Antioxidants

Antioxidant is substance that prevents or slows the breakdown of another substance by oxygen. Antioxidants are chemical substances that donate an electron to the free radical and convert it to a harmless molecule. Antioxidants are substances used by the body to protect itself from damage caused by oxidation. Oxidation is a process that causes damage in our tissues through the work of free radicals. An antioxidant is a chemical that prevents the oxidation of other chemicals. In the body, nutrient antioxidants such as beta-carotene (a vitamin A precursor), vitamin C, vitamin E, and selenium have been found to act as antioxidants.

Free radical production is actually a normal part of life, part of the equation of simply breathing in oxygen. The process of oxidation in the human body damages cell membranes and other structures including cellular proteins, lipids and DNA. When oxygen is metabolised, it creates 'free radicals' which steal electrons from other molecules, causing damage. The body can cope with some free radicals and needs them to function effectively. However, an overload of free radicals has been linked to certain diseases, including heart disease, liver disease and some cancers. Oxidation can be accelerated by stress, cigarette smoking, alcohol, sunlight, pollution and other factors. Antioxidants counteract these cellular by-products and bind with them before they can cause damage.

Free radicals

Harmful free radicals are toxic molecules of oxygen that damage every area of our bodies. A free radical is an unstable incomplete molecule because it is missing an electron which exists in pair in stable molecules. Free radicals steal an electron from another molecule, thereby create another free radical. This new free radical then duplicates the process, resulting in a chain reaction of events, which can ultimately damage the body. Free radicals are natural by-products of ongoing biochemical reactions in the body, including ordinary metabolic processes and immune system responses.

The common free radicals are oxygen reactive species (ROS), namely, superoxide radical, hydroxyl radical, and peroxyl radical which can be internally produced by cellular metabolism, inflammaiton by immune cells and externally by radiation, pharmaceuticals, hydrogen peroxide, toxic chemicals, smoke, alcohol, oxidized polyunsaturated fats and cooked food. Free radicals can cause damage to parts of cells such as proteins, DNA, and cell membranes by stealing their electrons through a process called oxidation. Free radicals may cause heart damage, cancer, cataracts, and a weak immune system.

The health benefits of antioxidants

Antioxidants work by neutralizing highly reactive, destructive compounds called free radicals. In biological systems, the normal processes of oxidation produce highly reactive free radicals. Antioxidants work by binding to the free radicals, they transforms them into non-damaging compounds or repairscellular damage. Antioxidants are able to easily donate electrons to molecules in need of an electron, such as free radicals, before they steal one from someplace else, thus stabilize and prevent a damaging chain reaction.

Antioxidants help neutralize the production of free radicals which are chemical complexes that cause harm to our cells and play a major role in the disease process. Antioxidants serve as a source of electrons that can be provided to free radicals without damaging the cell components. Antioxidants prevent unstable oxygen molecules (made unstable by loss of one electron) from interacting with other molecules (taking one of their electrons) and consequently causing them to become unstable, a process that starts the free-radical chain reaction.

Antioxidants help alleviate the symptoms and side effects of many of these diseases. According to the free radical theory, radicals damage cells in an organism, causing aging. Antioxidants break the free radical chain reaction by sacrificing electrons, and then humbly existing without stealing more. The body naturally circulates many nutrients for their antioxidant properties, and creates antioxidant enzymes just for the purpose of controlling free radicals and their chain reactions. Antioxidants are thought to thwart heart disease by preventing oxidation. Antioxidants combat chronic inflammation. Vitamin E suppresses platelet stickiness, acting as an anticoagulant to discourage the formation of clots that lead to heart attacks.

Vitamin C decreases a blood factor needed to build clots. Antioxidants neutralize free radicals as the natural by-product of normal cell processes.

Commonly used antioxidant supplements

Antioxidants are found in the nutrient antioxidants, vitamins A, C and E, and the minerals copper, zinc and selenium. Other dietary food compounds, such as the phytochemicals in plants and zoochemicals from animal products, are believed to have greater antioxidant effects than either vitamins or minerals. These are called the non-nutrient antioxidants and include phytochemicals, such as lycopenes in tomatoes, and anthocyanins found in cranberries.

Some antioxidants are made in our cells and include enzymes and the small molecules glutathione, uric acid, coenzyme Q10 and lipoic acid. Antioxidant compounds must be constantly replenished since they are "used up" (converted) in the process of neutralizing free radicals. Repair enzymes that can regenerate some antioxidants are superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), catalase and the other metalloenzymes.

Vitamin C (ascorbic acid)

Vitamin C neutralizes potentially harmful reactions in the watery parts of the body, such as the blood and the fluid inside and surrounding cells. Vitamin C may help decrease total and LDL cholesterol and triglycerides, as well as increase HDL levels. The antioxidant properties of vitamin C are thought to protect smokers, as well as people exposed to secondhand smoke, from the harmful effects of free radicals.

The body does not produce vitamin C. Foods containing the highest sources of vitamin C include green peppers, citrus fruits and juices, strawberries, tomatoes, broccoli, turnip greens and other leafy greens, sweet and white potatoes, and cantaloupe.

Vitamin E

Vitamin E is the most effective, fat-soluble antioxidant known to occur in the human body. Vitamin E is an antioxidant that prevents free radical damage in biological membranes. Free radicals can cause cell damage that may contribute to the development of cardiovascular disease and cancer. Vitamin E helps protect against heart disease by limiting the oxidation of LDL-cholesterol. Vitamin E helps prevent oxidation of lipoproteins, particularly in smokers, and reduces the stickiness of platelets in the bloodstream.

Vitamin E as an antioxidant helps to stabilize cell membranes and protect the tissues of the skin, eyes, liver, breast, and testes, which are more sensitive to oxidation. Vitamin E is found in many common foods, including vegetable oils (such as soybean, corn, cottonseed and safflower) and products made from these oils (such as margarine), wheat germ, nuts and green leafy vegetables, although the researchers evaluated only the pill form of the vitamin.

Beta-carotene

Consuming foods rich in beta-carotene appears to protect the body from damaging molecules called free radicals. Beta-carotene's antioxidant actions make it valuable in protecting against, and in some cases even reversing, precancerous conditions affecting the breast, mucous membranes, throat, mouth, stomach, prostate, colon, cervix, and bladder. The richest sources of beta-carotene are yellow, orange, and green leafy fruits and vegetables (such as carrots, spinach, lettuce, tomatoes, sweet potatoes, broccoli, cantaloupe, and winter squash).

Selenium

Selenium is a nonmetallic chemical element. Selenium is used in free radical elimination and other antioxidant enzymes, and also plays a role in the functioning of the thyroid gland. Selenium is the central element in glutathione peroxidase (GPx), an antioxidant enzyme that protects cells against the oxidative damage caused by peroxides and free radicals. Selenium forms part of the structure of the important antioxidant enzyme glutathione peroxidase, which in turn recycles glutathione. Dietary selenium comes from cereals, meat, fish, and eggs. Brazil nuts are a particularly rich source of selenium.

Superoxide dismutases (SOD) are a large and ubiquitous family of metalloenzymes that exist primarily to convert superoxide into hydrogen peroxide and water. This metal-containing antioxidant enzyme that reduces potentially harmful free radicals of oxygen formed during normal metabolic cell processes to oxygen and hydrogen peroxide. Hydrogen peroxide is always formed when superoxide is formed by way of the dismutation reaction. Most oxidases in the body directly reduce oxygen to hydrogen peroxide.

Oxidative metabolism in respiring cells generates highly reactive superoxide radicals which cause cellular damage. The presence of SOD has been shown to help protect many types of cells from the free radical damage that is important in aging, senescence, and ischemic tissue damage. SOD also helps protect cells from DNA damage, lipid peroxidation, ionizing radiation damage, protein denaturation, and many other forms of progressive cell degradation.

Several common forms of SOD exist: they are proteins cofactored with copper and zinc, or manganese, or iron. Copper/zinc SODs are typically found in the nuclei and cytosols of eukaryotic cells, iron SODs are typically found in prokaryotes, and manganese SODs are typically localized in the mitochondrial matrices of both eukaryotic and prokaryotic cells. Manganese superoxide dismutase and iron superoxide dismutase from some organisms (e.g. Escherichia coli) exhibit almost absolute metal specificity, while other enzymes, such as `cambialistic' superoxide dismutase from Propionibacterium shermanii, are active with either metal.

Manganese superoxide dismutase and iron superoxide dismutase occur as homodimers or homotetramers. Manganese superoxide dismutase and iron superoxide dismutase are unequally distributed throughout the kingdoms of living organisms and are located in different cellular compartments. In particular, iron superoxide dismutase is found in facultative aerobes, in the thylakoid membranes of cyanobacteria and the chloroplasts of higher plants, and in mitochondria of higher plants, fungi and animals.

The activity of the superoxide dismutases make them excellent candidates for therapeutic agents to counteract the toxic effects of the superoxide and other oxygen radicals. Pharmacologically, superoxide dismutase can serve as a medicine for treatment of inflammation caused by autoimmune diseases, and, recently, by use of superoxide dismutase, there have been attempts to develop medicines for the treatment of arthritis deformans and chronic rheumatism and for treatment of harmful side effects caused by radio therapy.

Manganese superoxide dismutase (MnSOD) is a very important antioxidant enzyme that catalyzes the conversion of superoxide radicals to hydrogen peroxide and molecular oxygen in the mitochondria. Alterations in MnSOD levels have been associated with a number of neurodegenerative diseases, including Parkinson’s disease, Duchenne muscular dystrophy, Charcot-Marie-Tooth disease, and Kennedy-Alter-Sung syndrome.