The effects of hyperglycemia on hypoxia-reoxygenation injury and remifentanil-preconditioning in cardiomyocytes

Abstract

Remifentanil has been reported to havecardioprotective effects against the ischemia-reperfusion injury. However, it has also been reported that hyperglycemia attenuates this cardioprotective effects by remifentanil in diabetic rats in vivo. In this study, the in vitro effect of hyperglycemia on hypoxia-reoxygenation and remifentanil-preconditioning induced cardioprotection in isolated neonatal rat ventricular myocytes (NRVMs) was evaluated, in particular, regarding to apoptotic signaling pathways and Ca2+ homeostasis. NRVMs were cultured in medium containing 5.5 mM (normoglycemic condition) or 25.5 mM (hyperglycemic condition) of glucose for 16 h. Then, NRVMs in hypoxia-reoxygenation groups were exposed to 1 h of hypoxia and 5 h of reoxygenation with or without remifentanil-preconditioning at 1 M for 1 h. Under these conditions, cell viability and apoptosis activity were evaluated with MTT assay and caspase-3 assay, respectively. To elucidate the mechanisms of remifentanil-preconditioning, Ca2+ homeostasis and signaling components which govern cell survival/apoptotic pathways were assessed.Remifentanil-preconditioning significantly improved the viability of cardiomyocytes and prevented the increase of caspase-3 activity and Ca2+ overload after hypoxia-reoxygenation injury. In addition, decrease in Akt, ERK1/2, and Bcl-2, and the increase in Bax by hypoxia- reoxygenation were significantly attenuated by remifentanil-preconditioning. On the contrary, under hyperglycemic condition, the viability was partially reduced by hypoxia-reoxygenation and not affected by remifentanil-preconditioning. In addition, apoptotic activity, Ca2+ concentration and apoptotic kinases except Akt were not affected by either hypoxia-reoxygenation or remifentanil-preconditioning. Akt phosphorylation was decreased by hypoxia-reoxygenation but not restored by remifentanil-preconditioning.

In conclusion, Remifentanil-preconditioning under normoglycemia renders NRVMs resistant to hypoxia-reoxygenation injury by inhibiting apoptosis and reducing the intracellular Ca2+ concentration. It is suggested that the mechanism of remifentanil preconditioning under normoglycemia involves modulation of Akt, ERK, Bcl-2 and Bax pathway. Under hyperglycemic condition, however, the protective effect of remifentanil preconditioning could not affirmatively evaluated because hyperglycemia itself mitigated hypoxia-reoxygenation injury in NRVMs. It is also suggested that hyperglycemia may reduce the protective effect of remifentanil-preconditioning associated with the Akt pathways because remifentanil preconditioning did not restore reduction of Akt activity under hyperglycemia.