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 6.4fold (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.

Study HighlightsWHAT IS THE CURRENT KNOWLEDGE ON THE TOPIC? Coproporphyrin I (CPI) and coproporphyrin III (CPIII) are promising biomarkers to measure organic anion transporting polypeptide (OATP) 1B activity in humans. In vitro data suggest that CPI and CPIII are better substrates for OATP1B1 than for OATP1B3. WHAT QUESTION DID THIS STUDY ADDRESS? Are CPI and CPIII sensitive OATP1B1 biomarkers in humans? What is the performance of CPI and CPIII compared with the highly specific and sensitive OATP1B1 endogenous probes glycochenodeoxycholate 3-O-glucuronide (GCDCA-3G) and glycodeoxycholate 3-O-glucuronide (GDCA-3G)?WHAT DOES THIS STUDY ADD TO OUR KNOWLEDGE? CPI clearly outperformed CPIII in distinguishing the genetically poor, decreased, increased, and highly increased OATP1B1 function groups, indicating higher sensitivity as an OATP1B1 biomarker. However, GCDCA-3G showed an even better sensitivity than CPI. Careful standardization of plasma CP handling and storing is needed for reliable quantification. HOW MIGHT THIS CHANGE CLINICAL PHARMA-COLOGY OR TRANSLATIONAL SCIENCE?  CPI may be a useful endogenous probe substrate along with the more sensitive GCDCA-3G for measuring OATP1B1 activity during drug development and in clinical practice.

To identify the genetic basis of interindividual variability in montelukast exposure, we determined its pharmacokinetics and sequenced 379 pharmacokinetic genes in 191 healthy volunteers. An intronic single nucleotide variation (SNV), strongly linked with UGT1A3*2, associated with reduced area under the plasma concentration–time curve (AUC0‐∞) of montelukast (by 18% per copy of the minor allele; P = 1.83 × 10−10). UGT1A3*2 was associated with increased AUC0‐∞ of montelukast acyl‐glucuronide M1 and decreased AUC0‐∞ of hydroxymetabolites M5R, M5S, and M6 (P < 10−9). Furthermore, SNVs in SLCO1B1 and ABCC9 were associated with the AUC0‐∞ of M1 and M5R, respectively. In addition, a candidate gene analysis suggested that CYP2C8 and ABCC9 SNVs also affect the AUC0‐∞ of montelukast. The found UGT1A3 and ABCC9 variants associated with increased expression of the respective genes in human liver samples. Montelukast and its hydroxymetabolites were glucuronidated by UGT1A3 in vitro. These results indicate that UGT1A3 plays an important role in montelukast pharmacokinetics, especially in UGT1A3*2 carriers.