Protection of human keratinocyte mtDNA by low-level nitric oxide

This study was designed to evaluate the DNA damaging effects of nitric oxide and to determine whether the endogenous generation of nitric oxide at low levels in the cell exerts a protective effect against this damage. Damage to mitochondrial and nuclear DNA in normal human epidermal keratinocytes (NHEK) was assessed after treatment of these cells with varying concentrations of S-nitroso-N-acetylpenicillamine, which decomposes to release nitric oxide. The results showed that mitochondrial DNA was more vulnerable to nitric oxide-induced damage than was a similarly sized fragment of the beta-globin gene. To evaluate the effects on DNA damage by pretreatment of cells with low-levels of nitric oxide, NHEK cells were treated with the prodrug V-PYRRO/NO. This agent is metabolized inside these cells and releases small quantities of nitric oxide. The cells then were exposed to damaging amounts of nitric oxide produced by S-nitroso-N-acetylpenicillamine. The results of these studies showed that pretreatment of NHEK cells with V-PYRRO/NO attenuated the mtDNA damage and loss of cell viability produced by exposure to S-nitroso-N-acetylpenicillamine.