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

Abstract

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 (O₂^•−), hydrogen peroxide (H₂O₂) 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 O₂^•− scavenger, and especially was almost completely blocked by pretreatment with FeTPPS (peroxynitrite scavenger). In contrast, although H₂O₂ scavenger potently scavenged SNP-induced H₂O₂ 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 O₂^•− elicited from SNP dominates the SNP-induced apoptosis of HepG2 cells, in which both iron ions and H₂O₂ are not involved.