Silver nanoparticles exert a long-lasting antiproliferative effect on human keratinocyte HaCaT cell line

For their antibacterial activity, silver nanoparticles (Ag NPs) are largely used in various commercially available products designed to come in direct contact with the skin. In this study we investigated the effects of Ag NPs on skin using the human-derived keratinocyte HaCaT cell line model. Ag NPs caused a concentration- and time-dependent decrease of cell viability, with IC50 values of 6.8 ± 1.3 μM (MTT assay) and 12 ± 1.2 μM (SRB assay) after 7 days of contact. A 24 h treatment, followed by a 6 day recovery period in Ag NPs-free medium, reduced cell viability with almost the same potency (IC50s of 15.3 ± 4.6 and 35 ± 20 μM, MTT and SRB assays, respectively). Under these conditions, no evidence of induction of necrotic events (propidium iodide assay) was found. Apocynin, NADPH-oxidase inhibitor, or N(G)-monomethyl-l-argynine, nitric oxide synthase inhibitor, did not prevent NPs-induced reduction of cell viability. TEM analysis of cells exposed to NPs for 24 h revealed alteration of nuclear morphology but only a marginal presence of individual NPs inside the cells. These results demonstrate that on HaCaT keratinocytes a relatively short time of contact with Ag NPs causes a long-lasting inhibition of cell growth, not associated with consistent Ag NPs internalization.

► In HaCaT cells silver nanoparticles caused a long-lasting inhibition of cell growth.
► Twenty-four hours treatment plus 6 days in nanosilver-free medium still reduced cell viability.
► No evidence of induction of necrotic events or of ROS production was found.
► NPs underwent to only a marginal internalization.