Peroxidase activity and glutathione content in the human first-trimester placenta and decidua

Recently, a novel pathway of xenobiotic oxidation by peroxidase in the placenta at term was described. Herein, we aim to determine the potential of the first-trimester placenta and decidua to activate carcinogens and mutagens by peroxidase and to scavenge free radicals by glutathione.

Placental and decidual peroxidase activity was measured using a sensitive, quantitative colorimetric kinetic assay, with O-phenylenediamine dihydrochloride (OPD) as substrate and H2O2 as co-substrate. Glutathione levels were measured using a colorimetric assay.

Peroxidase activity in cytosolic and CaCl2-extracted (membrane-bound) fractions was inhibited by a specific inhibitor, NaN3. The membrane-bound peroxidase activity was maximal at 12 weeks of gestation while cytosolic peroxidase activity did not change. Placental glutathione content remained unchanged during the first trimester. Decidual and placental peroxidase activities were similar; however decidual glutathione content was 15-fold lower, resulting in a higher decidual peroxidase activity/glutathione ratio (p < 0.03).

We report for the first time that peroxidase may be an important pathway for xenobiotic activation at the maternal-embryonal interface. It remains to be established whether the low glutathione content limits the ability of the decidua but not placenta to protect against genomic damage induced through xenobiotic oxidation.