Rhein reverses the diabetic phenotype of mesangial cells over-expressing the glucose transporter (GLUT1) by inhibiting the hexosamine pathway

Background and purpose: Rhein, an anthraquinone compound isolated from rhubarb, has been proved effective in treatment of experimental diabetic nephropathy (DN). To explore the mechanism of its therapeutic effect on DN, rhein was tested for its effect on the hexosamine pathway. Experimental approach: The influence of rhein on cellular hypertrophy, fibronectin synthesis, glucose uptake, glutamine: fructose 6-phosphate aminotransferase (GFAT) activity, UDP-N-acetylglucosamine (UDP-GlcNAc) level and TGF-beta 1 and p21 expression was evaluated in MCGT1 cells, a GLUT1 transgenic rat mesangial cell line. GFAT activity in normal rat mesangial cells in high glucose concentrations and in vitro was also measured. Key results: Significantly increased fibronectin synthesis, cellular hypertrophy, much higher GFAT activity and UDP-GIcNAc level and increased TGF-beta 1 and p21 expression were found in MCGT1 cells cultured in normal glucose concentration. Rhein treatment decreased all these features of MCGT1 cells but did not exert a direct effect on GFAT enzymatic activity. Conclusions and implications: There was over-activity of the hexosamine pathway in MCGT1 cells, which may explain the higher expression of TGF-beta 1 and p21, the cellular hypertrophy and the increased expression of extracellular matrix ( ECM) components in the cells. By inhibiting the increased activity the hexosamine pathway, rhein decreased TGF-beta 1 and p21 expression and thus contributed to the decreased cellular hypertrophy and ECM synthesis. Inhibition of the hexosamine pathway may be one of the mechanism through which rhein exerts its therapeutic role in diabetic nephropathy.