In vitro characterization of reactive oxygen species (ROS) generation by the commercially available Mesosilver™ dietary supplement

Silver nanoparticles (AgNPs) are frequently orally consumed as dietary supplements with various commercially available products (e.g., Nano-silver™ and Mesosilver™) claimed to yield health benefits across an array of areas. While the mechanism by which AgNPs might provide health benefits is unclear, these benefits could potentially be related to either the release of dissolved monovalent Ag species (such as Ag⁺) or the ability of AgNPs to generate reactive oxygen species (ROS) and subsequent influence on the gut microbiome or eukaryotic cells. In this study, we investigate the in vitro Ag(i) and ROS (particularly hydrogen peroxide (H₂O₂) and hydroxyl radicals (OH)) generation by Mesosilver™ over a range of pHs (2-7) typical of the human gut and upper digestive system. Our results show that Mesosilver™ undergoes rapid oxygen-mediated oxidative dissolution and associated H₂O₂ production with the generation rate of both Ag(i) and H₂O₂ increasing with decrease in pH and increase in NaCl concentration. No impact of increase in temperature from 22 °C to 37 °C was observed on the oxidative dissolution of Mesosilver™. Addition of H₂O₂ further accelerates the dissolution of Mesosilver™ and causes production of OH under all pH conditions investigated here. The presence of pepsin, an enzyme present in gastric fluid, resulted in a slight decrease in the extent of release of Ag(i) and H₂O₂ generation under acidic conditions. A kinetic model is developed based on our experimental results enabling prediction of the dissolved Ag(i) and ROS yield on dissolution of these nanoparticles under conditions typical of the human digestive system.