Transiently Increased Bone Density After Irradiation and the Radioprotectant Drug Amifostine in a Rat Model

Abstract

At therapeutic levels in pediatric patients, radiation causes damage to the growth plate and contributes to growth deformity and fractures. The purpose of this project was to examine the effects of x-ray irradiation on regional bone mineral density (BMD) and osteoclast histology of rat bone with and without radioprotectant amifostine (AMF) pretreatment. Seventy-two weanling rats had their right knee irradiated with single fraction 17.5 Gy, whereas the left leg was used as an internal control. Twelve animals were euthanized at each of 6 time periods (0.5-6 wk) after irradiation, half having received 100 mg/kg amifostine. BMD (g/cm3) was determined for both the right and left femurs using peripheral quantitative computed tomography (CT) (pQCT). Tibial sections were stained for osteoclasts/chondroclasts with tartrate-resistant acid phosphatase. Statistically significant increases in BMD within the radiation field were seen in the treatment groups' right irradiated legs over the control unirradiated left legs at all time points from 0.5 through 6 weeks. Anatomically, a peak in BMD occurs in the region immediately adjacent to the chondro-osseous junction at 2 weeks after irradiation and then moves proximally within the adjacent metaphysis after 3 weeks. Corresponding to these findings, histologically a 2-week nadir occurs after irradiation in osteoclasts/chondroclast numbers adjacent to the chondro-osseous junction with a 71.9% decrease compared with controls (p <0.05). At 3 weeks, the numbers of osteoclasts/chondroclasts in this region have increased to 47.4% greater than the control legs (p <0.03) The animals receiving amifostine had BMD that was consistently closer to controls only adjacent to the chondro-osseous junction at 0.5, 2, and 3 weeks and osteoclast/chondroclast numbers that were closer to controls only at 4 weeks.

The differential effects of the radioprotectant drugs amifostine and sodium selenite treatment in combination with radiation therapy on constituent bone cells, ewing's sarcoma of bone tumor cells, and rhabdomyosarcoma tumor cells in vitro

“…4 This increase in apoptosis observed in vitro corresponded to an increase in active caspase-3 fragment staining observed 48 h after irradiation in chondrocytes of the proliferative zone of the irradiated tibial growth plate. [2][3][4]8 In the current study, irradiation resulted in an RADIOPROTECTANT EFFECTS ON CELLS earlier significant increase in caspase-3 expression for the more radiosensitive endothelial cells 12 h following irradiation. The osteoblasts, the least radiosensitive cells examined in the current work, were observed to have a significant increase in caspase-3 expression 72 h after irradiation.…”

“…Osteoblasts and osteoclasts are located in close proximity to one another in vivo. 8 Osteoclasts produce free radical oxygen and nitrogen during resorption, similar to the free radicals produced after irradiation. 11 Chondrocytes within the proliferative zone of the growth plate are not located near osteoclasts in vivo, and as such, may not possess the machinery to respond to free radical damage; however, the above is entirely speculative.…”

“…4,8 Osteoclast number estimates were made through Cavalieri sampling and a modification of the fractionator technique. 4 For bone resorption, three bone slices were collected 21 days after irradiation and cells were removed by sonication in 1 M ammonium hydroxide.…”

SHIP1 Regulates MSC Numbers and Their Osteolineage Commitment by Limiting Induction of the PI3K/Akt/β-Catenin/Id2 Axis

“…Bone mineral density (BMD, g/cm 2 ), bone mineral content (BMC, grams), and body fat percent were assessed with dual-energy X-ray absorptiometry (DEXA) using a PixiMus scanner (GE Healthcare), according to previously published techniques [34]. Briefly, mice were anesthetized using 5% isoflurane and oxygen.…”

CORR Insights®: Development of a Mouse Model of Ischemic Osteonecrosis

“…O steonecrosis is a persistent and confounding orthopaedic pathology that can arise in any bone; common causes include compromised vasculature, exposure to radiation therapy, treatment with corticosteroids, or bisphosphonates treatment [2,5,6]. In the appendicular skeleton, osteonecrosis is managed surgically using total joint implants (among other approaches) while osteonecrosis of the jaw is treated with prophylactic antibiotic rinses followed by surgical resection when disease progression leads to substantial pain [1,3].…”