In Vitro Metabolism of Fipronil by Human and Rat Cytochrome P450 and Its Interactions with Testosterone and Diazepam

Details

• Personal Author:
  Hodgson E ; Rose RL ; Tang J ; Usmani A
• Description:
  Fipronil (5-amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl)sulfinyl]-1H-pyrazole-3-carbonitrile) is a highly active, broad spectrum insecticide from the phenyl pyrazole family, which targets the gamma-amino butyric acid (GABA) receptor. Although fipronil is presently widely used as an insecticide and acaricide, little information is available with respect to its metabolic fate and disposition in mammals. This study was designed to investigate the in vitro human metabolism of fipronil and to examine possible metabolic interactions that fipronil may have with other substrates. Fipronil was incubated with human liver microsomes (HLM) and several recombinant cytochrome P450 (CYP) isoforms obtained from BD Biosciences. HPLC was used for metabolite identification and quantification. Fipronil sulfone was the predominant metabolite via CYP oxidation. The Km and Vmax values for human liver microsomes are 27.2 microM and 0.11 nmol/mg protein min, respectively; for rat liver microsomes (RLM) the Km and Vmax are 19.9 microM and 0.39 nmol/mg protein min, respectively. CYP3A4 is the major isoform responsible for fipronil oxidation in humans while CYP2C19 is considerably less active. Other human CYP isoforms have minimal or no activity toward fipronil. Co-expression of cytochrome b5 (b5) is essential for CYP3A4 to manifest high activity toward fipronil. Ketoconazole, a specific inhibitor of CYP3A4, inhibits 78% of the HLM activity toward fipronil at a concentration of 2 microM. Oxidative activity toward fipronil in 19 single-donor HLMs correlated well with their ability to oxidize testosterone. The interactions of fipronil and other CYP3A4 substrates, such as testosterone and diazepam, were also investigated. Fipronil metabolism was activated by testosterone in HLM but not in CYP3A4 Supersomes(R). Testosterone 6beta-hydroxylation in HLM was inhibited by fipronil. Fipronil inhibited diazepam demethylation but had little effect on diazepam hydroxylation. The results suggest that fipronil has the potential to interact with a wide range of xenobiotics or endogenous chemicals that are CYP3A4 substrates and that fipronil may be a useful substrate for the characterization of CYP3A4 in HLM. [Description provided by NIOSH]
• Subjects:
  Animals Energy Metabolism Insecticides Occupational Health Safety
• Keywords:
  Animal Studies Author Keywords: Fipronil CYP3A4 Cytochrome P450 Human Liver Microsomes Interaction In Vitro Study Metabolic Study Metabolism Pesticides And Agricultural Chemicals
• ISSN:
  0009-2797
• Document Type:
  Text
• Funding:
  Cooperative Agreement
• Genre:
  Journal Article
• Place as Subject:
  North Carolina ; OSHA Region 4
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  319-329
• Volume:
  147
• Issue:
  3
• NIOSHTIC Number:
  nn:20062047
• Citation:
  Chem-Biol Interact 2004 Apr; 147(3):319-329
• Contact Point Address:
  Randy L. Rose, Department of Environmental and Molecular Toxicology, North Carolina State University, Raleigh, NC 27695, USA
• Email:
  randy_rose@ncsu.edu
• CAS Registry Number:
  Diazepam (CAS RN 439-14-5) ; Fipronil (CAS RN 120068-37-3)
• Federal Fiscal Year:
  2004
• Performing Organization:
  East Carolina University
• Peer Reviewed:
  True
• Start Date:
  20010930
• Source Full Name:
  Chemico-Biological Interactions
• End Date:
  20080929
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:9aa7517b19e46ae4cadd3dfc0c0dd114ef31a874a03e04ab6e5a7c6444aa36d2b6a1d0c00dd5cdc90ac9b1ba3ba53a4f95779b4ecb94dd0158d0e033d50f097f
• Download URL:
  https://stacks.cdc.gov/view/cdc/225369/cdc_225369_DS1.pdf
• File Type:
  [PDF - 153.89 KB ]