Are free radicals involved in tumor promotion?

W. J. Kozumbo, M. A. Trush, T. W. Kensler

Research output: Contribution to journalArticle

Abstract

Previously it was shown that lipophilic analogs of a free-radical scavenger, 2(3)-tert-butyl-4-hydroxyanisole (BHA), inhibit ornithine decarboxylase (ODC) activity which is induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) in mouse epidermis. With regard to this antitumor-promoting effect, eight analogs of BHA (2- and 3-BHA, 2-t-butyl-1, 4-dimethoxybenzene methyl-BHA), t-butylhydroquinone (t-BHQ), p-hydroquinone (HQ), 4-hydroxyanisole, phenol and 2-t-butylphenol) are evaluated herein for their antioxidant capacities for scavenging superoxide anions (O2-, of inhibiting lipid peroxidation and of inhibiting chemiluminescence (CL) in TPA-activated polymorphonuclear leukocytes (PMNs), an event associated with oxy-radical production. None of the analogs reacted with O2-, while 2- and 3-BHA suppressed the formation of O2- by TPA-activated PMNs. T-BHQ underwent autoxidation in aqueous solution, reducing molecular oxygen and increasing the levels of O2- that were formed chemically, enzymatically and cellularly. However, all of the phenolic antioxidant analogs of BHA inhibited TPA-stimulated CL in PMNs and ascorbate-initiated lipid peroxidation, while methyl-BHA (a non-antioxidant analog) was inactive. The inhibitory activities of these analogs for lipid peroxidation were related to both their lipophilic and antioxidant properties and corresponded favorably with their inhibitory activities for TPA-induced ODC activities in mouse epidermis. On the other hand, inhibition of the CL response by these antioxidants was independent of their lipophilicity and compared less favorably with their capacities to antagonize phorbol ester-induced ODC activity. These results imply that lipophilic BHA analogs inhibit TPA-induced ODC activity by scavenging free radicals other than O2-. Furthermore, the fact that t-BHQ was the most potent inhibitor of CL, lipid peroxidation and ODC activity and simultaneously reduced molecular oxygen, suggests the possibility that O2- may act as a precursor to the formation of free radicals which are reactive with t-BHQ and more directly involved in the process of tumor promotion.

Original languageEnglish (US)
Pages (from-to)199-207
Number of pages9
JournalChemico-Biological Interactions
Volume54
Issue numberC
DOIs
StatePublished - 1985

Keywords

  • Butylated hydroxyanisole
  • Chemiluminescence
  • Free radicals
  • Lipid peroxidation
  • Superoxide
  • Tumor promotion

ASJC Scopus subject areas

  • Toxicology

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