Discovery of novel plasma biomarkers for OATP1B1 activity using nontargeted metabolomics.

Organic anion transporting polypeptide (OATP) 1B1 is an influx transporter mediating the hepatic uptake of many compounds through the cell membrane. OATP1B1 activity fluctuates due to various factors; hence, evaluating OATP1B1 activity is important for pharmacokinetic studies and precision dosing of substrate drugs. This study aimed to discover novel biomarker candidates using nontargeted metabolomics. Blood samples of 432 individuals selected from the Japanese general population and 264 patients were analyzed. The samples were pretreated by more vigorous extraction methods than those conventionally used in metabolomics, and metabolites were measured comprehensively using ultraperformance liquid chromatography coupled to quadrupole time-of-flight mass spectrometry. These participants were classified by a major OATP1B1 polymorphism, the c.521T>C variant, into the OATP1B1 normal function group (c.521TT) and the decreased function group (c.521TC and c.521CC). Specific biomarker candidates were extracted from metabolome profiles by multivariate analyses in the general population and patients separately. Four novel candidate compounds were identified to be probably 13'-hydroxy-gamma-tocopherol, 6-deoxodolichosterone, (20R or 20S)-24-hydroxygeminivitamin D3, and glycochenodeoxycholate-3-O-glucuronide (GCDCA-3G). The intensities of the 4 compounds were compared between the OATP1B1 normal function group and the decreased function group and among 3 groups classified by OATP1B1 c.521T>C polymorphism. GCDCA-3G, 13'-hydroxy-gamma-tocopherol, and (20R or 20S)-24-hydroxygeminivitamin D3 clearly discriminated against differences among 3 c.521T>C genotype groups, whereas 6-deoxodolichosterone discriminated between the OATP1B1 normal function group and the decreased function group. These results confirm the robustness and specificity of GCDCA-3G as an OATP1B1 biomarker and propose 13'-hydroxy-gamma-tocopherol, 6-deoxodolichosterone, and (20R or 20S)-24-hydroxygeminivitamin D3 as potentially useful novel OATP1B1 functional biomarkers. SIGNIFICANCE STATEMENT: Endogenous biomarkers for drug transporters are valuable tools for predicting adverse events caused by substrate drugs. This study aimed to explore novel biomarker candidates for organic anion transporting polypeptide (OATP) 1B1 activity using the nontargeted metabolomics approach with more vigorous pretreatment using solid-phase extraction and liquid-liquid extraction. Three novel and one conventional OATP1B1 biomarker candidates were detected by our nontargeted metabolomics. These findings contribute to the advancement of biomarker research for OATP1B1 and support further exploration of novel biomarkers.