Regio- and stereoselectivity in propranolol metabolism by dog liver microsomes and the expressed dog CYP2D15.

We have studied the regio- and stereoselectivity of ring-hydroxylation and N-desisopropylation of S(-)- and R(+)-propranolol, using dog liver microsomes and the expressed dog CYP2D15 in insect cells. In dog liver microsomes, 4-hydroxylation was the preferred pathway in S(-)-propranolol oxidation, while N-desisopropylation was the preferred pathway in R(+)-propranolol oxidation. S(-)-Propranolol was preferred over R(+)-propranolol as substrate for 4- and 5-hydroxylations, while R(+)-propranolol was the preferred substrate for N-desisopropylation at higher substrate concentrations. The expressed CYP2D15 had high catalytic activities toward 4-, 5-hydroxylation, as well as N-desisopropylation of both enantiomers. At the substrate concentrations used, 4-hydroxylation was the preferred pathway for the metabolism of both enantiomers, and S(-)-propranolol was the preferred substrate over R(+)-propranolol for all three monooxygenations catalyzed by CYP2D15. Anti-CYP2D15 peptide antibody strongly inhibited 4- and 5-hydroxylation of both enantiomers in dog liver microsomes, while it did not inhibit their N-desisopropylation. These findings suggest that CYP2D15 is highly responsible for the stereoselective 4- and 5-hydroxylations of propranolol in dog liver microsomes.