Ultrafine Particles Cause Cytoskeletal Dysfunctions in Macrophages

Abstract

Essential cytoskeletal functions of macrophages are migration, phagocytosis of foreign materials, and intracellular transport and digestion The influence of fine and ultrafine test particles (UFP), such as TiO 2, elemental carbon, commercial carbon black, diesel exhaust particulate matter, and urban dust (UrbD), on cytoskeleton-related functions of macrophages, such as phagocytosis, phagosome transport mechanisms, and mechanical cytoskeletal integrity, were studied by flow cytometry and by cytomagnetometry. Additionally, necrosis and apoptosis caused by the test particles was detected. The diameter of the test particles ranged from 12 to 220 nm and the Brunauer–Emmet–Teller specific surface area ranged from 6 to 600 m 2/g. Primary alveolar macrophages from beagle dogs (BD-AM), obtained by bronchoalveolar lavage, were used as well as macrophages originating from the cell line J774A.1. For cytomagnetometry studies, spherical 1.8-μm ferromagnetic particles served as probes for cytoskeletal functions and were incubated together with the macrophages 24 h prior to UFP exposure. Macrophages were exposed in vitro with 10–320 μg UFP/ml/10 6 cells up to 24 h. In all experiments, J774A.1 macrophages were more sensitive than BD-AM to UFP exposure. Cytoskeletal dysfunctions evaluated by cytomagnetometry were an impaired phagosome transport and an increased cytoskeletal stiffness and occurred at concentrations of 100 μg UFP/ml/10 6 cells and above, in both BD-AM and J774A.1. Only fine TiO 2 did not show any effect. Urban dust (standard reference material 1649a) and diesel exhaust particles (DEP, standard reference material 1650) caused comparable cytoskeletal dysfunctions to elemental carbon with high specific surface area. Cytoskeletal dysfunctions induced by DEP or UrbD could be reduced after washing the particles by dichloromethane. UFP caused an impaired phagocytosis of 1-μm diameter fluorescent latex beads, inhibited cell proliferation, and decreased cell viability. All recorded cytotoxic parameters showed only weak correlations with the specific surface area or the total number of UFP, which can result from the different types of particles and different surface compositions. UFP cause cytoskeletal toxicity in vitro in macrophages, which can cause cellular dysfunctions, such as impaired proliferation, impaired phagocytic activity, and retarded intracellular transport processes as well as increased cell stiffness and can result in impaired defense ability in the lung.