LC/MS/MS Analysis of the Endogenous Dimethyltryptamine Hallucinogens, Their Precursors, and Major Metabolites in Rat Pineal Gland Microdialysate
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Research article Received: 20 March 2013, Revised: 20 May 2013, Accepted: 23 May 2013 Published online in Wiley Online Library: 23 July 2013 (wileyonlinelibrary.com) DOI 10.1002/bmc.2981 LC/MS/MS analysis of the endogenous dimethyltryptamine hallucinogens, their precursors, and major metabolites in rat pineal gland microdialysate Steven A. Barkera*, Jimo Borjiginb, Izabela Lomnickaa and Rick Strassmanc ABSTRACT: We report a qualitative liquid chromatography–tandem mass spectrometry (LC/MS/MS) method for the simulta- neous analysis of the three known N,N-dimethyltryptamine endogenous hallucinogens, their precursors and metabolites, as well as melatonin and its metabolic precursors. The method was characterized using artificial cerebrospinal fluid (aCSF) as the matrix and was subsequently applied to the analysis of rat brain pineal gland-aCSF microdialysate. The method de- scribes the simultaneous analysis of 23 chemically diverse compounds plus a deuterated internal standard by direct injection, requiring no dilution or extraction of the samples. The results demonstrate that this is a simple, sensitive, specific and direct approach to the qualitative analysis of these compounds in this matrix. The protocol also employs stringent MS confirmatory criteria for the detection and confirmation of the compounds examined, including exact mass measurements. The excellent limits of detection and broad scope make it a valuable research tool for examining the endogenous hallucinogen pathways in the central nervous system. We report here, for the first time, the presence of N,N-dimethyltryptamine in pineal gland microdialysate obtained from the rat. Copyright © 2013 John Wiley & Sons, Ltd. Keywords: N,N-dimethyltryptamines; pineal gland; microdialysis; rat brain; LC/MS/MS Introduction 1999), studies have now shown its presence in the central nervous system, including the pineal gland (Cozzi et al., 2011), In a recent review of 69 published studies reporting the detection motor neurons in the spinal cord (Mavlyutov et al., 2012; Cozzi of purported endogenous hallucinogens [N,N-dimethyltryptamine et al., 2011) and in the retina (Cozzi et al., 2011). While the en- (DMT); 5-hydroxy-DMT (HDMT, bufotenine); 5-methoxy-DMT zyme is present in these tissues, there has yet to be a definitive (MDMT)] in humans (Barker et al., 2012), it was concluded that determination of whether DMT is actually synthesized in these fi compelling mass spectral evidence exists for the con rmation of tissues and, if so, how it is utilized or released from the tissues fl their presence in certain human biological uids [cerebrospinal under normal or altered physiological conditions. fluid (CSF; DMT and MDMT), blood (DMT and HDMT) and urine (DMT and HDMT)]. There is as yet no definitive information as to the possible normal or pathophysiological roles of DMT, HDMT * Correspondence to: S. A. Barker, Department of Comparative Biomedical or MDMT in humans or other species owing, in part, to the lack Sciences, School of Veterinary Medicine, Louisiana State University, Baton of comprehensive methods to detect and unequivocally confirm Rouge, LA 70803, USA. E-mail: [email protected] the presence of these compounds in biological tissues and fluids a Department of Comparative Biomedical Sciences, School of Veterinary (Barker et al., 2012). Methodology to adequately assess their Medicine, Louisiana State University, Baton Rouge, LA, 70803, USA synthesis and turnover, simultaneously monitoring their precur- sors and metabolites, is also lacking. b Departments of Molecular & Integrative Physiology1 and Neurology2, Original interest in endogenous hallucinogens, and DMT in University of Michigan Medical School, Ann Arbor, MI, 48109, USA particular, was motivated by the hypothesis that these com- c Department of Psychiatry, University of New Mexico School of Medicine, pounds had a biochemical role in the heterogeneous disease Albuquerque, and Cottonwood Research Foundation, Gallup, New state of psychosis, especially schizophrenia (for a review see Mexico, USA Barker et al., 1981a, Barker et al., 2012). More recently, interest in DMT has been renewed owing to its characterization as a Abbreviations used: 2MTHBC, 2-methyl-1,2,3,4-THBC; CSF, cerebrospinal fluid; d4-MDMT, α,α,β,β-tetradeutero-5-methoxy-N,N-dimethyltryptamine; ligand for the sigma-1 (Fontanilla et al., 2009; Su et al., 2009) DMT, N,N-dimethyltryptamine; DMTNO, DMT-N-oxide; HDMT, 5-hydroxy- and trace amine receptors (Su et al., 2009). Recent studies DMT; HIAA, 5-hydroxy-IAA; HNATA, 5-hydroxy-N-acetyl-TA; HNMT, concerning the enzyme responsible for the biosynthesis of these 5-hydroxy-N-methyl-TA; HTA, 5-hydroxy-TA; HTHBC, 6-hydroxy-THBC; compounds have also drawn further attention. Although the en- HTRP, 5-hydroxy-tryptophan; IAA, indol-3-acetic acid; INMT, indole-N- methyltransferase; MAO, monoamine oxidase; MDMT, 5-methoxy-DMT; zyme for the synthesis of the DMTs, indole-N-methyltransferase MIAA, 5-methoxy-IAA; MNMT, 5-methoxy-N-methyl-TA;MTA,5-methoxy- (INMT), was not thought to occur to any significant extent in 1690 TA; MTHBC, 6-methoxy-THBC; NMT, N-methyl-TA; TA, tryptamine; THBC, brain (Thompson and Weinshilboum, 1998; Thompson et al., 1,2,3,4-tetrahydro-β-carboline; TRP, tryptophan. Biomed. Chromatogr. 2013; 27: 1690–1700 Copyright © 2013 John Wiley & Sons, Ltd. LC/MS/MS of endogenous DMTs in rat pineal gland microdialysate Given the reported expression of INMT in the mammalian provided ad libitum. All animal procedures were approved by pineal gland, the binding of DMT to the sigma-1 and trace amine the University Committee on Use and Care of Animals at the receptors, and the necessity for more comprehensive analytical University of Michigan. methodology to begin to assess the possible function of the DMTs in vivo, we undertook to develop a protocol to screen for Pineal microdialysis the presence of the DMTs, their precursors and metabolites in mammalian body fluids and tissues. We describe here the appli- Rats were implanted with linear microdialysis probes with a mo- cation of our method to rat pineal gland microdialysates using lecular weight cut-off of 13 kDa and a membrane length of liquid chromatography–tandem mass spectrometry (LC/MS/MS) 12–15 mm, manufactured in-house, as described previously for the qualitative analysis of the three known endogenous hal- (see Borjigin and Liu, 2008, for surgical techniques and probe lucinogens and of 20 compounds that constitute most of their preparation). The linear probe traversed both the pineal gland known precursors and major metabolites (Fig. 1), as well as as well as superficial layers of occipital cortex on either side of melatonin and its biochemical precursors. The method was the gland. The pineal location was ascertained in each rat by developed in artificial CSF (aCSF), which was used as the pineal the presence of melatonin in the dialysates (Borjigin and Liu, gland dialysate. The method described uses positive ion 2008). Following a recovery period of 2–3 days, animals were electrospray ionization, monitoring the protonated molecular placed in microdialysis chambers. The chambers consisted of ion (M + 1+) of each targeted analyte and corresponding frag- enclosed animal housing units equipped with their own lighting, ment ions (multiple reaction monitoring). It also applies strin- which was controlled by an on–off timer, and fitted with a venting gent analytical criteria for the detection and confirmation of fan. Sample collection was accomplished with the aid of a liquid these compounds in this matrix, including exact mass determi- swivel. Pineal microdialysis was performed with aCSF solution nation using high-resolution MS. The developed protocol was flowing continuously through the pineal gland at 2 μL/min for 2 h. applied to pineal gland-aCSF-microdialysates obtained from All sample collections were performed during daylight hours. Two freely moving rats. These studies revealed, for the first time, tubes of dialysate were collected, each of which contained 120 μL the presence of DMT in pineal gland microdialysate obtained collected over 1 h (2 μL/min). The pineal dialysates were collected from the rat. in microcentrifuge tubes on ice, capped and stored at À80 °C for 2–4 weeks prior to being shipped on dry-ice for further analysis. Samples experienced a single freeze–thaw cycle prior to analysis. Materials and methods Animals Analytical standards Adult (12 weeks of age), male, Wistar rats, weighing 300–350 g The following compounds were obtained from a commercial each, were obtained from Harlan Laboratories (Indianapolis, IN, source (Sigma Aldrich, St Louis, MO, USA), and were of the highest USA) and were housed in light–dark conditions of 12:12 h for available purity (>98%): DMT, MDMT, HDMT, tryptamine (TA), N- at least one week before experiments. Food and water was methyl-TA (NMT), 5-hydroxy-TA (serotonin; HTA), 5-hydroxy-N- 1691 Figure 1. Compounds examined. Biomed. Chromatogr. 2013; 27: 1690–1700 Copyright © 2013 John Wiley & Sons, Ltd. wileyonlinelibrary.com/journal/bmc S. A. Barker et al. methyl-TA (HNMT), 5-methoxy-TA (MTA), 5-methoxy-N-methyl-TA MS methods (MNMT), melatonin, tryptophan (TRP), 5-hydroxy-tryptophan The chromatography system was coupled to an ambient tem- (HTRP), 5-hydroxy-N-acetyl-TA (HNATA), indol-3-acetic acid perature electrospray ionization probe on the Quantum Access (IAA), 5-hydroxy-IAA (HIAA) and 5-methoxy-IAA (MIAA). The system. For analytes of interest, precursor-to-product ion transi- following compounds were synthesized (as noted) and their tions were established through direct infusion of neat standards structures and purity confirmed (>98%) by LC/MS/MS: DMT-N- of each compound into the ion source. Analytical standards oxide (DMTNO), HDMTNO, MDMTNO (N-oxides were prepared (1 μg/mL) were dissolved in water or methanol and co-infused as described by Fish et al., 1955), 1,2,3,4-tetrahydro-β-carboline into the mass spectrometer with mobile phase to obtain optimal (THBC), 2-methyl-1,2,3,4-THBC (2MTHBC), 6-hydroxy-THBC signal and fragmentation patterns/information (see Table 1).