Cytotoxicity and mutagenicity of retinol with ultraviolet A irradiation in mouse lymphoma cells

Vitamin A (all-trans-retinol; retinol) is an essential human nutrient and plays an important role in several biological functions. However, under certain circumstances, retinol treatment can cause free radical generation and induce oxidative stress. In this study, we investigated photocytotoxicity and photomutagenicity of retinol using L5178Y/Tk+/− mouse lymphoma cells concomitantly exposed to retinol and ultraviolet A (UVA) light. While the cells treated with retinol alone at the doses of 5 or 10 μg/ml in the absence of light did not increase the mutant frequency (MF) in the Tk gene, the treatment of the cells with 1–4 μg/ml retinol under UVA light (1.38 mW/cm2 for 30 min) increased the MF in the Tk gene in a dose–responsive manner. To elucidate the underlying mechanism of action, we also examined the mutational types of the Tk mutants by determining their loss of heterozygosity (LOH) at four microsatellite loci spanning the entire chromosome 11 on which the Tk gene is located. The mutational spectrum for the retinol + UVA treatment was significantly different from those of the control and UVA alone. More than 93% of the mutants from retinol + UVA treatment lost heterozygosity at the Tk1 locus and the major type (58%) of mutations was LOHs extending to D11Mit42, an alternation involving approximately 6 cM of the chromosome, whereas the main type of mutations in the control was non-LOH mutations. These results suggest that retinol is mutagenic when exposed to UVA in mouse lymphoma cells through a clastogenic mode-of-action.