High glucose solution and spent dialysate stimulate the synthesis of transforming growth factor-beta(1) of human peritoneal mesothelial cells: Effect of cytokine costimulation

Abstract

Objective:To investigate the effect of high glucose and spent peritoneal dialysate on the transforming growth factor-beta(1) (TGF beta(1)) synthesis of cultured human peritoneal mesothelial cells (HPMCs) and to examine the effect of costimulation with high glucose or spent dialysate, and cytokines, interleukin-1 beta (IL-1 beta), and tumor necrosis factor-alpha (TNF alpha) on TGF beta(1) synthesis of HPMCs. Design: HPMCs were exposed to different concentrations of glucose (30, 60, and 90 mmol/L) or spent peritoneal dialysate for 48 hours in the absence or presence of IL-1 beta (1 ng/mL) and TNF alpha(1 ng/mL). TGF beta(1) mRNA expression was assessed by Northern blot analysis and TGF beta(1) protein release by Western blot analysis and enzymelinked immunosorbent assay (ELISA). Results: Exposure of HPMCs to high glucose conditions (30, 60, and 90 mmol/L of D-glucose) induced 2.3-, 3.6-, and 4.0-fold increases in TGF beta(1) mRNA expression of HPMC with enhanced TGF beta(1) protein synthesis and secretion into the media, whereas there were no significant changes in TGF beta(1) synthesis with equimolar concentrations of D-mannitol. Incubation with spent dialysate also significantly increased TGF beta(1) mRNA expression and protein secretion compared to control media (p < 0.05). Stimulation with IL-1 beta (1 ng/mL) or TNF alpha (1 ng/mL) resulted in a significant increase in TGF beta(1) mRNA expression after 48 hours: 2.7 and 2.1 times the control level, respectively. However,TNF alpha-induced increase in TGF beta(1), mRNA expression was not translated into TGF beta(1) protein secretion, while IL-1 beta stimulation induced a significant increase in TGF beta(1) protein secretion as well as TGF beta(1) mRNA expression. Combined stimulation by high glucose or spent dialysate, together with IL-1 beta or TNF alpha showed a greater increase in TGF beta(1) mRNA expression and protein secretion compared to stimulation by high glucose or spent dialysate alone. Conclusion: Our results clearly show that high glucose solution and spent dialysate themselves might be sufficient to stimulate the production of TGF beta(1) by peritoneal mesothelial cells. In peritoneal dialysis patients, this state of chronic induction of TGF beta(1) is further exacerbated in the presence of peritonitis because of the stimulatory effeet of proinflammatory cytokines, resulting in augmented TGF beta(1) synthesis, thus promoting peritoneal fibrosis.