Hematologic, biochemical, and cardiopulmonary effects of l-arginine supplementation or phosphodiesterase 5 inhibition in patients with sickle cell disease who are on hydroxyurea therapy

Objectives: Fetal hemoglobin (HbF) induction involves NO-cGMP signaling pathways. l-arginine, an NO precursor, and the phosphodiesterase (PDE) 5 inhibitor sildenafil, which potentiates cGMP, were studied in adults with sickle cell disease (SCD) who were stably on HU. Methods: Twenty four courses of l-arginine (0.1-0.2 g/kg divided TID) or sildenafil (25-100 mg TID), assigned based on gender due to concerns about sildenafil-related priapism, were successfully completed. Biochemical assays, pulmonary pressures, and cardiopulmonary exercise capacity are reported from patients in whom serial values are available. Hematologic responses are reported in 14 subjects with HbSS who had stable baseline HbF levels. Results: l-arginine increased plasma arginine and ornithine, but not citrulline, suggesting diversion by plasma arginase from NO, and citrulline, generation. Glutathione increased only in patients on l-arginine. Sildenafil increased plasma cGMP and citrulline, but not other amino acids. Pulmonary pressures and 6-min walk distances improved only in patients on sildenafil. In subjects with stable baseline HbF levels, HbF levels changed little from a normalized baseline on l-arginine, decreasing by 2.9 ± 16.1%, n = 6; P = n.s., but increased on sildenafil, by 7.5 ± 11.7%, n = 8, P \u3c 0.05. Absolute reticulocyte counts initially decreased in patients on sildenafil. Conclusions: l-arginine, at doses that increase plasma arginine levels, altered redox potential in red cells. The lack of clinically detectable efficacy of l-arginine may be due to increased arginine metabolism in SCD patients. In vivo augmentation of the cyclic nucleotide pathway by PDE inhibition may induce HbF slightly, but strikingly improves hemodynamic and functional status in SCD. © 2009 John Wiley & Sons A/S

Combination erythropoietin-hydroxyurea therapy in sickle cell disease: Experience from the National Institutes of Health and a literature review

Erythropoietin is being used more widely in the management of sickle cell disease (SCD, inclusive of homozygous sickle beta, SS, and compound heterozygous sickle beta thalassemia, Sβ° thal), often in conjunction with hydroxyurea (HU). Herein, we summarize the published experience with erythropoietin use in SCD, in 39 patients (SS, n=30; Sβ° thal, n=9) who were treated between 1990 and 1996; and in 13 patients with sickle syndromes (SS, n=12, compound heterozygous SC disease, n=1) who were treated with erythropoietin or darbepoietin at the National Institutes of Health (NIH) since 2002. The dose range of erythropoietin for SCD in the published series, at a median of \u3e200 U/Kg/dose, is higher than that used in end-stage renal disease. The median duration of erythropoietin therapy was ≥3 months, with minimal reported side-effects. At the NIH, the median age of sickle syndrome patients who received erythropoietin or darbepoietin (both referred to as EPO in the NIH series) was 51 (24 to 70) years; 12/13 patients had sickle-associated pulmonary hypertension. Eleven out of the 13 patients were treated with both HU and EPO for \u3e 4 months (median of 11 months on EPO) without complication. Of the 13 patients, five (all SS) with pulmonary hypertension were given EPO for reticulocytopenia (\u3c100,000/μL) on HU; 5/13 patients (all SS), with pulmonary hypertension, were given EPO and HU concurrently, in the light of an estimated glomerular filtration rate of \u3c80 mL/minute. Three of the 13 patients (2 SS, 1 SC) were treated with EPO for miscellaneous reasons. Hematologic responses, detailed herein, suggest that EPO therapy may allow more aggressive HU dosing in high-risk SCD patients and in the setting of mild renal insufficiency, common to the aging sickle cell population. Furthermore EPO appears to be safe in SCD, particularly when used in conjunction with HU. We outline our current therapeutic strategy for EPO use in SCD. ©2006 Ferrata Storti Foundation