The peroxisomal proliferator clofibrate enhances the hepatic cytoplasmic movement of fatty acids in rats

The role of cytosolic fatty acid binding protein (FABP) in cellular fatty a cid metabolism remains poorly defined, The intracellular movement of fatty acids is thought to be facilitated through codiffusion with FABP, Peroxisom al proliferators like clofibrate induce FABP and may stimulate fatty acid u se by increasing cytoplasmic diffusion rates. Our aim was to determine if i nduction of FABP by clofibrate increases the cytoplasmic transport of a flu orescent fatty acid NBD-stearate. Male rats were fed clofibrate for 9 days to increase the hepatic concentration of FABP, Hepatocytes were isolated us ing collagenase perfusion. Cytosolic FABP was measured by enzyme-linked imm unosorbent assay (ELISA) using a specific antibody to hepatic FABP, Two-dim ensional laser photobleaching (FRAP) was used to measure the cytoplasmic mo vement of NBD-stearate in hepatocytes, Cytoplasmic transport of NBD-stearat e occurred by isotropic diffusion with no evidence for convective or direct ed transport. Treatment with clofibrate increased FABP levels, the fraction of NBD-stearate found in cytosol, and the observed cytoplasmic diffusion r ate, The increase in cytoplasmic movement exceeded that predicted from FABP binding changes suggesting that clofibrate also enhances fatty acid diffus ion within intracellular membranes. Nonspecific effects of clofibrate on cy toplasmic viscosity or pore size were not observed. These data suggest that clofibrate treatment induces cytosolic FABP and stimulates the intracellul ar movement of fatty acids by 2 distinct mechanisms. Soluble proteins like FABP promote the cytoplasmic transport of fatty acids by increasing diffusi on. These data further support a role for intracellular binding proteins in facilitating the intracellular movements of fatty acids.