Metallothionein blocks oxidative DNA damage in vitro

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.