Acetoacetate: A Cardioprotective Antioxidant

Squires, Jeffrey E., Acetoacetate: A Cardioprotective Antioxidant. Master of Science, June 2002, 100 pp., 1 table, 18 illustrations, bibliography, 70 titles. The purpose of this study was to test the effectiveness of acetoacetate and β-hydroxybutyrate as myocardial protectants following peroxide injury and to determine acetoacetate’s ability to potentiate β-adrenergic responsiveness following ischemia-reperfusion injury. This study utilized antegradely perfused isolated working hearts exercised from male guinea pigs and sustained with glucose-fortified Krebs-Henseleit. Hearts were challenged by either 10 min perfusion with 100 μM H2O2 or 45 min of low flow ischemia exacerbated by ι-norepinephrine infusion. H2O2-challenged hearts were treated with 5 mM acetoacetate or β-hydroxybutyrate, whereas hearts injured by ischemia/reperfusion were treated with 5 mM acetoacetate. In the case of the ischemically injured hearts, acetoacetate treatment was combined with 2 nM isoproterenol to delineate acetoacetate’s ability to enhance β-andrenergic responsiveness to submaximal inotropic stimulation. Data were compared to non-injured time control hearts and injured untreated hearts to determine the impact of ketone body treatment. Acetoacetate increased citrate and glucose 6-phosphate content, nearly restored power, and increased the glutathione antioxidant redox potential (GSH/GSSG) by 140% in H2O2-injured myocardium. Although β-hydroxybutyrate increased citrate, an activator of NADPH-generating pathways, and glucose 6-phosphate, the substrate for the hexose monophosphate shunt to the same extent as acetoacetate, β-hydroxybutyrate raised GSH/GSSG by only 60% and did not enhance cardiac power. Therefore, acetoacetate enhances contractile function by augmenting the glutathione redox potential, and does so by additional mechanisms independent of the citrate and hexose monophosphate pathway. In hearts stunned by ischemia/reperfusion, acetoacetate and isoproterenol each increased power and glutathione redox potential three-to-fourfold, but phosphocreatine potential was 70% higher in acetoacetate hearts. Combined, acetoacetate + isoproterenol synergistically increased power and GSH/GSSG 16- and 17- fold respectively, doubled {NADPH/NADP+}, and increased cyclic AMP content 30%. These findings support the conclusion that acetoacetate enhances myocardial sensitivity to β-adrenergic stimulation possibly by enhancing GSH/GSSG.