Early effects of parathyroid hormone on bisphosphonate/steroid-associated compromised osseous wound healing

Abstract

Summary: Administration of intermittent parathyroid hormone (PTH) promoted healing of tibial osseous defects and tooth extraction wounds and prevented the development of necrotic lesions in rats on a combined bisphosphonate and steroid regimen.

Introduction: Osteonecrosis of the jaw (ONJ) has emerged in association with antiresorptive therapies. The pathophysiology of ONJ is unknown and no established cure currently exists. Our objective was to determine the effect of intermittent PTH administration on early osseous healing in the jaw and long bones of rats receiving bisphosphonate and steroid treatment.

Methods: Ovariectomized rats received the combination therapy of alendronate and dexamethasone (ALN/DEX) for 12 weeks. Osseous wounds were created in the jaw and tibia. PTH was administered intermittently and healing at 2 weeks post-op was compared between the jaw and tibia by microcomputed tomography and histomorphometric analyses.

Results: ALN/DEX treatment was associated with necrotic open wounds in the jaw but had no negative effects on healing and promoted bone fill in tibial defects. PTH therapy prevented the development of necrotic lesions in the jaw and promoted healing of the tibial defects. PTH therapy was associated with the promotion of osteocyte survival in osseous wounds both in the jaw and tibia.

Conclusions: Wound healing was impaired in the jaw in rats on a combined bisphosphonate and steroid regimen, and PTH therapy rescued necrotic lesions. These findings suggest that PTH therapy could be utilized to prevent ONJ from occurring in patients on combination antiresorptive and steroid therapy.

Fig. 1

Experimental schedule. a Rats (n = 14) received ALN for 12 weeks and dexamethasone for 2 weeks before tooth extraction and osseous defect surgeries. Another14 rats received vehicle control (saline). Immediately after the surgeries, half of rats in each group received daily PTH administration (80 μg/kg) for 2 weeks and the remaining half vehicle control. b MicroCT scanning was performed in the proximal tibiae between 1.2 and 3.5 mm from the growth plate to determine the treatment effect on undisturbed trabecular bone. Scanning between 3.7 and 5.9 mm away from the growth plate was used to asses osseous healing (arrowhead). c The microCT scanning sites in the maxillae: tooth extraction wounds (arrow) and the interradicular bone (arrowhead) of the neighboring tooth. d A schematic drawing of a tooth extraction socket. Tissue area (TA) was defined as the area of an extraction socket and surrounding bone

Fig. 2

Treatment effect on undisturbed bone. a Representative longitudinal and cross-sectional images of the undisturbed tibiae. The ALN/DEX treatment resulted in significantly higher bone mass (b), trabecular numbers (c), BMD (f), and lower trabecular separation (e) compared with the VC treatment groups. PTH for 2 weeks significantly increased trabecular thickness regardless of the treatment (d). A nonsignificant increase by PTH was noted in bone mass (b) and BMD (f) in the ALN/DEX treatment group. When the bone mass increase by PTH was compared between the ALN/DEX and VC treatment groups, a significantly greater increase was noted in the ALN/DEX treatment group (g). *p < 0.05; **p < 0.01; ***p < 0.001 versus control (VC-VC)

Fig. 3

Treatment effect on the tibial defects. a Representative cross-sectional images of the tibial defects. Regardless of treatment, significantly higher bone mass (b), trabecular numbers (c), BMD (f), and lower trabecular separation (e) were noted in the treatment groups vs. control. PTH significantly increased trabecular thickness in the ALN/DEX and VC treatment groups but the ALN/DEX treatment alone had no effect on trabecular thickness (d). Although PTH further increased bone mass (b) and BMD (f) after the ALN/DEX treatment, an average bone mass increase by PTH was significantly less after ALN/DEX compared with VC (g). ***p < 0.001 versus control (VC-VC); ^††† p < 0.001 versus the ALN/DEX-VC group

Fig. 4

Histomorphometric assessments of tibial wound healing. a A diagram of the cross-sectional view of a tibial defect indicating the tissue area (TA). Both the ALN/DEX and PTH treatment resulted in significantly higher bone area vs. control (b). PTH after the ALN/DEX treatment significantly increased bone area. No differences were noted in periosteal callus formation between groups, but a trend of more periosteal callus in the ALN/DEX-PTH group vs. control was observed (c). The ALN/DEX treatment significantly suppressed osteoclast surface vs. control with further significant reduction in the ALN/DEX-PTH group (d). The ALN/DEX treatment had no effect on osteoblast surface vs. control. PTH significantly increased osteoblast surface after ALN/DEX (e). PTH therapy significantly suppressed the numbers of empty osteocyte lacunae and necrotic bone area regardless of other treatment (f, g). TUNEL⁺ cells in the bone marrow were significantly reduced by PTH compared with control (h). *p < 0.05; **p < 0.01; ***p < 0.001 versus control (VC-VC); ^† p < 0.05; ^†† p < 0.01 versus the ALN/DEX-VC group

Fig. 5

Treatment effect on the maxillae. a The result of microCT assessment of undisturbed maxillae. Regardless of treatment, significantly higher bone mass and BMD were found in the treatment groups vs. control. The ALN/DEX treatment significantly increased trabecular thickness and decreased trabecular separation compared with control. No PTH anabolic effect was observed after the ALN/DEX treatment, while PTH increased bone mass significantly after VC. b The result of microCT assessment of tooth extraction wounds. Both the ALN/DEX and PTH treatments resulted in significantly higher bone mass, trabecular thickness, and BMD than control. Although PTH significantly increased bone mass and BMD after ALN/DEX, an average increase in bone mass by PTH was significantly smaller after ALN/DEX than VC. *p < 0.05; **p < 0.01; ***p < 0.001 versus control (VC-VC); ^† p < 0.05 versus the ALN/DEX-VC group

Fig. 6

Histomorphometric assessments of extraction wound healing. (a) Representative images of frontal-sections of the extraction wounds. Six rats developed necrotic lesions in the ALN/DEX-VC group and only one in the ALN/DEX-PTH group. Both the ALN/DEX and PTH treatments resulted in significantly higher bone area vs. control (b). The ALN/DEX treatment significantly suppressed, and PTH after VC, significantly increased osteoclast surface (c). PTH significantly increased osteoblast surface after VC but not after ALN/DEX (d). Significantly higher numbers of empty osteocyte lacunae and necrotic bone area were noted in the ALN/DEX-VC group vs. control. PTH suppressed the numbers of empty lacunae and necrotic bone area significantly after ALN/DEX and after VC (e, f). PMN infiltration was significantly higher in the ALN/DEX-VC group versus control. PTH dramatically suppressed PMN infiltration when given after ALN/DEX (g). Significantly lower collagen apposition was noted in the ALN/DEX-VC group vs. control. PTH increased collagen apposition significantly after ALN/DEX and after VC (h). No treatment regimen altered blood vessel numbers (i). *p < 0.05; **p < 0.01; ***p < 0.001 versus control (VC-VC); †p < 0.05; ††p < 0.01 versus the ALN/DEX-VC group