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Human monoamine oxidase is inhibited by tobacco smoke (2005)

Human monoamine oxidase is inhibited by tobacco smoke (2005)

  1. Heretic.Ape.
    From biochemical and biophysical research communications 326 (2) pg:378 -386
    Brought to my attention by D-F member "Stuck"

    Herraiz, Tomas

    Monoamine oxidase (MAO) is a mitochondrial outer-membrane flavoenzyme involved in brain and peripheral oxidative catabolism of neurotransmitters and xenobiotic amines, including neurotoxic amines, and a well-known target for antidepressant and neuroprotective drugs. Recently, positron emission tomography imaging has shown that smokers have a much lower activity of peripheral and brain MAO-A (30%) and -B (40%) isozymes compared to non-smokers. This MAO inhibition results from a pharmacological effect of smoke, but little is known about its mechanism. Working with mainstream smoke collected from commercia cigarettes we confirmed that cigarette smoke is a potent inhibitor of human MAO-A and -B isozymes. MAO inhibition was partly reversible, competitive for MAO-A, and a mixed-type inhibition for MAO-B. Two b-carboline alkaloids, norharman (b-carboline) and harman (1-methyl-b-carboline), were identified by GC–MS, quantified, and isolated from the mainstream smoke by solid phase extraction and HPLC. Kinetics analysis revealed that b-carbolines from cigarette smoke were competitive, reversible, and potent inhibitors of MAO enzymes. Norharman was an inhibitor of MAO-A (Ki = 1.2 ± 0.18 lM) and MAO-B (Ki = 1.12 ± 0.19 lM), and harman of MAO-A (Ki = 55.54 ± 5.3 nM). b-Carboline alkaloids are psychopharmacologically active compounds that may occur endogenously in human tissues, including the brain. These results suggest that b-carboline alkaloids from cigarette smoke acting as potent reversible inhibitors of MAO enzymes may contribute to the MAO-reduced activity produced by tobacco smoke in smokers. The presence of MAO inhibitors in smoke like b-carbolines and others may help us to understand some of the purported neuropharmacological effects associated with smoking.