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Recent investigations indicate that innate immune "danger-signaling" pathways mediate metal implant debris induced-inflammatory responses, for example, NALP3 inflammasome. How the physical characteristics of particles (size, shape, and chemical composition) affect this inflammatory reactivity remains controversial. We examined the role of Cobalt-Chromium-Molybdenum (CoCrMo) alloy particle shape and size on human macrophage phagocytosis, lysosomal destabilization, and inflammasome activation. Round/smooth versus irregularly shaped/rough CoCrMo-alloy particles of ∼1 and 6-7 µm diameter were investigated for differential lysosomal damage and inflammasome activation in human monocytes/macrophages. While spherical/smooth 1 µm CoCrMo-alloy particles did not measurably affect macrophage IL-1β production, irregular 1 µm CoCrMo-alloy particles induced significant IL-1β increases over controls. Both round/smooth particles and irregular CoCrMo-alloy particles that were 6-7 µm in size induced >10-fold increases in IL-1β production compared to similarly shaped smaller particles (p 3-fold increase in IL-1β versus similarly sized round/smooth particles (at an equal dose, particles/cell). CoCrMo-alloy particle-size-induced IL-1β production was dependent on the lysosomal protease Cathepsin B, further supporting lysosomal destabilization as causative in inflammation. Phagocytosable larger/irregular shaped particles (6 µm) demonstrated the greatest lysosomal destabilization (observed immunofluorescently) and inflammatory reactivity when compared on an equal dose basis (particles/cell) to smaller/spherical 1 µm particles in vitro.
Caicedo et al. (Fri,) studied this question.