Microgram concentrations of norharman and harman were found and identified using HPLC-MS and RP-HPLC fluorescence in various types of coffee preparations. Instant coffee contained 3.8microg/g for NH and 1.5microg/g for H; brewed coffee measured in at 9.34microg g(-1)(NH) and 1.67microg g(-1). These two heterocyclic amines are pyrido-indole beta-carbolines, which are known to be biologically active. In another study, coffee brews showed inhibitory properties on the recombinant MAO A and MAO B isoenzymes catalyzing the oxidative deamination of kynuramine, suggesting coffee contains compounds acting as MAO inhibitors.
Coffee, along with tobacco smoke, make up most of our exogenous supply of these chemicals. A somewhat paradoxical study was conducted in rats who were given injections of harman and norharman and subsequently developed anxiety, tremors, and depressive behavior, which was attenuated by the administration of caffeine, an unlikely candidate to control anxiety and tremors. MAO A and B are well known therapeutic targets for antidepressant drugs. However, little research has been conducted on the antidepressant effects of harman and norharman in humans, in large part due to legal restrictions in many countries. This may be a dead end as far as a potential antidepressant agent, which is depressing because it's pharmacology is so seductive and perfect for such a function; despite lack of pharmacological data, other synthetic MAOI inhibitors are known that are less toxic. So, next time you grab a cup of freshly brewed coffee, you can rest assured that you're getting your daily dose of MAOIs, and an MOAI a day keeps the sadness away.
