Antioxidantsare substances that give protection to the cells from the damage caused byunstable molecules known as free radicals and they are able to slow or preventthe oxidation of other molecules.
Stabilization of free radicals occurs throughthe interaction with antioxidants and so prevents some of the damage freeradicals might produce such as cancer (Eraal, 2003). Examples of antioxidantsinclude beta-carotene, lycopene, vitamins C, E, A falvonoids, lipoic acid andglutathione. Oxidation is a chemical reaction that transfers electrons from asubstance to an oxidizing agent and can produce free radicals, which startchain reactions that damage cells. Antioxidants terminate these chain reactionsby removing free radical intermediates and inhibit other oxidation reactions bybeing oxidized (Ultraa, 2015). Cell damage caused by free radicals appears tobe a major contributor to aging and to degenerative diseases of aging such asparkinsonism, cancer, cardiovascular disease, cataracts, immune system decline,and brain dysfunction (Eraal, 2003). Overall, free radicals have beenimplicated in the pathogenesis of at least 50 diseases and so free radicalformation is controlled naturally by various beneficial compounds known asantioxidants. Once the availability of antioxidants is limited damage canbecome cumulative and debilitating (Erall, 2003).
Free radicals areelectrically charged molecules, so they have an unpaired electron, which causesthem to seek out and capture electrons from other substances in order toneutralize themselves. Although the initial attack causes the free radical tobecome neutralized, another free radical is formed in the process, causing achain reaction to occur and until produced free radicals are deactivated,thousands of free radical reactions can occur within seconds of the initialreaction making antioxidants able for stabilizing, or deactivating, freeradicals before they attack cells (Valko, 2015). Antioxidants are absolutelycritical substance in maintaining optimal cellular and systemic health andwell-being for humans.
Mechanism of action of antioxidant To defenseagainst the excessive production of free radical, the body has built protectivesystems and mechanisms against their toxic effects. Protection of the body’scells is organized on three levels:(a) Systemspreventing free radical FR formation, such as inhibitors of enzymes catalyzingfree radical formation. These enzymes may include xanthine oxidase producingsuperoxide and can be inhibited by allopurinol, chelating agents trapping ionsof transition metals and eliminating their catalytic activity during theproduction of free radical (Valko, 2015). (b) Whenthese initial protective systems are not enough and FR or RM have already beenformed, scavengers and trappers of FR becomes activated and eliminate the highreactivity of FR by turning them into non radical and nontoxic metabolites.
These compounds are generally called antioxidants and they prevent the oxidationof biologically important molecules by FR or RM (Valko, 2015). (c) Ifprotection fails at the above systems, then repair systems recognize impairedmolecules and decompose them, for instance, as in the case of lipases atoxidatively damaged lipids, proteinases at oxidatively modified proteins, orDNA repair systems at modified DNA bases (Eraal, 2003). 2.3.6.
B.Classification of antioxidantsFirst, primaryor natural antioxidantsThey arethe chain breaking antioxidants which react with lipid radicals and convertthem into more stable and highly reactive products. According to Ultra (2015), theyare mainly phenolic in structures and include the following types: (1)Antioxidants minerals – they called co factor of antioxidants enzymes and theirabsence will definitely affect metabolism of many large molecules such ascarbohydrates that include selenium, copper, iron, zinc and manganese.(2) Anti-oxidantsvitamins – It is needed for most body metabolic functions and include-vitaminC, vitamin E, vitamin B. (3)Phytochemicals – These are phenolic compounds that are neither vitamins norminerals and include flavonoids that are phenolic compounds which give the vegetablesand fruits their colours. Some examples of phenolic compounds found asphytochemical antioxidant: catechins, carotenoids and also herbs and spices-sourceinclude Diterpene, thyme, clove, black pepper, nutmeg, ginger, rosmariquinone, garlic,curcuma and their derivatives.
Second, secondaryor synthetic antioxidantsAs (Eraal,2003) Shows synthetic are phenolic compounds that perform the function of attackingfree radicals and stopping the chain reactions, these phenolic compoundsinclude:i.Butylated hydroxyl anisole (BHA).ii.Butylated hydroxyrotoluene (BHT).iii.
Propylgallate (PG) and metal chelating agent (EDTA).iv.Tertiary butyl hydroquinone (TBHQ).v.
Nor di-hydroguaretic acid (NDGA).2.3.6.
C.Antioxidants Protection:To protectthe cells and organ systems of the body against reactive oxygen species, humanshave synthesized a highly sophisticated and complex antioxidant protectionsystem. It involves a variety of components, both endogenous and exogenous inorigin, their function are to neutralize free radicals and they include:DietaryAntioxidantsVitamin C,vitamin E, and beta carotene are among the most widely used dietaryantioxidants. Vitamin C is considered the most important water-solubleantioxidant present in the extracellular fluids and able to regenerate vitaminE. Also, it is capable of neutralizing ROS in the aqueous phase before lipidperoxidation is initiated (Spenceer, 2010). Vitamin E, a major lipid-solubleantioxidant, is the most effective chain-breaking antioxidant within the cellmembrane in which it protects membrane fatty acids from lipid peroxidation (Spenceer,2010).
Betacarotene and other carotenoids are also consideredto provide antioxidant protection to lipid-rich tissues, so they need a highfat diet as well as for vitamin E absorption. The major sources of vitamin Cand carotenoids are fruits and vegetables, while major sources of vitamin E arewhole grains and high quality, properly extracted and protected vegetable oils (Spenceer,2010). .PhytonutrientsA number ofother dietary antioxidant substances exist other than the traditional vitaminsdiscussed above and called “Phytonutrients,” or “phytochemicals,” are becomingincreasingly known for their antioxidant protection activity. Phenoliccompounds such as flavonoids are being the most widely distributed among plantsand they account for approximately 3,000 substances (Spenceer, 2010).
Inplants, flavonoids serve as protectors against a wide variety of environmentalstresses while, in humans, flavonoids appear to function as “biological modifiers.”Flavonoids have many actions like antiallergenic, anti-viral, anti-inflammatory,anti-aging, and anti-carcinogenic activity (Spenceer, 2010). The significantand effective therapeutic uses of flavonoids can be largely accompanied totheir antioxidant properties. Also, they may exert protection against heartdisease through the inhibition of cyclooxygenase and lipoxygenase activities inplatelets and macrophages (Spenceer, 2010). The best way to ensure an adequateintake of phytonutrients is to eat a diet rich in a wide variety of freshfruits, vegetables or phytonutrient supplements (Spenceer, 2010). . EndogenousAntioxidantsIthas been suggested that an inadequate dietary intake of trace minerals such asselenium, iron, copper, zinc, and manganese may alter the effectiveness of endogenousantioxidant defense mechanisms.
The antioxidant enzymes are glutathioneperoxidase, Coenzyme Q10 (CoQ10), catalase, and superoxide dismutase (SOD)which metabolize oxidative toxic intermediates and require micronutrientcofactors (trace minerals) for significant catalytic activity (Spenceer, 2010).Glutathione, an important water-soluble antioxidant, is synthesized from theamino acids glycine, glutamate, and cysteine. Glutathione directlyquenches ROS such as lipid peroxides, and also plays a major role in xenobioticmetabolism (Spenceer, 2010). CoQ10 is a constituent of the mitochondrialelectron transport chain and enhance in ATP production. The completely reducedor oxidized form enables it to work in the electron transport chain as well as anantioxidant thus CoQ10 protect against loss of dopaminergic neurons and shows significantbeneficial effect on motor performance in the treatment of parkinsonism disease(Spenceer, 2010).