Tocotrienols Provide Radioprotection to Multiple Organ Systems through Complementary Mechanisms of Antioxidant and Signaling Effects

Tocotrienols have powerful radioprotective properties in multiple organ systems and are promising candidates for development as clinically effective radiation countermeasures. To facilitate their development as clinical radiation countermeasures, it is crucial to understand the mechanisms behind their powerful multi-organ radioprotective properties. In this context, their antioxidant effects are recognized for directly preventing oxidative damage to cellular biomolecules from ionizing radiation. However, there is a growing body of evidence indicating that the radioprotective mechanism of action for tocotrienols extends beyond their antioxidant properties. This raises a new pharmacological paradigm that tocotrienols are uniquely efficacious radioprotectors due to a synergistic combination of antioxidant and other signaling effects. In this review, we have covered the wide range of multi-organ radioprotective effects observed for tocotrienols and the mechanisms underlying it. These radioprotective effects for tocotrienols can be characterized as (1) direct cytoprotective effects, characteristic of the classic antioxidant properties, and (2) other effects that modulate a wide array of critical signaling factors involved in radiation injury.

The role of cytochrome P450 3A4-mediated metabolism in sorafenib and lapatinib hepatotoxicity

Tyrosine kinase inhibitors (TKIs) are increasingly popular drugs used to treat more than a dozen different diseases, including some forms of cancer. Despite having fewer adverse effects than traditional chemotherapies, they are not without risks. Liver injury is a particular concern. Of the FDA-approved TKIs, approximately 40% cause hepatotoxicity. However, little is known about the underlying pathophysiology. The leading hypothesis is that TKIs are converted by cytochrome P450 3A4 (CYP3A4) to reactive metabolites that damage proteins. Indeed, there is strong evidence for this bioactivation of TKIs in in vitro reactions. However, the actual toxic effects are underexplored. Here, we measured the cytotoxicity of several TKIs in primary mouse hepatocytes, HepaRG cells, and HepG2 cells with and without CYP3A4 modulation. To our surprise, the data indicate that CYP3A4 increases resistance to sorafenib and lapatinib hepatotoxicity. The results have implications for the mechanism of toxicity of these drugs in patients and underline the importance of selecting an appropriate experimental model.

Effect of Sirt3 on hippocampal MnSOD activity, mitochondrial function, physiology, and cognition in an aged murine model

The NAD(+)-dependent deacetylase SIRT3 is a proven mitochondrial metabolic stress sensor. It has been linked to the regulation of the mitochondrial acetylome and activation of several metabolic enzymes (e.g., manganese superoxide dismutase [MnSOD]) to protect mitochondrial function and redox homeostasis, which are vital for survival, excitability, and synaptic signaling of neurons mediating short- and long-term memory formation as well as retention. Eighteen-month-old male and female wild-type (WT) and Sirt3-/- mice were behaviorally tested for hippocampus-dependent cognitive performance in a Morris water maze paradigm. Cognitive impairment was displayed during the probe trial by female and male Sirt3-/- mice but not WT mice. Upon sacrifice, brains were fixed, and morphological assessments were conducted on hippocampal tissues. Both female and male Sirt3-/- mice demonstrated impaired spatial memory retention implying that SIRT3 plays a role in long-term memory function. Golgi-staining studies revealed decreased dendritic arborization and dendritic length in the hippocampi of male Sirt3-/- compared to WT animals. Sirt3 deletion significantly increased NR1, NR2A, and NR2B expression in the hippocampus of female mice only. Enzymatic activity of MnSOD, a major mitochondrial deacetylation target of SIRT3, was significantly decreased in both female and male Sirt3-/- mice. Similarly, both female and male Sirt3-/- mice demonstrated a significant decrease in their respiratory control ratio during Complex I-driven respiration, which was apparent only in female Sirt3-/- mice during Complex II-driven respiration.

Chemotherapy induced oxidative stress in the ovary: drug-dependent mechanisms and potential interventions†

Cancer incidence and relative survival are expected to increase over the next few decades. With the majority of patients receiving combinatorial chemotherapy, an increasing proportion of patients experience long-term side effects from treatment-including reproductive disorders and infertility. A limited number of studies have examined mechanisms of single-agent chemotherapy-induced gonadotoxicity, with chemotherapy-induced oxidative stress being implicated in the loss of reproductive functions. Current methods of female fertility preservation are costly, invasive, only moderately successful, and seldom presented to cancer patients. The potential of antioxidants to alleviate chemotherapy has been overlooked at a time when it is becoming increasingly important to develop strategies to protect reproductive functions during chemotherapy. This review will summarize the importance of reactive oxygen species homeostasis in reproduction, chemotherapy-induced mitochondrial dysfunction in oocytes, chemotherapy-induced oxidative stress, and several promising natural adjuvants.

Hematopoietic cytoplasmic adaptor protein Hem1 promotes osteoclast fusion and bone resorption in mice

Hem1 (hematopoietic protein 1), a hematopoietic cell-specific member of the Hem family of cytoplasmic adaptor proteins, is essential for lymphopoiesis and innate immunity as well as for the transition of hematopoiesis from the fetal liver to the bone marrow. However, the role of Hem1 in bone cell differentiation and bone remodeling is unknown. Here, we show that deletion of Hem1 resulted in a markedly increase in bone mass because of defective bone resorption in mice of both sexes. Hem1-deficient osteoclast progenitors were able to differentiate into osteoclasts, but the osteoclasts exhibited impaired osteoclast fusion and decreased bone-resorption activity, potentially because of decreased mitogen-activated protein kinase and tyrosine kinase c-Abl activity. Transplantation of bone marrow hematopoietic stem and progenitor cells from wildtype into Hem1 knockout mice increased bone resorption and normalized bone mass. These findings indicate that Hem1 plays a pivotal role in the maintenance of normal bone mass.

Parthenolide induces rapid thiol oxidation that leads to ferroptosis in hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is both a devastating and common disease. Every year in the United States, about 24,500 men and 10,000 women are diagnosed with HCC, and more than half of those diagnosed patients die from this disease. Thus far, conventional therapeutics have not been successful for patients with HCC due to various underlying comorbidities. Poor survival rate and high incidence of recurrence after therapy indicate that the differences between the redox environments of normal surrounding liver and HCC are valuable targets to improve treatment efficacy. Parthenolide (PTL) is a naturally found therapeutic with anti-cancer and anti-inflammatory properties. PTL can alter HCC's antioxidant environment through thiol modifications leaving tumor cells sensitive to elevated reactive oxygen species (ROS). Investigating the link between altered thiol mechanism and increased sensitivity to iron-mediated lipid peroxidation will allow for improved treatment of HCC. HepG2 (human) and McARH7777 (rat) HCC cells treated with PTL with increasing concentrations decrease cell viability and clonogenic efficiency in vitro. PTL increases glutathione (GSH) oxidation rescued by the addition of a GSH precursor, N-acetylcysteine (NAC). In addition, this elevation in thiol oxidation results in an overall increase in mitochondrial dysfunction. To elucidate if cell death is through lipid peroxidation, using a lipid peroxidation sensor indicated PTL increases lipid oxidation levels after 6 h. Additionally, western blotting reveals glutathione peroxidase 4 (GPx4) protein levels decrease after treatment with PTL suggesting cells are incapable of preventing lipid peroxidation after exposure to PTL. An elevation in lipid peroxidation will lead to a form of cell death known as ferroptosis. To further establish ferroptosis as a critical mechanism of death for HCC in vitro, the addition of ferrostatin-1 combined with PTL demonstrates a partial recovery in a colony survival assay. This study reveals that PTL can induce tumor cell death through elevations in intracellular oxidation, leaving cells sensitive to ferroptosis.

Transferrin receptor 1-mediated iron uptake regulates bone mass in mice via osteoclast mitochondria and cytoskeleton

Increased intracellular iron spurs mitochondrial biogenesis and respiration to satisfy high-energy demand during osteoclast differentiation and bone-resorbing activities. Transferrin receptor 1 (Tfr1) mediates cellular iron uptake through endocytosis of iron-loaded transferrin, and its expression increases during osteoclast differentiation. Nonetheless, the precise functions of Tfr1 and Tfr1-mediated iron uptake in osteoclast biology and skeletal homeostasis remain incompletely understood. To investigate the role of Tfr1 in osteoclast lineage cells in vivo and in vitro, we crossed Tfrc (encoding Tfr1)-floxed mice with Lyz2 (LysM)-Cre and Cathepsin K (Ctsk)-Cre mice to generate Tfrc conditional knockout mice in myeloid osteoclast precursors (Tfr1^ΔLysM) or differentiated osteoclasts (Tfr1^ΔCtsk), respectively. Skeletal phenotyping by µCT and histology unveiled a significant increase in trabecular bone mass with normal osteoclast number in long bones of 10-week-old young and 6-month-old adult female but not male Tfr1^ΔLysM mice. Although high trabecular bone volume in long bones was observed in both male and female Tfr1^ΔCtsk mice, this phenotype was more pronounced in female knockout mice. Consistent with this gender-dependent phenomena, estrogen deficiency induced by ovariectomy decreased trabecular bone mass in Tfr1^ΔLysM mice. Mechanistically, disruption of Tfr1 expression attenuated mitochondrial metabolism and cytoskeletal organization in mature osteoclasts in vitro by attenuating mitochondrial respiration and activation of the Src-Rac1-WAVE regulatory complex axis, respectively, leading to decreased bone resorption with little impact on osteoclast differentiation. These results indicate that Tfr1-mediated iron uptake is specifically required for osteoclast function and is indispensable for bone remodeling in a gender-dependent manner.

Ionizing Radiation Activates Mitochondrial Function in Osteoclasts and Causes Bone Loss in Young Adult Male Mice

The damaging effects of ionizing radiation (IR) on bone mass are well-documented in mice and humans and are most likely due to increased osteoclast number and function. However, the mechanisms leading to inappropriate increases in osteoclastic bone resorption are only partially understood. Here, we show that exposure to multiple fractions of low-doses (10 fractions of 0.4 Gy total body irradiation [TBI]/week, i.e., fractionated exposure) and/or a single exposure to the same total dose of 4 Gy TBI causes a decrease in trabecular, but not cortical, bone mass in young adult male mice. This damaging effect was associated with highly activated bone resorption. Both osteoclast differentiation and maturation increased in cultures of bone marrow-derived macrophages from mice exposed to either fractionated or singular TBI. IR also increased the expression and enzymatic activity of mitochondrial deacetylase Sirtuin-3 (Sirt3)-an essential protein for osteoclast mitochondrial activity and bone resorption in the development of osteoporosis. Osteoclast progenitors lacking Sirt3 exposed to IR exhibited impaired resorptive activity. Taken together, targeting impairment of osteoclast mitochondrial activity could be a novel therapeutic strategy for IR-induced bone loss, and Sirt3 is likely a major mediator of this effect.

Simulated Galactic Cosmic Rays Modify Mitochondrial Metabolism in Osteoclasts, Increase Osteoclastogenesis and Cause Trabecular Bone Loss in Mice

Space is a high-stress environment. One major risk factor for the astronauts when they leave the Earth's magnetic field is exposure to ionizing radiation from galactic cosmic rays (GCR). Several adverse changes occur in mammalian anatomy and physiology in space, including bone loss. In this study, we assessed the effects of simplified GCR exposure on skeletal health in vivo. Three months following exposure to 0.5 Gy total body simulated GCR, blood, bone marrow and tissue were collected from 9 months old male mice. The key findings from our cell and tissue analysis are (1) GCR induced femoral trabecular bone loss in adult mice but had no effect on spinal trabecular bone. (2) GCR increased circulating osteoclast differentiation markers and osteoclast formation but did not alter new bone formation or osteoblast differentiation. (3) Steady-state levels of mitochondrial reactive oxygen species, mitochondrial and non-mitochondrial respiration were increased without any changes in mitochondrial mass in pre-osteoclasts after GCR exposure. (4) Alterations in substrate utilization following GCR exposure in pre-osteoclasts suggested a metabolic rewiring of mitochondria. Taken together, targeting radiation-mediated mitochondrial metabolic reprogramming of osteoclasts could be speculated as a viable therapeutic strategy for space travel induced bone loss.

Role of miR-2392 in driving SARS-CoV-2 infection

MicroRNAs (miRNAs) are small non-coding RNAs involved in post-transcriptional gene regulation that have a major impact on many diseases and provide an exciting avenue toward antiviral therapeutics. From patient transcriptomic data, we determined that a circulating miRNA, miR-2392, is directly involved with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) machinery during host infection. Specifically, we show that miR-2392 is key in driving downstream suppression of mitochondrial gene expression, increasing inflammation, glycolysis, and hypoxia, as well as promoting many symptoms associated with coronavirus disease 2019 (COVID-19) infection. We demonstrate that miR-2392 is present in the blood and urine of patients positive for COVID-19 but is not present in patients negative for COVID-19. These findings indicate the potential for developing a minimally invasive COVID-19 detection method. Lastly, using in vitro human and in vivo hamster models, we design a miRNA-based antiviral therapeutic that targets miR-2392, significantly reduces SARS-CoV-2 viability in hamsters, and may potentially inhibit a COVID-19 disease state in humans.

The Great Deceiver: miR-2392's Hidden Role in Driving SARS-CoV-2 Infection

MicroRNAs (miRNAs) are small non-coding RNAs involved in post-transcriptional gene regulation that have a major impact on many diseases and provides an exciting avenue towards antiviral therapeutics. From patient transcriptomic data, we have discovered a circulating miRNA, miR-2392, that is directly involved with SARS-CoV-2 machinery during host infection. Specifically, we show that miR-2392 is key in driving downstream suppression of mitochondrial gene expression, increasing inflammation, glycolysis, and hypoxia as well as promoting many symptoms associated with COVID-19 infection. We demonstrate miR-2392 is present in the blood and urine of COVID-19 positive patients, but not detected in COVID-19 negative patients. These findings indicate the potential for developing a novel, minimally invasive, COVID-19 detection method. Lastly, using in vitro human and in vivo hamster models, we have developed a novel miRNA-based antiviral therapeutic that targets miR-2392, significantly reduces SARS-CoV-2 viability in hamsters and may potentially inhibit a COVID-19 disease state in humans.

Sex-dependent effects of genetic upregulation of activated protein C on delayed effects of acute radiation exposure in the mouse heart, small intestine, and skin

Accidental exposure to ionizing radiation may lead to delayed effects of acute radiation exposure (DEARE) in many organ systems. Activated protein C (APC) is a known mitigator of the acute radiation syndrome. To examine the role of APC in DEARE, we used a transgenic mouse model with 2- to 3-fold increased plasma levels of APC (high in APC, APCHi). Male and female APCHi mice and wild-type littermates were exposed to 9.5 Gy γ-rays with their hind-legs (bone marrow) shielded from radiation to allow long-term survival. At 3 and 6 months after irradiation, cardiac function was measured with ultrasonography. At 3 months, radiation increased cardiac dimensions in APCHi males, while decreases were seen in wild-type females. At this early time point, APCHi mice of both sexes were more susceptible to radiation-induced changes in systolic function compared to wild-types. At 6 months, a decrease in systolic function was mainly seen in male mice of both genotypes. At 6 months, specimens of heart, small intestine and dorsal skin were collected for tissue analysis. Female APCHi mice showed the most severe radiation-induced deposition of cardiac collagens but were protected against a radiation-induced loss of microvascular density. Both male and female APCHi mice were protected against a radiation induced upregulation of toll-like receptor 4 in the heart, but this did not translate into a clear protection against immune cell infiltration. In the small intestine, the APCHi genotype had no effect on an increase in the number of myeloperoxidase positive cells (seen mostly in females) or an increase in the expression of T-cell marker CD2 (males). Lastly, both male and female APCHi mice were protected against radiation-induced epidermal thickening and increase in 3-nitrotyrosine positive keratinocytes. In conclusion, prolonged high levels of APC in a transgenic mouse model had little effects on indicators of DEARE in the heart, small intestine and skin, with some differential effects in male compared to female mice.

Mitochondrial Sirt3 contributes to the bone loss caused by aging or estrogen deficiency

Altered mitochondria activity in osteoblasts and osteoclasts has been implicated in the loss of bone mass associated with aging and estrogen deficiency — the 2 most common causes of osteoporosis. However, the mechanisms that control mitochondrial metabolism in bone cells during health or disease remain unknown. The mitochondrial deacetylase sirtuin-3 (Sirt3) has been earlier implicated in age-related diseases. Here, we show that deletion of Sirt3 had no effect on the skeleton of young mice but attenuated the age-related loss of bone mass in both sexes. This effect was associated with impaired bone resorption. Osteoclast progenitors from aged Sirt3-null mice were able to differentiate into osteoclasts, though the differentiated cells exhibited impaired polykaryon formation and resorptive activity, as well as decreased oxidative phosphorylation and mitophagy. The Sirt3 inhibitor LC-0296 recapitulated the effects of Sirt3 deletion in osteoclast formation and mitochondrial function, and its administration to aging mice increased bone mass. Deletion of Sirt3 also attenuated the increase in bone resorption and loss of bone mass caused by estrogen deficiency. These findings suggest that Sirt3 inhibition and the resulting impairment of osteoclast mitochondrial function could be a novel therapeutic intervention for the 2 most important causes of osteoporosis.

Epigenetic Control of Cdkn2a.Arf Protects Tumor-Infiltrating Lymphocytes from Metabolic Exhaustion

T-cell exhaustion in cancer is linked to poor clinical outcomes, where evidence suggests T-cell metabolic changes precede functional exhaustion. Direct competition between tumor-infiltrating lymphocytes (TIL) and cancer cells for metabolic resources often renders T cells dysfunctional. Environmental stress produces epigenome remodeling events within TIL resulting from loss of the histone methyltransferase EZH2. Here, we report an epigenetic mechanism contributing to the development of metabolic exhaustion in TIL. A multiomics approach revealed a Cdkn2a.Arf-mediated, p53-independent mechanism by which EZH2 inhibition leads to mitochondrial dysfunction and the resultant exhaustion. Reprogramming T cells to express a gain-of-function EZH2 mutant resulted in an enhanced ability of T cells to inhibit tumor growth in vitro and in vivo. Our data suggest that manipulation of T-cell EZH2 within the context of cellular therapies may yield lymphocytes that are able to withstand harsh tumor metabolic environments and collateral pharmacologic insults. SIGNIFICANCE: These findings demonstrate that manipulation of T-cell EZH2 in cellular therapies may yield cellular products able to withstand solid tumor metabolic-deficient environments. GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/21/4707/F1.large.jpg.

Abstract 1029: Epigenetic control of tumor-infiltrating lymphocyte metabolic-exhaustion

Direct competition between tumor-infiltrating lymphocytes and cancer cells for metabolic resources often renders T cells dysfunctional. It is becoming clearer that T cell metabolic changes can precede functional exhaustion. In the case of solid tumors, the driving force of this dysfunction is thought to be a result of inhibitory metabolism (e.g. glucose deprivation and mitochondrial dysfunction). The mechanisms connecting inhibitory metabolism and T cell metabolic exhaustion are largely unknown. Interestingly, T cells undergo a loss of the histone methyltransferase EZH2 (H3K27me3) during tumor infiltration. Methyltransferases, like EZH2, depend on mitochondria to supply S-Adenosyl-L-Methionine (SAM), the primary methyl donor. We sought to determine if there was a link between EZH2 and mitochondrial function. In this work, we utilized highly specific EZH2 inhibitors to model acute inhibition of EZH2 in CD8+ and CD4+ T cells. Taking an unbiased, multi-omics approach (proteomics, RNAseq, ChIPseq) we fully interrogate the downstream consequences of EZH2 inhibition in T cells. The loss of H3K27me3 does indeed lead to an induction of mitochondrial dysfunction, which in turn, drives a dependency on glycolytic metabolism and sensitivity to glucose withdrawal. The metabolic shift phenotype was confirmed using extracellular metabolic flux analysis. In T cells, we found the loss of H3K27me3 repression of the Cdkn2aArf locus to be a major contributor to mitochondrial dysfunction, independent of the canonical role to stabilize p53. Furthermore, we show Arf-/- mice are resistant to EZH2-inhibition induced mitochondrial dysfunction. Reprogramming tumor-specific T cells to exogenously express a gain-of-function EZH2 mutant (Y641F) resulted in an enhanced ability of T cells to inhibit solid tumor growth. This work demonstrates the potential for manipulation of EZH2 in cellular therapies for solid tumors with harsh metabolic conditions and sheds light on the dynamic interplay of epigenetics and metabolic sufficiency.

Citation Format: Brian Koss, Bradley D. Shields, Erin M. Taylor, Aaron J. Storey, Stephanie D. Byrum, Allen J. Gies, Charity L. Washam, Samrat Roy Choudhury, Jeong Hyun Ahn, Hidetaka Uryu, Kimberly J. Krager, Tung-Chin Chiang, Samuel G. Mackintosh, Rick D. Edmondson, Nukhet Aykin-Burns, Gang Greg Wang, Alan J. Tackett. Epigenetic control of tumor-infiltrating lymphocyte metabolic-exhaustion [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1029.

Estrogens decrease osteoclast number by attenuating mitochondria oxidative phosphorylation and ATP production in early osteoclast precursors

Loss of estrogens at menopause is a major cause of osteoporosis and increased fracture risk. Estrogens protect against bone loss by decreasing osteoclast number through direct actions on cells of the myeloid lineage. Here, we investigated the molecular mechanism of this effect. We report that 17β-estradiol (E₂) decreased osteoclast number by promoting the apoptosis of early osteoclast progenitors, but not mature osteoclasts. This effect was abrogated in cells lacking Bak/Bax-two pro-apoptotic members of the Bcl-2 family of proteins required for mitochondrial apoptotic death. FasL has been previously implicated in the pro-apoptotic actions of E₂. However, we show herein that FasL-deficient mice lose bone mass following ovariectomy indistinguishably from FasL-intact controls, indicating that FasL is not a major contributor to the anti-osteoclastogenic actions of estrogens. Instead, using microarray analysis we have elucidated that ERα-mediated estrogen signaling in osteoclast progenitors decreases "oxidative phosphorylation" and the expression of mitochondria complex I genes. Additionally, E₂ decreased the activity of complex I and oxygen consumption rate. Similar to E₂, the complex I inhibitor Rotenone decreased osteoclastogenesis by promoting osteoclast progenitor apoptosis via Bak/Bax. These findings demonstrate that estrogens decrease osteoclast number by attenuating respiration, and thereby, promoting mitochondrial apoptotic death of early osteoclast progenitors.

Assessment of Cellular Oxidation using a Subcellular Compartment-Specific Redox-Sensitive Green Fluorescent Protein

Measuring the intracellular oxidation/reduction balance provides an overview of the physiological and/or pathophysiological redox status of an organism. Thiols are especially important for illuminating the redox status of cells via their reduced dithiol and oxidized disulfide ratios. Engineered cysteine-containing fluorescent proteins open a new era for redox-sensitive biosensors. One of them, redox-sensitive green fluorescent protein (roGFP), can easily be introduced into cells with adenoviral transduction, allowing the redox status of subcellular compartments to be evaluated without disrupting cellular processes. Reduced cysteines and oxidized cystines of roGFP have excitation maxima at 488 nm and 405 nm, respectively, with emission at 525 nm. Assessing the ratios of these reduced and oxidized forms allows the convenient calculation of redox balance within the cell. In this method article, immortalized human triple-negative breast cancer cells (MDA-MB-231) were used to assess redox status within the living cell. The protocol steps include MDA-MB-231 cell line transduction with adenovirus to express cytosolic roGFP, treatment with H2O2, and assessment of cysteine and cystine ratio with both flow cytometry and fluorescence microscopy.

PCB11 Metabolite, 3,3'-Dichlorobiphenyl-4-ol, Exposure Alters the Expression of Genes Governing Fatty Acid Metabolism in the Absence of Functional Sirtuin 3: Examining the Contribution of MnSOD

Although the production of polychlorinated biphenyls (PCBs) is prohibited, the inadvertent production of certain lower-chlorinated PCB congeners still threatens human health. We and others have identified 3,3’-dichlorobiphenyl (PCB11) and its metabolite, 3,3’-dichlorobiphenyl-4-ol (4OH-PCB11), in human blood, and there is a correlation between exposure to this metabolite and mitochondrial oxidative stress in mammalian cells. Here, we evaluated the downstream effects of 4OH-PCB11 on mitochondrial metabolism and function in the presence and absence of functional Sirtuin 3 (SIRT3), a mitochondrial fidelity protein that protects redox homeostasis. A 24 h exposure to 3 μM 4OH-PCB11 significantly decreased the cellular growth and mitochondrial membrane potential of SIRT3-knockout mouse embryonic fibroblasts (MEFs). Only wild-type cells demonstrated an increase in Manganese superoxide dismutase (MnSOD) activity in response to 4OH-PCB11–induced oxidative injury. This suggests the presence of a SIRT3-mediated post-translational modification to MnSOD, which was impaired in SIRT3-knockout MEFs, which counters the PCB insult. We found that 4OH-PCB11 increased mitochondrial respiration and endogenous fatty-acid oxidation-associated oxygen consumption in SIRT3-knockout MEFs; this appeared to occur because the cells exhausted their reserve respiratory capacity. To determine whether these changes in mitochondrial respiration were accompanied by similar changes in the regulation of fatty acid metabolism, we performed quantitative real-time polymerase chain reaction (qRT-PCR) after a 24 h treatment with 4OH-PCB11. In SIRT3-knockout MEFs, 4OH-PCB11 significantly increased the expression of ten genes controlling fatty acid biosynthesis, metabolism, and transport. When we overexpressed MnSOD in these cells, the expression of six of these genes returned to the baseline level, suggesting that the protective role of SIRT3 against 4OH-PCB11 is partially governed by MnSOD activity.

Deletion of ferroportin in murine myeloid cells increases iron accumulation and stimulates osteoclastogenesis in vitro and in vivo

Osteoporosis, osteopenia, and pathological bone fractures are frequent complications of iron-overload conditions such as hereditary hemochromatosis, thalassemia, and sickle cell disease. Moreover, animal models of iron overload have revealed increased bone resorption and decreased bone formation. Although systemic iron overload affects multiple organs and tissues, leading to significant changes on bone modeling and remodeling, the cell autonomous effects of excessive iron on bone cells remain unknown. Here, to elucidate the role of cellular iron homeostasis in osteoclasts, we generated two mouse strains in which solute carrier family 40 member 1 (Slc40a1), a gene encoding ferroportin (FPN), the sole iron exporter in mammalian cells, was specifically deleted in myeloid osteoclast precursors or mature cells. The FPN deletion mildly increased iron levels in both precursor and mature osteoclasts, and its loss in precursors, but not in mature cells, increased osteoclastogenesis and decreased bone mass in vivo Of note, these phenotypes were more pronounced in female than in male mice. In vitro studies revealed that the elevated intracellular iron promoted macrophage proliferation and amplified expression of nuclear factor of activated T cells 1 (Nfatc1) and PPARG coactivator 1β (Pgc-1β), two transcription factors critical for osteoclast differentiation. However, the iron excess did not affect osteoclast survival. While increased iron stimulated global mitochondrial metabolism in osteoclast precursors, it had little influence on mitochondrial mass and reactive oxygen species production. These results indicate that FPN-regulated intracellular iron levels are critical for mitochondrial metabolism, osteoclastogenesis, and skeletal homeostasis in mice.

Antioxidant Tocols as Radiation Countermeasures (Challenges to be Addressed to Use Tocols as Radiation Countermeasures in Humans)

Radiation countermeasures fall under three categories, radiation protectors, radiation mitigators, and radiation therapeutics. Radiation protectors are agents that are administered before radiation exposure to protect from radiation-induced injuries by numerous mechanisms, including scavenging free radicals that are generated by initial radiochemical events. Radiation mitigators are agents that are administered after the exposure of radiation but before the onset of symptoms by accelerating the recovery and repair from radiation-induced injuries. Whereas radiation therapeutic agents administered after the onset of symptoms act by regenerating the tissues that are injured by radiation. Vitamin E is an antioxidant that neutralizes free radicals generated by radiation exposure by donating H atoms. The vitamin E family consists of eight different vitamers, including four tocopherols and four tocotrienols. Though alpha-tocopherol was extensively studied in the past, tocotrienols have recently gained attention as radiation countermeasures. Despite several studies performed on tocotrienols, there is no clear evidence on the factors that are responsible for their superior radiation protection properties over tocopherols. Their absorption and bioavailability are also not well understood. In this review, we discuss tocopherol’s and tocotrienol’s efficacy as radiation countermeasures and identify the challenges to be addressed to develop them into radiation countermeasures for human use in the event of radiological emergencies.

Loss of C/EBPδ enhances IR-induced cell death by promoting oxidative stress and mitochondrial dysfunction

Exposure of cells to ionizing radiation (IR) generates reactive oxygen species (ROS). This results in increased oxidative stress and DNA double strand breaks (DSBs) which are the two underlying mechanisms by which IR causes cell/tissue injury. Cells that are deficient or impaired in the cellular antioxidant response are susceptible to IR-induced apoptosis. The transcription factor CCAAT enhancer binding protein delta (Cebpd, C/EBPδ) has been implicated in the regulation of oxidative stress, DNA damage response, genomic stability and inflammation. We previously reported that Cebpd-deficient mice are sensitive to IR and display intestinal and hematopoietic injury, however the underlying mechanism is not known. In this study, we investigated whether an impaired ability to detoxify IR-induced ROS was the underlying cause of the increased radiosensitivity of Cebpd-deficient cells. We found that Cebpd-knockout (KO) mouse embryonic fibroblasts (MEFs) expressed elevated levels of ROS, both at basal levels and after exposure to gamma radiation which correlated with increased apoptosis, and decreased clonogenic survival. Pre-treatment of wild type (WT) and KO MEFs with polyethylene glycol-conjugated Cu-Zn superoxide dismutase (PEG-SOD) and catalase (PEG-CAT) combination prior to irradiation showed a partial rescue of clonogenic survival, thus demonstrating a role for increased intracellular oxidants in promoting IR-induced cell death. Analysis of mitochondrial bioenergetics revealed that irradiated KO MEFs showed significant reductions in basal, adenosine triphosphate (ATP)-linked, maximal respiration and reserved respiratory capacity and decrease in intracellular ATP levels compared to WT MEFs indicating they display mitochondrial dysfunction. KO MEFs expressed significantly lower levels of the cellular antioxidant glutathione (GSH) and its precursor- cysteine as well as methionine. In addition to its antioxidant function, GSH plays an important role in detoxification of lipid peroxidation products such as 4-hydroxynonenal (4-HNE). The reduced GSH levels observed in KO MEFs correlated with elevated levels of 4-HNE protein adducts in irradiated KO MEFs compared to respective WT MEFs. We further showed that pre-treatment with the GSH precursor, N-acetyl L-cysteine (NAC) prior to irradiation showed a significant reduction of IR-induced cell death and increases in GSH levels, which contributed to the overall increase in clonogenic survival of KO MEFs. In contrast, pre-treatment with the GSH synthesis inhibitor- buthionine sulfoximine (BSO) further reduced the clonogenic survival of irradiated KO MEFs. This study demonstrates a novel role for C/EBPδ in protection from basal as well as IR-induced oxidative stress and mitochondrial dysfunction thus promoting post-radiation survival.

Recombinant Thrombomodulin (Solulin) Ameliorates Early Intestinal Radiation Toxicity in a Preclinical Rat Model

Intestinal radiation toxicity occurs during and after abdominopelvic radiotherapy. Endothelial cells play a significant role in modulating radiation-induced intestinal damage. We demonstrated that the endothelial cell surface receptor thrombomodulin (TM), a protein with anticoagulant, anti-inflammatory and antioxidant properties, mitigates radiation-induced lethality in mice. The goal of this study was to determine whether recombinant TM (Solulin) can protect the intestine from toxicity in a clinically relevant rat model. A 4 cm loop of rat small bowel was exposed to fractionated 5 Gy X radiation for 9 consecutive days. The animals were randomly assigned to receive daily subcutaneous injections of vehicle or Solulin (3 mg/kg/day or 10 mg/kg/day) for 27 days starting 4 days before irradiation. Early intestinal injury was assessed two weeks after irradiation by quantitative histology, morphometry, immunohistochemistry and luminol bioluminescence imaging. Solulin treatment significantly ameliorated intestinal radiation injury, made evident by a decrease in myeloperoxidase (MPO) activity, transforming growth factor beta (TGF-β) immunoreactivity, collagen-I deposition, radiation injury score (RIS) and intestinal serosal thickening. These findings indicate the need for further development of Solulin as a prophylactic and/or therapeutic agent to mitigate radiation-induced intestinal damage.

In Vitro Toxicity and Epigenotoxicity of Different Types of Ambient Particulate Matter

Exposure to ambient particulate matter (PM) has been associated with adverse health effects, including pulmonary and cardiovascular disease. Studies indicate that ambient PM originated from different sources may cause distinct biological effects. In this study, we sought to investigate the potential of various types of PM to cause epigenetic alterations in the in vitro system. RAW264.7 murine macrophages were exposed for 24 and 72 h to 5- and 50-μg/ml doses of the water soluble extract of 6 types of PM: soil dust, road dust, agricultural dust, traffic exhausts, biomass burning, and pollen, collected in January-April of 2014 in the area of Little Rock, Arkansas. Cytotoxicity, oxidative potential, epigenetic endpoints, and chromosomal aberrations were addressed. Exposure to 6 types of PM resulted in induction of cytotoxicity and oxidative stress in a type-, time-, and dose-dependent manner. Epigenetic alterations were characterized by type-, time-, and dose-dependent decreases of DNA methylation/demethylation machinery, increased DNA methyltransferases enzymatic activity and protein levels, and transcriptional activation and subsequent silencing of transposable elements LINE-1, SINE B1/B2. The most pronounced changes were observed after exposure to soil dust that were also characterized by hypomethylation and reactivation of satellite DNA and structural chromosomal aberrations in the exposed cells. The results of our study indicate that the water-soluble fractions of the various types of PM have differential potential to target the cellular epigenome.

The neuronal nitric oxide synthase inhibitor NANT blocks acetaminophen toxicity and protein nitration in freshly isolated hepatocytes

3-Nitrotyrosine (3NT) in liver proteins of mice treated with hepatotoxic doses of acetaminophen (APAP) has been postulated to be causative in toxicity. Nitration is by a reactive nitrogen species formed from nitric oxide (NO). The source of the NO is unclear. iNOS knockout mice were previously found to be equally susceptible to APAP toxicity as wildtype mice and iNOS inhibitors did not decrease toxicity in mice or in hepatocytes. In this work we examined the potential role of nNOS in APAP toxicity in hepatocytes using the specific nNOS inhibitor NANT (10 µM)(N-[(4S)-4-amino-5-[(2-aminoethyl)amino]pentyl]-N'-nitroguanidinetris (trifluoroacetate)). Primary hepatocytes (1 million/ml) from male B6C3F1 mice were incubated with APAP (1mM). Cells were removed and assayed spectrofluorometrically for reactive nitrogen and oxygen species using diaminofluorescein (DAF) and Mitosox red, respectively. Cytotoxicity was determined by LDH release into media. Glutathione (GSH, GSSG), 3NT, GSNO, acetaminophen-cysteine adducts, NAD, and NADH were measured by HPLC. APAP significantly increased cytotoxicity at 1.5-3.0 h. The increase was blocked by NANT. NANT did not alter APAP mediated GSH depletion or acetaminophen-cysteine adducts in proteins which indicated that NANT did not inhibit metabolism. APAP significantly increased spectroflurometric evidence of reactive nitrogen and oxygen formation at 0.5 and 1.0 h, respectively, and increased 3NT and GSNO at 1.5-3.0 h. These increases were blocked by NANT. APAP dramatically increased NADH from 0.5-3.0 h and this increase was blocked by NANT. Also, APAP decreased the Oxygen Consumption Rate (OCR), decreased ATP production, and caused a loss of mitochondrial membrane potential, which were all blocked by NANT.

A tocotrienol-enriched formulation protects against radiation-induced changes in cardiac mitochondria without modifying late cardiac function or structure

Radiation-induced heart disease (RIHD) is a common and sometimes severe late side effect of radiation therapy for intrathoracic and chest wall tumors. We have previously shown that local heart irradiation in a rat model caused prolonged changes in mitochondrial respiration and increased susceptibility to mitochondrial permeability transition pore (mPTP) opening. Because tocotrienols are known to protect against oxidative stress-induced mitochondrial dysfunction, in this study, we examined the effects of tocotrienols on radiation-induced alterations in mitochondria, and structural and functional manifestations of RIHD. Male Sprague-Dawley rats received image-guided localized X irradiation to the heart to a total dose of 21 Gy. Twenty-four hours before irradiation, rats received a tocotrienol-enriched formulation or vehicle by oral gavage. Mitochondrial function and mitochondrial membrane parameters were studied at 2 weeks and 28 weeks after irradiation. In addition, cardiac function and histology were examined at 28 weeks. A single oral dose of the tocotrienol-enriched formulation preserved Bax/Bcl2 ratios and prevented mPTP opening and radiation-induced alterations in succinate-driven mitochondrial respiration. Nevertheless, the late effects of local heart irradiation pertaining to myocardial function and structure were not modified. Our studies suggest that a single dose of tocotrienols protects against radiation-induced mitochondrial changes, but these effects are not sufficient against long-term alterations in cardiac function or remodeling.

BKCa channel inhibitor modulates the tumorigenic ability of hormone-independent breast cancer cells via the Wnt pathway

In breast cancers, the large conductance Ca2+ and voltage sensitive K+ (BKCa) channels have been hypothesized to function as oncoproteins, yet it remains unclear how inhibition of channel activity impacts oncogenesis. We demonstrated herein that iberiotoxin (IbTX), an inhibitor of BKCa channels, differentially modulated the in vitro tumorigenic activities of hormone-independent breast cancer cells. Specifically, in HER-2/neu-overexpressing UACC893 cells and triple‑negative MDA-MB-231 cells, IbTX selectively attenuated anchorage-independent growth with concomitant downregulation of β-catenin as well as total and phosphorylated Akt and HER-2/neu. By contrast, HER-2/neu-overexpressing SK-BR-3 cells were insensitive to IbTX. Molecular analyses showed an absence of β-catenin and a dose-dependent upregulation of total and phosphorylated Akt and HER-2/neu in these cells. Taken together, these studies identify β-catenin as a putative modulator of the inhibitory actions of IbTX in sensitive breast cancer cells.

Liver metabolomics reveals increased oxidative stress and fibrogenic potential in gfrp transgenic mice in response to ionizing radiation

Although radiation-induced tissue-specific injury is well documented, the underlying molecular changes resulting in organ dysfunction and the consequences thereof on overall metabolism and physiology have not been elucidated. We previously reported the generation and characterization of a transgenic mouse strain that ubiquitously overexpresses Gfrp (GTPH-1 feedback regulatory protein) and exhibits higher oxidative stress, which is a possible result of decreased tetrahydrobiopterin (BH4) bioavailability. In this study, we report genotype-dependent changes in the metabolic profiles of liver tissue after exposure to nonlethal doses of ionizing radiation. Using a combination of untargeted and targeted quantitative mass spectrometry, we report significant accumulation of metabolites associated with oxidative stress, as well as the dysregulation of lipid metabolism in transgenic mice after radiation exposure. The radiation stress seems to exacerbate lipid peroxidation and also results in higher expression of genes that facilitate liver fibrosis, in a manner that is dependent on the genetic background and post-irradiation time interval. These findings suggest the significance of Gfrp in regulating redox homeostasis in response to stress induced by ionizing radiation affecting overall physiology.

Characterization of transgenic Gfrp knock-in mice: implications for tetrahydrobiopterin in modulation of normal tissue radiation responses

AIMS

The free radical scavenger and nitric oxide synthase cofactor, 5,6,7,8-tetrahydrobiopterin (BH4), plays a well-documented role in many disorders associated with oxidative stress, including normal tissue radiation responses. Radiation exposure is associated with decreased BH4 levels, while BH4 supplementation attenuates aspects of radiation toxicity. The endogenous synthesis of BH4 is catalyzed by the enzyme guanosine triphosphate cyclohydrolase I (GTPCH1), which is regulated by the inhibitory GTP cyclohydrolase I feedback regulatory protein (GFRP). We here report and characterize a novel, Cre-Lox-driven, transgenic mouse model that overexpresses Gfrp.

RESULTS

Compared to control littermates, transgenic mice exhibited high transgene copy numbers, increased Gfrp mRNA and GFRP expression, enhanced GFRP-GTPCH1 interaction, reduced BH4 levels, and low glutathione (GSH) levels and differential mitochondrial bioenergetic profiles. After exposure to total body irradiation, transgenic mice showed decreased BH4/7,8-dihydrobiopterin ratios, increased vascular oxidative stress, and reduced white blood cell counts compared with controls.

INNOVATION AND CONCLUSION

This novel Gfrp knock-in transgenic mouse model allows elucidation of the role of GFRP in the regulation of BH4 biosynthesis. This model is a valuable tool to study the involvement of BH4 in whole body and tissue-specific radiation responses and other conditions associated with oxidative stress.

Radiation-induced alterations in mitochondria of the rat heart

Radiation therapy for the treatment of thoracic cancers may be associated with radiation-induced heart disease (RIHD), especially in long-term cancer survivors. Mechanisms by which radiation causes heart disease are largely unknown. To identify potential long-term contributions of mitochondria in the development of radiation-induced heart disease, we examined the time course of effects of irradiation on cardiac mitochondria. In this study, Sprague-Dawley male rats received image-guided local X irradiation of the heart with a single dose ranging from 3-21 Gy. Two weeks after irradiation, left ventricular mitochondria were isolated to assess the dose-dependency of the mitochondrial permeability transition pore (mPTP) opening in a mitochondrial swelling assay. At time points from 6 h to 9 months after a cardiac dose of 21 Gy, the following analyses were performed: left ventricular Bax and Bcl-2 protein levels; apoptosis; mitochondrial inner membrane potential and mPTP opening; mitochondrial mass and expression of mitophagy mediators Parkin and PTEN induced putative kinase-1 (PINK-1); mitochondrial respiration and protein levels of succinate dehydrogenase A (SDHA); and the 70 kDa subunit of complex II. Local heart irradiation caused a prolonged increase in Bax/Bcl-2 ratio and induced apoptosis between 6 h and 2 weeks. The mitochondrial membrane potential was reduced until 2 weeks, and the calcium-induced mPTP opening was increased from 6 h up to 9 months. An increased mitochondrial mass together with unaltered levels of Parkin suggested that mitophagy did not occur. Lastly, we detected a significant decrease in succinate-driven state 2 respiration in isolated mitochondria from 2 weeks up to 9 months after irradiation, coinciding with reduced mitochondrial levels of succinate dehydrogenase A. Our results suggest that local heart irradiation induces long-term changes in cardiac mitochondrial membrane functions, levels of SDH and state 2 respiration. At any time after exposure to radiation, cardiac mitochondria are more prone to mPTP opening. Future studies will determine whether this makes the heart more susceptible to secondary stressors such as calcium overload or ischemia/reperfusion.

Peroxynitrite induced mitochondrial biogenesis following MnSOD knockdown in normal rat kidney (NRK) cells

Superoxide is widely regarded as the primary reactive oxygen species (ROS) which initiates downstream oxidative stress. Increased oxidative stress contributes, in part, to many disease conditions such as cancer, atherosclerosis, ischemia/reperfusion, diabetes, aging, and neurodegeneration. Manganese superoxide dismutase (MnSOD) catalyzes the dismutation of superoxide into hydrogen peroxide which can then be further detoxified by other antioxidant enzymes. MnSOD is critical in maintaining the normal function of mitochondria, thus its inactivation is thought to lead to compromised mitochondria. Previously, our laboratory observed increased mitochondrial biogenesis in a novel kidney-specific MnSOD knockout mouse. The current study used transient siRNA mediated MnSOD knockdown of normal rat kidney (NRK) cells as the in vitro model, and confirmed functional mitochondrial biogenesis evidenced by increased PGC1α expression, mitochondrial DNA copy numbers and integrity, electron transport chain protein CORE II, mitochondrial mass, oxygen consumption rate, and overall ATP production. Further mechanistic studies using mitoquinone (MitoQ), a mitochondria-targeted antioxidant and L-NAME, a nitric oxide synthase (NOS) inhibitor demonstrated that peroxynitrite (at low micromolar levels) induced mitochondrial biogenesis. These findings provide the first evidence that low levels of peroxynitrite can initiate a protective signaling cascade involving mitochondrial biogenesis which may help to restore mitochondrial function following transient MnSOD inactivation.

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MnSOD knockdown in NRK cells results in a transient loss of MnSOD activity, increased nitrotyrosine and mitochondrial superoxide.

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MnSOD knockdown in NRK cells results in a transient induction of mitochondrial biogenesis.

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Nitric oxide synthase inhibition and Mitoquinone blocks mitochondrial biogenesis after MnSOD knockdown.

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Low doses of peroxynitrite induce biogenesis in NRK cells.

Selenoprotein P regulates 1-(4-Chlorophenyl)-benzo-2,5-quinone-induced oxidative stress and toxicity in human keratinocytes

Polychlorinated biphenyls and their metabolites are environmental pollutants that are believed to have adverse health effects presumably by inducing oxidative stress. To determine if 1-(4-Chlorophenyl)-benzo-2,5-quinone (4-ClBQ; metabolite of 4-monochlorobiphenyl, PCB3)-induced oxidative stress is associated with changes in the expression of specific antioxidant genes, mRNA levels of 92 oxidative stress-response genes were analyzed using TaqMan Array Human Antioxidant Mechanisms (Life Technologies), and results were verified by performing quantitative RT-PCR assays. The expression of selenoprotein P (sepp1) was significantly downregulated (8- to 10-fold) in 4-ClBQ-treated HaCaT human skin keratinocytes, which correlated with a significant increase in MitoSOX oxidation. Overexpression of Mn-superoxide dismutase or catalase or treatment with N-acetyl-l-cysteine suppressed 4-ClBQ-induced toxicity. Sodium selenite supplementation also suppressed 4-ClBQ-induced decrease in sepp1 expression, which was associated with a significant inhibition in cell death. Furthermore, HaCaT cells overexpressing sepp1 were resistant to 4-ClBQ-induced oxidative stress and toxicity. These results demonstrate that SEPP1 represents a previously unrecognized regulator of PCB-induced biological effects. These results support the speculation that selenoproteins can be an attractive countermeasure for PCB-induced adverse biological effects.

A new player in environmentally induced oxidative stress: polychlorinated biphenyl congener, 3,3'-dichlorobiphenyl (PCB11)

Recent analysis of air samples from Chicago and Lake Michigan areas observed a ubiquitous airborne polychlorinated biphenyl (PCB) congener, 3,3'-dichlorobiphenyl (PCB11). Our analysis of serum samples also revealed the existence of hydroxylated metabolites of PCB11 in human blood. Because PCBs and PCB metabolites have been suggested to induce oxidative stress, this study sought to determine whether environmental exposure to PCB11 and its 4-hydroxyl metabolite could induce alterations in steady-state levels of reactive oxygen species (ROS) and cytotoxicity in immortalized human prostate epithelial cells (RWPE-1). This study also examines if antioxidants could protect the cells from PCB11-induced cytotoxicity. Exponentially growing RWPE-1 cells were exposed to PCB11 and its metabolite, 3,3'-dichlorobiphenyl-4-ol (4-OH-PCB11), as well as an airborne PCB mixture resembling the Chicago ambient air congener profile, every day for 5 days. Results showed that 4-OH-PCB11 could significantly induce cell growth suppression and decrease the viability and plating efficiency of RWPE-1 cells. 4-OH-PCB11 also significantly increased steady-state levels of intracellular superoxide, O₂•⁻), as well as hydroperoxides. Finally, treatment with the combination of polyethylene glycol-conjugated CuZn superoxide dismutase and catalase added 1h after 4-OH-PCB11 exposures, significantly protected RWPE-1 cells from PCB toxicity. The results strongly support the hypothesis that exposure to a hydroxylated metabolite of PCB11 can inhibit cell proliferation and cause cytotoxicity by increasing steady-state levels of ROS. Furthermore, antioxidant treatments following PCBs exposure could significantly mitigate the PCB-induced cytotoxicity in exponentially growing human prostate epithelial cells.

Low-dose radiation-induced enhancement of thymic lymphomagenesis in Lck-Bax mice is dependent on LET and gender

The hypothesis that mitochondrial dysfunction and increased superoxide levels in thymocytes over expressing Bax (Lck-Bax1 and Lck-Bax38&1) contributes to lymphomagenesis after low-dose radiation was tested. Lck-Bax1 single-transgenic and Lck-Bax38&1 double-transgenic mice were exposed to single whole-body doses of 10 or 100 cGy of (137)Cs or iron ions (1,000 MeV/n, 150 keV/μm) or silicon ions (300 MeV/n, 67 keV/μm). A 10 cGy dose of (137)Cs significantly increased the incidence and onset of thymic lymphomas in female Lck-Bax1 mice. In Lck-Bax38&1 mice, a 100 cGy dose of high-LET iron ions caused a significant dose dependent acceleration of lymphomagenesis in both males and females that was not seen with silicon ions. To determine the contribution of mitochondrial oxidative metabolism, Lck-Bax38&1 over expressing mice were crossed with knockouts of the mitochondrial protein deacetylase, Sirtuin 3 (Sirt3), which regulates superoxide metabolism. Sirt3(-/-)/Lck-Bax38&1 mice demonstrated significant increases in thymocyte superoxide levels and acceleration of lymphomagenesis (P < 0.001). These results show that lymphomagenesis in Bax over expressing animals is enhanced by radiation exposure in both an LET and gender dependent fashion. These findings support the hypothesis that mitochondrial dysfunction leads to increased superoxide levels and accelerates lymphomagenesis in Lck-Bax transgenic mice.

Abstract 3729: Targeting breast cancer stem cells via oxidative stress with inhibitors of hydroperoxide metabolism and decyl-triphenylphosphonium

Cancer stem cells (CSCs) exhibit lower intracellular reactive oxygen species (ROS) levels than non-CSCs, which may be due to the increased expression of free radical scavenging systems. Exogenous agents may be useful to increase ROS and selectively kill CSCs by oxidative stress. Here we tested a combination approach to increase ROS as an effective strategy to eradicate breast CSCs and metastases. Buthionine sulfoximine (BSO) and auranofin (AU) were used to deplete glutathione (GSH) and inhibit thioredoxin reductase (TR), respectively, while mitochondrial-targeted decyltriphenylphosphonium (dTPP) was used to elevate ROS levels. In vitro clonogenicity assays using SUM159 cells showed that treatment with dTPP alone resulted in &lt;30% survival, while AU+BSO, BSO+dTPP and AU+BSO+dTPP all resulted in &lt;1% survival. These effects were reversible with N-acetylcysteine pre-treatment. The Aldefluor+ (CSC) population was also measured following drug treatment in vitro. dTPP or AU treatment alone resulted in &lt;50% of CSCs remaining, while BSO+AU or BSO+dTPP resulted in &lt;25% of CSCs remaining, and treatment with all three compounds resulted in &lt;1% of CSCs remaining. In a preclinical model of breast cancer metastasis, long-term adjuvant treatment with each individual compound significantly reduced the amount of metastases and increased survival, with dTPP treatment alone resulting in 100% survival rate. Interestingly, the combination of all three compounds resulted in increased metastases compared to the single agents. This may potentially be a stress-induced effect resulting from drug toxicity. In conclusion, the approach of increasing ROS in breast cancer cells may be an effective way to target CSCs and useful for adjuvant therapy to reduce metastases in patients.

Citation Format: Sarah J. Conley, Trenton Baker, Rebecca Theisen, Elizabeth Gheordunescu, Yueming Zhu, Nukhet Aykin-Burns, Melissa Fath, Douglas Spitz, Max Wicha. Targeting breast cancer stem cells via oxidative stress with inhibitors of hydroperoxide metabolism and decyl-triphenylphosphonium. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3729. doi:10.1158/1538-7445.AM2013-3729

Sirt3, mitochondrial ROS, ageing, and carcinogenesis

One fundamental observation in cancer etiology is that the rate of malignancies in any mammalian population increases exponentially as a function of age, suggesting a mechanistic link between the cellular processes governing longevity and carcinogenesis. In addition, it is well established that aberrations in mitochondrial metabolism, as measured by increased reactive oxygen species (ROS), are observed in both aging and cancer. In this regard, genes that impact upon longevity have recently been characterized in S. cerevisiae and C. elegans, and the human homologs include the Sirtuin family of protein deacetylases. Interestingly, three of the seven sirtuin proteins are localized into the mitochondria suggesting a connection between the mitochondrial sirtuins, the free radical theory of aging, and carcinogenesis. Based on these results it has been hypothesized that Sirt3 functions as a mitochondrial fidelity protein whose function governs both aging and carcinogenesis by modulating ROS metabolism. Sirt3 has also now been identified as a genomically expressed, mitochondrial localized tumor suppressor and this review will outline potential relationships between mitochondrial ROS/superoxide levels, aging, and cell phenotypes permissive for estrogen and progesterone receptor positive breast carcinogenesis.

An inhibitor of K+ channels modulates human endometrial tumor-initiating cells

Background

Many potassium ion (K⁺) channels function as oncogenes to sustain growth of solid tumors, but their role in cancer progression is not well understood. Emerging evidence suggests that the early progenitor cancer cell subpopulation, termed tumor initiating cells (TIC), are critical to cancer progression.

Results

A non-selective antagonist of multiple types of K⁺ channels, tetraethylammonium (TEA), was found to suppress colony formation in endometrial cancer cells via inhibition of putative TIC. The data also indicated that withdrawal of TEA results in a significant enhancement of tumorigenesis. When the TIC-enriched subpopulation was isolated from the endometrial cancer cells, TEA was also found to inhibit growth in vitro.

Conclusions

These studies suggest that the activity of potassium channels significantly contributes to the progression of endometrial tumors, and the antagonists of potassium channels are candidate anti-cancer drugs to specifically target tumor initiating cells in endometrial cancer therapy.

Oxygen tension changes the rate of migration of human skin keratinocytes in an age-related manner

Migration of keratinocytes to re-epithelialize wounds is a key step in dermal wound healing. In aged human skin, wound healing rates decrease and cellular damage by reactive oxygen species (ROS) accumulates. The relationship between age, ROS and human skin keratinocyte migration is not clearly understood. In this study, 4% and 21% oxygen tensions were used to modify levels of ROS produced by metabolism to model low and high oxidative stress conditions. When migration of keratinocytes from young and old primary skin was compared using an in vitro scratch assay, old keratinocytes migrated faster in high oxygen tension than did young keratinocytes, whereas young keratinocytes migrated faster in low oxygen tension. Although all young and old cells at the scratch margins showed intense increases in dihydroethidium oxidation immediately after scratching, the old keratinocytes grown at 21% oxygen demonstrated a greater decrease in the DHE oxidation following scratching and migrated the fastest. These results show that old and young keratinocytes respond to oxygen tension differently and support the hypothesis that keratinocyte migration is affected by the capacity to remove ROS.

The p53/p21(WAF/CIP) pathway mediates oxidative stress and senescence in dyskeratosis congenita cells with telomerase insufficiency

Telomere attrition is a natural process that occurs due to inadequate telomere maintenance. Once at a critically short threshold, telomeres signal growth arrest, leading to senescence. Telomeres can be elongated by the enzyme telomerase, which adds de novo telomere repeats to the ends of chromosomes. Mutations in genes for telomere binding proteins or components of telomerase give rise to the premature aging disorder dyskeratosis congenita (DC), which is characterized by extremely short telomeres and an aging phenotype. The current study demonstrates that DC cells signal a DNA damage response through p53 and its downstream mediator, p21(WAF/CIP), which is accompanied by an elevation in steady-state levels of superoxide and percent glutathione disulfide, both indicators of oxidative stress. Poor proliferation of DC cells can be partially overcome by reducing O(2) tension from 21% to 4%. Further, restoring telomerase activity or inhibiting p53 or p21(WAF/CIP) significantly mitigated growth inhibition as well as caused a significant decrease in steady-state levels of superoxide. Our results support a model in which telomerase insufficiency in DC leads to p21(WAF/CIP) signaling, via p53, to cause increased steady-state levels of superoxide, metabolic oxidative stress, and senescence.

Sensitivity to low-dose/low-LET ionizing radiation in mammalian cells harboring mutations in succinate dehydrogenase subunit C is governed by mitochondria-derived reactive oxygen species

It has been hypothesized that ionizing radiation-induced disruptions in mitochondrial O₂ metabolism lead to persistent heritable increases in steady-state levels of intracellular superoxide (O₂(•U+2212)) and hydrogen peroxide (H₂O₂) that contribute to the biological effects of radiation. Hamster fibroblasts (B9 cells) expressing a mutation in the gene coding for the mitochondrial electron transport chain protein succinate dehydrogenase subunit C (SDHC) demonstrate increases in steady-state levels of O₂•- and H₂O₂. When B9 cells were exposed to low-dose/low-LET radiation (5-50 cGy), they displayed significantly increased clonogenic cell killing compared with parental cells. Clones derived from B9 cells overexpressing a wild-type human SDHC (T4, T8) demonstrated significantly increased surviving fractions after exposure to 5-50 cGy relative to B9 vector controls. In addition, pretreatment with polyethylene glycol-conjugated CuZn superoxide dismutase and catalase as well as adenoviral-mediated overexpression of MnSOD and/or mitochondria-targeted catalase resulted in significantly increased survival of B9 cells exposed to 10 cGy ionizing radiation relative to vector controls. Adenoviral-mediated overexpression of either MnSOD or mitochondria-targeted catalase alone was equally as effective as when both were combined. These results show that mammalian cells over expressing mutations in SDHC demonstrate low-dose/low-LET radiation sensitization that is mediated by increased levels of O₂•- and H₂O₂. These results also support the hypothesis that mitochondrial O₂•- and H₂O₂ originating from SDH are capable of playing a role in low-dose ionizing radiation-induced biological responses.

2-deoxy-D-glucose induces oxidative stress and cell killing in human neuroblastoma cells

Malignant cells have a demonstrably greater sensitivity to glucose deprivation-induced cytotoxicity than normal cells. This has been hypothesized to be due to a higher level of reactive oxygen species (ROS) production in cancer cells leading to the increased need for reducing equivalents, produced by glucose metabolism, to detoxify hydroperoxides. Because complete glucose deprivation cannot be achieved in vivo, it has been proposed that agents that antagonize glucose metabolism, such as 2-deoxy-D-glucose (2DG), can mimic in vitro glucose deprivation that selectively kills cancer cells by oxidative stress. To test this hypothesis, neuroblastoma cell lines were treated with 2DG and the effects on clonogenic survival and the distribution of cellular phenotypes among surviving colonies was determined. The results showed that all three major cell types found in neuroblastoma (Schwann, Neuronal and Intermediate) were sensitive to 2DG-induced clonogenic cell killing. Furthermore, treatment with the thiol antioxidant, N-acetyl cysteine or with polyethylene glycol-conjugated superoxide dismutase and catalase, protected neuroblastoma cells from 2DG-induced cell killing. Finally normal non-immortalized neural precursor cells were relatively resistant to 2DG-induced cell killing when compared to neuroblastoma cell lines. These results support the hypothesis that inhibitors of glucose metabolism could represent useful adjuvants in the treatment of neuroblastoma by selectively enhancing metabolic oxidative stress.

SIRT3 is a mitochondria-localized tumor suppressor required for maintenance of mitochondrial integrity and metabolism during stress

The sirtuin gene family (SIRT) is hypothesized to regulate the aging process and play a role in cellular repair. This work demonstrates that SIRT3(-/-) mouse embryonic fibroblasts (MEFs) exhibit abnormal mitochondrial physiology as well as increases in stress-induced superoxide levels and genomic instability. Expression of a single oncogene (Myc or Ras) in SIRT3(-/-) MEFs results in in vitro transformation and altered intracellular metabolism. Superoxide dismutase prevents transformation by a single oncogene in SIRT3(-/-) MEFs and reverses the tumor-permissive phenotype as well as stress-induced genomic instability. In addition, SIRT3(-/-) mice develop ER/PR-positive mammary tumors. Finally, human breast and other human cancer specimens exhibit reduced SIRT3 levels. These results identify SIRT3 as a genomically expressed, mitochondria-localized tumor suppressor.

Polychlorinated-biphenyl-induced oxidative stress and cytotoxicity can be mitigated by antioxidants after exposure

PCBs and PCB metabolites have been suggested to cause cytotoxicity by inducing oxidative stress, but the effectiveness of antioxidant intervention after exposure has not been established. Exponentially growing MCF-10A human breast and RWPE-1 human prostate epithelial cells continuously exposed for 5 days to 3 microM PCBs [Aroclor 1254 (Aroclor), PCB153, and the 2-(4-chlorophenyl)-1,4-benzoquinone metabolite of PCB3 (4ClBQ)] were found to exhibit growth inhibition and clonogenic cell killing, with 4ClBQ having the most pronounced effects. These PCBs were also found to increase steady-state levels of intracellular O(2)(*-) and H(2)O(2) (as determined by dihydroethidium, MitoSOX red, and 5-(and 6)-carboxy-2',7'-dichlorodihydrofluorescein diacetate oxidation). These PCBs also caused 1.5- to 5.0-fold increases in MnSOD activity in MCF-10A cells and 2.5- to 5-fold increases in CuZnSOD activity in RWPE-1 cells. Measurement of MitoSOX red oxidation with confocal microscopy coupled with colocalization of MitoTracker green in MCF-10A and RWPE-1 cells supported the hypothesis that PCBs caused increased steady-state levels of O(2)(*-) in mitochondria. Finally, treatment with either N-acetylcysteine (NAC) or the combination of polyethylene glycol (PEG)-conjugated CuZnSOD and PEG-catalase added 1 h after PCBs significantly protected these cells from PCB toxicity. These results support the hypothesis that exposure of exponentially growing human breast and prostate epithelial cells to PCBs causes increased steady-state levels of intracellular O(2)(*-) and H(2)O(2), induction of MnSOD or CuZnSOD activity, and clonogenic cell killing that could be inhibited by a clinically relevant thiol antioxidant, NAC, as well as by catalase and superoxide dismutase after PCB exposure.

Mitochondrial complex II dysfunction can contribute significantly to genomic instability after exposure to ionizing radiation

Ionizing radiation induces chronic metabolic oxidative stress and a mutator phenotype in hamster fibroblasts that is mediated by H(2)O(2), but the intracellular source of H(2)O(2) is not well defined. To determine the role of mitochondria in the radiation-induced mutator phenotype, end points of mitochondrial function were determined in unstable (CS-9 and LS-12) and stable (114) hamster fibroblast cell lines derived from GM10115 cells exposed to 10 Gy X rays. Cell lines isolated after irradiation demonstrated a 20-40% loss of mitochondrial membrane potential and an increase in mitochondrial content compared to the parental cell line GM10115. Surprisingly, no differences were observed in steady-state levels of ATP (P > 0.05). Unstable clones demonstrated increased oxygen consumption (two- to threefold; CS-9) and/or increased mitochondrial electron transport chain (ETC) complex II activity (twofold; LS-12). Using Western blot analysis and Blue Native gel electrophoresis, a significant increase in complex II subunit B protein levels was observed in LS-12 cells. Furthermore, immunoprecipitation assays revealed evidence of abnormal complex II assembly in LS-12 cells. Treatment of LS-12 cells with an inhibitor of ETC complex II (thenoyltrifluoroacetone) resulted in significant decreases in the steady-state levels of H(2)O(2) and a 50% reduction in mutation frequency as well as a 16% reduction in CAD gene amplification frequency. These data show that radiation-induced genomic instability was accompanied by evidence of mitochondrial dysfunction leading to increased steady-state levels of H(2)O(2) that contributed to increased mutation frequency and gene amplification. These results support the hypothesis that mitochondrial dysfunction originating from complex II can contribute to radiation-induced genomic instability by increasing steady-state levels of reactive oxygen species.

Mitochondrial electron transport chain blockers enhance 2-deoxy-D-glucose induced oxidative stress and cell killing in human colon carcinoma cells

Increasing evidence suggests that cancer cells (relative to normal cells) have altered mitochondrial electron transport chains (ETC) that are more likely to form reactive oxygen species (ROS; i.e., O(2)(*-) and H(2)O(2)) resulting in a condition of chronic metabolic oxidative stress, that maybe compensated for by increasing glucose and hydroperoxide metabolism. In the current study, the ability of an inhibitor of glucose metabolism, 2-deoxy-D-glucose (2DG), combined with mitochondrial electron transport chain blockers (ETCBs) to enhance oxidative stress and cytotoxicity was determined in human colon cancer cells. Treatment of HT29 and HCT116 cancer cells with Antimycin A (Ant A) or rotenone (Rot) increased carboxy-dichlorodihydrofluorescein diacetate (H2DCFDA) and dihydroethidine (DHE) oxidation, caused the accumulation of glutathione disulfide and enhanced 2DG-induced cell killing. In contrast, Rot did not enhance the toxicity of 2DG in normal human fibroblasts supporting the hypotheses that cancer cells are more susceptible to inhibition of glucose metabolism in the presence of ETCBs. In addition, 2-methoxy-antimycin A (Meth A; an analog of Ant A that does not have ETCB activity) did not enhance 2DG-induced DHE oxidation or cytotoxicity in cancer cells. Finally, in HT29 tumor bearing mice treated with the combination of 2DG (500 mg/kg) + Rot (2 mg/kg) the average rate of tumor growth was significantly slower when compared to control or either drug alone. These results show that 2DG-induced cytotoxicity and oxidative stress can be significantly enhanced by ETCBs in human colon cancer cells both in vitro and in vivo.

Cisplatin combined with zidovudine enhances cytotoxicity and oxidative stress in human head and neck cancer cells via a thiol-dependent mechanism

Oxidative stress and mitochondrial dysfunction in cancer cells represent features that may be exploited therapeutically. We determined whether agents that induce mitochondrial dysfunction, such as zidovudine (AZT) and cisplatin (CIS), could enhance killing of human head and neck cancer cells via oxidative stress. AZT- and/or CIS-induced cytotoxicity was determined using clonogenic survival, mitochondrial membrane potential was analyzed to investigate mitochondrial function, and glutathione was measured to determine thiol metabolism perturbations. AZT+CIS significantly increased toxicity and reduced mitochondrial membrane potential in FaDu, Cal-27, and SQ20B head and neck cancer cells while increasing the percentage of glutathione disulfide (%GSSG). Treatment with the thiol antioxidant N-acetylcysteine (NAC) reversed the loss of mitochondrial membrane potential and the increase in %GSSG and partially protected FaDu and Cal-27 cells from AZT+CIS. Finally, an inhibitor of glutathione synthesis, l-buthionine-[S,R]-sulfoximine, sensitized the cells to AZT+CIS-induced cytotoxicity, which was partially reversed by NAC. These results suggest that exposure of cancer cells to agents that induce mitochondrial dysfunction, such as AZT, causes significant sensitization to CIS-induced toxicity via disruptions in thiol metabolism and oxidative stress. These findings provide a biochemical rationale for evaluating agents that induce mitochondrial dysfunction in combination with chemotherapy and inhibitors of glutathione metabolism in head and neck cancer.

Cigarette smoke induces cellular senescence via Werner's syndrome protein down-regulation

RATIONALE

Werner's syndrome is a genetic disorder that causes premature aging due to loss-of-function mutations in a gene encoding a member of the RecQ helicase family. Both Werner's syndrome and cigarette smoking accelerate aging. No studies have examined the effect of cigarette smoke on Werner's syndrome protein.

OBJECTIVES

To investigate the role of Werner's syndrome protein in cigarette smoke-induced cellular senescence.

METHODS

Cellular senescence and amounts of Werner's syndrome protein were measured in fibroblasts isolated from patients with emphysema and compared with age-matched nonsmokers. The in vitro effects of cigarette smoke on amounts of Werner's syndrome protein, function, and senescence were also evaluated in primary human lung fibroblasts and epithelial cells.

MEASUREMENTS AND MAIN RESULTS

Cultured lung fibroblasts isolated from patients with emphysema exhibited a senescent phenotype accompanied by a decrease in Werner's syndrome protein. Cigarette smoke extract decreased Werner's syndrome protein in cultured fibroblasts and epithelial cells. Werner's syndrome protein-deficient fibroblasts were more susceptible to cigarette smoke-induced cellular senescence and cell migration impairment. In contrast, exogenous overexpression of Werner's syndrome protein attenuated the cigarette smoke effects.

CONCLUSIONS

Cigarette smoke induces cellular senescence and cell migration impairment via Werner's syndrome protein down-regulation. Rescue of Werner's syndrome protein down-regulation may represent a potential therapeutic target for smoking-related diseases.

SIRT3 interacts with the daf-16 homolog FOXO3a in the mitochondria, as well as increases FOXO3a dependent gene expression

Cellular longevity is a complex process relevant to age-related diseases including but not limited to chronic illness such as diabetes and metabolic syndromes. Two gene families have been shown to play a role in the genetic regulation of longevity; the Sirtuin and FOXO families. It is also established that nuclear Sirtuins interact with and under specific cellular conditions regulate the activity of FOXO gene family proteins. Thus, we hypothesize that a mitochondrial Sirtuin (SIRT3) might also interact with and regulate the activity of the FOXO proteins. To address this we used HCT116 cells overexpressing either wild-type or a catalytically inactive dominant negative SIRT3. For the first time we establish that FOXO3a is also a mitochondrial protein and forms a physical interaction with SIRT3 in mitochondria. Overexpression of a wild-type SIRT3 gene increase FOXO3a DNA-binding activity as well as FOXO3a dependent gene expression. Biochemical analysis of HCT116 cells over expressing the deacetylation mutant, as compared to wild-type SIRT3 gene, demonstrated an overall oxidized intracellular environment, as monitored by increase in intracellular superoxide and oxidized glutathione levels. As such, we propose that SIRT3 and FOXO3a comprise a potential mitochondrial signaling cascade response pathway.