Abstract
Background and Aims
The composition of all currently available peritoneal dialysis (PD) fluids triggers morphological and functional changes in the peritoneal membrane. Periodic exposure leads to vasculopathy, hypervascularization, and diabetes-like damage of vessels, eventually leading to failure of the technique. Patients undergoing dialysis generally, have a high risk of cardiovascular events. It is currently unclear if there is a mechanistic link between peritoneal membrane failure and cardiovascular risk. In vitro and in vivo studies have shown that cytoprotective additives (e.g. dipeptide alanyl-glutamine (AlaGln) or kinase inhibitor lithium chloride (LiCl)) to PDF reduce peritoneal damage. Here, we developed an experimental model for investigating effects of these cytoprotective additives in PDF in the cardiovascular context.
Method
For modelling the peritoneal membrane in vitro, mesothelial and endothelial cells were co-cultured in transwell plates. Mesothelial cells were grown in the upper compartment and primary human umbilical vein endothelial cells (HUVEc) or primary microvascular cells were grown in the lower compartment. PDF with or without cytoprotective compounds, was added to the upper compartment to only expose mesothelial cells directly to different dilutions of the fluid. Effects on cell damage was assessed by quantification of lactate-dehydrogenase (LDH) release and live-dead staining of cells. Proteome profiles were analysed for both cell-types separately and in combination using two-dimensional difference gel electrophoresis (2D-DiGE) and liquid chromatography coupled to mass spectrometry (LC-MS). In vitro findings were related to PD-induced arteriolar changes based on abundance profiles of micro-dissected omental arterioles of children treated with conventional PD-fluids and age-matched controls with normal renal function.
Results
Marked cellular injury of HUVEc after PD-fluid exposure was associated with a molecular landscape of the enriched biological process clusters ‘glucose catabolic process’, ‘cell redox homeostasis’, ‘RNA metabolic process’, ‘protein folding’, ‘regulation of cell death’, and ‘actin cytoskeleton reorganization’ that characterize PD-fluid cytotoxicity and counteracting cellular repair process respectively. PDF-induced cell damage was reduced by AlaGln and LiCl both in mesothelial and endothelial cells. Proteome analysis revealed perturbation of major cellular processes including regulation of cell death and cytoskeleton reorganization. Selected markers of angiogenesis, oxidative stress, cell junctions and transdifferentiation were counter-regulated by the additives. Co-cultured cells yielded differently regulated pathways following PDF exposure compared to separate culture. Comparison to human arterioles confirmed overlapping protein regulation between endothelial cells in vitro and in vivo, proving harmful effects of PD-fluids on endothelial cells leading to drastic changes of the cellular process landscape.
Conclusion
In summary, this study shows harmful effects of PD-fluids also effecting endothelial cells and elucidates potential mechanisms by which cytoprotective additives may counteract the signalling axis between local peritoneal damage and systemic vasculopathy. An in vitro co-culture system may be an attractive approach to simulate the peritoneal membrane for testing direct and indirect effects of cytoprotective additives in PDF. When cultured and stressed in close proximity cells may respond differently. Characterisation of PD-induced perturbations will allow identifying molecular mechanisms linking the peritoneal and cardiovascular context, offering therapeutic targets to reduce current limitations of PD and ultimately decreasing cardiovascular risk of dialysis patients.
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