Lipoprotein lipase synthesis and secretion: effects of concentration and type of fatty acids in adipocyte cell culture.

Fatty acids (FA) were added to differentiating chick adipocytes to study their effects on the synthesis and secretion of avian lipoprotein lipase (LPL). Oleate (18:1n-9), eicosapentaenoate (EPA, 20:5n-3), and linoleate (18:2n-6) were complexed to fatty acid-free bovine serum albumin (BSA) and separately added to cells in RMPI-1640 media containing 0.5% delipidated hen serum. LPL secretion in the presence of 10 U/ml heparin was used as a means of estimating LPL synthesis. FA from 50 microM to 165 microM depressed LPL secretion for cells exposed to 20:5n-3 and 18:2n-6. The decrease in adipocyte LPL secretion was only observed with chronic administration of FA. In other experiments, the rate of LPL synthesis was estimated by incorporation of radiolabel (Tran 35S-label) in cells exposed to 50 microM FA. Total radioactivity incorporated into LPL, expressed as a percentage of total trichloroacetic acid (TCA)-precipitable radioactivity, was not affected in cells fed 18:1n-9 but was significantly decreased for cells fed 20:5n-3 (45%) or 18:2n-6 (67%) relative to controls given equimolar BSA (33 microM). Abundance of LPL message in similarly treated cells also decreased for cells incubated with 20:5n-3 or 18:2n-6 (35%) relative to controls and 18:1n-9-treated cells. A decrease in adipocyte LPL secretion was also observed with administration of lipoprotein (d < 1.006 g/ml) enriched in n-3 and n-6 fatty acids. LPL secretion of cells incubated with n-3 enriched lipoprotein at 50 microM and 75 microM triglyceride fatty acid equivalents was significantly greater than that of cells incubated with n-6-enriched lipoprotein. Interestingly, at the same concentrations of triglyceride fatty acids, lipoproteins enriched with n-9 fatty acids had no effect on LPL secretion relative to controls. These studies document that in cultured avian adipocytes, LPL secretion, synthesis, and level of message are decreased by chronic administration of n-3 and n-6 fatty acids. In contrast, in adipocytes supplemented with oleic acid there was no effect on LPL synthesis and secretion.