Antioxidants
Introduction
The chemical systems, existing in living organisms produce unstable molecules/particles called oxidants or free radicals. These unstable molecules can be lethal to the biological function of the organism. The response to these free radicals is found in the form of antioxidants. These are substances that retard the breakdown of another substance by oxygen. Antioxidants such as vitamin C (ascorbic acid), butylated hydroxytoluene (BHT), and butylated hydroxyanisole (BHA) are added to foods to prevent them from becoming sour through exposure to air. Endogenously produced, nutrients such as beta-carotene, vitamin C, vitamin E, and selenium have been found to play the role of antioxidants. Studies have suggested that the antioxidants that occur naturally in fresh fruits and vegetables have a protective effect. For example, vitamin E and beta-carotene appear to protect cell membranes; vitamin C removes free radicals from inside the cell.
The Mechanism
Cellular metabolism gives rise to ions called free radicals. These radicals play a crucial role in killing bacteria. Free radicals are not only by-products, but also play an important role in cell signal transduction, apoptosis and infection control (Bonnefoy M, Drai J, Kostka T, 2002). However, when the production of these radicals gets enhanced, the body stands the risk of damage to the biomolecules through pre-activated immune response. Consequently, the process of ageing is accelerated (Ansari, 1997). Continuous
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exposure to free radicals and other Reactive Oxygen Species (ROS) through external sources like sunlight, pollution and other forms of radiation and also endogenous generation leads to tissue injuries (Flora, 2007). The exposure of the biological unit or system to free radicals damages the integrity of the cell. When a cell’s integrity or quality has been compromised, it may result in cancer-proliferated and uncontrolled increase in cell size and number-, heart disease and stroke. Tissue damage eventually leads to diseases like Atherosclerosis, Diabetes, Cancer and Ageing and ultimately death (Flora, 2007). According to Flora (2007) ,“Radicals of oxygen (superoxide anion, hydroxyl radical, and peroxy- radicals), reactive non-radical oxygen species such as hydrogen peroxide and singlet oxygen, as well as carbon, nitrogen, and sulfur radicals comprise the variety of reactive molecules that can cause damage to cell” (p.2).
The body comprises of enzyme systems that destroy free radicals. However, the principal antioxidants are vitamin E, vitamin C, n-acetylcysteine and -lipoic acid. Selenium, a trace metal, is also a part of this system that aids in proper antioxidant system functioning.
A subtle balance needs to be maintained between the production of the ROS (Reactive Oxygen Species) and the compensating Endogenous Antioxidant system (Willcox JK, Ash SL & Catignani GL, 2004). The antioxidant system generates antioxidants that neutralize the radical ions by lending an electron. However, these antioxidants are stable and the neutralization process doesn’t turn them into free radicals. Failure of the antioxidant system leads to oxidative stress resulting in cardiovascular disease, cancer, and other chronic diseases that account for a major portion of deaths
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today (Willcox JK, Ash SL & Catignani GL, 2004). “Overwhelming production of free radicals in response to exposure to toxic chemicals and ageing may necessitate judicious antioxidant supplement to help alleviate free radical mediated damage” (Ansari, 1997)
Source
Antioxidants are organic molecules that are found in food as polyphenols, minerals, vitamins and carotenoids. The distinctive color of many foods – red for tomatoes and orange for carrots – can be attributed to the presence of antioxidants. The most common forms are; B-carotene; found in carrots and vegetables, the mineral selenium, in most herbs, and Vitamin A and C inmost fruits and vegetables.
Cancer and Ageing
“Life threatening human diseases, like atherosclerosis, diabetes, cancer, and ageing, have free radical reactions as an underlying mechanism of injury” (Flora, 2007). A lot of lives are lost to cancer every year. Premature ageing is also a major cause for concern in an era where science and medical technology are taking rapid strides towards the development of life-saving drugs. “Severe oxidative stress progressively leads to cell dysfunction and ultimately cell death. Oxidative stress is defined as an imbalance between pro-oxidants and/or free radicals on the one hand, and anti-oxidizing systems on the other” (Bonnefoy M, Drai J & Kostka T, 2002). Oxygen is a life-sustainer. However, the generation of free radicals is also attributed to Oxygen. Superoxide anions, hydroxyl radicals, peroxyl radicals, hydrogen peroxide, hydroperoxides and peroxinitrite anions are free radicals produced by oxygen and are toxic to the cells (Bonnefoy M, Drai J & Kostka T, 2002). These radicals damage the cells and attack DNA. The Antioxidant
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defense system constitutes enzymes that are readily oxidizable composites. “The free radical captor or neutralization systems of these ROS use a collection of mechanisms, vitamins (E and C), enzymes [superoxide dismutase (SOD), glutathion peroxidase (GPx) and others], and glutathion reductase (GSH), capable of neutralizing peroxinitrite” (Bonnefoy M, Drai J & Kostka T, 2002). However, the defense system is reliant on the DNA structure and the nutrition intake for the vitamins. Test studies reveal that oxidative stress and production of these free radicals can be contained by avoiding radiation, smoking, dietary carcinogens and other radical-favorable environmental conditions (Bonnefoy M, Drai J & Kostka T, 2002).
Cancer is initiated through a series of cellular and molecular changes that are triggered by diverse endogenous and exogenous stimuli. “One type of endogenous damage is that arising from intermediates of oxygen (dioxygen) reduction – oxygen-free radicals (OFR), which attacks not only the bases but also the deoxyribosyl backbone of DNA” (Valko M, Izakovic M, Mazur M, Rhodes CJ & Telser J, 2004). The effect of OFR is neutralized by the antioxidants, enzymatic and non-enzymatic. Non-enzymatic antioxidants are vitamin C, vitamin E, carotenoids (CAR), selenium,etc . However, it has been observed that under certain conditions, some antioxidants can also exhibit a pro-oxidant mechanism of action. For example, beta-carotene at high concentration and with increased partial pressure of dioxygen is known to behave as a pro-oxidant. Hence, biologists suggest that the optimal approach is to reduce endogenous and exogenous sources of oxidative stress, rather than increase intake of anti-oxidants (Valko M, Izakovic M, Mazur M, Rhodes CJ & Telser J, 2004)
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Conclusion
The use of anti-oxidant supplements is still not considered safe since there is insufficient knowledge on the pro-oxidant, oxidant and anti-oxidant properties of the supplements. However, studies do show that antioxidants have a positive impact on various age-related degenerative diseases. Antioxidant-rich fruit and vegetables go a long way in improving health and are recommended.
References
Haliwell.B, Okezie Aruoma, Molecular Biology of Free radicals in human diseases,
OICA (International), 1998, UK
Haliwell.B, Okezie Aruoma, DNA and Free radicals; Techniques, Mechanisms and applications, OICA (International), 1998, UK
Tokoyuni, Toshikazu Yoshikawa: Free radicals in chemistry, Biology and medicine,
OICA (International), 2000, UK
Okezie Aruoma, G Williams, Molecular drug Metabolism and Toxicology,
OICA (International), 2000, UK
Fuchs.D, Okezie Aruoma, Pharmacology of Infections, OICA (International), 2000, UK
The Columbia Encyclopedia, Sixth Edition. 2004.
Valko M, Izakovic M, Mazur M, Rhodes CJ, Telser J. Molecular and cellular
biochemistry. 2004 Nov;266(1-2):37-56.
Flora SJ. Cell and Molecular Biology (Noisy-le-grand). 2007 Apr 15;53-1:1-2.
Ansari.KN Indian Journal of Medical Sciences. 1997 Sep;51(9):319-36.
Willcox JK, Ash SL, Catignani GL.Critical Reviews in Food science and nutrition
2004; 44(4):275-95.
Bonnefoy M, Drai J, Kostka T. Presse Med. 2002 Jul 27; 31(25):1174-84.
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