Susceptibility of rat astrocytes to DNA strand scission induced by activation of NADPH oxidase and collateral resistance to the effects of peroxynitrite

Rat astrocytes accumulate extensive DNA single-strand breakage in response to agents promoting activation of NADPH oxidase. Proinflammatory stimuli, as bacterial lipopolysaccharide associated with interferon-γ, caused a rapid/robust burst of superoxide radicals, sensitive to NADPH oxidase inhibition, followed by dismutation to H2O2, the species resulting in DNA damage via a Fenton-type reaction. There was no contribution of superoxide radical/H2O2 of mitochondrial origin and there was no evidence for the formation/involvement of peroxynitrite. On the other hand, astrocytes were virtually invulnerable to the DNA-damaging effects of exogenous peroxynitrite, an agent causing DNA strand scission in other cell types, via the Ca2+-dependent mitochondrial formation of superoxide radical/H2O2. Resistance was not dependent on scavenging of peroxynitrite but, rather, on insufficient mitochondrial Ca2+ accumulation. Hence, different manipulations resulting in an increase of the mitochondrial Ca2+ pool were invariably associated with the formation of DNA-damaging levels of H2O2. In conclusion, it appears that the strategy adopted by astrocytes to avoid inflammation-dependent genotoxic events, in particular those mediated by peroxynitrite, is to prevent mitochondrial Ca2+ accumulation, critical for the formation of secondary species largely responsible for DNA damage induced by peroxynitrite.