U.S. flag An official website of the United States government.
Official websites use .gov

A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS

A lock ( ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

i

Direct Evidence for Recycling of Myeloperoxidase-Catalyzed Phenoxyl Radicals of a Vitamin E Homologue, 2,2, 5,7, 8-Pentamethyl-6-Hydroxy Chromane, by Ascorbate/Dihydrolipoate in Living HL-60 Cells

Public Domain


Details

  • Personal Author:
  • Description:
    Myeloperoxidase (MPO)-catalyzed one-electron oxidation of endogenous phenolic constituents (e.g., antioxidants, hydroxylated metabolites) and exogenous compounds (e.g., drugs, environmental chemicals) generates free radical intermediates: phenoxyl radicals. Reduction of these intermediates by endogenous reductants, i.e. recycling, may enhance their antioxidant potential and/or prevent their potential cytotoxic and genotoxic effects. The goal of this work was to determine whether generation and recycling of MPO-catalyzed phenoxyl radicals of a vitamin E homologue, 2,2,5,7,8-pentamethyl-6-hydroxychromane (PMC), by physiologically relevant intracellular reductants such as ascorbate/lipoate could be demonstrated in intact MPO-rich human leukemia HL-60 cells. A model system was developed to show that MPO/H(2)O(2)-catalyzed PMC phenoxyl radicals (PMC(z.rad;)) could be recycled by ascorbate or ascorbate/dihydrolipoic acid (DHLA) to regenerate the parent compound. Absorbance measurements demonstrated that ascorbate prevents net oxidation of PMC by recycling the phenoxyl radical back to the parent compound. The presence of DHLA in the reaction mixture containing ascorbate extended the recycling reaction through regeneration of ascorbate. DHLA alone was unable to prevent PMC oxidation. These conclusions were confirmed by direct detection of PMC(z.rad;) and ascorbate radicals formed during the time course of the reactions by EPR spectroscopy. Based on results in the model system, PMC(z.rad;) and ascorbate radicals were identified by EPR spectroscopy in ascorbate-loaded HL-60 cells after addition of H(2)O(2) and the inhibitor of catalase, 3-aminotriazole (3-AT). The time course of PMC(z.rad;) and ascorbate radicals was found to follow the same reaction sequence as during their recycling in the model system. Recycling of PMC by ascorbate was also confirmed by HPLC assays in HL-60 cells. Pre-loading of HL-60 cells with lipoic acid regenerated ascorbate and thus increased the efficiency of ascorbate in recycling PMC(z.rad;). Lipoic acid had no effect on PMC oxidation in the absence of ascorbate. Thus PMC phenoxyl radical does not directly oxidize thiols but can be recycled by dihydrolipoate in the presence of ascorbate. The role of phenoxyl radical recycling in maintaining antioxidant defense and protecting against cytotoxic and genotoxic phenolics is discussed. [Description provided by NIOSH]
  • Subjects:
  • Keywords:
  • ISSN:
    0304-4165
  • Document Type:
    Text
  • Genre:
    Journal Article
  • Place as Subject:
  • CIO:
    National Institute for Occupational Safety and Health (NIOSH)
  • Division:
    HELD - Health Effects Laboratory Division
  • Topic:
    Workplace Safety & Health
  • Location:
    North America
  • Pages in Document:
    72-84
  • Volume:
    1620
  • Issue:
    1
  • NIOSHTIC Number:
    nn:20022635
  • Citation:
    Biochim Biophys Acta 2003 Mar; 1620(1-3):72-84
  • Contact Point Address:
    Dr. Valerian E. Kagan, Department of Environmental and Occupational Health, University of Pittsburgh, 3343 Forbes Ave, Pittsburgh,PA 15260
  • Email:
    kagan@pitt.edu
  • Federal Fiscal Year:
    2003
  • NORA Priority Area:
    Disease and Injury: Allergic and Irritant Dermatitis
  • Peer Reviewed:
    True
  • Source Full Name:
    Biochimica et Biophysica Acta
  • Collection(s):
  • Main Document Checksum:
    urn:sha-512:52153470cc16456f6d7bbe4a64b150097d0c0591dce3f359aa0838f385a2f5261896747c0aa7dd80523c18d36112a78badc1fef1a48e5e2fc180c151d9fc0843
  • Download URL:
  • File Type:
    Filetype[PDF - 380.54 KB ]
PREVIOUS
ON THIS PAGE
Details
CDC STACKS serves as an archival repository of CDC-published products including scientific findings, journal articles, guidelines, recommendations, or other public health information authored or co-authored by CDC or funded partners.

As a repository, CDC STACKS retains documents in their original published format to ensure public access to scientific information.
BACK TO TOP