Empagliflozin, a sodium glucose cotransporter-2 inhibitor, ameliorates peritoneal fibrosis via suppressing TGF-β/Smad signaling

Sodium glucose cotransporter-2 (SGLT-2) inhibitor has been reported to exert a glucose-lowering effect in the peritoneum exposed to peritoneal dialysis solution. However, whether SGLT-2 inhibitors can regulate peritoneal fibrosis by suppressing TGF-β/Smad signaling is unclear. We aimed to (i) examine the effect of the SGLT-2 inhibitor empagliflozin in reducing inflammatory reaction and preventing peritoneal dialysis solution-induced peritoneal fibrosis and (ii) elucidate the underlying mechanisms. High-glucose peritoneal dialysis solution or transforming growth factor β1 (TGF-β1) was used to induce peritoneal fibrosis in vivo, in a mouse peritoneal dialysis model (C57BL/6 mice) and in human peritoneal mesothelial cells in vitro, to stimulate extracellular matrix accumulation. The effects of empagliflozin and adeno-associated virus-RNAi, which is used to suppress SGLT-2 activity, on peritoneal fibrosis and extracellular matrix were evaluated. The mice that received chronic peritoneal dialysis solution infusions showed typical features of peritoneal fibrosis, including markedly increased peritoneal thickness, excessive matrix deposition, increased peritoneal permeability, and upregulated α-smooth muscle actin and collagen I expression. Empagliflozin treatment or downregulation of SGLT-2 expression significantly ameliorated these pathological changes. Inflammatory cytokines (TNF-α, IL-1β, IL-6) and TGF-β/Smad signaling-associated proteins, such as TGF-β1 and phosphorylated Smad (p-Smad3), decreased in the empagliflozin-treated and SGLT-2 downregulated groups. In addition, empagliflozin treatment and downregulation of SGLT-2 expression reduced the levels of inflammatory cytokines (TNF-α, IL-1β, IL-6), TGF-β1, α-smooth muscle actin, collagen I, and p-Smad3 accumulation in human peritoneal mesothelial cells. Collectively, these results indicated that empagliflozin exerted a clear protective effect on high-glucose peritoneal dialysis-induced peritoneal fibrosis via suppressing TGF-β/Smad signaling.

MicroRNA-21 promotes the progression of peritoneal fibrosis through the activation of the TGF-β/Smad signaling pathway: An in vitro and in vivo study

The present study aimed to explore the roles of microRNA-21 (miR‑21) and the transforming growth factor-β (TGF-β)/Smad signaling pathway in the development of peritoneal fibrosis (PF). First, dialysis effluents from 30 patients with PF were collected, and after the establishment of a mouse model of PF, hematoxylin and eosin (H&E) and Masson's staining were used to observe peritoneal tissues, inflammatory cells and blood vessels. High glucose was used to stimulate human peritoneal mesothelial cell lines and these stimulated cells were then transfected with miR‑21 inhibitor. Immunofluorescence microscopy was applied for the observation of the transfected cells. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to detect the expression of miR‑21, and RT-qPCR and western blot analysis were used to detect the mRNA and protein expression of Zonula occludens-1 (ZO-1), TGF-β, Smad, vimentin and connective-tissue growth factor (CTGF). The mRNA and protein expression levels TGF-β, Smad-3, vimentin and CTGF were elevated, while ZO-1 mRNA and protein expression was decreased with the prolonged duration of dialysis treatment in the patients with PF. The experiments using the mouse model of PF revealed that the peritoneal connective tissue was thickened, while the numbers of inflammatory cells and blood vessels were increased. The expression levels of miR‑21, and the mRNA and protein expression levels of TGF-β, Smad-3, vimentin and CTGF were increased over time, whereas the mRNA and protein expression levels ZO-1 constantly decreased in the mice in the experimental group. Moreoever, the expression of miR‑21 positively correlated with the expression levels of TGF-β, Smad-3, vimentin and CTGF, while it negatively correlated with the expression of ZO-1. The results of H&E and Masson's staining revealed that miR‑21 expression was associated with the degree of PF. These findings thus indicate that miR‑21 promotes the progression of PF through the activation of the TGF-β/Smad signaling pathway.

Preservation of peritoneal morphology and function by pentoxifylline in a rat model of peritoneal dialysis: molecular studies

BACKGROUND

High-glucose (HG) content of dialysate accelerated peritoneal fibrosis. We investigated in vitro mechanisms and the in vivo potential of pentoxifylline (PTX) to prevent this fibrogenic process.

METHODS

For human peritoneal mesothelial cell (HPMC) culture, a normal-glucose (NG, 5.5 mM) or HG (138 mM) medium was established through pilot experiments. The rat peritoneal dialysis (PD) model consists of four groups (n = 8): group 1, intraperitoneal (IP) HG (4.25%) solution; group 2, as group 1 plus daily IP PTX (4 mg/in 1 h); group 3, IP PTX and group 4 as control.

RESULTS

In HPMC culture, PTX significantly prevented HG-stimulated gene and protein production of collagen and transforming growth factor-beta1 (TGF-ss1) (reduction rate of 72-81%). The p38 mitogen-activated protein kinase (MAPK) pathway was activated significantly in HG-treated HPMCs. Blockade of p38 MAPK by SB203580 (25 microM) or PTX (300 microg/ml) resulted in an effective suppression of collagen and TGF-ss1 gene expression in HG-cultured HPMCs. In PD experimental animals, peritoneal thickness and collagen expression in the peritoneum were significantly increased in HG-treated rats, and was attenuated by PTX (P < 0.01). Impaired peritoneal ultrafiltration (1.9 +/- 0.5 ml versus 2.4 +/- 0.4 ml, P < 0.05) and stimulated proinflammatory IL-6, MCP-1 and TGF-beta1 activation were observed in HG-treated rats. PTX well preserved the functional characteristics of peritoneum and cytokine profiles.

CONCLUSIONS

These in vitro and in vivo data suggest that PTX may have therapeutic benefits for the prevention or retardation of peritoneal fibrosis.