No abstract

Peritoneal fibrosis (PF) is an important complication of peritoneal dialysis (PD) therapy that often occurs in association with peritoneal high transport rate and ultrafiltration failure (UFF). To study the possible pathogenic role of connective tissue growth factor (CTGF) in the relationship of PF and UFF, dialysate CTGF contents (n = 178) and tissue CTGF expression (n = 61) were investigated by ELISA, real-time PCR, immunohistochemistry, and in situ hybridization. CTGF production with and without TGF-beta1 stimulation in human peritoneal mesothelial cells (HPMC) from the spent patients' peritoneal dialysate (n = 32) was studied in vitro. The dialysate-to-plasma ratio for creatinine (D/P Cr) was positively correlated to dialysate CTGF concentration and estimated local peritoneal production of CTGF. CTGF mRNA expression was 11.4-fold higher in peritoneal membranes with UFF than in pre-PD renal failure peritoneum and was correlated with thickness of the peritoneum. CTGF protein and mRNA were detected in mesothelium and in fibroblast-like cells. In cultured HPMC, TGF-beta(1)-induced expression of CTGF mRNA was increased at 12 and 24 h and was correlated with D/P Cr. In contrast, bone morphogenic protein-4 mRNA expression was inversely correlated with D/P Cr. Our results suggest that high peritoneal transport state is associated with fibrosis and increased peritoneal CTGF expression and production by mesothelial cells, which can be stimulated by TGF-beta1. Dialysate CTGF concentration could be a biomarker for both peritoneal fibrosis and membrane function. Functional alteration of mesothelial cells may be involved in progression of peritoneal fibrosis in high transport state.

Peritoneal fibrosis (PF) is an important complication of long-term peritoneal dialysis. Although mineralocorticoid and mineralocorticoid receptor (MR) have attracted increasing attention in the field of vascular injury, including the heart, kidney, and vessels, little is known about the role of mineralocorticoid in PF. This work was designed to explore the effects of MR blockade on PF. We developed a new model of PF in rats based on mechanical scraping of the peritoneum. This model is characterized by acute-phase inflammation (neutrophil and macrophage infiltration on days 0-3) and late-phase PF (alpha-smooth muscle actin-positive fibroblast infiltration, type III collagen accumulation, and neoangiogenesis on days 7-14). Peritoneal thickening peaked on day 14. MR was expressed in rat peritoneum and a rat fibroblast cell line. Expression of its effector kinase [serum- and glucocorticoid-induced kinase-1 (Sgk1)], transforming growth factor-beta (TGF-beta), plasminogen activator inhibitor-1 (PAI-1), and CD31-positive vessels increased during the course of PF. Rats were treated with spironolactone, angiotensin receptor blockade (ARB), or angiotensin-converting enzyme inhibitor (ACEI)-ARB-spironolactone starting at 6 h after peritoneal scraping. All parameters, including peritoneal thickening, number of macrophages and CD31-positive vessels, and expression of monocyte chemoattractant protein-1, TGF-beta, PAI-1, and Sgk1, were significantly suppressed by spironolactone (10 mg x kg(-1) x day(-1)). The effects of spironolactone (10 and 20 mg x kg(-1) x day(-1)) were very similar to those of triple blockade. ARB, but not ACEI, significantly reduced peritoneal thickening. Furthermore, peritoneal function assessed by peritoneal equilibration test was significantly improved by spironolactone. Our results suggest that MR is a potential target to prevent inflammation-induced PF in patients on peritoneal dialysis.

The characteristic features of chronic peritoneal injury with peritoneal dialysis (PD) are submesothelial fibrosis and neoangiogenesis. Transforming growth factor (TGF)β and vascular endothelial growth factor (VEGF)-A are the main mediators of fibrosis and neoangiogenesis, respectively; however, the effect of the interaction between them on the peritoneum is not well known. In this study, we investigated the relationship between TGF-β1 and VEGF-A in inducing peritoneal fibrosis by use of human tissues and dialysate, cultured cells, and animal models. The VEGF-A concentration correlated with the dialysate-to-plasma ratio of creatinine (D/P Cr) ( P < 0.001) and TGF-β1 ( P < 0.001) in human PD effluent. VEGF-A mRNA levels increased significantly in the peritoneal tissues of human ultrafiltration failure (UFF) patients and correlated with number of vessels ( P < 0.01) and peritoneal thickness ( P < 0.001). TGF-β1 increased VEGF-A production in human mesothelial cell lines and fibroblast cell lines, and TGF-β1-induced VEGF-A was suppressed by TGF-β receptor I (TGFβR-I) inhibitor. Incremental peak values of VEGF-A mRNA stimulated by TGF-β1 in human cultured mesothelial cells derived from PD patients with a range of peritoneal membrane functions correlated with D/P Cr ( P < 0.05). To evaluate the regulatory mechanisms of VEGF-A and neoangiogenesis in vivo, we administered TGFβR-I inhibitor intraperitoneally in a rat chlorhexidine-induced peritoneal injury (CG) model. TGFβR-I inhibitor administration in the CG model decreased peritoneal thickness ( P < 0.001), the number of vessels ( P < 0.001), and VEGF-A levels ( P < 0.05). These results suggest that neoangiogenesis is associated with fibrosis through the TGF-β1-VEGF-A pathway in mesothelial cells and fibroblasts. These findings are important when considering the strategy for management of UFF in PD patients.

The effect of prolonged application of isoprenaline on intracellular free‐Mg2+ concentration ([Mg2+]i) was examined by use of 31P‐nuclear magnetic resonance (31P‐n.m.r.) in rat isolated hearts. Left ventricular pressure (LVP) was simultaneously measured. [Mg2+]i was estimated from the separation of the α‐ and β‐ATP peaks, using the dissociation constant of MgATP 38 μm (established previously). In normal (phosphate‐free, Krebs‐Henseleit) solution, [Mg2+]i was approximately 0.4 mm. When isoprenaline was applied for 100 min, a transient increase in [Mg2+]i was observed during the initial 25 min, whilst concentrations of ATP ([ATP]) and phosphocreatine ([PCr]) decreased and [Pi] correspondingly increased. During the subsequent 75 min of isoprenaline application, [Mg2+]i decreased below its resting levels. Washout of isoprenaline restored [Mg2+]i and [PCr], but [ATP] remained low. These changes elicited by isoprenaline were not observed in the presence of propranolol, a typical α‐adrenoceptor blocker. Isoprenaline increased both LVP and heart rate. The increased LVP and heart rate slowly returned to lower values during prolonged application of isoprenaline, but remained higher than those before application. The transient rise in [Mg2+]i elicited by isoprenaline could be attributed to the decrease in [ATP] resulting in a release of Mg2+. The subsequent decrease in [Mg2+]i during the prolonged applications suggests that β‐adrenoceptor stimulation itself facilitates Mg2+‐extruding mechanism(s).