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Positional specificity for methyl-n-amylnitrosamine hydroxylation by cytochrome P-450 isozymes determined with monoclonal antibodies.
Cancer Res. 1991 Feb 15; 51(4):1059-64.CR

Abstract

Inhibitory monoclonal antibodies (MAbs) were used to determine the contribution of epitope-specific cytochrome P-450 isozymes in rat liver microsomes to hydroxylation of the esophageal carcinogen methyl-n-amylnitrosamine. These P-450-catalyzed reactions form 2-, 3-, 4-, and 5-hydroxymethyl-n-amylnitrosamine, formaldehyde (demethylation), and pentaldehyde (depentylation). With uninduced microsomes from male rats, MAb 1-68-11 inhibited 4-hydroxylation by 73% and demethylation by 46%. This indicated the major contribution of constitutive male-specific P-450 IIC11 to the metabolism. Inhibition studies with MAbs 2-66-3 and 1-91-3 indicated that P-450 IIB1 contributed 19% and IIE1 35% to demethylation. With uninduced microsomes from females, MAb 1-68-11 produced similar inhibitions to those in male rats, indicating that female-specific P-450 IIC12 (which is closely related to IIC11) also catalyzed 4-hydroxylation and demethylation. With microsomes from 3-methylcholanthrene-induced male rats, P-450 IA1 and/or IA2 were responsible for 60% of 3-hydroxylation and 40% of depentylation. With microsomes from phenobarbital-treated rats, P-450 IIB1 and IIB2 catalyzed all 6 reactions but especially 4-hydroxylation and depentylation, which were 50-75% inhibited by MAb 2-66-3. Microsomes from Aroclor-induced males behaved as if they were induced by both 3-methylcholanthrene and phenobarbital. After treatment with isoniazid (a P-450 IIE1 inducer), inhibition by MAb 1-91-3 indicated a 45% contribution of P-450 IIE1 to demethylation, and both P-450 IIE1 and IIB1 (or IIB2) appear to have been induced. A major finding with uninduced microsomes was the high specificity of MAb 1-68-11 for inhibiting 4-hydroxylation, indicating that P-450 IIC11 and IIC12 catalyzed most of this omega-1-hydroxylation. In microsomes from induced rats, the MAb inhibitions showed the role of the induced P-450 IA1 (or IA2), IIB1 (or IIB2), and IIE1 in methyl-n-amylnitrosamine hydroxylation at different positions, as well as the presence of P-450 IIC11. This study illustrates the usefulness of inhibitory MAbs for defining the contribution of individual P-450s to position-specific metabolism.

Authors+Show Affiliations

Eppley Institute for Research in Cancer, University of Nebraska Medical Center, Omaha 68105.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

1997155

Citation

Mirvish, S S., et al. "Positional Specificity for Methyl-n-amylnitrosamine Hydroxylation By Cytochrome P-450 Isozymes Determined With Monoclonal Antibodies." Cancer Research, vol. 51, no. 4, 1991, pp. 1059-64.
Mirvish SS, Huang Q, Ji C, et al. Positional specificity for methyl-n-amylnitrosamine hydroxylation by cytochrome P-450 isozymes determined with monoclonal antibodies. Cancer Res. 1991;51(4):1059-64.
Mirvish, S. S., Huang, Q., Ji, C., Wang, S., Park, S. S., & Gelboin, H. V. (1991). Positional specificity for methyl-n-amylnitrosamine hydroxylation by cytochrome P-450 isozymes determined with monoclonal antibodies. Cancer Research, 51(4), 1059-64.
Mirvish SS, et al. Positional Specificity for Methyl-n-amylnitrosamine Hydroxylation By Cytochrome P-450 Isozymes Determined With Monoclonal Antibodies. Cancer Res. 1991 Feb 15;51(4):1059-64. PubMed PMID: 1997155.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Positional specificity for methyl-n-amylnitrosamine hydroxylation by cytochrome P-450 isozymes determined with monoclonal antibodies. AU - Mirvish,S S, AU - Huang,Q, AU - Ji,C, AU - Wang,S, AU - Park,S S, AU - Gelboin,H V, PY - 1991/2/15/pubmed PY - 1991/2/15/medline PY - 1991/2/15/entrez SP - 1059 EP - 64 JF - Cancer research JO - Cancer Res VL - 51 IS - 4 N2 - Inhibitory monoclonal antibodies (MAbs) were used to determine the contribution of epitope-specific cytochrome P-450 isozymes in rat liver microsomes to hydroxylation of the esophageal carcinogen methyl-n-amylnitrosamine. These P-450-catalyzed reactions form 2-, 3-, 4-, and 5-hydroxymethyl-n-amylnitrosamine, formaldehyde (demethylation), and pentaldehyde (depentylation). With uninduced microsomes from male rats, MAb 1-68-11 inhibited 4-hydroxylation by 73% and demethylation by 46%. This indicated the major contribution of constitutive male-specific P-450 IIC11 to the metabolism. Inhibition studies with MAbs 2-66-3 and 1-91-3 indicated that P-450 IIB1 contributed 19% and IIE1 35% to demethylation. With uninduced microsomes from females, MAb 1-68-11 produced similar inhibitions to those in male rats, indicating that female-specific P-450 IIC12 (which is closely related to IIC11) also catalyzed 4-hydroxylation and demethylation. With microsomes from 3-methylcholanthrene-induced male rats, P-450 IA1 and/or IA2 were responsible for 60% of 3-hydroxylation and 40% of depentylation. With microsomes from phenobarbital-treated rats, P-450 IIB1 and IIB2 catalyzed all 6 reactions but especially 4-hydroxylation and depentylation, which were 50-75% inhibited by MAb 2-66-3. Microsomes from Aroclor-induced males behaved as if they were induced by both 3-methylcholanthrene and phenobarbital. After treatment with isoniazid (a P-450 IIE1 inducer), inhibition by MAb 1-91-3 indicated a 45% contribution of P-450 IIE1 to demethylation, and both P-450 IIE1 and IIB1 (or IIB2) appear to have been induced. A major finding with uninduced microsomes was the high specificity of MAb 1-68-11 for inhibiting 4-hydroxylation, indicating that P-450 IIC11 and IIC12 catalyzed most of this omega-1-hydroxylation. In microsomes from induced rats, the MAb inhibitions showed the role of the induced P-450 IA1 (or IA2), IIB1 (or IIB2), and IIE1 in methyl-n-amylnitrosamine hydroxylation at different positions, as well as the presence of P-450 IIC11. This study illustrates the usefulness of inhibitory MAbs for defining the contribution of individual P-450s to position-specific metabolism. SN - 0008-5472 UR - https://www.unboundmedicine.com/medline/citation/1997155/Positional_specificity_for_methyl_n_amylnitrosamine_hydroxylation_by_cytochrome_P_450_isozymes_determined_with_monoclonal_antibodies_ L2 - http://cancerres.aacrjournals.org/cgi/pmidlookup?view=long&pmid=1997155 DB - PRIME DP - Unbound Medicine ER -