Effect of xenobiotics on quinone reductase activity in first trimester explants.

The placental protective enzyme quinone reductase (QR) has recently been reported to be induced by exposure to mercury, which is a toxic metal in vitro at term. In the present study we have examined the effect of three groups of xenobiotics-carcinogens, chemoprotectors and a natural antioxidant, ascorbic acid (vitamin C) on this enzyme activity in the first trimester placenta in vitro. Incubations with the carcinogen benzo[a]pyrene (BP) at 10-50 microM doses increased the enzyme activity at 6 h. At 24 h the effect of 10 microM BP was significant while that of 50 microM BP was not consistent. On the other hand the effect of 50 microM 3-methylcholanthrene at both time points was not significant. Ascorbic acid (5-25 microM) added for 24 h caused a 2- and 4-fold increase in the enzyme activity, respectively (P < 0.005). Exposure to a 25 microM concentration of different classes of chemoprotectors 2(3)-tert-butyl-4-hydroxyl-anisole (BHA), dicoumarol and Sudan I caused a 2.5- to 3.6-fold significant increase in the enzyme activity after 24 h (P < 0.01). Present data suggest that QR activity in the early placenta is responsive to a wide variety of xenobiotics in vitro. Vitamin C in concentrations usually consumed, exerted a potent effect on local QR activity in vitro which may protect pregnant women and their conceptus in an adverse environment.