Chronic Ca2+/Calmodulin-Dependent Protein Kinase Ii Inhibition Rescues Advanced Heart Failure

Ca2+/calmodulin-dependent protein kinase II (CaMKII) is upregulated in congestive heart failure (CHF), contributing to electrical, structural, and functional remodeling. CaMKII inhibition is known to improve CHF, but its direct cardiac effects in CHF remain unclear. We hypothesized that CaMKII inhibition improves cardiomyocyte function, [Ca2+](i) regulation, and beta-adrenergic reserve, thus improving advanced CHF. In a 16-week study, we compared plasma neurohormonal levels and left ventricular (LV)-andmyocyte-functional and calciumtransient ([Ca2+](iT)) responses in male Sprague-Dawley rats (10/group) with CHF induced by isoproterenol (170 mg/kg sq for 2 days). In rats with CHF, we studied the effects of the CaMKII inhibitor KN-93 or its inactive analog KN-92 (n = 4) (70 mu g/kg per day, mini-pump) for 4 weeks. Compared with controls, isoproterenol-treated rats had severe CHF with 5-fold-increased plasma norepinephrine and about 50% decreases in ejection fraction (EF) and LV contractility [slope of LV end-systolic pressure-LV end-systolic volume relation (E-ES)] but increased time constant of LV relaxation (tau). They also showed significantly reduced myocyte contraction [maximum rate of myocyte shortening (dL/dt(max))], relaxation (dL/dt(max)), and [Ca2+](iT). Isoproterenol superfusion caused significantly fewer increases in dL/dt(max) and [Ca2+]iT. KN-93 treatment prevented plasma norepinephrine elevation, with increased basal and acute isoproterenol-stimulated increases in EF and EES and decreased t in CHF. KN-93 treatment preserved normal myocyte contraction, relaxation, [Ca2+](iT), and b-adrenergic reserve, whereas KN-92 treatment failed to improve LV and myocyte function, and plasma norepinephrine remained high in CHF. Thus, chronic CaMKII inhibition prevented CHF-induced activation of the sympathetic nervous system, restoring normal LV and cardiomyocyte basal and beta-adrenergic-stimulated contraction, relaxation, and [Ca2+](iT), thereby playing a rescue role in advanced CHF.SIGNIFICANCE STATEMENTWe investigated the therapeutic efficacy of late initiation of chronic Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibition on progression of advanced congestive heart failure (CHF). Chronic CaMKII inhibition prevented CHF-induced activation of the sympathetic nervous system and restored normal intrinsic cardiomyocyte basal and beta-adrenergic receptor-stimulated relaxation, contraction, and [Ca2+] i regulation, leading to reversal of CHF progression. These data provide new evidence that CaMKII inhibition is able and sufficient to rescue a failing heart, and thus cardiac CaMKII inhibition is a promising target for improving CHF treatment.