Inflammatory responses to metal oxide ceramic nanopowders

Ceramic orthopaedic implants are increasingly popular due to the need for robust total joint replacement implants that have a high success rate long-term and do not induce biological responses in patients. This study was designed to investigate the biological effects of ceramic nanopowders containing aluminium oxide or zirconium oxide to activate the human macrophage THP-1 cell line. In vitro investigation of pro-inflammatory gene expression and chemokine secretion was performed studied using RT-qPCR and ELISA, respectively. TLR4 inhibition, using a small-molecule inhibitor, was used to determine whether ceramic-mediated inflammation occurs in a similar manner to that of metals such as cobalt. THP-1 macrophages were primed with ceramics or LPS and then treated with ATP or ceramics, respectively, to determine whether these nanopowders are involved in the priming or activation of the NLRP3 inflammasome through IL-1β secretion. Cells treated with ceramics significantly increased pro-inflammatory gene expression and protein secretion which was attenuated through TLR4 blockade. Addition of ATP to cells following ceramic treatment significantly increased IL-1β secretion. Therefore, we identify the ability of ceramic metal oxides to cause a pro-inflammatory phenotype in THP-1 macrophages and propose the mechanism by which this occurs is primarily via the TLR4 pathway which contributes to inflammasome signalling.