Emodin ameliorates glucose-induced matrix synthesis in human peritoneal mesothelial cells

Abstract

Background. Prolonged exposure of human peritoneal mesothelial cells (HPMC) to high glucose concentrations in peritoneal dialysate is the principal factor leading to matrix accumulation and thickening of the peritoneal membrane, accompanied by progressive deterioration of transport functions. These changes are mediated in part through protein kinase C (PKC) activation and the induction of transforming growth factor-beta 1 (TGF-β1). Emodin (3-methyl-1,6,8 trihydroxyanthraquinone) has previously been demonstrated to reduce cell proliferation and fibronectin synthesis in cultured mesangial cells. How emodin modulates glucose-induced abnormalities in HPMC has not been elucidated and thus constitutes the theme of this study. Methods. We investigated the effects of emodin on the expression of PKCα, TGF-β1, fibronectin, and collagen type I in HPMC, and its effects on HPMC proliferation under physiologic (5 mmol) or high (30 mmol) glucose concentrations. Results. Exposure of HPMC cultured with 5 mmol or 30 mmol D-glucose to emodin (20 μg/mL) resulted in an initial lag of proliferation by 2.3 to 2.7 days, but did not affect cell viability or morphology at confluence. D-glucose (30 mmol) induced TGF-β1 secretion in a time-dependent manner (3.72 ± 0.29 and 4.30 ± 0.50 pg/μg cellular protein at 24 hours and 48 hours respectively, compared to 2.13 ± 0.23 and 2.65 ± 0.32 pg/μg cellular protein at 24 hours and 48 hours, respectively for 5 mmol glucose; P < 0.001 at both time points). Such induction was ameliorated by emodin (20 μg/mL) (TGF-β1 concentration 2.25 ± 0.15 and 2.96 ± 0.33 pg/μg cellular protein at 24 hours and 48 hours, respectively, in the presence of emodin and 30 mmol D-glucose; P < 0.001 compared to 30 mmol D-glucose alone at both time points). Induction of TGF-β1 synthesis by 30 mmol D-glucose was associated with induction of PKCα, phosphorylation of cAMP-responsive element binding protein (CREB) and activating transcription factor-1 (ATF-1), and increased fibronectin and type I collagen translation. Emodin abrogated all these effects of concentrated glucose. Immunohistochemical staining showed that 30 mmol D-glucose induced cytoplasmic, perinuclear, and extracellular fibronectin and type I collagen expression by HPMC. Emodin reduced 30 mmol D-glucose-induced cytoplasmic and extracellular matrix synthesis to near basal levels. Conclusion. Our findings demonstrate that emodin ameliorates the undesirable effects of concentrated glucose on HPMC via suppression of PKC activation and CREB phosphorylation, and suggest that emodin may have a therapeutic potential in the prevention or treatment of glucose-induced structural and functional abnormalities in the peritoneal membrane.