Free radicals and Antioxident (2024-11-19) d
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Oral Biology Department Nutrition course for first-year dental students.
Instructor: Prof. Samia Omar.
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Biological organization components in human bodies:
Organs
Tissues
Cells
Subcellular structures
Macromolecules
Micromolecules
Atoms
Nucleus and shell (multiple orbits)
Protons and neutrons in the nucleus
Electrons in orbits/shells
Each shell needs to be filled by a certain number of electrons for stability.
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Introduction to Free Radicals.
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Definition of Free Radicals:
Molecular atoms with unpaired electrons in their outer shells.
This unpaired state makes them highly reactive and unstable.
Free radicals can damage nucleic acids and membranes in cells.
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Production of Free Radicals:
Result from incompletely oxidized compounds during cellular metabolism.
Also known as reactive oxygen species (ROS).
Act as oxidants or reductants by donating or accepting electrons.
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Characterization of Free Radicals:
Compared to robbers, energy deficient seeking electrons from cells.
Damage to cellular membranes results from electron theft.
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Free radicals as central factors in cell injury:
Can cause damage through unwanted side reactions.
Excess leads to cell injury and possibly death, contributing to diseases.
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Types of Free Radicals:
Two main categories: Reactive Oxygen Species (ROS) and Reactive Nitrogen Species (RNS).
Important radical examples:
Superoxide anion (O2-)
Hydroxyl radicals (OH)
Peroxyl free radical (ROO)
Ozone (O3)
Singlet oxygen (1O2)
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Reactive Oxygen Species (ROS) act as oxidants by adding oxygen atoms to other substances.
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Generation of Free Radicals:
Mainly from cellular redox (oxidation-reduction) processes.
Reduction: Addition of hydrogen or removal of oxygen.
Oxidation: Addition of oxygen or removal of hydrogen.
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Formation of Free Radicals:
Occurs via:
Enzymatic reactions: Involves respiratory chain, phagocytosis, prostaglandin synthesis.
Non-enzymatic processes also contribute.
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Emphasis on enzymatic reactions and their endogenous role in Free Radical production.
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Energy extraction from food through gradual oxidation (respiration):
Combines carbon and hydrogen with oxygen to produce CO2 and H2O.
Incomplete reduction of O2 leads to the creation of reactive oxygen species (ROS).
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Mitochondrial structure:
Components include:
Respiratory chain, matrix, ribosomes, intermembrane space.
Role in oxidative phosphorylation and ATP production.
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Free radicals as byproducts of incompletely oxidized compounds during cellular respiration.
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Phagocytic cells (macrophages and neutrophils):
Detect and eliminate foreign organisms, releasing oxygen-derived free radicals during the process.
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Breakdown of cell membranes may expose arachidonic acid leading to:
Prostaglandin synthesis via cyclooxygenase and lipoxygenase actions.
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Causes of free radical formation include:
External factors: Oxygen reactions with organic compounds, radiation.
Internal factors: Mitochondrial oxidative phosphorylation (endogenous).
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Targets of Free Radicals:
Capable of damaging all types of biological molecules:
DNA, proteins, carbohydrates, lipids, leading to cell damage.
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Effects of Free Radicals:
1. Oxidative damage to proteins:
Can cause modifications, fragmentation, and inactivation.
Linked to aging processes.
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2. Lipid Peroxidation:
Occurs on fatty acids in membranes.
Associated with various diseases including neurodegenerative diseases, ischemic diseases, and type 2 diabetes.
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Free Radical Formation:
Electron loss leads to cell membrane free radical problems resulting in membrane erosion and damage to the cell interior.
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3. Oxidative damage to DNA:
DNA (and RNA) are susceptible to oxidative damage, linked to aging and cancer.
Mitochondrial DNA is particularly susceptible.
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Free Radicals in Biology:
Reactions produce cumulative adverse changes with age.
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Sources of Free Radicals:
Endogenous: Mitochondria, immune activation, stress, etc.
Exogenous: Pollution, smoke, radiation, etc.
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Exogenous Free Radical Production:
Influences from UV light, inflammation, and air pollution on DNA and metabolism.
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The Oral Cavity:
Subjected to various factors generating free radicals:
Food, air, microorganisms, cigarette smoke, dental materials, medications.
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Activities of Free Radicals and Oxidants:
Distinct beneficial and deleterious effects.
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Beneficial Activities:
Low/moderate ROS/RNS are crucial for:
Cell responses, maturation, and as defense mechanisms against pathogens.
Physiological roles in multiple cell signaling pathways.
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Deleterious Activities:
Excess leads to oxidative stress, potentially harming cell structures (proteins, lipids, DNA).
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Normal cell interactions vs. oxidative stress impact over time.
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Oxidative stress implications:
Contributes to systemic diseases affecting oral health, including obesity and diabetes.
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Significance of Oxidative Stress:
Linked to multiple chronic diseases, including cancer and cardiovascular issues.
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Oral health implications of oxidative stress:
Impacts salivary function, periodontitis, and oral cancers.
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Harmful Effects of Oxidative Stress:
Affects multiple systems and can lead to various health complications.
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Body’s Defensive Systems:
Free radical detoxifying enzymes.
Antioxidant production.
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Mechanisms to overcome the adverse effects of free radicals through antioxidants.
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Antioxidant Definition:
Low molecular weight molecules capable of neutralizing free radicals.
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Antioxidant Functions:
Donates electrons to free radicals preventing damage to vital molecules.
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Levels of Antioxidant Action:
Preventative, scavenging, repair mechanisms.
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Third and fourth lines of antioxidant defense include:
Repair systems and adaptive signaling for specific free radical responses.
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Antioxidants functionality:
Neutralize free radicals in different cellular environments.
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Summary of Antioxidant Features:
Levels of action, location, structural dependencies, and solubility classifications.
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Mechanisms of Antioxidant Production:
Endogenous (naturally produced) vs. Exogenous (dietary) sources.
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Endogenous Antioxidants:
Enzymatic.
Non-enzymatic.
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Major enzymatic antioxidants include:
Glutathione peroxidase and Superoxide dismutase.
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Non-Enzymatic Antioxidants:
Divided into:
A. Metabolic antioxidants (body-produced).
B. Nutritional antioxidants (diet obtained).
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Dietary and Plant-Derived Antioxidants:
Includes vitamins and minerals crucial for combating oxidative stress.
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Examples of Dietary Antioxidants:
Vitamin A, beta-carotene, Vitamin C, Vitamin E, selenium, lutein, lycopene, catechins.
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Ascorbic Acid (Vitamin C):
Important dietary antioxidant, cannot be synthesized by the body.
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Glutathione:
Synthesized in the body, antioxidant properties aid in neutralizing oxidative stress.
Melatonin:
A powerful antioxidant across membranes, supporting cellular protection.
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Antioxidant Supplementation Challenges:
Varied efficacy compared to natural sources and potential health risks associated with high dosages.
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Barriers to Antioxidant Supplement Use:
Research gaps, long-term effects, and dosing concerns affecting safety and efficacy.
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Usefulness of Supplements:
Can be essential for individuals with limited access to diverse diets or specific health needs.
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Acknowledgment: Thank you.