Cytochrome P450 isozymes involved in aromatic hydroxylation and side-chain N-desisopropylation of alprenolol in rat liver microsomes.
Alprenolol 4-hydroxylation and N-desisopropylation in liver microsomes from male Wistar rats were kinetically analyzed to be biphasic. In the 4-hydroxylation at a low substrate concentration (5 microM), significant strain [Wistar > Dark Agouti (DA)] and sex (male > female) differences were observed, and the differences decreased at a high substrate concentration (1 mM). In the N-desisopropylation, only a strain difference (Wistar > DA) was observed at the low substrate concentration. Cytochrome P450BTL (P450BTL, corresponding to CYP2D2) in a reconstituted system with 5 microM alprenolol had high 4-hydroxylase activity, which was about 10 times that of P450ml corresponding to CYP2C11, and N-desisopropylase activity at a similar extent to P450ml. The two microsomal activities at 5 microM alprenolol were efficiently decreased by antibodies against P450BTL and by sparteine, a typical substrate of the CYP2D subfamily. Polyclonal antibodies against P450ml and P450PB-1 (corresponding to CYP3A2) partially suppressed only N-desalkylation at 5 microM, whereas they reduced the two activities at 1 mM. P450ml showed a high N-desisopropylase activity at a substrate concentration of 1 mM, where the sex difference was not observed. Furthermore, P450PB-2 corresponding to CYP2C6, which is one of the major P450 isozymes in female rats, also had 4-hydroxylase and N-desalkylase activities. These results suggest that a CYP2D isozyme(s) is the primary enzyme in alprenolol 4-hydroxylation and N-desisopropylation in a lower substrate concentration range, and that the involvement of some male-specific P450 isozyme(s) other than CYP2C11 or CYP3A2 may cause the sex difference in the 4-hydroxylation. In a higher substrate concentration range, CYP2C11 is thought to play a major role particularly in N-desisopropylation in male rats.(ABSTRACT TRUNCATED AT 250 WORDS)
Narimatsu
S
S
Laboratory of Biopharmaceutics, Faculty of Pharmaceutical Sciences, Chiba University, Japan.
Tachibana
M
M
Masubuchi
Y
Y
Imaoka
S
S
Funae
Y
Y
Suzuki
T
T
D000526:Alprenolol / Q000378:metabolism*; D000818:Animals; D000906:Antibodies / Q000276:immunology; D003577:Cytochrome P-450 Enzyme System / Q000276:immunology / Q000378:metabolism*; D005260:Female; D006900:Hydroxylation; D007527:Isoenzymes / Q000276:immunology / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology*; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D012737:Sex Factors; D013034:Sparteine / Q000494:pharmacology; D013045:Species Specificity
D000906:Antibodies; D007527:Isoenzymes; D013034:Sparteine; D000526:Alprenolol; D003577:Cytochrome P-450 Enzyme System