(ES06-22) 6’,7’-dihydroxybergamottin (DHB) Affects UV-Induced DNA Damage of the Skin

Objectives: Epidemiological studies have found that high citrus fruit consumption was associated with higher risk of skin cancer, the most common cancer in the United States. Citrus fruits are rich in furocoumarins, which may interact with ultraviolet (UV) radiation to elevate risk of skin cancer. 6’,7’-dihydroxybergamottin (6’7’-DHB) is a furocoumarin commonly found in citrus fruits and its intake was associated with increased risk of basal cell carcinoma, a type of skin cancer. We aimed to determine whether 6’7’-DHB affects UVA-induced DNA damage in melanocytes, where melanoma originates.

Methods: Oxidative DNA damage phosphorylates H2AX (a member of the histone H2A family) and generates γ-H2AX. We assessed γ-H2AX as an indicator of DNA damage in human epidermal melanocytes untreated or treated with 50 µM 6’7’-DHB for 12 hours with or without 4J/cm2 UVA. Analysis of the experimental groups was done through western blots stained with H2AX and γ-H2AX antibodies. Immunostaining was quantified using ImageJ/FIJI software. To measure DNA damage, intensities of γ-H2AX bands were divided by that of H2AX bands (γ-H2AX/total H2AX). To see if 6’7’-DHB interacts with UV to influence DNA damage, the UV:Control ratios for untreated and 6’7’-DHB treated cells were calculated as the ratio of γ-H2AX/total H2AX in cells exposed to UV to that of cells without UV. T-tests were done to determine the significances of differences between γ-H2AX/total H2AX and between UV:Control ratios of the 4 groups.

Results: The mean UV:Control ratio for 6’7’-DHB treated cells (7.82) was nearly 7 times higher than the ratio for untreated cells (1.15), suggesting that 6’7’-DHB interacts with UV to increase DNA damage. The mean γ-H2AX/total H2AX for cells treated with 6’7’-DHB and exposed to UV (5.85) was higher than that of cells only exposed to UV (0.71), although the difference was not statistically significant (p=0.17).

Conclusions: 6’7’-DHB enhances UVA-induced DNA damage in melanocytes, which could suggest that 6’7’-DHB interacts with UV radiation to increase the risk of skin cancer. The potential carcinogenic properties of 6’7’-DHB, along with other dietary furocoumarins, should be further evaluated.

Funding Sources: Brown Cancer Center