Transcript Vitamins - Univerzita Karlova v Praze

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