Bone‐resorptive cytokine gene expression in periapical lesions in the rat

Abstract

Periapical bone destruction is an important pathogenic sequela of pulpal infection. Recent findings from this laboratory have demonstrated that most bone-resorbing activity in extracts of rat periapical lesions can be neutralized by an anti-interleukin (IL)-1 alpha antiserum. To further clarify pathogenic mechanisms, bone-resorptive cytokine messenger RNA (mRNA) expression was analyzed in developing rat periapical lesions. The molar teeth of 20 Sprague-Dawley rats were surgically exposed and left open to permit infection from the oral environment. Total cell RNA was isolated from periapical granuloma tissue obtained on days 3, 7, 15 and 30 after exposure. mRNA for IL-1 alpha, IL-1 beta and tumor necrosis factor alpha (TNF-alpha) was amplified by reverse transcription polymerase chain reaction, and levels were approximated by comparison to the parallel amplification of the housekeeping gene glyceraldehyde phosphate dehydrogenase. IL-1 alpha and TNF-alpha mRNA were both highly expressed beginning on day 7, increased on day 15, and declined somewhat on day 30. In contrast, IL-1 beta mRNA was expressed at much lower levels, but with similar kinetics. The kinetics of steady state IL-1 alpha and TNF-alpha mRNA levels were confirmed using the quantitative RNase protection assay, whereas IL-1 beta mRNA could not be detected by this technique. IL-1 alpha mRNA-expressing cells were identified using in situ hybridization and included infiltrating macrophages, as well as resident fibroblasts, endothelial cells and osteoclasts. These results demonstrate that the IL-1 alpha and TNF-alpha genes are highly expressed in developing periapical lesions in the rat and confirm previous studies at the protein level in this model.

Gamma Interferon (IFN-γ) and IFN-γ-Inducing Cytokines Interleukin-12 (IL-12) and IL-18 Do Not Augment Infection-Stimulated Bone Resorption In Vivo

“…Furthermore, rIL-12-infused mice failed to significantly up-regulate bone destruction compared to control mice. The local level of IL-1 in inflammatory lesions, previously found to be a primary mediator of infection-stimulated bone resorption (22,23), was significantly lower only in IL-12 Ϫ/Ϫ mice (data not shown). Taken together, these results suggest that, at least individually, endogenous IL-12, IL-18, and IFN-␥ do not appear to have a major, nonredundant effect on the pathogenesis of infection-stimulated bone resorption in vivo.…”

“…IL-1 mRNA and protein are markedly increased in infiltrating macrophages and polymorphonuclear leukocytes (23), and IL-1 levels generally correlate with the extent of bone destruction (15,22). Most bone-resorptive activity present in periapical granulomas is neutralized by anti-IL-1 antibodies, and bone resorption is significantly inhibited in vivo with IL-1 receptor antagonist (16,22).…”

Involvement of T-Lymphocytes in Periodontal Disease and in Direct and Indirect Induction of Bone Resorption

“…Further evidence indicates that in vivo administration of ILlot accelerates ligature-induced bone resorption in rats (Koide et al, 1995). TNF-ox (and PGE2) released from macrophages after phagocytosis of implant-derived particles seems to be responsible for the bone resorption induced in orthopedic implant osteolysis (Horowitz et al, 1998;Merkel et al, 1999 model, periapical bone resorption was associated with IL-liX and TNF-c (Wang and Stashenko, 1991;Wang et al, 1997). Also, inhibition of TNF-oc and IL-I resulted in inhibition of bone destruction in adjuvant arthritis in rats .…”

IL-10, But Not IL-4, Suppresses Infection-Stimulated Bone Resorption In Vivo

“…Macrophages are prominent in inflammatory periapical tissues, and produce large quantities of IL-1 (7,8). Therefore, we tested the ability of the four infecting pathogens to induce IL-1␣ by macrophages in vitro.…”