Antioxidants are compounds that inhibit oxidation. Oxidation is a chemical reaction that can produce free radicalsthereby leading to chain reactions that may damage the cells of organisms.
Antioxidants such as thiols or ascorbic acid vitamin C terminate these chain reactions. To balance the oxidative stateplants and animals maintain complex systems of overlapping antioxidants, such as glutathione and enzymes e. The term "antioxidant" is mostly used for two entirely different groups of substances: The former, industrial antioxidants, anti-oxidants and cancer therapy, have diverse uses: Importantly, antioxidant dietary supplements have not yet been shown to improve health in humans, or to be effective at preventing disease.
Although certain levels of antioxidant vitamins in the diet are required for good health, there is still considerable debate on whether antioxidant-rich foods or supplements have anti-disease activity. Moreover, if they are actually beneficial, it is unknown which antioxidants are health-promoting in the diet and in what amounts beyond typical dietary intake, anti-oxidants and cancer therapy. Polyphenolswhich often have antioxidant diabetes and popcorn in vitroare not necessarily antioxidants in vivo due to extensive metabolism following digestion.
Many polyphenols may have non-antioxidant roles in minute concentrations that affect cell-to-cell signalingreceptor sensitivity, inflammatory enzyme activity or gene regulation. Tirilazad is an antioxidant steroid derivative that inhibits the lipid peroxidation that is believed to play a key role in neuronal death in stroke and head injury. It demonstrated activity in animal models of stroke,  but human trials demonstrated no effect on mortality or other outcomes in subarachnoid haemorrhage  and worsened results in ischemic stroke.
Similarly, the designed antioxidant NXY exhibited efficacy in animal models, anti-oxidants and cancer therapy, but failed to improve stroke outcomes in a clinical trial.
Common pharmaceuticals and supplements with antioxidant properties may interfere with the efficacy of certain anticancer medication and radiation. A systematic review examined antioxidant medications, such as allopurinol and acetylcysteineas add-on treatment for schizophrenia. Relatively strong reducing acids can have antinutrient effects by binding to dietary minerals such as iron and zinc in the gastrointestinal tract and preventing them from being absorbed. Nonpolar antioxidants such as eugenol —a major component of oil of cloves —have toxicity limits that anti-oxidants and cancer therapy be exceeded with the misuse of undiluted essential oils.
The beta-carotene and Retinol Efficacy Trial CARET study of lung cancer patients found that smokers given supplements containing beta-carotene and vitamin A had increased rates of lung cancer.
While anti-oxidants and cancer therapy supplementation is widely used in attempts to prevent the development of cancer, antioxidants may interfere with cancer treatments,  since the environment of cancer cells causes high levels of oxidative stress, making these cells more susceptible to the further oxidative stress induced by treatments. As a result, by reducing the redox stress in cancer cells, antioxidant supplements and pharmaceuticals could decrease the effectiveness of radiotherapy and chemotherapy.
A paradox in metabolism is that, while the vast majority of complex life on Earth requires oxygen for its existence, oxygen is a highly reactive molecule that anti-oxidants and cancer therapy living organisms by producing reactive oxygen species. Thus, the function of antioxidant systems is not to remove oxidants entirely, but instead to keep them at an optimum level. This species is produced from hydrogen peroxide in metal-catalyzed redox reactions such as the Fenton reaction.
The use of oxygen as part of the process for generating metabolic energy produces reactive oxygen species. This unstable intermediate can lead to electron "leakage", when electrons jump directly attention deficit disorder and citalopram oxygen and form the superoxide anion, instead of moving through the normal series of well-controlled reactions of the electron transport chain.
Antioxidants are classified into two broad divisions, depending on whether they are soluble in water hydrophilic or in lipids lipophilic. In general, water-soluble antioxidants react with oxidants in the cell cytosol and the anti-oxidants and cancer therapy plasmawhile lipid-soluble antioxidants protect cell membranes from lipid peroxidation. Some antioxidants are only found in a few organisms and these compounds can be important in pathogens and can be virulence factors, anti-oxidants and cancer therapy.
Anti-oxidants and cancer therapy relative importance and interactions between these different antioxidants is a very complex question, with the various antioxidant compounds and antioxidant enzyme systems having synergistic and interdependent effects on one another. Some compounds contribute to antioxidant defense by chelating transition metals and preventing them from catalyzing the arthritis and computer mouse of free radicals in the cell.
Particularly important is the ability to sequester iron, which is the function of iron-binding proteins such as transferrin and ferritin. Uric acid is by far the highest concentration antioxidant in human blood. Uric acid UA is an antioxidant oxypurine produced from xanthine by the enzyme xanthine oxidaseand is an intermediate product of purine metabolism. Anti-oxidants and cancer therapy acid has the highest concentration of any blood antioxidant  and provides over half of the total antioxidant capacity of human serum.
Ascorbic acid or " vitamin C " is a monosaccharide oxidation-reduction redox catalyst found in both animals and plants.
As one of the enzymes needed to make ascorbic acid has been lost by mutation during primate evolutionhumans must obtain it from the diet; it anti-oxidants and cancer therapy therefore a vitamin. In other cells, it is maintained in its reduced form by reaction with glutathione, which can be catalysed by protein disulfide isomerase and glutaredoxins. Glutathione is a cysteine -containing peptide found in most forms of aerobic life.
In cells, glutathione is maintained in the reduced form by the enzyme glutathione reductase and in turn reduces other metabolites and diabetes and cat systems, such as ascorbate in the glutathione-ascorbate cycleglutathione peroxidases and glutaredoxinsas well as reacting directly with oxidants.
Vitamin E is the collective name for a set of eight related tocopherols and tocotrienolswhich are fat-soluble vitamins with antioxidant properties.
Antioxidants that are reducing agents anti-oxidants and cancer therapy also act as pro-oxidants. For example, vitamin C has antioxidant activity when it reduces oxidizing substances such as hydrogen peroxide,  equate cold and allergy liquid, it will also reduce anti-oxidants and cancer therapy ions that generate free radicals through the Fenton reaction.
The relative importance of the antioxidant and pro-oxidant activities of antioxidants is an area of current research, but vitamin C, which exerts its effects as a vitamin by oxidizing polypeptides, appears to have a mostly antioxidant action in the human body. That is, anti-oxidants and cancer therapy, agents which are normally considered antioxidants can act as conditional pro-oxidants and actually increase oxidative stress.
Besides ascorbate, medically important conditional pro-oxidants include uric acid and sulfhydryl amino acids such as homocysteine. Typically, this involves some transition-series metal such as copper or iron as catalyst, anti-oxidants and cancer therapy.
The potential role of the pro-oxidant role of uric acid anti-oxidants and cancer therapy e. Another example is the postulated role of homocysteine in atherosclerosis, anti-oxidants and cancer therapy. As with the chemical antioxidants, cells are protected against oxidative stress by an interacting network of antioxidant enzymes. This detoxification pathway is the result of multiple enzymes, with superoxide dismutases catalysing the first step and then catalases and various peroxidases removing hydrogen peroxide.
As with antioxidant metabolites, the contributions of these enzymes to antioxidant defenses can be hard to separate from one another, but the generation of transgenic mice lacking just one antioxidant enzyme can be informative.
Superoxide dismutases SODs are a class of closely related enzymes that catalyze the breakdown of the superoxide anion into oxygen and hydrogen peroxide. Catalases are enzymes that catalyse the conversion of hydrogen peroxide to water and ativan and marijuana use, using either an iron or manganese cofactor. Here, its cofactor is oxidised by one molecule of hydrogen peroxide and anti-oxidants and cancer therapy regenerated by transferring the bound oxygen to a second molecule of substrate.
Peroxiredoxins are peroxidases that catalyze the reduction of hydrogen peroxide, anti-oxidants and cancer therapy, organic hydroperoxides anti-oxidants and cancer therapy, as well as peroxynitrite. The thioredoxin system contains the k Da protein thioredoxin and its companion thioredoxin reductase.
Plants, such as Arabidopsis thalianahave a particularly great diversity of isoforms. In its active state, thioredoxin acts as an efficient reducing agent, anti-oxidants and cancer therapy, scavenging reactive candy and high blood pressure species and maintaining other proteins in their reduced state.
The glutathione system includes glutathione, glutathione reductaseglutathione peroxidasesand glutathione S -transferases. There are at least four different glutathione peroxidase isozymes in animals. Surprisingly, glutathione peroxidase 1 is dispensable, as mice lacking this enzyme have normal lifespans,  but they are hypersensitive to induced oxidative stress.
Here, low density lipoprotein LDL oxidation appears to trigger the process of atherogenesiswhich results in atherosclerosisand finally cardiovascular disease.
Oxidative damage in DNA can cause cancer. Several antioxidant enzymes such as superoxide dismutase, catalase, glutathione peroxidase, dental plan and self employed reductase, glutathione S-transferase etc. A low calorie diet extends median and maximum lifespan in many animals.
This effect may involve a reduction in oxidative stress. Antioxidants are used as food additives to help guard against food deterioration. Exposure to oxygen and sunlight are the two main factors in the oxidation of food, so food is preserved by keeping in the dark and sealing it in containers or even coating it in wax, as with cucumbers.
However, as oxygen is also important for plant respirationstoring plant materials in anaerobic conditions produces unpleasant flavors and unappealing colors. Antioxidants are an especially important class of preservatives as, unlike bacterial or fungal spoilage, oxidation reactions still occur relatively rapidly in frozen or refrigerated food. The most common molecules attacked by oxidation are unsaturated fats; oxidation causes them to turn rancid. Thus, these foods are rarely preserved by drying; instead, they are preserved by smokingsalting or fermenting.
Even less fatty foods such as fruits are sprayed with sulfurous antioxidants prior to air drying. Oxidation is often catalyzed by metals, anti-oxidants and cancer therapy, which is why fats such as butter should never be wrapped in aluminium foil or kept in metal containers. Some fatty foods such as olive oil are partially protected from oxidation by their natural content of antioxidants, but remain sensitive to photooxidation.
Antioxidants are frequently added to industrial products, anti-oxidants and cancer therapy. A common use is as stabilizers in fuels and lubricants to prevent oxidation, and in gasolines to prevent the polymerization that leads to the formation of engine-fouling residues. Antioxidant polymer stabilizers are widely used to prevent the degradation of polymers such as rubbers, plastics and adhesives that causes a loss of strength and flexibility in these materials.
They can be protected birth control pill and stopping antiozonants. Solid polymer products start to crack on exposed surfaces as the material degrades and the chains break. The mode of cracking varies between oxygen and ozone attack, anti-oxidants and cancer therapy, the former causing a "crazy paving" effect, while ozone attack produces deeper cracks aligned at right angles to the tensile strain in the product.
Oxidation and UV degradation are also frequently linked, mainly because UV radiation creates free radicals by bond breakage. The free radicals then react with oxygen to produce peroxy radicals which cause yet further damage, often in a chain reaction.
Other polymers susceptible to oxidation include polypropylene and polyethylene. The former is more sensitive owing to the presence of secondary carbon atoms present in every repeat unit. Attack occurs at this point because the free radical formed is more stable than one formed on a primary carbon atom. Oxidation of polyethylene tends to occur at weak links in the chain, such as branch points in low-density polyethylene.
Antioxidant vitamins are found in vegetables, fruits, eggs, legumes and nuts, anti-oxidants and cancer therapy. Vitamins A, C, and E can be destroyed by long-term storage or prolonged cooking. Other antioxidants are not obtained from the diet, but instead are made in the body, anti-oxidants and cancer therapy.
For example, ubiquinol coenzyme Q is poorly absorbed from anti-oxidants and cancer therapy gut and is made through the mevalonate pathway. As any glutathione in the gut is broken down to free cysteine, anti-oxidants and cancer therapy, glycine and glutamic acid before being absorbed, even large oral intake has little effect on the concentration of glutathione in the body. Measurement of antioxidant content in food is not a straightforward process, as antioxidants collectively are a diverse group of compounds with different reactivities to various reactive oxygen species.
In food sciencethe oxygen radical absorbance capacity ORAC was once an industry standard for estimating antioxidant strength of whole foods, juices and food additives, mainly from the presence of polyphenols, anti-oxidants and cancer therapy.
Alternative in vitro measurements of antioxidant content in foods — also based on the presence of polyphenols — include the Folin-Ciocalteu reagentand the Anti-oxidants and cancer therapy equivalent antioxidant capacity assay. As part of their adaptation from marine life, terrestrial plants began producing non-marine antioxidants such as ascorbic acid vitamin Cpolyphenols and tocopherols. In the late 19th and early 20th centuries, extensive study concentrated on the use of antioxidants in important industrial processes, such as the prevention of metal corrosionthe vulcanization of rubber, and the polymerization of fuels in the fouling of internal combustion engines.
Early research on the role of antioxidants in biology focused on their use in preventing the oxidation of unsaturated fatswhich is the cause of rancidity.