Uva-DARE (Digital Academic Repository)

UvA-DARE (Digital Academic Repository)

The human histaminergic system in health and neuropsychiatric disorders

Shan, L.

Publication date 2012

Link to publication

Citation for published version (APA): Shan, L. (2012). The human histaminergic system in health and neuropsychiatric disorders.

General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons).

Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: https://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible.

UvA-DARE is a service provided by the library of the University of Amsterdam (https://dare.uva.nl) Download date:28 Sep 2021 Chapter 10

General Discussion

L. Shan, A.M. Bao, and D.F. Swaab. Manuscript in preparation

127 Chapter 10

Content Summary and General Discussion 1. Physiology of neuronal histaminergic system 1.1 Age dependency 1.2 Sexual dimorphism 1.3 Diurnal differences in histamine production 2. Histaminergic system in neuropsychiatric disorders 2.1. Parkinson’s disease 2.2. Alzheimer’s disease 2.3. Huntington’s disease 2.4. Multiple sclerosis 2.5. Depression 2.6. Schizophrenia 3. Histamine receptor-3 antagonists/inverse agonists: clinical implications 4. Limitations of the thesis

Neuronal histamine is exclusively produced bels we obtain from the industry are often of low in the hypothalamic tuberomamillary nucleus quality, we routinely tested them, prior to a large (TMN) via the key enzyme histidine decarboxy- HDC experiment, for high abundant genes such lase (HDC). These histaminergic TMN neurons as vasopressin. project to a large number of brain areas (Haas et Using the optimized quantitative radioactive in al., 2008) where they play important roles in basic situ hybridization protocol, we investigated the physiological functions, such as the sleep-wake neuronal histaminergic system in non-neuro- cycle, energy and endocrine homeostasis, sensory psychiatric subjects in relation to age, sex, and and motor functions, cognition, attention, and le- day-night fluctuations, and in neuropsychiatric arning and memory (Haas et al., 2008). disorders including Parkinson’s disease, Alzhei- For the current thesis, we introduced a number mer’s disease, Huntington’s disease, depression of alterations in an otherwise routine protocol in and schizophrenia. order to create optimal in situ hybridization conditions for quantification of the mRNA expression of HDC in formalin-fixed, paraffin-embedded archival postmortem human brain tissue. These alterations included (1) omitting glycogen as a carrier for precipitation during purification of the oligo-probes, (2) dissolving the labeled probe contained within the pellet after precipitation first in water instead of in hybridization buffer (HBF), (3) increasing the dithiothreitol (DTT) concentration during hybridization, and (4) increasing the stringencies during hybridization and post-hybridization washes by increasing the temperature (Chapter 2). It should be noted that this optimized protocol is still very sensitive to the quality of the radioactive label. Since the la-

128 General Discussion

1. Physiology of neuronal Because our group has found that both estrogen histaminergic system in brain receptor (ER)-α and -β are expressed in human TMN neurons (Kruijver et al., 2003), it appears 1.1. Age dependency that the TMN is sensitive to sex hormones. In ad- The function of the neuronal histaminergic sys- dition, a stronger cytoplasmic ER-β staining was tem has been reported to be age-dependent. An observed in women than in men (Kruijver et al., age-related decline in histamine 1 receptor (H1R) 2003), which may be targeted by the fluctuating binding in the normal human brain was reported estrogen levels in women. Moreover, the hista- by a positron emission tomography (PET) study, mine receptors showed sexually dimorphic ex- especially in the prefrontal, temporal, cingulate pression levels. A PET study showed higher H1R and parahippocampal regions (Yanai et al., 1992). binding potential in human females compared Judging by the levels of the main histamine meta- to age-matched males (Yoshizawa et al., 2009). bolite tele-methylhistamine (t-MeHA), the neuro- Furthermore, also in the rat cerebral cortex H1R nal histaminergic system showed a developmental and H2R binding were higher in females than in pattern with peak level in infants (Kiviranta et al., males (Ghi et al., 1991). 1994), after which the levels of t-MeHA in cere- We reported a slightly but not significantly higher brospinal fluid (CSF) decreased to near-adult va- (32%) TMN neuron number in 4 females compa- lues in adolescent subjects. This study was done red with 5 male subjects. This was in agreement in 81 children with ages ranging from 3 months with HDC-mRNA expression, which showed sig- to 14.6 years (Kiviranta et al., 1994). In elderly nificantly higher (46%) levels in female than in subjects (97 non-demented controls, age range male subjects (Chapter 7 ). It should, however, 34-101 years), the t-MeHA levels were found to be noted that we did not observe such sexual di- be positively correlated with age (Motawaj et al., morphism of HDC-mRNA expression in a lar- 2011, Prell et al., 1988). ger group (n = 35, female = 11, male = 24) not However, we did not observe any age-related matched for brain weight or pH (Chapter 3). A changes in the level of HDC-mRNA expression slightly but not significantly higher histaminergic in the TMN for the combination of all our con- system activity in females was also revealed in the trol subjects (n = 35, age range 44-93, see Ge- higher (about 20%) levels of histamine main me- neral Introduction, Figure 5). It should thus be tabolite t-MeHA levels in CSF (n = 97, female = investigated whether the age-dependent changes 47, male = 50) (Motawaj et al., 2011, Prell et al., of the neuronal histaminergic system are exhibi- 1988). Apparently there are no large sex differen- ted exclusively in the event of inactive histamine ces in the histaminergic system in controls. in the brain. Interestingly, we found significant sex differences in the neuronal histaminergic system in 1.2. Sexual dimorphism Parkinson’s disease (Chapter 4). For the pooled PD group, which included clinical PD and pre- As mentioned above, the levels of CSF-t-MeHA clinical PD patients, female PD patients sho- reach peak levels in infants, then decrease to near- wed significantly lower HDC-mRNA expres- adult values in adolescent subjects. In adult cases sion than the pooled male PD patients (Mann a higher level of t-MeHA was observed in women Whitney U test P = 0.004), and lower than the than in men (Motawaj et al., 2011, Prell et al., pooled female controls (P = 0.035) (Figure 1). 1988). These data suggest a similar developmen- There was no significant difference in HDC- tal pattern of the neuronal histaminergic system to mRNA expression between the pooled male e.g. that of the sexually dimorphic nucleus of the PD patients and the pooled male controls (P = preoptic area, in which cell numbers reached peak 0.753) (Figure 1). The pooled data of female PD values at the postnatal age of 5 years, after which and female control subjects and the pooled data a sex difference arises (Swaab et al., 1988). of male PD and male control subjects were still

129 Chapter 10 well-matched (all P ≥ 0.165) for age, postmortem Our findings showed that HDC-mRNA expres- delay, fixation time, Braak stage for Alzheimer’s sion was significantly higher during the daytime disease (van de Nes et al., 1998) and clock time of (08:00-20:00 hr) than at night (20:00-08:00 hr) in death. A pooled data comparison was also perfor- the control group (Chapter 3) which agrees well med. However, because this study was not aimed with the rat data of Mochizuki et al. (Mochizuki at researching sex differences, the validation of et al., 1992), who showed that histamine release the sex difference we found needs to be performed increased in the active period (20:00-08:00 hr) as in a larger and well-matched group. compared to the sleep period (08:00-20:00 hr). The estimated acrophase of HDC-mRNA expres- 1.3. Diurnal rhythmicity of HDC-mRNA sion in controls at 18:09 hr in our study agrees also very well with the recent finding of an acrop- Accumulating results show that drugs that reduce hase for the histamine rhythm at 17:49 hr in diu- histamine signaling, including traditional antihis- rnal nonhuman squirrel monkeys (Zeitzer et al., tamines such as the H R antagonists diphenhydra- 1 2011). In addition, this day-night fluctuation was mine and pyrilamine, and low doses of doxepin found to be markedly different in patients with may increase sleep (Krystal et al., 2010, Lin et al., neurodegenerative diseases, including Parkin- 1988, Monti et al., 1986, Roehrs et al., 1984). In son’s disease, Alzheimer’s disease and Hunting- addition, mice lacking histamine show less wake ton’s disease patients with an acrophase at 8:56 hr fulness (Parmentier et al., 2002). These data sug- (Chapter 3). gest that the histaminergic system may be important for maintenance of wakefulness (Espana et Future Perspectives al., 2012). In many species, neuronal histamine displays a di- 1) Investigation of the development and sexual urnal rhythm with high levels during the waking dimorphism of the histamine production sys- period and low levels during the sleeping period tem in the human brain, will require larger (Haas et al., 2008, Lin, 2000). Increased hista- groups and bigger age ranges from both gen- mine release, TMN neuronal electrical activity, ders. and higher c-fos expression were shown during 2) Investigation of whether the neuronal hista- the dark period in the hypothalamus of nocturnal minergic system undergoes an age-dependent rodents (Mochizuki et al., 1992, Prast et al., 1992, change and to study these changes in health Takahashi et al., 2006). In addition, microdialysis and disease, histamine or histamine metabo- and quantitative radioenzymatic assays revealed lite levels in the CSF must be measured. The a considerably higher histamine concentration in Netherlands Brain Bank has collected a large the cat preoptic/anterior hypothalamic area during number of CSF samples from people with the waking stage as compared to the sleep stage neuropsychiatric disorders and from controls, (Strecker et al., 2002). One report showed that t- including the subjects whose HDC-mRNA MeHA levels in lumbar puncture CSF of febrile we measured. It would be of significance to children and infants are higher during the day study the relation between the histamine pro- time (06:00-20:00 hr) than at night (20:00-06:00 duction and the CSF-histamine levels. Howe- hr) (Kiviranta et al., 1994). Moreover, sleep-wake ver, it should be noted that, due to the fact that perturbations are frequently observed in people CSF-histamine levels are very low (at some using antihistaminergic medication (Espana et al., pg/ml concentration levels), the standard high- 2012) and patients suffering from neurodegenera- performance liquid chromatography (HPLC) tive disorders such as PD, AD and HD (Arnulf et could not offer a convenient and reliable mea- al., 2002, Aziz et al., 2011, Riemersma-van der surement. It is expected that HPLC combined Lek et al., 2008). with mass spectrum detector may be of assis- tance here.

130 General Discussion

3) To confirm the disturbed diurnal rhythm of the not influence HDC-mRNA expression during the neuronal histaminergic system in neurodege- course of PD (Chapter 4). In fact, there is incre- nerative disorders, a larger group of patients asing evidence that the presence of these com- with individual diseases have been collected pact inclusions represents a protective mechanism and should be studied. on the part of the surviving cells (Tanaka et al., 2004, Tompkins et al., 1997) and protects the cell, 2. Histaminergic system in e.g., by the uptake of misfolded and non-functio- neuropsychiatric disorders nal proteins (Olanow et al., 2004, Shults, 2006), whereas evidence that the α-synuclein aggre- 2.1. Parkinson’s disease (PD) gates in PD are neurotoxic is lacking (Lee et al., PD patients frequently show symptoms other than 2008). In addition, studies have reported on cell their motor problems, such as mood disorder, and animal models with different neurodegene- sleep problems, and cognitive decline (Boeve et rative diseases developing inclusion bodies that, al., 2007, Braak et al., 2006, Quelhas et al., 2009, conversely, correlate with cell death (Ross et al., Riedel et al., 2010), all of which involve functi- 2005). We found an unchanged HDC mRNA ex- ons that are at least partly regulated by histamine pression, not only in clinical PD, but also in pre- (Haas et al., 2003). In addition, the abundant ac- clinical PD (i.e. patients who did not have clinical cumulation of the characteristic neuropathologi- PD symptoms but in whom PD pathology was cal PD lesions, Lewy bodies (LBs) and Lewy neu- beginning to develop (Braak et al., 1996, Braak rites (LNs), in the TMN of PD patients presumed et al., 2003)), while there was no accumulation of a destruction of this nucleus in the course of the LBs and LNs in the TMN. There seems, therefore, disease (Braak et al., 1996, Braak et al., 2003). to be no enhancement of histamine production in Moreover, animal studies showed that endoge- the early stages of PD, as has been presumed on nous histamine might play an important role to the basis of animal experiments (Liu et al., 2007). accelerate the course of disease. In the 6-hydroxy- It is very meaningful that our study (Chapter 5) dopamine (6-OHDA)-lesioned rat, a classic PD showed that there was an up-regulation of HMT- model, an increase of endogenous histamine ap- mRNA in the putamen and SN of PD patients, peared to enhance the apomorphine-induced tur- which was in line with the increased histamine ning behavior and to increase the loss of tyrosine levels that were reported in the same brain areas hydroxylase (TH) in the SN (Liu et al., 2008). A of PD patients (Rinne et al., 2002). These results decrease of endogenous histamine by injection of plead for the possibility that histamine stimulates α-fluoromethylhistidine, an irreversible inhibitor the PD process in its projection brain areas. of HDC, strongly reduced rotation behavior and The up-regulation of HMT-mRNA may act as a prevented the loss of TH-expressing cells in an protective mechanism by metabolizing enhanced early stage of the 6-OHDA lesion in the rat (Liu levels of histamine in these brain areas. Such a et al., 2007). protective effect might be crucial, because pre- In contrast to the presumed degeneration of the vious animal experiments have shown that in- TMN in PD, no clear changes of HDC-mRNA creased histamine levels in the SN may cause were observed in the TMN in PD in our studies degeneration of dopaminergic neurons (Liu et al., (Chapter 4). This is in agreement with other stu- 2007, Vizuete et al., 2000). The significant inverse dies in PD patients showing an intact number of correlation between HMT-mRNA expression and histaminergic neurons (Nakamura et al., 1996), disease duration in the SN of PD patients suggests stable HDC enzyme activity (Garbarg et al., 1983) that the more serious (and thus the shorter lasting) and unaltered t-MeHA levels in the CSF (Prell et the disease, the more expression of HMT-mRNA, al., 1991) in PD. Our observations also showed which may be explained as a brain mechanism to - for the first time - that the accumulation of protect it against PD. Lewy bodies and Lewy neurites in the TMN did

131 Chapter 10

Future Perspectives cytoplasmic inclusions of mutant huntingtin, the neuropathological hallmark of HD (Aziz et al., 1) To investigate the functional relevance of the 2008) (General introduction Figure 7), so an in- increased HMT-mRNA in the SN and striatum volvement of the histaminergic system in HD was of PD patients, measurement of histamine and/ presumed. or histamine metabolite concentration in this We found an increase in HDC-mRNA levels in brain tissue may be of help, and may provide a the TMN and an increase in HMT-, H R- and better insight into local histamine alterations. 1 H R-mRNA levels in the inferior frontal gyrus 2) In the 6-hydroxydopamine (6-OHDA)-les- 3 (IFG) of HD patients. In addition, we observed ioned rat, a classic PD model, an increase of a significant negative correlation between age endogenous histamine appeared to enhance at onset of the disease and HMT-mRNA, which the apomorphine-induced turning behavior suggests that the more serious (thus the shorter and to increase the loss of tyrosine hydroxyla- lasting) the disease, the more HMT-mRNA is ex- se (TH) in SN (Liu et al., 2008). Furthermore, pressed. Since the levels of histamine metabolites a decrease of endogenous histamine by injec- in CSF have also been shown to be increased in tion of α-fluoromethylhistidine (α-FMH), an HD patients, it all points to an enhanced acti- irreversible inhibitor of HDC, strongly redu- vity of the neuronal histaminergic system in HD ced rotation behavior and prevented the loss (Chapter 6). of TH-expressing cells in an early stage of the These findings suggest a functional increase in 6-OHDA lesion in the rat (Liu et al., 2007). brain histaminergic signaling in HD, which may Although we showed that neuronal histamine contribute to sleep disturbances (Yanovsky et al., production in TMN was stable in an early 2011), weight loss or neuronal loss (Liu et al., stage of PD, it may also be possible that local 2007, Vizuete et al., 2000). In addition, our fin- augmentation of histamine transmission in SN dings provide a rationale for the use of H R ago- and putamen in PD happened in an early stage 3 nists in HD patients, since it may inhibit histamine of PD. Is so, it might contribute to SN degene- production. Recently Yanovsky et al. reported ration in the early stages of PD. To understand that dopamine could activate TMN neurons to in- alterations of the histaminergic system in an crease histamine release via Dopamine-2 receptor early stage of Parkinson’s disease, postmor- (Yanovsky et al., 2011). It is thus of interest to tem tissue from the SN and putamen should be notice that PET scanning revealed a loss/dysfunc- collected and the expression of histaminergic tion of Dopamine-2 receptor binding reported in genes should be measured. the hypothalamus of clinical HD patients and pre- 3) Histamine receptor-4 expression was consi- manifest HD patients (with abnormal CAG repeat derably higher - 6.3-fold in caudate nucleus numbers but no clinical symptoms yet) (Politis et and 4.3-fold in putamen in PD compared to al., 2008). These findings provide a potential ex- matched controls. However, only limited in- planation for the up-regulation of HDC-mRNA in formation is available on the function of H R 4 HD TMN. in the brain (Connelly et al., 2009). To find out whether the H R-mRNA upregulation plays a 4 Future Perspectives role in the pathology of PD in this brain area, the distribution and the compartments that 1) In order to correlate the cognitive impairment,

contribute to the H4R up-regulation in caudate sleep disturbances and weight loss in the last and putamen must be investigated. few years of a HD patient’s life with hypothalamic alterations, thorough documentation of 2.2. Huntington’s disease (HD) these parameters in donors is needed. Subse- quently the causality of such correlations and Of all the nuclei in the hypothalamus, the TMN the effect of histaminergic compounda may be shows the highest frequency of both nuclear and

132 General Discussion

studied. Unfortunately such physiological pa- expression level was only slightly (24%) and rameters were not documented in the clinical non-significantly decreased in the same patients histories of the HD patient whose post-mortem (Chapter 7). Interestingly, this seems to be in full material is available. The Netherlands Brain agreement with the previous finding of a slightly Bank has therefore begun to document the pa- but not significantly lower level of the histamine tients’ bodyweight at autopsies. metabolite t-MeHA (22%) in the lumbar CSF of 2) It would be of interest to study the mechanism AD patients (Motawaj et al., 2011). Our findings of histamine augmentation in the HD brain, suggest that the remaining TMN neurons in AD for which it is imperative to set up reliable and compensate for the loss in histamine neurons. valid HD animal models that show at least the Only in females did we find a significantly incre-

changes that are similar to neuronal histami- ased H3R-, HMT-,mRNA expression in the PFC, nergic changes. This is not the case with the which is one of the major projection areas of his- current mouse models (Williams et al., 2012). tamine produced in the TMN (Haas et al., 2008), 3) Based upon a recent acute rodent study that together with increased glial fibrillary acidic dopamine can activate TMN neurons to incre- protein (GFAP)-, Vimentin (VIM) and Proteoli- ase histamine release via the Dopamine-2 re- pid protein (PLP)-mRNA levels. Our findings in- ceptor (Yanovsky et al., 2011), PET scanning dicate that the histaminergic system as far as the revealed a loss/dysfunction of Dopamine-2 re- PFC is concerned is especially affected in female ceptor binding in the hypothalamus of both cli- AD patients. In addition, although we observed nical HD patients and premanifest HD patients a significant positive correlation between HMT, (with abnormal CAG repeat numbers but no GFAP and VIM-mRNA levels, both in controls clinical symptoms yet) (Politis et al., 2008). and AD patients, HMT-mRNA was exclusively This points to a potential mechanism for the located in neurons in the human PFC (Chapter HDC-mRNA upregulation we observed in the 7), and not in astrocytes, contrary to expectation TMN of HD and premanifest HD patients. To (Huszti et al., 1990, Nishibori et al., 2000, Rafa- investigate this, having access to HDC-mRNA lowska et al., 1987).

expression in postmortem premanifest HD It is known that H3R antagonists may increase the TMN would be of importance. release of histamine, acetylcholine, noradrenaline and dopamine, and it was therefore proposed to 2.3. Alzheimer’s disease (AD) modulate the cognitive processes in the PFC of AD patients. Regarding the rather small and fema- The accumulation of neurofibrillary tangles le-specific H R-mRNA increase we observed in (NFT) in the TMN takes place in the early stages 3 the PFC in AD patients, together with the finding of the AD process, i.e. in Braak stage 3 (Braak of insignificant changes of H R binding density in et al., 1993). In addition, a loss of large histami- 3 this area (Medhurst et al., 2009), the positive ef- nergic neurons has been described in the rostral fect of H R antagonists was, however, expected to TMN in AD (Nakamura et al., 1993). These ob- 3 be modest. This idea has recently been confirmed servations are in accordance with HPLC results by a clinical pilot study with one of the H R anta- showing that histamine levels, along with the de- 3 gonists/inverse agonists that appeared to be inef- creased neuronal metabolic activity of the TMN, fective in improving cognitive functions in mild to diminish in a number of brain areas, including the moderate AD patients (Egan et al., 2012). Further- hippocampus, frontal and temporal cortex, in AD more, it should be noted that, as the activity state (Mazurkiewicz-Kwilecki et al., 1989, Panula et of the remaining TMN neurons is supposed to be al., 1998). increased, a conservative application of H R anta- Surprisingly, our study showed that, although 3 gonists is in order if further degeneration of these there was a significant (57%) overall loss of neurons is to be prevented. TMN neurons in AD, the total HDC-mRNA

133 Chapter 10

Future Perspectives wed that decrements in DNA methylation status as measured by 5-methylcytosine and 1) The mechanism of the functional compen- 5-methylcytidine, as well as the immunore- sation of TMN neurons in AD is at present activity of all eight methylation stabilization unknown. My hypothesis is that a reduced factors were decreased in entorhinal cortex GABAergic inhibition (Gallopin et al., 2000) layer II in AD compared with matched con- may be the basis for the activation of TMN trols (Mastroeni et al., 2012). If such a decline neurons. A similar neuronal compensation has of DNA methylation activity also happened in been reported in AD in the locus coeruleus the TMN, this would greatly contribute to the (LC) where the small proportion of remaining higher HDC-mRNA expression in AD. Such noradrenergic neurons is hyperactive (Hoog- an epigenetic mechanism seems a worthwhile endijk et al., 1999, Raskind et al., 1999, Szot subject for future study. et al., 2006), indicating this may be a general 3) We found that the H R and HMT in PFC were mechanism in AD. The possible source of GA- 3 upregulated in both the preclinical (Braak BAergic projections for the TMN and locus stage III-IV) and clinical stages (Braak stage coeruleus in such compensatory mechanisms V-VI) of AD patients. This result, together is not clear, while the ventrolateral preoptic with the NFT accumulation in the TMN in nucleus (VLPO) (Chou et al., 2002, Steininger Braak stage III (Braak et al., 1993), seemed to et al., 2001), which sends GABAergic pro- imply that alteration of histamine production jections both to the TMN and to the LC in rat in TMN might start in an early stage of AD. could be a clue. It has been proposed that rat Counting TMN neurons and measuring HDC- VLPO is homologous to the human intermedi- mRNA in an early stage of AD TMN should be ate nucleus/ sexually dimorphic nucleus of the performed to test this possibility. preoptic area (SDN-POA)/ interstitial nucleus 4) Significantly increased H R, HMT and mRNA of the anterior hypothalamus-1 (INAH1), be- 3 expression in the course of AD was only found cause this nucleus is galanin positive (Gaus in the female PFC. The sex differences we et al., 2002, Saper et al., 2001). However, the reported deserve further study, due to possi- proposal that this human nucleus is homolo- ble clinical implications. Astrocyte markers, gous to the rat VLPO (Gaus et al., 2002, Saper GFAP, VIM-mRNA and oligodendrocyte mar- et al., 2001) appears to be at odds with other kers, and PLP-mRNA showed sex differences observations (Garcia-Falgueras et al., 2012). in PFC in AD as well. These findings need to The rat VLPO was localized much more ven- be confirmed on the protein level by means of trolaterally, i.e., lateral of the optic chiasm Western-blot and, if possible, by CSF measu- (Gaus et al., 2002), than the human interme- rements of astrocyte and oligodendrocyte mar- diate nucleus. The marker galanin is found kers. throughout the hypothalamus. A specific mar- 5) The novel histamine receptor H R was recent- ker for the intermediate nucleus is necessary 4 ly found to be functionally expressed in the to solve the problem regarding the possible human cortex (Connelly et al., 2009). We have homology with the rat VLPO. reported for the first time that the H R-mRNA 2) In mature mast cell lines and in an erythroblast 4 tended to be higher in the PFC in AD. The cell line it was found that demethylation in the functional meaning of such an up-regulation HDC promoter area increased HDC-mRNA should be elucidated with pharmacological expression and histamine content (Kuramasu studies in an animal model or cell line. This re- et al., 1998, Suzuki-Ishigaki et al., 2000). It ceptor should also be studied in other disease may therefore be of interest to investigate (see in PD) to gauge the quality/quantity of the whether HDC expression is regulated by me- changes. thylation in the TMN. Recently a report sho-

134 General Discussion

2.4. Multiple sclerosis (MS) and oxytocin-mRNA expression in the SON of the rat hypothalamus via both H R and H R, suppor- MS is an inflammatory disorder of the central ner- 1 2 ted this possibility (Kjaer et al., 1994). vous system associated with chronic and exten- However, our study on postmortem human brain sive neurodegeneration (Compston et al., 2008). material did not reveal any significant changes It should be noted that histamine can change the in the neuronal histaminergic system, either permeability of the blood brain barrier, which may in the rate-limiting enzyme, HDC, involved in lead to an elevation of infiltrating cells in the CNS its production or in its receptors and breaking- as well as to an increased risk of neuroinflamma- down enzyme in the two main projection sites, tion (Michelsen et al., 2005). the anterior cingulate cortex and the dorsola- In addition, histamine has shown to have positive teral prefrontal cortex(Chapter 8). effects in MS therapy by five possible mechanisms: 1) augmentation of subnormal cerebral tissue Future perspective levels of histamine, 2) improved electrical function of demyelinated fibers, 3) increased cerebral 1) Larger numbers of patients in the bipolar dis- blood flow, 4) suppression of autoimmune respon- order and major depression groups are needed ses, and 5) stimulation of remyelination (Gillson in order to see whether there is a change in et al., 2000). Although the effects of histamine the day-night fluctuations in HDC-mRNA in in MS patients are not yet clear, animal studies depression in the TMN. Measurements of his- (Musio et al., 2006) and human observations (Al- tamine or histamine metabolite levels in CSF onso et al., 2006, Lock et al., 2002) both show could also be instrumental here. that alterations in the histaminergic system may be involved in the progression of MS. 2.6. Schizophrenia Famotidine, a H R antagonist, was shown in se- Future perspective 2 veral open-label clinical trials to have antipsycho- To pave the road for the development of histami- tic effects and to reduce negative symptoms in ne-related therapeutic strategies, putative altera- schizophrenia (Kaminsky et al., 1990, Oyewumi tions in neuronal histamine production, release, et al., 1994, Rosse et al., 1996). For this reason, and breakdown, as well as in its receptors, should the histaminergic system has been thought to be be systematically studied in multiple sclerosis pa- involved in the pathophysiology of this disorder tients. The requirements for such studies i.e. ma- (Tandon, 1999). terial from the Netherlands Brain Bank and tech- Superior frontal gyrus (SFG) dysfunction has niques are in place. been implicated in the pathophysiology of schizophrenia (Smee et al., 2011). Our pilot study has 2.5. Depression shown, for the first time, that the histamine inactivating enzyme HMT-mRNA is up-regulated Due to the fact that hypothalamic histamine sig- twofold in the SFG of schizophrenia patients, nificantly increases when animals are exposed to whereas the histamine releasing factor HRF- acute stress (Mazurkiewicz-Kwilecki et al., 1986), mRNA tended to be elevated (Chapter 9). In ad- and as both acute and chronic stresses increase dition, the expression levels of the astrocyte-asso- histamine turnover (Ito, 2000), it was proposed ciated genes, including GFAP, VIM, were higher that the histaminergic system may be involved in in schizophrenia, which confirmed earlier findings the pathology of depression (Jin et al., 2009). The (Nanitsos et al., 2005, Rothermundt et al., 2009, observation that intracerebroventricularly infused Toro et al., 2006). The data obtained so far imply histamine increased the expression of stress-rela- an increased release and turnover of histamine in ted neuropeptides, such as CRH, arginine vaso- this brain area of schizophrenia patients. pression-mRNA and oxytocin-mRNA in the PVN

135 Chapter 10

Future perspectives nic for potential treatment of Alzheimer’s disease, Parkinson’s disease and schizophrenia (Brioni et 1) Our pilot provides a rationale for the explora- al., 2010, Passani et al., 2011), without taking into tion of histamine production in the hypothala- account the recent information on alterations in mus in schizophrenia and the levels of hista- the histaminergic system. mine and its metabolites in the CSF. Regarding Parkinson’s disease (Chapters 4 and 2) HRF was first discovered as the translational 5), we paid special attention to the ongoing Phase controlled tumor protein in Ehrlich ascites tu- III clinical trials of H R antagonist/inverse ago- mor cells and MacDonald characterized it as 3 nists (Benarroch, 2011, Passani et al., 2011), a histamine-releasing factor (see reviewed in which may potentially increase the histamine re- (Telerman et al., 2009)). Since a down-regula- lease and thus accelerate degeneration of neurons, tion of HRF protein expression was observed e.g. in the putamen or substantia nigra. in Alzheimer’s disease and Down’s syndrome, In Alzheimer’s disease (Chapter 7), because H R it has been proposed that reduced HRF is as- 3 antagonists increase the release of histamine, ace- sociated with cognitive and memory deficits tylcholine, noradrenalin and dopamine, they may (Kim et al., 2001). The previously reported in this way modulate cognitive processes in the down regulation of HRF-mRNA (1.4-1.9 fold) PFC of AD patients (Brioni et al., 2010, Passani et in the hippocampus of schizophrenic patients al., 2011). However, regarding the small and fe- (Chung et al., 2003), and our finding that HRF male-specific H R-mRNA increase we observed, tended to be upregulated in the PFC, supports 3 together with insignificant changes of binding the possibility of its involvement in cognition. density in this area (Medhurst et al., 2009), the It seems therefore of importance to determine positive effects of H R antagonists are expected this novel compound also in the PFC of neu- 3 to be modest. This presumption has already been rodegenerative disorders. Furthermore, in schi- supported by a recent clinical pilot study, which zophrenia, but not in controls, we observed showed that one of the H R antagonists/inverse a positive correlation between HRF and glia 3 agonists appeared to be ineffective with regard markers such as GFAP and VIM. This may to improving cognitive function in mild to mode- indicate that the upregulation of HRF comes rate AD patients (Egan et al., 2012). In addition, it largely from the glia compartment. These preli- should be noted that, because the activation state minary data thus ask for a localization of HRF of the remaining TMN neurons is already higher, at the messenger and protein level in the brain. the application of the H R antagonist should be on To delineate, in addition, the function of HRF 3 the conservative side in order to prevent accelera- in the brain, a HRF knock-out model is needed. ted degeneration of these neurons. 3. Histamine receptor-3 antagonists/ As far as schizophrenia was concerned (Chapter inverse agonists: clinical implications 9), our pilot study showed a significant increase of HMT-mRNA in the superior frontal cortex of schi- Recently a phase III Alzheimer’s disease trial with zophrenic patients, thus supporting the notion of Dimebon (latrepirdine), originally an antihista- an elevation of histamine (Prell et al., 1996, Prell mine compound used for allergy treatment, failed et al., 1995). Of course, a cohort has to be included to show any significant improvement in primary for the histamine production site TMN to warrant or secondary outcomes in 598 patients (Bezpro- future studies. However, the current pilot study, zvanny, 2010). The failure of Dimebon is presu- may already give arguments against clinical ap- med to be largely due to an insufficient understan- plication of H3R inverse agonist/antagonist in this ding of its mechanism (Jones, 2010). This topic, disorder (Brioni et al., 2010, Passani et al., 2011), therefore, seems to be especially timely, since because such compounds may potentially further histamine-3 receptor (H3R) antagonists/inverse increase histamine production and release (Brioni agonists are now making their way into the cli- et al., 2010, Passani et al., 2011). In addition, a

136 General Discussion recent preclinical pharmacological study failed to References show antipsychotic-like properties of H3R inverse Alonso, A., Jick, S.S., Hernan, M.A., 2006. Allergy, histamine agonist/antagonists (Burban et al., 2010). 1 receptor blockers, and the risk of multiple sclerosis. In general, our post-mortem data supported that Neurology. 66, 572-575. - as an adjunct form of medication - H R antago- Appl, H., Holzammer, T., Dove, S., Haen, E., Strasser, A., Sei- 3 fert, R., 2011. Interactions of recombinant human histami- nists might modulate the circadian rhythmicity of ne H(1), H (2), H antipsychotics. Naunyn Schmiedebergs neuropsychiatric disorders (Chapter 3). However, Arch Pharmacol. for improving cognitive impairment or locomoti- Arnulf, I., Konofal, E., Merino-Andreu, M., Houeto, J.L., Mesnage, V., Welter, M.L., et al., 2002. Parkinson’s on, the effects of H3R antagonists were modest or indirect, and warrants careful future studies. Last disease and sleepiness: an integral part of PD. Neurology. but not least, for this complex medication to be 58, 1019-1024. Aziz, A., Fronczek, R., Maat-Schieman, M., Unmehopa, U., used properly, the effects of H3R antagonists on Roelandse, F., Overeem, S., et al., 2008. Hypocretin and the modulation of histamine and other neurotrans- melanin-concentrating hormone in patients with Hunting- mitters in the human brain must be studied with ton disease. Brain Pathol. 18, 474-483. some urgency. Aziz, N.A., Anguelova, G.V., Marinus, J., Lammers, G.J., Roos, R.A., 2011. Sleep and circadian rhythm alterations correlate with depression and cognitive impairment 4. Limitations of the thesis in Huntington’s disease. Parkinsonism Relat Disord. 16, The other source of brain histamine, mast cells, 345-350. is not discussed in the current thesis because the Benarroch, E.E., 2011. Histamine in the CNS: multiple functions and potential neurologic implications. Neurology. 75, localizations are not well-documented in the hu- 1472-1479. man brain. However, it might be so that up to 50% Bezprozvanny, I., 2010. The rise and fall of Dimebon. Drug of whole brain histamine levels are made up of News Perspect. 23, 518-523. mast cells (Goldschmidt et al., 1985). In addition, Boeve, B.F., Silber, M.H., Saper, C.B., Ferman, T.J., Dickson, some medication showed interaction with hista- D.W., Parisi, J.E., et al., 2007. Pathophysiology of REM sleep behaviour disorder and relevance to neurodegenera- mine receptors (Appl et al., 2011, Jin et al., 2009) tive disease. Brain. 130, 2770-2788. or influenced the histamine levels in lumbar CSF Braak, H., Braak, E., Bohl, J., 1993. Staging of Alzheimer- (Kanbayashi et al., 2009, Zeitzer et al., 2011). For related cortical destruction. Eur Neurol. 33, 403-408. the study it was also therefore virtually impossible Braak, H., Braak, E., Yilmazer, D., de Vos, R.A., Jansen, E.N., to exclude the effects of medication. Bohl, J., 1996. Pattern of brain destruction in Parkinson’s and Alzheimer’s diseases. J Neural Transm. 103, 455-490. Braak, H., Del Tredici, K., Rub, U., de Vos, R.A., Jansen Steur, E.N., Braak, E., 2003. Staging of brain pathology related to sporadic Parkinson’s disease. Neurobiol Aging. 24, 197-211. Braak, H., Rub, U., Del Tredici, K., 2006. Cognitive decline correlates with neuropathological stage in Parkinson’s disease. J Neurol Sci. 248, 255-258. Brioni, J.D., Esbenshade, T., Garrison, T., Bitner, S., Cowart, M., 2010. H3 Receptor Miniseries: Discovery of histamine H3 antagonists for the treatment of cognitive disorders and Alzheimer’s disease. J Pharmacol Exp Ther. Burban, A., Sadakhom, C., Dumoulin, D., Rose, C., Le Pen, Figure 1 Box plots showing the median, 25th-75th percentiles G., Frances, H., et al., 2010. Modulation of prepulse inhi- and the range of radioactivity in arbitrary units. The total bition and stereotypies in rodents: no evidence for antipsy- amount of radioactivity of HDC mRNA expression appeared chotic-like properties of histamine H3-receptor inverse to be sex-specific. Female PD subjects show significantly agonists. Psychopharmacology (Berl). 210, 591-604. lower HDC-mRNA expression compared to control females Chou, T.C., Bjorkum, A.A., Gaus, S.E., Lu, J., Scammell, T.E., (* P=0.035) and compared to the group of male patients (** Saper, C.B., 2002. Afferents to the ventrolateral preoptic P= 0.004). There was no significant difference (P = 0.753) nucleus. J Neurosci. 22, 977-990. between the male controls and the male PD patients. 137 Chapter 10

Chung, C., Tallerico, T., Seeman, P., 2003. Schizophrenia hip- samples from subjects with psychiatric diseases. Br J pocampus has elevated expression of chondrex glycopro- Pharmacol. 157, 118-129. tein gene. Synapse. 50, 29-34. Jones, R.W., 2010. Dimebon disappointment. Alzheimers Res Compston, A., Coles, A., 2008. Multiple sclerosis. Lancet. Ther. 2, 25. 372, 1502-1517. Kaminsky, R., Moriarty, T.M., Bodine, J., Wolf, D.E., David- Connelly, W.M., Shenton, F.C., Lethbridge, N., Leurs, R., son, M., 1990. Effect of famotidine on deficit symptoms Waldvogel, H.J., Faull, R.L., et al., 2009. The histamine of schizophrenia. Lancet. 335, 1351-1352. H4 receptor is functionally expressed on neurons in the Kanbayashi, T., Kodama, T., Kondo, H., Satoh, S., Inoue, Y., mammalian CNS. Br J Pharmacol. 157, 55-63. Chiba, S., et al., 2009. CSF histamine contents in narco- Egan, M., Yaari, R., Liu, L., Ryan, M., Peng, Y., Lines, C., et lepsy, idiopathic hypersomnia and obstructive sleep apnea al., 2012. Pilot Randomized Controlled Study of a Hista- syndrome. Sleep. 32, 181-187. mine Receptor Inverse Agonist in the Symptomatic Treat- Kim, S.H., Cairns, N., Fountoulakisc, M., Lubec, G., 2001. ment of AD. Curr Alzheimer Res. Decreased brain histamine-releasing factor protein in Espana, R.A., Scammell, T.E., 2012. Sleep neurobiology from patients with Down syndrome and Alzheimer’s disease. a clinical perspective. Sleep. 34, 845-858. Neurosci Lett. 300, 41-44. Gallopin, T., Fort, P., Eggermann, E., Cauli, B., Luppi, P.H., Kiviranta, T., Tuomisto, L., Airaksinen, E.M., 1994. Diurnal Rossier, J., et al., 2000. Identification of sleep-promoting and age-related changes in cerebrospinal fluid tele-me- neurons in vitro. Nature. 404, 992-995. thylhistamine levels during infancy and childhood. Phar- Garbarg, M., Javoy-Agid, F., Schwartz, J.C., Agid, Y., 1983. macol Biochem Behav. 49, 997-1000. Brain histidine decarboxylase activity in Parkinson’s Kjaer, A., Larsen, P.J., Knigge, U., Warberg, J., 1994. Hista- disease. Lancet. 1, 74-75. minergic activation of the hypothalamic-pituitary-adrenal Garcia-Falgueras, A., Ligtenberg, L., Kruijver, F.P., Swaab, axis. Endocrinology. 135, 1171-1177. D.F., 2012. Galanin neurons in the intermediate nucleus Kruijver, F.P., Balesar, R., Espila, A.M., Unmehopa, U.A., (InM) of the human hypothalamus in relation to sex, age, Swaab, D.F., 2003. Estrogen-receptor-beta distribution and gender identity. J Comp Neurol. 519, 3061-3084. in the human hypothalamus: similarities and differences Gaus, S.E., Strecker, R.E., Tate, B.A., Parker, R.A., Saper, with ER alpha distribution. J Comp Neurol. 466, 251-277. C.B., 2002. Ventrolateral preoptic nucleus contains sleep- Krystal, A.D., Durrence, H.H., Scharf, M., Jochelson, P., active, galaninergic neurons in multiple mammalian spe- Rogowski, R., Ludington, E., et al., 2010. Efficacy and cies. Neuroscience. 115, 285-294. Safety of Doxepin 1 mg and 3 mg in a 12-week Sleep Ghi, P., Ferretti, C., Lupi, M.L., Blengio, M., Portaleone, P., Laboratory and Outpatient Trial of Elderly Subjects with 1991. Sexual dimorphism in [3H]histamine binding sites Chronic Primary Insomnia. Sleep. 33, 1553-1561. of rat cerebral cortex. Pharmacol Res. 23, 187-193. Kuramasu, A., Saito, H., Suzuki, S., Watanabe, T., Ohtsu, H., Gillson, G., Wright, J.V., DeLack, E., Ballasiotes, G., 2000. 1998. Mast cell-/basophil-specific transcriptional regu- Transdermal histamine in multiple sclerosis, part two: a lation of human L-histidine decarboxylase gene by CpG proposed theoretical basis for its use. Altern Med Rev. 5, methylation in the promoter region. J Biol Chem. 273, 224-248. 31607-31614. Goldschmidt, R.C., Hough, L.B., Glick, S.D., 1985. Rat brain Lee, J.T., Wheeler, T.C., Li, L., Chin, L.S., 2008. Ubiquitinati- mast cells: contribution to brain histamine levels. J Neu- on of alpha-synuclein by Siah-1 promotes alpha-synuclein rochem. 44, 1943-1947. aggregation and apoptotic cell death. Hum Mol Genet. 17, Haas, H., Panula, P., 2003. The role of histamine and the tu- 906-917. beromamillary nucleus in the nervous system. Nat Rev Lin, J.S., 2000. Brain structures and mechanisms involved in Neurosci. 4, 121-130. the control of cortical activation and wakefulness, with Haas, H.L., Sergeeva, O.A., Selbach, O., 2008. Histamine in emphasis on the posterior hypothalamus and histaminer- the nervous system. Physiol Rev. 88, 1183-1241. gic neurons. Sleep Med Rev. 4, 471-503. Hoogendijk, W.J., Feenstra, M.G., Botterblom, M.H., Gilhuis, Lin, J.S., Sakai, K., Jouvet, M., 1988. Evidence for histami- J., Sommer, I.E., Kamphorst, W., et al., 1999. Increased nergic arousal mechanisms in the hypothalamus of cat. activity of surviving locus ceruleus neurons in Alzhei- Neuropharmacology. 27, 111-122. mer’s disease. Ann Neurol. 45, 82-91. Liu, C.Q., Chen, Z., Liu, F.X., Hu, D.N., Luo, J.H., 2007. In- Huszti, Z., Magyar, K., Kalman, M., 1990. Contribution of volvement of brain endogenous histamine in the degene- glial cells to histamine inactivation. Agents Actions. 30, ration of dopaminergic neurons in 6-hydroxydopamine- 237-239. lesioned rats. Neuropharmacology. 53, 832-841. Ito, C., 2000. The role of brain histamine in acute and chronic Liu, C.Q., Hu, D.N., Liu, F.X., Chen, Z., Luo, J.H., 2008. Apo- stresses. Biomed Pharmacother. 54, 263-267. morphine-induced turning behavior in 6-hydroxydopami- Jin, C.Y., Anichtchik, O., Panula, P., 2009. Altered histamine ne lesioned rats is increased by histidine and decreased by H3 receptor radioligand binding in post-mortem brain histidine decarboxylase, histamine H(1) and H(2) receptor

138 General Discussion

antagonists, and an H(3) receptor agonist. Pharmacol Bio- of Na+/K+-dependent glutamate transport. J Biomed Sci. chem Behav. 12, 975-984. Lock, C., Hermans, G., Pedotti, R., Brendolan, A., Schadt, Nishibori, M., Tahara, A., Sawada, K., Sakiyama, J., Nakaya, E., Garren, H., et al., 2002. Gene-microarray analysis of N., Saeki, K., 2000. Neuronal and vascular localization of multiple sclerosis lesions yields new targets validated in histamine N-methyltransferase in the bovine central ner- autoimmune encephalomyelitis. Nat Med. 8, 500-508. vous system. Eur J Neurosci. 12, 415-424. Mastroeni, D., Grover, A., Delvaux, E., Whiteside, C., Cole- Olanow, C.W., Perl, D.P., DeMartino, G.N., McNaught, K.S., man, P.D., Rogers, J., 2012. Epigenetic changes in Alzhei- 2004. Lewy-body formation is an aggresome-related pro- mer’s disease: decrements in DNA methylation. Neuro- cess: a hypothesis. Lancet Neurol. 3, 496-503. biol Aging. 31, 2025-2037. Oyewumi, L.K., Vollick, D., Merskey, H., Plumb, C., 1994. Mazurkiewicz-Kwilecki, I.M., Nsonwah, S., 1989. Changes in Famotidine as an adjunct treatment of resistant schizophr- the regional brain histamine and histidine levels in post- enia. J Psychiatry Neurosci. 19, 145-150. mortem brains of Alzheimer patients. Can J Physiol Phar- Panula, P., Rinne, J., Kuokkanen, K., Eriksson, K.S., Sallmen, macol. 67, 75-78. T., Kalimo, H., et al., 1998. Neuronal histamine deficit in Mazurkiewicz-Kwilecki, I.M., Prell, G.D., 1986. Brain hista- Alzheimer’s disease. Neuroscience. 82, 993-997. mine response to stress in 12 month old rats. Life Sci. 38, Parmentier, R., Ohtsu, H., Djebbara-Hannas, Z., Valatx, J.L., 2339-2345. Watanabe, T., Lin, J.S., 2002. Anatomical, physiological, Medhurst, A.D., Roberts, J.C., Lee, J., Chen, C.P., Brown, and pharmacological characteristics of histidine decar- S.H., Roman, S., et al., 2009. Characterization of hista- boxylase knock-out mice: evidence for the role of brain mine H3 receptors in Alzheimer’s Disease brain and amy- histamine in behavioral and sleep-wake control. J Neuro- loid over-expressing TASTPM mice. Br J Pharmacol. 157, sci. 22, 7695-7711. 130-138. Passani, M.B., Blandina, P., 2011. Histamine receptors in the Michelsen, K.A., Lozada, A., Kaslin, J., Karlstedt, K., Kukko- CNS as targets for therapeutic intervention. Trends Phar- Lukjanov, T.K., Holopainen, I., et al., 2005. Histamine- macol Sci. immunoreactive neurons in the mouse and rat suprachias- Politis, M., Pavese, N., Tai, Y.F., Tabrizi, S.J., Barker, R.A., matic nucleus. Eur J Neurosci. 22, 1997-2004. Piccini, P., 2008. Hypothalamic involvement in Hunting- Mochizuki, T., Yamatodani, A., Okakura, K., Horii, A., In- ton’s disease: an in vivo PET study. Brain. 131, 2860- agaki, N., Wada, H., 1992. Circadian rhythm of histamine 2869. release from the hypothalamus of freely moving rats. Phy- Prast, H., Dietl, H., Philippu, A., 1992. Pulsatile release of siol Behav. 51, 391-394. histamine in the hypothalamus of conscious rats. J Auton Monti, J.M., Pellejero, T., Jantos, H., 1986. Effects of H1- and Nerv Syst. 39, 105-110. H2-histamine receptor agonists and antagonists on sleep Prell, G.D., Green, J.P., Elkashef, A.M., Khandelwal, J.K., and wakefulness in the rat. J Neural Transm. 66, 1-11. Linnoila, M., Wyatt, R.J., et al., 1996. The relationship Motawaj, M., Peoc’h, K., Callebert, J., Arrang, J.M., 2011. between urine excretion and biogenic amines and their CSF Levels of the Histamine Metabolite tele-Methylhista- metabolites in cerebrospinal fluid of schizophrenic pa- mine are only Slightly Decreased in Alzheimer’s Disease. tients. Schizophr Res. 19, 171-176. J Alzheimers Dis. Prell, G.D., Green, J.P., Kaufmann, C.A., Khandelwal, J.K., Musio, S., Gallo, B., Scabeni, S., Lapilla, M., Poliani, P.L., Morrishow, A.M., Kirch, D.G., et al., 1995. Histamine Matarese, G., et al., 2006. A key regulatory role for his- metabolites in cerebrospinal fluid of patients with chronic tamine in experimental autoimmune encephalomyelitis: schizophrenia: their relationships to levels of other ami- disease exacerbation in histidine decarboxylase-deficient nergic transmitters and ratings of symptoms. Schizophr mice. J Immunol. 176, 17-26. Res. 14, 93-104. Nakamura, S., Ohnishi, K., Nishimura, M., Suenaga, T., Aki- Prell, G.D., Khandelwal, J.K., Burns, R.S., Blandina, P., Mor- guchi, I., Kimura, J., et al., 1996. Large neurons in the rishow, A.M., Green, J.P., 1991. Levels of pros-methyli- tuberomammillary nucleus in patients with Parkinson’s midazoleacetic acid: correlation with severity of Parkin- disease and multiple system atrophy. Neurology. 46, son’s disease in CSF of patients and with the depletion 1693-1696. of striatal dopamine and its metabolites in MPTP-treated Nakamura, S., Takemura, M., Ohnishi, K., Suenaga, T., Ni- mice. J Neural Transm Park Dis Dement Sect. 3, 109-125. shimura, M., Akiguchi, I., et al., 1993. Loss of large Prell, G.D., Khandelwal, J.K., Burns, R.S., LeWitt, P.A., neurons and occurrence of neurofibrillary tangles in the Green, J.P., 1988. Elevated levels of histamine metaboli- tuberomammillary nucleus of patients with Alzheimer’s tes in cerebrospinal fluid of aging, healthy humans. Compr disease. Neurosci Lett. 151, 196-199. Gerontol [A]. 2, 114-119. Nanitsos, E.K., Nguyen, K.T., St’astny, F., Balcar, V.J., 2005. Quelhas, R., Costa, M., 2009. Anxiety, depression, and qua- Glutamatergic hypothesis of schizophrenia: involvement lity of life in Parkinson’s disease. J Neuropsychiatry Clin Neurosci. 21, 413-419.

139 Chapter 10

Rafalowska, U., Waskiewicz, J., Albrecht, J., 1987. Is neuro- transcriptional regulation by CpG methylation in the pro- transmitter histamine predominantly inactivated in astro- moter region. Nucleic Acids Res. 28, 2627-2633. cytes? Neurosci Lett. 80, 106-110. Swaab, D.F., Hofman, M.A., 1988. Sexual differentiation of Raskind, M.A., Peskind, E.R., Holmes, C., Goldstein, D.S., the human hypothalamus: ontogeny of the sexually dimor- 1999. Patterns of cerebrospinal fluid catechols support in- phic nucleus of the preoptic area. Brain Res Dev Brain creased central noradrenergic responsiveness in aging and Res. 44, 314-318. Alzheimer’s disease. Biol Psychiatry. 46, 756-765. Szot, P., White, S.S., Greenup, J.L., Leverenz, J.B., Peskind, Riedel, O., Klotsche, J., Spottke, A., Deuschl, G., Forstl, H., E.R., Raskind, M.A., 2006. Compensatory changes in the Henn, F., et al., 2010. Frequency of dementia, depression, noradrenergic nervous system in the locus ceruleus and and other neuropsychiatric symptoms in 1,449 outpatients hippocampus of postmortem subjects with Alzheimer’s with Parkinson’s disease. J Neurol. 257, 1073-1082. disease and dementia with Lewy bodies. J Neurosci. 26, Riemersma-van der Lek, R.F., Swaab, D.F., Twisk, J., Hol, 467-478. E.M., Hoogendijk, W.J., Van Someren, E.J., 2008. Effect Takahashi, K., Lin, J.S., Sakai, K., 2006. Neuronal activity of of bright light and melatonin on cognitive and noncogni- histaminergic tuberomammillary neurons during wake- tive function in elderly residents of group care facilities: a sleep states in the mouse. J Neurosci. 26, 10292-10298. randomized controlled trial. JAMA. 299, 2642-2655. Tanaka, M., Kim, Y.M., Lee, G., Junn, E., Iwatsubo, T., Mou- Rinne, J.O., Anichtchik, O.V., Eriksson, K.S., Kaslin, J., Tu- radian, M.M., 2004. Aggresomes formed by alpha-synu- omisto, L., Kalimo, H., et al., 2002. Increased brain his- clein and synphilin-1 are cytoprotective. J Biol Chem. tamine levels in Parkinson’s disease but not in multiple 279, 4625-4631. system atrophy. J Neurochem. 81, 954-960. Tandon, R., 1999. Cholinergic aspects of schizophrenia. Br J Roehrs, T.A., Tietz, E.I., Zorick, F.J., Roth, T., 1984. Daytime Psychiatry Suppl. 7-11. sleepiness and antihistamines. Sleep. 7, 137-141. Telerman, A., Amson, R., 2009. The molecular programme of Ross, C.A., Poirier, M.A., 2005. Opinion: What is the role of tumour reversion: the steps beyond malignant transforma- protein aggregation in neurodegeneration? Nat Rev Mol tion. Nat Rev Cancer. 9, 206-216. Cell Biol. 6, 891-898. Tompkins, M.M., Hill, W.D., 1997. Contribution of somal Rosse, R.B., Kendrick, K., Fay-McCarthy, M., Prell, G.D., Ro- Lewy bodies to neuronal death. Brain Res. 775, 24-29. senberg, P., Tsui, L.C., et al., 1996. An open-label study of Toro, C.T., Hallak, J.E., Dunham, J.S., Deakin, J.F., 2006. the therapeutic efficacy of high-dose famotidine adjuvant Glial fibrillary acidic protein and glutamine synthetase in pharmacotherapy in schizophrenia: preliminary evidence subregions of prefrontal cortex in schizophrenia and mood for treatment efficacy. Clin Neuropharmacol. 19, 341-348. disorder. Neurosci Lett. 404, 276-281. Rothermundt, M., Ahn, J.N., Jorgens, S., 2009. S100B in schi- van de Nes, J.A., Kamphorst, W., Ravid, R., Swaab, D.F., zophrenia: an update. Gen Physiol Biophys. 28 Spec No 1998. Comparison of beta-protein/A4 deposits and Alz- Focus, F76-81. 50-stained cytoskeletal changes in the hypothalamus and Saper, C.B., Chou, T.C., Scammell, T.E., 2001. The sleep adjoining areas of Alzheimer’s disease patients: amorphic switch: hypothalamic control of sleep and wakefulness. plaques and cytoskeletal changes occur independently. Trends Neurosci. 24, 726-731. Acta Neuropathol. 96, 129-138. Shults, C.W., 2006. Lewy bodies. Proc Natl Acad Sci U S A. Vizuete, M.L., Merino, M., Venero, J.L., Santiago, M., Cano, 103, 1661-1668. J., Machado, A., 2000. Histamine infusion induces a se- Smee, C., Krabbendam, L., O’Daly, O., Prins, A.M., Nalesnik, lective dopaminergic neuronal death along with an inflam- N., Morley, L., et al., 2011. An fMRI study of prefrontal matory reaction in rat substantia nigra. J Neurochem. 75, dysfunction and symptomatic recovery in schizophrenia. 540-552. Acta Psychiatr Scand. 123, 440-450. Williams, R.H., Morton, A.J., Burdakov, D., 2012. Paradoxical Steininger, T.L., Gong, H., McGinty, D., Szymusiak, R., 2001. function of orexin/hypocretin circuits in a mouse model of Subregional organization of preoptic area/anterior hypo- Huntington’s disease. Neurobiol Dis. 42, 438-445. thalamic projections to arousal-related monoaminergic Yanai, K., Watanabe, T., Yokoyama, H., Hatazawa, J., Iwata, cell groups. J Comp Neurol. 429, 638-653. R., Ishiwata, K., et al., 1992. Mapping of histamine H1 re- Strecker, R.E., Nalwalk, J., Dauphin, L.J., Thakkar, M.M., ceptors in the human brain using [11C]pyrilamine and po- Chen, Y., Ramesh, V., et al., 2002. Extracellular histamine sitron emission tomography. J Neurochem. 59, 128-136. levels in the feline preoptic/anterior hypothalamic area Yanovsky, Y., Li, S., Klyuch, B.P., Yao, Q., Blandina, P., Pas- during natural sleep-wakefulness and prolonged wakeful- sani, M.B., et al., 2011. L-Dopa activates histaminergic ness: an in vivo microdialysis study. Neuroscience. 113, neurons. J Physiol. 663-670. Yoshizawa, M., Tashiro, M., Fukudo, S., Yanai, K., Utsumi, Suzuki-Ishigaki, S., Numayama-Tsuruta, K., Kuramasu, A., A., Kano, M., et al., 2009. Increased brain histamine H1 Sakurai, E., Makabe, Y., Shimura, S., et al., 2000. The receptor binding in patients with anorexia nervosa. Biol mouse L-histidine decarboxylase gene: structure and Psychiatry. 65, 329-335.

140 General Discussion

Zeitzer, J.M., Kodama, T., Buckmaster, C.L., Honda, Y., Lyons, D.M., Nishino, S., et al., 2011. Time-course of cerebrospinal fluid histamine in the wake-consolidated squirrel monkey. J Sleep Res.

141

Summary The histaminergic system is involved in many brain functions, such as the sleep-wake cycle, energy and endocrine homeostasis, sensory and motor functions, cognition, attention, learning and memory. My interest in the functions of the histaminergic system in the brain was awakened when I noticed that traditional antihistamines, such as the histamine receptor antagonists diphenhydramine, pyrilamine and doxepin, which increase sleepiness and decrease attention, came with a caution about strong side effects . The posterior part of the hypothalamic tuberomamillary nucleus (TMN) is the exclusive source of neuronal histamine, produced by the key enzyme histidine decarboxylase (HDC). Four types of G-protein coupled HRs, i.e., H1-4R, have been found in the human brain. And histamine methyltransferase (HMT) is the inactivation enzyme for histamine in the brain. In the Introduction to this thesis (Chapter 1) we reviewed the data on the functions of the histaminergic system that are often gender and age-dependent and are disturbed in neuropsychiatric disorders such as Parkinson’s disease (PD), Huntington’s disease (HD), Alzheimer’s disease (AD), Multiple Sclerosis (MS), depression and schizophrenia. In addition, in this chapter we tried to bridge the gap between the fundamental features of the histaminergic system in experimental animals and the recently observed alterations in postmortem tissue of patients with neuropsychiatric disorders. We consider this a matter of some urgency, because histamine-3-receptor antagonists/inverse agonists are making their way into the clinic as a potential treatment for AD, PD and schizophrenia, while the insights on alterations in histamine production, breakdown and receptors recently obtained from postmortem studies yield crucial information on the potential effects and side effects of these compounds. Chapter 2 deals with an experiment in which a number of alterations were introduced into an otherwise routine protocol in order to create optimal in situ hybridization conditions for quantification of the messenger ribonucleic acid (mRNA) HDC in formalin-fixed, paraffin-embedded archival postmortem human brain tissue by radioactive probe. One of the most pronounced effects of neuronal histamine is its crucial role in maintaining wakefulness, also in human. In various species a diurnal fluctuation of histamine has been described, with high levels during the waking stage and low levels during the sleeping period. However, such information is still lacking for humans, both in physiology and in neurodegenerative disorders, where sleep-wake perturbations are a common feature. In Chapter 3, we showed - for the first time - diurnal fluctuations in human histamine production, i.e. higher HDC-mRNA levels during the wake stage (08:00-20:00 hr) than during the sleep stage (20:00- 08:00 hr) in control subjects. The estimation of the acrophase of HDC-mRNA expression in human healthy controls, i.e. at 18:09 hr, corresponded very well with the acrophase for the histamine rhythm at 17:49 hr in diurnal nonhuman squirrel monkeys. In addition, this day-night fluctuation was found to be strongly changed in patients with neurodegenerative diseases, i.e. in PD, AD and HD patients with an acrophase at 8:56 hr. Our observations thus add weight to the proposed ‘flip-flop’ hypothesis of the sleep switch, which says that TMN neurons may promote wakefulness in humans, too. Moreover, the inverted profile in neurodegenerative diseases may be involved in the restless nights and listless days that are so typical of these disorders. Previous animal studies have shown that in the 6-hydroxydopamine (6-OHDA)-lesion rat, a classic PD model, inhibition of endogenous histamine production in an early stage of the disorder put a halt to dopaminergic neuron degeneration. In agreement with this possibility and on the basis of the abundant accumulation of the characteristic neuropathological PD lesions, i.e. Lewy bodies (LBs) and Lewy neurites (LNs), a severe destruction of the histaminergic system was presumed to occur in the TMN of PD patients. However, surprisingly, we did not observe any quantitative changes in TMN HDC-mRNA

143 Summary in PD, which tallied with the intact number of histaminergic neurons, as well as with the unchanged enzyme activity of HDC and with the unaltered tele-methylhistamine (t-MeHA) levels in the CSF in PD. Our observation showed an unchanged TMN HDC-mRNA, not only in late stage PD, but also in a preclinical stage of this disease (Chapter 4). Furthermore, we observed that the expression of the histamine receptor-3 (H3R), which appeared to be localized immunocytochemically in the large pigmented neurons, was significantly decreased in the substantia nigra (SN) in PD (Chapter 5). In Chapter 5 we also showed that there was an up-regulation of HMT-mRNA in the SN and putamen of PD patients, which may act as a protective mechanism as it metabolizes enhanced histamine levels in these areas. Because animal experiments have shown that increased histamine levels may cause degeneration of dopaminergic neurons in the SN, such a protective effect might be of importance. Moreover, an inverse correlation between HMT-mRNA expression and disease duration was observed in the SN of PD patients, suggesting that the more serious (and thus the shorter lasting) the disease, the more HMT-mRNA was expressed, which further supports the notion of such a compensatory mechanism. Of all the nuclei in the hypothalamus, the TMN shows the highest presence of both nuclear and cytoplasmic inclusions of mutant huntingtin, the neuropathological hallmark of HD. Nevertheless, we found an increase in HDC-mRNA levels in the TMN and an increase in HMT-, H1R- and H3R-mRNA levels in the inferior frontal gyrus (IFG) of HD patients. In addition, we observed a significant negative correlation between age at onset of the disease and HMT-mRNA, which suggests that the more serious (and thus the shorter lasting) the disease, the more HMT-mRNA is expressed. Since the levels of histamine metabolites in CSF have also been shown to be increased in HD patients, all observations point to an enhanced activity of the neuronal histaminergic system in HD (Chapter 6). It is known that the accumulation of neurofibrillary tangles (NFT) in the TMN takes place in an early stage of the AD process, i.e. in Braak stage 3. Also, a loss of large histaminergic neurons has been reported in this nucleus in AD. Our study showed that the total HDC-mRNA expression level was only slightly (24%) and non-significantly decreased in the same patients, despite a significant (57%) overall loss of TMN neurons in AD (Chapter 7). Our findings suggest that the remaining TMN neurons in AD compensate for the loss of histamine neurons. Interestingly, when the TMN was divided into 3 parts, a significant reduction in the number of neurons was found in all 3 TMN sub-regions in AD patients, while a significantly lower HDC-mRNA expression was only found in the middle part of the TMN, and not in the rostral or caudal part. In addition, only in females did we find a significantly increased

H3R-, HMT-, mRNA expression in the prefrontal cortex, which is one of the major projection areas of histamine produced in the TMN, together with increased glial fibrillary acidic protein (GFAP)-, vimentin (VIM) and proteolipid protein (PLP)-mRNA levels. Moreover, and contrary to expectation, HMT-mRNA was exclusively located in neurons (Chapter 7), and not in astrocytes in the human PFC. However, we did observe a significant positive correlation between HMT, GFAP and VIM-mRNA levels in controls and AD patients . Our study on postmortem human depression brain material (Chapter 8) did not reveal any significant changes in the neuronal histaminergic system, either in the rate-limiting enzyme for histamine production, HDC, or in its receptors and breaking-down enzyme in the two main projection sites, the anterior cingulate cortex and the dorsolateral prefrontal cortex, despite the fact that animal experimental models for depression suggest the presence of changes in the histaminergic system. In schizophrenia (Chapter 9) we have shown, for the first time, that the histamine inactivating enzyme HMT-mRNA is up-regulated twofold in the superior frontal gyrus of schizophrenia patients, whereas the expression of a novel gene, the histamine-releasing factor (HRF), tended to be elevated (Chapter 9). HRF was proposed to be associated with cognitive deficits and histamine release. In the General discussion (Chapter 10), we showed alterations in the histaminergic system in day-night fluctuations and neuropsychiatric disorders. Ongoing clinical trials with H3R antagonists/inverse ago- 144 Summary nists in PD patients deal with the possibility that these (ant)agonists may potentially increase histamine release and thus accelerate the degeneration of neurons, e.g. in the putamen or substantia nigra in PD. In AD, the histamine-3 receptor antagonists are expected to be ineffective, or at best modestly effective, with regard to improving cognitive function in AD patients, since we have not seen any substantial alterations in the TMN or in the prefrontal cortex for H3R-mRNA. Histamine-3 receptor antagonists may, however, cause further degeneration of the remaining TMN neurons, because they are already hyper-activated. Our current schizophrenia study, which shows activation of the histaminergic system, may provide us with arguments against clinical application of H3R inverse agonist/antagonist in this disorder, because such compounds could potentially further increase histamine production and release.

In general, our post-mortem data supported our supposition that H3R antagonists, as an adjunct form of medication, might modulate the circadian rhythmicity of neuropsychiatric disorders. However, when it comes to improving cognitive impairment or locomotion, the effects of H3R antagonists are modest or indirect. Last but not least, we discussed the limitations of our work and proposed topics for future research.

145