Molecular and cellular pharmacologyHyperglycemia induced down-regulation of renal P-glycoprotein expression

The purpose of this study is to investigate the regulation of P-glycoprotein expression in the kidney under diabetic condition. Renal P-glycoprotein expression was examined in inbred mice with type 1 or type 2 diabetes by Western blotting. The underlying mechanisms of P-glycoprotein regulation were examined in Madin-Darby canine kidney type II (MDCK-II) cells by Western blotting or qRT-PCR. 3H-digoxin uptake was measured for P-glycoprotein activity in cells under various treatments. The results showed that P-glycoprotein expression was lower in kidneys of diabetic mice than in controls. In MDCK-II cells, treatments with insulin or IL-6 did not cause any change in P-glycoprotein expression, whereas TNF-α tended to increase P-glycoprotein expression at a concentration of 1 ng/ml. On the other hand, P-glycoprotein expression was reduced under high glucose conditions (450 mg/dl), while superoxide production was increased, and the reduction in P-glycoprotein expression was abolished by N-acetylcysteine (an antioxidant) and staurosporine (a nonselective PKC inhibitor). Treatment with oxidizing agents (H2O2, BSO) or PMA (a PKC activator) reduced P-glycoprotein expression. Antioxidant (N-acetylcysteine or glutathione) co-treatment abolished the H2O2-induced and BSO-induced reduction in P-glycoprotein expression, whereas it did not prevent the effect of PMA. The PMA-induced P-glycoprotein down-regulation was prevented by co-treatment of LY333531 (a PKC-β inhibitor). 3H-digoxin levels were higher in MDCK-II cells with high glucose, PMA or H2O2 treatments. In conclusion, P-glycoprotein expression is lower in kidneys of diabetic mice and in MDCK-II cells under high glucose conditions. Hyperglycemia induced reactive oxygen species and activated PKC in MDCK-II cells, leading to the decrease in P-glycoprotein expression.