Remote preconditioning: Evaluating the efficacy of cardioprotection in type-2 diabetes and exploring the mechanistic role of exosomes
Year: 2017
Type: dissertation
Abstract: Remote preconditioning is a promising and robust treatment for myocardial ischemia/reperfusion injury that evokes cardioprotection through endogenous neural and/or humoral signaling. A recent study has reported that protective signaling is mediated by exosomes through the circulation; however this concept is supported by limited and inconsistent evidence. Despite overwhelming success in preclinical studies, the efficacy of remote preconditioning in human studies is inconclusive. Importantly, the majority of remote preconditioning studies use healthy animal models despite growing evidence that comorbidities, such as type-2 diabetes, may negatively influence outcomes. Nonetheless, the efficacy of remote preconditioning in the setting of type-2 diabetes has not been investigated. Using an established model of myocardial ischemia/reperfusion in the Zucker model of type-2 diabetes and a model of hypoxia/reoxygenation in cultured HL-1 cardiomyocytes we tested four hypotheses: i. remote preconditioning is ineffective in early-stage type-2 diabetes in vivo; ii. the traditional ultracentrifugation technique for exosomes isolating is inadequate to isolate protective factor(s) from remote preconditioning; iii. enhanced ultracentrifugation technique for exosome isolation sequesters a protective fraction of serum; iv. the humoral component of remote preconditioning is defective in type-2 diabetes. In support of Hypothesis I, we demonstrate that remote preconditioning failed to reduce infarct size caused by ischemia/reperfusion in the Zucker model of early-stage type-2 diabetes. Our results illustrate that the loss in efficacy is not the result of hyperglycemia per se nor sensitization of the myocardium to ischemia/reperfusion. Subsequently, we sought to isolate a subfraction of serum from remote preconditioned rats which contained exosomes that could communicate protection and render HL-1 cardiomyocytes resistant to hypoxia/reoxygenation-induced cell death. In agreement with Hypothesis II, we report that the traditional ultracentrifugation isolation technique (100,000 xg for 2 hr) did not isolate the protective component with the exosome-rich pellet from serum, suggesting that the protective component remained in the supernatant. In accordance with these observations, we enhanced the ultracentrifugation technique to improve exosome sedimentation and obtain a protective sub-fraction of serum. In agreement with Hypothesis III, the enhanced ultracentrifugation technique (300,000 xg for 12 hr) isolated a protective exosome-rich supernatant fraction from remote preconditioned serum. However, our enhanced ultracentrifugation technique also yielded an additional, exosome-rich pellet and an exosome-depleted fraction, neither of which evoked protection. Lastly, in support of Hypothesis IV, we demonstrate that unfractionated serum and the exosome-rich supernatant fraction obtained from remote preconditioned diabetic Zucker Fatty rats did not protect HL-1 cardiomyocytes from hypoxia/reoxygenation. In conclusion, our results illustrate for the first time that the infarct-sparing efficacy of remote preconditioning is abolished in the setting of early-stage type-2 diabetes. We demonstrate that exosomes, although not sufficient for protection, may be requisite in the humoral component of remote preconditioning. Finally, we report that the humoral component of remote preconditioning is defective in the setting of type-2 diabetes – a defect that may contribute to the failure of remote conditioning to limit infarct size in this comorbid model.
Source: Human Biology
Author: Joseph M. Wider
Language: English
Subfield: Cardiology and Cardiovascular Medicine
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2613683196