Low-Dose X-Ray Irradiation Promotes Osteoblast Proliferation, Differentiation and Fracture Healing

Abstract

Great controversy exists regarding the biologic responses of osteoblasts to X-ray irradiation, and the mechanisms are poorly understood. In this study, the biological effects of low-dose radiation on stimulating osteoblast proliferation, differentiation and fracture healing were identified using in vitro cell culture and in vivo animal studies. First, low-dose (0.5 Gy) X-ray irradiation induced the cell viability and proliferation of MC3T3-E1 cells. However, high-dose (5 Gy) X-ray irradiation inhibited the viability and proliferation of osteoblasts. In addition, dynamic variations in osteoblast differentiation markers, including type I collagen, alkaline phosphatase, Runx2, Osterix and osteocalcin, were observed after both low-dose and high-dose irradiation by Western blot analysis. Second, fracture healing was evaluated via histology and gene expression after single-dose X-ray irradiation, and low-dose X-ray irradiation accelerates fracture healing of closed femoral fractures in rats. In low-dose X-ray irradiated fractures, an increase in proliferating cell nuclear antigen (PCNA)-positive cells, cartilage formation and fracture calluses was observed. In addition, we observed more rapid completion of endochondral and intramembranous ossification, which was accompanied by altered expression of genes involved in bone remodeling and fracture callus mineralization. Although the expression level of several osteoblast differentiation genes was increased in the fracture calluses of high-dose irradiated rats, the callus formation and fracture union were delayed compared with the control and low-dose irradiated fractures. These results reveal beneficial effects of low-dose irradiation, including the stimulation of osteoblast proliferation, differentiation and fracture healing, and highlight its potential translational application in novel therapies against bone-related diseases.

Periosteal Mesenchymal Progenitor Dysfunction and Extraskeletally-Derived Fibrosis Contribute to Atrophic Fracture Nonunion

“…A remarkably increased incidence of delayed and nonunion fracture within a prior irradiated bone has been a well‐known clinical observation for many years. Several previous rodent studies reported that radiation before or immediately after fracture causes alterations in the histology and radiology of the reparative processes . However, all those studies used whole‐body radiation, which limited the local radiation dosage that could be applied and was always accompanied by systematic effects, which primarily affect hematopoiesis and had abscopal effects on radiation‐shielded bones .…”

“…Several previous rodent studies reported that radiation before or immediately after fracture causes alterations in the histology and radiology of the reparative processes. (22)(23)(24) However, all those studies used whole-body radiation, which limited the local radiation dosage that could be applied and was always accompanied by systematic effects, which primarily affect hematopoiesis (25) and had abscopal effects on radiation-shielded bones. (26) Therefore, they do not faithfully mimic the clinical scenario of the primarily local problem of a traumatic fracture and ensuing nonunion.…”

Evaluation of longitudinal time-lapsedin vivomicro-CT for monitoring fracture healing in mouse femur defect models

“…As radiation effects are known to vary for different bone cell types and locations 30,34,35 , we assessed the four sub-volumes separately (Table 2). The applied micro-CT protocol did not significantly affect bone formation and resorption activities in the callus VOIs (DC, DP and FP) from week 5-6 with similar bone volume observed in week 5 and 6 for controls and scanned animals.…”

“…So far only few studies have focused on the underlying mechanisms of radiation-induced effects on bone mainly focusing on changes in expression profiles of osteoblast and osteoclast differentiation markers 30,35 . Recently, three consecutive in vivo studies by Chandra et al 36,53,54 showed, that radiation‐induced bone loss 53,54 is mediated via Sclerostin inhibition of osteoanabolic Wnt-signaling 36 .…”

Evaluating experimental molecular physics studies of radiation damage in DNA*

“…Also, it was demonstrated that SSB damage induced upon VUV irradiation has to date been significantly underestimated in radiotherapy models, which provided an explanation for the discrepancies obtained between theoretical and experimental data [116]. Such high levels of damage obtained upon high-dose radiation will be difficult to repair and might interfere with cell cycle progression, at which point cells undergo programmed cell death [117]. All the above allows to conclude that although AGE is popular, easy and inexpensive method, it should not be used for SSBs quantification.…”