Vitamin K

Question 1

What are the forms of vitmain K?

Answer 1

Menadione (synthetic form)
Phylloquinone (K1, natural plant form)
Menaquinone-7 (MK-7): bacterial form

Question 2

What are some natural sources of vitamin K? phylloquinones (k1)

Answer 2

Higher amount: leafy greens
Lesser amount: cereals, fruits, dairy, meats
Oils: canola sesame, peanut

heat and light sensitive
obligate and facultative anaerobic bacteria in GI tract (K2-bacterial)
K2: natto, cheese

Question 3

vitamin K DRIs?

Answer 3

felt bacterial generated menaquinones (k2) are not sufficient to maintain adequate vitamin K status

• AI may be sufficient for coagulation
• inadequate to max. carboxylation of proteins needed for bone health

Question 4

Absorption of natural vitamin k (Phylloquinone K1)

Answer 4

-does not require digestion: * jejunum (micelles)

some active transport in proximal SI

Question 5

what enhance the absorption of phylloquinone K1?

Answer 5

enhanced by:

• presence of dietary fat
• pancreatic lipase
• bile salts

Question 6

Absorption of menaquinones (K2, bacteria)

Answer 6

• passive diffusion
• facultative and obligate bacteria (anaerobic, lower GI tract)
• efficiency of absorption varies among individuals

Question 7

What is the fate of vitamin K within enterocytes?

Answer 7

K1 is incorporated into chylomicrons–>lymphatic system

-chylomicrons remnant: delivers any vit k not delivered to other tissues to liver

Question 8

How is vitamin k metabolized in the liver?

Answer 8

Metabolized and packaged into VLDL in the liver

Question 9

What is the average body pool size of vitamin K in body?

Answer 9

50-100 mg

turnover 1.5 days

Question 10

Where is vitamin K stored?

Answer 10

• minimal storage in liver

- bone marrow, kidneys, lymph nodes, adrenals, lungs

Question 11

What is the turnover fate of vit K?

Answer 11

rapid turnover

-taken up by tissues within 24h of appearance in blood

Question 12

What is the function of vitamin K?

Answer 12

necessary for post-translational carboxylation of specific glutamic acid residues in proteins

Question 13

What is the function of vitamin K?

Answer 13

Blood coagulation: activation of blood clotting proteins

-factor II, VII, IX, and X

Question 14

What is the function of vitamin K?

Answer 14

Bone proteins: osteocalcin (secreted from osteoblasts), matrix Gla protein (MGP)

Question 15

What is the process of blood clotting (involve vitamin K)?

Answer 15

fibronogen must be converted to fibrin (insoluble fiber network)
1. a series of rxns generates the inactive clotting factor X

2. vitamin K and calcium activate inactive clotting factors
3. Active clotting factor Xa–> converts prothrombin to thrombin
4. Thrombin and fibrin stabilizing factor XIIIa form fibrin–> aggregates to produce an insoluble clot and stops bleeding

Question 16

What is required for the coagulation of blood post-translationally?

Answer 16

post-translational carboxylation of glutamic acid residues on major proteins (e.g. factor II (prothrombin), VII, IX, X) activates these proteins

Question 17

What is the production process of gamma-carboxyglumatic acid (GLA) via vitamin K carboxylation?

Answer 17

1. vitamin K-dependent gamma-glutamyl carboxylase
   cause carboxylation of glutamic acid residue in peptide
2. GLA in peptide
3. GLA-proteins can bind calcium –>reacts with other cell components like phospholipids to affect blood clotting and bone mineralization among other processes

Question 18

What are some examples of anticoagulants?

Answer 18

warfarin, coumarin

Question 19

What is the mechanism of action of anticoagulants?

Answer 19

antagonize vitamin K activity
–>interfere w/ one of the steps in vitamin K cycle
(pathway to reduce vitamin K enabling its role in carboxylation rxns)

recommended to maintain constant vitamin K intake

Question 20

What are some vitamin K-dependent bone proteins?

Answer 20

Osteocalcin (bone GLA protein)

Matrix GLA protein (MGP)

Question 21

What are some facts of osteocalcin (Bone GLA proteins)

Answer 21

10-20% non-collagenous protein in bone

• synthesis stimulated by retinoic acid and calcitriol
• secreted byosteoblasts during bone ECM formation (bone modeling)
• regulates osteoclasts and precursors

Question 22

What are some facts of matrix GLA protein (MGP)?

Answer 22

• synthesis stimulated by retinoic acid and calcitriol
• found in: bone dentine and cartilage, associated w/ bone ECM (promotes calcification)

maybe: role in protection against soft tissue calcification

Question 23

Interactions w/ other nutrients:

What are come antagonists of vitamin K?

Answer 23

Vitamin A and E: affect vitamin K absorption (ant)

Vitamin E: thought involved in inhibition of vitamin K metabolism at high doses

Question 24

What are the inter-relationships b/w vitamin K, D, and A?

Answer 24

vitamin K, D, and A all involved w/ bone

• active vitamin D produces osteocalcin
• vitamin A (retinoic acid) may stimulate osteocalcin synthesis

active vit D acts on bone and kidneys (GGC in bone and kidneys)

Question 25

What is the excretion process of vitamin K phylloquinone (natural k1)?

Answer 25

Phylloquinone (K1, NATURAL) almost completely metabolized to a variety of metabolites prior to excretion
-excreted as glucoronides in urine or feces (via bile)

Question 26

What is the excretion process of vitamin K menaquinone (bacterial)?

Answer 26

excretion of menaquinone unknown

Question 27

What is the excretion process of vitamin K menadione (synthetic form)?

Answer 27

excreted as phosphate, sulfate, and glucuronide

Question 28

is vitamin K deficiency common?

Answer 28

uncommon