Iron Ion Induces Mitochondrial DNA Damage in HTC Rat Hepatoma Cell Culture-Role of Antioxidants in Mitochondrial DNA Protection from Oxidative Stresses

The mitochondrial DNA (mtDNA) is exposed to the reactive oxygen species generated in the mitochondrial electron transfer system. While mitochondrial superoxide dismicrotase (Mn-SOD) scavenges superoxide anions to prevent damage of mtDNA, excess amount of reactive oxygen generated by quinone compounds impairs the mtDNA, in which involvement of iron ion-catalyzed reactions is suggested. In this commicronication, we report that the mtDNA in HTC rat hepatoma cells was markedly damaged in the presence of either ferrous (Fe2+) or ferric (Fe3+) iron in the culture medium. The mtDNA of HTC cells was damaged in the presence of 100 μM of iron ions in the culture medium within 3 h. There was no significant difference in the potency of Fe2+ and Fe3+. Deferoxamine, a Fe3+-specific chelating reagent, blocked the iron ion-induced mtDNA damage completely. The mtDNA in rat hepatocyte primary culture was, on the other hand, not damaged by either Fe2+ or Fe3+. To understand the difference between iron ion-induced damage of mtDNA in HTC cells and in the primary hepatocytes, the Mn-SOD activity and lipid-soluble antioxidant contents were compared. The Mn-SOD activity in HTC cells was markedly lower (<0.02 U/mg cell protein) than that in rat hepatocyte primary cell cultures (1.5 U/mg cell protein). Immicronoreactive Mn-SOD content in HTC cells was also lower (21 ng/mg cell protein) than in the primary cultures (99 ng/mg cell protein). HTC cells contain microch smaller amounts (3-11% of that of normal rat hepatocytes) of α-tocopherol and coenzyme Q homologs (CoQn). These results suggest that reactive oxygen species produced by iron ion impaired mtDNA of HTC cells, in which antioxidant activity was markedly decreased.