Isoflurane induced eNOS signaling and cardioprotection:Preconditioning mechanisms under normal and hyperglycemic conditions

The main goal of the thesis was to evaluate the mechanisms conferring cardioprotection offered by anesthetic preconditioning (APC), i.e. the administration of inhalation anesthetics producing resistance to subsequent cessation of blood and oxygen supply, and to evaluate why this technique fails in diabetic conditions. We found that APC with isoflurane protected rat hearts by modulating nitric oxide (NO) synthesis through time-dependent changes in the expression of key NO regulatory proteins, including endothelial NO synthase (eNOS) and guanosine triphosphate cyclohydrolase (GTPCH)-1, the rate-limiting enzyme of tetrahydrobiopterin biosynthesis. Involvement of endothelial NO in APC was confirmed in co-cultures of endothelial and cardiac cells, which is dependent on maintenance of eNOS phosphorylation, partly via induction of hypoxia-inducible factor (HIF1α). APC is thought critically dependent on mitochondria. Given that diabetes alters mitochondrial bioenergetics and disrupts APC protection, contribution of proteins encoded by mitochondrial DNA was studied by using two strains of diabetic rats with the same nuclear but distinct mitochondrial genome. As APC protected hearts of only one of both strains from ischemia, with antioxidants having opposite effects, mitochondria and mitochondrial oxygen radical production seem critical in APC induced cardioprotection. Further mitochondrial adaptations that may abrogate APC induced cardioprotection in hyperglycemia and diabetes are reviewed in depth. Finally, we demonstrate that the ApoA1 mimetic, D-4F, restores APC evoked cardioprotection in hyperglycemia by maintaining a proper cellular localization of eNOS and limiting oxygen radical production. Collectively, this thesis discloses important signal transduction pathways involved in APC affected by diabetic conditions, and identifies a therapeutic strategy to counteract such loss for further clinical investigation