4.5. Establishment of the UV Irradiation-Induced Skin Photoaging Model

The objective of this experiment was to establish an animal model that, using complex ultraviolet, could be used to research the mechanism by which MAAs regulate tissue antioxidant enzyme levels and the expression of inflammatory factors, thereby protecting against UV irradiation-induced photoaging. The following methods were used for the irradiation of unhaired mouse skin, as in our previous report [12]: One 40 W UVB (UVB-313; wavelength range: 280–320 nm) and two 40 W UVA (UVA-340; wavelength range: 320–400 nm) lighting tubes (length and diameter of the light tube: 1200 × 38 mm) were used for simulating the ultraviolet light source. The distance from complex ultraviolet light source to the backs of the mice was 30 cm. Meanwhile, a radiometer was used to measure the practical ultraviolet intensity. With these conditions, the average UV radiation intensities were UVA 2.91 mw/cm² and UVB 18.07 mw/cm², which total radiation dose were radiation intensities and multiply by the time (irradiation duration was calculated by minimal erythemal dose). In the experiment, all mouse groups received identical doses of ultraviolet light as the distance between the model mice and the UV tubes was adjusted every five minutes. For this modeling process, the damage accumulation method was used to track the appropriate UV irradiation dosing as follows: 0.5 MED (minimal erythemal dose) for the first week, and then the UV irradiation intensity was increased per week up to 4 MED. Ultimately, all groups of mice received radiation dosages as follows: UVA: 20.81 J/cm², UVB: 0.47 J/cm². The irradiation experiment lasted for about one month.

All groups of mice were sacrificed after the last UV irradiation experiment, and dorsal skins were collected so that the level of antioxidant enzymes and inhibition of inflammation in the skin tissue could be further analyzed.