Simvastatin combined with aspirin increases the survival time of heart allograft by activating CD4+CD25+ Treg cells and enhancing vascular endothelial cell protection

ObjectiveThe objective was to investigate whether the combination of simvastatin and aspirin treatment prolongs the survival time of the heart allograft in rat and its underlying mechanism.MethodsHeterotopic heart transplantation was performed using Wistar rats as donors and Sprague-Dawley (SD) rats as recipients. The SD rats were randomly divided into five groups (n= 20/group): sham, HT (heart transplantation), HT+simvastatin (HT+S), HT+aspirin (HT+A), and HT+aspirin+simvastatin (HT+A+S). After transplantation, at 3, 7, 10, 15, 20, 30, and 40 days, the endothelial nitric oxide synthase (eNOS) expression was assessed by immunohistological staining; nitric oxide (NO) levels were analyzed by Griess assay; the activation of CD4+CD25+ T regulatory lymphocytes (Tregs) was analyzed by flow cytometry; and pathological changes in the graft heart were determined by histology.ResultsCombined treatment of hearts with simvastatin and aspirin significantly prolonged the mean survival time of heart allografts [8±1.2 days (n= 18), 20±3.4 days (n= 19), 21±2.8 days (n= 19), and 39±5.3 days (n= 19) for HT, HT+S, HT+A, and HT+A+S group, respectively; HT vs. HT+A+S, P< .001; HT vs. HT+S or HT+A, P< .05]. In addition,1.Treatment together with simvastatin and aspirin resulted in less pathological changes (inflammatory cell infiltration, myocardial and vascular damage) in graft hearts and reduced vascular damage.2.The eNOS expression and NO secretion were enhanced by the combined treatment of simvastatin and aspirin.3.The circulating level of CD4+CD25+ Tregs in HT+A+S rats was significantly increased [2.2%±0.5%, 2.9%±0.8%, 4.3%±1.0%, 8.3%±1.7%, and 14.3%±3.7% for sham, HT, HT+S, HT+A, and HT+A+S, respectively; HT vs. HT+A (P< .05) or HT+A+S (P< .01)].ConclusionsSimvastatin given in combination with aspirin delayed the development of pathological changes in the myocardium, reduced vascular damage and prolonged the survival time of cardiac allograft. The underlying mechanism is linked with CD4+CD25+-Treg-cell-induced immune tolerance and enhanced vascular endothelial cell protection.