Advanced Medical Biochemistry Lecture 6: Antioxidants PDF

Advanced Medical Biochemistry Dr. Ayman Mustafa Abu Mustafa Lecture 6: Antioxidants 1 Dr Ayman M Abu Mustafa PhD in...

Advanced Medical Biochemistry Dr. Ayman Mustafa Abu Mustafa Lecture 6: Antioxidants 1 Dr Ayman M Abu Mustafa PhD in Biochemistry Arab Diploma in Medical Statistics Msc & Bsc in Medical technology Mobile: 0599577280 WhatsApp: 00972599577280 Email: aymanayman20092009@hotmailcom 2 Dr. Ayman Mustafa Abu Mustafa 1  What Are Antioxidants? ❑ Definition ▪ Antioxidants are substances that inhibit or neutralize oxidative damage caused by free radicals, protecting cells, proteins, and DNA from harm. 3 Different between Free radical and Antioxidants Aspect Antioxidants Free Radicals Molecules that prevent or Unstable molecules that Definition reduce damage caused by damage cells through oxidation oxidation Highly reactive and Nature Stable molecules unstable molecules Protect cells by Cause oxidative stress, Role in the Body neutralizing free radicals leading to cell damage Formed naturally in the Found in healthy foods body or due to external Source like fruits, vegetables, and factors like pollution, nuts smoking Contribute to aging and Prevent aging and chronic Effect increase the risk of diseases diseases 4 Dr. Ayman Mustafa Abu Mustafa 2  Antioxidants vs. Free radical 5 Antioxidants vs. Free radical 6 Dr. Ayman Mustafa Abu Mustafa 3  Antioxidants vs. Free radical 7 Importance of Antioxidants ▪ Cellular Protection: Safeguard DNA, proteins, and lipids by neutralizing harmful free radicals. ▪ Oxidative Stress Reduction: Maintain balance between free radicals and antioxidants, reducing the risk of chronic conditions. ▪ Disease Prevention: Decrease risks of heart disease, cancer, neurodegenerative disorders, and boost immune function. ▪ Anti-Aging Benefits: Protect skin from UV damage and premature aging. ▪ Health Maintenance: Support cellular integrity for proper organ and tissue function. 8 Dr. Ayman Mustafa Abu Mustafa 4  Brief history: Discovery and relevance in health and science ❑ Early 20th Century: Free radicals were first identified as highly reactive molecules during chemical reactions. ▪ Initially studied in physical chemistry. ❑ 1954: Dr. Denham Harman proposed the Free Radical Theory of Aging, linking free radicals to cellular damage and aging. ❑ 1960s: Discovery of the role of free radicals in diseases like cancer, diabetes, and cardiovascular disorders. Also, Antioxidants were identified as protective agents against oxidative stress. ❑ Present Day: Free radicals are central to research in health, aging, and chronic diseases. Also, Their role in environmental damage and industrial applications is also widely studied. 9 Free Radicals and Oxidative Stress ❑ Definition ▪ Free Radicals: These are unstable molecules with unpaired electrons, making them highly reactive. They can damage cells by reacting with DNA, proteins, and lipids. Free radicals are produced naturally during metabolic processes and can also result from external factors like pollution, radiation, and smoking. ▪ Oxidative Stress: This occurs when there's an imbalance between the production of free radicals and the body's ability to neutralize them with antioxidants. When free radicals overwhelm the body's defenses, they cause oxidative stress, leading to cellular damage and contributing to various diseases and aging processes 10 Dr. Ayman Mustafa Abu Mustafa 5  11 12 Dr. Ayman Mustafa Abu Mustafa 6  Sources of Free Radicals ❑ Internal Sources ▪ Cellular Metabolism: Byproducts of energy production in mitochondria. ▪ Inflammation: Immune system response generates reactive oxygen species (ROS). ▪ Enzymatic Reactions: Natural biochemical processes create free radicals. ❑ External Sources ▪ Pollution: Airborne toxins and chemicals. ▪ Radiation: UV rays and other ionizing radiation. ▪ Smoking: Contains free radicals and increases oxidative stress. ▪ Chemical Exposure: Industrial chemicals and pesticides. 13 14 Dr. Ayman Mustafa Abu Mustafa 7  ROS (Reactive Oxygen Species) ❑ Divided into two categories: ❑ Free radicals: ▪ Superoxide (O₂·⁻) ▪ Hydroxyl radical (OH·) ▪ Peroxyl (ROO·) ▪ Alkoxyl (RO·) ▪ Hydroperoxyl (HO₂·) ❑ Particles that are not free radicals: ▪ Hydrogen peroxide (H₂O₂): Often involved in Fenton's reaction. ▪ Hypochlorous acid (HClO) ▪ Ozone (O₃) ▪ Singlet oxygen (O₂) 15 Impact of Oxidative Stress ❑ When free radicals outnumber antioxidants, they cause oxidative stress, leading to: ▪ Cell damage. ▪ Accelerated aging. ▪ Chronic diseases (e.g., cancer, cardiovascular disease). 16 Dr. Ayman Mustafa Abu Mustafa 8  Oxidative Stress: Mechanism and Consequences ❑ Mechanism of Oxidative Stress ▪ Occurs when the production of free radicals exceeds the capacity of antioxidants to neutralize them. ❑ Process: ▪ Free radicals seek to stabilize by stealing electrons from other molecules (e.g., DNA, proteins, lipids). ▪ This results in molecular damage and disruption of normal cellular functions. 17 Consequences of Oxidative Stress ❑ DNA Damage: ▪ Leads to mutations that can trigger cancer and other genetic disorders. ❑ Protein Damage: ▪ Alters protein structure and function, affecting enzymes and cellular signaling. ❑ Lipid Peroxidation: ▪ Free radicals attack lipids in cell membranes, leading to cell death and compromised cell integrity. ❑ Chronic Diseases: ▪Contributes to aging, cancer, cardiovascular diseases, diabetes, and neurodegenerative disorders (e.g., Alzheimer's). 18 Dr. Ayman Mustafa Abu Mustafa 9  Types of Antioxidants ❑ Endogenous Antioxidants ▪ Produced by the Body ❑ Exogenous Antioxidants ▪ Obtained from Diet 19 Endogenous Antioxidants ❑ Enzymatic Antioxidants: ▪ Superoxide Dismutase (SOD): Neutralizes superoxide radicals. ▪ Catalase: Breaks down hydrogen peroxide into water and oxygen. ▪ Glutathione Peroxidase: Reduces peroxides to protect cells. ❑ Non-Enzymatic Antioxidants: ▪ Glutathione: A master antioxidant that protects cells and regenerates other antioxidants. ▪ Coenzyme Q10: Protects mitochondria and supports energy production. 20 Dr. Ayman Mustafa Abu Mustafa 10  Endogenous Antioxidants ❑ Antioxidants: ▪ Cytochrome c ▪ Fixed in Membranes: ▪ Alpha-tocopherol (Vitamin E), Beta-carotene, Coenzyme Q10 ▪ Out of Membranes: ▪ Ascorbate (Vitamin C), Transferrin, Bilirubin 21 Exogenous Antioxidants ❑ Vitamins: ▪ Vitamin C: Neutralizes free radicals in the water-soluble environment. ▪ Vitamin E: Protects cell membranes from lipid peroxidation. ❑ Minerals: ▪ Selenium: A cofactor for antioxidant enzymes like glutathione peroxidase. ▪ Zinc: Supports enzymatic antioxidants and immune health. ❑ Phytochemicals: ▪ Flavonoids: Found in fruits and vegetables, combat oxidative stress. ▪ Carotenoids: Pigments like beta-carotene, protect against UV- induced damage. ▪ Polyphenols: Found in tea, coffee, and red wine, with strong antioxidant properties. 22 Dr. Ayman Mustafa Abu Mustafa 11  Exogenous Antioxidants: ❑ Drugs and Compounds Influencing FR Metabolism: ▪ Pharmaceutical and dietary compounds that modulate free radical activity and oxidative stress. 23 The Main Sources of Free Radicals ❑ Sources: ▪ Membrane enzymes and/or coenzymes with flavin structures. ▪ Hem coenzymes. ▪ Enzymes containing a copper (Cu) atom in their active site. 1. Respiratory Chain in Mitochondria: ▪ Produces superoxide and subsequently hydrogen peroxide (H₂O₂). ▪ Approx. 1-4% of O₂ enters the respiratory chain (mainly through complexes I and III). 24 Dr. Ayman Mustafa Abu Mustafa 12  Respiratory Chain in Mitochondria 25 The Main Sources of Free Radicals 2. Endoplasmic Reticulum: ▪ Generates superoxide through the activity of cytochrome P- 450 enzymes. 3. Special Cells (Leukocytes): ▪ Produce superoxide using NADP-oxidase as part of their immune defense mechanism. 4. Hemoglobin to Methemoglobin Oxidation: ▪ The oxidation of hemoglobin to methemoglobin generates radicals. ▪ Erythrocytes are "full" of antioxidants to counteract this. 26 Dr. Ayman Mustafa Abu Mustafa 13  Mechanism of Action: How Antioxidants Work 1. Donation of Electrons ▪ Antioxidants donate electrons to neutralize free radicals, stabilizing them without becoming reactive themselves. ▪ This prevents free radicals from stealing electrons from healthy molecules like DNA, proteins, and lipids. 2. Breaking the Chain Reaction ▪ Free radicals cause a chain reaction of oxidative damage by continuously stealing electrons. ▪ Antioxidants interrupt this process, stopping further cellular damage. 27 28 Dr. Ayman Mustafa Abu Mustafa 14  Free Radicals Physiological Function ▪ Usage: Free radicals are used in processes involving oxides and oxygen molecules. ❑ Cytochromoxidase ▪ Produces toxic intermediates such as H₂O₂ and superoxide. ▪ These intermediates are bound to an enzyme for controlled physiological functions. ❑ Monooxygenases: ▪ Activate O₂ in the liver endoplasmic reticulum (ER) or in adrenal gland mitochondria. ▪ Involved in hydroxylation reactions, which are critical for metabolic processes. 29 Free Radicals Physiological Function ❑ NADPH-oxidase: ▪ Found in leukocytes. ▪ Generates superoxide for antimicrobial defence. ❑ Myeloperoxidase: ▪ Catalyzes the reaction: H2O2+Cl−+H+→HClO+H2O ▪ Produces hypochlorous acid (HClO), a potent antimicrobial agent. 30 Dr. Ayman Mustafa Abu Mustafa 15  Free Radicals Physiological Function ❑ Signal Molecules: ▪ Free radicals act as intermediates in cellular signaling: ▪ First messenger → Second messenger → Information network. ▪ Cellular communication is influenced by the redox state. ❑ Redox State: ❑ Represents the balance between: ▪ Antioxidant capacity. ▪ Reduction equivalent availability. ▪ Rate of ROS and RNS production. ❑ ROS often act as second messengers in signal transduction. 31 Mechanism of Action: How Antioxidants Work 3. Synergistic Effects ▪ Different antioxidants work together to enhance protection: ▪ Vitamin C regenerates Vitamin E after it neutralizes free radicals. ▪ Enzymatic and non-enzymatic antioxidants support each other to maximize defense. ▪ This synergy provides comprehensive protection against oxidative stress. 32 Dr. Ayman Mustafa Abu Mustafa 16  Sources of Antioxidants 1. Dietary Sources ❑ Fruits: ▪ Rich in Vitamin C, flavonoids, and polyphenols. ▪ Examples: Berries, oranges, grapes. ❑ Vegetables: ▪ High in carotenoids, Vitamin E, and other phytochemicals. ▪ Examples: Spinach, broccoli, kale. ❑ Beverages: ▪ Packed with polyphenols and antioxidants. ▪ Examples: Green tea, coffee. 33 Sources of Antioxidants 3. Supplementation ▪ Convenient way to boost antioxidant levels. ▪ Useful for individuals with deficiencies or specific health needs. ▪ Excessive intake can disrupt natural oxidative balance, leading to pro- oxidant effects. ▪ Long-term reliance may reduce the body's endogenous antioxidant production. 34 Dr. Ayman Mustafa Abu Mustafa 17  Health Benefits of Antioxidants 1. Reducing the Risk of Chronic Diseases ❑ Cardiovascular Diseases: ▪ Antioxidants reduce oxidative stress, preventing LDL cholesterol oxidation and lowering the risk of heart disease. ❑ Cancer: ▪ Neutralize free radicals that can damage DNA and lead to mutations, reducing cancer risks. ❑ Neurodegenerative Diseases: ▪ Protect neurons from oxidative damage, potentially slowing the progression of Alzheimer’s and Parkinson’s diseases. 35 Health Benefits of Antioxidants 2. Skin Health ❑ Anti-Aging Properties: ▪ Reduce oxidative damage caused by UV exposure and pollution. ▪ Promote collagen production, improving skin elasticity and reducing wrinkles. 36 Dr. Ayman Mustafa Abu Mustafa 18  Health Benefits of Antioxidants Role of Antioxidants in Immune Health ▪ Neutralizing Free Radicals: Antioxidants protect immune cells by neutralizing harmful free radicals that can damage DNA and cell membranes. ▪ Reducing Inflammation: Help lower oxidative stress, which contributes to chronic inflammation, enhancing immune response. ▪ Boosting Immune Cells: Vitamin C, E, and selenium strengthen lymphocytes and macrophages, key players in fighting infections. ▪ Supporting Skin Barrier: Antioxidants promote the skin's defense system, the first line of immunity. ▪ Preventing Chronic Diseases: Limit oxidative damage linked to conditions that weaken immunity, such as diabetes and cardiovascular diseases. 37 Enzymes Defence Mechanism 38 Dr. Ayman Mustafa Abu Mustafa 19  Enzymes Defence Mechanism Glutathione Peroxidases 39 Enzymes Defence Mechanism ▪ Enzymes defence mechanism process in which reactive oxygen species (ROS) like superoxide and hydrogen peroxide are neutralized by antioxidant defense systems. Superoxide dismutase (SOD) and glutathione peroxidase (GSHPx) play critical roles in reducing ROS, while catalase provides an additional layer of protection by breaking down hydrogen peroxide into harmless products. The Fenton reaction, on the other hand, demonstrates how iron can contribute to ROS generation, amplifying oxidative damage. ▪ The glutathione cycle depicted is crucial in maintaining cellular defenses by regenerating antioxidants and ensuring that cells can protect themselves from oxidative damage. 40 Dr. Ayman Mustafa Abu Mustafa 20  Assignment (3) ❑ Free radicals and antioxidants" ▪ What is "free radical"? ▪ Reactive oxygen and nitrogen species (RNS and ROS ) ▪ Are the RNS and ROS always dangerous? ▪ Well-known term "oxidative stress" - what is it? ▪ What is Antioxidants - types and appearance ▪ What is Markers of oxidative stress ▪ What is Disorders associated with oxidative stress 41 Advanced Medical Biochemistry Dr. Ayman Mustafa Abu Mustafa 21