Simultaneous quantification of coproporphyrin-I and 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid in human plasma using ultra-high performance liquid chromatography coupled to tandem mass spectrometry.

In chronic kidney disease (CKD), organic anion transporting polypeptide (OATP)1B activity is reduced by mechanisms involving 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF), a uremic toxin. Coproporphyrin-I (CP-I) is a sensitive and specific endogenous probe for phenotyping OATP1B activity and a potentially useful tool to individualize the dosage of OATP1B substrates. In this study, we developed and validated an assay for simultaneous quantification of CP-I and CMPF in human plasma using ultra-high performance liquid chromatography with tandem mass spectrometry (UHPLC-MS/MS). The samples were prepared by solid phase extraction, and then subjected to UHPLC-MS/MS quantification. The assay fulfilled the requirements of the US Food and Drug Administration (FDA) guideline for assay validation, with a lower limit of quantification of 0.1 for CP-I and 50 ng/mL for CMPF. Recovery rates from human plasma ranged from 97.3%-109.8% for CP-I, and 94.1%-113.3% for CMPF. Matrix effects corrected by internal standards varied between 107.2 % and 119.3 % for CP-I, and between 90.4 % and 107.4 % for CMPF. The validated assay was applied to measurement of plasma CP-I and CMPF concentrations in 10 healthy volunteers, 14 stage 3-5 CKD patients, and 14 stage 5D CKD patients. The concentrations measured in all samples were within the calibration ranges. Our novel method may be clinically useful for simultaneous measurement of plasma CP-I and CMPF concentrations in human samples, and contribute to reveal the in vivo relationship of OATB1B activity with accumulation of CMPF in CKD patients.