Free Radical:A free radical is an atom capable of independent existence (hence the term “free”) that contains one or more unpaired electrons in its outer orbital.It is an electron-deficient species.It is represented by a superscript dot to the right.(R●) 6 Important characteristics Free radicals are:Highly reactive.Unstable and try to become stable.Short life span ( Short-lived ) as they tend to catch an electron from other molecules. 7 Types of Free Radicals Oxygen free radicals (OFR) Nitrogen free radicals (NFR)Lipid free radicals (LFR)Others: chlorine radicals(Cl ●) ,carbon radicals(CCl3●), sulfur radicals (RS ● ). 8 Oxygen free radicals (OFR) OFR is referred to oxygen-derived free radicals.The unpaired electron is located on O such as superoxideradical and hydroxyl radical▲ Reactive oxygen species (ROS)ROS is a collective term that includes both oxygen free radicals (OFR), and non radicals that are oxidizing agents and / or are easily converted into radicals such as hydrogen peroxide and singlet oxygen.H2O2、 1O2Non free radical ROSFree radical ROSROSOFR（O2、OH•）. 9 Nitrogen free radicals (NFR) NFR is defined as nitrogen-derived free radicals. RNS:NO•ONOO , NO2RNSLipid free radicals (LFR)Lipid free radicals are referred to middle metabolic products resulting from the chain reaction of lipid peroxidation, which is produced by interaction of OFR and unsaturated fatty acid.L•LO•LOO•LFR 10 Sources of Free Radicals Exogenous sources of free radicals:Ionizing radiationUltraviolet radiationChemicals, smokingPollutionDiet(fatty and processed foods)Endogenous sources of free radicals:RespirationMetabolism.InflammationPhagocytosis 12 Roles of Free Radicals in Biological Systems Like two-edged sword:It can be beneficial.It can be harmful.They play an important role in a number of biological processes, many of which are necessary for life.But they also cause damage and disease. 13 Free Radicals: Positive Effects The presence of low concentrations of free radicals is important for normal cellular redox status and immune function.Immune system: Free radicals are used by phagocytic cells to kill bacteria during infections. (Antimicrobial actions).Modify oxidation-reduction (redox) states.Nitric oxide (NO●) helps to regulate blood pressure .However, there is now clear evidence that ROS are not merely toxic species but also—within certain concentrations—useful signaling molecules regulating physiological processes.Nitric oxide (NO) derivatives and reactive oxygen species (ROS) modulate contractile function of respiratory and limb skeletal muscleDuring intense skeletal muscle contractile activity myotubes' mitochondria generate high ROS flows: this renders skeletal muscle a tissue where ROS hold a particular relevance 14 Free Radicals: Negative Effects Damage produced by FRsFree radicals attack the nearest stable molecule, "stealing" its electron.When the "attacked" molecule loses its electron, it becomes a free radical itself, beginning a chain reaction.Once the process is started, it can cascade, finally resulting in the disruption of a living cell.Almost all biological macromolecules are damaged by the free radicals 15 They attack sites of increased electron density such as: The nitrogen atom present in proteins and DNA predominantlyCarbon-carbon double bonds present in polyunsaturated fatty acids and phospholipidsto produce additional free radical, often reactive, intermediates.However, excessive production can provoke inflammation or altered cellular functions through:lipid peroxidationprotein modificationDNA modification (DNA is damaged by strand breaks)The DNA damage may directly cause inhibition of protein and enzyme synthesis and indirectly cause cell death or mutation and carcinogenesisWhich compromises cell function leading to cell death. 16 Mechanism of radical reactions Radicals are highly reactive speciesThree distinct stepsInitiation (homolytic covalent bonds cleavage)Propagation (chain propagation)Termination 17 Oxidative damage to lipids - Lipid peroxidation Peroxidation (auto-oxidation) of lipids exposed to oxygen is responsible not only for deterioration of foods (rancidity) but also for damage to tissues in vivo, where it may be a cause of cancer, inflammatory diseases, atherosclerosis, and aging.The deleterious effects are considered to be caused by free radicals (ROO•, RO•, OH•) produced during peroxide formation from fatty acids containing methylene-interrupted double bonds, ie, those found in the naturally occurring polyunsaturated fatty acids.Lipid peroxidation is a chain reaction providing a continuous supply of free radicals that initiate further peroxidation. 18 lipid peroxidation Initiation RH + X• R• + XH 2. Propagation R• + O ROO•ROO• + RH R• + ROOH , etc.3. TerminationROO• + ROO• ROOR + O2R• + ROO• ROORR• + R• RR 19 Counteracting free radical damage The human body has several mechanisms to counteract damage by free radicals and other reactive oxygen species.One important line of defense against free radical damage is the presence of antioxidants.Some such antioxidants, are produced during normal metabolism in the body.Other lighter antioxidants are found in the diet. 20 AntioxidantsSubstances that are able to neutralize reactive molecules and reduce oxidative damage.Result of metabolic processes and environmental sources.Certain antioxidant vitamins donate their electrons or hydrogen molecules to free radicals to stabilize them.Antioxidant minerals function within complex antioxidant enzyme systems that convert free radicals to less damageing substances that are excreted by our bodies. These enzymes also break down fatty acids that have become oxidized. In breaking down the fatty acids they destroy the free radicals associated with the oxidized fatty acids.SOD – converts free radicals to hydrogen peroxidecatalase – removes hydrogen peroxide from our bodies by converting it to water and hydrogenglutathione peroxidase – also removes hydrogen peroxide and stops the production of free radicals in lipidsAntioxidants, vit E, C possibly A, beta-carotene and seleniumCopper zinc and manganese are part of SOD.Iron cofactor for catalase antioxidant enzymeEnvironmental - air pollution, cigarette smokeEither act as antioxidant or are part of enxyme that does (Zn, Cu, Mn) 22 Pro-oxidant & Antioxidant Balance Damage(Pro-oxidants)Damage(Pro-oxidants)Defense(Antioxidants)Defense(Antioxidants)Decrease of antioxidant defense systemOxidative damage 23 Oxidative stress It is an excess of free-radicals damages cells. Oxidative stress has been identified as a causative factor in:Cognitive performanceAging processDevelopment of diseases such as cancer, arthritis, cataracts, and heart disease 24 Free Radical Diseases Stroke Alzheimer’s Parkinson’s Photo-aging (wrinkles)Macular Degeneration& CataractsPeriodontitisEmphysemaLung CancerCoronary Heart DiseaseDiabetesHypertension &Chronic Kidney DiseaseAlcohol &Viral Liver DiseasesProstate CancerRheumatoid ArthritisColo-rectal CancerPeripheral Vascular DiseaseSkin Cancer &MelanomaOsteoarthritis 25 Many of the changes associated with aging are actually due to the effects of free-radicals. As we age, the antioxidant enzyme systems work less efficiently. 26 Antioxidant System in our body The enzymatic antioxidants:Superoxide dismutase (SOD) eliminates the superoxide (O2-.).Catalase and the glutathione peroxidase eliminate hydrogenperoxide (H2O2).The non enzymatic antioxidants:Vitamins E, C, A or Pro vitamin A(beta-carotene). 27 Vitamin C Vitamin C, or ascorbic acid, is a water-soluble vitamin. This vitamin is a free radical scavenger.It is effective in protecting tissues against oxidative damage.Its protective effects extend to cancer, coronary artery disease, arthritis and aging. 28 Vitamin E Vitamin E is a fat-soluble substance It is a principal antioxidant in the body and protects polyunsaturated fatty acids in cell membranes from peroxidation. 29 2 types of Antioxidants (1) - Preventative antioxidants: Reduce the rate of chain initiatione.g.: catalase and other peroxidases that react with ROOH and chelators of metal ions such as EDTA(2) - Chain-breaking Antioxidants:Which interfere with chain propagation.e.g.: In vivo, superoxide dismutase, which acts in the aqueous phase to trap superoxide free radicals (O2 −•); perhaps urate ; and vitamin E, which acts in the lipid phase to trap ROO• radicals. 30 What do antioxidants do? Provides key nutrients needed by the body to neutralize free radicals.Aid the human body’s natural defenses.Repair oxidative damage.Slow or prevent damage to body cells.May exhibit anti-aging benefits.May improve immune function and lower risk for infection and cancer. 31 Table 1. Reactive Oxygen Species and Antioxidants that Reduce Them Reactive SpeciesAntioxidantSinglet oxygen 1O2Vitamin A, vitamin ESuperoxide radical (O2-)superoxide dismutase, vitamin CHydrogen peroxide (H2O2)Catalase; glutathione peroxidasePeroxyl radical (ROO)Vitamin C, vitamin ELipid peroxyl radical (LOO)Vitamin EHydroxyl radical (OH)Vitamin C 32 SummaryOne of the most significant sites of free radical damage is the cell membrane. May affect all systems affected by this cell.Other sites of damage include LDL, cell proteins and our genetic material (DNA). May increase our risk for heart disease and cancer and cause our cells to die prematurely. 33 ConclusionAntioxidant plays an important role to prevent cancer, and other disease. They also have role in slowing aging process and preventing heart disease. So antioxidant are very much necessary for our body .But our body can’t manufacture these chemicals, so they must be supplied through diet.