Effects of fibrates on human organic anion-transporting polypeptide 1B1-, multidrug resistance protein 2- and P-glycoprotein-mediated transport

A nonlinear least squares program (MULTI) for microcomputers was developed. The program is written in BASIC programming language. Four algorithms, (1) Gauss-Newton method, (2) damping Gauss-Newton method, (3) modified Marquardt method and (4) simplex method, can be used for nonlinear curve fitting in MULTI. Up to five pharmacokinetic equations, which are voluntarily defined by the user, are simultaneously fitted to observed time courses. The executions of MULTI are demonstrated for time courses of ampicillin and oxacillin in man.

Cyclosporine (INN, ciclosporin) increases the systemic exposure of all statins. Therefore rosuvastatin pharmacokinetic parameters were assessed in an open-label trial involving stable heart transplant recipients (> or =6 months after transplant) on an antirejection regimen including cyclosporine. Rosuvastatin has been shown to be a substrate for the human liver transporter organic anion transporting polypeptide C (OATP-C). Inhibition of this transporter could increase plasma concentrations of rosuvastatin. Therefore the effect of cyclosporine on rosuvastatin uptake by cells expressing OATP-C was also examined. Ten subjects were assessed while taking 10 mg rosuvastatin for 10 days; 5 of these were then assessed while taking 20 mg rosuvastatin for 10 days. Rosuvastatin steady-state area under the plasma concentration-time curve from time 0 to 24 hours [AUC(0-24)] and maximum observed plasma concentration (Cmax) were compared with values in controls (historical data from 21 healthy volunteers taking 10 mg rosuvastatin). Rosuvastatin uptake by OATP-C-transfected Xenopus oocytes was also studied by use of radiolabeled rosuvastatin with and without cyclosporine. In transplant recipients taking 10 mg rosuvastatin, geometric mean values and percent coefficient of variation for steady-state AUC(0-24) and Cmax were 284 ng. h/mL (31.3%) and 48.7 ng/mL (47.2%), respectively. In controls, these values were 40.1 ng. h/mL (39.4%) and 4.58 ng/mL (46.9%), respectively. Compared with control values, AUC(0-24) and Cmax were increased 7.1-fold and 10.6-fold, respectively, in transplant recipients. In transplant recipients taking 20 mg rosuvastatin, these parameters increased less than dose-proportionally. Rosuvastatin had no effect on cyclosporine blood concentrations. The in vitro results demonstrate that rosuvastatin is a good substrate for OATP-C-mediated hepatic uptake (association constant, 8.5 +/- 1.1 micromol/L) and that cyclosporine is an effective inhibitor of this process (50% inhibition constant, 2.2 +/- 0.4 micromol/L when the rosuvastatin concentration was 5 micromol/L). Rosuvastatin exposure was significantly increased in transplant recipients on an antirejection regimen including cyclosporine. Cyclosporine inhibition of OATP-C-mediated rosuvastatin hepatic uptake may be the mechanism of the drug-drug interaction. Coadministration of rosuvastatin with cyclosporine needs to be undertaken with caution.

Pitavastatin, a novel potent 3-hydroxymethylglutaryl-CoA reductase inhibitor, is selectively distributed to the liver in rats. However, the hepatic uptake mechanism of pitavastatin has not been clarified yet. In the present study, we investigated the contribution of organic anion transporting polypeptide 2 (OATP2/OATP1B1) and OATP8 (OATP1B3) to pitavastatin uptake using transporter-expressing HEK293 cells and human cryopreserved hepatocytes. Uptake studies using OATP2- and OATP8-expressing cells revealed a saturable and Na(+)-independent uptake, with K(m) values of 3.0 and 3.3 microM for OATP2 and OATP8, respectively. To determine which transporter is more important for its hepatic uptake, we proposed a methodology for estimating their quantitative contribution to the overall hepatic uptake by comparing the uptake clearance of pitavastatin with that of reference compounds (a selective substrate for OATP2 (estrone-3-sulfate) and OATP8 (cholecystokinin octapeptide) in expression systems and human hepatocytes. The concept of this method is similar to the so-called relative activity factor method often used in estimating the contribution of each cytochrome P450 isoform to the overall metabolism. Applying this method to pitavastatin, the observed uptake clearance in human hepatocytes could be almost completely accounted for by OATP2 and OATP8, and about 90% of the total hepatic clearance could be accounted for by OATP2. This result was also supported by estimating the relative expression level of each transporter in expression systems and hepatocytes by Western blot analysis. These results suggest that OATP2 is the most important transporter for the hepatic uptake of pitavastatin in humans.