Relevance of Caspase-1 and Nlrp3 Inflammasome on Inflammatory Bone Resorption in A Murine Model of Periodontitis.

This study investigates the role of NLRP3 inflammasome and its main effector Caspase-1 in inflammation and alveolar bone resorption associated with periodontitis. Heat-killed Aggregatibacter actinomycetemcomitans (Aa) was injected 3x/week (4 weeks) into gingival tissues of wild-type (WT), Nlrp3-KO and Caspase1-KO mice. Bone resorption was measured by µCT and osteoclast number was determined by tartrate-resistant acid phosphatase (TRAP) staining. Inflammation was assessed histologically (H/E staining and immunofluorescence of CD45 and Ly6G). In vitro studies determined the influence of Nlrp3 and Caspase-1 in Rankl-induced osteoclast differentiation and activity and on LPS-induced expression of inflammation-associated genes. Bone resorption was significantly reduced in Casp1-KO but not in Nlrp3-KO mice. Casp1-KO mice had increased in osteoclast numbers, whereas the inflammatory infiltrate or on gene expression were similar to those of WT and Nlrp3-KO mice. Strikingly, osteoclasts differentiated from Nlrp3-deficient macrophages had increased resorbing activity in vitro. LPS-induced expression of Il-10, Il-12 and Tnf-α was significantly reduced in Nlrp3- and Casp1-deficient macrophages. As an inceptive study, these results suggest that Nlrp3 inflammasome does not play a significant role in inflammation and bone resorption in vivo and that Caspase-1 has a pro-resorptive role in experimental periodontal disease.

NLRC4 inflammasome has a protective role on inflammatory bone resorption in a murine model of periodontal disease.

There is virtually no information on the role of NLRC4 inflammasome on bone resorption and inflammation associated with periodontitis. Bacterial-associated experimental periodontitis was induced in wild-type (WT) and Nlrc4-KO C57BL/6 mice. 3 µL of a 1 × 109 UFC/mL PBS suspension of heat-killed Gram-negative bacteria were injected (3x/week for 4 weeks) directly into the gingival tissues of WT and Nlrc4-KO mice (n = 6/genotype). Control animals were injected bilaterally (3x/week for 4 weeks) in the same sites with the same volume of the PBS vehicle. Alveolar bone resorption was quantified by µCT. Inflammatory infiltrate in the gingival tissues was assessed qualitatively in H&E-stained slides and by the detection of a pan-leukocyte marker (CD45) and a neutrophil marker (Ly6G) using immunofluorescence. Modulation of Rankl, Mmp-13, Tnf-a, Il-6 and Il-10 expression in the gingival tissues was determined by RT-qPCR. Osteoclastogenesis was assessed in vivo by biochemical staining for TRAP. The relevance of NLRC4 for RANKL-induced osteoclastic differentiation and activity was investigated in vitro using bone marrow-derived macrophages from WT and Nlrc4-KO mice. Bone resorption was significantly greater in Nlrc4-KO mice; however there were no differences between WT and Nlrc4-KO mice on osteoclast numbers and on the inflammatory infiltrate. In vitro, osteoclast activity was significantly enhanced in Nlrc4-deficient macrophages; whereas RANKL-induced differentiation was not affected. Expression of the selected candidate genes was also similarly increased by the induction of experimental periodontal disease, except for the expression of Tnf-alpha and Il-10, which was already significantly higher in the gingival tissues of Nlrc4-KO mice. We conclude that NLRC4 inflammasome has a protective role on inflammatory bone resorption in this experimental model. Furthermore, the bone-sparing effect may be related with the modulation of osteoclast activity.

Local administration of curcumin-loaded nanoparticles effectively inhibits inflammation and bone resorption associated with experimental periodontal disease.

There is evidence indicating that curcumin has multiple biological activities, including anti-inflammatory properties. In vitro and in vivo studies demonstrate that curcumin may attenuate inflammation and the connective tissue destruction associated with periodontal disease. Most of these studies use systemic administration, and considering the site-specific nature of periodontal disease and also the poor pharmacodynamic properties of curcumin, we conducted this proof of principle study to assess the biological effect of the local administration of curcumin in a nanoparticle vehicle on experimental periodontal disease. We used 16 rats divided into two groups of 8 animals according to the induction of experimental periodontal disease by bilateral injections of LPS or of the vehicle control directly into the gingival tissues 3×/week for 4 weeks. The same volume of curcumin-loaded nanoparticles or of nanoparticle vehicle was injected into the same sites 2×/week. µCT analysis showed that local administration of curcumin resulted in a complete inhibition of inflammatory bone resorption and in a significant decrease of both osteoclast counts and of the inflammatory infiltrate; as well as a marked attenuation of p38 MAPK and NF-kB activation. We conclude that local administration of curcumin-loaded nanoparticles effectively inhibited inflammation and bone resorption associated with experimental periodontal disease.