Modulation of oxidant formation in mouse skin in vivo by tumor-promoting phorbol esters

Area of Science:

• Biochemistry
• Toxicology
• Dermatology

Background:

• Benzo(a)pyrene (BP) is a polycyclic aromatic hydrocarbon found in environmental pollutants.
• Metabolism of BP can lead to the formation of reactive intermediates that bind to DNA, potentially initiating carcinogenesis.
• Understanding the specific pathways of oxidant generation during BP metabolism in the skin is crucial for assessing its carcinogenic potential.

Purpose of the Study:

• To investigate the specific pathways of oxidant generation during the metabolism of (7S,8S)-dihydroxy-7,8-dihydrobenzo(a)pyrene ((+)-BP-7,8-diol) in mouse epidermis.
• To determine the role of cytochrome P-450 and peroxyl radicals in the epoxidation of (+)-BP-7,8-diol.
• To examine the effect of tumor promoters, such as tetradecanoyl phorbol acetate (TPA), and other agents on oxidant generation and DNA adduct formation.

Main Methods:

• 32P-postlabeling analysis of diastereomeric DNA adducts.
• Investigation of DNA adduct patterns in epidermal scrapings from female CD-1 mice.
• Administration of (+)-BP-7,8-diol and various agents including TPA, 4-O-methyl-TPA, calcium ionophore A23187, fluocinolone acetonide, and all-trans-retinoic acid.

Main Results:

• Cytochrome P-450 was identified as the major oxidant in the absence of TPA pretreatment.
• TPA pretreatment significantly increased the contribution of peroxyl radicals to (+)-BP-7,8-diol epoxidation, with maximal effect at 24-72 hours post-treatment.
• The tumor-promoting activity of TPA correlated with increased radical-derived adducts, while the non-promoting analog 4-O-methyl-TPA did not.
• Specific timing of TPA administration and co-administration of other agents influenced radical generation and DNA adduct formation.

Conclusions:

• Tumor-promoting phorbol esters stimulate oxygen radical generation in mouse skin during BP metabolism.
• Peroxyl radicals play a significant role in (+)-BP-7,8-diol epoxidation, particularly after TPA treatment.
• Inhibitors of tumor promotion, like fluocinolone acetonide and all-trans-retinoic acid, can block specific pathways of radical generation and subsequent DNA adduct formation.