Toxicity and fate of silver nanoparticles from the food additive E174: Mitochondrial dynamics underlie their effects in intestinal epithelial cells

Abstract

The safety of silver nanoparticles (AgNPs) in the food additive E174 is poorly understood. We conducted a comparative analysis of the toxicity profiles of AgNPs extracted from commercially available E 174-containing confectionery (E174-AgNPs) and polyvinylpyrrolidone-coated AgNPs (PVP-AgNPs) by studying redox- and mitochondrial stress responses in Caco-2 cells. Integrating biological findings with physicochemical characterisation and intracellular fate analysis revealed time- and concentration-dependent membrane damage for both AgNPs types. This was accompanied by an adaptive response to oxidative stress, as evidenced by gene expression changes of heme oxygenase 1 and other genes, and altered mitochondrial homeostasis and function, shown by changes in mitochondrial footprint and network morphology. Qualitative STEM-EDX after 24 h exposure indicated transformed E174-AgNPs in endo-/autolysosomes and silver-containing particles of a few nm in size near these structures in the cytoplasm, which culminated in mitochondrial swelling and rupture. The concurrent observation of an enhanced mitochondrial network morphology suggested a compensatory response by the remaining mitochondria. This comparative analysis of the toxicity of E174-AgNPs and PVP-AgNPs underscores the urgent need to reassess the safety of the food additive E 174. Our study highlights the importance of a comprehensive and in-depth evaluation of AgNP properties for accurate and robust hazard and risk assessments.