Novel Azobenzene Compound to Extend and Reactivate UV Protection

May 1, 2014 | Contact Author | By: Jin-Ye Wang, PhD, and Shengyong Geng, Shanghai Jiao Tong University, Shanghai, China
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Title: Novel Azobenzene Compound to Extend and Reactivate UV Protection
azobenzene compoundsx liposomesx reversible photo-isomerizationx sunscreen cosmeticx cytotoxicityx
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Keywords: azobenzene compounds | liposomes | reversible photo-isomerization | sunscreen cosmetic | cytotoxicity

Abstract: Two azobenzene compounds were synthesized and combined in liposomal membranes. Their physico-chemical properties and biocompatibility were evaluated. The safer one was chosen, and its protective function for UVA and UVB were tested in vitro and in vivo. This azobenzene liposomal formulation provided good efficacy with longer shelf life, which could be utilized as a novel kind of repeated UV absorber.

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J-Y Wang and S Geng, Novel Azobenzene Compound to Extend and Reactivate UV Protection, Cosm & Toil 129(4) 84-95 (May 2014)

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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.

Experimental Design

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.

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Figure 1. Experimental design

Figure 1. Experimental design

Four test sites, 1-cm2 per site, were selected on the back of shaved rats or nude mice.

Figure 2. Isomerization of ACB-liposome under UV-Vis irradiation

Figure 2. Isomerization of ACB-liposome under UV-Vis irradiation

Isomerization of ACB-liposome under UV-Vis irradiation; isomerization rate (%) = 100 × At/A0, where A0 is the absorbance at the maximum absorption wavelength (λmax) of ACB-liposome in the initial state, and At is the absorbance at λmax at different irradiation time points.

Figure 3. Transmission electron micrographs of ACB-liposome

Figure 3. Transmission electron micrographs of ACB-liposome

Transmission electron micrographs of ACB-liposome: a) before and b) after ten cycles of periodic UV and visible irradiation; voltage was set at 200 kV and scale bar = 100 nm.

Figure 4. UVA protective effect of ACB-liposome in cream substrate

Figure 4. UVA protective effect of ACB-liposome in cream substrate

UVA protective effect of ACB-liposome when mixed with the cream substrate, as evaluated by critical wavelength method; area of the spectrum a) from 290–400 nm, b) from 290–390 nm, and c) from 290–389 nm.

Figure 5. Erythema and ambustion after UV irradiation for 5 hr and beyond

Figure 5. Erythema and ambustion after UV irradiation for 5 hr and beyond

Erythema and ambustion after UV irradiation for 5 hr, then observed after: a) 0 days, b) 1 day, c) 2 days and d) 3 days; a = avobenzone-liposome; b = ACB-liposome; c = PC-liposome; d = avobenzone; reproduced with permission from The Royal Society of Chemistry.

Figure 6. Observed skin states

Figure 6. Observed skin states

The skin states observed at: a) 0 days, b) 4 days, c) 5 days and d) 6 days after UV irradiation for 3.5 hr; a = avobenzone-liposome; b = ACB-liposome; c = PC-liposome; and d = avobenzone.

Figure 7. Fluorescent images of skin sections after applied samples for 2 hr

Figure 7. Fluorescent images of skin sections after applied samples

Fluorescent images of skin sections after applied samples onto the dorsal skin surface of nude mice for 2 hr; a) naked QDs; b) PC-QDs liposome; c) ACB-QDs liposome; and d) CAB-QDs liposome; scale bars = 100 μm; reproduced with permission from The Royal Society of Chemistry.

Figure 8. Fluorescent images of skin sections after applied samples for 8 hr

Figure 8. Fluorescent images of skin sections after applied samples for 8 hr

Fluorescent images of skin sections after applied samples onto the dorsal skin for 8 hr; a) naked QDs; b) PC-QDs liposome; c) ACB-QDs liposome; and d) CAB-QDs liposome; scale bars = 100 μm; reproduced with permission from The Royal Society of Chemistry.

Footntoes [Wang 129(4)]

a, e PC, CHOL, and 8-methoxypsoralen, Sigma (USA)
b Avobenzone, King Jack Int.
c Cream substrate, Shanghai Huashan Cosmetics Co., Ltd.
d QDs, Shen Zhen ZhongDS Investment Co., Ltd.
f Microplate reader, Stat Fax 2100
g Hg lamp, LCE-9, Zhengzhou, China
h Spectrophotometer, U3010, Hitachi
j Transpore tape, 3M
k TEK OCT, Sakura FineTek Inc.
m Cryostat CM3050S, Leica
n Fluorescence microscope BX51, Olympus
p DOTAP transfection reagent, Roche Diagnostics

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