Abstract 16683: Subcellular Changes in NF-κB p50-Dependent iNOS Regulation in Doxorubicin-Induced Cardiomyopathy (DIC)

A repeat use of doxorubicin (Dox), an anti-cancer drug, can cause heart failure in cancer patients. Dox-induced cardiac mitochondrial as well as ER damage due to oxidative and nitrosative stress (O/NS) has been widely studied. However, mechanism by which Dox exerts iNOS changes via mitochondrial damage and/or ER stress is yet to be elucidated. We investigated whether iNOS induced inflammatory changes in Dox exposed hearts involve mitochondrial and/or endoplasmic reticulum (ER) damage. A cumulative dose of Dox (15mg/kg B.W., ip) was given to Male Wistar rats. We noted an increase in cytC release in the cytoplasm due to O/NS indicating mitochondrial injury. Dox induced linking of chaperone binding immunoglobulin protein (Bip) to activating transcription factor 6 (ATF6) suggested an increased unfolded protein response (UPR) contributing to ER stress which was independent of upstream transcription factors inositol requiring enzyme 1 (IRE1) and protein kinase RNA-like ER kinase (PERK). ATF6-induced ER stress promoted NFκBp105/p50-induced expression of iNOS and NO production in the myocardium. The latter was associated with increased expression of TLR2 and TRAF2 together with NFκB105/50 expression suggesting that ER-stress promoted the inflammatory response in the myocardium. Co-localization of iNOS or TLR2 together with calnexin/grp78 (ER markers) but not with Tom20 (mitochondria marker) suggested that only ER stress promoted inflammatory response. The study suggests that inhibition of Bip binding to ATF6 may modulate ER-stress-mediated inflammation in DIC and presents a novel avenue for a development of the therapeutics for treatment of DIC.