Rat liver-mediated metabolism of hydroxyurea to nitric oxide

Effectiveness of Pharmacokinetic-Guided Hydroxyurea Dose Individualization in Patients with Sickle Cell Anemia: A Mini-Review

Inconsistent therapeutic responses have been observed among patients with sickle cell anemia (SCA) undergoing hydroxyurea (HU) following the adoption of the standardized protocol. Moreover, this treatment regimen necessitates a prolonged period to reach the maximum tolerated dose in which beneficial therapeutic effects are observed in most SCA patients. To overcome this limitation, several studies have performed HU dose adjustments in SCA patients based on individualized pharmacokinetic profiles. The present systematic mini-review aims to select and analyze published data to present an overview of HU pharmacokinetics studies performed in SCA patients, as well as evaluate the effectiveness of the dose adjustment strategy. A systematic search was performed in the Embase, Pubmed, Scopus, Web of Science, Scielo, Google Scholar, and the Virtual Library of Health databases from December 2020 to August 2022, with a total of five studies included. Inclusion criteria consisted of studies in which the dose adjustment was performed in SCA patients based on pharmacokinetic parameters. Quality analyzes were performed using QAT, while data synthesis was performed according to the Cochrane Manual of Systematic Reviews of Interventions. Analysis of the selected studies revealed improved HU treatment effectiveness using personalized dosages in SCA patients. Moreover, several laboratory parameters were utilized as biomarkers of the HU response, and methods designed to simplify the adoption of this practice were presented. Despite the scarcity of studies on this topic, HU-personalized treatment based on individualized pharmacokinetic profiles represents a viable alternative for SCA patients who are candidates for HU therapy, especially for pediatric patients. Registration number: PROSPERO CRD42022344512.

Stability evaluation of compounded hydroxyurea 100 mg/mL oral liquids using a novel analytical method involving chemical derivatization

This study assessed the stability of six extemporaneously compounded hydroxyurea oral liquids stored at room temperature. Hydroxyurea oral liquids (100 mg/mL) were prepared using three different mixing methods (mortar, mixer or QuartetRx) from either bulk powder, capsule content, or whole capsules. Two brands of capsules were tested in this study. All formulations were stored at room temperature (25°C / 60% RH) in amber plastic bottles for 90 days and amber plastic syringes for 14 days. Physical stability was assessed visually, while chemical stability was evaluated using a stability-indicating high-performance liquid chromatography method. Chemical derivatization with xanthydrol allowed the retention of hydroxyurea on a reverse-phase column. At least 93.9% and 97.0% of the initial concentration of hydroxyurea remained after 90 days in bottles and 14 days in syringes, respectively. There were no visual changes in formulations over the study period. Changes in pH up to 1.6 units were observed after 90 days of storage and were explained most likely by an ammonium generating degradation pathway. Ammonium was quantified and remained within safe levels in each HU 100 mg/mL oral preparations. Hydroxyurea oral liquids were all stable for 90 days in amber plastic bottles and 14 days in amber plastic syringes.

Protective potential of royal jelly against hydroxyurea -induced hepatic injury in rats via antioxidant, anti-inflammatory, and anti-apoptosis properties

Hydroxyurea (HDU) is a widely used medication for various malignancies, thalassemia, and sickle cell anemia with reported side effects. The current study investigated HDU- induced hepatic injury and the protective potential of the royal jelly (RJ) against this hepatotoxic effect in the light of hepatic oxidative/ antioxidative status, pro-inflammatory cytokine, apoptosis signaling pathway, and histopathology. Sixty albino rats were used (n = 10/group) for 60 days: control, RJ (100 mg/kg body weight, orally), HDU (225 mg/kg body weight, orally), 2HDU (450 mg/kg body weight, orally), and HDU + RJ groups. HDU-treated rats showed significant elevation of liver function tests as aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase, as well as malondialdehyde and nitric oxide (oxidative biomarkers) and significant decreased hepatic antioxidant molecules (reduced glutathione, superoxide dismutase, and glutathione peroxidase), compared to a control group, that more pronounced in the high dose of HDU. In addition, HDU induced significant upregulation of TNF-α and the Caspase-3 apoptotic pathway. Moreover, the liver of HDU treated groups showed various hepatic lesions from mild to severe necrotic changes related to the HDU dose. However, administration of RJ with HDU improved liver function tests, liver histology, and hepatic oxidative/antioxidative status concerning HDU groups. Furthermore, oral RJ administration with HDU significantly lessens the immune-expression area % of TNF-α and Caspase-3. Thus, the royal jelly has antioxidant, anti-inflammatory, and anti-apoptotic properties against HDU- induced hepatic injury and could be, therefore, used as adjuvant therapy in patients with long-term HDU medication.

Tolerability and age-dependent toxicokinetics following perinatal hydroxyurea treatment in Sprague Dawley rats

Hydroxyurea (HU) is a valuable therapy for individuals with sickle cell anemia. With increased use of HU in children and throughout their lives, it is important to understand the potential effects of HU therapy on their development and fertility. Thus, studies were conducted to identify appropriate doses to examine long‐term effects of prenatal and early postnatal HU exposure and to understand kinetics of HU at various life stages. Pregnant Sprague Dawley dams were administered HU (0–150 mg/kg/day) via oral gavage from gestation days 17 to 21 and during lactation. Pups were dosed with the same dose as their respective dam starting on postnatal day (PND) 10 and up to PND 34. There was minimal maternal toxicity, and no significant effects on littering at any dose of HU. Starting on ~PND 16, offspring displayed skin discoloration and alopecia at doses ≥75 mg/kg/day and lower body weight compared to controls at doses ≥100 mg/kg/day. Gestational transfer of HU was observed, but there was minimal evidence of lactational transfer. Our toxicokinetic studies suggest that the internal dose in offspring may be altered due to age, but not due to sex. The plasma area under the curve, a measure of systemic exposure, at doses tolerated by offspring was threefold to sevenfold lower than the internal therapeutic dose in humans. Therefore, strategies to establish clinically relevant exposures in animal studies are needed. Overall, these data are useful for the design of appropriate nonclinical studies in the future to evaluate the consequences of long‐term HU treatment starting in childhood.

Increased use of hydroxyurea (HU) to treat sickle cell disease in children and throughout their lives augments the importance of understanding potential effects of HU on development and fertility. To inform the design of studies to evaluate long‐term safety of HU use in children, tolerability of prenatal and early postnatal HU treatment was evaluated in Sprague Dawley rats. Additionally, studies investigating gestational and lactational transfer of HU and how toxicokinetics of HU vary with age were conducted.

Sickle Cell Anemia: Variants in the CYP2D6, CAT, and SLC14A1 Genes Are Associated With Improved Hydroxyurea Response

Differences in hydroxyurea response in sickle cell anemia may arise due to a series of factors with genetic factors appearing to be predominant. This study aims to investigate the effects of single nucleotide polymorphisms in genes encoding drug-metabolizing enzymes and solute carriers on hydroxyurea response, in patients with sickle cell anemia. For that purpose, a total number of 90 patients with sickle cell anemia were recruited, 45 were undergoing hydroxyurea treatment, while 45 were not under the treatment. Association analyses were performed between CYP3A4 (rs2740574), CYP2D6 (rs3892097), CAT (rs7943316 and rs1001179), and SLC14A1 (rs2298720) variants and laboratory parameters. According to our findings, patients with hydroxyurea treatment demonstrated higher HbF levels and a significant improvement in hemolytic, hepatic, inflammatory, and lipid parameters in comparison to those without the treatment. We also found significant associations between the CYP2D6 (rs3892097), CAT (rs7943316 and rs1001179), and SLC14A1 (rs2298720) variants and an improvement of the therapeutic effects, specifically the hemolytic, hepatic, inflammatory, lipid, and renal parameters. In conclusion, our results highlight the importance of the investigated variants, and their strong association with hydroxyurea efficacy in patients with sickle cell anemia, which may be considered in the future as genetic markers.

Drug Therapies for the Management of Sickle Cell Disease

Sickle cell disease (SCD) afflicts millions of people worldwide but is referred to as an orphan disease in the United States. Over the past several decades, there has been an increasing understanding of the pathophysiology of SCD and its complications. While most individuals with SCD in resource-rich countries survive into adulthood, the life expectancy of patients with SCD remains substantially shorter than for the general African-American population. SCD can be cured using hematopoietic stem cell transplantation and possibly gene therapy, but these treatment approaches are not available to most patients, the majority of whom reside in low- and middle-income countries. Until relatively recently, only one drug, hydroxyurea, was approved by the US Food and Drug Administration to ameliorate disease severity. Multiple other drugs (L-glutamine, crizanlizumab, and voxelotor) have recently been approved for the treatment of SCD, with several others at various stages of clinical testing. The availability of multiple agents to treat SCD raises questions related to the choice of appropriate drug therapy, combination of multiple agents, and affordability of recently approved products. The enthusiasm for new drug development provides opportunities to involve patients in low- and middle-income nations in the testing of potentially disease-modifying therapies and has the potential to contribute to capacity building in these environments. Demonstration that these agents, alone or in combination, can prevent or decrease end-organ damage would provide additional evidence for the role of drug therapies in improving outcomes in SCD.

An experimental erythrocyte rigidity index (Ri) and its correlations with Transcranial Doppler velocities (TAMMV), Gosling Pulsatility Index PI, hematocrit, hemoglobin concentration and red cell distribution width (RDW)

Brain artery velocities (Time-Averaged Maximum Mean Velocity, TAMMV) by Transcranial Doppler (TCD), hematocrit, hemoglobin, Red blood cell (RBC) Distribution Width (RDW) and RBC rigidity index (Ri), when reported together with their correlations, provide a accurate and useful diagnostic picture than blood viscosity measurements alone. Additionally, our study included a sixth parameter provided by TCD, the Gosling Pulsatility Index PI, which is an indicator of CBF (Cerebral Blood Flow) resistance. All these parameters are routine in Hematology except for values of Ri. The rigidity (Ri) of the RBC is the main rheological characteristic of the blood of Sickle Cell Anemia (SCA) patients and several pathologies. However, its quantification depends on many commercial and experimental techniques, none disseminated and predominant around the World. The difference in absorbance values of the blood, during the process of sedimentation in a microwell of a Microplate Reader, is a straightforward way of semi-quantifying the RBC rigidity Ri, since the fraction of irreversibly sickled red blood cells does not form rouleaux. Erythrocyte Rigidity Index (Ri) was calculated using initial absorbance A_initial (6 s) and final A_final (540 s), Ri = 1 / (Ai-Af). The Ri of 119 patients (2–17 y / o, M & F) SCA, SCC (Sickle Cell/hemoglobin C), SCD (Sickle Cell/hemoglobin D), Sβ0thal (Sickle Cell/hemoglobin Beta Zero Thalassemia) and 71 blood donors (20–65 y / o, M & F) were measured in our laboratory while the five parameters (TAMMV and PI by TCD, Hct, Hb and RDW) were obtained from medical records. The in vitro addition of hydroxyurea (HU, 50mg /dl, n = 51 patients, and n = 8 healthy donors) in the samples decreased the rouleaux adhesion strength of both donor and patients’ blood samples, leading to extraordinarily high Ri values. The correlation between the studied parameters was especially significant for the direct relationships between Ri, TAMMV, and PI.

Attenuation potentials of royal jelly against hydroxyurea-induced infertility through inhibiting oxidation and release of pro-inflammatory cytokines in male rats

Hydroxyurea (HDU), a class of antineoplastic drugs, has a powerful efficacy in the treatment of several types of malignancies. However, it has multiple adverse effects including reduced fertility, especially in males. Thus, 60 male albino rats were used to investigate the chemoprotective potentials of royal jelly on HDU-induced testicular damage. Animals were gastro-gavaged with HDU (225 or 450 mg kg^-1 bw day^-1) before royal jelly (100 mg kg^-1 bw day^-1) for 60 days. Blood samples and testicles were collected, and spermatozoon was obtained. In a dose-dependent manner, the sperm count, motility and liveability, and testosterone, GSH, and catalase concentrations were decreased in HDU groups, whereas MDA, FSH, LH, IL-6, and IFN-γ expression levels were increased. Germinal epithelium degeneration, germ cell sloughing, reduction in the number of luminal spermatozoa, interstitial congestion, and severe leukocyte infiltration besides no glandular secretion in most of the acini were identified. However, royal jelly intake in HDU-treated rats successfully improved sperm quality, hormonal and antioxidant status, and reproductive organ histoarchitecture. Thus, it could be concluded that royal jelly is endowed with antioxidative and anti-inflammatory activities and could be, therefore, used as an adjuvant remedy to improve HDU-induced male subfertility.

Decreased nitrite reductase activity of deoxyhemoglobin correlates with platelet activation in hemoglobin E/ß-thalassemia subjects

Nitric oxide (NO) can be generated from nitrite by reductase activity of deoxygenated hemoglobin (deoxyHb) apparently to facilitate tissue perfusion under hypoxic condition. Although hemoglobin E (HbE) solutions have been shown to exhibit decreased rate of nitrite reduction to NO, this observation has never been reported in erythrocytes from subjects with hemoglobin E/ß-thalassemia (HbE/ß-thal). In this study, we investigated the nitrite reductase activity of deoxyHb dialysates from 58 non-splenectomized and 23 splenectomized HbE/ß-thal subjects compared to 47 age- and sex-matched normal subjects, and examined its correlation with platelet activity. Iron-nitrosyl-hemoglobin (HbNO) was measured by tri-iodide reductive chemiluminescence as a marker of NO generation. HbNO produced from the reaction of nitrite with deoxyHb dialysate from both non-splenectomized and splenectomized HbE/ß-thal subjects was lower than that of normal (AA) hemoglobin subjects. P-selectin expression, a marker of platelet activation, at baseline and in reactivity to stimulation by adenosine diphosphate (ADP), were higher in HbE/ß-thal subjects than normal subjects. HbNO formation from the reactions of nitrite and deoxyHb inversely correlated with baseline platelet P-selectin expression, HbE levels, and tricuspid regurgitant velocity (TRV). Nitrite plus deoxygenated erythrocytes from HbE/ß-thal subjects had a lower ability to inhibit ADP-induced P-selectin expression on platelets than erythrocytes from normal subjects. We conclude that deoxyHb in erythrocytes from HbE/ß-thal subjects has a decreased ability to reduce nitrite to NO, which is correlated with increased platelet activity in these individuals.

Advances in new drug therapies for the management of sickle cell disease

Introduction

Sickle cell disease (SCD) is an orphan disease in the United States, but is highly prevalent worldwide. Only two drugs, hydroxyurea and L-glutamine, are approved for this disease. With an improved understanding of the pathophysiology of SCD as well as the success of several recently approved drugs for other orphan diseases, there is an increased interest in the development of drugs for SCD.

Areas covered

This review summarizes published studies of drug therapies and ongoing trials of novel agents.

Expert opinion

The development of drugs with different mechanisms of action offers opportunities for combination and individualized therapy in SCD. In addition to acute pain crisis, the evaluation of other SCD-related complications, exercise capacity, patient reported outcomes and validated surrogate endpoints are necessary to advance drug development. It is important to involve sites in sub-Saharan Africa and India, which have the highest burden of SCD, in trials of novel therapies.

Individual variability in response to a single sickling event for normal, sickle cell, and sickle trait erythrocytes

Hemoglobin S (Hb-S) polymerization is the primary event in sickle cell disease causing irreversible damage to red blood cell (RBC) membranes over repeated polymerization cycles. A single polymerization triggered by a hypoxic environment was reported to result in reversibly (upon reoxygenation) decreased RBC deformability and increased mechanical fragility (MF). Individualized responses have not been reported, although RBC fragility can vary significantly even among healthy individuals. This study evaluates individual variability in response to a single hypoxia-induced sickling event, through changes in RBC MF. Blood was drawn from 10 normal (AA), 11 sickle cell (SS), and 7 sickle trait (AS) subjects-with Hb-S fraction, osmotic fragility, and medical history also collected. Mechanical stress was applied using a bead mill at 50-Hz oscillation for 0.5-30 minutes. MF profiles here give percent hemolysis upon successive durations of stressing. MF was measured for AA, SS, and AS cells-each equilibrated (1) with air, (2) with nitrogen in an anaerobic chamber, and (3) with air after the hypoxic event. While AA subjects exhibited significantly different changes in fragility upon hypoxia, in all cases there was recovery to close to the initial MF values on reoxygenation. For AS subjects, recovery at reoxygenation was observed only in about half of the cases. Fragility of SS cells increased in hypoxia and decreased with reoxygenation, with significantly variable magnitude of recovery. The variability of response for individual AS and SS subjects indicates that some are potentially at higher risk of irreversible hypoxia-induced membrane damage.

A systematic review of known mechanisms of hydroxyurea-induced fetal hemoglobin for treatment of sickle cell disease

AIM

To report on molecular mechanisms of fetal hemoglobin (HbF) induction by hydroxyurea (HU) for the treatment of sickle cell disease.

STUDY DESIGN

Systematic review.

RESULTS

Studies have provided consistent associations between genomic variations in HbF-promoting loci and variable HbF level in response to HU. Numerous signal transduction pathways have been implicated, through the identification of key genomic variants in BCL11A, HBS1L-MYB, SAR1 or XmnI polymorphism that predispose the response to the treatment, and signal transduction pathways that modulate γ-globin expression (cAMP/cGMP; Giα/c-Jun N-terminal kinase/Jun; methylation and miRNA). Three main molecular pathways have been reported: i) Epigenetic modifications, transcriptional events and signaling pathways involved in HU-mediated response, ii) Signaling pathways involving HU-mediated response and iii) Post-transcriptional pathways (regulation by miRNAs).

CONCLUSIONS

The complete picture of HU-mediated mechanisms of HbF production in Sickle Cell Disease remains elusive. Research on post-transcriptional mechanisms could lead to therapeutic targets that may minimize alterations to the cellular transcriptome.

Endothelium-derived nitric oxide production is increased by ATP released from red blood cells incubated with hydroxyurea

Red blood cells (RBCs) release adenosine triphosphate (ATP) in response to a variety of stimuli, including flow-induced deformation. Hydroxyurea (HU), a proven therapy for individuals with sickle cell disease (SCD), is known to improve blood flow. However, the exact mechanism leading to the improved blood flow is incomplete. Here, we report that the incubation of human RBCs with HU enhances ATP release from these cells and that this ATP is capable of stimulating nitric oxide (NO) production in an endothelium. RBCs incubated with HU were pumped through micron-size flow channels in a microfluidic device. The release of ATP from the RBCs was measured using the luciferin-luciferase assay in detection wells on the device that were separated from the flow channels by a porous polycarbonate membrane. NO released from a layer of bovine artery endothelial cells (bPAECs) cultured on the polycarbonate membrane was also measured using the extracellular NO probe DAF-FM. ATP release from human RBCs incubated with 100 μM HU was observed to be 2.06±0.37-fold larger than control samples without HU (p<0.05, N ≥ 3). When HU-incubated RBCs were flowed under a layer of bPAECs, NO released from the bPAEC layer was measured to be 1.34±0.10-fold higher than controls. An antagonist of the P2Y receptor established that this extra 30% increase in NO release is ATP mediated. Furthermore, when RBCs were incubated with L-NAME, a significant decrease in endothelium-derived NO production was observed. Control experiments suggest that RBC-generated NO indirectly affects endothelial NO production via its effects on RBC-derived ATP release.

Organic anion transporting polypeptide 1B transporters modulate hydroxyurea pharmacokinetics

Hydroxyurea is currently the only FDA-approved drug that ameliorates the pathophysiology of sickle cell anemia. Unfortunately, substantial interpatient variability in the pharmacokinetics (PK) of hydroxyurea may result in variation of the drug's efficacy. However, little is known about mechanisms that modulate hydroxyurea PK. Recent in vitro studies identifying hydroxyurea as a substrate for organic anion transporting polypeptide (OATP1B) transporters prompted the current investigation assessing the role of OATP1B transporters in modulating hydroxyurea PK. Using wild-type and Oatp1b knockout (Oatp1b(-/-)) mice, hydroxyurea PK was analyzed in vivo by measuring [(14)C]hydroxyurea distribution in plasma, kidney, liver, urine, or the exhaled (14)CO2 metabolite. Plasma levels were significantly reduced by 20% in Oatp1b(-/-) mice compared with wild-type (area under the curve of 38.64 or 48.45 μg·h(-1)·ml(-1), respectively) after oral administration, whereas no difference was observed between groups following intravenous administration. Accumulation in the kidney was significantly decreased by twofold in Oatp1b(-/-) mice (356.9 vs. 748.1 pmol/g), which correlated with a significant decrease in urinary excretion. Hydroxyurea accumulation in the liver was also decreased (136.6 vs. 107.3 pmol/g in wild-type or Oatp1b(-/-) mice, respectively) correlating with a decrease in exhaled (14)CO2. These findings illustrate that deficiency of Oatp1b transporters alters the absorption, distribution, and elimination of hydroxyurea thus providing the first in vivo evidence that cell membrane transporters may play a significant role in modulating hydroxyurea PK. Future studies to investigate other transporters and their role in hydroxyurea disposition are warranted for understanding the sources of variation in hydroxyurea's PK.

Deprenyl enhances the teratogenicity of hydroxyurea in organogenesis stage mouse embryos

Hydroxyurea, an antineoplastic drug, is a model teratogen. The administration of hydroxyurea to CD1 mice on gestation day 9 induces oxidative stress, increasing the formation of 4-hydroxy-2-nonenal adducts to redox-sensitive proteins such as glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the caudal region of the embryo. GAPDH catalytic activity is reduced, and its translocation into the nucleus is increased. Because the nuclear translocation of GAPDH is associated with oxidative stress–induced cell death, we hypothesized that this translocation plays a role in mediating the teratogenicity of hydroxyurea. Deprenyl (also known as selegiline), a drug used as a neuroprotectant in Parkinson’s disease, inhibits the nuclear translocation of GAPDH. Hence, timed pregnant CD1 mice were treated with deprenyl (10mg/kg) on gestation day 9 followed by the administration of hydroxyurea (400 or 600mg/kg). Deprenyl treatment significantly decreased the hydroxyurea-induced nuclear translocation of GAPDH in the caudal lumbosacral somites. Deprenyl enhanced hydroxyurea-mediated caudal malformations, inducing specifically limb reduction, digit anomalies, tail defects, and lumbosacral vertebral abnormalities. Deprenyl did not augment the hydroxyurea-induced inhibition of glycolysis or alter the ratio of oxidized to reduced glutathione. However, it did dramatically increase cleaved caspase-3 in embryos. These data suggest that nuclear GAPDH plays an important, region-specific, role in teratogen-exposed embryos. Deprenyl exacerbated the developmental outcome of hydroxyurea exposure by a mechanism that is independent of oxidative stress. Although the administration of deprenyl alone did not affect pregnancy outcome, this drug may have adverse consequences when combined with exposures that increase the risk of malformations.

Low fixed-dose hydroxyurea in severely affected Indian children with sickle cell disease

There is limited data on the efficacy of hydroxyurea (HU) in Indian sickle cell anemia patients who have severe manifestations despite high fetal hemoglobin (Hb F). Sixty sickle cell anemia children (5-18 years) with more than three episodes of vasoocclusive crises or blood transfusions per year were randomized to receive HU (n = 30) or placebo (n = 30) therapy. Fixed dose (10 mg/kg/day) of HU was administered for 18 months and the patients were followed-up monthly with clinical assessment and laboratory monitoring. In the HU group, hemoglobin (Hb) and Hb F levels increased significantly along with a significant decrease in the number of painful crises, blood transfusion requirements and hospitalizations compared to the placebo group. No major adverse events were observed in this study. In conclusion, low-fixed dose HU therapy was effective for the treatment of Indian sickle cell anemia children. However, there is a need for long-term studies to evaluate the efficacy and toxicity in a larger number of Indian sickle cell anemia patients.

The proinflammatory cytokine GM-CSF downregulates fetal hemoglobin expression by attenuating the cAMP-dependent pathway in sickle cell disease

Although reduction in leukocyte counts following hydroxyurea therapy in sickle cell disease (SCD) predicts fetal hemoglobin (HbF) response, the underlying mechanism remains unknown. We previously reported that leukocyte counts are regulated by granulocyte-macrophage colony-stimulating factor (GM-CSF) in SCD patients. Here we examined the roles of GM-CSF in the regulation of HbF expression in SCD. Upon the analysis of retrospective data in 372 patients, HbF levels were inversely correlated with leukocyte counts and GM-CSF levels in SCD patients without hydroxyurea therapy, while HbF increments after hydroxyurea therapy correlated with a reduction in leukocyte counts, suggesting a negative effect of GM-CSF on HbF expression. Consistently, in vitro studies using primary erythroblasts showed that the addition of GM-CSF to erythroid cells decreased HbF expression. We next examined the intracellular signaling pathway through which GM-CSF reduced HbF expression. Treatment of erythroid cells with GM-CSF resulted in the reduction of intracellular cAMP levels and abrogated phosphorylation of cAMP response-element-binding-protein, suggesting attenuation of the cAMP-dependent pathway, while the phosphorylation levels of mitogen-activated protein kinases were not affected. This is compatible with our studies showing a role for the cAMP-dependent pathway in HbF expression. Together, these results demonstrate that GM-CSF plays a role in regulating both leukocyte count and HbF expression in SCD. Reduction in GM-CSF levels upon hydroxyurea therapy may be critical for efficient HbF induction. The results showing the involvement of GM-CSF in HbF expression may suggest possible mechanisms for hydroxyurea resistance in SCD.

Impact of hydroxyurea on perioperative management and outcomes in children with sickle cell anemia

Hydroxyurea has enhanced the treatment for children with sickle cell anemia. The objectives of this study were to compare perioperative transfusions and outcomes for children taking hydroxyurea versus those not taking hydroxyurea. We retrospectively reviewed perioperative management and outcomes for 51 children with sickle cell anemia (HbSS genotype) who underwent surgery in our center between January 2003 and April 2008. Of the 51 patients, 30 (59%) were taking hydroxyurea and 21 (41%) were not taking hydroxyurea. Eight of 30 (27%) in the hydroxyurea group were not transfused preoperatively, 12 of 30 (40%) received a single transfusion and 10 of 30 (33%) received serial transfusions, compared with 1 of 21 (5%) children in the nonhydroxyurea group who was not transfused, 2 of 21 (10%) who received a single transfusion and 18 of 21 (85%) who received serial transfusions or pheresis (P=0.004; for comparison across groups). One patient not taking hydroxyurea developed a delayed hyperhemolytic transfusion reaction, and 2 children taking hydroxyurea developed acute chest syndrome. Overall, children taking hydroxyurea had substantially fewer transfusions compared with children not taking hydroxyurea. Both groups of children had a low complication rate. Further research should be done to optimize perioperative management of children taking hydroxyurea.

Hydroxyurea enhances SMN2 gene expression through nitric oxide release

Small molecules that increase full-length survivor motor neuron (SMN) gene transcript are promising therapeutic candidates for spinal muscular atrophy (SMA). Hydroxyurea (HU) has recently been shown to increase full-length SMN transcript in cultured lymphocytes from patients with SMA. We investigate the mechanism by which HU enhances full-length SMN2 gene expression in SMA lymphocytes. Nitric oxide (NO) is a major intracellular metabolite of HU. We test whether NO donors can themselves enhance full-length SMN2 expression. Eighteen cell lines (five type I, five type II, six type III SMA, and two non-SMA controls) were treated with or without NO donors for 48 h. SMA cells treated with HU and three NO donors: two long-acting donors, Deta-NONOate and S-nitrosoglutathione, and one short-acting donor, 3-ethyl-3-(ethylaminoethyl)-1-hydroxy-2-oxo-1-triazene, resulted in significant increase in full-length SMN2 mRNA. These effects were abolished by co-treatment with an NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide. One short-acting NO donor, S-nitroso-N-acetyl-DL-penicillamine, failed to show significant effect on full-length SMN2 expression, possibly due to high degree of cytotoxicity. These results were observed using both densitometry and quantitative PCR methods. We conclude that HU enhances SMN2 expression through the release of NO. NO donors may themselves be considered as new therapeutic candidates for SMA.

How I use hydroxyurea to treat young patients with sickle cell anemia

Hydroxyurea has many characteristics of an ideal drug for sickle cell anemia (SCA) and provides therapeutic benefit through multiple mechanisms of action. Over the past 25 years, substantial experience has accumulated regarding its safety and efficacy for patients with SCA. Early proof-of-principle studies were followed by prospective phase 1/2 trials demonstrating efficacy in affected adults, then adolescents and children, and more recently infants and toddlers. The phase 3 National Heart, Lung and Blood Institute-sponsored Multicenter Study of Hydroxyurea trial proved clinical efficacy for preventing acute vaso-occlusive events in severely affected adults. Based on this cumulative experience, hydroxyurea has emerged as an important therapeutic option for children and adolescents with recurrent vaso-occlusive events; recent evidence documents sustained long-term benefits with prevention or reversal of chronic organ damage. Despite abundant evidence for its efficacy, however, hydroxyurea has not yet translated into effective therapy for SCA. Because many healthcare providers have inadequate knowledge about hydroxyurea, patients and families are not offered treatment or decline because of unrealistic fears. Limited support for hydroxyurea by lay organizations and inconsistent medical delivery systems also contribute to underuse. Although questions remain regarding its long-term risks and benefits, current evidence suggests that many young patients with SCA should receive hydroxyurea treatment.

Hydroxyurea for children with sickle cell disease

Hydroxyurea therapy offers promise for ameliorating the clinical course of children with sickle cell disease (SCD). Hydroxyurea is a prototypic therapeutic option; it can be administered with minimal side effects, has a relatively wide therapeutic window, and has mechanisms of action that address pathophysiologic pathways of sickling, vaso-occlusion, hemolysis, and organ damage. There are limited data regarding hydroxyurea's ability to prevent or diminish organ dysfunction, and the long-term risks of hydroxyurea therapy remain incompletely defined. Although clinical trials are underway to address long-term issues, hydroxyurea remains an effective but underutilized therapy for SCD.

Hydroxyurea generates nitric oxide in human erythroid cells: mechanisms for gamma-globin gene activation

Hydroxyurea (HU) induces fetal hemoglobin synthesis through activation of cyclic guanine monophosphate (cGMP) signaling. Studies in sickle cell patients demonstrated increased circulating nitric oxide (NO) levels after oral HU treatment. However, the direct measurement of NO in erythroid cells and its role in fetal hemoglobin induction have not been defined. Therefore, we quantified the level of nitrate and nitrite (NOx) generated by HU in human erythroid progenitors in the presence of three nitric oxide synthase inhibitors (NOS), including N(G)-monomethyl-L-arginine (L-NMMA). In addition, cGMP levels were measured in the presence or absence of the pathway inhibitor 1H-(1,2,4)ox-adiazolo(4,3-a)quinoxalin-1-one, which blocks soluble guanylyl cyclase formation. HU treatment increased NOx levels and gamma-globin transcription in K562 and primary erythroid cells, which was augmented when HU was combined with L-NMMA. Pretreatment with the cGMP pathway inhibitor reversed gamma-gene activation by HU. These data demonstrate the direct stimulation of cellular NO and cGMP signaling in erythroid progenitors by HU as a possible mechanism for gamma-globin gene activation.

Adverse effects of a clinically relevant dose of hydroxyurea used for the treatment of sickle cell disease on male fertility endpoints

Two experiments were conducted to determine: 1) whether the adult male transgenic sickle cell mouse (Tg58 x Tg98; TSCM), exhibits the patterns of reproductive endpoints (hypogonadism) characteristic of men with sickle cell disease (SCD) and 2) whether hydroxyurea (HU) exacerbates this condition. In Experiment 1, blood samples were collected from adult age-matched TSCM and ICR mice (ICRM) (N = 10/group) for plasma testosterone measurements. Subsequently, mice were sacrificed, testes excised and weighed and stored spermatozoa recovered for the determination of sperm density, progressive motility and percentage of spermatozoa with normal morphology. In experiment 2, adult male TSCM were orally treated with 25 mg HU/kg body weight/day for 28 or 56 days. Control mice received the vehicle for HU (saline) as described above. At the end of the treatment periods, blood samples were collected for quantification of circulating testosterone. Subsequently, mice were sacrificed, testes and epididymides were recovered and weighed and one testis per mouse was subjected to histopathology. Stored spermatozoa were recovered for the determination of indices of sperm quality mentioned in Experiment 1. Testis weight, stored sperm density, progressive motility, percentage of spermatozoa with normal morphology and plasma testosterone concentrations of TSCM were significantly lower by 40, 65, 40, 69 and 66%, respectively than those of ICRM. These data indicate that adult TSCM used in this study suffered from hypogonadism, characteristically observed among adult male SCD patients. In Experiment 2, HU treatment significantly decreased testis weight on day 28, (0.09 +/- 0.004 g) that was further decreased on day 56 (0.06 +/- 0.003 g; treatment x time interaction) compared with controls (day 28, 0.15 +/- 0.01 g; day 56, 2, 0.16 +/- 0.01 g). Concomitant with a 52% shrinkage (P<0.001) in area of testes in 56 days of HU treatment, testes from HU-treated TSCM exhibited significant atrophic degeneration in the seminiferous tubules compared with controls. Furthermore, treated TSCM had only Sertoli cells and cell debris remaining in most of the seminiferous tubules in comparison with controls. Leydig cell prominence and hyperplasia were more evident (P<0.05) in the steroidogenic compartments of testes of HU-treated TSCM compared with controls. However, plasma testosterone concentrations were reduced by HU treatment (P<0.05; treatment x time interaction) compared with controls on the two time periods studied. Epididymides from HU-treated TSCM sustained a 25% shrinkage (P<0.05), along with 69 (P<0.005) and 95% reduction (P<0.005), in stored sperm density and sperm progressive motility (treatment x time interaction P<0.05), respectively on day 56 of treatment compared with controls. These data demonstrate that TSCM used in this study exhibited SCD-induced hypogonadism, thus authenticating their use for studying the effect of HU on male reproductive endpoints observed in SCD patients. Secondarily, our data show that HU treatment exacerbated the already SCD-induced hypogonadism to gonadal failure.

Hydroxyurea for children with sickle cell disease

Hydroxyurea therapy offers promise for ameliorating the clinical course of children with sickle cell disease (SCD). Hydroxyurea is a prototypic therapeutic option; it can be administered with minimal side effects, has a relatively wide therapeutic window, and has mechanisms of action that address pathophysiologic pathways of sickling, vaso-occlusion, hemolysis, and organ damage. There are limited data regarding hydroxyurea's ability to prevent or diminish organ dysfunction, and the long-term risks of hydroxyurea therapy remain incompletely defined. Although clinical trials are underway to address long-term issues, hydroxyurea remains an effective but underutilized therapy for SCD.