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

Validation 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 E ₂ 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.