Read this article you will learn about Antioxidant. After reading this article you will learn about: 1. History of Antioxidant 2. Measurement of Antioxidants 3. Antioxidant Capacity 4. Classification.
History of Antioxidant:
The term antioxidant originally was used to refer specifically to a chemical that prevented the consumption of oxygen. In the late 19th and early 20th century, extensive study was devoted to the uses 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.
Antioxidant activity could be measured simply by placing the fat in a closed container with oxygen and measuring the rate of oxygen consumption. However, it was the identification of vitamins A, 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.
Research into how vitamin E prevents the process of lipid peroxidation led to the identification of antioxidants as reducing agents that prevent oxidative reactions, often by scavenging reactive oxygen species before they can damage cells.
Measurement of Antioxidants:
Measurement of antioxidants is not a clear-cut process, as this is a diverse group of compounds with different re-activities to different reactive oxygen species.
In food science, the oxygen radical absorbance capacity (ORAC) has become the current industry standard for assessing antioxidant strength of whole foods, juices and food additives. Other measurement tests include the Folin-Ciocalteu reagent, and the Trolox equivalent antioxidant capacity assay.
Antioxidants are found in varying amounts in foods such as vegetables, fruits, grain cereals, legumes and nuts. Some antioxidants such as lycopene and ascorbic acid can be destroyed by long-term storage or prolonged cooking. The polyphenols antioxidants in foods such as whole-wheat cereals and tea are more stable.
In general, processed foods contain fewer antioxidants than fresh and uncooked foods, since the preparation processes may expose the food to oxygen. The CAP-e assay measures antioxidants that are available to enter and protect live cells.
Total antioxidant capacity was based on ORAC assays. The fruits, nuts, rice bran and vegetables were freeze-dried before analysis. Brunette potato, broccoli, carrot and tomato, which were in their cooked form used for analysis. Total antioxidant capacity is summarized in Table 10.4.
The body has several mechanisms to counteract oxidative stress by producing antioxidants, either naturally generated in situ (endogenous antioxidants), or externally supplied through foods (exogenous antioxidants).
The roles of antioxidants are to neutralize the excess of free radicals, to protect the cells against their toxic effects and to contribute to disease prevention. Endogenous compounds in cells can be classified as enzymatic and non-enzymatic antioxidants.
The major enzymatic antioxidants directly involved in the neutralization of ROS and RNS are superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione reductase (GRx).
Superoxide dismutase (SOD) scavenges both extracellular and intracellular superoxide anion and prevents lipid peroxidation of the plasma membrane. It is first line enzyme of defense against free radicals, catalyzes the dis-mutation of superoxide anion radical (O2) into hydrogen peroxide (H2O2) by reduction.
The oxidant formed (H2O2) is transformed into water and oxygen (O2) by catalase or glutathione peroxidase. SOD also prevents premature hyper activation and capacitation induced by superoxide radicals before ejaculation.
Glutathione Peroxidase/Reductase System:
This system forms an excellent protection against lipid peroxidation of plasma membrane of spermatozoa. It scavenges lipid peroxides thereby arresting the progressive chain reaction of lipid peroxidation. It also scavenges hydrogen peroxide (H2O2), which is responsible for the initiation of lipid peroxidation. Glutathione reductase (GRx) stimulates the reduction of glutathione disulfide to reduced glutathione.
Glutathione reductase, a flavoprotein enzyme, regenerates reduced glutathione (GSH) from oxidized glutathione (GSSG), with NADPH as a source of reducing power. Besides hydrogen peroxide, GPx also reduces lipid or non-lipid hydro peroxides while oxidizing glutathione (GSH). This ensures a steady supply of the reductive substrate (NADPH) to glutathione peroxidase.
Catalase detoxifies both intracellular and extracellular H2O2 to water and oxygen (Baker et al., 1996). In addition, catalase activates NO-induced sperm capacitation, which is a complex mechanism involving H2O2.
The non-enzymatic antioxidants are also divided into metabolic and nutrient antioxidants. Metabolic antioxidants belonging to endogenous antioxidants, are produced by metabolism in the body, such as lipoid acid, glutathione, L-arginine, coenzyme Q10, melatonin, uric acid, bilirubin, metal- chelating proteins, transferrin, etc.
While nutrient antioxidants belonging to exogenous antioxidants, are compounds which cannot be produced in the body and must be provided through foods or supplements, such as vitamin E, vitamin C, carotenoids, trace metals (selenium, manganese, zinc), flavonoids, omega-3 and omega-6 fatty acids, etc. copper and iron.
Antioxidants from our diet play an important role in helping endogenous antioxidants for the neutralization of oxidative stress. The nutrient antioxidant deficiency is one of the causes of numerous chronic and degenerative pathologies. Each nutrient is unique in terms of its structure and antioxidant function which are discusses in below:
Vitamin E is a chiral compound with eight stereoisomers: α, β, y, δ-tocopherol and α, β, y, δ-to-cotrienol, which are fat-soluble vitamins with antioxidant properties. Among these stereoisomers, only α-tocopherol is the most bioactive and easily absorbing and metabolizing this form in the human body.
Studies in both animals and humans indicate that natural dextrorotary d-α-tocopherol is nearly twice as effective as synthetic racemic dl-α-tocopherol.
It has also been claimed that the α-tocophergl form is the most important lipid soluble antioxidant, and that it protects membranes from oxidation by reacting with lipid radicals produced in the lipid peroxidation chain reaction.
This reaction produces oxidized α-tocopheroxyl radicals that can be recycled back to the active reduced form through reduction by other antioxidants, such as ascorbate, retinol or ubiquinol. Vitamin E has also been claimed for the prevention against colon, prostate and breast cancers, cardiovascular diseases, ischemia, cataract, arthritis and certain neurological disorders.
In vitro studies show that vitamin E is a major chain-breaking antioxidant in the sperm membranes and it appears to have a dose dependent protective effect.
However, the roles and importance of the various forms of vitamin E are presently unclear and it has even been suggested that the most important function of α- tocopherol is as a signalling molecule, with this molecule having no significant role in antioxidant metabolism.
The functions of the other forms of vitamin E are even less well-understood, although α-tocopherol is a nucleophile that may react with electrophilic mutagens and tocotrienols may be important in protecting neurons from damage.
Vitamin C chemically known as ascorbic acid and is a water-soluble vitamin. It is a monosaccharide antioxidant found in both plants and animals. Animals except humans are able to produce this compound in their bodies and. do not require it in their diets.
In cells, it is maintained in its reduced form by reaction with glutathione, which can be catalysed by protein disulfide isomerase and glutaredoxins.
Ascorbic acid is a reducing agent and it reduce the reactive oxygen species like hydrogen peroxide. In addition to its direct antioxidant effects, ascorbic acid is also a substrate for the antioxidant enzyme ascorbate peroxidase, a function that is particularly important in stress resistance in plants.
Vitamin C is essential for collagen, carnitine and neurotransmitters biosynthesis and its beneficial effects are antioxidant, anti-atherogenic, anti- carcinogenic, immune modulator. A dose dependent effect of vitamin C on sperm motility has been demonstrated that at a dose of 1000 microgram/L, vitamin C positively influenced the motility of the spermatozoa.
However, above that level, vitamin C reduced the motility of the spermatozoa. On the other hand, doses fewer than 200 mg of vitamin C did not provide any benefit.
Dawson et al. (1992) reported that smokers receiving 1000 mg/day vitamin C showed improvement in sperm quality. Natural sources of vitamin Care acid fruits, green vegetables, tomatoes and it is a labile molecule, therefore it may be lost from during cooking.
Carotenoid and retinyl ester are two major pro-vitamins because they can be converted to active vitamin A. There are more than 600 carotenoid in nature of which six can be measured in blood. Carotenoid are fat soluble pigments which are found in fruits and vegetables like carrots, green plants, squash, spinach etc.
Carotenoids cannot be synthesized in animals or humans and therefore needs to be part of the dietary intake. α and β-carotene are the major carotenoids which are mainly composed of carbon and hydrogen atoms. In humans and animals, carotenoids play an important role in protection against photo oxidative processes by acting as oxygen and peroxyl radical scavengers.
Their synergistic action with other antioxidants makes them an even more potent compound.
Several studies have shown that less plant derived carotenoids is absorbed, cleaved, reduced and finally available as retinyl esters. Therefore, bioequivalence is less than predicted and factors such as food preparation, matrix properties, co-ingestion of fat, diseases of the gastrointestinal tract and malnutrition may be contributors.
Carotenoids have a wide range of protective properties against disease and aging and can act as a modulator for cellular processes and function. Some other studies have shown that carotenoids can protect against cancer and cardiovascular diseases.
Furthermore, dietary carotenoids can protect the skin against sun exposure, whilst antioxidant and cellular signalling effects have been shown in a number of studies.
However, beta-carotene supplement in doses of 20mg daily for 5-8 years has been associated with an increased risk of lung and prostate cancer and increased cardiovascular mortality in cigarette smokers.
Beta-carotene is a fat-soluble member of the carotenoids, which are considered pro-vitamins because they can be converted to active vitamin A. Beta-carotene is converted to retinol, which is essential for vision. It is a strong antioxidant and is the best quencher of singlet oxygen.
However, beta-carotene supplement in doses of 20 mg daily for 5-8 years has been associated with an increased risk of lung and prostate cancer and increased total mortality in cigarette smokers.
Beta-carotene 20-30 mg daily in smokers may also increase cardiovascular mortality by 12% to 26% . These adverse effects do not appear to occur in people who eat foods high in beta-carotene content. Beta-carotene is present in many fruits, grains, oil and vegetables (carrots, green plants, squash, spinach).
Curcumin [1, 7-bis (4-hydroxy-3-methoxy phenyl)- 1-6- hepatadine-3-5-dione] a member of curcuminoid family represents one of the yellow pigments isolated from turmeric. Turmeric is the dried rhizome of plant Curcuma longa and apart from its culinary appeal and common use as the spice, it is well known for its medicinal properties in Egyptian and Indian culture for more than 6000 year ago.
Its immunomodulatory properties including anti-oxidant, anti-inflammatory and anti-tumor properties are well-documented. The curcumin reduces nitric oxide (NO) and exerts beneficial effects in experimental colitis.
Ukil et al. (2003) repotted that the yellow pigment treats inflammatory bowl diseases due to the oxidative and nitrosative stresses. Recently the immuno-nutritional ability of curcumin demonstrating its active role in treatment of the allergic response has been highlighted in a review.
Lycopene, a member of the carotenoid family, is a fat-soluble pigment responsible for the red color of certain fruits and vegetables. Its pigment protects the plant from damage by oxygen and light. Lycopene possesses antioxidant and anti-proliferative properties in animal.
Lycopene has been found to be very protective, particularly for prostate cancer. Several prospective cohort studies have found associations between high intake of lycopene and reduced incidence of prostate cancer, though not all studies have produced consistent results.
The major dietary source of lycopene is tomatoes, with the lycopene in cooked tomatoes, tomato juice and tomato sauce included, being more bioavailable than that in raw tomatoes. The dietary antioxidant lycopene reduces oxidative stress and the levels of bone turnover markers in postmenopausal women, and may be beneficial in reducing the risk of osteoporosis.
Tea is one of the most consumed beverages of the world after water. Tea beverage is an infusion of the dried leaves of Camellia sinesis, a member of Theaceae family. Freshly harvested tea leaf is processed differently in different parts of the world to give oolong tea (2%), green tea (20%) or black tea (78%).
Green tea is prepared from the fresh tea leaf and widely consumed in Japan and China.
Western cultures favour black tea, which is prepared through the oxidation, curing process of maceration and exposure to atmospheric oxygen. Tea is linked to beneficial effects on human health with the polyphenols as the responsible constituents.
Fresh tea leaf is rich in water soluble polyphenols, particularly flavanols, flavanol gallate and flavanol glycosides.
The major tea catechins: α-epigallocatechin-3-gallate (EGCG), α-epigallocate- chin (EGC), epicatechin-3-gallate (ECG), α-epifltechin (EC), α-epicatechin-3-gallate (ECG), α- epicatechin (EC), α-gallocatechin and β-catechin; constitutes 30% to 42% of the green tea solids by weight.
These compounds are all potent antioxidant in vitro and, when consumed, may act as the free radical scavengers, which remove endogenously generated superoxide, peroxyl and hydroxyl radicals. Many in vitro and in vivo effects of tea polyphenols have been reported including antioxidant, anticar-cinogenic and hypolipidemic properties.
The powerful antioxidant properties of the tea are generally attributed to its flavonoids components; theaflavins, bisflavanols and theaflavic acids.
The antioxidant property of tea is coupled with several mechanisms e.g. depolarization of electrons, formation of intermolecular hydrogen bonds, rearrangement of the molecular structure.
The bioactive flavanol compounds of tea may also prevent oxidative reactions by chelating free copper and iron, which may catalyse the formation of reactive oxygen species in vitro.
Garlic (Allium sativum) is used universally as a traditional medicine, and a functional food to enhance physical and mental health. It is used for flavouring in cooking and is unique because of its high sulfur content. In addition to sulfur, garlic also contains arginine, oligosaccharides, flavonoids, and selenium, all of which may be beneficial to health.
The medicinal uses of garlic has a long history. Recent studies have validated many of the medicinal properties attributed to garlic and its potential to lower the risk of disease. Cancer-preventive actions of garlic, garlic extracts and its components have been demonstrated in animals.
Epidemiologic studies show an inverse correlation between garlic consumption and reduced risk of gastric and colon cancer. Garlic has been shown to have antithrombotic activity, lower blood lipids and have a cardio protective effect.
The mechanisms of garlic have been endorsed to its potent antioxidant action, its ability to stimulate immunological responsiveness and its modulation of prostanoid synthesis.
Aged garlic extract (AGE) is an odorless product resulting from prolonged extraction of fresh garlic at room temperature; it is highly bioavailable and has biological activity in vitro in both animals and humans.
AGE contains water-soluble allyl amino acid derivatives, which account for most of its organosulfur content, stable lipid-soluble allyl sulfides, flavonoids, saponins and essential macro-and micro- nutrients. The lipid-soluble volatile organosulfur compound allicin, which is produced enzymatically when garlic is cut or chopped, is absent in AGE.
Allicin is an unstable and transient compound with oxidant activity; it is virtually undetectable in blood circulation after garlic ingestion because it decomposes to form other organosulfur compounds.
The major unique organosulfur compounds in AGE are water-soluble 5-allyl-cysteine (SAC) and 5-allylmercaptocysteine (SAMC), which have potent antioxidant activity.
The content of SAC and SAMC in AGE is high because they are produced during the process of aging, thus providing AGE with higher antioxidant activity than fresh garlic and other commercial garlic supplements.
The anti-oxidative actions of AGE and its components are determined by their ability to scavenge ROS and inhibit the formation of lipid peroxides.
These effects are determined by measuring the decrease in ROS-induced chemiluminescence, inhibition of thiobarbituric acid reactive substances (lipid peroxides) (TBARS assay), and in vitro inhibition of the release of pentane, a product of oxidized lipids, in the breath of an animal exposed to oxidative stress.
Oxidation of lipids, notably oxidative modification of LDL, is implicated in the development of cardiovascular and cerebrovascular disease. Lipid oxidation products, including peroxides and toxic aldehydes such as malondialdehyde, can damage proteins and DNA and have been implicated in carcinogenesis.
AGE inhibits lipid oxidation and oxidative modification of LDL . Other protective actions of AGE include inhibition of platelet aggregation and suppression of prostanoid synthesis with subsequent anti-inflammatory, anti-athrogenic and antithrombotic effects.
The protection of endothelial cell integrity by inhibition of lipid peroxidation-induced injury and reduction in serum cholesterol and other lipids by AGE further add to its potential in helping prevent heart disease and stroke.
Cytosolic nuclear factor-B (NF-B) is a transcription factor that is regulated by the redox state of the cell and can be activated by mitogens, bacteria and viruses and by ROS-producing agents such as UV, ionizing radiation, hydrogen peroxide and tumor necrosis factor (TNF).
The major clinical significance of NF-B activation is its involvement in human immunodeficiency virus (HIV) gene expression. AGE and SAC inhibit TNF- and hydrogen peroxide-induced activation of NF-B in human T-cells, indicating their potent antioxidant function and suggesting a potential role for AGE in modulating HIV replication.
Oxidant-induced DNA damage and mutagenesis are determinants in the multistage process of cancer in animals and in vitro. Allixin, an active component in AGE, which has been shown to inhibits aflatoxin-induced DNA damage and mutagenesis in Salmonella typhimurium, in part by inhibiting cytochrome P450 activity.
Several group of workers reported that AGE inhibits both early and late stages of carcinogenesis of tumor growth in many tissues like colon, mammary glands, skin, stomach and esophagus.
Supplementation with AGE may have an important protective role against liver toxicity caused by a variety of medicinal and environmental substances. Tadi et al. (1991) reported that AGE protects against liver toxicity by benzo (a) pyrene and aflatoxin B1, two potent free radical-producing environmental carcinogens.
Studies in mice showed that SAC and SAMC were potent inhibitors of liver toxicity induced by the industrial oxidant carbon tetrachloride and by the commonly used analgesic agent, acetaminophen.