NF-κB involvement in hyperoxia-induced myocardial damage in newborn rat hearts.

Premature newborns are frequently exposed to hyperoxia ventilation and some literature data indicate the possibility of hyperoxia-induced myocardial damage. Since nuclear factor κB (NF-κB) is a crucial signaling molecule involved in physiological response to hyperoxia in different cell types as well as in various tissues, our attention has been focused on the role played by NF-κB pathway in response to moderate and severe hyperoxia exposure in rat neonatal heart tissue. Akt and IκBα levels, involved in NF-κB activation, along with the balance between apoptotic and survival pathways have also been investigated. Experimental design of the study has involved exposure of newborn rats to room air (controls), 60 % O2 (moderate hyperoxia), or 95 % O2 (severe hyperoxia) for the first two postnatal weeks. Morphological analysis shows a less compact tissue in rat heart exposed to moderate hyperoxia and a decreased number of nuclei in samples exposed to severe hyperoxia. A significant increase of NF-κB positive nuclei percentage and p-IκBα expression in samples exposed to 95 % hyperoxia compared to control and to 60 % hyperoxia is evidenced; in parallel, an increase of pAkt/Akt ratio in both samples exposed to 95 and 60 % hyperoxia is shown. Furthermore, a more evident cytochrome c/Apaf-1 immunocomplex and a decreased Bcl2 expression in 95 % hyperoxia-exposed sample compared to 60 % exposed one is evidenced. In conclusion, our findings suggest the involvement of the NF-κB pathway and Akt signaling in the mechanisms of myocardial hyperoxic damage in the newborns, with particular reference to the induction of oxidative stress-related apoptosis.