F-actin and α-actinin reorganization mediates initial fibroblast interaction with CoCr alloy particles in vitro

Asceptic loosening remains the primary cause for failure of joint implant. The active role of fibroblasts in mediating asceptic loosening is however not well documented. In this study the initial interactions of fibroblasts with metal particles was studied by evaluating changes in the cytoskeletal structure and cytokine level. Murine L929 fibroblasts cultured with cobalt chromium particles were observed by phase contrast and scanning electron microscopy (SEM). Changes in the cytoskeletal rearrangement of F-actin and α-actinin focal adhesion plaques were studied by confocal microscopy. Expression of the proinflammatory cytokines IL-6 and IL-1α were analyzed by ELISA. The role of actin filaments and microtubules in particle uptake were determined at low temperature and in presence of colchicine and cytochalasin B. Phase contrast and SEM studies reveal that the metal particles adhere to the fibroblasts. The cellular cytoplasm was observed to grow over the particles and is suggestive of particle uptake. Confocal microscopy shows the presence of voids within the F-actin cytoskeletal framework corresponding to areas occupied by the metal particles, indicating the possible uptake of these particles. Aggregates of α-actinin into patches at the cell surface were also noted. Adherence and uptake of particles did not occur at low temperature and in presence of cytochalasin B, indicating that it is an active energy-dependent process involving actin filaments. Changes in the levels of cytokine IL-6 and IL-1α were not observed suggesting the role of other cytokine molecules in mediating the inflammatory response to wear debri by fibroblasts.