Hydroxyurea is the standard disease-modifying therapy for sickle cell disease (SCD). Which primary mechanism explains its therapeutic benefit in SCD?
- A Direct inhibition of haemoglobin S polymerisation in the deoxy-conformation
- B Reduction of 2,3-BPG levels, improving haemoglobin-oxygen affinity
- C Blockade of P-selectin on RBCs, reducing vascular adhesion
- D Induction of fetal haemoglobin (HbF) synthesis via inhibition of ribonucleotide reductase and demethylation of gamma-globin gene promoter ✓
Explanation
Hydroxyurea's primary mechanism in SCD is induction of fetal haemoglobin (HbF, α2γ2) via ribonucleotide reductase inhibition and promotion of stress erythropoiesis; gamma-globin gene promoter demethylation also contributes. HbF dilutes HbS in the RBC and inhibits HbS polymer formation because the HbF γ-chain does not participate in the Glu6 (HbS) polymer contact. HbF >20% reduces sickling episodes significantly. Additional hydroxyurea effects include reduced neutrophil and reticulocyte adhesion, nitric oxide generation, and improved RBC hydration. Crizanlizumab specifically targets P-selectin. Voxelotor directly inhibits HbS polymerisation.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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