UVB Photoirradiation of Aloe Vera – Formation of Free Radicals, Singlet Oxygen, Superoxide, and Induction of Lipid Peroxidation
QINGSU XIA1, MARY D. BOUDREAU1, YU-TING ZHOU2, JUN-JIE YIN2 * AND PETER P. FU1
1. National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, U.S.A.
2. Center for Food Safety Applied Nutrition, U.S. Food and Drug Administration, College Park, U.S.A.
(Received: October 31, 2011; Accepted: November 7, 2011)
ABSTRACT
Aloe vera whole leaf extracts are incorporated into a wide variety of topically applied commercial products. Aloe vera whole leaf extracts contain anthraquinones, which can generate reactive oxygen species (ROS) upon UVA light irradiation. In this study, the phototoxicity of two Aloe vera whole leaf extracts, Aloe A and Aloe B, were examined. The Aloe B extract was prepared by treating the Aloe A extract with activated carbon (1%, wt/wt) and filtration to remove the Aloe latex components, including the anthraquinones. UVB irradiation of the Aloe vera whole leaf extracts induced lipid peroxidation in the presence of a lipid, methyl linoleate. The amounts of lipid peroxides formed were higher in the Aloe B, which contained lower amounts of anthraquinones than Aloe A. Sodium azide inhibited and deuterium oxide enhanced the formation of lipid peroxides by Aloe B, suggesting that singlet oxygen was involved in the mechanism. When superoxide dismutase was incorporated prior to irradiation, lipid peroxidation was inhibited, indicating that superoxide was produced during the photoirradiation of Aloe B. In addition, electron spin resonance (ESR) spectroscopy was also used to investigate the generation of free radicals by the UVB photoirradiated Aloe B. ESR measurements indicated that the UVB photoirradiation of Aloe B produced carbon-centered free radicals. These results suggested that, as with the exposure to UVA light, the exposure of Aloe vera whole leaf extracts to UVB light can also generate ROS and induce lipid peroxidation.
Key words: Aloe vera, UVB, Photoirradiation, Lipid peroxidation, Reactive oxygen species (ROS) , ESR