Identification of harman in the rat arcuate nucleus

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.

Increased beta-carboline 9N-methyltransferase activity in the frontal cortex in Parkinson's disease

Enzymatic beta-carboline N-methyltransferase activities generate N-methylated beta-carbolinium cations that are analogs of the parkinsonian-producing neurotoxin MPP+. We measured beta-carboline-2N-methyltransferase and beta-carboline-9N-methyltransferase activities in the supernatant and particulate fractions from postmortem human brains. These N-methyltransferase activities were assessed in the substantia nigra, putamen, and frontal cortex from control and Parkinson's disease cases. No significant differences were measured in any brain region in particulate and supernatant fraction beta-carboline 2N-methyltransferase activity or particulate fraction beta-carboline 9N-methyltransferase activity. Likewise, supernatant fraction beta-carboline 9N-methyltransferase activity was similar in the putamen and substantia nigra from Parkinson's disease and control cases. Unexpectedly, supernatant fraction beta-carboline 9N-methyltransferase activity was increased fourfold in Parkinson's disease frontal cortex (P < 0.05), suggesting that beta-carboline N-methylation may play a role in Parkinson's disease.

Characterization of brain beta-carboline-2-N-methyltransferase, an enzyme that may play a role in idiopathic Parkinson's disease

The activity of beta-carboline-2-N-methyltransferase results in the formation of neurotoxic N-methylated beta-carbolinium compounds. We have hypothesized that these N-methylated beta-carbolinium cations may contribute to the development of idiopathic Parkinson's disease. This report describes experiments undertaken to optimize assay conditions for bovine brain beta-carboline-2-N-methyltransferase activity. The activity of beta-carboline-2-N-methyltransferase is primarily localized in the cytosol, has a pH optimum of 8.5-9, and obeys Michaelis-Menten kinetics with respect to its substrates, 9-methylnorharman (9-MeNH) and S-adenosyl-L-methionine (SAM). Kinetic constants, KM and Vmax, with respect to 9-MeNH, are 75 microM and 48 pmol/h/mg protein, respectively. The KM for SAM is 81 microM and the Vmax is 53 pmol/h/mg protein. In addition, enzyme activity is inhibited by S-adenosyl-L-homocysteine (SAH) or zinc, and is increased 2-fold in the presence of iron or manganese. Enzyme characterization is a prerequisite to the purification of this N-methyltransferase from bovine brain as well as comparison of its activity in human brain from control and Parkinson's disease individuals.

Formaldehyde-derived tetrahydroisoquinolines and tetrahydro-beta-carbolines in human urine

Human urine samples were examined for the occurrence of formaldehyde-derived tetrahydroisoquinolines and tetrahydro-beta-carbolines generated by condensation of the methanol oxidation product with biogenic amines. Positive results were obtained for the tryptamine condensation product 1,2,3,4-tetrahydro-beta-carboline and the serotonine condensation product 6-hydroxy-1,2,3,4-tetrahydro-beta-carboline as well as for the condensation products with tyramine, dopamine, adrenaline and noradrenaline 1,2,3,4-tetrahydroisoquinoline, 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, N-methyl-4,6,7-trihydroxy-1,2,3,4-tetrahydroisoquinoline, 4,6,7-trihydroxy-1,2,3,4-tetrahydroisoquinoline, and the metabolite 6-methoxy-7-hydroxy-1,2,3,4-tetrahydroisoquinoline. Negative results were obtained for N-methyl-1,2,3,4-tetrahydroisoquinoline and 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline, N-methyl-1,2,3,4-tetrahydro-beta-carboline, 6-methyl-1,2,3,4-tetrahydro-beta-carboline, and 6-methoxy-1,2,3,4-tetrahydro-beta-carboline in samples of chronic alcoholics as well as in the urine of healthy volunteers. No correlation between alcohol ingestion or state of alcoholization could be demonstrated.

Action of harman (1-methyl-beta-carboline) on the brain: body temperature and in vivo efflux of 5-HT from hippocampus of the rat

Harman (1-methyl-beta-carboline) has been shown previously to act on the hippocampus of the rat in terms of its evocation of anxiogenic responses and induction of alcohol preference. In the present experiments, the localized perfusion of 200 microM harman in the dorsal hippocampus of freely moving rats increased the levels of serotonin (5-HT) but not 5-hydroxyindoleacetic acid (5-HIAA) in cerebral dialysates. The systemic administration of 5.0-20 mg/kg harman also enhanced 5-HT in the perfusates but reduced the levels of 5-HIAA in a dose-dependent manner, probably as a result of the inhibition of the enzyme monoamine oxidase type A (MAO-A). Harman given systemically in doses of 2.5-20 mg/kg induced an intense hypothermia, with a maximum fall produced by the 5.0 mg/kg dose. This fall in body temperature (Tb) induced by 5.0 mg/kg harman was not antagonized by 5.0 mg/kg of (+/-)-pindolol. Further, pretreatment of the rats with parachlorophenylalanine (pCPA) also failed to alter the harman-induced hypothermia. The systemic administration of 10 mg/kg of the MAO-A inhibitor, clorgyline, also lowered Tb significantly. Overall, the present experiments show that harman apparently influences 5-HT systems in the brain by its action in inhibiting MAO-A. This property is likely responsible also for the harman-induced increase of 5-HT in the hippocampus of the rats.

5-HT, dopamine, norepinephrine, and related metabolites in brain of low alcohol drinking (LAD) rats shift after chronic intra-hippocampal infusion of harman

Harman (1-methyl-beta-carboline) has been shown to induce preference for alcohol in the genetically bred, low alcohol drinking (LAD) rat. This study was undertaken in the LAD rat to determine whether monoamines and their metabolites in different regions of the brain are altered by harman infused chronically into the dorsal hippocampus. For this purpose, a cannula was implanted stereotaxically into the dorsal hippocampus. The cannula was attached to an osmotic minipump implanted subcutaneously within the intrascapular space. The pump was filled with either an artificial cerebrospinal fluid (CSF) vehicle or harman, which was delivered at a rate of 1.0 or 3.0 micrograms/h (i.e., 5.5 or 16.5 nmol/h, respectively) for a period of 14 days. Four days after surgery, a standard preference test for ethyl alcohol was given to the rats over 10 days in which concentrations were increased daily from 3%-30%. The higher concentration of harman infused into the hippocampus elevated the level of serotonin (5-HT), both ipsilateral and contralateral to the hippocampal site of infusion, as well as in the midbrain, frontal cortex, striatum and nucleus accumbens. Similarly, this treatment resulted in a rise in the levels of norepinephrine in the hippocampus and midbrain but decreases in dopamine levels in the pons. The levels of 5-hydroxyindoleacetic acid (5-HIAA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were diminished in the pons of rats given 3.0 micrograms/h harman, whereas both concentrations of the beta-carboline reduced the level of homovanillic acid (HVA) in the frontal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

N-Methyl-beta-carboline-3-carboxamide (FG 7142), an anxiogenic agent in airborne particles and cigarette smoke-polluted indoor air

beta-Carboline-3-carboxylic acid methylamide (FG 7142), an anxiogenic agent, has been measured in airborne particles, automobile-exhaust particles, incinerator ash, smoke condensate of tree leaves and cigarette-smoke-polluted indoor air by high-performance liquid chromatography. This compound has been detected in indoor as well as outdoor air. The source of this compound in indoor air was determined as cigarette smoke, identified from smoking machine studies. This anxiogenic agent was detected in smoke condensate of tree leaves and incinerator ash from garbage burning plants, but not in diesel-exhaust particles. Considering the present results, together with the previous finding that cigarette smoke contains this compound, FG 7142 is likely to be formed through combustion of plants. Our data also suggest that this compound may be widely distributed in the environment.

Increased alcohol intake in low alcohol drinking rats after chronic infusion of the beta-carboline harman into the hippocampus

Harman (1-methyl-beta-carboline) has been shown to induce volitional drinking of ethyl alcohol in the rat. The purpose of this study was to examine the long-term effect of sustained delivery of harman into the dorsal hippocampus on the subsequent preference for alcohol in the genetically bred low alcohol drinking (LAD) rat. The individual pattern of preference for alcohol was first determined following a standard 3-30% alcohol self-selection test for 10 days. Thereafter, a cerebral cannula for constant infusion was implanted stereotaxically into the dorsal hippocampus. The cannula was attached to an osmotic minipump implanted subcutaneously, which was filled with either an artificial cerebrospinal fluid (CSF) vehicle or harman. Harman was delivered at a rate of 1.0 or 3.0 micrograms/h (i.e., 5.5 or 16.5 nmol/h, respectively) for a period of 14 days. Four days after surgery, the rats underwent a second 3-30% alcohol preference test for 10 days. Both doses of harman induced a threefold increase in the voluntary consumption of alcohol, expressed as g/kg per day. This effect of the beta-carboline seems to be specific for ethanol because its intake by the LAD rats was increased significantly only when concentrations from 11% to 30% were presented. Harman also enhanced the daily intake of food in a dose-dependent manner, but did not affect body weights or the volumes of water and total fluid consumed. These results, thus, demonstrate that the long-term exposure of hippocampal neurons to harman induces a preference for high concentrations of alcohol even in a line of rats lacking such a genetic predisposition.

[3H]harman binding experiments. I: A reversible and selective radioligand for monoamine oxidase subtype A in the CNS of the rat

Harman (1-methyl-beta-carboline) is an endogenous compound with neurotropic properties in rats and humans. In a novel in vitro binding assay, the binding site of [3H]harman has been characterized in the rat crude mitochondrial (P2) fraction. The binding was saturable and reversible. Only a single high-affinity binding site was detected by kinetic, saturation, and displacement analyses in the cerebral cortex of the rat. The linear Scatchard plots revealed equilibrium dissociation constant (KD) values of approximately 2.5 nM at 0 degrees C, approximately 9 nM at 23 degrees C, and approximately 30 nM at 37 degrees C. Among six CNS regions (hypothalamus, hippocampus, cerebral cortex, striatum, cerebellum, and spinal cord), the highest density of binding sites (Bmax) was determined in the hypothalamus (approximately 5.5 pmol/mg of protein) and the lowest in the spinal cord (approximately 2.0 pmol/mg of protein). Several drugs known to affect serotonergic, adrenergic, dopaminergic, cholinergic, or GABAergic neurotransmission inhibited specific binding at best in the micromolar range. In contrast, potent and selective inhibitors of monoamine oxidase subtype A were active in the lower and middle nanomolar range. The displacing potency (apparent Ki) of substrates and inhibitors of monoamine oxidase correlated positively and highly significantly with the corresponding values of the inhibition of monoamine oxidase activity of subtype A (r = 0.92, p less than 0.001, n = 17) but not of subtype B (r = -0.47, p greater than 0.05, n = 15). In conclusion, [3H]harman was identified as a specific ligand of the active site of the A subtype of monoamine oxidase in rat brain.

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

Increased blood aldehyde levels, as occur in alcohol intoxication, could lead to the formation of beta-carbolines such as harmane by condensation with indoleamines. Endogenous beta-carbolines, therefore, should occur in specific brain areas where indoleamine concentrations are high, whilst exogenous beta-carbolines should exhibit an even distribution. The author presents direct and sensitive methods for assaying the beta-carbolines harmane, harmine and harmaline in brain tissue, cerebrospinal fluid and plasma at picogram sample concentrations using reversed-phase high-performance liquid chromatography with fluorimetric detection and minimal sample preparation. Using these assay methods, it was found that the distribution of beta-carbolines from a source exogenous to the brain results in a relatively even distribution within the brain tissue.

Harman in rat brain, lung and human CSF: effect of alcohol consumption

A simple, sensitive, HPLC method for the determination of harman has been developed and used to quantitate harman in rat brain (0.41 +/- 0.05 ng/g, n = 7) and rat lung (1.88 +/- 0.55 ng/g, n = 6). The definitive identification of harman in these tissues was accomplished by derivatizing the beta-carboline with pentafluorobenzyl bromide and using gas chromatography-electron capture chemical ionization mass spectrometry. Rats treated acutely with ethanol or subchronically with ethanol in the presence or absence of disulfiram did not have altered harman concentrations. Analysis of control human CSF samples and CSF samples taken from alcoholic patients (n = 8) at the time of intoxicated admission and one week later indicated a predominant absence of harman. These data suggest that harman is unlikely to be formed as a result of ethanol ingestion; its origin and pharmacological significance remain to be determined.

Harman in alcoholic beverages: pharmacological and toxicological implications

Harman, a beta-carboline compound, was identified and quantitated in beer and wine samples using a combination of high performance liquid chromatography with fluorescence detection and gas chromatography-negative chemical ionization mass spectrometry. The concentration of harman in beer (7.3-140.0 ng/ml) was greater than in wine (0.8-10.5 ng/ml) and was not related to alcohol content. The pharmacological and toxicological implications of harman in alcoholic beverages are discussed.

Measurement of beta-carbolines by high-performance liquid chromatography with fluorescence detection

A method using high-performance liquid chromatography with fluorescence detection was developed for the determination of beta-carboline compounds norharman, harman, norharmol, and harmol in lung. Aqueous derivatization with acetic anhydride was used to facilitate the isolation and separation of the phenolic compounds and to reduce the fluorescence background of the biological samples. Harman was identified and quantitated in rat lung (1.88 +/- 0.55 ng/g) using this method and its identity confirmed by means of gas chromatography-negative-ion chemical ionization mass spectrometry.

Effects of induction on the metabolism and cytochrome P-450 binding of harman and other beta-carbolines

1. The metabolism of harman by liver microsomes from non-induced, phenobarbitone (PB)-induced and 3-methylcholanthrene (MC)-induced mice was investigated. Initial reaction rates for harman disappearance were measured and showed a 4-fold induction by PB and a 10.6-fold induction by MC. 2. The major metabolite formed with each microsomal preparation was identified as 6-hydroxyharman. 3. Microsomal cytochrome P-450 binding was measured for harman and other beta-carbolines and both Type I and Type II binding spectra were observed, being dependent upon the mode of induction.

Demonstration of a distinct class of high-affinity binding sites for [3H]norharman [( 3H]beta-carboline) in the rat brain

Specific binding sites were demonstrated for some beta-carbolines in the rat brain with [3H]norharman as a ligand. The ligand displayed a high affinity for synaptosomal membranes which had been fractionated by a sucrose gradient. The calculated apparent KD value was 1.55 nmol/l and the maximum number of binding sites 148 fmol/mg protein. Displacement studies showed an exclusive specificity for a small group of beta-carbolines but not for the previously described inverse agonists at the benzodiazepine receptor nor for tryptamine and other indoles, as well as pargyline, a monoamine oxidase inhibitor. Further analysis revealed other binding sites for [3H]norharman, with an apparent KD value of 36 nmol/l that are presumably located on mitochondrial membranes. Binding to these sites was also not displaced by pargyline. Pargyline displaced [3H]norharman from a third population of binding sites on mitochondrial membranes with the apparent KD value of 46 nmol/l. These findings could explain the pharmacological effects of norharman and other beta-carbolines in vivo.

Formation of a beta-carboline (1,2,3,4-tetrahydro-1-methyl-beta-carboline-1-carboxylic acid) following intracerebroventricular injection of tryptamine and pyruvic acid

Tritium labelled 1-carboxy-tetrahydroharman was identified in rat brain following i.c.v.-injection of [3H]tryptamine and pyruvic acid. The animals had been treated with the MAO inhibitor pargyline (40 mg/kg) 30 min before i.c.v. injection. Under these conditions, only trace amounts of [3H]indole acetic acid could be detected in the brain. The formation of 1-CTHH was time-dependent. Five minutes following the i.c.v. injection, approximately 0.45% of the administered tryptamine was converted into 1-CTHH and 23% were still unchanged. The amount of the radioactive 1-CTHH increased slightly within 1 h (0.8%; [3H] tryptamine: 6%). Pretreatment of the rats with high doses of pargyline (75 mg/kg; 90 min before i.c.v. injection) prevented the formation of both [3H]1-CTHH and [3H]indole acetic acid (IAA) suggesting that high doses of pargyline inhibit the formation of 1-CTHH. As control for a possible non-enzymatic formation of 1-CTHH, [3H]tryptamine and various concentrations of pyruvic acid were incubated in phosphate buffer at pH 7.4. 1-CTHH was not detected under these conditions. However, the formation of 1-CTHH was observed at high pyruvic acid concentrations (final concentration = 100 mM) and low pH values (less than pH4). To support the assumption that the observed condensation of both precursors to 1-CTHH occurred intracellularly, the metabolism of tryptamine was studied. Two minutes after i.c.v. injection of [3H]tryptamine approximately 4% of the injected dose remained unchanged and 10% were metabolized to [3H]IAA. These findings suggest a rapid disappearance of [3H]tryptamine from the cerebrospinal fluid as well as a rapid penetration into the cerebral tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Mutagenicities of indole and 30 derivatives after nitrite treatment

Indole and 7-derivatives, L- and D-tryptophan and 9 derivatives, and beta-carboline (norharman) and 11 derivatives were tested for mutagenicity to Salmonella typhimurium TA100 and TA98 after nitrite treatment. 1-Methylindole, which is present in cigarette smoke condensate (Grob and Voellmin, 1970; Hoffmann and Rathkamp, 1970), was the most mutagenic to TA100 without S9 mix after nitrite treatment, inducing 615,000 revertants/mg. 2-Methylindole, 1-methyl-DL-tryptophan, harmaline and (-)-(1S,3S)-1,2-dimethyl-1,2,3,4-tetrahydro-beta-carboline-3- carboxylic acid also showed strong mutagenicity after nitrite treatment, inducing 129,000, 184,000, 103,000 and 197,000 revertants/mg, respectively. These mutagenic potencies were comparable with those of benzo[alpha]pyrene, 3-methylcholanthrene and 2-amino-9H-pyrido[2,3-b]indole (A alpha C) (Sugimura, 1982). Of 31 compounds tested, 22 were mutagenic after nitrite treatment. Since various indole compounds are ubiquitous in our environment, especially in plants, the presence of their mutagenicities after nitrite treatment warrants further studies, including those on their in vivo carcinogenicities.

Ethanol increases single unit activity in the inferior olivary nucleus

Single unit recording of rat inferior olivary nucleus neurons reveals significantly elevated discharge after acute intraperitoneal injection of 2 g/kg ethanol. This effect is consistent across 3 different methods of anesthesia and immobilization: local Xylocaine plus intraperitoneal D-tubocurare, intraperitoneal chloral hydrate and halothane vapor. In contrast, under urethane anesthesia acute ethanol produces significant depression of olivary discharge. Since this effect is opposite to that found under the other anesthetic conditions (including topical Xylocaine only), urethane anesthesia may compromise generalizations of electrophysiologic studies of ethanol. Neurons of the inferior olivary nucleus excite cerebellar Purkinje cells through a powerful afferent circuit; our data therefore suggest that ethanol-induced increases in cerebellar Purkinje cell complex (climbing fiber burst) spikes, obtained in our previous studies, are secondary to olivary activation.

Lack of specificity in cation effects on solubilized benzodiazepine receptor

Receptors for benzodiazepines (BZ) and beta-carboline-carboxylic acid ethyl ester (beta-CCE) has been solubilized with decanoly-N-methylglucamide (DMG), a new kind of nonionic detergent. The apparent dissociation constants of diazepam and beta-CCE for solubilized receptor were similar to those for synaptic membranes. Sucrose density gradient centrifugation of the solubilized receptor protein revealed that the binding profile of [3H]beta-CCE essentially parallels that of [3H]diazepam and that both sedimentation coefficients were 10.5S. Co2+ and Ni2+, which increase [3H]diazepam binding and decrease [3H]beta-CCE binding to synaptic membranes, remarkably increased the binding of both to the solubilized receptor. Mg2+ and Ca2+, which had no effect on membrane receptor binding, also enhanced [3H]diazepam and [3H]beta-CCE binding to the solubilized receptor. The increase in binding in the presence of these divalent cations was due to a change in the apparent number of binding sites, with no change in binding affinities. The relative lack of specificity in divalent cation effects on solubilized BZ receptor may be caused by separation or destruction of the cation recognition site or channel of the BZ receptor complex by solubilization of the synaptic membrane with DMG.

Ethanol induces an increase of harman in the brain and urine of rats

Harman occurs in rat brain, with the highest concentration in the cerebellum and the lowest in the striatum. 2 g/kg ethanol were ineffective with respect to the concentration of harman in the brain whereas 5 g/kg ethanol caused a time-dependent increase in the cerebral cortex as well as the cerebellum. A toxic dose (8 g/kg) of ethanol elicited no change of harman in the brain 3 h following the application. The rise in the harman concentration in the brain did not correlate with the increase of acetaldehyde in the blood after treatment with ethanol suggesting that several mechanisms are involved in the changes of the levels of harman. In subchronic experiments rats were treated with ethanol over a period of 5 or 6 days. Harman increased in the brain whereby the effect seemed to be more pronounced in the cerebellum than in the cerebral cortex. The concentration tended to increase over time and reached control levels again during withdrawal. The time course of the excretion of harman into the urine was similar to that of the brain in that it increased continuously during the period of ethanol treatment and reached control levels again during withdrawal.

Ethanol effects on harmaline-induced tremor and increase of cerebellar cyclic GMP

The spectra of pharmacological effects of ethanol and the benzodiazepine show a degree of overlap. Neurophysiological and neurochemical evidence indicates that both ethanol and benzodiazepines facilitate inhibitory neurotransmission mediated by GABA. Diazepam has been reported to inhibit both the tremor and mechanism of cerebellar cyclic GMP caused by harmaline by a neurotransmission in the cerebellum. Because of the similarities between ethanol and benzodiazepines, the effects of ethanol on harmaline-induced tremor and increase of cerebellar cyclic GMP were studied. Ethanol inhibited harmaline-induced tremor at doses as low as 0.1 g/kg. At this low dose, however, a dissociation between inhibition of harmaline tremor and inhibition of the harmaline-induced increase of cerebellar cyclic GMP was observed.

Picomole analyses of tryptophan by derivatization to 9-hydroxymethyl-beta-carboline

A new method specific for the determination of subpicomole quantities of tryptophan has been developed by elaboration of the Pictet-Spengler reaction. It permitted reproducible quantitation of tryptophan in less than 1 microliter of plasma ultrafiltrate or 1 mg of brain tissue. Samples deproteinized by trichloroacetic acid were boiled for 15 min with formaldehyde and potassium ferricyanide at controlled acidity, where tryptophan was converted to a single new product identified as 9-hydroxymethyl-beta-carboline. It was quantitated by either direct spectrofluorometry or a reversed-phase HPLC system developed for beta-carbolines. Under our conditions, peptides containing N-terminal tryptophan such as Trp-Leu and delta sleep-inducing peptide gave N-(9-hydroxymethyl-beta-carboline-3-carbonyl) peptides which retained all amino acid residues except tryptophan.

In vitro studies on the effect of beta-carbolines on the activities of acetylcholinesterase and choline acetyltransferase and on the muscarinic receptor binding of the rat brain

Acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7) activity and muscarinic receptor binding of homogenates from several brain structures were inhibited by beta-carbolines. The inhibition was of the noncompetitive type in the case of the enzyme and of the mixed type in the case of the receptor binding. This effect was most strongly manifested by pyridoindoles(harmane, norharmane), i.e., carbolines containing an aromatic C ring than by the corresponding piperidoindoles (tetrahydroharmane, tetrahydronorharmane), i.e., those with a reduced C ring. The activity of choline acetyltransferase (acetyl-CoA:choline O-acetyltransferase, EC 2.3.1.6) was not altered. These data are further evidence of the interactions between indoleamine derivatives and the cholinergic system. The results are discussed in terms of their possible biological significance.

Pharmacokinetics of tetrahydronorharmane (tetrahydro-beta-carboline) in rats

The distribution, metabolism and elimination into the urine of (14C)-tetrahydronorharmane (THN) as well as of (14C)-6-hydroxy-tetrahydronorharmane (6-OH-THN) are investigated in female and male rats. Following intravenous injection of (14C)-THN radioactivity was detected in all organs examined, namely blood, brain, lung, adrenal gland, small intestine, fat tissue, kidney and liver. In the brain the elimination half life of THN was calculated to be 1.8 h, the elimination half life of the radioactivity in the blood 6.24 h, and the accumulation half life in the urine 9.24 h. The elimination of 6-OH-THN into the urine is faster than that of THN. At least four metabolites of (14C)-THN were found in the urine of female rats. Two different metabolic pathways are discussed, firstly, hydroxylation followed by conjugation with glucuronic and sulfuric acids and secondly, dehydrogenation, followed by oxygenation. In female rats only traces of the conjugated metabolites are hydrolysed by arylsulfatase, whereas in male rats approximately 2/5 are cleaved by this enzyme. Pretreatment of male rats with 3-methylcholanthrene induced conjugation, whereas phenobarbital had no obvious effect on the pattern of metabolites. SKF 525 A and CFT 1201 both prevented almost completely the formation of conjugates from THN.

beta-Carbolines as selective monoamine oxidase inhibitors: in vivo implications

The inhibitory action of a range of beta-carbolines on human and rat monoamine oxidase (MAO) A and B has been studied. Concentrations of 5-hydroxytryptamine and phenylethylamine, approximately at their Km values, were used as substrates for MAO A and B respectively. A wide variation in selectivity was found, with harmaline being 10,000 times more potent an inhibitor of A than B whereas, using tetrahydro-beta-carboline and harmane, the difference was nearer to ten-fold. Of the carbolines which have been found endogenously, tetrahydro-beta-carboline, 6-methoxytetrahydro-beta-carboline and harmane are all sufficiently potent inhibitors of human MAO A, with I50 values of 5 X 10(-6), 10(-6), 5 X 10(-7) M respectively, for this property to be of possible physiological significance. Harmane, with an I50 of 5 X 10(-6) M, might also play a role as an inhibitor of MAO B.

The route and significance of endogenous synthesis of alkaloids in animals

There is now substantial evidence that several TIQs and beta-carbolines are present in vivo and increase during certain pathological conditions. It still remains to be determined, however, precisely what roles they play in endogenous functions and whether or not they are critical for the expression of these pathological conditions. Accumulating biochemical information continues to support the notion that these compounds can act as false transmitters. The exciting new findings, which will certainly receive a great deal more attention, concern the interaction of some of the beta-carbolines with the benzodiazepine receptor. Determining if a beta-carboline is an endogenous receptor ligand will attract further research interest on the theoretical and specifically clinically-directed levels. Biochemical, morphological, and behavioral data indicate that some of the condensation products can act as neurotoxins. Very few experiments have included an examination of long-term effects of exposure to one of these alkaloids, so the amount of information on this issue is limited. Chronic rather than acute administration of an alkaloid is more likely to mimic the pathological states in which these compounds are hypothesized to play a role. Biochemically, both the dopaminergic and serotonergic systems have been shown to be affected by chronic treatments with certain alkaloids. Progressive and long-term behavioral alterations also have been reported. Such changes may reflect an adaptation to an increase or decrease in activity of particular systems or a neurotoxic action.

Anticonvulsant effects of caerulein, cholecystokinin octapeptide (CCK-8) and diazepam against seizures produced in mice by harman, thiosemicarbazide and isoniazid

Caerulein, cholecystokinin octapeptide (CCK-8) and diazepam delayed the onset of seizures produced by harman and thiosemicarbazide (TSC). Caerulein had the potency of diazepam, whereas CCK-8 was less active by a factor of four. The convulsions induced by isoniazid (INH) were very resistant to both caerulein and diazepam; CCK-8 was not tested against isoniazid. Haloperidol did not influence the effect of TSC; it enhanced isoniazid-induced seizures, and antagonized the convulsant effect of harman.

Benzodiazepine antagonism by harmane and other beta-carbolines in vitro and in vivo

Harmane and other related beta-carbolines are putative endogenous ligands of the benzodiazepine receptor. Since the compounds are potent convulsants they may have agonist activities at the benzodiazepine receptor while the benzodiazepines may be antagonists. This hypothesis was proved by comparing the in vivo and in vitro antagonism of benzodiazepines by harmane and other beta-carbolines. Harmane is clearly a competitive inhibitor of benzodiazepine receptor binding in vitro. Moreover, harmane-induced convulsions can be inhibited reversibly by diazepam in a manner which is consistent with the assumption of competitive antagonism in vivo. For some beta-carboline derivatives a correlation was found between the affinity for the benzodiazepine receptor in vitro and the convulsive potency in vivo. Thus, the data reported suggest that harmane or other related beta-carbolines are putative endogenous agonists of the benzodiazepine receptor. This suggestion is further supported by the observation that diazepam is equally potent in inhibiting harmane- or picrotoxin-induced convulsions, indicating a convulsive mechanism within the GABA receptor-benzodiazepine receptor system.

[3H]propyl beta-carboline-3-carboxylate binds specifically to brain benzodiazepine receptors

Ethyl beta-carboline-3-carboxylate has recently been isolated from human urine and it was proposed that derivatives of this compound might be related to an endogenous ligand for benzodiazepine receptors. In the present study we investigated high-affinity binding of [3H]propyl beta-carboline-3-carboxylate ([3H]PrCC) to rat brain membranes. [3H]PrCC binds specifically and with high affinity (half-maximal binding at ca. 1nM) to rat brain membranes. The regional and subcellular distributions of specific [3H]PrCC binding are similar, but not identical, to the distributions of [3H]flunitrazepam or [3H]-diazepam binding. The total numbers of binding sites labelled by [3H]PrCC and [3H]flunitrazepam in rat cerebellum are closely similar, and both ligands bind to cerebellar membranes in a mutually exclusive way. The pharmacological selectivity of [3H]PrCC and [3H]diazepam binding is almost identical. Binding of [3H]PrCC like binding of [3H]diazepam, can be increased in vitro by muscimol, GABA and SQ 20.009. Although subtle differences in binding characteristics were observed, these results indicate that [3H]PrCC and benzodiazepines bind to a common recognition site on benzodiazepine receptors.

1-Methyl-beta-carboline (harmane), a potent endogenous inhibitor of benzodiazepine receptor binding

The interaction of several beta-carbolines with specific [3H]-flunitrazepam binding to benzodiazepine receptors in rat brain membranes was investigated. Out of the investigated compounds, harmane and norharmane were the most potent inhibitors of specific [3H]-flunitrazepam binding, with IC50-values in the micromolar range. All other derivatives, including harmine, harmaline, and several tetrahydroderivatives were at least ten times less potent. Harmane has been previously found in rat brain and human urine, so it is the most potent endogenous inhibitor of specific [3H]-flunitrazepam binding known so far, with a several fold higher affinity for the benzodiazepine receptor than inosine and hypoxanthine. Thus, we suggest that harmane or other related beta-carbolines could be potential candidates as endogenous ligands of the benzodiazepine receptor.

Effect of some beta-carbolines on phenylethylamine and apomorphine stereotypies in rats

Tetrahydro-beta-carbolines (THBC:s) have recently been shown to occur in the human body and their role in mental diseases has been discussed. The effect of THBC:s and some other beta-carbolines (25 mg/kg IP) were studied on the stereotypies caused by apomorphine (APO, 2 mg/kg IP) and phenylethylamine (PEA, 50 mg/kg IP) in rats. These effects of dopaminergic drugs like apomorphine as well as of phenylethylamine have sometimes been used as animal models of paranoid schizophrenia. Dose effect relationships were studied from ther most potent substances. All beta-carbolines studied significantly inhibited APO stereotypy. 6-Methoxyharmalan was most effective followed by beta-carboline (BC), tetrahydro-beta-carboline (THBC), 1-methyl-THBC, 6-methoxy-THBC and 6-hydroxy-THBC. 6-Methoxyharmalan, 6-hydroxy-THBC and BC inhibited also PEA stereotypy. Other substances studied were ineffective. beta-Carbolines did not inhibit PEA and APO stereotypies in the same way. Thus the mode of PEA and APO stereotypies seems to differ, and beta-carbolines seem influence these stereotypies by more than one mechanism. If dopamine hypothesis is valid, the beta-carbolines formed in human body may protect rather than worsen in paranoid psychoses.