leptin and 2-bromopalmitate

The effect of intracellular free fatty acid (FFA) accumulation on ob gene expression in adipocytes was examined. In fully differentiated 3T3-L1 adipocytes, triacsin C, a specific acyl CoA synthetase inhibitor with a K(i) of 8.97 microM, inhibited ob gene expression by 20% at 5 x 10(-5)M. At this concentration, triacsin C induced accumulation of intracellular FFA. Treatment with both chylomicron and triacsin C reduced ob gene expression more than treatment with triacsin C alone. Treatment with 2-bromopalmitate, a poorly metabolizable palmitate analog, reduced ob gene expression by 50% at 10(-4)M, but palmitate at the same concentration had no effect. This is the first demonstration that the ob gene is downregulated by intracellular FFA accumulation, thereby raising the possibility that ob product is regulated in response to lipolysis.

Topics: 3T3 Cells; Adipocytes; Animals; Blotting, Northern; Chromatography, Thin Layer; Chylomicrons; Dose-Response Relationship, Drug; Down-Regulation; Enzyme Inhibitors; Fatty Acids; Gene Expression; Hypoglycemic Agents; Kinetics; Leptin; Lipid Metabolism; Mice; Palmitates; Palmitic Acid; RNA; Triazenes

Free fatty acid (FFA) has been reported to decrease leptin mRNA levels in 3T3-L1 adipocytes. When using this cell line, it is difficult to determine the protein levels because a very small amount of leptin is secreted into the medium. The effect of FFA on leptin secretion from adipocytes has not yet been determined. In addition, in vivo studies have failed to demonstrate a FFA-induced decrease in plasma leptin levels. To clarify the effect of FFA on leptin production, we investigated the leptin protein level in the medium and the mRNA level in primary cultured rat adipocytes treated with triacsin C, which is a potent inhibitor of acyl-coenzyme A (CoA) synthetase, palmitate, and 2-bromopalmitate. Triacsin C (0 to 5 x 10(-5) mol/L) decreased leptin concentrations in the culture medium in a dose-dependent manner. Leptin mRNA levels were decreased to 10% of the control in the presence of triacsin C. The concentration of triacsin C needed to suppress leptin production was similar to the Ki value (approximately 10(-5) mol/L) for inhibition of acyl-CoA synthetase. Both palmitate and 2-bromopalmitate decreased leptin concentra-tions but did not affect the triacsin C-induced decrease in leptin additively. In conclusion, both protein and mRNA levels of leptin were decreased by triacsin C and FFA in primary cultured rat adipocytes. Our findings suggest that FFA is involved in the regulation of leptin production in adipocytes.

Topics: Adipocytes; Animals; Cells, Cultured; Coenzyme A Ligases; Enzyme Inhibitors; Epididymis; Gene Expression Regulation; Hypoglycemic Agents; Kinetics; Leptin; Male; Palmitates; Palmitic Acid; Rats; Rats, Sprague-Dawley; RNA, Messenger; Transcription, Genetic; Triazenes

Uncoupling protein-2 (UCP2) is a novel mitochondrial protein that may be involved in the control of energy expenditure. We have previously reported an upregulation of adipose tissue UCP2 mRNA expression during fasting in humans. Analysis of changes in metabolic parameters suggested that fatty acids may be associated with the increased UCP2 mRNA level. Culture of human adipose tissue explants was used to study in vitro regulation of adipocyte UCP2 gene expression. A 48-h treatment with BRL49653 and bromopalmitate, two potent activators of PPARgamma, resulted in a dose-dependent increase in UCP2 mRNA levels. The induction by BRL49653 was rapid (from 6 h) and maintained up to 5 days. TNFalpha provoked a 2-fold decrease in UCP2 mRNA levels. Human recombinant leptin did not affect UCP2 mRNA expression. The data support the hypothesis that fatty acids are involved in the control of adipocyte UCP2 mRNA expression in humans.

Topics: Adipocytes; Adipose Tissue; Adult; Cells, Cultured; Culture Techniques; Dose-Response Relationship, Drug; Female; Gene Expression Regulation; Humans; Ion Channels; Leptin; Membrane Transport Proteins; Middle Aged; Mitochondrial Proteins; Palmitates; Proteins; Receptors, Cytoplasmic and Nuclear; RNA, Messenger; Rosiglitazone; Thiazoles; Thiazolidinediones; Time Factors; Transcription Factors; Transcriptional Activation; Tumor Necrosis Factor-alpha; Uncoupling Protein 2