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Background: Mesothelial cell transplantation has been suggested to improve mesothelial repair after surgery, recurrent peritonitis and peritoneal dialysis., Methods: In this study we evaluated mesothelial cell transplantation during the resolution phase of experimentally thioglycollate-induced peritonitis in rats. To this end 4 x 10(6) DiO-labeled autologous mesothelial cells were transplanted 1 week after peritonitis induction. Peritoneal inflammation and permeability characteristics were evaluated after another week., Results: Mesothelial cell transplantation after peritonitis resulted in incorporation of these cells in the parietal mesothelial lining, leading to an acute transient submesothelial thickening which was not seen in transplanted animals without prior peritonitis induction. Long-term functioning of these repopulated mesothelial cells leaded to peritoneal activation as evidenced by a approximately twofold increase in peritoneal lymphocytes (P < 0.01) and omental mast cell counts (P < 0.05), accompanied by the induction of inflammation markers monocyte chemoattractant protein-1 (MCP-1) (P < 0.01) and hyaluronan (P < 0.01) in the transplanted peritonitis group, but not in rats with peritonitis without mesothelial cell transplantation or in control rats without mesothelial cell transplantation (all four parameters P < 0.01). In addition, trapping of transplanted mesothelial cells in the milky spots of omental tissue and lymphatic stomata of the diaphragm both in control and thioglycollate rats seems to increase microvascular permeability, reflected by apparent increased diffusion rates of small solutes and proteins., Conclusion: Altogether, our data underscore the importance of controlling peritoneal (patho)physiology and function in mesothelial transplantation protocols.

Background: Water transport in peritoneal dialysis (PD) patients is across the small pores and water channels, the latter allowing free water transport. The objective of the study was to investigate the contribution of each transport route on transcapillary ultrafiltration (TCUF)., Methods: Standard peritoneal permeability analyses of 80 stable PD patients were analyzed. Twenty-nine patients were followed longitudinally. Fluid transport through small pores (SPT) was assessed by the amount of transported sodium. Free water transport (FWT) was calculated by subtracting SPT from TCUF. The contribution of FWT and SPT to the TCUF and water transport rates at any time point was computed., Results: The ultrafiltered volume due to SPT increased gradually during the dwell, while FWT reached its maximum around 3 hours. The rate of FWT decreased continuously during the dwell. SPT decreased during the initial 2 hours and remained stable thereafter. At 60 minutes, the SPT (P < 0.05) and its contribution (P < 0.05) were positively related to the MTAC(creat). The contribution of FWT after 1 hour, but not the absolute amount, showed an inverse relationship. Peritoneal solute transport parameters (P < 0.01) and the contribution of SPT (P= 0.08), but none of the other fluid parameters showed a U-shape with the lowest values in the second year of PD (P < 0.01)., Conclusion: The dwell courses of water transport suggest that the activity of water channels is dependent and limited by the crystalloid osmotic pressure gradient, while other determinants are important in SPT. The time-course of SPT paralleled that of peritoneal solute transport parameters.

In a previous study, vascular endothelial growth factor (VEGF) was found to be locally produced in the peritoneal tissue of patients undergoing peritoneal dialysis (PD) who were being treated with glucose-containing PD solutions. Locally produced VEGF (LVEGF) was positively related to the mass transfer area coefficient (MTAC) of creatinine and to glucose absorption, both of which are representative of the peritoneal vascular surface area. It was therefore hypothesized that VEGF is involved in the peritoneal neoangiogenesis found in long-term PD. The aim of the present study was to investigate the time course of peritoneal VEGF levels in PD patients treated with glucose-based PD solutions during longitudinal follow-up. We also studied the effect of the switch to glucose-free PD treatment on VEGF production. Forty standard peritoneal permeability analyses (SPAs) with 3.86% glucose-containing dialysis solution were investigated. The SPAs were performed in 10 PD patients with a median number of three SPAs per patient during a follow-up of 23 months. Duration of PD treatment at the last SPA was 74 months. All patients were initially treated with glucose-containing dialysis solutions. Four patients switched after 114 months of glucose-based PD to glucose-free PD and were followed for 7 months. A PD regimen of icodextrin, glycerol, and amino acid-based dialysis solutions was applied in these patients. Four SPAs were performed per patient in this period. To predict the VEGF dialysate-to-serum ratio (D/S), when diffusion would be the only explanation for the VEGF dialysate concentration, we calculated the power relationship between D/S ratios of serum proteins that are only transported across the peritoneum and the molecular weights of those proteins. The measured VEGF D/S ratio was higher than expected (P <.001) in each observation, pointing to local production of VEGF. LVEGF increased with duration of glucose PD, 11.7 ng/L to 23.45 ng/L (P <.03). LVEGF decreased in all 4 patients undergoing glucose-free PD, from 57.35 ng/L to 23.10 ng/L. A correlation (r = 0.83, P <.001) was found be-tween the differences in MTAC creatinine between the first and last SPA during glucose-based PD and the difference in LVEGF between these observations. A similar correlation was present between the difference in glucose absorption and the difference in LVEGF (r = 0.85, P <.001). This supports a pathogenetic role of high glucose dialysate concentrations in the development of changes in the peritoneum that are found in long-term PD. Treatment with non-glucose-based PD solutions may inhibit further development of these alterations.

The morphologic alterations in the kidney and the retina that can be present in patients with diabetic microangiopathy are mediated by growth factors. Vascular endothelial growth factor (VEGF) is a mediator of neoangiogenesis in diabetic retinopathy. Transforming growth factor-beta (TGF-beta) is involved in the extracellular matrix proliferation in diabetic nephropathy. The aim of the present study was to investigate the presence of VEGF and TGF-beta1 in peritoneal effluents of patients undergoing continuous ambulatory peritoneal dialysis who are being treated with glucose-containing dialysis solutions in relation to parameters of peritoneal transport. Standard peritoneal permeability analyses with 3.86% glucose dialysate were performed in 16 stable patients undergoing peritoneal dialysis (PD) (median duration of PD 39 months, range 1 to 104 months). The power relationship that is present between dialysate/serum (D/S) ratios of serum proteins that are transported only across the peritoneal membrane and their molecular weights was used to predict the D/S ratios when diffusion would be the only explanation for the measured dialysate concentration. It was assumed that all TGF-beta1 in the circulation was bound to alpha2-macroglobulin. The D/S ratios of VEGF (P < .0005) and TGF-beta1 (P < .015) were significantly higher than expected when VEGF and TGF-beta1 would have been transported from the circulation only by diffusion. No relationship was present between the effluent concentration attributed to the local production of VEGF (LVEGF) and that of TGF-beta1 (LTGF-beta1). LVEGF correlated with the mass transfer area coefficient (MTAC) creatinine value (r = 0.69, P < .007), MTAC urate value (r = 0.60, P < .02), and glucose absorption value (r = 0.75, P < .004), all reflections of the peritoneal vascular surface area. A negative correlation was observed between the transcapillary ultrafiltration (926 mL/4 h, 394 to 1262 mL/4 h) and LVEGF (r = -0.52, P < .045). This negative tendency was also observed between the net ultrafiltration (622 mL/4 h, -43 to 938 mL/4 h) and LVEGF (r = -0.48) but did not reach significance. LVEGF and the duration of treatment did not correlate, possibly because of the relatively small number of patients. LTGF-beta1 showed no relationship with transport parameters or duration of treatment. In conclusion, we found evidence for the local production of both VEGF and TGF-beta1 in the peritoneal membrane of patients undergoing long-term peritoneal dialysis with glucose-based dialysate solutions. The analogy with VEGF in diabetic retinopathy suggests a pathogenetic role of high dialysate glucose concentrations in the development of these alterations in the peritoneal membrane.