In-vitro toxicity of molybdenum trioxide nanoparticles on human keratinocytes

Molybdenum trioxide (MoO3) nanoparticles (NPs) embedded in polymer films have been proposed as a cheap way of producing antibacterial coatings on external surfaces. Recently, we synthesized MoO3 nanowires in a unique shape and degree of anisotropy, which enables their fast water dissolution and quick antimicrobial reaction. Potential human health risks following the exposure to MoO3 NPs however need to be assessed prior their wide use. We therefore, investigated the biological effect of these newly synthesized MoO3 NPs on the human keratinocyte cell line HaCaT, used here as a model for the human skin. Exposure of HaCaT cells to 1 mg/mL MoO3 NPs concentration for 1 h showed no effect on cell survival, had no influence on reactive oxygen species production, expression of proteins involved in antioxidant defense, secretion of pro-inflammatory cytokines, nor induced DNA damage. Interestingly however, ERK and p38 MAP kinases were activated, and upon longer time exposure, induced a moderate release of the pro-inflammatory cytokine interleukin 6, increased DNA damage and increased the level of caspase independent cell death. Our study indicates that exposing HaCaT cells to antibacterial MoO3 NPs water-based solution in durations less than 1 h exhibits no cytotoxicity, but rather triggers cell signalling involved in cell survival and inflammation; which should be taken into consideration when evaluating MoO3 NPs for medical applications.