TGF-β1 Induced by High Glucose is Controlled by Angiotensin-Converting Enzyme Inhibitor and Angiotensin II Receptor Blocker on Cultured Human Peritoneal Mesothelial Cells

Abstract

Loss of peritoneal function is a major complication associated with long-term peritoneal dialysis. Observed changes include loss and degeneration of the mesothelium, submesothelial thickening, alterations in the structure and number of blood vessels, and reduplication of the vascular basement membrane. Exposure to high glucose concentrations in peritoneal dialysis solutions is known to cause injury to cultured human peritoneal mesothelial cells (HPMC) as a result of overexpression of transforming growth factor beta 1 (TGF-beta1). Previous studies have demonstrated that angiotensin II (AII) increases expression of TGF-beta1 in a number of different cell types; although this has not been demonstrated in HPMC. To clarify possible mechanisms involved in peritoneal fibrosis, we investigated whether HPMC expressed AII-forming pathway mRNA and whether increases in AII induced by high glucose contribute to the production of TGF-beta1. We also examined the effects of the angiotensin-converting enzyme inhibitor (ACEI) perindoprilat and the AII receptor blocker (ARB) candesartan on expression of TGF-beta1 and proliferation of HPMC. Expression of mRNA for the AII-forming pathway and TGF-beta1 in HPMC was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative RT-PCR. Levels of AII and TGF-beta1 following 48 hours of incubation of the cells in a range of glucose concentrations were measured by enzyme immunoassay and enzyme linked immunosorbent assay respectively. The effect of glucose on cell proliferation was examined using the water-soluble tetrazolium salt WST-1 and [3H]-thymidine uptake. We also investigated the effect of ACEI and ARB on the expression of TGF-beta1 and the proliferation of HPMC incubated at high glucose for 48 hours. AII-forming pathway mRNA was detected in HPMC, with expression of angiotensinogen, angiotensin-converting enzyme (ACE), AII type 1 receptor, and TGF-beta1 mRNA increasing following exposure to glucose according to glucose concentration. High glucose was also shown to increase the production of All and TGF-beta1 and decrease the proliferation of HPMC. In contrast, we found that both the ACEI and the ARB attenuated the increase in TGF-beta1 production and reduced cell proliferation caused by exposure to high glucose. These effects were greater with a combination of the two drugs. The present study provides evidence that (1) HPMC express mRNA for the AII-forming pathway; (2) ACEI and ARB inhibit the TGF-beta1 production induced by high glucose; (3) the AII-forming pathwayis one mechanism by which high glucose causes production of TGF-beta1. In addition to having antihypertensive and renal-protective effects, combination therapy with an ACEI and an ARB may also be effective in preventing loss of peritoneal function and decreasing peritoneal fibrosis.