Prevalence of Low Monoamine Oxidase Function in Alcoholism

Several studies have found a trend for low platelet monoamine oxidase activity (MAO) in alcoholism but with a great deal of overlap in MAO activity of alcoholics versus controls. The main objective of this study was to carry out a detailed assessment of MAO function that included the measurement of key kinetic parameters (i.e., K_m, V_max) in three groups of male subjects: (a) 51 hospitalized chronic alcoholics, (b) 16 recovering alcoholics with 2–10 years of abstinence, and (c) 21 controls. MAO activity was assayed radio-chemically with 14^C]tyramine as substrate (43–729 μM). The present study demonstrated that alcoholics had low platelet MAO activity (p < 0.05). Kinetic analysis revealed a substantial reduction (p < 0.01) in enzyme V_max values of chronic and recovering alcoholics. Greater than 95% of the alcoholics had V_max values lower than the smallest value of control subjects. Moreover, 100% of the alcoholics in both groups exhibited exceedingly low V_max values that were below the 25th percentile of controls. In summary, results of MAO V_max determinations provided us with a better separation of the alcoholics from controls. Measurements of platelet MAO function that include enzyme V_max may provide us a reliable biochemical marker for alcoholism.