Changes in peritoneal mesothelial cells phenotype after chronic exposure to glucose or N-acetylglucosamine

Protective role of N-acetylcysteine and Sulodexide on endothelial cells exposed on patients' serum after SARS-CoV-2 infection

Severe acute respiratory syndrome coronavirus-2 causes hyperinflammation and activation of coagulation cascade and, as a result, aggravates endothelial cell dysfunction. N-acetylcysteine and Sulodexide have been found to mitigate endothelial damage. The influence on coronary artery endothelial cells of serum collected after 4 ± 1 months from coronavirus infection was studied. The concentrations of serum samples of interleukin 6, von Willebrand Factor, tissue Plasminogen Activator, and Plasminogen Activator Inhibitor-1 were studied. The cultures with serum of patients after coronavirus infection were incubated with N-acetylcysteine and Sulodexide to estimate their potential protective role. The blood inflammatory parameters were increased in the group of cultures incubated with serum from patients after coronavirus infection. Supplementation of the serum from patients after coronavirus infection with N-acetylcysteine or Sulodexide reduced the synthesis of interleukin 6 and von Willebrand Factor. No changes in the synthesis of tissue Plasminogen Activator were observed. N-acetylcysteine reduced the synthesis of Plasminogen Activator Inhibitor-1. N-acetylcysteine and Sulodexide increased the tPA/PAI-1 ratio. N-acetylcysteine may have a role in reducing the myocardial injury occurring in the post-COVID-19 syndrome. Sulodexide can also play a protective role in post-COVID-19 patients.

Oxidative Stress-Induced Alterations of Cellular Localization and Expression of Aquaporin 1 Lead to Defected Water Transport upon Peritoneal Fibrosis

Being one of the renal replacement therapies, peritoneal dialysis (PD) maintains around 15% of end-stage kidney disease patients’ lives; however, complications such as peritoneal fibrosis and ultrafiltration failure during long-term PD compromise its application. Previously, we established a sodium hypochlorite (NaClO)-induced peritoneal fibrosis porcine model, which helped to bridge the rodent model toward pre-clinical human peritoneal fibrosis research. In this study, the peritoneal equilibration test (PET) was established to evaluate instant functional changes in the peritoneum in the pig model. Similar to observations from long-term PD patients, increasing small solutes transport and loss of sodium sieving were observed. Mechanistic investigation from both in vivo and in vitro data suggested that disruption of cytoskeleton induced by excessive reactive oxygen species defected intracellular transport of aquaporin 1, this likely resulted in the disappearance of sodium sieving upon PET. Functional interference of aquaporin 1 on free water transport would result in PD failure in patients.

Roles of the TGF-β⁻VEGF-C Pathway in Fibrosis-Related Lymphangiogenesis

Lymphatic vessels drain excess tissue fluids to maintain the interstitial environment. Lymphatic capillaries develop during the progression of tissue fibrosis in various clinical and pathological situations, such as chronic kidney disease, peritoneal injury during peritoneal dialysis, tissue inflammation, and tumor progression. The role of fibrosis-related lymphangiogenesis appears to vary based on organ specificity and etiology. Signaling via vascular endothelial growth factor (VEGF)-C, VEGF-D, and VEGF receptor (VEGFR)-3 is a central molecular mechanism for lymphangiogenesis. Transforming growth factor-β (TGF-β) is a key player in tissue fibrosis. TGF-β induces peritoneal fibrosis in association with peritoneal dialysis, and also induces peritoneal neoangiogenesis through interaction with VEGF-A. On the other hand, TGF-β has a direct inhibitory effect on lymphatic endothelial cell growth. We proposed a possible mechanism of the TGF-β–VEGF-C pathway in which TGF-β promotes VEGF-C production in tubular epithelial cells, macrophages, and mesothelial cells, leading to lymphangiogenesis in renal and peritoneal fibrosis. Connective tissue growth factor (CTGF) is also involved in fibrosis-associated renal lymphangiogenesis through interaction with VEGF-C, in part by mediating TGF-β signaling. Further clarification of the mechanism might lead to the development of new therapeutic strategies to treat fibrotic diseases.

"Biocompatible" Neutral pH Low-GDP Peritoneal Dialysis Solutions: Much Ado About Nothing?

Adverse outcomes in peritoneal dialysis (PD), including PD related infections, the loss of residual kidney function (RKF), and longitudinal, deleterious changes in peritoneal membrane function continue to limit the long-term success of PD therapy. The observation that these deleterious changes occur upon exposure to conventional glucose-based PD solutions fuels the search for a more biocompatible PD solution. The development of a novel PD solution with a neutral pH, and lower in glucose degradation products (GDPs) compared to its conventional predecessors has been labeled a "biocompatible" solution. While considerable evidence in support of these novel solutions' biocompatibility has emerged from cell culture and animal studies, the clinical benefits as compared to conventional PD solutions are less clear. Neutral pH low GDP (NpHLGDP) PD solutions appear to be effective in reducing infusion pain, but their effects on other clinical endpoints including peritoneal membrane function, preservation of RKF, PD-related infections, and technique and patient survival are less clear. The literature is limited by studies characterized by relatively few patients, short follow-up time, heterogeneity with regards to the novel PD solution type under study, and the different patient populations under study. Nonetheless, the search for a more biocompatible PD solution continues with emerging data on promising non glucose-based solutions.

Regulation of synthesis and roles of hyaluronan in peritoneal dialysis

Hyaluronan (HA) is a ubiquitous extracellular matrix glycosaminoglycan composed of repeated disaccharide units of alternating D-glucuronic acid and D-N-acetylglucosamine residues linked via alternating β-1,4 and β-1,3 glycosidic bonds. HA is synthesized in humans by HA synthase (HAS) enzymes 1, 2, and 3, which are encoded by the corresponding HAS genes. Previous in vitro studies have shown characteristic changes in HAS expression and increased HA synthesis in response to wounding and proinflammatory cytokines in human peritoneal mesothelial cells. In addition, in vivo models and human peritoneal biopsy samples have provided evidence of changes in HA metabolism in the fibrosis that at present accompanies peritoneal dialysis treatment. This review discusses these published observations and how they might contribute to improvement in peritoneal dialysis.

Mesothelial cells in tissue repair and fibrosis

Mesothelial cells are fundamental to the maintenance of serosal integrity and homeostasis and play a critical role in normal serosal repair following injury. However, when normal repair mechanisms breakdown, mesothelial cells take on a profibrotic role, secreting inflammatory, and profibrotic mediators, differentiating and migrating into the injured tissues where they contribute to fibrogenesis. The development of new molecular and cell tracking techniques has made it possible to examine the origin of fibrotic cells within damaged tissues and to elucidate the roles they play in inflammation and fibrosis. In addition to secreting proinflammatory mediators and contributing to both coagulation and fibrinolysis, mesothelial cells undergo mesothelial-to-mesenchymal transition, a process analogous to epithelial-to-mesenchymal transition, and become fibrogenic cells. Fibrogenic mesothelial cells have now been identified in tissues where they have not previously been thought to occur, such as within the parenchyma of the fibrotic lung. These findings show a direct role for mesothelial cells in fibrogenesis and open therapeutic strategies to prevent or reverse the fibrotic process.

N-Acetylglucosamine modulates function of the skin fibroblasts

BACKGROUND

Fibroblasts are an important component of the skin determining its properties. N-Acetylglucosamine (NAG) is the substrate for hyaluronan synthesis, and it also has anti-inflammatory and anti-senescent activity in mesothelial cells.

METHODS

We tested in in vitro-cultured human skin fibroblasts how supplementation of culture medium with NAG 10 mmol L(-1) changes properties of these cells.

RESULTS

Fibroblasts cultured in presence of NAG produced more proteins and that was mainly due to increased synthesis of collagen (+33% vs. control, P < 0.05). Hyaluronan synthesis was increased (+107% vs. control, P < 0.001), but interleukin-6 synthesis was reduced (-22% vs. control, P < 0.05). Fibroblasts cultured in medium with NAG 10 mmol L(-1) demonstrated improved ability to heal the injured layer of cells (+34% vs. control, P < 0.05). Additionally senescence of fibroblasts undergoing replicative ageing in the presence of NAG was less pronounced, as reflected by smaller increase in the population doubling time (-70% vs. control, P < 0.05).

CONCLUSION

We conclude that NAG induced changes in the skin fibroblasts' properties maybe important for prevention of the age-dependent changes in its structure and function.

Discovery and validation of a new class of small molecule Toll-like receptor 4 (TLR4) inhibitors

Many inflammatory diseases may be linked to pathologically elevated signaling via the receptor for lipopolysaccharide (LPS), toll-like receptor 4 (TLR4). There has thus been great interest in the discovery of TLR4 inhibitors as potential anti-inflammatory agents. Recently, the structure of TLR4 bound to the inhibitor E5564 was solved, raising the possibility that novel TLR4 inhibitors that target the E5564-binding domain could be designed. We utilized a similarity search algorithm in conjunction with a limited screening approach of small molecule libraries to identify compounds that bind to the E5564 site and inhibit TLR4. Our lead compound, C34, is a 2-acetamidopyranoside (MW 389) with the formula C17H27NO9, which inhibited TLR4 in enterocytes and macrophages in vitro, and reduced systemic inflammation in mouse models of endotoxemia and necrotizing enterocolitis. Molecular docking of C34 to the hydrophobic internal pocket of the TLR4 co-receptor MD-2 demonstrated a tight fit, embedding the pyran ring deep inside the pocket. Strikingly, C34 inhibited LPS signaling ex-vivo in human ileum that was resected from infants with necrotizing enterocolitis. These findings identify C34 and the β-anomeric cyclohexyl analog C35 as novel leads for small molecule TLR4 inhibitors that have potential therapeutic benefit for TLR4-mediated inflammatory diseases.

Effect of β-(3,4-dihydroxyphenyl)lactic acid on oxidative stress stimulated by high glucose levels in human peritoneal mesothelial cells

OBJECTIVE

To investigate the effects of β-(3,4-dihydroxyphenyl)lactic acid on oxidative stress stimulated by high glucose levels in human peritoneal mesothelial cells (HPMCs) in vitro.

METHODS

HPMCs were incubated with 100 mol/l glucose followed by 0.625-20 mg/ml β-(3,4-dihydroxyphenyl)lactic acid. Reactive oxygen species (ROS) were quantified by flow cytometry. Relative levels of fibronectin-1 (FN1), collagen-I α(1) (COL1A1), endothelin-1 (EDN1) and haem oxygenase-1 (HMOX1) mRNA and protein were quantified by real-time reverse transcription-polymerase chain reaction and Western blotting, respectively. Absolute levels of FN1 and COLIA1 were quantified by enzyme-linked immunosorbent assay.

RESULTS

β-(3,4-Dihydroxyphenyl)lactic acid significantly decreased ROS levels, and EDN1 mRNA and protein levels, in dose- and time-dependent manners. HMOX1 mRNA and protein levels were significantly increased by β-(3,4-dihydroxyphenyl)lactic acid in dose-dependent manners. COL1A1 and FN1 mRNA and protein levels were significantly decreased by β-(3,4-dihydroxyphenyl)lactic acid in dose- and time-dependent manners.

CONCLUSIONS

β-(3,4-Dihydroxyphenyl)lactic acid inhibited oxidative stress and reversed increases in FN1 and COLIA1 induced by high glucose levels in HPMCs. This may contribute to a protective role in peritoneal fibrosis.

Glucose but not N-acetylglucosamine accelerates in vitro senescence of human peritoneal mesothelial cells

BACKGROUND

Preservation of the mesothelial cells (MCs) is crucial for longevity of the peritoneal dialysis membrane. Glucose accelerates aging of MC and we tested whether N-acetylglucosamine (NAG) has an identical effect.

METHODS

Replicative aging of MCs was studied during 10 passages performed every three days in cells cultured in standard medium or in medium supplemented with Glucose 30 mmol/L or NAG 30 mmol/L. Changes in population doubling time and ß-galactosidase activity were used as an index of aging and compared with other cellular parameters.

RESULTS

Repeated passages of MC cause their aging, as reflected by prolongation of the population doubling time, increased ß-galactosidase activity, oxidative stress and release of cytokines. Healing of injured mesothelial monolayer is impaired in senescent cells. Glucose accelerates in vitro aging of MC, whereas NAG does not cause this effect.

CONCLUSIONS

Replacement of glucose with NAG in the dialysis fluid can slow down aging of MC.

Exogenous N-acetylglucosamine increases hyaluronan production in cultured human dermal fibroblasts

Application of hyaluronan (HA) containing cosmetic products to the skin is reported to moisturize and restore elasticity thereby achieving an antiwrinkle effect. In the skin, HA can be synthesized by dermal fibroblasts and N-acetylglucosamine (NAG) is a precursor for HA biosynthesis in the body. To study the effects of exogenous NAG on HA production in human dermal fibroblasts, HA production and HA-synthesizing enzymes 1, 2 and 3 mRNA expression in cultured human dermal fibroblasts were measured by ELISA and RT-PCR, respectively. The results showed that NAG promoted HA production while had no effect on the expression of HA-synthesizing enzymes 1, 2 and 3 mRNA in human dermal fibroblasts.