The hypothesis that the Akt inhibitor, perifosine (PER), combined with inhibitors of glutathione ... more The hypothesis that the Akt inhibitor, perifosine (PER), combined with inhibitors of glutathione (GSH) and thioredoxin (Trx) metabolism will induce cytotoxicity via metabolic oxidative stress in human head and neck cancer (HNSCC) cells was tested. PER induced increases in glutathione disulfide (%GSSG) in FaDu, Cal-27, and SCC-25 HNSCCs as well as causing significant clonogenic cell killing in FaDu and Cal-27, which was suppressed by simultaneous treatment with N-acetylcysteine (NAC). An inhibitor of GSH synthesis, buthionine sulfoximine (BSO), sensitized Cal-27 and SCC-25 cells to PER-induced clonogenic killing as well as decreased total GSH and increased %GSSG. Additionally, inhibition of thioredoxin reductase activity (TrxRed) with auranofin (AUR) was able to induce PER sensitization in SCC-25 cells that were initially refractory to PER. These results support the conclusion that PER induces oxidative stress and clonogenic killing in HNSCC cells that is enhanced with inhibitors of ...
Redox regulation of epidermal growth factor receptor (EGFR) signaling helps protect cells against... more Redox regulation of epidermal growth factor receptor (EGFR) signaling helps protect cells against oxidative stress. In this study, we investigated whether the cytotoxicity of an EGFR tyrosine kinase inhibitor, erlotinib (ERL), was mediated by induction of oxidative stress in human head and neck cancer (HNSCC) cells. ERL elicited cytotoxicity in vitro and in vivo while increasing a panel of oxidative stress parameters which were all reversible by the antioxidant N-acetyl cysteine. Knockdown of EGFR by using siRNA similarly increased these oxidative stress parameters. Overexpression of mitochondrial targeted catalase but not superoxide dismutase reversed ERL-induced cytotoxicity. Consistent with a general role for NADPH oxidase (NOX) enzymes in ERL-induced oxidative stress, ERL-induced cytotoxicity was reversed by diphenylene iodonium, a NOX complex inhibitor. ERL reduced the expression of NOX1, NOX2, and NOX5 but induced the expression of NOX4. Knockdown of NOX4 by using siRNA protec...
Ketogenic diets are low in carbohydrates and high in fat, which forces cells to rely more heavily... more Ketogenic diets are low in carbohydrates and high in fat, which forces cells to rely more heavily upon mitochondrial oxidation of fatty acids for energy. Relative to normal cells, cancer cells are believed to exist under a condition of chronic mitochondrial oxidative stress that is compensated for by increases in glucose metabolism to generate reducing equivalents. In this study we tested the hypothesis that a ketogenic diet concurrent with radiation and chemotherapy would be clinically tolerable in locally advanced non-small cell lung cancer (NSCLC) and pancreatic cancer and could potentially exploit cancer cell oxidative metabolism to improve therapeutic outcomes. Mice bearing MIA PaCa-2 pancreatic cancer xenografts were fed either a ketogenic diet or standard rodent chow, treated with conventionally fractionated radiation (2 Gy/fraction), and tumor growth rates were assessed daily. Tumors were assessed for immunoreactive 4-hydroxy-2-nonenal-(4HNE)-modfied proteins as a marker of ...
Purpose: Ketogenic diets are high in fat and low in carbohydrates as well as protein which forces... more Purpose: Ketogenic diets are high in fat and low in carbohydrates as well as protein which forces cells to rely on lipid oxidation and mitochondrial respiration rather than glycolysis for energy metabolism. Cancer cells (relative to normal cells) are believed to exist in a state of chronic oxidative stress mediated by mitochondrial metabolism. The current study tests the hypothesis that ketogenic diets enhance radio-chemo-therapy responses in lung cancer xenografts by enhancing oxidative stress. Experimental Design: Mice bearing NCI-H292 and A549 lung cancer xenografts were fed a ketogenic diet (KetoCal 4:1 fats: proteins+carbohydrates) and treated with either conventionally fractionated (1.8–2 Gy) or hypofractionated (6 Gy) radiation as well as conventionally fractionated radiation combined with carboplatin. Mice weights and tumor size were monitored. Tumors were assessed for immunoreactive 4-hydroxy-2-nonenal-(4HNE)–modified proteins as a marker of oxidative stress as well as prol...
Tumor cell proliferation, de-differentiation, and progression depend on a complex combination of ... more Tumor cell proliferation, de-differentiation, and progression depend on a complex combination of altered cell cycle regulation, excessive growth factor pathway activation, and decreased apoptosis. The understanding of these complex mechanisms should lead to the identification of potential targets for therapeutic intervention. Redox-sensitive signaling factors also regulate multiple cellular processes including proliferation, cell cycle, and pro-survival signaling cascades, suggesting their potential as molecular targets for anticancer agents. These observations suggest that redox-sensitive signaling factors may be potential novel molecular markers. We hypothesized that thioredoxin reductase-1 (TR), a component of several redox-regulated pathways, may represent a potential molecular target candidate in response to agents that induce oxidative stress. There have been numerous biological studies over the last decade investigating the cell biological, biochemical, and genetic properties of TR both in culture and in in vivo models. In addition, using a series of permanent cell lines that express either a wild-type TR or a dominant mutant TR gene or a chemical agent that inhibits TR we demonstrated that TR meets most criteria that would identify a molecular target. Based on these results we believe TR is a potential molecular target and discuss potential clinical possibilities.
The sirtuin gene family (SIRT) is hypothesized to regulate the aging process and play a role in c... more The sirtuin gene family (SIRT) is hypothesized to regulate the aging process and play a role in cellular repair. This work demonstrates that SIRT3 À/À 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 À/À MEFs results in in vitro transformation and altered intracellular metabolism. Superoxide dismutase prevents transformation by a single oncogene in SIRT3 À/À MEFs and reverses the tumor-permissive phenotype as well as stress-induced genomic instability. In addition, SIRT3 À/À 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.
Increasing evidence suggests that cancer cells (relative to normal cells) have altered mitochondr... more 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
Manganese superoxide dismutase (SOD2) is a nuclear encoded and mitochondria localized antioxidant... more Manganese superoxide dismutase (SOD2) is a nuclear encoded and mitochondria localized antioxidant enzyme that converts mitochondria derived superoxide to hydrogen peroxide. This study investigates the hypothesis that mitochondria derived reactive oxygen species (ROS) regulate ionizing radiation (IR) induced transformation in normal cells. Mouse embryonic fibroblasts (MEFs) with wild type SOD2 (+/+), heterozygous SOD2 (+/−), and homozygous SOD2 (−/−) genotypes were irradiated with equitoxic doses of IR, and assayed for transformation frequency, cellular redox environment, DNA damage, and cell cycle checkpoint activation. Transformation frequency increased (~ 5-fold) in SOD2 (−/−) compared to SOD2 (+/+) MEFs. Cellular redox environment (GSH, GSSG, DHE, and DCFH-oxidation) did not show any significant change within 24h post-IR. However, a significant increase in cellular ROS levels was observed at 72h post-IR in SOD2 (−/−) compared to SOD2 (+/+) MEFs, which was consistent with an increase in GSSG in SOD2 (−/−) MEFs. Late ROS accumulation was associated with an increase in micronuclei frequency in SOD2 (−/−) MEFs. Exit from G 2 was accelerated in irradiated SOD2 (+/−) and SOD2 (−/−) compared to SOD2 (+/+) MEFs. These results support the hypothesis that SOD2 activity and mitochondria generated ROS regulate IR induced transformation in mouse embryonic fibroblasts.
Malignant cells have a demonstrably greater sensitivity to glucose deprivation-induced cytotoxici... more 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.
Exposure of eukaryotic cells to ionizing radiation (IR) results in the immediate formation of fre... more Exposure of eukaryotic cells to ionizing radiation (IR) results in the immediate formation of free radicals that last a matter of milliseconds. It has been assumed that the subsequent alterations in multiple intracellular processes following irradiation is due to the initial oxidative damage caused by these free radicals. However, it is becoming increasingly clear that intracellular metabolic oxidation/reduction (redox) reactions can be affected by this initial IR-induced free radical insult and may remain perturbed for minutes, hours, or days. It would seem logical that these cellular redox reactions might contribute to the activation of protective or damaging processes that could impact upon the damaging effects of IR. These processes include redox sensitive signaling pathways, transcription factor activation, gene expression, and metabolic activities that govern the formation of intracellular oxidants and reductants. The physiological manifestations of these radiation-induced alterations in redox sensitive processes have been suggested to contribute to adaptive responses, bystander effects, cell cycle perturbations, cytotoxicity, heat-induced radiosensitization, genomic instability, inflammation, and fibrosis. While a great deal is known about the molecular changes associated with the initial production of free radicals at the time of irradiation, the contribution of perturbations in redox sensitive metabolic processes to biological outcomes following exposure to IR is only recently becoming established. This review will focus on evidence supporting the concept that perturbations in intracellular metabolic oxidation/reduction reactions contribute to the biological effects of radiation exposure as well as new concepts emerging from the field of free radical biology that may be relevant to future studies in radiobiology.
Cancer cells, relative to normal cells, demonstrate increased sensitivity to glucose deprivationi... more Cancer cells, relative to normal cells, demonstrate increased sensitivity to glucose deprivationinduced cytotoxicity. To determine if oxidative stress mediated by O 2
Chronic oxidative stress has been associated with genomic instability following exposure to ioniz... more Chronic oxidative stress has been associated with genomic instability following exposure to ionizing radiation (IR). However, data showing direct causal linkages between specific reactive oxygen species and the IR-induced mutator phenotype are lacking. The current study demonstrates that IRinduced genomically unstable cells (characterized by chromosomal instability and increased mutation and gene amplification frequencies) show a 3-fold increase in steady-state levels of hydrogen peroxide, but not superoxide. Furthermore, stable clones isolated from parallel studies showed significant increases in catalase and glutathione-peroxidase activity. Treatment of unstable cells with polyethylene glycol-conjugated catalase [PEG-CAT] reduced the mutation frequency and mutation rate in a dose dependent fashion. In addition, inhibiting catalase activity in the stable clones using 3-aminotriazole increased mutation frequency and rate. These results clearly demonstrate the causal relationship between chronic oxidative stress mediated by hydrogen peroxide and the mutator phenotype that persists many generations following exposure of mammalian cells to IR.
Biochemical and Biophysical Research Communications, 1997
Glutathione is synthesized by two enzymes, g-gluta-The gene GLCLC encodes the catalytic subunit o... more Glutathione is synthesized by two enzymes, g-gluta-The gene GLCLC encodes the catalytic subunit of mylcysteine synthetase, the rate limiting enzyme, and gamma-glutamylcysteine synthetase (glutamate-cysglutathione synthetase. g-Glutamylcysteine syntheteine ligase E.C. 6.3.2.2), the rate limiting enzyme for tase is a heterodimeric enzyme composed of a catalytic glutathione synthesis. When HepG2 cells were exposed subunit that exhibits GSH feedback inhibition, and a to the serine/threonine phosphatase inhibitor okadaic regulatory subunit that influences the K m for glutaacid (OA), increased expression of GLCLC was obmate binding (6).
, are large scale industrial chemicals but their disposition and toxicity are poorly understood d... more , are large scale industrial chemicals but their disposition and toxicity are poorly understood despite significant human exposure. The hypothesis that subacute exposure to N-EtFOSE, a weak peroxisome proliferator, causes a redox imbalance in vivo was tested using the known peroxisome proliferator, ciprofibrate, as a positive control. Female Sprague-Dawley rats were treated orally with N-EtFOSE, ciprofibrate or corn oil (vehicle) for 21 days, and levels of N-EtFOSE and its metabolites as well as markers of peroxisome proliferation and oxidative stress were assessed in serum, liver and/or uterus. The N-EtFOSE metabolite profile in liver and serum was in good agreement with reported in vitro biotransformation pathways in rats and the metabolite levels decreasing in the order perfluorooctanesulfonate ≫ perfluorooctanesulfonamide ∼ N-ethyl perfluorooctanesulfonamidoacetate ≫ perfluorooctanesulfonamidoethanol ∼ N-EtFOSE. Although N-EtFOSE treatment significantly decreased the growth rate, increased relative liver weight and activity of superoxide dismutases (SOD) in liver and uterus (total SOD, CuZnSOD and MnSOD), a metabolic study revealed no differences in the metabolome in serum from N-EtFOSE-treated and control animals. Ciprofibrate treatment increased liver weight and peroxisomal acyl Co-A oxidase activity in the liver and altered antioxidant enzyme activities in the uterus and liver. According to NMR metabolomic studies, ciprofibrate treated animals had altered serum lipid profiles compared to N-EtFOSE-treated and control animals, whereas putative markers of peroxisome proliferation in serum were not affected. Overall, this study demonstrates the biotransformation of N-EtFOSE to PFOS in rats that is accompanied by N-EtFOSE-induced alterations in antioxidant enzyme activity.
Archives of Environmental Contamination and Toxicology, 2000
Evidence implicating oxidative stress in toxicity during lead intoxication in vivo has opened new... more Evidence implicating oxidative stress in toxicity during lead intoxication in vivo has opened new avenues for investigation of the mechanisms of lead-induced immunosuppression. The current study explores the possibility that lead-induced oxidative stress contributes to the immunosuppression observed during lead poisoning. Fisher 344 rats were exposed to 2,000 ppm lead acetate in their drinking water for 5 weeks. One week following removal of lead from the drinking water, significant reductions in serum levels of IgA, IgM, and IgG were detected. Significant increases in oxidative damage, based on malondialdehyde (MDA) content, were observed in peripheral blood mononuclear cells (PMCs) collected during the same experiments. In addition, MDA content increased in livers from lead-exposed rats. Following 5 weeks of lead exposure, administration of either 5.5 mmol/kg N-acetylcysteine (NAC) or 1 mmol/kg meso-2,3-dimercaptosuccinic acid (DMSA) in the drinking water for 1 week significantly reversed the inhibitory effects of lead on serum immunoglobulin (Ig) levels. Also, all parameters indicative of oxidative stress returned to control levels. These results suggest that oxidative stress contributes to suppressed serum Ig levels during lead intoxication in vivo, and that intervention with either a thiol antioxidant (NAC) or a metal chelator (DMSA) will alleviate this lead-induced suppression by correcting the prooxidant/antioxidant imbalance caused by lead exposure.
Following exposure to 95% oxygen, clonogenic cell survival was assayed and qualitative morphologi... more Following exposure to 95% oxygen, clonogenic cell survival was assayed and qualitative morphologic changes were observed in a Chinese hamster fibroblast cell line (HA-1). The time in 95% O2 necessary to clonogenically inactivate 90% of the cells was inversely related to the cell density of the cultures at the beginning of hyperoxic exposure (from 1 to 6 X 10(4) cells/cm2). The O2-induced loss in clonogenicity and evidence of morphologic injury were shown to be significantly delayed (17-22 h) in an H2O2-resistant variant of the parental HA-1 cell line. After the delay in onset of clonogenic cell killing or morphologic injury, the process of injury proceeded in a similar fashion in both cell lines. The H2O2-resistant cell line demonstrated significantly greater catalase activity (20-fold), CuZn superoxide dismutase activity (2-fold), and Se-dependent glutathione peroxidase activity (1.5-fold). The greater activities of CuZn superoxide dismutase and catalase were accompanied by similarly greater quantities of immunoreactive protein as determined by immunoblotting. These data demonstrate that the cells adapted and/or selected for growth in a highly peroxidative environment also became refractory to O2-induced toxicity, which may be related to increased expression of antioxidant enzymes. However, the magnitude of this cross-resistance to O2 toxicity was less than the magnitude of the cellular resistance to the toxicity of exogenous H2O2, suggesting that in this system the toxicity of 95% oxygen is not identical to H2O2-mediated cytotoxicity.
The biological effects of ionizing radiation (IR) from environmental, medical, and man-made sourc... more The biological effects of ionizing radiation (IR) from environmental, medical, and man-made sources, as well as from space exploration are of broad health concern. During the last 40 years it has become evident that, in addition to short-lived free radical-mediated events initiated within microseconds of exposure and generally thought to dissipate within milliseconds, IR-induced production of reactive oxygen and nitrogen species as well as changes in redox signaling linked to disruption of metabolic processes persist long after radiation exposure. Furthermore, persistent IR-induced increases in the metabolic production of reactive oxygen and nitrogen species appear to significantly contribute to the delayed effects of IR exposure, including induction of adaptive responses at low doses as well as carcinogenesis, fibrosis, inflammation, genomic instability, and acceleration of the onset of degenerative tissue injury processes associated with aging. The ability to identify the specific metabolic mechanisms and dose-response relationships that contribute to adaptive responses as well as persistent IR-induced injury processes holds great promise for identifying novel strategies to mitigate the deleterious effects of IR exposure as well as for gathering mechanistic information critical for risk assessment. This Forum contains original and review articles authored by experts in the field of radiobiology focusing on novel mechanisms involving redox biology and metabolism that significantly contribute to the persistent biological effects seen following IR exposure.
Over the last three decades, it is has become increasing clear that intracellular signaling pathw... more Over the last three decades, it is has become increasing clear that intracellular signaling pathways are activated via changes in intracellular metabolic oxidation/reduction (redox) reactions involving reactive oxygen species (ROS; i.e., superoxide and hydrogen peroxide). The initial proposals hypothesized that signaling through metabolic oxidation/reduction (redox) reactions involving ROS could contribute to carcinogenesis and progression to malignancy. Strong evidence for this hypothesis was obtained from studies showing that environmental insults (i.e., ionizing radiation) as well as xenobiotics (i.e., polycyclic aromatic hydrocarbons and phorbol esters) capable of inducing steady-state increases in free radical production and ROS could act as both initiators and promoters of carcinogenesis. This Forum is directed at understanding possible redox signaling mechanisms governing cellular radiation response, tumor growth, and response to therapy, as well as the role of nitric oxide in cancer biology.
Mitochondrial reactive oxygen species (ROS) are mainly produced by the respiratory chain enzymes.... more Mitochondrial reactive oxygen species (ROS) are mainly produced by the respiratory chain enzymes. The sites for ROS production in mitochondrial respiratory chain are normally ascribed to the activity of Complex I and III. The presence of specific inhibitors modulates reactive oxygen species production in Complex I: inhibitors such as rotenone induce a strong ROS increase, while inhibitors such as stigmatellin prevent it. We have investigated the effect of hydrophilic quinones on Complex I ROS production in presence of different inhibitors. Some short chain quinones are Complex I inhibitors (CoQ2, idebenone and its derivatives), while CoQ1, decylubiquinone (DB) and duroquinone (DQ) are good electron acceptors from Complex I.
A method for the spectrophotometric determination of nitric oxide, nitrite, and nitrate in tissue... more A method for the spectrophotometric determination of nitric oxide, nitrite, and nitrate in tissue culture media is presented. The method is based on the nitric oxide-mediated nitrosative modification of sulfanilic acid that reacts with N-(1-naphthyl)ethylenediamine dihydrochloride forming an orange-colored product absorbing at 496 nm. Nitric oxide levels were determined in culture media from this absorbance measurement using chemiluminescence standardization. Extinction coefficients of 5400 and 6600 M ؊1 cm ؊1 were determined for the nitric oxide product in assay solutions containing 0.1 or 100 mM KPO 4 buffer (pH 7.4), respectively, with a limit of detection of 1 M. Acidification of these reactions (pH 2.4) generated a pinkcolored product absorbing at 540 nm allowing for quantitation of total nitric oxide/nitrite levels using extinction coefficients of 38,000 and 36,900 M ؊1 cm ؊1 , for the assay solutions described. The limit of detection of this assay was approximately 300 nM. Using the 100 mM KPO 4 buffer system, nitrate levels were determined following reduction to nitrite using a coppercoated cadmium reagent with an extinction coefficient of 29,500 M ؊1 cm ؊1 and a detection limit of 0.5 M. The utility of these assays was demonstrated in the standardization of nitric oxide-saturated cell culture media, and the release of nitric oxide by the NONOate compound DEA/NO.
The hypothesis that the Akt inhibitor, perifosine (PER), combined with inhibitors of glutathione ... more The hypothesis that the Akt inhibitor, perifosine (PER), combined with inhibitors of glutathione (GSH) and thioredoxin (Trx) metabolism will induce cytotoxicity via metabolic oxidative stress in human head and neck cancer (HNSCC) cells was tested. PER induced increases in glutathione disulfide (%GSSG) in FaDu, Cal-27, and SCC-25 HNSCCs as well as causing significant clonogenic cell killing in FaDu and Cal-27, which was suppressed by simultaneous treatment with N-acetylcysteine (NAC). An inhibitor of GSH synthesis, buthionine sulfoximine (BSO), sensitized Cal-27 and SCC-25 cells to PER-induced clonogenic killing as well as decreased total GSH and increased %GSSG. Additionally, inhibition of thioredoxin reductase activity (TrxRed) with auranofin (AUR) was able to induce PER sensitization in SCC-25 cells that were initially refractory to PER. These results support the conclusion that PER induces oxidative stress and clonogenic killing in HNSCC cells that is enhanced with inhibitors of ...
Redox regulation of epidermal growth factor receptor (EGFR) signaling helps protect cells against... more Redox regulation of epidermal growth factor receptor (EGFR) signaling helps protect cells against oxidative stress. In this study, we investigated whether the cytotoxicity of an EGFR tyrosine kinase inhibitor, erlotinib (ERL), was mediated by induction of oxidative stress in human head and neck cancer (HNSCC) cells. ERL elicited cytotoxicity in vitro and in vivo while increasing a panel of oxidative stress parameters which were all reversible by the antioxidant N-acetyl cysteine. Knockdown of EGFR by using siRNA similarly increased these oxidative stress parameters. Overexpression of mitochondrial targeted catalase but not superoxide dismutase reversed ERL-induced cytotoxicity. Consistent with a general role for NADPH oxidase (NOX) enzymes in ERL-induced oxidative stress, ERL-induced cytotoxicity was reversed by diphenylene iodonium, a NOX complex inhibitor. ERL reduced the expression of NOX1, NOX2, and NOX5 but induced the expression of NOX4. Knockdown of NOX4 by using siRNA protec...
Ketogenic diets are low in carbohydrates and high in fat, which forces cells to rely more heavily... more Ketogenic diets are low in carbohydrates and high in fat, which forces cells to rely more heavily upon mitochondrial oxidation of fatty acids for energy. Relative to normal cells, cancer cells are believed to exist under a condition of chronic mitochondrial oxidative stress that is compensated for by increases in glucose metabolism to generate reducing equivalents. In this study we tested the hypothesis that a ketogenic diet concurrent with radiation and chemotherapy would be clinically tolerable in locally advanced non-small cell lung cancer (NSCLC) and pancreatic cancer and could potentially exploit cancer cell oxidative metabolism to improve therapeutic outcomes. Mice bearing MIA PaCa-2 pancreatic cancer xenografts were fed either a ketogenic diet or standard rodent chow, treated with conventionally fractionated radiation (2 Gy/fraction), and tumor growth rates were assessed daily. Tumors were assessed for immunoreactive 4-hydroxy-2-nonenal-(4HNE)-modfied proteins as a marker of ...
Purpose: Ketogenic diets are high in fat and low in carbohydrates as well as protein which forces... more Purpose: Ketogenic diets are high in fat and low in carbohydrates as well as protein which forces cells to rely on lipid oxidation and mitochondrial respiration rather than glycolysis for energy metabolism. Cancer cells (relative to normal cells) are believed to exist in a state of chronic oxidative stress mediated by mitochondrial metabolism. The current study tests the hypothesis that ketogenic diets enhance radio-chemo-therapy responses in lung cancer xenografts by enhancing oxidative stress. Experimental Design: Mice bearing NCI-H292 and A549 lung cancer xenografts were fed a ketogenic diet (KetoCal 4:1 fats: proteins+carbohydrates) and treated with either conventionally fractionated (1.8–2 Gy) or hypofractionated (6 Gy) radiation as well as conventionally fractionated radiation combined with carboplatin. Mice weights and tumor size were monitored. Tumors were assessed for immunoreactive 4-hydroxy-2-nonenal-(4HNE)–modified proteins as a marker of oxidative stress as well as prol...
Tumor cell proliferation, de-differentiation, and progression depend on a complex combination of ... more Tumor cell proliferation, de-differentiation, and progression depend on a complex combination of altered cell cycle regulation, excessive growth factor pathway activation, and decreased apoptosis. The understanding of these complex mechanisms should lead to the identification of potential targets for therapeutic intervention. Redox-sensitive signaling factors also regulate multiple cellular processes including proliferation, cell cycle, and pro-survival signaling cascades, suggesting their potential as molecular targets for anticancer agents. These observations suggest that redox-sensitive signaling factors may be potential novel molecular markers. We hypothesized that thioredoxin reductase-1 (TR), a component of several redox-regulated pathways, may represent a potential molecular target candidate in response to agents that induce oxidative stress. There have been numerous biological studies over the last decade investigating the cell biological, biochemical, and genetic properties of TR both in culture and in in vivo models. In addition, using a series of permanent cell lines that express either a wild-type TR or a dominant mutant TR gene or a chemical agent that inhibits TR we demonstrated that TR meets most criteria that would identify a molecular target. Based on these results we believe TR is a potential molecular target and discuss potential clinical possibilities.
The sirtuin gene family (SIRT) is hypothesized to regulate the aging process and play a role in c... more The sirtuin gene family (SIRT) is hypothesized to regulate the aging process and play a role in cellular repair. This work demonstrates that SIRT3 À/À 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 À/À MEFs results in in vitro transformation and altered intracellular metabolism. Superoxide dismutase prevents transformation by a single oncogene in SIRT3 À/À MEFs and reverses the tumor-permissive phenotype as well as stress-induced genomic instability. In addition, SIRT3 À/À 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.
Increasing evidence suggests that cancer cells (relative to normal cells) have altered mitochondr... more 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
Manganese superoxide dismutase (SOD2) is a nuclear encoded and mitochondria localized antioxidant... more Manganese superoxide dismutase (SOD2) is a nuclear encoded and mitochondria localized antioxidant enzyme that converts mitochondria derived superoxide to hydrogen peroxide. This study investigates the hypothesis that mitochondria derived reactive oxygen species (ROS) regulate ionizing radiation (IR) induced transformation in normal cells. Mouse embryonic fibroblasts (MEFs) with wild type SOD2 (+/+), heterozygous SOD2 (+/−), and homozygous SOD2 (−/−) genotypes were irradiated with equitoxic doses of IR, and assayed for transformation frequency, cellular redox environment, DNA damage, and cell cycle checkpoint activation. Transformation frequency increased (~ 5-fold) in SOD2 (−/−) compared to SOD2 (+/+) MEFs. Cellular redox environment (GSH, GSSG, DHE, and DCFH-oxidation) did not show any significant change within 24h post-IR. However, a significant increase in cellular ROS levels was observed at 72h post-IR in SOD2 (−/−) compared to SOD2 (+/+) MEFs, which was consistent with an increase in GSSG in SOD2 (−/−) MEFs. Late ROS accumulation was associated with an increase in micronuclei frequency in SOD2 (−/−) MEFs. Exit from G 2 was accelerated in irradiated SOD2 (+/−) and SOD2 (−/−) compared to SOD2 (+/+) MEFs. These results support the hypothesis that SOD2 activity and mitochondria generated ROS regulate IR induced transformation in mouse embryonic fibroblasts.
Malignant cells have a demonstrably greater sensitivity to glucose deprivation-induced cytotoxici... more 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.
Exposure of eukaryotic cells to ionizing radiation (IR) results in the immediate formation of fre... more Exposure of eukaryotic cells to ionizing radiation (IR) results in the immediate formation of free radicals that last a matter of milliseconds. It has been assumed that the subsequent alterations in multiple intracellular processes following irradiation is due to the initial oxidative damage caused by these free radicals. However, it is becoming increasingly clear that intracellular metabolic oxidation/reduction (redox) reactions can be affected by this initial IR-induced free radical insult and may remain perturbed for minutes, hours, or days. It would seem logical that these cellular redox reactions might contribute to the activation of protective or damaging processes that could impact upon the damaging effects of IR. These processes include redox sensitive signaling pathways, transcription factor activation, gene expression, and metabolic activities that govern the formation of intracellular oxidants and reductants. The physiological manifestations of these radiation-induced alterations in redox sensitive processes have been suggested to contribute to adaptive responses, bystander effects, cell cycle perturbations, cytotoxicity, heat-induced radiosensitization, genomic instability, inflammation, and fibrosis. While a great deal is known about the molecular changes associated with the initial production of free radicals at the time of irradiation, the contribution of perturbations in redox sensitive metabolic processes to biological outcomes following exposure to IR is only recently becoming established. This review will focus on evidence supporting the concept that perturbations in intracellular metabolic oxidation/reduction reactions contribute to the biological effects of radiation exposure as well as new concepts emerging from the field of free radical biology that may be relevant to future studies in radiobiology.
Cancer cells, relative to normal cells, demonstrate increased sensitivity to glucose deprivationi... more Cancer cells, relative to normal cells, demonstrate increased sensitivity to glucose deprivationinduced cytotoxicity. To determine if oxidative stress mediated by O 2
Chronic oxidative stress has been associated with genomic instability following exposure to ioniz... more Chronic oxidative stress has been associated with genomic instability following exposure to ionizing radiation (IR). However, data showing direct causal linkages between specific reactive oxygen species and the IR-induced mutator phenotype are lacking. The current study demonstrates that IRinduced genomically unstable cells (characterized by chromosomal instability and increased mutation and gene amplification frequencies) show a 3-fold increase in steady-state levels of hydrogen peroxide, but not superoxide. Furthermore, stable clones isolated from parallel studies showed significant increases in catalase and glutathione-peroxidase activity. Treatment of unstable cells with polyethylene glycol-conjugated catalase [PEG-CAT] reduced the mutation frequency and mutation rate in a dose dependent fashion. In addition, inhibiting catalase activity in the stable clones using 3-aminotriazole increased mutation frequency and rate. These results clearly demonstrate the causal relationship between chronic oxidative stress mediated by hydrogen peroxide and the mutator phenotype that persists many generations following exposure of mammalian cells to IR.
Biochemical and Biophysical Research Communications, 1997
Glutathione is synthesized by two enzymes, g-gluta-The gene GLCLC encodes the catalytic subunit o... more Glutathione is synthesized by two enzymes, g-gluta-The gene GLCLC encodes the catalytic subunit of mylcysteine synthetase, the rate limiting enzyme, and gamma-glutamylcysteine synthetase (glutamate-cysglutathione synthetase. g-Glutamylcysteine syntheteine ligase E.C. 6.3.2.2), the rate limiting enzyme for tase is a heterodimeric enzyme composed of a catalytic glutathione synthesis. When HepG2 cells were exposed subunit that exhibits GSH feedback inhibition, and a to the serine/threonine phosphatase inhibitor okadaic regulatory subunit that influences the K m for glutaacid (OA), increased expression of GLCLC was obmate binding (6).
, are large scale industrial chemicals but their disposition and toxicity are poorly understood d... more , are large scale industrial chemicals but their disposition and toxicity are poorly understood despite significant human exposure. The hypothesis that subacute exposure to N-EtFOSE, a weak peroxisome proliferator, causes a redox imbalance in vivo was tested using the known peroxisome proliferator, ciprofibrate, as a positive control. Female Sprague-Dawley rats were treated orally with N-EtFOSE, ciprofibrate or corn oil (vehicle) for 21 days, and levels of N-EtFOSE and its metabolites as well as markers of peroxisome proliferation and oxidative stress were assessed in serum, liver and/or uterus. The N-EtFOSE metabolite profile in liver and serum was in good agreement with reported in vitro biotransformation pathways in rats and the metabolite levels decreasing in the order perfluorooctanesulfonate ≫ perfluorooctanesulfonamide ∼ N-ethyl perfluorooctanesulfonamidoacetate ≫ perfluorooctanesulfonamidoethanol ∼ N-EtFOSE. Although N-EtFOSE treatment significantly decreased the growth rate, increased relative liver weight and activity of superoxide dismutases (SOD) in liver and uterus (total SOD, CuZnSOD and MnSOD), a metabolic study revealed no differences in the metabolome in serum from N-EtFOSE-treated and control animals. Ciprofibrate treatment increased liver weight and peroxisomal acyl Co-A oxidase activity in the liver and altered antioxidant enzyme activities in the uterus and liver. According to NMR metabolomic studies, ciprofibrate treated animals had altered serum lipid profiles compared to N-EtFOSE-treated and control animals, whereas putative markers of peroxisome proliferation in serum were not affected. Overall, this study demonstrates the biotransformation of N-EtFOSE to PFOS in rats that is accompanied by N-EtFOSE-induced alterations in antioxidant enzyme activity.
Archives of Environmental Contamination and Toxicology, 2000
Evidence implicating oxidative stress in toxicity during lead intoxication in vivo has opened new... more Evidence implicating oxidative stress in toxicity during lead intoxication in vivo has opened new avenues for investigation of the mechanisms of lead-induced immunosuppression. The current study explores the possibility that lead-induced oxidative stress contributes to the immunosuppression observed during lead poisoning. Fisher 344 rats were exposed to 2,000 ppm lead acetate in their drinking water for 5 weeks. One week following removal of lead from the drinking water, significant reductions in serum levels of IgA, IgM, and IgG were detected. Significant increases in oxidative damage, based on malondialdehyde (MDA) content, were observed in peripheral blood mononuclear cells (PMCs) collected during the same experiments. In addition, MDA content increased in livers from lead-exposed rats. Following 5 weeks of lead exposure, administration of either 5.5 mmol/kg N-acetylcysteine (NAC) or 1 mmol/kg meso-2,3-dimercaptosuccinic acid (DMSA) in the drinking water for 1 week significantly reversed the inhibitory effects of lead on serum immunoglobulin (Ig) levels. Also, all parameters indicative of oxidative stress returned to control levels. These results suggest that oxidative stress contributes to suppressed serum Ig levels during lead intoxication in vivo, and that intervention with either a thiol antioxidant (NAC) or a metal chelator (DMSA) will alleviate this lead-induced suppression by correcting the prooxidant/antioxidant imbalance caused by lead exposure.
Following exposure to 95% oxygen, clonogenic cell survival was assayed and qualitative morphologi... more Following exposure to 95% oxygen, clonogenic cell survival was assayed and qualitative morphologic changes were observed in a Chinese hamster fibroblast cell line (HA-1). The time in 95% O2 necessary to clonogenically inactivate 90% of the cells was inversely related to the cell density of the cultures at the beginning of hyperoxic exposure (from 1 to 6 X 10(4) cells/cm2). The O2-induced loss in clonogenicity and evidence of morphologic injury were shown to be significantly delayed (17-22 h) in an H2O2-resistant variant of the parental HA-1 cell line. After the delay in onset of clonogenic cell killing or morphologic injury, the process of injury proceeded in a similar fashion in both cell lines. The H2O2-resistant cell line demonstrated significantly greater catalase activity (20-fold), CuZn superoxide dismutase activity (2-fold), and Se-dependent glutathione peroxidase activity (1.5-fold). The greater activities of CuZn superoxide dismutase and catalase were accompanied by similarly greater quantities of immunoreactive protein as determined by immunoblotting. These data demonstrate that the cells adapted and/or selected for growth in a highly peroxidative environment also became refractory to O2-induced toxicity, which may be related to increased expression of antioxidant enzymes. However, the magnitude of this cross-resistance to O2 toxicity was less than the magnitude of the cellular resistance to the toxicity of exogenous H2O2, suggesting that in this system the toxicity of 95% oxygen is not identical to H2O2-mediated cytotoxicity.
The biological effects of ionizing radiation (IR) from environmental, medical, and man-made sourc... more The biological effects of ionizing radiation (IR) from environmental, medical, and man-made sources, as well as from space exploration are of broad health concern. During the last 40 years it has become evident that, in addition to short-lived free radical-mediated events initiated within microseconds of exposure and generally thought to dissipate within milliseconds, IR-induced production of reactive oxygen and nitrogen species as well as changes in redox signaling linked to disruption of metabolic processes persist long after radiation exposure. Furthermore, persistent IR-induced increases in the metabolic production of reactive oxygen and nitrogen species appear to significantly contribute to the delayed effects of IR exposure, including induction of adaptive responses at low doses as well as carcinogenesis, fibrosis, inflammation, genomic instability, and acceleration of the onset of degenerative tissue injury processes associated with aging. The ability to identify the specific metabolic mechanisms and dose-response relationships that contribute to adaptive responses as well as persistent IR-induced injury processes holds great promise for identifying novel strategies to mitigate the deleterious effects of IR exposure as well as for gathering mechanistic information critical for risk assessment. This Forum contains original and review articles authored by experts in the field of radiobiology focusing on novel mechanisms involving redox biology and metabolism that significantly contribute to the persistent biological effects seen following IR exposure.
Over the last three decades, it is has become increasing clear that intracellular signaling pathw... more Over the last three decades, it is has become increasing clear that intracellular signaling pathways are activated via changes in intracellular metabolic oxidation/reduction (redox) reactions involving reactive oxygen species (ROS; i.e., superoxide and hydrogen peroxide). The initial proposals hypothesized that signaling through metabolic oxidation/reduction (redox) reactions involving ROS could contribute to carcinogenesis and progression to malignancy. Strong evidence for this hypothesis was obtained from studies showing that environmental insults (i.e., ionizing radiation) as well as xenobiotics (i.e., polycyclic aromatic hydrocarbons and phorbol esters) capable of inducing steady-state increases in free radical production and ROS could act as both initiators and promoters of carcinogenesis. This Forum is directed at understanding possible redox signaling mechanisms governing cellular radiation response, tumor growth, and response to therapy, as well as the role of nitric oxide in cancer biology.
Mitochondrial reactive oxygen species (ROS) are mainly produced by the respiratory chain enzymes.... more Mitochondrial reactive oxygen species (ROS) are mainly produced by the respiratory chain enzymes. The sites for ROS production in mitochondrial respiratory chain are normally ascribed to the activity of Complex I and III. The presence of specific inhibitors modulates reactive oxygen species production in Complex I: inhibitors such as rotenone induce a strong ROS increase, while inhibitors such as stigmatellin prevent it. We have investigated the effect of hydrophilic quinones on Complex I ROS production in presence of different inhibitors. Some short chain quinones are Complex I inhibitors (CoQ2, idebenone and its derivatives), while CoQ1, decylubiquinone (DB) and duroquinone (DQ) are good electron acceptors from Complex I.
A method for the spectrophotometric determination of nitric oxide, nitrite, and nitrate in tissue... more A method for the spectrophotometric determination of nitric oxide, nitrite, and nitrate in tissue culture media is presented. The method is based on the nitric oxide-mediated nitrosative modification of sulfanilic acid that reacts with N-(1-naphthyl)ethylenediamine dihydrochloride forming an orange-colored product absorbing at 496 nm. Nitric oxide levels were determined in culture media from this absorbance measurement using chemiluminescence standardization. Extinction coefficients of 5400 and 6600 M ؊1 cm ؊1 were determined for the nitric oxide product in assay solutions containing 0.1 or 100 mM KPO 4 buffer (pH 7.4), respectively, with a limit of detection of 1 M. Acidification of these reactions (pH 2.4) generated a pinkcolored product absorbing at 540 nm allowing for quantitation of total nitric oxide/nitrite levels using extinction coefficients of 38,000 and 36,900 M ؊1 cm ؊1 , for the assay solutions described. The limit of detection of this assay was approximately 300 nM. Using the 100 mM KPO 4 buffer system, nitrate levels were determined following reduction to nitrite using a coppercoated cadmium reagent with an extinction coefficient of 29,500 M ؊1 cm ؊1 and a detection limit of 0.5 M. The utility of these assays was demonstrated in the standardization of nitric oxide-saturated cell culture media, and the release of nitric oxide by the NONOate compound DEA/NO.
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