High glucose inhibits glucose uptake in renal proximal tubule cells by oxidative stress and protein kinase C

Abstract

Background. High glucose has been considered to play an important role in alteration of renal proximal tubule transporter's activity. This study examined the mechanism by which high glucose modulates α-methyl-D- glucopyranoside (α-MG) uptake in primary cultured rabbit renal proximal tubule cells (PTCs). Methods. PTCs were incubated with 25 mmol/L glucose alone or combined with taurine, ascorbic acid, catalase, staurosporine, and bisindolylmaleimide I. Then α-MG uptake and lipid peroxide (LPO) formation were examined. Results. Twenty-five mmol/L glucose from four hours, but not 25 mmol/L mannitol, inhibited α-MG uptake by 23% compared with 5 mmol/L glucose (control). In the study to examine the relationship of oxidative stress in the high-glucose-induced inhibition of α-MG uptake, 25 mmol/L glucose significantly increased LPO by 27% compared with control. However, 10 mmol/L glucose did not affect α-MG uptake and LPO formation. Taurine (2 mmol/L), ascorbic acid (1 mmol/L), endogenous antioxidants, or catalase (600 U/mL) significantly blocked 25 mmol/L glucose-induced increase of LPO formation and inhibition of α-MG uptake. In the experiment to examine the effects of protein kinase C on LPO formation, 12-O-tetradecanoylphorbol-13- acetate (TPA; 100 ng/mL) increased LPO formation, and staurosporine (10-7 mol/L) and bisindolylmaleimide I (10-6 mol/L) totally blocked 25 mmol/L glucose-induced increase of LPO formation and inhibition of α-MG uptake. In addition, taurine reduced TPA-induced increase of LPO formation and inhibition of α-MG uptake. Conclusion. High glucose induces, in part, the inhibition of α-MG uptake through LPO formation, and activation of protein kinase C may play a role in high-glucose-induced LPO formation in the primary cultured rabbit renal PTCs.