Gene Transfer of Transforming Growth Factor- 1 to the Rat Peritoneum: Effects on Membrane Function

Long-term peritoneal dialysis is limited by physiologic changes in the peritoneum that lead to ultrafiltration failure. To determine the role of profibrotic cytokines in the alteration of peritoneal transport, a rodent model of transforming growth factor(TGF)-mediated peritoneal fibrosis was established. An adenoviral vector driving the active form of TGF1 (AdTGF 1) was administered intraperitoneally, and peritoneal structure and function were evaluated for 28 d after infection. Seven days after AdTGF 1 infection, thickening of the peritoneum, with cellular proliferation and increased vascularization, was noted. By day 28, there was persistent thickening and extensive collagen deposition. The mesenteric collagen content was significantly elevated, compared with control adenovirus-treated animals, 21 d after infection (2.9 versus 1.8 mg hydroxyproline/g tissue, P 0.006). Blood vessel density, as measured using factor VIII immunohistochemical analyses, was significantly increased from day 4 to day 21 but decreased by day 28. Animals infected with AdTGF 1 demonstrated increased transport of solutes and decreased net ultrafiltration, which was maximal on day 7 and returned to baseline levels by day 28. It was demonstrated in vitro and in vivo that TGF1 induced production of vascular endothelial growth factor. Overexpression of TGF1 after adenovirus-mediated gene transfer causes peritoneal fibrosis, neoangiogenesis, and increased peritoneal membrane solute transport. This model should allow further delineation of the relative contributions of profibrotic and angiogenic cytokines to changes in peritoneal function and may lead to potential new interventions for peritoneal membrane failure. Peritoneal dialysis is an attractive option for the treatment of patients with end-stage renal disease. However, recurrent peritonitis and alterations in the peritoneal membrane transport of solutes complicate long-term peritoneal dialysis (1). The most common functional change in the peritoneal membrane with long-term peritoneal dialysis is ultrafiltration failure, which is the cause of technique failure for 9 to 27% of patients undergoing peritoneal dialysis (2). The relationship between the duration of peritoneal dialysis and ultrafiltration failure has been confirmed (1,3–5). In population-based studies, ultrafiltration was inversely correlated with increased peritoneal membrane transport of solutes (1,5,6). The pathophysiologic features of the changes in peritoneal membrane transport with time are not well understood. The main barrier to peritoneal transport of solutes seems to be the vascular wall (7,8). The observed changes in peritoneal membrane function with time are therefore attributable to increases in the permeability of individual blood vessels or increases in the total vascular surface of the peritoneum (9,10). Recent studies of human peritoneal biopsy samples demonstrated increases in the density of the peritoneal microvasculature with dialysis time (11,12). Human (13,14) and animal (15) biopsy samples revealed a generalized thickening of the submesothelial collagenous zone of the peritoneum, with connective tissue deposition and microvascular sclerosis, corresponding to the duration of dialysis. -Smooth muscle actin ( -SMA)-positive cells, suggesting myofibroblast differentiation induced by fibrogenic cytokines (16), were identified in the peritoneum and were correlated with the degree of fibrosis and the density of blood vessels (13). The role of increased peritoneal vascular area in ultrafiltration failure suggests that angiogenic cytokines such as vascular endothelial growth factor (VEGF) are upregulated in the process of peritoneal dialysis. VEGF has been identified, by both immunohistochemical and immunoblot analyses, in biopsy samples from patients undergoing long-term dialysis (11). VEGF concentrations in dialysate fluid have been correlated with measures of solute transport among patients undergoing chronic peritoneal dialysis who are in stable condition (17). VEGF may be induced directly in the peritoneum of patients undergoing peritoneal dialysis. Glucose degradation products, formed by heat-sterilization of dialysate, have been demonstrated to be toxic to mesothelial cells (18) but also enhance the production of VEGF by those cells (19). Rats with streptozocin-induced diabetes mellitus exhibit changes in peritoneal membrane transport similar to those of patients undergoing Received November 6, 2000. Accepted March 29, 2001. Correspondence to Dr. Jack Gauldie, Department of Pathology and Molecular Medicine, McMaster University, 1200 Main Street W. , Room 2N16, Hamilton, Ontario, Canada L8N 3Z5. Phone: 905-521-2100, ext. 76332; Fax: 905-5770198; E-mail: gauldie@mcmaster.ca