Mitochondrial dysfunction, a probable cause of persistent oxidative stress after exposure to ionizing radiation

Radiation-induced translational control of gene expression

Radiation-induced gene expression has long been hypothesized to protect against cell death. Defining this process would provide not only insight into the mechanisms mediating cell survival after radiation exposure, but also a novel source of targets for radiosensitization. However, whereas the radiation-induced gene expression profiles using total cellular mRNA have been generated for cell lines as well as normal tissues, with few exception, the changes in mRNA do not correlate with changes in the corresponding protein. The traditional approach to profiling gene expression, i.e., using total cellular RNA, does not take into account posttranscriptional regulation. In this review, we describe the use of gene expression profiling of polysome-bound RNA to establish that radiation modifies gene expression via translational control. Because changes in polysome-bound mRNA correlate with changes in protein, analysis of the translational profiles provides a unique data set for investigating the mechanisms mediating cellular radioresponse.

The activity and tissue distribution of thioredoxin reductase in basal cell carcinoma

PURPOSE

Basal cell carcinoma (BCC) is the most prevalent cancer worldwide. Different mechanisms are proposed to be involved in its pathogenesis such as oxidative stress. Oxidative stress, which is the consequence of the disruption of redox balance in favor of oxidants, is involved in the initiation or progression of many tumors. Thioredoxin reductase (TrxR) is a key enzyme of the thioredoxin (Trx) system, containing Trx and TrxR and NADPH, which is one of the main cellular oxidoreductases with an essential role in cellular health and survival through providing and maintaining redox balance. Therefore, we aimed to study and compare the activity and tissue distribution of TrxR in tumoral tissue and its healthy margin in patients with BCC.

METHODS

After biopsy and taking samples from 18 patients, TrxR activity was measured using a commercial kit and its tissue distribution was assessed immunohistochemically.

RESULTS

Both the activity and tissue distribution of TrxR in tumoral tissues were significantly higher compared to their healthy margins. Regarding the tissue distribution, this significant increase in TrxR in tumoral tissues was documented based on both staining intensity and abundance of positive cells in immunohistochemistry.

CONCLUSIONS

Based on these results, it is concluded that TrxR is involved in the pathogenesis of BCC; however, more investigations are required to clarify whether this increase is a consequence of BCC or it is an initiating mechanism.

The Hallmarks of Cancer from a Redox Perspective

SIGNIFICANCE

For a healthy cell to turn into a cancer cell and grow out to become a tumor, it needs to undergo a series of complex changes and acquire certain traits, summarized as "The Hallmarks of Cancer." These hallmarks can all be regarded as the result of altered signal transduction cascades and an understanding of these cascades is essential for cancer treatment.

RECENT ADVANCES

Redox signaling is a long overlooked form of signal transduction that proceeds through the reversible oxidation of cysteines in proteins and that uses hydrogen peroxide as a second messenger.

CRITICAL ISSUES

In this article, we provide examples that show that redox signaling is involved in the regulation of proteins and signaling cascades that play roles in every hallmark of cancer.

FUTURE DIRECTIONS

An understanding of how redox signaling and "classical" signal transduction are intertwined could hold promising strategies for cancer therapy in the future. Antioxid. Redox Signal. 25, 300-325.

Cancer drug resistance: redox resetting renders a way

Disruption of redox homeostasis is a crucial factor in the development of drug resistance, which is a major problem facing current cancer treatment. Compared with normal cells, tumor cells generally exhibit higher levels of reactive oxygen species (ROS), which can promote tumor progression and development. Upon drug treatment, some tumor cells can undergo a process of 'Redox Resetting' to acquire a new redox balance with higher levels of ROS accumulation and stronger antioxidant systems. Evidence has accumulated showing that the 'Redox Resetting' enables cancer cells to become resistant to anticancer drugs by multiple mechanisms, including increased rates of drug efflux, altered drug metabolism and drug targets, activated prosurvival pathways and inefficient induction of cell death. In this article, we provide insight into the role of 'Redox Resetting' on the emergence of drug resistance that may contribute to pharmacological modulation of resistance.

Radiation Exposure Decreases the Quantity and Quality of Cardiac Stem Cells in Mice

Radiation exposure may increase cardiovascular disease risks; however, the precise molecular/cellular mechanisms remain unclear. In the present study, we examined the hypothesis that radiation impairs cardiac stem cells (CSCs), thereby contributing to future cardiovascular disease risks. Adult C57BL/6 mice were exposed to 3 Gy γ-rays, and heart tissues were collected 24 hours later for further experiments. Although c-kit-positive cells were rarely found, radiation exposure significantly induced apoptosis and DNA damage in the cells of the heart. The ex vivo expansion of CSCs from freshly harvested atrial tissues showed a significantly lower production of CSCs in irradiated mice compared with healthy mice. The proliferative activity of CSCs evaluated by Ki-67 expression was not significantly different between the groups. However, compared to the healthy control, CSCs expanded from irradiated mice showed significantly lower telomerase activity, more 53BP1 foci in the nuclei, lower expression of c-kit and higher expression of CD90. Furthermore, CSCs expanded from irradiated mice had significantly poorer potency in the production of insulin-like growth factor-1. Our data suggest that radiation exposure significantly decreases the quantity and quality of CSCs, which may serve as sensitive bio-parameters for predicting future cardiovascular disease risks.

Accelerated Regeneration of ATP Level after Irradiation in Human Skin Fibroblasts by Coenzyme Q10

Human skin is exposed to a number of harmful agents of which the ultraviolet (UV) component of solar radiation is most important. UV-induced damages include direct DNA lesions as well as oxidative damage in DNA, proteins and lipids caused by reactive oxygen species (ROS). Being the main site of ROS generation in the cell, mitochondria are particularly affected by photostress. The resulting mitochondrial dysfunction may have negative effects on many essential cellular processes. To counteract these effects, coenzyme Q10 (CoQ10 ) is used as a potent therapeutic in a number of diseases. We analyzed the mitochondrial respiration profile, the mitochondrial membrane potential and cellular ATP level in skin fibroblasts after irradiation. We observed an accelerated regeneration of cellular ATP level, a decrease in mitochondrial dysfunction as well as a preservation of the mitochondrial membrane potential after irradiation in human skin fibroblasts by treatment with CoQ10 . We conclude that the faster regeneration of the ATP level was achieved by a preservation of mitochondrial function by the addition of CoQ10 and that the protective effect of CoQ10 is primarily mediated via its antioxidative function. We suggest also that it might be further dependent on a stimulation of DNA repair enzymes by CoQ10 .

Polysome Profiling Links Translational Control to the Radioresponse of Glioblastoma Stem-like Cells

Changes in polysome-bound mRNA (translatome) are correlated closely with changes in the proteome in cells. Therefore, to better understand the processes mediating the response of glioblastoma to ionizing radiation (IR), we used polysome profiling to define the IR-induced translatomes of a set of human glioblastoma stem-like cell (GSC) lines. Although cell line specificity accounted for the largest proportion of genes within each translatome, there were also genes that were common to the GSC lines. In particular, analyses of the IR-induced common translatome identified components of the DNA damage response, consistent with a role for the translational control of gene expression in cellular radioresponse. Moreover, translatome analyses suggested that IR enhanced cap-dependent translation processes, an effect corroborated by the finding of increased eIF4F-cap complex formation detected after irradiation in all GSC lines. Translatome analyses also predicted that Golgi function was affected by IR. Accordingly, Golgi dispersal was detected after irradiation of each of the GSC lines. In addition to the common responses seen, translatome analyses predicted cell line-specific changes in mitochondria, as substantiated by changes in mitochondrial mass and DNA content. Together, these results suggest that analysis of radiation-induced translatomes can provide new molecular insights concerning the radiation response of cancer cells. More specifically, they suggest that the translational control of gene expression may provide a source of molecular targets for glioblastoma radiosensitization. Cancer Res; 76(10); 3078-87. ©2016 AACR.

Low temperature plasmas as emerging cancer therapeutics: the state of play and thoughts for the future

The field of plasma medicine has seen substantial advances over the last decade, with applications developed for bacterial sterilisation, wound healing and cancer treatment. Low temperature plasmas (LTPs) are particularly suited for medical purposes since they are operated in the laboratory at atmospheric pressure and room temperature, providing a rich source of reactive oxygen and nitrogen species (RONS). A great deal of research has been conducted into the role of reactive species in both the growth and treatment of cancer, where long-established radio- and chemo-therapies exploit their ability to induce potent cytopathic effects. In addition to producing a plethora of RONS, LTPs can also create strong electroporative fields. From an application perspective, it has been shown that LTPs can be applied precisely to a small target area. On this basis, LTPs have been proposed as a promising future strategy to accurately and effectively control and eradicate tumours. This review aims to evaluate the current state of the literature in the field of plasma oncology and highlight the potential for the use of LTPs in combination therapy. We also present novel data on the effect of LTPs on cancer stem cells, and speculatively outline how LTPs could circumvent treatment resistance encountered with existing therapeutics.

Ionizing Radiation Induces Altered Neuronal Differentiation by mGluR1 through PI3K-STAT3 Signaling in C17.2 Mouse Neural Stem-Like Cells

Most studies of IR effects on neural cells and tissues in the brain are still focused on loss of neural stem cells. On the other hand, the effects of IR on neuronal differentiation and its implication in IR-induced brain damage are not well defined. To investigate the effects of IR on C17.2 mouse neural stem-like cells and mouse primary neural stem cells, neurite outgrowth and expression of neuronal markers and neuronal function-related genes were examined. To understand this process, the signaling pathways including PI3K, STAT3, metabotrophic glutamate receptor 1 (mGluR1) and p53 were investigated. In C17.2 cells, irradiation significantly increased the neurite outgrowth, a morphological hallmark of neuronal differentiation, in a dose-dependent manner. Also, the expression levels of neuronal marker proteins, β-III tubulin were increased by IR. To investigate whether IR-induced differentiation is normal, the expression of neuronal function-related genes including synaptophysin, a synaptic vesicle forming proteins, synaptotagmin1, a calcium ion sensor, γ-aminobutyric acid (GABA) receptors, inhibitory neurotransmitter receptors and glutamate receptors, excitatory neurotransmitter receptors was examined and compared to that of neurotrophin-stimulated differentiation. IR increased the expression of synaptophysin, synaptotagmin1 and GABA receptors mRNA similarly to normal differentiation by stimulation of neurotrophin. Interestingly, the overall expression of glutamate receptors was significantly higher in irradiated group than normal differentiation group, suggesting that the IR-induced neuronal differentiation may cause altered neuronal function in C17.2 cells. Next, the molecular mechanism of the altered neuronal differentiation induced by IR was studied by investigating signaling pathways including p53, mGluR1, STAT3 and PI3K. Increases of neurite outgrowth, neuronal marker and neuronal function-related gene expressions by IR were abolished by inhibition of p53, mGluR-1, STAT3 or PI3K. The inhibition of PI3K blocked both p53 signaling and STAT3-mGluR1 signaling but inhibition of p53 did not affect STAT3-mGluR1 signaling in irradiated C17.2 cells. Finally, these results of the IR-induced altered differentiation in C17.2 cells were verified in ex vivo experiments using mouse primary neural stem cells. In conclusion, the results of this study demonstrated that IR is able to trigger the altered neuronal differentiation in undifferentiated neural stem-like cells through PI3K-STAT3-mGluR1 and PI3K-p53 signaling. It is suggested that the IR-induced altered neuronal differentiation may play a role in the brain dysfunction caused by IR.

Estrogen deficiency heterogeneously affects tissue specific stem cells in mice

Postmenopausal disorders are frequently observed in various organs, but their relationship with estrogen deficiency and mechanisms remain unclear. As tissue-specific stem cells have been found to express estrogen receptors, we examined the hypothesis that estrogen deficiency impairs stem cells, which consequently contributes to postmenopausal disorders. Six-week-old C57BL/6 female mice were ovariectomized, following which they received 17β-estradiol replacement or vehicle (control). Sham-operated mice were used as healthy controls. All mice were killed for evaluation 2 months after treatments. Compared with the healthy control, ovariectomy significantly decreased uterine weight, which was partially recovered by 17β-estradiol replacement. Ovariectomy significantly increased the numbers of c-kit-positive hematopoietic stem/progenitor cells in bone marrow, but impaired their capacity to grow mixed cell-type colonies in vitro. Estrogen replacement further increased the numbers of c-kit-positive hematopoietic stem/progenitor cells in bone marrow, without significantly affecting colony growth in vitro. The number of CD105-positive mesenchymal stem cells in bone marrow also significantly decreased after ovariectomy, but completely recovered following estrogen replacement. Otherwise, neither ovariectomy nor estrogen replacement changed the number of Pax7-positive satellite cells, which are a skeletal muscle-type stem cell. Estrogen deficiency heterogeneously affected tissue-specific stem cells, suggesting a likely and direct relationship with postmenopausal disorders.

Increased Oxidative Stress as a Selective Anticancer Therapy

Reactive oxygen species (ROS) are closely related to tumorgenesis. Under hypoxic environment, increased levels of ROS induce the expression of hypoxia inducible factors (HIFs) in cancer stem cells (CSCs), resulting in the promotion of the upregulation of CSC markers, and the reduction of intracellular ROS level, thus facilitating CSCs survival and proliferation. Although the ROS level is regulated by powerful antioxidant defense mechanisms in cancer cells, it is observed to remain higher than that in normal cells. Cancer cells may be more sensitive than normal cells to the accumulation of ROS; consequently, it is supposed that increased oxidative stress by exogenous ROS generation therapy has an effect on selectively killing cancer cells without affecting normal cells. This paper reviews the mechanisms of redox regulation in CSCs and the pivotal role of ROS in anticancer treatment.

Ionizing radiation induces neuronal differentiation of Neuro-2a cells via PI3-kinase and p53-dependent pathways

PURPOSE

The influence of ionizing radiation (IR) on neuronal differentiation is not well defined. In this study, we investigated the effects of IR on the differentiation of Neuro-2a mouse neuroblastoma cells and the involvement of tumor protein 53 (p53) and mitogen-activated protein kinases (MAPK) during this process.

MATERIALS AND METHODS

The mouse neuroblastoma Neuro-2a cells were exposed to (137)Cs γ-rays at 4, 8 or 16 Gy. After incubation for 72 h with or without inhibitors of p53, phosphatidylinositol-4, 5-bisphosphate 3-kinase (PI3K) and other kinases, the neuronal differentiation of irradiated Neuro-2a cells was examined through analyzing neurite outgrowth and neuronal maker expression and the activation of related signaling proteins by western blotting and immunocytochemistry. Mouse primary neural stem cells (NSC) were exposed to IR at 1 Gy. The change of neuronal marker was examined using immunocytochemistry.

RESULTS

The irradiation of Neuro-2a cells significantly increased the neurite outgrowth and the expression of neuronal markers (neuronal nuclei [NeuN], microtubule-associated protein 2 [Map2], growth associated protein-43 [GAP-43], and Ras-related protein 13 [Rab13]). Immunocytochemistry revealed that neuronal class III beta-tubulin (Tuj-1) positive cells were increased and nestin positive cells were decreased by IR in Neuro-2a cells, which supported the IR-induced neuronal differentiation. However, the IR-induced neuronal differentiation was significantly attenuated when p53 was inhibited by pifithrin-α (PFT-α) or p53-small interfering RNA (siRNA). The PI3K inhibitor, LY294002, also suppressed the IR-induced neurite outgrowth, the activation of p53, the expression of GAP-43 and Rab13, and the increase of Tuj-1 positive cells. The increase of neurite outgrowth and Tuj-1 positive cells by IR and its suppression by LY294002 were also observed in mouse primary NSC.

CONCLUSION

These results suggest that IR is able to trigger the neuronal differentiation of Neuro-2a cells and the activation of p53 via PI3K is an important step for the IR-induced differentiation of Neuro-2a cells.

Low-dose ionizing radiation rapidly affects mitochondrial and synaptic signaling pathways in murine hippocampus and cortex

The increased use of radiation-based medical imaging methods such as computer tomography is a matter of concern due to potential radiation-induced adverse effects. Efficient protection against such detrimental effects has not been possible due to inadequate understanding of radiation-induced alterations in signaling pathways. The aim of this study was to elucidate the molecular mechanisms behind learning and memory deficits after acute low and moderate doses of ionizing radiation. Female C57BL/6J mice were irradiated on postnatal day 10 (PND10) with gamma doses of 0.1 or 0.5 Gy. This was followed by evaluation of the cellular proteome, pathway-focused transcriptome, and neurological development/disease-focused miRNAome of hippocampus and cortex 24 h postirradiation. Our analysis showed that signaling pathways related to mitochondrial and synaptic functions were changed by acute irradiation. This may lead to reduced mitochondrial function paralleled by enhanced number of dendritic spines and neurite outgrowth due to elevated long-term potentiation, triggered by increased phosphorylated CREB. This was predominately observed in the cortex at 0.1 and 0.5 Gy and in the hippocampus only at 0.5 Gy. Moreover, a radiation-induced increase in the expression of several neural miRNAs associated with synaptic plasticity was found. The early changes in signaling pathways related to memory formation may be associated with the acute neurocognitive side effects in patients after brain radiotherapy but might also contribute to late radiation-induced cognitive injury.

Ionizing radiation-induced cell death is partly caused by increase of mitochondrial reactive oxygen species in normal human fibroblast cells

Radiation-induced cell death is thought to be caused by nuclear DNA damage that cannot be repaired. However, in this study we found that a delayed increase of mitochondrial reactive oxygen species (ROS) is responsible for some of the radiation-induced cell death in normal human fibroblast cells. We have previously reported that there is a delayed increase of mitochondrial (·)O2(-), measured using MitoSOX™ Red reagent, due to gamma irradiation. This is dependent on Drp1 localization to mitochondria. Here, we show that knockdown of Drp1 expression reduces the level of DNA double-strand breaks (DSBs) remaining 3 days after 6 Gy irradiation. Furthermore, cells with knockdown of Drp1 expression are more resistant to gamma radiation. We then tested whether the delayed increase of ROS causes DNA damage. The antioxidant, 2-glucopyranoside ascorbic acid (AA-2G), was applied before or after irradiation to inhibit ROS production during irradiation or to inhibit delayed ROS production from mitochondria. Interestingly, 1 h after exposure, the AA-2G treatment reduced the level of DSBs remaining 3 days after 6 Gy irradiation. In addition, irradiated AA-2G-treated cells were more resistant to radiation than the untreated cells. These results indicate that delayed mitochondrial ROS production may cause some of the cell death after irradiation.

From radioresistance to radiosensitivity: In vitro evolution of L5178Y lymphoma

PURPOSE

To discuss the possible reasons for the loss of tumourigenicity and the acquisition of new phenotypic features (among them, sensitivity to X and UVC radiations) as a result of in vitro cultivation of L5178Y lymphoma cells.

RESULTS

Ten years ago the phenotypic differences between LY-R (original L5178Y maintained in vivo and examined in vitro) and LY-S lines were reviewed in detail by the author. The loss of tumourigenicity of LY-R cells upon in vitro cultivation accompanying the acquirement of the LY-S phenotype had been described earlier by Beer et al. (1983). In spite of their common origin, the sublines were shown to differ in their relative sensitivity to a number of DNA damaging agents and in numerous other features. Here, selected differences between LY-R and LY-S lines are briefly reviewed. It is proposed that Wallace's concept (2010a) that mitochondria are the interface between environmental conditions and the genome may explain the LY-R-LY-S conversion under prolonged in vitro cultivation.

CONCLUSION

The differences between the LY lines were probably of epigenetic rather than genetic character. The properties of LY-R cells changed as a result of exposure to an oxic in vitro milieu. The changes could be preconditioned by heteroplasmy and the selection of cells endowed with mitochondria best fitted to a high oxygen-low carbon dioxide environment.

Cellular oxidative stress response mediates radiosensitivity in Fus1-deficient mice

Mechanism of radiosensitivity of normal tissues, a key factor in determining the toxic side effects of cancer radiotherapy, is not fully understood. We recently demonstrated that deficiency of mitochondrial tumor suppressor, Fus1, increases radiosensitivity at the organismal, tissue and cellular levels. Since Fus1-deficient mice and cells exhibit high levels of oxidative stress, we hypothesized that dysregulation of cellular antioxidant defenses may contribute to the increased radiosensitivity. To address this potential mechanism, we treated the Fus1 KO mice with an inhibitor of pathogenic oxidative reactions, pyridoxamine (PM). Treatment with PM ameliorated IR-induced damage to GI epithelium of Fus1 KO mice and significantly increased the survival of irradiated mice. In cultured Fus1 KO epithelial cells, IR-induced oxidative stress was enhanced because of inadequate cellular antioxidant defenses, such as low levels and/or activities of cytochrome C, Sod 2 and STAT3. This resulted in dysregulation of IR-induced DNA-damage response and DNA synthesis. Treatment of Fus1 KO cells with PM or Sod 2 mimetic Tempol normalized the oxidative stress response, thus compensating to a significant degree for inadequate antioxidant response. Our findings using Fus1 KO radiosensitive mice suggest that radiosensitivity is mediated via dysregulation of antioxidant response and defective redox homeostasis.

Sensitivity and dose dependency of radiation-induced injury in hematopoietic stem/progenitor cells in mice

We evaluated the sensitivity and dose dependency of radiation-induced injury in hematopoietic stem/progenitor cells. Adult C57BL/6 mice were daily exposed to 0, 2, 10, 50, and 250 mGy γ-ray for 1 month in succession, respectively. The damage of hematopoietic stem/progenitor cells in bone marrow were investigated within 2 hours (acute phase) or at 3 months (chronic phase) after the last exposure. Daily exposure to over 10 mGy γ-ray significantly decreased the number and colony-forming capacity of hematopoietic stem/progenitor cells at acute phase, and did not completely recover at chronic phase with 250 mGy exposure. Interestingly, the daily exposure to 10 or 50 mGy γ-ray decreased the formation of mixed types of colonies at chronic phase, but the total number of colonies was comparable to control. Immunostaining analysis showed that the formation of 53BP1 foci in c-kit⁺ stem/progenitor cells was significantly increased with daily exposure to 50 and 250 mGy at acute phase, and 250 mGy at chronic phase. Many genes involved in toxicity responses were up- or down-regulated with the exposures to all doses. Our data have clearly shown the sensitivity and dose dependency of radiation-induced injury in hematopoietic stem/progenitor cells of mice with daily exposures to 2 ~ 250 mGy γ-ray.

Melatonin blunts the mitochondrial/NLRP3 connection and protects against radiation-induced oral mucositis

Mucositis is a common and distressing side effect of chemotherapy or radiotherapy that has potentially severe consequences, and no treatment is available. The purpose of this study was to analyze the molecular pathways involved in the development of oral mucositis and to evaluate whether melatonin can prevent this pathology. The tongue of male Wistar rats was subjected to irradiation (X-ray YXLON Y.Tu 320-D03 irradiator; the animals received a dose of 7.5 Gy/day for 5 days). Rats were treated with 45 mg/day melatonin or vehicle for 21 days postirradiation, either by local application into their mouths (melatonin gel) or by subcutaneous injection. A connection between reactive oxygen species, generating mitochondria and the NLRP3 (NLR-related protein 3 nucleotide-binding domain leucine-rich repeat containing receptor-related protein 3) inflammasome, has been reported in mucositis. Here, we show that mitochondrial oxidative stress, bioenergetic impairment and subsequent NLRP3 inflammasome activation are involved in the development of oral mucositis after irradiation and that melatonin synthesized in the rat tongue is depleted after irradiation. The application of melatonin gel restores physiological melatonin levels in the tongue and prevents mucosal disruption and ulcer formation. Melatonin gel protects the mitochondria from radiation damage and blunts the NF-κB/NLRP3 inflammasome signaling activation in the tongue. Our results suggest new molecular pathways involved in radiotherapy-induced mucositis that are inhibited by topical melatonin application, suggesting a potential preventive therapy for mucositis in patients with cancer.

Radioprotective effects of mitochondria-targeted antioxidant SkQR1

We show here that mitochondria-targeted antioxidant composed of plastoquinone conjugated through hydrocarbon linker with cationic rhodamine 19 (SkQR1) protected against nuclear DNA damage induced by gamma radiation in K562 erythroleukemia cells. We also demonstrate that SkQR1 prevented the early (1 h postirradiation) accumulation of phosphorylated histone H2AX (γ-H2AX) an indicator of DNA double-strand break formation, as well as the radiation-induced increase in chromosomal aberrations. These data suggested that nuclear DNA damage induced by gamma radiation may be mediated by mitochondrial reactive oxygen species (ROS) production. We show that SkQR1 suppressed delayed accumulation of ROS 32 h after irradiation probably by inhibiting mitochondrial ROS-induced ROS release mechanisms. This suggests that mitochondria-targeted antioxidants may protect cells from the late consequences of radiation exposure related to delayed oxidative stress. We have previously reported that SkQRl is the substrate of multidrug resistance pump P-glycoproten (Pgp 170) and selectively protects Pgp 170-negative cells against oxidative stress. In line with this finding, we demonstrate here that SkQR1 did not protect Pgp170-positive K562 subline against DNA damage induced by gamma radiation. The selective radioprotection of normal Pgp 170-negative cells by mitochondria-targeted antioxidants could be a promising strategy to increase the efficiency of radiotherapy for multidrug-resistant tumors.

Intraclonal recovery of 'slow clones'-a manifestation of genomic instability: are mitochondria the key to an explanation?

Intraclonal recovery following X-irradiation in an in vitro study of L5178Y-S murine leukaemic cells is reviewed. This phenomenon was first described in 1994 occurring in the slowly growing clones ('slow clones') present among the survivors in irradiated cell populations. An attempt to explain these experimental data is given in terms of the present knowledge of the role of mitochondria in nontargeted radiation effects, with the focus on genomic instability and mtDNA-related epigenetic modifications of the nuclear genome. An understanding of this intraclonal recovery may be important in preventing tumour regrowth following radiotherapy, as well as in decreasing the risk of secondary radiation-induced malignancies.

Redox-mediated and ionizing-radiation-induced inflammatory mediators in prostate cancer development and treatment

SIGNIFICANCE

Radiation therapy is widely used for treatment of prostate cancer. Radiation can directly damage biologically important molecules; however, most effects of radiation-mediated cell killing are derived from the generated free radicals that alter cellular redox status. Multiple proinflammatory mediators can also influence redox status in irradiated cells and the surrounding microenvironment, thereby affecting prostate cancer progression and radiotherapy efficiency.

RECENT ADVANCES

Ionizing radiation (IR)-generated oxidative stress can regulate and be regulated by the production of proinflammatory mediators. Depending on the type and stage of the prostate cancer cells, these proinflammatory mediators may lead to different biological consequences ranging from cell death to development of radioresistance.

CRITICAL ISSUES

Tumors are heterogeneous and dynamic communication occurs between stromal and prostate cancer cells, and complicated redox-regulated mechanisms exist in the tumor microenvironment. Thus, antioxidant and anti-inflammatory strategies should be carefully evaluated for each patient at different stages of the disease to maximize therapeutic benefits while minimizing unintended side effects.

FUTURE DIRECTIONS

Compared with normal cells, tumor cells are usually under higher oxidative stress and secrete more proinflammatory mediators. Thus, redox status is often less adaptive in tumor cells than in their normal counterparts. This difference can be exploited in a search for new cancer therapeutics and treatment regimes that selectively activate cell death pathways in tumor cells with minimal unintended consequences in terms of chemo- and radio-resistance in tumor cells and toxicity in normal tissues.

Modulation of oxidative stress as an anticancer strategy

The regulation of oxidative stress is an important factor in both tumour development and responses to anticancer therapies. Many signalling pathways that are linked to tumorigenesis can also regulate the metabolism of reactive oxygen species (ROS) through direct or indirect mechanisms. High ROS levels are generally detrimental to cells, and the redox status of cancer cells usually differs from that of normal cells. Because of metabolic and signalling aberrations, cancer cells exhibit elevated ROS levels. The observation that this is balanced by an increased antioxidant capacity suggests that high ROS levels may constitute a barrier to tumorigenesis. However, ROS can also promote tumour formation by inducing DNA mutations and pro-oncogenic signalling pathways. These contradictory effects have important implications for potential anticancer strategies that aim to modulate levels of ROS. In this Review, we address the controversial role of ROS in tumour development and in responses to anticancer therapies, and elaborate on the idea that targeting the antioxidant capacity of tumour cells can have a positive therapeutic impact.

Effects of antioxidants on the quality and genomic stability of induced pluripotent stem cells

Effects of antioxidants on the quality and genomic stability of induced pluripotent stem (iPS) cells were investigated with two human iPS cell lines (201B7 and 253G1). Cells used in this study were expanded from a single colony of each cell line with the addition of proprietary antioxidant supplement or homemade antioxidant cocktail in medium, and maintained in parallel for 2 months. The cells grew well in all culture conditions and kept “stemness”. Although antioxidants modestly decreased the levels of intracellular reactive oxygen species, there were no differences in the expression of 53BP1 and pATM, two critical molecules related with DNA damage and repair, under various culture conditions. CGH analysis showed that the events of genetic aberrations were decreased only in the 253G1 iPS cells with the addition of homemade antioxidant cocktail. Long-term culture will be necessary to confirm whether low dose antioxidants improve the quality and genomic stability of iPS cells.

Effects of ionizing radiation on mitochondria

The current concept of radiobiology posits that damage to the DNA in the cell nucleus is the primary cause for the detrimental effects of radiation. However, emerging experimental evidence suggests that this theoretical framework is insufficient for describing extranuclear radiation effects, particularly the response of the mitochondria, an important site of extranuclear, coding DNA. Here, we discuss experimental observations of the effects of ionizing radiation on the mitochondria at (1) the DNA and (2) functional levels. The roles of mitochondria in (3) oxidative stress and (4) late radiation effects are discussed. In this review, we summarize the current understanding of targets for ionizing radiation outside the cell nucleus. Available experimental data suggest that an increase in the tumoricidal efficacy of radiation therapy might be achievable by targeting mitochondria. Likewise, more specific protection of mitochondria and its coding DNA should reduce damage to healthy cells exposed to ionizing radiation.

HIV-TAT mediated protein transduction of Cu/Zn-superoxide dismutase-1 (SOD1) protects skin cells from ionizing radiation

Background

Radiation-induced skin injury remains a serious concern during radiotherapy. Cu/Zn-superoxide dismutase (Cu/Zn-SOD, SOD₁) is a conserved enzyme for scavenging superoxide radical in cells. Because of the integrity of cell membranes, exogenous molecule is not able to be incorporated into cells, which limited the application of natural SOD₁. The aim of this study was to evaluate the protective role of HIV-TAT protein transduction domain mediated protein transduction of SOD₁ (TAT-SOD₁) against ionizing radiation.

Methods

The recombinant TAT-SOD₁ and SOD₁ were obtained by prokaryotic–based protein expression system. The transduction effect and biological activity of TAT-SOD₁ was measured by immunofluorescence and antioxidant capability assays in human keratinocyte HaCaT cells. Mito-Tracker staining, reactive oxygen species (ROS) generation assay, cell apoptosis analysis and malondialdehyde (MDA) assay were used to access the protective effect of TAT- SOD₁.

Results

Uptake of TAT-SOD₁ by HaCaT cells retained its biological activity. Compared with natural SOD₁, the application of TAT-SOD₁ significantly enhanced the viability and decreased the apoptosis induced by X-ray irradiation. Moreover, TAT-SOD₁ reduced ROS and preserved mitochondrial integrity after radiation exposure in HaCaT cells. Radiation-induced γH2AX foci, which are representative of DNA double strand breaks, were decreased by pretreatment with TAT-SOD₁. Furthermore, subcutaneous application of TAT-SOD₁ resulted in a significant decrease in 45 Gy electron beam-induced ROS and MDA concentration in the skins of rats.

Conclusions

This study provides evidences for the protective role of TAT-SOD₁ in alleviating radiation-induced damage in HaCaT cells and rat skins, which suggests a new therapeutic strategy for radiation-induced skin injury.

Suppression of E. multilocularis hydatid cysts after ionizing radiation exposure

Background

Heavy-ion therapy has an advantage over conventional radiotherapy due to its superb biological effectiveness and dose conformity in cancer therapy. It could be a potential alternate approach for hydatid cyst treatment. However, there is no information currently available on the cellular and molecular basis for heavy-ion irradiation induced cell death in cystic echinococcosis.

Methododology/Principal Findings

LD50 was scored by protoscolex death. Cellular and ultrastructural changes within the parasite were studied by light and electron microscopy, mitochondrial DNA (mtDNA) damage and copy number were measured by QPCR, and apoptosis was determined by caspase 3 expression and caspase 3 activity. Ionizing radiation induced sparse cytoplasm, disorganized and clumped organelles, large vacuoles and devoid of villi. The initial mtDNA damage caused by ionizing radiation increased in a dose-dependent manner. The kinetic of DNA repair was slower after carbon-ion radiation than that after X-rays radiation. High dose carbon-ion radiation caused irreversible mtDNA degradation. Cysts apoptosis was pronounced after radiation. Carbon-ion radiation was more effective to suppress hydatid cysts than X-rays.

Conclusions

These studies provide a framework to the evaluation of attenuation effect of heavy-ion radiation on cystic echinococcosis in vitro. Carbon-ion radiation is more effective to suppress E. multilocularis than X-rays.

Surgical removal of cysts may be impractical in cases that cysts are in multiple organs or tissues, or in risky locations. In that case, alternative treatment should be employed. Heavy-ion radiation could be an effective way for treatment of hydatid cysts, taking its full advantage of well-defined range, small lateral beam spread and an enhanced biological effectiveness. In this study, we found that carbon-ion radiation could result in extensive mitochondrial DNA damage and apoptosis in hydatid cysts. Cellular and ultrastructural changes were observed after ionizing radiation, which were indicative of cysts growth inhibition. To our knowledge, this is the first study reporting the biological effect of carbon-ion radiation on E. multilocularis hydatid cysts.

Ionizing irradiation-induced radical stress stalls live meiotic chromosome movements by altering the actin cytoskeleton

Meiosis generates haploid cells or spores for sexual reproduction. As a prelude to haploidization, homologous chromosomes pair and recombine to undergo segregation during the first meiotic division. During the entire meiotic prophase of the yeast Saccharomyces cerevisiae, chromosomes perform rapid movements that are suspected to contribute to the regulation of recombination. Here, we investigated the impact of ionizing radiation (IR) on movements of GFP-tagged bivalents in live pachytene cells. We find that exposure of sporulating cultures with >40 Gy (4-krad) X-rays stalls pachytene chromosome movements. This identifies a previously undescribed acute radiation response in yeast meiosis, which contrasts with its reported radioresistance of up to 1,000 Gy in survival assays. A modified 3'-end labeling assay disclosed IR-induced dsDNA breaks (DSBs) in pachytene cells at a linear dose relationship of one IR-induced DSB per cell per 5 Gy. Dihydroethidium staining revealed formation of reactive oxygen species (ROS) in irradiated cells. Immobility of fuzzy-appearing irradiated bivalents was rescued by addition of radical scavengers. Hydrogen peroxide-induced ROS did reduce bivalent mobility similar to 40 Gy X IR, while they failed to induce DSBs. IR- and H2O2-induced ROS were found to decompose actin cables that are driving meiotic chromosome mobility, an effect that could be rescued by antioxidant treatment. Hence, it appears that the meiotic actin cytoskeleton is a radical-sensitive system that inhibits bivalent movements in response to IR- and oxidant-induced ROS. This may be important to prevent motility-driven unfavorable chromosome interactions when meiotic recombination has to proceed in genotoxic environments.

Role of reactive oxygen species in the radiation response of human hematopoietic stem/progenitor cells

Hematopoietic stem/progenitor cells (HSPCs), which are present in small numbers in hematopoietic tissues, can differentiate into all hematopoietic lineages and self-renew to maintain their undifferentiated phenotype. HSPCs are extremely sensitive to oxidative stressors such as anti-cancer agents, radiation, and the extensive accumulation of reactive oxygen species (ROS). The quiescence and stemness of HSPCs are maintained by the regulation of mitochondrial biogenesis, ROS, and energy homeostasis in a special microenvironment called the stem cell niche. The present study evaluated the relationship between the production of intracellular ROS and mitochondrial function during the proliferation and differentiation of X-irradiated CD34⁺ cells prepared from human placental/umbilical cord blood HSPCs. Highly purified CD34⁺ HSPCs exposed to X-rays were cultured in liquid and semi-solid medium supplemented with hematopoietic cytokines. X-irradiated CD34⁺ HSPCs treated with hematopoietic cytokines, which promote their proliferation and differentiation, exhibited dramatically suppressed cell growth and clonogenic potential. The amount of intracellular ROS in X-irradiated CD34⁺ HSPCs was significantly higher than that in non-irradiated cells during the culture period. However, neither the intracellular mitochondrial content nor the mitochondrial superoxide production was elevated in X-irradiated CD34⁺ HSPCs compared with non-irradiated cells. Radiation-induced gamma-H2AX expression was observed immediately following exposure to 4 Gy of X-rays and gradually decreased during the culture period. This study reveals that X-irradiation can increase persistent intracellular ROS in human CD34⁺ HSPCs, which may not result from mitochondrial ROS due to mitochondrial dysfunction, and indicates that substantial DNA double-strand breakage can critically reduce the stem cell function.

Loss of TRPM2 function protects against irradiation-induced salivary gland dysfunction

Xerostomia as a result of salivary gland damage is a permanent and debilitating side effect of radiotherapy for head and neck cancers. Effective treatments for protecting, or restoring, salivary gland function are not available. Here we report that irradiation treatment leads to activation of the calcium-permeable channel, transient potential melastatin-like 2 (TRPM2), via stimulation of poly-ADP-ribose polymerase. Importantly, irradiation induced an irreversible loss of salivary gland fluid secretion in TRPM2+/+ mice while a transient loss was seen in TRPM2-/- mice with >60% recovery by 30 days after irradiation. Treatment of TRPM2+/+ mice with the free radical scavenger Tempol or the PARP1 inhibitor 3-aminobenzamide attenuated irradiation-induced activation of TRPM2 and induced significant recovery of salivary fluid secretion. Furthermore, TPL (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl) induced complete recovery of function in irradiated TRPM2-/- mice. These novel data demonstrate that TRPM2 is activated by irradiation, via PARP1 activation, and contributes to irreversible loss of salivary gland function.

Baicalein attenuates impaired hippocampal neurogenesis and the neurocognitive deficits induced by γ-ray radiation

BACKGROUND AND PURPOSE

Whole-brain irradiation (WBI) therapy produces learning and memory deficits in patients with brain tumours. Although the pathological cascade of cognitive deficits remains unknown, it may involve reduced neurogenesis within the hippocampus. Baicalein is a flavonoid derived from the roots of Huangqin, Scutellaria baicalensis Georgi, and has been shown to have antioxidant effects. Here, we have investigated the protective effects of baicalein on irradiation-induced impairments in hippocampal neurogenesis and cognitive function.

EXPERIMENTAL APPROACH

Radioprotective effects of baicalein were evaluated in C17.2 neural progenitor cells and 6-week-old male C57BL/6 mice during hippocampal neurogenesis. Mice were given a single dose of 5 Gy WBI. Changes in hippocampal neurogenesis, oxidative stress and BDNF-pCREB signalling were evaluated. Morris water maze and passive avoidance test were used to assess learning and memory.

KEY RESULTS

Baicalein protected neural progenitor cells against irradiation-induced necrotic cell death. Pretreatment with baicalein attenuated the irradiation-induced impairment of hippocampal neurogenesis by modulating oxidative stress and elevating BDNF-pCREB signalling. Furthermore, baicalein prevented the spatial learning and memory retention deficits follwing WBI.

CONCLUSIONS AND IMPLICATIONS

Our findings suggest that baicalein can be viewed as a potential therapeutic agent that protects against the impaired neurogenesis induced by WBI, and its neurocognitive consequences.

Nicaraven attenuates radiation-induced injury in hematopoietic stem/progenitor cells in mice

Nicaraven, a chemically synthesized hydroxyl radical-specific scavenger, has been demonstrated to protect against ischemia-reperfusion injury in various organs. We investigated whether nicaraven can attenuate radiation-induced injury in hematopoietic stem/progenitor cells, which is the conmen complication of radiotherapy and one of the major causes of death in sub-acute phase after accidental exposure to high dose radiation. C57BL/6 mice were exposed to 1 Gy γ-ray radiation daily for 5 days in succession (a total of 5 Gy), and given nicaraven or a placebo after each exposure. The mice were sacrificed 2 days after the last radiation treatment, and the protective effects and relevant mechanisms of nicaraven in hematopoietic stem/progenitor cells with radiation-induced damage were investigated by ex vivo examination. We found that post-radiation administration of nicaraven significantly increased the number, improved the colony-forming capacity, and decreased the DNA damage of hematopoietic stem/progenitor cells. The urinary levels of 8-oxo-2′-deoxyguanosine, a marker of DNA oxidation, were significantly lower in mice that were given nicaraven compared with those that received a placebo treatment, although the levels of intracellular and mitochondrial reactive oxygen species in the bone marrow cells did not differ significantly between the two groups. Interestingly, compared with the placebo treatment, the administration of nicaraven significantly decreased the levels of the inflammatory cytokines IL-6 and TNF-α in the plasma of mice. Our data suggest that nicaraven effectively diminished the effects of radiation-induced injury in hematopoietic stem/progenitor cells, which is likely associated with the anti-oxidative and anti-inflammatory properties of this compound.

Placental extract protects bone marrow-derived stem/progenitor cells against radiation injury through anti-inflammatory activity

Placental extracts have been reported to have anti-oxidative and anti-inflammatory activities. Because there is increasing evidence that ionizing radiation induces the release of reactive oxygen species (ROS) and inflammatory cytokines, we examined the protective effects of a placental extract against radiation injury. C57BL/6 mice were exposed to 1 Gy of γ-ray radiation every day for 5 days, and placental extract (1 mg/day) was administrated orally soon after each exposure. At 2 days after the last irradiation, mice were euthanized to examine the numbers, colony-forming capacity, and DNA damage of stem/progenitor cells in the peripheral blood and bone marrow. To understand the related mechanisms, we also measured the levels of intracellular and mitochondrial ROS, and 8-OHdG in the plasma and urine, and IL-6 and TNF-α in the plasma. Compared with the placebo treatment, oral administration of placental extract significantly increased the number and colony-forming capacity, but decreased the DNA damage of bone marrow stem/progenitor cells. However, neither the levels of intracellular and mitochondrial ROS in bone marrow cells, nor the levels of 8-OHdG in the urine and plasma significantly differed between groups. Interestingly, in comparison with the placebo treatment, placental extract significantly decreased the levels of the inflammatory cytokines IL-6 and TNF-α in the plasma. Placental extract significantly attenuated the acute radiation injury to bone marrow-derived stem/progenitor cells, and this protection is likely to be related to the anti-inflammatory activity of the placental extract.

Exposure to heavy ion radiation induces persistent oxidative stress in mouse intestine

Ionizing radiation-induced oxidative stress is attributed to generation of reactive oxygen species (ROS) due to radiolysis of water molecules and is short lived. Persistent oxidative stress has also been observed after radiation exposure and is implicated in the late effects of radiation. The goal of this study was to determine if long-term oxidative stress in freshly isolated mouse intestinal epithelial cells (IEC) is dependent on radiation quality at a dose relevant to fractionated radiotherapy. Mice (C57BL/6J; 6 to 8 weeks; female) were irradiated with 2 Gy of γ-rays, a low-linear energy transfer (LET) radiation, and intestinal tissues and IEC were collected 1 year after radiation exposure. Intracellular ROS, mitochondrial function, and antioxidant activity in IEC were studied by flow cytometry and biochemical assays. Oxidative DNA damage, cell death, and mitogenic activity in IEC were assessed by immunohistochemistry. Effects of γ radiation were compared to ⁵⁶Fe radiation (iso-toxic dose: 1.6 Gy; energy: 1000 MeV/nucleon; LET: 148 keV/µm), we used as representative of high-LET radiation, since it's one of the important sources of high Z and high energy (HZE) radiation in cosmic rays. Radiation quality affected the level of persistent oxidative stress with higher elevation of intracellular ROS and mitochondrial superoxide in high-LET ⁵⁶Fe radiation compared to unirradiated controls and γ radiation. NADPH oxidase activity, mitochondrial membrane damage, and loss of mitochondrial membrane potential were greater in ⁵⁶Fe-irradiated mice. Compared to γ radiation oxidative DNA damage was higher, cell death ratio was unchanged, and mitotic activity was increased after ⁵⁶Fe radiation. Taken together our results indicate that long-term functional dysregulation of mitochondria and increased NADPH oxidase activity are major contributing factors towards heavy ion radiation-induced persistent oxidative stress in IEC with potential for neoplastic transformation.