Vitamin K Flashcards
What are the forms of vitmain K?
Menadione (synthetic form)
Phylloquinone (K1, natural plant form)
Menaquinone-7 (MK-7): bacterial form
What are some natural sources of vitamin K? phylloquinones (k1)
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
vitamin K DRIs?
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
Absorption of natural vitamin k (Phylloquinone K1)
-does not require digestion: * jejunum (micelles)
some active transport in proximal SI
what enhance the absorption of phylloquinone K1?
enhanced by:
- presence of dietary fat
- pancreatic lipase
- bile salts
Absorption of menaquinones (K2, bacteria)
- passive diffusion
- facultative and obligate bacteria (anaerobic, lower GI tract)
- efficiency of absorption varies among individuals
What is the fate of vitamin K within enterocytes?
K1 is incorporated into chylomicrons–>lymphatic system
-chylomicrons remnant: delivers any vit k not delivered to other tissues to liver
How is vitamin k metabolized in the liver?
Metabolized and packaged into VLDL in the liver
What is the average body pool size of vitamin K in body?
50-100 mg
turnover 1.5 days
Where is vitamin K stored?
- minimal storage in liver
- bone marrow, kidneys, lymph nodes, adrenals, lungs
What is the turnover fate of vit K?
rapid turnover
-taken up by tissues within 24h of appearance in blood
What is the function of vitamin K?
necessary for post-translational carboxylation of specific glutamic acid residues in proteins
What is the function of vitamin K?
Blood coagulation: activation of blood clotting proteins
-factor II, VII, IX, and X
What is the function of vitamin K?
Bone proteins: osteocalcin (secreted from osteoblasts), matrix Gla protein (MGP)
What is the process of blood clotting (involve vitamin K)?
fibronogen must be converted to fibrin (insoluble fiber network)
1. a series of rxns generates the inactive clotting factor X
- vitamin K and calcium activate inactive clotting factors
- Active clotting factor Xa–> converts prothrombin to thrombin
- Thrombin and fibrin stabilizing factor XIIIa form fibrin–> aggregates to produce an insoluble clot and stops bleeding
What is required for the coagulation of blood post-translationally?
post-translational carboxylation of glutamic acid residues on major proteins (e.g. factor II (prothrombin), VII, IX, X) activates these proteins
What is the production process of gamma-carboxyglumatic acid (GLA) via vitamin K carboxylation?
- vitamin K-dependent gamma-glutamyl carboxylase
cause carboxylation of glutamic acid residue in peptide - GLA in peptide
- GLA-proteins can bind calcium –>reacts with other cell components like phospholipids to affect blood clotting and bone mineralization among other processes
What are some examples of anticoagulants?
warfarin, coumarin
What is the mechanism of action of anticoagulants?
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
What are some vitamin K-dependent bone proteins?
Osteocalcin (bone GLA protein)
Matrix GLA protein (MGP)
What are some facts of osteocalcin (Bone GLA proteins)
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
What are some facts of matrix GLA protein (MGP)?
- 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
Interactions w/ other nutrients:
What are come antagonists of vitamin K?
Vitamin A and E: affect vitamin K absorption (ant)
Vitamin E: thought involved in inhibition of vitamin K metabolism at high doses
What are the inter-relationships b/w vitamin K, D, and A?
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)
What is the excretion process of vitamin K phylloquinone (natural k1)?
Phylloquinone (K1, NATURAL) almost completely metabolized to a variety of metabolites prior to excretion
-excreted as glucoronides in urine or feces (via bile)
What is the excretion process of vitamin K menaquinone (bacterial)?
excretion of menaquinone unknown
What is the excretion process of vitamin K menadione (synthetic form)?
excreted as phosphate, sulfate, and glucuronide
is vitamin K deficiency common?
uncommon
