Quantitative histologic evidence of amifostine-induced cytoprotection in an irradiated murine model of mandibular distraction osteogenesis

Radioprotective role of amifostine on osteointegration of titanium implants in the tibia of rats

BACKGROUND

Titanium is the most widely used metal for bone integration, especially for cancer patients receiving ionizing radiation. This study aimed to investigate the amifostine administration that would reduce the effects of radiation on bone healing and osseointegration in rat models.

OBJECTIVES

It is aimed that the application of amifostine in rats receiving radiotherapy treatment will reduce the negative effects of ionizing radiation on the bone.

METHODS

Thirty-five adult male Wistar rats were randomly divided into one healthy and four experimental groups. In three consecutive days, two experimental groups of rats (AMF-RT-IMP and RT-IMP) were exposed to radiation (15 Gy/3 fractions of 5 Gy each). Then the titanium implants were inserted into the left tibia. Before the radiotherapy process, a 200 mg/kg dose of amifostine (AMF) was administered to the rats in the AMF-IMP and AMF-RT-IMP groups. Twenty-eight days after the screw implant, all rats were sacrificed, and their blood samples and tibia bones were collected for analysis.

RESULTS

The results indicated an accelerated bone formation and a more rapid healing process in the screw implants in the AMF-IMP, AMF-RT-IMP, and AMF-RT groups than in the RT-IMP group. Also, bone-implant contact area measurement and inflammation decreased with amifostine treatment in the implants subjected to irradiation (p < 0.05).

CONCLUSIONS

The results obtained in the present study suggested that amifostine prevents the losses of bone minerals, bone integrity, and implant position from ionizing-radiation when given before exposure.

Nonvascularized Bone Graft Reconstruction of the Irradiated Murine Mandible: An Analogue of Clinical Head and Neck Cancer Treatment

Nonvascularized bone grafts (NBGs) represent a practical method of mandibular reconstruction that is precluded in head and neck cancer patients by the destructive effects of radiotherapy. Advances in tissue-engineering may restore NBGs as a viable surgical technique, but expeditious translation demands a small-animal model that approximates clinical practice. This study establishes a murine model of irradiated mandibular reconstruction using a segmental iliac crest NBG for the investigation of imperative bone healing strategies. Twenty-seven male isogenic Lewis rats were divided into 2 groups; control bone graft and irradiated bone graft (XBG). Additional Lewis rats served as graft donors. The XBG group was administered a fractionated dose of 35Gy. All rats underwent reconstruction of a segmental, critical-sized defect of the left hemi-mandible with a 5 mm NBG from the iliac crest, secured by a custom radiolucent plate. Following a 60-day recovery period, hemi-mandibles were evaluated for bony union, bone mineralization, and biomechanical strength (P < 0.05). Bony union rates were significantly reduced in the XBG group (42%) compared with controls (80%). Mandibles in the XBG group further demonstrated substantial radiation injury through significant reductions in all metrics of bone mineralization and biomechanical strength. These observations are consistent with the clinical sequelae of radiotherapy that limit NBGs to nonirradiated patients. This investigation provides a clinically relevant, quantitative model in which innovations in tissue engineering may be evaluated in the setting of radiotherapy to ultimately provide the advantages of NBGs to head and neck cancer patients and reconstructive surgeons.

Radioprotection With Amifostine Enhances Bone Strength and Regeneration and Bony Union in a Rat Model of Mandibular Distraction Osteogenesis

BACKGROUND

Using distraction osteogenesis (DO) to regenerate robust endogenous bone could greatly enhance postoncologic reconstruction of head and neck cancer. However, radiation (XRT) corrosive effects still preclude DO's immense potential. We posit that adjunctive pretreatment with the radioprotectant amifostine (AMF) can optimize wound healing and allow for successful DO with quantifiable enhancements in bony union and strength despite previous surgical bed irradiation.

METHODS

Two groups of murine left hemimandibles were exposed to a human equivalent radiation dosage fractionated over 5 daily doses of 7 Gy. AMF-XRT-DO (n = 30) received AMF before radiation, whereas XRT-DO (n = 22) was untreated. All animals underwent left hemimandibular osteotomy and external fixator placement, followed by distraction to a 5.1-mm gap. Left hemimandibles were harvested and mechanically tested for parameters of strength, yield, and breaking load.

RESULTS

Radiation-related complications such as severe alopecia were significantly increased in XRT-DO compared with the AMF-treated group (P = 0.001), whereas infection and death were comparable (P = 0.318). Upon dissection, bony defects were grossly visible in XRT-DO distraction gap compared with AMF-XRT-DO, which exhibited significantly more complete unions (P = 0.004). Those results were significantly increased in the specimens prophylactically treated with AMF (yield: 39.41 N vs 21.78 N, P = 0.023; breaking load: 61.74 N vs 34.77 N, P = 0.044; respectively).

CONCLUSIONS

Our study revealed that AMF enhances biomechanical strength, regeneration, and bony union after radiation in a murine model of DO. The use of prophylactic AMF in combination with DO offers the promise of an alternative reconstructive option for patients afflicted with head and neck cancer.

Novel Formulation Strategy to Improve the Feasibility of Amifostine Administration

PURPOSE

Amifostine (AMF), a radioprotectant, is FDA-approved for intravenous administration in cancer patients receiving radiation therapy (XRT). Unfortunately, it remains clinically underutilized due to adverse side effects. The purpose of this study is to define the pharmacokinetic profile of an oral AMF formulation potentially capable of reducing side effects and increasing clinical feasibility.

METHODS

Calvarial osteoblasts were radiated under three conditions: no drug, AMF, and WR-1065 (active metabolite). Osteogenic potential of cells was measured using alkaline phosphatase staining. Next, rats were given AMF intravenously or directly into the jejunum, and pharmacokinetic profiles were evaluated. Finally, rats were given AMF orally or subcutaneously, and blood samples were analyzed for pharmacokinetics.

RESULTS

WR-1065 preserved osteogenic potential of calvarial osteoblasts after XRT to a greater degree than AMF. Direct jejunal AMF administration incurred a systemic bioavailability of 61.5%. Subcutaneously administrated AMF yielded higher systemic levels, a more rapid peak exposure (0.438 vs. 0.875 h), and greater total systemic exposure of WR-1065 (116,756 vs. 16,874 ng*hr/ml) compared to orally administered AMF.

CONCLUSIONS

Orally administered AMF achieves a similar systemic bioavailability and decreased peak plasma level of WR-1065 compared to intravenously administered AMF, suggesting oral AMF formulations maintain radioprotective efficacy without causing onerous side effects, and are clinically feasible.

Significant Differences in the Bone of an Isogenic Inbred Versus Nonisogenic Outbred Murine Mandible: A Study in Rigor and Reproducibility

Inattention to differences between animal strains is a potential cause of irreproducibility of basic science investigations. Accordingly, the authors' laboratory sought to ensure that cross-comparisons of results generated from studies of mandibular physiology utilizing the Sprague Dawley and Lewis rat strains are valid. The authors specifically investigated baseline histomorphometrics, bone mineral density, and biomechanical strength of the unaltered endogenous mandibles of the inbred, isogenic Lewis rat, and the outbred, nonisogenic Sprague Dawley rat to determine if they are indeed equal. The authors hypothesized that little difference would be found within these metrics.The authors' study utilized 20 male Lewis and Sprague Dawley rats, which underwent no manipulation other than final dissection and analysis. Ten rats from each strain underwent bone mineral density and biomechanical strength analysis. The remaining rats underwent histological analysis. Descriptive and bivariate statistics were computed and the P value was set at 0.05.Lewis rats had a significantly greater number of empty lacunae. Sprague Dawley rats exhibited a significantly greater ratio of bone volume-to-total volume, bone mineral density, tissue mineral density, bone volume fraction, and total mineral content. No differences were found during biomechanical testing.This study demonstrates that differences exist between the Lewis and Sprague Dawley rat within unaltered baseline mandibular tissue. However, these differences appear to have limited functional impact, as demonstrated by similar biomechanical strength metrics. Other specific differences not addressed in this manuscript may exist. However, the authors believe that researchers may confidently cross-compare results between the 2 strains, while taking into account the differences found within this study.

Prevention of radiation-induced bone pathology through combined pharmacologic cytoprotection and angiogenic stimulation

Pathologic fractures and associated non-unions arising in previously irradiated bone are severely debilitating diseases. Although radiation is known to have deleterious effects on healthy tissue cellularity and vascularity, no clinically accepted pharmacologic interventions currently exist to target these destructive mechanisms within osseous tissues. We utilized amifostine-a cellular radioprotectant-and deferoxamine-an angiogenic stimulant-to simultaneously target the cellular and vascular niches within irradiated bone in a rat model of mandibular fracture repair following irradiation. Rats treated with combined therapy were compared to those undergoing treatment with singular amifostine or deferoxamine therapy, nontreated/irradiated animals (XFx) and non-treated/non-irradiated animals (Fx). 3D angiographic modeling, histology, Bone Mineral Density Distribution and mechanical metrics were utilized to assess therapeutic efficacy. We observed diminished metrics for all outcomes when comparing XFx to Fx alone, indicating the damaging effects of radiation. Across all outcomes, only the combined treatment group improved upon XFx levels, normalized all metrics to Fx levels, and was consistently as good as, or superior to the other treatment options (p<0.05). Collectively, our data demonstrate that pharmacologically targeting the cellular and vascular environments within irradiated bone prevents bone injury and enhances fracture healing.

Prophylactic amifostine prevents a pathologic vascular response in a murine model of expander-based breast reconstruction

BACKGROUND

Although expander-based breast reconstruction is the most commonly used method of reconstruction worldwide, it continues to be plagued with complication rates as high as 60% when radiotherapy is implemented. We hypothesized that quantitative measures of radiotherapy-induced vascular injury can be mitigated by utilizing amifostine in a murine model of expander-based breast reconstruction.

METHODS

30 rats were divided into three groups: expander placement (Control), expander placement followed by radiotherapy (XRT), and expander placement followed by radiotherapy with amifostine (AMF/XRT). All groups underwent placement of a sub-latissimus tissue expander. After a 45 day recovery period, all groups underwent vascular perfusion and micro-CT analysis.

RESULTS

Micro-CT analysis was used to calculate vessel volume fraction (VVF), vessel number (VN), and vessel separation (VSp). A significant increase in VN was seen in the XRT group as compared to the Control (p = 0.021) and the AMF/XRT (p = 0.027). There was no difference between Control and AMF/XRT (p = 0.862). VVF was significantly higher in XRT than either Control (p = 0.043) and AMF/XRT (p = 0.040), however no difference was seen between Control and AMF/XRT (p = 0.980). VSp of XRT was smaller when compared to both Control and AMF/XRT specimens (p = 0.05 and p = 0.048, respectively), and no difference was seen between Control and AMF/XRT (p = 0.339).

CONCLUSIONS

Amifostine administered prior to radiotherapy preserved vascular metrics similar to those of non-radiated specimens. Elevated vascularity demonstrated within the XRT group was not seen in either the Control or AMF/XRT groups. These results indicate that amifostine protects soft tissue in our model from a radiotherapy-induced pathologic vascular response.

Prophylactic administration of Amifostine protects vessel thickness in the setting of irradiated bone

Although often beneficial in the treatment of head and neck cancer (HNC), radiation therapy (XRT) leads to the depletion of vascular supply and eventually decreased perfusion of the tissue. Specifically, previous studies have demonstrated the depletion of vessel volume fraction (VVF) and vessel thickness (VT) associated with XRT. Amifostine (AMF) provides protection from the detrimental effects of radiation damage, allowing for reliable post-irradiation fracture healing in the murine mandible. The purpose of this study is to investigate the prophylactic ability of AMF to protect the vascular network in an irradiated field. Sprague-Dawley rats (n = 17) were divided into 3 groups: control (C, n = 5), radiated (XRT, n = 7), and radiated mandibles treated with Amifostine (AMF XRT, n = 5). Both groups receiving radiation underwent a previously established, human equivalent dose of XRT totaling 35 Gy, equally fractionated over 5 days. The AMF XRT group received a weight dependent (0.5 mg AMF/5 g body weight) subcutaneous injection of AMF 45 min prior to XRT. Following a 56-day recovery period, mandibles were perfused, dissected, and imaged with μCT. ANOVA was used for comparisons between groups and p < 0.05 was considered statistically significant. Stereologic analysis demonstrated a significant and quantifiable restoration of VT in AMF treated mandibles as compared to those treated with radiation alone (0.061 ± 0.011 mm versus 0.042 ± 0.004 mm, p = 0.027). Interestingly, further analysis demonstrated no significant difference in VT between control mandibles and those treated with AMF (0.067 ± 0.016 mm versus 0.061 ± 0.011 mm, p = 0.633). AMF treatment also showed an increase in VVF, however those results were not statistically significant from VVF values demonstrated by the XRT group. Our data support the contention that AMF therapy acts prophylactically to protect vessel thickness. Based on these findings, we support the continued investigation of this treatment paradigm in its potential translation for the prevention of vascular depletion after radiotherapy.

Prophylactic amifostine preserves the biomechanical properties of irradiated bone in the murine mandible

BACKGROUND

The authors have previously demonstrated that amifostine prophylaxis mitigates the pernicious effects of radiation in settings of fracture repair and distraction osteogenesis. Expanding on these studies, the authors examined the biomechanical properties of uninjured bone exposed to both radiation and amifostine. The authors hypothesize that radiation will degrade the biomechanical properties of native bone, and further hypothesize that prophylactic amifostine will preserve biomechanical properties to levels of normal bone and protect against radiation-induced morbidities.

METHODS

Rats were randomized into control, irradiated, and amifostine pretreatment plus radiation (amifostine-pretreated) groups. Irradiated animals received a fractionated dosing schedule of 35 Gy, with amifostine-pretreated animals receiving amifostine before irradiation. Hemimandibles were harvested at 8 and 18 weeks for biomechanical testing and micro-computed tomographic analysis.

RESULTS

At 8 weeks, irradiated specimens displayed elevations above controls for all biomechanical properties. At 18 weeks, the biomechanical properties of irradiated specimens degraded in comparison with controls; at both time points, amifostine-pretreated specimens were maintained at levels comparable to controls. There was a significant decrease in tissue mineral density from 8- to 18-week irradiated specimens, whereas no such change existed for control and amifostine-pretreated specimens.

CONCLUSIONS

The authors' findings demonstrate paradoxical and transient elevations in the initial biomechanical properties of irradiated specimens that were not sustained through the later study time point. Amifostine pretreatment, however, provided uninterrupted preservation of the biomechanical properties of normal, native bone at both time points. This supports the contention that amifostine is capable of providing continuous protection to bone against the untoward effects of radiation therapy.

Amifostine protects vascularity and improves union in a model of irradiated mandibular fracture healing

BACKGROUND

Pathologic fractures of the mandible can be devastating to cancer patients and are due in large part to the pernicious effects of irradiation on bone vascularity. The authors' aim was to ascertain whether amifostine, a radioprotective drug, will preserve vascularity and improve bone healing in a murine model of irradiated mandibular fracture repair.

METHODS

Rats were randomized into three groups: nonirradiated fracture (n = 9), irradiation/fracture (n = 5), and amifostine/irradiation/fracture (n = 7). Animals in the irradiation groups underwent a human equivalent dose of radiation directed at the left hemimandible. Animals treated in the amifostine group received amifostine concomitantly with radiation. All animals underwent unilateral left mandibular osteotomy with external fixation set to a 2.1-mm fracture gap. Fracture healing was allowed for 40 days before perfusion with Microfil. Vascular radiomorphometrics were quantified with micro-computed tomography.

RESULTS

When compared with the irradiated/fractured group, amifostine treatment more than doubled the rate of fracture unions to 57 percent. Amifostine treatment also resulted in an increase in vessel number (123 percent; p < 0.05) and a corresponding decrease in vessel separation (55.5 percent; p < 0.05) there was no statistical difference in the vascularity metrics between the amifostine/irradiation/fracture group and the nonirradiated/fracture group.

CONCLUSIONS

Amifostine prophylaxis during radiation maintains mandibular vascularity at levels observed in nonirradiated fracture specimens, corresponding to improved unions. These results set the stage for clinical exploration of this targeted therapy alone and in combination with other treatments, to mitigate the effects of irradiation on bone healing and fracture repair.

Amifostine preserves osteocyte number and osteoid formation in fracture healing following radiotherapy

PURPOSE

Radiation is known to decrease osteocyte count and function, leading to bone weakening. A treatment strategy to mitigate these consequences could have immense therapeutic ramifications. The authors previously reported significantly decreased osteocyte count and mineralization capacity in a rat model of fracture healing after radiotherapy. They hypothesized that amifostine (AMF) would preserve osteocyte number and function in this model.

MATERIALS AND METHODS

Thirty-six rats were divided into 3 groups: fracture, radiated fracture, and radiated fracture with AMF. Radiated groups underwent human-equivalent radiotherapy to the mandible before fixator placement and mandibular osteotomy. The AMF group received a subcutaneous injection before each dose of radiotherapy. After 40 days, mandibles were harvested for histologic processing. Quantification of osteocyte count (Oc), empty lacunae (EL), and osteoid ratio (osteoid volume [OV] to tissue volume [TV]) was performed and the results were compared using analysis of variance (P < .05).

RESULTS

Radiated fractures showed significantly decreased Oc, increased EL, and a decreased capacity to produce new osteoid at the fracture site as measured with OV/TV compared with nonradiated fractures. In mandibles treated with AMF, these metrics were not statistically different than the control, indicating a preservation of osteocyte number and function.

CONCLUSIONS

These results support the hypothesis that AMF preserves osteocyte number and function, thereby preventing the pernicious effects of radiotherapy on the cellular environment of fracture healing. Based on these findings, the authors encourage future investigation of this promising therapy for use in the prevention of pathologic fractures and osteoradionecrosis.

The effect of Amifostine prophylaxis on bone densitometry, biomechanical strength and union in mandibular pathologic fracture repair

BACKGROUND

Pathologic fractures (Fx) of the mandibles are severely debilitating consequences of radiation (XRT) in the treatment of craniofacial malignancy. We have previously demonstrated Amifostine's effect (AMF) in the remediation of radiation-induced cellular damage. We posit that AMF prophylaxis will preserve bone strength and drastically reverse radiotherapy-induced non-union in a murine mandibular model of pathologic fracture repair.

MATERIALS AND METHODS

Twenty-nine rats were randomized into 3 groups: Fx, XRT/Fx, and AMF/XRT/Fx. A fractionated human equivalent dose of radiation was delivered to the left hemimandibles of XRT/Fx and AMF/XRT/Fx. AMF/XRT/Fx was pre-treated with AMF. All groups underwent left mandibular osteotomy with external fixation and setting of a 2.1mm fracture gap post-operatively. Utilizing micro-computed tomography and biomechanical testing, the healed fracture was evaluated for strength.

RESULTS

All radiomorphometrics and biomechanical properties were significantly diminished in XRT/Fx compared to both Fx and AMF/XRT/Fx. No difference was demonstrated between Fx and AMF/XRT/Fx in both outcomes.

CONCLUSION

Our investigation establishes the significant and substantial capability of AMF prophylaxis to preserve and enhance bone union, quality and strength in the setting of human equivalent radiotherapy. Such novel discoveries establish the true potential to utilize pharmacotherapy to prevent and improve the treatment outcomes of radiation-induced late pathologic fractures.

Raman spectroscopy demonstrates Amifostine induced preservation of bone mineralization patterns in the irradiated murine mandible

PURPOSE

Adjuvant radiotherapy in the management of head and neck cancer remains severely debilitating. Fortunately, newly developed agents aimed at decreasing radiation-induced damage have shown great promise. Amifostine (AMF) is a compound, which confers radio-protection to the exposed normal tissues, such as bone. Our intent is to utilize Raman spectroscopy to demonstrate how AMF preserves the mineral composition of the murine mandible following human equivalent radiation.

METHODS

Sprague Dawley rats were randomized into 3 experimental groups: control (n=5), XRT (n=5), and AMF-XRT (n=5). Both XRT and AMF groups underwent bioequivalent radiation of 70Gy in 5 fractions to the left hemimandible. AMF-XRT received Amifostine prior to radiation. Fifty-six days post-radiation, the hemimandibles were harvested, and Raman spectra were taken in the region of interest spanning 2mm behind the last molar. Bone mineral and matrix-specific Raman bands were analyzed using one-way ANOVA, with statistical significance at p<0.05.

RESULTS

The full-width at half-maximum of the primary phosphate band (FWHM) and the ratio of carbonate/phosphate intensities demonstrated significant differences between AMF-XRT versus XRT (p<0.01) and XRT versus control (p<0.01). There was no difference between AMF-XRT and control (p>0.05) in both Raman metrics. Computer-aided spectral subtraction further confirmed these results where AMF-XRT was spectrally similar to the control. Interestingly, the collagen cross-link ratio did not differ between XRT and AMF-XRT (p<0.01) but was significantly different from the control (p<0.01).

CONCLUSION

Our novel findings demonstrate that AMF prophylaxis maintains and protects bone mineral quality in the setting of radiation. Raman spectroscopy is an emerging and exceptionally attractive clinical translational technology to investigate and monitor both the destructive effects of radiation and the therapeutic remediation of AMF on the structural, physical and chemical qualities of bone.