Antioxidants are those substances that reduce the harmful effects of free radicals on the body. There are two types of antioxidants: Preventive antioxidants and chain breaking antioxidants.
Preventive antioxidants – They inhibit the initial production of free radicals. They include catalase, glutathione peroxidase, diethyl triamine penta – acetate (DTPA) and ethylene diamine tetra-acetate (EDTA).
Chain breaking Antioxidants – They inhibit the damaging phase of free radicals. They include superoxide dismutase, uric acid and vitamin E. Alpha tocopherol acts as the most effective naturally occurring chain breaking antioxidants in body tissues. Only traces of tocopherol are required to protect the body from considerable amounts of poly unsaturated fat.
Damaging effects of free radicals:
Free radicals are also called reactive oxygen species (ROS). They are characterized by extreme reactivity, short life span, generation of new ROS by chain reaction and damage to various body tissues. They are constantly produced during the normal oxidation of food stuffs due to leaks in the electron transport chain in the mitochondria. About one to four percent of oxygen taken up by the body is converted into free radicals. Macrophages also produce nitrogen oxide from arginine by the enzyme nitric oxide synthase. Ionizing radiation damages tissues by producing hydroxyl radicals, hydrogen peroxide and super oxide anion. Cigarette smoke contains high concentration of various free radicals. Other toxic compounds such as carbon tetrachloride, drugs and inhalation of air pollution increase the production of free radicals. There are a number of harmful effects of free radicals on the body such as damage to the cell membrane, genetic defects and diseases like cancer, bronchitis etc.
Chronic inflammation:
Chronic inflammatory diseases such as rheumatoid arthritis are self-perpetuated by free radicals released by neutrophils. Both corticosteroids and non-steroid anti- inflammatory drugs interfere with the formation of free radicals and interrupt with the disease formation process. Respiratory diseases from breathing 100% oxygen for more than 24 hours produce destruction of endothelium and lung edema. This is due to the release of free radicals by activated neutrophils. In premature new born infants, prolonged exposure to high oxygen concentration is responsible for bronco-pulmonary dysphasia. Adult respiratory distress syndrome (ARDS) is characterized by pulmonary edema.
Cigarette Smoking:
This enhances the emphysema in alpha-1 protease inhibitor deficiency. Cigarette smoke releases free radicals which attract neutrophils and releases more free radicals leading to lunge damage.
Diseases of the eye:
Retrolental fibroplasias or retinopathy of prematurity is a condition seen in prematurances treated with pure oxygen for a long time. It is caused by free radicals resulting in thromboxane release, sustained vascular contracture and cellular injury. Cataract formation is related with the ageing process which results partly due to photochemical generation of free radicals. Tissues of the eye including the lance, have high concentration of free radicals scavenging enzymes.
Shock related injury:
Free radicals damage cell membranes by the process of lipid peroxidation causing increased vascular permeability resulting in tissue edema.
Atherosclerosis and Myocardial Infarction:
Low density lipoproteins (LDL) promote atherosclerosis. They are deposited under the endothelial cells, which undergo oxidation by free radicals released from endothelial cells. Alpha tocopherol has a protective effect on the body.
Peptic Ulcer: It is produced by the erosion of gastric mucosa by hydrochloric acid. This infection promotes a burst of free radicals leading to tissue destructions.
Skin Diseases: Free radicals contribute to the development of various skin diseases such as psoriasis, leukoderma and skin cancer.
Cancer: Free radicals are responsible for the development of cancers due to their mutagenic property. They produce DNA damage, and accumulated damages leading to somatic mutations and malignancy. Free radicals also play a crucial role in the formation of degenerative brain disorders such as Parkinson’s, Alzheimer’s, dementia, multiple sclerosis etc. Cumulative effects of free radicals injury are the underline cause for gradual deterioration of the ageing process. Free radicals are involved in alcoholic liver cirrhosis, muscular dystrophies, malignant hypertension, male infertility, toxemia of pregnancy and hearing loss associated with antibiotics.
Benefits of antioxidants: The damage produced by reactive oxygen species may be prevented by antioxidants. They reduce the destructive effects of free radicals and inhibit their formation. Antioxidants can be consumed as dietary supplements or as pills. These include vitamin E, Vitamin C, Vitamin K, dimethyl thiourea, dimethyl sulfoxide, mannitol, allopurinol and superoxide dismutase. Antioxidants are regularly used in the food industry to increase the shelf life of products. Commercially used food preservatives are Vitamin E, propyl gallate, butylated, chydroxy anisole (BHA) and butylated hydropsy toluene (BHT). Antioxidants prevent the damage of oils and rancidity.
Vitamin C is an important aqueous phase antioxidant. Ceruloplasmin can act as an antioxidant in extra cellular fluid. Caffeine and uric acid are good antioxidants. Cysteine, glutathione and vitamin A are good antioxidants that block the effects of free radicals. Beta carotene is a chain breaking antioxidant but is less effective than alpha tocopherol. Transparent ferritin and bilirubin are mild antioxidants
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