Introduction

Antioxidants are the opposite of free Radicals. They prevent the free radicals from damaging our cells and their constituents. Free radicals are continuously produced in the body as a part of metabolic process, external pollution, UV light, cigarette smoke etc. These free radicals can damage the cells alter their function and cause diseases. To protect from free radicals there is a system known as antioxidant defense mechanism.

Our body has several antioxidants of different types which act as scavengers of free radicles. These antioxidants may be enzymic or non enzymic antioxidants, that help the body from the deleterious effect of free radicles. They help the body to reduce oxidative stress and prevent the body from causing various chronic diseases.

In this article, you will learn about the antioxidants that are present in the body that help us neutralize free radicles. If free radicles are controlled, then the cells of our body perform their functions properly and offer several health benefits.

What are antioxidants?

Antioxidants are nutrients that can slow oxidative damage to our body’s tissues. Antioxidants can help prevent cancer and a range of other health problems. Our body has a few antioxidants of different types to protect us from oxidative damage.

They are substances which inhibit or decreases the oxidation of compounds. They donate an electron to the free radical which has an unpaired electron. On receiving the electron, the free radical gets neutralized and becomes inactive.

Examples .. Vitamin C is an important antioxidant. It easily donates an electron to the free radical. Another important example of an antioxidant is Vitamin E.

They are also found in fruits and vegetables, especially in the skin of fruits and vegetables. Some antioxidants, such as phytochemicals, are found in beverages such as wine and tea

Antioxidant defense system

Our body contains several antioxidants of different types and they take care of different types of free radicals produced in the body.  Antioxidants act as radical scavenger, hydrogen donor, electron donor, peroxide decomposer, singlet oxygen quencher, enzyme inhibitor, synergist, and metal-chelating agents. Both enzymatic and nonenzymatic antioxidants exist in the intracellular and extracellular environment to detoxify ROS.[Ref 1]

Mechanism of action of antioxidants

How do antioxidants manage to neutralize the free radicles? What is their mechanism? There are two principle mechanisms of action that have been proposed for antioxidants: [ref 2]

The first is a chain- breaking mechanism by which the primary antioxidant donates an electron to the free radical present in the systems.

The second mechanism involves removal of ROS/reactive nitrogen species initiators (secondary antioxidants) by quenching chain-initiating catalyst.

Antioxidants may exert their effect on biological systems by different mechanisms including electron donation, metal ion chelation, co-antioxidants, or by gene expression regulation. [Ref 3]

Types of Antioxidants

A variety of antioxidants are present in the body and they can be classified into two types:

1. Enzymatic antioxidants and
2. Non-enzymatic antioxidants

Enzymic antioxidants:

1. Superoxide dismutase;
2. Catalase
3. Gluthione peroxidase and
4. Gluthione Reductases

Non-enzymic antioxidants:

These are of two types: 

1. Nutritional antioxidants: Vitamin C, Vitamin E (alpha tocopherol), and beta carotene;; zinc copper, Mn and selenium
2. Endogenous: ceruloplasmin, UA, Transferrin, Bilirubin, Ferritin, Lipoic acid and Ubiquinone

Superoxide Dismutase: The Body’s First Line of Defense Against Free Radicals

Superoxide dismutase (SOD) is a family of enzymes that are essential for protecting cells from damage caused by free radicals. Free radicals are unstable molecules that can damage cells, leading to a variety of health problems. SOD enzymes help to neutralize free radicals by converting them into oxygen and hydrogen peroxide.

There are three major types of SOD enzymes: Cu/Zn-SOD, Fe-SOD, and Mn-SOD. Cu/Zn-SOD is the most common type of SOD enzyme and is found in the cytoplasm, mitochondria, and extracellular fluids. Fe-SOD is found mainly in chloroplasts, but it is also found in peroxisomes. Mn-SOD is found in mitochondria and peroxisomes.

In humans, there are three forms of SOD enzymes: SOD1, SOD2, and SOD3. SOD1 is located in the cytoplasm, SOD2 is located in the mitochondria, and SOD3 is extracellular. SOD1 and SOD3 contain copper and zinc, while SOD2 has manganese in its reactive center.

SOD enzymes play a critical role in protecting cells from damage caused by free radicals. They are essential for maintaining good health and preventing a variety of diseases.

Here are some additional facts about superoxide dismutase:

SOD enzymes are found in almost all aerobic cells.

SOD enzymes are thought to be one of the most important antioxidants in the body.

SOD enzymes can help to protect cells from damage caused by environmental pollutants, cigarette smoke, and radiation.

SOD enzymes may also play a role in preventing cancer and other diseases

Catalase: The Body’s Natural Defense Against Hydrogen Peroxide

Catalase is an enzyme found in nearly all living organisms that are exposed to oxygen. It helps to protect cells from damage caused by hydrogen peroxide, a harmful by-product of many normal metabolic processes.

Hydrogen peroxide is a reactive molecule that can damage cells by oxidizing proteins, lipids, and DNA. Catalase helps to neutralize hydrogen peroxide by catalyzing its decomposition into water and oxygen. This reaction occurs very quickly, and catalase is able to convert large amounts of hydrogen peroxide into harmless substances.

Catalase is found in all known animals, with particularly high concentrations occurring in the liver. The liver is a major site of hydrogen peroxide production, so it is important that the liver has a high level of catalase to protect itself from damage.

Catalase is also found in other organs, including the kidneys, lungs, and spleen. It is also found in some plants and bacteria.

Catalase is an important enzyme that helps to protect cells from damage caused by hydrogen peroxide. It is a vital part of the body’s natural defense system.

Here are some additional facts about catalase:

Catalase is a tetramer, meaning that it is made up of four protein subunits.

The active site of catalase contains four iron atoms that are arranged in a tetrahedral structure.

Catalase is a very efficient enzyme, and it can decompose hydrogen peroxide at a rate of millions of molecules per second.

Catalase is essential for life, and it is present in all known animals.

The Glutathione System: Your Body’s Natural Defense Against Oxidative Stress

The glutathione system is a network of enzymes and molecules that help to protect cells from damage caused by oxidative stress. Oxidative stress is a condition that occurs when there is an imbalance between the production of free radicals and the body’s ability to neutralize them. Free radicals are unstable molecules that can damage cells by oxidizing proteins, lipids, and DNA.

The glutathione system helps to neutralize free radicals by converting them into harmless substances. The system includes glutathione, glutathione reductase, glutathione peroxidases, and glutathione S-transferases.

Glutathione is a tripeptide that is made up of the amino acids cysteine, glycine, and glutamic acid. It is the most abundant antioxidant in the body, and it plays a role in many different cellular processes.

Glutathione reductase is an enzyme that helps to regenerate glutathione. It does this by reducing oxidized glutathione back to its active form.

The following is the structure of Glutathione reductase:

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Glutathione peroxidases are enzymes that help to break down hydrogen peroxide and organic hydroperoxides. Hydrogen peroxide is a free radical that can damage cells, and organic hydroperoxides are produced as a byproduct of many metabolic processes.

Glutathione S-transferases are enzymes that help to detoxify harmful substances. They do this by attaching glutathione to the harmful substances, making them less harmful and easier for the body to excrete.

The glutathione system is found in all living cells, and it is particularly important in the liver, where it helps to protect cells from damage caused by toxins and other harmful substances.

Here are some additional facts about the glutathione system:

The glutathione system is essential for maintaining good health.

Low levels of glutathione have been linked to a number of diseases, including cancer, heart disease, and neurodegenerative disorders.

There are a number of ways to boost glutathione levels, including eating a healthy diet, taking supplements, and reducing stress.

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Vitamin C as an Antioxidant in Human Biology

Vitamin C in humans must be ingested for survival. Vitamin C is an electron donor, and this property accounts for all its known functions. As an electron donor, vitamin C is a potent water-soluble antioxidant in humans.

Antioxidant effects of vitamin C have been demonstrated in many experiments in vitro. Human diseases such as atherosclerosis and cancer might occur in part from oxidant damage to tissues.

Vitamin C is a powerful antioxidant that can protect cells from damage caused by free radicals. It is classified as a nutritional antioxidant

Vitamin C can be oxidized by many different species, including:

1. Free radicals, such as superoxide, hydroxyl radical, and peroxyl radicals.
2. Reactive nitrogen species, such as nitric oxide and peroxynitrite.
3. Reactive halogen species, such as hypochlorous acid and nitrosamines.
4. Transition metal-mediated radicals, such as those generated by iron and copper.
5. When vitamin C is oxidized, it donates an electron to the free radical, thereby neutralizing it. This prevents the free radical from reacting with other molecules and causing damage.
6. Vitamin C is also involved in the regeneration of other antioxidants, such as alpha-tocopherol (Vitamin E). Alpha-tocopherol is a fat-soluble antioxidant that protects cell membranes from damage. When alpha-tocopherol is oxidized, it can be reduced back to its active form by vitamin C.

The antioxidant properties of vitamin C have been linked to a number of health benefits, including:

1. Reduced risk of chronic diseases, such as heart disease, stroke, and cancer.
2. Improved immune function.
3. Protection against oxidative stress, which can lead to premature aging and other health problems.

Good sources of vitamin C include citrus fruits, berries, tomatoes, broccoli, and potatoes. You can also get vitamin C from supplements.

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Vitamin E: An Antioxidant with Potential Health Benefits

Vitamin E is a fat-soluble vitamin with antioxidant properties. It is classified as a nutritional antioxidant. It is a chiral compound with eight stereoisomers, but only α-tocopherol is the most bioactive form in humans.

α-Tocopherol protects cell membranes from damage by free radicals. Free radicals are unstable molecules that can react with other molecules, causing damage to DNA, proteins, and lipids.

The antioxidant function of vitamin E mainly resides in the protection against lipid peroxidation. Lipid peroxidation is a process that can damage cell membranes and lead to a number of health problems, including cancer, heart disease, and stroke.

Vitamin E has been proposed for the prevention of a number of diseases, including colon, prostate, and breast cancer, cardiovascular disease, ischemia, cataract, arthritis, and certain neurological disorders. However, a recent trial found that daily α-tocopherol doses of 400 IU or more can increase the risk of death. In contrast, there is no increased risk of death with a dose of 200 IU per day or less.

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Beta Carotene a nutritional antioxidant:

Beta-carotene is a pigment found in plants that gives them their color. The name beta-carotene is derived from the Latin name for carrot. It gives yellow and orange fruits and vegetables their rich hues. Beta-carotene is also used to color foods such as margarine.

Beta-carotene is transformed into vitamin A (retinol) in the body. For clear eyesight and healthy eyes, a robust immune system, and healthy skin and mucous membranes, we require vitamin A. Vitamin A in large levels can be poisonous, but your body only makes as much of the vitamin from beta-carotene as is required. In light of this, beta-carotene is regarded as a secure source of vitamin A

Beta-carotene is an antioxidant. It protects the body from damaging molecules called free radicals. Free radicals damage cells through a process known as oxidation. Over time, this damage can lead to a number of chronic illnesses. There is good evidence that eating more antioxidants from foods helps boost your immune system, protect against free radicals, and may lower your risk of heart disease and cancer.

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Lycopene: An Antioxidant that Can Neutralize Free Radicals

Lycopene is a carotenoid, which is a type of pigment that gives fruits and vegetables their bright red color. It is also an antioxidant, which means that it can help protect cells from damage caused by free radicals.
Lycopene is one of the most powerful antioxidants known. It is more efficient at scavenging free radicals than other carotenoids, such as beta-carotene and alpha-carotene. Lycopene is also more soluble in fat than other carotenoids, which means that it can more easily enter and protect cell membranes.

There is a growing body of evidence that lycopene can help protect against a number of diseases, including cancer, heart disease, and stroke. Lycopene has also been shown to improve skin health and may help protect against age-related macular degeneration (AMD).
Good sources of lycopene include tomatoes, tomato products, watermelon, guava, and apricots. You can also get lycopene from supplements.[Ref 4]

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Glutathione

Glutathione is a cysteine-containing peptide found in mostforms of aerobic life.

It is not required in the diet and is instead synthesized in cells from its constituent amino acids.

Glutathione has antioxidant properties since the thiol group in its cysteine moiety is a reducing agent and can be reversibly oxidized and reduced.

In cells, glutathione is maintained in the reduced form by the enzyme glutathione reductase and in turn reduces other metabolites and enzyme systems as well as reacting directly with oxidants.

Due to its high concentration and central role in maintaining the cell’s redox state, glutathione is one of the most important cellular antioxidants

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Selenium as an Antioxidant

Selenium (Se) is an essential trace element that is important for human health. It is a component of several antioxidant enzymes, including glutathione peroxidase (GPx), thioredoxin reductase (TrxR), and iodothyronine deiodinases (IDD). These enzymes help protect cells from damage caused by free radicals.

Selenium deficiency can cause a number of health problems, including Keshan disease, a type of heart disease that is common in areas with low soil Se levels. Se deficiency can also impair the function of the immune system.

There is a growing body of evidence that Se can help protect against a number of diseases, including cancer, heart disease, and stroke. Se has also been shown to improve immune function and may help protect against age-related macular degeneration (AMD) [Ref 5]

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Metal Binding Proteins as Antioxidants:

Cerruloplasmin

1. Ferritin
2. Lactoferrin
3. Metallotheinein
4. Transferrin
5. Haemoglobin
6. Myoglobin

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Related Articles:

Free Radicals: Definition, Types of free radicals, their Structure and Impact! https://maintaincholesterol.com/blog/free-radicals/

The Dangerous Link Between Smoking and Nutrient Depletion: https://maintaincholesterol.com/blog/smoking-and-nutrient-depletion/

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References

1. Frie B, Stocker R, Ames BN. Antioxidant defences and lipid peroxidation in human blood plasma. https://pubmed.ncbi.nlm.nih.gov/3200852/
2. Rice-Evans CA, Diplock AT. Current status of antioxidant therapy. https://pubmed.ncbi.nlm.nih.gov/8359712/
3. Krinsky NI. Mechanism of action of biological antioxidants. https://pubmed.ncbi.nlm.nih.gov/1579590/
4. Lycopene as a Natural Antioxidant Used to Prevent Human Health: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7464847/
5. Selenium: its role as antioxidant in human health: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2698273/
6. Free radicals, antioxidants and functional foods: Impact on human health: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3249911/#ref3
7. How do free radicals affect the body? https://www.medicalnewstoday.com/articles/318652
8. Free Radicals, Antioxidants in Disease and Health https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3614697/
9. Antioxidants: https://www.slideshare.net/pharmacologyseminars/antioxidants-9122878

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