Ultraviolet (UV) radiation induces DNA damage, oxidative stress, and inflammatory processes in human keratinocytes, resulting in skin
inflammation, photoaging, and photocarcinogenesis. Adequate protection of skin against the harmful effects of UV irradiation is essential. Therefore, in this study, we investigated the protective effects of
afzelin, one of the
flavonoids, against UV irradiation in human keratinocytes and epidermal equivalent models. Spectrophotometric measurements revealed that the
afzelin extinction maxima were in the UVB and UVA range, and UV transmission below 376 nm was <10%, indicating UV-absorbing activity of
afzelin. In the
phototoxicity assay using the 3T3 NRU
phototoxicity test (3T3-NRU-PT),
afzelin presented a tendency to no phototoxic potential. In addition, in order to investigate cellular functions of
afzelin itself, cells were treated with
afzelin after UVB irradiation. In human keratinocyte,
afzelin effectively inhibited the UVB-mediated increase in lipid peroxidation and the formation of
cyclobutane pyrimidine dimers.
Afzelin also inhibited UVB-induced cell death in human keratinocytes by inhibiting intrinsic apoptotic signaling. Furthermore,
afzelin showed inhibitory effects on UVB-induced release of pro-inflammatory mediators such as
interleukin-6,
tumor necrosis factor-α, and prostaglandin-E2 in human keratinocytes by interfering with the p38 kinase pathway. Using an epidermal equivalent model exposed to UVB radiation, anti-apoptotic activity of
afzelin was also confirmed together with a photoprotective effect at the morphological level. Taken together, our results suggest that
afzelin has several cellular activities such as
DNA-protective,
antioxidant, and anti-inflammatory as well as UV-absorbing activity and may protect human skin from UVB-induced damage by a combination of UV-absorbing and cellular activities.