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

• Published in: Circulation research Vol. 104; no. 6; pp. 805 - 812
• Main Authors: Pound, Kayla M, Sorokina, Natalia, Ballal, Kalpana, Berkich, Deborah A, Fasano, Mathew, LaNoue, Kathryn F, Taegtmeyer, Heinrich, OʼDonnell, J Michael, Lewandowski, E Douglas
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD American Heart Association, Inc 27.03.2009; Lippincott Williams & Wilkins
• Subjects: Animals; Biological and medical sciences; Cardiomegaly - enzymology; Citric Acid Cycle; Dichloroacetic Acid - pharmacology; Fundamental and applied biological sciences. Psychology; Humans; Ketone Oxidoreductases - metabolism; Malate Dehydrogenase - metabolism; Male; Myocardium - enzymology; NADP - metabolism; Perfusion; Pyruvic Acid - metabolism; Rats; Rats, Sprague-Dawley; Triglycerides - metabolism; Vertebrates: cardiovascular system; Hypertrophied heart; Rat; Enzyme; Rodentia; Flux; Lipids; triglycerides; Triglyceride; Vertebrata; Mammalia; anaplerosis; Circulatory system; cardiac hypertrophy
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/CIRCRESAHA.108.189951

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 C-palmitate plus glucose or C 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 activationHYP=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.