ENZYMATIC FORMATION OF TETRAHYDRO-?-CARBOLINE FROM TRYPTAMINE AND 5-METHYLTETRAHYDROFOLIC ACID IN RAT BRAIN FRACTIONS: REGIONAL AND SUBCELLULAR DISTRIBUTION

Activity of 5-formyl tetrahydrofolate cyclodehydrase and 5,10-methenyl tetrahydrofolate cyclohydrolase in primary brain tumors in children

The activity of the enzymes 5-formyl tetrahydrofolate cyclodehydrase and 5,10-methenyl tetrahydrofolate cyclohydrolase has been studied cytochemically in children's primary brain tumors. These enzymes play a significant role in purine biosynthesis. Thirty children, aged 1-12 years, were studied, 12 with medulloblastoma, 14 with glioma grade I-IV, and 4 with ependymoma. The activity of the enzymes was apparent as cytoplasmic granules that sometimes overlie the nucleus of the tumor cells. This coincidence showed that different types of brain tumors exhibit different degrees of enzymic activity, which in some cases correlated positively with the malignant potential of the tumor. Approximately one third of the cases were negative for any activity of these enzymes. The intensity of the staining of 5,10-methenyl tetrahydrofolate cyclohydrolase activity was actually higher than that of 5-formyl tetrahydrofolate cyctodehydrase. The clinical or prognostic significance of these findings remains to be clarified, but we believe that cylochemistry provides a sensitive technique for the detection, localization, and description of these enzymes in brain tumor cells. A clear understanding of the mode of action of these enzymes may contribute to devising novel therapeutic strategies.

Inhibition of monoamine oxidase from bovine retina by beta-carbolines

The behaviour of some beta-carboline derivatives as inhibitors of monoamine oxidase has been studied in bovine retina. Inhibition was found not to show any significant time dependence. Di- and tetrahydro-beta-carbolines were shown to behave as reversible and competitive inhibitors. In contrast, the fully unsaturated beta-carbolines harmane, harmine and harmaline, which showed deviation from linearity at high substrate concentrations, behaved as tight-binding inhibitors. In these cases, the concentration of the enzyme and the inhibitor were of the same order. This was confirmed by the Ki values for these compounds in the nanomolar concentration range. Consistent with this was that inhibition was only partly reversed by dialysis for 18 h at 4 degrees C, although complete reversal was observed after dialysis for the same period at 37 degrees C. Structure-activity relationships indicated that substitution of a methoxy group at the C7 position of the aromatic ring is determinant for this tight-binding behaviour; a substitution of this group at the C6 position greatly reduced inhibition. Since beta-carbolines have been reported to be formed endogenously, this suggests that they might have important physiological actions on monoamine oxidase activity in-vivo. In contrast, all the beta-carbolines investigated in this study had low potencies as inhibitors of monoamine oxidase B.

Formation of a new biogenic aldehyde adduct by incubation of tryptamine with rat brain tissue

Tryptamine was degraded by incubation with rat brain homogenate to an unknown product. The reaction was stimulated by the nonionic detergents Triton X-100 and Lubrol PX and less by the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]1-propanesulfonate (CHAPS). The same results were obtained with pig brain and bovine brain. The monoamine oxidase inhibitor pargyline inhibited the reaction strongly, indicating the participation of the enzyme on the reaction. Addition of 17,000 g supernatant from rat brain homogenate increased the formation effectively whereas phospholipids or chloroform/methanol (7:3) extract from the 17,000 g supernatant showed only little or no effect. Chromatographic and electrophoretic properties as well as the chemical reaction of the product with specific reagents suggest that the compound consists of an indole part and an amino acid part. The product could be identified by fast atom bombardment mass spectrometry and by comparison with the synthetic substance (4R)-2-(3-indolylmethyl)-1,3-thiazolidine-4-carboxylic acid. It is formed by the enzymatic oxidation of tryptamine producing indole-3-acetaldehyde which spontaneously cyclizes with free L-cysteine from the tissue. The results suggest that the reaction of biogenic aldehydes with brain macromolecules may proceed via an analogous reaction.

Endocrine effects of 5-methoxytryptoline, 5-hydroxytryptoline and tryptoline, putative modulators of rat serotonergic system

The effects of tryptolines (TH beta Cs), putative endogenous compounds acting on the serotonergic function, have been studied on endocrine parameters in rats. In particular, graded doses of 5-methoxytryptoline (5-MeOT), 5-hydroxytryptoline (5-OHT) and tryptoline (Tp) were ip or iv administered to the animals and the circulating titers of prolactin (PRL), growth hormone (GH) and luteinizing hormone (LH) were assayed either at 20 min or at various times after the injection of the compounds. The data herein reported show that TH beta Cs exert endocrine effects, at least in a pharmacological condition. However, the three compounds unequally affect anterior pituitary function. In fact, while 5-MeOT, 5-OHT and Tp all enhance plasma PRL concentrations in a quick, short lasting and dose-related manner, 5-MeOT and Tp induce also decreases of serum LH levels in ovariectomized rats, and 5-MeOT only is able to diminish plasma GH titers. These findings underline an endocrine effect for TH beta Cs in pharmacological conditions and may suggest a functional role for these compounds in the control of anterior pituitary function.

Multiple forms of aryl acylamidase in regional tissues of developing rat brain

The specific activities of two forms of aryl acylamidase (AAA) were examined in 7 regions of the developing rat brain, plus the remainder of the brain and the whole brain. AAA-1 activity peaked at 15 days old in all brain regions studied except the whole brain where it peaked at 22 days of age. AAA-2 activity peaked between 15 and 29 days old in most brain regions studied except corpus striatum and hippocampus where the AAA-2 activity peaked before 15 days old. In all areas and at all time periods, with the exception of CS after 15 days of age, AAA-2 activity was much higher than that of AAA-1. The developmental pattern of AAA-1 is generally the same in the different brain regions while that of AAA-2 shows more regional specificity. These results indicate that neither AAA-1 nor AAA-2 may be associated with amine N-acetyltransferase in the brain which has an entirely different developmental pattern.

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.

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.

Aromatic alkylamine N-acetyltransferase in regional tissues in developing rat brain

The specific activities of N-acetyltransferase (EC 2.3.1.5) were examined in several regions of rat brain of both sexes at various times after birth. The enzyme activity increased with development in whole brain, hippocampus, midbrain, cerebellum and the remainder of brain, peaking around 36 days of age. Lineweaver-Burk plots indicated linear kinetics for N-acetyltransferase in dialyzed supernatant and ammonium sulfate precipitates from the newborn rat brain, whereas enzyme preparation further purified by Bio Gel yielded biphasic kinetics. These data remain consistent with the possibility that there are two forms of N-acetyltransferase in rat brain even from birth.

Tetrahydro-beta-carbolines and corresponding tryptamines: In vitro inhibition of serotonin, dopamine and noradrenaline uptake in rat brain synaptosomes

The structure activity relationships of tryptolines and some other beta-carbolines and tryptamines as inhibitors of serotonin (5-HT), dopamine (DA) and noradrenaline (NA) uptake were studied in rat brain synaptosomes. All beta-carbolines inhibited to higher degree the uptake of 5-HT than that of DA or NA(IC50's 5-100 times lower). The most potent tryptoline derivative was 6-hydroxy-tetrahydro-beta-carboline (5-hydroxytryptoline, 6-OH-THBC) with an IC50 of 5.0 x 10(-7) M at a 5-HT concentration of 10(-7) M. 6-Methoxy-tetrahydro-beta-carboline (5-methoxytryptoline) was slightly weaker; the inhibition of 5-HT uptake and DA uptake being competitive. Also tetrahydro-beta-carboline (tryptoline) was more potent than its 1-methylderivative, tetrahydroharmane (methtryptoline) or norharmane (beta-carboline). All of them were, however, weaker inhibitors of 5-HT uptake than the freely rotating indoleamines N-methyl-tryptamine (N-Me-T) or 5-HT itself. N-Me-T and 5-HT were also more potent inhibitors of DA and NA uptake than most of the beta-carbolines, DA uptake, however, was inhibited better by 6-OH-THBC than by 5-HT or N-ME-T. Tetrahydro-beta-carbolines may inhibit 5-HT uptake also in vivo but is unlikely that catecholamine uptake is affected.

Identification of tetrahydronorharmane (tetrahydro-beta-carboline) in human blood platelets

The present paper shows that tetrahydronorharmane (tetrahydro-beta-carboline) exists in human platelets. The concentration of tetrahydronorharmane in platelets from 10 ml platelet rich plasma was in the range of 9.3 to 25.6 pmol (n=8). Ingestion of tryptamine hydrochloride (n=4) three times daily for three consecutive days and of 19.6 mmol D,L-tryptophan (n=7) the evening (10 p.m.) before the blood collection did not lead to an increase of tetrahydronorharmane in platelets.

Tetrahydronorharmane modulates the depolarisation-induced efflux of 5-hydroxytryptamine and dopamine and is released by high potassium concentration from rat brain slices

Tetrahydronorharmane (THN), a compound which occurs in man and in rats is supposed to act as a modulator of 5-hydroxytryptaminergic neurones. It is reported here that THN stimulated the potassium-induced release of the neurotransmitter from brain slices. This suggests enhancement of the efflux as a mechanism for the 5-hydroxytryptamine-like action of THN in pharmacological experiments. Furthermore, THN decreased the potassium-evoked efflux of (3H)-dopamine. This is consistent with the inhibition of dopaminergic neurones by THN as seen previously in various in vivo experiments. Finally it is demonstrated that a high concentration of potassium evokes the efflux of (14C)-THN from brain slices. This finding suggests that THN is taken up into neurones and exerts its modulating action on serotonergic neurones either inside or outside the cell.

Tetrahydronorharmane (tetrahydro-beta-carboline), a physiologically occurring compound of indole metabolism

In the present paper a sensitive method is described to measure tetrahydronorharmane (THN) in the urine of man and rats as well as in the forebrain of rats. The compound is extracted into diethyl ether, separated by thin layer chromatography (TLC), acetylated with radiolabelled acetic anhydride and further isolated by two-dimensional TLC development. The existence of THN in urine of man was proven by using chromatography with different solvent systems, cocristallisation, isotope dilution technique as well as mass-spectrometry. The amount of THN in the urine varied over a wide range. With the same method it was demonstrated that THN occurs also in the forebrain of rats. The concentration increases after loading with tryptamine. The findings are discussed in view of the hypothesis that THN acts as a compound modulating neuronal mechanism.

Inhibition of 5-hydroxytryptamine uptake by tetrahydronorharmane in vivo

Injection of tetrahydronorharmane (THN) elicited a dose-dependent increase of the level of 5-hydroxytryptamine (5-HT) and a fall of 5-hydroxyindoleacetic acid in the rat brain whereas noradrenaline and dopamine levels remained unchanged. The effect on indoles was shortlasting which may be explained by the short half life of THN or its metabolization to 6-OH-THN. The 5-HT depleting action of parachloro-N-methylamphetamine (CMA) was used to study uptake inhibition in vivo. The results support the notion that THN acts as an inhibitor of the reuptake of 5-HT in vivo. Further evidence for this hypothesis was obtained by intraventricular injection of radiolabelled 5-HT. The disappearance of (3H)-5-HT from brain tissue was reduced by THN. Thus, THN may exert its central 5-HT-like effects in pharmacological experiments by preventing 5-HT from being removed from the synaptic cleft.

Inhibition of the reuptake of serotonin by tryptoline

Tryptoline, a metabolite of tryptamine, competitively inhibits serotonin accumulation in nuclei-free homogenate of rat "forebrains". After intraventricular injection the drug elicits an increase of serotonin levels in the same part of the brain whereas the monoamine oxidase activity is not altered.