Fipronil Induces CYP Isoforms and Cytotoxicity in Human Hepatocytes

Details

• Personal Author:
  Cao Y ; Cherrington N ; Das PC ; Hodgson E ; Rose RL
• Description:
  Recent studies have demonstrated the potential of pesticides to either inhibit or induce xenobiotic metabolizing enzymes in humans. Exposure of human hepatocytes to doses of fipronil (5-amino-1-[2,6-dichloro-4-(trifluoromethyl)phenyl]-4-[(trifluoromethyl) sulfinyl]-1H-pyrazole-3-carbonitrile) ranging from 0.1 to 25 µM resulted in a dose dependent increase in CYP1A1 mRNA expression (3.5 to approximately 55-fold) as measured by the branched DNA assay. In a similar manner, CYP3A4 mRNA expression was also induced (10-30-fold), although at the higher doses induction returned to near control levels. CYP2B6 and 3A5 were also induced by fipronil, although at lower levels (2-3-fold). Confirmation of bDNA results were sought through western blotting and/or enzyme activity assays. Western blots using CYP3A4 antibody demonstrated a dose responsive increase from 0.5 to 1 µM followed by decreasing responses at higher concentrations. Similar increases and decreases were observed in CYP3A4-specific activity levels as measured using 6ß-hydroxytestosterone formation following incubation with testosterone. Likewise, activity levels for a CYP1A1-specific substrate, luciferin CEE, demonstrated that CYP1A1 enzyme activities were maximally induced by 1 µM fipronil followed by dramatically declining activity measurements at 10 and 25 µM. Cytotoxic effects of fipronil and fipronil sulfone were examined using the adenylate kinase and the trypan blue exclusion assays in HepG2 cells and human hepatocytes. The results indicate both that HepG2 cells and primary human hepatocytes are sensitive to the cytotoxic effects of fipronil. The maximum induction of adenylate kinase was ca. 3-fold greater than the respective controls in HepG2 and 6-10-fold in the case of primary hepatocytes. A significant time- and dose-dependent induction of adenylate kinase activity in HepG2 cells was noted from 0.1 to 12.5 µM fipronil followed by decreasing activities at 25 and 50 µM. For fipronil sulfone, cytotoxic effects increased throughout the dose range. The trypan blue assay indicated that cytotoxic effects contributing to an increase of greater than 10% of control values was indicated at doses above 12.5 µM. However, fipronil sulfone induced cytotoxic effects at lower doses. The possibility that cytotoxic effects were due to apoptosis was indicated by significant time- and dose-dependent induction of caspase-3/7 activity in both HepG2 cells and human hepatocytes. Fipronil mediated activation of caspase-3/7 in concurrence with compromised ATP production and viability are attributed to apoptotic cell death. [Description provided by NIOSH]
• Subjects:
  Insecticides Liver Occupational Health Safety
• Keywords:
  Hepatocytes Hepatotoxicity Hepatotoxins Humans Pesticides Pesticides-and-agricultural-chemicals
• ISSN:
  0009-2797
• Document Type:
  Text
• Funding:
  Cooperative Agreement
• Genre:
  Journal Article
• Place as Subject:
  Arizona ; North Carolina ; OSHA Region 4 ; OSHA Region 9
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  200-214
• Volume:
  164
• Issue:
  3
• NIOSHTIC Number:
  nn:20031505
• Citation:
  Chem-Biol Interact 2006 Dec; 164(3):200-214
• Contact Point Address:
  Department of Environmental and Molecular Toxicology, North Carolina State University, Raleigh, NC 27695-7633, USA
• Email:
  ernest_hodgson@ncsu.edu
• CAS Registry Number:
  Fipronil (CAS RN 120068-37-3) ; Sulfur (CAS RN 7704-34-9)
• Federal Fiscal Year:
  2007
• 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:c63db9fe9e7dbaafd2c0efe8a9c673f4975dd2526e2e6cba2e40082a5550242473af20d72d11c0615ccde5e921798b7d9809009e08c79275665a3fbde1f6adf2
• Download URL:
  https://stacks.cdc.gov/view/cdc/185774/cdc_185774_DS1.pdf
• File Type:
  [PDF - 1.12 MB ]