Micronutrient and Antioxidant Introduction Flashcards
What is the NPSC
The nutrient profiling scoring criterion is a system to determine the nutrient composition of a food and the kind of health claims that can be made on the food label as defined by FSANZ. The NPSC is primarily concerned about nutrients that should not be present in too large quantity (saturated fat, sodium, added sugar)
Requires a score less than 4 to be eligible
What is mandatory fortification and what are some examples?
Includes replacing nutrients lost by food processing and where there is robust evidence of requirement (e.g. folic acid added to bread making flour, iodine added in break-making salt)
What is voluntary fortification and what are some examples?
Where manufacturers are allowed under specific regulations to add selected nutrients to “enhance” their product (e.g. iron in cereals, calcium in orange juice, n-3 FA in margarine)
Must comply with claims regulations of quantity added (ratio of NRV, not above UL per serve etc.), and must comply with NPSC
What classifies an essential micronutrient?
Vitamins:
14 essential organic (not produced endogenously beside a couple exceptions) components required in very small amounts
Don’t yield energy but play a vital role in energy metabolism, growth, development, sustenance of health
Minerals:
14 essential major and minor (trace) minerals: essential to humans because they are not produced endogenously
If needed at >100mg per day = major minerals
If needed at <100mg per day = minor (or trace) minerals
Major minerals are found in the body structures in larger amounts than minor minerals (e.g. calcium vs copper)
Toxicity potential + competition in absorption = caution when using multi-minerals supplements
What are the 7 possible risks for deficiency?
- Is the dietary intake adequate/sufficient?
- Is the nutrient available for absorption? (i.e. is digestion of food optimal?)
- Is absorption optimal?
- Is conversion to the biologically active form optimal?
- Is the nutrient available to the cells? (i.e. are transport proteins available?)
- Is excretion increased?
- Are there any reasons for increased requirements? (e.g. pregnancy, athlete, elderly)
What are free radicals are how are they produced?
An atom with an unpaired electron pair in its outer shell. Many different types
- ROS = reactive oxygen species (free radical with oxygen)
Formed via many processes. Mitochondria large role
How can free radicals lead to disease?
Free radicals attack amino acids in proteins, lipids in cell membranes, nucleic acids in the DNA, and damage lysosomes. Over time, this damage can cause certain diseases
What are some endogenous and exogenous sources of free radicals?
Endogenous = metabolic processes requiring O (oxphos), exercising, inflammation, obesity, high energy diets
Exogenous = radiation, smoking, pollution, pesticides
What is oxidative stress?
When pro-oxidants outweigh anti-oxidants
Describe the enzymatic defence system in detail
Superoxide dismutase (SOD) converts superoxide (e.g. from oxidative phosphorylation) to hydrogen peroxide
- SOD1: is Cu and Zn dependent - SOD2: is Mn dependent - SOD3: is Fe dependent
Catalase converts hydrogen peroxide to water and oxygen. Present in energy organ, but especially in the liver
Glutathione enzyme system: reductases, peroxidases (GPX, Se dependant), and S-transferases. Continuously regenerates itself as to be always active
- GPX (glutathione peroxidase) catalases the breakdown of hydrogen peroxides, lipid peroxides etc., and also reduces glutathione - Selenium dependent
Role of Nrf2 in the enzymatic antioxidant defence system:
- Nrf2 is a transcription factor that promotes the expression of genes coding for antioxidant enzymes
- Nrf2 is activated when there is an increase in free radicals (e.g. ROS) in the cell, and by some phytochemicals ("Nrf2 activators")
- When activated, Nrf2 moves to the nucleus where it binds to the antioxidant response element (ARE) in DNA, to promote the expression of antioxidant enzymes genes. Endogenous ability to respond to ROS during exercise
- Antioxidant supplements don’t allow for Nrf2 to be activated (they convert ROS before it has the ability to activate Nrf2). Activation leads to production of enzymes that can work in various locations
Describe the enzymatic defence system in detail
Superoxide dismutase (SOD) converts superoxide (e.g. from oxidative phosphorylation) to hydrogen peroxide
- SOD1: is Cu and Zn dependent - SOD2: is Mn dependent - SOD3: is Fe dependent
Catalase converts hydrogen peroxide to water and oxygen. Present in energy organ, but especially in the liver
Glutathione enzyme system: reductases, peroxidases (GPX, Se dependant), and S-transferases. Continuously regenerates itself as to be always active
- GPX (glutathione peroxidase) catalase the breakdown of hydrogen peroxides and oxidises glutathione (selenium dependent) - Glutathione reductase reduces oxidised glutathione (riboflavin FAD dependent)
Role of Nrf2 in the enzymatic antioxidant defence system:
- Nrf2 is a transcription factor that promotes the expression of genes coding for antioxidant enzymes
- Nrf2 is activated when there is an increase in free radicals (e.g. ROS) in the cell, and by some phytochemicals ("Nrf2 activators")
- When activated, Nrf2 moves to the nucleus where it binds to the antioxidant response element (ARE) in DNA, to promote the expression of antioxidant enzymes genes = endogenous ability to respond to ROS during exercise
- Antioxidant supplements block this activation
Describe the non-enzymatic defence system in detail
Alpha-tocopherol (vitamin E) removes free radical intermediates by donation of hydrogen, thus preventing propagation reaction to continue. This produces oxidised alpha-tocopheryl radicals that can be recycled through reduction by other antioxidants (ascorbate, retinal, ubiquinol)
Ascorbic acid (vitamin C) reduces and neutralises ROS by donating electrons (e.g. to hydrogen peroxide). It is then returned and maintained in reduced form by reaction with glutathione
Glutathione is the most important cellular antioxidant
- It is a tripeptide formed from cellular cysteine, glutamate and glycine
- The thiol group in cysteine is a reducing agent (electron donor to inhibit reactive oxygen and nitrogen species)
- Glutathione is also a component of the enzymatic antioxidant glutathione system
- Glutathione is kept reduced in cells by glutathione reductase
Bilirubin, albumin, and thiols are hydrophilic radical scavengers, and vitamin E and ubiquinol are lipophilic scavengers
Uric acid = 50% of antioxidant ability of plasma because present in high concentration proportionally to other antioxidant compounds. Scavenger of singlet oxygen, as well as other radicals
Melatonin acts in the mitochondria as an electron donor, and also crosses the cell membrane and blood brain barrier. Once oxidises it cannot be reduced to its former state because it forms end-products with free radicals (= “suicidal antioxidant”) (unlike vitamin E and C which can be reduced again). Melatonin appears to boost the activity of antioxidant enzymes SOD and GPX via signalling
Describe the free radical theory of ageing
Cells continuously produce free radicals via normal metabolism and oxidation of organic compounds and these free radicals damage cellular macromolecules (like DNA, lipids, protein) and accumulation of this damage over time causes ageing
What are the broad differences between the two antioxidant defence systems?
- Enzymatic system
- Composed of gene products (enzymes). E.g. catalases, superoxide dismutase, glutathione peroxidase, hemoxygenase etc.
- Deactivate free radicals in a number of processes. (e.g. conversion to water and O2)
- Require co-factors for function (zinc, copper, iron, manganese, selenium from diet)
- Non-enzymatic system
- Composed of plasma constituents:
§ E.g. bilirubin, uric acid, melatonin, albumin, glutathione
§ Act as electron donors primarily (and by other mechanisms too) - Composed of food constituents:
§ Vitamins
→ E and C are electron donors
§ Minerals
→ Zn, Cu, Fe, Mn, Se are co-factors in the enzymatic system
§ Phytochemicals
→ Carotenoids, flavonoids, epicatechins, resveratrol etc.
→ Mild electron donors
→ Signal gene transcription of enzymatic system via Nrf2 activation
- Composed of plasma constituents:
