The Important Antioxidant Vitamins - Assignment Example

Vitamins and Minerals as Antioxidants Antioxidant vitamins and minerals which are present in natural food sources are important inprotecting the body from free radicals. Free radicals are atoms or groups of atoms containing unpaired electrons (namely the superoxide anion, hydroxyl free radical and hydrogen peroxide) that can cause damage to cells, impairs the immune system and leads to various degenerative diseases like spinal cord injury, heart diseases, atherosclerosis, cancer, arthritis, emphysema, retinopathy and optical cataracts(Sies,1997). The unpaired electron can accept protons from other bio-molecules present in the cellular structures like the cell membrane and DNA, leading to their destruction through oxidative damage (Knight, 1998). The important antioxidant vitamins are vitamin A, beta carotene, vitamin C and vitamin E while the important antioxidant minerals are Selenium, Zinc, Manganese and Copper. These vitamins and minerals are an integral part of the free radicals scavenging enzyme system. The four significant antioxidant enzymes that neutralize the free radicals are superoxide dismutase, catalase, methionine reductase and glutathione peroxidase. Most minerals and vitamins might not be effective alone in scavenging free radicals, but can act as effective antioxidants in a synchronized manner. Major sources of antioxidant vitamins and minerals are fish oils, avocados, pomegranate, banana, raspberries, mango, spirulina and pumpkin. Most nuts and seeds also serve as a major source of antioxidant minerals (Benzie, 2003). The oxygen free radicals are neutralized by vitamins and minerals in a concerted way. Free radicals are formed due to many reasons either by cleaving water molecules into the hydroxyl free radical superoxide radicals and lipid peroxides by the action of ionizing radiations, and toxic pollutants. The fat molecules are broken down to liberate the reactive fatty acid peroxy radical. The free radicals have one unpaired electron in outermost valence shell, so in order to become stabilized it can accept protons from other bio-molecules present in the cellular structures like the cell membrane and DNA, leading to their destruction through oxidative damage (Knight, 1998). Free radicals can also be liberated from the diet we consume. A fat rich diet can increase free radical activity because fatty acids are readily oxidized to fatty acid free radicals. Cooking fats at high temperatures, mainly frying foods in oil, may produce large number of free radicals. Hence if the diet does not contain enough antioxidant vitamins and minerals, then it might lead to mutations which can cause irreversible damage to the body. Changes in the structure of the proteins may result from the errors in protein synthesis caused by mutation of free radicals on the DNA. The immune system might recognize this altered protein as a foreign substance and try to destroy it. These damaged proteins lead to cancer, autoimmune diseases and many degenerative diseases (Chaudiere and Ferrari, 1999). The roles of various vitamins as antioxidants are described as follows. Vitamins A are polyisoprenoids each with a beta-ionone or cyclohexenyl ring with many double bonds. Vitamin A and Beta Carotene are effective antioxidants for destroying singlet oxygen 1O2 while Beta Carotene is more effective in scavenging superoxide free radical and proxy free radical. Thus these vitamins reduce the carcinogenic effects of many pollutants and together with vitamin E acts as lipid antioxidants. Organic free radicals gets mopped up from tissues by getting bound to the conjugated alkyl molecular chain of Beta Carotene as resonance stabilized and carbon –centered substituent which traps the free radicals and prevents them from destroying membranes and tissues (Wang and Quinn, 1999). Tocopherols or Vitamin E are thermostable vitamins having a chromane nucleus with a phenolic hydroxyl group and an isoprenoid sidechain. The chromanol ring of the tocopherol donates its phenolic hydrogen to reduce a free radical such as a fatty acid peroxy free radical and itself is oxidized to phenoxytocopheryl free radical. The latter has two fates, i) it may be reduced back to tocopherol by electrons transferred from L-ascorbate (Vitamin C) which plays a supportive role in the antioxidant activity of vitamin E and ii) it might get its polyisoprenyl sidechain and chromane ring oxidized to form a non free radical oxidized product while reducing another free radical. The non free radical gets excreted as a glucoronide in the bile. The hydroperoxy fatty acid, formed in a membrane lipid by such antioxidant reaction is released into the cytosol by phospholipase A2 and reduced to hydroxy fatty acid by a selenium enzyme glutathione peroxidase , using glutathione as the electron donor. Hence selenium acts synergistically with tocopherol to protect the cell components from hydroperoxides, selenium also helps to maintain normal intestinal absorption of tocopherol while vitamin E protect selenium of membrane selenoproteins from the action of free radicals (Wang and Quinn, 1999). Vitamin A and Beta Carotene are effective antioxidants for destroying singlet oxygen 1O2 at low partial pressures of oxygen while tocopherol does the same when the partial pressure of oxygen is high. By such scavenging action tocopherols prevent muscular dystrophy and peroxidation of poly unsaturated fatty acids in lysosomal membranes, so the lysosomal enzymes like hydrolases will not be released to destroy the muscle fibers. By preventing peroxidative changes in mitochondrial membranes, tocopherols maintain the translocation of phosphate ions and ADP into mitochondria and may enhance oxidative phosphorylation. Tocopherols might also prevent the oxidation of sulfhydryl enzymes participating in mitochondrial oxidation. Vitamin E also prevents ageing; prevent hepatic necrosis and anticancer effects by preventing free radical mediated mutations. Vitamin C or L ascorbate is the gamma lactone of a C6 with C2-C3 double bond. Being an electron donor vitamin C is a potent antioxidant in humans (Wang and Quinn, 1999). The minerals also serve the role as antioxidants in conjugation with the vitamins discussed. The cytoplasmic superoxide dismutase is a copper-zinc protein of liver, erythrocytes, phagocytic lymphocytes and neurons which acts as an oxidant and reductant in converting superoxide anion free radical into hydrogen peroxide. This copper zinc enzyme works together with tocopherols , selenium, ascorbate and carotene in removing free radicals(Chaudiere and Ferrari, 1999). Selenium mainly occurs as selenocysteine residues of tissue and membrane proteins replacing the sulfur in cysteine. It is an integral part of the enzyme called glutathione peroxidase which occurs in plasma, erythrocytes and pulmonary cells. The erythrocyte isozyme is a tetrameric protein with one selenocysteine residue in each peptide unit. The enzyme glutathione is the reducing agent for reducing hydrogen peroxide to water or polyunsaturated hydroperoxy fatty acids to hydroxyl fatty acids. Glutathione gets oxidized to oxidized glutathione. This selenoprotein enzyme thus protects lipids, proteins and nucleic acids from oxidative damage (Chaudiere and Ferrari, 1999). The molecular weights of these antioxidant enzymes are quite high. The copper-zinc containing cytoplasmic superoxide dismutase has a molecular weight of over 30,000 daltons, while the manganese SOD bears a weight in excess of 60,000 daltons. These structures have molecular weights which far exceeds the limit that the body and cells will be able to absorb intact without digestion, ultimately resulting in the destruction of the enzyme. The maximum molecular weight required for intact absorption by the cells is around 1500 daltons. In view of the above discussion the typical superoxide dismutase supplements found in the market have little or no value. Our body requires the supplementation of these vitamins and minerals in a proper balance to synthesize the proper amount of SOD enzymes needed to scavenge the free radicals and prevent their detrimental effects on the body (Brigelius, 1999). There are at present 3 superoxide dismutase enzymes identified that the body is able to manufacture with the proper intake of vitamins and minerals. These are Cytosolic Copper/Zinc SOD, Mitochondrial manganese SOD and the Erythrocyte Copper/Zinc SOD (Chaudiere and Ferrari, 1999). The superoxide anion is catalytically converted by the SOD to hydrogen peroxide which gets converted to water by the actions of glutathione peroxidase and catalase. If the antioxidant vitamins and minerals are not made bio-available to the body, then the superoxide anions becomes unstable and becomes reactive and generate the so called free radicals which causes the harmful effects (Knight, 1998). From the above discussion it is noted that the important antioxidant vitamins are vitamin A, beta carotene, vitamin C and vitamin E while the important antioxidant minerals are Selenium, Zinc, Manganese and Copper. These vitamins and minerals are an integral part of the free radicals scavenging enzyme system which are superoxide dismutase, catalase, methionine reductase and glutathione peroxidase. They needs to be supplemented in proper ratio through foods like fish oils, avocados, pomegranate, banana, raspberries, mango, and nuts to maintain the proper levels of the antioxidant enzymes in the body so as to protect the body from the detrimental effects of free radicals. References Brigelius-Flohé R (1999). "Tissue-specific functions of individual glutathione peroxidases". Free Radic Biol Med 27 (9–10): 951–65 Benzie, I (2003). "Evolution of dietary antioxidants". Comparative Biochemistry and Physiology 136 (1): 113–26 Chaudiere, J; Ferrari-Iliou, R (1999). "Intracellular Antioxidants: From Chemical to Biochemical Mechanisms". Food and Chemical Toxicology 37 (9–10): 949–62 Knight, JA (1998). "Free radicals: Their history and current status in aging and disease". Annals of Clinical and Laboratory Science 28 (6): 331–46 Sies, Helmut (1997). "Oxidative stress: Oxidants and antioxidants". Experimental physiology 82 (2): 291–5. . Wang, Xiaoyuan; Quinn, Peter J. (1999). "Vitamin E and its function in membranes". Progress in Lipid Research 38 (4): 309–36. Read More