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HUNT 241 > Lecture 4 - Selenium > Flashcards

Lecture 4 - Selenium Flashcards

1
Q

selenium is a what type of element and what does this mean

A

trace element = found in very small amounts in the body

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2
Q

what is the geographic intake of selenium intake like

A

large variations from deficiency to toxicity

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3
Q

what is the RDI of selenium for men and women

A

women is 60ug/day

men is 70ug/day

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4
Q

what is the New Zealand upper limit for selenium

A

400ug/day

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5
Q

there are different species of selenium, what are the ones that we need to remember

A

the organic ones

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6
Q

what are the organic species of selenium and their sources

A
  • selenocysteine (SeCys) = animal products
  • selenomethionine (SeMet) = plant products
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7
Q

in where is the selenium incorporated in a selenium protein

A

selenium is incorporated in the amino acid in place of sulfur

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8
Q

where does selenium enter the food chain and how does it get to us

A

enters the food chain through plants
- animals eat plants
- we eat animals and plants

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9
Q

Se content of plants is affected by what

A

availability of Se in soil

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10
Q

what is the availability of Se in soil limited by

A

total soil Se content

bioavailability of Se to the plant

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11
Q

what makes Se less bioavailable to a plant

A

organic matter in soil absorbs Se ( makes it not available for the plant to take up )

Fe hydroxides, clay minerals bind Se (makes them unavailable)

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12
Q

how does pH of soil and selenium species affect the bioavailability

A
  • alkaline soils favour selenate > more bioavailable
  • acidic neutral soils favour selenide = less bioavailable
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13
Q

what are hyperaccumulators of selenium

A

accumulate > 1000mg Se/Kg DW in Se rich soils

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14
Q

example of hyperaccumulators of selenium

A

brazil nuts = very efficient way to increase intake of selenium

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15
Q

what are secondary accumulators of selenium

A

accumulate up to 100-1000 mg Se/Kg DW

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16
Q

examples secondary accumulators of selenium

A

brassica (broccoli, cabbage)

allium (garlic, onions, leeks)

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17
Q

what are non accumulators of selenium

A

accumulate <100 mg Se/Kg DW

will only draw up small amount of selenium = how ever we eat a lot of them

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18
Q

examples non accumulators of selenium

A

wheat crops (wheat, oats, barley, rye)

rice

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19
Q

examples of Se low regions

A

NZ, Korea, Finland

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20
Q

examples of Se rich regions

A

USA, Canada, Japan, China

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21
Q

examples of Se deficient regions

A

certain regions of China, Nepal, UK, France, India

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22
Q

common food sources of selenium

A

brazil nuts

mussels

lamb kidney

blue cod

mushroom

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23
Q

what is the intake of Se like in New Zealand

A

low soil in NZ = low intakes however this changes throughout the country

but the intake in 2008 nutrition survey was pretty close to the RDI

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24
Q

in the 2008 nutrition survey what was the main source of selenium in NZ

A

bread = not super high in selenium but we consume a lot of it

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25
Q

why does selenium intake heavily change throughout the country

A

south island has lower levels of Se

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26
Q

why is the Se content of animal products more reliable than plants

A

animals have an absolute requirement for Se, so the content will reflect what you eat but plants depend on bioavailability

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27
Q

what is the absorption of selenium like (%)

A

absorption of selenium is high (80% from food)

28
Q

where is the main place selenium is absorbed

A

in the duodenum

29
Q

what are the inorganic forms of selenium

A

selenate (SeO2 - 4)

selenide (SeO2 - 3)

30
Q

inorganic and organic selenium is converted to what in the enterocyte

A

converted to hydrogen selenite

31
Q

hydrogen selenite is packaged into what and transported where from the enterocyte

A

packaged into LDL and VLDL (lipoproteins) that transport selenium to the liver

32
Q

what is hydrogen selenite converted to in the liver

A

converted to functioning selenoprotein

33
Q

what is the form of selenium that does the biological functions of selenium

A

selenoprotein

34
Q

what does a selenoprotein do

A

transport protein = takes the selenium from the liver to the tissues in the body that need it

35
Q

how many known classes are there of selenoproteins and what do they mediate

A

mediate Se biological functions
- 25 known classes

36
Q

biological processes that selenoproteins are involved in

A
  • antioxidant defences
  • inflammation
  • muscle development and function
  • reproduction
  • thyroid hormone metabolism
  • immune function
37
Q

two important selenoprotein classes

A

glutathione peroxidases

thioredoxin reductases

38
Q

selenoprotein synthesis is what

A

high regulated

39
Q

up to a certain level of selenium intake your what will increase until you get to a certain level of intake

A

your selenoprotein synthesis will increase until you get to a certain intake where it will not increase anymore (it is maximised)

40
Q

what is the active part of selenoprotein

A

selenocysteine (inorganic selenium species)

41
Q

what can impact the functions of the selenoprotein

A

within the 3 UTR part of the mRNA, you can sometimes get differences in single nucleotide polymorphisms where you have different types of amino acids placed in different areas

42
Q

what are the isoforms of GPx (glutathione peroxidases) and their locations

A

GPx1 - cytosol

GPx3 - extracellular (plasma, extracellular fluid)

GPx4 - phospholipid

43
Q

what are the antioxidant defences of glutathione peroxidases

A
  • reduce hydrogen peroxide and other organic hydroperoxides
  • protect tissues from inflammatory and oxidative damage
44
Q

in the glutathione peroxidase cycle H2O2 oxidises the selenol of SeCys to form what

A

selenic acid (SeOH)

45
Q

in the glutathione peroxidase cycle what reacts with selenic acid and what does this form

A

glutathione molecule reacts with selenic acid to form Se-SR intermediate and water

46
Q

in the glutathione peroxidase cycle what reduces the Se-SR intermediate back to selenol and what is released

A

another glutethione molecule reduces the Se-SR intermediate back to selenol releasing oxidised gluthethione

47
Q

in the glutathione peroxidase cycle glutathione is restored by what

A

NADPH dependent glutathione reductase

48
Q

thioredoxin reductases are involved in what

A

vital cell processes

49
Q

what influence does liver disease have on selenoprotein synthesis

A

reduces SelP

50
Q

what influence does kidney disease have on selenoprotein synthesis

A

reduces GPx3

51
Q

what influence does inflammation have on selenoprotein synthesis

A

plasma Se reduced during the acute phase

52
Q

what up-regulates selenoprotein synthesis

A

oxidative stress

53
Q

selenium containing compounds differs from what

A

differs from selenoproteins

54
Q

what are selenium containing compounds

A

SeMet is non-specifically incorporated into body proteins

55
Q

when Se availability is limited what is prioritised

A

incorporation of Se into individual selenoproteins is prioritised

56
Q

when Se availability is limited what selenoprotein is prioritised and what isnt (what happens to activities of them)

A

GPx4 near top of hierarchy (activities maintained)

GPx1 near bottom of hierarchy (activities drop rapidly)

57
Q

what body tissues are prioritised when Se availability is limited

A

brain, endocrinological, reproductive tissues top of hierarchy (Se levels preserved)

heart, liver, kidney, lung tissues bottom of hierarchy (Se levels decrease)

58
Q

once selenium is absorbed by the body where is it taken

A

to the liver

59
Q

in the liver selenium is converted to what or excreted when ……. or ….

A

converted to selenoproteins (the essential active enzymes)

or excreted if too much

or incorporated into other body proteins (no biological importance of these)

60
Q

you can have high levels of body tissue selenium methionine but that doesn’t mean ….

A

that doesn’t mean you have high functioning selenium status

61
Q

long term Se concentration can be measured in

A

urine, toenails and hair

62
Q

what is medium / short term selenium intake usually measured in

A

plasma / serum concentration

63
Q

what are functional biomarkers of selenium

A

plasma selnoproteins (SelP - reflects liver and GPx3 - reflects kidneys)

64
Q

what can use to estimate selenium intake from plasma selenium concentrations

A

formulas

65
Q

study on men with low baseline selenium status found what reduction in prostate cancer due to supplementation

A

50% reduction in prostate cancer

66
Q

what is the shape of the relationship between Se and disease risk and why

A

U-shaped relationship

when you are deficient or have excessive levels you are most at risk

HUNT 241 (19 decks)

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