Antioxidants Flashcards
What are antioxidants?
Vitamins: fat-soluble (beta-carotene, E & A); water-soluble (C)
Minerals: trace (Selenium, Copper, Zinc, Manganese, and Iron)
What are free radicals?
- unstable atoms that contain an unpaired electron in the outer orbital (shell)
What function do antioxidants serve?
Antioxidants reduce naturally-occurring reactive oxidizing species (ROS), or damage caused by ROS that have one unpaired electron in their outer orbital.
- Neutralize free radicals
- Inhibit oxidant formation
- Intercept oxidants once they are formed
- Repair oxidant-induced damage
Name three enzymes that require mineral antioxidants to function.
- glutathione peroxidase (requires Se)
- superoxide dismutase (requires Cu, Zn, Mn)
- catalase (requires Fe)
Compare the vitamin antioxidants with the mineral antioxidants.
Vitamin antioxidants donate their electrons to the unpaired electron in the outer orbital of the free radical, thereby neutralizing the free radical and ending the chain reaction.
Mineral antioxidants activate enzymes to destroy free radicals (converted to less damaging molecules that are excreted from the body).
What substances do free radicals target?
Free radicals destabilize other molecules and damage:
- cell membranes (lipids)
- cellular proteins
- blood LDL lipoproteins
- nuclear DNA
How are free radicals formed?
- endogenously: normal products of metabolic processes (eg - oxidizing macronutrients, immune responses, production of ATP)
- exogenously: environmental (eg - radiation from the sun, pollution, tobacco smoke, etc…)
Provide examples of free radicals.
- superoxide radical (O2- )
- hydroxyl radical (OH)
- nitric oxide (NO)
Describe the interrelationship between vitamin E and C.
- Active vitamin E (an antioxidant) donates one of its hydrogen atoms (with accompanying electron) to a lipid radical.
- Vitamin E is no longer active, but it has stopped the lipid radical from creating further camage and generating more free radicals.
- Vitamin E can be reactivated by accepting a hydrogen atom from vitamin C (ascorbic acid).
- Both the reduced & oxidized forms of vitamin C are stable.
Provide three rich sources of vitamin C.
- kale
- red bell pepper
- guava
- kiwi
- broccoli
- tomato
- blueberries
- oranges
Provide three rich sources of vitamin E.
- brazil nuts
- sunflower seeds
- wheat germ
(nuts, seeds)
Provide three rich sources of beta-carotene.
- carrots
- yams
- kale
- tomatoes
- kale
(leafy greens, red/orange veggies)
Provide three rich sources of iron.
- lentils
- hempseeds, linseed
- pumpkin seeds
- kale
- beans
- tofu
- oats
- spinach
- red meat, shellfish (disgusting)
Provide three rich sources of copper.
- spirulina
- nuts and seeds
- leafy greens
- dark chocolate
- shiitake mushrooms
Provide three rich sources of selenium.
- brazil nuts
- pork, beef, turkey, chicken, fish, and eggs. (ewwww)
Provide three rich sources of manganese.
- brown rice
- almonds, pecans
- pinto beans, legumes
- oatmeal,
- leafy green vegetables
- pineapple
- dark chocolate
Provide three rich sources of zinc.
- chickpeas
- lentils, and beans
- nuts and seeds
- whole grains
- meat, shellfish, dairy, eggs (nasty af don’t support this!)
What are the two stable forms of vitamin C?
Ascorbic acid (reduced form)
Dehydroascorbic acid (oxidized form)
What are the 3 ‘natural sets’ of antioxidant nutrients a la FNH 250?
- Vitamin E, Selenium & Vitamin C
- Beta-Carotene & Vitamin A
- Copper, Zinc, Manganese, & Iron
Is taking antioxidant supplements a good idea?
Myths:
- Antioxidants are all vitamins
- All antioxidants are created equal
- It’s important to eat “super fruits”
- You should amp up your intake with supplements
- If some antioxidants are good, more are better
- Packaged food with labels touting antioxidants will boost your health.
How many forms of tocopherols are there?
- tocopherols “to bring forth birth” (aka Vitamin E) has 8 forms
What form of vitamin E has effective biological activity?
alpha-tocopherol
What is the bioavailability of vitamin E and where is it stored in the body?
- moderate bioavailability (~20-70%)
- mostly stored in adipose (~90%), some in cell membranes, little in liver
What are the fat-soluble vitamins?
beta-carotene, E, and A
What are the water-soluble vitamins?
C
Define: bioavailability.
The proportion of a drug or other substance (eg - nutrients in food) which enters the circulation when introduced into the body and so is able to have an active effect.
Give an introduction for selenium, (trace mineral).
- high bioavailability (~60-90%)
- homeostasis regulated by the kidneys
- high potential for toxicity with supplements
There are 25 selenoproteins (proteins bound to selenium) known in humans. What are the most common?
- selenocysteine (active Se)
- selenomethionine (storage Se)
How is vitamin E lost during food preparation?
Vitamin E is readily destroyed by heat (eg - deep frying), and exposure oxygen & light.
Keep oils in cool, dark cupboard or fridge.
What is the primary action of vitamin C?
Vitamin C primarily acts as a reducing agent (electron donor).
Discuss the absorption of vitamin C in the body.
Absorption (<100mg): 80+%
Absorption (1000mg): ~50%
Excess vitamin C is excreted in urine.
What are the antioxidant roles of Vitamin E?
Vitamin E maintains membrane integrity:
- in cell membranes - neutralizes free radicals, maintains integrity of membranes (especially lung)
- in nuclear and mitochondrial membranes - protects DNA and other celluar compounds from oxidative damage.
What is the antioxidant role of selenium?
Selenium, through its role in glutathione peroxidase, reduces production of free radicals, and spares use of vitamin E.
- Cofactor for glutathione peroxidase enzyme (riboflavin is a necessary coenzyme) - protects cell membranes.
What is the antioxidant role of vitamin C?
Vitamin C donates an electron to a free radical to stop damage. Vitamin C also:
- restores vitamin E to active antioxidant form
- acts in intracellular and extracellular fluid compartments
- keeps folate (a B vitamin) coenzyme intact
What are the non-antioxidant roles of Vitamin E?
Vitamin E reduces platelet aggregation by inhibition of enzyme protein kinase C required for platelet aggregation.
Vitamin E (along with sufficient fat in the body) is also required for successful reproduction.
Other roles include:
- protects LDL from oxidation
- protects lung cell membranes from oxidation
- iron metabolism (RBC membrane integrity)
- immune function (protects WBC)
What are the non-antioxidant roles of selenium?
Thyroid hormones
- Se is needed for the enzyme that converts T4 (thyroxine) to T3 (triiodothyronine): T3 has greatest biological activity.
- thyroid hormones help regulate basal metabolism, growth and development, as well as body temperature.
What are the non-antioxidant roles of vitamin C?
Vitamin C enhances iron absorption.
- increases absorption of non-heme iron (Fe3+, ferric) found in plant foods
- keeps dietary iron in reduced oxidation state (Fe2+, ferrous) for increased absorption
Vitamin C synthesizes collagen.
- collagen maintains integrity of connective tissue, skin, tendons, scar tissue, blood vessels, gum tissue
- collagen helps prevent bruising and ensures proper wound healing
Other roles include:
- immune cell action and function
- thyroid hormon, thyrozine - helps regulate BMR and maintain body temperature
- steroid hormones (eg - cortisol)
- neurotransmitters - epinephrine
- compounds used for DNA synthesis
What demographic is at greatest risk for vitamin E deficiency?
Preterm infants - born before 37 weeks of gestation
- transfer of vitamin E from mother to fetus normally occurs during last few weeks of pregnancy; thus, low stores, increased need for growth, if preterm
- preterm infants often placed in incubator - a high oxygen environment, increased oxidative stress on lung membranes, increased need for vitamin E - use oral supplementation to correct.
What are the consequences of a vitamin E deficiency?
Hemolytic Anemia
- lose integrity of red blood cell membrane, so red blood cells are unable to carry sufficient oxygen to cells for use in generating energy from macronutrients
Symptoms of anemia - fatigue, lethargy
What are the consequences of selenium deficiency?
- Deficiency is seen in areas where people primarily eat local foods and soil is depleted of selenium.
- Those who are deficient develop severe joint pain and heart muscle disease - cardiomyopathy - known as Keshan’s disease.
What demographics are at risk of vitamin C deficiency?
- alcoholics - at risk, if consuming a nutrient-poor diet (likely)
- smokers - vitamin C used to combat the multitude of antioxidants produced by cigarette smoking leading to lower levels in the body (RDA: +35 mg/day more than a non-smoker)
- burn patients - needed for would healing, skin repair
- old timey sailors
What are the consequences of a vitamin C deficiency?
Scurvy
Symptoms:
- weakness
- petechiae - pinpoint hemorrhages on face and limbs
- bleeding gums, loose teeth
- painful joints
- failure of wounds to heal (not unique to vitamin C)
Treatment:
- ~5 days @ 100 mg/day intake will reverse symptoms
Also - widespread tissue breakdown - due to vitamin C’s role in the synthesis of collagen
What are the consequences of selenium toxicity?
- only a concern for supplement use, safe from food sources
- symptoms: nausea, vomiting, irritability
What are the causes and consequences of vitamin E toxicity?
Causes:
food intake - safe, not toxic
supplement use - most likely reason for increased risk of toxicity (seen at continued intakes of 800-1200 mg/day (RDA: 15 mg/day)
Symptoms:
- muscle weakness, fatigue, nausea, diarrhea
- vitamin E augments the effect of anticoagulants (eg - aspirin); can lead to uncontrolled bleeding
Briefly discuss the SELECT (SELenium &/or vitamin E) Cancer Trial.
Define: megadose.
>10X DRI
Since excess vitamin C is excreted in urine, is toxicity possible?
Yes, megadoes (>10X DRI) can cause diarrhea.
Vitamin C can also act as a pro-oxidant in high doses. High doses of vitamin C can release iron from protein. Free iron can cause cellular damage, acting as a catalyst to promote free radicals.
In addition, when high intakes of vitamin C are quickly reduced to normal, rebound scurvy may occur.
Furthermore, high vitamin C intake increases risk of kidney stone formation.
To reiterate: what are food sources for vitamin E, Selenium & vitamin C?
Legend:
- Vitamin E
* Selenium
t Vitamin C
Are trace minerals lost during food preparation?
Trace minerals are stable to food preparation processes.
How is vitamin C lost during food preparation?
Think back to Chem 123 lab! :)
Vitamin C is easily lost in food processing & cooking.
Susceptible to loss with exposure to:
- excessive heat, air (oxygen), baking soda.
- Try to consume fresh fruits.*
What are the recommendations for vitamin E intake?
What are the recommended intakes for vitamin C?
What are the recommended dietary intakes for selenium?
Introduce Vitamin A.
Retinoids + Carotenoids = “Vitamin A”
Retinoids - pre-formed vitamin A (animal foods)
- retinol (alcohol form) - reproduction
- retinal (aldehyde form) - vision
- retinoic acid (carboxylic acid form) - growth & development
Carotenoids - pro-form of vitamin A (plant foods)
- ß-carotene - greatest biological activity of carotenoids
Discuss the interconversion of Vitamin A Compounds in the body.
Notice the directionality of the arrows.
Where is vitamin A stored in the body?
Retinol is stored mostly (~90%) in the liver, a little in adipose tissue.
ß-carotene can accumulate in the subcutaneous fat layer under the skin, giving skin a yellow colour (hypercarotenemia)
What is the ratio of biological activity when comparing ß-carotene to retinol?
12 µg of ß-carotene is equivalent to 1 µg of retinol. (conversion of other carotenoids to retinol is less efficient)
- use RAE (retinol activity equivalents)
Provide a brief introduction for ß-carotene.
- >600 different carotenoid pigments
- ~50 common in human diet (eg - ß-carotene, lutein, lycopene, cryptoxanthin, zeaxanthin)
- ~20-40% absorbed, with fat
- stored in adipose tissue, subcutaneous fat layer & liver
- liver converts ß-carotene to retinol; no DRI
- carotenoids have antioxidant properties
What is the antioxidant role of ß-carotene?
- clear in-vitro antioxidant function; not as clear antioxidant function in humans
- fat-soluble: protects against oxidation of cell membranes and Low Density Lipoproteins (LDL)
- relatively weak antioxidant compared to vitamin E
What is the antioxidant role of retinol (vitamin A)?
- retinol quenches free radicals
- protects LDL from oxidation to reduce risk of heart disease
- may decrease initiation of cancer & atherosclerosis
What are the non-antioxidant roles of ß-carotene?
What are the non-antioxidant roles of Vitamin A?
How does Vitamin A support your vision?
Retina - lining at the back of the eye:
- rods - allow us to see in black and white
- cones - allow us to see in colour
- light strikes retina and converts cis-retinal to trans-retinal in visual pigment rhodopsin, causing a nerve impulse to the brain to interpret the object
Cornea - clear membrane at front of eye
Macula - ß-carotene rich; central vision
How does Vitamin A support growth, development & reproduction?
How does Vitamin A support the health of mucous membranes in epithelial tissue?
How does Vitamin A support immune function?
What are the consequences of ß-carotene deficiency?
- there is no DRI for ß-carotene since there are no known deficiency symptoms; non-essential nutrient!
- may contribute to increased damage to DNA and onset of epithelial cancers, and heart disease
What are the consequences of Vitamin A deficiency?
- Vision (retina)
- night blindness: slow sight recovery from flashes of light under dim conditions
- Xerophthalmia (dry eye): leads to blindness in >350,000 children each year
- Growth, Development & Reproduction
- animals can’t reproduce
- children fail to grow properly
- deficiencies early in life can affect jaw development - causes poor dental and nutritional health throughout life
- Health of Mucous Membranes in Epithelial Tissues
- decreased mucous production
- keratinization of cells occurs, hardening of epithelial cells, increased risk of infection (eg - eye, respiratory, urinary, GI), decreased absorption through intestinal cells
-
Immune Function
* children in developing countries have a high incidence of measles (viral infection) - severity of infection correlates with deficiency since vitamin A is required to activate T-cells of immune system.
What are the consequences of ß-carotene toxicity?
Hypercarotenemia - high intakes can cause skin to turn orange; reversible, harmless
Briefly discuss the ATBC & CARET trials.
What are the consequences of Vitamin A toxicity?
Symptoms:
- loss of appetite, nausea, headaches
- dry skin
- enlarged liver, spleen
- bone defects - can reduce bone density
What are the causes of Vitamin A toxicity?
What are the types of Vitamin A toxicity?
To reiterate; what are some food sources for ß-carotene and Vitamin A?
What are the dietary recommendations for ß-carotene & Vitamin A?
What are the antioxidant roles of Copper, Zinc, and Manganese?
- Required as cofactors by the superoxide dismutase enzyme to protect against oxidative damage in the cytoplasm (Cu, Zn) and in the mitochondria (Mn) of cells.
Each one of these trace minerals has multiple other roles in the body.
What are the antixodant roles of Iron?
- Integral component of catalase antioxidant enzyme, decreases damaging action of hydrogen peroxide being converted into hydroxyl radicals (OH*)
- Iron has multiple other roles in the body as well.*
What are Dr. Hammond’s (FNH 250 prof!) recommendations for antioxidants?
Provide two foods rich in beta-carotene.
Yams
Squash
Carrots
Sweet Potato
Pumpkin
Red blood cells are susceptible to disruption when there is a deficiency of:
- vitamin C?
- beta-carotene?
- sodium?
- potassium?
- vitamin E?
Vitamin E
[…] are characterized by having an unpaired electron in their outer orbital.
Reactive Oxidizing Species (ROS) / Free Radicals
What does the turnover of bone tissue relies on adequate:
- sodium?
- vitamin E?
- vitamin A?
- potassium?
- chloride?
Vitamin A
What vitamin deficiences causes the breakdown of collagen?
- vitamin A
- vitamin C
- vitamin E
- potassium
- phosphorus
Vitamin C
