Fat Soluble Vitamins

What are the fat-soluble vitamins?

A, D, E, K

What do fat-soluble vitamins requre for absorption?

lipid - bile

Do fat-soluble vitamins act as coenzymes?

No, they bind directly to receptor

What two vitamins are stored in the liver?

Vitamins A and D

What is the alcohol form of vitamin A?

Retinol

What is the aldehyde form of vitamin A?

Retinal

What is the acid form of vitamin A?

Retinoic Acid

What is the Vitamin A precursor (2 retinals combined head-to-tail)?

Beta-carotene

Another name for Beta-carotene?

provitamin form of vitamin A

Cleavage at which position of Beta-carotene yields two molecules of Vitamin A?

Position 15

Trans form of retinal

ALL double bonds will be trans

Cis form of retinal

Doubld bond at position 11 will be cis (11-cis-retinal)

What type of foods do Retinoids come from?

• animals/meat/cheese

What type of foods do Cartenoids come from?

• plants = fruits and veggies

What happens to ingested β-carotene in the intestine?

β-carotene is cleaved in the intestinal lumen by β-carotene dioxygenase to yield retinal

What enzyme cleaves β-carotene?

β-carotene dioxygenase

What does cleaving β-carotene yield?

Retinal

How is retinal converted to retinol?

Retinal is reduced to retinol by retinaldehyde reductase, an NADPH-dependent enzyme.

What enzyme reduces retinal to retinol?

retinaldehyde reductase

How is retinol converted to palmitic acid?

It is esterified

How is retinol deleived to the blood?

Retinol is coverted into palmitic acid, then delivered to the blood bia chylomicrons

How does retinol reach the liver?

Chylomicron remnants are taken up by the liver, delivering the retinols along with them

How is retinol stored in the liver?

Retinol is stored as a lipid ester within liver lipocytes.

How is retinol transported from the liver to extrahepatic tissues?

Retinol binds to retinol-binding protein (RBP) and is transported in the blood.

How is the retinol-RBP complex secreted from cells?

The retinol-RBP complex is transported to the cell surface via the Golgi and then secreted.

How is retinol handled in extrahepatic tissues?

Retinol binds to cellular retinol-binding protein (CRBP) within tissues.

How is retinoic acid transported in plasma?

Retinoic acid is transported in plasma bound to albumin.

Why cant the vitamins go to the blood vessels?

They are too large

What does retinol help with?

• Supports reproduction

• Major transport and storage form

What does retinal help with?

active in vision

What does Retinoic acid help with?

regulates cell differentiation, growth, and embryonic developmen

What Retinoid convertion is irreversible?

Retinal → retinoic acid

What does beta-carotene help with?

Works as an antioxidant

What form of Retenoid should be avoided during pregnancy?

Retinoic Acid

Which molecule/medication closely ressembles retinoic acid?

Isotretinoin also knows as Accutane (brand name)

What is another name for Isotretinoin?

12-cis-retinoic acid

When should Isotretinoin be avoided?

During pregnancy

What drug is is used for the treatment of acne, photoaging (cream, gel or ointment) and acute promyelocytic leukemia?

all-trans retinoic acid (ATRA)

What drug is a synthetic retinoid derivative and potentially used in the treatment of cancer, cystic fibrosis, rheumatoid arthritis, acne, and psoriasis?

Fenretinide

What is Fenretinide also known as?

N-(4-hydroxyphenyl)retinamide; 4-HPR (INN)

How does Fenretinide aid in cancer treatmenrt?

• causes ceramide build up in tumor cells

• increases reactive oxygen species (ROS) → resulting in cell death through apoptosis and/or necrosis.

What happens to the cells structure and function in the absence of vitamin A?

Impained mucous membrane → mucus basically dries up

What two things does the light hit in the retina to help with vision?

Rod and cone cells

What molecules in the rod cells does the light interact with?

Rhodopsin molecules

What is Rhodopsin made of?

Opsin (a protein) + cis-retinal

What happens to the rhodopsin when light hits the rod cells?

The cis-retinal is converted to trans-retinal

What happens after the cis-retinal is converted to trans-retinal?

The Rhodopsin is split into two seperate pieces: opsin and trams-retinal

What happens when Rhodopsin is split into two parts?

A neural signal is sent to the brain which allows to brain to “see’ the image

What happens to the trans-retinal after it splits from the opsin?

It is converted to EITHER cis-retinal OR Retinoic acid

How is rhodopsin reformed?

Opsin (that was seperated from the trans-retinal) conbined with cis-retinal

What is the Sunshine Vitamin?

Vitamin D

What type of harmone is Vitamin D?

A steroid harmone

What is the function of vitamin D?

To rgulate specific gene expression following interaction with its intracellular receptor

What is the active form of Vitamin D?

1,25-dihydroxy vitamin D3 (1,25-(OH)2D3 aks calcitirol

What is another name for calcitroil?

1,25-dihydroxy vitamin D3 (1,25-(OH)2D3

What is the primary functions of Calcitriol?

To regulate calcium and phosphorous homeostasis

What is the role of calcitriol in calcium and phosphorus regulation?

Calcitriol functions with parathyroid hormone (PTH) and calcitonin to regulate serum calcium and phosphorus levels.

What does Calcitriol function with to regulate calcium and phosphorus levels?

Parathyroid hormone (PTH) and calcitonin

When is PTH released?

PTH is released in response to low serum calcium

What does PTH release induce?

The production of calcitriol

How does calcitriol affect intestinal calcium absorption?

Calcitriol acts as a steroid hormone in the intestinal epithelium, inducing the expression of calbindinD28K

What is calbindinD28K?

a protein involved in the intestinal calcium absorption

Why is a counter ion required during calcium absorption in the intestine?

Calcium absorption requires concomitant absorption of a negatively charged counter ion (phosphate, Pi) to maintain electrical neutrality.

What are the major sites of action of calcitriol and PTH when plasma calcium falls?

• Bone: stimulate bone resorption (low calcium = brittle bones)

• Kidneys: inhibit calcium excretion by promoting reabsorption in distal tubules

How is elevated serum calcium decreased?

Calcitonin decreases elevated serum calcium levels by inhibiting bone resorption.

What are some of the immune-related functions of calcitriol?

• Supports immune function by acting as cold/flu defence

• reduces inflammation and apoptosis

What is 7-Dehydrocholesterol?

Initial precursor for Vitamin D3

What happens when UV light hits 7-Dehydrocholesterol?

It is converted to Previtamin D3

What is another name for Previtamin D3?

Precalciferol

What is Previtamin D3 converted to in the skin?

Vitamin D3 aka cholecalciferol

In periods of low calcium, what harmone does the parathyroid gland secrete?

parathyroid harmone (PTH)

What gland secretes the harmone parathyroid harmone (PTH)?

The parathyroid gland

When does the parathyroid gland secrete PTH?

When blood calcium is low

What does the liver convert Vitamin D3 (cholecaliferol) to?

25-(OH)D3

• by adding an -OH to the 25th position

What does the kidneys convert 25-(OH)D3 to?

1,25-(OH)D3 aka calcitroil

• adds another -OH to the first (1) carbon

After 1,25-(OH)D3 is formed, where does it go?

travels through the blood vessel along with a Vitamin D binding Protein (DBP)

Where does 1,25-(OH)D3 go after traveling through the blood vessels?

To its target cell, where it enters the nucleus and impacts gene expression

Which vitamin acts as an Antioxidant that Protects Biological Membranes

Vitamin E

Vitamin E is a mixture of several related compounds known as?

tocopherols

What molecule is the most potent of the tocopherols?

α-tocopherol

When vitamin E is absorbed from the intestines, it is packed in?

chylomicrons

How is vitamin E delivered to the tissues?

Via chylomicron transport

How is vitamin E delivered back to the liver?

Through chylomicron remnant uptake

What does the liver export Vitamin E, due to its lipophilic nature?

In VLDLs

Where does vitamin E accumulate in?

Vtamin E accumulates in

• cellular membranes

• fat deposits

• other circulating lipoproteins

What is the major site of vitamin E storage?

In adipose tissues

What is the major function of vitamin E?

to act as a natural antioxidant by scavenging free radicals and molecular oxygen.

What does Viitamin E prevent peroxidation of?

polyunsaturated membrane fatty acid

How are vitamins E and C interrelated?

Through their antioxidant capabilities

How can active α-tocopherol be regenerated?

by interaction with vitamin C following scavenge of a peroxy free radical

What is another way α-tocopherol can be regenerated?

scavenge two peroxy free radicals and then be conjugated to glucuronate for excretion in the bile.

How do antioxidants like Vitamin E neutralize free radicals?

By donating one of its own electrons

What happens to Vitamin E after it donates its electron?

It becomes inactive

How does Vitamin E restore its active form?

With the help of vitamin C