Abstract 222: Inhibition Of Class I But Not Class IIb Lysine Deacetylases Is Responsible For Cardioprotection From Ischemia-Reperfusion.

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Background: While dual inhibition of class I/IIb KDACs protects the mammalian heart from ischemia-reperfusion (IR) injury, class-specific effects have not been examined. Hypothesis: We hypothesized that specific inhibition of class I KDACs would preserve left ventricular (LV) function following IR in isolated hearts. Methods: Male Sprague-Dawley rats (n=4 per group) were injected with vehicle, the class I KDAC inhibitor entinostat, the class IIb inhibitor tubastatin A, or the class I/IIb inhibitor trichostatin A (TSA). After 18 h, hearts were isolated and perfused in Langendorff mode. A saline-filled balloon was placed in the LV to monitor contractile function. Following IR (30/120 min), LV free wall tissue was assayed for activation of pro-survival proteins. Group results are reported vs vehicle as mean±SE. Results: There were no differences between groups in LV function before ischemia. At the end of reperfusion, rate pressure product (mm hg/min) was improved with entinostat (27392±3474, p<0.001) and TSA (22980±3226, p<0.05) vs vehicle (11,352±1977), as were +dP/dt max and -dP/dt max . Most notably, entinostat alone blunted the rise in end diastolic pressure (mm Hg) during reperfusion (18.6±1.4 vs. 45.3±4.1, p<0.001), and completely prevented diastolic contracture (mm Hg) in reperfusion for up to one hour (12.4±2.0 vs pre-ischemia=8.7±1.7, p=0.21). Contractile function was not significantly preserved in hearts treated with tubastatin A. Entinostat reduced phosphorylation at the eNOS inhibitory site, and increased phosphorylation at the eNOS activation site, and Src activation was dramatically reduced. TSA increased activation of Src, p38, and ERK 1/2, and increased phosphorylation of eNOS at both the activation (Ser1177) and inhibition site (Thr495). Tubastatin A reduced activation of p38, ERK 1/2, and eNOS, but not Src. Conclusions: Inhibition of class I KDACs was most effective at preserving contractile function following IR in isolated hearts, notably through prevention of LV contracture during reperfusion. Class I KDAC inhibition may preserve LV function by differentially modulating Src and eNOS activities. These results suggest that the protective effects of KDAC inhibitors in IR can be ascribed to specific inhibition of class I KDACs.