Palmitate-induced cardiac apoptosis is mediated through CPT-1 but not influenced by glucose and insulin

Abstract

Kong, Jennifer Y., and Simon W. Rabkin. Palmitateinduced cardiac apoptosis is mediated through CPT-1 but not influenced by glucose and insulin. Am J Physiol Heart Circ Physiol 282: H717-H725, 2002; 10.1152/ajpheart.00257. 2001.-To test the hypothesis that regulation of palmitate metabolism, through carnitine palmitoyl transferase-1 (CPT-1) or through alterations of glycolysis, was involved in the pathway of palmitate-mediated cell death, cardiomyocytes were cultured from 7-day-old chick embryos. Palmitateinduced cell death, assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay, was enhanced by carnitine, a cofactor needed for palmitate transport into mitochondria via CPT-1. Carnitine co-incubation with palmitate significantly (P Ͻ 0.01) increased the amount of apoptotic cells, assessed by propidium iodine staining and fluorescent-activated cell sorting analysis compared with treatment with either palmitate or carnitine alone. The CPT-1 inhibitor oxfenicine significantly (P Ͻ 0.05) blocked the cell death induced by the combination of palmitate and carnitine. The short-chain saturated fatty acid capric acid (100 M), which is not likely transported by CPT-1, did not significantly affect cell viability, whereas the C18 saturated fatty acid stearic (100 M) significantly (P Ͻ 0.01) reduced cell viability and to a similar extent as palmitate. In contrast, there was no significant alteration of palmitate-induced cell death by cotreatment with 100 nM insulin ϩ 2 g/l glucose or 1 mM lactate, which promote ATP generation by glycolysis rather than fatty acid oxidation. Fumonisin did not alter palmitate-induced cell death or apoptosis, suggesting that the effect of palmitate was not operative through increased ceramide synthesis. These results suggest that oxidation of palmitate through CPT-1 is involved in the production of apoptosis in cardiomyocytes.carnitine; fatty acid metabolism; oxfenicine; fumonisin; palmitate; capric acid FATTY ACIDS ARE A PRINCIPAL source of energy for the heart, and the metabolism of fatty acids is of fundamental importance for cardiac function (for reviews, see Refs. 23,24,48). Briefly, fatty acid metabolism involves fatty acids binding to carrier binding proteins that are transported across the sarcolemmal membrane, and once inside the cell are metabolized to long chain acyl-CoA by acyl-CoA synthetase (23,24,48). The acyl moieties are transferred to the mitochondria by a series of enzymes involving carnitine palmitoyl transferase-1 and -2 (CPT-1 and -2) as well as carnitine-acylcarnitine translocase. In the mitochondria, long-chain acyl-CoA is subjected to ␤-oxidation-producing acetyl CoA, a fatty acyl moiety less two carbons, and the by-products, reduced flavin adenine dinucleotide and reduced nicotinamide adenine dinucleotide. Fatty acid oxidation also occurs in peroxisomes (23,24,48) but the amount is small (9).

Myocardium of type 2 diabetic and obese patients is characterized by alterations in sphingolipid metabolic enzymes but not by accumulation of ceramide

“…This suggests that in the human heart or at least in the atrium, ceramide is not a major mediator of cardiomyocyte apoptosis associated with obesity and type 2 diabetes and that other factors play a dominant role in this process. It was shown that palmitate can induce cardiomyocyte apoptosis independently of ceramide via generation of reactive oxygen species resulting from increased cycling through mitochondrial ␤ -oxidation pathway ( 32,33 ). In addition, apoptosis of cardiomyocytes is activated by hyperglycemia through a mechanism involving excessive protein O-glycosylation ( 34 ).…”

Regular exercise is associated with a protective metabolic phenotype in the rat heart

“…In contrast, oxidation of glucose to CO2 yields 0 mol H ϩ /mol glucose (15,37). Therefore, the overall rate of H ϩ production derived from glucose utilization was determined as follows (3,21,24):…”

“…On the basis of the different proton stoichiometry of glucose fermentation compared with oxidation (15,37), this protective effect has been suggested to be related to a reduction in net proton production from glucose catabolism (2,3,21,24,25,45). Such a reduction was shown to favor the recovery of intracellular pH, which could limit calcium overload by way of successive trans-sarcolemmal H ϩ /Na ϩ and Na ϩ /Ca 2ϩ exchange and therefore reduce the energetic cost associated with the maintenance of ion homeostasis (21,24). This would in turn lead to improved postischemic contractile function and efficiency (see Refs.…”

Mitochondrial energy metabolism in heart failure: a question of balance

“…These hearts display evidence of myocyte dropout due to activation of apoptotic pathways. Indeed, direct treatment with saturated long-chain FAs has been shown to trigger apoptosis in cardiac myocytes as well as in other cell types in culture via mechanisms that may involve generation of reactive oxygen species (105)(106)(107). Collectively, observations in mice and humans indicate that severe reduction in mitochondrial FAO capacity sets the stage for cardiac lipotoxic effects related to lipid intermediates that accumulate in the context of impaired catabolism.…”