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Research ArticleArticle

MALATHION BIOACTIVATION IN THE HUMAN LIVER: THE CONTRIBUTION OF DIFFERENT CYTOCHROME P450 ISOFORMS

Franca M. Buratti, Alessandra D'Aniello, Maria Teresa Volpe, Annarita Meneguz and Emanuela Testai
Drug Metabolism and Disposition March 2005, 33 (3) 295-302; DOI: https://doi.org/10.1124/dmd.104.001693
Franca M. Buratti
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Alessandra D'Aniello
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Maria Teresa Volpe
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Annarita Meneguz
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Emanuela Testai
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Abstract

Among organophosphorothioate (OPT) pesticides, malathion is considered relatively safe for use in mammals. Its rapid degradation by carboxylesterases competes with the cytochrome P450 (P450)-catalyzed formation of malaoxon, the toxic metabolite. However, impurities in commercial formulations are potent inhibitors of carboxylesterase, allowing a dramatic increase in malaoxon formation. Malathion desulfuration has been characterized in human liver microsomes (HLMs) with a method based on acetylcholinesterase inhibition that is able to detect nanomolar levels of oxon. The active P450 isoforms have been identified by means of a multifaceted strategy, including the use of cDNA-expressed human P450s and correlation, immunoinhibition, and chemical inhibition studies in a panel of phenotyped HLMs. HLMs catalyzed malaoxon formation with a high level of variability (>200-fold). One or two components (Kmapp1 = 53–67 μM; Kmapp2 = 427-1721 μM) were evidenced, depending on the relative specific P450 content. Results from different approaches indicated that, at low malathion concentration, malaoxon formation is catalyzed by CYP1A2 and, to a lesser extent, 2B6, whereas the role of 3A4 is relevant only at high malathion levels. These results are in line with those found with chlorpyrifos, diazinon, azynphos-methyl, and parathion, characterized by the presence of an aromatic ring in the molecule. Since malathion has linear chains as substituents at the thioether sulfur, it can be hypothesized that, independently from the chemical structure, OPTs are bioactivated by the same P450s. These results also suggest that CYP1A2 and 2B6 can be considered as possible metabolic biomarkers of susceptibility to OPT-induced toxic effects at actual human exposure levels.

Footnotes

  • This work has been partially supported by Istituto Superiore di Sanitá Projects 3AAS and 3AG/F11. Preliminary results were presented at the 8th European ISSX Meeting in Dijon, France, April 27 to May 1, 2003.

  • Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.

  • doi:10.1124/dmd.104.001693.

  • ABBREVIATIONS: OPT, organophosphothionate; P450, cytochrome P450 isoform; HLM, human liver microsome; CLi, intrinsic clearance; AChE, acetylcholinesterase; iso-OMPA, tetraisopropyl-pyrophosphoramide; Ab, antibody.

    • Received July 30, 2004.
    • Accepted November 17, 2004.
  • The American Society for Pharmacology and Experimental Therapeutics
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Drug Metabolism and Disposition: 33 (3)
Drug Metabolism and Disposition
Vol. 33, Issue 3
1 Mar 2005
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Research ArticleArticle

MALATHION BIOACTIVATION IN THE HUMAN LIVER: THE CONTRIBUTION OF DIFFERENT CYTOCHROME P450 ISOFORMS

Franca M. Buratti, Alessandra D'Aniello, Maria Teresa Volpe, Annarita Meneguz and Emanuela Testai
Drug Metabolism and Disposition March 1, 2005, 33 (3) 295-302; DOI: https://doi.org/10.1124/dmd.104.001693

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Research ArticleArticle

MALATHION BIOACTIVATION IN THE HUMAN LIVER: THE CONTRIBUTION OF DIFFERENT CYTOCHROME P450 ISOFORMS

Franca M. Buratti, Alessandra D'Aniello, Maria Teresa Volpe, Annarita Meneguz and Emanuela Testai
Drug Metabolism and Disposition March 1, 2005, 33 (3) 295-302; DOI: https://doi.org/10.1124/dmd.104.001693
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