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Mass Spectrometry and Luminogenic-based Approaches to Characterize Phase I Metabolic Competency of In Vitro Cell Cultures
Published on: March 28, 2017
Endogenous melatonin partial metabolic clearance as a potential endogenous marker of CYP1A2 activity
Akitomo Yokokawa1, Hayato Shimazaki1, Shunji Igarashi1
1Laboratory of Clinical Pharmacy and Experimental Therapeutics, School of Pharmacy, Tokyo University of Pharmacy and Life Sciences, Tokyo, Japan.
Aims:
Cytochrome P450 1A2 (CYP1A2) exhibits substantial interindividual variability, necessitating appropriate phenotyping strategies for personalized pharmacotherapy. This study evaluated endogenous melatonin partial metabolic clearance (CLm(MEL)), calculated from urinary 6-hydroxymelatonin (6-O-MEL) excretion and plasma melatonin (MEL) exposure, as a potential endogenous marker of CYP1A2 activity and compared it with caffeine (CA)-based indexes.
Methods:
Eighteen healthy adults received 142-146 mg of CA following 48 h of CA abstinence. Blood samples were collected at 4, 6, 24 and 26 h post-dose, and urine was collected over two 2-h intervals (4-6 and 24-26 h). CA clearance (CLCA) was derived from the plasma CA AUC using noncompartmental analysis, and CLm(MEL) was calculated as urinary 6-hydroxymelatonin excretion divided by the corresponding plasma melatonin AUC.
Results:
Mean CLCA was 4.71 ± 2.97 L/h. CLm(MEL) values were comparable between sampling intervals (54.65 ± 15.87 vs. 53.66 ± 25.81 L/h) and showed significant correlations with CLCA (r = 0.57 and 0.67) and plasma paraxanthine/CA (PX/CA) ratios (r = 0.63 and 0.65).
Conclusions:
Endogenous CLm(MEL) correlates with established caffeine-derived CYP1A2 phenotyping indexes and may represent a probe-free approach for CYP1A2 phenotyping. Further validation under CYP1A2 induced and inhibited conditions is warranted.
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