Regulation of Malonyl-CoA Concentration and Turnover in the Normal Heart

Abstract

The goal of this study was to test the relationship between malonyl-CoA concentration and its turnover measured in isolated rat hearts perfused with NaH 13 CO 3 . This turnover is a direct measurement of the flux of acetyl-CoA carboxylation in the intact heart. It also reflects the rate of malonyl-CoA decarboxylation, i.e. the only known fate of malonyl-CoA in the heart. Conditions were selected to result in stable malonyl-CoA concentrations ranging from 1.5 to 5 nmol⅐g wet weight؊ 1 . The malonyl-CoA concentration was directly correlated with the turnover of malonyl-CoA, ranging from 0.7 to 4.2 nmol⅐min ؊1 ⅐g wet weight ؊1 (slope ‫؍‬ 0.98, r 2 ‫؍‬ 0.94). The V max activities of acetyl-CoA carboxylase and of malonylCoA decarboxylase exceeded the rate of malonyl-CoA turnover by 2 orders of magnitude and did not correlate with either concentration or turnover of malonyl-CoA. However, conditions of perfusion that increased acetylCoA supply resulted in higher turnover and concentration, demonstrating that malonyl-CoA turnover is regulated by the supply of acetyl-CoA. The only condition where the activity of malonyl-CoA decarboxylase regulated malonyl-CoA kinetics was when the enzyme was pharmacologically inhibited, resulting in increased malonyl-CoA concentration and decreased turnover. Our data show that, in the absence of enzyme inhibitors, the rate of acetyl-CoA carboxylation is the main determinant of the malonyl-CoA concentration in the heart.Malonyl-CoA is a key intermediate of fatty acid synthesis in lipogenic organs. It is also an inhibitor of carnitine palmitoyltransferase I, a regulator of fatty acid oxidation in most tissues (1-3). A number of studies have documented the modulation by malonyl-CoA of fatty acid oxidation in the heart under physiological and pathological conditions, such as maturation (4), diabetes (5), increased cardiac work (6), and postischemic reperfusion (7). In the heart, malonyl-CoA formed by cytosolic acetyl-CoA carboxylase (ACC) 1 is, as far as is known, disposed only via decarboxylation catalyzed by malonyl-CoA decarboxylase (MCD). Thus, cytosolic acetyl-CoA and malonyl-CoA are the two components of a substrate cycle that regulates carnitine palmitoyltransferase I activity and the rate of mitochondrial fatty acid oxidation in the heart.No information is available on the relationship between the concentration of malonyl-CoA and its turnover, i.e. with the flux of ACC in the intact heart. The rate of turnover of malonyl-CoA is likely to be regulated by the cytosolic acetyl-CoA concentration and by the activities of ACC and MCD. The concentrations of cytosolic acetyl-CoA and malonyl-CoA in the heart are much lower than the K m of the two enzymes for their respective substrates (6, 8). Thus, it is unlikely that the modulation of ACC and MCD activities exerts a tight control on malonyl-CoA turnover. It was previously shown that the myocardial content of malonylCoA is elevated when acetyl-CoA levels are increased by either activation of pyruvate dehydrogenase (8, 9) or by perfusing the ...

Peroxisomal and Mitochondrial Oxidation of Fatty Acids in the Heart, Assessed from the 13C Labeling of Malonyl-CoA and the Acetyl Moiety of Citrate

“…To test whether the peroxisomes of the intact heart can oxidize octanoate, we perfused hearts with increasing concentrations of [1][2][3][4][5][6][7][8][9][10][11][12][13] C]octanoate (Fig. 4).…”

“…4 -8. Because the cytosolic concentrations of acetyl-CoA and malonyl-CoA are much lower than the K m of acetyl-CoA carboxylase and malonyl-CoA decarboxylase for their corresponding substrates, the concentrations of these substrates may regulate the fluxes through the enzymes. We recently measured the turnover of malonyl-CoA in isolated rat hearts perfused with NaH 13 CO 3 (9). Under conditions where the malonyl-CoA concentration varied over a 5-fold range, this concentration was directly proportional to the acetyl-CoA carboxylase flux, but the total activities of acetyl-CoA carboxylase and malonyl-CoA decarboxylase (measured in tissue extracts) did not vary.…”

“…The 13 C labeling of the acetyl moiety of heart citrate (a probe of mitochondrial acetyl-CoA) was assayed by cleaving citrate with ATP-citrate lyase isolated from rat liver (15) and analyzing acetyl-CoA by ion trap liquid chromatography-mass spectrometry (10). Because of the poor solubility of [1][2][3][4][5][6][7][8][9][10][11][12][13] C]docosanoate, its perfusate concentration was assayed (as the trimethylsilyl derivative) using a standard curve built with unlabeled docosanoate and an internal standard of [1,2,3,4-13 C 4 ]docosanoate. In some experiments, the 13 C labeling of acetate in the effluent perfusate (16) of tissue succinyl-CoA (17), acetylcarnitine (18), and citrate (10) were assayed as described previously.…”

Metabolic response to an acute jump in cardiac workload: effects on malonyl-CoA, mechanical efficiency, and fatty acid oxidation

“…Malonyl-CoA inhibits CPT-I on the cytosolic side of the enzyme (22,44) and is produced in the cytosol and mitochondrial matrix from acetyl-CoA (44). The supply of acetyl-CoA is a major regulator of malonyl-CoA formation (36,37). The increase in workload in the present experiment caused a 50% increase in the acetyl-CoA concentration (48), presumably due to the rapid stimulation of acetyl-CoA formation by pyruvate dehydrogenase, which may have triggered a selective increase of malonyl-CoA in the mitochondrial matrix.…”

Myocardial Hypertrophy and the Maturation of Fatty Acid Oxidation in the Newborn Human Heart

“…Malonyl CoA is a potent inhibitor of carnitine palmitoyl transferase-1 (CPT-1), the rate limiting enzyme of mitochondrial fatty acid uptake (12). Acetyl CoA Carboxylase (ACC), is responsible for the synthesis of cardiac malonyl CoA (5,10,(13)(14)(15) (Fig. 1), whereas malonyl CoA decarboxylase (MCD), is primarily responsible for the degradation of cardiac malonyl CoA (16).…”