Natural Antioxidants In Human Health And Disease Pdf

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The overproduction of reactive oxygen species ROS has been implicated in the development of various chronic and degenerative diseases such as cancer, respiratory, neurodegenerative, and digestive diseases. Under physiological conditions, the concentrations of ROS are subtlety regulated by antioxidants, which can be either generated endogenously or externally supplemented. A combination of antioxidant-deficiency and malnutrition may render individuals more vulnerable to oxidative stress, thereby increasing the risk of cancer occurrence.

Natural Antioxidants: A Review of Studies on Human and Animal Coronavirus

Antioxidants are compounds that inhibit oxidation. Oxidation is a chemical reaction that can produce free radicals , thereby 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 stress , plants 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: industrial chemicals that are added to products to prevent oxidation, and naturally occurring compounds that are present in foods and tissue. The former, industrial antioxidants, have diverse uses: acting as preservatives in food and cosmetics, and being oxidation -inhibitors in rubber, synthetic plastics, and fuels.

Antioxidant dietary supplements have not 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.

Common pharmaceuticals and supplements with antioxidant properties may interfere with the efficacy of certain anticancer medication and radiation therapy. 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. However, germination, soaking, or microbial fermentation are all household strategies that reduce the phytate and polyphenol content of unrefined cereal.

Increases in Fe, Zn and Ca absorption have been reported in adults fed dephytinized cereals compared with cereals containing their native phytate. High doses of some antioxidants may have harmful long-term effects.

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 element that damages 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 to 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 blood plasma , while 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.

The 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 production 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 oxidase , and is an intermediate product of purine metabolism. Uric acid has the highest concentration of any blood antioxidant [58] 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.

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 enzyme systems, such as ascorbate in the glutathione-ascorbate cycle , glutathione peroxidases and glutaredoxins , as well as reacting directly with oxidants. Vitamin E is the collective name for a set of eight related tocopherols and tocotrienols , which are fat-soluble vitamins with antioxidant properties.

Antioxidants that are reducing agents can also act as pro-oxidants. For example, vitamin C has antioxidant activity when it reduces oxidizing substances such as hydrogen peroxide; [] however, it will also reduce metal 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, paradoxically, 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. The potential role of the pro-oxidant role of uric acid in e. Another example is the postulated role of homocysteine in atherosclerosis.

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 oxygen, using either an iron or manganese cofactor. Here, its cofactor is oxidised by one molecule of hydrogen peroxide and then regenerated by transferring the bound oxygen to a second molecule of substrate. Peroxiredoxins are peroxidases that catalyze the reduction of hydrogen peroxide, organic hydroperoxides , as well as peroxynitrite.

The thioredoxin system contains the k Da protein thioredoxin and its companion thioredoxin reductase. Plants, such as Arabidopsis thaliana , have a particularly great diversity of isoforms.

In its active state, thioredoxin acts as an efficient reducing agent, scavenging reactive oxygen species and maintaining other proteins in their reduced state. The glutathione system includes glutathione, glutathione reductase , glutathione peroxidases , and 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.

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 respiration , storing 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 smoking , salting or fermenting. Even less fatty foods such as fruits are sprayed with sulfurous antioxidants prior to air drying. Oxidation is often catalyzed by metals, 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. 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 by 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, 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. 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. For example, ubiquinol coenzyme Q is poorly absorbed from the gut and is made through the mevalonate pathway. As any glutathione in the gut is broken down to free cysteine, glycine and glutamic acid before being absorbed, even large oral intake has little effect on the concentration of glutathione in the body. Measurement of polyphenol and carotenoid 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 science analyses in vitro, the 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.

Alternative in vitro measurements of antioxidant content in foods — also based on the presence of polyphenols — include the Folin-Ciocalteu reagent , and the Trolox equivalent antioxidant capacity assay. As part of their adaptation from marine life, terrestrial plants began producing non-marine antioxidants such as ascorbic acid vitamin C , polyphenols 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 corrosion , the 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 fats , which is the cause of rancidity.

However, it was the identification of vitamins C and E as antioxidants that revolutionized the field and led to the realization of the importance of antioxidants in the biochemistry of living organisms. From Wikipedia, the free encyclopedia. Compound that inhibits the oxidation of other molecules. See also: Antioxidative stress. Further information: Oxidative stress. Further information: Pro-oxidant.

Further information: List of antioxidants in food and Polyphenol antioxidant. Ullmann's Encyclopedia of Industrial Chemistry. June Archived from the original on 25 August Retrieved 20 June Bibcode : PLoSO Current Aging Science. The Cochrane Database of Systematic Reviews.

Natural Antioxidants in Human Health and Disease

Free radicals and oxidants play a dual role as both toxic and beneficial compounds, since they can be either harmful or helpful to the body. They are produced either from normal cell metabolisms in situ or from external sources pollution, cigarette smoke, radiation, medication. When an overload of free radicals cannot gradually be destroyed, their accumulation in the body generates a phenomenon called oxidative stress. This process plays a major part in the development of chronic and degenerative illness such as cancer, autoimmune disorders, aging, cataract, rheumatoid arthritis, cardiovascular and neurodegenerative diseases. This mini-review deals with the taxonomy, the mechanisms of formation and catabolism of the free radicals, it examines their beneficial and deleterious effects on cellular activities, it highlights the potential role of the antioxidants in preventing and repairing damages caused by oxidative stress, and it discusses the antioxidant supplementation in health maintenance. Oxygen is an element indispensable for life. When cells use oxygen to generate energy, free radicals are created as a consequence of ATP adenosine triphosphate production by the mitochondria.


In addition to vitamins C, A and E the most important naturally occurring plant substances showing antioxidant activity are carotenoids, flavonoids and other simple.


Free radicals, oxidative stress, and antioxidants in human health and disease

Antioxidants are compounds that inhibit oxidation. Oxidation is a chemical reaction that can produce free radicals , thereby 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 stress , plants and animals maintain complex systems of overlapping antioxidants, such as glutathione and enzymes e.

Role of ROS and Nutritional Antioxidants in Human Diseases

Free radicals and other reactive oxygen species ROS are constantly formed in the human body. Free-radical mechanisms have been implicated in the pathology of several human diseases, including cancer, atherosclerosis, malaria, and rheumatoid arthritis and neurodegenerative diseases. Catalases in peroxisomes convert H 2 O 2 into water and O 2 and help to dispose of H 2 O 2 generated by the action of the oxidase enzymes that are located in these organelles.

Everything You Should Know About Oxidative Stress

Often used as a marketing buzzword, learn about the role of antioxidants beyond the hype, and some of the research on health and disease prevention. Jump to: — What are antioxidants?

We include products we think are useful for our readers. If you buy through links on this page, we may earn a small commission. Antioxidants are substances that can prevent or slow damage to cells caused by free radicals, unstable molecules that the body produces as a reaction to environmental and other pressures. The sources of antioxidants can be natural or artificial. Certain plant-based foods are thought to be rich in antioxidants.

Antioxidant

Free radicals and other reactive oxygen species ROS are constantly formed in the human body. Free-radical mechanisms have been implicated in the pathology of several human diseases, including cancer, atherosclerosis, malaria, and rheumatoid arthritis and neurodegenerative diseases. Catalases in peroxisomes convert H 2 O 2 into water and O 2 and help to dispose of H 2 O 2 generated by the action of the oxidase enzymes that are located in these organelles.

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