Syringic acid prevents skin carcinogenesis via regulation of NoX and EGFR signaling

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Graphical abstractValidation of nutraceutical and pharmaceutical targets is essential for the prediction of physiological and side effects. Epidemiologic evidence and molecular studies suggest that non-melanoma skin cancer is directly associated with excessive exposure to ultraviolet (UV) radiation. The aim of the present study was to evaluate the inhibitory effects of syringic acid on UVB-induced signaling and skin carcinogenesis, and determine the molecular targets. Treatment of human epidermal keratinocytes (HaCaT) cells with syringic acid resulted in the suppression of UVB-induced cyclooxygenase-2, matrix metalloproteinase-1, and prostaglandin E2 expression as well as activator protein-1 activity. Moreover, syringic acid inhibited the UVB-induced phosphorylation of mitogen-activated protein kinases and Akt signaling pathways as well as epidermal growth factor receptor (EGFR). Syringic acid treatment further inhibited intracellular reactive oxygen species and protein-tyrosine phosphatase-κ activity, a regulator of EGFR activation. Syringic acid and the antioxidant N-acetyl-l-cysteine inhibited UVB-induced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity. In vivo, pretreatment of mouse skin with syringic acid significantly suppressed UVB-induced skin tumor incidence in a dose-dependent manner. Overall, these results indicate that syringic acid exerts potent chemopreventive activity in skin carcinogenesis mainly by inhibition of the Nox/PTP-κ/EGFR axis. Syringic acid might serve as an effective chemopreventive and therapeutic agent against UVB-mediated skin cancer.

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