Irreversible inhibition of monoamine oxidase by some components of cigarette smoke.

Inhibitory activity towards monoamine oxidase has been found in a solution of cigarette smoke. The inhibition was irreversible. When tissue slices of rat lung were incubated in the cigarette smoke solution or alternatively, exposed directly to cigarette smoke, monoamine oxidase activities were reduced drastically. Similarly, human saliva after cigarette smoking also exhibits considerable MAO inhibitory activity. When the amine substrates p-tyramine, serotonin and beta-phenylethylamine were incubated with the cigarette smoke solution, lipophilic adducts were formed non-enzymatically. The irreversible inhibition of MAO by cigarette smoke may well be related to the low platelet MAO associated with cigarette smokers as previously reported. The implication of such cigarette smoke-caused reduction of MAO activity in relation to Parkinsonism is discussed.