Increasing both CoCrMo‐alloy particle size and surface irregularity induces increased macrophage inflammasome activation in vitro potentially through lysosomal destabilization mechanisms

Abstract

Recent investigations indicate that innate immune “danger-signaling” pathways mediate metal implant debris induced-inflammatory responses, e.g. 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 vs. irregularly shaped/rough CoCrMo-alloy particles of ~1µm and 6 to 7µm diameter were investigated for differential lysosomal damage and inflammasome activation in human monocytes/macrophages. While spherical/smooth 1µm CoCrMo-alloy particles did not measurably affect macrophage IL-1β production, irregular 1µm CoCrMo-alloy particles induced significant IL-1β increases over controls. Both round/smooth particles and irregular CoCrMo-alloy particles that were 6 to 7µ min size induced >10-fold increases in IL-1β production compared to similarly shaped smaller particles (p<0.05). Larger irregular particles induced a greater degree of intracellular lysosomal damage and a >3-fold increase in IL-1β vs. 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 (6µm) demonstrated the greatest lysosomal destabilization (observed immunofluorescently) and inflammatory reactivity when compared on an equal dose basis (particles/cell) to smaller/spherical 1µm particles in vitro.

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“…Under these conditions, inflammasome activity was clearly induced by apatite. Inflammasome activation by particles can be due to particle-induced reactive oxygen species and phagolysosomal destabilization [32][33][34] and, in some circumstances, lead to cell death. Incubation of mononuclear cells with apatite for long periods could therefore result in artefactual particle 'gorging', lysosomal disruption and cell death [2].…”

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