No abstract

Ultrafiltration (UF) failure is a consequence of long-term peritoneal dialysis (PD). Fibrosis, angiogenesis, and vasculopathy are causes of this functional disorder after 3-8 years on PD. Epithelial-to-mesenchymal transition (EMT) of mesothelial cell (MC) is a key process leading to peritoneal fibrosis with functional deterioration. Our purpose was to study the peritoneal anatomical changes during the first months on PD, and to correlate them with peritoneal functional parameters. We studied 35 stable PD patients for up to 2 years on PD, with a mean age of 45.3+/-14.5 years. Seventy-four percent of patients presented loss of the mesothelial layer, 46% fibrosis (>150 microm) and 17% in situ evidence of EMT (submesothelial cytokeratin staining), which increased over time. All patients with EMT showed myofibroblasts, while only 36% of patients without EMT had myofibroblasts. The number of peritoneal vessels did not vary when we compared different times on PD. Vasculopathy was present in 17% of the samples. Functional studies were used to define the peritoneal transport status. Patients in the highest quartile of mass transfer area coefficient of creatinine (Cr-MTAC) (>11.8 ml min(-1)) showed significantly higher EMT prevalence (P=0.016) but similar number of peritoneal vessels. In the multivariate analysis, the highest quartile of Cr-MTAC remained as an independent factor predicting the presence of EMT (odds ratio 12.4; confidence interval: 1.6-92; P=0.013) after adjusting for fibrosis (P=0.018). We concluded that, during the first 2 PD years, EMT of MCs is a frequent morphological change in the peritoneal membrane. High solute transport status is associated with its presence but not with increased number of peritoneal vessels.

The preservation of the peritoneal membrane is crucial for long-term survival in peritoneal dialysis. Epithelial-to-mesenchymal transition (EMT) is a process demonstrated in mesothelial cells (MC), responsible for negative peritoneal changes and directly related to PD. EMT enables neovascularization and fibrogenic capabilities in MC. Vascular endothelial growth factor (VEGF) is the mediator for neo-vascularization. Rapamycin is a potent immunosuppressor with antifibrotic action in renal allografts and has a demonstrated anti-VEGF effect. We performed this study with the hypothesis that rapamycin may regulate the EMT of MC. MC from human omentum were cultured. When mesothelial cells reached confluence, some of them were stimulated with r-TGF-ß (1 ng/mL) to induce EMT, co-administered with rapamycin (0.2, 2, 4, 20 and 40 nM). Other groups of cells received similar doses of rapamycin or r-TGF-ß, separately. Cells were analyzed at 6, 24, 48 hours and 7 days. As markers of EMT we included α-SMA, E-cadherin and snail nuclear factor by quantitative RT-PCR. EMT markers and regulators demonstrated the following changes with rapamycin: E-cadherin (a protective gene for EMT) increased 2.5-fold relative to controls under 40 nM, at 24h. Importantly, rapamycin inhibited snail expression induced by TGF-ß at 6h, whereas TGF-ß increased snail 10fold. At day 7, rapamycin showed no anti-EMT properties. An important decrease in α-SMA expression by MC after rapamycin addition was observed. In conclusion, rapamycin shows a mild protective effect on EMT, as it increases E-cadherin and decreases α-SMA expression. Consequently, rapamycin might partially regulate the epithelial-to-mesenchymal transition of mesothelial cells.