These data identify that the formaldehyde and 3,4-DGE present in heat-sterilized peritoneal dialysis solutions are important in reducing mesothelial cell regeneration. Specifically targeting their removal may have major benefits in preserving the mesothelium during long-term peritoneal dialysis.

Structural and functional alterations of the peritoneal membrane are a significant problem in long-term peritoneal dialysis patients. The present study has established a 3-dimensional (3D) cell culture system to study the human peritoneal fibroblast (HPFB) and to examine its proliferative responses to cytokines and growth factors as well as dialysis effluent obtained from patients during peritoneal infection. PDGF-AB, basic FGF and IL-1 beta induced a time and dose dependent increase in 3D-HPFB proliferation. At day 9 proliferation, as assessed by MTT uptake, was increased by 2.4-, 2.3- and 1.5-fold above control by PDGF-AB (50 ng/ml), bFGF (50 ng/ml) and IL-1 beta (10 ng/ml), respectively (N = 5, P = 0.04 for all). These effects could be inhibited by co-incubation with anti-PDGF-AB antibody, anti-bFGF or IL-1ra, respectively. Exposure of 3D-HPFB to TGF-beta 1 did not result in an increase in cell proliferation. Incubation of 3D-HPFB with peritoneal macrophage (PMø) or human peritoneal mesothelial cell (HPMC) conditioned medium also resulted in a time and dose dependent increase in proliferation. At day 9, proliferation was maximally increase 1.65- and 1.92-fold by peritoneal macrophage- and mesothelial cell-conditioned medium, respectively. Cell free PDE, obtained from CAPD patients during episodes of peritonitis, induced 3D-HPFB proliferation above control values (2- to 6.5-fold increases, N = 5, P < 0.05 for all). This mitogenic potential of PDE was reduced following dilution, and with time following peritonitis there was a gradual decrease in the mitogenic effect of PDE. The proliferative potential of PDE was significantly reduced following co-incubation with IL-1ra (45.7% inhibition), anti-bFGF (34.9% inhibition) and anti PDGF-AB (27.4% inhibition). These data indicate that infected PDE causes fibroblast hyperplasia which might potentially contribute to pro-fibrotic processes during CAPD.

In the present study a newly formulated dialysis solution (HDF) was tested for its effects on phagocyte viability and function as well as its ability to support bacterial growth. This solution differs from standard CAPD solution (NPD) by the inclusion of histidine to buffer the fluid to pH 6.7. Low-dextrose HDF (1.36% w/v dextrose) did not significantly decrease the viability or inhibit any of the PMN functional parameters measured (phagocytosis, LTB4 release or respiratory burst activation) when compared to control buffer. NPD (1.36% w/v dextrose) at low pH as well as all high-dextrose dialysis solutions (NPD and HDF) significantly inhibited most PMN functions independently of reduced viability. Peritoneal mesothelial cell viability was unaffected by either low- or high-dextrose HDF but was significantly reduced by NPD (1.36 and 3.86% dextrose) at pH 5.2. The inhibitory effects of low dextrose dialysis solutions were confirmed as being partly related to their low initial pH. High-dextrose dialysis fluids, however, inhibit PMN function by a mechanism which, in addition to initial pH, appears to be directly related to their dextrose content but not their osmolality.

Background. In a fibrotic process the interaction between resident cells and extracellular matrices is important in the control of cell function. Our preliminary experiments indicated that concentrated peritoneal dialysis effluent caused contraction of collagen matrices by peritoneal fibroblasts. In this study we attempted to mimic the inflammatory milieu present during peritoneal inflammation and assessed its effect on fibroblast activation. Methods. Rat peritoneal fibroblasts (RPFB) were isolated by a time-elapsed differential subculture from mixtures of primary cultures of peritoneal resident cells, and then cultured in collagen matrices. Various inflammatory mediators, known to be present in the peritoneal cavity during inflammation, (i.e., interleukin-6 [IL-6], IL-1 , and tumor necrosing factor (TNF)α were added to three-dimensional-RPFB cultures (1 ϫ 10 5 /ml) prior to their incubation for either 48 h or 10 days. The contractility of collagen matrices over this time period was monitored, as was the expression of transforming growth factor (TGF)-1 mRNA. Experimental conditions were: (i) control gels, (ii) gels with IL-6, (iii) gels with IL-1 , (iv) gels with TNFα, (v) gels with each cytokine plus glucose (90 mM). Results. With 48 h stimulation, a greater than tenfold increase in TGF-1 mRNA expression (measured as the ratio to TGF-1/glyceraldehyde 3-phosphate dehydrogenase [GAPDH] mRNA) was observed compared with the control, and this was accompanied by gel contraction. With 10-day stimulation, both IL-1 and TNFα suppressed the expression of TGF-1 mRNA as well as suppressing gel contraction. There was a 30% to 40% gel contraction accompanied by elongation of RPFB morphology in the IL-6 and control groups. The addition of glucose promoted the extension of RPFB and gel contraction by up to 60% in both the IL-1 -and TNFα-supplemented groups. Conclusion. These in vitro findings suggest that a balance of inflammatory cytokines influences rat peritoneal fibroblast (RPFB) gene expression, causing changes in the interaction between extracellular matrices and peritoneal fibroblasts.