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Antioxidants

(+ selenium)

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Free Radicals

  • Highly Reactive Molecules

    • Formed from interactions with oxygen (oxidative stress)

    • Also called Reactive Oxygen Species (ROS)

    • Can start chain reactions with molecules in the body

      • Leads to destruction of cells

    • Electrons

      • usually in pairs

      • each pair moves around the nucleus in a defined space (orbital)

    • Free radicals (atom or molecule) have one or more unpaired electrons)

      • if an atom loses one electron, it has become a free radical​

      • it tries to steal an electrons from a healthy atom or molecule because it wants to have pairs, which leads to destruction

      • free radicals are identified by a dot in the upper right corner

        • ex.​

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Types of Free Radicals

  • Superoxide Radical

    • made as apart of normal metabolism​

    • made by phagocytic cells (neutrophils, monocytes, macrophages and eosinophils) to kill invading organisms

  • Hydroxyl Radical

    • highly reactive​

    • formed from superoxide radical and H2O2 in the presence of metals

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study question: 

  • do we want zero free radicals in our body?

  • Nitric Oxide

    • good functions​

      • produced by NK cells to kill invaders​

      • vasodilation, vasorelaxation

      • mediates cell signals

    • bad functions

      • overproduction can kills immune cells​

      • signal transduction trigger

​

  • Peroxyl Radical

    • can be formed directly by interaction of O2 with the double bond of a FA or as part of a chain reaction with another ROO​

    • targets unsat lipids

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Diseases Associated with Free Radicals

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Antioxidants

  • —Reduce oxidative stress (Redox Agents)

    • —Help control and eliminate free radicals

    • —Vitamins and other compounds

    • —Need regeneration themselves​

  • —Antioxidants work by giving up one of their own electrons so that the free radical has a pair again

    • —Enzyme systems

      • —In all cells of the body

    • —Outside sources

      • —Diet (food sources)

      • —Dietary supplements

study question: 

  • describe how antioxidants are able to neutralize free radicals

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Antioxidant Defenses

  • Endogenous Enzyme Systems

    • superoxide dismutase (SOD)​

    • catalase

    • glutathione peroxidase + reductase

  • Exogenous

    • diet (food sources)​

      • fruits and vegetables​

    • dietary supplements

    • vitamin E, vitamin C, carotenoids, bioflavonoids

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SOD

  • primary defense

  • present in plasma, cytoplasm (needs Zn and Cu) and mitochondria (needs Mn)

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catalase

  • present in peroxisomes (some in cytoplasm, heme iron dependant)

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Glutathione peroxidase (Se) and reductase (FAD)

  • principle antioxidant defense

  • plasma, cytosol and mitochondria

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Vitamin E

  • lipid soluble

  • free radical scavenger

  • important in protecting membrane structure

  • works to terminate chain reactions involving lipid peroxides

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study questions: 

  • describe how glucose metabolism plays a role in antioxidant defense

  • what other vitamins play a role?

  • why is solubility important?

Vitamin C

  • ascorbic acid (AA)

  • water soluble

  • free radical scavenger

  • helps recycle vitamin E

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Coordination of Nutrients

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study question: 

  • using both this image and the image above, describe how different nutrients work together in antioxidant defense

Antioxidant Defense Cont.

Carotenoids

  • lipid soluble

  • Can neutralize free radicals in vitro

  • Antioxidant role in vivo remains unclear

  • Epidemiological evidence points to a protective role against diseases associated with oxidative stress

Bioflavonoids

  • Epidemiological evidence points to a protective role against diseases associated with oxidative stress

    • French paradox—red wine

    • Colored foods: blueberries, strawberries, grapes

  • Antioxidant activity demonstrated in vitro

Flavonoids

  • Flavonoids in teas and chocolate

  • Improved blood flow, reduced blood pressure, anti-inflammatory effects, antioxidant effects

Selenium

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  • Se occurs naturally in food mostly as selenoamino acids

    • selenomethionine (primarily in plants) and

    • selenocycteine (mostly in animal products

  • Inorganic forms can be found in vegetables

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Se Absorption

  • —Efficient absorption in the small intestine, esp duodenum

  • —Organic selenium (selenoamino acids) are absorbed via amino acid transporter

  • —Enhancers include

    • —Vitamins A, C, E; reduced glutathione

  • —Inhibitors include

    • —Phytate, heavy metal​

Se Transport and Storage

  • ​Se binds to plasma proteins for travel through the liver and other tissues

  • —Selenoprotein P is the major Se-containing protein in plasma, representing >50% of  Se in circulation

  • Tissues with high Se levels includes

    • Thyroid gland, kidney, liver, heart, pancreas, and muscle

Selenium Functions

  • Selenium is a cofactor of some enzymes and play roles as anti-oxidant, in immune function, in pancreatic function, in DNA repair, etc

  • Glutathione peroxidase (GPX)

    • GPX removes hydrogen peroxides and hydroperoxides from tissue è is an important player in presenting/controlling damage caused by oxidative stress

    • —There are different isoforms

      • —GPX1~4 are Se-dependent

    • —Within cells

      • —GPX is found mainly in cytoplasm, and in mitochondrial matrix as well

      • —GPX4 is associated with cell membrane

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Selenium Deficiency 

  • —RDA has been established

  • —Risk factors

    • —Living in areas where Se is very low in soil

    • —Increased needs/turnover

      • —Smoking, strenuous exercise, increased expose to pollutants such as heavy metals

      • —Malabsorption

      • —On total parenteral nutrition

  • —Keshan Disease

    • —Keshan is the name of a county in NE China

    • —Affecting young women and children

    • —Features

      • —Cardiomyopathy

      • —Congestive heart failure

      • —Multifocal necrosis of heart tissue (replaced by fibrous tissue)

    • —Coxsachie virus appears to be involved

      • —The virus becomes more virulent under Se deficiency

Selenium Toxicity 

  • UL has been established

  • In miners and those who consume large doses of Se supplement

  • Signs and symptoms

    • Nausea, vomiting, diarrhea

    • Hair loss

    • Fatigue

    • Peripheral neuropathy

©2023 by Syracuse University Dr.Margaret Voss

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