Contribution of mammalian target of rapamycin in the pathophysiology of cirrhotic cardiomyopathy

摘要

AIM: To explore the role of mammalian target of rapamycin(m TOR) in the pathogenesis of cirrhotic cardiomyopathy and the potential of rapamycin to improve this pathologic condition.METHODS: Male albino Wistar rats weighing 100-120 g were treated with tetrachloride carbon(CCl_4) for 8 wk to induce cirrhosis. Subsequently, animals were administered rapamycin(2 mg/kg per day). The QT_c intervals were calculated in a 5-min electrocardiogram. Then, the left ventricular papillary muscles wereisolated to examine inotropic responsiveness to β-adrenergic stimulation using a standard organ bath equipped by Powerlab system. Phosphorylated-m TOR localization in left ventricles was immunohistochemically assessed, and ventricular tumor necrosis factor(TNF)-α was measured. Western blot was used to measure levels of ventricular phosphorylated-m TOR protein.RESULTS: Cirrhosis was confirmed by hematoxylin and eosin staining of liver tissues, visual observation of lethargy, weight loss, jaundice, brown urine, ascites, liver stiffness, and a significant increase of spleen weight(P < 0.001). A significant prolongation in QTc intervals occurred in cirrhotic rats exposed to CCl_4(P < 0.001), while this prolongation was decreased with rapamycin treatment(P < 0.01). CCl_4-induced cirrhosis caused a significant decrease of contractile responsiveness to isoproterenol stimulation and a significant increase in cardiac TNF-α. These findings were correlated with data from western blot and immunohistochemical studies on phosphorylated-m TOR expression in left ventricles. Phosphorylated-m TOR was significantly enhanced in cirrhotic rats, especially in the endothelium, compared to controls. Rapamycin treatment significantly increased contractile force and myocardial localization of phosphorylated-m TOR and decreased cardiac TNF-α concentration compared to cirrhotic rats with no treatment. CONCLUSION: In this study, we demonstrated a potential role for cardiac m TOR in the pathophysiology of cirrhotic cardiomyopathy. Rapamycin normalized the inotropic effect and altered phosphorylated-m TOR expression and myocardial localization in cirrhotic rats.