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Nutrition 522 > Selenium > Flashcards

Selenium Flashcards

1
Q

Selenium is an…

A

Essential trace element

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2
Q

Primary function of Se

A

Incorporation into selenoproteins (25)

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3
Q

Inorganic selenium is found in…

A

Soil

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4
Q

Selenite

A

SeO32

(Inorganic)

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5
Q

Selenous acid

A

H2SeO3

(Inorganic)

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6
Q

Selenate

A

SeO42

(Inorganic)

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7
Q

Organic selenium is found in…

A

Plants & animals

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8
Q

Describe formation of organoselenium compounds (i.e. SeCys, SeMet)

A

Plants/microorganisms replace sulfur with selenium in the biosynthetic pathways for cysteine and methionine (sulfur-containing amino acids)

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9
Q

Selenoamino acids are defined as…

A

Se covalently bonded with carbon atoms (i.e. SeMet, SeCys)

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10
Q

Selenomethionine (SeMet) synthesis

A

Synthesized by plants/microorganisms

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11
Q

Selenocysteine (SeCys) synthesis?

A

Co-translationally synthesized in animals/humans

Inorganic selenide is activated and added in a co-translational conversion of serene –> SeCys while the AA is bound to a specific tRNA coding for the selenoprotein

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12
Q

Methionine =

A

Essential amino acid in humans/animals (diet only)

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13
Q

Cysteine =

A

Synthesized from methionine

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14
Q

Selenium RDA is…

A

Adults: 55 mcg/day

Infants: 15 mcg/day up to 20 mcg/day after 6 mos (based on breast milk)

Children: 20-40 mcg/day

Pregnancy: 60 mcg/day Lactation: 70 mcg/day

Selenium intakes of most Americans exceed the RDA

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15
Q

Selenium RDA mostly based on…

A

Maximal expression of glutathione peroxidase 3

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16
Q

What determines selenium content of plant-based foods?

A

Varies according to soil Se levels, which are affected by:

Soil pH

Organic matter in dirt

Form of selenium present

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17
Q

Se content of foods tends to correlate with…

A

Protein content; because SeCys and SeMet are mostly incorporated into proteins

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18
Q

Muscle meats contain…

A

0.3 to 0.5 mg Se/kg (fresh weight)

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19
Q

Organ meats contain __x higher/lower concentrations of Se

A

4x to 15x higher

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20
Q

Foods high in selenium

A

Brazil nuts, fish, organ meats, muscle meats, high protein foods

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21
Q

Absorption of inorganic Se from food is __% (selenite)

A

84%

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22
Q

Absorption of organic Se from food is __% for SeMet

A

98%

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23
Q

Inorganic Se (selenate/selenite) absorbed via…

A

Diffusion

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24
Q

Selenoaminoacids absorbed via…

A

Transport by amino acid transporters

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25
Q

Bioavailability of selenoamino acids from plants/animals depends on…

A

Digestibility of these proteins

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26
Q

Fate of ingested SeMet

A

Incorporated into body proteins non-specifically in place of methionine based on protein methionine content

Metabolized to selenide via same pathway which converts Met to Cys

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27
Q

Fate of ingested SeCys

A

Incorporate selenium indirectly as SeCys as residues in new selenoproteins

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28
Q

Fate of ingested inorganic Se (selenite or selanate)

A

Se incorporated as SeCys residues in new selenoproteins)

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29
Q

Describe the circulating plasma pool of Se

A
  1. SepP1 and GPX3 (contain ~50-60% of total plasma Se)
  2. Non-specific SeMet in albumin & other plasma proteins
  3. A small amount of selenosugars
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30
Q

Plasma Se taken up by the liver and re-enters circulation as…

A

Selenoprotein P (SepP) for distribution of Se to extrahepatic tissues

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31
Q

General function of selenoproteins (3)

A
  1. Cellular protection from oxidative stress
  2. Thyroid hormone metabolism
  3. Reproduction

Much more!

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32
Q

Maximal plasma selenoprotein levels occurs at…

A

Se intakes yielding plasma levels > 70 ng/mL

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33
Q

List selenoproteins (4):

A

Glutathione peroxidases (GPX) Thioredoxin reductase Selenoprotein P Selenoprotein W

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34
Q

GPX

A

Glutathione peroxidase

Antioxidant enzymes that reduce ROS (e.g H2O2) by coupling their reaction with the oxidation of reduced glutathione

6 isoforms in animals

GPX activity depends on selenium status; used as a biomarker

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35
Q

Thioredoxin reductase

A

Regenerates several antioxidants, including Vit C

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36
Q

Selenoprotein P

A

Antioxidant Found in plasma and endothelial cells Transport protein for Se

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37
Q

Selenoprotein W

A

Found in muscle Thought to play a role in muscle metabolism

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38
Q

Se excretion

A

Poorly digested Se-containing proteins and insoluble Se compounds will pass through the intestinal lumen and be excreted in feces

Digested/absorbed Se excreted via the kidney, mostly as selenosugars

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39
Q

Short-term selenium intake measured in:

A

Blood and urine selenium concentration

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40
Q

Long-term selenium intake measured in:

A

Hair/nail selenium status

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41
Q

T/F: Neither SeCys from the diet nor SeCys formed in the body during SeMet catabolism or muscle catabolism can be used directly for the incorporation of SeCys into selenoproteins

A

True

42
Q

Ox/Redox general principle

A

OILRIG

Oxidation is loss

Reduction is Gain

43
Q

Glutathione function

A

Major participant in cellular antioxidant systems

Can detoxify both soluble and lipid peroxides in cytoplasm, nuclei, and mitochondria (dominant soluble antioxidant in these compartments)

Oxidation (loss of one electron) easily accommodated by sulfur

44
Q

Describe glutathione oxidation cycle

A
45
Q

Desribe glutathione peroxidase-mediated reaction

A

2(GSH) + H2O2 –> GSSG + H2O

GSH is oxidized to GSSG

46
Q

Describe glutathione reductase-mediated reaction

A

GSSG + NADPH+H –> GSH + NADP

GSSG is reduced to GSH

47
Q

GSH

A

Reduced glutathione

48
Q

What is GSSG?

A

Oxidized glutathione

49
Q

Enzymatic activity of glutathione reductase is dependant on what cofactor?

A

Riboflavin (FAD)

50
Q

Draw glutathione oxidation cycle

A
51
Q

How does selenium work with vitamin E?

A

One or more SeCys residues in redox-active selenoproteins work to regenerates vit E

Combined deprivation of Vit E and Se yields increased free radical attack on PUFAs

52
Q

Draw antioxidant network in general terms

A
53
Q

GPX1

A

Highly specific for GSH as the donor of reducing equivalents

54
Q

GPX2

A

Found primarily in GI cells and liver

55
Q

GPX3

A

Found in plasma & extracellular fluids

56
Q

GPX4

A

Associated with cell membranes

Detoxifies H2O2s which impair membrane function & is important for sperm production

Knocking out GPX4 is embryonically lethal

57
Q

Iodothyronine 5’-Deiodinases

A

Selenoprotein enzyme that converts T4 –> T3

Selenium deficiency results in elevated levels of thyroid hormone thyroxine (T4) w/low active thyroid hormone (T3)

58
Q

Diseases associated with selenium deficiency (2)

A

Keshan disease

Kashin-Beck disease

59
Q

Keshan Disease

A

Cardiomyopathy mainly affecting children and young women residing in regions of China/Russia where soil Se and subsuquent dietary Se intake is very low

Acute or chronic cardiac insufficiency

Cardiac enlargement

Arrhythmias

EKG abnormalities

Largely eliminated through selenium supplementation •

May be caused by cardiophilic RNA viruses

Selenium deficiency may exacerbate RNA attack through increased viral mutation

60
Q

Kashin-Beck Disease

A

Ostearthropathy affecting the epiphyseal growth plates and articular cartilage

Enlarged joints (especially of the fingers, toes and knees)

Shortened fingers, toes, and extremities

Sometimes dwarfism

Iodine deficiency, fungal toxins, & impaired thyroid hormone metabolism may be involved

A meta analysis of 15 clinical trials suggested some beneficial effect of Se supplementation

61
Q

Symptoms of acute selenotoxicity

A

Severe GI symptoms, neurological symptoms, & acute cardiac/respiratory/renal failure

Due to accidental overexposure (to gram quantities of Se) to high-Se compounds such as anti-dandruff shampoo

62
Q

Symptoms of chronic selenosis

A

Hair loss, nail changes, skin sensitivity

63
Q

FDA “no observed adverse effect level”

A

0.8 mg/day

64
Q

Se TUL

A

0.4 mg/day

65
Q

Selenium and cancer

A

Anti-tumorigenic effects of Se supp noted in animal studies

Epi studies observed lower cancer incidence with higher selenium status

Nutritional Prevention of Cancer (NPC) Trial found no effect of selenium on skin cancer, yet found a decrease in overall cancer mortality, total cancer incidence, and incidence of lung, colorectal and prostate cancers (6 years)

SELECT Prostate Cancer Prevention Trial found no effect on the incidence of prostate cancer over 5-yr intervention

Effects may only be observed in those with low Se levels at baseline

66
Q

(Reversed)

SeO32- (I)

A

Selenite

67
Q

(Reversed)

H2SeO3 (I)

A

Selenous acid

68
Q

(Reversed)

SeO42- (I)

A

Selenate

69
Q

(Reversed)

Adults: 55 mcg/day Infants: 15 mcg/day up to 20 mcg/day after 6 mos (based on breast milk) Children: 20-40 mcg/day Pregnancy: 60 mcg/day Lactation: 70 mcg/day Selenium intakes of most Americans exceed the RDA

A

Selenium RDA is…

70
Q

(Reversed)

0.3 to 0.5 mg Se/kg (fresh weight)

A

Muscle meats contain…

71
Q

(Reversed)

4x to 15x higher

A

Organ meats contain __x higher/lower concentrations of Se

72
Q

(Reversed)

84%

A

Absorption of inorganic Se from food is __% (selenite)

73
Q

(Reversed)

98%

A

Absorption of organic Se from food is __% for SeMet

74
Q

(Reversed)

Diffusion

A

Inorganic Se (selenate/selenite) absorbed via…

75
Q

(Reversed)

Transport by amino acid transporters

A

Selenoaminoacids absorbed via…

76
Q

(Reversed)

Digestibility of these proteins

A

Bioavailability of selenoamino acids from plants/animals depends on…

77
Q

(Reversed)

incorporated into body proteins non-specifically in place of methionine based on protein methionine content Metabolized to selenide via same pathway which converts Met to Cys

A

Fate of ingested SeMet

78
Q

(Reversed)

Incorporate selenium indirectly as SeCys as residues in new selenoproteins

A

Fate of ingested SeCys

79
Q

(Reversed)

Se incorporated as SeCys residues in new selenoproteins)

A

Fate of ingested inorganic Se (selenite or selanate)

80
Q

(Reversed)

Glutathione peroxidases (GPX) Thioredoxin reductase Selenoprotein P Selenoprotein W

A

List selenoproteins (4):

81
Q

(Reversed)

Glutathione peroxidase

Antioxidant enzymes that reduce ROS (e.g H2O2) by coupling their reaction with the oxidation of reduced glutathione

6 isoforms in animals

GPX activity depends on selenium status; used as a biomarker

A

GPX

82
Q

(Reversed)

Regenerates several antioxidants, including Vit C

A

Thioredoxin reductase

83
Q

(Reversed)

Antioxidant Found in plasma and endothelial cells Transport protein for Se

A

Selenoprotein P

84
Q

(Reversed)

Found in muscle Thought to play a role in muscle metabolism

A

Selenoprotein W

85
Q

(Reversed)

Poorly digested Se-containing proteins and insoluble Se compounds will pass through the intestinal lumen and be excreted in feces Digested/absorbed Se excreted via the kidney, mostly as selenosugars

A

Se excretion

86
Q

(Reversed)

Blood and urine selenium concentration

A

Short-term selenium intake measured in:

87
Q

(Reversed)

Hair/nail selenium status

A

Long-term selenium intake measured in:

88
Q

(Reversed)

Reduced glutathione

A

GSH

89
Q

(Reversed)

Oxidized glutathione

A

What is GSSG?

90
Q

(Reversed)

Highly specific for GSH as the donor of reducing equivalents

A

GPX1

91
Q

(Reversed)

Found primarily in GI cells and liver

A

GPX2

92
Q

(Reversed)

Found in plasma & extracellular fluids

A

GPX3

93
Q

(Reversed)

Associated with cell membranes

Detoxifies H2O2s which impair membrane function & is important for sperm production

Knocking out GPX4 is embryonically lethal

A

GPX4

94
Q

(Reversed)

Selenoprotein enzyme that converts T4 –> T3

Selenium deficiency results in elevated levels of thyroid hormone thyroxine (T4) w/low active thyroid hormone (T3)

A

Iodothyronine 5’-Deiodinases

95
Q

(Reversed)

Cardiomyopathy mainly affecting children and young women residing in regions of China/Russia where soil Se and subsuquent dietary Se intake is very low

Acute or chronic cardiac insufficiency

Cardiac enlargement

Arrhythmias

EKG abnormalities

Largely eliminated through selenium supplementation •

May be caused by cardiophilic RNA viruses

Selenium deficiency may exacerbate RNA attack through increased viral mutation

A

Keshan Disease

96
Q

(Reversed)

Ostearthropathy affecting the epiphyseal growth plates and articular cartilage

Enlarged joints (especially of the fingers, toes and knees)

Shortened fingers, toes, and extremities

Sometimes dwarfism

Iodine deficiency, fungal toxins, & impaired thyroid hormone metabolism may be involved

A meta analysis of 15 clinical trials suggested some beneficial effect of Se supplementation

A

Kashin-Beck Disease

97
Q

(Reversed)

Severe GI symptoms, neurological symptoms, & acute cardiac/respiratory/renal failure

Due to accidental overexposure (to gram quantities of Se) to high-Se compounds such as anti-dandruff shampoo

A

Symptoms of acute selenotoxicity

98
Q

(Reversed)

Hair loss, nail changes, skin sensitivity

A

Symptoms of chronic selenosis

99
Q

(Reversed)

0.8 mg/day

A

FDA “no observed adverse effect level”

100
Q

(Reversed)

0.4 mg/day

A

Se TUL

Nutrition 522 (1 decks)

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