Combined Effect of Silybin and Sodium Acetylated Hyaluronate on UV-Induced Photoaging

Exposure to solar ultraviolet (UV) radiation is a major cause of skin photoaging, which is characterized by decreased collagen levels in the dermis. Both silybin and sodium acetylated hyaluronate (HA) are potential anti-aging compounds. However, when used alone, both agents show limited anti-aging efficacy. This study aimed to examine the combined effects of silybin and HA on UV-induced skin photoaging and elucidate the underlying mechanisms.

In this study, cytotoxicities of silybin and HA were assessed across a range of concentrations, both with and without UV exposure. We quantified mRNA levels of matrix metalloproteinase-1 (MMP-1), collagen type I (Col I), and collagen type III (Col III) after silybin and HA treatment to study their collagen synthesis promotion and degradation inhibition effects. Reducibility and reactive oxygen species (ROS) scavenging activity were also characterized for each compound. Collagen protein content was then measured after individual and combined treatments.

Silybin showed obvious cytotoxicity when its concentration reached 0.01%, while HA remained largely non-toxic even at concentrations of 1%. UV irradiation slightly increased the cytotoxicity of both silybin and HA. Notably, silybin effectively inhibited collagen degradation by downregulating MMP-1 mRNA expression, although it failed to upregulate Col I and III mRNA levels. In contrast, HA did not inhibit, and at higher concentrations slightly elevated, MMP-1 mRNA expression, while it was efficient in promoting Col I and III mRNA expression. Therefore, combined treatment with silybin and HA led to the downregulation of MMP-1 mRNA levels and upregulation of Col I and III mRNA levels. Silybin also showed high reducibility and therefore provided strong ROS scavenging capacity. As MMP-1 synthesis is primarily induced by ROS, silybin exhibited strong MMP-1 inhibition. Meanwhile, HA showed weak ROS scavenging capacity owing to its low reducibility. Nevertheless, the combination of silybin and HA inhibited collagen degradation (primarily via silybin) and promoted Col I and III mRNA expression and protein synthesis (primarily via HA), thereby increasing overall collagen protein levels.

This study reveals the complementary mechanisms through which silybin and HA collectively increase dermal collagen levels-silybin by protecting existing collagen from degradation and HA by promoting collagen synthesis-guiding their combined use in cosmetics to protect the skin from UV-induced photoaging.