BONE-RESORPTIVE CYTOKINE GENE-EXPRESSION IN PERIAPICAL LESIONS IN THERAT

Periapical bone destruction is an important pathogenic sequela of pulp al infection. Recent findings from this laboratory have demonstrated t hat 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 cy tokine messe nger RNA (mRNA) expression was analyzed in developing rat periapical l esions. The molar teeth of 20 Sprague-Dawley rats were surgically expo sed and left open to permit infection from the oral environment. Total cell RNA was isolated from periapical granuloma tissue obtained on da ys 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 trans cription polymerase chain reaction, and levels were approximated by co mparison to the parallel amplification of the housekeeping gene glycer aldehyde phosphate dehydrogenase. IL-1 alpha and TNF-alpha mRNA were b oth highly expressed beginning on day 7, increased on day 15, and decl ined somewhat on day 30. In contrast; IL-1 beta mRNA was expressed at much lower levels, but with similar kinetics. The kinetics of steady s tate IL-1 alpha and TNF-alpha mRNA levels were confirmed using the qua ntitative RNase protection assay, whereas IL-1 beta mRNA could not be detected by this technique. IL-1 alpha mRNA-expressing cells were iden tified using in situ hybridization and included infiltrating macrophag es, as well as resident fibroblasts, endothelial cells and osteoclasts . These results demonstrate that the IL-1 alpha and TNF-alpha genes ar e highly expressed in developing periapical lesions in the rat and con firm previous studies at the protein level in this model.