oxidants and antioxidants

ion vs radical, oxidation vs reduction
the oxidants, their origin, their normal uses/ roles
harms caused by oxidants
antioxidants: how the body protects itself from oxidants
clinical uses of antioxidants

Oxidants are compounds which oxidize other molecules. In the biological context, oxidants are molecules which are relatively strong oxidizing agents, strong enough to do damage if allowed to accumulate unchecked. 

ion vs radical, oxidation vs reduction

An ion is a charged particle. In a molecule this means that the total number of electrons and protons are unequal. Ions may be cations or anions.
A radical is an atom or molecule that has at least one unpaired electron. In terms of atomic and molecular structure, electrons try to form pairs. The presence of an unpaired electron makes that atom or molecule highly reactive. The oxygen atom has two unpaired electrons, while the oxygen molecule has none. Conventionally the presence of an unpaired electron is written as a dot, eg O2s- which is a molecule with an unpaired electron and a negative charge (an anion).

Oxidation is loss of electrons. When a molecule or atom is oxidized, it loses electrons, and vice versa. Reduction is gain of electrons. 


the oxidants, their origin, their normal roles

The important oxidants that are known to be formed during enzymatic reactions in the body are:
a. the superoxide anion radical, O2s-
b. hydrogen peroxide, H2O2
c. hydroxyl radical, OHs
d. hypochlorous acid and hypochlorite ion, HClO, ClO-
e. peroxynitrite ion, ONOO-

Not all of these are radicals.
The reactions that generate large amounts of oxidants take place mainly in white blood cells (neutrophils)
Agents that increase production of oxidants in the body include any radiation, estrogens, gentamicin, chemotherapy drugs and bacterial toxins.

Normal roles of oxidants. Oxidants are there for a purpose, and are obviously not produced by the cells merely to cause harm to the body. They are byproducts of some metabolic processes, in particular during the metabolism of respiratory oxygen. Their main function appears to be to kill germs. In infections, by a process called a "respiratory burst", large amounts of oxidants are produced, especially in the white blood cells. This huge production of oxidants helps to kill micro-organisms. In diseases in which there is a deficiency of enzymes that produce these oxidants, immunity is depressed. Oxidants are produced in other metabolic processes in the body as well. 


harms caused by oxidants

Although oxidants have their uses, sometimes the oxidants may escape the normal protective backup devices and attack proteins, carbohydrates and fats to cause harm. 

Excessive inflammation. Oxidants may stimulate white cells to release hormones and other chemicals in such large quantities that there can be inflammation in the entire body. Such a situation is called the Systemic Inflammatory Response Syndrome, SIRS, and is a very dangerous condition. 

Several diseases. Oxidative damage to cells has been implicated in the causation of several conditions, including heart disease, atherosclerosis, amyotrophic lateral sclerosis, stomach ulcers, birth defects (interestingly, thalidomide, a drug which was associated with birth defects, is a oxidant inducer), sperm defects, infertility, and also several eye diseases including cataracts and macular degeneration. 

Aging. There is evidence that prolonged oxidant attacks over a period of years causes aging. Changes in brains from oxidation are similar to those that are present in aging brains. Animal species with low levels of antioxidant enzymes and low rates of oxygen radical production in mitochondria live longest, and within a given species the same applies.

Cancer. Oxidants may attack DNA in the nuclei of cells, causing changes that may eventually lead to the development of cancer. Carcinogens such as cigarette smoke, asbestos, gamma and UV rays, nitrosamines (present in burnt food) and hydrocarbons such as benzanthracene, all produce oxidants. It was shown that women whose DNA is getting oxidized tend to develop breast cancer after some years. Epidemiological and case control studies indicate that high intake of ascorbic acid, alpha tocopherol, selenium, beta carotene, vegetables containing A, C, E may lower mortality rates for certain cancers in humans. 


antioxidants: how the body protects itself

Once an oxidizing molecule is produced, the body recognizes that it can do harm. It therefore makes efforts to neutralize the oxidants with different anti-oxidants. Some protective compounds in made by the body are superoxide dismutase, glutathione, catalase, melatonin and antiproteinases. There are many others, not produced by the body. These include Vit A, C, E, some drugs (eg carvedilol used in heart disease), catechins in tea (especially green tea), and some compounds in honey. The oxidants can be reduced, or incorporated into large molecules within which their oxidizing capacity becomes greatly decreases.. 


clinical uses of antioxidants

Antioxidants have been studied in great detail, but information is mostly indirect. They, and their metabolites, can be useful in 

  • improving immunity: vitamin C has been shown to be useful in colds

    heart disease: Vit A, and carotenoids protect against and in heart disease. Some drugs (such as carvedilol) have anti-oxidant properties in addition to their beta blocker effects

    brain disease: some anti-oxidants such as vitamin C and Vitamin E, and others, appear to have protective effects in Alzheimer's and Parkinson's diseases, stroke and other neurological disorders. Anti-oxidants also appear to reduce the incidence and severity of gastric ulcers and prevented severe symptoms of colitis, such as mucosal lesions and diarrhea, to protect patients during hemodialysis, to protect the liver, eg from developing cirrhosis

    to protect against aging and cancer: experimental evidence suggests that aging is slowed when oxidative processes are less. A large body of human epidemiological evidence which suggests that incidence of cancer is lower in populations having a high level of antioxidants,such as vitamin E, in their diet, or who have taken steps to enhance their level of intake of the vitamin by taking dietary supplements. There is also some evidence which suggests that intervention with dietary supplements of vitamin E can result in a lowered risk of disease, in particular of cardiovascular disease 

Should antioxidants be used clinically? The answer is probably yes. Vitamin C is safe at levels of supplementation up to 600 mg/d, and higher levels, up to 2000 mg/d, are without risk. Vitamin E has a very low human toxicity and an intake of 30 mg/ day is the recommended daily allowance (RDA). Some studies could not detect vitamin E toxicity even at doses as high as 1000 mg/d. 
The best advice against aging is to avoid toxins such as preservatives and pollutants, to drink tea instead of coffee, and to eat liberal amounts of fruit,vegetables, nuts, soya beans and lentils.



Dr Suneet Sood, MBBS (AIIMS), MS (AIIMS), MAMS, is a practising surgeon attached to Dharamshila Cancer Hospital, Sir Ganga Ram Hospital and to Noida Medicare Center. Formerly Professor of Surgery, Himalayan Institute of Medical Sciences, Dehradun, Dr Sood has a special interest in gastrointestinal surgery. He has had an active academic career, has published several papers in national and international journals, and is the Editor (with Dr Anurag Krishna) of a widely acclaimed book titled Surgical Diseases in Tropical Countries. 
Contact Nos: 2486788, 9811052966, suneetsood@vsnl.com

Editorial board: 

Dr Suneet Sood,MS, MAMS, Editor in chief
Dr Anurag Krishna, MS, MCh, MAMS
Dr Ivan Singh, MS, MAMS

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Last revised: May 12, 2000