Intestinal epithelial cell dysfunction is mediated by an endothelial-specific radiation-induced bystander effect

Single-cell and bulk transcriptional profiling of mouse ovaries reveals novel genes and pathways associated with DNA damage response in oocytes

Immature oocytes enclosed in primordial follicles stored in female ovaries are under constant threat of DNA damage induced by endogenous and exogenous factors. Checkpoint kinase 2 (CHEK2) is a key mediator of the DNA damage response in all cells. Genetic studies have shown that CHEK2 and its downstream targets, p53 and TAp63, regulate primordial follicle elimination in response to DNA damage, however the mechanism leading to their demise is still poorly characterized. Single-cell and bulk RNA sequencing were used to determine the DNA damage response in wildtype and Chek2-deficient ovaries. A low but oocyte-lethal dose of ionizing radiation induces a DNA damage response in ovarian cells that is solely dependent on CHEK2. DNA damage activates multiple ovarian response pathways related to apoptosis, p53, interferon signaling, inflammation, cell adhesion, and intercellular communication. These pathways are differentially employed by different ovarian cell types, with oocytes disproportionately affected by radiation. Novel genes and pathways are induced by radiation specifically in oocytes, shedding light on their sensitivity to DNA damage, and implicating a coordinated response between oocytes and pre-granulosa cells within the follicle. These findings provide a foundation for future studies on the specific mechanisms regulating oocyte survival in the context of aging, as well as therapeutic and environmental genotoxic exposures.

Radiobiological Studies of Microvascular Damage through In Vitro Models: A Methodological Perspective

Ionizing radiation (IR) is used in radiotherapy as a treatment to destroy cancer. Such treatment also affects other tissues, resulting in the so-called normal tissue complications. Endothelial cells (ECs) composing the microvasculature have essential roles in the microenvironment's homeostasis (ME). Thus, detrimental effects induced by irradiation on ECs can influence both the tumor and healthy tissue. In-vitro models can be advantageous to study these phenomena. In this systematic review, we analyzed in-vitro models of ECs subjected to IR. We highlighted the critical issues involved in the production, irradiation, and analysis of such radiobiological in-vitro models to study microvascular endothelial cells damage. For each step, we analyzed common methodologies and critical points required to obtain a reliable model. We identified the generation of a 3D environment for model production and the inclusion of heterogeneous cell populations for a reliable ME recapitulation. Additionally, we highlighted how essential information on the irradiation scheme, crucial to correlate better observed in vitro effects to the clinical scenario, are often neglected in the analyzed studies, limiting the translation of achieved results.

Atorvastatin Inhibits Endothelial PAI-1-Mediated Monocyte Migration and Alleviates Radiation-Induced Enteropathy

Intestinal injury is observed in cancer patients after radiotherapy and in individuals exposed to radiation after a nuclear accident. Radiation disrupts normal vascular homeostasis in the gastrointestinal system by inducing endothelial damage and senescence. Despite advances in medical technology, the toxicity of radiation to healthy tissue remains an issue. To address this issue, we investigated the effect of atorvastatin, a commonly prescribed hydroxy-3-methylglutaryl-coenzyme A reductase inhibitor of cholesterol synthesis, on radiation-induced enteropathy and inflammatory responses. We selected atorvastatin based on its pleiotropic anti-fibrotic and anti-inflammatory effects. We found that atorvastatin mitigated radiation-induced endothelial damage by regulating plasminogen activator inhibitor-1 (PAI-1) using human umbilical vein endothelial cells (HUVECs) and mouse model. PAI-1 secreted by HUVECs contributed to endothelial dysfunction and trans-endothelial monocyte migration after radiation exposure. We observed that PAI-1 production and secretion was inhibited by atorvastatin in irradiated HUVECs and radiation-induced enteropathy mouse model. More specifically, atorvastatin inhibited PAI-1 production following radiation through the JNK/c-Jun signaling pathway. Together, our findings suggest that atorvastatin alleviates radiation-induced enteropathy and supports the investigation of atorvastatin as a radio-mitigator in patients receiving radiotherapy.

The role of connexin proteins and their channels in radiation-induced atherosclerosis

Radiotherapy is an effective treatment for breast cancer and other thoracic tumors. However, while high-energy radiotherapy treatment successfully kills cancer cells, radiation exposure of the heart and large arteries cannot always be avoided, resulting in secondary cardiovascular disease in cancer survivors. Radiation-induced changes in the cardiac vasculature may thereby lead to coronary artery atherosclerosis, which is a major cardiovascular complication nowadays in thoracic radiotherapy-treated patients. The underlying biological and molecular mechanisms of radiation-induced atherosclerosis are complex and still not fully understood, resulting in potentially improper radiation protection. Ionizing radiation (IR) exposure may damage the vascular endothelium by inducing DNA damage, oxidative stress, premature cellular senescence, cell death and inflammation, which act to promote the atherosclerotic process. Intercellular communication mediated by connexin (Cx)-based gap junctions and hemichannels may modulate IR-induced responses and thereby the atherosclerotic process. However, the role of endothelial Cxs and their channels in atherosclerotic development after IR exposure is still poorly defined. A better understanding of the underlying biological pathways involved in secondary cardiovascular toxicity after radiotherapy would facilitate the development of effective strategies that prevent or mitigate these adverse effects. Here, we review the possible roles of intercellular Cx driven signaling and communication in radiation-induced atherosclerosis.

Citrulline, A Potential Biomarker of Radiation-Induced Small Intestine Damage

Radiation damage assessment of the small intestine is important in nuclear accidents or routine radiotherapy of abdominal tumors. This article reviews the clinical symptoms and molecular mechanisms of radiation-induced small intestinal damage and summarizes recent research on biomarkers of such damage. Citrulline is the most promising biomarker for the evaluation of radiation-induced small intestinal damage caused by radiotherapy and nuclear accidents. This article also summarizes the factors influencing plasma citrulline measurement investigated in the latest research, as well as new findings on the concentration of citrulline in saliva and urine after different types of radiation.

Secretion of Acid Sphingomyelinase and Ceramide by Endothelial Cells Contributes to Radiation-Induced Intestinal Toxicity

Ceramide-induced endothelial cell apoptosis boosts intestinal stem cell radiosensitivity. However, the molecular connection between these two cellular compartments has not been clearly elucidated. Here we report that ceramide and its related enzyme acid sphingomyelinase (ASM) are secreted by irradiated endothelial cells and act as bystander factors to enhance the radiotoxicity of intestinal epithelium. Ceramide and the two isoforms of ASM were acutely secreted in the blood serum of wild-type mice after 15 Gy radiation dose, inducing a gastrointestinal syndrome. Interestingly, serum ceramide was not enhanced in irradiated ASMKO mice, which are unable to develop intestinal failure injury. Because ASM/ceramide were secreted by primary endothelial cells, their contribution was studied in intestinal epithelium dysfunction using coculture of primary endothelial cells and intestinal T84 cells. Adding exogenous ASM or ceramide enhanced epithelial cell growth arrest and death. Conversely, blocking their secretion by endothelial cells using genetic, pharmacologic, or immunologic approaches abolished intestinal T84 cell radiosensitivity. Use of enteroid models revealed ASM and ceramide-mediated deleterious mode-of-action: when ceramide reduced the number of intestinal crypt-forming enteroids without affecting their structure, ASM induced a significant decrease of enteroid growth without affecting their number. Identification of specific and different roles for ceramide and ASM secreted by irradiated endothelial cells opens new perspectives in the understanding of intestinal epithelial dysfunction after radiation and defines a new class of potential therapeutic radiomitigators. SIGNIFICANCE: This study identifies secreted ASM and ceramide as paracrine factors enhancing intestinal epithelial dysfunction, revealing a previously unknown class of mediators of radiosensitivity.

Radiation-Induced Bystander Effect is Mediated by Mitochondrial DNA in Exosome-Like Vesicles

Exosome-like vesicles (ELV) are involved in mediating radiation-induced bystander effect (RIBE). Here, we used ELV from control cell conditioned medium (CCCM) and from 4 Gy of X-ray irradiated cell conditioned medium (ICCM), which has been used to culture normal human fibroblast cells to examine the possibility of ELV mediating RIBE signals. We investigated whether ELV from 4 Gy irradiated mouse serum mediate RIBE signals. Induction of DNA damage was observed in cells that were treated with ICCM ELV and ELV from 4 Gy irradiated mouse serum. In addition, we treated CCCM ELV and ICCM ELV with RNases, DNases, and proteinases to determine which component of ELV is responsible for RIBE. Induction of DNA damage by ICCM ELV was not observed after treatment with DNases. After treatment, DNA damages were not induced in CCCM ELV or ICCM ELV from mitochondria depleted (ρ0) normal human fibroblast cells. Further, we found significant increase in mitochondrial DNA (mtDNA) in ICCM ELV and ELV from 4 Gy irradiated mouse serum. ELV carrying amplified mtDNA (ND1, ND5) induced DNA damage in treated cells. These data suggest that the secretion of mtDNA through exosomes is involved in mediating RIBE signals.

Radiation-induced bystander effect in large Japanese field mouse (Apodemus speciosus) embryonic cells

Although evidence suggests that ionizing radiation can induce the bystander effect (radiation-induced bystander effect: RIBE) in cultured cells or mouse models, it is unclear whether the effect occurs in cells of wild animals. We investigated medium-mediated bystander micronucleus (MN) formation and DNA damage in un-irradiated cells from a large Japanese field mouse (Apodemus speciosus). We isolated four clones of A. speciosus embryonic fibroblasts (A603-1, A603-2, A603-3, and A603-4) derived from the same mother, and examined their radiation sensitivity using the colony-forming assay. A603-3 and A603-4 were similar, and A603-1 and A603-2 were highly sensitive compared with A603-3 and A603-4. We examined RIBE in the four clones in autologous medium from cell cultures exposed to 2 Gy X-ray radiation (irradiated cell conditioned medium: ICCM). We only observed increased MN prevalence and induction of DNA damage foci in A603-1 and A603-3 cells after ICCM transfer. The ICCM of A603-3 (RIBE-induced) was able to induce MN in A603-4 (not RIBE-induced). To assess the possible contribution of reactive oxygen species (ROS) or nitric oxide (NO) in medium-mediated RIBE, dimethyl sulfoxide (DMSO; a ROS scavenger) or 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO; an NO scavenger) were added to the medium. A suppressive effect was observed after adding DMSO, but there was no effect after treatment with c-PTIO. These results suggest that an enhanced radiosensitivity may not be directly related to the induction of medium-mediated RIBE. Moreover, ROS are involved in the transduction of the RIBE signal in A. speciosus cells, but NO is not. In conclusion, our results suggest that RIBE may be conserved in wild animals. The results contribute to better knowledge of radiation effects on wild, non-human species.

Late-onset cystic brain necrosis after radiotherapy for nasopharyngeal carcinoma

Background

Cystic brain radionecrosis (CBRN) is a late-onset devastating complication after radiotherapy for head and neck neoplasms, especially for nasopharyngeal carcinoma (NPC). To our knowledge, it has scarcely been reported.

Methods

We retrospectively reviewed all available medical records of NPC patients with CBRN who were treated with surgical intervention.

Results

Sixteen patients were identified in this study and the mean latency of CBRN was 9.2 ± 0.9 years. The total irradiation dose of the nasopharynx ranged from 60 to 78 Gy. Cyst-like lesions were observed and there were slightly enhancements on the cyst wall in five patients on patients' brain MRI. All the included patients underwent surgical resection of the cystic necrotic lesion thought temporal approach. Specimens from surgery revealed reactive gliosis and immunopositive cytokines including TNF-α, IL-6 and HIF-2α. Only one patient experienced recurrence and received reoperation after surgery. All the other patients made a good recovery and no operation-related mortality was observed.

Conclusions

CBRN is a delayed but irreversible neurological sequel in irradiated NPC patients. Post-radiotherapy follow-up is quite necessary for those with high risk of CBRN. Proper treatment is needed for early CBRN patients to suppress inflammation in the brain. Timely neurosurgery may benefit patients with late-stage CBRN by alleviating increased intracranial pressure and inflammatory responses.

Fractionated abdominal irradiation induces intestinal microvascular changes in an in vivo model of radiotherapy-induced gut toxicity

PURPOSE

Radiotherapy-induced gut toxicity (RIGT) is associated with diarrhoea, pain and rectal bleeding and can occur as an acute or chronic toxicity. The microvasculature has been shown to be altered in the development of RIGT; however, the features are not yet characterized. We hypothesized that apoptosis of microvascular cells would occur early in the gastrointestinal tract following fractionated irradiation, followed by late microvascular changes, including sclerosis and telangiectasis.

METHODS

Female Dark Agouti rats were treated with a 6-week fractionated radiation schedule of 3 × 2.5 Gy doses per week localized to the abdomen. At 3, 6 and 15 weeks, the intestines were assessed for markers of acute and chronic injury including morphological changes, collagen deposition, apoptosis and proliferation.

RESULTS

Apoptosis of microvascular cells significantly increased at 6 and 15 weeks in the jejunum (p = 0.0026 and p = 0.0062, respectively) and at 6 and 15 weeks in the colon (p < 0.0001 and p = 0.0005, respectively) in rats receiving fractionated radiation to the abdomen. Histopathological changes of the colon microvasculature were also seen from week 3, including thickening of the lamina propria and dilated, thickened, telangiectatic vessels.

CONCLUSIONS

Findings of this study provide evidence of regional and timing-specific changes in the intestinal microvasculature in response to fractionated radiotherapy which may play a role in development of both acute and chronic RIGT.

Computer aided prognosis for cell death categorization and prediction in vivo using quantitative ultrasound and machine learning techniques

PURPOSE

At present, a one-size-fits-all approach is typically used for cancer therapy in patients. This is mainly because there is no current imaging-based clinical standard for the early assessment and monitoring of cancer treatment response. Here, the authors have developed, for the first time, a complete computer-aided-prognosis (CAP) system based on multiparametric quantitative ultrasound (QUS) spectroscopy methods in association with texture descriptors and advanced machine learning techniques. This system was used to noninvasively categorize and predict cell death levels in fibrosarcoma mouse tumors treated using ultrasound-stimulated microbubbles as novel endothelial-cell radiosensitizers.

METHODS

Sarcoma xenograft tumor-bearing mice were treated using ultrasound-stimulated microbubbles, alone or in combination with x-ray radiation therapy, as a new antivascular treatment. Therapy effects were assessed at 2-3, 24, and 72 h after treatment using a high-frequency ultrasound. Two-dimensional spectral parametric maps were generated using the power spectra of the raw radiofrequency echo signal. Subsequently, the distances between "pretreatment" and "post-treatment" scans were computed as an indication of treatment efficacy, using a kernel-based metric on textural features extracted from 2D parametric maps. A supervised learning paradigm was used to either categorize cell death levels as low, medium, or high using a classifier, or to "continuously" predict the levels of cell death using a regressor.

RESULTS

The developed CAP system performed at a high level for the classification of cell death levels. The area under curve of the receiver operating characteristic was 0.87 for the classification of cell death levels to both low/medium and medium/high levels. Moreover, the prediction of cell death levels using the proposed CAP system achieved a good correlation (r = 0.68,  p < 0.001) with histological cell death levels as the ground truth. A statistical test of significance between individual treatment groups with the corresponding control group demonstrated that the predicted levels indicated the same significant changes in cell death as those indicated by the ground-truth levels.

CONCLUSIONS

The technology developed in this study addresses a gap in the current standard of care by introducing a quality control step that generates potentially actionable metrics needed to enhance treatment decision-making. The study establishes a noninvasive framework for quantifying levels of cancer treatment response developed preclinically in tumors using QUS imaging in conjunction with machine learning techniques. The framework can potentially facilitate the detection of refractory responses in patients to a certain cancer treatment early on in the course of therapy to enable switching to more efficacious treatments.

Nuclear Countermeasure Activity of TP508 Linked to Restoration of Endothelial Function and Acceleration of DNA Repair

There is increasing evidence that radiation-induced damage to endothelial cells and loss of endothelial function may contribute to both acute radiation syndromes and long-term effects of whole-body nuclear irradiation. Therefore, several drugs are being developed to mitigate the effects of nuclear radiation, most of these drugs will target and protect or regenerate leukocytes and platelets. Our laboratory has demonstrated that TP508, a 23-amino acid thrombin peptide, activates endothelial cells and stem cells to revascularize and regenerate tissues. We now show that TP508 can mitigate radiation-induced damage to endothelial cells in vitro and in vivo. Our in vitro results demonstrate that human endothelial cells irradiation attenuates nitric oxide (NO) signaling, disrupts tube formation and induces DNA double-strand breaks (DSB). TP508 treatment reverses radiation effects on NO signaling, restores tube formation and accelerates the repair of radiation-induced DSB. The radiation-mitigating effects of TP508 on endothelial cells were also seen in CD-1 mice where systemic injection of TP508 stimulated endothelial cell sprouting from aortic explants after 8 Gy irradiation. Systemic doses of TP508 that mitigated radiation-induced endothelial cell damage, also significantly increased survival of CD-1 mice when injected 24 h after 8.5 Gy exposure. These data suggest that increased survival observed with TP508 treatment may be due to its effects on vascular and microvascular endothelial cells. Our study supports the usage of a regenerative drug such as TP508 to activate endothelial cells as a countermeasure for mitigating the effects of nuclear radiation.

The role of oxidative DNA damage in radiation induced bystander effect

Ionizing radiation (IR) has been described as a double-edged sword, since it is used for diagnostic and therapeutic medical applications, and at the same time it is a well known human mutagen and carcinogen, causing wide-ranging chromosomal aberrations. It is nowadays accepted that the detrimental effects of IR are not restricted only in the irradiated cells, but also to non-irradiated bystander or even distant cells manifesting various biological effects. This review presents the role of oxidative stress in the induction of bystander effects referring to the types of the implicated oxidative DNA lesions, the contributing intercellular and intracellular stress mediators, the way they are transmitted from irradiated to bystander cells and finally, the complex role of the bystander effect in the therapeutic efficacy of radiation treatment of cancer.

Radiation-Induced Bystander Response: Mechanism and Clinical Implications

Significance: Absorption of energy from ionizing radiation (IR) to the genetic material in the cell gives rise to damage to DNA in a dose-dependent manner. There are two types of DNA damage; by a high dose (causing acute or deterministic effects) and by a low dose (related to chronic or stochastic effects), both of which induce different health effects. Among radiation effects, acute cutaneous radiation syndrome results from cell killing as a consequence of high-dose exposure. Recent advances: Recent advances in radiation biology and oncology have demonstrated that bystander effects, which are emerged in cells that have never been exposed, but neighboring irradiated cells, are also involved in radiation effects. Bystander effects are now recognized as an indispensable component of tissue response related to deleterious effects of IR. Critical issues: Evidence has indicated that nonapoptotic premature senescence is commonly observed in various tissues and organs. Senesced cells were found to secrete various proteins, including cytokines, chemokines, and growth factors, most of which are equivalent to those identified as bystander factors. Secreted factors could trigger cell proliferation, angiogenesis, cell migration, inflammatory response, etc., which provide a tissue microenvironment assisting tissue repair and remodeling. Future directions: Understandings of the mechanisms and physiological relevance of radiation-induced bystander effects are quite essential for the beneficial control of wound healing and care. Further studies should extend our knowledge of the mechanisms of bystander effects and mode of cell death in response to IR.

Non-targeted radiation effects in vivo: a critical glance of the future in radiobiology

Radiation-induced bystander effects (RIBE), demonstrate the induction of biological non-targeted effects in cells which have not directly hit by radiation or by free radicals produced by ionization events. Although RIBE have been demonstrated using a variety of biological endpoints the mechanism(s) of this phenomenon still remain unclear. The controversial results of the in vitro RIBE and the evidence of non-targeted effects in various in vivo systems are discussed. The experimental evidence on RIBE, indicate that a more analytical and mechanistic in depth approach is needed to secure an answer to one of the most intriguing questions in radiobiology.

Alpha particle-induced bystander effect is mediated by ROS via a p53-dependent SCO2 pathway in hepatoma cells

PURPOSE

The radiation-induced bystander effect (RIBE) has important implications for the efficiency of radiotherapy but the underlying role of cellular metabolism is widely unknown. The roles of synthesis of cytochrome c oxidase 2 (SCO2), a key effector for respiratory chain, and related signaling factors in α-particle-induced bystander damage were currently investigated in a liver cell co-culture system.

MATERIALS AND METHODS

Human hepatoma cells of HepG2 with wild-type p53 (wtp53) and Hep3B (p53 null) were irradiated with 0.4 Gy of α-particles and co-cultured with non-irradiated normal liver cells HL-7702 for 6 h, then the incidence of micronucleus (MN) in the bystander HL-7702 cells was analyzed. The expressions of total P53, phospho-P53 (p-P53), SCO2, and reactive oxygen species (ROS) in the irradiated hepatoma cells were detected. In some experiments, the hepatoma cells were respectively treated with p53 siRNA, SCO2 siRNA, or dimethyl sulfoxide (DMSO) before irradiation.

RESULTS

Bystander damage in HL-7702 cells was induced by α-irradiated HepG2 cells but not by α-irradiated Hep3B cells, and this bystander effect was diminished when the irradiated HepG2 cells were pretreated with p53 siRNA, SCO2 siRNA, or DMSO. Meanwhile, the expressions of p-P53 protein and SCO2 mRNA, the activity of SCO2 protein, and intracellular ROS were all increased in the irradiated HepG2 cells but not Hep3B cells and these expressions were eliminated by p53 siRNA treatment. Moreover, the radiation-enhanced expressions of SCO2 and ROS were inhibited by SCO2 siRNA.

CONCLUSION

α-particle-induced bystander effect was regulated by p53 and its downstream SCO2 in the irradiated hepatoma cells, and ROS generation could be an early event for triggering this bystander response.

Enhanced and aberrant T cell trafficking following total body irradiation: a gateway to graft-versus-host disease?

Pre-transplant conditioning regimens play a major role in triggering graft-versus-host disease (GVHD). This study investigated the effect of irradiation on donor T cell trafficking to lymphoid and non-lymphoid tissues by comparing the migration of carboxy-fluorescein diacetate succinimidyl ester-labelled, naïve donor T lymphocytes in vivo in irradiated and non-irradiated syngeneic mice recipients. Recruitment of adoptively transferred naïve T cells to secondary lymphoid organs was increased in irradiated mice and naïve T cells also aberrantly localized to non-lymphoid tissues. Irradiation also induced aberrant effector memory T cell migration into lymph nodes and their localization to homing-privileged non-lymphoid sites, such as the gut. The presence of a minor histocompatibility mismatch further enhanced the aberrant accumulation of T cells in both lymphoid and non-lymphoid tissue, whilst their migratory pattern was not modified as compared to fully matched irradiated recipients. These effects correlated with decreased permeability of, and the secretion of chemotactic factors by the endothelium. Our findings are consistent with the possibility that excessive, dysregulated extravasation of T cells induced by irradiation promotes the development of GVHD.

Anti-Gb3 monoclonal antibody inhibits angiogenesis and tumor development

Inhibiting the growth of tumor vasculature represents one of the relevant strategies against tumor progression. Between all the different pro-angiogenic molecular targets, plasma membrane glycosphingolipids have been under-investigated. In this present study, we explore the anti-angiogenic therapeutic advantage of a tumor immunotherapy targeting the globotriaosylceramide Gb3. In this purpose, a monoclonal antibody against Gb3, named 3E2 was developed and characterized. We first demonstrate that Gb3 is over-expressed in proliferative endothelial cells relative to quiescent cells. Then, we demonstrate that 3E2 inhibits endothelial cell proliferation in vitro by slowing endothelial cell proliferation and by increasing mitosis duration. Antibody 3E2 is further effective in inhibiting ex vivo angiogenesis in aorta ring assays. Moreover, 3E2 treatment inhibits NXS2 neuroblastoma development and liver metastases spreading in A/J mice. Immunohistology examination of the NXS2 metastases shows that only endothelial cells, but not cancer cells express Gb3. Finally, 3E2 treatment diminishes tumor vessels density, proving a specific therapeutic action of our monoclonal antibody to tumor vasculature. Our study demonstrates that Gb3 is a viable alternative target for immunotherapy and angiogenesis inhibition.

Vascular Strategies for Enhancing Tumour Response to Radiation Therapy

Radiation therapy is prescribed to more than 50% of patients diagnosed with cancer. Although mechanisms of interaction between radiation and tumour cells are well understood on a molecular level, much remains uncertain concerning the interaction of radiation with the tumour as a whole. Recent studies have demonstrated that single large doses of radiation (8–20 Gy) may primarily target tumour endothelial cells, leading to secondary tumour clonogenic cell death. These studies suggest that blood vessels play an important role in radiation response. As a result, various strategies have been proposed to effectively combine radiation with vascular targeting agents. While most proposed schemes focus on methods to disrupt tumour blood vessels, recent evidence supporting that some anti-angiogenic agents may “normalize” tumour blood vessels, in turn enhancing tumour oxygenation and radiosensitivity, indicates that there may be more efficient strategies. Furthermore, vascular targeting agents have recently been demonstrated to enhance radiation therapy by targeting endothelial cells. When combined with radiation, these agents are believed to cause even more localized vascular destruction followed by tumour clonogenic cell death. Taken together, it is now crucial to elucidate the role of tumour blood vessels in radiation therapy response, in order to make use of this knowledge in developing therapeutic strategies that target tumour vasculature above and beyond classic clonogenic tumour cell death. In this report, we review some major developments in understanding the importance of tumour blood vessels during radiation therapy. A discussion of current imaging modalities used for studying vascular response to treatments will also be presented.

Bystander effects induced by direct and scattered radiation generated during penetration of medium inside a water phantom

BACKGROUND

The biological effects of ionizing radiation have long been thought to results from direct targeting of the nucleus leading to DNA damage. Over the years, a number of non-targeted or epigenetic effects of radiation exposure have been reported where genetic damage occurs in cells that are not directly irradiated but respond to signals transmitted from irradiated cells, a phenomenon termed the "bystander effects".

AIM

We compared the direct and bystander responses of human A 549, BEAS-2-B and NHDF cell lines exposed to both photon (6 MV) and electron (22 MeV) radiation inside a water phantom. The cultures were directly irradiated or exposed to scattered radiation 4 cm outside the field. In parallel, non-irradiated cells (termed bystander cells) were incubated in ICM (irradiation conditioned medium) collected from another pool of irradiated cells (termed donor cells).

MATERIALS AND METHODS

In directly irradiated cells as well as ICM-treated cells, the frequency of micronuclei and condensation of chromatin characteristic for the apoptotic process were estimated using the cytokinesis-block micronucleus test.

RESULTS

In all tested cell lines, radiation induced apoptosis and formation of micronuclei. A549 and BEAS-2B cells cultured in ICM showed increased levels of micronuclei and apoptosis, whereas normal human fibroblasts (NHDF line) were resistant to bystander response. In A549 and BEAS-2B cells placed outside the radiation field and exposed to scattered radiation the formation of micronuclei and induction of apoptosis were similar to that after ICM-treatment.

CONCLUSION

Results suggest that the genetic damage in cells exposed to scattered radiation is caused by factors released by irradiated cells into the medium rather than by DNA damage induced directly by X rays. It seems that bystander effects may have important clinical implications for health risk after low level radiation exposure of cells lying outside the radiation field during clinical treatment.

Radiation-induced bystander effects: what are they, and how relevant are they to human radiation exposures?

The term radiation-induced bystander effect is used to describe radiation-induced biological changes that manifest in unirradiated cells remaining within an irradiated cell population. Despite their failure to fit into the framework of classical radiobiology, radiation-induced bystander effects have entered the mainstream and have become established in the radiobiology vocabulary as a bona fide radiation response. However, there is still no consensus on a precise definition of radiation-induced bystander effects, which currently encompasses a number of distinct signal-mediated effects. These effects are classified here into three classes: bystander effects, abscopal effects and cohort effects. In this review, the data have been evaluated to define, where possible, various features specific to radiation-induced bystander effects, including their timing, range, potency and dependence on dose, dose rate, radiation quality and cell type. The weight of evidence supporting these defining features is discussed in the context of bystander experimental systems that closely replicate realistic human exposure scenarios. Whether the manifestation of bystander effects in vivo is intrinsically limited to particular radiation exposure scenarios is considered. The conditions under which radiation-induced bystander effects are induced in vivo will ultimately determine their impact on radiation-induced carcinogenic risk.

Bleomycin, neocarzinostatin and ionising radiation-induced bystander effects in normal diploid human lung fibroblasts, bone marrow mesenchymal stem cells, lung adenocarcinoma cells and peripheral blood lymphocytes

PURPOSE

To determine whether the bystander effects induced by chemotherapeutic agents are similar to those induced by ionising radiation and to analyse the cell dependency, if any, in different human cell types such as normal lung fibroblasts (WI-38), human bone marrow mesenchymal stem cells (hBMSC), lung adenocarcinoma (A-549, NCI-H23) and peripheral blood lymphocytes (PBL).

MATERIALS AND METHODS

The cells mentioned above were exposed to two different concentrations of bleomycin (BLM) and neocarzinostatin (NCS) and to X-irradiation. Co-culture methodology was adopted to study the in vitro bystander effects. DNA damage was measured using a micronucleus (MN) assay as an endpoint to study the bystander response. High performance liquid chromatography (HPLC) was performed to rule out any residual activity of BLM and NCS. To further investigate if this bystander response is mediated through reactive oxygen species (ROS), the bystander cells were pretreated with dimethyl sulphoxide (DMSO), an ROS scavenger, and co-cultured with cells exposed to BLM.

RESULTS

Bystander response was observed in all five types of human cells (WI-38, hBMSC, NCI-H23, A-549 and PBL) co-cultured with exposed cells. While all cell types showed a bystander response, undifferentiated hBMSC and PBL showed a higher magnitude of bystander response. A reduction in the MN frequency was observed in co-cultured hBMSC and PBL pretreated with DMSO.

CONCLUSION

These results suggest that the chemotherapeutic agents, BLM and NCS, induce bystander response which is similar to that induced by radiation. Furthermore, it is observed that the bystander effect is independent of the cell type studied. Our results further support the involvement of ROS in mediating the bystander response induced by BLM.

Sphingosine-1-phosphate activates the AKT pathway to protect small intestines from radiation-induced endothelial apoptosis

A previous in vitro study showed that sphingosine-1-phosphate (S1P), a ceramide antagonist, preserved endothelial cells in culture from radiation-induced apoptosis. We proposed to validate the role of S1P in tissue radioprotection by inhibiting acute gastrointestinal (GI) syndrome induced by endothelial cell apoptosis after high dose of radiation. Retro-orbital S1P was injected in mice exposed to 15 Gy, a dose-inducing GI syndrome within 10 days. Overall survival and apoptosis on intestines sections were studied. Intestinal cell type targeted by S1P and early molecular survival pathways were researched using irradiated in vitro cell models and in vivo mouse models. We showed that retro-orbital S1P injection before irradiation prevented GI syndrome by inhibiting endothelium collapse. We defined endothelium as a specific therapeutic target because only these cells and not intestinal epithelial cells, or B and T lymphocytes, were protected. Pharmacologic approaches using AKT inhibitor and pertussis toxin established that S1P affords endothelial cell protection in vitro and in vivo through a mechanism involving AKT and 7-pass transmembrane receptors coupled to Gi proteins. Our results provide strong pharmacologic and mechanistic proofs that S1P protects endothelial cells against acute radiation enteropathy.

microRNAome changes in bystander three-dimensional human tissue models suggest priming of apoptotic pathways

The radiation-induced bystander effect (RIBE) is a phenomenon whereby unexposed cells exhibit molecular symptoms of stress exposure when adjacent or nearby cells are traversed by ionizing radiation (IR). Recent data suggest that RIBE may be epigenetically mediated by microRNAs (miRNAs), which are small regulatory molecules that target messenger RNA transcripts for translational inhibition. Here, we analyzed microRNAome changes in bystander tissues after α-particle microbeam irradiation of three-dimensional artificial human tissues using miRNA microarrays. Our results indicate that IR leads to a deregulation of miRNA expression in bystander tissues. We report that major bystander end points, including apoptosis, cell cycle deregulation and DNA hypomethylation, may be mediated by altered expression of miRNAs. Specifically, c-MYC-mediated upregulation of the miR-17 family was associated with decreased levels of E2F1 and RB1, suggesting a switch to a proliferative state in bystander tissues, while priming these cells for impending death signals. Upregulation of the miR-29 family resulted in decreased levels of its targets DNMT3a and MCL1, consequently affecting DNA methylation and apoptosis. Altered expression of miR-16 led to changes in expression of BCL2, suggesting modulation of apoptosis. Thus, our data clearly show that miRNAs play a profound role in the manifestation of late RIBE end points. In summary, this study creates a roadmap for understanding the role of microRNAome in RIBE and for developing novel RIBE biomarkers.

Investigation of bystander effects in hybrid cells by means of cell fusion and premature chromosome condensation induction

The established dogma in radiation sciences that underlies radiation protection and therapeutic applications is that radiation effects require induction of DNA damage only in cells that are directly hit by the radiation. However, extensive work during the last decade demonstrates that DNA damage responses can be detected in cells that are only bystanders. Such effects include cell killing and responses associated with DNA and chromosome damage. Here, we developed a strategy for investigating bystander effects on chromosomal integrity by premature chromosome condensation using hybrid cell formation between nontargeted human lymphocytes and targeted CHO cells or vice versa. We reasoned that signaling molecules generated in the targeted component of the hybrid will transfer to the nontargeted cell, inducing damage detectable at the chromosomal level. The results indicate that bystander cytogenetic effects between CHO and human lymphocytes cannot be detected under the experimental conditions used. This may be due either to the lack of communication of such responses between the components of the hybrid or to their abrogation by the experimental manipulations. These observations and the methodology developed should be useful in the further development of protocols for investigating bystander responses and for elucidating the underlying mechanisms.

Bystander effects and their implications for clinical radiotherapy

Radiation-induced bystander effects are defined as those biological effects expressed, after irradiation, by cells whose nuclei have not been directly irradiated. Radiation oncologists are only gradually beginning to appreciate the clinical relevance of radiation-induced bystander effects and associated phenomena: adaptive responses, genomic instability and abscopal effects. Incorporating bystander effects into the science underpinning clinical radiotherapy will involve moving beyond simple mechanistic models and towards a more systems-based approach. It is, given the protean nature of bystander effects, difficult to devise a coherent research strategy to investigate the clinical impact and relevance of bystander phenomena. Epidemiological approaches will be required, the traditional research models based on randomised controlled trials are unlikely to be adequate for the task. Any consideration of bystander effects challenges not only clinicians' preconceptions concerning the effects of radiation on tumours and normal tissues but also their ingenuity. This review covers, from a clinical perspective, the issues and problems associated with radiation-induced bystander effects.

Radiation-induced bystander signalling in cancer therapy

Our understanding of how radiation kills normal and tumour cells has been based on an intimate knowledge of the direct induction of DNA damage and its cellular consequences. What has become clear is that, as well as responses to direct DNA damage, cell-cell signalling -- known as the bystander effect -- mediated through gap junctions and inflammatory responses may have an important role in the response of cells and tissues to radiation exposure and also chemotherapy agents. This Review outlines the key aspects of radiation-induced intercellular signalling and assesses its relevance for existing and future radiation-based therapies.

Radiation-induced bystander effects in vivo are epigenetically regulated in a tissue-specific manner

Exposure of animal body parts to ionizing radiation (IR) can lead to molecular changes in distant shielded "bystander" tissues and organs. Nevertheless, tissue specificity of bystander responses within the same organism has not been examined in detail. Studies on in vivo bystander effect conducted so far analyzed changes induced by single-dose exposure. The potential of fractionated irradiation to induce bystander effects in vivo has never been studied. We analyzed changes in global DNA methylation and microRNAome in skin and spleen of animals subjected to single-dose (acute or fractionated) whole-body or cranial exposure to 0.5 Gy of X-rays. We found that IR-induced DNA methylation changes in bystander spleen and skin were distinct. Acute radiation exposure resulted in a significant loss of global DNA methylation in the exposed and bystander spleen 6 hr, 96 hr, and 14 days after irradiation. Fractionated irradiation led to hypomethylation in bystander spleen 6 hr after whole-body exposure, and 6 hr, 96 hr, and 14 days after cranial irradiation. Contrarily, changes in the skin of the same animals were seen only 6 hr after acute whole-body and head exposure. DNA hypomethylation observed in spleen was paralleled by a reduction of methyl-binding protein MeCP2 expression. Irradiation also induced tissue-specific microRNAome alterations in skin and spleen. For the first time, we have shown that IR-induced epigenetic bystander effects that occur in the same organism are triggered by both acute and fractionated exposure and are very distinct in different bystander organs. Future studies are clearly needed to address organismal and carcinogenic repercussions of those changes.

Radiation-induced bystander effects in vivo are sex specific

Ionizing radiation (IR) effects span beyond the area of direct exposure and can be observed in neighboring and distant naïve cells and organs. This phenomenon is termed a 'bystander effect'. IR effects in directly exposed tissue in vivo are epigenetically mediated and distinct in males and females. Yet, IR-induced bystander effects have never been explored in a sex-specificity domain. We used an in vivo mouse model, whereby the bystander effects are studied in spleen of male and female animals subjected to head exposure when the rest of the body is protected by a medical-grade lead shield. We analyzed the induction of DNA damage and alterations in global DNA methylation. Molecular parameters were correlated with cellular proliferation and apoptosis levels. The changes observed in bystander organs are compared to the changes in unexposed animals and animals exposed to predicted and measured scatter doses. We have found the selective induction of DNA damage levels, global DNA methylation, cell proliferation and apoptosis in exposed and bystander spleen tissue of male and female mice. Sex differences were significantly diminished in animals subjected to a surgical removal of gonads. These data constitute the first evidence of sex differences in radiation-induced bystander effects in mouse spleen in vivo. We show the role of sex hormones in spleen bystander responses and discuss implications of the observed changes.

Epigenetic changes and nontargeted radiation effects--is there a link?

It is now well accepted that the effects of ionizing radiation (IR) exposure can be noticed far beyond the borders of the directly irradiated tissue. IR can affect neighboring cells in the proximity, giving rise to a bystander effect. IR effects can also span several generations and influence the progeny of exposed parents, leading to transgeneration effects. Bystander and transgeneration IR effects are linked to the phenomenon of the IR-induced genome instability that manifests itself as chromosome aberrations, gene mutations, late cell death, and aneuploidy. While the occurrence of the above-mentioned phenomena is well documented, the exact mechanisms that lead to their development have still to be delineated. Evidence suggests that the IR-induced genome instability, bystander, and transgeneration effects may be epigenetically mediated. The epigenetic changes encompass DNA methylation, histone modification, and RNA-associated silencing. Recent studies demonstrated that IR exposure alters epigenetic parameters in the directly exposed tissues and in the distant bystander tissues. Transgeneration radiation effects were also proposed to be of an epigenetic nature. We will discuss the role of the epigenetic mechanisms in radiation responses, bystander effects, and transgeneration effects.