Irradiation increases manganese superoxide dismutase mRNA levels in human fibroblasts. Possible mechanisms for its accumulation

Enzymatic Depletion of Mitochondrial Inorganic Polyphosphate (polyP) Increases the Generation of Reactive Oxygen Species (ROS) and the Activity of the Pentose Phosphate Pathway (PPP) in Mammalian Cells

Inorganic polyphosphate (polyP) is an ancient biopolymer that is well preserved throughout evolution and present in all studied organisms. In mammals, it shows a high co-localization with mitochondria, and it has been demonstrated to be involved in the homeostasis of key processes within the organelle, including mitochondrial bioenergetics. However, the exact extent of the effects of polyP on the regulation of cellular bioenergetics, as well as the mechanisms explaining these effects, still remain poorly understood. Here, using HEK293 mammalian cells under Wild-type (Wt) and MitoPPX (cells enzymatically depleted of mitochondrial polyP) conditions, we show that depletion of polyP within mitochondria increased oxidative stress conditions. This is characterized by enhanced mitochondrial O2- and intracellular H2O2 levels, which may be a consequence of the dysregulation of oxidative phosphorylation (OXPHOS) that we have demonstrated in MitoPPX cells in our previous work. These findings were associated with an increase in basal peroxiredoxin-1 (Prx1), superoxide dismutase-2 (SOD2), and thioredoxin (Trx) antioxidant protein levels. Using 13C-NMR and immunoblotting, we assayed the status of glycolysis and the pentose phosphate pathway (PPP) in Wt and MitoPPX cells. Our results show that MitoPPX cells display a significant increase in the activity of the PPP and an increase in the protein levels of transaldolase (TAL), which is a crucial component of the non-oxidative phase of the PPP and is involved in the regulation of oxidative stress. In addition, we observed a trend towards increased glycolysis in MitoPPX cells, which corroborates our prior work. Here, for the first time, we show the crucial role played by mitochondrial polyP in the regulation of mammalian redox homeostasis. Moreover, we demonstrate a significant effect of mitochondrial polyP on the regulation of global cellular bioenergetics in these cells.

Expression profiles of genes associated with inflammatory responses and oxidative stress in lung after heat stroke

BACKGROUND

Heat stroke (HS) is a physically dysfunctional illness caused by hyperthermia. Lung, as the important place for gas-exchange and heat-dissipation organ, is often first to be injured. Lung injury caused by HS impairs the ventilation function of lung, which will subsequently cause damage to other tissues and organs. Nevertheless, the specific mechanism of lung injury in heat stroke is still unknown.

METHODS

Rat lung tissues from controls or HS models were harvested. The gene expression profile was identified by high-throughput sequencing. DEGs were calculated using R and validated by qRT-PCR. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and cell-enrichment were performed using differential expression genes (DEGs). Finally, lung histopathology was accessed by H&E staining.

RESULTS

About 471 genes were identified to be DEGs, of which 257 genes were up-regulated, and 214 genes were down-regulated. The most up-regulated and down-regulated DEGs were validated by qRT-PCR, which confirmed the tendency of expression. GO, KEGG, and protein-protein interaction (PPI)-network analyses disclosed DEGs were significantly enriched in leukocyte migration, response to lipopolysaccharide, NIK/NF-kappaB signaling, response to reactive oxygen species, response to heat, and the hub genes were Tnf, Il1b, Cxcl2, Ccl2, Mmp9, Timp1, Hmox1, Serpine1, Mmp8 and Csf1, most of which were closely related to inflammagenesis and oxidative stress. Finally, cell-enrichment analysis and histopathologic analysis showed Monocytes, Megakaryotyes, and Macrophages were enriched in response to heat stress.

CONCLUSIONS

The present study identified key genes, signal pathways and infiltrated-cell types in lung after heat stress, which will deepen our understanding of transcriptional response to heat stress, and might provide new ideas for the treatment of HS.

Superoxide Dismutase 2 (SOD2) in Vascular Calcification: A Focus on Vascular Smooth Muscle Cells, Calcification Pathogenesis, and Therapeutic Strategies

Vascular calcification (VC) describes the pathophysiological phenotype of calcium apatite deposition within the vascular wall, leading to vascular stiffening and the loss of compliance. VC is never benign; the presence and severity of VC correlate closely with the risk of myocardial events and cardiovascular mortality in multiple at-risk populations such as patients with diabetes and chronic kidney disease. Mitochondrial dysfunction involving each of vascular wall constituents (endothelia and vascular smooth muscle cells (VSMCs)) aggravates various vascular pathologies, including atherosclerosis and VC. However, few studies address the pathogenic role of mitochondrial dysfunction during the course of VC, and mitochondrial reactive oxygen species (ROS) seem to lie in the pathophysiologic epicenter. Superoxide dismutase 2 (SOD2), through its preferential localization to the mitochondria, stands at the forefront against mitochondrial ROS in VSMCs and thus potentially modifies the probability of VC initiation or progression. In this review, we will provide a literature-based summary regarding the relationship between SOD2 and VC in the context of VSMCs. Apart from the conventional wisdom of attenuating mitochondrial ROS, SOD2 has been found to affect mitophagy and the formation of the autophagosome, suppress JAK/STAT as well as PI₃K/Akt signaling, and retard vascular senescence, all of which underlie the beneficial influences on VC exerted by SOD2. More importantly, we outline the therapeutic potential of a novel SOD2-targeted strategy for the treatment of VC, including an ever-expanding list of pharmaceuticals and natural compounds. It is expected that VSMC SOD2 will become an important druggable target for treating VC in the future.

Decoding the role of SOD2 in sickle cell disease

Sickle cell disease (SCD) is an inherited hemoglobinopathy caused by a single point mutation in the β-globin gene. As a consequence, deoxygenated hemoglobin polymerizes triggering red blood cell sickling and hemolysis, vaso-occlusion, and ischemia/reperfusion. Allied to these pathologies is the overproduction of reactive oxygen species driven by hemoglobin Fenton chemistry and peroxidase reactions as well as by secondary activation of vascular oxidases, including NAD(P)H oxidase and xanthine oxidase. In addition, hypoxia, produced by sickle red blood cell occlusion, disrupts mitochondrial metabolism and generates excess superoxide through electron leak from the mitochondrial respiratory chain. Superoxide dismutase 2 (SOD2) is a mitochondrial-specific antioxidant enzyme that dismutates superoxide to hydrogen peroxide, which is then converted to water by catalase and glutathione peroxidase. In SCD, the antioxidant defense system is significantly diminished through decreased expression and activity levels of antioxidant enzymes, including superoxide dismutase, catalase, and glutathione peroxidase. From a translational perspective, genetic variants including a missense variant in SOD2 (valine to alanine at position 16) are present in 45% of people with African ancestry and are associated with increased sickle complications. While it is known that there is an imbalance between oxidative species and antioxidant defenses in SCD, much more investigation is warranted. This review summarizes our current understanding of antioxidant defense systems in SCD, particularly focused on SOD2, and provides insight into challenges and opportunities as the field moves forward.

Association of SOD2 p.V16A polymorphism with Parkinson's disease: A meta-analysis in Han Chinese

BACKGROUND

Oxidative stress could participate in the pathogenesis of Parkinson's disease (PD). However, the role of genetic variation of superoxide dismutase 2 (SOD2), an important regulator against oxidative stress, in PD remains to be elucidated.

METHODS

We screened SOD2 gene variation by sequencing cDNA from 72 patients with early onset PD. A cohort of PD (n = 609) and ethnically matched controls (n = 681) were further examined for the identified sequence variant by PCR and NaeI restriction analysis.

RESULTS

Only a reported c.47T>C polymorphism (rs4880, SOD2 p.V16A) was found by cDNA sequencing. Case-control study of c.47T>C revealed that genotype and allele frequencies were in Hardy-Weinberg equilibrium in both patients and healthy controls. In a recessive model, those with CC genotype had a 2.61-fold increased risk of PD (95% CI: 1.08-6.30, P = 0.03) compared to subjects with TT and TC genotypes. Significant association between CC genotype and PD in non-smokers was also observed after stratification according to the history of smoking (3.54-fold increased risk of PD, 95% CI: 1.17-10.72, P = 0.02). Meta-analysis by combining studies of Chinese in China, Singapore, and Taiwan (total 2302 cases and 2029 controls) consistently showed CC genotype with increased risk of PD (OR = 1.77, 95% CI: 1.15-2.71, P = 0.01).

CONCLUSION

Our findings demonstrate that SOD2 p.V16A may play a role in the susceptibility of PD in Han Chinese.

Brain Overexpression of Uncoupling Protein-2 (UCP2) Delays Renal Damage and Stroke Occurrence in Stroke-Prone Spontaneously Hypertensive Rats

The downregulation of uncoupling protein-2 (UCP2) is associated with increased brain and kidney injury in stroke-prone spontaneously hypertensive rats (SHRSP) fed with a Japanese style hypersodic diet (JD). Systemic overexpression of UCP2 reduces organ damage in JD-fed SHRSP. We examined the effect of brain-specific UCP2 overexpression on blood pressure (BP), stroke occurrence and kidney damage in JD-fed SHRSP. Rats received a single i.c.v. injection of a lentiviral vector encoding UCP2 (LV-UCP2), or an empty vector. The brain delivery of LV-UCP2 significantly delayed the occurrence of stroke and kidney damage. The large reduction of proteinuria observed after LV-UCP2 injection was unexpected, because BP levels were unchanged. At the time of stroke, rats treated with LV-UCP2 still showed a large UCP2 upregulation in the striatum, associated with increases in OPA1 and FIS1 protein levels, and reductions in PGC1-α, SOD2, TNFα mRNA levels and NRF2 protein levels. This suggested UCP2 overexpression enhanced mitochondrial fusion and fission and reduced oxidative damage and inflammation in the striatum of JD-fed SHRSP rats. Our data suggest the existence of central mechanisms that may protect against hypertension-induced organ damage independently of BP, and strengthen the suitability of strategies aimed at enhancing UCP2 expression for the treatment of hypertensive damage.

Gene therapy and cell therapy for the management of radiation damages to healthy tissues: Rationale and early results

Nowadays, ionizing radiations have numerous applications, especially in medicine for diagnosis and therapy. Pharmacological radioprotection aims at increasing detoxification of free radicals. Radiomitigation aims at improving survival and proliferation of damaged cells. Both strategies are essential research area, as non-contained radiation can lead to harmful effects. Some advances allowing the comprehension of normal tissue injury mechanisms, and the discovery of related predictive biomarkers, have led to developing several highly promising radioprotector or radiomitigator drugs. Next to these drugs, a growing interest does exist for biotherapy in this field, including gene therapy and cell therapy through mesenchymal stem cells. In this review article, we provide an overview of the management of radiation damages to healthy tissues via gene or cell therapy in the context of radiotherapy. The early management aims at preventing the occurrence of these damages before exposure or just after exposure. The late management offers promises in the reversion of constituted late damages following irradiation.

Mitochondrial superoxide dismutase 2 mediates γ-irradiation-induced cancer cell invasion

Sublethal doses of γ-rays promote cancer cell invasion by stimulating a signaling pathway that sequentially involves p53, sulfatase 2 (SULF2), β-catenin, interleukin-6 (IL-6), signal transducer and activator of transcription 3 (STAT3), and Bcl-X_L. Given that Bcl-X_L can increase O₂^•− production by stimulating respiratory complex I, the possible role of mitochondrial reactive oxygen species (ROS) in γ-irradiation-induced cell invasion was investigated. Indeed, γ-irradiation promoted cell invasion by increasing mitochondrial ROS levels, which was prevented by metformin, an inhibitor of complex I. γ-Irradiation-stimulated STAT3 increased the expression of superoxide dismutase 2 (SOD2), a mitochondrial enzyme that catalyzes the conversion of O₂^•− to hydrogen peroxide (H₂O₂). In contrast to O₂^•−, H₂O₂ functions as a signaling molecule. γ-Irradiation consistently stimulated the Src-dependent invasion pathway in a manner dependent on both complex I and SOD2. SOD2 was also essential for the invasion of un-irradiated cancer cells induced by upregulation of Bcl-X_L, an intracellular oncogene, or extracellular factors, such as SULF2 and IL-6. Overall, these data suggested that SOD2 is critical for the malignant effects of radiotherapy and tumor progression through diverse endogenous factors.

A drug usually used to treat type 2 diabetes may also help to prevent cancer relapse following radiotherapy, which is commonly used to kill cancer cells. However, any tumor cells that survive radiation are highly invasive, sometimes causing tumors to spread. Hong-Duck Um and co-workers at the Korea Institute of Radiological & Medical Sciences in Seoul, South Korea, noticed that the surviving cells often showed higher levels of a key enzyme, superoxide dismutase 2 (SOD2), which is involved in energy production in the cellular powerhouse, the mitochondria. Artificially increasing levels of SOD2, without radiation, made cells more invasive. Treatment with metformin, which prevents production of the molecule that SOD2 acts on, prevented cells from becoming invasive. SOD2 has been implicated in many cancers, and is therefore a very promising therapeutic target.

Peroxiredoxins in Colorectal Cancer: Predictive Biomarkers of Radiation Response and Therapeutic Targets to Increase Radiation Sensitivity?

Colorectal cancer (CRC) is the third most common cancer in the Western world, with one-third of cases located in the rectum. Preoperative radiotherapy is the standard of care for many patients with rectal cancer but has a highly variable response rate. The ability to predict response would be of great clinical utility. The response of cells to ionizing radiation is known to involve immediate damage to biomolecules and more sustained disruption of redox homeostasis leading to cell death. The peroxiredoxins are an important group of thiol-dependent antioxidants involved in protecting cells from oxidative stress and regulating signaling pathways involved in cellular responses to oxidative stress. All six human peroxiredoxins have shown increased expression in CRC and may be associated with clinicopathological features and tumor response to ionizing radiation. Peroxiredoxins can act as markers of oxidative stress in various biological systems but they have not been investigated in this capacity in CRC. As such, there is currently insufficient evidence to support the role of peroxiredoxins as clinical biomarkers, but it is an area worthy of investigation. Future research should focus on the in vivo response of rectal cancer to radiotherapy and the redox status of peroxiredoxins in rectal cancer cells, in order to predict response to radiotherapy. The peroxiredoxin system is also a potential therapeutic target for CRC.

Manganese elevates manganese superoxide dismutase protein level through protein kinase C and protein tyrosine kinase

Three experiments were conducted to investigate the effects of inorganic and organic Mn sources on MnSOD mRNA, protein and enzymatic activity and the possible signal pathways. The primary broiler myocardial cells were treated with MnCl2 (I) or one of organic chelates of Mn and amino acids with weak, moderate (M) or strong (S) chelation strength for 12 and 48 h. Cells were preincubated with superoxide radical anions scavenger N-acetylcysteine (NAC) or specific inhibitors for MAPKs and protein tyrosine kinase (PTK) or protein kinase C (PKC) for 30 min before treatments of I and M. The MnSOD mRNA, protein and enzymatic activity, phosphorylated MAPKs or protein kinases activations were examined. The results showed that additions of Mn increased (P < 0.05) MnSOD mRNA levels and M was more effective than I. Additions of Mn elevated (P < 0.05) MnSOD protein levels and enzymatic activities, and no differences were found among I and M. Addition of NAC did not decrease (P > 0.05) Mn-induced MnSOD mRNA and protein levels. None of the three MAPKs was phosphorylated (P > 0.05) by Mn. Additions of Mn decreased (P < 0.05) the PTK activities and increased (P < 0.05) the membrane PKC contents. Inhibitors for PTK or PKC decreased (P < 0.05) Mn-induced MnSOD protein levels. The results suggested that Mn-induced MnSOD mRNA and protein expressions be not related with NAC, and MAPK pathways might not involve in Mn-induced MnSOD mRNA expression. PKC and PTK mediated the Mn-induced MnSOD protein expression.

Gene therapy for radioprotection

Radiation therapy is a critical component of cancer treatment with over half of patients receiving radiation during their treatment. Despite advances in image-guided therapy and dose fractionation, patients receiving radiation therapy are still at risk for side effects due to off-target radiation damage of normal tissues. To reduce normal tissue damage, researchers have sought radioprotectors, which are agents capable of protecting tissue against radiation by preventing radiation damage from occurring or by decreasing cell death in the presence of radiation damage. Although much early research focused on small-molecule radioprotectors, there has been a growing interest in gene therapy for radioprotection. The amenability of gene therapy vectors to targeting, as well as the flexibility of gene therapy to accomplish ablation or augmentation of biologically relevant genes, makes gene therapy an excellent strategy for radioprotection. Future improvements to vector targeting and delivery should greatly enhance radioprotection through gene therapy.

Effects of ionizing radiation on mitochondria

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

Manganese superoxide dismutase regulation and cancer

Mitochondria are the power plants of the eukaryotic cell and the integrators of many metabolic activities and signaling pathways important for the life and death of a cell. Normal aerobic cells use oxidative phosphorylation to generate ATP, which supplies energy for metabolism. To drive ATP production, electrons are passed along the electron transport chain, with some leaking as superoxide during the process. It is estimated that, during normal respiration, intramitochondrial superoxide concentrations can reach 10⁻¹² M. This extremely high level of endogenous superoxide production dictates that mitochondria are equipped with antioxidant systems that prevent consequential oxidative injury to mitochondria and maintain normal mitochondrial functions. The major antioxidant enzyme that scavenges superoxide anion radical in mitochondria is manganese superoxide dismutase (MnSOD). Extensive studies on MnSOD have demonstrated that MnSOD plays a critical role in the development and progression of cancer. Many human cancer cells harbor low levels of MnSOD proteins and enzymatic activity, whereas some cancer cells possess high levels of MnSOD expression and activity. This apparent variation in MnSOD level among cancer cells suggests that differential regulation of MnSOD exists in cancer cells and that this regulation may be linked to the type and stage of cancer development. This review summarizes current knowledge of the relationship between MnSOD levels and cancer with a focus on the mechanisms regulating MnSOD expression.

Mitochondria-targeted superoxide dismutase (SOD2) regulates radiation resistance and radiation stress response in HeLa cells

Reactive oxygen species (ROS) act as a mediator of ionizing radiation-induced cellular damage. Previous studies have indicated that MnSOD (SOD2) plays a critical role in protection against ionizing radiation in mammalian cells. In this study, we constructed two types of stable HeLa cell lines overexpressing SOD2, HeLa S3/SOD2 and T-REx HeLa/SOD2, to elucidate the mechanisms underlying the protection against radiation by SOD2. SOD2 overexpression in mitochondria enhanced the survival of HeLa S3 and T-REx HeLa cells following γ-irradiation. The levels of γH2AX significantly decreased in HeLa S3/SOD2 and T-REx HeLa/SOD2 cells compared with those in the control cells. MitoSox(TM) Red assays showed that both lines of SOD2-expressing cells showed suppression of the superoxide generation in mitochondria. Furthermore, flow cytometry with a fluorescent probe (2',7'-dichlorofluorescein) revealed that the cellular levels of ROS increased in HeLa S3 cells during post-irradiation incubation, but the increase was markedly attenuated in HeLa S3/SOD2 cells. DNA microarray analysis revealed that, of 47,000 probe sets analyzed, 117 and 166 probes showed more than 2-fold changes after 5.5 Gy of γ-irradiation in control and HeLa S3/SOD2 cells, respectively. Pathway analysis revealed different expression profiles in irradiated control cells and irradiated SOD2-overexpressing cells. These results indicate that SOD2 protects HeLa cells against cellular effects of γ-rays through suppressing oxidative stress in irradiated cells caused by ROS generated in the mitochondria and through regulating the expression of genes which play a critical role in protection against ionizing radiation.

Exogenously-added copper/zinc superoxide dismutase rescues damage of endothelial cells from lethal irradiation

The vascular endothelium is important for the early and late effects observed in lethally irradiated tissue and organs. We examined the effects of exogenously added superoxide dismutase on cell survival and angiogenesis in lethally irradiated human primary umbilical vein endothelial cells. Cell survival was significantly improved in superoxide dismutase-treated cells; the addition of superoxide dismutase to cells after irradiation was also effective for increased survival, as it was before irradiation. Moreover, treatment of cells with superoxide dismutase enhanced the phosphorylation of mitogen-activated protein/extracellular signal-regulated kinase/extracellular signal regulated kinases 1 and 2 in human primary umbilical vein endothelial cells. The addition of superoxide dismutase to cells after irradiation attenuated the reduction of angiogenesis by irradiation, and inhibition of the mitogen-activated protein/extracellular signal-regulated kinase/extracellular signal regulated kinases signaling pathway abrogated the rescue effect of superoxide dismutase. Our results suggest that superoxide dismutase rescues human primary umbilical vein endothelial cells from endothelial dysfunction caused by irradiation via a pathway requiring activation of mitogen-activated protein/extracellular signal-regulated kinase/extracellular signal regulated kinases 1 and 2.

Preferential selection of MnSOD transcripts in proliferating normal and cancer cells

Manganese superoxide dismutase (MnSOD) is a nuclear encoded and mitochondrial matrix localized redox enzyme that is known to regulate cellular redox environment. Cellular redox environment changes during transitions between quiescent and proliferative cycles. Human MnSOD has two poly(A) sites resulting in two transcripts: 1.5 and 4.2 kb. The present study investigates if the 3'-untranslated region (UTR) of MnSOD regulates its expression during transitions between quiescent and proliferating cycles, and in response to radiation. A preferential increase in the 1.5 kb MnSOD transcript levels was observed in quiescent cells, while the abundance of the longer transcript showed a direct correlation with the percentage of S-phase cells. Log transformed expression ratio of the longer to shorter transcript was also higher in proliferating normal and cancer cells. Deletion and reporter assays showed a significant decrease in reporter activity in constructs carrying multiple AU-rich sequence that are present in the 3'-UTR of the longer MnSOD transcript. Overexpression of the MnSOD 3'-UTR representing the longer transcript enhanced endogenous MnSOD mRNA levels, which was associated with an increase in MnSOD protein levels and a decrease in the percentage of S-phase cells. Irradiation increases the mRNA levels of the 1.5 kb MnSOD transcript, which was consistent with a significant increase in reporter activity of the construct carrying the 3'-UTR of the shorter transcript. We conclude that the 3'-UTR of MnSOD regulates MnSOD expression in response to different growth states and radiation.

Dual function of protein kinase C (PKC) in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced manganese superoxide dismutase (MnSOD) expression: activation of CREB and FOXO3a by PKC-alpha phosphorylation and by PKC-mediated inactivation of Akt, respectively

12-O-tetradecanoylphorbol-13-acetate (TPA) has been shown to induce transcriptional activation of human manganese superoxide dismutase (MnSOD) mRNA in human lung carcinoma cells, A549, mediated by a protein kinase C (PKC)-dependent activation of cAMP-responsive element-binding protein (CREB)-1/ATF-1-like factors. In this study, we showed that MnSOD protein expression was elevated in response to TPA or TNF-α, but not to hydrogen peroxide treatment. TPA-induced generation of reactive oxygen species (ROS) was blocked by pretreatment of the PKC inhibitor BIM and NADPH oxidase inhibitor DPI. Small interfering RNA (siRNA) experiments indicated that knocking down the NADPH oxidase components e.g. Rac1, p22(phox), p67(phox), and NOXO1 in A549 cells impaired TPA-induced MnSOD expression. To identify the PKC isozyme involved, we used a sod2 gene response reporter plasmid, pSODLUC-3340-I2E-C, capable of sensing the effect of TNF-α and TPA, to monitor the effects of PKC isozyme-specific inhibitors and siRNA-induced knockdown of specific PKC isozyme. Our data indicate that TPA-induced MnSOD expression was independent of p53 and most likely mediated by PKC-α-, and -ε-dependent signaling pathways. Furthermore, siRNA-induced knock-down of CREB and Forkhead box class O (FOXO) 3a led to a reduction in TPA-induced MnSOD gene expression. Together, our results revealed that TPA up-regulates, in part, two PKC-dependent transcriptional pathways to induce MnSOD expression. One pathway involves PKC-α catalyzed phosphorylation of CREB and the other involves a PKC-mediated the PP2A catalyzed dephosphorylation of Akt at Ser(473) which in turn leads to FOXO3a Ser(253) dephosphorylation and its activation.

The role of manganese superoxide dismutase in skin cancer

Recent studies have shown that antioxidant enzyme expression and activity are drastically reduced in most human skin diseases, leading to propagation of oxidative stress and continuous disease progression. However, antioxidants, an endogenous defense system against reactive oxygen species (ROS), can be induced by exogenous sources, resulting in protective effects against associated oxidative injury. Many studies have shown that the induction of antioxidants is an effective strategy to combat various disease states. In one approach, a SOD mimetic was applied topically to mouse skin in the two-stage skin carcinogenesis model. This method effectively reduced oxidative injury and proliferation without interfering with apoptosis. In another approach, Protandim, a combination of 5 well-studied medicinal plants, was given via dietary administration and significantly decreased tumor incidence and multiplicity by 33% and 57%, respectively. These studies suggest that alterations in antioxidant response may be a novel approach to chemoprevention. This paper focuses on how regulation of antioxidant expression and activity can be modulated in skin disease and the potential clinical implications of antioxidant-based therapies.

Low-dose γ-radiation-induced oxidative stress response in mouse brain and gut: regulation by NFκB-MnSOD cross-signaling

Radiation-induced amplification of reactive oxygen species (ROS) may be a sensing mechanism for activation of signaling cascades that influence cell fate. However, the regulated intrinsic mechanisms and targets of low-dose ionizing radiation (LDIR) are still unclear. Accordingly, we investigated the effects of LDIR on NFκB signal transduction and manganese superoxide dismutase (SOD2) activity in mice brain and gut. LDIR resulted in both dose-dependent and persistent NFκB activation in gut and brain. QPCR displayed a dose- and tissue-dependent differential modulation of 88 signaling molecules. With stringent criteria, a total of 15 (2cGy), 43 (10cGy) and 19 (50cGy) genes were found to be commonly upregulated between brain and gut. SOD2 immunostaining showed a LDIR-dose dependent increase. Consistent with the NFκB results, we observed a persistent increase in SOD2 activity after LDIR. Moreover, muting of LDIR-induced NFκB attenuated SOD2 transactivation and cellular localization. These results imply that exposure of healthy tissues to LDIR results in induced NFκB and SOD2 activity and transcriptional activation of NFκB-signal transduction/target molecules. More importantly, the results suggest that NFκB initiates a feedback response through transcriptional activation of SOD2 that may play a key role in the LDIR-induced oxidative stress response and may control the switch that directs cell fate.

Reperfusion and neurovascular dysfunction in stroke: from basic mechanisms to potential strategies for neuroprotection

Effective stroke therapies require recanalization of occluded cerebral blood vessels. However, reperfusion can cause neurovascular injury, leading to cerebral edema, brain hemorrhage, and neuronal death by apoptosis/necrosis. These complications, which result from excess production of reactive oxygen species in mitochondria, significantly limit the benefits of stroke therapies. We have developed a focal stroke model using mice deficient in mitochondrial manganese-superoxide dismutase (SOD2-/+) to investigate neurovascular endothelial damage that occurs during reperfusion. Following focal stroke and reperfusion, SOD2-/+ mice had delayed blood-brain barrier breakdown, associated with activation of matrix metalloproteinase and high brain hemorrhage rates, whereas a decrease in apoptosis and hemorrhage was observed in SOD2 overexpressors. Thus, induction and activation of SOD2 is a novel strategy for neurovascular protection after ischemia/reperfusion. Our recent study identified the signal transducer and activator of transcription 3 (STAT3) as a transcription factor of the mouse SOD2 gene. During reperfusion, activation of STAT3 and its recruitment into the SOD2 gene were blocked, resulting in increased oxidative stress and neuronal apoptosis. In contrast, pharmacological activation of STAT3 induced SOD2 expression, which limits ischemic neuronal death. Our studies point to antioxidant-based neurovascular protective strategies as potential treatments to expand the therapeutic window of currently approved therapies.

Clair DK. Regulation of superoxide dismutase genes: implications in disease

Numerous short-lived and highly reactive oxygen species (ROS) such as superoxide (O2(.-)), hydroxyl radical, and hydrogen peroxide are continuously generated in vivo. Depending upon concentration, location, and intracellular conditions, ROS can cause toxicity or act as signaling molecules. The cellular levels of ROS are controlled by antioxidant enzymes and small-molecule antioxidants. As major antioxidant enzymes, superoxide dismutases (SODs), including copper-zinc superoxide dismutase (Cu/ZnSOD), manganese superoxide dismutase, and extracellular superoxide dismutase, play a crucial role in scavenging O2(.-). This review focuses on the regulation of the sod genes coding for these enzymes, with an emphasis on the human genes. Current knowledge about sod structure and regulation is summarized and depicted as diagrams. Studies to date on genes coding for Cu/ZnSOD (sod1) are mostly focused on alterations in the coding region and their associations with amyotrophic lateral sclerosis. Evaluation of nucleotide sequences reveals that regulatory elements of the sod2 gene reside in both the noncoding and the coding region. Changes associated with sod2 lead to alterations in expression levels as well as protein function. We also discuss the structural basis for the changes in SOD expression associated with pathological conditions and where more work is needed to establish the relationship between SODs and diseases.

Reactive oxygen species controls endometriosis progression

Endometriosis is associated with chronic inflammation, and reactive oxygen species (ROS) are proinflammatory mediators that modulate cell proliferation. We have investigated whether the dysregulation of ROS production in endometriotic cells correlates with a pro-proliferative phenotype and can explain the spreading of this disease. Stromal and epithelial cells were purified from ovarian endometrioma and eutopic endometrium from 14 patients with endometriosis to produce four primary cell lines from each patient. ROS production, detoxification pathways, cell proliferation, and mitogen-activated protein kinase pathway activation were studied and compared with epithelial and stromal cell lines from 14 patients without endometriosis. Modulation of the proliferation of endometriosis by N-acetyl-cysteine, danazol, and mifepristone was tested in vitro and in 28 nude mice implanted with endometriotic tissue of human origin. Endometriotic cells displayed higher endogenous oxidative stress with an increase in ROS production, alterations in ROS detoxification pathways, and a drop in catalase levels, as observed for tumor cells. This increase in endogenous ROS correlated with increased cellular proliferation and activation of ERK1/2. These phenomena were abrogated by the antioxidant molecule N-acetyl-cysteine both in vitro and in a mouse model of endometriosis. Human endometriotic cells display activated pERK, enhanced ROS production, and proliferative capability. Our murine model shows that antioxidant molecules could be used as safe and efficient treatments for endometriosis.

Increased superoxide formation induced by irradiation preconditioning triggers kidney resistance to ischemia-reperfusion injury in mice

One of the obstacles in irradiation therapy is cytoresistance, acquired by activation of self-defense systems, such as antioxidant or molecular chaperone systems, to cope with stress. We investigated whether irradiation preconditioning (IP) rendered resistance of the kidney against subsequent ischemia-reperfusion (I/R) and attempted to elucidate any such protective mechanisms. Mice were irradiated with a total of 4, 6, or 8 Gy using a cesium-137 source irradiator and then, 6 days later, were subjected to 28 min of bilateral renal ischemia followed by reperfusion. Eight Gy of IP significantly attenuated the increases in plasma creatinine (PCr) and blood urea nitrogen (BUN) concentration, structural damage, lipid peroxidation, superoxide formation, expression and activity of NADPH oxidase (NOX)-2, nitrotyrosine level, and hydrogen peroxide production after I/R in kidney tissues, indicating that IP protects the kidneys from I/R injury. IP markedly increased the activity of NOX, resulting in increased superoxide formation, manganese superoxide dismutase (MnSOD) activity and expression, and heat shock protein (HSP)-27 expression in kidneys. However, it did not change expressions of catalase, copper-zinc superoxide dismutase (CuZnSOD), and HSP-72. To investigate whether the protection afforded by IP was associated with increases in MnSOD and HSP-27 expression triggered by increased superoxide formation after IP, we administered manganese (III) tetrakis(1-methyl-4-pyridyl)porphyrin, a superoxide scavenger, to IP mice. This administration blocked superoxide formation and subsequent increases in MnSOD and HSP-27 expression and accelerated the post-I/R increases in PCr and BUN. In conclusion, IP renders kidney resistance to I/R injury, and this resistance is mediated by increased superoxide formation, which activates MnSOD activity and expression as well as HSP-27 expression.

Overexpression of manganese superoxide dismutase in human dermal fibroblasts enhances the contraction of free floating collagen lattice: implications for ageing and hyperplastic scar formation

Cell-matrix interactions are of significant importance for tissue homeostasis of the skin and, if disturbed, may lead to ageing and hyperplastic scar formation. We have studied fibroblasts stably overexpressing manganese superoxide dismutase (MnSOD) with a defined capacity for the removal of superoxide anions and concomitant accumulation of hydrogen peroxide to evaluate the role of enhanced MnSOD activity on the dynamics of cell-matrix interactions in the three-dimensional collagen lattice contraction assay. MnSOD overexpressing fibroblast populated collagen lattices revealed a significantly enhanced contraction compared to collagen lattices populated with vector control cells. The enhanced collagen lattice contraction was in part due to an increase in active TGF-beta1 and the accumulation of H2O2 in MnSOD overexpressing fibroblasts populated collagen lattices. Inhibition of TGF-beta1 signalling by the ALK4,5,7 kinases' inhibitor SB431542 at least partly inhibited the enhanced collagen lattice contraction of MnSOD overexpressing fibroblasts populated lattices. In addition, supplementation of vector control fibroblast populated collagen lattices with recombinant TGF-beta1 concentration dependently enhanced the collagen lattice contraction. In the presence of the antioxidant Ebselen, a mimic of H2O2 and other hydroperoxides/peroxynitrite-detoxifying glutathione peroxidase, collagen lattice contraction and the activation of TGF-beta1 were significantly reduced in collagen lattices populated with MnSOD overexpressing fibroblasts. Collectively, these data suggest that H2O2 or other hydroperoxides or peroxynitrite or a combination thereof may function as important second messengers in collagen lattice contraction and act at least in part via TGF-beta1 activation.

Antioxidant activity of Bol d'Air Jacquier breathing sessions in Wistar rats--first studies

OBJECTIVES

The Bol d'Air Jacquier is used to create a molecule able to deliver oxygen at the cellular level to manage hypoxia due to environmental pollution, ageing, or inflammatory disease. This study was designed to determine, firstly, whether the device generated oxidative stress and, secondly, whether it might induce an antioxidant effect.

MATERIAL AND METHODS

Over a period of 62 weeks, 10 male Wistar rats were randomized into two groups: the Bol d'Air group (BA) regularly breathed peroxidizing terpens delivered by the device and the control group breathed water vapour during 9-min sessions, at the frequency of 1-12 per month. Several antioxidant compounds and KRL levels were determined in the blood and major organs.

RESULTS

The results showed that the two groups did not differ with respect to the organ concentrations of Cu, Zn SOD, GPx, GSH, GSSG and TBARS. The device might have a weak slimming effect over time. The BA group presented a significantly higher GR level in plasma throughout the experiment, and in the muscle at the end of the study. In the BA group, the plasma Cu, Zn SOD level was related to the number of breathing sessions per week before blood collection. The BA group also had a higher KRLantioxidant status at two different time-points: at the onset of the study, in the blood of young rats; and after three breathing sessions per week, in the blood and RBCs of old rats.

CONCLUSIONS

The device did not generate oxidative stress and seemed to produce global antioxidant effect depending on the number of sessions per week, especially in old rats.

Chronic exposure to 12-O-tetradecanoylphorbol-13-acetate represses sod2 induction in vivo: the negative role of p50

It is well documented that the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) can activate manganese superoxide dismutase (MnSOD) expression. However, it is unclear how repeated exposure to TPA following a single application of tumor initiator 7,12-dimethylbenz-(a)-anthracene causes tumor development. We generated transgenic mice expressing human MnSOD promoter- and enhancer-driven luciferase reporter gene and used a non-invasive imaging system to investigate the effects of TPA on MnSOD expression in vivo. Our data indicate that TPA initially activates MnSOD expression, but this positive effect declines after repeated applications. Changes in MnSOD expression in vivo were verified by measuring MnSOD mRNA and protein levels. Using chromatin immunoprecipitation coupled to Western analysis of the transcription factors known to be essential for the constitutive and TPA-induced transcription of MnSOD, we found that TPA treatment leads to both activation and inactivation of MnSOD gene transcription. During the activation phase, the levels of p50, p65, specificity protein 1 (Sp1) and nucleophosmin (NPM) increase after TPA treatments. Sustained treatments with TPA lead to further increase of p50 but not p65, Sp1 or NPM, suggesting that excess p50 may have inhibitory effects leading to the suppression of MnSOD. Alteration of p50 levels by expressing p50 cDNA or p50 small interfering RNA in mouse epithelial (JB6) cells confirms that p50 is inhibitory to MnSOD transcription. These findings identify p50 as having a negative effect on MnSOD induction upon repeated applications of TPA and provide an insight into a cause for the reduction of MnSOD expression during early stages of skin carcinogenesis.

P21/WAF1 is an independent survival prognostic factor for patients with hepatocellular carcinoma after resection

BACKGROUND/AIMS

The cyclin kinase inhibitor p21/WAF1 is regulated by p53-dependent or independent pathways and inhibits the action of proliferating cell nuclear antigen (PCNA). The prognostic role of p21/WAF1 in hepatocellular carcinoma (HCC) is ambiguous. To further clarify this, we examined the expression of three genes in HCC.

METHODS

A total of 122 resected HCC specimens were collected from 1987 to 1998. Expression of p21/WAF1, p53, and PCNA in HCC was analysed by immunohistochemistry.

RESULTS

Immunoreactivity was detectable for p21/WAF1 in 37%, and for p53 in 41.8% of HCCs. Positive expression of both genes does not relate to each other, but both are associated with a high PCNA labelling index (LI) (P<0.05) in tumour. p53 (+) is also associated with high serum alpha-foetoprotein (alphaFP) (P<0.001), tumour dedifferentiation (P=0.001) and advanced pathologic stages (P=0.017). However, p21/WAF1 (+) did not show clinicopathologic significance. Survival analysis indicated that poor prognostic factors were p21/WAF1 (-) (P=0.024), p53 (+) (P=0.008), high PCNA (P<0.001), tumour without capsule (P=0.001), poor tumour differentiation (P=0.004), advanced pathologic stage (P<0.001), and high serum alphaFP(P<0.001). Independent factors were p21/WAF1 expression, pathologic stage, and PCNA.

CONCLUSION

In HCC, increased proliferation index PCNA is significantly associated with positive p53 and p21/WAF1. But p21/WAF1 expression did not relate to p53 expression. P21/WAF1 (+) is a good event and serves as an independent survival prognostic factor for HCC, which is a novel finding apart from previous reports.

Manganese superoxide dismutase (SOD2)-mediated delayed radioprotection induced by the free thiol form of amifostine and tumor necrosis factor alpha

RKO36 cells, a subclone of RKO colorectal carcinoma cells that have been stably transfected with the pCMV-EGFP2Xho vector, were grown to confluence and then exposed to either the radioprotector WR-1065, i.e. the active thiol form of amifostine, for 30 min at doses of 40 microM and 4 mM or the cytokine tumor necrosis factor alpha (TNFalpha, TNFA) for 30 min at a concentration of 10 ng/ml and then washed. Total protein was isolated as a function of time up to 32 h after these treatments. Both doses of WR-1065 as well as the concentration of TNFalpha used were effective in elevating intracellular levels of the antioxidant protein SOD2 (also known as MnSOD) at least 15-fold over background levels as determined by Western blot analysis, while measured SOD2 activity was elevated between 5.5- and 6.9-fold. SOD2 reached a maximal level 24 h and 20 h after WR-1065 and TNFalpha treatments, respectively. The antioxidant proteins catalase and glutathione peroxidase (GPX) were also monitored over the 32-h period. In contrast to the robust changes observed in intracellular levels of SOD2 as a function of time after exposure of cells to WR-1065, catalase levels were elevated only 2.6-fold over background as determined by Western blot analysis, while GPX activity was unaffected by WR-1065 exposure. GPX protein levels were extremely low in cells, and analysis of GPX activity using a spectrophotometric method based on the consumption of reduced NADPH also revealed no measurable change as a function of WR-1065 or TNFalpha exposure. RKO36 cells either were irradiated with X rays in the presence of either 40 microM or 4 mM WR-1065 or 10 ng/ml TNFalpha or were irradiated 24 or 20 h later, respectively, when SOD2 protein levels were most elevated. The concentrations and exposure conditions used for WR-1065 and TNFalpha were not cytotoxic and had no effect on plating efficiencies or cell survival compared to untreated controls. No protection or sensitization was observed for cells irradiated in the presence of 40 microM WR-1065 or TNFalpha. Survival was elevated 1.90-fold for cells irradiated in the presence of 4 mM WR-1065. When RKO36 cells were irradiated with 2 Gy 24 h after 40 microM or 4 mM WR-1065 and 20 h after TNFalpha treatments when SOD2 levels were the most increased, survival was elevated 1.42-, 1.48- and 1.36-fold, respectively. This increased survival represents a SOD2-mediated delayed radioprotective effect. SOD2 appears to be an important antioxidant gene whose inducible expression is an important element in adaptive cellular responses in general, and the delayed radioprotective effect in particular. It can be induced by a range of agents including cytoprotective nonprotein thiols such as WR-1065 and pleiotropic cytokines such as TNFalpha.

Gene Expression of Manganese-Containing Superoxide Dismutase as a Biomarker of Manganese Bioavailability for Manganese Sources in Broilers

The goal of this study was to determine whether Mn-containing superoxide dismutase (MnSOD) gene expression in heart tissue would reflect differences among bioavailabilities of Mn sources earlier than other indices. Broilers were divided into 5 groups and fed a Mn-unsupplemented basal diet (control) or the basal diet supplemented with 120 mg of Mn/kg as Mn sulfate or Mn methionine E (Mn Met E), Mn amino acid B (Mn AA B), or Mn amino acid C (Mn AA C) with weak, moderate, or strong chelation strength, respectively. Heart MnSOD mRNA levels were analyzed using quantitative reverse transcription-PCR at 7, 14, or 21 d. The results showed that heart MnSOD mRNA level increased as dietary Mn level increased at any age. At 7 d, chicks fed the diet supplemented with Mn AA B had higher MnSOD mRNA levels than those fed the diet supplemented with Mn sulfate and Mn Met E, and the same tendency was observed at 14 or 21 d. The results suggest that MnSOD gene expression, which is regulated by dietary Mn at transcriptional level, could reflect differences among bio-availabilities of organic Mn sources as early as 7 d. Therefore, the estimation of relative bioavailabilities of Mn sources based on heart MnSOD mRNA level could require a shorter experimental period and a smaller number of animals, and thus less cost.

Do altered activities of superoxide dismutases and the level of Nf-κB modulate the effects of gamma radiation in HeLaS3 cells?

Most experimental models, including cell culture studies, have demonstrated that over-expression of manganese superoxide dismutase (MnSOD) in cells bearing a carcinoma phenotype has anti-proliferative and tumour suppression characteristics. In contrast, when cervical carcinoma biopsies express MnSOD, there is a poor prognosis and resistance to radiation therapy. The results herein indicate that human cervical adenocarcinoma (HeLaS3) cells have increased MnSOD activity (up to 50 % of the total SOD activity) due to low expression of its repressor p53 and a high level of oxidative stress arising from the cell culture conditions. High MnSOD activity may be related to HeLaS3 cell radioresistance, illustrated by a high IC50 of 3.4 Gy and by a relatively high level of cell viability after gamma irradiation. In contrast to MnSOD activity, cytosolic CuZnSOD activity decreased after ionising radiation. The catalase (Cat) activity was unchanged. IR also increased the nitric oxide synthase (NOS) activity. Such conditions lead to increased concentrations of the superoxide radical, hydrogen peroxide and NO?, which together may be responsible for the decreased expression of NF-?B and unaltered Cat activity. Therefore, the disturbed redox balance within HeLaS3 cells may be responsible for the cytotoxicity observed at higher irradiation doses. It could be concluded that inhibition of the CuZnSOD activity may be an important target for the selective killing of radioresistant cancer cells.

Enhanced ROS production and antioxidant defenses in cybrids harbouring mutations in mtDNA

It has been suggested that mutations in mitochondrial DNA (mtDNA) can produce an increase in reactive oxygen species (ROS) and that this can play a major role in the pathogenic mechanisms of mitochondrial encephalomyopathies. Many studies exist using electron transport chain (ETC) inhibitors, however there are only a few studies that examine ROS production associated with mutations in the mtDNA. To investigate this issue, we have studied ROS production, antioxidant defences and oxidative damage to lipids and proteins in transmitochondrial cybrids carrying different mtDNA mutations. Here, we report that two different mutant cell lines carrying mutations in their mitochondrial tRNA genes (A3243G in tRNA LeuUUR and A8344G in tRNA Lys) showed an increased ROS production with a parallel increase in the antioxidant enzyme activities, which may protect cells from oxidative damage in our experimental conditions (no overt oxidative damage to lipids and proteins has been observed). In contrast, cytochrome c oxidase (COX) mutant cybrids (carrying the stop-codon mutation G6930A in the COXI gene) showed neither an increase in ROS production nor elevation of antioxidant enzyme activities or oxidative damage. These results suggest that the specific location of mutations in mtDNA has a strong influence on the phenotype of the antioxidant response. Therefore, this issue should be carefully considered when antioxidant therapies are investigated in patients with mitochondrial disorders.

Modulation of radiation-induced disturbances of antioxidant defense systems by ginsan

There are numerous studies to indicate that irradiation induces reactive oxygen species (ROS), which play an important causative role in radiation damage of the cell. We evaluated the effects of ginsan, a polysaccharide fraction extracted from Panax ginseng, on the γ-radiation induced alterations of some antioxidant systems in the spleen of Balb/c mice. On the 5th day after sublethal whole-body irradiation, homogenized spleen tissues of the irradiated mice expressed only marginally increased mRNA levels of Mn-SOD (superoxide dimutase) in contrast to Cu/Zn-SOD, however, catalase mRNA was decreased by ∼50% of the control. In vivo treatment of non-irradiated mice with ginsan (100 mg kg⁻¹, intraperitoneal administration) had no significant effect, except for glutathione peroxidase (GPx) mRNA, which increased to 144% from the control. However, the combination of irradiation with ginsan effectively increased the SODs and GPx transcription as well as their protein expressions and enzyme activities. In addition, the expression of heme oxygenase-1 and non-protein thiol induced by irradiation was normalized by the treatment of ginsan. Evidence indicated that transforming growth factor-β and other important cytokines such as IL-1, TNF and IFN-γ might be involved in evoking the antioxidant enzymes. Therefore, we propose that the modulation of antioxidant enzymes by ginsan was partly responsible for protecting the animal from radiation, and could be applied as a therapeutic remedy for various ROS-related diseases.

Levels of reactive oxygen species and primary antioxidant enzymes in WI38 versus transformed WI38 cells following bleomcyin treatment

Bleomycin (BLM) is an anticancer drug that generates reactive oxygen species (ROS) after interacting with iron and oxygen. We hypothesized that BLM could cause a different status of oxidative stress in normal versus tumor cells due to possible altered redox status and gene expression in cells following transformation. In this study, the extent of cytotoxicity, levels of ROS, and activities of antioxidant enzymes were compared between normal WI38 cells and SV40-transformed WI38 (VA13) cells following BLM treatment. Basal activities of MnSOD and catalase were lower in VA13 cells and basal ROS levels were higher in VA13 cells. Although BLM caused greater growth inhibition and apoptosis in VA13 cells, it increased ROS levels at an earlier time point in WI38 cells. Moreover, BLM treatment (100 microg/ml) had no effect on the activities of MnSOD, CuZnSOD, and catalase, but increased the activities of glutathione peroxidase (GPX) in WI38 cells after a 48-h treatment and in VA13 cells after a 24- and 48-h treatment. Northern blot analysis indicated that the increase in GPX activities was due to increased transcript levels of GPX1 but not GPX4 in both cells. Our results indicate selective induction of the GPX1 gene by BLM and different redox responses to BLM between WI38 and VA13 cells.

An examination of radiation hormesis mechanisms using a multistage carcinogenesis model

A multistage cancer model that describes the putative rate-limiting steps in carcinogenesis is developed and used to investigate the potential impact on cumulative lung cancer incidence of the hormesis mechanisms suggested by Feinendegen and Pollycove. In the model, radiation and endogenous processes damage the DNA of target cells in the lung. Some fraction of the misrepaired or unrepaired DNA damage induces genomic instability and, ultimately, leads to the accumulation of malignant cells. The model explicitly accounts for cell birth and death processes, the clonal expansion of initiated cells, malignant conversion, and a lag period for tumor formation. Radioprotective mechanisms are incorporated into the model by postulating dose and dose-rate-dependent radical scavenging. The accuracy of DNA damage repair also depends on dose and dose rate. As currently formulated, the model is most applicable to low-linear-energy-transfer (LET) radiation delivered at low dose rates. Sensitivity studies are conducted to identify critical model inputs and to help define the shapes of the cumulative lung cancer incidence curves that may arise when dose and dose-rate-dependent cellular defense mechanisms are incorporated into a multistage cancer model. For lung cancer, both linear no-threshold (LNT-), and non-LNT-shaped responses can be obtained. If experiments demonstrate that the effects of DNA damage repair and radical scavenging are enhanced at least three-fold under low-dose conditions, our studies would support the existence of U-shaped responses. The overall fidelity of the DNA damage repair process may have a large impact on the cumulative incidence of lung cancer. The reported studies also highlight the need to know whether or not (or to what extent) multiply damaged DNA sites are formed by endogenous processes. Model inputs that give rise to U-shaped responses are consistent with an effective cumulative lung cancer incidence threshold that may be as high as 300 mGy (4 mGy per year for 75 years) for low-LET radiation.

Identification of nucleophosmin as an NF-kappaB co-activator for the induction of the human SOD2 gene

Manganese superoxide dismutase (MnSOD) is an antioxidant enzyme essential for the survival of life. We have reported that NF-kappaB is essential but not sufficient for the synergistic induction of MnSOD by phorbol 12-myristate 13-acetate and cytokines. To further identify transcription factors and co-activators that participate in the induction of MnSOD, we used NF-kappaB affinity chromatography to isolate potential NF-kappaB interacting proteins. Proteins eluted from the NF-kappaB affinity column were subjected to proteomic analysis and verified by Western analysis. Nucleophosmin (NPM), a nucleolar phosphoprotein, is the most abundant single protein identified. Co-immunoprecipitation studies suggest a physical interaction between NPM and NF-kappaB proteins. To verify the role of NPM on MnSOD gene transcription, cells were transfected with constructs expressing NPM in sense or antisense orientation as well as interference RNA. The results indicate that an increase NPM expression leads to increased MnSOD gene transcription in a dose-dependent manner. Consistent with this, expression of small interfering RNA for NPM leads to inhibition of MnSOD gene transcription but does not have any effect on the expression of interleukin-8, suggesting that the effect of NPM is selective. These results identify NPM as a partner of the NF-kappaB transcription complex in the induction of MnSOD by phorbol 12-myristate 13-acetate and cytokines.

Superoxide dismutases in malignant cells and human tumors

Reactive oxygen metabolites have multifactorial effects on the regulation of cell growth and the capacity of malignant cells to invade. Overexpression of the superoxide dismutases (SODs) in vitro increases cell differentiation, decreases cell growth and proliferation, and can reverse a malignant phenotype to a nonmalignant one. The situation in vivo is more complex due to multiple interactions of tumor cells with their environment. Numerous in vivo studies show that the superoxide dismutases can be highly expressed in aggressive human solid tumors. Furthermore, high SOD has occasionally been associated with a poor prognosis and with resistance to cytotoxic drugs and radiation. Most of the apparent conflicts between the above in vitro and in vivo observations can be reconciled by considering the net redox status of tumor cells in different environments. Administering high concentrations of SOD to cells in vitro is usually associated with a non- or less malignant phenotype, whereas secondary induction of SOD in tumors in vivo can be associated with an aggressive malignant transformation probably due to the altered (oxidative) redox state in the malignant cells. This concept suggests that for many types of tumors antioxidants could be used to diminish the invasive capability of malignant cells.

Polyphenol (−)-epigallocatechin gallate inhibits apoptosis induced by irradiation in human HaCaT keratinocytes

Green tea is a rich source of polyphenols, and (-)-epigallocatechin-3-gallate (EGCG) is a major constituent of green tea polyphenols. In the present study, we investigated the effect of EGCG on apoptosis induced by irradiation in the human keratinocytic cell line HaCaT. Irradiation by gamma-ray induced apoptosis with concomitant cleavage of caspase-3 and its in vivo substrate poly(ADP-ribose) polymerase. Treatment of cells with EGCG inhibited irradiation-induced apoptosis as detected by Hoechst staining and internucleosomal cleavage of DNA, and prevented the cleavage of these proteins by irradiation. We also found that the treatment of cells with EGCG alone suppressed cell growth and induced apoptosis in these cells. Our results suggest that EGCG inhibits irradiation-induced apoptosis by inactivating the caspase pathway in HaCaT cells. Our study also indicates that EGCG has a dual effect on the survival of these keratinocytes.

Endogenous production of TNFalpha is a potent trigger of NFkappaB activation by irradiation in human monocytic cells THP-1

Irradiation causes DNA damage and induces neoplastic transformation. In response to irradiation, cells induce genes or activate proteins that protect themselves from the external insult. Nuclear factor kappaB (NFkappaB) activates transcription of target genes and plays important roles in inflammation. We studied the mechanism(s) for activation of NFkappaB by irradiation in human monocytic cells THP-1. Gel mobility shift assays showed that irradiation stimulated the NFkappaB-DNA binding activity of nuclear extracts from these cells. Western blot analysis using polyclonal antibody against phosphorylated IkappaB protein showed that irradiation increased the levels of phosphorylated IkappaB. The production of tumor necrosis factor alpha (TNFalpha) was stimulated by irradiation in these cells. Treatment with exogenously added TNFalpha also stimulated the NFkappaB binding activity with concomitant degradation of IkappaB. Further study found that the activation of NFkappaB by irradiation was inhibited by a neutralizing anti-TNFalpha antibody. Macrophages from TNFalpha-deficient mice were also defective in the irradiation-induced activation of NFkappaB. These results indicate that endogenous production of TNFalpha in macrophages/monocytes is required for NFkappaB activation by irradiation. Our data also suggest that TNFalpha in monocytes/macrophages exposed to irradiation is involved in signal transduction network initiation.

HSP25 overexpression attenuates oxidative stress-induced apoptosis: roles of ERK1/2 signaling and manganese superoxide dismutase

HSP25 has been shown to induce resistance to radiation and oxidative stress; however, its exact mechanisms remain unclear. In the present study, a high concentration of H2O2 was found to induce DNA fragmentation in L929 mouse fibroblast cells, and HSP25 overexpression attenuated this phenomenon. To elucidate the mechanisms of H2O2-mediated cell death, ERK1/2, p38 MAPK, and JNK1/2 phosphorylation in the cells after treatment with H2O2 were examined. ERK1/2 and JNK1/2 were activated by H2O2; ERK1/2 activation was inhibited in HSP25-overexpressed cells, while JNK1/2 was indifferent. Inhibition of ERK1/2 activation by treatment of the cells with PD98059 or dominant-negative ERK2 transfection blocked H2O2-induced cell death; similarly treated HSP25-overexpressed cells were not at all affected. Moreover, inhibition of JNK1/2 by dominant-negative JNK1 or JNK2 transfection did not affect H2O2-mediated cell death in control cells. Dominant-negative Ras or Raf transfection inhibited H2O2-mediated ERK1/2 activation and cell death in control cells. On the contrary, HSP25-overexpressed cells did not show any differences. Upstream pathways of H2O2-mediated ERK1/2 activation and cell death involved both tyrosine kinase (PDGFbeta receptor and Src) and PKCdelta, while in HSP25-overexpressed cells these kinases did not respond to H2O2 treatment. Since HSP25 overexpression reduced reactive oxygen species (ROS), increased manganese superoxide dismutase (MnSOD) gene expression, and increased enzyme activity, involvement of MnSOD in HSP25-mediated attenuation of H2O2-mediated ERK1/2 activation and cell death was examined. Blockage of MnSOD with antisense oligonucleotides prevented DNA fragmentation and returned the ERK1/2 activation to the control level. Indeed, when MnSOD was overexpressed in L929 cells, similar to in HSP25-overexpressed cells, DNA fragmentation and ERK1/2 activation were reduced. From the above results, we suggest for the first time that reduced oxidative damage by HSP25 was due to MnSOD-mediated downregulation of ERK1/2.

Role of the intronic enhancer in tumor necrosis factor-mediated induction of manganous superoxide dismutase

Manganous superoxide dismutase (Mn-SOD), a tumor necrosis factor (TNF)-inducible gene product, plays an important role in removing superoxide anions produced inside mitochondria. Two regulatory regions, the proximal promoter region (PPR), which is upstream from the transcription initiation site, and the TNF-responsive element (TNFRE), which is inside intron 2, are responsible for Mn-SOD expression. To understand how each of these regions contributes to the transcription of Mn-SOD, quantitative reverse transcription-PCR, chromatin immunoprecipitations, and in vivo nuclease sensitivity assays were performed on the murine Mn-SOD gene. These assays demonstrate that Sp1 and nuclear factor (NF)-kappaB p65 are required for Mn-SOD induction by TNF. Sp1 bound the PPR constitutively, whereas NF-kappaB p65 and C/EBP-beta bound the TNFRE only after TNF treatment. Binding of C/EBP-beta to the TNFRE was dependent on the presence of NF-kappaB p65. The chromatin structure within the TNFRE became more accessible to nuclease digestion after TNF treatment. This accessibility required Sp1 and NF-kappaB p65. Treatment of cells with an inhibitor of histone deacetylation, or transient transfection with coactivator-expressing plasmids, enhanced the expression of Mn-SOD. NF-kappaB p65 binding was required for acetylation of histones H3 and H4 at the PPR and the TNFRE. Together, these data suggest communication between the PPR and the TNFRE which involves chromatin remodeling and histone acetylation during the induction process of Mn-SOD in response to TNF.

Radioprotective effects of ginsan, an immunomodulator

We previously reported that ginsan, a purified polysaccharide isolated from Panax ginseng, had a mitogenic activity, induced LAK cells, and increased levels of several cytokines. In an effort to identify other immunostimulatory effects, we evaluated the protective effects of ginsan injected in vivo against radiation by measuring its effects on the CFU-S bone marrow cells and spleen cells. Ginsan was found to significantly increase the number of bone marrow cells, spleen cells, granulocyte-macrophage colony-forming cells (GM-CFC), and circulating neutrophils, lymphocytes and platelets in irradiated mice. In addition, ginsan induced the endogenous production of cytokines such as Il1, Il6, Ifng and Il12, which are required for hematopoietic recovery, and was able to enhance Th1 function while interfering with the Th2 response in irradiated mice. We demonstrated that pretreatment with ginsan protected mice from the lethal effects of ionizing radiation more effectively than when it was given immediately after or at various times after irradiation. A significant increase in the LD(50/30) from 7.54 Gy for PBS injection to 10.93 Gy for mice pretreated with 100 mg/kg ginsan was observed. These findings indicate that ginsan may be a useful agent to reduce the time necessary for reconstituting hematopoietic cells after irradiation.

M-LP, Mpv17-like protein, has a peroxisomal membrane targeting signal comprising a transmembrane domain and a positively charged loop and up-regulates expression of the manganese superoxide dismutase gene

M-LP (Mpv17-like protein) has been identified as a new protein that has high sequence homology with Mpv17 protein, a peroxisomal membrane protein involved in the development of early onset glomerulosclerosis. In this study, we verified the peroxisomal localization of M-LP by performing dual-color confocal analysis of COS-7 cells cotransfected with green fluorescent protein-tagged M-LP and DsRED2-PTS1, a red fluorescent peroxisomal marker. To characterize the peroxisomal membrane targeting signal, we examined the intracellular localizations of several green fluorescent protein-tagged deletion mutants and demonstrated that, of the three transmembrane segments predicted, the first near the NH(2) terminus and NH(2)-terminal half of the following loop region, which is abundant in positively charged amino acids, were necessary and sufficient for peroxisomal targeting. To elucidate the function of M-LP, we examined the activities of several enzymes involved in reactive oxygen species metabolism in COS-7 cells and found that transfection with M-LP increased the superoxide dismutase activity significantly. Quantitative real-time PCR analysis revealed that the manganese SOD (SOD2) mRNA level of COS-7 cells transfected with M-LP was elevated. These results indicate that M-LP participates in reactive oxygen species metabolism.

Cell phenotype specific kinetics of expression of intratracheally injected manganese superoxide dismutase-plasmid/liposomes (MnSOD-PL) during lung radioprotective gene therapy

Intratracheal (IT) injection of manganese superoxide dismutase-plasmid/liposome (MnSOD-PL) complexes prior to whole lung irradiation of C57BL/6J mice provides significant protection from acute and chronic irradiation damage. We determined the duration of increased MnSOD biochemical activity and differential expression of a hemagglutinin (HA) epitope-tagged MnSOD transgene. HA-MnSOD-PL was IT injected at doses of 0-1000 microg, and mice were killed 1,2,3 or 4 days later. Other groups of mice were irradiated to 20 Gy to the pulmonary cavity 24 h after injection and killed at the same time points as non-irradiated mice. Both non-irradiated and irradiated groups of mice showed increased MnSOD biochemical activity with plasmid dose that plateaued at 100 microg of MnSOD plasmid DNA. In control mice, MnSOD biochemical activity decreased at 2, 3 or 4 days after injection. In irradiated mice, MnSOD biochemical activity decreased at day 2 but increased on days 3 and 4. HA-MnSOD expression decreased in broncheoalveolar macrophages and alveolar type-II cells 3 days after injection in non-irradiated and irradiated mice, but remained elevated in endothelial and epithelial cells past 4 days. The data provide a rationale for every second-day administration of intrapulmonary MnSOD-PL in clinical trials of radioprotective gene therapy. This should be sufficient to provide radioprotection during radiation treatments.