Effect of Noble Metal Nanomaterials on Endogenous and Dietary Antioxidants and their Combined Interaction with Reactive Oxygen Species
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In the last decade, nanotechnology has been extensively exploited in a variety of areas because nanoscaled materials provide a wide range of benefits that bulk materials do not possess. In spite of its advent, when applied to consumer related products, the new technology inevitably brings about side effect especially to biological or environment systems. Many have already determined that the damaging effect of nanomaterials in cell lines is caused by oxidative stress as a result of overproduction of reactive oxygen species (ROS). The present study aims at evaluating the role of noble metal nanomaterials in the generation and scavenging of ROS. It is noteworthy that the behavior of silver nanoparticles (Ag NPs) in the presence of hydrogen peroxide, a continuously generated component in biological systems, is adjusted by the mimetic microenvironment. These Ag NPs were found to be capable of inducing production of ROS hydroxyl radicals and oxygen in acidic and alkaline environments, respectively. The Ag NPs were oxidized to ions at pH 4.6 while they have been found to participate in Ag<super>0</super>-Ag<super>1</super>-Ag<super>0</super> cyclic reaction at pH 11. As a promising antimicrobial agent, Ag NPs alone barely scavenge free radicals, but they are found to moderate the scavenging capability of thiol-based antioxidants, essential endogenous antioxidants, due to their formation of Ag-S bond. In addition, Platinum nanoparticles (Pt NPs) have been mostly used as catalysts in many chemical reactions. While recent reports suggest antioxidant activity of Pt NPs due to their peroxidase-like activity, there are limitations in the use of Pt NPs as an antioxidant in scavenging hydroxyl radicals. Alternatively, owing to their ascorbate oxidase-like activity, Pt NPs reduce the antioxidant ability of ascorbic acid, an important antioxidant participating in many biological reactions. In addition, they exert tyrosinase-like activity in catalyzing the oxidation of (-)-Epicatechin, caffeic acid, and resveratrol to form pigment compounds. Therefore, Pt NPs vary in their effect on the antioxidant activity of phenolics against various radicals (DPPH radicals > hydroxyl radicals >superoxide radicals). Our study may provide insights for finding new applications for noble metal nanoparticles and for risk assessment.