, Volume 259, Issue 1-2, pp 115-129

Liver fatty acid binding protein expression enhances branched-chain fatty acid metabolism

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Although liver fatty acid binding protein (L-FABP) is known to enhance uptake and esterification of straight-chain fatty acids such as palmitic acid and oleic acid, its effects on oxidation and further metabolism of branched-chain fatty acids such as phytanic acid are not completely understood. The present data demonstrate for the first time that expression of L-FABP enhanced initial rate and average maximal oxidation of [2,3−3H] phytanic acid 3.5− and 1.5−fold, respectively. This enhancement was not due to increased [2,3−3H] phytanic acid uptake, which was only slightly stimulated (20%) in L-FABP expressing cells after 30 min. Similarly, L-FABP also enhanced the average maximal oxidation of [9,10−3H] palmitic acid 2.2−fold after incubation for 30 min. However, the stimulation of L-FABP on palmitic acid oxidation nearly paralleled its 3.3−fold enhancement of uptake. To determine effects of metabolism on fatty acid uptake, a non-metabolizable fluorescent saturated fatty acid, BODIPY-C16, was examined by laser scanning confocal microscopy (LSCM). L-FABP expression enhanced uptake of BODIPY-C16 1.7−fold demonstrating that L-FABP enhanced saturated fatty acid uptake independent of metabolism. Finally, L-FABP expression did not significantly alter [2,3−3H] phytanic acid esterification, but increased [9,10−3H] palmitic acid esterification 4.5−fold, primarily into phospholipids (3.7−fold) and neutral lipids (9−fold). In summary, L-FABP expression enhanced branched-chain phytanic acid oxidation much more than either its uptake or esterification. These data demonstrate a potential role for L-FABP in the peroxisomal oxidation of branched-chain fatty acids in intact cells.