Capillary gas chromatography of carbolines

Exposure to beta-carbolines norharman and harman

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

Formation of tetrahydro-beta-carbolines in human saliva

When human saliva obtained after cigarette smoking was incubated in the presence of tryptamine, the formation of 1,2,3,4-tetrahydro-beta-carboline (TBC) and 1-methyl-1,2,3,4-tetrahydro-beta-carboline (MTBC) was observed in a short time. After incubation with tryptamine (2.5 micrograms/microliter) for 10 min, the concentrations of TBC and MTBC formed were 3.27 +/- 0.94 and 0.35 +/- 0.17 ng/microliter, respectively. The formation of TBC and MTBC in intact saliva and in saliva heated at 100 degrees for 10 min was compared, but no significant difference was found. The analysis of foodstuffs showed that significant amounts of tryptamine were contained in various foods and beverages. The analysis of cigarette smoke solutions and immersion solutions of denture-base acrylic resins showed that ng-micrograms/microliter levels of formaldehyde and acetaldehyde were contained in cigarette smoke and leached from dental resins. These results indicate that both precursors, tryptamine and aldehydes, coexist in oral environments and that their interaction to form TBC and MTBC potentially occurs in human saliva without participation of salivary enzyme.

Genotoxic potential of beta-carbolines: a review

The mutagenic and co-mutagenic properties of harman, norharman and of some of their pharmacologically important derivatives are reviewed. These compounds do not behave as true mutagens, but rather interact, directly or indirectly with DNA, leading to various consequences. This unusual behaviour is most probably related to the particular structure of the chemical nucleus common to all beta-carbolines which confers to the different derivatives the property to interact with various macromolecules and enzymatic systems. These interactions are compiled and discussed in this review. The alterations, by beta-carbolines, of some important enzymatic systems, e.g. cytochrome P-450, have been clearly demonstrated, yet many discrepancies and contradictions exist so that an interpretation of the results and the definition of some common mechanism appears premature. Since beta-carbolines are widely distributed in tissues and since they may modify and increase genotoxic and toxic consequences of other compounds, these interactions need to be clarified.

Novel S-adenosylmethionine-dependent indole-N-methylation of beta-carbolines in brain particulate fractions

Guinea pig brain S-adenosylmethionine (SAM)-dependent N-methyltransferase activity toward physiologically relevant beta-carboline (BC) substrates was examined with reverse-phase HPLC and radiochemical detection. Representative BCs, norharman and harmine, were enzymatically methylated on the 2[beta]-nitrogen by [3H]CH3-SAM in undialyzed homogenates to yield 2[beta]-methylated BCs and subsequently on the 9[indole]-nitrogen to generate 2,9-dimethylated BC products. This may be the first account of mammalian indole N-methyl transfer. There was no HPLC evidence for 9-methyl BC or (from carbon methylation) 2,6-dimethyl BC products. Capillary gas chromatography-mass spectrometry analysis confirmed the structures of the 2,9-dimethyl and 2-methyl products of norharman. The 2[beta]- and 9[indole]-N-methylation activities were mainly in the nuclear fractions and were negligible in undialyzed cytosol. This differs from the cytosolic SAM-dependent N-methylations reported with other azaheterocyclics, including 1,2,3,4-tetrahydro-BCs. The involvement of a single enzyme was suggested because the two N-methyl transfers with BC substrate had similar subcellular activity patterns, regional brain distributions, and Km and Vmax values. Sequential N-methylation of various BCs that have been observed in vivo may be a unique route to centrally retained N2,N9-dimethylated beta-carbolinium ions. Because they resemble the synthetic parkinsonian toxicant, N-methyl-4-phenylpyridinium, with respect to structure and neurotoxic activity, such "bioactivated" carbolinium ions could be endogenous causative factors in Parkinson's disease.

[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.

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.