Nitric oxide differentially regulates renal ATP-binding cassette transporters during endotoxemia

Nitric oxide (NO) is an important regulator of renal transport processes. In the present study, we investigated the role of NO, produced by inducible NO synthase (iNOS), in the regulation of renal ATP-binding cassette (ABC) transporters in vivo during endotoxemia. Wistar–Hannover rats were injected with lipopolysaccharide (LPS+) alone or in combination with the iNOS inhibitor, aminoguanidine. Controls received detoxified LPS (LPS−). After LPS+, proximal tubular damage and a reduction in renal function were observed. Furthermore, iNOS mRNA and protein, and the amount of NO metabolites in plasma and urine, increased compared to the LPS− group. Coadministration with aminoguanidine resulted in an attenuation of iNOS induction and reduction of renal damage. Gene expression of 20 ABC transporters was determined. After LPS+, a clear up-regulation in Abca1, Abcb1/P-glycoprotein (P-gp), Abcb11/bile salt export pump (Bsep), and Abcc2/multidrug resistance protein (Mrp2) was found, whereas Abcc8 was down-regulated. Up-regulation of Abcc2/Mrp2 was accompanied by enhanced calcein excretion. Aminoguanidine attenuated the effects on transporter expression. Our data indicate that NO, produced locally by renal iNOS, regulates the expression of ABC transporters in vivo. Furthermore, we showed, for the first time, expression and subcellular localization of Abcb11/Bsep in rat kidney

Renal glucuronidation and multidrug resistance protein 2-/ multidrug resistance protein 4-mediated efflux of mycophenolic acid : interaction with cyclosporine and tacrolimus

Mycophenolic acid (MPA) is an immunosuppressant used in transplant rejection, often in combination with cyclosporine (CsA) and tacrolimus (Tac). The drug is cleared predominantly via the kidneys, and 95% of the administered dose appears in urine as 7-hydroxy mycophenolic acid glucuronide (MPAG). The current study was designed to unravel the renal excretory pathway of MPA and MPAG, and their potential drug-drug interactions. The role of multidrug resistance protein (MRP) 2 and MRP4 in MPA disposition was studied using human embryonic kidney 293 (HEK293) cells overexpressing the human transporters, and in isolated, perfused kidneys of Mrp2-deficient rats and Mrp4-deficient mice. Using these models, we identified MPA as substrate of MRP2 and MRP4, whereas its MPAG appeared to be a substrate of MRP2 only. CsA inhibited MPAG transport via MRP2 for 50% at 8 μM (P < 0.05), whereas Tac had no effect. This was confirmed by cell survival assays, showing a 10-fold increase in MPA cytotoxicity (50% reduction in cell survival changed from 12.2 ± 0.3 μM to 1.33 ± 0.01 μM by MPA + CsA; P < 0.001) and in perfused kidneys, showing a 50% reduction in MPAG excretion (P < 0.05). The latter effect was observed in Mrp2-deficient animals as well, supporting the importance of Mrp2 in MPAG excretion. CsA, but not Tac, inhibited MPA glucuronidation by rat kidney homogenate and human uridine 5'-diphospho-glucuronosyltransferase-glucuronosyltransferase 1A9 (P < 0.05 and P < 0.01, respectively). We conclude that MPA is a substrate of both MRP2 and MRP4, but MRP2 is the main transporter involved in renal MPAG excretion. In conclusion, CsA, but not Tac, influences MPA clearance by inhibiting renal MPA glucuronidation and MRP2-mediated MPAG secretion