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Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. Autoxidation leads to degradation of organic compounds, including living matter. Antioxidants are frequently added to industrial products, such as polymers, fuels, and lubricants, to extend their usable lifetimes. Foods are also treated with antioxidants to forestall spoilage, in particular the rancidification of oils and fats. In cells, antioxidants such as glutathione, mycothiol, or bacillithiol, and enzyme systems like superoxide dismutase, can prevent damage from oxidative stress.
Superoxide dismutase (SOD, EC 1.15.1.1) is an enzyme that alternately catalyzes the dismutation (or partitioning) of the superoxide (O−
2) anion radical into normal molecular oxygen (O2) and hydrogen peroxide (H
2O
2). Superoxide is produced as a by-product of oxygen metabolism and, if not regulated, causes many types of cell damage. Hydrogen peroxide is also damaging and is degraded by other enzymes such as catalase. Thus, SOD is an important antioxidant defense in nearly all living cells exposed to oxygen. One exception is Lactobacillus plantarum and related lactobacilli, which use a different mechanism to prevent damage from reactive O−
2.
In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula O−2. The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of the one-electron reduction of dioxygen O2, which occurs widely in nature. Molecular oxygen (dioxygen) is a diradical containing two unpaired electrons, and superoxide results from the addition of an electron which fills one of the two degenerate molecular orbitals, leaving a charged ionic species with a single unpaired electron and a net negative charge of −1. Both dioxygen and the superoxide anion are free radicals that exhibit paramagnetism. Superoxide was historically also known as "hyperoxide".
The free radical theory of aging states that organisms age because cells accumulate free radical damage over time. A free radical is any atom or molecule that has a single unpaired electron in an outer shell. While a few free radicals such as melanin are not chemically reactive, most biologically relevant free radicals are highly reactive. For most biological structures, free radical damage is closely associated with oxidative damage. Antioxidants are reducing agents, and limit oxidative damage to biological structures by passivating them from free radicals.
In chemistry and biology, reactive oxygen species (ROS) are highly reactive chemicals formed from diatomic oxygen (O2), water, and hydrogen peroxide. Some prominent ROS are hydroperoxide (O2H), superoxide (O2-), hydroxyl radical (OH.), and singlet oxygen. ROS are pervasive because they are readily produced from O2, which is abundant. ROS are important in many ways, both beneficial and otherwise. ROS function as signals, that turn on and off biological functions. They are intermediates in the redox behavior of O2, which is central to fuel cells. ROS are central to the photodegradation of organic pollutants in the atmosphere. Most often however, ROS are discussed in a biological context, ranging from their effects on aging and their role in causing dangerous genetic mutations.
Obligate anaerobes are microorganisms killed by normal atmospheric concentrations of oxygen (20.95% O2). Oxygen tolerance varies between species, with some species capable of surviving in up to 8% oxygen, while others lose viability in environments with an oxygen concentration greater than 0.5%.
Respiratory burst is the rapid release of the reactive oxygen species (ROS), superoxide anion and hydrogen peroxide, from different cell types.
NADPH oxidase is a membrane-bound enzyme complex that faces the extracellular space. It can be found in the plasma membrane as well as in the membranes of phagosomes used by neutrophil white blood cells to engulf microorganisms. Human isoforms of the catalytic component of the complex include NOX1, NOX2, NOX3, NOX4, NOX5, DUOX1, and DUOX2.
Oxidative stress reflects an imbalance between the systemic manifestation of reactive oxygen species and a biological system's ability to readily detoxify the reactive intermediates or to repair the resulting damage. Disturbances in the normal redox state of cells can cause toxic effects through the production of peroxides and free radicals that damage all components of the cell, including proteins, lipids, and DNA. Oxidative stress from oxidative metabolism causes base damage, as well as strand breaks in DNA. Base damage is mostly indirect and caused by the reactive oxygen species generated, e.g., O2− (superoxide radical), OH (hydroxyl radical) and H2O2 (hydrogen peroxide). Further, some reactive oxidative species act as cellular messengers in redox signaling. Thus, oxidative stress can cause disruptions in normal mechanisms of cellular signaling.
Myricetin is a member of the flavonoid class of polyphenolic compounds, with antioxidant properties. Common dietary sources include vegetables, fruits, nuts, berries, tea, and red wine.
Superoxide dismutase [Cu-Zn] also known as superoxide dismutase 1 or hSod1 is an enzyme that in humans is encoded by the SOD1 gene, located on chromosome 21. SOD1 is one of three human superoxide dismutases. It is implicated in apoptosis, familial amyotrophic lateral sclerosis and Parkinson's disease.
Superoxide dismutase 2, mitochondrial (SOD2), also known as manganese-dependent superoxide dismutase (MnSOD), is an enzyme which in humans is encoded by the SOD2 gene on chromosome 6. A related pseudogene has been identified on chromosome 1. Alternative splicing of this gene results in multiple transcript variants. This gene is a member of the iron/manganese superoxide dismutase family. It encodes a mitochondrial protein that forms a homotetramer and binds one manganese ion per subunit. This protein binds to the superoxide byproducts of oxidative phosphorylation and converts them to hydrogen peroxide and diatomic oxygen. Mutations in this gene have been associated with idiopathic cardiomyopathy (IDC), premature aging, sporadic motor neuron disease, and cancer.
Irwin Fridovich was an American biochemist who, together with his graduate student Joe M. McCord, discovered the enzymatic activity of copper-zinc superoxide dismutase (SOD),—to protect organisms from the toxic effects of superoxide free radicals formed as a byproduct of normal oxygen metabolism. Subsequently, Fridovich's research group also discovered the manganese-containing and the iron-containing SODs from Escherichia coli and the mitochondrial MnSOD (SOD2), now known to be an essential protein in mammals. He spent the rest of his career studying the biochemical mechanisms of SOD and of biological superoxide toxicity, using bacteria as model systems. Fridovich was also Professor Emeritus of Biochemistry at Duke University.
Extracellular superoxide dismutase [Cu-Zn] is an enzyme that in humans is encoded by the SOD3 gene.
All living cells produce reactive oxygen species (ROS) as a byproduct of metabolism. ROS are reduced oxygen intermediates that include the superoxide radical (O2−) and the hydroxyl radical (OH•), as well as the non-radical species hydrogen peroxide (H2O2). These ROS are important in the normal functioning of cells, playing a role in signal transduction and the expression of transcription factors. However, when present in excess, ROS can cause damage to proteins, lipids and DNA by reacting with these biomolecules to modify or destroy their intended function. As an example, the occurrence of ROS have been linked to the aging process in humans, as well as several other diseases including Alzheimer's, rheumatoid arthritis, Parkinson's, and some cancers. Their potential for damage also makes reactive oxygen species useful in direct protection from invading pathogens, as a defense response to physical injury, and as a mechanism for stopping the spread of bacteria and viruses by inducing programmed cell death.
Oxidation response is stimulated by a disturbance in the balance between the production of reactive oxygen species and antioxidant responses, known as oxidative stress. Active species of oxygen naturally occur in aerobic cells and have both intracellular and extracellular sources. These species, if not controlled, damage all components of the cell, including proteins, lipids and DNA. Hence cells need to maintain a strong defense against the damage. The following table gives an idea of the antioxidant defense system in bacterial system.
Nickel superoxide dismutase (Ni-SOD) is a metalloenzyme that, like the other superoxide dismutases, protects cells from oxidative damage by catalyzing the disproportionation of the cytotoxic superoxide radical to hydrogen peroxide and molecular oxygen. Superoxide is a reactive oxygen species that is produced in large amounts during photosynthesis and aerobic cellular respiration. The equation for the disproportionation of superoxide is shown below:
Superoxide dismutase (SOD) mimetics are synthetic compounds that mimic the native superoxide dismutase enzyme. SOD mimetics effectively convert the superoxide anion, a reactive oxygen species, into hydrogen peroxide, which is further converted into water by catalase. Reactive oxygen species are natural byproducts of cellular respiration and cause oxidative stress and cell damage, which has been linked to causing cancers, neurodegeneration, age-related declines in health, and inflammatory diseases. SOD mimetics are a prime interest in therapeutic treatment of oxidative stress because of their smaller size, longer half-life, and similarity in function to the native enzyme.
The mitochondrial theory of ageing has two varieties: free radical and non-free radical. The first is one of the variants of the free radical theory of ageing. It was formulated by J. Miquel and colleagues in 1980 and was developed in the works of Linnane and coworkers (1989). The second was proposed by A. N. Lobachev in 1978.
Iron superoxide dismutase (FeSOD) is a metalloenzyme that belongs to the superoxide dismutases family of enzymes. Like other superoxide dismutases, it catalyses the dismutation of superoxides into diatomic oxygen and hydrogen peroxide. Found primarily in prokaryotes such as Escherichia coli and present in all strict anaerobes, examples of FeSOD have also been isolated from eukaryotes, such as Vigna unguiculata.
References
- ↑ C. Muth; Y. Glenz; M. Klaus; P. Radermacher; Guenter Speit; X. Leverve (2004). "Influence of an orally effective SOD on hyperbaric, oxygen related cell damage". Free Radical Research. 38 (9): 927–32. CiteSeerX 10.1.1.554.9017 . doi:10.1080/10715760412331273197. PMID 15621710. S2CID 22421934.
- ↑ S. Arent, D. DiFabio, J. Greenwood, J. Pellegrino, C. Williams (2005). “Nutritional Supplementation In Male College Soccer Players: Effects On Performance And Oxidative Stress Archived 2008-08-27 at the Wayback Machine ,” Human Performance Lab, Rutgers University, New Brunswick, NJ.