Oxygen Radical

 

Oxygen Radical

PKGhatak, MD

The word radical means extreme - very different from usual or traditional, and generally implies harmful. In biological systems radicals are any molecule containing unpaired electron and that makes them very reactive. When O2 receives an electron, the oxygen is said to have reduced when donates electron oxygen is oxidized. Radicals can damage the RNA and DNA and eventually  can kill a cell.

Basic science of Oxygen.

Oxygen is the most abundant element in our body, and accounts  75% of the body weight. Air contains 21% Oxygen. In the air the oxygen is present in three different forms -

1. Oxygen molecule( O2,) 

2. Oxygen atom( O1)

 3. Ozone (O3).

Oxygen is the 16^th element on the Periodic Table. In the nucleus of an atom it has 8 protons  and 8 electrons in the orbit. Oxygen is a diatom, meaning two atoms are bound together by a covalent double bond, and  is expressed as O2 (oxygen molecule). Oxygen is a primary reactant and the reaction gives out heat and it is called exothermic. 

Tissue respiration:

Mitochondria is the main metabolic center of the cells, more active the cell is the more chance of generating radicals. The next order of cellular active sites are endoplasmic reticulum, cytosol and cell membrane.

Mitochondrial enzymes transfer electron from food substrate in a series of enzymes and finally to the oxygen . Substrate –> Nicotinamide dehydrogenase –> Flavoproteins -> Cytochromes –> Oxygen.

Source of Oxygen Radical:

 Radicals are generated: Two sources - cellular and extracellular.

A. The cellular.  As stated above.

B. Non-cellular.  Air pollution, cigarette smoke, alcohol, Ozone, heavy metals, radiation, drugs, industrial solvents, pesticides and herbicides are the main sources.

Nitrogenous radicals:

Oxygen radicals react with Nitric oxide to form peroxynitrite. Peroxynitrite reacts with membrane lipids and from highly reactive lipid-peroxynitrite. . In the respiratory tract radical Nitric oxide produce bronchodilatation.

Protein oxidation, carbonyl and nitrotyrosine formation impair many enzymes, normal cell division, and cell growth. Lipid oxidation leads to cell death by ceramide formation via sphingomyelinase activation. NOX reacts with the Nucleic acid of the cells and damages DNA and RNA leading to premature aging and cell death. In phagocytes and neutrophils, ROS enhances bacterial digestion by increasing NO.

Free radicals and  Non-radical:

Derivatives of free radicals are less active but more harmful to the body and are called Oxidants. A chart below lists the Free radicals and non-radicals:

Oxygen Radicals and non-radical Oxidants.

Radical	Symbol	Oxidants	Symbol
Superoxide	O*-	Hydrogen peroxide	H2O2
Hydroxyl	*OH	Single Oxygen	1O2
Peroxyl	R00*	Ozone	O3
		Organic peroxide	ROOH
		Hypocaloric acid	HOCl
		Hypo bromic acid	HOBm

Nitrogenous Radicals and Oxidants.

Radical	Symbol	Oxidants	Symbol
Nitric acid	NO*	Peroxyl nitrogen	ONOO
Nitrogen dioxide	NO*2	Nitrosyl anions	NO
		Dinitro tetraoxide	N2O4
		Peroxyl nitrous acid	OHOOH
		Nitryl chloride	NO2Cl

Body's defense against radicals:

Human body employs Enzymes and Non-Enzymes to neutralize free radical and oxidants.

A list of enzymes act as antiradicals and antioxidants - Superoxide dismutase, Catalase, Glutathione peroxidase,  and Glutathione reductase.

The Non-enzyme antioxidants are Vitamin E, Vitamin C, Carotenoids,  Trace metals Selenium and Zinc, Flavonoids, Omega 3 and Omega 6 fatty acids, L-arginine, Coenzyme Q10, and Melatonin.

An example of Enzymatic action against Radical:

Glutathione reductase breaks down superoxide anion radical into Hydrogen peroxide (H2O2), then Glutathione peroxidase breaks up H2O2 into H20 and O2.

Non- enzyme antioxidants:

Vitamin E has many chimeric forms of which  Alpha tocopherol is most active against radicals. It prevents damage to the cells membrane by neutralizing Lipid peroxidase.

Omega 3 and Omega 5 Fatty acids.

These are long change polyunsaturated fatty acids. The omega 3 is cardioprotective  and prevents atheroma formation in coronary vessels.

Selenium. It conjugates with many enzymes and prevents cancer development.

Diseases caused by radical in humans:

Age related conditions- 

Loss of skin elasticity, wrinkles, cataracts, graying hairs and loss of hairs.

Neurogenerative diseases-

Parkinson's diseases and Huntington disease.

Autoimmune diseases-

Rheumatoid arthritis and various cancers.

Cardiovascular -

Coronary artery diseases.

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