6-Hydroxy-tetrahydronorharmane (6-hydroxy-tetrahydro-beta-carboline), a new active metabolite of indole-alkylamines in man and rat

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.

Gas chromatographic-mass spectrometric screening procedure for the identification of formaldehyde-derived tetrahydro-beta-carbolines in human urine

A gas chromatographic-mass spectrometric method for the identification of 1,2,3,4-tetrahydro-beta-carboline and four metabolites extracted from urine is described. In a first step the substances, formed by reaction of formaldehyde with biogenic amines, were derivatized in aqueous solution with methyl chloroformate to eliminate an artificial formation of these compounds via condensation of endogenous indole ethylamines with aldehydes or alpha-keto acids during the work-up procedure. This initial derivatization formed stable hydrophobic compounds and improved the extractability for a liquid-liquid extraction. Further clean-up was performed by solid-phase extraction on C18 sample preparation columns. The method can identify these compounds in the picogram range.

The use of microwave irradiation with low formalin concentrations to enhance the conversion of dopamine into norsalsolinol in rat brain: a pilot study

The fixation of the neurotransmitter dopamine in the central nervous system by perfusion with formalin solutions seems to take place mainly via the formalin-induced condensation product norsalsolinol. In the present investigation the influence of microwave irradiation of the formalin-induced condensation of dopamine was studied in vitro and in vivo by making use of different, relatively low, formalin concentrations. It appeared that in vitro and in vivo the dopamine conversion was complete with 4% formalin and no influence of microwaves was noted. However, by making use of much lower formalin concentrations (0.2% and 0.4%) the condensation of dopamine was strongly augmented, in vitro (200%) and in vivo (at least 500%) using microwave techniques. There was a considerable loss in non-microwaved tissue (30%) after perfusion in vivo. This was lower (10%) in microwaved tissue. In experiments with perfused brain tissue which allowed a more complete calculation, a loss was found. This might be caused by a strong binding of dopamine and/or norsalsolinol to tissue components or to side reactions that could not be traced by the present experimental techniques.

Behavioural and electrocortical power spectrum effects of 5-methoxytryptoline and other analogs after intraventricular administration in rats

The behavioural and electrocortical power spectrum effects of tryptoline and the 5-hydroxy and 5-methoxy derivatives were studied after microinjection of the drugs into the third cerebral ventricle in freely moving rats. The three compounds produced a dose-dependent desynchronication in electrocortical activity with a concomitant syndrome of behavioural stimulation. The most potent compound was 5-methoxytryptoline, already active at 4 nmol. When given into the third cerebral ventricle, 5-methoxytryptoline antagonized the sedation and hypothermia induced by reserpine. The relative order of potencies was 5-methoxytryptoline greater than 5-hydroxytryptoline greater than tryptoline. Melatonin, the 5-methoxy-N-acetyl derivative of serotonin, when injected into the third cerebral ventricle, did not produce desynchronization and elicited only mild sedation. The high potency of 5-methoxytryptoline following injection into the third cerebral ventricle and the relative order of potencies with 5-hydroxytryptoline and tryptoline is compared to the affinity of these compounds for the modulatory site of the serotonin transporter which was labelled with [3H]imipramine or [3H]paroxetine.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC and related agents: II

Antipyretics, in particular acetaminophen, aspirin and ibuprofen, constitute the single most important class of drugs used therapeutically for an effect on body temperature. Hallucinogens exert prominent actions on the central nervous system, and it is not surprising that, like so many other centrally-acting agents, they too often affect temperature. This compilation primarily covers the considerable amount of data published from 1981 through 1985 on the interactions of these drugs and thermoregulation, but data from many earlier papers not included in a previous compilation are also tabulated. The effects of agents not classically considered as antipyretics on temperatures of febrile subjects are also covered. The information listed includes the species used, the route of administration and dose of drug, the environmental temperature at which experiments were performed, the number of tests, the direction and magnitude of change in body temperature and remarks on special conditions, such as age or brain lesions. Also indicated is the influence of other drugs, such as antagonists, on the response to the primary agent.

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.

Decarboxylation of 1,2,3,4-tetrahydro-beta-carboline-1-carboxylic acids in brain homogenate and catalysis by pyridoxal-5'-phosphate

[Carboxyl-14C] labelled 1,2,3,4-tetrahydro-beta-carboline-1-carboxylic acid (I) and 1-methyl-1,2,3,4-tetrahydro-beta-carboline-1-carboxylic acid (II) were synthesized and their decarboxylation was studied in mouse brain homogenate and buffer. The decarboxylation rates of (I) and (II) in the homogenate were about 6-fold and 4-fold, respectively, as compared with the rates in phosphate buffer. The increase could not be prevented by preheating the homogenate, but was partially abolished by addition of 1 mM EDTA. The decarboxylation was increased dose-dependently when pyridoxal-5'-phosphate was included in the buffer, 400 microM being sufficient to exceed the rate in homogenate for both (I) and (II). Mass spectrometric examination of the decarboxylation products indicated that both (I) and (II) were degraded mainly to corresponding 1,2,3,4-tetrahydro-beta-carbolines, but some 3,4-dihydro analogues also were detectable. In conclusion, the results outline a way through which these pharmacologically active beta-carbolines are readily formed under conditions that may be regarded as physiological.

Biochemical basis of alcoholism: statements and hypotheses of present research

Experimental results and theoretical considerations on the biology of alcoholism are devoted to the following topics: genetically determined differences in metabolic tolerance; participation of the alternative alcohol metabolizing systems in chronic alcohol intake; genetically determined differences in functional tolerance of the CNS to the hypnotic effect of alcohol; cross tolerance between alcohol and centrally active drugs; dissociation of tolerance and cross tolerance from physical dependence; permanent effect of uncontrolled drinking behavior induced by alkaloid metabolites in the CNS; genetically determined alterations in the function of opiate receptors; and genetic predisposition to addiction due to innate endorphin deficiency. For the purpose of introducing the most important research teams and their main work, statements from selected publications of individual groups have been classified as to subject matter and summarized. Although the number for summary-quotations had to be restricted, the criterion for selection was the relevance to the etiology of alcoholism rather than consequences of alcohol drinking.

[Simple compounds with high pharmacologic potential: beta-carbolines. Origins, syntheses, biological properties]

We reviewed the origins, the synthetic pathways and the biological properties of beta-carbolines, the condensation products of tryptophan and indole alkylamines with aldehydes. They were found in many plants, some of which have been used as hallucinogens. They also occur as minor constituents in tobacco smoke. In mammalian body, beta-carboline derivatives occur normally in plasma, platelets and urine, moreover it seems that some are formed in human body after alcohol intake. Due to interesting biological effects described in recent years (inhibition of monoamine oxidase, binding to benzodiazepine receptors, comutagenic and carcinogenic properties, 5-hydroxy tryptamine uptake inhibition), many attempts were made to prepare beta-carbolines starting from various indole derivatives. We reviewed the published methods up to 1975 and summarized the main patents related with pharmacological properties of synthetic beta-carbolines.

Derivatization in aqueous solution, isolation and separation of tetrahydro-beta-carbolines and their precursors by liquid chromatography

Derivatization of indole ethylamines and 1,2,3,4-tetrahydro-beta-carbolines in aqueous solution with methyl chloroformate has been used to facilitate the isolation of these compounds. The initial derivatization eliminated the potential for the artifactual formation of these compounds via the condensation of the indole ethylamine with an aldehyde or alpha-keto acid during the work-up procedure. The derivatized compounds possessed improved chromatographic properties which allowed for their facile separation by reversed-phase liquid chromatography and their fluorescent detection at the nanogram level.

High-performance liquid chromatography of tetrahydro-beta-carbolines extracted from plasma and platelets

A fast method for extraction and concentration of tryptamine (TA), 5-hydroxy-TA, and 5-methoxy-TA was developed using reverse-phase C-18 sample preparation columns in combination with an ion-pairing reagent. Using this method, 1,2,3,4-tetrahydro-beta-carboline (THBC), 6-hydroxy-THBC, and 6-methoxy-THBC, the respective reaction products formed after reaction of formaldehyde with the primary amines mentioned above, and beta-carboline (BC, norharman) and 1-methyl-beta-carboline (1-Me-BC, harman) could also be extracted from human and rat platelets and platelet-poor plasma (PPP). A HPLC method combined with fluorometric detection was developed for the quantitative determination of these compounds in the picomole range. The formation of beta-carbolines during the extraction procedure was below the limit of detection of the assay procedure. 6-OH-THBC, THBC, 1-Me-BC, and 5-HT were identified as normal constituents of human platelets, whereas only 5-hydroxytryptamine (5-HT) and 6-OH-THBC could be identified in human PPP. In rat platelets and PPP 5-HT, but no THBCs, could be detected.

Light microscopic autoradiography of rat retinae after intravitreal injection of [3H]6-methoxy-tetrahydro-beta-carboline

Many beta-carbolines have recently been shown to occur in the human body and animals. beta-carbolines may act as neuromodulators although their physiological role is not known. We have studied the autoradiographic retinal distribution of intravitreally injected [3H]6-methoxy-tetrahydro-beta-carboline (6-MeO-THBC) in rats. The synaptic and ganglion cell layers accumulate pronounced radioactivity, as do some intra- and extracellular locations in the inner nuclear layer and the outer segments of the photoreceptors. The pigment epithelium gradually accumulates a very dense band of radioactivity. 6-MeO-THBC (pinoline, 5-methoxytryptoline, 6-methoxy-1,2,3,4-tetrahydronorharmane) has been shown to possess many important biochemical and pharmacological properties. It has been demonstrated to occur as a normal constituent in the retina of some animals. The relationship between 6-MeO-THBC, melatonin and other 5-methoxy-indoles is discussed.

Distribution of 1,2,3,4-tetrahydro-beta-carboline and 6-methoxy-1,2,3,4-tetrahydro-beta-carboline in mice

The distribution of radioactivity after intravenous injection of 14C-labelled 1,2,3,4-tetrahydro-beta-carboline (THBC) and 6-methoxy-1,2,3,4-tetrahydro-beta-carboline (6-MeO-THBC) was studied on mice by whole-body autoradiography and by liquid scintillation counting (LSC). Following intravenous injection they rapidly distributed into different organs and were excreted into urine and the gut contents. A considerable uptake of the compounds was seen in the lungs, kidney, liver, bone marrow, urinary bladder, gastrointestinal tract and in various glands e.g. adrenal, Harderian and salivary glands. THBC moderately penetrated the blood-brain barrier and the placenta but 6-MeO-THBC seemed to penetrate poorly both. At early stages of the experiment the values of tissue radioactivity in LSC were generally much higher in the THBC group but 24 hours following injections the reverse was true with higher activities in the 6-MeO-THBC group. The initial excretion of 6-MeO-THBC seemed to be more rapid judged by the superfluous accumulation of activity in the bladder and a high accumulation of activity into the gut contents.

Two metabolic pathways of tetrahydronorharmane (tetrahydro-beta-carboline) in rats

Metabolites of (14C) tetrahydronorharmane (THN, tetrahydro-beta-carboline) have been identified by mass spectrometry and nuclear magnetic resonance spectroscopy. Two metabolic pathways are suggested: Hydroxylation of the benzene ring--most probably with an epoxide as intermediate--though no hydroxylated THN could be detected in the urine samples of male and female rats but conjugated compounds as the main metabolites. The intermediary epoxide is supported by the fact, that the hydroxy substituent of THN is positioned on C-6 or C-7 with a ratio of 55:45 in female rats and of 45:55 in male rats. Dehydrogenation yielding norharmane. This substance possibly gives rise to another metabolite--1,2-dihydro-beta-carboline-1-one. The pharmacological and toxicological implications of these findings are discussed.

Effects of 6-methoxytetrahydro-beta-carboline on 5-hydroxytryptamine binding in rat brain

6-MeOTHBC competes for 5-HT binding sites in rat brain in-vitro and in-vivo. The beta-carboline is significantly more active at the type 1 [3H]-5-HT, than the type 2 [3H]spiperone receptors, in-vitro. Following injection, 6-MeOTHBC significantly decreases [3H]-5-HT binding in the cortex. The ineffectiveness on [3H]spiperone binding in-vivo corresponds with the low affinity in-vitro. The effect of 6-MeOTHBC on central 5-HT binding may be a significant aspect of its 5-HT-ergic activity.

[14C]6-methoxy-1,2,3,4-tetrahydro-beta-carboline in retinal and other tissues after intravascular and intravitreal injections in mice and rats

6-Methoxy-1,2,3,4-tetrahydro-beta-carboline (6-MeO-THBC) is a condensation product of 5-methoxytryptamine and formaldehyde. It possesses diverse biochemical and pharmacological properties and has been suggested to act as a neuromodulator. 6-MeO-THBC has been shown to occur in various tissues including the retina in animals and human beings. The present results show that the mouse and rat retina as well as other tissues take up 14C-labelled 6-MeO-THBC injected intravenously or intravitreally. The retinal concentrations show a prompt rise after the injection and significant levels are maintained after 2 days.

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.

Presence of formaldehyde in biological media and organic solvents: artifactual formation of tetrahydro-beta-carbolines

A gas chromatography-mass spectrometry method is described for the identification and quantitation of 6-hydroxy-1,2,3,4-tetrahydro-beta-carboline (6OHTHBC). During the analysis of 6OHTHBC in human platelets, the artifactual formation of 6OHTHBC was observed and shown to be due to the presence of formaldehyde in both organic solvents and in platelet homogenates. Formaldehyde was facilely removed from the organic solvent via a Pictet-Spengler reaction; however, removal from tissue homogenates was not possible by using conventional aldehyde-trapping agents. The solution of these problems and their consequences for persons attempting to establish the in vivo presence of tetrahydro-beta-carbolines or biochemically study tissue preparations are discussed.

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.

Identification and measurement of 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-beta-carboline by gas chromatography-mass spectrometry

A glass capillary gas chromatographic-mass spectrometric method for the analysis of 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-beta-carboline in urine, plasma and blood platelets was developed. The method involves the use of a deuterated analogue as internal standard, addition of semicarbazide, extraction with methylene chloride and formation of pentafluoropropionyl derivatives. The 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-beta-carboline was found to occur in the urine of controls and alcoholics as both the free and conjugated compound. In the controls the mean level of free and conjugated 60MTHBC was 75 +/- 20 nmole/l. When intoxicated, the alcoholics had a statistically higher excretion rate of the conjugate(s) than the controls. The compound was not detectable in blood platelets or plasma.

In vitro studies of 5, 10-methylenetetrahydrofolate reductase: inhibition by folate derivatives, folate antagonists, and monoamine derivatives

Folate monoglutamates and folate antagonists have an inhibitory action on the activity of 5,10-methylenetetrahydrofolate reductase in rat brain. The type of inhibition was studied for dihydrofolic acid using the Lineweaver--Burk transformation. Some of the monoamine alkaloids, the in vitro products of 5,10-methylenetetrahydrofolate reductase, have either a stimulatory or inhibitory effect on the enzyme activity.

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.

Identification by selective ion monitoring of 1-methyl-1,2,3,4-tetrahydro-beta-carboline in human platelets and plasma after ethanol intake

1-Methyl-1,2,3,4-tetrahydro-beta-carboline (tetrahydroharman) has been quantified in human platelets and plasma following acute intake of ethanol using a selective ion monitoring method. It was not possible to detect this compound before ethanol intake.

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.

Tetrahydro-beta-carbolines elevate plasma prolactin in male rats

The effects of systemic administration of three tetrahydro-beta-carbolines (TH beta C's) on plasma prolactin were determined in male rats. After intraperitoneal administration, 6-methoxy-TH beta C (6-MeO-TH beta C; 80 mg/kg) significantly elevated prolactin levels for 6 min. After intravenous administration via an indwelling jugular cannula, 6-MeO-TH beta C (20 mg/kg but not 2.0 mg/kg), TH beta C (20 mg/kg) and 6-OH-TH beta C (20 mg/kg) all produced a significant elevation in plasma prolactin for 30 min. with the latter compound effective for 60 min. Previous evidence indicated that the TH beta C's interact relatively selectively with the serotonergic neurotransmitter system to increase serotonergic function. Thus, the present data are consistent with previous studies which indicated that increased serotonergic activity resulted in enhanced prolactin secretion.