Photoprotective Effects of Germinated and Fermented Soybean Extract on UVB-irradiated SKH-1 Hairless Mice

Abstract

Ultraviolet (UV) radiation is a primary contributor to skin aging, accounting for approximately 90% of signs of premature aging. Continuous ultraviolet irradiation rapidly induces a large accumulation of reactive oxygen species (ROS) in the body, causing various metabolic diseases and causing direct damage to skin cells due to oxidative stress. The phytochemical isoflavones present in soybeans are recognized for exerting physiological effects, including anti-tumor, anti-obesity, and especially anti-aging properties. However, there is currently limited research on phytoestrogens, including the ability of phytochemicals to improve skin aging functions. This study was to evaluate the anti-inflammatory and potent antioxidant properties of germinated and fermented soybean extract (GFSE) in improving photoaging induced by continuous UVB irradiation in hairless mouse. Photoaging was induced in hairless mice by irradiating UVB for 8 weeks, and GFSE was orally administered daily (250 and 500 mg/kg). The skin was collected and parameters and wrinkle formation analysis and histopathological analysis were performed to indirectly assess the effects on skin conditions. Additionally, skin hyaluronic acid (HA) content, protein expression, and mRNA were evaluated for the photoprotective effects of GFSE through molecular biological approaches. GFSE significantly improved UVB-induced skin parameters and wrinkle index and reduced the increased thickness of the epidermis. In addition, the HA content reduced by UVB was increased. GFSE decreased the expression of matrix metalloproteinases, which were increased by UVB, and increased tissue metallopeptidase inhibitors and collagen type 1α1, which were decreased by UVB. It also increased antioxidant-related factors such as superoxide dismutase 1, catalase, and glutathione peroxidase, and increased factors related to the skin barrier and selective skin moisture absorption, such as involucrin, filaggrin, and aquaporin 3. GFSE administration reduced interleukin-1β, cyclooxygenase 2, and tumor necrosis factor-α which are inflammatory cytokines produced due to photoaging. Moreover, UVB reduced phosphorylated protein levels of Jun N-terminal kinase, extracellular signaling regulatory kinase, and p38, as well as cyclooxygenase 2 and inducible nitric oxide synthase protein levels. GFSE significantly improved skin photoaging and reduced the extent of skin damage in hairless mice exposed to UVB irradiation. These findings suggest that GFSE may be a functional food ingredient for alleviating skin photoaging.