Original Article
Treatment of Sickle Cell Anemia with Hydroxyurea and Erythropoietin
N Engl J Med 1990; 323:366-372August 9, 1990
- Abstract
- Abstract
Background.
Hydroxyurea increases the production of fetal hemoglobin (hemoglobin F) in patients with sickle cell anemia and therefore has the potential for alleviating both the hemolytic and vaso-occlusive manifestations of the disease. There is preliminary evidence that recombinant human erythropoietin may also increase hemoglobin F production.
Methods and Results.
We treated five patients with sickle cell disease with escalating doses of intravenous erythropoietin for eight weeks. Three of these patients were subsequently treated with daily doses of oral hydroxyurea. After the optimal dose was determined, erythropoietin was then given along with hydroxyurea for four weeks.
Treatment with erythropoietin, either alone or in combination with hydroxyurea, had no significant effect on the percentage of hemoglobin F—containing reticulocytes (F reticulocytes) or red cells (F cells). In contrast, hydroxyurea treatment was associated with a 3-to-25-fold increase in F reticulocytes, a 1.6-to-7-fold increase in F cells, and a 2.3-to-16-fold increase in the percentage of hemoglobin F. In all three patients given hydroxyurea, treatment with this drug was associated with reduced hemolysis, shown by decreases in serum bilirubin and lactic dehydrogenase and prolongation of red-cell survival. Hydroxyurea treatment also resulted in a decrease in the percentage of irreversibly sickled cells and sickling at partial oxygen saturation, an increase in oxygen affinity and total red-cell cation content, and a reduction in potassium-chloride cotransport. All three patients had a decrease in the number of pain crises.
Conclusions.
This study confirms that hydroxyurea therapy increases hemoglobin F production and provides objective evidence that hydroxyurea reduces the rate of hemolysis and intracellular polymerization of hemoglobin S. In contrast, recombinant human erythropoietin, whether alone or in combination with hydroxyurea, offers no measurable benefit. (N Engl J Med 1990; 323:366–72.)
Media in This Article
Figure 1
Effect of Recombinant Human Erythropoietin on the Percentage of F Reticulocytes (Solid Lines) and F Cells (Dashed Lines) in Five Patients with Sickle Cell Disease.Figure 2
Effect of Hydroxyurea and Erythropoietin on the Percentage of Hemoglobin F (▲) and F Cells (□) in Three Patients with Sickle Cell Disease.Article Activity
- Article
CURRENT understanding of the molecular and cellular pathogenesis of sickle cell disease1 2 3 4 has led to three independent approaches to therapy: chemical inhibition of hemoglobin S polymerization, reduction of the intracellular hemoglobin concentration, and pharmacologic increase in fetal hemoglobin (hemoglobin F) production. Knowledge of the three-dimensional structure of the hemoglobin S polymer5 , 6 has facilitated the design and development of compounds that react at specific sites on hemoglobin S, thereby inhibiting the assembly or growth of polymers (or both).7 8 9 Unfortunately, no antisickling agents tested thus far can be regarded as both safe and effective. Because the rate of polymerization is so exquisitely dependent on the hemoglobin S concentration,10 any treatment that lowers the mean corpuscular hemoglobin concentration has a sound rationale. The simplest approach, and the only one to have been tested in clinical trials, is the induction of hyponatremia, which causes osmotic swelling of red cells.11 Although this treatment appears to be effective when it is carefully monitored, it is too cumbersome and risky to be adapted to long-term outpatient care.12
Because hemoglobin F is an effective inhibitor of polymerization of deoxyhemoglobin S,13 14 15 16 therapeutic agents that increase hemoglobin F production would be expected to benefit patients with sickle cell disease. A variety of antitumor agents, including 5–azacytidine,17 18 19 20 cytarabine,21 , 22 and hydroxyurea,22 23 24 25 26 27 28 have been shown to increase production of fetal hemoglobin in nonhuman primates17 , 21 , 23 as well as in humans.18 19 20 , 22 , 24 25 26 27 28 Recent interest has focused on hydroxyurea, since it is relatively nontoxic, its myelo-suppressive effects are readily reversible, and it is not known to induce secondary neoplasms. Currently, the principal use of hydroxyurea is in the treatment of patients with myeloproliferative diseases, in whom it has been shown to induce moderate increases in hemoglobin F levels.29 Much more impressive increases in hemoglobin F levels have been noted in patients with sickle cell disease.24 25 26 27 28 In view of concern about the long-term administration of any antitumor drug to patients with a congenital nonmalignant disorder, there is considerable interest in identifying safe alternatives for increasing hemoglobin F production. Recombinant human erythropoietin has proved to be both extremely effective and remarkably nontoxic therapy for the anemia of chronic renal disease.30 31 32 There is preliminary evidence that it may stimulate hemoglobin F production not only in nonhuman primates33 but also in patients with sickle cell anemia.34 Since the clinical manifestations of sickle cell disease are episodic and largely subjective, the evaluation of new kinds of therapy requires rigorous objective measurements. Recent reports show quite convincingly that hydroxyurea increases the number of red cells containing hemoglobin F (F cells), the percentage of hemoglobin F,26 27 28 and the amount of hemoglobin F per F cell.28 However, except for the recent study of two patients by Balas et al.,35 there is almost no information on whether this treatment inhibits sickling and prolongs red-cell survival. We have performed a battery of in vivo and in vitro studies in three patients with sickle cell disease, before and after treatment with high doses of recombinant human erythropoietin, oral hydroxyurea, and a combination of the two agents. Two other patients were treated with erythropoietin alone. The results provide strong evidence that hydroxyurea, but not recombinant erythropoietin, significantly decreases both the rate of hemolysis and the intracellular polymerization of hemoglobin S in patients with sickle cell anemia.
Methods
Patients
Three patients at Brigham and Women's Hospital (Patients 1, 2, and 3) and two patients at Johns Hopkins Hospital (Patients 4 and 5) were enrolled in the study. All five patients had been documented as homozygous for sickle cell anemia. Before treatment, four patients had frequent episodes of vaso-occlusion manifested primarily by pain crises. One (Patient 4) had mild chronic renal insufficiency (serum creatinine level, 150 to 177 μmol per liter) and severe anemia (hemoglobin level, 2.3 to 2.8 mmol per liter). All the patients were cooperative and free of dependence on analgesics or narcotics. Their condition was otherwise clinically stable as documented by medical history, complete physical examination, serum chemistry profile (electrolyte measurements, liver-function tests, and measurement of blood urea nitrogen and creatinine), complete blood counts, and 12-lead electrocardiography. The patients had no clinically important abnormalities on chest radiography performed within the six months before study entry. The use and dosages of medications were kept constant for at least two weeks before entry, and every attempt was made to continue a regimen of these drugs throughout the study.
Approval was obtained from the institutional review board of each institution before the study began. Written informed consent was obtained from each participant after the nature of the study had been fully explained by one of the investigators.
Study Protocol
The following studies were performed in all patients on entry and in most instances during the various treatments: complete and differential blood counts, determination of the percentage of reticulocytes, F reticulocytes,36 and F cells37 and the percentage of hemoglobin F by high-performance liquid chromatography,38 and measurement of serum erythropoietin,39 , 40 ferritin, and iron. Additional variables measured in the three Boston patients included the percentage of hemoglobin F determined by alkali denaturation, the survival of 51Cr-labeled red cells, the percentage of irreversibly sickled cells on Wright-stained blood films, whole-blood oxygen equilibria and sickling of partially oxygenated cells,11 the phthalate density-gradient profile, the total red-cell cation content, and potassium-chloride cotransport. Methodologic details of these latter studies are presented below. Recombinant human erythropoietin was then administered intravenously twice a day (six to eight hours apart) one day a week for eight weeks, according to a schedule for dose escalation (weeks 1 and 2, 600 U per kilogram of body weight; weeks 3 and 4, 1100 U per kilogram; and weeks 5 through 8, 1500 U per kilogram).
Five to seven weeks after treatment with erythropoietin ended, the three Boston patients were treated with oral hydroxyurea. The initial dose was determined on the basis of a hydroxyurea-clearance test.27 The drug was prepared as 100-mg and 500-mg tablets in order to permit small changes in the dosage. Daily therapy was instituted, since recent clinical trials41 have shown it to be at least as effective as pulse therapy24 or therapy given four days a week.28 The dose was gradually escalated until moderate neutropenia developed (a 30 to 60 percent decrease in the absolute neutrophil count). When the levels of hemoglobin F and F cells reached a plateau, the measurements of red-cell survival and in vitro sickling were repeated.
In the third phase of the study, hydroxyurea therapy was continued and intravenous recombinant erythropoietin treatment was reinstituted with a dose of 1500 U per kilogram, given twice a day one day a week for four weeks. Two patients received a final dose of 1500 U per kilogram twice a day, four days after the previous dose.
Oxygen Equilibria and Morphologic Sickling
Red cells were incubated at a hematocrit of 20 percent in a medium containing 120 mM sodium chloride, 28 mM sodium bicarbonate, 5 mM potassium chloride, 2 mM sodium phosphate buffer (pH 7.40), 1 mM magnesium chloride, 1 mM calcium chloride, and 5 mM glucose. Aliquots of this suspension (each 1.5 ml) were transferred to 25-ml Erlenmeyer flasks and equilibrated for five minutes at room temperature with the desired gas mixture. The gas mixtures used contained 5 percent carbon dioxide and varying percentages of oxygen (0, 1, 2, 3, 5, 7, and 15 percent), with nitrogen as the balancing gas. Gases were hydrated with the same buffer to avoid alteration of cell water content. The flasks were subsequently incubated at 37°C for 30 minutes in a shaking water bath. Samples were obtained for measurements of oxygen saturation (Corning 2500 CO-oximeter), the partial pressure of oxygen and carbon dioxide, and pH (IL Model 1304 pH/Blood Gas Analyzer). Triplicate readings were performed for each flask. At the end of the 30-minute incubation at 37°C, 50 μl of cells was taken from each flask used for oxygen-equilibria measurements and transferred to a flask containing 4 ml of medium containing 1 percent glutaraldehyde and 0.2 percent albumin. This flask had been incubated for 30 minutes at 37°C with the same gas mixture used in the oxygen-equilibria studies. The cells were transferred to 5-ml plastic tubes and maintained at 4°C for subsequent determination of the percentage of sickle cells. Samples were coded and analyzed in a blinded fashion by a single observer. For each sample, 500 cells were counted in duplicate and scored as normal, deformed, or sickled according to morphologic criteria previously described.11 The percentage of deformed cells was less than 10 percent in all specimens.
Red-Cell Cation Content and Phthalate Density Profile
Blood samples were centrifuged in a refrigerated centrifuge (RC5B, Dupont Instruments, Sorvall Biomedical, Newtown, Conn.) at 5°C for 10 minutes at 3000×g, and the cells were washed five times with a solution containing 152 mM choline chloride, 1 mM magnesium chloride, and 10 mM TRIS—MOPS (MOPS is 3-(N-morpholino) propanosulfonic acid) (pH 7.4) at 4°C. The following measurements were made in an aliquot of cells suspended in an approximately equal volume of choline washing solution: hematocrit, cell sodium (1:50 dilution in 0.02 percent Acationox, American Scientific Products, McGaw Park, Ill.), cell potassium (1:500 dilution), hemoglobin (optical density at 540 nm in Drabkin's solution), and phthalate density profile42 after centrifugation in microhematocrit tubes. The erythrocyte sodium and potassium contents were determined in an atomic absorption spectrophotometer (Model 5000, Perkin—Elmer, Norwalk, Conn.) with the use of standards in double-distilled water. Since phthalate density is markedly temperature dependent, the red cells were equilibrated at room temperature before centrifugation. Centrifugation lasted 6 to 7 minutes, with 15 minutes between centrifugations to allow the microcentrifuge head to cool. The median density (D50) and middle 60 percent density range (R60) of the phthalate density profiles were determined according to the technique of Rodgers et al.42
Potassium—Chloride Cotransport Activity in Sickle Cells
Measurements of potassium transport were performed in carbon monoxide-treated sickle cells. The erythrocytes were suspended at 10 percent hematocrit in choline washing solution at 4°C and were equilibrated for 20 minutes with carbon monoxide, which was bubbled in a flask containing choline washing solution at 4°C. The percentage of carboxyhemoglobin was measured at the end of incubation. Potassium efflux was measured from fresh, untreated sickle cells and from nystatin-treated sickle cells. The nystatin loading procedure and the protocol for measuring potassium efflux were performed as described previously.43 , 44 The flux mediums contained 140 mM or 100 mM sodium, 1 mM magnesium (with either chloride or nitrate as the anion), 10 mM glucose, 0.1 mM ouabain, 0.01 mM bumetanide, and TRIS-MOPS (pH 7.0 or 7.40 at 37°C). Chloride-dependent potassium flux was calculated as the difference in potassium efflux between the chloride and the nitrate mediums. Swelling-induced potassium flux was calculated as the difference between the potassium efflux in hypotonic chloride medium and efflux in isotonic medium. To allow cells with different mean corpuscular hemoglobin concentrations to be compared, flux was expressed per liter of original cells.
Results
Five patients with homozygous sickle cell anemia were treated with recombinant human erythropoietin. The administration of high doses did not significantly change the level of F reticulocytes or F cells (Fig. 1Figure 1
Effect of Recombinant Human Erythropoietin on the Percentage of F Reticulocytes (Solid Lines) and F Cells (Dashed Lines) in Five Patients with Sickle Cell Disease.) or hemoglobin F (data not shown). Since it is very unlikely that erythropoietin affected sickling in vivo or in vitro without affecting hemoglobin F, we did not perform a full battery of tests after the completion of the trial with erythropoietin and before the start of hydroxyurea therapy. None of the patients had significant changes in either the hemoglobin level or the percentage of reticulocytes during or after erythropoietin therapy. Three patients had normal serum iron and ferritin levels, and two had iron overload and ferritin levels above 1000 μg per liter (Patient 2) and 580 μ.g per liter (Patient 4). Therefore, it is very unlikely that the lack of response to erythropoietin in any patient was due to a limitation of the availability of iron. All five had elevated serum levels of erythropoietin before treatment, but four had values somewhat lower than those expected for their degree of anemia — a finding consistent with previous reports.45 , 46 Unlike some patients with uremia,32 none of our patients with sickle cell disease had any increase in blood pressure after receiving infusions of erythropoietin. Two (Patients 2 and 5) had severe pain crises coincident with the erythropoietin therapy. Patient 2 requested that erythropoietin treatment be discontinued after the fourth week (1100 U per kilogram).Table 1Table 1
Laboratory Values before and after Treatment with Hydroxyurea.* summarizes the laboratory values obtained before and during hydroxyurea treatment in the three patients who received this drug (Patients 1, 2, and 3). Unless otherwise stated, the data in Table 1 are the means (±1 SD) of three to five values obtained three to four weeks apart before therapy and of three to five values obtained at three-to-four-week intervals after the optimal dose of hydroxyurea had been determined. In contrast to erythropoietin treatment, hydroxyurea therapy resulted in substantial increases in the levels of F reticulocytes, F cells, and hemoglobin F and in the amount of hemoglobin F per F cell in all three patients (Table 1 and Fig. 2Figure 2Effect of Hydroxyurea and Erythropoietin on the Percentage of Hemoglobin F (▲) and F Cells (□) in Three Patients with Sickle Cell Disease.). In Patients 1 and 2, the levels of hemoglobin F and F cells reached a plateau (Fig. 2), whereas in Patient 3 it is possible that the levels did not reach equilibrium. The marked rise in the red-cell mean corpuscular volume, along with the reduction in the absolute neutrophil count, demonstrated that when the measurements shown in Table 1 were obtained, the dose of hydroxyurea had been increased so that it induced an appropriate degree of myelosuppression. The final doses of hydroxyurea (per kilogram per day) were 11 mg in Patient 1, 9 mg in Patient 2, and 23 mg in Patient 3.In all three patients, hydroxyurea treatment was associated with a significant decrease in serum levels of bilirubin and lactic dehydrogenase, indicative of a reduction in hemolysis. Patients 1 and 2 had a significant and sustained increase in the hemoglobin level and a decrease in the reticulocyte count that began about eight weeks after the initiation of hydroxyurea therapy, again suggesting a decrease in the hemolysis rate. After treatment, all three patients had a significant decrease in the percentage of irreversibly sickled cells on peripheral-blood films, as well as in prolongation of the survival of 51Cr-labeled endogenous red cells (Table 1). In Patients 1 and 2, the red-cell survival curves were biphasic. It is very likely that the initial, rapid decay represented the destruction of dense cells, including irreversibly sickled cells, that did not contain hemoglobin F.
Before treatment we observed the expected "shift to the right" in the curves for whole-blood oxyhemoglobin binding, which was due in large part to the polymerization of hemoglobin S. In all three patients, the oxygen affinity increased toward normal after treatment with hydroxyurea (Table 1). These changes were accompanied by significant reductions in the percentage of sickled cells observed after equilibration with gas mixtures containing 1 to 7 percent oxygen (Fig. 3Figure 3
Effect of Hydroxyurea Therapy on the Percentage of Sickled Cells in Red-Cell Suspensions Incubated at Reduced Oxygen Tension.). Hydroxyurea treatment was also associated with a reduction in the number of dense red cells that have a high propensity for polymer formation. This is demonstrated in Table 1 by the decrease in the red-cell density-distribution width and the increase in red-cell cation content. This increment in cell hydration correlated with a reduction in potassium-chloride cotransport toward the normal range (Fig. 4Figure 4
Effect of Hydroxyurea Therapy on Red-Cell Potassium−Chloride Cotransport.), a phenomenon that may contribute to progressive loss of potassium and water from sickled red cells.43 , 44 In the three patients maintained on optimal doses of hydroxyurea for two to four months, repeat treatment with infusions of erythropoietin in the same doses as those used initially again had no detectable effect on the levels of F cells, hemoglobin F (Fig. 2), or F reticulocytes. This negative result contrasts with recent results in baboons,47 in which the addition of treatment with recombinant human erythropoietin to continuous treatment with hydroxyurea caused further stimulation of F-cell production. In all five patients we studied, erythropoietin was ineffective whether administered alone or in combination with hydroxyurea.
Discussion
All three patients with sickle cell anemia treated with hydroxyurea over a period of 11 to 13 months had a virtual cessation of vaso-occlusive episodes and pain crises (Fig. 2). We stress that ours was an open trial in a small number of patients. The subsidence of episodes of pain could be coincidental or related in part to increased medical attention during the study. Because of the subjective and episodic nature of pain crises, more patients need to be evaluated in a controlled fashion over a longer period before firm conclusions can be drawn about how hydroxyurea treatment affects the clinical course of sickle cell anemia.
More convincing is the improvement in various objective indexes of red-cell survival and intracellular polymerization of hemoglobin S. Replicate laboratory tests were performed before therapy was begun and again after the patients had been treated with hydroxyurea long enough for steady-state values to be reached. Thus, each patient served as his or her own control. As in studies in larger numbers of patients,26 27 28 , 41 hydroxyurea treatment resulted in substantial increments in the percentage of hemoglobin F and F cells in all three of our patients given this drug, as well as significant increases in the amount of hemoglobin F per F cell (Table 1 and Fig. 2). Unlike some patients,48 these three patients had preferential survival of F cells before hydroxyurea treatment, documented by a substantially higher percentage of F cells than of F reticulocytes. Therefore, it is not surprising that the increase in F cells as well as in the amount of hemoglobin F per F cell induced by hydroxyurea treatment was accompanied by evidence of prolongation of red-cell survival. The two patients who had early and sustained increments of F cells (Patients 1 and 2) also had the most improvement in red-cell survival. After hydroxyurea treatment, all three patients had significant decreases in serum bilirubin and lactic dehydrogenase levels. A twofold decrease in the reticulocyte count, noted in all three patients, was accompanied by an increase in the hemoglobin level of 16 to 21 percent, again indicating a significant decrease in the rate of hemolysis. The two patients studied by Ballas et al.35 also had significant prolongation of red-cell survival after hydroxyurea therapy.
In all three patients, hydroxyurea treatment appeared to decrease polymerization of hemoglobin S. The oxygen-binding curve provides a simple and reliable, although indirect, measurement of the amount of intracellular polymer at partial oxygen saturation.49 50 51 Since the deoxyhemoglobin S polymer has a very low affinity for oxygen, the oxygen affinity of sickled red cells is lowered in proportion to the amount of polymer. As shown in Table 1, treatment was associated with a substantial increase in oxygen affinity (decreased oxygen pressure at 50 percent hemoglobin saturation), indicating inhibition of polymerization. This conclusion is supported by direct morphologic analysis of fixed cells after equilibration at partial oxygen saturation. The increased oxygen affinity of the new F cells, which sickle either slowly or not at all, may impose a "steal" of oxygen from the few remaining cells with low oxygen affinity that are not F cells. These cells would be expected to undergo more cycles of sickling and unsickling, and rapid induction of the membrane damage characteristic of irreversibly sickled cells. Therefore, the reduction in the percentage of irreversibly sickled cells noted in all three patients may be due not only to dilution but also to more rapid damage and accelerated destruction of the non-F cells.
The red cells of patients with sickle cell disease generally have a broad density distribution.52 , 53 As in other types of severe hemolytic anemia, a predominance of young red cells (reticulocytes) increases the proportion of low-density cells. The dehydrated, irreversibly sickled cells increase the proportion of high-density cells. In agreement with the study of two patients by Ballas et al.,35 hydroxyurea therapy resulted in a decrease in the red-cell density-distribution width in all three of our patients (Table 1), due to a reduction in the number ofreticulocytes as well as very dense cells, including irreversibly sickled cells. The increase in red-cell cations — an index of cell hydration — noted in all three patients (as well as in the two studied by Ballas et al.35) provides further evidence of a reduction in the dense-cell population. This treatment-induced increase in cell hydration was accompanied by a marked reduction toward normal in potassium−chloride cotransport, a pathway that may be a major factor contributing to potassium and water loss in sickled red cells.44
These results raise questions about the mechanism of action of hydroxyurea. In Patients 1 and 2, the substantial and prolonged increase in F cells and hemoglobin F was probably a major contributor. However, in Patient 3, a significant reduction occurred in both the hemolysis rate and intracellular polymerization before a substantial increase in the hemoglobin F level began. It is possible that the increased mean corpuscular volume, which has been observed in nearly all patients treated with hydroxyurea, has a favorable influence on the rheologic behavior of the cell. Alternatively, hydroxyurea therapy may result in decreased interactions between sickled red cells and small-vessel endothelium54 or macrophages,55 thereby reducing the number of vaso-occlusive episodes and hemolysis.
In contrast to hydroxyurea, recombinant human erythropoietin, whether given alone or in combination with hydroxyurea, was ineffective in increasing the hemoglobin F level, even in doses 20-fold higher than those generally given to patients with the anemia of uremia.30 31 32 It is possible that the use of even higher doses of erythropoietin or more frequent administration may stimulate F-cell production, but the cost of long-term treatment at current market prices might be prohibitive. More important, there is no rational basis for the use of erythropoietin to benefit patients with sickle cell disease other than to increase the level of hemoglobin F. Indeed, an acute increase in red-cell mass could be deleterious. One of our patients (Patient 2) could not complete the full dose schedule because of severe crises coincident with the initiation of erythropoietin therapy.
All three patients given hydroxyurea had significant objective and subjective improvement. These data support the need for large-scale studies of the efficacy and safety of hydroxyurea in the treatment of sickle cell disease.
Supported in part by grants from the National Institutes of Health (HL-15157–18, to the Boston Sickle Cell Center [Drs. Brugnara and Bunn]; 5–M01–RR-02635–05, a Clinical Research Center grant, to Brigham and Women's Hospital; R01-HL-42949–01 [Dr. Bunn]; R01-HL-28028 [Dr. Dover]; R01-HL-40002 [Dr. Charache]; RR-0035 and RR-00722, Clinical Research Center grants, to Johns Hopkins Hospital; and DK-01401 (Dr. Goldberg]) and by the Cowan Foundation.
We are indebted to Ortho Pharmaceutical Corporation for their generous gift of recombinant human erythropoietin used in this clinical trial; to Susan Fisher, R.N., Ms. Susan Weiner, and Mr. Robert Palombo for their assistance; to Dr. David Drum for measuring red-cell survival; to Drs. Kenneth Bridges and Robert Handin for their helpful advice; and most especially to the patients who participated in this study for their cooperation and goodwill.
Source Information
From the Hematology Division, Department of Medicine (M.A.G., L.S., H.F.B.), and the Department of Pathology (C.B.), Brigham and Women's Hospital and Harvard Medical School, Boston; and the Departments of Pediatrics (G.J.D.) and Medicine (S.C), Johns Hopkins University School of Medicine, Baltimore. Address reprint requests to Dr. Bunn at the Hematology Division, Thorn 919, Brigham and Women's Hospital, 75 Francis St., Boston, MA 02115.
- References
References
1
Eaton
Web of Science | Medline2
Nagel RL, Fabrey ME. The Hb S containing cell. In: Nagel RL, ed. Genetically abnormal red cells. Vol. 1. Boca Raton, Fla.: CRC Press. 1988:71.
3
Bunn HF, Forget BG. Hemoglobin: molecular, genetic and clinical aspects. Philadelphia: W.B. Saunders, 1986.
4
Embury
CrossRef | Web of Science | Medline5
Padlan
Web of Science | Medline6
Edelstein
CrossRef | Web of Science | Medline7
Cerami
CrossRef | Web of Science | Medline8
Walder
CrossRef | Web of Science | Medline9
Abraham
CrossRef | Web of Science | Medline10
Hofrichter
CrossRef | Web of Science | Medline11
Rosa
Full Text | Web of Science | Medline12
Charache
Web of Science | Medline13
Bookchin
CrossRef | Web of Science | Medline14
Goldberg
Web of Science | Medline15
Benesch
CrossRef | Web of Science | Medline16
Sewchand
Medline17
DeSimone
CrossRef | Web of Science | Medline18
Ley
Web of Science | Medline19
Charache
CrossRef | Web of Science | Medline20
Dover
Web of Science | Medline21
Papayannopoulou
CrossRef | Web of Science | Medline22
Veith
Full Text | Web of Science | Medline23
Letvin
Full Text | Web of Science | Medline24
Platt
CrossRef | Web of Science | Medline25
Sumoza 26
Dover
Web of Science | Medline27
Charache
Web of Science | Medline28
Rodgers
Full Text | Web of Science | Medline29
Alter
Web of Science | Medline30
Eschbach
Full Text | Web of Science | Medline31
Winearls
CrossRef | Web of Science | Medline32
Eschbach
Full Text | Web of Science | Medline33
Al-Khatti
Full Text | Web of Science | Medline34
Al-Khatti
Medline35
Bailas
CrossRef | Web of Science | Medline36
Dover
Web of Science | Medline37
Dover
Web of Science | Medline38
Wilson
Medline39
Egrie
CrossRef | Web of Science | Medline40
Goldberg
CrossRef | Web of Science | Medline41
Dover GJ, Charache S. Stimulation of fetal hemoglobin production by hydroxyurea in sickle cell anemia. In: Stamatoyannopoulos G, Nienhuis A, eds. Hemoglobin switching: proceedings of the sixth conference on hemoglobin switching, held in Airlie, Virginia, September 24−27, 1988. Part B: cellular and molecular mechanisms. New York: Alan R. Liss, 1989:295–306.
42
Rodgers
Medline43
Brugnara
CrossRef | Web of Science | Medline44
Brugnara
CrossRef | Web of Science | Medline45
Sherwood
Web of Science | Medline46
Dover 47
Al-Khatti
Web of Science | Medline48
Dover
Full Text | Web of Science | Medline49
Winslow RM. Hemoglobin interactions and whole blood oxygen equilibrium curves in sickling disorders. In: Caughey WS, ed. Clinical and biochemical aspects of hemoglobin abnormalities. New York: Academic Press, 1978:369–77.
50
Gill
CrossRef | Web of Science | Medline51
Benesch
CrossRef | Web of Science | Medline52
Clark
Web of Science | Medline53
Fabry
Medline54
Hebbel
Full Text | Web of Science | Medline55
Hebbel
Web of Science | Medline
- Citing Articles (53)
Citing Articles
1
Joshua J. Field, David G. Nathan, Joel Linden. (2011) Targeting iNKT cells for the treatment of sickle cell disease. Clinical Immunology 140:2, 177-183
CrossRef2
Wally R. Smith, Samir K. Ballas, William F. McCarthy, Robert L. Bauserman, Paul S. Swerdlow, Martin H. Steinberg, Myron A. Waclawiw, . (2011) The Association Between Hydroxyurea Treatment and Pain Intensity, Analgesic Use, and Utilization in Ambulatory Sickle Cell Anemia Patients. Pain Medicine 12:5, 697-705
CrossRef3
Santosh Saraf, Mohammed Farooqui, Giovanni Infusino, Bharvi Oza, Seema Sidhwani, Michel Gowhari, Stephen Vara, Weihua Gao, Lani Krauz, Donald Lavelle, Joseph DeSimone, Robert Molokie, Yogen Saunthararajah. (2011) Standard clinical practice underestimates the role and significance of erythropoietin deficiency in sickle cell disease. British Journal of Haematology 153:3, 386-392
CrossRef4
Michelle Y. Owens, James N. Martin. 2010. Sickle Cell Crisis. , 391-399.
CrossRef5
Hind Sassi, Dora Bachir, Anoosha Habibi, Alain Astier, Frédéric Galactéros, Anne Hulin. (2010) No effect of CYP450 and P-glycoprotein on hydroxyurea in vitro metabolism. Fundamental & Clinical Pharmacology 24:1, 83-90
CrossRef6
V. R. Gordeuk, A. Campbell, S. Rana, M. Nouraie, X. Niu, C. P. Minniti, C. Sable, D. Darbari, N. Dham, O. Onyekwere, T. Ammosova, S. Nekhai, G. J. Kato, M. T. Gladwin, O. L. Castro. (2009) Relationship of erythropoietin, fetal hemoglobin, and hydroxyurea treatment to tricuspid regurgitation velocity in children with sickle cell disease. Blood 114:21, 4639-4644
CrossRef7
Jane Hankins, Banu Aygun. (2009) Pharmacotherapy in sickle cell disease - state of the art and future prospects. British Journal of Haematology 145:3, 296-308
CrossRef8
Nathalie Dauphin-McKenzie, Jerry M. Gilles, Elvire Jacques, Thomas Harrington. (2006) Sickle Cell Anemia in the Female Patient. Obstetrical & Gynecological Survey 61:5, 343-352
CrossRef9
F. Pasquier, C. Croxo, H. Melliez, H. Porte, E. Bourgeois-Petit, N. Cambier, C. Rose. (2006) L'aspergillome pulmonaire : une complication possible de la drépanocytose. La Revue de Médecine Interne 27:3, 260-263
CrossRef10
Michael Heuser, Arnold Ganser. (2006) Recombinant human erythropoietin in the treatment of nonrenal anemia. Annals of Hematology 85:2, 69-78
CrossRef11
Janie A. Ho, Chrisley V. Pickens, Michael P. Gamscik, O.Michael Colvin, Russell E. Ware. (2003) In vitro induction of fetal hemoglobin in human erythroid progenitor cells. Experimental Hematology 31:7, 586-591
CrossRef12
Vladan P. Cokic, Reginald D. Smith, Bojana B. Beleslin-Cokic, Joyce M. Njoroge, Jeffery L. Miller, Mark T. Gladwin, Alan N. Schechter. (2003) Hydroxyurea induces fetal hemoglobin by the nitric oxide–dependent activation of soluble guanylyl cyclase. Journal of Clinical Investigation 111:2, 231-239
CrossRef13
Mara Prengler, Steven G. Pavlakis, Isak Prohovnik, Robert J. Adams. (2002) Sickle cell disease: The neurological complications. Annals of Neurology 51:5, 543-552
CrossRef14
Luciana de Feltran, Jo??o Thom??s Carvalhaes, Ricardo Sesso. (2002) Renal Complications of Sickle Cell Disease. Pediatric Drugs 4:1, 29-36
CrossRef15
Ione C. Barbosa, Oladapo A. Ladipo, Maria de Lourdes, P. Nascimento, Célia Athayde, Cristina Hirsch, Renata Lopes, Bruno Matias, Elsimar Coutinho. (2001) Carbohydrate metabolism in sickle cell patients using a subdermal implant containing nomegestrol acetate (Uniplant). Contraception 63:5, 263-265
CrossRef16
Donald Lavelle, Robert Molokie, Janice Ducksworth, Joseph DeSimone. (2001) Effects of hydroxurea, stem cell factor, and erythropoietin in combination on fetal hemoglobin in the baboon. Experimental Hematology 29:2, 156-162
CrossRef17
Roger S. Riley, Jonathan M. Ben-Ezra, Rajat Goel, Ann Tidwell. (2001) Reticulocytes and reticulocyte enumeration. Journal of Clinical Laboratory Analysis 15:5, 267-294
CrossRef18
S.Tsuyoshi Ohnishi, Tomoko Ohnishi, Gabriel B Ogunmola. (2000) Sickle cell anemia: a potential nutritional approach for a molecular disease. Nutrition 16:5, 330-338
CrossRef19
Arlene M Buller, Howard L Elford, Charles C DuBois, Joanne Meyer, Joyce A Lloyd. (1999) A Combination of Hydroxyurea and Isobutyramide to Induce Fetal Hemoglobin in Transgenic Mice Is More Hematotoxic Than the Individual Agents. Blood Cells, Molecules, and Diseases 25:4, 255-269
CrossRef20
Samir Ballas, Mary Marcolina, George Dover, Franca Barton, . (1999) Erythropoietic activity in patients with sickle cell anaemia before and after treatment with hydroxyurea. British Journal of Haematology 105:2, 491-496
CrossRef21
Wood, Alastair J.J., , Steinberg, Martin H., . (1999) Management of Sickle Cell Disease. New England Journal of Medicine 340:13, 1021-1030
Full Text22
C. Breymann, E. Fibach, E. Visca, C. Huettner, A. Huch, R. Huch. (1999) Induction of fetal hemoglobin synthesis with recombinant human erythropoietin in anemic patients with heterozygous beta-thalassemia during pregnancy. The Journal of Maternal-Fetal Medicine 8:1, 1-7
CrossRef23
Maria de Lourdes Pires Nascimento, Oladipo A. Ladipo, Elsimar M. Coutinho. (1998) Nomegestrol acetate contraceptive implant use by women with sickle cell disease*. Clinical Pharmacology & Therapeutics 64:4, 433-438
CrossRef24
Filippo Salvati, Mario Liani. (1998) Erythropoietin and thrombotic events. The Lancet 352:9138, 1471
CrossRef25
ELIEZER A. RACHMILEWITZ, MEMET AKER. (1998) The Role of Recombinant Human Erythropoietin in the Treatment of Thalassemia. Annals of the New York Academy of Sciences 850:1 COOLEY'S ANEM, 129-138
CrossRef26
Samir K. Ballas. (1998) 7 Sickle cell disease: clinical management. Baillière's Clinical Haematology 11:1, 185-214
CrossRef27
Griffin P. Rodgers. (1998) 9 Pharmacological therapy. Baillière's Clinical Haematology 11:1, 239-255
CrossRef28
Yih-Ming Yang, Betty Pace, David Kitchens, Samir K. Ballas, Arvind Shah, B. Surendra Baliga. (1997) BFU-E colony growth in response to hydroxyurea: Correlation between in vitro and in vivo fetal hemoglobin induction. American Journal of Hematology 56:4, 252-258
CrossRef29
Epstein, Franklin H., , Bunn, H. Franklin, . (1997) Pathogenesis and Treatment of Sickle Cell Disease. New England Journal of Medicine 337:11, 762-769
Full Text30
Stacy J. Marcus, Thomas R. Kinney, William H. Schultz, Erin E. O'Branski, Russell E. Ware. (1997) Quantitative analysis of erythrocytes containing fetal hemoglobin (F cells) in children with sickle cell disease. American Journal of Hematology 54:1, 40-46
CrossRef31
Michael Edmond, Mary Pat Clements, Richard Wenzel. (1997) A 27-Year-Old Man With Hematuria. The American Journal of the Medical Sciences 313:1, 58-63
CrossRef32
Samuel Charache. (1996) EXPERIMENTAL THERAPY. Hematology/Oncology Clinics of North America 10:6, 1373-1382
CrossRef33
Kristen S. Montgomery. (1996) Caring for the Pregnant Woman with Sickle Cell Disease. The American Journal of Maternal/Child Nursing 21:5, 224-228
CrossRef34
Anita Catlin. (1996) The dilemma of Jehovah's Witness children who need blood to survive. Hec Forum 8:4, 195-207
CrossRef35
Cleveland M Moore, Mohammad Ehlayel, Lily E Leiva, Ricardo U Sorensen. (1996) New Concepts in the Immunology of Sickle Cell Disease. Annals of Allergy, Asthma & Immunology 76:5, 385-403
CrossRef36
Russell E. Ware, Martin H. Steinberg, Thomas R. Kinney. (1995) Hydroxyurea: An alternative to transfusion therapy for stroke in sickle cell anemia. American Journal of Hematology 50:2, 140-143
CrossRef37
Griffin P. Rodgers, Eliezer A. Rachmilewitz. (1995) NOVEL TREATMENT OPTIONS IN THE SEVERE β-GLOBIN DISORDERS. British Journal of Haematology 91:2, 263-268
CrossRef38
Kazumi Horiuchi, Melissa L. Osterhout, Hiroshi Kamma, Nicoletta A. Bekoe, Kevin J. Hirokawa. (1995) Estimation of fetal hemoglobin levels in individual red cells via fluorescence image cytometry. Cytometry 20:3, 261-267
CrossRef39
YI-TAO ZENG, SHU-ZHEN HUANG, ZHAO-RUI REN, ZHI-HONG LU, FAN-YI ZENG, ALAN N. SCHECHTER, GRIFFIN P. RODGERS. (1995) Hydroxyurea therapy in β-thalassaemia intermedia: improvement in haematological parameters due to enhanced β-globin synthesis. British Journal of Haematology 90:3, 557-563
CrossRef40
CARLO BRUGNARA, LUCIA FRANCESCHI, CARRIE C. ARMSBY, NACERA SAADANE, MARIE TRUDEL, YVES BEUZARD, ANN RITTENHOUSE, NADER RIFAI, ORAH PLATT, SETH L. ALPER. (1995) A New Therapeutic Approach for Sickle Cell Disease.. Annals of the New York Academy of Sciences 763:1 The Imidazoli, 262-271
CrossRef41
Charache, Samuel, Terrin, Michael L., Moore, Richard D., Dover, George J., Barton, Franca B., Eckert, Susan V.McMahon, Robert P., Bonds, Duane R., the Investigators of the Multicenter Study of Hydroxyurea in Sickle Cell Anemia. (1995) Effect of Hydroxyurea on the Frequency of Painful Crises in Sickle Cell Anemia. New England Journal of Medicine 332:20, 1317-1322
Full Text42
Orah S. Platt. (1995) Sickle cell paths converge on hydroxyurea. Nature Medicine 1:4, 307-308
CrossRef43
L. Luzzatto. (1995) About hemoglobins, G6PD and parasites in red cells. Experientia 51:3, 206-208
CrossRef44
Eitan Fibach, Alan N. Schechter, Constance T. Noguchi, Griffen P. Rodgers. (1994) Reducing erythropoietin in cultures of human erythroid precursors elevates the proportion of fetal haemoglobin. British Journal of Haematology 88:1, 39-45
CrossRef45
Martin S. Blumenreich, Michael J. Kellihan, U. Geetha Joseph, Kim A. Lalley, Eliza J. Sherrill, Daniel M. Sullivan, John T. Hamm, Patrick S. Gentile, Subash P. Sheth, Janell Seeger, Thomas M. Woodcock. (1993) Long-term intravenous hydroxyurea infusions in patients with advanced cancer. A phase I trial. Cancer 71:9, 2828-2832
CrossRef46
Carlo Brugnara, Margot S. Kruskall, Rose M. Johnstone. (1993) Membrane properties of erythrocytes in subjects undergoing multiple blood donations with or without recombinant erythropoietin. British Journal of Haematology 84:1, 118-130
CrossRef47
Rodgers, Griffin P.Dover, George J.Uyesaka, NobuhiroNoguchi, Constance T.Schechter, Alan N.Nienhuis, Arthur W.. (1993) Augmentation by Erythropoietin of the Fetal-Hemoglobin Response to Hydroxyurea in Sickle Cell Disease. New England Journal of Medicine 328:2, 73-80
Full Text48
A. D. Adekile, T. H. J. Huisman. (1993) Hb F in sickle cell anemia. Experientia 49:1, 16-27
CrossRef49
C. D. L. Reid. (1992) IN VITRO STUDIES OF NORMAL AND PATHOLOGICAL ERYTHROPOIESIS. British Journal of Haematology 82:3, 483-487
CrossRef50
Mario Cazzola, Yves Beguin. (1992) NEW TOOLS FOR CLINICAL EVALUATION OF ERYTHRON FUNCTION IN MAN. British Journal of Haematology 80:3, 278-284
CrossRef51
(1991) Erythropoietin in Anemia of Renal Failure in Sickle Cell Disease. New England Journal of Medicine 325:16, 1175-1176
Full Text52
John C. Morrison, Francis S. Morrison, Randall C. Floyd, William E. Roberts, L. Wayne Hess, Winfred L. Wiser. (1991) Use of continuous flow erythrocytapheresis in pregnant patients with sickle cell disease. Journal of Clinical Apheresis 6:4, 224-229
CrossRef53
Armando R. Orlina, Steven D. Sosler, Mabel Koshy. (1991) Problems of chronic transfusion in sickle cell disease. Journal of Clinical Apheresis 6:4, 234-240
CrossRef
