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Common Types of Free Radicals That Cause Oxidation and Cytotoxicity

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By Kyle J. Norton


Free radicals are atoms, molecules, or ions with unpaired electrons through chemical bonds with other atoms or molecules during a chemical reaction. As oxidants or reductants, they can donate or accept an electron from other molecules to exhibit chain and domino’s effects.

They may have positive, negative or zero charge. 


The unpaired electrons cause radicals to be highly chemically reactive in the human body, leading to aging and cancers.

However, injection of free radicals into cancer cells may induce cells death and inhibit tumor proliferation.

These results suggested that free radicals have a duo function in mediated cellular processes. On one hand, they cause alternation of DNA of healthy cells into cancerous cells. On the other hand, free radical can cause apoptosis of cancer cells through cytotoxicity(1).

Some researchers went even further to suggest that free radical such as H2O2 signaling pathway plays an essential role in creation of a bridge between insulin receptor and mitochondrial function in neurons(1)


And, over expression of antioxidant caused by intake of supplementation  can also be dangerous to signaling role in cells(2) and increase risk motility(3). For example, integral mitochondrial Manganese superoxide dismutase µMnSOD) protein possesses peroxidase activity when the enzyme is over expressed in mitochondria(2).



Most common Types of Free radical include
1. Hydroxyl radical (OH•)
The hydroxyl radical, is the neutral form of the hydroxide ion (OH–). It is produced from the decomposition of hydroperoxides (ROOH) by the reaction of an elevation in energy level above an arbitrary baseline energy state molecular oxygen with water.
The hydroxyl radical is highly reactive and has a very short in vivo half-life of approx. 10−9 s This makes it a very dangerous compound to the organism. Hydroxyl radical cannot be eliminated by an enzymatic reaction and can damage virtually all types of macromolecules: carbohydrates, nucleic acids (mutations), lipids (lipid peroxidation) and amino acids, that makes it a very danger compound to shorten the life span of human being.

2. Superoxide anion radical (O2–•)
A superoxide anion is a compound that possesses an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge with the chemical formula O2− with one unpaired electron, leading to the generating of superoxide anion free radical.
Mutations in the gene coding for the NADPH oxidase cause immune deficiency chronic granulomatous disease, leading to extreme susceptibility to infection and pathogenesis of many diseases, including aging.

3. Singlet oxygen
Singlet oxygen is the common name used for the diamagnetic form of molecular oxygen (O2), which is less stable than the normal triplet oxygen. In biological study, species, Singlet oxygen causes oxidation of LDLcholesterol and resultant cardiovascular effects.

Since singlet oxygen with activation by light can produce severe photosensitivity of skin, leading to skin defects.

4. Hydrogen peroxide
Hydrogen peroxide (H2O2) is the simplest peroxide, a clear liquid, slightly more viscous than water, that appears colorless in dilute solution. 


It is considered a highly reactive oxygen species because of its strong oxidizing capacity.

A study published in Nature found that hydrogen peroxide plays a role in the immune system by signaling the white blood cells to converge on the site of damage. The process leads to white blood cells did not accumulate at the site of damage, but somewhere else if the gene in production of hydrogen peroxide is altered, causing higher levels of hydrogen peroxide and white blood cells in their lungs accumulation in the lung than healthy people.

5. Lipid peroxyl free radical
Lipid peroxidation is a process in which free radicals steal electrons from the lipids in cell membranes, most often affecting polyunsaturated fatty acids, resulting in damaging to the cell membrane, which consists mainly of lipids, because of chain reaction after initial oxidating by producing even more lipid peroxyl free radicals if not bought under controlled fast enough.

6. Nitric oxide
Nitric oxide is a chemical compound with chemical formula NO. Even though low levels of NO production are important in protecting liver from ischemic damage and contribute to proper smooth muscle contraction and growth, but its free radical and toxic nature can cause DNA damage and inflammation.

7. Alkoxyl radical
Alkoxyl radical which is an alkyl (carbon and hydrogen chain) group singular bonded to oxygen can result in cellular damage caused by oxyfluorfen, a herbicide.

8. Peroxynitrite
Peroxynitrite is the anion with the formula ONOO−reacted quikly with carbon dioxide, leading to forming of carbonate and nitrogen dioxide radicals.


If the two radicals do not recombine to form carbon dioxide and nitrate, they can cause peroxynitrite-related cellular damage.



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Kyle J. Norton
Health article writer and researcher; Over 10.000 articles and research papers have been written and published on line, including world wide health, ezine articles, article base, healthblogs, selfgrowth, best before it’s news, the karate GB daily, etc.,.
Named TOP 50 MEDICAL ESSAYS FOR ARTISTS & AUTHORS TO READ by Named 50 of the best health Tweeters Canada – Huffington Post
Nominated for shorty award over last 4 years
Some articles have been used as references in medical research, such as international journal Pharma and Bio science, ISSN 0975-6299.
(1) Recognition of Functional Roles of Free Radicals by István Bókkon(PMC)

(2) The peroxidase activity of mitochondrial superoxide dismutase. Free Radic Biol. by Ansenberger-Fricano K, Silva Ganini DD, Mao M, Chatterjee S, Dallas S, Mason RP, Stadler K, Santos JH, Bonini MG(PubMed)

(3)  The neglected significance of “antioxidative stress”.by Poljsak B, Milisav I (PubMed)

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