Editor’s note: While Cosmetics & Toiletries acknowledges that animal testing is a sensitive issue to many readers worldwide, it is important to note that in China, where these authors conducted their research, it is currently legally required. All animal experiments involved in this study were performed in accordance with Regulations for the Administration of Affairs Concerning Experimental Animals of China.
UV radiation can be absorbed by different chromophores in the skin, and absorption of UV photons by these chromophores results in different photochemical reactions and secondary interactions involving reactive oxygen species (ROS), which result in harmful effects. UV radiation is comprised of 98% UVA (320–400 nm) and 2% UVB (290–320 nm). UVB radiation is mainly responsible for the most severe damage: acute damage such as sunburn and long-term damage, including cancer. It has a direct impact on cell DNA and proteins. Unlike UVB, UVA radiation is not directly absorbed by biological targets, but can still dramatically impair cell and tissue functions.
An ideal sunscreen should provide uniform UVB/UVA protection, and remain unchanged after UV irradiation. Another consideration is safety; this is a fundamental point in the field of cosmetics. Skin presents a significant barrier for most substances applied. Typically, one wants UV filters to stay on the surface or to not permeate lower than the upper epidermis; certainly not to the vascular dermis.
In the present study, two photosensitive compounds, i.e., 4-cholesterocarbonyl-4’-(N,N’-diethylaminobutyloxy) azobenzene (ACB) and 4-cholesterocarbonyl-4’-(N,N,N-triethylamine butyloxyl bromide) azobenzene (CAB), were synthesized. The phototoxicity of the two compounds was first evaluated in animal models. The cytotoxicity after combined either ACB or CAB into liposomes was then compared with NIH3T3 cells. In addition, their skin permeation ability was assessed. Finally, ACB, the safer of the two, was studied in greater depth for its stability under UV and visible light irradiation, as well as its UVA and UVB protective efficacy.
Materials: Egg phosphatidylcholine (PC) and cholesterol (CHOL) were purchased. The commercial sunscreen 4-tert-butyl-4’-methoxydibenzoylmethane—also known as avobenzone (C20H22O3)—also was obtained. The cream substrate used was provided gratis, and water-soluble CdTe630 quantum dots (QDs) were purchased. Finally, ACB (C48H71N3O3, Mw 737) and CAB (C50H76N3O3+, Mw 766) were synthesized.