In vivo administration of IL‐1β accelerates silk ligature‐induced alveolar bone resorption in rats

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Abstract
The effects of recombinant human interleukin‐1β (rhIL‐1β) on alveolar bone resorptive activity in rats were examined. Continuous administration of rhIL‐1β or phosphate‐buffered saline (PBS) was given via osmotic pumps for 3, 7 and 14 days to rats with silk ligatures around second maxillary molars. Other animals without ligatures received insertion of pumps containing rhIL‐lp or remained untreated. Sections were subject to three different stains:–hematoxylin and eosin (H‐E) for histology, acid phosphatase (ACPase) activity for osteoclast detection, and immunohistochemistry using anti‐rat monocyte/macrophage monoclonal antibody (ED 1). In addition, body weight, plasma calcium and phosphorus levels were monitored. The mean body weight of rats receiving rhIL‐lp was significantly lower (P < 0.05 to P < 0.01) compared with untreated rats throughout the experimental period. On Day 7, plasma calcium and phosphorus levels were significantly lower in rats receiving rhIL‐1β than in rats receiving PBS only (P < 0.05). Sections revealed a moderate inflammatory cell infiltrate reaching near the alveolar crest in both groups with ligatures on Day 3. Only rats receiving rhIL‐lp exhibited enhancement of inflammatory cell invasion on Days 7 and 14. In rats receiving rhIL‐lp with ligatures, numerous resorption lacunae containing ACPase‐positive multinucleated giant cells (MNGCs), coinciding with ED1‐positive cells, were located on the mesial side of the septum where extensive bone resorption had occurred throughout the experimental period. In animals receiving rhIL‐β without ligatures, compared with untreated rats, increased ACPase‐positive cells were observed on the mesial side of the septum on Day 3. In animals receiving PBS only, a few ACPase‐positive cells were observed confined to the mesial regions where slight bone resorption occurred on Days 7 and 14. These results indicate that the administration of rhIL‐1β accelerated alveolar bone destruction in ligature‐induced periodontal tissue inflammation over a two‐week period.