Iron-deficiency anemia (IDA)
The development of this condition is caused by a shortage of the trace element or impaired its utilization. Main causes include regular blood loss, increased bodily demand (e.g., during pregnancy), and dietary deficiency—insufficient intake of iron with food.
For correction, complex preparations are used, whose components cover different biochemical needs of erythropoiesis:
- Iron sulfate ($FeSO_4$): supplies exogenous divalent iron ($Fe^{2+}$), serving as a direct substrate for the synthesis of heme and hemoglobin molecules.
- Ascorbic acid (Vitamin C): acts as a reducing agent in the gastrointestinal tract, converting $Fe^{3+}$ into the absorbable form $Fe^{2+}$. It is also essential for mobilizing iron stores from the intracellular protein ferritin.
- Folic acid (Vitamin $B_9$): indispensable for the synthesis of purine and pyrimidine nucleotides (DNA), ensuring active proliferation of erythroid cells.
- Cyanocobalamin (Vitamin $B_{12}$): a cofactor that converts folic acid into its active form, tetrahydrofolate. It participates in the conversion of homocysteine to methionine and protects against the development of megaloblastic anemia.
Hemochromatosis (iron overload)
A pathology diametrically opposed to deficiency, characterized by the excessive accumulation of iron. Excess amounts are deposited as hemosiderin pigment granules inside cells of the reticuloendothelial system, primarily in the liver and spleen.
Hemosiderin accumulation is toxic and eventually leads to severe organ damage. The main causes of such overload are frequent blood transfusions or a pathological increase in intestinal iron absorption.
Iron transport and Heilmeyer's disease
Iron delivery into the cell is carried out via the receptor-mediated endocytosis mechanism:
- The complex consisting of transferrin and $Fe^{3+}$ binds to a specific receptor on the cell membrane.
- The membrane invaginates, forming an intracellular vesicle—an endosome.
- The $H^+$-ATPase enzyme pumps protons into the endosome, acidifying the medium.
- In the acidic environment, iron dissociates from transferrin and enters the cytosol for cellular needs.
An inherited impairment of transferrin synthesis is called atransferrinemia (Heilmeyer's disease). This pathology presents a paradox: tissues experience severe iron deficiency despite its actual presence in the body.
Briefly: answers to topical questions
Which laboratory blood parameters are used for the differential diagnosis of iron-deficiency anemia?
Biochemical markers of iron metabolism that assess depletion of stores and transport capacity are used for the differential diagnosis of iron-deficiency anemia.
Markers that decrease:
- Serum iron — an indicator of circulating iron.
- Serum ferritin — the main indicator of tissue iron stores.
- Transferrin saturation percentage — calculated from serum iron and TIBC.
Markers that compensatorily increase:
- Total iron-binding capacity (TIBC) — reflects an increase in transport capacity.
- Latent iron-binding capacity (UIBC).
These parameters respond to deficiency at early stages and change unidirectionally.
Which copper-containing enzyme catalyzes the oxidation of Fe2+ to Fe3+ for binding with transferrin in plasma?
The oxidation of iron for its subsequent binding to transferrin is catalyzed by the enzyme ferroxidase (ceruloplasmin).
After oxidation, iron binds to the transport glycoprotein—transferrin. The iron-transferrin complex is carried by the bloodstream to tissues. Next, the transferrin complex binds to a specific transferrin receptor on the surface of target cells, is internalized by the cell to form an endosome, and intracellular iron is released as Fe2+ and used for the synthesis of iron-containing proteins or stored as ferritin.
Composition of IDA combination drugs: Iron builds heme, vitamin C aids absorption (Fe3+ → Fe2+), while B9 and B12 divide blood cells and protect against megaloblastic anemia.
Class and exam questions
Why is ascorbic acid added to iron preparations?
Vitamin C reduces ferric iron to ferrous iron. This is critically important for its absorption in the gastrointestinal tract and also helps release iron stores from ferritin.
What is atransferrinemia (Heilmeyer's disease)?
This is an inherited pathology in which the synthesis of the carrier protein transferrin is impaired. As a result, tissues experience an iron shortage even when there is enough of it in the body itself.
How does iron dissociate from transferrin inside the cell?
The complex is taken up via endocytosis. Inside the resulting endosome, the environment is acidified using a proton pump ($H^+$-ATPase), which leads to the dissociation of iron from the protein and its release into the cytosol.
What else to study on this topic
- Biochemistry of purine and pyrimidine nucleotide synthesis involving folic acid
- The role of vitamin B12 in the metabolism of homocysteine to methionine
- Heme structure and hemoglobin synthesis mechanisms
- Mechanism of action of $H^+$-ATPase in endosomal membranes
- Differences between ferritin and hemosiderin
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