Role of oxygen free radical species in in vitro models of proximal tubular ischemia.

Lipid peroxidation (LP) of cell membranes by oxygen free radical species (OFRS) during reflow may be a mechanism for progressive proximal tubule injury after ischemia. We examined the relationship between tubule function and an endproduct of LP, malondialdehyde (MDA), in two in vitro models using a suspension of rat proximal tubule segments (PTS). Exposure of PTS to tert-butyl hydroperoxide (tBHP), a potent oxidant, induced dose-dependent decrements in the PTS respiration (QO2) but was associated with a progressive increase in MDA. The relationship between increasing doses of tBHP, QO2, and MDA content, as well as that between MDA and QO2 were highly correlated (r greater than or equal to 0.89, n = 6). Dithiothreitol (1 mM), a sulfhydryl reagent, prevented the tBHP-induced changes in both QO2 and LP. In the second model, 45-min O2 deprivation followed by 30 min of reoxygenation produced similar decrements in QO2 as did 0.75 mM tBHP but without a rise in MDA (n = 9). Mitochondria isolated from ischemic PTS had a 49 +/- 8.2% decrement in state III respiration (P less than 0.006, n = 4) but their MDA content was unchanged. Furthermore, allopurinol, superoxide dismutase, and catalase, agents that reduce tissue OFRS, did not attenuate ischemic tubular injury (n = 9). These results suggest that OFRS do not mediate transient O2 deprivation injury to the proximal tubule.