Long-term effects of silver nanoparticles in caco-2 cells

The high success of silver nanoparticles (AgNPs), mainly associated with their proved antimicrobial properties, has led to an increasing spread in our close environment. Although many studies have been carried out to detect potential toxicity of AgNPs, most of them have been developed under unrealistic exposure conditions. In terms of human risk, the evaluation of long-term exposures to subtoxic doses of NPs remains a challenge. Here, we have determined different transformation-related end points under a scenario of 6 weeks long-term exposure to low noncytotoxic AgNPs concentrations (0.5 and 1 μg/mL) in Caco-2 cells. A significant uptake of AgNPs was demonstrated by using confocal microscopy showing a high presence of AgNPs in both the cytoplasm and the nucleus. As for the assayed parameters of cell transformation such as ability to growth without requiring adherence to a surface (soft-agar assay), the secretion of extracellular matrix metalloproteinase to the medium (zymography), migration capacity and ability of the secretome of exposed cells to promote tumor growth, significant effects were detected in all cases, with the exception of the extracellular matrix metalloproteinases (MMP2 and MMP9) secretion. Our results point out the potential carcinogenic risk associated with AgNPs exposure under long-term exposure conditions, as well as the importance of using realistic exposure scenarios to test nanomaterials.