Validated LC-MS/MS method for profiling endogenous probes of OATP1B during pregnancy: Simultaneous quantification of...

The activity of organic anion-transporting polypeptide (OATP) 1B can fluctuate during pregnancy, affecting the kinetics of various drugs and endogenous substrates. Endogenous probes for OATP1B are essential for predicting transporter activity in pregnant women, thereby avoiding the use of embryotoxic exogenous probes like statins. This study aimed to establish a rapid and safe method for evaluating OATP1B activity in pregnant women by measuring plasma bile acid-O-sulfates, which are potential endogenous probes for OATP1B. Plasma concentrations of glycolithocholic acid 3-O-sulfate (GLCA-S) and glycochenodeoxycholic acid 3-O-sulfate (GCDCA-S) were quantified using liquid chromatography-tandem mass spectrometry. GLCA-S and GCDCA-S were separated on a metal-free column coated with polyether ether ketone. Calibration curves for GLCA-S and GCDCA-S exhibited linearity over a concentration range of 25-1500 ng/mL, with efficient separation within 10 min and no significant peak tailing. All analytical parameters met the International Council for Harmonisation M10 guideline. Using this method, the highest median concentration of GLCA-S was observed in the second trimester of pregnancy (95.7 ng/mL), which decreased in the third trimester (39.3 ng/mL) and postpartum period (44.4 ng/mL) (P = 0.05), suggesting reduced OATP1B activity during pregnancy. Median GCDCA-S concentrations in the second and third trimesters and the postpartum period were 38.7 ng/mL, 78.1 ng/mL, and 57.3 ng/mL, respectively (P = 0.37). In conclusion, this method offers a safe alternative approach for evaluating OATP1B activity in pregnant women without embryotoxic exogenous probes like statins.