2-bromooctanoic-acid and 2-bromopalmitate

The effect of palmitate and metabolizable and nonmetabolizable monosacharides (D-glucose, D-fructose and 2-deoxy-D-glucose = 2-DG) on the membrane potential (Vm) of mouse hepatocytes was investigated employing a superfused mouse liver slice technique. Palmitate hyperpolarized the liver cell membrane in a concentration dependent manner whereas the monosaccharides tested did not. When mice were fed a fat-rich diet, the hyperpolarisation was greater in comparison to mice fed a low fat diet. The hyperpolarization was reversed by ouabain, an inhibitor of the Na+/K(+)-ATPase, by the K(+)-channel blockers tetra-ethyl-ammonium (TEA) and cetiedil and by three inhibitors of fatty acid oxidation (2-bromopalmitate, 2-bromooctanoate and 4-pentenoate). The results suggest that hyperpolarization of the liver cell membrane is due to fatty acid oxidation and that both activation of Na+/K(+)-ATPase and opening of K(+)-channels are involved. The implications of these findings with regard to control of food intake by fatty acid oxidation are discussed. The results are consistent with a role of the hepatic membrane potential in control of food intake by fatty acid oxidation.

Topics: Animals; Caprylates; Deoxyglucose; Dietary Fats; Fatty Acids; Fatty Acids, Monounsaturated; Female; Fructose; Glucose; In Vitro Techniques; Liver; Male; Membrane Potentials; Mice; Ouabain; Oxidation-Reduction; Palmitates

Metabolism-dependent inactivators of 3-ketothiolase I and carnitine acyltransferase I (CAT I) have been used to study the oxidation of fatty acids in intact hepatocytes. 2-Bromooctanoate inactivates mitochondrial and peroxisomal 3-ketothiolases I in a time-dependent manner. During the first 5 min of incubation, inactivation of 3-ketothiolase in mitochondria is five times faster than its inactivation in peroxisomes. Almost complete inactivation of 3-ketothiolase I in both types of organelle is achieved after incubation with 1 mM 2-bromooctanoate for 40 min. The inactivation is not affected by preincubating hepatocytes with 20 microM tetradecylglycidate (TDGA), an inactivator of CAT I, under conditions which cause greater than 95% inactivation of CAT I. 2-Bromododecanoate (1 mM) causes 60% inactivation of mitochondrial and peroxisomal 3-ketothiolases I in 40 min. These inactivations are greatly reduced by preincubating hepatocytes with 20 microM TDGA, demonstrating that 2-bromododecanoate enters both mitochondria and peroxisomes via its carnitine ester. 2-Bromopalmitate (1 mM) causes less than 5% inactivation of mitochondrial and peroxisomal 3-ketothiolases I in 40 min, but causes 95% inactivation of CAT I during this time. Incubation of hepatocytes with 10-200 microM 2-bromopalmitoyl-L-carnitine causes inactivation of mitochondrial and peroxisomal 3-ketothiolases I at similar rates. This inactivation is decreased by palmitoyl-D-carnitine during the first 5 min of incubation. Pretreating hepatocytes with 20 microM TDGA does not affect the inactivation of mitochondrial or peroxisomal 3-ketothiolase I by 2-bromopalmitoyl-L-carnitine. These results demonstrate that in intact hepatocytes, peroxisomes oxidize fatty acids of medium-chain length by a carnitine-independent mechanism, whereas they oxidize long-chain fatty acids by a carnitine-dependent mechanism.

Topics: Acetyl-CoA C-Acyltransferase; Animals; Caprylates; Carnitine; Carnitine Acyltransferases; Cells, Cultured; Esters; Fatty Acids; Lauric Acids; Liver; Microbodies; Mitochondria, Liver; Oxidation-Reduction; Palmitates; Rats

1. The induction of peroxisomal beta-oxidation activities by bezafibrate in cultured rat hepatocytes and in the rat in vivo was prevented by inhibitors of carnitine acyltransferase, e.g. 2-bromopalmitate, 2-[5-(4-chlorophenyl)pentyl]oxirane-2-carboxylate or 2-tetradecylglycidic acid. 2. The prevention of peroxisomal proliferation by carnitine palmitoyltransferase inhibitors could not be accounted for by inhibition of mitochondrial beta-oxidation, since 2-bromo-octanoate, acting as an inhibitor of beta-oxidation, did not prevent the induction of peroxisomal activities in cultured rat hepatocytes. 3. The putative role of the acylcarnitine derivative of bezafibrate was analysed by studying the formation of bezafibroylcarnitine with bezafibroyl-CoA as substrate. However, no bezafibroylcarnitine formation was demonstrated in the presence of rat liver preparations capable of catalysing transfer to carnitine of medium- or long-chain fatty acids. 4. The prevention of peroxisomal proliferation by carnitine acyltransferase inhibitors may help in dissecting the causal relationship between the multiple effects mediated by peroxisomal proliferators.

Topics: Acyltransferases; Animals; Bezafibrate; Caprylates; Carnitine O-Palmitoyltransferase; Cells, Cultured; Epoxy Compounds; Fatty Acids; Glycerol; Liver; Microbodies; Palmitates; Palmitic Acid; Palmitic Acids; Rats