Iron homeostasis Flashcards
What are dietary sources of iron?
- meat and fish contain ham iron
- green veg, tofu, beans and pulses are rich in non-ham iron
What is the total dietary uptake of iron?
1-2mg/day
What transition state is most dietary iron found in?
Fe(III) and then converted to Fe(II) in the gut
What is iron involved in in the body?
- cofactor of Hb
- component of iron-sulfur proteins in the ETC → cytochromes
- acts as a co-factor in many enzymes, facilitating redox reactions - catalase and peroxidase
When can iron be toxic?
can be toxic in excess, participating in intracellular ‘Fenton Reactions’ (e.g. reacting with hydrogen peroxide to produce 2OH-) which can generate harmful free radicals and cause tissue damage
What exclusively takes up iron?
Duodenum
Describe excretion of iron
the body has no pathway for iron excretion, so absorption is the key regulatory step in controlling body iron
(unless mensuration)
What may happen to iron following uptake?
May be stored as ferritin in enterocytes (and subsequently lost via cell shedding) or absorbed via the ferroportin transporter (in the BL membrane)
What promotes iron uptake and how?
vitamin C - converts it to harm iron
What transition state must iron be in before uptake into enterocytes by DMT-1?
FeII
Which are the only cells that ferroportin is found in?
enterocytes and splenic reticuloendothelial macrophages involved in RBC turnover
Discuss transition states require for iron export from enterocyte
Must be converted to Fe(III) by hephaestin
How does iron then travel in the plasma?
Bound to transferrin
Describe transferrin
Liver-derived glycoprotein with binding sites for two Fe(III)
Serum transferrin concentration rises in response to iron deficiency and is often quantified
as ‘total iron-binding capacity’
Free serum iron levels are variable, and alone rarely a good index of iron status
Transferrin saturation (serum iron/TIBC x 100) is usually around 20-30%, and is often used as an index of iron availability
What do target cells of transferrin express? Describe
Cell surface transferrin receptors TfR1 which can bind and internalise the Fe(III)-transferrin complex
Liver cells also expression TfR2 with may be important in sensing iron availability