Beta-carbolines, psychoactive compounds in the mammalian body. Part I: Occurrence, origin and metabolism.

We review the occurrence in nature and the formation and biotransformation in mammals of beta-carbolines, the condensation products of tryptophan and indolealkylamines with aldehydes, with special reference to their possible role in man. They are found in many plants, some of which have been used as hallucinogens and drugs. They also occur as minor constituents in tobacco smoke. In man tetrahydro-beta-carboline (tetrahydronorharman), formed from tryptamine condensed with formaldehyde, occurs normally in plasma and is highly concentrated in platelets. The corresponding products from 5-hydroxytryptamine and 5-methoxytryptamine have been identified in rats but their concentrations in man have not yet been assessed. 1-Methyltetrahydro-beta-carboline (tetrahydroharman) is formed in the body as the acetaldehyde condensate after alcohol intake and its concentration is usually greatest at the time of hang-over. Its oxidation product, 1-methyl-beta-carboline (harman), has also been found in human urine and platelets. Tetrahydro-beta-carbolines may be oxidized to corresponding dihydro-beta-carbolines and beta-carbolines, at least in vitro. Due to the interesting biochemical and pharmacological effects (see part II) of beta-carbolines, several hypotheses about their role in the body can be made. The concentrations and roles of beta-carbolines in different neuropsychiatric diseases, however, remain to be determined, as suitable evaluation methods have only been developed in recent years.