Iron Flashcards
What is the physiological importance and functions of iron?
- oxygen utilization, enzymatic systems, overall cell function/growth/transcription
- brain/neural development
- fight pathogens, energy/nutrient storage
What are the primary molecules that utilize iron?
- iron transport/storage proteins
- transferrin-binding proteins
- proteins of iron recycling
- functional/heme/non-heme proteins
How is heme vs non-heme iron absorbed?
h: ~25% absorbed, hydrolyzed from hgb/mgb via HCl/proteases, absorbed intact by hcp1, hydrolyzed to inorganic Fe2 + protoporphyrin
nh: <17% absorbed, hydrolyzed from food components as mainly Fe3 released in SI (absorption increased by acidic environment + chelation of Fe) + some Fe2 absorbed via DMT1
How is iron status regulated?
What is the relative efficiency vs intake of iron?
Fe3 is less bioavailable than Fe2
- heme iron: ~25% absorbed intact, hydrolyzed to Fe2
- non-heme iron: <17% absorbed, mostly Fe3
What are some food sources of iron + their bioavailability?
meat - higher bioavailability due to heme: oysters 6mg/3oz, beef liver 5mg/30z
legumes/vegetables - lower bioavailability due to lack of heme: soybean 4.5mg/0.5 cup, raisins 1.8mg/0.5 cup
enriched cereal/grains - bioavailability depends on type of iron its enriched with: 4-18mg/cup varying cereals
what is the definition of iron status/assessments?
iron status = serum ferritin levels that represent amount of Fe stored in body - via blood tests
why do EAR/RDA values vary between groups?
m: 6mg/day (EAR) \ 8mg/day (RDA)
f: 8mg/day (EAR) \ 18mg/day (RDA) - higher due to menstruation
pregnancy 22mg/day (EAR) \ 27mg/day (RDA) - higher due to RBC and fetal development
f on bc: 11mg/day (RDA) - higher due to shorter/lighter menses
What are the cause of iron excess + consequences?
hemochromatosis
cause: HFE mutations (unable to sense iron stores/hepcidin not released), increased transferrin saturation + ferritin = increased reactive free iron
cons: >60% TSAT, pain, TD2, heart/liver failure
What are the cause of iron deficiency + consequences?
how does iron help protect against pathogens?
is a key element in supporting growth, cells sequester it to keep it away from the pathogens and limit their growth + hepcidin as an antimicrobial peptide
what enhances iron absorption?
sugars, acids, acidic pH, mucin, meat factor proteins
what inhibits iron absorption?
alkaline pH, polyphenols, oxalic/phytic acids, divalent cations
what is iron chelation + impacts of it?
chelators bind metal ions
- loose chelation = solubilizes and make iron unavailable for other systems
- tight chelation = prevents it from being used
iron status is regulated/controlled by ____?
absorption
what is the role of hepcidin
innate immunity, lowers ECF iron concentrations to limit microbial growth
what is the role of ferroportin
exports ferrous/Fe2 across basolateral membrane of duodenal enterocytes (how iron gets out of the cell) + exports ferrous/Fe2 from macrophages/hepatocytes
what is the role of ferritin
store iron in cell cytosol, synthesis can be regulated by iron regulatory protein/element
what is the role of transferrin
transports iron in circulation/supplies iron to cells
what are the different types of iron-containing proteins
- heme proteins
- iron-sulfur clusters
- mononuclear nonheme iron proteins
- dinuclear nonheme iron proteins
what types of proteins are involved in iron transport/storage/recycling
transport/storage: transferrin, lactoferrin, DMT1, ferroportin, ferritin, hemosiderin
transferrin-binding (transport): TR1, TR2
recycling: ceruloplasmin, hephaestin, duodenal cytochrome b, STEAP
what is the role of ceruloplasmin and hephaestin
oxidize Fe2 to Fe3 before incorporation into apotransferrin
what is the role of duodenal cytochrome b and STEAP
reduce Fe3 to Fe2 before DMT1 transport
how do transferrin receptor (TfR) 1 and 2 differ?
1: principal protein for transferrin iron uptake + subject to regulation by iron regulatory proteins
2: secondary protein for transferrin iron uptake + not subject to regulation by iron regulatory proteins + involved in hepcidin transcription regulation
