Bioactive-rich kale extracts protect against UV-induced oxidative stress and DNA damage in human skin fibroblasts

Exposure to ultraviolet (UV) radiation causes oxidative stress and DNA damage in skin cells. This study investigated the protective effects of bioactive-rich extracts prepared from upcycled kale powder using UV-induced human skin fibroblasts (WS1 cells) in vitro. The extracts were prepared using ultrasound-assisted extraction [K(U)] and microwave-assisted extraction [K(M)]. The Fourier transform infrared spectroscopy (FT-IR) and ultra-high-performance liquid chromatography electrospray ionization mass spectrometry (UPLC-ESI-MS) demonstrated that K(M) contains higher concentrations of major bioactive phytochemicals, including phenolic acids, carotenoids, glucosinolates and flavonoids, than K(U). Both extracts contributed to higher cell viability (>80%) at concentrations of 1, 10, and 100 µg/mL compared to the UV-exposed control. Furthermore, the kale extracts and all tested phytochemicals (0.001-100 µg/mL) significantly reduced UV-induced reactive oxygen species (p < 0.05) compared to the UV-treated control. UV irradiation increased DNA damage, while K(U) at 0.01 and 0.1 µg/mL, chlorogenic acid at 0.1 µg/mL, and sulforaphane at 0.001 and 0.01 µg/mL significantly reduced DNA damage compared to the UV-treated control, as determined using phosphorylated H2A histone (γ-H2AX) immunofluorescence assay. Therefore, phytochemical-rich kale extracts demonstrate potential in protecting skin fibroblasts from UV-induced oxidative stress and DNA damage, suggesting potential applications in cosmeceutical formulations for skin protection against UV radiation.