Comparison of the radiosensitivities of neurons and glial cells derived from the same rat brain

Determinants of cerebral radionecrosis in animal models: A systematic review

BACKGROUND

Radionecrosis is a common complication in radiation oncology, while mechanisms and risk factors have yet to be fully explored. We therefore conducted a systematic review to understand the pathogenesis and identify factors that significantly affect the development.

METHODS

We performed a systematic literature search based on the PRISMA guidelines using PubMed, Ovid, and Web of Science databases. The complete search strategy can be found as a preregistered protocol on PROSPERO (CRD42023361662).

RESULTS

We included 83 studies, most involving healthy animals (n = 72, 86.75 %). High doses of hemispherical irradiation of 30 Gy in rats and 50 Gy in mice led repeatedly to radionecrosis among different studies and set-ups. Higher dose and larger irradiated volume were associated with earlier onset. Fractionated schedules showed limited effectiveness in the prevention of radionecrosis. Distinct anatomical brain structures respond to irradiation in various ways. White matter appears to be more vulnerable than gray matter. Younger age, more evolved animal species, and genetic background were also significant factors, whereas sex was irrelevant. Only 13.25 % of the studies were performed on primary brain tumor bearing animals, no studies on brain metastases are currently available.

CONCLUSION

This systematic review identified various factors that significantly affect the induction of radionecrosis. The current state of research neglects the utilization of animal models of brain tumors, even though patients with brain malignancies constitute the largest group receiving brain irradiation. This latter aspect should be primarily addressed when developing an experimental radionecrosis model for translational implementation.

Radiation necrosis after radiation therapy treatment of brain metastases: A computational approach

Metastasis is the process through which cancer cells break away from a primary tumor, travel through the blood or lymph system, and form new tumors in distant tissues. One of the preferred sites for metastatic dissemination is the brain, affecting more than 20% of all cancer patients. This figure is increasing steadily due to improvements in treatments of primary tumors. Stereotactic radiosurgery (SRS) is one of the main treatment options for patients with a small or moderate number of brain metastases (BMs). A frequent adverse event of SRS is radiation necrosis (RN), an inflammatory condition caused by late normal tissue cell death. A major diagnostic problem is that RNs are difficult to distinguish from BM recurrences, due to their similarities on standard magnetic resonance images (MRIs). However, this distinction is key to choosing the best therapeutic approach since RNs resolve often without further interventions, while relapsing BMs may require open brain surgery. Recent research has shown that RNs have a faster growth dynamics than recurrent BMs, providing a way to differentiate the two entities, but no mechanistic explanation has been provided for those observations. In this study, computational frameworks were developed based on mathematical models of increasing complexity, providing mechanistic explanations for the differential growth dynamics of BMs relapse versus RN events and explaining the observed clinical phenomenology. Simulated tumor relapses were found to have growth exponents substantially smaller than the group in which there was inflammation due to damage induced by SRS to normal brain tissue adjacent to the BMs, thus leading to RN. ROC curves with the synthetic data had an optimal threshold that maximized the sensitivity and specificity values for a growth exponent β* = 1.05, very close to that observed in patient datasets.

Pentoxifylline and Vitamin E Can Restrict Radiation Necrosis via Vascular Pathways, Experimental Study in an Animal Model

OBJECTIVE

Radiation necrosis (RN) is a long-term side effect of Gamma Knife stereotactic radiosurgery that may require surgical intervention. Pentoxifylline and vitamin E have previously been shown to be effective in the treatment of RN in the published literature, but there are no data on the prophylactic use of these molecules or, more importantly, whether prophylaxis is required.

METHODS

The iatrogenic RN model included 50 Sprague-Dawley rats of both sexes. There were 7 treatment subgroups established. Gamma-Plan 8.32 was used to plan after magnetic resonance scans were performed in a specially designed frame. The injection doses used in the treatment groups were vitamin E (30 mg/kg/day in a single dose) and pentoxifylline (50 mg/kg/day in 2 doses). Control magnetic resonance scans were performed at the end of a 16-week treatment, and the subjects were decapitated for pathological evaluations.

RESULTS

The intensity of hypoxia - inducible factor 1α immunoreactivity is statistically significantly lower in the therapeutic vitamin E, prophylactic pentoxifylline and vitamin E, and therapeutic pentoxifylline and vitamin E groups than in the other groups. Similarly, the intensity of vascular endothelial growth factor immunoreactivity was reduced in the therapeutic vitamin E and prophylactic pentoxifylline and vitamin E treatment modality groups. When compared with other groups, the therapeutic pentoxifylline group had significantly fewer vascular endothelial growth factor-immunoreactive cells in the perinecrotic area, with an accompanying decreased contrast enhancement pattern.

CONCLUSIONS

Both vitamin E and pentoxifylline are effective for the treatment and/or restriction of RN, either alone or in combination. The use of these molecules as a preventive measure did not outperform the therapeutic treatment.

Radiosurgery for Brain Metastases: Challenges in Imaging Interpretation after Treatment

Stereotactic radiosurgery (SRS) has transformed the management of brain metastases by achieving local tumor control, reducing toxicity, and minimizing the need for whole-brain radiation therapy (WBRT). This review specifically investigates radiation-induced changes in patients treated for metastasis, highlighting the crucial role of magnetic resonance imaging (MRI) in the evaluation of treatment response, both at very early and late stages. The primary objective of the review is to evaluate the most effective imaging techniques for assessing radiation-induced changes and distinguishing them from tumor growth. The limitations of conventional imaging methods, which rely on size measurements, dimensional criteria, and contrast enhancement patterns, are critically evaluated. In addition, it has been investigated the potential of advanced imaging modalities to offer a more precise and comprehensive evaluation of treatment response. Finally, an overview of the relevant literature concerning the interpretation of brain changes in patients undergoing immunotherapies is provided.

Does protracted radon exposure play a role in the development of dementia?

Radon is a ubiquitous radioactive gas that decays into a series of solid radioactive decay products. Radon, and its decay products, enter the human body primarily through inhalation and can be delivered to various tissues including the brain through systemic circulation. It can also reach the brain by neuronal pathways via the olfactory system. While ionizing radiation has been suggested as a risk factor of dementia for decades, studies exploring the possible role of radon exposure in the development of Alzheimer's Diseases (AD) and other dementias are sparse. We systematically reviewed the literature and found several lines of evidence suggesting that radon decay products (RDPs) disproportionally deposit in the brain of AD patients with selective accumulation within the protein fractions. Ecologic study findings also indicate a significant positive correlation between geographic-level radon distribution and AD mortality in the US. Additionally, pathologic studies of radon shed light on the potential pathways of radon decay product induced proinflammation and oxidative stress that may result in the development of dementia. In summary, there are plausible underlying biological mechanisms linking radon exposure to the risk of dementia. Since randomized clinical trials on radon exposure are not feasible, well-designed individual-level epidemiologic studies are urgently needed to elucidate the possible association between radon (i.e., RDPs) exposure and the onset of dementia.

Treatment of Radiation-Induced Brain Necrosis

Radiation-induced brain necrosis (RBN) is a serious complication of intracranial as well as skull base tumors after radiotherapy. In the past, due to the lack of effective treatment, radiation brain necrosis was considered to be progressive and irreversible. With better understanding in histopathology and neuroimaging, the occurrence and development of RBN have been gradually clarified, and new treatment methods are constantly emerging. In recent years, some scholars have tried to treat RBN with bevacizumab, nerve growth factor, and gangliosides and have achieved similar results. Some cases of brain necrosis can be repairable and reversible. We aimed to summarize the incidence, pathogenesis, and treatment of RBN.

Risk of radiation necrosis after stereotactic radiosurgery for melanoma brain metastasis by anatomical location

PURPOSE

In this retrospective study, we have explored the anatomical factors that lead to the development of radiation necrosis (RN) in the setting of stereotactic radiosurgery (SRS) for melanoma brain metastases (MBM).

METHODS

Between 2014 and 2018, 137 patients underwent SRS for 311 MBM. Lesions were assessed according to anatomical zones: zone 1-peripheral grey-white matter junction and cortical mantle, zone 2-deep white matter, including tumours located at base of sulci, zone 3-tumours adjacent to ependymal lining or in deep locations such as brainstem, basal ganglia and thalamus. Other anatomical factors including lobes, medial-peripheral, supra or infratentorial locations were also recorded.

RESULTS

In all, 12.4% (n = 17) of patients and 6.1% (n = 20) of lesions developed RN, actuarial incidence of RN at 12 and 24 months was 10% and 14.2% respectively. Zone 2 lesions recorded the highest rate of development of RN (n = 7/19; 36%), zone 3 (N = 4/24; 16%) and zone 1 (n = 9/268; 3%). Five of 17 patients developed symptomatic RN and 7/17 patients underwent surgery for RN.

CONCLUSION

This study raises awareness of the increased likelihood of deep lesions particularly in white matter structures to develop RN after SRS. Further studies including larger cohorts would be useful in identifying statistical differences in the rate of development of RN in different anatomical zones.

Stem-Cell Therapy as a Potential Strategy for Radiation-Induced Brain Injury

Radiation therapy is a standard and effective non-surgical treatment for primary brain tumors and metastases. However, this strategy inevitably results in damage of normal brain tissue, causing severe complications, especially the late-delayed cognitive impairment. Due to the multifactorial and complex pathological effects of radiation, there is a lack of effective preventative and restorative treatments for the irradiated brain. Stem-cell therapy has held considerable promise for decades in the treatment of central nervous system (CNS) disorders because of its unique capacity for tissue repair and functional integrity. Currently, there is growing interest in using stem cells as a novel option to attenuate the adverse effects of irradiation. In the present review, we discuss recent studies evaluating stem-cell therapies for the irradiated brain and their therapeutic effects on ameliorating radiation-related brain injury as well as their potential challenges in clinical applications. We discuss these works in context of the pathogenesis of radiation-induced injury to CNS tissue in an attempt to elucidate the potential mechanisms of engrafted stem cells to reverse radiation-induced degenerative processes.

Hibernation as a Tool for Radiation Protection in Space Exploration

With new and advanced technology, human exploration has reached outside of the Earth's boundaries. There are plans for reaching Mars and the satellites of Jupiter and Saturn, and even to build a permanent base on the Moon. However, human beings have evolved on Earth with levels of gravity and radiation that are very different from those that we have to face in space. These issues seem to pose a significant limitation on exploration. Although there are plausible solutions for problems related to the lack of gravity, it is still unclear how to address the radiation problem. Several solutions have been proposed, such as passive or active shielding or the use of specific drugs that could reduce the effects of radiation. Recently, a method that reproduces a mechanism similar to hibernation or torpor, known as synthetic torpor, has started to become possible. Several studies show that hibernators are resistant to acute high-dose-rate radiation exposure. However, the underlying mechanism of how this occurs remains unclear, and further investigation is needed. Whether synthetic hibernation will also protect from the deleterious effects of chronic low-dose-rate radiation exposure is currently unknown. Hibernators can modulate their neuronal firing, adjust their cardiovascular function, regulate their body temperature, preserve their muscles during prolonged inactivity, regulate their immune system, and most importantly, increase their radioresistance during the inactive period. According to recent studies, synthetic hibernation, just like natural hibernation, could mitigate radiation-induced toxicity. In this review, we see what artificial hibernation is and how it could help the next generation of astronauts in future interplanetary missions.

Pathological changes in the central nervous system following exposure to ionizing radiation

Experimental studies in animals provide relevant knowledge about pathogenesis of radiation-induced injury to the central nervous system. Radiation-induced injury can alter neuronal, glial cell population, brain vasculature and may lead to molecular, cellular and functional consequences. Regarding to its fundamental role in the formation of new memories, spatial navigation and adult neurogenesis, the majority of studies have focused on the hippocampus. Most recent findings in cranial radiotherapy revealed that hippocampal avoidance prevents radiation-induced cognitive impairment of patients with brain primary tumors and metastases. However, numerous preclinical studies have shown that this problem is more complex. Regarding the fact, that the radiation-induced cognitive impairment reflects hippocampal and non-hippocampal compartments, it is highly important to investigate molecular, cellular and functional changes in different brain regions and their integration at clinically relevant doses and schedules. Here, we provide a literature review in order support the translation of preclinical findings to clinical practice and improve the physical and mental status of patients with brain tumors.

Cerebral Radiation Necrosis: Incidence, Pathogenesis, Diagnostic Challenges, and Future Opportunities

PURPOSE OF REVIEW

Cerebral radiation necrosis (CRN) is a major dose-limiting adverse event of radiotherapy. The incidence rate of RN varies with the radiotherapy modality, total dose, dose fractionation, and the nature of the lesion being targeted. In addition to these known and controllable features, there is a stochastic component to the occurrence of CRN-the genetic profile of the host or the lesion and their role in the development of CRN.

RECENT FINDINGS

Recent studies provide some insight into the genetic mechanisms underlying radiation-induced brain injury. In addition to these incompletely understood host factors, the diagnostic criteria for CRN using structural and functional imaging are also not clear, though multiple structural and functional imaging modalities exist, a combination of which may prove to be the ideal diagnostic imaging approach. As the utilization of novel molecular therapies and immunotherapy increases, the incidence of CNR is expected to increase and its diagnosis will become more challenging. Tissue biopsies can be insensitive and suffer from sampling biases and procedural risks. Liquid biopsies represent a promising, accurate, and non-invasive diagnostic strategy, though this modality is currently in its infancy. A better understanding of the pathogenesis of CRN will expand and optimize the diagnosis and management of CRN by better utilizing existing treatment options including bevacizumab, pentoxifylline, hyperbaric oxygen therapy, and laser interstitial thermal therapy.

Glial U87 cells protect neuronal SH-SY5Y cells from indirect effect of radiation by reducing oxidative stress and apoptosis

Recent studies have demonstrated the role of indirect effect of radiation in neurodegeneration. However, the role of glial cells in neuroprotection against indirect effect of radiation is still not clear, although they are known to protect neurons under stress conditions in central nervous system. Our study showed that indirect effect of radiation increased the oxidative stress that further enhances the expression of key apoptotic proteins and leads to neuronal cell death. We also investigated the indirect effect of radiation on neuronal cells in the presence of glial cells in a transwell co-culture system, while our analysis was focused on neuronal cells. Irradiated cell-conditioned medium (ICCM) was used as source of indirect radiation and neuroprotective effect was analyzed by various endpoints. It was observed that ICCM-induced reactive oxidative species level was significantly reduced in SH-SY5Y cells co-cultured with glial U87 cells, which might help to maintain the integrity of mitochondrial membrane potential. Increased levels of antioxidant enzyme superoxide dismutase and antioxidant glutathione were observed in SH-SY5Y cells co-cultured with glial U87 cells. Moreover, it was also observed that co-culture with glial cells inhibits the expression of ICCM-induced apoptotic proteins, i.e. Bax, cytochrome c, and caspase-3 in SH-SY5Y cells. Hence, it can be speculated that in co-culture system glial cells may protect the neuronal SH-SY5Y cells by reducing the ICCM-induced oxidative stress and apoptotic death.