Toxic Metals and Oxidative Stress Part I: Mechanisms Involved in Me-tal induced Oxidative Damage

Abstract

Toxic metals (lead, cadmium, mercury and arsenic) are widely found in our environment. Humans are exposed to these metals from numerous sources, including contaminated air, water, soil and food. Recent studies indicate that transition metals act as catalysts in the oxidative reactions of biological macromolecules therefore the toxicities associated with these metals might be due to oxidative tissue damage. Redox-active metals, such as iron, copper and chromium, undergo redox cycling whereas redox-inactive metals, such as lead, cadmium, mercury and others deplete cells' major antioxidants, particularly thiol-containing antioxidants and enzymes. Either redox-active or redox-inactive metals may cause an increase in production of reactive oxygen species (ROS) such as hydroxyl radical (HO.), superoxide radical (O2.-) or hydrogen peroxide (H2O2). Enhanced generation of ROS can overwhelm cells' intrinsic antioxidant defenses, and result in a condition known as "oxidative stress". Cells under oxidative stress display various dysfunctions due to lesions caused by ROS to lipids, proteins and DNA. Consequently, it is suggested that metal-induced oxidative stress in cells can be partially responsible for the toxic effects of heavy metals. Several studies are underway to determine the effect of antioxidant supplementation following heavy metal exposure. Data suggest that antioxidants may play an important role in abating some hazards of heavy metals. In order to prove the importance of using antioxidants in heavy metal poisoning, pertinent biochemical mechanisms for metal-induced oxidative stress should be reviewed.

RETRACTED: Effects of <i>Annona squamosa</i> Seed Extract on <i>Mus musculus</i> Exposed to Mercuric Chloride: Evaluations of Metal-Induced Oxidative Stress and Its Developmental Outcomes

“…These interfering effects of anti-oxidants on the damaging effects of sulfhydryl reactive metals have significant consequences on the developing embryo. It has been proposed that plants with potent anti-oxidant properties may also have the potential to interfere, and hence mediate the effects of heavy metal toxicity [2] [14].…”

Generation of reactive oxygen species in relevant cell lines as a bio-indicator of oxidative effects caused by acid mine water

“…Of the metals present in the effluent, Fe, Cu, Cr and Ar are reported to generate ROS by redox recycling, while Hg depletes GSH and thiol-containing antioxidant enzymes. Both processes result in an increase in ROS production (see review by Ercal et al, 2001). …”

Bird Glutathione S-transferases: Endogenous and Exogenous Toxic Insults Read more at http://nexusacademicpublishers.com/table_contents_detail/4/872/html#CUM6EltbRFTzsEeL.99

“…That the individuals which are living in polluted environments can exposed to a mixture of pollutants at sub lethal concentrations which shows synergistic, antagonistic effects. Based on oxidative potential and reactivity with biomolecules the hydroxyl radicals are the most important in biological and toxicological terms (Ercal et al, 2001). Little attention was paid on the function of antioxidant enzymatic system and it's levels in different bird species as an indicators of oxidative stress in polluted environments (Berglund et al, 2007;Norte et al, 2009;Hegseth et al, 2011).…”