Background: Peritoneal dialysis (PD) is a renal replacement technique that requires repeated exposure of the peritoneum to hyperosmolar PD fluids (PDFs). Unfortunately, it promotes alterations of the peritoneal membrane (PM) that affects its functionality, including mesothelial-mesenchymal transition (MMT) of mesothelial cells (MCs), inflammation, angiogenesis, and fibrosis. Glucose is the most used osmotic agent, but it is known to be at least partially responsible, together with its degradation products (GDP), for those changes. Therefore, there is a need for more biocompatible osmotic agents to better maintain the PM. Herein we evaluated the biocompatibility of Steviol glycosides (SG)-based fluids.Methods: The ultrafiltration and transport capacities of SG-containing and glucose-based fluids were analyzed using artificial membranes and an in vivo mouse model, respectively. To investigate the biocompatibility of the fluids, Met-5A and human omental peritoneal MCs (HOMCs) were exposed in vitro to different types of glucose-based PDFs (conventional 4.25% glucose solution with high-GDP level and biocompatible 2.3% glucose solution with low-GDP level), SG-based fluids or treated with TGF-β1. Mice submitted to surgery of intraperitoneal catheter insertion were treated for 40 days with SG- or glucose-based fluids. Peritoneal tissues were collected to determine thickness, MMT, angiogenesis, as well as peritoneal washings to analyze inflammation.Results: Dialysis membrane experiments demonstrated that SG-based fluids at 1.5%, 1%, and 0.75% had a similar trend in weight gain, based on curve slope, as glucose-based fluids. Analyzing transport capacity in vivo, 1% and 0.75% SG-based fluid-exposed nephrectomized mice extracted a similar amount of urea as the glucose 2.3% group. In vitro, PDF with high-glucose (4.25%) and high-GDP content induced mesenchymal markers and angiogenic factors (Snail1, Fibronectin, VEGF-A, FGF-2) and downregulates the epithelial marker E-Cadherin. In contrast, exposition to low-glucose-based fluids with low-GDP content or SG-based fluids showed higher viability and had less MMT. In vivo, SG-based fluids preserved MC monolayer, induced less PM thickness, angiogenesis, leukocyte infiltration, inflammatory cytokines release, and MMT compared with glucose-based fluids.Conclusion: SG showed better biocompatibility as an osmotic agent than glucose in vitro and in vivo, therefore, it could alternatively substitute glucose in PDF.
BACKGROUND AND AIMS Peritoneal dialysis (PD) is a renal replacement technique that requires repeated contact of the peritoneum with hyperosmolar fluids. Unfortunately, it generates metabolic and biomechanical insults that promote structural and functional alterations of the peritoneal membrane (PM). PM is lined by a mesothelial cells (MCs) monolayer that is in direct contact with the PD fluids (PDFs). Repeated PDF exposure causes a mesothelial–mesenchymal transition (MMT) of the MCs, as well as an inflammatory response, angiogenesis and fibrosis of the peritoneal tissue. For decades, glucose (Gl) has been the most commonly used osmotic agent, and Gl itself is responsible for the aforementioned changes. Furthermore, Gl degradation products (GDPs) contribute to deleterious effects on the PM [1]. Therefore, there is an unmet need for more biocompatible osmotic agents able to better maintain the structure and function of the PM. Here we evaluated the biocompatibility of Stevia (STV), a compound of natural origin with a mixture of glycosides. STV has a molecular weight close to the theoretical ideal weight for an osmotic agent in PD [2] and it was used instead of Gl for PDF. METHODS The osmotic capacity of STV-containing fluids was analysed using an in vitro device with artificial membranes and compared to Gl-based fluids. In order to investigate the STV biocompatibility, human omental peritoneal mesothelial cells (HOMCs) were cultured in the presence of different types of Gl-based PDFs (Conventional 4.25% Gl solution with a high GDP level and biocompatible 2.3% Gl solution with low GDPs level), STV-based fluids or TGF-b for 48 h. Mice submitted to surgery of an intraperitoneal catheter insertion were treated for 40 days with STV- or Gl-based PDFs. Peritoneal tissues were collected to determine thickness, MMT, angiogenesis and inflammatory markers, as well as effluents to analyse infiltrating cells. RESULTS Experimentally, using artificial membranes we demonstrated that 1, 0.75 and 0.5% STV-based fluids have a maintained and prolonged osmotic capacity similar to commercial PDFs containing Gl concentrations between 1.5 and 2.3%. Moreover, 1.5% STV-based fluid showed an osmotic capacity higher than a PDF with Gl 2.3% and reached values similar to Gl 4.25% at longer time points. In addition, HOMCs exposed to STV-based fluids showed higher viability and did not induce MMT. Gl-based fluids induced upregulation of mesenchymal markers (VEGF, fibronectin, snail) and also downregulation of the epithelial marker E-cadherin in the case of the highest concentration of Gl (4.25%). None of these markers were significantly affected by STV treatment. In vivo, STV-based fluids preserved MCs monolayer and induced less PM thickness (Figure 1), angiogenesis, leukocyte infiltration and MMT than Gl-based fluids. Furthermore, STV solutions did not promote the release of pro-inflammatory cytokines by HOMCs nor by cells present in mice parietal peritoneal tissue in contrast to Gl-based PDFs. CONCLUSIONS STV-based fluids showed better biocompatibility than Gl-based PDFs in vivo and ex vivo since STV did not induce PM thickness, MMT, angiogenesis or the release of pro-inflammatory cytokines.
BACKGROUND AND AIMS Peritoneal dialysis (PD) is the current replacement therapy for end-stage renal disease (ESRD) patients until renal transplantation can be achieved. However, chronic exposure to non-physiological PD fluids (PDF) and occasional infection episodes may lead to peritoneal damage and membrane transport failure. Chronic inflammation, together with mesothelial-to-mesenchymal transition (MMT) and submesothelial fibrosis, is a hallmark of PDF-associated peritoneal damage whose intrinsic mechanisms are still expected to be disclosed [1–2]. Activation of the innate immunity is the cornerstone for infectious agents’ elimination, also enrolled in response to damage-associated molecular patterns (DAMPs) released from stressed or injured host cells. Leakage of DNA from stressed mitochondria and damaged genomic DNA may act as DAMPs that are recognized by cytosolic double-strand DNA sensors, like the stimulator of interferon gene (STING), to mount an inflammatory response [3]. Excessive activation of STING is involved in autoinflammatory, autoimmune, and increasingly related to several chronic inflammatory conditions [4]. Thus, this study aimed to investigate the role of STING in experimental peritoneal damage. METHOD We induced peritoneal fibrosis in wild-type and STING-KO mice by intraperitoneal administration of 0.1% chlorhexidine gluconate (CHX) daily for 4 weeks. No treated WT and STING-KO mice were used as control. Then, mice were euthanized, and peritoneal tissue and peritoneal lavage fluids were recollected for the following experiments. STING mRNA (Tmem173) and protein levels in control and CHX-treated wild-type were measured by RT-qPCR, western blot and immunohistochemistry. Peritoneal levels of the STING downstream proteins TBK1 and IRF3 and their phosphorylated isoforms were assayed by western blot. Peritoneal membrane thickness was measured in formalin-fixed paraffin-embedded tissues stained with Masson's trichrome stain. Fibronectin protein levels were evaluated by western blot and MMT, fibrosis, and inflammation markers were determined by RT-qPCR. Inflammatory cells present in peritoneal effluents were assayed by flow cytometry. RESULTS We found that in the peritoneum of CHX-treated wild-type mice both Tmem173 expression and STING protein levels were increased. Interestingly, STING-positive cells were located in areas of peritoneal thickness and immune infiltration. Moreover, the protein levels of IRF3, p-IRF3, TBK1 and p-TBK1 were increased, indicating that the STING pathway is activated in experimental peritoneal damage. In STING-KO mice, CHX-induced peritoneal damage was prevented. STING-KO mice under CHX treatment showed decreased peritoneal membrane thickness and attenuated CHX-induced expression of fibrosis and MMT markers, such as Tgb1, Snai1, Cdh2, Col1a1, Fn1 and fibronectin protein when compared with CHX-treated WT mice. The absence of STING also prevented the gene expression of cytokines (Il1b, Il6 and Ifng) and chemokines (Ccl5, Ccl2 and Ccl19) and macrophages infiltration into the peritoneum. Inflammatory cell recruitment into the peritoneal cavity was also decreased in STING-KO mice, including CD3+CD4+ lymphocytes and CD11b+F4/80+ macrophages. CONCLUSION In summary, STING absence prevents peritoneal membrane thickness, fibrosis, and inflammation induced by CHX in a mice model. These results suggest that STING plays a key role in peritoneal membrane injury. Therefore, STING may become a new potential therapeutic target in PD-associated peritoneal damage.
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