Glutathione S-epoxidetransferase in the human placenta at different stages of pregnancy.

The results show that placental tissue catalyzes not only the formation of previously demonstrated reactive metabolites but also the further metabolism of such metabolites via conjugation with glutathione, suggesting that the balance between the placental formation of toxic metabolites and their further degradation is important in regulation of the quantities ofsuch metabolites that reach the fetal compartment.

Abstract

Glutathione S-transferase activity with styrene 7,8-oxide as substrate was studied in the soluble fraction of human placentas. Measurable enzyme activities were noted in all placental specimens studied. The mean activity was 5.61 +/- 0.59 (SE) nmol of conjugate formed per min per mg of microsomal protein in midgestational placentas obtained between the 8th and 25th weeks of gestation. The corresponding activity was only 2.07 +/- 0.34 (SE) in four term placental specimens. In this material no relation between the enzyme activities and the smoking habits of the women was observed. Linear kinetics of the enzyme were observed both with respect to styrene 7,8-oxide and glutathione as substrates. Our results show that placental tissue catalyzes not only the formation of previously demonstrated reactive metabolites but also the further metabolism of such metabolites via conjugation with glutathione. The clinical significance of our findings is unclear, but one may speculate that the balance between the placental formation of toxic metabolites and their further degradation is important in regulation of the quantities of such metabolites that reach the fetal compartment.