FATTY-ACID-BINDING PROTEINS REDUCE 15-LIPOXYGENASE-INDUCEDOXYGENATIONOF LINOLEIC-ACID AND ARACHIDONIC-ACID

Free fatty acids in plasma and cells are mainly bound to membranes and proteins such as albumin and fatty acid binding proteins (FABP), whic h can regulate their biological activities and metabolic transformatio ns. We have investigated the effect of FABP and albumin on the peroxid ation of linoleic acid (18:2) and arachidonic acid (20:4) by 15-lipoxy genase (15-LO). Rabbit reticulocyte 15-LO produced a rapid conversion of [1-C-14]18:2 to 13-hydroxyoctadecadienoic acid (13-HODE) and [H-3]2 0:4 to 15-hydroxyeicosatetraenoic acid(15-HETE). 13-HODE formation was reduced when intestinal FABP (I-FABP), liver FABP (L-FABP) or albumin was added. The relative ability of these proteins to reduce 15-LO ind uced formation of 13-HODE and 15-HETE was BSA>L-FABP>I-FABP. Smaller r eductions in activity were observed with 20:4 as compared to 18:2. The IC50-values of I-FABP and L-FABP, using either 18:2 (3.4 mu M) or 20: 4 (3.4 mu M), were 4.6 +/- 0.6 and 1.9 +/- 0.2 mu M, respectively, for reduction of 13-KODE and 6.8 +/- 0.3 and 3.1 +/- 0.2 mu M, respective ly, for reduction of 15-HETE formation. The smaller 15-HETE reduction correlated with decreased binding of 20:4 to the FABP. Titration calor imetry also showed that the I-FABP IC50 for 18:2, 0.25 mu M, was lower then for 20:4, 0.6 mu M. Thus the reduction in fatty acid lipid perox idation relates to the binding capacity of each FABP. We also demonstr ated that 18:2 rapidly diffuses (flip-flops) across the phospholipid b ilayer of small unilamellar vesicles (SUV) and measured partitioning o f 18:2 between proteins and SW by the pyranin fluorescence method [Kam p, F. and Hamilton, J.A. (1992) Proc. Natl, Acad, Sci. U.S.A. 89, 1136 7-11370]. Addition of proteins to SUV in buffer resulted in a complete desorption of 18:2 from SUV with a relative effect of BSA > L-FABP > I-FABP, This suggests that the relative effects of these proteins on 1 8:2, peroxidation will not be altered by the presence of membranes. Ou r results indicate that FAPBs protect intracellular polyunsaturated fa tty acids against peroxidation and, through differential binding of 18 :2 and 20:4, they may modulate the availability of these polyunsaturat ed fatty acids to intracellular oxidative pathways. (C) 1997 Elsevier Science B.V.