Amplification of the gamma-irradiation-induced cell death pathway by reactive oxygen species in human U937 cells

Biomarkers of mitochondrial stress and DNA damage during pediatric catheter-directed neuroangiography - a prospective single-center study

BACKGROUND

Neuroangiography represents a critical diagnostic and therapeutic imaging modality whose associated radiation may be of concern in children. The availability of in vivo radiation damage markers would represent a key advancement for understanding radiation effects and aid in the development of radioprotective strategies.

OBJECTIVE

Determine if biomarkers of cellular damage can be detected in the peripheral blood mononuclear cells (PBMC) of children undergoing neuroangiography.

MATERIALS AND METHODS

Prospective single-site study of 27 children. Blood collected pre and post neuroangiography, from which PBMC were isolated and assayed for biomarkers of mitochondrial stress (mitochondrial membrane potential (MMP), reactive oxygen species (ROS), and mitochondrial DNA (mtDNA)) and DNA damage (γH2AX). Dose response of biomarkers vs. radiation dose was analyzed using linear regressions. The cohort was divided into higher (HD) and lower dose (LD) groups and analyzed using linear mixed models and compared using Welch's t-tests.

RESULTS

No biomarker exhibited a dose-dependent response following radiation (γH2AX: R2 = 0.0012, P = 0.86; MMP: R2 = 0.016, P = 0.53; mtDNA: R2 = 0.10, P = 0.11; ROS: R2 = 0.0023, P = 0.81). Groupwise comparisons showed no significant differences in γH2AX or ROS after radiation (γH2AX: LD: 0.6 ± 6.0, P = 0.92; HD: -7.5 ± 6.3 AU, P = 0.24; ROS: LD: 1.3 ± 2.8, P = 0.64; HD: -3.6 ± 3.0 AU, P = 0.24). Significant changes were observed to mitochondrial markers MMP (-53.7 ± 14.7 AU, P = 0.0014) and mtDNA (-1.1 ± 0.4 AU, P = 0.0092) for HD, but not the LD group (MMP: 26.1 ± 14.7 AU, P = 0.090; mtDNA: 0.2 ± 0.4, P = 0.65).

CONCLUSIONS

Biomarkers of mitochondrial stress in PBMC were identified during pediatric neuroangiography and warrant further investigation for radiation biodosimetry. However, isolating radiation-specific effects from those of procedural stress and general anesthesia requires further investigation.

Mitochondrial reactive oxygen species impact human fibroblast responses to protracted γ-ray exposures

Purpose: Continuous exposure to ionizing radiation at a low dose rate poses significant health risks to humans on deep space missions, prompting the need for mechanistic studies to identify countermeasures against its deleterious effects. Mitochondria are a major subcellular locus of radiogenic injury, and may trigger secondary cellular responses through the production of reactive oxygen species (mtROS) with broader biological implications. Methods and Materials: To determine the contribution of mtROS to radiation-induced cellular responses, we investigated the impacts of protracted γ-ray exposures (IR; 1.1 Gy delivered at 0.16 mGy/min continuously over 5 days) on mitochondrial function, gene expression, and the protein secretome of human HCA2-hTERT fibroblasts in the presence and absence of a mitochondria-specific antioxidant mitoTEMPO (MT; 5 µM). Results: IR increased fibroblast mitochondrial oxygen consumption (JO2) and H2O2 release rates (JH2O2) under energized conditions, which corresponded to higher protein expression of NADPH Oxidase (NOX) 1, NOX4, and nuclear DNA-encoded subunits of respiratory chain Complexes I and III, but depleted mtDNA transcripts encoding subunits of the same complexes. This was associated with activation of gene programs related to DNA repair, oxidative stress, and protein ubiquination, all of which were attenuated by MT treatment along with radiation-induced increases in JO2 and JH2O2. IR also increased secreted levels of interleukin-8 and Type I collagens, while decreasing Type VI collagens and enzymes that coordinate assembly and remodeling of the extracellular matrix. MT treatment attenuated many of these effects while augmenting others, revealing complex effects of mtROS in fibroblast responses to IR. Conclusion: These results implicate mtROS production in fibroblast responses to protracted radiation exposure, and suggest potentially protective effects of mitochondrial-targeted antioxidants against radiogenic tissue injury in vivo.

Targeting serine/glycine metabolism improves radiotherapy response in non-small cell lung cancer

BACKGROUND

Lung cancer is the most lethal cancer, and 85% of cases are classified as non-small cell lung cancer (NSCLC). Metabolic rewiring is a cancer hallmark that causes treatment resistance, and lacks insights into serine/glycine pathway adaptations upon radiotherapy.

METHODS

We analyzed radiotherapy responses using mass-spectrometry-based metabolomics in NSCLC patient's plasma and cell lines. Efficacy of serine/glycine conversion inhibitor sertraline with radiotherapy was investigated by proliferation, clonogenic and spheroid assays, and in vivo using a serine/glycine dependent NSCLC mouse model by assessment of tumor growth, metabolite and cytokine levels, and immune signatures.

RESULTS

Serine/glycine pathway metabolites were significantly consumed in response to radiotherapy in NSCLC patients and cell models. Combining sertraline with radiotherapy impaired NSCLC proliferation, clonogenicity and stem cell self-renewal capacity. In vivo, NSCLC tumor growth was reduced solely in the sertraline plus radiotherapy combination treatment group. Tumor weights linked to systemic serine/glycine pathway metabolite levels, and were inhibited in the combination therapy group. Interestingly, combination therapy reshaped the tumor microenvironment via cytokines associated with natural killer cells, supported by eradication of immune checkpoint galectin-1 and elevated granzyme B levels.

CONCLUSION

Our findings highlight that targeting serine/glycine metabolism using sertraline restricts cancer cell recovery from radiotherapy and provides tumor control through immunomodulation in NSCLC.

Mitophagy plays a "double-edged sword" role in the radiosensitivity of cancer cells

Mitochondria are organelles with double-membrane structure of inner and outer membrane, which provides main energy support for cell growth and metabolism. Reactive oxygen species (ROS) mainly comes from mitochondrial and can cause irreversible damage to cells under oxidative stress. Thus, mitochondrial homeostasis is the basis for maintaining the normal physiological function of cells and mitophagy plays a pivotal role in the maintenance of mitochondrial homeostasis. At present, to enhance the sensitivity of cancer cells to radiotherapy and chemotherapy by regulating mitochondria has increasingly become a hot spot of cancer therapy. It is particularly important to study the effect of ionizing radiation (IR) on mitochondria and the role of mitophagy in the radiosensitivity of cancer cells. Most of the existing reviews have focused on mitophagy-related molecules or pathways and the impact of mitophagy on diseases. In this review, we mainly focus on discussing the relationship between mitophagy and radiosensitivity of cancer cells around mitochondria and IR.

The role of PKC in X-ray-induced megakaryocyte apoptosis and thrombocytopenia

Thrombocytopenia is a critical complication after radiation therapy and exposure. Dysfunction of megakaryocyte development and platelet production are key pathophysiological stages in ionizing radiation (IR)-induced thrombocytopenia. Protein kinase C (PKC) plays an important role in regulating megakaryocyte development and platelet production. However, it remains unclear how PKC regulates IR-induced megakaryocyte apoptosis. In this study, we found that pretreatment of PKC pan-inhibitor Go6983 delayed IR-induced megakaryocyte apoptosis, and inhibited IR-induced mitochondrial membrane potential and ROS production in CMK cells. Moreover, suppressing PKC activation inhibited cleaved caspase3 expression and reduced p38 phosphorylation levels, and IR-induced PKC activation might be regulated by p53. In vivo experiments confirmed that Go6983 promoted platelet count recovery after 21 days of 3 Gy total body irradiation. Furthermore, Go6983 reduced megakaryocyte apoptosis, increased the number of megakaryocyte and polyploid formation in bone marrow, and improved the survival rate of 6 Gy total body irradiation. In conclusion, our results provided a potential therapeutic target for IR-induced thrombocytopenia.

Possible relationship between mitochondrial changes and oxidative stress under low dose-rate irradiation

Objectives: High dose-rate ionizing radiation (IR) causes severe DSB damage, as well as reactive oxygen species (ROS) accumulation and oxidative stress. However, it is unknown what biological processes are affected by low dose-rate IR; therefore, the molecular relationships between mitochondria changes and oxidative stress in human normal cells was investigated after low dose-rate IR.Methods: We compared several cellular response between high and low dose-rate irradiation using cell survival assay, ROS/RNS assay, immunofluorescence and western blot analysis.Results: Reduced DSB damage and increased levels of ROS, with subsequent oxidative stress responses, were observed in normal cells after low dose-rate IR. Low dose-rate IR caused several mitochondrial changes, including morphology mass, and mitochondrial membrane potential, suggesting that mitochondrial damage was caused. Although damaged mitochondria were removed by mitophagy to stop ROS leakage, the mitophagy-regulatory factor, PINK1, was reduced following low dose-rate IR. Although mitochondrial dynamics (fission/fusion events) are important for the proper mitophagy process, some mitochondrial fusion factors decreased following low dose-rate IR.Discussion: The dysfunction of mitophagy pathway under low dose-rate IR increased ROS and the subsequent activation of the oxidative stress response.

Role of Mitochondria in Radiation Responses: Epigenetic, Metabolic, and Signaling Impacts

Until recently, radiation effects have been considered to be mainly due to nuclear DNA damage and their management by repair mechanisms. However, molecular biology studies reveal that the outcomes of exposures to ionizing radiation (IR) highly depend on activation and regulation through other molecular components of organelles that determine cell survival and proliferation capacities. As typical epigenetic-regulated organelles and central power stations of cells, mitochondria play an important pivotal role in those responses. They direct cellular metabolism, energy supply and homeostasis as well as radiation-induced signaling, cell death, and immunological responses. This review is focused on how energy, dose and quality of IR affect mitochondria-dependent epigenetic and functional control at the cellular and tissue level. Low-dose radiation effects on mitochondria appear to be associated with epigenetic and non-targeted effects involved in genomic instability and adaptive responses, whereas high-dose radiation effects (>1 Gy) concern therapeutic effects of radiation and long-term outcomes involving mitochondria-mediated innate and adaptive immune responses. Both effects depend on radiation quality. For example, the increased efficacy of high linear energy transfer particle radiotherapy, e.g., C-ion radiotherapy, relies on the reduction of anastasis, enhanced mitochondria-mediated apoptosis and immunogenic (antitumor) responses.

Weak Magnetic Fields Enhance the Efficacy of Radiation Therapy

Purpose

The clinical efficacy of radiation therapy is mechanistically linked to ionization-induced free radicals that cause cell and tissue injury through direct and indirect mechanisms. Free radical reaction dynamics are influenced by many factors and can be manipulated by static weak magnetic fields (WMF) that perturb singlet-triplet state interconversion. Our study exploits this phenomenon to directly increase ionizing radiation (IR) dose absorption in tumors by combining WMF with radiation therapy as a new and effective method to improve treatment.

Methods and Materials

Coils were custom made to produce both homogeneous and gradient magnetic fields. The gradient coil enabled simultaneous in vitro assessment of free radical/reactive oxygen species reactivity across multiple field strengths from 6 to 66 G. First, increases in IR-induced free radical concentrations using oxidant-sensitive fluorescent dyes in a cell-free system were measured and verified. Next, human and murine cancer cell lines were evaluated in in vitro and in vivo models after exposure to clinically relevant doses of IR in combination with WMF.

Results

Cellular responses to IR and WMF were field strength and cell line dependent. WMF was able to enhance IR effects on reactive oxygen species formation, DNA double-strand break formation, cell death, and tumor growth.

Conclusions

We demonstrate that the external presence of a magnetic field enhances radiation-induced cancer cell injury and death in vitro and in vivo. The effect extends beyond the timeframe when free radicals are induced in the presence of radiation into the window when endogenous free radicals are produced and therefore extends the applicability of this novel adjunct to cancer therapy in the context of radiation treatment.

Role of Commensal Microbes in the γ-Ray Irradiation-Induced Physiological Changes in Drosophila melanogaster

Ionizing radiation induces biological/physiological changes and affects commensal microbes, but few studies have examined the relationship between the physiological changes induced by irradiation and commensal microbes. This study investigated the role of commensal microbes in the γ-ray irradiation-induced physiological changes in Drosophila melanogaster. The bacterial load was increased in 5 Gy irradiated flies, but irradiation decreased the number of operational taxonomic units. The mean lifespan of conventional flies showed no significant change by irradiation, whereas that of axenic flies was negatively correlated with the radiation dose. γ-Ray irradiation did not change the average number of eggs in both conventional and axenic flies. Locomotion of conventional flies was decreased after 5 Gy radiation exposure, whereas no significant change in locomotion activity was detected in axenic flies after irradiation. γ-Ray irradiation increased the generation of reactive oxygen species in both conventional and axenic flies, but the increase was higher in axenic flies. Similarly, the amounts of mitochondria were increased in irradiated axenic flies but not in conventional flies. These results suggest that axenic flies are more sensitive in their mitochondrial responses to radiation than conventional flies, and increased sensitivity leads to a reduced lifespan and other physiological changes in axenic flies.

STK11/LKB1 Mutations in NSCLC Are Associated with KEAP1/NRF2-Dependent Radiotherapy Resistance Targetable by Glutaminase Inhibition

PURPOSE

Radiotherapy with or without chemotherapy is a mainstay of treatment for locally advanced non-small cell lung cancer (NSCLC), but no predictive markers are currently available to select patients who will benefit from these therapies. In this study, we investigated the association between alterations in STK11/LKB1, the second most common tumor suppressor in NSCLC, and response to radiotherapy as well as potential therapeutic approaches to improve outcomes.

EXPERIMENTAL DESIGN

We conducted a retrospective analysis of 194 patients with stage I-III NSCLC, including 164 stage III patients bearing mutant or wild-type STK11/LKB1 treated with radiotherapy, and assessed locoregional recurrence (LRR), distant metastasis rates, disease-free survival (DFS), and overall survival (OS), and we investigated the causal role of LKB1 in mediating radiotherapy resistance using isogenic pairs of NSCLC cell lines with LKB1 loss or gain.

RESULTS

In stage III patients, with 4 years median follow-up, STK11/LKB1 mutations were associated with higher LRR (P = 0.0108), and shorter DFS (HR 2.530, P = 0.0029) and OS (HR 2.198, P = 0.0263). LKB1 loss promoted relative resistance to radiotherapy, which was dependent on the KEAP1/NRF2 pathway for redox homeostasis. Suppression of the KEAP1/NRF2 pathway via KEAP1 expression, or pharmacologic blockade of glutaminase (GLS) 1 sensitized LKB1-deficient tumors to radiotherapy.

CONCLUSIONS

These data provide evidence that LKB1 loss is associated with LRR and poor clinical outcomes in patients with NSCLC treated with radiotherapy and that targeting the KEAP1/NRF2 pathway or GLS inhibition are potential approaches to radiosensitize LKB1-deficient tumors.

Degradation of nuclear and mitochondrial DNA after γ-irradiation and its effect on forensic genotyping

Forensic genotyping can be impeded by γ-irradiation of biological evidence in the event of radiological crime; that is, criminal activity involving radioactive material. Oxidative effects within the mitochondria of living cells elicits greater damage to mitochondrial DNA (mtDNA) than nuclear DNA (nuDNA) at low doses. This study presents a novel approach for the assessment of nuDNA versus mtDNA damage from a comparison of genotype and quantity data, while exploring likely mechanisms for differential damage after high doses of γ-irradiation. Liquid (hydrated) and dried (dehydrated) whole blood samples were exposed to high doses of γ-radiation (1-50 kilogray, kGy). The GlobalFiler PCR Amplification Kit was used to evaluate short tandem repeat (STR) genotyping efficacy and nuDNA degradation; a comparison was made to mtDNA degradation measured using real-time PCR assays. Each assay was normalized before comparison by calculation of integrity indices relative to unirradiated controls. Full STR profiles were attainable up to the highest dose, although DNA degradation was noticeable after 10 and 25 kGy for hydrated and dehydrated blood, respectively. This was manifested by heterozygote imbalance more than allele dropout. Degradation was greater for mtDNA than nuDNA, as well as for hydrated than dehydrated cells, after equivalent doses. Oxidative effects due to water radiolysis and mitochondrial function are dominant mechanisms of differential damage to nuDNA versus mtDNA after high-dose γ-irradiation. While differential DNA damage was reduced by cell desiccation, its persistence after drying indicates innate differences between nuDNA and mtDNA radioresistance and/or continued oxidative effects within the mitochondria.

Phlorotannins from Undaria pinnatifida Sporophyll: Extraction, Antioxidant, and Anti-Inflammatory Activities

Undaria pinnatifida sporophyll (U. pinnatifida) is a major byproduct of U. pinnatifida (a brown algae) processing. Its phenolic constituents, phlorotannins, are of special interest due to their intrinsic ability to precipitate proteins. Herein, a high-temperature extraction procedure was used to isolate these biologically active compounds. The heating temperature, heating time, and extraction solvent (ethanol) concentration were examined with response surface analysis to determine the optimal conditions to achieve the maximum extraction rate. The analysis revealed the optimal conditions to be: 170 °C of heating temperature, 5.2 h of heating time, and 52% ethanol concentration for a yield of 10.7 ± 0.2 mg gallic acid equivalent/g dry weight (GAE/g DW) of sample. Compared to epigallocatechin gallate (EGCG), the extracted phlorotannins displayed higher antioxidant activity on H2O2-induced RAW 264.7 cells with improved efficiency. Furthermore, the compounds exhibited strong anti-inflammatory activity. These findings potentially can be utilized to guide development of novel functional foods and food supplements from sea-originated resources such as brown algae.

Slowly Reducible Genetically Encoded Green Fluorescent Indicator for In Vivo and Ex Vivo Visualization of Hydrogen Peroxide

Hydrogen peroxide (H₂O₂) plays an important role in modulating cell signaling and homeostasis in live organisms. The HyPer family of genetically encoded indicators allows the visualization of H₂O₂ dynamics in live cells within a limited field of view. The visualization of H₂O₂ within a whole organism with a single cell resolution would benefit from a slowly reducible fluorescent indicator that integrates the H₂O₂ concentration over desired time scales. This would enable post hoc optical readouts in chemically fixed samples. Herein, we report the development and characterization of NeonOxIrr, a genetically encoded green fluorescent indicator, which rapidly increases fluorescence brightness upon reaction with H₂O₂, but has a low reduction rate. NeonOxIrr is composed of circularly permutated mNeonGreen fluorescent protein fused to the truncated OxyR transcription factor isolated from E. coli. When compared in vitro to a standard in the field, HyPer3 indicator, NeonOxIrr showed 5.9-fold higher brightness, 15-fold faster oxidation rate, 5.9-fold faster chromophore maturation, similar intensiometric contrast (2.8-fold), 2-fold lower photostability, and significantly higher pH stability both in reduced (pK_a of 5.9 vs. ≥7.6) and oxidized states (pK_a of 5.9 vs.≥ 7.9). When expressed in the cytosol of HEK293T cells, NeonOxIrr demonstrated a 2.3-fold dynamic range in response to H₂O₂ and a 44 min reduction half-time, which were 1.4-fold lower and 7.6-fold longer than those for HyPer3. We also demonstrated and characterized the NeonOxIrr response to H₂O₂ when the sensor was targeted to the matrix and intermembrane space of the mitochondria, nucleus, cell membranes, peroxisomes, Golgi complex, and endoplasmic reticulum of HEK293T cells. NeonOxIrr could reveal endogenous reactive oxygen species (ROS) production in HeLa cells induced with staurosporine but not with thapsigargin or epidermal growth factor. In contrast to HyPer3, NeonOxIrr could visualize optogenetically produced ROS in HEK293T cells. In neuronal cultures, NeonOxIrr preserved its high 3.2-fold dynamic range to H₂O₂ and slow 198 min reduction half-time. We also demonstrated in HeLa cells that NeonOxIrr preserves a 1.7-fold ex vivo dynamic range to H₂O₂ upon alkylation with N-ethylmaleimide followed by paraformaldehyde fixation. The same alkylation-fixation procedure in the presence of NP-40 detergent allowed ex vivo detection of H₂O₂ with 1.5-fold contrast in neuronal cultures and in the cortex of the mouse brain. The slowly reducible H₂O₂ indicator NeonOxIrr can be used for both the in vivo and ex vivo visualization of ROS. Expanding the family of fixable indicators may be a promising strategy to visualize biological processes at a single cell resolution within an entire organism.

Protective Effect of Antrodia cinnamomea Extract against Irradiation-Induced Acute Hepatitis

Radiotherapy for treatment of hepatocellular carcinoma causes severe side effects, including acute hepatitis and chronic fibrosis. Complementary and alternative medicine (CAM) has emerged as an important part of integrative medicine in the management of diseases. Antrodia cinnamomea (AC), a valuable medicinal fungus originally found only in Taiwan, has been shown to possess anti-oxidation, vaso-relaxtation, anti-inflammation, anti-hepatitis, and anti-cancer effects. In this paper we evaluate the protective effects of ethanol extract of Antrodia cinnamomea (ACE) against radiotoxicity both in normal liver cell line CL48 and in tumor-bearing mice. In CL48, ACE protects cells by eliminating irradiation-induced reactive oxygen species (ROS) through the induction of Nrf2 and the downstream redox system enzymes. The protective effect of ACE was also demonstrated in tumor-bearing mice by alleviating irradiation-induced acute hepatitis. ACE could also protect mice from CCl₄-induced hepatitis. Since both radiation and CCl₄ cause free radicals, these results indicate that ACE likely contains active components that protect normal liver cells from free radical attack and can potentially benefit hepatocellular carcinoma (HCC) patients during radiotherapy.

Hydroxysafflor yellow A attenuates high glucose-induced pancreatic β-cells oxidative damage via inhibiting JNK/c-jun signaling pathway

Pancreatic β-cells apoptosis and dysfunction induced by glucose toxicity were attributed to the formation of excess oxidative damage. Some studies have found that hydroxysafflor yellow A has strong effects to scavenge oxidative stress and inhibit apoptosis. In order to explore the influence of HSYA on oxidative stress induced by high glucose and the potential mechanisms, we set up a high glucose damage model and induced oxidative stress in INS-1 rat insulinoma cells. N-acetylcysteine was added as a group of oxidative stress scavenger. After 72 h of cultivation, the related indexes of oxidative stress (reactive oxygen species, catalase, glutathione peroxidase, lipid peroxidation, and superoxide dismutase), apoptosis (caspase3, parp) and the function of glucose stimulated insulin secretion were determined. In addition, the signaling pathway proteins of C-Jun NH2 -terminal kinases (JNK), phosphorylated JNK, C-jun, phosphorylated C-jun were evaluated. Fluorescence microscopy, qRT-PCR, western blotting were the main methods used in the experiment. Our results showed that hydroxysafflor yellow A reduced pancreatic β-cells apoptosis by attenuating oxidative damage, and JNK/c-Jun signaling pathway was involved. It indicated a significant mechanism for the positive impacts of HSYA on oxidative stress induced by high glucose, and provide important basis for using HSYA in diabetic prevention and therapy.

Potential relationship between the biological effects of low-dose irradiation and mitochondrial ROS production

Exposure to ionizing radiation (IR) induces various types of DNA damage, of which DNA double-strand breaks are the most severe, leading to genomic instability, tumorigenesis, and cell death. Hence, cells have developed DNA damage responses and repair mechanisms. IR also causes the accumulation of endogenous reactive oxidative species (ROS) in the irradiated cells. Upon exposure to low-dose irradiation, the IR-induced biological effects mediated by ROS were relatively more significant than those mediated by DNA damage. Accumulating evidence suggests that such increase in endogenous ROS is related with mitochondria change in irradiated cells. Thus, in this review we focused on the mechanism of mitochondrial ROS production and its relationship to the biological effects of IR. Exposure of mammalian cells to IR stimulates an increase in the production of endogenous ROS by mitochondria, which potentially leads to mitochondrial dysfunction. Since the remains of damaged mitochondria could generate or leak more ROS inside the cell, the damaged mitochondria are removed by mitophagy. The disruption of this pathway, involved in maintaining mitochondrial integrity, could lead to several disorders (such as neurodegeneration) and aging. Thus, further investigation needs to be performed in order to understand the relationship between the biological effects of low-dose IR and mitochondrial integrity.

JNK Inhibitor SP600125 Attenuates Paraquat-Induced Acute Lung Injury: an In Vivo and In Vitro Study

Acute lung injury (ALI) is a major complication soon after paraquat poisoning and rapidly progresses with high mortality. However, the specific mechanism underlying paraquat-induced ALI is still unclear. In this study, the mechanism underlying the protective effects of SP600125 on paraquat-induced ALI was investigated according to oxidative stress, inflammation, and apoptosis. The rats were randomly assigned into the control group (CON), the paraquat poisoning group (PQ), and the PQ + SP600125 group (SP). A549 cells were divided into the Con group, Pq group, and Sp group. H&E staining and detection of lung wet/dry ratio were employed to evaluate lung injury. Annexin V-PI staining was done to evaluate A549 cell apoptosis. Dihydroethidium fluorescence was used to measure reactive oxygen species (ROS) in the lungs and A549 cells. ELISA was performed to detect TNF-α and IL-6 in the supernatant of bronchoalveolar lavage fluid (BALF) and A549 cells. RT-qPCR was done to measure the messenger RNA (mRNA) expression of TNF-α and IL-6 in the lungs and A549 cells. Western blotting assay was performed to detect the protein expression of phospho-JNK, total JNK, and cleaved caspase-3. Electrophoretic mobility shift assay was employed to detect the DNA binding activities of AP-1 and P-p65. JNK inhibitor SP600125 reduced JNK phosphorylation, downregulated cleaved caspase-3 protein level, decreased AP-1 transcriptional activity and ROS level, and reduced the transcription and expression of TNF-α and IL-6, which improved ALI and cell apoptosis after paraquat poisoning. Our results indicate that JNK/AP-1 mediates ALI as well as oxidative stress and inflammation deterioration secondary to paraquat poisoning.

Calcifying nanoparticles induce cytotoxicity mediated by ROS-JNK signaling pathways

Calcifying nanoparticles (CNPs) play an important role in kidney stone formation, but the mechanism(s) are unclear. CNPs were isolated and cultured from midstream urine of patients with kidney stones. CNP morphology and characteristics were examined by electron microscopy and electrophoresis analysis. Chemical composition was analyzed using energy-dispersive X-ray microanalysis and Western blotting. Human renal proximal convoluted tubule cell (HK-2) cultures were exposed to CNPs for 0, 12 and 72 h, and production of reactive oxygen species (ROS), mitochondrial membrane potential and apoptosis levels were evaluated. CNPs isolated from patients showed classical morphology, the size range of CNPs were 15-500 nm and negative charge; they were found to contain fetuin-A. Exposure of HK-2 cells to CNPs induced ROS production, decreased mitochondrial membrane potential and decreased cell viability. Transmission electron microscopy showed that CNPs can enter the cell by phagocytosis, and micrographs revealed signs of apoptosis and autophagy. CNPs increased the proportion of apoptotic cells, down-regulated Bcl-2 expression and up-regulated Bax expression. CNPs also up-regulated expression of LC3-B, Beclin-1and p-JNK.CNPs are phagocytosed by HK-2 cells, leading to autophagy, apoptosis and ROS production, in part through activation of JNK signaling pathways. ROS and JNK pathways may contribute to CNP-induced cell injury and kidney stone formation.

AMRI-59 functions as a radiosensitizer via peroxiredoxin I-targeted ROS accumulation and apoptotic cell death induction

Previously, we identified AMRI-59 as a specific pharmaceutical inhibitor of peroxiredoxin (PRX) I enzyme activity. In this study, we examined whether AMRI-59 acts as a radiosensitizer in non-small cell lung cancer cells using clonogenic assays. The intracellular mechanisms underlying the radiosensitization effect of AMRI-59 were determined via immunoblotting in addition to measurement of ROS generation, mitochondrial potential and cell death. AMRI-59 activity in vivo was examined by co-treating nude mice with the compound and γ-ionizing radiation (IR), followed by measurement of tumor volumes and apoptosis. The dose enhancement ratios of 30 μM AMRI-59 in NCI-H460 and NCI-H1299 were 1.51 and 2.12, respectively. Combination of AMRI-59 with IR augmented ROS production and mitochondrial potential disruption via enhancement of PRX I oxidation, leading to increased expression of γH2AX, a DNA damage marker, and suppression of ERK phosphorylation, and finally, activation of caspase-3. Notably, inhibition of ROS production prevented ERK suppression, and blockage of ERK in combination with AMRI-59 and IR led to enhanced caspase-3 activation and apoptosis. In a xenograft assay using NCI-H460 and NCI-H1299, combined treatment with AMRI-59 and IR delayed tumor growth by 26.98 and 14.88 days, compared with controls, yielding enhancement factors of 1.73 and 1.37, respectively. Taken together, the results indicate that AMRI-59 functions as a PRX I-targeted radiosensitizer by inducing apoptosis through activation of the ROS/γH2AX/caspase pathway and suppression of ERK.

Lycium barbarum Polysaccharides Protect Rat Corneal Epithelial Cells against Ultraviolet B-Induced Apoptosis by Attenuating the Mitochondrial Pathway and Inhibiting JNK Phosphorylation

Lycium barbarum polysaccharides (LBPs) have been shown to play a key role in protecting the eyes by reducing the apoptosis induced by certain types of damage. However, it is not known whether LBPs can protect damaged corneal cells from apoptosis. Moreover, no reports have focused on the role of LBPs in guarding against ultraviolet B- (UVB-) induced apoptosis. The present study aimed to investigate the protective effect and underlying mechanism of LBPs against UVB-induced apoptosis in rat corneal epithelial (RCE) cells. The results showed that LBPs significantly prevented the loss of cell viability and inhibited cell apoptosis induced by UVB in RCE cells. LBPs also inhibited UVB-induced loss of mitochondrial membrane potential, downregulation of Bcl-2, and upregulation of Bax and caspase-3. Finally, LBPs attenuated the phosphorylation of c-Jun NH₂-terminal kinase (JNK) triggered by UVB. In summary, LBPs protect RCE cells against UVB-induced damage and apoptosis, and the underlying mechanism involves the attenuation of the mitochondrial apoptosis pathway and the inhibition of JNK phosphorylation.

Bcl-2 family proteins as regulators of cancer cell invasion and metastasis: a review focusing on mitochondrial respiration and reactive oxygen species

Although Bcl-2 family proteins were originally identified as key regulators of apoptosis, an impressive body of evidence has shown that pro-survival members of the Bcl-2 family, including Bcl-2, Bcl-X_L, and Bcl-w, can also promote cell migration, invasion, and cancer metastasis. Interestingly, cell invasion was recently found to be suppressed by multidomain pro-apoptotic members of the Bcl-2 family, such as Bax and Bak. While the mechanisms underlying these new functions of Bcl-2 proteins are just beginning to be studied, reactive oxygen species (ROS) have emerged as inducers of cell invasion and the production of ROS from mitochondrial respiration is known to be promoted and suppressed by the pro-survival and multidomain pro-apoptotic Bcl-2 family members, respectively. Here, I review the evidence supporting the ability of Bcl-2 proteins to regulate cancer cell invasion and metastasis, and discuss our current understanding of their underlying mechanisms, with a particular focus on mitochondrial respiration and ROS, which could have implications for the development of strategies to overcome tumor progression.

Miltirone Is a Dual Inhibitor of P-Glycoprotein and Cell Growth in Doxorubicin-Resistant HepG2 Cells

Miltirone (1), an abietane-type diterpene quinone isolated from Salvia miltiorrhiza, possesses anticancer activity in p-glycoprotein (P-gp)-overexpressing human cancer cells. Results of the current study suggest a dual effect of miltirone on P-gp inhibition and apoptotic induction in a human hepatoma HepG2 cell line and its P-gp-overexpressing doxorubicin-resistant counterpart (R-HepG2). Miltirone (1) elicited a concentration-dependent cytotoxicity, with a similar potency (EC50 ≈ 7-12 μM), in HepG2 and R-HepG2 cells. Miltirone (1) (1.56-6.25 μM) produced synergistic effects on doxorubicin (DOX)-induced growth inhibition of R-HepG2 (synergism: 0.3 < combination index < 0.5). Molecular docking studies illustrated that miltirone (1) interacted with the active site of P-gp with a higher binding affinity than DOX, suggesting that it was a P-gp inhibitor. Flow cytometric analysis confirmed miltirone (1) as a competitive inhibitor of P-gp. At non-necrotic concentrations (1.56-25 μM), miltirone (1) activated caspase-dependent apoptotic pathways and triggered the generation of reactive oxygen species (ROS) and ROS-mediated mitogen-activated protein kinase (MAPK) signaling pathways (e.g., p38 MAPK, stress-activated protein kinase/c-Jun N-terminal kinase, and extracellular regulated kinase 1/2) in both HepG2 and R-HepG2 cells. Thus, we conclude that miltirone (1) is a dual inhibitor of P-gp and cell growth in human drug-resistant hepatoma cells.

Irradiation of necrotic cancer cells, employed for pulsing dendritic cells (DCs), potentiates DC vaccine-induced antitumor immunity against high-grade glioma

Dendritic cell (DC)-based immunotherapy has yielded promising results against high-grade glioma (HGG). However, the efficacy of DC vaccines is abated by HGG-induced immunosuppression and lack of attention toward the immunogenicity of the tumor lysate/cells used for pulsing DCs. A literature analysis of DC vaccination clinical trials in HGG patients delineated the following two most predominantly applied methods for tumor lysate preparation: freeze-thaw (FT)-induced necrosis or FT-necrosis followed by X-ray irradiation. However, from the available clinical evidence, it is unclear which of both methodologies has superior immunogenic potential. Using an orthotopic HGG murine model (GL261-C57BL/6), we observed that prophylactic vaccination with DCs pulsed with irradiated FT-necrotic cells (compared to FT-necrotic cells only) prolonged overall survival by increasing tumor rejection in glioma-challenged mice. This was associated, both in prophylactic and curative vaccination setups, with an increase in brain-infiltrating Th1 cells and cytotoxic T lymphocytes (CTL), paralleled by a reduced accumulation of regulatory T cells, tumor-associated macrophages (TAM) and myeloid-derived suppressor cells (MDSC). Further analysis showed that irradiation treatment of FT-necrotic cells considerably increased the levels of carbonylated proteins — a surrogate-marker of oxidation-associated molecular patterns (OAMPs). Through further application of antioxidants and hydrogen peroxide, we found a striking correlation between the amount of lysate-associated protein carbonylation/OAMPs and DC vaccine-mediated tumor rejection capacity thereby suggesting for the first time a role for protein carbonylation/OAMPs in at least partially mediating antitumor immunity. Together, these data strongly advocate the use of protein oxidation-inducing modalities like irradiation for increasing the immunogenicity of tumor lysate/cells used for pulsing DC vaccines.

Nuclear and cytoplasmic p53 suppress cell invasion by inhibiting respiratory complex-I activity via Bcl-2 family proteins

Although the p53 tumor suppressor/transcription factor often accumulates in the cytoplasm of healthy cells, limited information is available on the cytoplasmic function of p53. Here, we show that cytoplasmic p53 suppresses cell invasion by reducing mitochondrial reactive oxygen species (ROS) levels. Analysis revealed that this function is mediated by Bcl-2 family proteins: Cytoplasmic p53 binds Bcl-w, liberating Bax, which then binds ND5, a subunit of respiratory complex-I, thereby suppressing complex-I activity and thus ROS production. The G13289A mutation of ND5, identified in cancer patients, prevents Bax/ND5 interactions and promotes ROS production and cell invasion. We also showed that Bcl-XL and Bak can substitute for Bcl-w and Bax, respectively, regulating complex-I activity and supporting the cytoplasmic function of p53; nuclear p53 also suppresses complex-I activity by inducing Bax expression. Studies in animal models support the notion that p53 and Bcl-2 family proteins exhibit these functions in vivo. This study demonstrates a link between p53 and Bcl-2 proteins as regulators of ROS production and cellular invasiveness, and reveals complex-I, especially ND5, as their functional target.

Role of the MAPK pathway in the observed bystander effect in lymphocytes co-cultured with macrophages irradiated with γ-rays or carbon ions

AIMS

The radiation-induced bystander effect (RIBE) has potential implications in cancer risks from space particle radiation; however, the mechanisms underlying RIBE are unclear. The role of the MAPK pathway in the RIBEs of different linear energy transfer (LET) was investigated.

MAIN METHODS

Human macrophage U937 cells were irradiated with γ-rays or carbon ions and then co-cultured with nonirradiated HMy2.CIR (HMy) lymphocytes for different periods. The activation of MAPK proteins and the generation of intracellular nitric oxide (NO) and reactive oxygen species (ROS) in the irradiated U937 cells were measured. Micronuclei (MN) formation in the HMy cells was applied to evaluate the bystander damage. Some U937 cells were pretreated with different MAPK inhibitors before irradiation.

KEY FINDINGS

Additional MN formation was induced in the HMy cells after co-culturing with irradiated U937 cells, and the yield of this bystander MN formation was dependent on the co-culture period with γ-ray irradiation but remained high after 1h of co-culture with carbon irradiation. Further investigations disclosed that the time response of the RIBEs had a relationship with LET, where ERK played a different role from JNK and p38 in regulating RIBEs by regulating the generation of the bystander signaling factors NO and ROS.

SIGNIFICANCE

The finding that the RIBE of high-LET radiation could persist for a much longer period than that of γ-rays implies that particle radiation during space flight could have a high risk of long-term harmful effects. An appropriate intervention targeting the MAPK pathway may have significant implications in reducing this risk.

Podophyllotoxin acetate enhances γ-ionizing radiation-induced apoptotic cell death by stimulating the ROS/p38/caspase pathway

To develop a new radiosensitizer against non-small cell lung cancer cells, we screened a natural product library for growth-inhibitory compounds. PA was found to be cytotoxic toward NCI-H460 cells, and its IC₅₀ value was determined. The radiosensitizer effects of PA were tested at its IC₅₀ value in clonogenic and cell-counting assays. The intracellular mechanism underlying this effect was determined by immunoblotting and by measuring propidium iodide uptake and ROS generation. The radiosensitizer activity of PA in vivo was tested in nude mice by treating with PA and IR, and measuring tumor volume and assessing apoptosis. PA, tested at its experimentally determined IC₅₀ value (12 nM), enhanced IR-induced death of NCI-H460 cells by increasing apoptosis, yielding a mean calculated dose-enhancement ratio of 1.67. Combination with PA and IR also increased the production of ROS, which subsequently induced phosphorylation of p38, suppressed phosphorylation of ERK, and activated caspase-3, -8, and -9. Notably, inhibition of ROS production prevented p38 phosphorylation, and inhibition of ROS production or p38 activation blocked caspase activation and apoptosis. In a xenograft assay, combination with PA and IR delayed tumor growth by 11.4 days compared with controls, yielding an enhancement factor of 1.48. Collectively, these results indicate that PA functions as a radiosensitizer by enhancing apoptosis through activation of a ROS/p38/caspase pathway and suppression of ERK.

Mitigation of radiation injury by selective stimulation of the LPA(2) receptor

Due to its antiapoptotic action, derivatives of the lipid mediator lysophosphatidic acid (LPA) provide potential therapeutic utility in diseases associated with programmed cell death. Apoptosis is one of the major pathophysiological processes elicited by radiation injury to the organism. Consequently, therapeutic explorations applying compounds that mimic the antiapoptotic action of LPA have begun. Here we present a brief account of our decade-long drug discovery effort aimed at developing LPA mimics with a special focus on specific agonists of the LPA(2) receptor subtype, which was found to be highly effective in protecting cells from apoptosis. We describe new evidence that 2-((3-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)propyl)thio)benzoic acid (GRI977143), a prototypic nonlipid agonist specific to the LPA(2) receptor subtype, rescues apoptotically condemned cells in vitro and in vivo from injury caused by high-dose γ-irradiation. GRI977143 shows the features of a radiomitigator because it is effective in rescuing the lives of mice from deadly levels of radiation when administered 24h after radiation exposure. Our findings suggest that by specifically activating LPA(2) receptors GRI977143 activates the ERK1/2 prosurvival pathway, effectively reduces Bax translocation to the mitochondrion, attenuates the activation of initiator and effector caspases, reduces DNA fragmentation, and inhibits PARP-1 cleavage associated with γ-irradiation-induced apoptosis. GRI977143 also inhibits bystander apoptosis elicited by soluble proapoptotic mediators produced by irradiated cells. Thus, GRI977143 can serve as a prototype scaffold for lead optimization paving the way to more potent analogs amenable for therapeutic exploration. This article is part of a Special Issue entitled Advances in Lysophospholipid Research.

Immunogenic cell death and DAMPs in cancer therapy

Although it was thought that apoptotic cells, when rapidly phagocytosed, underwent a silent death that did not trigger an immune response, in recent years a new concept of immunogenic cell death (ICD) has emerged. The immunogenic characteristics of ICD are mainly mediated by damage-associated molecular patterns (DAMPs), which include surface-exposed calreticulin (CRT), secreted ATP and released high mobility group protein B1 (HMGB1). Most DAMPs can be recognized by pattern recognition receptors (PRRs). In this Review, we discuss the role of endoplasmic reticulum (ER) stress and reactive oxygen species (ROS) in regulating the immunogenicity of dying cancer cells and the effect of therapy-resistant cancer microevolution on ICD.

Establishment of animal model for the analysis of cancer cell metastasis during radiotherapy

Background

Γ-Ionizing radiation (IR) therapy is one of major therapeutic tools in cancer treatment. Nevertheless, γ-IR therapy failed due to occurrence of metastasis, which constitutes a significant obstacle in cancer treatment. The main aim of this investigation was to construct animal model which present metastasis during radiotherapy in a mouse system in vivo and establishes the molecular mechanisms involved.

Materials and methods

The C6L transfectant cell line expressing firefly luciferase (fLuc) was treated with γ-IR, followed by immunoblotting, zymography and invasion assay in vitro. We additionally employed the C6L transfectant cell line to construct xenografts in nude mice, which were irradiated with γ-IR. Irradiated xenograft-containing mice were analyzed via survival curves, measurement of tumor size, and bioluminescence imaging in vivo and ex vivo. Metastatic lesions in organs of mice were further assessed using RT-PCR, H & E staining and immunohistochemistry.

Results

γ-IR treatment of C6L cells induced epithelial-mesenchymal transition (EMT) and increased cell invasion. In irradiated xenograft-containing mice, tumor sizes were decreased dramatically and survival rates extended. Almost all non-irradiated xenograft-containing control mice had died within 4 weeks. However, we also observed luminescence signals in about 22.5% of γ-IR-treated mice. Intestines or lungs of mice displaying luminescence signals contained several lesions, which expressed the fLuc gene and presented histological features of cancer tissues as well as expression of EMT markers.

Conclusions

These findings collectively indicate that occurrences of metastases during γ-IR treatment accompanied induction of EMT markers, including increased MMP activity. Establishment of a murine metastasis model during γ-IR treatment should aid in drug development against cancer metastasis and increase our understanding of the mechanisms underlying the metastatic process.

Neuroprotective effects of phlorotannins isolated from a brown alga, Ecklonia cava, against H2O2-induced oxidative stress in murine hippocampal HT22 cells

Exposure of neurons to hydrogen peroxide (H(2)O(2)) results in oxidative stress and the activation of a cascade of intracellular toxic events resulting in oxidation, lipid peroxidation, and Ca(2+) elevation, ultimately resulting in cell death. In this study, we attempted to characterize the neuroprotective effects of phlorotannins isolated from Ecklonia cava, including phloroglucinol, eckol, triphloroethol A, eckstolonol, and dieckol, against H(2)O(2)-induced cell damage in murine hippocampus neuronal (HT22) cells. We measured the reactive oxygen species (ROS) and lipid peroxidation levels and evaluated the resultant cell death and alterations in Ca(2+)-concentrations. All phlorotannins were to scavenge intracellular ROS and repress ROS accumulation, thus preventing lipid peroxidation. Consquently, all phlorotannins reduced H(2)O(2)-induced cell death in HT22 cells. Moreover, phlorotannins inhibited H(2)O(2)-induced Ca(2+) release. This study provides a new useful strategy for preventing neuronal H(2)O(2)-induced oxidative stress.

Short-term anoxic conditioning hormesis boosts antioxidant defenses, lowers oxidative damage following irradiation and enhances male sexual performance in the Caribbean fruit fly, Anastrepha suspensa

Most organisms are repeatedly exposed to oxidative stress from multiple sources throughout their lifetimes, potentially affecting all aspects of organismal performance. Here we test whether exposure to a conditioning bout of anoxia early in adulthood induces a hormetic response that confers resistance to oxidative stress and enhances male sexual performance later in life in the Caribbean fruit fly, Anastrepha suspensa. Anoxic conditioning of adults prior to emergence led to an increase in antioxidant capacity driven by mitochondrial superoxide dismutase and glutathione peroxidase. When exposed to gamma irradiation, a strong oxidative stressor, males that received anoxic conditioning had lower lipid and protein oxidative damage at sexual maturity. Anoxia conditioning led to greater male sexual competitiveness compared with unconditioned males when both were irradiated, although there was no effect of anoxia conditioning on mating competitiveness in unirradiated males. Anoxia also led to higher adult emergence rates and greater flight ability in irradiation-stressed flies while preserving sterility. Thus, hormetic treatments that increased antioxidant enzyme activity also improved male performance after irradiation, suggesting that antioxidant enzymes play an important role in mediating the relationship between oxidative stress and sexual selection. Furthermore, our work has important applied implications for the sterile insect technique (SIT), an environmentally friendly method of insect pest control where males are sterilized by irradiation and deployed in the field to disrupt pest populations via mating. We suggest that hormetic treatments specifically designed to enhance antioxidant activity may produce more sexually competitive sterile males, thus improving the efficacy and economy of SIT programs.

Effect of Emblica officinalis (fruit) against UVB-induced photo-aging in human skin fibroblasts

ETHNOPHARMACOLOGICAL RELEVANCE

Emblica officinalis fruit (EO), commonly known as Amla is a reputed traditional medicine and functional food used in Indian subcontinent. It has long been used in Indian folk medicine to treat liver diseases, stomach ulcers, inflammatory diseases, metabolic disorders, geriatric complaints, skin disorders and beauty care.

AIM OF THE STUDY

Recently, it has been shown to promote pro-collagen content and inhibit matrix metalloproteinase levels in skin fibroblast. The aim of the present study was to investigate the efficacy of EO to inhibit UVB-induced photo-aging in human skin fibroblasts.

MATERIALS AND METHODS

Mitochondrial activity of human skin fibroblasts was measured by MTT-assay. Quantifications of pro-collagen 1 and matrix metalloproteinase 1 (MMP-1) release were performed by immunoassay techniques. Hyaluronidase inhibition assay was studied in vitro using bovine testicular hyaluronidase and human umbilical cord hyaluronic acid. Cell cycle analysis was performed by flowcytometry using propidium iodide.

RESULTS

EO stimulated, the otherwise UVB inhibited cellular proliferation and protected pro-collagen 1 against UVB-induced depletion via inhibition of UVB-induced MMP-1 in skin fibroblasts (10-40 μg/mL, p>0.001). EO exhibited inhibitory activity of hyaluronidase (10-40 μg/mL, p>0.001). Treatment with EO also prevented UVB disturbed cell cycle to normal phase.

CONCLUSION

The results of the present study suggests that EO effectively inhibits UVB-induced photo-aging in human skin fibroblast via its strong ROS scavenging ability and its therapeutic and cosmetic applications remain to be explored.

Effect of phlorotannins isolated from Ecklonia cava on melanogenesis and their protective effect against photo-oxidative stress induced by UV-B radiation

In the present study, three kinds of phlorotannins, marine algal polyphenol, were isolated from a brown alga Ecklonia cava, and their inhibitory effect on melanogenesis as well as the protective effect against photo-oxidative stress induced by UV-B radiation was investigated. The effect on melanogenesis was evaluated via the inhibitory effects of tyrosinase and melanin synthesis. Among the phlorotannins, dieckol showed higher effect than that of the other phlorotannins in the both assays; especially the value of dieckol in the tyrosinase inhibition assay was relatively higher than that of a commercial tyrosinase inhibitor (kojic acid). The UV-B protection effect was evaluated via DCFH-DA, MTT, comet assays, and morphological changes in fibroblast. Intracellular ROS induced by UV-B radiation was reduced by the addition of phlorotannins and cell viability was dose-dependently increased. Moreover, dieckol demonstrated strong protective properties against UV-B radiation-induced DNA damage via damaged tail intensity and morphological changes in fibroblast. Hence, these results indicated that dieckol isolated from E. cava has potential whitening effects and prominent protective effects on UV-B radiation-induced cell damages, which might be used in pharmaceutical and cosmeceutical industries.

Reactive oxygen species: A double-edged sword in oncogenesis

Reactive oxygen species (ROS) are molecules or ions formed by the incomplete one-electron reduction of oxygen. Of interest, it seems that ROS manifest dual roles, cancer promoting or cancer suppressing, in tumorigenesis. ROS participate simultaneously in two signaling pathways that have inverse functions in tumorigenesis, Ras-Raf-MEK1/2-ERK1/2 signaling and the p38 mitogen-activated protein kinases (MAPK) pathway. It is well known that Ras-Raf-MEK1/2-ERK1/2 signaling is related to oncogenesis, while the p38 MAPK pathway contributes to cancer suppression, which involves oncogene-induced senescence, inflammation-induced cellular senescence, replicative senescence, contact inhibition and DNA-damage responses. Thus, ROS may not be an absolute carcinogenic factor or cancer suppressor. The purpose of the present review is to discuss the dual roles of ROS in the pathogenesis of cancer, and the signaling pathway mediating their role in tumorigenesis.