Size-dependent effects of tungsten carbide–cobalt particles on oxygen radical production and activation of cell signaling pathways in murine epidermal cells

Hard metal or cemented carbide consists of a mixture of tungsten carbide (WC) (85%) and metallic cobalt (Co) (5–15%). WC–Co is considered to be potentially carcinogenic to humans. However, no comparison of the adverse effects of nano-sized WC–Co particles is available to date. In the present study, we compared the ability of nano- and fine-sized WC–Co particles to form free radicals and propensity to activate the transcription factors, AP-1 and NF-κB, along with stimulation of mitogen-activated protein kinase (MAPK) signaling pathways in a mouse epidermal cell line (JB6 P +). Our results demonstrated that nano-WC–Co generated a higher level of hydroxyl radicals, induced greater oxidative stress, as evidenced by a decrease of GSH levels, and caused faster JB6 P + cell growth/proliferation than observed after exposure of cells to fine WC–Co. In addition, nano-WC–Co activated AP-1 and NF-κB more efficiently in JB6 +/+ cells as compared to fine WC–Co. Experiments using AP-1-luciferase reporter transgenic mice confirmed the activation of AP-1 by nano-WC–Co. Nano- and fine-sized WC–Co particles also stimulated MAPKs, including ERKs, p38, and JNKs with significantly higher potency of nano-WC–Co. Finally, co-incubation of the JB6 +/+ cells with N-acetyl-cysteine decreased AP-1 activation and phosphorylation of ERKs, p38 kinase, and JNKs, thus suggesting that oxidative stress is involved in WC–Co-induced toxicity and AP-1 activation.