Peroxynitrite dominates sodium nitroprusside-induced apoptosis in human hepatocellular carcinoma cells

This study aims to explore which radicals dominate sodium nitroprusside (SNP)-induced cytotoxicity in human hepatocellular carcinoma (HCC) cells (HepG2 and Hep3B). Exposure of SNP to cell medium produced abundant nitric oxide (NO), superoxide anion (O(2)(·−)), hydrogen peroxide (H(2)O(2)) and iron ions. SNP potently induced caspases activation, mitochondrial membrane permeabilization and apoptosis in HCC cells. In Hep3B cells, pretreatment with NO scavenger (PTIO) did not prevent SNP-induced cytotoxicity. However, in HepG2 cells, SNP-induced cytotoxicity was prevented significantly by pretreatment with PTIO and O(2)(·−) scavenger, and especially was almost completely blocked by pretreatment with FeTPPS (peroxynitrite scavenger). In contrast, although H(2)O(2) scavenger potently scavenged SNP-induced H(2)O(2) production, it did not prevent SNP-induced cytotoxicity in HepG2 cells. In addition, pretreatment with DFO (iron ions chelator) and iron-saturated DFO respectively completely prevented SNP-induced cytotoxicity in HepG2 cells. Collectively, peroxynitrite from the reaction between NO and O(2)(·−) elicited from SNP dominates the SNP-induced apoptosis of HepG2 cells, in which both iron ions and H(2)O(2) are not involved.