Evaluation of silver nanoparticle toxicity in skin in vivo and keratinocytes in vitro

Abstract

INTRODUCTION: Products using the antimicrobial properties of silver nanoparticles (Ag-nps) may be found in health and consumer products that routinely contact skin. OBJECTIVES: This study was designed to assess the potential cytotoxicity of Ag-nps in human epidermal keratinocytes (HEKs) and their inflammatory and penetrating potential into porcine skin in vivo. MATERIALS AND METHODS: We used eight different Ag-nps in this study [unwashed/uncoated (20, 50, and 80 nm particle diameter), washed/uncoated (20, 50, and 80 nm), and carbon-coated (25 and 35 nm)]. Skin was dosed topically for 14 consecutive days. HEK viability was assessed by MTT, alamarBlue (aB), and CellTiter 96 AQueous One (96AQ). Release of the pro inflammatory mediators interleukin (IL)-1β, IL-6, IL-8, IL-10, and tumor necrosis factor-α (TNF-α) were measured. RESULTS: The effect of the unwashed Ag-nps on HEK viability after a 24-hr exposure indicated a significant dose-dependent decrease (p < 0.05) at 0.34 μg/mL with aB and 96AQ and at 1.7 μg/mL with MTT. However, both the washed Ag-nps and carbon-coated Ag-nps showed no significant decrease in viability at any concentration assessed by any of the three assays. For each of the unwashed Ag-nps, we noted a significant increase (p < 0.05) in IL-1β, IL-6, IL-8, and TNF-α concentrations. We observed localization of all Ag-nps in cyto plasmic vacuoles of HEKs. Macroscopic observations showed no gross irritation in porcine skin, whereas microscopic and ultrastructural observations showed areas of focal inflammation and localization of Ag-nps on the surface and in the upper stratum corneum layers of the skin. CONCLUSION: This study provides a better understanding Ag-nps safety in vitro as well as in vivo and a basis for occupational and risk assessment. Ag-nps are non toxic when dosed in washed Ag-nps solutions or carbon coated.