Selective induction of apoptosis in mouse and human lung epithelial cell lines by the tert-butyl hydroxylated metabolite of butylated hydroxytoluene: a proposed role in tumor promotion

Toxicology. 1998 Sep 15;130(2-3):115-27. doi: 10.1016/s0300-483x(98)00102-4.

Abstract

Butylated hydroxytoluene (BHT) causes lung injury in mice and promotes tumor formation. Hydroxylation of a tert-butyl group on BHT to yield the metabolite, 6-tert-butyl-2-[2'-(2'-hydroxymethyl)-propyl]-4-methylphenol (BHTOH), may be required. BHTOH is more potent than BHT on an equimolar basis in causing lung damage, enhancing lung tumor development, killing isolated bronchiolar non-ciliated Clara cells, and inhibiting lung epithelial gap junctional intercellular communication. One mechanism proposed for tumor promoting agents is selective cytotoxicity; killing normal cells allows uninhibited clonal expansion of neighboring initiated cells. We compared the abilities of BHT, BHTOH, and other BHT metabolites to kill non-tumorigenic and tumorigenic mouse and human lung cell lines, and examined the contribution of apoptosis to this cytotoxicity. These cells lack the cytochrome P450 2B isozyme necessary for converting BHT to BHTOH. BHTOH and 4-hydroperoxy-4-methyl-2,6-di-tert-butyl-2,5-cyclohex-adienone+ ++ (BHTOOH) were most toxic, BHT and 2,6-di-tert-butyl-1,4-benzoquinone (BHTQu) were less potent, and 4-methyl BHT metabolites that are not pneumotoxic were ineffective. BHTOH most strongly induced apoptosis, based on nuclear condensation and transmission electron microscopy. Non-tumorigenic cells were as susceptible to cell death as the neoplastic cell lines when apoptosis and necrosis are not distinguished, but more sensitive to BHTOH-induced apoptosis. An apoptotic mechanism may underlie the lung tumor promoting actions of BHTOH.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Apoptosis / drug effects*
  • Bronchi / cytology
  • Bronchi / drug effects
  • Butylated Hydroxytoluene / analogs & derivatives*
  • Butylated Hydroxytoluene / chemistry
  • Butylated Hydroxytoluene / toxicity
  • Carcinogens / toxicity*
  • Cell Count
  • Cell Nucleus / drug effects
  • Cell Nucleus / ultrastructure
  • Cell Transformation, Neoplastic / drug effects*
  • Cell Transformation, Neoplastic / pathology
  • Cytochrome P-450 CYP2B1 / deficiency
  • Cytochrome P-450 CYP2B1 / metabolism
  • Epithelial Cells / drug effects*
  • Epithelial Cells / enzymology
  • Epithelial Cells / pathology
  • Humans
  • Lung / drug effects*
  • Lung / enzymology
  • Lung / pathology
  • Lung Neoplasms
  • Mice
  • Mice, Inbred Strains
  • Tumor Cells, Cultured

Substances

  • Carcinogens
  • Butylated Hydroxytoluene
  • Cytochrome P-450 CYP2B1
  • 2,6-di-tert-butyl-4-hydroxy-4-methyl-2,5-cyclohexadien-1-one