Abstract: In order to evaluate the effect of oral supplementation of four kinds of food-derived bioactive peptides on improving the elasticity of photoaged skin in SD rats and to explore the underlying mechanical mechanism, healthy adult female SD rats were randomly divided into normal control group, ultraviolet (UV) exposure group and four bioactive peptide administration groups. All animals except those in the normal control group were exposed to UVA radiation in combination with UVB. Water solutions of each bioactive peptide were prepared in at concentrations of 0.3, 0.9, and 1.5 g/L for the low, middle and high-dose peptide treatment groups, respectively. The model and peptide treatment groups were exposed to UV irradiation thrice weekly for 18 consecutive weeks until the photoaging model was established. The elasticity of dorsal skin in each animal group was detected with a skin analyzer and then the rats were sacrificed. Approximately 1 g of dorsal skin samples were mixed into 10 mL of buffer solution and homogenized, and then the homogenate was prepared for biochemical measurements. The contents of hydroxyproline and hyaluronic acid (HA) were determined by biochemical assays, and the contents of type I and III collagen, and the activity of matrix metalloproteinase-1 (MMP-1) were determined by enzyme-linked immunosorbent assay. Paraffin-embedded sections of skin tissue were prepared and stained with hematoxylin and eosin for histochemical observation. Results showed that skin elasticity and the contents of collagen I, hydroxyproline and HA in rat skin from the model group were significantly decreased when compared with the normal group, while the content of collagen III and the activity of MMP-1 were significantly increased. Histochemical assays showed epidermal hyperplasia and disorderly arrangement of collagen fibers in the dermis which were broken into fragments aggregated and distorted, together with solubilization and flattening of the basement membrane. In comparison with the model group, skin elasticity in all peptide supplementation groups was improved to some different degrees, with elastinderived peptide showing the best effect, which significantly increased the contents of collagen I, hydroxyproline and HA and significantly decreased the content of collagen III and the activity of MMP-1 (P < 0.05). Histochemical assays demonstrated that elastin-derived peptide markedly improved epidermal hyperplasia, increased the thickness of the dermis and the amount of collagen fibers and restored collagen fibers to the uniform compact wave-like arrangement of the blank control, suggesting that the mechanism of action of elastin-derived peptide was enhancing the biosynthesis of extracellular matrix (ECM) and inhibiting the degradation of ECM by MMP-1 as well as restoring the mechanical structure of photodamaged skin.

Key words: bioactive peptides, oral exposure, SD rat, skin photoaging