Vitamins and trace elements
Vitamins
• Hypovitaminosis - a reduced amount of
vitamins, usually without clinical
manifestations
• Avitaminosis - complete lack of vitamins
(clinically manifested)
Measuring the concentration
of vitamins
• Directly (vit E, provitamin A = beta carotene,
B12, folates).
• Indirectly by concentrations of the
accumulating vitamin metabolite
• Saturation tests (administration of vit. C, if the
organism is saturated with vitamin, it appears
in the urine).
Fat soluble vitamins
• A (retinol) - taken in the form of provitamin A - betacarotene.
It binds to retinol binding protein (RBP). The active
form = 11-cis-retinal is essential for vision and for the proper
function of skin and mucous membranes. Antioxidant.
• D (cholecalciferol D3, from animal food, ergocalciferol D2,
from plant food or endogenously by UV) - vitamin D is
formed in the skin by UV from 7 - dehydrocholesterol, partly
ingested by food (D2, D3). It affects the metabolism of Ca and
P. Vit. D is formed only after double hydroxylation at position
25 in the liver (from cholecalciferol 25 hydroxycholecalciferol
= calcidiol is formed) and then in the kidneys hydroxylation at
position 1 (calcitriol = 1,25 dihydroxycholecalciferol is
formed).
Fat soluble vitamins
• There are several E (alpha - tocopherol) isomers.
Antioxidant. Protects LDL from oxidation. By
scavenging radicals, it itself becomes a radical, it is
renewed with the help of vitamin C.
• K (menadiol) - used for post-translational
modification of vitamin K-dependent coagulation
factors.
Warfarin (Coumadin)
• Anticoagulant
• It binds vitamin K
Water soluble vitamins - group B
• B1 thiamine (part of enzymes, deficiency manifests
as beriberi, neurological deficits)
• B2 riboflavin (part of FAD, FMN, electron transfer in
the respiratory chain)
• B5 pantothenic (part of CoA)
• B6 pyridoxine - part of aminotransferases
• B12 cyanocobalamin, necessary for nucleic acid
synthesis, deficiency = pernicious anemia
Water soluble vitamins
• Folic acid - deficiency = megaloblastic anemia.
• Niacin (NAD) - part of NAD, NADP
• H (Biotin) - part of the Krebs cycle
• C (ascorbic acid) - antioxidant. Deficiency = scurvy
Scurvy
Trace elements
• in the body are in trace amounts
• some elements (Pb, Hg, Cd) are the cause of
chronic poisoning.
Fe metabolism
• absorption (in the form of Fe2+) in the upper part of the
small intestine in the presence of acidic gastric juice
• absorption is forced by apoferritin, the protein of the
intestinal mucosa, which binds iron in trivalent form
(Fe3+) as ferritin.
• In plasma, iron as trivalent Fe3+ is bound to the β1
transport globulin - transferrin.
• Iron enters cells through transferrin receptors (TfRs). It
is again stored in the tissues in the form of ferritin
(storage form) or hemosiderin (unusable form).
Fe metabolism
• About 4 grams of Fe in the body, of which 3
grams are in hemoglobin.
• Oxygen binding and its transport in
hemoglobin, for some redox processes (it is
part of cytochromes).
Fenton's reaction
• formation of hydroxyl radical →
lipoperodixation
• this reaction is prevented by transferrin, which
binds free iron.
H2O2 + Fe2+ → OH- + ∙OH + Fe3+
Fe deficiency
• insufficient food intake (rarely),
• resorption disorder due to achlorhydria
(decreased production of acidic gastric juice).
• increased iron loss during chronic bleeding
(enterorrhagia - due to ca colorectum,
metrorrhagia).
Microcytic hypochromic anemia
• increased free plasma binding capacity for iron
(free transferrin = sign of chronic condition and
decreased plasma ferritin concentration = sign of
acute condition).
• The most sensitive indicator of iron deficiency in
cells are soluble transferrin receptors (sTfR) - in
the case of Fe deficiency, the cell produces up to
twice the amount of transferrin receptors and
releases large amounts into the blood.
Fe toxicity
Hemochromatosis
• an inherited disease caused by a defect in the
regulation of iron absorption in the small
intestine.
• Fe is stored in the organs.
Hemosiderosis
• it occurs iatrogenically with prolonged excessive
parenteral Fe supply.
Other trace elements
• Cu - bound to albumin in the blood. In the liver, it is
incorporated into ceruloplasmin, through which it is distributed
to tissues. Cofactor of enzymes, antioxidant. It is excreted in
the bile. Daily dose 15-30 mg for an adult. Deficiency leads to
mental retardation, skeletal involvement, CNS. Excess =
Wilson's disease. Tremor, ataxia, increased urinary excretion of
Cu.
• Zn - most is in a meat diet. It is excreted in pancreatic juice and
bile. Daily need 12-19 mg for an adult. Zn is part of
metalloenzymes (carbonic anhydridase, LD, ALP, AMS, SOD, is
used in the stabilization of DNA and RNA. Necessary for sperm
production. Lack of Zn in catabolism, malnutrition, burns,
nephrotic sy (binds to albumin). Diarrhea, vomiting.
Other trace elements
• Se - is not stored in the body. Contained in glutathione
peroxidase and protects the body from oxidative
damage. Selenium deficiency leads to cardiomyopathy
and muscle damage. Toxicity - the smell of garlic.
• Cr - mutagen, a carcinogen (if hexavalent), as a
trivalent regulates the effect of insulin, improves
glucose tolerance in diabetics.
Other elements
• F - deficiency leads to dental caries
• I - necessary for the synthesis of thyroid hormones
• Co - part of vit B12.