INTRACELLULAR HIGH-ENERGY METABOLITE DEPLETION AND CELL-MEMBRANE INJURY WITH ANTIOXIDANT ENZYMES DURING OXIDANT EXPOSURE IN-VITRO

We compared oxidant-induced intracellular adenine nucleotide catabolis m and cell membrane injury in 4 different human cell types. Responses to oxidant exposure were correlated with endogenous antioxidant enzyme activities in these cells. Blood monocytes, amniotic fibroblasts, umb ilical vein endothelial cells in primary culture, and transformed bron chial epithelial cells (BEAS 2B) were exposed to 0.1-5 mM hydrogen per oxide (H2O2) for 4 h. Some experiments were conducted in cells pretrea ted with 3-amino I:2,4-triazole (ATZ) to inactivate catalase or with 1 ,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) to inactivate glutathione ( GSH) reductase. Depletion of adenine nucleotides and accumulation of t heir catabolic products (hypoxanthine, xanthine and uric acid) occurre d to varying extent, monocytes being the most resistant. There was a m utual relationship between catalase and GSH reductase activities and m aintenance of cellular adenine nucleotide levels during H2O2 exposure. GSH reductase inhibition rendered BEAS 2B cells susceptible to lytic injury by H2O2, assessed by release of lactate dehydrogenase and intac t nucleotides into the medium, there was no correlation between these markers of such injury and endogenous antioxidant enzymes. We conclude that adenine nucleotide depletion and nucleotide catabolite accumulat ion relate closely with the antioxidant enzyme activities, whereas the lack of a similar correlation between the enzyme levels and markers o f lytic cell injury suggest that intracellular antioxidant enzymes do not protect cells from membrane damage due to extracellular oxidants.