Preliminary assessment of inhaled nitric oxide for acute vaso-occlusive crisis in pediatric patients with sickle cell disease

Pharmacogenomics of Drugs Used in β-Thalassemia and Sickle-Cell Disease: From Basic Research to Clinical Applications

In this short review we have presented and discussed studies on pharmacogenomics (also termed pharmacogenetics) of the drugs employed in the treatment of β-thalassemia or Sickle-cell disease (SCD). This field of investigation is relevant, since it is expected to help clinicians select the appropriate drug and the correct dosage for each patient. We first discussed the search for DNA polymorphisms associated with a high expression of γ-globin genes and identified this using GWAS studies and CRISPR-based gene editing approaches. We then presented validated DNA polymorphisms associated with a high HbF production (including, but not limited to the HBG2 XmnI polymorphism and those related to the BCL11A, MYB, KLF-1, and LYAR genes). The expression of microRNAs involved in the regulation of γ-globin genes was also presented in the context of pharmacomiRNomics. Then, the pharmacogenomics of validated fetal hemoglobin inducers (hydroxyurea, butyrate and butyrate analogues, thalidomide, and sirolimus), of iron chelators, and of analgesics in the pain management of SCD patients were considered. Finally, we discuss current clinical trials, as well as international research networks focusing on clinical issues related to pharmacogenomics in hematological diseases.

Mouse models of sickle cell disease: Imperfect and yet very informative

The root cause of sickle cell disease (SCD) has been known for nearly a century, however, few therapies to treat the disease are available. Over several decades of work, with advances in gene editing technology and after several iterations of mice with differing genotype/phenotype relationships, researchers have developed humanized SCD mouse models. However, while a large body of preclinical studies has led to huge gains in basic science knowledge about SCD in mice, this knowledge has not led to the development of effective therapies to treat SCD-related complications in humans, thus leading to frustration with the paucity of translational progress in the SCD field. The use of mouse models to study human diseases is based on the genetic and phenotypic similarities between mouse and humans (face validity). The Berkeley and Townes SCD mice express only human globin chains and no mouse hemoglobin. With this genetic composition, these models present many phenotypic similarities, but also significant discrepancies that should be considered when interpreting preclinical studies results. Reviewing genetic and phenotypic similarities and discrepancies and examining studies that have translated to humans and those that have not, offer a better perspective of construct, face, and predictive validities of humanized SCD mouse models.

Using disease-modifying therapies in sickle cell disease

As curative therapy using allogeneic hematopoietic stem cell transplantation as well as gene therapy and gene editing remains inaccessible to most patients with sickle cell disease, the availability of drug therapies that are safe, efficacious, and affordable is highly desirable. Increasing progress is being made in developing drug therapies based on our understanding of disease pathophysiology. Four drugs, hydroxyurea, L-glutamine, crizanlizumab, and voxelotor, are currently approved by the US Food and Drug Administration, with multiple others at various stages of testing. With the limited efficacy of individual agents, combinations of agents will likely be required for optimal outcomes.

Emerging drugs for the treatment of sickle cell disease: a review of phase II/III trials

INTRODUCTION

The substitution of glutamic acid by valine on the ß-globin gene produces the hemoglobin S variant responsible for sickle cell disease (SCD), a disorder that affects millions of people worldwide and leads to acute and cumulative organ damage. Even though life expectancy has significantly improved where the best medical care is available, there are still few therapeutic options for SCD and those are limited by their availability, cost, and individual toxicities.

AREAS COVERED

This review summarizes the clinical data on current treatments for SCD and emerging therapies studied in the acute setting as well as potential disease-modifying agents, with an emphasis on the FDA-approved agents.

EXPERT OPINION

Hydroxyurea has been a gold standard for two decades, showing benefits in acute complications and overall survival in sickle cell anemia, although data is lacking for certain genotypes such as hemoglobin SC. As progress is made in our understanding of the pathophysiological networks characterizing SCD, numerous pathways appear to be targetable, with L-glutamine, Crizanlizumab and Voxelotor now approved by the FDA. Pursuing a multi-agent approach could alter the disease course in a more effective fashion and provide an alternative option to curative therapies, but longer clinical studies are needed.

Inhaled nitric oxide for treating pain crises in people with sickle cell disease

BACKGROUND

In people with sickle cell disease, sickled red blood cells cause the occlusion of small blood vessels, which presents as episodes of severe pain known as pain crises or vaso-occlusive crises. The pain can occur in the bones, chest, or other parts of the body, and may last several hours to days. Pain relief during crises includes both pharmacologic and non-pharmacologic treatments. The efficacy of inhaled nitric oxide in pain crises has been a subject of controversy; hypotheses have been made suggesting a beneficial response due to its vasodilator properties, yet no conclusive evidence has been presented. This review aimed to evaluate the available randomised controlled studies addressing this topic.

OBJECTIVES

To capture the body of evidence evaluating the efficacy and safety of the use of inhaled nitric oxide in treating pain crises in people with sickle cell disease, and to assess the relevance, robustness, and validity of the treatment to better guide medical practice in the fields of haematology and palliative care (since the recent literature seems to favour the involvement of palliative care for such people).

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Haemoglobinopathies Trials Register. We searched for unpublished work in the abstract books of the European Haematology Association conference, the American Society of Hematology conference, the British Society for Haematology Annual Scientific Meeting, the Caribbean Health Research Council Meetings, and the National Sickle Cell Disease Program Annual Meeting. The most recent search was conducted on 1 September 2021. We also searched ongoing study registries on 19 November 2021.

SELECTION CRITERIA

Randomised and quasi-randomised trials comparing inhaled nitric oxide with placebo for treating pain crises in people with sickle cell disease.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data (including adverse event data), with any disagreements resolved by consulting a third review author. When the data were not reported in the text, we attempted to extract the data from available tables or figures. We contacted trial authors for additional information. We assessed the certainty of the evidence using the GRADE criteria.

MAIN RESULTS

We included three trials involving a total of 188 participants in the review. There were equal numbers of males and females. Most participants were adults, although one small trial was conducted in a children's hospital and recruited children over the age of 10 years. All three parallel trials compared inhaled nitric oxygen (80 parts per million (ppm)) to placebo (nitrogen gas mixed with oxygen or room air) for four hours; one trial continued administering nitric oxide (40 ppm) for a further four hours. This extended trial had an overall low risk of bias; however, we had concerns about risk of bias for the remaining two trials due to their small sample size, and additionally a high risk of bias due to financial conflicts of interest in one of these smaller trials. We were only able to analyse some limited data from the eight-hour trial, reporting the remaining results narratively. Evidence from one trial (150 participants) suggested that inhaled nitric oxide may not reduce the time to pain resolution: inhaled nitric oxide median 73.0 hours (95% confidence interval (CI) 46.0 to 91.0) and with placebo median 65.5 hours (95% CI 48.1 to 84.0) (low-certainty evidence). No trial reported on the duration of the initial pain crisis. Only one large trial reported on the frequency of pain crises in the follow-up period and found there may be little or no difference between the inhaled nitric oxide and placebo groups for return to the emergency department (risk ratio (RR) 0.73, 95% CI 0.31 to 1.71) and rehospitalisation (RR 0.53, 95% CI 0.25 to 1.11) (150 participants; low-certainty evidence). There may be little or no difference between treatment and placebo in terms of reduction in pain score at any time point up to eight hours (150 participants). The two smaller trials reported a beneficial effect of inhaled nitric oxide in reducing the visual analogue pain score after four hours of the intervention. Analgesic use was reported not to differ greatly between the inhaled nitric oxide group and placebo group in any of the three trials, but no analysable data were provided. Two trials reported the median duration of hospitalisation: in the largest trial the placebo group had the shorter duration, whilst in the second smaller (paediatric) trial hospitalisation was shorter in the treatment group. Only the largest trial (150 participants) reported serious adverse events, with no increase in the inhaled nitric oxide group during or after the intervention compared to the control group (acute chest syndrome occurred in 5 out of 75 participants from each group, pyrexia in 1 out of 75 participants from each group, and dysphagia and a drop in haemoglobin were each reported in 1 out of 75 participants in the inhaled nitric oxide group) (low-certainty evidence).

AUTHORS' CONCLUSIONS

The currently available evidence is insufficient to determine the effects (benefits or harms) of using inhaled nitric oxide to treat pain (vaso-occlusive) crises in people with sickle cell disease. Large-scale, long-term trials are needed to provide more robust data in this area. Patient-important outcomes (e.g. measures of pain and time to pain resolution and amounts of analgesics used), as well as use of healthcare services, should be measured and reported in a standardised manner.

Inhaled pulmonary vasodilators: a narrative review

Pulmonary hypertension (PH) is a severe disease that affects people of all ages. It can occur as an idiopathic disorder at birth or as part of a variety of cardiovascular and pulmonary disorders. Inhaled pulmonary vasodilators (IPV) can reduce pulmonary vascular resistance (PVR) and improve RV function with minimal systemic effects. IPV includes inhaled nitric oxide (iNO), inhaled aerosolized prostacyclin, or analogs, including epoprostenol, iloprost, treprostinil, and other vasodilators. In addition to pulmonary vasodilating effects, IPV can also be used to improve oxygenation, reduce inflammation, and protect cell. Off-label use of IPV is common in daily clinical practice. However, evidence supporting the inhalational administration of these medications is limited, inconclusive, and controversial regarding their safety and efficacy. We conducted a search for relevant papers published up to May 2020 in four databases: PubMed, Google Scholar, EMBASE and Web of Science. This review demonstrates that the clinical using and updated evidence of IPV. iNO is widely used in neonates, pediatrics, and adults with different cardiopulmonary diseases. The limitations of iNO include high cost, flat dose-response, risk of significant rebound PH after withdrawal, and the requirement of complex technology for monitoring. The literature suggests that inhaled aerosolized epoprostenol, iloprost, treprostinil and others such as milrinone and levosimendan may be similar to iNO. More research of IPV is needed to determine acceptable inclusion criteria, long-term outcomes, and management strategies including time, dose, and duration.

Hydroxyurea improves nitric oxide bioavailability in humanized sickle cell mice

Despite advancements in disease management, sickle cell nephropathy, a major contributor to mortality and morbidity in patients, has limited therapeutic options. Previous studies indicate hydroxyurea, a commonly prescribed therapy for sickle cell disease (SCD), can reduce renal injury in SCD but the mechanisms are uncertain. Because SCD is associated with reduced nitric oxide (NO) bioavailability, we hypothesized that hydroxyurea treatment would improve NO bioavailability in the humanized sickle cell mouse. Humanized male 12-wk-old sickle (HbSS) and genetic control (HbAA) mice were treated with hydroxyurea or regular tap water for 2 wk before renal and systemic NO bioavailability as well as renal injury were assessed. Untreated HbSS mice exhibited increased proteinuria, elevated plasma endothelin-1 (ET-1), and reduced urine concentrating ability compared with HbAA mice. Hydroxyurea reduced proteinuria and plasma ET-1 levels in HbSS mice. Untreated HbSS mice had reduced plasma nitrite and elevated plasma arginase concentrations compared with HbAA mice. Hydroxyurea treatment augmented plasma nitrite and attenuated plasma arginase in HbSS mice. Renal vessels isolated from HbSS mice also had elevated nitric oxide synthase 3 (NOS3) and arginase 2 expression compared with untreated HbAA mice. Hydroxyurea treatment did not alter renal vascular NOS3, however, renal vascular arginase 2 expression was significantly reduced. These data support the hypothesis that hydroxyurea treatment augments renal and systemic NO bioavailability by reducing arginase activity as a potential mechanism for the improvement on renal injury seen in SCD mice.

Hemodynamics in acute stroke: Cerebral and cardiac complications

Hemodynamics is the study of blood flow, where parameters have been defined to quantify blood flow and the relationship with systemic circulatory changes. Understanding these perfusion parameters, the relationship between different blood flow variables and the implications for ischemic injury are outlined in the ensuing discussion. This chapter focuses on the hemodynamic changes that occur in ischemic stroke, and their contribution to ischemic stroke pathophysiology. We discuss the interaction between cardiovascular response and hemodynamic changes in stroke. Studying hemodynamic changes has a key role in stroke prevention, therapeutic implications and prognostic importance in acute ischemic stroke: preexisting hemodynamic and autoregulatory impairments predict the occurrence of stroke. Hemodynamic failure predisposes to the formation of thromboemboli and accelerates infarction due to impairing compensatory mechanisms. In ischemic stroke involving occlusion of a large vessel, persistent collateral circulation leads to preservation of ischemic penumbra and therefore justifying endovascular thrombectomy. Following thrombectomy, impaired autoregulation may lead to reperfusion injury and hemorrhage.

Analgesic management of uncomplicated acute sickle-cell pain crisis in pediatrics: a systematic review and meta-analysis

OBJECTIVES

To capture evidence of the efficacy and safety of pharmacological analgesia for uncomplicated acute sickle-cell pain in pediatric patients compared to placebo.

SOURCES OF DATA

Searches for key evidence were performed from March 1 to 31, 2018, for randomized controlled trials of pharmacological analgesia compared to placebo for uncomplicated acute sickle-cell pain in a pediatric sample. The authors searched ten scientific databases including, among others, PubMed, MEDLINE, Embase, and Clinicaltrials.gov for this systematic review and meta-analysis.

SUMMARY OF THE FINDINGS

Four trials (n=227) were selected by the inclusion criteria (intranasal fentanyl, intravenous magnesium, arginine, and inhaled nitric oxide). The quality of evidence ranged from low to moderate for each outcome. Meta-analysis of changes in the ladder of pain score (p=0.72), length-of-stay in hospital (p=0.65), and amount of narcotics used during the study (p=0.10) showed non-statistically significant differences and a lack of amelioration provided by pharmaceutical analgesics in treatment group. The adverse events reported that more participants in the intervention arm underwent pain, with statistically significant differences at the drug delivery site in studies using intranasal fentanyl and intravenous magnesium (p=0.03).

CONCLUSIONS

Pharmacological analgesia appears to be uncertain in improving the intensity and providing relief of acute pain crisis in pediatric patients with sickle-cell anemia. With respect to clinical advantage, no decisive deduction about the clinical efficacy may be made regarding these medications in acute sickle-cell pain management in the pediatric age group.

Sickle cell disease subjects and mouse models have elevated nitrite and cGMP levels in blood compartments

The hypothesis of decreased nitric oxide (NO) bioavailability in sickle cell disease (SCD) proposes that multiple factors leading to decreased NO production and increased consumption contributes to vaso-occlusion, pulmonary hypertension, and pain. The anion nitrite is central to NO physiology as it is an end product of NO metabolism and serves as a reservoir for NO formation. However, there is little data on nitrite levels in SCD patients and its relationship to pain phenotype. We measured nitrite in SCD subjects and examined its relationship to SCD pain. In SCD subjects, median whole blood, red blood cell and plasma nitrite levels were higher than in controls, and were not associated with pain burden. Similarly, Townes and BERK homozygous SCD mice had elevated blood nitrite. Additionally, in red blood cells and plasma from SCD subjects and in blood and kidney from Townes homozygous mice, levels of cyclic guanosine monophosphate (cGMP) were higher compared to controls. In vitro, hemoglobin concentration, rather than sickle hemoglobin, was responsible for nitrite metabolism rate. In vivo, inhibition of NO synthases and xanthine oxidoreductase decreased nitrite levels in homozygotes but not in control mice. Long-term nitrite treatment in SCD mice further elevated blood nitrite and cGMP, worsened anemia, decreased platelets, and did not change pain response. These data suggest that SCD in humans and animals is associated with increased nitrite/NO availability, which is unrelated to pain phenotype. These findings might explain why multiple clinical trials aimed at increasing NO availability in SCD patients failed to improve pain outcomes.

Inhaled nitric oxide for treating pain crises in people with sickle cell disease

BACKGROUND

In people with sickle cell disease, sickled red blood cells cause the occlusion of small blood vessels which presents as episodes of severe pain known as pain crises or vaso-occlusive crises. The pain can occur in the bones, chest, or other parts of the body, and may last several hours to days. Pain relief during crises includes both pharmacologic and non-pharmacologic treatments. The efficacy of inhaled nitric oxide in pain crises has been a controversial issue and hypotheses have been made suggesting a beneficial response due to its vasodilator properties. Yet no conclusive evidence has been presented.This review aims to evaluate the available randomised controlled studies which address this topic.

OBJECTIVES

To capture the available body of evidence evaluating the efficacy and safety of the use of inhaled nitric oxide in treating pain crises in people with sickle cell disease; and to assess the treatment's relevance, robustness, and validity, in order to better guide medical practice in the fields of haematology and palliative care (since recent literature seems to favour the involvement of palliative care for those people).

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register. Unpublished work is identified by searching the abstract books of the European Haematology Association conference; the American Society of Hematology conference; the British Society for Haematology Annual Scientific Meeting; the Caribbean Health Research Council Meetings; and the National Sickle Cell Disease Program Annual Meeting.Date of most recent search: 19 September 2019.We also searched ongoing study registries, date of most recent search: 26 September 2019.

SELECTION CRITERIA

Randomised and quasi-randomised trials comparing inhaled nitric oxide with placebo, or standardized way of treatment of pain crises in people with sickle cell disease.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data (including adverse event data). A third author helped clarify any disagreement. When the data were not reported in the text, we attempted to extract the data from any table or figure available. We contacted trial authors for additional information. We assessed the quality of the evidence using the GRADE criteria MAIN RESULTS: We identified six trials, three of which (188 participants) were eligible for inclusion in the review. There were equal numbers of males and females; and most participants were adults, although one small trial was conducted in a children's hospital and recruited children over the age of 10 years. All three parallel trials compared inhaled nitric oxygen (80 ppm) to placebo (room air) for four hours; one trial continued administering nitric oxide (40 ppm) for a further four hours. This extended trial had an overall low risk of bias; however, in the remaining two trials we had concerns about the risk of bias from the small sample size and additionally a high risk of bias due to financial conflicts of interest in one of these smaller trials. We were only able to analyse some limited data from the eight-hour trial and report the remaining results narratively.The time to pain resolution was only reported in one trial (150 participants), showing there may be little or no difference between the two groups: with inhaled nitric oxide median 73.0 hours (95% confidence interval (CI) 46.0 to 91.0) and with placebo median 65.5 hours (95% CI 48.1 to 84.0) (low-quality evidence). No trial reported on the duration of the initial pain crisis. Only one large trial reported on the frequency of pain crises in the follow-up period and found there may be little or no difference between the inhaled nitric oxide and placebo groups for a return to the ED, risk ratio 0.73 (95% CI 0.31 to 1.71) or for re-hospitalisation, risk ratio 0.53 (95% CI 0.25 to 1.11) (150 participants; low-quality evidence).There may be little or no difference between treatment and placebo in terms of reduction in pain score at any time point up to eight hours (150 participants). The two smaller trials reported a beneficial effect of inhaled nitric oxide in reducing the visual analogue pain score after four hours of the intervention, but these trials were small and limited compared to the first trial.Analgesic use was reported not to differ greatly between the inhaled nitric oxide group and placebo group in any of the three trials, but no analysable data were provided. The median duration of hospitalisation was reported by two trials, in the largest trial the placebo group had the shorter duration and in the second smaller (paediatric) trial hospitalisation was shorter in the treatment group.Only the largest trial (150 participants) reported serious adverse events, with no increase in the inhaled nitric oxide group during or after the intervention compared to the control group (acute chest syndrome occurred in 5 out of 75 participants from each group, pyrexia in 1 out of 75 participants from each group, dysphagia and a drop in haemoglobin were each reported in 1 out of 75 participants in the inhaled nitric oxide group, but not in the placebo group) (low-quality evidence).

AUTHORS' CONCLUSIONS

The currently available trials do not provide sufficient evidence to determine the effects (benefits or harms) of using inhaled nitric oxide to treat pain (vaso-occlusive) crises in people with sickle cell disease. Large-scale, long-term trials are needed to provide more robust data in this area. Patient-important outcomes (e.g. measures of pain and time to pain resolution and amounts of analgesics used), as well as use of healthcare services should be measured and reported in a standardized form.

PROMIS pediatric measures validated in a longitudinal study design in pediatric oncology

PURPOSE

This study assessed the responsiveness to change over time and theorized associations of Patient-Reported Outcomes Measurement Information System (PROMIS) pediatric measures in children and adolescents in treatment for cancer to determine measure readiness for use in cancer clinical trials.

METHODS

We administered eight PROMIS (three symptom, two psychological, and three performance) pediatric short-form measures and the Symptom Distress Scale (SDS) to 96 pediatric oncology patients at three time points during a course of chemotherapy. We assessed responsiveness using paired t tests and generalized estimating equation (GEE) models, calculated standardized response mean (SRM) values for PROMIS measures, and examined scores over three data points (T1-T3). Guided by the theory of unpleasant symptoms (TOUS), we examined associations among the PROMIS measures, the SDS, and other variables using GEE.

RESULTS

The paired t tests showed statistically significant changes in two psychological measures and one performance measure from T1 to T2; three symptom, two psychological and two performance measures from T2 to T3; and three symptom and two psychological measures from T1 to T3. Findings from GEE models indicate PROMIS pediatric measures had statistically significant short-term and long-term changes, controlling for demographic and clinical variables. One performance measure did not achieve significant change at any time point. We found positive support for theorized relationships in the TOUS.

CONCLUSIONS

Most of the PROMIS pediatric measures demonstrated changes over time and had significant relationships as theorized, thus supporting concurrent and construct validity of these measures when administered to pediatric oncology patients during a course of chemotherapy. This evidence supports the measures' readiness for use in clinical trials.

Successful Use of Pulmonary Vasodilators in Acute Chest Syndrome Complicated by Persistent Right Ventricular Failure

Pulmonary hypertension (PH) is a known consequence of sickle cell disease (SCD) and is associated with increased mortality and more frequent episodes of acute chest syndrome (ACS). Pulmonary pressures are known to increase during ACS, and right ventricular (RV) failure has been described as a significant cause of mortality in this condition. Management of ACS includes exchange transfusion, pain control, and prevention of hypovolemia and hypoxemia. However, in patients with a history of precapillary PH in whom ACS is complicated by persistent RV failure and cardiogenic shock, RV afterload reduction with pulmonary vasodilators may be an effective treatment strategy. Here, we present a case of a young man with SCD-associated PH and ACS who was successfully managed with inhaled and oral pulmonary vasodilators in the setting of persistent elevations in pulmonary vascular resistance leading to acute RV failure and cardiogenic shock.

Double-Blind Clinical Trial of Arginine Supplementation in the Treatment of Adult Patients with Sickle Cell Anaemia

Background

Sickle cell anaemia (SCA) is the most prevalent monogenic disease in Brazil. In SCA, haemoglobin S (HbS) is formed, which modifies red blood cell morphology. Intravascular haemolysis occurs, in which free Hb and free radicals degrade nitric oxide (NO) and release arginase, which reduces arginine levels. Because arginine is a substrate for NO formation, this decrease leads to reduced NO (vasodilator) synthesis. SCA treatment uses hydroxyurea (HU) to maintain high foetal haemoglobin (HbF) levels and reduces HbS to avoid haemolytic episodes.

Objective

To analyse the efficacy of L-arginine as an adjuvant in the treatment of SCA patients.

Setting

The State Blood Centre of Ceará, Brazil.

Methods

This was a randomized double-blind clinical study of adults with SCA with continuous use of HU at the State Blood Centre of Ceará. The clinical study enrolled 25 patients receiving HU + L-arginine (500 mg) and 25 patients receiving HU + placebo. The treatment was carried out over four months. Laboratory tests were performed to determine the levels of the following: (1) complete blood count; (2) nitrite + nitrate; (3) HbF; and (4) reticulocytes. The clinical experiments were performed by a haematologist. The main outcome measures were nitrite and pain.

Results

Statistical analysis showed that the levels of NO were increased in the study group, and there was also a reduction in pain frequency using a pain frequency scale by day, week, and month. The levels of nitrite plus nitrate in the group receiving placebo plus HU did not change among the times evaluated (38.27 ± 17.27 mg/L, 39.49 ± 12.84 mg/L, 34.45 ± 11.25 mg/L, p >0.05), but in the patients who received supplementation with L-arginine plus HU, a significant increase in nitrite plus nitrate levels was observed between M0 and M4 (36.55 ± 20.23 mg/L versus 48.64 ± 20.63 mg/L, p =0.001) and M2 and M4 (35.71 ± 15.11 mg/L versus 48.64 ± 20.63 mg/L, p <0.001). It is important to note that the increase in nitrite plus nitrate levels occurred only in the fourth month of follow-up of patients in the treatment group, showing that at least 4 months of supplementation with L-arginine is necessary to show an increase in these metabolites in the serum.

Conclusion

The use of L-arginine as a coadjuvant in the treatment of sickle cell anaemia may function as a potential tool for pain relief, consequently improving the life of patients.

cGMP modulation therapeutics for sickle cell disease

IMPACT STATEMENT

Sickle cell disease (SCD) is one of the most common inherited diseases and is associated with a reduced life expectancy and acute and chronic complications, including frequent painful vaso-occlusive episodes that often require hospitalization. At present, treatment of SCD is limited to hematopoietic stem cell transplant, transfusion, and limited options for pharmacotherapy, based principally on hydroxyurea therapy. This review highlights the importance of intracellular cGMP-dependent signaling pathways in SCD pathophysiology; modulation of these pathways with soluble guanylate cyclase (sGC) stimulators or phosphodiesterase (PDE) inhibitors could potentially provide vasorelaxation and anti-inflammatory effects, as well as elevate levels of anti-sickling fetal hemoglobin.

Inhaled nitric oxide

Nitric oxide (NO) is a gas that induces relaxation of smooth muscle cells in the vasculature. Because NO reacts with oxyhaemoglobin with high affinity, the gas is rapidly scavenged by oxyhaemoglobin in red blood cells and the vasodilating effects of inhaled NO are limited to ventilated regions in the lung. NO therefore has the unique ability to induce pulmonary vasodilatation specifically in the portions of the lung with adequate ventilation, thereby improving oxygenation of blood and decreasing intrapulmonary right to left shunting. Inhaled NO is used to treat a spectrum of cardiopulmonary conditions, including pulmonary hypertension in children and adults. However, the widespread use of inhaled NO is limited by logistical and financial barriers. We have designed, developed and tested a simple and economic NO generation device, which uses pulsed electrical discharges in air to produce therapeutic levels of NO that can be used for inhalation therapy. LINKED ARTICLES: This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc.

New Therapeutic Options for the Treatment of Sickle Cell Disease

Sickle cell disease (SCD; ORPHA232; OMIM # 603903) is a chronic and invalidating disorder distributed worldwide, with high morbidity and mortality. Given the disease complexity and the multiplicity of pathophysiological targets, development of new therapeutic options is critical, despite the positive effects of hydroxyurea (HU), for many years the only approved drug for SCD. New therapeutic strategies might be divided into (1) pathophysiology-related novel therapies and (2) innovations in curative therapeutic options such as hematopoietic stem cell transplantation and gene therapy. The pathophysiology related novel therapies are: a) Agents which reduce sickling or prevent sickle red cell dehydration; b) Agents targeting SCD vasculopathy and sickle cell-endothelial adhesive events; c) Anti-oxidant agents. This review highlights new therapeutic strategies in SCD and discusses future developments, research implications, and possible innovative clinical trials.

Drugs for preventing red blood cell dehydration in people with sickle cell disease

BACKGROUND

Sickle cell disease is an inherited disorder of hemoglobin, resulting in abnormal red blood cells. These are rigid and may block blood vessels leading to acute painful crises and other complications. Recent research has focused on therapies to rehydrate the sickled cells by reducing the loss of water and ions from them. Little is known about the effectiveness and safety of such drugs. This is an updated version of a previously published review.

OBJECTIVES

To assess the relative risks and benefits of drugs to rehydrate sickled red blood cells.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register. We also searched online trials registries for any ongoing trials (01 July 2018).Last search of the Group's Haemoglobinopathies Trials Register: 08 October 2018.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of drugs to rehydrate sickled red blood cells compared to placebo or an alternative treatment.

DATA COLLECTION AND ANALYSIS

Both authors independently selected studies for inclusion, assessed study quality and extracted data.

MAIN RESULTS

Of the 51 studies identified, three met the inclusion criteria, including 524 people with sickle cell disease aged between 12 and 65 years of age. One study tested the effectiveness of zinc sulphate as compared to placebo and the remaining two assessed senicapoc versus placebo. No deaths were seen in any of the studies (low-quality evidence). The zinc sulphate study showed a significant reduction in painful crises (in a total of 145 participants) over one and a half years, mean difference -2.83 (95% confidence interval -3.51 to -2.15) (moderate-quality evidence). However, analysis was restricted due to limited statistical data. Changes to red blood cell parameters and blood counts were inconsistent (very low-quality evidence). No serious adverse events were noted in the study. The Phase II dose-finding study of senicapoc (a Gardos channel blocker) compared to placebo showed that the high dose senicapoc showed significant improvement in change in hemoglobin level, the number and proportion of dense red blood cells, red blood cell count and indices and hematocrit value (very low-quality evidence). The results with low-dose senicapoc were similar to the high-dose senicapoc group but of lesser magnitude. There was no difference in the frequency of painful crises between the three groups (low-quality evidence). A subsequent Phase III study of senicapoc was terminated early since there was no difference observed between the treatment and control groups in the primary end point of painful crises.

AUTHORS' CONCLUSIONS

While the results of zinc for reducing sickle-related crises are encouraging, larger and longer-term multicenter studies are needed to evaluate the effectiveness of this therapy for people with sickle cell disease.While the Phase II and the prematurely terminated phase III studies of senicapoc showed that the drug improved red blood cell survival (depending on dose), this did not lead to fewer painful crises.Given this is no longer an active area of research, this review will no longer be regularly updated.

Nitric oxide in red blood cell adaptation to hypoxia

Nitric oxide (NO) appears to be involved in virtually every aspect of cardiovascular biology. Most attention has been focused on the role of endothelial-derived NO in basal blood flow regulation by relaxing vascular smooth muscle; however, it is now known that NO derived from red blood cells (RBCs) plays a fundamental role in vascular homeostasis by enhancing oxygen (O2) release at the cellular and physiological level. Hypoxia is an often seen problem in diverse conditions; systemic adaptations to hypoxia permit people to adjust to the hypoxic environment at high altitudes and to disease processes. In addition to the cardiopulmonary and hematologic adaptations that support systemic O2 delivery in hypoxia, RBCs assist through newly described NO-based mechanisms, in line with their vital role in O2 transport and delivery. Furthermore, to increase the local blood flow in proportion to metabolic demand, NO regulates membrane mechanical properties thereby modulating RBC deformability and O2 carrying-releasing function. In this review article, we focus on the effect of NO bioactivity on RBC-based mechanisms that regulate blood flow and RBC deformability. RBC adaptations to hypoxia are summarized, with particular attention to NO-dependent S-nitrosylation of membrane proteins and hemoglobin (S-nitrosohemoglobin). The NO/S-nitrosylation/RBC vasoregulatory cascade contributes fundamentally to the molecular understanding of the role of NO in human adaptation to hypoxia and may inform novel therapeutic strategies.

Nitric oxide pathology and therapeutics in sickle cell disease

Sickle cell disease is caused by a mutant form of hemoglobin that polymerizes under hypoxic conditions which leads to red blood cell (RBC) distortion, calcium-influx mediated RBC dehydration, increased RBC adhesivity, reduced RBC deformability, increased RBC fragility, and hemolysis. These impairments in RBC structure and function result in multifaceted downstream pathology including inflammation, endothelial cell activation, platelet and leukocyte activation and adhesion, and thrombosis, all of which contribute vascular occlusion and substantial morbidity and mortality. Hemoglobin released upon RBC hemolysis scavenges nitric oxide (NO) and generates reactive oxygen species (ROS) and thereby decreases bioavailability of this important signaling molecule. As the endothelium-derived relaxing factor, NO acts as a vasodilator and also decreases platelet, leukocyte, and endothelial cell activation. Thus, low NO bioavailability contributes to pathology in sickle cell disease and its restoration could serve as an effective treatment. Despite its promise, clinical trials based on restoring NO bioavailability have so far been mainly disappointing. However, particular "NO donating" agents such as nitrite, which unlike some other NO donors can improve sickle RBC properties, may yet prove effective.

The cerebral collateral circulation: Relevance to pathophysiology and treatment of stroke

The brain's collateral circulation consists of arterial anastomotic channels capable of providing nutrient perfusion to brain regions whose normal sources of flow have become compromised, as occurs in acute ischemic stroke. Modern CT-based neuroimaging is capable of providing detailed information as to collateral extent and sufficiency and is complemented by magnetic resonance-based methods. In the present era of standard-of-care IV thrombolysis for acute ischemic stroke, and following the recent therapeutic successes of randomized clinical trials of acute endovascular intervention, the sufficiency of the collateral circulation has been convincingly established as a key factor influencing the likelihood of successful reperfusion and favorable clinical outcome. This article reviews the features of the brain's collateral circulation; methods for its evaluation in the acute clinical setting; the relevance of collateral circulation to prognosis in acute ischemic stroke; the specific insights into the collateral circulation learned from recent trials of endovascular intervention; and the major influence of genetic factors. Finally, we emphasize the need to develop therapeutic approaches to augment collateral perfusion as an adjunctive strategy to be employed along with, or prior to, thrombolysis and endovascular interventions, and we highlight the possible potential of inhaled nitric oxide, albumin, and other approaches. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Socio-environmental exposures and health outcomes among persons with sickle cell disease

There is much variability in the expression of sickle cell disease (SCD) and recent works suggest that environmental and social factors may also influence this variability. This paper aims to use geographic information systems technology to examine the association between socio-environmental exposures and health outcomes in all persons who have attended or currently attend the Sickle Cell Unit in Jamaica. Rural patients presented for clinical care at older ages and had less annual visits to clinic. Persons travelled relatively long distances to seek SCD care and those travelling longer had less health maintenance visits. Urban patients had a higher prevalence of significant pain crises (69.4% vs. 55.8%, p value<0.001) and respiratory events (21.2% vs. 14%, p value<0.001). Prevalence of leg ulcers did not vary between rural and urban patients but was higher in males than in females. Females also had lower odds of having respiratory events but there was no sex difference in history of painful crises. Persons with more severe genotypes lived in higher poverty and travelled longer for healthcare services. Persons in areas with higher annual rainfall, higher mean temperatures and living farther from factories had less painful crises and respiratory events. The paper highlights a need for better access to healthcare services for Jamaicans with SCD especially in rural areas of the island. It also reports interesting associations between environmental climatic exposures and health outcomes.

Expanding the concept of neuroprotection for acute ischemic stroke: The pivotal roles of reperfusion and the collateral circulation

This review surveys the efforts taken to achieve clinically efficacious protection of the ischemic brain and underscores the necessity of expanding our purview to include the essential role of cerebral perfusion and the collateral circulation. We consider the development of quantitative strategies to measure cerebral perfusion at the regional and local levels and the application of these methods to elucidate flow-related thresholds of ischemic viability and to characterize the ischemic penumbra. We stress that the modern concept of neuroprotection must consider perfusion, the necessary substrate upon which ischemic brain survival depends. We survey the major mechanistic approaches to neuroprotection and review clinical neuroprotection trials, focusing on those phase 3 multicenter clinical trials for acute ischemic stroke that have been completed or terminated. We review the evolution of thrombolytic therapies; consider the lessons learned from the initial, negative multicenter trials of endovascular therapy; and emphasize the highly successful positive trials that have finally established a clinical role for endovascular clot removal. As these studies point to the brain's collateral circulation as key to successful reperfusion, we next review the anatomy and pathophysiology of collateral perfusion as it relates to ischemic infarction, as well as the molecular and genetic influences on collateral development. We discuss the current MR and CT-based diagnostic methods for assessing the collateral circulation and the prognostic significance of collaterals in ischemic stroke, and we consider past and possible future therapeutic directions.

Supplementation with l-arginine stabilizes plasma arginine and nitric oxide metabolites, suppresses elevated liver enzymes and peroxidation in sickle cell anaemia

The effect of l-arginine on liver function in SCD has received little or no attention. The effect of a chronic, oral, low-dose supplementation with l-arginine (1gm/day for 6 weeks) on some liver enzymes, lipid peroxidation and nitric oxide metabolites was studied in 20 normal (non-sickle cell anaemia; NSCA) subjects and 20 sickle cell anaemia (SCA) subjects. Ten milliliters of blood was withdrawn from an ante-cubital vein for the estimation of plasma arginine concentration ([R]), alanine aminotransaminase (ALT), aspartate aminotransaminase (AST) and alkaline phosphatase (ALP), plasma total bilirubin concentration [TB], malondialdehyde concentration [MDA] and nitric oxide metabolites concentration [NOx]. Before supplementation, ALT, AST, ALP (p<0.05 respectively) and TB (p<0.001) were higher in SCA subjects than in NSCA subjects. [R] and [NOx] were higher in NSCA subjects (p<0.001 and p<0.05 respectively). Supplementation caused greater percent increases in [R], and [NOX] in SCA than in NSCA subjects (p<0.001 in each case). l-Arginine caused greater percent reductions in ALT and AST in SCA subjects but greater percent reduction in ALP in NSCA subjects (p<0.001 in each case). Changes in [MDA] and [TB] in the two groups were similar. Study shows that chronic, oral, low-dose supplementation with l-arginine improved liver function, oxidative stress, plasma arginine concentration and nitric oxide metabolites levels in NSCA and SCA subjects. Responses in SCA subjects to l-arginine were more sensitive than in NSCA subjects.

New strategies for the treatment of pulmonary hypertension in sickle cell disease : the rationale for arginine therapy

Nitric oxide (NO) is inactivated in sickle cell disease (SCD), while bioavailability of arginine, the substrate for NO synthesis, is diminished. Impaired NO bioavailability represents the central feature of endothelial dysfunction, and is a key factor in the pathophysiology of SCD. Inactivation of NO correlates with the hemolytic rate and is associated with erythrocyte release of cell-free hemoglobin and arginase during hemolysis. Accelerated consumption of NO is enhanced further by the inflammatory environment of oxidative stress that exists in SCD. Based upon its critical role in mediating vasodilation and cell growth, decreased NO bioavailability has also been implicated in the pathogenesis of pulmonary arterial hypertension (PHT). Secondary PHT is a common life-threatening complication of SCD that also occurs in most hereditary and chronic hemolytic disorders. Aberrant arginine metabolism contributes to endothelial dysfunction and PHT in SCD, and is strongly associated with prospective patient mortality. The central mechanism responsible for this metabolic disorder is enhanced arginine turnover, occurring secondary to enhanced plasma arginase activity. This is consistent with a growing appreciation of the role of excessive arginase activity in human diseases, including asthma and PHT. Decompartmentalization of hemoglobin into plasma consumes endothelial NO and thus drives a metabolic requirement for arginine, whose bioavailability is further limited by arginase activity. New treatments aimed at maximizing both arginine and NO bioavailability through arginase inhibition, suppression of hemolytic rate, or oral arginine supplementation may represent novel therapeutic strategies.

Drugs for preventing red blood cell dehydration in people with sickle cell disease

BACKGROUND

Sickle cell disease is an inherited disorder of hemoglobin, resulting in abnormal red blood cells. These are rigid and may block blood vessels leading to acute painful crises and other complications. Recent research has focused on therapies to rehydrate the sickled cells by reducing the loss of water and ions from them. Little is known about the effectiveness and safety of such drugs. This is an updated version of a previously published review.

OBJECTIVES

To assess the relative risks and benefits of drugs to rehydrate sickled red blood cells.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register.Last search of the Group's Trials Register: 28 November 2015.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of drugs to rehydrate sickled red blood cells compared to placebo or an alternative treatment.

DATA COLLECTION AND ANALYSIS

Both authors independently selected studies for inclusion, assessed study quality and extracted data.

MAIN RESULTS

Of the 51 studies identified, three met the inclusion criteria. The first study tested the effectiveness of zinc sulphate to prevent sickle cell-related crises in a total of 145 participants and showed a significant reduction in painful crises over one and a half years, mean difference -2.83 (95% confidence interval -3.51 to -2.15). However, analysis was restricted due to limited statistical data. Changes to red cell parameters and blood counts were inconsistent. No serious adverse events were noted in the study.The second study was a Phase II dose-finding study of senicapoc (a Gardos channel blocker) compared to placebo. Compared to the placebo group the high dose senicapoc showed significant improvement in change in hemoglobin level, number and proportion of dense red blood cells, red blood cell count and indices and hematocrit. The results with low-dose senicapoc were similar to the high-dose senicapoc group but of lesser magnitude. There was no difference in the frequency of painful crises between the three groups. A subsequent Phase III study of senicapoc was terminated early since there was no difference observed between the treatment and control groups in the primary end point of painful crises.

AUTHORS' CONCLUSIONS

While the results of zinc for reducing sickle-related crises are encouraging, larger and longer-term multicenter studies are needed to evaluate the effectiveness of this therapy for people with sickle cell disease.While the Phase II and the prematurely terminated phase III studies of senicapoc showed that the drug improved red cell survival (depending on dose), this did not lead to fewer painful crises.We will continue to run searches to identify any potentially relevant trials; however, we do not plan to update other sections of the review until new trials are published.

2015 Clinical trials update in sickle cell anemia

Polymerization of HbS and cell sickling are the prime pathophysiological events in sickle cell disease (SCD). Over the last 30 years, a substantial understanding at the molecular level has been acquired on how a single amino acid change in the structure of the beta chain of hemoglobin leads to the explosive growth of the HbS polymer and the associated changes in red cell morphology. O2 tension and intracellular HbS concentration are the primary molecular drivers of this process, and are obvious targets for developing new therapies. However, polymerization and sickling are driving a complex network of associated cellular changes inside and outside of the erythrocyte, which become essential components of the inflammatory vasculopathy and result in a large range of potential acute and chronic organ damages. In these areas, a multitude of new targets for therapeutic developments have emerged, with several ongoing or planned new therapeutic interventions. This review outlines the key points of SCD pathophysiology as they relate to the development of new therapies, both at the pre-clinical and clinical levels.

Endothelial Function and Vascular Properties in Children with Sickle Cell Disease

BACKGROUND

Sickle cell disease (SCD) is an inherited disorder characterized by recurrent painful crises with ischemia resulting from vascular occlusion. Adults with SCD have increased arterial stiffness and reduced flow-mediated dilation (FMD), due to impaired release of substances such as nitric oxide.

AIM

We aimed to assess the vascular properties of carotid and brachial arteries in children with SCD compared with a control group without cardiovascular risk factors.

METHODS

Thirty patients with SCD, mean age 12.3 ± 4.5 years, were prospectively enrolled. A control group was made up of 30 age- and gender-matched healthy subjects. Carotid intima-media thickness (IMT), cross-sectional compliance (CSC), cross-sectional distensibility (CSD), diastolic wall stress (DWS), incremental elastic modulus (Einc), and FMD were determined in both groups.

RESULTS

There was no significant difference in FMD between the two groups (8.2 ± 5.0% in the SCD group vs. 9.3 ± 4.2% in the control group, P = 0.15). There was no significant correlation between FMD and age, hemoglobin, LDH level, or transcranial Doppler findings. CSD was significantly elevated in the SCD group (0.96 ± 0.44 vs. 0.59 ± 0.21, P = 0.0002), whereas DWS and Einc were significantly lower in the SCD group. CSC did not differ significantly between the two groups.

CONCLUSIONS

Children with SCD have no marked endothelial dysfunction or change in arterial stiffness. These manifestations may be related to disease severity and duration. Changes may become evident later in life as the disease progresses.

Overlapping biological mechanisms underlying sickle cell disease, stress, and depression: a stress-vulnerability framework

After participating in this activity, learners should be better able to:1. Evaluate the overlap between sickle cell disease (SCD) and depression.2. Identify sources of psychological stress and biological vulnerabilities toward developing depression in patients with SCD.3. Assess the potential mechanisms underlying SCD, stress, and depression.Depression is a common co-occurring disorder in persons with sickle-cell disease (SCD). Individuals with this chronic illness may be particularly vulnerable to depression. In addition to risk factors for depression specifically related to SCD, these individuals typically experience further psychological stress due to multiple risk factors in their environment. To date, however, little research has focused on the co-occurring biological mechanisms across these conditions and how those mechanisms may interact to produce depressive symptoms. In this review we use a stress-vulnerability framework to describe the sources of psychological stress and the SCD factors that increase the risk of depression. We suggest that several biological factors, such as nitric oxide and cytokines, may play an important role in co-occurring stress, SCD, and depression. The interaction of these factors may be of particular importance for understanding the comorbidity of SCD and depression. Implications for current treatment and future research are discussed.

Glycosylation inhibitors efficiently inhibit P-selectin-mediated cell adhesion to endothelial cells

Adhesion molecules play a critical role in the adhesive interactions of multiple cell types in sickle cell disease (SCD). We previously showed that anti-P-selectin aptamer efficiently inhibits cell adhesion to endothelial cells (ECs) and permits SCD mice to survive hypoxic stress. In an effort to discover new mechanisms with which to inhibit P-selectin, we examined the role of glycosylation. P-selectin is a 90 kDa protein but was found to migrate as 90 and 140 kDa bands on gel electrophoresis. When P-selectin isolated from ECs was digested with peptide N-glycosidase F, but not O-glycosidase, the 140 kDa band was lost and the 90 kDa band was enhanced. Treatment of ECs with tunicamycin, an N-glycosylation inhibitor, suppressed CD62P (P-selectin) expression on the cell surface as well as the 140 kDa form in the cytoplasm. These results indicate that the 140 kDa band is N-glycosylated and glycosylation is critical for cell surface expression of P-selectin in ECs. Thrombin, which stimulates P-selectin expression on ECs, induced AKT phosphorylation, whereas tunicamycin inhibited AKT phosphorylation, suggesting that AKT signaling is involved in the tunicamycin-mediated inhibition of P-selectin expression. Importantly, the adhesion of sickle red blood cells (sRBCs) and leukocytes to ECs induced by thrombin or hypoxia was markedly inhibited by two structurally distinct glycosylation inhibitors; the levels of which were comparable to that of a P-selectin monoclonal antibody which most strongly inhibited cell adhesion in vivo. Knockdown studies of P-selectin using short-hairpin RNAs in ECs suppressed sRBC adhesion, indicating a legitimate role for P-selectin in sRBC adhesion. Together, these results demonstrate that P-selectin expression on ECs is regulated in part by glycosylation mechanisms and that glycosylation inhibitors efficiently reduce the adhesion of sRBCs and leukocytes to ECs. Glycosylation inhibitors may lead to a novel therapy which inhibits cell adhesion in SCD.

Molecular mechanisms underlying synergistic adhesion of sickle red blood cells by hypoxia and low nitric oxide bioavailability

The molecular mechanisms by which nitric oxide (NO) bioavailability modulates the clinical expression of sickle cell disease (SCD) remain elusive. We investigated the effect of hypoxia and NO bioavailability on sickle red blood cell (sRBC) adhesion using mice deficient for endothelial NO synthase (eNOS) because their NO metabolite levels are similar to those of SCD mice but without hypoxemia. Whereas sRBC adhesion to endothelial cells in eNOS-deficient mice was synergistically upregulated at the onset of hypoxia, leukocyte adhesion was unaffected. Restoring NO metabolite levels to physiological levels markedly reduced sRBC adhesion to levels seen under normoxia. These results indicate that sRBC adherence to endothelial cells increases in response to hypoxia prior to leukocyte adherence, and that low NO bioavailability synergistically upregulates sRBC adhesion under hypoxia. Although multiple adhesion molecules mediate sRBC adhesion, we found a central role for P-selectin in sRBC adhesion. Hypoxia and low NO bioavailability upregulated P-selectin expression in endothelial cells in an additive manner through p38 kinase pathways. These results demonstrate novel cellular and signaling mechanisms that regulate sRBC adhesion under hypoxia and low NO bioavailability. Importantly, these findings point us toward new molecular targets to inhibit cell adhesion in SCD.

Oxidative stress in sickle cell disease: an overview of erythrocyte redox metabolism and current antioxidant therapeutic strategies

Erythrocytes have an environment of continuous pro-oxidant generation due to the presence of hemoglobin (Hb), which represents an additional and quantitatively significant source of superoxide (O2(-)) generation in biological systems. To counteract oxidative stress, erythrocytes have a self-sustaining antioxidant defense system. Thus, red blood cells uniquely function to protect Hb via a selective barrier allowing gaseous and other ligand transport as well as providing antioxidant protection not only to themselves but also to other tissues and organs in the body. Sickle hemoglobin molecules suffer repeated polymerization/depolymerization generating greater amounts of reactive oxygen species, which can lead to a cyclic cascade characterized by blood cell adhesion, hemolysis, vaso-occlusion, and ischemia-reperfusion injury. In other words, sickle cell disease is intimately linked to a pathophysiologic condition of multiple sources of pro-oxidant processes with consequent chronic and systemic oxidative stress. For this reason, newer therapeutic agents that can target oxidative stress may constitute a valuable means for preventing or delaying the development of organ complications.

Updated role of nitric oxide in disorders of erythrocyte function

Nitric oxide is a potent vasodilator that plays a critical role in disorders of erythrocyte function. Sickle cell disease, paroxysmal nocturnal hemoglobinuria and banked blood preservation are three conditions where nitric oxide is intimately related to dysfunctional erythrocytes. These conditions are accompanied by hemolysis, thrombosis and vasoocclusion. Our understanding of the interaction between nitric oxide, hemoglobin, and the vasculature is constantly evolving, and by defining this role we can better direct trials aimed at improving the treatments of disorders of erythrocyte function. Here we briefly discuss nitric oxide's interaction with hemoglobin through the hypothesis regarding Snitrosohemoglobin, deoxyhemoglobin, and myoglobin as nitrite reductases. We then review the current understanding of the role of nitric oxide in sickle cell disease, paroxysmal nocturnal hemoglobinuria, and banked blood, and discuss therapeutics in development to target nitric oxide in the treatment of some of these disorders.

A pilot study of eptifibatide for treatment of acute pain episodes in sickle cell disease

INTRODUCTION

The contribution of platelet activation to the pathogenesis of sickle cell disease (SCD) remains uncertain. We evaluated the safety and efficacy of eptifibatide, a synthetic peptide inhibitor of the αIIbβ3 receptor, in SCD patients during acute painful episodes.

MATERIALS AND METHODS

In this single site, double-blind, placebo-controlled trial, eligible patients with SCD admitted for acute painful episodes were randomized to receive eptifibatide or placebo at a ratio of 2:1.

RESULTS

Thirteen patients (SS - 10, Sβ(0) - 2, SC - 1) were randomized to receive either eptifibatide (N=9; 6 females; median age - 25years) or placebo (N=4; 3 females; median age - 31years). In the intent-to-treat analysis, there were no major bleeding episodes in either the eptifibatide or placebo arms (point estimate of difference: 0.00, 95% CI; -0.604, 0.372). There was one minor bleeding episode in the eptifibatide arm (point estimate of difference for any bleeding: 0.11, 95% CI: -0.502, 0.494). There was no significant difference in the proportion of patients with thrombocytopenia between the treatment groups (point estimate of difference: 0.11, 95% CI: -0.587, 0.495). There were no differences in the median times to discharge, median times to crisis resolution or the median total opioid use.

CONCLUSIONS

In this small study, eptifibatide appeared to be safe, but did not improve the times to crisis resolution or hospital discharge. Adequately powered studies are required to evaluate the safety and efficacy of eptifibatide in SCD. Clinicaltrials.gov Identifier: NCT00834899.

Biologic complexity in sickle cell disease: implications for developing targeted therapeutics

Current therapy for sickle cell disease (SCD) is limited to supportive treatment of complications, red blood cell transfusions, hydroxyurea, and stem cell transplantation. Difficulty in the translation of mechanistically based therapies may be the result of a reductionist approach focused on individual pathways, without having demonstrated their relative contribution to SCD complications. Many pathophysiologic processes in SCD are likely to interact simultaneously to contribute to acute vaso-occlusion or chronic vasculopathy. Applying concepts of systems biology and network medicine, models were developed to show relationships between the primary defect of sickle hemoglobin (Hb S) polymerization and the outcomes of acute pain and chronic vasculopathy. Pathophysiologic processes such as inflammation and oxidative stress are downstream by-products of Hb S polymerization, transduced through secondary pathways of hemolysis and vaso-occlusion. Pain, a common clinical trials endpoint, is also complex and may be influenced by factors outside of sickle cell polymerization and vascular occlusion. Future sickle cell research needs to better address the biologic complexity of both sickle cell disease and pain. The relevance of individual pathways to important sickle cell outcomes needs to be demonstrated in vivo before investing in expensive and labor-intensive clinical trials.

Beyond the definitions of the phenotypic complications of sickle cell disease: an update on management

The sickle hemoglobin is an abnormal hemoglobin due to point mutation (GAG → GTG) in exon 1 of the β globin gene resulting in the substitution of glutamic acid by valine at position 6 of the β globin polypeptide chain. Although the molecular lesion is a single-point mutation, the sickle gene is pleiotropic in nature causing multiple phenotypic expressions that constitute the various complications of sickle cell disease in general and sickle cell anemia in particular. The disease itself is chronic in nature but many of its complications are acute such as the recurrent acute painful crises (its hallmark), acute chest syndrome, and priapism. These complications vary considerably among patients, in the same patient with time, among countries and with age and sex. To date, there is no well-established consensus among providers on the management of the complications of sickle cell disease due in part to lack of evidence and in part to differences in the experience of providers. It is the aim of this paper to review available current approaches to manage the major complications of sickle cell disease. We hope that this will establish another preliminary forum among providers that may eventually lead the way to better outcomes.

Drugs for preventing red blood cell dehydration in people with sickle cell disease

BACKGROUND

Sickle cell disease is an inherited disorder of hemoglobin, resulting in abnormal red blood cells. These are rigid and may block blood vessels leading to acute painful crises and other complications. Recent research has focused on therapies to rehydrate the sickled cells by reducing the loss of water and ions from them. Little is known about the effectiveness and safety of such drugs.

OBJECTIVES

To assess the relative risks and benefits of drugs to rehydrate sickled red blood cells.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register.Last search of the Group's Trials Register: 25 October 2011.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of drugs to rehydrate sickled red blood cells compared to placebo or an alternative treatment.

DATA COLLECTION AND ANALYSIS

Both authors independently selected studies for inclusion, assessed study quality and extracted data.

MAIN RESULTS

Of the 51 studies identified, three met the inclusion criteria. The first study tested the effectiveness of zinc sulphate to prevent sickle cell-related crises in a total of 145 participants and showed a significant reduction in painful crises over one and a half years, mean difference -2.83 (95% confidence interval -3.51 to -2.15). However, analysis was restricted due to limited statistical data. Changes to red cell parameters and blood counts were inconsistent. No serious adverse events were noted in the study.The second study was a Phase II dose-finding study of senicapoc (a Gardos channel blocker) compared to placebo. Compared to the placebo group the high dose senicapoc showed significant improvement in change in hemoglobin level, number and proportion of dense red blood cells, red blood cell count and indices and hematocrit. The results with low-dose senicapoc were similar to the high-dose senicapoc group but of lesser magnitude. There was no difference in the frequency of painful crises between the three groups. A subsequent Phase III study of senicapoc was terminated early since there was no difference observed between the treatment and control groups in the primary end point of painful crises.

AUTHORS' CONCLUSIONS

While the results of zinc for reducing sickle-related crises are encouraging, larger and longer-term multicenter studies are needed to evaluate the effectiveness of this therapy for people with sickle cell disease.While the Phase II and the prematurely terminated phase III studies of senicapoc showed that the drug improved red cell survival (depending on dose), this did not lead to fewer painful crises.

Unlocking the binding and reaction mechanism of hydroxyurea substrates as biological nitric oxide donors

Hydroxyurea is the only FDA approved treatment of sickle cell disease. It is believed that the primary mechanism of action is associated with the pharmacological elevation of nitric oxide in the blood; however, the exact details of this are still unclear. In the current work, we investigate the atomic level details of this process using a combination of flexible-ligand/flexible-receptor virtual screening coupled with energetic analysis that decomposes interaction energies. Utilizing these methods, we were able to elucidate the previously unknown substrate binding modes of a series of hydroxyurea analogs to hemoglobin and the concomitant structural changes of the enzyme. We identify a backbone carbonyl that forms a hydrogen bond with bound substrates. Our results are consistent with kinetic and electron paramagnetic resonance (EPR) measurements of hydroxyurea-hemoglobin reactions, and a full mechanism is proposed that offers new insights into possibly improving substrate binding and/or reactivity.

Pulmonary complications of sickle cell disease

Sickle cell disease (SCD) is a common monogenetic disorder with high associated morbidity and mortality. The pulmonary complications of SCD are of particular importance, as acute chest syndrome and pulmonary hypertension have the highest associated mortality rates within this population. This article reviews the pathophysiology, diagnosis, and treatment of clinically significant pulmonary manifestations of SCD, including acute chest syndrome, asthma, and pulmonary hypertension in adult and pediatric patients. Clinicians should be vigilant in screening and treating such comorbidities to improve patient outcomes.

Management of children with sickle cell disease: a comprehensive review of the literature

OBJECTIVE

Sickle cell disease (SCD) affects 70 000 to 100 000 people in the United States, and 2000 infants are born with the disease each year. The purpose of this study was to review the quality of the literature for preventive interventions and treatment of complications for children with SCD to facilitate the use of evidence-based medicine in clinical practice and identify areas in need of additional research.

METHODS

We searched the Ovid Medline database and the Cochrane Library for articles published between January 1995 and April 2010 for English-language abstracts on 28 topics thought to be important for the care of children with SCD. We also added pertinent references cited by studies identified in our search. Each abstract was reviewed independently by 2 authors. Data from articles retrieved for full review were abstracted by using a common form.

RESULTS

There were 3188 abstracts screened, and 321 articles underwent full review. Twenty-six articles (<1% of abstracts initially screened), which consisted of 25 randomized controlled trials and 1 meta-analysis, were rated as having level I evidence. Eighteen of the 28 topics selected for this review did not have level I evidence studies published. The management and prevention of pain episodes accounted for more than one-third of the level I studies.

CONCLUSIONS

Although significant strides have been made in the care of children with SCD in the past 2 decades, more research needs to be performed, especially for acute events associated with SCD, to ensure that the health and well-being of children with SCD continues to improve.