ABSTRACT: Loss of ultrafiltration capacity in peritoneal dialysis (PD) patients is often associated with peritoneal vascular changes, manifest as diabetes-like vasculopathy and angiogenesis. The endothelial monolayer lining the vessel lumen controls vessel barrier function and thereby influences peritoneal substrate transport and ultrafiltration. In this study, we investigated the influence of exposure of human umbilical vein endothelial cells (HUVEC) to different PD fluids. HUVECs were exposed to experimental solutions for up to 24 h. All test fluids were sterile-filtered before usage. Each experiment consisted of three independent samples in biological replicates on separate culture plates. For PD fluid incubation, cells were first exposed to pure PD fluids (Dianeal PD4 3.86% glucose, Physioneal 3.86% glucose, Extraneal, all Baxter, Castlebar, Ireland), or to a lab-made GDP-free PD fluid or to normal medium without growth factors as control. Cells were subsequently exposed for 24 h to the above solutions diluted 1:1 with culture medium and brought to 2% FCS. Cells were then washed three times (250 mM sucrose, 10 mM Tris/HCl, pH 7) and lysed in 125 µL per well of lysis buffer (30 mM Tris, pH 8.5, 7 M urea, 2 M thiourea, 4% CHAPS, 1 mM EDTA, one tablet of Complete Protease Inhibitor (Roche, Basel; Switzerland) per 100 ml, and one tablet of PhosStop Protease Inhibitor (Roche) per 100 mL). Total protein concentration was determined with the Pierce 660 Kit (Thermo) per manufacturer’s manual. Lysates were stored at -80°C until further processing. We investigated the molecular mechanisms of endothelial cell pathology during in vitro PD fluid exposure by proteomic and bioinformatic analysis of the endothelial cell response to the PD fluid induced stress, integrating current understanding of PD-related cellular injury and stress responses (Bender et al., Nephrol Dial Transplant, 2011, doi:10.1093/ndt/gfq484; Kratochwill et al., BioMed research international, 2015, doi:10.1155/2015/628158; Kratochwill et al., J Proteome Res, 2009, doi:10.1021/pr800916s; Lechner et al., J Proteome Res, 2010, doi:10.1021/pr9011574). We then evaluated the effect of AlaGln addition to conventional PD fluid on these parameters in endothelial cells. This strategy allowed characterization of endothelial cell injury and stress responses during exposure to different PD fluid.