Vitamin K- Chemistry functions and Clinical significance

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An overview of vitamin k- Structure, functions and deficiency

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Vitamin K- Chemistry functions and Clinical significance

  1. 1. By- Professor (Dr. )Namrata Chhabra Biochemistry For Medics- Lecture notes 8/6/2014 1 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  2. 2. Vitamin K- Chemistry Vitamin K represents a group of lipophilic and hydrophobic vitamins. Three compounds have the biological activity of vitamin K Phylloquinone (Vitamin K1), the normal dietary source, found in green vegetables Menaquinones (vitamin K2), synthesized by intestinal bacteria, with differing lengths of side chain; and Menadione and menadiol diacetate, synthetic compounds that can be metabolized to phylloquinone. 8/6/2014 2 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  3. 3. Vitamin K- Chemistry 8/6/2014 3 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  4. 4. Vitamin K- Chemistry Vitamin K family are naphthoquinone derivatives . Phylloquinone and menaquinones, both have a long isoprenoid side chain. The length of the side chain differs. Phylloquinone have a 20 C side chain , whereas menaquinones have a 30 C side chain. The isoprenoid chain makes these vitamin hydrophobic or lipophilic. The synthetic vitamin K (menadione, menadiol diacetate) have only hydrogen in place of isoprenoid side chain that makes these vitamin water-soluble. 8/6/2014 4 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  5. 5. Dietary Sources Vitamin K is found in green leafy vegetables such as kale and spinach, and Appreciable amounts are also present in margarine and liver. Vitamin K is present in vegetable oils and is particularly rich in olive, canola, and soybean oils. Some amount is contributed by intestinal bacteria 8/6/2014 5 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  6. 6. Dietary Sources 8/6/2014 6 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  7. 7. Absorption, Transportation and Storage Absorption takes place in intestine in the presence of bile salts. The transportation from intestine is carried out through chylomicrons. Storage occurs in liver and from liver transportation to peripheral cells is carried out bound with beta lipoproteins. 8/6/2014 7 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  8. 8. Impaired absorption of vitamin K Fat malabsorption is associated with impaired absorption of vitamin K and other fat soluble vitamins. Vitamin K is important for the coagulation process. In its deficiency coagulation process is grossly affected resulting in tendency for bleeding and hemorrhages. Absorption of vitamin K may also be decreased by mineral oil, bile acid sequestrants (Cholestyramine, Colestipol) and Orlistat (weight loss medication). 8/6/2014 8 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  9. 9. Impaired absorption of vitamin K 8/6/2014 Biochemistry for medics- Lecture Notes- Namrata Chhabra 9
  10. 10. Recommended daily allowance The average daily allowance is 50-100 mg/day. Requirement increases in – Liver disorders Patients on prolonged antibiotic therapy, bile acid sequestrants (Cholestyramine, colestipol) and Orlistat (weight loss medication) 8/6/2014 10 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  11. 11. Functions of vitamin K Carboxylation of Glutamate in post synthetic modification of calcium binding proteins The only known biological role of vitamin K is as a cofactor for an enzyme (Carboxylase) that catalyzes the carboxylation of the amino acid, glutamic acid, resulting in its conversion to gamma-carboxy glutamic acid (Gla). Although vitamin K-dependent gamma-carboxylation occurs only on specific glutamic acid residues in a small number of vitamin K-dependent proteins, it is critical to the calcium-binding function of those proteins. 8/6/2014 11 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  12. 12. Vitamin K-dependent gamma- carboxylation 8/6/2014 Biochemistry for medics- Lecture Notes- Namrata Chhabra 12
  13. 13. Functions of vitamin K Calcium binding proteins Vitamin K–dependent proteins are a heterogeneous group, including = clotting factor proteins and proteins found in bone lung kidney, and placenta. 8/6/2014 13 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  14. 14. 1) Role of vitamin K in coagulation The ability to bind calcium ions (Ca2+) is acquired by the activation of the vitamin K-dependent clotting factors, or proteins, in the coagulation cascade. Factors II (prothrombin), VII, IX, and X make up the core of the coagulation cascade. These factors are synthesized in the liver in the inactive form. They undergo post translational modifications, gamma carboxylation of glutamic acid residues. This process of gamma carboxylation of glutamic acid residues imparts another negative charge, so as to promote the effective binding of these factors/proteins to calcium ions. 8/6/2014 14 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  15. 15. 8/6/2014 15 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  16. 16. Vitamin K cycle Vitamin K is a fat-soluble vitamin, the body stores very little of it, and its stores are rapidly depleted without regular dietary intake. Because of its limited ability to store vitamin K, the body recycles it through a process called the vitamin K cycle. The vitamin K cycle allows a small amount of vitamin K to function in the gamma-carboxylation of proteins many times, decreasing the dietary requirement. 8/6/2014 16 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  17. 17. Vitamin K cycle Reduced lipoamide is required for the activity of Epoxide reductase whereas NADPH is needed for the action of vitamin K reductase. 8/6/2014 17 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  18. 18. Vitamin K cycle Vitamin K hydroquinone (active form) is oxidized to the Epoxide form during the process of enzymatic reaction. The initial form (hydroquinone form) is regenerated by two steps process. Vitamin K Epoxide is reduced to the quinone by a Epoxide reductase, and the quinone is reduced to the active hydroquinone by either the same reductase or by a vitamin K reductase(quinone reductase). 8/6/2014 18 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  19. 19. Role of vitamin K in coagulation Prothrombin and several other proteins of the blood clotting system (Factors VII, IX, and X, and proteins C and S) each contain 4–6 γ-carboxyglutamate residues. γ-Carboxyglutamate chelates calcium ions, and so permits the binding of the blood clotting proteins to membranes. 8/6/2014 19 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  20. 20. Vitamin K Antagonists Dicumarol and Warfarin, inhibit coagulation through antagonism of the action of vitamin K. Warfarin prevents the recycling of vitamin K by inhibiting two important reactions and creating a functional vitamin K deficiency Warfarin is a competitive inhibitor of Epoxide reductase. In the presence of Warfarin, vitamin K epoxides cannot be reduced, they accumulate and are excreted. 8/6/2014 20 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  21. 21. Vitamin K Antagonists Abnormal precursor of prothrombin (preprothrombin) containing little or no carboxyglutamate, and incapable of chelating calcium, is released into the circulation Thus, in the presence of Warfarin or in vitamin K deficiency the process of coagulation is inhibited, 8/6/2014 Biochemistry for medics- Lecture Notes- Namrata Chhabra 21
  22. 22. Vitamin K Antagonists Large quantities of dietary or supplemental vitamin K can overcome the anticoagulant effect of vitamin K antagonists patients taking these drugs are cautioned against consuming very large or highly variable quantities of vitamin K in their diets. Like all anticoagulants, the major side effect of Warfarin is bleeding. Treatment of pregnant women with Warfarin can lead to fetal bone abnormalities (Fetal Warfarin syndrome) 8/6/2014 22 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  23. 23. Synthesis of Bone Calcium-Binding Proteins Vitamin K is also important in synthesis of two proteins that contain γ-carboxyglutamate that are present in bone- osteocalcin and bone matrix Gla protein. Osteocalcin is a protein synthesized by osteoblasts. The synthesis of osteocalcin by osteoblasts is regulated by the active form of vitamin D, 1,25(OH)2D3 or calcitriol. The mineral-binding capacity of osteocalcin requires vitamin K-dependent gamma-carboxylation of three glutamic acid residues. 8/6/2014 23 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  24. 24. Synthesis of Bone Calcium-Binding Proteins After gamma carboxylation osteocalcein binds tightly to calcium. Osteocalcin also contains hydroxy proline, so its synthesis is dependent on both vitamins K and C; in addition, its synthesis is induced by vitamin D. The release into the circulation of osteocalcin provides an index of vitamin D status. 8/6/2014 24 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  25. 25. Synthesis of Bone Calcium-Binding Proteins Matrix Gla protein- MGP has been found in bone, cartilage, and soft tissue, including blood vessels. MGP prevents the calcification of soft tissues and cartilages, while facilitating normal bone growth and development. Protein S- The vitamin K-dependent anticoagulant protein S is also synthesized by osteoblasts, but its role in bone metabolism is unclear. Children with inherited protein S deficiency suffer complications related to increased blood clotting as well as decreased bone density. 8/6/2014 25 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  26. 26. Synthesis of Bone Calcium-Binding Proteins 8/6/2014 Biochemistry for medics- Lecture Notes- Namrata Chhabra 26
  27. 27. Vitamin K- dependent proteins 8/6/2014 Biochemistry for medics- Lecture Notes- Namrata Chhabra 27
  28. 28. Vitamin K deficiency Causes Lack of vitamin K in the diet Fat malabsorption and that thus reduce the absorption of vitamin K Disease or surgical interventions that affect the ability of the intestinal tract to absorb vitamin K Chronic liver diseases 8/6/2014 28 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  29. 29. Vitamin K deficiency in the newborn • Maternal medications that interfere with vitamin K stores or function (e.g., carbamazepine, phenytoin, barbiturates, some Cephalosporins, rifampin, Isoniazid, Warfarin or Warfarin like drugs) can result in vitamin K deficiency bleeding in the infant. •Transplacental transfer of vitamin K is very limited during pregnancy, •The storage of vitamin K in neonatal liver is also limited. •Breast milk is a poor source of vitamin K. 8/6/2014 29 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  30. 30. Vitamin K deficiency in infants Diarrhea Hepatitis Cystic fibrosis Celiac disease Short bowel syndrome Chronic exposure to broad spectrum antimicrobials 8/6/2014 30 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  31. 31. Clinical Manifestations The main symptom is bleeding (hemorrhage)—into the skin (causing bruises), from the nose, from a wound, in the stomach, or in the intestine. Blood may be seen in the urine or stool. In newborns, life-threatening bleeding within or around the brain may occur. Having a liver disorder increases the risk of bleeding because proteins that help blood clot (clotting factors) are made in the liver. Vitamin K deficiency may also weaken bones. 8/6/2014 31 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  32. 32. Clinical Manifestations Most newborn infants are healthy upon examination, however, intracranial hemorrhage can occur during the delivery process and can lead to severe complications. Internal hemorrhage of organs other than the brain may be difficult to detect; however, if they are suspected, careful physical monitoring and serial imaging after birth are indicated. Soft tissue hemorrhages may be there. 8/6/2014 32 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  33. 33. Clinical Manifestations A deficiency of vitamin K can lead to extreme bleeding, which can begin as a gum or nose discharge or bruising 8/6/2014 33 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  34. 34. Laboratory Studies A Prothrombin time (PT), activated partial Thromboplastin time (aPTT), fibrinogen levels, and a platelet count should be included in the initial workup for vitamin K deficiency bleeding (VKDB) in a newborn. 8/6/2014 34 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  35. 35. Laboratory Studies A prolonged PT is usually the first laboratory test result to be abnormal in vitamin K deficiency bleeding due to reduction in Prothrombin, FVII, FIX, and FX levels. 8/6/2014 35 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  36. 36. Laboratory Studies The diagnosis of vitamin K deficiency bleeding is confirmed if administration of vitamin K halts the bleeding and reduces the PT value. Infants with vitamin K deficiency bleeding typically have a prolonged PT with platelet counts and fibrinogen levels within the normal range for newborns. 8/6/2014 36 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  37. 37. Imaging Studies MRI exposes the neonate to no radiation and is becoming the preferred way to study the brain because tissue damage can be better defined. 8/6/2014 37 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  38. 38. Other Tests A full coagulopathy work-up and hematology consultation are required if clinical and laboratory findings are suggestive of non–vitamin K deficiency bleeding. A work-up that includes functional tests and imaging are mandatory if liver disease is suspected. Hereditary defects in the coagulation system must always be considered among the differential diagnoses. 8/6/2014 38 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  39. 39. Treatment A vitamin K injection in the muscle is recommended for all newborns to reduce the risk of bleeding within the brain after delivery. 8/6/2014 39 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  40. 40. Treatment For patients with chronic malabsorption, 1–2 mg/d of vitamin K should be given orally, or 1–2 mg/week can be taken parenterally. 8/6/2014 40 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  41. 41. Treatment Patients with liver disease may have an elevated prothrombin time because of liver cell destruction as well as vitamin K deficiency. If an elevated prothrombin time does not improve on vitamin K therapy, it can be deduced that it is not the result of vitamin K deficiency. 8/6/2014 41 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  42. 42. Treatment People who have vitamin K deficiency and a severe liver disorder may also need blood transfusions to replenish the clotting factors. A damaged liver may be unable to synthesize clotting factors even after vitamin K injections are given. The reversal of excessive anticoagulant therapy with Warfarin or Warfarin-like drugs can be achieved by minimal doses of vitamin K (1 mg orally or by intravenous injection) for asymptomatic patients. 8/6/2014 42 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  43. 43. Toxicity Toxicity from dietary phylloquinone and menaquinones has not been described. High doses of vitamin K can impair the actions of oral anticoagulants. 8/6/2014 43 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  44. 44. Prevention Intramuscular (IM) vitamin K prophylaxis at birth is the standard of care. Commercial infant formulas contain supplemental vitamin K. These measures have served to make vitamin K deficiency bleeding a rarity. However, parental refusal of prophylaxis and an increasing frequency of breastfeeding may cause a resurgence of vitamin K deficiency bleeding in developed countries. 8/6/2014 44 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  45. 45. Prognosis In the absence of intracranial hemorrhage, the prognosis for vitamin K deficiency bleeding in an otherwise healthy infant is excellent. Prognosis after intracranial hemorrhage depends on the extent and location of the hemorrhage. 8/6/2014 45 Biochemistry for medics- Lecture Notes- Namrata Chhabra
  46. 46. Summary Vitamin K is a fat soluble vitamin Phylloquinone, Menaquinone and Menadione are the members of vitamin K family Vitamin K acts as a coenzyme for the gamma carboxylation of glutamic residues of Calcium binding proteins Plays an important role in blood clotting, bone formation and prevention of calcification of soft tissues Deficiency of vitamin K is manifested in the form of bleeding tendencies and hemorrhages Oral or injectable vitamin K can be recommended depending upon the severity of the disease. 8/6/2014 46 Biochemistry for medics- Lecture Notes- Namrata Chhabra

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