Fatty acid cycling in human hepatoma cells and the effects of troglitazone.
Fatty acid cycling by chain shortening/elongation in the peroxisomes is an important source of fatty acids for membrane lipid synthesis. Its role in the homeostasis of nonessential fatty acids is poorly understood. We report here a study on the cycling of saturated fatty acids and the effects of troglitazone in HepG2 cells in culture using [U-13C]stearate or [U-13C]oleate and mass isotopomer analysis. HepG2 cells were grown in the presence of 0.7 mmol/liter [U-13C]stearate or [U-13C]oleate, and in the presence and absence of 50 microM troglitazone for 72 h. Fatty acids extracted from cell pellets after saponification were analyzed by gas chromatography/mass spectrometry. Peroxisomal beta-oxidation of uniformly 13C-labeled stearate (C18:0) and oleate (C18:1) resulted in chain shortening and produced uniformly labeled palmitate (C16:0) and palmitoleate (C16:1). In untreated cells, 16% of C16:0 was derived from C18:0 and 26% of C16:1 from C18:1 by chain shortening. Such contributions were significantly increased by troglitazone to 23.6 and 36.6%, respectively (p < 0.001). Desaturation of stearate contributed 67% of the oleate, while reduction of oleate contributed little to stearate (2%). The desaturation of C18:0 to C18:1 was not affected by troglitazone. Our results demonstrated a high degree of recycling of C18:0 and C18:1 to C16:0 and C16:1 through chain shortening and desaturation. Chain shortening was accompanied by chain elongation in the synthesis of other long chain fatty acids. Troglitazone specifically increased recycling by peroxisomal beta-oxidation of C18 to C16 fatty acids, and the interconversion of long chain fatty acids was associated with reduced de novo lipogenesis.
Harbor-UCLA Medical Center, Torrance, California 90502, USA. lee@gcrc.humc.edu
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Lee
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Lim
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Bassilian
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Bergner
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Edmond
D006528:Carcinoma, Hepatocellular / Q000378:metabolism* / Q000473:pathology; D002839:Chromans / Q000494:pharmacology*; D005227:Fatty Acids / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism* / Q000473:pathology; D010084:Oxidation-Reduction; D013844:Thiazoles / Q000494:pharmacology*; D045162:Thiazolidinediones; D000077288:Troglitazone; D014407:Tumor Cells, Cultured
D002839:Chromans; D005227:Fatty Acids; D013844:Thiazoles; D045162:Thiazolidinediones; D000077288:Troglitazone