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Title: Metabolism of aflatoxin B{sub 1} in Turkey liver microsomes: The relative roles of cytochromes P450 1A5 and 3A37

Abstract

The extreme sensitivity of turkeys to aflatoxin B{sub 1} (AFB{sub 1}) is associated with efficient epoxidation by hepatic cytochromes P450 (P450) 1A5 and 3A37 to exo-aflatoxin B{sub 1}-8,9-epoxide (exo-AFBO). The combined presence of 1A5 and 3A37, which obey different kinetic models, both of which metabolize AFB{sub 1} to the exo-AFBO and to detoxification products aflatoxin M{sub 1} (AFM{sub 1}) and aflatoxin Q{sub 1} (AFQ{sub 1}), respectively, complicates the kinetic analysis of AFB{sub 1} in turkey liver microsomes (TLMs). Antisera directed against 1A5 and 3A37, thereby individually removing the catalytic contribution of these enzymes, were used to identify the P450 responsible for epoxidating AFB{sub 1} in TLMs. In control TLMs, AFB{sub 1} was converted to exo-AFBO in addition to AFM{sub 1} and AFQ{sub 1} confirming the presence of functional 1A5 and 3A37. Pretreatment with anti-1A5 inhibited exo-AFBO formation, especially at low, submicromolar ({approx} 0.1 {mu}M), while anti-3A37, resulted in inhibition of exo-AFBO formation, but at higher (> 50 {mu}M) AFB{sub 1} concentrations. Metabolism in immunoinhibited TLMs resembled that of individual enzymes: 1A5 produced exo-AFBO and AFM{sub 1}, conforming to Michaelis-Menten, while 3A37 produced exo-AFBO and AFQ{sub 1} following the kinetic Hill equation. At 0.1 {mu}M AFB{sub 1}, close to concentrations inmore » livers of exposed animals, 1A5 contributed to 98% of the total exo-AFBO formation. At this concentration, 1A5 accounted for a higher activation:detoxification (50:1, exo-AFBO: AFM{sub 1}) compared to 3A37 (0.15: 1, exo-AFBO: AFQ{sub 1}), suggesting that 1A5 is high, while 3A4 is the low affinity enzyme in turkey liver. The data support the conclusion that P450 1A5 is the dominant enzyme responsible for AFB{sub 1} bioactivation and metabolism at environmentally-relevant AFB{sub 1} concentrations in turkey liver. - Graphical abstract: Display Omitted Highlights: > Efficient bioactivation by P450s 1A5 and 3A4 associated with extreme aflatoxin B{sub 1} sensitivity in turkeys. > These P450s exhibit different metabolite profiles and enzyme kinetic models toward AFB{sub 1}. > Study conducted to determine which P450 is primary bioactivator in turkey liver. > Immunoinhibition studies show 1A5 predominates at low, environmentally-relevant AFB{sub 1} concentrations. > 3A37 predominates at only at very high AFB{sub 1} concentrations, not relevant to liver in vivo.« less

Authors:
;
Publication Date:
OSTI Identifier:
21587800
Resource Type:
Journal Article
Journal Name:
Toxicology and Applied Pharmacology
Additional Journal Information:
Journal Volume: 254; Journal Issue: 3; Other Information: DOI: 10.1016/j.taap.2011.05.010; PII: S0041-008X(11)00181-5; Copyright (c) 2011 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0041-008X
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; AFLATOXINS; ANIMALS; CONTROL; CYTOCHROMES; DETOXIFICATION; ENZYMES; EPOXIDES; GLUTATHIONE; GLUTATHIONE CONJUGATES; HILL EQUATION; IN VIVO; LIVER; METABOLISM; MICROSOMES; SENSITIVITY; TURKEY; ANTIGENS; ASIA; BODY; CELL CONSTITUENTS; DEVELOPING COUNTRIES; DIFFERENTIAL EQUATIONS; DIGESTIVE SYSTEM; DRUGS; EQUATIONS; GLANDS; HAZARDOUS MATERIALS; MATERIALS; METABOLITES; MIDDLE EAST; MYCOTOXINS; ORGANIC COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; ORGANS; PEPTIDES; PIGMENTS; POLYPEPTIDES; PROTEINS; RADIOPROTECTIVE SUBSTANCES; RESPONSE MODIFYING FACTORS; RIBOSOMES; TOXIC MATERIALS; TOXINS

Citation Formats

Rawal, Sumit, and Coulombe, Roger A., E-mail: roger@usu.edu. Metabolism of aflatoxin B{sub 1} in Turkey liver microsomes: The relative roles of cytochromes P450 1A5 and 3A37. United States: N. p., 2011. Web. doi:10.1016/j.taap.2011.05.010.
Rawal, Sumit, & Coulombe, Roger A., E-mail: roger@usu.edu. Metabolism of aflatoxin B{sub 1} in Turkey liver microsomes: The relative roles of cytochromes P450 1A5 and 3A37. United States. doi:10.1016/j.taap.2011.05.010.
Rawal, Sumit, and Coulombe, Roger A., E-mail: roger@usu.edu. Mon . "Metabolism of aflatoxin B{sub 1} in Turkey liver microsomes: The relative roles of cytochromes P450 1A5 and 3A37". United States. doi:10.1016/j.taap.2011.05.010.
@article{osti_21587800,
title = {Metabolism of aflatoxin B{sub 1} in Turkey liver microsomes: The relative roles of cytochromes P450 1A5 and 3A37},
author = {Rawal, Sumit and Coulombe, Roger A., E-mail: roger@usu.edu},
abstractNote = {The extreme sensitivity of turkeys to aflatoxin B{sub 1} (AFB{sub 1}) is associated with efficient epoxidation by hepatic cytochromes P450 (P450) 1A5 and 3A37 to exo-aflatoxin B{sub 1}-8,9-epoxide (exo-AFBO). The combined presence of 1A5 and 3A37, which obey different kinetic models, both of which metabolize AFB{sub 1} to the exo-AFBO and to detoxification products aflatoxin M{sub 1} (AFM{sub 1}) and aflatoxin Q{sub 1} (AFQ{sub 1}), respectively, complicates the kinetic analysis of AFB{sub 1} in turkey liver microsomes (TLMs). Antisera directed against 1A5 and 3A37, thereby individually removing the catalytic contribution of these enzymes, were used to identify the P450 responsible for epoxidating AFB{sub 1} in TLMs. In control TLMs, AFB{sub 1} was converted to exo-AFBO in addition to AFM{sub 1} and AFQ{sub 1} confirming the presence of functional 1A5 and 3A37. Pretreatment with anti-1A5 inhibited exo-AFBO formation, especially at low, submicromolar ({approx} 0.1 {mu}M), while anti-3A37, resulted in inhibition of exo-AFBO formation, but at higher (> 50 {mu}M) AFB{sub 1} concentrations. Metabolism in immunoinhibited TLMs resembled that of individual enzymes: 1A5 produced exo-AFBO and AFM{sub 1}, conforming to Michaelis-Menten, while 3A37 produced exo-AFBO and AFQ{sub 1} following the kinetic Hill equation. At 0.1 {mu}M AFB{sub 1}, close to concentrations in livers of exposed animals, 1A5 contributed to 98% of the total exo-AFBO formation. At this concentration, 1A5 accounted for a higher activation:detoxification (50:1, exo-AFBO: AFM{sub 1}) compared to 3A37 (0.15: 1, exo-AFBO: AFQ{sub 1}), suggesting that 1A5 is high, while 3A4 is the low affinity enzyme in turkey liver. The data support the conclusion that P450 1A5 is the dominant enzyme responsible for AFB{sub 1} bioactivation and metabolism at environmentally-relevant AFB{sub 1} concentrations in turkey liver. - Graphical abstract: Display Omitted Highlights: > Efficient bioactivation by P450s 1A5 and 3A4 associated with extreme aflatoxin B{sub 1} sensitivity in turkeys. > These P450s exhibit different metabolite profiles and enzyme kinetic models toward AFB{sub 1}. > Study conducted to determine which P450 is primary bioactivator in turkey liver. > Immunoinhibition studies show 1A5 predominates at low, environmentally-relevant AFB{sub 1} concentrations. > 3A37 predominates at only at very high AFB{sub 1} concentrations, not relevant to liver in vivo.},
doi = {10.1016/j.taap.2011.05.010},
journal = {Toxicology and Applied Pharmacology},
issn = {0041-008X},
number = 3,
volume = 254,
place = {United States},
year = {2011},
month = {8}
}