Effect of mechanical perturbation on the release of PGE2 by macrophages in vitro

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Abstract
Macrophages play numerous roles in both physiologic and pathologic processes. Along with fibroblasts, they comprise the synovial tissue that forms the lining of musculoskeletal joint capsules and bursae, and they often envelop implants. During the process of phagocytosing prosthesis‐related particles, macrophages in peri‐implant tissue release inflammatory mediators. Little is known, however, about the response of these cells to mechanical perturbation, which often is a component of the physical environment of the cell. Mouse peritoneal macrophages were grown on a flexible membrane in vitro and a dynamic 1‐Hz spatially uniform sinusoidal strain pattern imparted to the elastomeric substrate. The effect of mechanical strain on prostaglandin (PG) E2 release was evaluated using cells that were activated by lipopolysaccharide (LPS) as well as by those that were not. The results are compared with the levels of PGE2 stimulated by metallic particles. Strain magnitudes of 4 and 8% applied for 1 h resulted in almost a twofold increase in the release of PGE2 from LPS‐stimulated cells (p < 0.05) and nonstimulated macrophages (p < 0.07), compared with nonperturbated controls. No release was elicited by a challenge of metal particles. These findings demonstrate for the first time an effect of mechanical force on the release of an inflammatory mediator by macrophages. This response may help to explain the macrophage‐mediated processes underlying the osteolysis associated with loose prostheses in bone and suggests a mechanism for the inflammation of synovial tissues by excessive mechanical strain. © 2001 Wiley Periodicals, Inc. J Biomed Mater Res 59: 288–293, 2002