Heme oxygenase-1 (HO-1) plays a preventive role in oxidative stress. In contrast, COX-2 is involved in the pathogenesis of many inflammatory diseases, thus COX-2 inhibitor is believed to exert anti-inflammatory properties by blocking COX-2. Recently, however, salicylate the active metabolite of aspirin showed COX-independent anti-inflammatory effects through induction of HO-1. Thus, we hypothesized that HO-1 are induced as an adaptive response to sodium nitroprusside (SNP) and play a protective role against cytotoxicity. Moreover, we investigated the protective effect of NS398 known as a selective COX-2 inhibitor on SNP-mediated cytotoxicity, and whether the protective effect of NS398 is due to COX-2 inhibition or not. SNP induced cytotoxicity in a dose-dependent manner, which was enhanced by inhibition of HO-1, suggesting that HO-1 acts in an adaptive response to SNP. Interestingly, NS398 decreased SNP-mediated cytotoxicity whereas COX-2 siRNA did not. Furthermore, NS398 enhanced SNP-induced HO-1 induction even though NS398 alone failed to induce HO-1 protein expression. In addition, NS398 enhanced SNP-induced COX-2, even though NS398 effectively inhibited SNP-mediated PGE(2) production. These results demonstrate that NS398 exerts cytoprotective effects by inducing HO-1 independent of COX-2 inhibition.