Cobalt Alloy Implant Debris Induces Inflammation and Bone Loss Primarily through Danger Signaling, Not TLR4 Activation: Implications for DAMP-ening Implant Related Inflammation

Abstract

Cobalt alloy debris has been implicated as causative in the early failure of some designs of current total joint implants. The ability of implant debris to cause excessive inflammation via danger signaling (NLRP3 inflammasome) vs. pathogen associated pattern recognition receptors (e.g. Toll-like receptors; TLRs) remains controversial. Recently, specific non-conserved histidines on human TLR4 have been shown activated by cobalt and nickel ions in solution. However, whether this TLR activation is directly or indirectly an effect of metals or secondary endogenous alarmins (danger-associated molecular patterns, DAMPs) elicited by danger signaling, remains unknown and contentious. Our study indicates that in both a human macrophage cell line (THP-1) and primary human macrophages, as well as an in vivo murine model of inflammatory osteolysis, that Cobalt-alloy particle induced NLRP3 inflammasome danger signaling inflammatory responses were highly dominant relative to TLR4 activation, as measured respectively by IL-1β or TNF-α, IL-6, IL-10, tissue histology and quantitative bone loss measurement. Despite the lack of metal binding histidines H456 and H458 in murine TLR4, murine calvaria challenge with Cobalt alloy particles induced significant macrophage driven in vivo inflammation and bone loss inflammatory osteolysis, whereas LPS calvaria challenge alone did not. Additionally, no significant increase (p<0.05) in inflammation and inflammatory bone loss by LPS co-challenge with Cobalt vs. Cobalt alone was evident, even at high levels of LPS (i.e. levels commiserate with hematogenous levels in fatal sepsis, >500pg/mL). Therefore, not only do the results of this investigation support Cobalt alloy danger signaling induced inflammation, but under normal homeostasis low levels of hematogenous PAMPs (<2pg/mL) from Gram-negative bacteria, seem to have negligible contribution to the danger signaling responses elicited by Cobalt alloy metal implant debris. This suggests the unique nature of Cobalt alloy particle bioreactivity is strong enough to illicit danger signaling that secondarily activate concomitant TLR activation, and may in part explain Cobalt particulate associated inflammatory and toxicity-like reactions of specific orthopedic implants.

Inflammatory osteolysis: a conspiracy against bone

“…The NLRP3 inflammasome, however, appears to supersede TLR4 signaling in prosthetic-wear particle-induced osteolysis (147). On the other hand, the non-NLR inflammasome AIM2 and not NLRP3 may mediate the acute phase of PMMA-induced foreign body responses (148).…”

Stainless steel wear debris of a scoliotic growth guidance system has little local and systemic effect in an animal model

“…It may be misleading that several past investigations have shown that smaller particles (e.g., 0.4 μm) produce a greater inflammatory response than larger particles (e.g., 7.5μm), because in these past studies equal mass of debris was used which generally resulted in >1,000‐fold higher dose of smaller particles per cell than larger particles per cell. Thus, the >0.8 μm sized stainless steel particles used in this investigation, while not nanometer in size (<300 nm), fall into the smaller sub‐micron ranges of particles that have been reported as optimally reactive and are in the range of TJA implant particulate debris.…”

Effect of cobalt ions on the interaction between macrophages and titanium

“…Aseptic loosening of orthopedic implants is described as a immunological response against wear particles eroded from the implant and was first reported by Harris et al21 It is well established in orthopedic research that wear debris and nanoparticles from different metals can cause osteolysis by activation and secretion of the pro‐inflammatory cytokines (for example, interleukin (IL)‐1β, IL‐6, tumor necrosis factor (TNF)‐α, and prostaglandin E2 (PGE2) 22, 23, 24, 25, 26, 27, 28…”

“…Aseptic loosening of orthopedic implants is described as a immunological response against wear particles eroded from the implant and was first reported by Harris et al 21 It is well established in orthopedic research that wear debris and nanoparticles from different metals can cause osteolysis by activation and secretion of the pro-inflammatory cytokines (for example, interleukin (IL)-1b, IL-6, tumor necrosis factor (TNF)-a, and prostaglandin E2 (PGE2). [22][23][24][25][26][27][28] In dentistry, very little has been discussed about this particle-induced inflammatory process that could occur around a dental implant. As in osteolysis around an orthopedic implant, 29 peri-implantitis shows a similar infiltration of macrophages, and the macrophage infiltration is more pronounced in peri-implantitis than in an infectious disease such as periodontitis.…”