Antioxidant activity and anti-melanogenic of the exopolysaccharide EPS-HuA40 from Mesonia sp. HuA40

• EPS-HuA40 scavenges DPPH, ·OH, and ROO· radicals effectively. • EPS-HuA40 is non-cytotoxic, reduces ROS in cells by promoting CAT/SOD production. • EPS-HuA40 inhibits B16-F10 melanogenesis by blocking tyrosinase and related genes. The growing demand for antioxidant and whitening skincare products has driven the development of eco-friendly natural ingredients. Marine microorganisms represent a rich source of novel bioactive molecules. This study investigated the antioxidant and melanogenesis-inhibitory activities of EPS-HuA40, an exopolysaccharide from the marine bacterium Mesonia sp. HuA40. EPS-HuA40 demonstrated significant dose-dependent scavenging activities against multiple free radicals, with a scavenging rate reaching up to 86.05%, which is comparable to that of the positive control antioxidant Vc (88.13%) at the same mass concentration. In HaCaT, HDF, and HUVEC cells, treatment with EPS-HuA40 significantly inhibited the production of intracellular ROS due to oxidative stress, without exhibiting cytotoxicity. And it enhanced the activities of intracellular antioxidant enzymes such as CAT and SOD to bolster cellular antioxidant capacity, protecting cells against adverse environments. Furthermore, EPS-HuA40 effectively reduced α-MSH-induced melanin production in B16-F10 cells by indirectly suppressing tyrosinase activity and downregulating melanogenesis-related gene expression. The results suggested that EPS-HuA40 exhibits significant antioxidant activity and reduces hyperpigmentation. Therefore, it holds potential for future application in skincare formulations.