Ramipril inhibits in vitro human mesangial cell proliferation and platelet-derived growth factor expression

Angiotensin-converting enzyme (ACE) inhibitors are antihypertensive drugs that have been shown to reduce proteinuria and to slow down the progression of renal function deterioration in different models of chronic glomerular disease. Major pathogenetic features of progressive glomerular injury leading to glomerulosclerosis are mesangial cell proliferation and platelet-derived growth factor (PDGF) expression. The aim of the present study was to evaluate the effect of ramipril, an ACE inhibitor, on these two potential therapeutic targets. Thus, the effect of ramipril on DNA synthesis, cell proliferation and PDGF A and B chain gene expression in fetal calf serum (FCS)-activated cultured human glomerular mesangial cells was investigated. DNA synthesis was evaluated by tritiated thymidine incorporation, cell proliferation by direct cell counting and cell viability by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT). PDGF A and B chain gene expressions were studied by Northern blot and RT-PCR, respectively. In a dose-dependent manner ramipril inhibited the FCS-induced DNA synthesis and cell proliferation. This effect was not dependent upon a toxic effect as demonstrated by MTT. The antiproliferative effect of ramipril was most likely independent of its ability to inhibit ACE present in the FCS and/or expressed by the cells, since a synthetic peptide that specifically inhibits ACE, at the same molar concentrations, did not inhibit FCS-stimulated DNA synthesis. Moreover, ramipril significantly reduced FCS-induced PDGF A and B chain gene expression. Finally, ramipril completely abolished the PDGF A and B chain gene expression induced by phorbol 12-myristate 13-acetate, a specific protein kinase C activator, suggesting a site of action downstream of this enzyme in the mitogenic signal transduction pathway. Our study would suggest that the modulatory action of ramipril on activated mesangial cell proliferation and PDGF expression is independent of its ability to inhibit ACE and could represent an additional mechanism in the renal protective effects of this drug.