Encapsulating peritoneal sclerosis (EPS) is a rare but severe complication of peritoneal dialysis (PD) characterized by extensive fibrosis of the peritoneum. Changes in peritoneal water transport may precede EPS, but the mechanisms and potential predictive value of that transport defect are unknown. Among 234 patients with ESRD who initiated PD at our institution over a 20-year period, 7 subsequently developed EPS. We evaluated changes in peritoneal transport over time on PD in these 7 patients and in 28 matched controls using 3.86% glucose peritoneal equilibration tests. Compared with long-term PD controls, patients with EPS showed early loss of ultrafiltration capacity and sodium sieving before the onset of overt EPS. Multivariate analysis revealed that loss of sodium sieving was the most powerful predictor of EPS. Compared with long-term PD control and uremic peritoneum, EPS peritoneum showed thicker submesothelial fibrosis, with increased collagen density and a greater amount of thick collagen fibers. Reduced osmotic conductance strongly correlated with the degree of peritoneal fibrosis, but not with vasculopathy. Peritoneal fibrosis was paralleled by an excessive upregulation of vascular endothelial growth factor and endothelial nitric oxide synthase, but the expression of endothelial aquaporin-1 water channels was unaltered. Our findings suggest that an early and disproportionate reduction in osmotic conductance during the course of PD is an independent predictor of EPS. This functional change is linked to specific alterations of the collagen matrix in the peritoneal membrane of patients with EPS, thereby validating the serial three-pore membrane/fiber matrix and distributed models of peritoneal transport.

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Bacterial peritonitis remains the main cause of technique failure in peritoneal dialysis (PD). During peritonitis, the peritoneal membrane undergoes structural and functional alterations that are mediated by IL-1 The NLRP3 inflammasome is a caspase-1-activating multiprotein complex that links sensing of microbial and stress products to activation of proinflammatory cytokines, including IL-1 The potential roles of the NLRP3 inflammasome and IL-1 in the peritoneal membrane during acute peritonitis have not been investigated. Here, we show that the NLRP3 inflammasome is activated during acute bacterial peritonitis in patients on PD, and this activation associates with the release of IL-1 in the dialysate. In mice, lipopolysaccharide- or -induced peritonitis led to IL-1 release in the peritoneal membrane. The genetic deletion of , which encodes NLRP3, abrogated defects in solute transport during acute peritonitis and restored ultrafiltration. In human umbilical vein endothelial cells, IL-1 treatment directly enhanced endothelial cell proliferation and increased microvascular permeability. These effects require endothelial IL-1 receptors, shown by immunofluorescence to be expressed in peritoneal capillaries in mice. Furthermore, administration of the IL-1 receptor antagonist, anakinra, efficiently decreased nitric oxide production and vascular proliferation and restored peritoneal function in mouse models of peritonitis, even in mice treated with standard-of-care antibiotherapy. These data demonstrate that NLRP3 activation and IL-1 release have a critical role in solute transport defects and tissue remodeling during PD-related peritonitis. Blockade of the NLRP3/IL-1 axis offers a novel method for rescuing morphologic alterations and transport defects during acute peritonitis.

These findings suggest that changes in intraperitoneal pH during PD are mediated by bidirectional buffer transport and by CA-mediated production of HCO3- in the membrane. The use of acidic solutions enhances acid excretion through respiratory and renal responses, which should be considered in patients with renal failure.