Cytochrome P450 isozymes involved in aromatic hydroxylation and side- chain N-desisopropylation of alprenolol in rat liver microsomes

S. Narimatsu, M. Tachibana, Y. Masubuchi, S. Imaoka, Y. Funae, T. Suzuki

Research output: Contribution to journalArticle

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Abstract

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 μM), 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 μM 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 μM 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 μM, 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. In female rats, some major constitutive P450 isozyme(s) with a relatively high K(m) value (e.g., CYP2C6) may be involved in the metabolism of alprenolol, resulting in the disappearance of the sex difference.

Original languageEnglish
Pages (from-to)1060-1065
Number of pages6
JournalBiological and Pharmaceutical Bulletin
Volume18
Issue number8
Publication statusPublished - 1995
Externally publishedYes

Fingerprint

Alprenolol
Liver Microsomes
Hydroxylation
Cytochrome P-450 Enzyme System
Isoenzymes
Sex Characteristics
Mixed Function Oxygenases
Sparteine
Antibodies
Cytochromes
Wistar Rats
Enzymes

Keywords

  • alprenolol 4-hydroxylation
  • CYP2D2
  • N-desisopropylation
  • sex difference
  • strain difference
  • Wistar > Dark Agouti rat

ASJC Scopus subject areas

  • Molecular Medicine
  • Pharmacology, Toxicology and Pharmaceutics(all)

Cite this

Cytochrome P450 isozymes involved in aromatic hydroxylation and side- chain N-desisopropylation of alprenolol in rat liver microsomes. / Narimatsu, S.; Tachibana, M.; Masubuchi, Y.; Imaoka, S.; Funae, Y.; Suzuki, T.

In: Biological and Pharmaceutical Bulletin, Vol. 18, No. 8, 1995, p. 1060-1065.

Research output: Contribution to journalArticle

Narimatsu, S, Tachibana, M, Masubuchi, Y, Imaoka, S, Funae, Y & Suzuki, T 1995, 'Cytochrome P450 isozymes involved in aromatic hydroxylation and side- chain N-desisopropylation of alprenolol in rat liver microsomes', Biological and Pharmaceutical Bulletin, vol. 18, no. 8, pp. 1060-1065.
Narimatsu, S. ; Tachibana, M. ; Masubuchi, Y. ; Imaoka, S. ; Funae, Y. ; Suzuki, T. / Cytochrome P450 isozymes involved in aromatic hydroxylation and side- chain N-desisopropylation of alprenolol in rat liver microsomes. In: Biological and Pharmaceutical Bulletin. 1995 ; Vol. 18, No. 8. pp. 1060-1065.
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abstract = "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 μM), 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 μM 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 μM 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 μM, 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. In female rats, some major constitutive P450 isozyme(s) with a relatively high K(m) value (e.g., CYP2C6) may be involved in the metabolism of alprenolol, resulting in the disappearance of the sex difference.",
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AU - Narimatsu, S.

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AU - Masubuchi, Y.

AU - Imaoka, S.

AU - Funae, Y.

AU - Suzuki, T.

PY - 1995

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N2 - 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 μM), 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 μM 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 μM 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 μM, 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. In female rats, some major constitutive P450 isozyme(s) with a relatively high K(m) value (e.g., CYP2C6) may be involved in the metabolism of alprenolol, resulting in the disappearance of the sex difference.

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KW - sex difference

KW - strain difference

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