Understanding and targeting the molecular basis of peritoneal solute and protein transport is essential to improve peritoneal dialysis (PD) efficacy and patient outcome. Supplementation of PD fluids (PDF) with alanyl-glutamine (AlaGln) increased small solute transport and reduced peritoneal protein loss in a recent clinical trial. Transepithelial resistance and 10 kDa and 70 kDa dextran transport were measured in primary human endothelial cells (HUVEC) exposed to conventional acidic, glucose degradation products (GDP) containing PDF (CPDF) and to low GDP containing PDF (LPDF) with and without AlaGln. Zonula occludens-1 (ZO-1) and claudin-5 were quantified by Western blot and immunofluorescence and in mice exposed to saline and CPDF for 7 weeks by digital imaging analyses. Spatial clustering of ZO-1 molecules was assessed by single molecule localization microscopy. AlaGln increased transepithelial resistance, and in CPDF exposed HUVEC decreased dextran transport rates and preserved claudin-5 and ZO-1 abundance. Endothelial clustering of membrane bound ZO-1 was higher in CPDF supplemented with AlaGln. In mice, arteriolar endothelial claudin-5 was reduced in CPDF, but restored with AlaGln, while mesothelial claudin-5 abundance was unchanged. AlaGln supplementation seals the peritoneal endothelial barrier, and when supplemented to conventional PD fluid increases claudin-5 and ZO-1 abundance and clustering of ZO-1 in the endothelial cell membrane.

Rationale: Patients with chronic kidney disease (CKD) have an exceedingly high cardiovascular risk; which further increases in patients on peritoneal dialysis (PD). The pathophysiological role of reactive metabolites accumulating in CKD such as glucose degradation products (GDP) is uncertain. Objective: Delineating the impact of GDP present in PD fluids in accelerated vasculopathy development in patients with CKD. Methods and Results: Omental and parietal peritoneal tissues were obtained from 107 children with CKD before dialysis and 90 children on chronic PD with PD fluids containing very low or high concentrations of GDP. Omental arterioles, protected from local PD fluid exposure by surrounding fat, were microdissected for multiomics analyses. High-GDP exposed omental arterioles exhibited 3-fold higher advanced glycation endproduct concentrations and upregulated genes involved in cell death/apoptosis and suppressed genes related to cell viability/survival, cytoskeleton organization, and immune response biofunctions. Vasculopathy-associated canonical pathways concordantly regulated on gene and protein level with high-GDP exposure included cell death/proliferation, apoptosis, cytoskeleton organization, metabolism and detoxification, cell junction signaling, and immune response. Parietal peritoneal arterioles of patients exposed to high-GDP fluids exhibited lumen narrowing compared to patients with CKD stage 5 (end-stage kidney disease) and patients on low-GDP PD, intima thickness was increased. Protein quantification verified increased proapoptotic activity and cytoskeleton disintegration, single-molecule-localization microscopy demonstrated arteriolar endothelial ZO-1 (zonula occludens-1) disruption. Absolute and per endoluminal surface length, arteriolar endothelial cell counts inversely correlated with GDP exposure, caspase-3, TGF (transforming growth factor)-β–induced pSMAD2/3 (phosphorylated SMAD2/3), interleukin-6, ZO-1 abundance, and lumen narrowing. In vitro, 3,4-dideoxyglucosone-3-ene reduced lamin-A/C and membrane ZO-1 assembly, increased pSMAD2/3, and ionic and 4 and 10 kDa permeability of arterial endothelial cells. Conclusions: Our findings indicate a fundamental role of GDP in PD-associated vasculopathy, exerted by endothelial cell junction and cytoskeleton disruption, and induction of apoptosis. They should redirect the focus of research and intervention on targeting reactive metabolite overload in CKD and PD. Registration: URL: https://www.clinicaltrials.gov ; Unique identifier: NCT01893710.

Endothelial and epithelial barrier function is crucial for the maintenance of physiological processes. The barrier paracellular permeability depends on the composition and spatial distribution of the cell-to-cell tight junctions (TJ). Here, we provide an experimental workflow that yields several layers of physiological data in the setting of a single endothelial cell monolayer. Human umbilical vein endothelial cells were grown on Transwell filters. Transendothelial electrical resistance (TER) and 10 kDa FITC dextran flux were measured using Alanyl-Glutamine (AlaGln) as a paracellular barrier modulator. Single monolayers were immunolabelled for Zonula Occludens-1 (ZO-1) and Claudin-5 (CLDN5) and used for automated immunofluorescence imaging. Finally, the same monolayers were used for single molecule localization microscopy (SMLM) of ZO-1 and CLDN5 at the nanoscale for spatial clustering analysis. The TER increased and the paracellular dextran flux decreased after the application of AlaGln and these functional changes of the monolayer were mediated by an increase in the ZO-1 and CLDN5 abundance in the cell–cell interface. At the nanoscale level, the functional and protein abundance data were accompanied by non-random increased clustering of CLDN5. Our experimental workflow provides multiple data from a single monolayer and has wide applicability in the setting of paracellular studies in endothelia and epithelia.

In vitro studies are essential in pre-clinical research. While choice of cell lines is often driven by handling and cost-effectiveness, in-depth knowledge on specific characteristics is scant. Mesothelial cells, which interact with endothelial cells, are widely used in research, including cancer and drug development, but have not been comprehensively profiled. We therefore performed RNA sequencing of polarized, primary peritoneal (HPMC) and immortalized pleural mesothelial cells (MeT-5A), and compared them to endothelial cells from umbilical vein (HUVEC) and cardiac capillaries (HCMEC). Seventy-seven per cent of 12,760 genes were shared between the 4 cell lines, 1003 were mesothelial and 969 were endothelial cell specific. The transcripts reflected major differences between HPMC and MeT-5A in DNA-related processes, extracellular matrix, migration, proliferation, adhesion, transport, growth factor- and immune response, and between HUVEC and HCMEC in DNA replication, extracellular matrix and adhesion organization. Highly variable shared genes were related to six clusters, cell tissue origin and immortalization, but also cell migration capacity, cell adhesion, regulation of angiogenesis and response to hypoxia. Distinct, cell type specific biological processes were further described by cellular component-, molecular function- and Reactome pathway analyses. We provide crucial information on specific features of the most frequently used mesothelial and endothelial cell lines, essential for appropriate use.

Peritoneal dialysis (PD) is limited by insufficient phosphate removal, leading to adverse cardiovascular outcomes in patients with chronic kidney disease. To advance the understanding of the molecular mechanisms of peritoneal phosphate transport, RNAseq data of phosphate transporters in four PD-relevant cell lines were analyzed. The expression and localization of the respective proteins were validated by immunostaining in these cells. The transcriptomics of omental arterioles from children on PD were analyzed. In vitro Transwell models of an immortalized mesothelial cell line (MeT-5A) and human umbilical vein endothelial cells (HUVECs) and respective co-cultures were established, enabling quantification of phosphate transport across mesothelial and endothelial monolayers. Sodium phosphonoformate tribasic hexahydrate (PFA) and Tenapanor were used to inhibit transcellular and paracellular transport pathways. Cell viability and integrity markers were measured over the experimental periods. SLC20A1 and SLC20A2 were expressed across all studied cell types, while SLC34A2 and SLC34A3 were mesothelial cell-specific. Omental arterioles of children on low-glucose-degradation-product (GDP) PD showed higher SLC20A1 expression vs. stage 5 chronic kidney disease (CKD5) and healthy controls. Permeability for phosphate was lower across MeT-5A compared with HUVEC monolayers and was not further reduced in co-culture. Inhibitors reduced both transcellular and paracellular transport to 75% in MeT-5A and 65% in co-cultures, while no effects were observed in HUVEC alone, suggesting the mesothelial cell layer as a significant barrier for phosphate transport. Our studies provide first analyses combining findings on molecular phosphate transporters in peritoneal cells and arterioles and introducing a Transwell model for quantitative studies of phosphate kinetics.

For patients with kidney failure, peritoneal dialysis (PD) is an alternative kidney replacement therapy to hemodialysis. Long-term PD efficacy is limited by multicellular pathologies induced by the hyperosmotic PD fluids, including vasculopathy and fibroangiogenic remodeling of the peritoneum, which lack targeted pharmacological interventions. We developed a deep secretome profiling workflow in a coculture system using a human peritoneal mesothelial cell line and primary human lymphatic endothelial cells to characterize the influence of PD fluid on communication between these cell types. This approach uncovered extracellular and intracellular signaling patterns absent in standard monocultures and identified 1910 human proteins that revealed extracellular regulatory processes central to PD-associated peritoneal pathology. Integration of the coculture secretome and cellular proteomes with effluent and plasma proteomes derived from patients with PD revealed cell type–specific signaling networks and groups of proteins correlating with clinical parameters such as ultrafiltration capacity, transport kinetics, and inflammation. Functional validation demonstrated that lithium chloride supplementation partially counteracted fibroangiogenic signaling and affected key PD fluid–induced processes, including PDGFC-driven lymphangiogenesis, syndecan-4 ectodomain shedding by endothelial cells, and a mesothelial switch from NOTCH1 to NOTCH3 synthesis. These findings suggest new potential pharmacological strategies to mitigate peritoneal fibrosis and vasculopathy, offering a framework for future therapeutic innovation in PD and beyond.