Identification of Glycochenodeoxycholate 3‐O‐Glucuronide and Glycodeoxycholate 3‐O‐Glucuronide as Highly Sensitive and Specific OATP1B1 Biomarkers

The aim of this study was to investigate the sensitivity and specificity of endogenous glycochenodeoxycholate and glycodeoxycholate 3‐O‐glucuronides (GCDCA‐3G and GDCA‐3G) as substrates for organic anion transporting polypeptide 1B1 (OATP1B1) in humans. We measured fasting levels of plasma GCDCA‐3G and GDCA‐3G using liquid chromatography‐tandem mass spectrometry in 356 healthy volunteers. The mean plasma levels of both compounds were ~ 50% lower in women than in men (P = 2.25 × 10(−18) and P = 4.73 × 10(−9)). In a microarray‐based genome‐wide association study, the SLCO1B1 rs4149056 (c.521T>C, p.Val174Ala) variation showed the strongest association with the plasma GCDCA‐3G (P = 3.09 × 10(−30)) and GDCA‐3G (P = 1.60 × 10(−17)) concentrations. The mean plasma concentration of GCDCA‐3G was 9.2‐fold (P = 8.77 × 10(−31)) and that of GDCA‐3G was 6.4‐fold (P = 2.45x10(−13)) higher in individuals with the SLCO1B1 c.521C/C genotype than in those with the c.521T/T genotype. No other variants showed independent genome‐wide significant associations with GCDCA‐3G or GDCA‐3G. GCDCA‐3G was highly efficacious in detecting the SLCO1B1 c.521C/C genotype with an area under the receiver operating characteristic curve of 0.996 (P < 0.0001). The sensitivity (98–99%) and specificity (100%) peaked at a cutoff value of 180 ng/mL for men and 90 ng/mL for women. In a haplotype‐based analysis, SLCO1B1*5 and *15 were associated with reduced, and SLCO1B1 *1B, *14, and *35 with increased OATP1B1 function. In vitro, both GCDCA‐3G and GDCA‐3G showed at least 6 times higher uptake by OATP1B1 than OATP1B3 or OATP2B1. These data indicate that the hepatic uptake of GCDCA‐3G and GDCA‐3G is predominantly mediated by OATP1B1. GCDCA‐3G, in particular, is a highly sensitive and specific OATP1B1 biomarker in humans.