Female headstart in resistance to hyperoxia-induced oxidative stress in mice.

Increased oxygen concentration (hyperoxia) induces oxidative damage of tissues and organs. Oxygen toxicity in hyperoxia is controlled by factors such as sex, age, tissue, strain and hormones. In most species females show lower incidence of some age-related pathologies linked with oxidative stress, which has been attributed to a beneficial effect of ovarian hormones. In this study we found that hyperoxia induced hepatic oxidative damage exclusively in male CBA/H mice, followed by their decreased survival. Histopathological examination revealed that the observed differences in survival were not the consequence of acute lung injury induced by hyperoxia. Next, we observed that an increased Sirt1 protein level in hyperoxia-exposed female CBA/H mice correlated with their lower PPAR-γ and higher eNOS and Sod2 protein levels. In males, higher PPAR-γ and lower Sod2 protein levels were associated with unchanged Sirt1 expression. Although these results are of a correlative nature only, they clearly show that females show better survival, increased resistance to hyperoxia and have generally more efficient defense systems, which suggests that their headstart in resistance to hyperoxia could be a consequence of the beneficial effect of ovarian hormones.