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

Abstract

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. Palmitate-induced 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 < 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 < 0.05) blocked the cell death induced by the combination of palmitate and carnitine. The short-chain saturated fatty acid capric acid (100 μM), which is not likely transported by CPT-1, did not significantly affect cell viability, whereas the C18 saturated fatty acid stearic (100 μM) significantly ( P < 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 + 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.