Mechanistic relationships between hepatic genotoxicity and carcinogenicity in male B6C3F1 mice treated with polycyclic aromatic hydrocarbon mixtures.

The genotoxicity of a complex mixture [neutral fraction (NF)] from a wood preserving waste and reconstituted mixture (RM) mimicking the NF with seven major polycyclic aromatic hydrocarbons (PAHs) and benzo(a)pyrene (BaP) was investigated by determining DNA adducts and tumor incidence in male B6C3F1 mice exposed to three different doses of the chemical mixtures. The peak values of DNA adducts were observed after 24 h, and the highest levels of PAH-DNA adducts were exhibited in mice administered NF + BaP, and the highest tumor incidence and mortality were also observed in this group. DNA adduct levels after 1, 7, or 21 days were significantly correlated with animal mortality and incidence of total tumors including liver, lung, and forestomach. However, only hepatic DNA adducts after 7 days significantly correlated with liver tumor incidence. Most proteins involved in DNA repair including ATM, pATR, Chk1, pChk1, DNA PKcs, XRCC1, FANCD2, Ku80, Mre11, and Brca2 were significantly lower in liver tumor tissue compared to non-tumor tissue. Expressions of proteins involved in apoptosis and cell cycle regulation were also significantly different in tumor versus non-tumor tissues, and it is possible that PAH-induced changes in these gene products are important for tumor development and growth.

Effects of dietary fish oil on the depletion of carcinogenic PAH-DNA adduct levels in the liver of B6C3F1 mouse.

Many carcinogenic polycyclic aromatic hydrocarbons (PAHs) and their metabolites can bind covalently to DNA. Carcinogen-DNA adducts may lead to mutations in critical genes, eventually leading to cancer. In this study we report that fish oil (FO) blocks the formation of DNA adducts by detoxification of PAHs. B6C3F1 male mice were fed a FO or corn oil (CO) diet for 30 days. The animals were then treated with seven carcinogenic PAHs including benzo(a)pyrene (BaP) with one of two doses via a single intraperitoneal injection. Animals were terminated at 1, 3, or 7 d after treatment. The levels of DNA adducts were analyzed by the (32)P-postlabeling assay. Our results showed that the levels of total hepatic DNA adducts were significantly decreased in FO groups compared to CO groups with an exception of low PAH dose at 3 d (P = 0.067). Total adduct levels in the high dose PAH groups were 41.36±6.48 (Mean±SEM) and 78.72±8.03 in 10(9) nucleotides (P = 0.011), respectively, for the FO and CO groups at 7 d. Animals treated with the low dose (2.5 fold lower) PAHs displayed similar trends. Total adduct levels were 12.21±2.33 in the FO group and 24.07±1.99 in the CO group, P = 0.008. BPDE-dG adduct values at 7 d after treatment of high dose PAHs were 32.34±1.94 (CO group) and 21.82±3.37 (FO group) in 10(9) nucleotides with P value being 0.035. Low dose groups showed similar trends for BPDE-dG adduct in the two diet groups. FO significantly enhanced gene expression of Cyp1a1 in both the high and low dose PAH groups. Gstt1 at low dose of PAHs showed high levels in FO compared to CO groups with P values being 0.014. Histological observations indicated that FO played a hepatoprotective role during the early stages. Our results suggest that FO has a potential to be developed as a cancer chemopreventive agent.

Toxicity characterization of complex mixtures using biological and chemical analysis in preparation for assessment of mixture similarity.

In the United States, several proposed approaches for using bioassays for the risk assessment of complex hazardous mixtures require that selected mixtures be "sufficiently similar" to each other. The goal of this research was to evaluate the utility of a protocol using in vitro bioassays and chemical analysis as a basis for assessing mixture similarity. Two wood preserving wastes (WPWs) containing polycyclic aromatic hydrocarbons and pentachlorophenol were extracted and fractionated to generate potentially similar mixtures. Chemical analysis was conducted using gas chromatography/mass spectrometry. Genotoxicity was evaluated using the Salmonella/microsome and Escherichia coli prophage induction assays. The crude extract of one WPW was also tested in the chick embryotoxicity screening test (CHEST) assay. The CHEST assay provided the most sensitive measurement of toxicity. Overall, the biological potency of the samples was not well correlated with predicted potency based on chemical analysis. Although several mixtures appeared similar based on chemical analysis, the magnitude of the response in bioassays was often dissimilar. Fractionation was required to detect the genotoxicity of mixture components in vitro. The results confirm the need for an integrated protocol, combining chemical analysis, fractionation, and biological testing to characterize the risk associated with complex mixtures.