Preventive effect of culture supernatant of epithelial-like peritoneal mesothelial cells on peritoneal fibrosis.

Peritoneal fibrosis (PF) is a primary reason for discontinuing peritoneal dialysis, which involves characteristic changes of peritoneal mesothelial cells (PMCs). We previously reported preventive effects of implanting human epithelial-like PMCs (P-Epi) for mouse PF caused by mechanical peritoneum scrapings. In the present study, we analysed the preventive effects of culture supernatant of P-Epi in PF. Concentrated culture supernatant of P-Epi or human fibroblast-like PMCs (P-Fibro) or vehicles was injected into nude mice that had undergone mechanical scraping of the parietal and visceral peritoneum, and thickness and amount of adhesions were analysed. Although increased peritoneal adhesions and peritoneum thickening were observed in the vehicle-injected positive control group compared to the sham operation group, fewer number of adhesions and less thickness were observed in the mice treated with culture supernatant of P-Epi, but not P-Fibro, compared to the vehicle-injected positive controls. Immunofluorescent analysis revealed that the expression of extracellular matrix, type I collagen and fibronectin, was lower in the mice treated with culture supernatant of P-Epi than in the vehicle-injected positive controls. In addition, exosomes from P-Epi significantly reduced transforming growth factor-β (TGF-β)-induced expressions of type I collagen and fibronectin in 3T3 fibroblast cells. Collectively, culture supernatant of P-Epi has preventive effects on PF, thus cell therapy is not necessarily required. Further exploration of substances secreted by P-Epi and their protective mechanisms could lead to the development of therapeutic strategies to limit PF.