Quinone reductase activity in the first trimester placenta: effect of cigarette smoking and polycyclic aromatic...

Quinone reductase (QR) is considered a major protective enzyme against cancer in the organism. In this study, the activity of QR was measured in first trimester placental tissue using colorimetric techniques. There were no significant differences between the mean enzyme activity of women who smoked more than 20 cigarettes per day during pregnancy and of nonsmokers (0.50 +/- 0.09 compared with 0.51 +/- 0.15 mumol/mg protein/10 min, respectively). Among the polycyclic aromatic hydrocarbons (PAH) studied, dimethyl benzanthracene (DMBA) increased QR activity in a dose-dependent manner in the first trimester placental explants at the 10- to 100-microM range after 6 h of incubation (440% increase) with the highest concentration. The effect of other PAH of different potency added at 50-microM concentrations showed that benz(a)anthracene (BA), dibenzo(a,h)anthracene (DBHA), dibenzo(a,c)anthracene (DBCA), or chrysene (CH) caused a significant 2- to 3-fold increase in the enzymatic activity after 6 h of incubation. At 24 h 50-microM DBCA effect was also stimulatory, while the 10-microM DMBA effect almost reached statistical significance. However, no differences were encountered in the response of placental tissues to PAH between cigarette smokers and nonsmokers at 6 and 24 h. The present data indicate that placental QR activity is increased by exposure to PAH in vitro, but it does not appear to be affected by in vivo exposure to cigarette smoking. Thus, the early placenta appears to have a significant potential to inactivate carcinogens/mutagens locally, thereby limiting their transfer to the embryo.