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HUN 4221 Exam 2 > Vitamin A > Flashcards

Vitamin A Flashcards

1
Q

Who was Paul Karrer?

A

Awarded for his investigations on carotenoids.

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2
Q

What are the different forms of retinoids?

A

All-trans-retinol
Retinal
Retinoic Acid
Retinyl ester

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3
Q

What are the interconversions of the retinoids?

A 
Retinol  Retinal (can be reversibly oxidized)
Retinal ----> Retinoic Acid (can be irreversibly oxidized)
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4
Q

Retinal —> Retinoic acid is active in what?

A

Active in growth but not vision or reproduction

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5
Q

What is the enzyme that oxidizes Retinal to Retinoic Acid?

A

Retinal Oxidase

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6
Q

What are the different forms of carotenoids?

A

Beta-carotene- most common in foods
Alpha-carotene
Gamma-carotene

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7
Q

What is Vitamin A

A

It is the generic descriptor for compounds exhibiting the biological activity of retinoids and some provitamin A carotenoids

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8
Q

Retionol (as all-trans) is usually bound to?

A

Fatty acid esters (palmitate)

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9
Q

Retinyl Palmitate and carotenoids are usually bound to what?

A

Protein

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10
Q

What are the food forms of Vitamin A?

A

Retinyl Palmitate and Beta-Carotene

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11
Q

What is CRBPII?

A

Cellular retinol-binding protein II
Abundant in small intestine
Binds retinol and retinal (makes them soluble)
-this controls free retinol concentrations and protects it from oxidation.
-directs the reduction of retinal to retinol
-Escorts retinol to LRAT

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12
Q

What is LRAT?

A

Lecithin retinol acyl transferase

Adds fatty acids (mainly palmitate) to retinol to form retinyl esters

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13
Q

What does the formation of the trimolecular complex do?

A

It reduces glomerular filtration and thus renal catabolism

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14
Q

Vitamin A functions metabolically in…?

A

Vision, cellular differentiation & gene expression, growth, immune system, bone development, reproduction.

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15
Q

What is Vitamin A’s role in vision?

A

Serves as the photosensitive chromophoric group of rhodopsin found in rod cells of the retina.

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16
Q

What does rhodopsin detect?

A

Small amounts of light important for night vision

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17
Q

What is the purpose of the visual cycle?

A

To regenerate 11-cis-retinal

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18
Q

What must happened in order to regenerate rhodopsin?

A

All-trans-retinal must be converted back to 11-cis-retinal

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19
Q

How can stored retinyl esters be used to produce 11-cis-retinal?

A

They can hydrolyzed, isomerized, oxidized to 1–cis-retinal and shuttled to rod cell.

If storage is deficient, cannot regenerate sufficient 11-cis retinal

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20
Q

Failure to regenerate 11-cis-retinal results in?

A

Night blindness

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21
Q

What is cellular differentiation?

A

Process whereby an immature cell is transformed into a specific type of mature cell

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22
Q

What is the reaction in cell differentiation that Vitamin A is involved in?

A

Keratinocytes ——–> (Retinoic acid)——> epidermal cells (immature skin cells)

Squamous epithelial keratinizing cells —–> (retinoic acid) —–> Mucous-secreting cells
*If retanoic acid is not there, the squamous epithelial keratinizing cells replace the mucous secreting cells and cause keratinization, which is the dry, rough, and scaly skin.

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23
Q

Cell differentiation is important for what?

A

Bronchial passages which a barrier function which include mucous-secreting cells nd ciliated cells.

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24
Q

A deficiency in Vitamin A may compromise what in regards to immunity and increase what?

A

Comprimise barrier function and increase risk of infection.

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25
Q

What does CRABP stand for and what does it serve for?

A

Cellular retinoic acid binding protein and it serves as a chaperone that binds to All-trans-retinoic acid and 9-cis retinoic acid and translocates them into the nucleus

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26
Q

What does CRBP serve for?

A

serves for storage and transport for retinol

27
Q

How does Vitamin A affect gene expression?

A
  1. All-trans retinoic acid or 9-cis retinoic acid bound to CRABP will enter the nucleus of a cell.
  2. RAR or RXR respectively will bind to the retinoic acid form without CRABP.
  3. This complex will bind to RARE (Retinoic Acid response element)
  4. This enhances the transcription of certain genes
28
Q

What does RAR (alpha, beta, or gamma) and RXR (alpha, beta, or gamma) specific for?

A 
RAR = Specific for all-trans-retinoic acid
RXR = specific for 9-cis-retinoic acid
29
Q

Vitamin A bound RAR or RXR bind to DNA at what specific site?

A

RARE- Retinoic acid response elements, located in promoter regions of specific genes.

30
Q

Binding to RARE sites results in what?

A

Increased transcription of specific genes (gene expression)

31
Q

Retinoids bound to RAR/RXR act as what?

A

Trancription factors regulating either the activation or repression of mRNA formation in nuclei

32
Q

How does retinoic acid stimulate growth?

A

Increases expression of growth receptors on cell surface

33
Q

What is bilateral keratomalacia?

A

Irreversible blindness due to Vitamin A deficiency

34
Q

What are sources of Vitamin A?

A

Dark leafy greens, carrots.

35
Q

Vitamin A deficiency results in abnormalities in immunity which are?

A

Hematopoiesis and blood and lymphoid organ cell populations

36
Q

Immunity: Vitamin A and it’s metabolites are involved in?

A
  • Antibody responses to T-cell dependent antigens
  • Increasing lymphocyte proliferation responses to antigens
  • Maintaining the integrity/function of mucosal surfaces by upregulating expression of mRNA by retinoic acid for mucin proteins of respiratory tract
37
Q

What is Isotretinoin?

A

Accutane
Normalizes epidermis cell differentiation
Reduces synthesis of sebum

38
Q

When is Accutane dangerous?

A

In 1st trimester of pregnancy.
Excessive Vitamin A intake increases congenital defects for baby (teratogenicity-capability of producing fetal malformations)

39
Q

Excessive Accutane in pregnant women can cause?

A

Malformations
Craniofacial with low set, small or absent ears
Malformed facial bones
Defects in cardiac thymus, central nercous system

40
Q

Subclinical Deficiency of Vitamin A can lead to?

A

Increased risk of respiratory and diarrheal infections
Decreased growth rates
Slow bone development
Decreased survival from serious illness

41
Q

What are status indicators of Vitamin A?

A

Liver biopsy
Plasma retinol: POOR indicator of low status unless severe deficiency
Relative dose response (RDR) test: magnitude of increase in RBP following supplementation
Conjunctival impression cytology- field test

42
Q

What is the RDA of Vitamin A?

A

Males- 900 micrograms

Females- 700 micrograms

43
Q

Hypervitaminosis A results in?

A 
Symptoms- 
nausea & vomiting
headache
dizziness
blurred vision
lack of muscular coordination
abnormal liver function
pain in bone and joints
44
Q

Hypervitaminosis A can be caused by

A

Inappropriate use of retinoid supplements and can occur from excess consumption of liver

45
Q

Beta-carotene toxicity

A

Considered to be non-toxic but may cause skin discoloration

46
Q

What is beta carotene?

A

Two vitamin As put together

47
Q

How is vitamin A found in food?

A

Esterified as retinyl palmitate

48
Q

How is vitamin A absorbed in the intestine?

A
  1. CRBPII binds to both retinol and retinal
  2. CRBPII-Retinal will be converted to CRBPII-retinol
  3. (Lecithin retinol acyl transferase (LRAT) esterifies a fatty acid (palmitic acid) onto CRBP-retinol to form CRBP-reitnylpalmitate
  4. Added to other stuff in a chylomicron
  5. Chylomicron leaves the intestinal cell and enters the lymph system and ultimately the blood.
  6. Retinoic acid can directly enter the blood where it attaches to albumin for transport to the liver.
49
Q

In order for retinol to exit the intestinal cell it must be what?

A

Retinol must be esterified to exit intestinal cell by LRAT

50
Q

How is Vitamin A taken up and stored in the liver?

A
  1. Retinyl esters are taken up by parenchymal cells of the liver.
  2. Esters are hydrolyzed in parenchymal cells and stored in stellate cells as retinyl esters. LRAT is involved in forming the ester.
  3. Within the cell retinol binds to CRBPI and has many options from there
51
Q

How is vitamin A released from the liver?

A
  1. Retinol binds to retinol-binding protein (RBP) in the liver and forms Holo-RBP
  2. Holo-RBP is then released into the blood where is binds to the transthyretin and thyroxin to form a trimolecular complex.
52
Q

How is vitamin A transported in the plasma?

A

Retinol is bound to TTR creating the holo-rbp-ttr and then it binds to T4 creating the trimolecular complex.

53
Q

How is retinol taken up by cells?

A
  1. TTR disassociates from the holo-RBP complex and binds to RBP receptor.
  2. Complex is endocytosed and released is retinol and apo(without)-RBP
54
Q

Vitamin A acts as a what affecting signaling pathways?

A

A hormone

55
Q

Vitamin A- DNA complexes are proposed to affect a large variety of what cellular processes?

A
  • cell differentiation

- apoptosis

56
Q

Vitamin A functioning in gene expression regulates what?

A

Regulates genes that code for proteins including enzymes and transcription factors required for cell differentiation and growth

57
Q

Vitamin A deficiency impairs what?

A

Growth, which is stimulated by retinol or retinoic acid

58
Q

How does Vitamin A maintain normal eye tissue?

A

Retinoic Acid maintains normal differentiation of cells including the conjunctival membranes

It prevents xerophthalmia by upregulating expression of mRNA by retinoic acid for mucin proteins of the conjunctive

59
Q

What are the stages of xeropthalmia?

A

Stage 1. Xerosis: dryness of the conjunctiva, bitot’s spots (grey,white foamy greasy deposits.)
Stage 2. Keatomalacia: softening of the cornea, ultimate involvement of iris/lens, secondary infection

60
Q

After night blindeness what is the worst thing that can happen to your eyes?

A

Xeropthalmia

61
Q

What is the main roles of Vitamin A in Immunity?

A

Ability to respond to pathogens, antigens,
increases and decreases in number and function of B cells, T cells, natural killer cells, antigen-presenting cells, and macrophages

62
Q

Vitamin A deficiency is mainly seen in people who?

A

Eat low fat/ plant based diets and have protein-calorie malnutrition

63
Q

How is mortality in developing countries reduced?

A

Byt adminstering retiny palmitate orally every six months infants, children, and pregnant women

64
Q

Children with measles are recommended by WHO/UNICEF to be given what?

A

Vitamin A

HUN 4221 Exam 2 (7 decks)

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