Platelet monoamine oxidase B activity is inversely associated with plasma cotinine concentration

Cigarette smoke but not nicotine inhibits irreversibly platelet monoamine oxidase B (MAO-B) activity. Current smokers have decreased platelet MAO-B activity which normalizes when smokers quit. Normalization of platelet MAO-B activity probably depends on platelet turnover. Platelet MAO-B activity has been found to be correlated with plasma thiocyanate concentration. The aim of this study was to investigate in smokers whether platelet MAO-B activity is related to plasma cotinine concentration, an indirect index of use of smoked tobacco. We determined simultaneously plasma cotinine concentration and platelet MAO-B activity in 85 cigarette smokers [mean (+/- SD) age 39 +/- 8.8 years, 55 men]. Platelet MAO-B activity was lower in male than in female smokers (14.1 +/- 7.9 versus 17.8 +/- 7.2 nmol/h/10(9) platelets, p = 0.03). Platelet MAO-B activity correlated positively with age (r = 0.26, p = 0.01) and inversely with plasma cotinine concentration (r = -0.32, p = 0.002) but not with number of cigarettes smoked or with Fagerström Tolerance Questionnaire score. Multiple linear regression analysis showed that 49% of the age-adjusted variance in platelet MAO-B activity (R2 = 0.489, p < 0.0001) was explained by plasma cotinine concentration (p < 0.001) and gender (p = 0.037). It was concluded that platelet MAO-B activity in smokers is inversely associated with plasma cotinine level, an index of smoked tobacco use. Further studies are needed to investigate whether measurement of platelet MAO-B activity can be used as a long-term index of tobacco use and smoke exposure.