![]() #Ho cosmic view 108 freeSoon thereafter Denham Harman, in 1956, proposed the “free radical theory of aging”, which states that free radicals play a central role in the aging process. ![]() 1954 confirmed the presence of free radicals in biological materials. In the same year, the electron paramagnetic resonance (EPR) studies by Commoner et al. Later in 1954, Gershman proposed “free radical theory of oxygen toxicity”, according to which, the toxicity of oxygen is due to its ability to form free radicals. For the first time in 1900, Moses Gomberg, Professor of Chemistry at the University of Michigan, speculated the existence of an organic free radical, triphenyl methyl radical (Ph3C In recent years there is an ever-increasing curiosity in studying the role of free radicals in biology, because of their pivotal role in various physiological conditions as well as their involvement in a diverse range of diseases. This review deals with chemistry, formation and sources, and molecular targets of free radicals and it provides a brief overview on the pathogenesis of various diseased conditions caused by ROS/RNS. The free radicals induced oxidative stress has been reported to be involved in several diseased conditions such as diabetes mellitus, neurodegenerative disorders (Parkinson’s disease-PD, Alzheimer’s disease-AD and Multiple sclerosis-MS), cardiovascular diseases (atherosclerosis and hypertension), respiratory diseases (asthma), cataract development, rheumatoid arthritis and in various cancers (colorectal, prostate, breast, lung, bladder cancers). Free radicals can adversely affect various important classes of biological molecules such as nucleic acids, lipids, and proteins, thereby altering the normal redox status leading to increased oxidative stress. The free radicals, both the reactive oxygen species (ROS) and reactive nitrogen species (RNS), are derived from both endogenous sources (mitochondria, peroxisomes, endoplasmic reticulum, phagocytic cells etc.) and exogenous sources (pollution, alcohol, tobacco smoke, heavy metals, transition metals, industrial solvents, pesticides, certain drugs like halothane, paracetamol, and radiation). Free radicals and other oxidants have gained importance in the field of biology due to their central role in various physiological conditions as well as their implication in a diverse range of diseases.
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