The Promoting Effect of Radiation on Glucose Metabolism in Breast Cancer Cells under the Treatment of Cobalt Chloride

Evaluation of the effects of simulated hypoxia by CoCl2 on radioresistance and change of hypoxia-inducible factors in human glioblastoma U87 tumor cell line

PURPOSE

Glioblastoma (GBM) is considered the most common and lethal type of brain tumor with a poor prognosis. GBM treatment has challenges due to its aggressive nature, which often causes treatment failure and recurrence. Hypoxia is one of the characteristics of glioblastoma tumors that contribute to radioresistance and malignant phenotypes of GBM. In this study, we aimed to determine the effects of hypoxia on the radiosensitivity of U87 GBM cells by the hypoxia-mimicking model.

METHODS

Following the treatment of cells with different concentrations of CoCl2, an MTT assay was used to evaluate the cytotoxicity of CoCl2. To understand the effects of Ionizing radiation on CoCl2-treated groups, cells were exposed to irradiation after pretreating with 100 μM CoCl2, and a clonogenic survival assay was performed to determine the radiosensitivity of U87 cells. Also, the intracellular Reactive oxygen level was measured by 2',7'-dichlorofluorescein diacetate (DCFDA) probe staining. Additionally, the expression of hypoxia-associated genes, including HIF-1α, HIF-2α, and their target genes (GLUT-1), was monitored by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Our study revealed that the cell viability of CoCl2-treated cells was decreased in a concentration-dependent manner. Also, CoCl2 did not cause any cytotoxicity on U87 cells at a concentration of 100 μM after treatment for 24 h. Colony formation assay showed that CoCl2 pretreatment induced radioresistance of tumor cells compared to non-treated cells. Also, CoCl2 can protect cells against irradiation by the clearance of ROS. Moreover, Real-time results showed that the mRNA expression of HIF-1α and GLUT-1 were significantly upregulated following hypoxia induction and/or irradiation condition. However, the level of HIF-2α mRNA did not change significantly in hypoxia or irradiation alone conditions, but it increased significantly only in hypoxia + irradiation conditions.

CONCLUSION

Taken together, our results indicated that simulating hypoxia by CoCl2 can effectively increase hypoxia-associated genes, specially HIF-1α and GLUT-1, but did not affect HIF-2α gene expression. Also, it can increase the clearance of ROS, respectively, and it leads to inducing radioresistance of U87 cells.

IDH2: A novel biomarker for environmental exposure in blood circulatory system disorders (Review)

As the risk of harmful environmental exposure is increasing, it is important to find suitable targets for the diagnosis and treatment of the diseases caused. Isocitrate dehydrogenase 2 (IDH2) is an enzyme located in the mitochondria; it plays an important role in numerous cell processes, including maintaining redox homeostasis, participating in the tricarboxylic acid cycle and indirectly taking part in the transmission of the oxidative respiratory chain. IDH2 mutations promote progression in acute myeloid leukemia, glioma and other diseases. The present review mainly summarizes the role and mechanism of IDH2 with regard to the biological effects, such as the mitophagy and apoptosis of animal or human cells, caused by environmental pollution such as radiation, heavy metals and other environmental exposure factors. The possible mechanisms of these biological effects are described in terms of IDH2 expression, reduced nicotine adenine dinucleotide phosphate content and reactive oxygen species level, among other variables. The impact of environmental pollution on human health is increasingly attracting attention. IDH2 may therefore become useful as a potential diagnostic and therapeutic target for environmental exposure-induced diseases.

5-Aminolevulinic acid overcomes hypoxia-induced radiation resistance by enhancing mitochondrial reactive oxygen species production in prostate cancer cells

Background

The naturally occurring amino acid 5-aminolevulinic acid (5-ALA) is a precursor of protoporphyrin IX (PpIX) biosynthesised in the mitochondria. When accumulated PpIX is excited by light (wavelength of 625–635 nm), reactive oxygen species (ROS) are generated. Here, we investigated whether 5-ALA may increase the sensitisation of prostate cancer (PCA) cells to radiotherapy through the generation of ROS via its metabolite, PpIX.

Methods

Effect of 5-ALA on PC-3 and DU-145 PCA cell lines treated with ionising radiation (IR) was examined in vitro and in vivo with assessment by clonogenic assay, mitochondrial function and ROS production under normoxia or hypoxia condition.

Results

5-ALA enhanced intra-mitochondrial ROS production immediately after exposure to IR and decreased mitochondrial membrane potential via increase of intra-cellular PpIX. IR with 5-ALA induced mitochondrial dysfunction and increased ATP production, switching energy metabolism to the quiescence. Under hypoxic condition, ROS burst and mitochondrial dysfunction were induced by IR with 5-ALA resulting reducing cancer stemness and radiation resistance.

Conclusion

These results suggest that combined therapy with 5-ALA and radiation therapy is a novel strategy to improve the anti-cancer effects of radiation therapy for PCA.

Metabolic response to radiation therapy in cancer

Tumor metabolism has emerged as a hallmark of cancer and is involved in carcinogenesis and tumor growth. Reprogramming of tumor metabolism is necessary for cancer cells to sustain high proliferation rates and enhanced demands for nutrients. Recent studies suggest that metabolic plasticity in cancer cells can decrease the efficacy of anticancer therapies by enhancing antioxidant defenses and DNA repair mechanisms. Studying radiation-induced metabolic changes will lead to a better understanding of radiation response mechanisms as well as the identification of new therapeutic targets, but there are few robust studies characterizing the metabolic changes induced by radiation therapy in cancer. In this review, we will highlight studies that provide information on the metabolic changes induced by radiation and oxidative stress in cancer cells and the associated underlying mechanisms.

Mitochondrial miR-1285 regulates copper-induced mitochondrial dysfunction and mitophagy by impairing IDH2 in pig jejunal epithelial cells

Copper (Cu), a hazardous heavy metal, can lead to toxic effects on host physiology. Recently, specific mitochondria-localized miRNAs (mitomiRs) were shown to modulate mitochondrial function, but the underlying mechanisms remain undefined. Here, we identified mitomiR-1285 as an important molecule regulating mitochondrial dysfunction and mitophagy in jejunal epithelial cells under Cu exposure. Mitochondrial dysfunction and mitophagy were the important mechanisms of Cu-induced pathological damage in jejunal epithelial cells, which were accompanied by significant increase of mitomiR-1285 in vivo and in vitro. Knockdown of mitomiR-1285 significantly attenuated Cu-induced mitochondrial respiratory dysfunction, ATP deficiency, mitochondrial membrane potential reduction, mitochondrial reactive oxygen species accumulation, and mitophagy. Subsequently, bioinformatics analysis and luciferase reporter assay demonstrated that IDH2 was a direct target of mitomiR-1285. RNA interference of IDH2 dramatically reversed the effect that mitomiR-1285 knockdown relieved mitochondrial dysfunction and mitophagy induced by Cu, and the opposite effect was shown by overexpression of IDH2. Therefore, our results suggested that mitomiR-1285 aggravated Cu-induced mitochondrial dysfunction and mitophagy via suppressing IDH2 expression. These findings identified the important mechanistic connection between mitomiRs and mitochondrial metabolism under Cu exposure, providing a new insight into Cu toxicology.

Canagliflozin, a SGLT-2 inhibitor, relieves ER stress, modulates autophagy and induces apoptosis in irradiated HepG2 cells: Signal transduction between PI3K/AKT/GSK-3β/mTOR and Wnt/β-catenin pathways; in vitro

Background and Objectives

Metabolic shifting from mitochondrial respiration to glycolysis characterizes malignant cells from its normal counterparts and is attributed to overactivation of oncogenic signaling pathways. Hence, this study intended to investigate the influence of canagliflozin (CAN) and/or γ-irradiation (γ-IR) on HepG2 cell proliferation, crosstalk between phosphatidylinositol 3-kinases (PI3K)/AKT/glycogen synthase kinase-3-β (GSK3-β)/mTOR and Wnt/β-catenin signaling pathways, and their regulation of diverse processes, such as endoplasmic reticulum (ER) stress, autophagy, and apoptosis.

Materials and Methods

HepG2 cells were treated with different doses of CAN and then exposed to different doses of γ-IR to achieve optimization that was based on cytotoxicity and clonogenic assays, respectively. The effects of CAN and/or γ-IR on glycolytic metabolism, cellular bioenergetics, oxidative stress, ER stress and autophagy biomarkers, expression of PI3K/AKT/GSK3-β/mTOR and Wnt/β-Catenin signaling pathways, and apoptotic markers were monitored.

Results

CAN enhanced the antitumor potential of γ-IR as displayed by a significant inhibition of clonogenic survival in HepG2 cells via inhibition of glucose uptake, lactate release, and modulation of ER stress-mediated autophagy; switched it to apoptosis; as well as disabled signaling pathways which contribute to metabolic reprogramming and tumor progression induced by γ-IR that confer radioresistance and treatment failure.

Conclusion

Our study sheds light on the effective combination of CAN and γ-IR in hepatocellular carcinoma treatment and necessitates CAN treatment prior to γ-IR to overcome metabolic reprogramming-associated radioresistance and improve curative outcomes.

Targeting of cellular redox metabolism for mitigation of radiation injury

Accidental exposure to ionizing radiation is a serious concern to human life. Studies on the mitigation of side effects following exposure to accidental radiation events are ongoing. Recent studies have shown that radiation can activate several signaling pathways, leading to changes in the metabolism of free radicals including reactive oxygen species (ROS) and nitric oxide (NO). Cellular and molecular mechanisms show that radiation can cause disruption of normal reduction/oxidation (redox) system. Mitochondria malfunction following exposure to radiation and mutations in mitochondria DNA (mtDNA) have a key role in chronic oxidative stress. Furthermore, exposure to radiation leads to infiltration of inflammatory cells such as macrophages, lymphocytes and mast cells, which are important sources of ROS and NO. These cells generate free radicals via upregulation of some pro-oxidant enzymes such as NADPH oxidases, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Epigenetic changes also have a key role in a similar way. Other mediators such as mammalian target of rapamycin (mTOR) and peroxisome proliferator-activated receptor (PPAR), which are involved in the normal metabolism of cells have also been shown to regulate cell death following exposure to radiation. These mechanisms are tissue specific. Inhibition or activation of each of these targets can be suggested for mitigation of radiation injury in a specific tissue. In the current paper, we review the cellular and molecular changes in the metabolism of cells and ROS/NO following exposure to radiation. Furthermore, the possible strategies for mitigation of radiation injury through modulation of cellular metabolism in irradiated organs will be discussed.

Cellular adaptive response and regulation of HIF after low dose gamma-radiation exposure

PURPOSE

Cellular damage due to low dose of γ-radiation (≤0.1 Gy) is generally extrapolated from observing the effects at higher doses. These estimations are not accurate. This has led to uncertainties while assessing the radiation risk factors at low doses. Although there are reports on the radiation induced adaptive response, the mechanism of action is not fully elucidated, leading to the uncertainties. One of the outcomes of low dose radiation exposure is believed to be an adaptive response. The mechanism of adaptive response is not fully understood. Therefore, the study was undertaken to understand the role of hypoxia inducible factor (HIF) on radiation induced adaptive response.

MATERIALS AND METHODS

Human breast cancer cell line MCF-7 cells pre-exposed to low dose γ-radiation (0.1 Gy; priming dose) were exposed to 2 Gy (challenging dose) 8 h after the priming dose and studied for the adaptive response. Cell death was measured by 3-(4,5-dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide (MTT) assay and apoptosis was measured by fluorescence-activated cell sorting analysis. DNA damage was measured by alkaline comet assay. HIF transcription activity was assayed using transiently transfected plasmid having HIF consensus sequence and luciferase as the reporter gene.

RESULTS

Cells when exposed to 0.1 Gy priming dose 8 h prior to the higher dose (2 Gy; challenging dose) results in lower amount of radiation induced damages compared to the cells exposed to 2 Gy alone. Cobalt chloride treatment in place of priming dose also results in the protection to cells when exposed to challenging dose. There was up-regulation of HIF activity when cells were exposed to priming dose, indicating the role of HIF in radiation induced response.

CONCLUSION

Results indicate the γ-radiation induced adaptive response. One of the mechanism proposed is up-regulation of HIF after low dose exposure, which protects the cells from damages when they are exposed to challenging dose of 2 Gy radiation.