Nitric oxide synthase-mediated alteration of intestinal P-glycoprotein under hyperglycemic stress

P-glycoprotein (P-gp), one of the important drug-efflux pumps, is known to be affected by pathological conditions such as inflammation or infection. Recently, it is reported that high glucose or hyperglycemia can alter P-gp expression levels at the blood-brain barrier or in kidney, although the details are still unknown. Here, we analyzed the alteration of intestinal P-gp expression and function in the development of diabetes and elucidated the mechanisms. Type 1 diabetes was induced in male ddY mice by an i.p. injection of streptozotocin (STZ) (230 mg/kg). We analyzed ileal P-gp expression and drug efflux activity using western blot analysis and an in situ closed loop method, respectively. Additionally, we analyzed ileal nitric oxide synthase (NOS) activity using colorimetric method. A significant reduction of P-gp expression level in ileum was found on day 9 after STZ administration. In contrast, a remarkable decrease in drug efflux activity was observed on days 3 and 9. Interestingly, NOS activity in ilea was significantly increased on day 9. The decrease of P-gp expression levels observed on day 9 was completely suppressed by L-NG-nitroarginine methyl ester (L-NAME), a broad range NOS inhibitor, or aminoguanidine, a specific inducible NOS (iNOS) inhibitor. In addition, P-gp expression level in ileum was significantly decreased by administration of NOR5, a NO donor. These results indicate the possibility that NO, produced by iNOS in the ileum, is involved in the alteration of ileal P-gp expression and function under STZ-induced diabetic conditions.