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Biochemisty: Vitamin A and Carotenoids
Vitamin A and Carotenoids
92
Chemistry
Graduate
05/14/2010

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Term
What is generic descriptor of Vit A
Definition
Retinoids
Term
Retinoids exhibit biological activity for retinOL or retinAL?
Definition
retiNOL
Term
Beta-ionine ring, isopreponoid units and conjugated double bond system are characteristics of what vitamin?
Definition
Carotenoids
Term
Which three types of forms of does vit A come in?
Definition
Retinoid, Precursors or provitamins, synthetic form
Term
What are examples of retinoids and their chemical formula?
Definition
- all trans- retiNOL (R- CH2OH)
- RetiNAl (R-CHO)
- Retinoic Acid ( R-COOH)
Term
Parent compounds have all cis or all trans configuration?
Definition
All trans
Term
What are examples of precursors or provitamins?
Definition
- β-carotene
- other carotenoids
Term
What is Tretinoin and what is it used for?
Definition
Tretinoin is all –trans retinoic acid used to treat
PSORASIS (skin condition that causes skin redness and irritation) and
APL (acute promyelocytic leukemia)
Term
What is Etretinate or Accutane and what is it used for?
Definition
It is a 13- cis retinoic acid used to treat ACNE
Term
What carotenoids are MOST prevalent in diet? (six)
Definition
alpha carotene beta carotene
Lycopene Lutein
Zeaxanthin beta-cryptozanthin
Term
Which carotenoids are Provitamin A carotenoids? (3)
Definition
a-carotene
b-carotene
b-cryptoxanthin
Term
Natural occurring are carotenoids in which form?
Definition
all-trans-configuration
Term
What is dietary source of beta carotene?
Definition
- green leafy vegetables, carrots, red palm oil.
Fruits: peaches, apricots, mango, papaya
- yellow orange veggies: sweet potato, squash, cassava
- High carotenoid rice
Term
What are dietary sources of alpha carotene?
Definition
- green leafy vegetables, carrots, red palm oil.
Fruits: peaches, apricots, mango, papaya
- yellow orange veggies: sweet potato, squash, cassava
- High carotenoid rice
Term
Lutein is found in?
Definition
Green leafy vegetables, peas, pepper, egg yolk
Term
Zeaxanthin is found in ?
Definition
citrus fruit, maize
Term
Lycopene is found in?
Definition
tomato, watermelon, pink grapefruit
Term
In the conversion of beta carotene to retiNOL,what enzymes are present and their function?
Definition
Cleavage enzyme: 15,15- dioxygenase (in cytosol of mucosal cells- intestines)

Reduction enzyme: retinaldehyde reductase
Term
15,15 dioxygenase and retinaldehyde reductase are involved in which reaction?
Definition
Conversion of beta carotene to retoNOL
Term
1 μg retoNOL= how many IU
Definition
3.33 IU vit A from retinol
Term
1 RE = how many μg of all trans retinol?
Definition
1 RE = 1 μg of all trans retinol
Term
1 RE = how many μg of beta carotene?
Definition
1 RE= 6 μg of beta carotene
Term
1 RE = how many μg of other provitamin A carotenoids?
Definition
1 RE = 12 μg of other provitamin carotenoids
Term
1 RAE = ___ μg all trans retinol
Definition
1 RAE = 1 μg all trans retinol
Term
1 RAE= ____ μg of all trans beta carotene in OIL
Definition
1 RAE = 2 μg of all trans beta carotene in OIL
Term
1 RAE= ____ μg of FOOD BASED all trans beta carotene
Definition
1 RAE = 12 μg of FOOD BASED all trans beta carotene
Term
1 RAE = ___ μg of other food based pro vitamin A carotenoids
Definition
1 RAE= 24 μg of other food based pro vitamin A carotenoids
Term
1 RE = ____
Definition
1 μg all trans retinol
6 μg beta carotene
12 μg of other provitamin A carotenoids
1-6-12
Term
1 RAE= ____
Definition
1 μg all trans
2 μg all trans beta carotene in OIL
12 μg FOOD BASED all trans beta carotene
24 μg of other food based PROVITAMIN A carotenoids

1-2-12-24
Term
The RDA vit A for Male is?
Definition
900 RAE
Term
The RDA Vit A for Female is?
Definition
700 RAE
Term
Daily value for Vit A is?
Definition
5000 IU
Term
10 IU of beta carotene =____ IU retinol
Definition
10 IU of beta carotene = 3.33 IU of retinol
Term
When converting from IU beta carotene from fruits to vegetables to μg RAE, IU is divided by ___? (page 7 notes)
Definition
IU is divided by 20 (2x10)
Term
Compare Preformed vit A (retiNOL) with provitamin A?
Definition
Preformed:
- animal food as retinol and retinyl ester
- toxic
- highly absorptive (70-90%)

Provitamin A:
- plant food as beta carotene and other carotenoids
- limited conversion to vit A
- carotenodermia is benign
- low absorptive efficiency
Term
What are some of the chemical properties of retinoids?
Definition
Color: light yellow to redding
- soluble in organic solvents
- sensitive to oxidation, isomerization and polymerization by light, oxygen, and high temperatures
- stable in crystalline form and as an OIL stored in dark, cool place
- characteristics UV absorption spectrum
Term
What is REH and what role does it play in metabolism of retinoids?
Definition
REH is Retinyl Ester Hydrolase, it is found in pancreatic juices and it hydrolyzes retinyl esters
Term
Which enzymes are required to release proteins from vit A?
Definition
Release from protein requires PEPSIN and PROTEOLYTIC enzymes
Term
Which complex carries retinoids to different parts of the body?
Definition
TTR RBP 1:1 ratio (transthyretin or prealbumin) binds thyroxin
Term
LRAT catalyzes what?
Definition
Re-esterification of retinol
LRAT (lecithing: retinol acyl transferase)
Term
Once retinol is re-esterified, it gets packaged into chylomicrons. T or F
Definition
True. its called Chylo RE (p 10)
Term
How are Chylo RE carried to the liver?
Definition
By lymph
Term
How are Chylo RE taken up by the liver?
Definition
Chylo RE taken up by the liver in association with chylomicron remnant by RECEPTOR-MEDIATED ENDYCYTOSIS
Term
Where does hydrolysis and esterification of retinoids occur?
Definition
LIVER
Term
What are two (2) esterificaton enzymes for retinoids and give brief description.
Definition
1. LRAT
- uses ACYL groups from phosphotidylcholine
- high affinity
- involves retinol complexed to CRBP II
2. ARAT
- uses acyl groups from CoA
- low affinity
- non specific binding
Term
LRAT
Definition
LRAT: lecithin
- esterification enzyme
- uses ACYL groups from phosphotidylcholine
- high affinity
- involves retinol complexed to CRBP II
Term
ARAT
Definition
ARAT
- esterification enzyme
- uses acyl groups from CoA
- low affinity
- non specific binding
Term
ARAT vs LRAT
a. Which one is high affinity enzyme?
b. Which one uses acyl group from CoA?
c. Which one envolves renitol complexed to CRBP II?
Definition
a. LRAT
b. ARAT
c. LRAT
Term
Where is most (50-85 %) of Vit A stored? In what form?
Definition
Mostly as RE stored in LIVER hepatic stellate cells
Term
Vit A is excreted in bile but only after _______ and _______ ?
Definition
hydroxylation and glucoronidation
Term
Vit A is excreted in bile but only after _______ and _______ ?
Definition
hydroxylation and glucoronidation
Term
Vit A is excreted in bile but only after _______ and _______ ?
Definition
hydroxylation and glucoronidation
Term
Where is apo-retinol binding protein (apo- RBP) synthesized and what does it combine with to form a 1:1 complex?
Definition
apo-RBP is synthesized by hepatocytes and apo RBP combines with retinOL to form 1:1 complex called holo-RBP
Term
Draw diagram of transport and cellular metabolism in intestine, liver and target organs (VIt A) (p 10)
Definition
Term
Where is RBP- TTR complex formed?
Definition
Plasma
Term
What is Transthyretin?
Definition
Transthyretin is a tetrameric protein whihc strongly binds four thyroxine molecules
Term
What is RBP (retinold binding protein) function in plasma?
Definition
to solubilize retinol and deliver it to cells
Term
Which protein limit "free" retinoid?
Definition
RBP
Term
Which protein channels retinoids to specific enzymes responsible for metabolic transformation and limits 'free' retinoids?
Definition
RBP
Term
In the nuclei, specific retinoid-receptor proteins have what function?
Definition
To regulate the activity of retinoid- responsive genes
Term
Retinoid- binding protein and receptors?
a. in PLASMA
b. in CELLS
c. in NUCLEI
Definition
1. in plasma RPB functions to solubilize retinOL and deliver it to cells
2. in CELLS: cellular retinoid binding protein limit "free" retinoid and channel retinoids to specific enzymes responsible for metabolic transformation
3. in NUCLEI: specific retinoid receptor protein regulate the activity of retinoid responsive genes
Term
Draw retinoid conversion reactions. Vit a (page 13)
Definition
Term
What are functions of vit A?
Definition
a. 11-cis retinAL fucntions in retina. Convert light into neural signals necessary for vision
b. Ret. Acid maintains normal differentiation of the conjuctival membranes, cornea, and other cells to prevent xerophthalmia.
- cellular differentiation
- Development
- Immunity
Term
11-cis-retiNAL (function in vision)
Definition
11-cis retinAL fucntions in retina. Convert light into neural signals
Term
Retinoic Acid (function in vision)
Definition
Ret. Acid maintains normal differentiation of the conjuctival membranes, cornea, and other cells to prevent xerophthalmia.
Term
Function of Vit A in vision
Definition
Light absorbing unit (chromophore): 11 cis retinal bound to opsin
- disk contain "visual pigment" or rhodopsin (in rods) and iodopsins (in cones)
-absorption of a photon light catalyzes the isomerization of 11-cis-retinal to all trans retinal and its release from opsin.
- this triggers a neuronal signaling cascase
- regeneration occurs in RPE (retinal pigment epithelium)
Term
Draw visual cycle . Vit A page 14
Definition
Term
+ or - Vitamin A in Basal Cells: cell differention
Definition
+ A: Cuboidal, columnar, and goblet cells
- A: squamous (scale like) cells
Term
Role of Vit A (RA) in gene expression?
Definition
1. Binding of RA to its nuclear receptor
2. Activation of receptor
3. Binding of the receptor to a RARE
4. Regulation of the expression of genes downstream
Term
Retinoic Acid:
RAR, RXR: what do they bind?
Definition
RAR: binds RA and 9-cis-RA
RXR: binds 9-cis-RA
Term
Genes with RARE?
Definition
Skin(keratin)
Matrix (laminin)
Enzymes( alcohol dehydrogenatse, etc)
Term
Xerophthalmia
Definition
Drying and ulceration of cornea
- night blindness
- conjuctival xerosis
- bitot's spots
- corneal xerosis
- ulceration
- necrosis/keratomalacia
Term
Immune function and Vit A
Definition
Effects on the immune system
- infection
- morbidity
- growth
- mortality (Inf and Children, women of reproductive age)
Term
Follicular hyperkeratosis
Definition
in deficiency of Vit A, mucous secreting epithelial cells become keratinized
Term
Xerophthalamia: clinical deficiency and progression
Definition
Clinical deficiency:
conjuctival xerosis, bitot spots
progression: corneal xerosis, ulceration, keratomalacia, blindness
Term
Beta carotene and cancer
Definition
Beta carotene:
- 18 % incr. lung cancer
- 8 % incre in lung cancer mortality
- more heart disease

Vit E:
- no effect in lung cancer mortality
- decrease death from eschemic heard disease and stroke
- increase death from hemorrhagic stroke
Term
Vit A deficiency?
Who's at risk?
Consequences?
Definition
125,000 to 250,000 million children (pre-school) and pregnant and lactating women
Consequences:
Leading cause of preventable childhood blindness
- night blindness and xerophthalmia
- 250,000-500,000 per year
Increase risk of mortality and morbidity in pre school children, and most likely in pregnant women
- Incresse risk of dying from childhood infections
Term
Where is Vit A deficiency in pre school children most prevalent *region
Definition
south east asia . 127 million
Term
What are contributing factors to Vit A deficiency?
Definition
Low intake in diet or breast milk
High demand during infection
High losses with diarhhea
Term
How does immune responce changes due to Vit A deficiency?
Definition
Lymphoid cellularity
- thymic atrophy
- reduced number of spleen cells
- reduced lymphocytes etc

Antibody responses
- reduced T cell dependent antigens

Cell mediated immunity
- reduced cytoxicity
- alterations in cytokine production

Innate Immunity
- decreased number of natural killer cells
- Reduced phagocytosis by macrophages
Term
What are risk factors of Vit A deficiency?
Definition
Age
Gender
Physiological status
Diet
Socioeconomic conditions
Clusterin
Term
Evaluation of Vit A status:
Clinical
Histological
Biochemical
Definition
Clinical
- night blindness
- dark adaptaion tests
Histological
- conjuctival impression cytology

Biochemical:
Retinol levels in serum
Relative Dose Response (RDR)
Modified Relative Dose Response (MRDR)
Term
Relative Dose Response Test *Vit A assessment status
Definition
Relative Dose Response Test:

As liver reserves of Vit A become low, conservation starts to increase efficiency of Vit A.
- At critical threshhold , rate of release is dimineshed and blood levels are low
- BUT, synthesis of carier protein RBP continues
- SO accumulation of a pool of preformed RBP

Procedure:
- Fasting blood sample is taken
- oily solution w/450-1000 micrograms of RETINYL PALMITATE is given orally
- Small meal with some fat is given
- After 5 hours, second blood test
- Blood analyzed and RDR is calculated:
RDR= ret (5 hr)- ret (0 hr)/ ret (5 hr)

RDR > 20% indicates of INAdequate hepatic stores
Term
Modified Relative dose response: Vit A assessment
Definition
- uses DEHYDRO- RETINOL for dosing and a single blood sample at 5 hours post dosing
Term
Public Health Measures to correct Vit A deficiency (3)
Definition
Food Fortification
Supplementation
Dietary Diversificaton
Term
Supplement of Vit A (+ and -)
Definition
+:
easy to implement
fast improvement in Vit A status
Easy to target vulnearable pop
low cost
easy to do
-:
short term approach
distribution every 6 months
requires heaby logistics
Term
What children are at high risk of deficiency of vit A?
Definition
measles
diarrhea
chicken pox
protein energy malnutrition
severe infection
Term
Food Fortification of Vit A (+, -, main issues)
Definition
+ :
- wide coverage
- easy to implement
- does not depend on active participation
- inexpensive

- :
- entire pop exposed
- target pop may not be reached
- requires a centralized food industry
- need effective surveillance

Main issues:

- selection of appropriate food vehicle
- Selection of appropriate level of fortification
- need for regulation
- sustanability
- economic implications
Term
What are clinical indicators to assess vit A deficiency?
Definition
Clinical:
pre school: night blindress < 6 yo: >1 %
bitot spots (<6 yo: >0.5 %)

Pregnant women: night blindness (> 6%)

Sub clinical:
pre school: serum retinol <6 yo >20 %
Term
Draw deficiency to toxicity curve of Vit A
page. 28
Definition
Term
Toxicity and Vit A (symptoms)
Definition
Hypervtiaminosis A
- bright red marginal discoloration of the gingiva
- Retinoid Embryopathy (during 1st trimester)
- malformation (limb)
- craniofacial defects in bones and oral clef
- cardiac, thymic, CNS defect
- microtia/anotia (ear)
-
Term
Vit A and Osteoporosis?
Definition
Excess intake of Vit A leads to incrased risk of osteoporosis.

- May impair the ability of vit D to promote calcium absorption
- 1500 mcg/day --> reduced bone mineral density compare with who consumed <500 mcg
- effect of retinols is decresed with use of estrogens
- High vit A does not equal to high blood levels of retinol
- beta carotene intake is ok, esp from fruits and veggies
- only problems with retiNOL
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