Background: Post-burn cardiac shock causes myocardial damage and cardiac dysfunction at the early stage of severe burns. We showed that remote ischemic preconditioning(RIPC) protects heart against myocardial I/R injury. However, little is known regarding the effect of RIPC on heart after severe burn. We proposed the existence of RIPC-induced cardioprotection in severely burned rats and further investigate the underlying mechanisms.
Methods: Male Sprague Dawley rats were assigned to sham-burn,control(CON), limb ischemic preconditioning group (RIPC), each group, n=8. Rats were inflicted with 30% total body surface area full-thickness burn in a 97℃ water bath for 18 s except for the sham rats. Immediately after burn injury, all rats were resuscitated with Ringer's lactate solution (4.0ml/kg/1%TBSA,i.p.). For RIPC intervention, rats received four cycles of 5 min of limb ischemia with 5 min reperfusions at 24 hours and 1 hour before burn injury. Hemodynamics were measured. 3 hours post-burn, hearts were taken for apoptosis measurements and westernblotting analysis. Myocardial mitochondria and cytosol were isolated to determine mitochondrial energy metabolism, cytochrome c release and mitochondrial membrane potential (ΔΨm). Blood samples were taken for serum levels of lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) determination. 

Results: RIPC restored cardiac function, increased Bcl-2 expression while decreasing Bax and Caspase-3 expression and enhancing Bcl-2/Bax ratios(P<0.05 vs CON). RIPC preserved post-burn cardiac mitochondrial function by recovering ATP concentrations and decreasing AMP/ATP ratio (P<0.05 vs. CON). RIPC up-regulated ΔΨm from 11.2±2 in the CON to 17.2±1.1μg/mL (P<0.05). RIPC caused a 40% lower of cytochrome c, than rats in CON (P<0.01). Serum levels of cardiac enzyme leakage were reduced in RIPC group (P<0.05 vs CON). Meanwhile, RISK pathway (Akt, ERK1/2, and GSK3β) phosphorylation was enhanced in RIPC-treated hearts compared to non-treated control groups (P<0.05), highlighting the crucial role of the RISK pathway in RIPC-induced heart protection after severe burn injury. 

Conclusion: Limb ischemic conditioning effectively improves cardiac function, ameliorates myocardial damage and preserves mitochondrial function after severe burn injury. The underlying mechanism may involve RISK signaling pathways. 


02 / Limb Ischemic Preconditioning Reduces Heart Injury after Severe Burn Injury in Rats