Protective effects of dihydropyridine Ca-blockers against endothelial cell oxidative injury due to combined nitric oxide and superoxide

Nitric oxide (NO) and superoxide anions (·O− 2 ), which are known to be generated by inflammatory cells under certain pathological conditions, may be cytotoxic to the endothelial cells (ECs) due to peroxynitrite formation. We reported previously that certain lipophilic dihydropyridine (DHP) Ca-blockers exhibit antioxidant activities. In the present study, the extent of antioxidant protection by nisoldipine against combined NO / ·O− 2 or peroxynitrite-mediated EC injury was assessed and compared with nicardipine, nifedipine and Trolox (water-soluble vitamin E). When confluent bovine aortic ECs were exposed to combined NO / ·O− 2 (generated from 0.25 mM SIN-1), dramatic loss of cell GSH (53 ± 8% ) occurred in 60 min; cell survival/viability, determined 24 h later by the tetrazolium MTT assay, decreased by 45 ± 6 %. NO alone or ·O− 2 alone were ineffective. Nisoldipine pretreatment (30 min) of the cells concentration dependently (0.3–10 μ M) attenuated the SIN-1-induced GSH loss: the EC50value was 4.7 μ M and the corresponding values for nicardipine and nifedipine were 7.8 μ M and >20 μ M, respectively, and that for Trolox was 5.2 μ M. These agents (10μ M) also protected against the loss of cell viability: nisoldipine, 86 ± 8 %; nicardipine, 60 ± 7 %; nifedipine, 35 ± 5 %, and Trolox, 78 ± 9 %. In addition, significant losses of GSH and viability could be induced by incubation of the EC monolayers with purified peroxynitrite (25 μ M). Attenuation of these peroxynitrite-mediated GSH and viability losses was observed with the following order of efficacy: nisoldipine ≥ Trolox > nicardipine ⪢ nifedipine. In a cell-free system containing 0.05 mM GSH, none of the agents (10 μ M) were able to inhibit SIN-1- (0.25 mM) or peroxynitrite- (25μ M) induced depletion ( ∼50%) of GSH. However, with a purified microsomal membrane system, all four agents inhibited the SIN-1- (or peroxynitrite-) induced lipid peroxidation (TBARS) with the followingIC50 values: nisoldipine, 6.3 μ M; nicardipine, 10.6 μ M; nifedipine, >20μ M, and Trolox, 6.5 μ M. In conclusion, nisoldipine, a vascular selective DHP calcium channel-blocker, demonstrated the greatest protection against the EC injury induced either by SIN-1 or peroxynitrite. The protective mechanism against the cytotoxicity is most likely through a lipophilic ‘chain-breaking’ antiperoxidative action against the ‘OH-like species’ released from peroxynitrite or SIN-1.