Condensed tannins from Acer palmatum seed coats attenuate UVB-induced skin hyperpigmentation and oxidative stress

Ultraviolet B (UVB) radiation is a major environmental stressor implicated in cutaneous hyperpigmentation and oxidative damage. In this study, we investigated the protective effects and underlying mechanisms of Acer palmatum seed coat-derived condensed tannins (CTs) against UVB-induced skin injury. The results revealed that A. palmatum CTs, predominantly consisting of B-type procyanidins based on (epi)catechin subunits, exhibit potent anti-tyrosinase activity (IC 50 = 22.53 ± 2.06 μg/mL) and antioxidant capacity (IC 50 187.47 ± 6.10 to 244.79 ± 1.73 μg/mL). In a UVB-irradiated B16F10 melanoma cell model, CTs produced a dose-dependent suppression of melanin synthesis (up to 48.34% reduction) and tyrosinase activity (up to 31.84% inhibition), which was accompanied by a 61.56% ± 1.99% decrease in intracellular reactive oxygen species (ROS). Further mechanistic studies demonstrated that A. palmatum CTs alleviated oxidative stress by restoring redox balance via enhancing catalase (CAT) and superoxide dismutase (SOD) activities while normalizing glutathione (GSH) and malondialdehyde (MDA) levels. Simultaneously, CTs attenuated melanogenesis by downregulating the expression of MITF, TYR, TRP-1, and TRP-2. We further elucidated that these effects are mediated through the suppression of the MAPK signaling pathway and the activation of the NRF2/HO-1 antioxidant axis, with evidence of NRF2-mediated crosstalk leading to MITF repression. These findings were corroborated by an in vivo mouse model, where topical application of CTs significantly ameliorated UVB-induced skin damage and oxidative stress. Collectively, our findings substantiate the potential of A. palmatum CTs as a promising multi-mechanistic and dual-functional natural agent for cosmeceutical applications targeting both hyperpigmentation and oxidative stress.