Antioxidants
are substances that give protection to the cells from the damage caused by
unstable molecules known as free radicals and they are able to slow or prevent
the oxidation of other molecules. Stabilization of free radicals occurs through
the interaction with antioxidants and so prevents some of the damage free
radicals might produce such as cancer (Eraal, 2003). Examples of antioxidants
include beta-carotene, lycopene, vitamins C, E, A falvonoids, lipoic acid and
glutathione. Oxidation is a chemical reaction that transfers electrons from a
substance to an oxidizing agent and can produce free radicals, which start
chain reactions that damage cells. Antioxidants terminate these chain reactions
by removing free radical intermediates and inhibit other oxidation reactions by
being oxidized (Ultraa, 2015). Cell damage caused by free radicals appears to
be a major contributor to aging and to degenerative diseases of aging such as
parkinsonism, cancer, cardiovascular disease, cataracts, immune system decline,
and brain dysfunction (Eraal, 2003). Overall, free radicals have been
implicated in the pathogenesis of at least 50 diseases and so free radical
formation is controlled naturally by various beneficial compounds known as
antioxidants. Once the availability of antioxidants is limited damage can
become cumulative and debilitating (Erall, 2003). Free radicals are
electrically charged molecules, so they have an unpaired electron, which causes
them to seek out and capture electrons from other substances in order to
neutralize themselves. Although the initial attack causes the free radical to
become neutralized, another free radical is formed in the process, causing a
chain reaction to occur and until produced free radicals are deactivated,
thousands of free radical reactions can occur within seconds of the initial
reaction making antioxidants able for stabilizing, or deactivating, free
radicals before they attack cells (Valko, 2015). Antioxidants are absolutely
critical substance in maintaining optimal cellular and systemic health and
well-being for humans.

2.3.6.A.
Mechanism of action of antioxidant

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To defense
against the excessive production of free radical, the body has built protective
systems and mechanisms against their toxic effects. Protection of the body’s
cells is organized on three levels:

(a) Systems
preventing free radical FR formation, such as inhibitors of enzymes catalyzing
free radical formation. These enzymes may include xanthine oxidase producing
superoxide and can be inhibited by allopurinol, chelating agents trapping ions
of transition metals and eliminating their catalytic activity during the
production of free radical (Valko, 2015).

(b) When
these initial protective systems are not enough and FR or RM have already been
formed, scavengers and trappers of FR becomes activated and eliminate the high
reactivity of FR by turning them into non radical and nontoxic metabolites.
These compounds are generally called antioxidants and they prevent the oxidation
of biologically important molecules by FR or RM (Valko, 2015).

(c) If
protection fails at the above systems, then repair systems recognize impaired
molecules and decompose them, for instance, as in the case of lipases at
oxidatively damaged lipids, proteinases at oxidatively modified proteins, or
DNA repair systems at modified DNA bases (Eraal, 2003).

2.3.6. B.
Classification of antioxidants

First, primary
or natural antioxidants

They are
the chain breaking antioxidants which react with lipid radicals and convert
them into more stable and highly reactive products. According to Ultra (2015), they
are mainly phenolic in structures and include the following types:

(1)
Antioxidants minerals – they called co factor of antioxidants enzymes and their
absence will definitely affect metabolism of many large molecules such as
carbohydrates that include selenium, copper, iron, zinc and manganese.

(2) Anti-oxidants
vitamins – It is needed for most body metabolic functions and include-vitamin
C, vitamin E, vitamin B.

(3)
Phytochemicals – These are phenolic compounds that are neither vitamins nor
minerals and include flavonoids that are phenolic compounds which give the vegetables
and fruits their colours. Some examples of phenolic compounds found as
phytochemical antioxidant: catechins, carotenoids and also herbs and spices-source
include Diterpene, thyme, clove, black pepper, nutmeg, ginger, rosmariquinone, garlic,
curcuma and their derivatives.

Second, secondary
or synthetic antioxidants

As (Eraal,
2003) Shows synthetic are phenolic compounds that perform the function of attacking
free radicals and stopping the chain reactions, these phenolic compounds
include:

i.
Butylated hydroxyl anisole (BHA).

ii.
Butylated hydroxyrotoluene (BHT).

iii. Propyl
gallate (PG) and metal chelating agent (EDTA).

iv.
Tertiary butyl hydroquinone (TBHQ).

v. Nor di-hydro
guaretic acid (NDGA).

2.3.6. C.
Antioxidants Protection:

To protect
the cells and organ systems of the body against reactive oxygen species, humans
have synthesized a highly sophisticated and complex antioxidant protection
system. It involves a variety of components, both endogenous and exogenous in
origin, their function are to neutralize free radicals and they include:

Dietary
Antioxidants

Vitamin C,
vitamin E, and beta carotene are among the most widely used dietary
antioxidants. Vitamin C is considered the most important water-soluble
antioxidant present in the extracellular fluids and able to regenerate vitamin
E. Also, it is capable of neutralizing ROS in the aqueous phase before lipid
peroxidation is initiated (Spenceer, 2010). Vitamin E, a major lipid-soluble
antioxidant, is the most effective chain-breaking antioxidant within the cell
membrane in which it protects membrane fatty acids from lipid peroxidation (Spenceer,
2010).

Beta
carotene and other carotenoids are also considered
to provide antioxidant protection to lipid-rich tissues, so they need a high
fat diet as well as for vitamin E absorption. The major sources of vitamin C
and carotenoids are fruits and vegetables, while major sources of vitamin E are
whole grains and high quality, properly extracted and protected vegetable oils (Spenceer,
2010).  .

Phytonutrients

A number of
other dietary antioxidant substances exist other than the traditional vitamins
discussed above and called “Phytonutrients,” or “phytochemicals,” are becoming
increasingly known for their antioxidant protection activity. Phenolic
compounds such as flavonoids are being the most widely distributed among plants
and they account for approximately 3,000 substances (Spenceer, 2010). In
plants, flavonoids serve as protectors against a wide variety of environmental
stresses 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 significant
and effective therapeutic uses of flavonoids can be largely accompanied to
their antioxidant properties. Also, they may exert protection against heart
disease through the inhibition of cyclooxygenase and lipoxygenase activities in
platelets and macrophages (Spenceer, 2010). The best way to ensure an adequate
intake of phytonutrients is to eat a diet rich in a wide variety of fresh
fruits, vegetables or phytonutrient supplements (Spenceer, 2010).  .

Endogenous
Antioxidants

It
has been suggested that an inadequate dietary intake of trace minerals such as
selenium, iron, copper, zinc, and manganese may alter the effectiveness of endogenous
antioxidant defense mechanisms. The antioxidant enzymes are glutathione
peroxidase, Coenzyme Q10 (CoQ10), catalase, and superoxide dismutase (SOD)
which metabolize oxidative toxic intermediates and require micronutrient
cofactors (trace minerals) for significant catalytic activity (Spenceer, 2010).
Glutathione, an important water-soluble antioxidant, is synthesized from the
amino acids glycine, glutamate, and cysteine. Glutathione directly
quenches ROS such as lipid peroxides, and also plays a major role in xenobiotic
metabolism (Spenceer, 2010). CoQ10 is a constituent of the mitochondrial
electron transport chain and enhance in ATP production. The completely reduced
or oxidized form enables it to work in the electron transport chain as well as an
antioxidant thus CoQ10 protect against loss of dopaminergic neurons and shows significant
beneficial effect on motor performance in the treatment of parkinsonism disease
(Spenceer, 2010).