Concentrations of tryptoline and methtryptoline in rat brain

Tetrahydro-beta-carboline alkaloids occur in fruits and fruit juices. Activity as antioxidants and radical scavengers

Tetrahydro-beta-carbolines are biologically active alkaloids that occur and accumulate in mammalian tissues, fluids, and brain, but their ultimate origin or biological role is still uncertain. Four tetrahydro-beta-carboline alkaloids: 1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid, 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid, 1-methyl-1,2,3,4-tetrahydro-beta-carboline, and 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-beta-carboline, are found as naturally occurring substances in some fruit and fruit juices. These compounds occur in the microg/g level in those products, and a characteristic and distinct profile appears to exist depending on the type of fruit and juice involved. Thus, 1-methyl-1,2,3,4-tetrahydro-beta-carboline may appear in tomato, tomato juice, and kiwi; 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-beta-carboline in bananas, pineapple, tomato, and their corresponding juices; and 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid in oranges and grapefruits, although it also occurred in most juices. Fruit-occurring tetrahydro-beta-carboline alkaloids acted as antioxidants and free radical scavengers in the ABTS assay when compared with ascorbic acid and Trolox. This suggests that tetrahydro-beta-carboline alkaloids might act as antioxidants when absorbed and accumulated in the body, contributing to the antioxidant effect of fruit products containing these compounds.

Phenylethanolamine N-methyltransferase has beta-carboline 2N-methyltransferase activity: hypothetical relevance to Parkinson's disease

Mammalian brain has a beta-carboline 2N-methyltransferase activity that converts beta-carbolines, such as norharman and harman, into 2N-methylated beta-carbolinium cations, which are structural and functional analogs of the Parkinsonian-inducing toxin 1-methyl-4-phenylpyridinium cation (MPP+). The identity and physiological function of this beta-carboline 2N-methylation activity was previously unknown. We report pharmacological and biochemical evidence that phenylethanolamine N-methyltransferase (EC 2.1.1.28) has beta-carboline 2N-methyltransferase activity. Specifically, purified phenylethanolamine N-methyltransferase (PNMT) catalyzes the 2N-methylation (21.1 pmol/h per unit PNMT) of 9-methylnorharman, but not the 9N-methylation of 2-methylnorharmanium cation. LY134046, a selective inhibitor of phenylethanolamine N-methyltransferase, inhibits (IC50 1.9 microM) the 2N-methylation of 9-methylnorharman, a substrate for beta-carboline 2N-methyltransferase. Substrates of phenylethanolamine N-methyltransferase also inhibit beta-carboline 2N-methyltransferase activity in a concentration-dependent manner. beta-Carboline 2N-methyltransferase activity (43.7pmol/h/mg protein) is present in human adrenal medulla, a tissue with high phenylethanolamine N-methyltransferase activity. We are investigating the potential role of N-methylated beta-carbolinium cations in the pathogenesis of idiopathic Parkinson's disease. Presuming that phenylethanolamine N-methyltransferase activity forms toxic 2N-methylated beta-carbolinium cations, we propose a novel hypothesis regarding Parkinson's disease-a hypothesis that includes a role for phenylethanolamine N-methyltransferase-catalyzed formation of MPP+ -like 2N-methylated beta-carbolinium cations.

Protective effect of beta-carbolines and other antioxidants on lipid peroxidation due to hydrogen peroxide in rat brain homogenates

Tryptoline and pinoline are two beta-carbolines isolated from the nervous system of mammals. We investigated the ability of these compounds to prevent lipid peroxidation induced by hydrogen peroxide in rat brain homogenates. We also compared their effects with other known antioxidants including melatonin, trolox and ascorbic acid. Lipid peroxidation was assessed by measuring malonaldehyde (MDA) and 4-hydroxy-alkenals (4-HDA) concentrations in the brain homogenates. Incubation with hydrogen peroxide (5 mM) increased MDA+4-HDA levels, which were totally prevented by tryptoline, pinoline, melatonin and trolox in a concentration-dependent manner. By contrast, higher MDA-4-HDA concentrations compared with control experiments were found after incubation with ascorbic acid, thus reflecting an increase of lipid peroxidation induced by this compound. Although in vivo studies are needed, the data suggest that these beta-carbolines may be potential neuroprotective agents because of their antioxidant activities.

A possible link between beta -carboline metabolism and infantile autism

Benzodiazepine receptors and abnormal hepatic metabolism have been suggested to participate in several neuropsychiatric disorders including autism. Neuropsychoactive beta-carboline alkaloids as the potent ligands for benzodiazepine receptors are endogenously produced and exogenously supplied much more than benzodiazepines. 1-Methyl-1,2,3,4-tetrahydro-beta-carboline, a predominant alkaloid in humans and foodstuffs, is metabolically hydroxylated in liver. Although its in vivo levels show no difference between autistic and healthy children, the metabolic 6-hydroxylation is significantly decreased in autistic subjects. Therefore, it could be hypothesized that the reduced hepatic metabolism of 1-methyl-1,2,3, 4-tetrahydro-beta-carboline to 6-hydroxyl metabolite may be linked to the pathogenesis of infantile autism as suggested for autistic occurrence to involve the pathology similar to hepatic encephalopathy.

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.

Studies on the interaction between 1,2,3,4-tetrahydro-beta-carboline and cigarette smoke: a potential mechanism of neuroprotection for Parkinson's disease

1,2,3,4-Tetrahydro-beta-carboline (TH beta C) is an endogenous or environmental neurotoxic factor putatively involved in the development of Parkinson's disease (PD). As part of our efforts to characterize the mechanism of the reported protection of smoking against PD, we have examined the interaction between TH beta C and cigarette smoke. We found that TH beta C reacts in vitro and under physiological conditions with some components of cigarette smoke to form N2-(cyanomethyl)-TH beta C (CM-TH beta C), N2-(gamma-cyanoethyl)-TH beta C (CE-TH beta C), N2-(1'-cyanopropyl)-TH beta C (CP-TH beta C), N2-(1'-cyanobutyl)-TH beta C (CB-TH beta C) and N2-formyl-TH beta C (F-TH beta C). Significant differences in the recovery of some of these TH beta C-derivatives were obtained for Burley and Bright tobacco. Several of the reported compounds showed reversible and competitive MAO-A inhibitory properties. The detection of some of these compounds in rat brain after chronic administration of TH beta C and a solution of cigarette smoke proved that the reported interactions also occur in vivo. These results are discussed as a potential mechanism of neuroprotection in the development of PD.

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.

Structural studies of condensation products of biogenic amines as inhibitors of tryptophan hydroxylase

The effects of condensation products of dopamine and indoleamines on the activity of tryptophan hydroxylase (TPH) were evaluated to determine the structures associated with modulation of this enzyme activity. The compounds having a catechol structure, such as 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline, markedly inhibited the activity of the enzyme prepared from the rat brain. The inhibition was non-competitive in terms of both the biopterin cofactor and the substrate L-tryptophan. Substitution on the one or two positions of catechol isoquinolines did not affect the inhibitory activity towards TPH. Among these compounds, a charged substance, 1,2[N]-dimethyl-6,7-dihydroxy-isoquinolinium ion, was an extremely potent inhibitor; the Ki values were 0.88 +/- 0.17 and 0.64 +/- 0.08 microM (mean +/- S.D.) in terms of the substrate and cofactor, respectively. By contrast, the condensation products of tryptophan and tryptamine with acetaldehyde scarcely affected TPH activities. 1-Methyl-1,2,3,4-tetrahydroisoquinoline, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-phenylpyridinium ion (MPP+) were almost inactive. These results indicated that the catechol structure recognized and combined with TPH at a binding site different from that of the substrate or cofactor and the positive charge on the dopamine-derived substance enhanced the affinity to TPH. The selective inhibition of TPH by dopamine-derived catechol isoquinolines was discussed in relationship to the interactions between catecholamines, indoleamines and their metabolites in the brain under physiological and pathological conditions.

Potential bioactivated neurotoxicants, N-methylated beta-carbolinium ions, are present in human brain

Potential bioactivated neurotoxicants, 2-N-methyl-beta-carbolinium and 2,9-N,N'-dimethyl-beta-carbolinium ions, as well as N-methylation activities which form these charged species, were analyzed for the first time in the parietal association cortex and the substantia nigra of human brain using GC/MS and HPLC. The brains were taken during forensic autopsies from corpses without obvious degeneration of substantia nigra. In the cortex, 2-methyl-norharmanium ion (2-MeNH) and 2,9-dimethyl-norharmanium ion (2,9-Me2NH) were detected in almost all samples. 2-Methyl-harmanium ions (2-MeHA) and 2,9-dimethyl-harmanium ions (2,9-Me2HA) were detectable in only two samples. In substantia nigra samples pooled from 3 or 4 brains for analysis, 2-MeNH and 2,9-Me2NH levels were higher than those in the cortex, whereas 2-MeHA and 2,9-Me2HA were below detection limits. Their precursors, norharman (NH) and harman (HA), were also measured using HPLC/fluorescence detection. In both regions, NH and HA were present in almost all samples; levels of NH and HA were also significantly higher in the nigra than in the cortex. Using 9-methyl-NH and 2-MeNH as substrates, in vitro N-methylation of the 2[beta] and 9[indole] nitrogens toward beta-carbolines was measured both in the cortex and in the nigra. 2[beta]-N-Methylation activity was significantly higher than 9[indole]-N-methylation activity in both regions. Recent studies show that beta-carbolinium ions resemble the synthetic parkinsonian toxicant, MPP+, with respect to structure and neurotoxic activity. Such 'bioactivated' carbolinium ions could be endogenous causative factors in Parkinson's disease.

Tryptamine: a metabolite of tryptophan implicated in various neuropsychiatric disorders

Although early interest in the biomedical relevance of tryptamine has waned in recent years, it is clear from the above discussion that the study of tryptamine is worthy of serious consideration as a factor in neuropsychiatric disorders. The study of [3H]-tryptamine binding sites indicates an adaptive responsiveness characteristic of functional receptors. The question raised by Jones (1982d) on whether tryptamine is acting centrally as a neurotransmitter or a neuromodulator still remains mostly unanswered, although the evidence cited within this review strongly suggests a modulatory role for this neuroactive amine (see also Juorio and Paterson, 1990). The synthesis and degradative pathways of tryptamine, as well as the intricate neurochemical and behavioral consequences of altering these pathways, are now more fully understood. It is not yet clear what the role of tryptamine is under normal physiological [homeostatic] conditions, however, its role during pathological conditions such as mental and physical stress, hepatic dysfunction and other disorders of metabolism (i.e. electrolyte imbalance, increased precursor availability, enzyme induction or alterations in enzyme co-factor availability) may be quite subtle, perhaps accounting for various sequelae hitherto considered idiopathic. The evidence for a primary role for tryptamine in the etiology of mental or neurological diseases is still relatively poor, although the observations that endogenous concentrations of tryptamine are particularly susceptible to pharmacological as well as physiological manipulations serve to reinforce the proposition that this indoleamine is not simply a metabolic accident but rather a neuroactive compound in its own right. Finally, one might wonder what proportion of the data attributed to modifications of 5-HT metabolism might, in fact, involve unrecognized changes in the concentrations of other neuroactive metabolites of tryptophan such as tryptamine.

Mono-N-methylation of 1,2,3,4-tetrahydro-beta-carbolines in brain cytosol: absence of indole methylation

In an accompanying report we demonstrated enzyme activity in guinea pig brain cell nuclei that catalyzes S-adenosylmethionine (SAM)-dependent N-methylations of heteroaromatic beta-carbolines (BCs) on the 2[beta]-nitrogen and subsequently on the 9[indole]-nitrogen, ultimately yielding N2,N9-dimethylated BCs. Presented here are the results of a parallel study of the N-methylation of 1,2,3,4-tetrahydro-BCs (THBCs), which form endogenously via condensations of tryptophan and its derived indoles with carbonyl compounds or, like their BC oxidation products, are environmental constituents and plant alkaloids. THBCs were enzymatically methylated on the 2[beta]-nitrogen by [3H]-SAM in undialyzed homogenates of rat or guinea pig brain, but [3H]methyl transfer to the 9[indole]-nitrogen was not observed. The structure of the 2[beta]-methyl THBC product was verified with capillary gas chromatography-mass spectrometry. Furthermore, whereas BC N-methylation was largely particulate and displayed micromolar Km values for BC substrate, THBC 2[beta]-N-methylation activity was cytosolic and displayed a relatively high (millimolar) Km for THBC substrate. The N-methylation of THBCs may be due to cytosolic N-methyltransferases that others have studied using different azaheterocyclics. Our overall studies indicate that N2,N9-dimethylated BCs could be unique neurotoxic factors that are bioactivated within brain by sequential N-methylations of BCs. These results suggest the possibility of an additional route to the putative 2,9-dimethylated toxins involving, as a first step, 2[beta]-N-methylation of environmental or endogenously derived THBCs in the brain and perhaps other organs.

1-Methyl-tetrahydro-beta-carboline-3-carboxylic acid is present in the rat brain and is not increased after acute ethanol injection with cyanamide treatment

We conducted analyses of 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (1Me3C-THBC) by gas chromatography-mass spectrometry (negative chemical ionization mode) to investigate its presence and the in vivo condensation between tryptophan and AcH. 1Me3C-THBC was found in the cerebellum and the cerebrum of normal rat [117.0 +/- 41.7 and 46.5 +/- 13.9 pmol/g tissue (mean +/- SEM), respectively]. The concentrations of 1Me3C-THBC and tryptophan were higher in the cerebellum than those in the cerebrum. The level of 1Me3C-THBC in both regions remained unchanged following a single oral ethanol administration alone or with cyanamide pretreatment. These data suggest that acetaldehyde is an unlike precursor of 1Me3C-THBC as a result of ethanol ingestion. 1Me3C-THBC also existed in the rat chow (282.0 +/- 24.2 pmol/g), so that most of brain 1Me3C-THBC detected in the rat brain might have originated from dietary sources. However, the possibility of a biosynthesis from tryptophan and alpha-keto acid still remained, especially after long-term ethanol treatment.

Mitochondrial respiratory inhibition by N-methylated beta-carboline derivatives structurally resembling N-methyl-4-phenylpyridine

Mitochondrial accumulation and respiratory inhibition are critical steps in the actions of N-methyl-4-phenylpyridinium ion (MPP+), the toxic metabolite of the parkinsonism-inducing agent, N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. We examined the respiratory characteristics of 2-methylated beta-carbolines (2-Me beta Cs) and 2-methylated 3,4-dihydro-beta-carbolines (2-MeDH beta Cs), which encompass the MPP+ structure. As indoleamine derivatives, they could have endogenous roles in idiopathic parkinsonism. With rat liver mitochondria, the order for inhibition of NAD(+)-linked O2 consumption (6-min preincubations) was as follows: MPP+ = 2-methylharmine greater than 2-methylharmol = 2-methylharmaline much greater than 2-methylharmalol greater than 2-methylnorharman greater than 6-OH-2-methylharmalan much greater than 2-methylharman. Similar to MPP+, 2-MeDH beta C/2-Me beta C inhibition was potentiated by tetraphenylboron and reversed by dinitrophenol, consistent with the involvement of cationic forms. However, the participation of neutral forms was indicated by the 2-MeDH beta C/2-Me beta C inhibitory time courses, which were unlike MPP+. The neutral forms probably arise via indolic nitrogen deprotonation because the characteristics of a cationic beta-carboline that cannot N-deprotonate, 2,9-dimethylnorharman, mirrored MPP+ rather than 2-Me beta Cs. Succinate-supported respiration was also significantly blocked by 2-MeDH beta Cs/2-Me beta Cs, but results with tetraphenylboron and 2,9-dimethylnorharman indicated that cationic forms were less important than in the inhibition of NAD(+)-linked respiration. We suggest that the relatively potent inhibition by certain 2-MeDH beta Cs/2-Me beta Cs involves neutral forms for passive mitochondrial entry and cationic as well as neutral forms that act at several respiratory sites. Respiratory inhibition could reasonably underlie the reported neurotoxicity of 2-Me beta Cs.

Modulation of calcium fluxes across synaptosomal plasma membrane by local anesthetics

We have studied the effects of local anesthetics (dibucaine, tetracaine, lidocaine, and procaine) on calcium fluxes through the plasma membrane of synaptosomes. All these local anesthetics inhibit the ATP-dependent calcium uptake by inverted plasma membrane vesicles at concentrations close to those that promote an effective blockade of the action potential. The values obtained for the K0.5 of inhibition of calcium uptake are the following: 23 microM (dibucaine), 0.44 mM (lidocaine), 1.5 mM (procaine), and 0.8 mM (tetracaine). There is a good correlation between these K0.5 values and the concentrations of the local anesthetics that inhibit the Ca2(+)-dependent Mg2(+)-ATPase of these membranes. In addition, except for procaine, these local anesthetics stimulate severalfold the Ca2+ outflow via the Na+/Ca2+ exchange in these membranes. This effect, however, is observed at concentrations slightly higher than those that effectively inhibit the ATP-dependent Ca2+ uptake, e.g., 80-700 microM dibucaine, 2-10 mM lidocaine, and 1-3 mM tetracaine. The results suggest that the Ca2+ buffering of neuronal cytosol is altered by these anesthetics at pharmacological concentrations.