Properties of radicals pdf

Upon oxidative stress, p66Shc translocates to mitochondrial intermembrane space, where it associates with cytochrome-c, thus inducing ROS generation [ 65 ]. In peroxisomes the respiratory pathway involves the transfer of electrons from various metabolites to the oxygen leads to H 2 O 2 formation [ 66 ], but is not coupled to oxidative phosphorylation to produce ATP instead free energy is released in the form of heat. The enzymes of endoplasmic reticulum such as cytochrome p and b5 enzymes and diamine oxidase contribute to the formation of ROS [ 68 ].

Another important thiol oxidase enzyme, Erop1p catalyses the transfer of electrons from dithiols to molecular oxygen results in the formation of H 2 O 2 [ 69 ]. The other endogenous sources of ROS include prostaglandin synthesis, auto-oxidation of adrenalin, phagocytic cells, reduced riboflavin, FMNH 2 , FADH 2 , cytochrome P , immune cell activation, inflammation, mental stress, excessive exercise, infection, cancer, aging, ischemia etc. On the other hand, ROS are also produced in the biological systems by various exogenous sources shown in Table 3 [ 10 ].

Since these free radicals are highly reactive, they can damage all the three important classes of biological molecules including nucleic acids, proteins, and lipids [ 70 ].

The purine adducts formed by hydroxyl radical attack include, 8-hydroxydeoxy guanosine, 8-hydroxy deoxy adenosine, 2,6-diaminohydroxyformamidopyrimidine. The other free radical induced adducts of DNA bases include, 5-formyl uracil, cytosine glycol, 5,6-dihydrothyronine, 5-hydroxyhydro-cytosine, 5-hydroxyhydro uracil, uracil glycol, and alloxan [ 72 ]. The major free radical induced adducts of the sugar moiety in DNA include glycolic acid, 2-deoxytetrodialdose, erythrose, 2-deoxypentonic acid lactone, 2-deoxypentoseulose [ 72 ].

Conversely adenine can be paired with 8-nitroguanine during DNA synthesis resulting in a G-T transversions [ 76 ]. Accordingly 8-nitroguanine is a mutagenic DNA lesion involved in carcinogenesis.

The membrane lipids, especially the polyunsaturated fatty acid residues of phospholipids are more susceptible to oxidation by free radicals [ 83 ].

The lipid peroxidation is very important in vivo because of its involvement in various pathological conditions. The lipid peroxidation results in the loss of membrane functioning, for example, decreased fluidity, inactivation of membrane bound enzymes and receptors [ 84 ]. These lipid peroxyl radicals can further propagate the peroxidation process by abstracting hydrogen atoms from the other lipid molecules. Isoprostanes prostaglandin like substances produced by in the body by the esterfication of arachidonic acid constitute the important product of lipid peroxidation of arachidonic acid and are considered as the makers of the oxidative lipid damage [ 86 ].

ROS oxidize different amino acids present in the proteins, causing formation of protein—protein cross linkages, results in the denaturing and loss of functioning of proteins, loss of enzyme activity, loss of function of receptors and transport proteins [ 88 ].

The sulphur containing amino acids such as methionine and cysteine are more susceptible to oxidation by ROS and are converted to disulphides and methionine sulphoxide [ 89 , 90 ] respectively. However in biological systems, only these two oxidized forms of proteins can be converted back to their native form by two different enzymes namely disulfide reductases and methionine sulfoxide reductases respectively [ 91 — 94 ].

The ROS mediated attack of different amino acids results in the formation of different oxidation products such as, tryptophan forms nitrotryptophan, kynurenine, formylkynurinine; Phenylalanine forms 2,3-Dihydroxyphenylalanine, 2-, 3-, and 4-hydroxyphenylalanine; Tyrosine forms 3,4-Dihydroxyphenylalanine, tyrosine—tyrosine cross-linkages, Tyr-O-Tyr, cross-linked nitrotyrosine; Histidine forms 2-Oxohistidine, asparagine, aspartic acid; Arginine forms glutamic semialdehyde; Lysine forms a-Aminoadipic semialdehyde; Proline forms 2-Pyrrolidone, 4- and 5-hydroxyproline pyroglutamic acid, glutamic semialdehyde; threonine forms 2-Aminoketobutyric acid; leucine and valine residues form hydroxyl residues [ 91 ].

The ROS induced oxidative damage of amino acid residues such as lysine, proline, threonine and arginine yields carbonyl derivatives.

The presence of carbonyl groups in proteins has been considered as the marker of ROS mediated protein oxidation [ 95 ]. The other specific markers of protein oxidation are O-tyrosine a marker for hydroxyl radical and 3-nitrotyrosine a marker for RNS. Free radicals are involved in many pathological conditions such as many types of diabetes, neurodegenerative diseases, cardiovascular diseases CVDs , cancer, cataracts, asthma, rheumatoid arthritis, inflammation, burns, intestinal tract diseases, progerias and ischemic and post-ischemic pathologies.

The role of free radicals in some of the important disease conditions see Fig. Diabetes mellitus is heterogeneous group of chronic disorders characterized by enhanced blood glucose levels hyperglycemia resulting from defective insulin secretion in type I diabetes , resistance to insulin action in type II diabetes or both [ ].

The major symptoms are thirst, hunger, emaciation, and weakness, eventually lead to coma. DM is associated with the increased production of free radicals or decreased activity of the antioxidant systems, which leads to development of oxidative stress [ , ].

Under normal conditions, the electron transport chain complexes I and III are the key sites of superoxide production [ ]. However, the increased glucose levels in DM lead to increased glycolysis resulting in the augmented generation of pyruvate, thus raising the inner mitochondrial membrane potential upwards, followed by mitochondrial dysfunction and increased ROS production at electron transport chain complex II [ ]. The central nervous system CNS is particularly susceptible to the oxidants due to the presence of high lipid content, high consumption of oxygen, and low levels of antioxidant enzymes, for example, SOD is localized primarily in neurons, and GSH and GPx are localized in astrocytes [ ].

The regions of the brain such as hippocampus, substantia nigra, and the striatum are particularly susceptible to attack by free radicals [ , ]. The redox imbalance causes oxidative damage to these neurons and begins to alter the synthesis and metabolic pathway of dopamine leads to a further increase in oxidative stress because of quinine formation [ ].

The characteristic clinical symptoms of PD include, jerky movements, trembling of the hands and lips, and tremors [ ]. Dopamine, a neurotransmitter, can also act as a metal chelator, has the ability to generate H 2 O 2 via Fenton reaction.

Ceruloplasmin an extracellular ferroxidase required for regulating cellular iron load and transport oxidation results in the decreased ferroxidase activity followed by the accumulation of intracellular iron in neurons in PD. The other oxidative markers of protein damage such as protein carbonyls and 3-nitrotyrosine have been also observed in AD patients [ ]. MS is an autoimmune neuronal disorder characterized by impaired nerve conduction due to demylination of central nervous system CNS.

Apart from ROS generation, an impaired iron metabolism has been also considered to play a major role in pathogenesis of disease. It is one of the leading causes of death in humans. Free radicals cause different types of chemical changes in DNA, thus they could be mutagenic and involved in the etiology of cancer [ , ].

Cancer cells in particular, in comparison to normal cells, have higher levels of ROS and are more susceptible to mitochondrial dysfunction due to their higher metabolic rate [ ]. Cancer cells display elevated levels of oxidative stress due to activation of oncogenes and loss of tumor suppressors [ ]. ROS by altering the growth signals and gene expression cause continuous proliferation of cancer cells [ ]. ROS can damage DNA by inducing base modifications, deletions, strand breakage, chromosomal rearrangements and hyper- and hypo-methylation of DNA [ ].

Colorectal cancer CRC is the third most common cancer worldwide, accounting for , deaths per year [ ]. The gastrointestinal tract, particularly the colon and rectum, is continuously exposed to ROS originating from both endogenous and exogenous sources [ ]. Colon cancer originates from the epithelial cells that line the bowel. These cells divide rapidly and have a high metabolic rate [ ]. Since the intestinal mucosa is constantly confronting with diet and bacterial-derived oxidants and carcinogens, an unrestrained production of free radicals, redox imbalance, and DNA damage occurs, finally leads to an altered intestinal metabolic homeostasis with cancer as an endpoint [ ].

The human colorectal tumors have increased levels of nitric oxide NO [ ], 8-oxodG in DNA [ ], and lipid peroxides [ ]. Suzuki et al. Damage to the breast epithelium by ROS can lead to fibroblasts proliferation, hyperplasia of epithelium, cellular atypia and breast cancer [ ]. In majority of breast carcinomas the oxidative stress can be induced by the over expression of thymidine phosphorylase enzyme which catabolizes thymidine to thymine and 2-deoxy-D-ribosephosphate; the latter is a powerful reducing sugar that rapidly glycates proteins, generating oxygen radicals within the carcinoma cell [ ].

The ROS produced are responsible for the cellular proliferation of prostate cancer cells [ ]. The superoxide produced by NOX in prostate cancer cells facilitates cellular immortality through resistance to programmed cell death which results in cancer-promoting effect [ ]. Kumar et al. Veeramani et al. Lung cancer has been the most commonly diagnosed cancer and is the central cause of cancer death in men worldwide [ ]. Oxidative stress plays an important role in lung inflammation and lung cancer [ ].

Cigarette Smoking is the most crucial environmental risk factor in lung cancer etiology. Cigarette smoke particulate matter contains complex mixture of numerous carcinogens and stable ROS with very long half-lives. These ROS can damage the tissues resulting in progressive transformation of cells into the malignant form, which leads to increased frequency of mutations by the oxidative damage to DNA and, eventually leading to lung cancer [ ]. Smokers develop lung cancer a fold higher than non-smokers.

Bladder cancer is one of the most common cancers across the world, ranking the fourth and tenth in men and women, respectively [ ]. The most common risk factors for bladder cancer are cigarette smoking, exposure to industrial carcinogens aromatic amines , high levels of arsenic intake and diet [ ].

Oxidative stress critically contributes to the development of bladder cancer [ ]. Various lines of evidence reported an increased oxidative stress in patients with breast cancer [ , ]. Increased NO levels have been reported in bladder cancer patients [ ]. This NO stimulates matrix metalloproteinases MMPs , especially prolidase activity, which is involved in the terminal step of collagen degradation.

Significantly higher serum prolidase activities were reported in patients with bladder cancer than healthy controls [ ]. Therefore, increased prolidase activity may, in part, play a role in the pathogenesis of bladder cancer. Epidemiological studies reveal that low levels of antioxidants are associated with an increased risk of cancer. Significant increase in total oxidant status levels and decrease in total antioxidant status were observed in patients with bladder cancer [ ].

Significantly lower levels of plasma protein, total thiol groups and protein-bound thiol groups and elevated levels of Protein carbonyl groups were observed in bladder cancer patients than in healthy controls [ ]. Cardiovascular diseases are a class of pathologies involving the heart and blood vessels arteries, capillaries, and veins. They include cardiac diseases, vascular diseases of the brain and kidney, and peripheral arterial disease. Most of the people are dying due to CVDs compared to other diseases [ ].

Atherosclerosis is a condition commonly referred to as hardening of the arteries. Hyperlipidemia is a major risk factor for atherosclerosis. Elevated levels of oxidized low density lipoprotein LDL , glucose and free fatty acids are found in patients with atherosclerosis, T2D, and obesity [ ]. A profound imbalance of oxidants and antioxidants resulting in oxidative stress is observed in atherosclerosis.

In the vessel wall, endothelial cells, smooth muscle cells SMCs and macrophages are sources of free radicals [ ]. Endothelial dysfunction leads to increased endothelial permeability, up regulation of endothelial adhesion molecules, and inflammatory cell infiltration into the arterial wall [ ].

A substantial data has been shown that ROS are involved in endothelial injury, dysfunction, and lesion progression [ ]. The ROS dependent activation of the MMPs results in the degradation of intimal extracellular matrices and promotes smooth muscle cell migration [ ].

Cigarette smoking contain large amount of free radicals and may down-regulate key exogenous and endogenous antioixdants such as vitamin-D, carotenes, GPx and SOD and can lead to the dysfunction of monocytes and vascular smooth muscle cells [ ]. The proatherogenic agents such as oxidaised lipids, high glucose and cigarette constituents give rise to increased free radical production.

ONOO - reduces the bioavailability of NO leading to reduced endothelial vascular regulatory capacity and increased vascular dysfunction. Mitochondrial DNA damage is frequently observed in human atherosclerosis in both circulating and vessel wall cells [ ]. Oxidative stress mediated damaged mitochondrial DNA that escape autophagy induces a potent inflammatory response in atherosclerosis [ ].

Malfunction of DNA repair leads to defects in cell proliferation, apoptosis, and mitochondrial dysfunction, which in turn leads to ketosis, hyperlipidemia, and increased fat storage, promoting atherosclerosis and the metabolic syndrome [ ].

Persons with hypertension are at an increased risk for stroke, heart disease, kidney failure, and premature mortality. Free radical induced oxidative stress in part contributes to endothelial dysfunction and development of hypertension [ ]. A decrease in NO bioavailability and an increase in oxidative stress are present in human hypertension [ ]. Oxidation-induced impairment of NO also results in reduced opposition to the vasoconstrictive and hypertensive effects of angiotensin II.

Angiotensin II decreases NO bioavailability by promoting oxidative stress [ ]. It is the most common cause of the visual impairment affecting about 25 million people throughout the world, with the highest incidence occurring in developing countries [ , ]. It is characterized by opacity of the eye lens that reduces the amount of incoming light and results in visual impairment [ ]. Although a number of factors such as genetic factors, diabetes, aging, smoking, drugs, malnutrition, radiation x-rays and UV rays and alteration in both endocrine and enzymatic equilibrium have been implicated in cataract formation [ ], the free radical induced oxidative stress is considered as one of the major underlying mechanism of cataract disorder [ ].

Oxidation of proteins, lipids and DNA is seen in cataract lenses. Proteins lose sulfhydryl —SH groups become cross linked by non disulfide bonds, form high molecular aggregates and become insoluble [ ]. The oxidative stress induced lipid peroxidation toxic product such as HNE induce the fragmentation of lens proteins contributing towards the opacity of the lens [ ]. Oxidative stress has been shown to induce lens opacification both in experimental animal models and cultured lens systems [ ].

The cornea absorbs the light in the range of above nm results in the activation of tryptophan, to form N-formyl kynurenine, 3-hydroxy kynurenine and other photoproducts [ , ]. These photoproducts gradually accumulate in the centre of the lens are capable of generating singlet oxygen which induce protein damage leading to the loss of transparency [ ].

Cataract lens have an intracellular ionic imbalance i. Elevated levels of H 2 O 2 were observed in cataract lenses than normal lenses [ , ]. The disease is characterized by synovial and systemic inflammation with joint swelling, morning stiffness, destruction of articular tissues, joint deformities, fatigue, loss of appetite and weakness [ — ]. It is believed to be a T-lymphocyte driven disease in which a sudden influx of T-cells into the affected joints is followed by an increased number of macrophages and fibroblasts drawn the release of cytokines particularly IL-1 and TNF-alpha.

This cytokine release and subsequent migration is thought to be responsible for the chronic inflammation and characteristic changes in RA [ ]. Several lines of evidence suggest a role for oxidative stress in the pathogenesis of RA. Tissue injury in inflammation results in NO. The HOCl, produced by myeloperoxidase MPO in neutrophils, chlorinate the tyrosine residues to form 3-chlorotyrosine and damage the collagen, thus implicated in arthritogensis.

RA patients have increased plasma MPO concentrations [ ]. These oxidized LDL can be ingested in large quantities by monocytes results in the formation of Foam cells that are present in atherosclerotic plaques of vessles and have also been found in RA synovial fluid [ ]. Cigarette smoking is also considered as the most established environmental factor for RA.

Both particulate and gaseous phases of smoke contain high concentrations of free radicals that can interact with DNA and could cause genetic mutations and activation responsible for the development of RA [ ]. Free radicals are involved in various respiratory diseases such as respiratory distress syndrome, chronic obstructive pulmonary disease, chronic bronchitis, asthma [ ]. Asthma is the most common disorders of the airways of the lungs and is one of the major global health problems [ ].

It is characterized by chronic inflammation of the airways involving variable and recurrent airflow obstruction and bronchial hyperreactivity associated with airway remodelling [ , ].

Airway remodeling is a dynamic process involving mucous hypersecretion, collagen deposition, wall thickening, myocyte hypertrophy and hyperplasia, myofibroblast hyperplasia, vascular proliferation and alterations in airway elastic fibers, all of which culminate in persistent structural alterations of the airway [ ].

NO is endogenously produced in mammalian airways by NOS and is known to regulate many aspects of human asthma, including modulation of airway and vascular smooth muscle tone and the inflammation. Increased production of airway NO is a key factor in the development of airway hyperresponsiveness [ ].

ROS are produced both intracellularly by lung parenchymal cells and extracellularly by lung macrophages. Increased generation of oxidants have been reported in asthma patients than in healthy individuals [ ] which provoked airway inflammation by inducing diverse pro-inflammatory mediators including macrophages, neutrophils and eosinophils [ ].

Numerous studies have suggested that oxidative stress is caused by overproduction of various free radicals or by an insufficient antioxidant defense system in asthma and thus it contributes to the tissue damage which is induced by inflammatory cells [ ].

Elevated levels of oxidative stress markers such as H 2 O 2 , 8-isoprostane, nitric oxide, and carbon monoxide were reported in exhaled air of asthmatic patients [ ]. Increased MDA levels, and Protein carbonyls; decreased protein sulfhydryl and antioxidant activity were observed in plasma, bronchoalveolar lavage BAL fluid and exhaled air of asthamatic patients [ — ].

When there is an imbalance between the antioxidants and oxidants, the fee radicals accumulate leading to vigorous damage to macromolecules such as nucleic acids, proteins and lipids. This leads to tissue damage in various disease conditions such as diabetes mellitus, neurodegenerative diseases, cancer, cardiovascular diseases, cataracts, rheumatoid arthritis, asthma etc.

Alugoju Phaniendra, Email: moc. Dinesh Babu Jestadi, Email: moc. Latha Periyasamy, Email: ni. National Center for Biotechnology Information , U. Indian J Clin Biochem. Published online Jul Author information Article notes Copyright and License information Disclaimer.

Corresponding author. Received Oct 2; Accepted May This article has been cited by other articles in PMC. Abstract 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. History 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.

Introduction Free radicals are the products of normal cellular metabolism. Open in a separate window. Singlet Oxygen 1 O 2 It is an electronically high excited, meta-stable state of molecular oxygen and is a highly reactive toxic reactive oxygen species [ 35 ].

Ozone O 3 Ozone is a powerful oxidant may be produced in vivo by antibody catalyzed water oxidation pathway which plays an important role in inflammation [ 43 ]. Hypochlorous Acid HOCl It is a major oxidant produced by the activated neutrophils at the site of inflammation from hydrogen peroxide and chloride in a reaction catalyzed by the enzyme myeloperoxidase [ 49 ].

Peroxisomes In peroxisomes the respiratory pathway involves the transfer of electrons from various metabolites to the oxygen leads to H 2 O 2 formation [ 66 ], but is not coupled to oxidative phosphorylation to produce ATP instead free energy is released in the form of heat.

Table 2 ROS producing enzymes in peroxisomes. Endoplasmic Reticulum The enzymes of endoplasmic reticulum such as cytochrome p and b5 enzymes and diamine oxidase contribute to the formation of ROS [ 68 ]. Table 3 ROS generated from exogenous sources. Lipids The membrane lipids, especially the polyunsaturated fatty acid residues of phospholipids are more susceptible to oxidation by free radicals [ 83 ].

Free Radicals and Diseases Free radicals are involved in many pathological conditions such as many types of diabetes, neurodegenerative diseases, cardiovascular diseases CVDs , cancer, cataracts, asthma, rheumatoid arthritis, inflammation, burns, intestinal tract diseases, progerias and ischemic and post-ischemic pathologies.

Diabetes Mellitus Diabetes mellitus is heterogeneous group of chronic disorders characterized by enhanced blood glucose levels hyperglycemia resulting from defective insulin secretion in type I diabetes , resistance to insulin action in type II diabetes or both [ ].

Neurodegenrative Diseases The central nervous system CNS is particularly susceptible to the oxidants due to the presence of high lipid content, high consumption of oxygen, and low levels of antioxidant enzymes, for example, SOD is localized primarily in neurons, and GSH and GPx are localized in astrocytes [ ].

Multiple Sclerosis MS MS is an autoimmune neuronal disorder characterized by impaired nerve conduction due to demylination of central nervous system CNS. Cancer It is one of the leading causes of death in humans. Colorectal Cancer Colorectal cancer CRC is the third most common cancer worldwide, accounting for , deaths per year [ ]. Breast Cancer Damage to the breast epithelium by ROS can lead to fibroblasts proliferation, hyperplasia of epithelium, cellular atypia and breast cancer [ ].

Prostate Cancer The ROS produced are responsible for the cellular proliferation of prostate cancer cells [ ]. Lung Cancer Lung cancer has been the most commonly diagnosed cancer and is the central cause of cancer death in men worldwide [ ]. Bladder Cancer Bladder cancer is one of the most common cancers across the world, ranking the fourth and tenth in men and women, respectively [ ].

Cardiovascular Diseases CVDs Cardiovascular diseases are a class of pathologies involving the heart and blood vessels arteries, capillaries, and veins. Atherosclerosis Atherosclerosis is a condition commonly referred to as hardening of the arteries.

Cataract It is the most common cause of the visual impairment affecting about 25 million people throughout the world, with the highest incidence occurring in developing countries [ , ].

Asthma Free radicals are involved in various respiratory diseases such as respiratory distress syndrome, chronic obstructive pulmonary disease, chronic bronchitis, asthma [ ]. Contributor Information Alugoju Phaniendra, Email: moc. References 1. Gomberg M. An Incidence of Trivalent Carbon Trimethylphenyl. J Am Chem Soc. Oxygen poisoning and x-irradiation-A mechanism in common. Free radicals in biological materials.

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An introduction to free radical biochemistry. Br Med Bull. Generating disulfides enzymatically: reaction products and electron acceptors of the endoplasmic reticulum thiol oxidase Ero1p. Droge W. Review Free radicals in the physiological control of cell function. The square root of a perfect square is always a rational number. The square root of an even perfect square number is always even and the square root of an odd perfect square number is always is odd.

Square root of a negative number is considered to be an imaginary value. Problem 1 :. Simplify :. Solution :. Problem 2 :. Problem 3 :. Decompose and 68 into prime factors using synthetic division. Decompose , 12 and 27 into prime factors using synthetic division. Apart from the stuff given above , if you need any other stuff in math, please use our google custom search here. Kindly mail your feedback to v4formath gmail. We always appreciate your feedback. Read More.