Manganese-containing superoxide dismutase (MnSOD) is an essential primary antioxidant enzyme that converts superoxide radical to hydrogen peroxide and molecular oxygen within the mitochondrial ...matrix. Cytosolic glutathione peroxidase (GPX) converts hydrogen peroxide into water. MnSOD is reduced in a variety of tumor types and has been proposed to be a new kind of tumor suppressor gene, but the mechanism(s) by which MnSOD suppresses malignancy is unclear. According to the enzymatic reactions catalyzed by MnSOD and cytosolic GPX, change in the cellular redox status, especially change attributable to accumulation of hydrogen peroxide or other hydroperoxides, is a possible reason to explain the suppression of tumor growth observed in MnSOD-overexpressing cells. To test this possible mechanism, we transfected human cytosolic GPX cDNA into human glioma cells overexpressing MnSOD. The results showed that GPX overexpression not only reversed the tumor cell growth inhibition caused by MnSOD overexpression but also altered the cellular contents of total glutathione, reduced glutathione, oxidized glutathione, and intracellular reactive oxygen species. Overexpression of GPX also inhibited degradation of the inhibitory subunit alpha of nuclear factor-KB. These results suggest that hydrogen peroxide or other hydroperoxides appear to be key reactants in the tumor suppression by MnSOD overexpression, and growth inhibition correlates with the intracellular redox status. This work suggests that manipulations that inhibit peroxide removal should enhance the tumor suppressive effect of MnSOD overexpression.
Mice deficient in CuZn superoxide dismutase (CuZnSOD) showed no overt abnormalities during development and early adulthood, but had a reduced lifespan and increased incidence of neoplastic changes in ...the liver. Greater than 70% of Sod1-/- mice developed liver nodules that were either nodular hyperplasia or hepatocellular carcinoma (HCC). Cross-sectional studies with livers collected from Sod1-/- and age-matched +/+ controls revealed extensive oxidative damage in the cytoplasm and, to a lesser extent, in the nucleus and mitochondria from as early as 3 months of age. A marked reduction in cytosolic aconitase, increased levels of 8-oxo dG and F2-isoprostanes, and a moderate reduction in glutathione peroxidase activities and porin levels were observed in all age groups of Sod1-/- mice examined. There were also age-related reductions in Mn superoxide dismutase activities and carbonic anhydrase III. Parallel to the biochemical changes, there were progressive increases in the DNA repair enzyme APEX1, the cell cycle control proteins cyclin D1 and D3, and the hepatocyte growth factor receptor Met. Increased cell proliferation in the presence of persistent oxidative damage to macromolecules likely contributes to hepatocarcinogenesis later in life.
Manganese superoxide dismutase (MnSOD) has been previously shown to suppress the malignant phenotype of human melanoma and breast cancer cells. To test the possible role of MnSOD in glioma ...malignancy, MnSOD was overexpressed in wild type human glioma U118 cells and subcloned U118-9 cells by transfection of human MnSOD cDNA. The MnSOD-transfected cell lines demonstrated expression of exogenous (plasmid) MnSOD mRNA, increase in MnSOD immunoreactive protein, and a three- to eightfold increase in MnSOD enzymatic activity. The MnSOD overexpressing cell lines became less malignant as demonstrated by requiring a higher serum concentration to grow in vitro and much slower tumor growth in nude mice than the parental and neo control cell lines. These findings further support the hypothesis that MnSOD may be a tumor suppressor gene in a wide variety of human tumors.
Inhaled diesel exhaust particles (DEP) exert proinflammatory effects in the respiratory tract. This effect is related to the particle content of redox cycling chemicals and is involved in the ...adjuvant effects of DEP in atopic sensitization. We demonstrate that organic chemicals extracted from DEP induce oxidative stress in normal and transformed bronchial epithelial cells, leading to the expression of heme oxygenase 1, activation of the c-Jun N-terminal kinase cascade, IL-8 production, as well as induction of cytotoxicity. Among these effects, heme oxygenase 1 expression is the most sensitive marker for oxidative stress, while c-Jun N-terminal kinase activation and induction of apoptosis-necrosis require incremental amounts of the organic chemicals and increased levels of oxidative stress. While a macrophage cell line (THP-1) responded in similar fashion, epithelial cells produced more superoxide radicals and were more susceptible to cytotoxic effects than macrophages. Cytotoxicity is the result of mitochondrial damage, which manifests as ultramicroscopic changes in organelle morphology, a decrease in the mitochondrial membrane potential, superoxide production, and ATP depletion. Epithelial cells also differ from macrophages in not being protected by a thiol antioxidant, N-acetylcysteine, which effectively protects macrophages against cytotoxic DEP chemicals. These findings show that epithelial cells exhibit a hierarchical oxidative stress response that differs from that of macrophages by more rapid transition from cytoprotective to cytotoxic responses. Moreover, epithelial cells are not able to convert N-acetylcysteine to cytoprotective glutathione.
1 Department of Exercise Science, and 2 Radiation
Research Laboratory, The University of Iowa, Iowa City, Iowa 52242;
3 Department of Pathology and Veterans Affairs Hospitals and
Clinics, ...University of Wisconsin, Madison, Wisconsin 53705; and
4 Department of Internal Medicine and Laboratory of
Environmental Stress and Adaptation, University of New Mexico,
Albuquerque, New Mexico 87131
A decline in an organism's ability to
cope with stress through acute response protein expression may
contribute to stress intolerance with aging. We investigated the
influence of aging on stress tolerance and the capacity to synthesize
the 70-kDa heat shock protein (HSP70) in young and old rats exposed to
an environmental heating protocol. Livers were assessed for injury and
HSP70 expression after heat stress by use of immunohistochemical and
immunoblotting techniques. The inducible HSP70 response in the
cytoplasm and nucleus was markedly reduced with age at several time
points over a 48-h recovery period, although senescent rats were able
to strongly express HSP70 early in recovery. Older animals had
extensive zone-specific liver injury, which corresponded to the
diminished HSP70 response observed in these regions, and a significant
reduction in thermotolerance compared with their young counterparts.
These data highlight the regional nature of stress-induced injury and
HSP70 expression in the liver and the impact of aging on these
responses. Furthermore, the results suggest a functional link between
the age-related decrements in the expression of inducible HSP70 and the
pathophysiological responses to heat stress.
heat shock proteins; hyperthermia; environmental stress
Antioxidant enzyme levels in cancer Oberley, T D; Oberley, L W
Histology and histopathology,
04/1997, Letnik:
12, Številka:
2
Journal Article
Recenzirano
Normal cells are protected by antioxidant enzymes from the toxic effects of high concentrations of reactive oxygen species generated during cellular metabolism. Even though cancer cells generate ...reactive oxygen species, it has been demonstrated biochemically that antioxidant enzyme levels are low in most animal and human cancers. However, a few cancer types have been found to have elevated levels of antioxidant enzymes, particularly manganese superoxide dismutase. Morphologic studies of animal and human cancer have confirmed that although the majority of tumor cell types from several organ systems have low antioxidant enzymes, adenocarcinomas may have elevated manganese superoxide dismutase and catalase levels. However, all cancers examined to date have some imbalance in antioxidant enzyme levels compared with the cell of origin. Antioxidant enzyme importance in cancer genesis has been difficult to evaluate in early cancerous lesions using biochemical techniques because such lesions are small and therefore below the level of detection. Using immunohistochemical techniques, early lesions of human and animal cancers were demonstrated to have low antioxidant enzymes, thus suggesting a role for these enzymes both in the genesis of cancer and the malignant phenotype. All but one human cancer cell type (the granular cell variant of human renal adenocarcinoma) examined showed both low catalase and glutathione peroxidase levels, suggesting that most cancer cell types cannot detoxify hydrogen peroxide. Our results to date are used to propose new cancer therapies based on modulation of cellular redox state.
Two polymorphic variants of manganese superoxide dismutase (MnSOD), with either Ile or Thr at amino acid 58, (Ile58MnSOD or Thr58MnSOD), have been found in the human population. The MnSOD activity of ...these two variants and their effects on the malignant phenotype of human breast cancer MCF-7 cells were compared. It was demonstrated that MnSOD-overexpressing clones obtained from transfection of the two MnSOD cDNAs into MCF-7 cells had increased MnSOD immunoreactive protein and increased MnSOD activity. Cells overexpressing Ile58MnSOD had 3-fold higher MnSOD activity than cells overexpressing Thr58MnSOD in vivo at an equal MnSOD protein level. Tumor-suppressive effects of MnSOD-overexpressing cells were indicated by: (a) decreased plating efficiency; (b) elongated cell population doubling time; (c) lower clonogenic fraction in soft agar; and (d) complete inhibition or delayed onset of tumor formation in nude mice. When compared on the same activity basis, the suppressive effects of Ile58MnSOD were similar to those of Thr58MnSOD. However, far more Thrs58MnSOD protein was required to obtain the same amount of MnSOD activity, making the Thr58MnSOD far less effective. A dose-response suppressive effect was observed when the increase of MnSOD activity was moderate. We conclude that MnSOD is a tumor suppressor in human breast cancer, but the Thr58 form of the protein is a much less effective tumor suppressor than the Ile58 form of the protein.
Background: The antioxidant enzymes (manganese‐ and copper‐zinc‐containing superoxide dismutases, catalast and glutathione peroxidase) limit cell injury induced by reactive oxygen species. The ...purpose of the study was to determine whether human oral squamous cell carcinomas have altered antioxidant enzyme levels. This study is the first to undertake this task in human oral mucosa and squamous cell carcinoma.
Methods: Semiquantitative immunohistochemistry was used to examine 26 archived oral squamous cell carcinoma biopsies. Fourteen well‐differentiated and 12 poorly differentiated tumors were examined, as were 12 specimens of oral mucosa. All sections were reviewed by two oral and maxillofacial pathologists, and image analysis of the immunostained sections was performed using NIH Image. Antioxidant enzyme staining intensities were compared in the different groups by Duncan's multiple range test.
Results: In general, mucosal basal cells displayed lower antioxidant enzyme levels than spinous cells, and primary tumor cells displayed lower antioxidant enzyme staining intensities than did their normal cell counterparts. Moreover, poorly differentiated tumor cells showed lower antioxidant enzyme staining intensities than well‐differentiated tumor cells. Manganese‐containing superoxide dismutase staining intensities were, however, higher in well‐differentiated oral squamous cell carcinomas than their normal cells of origin.
Conclusions: Detection of antioxidant enzymes may be a useful future marker in the molecular diagnosis of the oral cancer. Moreover, it may be possible to not only monitor the effectiveness of chemopreventitive and therapeutic strategies in oral cancer using these enzymes, but to monitor tumor recurrence.
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