Effect of niacin supplementation on UV-induced DNA damage in fish and mammalian cell lines

Ultraviolet radiation (UVR) is becoming recognised as a potential stress factor in aquatic systems, which may have deleterious consequences for finfish aquaculture. Most significantly, UVR is able to induce photochemical changes in DNA, either through direct absorption of incident photons or through the generation of reactive oxygen species. In mammals, it is recognised that a sufficient supply of dietary niacin is necessary for the maintenance of genomic stability, although such information is not available for fish. Therefore, this study investigates the induction of DNA damage by UVR in a representative fish (EPC-A1) and mammalian cell line (CHO-K1) and whether dietary niacin supplementation can ameliorate these effects. To this end the single cell gel electrophoresis (SCGE) or 'comet' assay was used to quantify the induction of DNA SSBs. The assay was first optimised and validated using reference chemical genotoxins (H20 2, EMS), before UVR-induced DNA damage was assessed. Subsequently, the efficacy of niacin supplementation (0.18, 0.56, 1.0 mM) in reducing UYR-induced DNA damage was evaluated. During these experiments it was found that that both the reference genotoxins (H20 2, EMS) and UVR were capable of inducing increased levels of DNA SSBs in fish and mammalian cells, in comparison to untreated controls. However, optimisation results showed that neither increasing unwinding nor electrophoresis time increased the extent DNA strand migration. Validation with EMS showed no significant differences in sensitivity to chemically-induced DNA damage between the two cell lines, although EPC-A1 cells where found to be more sensitive to UYR-induced DNA damage. This was exhibited as a significant increase in DNA damage at a lower dose of UVR than in the CHO-K1 cells (120 J/m² compared to 180 J/m² ). Niacin supplementation was effective in reducing UVR-induced DNA damage to background levels in the CHO-K1 cells. Contrastingly, niacin supplementation made no significant difference to UVR-induced DNA damage in EPC-A1 cells. These results confirm that niacin is important for the maintenance of genomic stability in mammalian cells. The possible beneficial effect of dietary micronutrient supplementation for reducing UYR-induced DNA damage in farmed finfish remains undefined. Recommendations for further research are suggested