Quercitrin Functions as an Antioxidant and Protects UV-Induced Carcinogenesis

Abstract Reactive oxygen species (ROS) and related oxidative stress are linked with various diseases including cardiovascular disease, cancer, chronic lung diseases, and diabetes mellitus. Interventions favoring the scavenging of ROS to attenuate the oxidative stress may prevent oxidant stress associated diseases. Recent studies suggest that various fruits and vegetables contain high concentrations of antioxidants. Quercitrin is a glycosylated form of flavonoid compounds, widely distributed in nature, and is ubiquitous in plants, fruits, seeds, and vegetables. Our preliminary studies show that this compound displayed a stronger antioxidant activity than that of ascorbic acid over the same concentration range. It blocked TPA-induced neoplastic transformation in JB6 p+ cells. Pretreatment of JB6 cells with quercitrin down-regulated activation of AP-1, NFKB induced by UVB or TPA. In the skin of AP-1-luciferase transgenic mice, topical treatment of mouse with quercitrin markedly blocked the TPA-induced AP-1 activation. Further studies indicated that these inhibitory actions appear to be mediated through the inhibition of MAPKs phosphorylation, including ERKs, p38 kinase, and JNKs. In addition, quercitrin stimulated the activation of NF-E2-related factor (Nrf2) and GST AREluciferase activity. Comet assays showed that quercitrin could block DNA damage induced by UVB. These preliminary studies indicate that quercitrin may function as a potential chemopreventive and chemotherapeutic agent. The overall hypothesis of this application is that quercitrin functions as an antioxidant and protects UVinduced carcinogenesis. The goal of this proposal is to test this hypothesis. Aim 1 will investigate the antioxidant properties of quercitrin in both non-cellular and ce"ular. We will study whether quercitrin scavenges free radicals or inhibits their generation and determine reaction rate constants of the reactions between quercitrin and oxygen radicals. Moreover, we will detect the UV-induced free radical generation from UVirradiated skin of living animal using in vivo electron spin resonance (ESR) spin trapping and identify the radicals generated. Aim 2 will investigate the inhibitory effects of quercitrin against the UV -induced oxidative damage to lipid, protein, and DNA, and UV-induced tumorigenesis and cell proliferation in SKH-1 hairless mice. This study represents first detection of free radicals generated by UV-irradiated skin of living animals and may potentially open a new avenue to evaluate the properties of antioxidant against free radicals generated in living animals. Another significance of the study is the identification of qucertrin as a preventive agent against UV-induced skin cancers.