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SIGMA RECEPTORS AND THE IMMUNE SYSTEM
DISSERTATION
Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in the Graduate School of the Ohio State University
By
Yuhong Liu, B.M. (Bachelor of Medicine)
The Ohio State University 1995
Dissertation Committee: Approved by
Dr. S. A. Wolfe, Jr. Dr. M. S. O’Dorisio Research Advisor Dr. R. H. Fertel Dr. W. P. Lafuse ft)/I Dr. J. F. Sheridan Aavisorof Record Department of Medical Microbiology and Immunology UMI Number: 9612230
UMI Microform 9612230 Copyright 1996/ by OMI Company. All rights reserved.
This microform edition is protected against unauthorized copying under Title 17, United States Code.
UMI 300 North Zeeb Road Ann Arbor, MI 48103 To My Parents,
My Husband Willie and My Daughter Ellen,
For Your Unfailing Love, Support, and Understanding.
ii ACKNOWLEDGMENTS
I would like to express my sincere appreciation to my
research advisor, Dr. Seth Wolfe, for his guidance and insight
throughout this project, his unshakable belief in me and this
research endeavor, and his and Dr. Charity Fox’s support and
friendship. I offer my sincere thanks to the other members of my
advisory committee, Dr. Richard Fertel, Dr. William Lafuse, Dr. Sue
O’Dorisio, and Dr. John Sheridan, for their invaluable suggestions
and comments. Special thanks go to Dr. O’Dorisio for her support
and encouragement when they were most needed, and to Dr. Fertel
for his professional insight and intellectual support. Also, I would
like to express gratitude to Joseph Pultz and Dr. Dennis Pearl for
their assistance in statistical analysis of our data. Finally, I would
like to express my deepest appreciation to my husband and
daughter, my parents, my brother, my father- and mother-in-law, for their support and understanding throughout this experience. VITA
February 20, 1964 ...... Born, Changchun, P.R. China
1987 ...... Bachelor of Medicine, Basic Medicine, Beijing Medical University, Beijing, P.R. China
1987-1989 ...... Teaching Assistant, Department of Immunology, Beijing Medical University, Beijing, P.R. China
1989-1995 ...... Graduate Research Associate Department of Medical Microbiology and Immunology, The Ohio State University, College of Medicine, Columbus, Ohio
PUBLICATIONS
Liu, Y. and Y. Qian. 1989. The experimental studies of IL-3. Progress in Physiological Sciences 20(1 ):17
Liu, Y., Q. Gong and T. Tong. 1989. Isolation and characterization of high molecular weight DNA binding protein from serum of mice with H22 ascites hepatoma. J. Beijing Med. Univ. 21(5):372
Liu, Y., Q. Gong and T. Tong. 1990. Isolation and characterization of high molecular weight DNA binding protein from ascites of mice with Ehrlich ascites carcinoma. Chinese Biochem. J. 6(3):264
Wang, D., S. Yang, Y. Qian and Y. Liu. 1990. Establishment and characterization of an acute myelogenous leukemia cell line. J. Beijing Med. Univ. 22(5):331
iv Liu, Y., B. B. Whitlock, J. A. Pultz and S. A. Wolfe, Jr. 1995. Sigma-1 receptors modulate functional activity of rat splenocytes. J. Neuroimmunology 59: 143-154
Liu, Y. and S. A. Wolfe, Jr. 1995. Haloperidol and spiperone potentiate murine splenic B cell proliferation. Imuunopharmacology submitted
FIELDS OF STUDY
Major Field: Medical Microbiology and Immunology Studies in sigma receptors in immune system with Dr. Seth A. Wolfe, Jr. TABLE OF CONTENTS
DEDICATION...... ii
ACKNOWLEDGMENTS ...... iii
VITA ...... iv
LIST OF TABLES ...... vii
LIST OF FIGURES ...... viii
CHAPTER PAGE
I INTRODUCTION ...... 1
II MATERIALS AND METHODS ...... 13
III RESULTS ...... 23
IV DISCUSSION ...... 75
LIST OF REFERENCES ...... 94 LIST OF TABLES
TABLE PAGE
1. Pharmacological specificity of [3H]haloperidol- labeled sigma-1 receptors in rat spleen ( K j ) and potency of drugs suppressing ConA-induced proliferation of rat splenocytes (EC 50) ...... 29
2. Splenic [3H]haloperidol binding sites are present on isolated splenocytes ...... 39
3. Drugs that do not enhance anti-p induced murine splenic B cell proliferation ...... 74
vii LIST OF FIGURES
FIGURE PAGE
1. ConA induced rat splenocyte proliferation dose response cuive ...... 25
2. Three classical sigma agonists suppress ConA-induced ratsplenocyte proliferation ...... 27
3. (-)-Sulpiride has no effect on ConA-induced ratsplenocyte proliferation ...... 31
4. Specific binding sites for pHJhaloperidol are piesenton membranesofratspleen(A)andratsplenocytes(B) ...... 3 3 , 34
5. Isolated ratsplenocytes (A) had higher densities (Bma*) of pH]haloperidol binding sites than the rat spleens (B)ftom which they were obtained ...... 3 7 , 38
6. Competition binding assaysofthree prototype sigma ligands against pH]haloperidol in ratspleen ...... 41
7. The ability of seven reference sigma agonists, to suppress Con A-induced proliferation correlated highly with theirpotency in binding pHJhaloperidol-labeled splenic sigma-1 receptors ...... 46
8. Correlation between EC 50 and Kjofall fifteen drugstested ...... 48
9. Speafic binding sites for pH]haloperidol are piesenton membranes of mouse B lymphoma cell line, A20 cells ...... 50
10. Rosenthal plotsofthe same data as in Rgure 9 ...... 52
11. Haloperidol and spiperone enhance anti-ju. induced B cell proliferation in a dose-dependent manner ...... 55
v iii LIST OF FIGURES
FIGURE PAGE
12. Haloperidol and spiperone lowerthe threshold of anti-jj. needed to trigger Boell proliferation ...... 5 8 , 59
13. Dopamine inhibits anti-p. induced Bcell proliferation ...... 62
14. Norepinephrineinhibitsanti-pinduced Bcellproliferation ...... 6 4
15. Serotonin enhancesanti-pinduoed Bcell proliferation at 104 M ...... 66
16. Spiperone and dopamine antagonize each other’s effects on anti-p induced Bcell proliferation ...... 6 8 , 69
17. Spiperone and norepinephrine antagonize each other’s effects on anti-p induced B cell proliferation ...... 71,72
ix CHAPTER I INTRODUCTION
The Nature of Sigma Receptors
The existence of sigma receptors was first postulated by
Martin et al. in 1976 as a result of canine physiological studies with racemic mixtures of the opiate benzomorphan, N-allynormetazocine
(SKF 10,047, or NANM) (1). SKF 10,047 and related benzomorphans cause canine delirium and produce psychotomimetic effects in humans (2). It was originally thought that a novel type of ‘opiate’ receptor, sigma (a) opiate receptors, mediated the phenomena. However, further studies revealed that naltrexone, a classical opioid antagonist, could not block the effects of SKF 1 0,047 in dogs (3). Therefore, it was clear that the sigma ‘opiate’ receptor should not be classified as a type of opiate receptor after all. But the designation sigma receptor was retained.
[3H]SKF 10,047 labeled etorphine-inaccessible sigma sites were subsequently described by Su in guinea pig brain (4,5).
Sigma receptors bind psychotomimetic drugs. For example:
1 2
1. Opiate-related compounds. The opiate benzomorphans
N-allylnormetazocine (SKF 10,047), pentazocine,
ethylketocyclazocine and cyclazocine, bind to both opiate receptors
and sigma receptors. But these two kinds of receptors have
opposite stereoselectivity. Opiate receptors bind to
(-)-benzomorphans better, whereas sigma receptors prefer
(+)-benzomorphans;
2. Phencyclidine-related compounds. In some early studies
sigma receptors were believed to be identical to PCP receptors
based on the displacement of [3H]PCP binding by the sigma ligand
(+)-SKF 1 0,047 (6, 7). Later it was found that the drug selectivity
and the anatomical distribution of sigma receptors and PCP
receptors are distinct from each other. It is now known that PCP
and its derivative, TCP, bind to PCP receptors (in the ion channels
of NMDA receptors) with high affinities, while their binding affinity to sigma receptors is relatively low (8);
3. Guanidines. 1,3-Di(2-tolyI)guanidine (DTG) binds to sigma
receptors selectively and with high affinity. Ligands for other
receptors are very weak in displacing [3H]DTG binding (9);
4. 3-Phenylpiperidines.
3-(3-hydroxyphenyl)-N-propylpiperidine (3-PPP) binds to both sigma receptors (10) and dopamine D 2 receptors (11). But (+)-3-PPP binds to sigma receptors with higher affinity, (-)-3-PPP is more potent at dopamine D 2 receptors (11);
5. Miscellaneous compounds. Haloperidol binds to sigma receptors, serotonin 5-HT2 and dopamine D2 receptors with high 3
affinity (12). (-)-Butaclamol binds to sigma receptors with high
affinity, while its (+)-enantiomer binds to D 2 receptors and
serotonin receptors with high affinity (13). A novel antipsychotic
drug, rimcazole, also binds to sigma receptors, but with relatively
low affinity (14).
Recently, it has been found that there is more than one type
of sigma receptor. A second type of sigma receptor was first found
in rat PC 1 2 cells, a tumor cell line that has the phenotype of
sympathetic neurons (15). This new sigma site has an overlapping
pharmacology with the previously described ( 0 1 ) sigma receptors.
It has substantially lower affinity for (+)-benzomorphans, and its
affinity for (-)-benzomorphans is greater than for
(+)-benzomorphans. Researchers have come to agreement on the
nomenclature and labeling conditions for the two subtypes of sigma
receptors, which are now known as sigma-1 ( 0 1 ) and sigma-2 ( 0 2 )
(16). These can coexist in tissues. For example, rat liver contains approximately 25% sigma-1 sites and 75% sigma-2 sites (17); rat brain also contains both sites (18). Furthermore, studies done in our laboratory indicated that there might be a third type of saturable and specific binding site for sigma ligands in rat spleen and human peripheral blood leukocytes (Whitlock and Wolfe, unpublished data).
Little is known about the structure of sigma receptors. Sigma binding sites are sensitive to temperature, pH, and protein-modifying agents, which suggests that sigma receptors are proteins (5, 19). Several attempts have been made to determine the 4 molecular weight of sigma receptors (15,20-22). A single polypeptide of 29 KD was found in guinea pig brain using azido-DTG to label sigma-1 sites, while two polypeptides with molecular weights of 18 KD and 21 KD were discovered in PC1 2 cells. Because no or very few sigma-1 receptors are found on
PC12 cells, these two polypeptides may represent sigma-2 receptors. In addition, McCann and Su identified a
CHAPS-solubilized sigma-1 complex with a molecular weight of
450 KD from rat liver membrane (23). Another group has isolated and sequenced a 28 KD, cyclophilin-like protein from rat liver membrane that may be a component of sigma receptors (24). These discrepancies regarding the molecular weight of sigma-1 receptors might be due to species differences or the difference between a single subunit and a whole receptor complex. So far, sigma receptors have not been cloned.
There have been several studies on the signal transduction mechanisms of sigma receptors. One group reported that sigma receptors might be coupled to guanine nucleotide-binding proteins
(25, 26). As observed with other G protein-coupled receptors, guanosine triphosphate and Gpp(NH)p, a non-hydrolyzable analog of GTP, inhibited the binding of [3H](+)-3-PPP to rat brain membranes. Pertussis toxin and cholera toxin also decreased binding by [3H](+)-3-PPP (26,27), which indicated that sigma receptors may interact both with Gj and G0, as well as Gs proteins.
Further studies also showed that in rat brain only [3H](+)-3-PPP binding sites were sensitive to guanine nucleotides, while [3H]DTG 5
binding sites were not (28). This suggests that subtypes of sigma
receptors may have different signal transduction mechanisms.
Also, Bowen and coworkers found that although sigma ligands did
not have direct effects on phosphoinositide (PI) turnover in rat
brain, they did inhibit inositol phosphate (IP 1 ) production following
the stimulation of muscarinic receptors by either carbachol or
oxotremorine-M in synaptoneurosomes from whole rat brain (29, 30).
This implies that, in brain, sigma receptors can modulate the
phosphoinositide secondary messenger system.
Physiological Functions of Sigma Receptors
Evidence for the existence of endogenous sigma ligands has
been observed in several laboratories. Preliminary reports of
partially purified extracts from brain and liver have shown both
peptides and non-peptides with the binding characteristics of sigma
ligands (31-33). Many known endogenous substances have been
screened and proven to be ineffective in inhibiting binding at sigma
receptors (reviewed in 34). But there are a few exceptions. Roman
et al. reported that the peptides, neuropeptide Y (NPY) and peptide
YY (PYY), have high affinity for rat brain sigma receptors labeled with [3H](+)-SKF 10,047 (35), although others have reported that they have no such activity (23, 36). Progesterone, another candidate for sigma endogenous ligand, was reported to inhibit [3H](+)-SKF
10,047 binding in guinea pig brain and spleen, with a K j of 268nM
(37). Also, Zn++ has been proposed to be an endogenous ligand for sigma-2 receptors in rat brain (38). However, none of these has been conclusive, and the true identity of the sigma endogenous
ligand(s) remains unknown.
Sigma receptors are widely distributed in the central nervous
system (39), endocrine tissues (40-42), gastrointestinal tract (43),
liver (44) and immune system (45, 46). However, the physiological
functions of sigma receptors are poorly understood, mainly due to
the lack of selective ligands for sigma receptors. For example,
conclusions about the functions of sigma receptors based on the
actions of SKF 10,047 must be viewed with caution, because this
compound acts at several different sites, i.e. PCP receptors, opiate
receptors and sigma receptors. Although much effort has recently
been devoted to developing more selective compounds (47-49, and
numerous articles by De Costa and colleagues, reviewed in 50),
most of them have not been well characterized enough,
pharmacologically and physiologically, to be recognized as
selective ligands for sigma receptors.
Despite these difficulties, sigma receptors have been linked to phenomena in the central nervous system and in peripheral tissues. (+)-Pentazocine has been shown to increase local cerebral glucose utilization in brain areas that are rich in sigma receptors (51). Steinfels et al., found that (+)-pentazocine produced a sigma-selective discriminative stimulus cue in rats, enabling them to discriminate non-sigma drugs from the training drug ,
(+)-pentazocine (52). Sigma receptors have also been implicated in the etiology of schizophrenia. Both autoradiographic and homogenate radioligand binding studies showed dramatic reductions of sigma receptors in several brain regions from autopsy
samples of schizophrenic patients (53, 54). Other studies have
provided evidence that sigma receptors may be also involved in
certain movement disorders such as dystonia (55). In the periphery,
Campbell and colleagues showed that sigma ligands blocked
electrically or 5-HT-induced contractions of the isolated guinea pig
ileum/myenteric plexus preparation (56). Also, electrically induced
twitches of isolated guinea-pig vas deferens were potentiated by
sigma agonists (42). Sigma agonists blocked a tonic, outward
potassium current in NCB-20 neuroblastoma cells (57). In an in
vitro assay system using bovine adrenal chromaffin cells, sigma
ligands were shown to noncompetitively inhibit nicotine-stimulated
catecholamine release (58).
Role of Sigma Receptors in the Immune System
Sigma receptors may be of importance for the immune system
as well. Fudenberg, Whitten and Khansari found that high
concentrations of PCP (10'5M) could inhibit functional activities of
human peripheral blood leukocytes (HPBL) in vitro, and they
detected specific binding sites for [3H]PCP on HPBL (59, 60). In
1987, Dornand and colleagues reported that PCP and PCP analogs
suppressed mitogen-induced proliferation of murine splenocytes
(61). They found that, at high doses (10‘6M to 10"5M), PCP analogs caused a reduction in the resting potential of splenocytes, and
reduced the ability of these cells to depolarize and elevate their intracellular calcium levels in response to stimulation with 8
concanavalin A (ConA). However, in previous studies, Wolfe and
associates could not detect high affinity PCP receptors (PCP-i) in
rat spleen or HPBL, while they did find strikingly high
concentrations of sigma receptors in both of these tissues (45, 46).
This suggests that the effect of PCP on immune cells may be
mediated through sigma receptors. Recently, Carr et al., reported
that the sigma agonists 1 ,3-di(2-tolyl)guanidine (DTG), haloperidol,
and (+)-pentazocine suppressed ConA-induced proliferation of
murine splenocytes. In contrast, bacterial lipopolysaccharide
(LPS)-induced proliferation was enhanced by these drugs (62).
They also reported that pokeweed mitogen (PWM)-induced and
LPS-induced immunoglobulin production was either enhanced or
suppressed by sigma agonists, depending on the mitogen and
concentration of the drug. In addition, they have shown that sigma
agonists may also modulate murine splenic natural killer activity
and forskolin-induced cAMP production in splenocytes (63). More
recently, Garza et al., found that high concentrations (10_6M to
10_5M) of haloperidol and the novel sigma ligand
(+)-azidophenazocine (64) suppressed ConA-induced interferon
production. However, in their hands, the sigma agonists DTG,
(+)-pentazocine, and (+)-1-propyl-3-(3-hydroxyphenyl)piperidine
((+)-3-PPP) did not significantly affect interferon production (65),
which suggests that this may not have been a sigma receptor-
mediated effect. More recently, drug binding and modulation of
several in vivo and in vitro functional assays have been reported for a novel sigma ligand, SR 31747 (66, 67). SR 31747 inhibited 9
mitogen induced lymphocyte proliferation, and prevented both
graft-versus-host disease and delayed-type hypersensitivity granuloma formation in vivo. The same group also reported that
SR 31747 given in vivo caused an indirect inhibition of
lipopolysaccharide-induced production of interleukin (IL)-1, IL-6
and tumor necrosis factor-a, due to an elevation of the level of
corticosteroids (68).
Collectively, these data suggest that sigma receptors are
present on lymphocytes, and that these receptors may regulate both T cell and B cell functions. However, there are several major problems with the studies mentioned above:
1. In lymphocyte proliferation assays, mitogens that could activate multiple types of cells were used on mixed cell populations, such as lipopolysacharride (LPS) which could act on both B cells and macrophages, and pokeweed mitogen (PWM) which could act on both B cells and T cells. This makes it hard to interpret which subpopulation of cells were responding to sigma agonists.
2. Sigma agonists do not act exclusively at sigma receptors, but can also be quite potent at a multitude of other sites, including ion channels, dopamine receptors, serotonin receptors, opiate receptors, phencyclidine receptors, ai adrenergic receptors, and uptake sites for serotonin and dopamine (reviewed in 69). Many of these sites have been identified on immune cells, among them adrenergic receptors (70-72), dopamine receptors (73-81), serotonin receptors (82, 83), and opioid receptors (reviewed in 84). Therefore, 10
immune modulation by putative sigma agonists might actually be
the result of drug actions at a multitude of receptors on immune
cells. In most of the existing studies, attempts to discriminate
between the effects through sigma receptors and other receptors
were not made. In addition, the subtypes of sigma receptors,
sigma-1 and sigma-2, which have overlapping pharmacology, were
not distinguished from one another.
3. SR 31747, a recently described putative sigma ligand, has
a very different pharmacological profile from either sigma-1 or
sigma-2 (67). The authors argued that it might bind to an allosteric
modulation site of sigma receptors. Although SR 31747 has been
shown to have immunomodulatory effects (66, 68), many questions
still remain as to how this is related to sigma receptors.
In order to demonstrate that sigma receptors modulate a
biological function, the receptors must be identified, quantitated,
and characterized kinetically and pharmacologically in the cells
and tissues of interest. Sigma agonists must modulate functional
activity in those cells or tissues, and the ability of drugs to
modulate function must correlate with drug binding potency at the
receptor. (It is to be expected that some compounds may fall
outside the correlation due to additional actions at other receptors.)
This has been accomplished in other systems in which sigma
receptors have been reported to act (55, 56, 58, 85), but these criteria
have not yet been met in the immune system. In the immune
system, several laboratories have demonstrated drug binding sites and/or have shown modulation of functional activities by sigma 11
agonists (45, 46, 59-63, 65-67), but a mathematical correlation
between drug binding at the receptor and the pharmacology of the
biological responses has not been demonstrated.
Hypothesis and Significance
A significant recent development in immunology is a growing
appreciation that the immune system functions as part of a
complex, interactive network consisting of the immune, endocrine,
and nervous systems. Together, these systems deal with external
and internal stimuli, and maintain homeostasis under dynamic
conditions. There is a considerable body of evidence that the
immune system is modulated by endocrine and nervous inputs, and that it in turn causes changes in endocrine status and central
nervous system activity (reviewed in 86). The mechanisms of this communication, -neurotransmitters, hormones, “immune" cytokines and their receptors, - are shared among these three systems (87).
Although characterization of endogenous sigma ligand(s) is still in preliminary stages, the underlying premise of our investigations is that the endogenous sigma ligand(s) is one of these mediators. The presence of sigma receptors in high density in the central nervous system, the endocrine system and the immune system suggests that endogenous sigma ligand(s) may have a special role in coordinating the responses of these three systems to environmental stimuli.
The present study was undertaken to determine whether sigma agonists have direct effects on T cell and B cell function. 12
The objective was to identify sigma receptors on immune cells pharmacologically, using radioligand binding assays. As mentioned before, due to the cross reactivity of sigma ligands, a series of sigma ligands were employed to characterize sigma receptors on immune cells. The same group of drugs were also tested in in vitro assays, for their effects on a commonly used measure of T and B cell responsiveness: mitogen-induced proliferation. If sigma agonists do influence T or B cell proliferation, we would try to correlate their ability to modulate function with their binding potency at sigma receptors. We would be able to conclude whether sigma receptors could mediate immunomodulatory effects, based on the outcome of the correlation. We believe this study is the first definitive study on whether sigma receptors in the immune system have functional significance. CHAPTER II MATERIALS AND METHODS
Animals
Male Sprague-Dawley rats (Harlan Sprague-Dawley Inc.,
Indianapolis, IN), 150 - 300 gram, were used for radioligand binding assays and ConA-induced splenocyte proliferation assays.
Animals were housed three to four per cage.
Male C57BL/6J mice (Jackson Laboratories, Bar Harbor, ME),
8-12 weeks old, were used in splenic B cell proliferation assays.
Animals were housed ten per cage.
All animals had access to food and water ad libitum, and were maintained on a 12 hour light/dark cycle at a room temperature of 22°C. All animals were treated in accordance with
National Institute of Health animal care guidelines.
Cell Cultures
The mouse B lymphoma cell line, A20, was obtained from
American Type Culture Collection (Rockville, MD). Cells were
13 14
maintained in suspension in RPMI 1640 medium (GIBCO BRL Life
Technologies, Inc., Gaithersburg, MD) containing 10% fetal bovine
serum (FBS, defined grade, HyClone Laboratories, Inc., Logan, UT), 50 |a.g/ml gentamycin (GIBCO), and 5 x 10_5M
2-mercaptoethanol (BIO-RAD Laboratories, Richmond, CA). Cells
were seeded at 2 x 105 viable cells/ml in 150 cm2 tissue culture
flasks (Corning Inc., Corning, NY), and harvested and passed every
three days. Harvested cells were washed once in Ca2+/Mg2+-free
Hank’s Balanced Salt Solution (HBSS, GIBCO), and counted. Cell
pellets were stored at -80°C until use in binding assays.
Drugs and Reagents
Haloperidol, haloperidol metabolite I (4-(4-chlorophenyl)-4-
hydroxypiperidine), haloperidol metabolite II ((±)-4-(4-chlorophenyl)-a-(4-fluorophenyl)-4-hydroxy-1 - piperidinebutanol), (+) and (-)-pentazocine, (+) and (-)-butaclamol,
(+) and (-)-3-PPP hydrochloride (3-(3-hydroxyphenyl)-N- propylpiperidine hydrocloride), (+) and (-)-SKF 10,047
(N-allynormetazocine hydrochloride), DTG (1,3-di(2-tolyI) guanidine), rimcazole dihydrochloride, TCP hydrochloride
(tenocyclidine hydrochloride, 1 -[1 -(2-thienyl)cyclohexyl]piperidine hydrochloride), PCP hydrochloride (phencyclidine hydrochloride,
1-(1-phenylcyclohexyl)piperidine hydrochloride), spiperone hydrochloride, (-)-sulpiride, pindobind-5HT1 A, (+)-SCH-23390 hydrochloride, ritanserin, LY-53,857 maleate, WB-4101 hydrochloride, 5-methyl-urapidil, dopamine hydrochloride, 15
(-)-norepinephrine bitartrate, and serotonin hydrochloride were
purchased from Research Biochemicals, Inc. (Natick, MA).
Phentolamine hydrochloride, methoxamine, clonidine and
concanavalin A (ConA) were purchased from Sigma Chemical Co.
(S t. Louis, MO). Affinity-purified F(ab ’)2 fragment goat anti-mouse IgM (anti-p) antibodies were purchased from Jackson
ImmunoResearch Laboratories, Inc. (West Grove, PA).
Preparation of Rat Spienocytes
Spleens from C02-ki I led Sprague-Dawley rats were removed
and teased into single-cell suspensions by pressing them through a
stainless steel mesh. Spienocytes were suspended in Ca2+ and
Mg2+ free HBSS (GIBCO), layered over 70% Percoll (Pharmacia,
LKB Biotechnology, Uppsala, Sweden), and centrifuged at 1000 x g
for 15 min., at 4°C. Spienocytes were collected from the
HBSS-Percoll interface, washed twice by centrifugation in HBSS,
and suspended in RPMI 1640 medium (BioWhittaker, Inc.,
Walkersville, MD) containing 10% fetal bovine serum (FBS, defined grade, HyClone), 50 pg/ml gentamycin (GIBCO), and 5 x 10‘5 M
2-mercaptoethanol (BIO-RAD).
B Cell Preparation
Spleens from C02-ki I led C57BL/6J mice were removed and teased into single-cell suspensions by pressing them through a
stainless steel mesh. Spienocytes were suspended in
Ca2+/Mg2+-free HBSS (GIBCO), layered over a discontinuous 16
55%/70% Percoll gradient, and centrifuged at 1000 x g for 15 min.
at 4°C. Cells were collected from the 55% /7 0% Percoll interface,
washed twice by centrifugation in HBSS, and suspended at 2 x 107
cells/ml in Dulbecco’s phosphate-buffered saline (D-PBS, GIBCO)
containing 0.1% bovine serum albumin (BSA, Sigma). The cells were incubated for 30 min. at 4°C with 20 pg/ml biotinylated anti-
Thy1.2 (CD90) and biotinylated anti-Mac-1, ccm chain (CD11 b)
monoclonal antibodies (PharMingen, San Diego, CA), and washed
twice by centrifugation through D-PBS/0.1 % BSA. They were then
incubated with streptavidin-conjugated magnetic beads
(Dynabeads M-280 streptavidin, Dynal, Inc., Lake Success, NY)
(1 x 1 07 cells in 0.5 ml, at a celhbead ratio of 1:5). After incubation
at 4°C for 15 min., 3 ml of D-PBS/0.1 % BSA was added to the
mixture of cells and beads, and bead-coupled Thy1.2+ and Mac-1 +
cells were removed by placing the tubes on a magnetic particle
concentrator (Dynal) for 3 min. Supernatant medium and
non-labeled cells were decanted, and the magnetically entrapped cells and beads were resuspended three times with 3 ml of
D-PBS/0.1% BSA, and re-separated using the magnet.
Supernatants were pooled and separated again using the magnet.
The composition of the negatively-selected B cell populations was then assessed by flow cytometry. The enriched B cell populations were found to be contaminated less than 5% by Thy1.2+ and
Mac-1 + cells. 17
ConA-induced Proliferation of Rat Spienocytes
Rat spienocytes (2.5 x 1 05 cells/well) were added to
flat-bottom 96-well microtiter plates (Becton Dickinson, Lincoln
Park, NJ) and incubated at 37°C for two hours with varying
concentrations of drugs, after which ConA (final concentration, 0.5
|ig/ml) was added to all wells. The cells were then incubated at
37°C in 5% C02/95% air for 48 hours, and [3H]thymidine (0.5
pCi/well, Amersham Corp., Arlington Heights, IL) was added during the last 4-8 hours of culture. Cultures were harvested on Whatman
GF/B glass fiber filters in a cell harvester (Biomedical Research and Development Laboratories, Inc., Gaithersburg, MD), washed with distilled water. Filter discs were collected in 6 ml liquid scintillation vials (Wheaton Scientific, Millville, NJ), and 3 ml liquid scintillation cocktail (Formula-989, Biotechnology systems, NEN
Research Products, Boston, MA) was added to each vial. Liquid scintillation vials were then counted in a scintillation counter
(Beckman LS6000IC) to measure [3H]thymidine incorporation as an index of cell proliferation. Drugs used in these assays were: haloperidol, haloperidol metabolite I, haloperidol metabolite II,
(+) and (-)-pentazocine, (+) and (-)-butaclamol, (+) and (-)-3-PPP,
(+) and (-)-SKF 10,047, DTG, rimcazole, TCP, and PCP.
B cell proliferation assay
Enriched B cells were suspended in RPMI 1640 medium
(GIBCO) containing 10% fetal bovine serum (FBS, defined grade, HyClone), 50 pg/ml gentamycin (GIBCO), and 5 x 10~5 M 18
2-mercaptoethanol (BIO-RAD). B cells (1 x 105/well) were
incubated in flat-bottom 96-well microtiter plates (Corning Glass
Works, Corning, New York) at 37°C for 1 hour with varying concentrations of drugs, after which anti-p antibody (final concentration, 0.5 pg/ml) was added to all wells. The cells were then incubated at 37°C in 5% C02/95% air for 48 hours, after which [3H]thymidine (0.5 (iCi/well, Amersham) was added, and cells were incubated for another 16-18 hours. Using a cell harvester
(Biomedical Research and Development Laboratories), cultures were harvested and washed with distilled water by filtration on glass fiber filters (Whatman GF/B, Biomedical Research and
Development Laboratories). Filter discs were collected in 6 ml liquid scintillation vials (Wheaton Scientific, Millville, NJ), and 3 ml liquid scintillation cocktail (Formula-989, Biotechnology systems,
NEN Research Products, Boston, MA) was added to each vial.
Liquid scintillation vials were then counted in a scintillation counter
(Beckman LS6000IC) to measure [3H]thymidine incorporation as an index of cell proliferation. Drugs used in these assays were: haloperidol, spiperone, DTG, (+) and (-)-pentazocine, (+) and
(-)-butaclamol, (+)-SCH-23390, (-)-sulpiride, ritanserin, LY-53,857, pindobind-5HT1 A, WB-4101, 5-methyl-urapidil, phentolamine, methoxamine, clonidine, serotonin, dopamine, and
(-)-norepinephrine. 19
Preparation of Rat Spleen, Rat Spienocytes, and A20 cell membranes
Rats were killed with CO2 and their spleens were dissected.
For radioligand binding assays in which whole spleens were used,
spleens were frozen rapidly on dry ice, then stored at -80°C. For
assay, frozen spleens were disrupted with a Polytron tissue
homogenizer (Brinkman Instruments, Westbury, NY) in 25-50
volumes of ice-cold 50 mM Tris-HCI buffer (pH 7.7 at 4°C).
Membranes were pelleted by centrifugation at 40,000 x g for 10
min. at 4°C, and washed twice by resuspension in the same buffer
and recentrifugation. After the second wash they were
resuspended in 50 mM Tris-HCI buffer (pH 7.7 at 22°C) and kept on
ice until placed in binding assays. To prepare washed splenocyte
membranes for binding assays, cells were teased from freshly dissected spleens and isolated on Percoll gradients as described for ConA-induced proliferation assays, above. Isolated spienocytes were then frozen on dry ice and stored at -80°C. For assay, frozen spienocytes and A20 cells (prepared as described previously), were thawed, subjected to homogenization, centrifuged, washed and resuspended in a manner identical to the procedure described for whole spleen. Protein content of the membrane suspensions was determined using commercial protein assay kit (Sigma, Cat.
No. P5656). 20
Characterization of [3H]Haloperidol Binding to Sigma-1 Sites in Rat Spleen, Rat Spienocytes, and A20 Cells
For saturation binding assays (16, 45, 88), membrane
preparations equivalent to 5.0 mg wet weight of rat spleen/tube,
2 x 107 rat splenocytes/tube, or 1 x 107 A20 cells/tube, were
incubated at room temperature in total volume of 2.5 ml 50 mM
Tris-HCI buffer (pH 7.7), with increasing concentrations (0.1-10 nM)
of [3H]haloperidol (Specific Activity, 50 Ci/mmol, New England
Nuclear, Boston, MA). Spiperone (50 times the [3H]haloperidol
concentration) was included in all incubations in order to block
[3H]haloperidol binding to D 2 dopamine and 5 -HT2 serotonin
receptors (89, 90). Non-specific binding was defined by the
presence of 10 pM DTG. After a 90 min. incubation,
membrane-bound [3H]haloperidol was separated from free
radioligand in a cell harvester (Biomedical Research and
Development Laboratories) by rapid filtration through Whatman
GF/B glass fiber filters (Biomedical Research and Development
Laboratories) that had been pretreated with 0.001% or 0.5% polyethylenimine (PEI) to reduce non-specific binding. The filters and entrapped membranes were washed at room temperature for
10 seconds with 5 mM Tris-HCI buffer (pH 8.0). Filter discs were collected in 6 ml liquid scintillation vials (Wheaton Scientific,
Millville, NJ), and 3 ml liquid scintillation cocktail (Formula-989,
Biotechnology systems, NEN Research Products, Boston, MA) was added to each vial. Liquid scintillation vials were then counted in a scintillation counter (Beckman LS6000IC). For competition binding assays, rat spleen membranes (5 mg
wet weight/tube) were incubated under the conditions described
above with 0.7 nM [3H]haloperidol in the presence of 35 nM
spiperone plus increasing concentrations of competing drugs.
Non-specific binding again was defined as that occurring in the presence of 10 jo.M DTG. The following drugs were used in
competition binding assays: haloperidol metabolite I, haloperidol
metabolite II, (+) and (-)-pentazocine, (+) and (-)-butaclamol,
(+) and (-)-3-PPP, (+) and ( - ) - S K F 10,047, DTG, rimcazole, TCP,
and PCP.
Data Analysis
Saturation binding and drug competition data were analyzed
using the MacLIGAND nonlinear curve fitting program (91) in order to obtain Kd (ligand concentration at which 50% of binding sites are
occupied at steady state), K j and Bmax (number of binding sites per
cell or unit protein) values for drugs. A least squares fit to a
logarithm-probit analysis was used to calculate EC 50 (drug concentration at which 50% of maximum effect is achieved) values for drugs in suppression of ConA-induced proliferation assays.
Analysis of the relationship between drug potencies in binding and proliferation experiments was performed using PROC REG in the
SAS computer package. Because we expected relationships to be relative, rather than absolute, data were examined in a logarithmic format, comparing geometric, rather than arithmetic means.
Although a total of 15 compounds were tested in proliferation and competition assays, seven were used to test whether sigma receptors modulate cell function. These reference compounds were chosen before this series of experiments was performed.
They were haloperidol, haloperidol metabolite II, DTG,
(+)-pentazocine, (+)-SKF 10,047, (+)-3-PPP, and (-)-butaclamol.
These seven reference compounds were examined with a linear regression analysis. The leverage of individual points was examined to determine their influence on the regression. Cook’s distance statistic was used as a test for outliers. The remaining drugs were then compared to the regression in order to determine whether they fell within the 95% prediction interval of the reference compounds. Unpaired t-te s t was performed using StatView 4.0 for
B cell proliferation assays. CHAPTER III RESULTS
A. Sigma Receptors and T Cell Function
Sigma Agonists Modulate ConA-induced Splenocyte Proliferation
A series of fifteen compounds were tested as described in
Materials and Methods for their ability to influence ConA-induced rat splenocyte proliferation in vitro, which is a commonly used measure of T cell activation. A stimulus of 0.5 pg/ml ConA was used for all experiments. This concentration was in the linear range of the ConA dose response, and induced somewhat less than
50% of the maximum proliferative response that could be obtained using higher lectin concentrations (Figure 1). In this system, all fifteen drugs suppressed mitogenic responses in a dose-dependent manner. Representative experiments with the prototypic sigma agonists haloperidol , (+)-pentazocine and DTG are shown in
Figure 2. Controls were performed for all diluents required to solublize drugs, which were the combination of ethanol, 100 mM
23 Figure 1. ConA-induced rat splenocyte proliferation dose response curve. The concentration of ConA used in subsequent experiments, was 0.5 |ig/ml, which was in the linear range of the curve and induced somewhat less than 50% of the maximum proliferative response. The figure is a representative experiment, which was replicated five times.
24 100000
8 0 0 0 0
6 0 0 0 0 E Q. O 4 0 0 0 0
experimental 20000 condition 0.5 ]ig/ml
.01 100
Figure 1
NJ t n Figure 2. Three classical sigma agonists, — haloperidol, (+)- pentazocine and DTG, — suppress Con A-induced rat splenocyte proliferation in a dose-dependent manner. Conditions were as specified in Materials and Methods. Data shown are from a representative experiment. Each point represents average values of three replicates, and each titration curve was repeated three times. The other twelve drugs were tested in an identical manner.
26 %Control [3H]Thymidine 0 0 1 120 0 8 0 4 0 6 20 0 10 -10
a □ (+)- (+)- Pentazocine □ Haloperidol • DTG
10 -9
10 -8
10 Figure 2 rg (M) Drug
-7
10 -6
10
-5
10 -4 28 acetic acid or deionized water. The cpm values of experimental group were then compared to those of control group which contained vehicle(s) only and was considered as 100% proliferation. The EC 50 values of the drugs ranged from 2 x10'7 M to 6 x1 O'5 M. The rank order of drug potencies (from most to least potent) was: haloperidol metabolite II > haloperidol > rimcazole >
(+)-butaclamol > TCP > (-)-butaclamol > PCP > (+)-pentazocine =
DTG > haloperidol metabolite I > (+)-3-PPP > (-)-pentazocine >
(+)-SKF 10,047 > (-)-SKF 10,047 > (-)-3-PPP (Table 1).
Haloperidol, one of the most potent drugs at suppressing
ConA-induced proliferation of rat spienocytes, also is a potent antipsychotic drug which a c ts as a D2 dopamine receptor antagonist (13). Since haloperidol binds to sigma and D 2 receptors with similar affinity, some of the immunosuppressive effects of haloperidol might have been mediated through its actions at D 2 receptors. This does not appear to be the case, as (-)-sulpiride, a potent D 2 antagonist, had no effect on ConA-induced proliferation
(Figure 3).
Spienocytes Have [3H]Haloperidol-labelable Sigma-1 Receptors
Although sigma-1 receptors have been previously identified and characterized on human peripheral blood leukocytes and in rat spleen (45, 46), their presence had not been demonstrated on the isolated rat spienocytes used for the present functional assays. As may be seen in Figure 4A and B, washed membranes of spienocytes isolated on 70% Percoll gradients bound 29
Table 1. Pharmacological specificity of [ 3H]haloperidol-labeled sigma-1 receptors in rat spleen ( K j ) and potency of drugs suppressing ConA-induced proliferation of rat spienocytes (EC 50)
Drug EC 50 (a) (|iM) K|(a) (nM)
1. haloperidol metabolite II .197 ± .081 ( 4 ) 5.67 ± 0.16 ( 3 ) 2 . haloperidol .260 ± .053 ( 3 ) .654 ±.012 (b)(3) 3. rimcazole .290 ± .036 ( 3 ) 448 ± 117 ( 3 ) 4. (+)-butaclamol 4.00 ± 1.21 ( 3 ) 1420 ± 180 ( 3 ) 5. TCP 5.48 ± 1.70 ( 4 ) 2530 ± 280 ( 3 ) 6 . (-)-butaclamol 5.90 ± 1.83 ( 3 ) 31.0 ± 4.0 (3) 7. PCP 9.82 ± 2.44 (5) 5980 ± 1690 (3) 8 . (+)-pentazocine 12.8 ± 4.8 (3) 20.3 ± 3.6 (3) 9. DTG 12.9 ± 2.9 (3) 69.6 ± 12.5 ( 3 ) 10. haloperidol metabolite I 20.4 ± 6.4 (3) 389 ± 23 (3) 11. (+)-3-PPP 26.5 ± 17.5 (3) 68.9 ± 23.8 ( 3 ) 12. (-)-pentazocine 30.7 ± 10.5 (3) 28.5 ± 3.8 ( 3 ) 13. (+)-SKF 10,047 31.2 ± 9.9 (3) 233 ± 20 (3) 14. (-)-SKF 10,047 55.6 ± 36.9 (3) 2110 ± 310 ( 3 ) 15. (-J-3-PPP 57.7 ± 26.7 (3) 207 ± 41 ( 3 )
(a) Values represent arithmetic means ± SEM of (number of independent experiments). (b) This is a Kd value. Figure 3. The classical dopamine D 2 receptor antagonist,
(-)-sulpiride, has no effect on ConA-induced rat splenocyte proliferation. Conditions were as specified in Materials and
Methods. Each point represents average values of three replicates.
The figure is a representative experiment, which was replicated twice.
30 200
CD 1 5 0 C
E >, sz h; 100 roX
c o 5 0 CJNO 0s
0 i______-7 -6 -5 10 10 10 10 ' 4 10 ~3
(-)-Sulpiride (M)
Figure 3
03 Figure 4. Specific binding sites for [3H]haloperidol are present on membranes of rat spleen (A) and rat spienocytes (B). As described in Materials and Methods, membrane preparations were incubated with 0.078-10 nM [3H]haloperidol in the presence of 50-fold excess spiperone (3.9-500 nM) to block dopamine and serotonin receptors, and nonspecific binding was defined using 10 pM DTG. The figures shows the pooled data from three experiments for each tissue.
32 Bound [3H]Haloperidol (fmol/mg protein) 2000 Cn O Cn O O O O O O
r \ j
co n: :c n Q)_ <5‘ o c T3 “T (D
oo
o
ee Bound [3HJHaloperidol (fmol/mg protein) 0 0 0 3 2000 1000 0 i 0 . SpienocytesB. 3H]Haloperidol [3 Figure 4BFigure 6 4 (nM) A A ■A— 8 10 35
[3H]haloperidol in a manner comparable to membranes derived
from whole spleen. In both tissues, binding data gave linear
Rosenthal plots (Figure 5A and B ) , indicating the presence of a
single class of sites, with Kd values (mean + S.E.M.) of 0.65 ± 0.12
nM and 1.07 + 0.27 nM in whole rat spleen and rat spienocytes,
respectively. As may be seen from the B m a x values (the number of
binding sites/unit tissue) in Table 2 , there was an enrichment of
binding sites in spienocytes relative to whole spleen, indicating
that the cells we isolated, rather than structural elements of the
spleen, were a major source of sigma-1 receptors in this tissue.
Regulation of ConA-induced Rat Splenocyte Proliferation by
Sigma Agonists Correlates with the Pharmacology of Splenic
Sigma-1 Receptors
The ability of our te s t compounds to compete with
[3H]haloperidol for binding at sigma-1 receptors was determined in competition binding assays, as illustrated in Figure 6. K j values at
[3H]haloperidol-labeled sigma-1 receptors (mathematically equal to the drugs’ Kd values) were determined for each compound tested in the ConA proliferation assays. In accordance with previous studies
(46), the [3H]haloperidol-labeled sites in rat spleen displayed a pattern of drug potency typical of the pharmacology of sigma-1 receptors. Haloperidol was the most potent compound, while PCP and TCP were least potent. Furthermore, there was selectivity for
(+)-stereoenantiomers of pentazocine, SKF 10,047 and 3-PPP, and for (-)-butaclamol. The rank order of potency in the binding assay Figure 5. Rosenthal plots of the same data as in Figure 4, which show straight lines, indicative of a single class of drug binding site.
Isolated rat spienocytes (A) had higher densities (Bmax) of
[3H]haloperidol binding sites than the rat spleens (B) from which they were obtained. Data from three experiments are shown, each point being the average of three replicates within one experiment.
36 3000
2 5 0 0 -
CD CD
"O C 3 O CO 1 5 0 0 o
§_ 1 0 0 0 c o
5 0 0 '
1000 2000 3 0 0 0
Specific Bound
Figure 5A
CO-'si 3000
2 5 0 0 B
2000
1 5 0 0
A 1000
A 5 0 0
■------1------1_____ i_\ ■ 2 0 0 0 3 0 0 0 4 0 0 0
Specific Bound Figure 5B
CO 00 39
Table 2. Splenic [3H]haloperidol binding sites are present on
isolated splenocytes
Tissue Kd ______loM ) (fmol/mg protein) Spleen 0.65 + 0.12 1377 ±183 Splenocytes 1.07 + 0.27 2560 ± 502 (b) (a) Values represent simultaneous analysis ± SEM of three independent experiments. (b) Splenocyte Bmax is equivalent to 2582 ± 506 sites/cell. Figure 6. Using competition binding assays, splenic binding sites for 0.7 nM [3H]haloperidol (in the presence of 35 nM spiperone) were demonstrated to have the pharmacology of sigma-1 receptors. Representative curves using the prototypic sigma ligands haloperidol, (+)-pentazocine and DTG are shown in the figure. The other twelve drugs were tested in an identical manner. Experiments were carried out as described in Materials and Methods. Each point represents triplicate measurements, and all experiments were repeated three times. 40 120 100 - T3 C 3 O “ 80 - o ■g ‘i— I 4 0 ' • Hal oper idol < £ ° (+)Pentazoci ne 20 - A DTG 0 -14 -12 -10 -8 -6 -4 10 10 10 10 10 10 Drug (M) Figure 6 -p>. 42 (from most to least) was: haloperidol > haloperidol metabolite II > (+)-pentazocine > (-)-pentazocine >_(-)-butaclamol > (+)-3-PPP > DTG > (-)-3-PPP > (+)-SKF 10,047 > haloperidol metabolite I > rimcazole > (+)-butaclamol > (-)-SKF 10,047 > TCP > PCP (Table 1 )- Competition binding assays were performed using membrane preparations from homogenized spleens, whereas proliferation assays utilized splenocytes teased from spleen and isolated on Percoll gradients. Since saturation binding studies demonstrated the existence of only a single class of binding sites in spleen, and this site also occurred on isolated splenocytes derived from whole spleen (Figure 4 and 5, Table 2), we did not deem it necessary to repeat the pharmacological characterization of drug binding sites using isolated splenocytes as a tissue source. Of the fifteen compounds tested, the seven most sigma-1 selective agonists, haloperidol, haloperidol metabolite II, DTG, (+)-pentazocine, (+)-SKF 10,047, (+)-3-PPP, and (-)-butaclamol, were chosen as reference compounds. Five drugs, (-)-pentazocine, (-)-SKF 10,047, (-)-3-PPP, (+)-butaclamol, and haloperidol metabolite I, were chosen to serve as contrasting, less potent stereoenantiomers or metabolites of the reference compounds. Although it is a weak sigma agonist and is considerably more potent at modulating several ion channels in cells (92, 93), PCP was also te s te d because of its historical association with sigma receptors (94) and immune modulation (59-61). TCP (95) and 43 rimcazole (14, 96, 97) were selected as a PCP analog and newly described sigma antagonist, respectively. To determine whether the biological effect was due to actions at sigma-1 receptors, drugs’ EC 50 values in the proliferative assay were compared on a logarithmic scale with their binding assay K j values at sigma-1 receptors. These values are listed in Table 1. Because of the actions of sigma agonists at multiple receptors (discussed in Introduction), only the seven most sigma-1 selective te s t compounds, haloperidol, haloperidol metabolite II, DTG, (+)-pentazocine, (+)-SKF 10,047, (+)-3-PPP, and (-)-butaclamol, were used to establish this correlation, which was quite strong (adjusted r = 0.86). The slope of the correlation line (0.98) had a value approaching unity (Figure 7). As previously stated, PCP was initially included in the reference group because of its historical role in the field of sigma receptors (see Introduction). By this analysis, a weak, but marginally significant regression (r = 0.63, P approx. 0.05) was obtained. However, PCP seemed to fall outside the pattern of the other compounds. The average leverage of the points was 0.25, but the leverage of PCP was 0.6, indicating that PCP exerted an unusually large influence on the position of the line. A statistical te s t to determine whether PCP could be declared an outlier was inconclusive (P = 0.148, F ^ j) statistic forthe size of Cook’s distance = 2.67). Because in non-immune cells PCP is known to have a variety of actions in addition to those at sigma receptors (92, 93), we felt it should be removed from the reference group if there 44 was any question as to its actions in this system. As discussed above, this resulted in a strong correlation (adjusted r = 0.86) between binding and function for the remaining seven compounds (Figure 7) When the compounds not used to make the correlation were considered, four, (-)-pentazocine, (-)-SKF 10,047, (-)-3-PPP and haloperidol metabolite I, fell within the 95% prediction interval of the seven reference standards. Three, (+)-butaclamol, PCP and TCP, fell at the borders of the prediction interval, and rimcazole (a putative antagonist) was clearly an outlier (Figure 8). B. Sigma Receptors and B Cell Function Mouse B lymphoma Cell Line A20 Has [3H]Haloperidol-labelable Sigma-1 Receptors A20, a commonly used B lymphoma cell line, was used as a source of pure B lymphocytes. Saturation binding assays using the membrane preparations from these cells were performed under the same conditions used for rat spleen and rat splenocytes. Specific and saturable binding was obtained, and nonlinear curve fitting data analysis indicated the presence of a single class of sites, with Kd value (mean + S.E.M.) of 1.09 ± 0 .3 5 nM and Bmax value of 8 8 .7 ± 21.5 f mo l/mg protein or 17826± 4323 sites/cell (Figures 9 and 10). Although A20 is a mouse B cell line, its binding of [3H]Haloperidol was comparable to that of rat spleen and rat Figure 7. The ability of seven reference sigma agonists, haloperidol metabolite II (1), haloperidol (2), (-)-butaclamol (6), (+)-pentazocine (8), DTG (9), (+)-3-PPP (11) and ( + ) - S K F 1 0 , 0 4 7 (13), to suppress Con A-induced proliferation (EC 50 values) correlated highly (r = 0.86) with their potency in binding [3H]haloperidol-labeled splenic sigma-1 receptors ( K j values). The 9 5 % prediction interval of the regression is indicated by the dashed lines. Numbers refer to drug’s potency rank in suppressing ConA-induced proliferation (Table 1 ) . 45 o> oLD CJ LU Slope = 0.98 r = 0.86 -10 9 8 7 6 5 Ki (log M) Figure 7 CD Figure 8. Haloperidol metabolite I (10), (-)-pentazocine (12), (-)-SKF 10,047 (14) and (-)-3-PPP (15) fell within the 95% prediction interval (dashed lines) of the regression line of the seven reference sigma agonists (circled numbers, see Fig. 7). Numbers identify drugs by their relative potencies to suppress Con A-induced splenocyte proliferation (Table 1). PCP (7), TCP (5) and (+)-butaclamol (4), fell at the limits of the prediction interval. The putative sigma antagonist rimcazole (3) was, as expected, an outlier in this relationship. 47 -3 - 4 m - 5 O) =2o -6 o LO o LU - 7 -8 / / - 9 -J ------1------1------1______i______L. -10 - 9 - 8 - 7 -6 Ki (log M) Figure 8 Figure 9. Specific binding sites for [3H]haloperidol are present on membranes of mouse B lymphoma cell line, A20 cells. As described in Materials and Methods, membrane preparations were incubated with 0.078-10 nM [3H]haloperidol in the presence of 50-fold excess spiperone (3.9-500 nM) to block dopamine and serotonin receptors, and nonspecific binding was defined using 10 pM DTG. The figure is a representative experiment, which was replicated three times. 49 250 200 o S - C 1 5 0 a'® J2 o ro k X D) 100 ro E 13 M— E o w / CD 5 0 0 *f -----■------L. -1 ______I______I______I 0 4 6 . 8 [3H]Haloperidol (nM) Figure 9 Figure 10. Rosenthal plots of the same data as in Figure 9, which show straight lines, indicative of a single class of drug binding site. Data from a representative experiment are shown, each point being the average of three replicates within one experiment. 51 —I______1______1______I_ 50 TOO 150 200 Specific Bound Figure 10 cro n 53 splenocytes. Their Kd values are very close, all around 1 nM. A20 cells had more binding sites per cell, but less binding sites per mg of protein compared to rat splenocytes. This is probably due to the size of A20 cells. Because A20 cells are constantly dividing cells, they appear under the microscope to be much larger than splenocytes. Larger cell size would cause greater membrane surface, and space to have more binding sites per cell, but their higher cell membrane mass per cell resulted in less binding sites per unit protein. Haloperidol and Spiperone Modulate Splenic B Cell Proliferation, But Not Through Sigma Receptors A series of sigma agonists, haloperidol, DTG, (+) and (-)-pentazocine, and (-)-butaclamol were tested as described in Materials and Methods for their ability to influence anti-p induced murine splenic B cell proliferation in vitro. A suboptimal concentration of 0.5 pg/ml anti-p antibody was used in these experiments. Unlike the case with ConA-induced T cell proliferation, which was suppressed by sigma agonists, proliferation of B cells was enhanced by haloperidol in a dose dependent manner (Figure 11). However, the other sigma agonists mentioned above did not have any effect, indicating that haloperidol did not exert its effect through sigma receptors in this case. Later, we found spiperone was another drug that had the same effect as haloperidol did on anti-p induced B cell proliferation Figure 11. Haloperidol and spiperone enhance anti-p induced B cell proliferation in a dose-dependent manner. Conditions were as specified in Materials and Methods. * p<0.02, ** p<0.0005, *** p<0.0001 as determined by unpaired t-test comparing control and drug treated cells. The figure is a representative experiment, which was replicated five times. Each point in the figure represents average values of three replicates. If error bar is not visible, it is smaller than the symbol. 54 20000 * * * 1 6 0 0 0 spiperone 12000 * * 8 0 0 0 haloperidol 4 0 0 0 0 10'7 10'6 TO'5 Drug (M) Figure 11 56 (Figure 11). In the absence of anti-p antibody, neither haloperidol nor spiperone triggered B cell proliferation. Haloperidol and spiperone were then tested for their ability to influence the threshold concentration of anti-p antibody needed to trigger proliferation. Haloperidol or spiperone (10 pM) were incubated at 37°C with cells in microtiter plates for one hour, after which doubling concentrations of anti:p antibodies (0.078 - 1.25 pg/ml) were added to the wells. A constant amount of vehicle used to solublize drugs was present in all experimental and control groups. As shown in Figures 12A and 12B, in the absence of drugs, 0.31 2 pg/ml of antibody was required to produce significant [3H]thymidine uptake, while in the presence of 10 pM haloperidol or spiperone this threshold was reduced to 0.156 pg/ml. Again, neither haloperidol nor spiperone caused significant changes in [3H]thymidine incorporation in the absence of anti-p antibody (Figures 12A and 12B). Dopamine, Norepinephrine and Serotonin Modulate Anti-p Induced B Cell Proliferation Haloperidol and spiperone have similar pharmacological profiles. They are potent neuroleptics that bind to multiple receptors. They can act as D2 , 5HT2, and ai antagonists. Therefore we determined whether the endogenous ligands of D 2 receptors - dopamine, ai receptors - norepinephrine, and 5 HT2 receptors - serotonin, modulated anti-p induced B cell proliferation. Dopamine inhibited anti-p induced B cell proliferation in a Figure 12. Haloperidol and spiperone lower the threshold of anti-p needed to trigger B cell proliferation from 0.312 pg/ml to 0.156 pg/ml. (A): 10 pM haloperidol; (B): 1 0 pM spiperone. Conditions were as specified in Materials and Methods. * p<0.003, ** p<0.001, *** p<0.0001 as determined by unpaired t-test comparing control and drug treated cells. Representatives of two replicate experiments are shown. The bars in the figures represent average values of three replicates. 57 2 4 0 0 0 □ control 20000 ^ haloperidol Q. O a) 1 6 0 0 0 c * * * E >> 12000 JZ r—■M i x CO 8 0 0 0 I! * * 8 ? u a.CD 4 0 0 0 co 0 1------1______I______1___ 0 0 . 0 7 8 0.156 0.312 0.625 1.25 Anti-|i((xg/ml) Figure 12A Ol 00 24000 20000 □ control £ B Q. spiperone a g 16000 ig I 12000 x on 8000 y h — ‘o a ) Q. 4000 C/3 o 0 0.078 0.156 0.312 0.625 1.25 Anti-|i(|ig/ml) Figure 12B Ul CD dose-dependent manner (Figure 13), as did norepinephrine (Figure 14). In contrast, serotonin had no effect at 10‘8 M through 1 0-5 M concentrations, while at 10'4 M, serotonin caused a slight increase in [3H]thymidine incorporation (Figure 15). This unusual dose-response could be accounted for by the presence of serotonin in the fetal bovine serum used for our culture medium. Using a commercially available serotonin assay kit (Immunotech Inc., Westerbrook, ME), serotonin levels in the culture medium were found to be 3.4 - 3.7 pM. These results were consistent with haloperidol and spiperone modulating B cell proliferation by acting as antagonists at dopamine or norepinephrine receptors, but were not consistent with modulation of proliferation via antagonist actions at serotonin receptors. Spiperone Antagonizes the inhibitory Effect of Dopamine and Norepinephrine on Anti-p Induced B cell Proliferation To determine whether spiperone could antagonize the effects of dopamine and norepinephrine, B cells were co-incubated with varying concentrations of spiperone and these two endogenous agonists. Spiperone was used in these assays because it had a stronger modulating effect than haloperidol on B cell proliferation. As shown in Figures 1 6 and 1 7, proliferation at all concentrations of spiperone was reduced by the presence of either dopamine or norepinephrine. Conversely, the [3H]thymidine incorporation at all Figure 13. Dopamine inhibits anti-p induced B cell proliferation. Conditions were as specified in Materials and Methods. Figure is a representative experiment, which was replicated four times. Each point in the figure represents average values of three replicates. 61 6000 5000 £ Q. a 4000 a? c '-O £ 3000 -C 4—1 X 2000 co y 4— ' o 1000 -//- 0 10'7 10‘6 Dopamine (M) Figure 13 O) co Figure 14. Norepinephrine inhibits anti-p induced B cell proliferation. Conditions were as specified in Materials and Methods. Figure is a representative experiment, which was replicated four times. Each point in the figure represents average values of three replicates. 63 6000 5000 - 4000 - 3000 - 2000 - 1000 - 0 - Norepinephrine (M) Figure 14 Figure 15. Serotonin enhances anti-p induced B cell proliferation at 10'4 M. Conditions were as specified in Materials and Methods. Figure is a representative experiment, which was replicated three times. Each point in the figure represents average values of three replicates. 65 6000 5000 4000 3000 2000 1000 0 -// _i______i 0 10'7 10'6 10 ' 5 10 ' 4 5-HT (M) Figure 15 o> 0 5 Figure 16. Spiperone and dopamine antagonize each other’s effects on anti-p induced B cell proliferation. (A) 1 pM dopamine reduces [3H]thymidine incorporation in the presence of various concentrations of spiperone; (B) 5 pM spiperone increases [3H]thymidine incorporation in the presence of various concentrations of dopamine. Conditions were as specified in Materials and Methods. * p<0.02, ** p<0.003, *** p<0.0002 as determined by unpaired t-test comparing control (one-drug-treated) and two-drug-treated cells. Each figure is a representative experiment, which was replicated twice. Each point in the figure represents average values of three replicates. 67 Specific [3H]thymidine (cpm) 0 0 0 0 2000 0 0 0 4 0 0 0 6 0 0 0 8 0 Spiperone(M) Figure 16A Figure control 1|iM dopamine 1 4 0 0 0 * * * * * 5(iM spiperone 12000 ------// ■ i * * * Q. O 10000 Dopamine (M) Figure 16B CO CD Figure 17. Spiperone and norepinephrine antagonize each other’s effects on anti-p induced B cell proliferation. (A) 1 pM norepinephrine reduces [3H]thymidine incorporation in the presence of various concentrations of spiperone; (B) 5 pM spiperone increases [3H]thymidine incorporation in the presence of various concentrations of norepinephrine. * p<0.03, ** p<0.01, *** p<0.0002 as determined by unpaired t-test comparing control (one- drug-treated) and two-drug-treated cells. Conditions were as specified in Materials and Methods. Each figure is a representative experiment, which was replicated twice. Each point in the figure represents average values of three replicates. 70 Specific [3H]thymidine (cpm) 12000 10000 0 0 0 4 0 0 0 8 2000 0 0 0 6 Spiperone(M) Figure 17A Figure * * * 1|iM norepinephrine 1|iM control ** £ 14000 12000 10000 ^ *** 8000 6000 4000 control £ 2000 0 /A 10 ' 7 10 ' 6 10 ' 5 Norepinephrine (M) Figure 17B 73 concentrations of dopamine and norepinephrine was increased in the presence of spiperone (Figures 16 and 17). D2 antagonists, 5HT2 antagonists, andai Antagonists Do Not Enhance Anti-p Induced B Cell Proliferation In an attempt to mimic the actions of spiperone and haloperidol, we then tested a variety of dopamine, serotonin (5HT), and ai adrenergic receptor antagonists. These compounds included D-|, D 2 , D3 , D5 antagonists [(+)-SCH 23390, (-)-sulpiride, (+)-butaclamol], 5 HT2 and 5HT-|a antagonists [ritanserin, LY-53,857, pindobind-5HT1 A], ai antagonists [phentolamine, WB-4101 and 5-methyl-urapidil], and a agonists [methoxamine and clonidine]. Over a concentration range of 10'7 M to 1 0*5 M, none of these drugs enhanced anti-p induced B cell proliferation (Table 3). 74 Table 3. Drugs that do not enhance anti-jj. induced murine splenic B cell proliferation* sigma agonists DTG (+)-pentazocine (-)-pentazocine (-)-butaclamol Di antagonist (+)-SCH-23390 D2 antagonists (-)-sulpiride (+)-butaclamol D3 antagonist (-)-sulpiride D5 antagonist (+)-SCH-23390 5 HT2 antagonists ritanserin LY-53,857 5HTi a antagonist pindobind-5HT1 A ai antagonists WB-4101 5-methyl-urapidil phentolamine a agonists methoxamine clonidine * Enriched splenic B cells were cultured with drugs, stimulated with anti-p, pulsed with [3 H]thymidine, and harvested as described in Materials and Methods in a manner identical to that of the experiments shown in Figurel 1. Compounds were tested at 10'7, 10 '6 and 10 _5 M concentrations. Within each experiment, triplicate determinations were made for each drug concentration, and all experiments were replicated at least twice. CHAPTER VI DISCUSSION The present study is composed of two major parts. The first part is about the influence of sigma receptors on a commonly used measure of T cell responsiveness - ConA-induced proliferation. The second part is about the influence of sigma receptors on B cell proliferation. Sigma-1 Receptors Modulate T Cell Proliferation Our study on the effect of sigma receptors on T cell function resulted in three main observations: (i) sigma-1 receptors are present in rat spleen and on isolated splenocytes; (ii) a series of 1 5 sigma agonists and related compounds suppressed ConA-induced proliferation in a dose-dependent manner; (iii) drug suppression of ConA-induced proliferation correlated highly with the pharmacology of sigma-1 receptors in spleen. The regression of EC 50 values in bioassay versus K j values in binding assays had a slope approaching unity, which is suggestive of a one-for-one 75 relationship between sigma-1 receptor binding events and biological responses. The reliability of measurements was high for both Kj and EC 50 values. On a logarithmic scale, the standard errors of Kj and EC 50 values were 0.07 and 0.19 orders of magnitude, respectively. Therefore, the correlation was not significantly biased by errors in measurement. These results strongly support the hypothesis that drugs can modulate T cell functional activities via actions at sigma-1 receptors. It has been reported for more than a decade that PCP and PCP analogs can depress lymphocyte proliferation and alter secretion of antibody, IL-1 and IL-2 in vitro (60, 61), and that PCP can act at sigma receptors (94, 98). At the time of these initial observations, the presumed site of action of these drugs was referred to as the sigma/PCP receptor (98). Subsequently, two distinct receptors were recognized that could bind PCP (94). These are now termed sigma and PCP receptors. Although certain drugs can bind to both of these, the affinities of binding and the rank order of potency of compounds are distinctive for each (94). With the advent of more selective labels for PCP and sigma receptors, Wolfe and associates were able to examine the immune system and to determine that sigma receptors were present in abundance in both rat spleen and human circulating leukocytes, while PCP receptors were absent or below the threshold of detectability in these tissues (45,46). However, PCP and TCP have additional actions at a variety of other non-sigma sites, including several potassium channels (92, 93). Since these drugs fell right at the 77 confidence limit of our correlation, we can neither hypothesize, nor rule out, a contribution by other, non-sigma-1 receptors to the inhibition of proliferation caused by PCP and TCP. Because most sigma agonists also act at other receptors, it would be unrealistic to expect a perfect correlation between modulation of cell proliferation and drug binding potency at sigma-1 receptors. Nonetheless, all but three of the fourteen tested agonists clearly fell within the 95% confidence limits of the correlation, and gave a collective r value of 0.84, inclusive with the reference group (r value of the reference group alone was 0.86). Most significantly, none of the compounds tested were less potent in suppressing proliferation than was predicted by their relative binding potencies at sigma-1 sites. We interpret this as very strong, if not definitive, evidence that sigma-1 receptors on rat splenocytes are physiologically active. In our hands, the immunosuppressive effect of sigma agonists required drug concentrations several orders of magnitude greater than their K d or K j values in binding assays. This is common in other bioassays of sigma agonists as well (58, 60-62). Five possible explanations for this are: 1) The buffer used for binding assays is different from tissue culture medium in many respects, such as pH, ionic strength, the presence of specific ions, and the presence of exogenous proteins in serum. In the tissue culture medium in which the cells encountered drugs, the binding affinities of sigma 78 agonists may be lower than the Kd and Kj values obtained under optimized binding conditions. 2) Over the course of two-day cultures with live cells, sigma agonists may be metabolized into inactive forms. Therefore, higher initial drug concentrations may be required in order to maintain effective drug levels for the duration of the cultures. 3) Binding sites for sigma ligands have been reported to reside within cells, as well as on the external surfaces of the plasma membranes (99). Proliferation assays used intact cells, while binding assays were done with disrupted cytoplasmic membranes plus internal membranes and nuclei. If the biologically active sigma receptors reside within cells, and if the cytoplasmic membrane is not completely permeable to the drugs, elevated drug concentrations in the medium may be required to reach effective levels at the site of the active receptors within cells. 4) Since we observed an inhibition of activity, it might be a nonspecific toxic, rather than a receptor-mediated effect. Sigma agonists have been reported to be toxic to glioma cells over periods of about one week in culture (100). W e saw no short-term drug toxicity evidenced by trypan blue vital dye exclusion. However, in the absence of stimulation, lymphocytes tend to gradually die off in culture, and it is difficult to distinguish between slow toxic effects and a drug-mediated blockade of the mitogenic stimulus (Con A). Recently, Casellas and associates (66) reported that a novel 79 sigma ligand, SR 31747, could suppress proliferation of human lymphocytes, and argued that this suppression was not due to toxicity, because after 1 20 hours of drug-induced suppression the cells could be restored to full mitogenic responsiveness by removal of the drug. Regardless, the correlation of biologic effect with the pharmacology of sigma-1 receptors in our hands indicates that if this is a toxic effect, it is mediated through drug actions at sigma-1 receptors. 5) Suppression of ConA-induced proliferation may not occur unless a very high percentage of sigma-1 receptors are occupied. Scenario #1, above, seems improbable because we have performed binding studies in RPMI-1640 culture medium with the identical additives as were used for cell cultures, and we observed no significant changes in affinities of drug binding. At this time, we cannot distinguish among the remaining four possibilities. Sigma-1 receptors are selective for the (+)-stereoenantiomers of 3-PPP and the psychotomimetic benzomorphans (pentazocine and SKF 10,047), while sigma-2 receptors display minimal, or the reverse, selectivity (16). In the proliferation assay, (+)-pentazocine, (+)-SKF 10,047 and (+)-3-PPP were invariably more biologically potent than their (-)-stereoenantiomers in all experiments, although the differences were less pronounced than expected by their relative binding affinities (Table 1 and Figure 8). It should be emphasized that all stereoisomers of these compounds fell within the 95% prediction interval of the correlation. Therefore, no actions by these compounds at non-sigma-1 sites are predicted or supported by our data. However, it is tempting to suggest possible explanations for this reduction of stereoselectivity. One of these is that the stereoselectivity that we observed in binding assays is an artifact of the buffer conditions, and that the receptor is less stereoselective in physiological buffers. However, in our hands, competition binding revealed no diminution of stereoselectivity in tissue culture medium. Therefore, we consider it more probable that other receptors may have made minor contributions to our proliferative assays. Receptors of particular interest in this regard are sigma-2, dopamine, and opiate receptors. There is evidence that both sigma-1 and sigma-2 receptors are biologically active. Sigma-1 sites appear to mediate the inhibition of electrically- and 5-HT-induced contractions of guinea pig ileum (56), the modulation of muscarinic acetylcholine receptor-triggered phosphoinositide turnover in brain (29, 30), and nicotinic receptor function in adrenal chromaffin cells (58). On the other hand, it is most likely that the dystonia from microinjection of sigma agonists into the rat red nucleus (55), and modulation of potassium channels (16, 85) are mediated through sigma-2 sites. Interestingly, sigma-1 and sigma-2 receptors can coexist. For example, rat liver contains approximately 25% sigma-1 sites and 75% sigma-2 sites (17); rat brain also contains both sites (101). Our preliminary experiments support the notion that sigma-2 receptors are also present along with sigma-1 receptors in immune tissues. Using [3H]DTG under sigma-2 receptor-selective conditions (16), we have labeled specific binding sites in splenic homogenates, isolated splenocytes, and T and B cell lines (Wolfe et al., unpublished). However, the data we present here do not correlate with the pharmacological profile of sigma-2 receptors (18). Therefore, while a minor contribution by these receptors cannot be excluded, the overall pattern that we observed cannot be accounted for on the basis of drug actions at sigma-2 sites. There is overlapping drug specificity between dopamine, 5 -HT2 (serotonin) receptors and sigma receptors. Haloperidol is most commonly known for its actions as a dopamine receptor antagonist (reviewed in 13). However, the carbonyl-reduced metabolite of haloperidol (haloperidol metabolite II) has almost the same affinity to sigma receptors as haloperidol, but an 85-fold lower affinity to dopamine receptors; the chlorophenyl-hydroxy- piperidine metabolite of haloperidol (haloperidol metabolite I) lacks affinity for dopamine receptors, but has a moderate affinity for sigma receptors (102). Both of these haloperidol metabolites were immunosuppressive (Table 1), and fell within our correlation (Figure 8). Furthermore, the D 2 dopamine antagonist (-)-sulpiride failed to affect proliferation. Thus, it seems unlikely that D 2 receptors had a significant contribution to the immunosuppressive effect we observed. At this time, we cannot rule out a minor contribution by D 5 dopamine receptors (80), but it should be emphasized that our over-all correlation of suppression of proliferation with sigma-1 receptor binding indicates that sigma-1 82 sites play the predominant role in the present study. We obtained highly selective labeling of sigma-1 receptors with [3H]haloperidol by blocking dopamine and 5 -HT2 (serotonin) receptors with excess spiperone in all radioligand binding assays. We demonstrated the sigma-1 pharmacology of the sites labeled in this manner (Table 1), and showed a correlation between these drug binding sites and regulation of cell proliferation. Therefore, contributions by dopamine and serotonin receptors to the present findings must be minimal. Opiate receptors are known to be present on immune cells, and to affect a variety of functional activities, but the literature in this field is inconsistent. Our data are consistent with drug actions via sigma-1 receptors. However, we consider it probable that interactions of opiate compounds with sigma-1 receptors, such as was the case with (-)-pentazocine and (-)-SKF 10,047 in this study, may be responsible for some of the confusion in the opiate literature. Rimcazole is a putative sigma antagonist (14,96,97). As such, it should have had no effect in this system unless endogenous sigma agonists were present in the culture medium, or were generated by the cells in culture. Although, as expected, rimcazole was the only clear outlier, it was not expected to affect the system in the same direction as the agonists. We must assume that this relatively uncharacterized compound has additional, non-sigma actions that have yet to be described. 83 The mechanism by which sigma-1 receptors modulate T cell proliferation is unknown, though one might speculate an inhibitory action on T cell phosphoinositide turnover in splenocytes. Such an action would be similar to that reported for rat synaptoneurosomes (29) rat cortical brain slices (103) and pheochromocytoma cells (101). There have been reports of sigma-1 receptor coupling to guanine regulatory proteins (25, 26), but no evidence for this was found in other studies. Dornand and associates (61), found that PCP prevented resting splenocytes from hyperpolerizing, and reduced subsequent mitogen-induced depolarization and calcium mobilization. However, our data indicate that PCP and TCP may have additional, non-sigma-1 actions on splenocytes. Thus, it is not clear which receptors are responsible for the phenomena reported by Dornand and associates. It is clear that a major obstacle to investigations into the physiologic role of sigma receptors is the broad cross-reactivity of many or most sigma agonists and antagonists with other, non sigma receptors. Much effort has recently been devoted to developing and characterizing more sigma-selective compounds (47-50). The intent of the present study was to correlate function with the “classical” pharmacology which has been reported for sigma binding sites. Based on this approach, we did find that sigma-1 receptors modulate ConA-induced T cell proliferation. Future studies in the immune system, in particular examination of cell signaling and early gene activation, are planned which will utilize several of these newly-developed compounds. 84 Sigma Receptors Do Not Modulate B Ceil Proliferation The second part of our investigation is about the influence of sigma receptors on B cell proliferation. This was carried out with enriched murine B cells from spleen. What we found was: (i) sigma -1 receptors are present in mouse whole spleen (Whitlock and Wolfe, unpublished data); (ii) sigma-1 receptors are present in a mouse B lymphoma cell line, A20; (iii) sigma receptors did not modulate anti-p induced murine splenic B cell proliferation; (iv) the neuroleptics haloperidol and spiperone potentiated anti-p induced murine B lymphocyte proliferation in vitro, and lowered the threshold of antibody needed to trigger proliferation. However, their actions are not due to actions at known dopamine, serotonin, a1 adrenergic, or sigma receptors. As mentioned above we have identified sigma-1 receptors in rat splenocytes, and demonstrated that sigma agonists could modulate T cell function through these receptors. The second part of our study was undertaken to determine whether sigma receptors have comparable physiologic effects on B cells. Our laboratory has shown that sigma-1 receptors are also present in mouse whole spleen membrane preparations (Whitlock and Wolfe, unpublished data). Because of the great difficulty obtaining a large number of purified B cells from mouse spleen, we used a mouse B lymphoma cell line, A20, as a pure source of mouse B cells, for radioligand binding assays. The reason that we switched to a mouse system was that two previous studies on sigma receptors and B cell 85 functions were done with mouse spleen B cells (62, 63). We felt that we would be able to compare our finding with their results better if we use mouse instead of rat. Sigma receptors were reported by Carr and associates (62, 63) to regulate proliferation and immunoglobulin production by B cells in vitro. These investigators found that the sigma agonists DTG, (+)-pentazocine, (-)-pentazocine, and haloperidol could enhance LPS-induced mouse splenocyte proliferation. However, these studies were performed with unfractionated splenocyte populations. Because LPS is not only a B cell mitogen, but also activates monocytes and macrophages, it is highly likely that cell cross-talk via cytokine secretion occurred in these cultures. Therefore it is difficult to conclude from these studies that the reported effects were due solely to direct actions of drugs at sigma receptors on B cells. Furthermore, using either all splenocytes or adherent cell- depleted splenocytes stimulated by LPS, we could not repeat the results reported by Carr and associates (62). The report by Carr and associates on modulation of antibody production by sigma receptors is also questionable. Their dose-response curves were uninterpretable to us, and while some sigma agonists enhanced LPS- or PWM- induced immunoglobulin production, others did not have any effect or even caused inhibition (63). Therefore we consider the effect of sigma receptors on B cell functions to be unsettled. In the present study, we have sought to minimize the effects of other cells on the measured B cell responses by: 1) removing T 86 cells, macrophages and monocytes, and using enriched B cell populations; and 2) using anti-p antibody, which provides a more selective B cell proliferative stimulus than does LPS. Although we have identified sigma receptors on mouse spleen and the A20 B lymphoma cell line, in our studies the classical sigma ligands DTG, (+)-pentazocine, (-)-pentazocine, and (-)-butaclamol had no effect on anti-p triggered B cell proliferation. We conclude that either: 1) the modulation of proliferation reported by Carr and associates (62) was due to drug actions at sigma receptors on contaminating non-B cells in their cultures; or 2) since LPS and anti-p activate different intracellular signals, it might be the case that LPS-stimulated B cell triggering events are susceptible to modulation by sigma receptors, while those initiated by crosslinking of cell surface IgM with anti-p antibody are not. In addition, 3) it may be that differentiation and maturation of B cells to antibody production (63) is sigma receptor- sensitive, while proliferation of B cells is not. Future experiments are planned to distinguish among these three possibilities. Haloperidol is a potent ligand at sigma receptors (88), at which spiperone may also bind (104). Haloperidol-displaceable [3H]spiperone binding sites have been observed on lymphocytes (73), primarily on B cells (74). In the present study, we found that haloperidol and spiperone could modulate B cell proliferation in vitro. Unlike the case with T cells, which are suppressed by sigma agonists, proliferation of B cells was enhanced in a dose-dependent manner by these two compounds. However, other sigma agonists had no effect on anti-p induced B cell proliferation, 87 indicating that haloperidol and spiperone did not exert their effects through sigma receptors in this case. Haloperidol and spiperone are largely used as antagonists of dopaminergic-D 2 and serotonergic-5HT2 receptors in the central nervous system (CNS). Because of its strong antagonism at CNS D2 receptors, haloperidol is a commonly prescribed neuroleptic used in the treatment of psychotic disorders. Haloperidol and spiperone also have moderate affinity at ai adrenergic receptors. The present findings indicate that haloperidol and spiperone act not only in the CNS, but also directly on B lymphocytes. Therefore, our next working hypothesis was that haloperidol and spiperone act on B cells through one of the major non-sigma receptors, at which they are known to act in non-immune cells: dopamine (D 2 ), serotonin ( 5 HT2 ), or adrenergic (ai) receptors (12, 105). Dopaminergic, serotonergic and adrenergic receptors are known to be present on immune cells. Although the existence of dopamine D 2 receptors on immune cells is still a matter of debate (76, 79), D 3 and D 5 receptors have been identified on human peripheral blood lymphocytes by both molecular biology and radioligand binding techniques (77, 78, 80, 81). Serotonin has been shown to regulate the functions of T cells, pre-B cells, macrophages, and NK cells (82, 83, 106-108), and serotonin 5HTia receptors have been identified on activated human T cells (83). (3-Adrenergic receptors have been demonstrated on lymphocytes, macrophages and granulocytes (70, 72,109). Although evidence for the presence of a-adrenergic receptors on immune cells is mostly 88 indirect (71,110-112), they may be present on low frequency cell subpopulations. Consistent with the notion that haloperidol and spiperone might be acting as dopaminergic or adrenergic antagonists in our system, we found that the endogenous agonists for these receptors (i.e., dopamine and norepinephrine) down-regulated B cell proliferation (Figures 13 and 14). Spiperone reversed the effects of both dopamine and norepinephrine in that it increased [3H]thymidine incorporation (Figures 16 and 17). However these experiments did not produce definitive shifts to the right in dose-response curves as expected for receptor antagonism. These experiments (Figures 16 and 17) are consistent with two interpretations, either: 1) the measured responses are simply the additive effects of actions at two or more entirely different receptor systems, or 2) agonist (dopamine or norepinephrine) is present in the culture medium, or is released in an autocrine manner by the cells in culture. To test this, other adrenergic and dopaminergic antagonists were screened in order to determine whether they could mimic the effects of haloperidol and spiperone. Li and associates (113) demonstrated that norepinephrine inhibits anti-jo. induced B cell proliferation by acting on P-adrenergic receptors. However, since haloperidol and spiperone have little or no activity at p-receptors (12,105), they most likely act through a different mechanism in our system. Therefore we tested the a-adrenergic antagonists phentolamine, WB-4101 and 5-methyl-urapidil. These compounds had no effect on B cell 89 proliferation; nor did the a-adrenergic agonists methoxamine and clonidne (Table 1). Therefore, it is likely that haloperidol's and spiperone's effect is not mediated by a or p-adrenergic receptors. Haloperidol and spiperone are antagonists with high affinity at dopamine D 2 receptors, and moderate to low affinity at D 3 and D5 sites. However, because the D2 antagonist (+)-butaclamol, the D2 /D3 antagonist (-)-sulpiride, and the D 1/D5 antagonist (+)-SCH-23390 had no effect (Table 3), it is most likely that haloperidol and spiperone did not potentiate B cell proliferation in our cultures through antagonist actions at D-|, D 2 D3 or D 5 receptors. This does not indicate, however, that dopamine receptors are absent from or do not modulate the functions of murine B cells, or that haloperidol and spiperone could not act at those receptors to modulate function if dopamine were present in our cultures. To the contrary, exogenously added dopamine was found to suppress proliferation (Figure 13), and spiperone opposed this effect (Figures 1 6 A and 16B). Interestingly, it may be that dopamine inhibits proliferation indirectly, by suppressing autocrine production of prolactin and thyrotropin by B cells in culture. Prolactin is an immunopermissive hormone (114-116), and thyrotropin can enhance lymphocyte proliferation (117). These hormones are made by lymphoid cells, and dopamine has been reported to cause B lymphoma cell death by inhibiting prolactin and thyrotropin release (118). Regardless, our results suggest that dopamine was not present in our culture medium, and was not 90 secreted by the cells in an autocrine manner. Thus, in the absence of agonist, no alteration of functional activity would be expected by dopamine antagonists. Exogenous serotonin (5-hydroxytryptamine, 5HT) did not suppress proliferation. It had no effect on B cell proliferation at 10 (iM or lower concentrations, while at 100 pM a slightenhan cement was observed. This dose-response was probably due to the presence of serotonin in the fetal bovine serum used for cultures, which we determined to be at a final concentration in the medium of 3.4 - 3.7 pM. Regardless, because the 5HT2 antagonists ritanserin and LY-53,857 failed to mimic the actions of haloperidol and spiperone, and because exogenous serotonin influenced the proliferative response in the same direction as did haloperidol and spiperone, it is unlikely that serotonin receptor antagonism is the basis of haloperidol's and spiperone's actions in this system. It is possible that haloperidol and spiperone act on B cells through separate mechanisms. Although these two compounds bind almost the same receptors, there are exceptions. Most importantly, spiperone is a potent 5 HTia receptor antagonist, while haloperidol has low affinity at this site (12, 105). To this end, the 5HT-ia receptor antagonist pindobind-5HT1 A was tested, and found not to enhance B cell proliferation. Therefore, we do not believe the present phenomenon was mediated by 5 HTia receptors on B cells. There have been previous reports of effects of haloperidol or spiperone on immune activities. As mentioned above, our studies have shown that haloperidol can act at sigma-1 receptors to inhibit ConA-induced rat splenocyte (presumably, T cell) proliferation. Others have found that haloperidol could inhibit natural killer activity or Epstein-Barr virus infection of B lymphocytes (119, 120). Sharpe and associates (121), found that systemic or topical spiperone could inhibit cutaneous contact hypersensitivity in mice, and that its mechanism of action was apparently independent of either dopamine or serotonin receptors. In the present investigation, haloperidol and spiperone modulated B cell proliferation by an unkown mechanism. Summary And Conclusions In summary, we have found that suppression of ConA-induced proliferation correlates with the pharmacology of sigma-1 receptors on splenocytes. Most other physiological assays involving sigma receptors have utilized preparations containing neuronal elements, and elicited responses with electrical stimulation or by means of neurotransmitters such as norepinephrine or 5-HT (29, 56, 58, 122-124). To the best of our knowledge, the splenocyte proliferative response to the mitogen, Con A, is the first demonstration of sigma receptors modulating a function that does not involve neuronal elements or induction of responses by neurotransmitters or neuroactive drugs. This implies that sigma agonists have a direct effect on immune cells. Since sigma receptors have been identified in the nervous, endocrine and immune systems (40,45,46), it is 92 reasonable to suggest that endogenous sigma ligands may play a important role in neuroimmune modulation. Also, we have shown that sigma receptors have no effect on anti-p induced B cell proliferation. This finding is in contrast to other reports (62, 63) that sigma receptors modulate proliferation and immunoglobulin production by heterogeneous splenocyte populations stimulated with LPS. In addition, the present study reports that the neuroleptics haloperidol and spiperone enhance mouse splenic B cell proliferation triggered by anti-p antibody. Among the endogenous agonists haloperidol and spiperone are known to antagonize, dopamine and norepinephrine inhibited and serotonin enhanced B cell proliferation in our system. Although in our hands spiperone could oppose the suppression of proliferation by dopamine and norepinephrine, the inability of other antagonists to enhance proliferation suggests it is unlikely that the effects of haloperidol and spiperone in this system are due to actions at Di, □ 2 . D3 . D5 , o ra i, receptors. By the same logic, it is also unlikely that the enhancement of proliferation was caused by actions at 5 HT2 , 5HTi a or sigma receptors. The specific mechanism by which haloperidol and spiperone modulate anti-p induced mouse splenic B cell proliferation remains to be determined. There is significant exposure of humans to compounds that can act at sigma receptors. Among these are the prescribed drugs haloperidol (haldol), chlorpromazine (thorazine), perphenizine, thioridazine, pentazocine and antiinflammatory steroids, and the abused drugs PCP, cocaine, and possibly anabolic steroids. Except for steroids, these drugs are used primarily for their effects at other receptors in the brain. 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