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Title: Characterization of deltamethrin metabolism by rat plasma and liver microsomes

Abstract

Deltamethrin, a widely used type II pyrethroid insecticide, is a relatively potent neurotoxicant. While the toxicity has been extensively examined, toxicokinetic studies of deltamethrin and most other pyrethroids are very limited. The aims of this study were to identify, characterize, and assess the relative contributions of esterases and cytochrome P450s (CYP450s) responsible for deltamethrin metabolism by measuring deltamethrin disappearance following incubation of various concentrations (2 to 400 {mu}M) in plasma (esterases) and liver microsomes (esterases and CYP450s) prepared from adult male rats. While the carboxylesterase metabolism in plasma and liver was characterized using an inhibitor, tetra isopropyl pyrophosphoramide (isoOMPA), CYP450 metabolism was characterized using the cofactor, NADPH. Michaelis-Menten rate constants were calculated using linear and nonlinear regression as applicable. The metabolic efficiency of these pathways was estimated by calculating intrinsic clearance (Vmax/Km). In plasma, isoOMPA completely inhibited deltamethrin biotransformation at concentrations (2 and 20 {mu}M of deltamethrin) that are 2- to 10-fold higher than previously reported peak blood levels in deltamethrin-poisoned rats. For carboxylesterase-mediated deltamethrin metabolism in plasma, Vmax = 325.3 {+-} 53.4 nmol/h/ml and Km = 165.4 {+-} 41.9 {mu}M. Calcium chelation by EGTA did not inhibit deltamethrin metabolism in plasma or liver microsomes, indicating that A-esterases do notmore » metabolize deltamethrin. In liver microsomes, esterase-mediated deltamethrin metabolism was completely inhibited by isoOMPA, confirming the role of carboxylesterases. The rate constants for liver carboxylesterases were Vmax = 1981.8 {+-} 132.3 nmol/h/g liver and Km = 172.5 {+-} 22.5 {mu}M. Liver microsomal CYP450-mediated biotransformation of deltamethrin was a higher capacity (Vmax = 2611.3 {+-} 134.1 nmol/h/g liver) and higher affinity (Km = 74.9 {+-} 5.9 {mu}M) process than carboxylesterase (plasma or liver) detoxification. Genetically engineered individual rat CYP450s (Supersomes) were used to identify specific CYP450 isozyme(s) involved in the deltamethrin metabolism. CYP1A2, CYP1A1, and CYP2C11 in decreasing order of importance quantitatively, metabolized deltamethrin. Intrinsic clearance by liver CYP450s (35.5) was more efficient than that by liver (12.0) or plasma carboxylesterases (2.4)« less

Authors:
 [1];  [2];  [3];  [4];  [2];  [5];  [3]
  1. Department of Pharmaceutical and Biomedical Sciences, College of Pharmacy, University of Georgia, Athens, GA 30602 (United States). E-mail: sanand@rx.uga.edu
  2. Department of Pharmaceutical and Biomedical Sciences, College of Pharmacy, University of Georgia, Athens, GA 30602 (United States)
  3. Neurotoxicology Division, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711 (United States)
  4. (United States)
  5. Department of Environmental Health Science, School of Public Health, University of Georgia, Athens, GA 30602 (United States)
Publication Date:
OSTI Identifier:
20783463
Resource Type:
Journal Article
Resource Relation:
Journal Name: Toxicology and Applied Pharmacology; Journal Volume: 212; Journal Issue: 2; Other Information: DOI: 10.1016/j.taap.2005.07.021; PII: S0041-008X(05)00425-4; Copyright (c) 2005 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; AFFINITY; BLOOD; CARBOXYLESTERASES; CLEARANCE; DETOXIFICATION; EGTA; INSECTICIDES; LIVER; METABOLISM; MICROSOMES; RATS; TOXICITY

Citation Formats

Anand, Sathanandam S., Bruckner, James V., Haines, Wendy T., Curriculum in Toxicology, UNC-CH, NC 27514, Muralidhara, Srinivasa, Fisher, Jeffrey W., and Padilla, Stephanie. Characterization of deltamethrin metabolism by rat plasma and liver microsomes. United States: N. p., 2006. Web. doi:10.1016/j.taap.2005.07.021.
Anand, Sathanandam S., Bruckner, James V., Haines, Wendy T., Curriculum in Toxicology, UNC-CH, NC 27514, Muralidhara, Srinivasa, Fisher, Jeffrey W., & Padilla, Stephanie. Characterization of deltamethrin metabolism by rat plasma and liver microsomes. United States. doi:10.1016/j.taap.2005.07.021.
Anand, Sathanandam S., Bruckner, James V., Haines, Wendy T., Curriculum in Toxicology, UNC-CH, NC 27514, Muralidhara, Srinivasa, Fisher, Jeffrey W., and Padilla, Stephanie. Sat . "Characterization of deltamethrin metabolism by rat plasma and liver microsomes". United States. doi:10.1016/j.taap.2005.07.021.
@article{osti_20783463,
title = {Characterization of deltamethrin metabolism by rat plasma and liver microsomes},
author = {Anand, Sathanandam S. and Bruckner, James V. and Haines, Wendy T. and Curriculum in Toxicology, UNC-CH, NC 27514 and Muralidhara, Srinivasa and Fisher, Jeffrey W. and Padilla, Stephanie},
abstractNote = {Deltamethrin, a widely used type II pyrethroid insecticide, is a relatively potent neurotoxicant. While the toxicity has been extensively examined, toxicokinetic studies of deltamethrin and most other pyrethroids are very limited. The aims of this study were to identify, characterize, and assess the relative contributions of esterases and cytochrome P450s (CYP450s) responsible for deltamethrin metabolism by measuring deltamethrin disappearance following incubation of various concentrations (2 to 400 {mu}M) in plasma (esterases) and liver microsomes (esterases and CYP450s) prepared from adult male rats. While the carboxylesterase metabolism in plasma and liver was characterized using an inhibitor, tetra isopropyl pyrophosphoramide (isoOMPA), CYP450 metabolism was characterized using the cofactor, NADPH. Michaelis-Menten rate constants were calculated using linear and nonlinear regression as applicable. The metabolic efficiency of these pathways was estimated by calculating intrinsic clearance (Vmax/Km). In plasma, isoOMPA completely inhibited deltamethrin biotransformation at concentrations (2 and 20 {mu}M of deltamethrin) that are 2- to 10-fold higher than previously reported peak blood levels in deltamethrin-poisoned rats. For carboxylesterase-mediated deltamethrin metabolism in plasma, Vmax = 325.3 {+-} 53.4 nmol/h/ml and Km = 165.4 {+-} 41.9 {mu}M. Calcium chelation by EGTA did not inhibit deltamethrin metabolism in plasma or liver microsomes, indicating that A-esterases do not metabolize deltamethrin. In liver microsomes, esterase-mediated deltamethrin metabolism was completely inhibited by isoOMPA, confirming the role of carboxylesterases. The rate constants for liver carboxylesterases were Vmax = 1981.8 {+-} 132.3 nmol/h/g liver and Km = 172.5 {+-} 22.5 {mu}M. Liver microsomal CYP450-mediated biotransformation of deltamethrin was a higher capacity (Vmax = 2611.3 {+-} 134.1 nmol/h/g liver) and higher affinity (Km = 74.9 {+-} 5.9 {mu}M) process than carboxylesterase (plasma or liver) detoxification. Genetically engineered individual rat CYP450s (Supersomes) were used to identify specific CYP450 isozyme(s) involved in the deltamethrin metabolism. CYP1A2, CYP1A1, and CYP2C11 in decreasing order of importance quantitatively, metabolized deltamethrin. Intrinsic clearance by liver CYP450s (35.5) was more efficient than that by liver (12.0) or plasma carboxylesterases (2.4)},
doi = {10.1016/j.taap.2005.07.021},
journal = {Toxicology and Applied Pharmacology},
number = 2,
volume = 212,
place = {United States},
year = {Sat Apr 15 00:00:00 EDT 2006},
month = {Sat Apr 15 00:00:00 EDT 2006}
}
  • The metabolism of the PAF antagonists kadsurenone and tritium-labeled 9,10-dihydrokadsurenone was studied in rhesus monkeys and rat liver microsomes. The monkey metabolites of the two drugs were isolated as their glucuronide conjugates from the urine of iv dosed males. The metabolites from both monkey and microsomal metabolism were purified by reverse phase HPLC and identified by spectral (NMR, UV, and mass spectrometric) analysis. The principal pathway of biotransformation of the tritium-labeled 9,10-dihydrokadsurenone in monkeys was hydroxylation of the C-5 propyl side chain to give two metabolites, 10-hydroxy-9,10-dihydrokadsurenone and 9-hydroxy-9,10-dihydrokadsurenone. These compounds were excreted as glucuronides. Microsomal incubation of tritium-labeled 9,10-dihydrokadsurenonemore » yielded the 10-, 9-, and 8-hydroxy-9,10-dihydrokadsurenone as major metabolites. Kadsurenone was also metabolized at the C-5 side chain, an allyl group. The monoglucuronide of 9,10-dihydroxykadsurenone was isolated from monkey urine. Spectral analysis was not definitive as to the site of conjugation, and the structure of the metabolite was assigned as the C-10 conjugate. A major metabolite of rat liver microsomal incubation of kadsurenone was 9,10-dihydroxykadsurenone.« less
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