MODULATION OF PROCOAGULANT AND FIBRINOLYTIC SYSTEM COMPONENTS OF MESOTHELIAL CELLS BY INFLAMMATORY MEDIATORS

Human peritoneal mesothelial cells (HMC) play a critical role in maint aining the intraperitoneal balance between fibrinolysis and coagulatio n by expressing the fibrinolytic enzyme tissue-type plasminogen activa tor (t-PA) as well as a specific plasminogen activator inhibitor, PAI- 1, and the procoagulant protein tissue factor (TF). Of three compounds known to stimulate t-PA synthesis in cultured human endothelial cells , i.e., retinoic acid, the protein kinase C activator 4 beta-phorbol 1 2-myristate 13-acetate (PMA), and sodium butyrate, only butyrate (1 mM ) caused about a threefold increase in t-PA synthesis and mRNA express ion in HMC after 24 h of incubation, without markedly affecting PAI-1 synthesis. PMA (10 nM) induced a threefold increase in urokinase-type plasminogen activator (u-PA) mRNA, but u-PA antigen levels in the HMC conditioned media remained below the detection level (0.5 ng/ml), poss ibly as a result of rapid uptake and degradation by the u-PA receptor. The u-PA receptor mRNA levels were about fivefold enhanced above cont rol levels after PMA treatment of the cells. An increase in intracellu lar adenosine 3',5'-cyclic monophosphate levels by forskolin (10 mu M) diminished t-PA and PAI-1 levels 43 and 17%, respectively. Among the inflammatory mediators tested [tumor necrosis factor-alpha (TNF-alpha) , interleukin-1 alpha, and bacterial lipopolysaccharide], TNF-alpha (1 0-1,000 U/ml) showed the strongest procoagulant effects. We found that the Isoflavone compound genistein (25 mu g/ml) prevented the TNF-alph a-induced expression of PAI-1 and TF while also slightly counteracting the decrease in t-PA synthesis. The protein kinase C inhibitor Re-318 220 (3 mu M) only moderately opposed the TNF-alpha-induced changes in t-PA and PAI-1 synthesis but completely prevented the induction of TF mRNA. In summary, our results demonstrate that t-PA synthesis in HMC i s relatively insensitive to pharmacological stimulation. To restore th e balance between fibrinolysis and coagulation under inflammatory cond itions, attempts to interfere with the TNF-alpha-signaling pathway wer e more successful.