Potency shift in immunomodulatory activities of zinc oxide (ZnO) nanoparticles in THP-1 cells is associated with cytotoxicity

Two zinc oxide nanoparticles (ZnO NPs) with different physicochemical properties (ZnO(α) and ZnO(Σ)) were examined in THP-1 cells to investigate their effects on cellular immunomodulation and cytotoxicity. THP-1 cells were cultured in the presence of ZnO(α) or ZnO(Σ) for 48 hr, and the expression of proinflammatory cytokines and immune cell surface antigens was examined. ZnO(α) and ZnO(Σ) reduced cell viability in a concentration- and time-dependent manner, with the latter being more potent. ZnO(α) and ZnO(Σ) increased the expression of CD54, IL-8, and TNF-α to the same extent between 24 and 48 hr. While ZnO(Σ) was more potent at effective concentrations, this potency was comparable between ZnO(α) and ZnO(Σ) when normalized to their cytotoxic concentrations (LC50, LC25, or LC5). It was considered that there was a potency shift that is associated with cytotoxicity and physicochemical properties, in immunomodulatory activities in THP-1 cells between ZnO NPs.