Nutrition Lecture 4: Selenium

Question 1

What is selenium?

Answer 1

An essential trace element

Question 2

How does selenium intake range globally?

Answer 2

Large geographical intakes from deficiency to toxicity - China’s intake is extremely high

Question 3

What is the RDI for selenium?

Answer 3

Women = 60ug/day
Men = 70ug/day

Question 4

What are the different species of selenium?

Answer 4

Organic and Inorganic

Question 5

What are the two organic forms of selenium?

Answer 5

SeCys and SeMet

Question 6

What form of selenium is found in animal products?

Answer 6

SeCys

Question 7

What form of selenium is found in plant products?

Answer 7

SeMet

Question 8

What are the two inorganic forms of selenium?

Answer 8

Selenate (SeO2- 4)
Selenide (SeO2- 3)

Question 9

What is the active part of selenium?

Answer 9

SeCys - responsible for 99% of the metabolic actions

Question 10

What are inorganic forms of selenium not attached to?

Answer 10

Not attached to amino acids

Question 11

How does Se enter the food chain?

Answer 11

Through plants

Question 12

What is the Se content of plants affected by?

Answer 12

Availability of Se in soil

Question 13

What matter in soil absorbs Se?

Answer 13

Organic matter

Question 14

What binds Se?

Answer 14

Clay minerals

Question 15

What form of Se do alkaline soils favour?

Answer 15

Selenate - more bioavailable

Question 16

What form of Se fo acidic-neutral soils favour?

Answer 16

Selenide - less bioavailable

Question 17

What are the three classifications of Se accumulation in plants?

Answer 17

1. Hyperaccumulators
2. Secondary-accumulators
3. Non-accumulators

Question 18

What are hyperaccumulators?

Answer 18

Accumulate >1000mg/Se/kg

Question 19

What is an example of a hyperaccumulator plant?

Answer 19

Brazil nuts

Question 20

What are secondary-accumulators?

Answer 20

Accumulate up to 100-1000mg/Se/kg

Question 21

What are examples of secondary-accumulators?

Answer 21

Brassica (rapeseed, broccoli, cabbage) Allium (garlic, onions, leeks)

Question 22

What are non accumulators?

Answer 22

Accumulate <100mg/Se/kg

Question 23

What are examples of non-accumulators?

Answer 23

Wheat crops (wheat, oats, barley, rye) Rice

Question 24

Is NZ considered a deficient, low or rich region of Se?

Answer 24

Low region - we have moderate to low intakes

Question 25

What are good food sources of Se?

Answer 25

Brazil nuts, Seafood, kidney, livers and brains

Question 26

What food sources do NZ'ers get their Se from?

Answer 26

Bread, seafood, chicken

Question 27

What are the regional differences in Se intake in NZ?

Answer 27

Intake is significantly higher in the North Island

Question 28

Why are animal sources of Se more reliable than plant sources?

Answer 28

Plant sources are affected by soil variability, whereas animals have an absolute requirement for Se - If the soil is deficient in selenium, the animals must be fed it from somewhere else

Question 29

What is the absorption of Se?

Answer 29

High - 80% from food sources

Question 30

Where is selenium processed?

Answer 30

In enterocytes

Question 31

What is organic selenium converted into?

Answer 31

Into H2Se and then packaged into lipoproteins

Question 32

After selenium is packaged into lipoproteins where does it go?

Answer 32

Taken into the liver and converted into a functional protein - selenoprotein

Question 33

What does organic Se need to be converted into before it can be used in the body?

Answer 33

Selenoprotein

Question 34

What are inhibitors of Se absorption?

Answer 34

None are known

Question 35

How many classes of selenoproteins are there?

Answer 35

25 known classes

Question 36

What are the biological processes of selenoproteins?

Answer 36

- Antioxidant defence - Inflammation - Muscle development - Reproduction - Thyroid hormone metabolism - Immune function

Question 37

What is selenocysteine?

Answer 37

The active part of a selenoprotein - an essential amino acid component in selenoproteins

Question 38

Is selenoprotein synthesis regulated?

Answer 38

Highly regulated - there is a maximum amount of selenoproteins that we can and will synthesise

Question 39

How do differences arise in selenoprotein function and usage between people?

Answer 39

Within the 3UTR you can sometimes get differences in polymorphisms which affects the function of the protein

Question 40

What are glutathione peroxidases (GPx)

Answer 40

selenium-containing antioxidant enzymes

Question 41

What are the different forms of GPx?

Answer 41

GPx1 GPx3 GPx4

Question 42

Where is GPx1 found?

Answer 42

in the cytosol of cells

Question 43

Where is GPx3 found?

Answer 43

is extracellular in the blood and plasma, and ECF

Question 44

Where is GPx4 found?

Answer 44

in phospholipids

Question 45

What is the main function of GPx?

Answer 45

Antioxidant defences

Question 46

What 2 main antioxidant defences does GPx carry out?

Answer 46

- Reduces hydrogen peroxide and other organic hydroperoxides - Protects tissues from inflammatory and oxidative damage

Question 47

What are thioredoxin reductases?

Answer 47

Selenium containing enzymes

Question 48

What is the function of Thioredoxin reductases?

Answer 48

involved in vital cell processes, found everywhere

Question 49

What does liver disease reduce?

Answer 49

reduces selenoproteins

Question 50

What does kidney disease reduce?

Answer 50

GPx3

Question 51

What type of stress upregulates selenoprotein synthesis?

Answer 51

Oxidative stress

Question 52

What does inflammation reduce?

Answer 52

Plasma Se is reduced during acute phase

Question 53

What are selenium-containing proteins?

Answer 53

Differ from selenoproteins, proteins in the body that incorperate seleno-methionine

Question 54

What does SeMet stand for?

Answer 54

Seleno-methionine

Question 55

What happens when Se availability is limited?

Answer 55

Incorporation of Se into individual selenoproteins is prioritised

Question 56

What selenoprotein is at the top of the hierarchy (activities maintained when deficient)?

Answer 56

GPx4

Question 57

What selenoprotein is at the bottom of the hierarchy (activities drop when deficient)?

Answer 57

GPx1

Question 58

What body tissues does Se prioritise when deficient?

Answer 58

Brain, endocrinological, reproductive tissues

Question 59

What body tissues does Se disregard when deficient?

Answer 59

Heart, liver, kidney, lung tissues

Question 60

What body parts can Se concentration be measured in? (long term intake)

Answer 60

Urine, toenails, hair

Question 61

How is Se commonly measured? (short-medium term intake)

Answer 61

Plasma/serum Se concentration (SelP and GPx3)

Question 62

What plasma selenoprotein reflects liver concentration?

Answer 62

SelP

Question 63

What plasma selenoprotein reflects kidney concentration?

Answer 63

GPx3

Question 64

What is the relationship between plasma Se and dietary intake?

Answer 64

Plasma Se concentrations increase with increasing Se intake

Question 65

When do we see a sharper increase in plasma Se?

Answer 65

When Se intakes are less than 70ug/day

Question 66

When do plasma Se concentrations decrease?

Answer 66

During acute phase (inflammation/sickness)

Question 67

When does plasma GPx activity reach maximum? (plateus)

Answer 67

at Se intakes of 40-60ug/day (plasma Se of 85ug/L)

Question 68

When does plasma SelP concentration reach maximum? (plateus)

Answer 68

at Se intakes of 95ug/day (plasma Se of 120ug/day

Question 69

What is the relationship between selenium and all-cause mortality?

Answer 69

Risk of all cause mortality is highest risk at low and high concentrations - want to sit at recommended (U shape relationship)