Manbir Online ... Free Radicals and Antioxidants

Free Radicals and Antioxidants

A free radical is a substance that contains one or more unpaired electrons, which is capable of independent existance. They are highly reactive molecules. They may be formed physiologically as in neutropils during intracellular killing or micro organisms or may be formed pathologically in an atherosclerotic plaque.
A stable molucle has no unpaired electron in its electron orbit. In afree radical however the presence of unpaired electron makes it energetically unstaable. It will quickly pair with an electron in the surrounding molecule to give it stability. This oxidises the surrounding molecule. This oxidation has two effects on the taaget molecule - it is chemically modified and it will also become reactive as it now has an unpaired electron. This will lead to oxidation of another surrounding molecule ans a chain reaction will set in generating and regenerationg free radicals, thus destroying large number of cell components.

Free radicals are very short lived. Most of the free radicals are formed in the body from oxygen.

Superoxide (O2) ion
Hydroxyl group (OH)
Nitric Oxide (NO)
Singlet oxygen (O)
Peroxyl radicals (ROO)
Hydrogen Peroxide (H2O2)

Free radicals are being constantly formed in the body because of endogenous metabolic processes or due to environmental exposures - smoking, pollution.

Free radicals are generated in any of the three major cell types of the arterial wall : - endothelial cells, smooth muscle cells and macrophages. The free radicals and the LDL ( Low density lipids ) are involved in processes which finally lead to the formation of 'Foam Cells' from which atherosclerotic plaques evolve.
Oxidised LDL also exerts other actions that add to the development of atherosclerosis. Free radicals also stimulate production of prostaglandins that cause vaso-constriction and also help in the aggregation of the platelets.

Although high levels of native LDL are associated with atherosclerosis, it is the oxidation of LDL by the free radicals that is crucial to its initiation and progression.

Antioxidants

We know that the free radicals are formed in the body constantly. Surely the body has mechanisms to take care of the oxidative stress. All cells have defences against the free radicals and these defences are antioxidants.
There are three types of natural antioxidants :-
1. Antioxidant enzymes : superoxide dismutase, catalase, glutathiaone peroxidase.
2. Preventive antioxidants : transferrin, lactoferrin, ceruloplasmin.
3. Scavenging antioxidants : vitamin C, E,A.

The antioxidants particitipate in reducing the oxidative stress by themselves getting oxidised, thereby protecting the target cells. The free radicals attempt to react with the target cells but in the presence of the antioxidants they react with the antioxidants.

Important Antioxidants
Vitamin A ( ß - carotene )
Vitamin E ( Alpha - tocopherol )
Vitamin C (Ascorbic acid )
Selenium