Phagocytic osteoclasts in the alveolar bone of diabetic rats with periodontitis

Periodontitis is a bacteria-induced inflammatory disease associated with alveolar bone loss. Osteoclast is a macrophage-lineage cell that exhibits phagocytic activity; however, osteoclast phagocytic activity has not been demonstrated under pathological conditions. Diabetes is a pathological condition that exacerbates alveolar bone loss via periodontitis; therefore, we examined phagocytic osteoclasts in diabetic rats that had periodontitis. The rats were divided into the control (C), periodontitis (P), and diabetes with periodontitis (DP) groups. Diabetes and periodontitis were induced by streptozotocin injection and ligature of the mandibular first molars, respectively. On days 3 and 20 after the ligature, the rats were sacrificed, and osteoclasts containing inclusions were quantified by tartrate-resistant acid phosphatase staining. On day 3, there were more osteoclasts containing inclusions in the DP group than in the C group. Among inclusions, osteocyte-like cells and dense bodies were more frequently observed in the DP group than in the C group. Cytoplasm-like structures were elevated more in the DP group than in the C and P groups. However, no differences were observed on day 20. Interestingly, some osteoclasts were in contact with the osteocytes within the exposed lacunae and contained several inclusions within a large vacuole. Thus, the elevation of phagocytic osteoclasts in rats with diabetes and periodontitis provides insight into the role of osteoclast phagocytic activity under pathological conditions.