Abstract

Coumarin has been reported to be a reliable probe for the determination of human microsomal CYP2A6 activity. Coumarin is converted to 7-hydroxycoumarin by CYP2A6. A high pressure liquid chromatographic assay for the estimation of CYP2A6 activity in microsomes was evaluated. A RP C-18 Novapak Waters (15 cm x 3.9 mm, 5 µm) column was used for the assay. The mobile phase composition was methanol : 1% glacial acetic acid (35:65 v/v) (pH~3.1), with a flow rate of 0.6 ml/min, injection volume of 100 µl and detection at 320 nm. The retention times for coumarin and 7-hydroxycoumarin were 8.7 min and 5.3 min, respectively. The limit of detection (LOD) was 0.05 µM, and the limit of quantitation (LOQ) was 0.1 µM, for 7-hydroxycoumarin. The percent coefficient of variation associated with 7-hydroxycoumarin determination after duplicate estimation was found to be in the range 0.03 to 3.6% for buffer matrix and 0.1 to 6.5% for microsomal matrix. The mean rate of 7-hydroxycoumarin formation in guinea pig liver microsomes was 0.084 nmol/min/nmol P450. Coumarin 7-hydroxylase activity was absent in rat liver microsomes. No interference was observed from incubation mixture components.