TLR4 (not TLR2) dominate cognate TLR activity associated with CoCrMo implant particles

Abstract

Innate immune reactions to orthopedic implant debris are the primary cause of total joint replacement (TJR) failure over the long term (15-20 years). The role of pathogen associated pattern recognition receptors (i.e., TLRs) in regulating immune reactivity to metal implant particles remains controversial. Do different TLRs (i.e., TLR2 vs. TLR4) activated by their respective ligands in concert with metal implant debris elicit equivalent innate immune responses? In this investigation, our in vitro and in vivo data indicate that Gram-negative PAMPs are more pro-inflammatory than Gram-positive PAMPs. In vitro results indicated TLR4 activation in concert with CoCrMo orthopedic implant debris (CoCrMo/LPS+) challenged primary macrophages resulted in significantly greater inflammatory responses than CoCrMo/PAM3CSK+ (TLR2). Similarly, in vivo results indicated CoCrMo/LPS+ TLR4 challenge induced a twofold increase in inflammation-induced bone resorption (osteolysis) than CoCrMo/PAM3CSK+ (p < 0.01) or CoCrMo (p < 0.03) alone in an established murine calvaria model. This points to a more potent TLR4-based effect of CoCrMo/LPS+ on innate immune responses, that is, IL-1ß, TNF-α, and resulting osteolysis. Differential CoCrMo/LPS+ induced osteolysis compared to CoCrMo/PAM3CSK+, reveals inherent differences in TLR4 versus TLR2 activation which are relevant to (i) how different types of implant debris elicit differential reactivity, (ii) how TLR2 Gram-positive bacteria benefits from less immune activation possibly due to the down-regulation of TLR2 surface expression, that subsequently impacts Gram-positive infections in TJRs, and (iii) how using TLR4 LPS (a Gram-negative agonist) may not accurately model Gram-positive bacteria responses, alone and/or with specific types of implant particles, particularly CoCrMo alloy. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1007-1017, 2017.

NOD2 negatively regulated titanium particle-induced osteolysis in mice

“…11 But in recent studies, PRRs, especially TLRs, have been widely reported to recognize a variety of metals from the prosthesis, such as titanium particles, cobalt ions and CoCrMo implant particles and to respond by the activation of different inflammation pathways, and then cause the secretion of proinflammatory cytokines. 8,12,13 In our previous studies, we overexpressed the small heterodimer partner (SHP), an orphan nuclear receptor that negatively regulates the TLR4/NF-κB pathway and down-regulates the P65 expression of NF-κB. The expression of NF-κB was suppressed and the expression of proinflammatory cytokines was partly reduced.…”

Gene expression in adverse reaction to metal debris around metal-on-metal arthroplasty: An RNA-Seq-based study

“…In the literature, the biochemical mechanisms of cobalt-induced toxicity appear to be more comprehensively characterized than those of chromium. In addition, cobalt may activate macrophages directly through TLR4 [17]. It also modifies macrophage phenotype [45] and causes strong oxidative stress [46].…”

“…Their direct cytotoxic effects can also cause tissue necrosis, which in turn may attract macrophages and lead to granulomatous responses [15] and osteolysis [16]. Cobalt may also stimulate macrophages through direct activation of Toll-like receptor 4 (TLR4) [17] and/or so-called danger signaling [18].…”

Endotoxin Contributes to Artificial Loosening of Prostheses Induced by Titanium Particles

“…Because of the many similarities between endotoxin and abrasive particles, we speculated that endotoxins participate in the biological response caused by wear particles [ 11 ]. For example, endotoxin and wear particles activate similar signal transduction pathways, increase production of prostaglandins and proinflammatory cytokines, and stimulate bone resorption.…”