Chemical Structures of Polyphenols That Critically Influence the Toxicity of ZnO Nanoparticles.

Recent studies suggested that phytochemicals as natural antioxidants in food could alleviate nanoparticle (NP) toxicity. This study investigated the combined toxicity of ZnO NPs and a panel of polyphenols. Surprisingly, polyphenols with both high and almost no radical scavenging activities could elicit cytoprotective effects against NP exposure in Caco-2 cells, which were primarily influenced by the positions of the hydroxyl group. Polyphenols with different chemical structures variously influenced the hydrodynamic size, zeta potential, and solubility of ZnO NPs as well as NP-induced intracellular superoxide and Zn ions, which could all contribute to the combined effects. Responses of human endothelial cells appeared to be different from the responses of Caco-2 cells, which may indicate cell-type dependent responses to combined exposure of NPs and phytochemicals. In conclusion, the data from this study suggested a pivotal role of chemical structures of phytochemicals in determining their capacity to affect ZnO NP toxicity.