Long term exposure to benzo[b]fluoranthene does not induce mutations in Mutamouse male germ cells

Abstract

Germ cell mutations can be inherited and lead to genetic disorders in the offspring. Thus, it is critical to identify environmental exposures that impact the germline. Polycyclic aromatic hydrocarbons (PAHs) are widespread combustion by-products found in food, tobacco smoke, and urban air. Benzo[b]fluoranthene (BbF) is a PAH that is classified as a possible human carcinogen. Studies using the transgenic mouse lacZ assay and duplex sequencing (DS), an error-corrected sequencing technology, have demonstrated that BbF robustly induces mutations in somatic tissues. However, the mutagenic effects of BbF on germ cells are unknown. We investigated whether long-term exposure to BbF induces mutations in male germ cells. Adult MutaMouse males were orally exposed to BbF in olive oil at doses of 0, 3.25, 6.25, 12.5, 25, or 50 mg/kg body weight per day (BW/day) for 90 days, or to 0, 1.56, 3.125, 6.25, 12.5, or 25 mg/kg BW/day for 180 days. Mutant frequencies were determined using the lacZ assay (n = 8 per group). Control and high dose groups at each time point were then sequenced to detect mutations using DS (n = 6 per group). Neither method detected significant increases in mutations following BbF exposure. Similarly, there was no increase in C:G > A:T transversions at either time point, the main mutation subtype induced by BbF in somatic tissues. These results suggest that BbF or its active metabolites are not present in germ cells at amounts sufficient to cause mutations, and/or DNA damage repair mechanisms in germ cells effectively repair BbF-induced damage.