Metallothionein Suppresses Angiotensin II-Induced Nicotinamide Adenine Dinucleotide Phosphate Oxidase Activation, Nitrosative Stress, Apoptosis, and Pathological Remodeling in the Diabetic Heart

Objectives: We evaluated metallothionein (MT)-mediated cardioprotection from angiotensin II (Ang II)-induced pathologic remodeling with and without underlying diabetes. Background: Cardiac-specific metallothionein-overexpressing transgenic (MT-TG) mice are resistant to diabetic cardiomyopathy largely because of the antiapoptotic and antioxidant effects of MT. Methods: The acute and chronic cardiac effects of Ang II were examined in MT-TG and wild-type (WT) mice, and the signaling pathways of Ang II-induced cardiac cell death were examined in neonatal mouse cardiomyocytes. Results: Acute Ang II administration to WT mice or neonatal cardiomyocytes increased cardiac apoptosis, nitrosative damage, and membrane translocation of the nicotinamide adenine dinucleotide phosphate oxidase (NOX) isoform p47^phox. These effects were abrogated in MT-TG mice, MT-TG cardiomyocytes, and WT cardiomyocytes pre-incubated with peroxynitrite or superoxide scavengers and NOX inhibitors, suggesting a critical role for NOX activation in Ang II-mediated apoptosis. Prolonged administration of subpressor doses of Ang II (0.5 mg/kg every other day for 2 weeks) also induced apoptosis and nitrosative damage in both diabetic and nondiabetic WT hearts, but not in diabetic and nondiabetic MT-TG hearts. Long-term follow-up (1 to 6 months) of both WT and MT-TG mice after discontinuing Ang II administration revealed progressive myocardial fibrosis, hypertrophy, and dysfunction in WT mice but not in MT-TG mice. Conclusions: Metallothionein suppresses Ang II-induced NOX-dependent nitrosative damage and cell death in both nondiabetic and diabetic hearts early in the time course of injury and prevents the late development of Ang II-induced cardiomyopathy.