Hydroxyurea promotes the reduction of spontaneous BFU-e to normal levels in SS and S/beta thalassemic patients

Clinical experience with fetal hemoglobin induction therapy in patients with β-thalassemia

Recent molecular studies of fetal hemoglobin (HbF) regulation have reinvigorated the field and shown promise for the development of clinical HbF inducers to be used in patients with β-thalassemia and sickle cell disease. However, while numerous promising inducers of HbF have been studied in the past in β-thalassemia patient populations, with limited success in some cases, no universally effective agents have been found. Here we examine the clinical studies of such inducers in an attempt to systematically review the field. We examine trials of agents, including 5-azacytidine, hydroxyurea, and short-chain fatty acids. This review highlights the heterogeneity of clinical studies done on these agents, including both the patient populations examined and the study end points. By examining the published studies of these agents, we hope to provide a resource that will be valuable for the design of future studies of HbF inducers in β-thalassemia patient populations.

Peripheral blood haematopoietic progenitor cells in patients with beta thalassaemia major receiving desferrioxamine or deferiprone as chelation therapy

OBJECTIVES

The main adverse effect of deferiprone is the development of neutropenia, which occurs via an unknown mechanism. We aimed to gain insight into the pathogenesis of deferiprone-induced neutropenia by assessing the peripheral blood haematopoietic progenitor cells.

METHODS

Sixteen patients with beta thalassaemia were studied; nine (Group A) were receiving desferrioxamine and seven (Group B) deferiprone. Ten healthy individuals comprised the control group (Group C).

RESULTS

Granulocyte-erythrocyte-monocyte-megakaryocyte colony forming units were significantly more in Groups A and B compared with Group C. Granulocyte-macrophage colony forming units (CFU-GM) were significantly more in Group B compared with Group C. Macrophage colony forming units were significantly less in Group B compared with Group C. Granulocyte colony forming units (CFU-G) were significantly more in Group A compared with Group C. We found a trend in the difference in the number of CFU-G between patients' groups (P = 0.123). Adding serum from patients receiving deferiprone to cultures of controls resulted in a maturation arrest of the granulocytic lineage.

CONCLUSION

Our findings point to a maturation arrest at the level of CFU-GM as a potential mechanism of deferiprone-induced neutropenia.

Zileuton induces hemoglobin F synthesis in erythroid progenitors: role of the L-arginine-nitric oxide signaling pathway

Induction of fetal hemoglobin (Hb F) is an important therapeutic tool in ameliorating complications of sickle cell disease. Nitric oxide has been implicated in the mechanism of Hb F synthesis induced by hydroxyurea (HU). This study examined whether zileuton (ZL), a structural analog of hydroxyurea, possessed Hb F-inducing properties and the potential role nitric oxide plays. ZL caused a dose-dependent increase in gamma-globin expression in K562 cells. This effect was confirmed by a dose-dependent increase in Hb F synthesis in erythroid progenitors from individuals with sickle cell anemia and normal hemoglobin genotypes. l-arginine had no effect on Hb F production; however, it dose-dependently inhibited ZL's ability to induce Hb F. The nitric oxide synthase inhibitor N(G)-monomethyl-l-arginine (l-NMMA) inhibited l-arginine's effect and restored ZL-mediated increase in Hb F synthesis. In addition, 8-PCPT-cGMP (8-(4-chlorophenylthio)guanosine 3',5'-cyclic monophosphate) inhibited ZL-mediated induction of Hb F synthesis. When comparing l-NMMA effects alone on ZL and HU, a partial reversal of increased Hb F synthesis was seen only with HU. Neither l-arginine alone nor l-arginine in combination with l-NMMA effected hydroxyurea-mediated induction of Hb F synthesis. This study demonstrates that ZL induces Hb F through a mechanism that involves l-arginine/nitric oxide/cGMP in a manner distinctly different from HU.

Renal complications of sickle cell disease: managing for optimal outcomes

A broad spectrum of renal changes is observed in patients with sickle cell anemia, and ideal therapeutic measures for the management of these alterations are still being studied. Affected patients have deficient urinary concentration and potassium excretion. Perhaps owing to a compensatory mechanism, the proximal tubules are in a condition of "hyperfunction", with increased sodium and phosphorus reabsorption and greater creatinine and uric acid secretion. Mild tubular acidosis may be present. No treatment has been reported for these tubular changes, except for care in the maintenance of hydration. The use of anti-inflammatory drugs is being studied in order to inhibit the prostaglandins involved in the process. Increased renal blood flow, glomerular filtration rate, and filtration fraction are frequent findings. Hematuria commonly occurs as a consequence of red blood cell sickling in the renal medulla, papillary necrosis, or even renal medullary carcinoma. Measures such as increased fluid ingestion, urine alkalinization and, if necessary, administration of epsilon-aminocaproic acid and certain invasive procedures have been proposed to treat hematuria. Nephropathy in patients with sickle cell anemia can be manifested by proteinuria and, more rarely, nephrotic syndrome. Drugs such as prednisone and cyclophosphamide are ineffective for the treatment of patients with nephrotic syndrome. Angiotensin converting enzyme inhibitors decrease proteinuria, but their long-term effect in preventing the progression of glomerular disease has not been established. Chronic renal failure, although infrequent, may be one of the manifestations of this disease. Hemodialysis and transplantation are satisfactory therapeutic options for patients with end-stage renal disease.