In early clinical testing, acute addition of alanyl-glutamine (AlaGln) to glucose-based peritoneal dialysis (PD) fluids restored peritoneal cellular stress responses and leukocyte function. This study was designed to test the effect of extended treatment with AlaGln-supplemented PD fluid on biomarkers of peritoneal health. In a double-blinded, randomized crossover design, stable PD patients were treated with AlaGln (8 mM) or placebo added to PD fluid for eight weeks. As primary outcome measures, dialysate cancer-antigen 125 (CA-125) appearance rate and ex vivo stimulated interleukin-6 (IL-6) release were assessed in peritoneal equilibration tests. In 8 Austrian centers, 54 patients were screened, 50 randomized, and 41 included in the full analysis set. AlaGln supplementation significantly increased CA-125 appearance rate and ex vivo stimulated IL-6 release. AlaGln supplementation also reduced peritoneal protein loss, increased ex vivo stimulated tumor necrosis factor (TNF)-α release, and reduced systemic IL-8 levels. No adverse safety signals were observed. All 4 peritonitis episodes occurred during standard PD fluid treatment. A novel AlaGln-supplemented PD fluid improves biomarkers of peritoneal membrane integrity, immune competence, and systemic inflammation compared to unsupplemented PD fluid with neutral pH and low-glucose degradation. A phase 3 trial is needed to determine the impact of AlaGln supplementation on hard clinical outcomes.

Exposure of mesothelial cells to peritoneal dialysis fluids (PDF) results in cytoprotective cellular stress responses (CSR) that counteract PDF-induced damage. In this study, we tested the hypothesis that the CSR may be inadequate in relevant models of peritoneal dialysis (PD) due to insufficient levels of glutamine, resulting in increased vulnerability against PDF cytotoxicity. We particularly investigated the role of alanyl-glutamine (Ala-Gln) dipeptide on the cytoprotective PDF stress proteome. Adequacy of CSR was investigated in two human in vitro models (immortalized cell line MeT-5A and mesothelial cells derived from peritoneal effluent of uraemic patients) following exposure to heat-sterilized glucose-based PDF (PD4-Dianeal, Baxter) diluted with medium and, in a comparative proteomics approach, at different levels of glutamine ranging from depletion (0 mM) via physiological (0.7 mM) to pharmacological levels (8 mM administered as Ala-Gln). Despite severe cellular injury, expression of cytoprotective proteins was dampened upon PDF exposure at physiological glutamine levels, indicating an inadequate CSR. Depletion of glutamine aggravated cell injury and further reduced the CSR, whereas addition of Ala-Gln at pharmacological level restored an adequate CSR, decreasing cellular damage in both PDF exposure systems. Ala-Gln specifically stimulated chaperoning activity, and cytoprotective processes were markedly enhanced in the PDF stress proteome. Taken together, this study demonstrates an inadequate CSR of mesothelial cells following PDF exposure associated with low and physiological levels of glutamine, indicating a new and potentially relevant pathomechanism. Supplementation of PDF with pharmacological doses of Ala-Gln restored the cytoprotective stress proteome, resulting in improved resistance of mesothelial cells to exposure to PDF. Future work will study the clinical relevance of CSR-mediated cytoprotection.

Peritonitis and ultrafiltration failure remain serious complications of chronic peritoneal dialysis (PD). Dysfunctional cellular stress responses aggravate peritoneal injury associated with PD fluid exposure, potentially due to peritoneal glutamine depletion. In this randomized cross-over phase I/II trial we investigated cytoprotective effects of alanyl-glutamine (AlaGln) addition to glucose-based PDF. In a prospective randomized cross-over design, 20 stable PD outpatients underwent paired peritoneal equilibration tests 4 weeks apart, using conventional acidic, single chamber 3.86% glucose PD fluid, with and without 8 mM supplemental AlaGln. Heat-shock protein 72 expression was assessed in peritoneal effluent cells as surrogate parameter of cellular stress responses, complemented by metabolomics and functional immunocompetence assays. AlaGln restored peritoneal glutamine levels and increased the primary outcome heat-shock protein expression (effect 1.51-fold, CI 1.07–2.14; p = 0.022), without changes in peritoneal ultrafiltration, small solute transport, or biomarkers reflecting cell mass and inflammation. Further effects were glutamine-like metabolomic changes and increased ex-vivo LPS-stimulated cytokine release from healthy donor peripheral blood monocytes. In patients with a history of peritonitis (5 of 20), AlaGln supplementation decreased dialysate interleukin-8 levels. Supplemented PD fluid also attenuated inflammation and enhanced stimulated cytokine release in a mouse model of PD-associated peritonitis. We conclude that AlaGln-supplemented, glucose-based PD fluid can restore peritoneal cellular stress responses with attenuation of sterile inflammation, and may improve peritoneal host-defense in the setting of PD.

Lithium added to peritoneal dialysis fluid protects mesothelial cells and attenuates peritoneal fibrosis and angiogenesis by reducing αB-crystallin.