Dipyridamole inhibits PDGF-stimulated human peritoneal mesothelial cell proliferation

Background. It has been proposed that proliferation of human peritoneal mes othelial cells (HPMCs) accompanied by collagen synthesis may contribute to the development of peritoneal fibrosis (PF) in patients of long-term contin uous ambulatory peritoneal dialysis (CAPD). However, the precise molecular mechanism regulating HPMC proliferation has never been reported. Dipyridamo le has been reported to have potential as an antiproliferative and antifibr otic agent. We investigated the mechanism and effect of dipyridamole in reg ulation of HPMC proliferation. Methods. HPMCs were cultured from human omentum by an enzyme digestion meth od. Cell proliferation was measured by the methyltetrazolium assay and intr acellular cAMP was measured using an enzyme immunoassay kit. Cell-cycle dis tribution of HPMC was analyzed by flow cytometry. Extracellular signal-regu lated protein kinase (p44/p42 ERK) activity and expressions of cell-cycle p roteins (cyclin D-1, CDK4, pRB and p27(Kip1)) were determined by Western bl otting. Results. The addition of DP suppressed PDGF-stimulated HPMC proliferation b y cell-cycle arrest at the G(1) phase. The antimitogenic effect of dipyrida mole was mediated through the cAMP pathway. PDGF (25 ng/mL) increased the E RK1/2 activity of HPMC within 15 minutes, which maximized at 30 minutes, an d the pretreatment with dipyridamole (17 mug/mL) substantially reduced the ERK response to PDGF by approximately 78.5%. PDGF induced elevated protein levels of cyclin D1, but the CDK4 protein level did not change. Dipyridamol e and DBcAMP had no effect on the levels of cyclin D-1 and CDK4 in PDGFstim ulated HPMC. PDGF decreased p27(Kip1) and induced pRB phosphorylation of HP MC. In contrast, dipyridamole prevented PDGF-induced p27(Kip1) degradation and attenuated PDGFstimulated pRB phosphorylation. Conclusion. Dipyridamole appears to inhibit PDGF-stimulated HPMC proliferat ion through attenuated ERK activity, preservation of p27 Kip1, and decrease d pRB phosphorylation. Thus, dipyridamole may have therapeutic efficacy to prevent or alleviate PF.