Is the toxic potential of nanosilver dependent on its size?

Anna Huk,Albert Duschl,Maria Dušinska,Emilia Izak-Nau,Bogumila Reidy,Iseult Lynch,Matthew Boyles

doi:10.1186/s12989-014-0065-1

Abstract

BackgroundNanosilver is one of the most commonly used engineered nanomaterials (ENMs). In our study we focused on assessing the size-dependence of the toxicity of nanosilver (Ag ENMs), utilising materials of three sizes (50, 80 and 200 nm) synthesized by the same method, with the same chemical composition, charge and coating.MethodsUptake and localisation (by Transmission Electron Microscopy), cell proliferation (Relative growth activity) and cytotoxic effects (Plating efficiency), inflammatory response (induction of IL-8 and MCP-1 by Enzyme linked immune sorbent assay), DNA damage (strand breaks and oxidised DNA lesions by the Comet assay) were all assessed in human lung carcinoma epithelial cells (A549), and the mutagenic potential of ENMs (Mammalian hprt gene mutation test) was assessed in V79-4 cells as per the OECD protocol. Detailed physico-chemical characterization of the ENMs was performed in water and in biological media as a prerequisite to assessment of their impacts on cells. To study the relationship between the surface area of the ENMs and the number of ENMs with the biological response observed, Ag ENMs concentrations were recalculated from μg/cm2 to ENMs cm2/cm2 and ENMs/cm2.ResultsStudied Ag ENMs are cytotoxic and cytostatic, and induced strand breaks, DNA oxidation, inflammation and gene mutations. Results expressed in mass unit [μg/cm2] suggested that the toxicity of Ag ENMs is size dependent with 50 nm being most toxic. However, re-calculation of Ag ENMs concentrations from mass unit to surface area and number of ENMs per cm2 highlighted that 200 nm Ag ENMs, are the most toxic. Results from hprt gene mutation assay showed that Ag ENMs 200 nm are the most mutagenic irrespective of the concentration unit expressed.ConclusionWe found that the toxicity of Ag ENMs is not always size dependent. Strong cytotoxic and genotoxic effects were observed in cells exposed to Ag ENMs 50 nm, but Ag ENMs 200 nm had the most mutagenic potential. Additionally, we showed that expression of concentrations of ENMs in mass units is not representative. Number of ENMs or surface area of ENMs (per cm2) seem more precise units with which to compare the toxicity of different ENMs.Electronic supplementary materialThe online version of this article (doi:10.1186/s12989-014-0065-1) contains supplementary material, which is available to authorized users.

Highlights

Nanosilver is one of the most commonly used engineered nanomaterials (ENMs)
We did not study possible interference of PVP coated ENMs with Enzyme-linked immunosorbent assay (ELISA), we found that PVP immobilized at ENM surfaces reduces protein binding, suggesting that the likelihood of such interference is low [33]
We were interested to see if ENMs with the same shape, charge and chemical composition but with different sizes resulted in similar toxicity responses in mammalian cells

Summary

Introduction

Nanosilver is one of the most commonly used engineered nanomaterials (ENMs). In our study we focused on assessing the size-dependence of the toxicity of nanosilver (Ag ENMs), utilising materials of three sizes (50, 80 and 200 nm) synthesized by the same method, with the same chemical composition, charge and coating. Ag ENMs did not cause toxic effects in bone marrow cells, erythrocytes or human keratinocytes [16,17] These discrepancies in toxicology studies may be explained by cell-type specific responses or coupled with the huge differences in the properties of the Ag ENMs used [18]. One of the main reasons for discrepancies between results in nanotoxicology studies in vitro is the lack of characterization of ENMs, especially under the actual exposure conditions in the relevant culture media This includes a lack of information about biological and chemical contamination of ENMs in the samples, and differences in experimental conditions such as in amount of protein in the cell culture media and whether the serum was heat inactivated or not [19,20,21,22,23].

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