Ti Ions Induce IL-1β Release by Activation of the NLRP3 Inflammasome in a Human Macrophage Cell Line

Abstract

The aim of the present study was to investigate whether titanium (Ti)-induced release of interleukin (IL)-1β acts through the assembly of the NACHT, LRR, and PYD domain-containing protein 3 (NLRP3) inflammasome. In addition, we examined whether particulate Ti or TiO2 activates the same intracellular pathways with the assembly of the NLRP3 inflammasome as Ti ions. Ti ions are known to induce IL-1β maturation and release by the formation of metal–protein aggregates. Wild-type THP-1 (wt.) cells and NLRP3− and ASC− (apoptosis-associated speck-like protein containing caspase recruitment domain (CARD)) knockdown cells were used in the experimental analyses. Macro- and nanoparticles (NPs) of both Ti and TiO2 were used as test agents. IL-1β release as a biomarker for inflammasome activation and cell viability was also analyzed. Periodate-oxidized adenosine triphosphate (oATP) was used to attenuate downstream signaling in NLRP3 inflammasome activation. Cellular uptake of Ti was examined using transmission electron microscopy. Cells exposed to the Ti-ion solution showed a dose-dependent increase in the release of IL-1β; conversely, exposure to particulate Ti did not result in increased IL-1β release. Cell viability was not affected by particulate Ti. Knockdown cells exposed to Ti showed a statistically significant reduction in the release of IL-1β compared with wt. cells (p < 0.001). Cellular uptake was detected in all Ti mixtures, and aggregates with various structures were observed. Ti ion–induced release of bioactive IL-1β in THP-1 cells involves the assembly of the NLRP3 inflammasome.

A Mapping Review of the Pathogenesis of Peri-Implantitis: The Biofilm-Mediated Inflammation and Bone Dysregulation (BIND) Hypothesis

“…Although regarded as being biocompatible, commercial grade titanium is not fully inert. Titanium can act as an abiotic stimulus to macrophages and activate the release of the NLRP3 inflammasome complex assembly [112]. Inflammation also impairs osteoblast attachment and function, and a pro-osteoclastic phenotype has been described on infected implant surfaces [113].…”

Subgingival titanium wire implantation induces weak inflammatory responses but does not promote substantial T cell activation

“…In addition, nickel ions were shown to bind directly to CXCL4, an inflammatory chemokine, and exacerbate skin inflammation in a murine model of nickel-induced CHS using LPS as an adjuvant 31) . On the other hand, although the direct recognition mechanism of titanium is unknown, both titanium ions and nanoparticles were reported to induce cellular activity [7][8][9][10][11][12][13] . In our experimental model, small amounts of ions or particles may have been released from implanted titanium or nickel wire, helping induce biological responses to implanted wires.…”

“…In addition to titanium particles, titanium ions also enhance immunoreactivity. Titanium ion exposure enhances proinflammatory cytokine production in macrophages via activation of NLRP3 or NF-κB 11,12) . Other studies showed that titanium ions also decrease the viability and inhibit the differentiation of osteoblastlike MC3T3-E1 cells 13) .…”

NLRP3 inflammasome activation in response to metals

“…However, none of these is recognized as a common event induced by all the NLRP3 inflammasome stimuli (21,25). To date, studies on metal-activated inflammasomes have mainly focused on the NLRP3 inflammasome (26,27). Details of these studies are discussed in the following sections and are summarized in Figure 2.…”