Protein-Kinase-C inhibitors and gemfibrozil prevent the enhancing effect of very low density lipoproteins on the biosynthesis of plasminogen activator inhibitor type 1 by HepG2 cells

Triglyceride-rich lipoproteins (VLDL) have been previously shown to enhance the biosynthesis of plasminogen activator inhibitor type 1 (PAl-1) by HepG2 cells. This study was undertaken to assess whether the effect of VLDL on PAI-1 antigen and mRNA induction could be by protein kinase C (PKC) signaling pathway. To this end confluent HepG2 cells were first incubated for 16 h with VLDL isolated from normal donors, at the 100 µg/ml concentration with or without inhibitors of PKC. At the end of incubation PAI-1 antigen released in the conditioned medium was determined by ELISA and PAI-1 mRNA expression was assessed by Northern analysis. Exposure of HepG2 cells to 100 µg/ml VLDL resulted in a twofold increase in PAI-1 antigen release and total PAI-1 mRNA expression. H7 (50 11M) and sphingosine (3-5 µM) almost completely prevented (> 80%) the effect of VLDL on PAI-1 antigen release and total PAI-1 mRNA accumulation. In addition down regulation of PKC, obtained by preincubation of HepG2 cells with PMA (100 nM) for 24h, prevented the effect of VLDL on PAI-1 biosynthesis. Established that the effect of VLDL on PAI-1 biosynthesis was mediated by activation of PKC signaling pathway we evaluated whether fibric acid derivatives influenced PAI-1 biosynthesis in unstimulated HepG2 cells and in cells exposed to VLDL. In unstimulated HepG2 cells, Gemfibrozil (0.1-0.75 mM) significantly reduced PAI-1 antigen release (-85% at the 0.75 mM concentration) and mRNA expression, whereas Bezafibrate at the highest concentration used (1 mM) reduced PAI-1 antigen release by 20%, with no effect on PAI-1 mRNA expression. In VLDL treated cells, only Gemfibrozil, at the 0 .75 mM concentration, attenuated (-50%) the biosynthesis of PAI-1 as induced by VLDL (100 µg/ml) . It is concluded that VLDL enhance PAI-1 biosynthesis through activation of PKC and that Gemfibrozil, but not Bezafibrate, attenuates PAI-1 induction in these cells.