Regulation of iNOS expression and glutathione levels in rat liver by oxygen tension

Molecular oxygen (O-2) regulates the expression of a variety of genes. We h ypothesized that O-2 tension may regulate iNOS expression in rat liver thro ugh the production of reactive oxygen species (ROS) and the reduction of in tracellular glutathione (GSH) levels. To investigate this hypothesis, we de termined the effects of hyperoxia upon iNOS induction (both at the protein and mRNA level) and the intracellular concentration of GSH in an isolated i n vitro perfused rat liver preparation. To study the potential involvement of ROS in the intracellular signaling pathway linking changes in oxygen ten sion to gene expression, we repeated these determinations in the presence o f the thiol antioxidant N-acetyl-L-cysteine (NAC). We found that 95'% O-2 t ension caused a significant induction of the iNOS protein and mRNA levels p aralleled by a significant fall in intracellular GSH concentration. The add ition of NAC (1 mM) to the perfusate during hyperoxia blocked the induction of iNOS and restored GSH levels. These results indicate that molecular O-2 regulates the expression of iNOS in rat liver at the transcriptional level , most likely through the production of ROS and the reduction of intracellu lar GSH levels. (C) 2000 Federation of European Biochemical Societies. Publ ished by Elsevier Science B.V. All rights reserved.