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Antioxidant enzyme levels in cancer
T.O. Oberley1,2 and l.W. Oberley3
1Pathology and Laboratory Medicine Service, William S. Middleton Memorial Veterans Hospital, 2Department of Pathology and Laboratory Medicine, University of Wisconsin Medical School Madison, Wisconsin and 3Radiation Research Laboratory, University of Iowa College of Medicine, Iowa city, Iowa, USA
Offprint requests to: Professor Terry D. Oberley, M.D., Ph.D., Pathology
and Laboratory Medicine Service, William S. Middleton Memorial
Veterans Hospital, 2500 Overlook Terrace, Madison, WI 53705,
USA
Summary. 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. Histol Histopathol 12, 525-535
(1997)
Key words: Antioxidant enzymes, Reactive oxygen
species, Superoxide dismutase, Carcinogenesis, Malignant phenotype
DOI: 10.14670/HH-12.525
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