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(Circulation Research. 2009;104:805.)
© 2009 American Heart Association, Inc.

Integrative Physiology

Substrate–Enzyme Competition Attenuates Upregulated Anaplerotic Flux Through Malic Enzyme in Hypertrophied Rat Heart and Restores Triacylglyceride Content

Attenuating Upregulated Anaplerosis in Hypertrophy

Kayla M. Pound, Natalia Sorokina, Kalpana Ballal, Deborah A. Berkich, Mathew Fasano, Kathryn F. LaNoue, Heinrich Taegtmeyer, J. Michael O'Donnell, E. Douglas Lewandowski

From the Program in Integrative Cardiac Metabolism (K.M.P., N.S., M.F., J.M.O., E.D.L.), Center for Cardiovascular Research, University of Illinois at Chicago, College of Medicine; Department of Internal Medicine (K.B., H.T.), Division of Cardiology, University of Texas Houston Medical School, Houston; and Department of Molecular and Cellular Physiology (D.A.B., K.F.L.), Pennsylvania State University Medical School, Hershey.

Correspondence to E. Douglas Lewandowski, PhD, Department of Physiology and Biophysics, MC 901, UIC College of Medicine, 835 S Wolcott Ave, Chicago, IL 60612. E-mail dougl{at}uic.edu

Recent work identifies the recruitment of alternate routes for carbohydrate oxidation, other than pyruvate dehydrogenase (PDH), in hypertrophied heart. Increased carboxylation of pyruvate via cytosolic malic enzyme (ME), producing malate, enables "anaplerotic" influx of carbon into the citric acid cycle. In addition to inefficient NADH production from pyruvate fueling this anaplerosis, ME also consumes NADPH necessary for lipogenesis. Thus, we tested the balance between PDH and ME fluxes in hypertrophied hearts and examined whether low triacylglyceride (TAG) was linked to ME-catalyzed anaplerosis. Sham-operated (SHAM) and aortic banded rat hearts (HYP) were perfused with buffer containing either ¹³C-palmitate plus glucose or ¹³C glucose plus palmitate for 30 minutes. Hearts remained untreated or received dichloroacetate (DCA) to activate PDH and increase substrate competition with ME. HYP showed a 13% to 26% reduction in rate pressure product (RPP) and impaired dP/dt versus SHAM (P<0.05). DCA did not affect RPP but normalized dP/dt in HYP. HYP had elevated ME expression with a 90% elevation in anaplerosis over SHAM. Increasing competition from PDH reduced anaplerosis in HYP+DCA by 18%. Correspondingly, malate was 2.2-fold greater in HYP than SHAM but was lowered with PDH activation: HYP=1419±220 nmol/g dry weight; HYP+DCA=343±56 nmol/g dry weight. TAG content in HYP (9.7±0.7 µmol/g dry weight) was lower than SHAM (13.5±1.0 µmol/g dry weight). Interestingly, reduced anaplerosis in HYP+DCA corresponded with normalized TAG (14.9±0.6 µmol/g dry weight) and improved contractility. Thus, we have determined partial reversibility of increased anaplerosis in HYP. The findings suggest anaplerosis through NADPH-dependent, cytosolic ME limits TAG formation in hypertrophied hearts.

Key Words: anaplerosis • cardiac hypertrophy • triglycerides

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