More on antioxidant defence system

FREE radicals play very far-reaching roles in causing diseases in the body; much more than individuals and even practitioners know. Knowledge of these elements and compounds and their actions, will go a long way in identifying the diseases caused by free radicals and how to prevent and combat them.

  Free radicals, as you may know, are highly reactive and unstable oxygen (nitrogen) intermediates released during normal chemical reactions in the body. During the metabolic process of energy production in the mitochondria of a cell, oxygen is reduced to water. 

  On some occasions, the reduction of oxygen is not complete and oxygen ions with a single electron in the outer orbit is released. Usually, there is a paired set of electrons in the outer orbit. The free radical thus released begins to seek out an electron from surrounding tissues so as to become paired. 

  As the free radical becomes stable after its electron has been paired, the tissue from which it got the electron becomes an unstable free radical. A chain reaction becomes established with the generation of free radicals and stable atoms or compounds. 

  The antioxidant defence system is the inborn system in the body that checks the free radicals. The components of the system donate electrons to the free radicals in order to stabilize them. Tissues and nutrients that are frequently attacked by free radicals are lipids (LDLs), proteins in the lipid bi-layered cell membranes, carbohydrates and DNA. 

  More often than not, the antioxidant defence system neutralizes and stabilizes the free radicals completely and prevents tissue damage. However, on certain occasions, the capability of the defence system becomes compromised and free radicals begin to accumulate and cause damage.

  The major free radical produced in the body is the superoxide radical. When these accumulate as in a situation where the antioxidant defence has been overwhelmed, they can react with free fatty acids a chain reaction to form fatty acid hydroperoxides and other free radicals. 

  As these accumulate in the absence of antioxidants the surrounding structures will begin to suffer from oxidative stress damage. 

Components of the antioxidant defence system

The antioxidant defence system is made up of: 1. Vitamins E, C, A and the carotenoids. Vitamin E being a fat soluble vitamin is found predominantly in the lipid membranes of cells and organelles. In these membranes, Vitamin E neutralizes fatty acid hydroperoxide free radicals. It prevents lipid oxidation in cell membranes and protects them against damage.

  Vitamin C is the predominant antioxidant in the extracellular fluid compartment. It neutralizes free radicals by ‘donating’ electrons to them. Vitamin C also donates electrons to Vitamin E antioxidants that have lost their electrons to free radicals. In other words, Vitamin C helps to regenerate Vitamin E and prolongs its ability to prevent lipid damage in the cell membrane. Carotenoids stabilize singlet oxygen and prevent lipid oxidation.

  2. Enzymes. These are protein compounds produced in the body that catalyze chemical, reactions. The main enzymes in this group of antioxidants are,

Superoxide dismutase. A lot was written about it in last week Thursday’s edition of the Guardian Newspaper. 

  Glutathione peroxidase. This is a group of enzymes of the peroxidase family. It is made up of about 8 sub-groups and selenium is the trace element that acts as a co-factor to these group of enzymes. The different sub-groups of enzymes that make up gutathione peroxidase function in different parts of the body. 

  Five of such subgroups have been extensively studied by researchers. Their findings are as follows: The first sub-group GP-1 is found in almost all the cells of the body. GP-2 is found mainly in the cells of the intestines and in the extracellular fluid. GP-3 is located mainly in the plasma. GP-4 is also found in all the cells in the body and GP-5 is an androgen-related protein located in the epididymal cells of the testicles.

  All these peroxidase enzymes catalyze the conversion of hydrogen peroxide to water and oxygen. They are also involved in the conversion of lipid hydroperoxide to their corresponding alcohol. In all of these reactions, they protect the tissues in the parts of the body where they are found against oxidative damage. 

  3. Trace minerals: Certain minerals required in very minute amounts take part in the enzymatic reactions involving the antioxidant enzyme system. As I wrote last week, zinc and copper (magnesium) are co-factors in the reactions that the superoxide dismutase enzyme catalyses. Selenium is a co-factor in glutathione peroxidase enzyme reactions, while iron is involved with catalase.

  Next week Thursday, we shall look at sources of all these vitamins and minerals and how we can eliminate or minimize the scourge of free radicals.