抄録
Enantio and regioselectivity of adrenoceptor blocking agents [propranolol (PL) and bunitrolol (BTL)] was examined for CYP2D6 expressed in various heterologous expression systems. In human liver microsomes, propranolol was oxidized at 4 and 5-position of the naphthalene ring and at the side chain to form 4-hydroxypropranolol, 5-hydroxypropranolols and N-desisopropyl-propranolol, respectively. BTL was oxidized to 4-hydroxybunitrolol by human liver microsomes. At a lower concentration range of PL or BTL, the ring hydroxylation of the substrates is mainly mediated by CYP2D6 in human liver.
As for the enantioselectivity, CYP2D6 expressed in Sf9 insect cells showed enantioselectivity of R(+)<S(-) for PL oxidation consisting of aromatic ring 4 and 5-hydroxylations and side-chain Ndesisopropylation, which was reverse of human liver microsomes at a low PL concentration range [R(+)>S(-)]. CYP2D6 expressed in Escherichia coli also gave the same results. This was proved to be caused by the change of an amino acid residue at position 374 of CYP2D6 from valine as wildtype to methionine as allelic variant.
As for the regioselectivity, CYP2D6 expressed in lymphoblastoid cells had PL 4- and 5-hydroxylase, and BTL 4-hydroxylase activities, but did not show PL N-desisopropylase activity, on the one hand. CYP2D6 expressed in E. coli had PL 4- and 5-hydroxylase, and N-desalkylase activities but did not exhibit BTL 4-hydroxylase activity, on the other. These results suggest that different environment surrounding the CYP2D6 proteins expressed in heterologous cells or N-truncation of the enzyme to yield high efficiency in expression in E. coli. affects the properties of CYP2D6 proteins.
