Free radical-induced endothelial membrane dysfunction at the site of blood-brain barrier: Relationship between lipid peroxidation, Na,K-ATPase activity, and Cr-51 release

Na,K-ATPase activity, membrane lipid peroxidation (TBARM), and membrane 'leakiness' for small molecules were examined in rat cerebromicrovascular endothelial cells (RCEC) following exposure to hydrogen peroxide and xanthine/xanthine oxidase. Whereas short-term (15-30 min) exposure to either oxidant decreased ouabain-sensitive Rb-86 uptake and increased TBARM in a concentration-dependent fashion, significant release of Cr-51 (30-40%) from cells was observed only after one hour exposure to the oxidants. By comparison, much longer exposure times (i.e., 4 hours) were needed to induce significant lactate dehydrogenase release from oxidant-treated cells. The oxidant-evoked decrease in Na,K-ATPase activity and increases in TBARM and RCEC 'permeability' were abolished in the presence of the steroid antioxidants U-74500A and U-74389G (5-20 mu M). Reduced glutathione (4 mM) partially attenuated oxidant-induced changes, whereas ascorbic acid (2 mM) and the disulfide bond-protecting agent, dithiothreitol (1 mM), were ineffective. These results suggest that the oxidant-induced loss of Na,K-ATPase activity in RCEC results primarily from changes in membrane lipids, and implicate both the inhibition of Na,K-ATPase and membrane lipid peroxidation in the mechanism responsible for the delayed free radical-induced increase in RCEC membrane 'permeability'.