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Vitamins František Duška Nomenclature • Definition: compound indispensable for metabolism (usually co-enzyme), which cannot be synthetized in the body • Nomenclature: – is historical and therefore confusing – according to order of discovery – a letter covers whole group of compounds Vitamins: • Water soluble: – indispensible for the intermediary metabolism – anemia preventing – vitamin C • Lipid soluble: A, D, E, K Lipid-Soluble Vitamins • Resorption from the gut is coupled with the absorption of fat • Fat malabsorption (e.g. pancreatic insuficiency, xenical) can lead to vitamin deficiency • Hypervitaminosis is possible due to poor water-solubility and slow renal excretion Water-Soluble Vitamins • Deficiencies can occure relatively quickly (except B12) • Readily exreted by the kidney when surpassing the renal threshold toxicity is rare Vitamin A - Retinol -caroten: yellow and green vegetable cleavage (6mg to 1mg) Retinol/-al/-ic acid: liver, yolk, milk Vitamin A - Functions • Both -caroten and retinol are antioxidants • Retinol-P as a glycosyl donor for the synthesis of glycoproteins and proteoglycans • Steroid-hormone-like action • Vision Vitamin A - Deficiency and Toxicity • Deficiency: – hyperkeratosis due to impaired epithelial regeneration and mucus sercetion – imunity disturbancies and anemia – night-blindness • Toxicity: !!! teratogenic!!! – “polar-bear liver eaters“, otherwise uncommon Vitamin D • Is rather a hormone than a vitamin: can be synthetized in the body from 7dehydrocholesterol (UV light is recquired) Cholecalciferol - saltwater fish, liver, egg (liver) 25-hydroxycholecalciferol (kidney - PTH) 1,25-dihydroxycholecalciferol = calcitriol Vitamin D - Action • Increase calcium absorbtion (calbinden expression in the enterocyte) • Promotes bone resorbtion (with PTH) • Inhibits Ca excretion by the kidney Vitamin D - Deficiency and Toxicity • Deficiency: – fat malabsorption, vegans, the eldery, renal failure (impaired 25-hydroxylation) – rickets in children and osteomalacia in adults (soft bones due to impaierd mineralization of normal organic matrix) • Toxicity: – hypercalcemia with hypercalciuria (!stones), bone demineralization Vitamin E • a mixture of tocopherols • Function: – antioxidant: O. scavenger – possible role in the respiratory chain or heme synthesis – helps to prevent atherosclerosis • Deficiency and toxicity: unknown Tocopherol František Duška: carboxylation of Glu residues to gama-carboxyglutamic acid form a chelat-like comp., indispensable for Ca binding Vitamin K • A group of quinone derivates: – K1(phytylmetaquinone) from green veg. – K2(multiprenylmenaquinone) syntethized by the intestinal bacteria • Function: – recquired for the synthesis of clotting factors II., VII, IX and X. – indispensable for osteocalcin synthesis (= Ca-binding protein of the bone matrix) Vitamin K Vitamin K (cont.) • Deficiency: – increase coagulation time (Quick test), i.e. increase the risk of hemorhage and decrease th risk of thrombosis – newborns or long-term antibiotic treatment, fat malabsorbtion • Vitamin K antagonists (Warfarine) are widely used as an anticoagulant drug. Water-Soluble Vitamins It’s useful to learn features common for whole group of vitamins! Water-Soluble Vitamins 1. For energy metabolism: – B1, B2, B6 and niacin – pantothenic acid and biotine 2. Hematopoetic vitamins: – Folic acid and B12 3. Vitamin C “Energy-Releasing Vitamins“ • Are turned to co-enzymes of key reactions of energy metabolism • Sources: whole-grain cereals, meat, yolk, yeasts • For B1, B2 and B6 is recommended daily dose 1 to 2 mg for the normal adult. “Energy-Releasing Vitamins“ • Deficiencies can appear in alcoholics – otherwise rare: extreme diets, the eldery, increased recquirements (pregnancy…) • Symptoms are derived from impaired energy metabolism: – rapidly growing tissues (cheilitis, dermatitis, diarhoea) – peripheral and central nervous system – malaise Vitamin B1 (Thiamine) • is a precursor for TDP: co-enzyme of: – PDH and KG-DH (Krebs cycle) – transketolase (pentose-P pathway) – ? possible role in nerve transmission • Recomended daily dose is dependent oncarbohydrate and alcohol intake • Sources: whole-grain cereals (incl. flour), yeast etc. Thiamine deficiency • In whom? – alcoholics – polished rice as a major source of energy • Beri-beri: impairment of nervous tissue, heart failure, muscle weakness Vitamin B2 Riboflavine • As a part of FMN and FAD • Important for respiratory chain and various red-ox reactions • Deficiency in alcoholics, impairment of the skin and mucous membranes Niacin = Nicotinic Acid • a part of NADH & NADPH molecules in the form of nicotinamid • can be synthetized from tryptophan • Deficiency = pelagra = 3Ds: – dermatitis – diarhoea – dementia Vitamin B6 (Pyridoxin) • Pyridoxin, pyridoxal, pyridoxamin are all turned to pyridoxalphosphate (PLP) • Recquired for: – transamination – other reactions (e.g. serotonin and catecholamine synthesis, -ALA synthesis, homocystein breakdown) • Deficiency causes neurologic symtoms Panthotenic Acid Biotin • Panthotenic acid is a part of CoA – used by more than 70 enzymes – widespread in all food, deficiency not described • Biotin is a co-enzyme of carboxylation – pyruvatecarboxylase: anaplerotic for Krebs cycle and gluconeogenesis – AcCoA carboxylase: FA syntesis “Hematopoetic vitamins“ The lack of B12 and/or folate causes macrocytic anemia. “Hematopoetic vitamins” • Both co-operate in one-carbon metabolism, recquired for: – purines and dTMP (i.e. nucleic acids) – conversion of homocystein to Met – other: choline, Ser, Gly • Deficiency leads to: – macrocytic anemia (impaired DNA synthesis) – hyperhomocysteinemia (risk factor of atherosclerosis) Folic Acid • Absorbed and stored as polyglutamate reductase dihydroholate (FH2) reductase tetrahydrofolate (FH4) = active form Vitamin B12 • Cyanocobalamin