Foreign body reaction to biomaterials.

Macrophage polarization: an opportunity for improved outcomes in biomaterials and regenerative medicine.

The role of macrophages in osteolysis of total joint replacement.

In vitro assessments of nanomaterial toxicity

Today, aseptic loosening is the most common cause of revision of major arthroplasties. Aseptic loosening accounts for more than two-thirds of hip revisions and almost one-half of knee revisions in Sweden. Several theories on the cause of aseptic loosening have been proposed. Most of these theories, however, are based on empiric observations, experimental animal models or anecdotal cases. In this review, we discuss the most common theories concerning aseptic loosening. It emerges from this review that aseptic loosening has a multifactorial etiology and cannot be explained by a single theory.

https://www.tandfonline.com/doi/pdf/10.1080/17453670610045902

Aseptic loosening, not only a question of wear: a review of different theories.

Aseptic loosening of orthopedic implants is thought to be caused primarily by osteoclast differentiation induced by bone resorptive cytokines produced in response to phagocytosis of implant-derived wear particles. This study examined whether adherent endotoxin on the wear particles is responsible for inducing osteoclast differentiation as well as production of interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor a (TNF-alpha). Removal of adherent endotoxin almost completely inhibited the responses to titanium (Ti) particles by both murine marrow cells and human peripheral blood monocytes. In vivo experiments showed that endotoxin removal reduced particle-induced osteolysis by 50-70%. Addition of lipopolysaccharide (LPS) to the "endotoxin-free" particles restored their ability to induce cytokine production and osteoclast differentiation in vitro. Moreover, marrow cells from mice that are hyporesponsive to endotoxin because of mutation of Toll-like receptor 4 induced significantly less cytokine production and osteoclast differentiation in response to Ti particles with adherent endotoxin than did marrow cells from normoresponsive mice. This mutation also resulted in significantly less particle-induced osteolysis in vivo. Taken together, these results show that adherent endotoxin is involved in many of the biological responses induced by orthopedic wear particles and should stimulate development of new approaches designed to reduce the activity of adherent endotoxin in patients with orthopedic implants.

Adherent Endotoxin on Orthopedic Wear Particles Stimulates Cytokine Production and Osteoclast Differentiation

Aseptic loosening of orthopedic implants caused by wear particles is a major clinical problem. This review examines the hypothesis that bacterial endotoxin contributes to aseptic loosening. Clinical findings support this hypothesis: bacterial biofilms exist on many implants from patients with aseptic loosening and antibiotics in bone cement reduce the rate of aseptic loosening. Three approaches were used to demonstrate that adherent endotoxin increases bioactivity of titanium particles. These experiments measured cytokine production and osteoclast differentiation in vitro and murine calvarial osteolysis in vivo. First, removal of >99.9% of the adherent endotoxin from titanium particles significantly ablates their biological activity. Second, adding lipopolysaccharide back to these "endotoxin-free" particles restores their biological activity. Third, cells or mice that are genetically hyporesponsive to endotoxin are significantly less responsive to titanium particles than are wild-type controls. Other investigators have confirmed and extended these results to include virtually all orthopedically relevant types of particles, including authentic titanium alloy particles retrieved from patients with loosening. Our recent studies suggest that adherent endotoxin on orthopedic implants may also inhibit initial osseointegration of the implants. Taken together, these studies suggest that bacterial endotoxin may have a significant role in induction of aseptic loosening.

Joscelyn M. Seabold

Papers

Adherent Endotoxin on Orthopedic Wear Particles Stimulates Cytokine Production and Osteoclast Differentiation

Does endotoxin contribute to aseptic loosening of orthopedic implants