Antioxidants are substances that may protect cells from the damage caused by unstable molecules known as free radicals. Antioxidants interact with and stabilize free radicals and may prevent some of the damage free radicals might otherwise cause.
Free radical damage may lead to cancer. An antioxidant is a molecule capable of slowing or preventing the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons from a substance to an oxidizing agent. Oxidation reactions can produce free radicals, which start chain reactions that damage cells. Antioxidants terminate these chain reactions by removing free radical intermediates and inhibit other oxidation reactions by being oxidized themselves. As a result, antioxidants are often reducing agents such as thiols, ascorbic acid or polyphenols . Although oxidation reactions are crucial for life, they can also be damaging; hence, plants and animals maintain complex systems of multiple types of antioxidants, such as glutathione, vitamin C and vitamin E as well as enzymes such as catalase, superoxide dismutase and various peroxidases.
Low levels of antioxidants, or inhibition of the antioxidant enzymes, causes oxidative stress and may damage or kill cells. As oxidative stress might be an important part of many human diseases, the use of antioxidants in pharmacology is intensively studied, particularly as treatments for stroke and neurodegenerative diseases. However, it is unknown whether oxidative stress is the cause or the consequence of disease.
Antioxidants are also widely used as ingredients in dietary supplements in the hope of maintaining health and preventing diseases such as cancer and coronary heart disease. Although initial studies suggested that antioxidant supplements might promote health, later large clinical trials did not detect any benefit and suggested instead that excess supplementation may be harmful.
In addition to these uses of natural antioxidants in medicine, these compounds have many industrial uses, such as preservatives in food and cosmetics and preventing the degradation of rubber and gasoline. For many years chemists have known that free radicals cause oxidation which can be controlled or prevented by a range of antioxidants. It is vital that lubrication oils should remain stable and liquid should not dry up like paints. For this reason, such oil usually has small quantities of antioxidants such as phenol or amine derivatives, added to them. Although plastics are often formed by free radical action, they can also be broken down by the same process, so they too, require protection by antioxidants like phenols or naphthol. Low density polythene is also of protected by carbon black which absorbs the ultraviolet light which causes radical production.
Antioxidants block the process of oxidation by neutralizing free radicals. In doing so, the antioxidants themselves become oxidized. The two ways by which they act are-
Antioxidants can be classified into two groups on the basis of enzymatic nature-
The antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx), glutathione reductase, thioredoxin reductase, heme oxygenase and biliverdin reductase serve as primary line of defense in destroying free radicals.
They are classified into two groups:
The major extracellular endogenous antioxidants found in human plasma are the transition metal binding proteins i.e. ceruloplasmin, transferrin, hepatoglobin and albumin. They bind with transition metals and control the production of metal catalyzed free radicals. Albumin and ceruloplasmin are the copper ions sequesters. Hepatoglobin binds with hemoglobin, ferritin and transferrin with free iron. Lipoic and uric acids, bilirubin, ubiquinone and glutathione are non protein endogenous antioxidants which inhibit the oxidation processes by scavenging free radicals.
Antioxidants are very important in the treatment of fried Reich ataxia, a rare progressive condition that causes damage to the nervous system. It is inherited in an autosomal recessive pattern, meaning that, an affected gene must be inherited from each parent for the disease to develop in their child it is most common recessively inherited worldwide. The progression of the disease cannot be easily assessed by clinical examination test. Evaluation of diseases is done by standard neurological scales. Abnormal high levels, oxidative damage to the cells occurs leading to several pathological conditions, rheumatoid arthritis, hemorrhagic shock, cardiovascular system disorder, cystic fibrosis, metabolic disorder, gastrointestinal, ulcerogenesis and acquired immunodeficiency. Pharmacological applications of leutinide are as agent in radio immunotherapy and photodynamic.
Antioxidants therapy in acute central nervous system injury : Free radicals are highly reactive molecules generated predominantly during cellular respiration and normal metabolism imbalance between cellular production of free radicals and ability of cells to defend against them is referred to as oxidative stress (OS) (Gutter, 1991). OS has been implicated as a potential contributor to acute central nervous system (CNS) injury by ischemic or hemorrhagic stroke or trauma. The production of reactive oxygen species (ROS) may increase, sometimes drastically leading to tissues damage via several different cellular molecular pathways. Radicals can cause damage to cardinal cellular components such as lipids, proteins and nucleic acid e.g DNA leading to subsequent cell death by modes of necrosis or apoptosis. The damage can become more widespread due to weakened cellular antioxidant defense systems. Moreover, acute brain injury increases the level of excitoxic amino acids (such as glutamate), which also produce ROS, thereby promoting parenchymatous destruction. Therefore, treatment with antioxidants may theoretically act as tissue damage and improve both the survival and neurological outcome, several such agents of widely varying chemical structures have been investigated as therapeutic agents for acute CNS injury, although, a few of the antioxidants showed some efficacy in animal models or in smal clinical studies. Better understanding of the pathological mechanisms of acute CNS injury would characterize the exact primary targets for drug intervention improved antioxidant design should take into consideration the relevant and specific harmful free radical.
A vast amount of circumstantial evidence implicates oxygen-derived free radicals (especially superoxide and hydroxyl radicals) and high-energy oxidants such as peroxynitrite as mediators of inflammation, shock and ischemia/reperfusion injury.
Chitra, K., and Pillai, K.S. (2002) Antioxidant in health, Indian Journal of Physiology and Pharmacology 46(1): 1-5.
Gutter RG (1991). Antioxidants and ageing. The American Journal of Clinical Nutrition
Halliwell B (1996). Antioxidants in human health and disease. Annal Review of Nutrition 16: 33-50.
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