Metallothionein blocks oxidative DNA damage in vitro
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Updated: May 19, 2026
Quantification of three DNA Lesions by Mass Spectrometry and Assessment of Their Levels in Tissues of Mice Exposed to Ambient Fine Particulate Matter
Published on: May 29, 2019
Wei Qu1, Jingbo Pi, Michael P Waalkes
1Inorganic Toxicology Group, National Toxicology Program Laboratory, Division of the National Toxicology Program, National Institute of Environmental Health Sciences, Research Triangle Park, NC 27709, USA.
Abstract:
The role of metallothionein (MT) in mitigation of oxidative DNA damage (ODD) induced by either cadmium (Cd) or the direct oxidant hydrogen peroxide (H(2)O(2)) was systematically examined using MT-I/II double knockout (MT-null) or MT-competent wild-type (WT) cells. Both toxicants were much more lethal to MT-null cells (Cd LC(50) = 6.6 microM; H(2)O(2) LC(50) = 550 microM) than to WT cells (Cd LC(50) = 16.5 microM; H(2)O(2) LC(50) = 930 microM). Cd induced concentration-related MT increases in WT cells, while the basal levels were undetectable and not increased by Cd in MT-null cells. ODD, measured by the immuno-spin trapping method, was minimally induced by sub-toxic Cd levels (1 or 5 microM; 24 h) in WT cells, but markedly increased in MT-null cells (>430 %). Similarly, ODD was induced to higher levels by lower concentrations of H(2)O(2) in MT-null cells than WT cells. Transfection of MT-I into MT-null cells reduced both Cd- and H(2)O(2)-induced cytolethality and ODD. Cd increased the expression of the oxidant defense genes, HO-1, and GSTa2 to a much greater extent in MT-null cells than in WT. Cd or H(2)O(2) exposure increased the expression of key transport genes, Mrp1 and Mrp2, in WT cells but not in MT-null cells. MT protects against Cd- and H(2)O(2)-induced ODD in MT-competent cells possibly by multiple mechanisms, potentially including direct metal ion sequestration and sequestration of oxidant radicals by MT. MT-deficient cells appear to adapt to Cd primarily by turning on oxidant response systems, while MT-competent cells activate MT and transport systems.
Insights
Metallothionein (MT) protects cells from oxidative DNA damage (ODD) caused by cadmium (Cd) and hydrogen peroxide (H2O2). MT-deficient cells show increased ODD and altered gene expression responses to these toxicants.
Area of Science:
- Biochemistry
- Cell Biology
- Toxicology
Background:
- Metallothionein (MT) is a protein involved in metal homeostasis and protection against oxidative stress.
- Oxidative DNA damage (ODD) is a critical factor in cellular toxicity and disease.
- Cadmium (Cd) and hydrogen peroxide (H2O2) are known inducers of oxidative stress.
Purpose of the Study:
- To investigate the role of metallothionein (MT) in mitigating oxidative DNA damage (ODD) induced by cadmium (Cd) and hydrogen peroxide (H2O2).
- To compare the cellular responses to these toxicants in MT-deficient (MT-null) and MT-competent (wild-type, WT) cells.
Main Methods:
- Utilized MT-I/II double knockout (MT-null) and wild-type (WT) cells.
- Assessed cytolethality using lethal concentration 50% (LC50) values.
- Measured ODD using the immuno-spin trapping method.
- Analyzed gene expression of oxidant defense (HO-1, GSTa2) and transport (Mrp1, Mrp2) genes.
- Investigated the effect of MT-I gene transfection into MT-null cells.
Main Results:
- MT-null cells exhibited significantly higher sensitivity (lower LC50) to both Cd and H2O2 compared to WT cells.
- MT-null cells showed markedly increased ODD under Cd and H2O2 exposure, while WT cells showed minimal ODD at sub-toxic levels.
- Cd induced significant increases in MT levels in WT cells, but not in MT-null cells.
- Transfection of MT-I into MT-null cells restored protection against cytolethality and ODD.
- MT-null cells upregulated oxidant defense genes (HO-1, GSTa2) more significantly in response to Cd than WT cells.
- WT cells increased expression of transport genes (Mrp1, Mrp2) upon Cd or H2O2 exposure, unlike MT-null cells.
Conclusions:
- Metallothionein (MT) plays a crucial protective role against Cd- and H2O2-induced oxidative DNA damage (ODD) in cells.
- MT may exert protection through direct sequestration of metal ions and oxidant radicals.
- MT-deficient cells adapt to Cd primarily by activating oxidant response systems.
- MT-competent cells utilize MT and transport systems for protection against these toxicants.
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