1,4-Naphthoquinones as inducers of oxidative damage and stress signaling in HaCaT human keratinocytes

Selected biological effects of 1,4-naphthoquinone, menadione (2-methyl-1,4-naphthoquinone) and structurally related quinones from natural sources - the 5-hydroxy-naphthoquinones juglone, plumbagin and the 2-hydroxy-naphthoquinones lawsone and lapachol - were studied in human keratinocytes (HaCaT). 1,4-naphthoquinone and menadione as well as juglone and plumbagin were highly cytotoxic, strongly induced reactive oxygen species (ROS) formation and depleted cellular glutathione. Moreover, they induced oxidative DNA base damage and accumulation of DNA strand breaks, as demonstrated in an alkaline DNA unwinding assay. Neither lawsone nor lapachol (up to 100 μM) were active in any of these assays. Cytotoxic and oxidative action was paralleled by stimulation of stress signaling: all tested quinones except lawsone and lapachol strongly induced phosphorylation of the epidermal growth factor receptor (EGFR) and the related ErbB2 receptor tyrosine kinase. EGFR activation by plumbagin, juglone and menadione was attenuated by a superoxide dismutase mimetic, indicating that ROS-related mechanisms contribute to EGFR activation by these naphthoquinones.