Myocardial ischaemia – reperfusion injury and its reduction by remote ischaemic preconditioning in health and diabetes mellitus

Myocardial infarction is the main cause of death in the United Kingdom. Early reperfusion of coronary artery occlusion has greatly improved mortality, though restoration of blood supply may perpetuate cell death through reperfusion injury. Preconditioning is a potent endogenous form of cardioprotection triggered through preceding brief nonperfusion of the heart’s blood supply. In remote conditioning it is triggered by intermittent tourniquet ischaemia of a limb. However a limited understanding of the mechanisms underlying transfer of a signal from the peripheries, its reception in the heart, and the impact of comorbid disease on this process hinders its application to the clinical setting of myocardial infarction. This work trials several models of reperfusion injury, and optimises a method of centrifugation of adult rat ventricular myocytes into a dense pellet to induce ischaemia, and simulate reperfusion by its dispersal. Remote preconditioning is evoked by preincubation of myocytes with serum samples taken from participants. This is used as a screening tool in order to test serum samples acquired from volunteers in control and disease states undergoing tourniquet ischaemia of a peripheral limb to reproduce the stimulus of remote preconditioning. A protective signal was seen in serum taken from healthy subjects following remote preconditioning versus baseline serum (20.5±3.3 vs 37.2±4.5 % necrosis respectively, n = 21, p < 0.001). Protection is absent in diabetes mellitus type 1 (51.5±4.6% necrosis, n = 14) and type 2 (51.3±8.2% necrosis, n = 10). The protective signal is preserved with age in healthy male participants, though appears to decline with age in a preliminary cohort of female participants. On assay of putative mechanisms of remote preconditioning, serum nitrite did not change with preconditioning in healthy volunteers, though it was found to significantly decrease in diabetes mellitus type 1. The implications for the application of this powerful yet elusive form of innate cardiac protection are considered.