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 similar to 50% lower in women than in men (P = 2.25 x 10(-18) and P = 4.73 x 10(-9)). In a microarray-based genome-wide association study, theSLCO1B1rs4149056 (c.521T>C, p.Val174Ala) variation showed the strongest association with the plasma GCDCA-3G (P = 3.09 x 10(-30)) and GDCA-3G (P = 1.60 x 10(-17)) concentrations. The mean plasma concentration of GCDCA-3G was 9.2-fold (P = 8.77 x 10(-31)) and that of GDCA-3G was 6.4-fold (P = 2.45x10(-13)) higher in individuals with theSLCO1B1c.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 theSLCO1B1c.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*5and*15were associated with reduced, andSLCO1B1*1B, *14, and *35with 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.