Lecture 43: Fat Soluble Vitamins 3 (Vitamins K and E) PDF

Lecture 43 Fat Soluble Vitamins 3 Vitamins K and E 1  Specific Objectives By the end of this lecture students can be able to: Understand the importance of both vitamins K and E in the body. Explain symptoms of deficiency of vitamin K in the newborn. Discuss the...

Lecture 43 Fat Soluble Vitamins 3 Vitamins K and E 1  Specific Objectives By the end of this lecture students can be able to: Understand the importance of both vitamins K and E in the body. Explain symptoms of deficiency of vitamin K in the newborn. Discuss the toxicity symptoms of both vitamins K and E. 2 VITAMIN K Vitamin K exists in several forms, for example, in plants as phylloquinone (or vitamin K1), and in intestinal bacterial flora as menaquinone (or vitamin K2). A synthetic form of vitamin K, menadione. 3 Function of vitamin K Vitamin K is required in the hepatic synthesis of prothrombin and blood clotting factors II, VII, IX, and X by carboxylation of glutamic acid residues to Gamma-carboxyglutamate (GLA) residues. 4  The formation of Gla is sensitive to inhibition by dicumarol, an anticoagulant occurring naturally in spoiled sweet clover, and by warfarin, a synthetic analog of vitamin K. 5 Distribution and requirement of vitamin K Vitamin K is found in cabbage, kale, spinach, egg yolk, and liver. There is also extensive synthesis of the vitamin by the bacteria in the gut. AI for vitamin K is 120 µg/day for adult 6 males and 90 µg for adult females. Clinical indications A true vitamin K deficiency is unusual because adequate amounts are generally produced by intestinal bacteria or obtained from the diet. If the bacterial population in the gut is decreased, for example, by antibiotics, the amount of endogenously formed vitamin is depressed. This can lead to hypoprothrombinemia in the marginally malnourished individual, for example, a debilitated geriatric patient. 7 8 Deficiency of vitamin K in the newborn: Newborns have sterile intestines and so initially lack the bacteria that synthesize vitamin K. Because human milk provides only about one fifth of the daily requirement for vitamin K, it is recommended that all newborns receive a single intramuscular dose of vitamin K as prophylaxis against hemorrhagic disease. 9 Toxicity of vitamin K Prolonged administration of large doses of synthetic vitamin K (menadione) can produce hemolytic anemia and jaundice in the infant, due to toxic effects on the membrane of red blood cells; therefore, it is no longer used to treat vitamin K deficiency. 10  VITAMIN E The E vitamins consist of eight naturally occurring tocopherols, of which α-tocopherol is the most active. The primary function of vitamin E is as an antioxidant in prevention of the nonenzymatic oxidation of cell components, for example, polyunsaturated fatty acids, by molecular oxygen and free radicals. 11  Distribution and requirements of vitamin E Vegetable oils are rich sources of vitamin E, whereas liver and eggs contain moderate amounts. The RDA for α -tocopherol is 15 mg for adults. The vitamin E requirement increases as the intake of polyunsaturated fatty acid increases 12  Deficiency of vitamin E Vitamin E deficiency is almost entirely restricted to premature infants. When observed in adults, it is usually associated with defective lipid absorption or transport. The signs of human vitamin E deficiency include sensitivity of erythrocytes to peroxide, and the appearance of abnormal cellular membranes. 13 14  Toxicity of vitamin E Vitamin E is the least toxic of the fat-soluble vitamins, and no toxicity has been observed at doses of 300 mg/day. Populations consuming diets high in fruits and vegetables show decreased incidence of some chronic diseases. 15 A 27-year-old woman with epilepsy has been taking phenytoin to control her seizures. She is now pregnant, and her physician is considering changing her medication to prevent potential bleeding episodes in the infant. What is the biochemical activity might be deficient in the infant if her medication is continued? A) Hydroxylation of proline B) Glucuronidation of bilirubin C) Reduction of glutathione D) Gamma-Carboxylation of glutamate E) Oxidation of lysine 16  76-year-old female patient is diagnosed with atrial fibrillation and an enlarged left atrium. Apart from this the patient is healthy and her family medical history does not show any peculiarities. The patient is eligible for a prolonged anti-coagulation therapy. Which of the following drugs is the best option in this case? A) Acetylsalicylic acid B) Clopidogrel C) Heparin D) Warfarin 17 Reference Book: Vasudevan, D. M., Sreekumari, S., and Kannan, V.., 2011. Textbook of biochemistry for medical students, 6th Edition. 18