Immunotoxicity of Zinc Oxide (ZnO) Nanoparticles (NPs) in vitro and in vivo
Dept. of Medicine/석사
While Zinc Oxide (ZnO) nanoparticle (NP) has been recognized to have promising applications in biomedicine, its immunotoxicity has been inconsistent and even contradictory. To address this issue, we investigated whether ZnO NPs with different sizes (20 nm or 100 nm) and electrostatic charges (negative or positive) would cause immunotoxicity in vitro and in vivo, and explored their underlying molecular mechanism. Using Raw 264.7 cell line, we examined cell viability, reactive oxygen species (ROS) generation, mitochondrial membrane potential (MMP), and antioxidant enzyme activity to explore the immunotoxicity mechanism of ZnO NPs in vitro. We found that in cell viability assay (CCK-8, real-time xCelligence) ZnO NPs with different size and charge could induce differential cytotoxicity to Raw 264.7 cells. Specifically, the positively charged ZnO NPs exerted higher cytotoxicity than the negatively charged one. Molecular study to unravel the mechanism of immune cell toxicity showed that overall, treatment of ZnO NPs decreased MMP, generated intracellular ROS, and reduced antioxidant enzyme activity such as glutathione peroxidase (GPx). Next, to gauge systemic immunotoxicity, we assessed immune responses of C57BL/6 mice after orally administration of sub-lethal dose of ZnO NPs for two weeks. Oral intake of ZnO NPs significantly decreased body weight gain. In parallel, ZnO NPs did not alter the cell-mediated immune response in mice but suppressed innate immunity such as NK cell activity. The CD4+/CD8+ ratio was slightly reduced which implies the alteration of immune status induced by ZnO NPs. Accordingly, nitric oxide (NO) production from splenocyte culture supernatant in ZnO NP-fed mice was lower than control. Consistently, serum levels of pro/anti-inflammatory (IL-1, TNF-α, and IL-10) and Th1 cytokines (IFN-γ, IL-12) in ZnO NP-fed mice were significantly suppressed. Collectively, our results indicate that different sized- and charged-ZnO NPs would cause in vitro and in vivo immunotoxicity, of which nature is a minor immunosuppression. This has important implications for individuals who may be chronically exposed to ZnO NPs.