Intermittent administration of parathyroid hormone ameliorates periapical lesions in mice

Abstract

Introduction: Intermittent administration of parathyroid hormone (PTH) promotes oral osseous wound healing and protects against ligature-induced alveolar bone loss. However, its therapeutic value on periapical periodontitis is unknown. The goal of this study was to determine the effect of intermittent PTH administration on the progression of periapical periodontitis.

Methods: Seven lymphotoxin alpha-deficient mice received pulp exposures of mandibular first and second molars. Exposed pulp in the right mandible was covered with plaque-contaminated fibrin, whereas exposed pulp in the left mandible was left open. After 4 weeks, the periapical tissues were examined to determine the effect of plaque-contaminated fibrin to induce periapical lesions. Fourteen mice received pulp exposure covered with plaque-contaminated fibrin. PTH (40 μg/kg/d) was administered intermittently to half of the mice for 3 weeks beginning 1 week after pulp exposure. The remaining half received saline injections as the vehicle control. At sacrifice, mandibles and tibiae were harvested and processed for histologic examination. Evaluation of neutrophils and blood vessels was performed after staining with immunofluorescence, and periradicular bone was histomorphometrically analyzed.

Results: The exposed pulp covered with plaque-contaminated fibrin resulted in significantly larger periapical lesions compared with the control. Intermittent PTH administration reduced the size of periapical lesions significantly. Significantly less neutrophil infiltration around the root apex was found in PTH-treated animals compared with the control.

Conclusions: PTH treatment suppressed periapical inflammation by reducing neutrophil infiltration and protected against tissue destruction by periapical periodontitis.

Keywords: Lymphotoxin alpha; neutrophil infiltration; parathyroid hormone; periapical periodontitis.

Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Figures

Figure 1. Exposed pulp covered with plaque-contaminated fibrin induced large periapical lesions

(A) Distance between the root apex and the surface of periradicular bone was measured at seven points and results averaged. The average was used as a representative distance to estimate the size of the lesion. (B) The bone tissue within 0.4 mm of the bone surface was defined as the area of Interest (AOI) for the measurements of the numbers of bone fragments, BA/TA, and Oc.N/BS. (C) The periapical soft tissue area in a semicircle with a radius of 0.6mm was defined as the AOI for the assessment of inflammatory cells and neutrophils. (D,E) Representative photomicrographs of HE-stained sections of periapical lesions (original magnification, x100). Arrowheads indicate inflammatory cell infiltration. (F) Tissue areas occupied by inflammatory cells were measured. Significantly larger inflammatory cell area was noted in the plaque-contaminated fibrin group than control. (G) Size of periapical lesions were assessed by measuring the distance between the apex and bone surface. Significantly larger periapical lesions were found in the plaque-contaminated fibrin group than control. (H) Ly6G(+) cells, which represent neutrophils, were assessed next to the apex. Significantly more neutrophils were observed in the plaque-contaminated fibrin group than control. (N=7/group; Paired t-test; *p<0.05, **p<0.01)

Figure 2. PTH treatment protected periapical tissues from destruction

(A, B) Representative photomicrographs of HE-stained sections of periapical lesions (original magnification, x100). VC: Vehicle control (Saline) treatment, PTH: PTH treatment. Arrow heads indicate inflammatory cell infiltration. (C) The inflammatory cell area was significantly smaller in PTH-treated animals vs. control. (D) Size of periapical lesions were assessed by measuring the distance between the apex and bone surface. Significantly smaller periapical lesions were found in the PTH than VC group. (E) Periradicular bone was significantly denser in the PTH group compared to VC. (F) The numbers of osteoclasts per linear bone perimeters were measured. There was no difference between PTH-treated animals vs. control. (G, H) Representative photomicrographs of TRAP-stained sections of periapical lesions (original magnifications, x100). (N=7/group; Student t-test; *p<0.05, **p<0.01)

Figure 3. PTH treatment resulted in reduced neutrophil infiltration and blood vessels

(A, B) Representative immunofluorescent photomicrographs of Ly6G-stained sections of periapical lesions (bottom). DAPI staining was used for nuclei visualization (top) (original magnification, x200). VC: Vehicle control (Saline) treatment, PTH: PTH treatment. Dotted line indicates the tooth root near the apex. Arrow heads indicate inflammatory cell infiltration. Significantly smaller neutrophil area was found in the PTH-treated group than VC (E). (C, D) Representative immunofluorescent photomicrographs of CD31-stained sections of periapical lesions (bottom). DAPI staining was used for nuclei visualization (top) (original magnification, x200). No blood vessels were observed within the lesions. The numbers and areas of blood vessels around the lesions were significantly less in the PTH-treated group than VC (F, G). (N=7/group; Student t-test; *p<0.05, ***p<0.001)

Figure 4. PTH treatment increased bone area in long bones of LTA deficient mice

(A, B) Representative photomicrographs of HE-stained sections of proximal tibiae (original magnification, x40). VC: Vehicle control (Saline) treatment, PTH: PTH treatment. PTH treatment for 3 weeks significantly increased bone mass in the proximal tibia (C) with significantly more osteoclasts compared to VC (D). (N=7/group, student t-test, ***p<0.001)