Obesity improves myocardial ischaemic tolerance and RISK signalling in insulin-insensitive rats

Obesity with associated metabolic disturbances worsens ischaemic heart disease outcomes, and rodent studies confirm that obesity with insulin-resistance impairs myocardial resistance to ischemia-reperfusion (I-R) injury. However, the effects of obesity per se are unclear, with some evidence for paradoxic cardioprotection (particularly in older subjects). We tested the impact of dietary obesity on I-R tolerance and reperfusion injury salvage kinase (RISK) signalling in hearts from middle-aged (10 months old) insulin-insensitive rats. Hearts from Wistar rats on either a 32-week control (CD) or high carbohydrate obesogenic (OB) diet were assessed for I-R resistance in vivo (45 minutes left anterior descending artery occlusion and 120 minutes reperfusion) and ex vivo (25 minutes ischemia and 60 minutes reperfusion). Expression and δ-opioid receptor (δ-OR) phospho-regulation of pro-survival (Akt/PKB, Erk1/2, eNOS) and pro-injury (GSK3β) enzymes were also examined. OB rats were heavier (764±25 versus 657±22 g for CD; P<0.05), hyperleptinaemic (11.1±0.7 versus 5.0±0.7 for CD; P<0.01) and comparably insulin-insensitive (HOMA-IR of 63.2±3.3 versus 63.2±1.6 for CD). In vivo infarction was more than halved in OB (20±3%) versus CD rats (45±6% P<0.05), as was post-ischaemic lactate dehydrogenase efflux (0.4±0.3 mU/ml versus 5.6±0.5 mU/ml; P<0.02) and ex vivo contractile dysfunction (62±2% versus 44±6% recovery of ventricular force; P<0.05). OB hearts exhibited up to 60% higher Akt expression, with increased phosphorylation of eNOS (+100%), GSK3β (+45%) and Erk1/2 (+15%). Pre-ischaemic δ-OR agonism with BW373U86 improved recoveries in CD hearts in association with phosphorylation of Akt (+40%), eNOS (+75%) and GSK3β (+30%), yet failed to further enhance RISK-NOS activation or I-R outcomes in OB hearts. In summary, dietary obesity in the context of age-related insulin-insensitivity paradoxically improves myocardial I-R tolerance, in association with moderate hyperleptinaemic and enhanced RISK expression and phospho-regulation. However, OB hearts are resistant to further RISK modulation and cardioprotection via acute δ-OR agonism.