Effects of phenytoin on glutathione status and oxidative stress biomarker gene mRNA levels in cultured precision human liver slices

Abstract

Cellular production of reactive oxygen species (ROS) has been implicated as an important mechanism of chemical teratogenesis and developmental toxicity. Unfortunately, the lack of relevant model systems has precluded studies targeting the role of ROS in human teratogenesis and prenatal toxicity. In the current study, we have used cultured precision human prenatal liver slices to study the effects of the human teratogen phenytoin (diphenylhydantoin; Dilantin) on cell toxicity, glutathione redox status, and steady-state mRNA expression of a panel of oxidative stress-related biomarker genes. The biomarker genes analyzed were p53, bcl-2, alpha class glutathione S-transferases isozymes A1 and A4 (hGSTA1 and hGSTA4), and the catalytic subunit of γ-glutamyl-cysteine synthetase (γGCS-HS). Liver slices (200 μm) were prepared from second trimester prenatal livers and cultured in the presence of 0, 250 μM, and 1000 μM phenytoin for 18 h. Exposure to 1000 μM phenytoin elicited 41% and 34% reductions in slice intracellular potassium and reduced glutathione (GSH) concentrations, respectively. The reduction in slice GSH concentrations at 1000 μM phenytoin was accompanied by a 2.2-fold increase in the percentage of total slice glutathione consisting of GSSG, and a 3.9-fold increase in hGSTA1 steady-state mRNA expression. Exposure to 250 μM or 1000 μM phenytoin also elicited a relatively minor (less than 2-fold) but significant increase in p53 steady-state mRNA expression. In contrast, the steady-state levels of γGCS-HS, hGSTA4, and bcl-2 mRNAs were not affected by phenytoin exposure. Our findings in a relevant human model system are supportive of a protective role of GSH and hGSTA1 against phenytoin toxicity and teratogenesis. These studies also demonstrate the utility of using cultured human prenatal liver slices as a relevant tool for developmental toxicology studies.