SEMINAR ON OXYGEN FREE RADICALS

RAJIV GANDHI UNIVERSUTY OF HEALTH SCIENCES, BANGALORE, KARNATAKA : 

RAJIV GANDHI UNIVERSUTY OF HEALTH SCIENCES, BANGALORE, KARNATAKA A SEMINAR ON OXYGEN FREE RADICALS AND THEIR SCAVENGERS PRESENTED BY: AAFTAB ANWAR M.PHARM PHARMACOLOGY

۩ Free Radicals….??? : 

۩ Free Radicals….??? Free radicals are organic molecules responsible for ageing, tissue damage, and possibly some diseases. These molecules are very unstable, therefore they look to bond with other molecules, destroying their vigor and perpetuating the detrimental process. Antioxidants, present in many foods, are molecules that prevent free radicals from harming healthy tissue.

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Free radical, radical (an atom or group of atoms with at least one unpaired electron. In the body it is usually an oxygen molecule that has lost an electron and will stabilize itself by stealing an electron from a nearby molecule. “In the body free radicals are high-energy particles that ricochet wildly and damage cells"

۩ FREE RADICAL FORMATION : : 

۩ FREE RADICAL FORMATION : Atoms are most stable in the ground state. An atom is considered to be "ground" when every electron in the outermost shell has a complimentary electron that spins in the opposite direction. By definition a free radical is any atom (e.g. oxygen, nitrogen) with at least one unpaired electron in the outermost shell, and is capable of independent existence. A free radical is easily formed when a covalent bond between entities is broken and one electron remains with each newly formed atom. Free radicals are highly reactive due to the presence of unpaired electron(s).

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Any free radical involving oxygen can be referred to as reactive oxygen species (ROS). Oxygen centered free radicals contain two unpaired electrons in the outer shell. When free radicals steal an electron from a surrounding compound or molecule a new free radical is formed in its place. In turn the newly formed radical then looks to return to its ground state by stealing electrons with antiparallel spins from cellular structures or molecules.

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Thus the chain reaction continues and can be "thousand of events long. The electron transport chain (ETC), which is found in the inner mitochondrial membrane, utilizes oxygen to generate energy in the form of adenosine triphosphate (ATP). Oxygen acts as the terminal electron acceptor within the ETC.

۩ TYPES OF FREE RADICALS : : 

۩ TYPES OF FREE RADICALS : The most common ROS include: the superoxide anion (O2-), the hydroxyl radical (OH ·), singlet oxygen (1O2 ), and hydrogen peroxide (H2O2)

1. Superoxide anion (O2-) : : 

1. Superoxide anion (O2-) : Superoxide anions are formed when oxygen (O2) acquires an additional electron, leaving the molecule with only one unpaired electron. Within the mitochondria O2- ·is continuously being formed

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Hydroxyl radicals are short-lived, but the most damaging radicals within the body. This type of free radical can be formed from O2- and H2O2 via the Harber-Weiss reaction. The interaction of copper or iron and H2O2 also produce OH · as first observed by Fenton. 2. HYDROXYL RADICAL (OH- .) :

3. HYDROGEN PEROXIDE (H2O2) : : 

3. HYDROGEN PEROXIDE (H2O2) : Hydrogen peroxide is produced in vivo by many reactions. Hydrogen peroxide is unique in that it can be converted to the highly damaging hydroxyl radical or be catalyzed and excreted harmlessly as water. Glutathione peroxidase is essential for the conversion of glutathione to oxidized glutathione, during which H2O2 is converted to water (2). If H2O2 is not converted into water 1O2 (singlet oxygen) is formed.

4. SINGLET OXYGEN (1O2) : : 

4. SINGLET OXYGEN (1O2) : Singlet oxygen is not a free radical, but can be formed during radical reactions and also cause further reactions. Singlet oxygen violates Hund's rule of electron filling in that it has eight outer electrons existing in pairs leaving one orbital of the same energy level empty. When oxygen is energetically excited one of the electrons can jump to empty orbital creating unpaired electrons. Singlet oxygen can then transfer the energy to a new molecule and act as a catalyst for free radical formation. The molecule can also interact with other molecules leading to the formation of a new free radical.

۩ PHYSIOLOGICAL EFFECTS : : 

۩ PHYSIOLOGICAL EFFECTS : Under normal conditions (at rest) the antioxidant defense system within the body can easily handle free radicals that are produced. During times of increased oxygen flux (i.e. exercise) free radical production may exceed that of removal ultimately resulting in lipid peroxidation. Free radicals have been implicated as playing a role in the - etiology of cardiovascular disease, cancer, Alzheimer's disease, and Parkinson's disease.

۩ IMPORTANCE OF FREE RADICALS : : 

۩ IMPORTANCE OF FREE RADICALS : Free radicals are naturally produced by some systems within the body and have beneficial effects that cannot be overlooked. The immune system is the main body system that utilizes free radicals. Foreign invaders or damaged tissue is marked with free radicals by the immune system. This allows for determination of which tissue need to be removed from the body. Because of this some question the need for antioxidant supplementation, as they believe supplementation can actually decrease the effectiveness of the immune system.

How Antioxidants May Prevent Against Free Radical Damage : : 

How Antioxidants May Prevent Against Free Radical Damage : The vitamins C and E, are thought to protect the body against the destructive effects of free radicals. Antioxidants neutralize free radicals by donating one of their own electrons, ending the electron-"stealing" reaction. The antioxidant nutrients themselves don't become free radicals by donating an electron because they are stable in either form. They act as scavengers, helping to prevent cell and tissue damage that could lead to cellular damage and disease.

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Vitamin E : The most abundant fat-soluble antioxidant in the body. One of the most efficient chain-breaking antioxidants available. Primary defender against oxidation. Primary defender against lipid peroxidation (creation of unstable molecules containing more oxygen than is usual).

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Vitamin C : The most abundant water-soluble antioxidant in the body. Acts primarily in cellular fluid Of particular note in combating free-radical formation caused by pollution and cigarette smoke. Also helps return vitamin E to its active form.

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Our bodies use oxygen to convert food items such as fat and sugar into energy, in this process, oxygen is converted to water, and each water molecule normally takes up four electrons.  However some oxygen may escape before the conversion is complete, and this results in about 2% of the oxygen having an electron deficit.  These particles are called free radicals or super oxide radicals (Oxygen Free Radicals) ۩ THE ROLE OF OXYGEN FREE RADICALS :

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They may also be formed in the human body through other processes, such as air pollution, smoking and exposure to radiation.  Free oxygen radicals are extremely reactive and can cause damage to body proteins and fats, and also to the hereditary material of cells, known as DNA.  The oxygen free radical (super oxide radical) can be converted to even more damaging radicals by a chain reaction.

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Fortunately our bodies have some protective mechanisms against the harmful effects of free oxygen radicals and other even more powerful radicals such as the so-called peroxides and hydroxyl radicals.  The protective mechanisms are enzymes and antioxidants.

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Some enzymes in the human body are capable of neutralizing the oxygen free radicals as soon as they are formed.  The best known of such enzymes is called SOD (super oxide dismutase).  SOD and other enzymes convert super oxide and damage to lipids and to DNA.

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This mechanism slows down in later life, so that the damage may accumulate and become visible as the process of ageing, when tissues lose their elasticity.  Damage to the hereditary material (DNA) in a normal cell may cause it to become a cancer cell.  It  is also thought that free radicals may play a role in the development of cardiovascular disease such as atherosclerosis [here the coronary arteries become blocked by a gradual thickening of the wall].

Role of oxygen free radicals in carcinogenesis and brain ischemia : : 

Role of oxygen free radicals in carcinogenesis and brain ischemia : Even though oxygen is necessary for aerobic life, it can also participate in potentially toxic reactions involving oxygen free radicals and transition metals such as Fe that damage membranes, proteins, and nucleic acids. Oxygen free radical reactions and oxidative damage are in most cases held in check by antioxidant defense mechanisms. But where an excessive amount of oxygen free radicals are produced or defense mechanisms are impaired, oxidative damage may occur and this appears to be important in contributing to several pathological conditions including aging, carcinogenesis, and stroke. RA Floyd, Molecular Toxicology Research Group, Oklahoma Medical Research Foundation, Oklahoma City 73104.

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FREE RADICAL DAMAGE TO MOTOR NEURONS

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Several newer methods, such as in vivo spin-trapping, have become available to monitor oxygen free radical flux and quantitate oxidative damage. Using a combination of these newer methods collectively focused on one model, recent results show that oxidative damage plays a key role in brain injury that occurs in stroke. Subtle changes, such as oxidative damage-induced loss of glutamine synthetase activity, may be a key event in stroke-induced brain injury. Oxygen free radicals may play a key role in carcinogenesis by mediating formation of base adducts, such as 8-hydroxyguanine, which can now be quantitated to very low levels.

۩ Science news articles about oxygen free radicals : : 

۩ Science news articles about oxygen free radicals : “ BRAIN PLAYS AN IMP KEY ROLE IN APPETITE BY REGULATING O.F.R. ” Researchers at Yale School of Medicine have found the brain's appetite centre uses fat for fuel by involving oxygen free radicals - molecules associated with ageing and neurodegeneration. The findings, reported in the journal Nature, suggest that antioxidants could play a role in weight control..

Oxygen free radicals don't cause aging, Guarente research shows.. : 

Oxygen free radicals don't cause aging, Guarente research shows.. Professor Lenny Guarente examines his latest generation of yeast under the microscope. “In results that counter the idea that oxygen free radicals cause aging, an MIT researcher reports in the July 18 issue of Nature that calorie restriction prolongs life because it increases respiration, not because it decreases oxygen free radicals….” NEW DISCOVERY 18 July - 2009 www.nature.com

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MIT biologist Leonard Guarente believes; “ The conventional wisdom on oxygen radicals is dead wrong. Our results (in yeast) are contrary to the frequent suggestion that calorie restriction functions by slowing metabolism and thereby slowing the generation of free radicals…”

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Guarente, who is working on a book on aging to be published this fall, discovered in 2000 that calorie restriction activates the silenced information regulator (SIR2) gene, which has the apparent ability to slow aging. This gene makes a protein called Sir2, which Guarente has shown is integrally tied to extending life span in yeast and in the roundworm. Humans carry a similar gene.

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Rather than a slower metabolism leading to a slower rate of respiration, it turns out that respiration in yeast cells under calorie restriction goes up, not down. "The increase in anti-oxidant enzymes that is reported to occur during calorie restriction in animals may be a result of an increase in respiration rather than a cause of the observed longevity……" Guarente said.

OXYGEN FREE RADICAL SCAVENGING ABILITIES OF VIT. C,E, ®-CAROTENE, PYCNOGENOL, GRAPE SEED PROANTHOCYANIDIN EXTRACT & ASTAXANTHINS IN VITRO : 

OXYGEN FREE RADICAL SCAVENGING ABILITIES OF VIT. C,E, ®-CAROTENE, PYCNOGENOL, GRAPE SEED PROANTHOCYANIDIN EXTRACT & ASTAXANTHINS IN VITRO Free radicals have been implicated in more than one hundred disease conditions in humans, including….; arthritis, hemorrhagic shock, atherosclerosis, aging, ischemia and reperfusion injury of many tissues, central nervous system injury, gastritis, tumor promotion and carcinogenesis, and AIDS. This wide range of diseases implies that enhanced free radical formation accompanies tissue and cellular injury in most, if not all, human diseases.

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In most cases, free radicals and their metabolites are increasingly recognized for their contribution to tissue injury leading to both initiation and promotion of multistage carcinogenesis, which ultimately leads to cancer. Free radical production is also enhanced by carcinogen exposure as well as under the conditions of stress

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Antioxidants/free radical scavengers function as inhibitors at both initiation and promotion/propagation/transformation stage of tumor promotion/carcinogenesis and protect cells against oxidative damage. Antioxidants have been shown to inhibit both initiation and promotion in carcinogenesis and counteract cell immortalization and transformation.

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There is considerable evidence for a role of antioxidant nutrients including vitamins C and E, and ®-carotene, in the maintenance of health in contributing to the decreased incidence of free radical-induced diseases. The consumption of edible plants, fruits and vegetables has been repeatedly demonstrated to prevent the occurrence of a number of diseases in humans and animals. Vegetables, fruits and their seeds are rich sources of vitamins C, E and ®-carotene, and/or protease inhibitors, compounds which might protect the organism against free radical-induced injury and diseases.

SCAVENGERS OF OXYGEN FREE RADICALS : : 

SCAVENGERS OF OXYGEN FREE RADICALS : Biology of free radical scavengers: an evaluation of ascorbate Reactive free radical species (R.) are associated with several forms of tissue damage and disease, and also with the process of aging. Protection is thought to be available in the form of endogenous compounds that react with and thereby "scavenge" the R.. Because many R. are reactive forms of oxygen, an effective scavenger is often referred to as an antioxidant. RC Rose and AM Bode; Department of Physiology and Biophysics, Chicago Medical School, Illinois 60064.

۩ Properties of an ideal ANTI OXIDANTS : : 

۩ Properties of an ideal ANTI OXIDANTS : To be an effective antioxidant physiologically, a substance must have certain chemical and biological properties: It must be present in adequate amounts in the body; It must react with a variety of R.; It must be suitable for compartmentation; It must be readily available; It might be suitable for regeneration; It must be conserved by the kidneys; and It must have tolerable toxicity.

Carvedilol, a new vasodilator and beta adrenoceptor antagonist, is an antioxidant and free radical scavenger : : 

Carvedilol, a new vasodilator and beta adrenoceptor antagonist, is an antioxidant and free radical scavenger : The antioxidant effect of carvedilol, a new vasodilating, beta adrenoceptor blocker was studied and compared with five other beta blockers. Carvedilol rapidly inhibited Fe(++)-initiated lipid peroxidation, measured as thiobarbituric acid reactive substance (TBARS), in rat brain homogenate with an IC50 of 8.1 microM. Under the same conditions, the IC50 values of atenolol, pindolol propranolol, celiprolol and labetalol were over 1.0 mM. Division of Pharmacology, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania. TL Yue, HY Cheng, PG Lysko, PJ McKenna, R Feuerstein, JL Gu, KA Lysko, LL Davis

Oxygen free radical scavengers protect rat islet cells from damage by cytokines : : 

Oxygen free radical scavengers protect rat islet cells from damage by cytokines : Summary:    A possible role for oxygen free radicals in mediating the cytotoxic effects of cytokines in islets was sought by the use of agents that scavenge free radicals. Rat islet cell monolayer cultures were incubated for 6 days with t-butylhy-droperoxide, alloxan, streptozotocin, or the cytokines, interleukin 1, tumor necrosis factor, and interferon gamma, without and together with the oxygen free radical scavenger combination of dimethylthiourea and citiolone. Islet cell lysis was measured in a 15chromium cytotoxicity assay. Department of Medicine, University of Alberta, Edmonton, Alberta, Canada

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The free radical scavengers significantly inhibited the islet cell cytotoxic effects of t-butylhydroperoxide and alloxan, but not streptozotocin. Similarly, the cytotoxic effects of the cytokine combinations of interleukin 1 plus tumor necrosis factor, interferon gamma plus tumor necrosis factor, and interferon gamma plus interleukin 1 were significantly inhibited by the free radical scavenger combination of dimethylthiourea and citiolone.

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These results suggest that the cytokine products of macrophages and lymphocytes infiltrating islets in Type 1 (insulin-dependent) diabetes may contribute to B-cell damage by inducing the production of oxygen free radicals in the islet cells. Source: University of Gothenburg

FREE RADICAL SCAVENGER IN STROKE : : 

FREE RADICAL SCAVENGER IN STROKE : : INVESTIGATIONAL THERAPY : As knowledge of pathophysiologic processes involved has increased, number of potential targets for therapy have multiplied. Strategies aimed at restoring blood flow to the ischemic brain have been most promising. “ANCORD” – a defibrogenating agent has been shown to improve 90 days outcome when initiated within 3 hrs of onset of symptoms. Pro –urokinase, when administered intra arterially to patients with large strokes within 6 hrs of symptoms onset, also has been Shawn to improve stroke outcome at 90 days.

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Intra arterially thrombolysis is more effective than intra venous therapy – in patients with large clots. Other strategies under investigations to open the artery include; Laser Embolectonomy, Intracranial angioplasty and Suction Embolectonomy. Neuro protective therapy has shown less promise, although many compounds have been neuro protective in animals. Some reasons for the lack of success may be an inability to give the drug early enough in complete delivery of drugs to the site of action.

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Compounds under study are Glutamate antagonists, Gamma Amino Butyric acid Agonist (GABA), Ion channel modulators, and free radical scavengers. Area of intense interest is recovery enhancement. Investigators are interested in facilitating this recovery enhancing it, making it and available to all stroke victims, regardless of how long it has been.

FREE RADICAL SCAVENGER IN HEAD INJURY : : 

FREE RADICAL SCAVENGER IN HEAD INJURY : Potential role of O.F.R. in the pathophysiology of head injury has stimulated interest in the use of Antioxidants to interrupt self perpetuating cycle of membrane destruction in these patients. TIRILAZAD – a 21 amino steroid is one such antioxidants that has undergone phase-3 testing in head injury, stroke and t-SAH patients.

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An attractive feature : although it is a potent inhibitor of lipid peroxidation, its essentially devoid of Glucocorticoid activity. Unfortunately, 2 major trials of “TIRILAZAD” in head injury patients were unable to demonstrate the efficacy compared with placebo. FINISHED

۩ REFERENCES: : 

۩ REFERENCES: Review; Volume 263, Issue 1, pp. 92-98, 10/01/1992Copyright © 1992 by American Society for Pharmacology and Experimental Therapeutics. Journal review; The FASEB Journal, Vol 4, 2587-2597, Copyright © 1990 by The Federation of American Societies for experimental biology. Journal DIABETOLOGIA, Volume 32, number 11/ November 1989 Text book of Pharmacotherapy and physiological approach , JOSHEP T DIPIRO, 5th edition, pg no – 390 and 1085 www.google.com www.wikipedia.com

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Thank You ! DATE: 23/07/2009