Cytokine and NO release from peripheral blood neutrophils after exposure to metal nanoparticles: in vitro and ex vivo studies

We have observed that nano-size metal particles such as nickel (Nano-Ni), cobalt (Nano-Co), and titanium dioxide (Nano-TiO2) have much more toxic effects on rat lungs than standard-size Ni, Co, and TiO2 particles. Recent evidence indicates that inhaled nanoparticles can penetrate alveolar membranes and enter the circulation, which may result in adverse effects in extra-pulmonary organs. We have proposed that metal nanoparticles may directly or indirectly activate peripheral blood neutrophils after they have translocated from the lungs to the circulation. The neutrophils are the most numerous phagocytes in the body, whose function is not only to defense against bacterial and viral infection, but also to be capable of ingesting particles. Neutrophils contain enzymes that may cause tissue damage if they are excessive or inappropriate activated. In this study, we determined the release of cytokines and nitrite from neutrophils after exposure to metal nanoparticles in vitro and ex vivo. The results showed dose-related increases of TNF-alpha, MIP-2, and nitrite levels in the supernatants of neutrophils treated with various doses of Nano-Ni and Nano-Co. Neutrophils treated with Nano-Ni and Nano-Co released significantly higher levels of TNF-alpha, MIP-2, and nitrite than those treated with Nano-TiO2 and the control. The above results were further confirmed by ex vivo experiments that showed dose-related increases in TNF-alpha, MIP-2, and nitrite release from neutrophils from rats exposed to Nano-Ni and Nano-Co. The level of TNF-alpha and MIP-2 reached their highest level after 24 h exposure, while the level of nitrite continued to increase, reaching its highest level after 48 h exposure. The levels of TNF-alpha, MIP-2, and nitrite released by neutrophils from rats intratracheally instilled with Nano-Ni and Nano-Co were consistently significantly higher than those from rats instilled with physiological saline and Nano-TiO2. These results indicate that Ni, Co, and TiO2 nanoparticles of the similar diameter are dramatically different in their ability to activate neutrophils to release cytokines and nitrite, and each metal exerts a different effect.