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Covalent binding of polycyclic aromatic hydrocarbon components of coal tar to DNA in mouse skin
1Haddow Laboratories, Institute of Cancer Research, Sutton, Surrey, UK.
Abstract:
Treatment of mouse skin with coal tar is known to initiate tumour formation, with the carcinogenic activity associated mainly with polycyclic aromatic hydrocarbons (PAHs). A sample of pharmaceutical coal tar was analysed by gas chromatography and 19 major PAHs were identified. 32P-postlabelling analysis was used to characterize those PAHs that are responsible for the DNA binding of coal tar and, by inference, its biological activity. PAHs were grouped according to their reported carcinogenic activities and applied as mixtures to mouse skin. Group A contained all of the 19 PAHs, group B seven PAHs for which there is sufficient evidence for carcinogenicity and group C 12 PAHs with only limited or inadequate evidence of carcinogenicity in experimental animals. 32P-Labelled DNA adducts formed by coal tar were resolved on TLC into a pattern of three discrete spots (2, 4 and 6) and four areas of diffuse radioactivity (1, 3, 5 and 7). By comparison of the pattern of adducts formed by coal tar with those formed by the synthetic mixtures it appeared that PAHs in group B formed coal tar-DNA adduct spots 4 and 6, and that adduct spot 2 was formed by PAHs in group C. Attempts to identify those PAHs responsible for the formation of coal tar-DNA adducts 4 and 6 were made by comparing the chromatographic mobilities of 32P-labelled coal tar-derived DNA adducts formed in mouse skin, using TLC and HPLC, with those formed by PAHs in group B. As benzo[ghi]perylene (B[ghi]P), a component of group C, has been demonstrated to exhibit significant DNA binding ability previously, the chromatographic mobility of coal tar-DNA adduct spot 2 was compared to that of the major DNA adducts formed by B[ghi]P in vivo and in vitro. It appeared that coal tar adduct spot 2 was the major adduct formed by B[ghi]P in vitro and that benzo[a]pyrene, benzo[b]fluoranthene, benzo [j]fluoranthene and benzo[k]fluoranthene contributed to the formation of adduct spot 6. None of the PAHs examined appeared to be responsible for the formation of adduct spot 4.
Insights
Coal tar initiates tumors via polycyclic aromatic hydrocarbons (PAHs). This study identified specific PAHs responsible for DNA binding and tumor formation in mice, pinpointing benzo[ghi]perylene and other PAHs to specific DNA adducts.
Area of Science:
- Environmental Health
- Toxicology
- Molecular Biology
Background:
- Coal tar is a known carcinogen, primarily due to its polycyclic aromatic hydrocarbon (PAH) content.
- Pharmaceutical coal tar contains 19 identified major PAHs.
- Understanding which specific PAHs contribute to DNA binding is crucial for assessing carcinogenic risk.
Purpose of the Study:
- To identify the specific polycyclic aromatic hydrocarbons (PAHs) in coal tar responsible for DNA binding and subsequent tumor initiation.
- To correlate specific PAHs with the formation of distinct DNA adducts observed in mouse skin treated with coal tar.
Main Methods:
- Gas chromatography was used to identify 19 major PAHs in pharmaceutical coal tar.
- 32P-postlabelling analysis was employed to detect and characterize DNA adducts formed by coal tar and synthetic PAH mixtures in mouse skin.
- Thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC) were used to compare DNA adduct patterns.
Main Results:
- Coal tar formed distinct DNA adduct spots (2, 4, 6) and diffuse areas.
- PAHs with sufficient carcinogenic evidence (Group B) were linked to adduct spots 4 and 6.
- PAHs with limited evidence (Group C), including benzo[ghi]perylene, were associated with adduct spot 2.
- Benzo[ghi]perylene was identified as a major contributor to adduct spot 2, while benzo[a]pyrene and related compounds contributed to adduct spot 6.
Conclusions:
- Specific PAHs within coal tar exhibit differential DNA binding capabilities.
- Benzo[ghi]perylene is a significant contributor to coal tar-induced DNA adduct formation.
- The study elucidates the molecular mechanisms of coal tar carcinogenicity by linking specific PAHs to DNA adducts.