Ascorbic acid prevents zinc oxide nanoparticle-induced intracellular oxidative stress and inflammatory responses

Exposure to zinc oxide nanoparticles (ZnO NPs) promotes acute pulmonary toxicity through oxidative stress and inflammation. Furthermore, dissolved zinc from ZnO NPs induces the formation of intracellular reactive oxygen species (ROS). We previously reported that supplemental ascorbic acid (AA) inhibits ZnO NP-induced acute pulmonary toxicity in a rat model; however, the mechanism of this action remains unclear. Therefore, we investigated the effects of AA on ZnO NP-induced cytotoxicity in human lung carcinoma A549 cells. AA was found to suppress intracellular production of ROS, and thus reduce the subsequent inflammation of ZnO NPs. However, intracellular Zn²⁺ concentrations were higher in AA-treated cells than in AA-untreated cells. AA was found to react with Zn²⁺ but not with the ZnO NPs themselves. These results suggest the possibility that AA-chelated extracellular Zn²⁺ and the Zn-AA complex was readily taken up into cell. Even if the intracellular Zn²⁺ level was high, cytotoxicity might be reduced because the Zn-AA complex was stable. Co-treatment of AA to A549 inhibited ROS production and subsequent intracellular inflammatory responses. These results are consistent with those previously reported from an in vivo model. Thus, two possibilities can be considered about the cytotoxicity-reducing the effect of AA: antioxidant efficacy and chelating effect.