Comparison of the hydroxylation of zoxazolamine and benzo[a]pyrene in human placenta: Effect of cigarette smoking

The in vitro hydroxylation of zoxazolamine was compared with the hydroxylation of benzo[a]pyrene (BP) in full-term placentas from 11 nonsmokers and from 13 women who smoked cigarettes during pregnancy. Cigarette smoking increased the average zoxazolamine and benzo[a]pyrene hydroxylase activities 13- and 39 fold, respectively. A 59-fold range in benzo[a]pyrene hydroxylase activity and a 28 fold range in zoxazolamine hydroxylase activity were found! in the placentas of cigarette smokers. A plot of these two enzyme activities showed that zoxazolamine hydroxylase activity was highly correlated, with benzo[a]pyrene hydroxylase activity in the 24 placentas studied (r = 0.98; p < 0.001). A strong correlation between the above enzymatic activities was also found in 8 placentas which had been stored for 2 yr at -20° C (r = 0.95; p < 0.001). The results suggest that benzo[a]pyrene and zoxazolamine are metabolized in the human placenta by the same enzyme system or by different systems that are under the same regulatory control.