RT Journal Article
SR Electronic
T1 A sensitive method for determination of cytochrome P4502D6 activity in vitro using bupranolol as substrate.
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 303
OP 306
VO 24
IS 3
A1 Appanna, G
A1 Tang, B K
A1 Mller, R
A1 Kalow, W
YR 1996
UL http://dmd.aspetjournals.org/content/24/3/303.abstract
AB Previous studies have shown that bupranolol, a beta-adrenoceptor blocker, is a substrate of cytochrome P4502D6 (CYP2D6). A sensitive in vitro assay was developed to quantify the formation of hydroxybupranolol using HPLC. A TLC method, using radiolabeled bupranolol, was also developed to test the reproducibility of the two methods. Both of them gave virtually identical results; however, the HPLC method was sensitive to 20 pmol and the TLC with radiolabeled substrate to <1 pmol of hydroxybupranolol. The KM value for bupranolol was lower than that reported for any other substrate of CYP2D6. The KM value in microsomes of a typical human liver (L-1) was 0.272 +/- 0.02 (SE) mu M and the Vmax was 360 +/- 10 (SE) pmol/mg/min (0.83 +/- 0.02 pmol/pmol cytochrome P450/min). The KM value for the CYP2D6 expressed in yeast was 0.076 +/- 0.003 (SE) mu M, and the Vmax was 43 +/- 1 (SE) pmol/mg/min (0.64 +/- 0.01 pmol/pmol cytochrome P450/min). Quinidine competitively inhibited the formation of hydroxybupranolol, with Ki values of 5 nM in expressed CYP2D6 and 14.05 nM in human liver (L-1).