LAUSR

Multiple endogenous compounds have been proposed as candidate biomarkers to monitor organic anion transporting polypeptide (OATP) function in preclinical species or humans. Previously, we demonstrated that coproporphyrins (CPs) I and III are appropriate clinical markers to evaluate OATP inhibition and recapitulate clinical drug-drug interactions (DDIs). In the present study, we investigated bile acids (BAs) dehydroepiandrosterone sulfate (DHEAS), hexadecanedioate (HDA), and tetradecanedioate (TDA) in plasma as endogenous probes for OATP inhibition and compared these candidate probes to CPs. All probes were determined in samples from a single study that examined their behavior and their association with rosuvastatin (RSV) pharmacokinetics after administration of an OATP inhibitor rifampin (RIF) in healthy subjects. Among endogenous probes examined, RIF significantly increased maximum plasma concentration (Cmax) and area under the concentration-time curve (AUC)(0–24h) of fatty acids HDA and TDA by 2.2- to 3.2-fold. For the 13 bile acids in plasma examined, no statistically significant changes were detected between treatments. Changes in plasma DHEAS did not correlate with OATP1B inhibition by RIF. On the basis of the magnitude of effects for the endogenous compounds that demonstrated significant changes from baseline over interindividual variations, the overall rank order for the AUC change was found to be CP I > CP III > HDA ≈ TDA ≈ RSV > > BAs. Collectively, these results reconfirmed that CPs are novel biomarkers suitable for clinical use. In addition, HDA and TDA are useful for OATP functional assessment. Since these endogenous markers can be monitored in conjunction with pharmacokinetics analysis, the CPs and fatty acid dicarboxylates, either alone or in combination, offer promise of earlier diagnosis and risk stratification for OATP-mediated DDIs.