From the Edited Volume

1. Introduction

During regular metabolic functions, highly reactive link called complimentary radicals are generated in the body; however, castle may additionally be introduced from the environment. These molecules are naturally unstable together they possess lone pair of electrons and hence end up being highly reactive. Castle react v cellular molecule such as proteins, lipids and also carbohydrates, and denature them. Together a result of this, an important cellular structures and also functions are lost and ultimately leading to various pathological conditions.

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Antioxidant enzyme are capable of stabilizing, or deactivating totally free radicals before they assault cellular components. They plot by reducing the energy of the totally free radicals or by offering up some of their electrons for its use, thereby bring about it to become stable. In addition, lock may also interrupt with the oxidizing chain reaction to minimization the damage caused by cost-free radicals. Because that the past decade, many studies have actually been specialized to the useful effects of antioxidant enzymes. It has been uncovered that a an extensive link exists between cost-free radicals and much more than sixty different health conditions, consisting of the aging process, cancer, diabetes, Alzheimer’s disease, strokes, love attacks and also atherosclerosis. By reduce exposure to totally free radicals and increasing the entry of antioxidant enzyme rich foods items or antioxidant enzyme supplements, our body’s potential to reducing the danger of complimentary radical connected health troubles is made more palpable <1>. Antioxidant enzymes are, therefore, absolutely an essential for preserving optimal cellular and systemic health and well being. This chapter reviews the pathophysiological function of few of the vital enzymes associated in totally free radical scavenging through their clinical applications.


2. Complimentary radicals and also their scavengers

Free radicals are electrically fee molecules, i.e., they have actually an unpaired electron, which reasons them to look for out and capture electron from other substances in order to neutralize themselves. Back the initial assault causes the totally free radical to end up being neutralized, another totally free radical is created in the process, leading to a chain reaction come occur. And until subsequent cost-free radicals room deactivated, thousands of cost-free radical reaction can take place within seconds of the early reaction.

The ability of the cell to make use of oxygen has detailed humans through the benefit of metabolizing fats, proteins, and carbohydrates because that energy; however, that does not come there is no cost. Oxygen is a highly reactive atom that is capable of becoming component of perhaps damaging molecules frequently called totally free radical or reactive oxygen varieties (ROS). About 5% or more of the inhaled O2 is converted to ROS such together superoxide, hydrogen peroxide, and also hydroxyl radicals through univalent palliation of O2.<2> for this reason cells under aerobic problem are always threatened with the insult of ROS, which but are properly taken care of through the highly powerful antioxidant equipment of the cabinet without any kind of untoward effect. This antioxidant system includes, antioxidant enzymes (e.g., SOD, GPx and reductase, CAT, etc.), nutrient-derived antioxidant (e.g., ascorbic acid, tocopherols and tocotrienols, carotenoids, glutathione and lipoic acid), metal binding proteins (e.g., ferritin, lactoferrin, albumin, and also ceruloplasmin) and also numerous various other antioxidant phytonutrients present in a wide selection of plant foods. Whenever the balance between ROS production and also antioxidant defence is lost, ‘oxidative stress’ results which through a series of occasions deregulates the cellular features leading to various pathological conditions.<3,4>

3. Reactive Oxygen Species

Reactive oxygen types (ROS) is a hatchet that incorporates all extremely reactive, oxygen containing molecules, including complimentary radicals. Species of ROS encompass the hydroxyl radical, the superoxide anion radical, hydrogen peroxide, singlet oxygen, nitric oxide radical, hypochlorite radical, and also various lipid peroxides. Every are capable of reacting with membrane lipids, nucleic acids, proteins and also enzymes, and also other little molecules, resulting in cellular damage. ROS are produced by a variety of pathways. Many of the oxidants developed by cells happen as:

A an effect of regular aerobic metabolism: approximately 90% the the oxygen made use of by the cell is spend by the mitochondrial electron move system.

Oxidative burst indigenous phagocytes (white blood cells) as part of the mechanism by which bacteria and viruses are killed, and also by which international proteins (antigens) are denatured.

Xenobiotic metabolism, i.e., detoxification of toxicity substances.

Consequently, things prefer vigorous exercise, which speeds up cellular metabolism; chronic inflammation, infections, and other illnesses; exposure come allergens and the presence of “leaky gut” syndrome; and also exposure to medicine or toxin such as cigarette smoke, pollution, pesticides, and also insecticides might all add to rise in the body’s oxidant load.

3.1. After-effects of generation the ROS

Although O2 have the right to behave choose a radical (a diradical) owing to presence of 2 unpaired electrons of parallel spin, it does no exhibit too much reactivity because of quantum mechanically restrictions. Its digital structure result in development of water by palliation with four electrons, i.e.:


In the sequential univalent procedure by which O2 experience reduction, number of reactive intermediates space formed, such together superoxide (O2-), hydrogen peroxide (H2O2), and the incredibly reactive hydroxy radical (°OH): jointly termed as the reactive oxygen species, the procedure can be stood for as:


For the production of O2-, typically the propensity of univalent reduction of O2 in respiring cells is restricted by cytochrome oxidase the the mitochondrial electron carry chain, which reduces O2 by four electrons to H2O there is no releasing either O2- or H2O2. However, O2- is invariably produced in respiring cells. This is due to the probable leak of solitary electron at the details site of the mitochondrial electron transfer chain, bring about the appropriate single electron reduction of oxygen come O2-. Once the electron transport chain is extremely reduced, and the respiratory price is dependent on ADP availability; leakage of electrons at the ubisemiquinone and also ubiquinone sites boosts so together to result in manufacturing of O2- and also H2O2.

For the manufacturing of H2O2, peroxisomal oxidases and also flavoprotein, as well as D-amino mountain oxidase, L-hydroxy acid oxidase, and fatty acyl oxidase participate. Cytochrome P-450, P-450 reductase and also cytochrome b-5 reductase in the absorbent reticulum under details conditions create O2-, and also H2O2. During their catalytic cycles, likewise, the catalytic bicycle of xanthine oxidase has arised as important source of O2- and also H2O2 in a variety of different organization injuries.

Finally, because that the manufacturing of ºOH, except during abnormal exposure to ionization radiation, generation the ºOH in vivo requires the existence of trace amount of H2O2 and also Fe2+ salt forms ºOH, together given adhering to Fenton reaction: <2>


Reactive oxygen species can attack critical cell components like polyunsaturated fat acids, proteins, and nucleic acids. To a lesser extent, carbohydrates are likewise the targets the ROS. These reactions can change intrinsic membrane properties favor fluidity, ion transport, ns of enzyme activity, protein synthesis, DNA damage; ultimately resulting in cell fatality (fig.01).<2>

Damage come cells led to by totally free radicals is believed to pat a central role in various person disorders favor rheumatoid arthritis, hemorrhagic shock, cardiovascular disease, cystic fibrosis, metabolic disorders, neurodegenerative disease, cradle ulcerogenesis, and also AIDS. Some particular examples of ROS mediated an illness are Alzheimer’s disease, Parkinson’s disease, oxidative modification of low-density lipoprotein in atherosclerosis, cancer, Down’s syndrome, and also ischemic reperfusion injury in various tissues consisting of heart, brain, kidney, liver, and also gastrointestinal tract. Amongst these, function of ROS in atherosclerosis and also ischemic injury in love and brain studied extensively. <2,3>


4. Antioxidant defense system

To safeguard the cells and also organ solution of the body versus reactive oxygen species (ROS), human beings have progressed a highly sophisticated and facility antioxidant security system. It requires a selection of components, both endogenous and also exogenous in origin, that duty interactively and synergistically come neutralize cost-free radicals (Table 1)<5> These materials include:

Endogenous Antioxidants


Thiols, e.g., glutathione, lipoic acid, N-acetyl cysteine

NADPH and also NADH

Ubiquinone (coenzyme Q10)

Uric acid


copper/zinc and also manganese-dependent superoxide dismutase

iron-dependent catalase

selenium-dependent glutathione peroxidase

Dietary Antioxidants

Vitamin C

Vitamin E

Beta carotene and other carotenoids and also oxycarotenoids, e.g., lycopene and also lutein

Polyphenols, e.g., flavonoids, flavones, flavonol’s, and Proanthocyanidins

Metal Binding Proteins

Albumin (copper)

Ceruloplasmin (copper)

Metallothionein (copper)

Ferritin (iron)

Myoglobin (iron)

Transferrin (iron)

Hydroxyl radicalVitamin C, Glutathione Flavonoids, Lipoic acid
Superoxide radicalVitamin C, Glutathione, Flavonoids, SOD
Hydrogen peroxideVitamin C, Glutathione, beta carotene, Vitamin-E, flavonoids, lipoic acid
Lipid peroxidesBeta-carotene, Vitamin-E, Ubiquinone, flavonoids, Glutathione peroxidase

Table 1.

Various ROS and also corresponding neutralizing antioxidants

Defence mechanisms against cost-free radical-induced oxidative damage include the following:

catalytic remove of complimentary radicals and also reactive types by factors such together CAT, SOD, GPx and thiol-specific antioxidants;

binding of protein (e.g., transferrin, metallothionein, haptoglobins, caeroplasmin) come pro-oxidant metal ions, such as iron and also copper;

protection versus macromolecular damage by proteins such as anxiety or warm shock proteins; and

Animal CAT space heme-containing enzyme that transform hydrogen peroxide (H2O2) to water and O2, and they are largely localized in subcellular organelles such together peroxisomes. Mitochondria and also the endoplasmic reticulum contain tiny CAT. Thus, intracellular H2O2 cannot be got rid of unless that diffuses to the peroxisomes <6>. GSH-Px gets rid of H2O2 by coupling that reduction with the oxidation that GSH. GSH-Px can additionally reduce various other peroxides, such as fatty acid hydro peroxides. This enzymes are current in the cytoplasm at millimolar concentrations and additionally present in the mitochondrial matrix. Most pet tissues save on computer both CAT and also GSH-Px activity.

SODs space metal-containing proteins the catalyze the removed of superoxide, generating water peroxide as a final product the the dismutation. 3 isoforms have actually been identified, and they all are existing in all eukaryotic cells. The copper-zinc SOD isoform is existing in the cytoplasm, nucleus, and plasma. Top top the various other hand, the manganese SOD isoform is primarily situated in mitochondria.

Dietary micronutrients also contribute to the antioxidant defence system. These incorporate β - carotene, vitamin C, and also vitamin E (the vitamin E family members comprises both tocopherols and tocotrienols, v α- tocopherol being the predominant and most active form). Water-soluble molecules, such as vitamin C, space potent radical scavenging agents in the aqueous phase of the cytoplasm, whereas lipid dissolve forms, such as vitamin E and also β- carotene, act as antioxidants within lipid environments. Selenium, copper, zinc, and manganese are additionally important elements, due to the fact that they act together cofactors for antioxidant enzymes. Selenium is considered specifically important in protecting the lipid environment versus oxidative injury, as it serves as a cofactor for GSH-Px <6–8>.

The many abundant to move antioxidant is the tripeptide, GSH(l-L-γ-glutamyl-l-cysteinyl glycine). GSH is synthesized in 2 steps. First, γ-glutamyl cysteine synthetase (γ-GCS) forms a γ-peptide bond in between glutamic acid and also cysteine, and then GSH synthetase adds glycine. GSH avoids the oxidation that protein thiol groups, either straight by reacting v reactive varieties or indirectly with glutathione transferases <6-8>.

5. Antioxidant enzymes in health

Antioxidants are of different species so the they can be easily accessible for action when and also where they space needed. Castle are organic (enzymes antioxidants and metal carrier proteins in the body), scavenging or chain breaking (like vitamin A, C, beta-carotene, etc.), pharmacologic antioxidants and others. Antioxidant compounds have to be up’’ (converted) in the procedure of neutralizing complimentary radicals. Therefore, one must continually produce more of the antioxidant in the human body or ingest them one of two people in diet or by supply mentation. The fix enzymes that deserve to regrate some antioxidants are SOD, GPx, glutathione reductase (GR), CAT and the other metalloenzymes.

SOD, CAT, and also GPx constitute a support supportive team that defence versus ROS. If SOD lowers the steady-state level that O2-, catalase and also peroxidases carry out the very same for H2O2.


Catalytic remove of ROS by antioxidant enzyme

Endogenous Antioxidants

In addition to diet antioxidants, the body depends on several endogenous defence instrument to aid protect against cost-free radical-induced cell damage. The antioxidant enzyme – GPx, heme peroxidase, CAT, and SOD – metabolize oxidative toxicity intermediates and require micronutrient cofactors such together selenium, iron, copper, zinc, and manganese because that optimum catalytic activity. Glutathione, an important water-soluble antioxidant, is synthesized from the amino mountain glycine, glutamate, and cysteine. Glutathione straight quenches ROS such together lipid peroxides, and likewise plays a significant role in xenobiotic metabolism. Exposure the the liver to xenobiotic substances root cause oxidative reactions with the increase regulation that detoxification enzymes, i.e., cytochrome P-450 mixed-function oxidase. Once an separation, personal, instance is exposed to high level of xenobiotics, an ext glutathione is utilized for link (a an essential step in the body’s detoxification process) making it less accessible to serve as an antioxidant. Research suggests that glutathione and vitamin C work interactively come quench totally free radicals and that they have a sparing result upon every other. Lipoic acid, yet another important endogenous antioxidant, categorized as a “thiol” or “biothiol,” is a sulphur-containing molecule the is known for its involvement in the reaction the catalyzes the oxidative decarboxylation the alpha-keto acids, such together pyruvate and also alphaketoglutarate, in the Krebs cycle. Lipoic acid and also its diminished form, dihydrolipoic acid (DHLA), are qualified of quenching totally free radicals in both lipid and aqueous domains and also as such has been dubbed a “universal antioxidant.” Lipoic acid may additionally exert that antioxidant impact by cheating through pro-oxidant metals. Study further says that lipoic acid has a sparing result on other antioxidants. Pet studies have demonstrated supplemental lipoic acid to protect against the symptom of vitamin E or vitamin C deficiency.

Superoxide dismutase

In 1967 biochemist Irwin Fridovitch of duke University and Joe McCord found the antioxidant enzyme SOD, which provides an important means of cellular defence against free radical damage. This breakthrough brought about medical researchers to begin to look serious at complimentary radicals. In most cases the process is automatically controlled and the number of cost-free radicals walk not end up being dangerously high. Fortunately, the body has, transparent the food of countless years of evaluation become accustomed to coping with cost-free radicals and also has evolved various schemes for doing this <3>.

SOD (EC is the antioxidant enzyme the catalysed the dismutation of the highly reactive superoxide anion come O2 and also to the much less reactive varieties H2O2. Peroxide have the right to be ruined by CAT or GPX reactions <9-11>.


In humans, there are three develops of SOD: cytosolic Cu/Zn-SOD, mitochondrial Mn-SOD, and also extracellular SOD (EC-SOD) <12,13>. SOD destroys O2- by successive oxidation and also reduction the the shift metal ion in ~ the active site in a Ping Pong form mechanism with remarkably high reaction rates <14>. All varieties of SOD bind single charged anions such together azide and also fluoride, yet distinct distinctions have been provided in the susceptibilities that Fe-, Mn- or Cu/Zn-SODs. Cu/Zn-SOD is competitively inhibited through N3-, CN- <15>, and also by F- <16>.

Mn-SOD is a homotetramer (96 kDa) comprise one manganese atom every subunit those cycles from Mn (III) come Mn (II) and back to Mn (III) throughout the two action dismutation the superoxide <17>. The respiratory tract chain in mitochondria is a significant source the oxygen radicals. Mn-SOD has actually been shown to be considerably induced and also depressed by cytokines, yet is only moderately influenced by oxidants <17>. Inactivation that recombinant human being mitochondrial Mn- SOD by peroxynitrite is resulted in by nitration that a certain tyrosine residue <18>.

The biological importance of Mn-SOD is demonstrated amongst others through the following observations: (a) inactivation of Mn-SOD genes in Escherichia coliincreases mutation frequency when grown under aerobic conditions <19>; (b) removed of the gene in Saccharomyces cerevisiaeincreases that sensitivity to oxygen <20>, (c) lack of expression in Mn-SOD knockout mice results in dilated cardiomyopathy and neonatal lethality <21>; (d) tumor necrosis element (TNF) selectively root cause Mn-SOD, but not Cu/Zn- SOD, CAT or GPX mRNA in assorted mouse tissues and cultured cell <22,23>; (e) transection of Mn- SOD cDNA into cultured cell rendered the cell resistant come parquet, TNF and Adriamycin-induced cytotoxicity, and radiation induced-neoplastic change <24>; f) expression of person Mn-SOD genes in transgenic mouse protects versus oxygen induced pulmonary injury and also Adriamycin-induced cardiac toxicity <25>.

Cu/Zn-SOD (SOD-1) is another type of enzyme that has been conserved throughout evolution. These enzymes have actually two identical subunits of around 32 kDa, back a monomeric structure deserve to be discovered in a high protein concentration indigenous E. Coli<26>. Every subunit consists of a steel cluster, the energetic site, made up by a copper and also a zinc atom connected by a histamine residue <27,28,29>.

Cu/Zn-SOD is believed to beat a significant role in the first line of antioxidant defence. Calves the were fed milk supplemented v 25 ppm Cu and also 100 ppm Zn confirmed a stronger immune solution and a greater SOD task <30>. Other recent reports including SOD knock-outs have revealed that Mn- SOD is important for life vice versa, Cu/Zn-SOD is not. Cu/Zn-SOD knock-out mice appear normal and also exhibit distinctions only after traumatic injury, whereas Mn-SOD knockouts execute not survive past 3 mainly of period <31>. Among various human being tissues Mn-SOD contents were approximately one-half as big as the Cu/Zn-SOD materials <31>. Extracellular superoxide dismutase (EC-SOD) is a secretory, tetrameric, copper and also zinc include glycoprotein; through a high affinity for certain glycosaminoglycans such together heparin and heparin sulphate. EC-SOD was uncovered in the interstitial spaces of tissues and also in extracellular fluids, accountancy for the bulk of the SOD activity in plasma, lymph, and synovial fluid. EC-SOD is not induced by its substrate or by other oxidants and also its regulation in mammalian tissues mostly occurs in a manner coordinated by cytokines, rather than together a an answer of individual cells to oxidants <32>.


This enzyme has actually been known to encourage the rejuvenation and also repair that cells, while reducing the damages brought about by complimentary radicals. SOD is discovered in ours skin and also it is crucial in order for our body to generate adequate amounts of skin-building cells referred to as fibroblasts. Among the common natural resources of SOD are cabbage, Brussels sprouts, wheat grass, barley grass and also broccoli. SOD theatre a far-ranging role in staying clear of the development of the Lou Gehrig’s disease, also known together Amyotrophic Lateral Sclerosis (ALS). This sort of disease can cause death because it influence the nerve cells in the spinal cord and also the brain. Except that, this enzyme is additionally used for therapy of inflammatory diseases, burn injuries, prostate problems, arthritis, corneal ulcer, and reversing the long term results of radiation and also smoke exposure. Additionally, if superoxide dismutase is made right into a lotion and also applied come the skin, it will protect against the formation of wrinkles. That will also heal wounds, alleviate the illustration of scars, and lighten skin pigmentation that has actually been caused by UV rays.

SOD is likewise known to help carry nitric oxide right into our hair follicles. This is useful for people who space experiencing premature hair loss as result of a genetic predisposition or cost-free radicals. Since this enzyme is a really potent antioxidant, SOD combats the results of complimentary radicals the are bring about hair follicles come die. Due to the fact that nitric oxide relaxes the blood vessels and also allows more blood to circulate come the hair follicles and also SOD helps to remove the totally free radicals, hair loss deserve to be prevented and even reversed. Taking dietary additionally that administer an adequate supply the Superoxide dismutase will be useful in maintaining all at once well being and also health because it protects our entire body from the harmful effects of free radicals.


Catalase (CAT) is one enzyme responsible for the degradation of hydrogen peroxide. It is a security enzyme present in almost all pet cells.

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The reaction that CAT occurs in two steps. A molecule the hydrogen peroxide oxidizes the heme come an oxyferryl species. A porphyrin cation radical is generated when one oxidation indistinguishable is gotten rid of from iron and also one from the porphyrin ring. A second hydrogen peroxide molecule acts as a reducing agent to regenerate the resting state enzyme, developing a molecule the oxygen and also water.