Determination of pharmacological levels of harmane, harmine and harmaline in mammalian brain tissue, cerebrospinal fluid and plasma by high-performance liquid chromatography with fluorimetric detection

Simple naturally occurring β-carboline alkaloids – role in sustainable theranostics

This review is a brief treatise on some simple β-carboline alkaloids that are abundantly available in plants, animals and foodstuff. These alkaloids are well known for their pharmacological action as well as their allelopathic behaviour. The focus of this review is on sustainable use of naturally occurring compounds in safeguarding human health and protecting our environment at large i.e. the prospective applications of these molecules for Sustainable Theranostics. The review commences with an initial introduction to the β-carboline alkaloids, followed by an outlay of their geographical distribution and natural abundance, then the basic structure and building units of the simplest β-carboline alkaloids have been mentioned. This is followed by a discussion on the important methods of extraction from natural sources both plants and animals. Then the foundation for the use of these alkaloids in Sustainable Theranostics has been built by discussing their interesting photophysics, interactions with important biological molecules and an extensive survey of their therapeutic potential and allelopathic behaviour. Finally the review ends with a silver lining mentioning the future prospective applications of these alkaloids with special relevance to sustainability issues.

Human CYP2D6 in the Brain Is Protective Against Harmine-Induced Neurotoxicity: Evidence from Humanized CYP2D6 Transgenic Mice

CYP2D6 metabolically inactivates several neurotoxins, including beta-carbolines, which are implicated in neurodegenerative diseases. Variation in CYP2D6 within the brain may alter local inactivation of neurotoxic beta-carbolines, thereby influencing neurotoxicity. The beta-carboline harmine, which induces hypothermia and tremor, is metabolized by CYP2D6 to the non-hypothermic/non-tremorgenic harmol. Transgenic mice (TG), expressing human CYP2D6 in addition to their endogenous mouse CYP2D, experience less harmine-induced hypothermia and tremor compared with wild-type mice (WT). We first sought to elucidate the role of CYP2D in general within the brain in harmine-induced hypothermia and tremor severity. A 4-h intracerebroventricular (ICV) pretreatment with the CYP2D inhibitor propranolol increased harmine-induced hypothermia and tremor in TG and increased harmine-induced hypothermia in WT. We next sought to specifically demonstrate that human CYP2D6 expressed in TG brain altered harmine response severity. A 24-h ICV propranolol pretreatment, which selectively and irreversibly inhibits human CYP2D6 in TG brain, increased harmine-induced hypothermia. This 24-h pretreatment had no impact on harmine response in WT, as propranolol is not an irreversible inhibitor of mouse CYP2D in the brain, thus confirming no off-target effects of ICV propranolol pretreatment. Human CYP2D6 activity in TG brain was sufficient in vivo to mitigate harmine-induced neurotoxicity. These findings suggest that human CYP2D6 in the brain is protective against beta-carboline-induced neurotoxicity and that the extensive interindividual variability in CYP2D6 expression in human brain may contribute to variation in susceptibility to certain neurotoxin-associated neurodegenerative disorders.

Pre-clinical investigations of β-carboline alkaloids as antidepressant agents: A systematic review

Depressive disorders remain a current public health problem whose prevalence has increased in the past decades. In the constant search for new therapeutic alternatives, β-carboline alkaloids have been identified as good candidates for new antidepressant drugs. In this systematic review, we summarized all pre-clinical investigations involving the use of natural or semisynthetic β-carboline in depression models. A literature search was conducted in August 2018, using PubMed, Scopus and Science Direct databases. All reports were carefully analyzed, and data extraction was conducted through standardized forms. Methodological quality assessment of in vivo studies was also performed. The entire systematic review was performed according to PRISMA statement. From a total of 373 articles, 26 met all inclusion criteria. In vitro and in vivo studies have evaluated a wide variety of β-carbolines through enzymatic and binding assays, and acute or chronic animal models. Most of the in vivo and in vitro studies is concentrated on two molecules: harman and harmine. They have been investigated in several animal models and some mechanisms of action have been proposed for their antidepressant activity. In general, β-carbolines modulate 5-HT and GABA systems, promote neurogenesis, induce neuroendocrine response and restore astrocytic function, being effective when administrated acutely or chronically in different animal models, including chronic mild stress protocols. In short, β-carbolines are multi-target antidepressant compounds and may be useful in the treatment of depressive disorders.

Copper amine oxidases catalyze the oxidative deamination and hydrolysis of cyclic imines

Although cyclic imines are present in various bioactive secondary metabolites, their degradative metabolism remains unknown. Here, we report that copper amine oxidases, which are important in metabolism of primary amines, catalyze a cyclic imine cleavage reaction. We isolate a microorganism (Arthrobacter sp. C-4A) which metabolizes a β-carboline alkaloid, harmaline. The harmaline-metabolizing enzyme (HarA) purified from strain C-4A is found to be copper amine oxidase and catalyze a ring-opening reaction of cyclic imine within harmaline, besides oxidative deamination of amines. Growth experiments on strain C-4A and Western blot analysis indicate that the HarA expression is induced by harmaline. We propose a reaction mechanism of the cyclic imine cleavage by HarA containing a post-translationally-synthesized cofactor, topaquinone. Together with the above results, the finding of the same activity of copper amine oxidase from E. coli suggests that, in many living organisms, these enzymes may play crucial roles in metabolism of ubiquitous cyclic imines.

Elevated blood harmane (1-methyl-9H-pyrido[3,4-b]indole) concentrations in Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is a late-life neurodegenerative disease. Genetic and environmental factors play an etiological role. Harmane (1-methyl-9H-pyrido[3,4-b]indole) is a potent tremor-producing neurotoxin that shows structural resemblance to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

OBJECTIVES

In 2002 and 2007, we demonstrated elevated blood harmane concentrations [HA] in essential tremor (ET) cases. We now assessed whether blood [HA] were elevated in Parkinson's disease (PD) as well.

METHODS

Blood [HA] were quantified by high performance liquid chromatography. Subjects comprised 113 PD cases and 101 controls.

RESULTS

Mean log blood [HA] in PD cases was double that of controls (0.59±0.63 g(-10)/ml vs. 0.27±0.63 g(-10)/ml, p<0.001). A non-parametric test on non-transformed data (median blood [HA]=3.31 g(-10)/ml in cases and 1.44 g(-10)/ml in controls) also showed this difference (p<0.001). In unadjusted and then adjusted logistic regression analyses, log blood [HA] was associated with PD (odds ratio [OR]unadjusted 2.31, 95% confidence interval [CI] 1.46-3.67, p<0.001; OR(adjusted) 2.54, 95% CI 1.55-4.16, p<0.001). In PD, log blood [HA] co-varied with family history, being lowest in PD cases with no family history (0.54±0.60 g(-10)/ml) and highest in PD cases with a family history of both ET and PD (0.84±0.68 g(-10)/ml) (p=0.06).

CONCLUSIONS

Blood harmane appears to be elevated in PD. The finding needs to be reproduced in additional cohorts to assess its generalizability. The higher concentration in familial PD suggests that the mechanism may involve genetic factors.

Elevated brain harmane (1-methyl-9H-pyrido[3,4-b]indole) in essential tremor cases vs. controls

BACKGROUND

Harmane (1-methyl-9H-pyrido[3,4-β]indole), a potent neurotoxin that has tremor-producing properties in animal models, is present in many foods; although we have demonstrated a difference in tissue harmane concentrations in ET cases vs. controls, all work to date has involved blood samples.

OBJECTIVES

We quantified harmane concentrations in human cerebellum, a brain region of particular pathogenic interest in essential tremor (ET), comparing ET to control brains.

METHODS

Cerebellar cortex was snap frozen and stored at -80°C in aliquots for biochemical analyses. Harmane concentration was assessed using high performance liquid chromatography.

RESULTS

Geometric mean brain harmane concentrations (adjusted for postmortem interval [PMI] and freezer time) were higher in ET cases than controls: 1.0824 (95% confidence interval=0.9405-1.2457) vs. 0.8037 (0.6967-0.9272), p=0.004. Geometric mean of brain harmane concentrations (adjusting for PMI and freezer time) was highest in ET cases who reported other relatives with tremor (1.2005 [0.8712-1.6541]), intermediate in ET cases without family history (1.0312 ([0.8879-1.1976]), and both were significantly higher than controls (p=0.02).

CONCLUSIONS

This study provides additional evidence of a possible etiological importance of this toxin in some cases of the human disease ET.

Blood harmane (1-methyl-9H-pyrido[3,4-b]indole) concentration in essential tremor cases in Spain

BACKGROUND

Environmental correlates for essential tremor (ET) are largely unexplored. The search for such environmental factors has involved the study of a number of neurotoxins. Harmane (1-methyl-9H-pyrido[3,4-b]indole) is a potent tremor-producing toxin. In two prior case-control studies in New York, we demonstrated that blood harmane concentration was elevated in ET patients vs. controls, and especially in familial ET cases. These findings, however, have been derived from a study of cases ascertained through a single tertiary referral center in New York.

OBJECTIVE

Our objective was to determine whether blood harmane concentrations are elevated in familial and sporadic ET cases, ascertained from central Spain, compared to controls without ET.

METHODS

Blood harmane concentrations were quantified by a well-established high performance liquid chromatography method.

RESULTS

The median harmane concentrations were: 2.09 g(-10)/ml (138 controls), 2.41 g(-10)/ml (68 sporadic ET), and 2.90 g(-10)/ml (62 familial ET). In an unadjusted logistic regression analysis, log blood harmane concentration was not significantly associated with diagnosis (familial ET vs. control): odds ratio=1.56, p=0.26. In a logistic regression analysis that adjusted for evaluation start time, which was an important confounding variable, the odds ratio increased to 2.35, p=0.049.

CONCLUSIONS

Blood harmane levels were slightly elevated in a group of familial ET cases compared to a group of controls in Spain. These data seem to further extend our observations from New York to a second cohort of ET cases in Spain. This neurotoxin continues to be a source of interest for future confirmatory research.

Blood harmane (1-methyl-9H-pyrido[3,4-b]indole) concentrations in essential tremor: repeat observation in cases and controls in New York

Essential tremor (ET) is a widespread late-life neurological disease. Genetic and environmental factors are likely to play important etiological roles. Harmane (1-methyl-9H-pyrido[3,4-b]indole) is a potent tremor-producing neurotoxin. Previously, elevated blood harmane concentrations were demonstrated in ET cases compared to controls, but these observations have all been cross-sectional, assessing each subject at only one time point. Thus, no one has ever repeat-assayed blood harmane in the same subjects twice. Whether the observed case-control difference persists at a second time point, years later, is unknown. The current goal was to reassess a sample of our ET cases and controls to determine whether blood harmane concentration remained elevated in ET at a second time point. Blood harmane concentrations were quantified by a well-established high-performance liquid chromatography method in 63 ET cases and 70 controls. A mean of approximately 6 yr elapsed between the initial and this subsequent blood harmane determination. The mean log blood harmane concentration was significantly higher in cases than controls (0.30 ± 0.61 g(-10)/ml versus 0.08 ± 0.55 g(-10)/ml), and the median value in cases was double that of controls: 0.22 g(-10)/ml versus 0.11 g(-10)/ml. The log blood harmane concentration was highest in cases with a family history of ET. Blood harmane concentration was elevated in ET cases compared to controls when reassessed at a second time point several years later, indicating what seems to be a stable association between this environmental toxin and ET.

Relationship between blood harmane and harmine concentrations in familial essential tremor, sporadic essential tremor and controls

INTRODUCTION

Harmane, a potent tremor-producing β-carboline alkaloid, may play a role in the etiology of essential tremor (ET). Blood harmane concentrations are elevated in ET cases compared with controls yet the basis for this elevation remains unknown. Decreased metabolic conversion (harmane to harmine) is one possible explanation. Using a sample of >500 individuals, we hypothesized that defective metabolic conversion of harmane to harmine might underlie the observed elevated harmane concentration in ET, and therefore expected to find a higher harmane to harmine ratio in familial ET than in sporadic ET or controls.

METHODS

Blood harmane and harmine concentrations were quantified by high performance liquid chromatography.

RESULTS

There were 78 familial ET cases, 187 sporadic ET cases, and 276 controls. Blood harmane and harmine concentrations were correlated with one another (Spearman's r=0.24, p<0.001). The mean (±SD) harmane/harmine ratio=23.4±90.9 (range=0.1-987.5). The harmane/harmine ratio was highest in familial ET (46.7±140.4), intermediate in sporadic ET (28.3±108.1), and lowest in controls (13.5±50.3) (p=0.03). In familial ET cases, there was no association between this ratio and tremor severity (Spearman's r=0.08, p=0.48) or tremor duration (Spearman's r=0.14, p=0.24).

CONCLUSION

The basis for the elevated blood harmane concentration, particularly in familial ET, is not known, although the current findings (highest harmane/harmine ratio in familial ET cases) lends support to the possibility that it could be the result of a genetically-driven reduction in harmane metabolism.

Environmental epidemiology of essential tremor

BACKGROUND

Essential tremor (ET) is one of the most common neurological disorders. Despite this, the disease mechanisms and etiology are not well understood. While susceptibility genotypes undoubtedly underlie many ET cases, no ET genes have been identified thus far. As with many other progressive, degenerative neurological disorders, it is likely that environmental factors contribute to the etiology of ET. Environmental epidemiology is the study in specific populations or communities of the effect on human health of physical, biologic and chemical factors in the external environment. The purpose of this article is to review current knowledge with regards to the environmental epidemiology of ET.

RESULTS

As will be discussed, a series of preliminary case-control studies in recent years has begun to explore several candidate toxins/exposures, including harmane (1-methyl-9H-pyrido[3,4-b]indole), lead and agricultural exposures/pesticides.

CONCLUSIONS

While several initial results are promising, as will be discussed, additional studies are needed to more definitively establish whether these exposures are associated with ET and if they are of etiological importance.

Elevated blood harmane (1-methyl-9H-pyrido[3,4-b]indole) concentrations in essential tremor

Essential tremor (ET) is a widespread late-life neurological disease. Genetic and environmental factors likely play an etiological role. Harmane (1-methyl-9H-pyrido[3,4-b]indole) is a potent tremor-producing neurotoxin. In 2002, we demonstrated elevated blood harmane concentrations in an initial sample of 100 ET cases compared to 100 controls. Between 2002 and 2007, we assembled a new and larger sample of ET cases and controls. We now attempt to replicate our previous findings. Cases and controls were frequency-matched on age, gender, and race. Blood harmane concentrations were quantified by high-performance liquid chromatography. Subjects comprised 150 ET cases and 135 controls (mean age 65.3+/-15.5 vs. 65.5+/-14.2 years, p=0.94). Mean log blood harmane concentration was approximately 50% higher in cases than controls (0.50+/-0.54g(-10)/ml vs. 0.35+/-0.62g(-10)/ml, p=0.038). In a logistic regression analysis, log blood harmane concentration was associated with ET (OR(adjusted) 1.56, 95% CI 1.01-2.42, p=0.04), and odds of ET was 1.90 (95% CI 1.07-3.39, p=0.029) in the highest versus lowest log blood harmane tertile. Log blood harmane was highest in ET cases with familial ET (0.53+/-0.57g(-10)/ml), intermediate in cases with sporadic ET (0.43+/-0.45g(-10)/ml) and lowest in controls (0.35+/-0.62g(-10)/ml) (test for trend, p=0.026). Blood harmane appears to be elevated in ET. The higher concentrations in familial ET suggests that the mechanism may involve genetic factors.

Antidepressant-like effect of harmane and other beta-carbolines in the mouse forced swim test

The purpose of the present study was to determine the effects of harmane, norharmane and harmine on the immobility time in the mouse forced swim test (FST) - an animal model of depression. After 30 min of the beta-carbolines injections, mice were placed individually in a vertical glass cylinder (height, 25 cm; diameter, 12 cm) containing water about 15 cm deep at 22+/-1 degrees C and forced to swim. Treatment of animals with harmane (5-15 mg/kg, i.p.), norharmane (2.5-10 mg/kg, i.p.) and harmine (5-15 mg/kg, i.p.) reduced dose-dependently the time of immobility. Their antidepressant-like effects were not affected by pretreatment with reserpine at the dose of 5 mg/kg, i.p., 18 h before the test, which did not modify the immobility time. Conversely, when flumazenil (5 mg/kg, i.p.) was administered 30 min before the test, it was able to antagonize completely the antidepressant-like effects of harmane, norharmane and harmine. It was concluded that harmane, norharmane and harmine reduce the immobility time in this test, suggesting an antidepressant-like effect, via an inverse-agonistic mechanism located in the benzodiazepine receptors.

Harmane inhibits serotonergic dorsal raphe neurons in the rat

RATIONALE

Harmane and norharmane (two beta-carbolines) are tobacco components or products. The effects of harmane and norharmane on serotonergic raphe neurons remain unknown. Harmane and norharmane are inhibitors of the monoamine oxidases A (MAO-A) and B (MAO-B), respectively.

OBJECTIVES

To study the effects of harmane, norharmane, befloxatone (MAOI-A), and selegiline (MAOI-B) on the firing of serotonergic neurons. To compare the effects of these compounds to those of nicotine (whose inhibitory action on serotonergic neurons has been previously described). The effects of cotinine, a metabolite of nicotine known to interact with serotonergic systems, are also tested.

METHODS

In vivo electrophysiological recordings of serotonergic dorsal raphe neurons in the anaesthetized rat.

RESULTS

Nicotine, harmane, and befloxatone inhibited serotonergic dorsal raphe neurons. The other compounds had no effects. The inhibitory effect of harmane (rapid and long-lasting inhibition) differed from that of nicotine (short and rapidly reversed inhibition) and from that of befloxatone (slow, progressive, and long-lasting inhibition). The inhibitory effects of harmane and befloxatone were reversed by the 5-HT1A antagonist WAY 100 635. Pretreatment of animals with p-chlorophenylalanine abolished the inhibitory effect of befloxatone, but not that of harmane.

CONCLUSIONS

Nicotine, harmane, and befloxatone inhibit the activity of raphe serotonergic neurons. Therefore, at least two tobacco compounds, nicotine and harmane, inhibit the activity of serotonergic neurons. The mechanism by which harmane inhibits serotonergic dorsal raphe neurons is likely unrelated to a MAO-A inhibitory effect.

In vitro and ex vivo distribution of [3H]harmane, an endogenous beta-carboline, in rat brain

The endogenous beta-carboline, harmane, has been shown to bind to monoamine oxidase A (MAO-A) and a separate, high affinity, non-MAO site. Research in our laboratory has shown that harmane is an active component of clonidine-displacing substance (CDS), the proposed endogenous ligand for imidazoline binding sites (IBS). In the present study we have investigated the distribution of [3H]harmane in rat brain, and related the binding profile to the distribution of the MAO-A selective ligand [3H]Ro41-1049 and the I2BS ligand [3H]2-BFI. The in vivo distribution of [3H]harmane following intravenous administration was also investigated. Receptor autoradiography revealed a highly significant correlation for the distribution of [3H]harmane and [3H]Ro41-1049, and a significant correlation for [3H]harmane and the I2BS ligand [3H]2-BFI. The in vivo distribution of [3H]harmane suggests that the ligand accumulates in the adrenal gland and throughout the brain with the primary route of excretion occurring via the duodenum. In conclusion, these studies have shown that [3H]harmane labels a population of binding sites that reflect the distribution of MAO-A. Further evidence for a non-MAO, IBS [3H]harmane population has not been shown but the high level of expression of the MAO-A site is likely to have masked the much smaller population of I2BS.

Exposure to beta-carbolines norharman and harman

The aromatic beta-carbolines norharman and harman have been implicated in a number of human diseases including Parkinson's disease, tremor, addiction and cancer. It has been shown that these compounds are normal body constituents formed endogenously but external sources have been identified. Here, we summarise literature data on levels of norharman and harman in fried meat and fish, meat extracts, alcoholic drinks, and coffee brews. Other sources include edible and medicinal plants but tobacco smoke has been identified as a major source. Exposure levels from these different dietary sources are estimated to a maximum of 4 microg norharman per kg body weight (bw) per day and 1 microg harman per kg bw per day. Exposure via tobacco smoke depends on smoking habits and type of cigarettes but can be estimated to 1.1 microg/kg bw for norharman and 0.6 microg/kg bw for harman per package of cigarettes smoked. Studies on toxicokinetics indicate that inhalative exposure leads to a rapid increase in plasma levels and high bioavailability of norharman and harman. Oral bioavailability is lower but there are indications that sublingual absorption may increase dietary uptake of beta-carbolines. Endogenous formation can be estimated to be 50-100 ng/kg bw per day for norharman and about 20 ng/kg bw per day for harman but these rates may increase with high intake of precursors. Biomarker studies on plasma levels of beta-carbolines reported on elevated levels of norharman, harman or both in diseased patients, alcoholics and following tobacco smoking or consumption of beta-carboline-containing food. Cigarette smoking has been identified as major influence but dietary exposure may contribute to exposure.

Detection and characterization of cyclodextrin complexes with beta-carboline derivatives by spectroscopic techniques

beta-Carboline alkaloids exhibit a great variety of pharmacological activities. The solid inclusion complexes of harmane and harmine with beta-cyclodextrin and also with hydroxypropyl-beta-cyclodextrin, have been prepared following different procedures. IR and NMR spectroscopies were employed to verify the interaction of the guest molecules with the cyclodextrin cavities. The differences observed in the IR and NMR spectra are in agreement with those described in the literature for other guest molecules. The shifts in the 13C- and 1H-NMR spectra confirm the existence of the inclusion complexes. The fluorescence emission spectra of these complexes dissolved in buffered aqueous solution (pH 7.3) exhibit the characteristic peaks of the cationic form for harmane alkaloids. The neutral bands are not present for the free alkaloids in aqueous solutions. Fluorescence quenching emission of the complexes is compared to that of the corresponding free alkaloids.

Identification and occurrence of the bioactive beta-carbolines norharman and harman in coffee brews

Norharman and harman, two heterocyclic beta-carboline alkaloids with biological activity, were found in brewed coffee. Identification and analysis were carried out by HPLC-MS and RP-HPLC-fluorescence, respectively. All tested samples of brewed coffee including ground coffee, decaffeinated coffee, instant coffee and espresso contained both norharman and harman in variable amounts. Norharman was the major beta-carboline alkaloid in brewed coffee at levels up to 9.34 microg g(-1) in instant ground coffee compared with harman, which had levels up to 1.67 microg g(-1). The two beta-carbolines appeared to be formed during roasting of the coffee beans. It is concluded that drinking coffee is a major exogenous dietary source of these bioactive beta-carboline alkaloids previously reported as mild psychoactive compounds in animal studies and in vitro co-mutagens. These results support our previous conclusion that foods containing beta-carbolines are an important exogenous source of these alkaloids in humans.

Stimulatory effect of harmane and other beta-carbolines on locus coeruleus neurons in anaesthetized rats

Harmane, harmaline and norharmane are beta-carboline related compounds which have been proposed to be endogenous ligands for imidazoline receptors. The effect of these compounds on the activity of locus coeruleus (LC) neurons was studied by extracellular recordings techniques. Intracerebroventricular administration of harmane and harmaline increased the firing rate of LC neurons. Systemic administration of efaroxan, a mixed alpha(2)-adrenoceptor/I(1)-imidazoline antagonist or vagotomy failed to modify the harmane effect. Furthermore, local applications of harmane and harmaline increased the firing rate of LC neurons in a dose-related manner. Finally, intravenous administration of norharmane also increased the activity of LC neurons. Our results demonstrate that beta-carbolines stimulate LC neuron activity and indicate that this stimulation occurs directly in the LC by a mechanism independent of I(1)- and I(2)-imidazoline receptors.

Determination of harmane and harmine in human blood using reversed-phased high-performance liquid chromatography and fluorescence detection

A number of tremorogenic beta-carboline alkaloids have been found in common plant-derived foodstuffs, beverages, and inhaled substances. Because of their natural presence in the food chain, there is a growing concern regarding the potential risks of certain essential tremors associated with the long-term, low-level dietary exposure to these alkaloids. The purpose of this study was to develop an effective analytical method to determine blood levels of two major beta-carboline derivatives, harmane and harmine. Human blood was extracted with ethyl acetate and methyl-t-butyl ether (2:98) under an alkaline condition. After evaporation of organic solvent, the samples were reconstructed in methanol. The samples were fractionated on a 250 x 4.6-mm C18 reversed-phase column with an isocratic mobile system consisting of 17.5 mM potassium phosphate buffer (ph 6.5) and methanol (30:70), followed by an on-line fluorescence detection. The method had the detection limit to determine 206 and 81 pg/ml of harmane and harmine, respectively, in 10 ml of human blood. The intraday precision (C.V.) at 25 ng/ml was less than 6.7 and 3.4% for harmane and harmine, respectively. The interday precision was 7.3% for harmane and 5.4% for harmine. The method has proven sensitive, reproducible, and thus useful for both laboratory and clinical studies of beta-carboline toxicities.

Harmane produces hypotension following microinjection into the RVLM: possible role of I(1)-imidazoline receptors

The beta-carboline, harmane (0.1 - 1.0 nmol) produces dose dependent hypotension when microinjected unilaterally into the rostral ventrolateral medulla (RVLM) of the anaesthetized rat. The potency of harmane on blood pressure is similar to that of the imidazoline, clonidine. The hypotensive effects of both clonidine and harmane are reversed by microinjection of the relatively I(1)-receptor selective antagonist efaroxan (20 nmol). These results are consistent with harmane acting at an I(1)-receptor in the RVLM. This is the first report of an endogenous ligand for I(1)-receptors that has central effects on blood pressure.

Metabolic hydroxylation of 1-methyl-1,2,3,4-tetrahydro-beta-carboline in humans

We characterized the metabolites of 1-methyl-1,2,3,4-tetrahydro-beta-carboline (MTBC) in human urine by gas chromatography-negative ion chemical ionization mass spectrometry (GC-NICIMS) and developed an analytical method using GC-NICIMS for their quantitative determination. When tetradeuterated MTBC was orally administered to a human subject, two peaks of the deuterated metabolites appeared on mass fragmentograms of the urine samples after administration. They were identified as tetradeuterated 6-hydroxy-MTBC (6-OH-MTBC) and 7-hydroxy-MTBC (7-OH-MTBC), indicating that MTBC was metabolically hydroxylated in humans. The proposed GC-NICIMS method could sensitively and selectively determine urinary 6-OH-MTBC and 7-OH-MTBC without interference from their artifactual formation during analysis. Its application to urine analysis has revealed that MTBC is excreted in human urine predominantly as the two hydroxylated metabolites, in which 6-OH-MTBC is present in both free and conjugated forms, whereas the 7-OH-MTBC of a conjugated form is much more than the 7-OH-MTBC of a free form.

Determination of tetrahydro-beta-carbolines in rat brain by gas chromatography-negative-ion chemical ionization mass spectrometry without interference from artifactual formation

This paper describes a quantitative method for neuroactive alkaloids, 1-methyl-1,2,3,4-tetrahydro-beta-carboline (MTBC) and 1,2,3,4-tetrahydro-beta-carboline (TBC), in rat brain by gas chromatography-negative-ion chemical ionization mass spectrometry (GC-NICIMS). After addition of tetradeuterated MTBC and TBC (internal standards), the samples were subjected to deproteinization, reaction with fluorescamine, solvent extractions, trifluoroacetylation and GC-NICIMS analysis. In contrast to the other previous methods, the artifactual formation during analysis did not interfere with the determination of MTBC and TBC because their precursor tryptamine was removed as a fluorescamine derivative from the analytical system at the first step of pretreatment. MTBC and TBC were specifically and reliably determined in the range of pg-ng/sample. Application of the proposed method has revealed that the MTBC and TBC contents in rat brain significantly increase after intraperitoneal administration of MTBC and TBC, indicating their ability to easily cross the blood-brain barrier.

Determination of tetrahydro-beta-carbolines in urine by high-performance liquid chromatography with suppression of artefact formation

A high-performance liquid chromatographic method has been developed for the determination of urinary tetrahydro-beta-carbolines. When standing tryptamine with formaldehyde and acetaldehyde under extraction conditions, the significant amounts of artefact 1,2,3,4-tetrahydro-beta-carboline (TBC) and 1-methyl-1,2,3,4-tetrahydro-beta-carboline (MTBC) were formed in a short time. Urine samples added with 2-ethyl-1,2,3,4-tetrahydro-beta-carboline (an internal standard) were treated with fluorescamine, and then with glycine, followed by serial solvent extractions. Such a pretreatment using two-step reactions removed a precursor (trypamine) by extracting its fluorescamine derivative, and enhanced the detection response by consuming excess fluorescamine. It solved the analytical problem that artefact TBC and MTBC are formed during analysis. Reversed-phase ion-pair chromatography using a C8-column and trifluoroacetic acid as a counter ion completed a base-line separation of three analytes within 10 min. The calibration graphs showed a good linearity in the range 0.1-50.0 ng ml-1 of urine samples spiked with standard TBC and MTBC. In the spike experiment, the recovery and relative standard deviation were almost 100% and less than 3.0%, respectively, for both TBC and MTBC. The proposed method enables the determination of the genuine urinary concentrations of TBC and MTBC without involving their artefacts.