The role of adsorbed endotoxin in particle‐induced stimulation of cytokine release

Abstract

Numerous in vitro models have demonstraed the capacity of wear particles to stimulate the release of soluble pro‐inflammatory products with the ability to induce local bone resorption. Recent observations have demonstrated that binding of lipopolysaccharide (LPS) to particulate wear deris can significantly modulate the pattern of cell response in the in vitro models. These findings raise concerns over the possible role of LPS in the athogenesis of aseptic looseing after total joint replacements, and also indicates the importance of controlling for possible confounding effects of LPS contamination in the in vitro models used to study the reactive nature of wear debris. Our studies were undertaken to rigorously analyze the effects of particle‐associated LPS on cell responses and to assess the efficacy ofdifferent treatment protocols to inactivate LPS associated with different particulate materials. Particles of cobalt‐chrome alloy, titanium‐6‐aluminum‐4‐vanadium, titanium nitride and silica were pretreated with LPS and exposed to multiple treatment protocols. When cells were treated with „as‐received”︁ particles prepared by washing in ethanol, small amounts of TNF‐α, IL‐1β, and IL‐1α were detected. In contrast, all particle species pretreated with LPS produced marked increases in TNF‐α, IL‐1α, and IL‐1β release, as well as upregulation of corresponding mRNa levels even after ethanol washing. Boiling the LPS‐pretreated particles in 1% acetic acid or autoclaving and baking the particles also markedly reduced and in some instances abolished the effect of the LPS‐pretreatment. This indicates that LPS binds to the surface of particles of diverse composition and that the bound LPS is biologically active. Treatment protocols to inactivate particle‐associated LPS demonstrated significant differences in effcacy. When the most rigorous treatments were utilized, essentially all LPS activity could be eliminated. Particles treated with these methods retained some capacity to stimulated cytokine release, but activities were markedly reduced. These results provide further evidnce indicating that LPS contamination of particulate materials can markedly enhance their biological activity. This potential confounding effect needs to be carefully monitored and controlled in the in vitro model systems systems used to evaluate wear particles. Furthermore, the presence of particle‐associated endotoxin at the bone‐implant interface in vivo could markedly enhance the adverse biological activity of particulate wear debris. © 2002 Published by Elsevier Science Ltd. On behalf of Orthopaedic Research Society.

Individual susceptibility to periprosthetic osteolysis is associated with altered patterns of innate immune gene expression in response to pro‐inflammatory stimuli

“…The polyethylene wear rate was greater in osteolysis-susceptible subjects then in the controls, and the severity of pelvic osteolytic defects by AAOS grade was strongly correlated with polyethylene wear rate. The above findings are consistent with other investigators who have shown that the biological activity of particulate wear debris is strongly dependent on adherent endotoxin, 18 that ex vivo responses of human PBMCs to particulate stimuli can be affected by the presence of indwelling metallic prostheses, 19 and that polyethylene wear rate modulates both the risk of osteolysis, and the severity of osteolytic lesions. 6 For these reasons polyethylene wear rate and clinical titanium exposure were included as covariates in our multivariate analysis model.…”

Effects of polyethylene and TiAIV wear particles on expression of RANK, RANKL and OPG mRNA

“…These findings are supported by another study (Chiang et al 1999) showing that LPSinduced bone resorption is substantially mediated by TNFα and IL-1 receptor signaling. Moreover, the different time courses of expression of mRNA for OPG and RANK between groups indicate that the particle effects demonstrated are not due to LPS-contaminated particles or particle-associated endotoxin, as has been postulated by other authors (Bi et al 2001, Brooks et al 2002, Cho et al 2002.…”

The effectiveness of polyethylene versus titanium particles in inducing osteolysis in vivo

“…The protocols we followed for sterilization and endotoxin removal for both titanium and polyethylene particles were different than in studies published by other investigators [5,8,13,15,18,20]. We used loo'%, ethanol for 48 h for sterilization and significant reduction of endotoxin.…”