Alanyl-Glutamine Restores Tight Junction Organization after Disruption by a Conventional Peritoneal Dialysis Fluid

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.This work is part of the IMPROVE-PD project that has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie grant agreement number 812699. M.B. is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Projektnummer 419826430. R.H. was supported by a research fellowship of the European Renal Association and European Dialysis and Transplant Association (ERA-EDTA). E.L. was supported by the ÚNKP-18-2 New National Excellence Program of the Ministry of Human Capacities, Hungary. E.L. and H.J. were supported by Jellinek-Harry scholarship. S.G.Z. acknowledges the Alexander von Humboldt Stiftung/Foundation for an Experienced Researcher Fellowship (2019–2021) and the International Peritoneal Dialysis Society (ISPD) for an International Cooperation Research Grant (2019–2021). C.P.S. has obtained funding from European Nephrology and Dialysis Institute (ENDI).Peer reviewe

Human peritoneal tight junction, transporter and channel expression in health and kidney failure, and associated solute transport

Abstract Next to the skin, the peritoneum is the largest human organ, essentially involved in abdominal health and disease states, but information on peritoneal paracellular tight junctions and transcellular channels and transporters relative to peritoneal transmembrane transport is scant. We studied their peritoneal localization and quantity by immunohistochemistry and confocal microscopy in health, in chronic kidney disease (CKD) and on peritoneal dialysis (PD), with the latter allowing for functional characterizations, in a total of 93 individuals (0–75 years). Claudin-1 to -5, and -15, zonula occludens-1, occludin and tricellulin, SGLT1, PiT1/SLC20A1 and ENaC were consistently detected in mesothelial and arteriolar endothelial cells, with age dependent differences for mesothelial claudin-1 and arteriolar claudin-2/3. In CKD mesothelial claudin-1 and arteriolar claudin-2 and -3 were more abundant. Peritonea from PD patients exhibited increased mesothelial and arteriolar claudin-1 and mesothelial claudin-2 abundance and reduced mesothelial and arteriolar claudin-3 and arteriolar ENaC. Transperitoneal creatinine and glucose transport correlated with pore forming arteriolar claudin-2 and mesothelial claudin-4/-15, and creatinine transport with mesothelial sodium/phosphate cotransporter PiT1/SLC20A1. In multivariable analysis, claudin-2 independently predicted the peritoneal transport rates. In conclusion, tight junction, transcellular transporter and channel proteins are consistently expressed in peritoneal mesothelial and endothelial cells with minor variations across age groups, specific modifications by CKD and PD and distinct associations with transperitoneal creatinine and glucose transport rates. The latter deserve experimental studies to demonstrate mechanistic links. Clinical Trial registration: The study was performed according to the Declaration of Helsinki and is registered at www.clinicaltrials.gov (NCT01893710)

Cisplatin and siRNA interference with structure and function of Wnt-5a mRNA: design and in vitro evaluation of targeting AU-rich elements in the 3' UTR.

Wnt-5a is a secreted glycoprotein which has been shown to be involved in the regulation of cell adhesion and motility, processes which are of importance in metastasis formation by cancer cells. We here present an initial study aiming at evaluating whether small interfering RNA (siRNA) in combination with cisplatin can be used to modulate protein expression levels under in vitro conditions. For this purpose, an AU-rich region corresponding to the initial 260 bases of the Wnt-5a 3' untranslated region was chosen as the target. The effect of four different siRNAs was evaluated by analysis of protein suppression levels in rabbit reticulocyte lysate (RRL) and an immortalized noncancerous mammary epithelial (HB2) cell line by monitoring the activity of transiently expressed luciferase. The specificity and kinetics for hybridization of the siRNA with the messenger RNA target were followed by digestion techniques and analysis by polyacrylamide gel electrophoresis. Specific and temperature-dependent hybridization was observed, with a half-life of approximately 0.5 h at 4 degrees C. Significant downregulation of luciferase activity was obtained in the micromolar and nanomolar range, for RRL and HB2, respectively. In addition, the downregulation of protein production caused by addition of cisplatin could be further potentiated by addition of siRNA in a selective manner. The latter observation suggests that combined use of cisplatin and siRNA could be a method to decrease therapeutically used cisplatin concentrations. Thus, toxic side effects could be minimized while key proteins are targeted in a highly specific manner