The antioxidant enzyme defence system and trace minerals
Diseases caused by the accumulation of free radicals (oxidative stress)
ENZYMES are protein compounds produced in the body that catalyze chemical reactions. The main enzymes in this group of antioxidants are,
The superoxide dismutase (SOD), is one of the most powerful natural antioxidant enzymes found in the body. It is an enzyme that is found in all living cells, located both inside and outside the cell membranes. Superoxide dismutase is an internal antioxidant defence system that is closely associated with the catalase system. It works against the superoxide radicals, which can easily be described as the body’s most dangerous free radicals. SOD converts the superoxide radical to oxygen and hydrogen peroxide through a process known as dismutation and hence the name. The hydrogen peroxide so produced is also a free radical, but it is not as harmful as superoxide. Catalase and glutathione peroxidase, the other two enzymes in the enzyme antioxidant defence system act further on the hydrogen peroxide converting it to oxygen and water. Zinc and copper are the two trace minerals that act as co-factors to SOD.
Glutathione peroxidase. This is a group of enzymes of the peroxidase family. It is made up of about eight sub-groups and selenium is the trace element that acts as a co-factor to these groups of enzymes. The different sub-groups of enzymes that make up glutathione peroxidase function in different parts of the body. Researchers have extensively studied five of such subgroups. 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.
Certain minerals required in very minute amounts take part in the enzymatic reactions involving the antioxidant enzyme system. These include zinc and copper (magnesium) which act as co-factors in reactions catalyzed by the superoxide dismutase enzyme. Selenium is a co-factor in glutathione peroxidase enzyme systems, while the iron is involved with catalase.
These trace minerals are very important in the chemical reactions catalyzed by the antioxidant enzyme defence systems. In fact, absence of the minerals is a limiting factor to the function of the enzymes, which easily lead to failure and free radical accumulation. Excessive damage of tissues by oxidative stress becomes inevitable.
Diseases caused by oxidative stress (free radical accumulation)
Free radicals attack mostly the lipids in the bilayer membranes of cells, the lipoproteins, particularly the low-density lipoproteins (LDLs), proteins (structural and enzymes) and DNA.
This is a term that describes the oxidative degradation of lipids (fats) by free radicals as they seek to balance their electrons from the lipids in the cell membranes. This results in extensive damage to the membranes and cells. Polyunsaturated fatty acids are the lipids most often attacked. In what is known as a chain reaction mechanism, ROS such as OH- and HO2 combine with one hydrogen atom to form water and a fatty acid radical. This chain reaction continues and as it does so, different fatty acid radicals and lipid peroxide are produced. This reaction will continue for as long as the free radicals react with the fatty acids and can only be terminated when two free radicals react together. It is the role of antioxidants like Vitamin E to provide the enabling environment for the termination of this chain reaction. If the reaction is allowed to go on, the end results are certain cytotoxic and mutagenic compounds, which can cause cancer and other degenerative diseases.
Damage to proteins by free radicals can lead to certain structural damage and enzyme deficiency and alteration of enzymatic processes.
Oxidative damage to DNA can cause mutation, which can easily lead to cancer.
If these different mechanisms of attack go on unabated, they will lead to the development of various kinds of degenerative diseases affecting different parts and organs of the body.
Ongoing research which started about 50 years ago has shown that oxidative stress is the cause of several chronic degenerative diseases that afflict the human being. These diseases include cardiovascular conditions such as arteriosclerosis, hypertension, heart attack and heart failure. Others are glomerulonephritis, chronic renal failure, Alzheimer’s disease, Parkinson’s disease, stroke, and depression. Also included in the list, are such conditions as rheumatoid arthritis, inflammation, diabetes, ageing and cancer. Macular degeneration, cataract and pre-eclampsia are also known to be associated with oxidative stress.