The Effects of Bovine Serum Albumin on Kinetic Characterization of Human Liver Microsomal CYP2C19 and CYP2E1 Activities

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Nitsupa Wattanachai
Wongwiwat Tassaneeyakul
Wichittra Tassaneeyakul


The addition of bovine serum albumin (BSA) to incubations of HLM or recombinant enzymes enhances the activities of several human cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) enzymes, including CYP1A2, CYP2C8, CYP2C9, UGT1A8, UGT1A9, UGT1A10, UGT2A1, UGT2B4, UGT2B7, and UGT2B15. Available evidence suggests that BSA increases the activities of these drug metabolizing enzymes by sequestering polyunsaturated fatty acids that are released from membranes, especially when using human liver microsomes (HLM) as the enzyme source.  Despite the importance of the ‘albumin effect’ for the accurate determination of kinetic parameters, the effects of BSA on CYP enzymes other than CYP1A2, CYP2C8, and CYP2C9 are yet to be investigated. This study aimed to investigate the effects of BSA on kinetic characterization of human liver microsomal omeprazole (OMP) 5¢-hydroxylation and chlorzoxazone (CZX) 6-hydroxlation pathways which are catalyzed by CYP2C19 and CYP2E1, respectively.  When BSA (2% w/v) was added to incubations, the Km and Vmax valuesfor CYP2C19-catalyzed OMP 5¢-hydroxylation were decreased by approximately 75% and 50%, resulting in a 2-fold increase in CLint.  By contrast, BSA had a minimal effect on the Km, Vmax, and CLint values for human liver microsomal CYP2E1-catalyzed CZX 6-hydroxylation.  These data confirm that BSA selectively affects human liver microsomal CYP activities.  

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