Table of Contents  
REVIEW ARTICLE
Year : 2015  |  Volume : 7  |  Issue : 2  |  Page : 71-75

Role of antioxidants in facilitating the body functions: A review


Department of Oral Pathology and Microbiology, SIBAR Institute of Dental Sciences, Tekallapadu, Guntur, Andhra Pradesh, India

Date of Web Publication17-Nov-2015

Correspondence Address:
Dr. Kiran Kumar Kattappagari
Department of Oral Pathology and Microbiology, SIBAR Institute of Dental Sciences, Tekallapadu, Guntur, Andhra Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0975-8844.169745

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  Abstract 

The cell damage will cause the release of free radicals. These free radicals will play an important role in any bioactive process of the cells. Antioxidants are one of the important components which plays a critical role to maintain the cell functioning and integrity of the cells. Antioxidants play an important role against the reactive oxygen species and maintain the normal activity of the cell. Antioxidants are preventing the free radical configuration tissue damage by preventing the formation of radicals or promoting their breakdown of free radical species. The review article explains the role of antioxidants in normal healthy conditions as well as diseases.

Keywords: Antioxidants, health, diseases, free radical, reactive oxygen species


How to cite this article:
Kattappagari KK, Ravi Teja C S, Kommalapati RK, Poosarla C, Gontu SR, Reddy BV. Role of antioxidants in facilitating the body functions: A review. J Orofac Sci 2015;7:71-5

How to cite this URL:
Kattappagari KK, Ravi Teja C S, Kommalapati RK, Poosarla C, Gontu SR, Reddy BV. Role of antioxidants in facilitating the body functions: A review. J Orofac Sci [serial online] 2015 [cited 2017 Dec 11];7:71-5. Available from: http://www.jofs.in/text.asp?2015/7/2/71/169745


  Introduction Top


Aerobic life is connected with the continuous production of free radicals, particularly reactive oxygen species (ROS) or free radicals. This ROS is formed within the body. These ROS are the components formed normally in the body as a response to stress, but they damage healthy cells by attacking the cell membrane and damaging it. Free radicals are produced from exposure to various factors such as smoking, chewing tobacco, excessive exposure to sunlight and exposure to heavy metals for a long duration. [1]

Antioxidants are the components produced by the body to neutralize the effect of free radicals, but the effect will be limited to specific antioxidants. In human body oxidants and anti oxidate ratio will be maintained, any alteration in these oxidants and antioxidate will causes accumulation of ROS within the body, this process is called as oxidative stress. Oxidative stress has an important role in tissue damage and leads to pathological conditions such as cancer. [2] Oxidants and antioxidants may play a role in the last stages of cancer development. At this stage the levels of antioxidants play a very crucial role in prevention and progression of carcinogenesis. The human body has an inherent mechanism for protection against free radicals and other ROS called as antioxidant stress, it is defined as a "persistent imbalance between antioxidants and pro-oxidants in favor of the latter, resulting in irreversible cellular damage." They act by scavenging them, suppressing their formation or opposing their action [Figure 1] and [Figure 2]. Few literature shown that high level of pro-oxidants and deficiency of antioxidant levels are likely to play an important role in the progression of precancer to cancer. [3]
Figure 1: Sources of free radical helps in tissue repair mechanism[6]

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Figure 2: Sources of free radical helps in tissue repair mechanism[6]

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  Functions of Antioxidants Top


  • It reduces the free radicals.
  • It stimulates the growth of normal cells.
  • Protects cells against premature and abnormal ageing.
  • Helps fight age related molecular degeneration.
  • It supports the body immune system. [4]


Classifications

Broadly divided into two types depending upon enzymes:

  1. Enzymatic antioxidants.
  2. Nonenzymatic antioxidants.


Enzymatic antioxidants are again divided into primary and secondary antioxidants:

  1. Primary antioxidants: Superoxide dismutase, glutathione peroxidase.
  2. Secondary antioxidants: Glutathione reductase, glucose 6 - phosphate dehydrogenase.


Nonenzymatic antioxidants

  1. Minerals: Zinc, selenium.
  2. Vitamins: Vitamins A, C, E.
  3. Carotenoids: Beta carotene, lycopene, lutein, zeaxanthin.
  4. Low molecular weight antioxidants: Glutathione, uric acid.
  5. Organo sulfur compounds: Allium, allyl sulfide, indoles.
  6. Antioxidants cofactors: Coenzyme O 10.
  7. Polyphenols: Flavonoids, phenolic acid.


Under flavonoids

  1. Xanthones - Mangostin.
  2. Flavonoids - Quercein, kaempferol.
  3. Flavanols - Catechin, EGCG.
  4. Flavanones - Hesperetin.
  5. Flavones - Chrysin, isoflavanoids - genistein.
  6. Anthocyanidines - Cyanidin, pelagonidin.


Under phenolic acid

  1. Hydroxycinnamic acid: Ferulic, P-coumaric.
  2. Hydroxybenzoic acid: Gallic acid, ellagic acid.
  3. Gingerol, curcumin. [5]


The free radicals react in an indiscriminant manner leading to damage to the cells and its cellular components. An extensive variety of antioxidant defense is present in the body, both endo and exogenous. These endogenous and exogenous components protect the cellular components from free radical induced damage. This process can be divided into three phases.

  1. Antioxidant enzyme.
  2. Chain breaking antioxidants.
  3. Transition metal binding proteins. [7]


Antioxidant enzyme

These enzymes mainly act on the free radicals.

Catalase

It is the first antioxidant enzyme that comes into action. It has two functions, one is the conversion of hydrogen peroxide to water and oxygen.

Catalase - Fe (III) + H 2 O ---- Compound I (hydrogen peroxide)

Compound I + H 2 O ---- Catalase - Fe (III) + 2 H 2 O +O 2

Catalase consists of four protein subunits, each of which contains haem group and molecules of NADPH. [8] This enzyme is mainly present in the peroxisomes within the cell, along with catalase and some other enzymes such as hydrogen peroxide. These catalases which are present in the lysosomes are very easily ruptured during minor exploitation of cells. The greatest activity is present in liver and erythrocytes but some of the catalases are found in all tissues. [8]

Glutathione peroxidase and glutathione reductase

Glutathione peroxidase catalyzes the oxidation of glutathione at the cost of a hydroperoxidase, which might be hydrogen peroxide. ROOH + 2 GSH ---- GSSG + H 2 O + ROH.

Lipid hydroperoxides plays an important role in repairing damage cell resulting from lipid peroxidation. Selenium is required for activation glutathione peroxidase. If deficiency of selenium may causes decreases concentration of glutathione peroxidase. Glutathione peroxides mainly synthesis in the kidney. Within the tissue liver cells will have highest concentration, predominantly distribution in cytosol and mitochondria. The activity of this particular enzyme is reduction of glutathione. [9]

Superoxide dismutase

There are three forms of superoxide dismutase:

  1. Copper-zinc superoxide dismutase (Cu Zn SOD).
  2. Manganese superoxide dismutase (Mn SOD).
  3. Extra cellular superoxide dismutase (EC SOD).


Copper zinc superoxide dismutase

It is mainly seen within cell, especially cytoplasm and other organelles. Cu Zn SOD has a molecular weight of 32,000 KDa with two proteins subunits, each one containing a catalase, which gets activated by copper and zinc molecules. [10]

Manganese superoxide dismutase

Mn SOD is predominantly present in the mitochondria with a molecular weight of 40,000 KDa. The sequence of amino acids of Mn SOD is entirely different from Cu Zn SOD. [11]

Extra cellular superoxidase dismutase

EC SOD first described by Marklund in the year 1982. [12] EC SOD also contains copper and zinc, but is distinct from Cu Zn SOD. EC SOD is synthesized by only a few cell types such as fibroblasts and endothelial cells. EC SOD also expresses heparin sulfate on the cell surface. EC SOD is one of the major SOD traced in extracellular fluids and is released into the circulation from the surface of vascular endothelium. [13] EC SOD plays a role in the regulation of vascular tone, because an endothelial derived relaxing factor is neutralized in the plasma by superoxide. [14]

The chain breaking antioxidants

α topocherol, carotenoids, flavonoids, ubiquinol.

During any external stimulation these antioxidants allow free radicals to interact with other molecules and the secondary radicals generated that can then react with other target molecules to produce more free radicals within the cell. Chain reactions where lipid peroxidation occur, propagate until two radicals combine and form stable radicals which are neutralized by chain-breaking antioxidants. [15] These antioxidants are small molecules that can receive an electron from a radical and also donate an electron to the free radicals with the formation of stable energy. Unpaired electrons become disassociated and donate an electron to another molecule, preventing the further propagation of the chain reaction. This is known as the antioxidant phase or lipid phase. [16]

Lipid phase chain braking antioxidants: T

These are the scavenger radicals present in the membrane and lipid protein particles which prevent lipid peroxidation. Vitamin E is one of the lipid phase antioxidants. Vitamin E has very important role in stabilizing cell membranes. [17] Metabolism of Vitamin E is not well understood, but in cell membrane and lipoprotein it has an antioxidant function. Vitamin E is utilized to trap peroxyl radicals and to break the chain reaction of lipid peroxidation. Vitamin E cannot stop the initial formation of carbon-centered radical in a lipid-rich environment, but it reduces the formation of secondary radicals. α tocopherol is one of the important antioxidants which reacts quickly with the peroxyl radical to form a stable tocopherol, which has excess electrons across the chromanol ring. This resonance stabilized radical might subsequently react in one of the several ways. α tocopherol may react at the aqueous interface with ascorbate. [18] Carotenoids are lipid-soluble antioxidants based around an isoprenoid carbon skeleton. [19] These carotenoids are mainly present in the cell membrane and lipoproteins. They are efficient scavengers of singlet oxygen, [20] but it can also trap peroxyl radicals at low oxygen pressure with efficiency at least as great as that of α tocopherol. The carotenoids might play a role in preventing lipid peroxidation. [21] Other carotenoids are retinol (Vitamin A) which also has antioxidant properties, [22] flavonoids are polyphenolic antioxidants found in fruits, vegetables and beverages such as wine and fruit juice. [23] Over 4,000 flavonoids have been identified and they are divided into several groups according to their biochemical structure; flavonols (Quercetin and Kaempherol), flavonoids (catechins), flavones (apigenin) and isoflavonols (genistrin). The absorption, metabolism of flavonoids and epidemiological association might be a consequence of various other factors. Very few studies show the relationship between flavonoids with coronary heart diseases. [24] Flavonoids are very low in plasma, but some of the studies show that the intake of flavonoids might improve biochemical damage produced by oxidative stress. [25] Ubiquinol - 10 is a reduced form of coenzyme Q 10. It is an effective lipid soluble chain breaking antioxidant. [26] Ubiquinol - 10 will be lower concentration than alpha tocopherol. It can scavenge lipid peroxyl radicals with higher efficiency than alpha tocopherol and carotenoids. [27] Low density lipoprotein (LDL) which is present in the plasma, will expose the radicals generated in the lipid phase to ubiquinol 10 which is the first antioxidant that prevents the propagation of lipid peroxidation. [28]

Aqueous phase chain breaking antioxidants

Antioxidants will directly scavenge the radicals present in the aqueous compartment. Qualitatively the most important antioxidant of this type is Vitamin C (ascarbate). This ascorbate acts as a co factor for several enzyme catalyzing hydroxylation reactions, prolyl and lysyloxidase and in the synthesis of collagen. In addition to this there are some other biochemical pathways which depend upon the presence of ascorbate. [29] This ascorbic acid acts s a scavenger to superoxide, hydrogen peroxide, the hydroxyl radicals, hypochlorous acid and singlet oxygen. Ascorbic acid will change into dehydroascorbate which is relatively unstable and easily undergoes conversion into oxalic acid. This takes place in two mechanisms; seleno enzyme thioredoxin reductase reaction and a nonenzyme mediated reaction that causes reduction of glutathione. [30] Other aqueous phase chain breaking antioxidants are uric acid, plasma protein bound thiol group, and albumin reduced glutathione. [30] Most important free radicals in many diseases are oxygen derivatives such as superoxide and the hydroxyl radicals. The radical formation in the body occurs in several mechanisms [Table 1].
Table 1: Sources of food which have rich antioxidants

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Types of antioxidants

  • Vitamins A, C, E.
  • Anthocyanins.
  • Beta carotene.
  • Catechins.
  • Elligic acid.
  • Lycopene.
  • Selenium.


Food may contain other antioxidants and eating a wide variety of foods will help get full benefit of these antioxidants [Table 1]. [31]

Antioxidant protection system

Antioxidant protection system divided into three:

  1. Endogenous antioxidants.
  2. Dietary antioxidant.
  3. Metal binding proteins [Table 2]. [32]
Table 2: Varies antioxidant with protective mechanism

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Oxidative stress and human diseases

When stress or any other biochemical reaction increases the oxidative stress, damage to DNA occurs within the cell. Along with damage to DNA proteins, damage to the macromolecules has been implemented in the pathogenesis of abundant diseases including cancer and cardiac diseases [33] [Table 3]. There are few epidemiological and clinical intervention studies which suggest that antioxidants play a major role in preventing the cardiac diseases and some cancers. [34],[35]
Table 3: Various conditions which are associated with Oxidative damage

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  Conclusions Top


Free radical can damage the cell, it can be reversible or irreversible this will be depending up on external factors such as environmental or biochemical agents. The damage to the cell is reversible depending up on the levels of antioxidant stress. Antioxidants acts like first line of defense for protection of cells. Increased intake of antioxidants in the diet will help maintain cell integrity and also the normal physiological and biochemical functions of living system. The antioxidants help in neutralizing the free radicals and thus protect the cells.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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