Indolethylamine-N-methyltransferase Polymorphisms: Genetic and Biochemical Approaches for Study of Endogenous N,N,-dimethyltryptamine

Detailed resume of S-methyltransferases: Categories, structures, biological functions and research advancements in related pathophysiology and pharmacotherapy

Methylation is a vital chemical reaction in the metabolism of many drugs, neurotransmitters, hormones, and exogenous compounds. Among them, S-methylation plays a significant role in the biotransformation of sulfur-containing compounds, particularly chemicals with sulfhydryl groups. Currently, only three S-methyltransferases have been reported: thiopurine methyltransferase (TPMT), thiol methyltransferase (TMT), and thioether methyltransferase (TEMT). These enzymes are involved in various biological processes such as gene regulation, signal transduction, protein repair, tumor progression, and biosynthesis and degradation reactions in animals, plants, and microorganisms. Furthermore, they play pivotal roles in the metabolic pathways of essential drugs and contribute to the advancement of diseases such as tumors. This paper reviews the research progress on relevant structural features, metabolic mechanisms, inhibitor development, and influencing factors (gene polymorphism, S-adenosylmethionine level, race, sex, age, and disease) of S-methyltransferases. We hope that a better comprehension of S-methyltransferases will help to provide a reference for the development of novel strategies for related disorders and improve long-term efficacy.

Hypothetical biosynthetic pathways of pharmaceutically potential hallucinogenic metabolites in Myristicaceae, mechanistic convergence and co-evolutionary trends in plants and humans

The family Myristicaceae harbour mind-altering phenylpropanoids like myristicin, elemicin, safrole, tryptamine derivatives such as N,N-dimethyltryptamine (DMT) and 5-methoxy N,N-dimethyltryptamine (5-MeO-DMT) and β-carbolines such as 1-methyl-6-methoxy-dihydro-β-carboline and 2-methyl-6-methoxy-1,2,3,4-tetrahydro-β-carboline. This study aimed to systematically review and propose the hypothetical biosynthetic pathways of hallucinogenic metabolites of Myristicaceae which have the potential to be used pharmaceutically. Relevant publications were retrieved from online databases, including Google Scholar, PubMed Central, Science Direct and the distribution of the hallucinogens among the family was compiled. The review revealed that the biosynthesis of serotonin in plants was catalysed by tryptamine 5-hydroxylase (T5H) and tryptophan 5-hydroxylase (TPH), whereas in invertebrates and vertebrates only by tryptophan 5-hydroxylase (TPH). Indolethylamine-N-methyltransferase catalyses the biosynthesis of DMT in plants and the brains of humans and other mammals. Caffeic acid 3-O-methyltransferase catalyses the biosynthesis of both phenylpropanoids and tryptamines in plants. All the hallucinogenic markers exhibited neuropsychiatric effects in humans as mechanistic convergence. The review noted that DMT, 5-MeO-DMT, and β-carbolines were natural protectants against both plant stress and neurodegenerative human ailments. The protein sequence data of tryptophan 5-hydroxylase and tryptamine 5-hydroxylase retrieved from NCBI showed a co-evolutionary relationship in between animals and plants on the phylogenetic framework of a Maximum Parsimony tree. The review also demonstrates that the biosynthesis of serotonin, DMT, 5-MeO-DMT, 5-hydroxy dimethyltryptamine, and β-carbolines in plants, as well as endogenous secretion of these compounds in the brain and blood of humans and rodents, reflects co-evolutionary mutualism in plants and humans.

A mechanistic insight for the biosynthesis of N,N-dimethyltryptamine: An ONIOM theoretical approach

Psychoactive natural products are potent serotonergic agonists capable of modulating brain functions such as memory and cognition. These substances have shown therapeutic potential for treating various mental disorders. The fact that N,N-dimethyltryptamine (DMT) is produced endogenously in several plants and animals, including humans, makes it particularly attractive. As an amino acid-derived alkaloid, the DMT biosynthetic pathway is part of the L-tryptophan biochemical cascade and can be divided into the decarboxylation by an aromatic L-amino acid decarboxylase (AADC) for tryptamine formation and the subsequent double-methylation by the indolethylamine-N-methyltransferase (INMT) through the cofactor S-adenosyl-L-methionine (SAM), a methyl donor. Unlike the decarboxylation mechanism of L-tryptophan, the molecular details of the double methylation of tryptamine have not been elucidated. Therefore, we propose an in silico model using molecular dynamics (MD), non-covalent interaction index (NCI) and density functional theory (DFT) calculations with the ONIOM QM:MM B3LYP/6-31+G(d,p):MM/UFF level of theory. Based on the obtained energetic data, the potential energy surface (PES) indicates an SN2 mechanism profile, with the second methylation energy barrier being the rate-limiting step with δG‡=60kJ∙mol-1 larger than the previous methylation, following the NCI analysis showing more repulsive interactions for the second transition state. In addition, the hybridization information of each reaction step provides geometric details about the double-methylation.

An experimental platform for stochastic analyses of single serotonergic fibers in the mouse brain

The self-organization of the serotonergic matrix, a massive axon meshwork in all vertebrate brains, is driven by the structural and dynamical properties of its constitutive elements. Each of these elements, a single serotonergic axon (fiber), has a unique trajectory and can be supported by a soma that executes one of the many available transcriptional programs. This "individuality" of serotonergic neurons necessitates the development of specialized methods for single-fiber analyses, both at the experimental and theoretical levels. We developed an integrated platform that facilitates experimental isolation of single serotonergic fibers in brain tissue, including regions with high fiber densities, and demonstrated the potential of their quantitative analyses based on stochastic modeling. Single fibers were visualized using two transgenic mouse models, one of which is the first implementation of the Brainbow toolbox in this system. The trajectories of serotonergic fibers were automatically traced in the three spatial dimensions with a novel algorithm, and their properties were captured with a single parameter associated with the directional von Mises-Fisher probability distribution. The system represents an end-to-end workflow that can be imported into various studies, including those investigating serotonergic dysfunction in brain disorders. It also supports new research directions inspired by single-fiber analyses in the serotonergic matrix, including supercomputing simulations and modeling in physics.

A cane toad (Rhinella marina) N-methyltransferase converts primary indolethylamines to tertiary psychedelic amines

Psychedelic indolethylamines have emerged as potential medicines to treat several psychiatric pathologies. Natural sources of these compounds include 'magic mushrooms' (Psilocybe spp.), plants used to prepare ayahuasca, and toads. The skin and parotid glands of certain toads accumulate a variety of specialized metabolites including toxic guanidine alkaloids, lipophilic alkaloids, poisonous steroids, and hallucinogenic indolethylamines such as DMT, 5-methoxy-DMT, and bufotenin. The occurrence of psychedelics has contributed to the ceremonial use of toads, particularly among Mesoamerican peoples. Yet, the biosynthesis of psychedelic alkaloids has not been elucidated. Herein, we report a novel indolethylamine N-methyltransferase (RmNMT) from cane toad (Rhinella marina). The RmNMT sequence was used to identify a related NMT from the common toad, Bufo bufo. Close homologs from various frog species were inactive, suggesting a role for psychedelic indolethylamine biosynthesis in toads. Enzyme kinetic analyses and comparison with functionally similar enzymes showed that recombinant RmNMT was an effective catalyst and not product inhibited. The substrate promiscuity of RmNMT enabled the bioproduction of a variety of substituted indolethylamines at levels sufficient for purification, pharmacological screening, and metabolic stability assays. Since the therapeutic potential of psychedelics has been linked to activity at serotonergic receptors, we evaluated binding of derivatives at 5-HT1A and 5-HT2A receptors. Primary amines exhibited enhanced affinity at the 5-HT1A receptor compared with tertiary amines. With the exception of 6-substituted derivatives, N,N-dimethylation also protected against catabolism by liver microsomes.

N, N-Dimethyltryptamine (DMT)-Occasioned Familiarity and the Sense of Familiarity Questionnaire (SOF-Q)

This study investigated the sense of familiarity attributed to N, N-dimethyltryptamine (DMT) experiences. 227 naturalistic inhaled-DMT experiences reporting a sense of familiarity were included. No experiences referenced a previous DMT or psychedelic experience as the source of the familiarity. A high prevalence of concomitant features discordant from ordinary consciousness were identified: features of a mystical experience (97.4%), ego-dissolution (16.3%), and a "profound experience of death" (11.0%). The Sense of Familiarity Questionnaire (SOF-Q) was developed assessing 19 features of familiarity across 5 themes: (1) Familiarity with the Feeling, Emotion, or Knowledge Gained; (2) Familiarity with the Place, Space, State, or Environment; (3) Familiarity with the Act of Going Through the Experience; (4) Familiarity with Transcendent Features; and (5) Familiarity Imparted by an Entity Encounter. Bayesian latent class modeling yielded two stable classes of participants who shared similar SOF-Q responses. Class 1 participants responded, "yes" more often for items within "Familiarity Imparted by an Entity Encounter" and "Familiarity with the Feeling, Emotion, or Knowledge Gained." Results catalogued features of the sense of familiarity imparted by DMT, which appears to be non-referential to a previous psychedelic experience. Findings provide insights into the unique and enigmatic familiarity reported during DMT experiences and offer a foundation for further exploration into this intriguing phenomenon.

An encounter with the self: A thematic and content analysis of the DMT experience from a naturalistic field study

Introduction

N,N-Dimethyltryptamine (DMT) is an endogenous serotonergic psychedelic capable of producing radical shifts in an experience that have significant implications for consciousness and its neural correlates, especially given the “disconnected consciousness” suggested by the “breakthrough” DMT state. Its increasing usage and clinical trial indicate the growing importance of a thorough elucidation of the experience's qualitative content, over and above the phenomenological structure. This is particularly in light of the intensely pervasive effects of DMT occasions in all dimensions of the self, which are often ontologically challenging yet potentially transformative.

Methods

This is the second report on the first naturalistic field study of DMT use exploring its qualitative analysis. Screened, healthy, anonymized, and experienced DMT users were observed during their non-clinical use of the drug at home (40–75-mg inhaled). In-depth semi-structured interviews, inspired by the micro-phenomenological technique, were employed immediately after their experience. This study reports on the thematic and content analysis of one major domain of the breakthrough experiences elicited, the “self”; where analyses of the “other” were previously reported. A total of 36 post-DMT experience interviews with mostly Caucasian (83%) men (eight women) of a mean of 37 years were predominantly inductively coded.

Results

Invariably, profound and highly intense experiences occurred. The first overarching category comprised the onset of effects, encompassing super-ordinate themes including sensory, emotion and body, and space-time shifts; the second category comprised bodily effects, encompassing themes including pleasurable, neutral/both, and uncomfortable; the third category comprised the sensorial effects, encompassing open-eye, visual, and cross-modal and other; the fourth comprised the psychological effects, encompassing memory and language, awareness and sense of self, and time distortions; and the fifth comprised the emotional effects, encompassing positive, neither/both, and challenging experiences. Many further subthemes also illuminate the rich content of the DMT experience.

Discussion

The present study provides a systematic and nuanced analysis of the content of the breakthrough DMT state pertaining to one's personal and self-referential experiences of the body, senses, psychology, and emotions. The resonances both with previous DMT studies and other types of extraordinary experiences, such as the alien abduction, shamanic and near-death experiences, are also elaborated upon. Putative neural mechanisms and their promise as a psychotherapeutic agent, especially owing to deep emotional impact, are discussed.

Unravelling the limb regeneration mechanisms of Polypedates maculatus, a sub-tropical frog, by transcriptomics

BACKGROUND

Regeneration studies help to understand the strategies that replace a lost or damaged organ and provide insights into approaches followed in regenerative medicine and engineering. Amphibians regenerate their limbs effortlessly and are indispensable models to study limb regeneration. Xenopus and axolotl are the key models for studying limb regeneration but recent studies on non-model amphibians have revealed species specific differences in regeneration mechanisms.

RESULTS

The present study describes the de novo transcriptome of intact limbs and three-day post-amputation blastemas of tadpoles and froglets of the Asian tree frog Polypedates maculatus, a non-model amphibian species commonly found in India. Differential gene expression analysis between early tadpole and froglet limb blastemas discovered species-specific novel regulators of limb regeneration. The present study reports upregulation of proteoglycans, such as epiphycan, chondroadherin, hyaluronan and proteoglycan link protein 1, collagens 2,5,6, 9 and 11, several tumour suppressors and methyltransferases in the P. maculatus tadpole blastemas. Differential gene expression analysis between tadpole and froglet limbs revealed that in addition to the expression of larval-specific haemoglobin and glycoproteins, an upregulation of cysteine and serine protease inhibitors and downregulation of serine proteases, antioxidants, collagenases and inflammatory genes in the tadpole limbs were essential for creating an environment that would support regeneration. Dermal myeloid cells were GAG+, EPYC+, INMT+, LEF1+ and SALL4+ and seemed to migrate from the unamputated regions of the tadpole limb to the blastema. On the other hand, the myeloid cells of the froglet limb blastemas were few and probably contributed to sustained inflammation resulting in healing.

CONCLUSIONS

Studies on non-model amphibians give insights into alternate tactics for limb regeneration which can help devise a plethora of methods in regenerative medicine and engineering.

Significance of mammalian N, N-dimethyltryptamine (DMT): A 60-year-old debate

N,N-dimethyltryptamine (DMT) is a potent psychedelic naturally produced by many plants and animals, including humans. Whether or not DMT is significant to mammalian physiology, especially within the central nervous system, is a debate that started in the early 1960s and continues to this day. This review integrates historical and recent literature to clarify this issue, giving special attention to the most controversial subjects of DMT's biosynthesis, its storage in synaptic vesicles and the activation receptors like sigma-1. Less discussed topics, like DMT's metabolic regulation or the biased activation of serotonin receptors, are highlighted. We conclude that most of the arguments dismissing endogenous DMT's relevance are based on obsolete data or misleading assumptions. Data strongly suggest that DMT can be relevant as a neurotransmitter, neuromodulator, hormone and immunomodulator, as well as being important to pregnancy and development. Key experiments are addressed to definitely prove what specific roles DMT plays in mammalian physiology.

Downregulation of Indolethylamine N-methyltransferase is an early event in the rat hepatocarcinogenesis and is associated with poor prognosis in hepatocellular carcinoma patients

Hepatocellular carcinoma (HCC) is one of the deadliest cancers worldwide, often preceded by cirrhosis and usually diagnosed at advanced stages; therefore, identifying molecular changes at early stages is an attractive strategy for detection and timely treatment. Here, we investigated the progressive transcriptomic changes during experimental hepatocarcinogenesis to identify novel early tumor markers in an HCC model induced by chronic administration of sublethal doses of diethylnitrosamine. An analysis of differentially expressed genes showed that four processes associated with oxidation-reduction and detoxification were significantly overrepresented during hepatocarcinogenesis progression, of which the Nuclear Factor, Erythroid 2 Like 2 (NRF2) pathway showed several dysregulated genes. Interestingly, we also identified 91 genes dysregulated at early HCC stages, but the expression of the indolethylamine N-methyltransferase gene (Inmt), as well as the level of its encoding protein, were strongly downregulated. INMT was increased in perivenular hepatocytes of normal livers but decreased in livers of experimental HCC. Furthermore, a gene expression and survival analysis performed using data from the liver hepatocellular carcinoma project of The Cancer Genome Atlas Program revealed that INMT is also significantly downregulated in human HCC and is associated with poor overall survival. In conclusion, by performing a transcriptome analysis of the HCC progression, we identified that INMT is early downregulated in the rat hepatocarcinogenesis and is associated with poor prognosis in human HCC, suggesting that INMT downregulation may be a promising prognostic marker for HCC in high-risk populations.

N,N-dimethyltryptamine and Amazonian ayahuasca plant medicine

OBJECTIVE

Reports have indicated possible uses of ayahuasca for the treatment of conditions including depression, addictions, post-traumatic stress disorder, anxiety and specific psychoneuroendocrine immune system pathologies. The article assesses potential ayahuasca and N,N-dimethyltryptamine (DMT) integration with contemporary healthcare. The review also seeks to provide a summary of selected literature regarding the mechanisms of action of DMT and ayahuasca; and assess to what extent the state of research can explain reports of unusual phenomenology.

DESIGN

A narrative review.

RESULTS

Compounds in ayahuasca have been found to bind to serotonergic receptors, glutaminergic receptors, sigma-1 receptors, trace amine-associated receptors, and modulate BDNF expression and the dopaminergic system. Subjective effects are associated with increased delta and theta oscillations in amygdala and hippocampal regions, decreased alpha wave activity in the default mode network, and stimulations of vision-related brain regions particularly in the visual association cortex. Both biological processes and field of consciousness models have been proposed to explain subjective effects of DMT and ayahuasca, however, the evidence supporting the proposed models is not sufficient to make confident conclusions. Ayahuasca plant medicine and DMT represent potentially novel treatment modalities.

CONCLUSIONS

Further research is required to clarify the mechanisms of action and develop treatments which can be made available to the general public. Integration between healthcare research institutions and reputable practitioners in the Amazon is recommended.

Administration of N,N-dimethyltryptamine (DMT) in psychedelic therapeutics and research and the study of endogenous DMT

As with all drugs, the route, form, and/or dose of a substance administered or applied can play a defining role in its overall pharmacology and use as a therapeutic. This review will focus on these factors as they relate to the psychedelic N,N-dimethyltryptamine (DMT). It will examine the positive and negative aspects of different formulations and routes of administration of DMT and the observed effects from such administrations in the form of ayahuasca teas; oral "pharmahuasca"; injections by intravenous (IV) and intramuscular (IM) routes; inhalation, insufflation; and other routes; and high-dose, low-dose, and "micro-dose" effects. The review will consider possible oral route of administration alternatives that would not require concomitant use of a monoamine oxidase inhibitor. The review will then address the current research findings for DMT from in vivo and in vitro studies as well as the possibility that these findings may be revealing the role of endogenous DMT in normal brain function.

An Encounter With the Other: A Thematic and Content Analysis of DMT Experiences From a Naturalistic Field Study

Introduction: N,N-dimethyltryptamine (DMT) is an endogenous serotonergic psychedelic capable of producing radical shifts in conscious experience. Increasing trends in its use, as well as new trials administering DMT to patients, indicate the growing importance of a thorough elucidation of the qualitative content, over and above structure, which the drug occasions. This is particularly in light of the hyper-real, otherworldly, and often ontologically challenging yet potentially transformative, nature of the experience, not least encounters with apparently non-self social agents. Laboratory studies have been limited by clinical setting and lacking qualitative analyses of experiential content, while online surveys' limitations lie in retrospective design, uncontrolled use, and both of which not guaranteeing 'breakthrough' experiences, i.e., producing very strong psychoactive effects. Methods: We report on the first naturalistic field study of DMT use including its qualitative analysis. Screened, healthy, anonymised and experienced DMT users were observed during their non-clinical use of the drug at home (40-75 mg inhaled). In-depth semi-structured interviews (inspired by the micro-phenomenological technique) were employed immediately after their experience. This paper reports on the thematic analysis of one major domain of the breakthrough experiences elicited, the 'other'. Thirty-six post-DMT experience interviews with mostly Caucasian (83%) males (eight female) of average 37 years were predominantly inductively coded. Results: Invariably, profound and highly intense experiences occurred. The first overarching category comprised the encounter with other 'beings' (94% of reports), encompassing super-ordinate themes including the entities' role, appearance, demeanour, communication and interaction; while the second overarching category comprised experiences of emerging into other 'worlds' (100% of reports), encompassing super-ordinate themes of the scene, the contents and quality of the immersive spaces. Many further mid-level themes and subthemes also illuminate the rich content of the DMT experience. Discussion: The present study provides a systematic and in-depth analysis of the nuanced content of the otherworldly encounter within the breakthrough DMT experience, as well as elaborating on the resonances both with previous DMT studies focusing on entity encounters and other types of extraordinary experiences entailing such encounters. These include the alien abduction, folkloric, shamanic and near-death experience. Putative neural mechanisms of these features of the DMT experience and its promise as a psychotherapeutic agent are discussed in light of such findings.

Insights into S-adenosyl-l-methionine (SAM)-dependent methyltransferase related diseases and genetic polymorphisms

Enzymatic methylation catalyzed by methyltransferases has a significant impact on many human biochemical reactions. As the second most ubiquitous cofactor in humans, S-adenosyl-l-methionine (SAM or AdoMet) serves as a methyl donor for SAM-dependent methyltransferases (MTases), which transfer a methyl group to a nucleophilic acceptor such as O, As, N, S, or C as the byproduct. SAM-dependent methyltransferases can be grouped into different types based on the substrates. Here we systematically reviewed eight types of methyltransferases associated with human diseases. Catechol O-methyltransferase (COMT), As(III) S-adenosylmethionine methyltransferase (AS3MT), indolethylamine N-methyltransferase (INMT), phenylethanolamine N-methyltransferase (PNMT), histamine N-methyltransferase (HNMT), nicotinamide N-methyltransferase (NNMT), thiopurine S-methyltransferase (TPMT) and DNA methyltansferase (DNMT) are classic SAM-dependent MTases. Correlations between genotypes and disease susceptibility can be partially explained by genetic polymorphisms. The physiological function, substrate specificity, genetic variants and disease susceptibility associated with these eight SAM-dependent methyltransferases are discussed in this review.

Further development of a liquid chromatography-high-resolution mass spectrometry/mass spectrometry-based strategy for analyzing eight biomarkers in human urine indicating toxic mushroom or Ricinus communis ingestions

Recently, we presented a strategy for analysis of eight biomarkers in human urine to verify toxic mushroom or Ricinus communis ingestions. However, screening for the full panel is not always necessary. Thus, we aimed to develop a strategy to reduce analysis time and by focusing on two sets of analytes. One set (A) for biomarkers of late-onset syndromes, such as phalloides syndrome or the syndrome after castor bean intake. Another set (B) for biomarkers of early-onset syndromes, such as pantherine-muscaria syndrome and muscarine syndrome. Both analyses should be based on hydrophilic-interaction liquid chromatography coupled with high-resolution mass spectrometry (MS)/MS (HILIC-HRMS/MS). For A, urine samples were prepared by liquid-liquid extraction using dichloromethane and subsequent solid-phase extraction of the aqueous supernatant. For B urine was precipitated using acetonitrile. Method A was validated for ricinine and α- and β-amanitin and method B for muscarine, muscimol, and ibotenic acid according to the specifications for qualitative analytical methods. In addition, robustness of recovery and normalized matrix factors to matrix variability measured by urinary creatinine was tested. Moreover, applicability was tested using 10 urine samples from patients after suspected mushroom intoxication. The analytes α- and β-amanitin, muscarine, muscimol, and ibotenic acid could be successfully identified. Finally, psilocin-O-glucuronide could be identified in two samples and unambiguously distinguished from bufotenine-O-glucuronide via their MS² patterns. In summary, the current workflow offers several advantages towards the previous method, particularly being more labor-, time-, and cost-efficient, more robust, and more sensitive.

Molecular and Functional Imaging Studies of Psychedelic Drug Action in Animals and Humans

Hallucinogens are a loosely defined group of compounds including LSD, N,N-dimethyltryptamines, mescaline, psilocybin/psilocin, and 2,5-dimethoxy-4-methamphetamine (DOM), which can evoke intense visual and emotional experiences. We are witnessing a renaissance of research interest in hallucinogens, driven by increasing awareness of their psychotherapeutic potential. As such, we now present a narrative review of the literature on hallucinogen binding in vitro and ex vivo, and the various molecular imaging studies with positron emission tomography (PET) or single photon emission computer tomography (SPECT). In general, molecular imaging can depict the uptake and binding distribution of labelled hallucinogenic compounds or their congeners in the brain, as was shown in an early PET study with N1-([11C]-methyl)-2-bromo-LSD ([11C]-MBL); displacement with the non-radioactive competitor ketanserin confirmed that the majority of [11C]-MBL specific binding was to serotonin 5-HT2A receptors. However, interactions at serotonin 5HT1A and other classes of receptors and pleotropic effects on second messenger pathways may contribute to the particular experiential phenomenologies of LSD and other hallucinogenic compounds. Other salient aspects of hallucinogen action include permeability to the blood-brain barrier, the rates of metabolism and elimination, and the formation of active metabolites. Despite the maturation of radiochemistry and molecular imaging in recent years, there has been only a handful of PET or SPECT studies of radiolabeled hallucinogens, most recently using the 5-HT2A/2C agonist N-(2[11CH3O]-methoxybenzyl)-2,5-dimethoxy- 4-bromophenethylamine ([11C]Cimbi-36). In addition to PET studies of target engagement at neuroreceptors and transporters, there is a small number of studies on the effects of hallucinogenic compounds on cerebral perfusion ([15O]-water) or metabolism ([18F]-fluorodeoxyglucose/FDG). There remains considerable scope for basic imaging research on the sites of interaction of hallucinogens and their cerebrometabolic effects; we expect that hybrid imaging with PET in conjunction with functional magnetic resonance imaging (fMRI) should provide especially useful for the next phase of this research.

Hypoxia Routes Tryptophan Homeostasis Towards Increased Tryptamine Production

The liver is the central hub for processing and maintaining homeostatic levels of dietary nutrients especially essential amino acids such as tryptophan (Trp). Trp is required not only to sustain protein synthesis but also as a precursor for the production of NAD, neurotransmitters and immunosuppressive metabolites. In light of these roles of Trp and its metabolic products, maintaining homeostatic levels of Trp is essential for health and well-being. The liver regulates global Trp supply by the immunosuppressive enzyme tryptophan-2,3-dioxygenase (TDO2), which degrades Trp down the kynurenine pathway (KP). In the current study, we show that isolated primary hepatocytes when exposed to hypoxic environments, extensively rewire their Trp metabolism by reducing constitutive Tdo2 expression and differentially regulating other Trp pathway enzymes and transporters. Mathematical modelling of Trp metabolism in liver cells under hypoxia predicted decreased flux through the KP while metabolic flux through the tryptamine branch significantly increased. In line, the model also revealed an increased accumulation of tryptamines under hypoxia, at the expense of kynurenines. Metabolic measurements in hypoxic hepatocytes confirmed the predicted reduction in KP metabolites as well as accumulation of tryptamine. Tdo2 expression in cultured primary hepatocytes was reduced upon hypoxia inducible factor (HIF) stabilisation by dimethyloxalylglycine (DMOG), demonstrating that HIFs are involved in the hypoxic downregulation of hepatic Tdo2. DMOG abrogated hepatic luciferase signals in Tdo2 reporter mice, indicating that HIF stability also recapitulates hypoxic rewiring of Trp metabolism in vivo. Also in WT mice HIF stabilization drove homeostatic Trp metabolism away from the KP towards enhanced tryptamine production, leading to enhanced levels of tryptamine in liver, serum and brain. As tryptamines are the most potent hallucinogens known, the observed upregulation of tryptamine in response to hypoxic exposure of hepatocytes may be involved in the generation of hallucinations occurring at high altitude. KP metabolites are known to activate the aryl hydrocarbon receptor (AHR). The AHR-activating properties of tryptamines may explain why immunosuppressive AHR activity is maintained under hypoxia despite downregulation of the KP. In summary our results identify hypoxia as an important factor controlling Trp metabolism in the liver with possible implications for immunosuppressive AHR activation and mental disturbances.

Human indole(ethyl)amine-N-methyltransferase (hINMT) catalyzed methylation of tryptamine, dimethylsulfide and dimethylselenide is enhanced under reducing conditions - A comparison between 254C and 254F, two common hINMT variants

Phenylalanine and cysteine comprise common miss-sense variants (i.e., single nucleotide polymorphisms [SNPs]) at amino acid position 254 of the human indole(ethyl)amine-N-methyltransferase (hINMT). The phenylalanine variant, which occurs in linkage disequilibrium with two 3’ UTR SNPs, has been reported to associate with elevated urine levels of trimethylselenonium (TMSe), the Se-methylated product of volatile dimethylselenide. hINMT allozymes expressing either cysteine (254C) or phenylalanine (254F) at position 254 were compared for enzyme activity (i.e., K_m and V_max) towards the INMT substrates tryptamine, dimethylsulfide (DMS) and dimethylselenide (DMSe) in vitro. The SNP 254C had a higher V_max for DMS and tryptamine in the presence of reducing agent than in its absence. Conversely, V_max for 254F was insensitive to the presence or absence of reducing agent for these substrates. SNP 254F showed a lower K_m for tryptamine in the absence of reducing agent than 254C. No statistically significant difference in V_max or K_m was observed between 254C and 254F allozymes in the presence of reducing agent for DMSe, The K_m values for DMSe methylation were about 10-fold (254C) or 6-fold (254F) more favorable than for tryptamine methylation with reducing agent present. These findings indicated that: 1) That phenylalanine at position 254 renders hINMT methylation of substrates DMS and tryptamine insensitive to a non reducing environment. 2) That human INMT harbors significant thioether-S-methyltransferase (TEMT) activity with a higher affinity for DMSe than tryptamine, 3) The reduction of a 44C/254C disulfide bond in hINMT that increases V_max is proposed.

Updated View on the Relation of the Pineal Gland to Autism Spectrum Disorders

Identification of the biological features of autism is essential for designing an efficient treatment and for prevention of the disorder. Though the subject of extensive research, the neurophysiological features of autism remain unclear. One of the proposed biological causes of autism is malfunction of the pineal gland and deficiency of its principal hormone, melatonin. The main function of melatonin is to link and synchronize the body's homeostasis processes to the circadian and seasonal rhythms, and to regulate the sleep-wake cycle. Therefore, pineal dysfunction has been implicated based on the common observation of low melatonin levels and sleep disorders associated with autism. In this perspective, we highlight several recent findings that support the hypothesis of pineal gland/melatonin involvement in autism. Another common symptom of autism is abnormal neuroplasticity, such as cortical overgrowth and dendritic spine dysgenesis. Here, we synthesize recent information and speculate on the possibility that this abnormal neuroplasticity is caused by hyperactivity of endogenous N,N-dimethyltryptamine (DMT). The pineal gland was proposed as the source of DMT in the brain and therefore, our assumption is that besides melatonin deficiency, pineal dysfunction might also play a part in the development of autism through abnormal metabolism of DMT. We hope that this manuscript will encourage future research of the DMT hypothesis and reexamination of several observations that were previously attributed to other factors, to see if they could be related to pineal gland/melatonin malfunction. Such research could contribute to the development of autism treatment by exogenous melatonin and monitored light exposure.