Antioxidants and Free Radicals Quiz

Advanced Medical Biochemistry - Lecture 6: Antioxidants

• Antioxidants are substances that inhibit or neutralize oxidative damage caused by free radicals. These protect cells, proteins, and DNA from harm.
• Free radicals are unstable molecules with unpaired electrons, making them highly reactive and capable of damaging cells via oxidation.
• Oxidative stress occurs when the body produces more free radicals than it can neutralize with antioxidants. This imbalance can lead to cellular damage and contribute to various diseases and aging processes.

Different between Free radical and Antioxidants

• Definition: Antioxidants prevents/reduces damage caused by oxidation; Free radicals are highly reactive molecules that damage cells via oxidation
• Nature: Antioxidants are stable; Free radicals are highly unstable.
• Role in the Body: Antioxidants protects cells by neutralizing free radicals; Free radicals cause oxidative stress leading to cell damage.
• Source: Antioxidants are found in healthy foods, fruits, vegetables, and nuts; Free radicals are formed naturally in the body or by external factors like pollution or smoking.
• Effect: Antioxidants prevent aging and chronic diseases; Free radicals contribute to aging and increase the risk of diseases.

Antioxidants vs. Free radical

• Free radicals are unstable molecules with unpaired electrons. Antioxidants are stable molecules.

Importance of Antioxidants

• Cellular Protection: Antioxidants neutralize harmful free radicals protecting DNA, proteins, and lipids.
• Oxidative Stress Reduction: Maintaining a balance between free radicals and antioxidants reduces risk of chronic conditions.
• Disease Prevention: Antioxidant intake can decrease risks of heart disease, cancer, neurodegenerative disorders, and boost immune function.
• Anti-Aging Benefits: Antioxidants prevent damage from UV exposure and premature aging.
• Health Maintenance: Antioxidants support proper cellular integrity and organ/tissue function.

Brief History: Discovery and Relevance in Health and Science

• Early 20th Century: Free radicals were identified as highly reactive molecules in chemical reactions.
• 1954: Dr. Denham Harman proposed the Free Radical Theory of Aging, linking free radicals to cellular damage and aging.
• 1960s: Discovery of free radicals' role in diseases like cancer, diabetes, and cardiovascular disorders. Antioxidants were identified as protective agents against oxidative stress.
• Present Day: Free radicals are central to research in health, aging, and chronic diseases. Their role in environmental damage and industrial applications is widely studied.

Free Radicals and Oxidative Stress

• Definition: Free radicals are unstable molecules with unpaired electrons making them highly reactive. Oxidation is the process where atoms lose electrons.
• Oxidative Stress: Imbalance between free radical production and the body's antioxidant capacity. Oxidative stress causes cellular damage contributing to diseases and aging.

Sources of Free Radicals

• Internal Sources: Cellular metabolism (byproducts of energy production in mitochondria), inflammation (immune response generates reactive oxygen species), and enzymatic reactions (natural biochemical processes).
• External Sources: Pollution, ultraviolet radiation, radiation, smoking, industrial/chemical exposures, and pesticides.

ROS (Reactive Oxygen Species)

• Divided into two categories: free radicals (superoxide, hydroxyl radical, peroxyl, alkoxyl, and hydroperoxyl) and particles that are not free radicals (hydrogen peroxide, hypochlorous acid, ozone, and singlet oxygen).

Impact of Oxidative Stress

• Cell damage
• Accelerated aging
• Chronic diseases (cancer, cardiovascular disease)

Oxidative Stress: Mechanism and Consequences

• Oxidative stress occurs when the production of free radicals exceeds the body's ability to neutralize them.
• Free radicals damage DNA, proteins, and lipids and disrupt normal cellular functions.
• DNA damage can lead to mutations, increasing the risk of cancer.
• Alters protein structure and function, impacting enzyme and cellular signaling.
• Free radicals attack lipids in cell membranes causing cell death and compromising cell integrity.
• Contributes to aging, and chronic diseases (cardiovascular disease, diabetes, and neurodegenerative disorders like Alzheimer's).

Types of Antioxidants

• Endogenous: Produced by the body.
  • Enzymatic: Superoxide dismutase (SOD), catalase, and glutathione peroxidase.
  • Non-enzymatic: Glutathione, Coenzyme Q10.
• Exogenous: Obtained from diet.
  • Vitamins: Vitamin C, Vitamin E,
  • Minerals: Selenium, Zinc.
  • Phytochemicals: Flavonoids, carotenoids, and polyphenols.

Exogenous Antioxidants

• Drugs and compounds that influence free radical metabolism.
• Pharmaceutical and dietary compounds that modulate free radical activity and oxidative stress.

The Main Sources of Free Radicals

• Respiratory Chain in Mitochondria: Produces superoxide and hydrogen peroxide.
• Endoplasmic Reticulum: Generates superoxide through cytochrome P-450 enzymes.
• Special Cells (Leukocytes): Produce superoxide using NADPH-oxidase as part of their immune defense mechanism.
• Hemoglobin to Methemoglobin Oxidation: Oxidation of hemoglobin generates radicals. Erythrocytes are full of antioxidants to counteract this.

Mechanism of Action: How Antioxidants Work

• Electron Donation: Antioxidants donate electrons to neutralize free radicals, stabilizing them without becoming reactive.
• Breaking the Chain Reaction: Free radicals cause a chain reaction of oxidative damage by stealing electrons. Antioxidants interrupt this process, stopping further cellular damage.

Free Radicals Physiological Function

• Usage in processes involving oxides and oxygen molecules
• Cytochromoxidase: Produces toxic intermediates (H2O2, superoxide).
• Monooxygenases: Activate O2 in the liver or adrenal gland mitochondria, involved in hydroxylation.
• NADPH-oxidase: Found in leukocytes, generates superoxide (antimicrobial function).
• Myeloperoxidase: Catalyzes H2O2 + Cl+H+→ HClO + H2O (potent antimicrobial HClO)

Free Radicals Physiological Function (Signal Molecules, Redox State)

• Signal Molecules: Free radicals act as intermediates in cellular signaling.
• Redox State: Balances antioxidant capacity, reduction equivalent availability, and ROS and RNS production. ROS often act as second messengers in signal transduction.

Mechanism of Action: How Antioxidants Work (Synergistic Effects)

• Different antioxidants work together to enhance protection. For example, vitamin C regenerates vitamin E.
• Enzymatic and nonenzymatic support each other to maximize defense.
• This synergy provides comprehensive protection against oxidative stress.

Sources of Antioxidants

• Dietary: Fruits, vegetables, beverages like green tea and coffee.
• Supplementation: Convenient way to boost levels, though there are caveats.

Health Benefits of Antioxidants

• Reduce risk of chronic diseases (cardiovascular, cancer, neurodegenerative).
• Promote skin health, and reduce oxidative damage.
• Boost immune health and support immune response.

Role of Antioxidants in Immune Health

• Neutralizing free radicals protecting immune cells and cell membranes.
• Reducing inflammation and enhancing immune response.
• Boosting immune cells (lymphocytes and macrophages).
• Supporting skin barrier immunity.
• Preventing chronic diseases linked to weakened immunity.

Enzymes Defence Mechanism

• Enzymes like Superoxide dismutase (SOD) and catalyse break down hydrogen peroxide and reactive oxygen species.
• Glutathione cycle depicted is crucial in maintaining cellular defenses by regenerating antioxidants.

Assignment (3): Free radicals and antioxidants

• Definition of Free radical and reactive oxygen species (ROS) and nitrogen species (RNS).
• Are RNS and ROS always dangerous?
• Definition and significance of oxidative stress
• Types and characteristics of antioxidants.
• Markers of oxidative stress.
• Diseases associated with oxidative stress.

Test your knowledge on the roles of antioxidants and free radicals in the body. This quiz covers their functions, sources, and effects on aging and cellular signaling. Perfect for understanding the importance of redox state in physiology!