Extended-term effects of head and neck irradiation in a rodent

Neurologic Changes Induced by Whole-Brain Synchrotron Microbeam Irradiation: 10-Month Behavioral and Veterinary Follow-Up

PURPOSE

Novel radiation therapy approaches have increased the therapeutic efficacy for malignant brain tumors over the past decades, but the balance between therapeutic gain and radiotoxicity remains a medical hardship. Synchrotron microbeam radiation therapy, an innovative technique, deposes extremely high (peak) doses in micron-wide, parallel microbeam paths, whereas the diffusing interbeam (valley) doses lie in the range of conventional radiation therapy doses. In this study, we evaluated normal tissue toxicity of whole-brain microbeam irradiation (MBI) versus that of a conventional hospital broad beam (hBB).

METHODS AND MATERIALS

Normal Fischer rats (n = 6-7/group) were irradiated with one of the two modalities, exposing the entire brain to MBI valley/peak doses of 0/0, 5/200, 10/400, 13/520, 17/680, or 25/1000 Gy or to hBB doses of 7, 10, 13, 17, or 25 Gy. Two additional groups of rats received an MBI valley dose of 10 Gy coupled with an hBB dose of 7 or 15 Gy (groups MBI17* and MBI25*). Behavioral parameters were evaluated for 10 months after irradiation combined with veterinary observations.

RESULTS

MBI peak doses of ≥680 Gy caused acute toxicity and death. Animals exposed to hBB or MBI dose-dependently gained less weight than controls; rats in the hBB25 and MBI25* groups died within 6 months after irradiation. Increasing doses of MBI caused hyperactivity but no other detectable behavioral alterations in our tests. Importantly, no health concerns were seen up to an MBI valley dose of 17 Gy.

CONCLUSIONS

While acute toxicity of microbeam exposures depends on very high peak doses, late toxicity mainly relates to delivery of high MBI valley doses. MBI seems to have a low impact on normal rat behavior, but further tests are warranted to fully explore this hypothesis. However, high peak and valley doses are well tolerated from a veterinary point of view. This normal tissue tolerance to whole-brain, high-dose MBI reveals a promising avenue for microbeam radiation therapy, that is, therapeutic applications of microbeams that are poised for translation to a clinical environment.

Side effects of different head and neck radiotherapy doses on wistar rat's behavior

Radiotherapy (RT) is a common treatment for head and neck tumors. However, it causes several physical and behavioral side effects, and no study has assessed the emotional effects in rats. Therefore, the present study evaluated the influence of head and neck RT on the behavior and body weight gain in Wistar rats. Fifty-four male Wistar rats were allocated into six groups (n = 9) according to the irradiation dose, which was applied at the first day of the experiment: RT-7.5 (single dose of 7.5 Gy); RT-10 (single dose of 10 Gy); RT-15 (single dose of 15 Gy); RT-30 (single dose of 30 Gy); Control (without RT). The animals were irradiated in the region of the right face, and behavioral tests and weighing were performed on days one, seven, and 28. The open field and Y-maze tests were undertaken to analyze the animal's behavior. The dose of 30 Gy was lethal when applied to the head and neck region. The irradiated animals had less weight gain when compared to the control ones, but there was no statistical difference. In the open field and Y-maze tests, lower mobility of animals in the RT groups was observed both on day seven and at the end of the experiment (day 28) when compared to the control rats (p < 0.05). It was possible to conclude that the different doses of radiation induced depressive behavior in the animals, and that the weight gain tended to be lower in the irradiated groups, however, without statistical difference.

Modulation of the Nitric Oxide/BH4 Pathway Protects Against Irradiation-Induced Neuronal Damage

The kynurenine pathway (KP, IDO/Kyn pathway) is an important metabolic pathway related to many diseases. Although cranial radiotherapy is the mainstay in metastatic tumors management, its efficacy is limited owing to the associated neuropsychiatric disorders. Sildenafil (SD) and simvastatin (SV) were reported to have antioxidant/anti-inflammatory effects and to serve as NO donor/BH4 regulator, respectively. Fluoxetine (Fx) is an FDA-approved anti-depressant agent and one of the selective serotonin reuptake inhibitor drugs (SSRI), used in neurological disorder treatment. The study objective was to investigate the role of cranial irradiation (C-IR) on KP signaling impairment and the possible intervention by SD and/or SV (as nitric oxide (NO) donor/Tetrahydrobiopterin (BH4) regulatory) on KP following C-IR-induced disruption compared with Fx (as standard drug).Herein, rats were exposed to C-IR at a single dose level of 25 Gy, then treated with sildenafil (SD) and/or simvastatin (SV), and fluoxetine (Fx) at doses of 75, 20, 10 mg/kg/day, respectively. The body weight gain and forced swimming test (FST) were used for evaluation along with the biochemical quantifications of KP intermediates and histopathological examination of cortex and hippocampus. The results indicated a significant activation of KP following C-IR as manifested by decreased Trp content and increased activities of indoleamine 2,3-dioxygenase (IDO) and tryptophan 2,3-dioxygenase (TDO) with a rise in kynurenine (KYN) and quinolinic acid (QA) hippocampal contents. In addition, a state of C-IR-induced oxidative stress, inflammation, NO-pathway dysregulation and neuronal apoptosis were observed as compared to the control group. However, significant modulations were recorded after the combined administration of SD and SV than those offered by each of them alone and by Fx. The biochemical assessment results were supported by the histopathological tissue examination. It could be concluded that the co-administration of SV and SD offers a neuroprotective effect against irradiation-induced brain injury due to its NO donor/BH4 regulatory activities, anti-inflammatory and antioxidant properties that modulate IDO/KYN pathway.

Effect of fractionated whole-brain irradiation on brain and plasma in a rat model: Metabolic, volumetric and histopathological changes

In the present study, we investigated the correlation between histopathological, metabolic, and volumetric changes in the brain and plasma under experimental conditions. Adult male Wistar rats received fractionated whole-brain irradiation (fWBI) with a total dose of 32 Gy delivered in 4 fractions (dose 8 Gy per fraction) once a week on the same day for 4 consecutive weeks. Proton magnetic resonance spectroscopy (¹H MRS) and imaging were used to detect metabolic and volumetric changes in the brain and plasma. Histopathological changes in the brain were determined by image analysis of immunofluorescent stained sections. Metabolic changes in the brain measured by ¹H MRS before, 48 h, and 9 weeks after the end of fWBI showed a significant decrease in the ratio of total N-acetylaspartate to total creatine (tNAA/tCr) in the corpus striatum. We found a significant decrease in glutamine + glutamate/tCr (Glx/tCr) and, conversely, an increase in gamma-aminobutyric acid to tCr (GABA/tCr) in olfactory bulb (OB). The ratio of astrocyte marker myoinositol/tCr (mIns/tCr) significantly increased in almost all evaluated areas. Magnetic resonance imaging (MRI)-based brain volumetry showed a significant increase in volume, and a concomitant increase in the T₂ relaxation time of the hippocampus. Proton nuclear magnetic resonance (¹H NMR) plasma metabolomics displayed a significant decrease in the level of glucose and glycolytic intermediates and an increase in ketone bodies. The histomorphological analysis showed a decrease to elimination of neuroblasts, increased astrocyte proliferation, and a mild microglia response. The results of the study clearly reflect early subacute changes 9-11 weeks after fWBI with strong manifestations of brain edema, astrogliosis, and ongoing ketosis.

Effect of Previous Irradiation on Vascular Thrombosis of Microsurgical Anastomosis: A Preclinical Study in Rats

BACKGROUND

The objective of the present investigation was to compare the effect of neoadjuvant irradiation on the microvascular anastomosis in cervical bundle using an experimental model in rats.

METHODS

One hundred forty male Sprague-Dawley rats were allocated into 4 groups: group I, control, arterial microanastomosis; group II, control, venous microanastomosis; group III, arterial microanastomosis with previous irradiation (20 Gy); and group IV, venous microanastomosis with previous irradiation (20 Gy). Clinical parameters, technical values of anastomosis, patency, and histopathological parameters were evaluated.

RESULTS

Irradiated groups (III and IV) and vein anastomosis groups (II and IV) showed significantly increased technical difficulties. Group IV showed significantly reduced patency rates (7/35) when compared with the control group (0/35). Radiotherapy significantly decreased the patency rates of the vein (7/35) when compared with the artery (1/35). Groups III and IV showed significantly reduced number of endothelial cells and also showed the presence of intimal thickening and adventitial fibrosis as compared with the control group.

CONCLUSION

Neoadjuvant radiotherapy reduces the viability of the venous anastomosis in a preclinical rat model with a significant increase in the incidence of vein thrombosis.

New and safe experimental model of radiation-induced neurovascular histological changes for microsurgical research

The aim is to create a new and safe experimental model of radiation-induced neurovascular histological changes with reduced morbidity and mortality for use with experimental microsurgical techniques. Seventy-two Sprague-Dawley rats (250-300 g) were divided as follows: Group I: control group, 24 rats clinically evaluated during six weeks; Group II: evaluation of acute side-effects (two-week follow-up period), 24 irradiated (20 Gy) rats; and Group III: evaluation of subacute side-effects (six-week follow-up period), 24 irradiated (20 Gy) rats. Variables included clinical assessments, weight, vascular permeability (arterial and venous), mortality and histological studies. No significant differences were observed between groups with respect to the variables studied. Significant differences were observed between groups I vs II-III regarding survival rates and histological changes to arteries, veins and nerves. Rat body weights showed progressive increases in all groups, and the mortality rate of the present model is 10.4% compared with 30-40% in the previous models. In conclusion, the designed model induces selective changes by radiotherapy in the neurovascular bundle without histological changes affecting the surrounding tissues. This model allows therapeutic experimental studies to be conducted, including the viability of microvascular and microneural sutures post radiotherapy in the cervical neurovascular bundle.

Molecular, Cellular and Functional Effects of Radiation-Induced Brain Injury: A Review

Radiation therapy is the most effective non-surgical treatment of primary brain tumors and metastases. Preclinical studies have provided valuable insights into pathogenesis of radiation-induced injury to the central nervous system. Radiation-induced brain injury can damage neuronal, glial and vascular compartments of the brain and may lead to molecular, cellular and functional changes. Given its central role in memory and adult neurogenesis, the majority of studies have focused on the hippocampus. These findings suggested that hippocampal avoidance in cranial radiotherapy prevents radiation-induced cognitive impairment of patients. However, multiple rodent studies have shown that this problem is more complex. As the radiation-induced cognitive impairment reflects hippocampal and non-hippocampal compartments, it is of critical importance to investigate molecular, cellular and functional modifications in various brain regions as well as their integration at clinically relevant doses and schedules. We here provide a literature overview, including our previously published results, in order to support the translation of preclinical findings to clinical practice, and improve the physical and mental status of patients with brain tumors.

The effect of radiation dose on mouse skeletal muscle remodeling

Background

The purpose of this study was to determine the effect of two clinically relevant radiation doses on the susceptibility of mouse skeletal muscle to remodeling.

Materials and methods.

Alterations in muscle morphology and regulatory signaling were examined in tibialis anterior and gastrocnemius muscles after radiation doses that differed in total biological effective dose (BED). Female C57BL/6 (8-wk) mice were randomly assigned to non-irradiated control, four fractionated doses of 4 Gy (4x4 Gy; BED 37 Gy), or a single 16 Gy dose (16 Gy; BED 100 Gy). Mice were sacrificed 2 weeks after the initial radiation exposure.

Results

The 16 Gy, but not 4x4 Gy, decreased total muscle protein and RNA content. Related to muscle regeneration, both 16 Gy and 4x4 Gy increased the incidence of central nuclei containing myofibers, but only 16 Gy increased the extracellular matrix volume. However, only 4x4 Gy increased muscle 4-hydroxynonenal expression. While both 16 Gy and 4x4 Gy decreased IIB myofiber mean cross-sectional area (CSA), only 16 Gy decreased IIA myofiber CSA. 16 Gy increased the incidence of small diameter IIA and IIB myofibers, while 4x4 Gy only increased the incidence of small diameter IIB myofibers. Both treatments decreased the frequency and CSA of low succinate dehydrogenase activity (SDH) fibers. Only 16 Gy increased the incidence of small diameter myofibers having high SDH activity. Neither treatment altered muscle signaling related to protein turnover or oxidative metabolism.

Conclusions

Collectively, these results demonstrate that radiation dose differentially affects muscle remodeling, and these effects appear to be related to fiber type and oxidative metabolism.

Systemic effects of fractionated, whole-brain irradiation in young adult and aging rats

Cranial irradiation is a critical and effective treatment for primary brain tumors and metastases. Unfortunately, most patients who are treated and survive for more than a few months develop neural and cognitive problems as the result of radiation-induced normal tissue injury. The neurobiological mechanisms underlying these cognitive deficits remain largely unknown and there are no validated treatments to prevent or ameliorate them; thus, there is a significant and continuing need for preclinical studies in animal models. Investigations from several laboratories have demonstrated neurobiological changes after cranial irradiation in rodents. To date, however, experimental studies in animal models have included little assessment of the systemic effects of cranial irradiation, despite evidence from the clinic that cranial irradiation results in changes throughout the body and recognition that systemic responses may influence the development of neural and cognitive deficits. This study evaluated systemic effects of clinically relevant, fractionated whole-brain irradiation in adult rats and demonstrates effects on the growth hormone/insulin-like growth factor-I axis, which may contribute to the development of neural changes. These and other systemic responses are important to consider in ongoing efforts to understand the mechanisms of radiation-induced normal tissue injury.

Effect of emaciation and obesity on small-animal internal radiation dosimetry for positron-emitting radionuclides

PURPOSE

Rats are widely used in biomedical research involving molecular imaging and therefore the radiation dose to animals has become a concern. The weight of laboratory animals might change through emaciation or obesity as a result of their use in various research experiments including those investigating different diet types. In this work, we evaluated the effects of changes in body weight induced by emaciation and obesity on the internal radiation dose from common positron-emitting radionuclides.

METHODS

A systematic literature review was performed to determine normal anatomical parameters for adult rats and evaluate how organs change with variations in total body weight. The ROBY rat anatomical model was then modified to produce a normal adult rat, and mildly, moderately and severely emaciated and obese rats. Monte Carlo simulations were performed using MCNPX to estimate absorbed fractions, specific absorbed fractions (SAFs) and S-values for these models using different positron-emitting radionuclides. The results obtained for the different models were compared to corresponding estimates from the normal rat model.

RESULTS

The SAFs and S-values for most source-target pairs between the various anatomical models were not significantly different, except where the intestine and the total body were considered as source regions. For the intestine, irradiating other organs in the obese model, the SAFs in organs in the anterior region of the splanchnocoele (e.g. kidney, liver and stomach) increased slightly, whereas the SAFs in organs in the posterior region of the splanchnocoele (e.g. bladder and testes) decreased owing to the increase in the distance separating the intestine and posterior abdominal organs because of the rat epididymal fat pad. For the total body, irradiating other organs, the SAFs and S-values were inversely related to body weight.

CONCLUSION

The effect of obesity on internal radiation dose is insignificant in most conditions for common positron-emitting radionuclides. Emaciation increases the cross-absorbed dose to organs from surrounding tissues, which might be a notable issue in laboratory animal internal dosimetry.

Quantitative analysis of myosin heavy chain expression change in laryngeal muscle after irradiation in rats

PURPOSE

Radiotherapy for head and neck cancer does not impair the voice quality as much as laser treatment or surgery, but it can induce muscle wasting and fibrosis and symptoms of dry mouth. We investigated the effect of irradiation on the myosin heavy chain (MyHC) expression in laryngeal muscles.

MATERIALS AND METHODS

Rats were irradiated with one dose of 10, 15, 20, 25, 30, or 35 Gy and other rats were irradiated with 20 Gy. The thyroarytenoid (TA), posterior cricoarytenoid (PCA), and cricothyroid (CT) muscles were subjected to reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Two weeks after irradiation with 10, 15, or 20 Gy, all the MyHC type expressions had decreased in a dose-dependent manner in the TA, PCA, and CT muscles, and especially the expression of MyHC IIa decreased much more than the expressions of the other MyHC isoforms in all muscles. In the 20 Gy-irradiated rats, almost all the MyHC isoform expressions declined over 12 weeks in the TA, PCA, and CT muscles, except for the MyHC I expression in the PCA and CT muscle. The MyHC IIa expression was markedly decreased in all the muscles.

CONCLUSION

The laryngeal muscles responded differently to radiation, but they showed a time-dependent and long-lasting decrease in the expressions of all the MyHC isoforms in the TA, PCA, and CT muscles. In particular, the expression of the MyHC IIa isoform in all the muscles may be more sensitive to irradiation than the expressions of the other MyHC isoforms.

The effects of methylprednisolone and halofuginone on preventing esophageal and hypopharyngeal fibrosis in delivered radiotherapy

In this study, we assessed the effects of halofuginone and methylprednisolone on hypopharyngeal and esophageal stricture that can develop following radiation to the head and neck of rats. Rats were divided into four groups randomly and 18 Gy radiation was given to the head and neck regions of all rats except the control group. Group 1 (Control Group): No radiation or drugs were administered. Group 2 (Radiation Group): only radiation was applied without any drugs. Group 3 (Halofuginone Group): halofuginone 100 microg/kg per day was given intraperitoneally. Group 4 (Methylprednisolone Group): methylprednisolone 1 mg/kg per day was administered intramuscularly. In all groups, 90 days after application of radiation, sections of the proximal esophagus and hypopharynx were examined for fibrosis, fibroblast proliferation, vascularization, epithelial atypia, necrosis, polymorphonuclear leukocytes, mononuclear cells, and stenosis index by light microscope and the hydroxyproline levels were assessed biochemically. Fibrosis, epithelial atypia and hydroxyproline levels were found to be significantly higher in the radiation group compared to the control group (P < 0.05). We did not observe fibrosis in either the halofuginone or the control groups. Fibrosis was also significantly lower in the methylprednisolone group than the radiation group (P < 0.05). The differences of the stenosis index scores between the groups were not statistically significant (P < 0.05). Vascularization was similar in all groups. We think that especially halofuginone is a drug that can be used safely to prevent fibrosis due to radiotherapy, but further studies are needed.

Structural and functional characteristics of irradiation damage to parotid glands in the miniature pig

PURPOSE

To evaluate the effects of a solitary megadose protocol of ionizing radiation (IR) on the structure and function of the miniature pig (minipig) parotid gland.

METHODS AND MATERIALS

Fourteen minipigs were subjected to either 15 or 20 Gy to one parotid gland with a linear accelerator, whereas another four minipigs served as non-IR controls. Salivary flow rates and salivary chemistries were measured pre-IR and 4 and 16 weeks post-IR. A quantitative assessment of gland weight and acinar area and detailed serum chemistry and hematologic analyses were also performed.

RESULTS

Parotid flow rates decreased by approximately 50% either with 20 Gy at 4 weeks, or 15 Gy at 16 weeks post-IR. In the 20 Gy group, salivary flow rates were reduced by approximately 80% at 16 weeks post-IR. A significant decrease in salivary calcium and amylase and an increase of salivary potassium levels were found in both IR groups. There were also transient alterations in serum chemistry and hematology parameters post-IR. Parotid gland weights were significantly decreased (-50%) in the 15 and 20 Gy groups at 4 and 16 weeks post-IR. Additionally, the acinar cell area in glands of both IR groups was significantly reduced from that in control glands at both the 4 and 16 weeks time points.

CONCLUSION

Structural changes in salivary gland parenchyma occurred relatively early after IR, whereas the alterations in salivary output were relatively delayed. Further, reductions in salivary flow were not proportional to acinar cell area loss. Together, these findings suggest that nonparenchymal IR damage likely contributes to IR-induced salivary hypofunction.

Oral sequelae of head and neck radiotherapy

In addition to anti-tumor effects, ionizing radiation causes damage in normal tissues located in the radiation portals. Oral complications of radiotherapy in the head and neck region are the result of the deleterious effects of radiation on, e.g., salivary glands, oral mucosa, bone, dentition, masticatory musculature, and temporomandibular joints. The clinical consequences of radiotherapy include mucositis, hyposalivation, taste loss, osteoradionecrosis, radiation caries, and trismus. Mucositis and taste loss are reversible consequences that usually subside early post-irradiation, while hyposalivation is normally irreversible. Furthermore, the risk of developing radiation caries and osteoradionecrosis is a life-long threat. All these consequences form a heavy burden for the patients and have a tremendous impact on their quality of life during and after radiotherapy. In this review, the radiation-induced changes in healthy oral tissues and the resulting clinical consequences are discussed.