Micro-computed tomographic, histological, and immunohistochemical evaluation of the effects of phosphodiesterase-4 inhibition on experimental periodontitis in rats

Objective

The aim of this study was to evaluate the effects of Apremilast on periodontal inflammation, alveolar bone loss, and osteoclastic and osteoblastic activity in a ligature-induced experimental periodontitis model using micro-computed tomography (micro-CT), histological, and immunohistochemical analyses.

Materials and Methods

Forty-five male Wistar albino rats (250–300 g) were included in the study. Of these, 42 animals were allocated to the experimental periodontitis groups, while three non-ligated healthy animals were included solely to provide descriptive physiological reference values for linear alveolar bone level (CEJ–ABC distance). The 42 experimental animals were randomly assigned to an experimental periodontitis (EP) group (n = 21) or an experimental periodontitis plus Apremilast (EP + APR) group (n = 21). Experimental periodontitis was induced by placing 4–0 silk ligatures around the bilateral maxillary second molars. During the experimental period, two animals were excluded from the final analysis: one died due to an infection, and one exhibited excessive periodontal destruction that was considered inconsistent with the intended experimental periodontitis model. Consequently, 40 experimental animals were included in the final analyses and euthanized according to their assigned experimental time points on days 8, 15, and 29. The EP + APR group received Apremilast at 5 mg/day by oral gavage, whereas the EP group received no treatment. Histological analyses assessed inflammatory cell infiltration and connective tissue organization, while immunohistochemistry evaluated tartrate-resistant acid phosphatase (TRAP) and alkaline phosphatase (ALP) expression. Micro-CT was used to analyze linear alveolar bone loss, bone mineral density, and trabecular bone microarchitecture. Statistical significance was set at p < 0.05.

Results

Compared with the EP group, the EP + APR group demonstrated reduced inflammatory cell infiltration, better-preserved connective tissue organization, and a more regular alveolar bone surface morphology. On day 29, the number of TRAP-positive cells was significantly lower in the EP + APR group (p = 0.008). No significant group differences were observed in ALP expression, BMD, or trabecular bone microarchitecture. Although a significant overall group effect was detected for CEJ–ABC distance, the group × time interaction was not significant (p = 0.836). Linear alveolar bone loss increased over time in both groups.

Conclusion

Apremilast reduced inflammatory cell infiltration and osteoclastic activity but did not produce significant improvements in alveolar bone loss or trabecular bone microarchitecture. These findings indicate that Apremilast exerted anti-inflammatory and anti-osteoclastic biological effects under the present experimental conditions; however, these effects did not translate into measurable structural protection of alveolar bone.