Pathophisiology of sickle cell disease and new drugs for the treatment

Evaluating sheep hemoglobins with MD simulations as an animal model for sickle cell disease

Sickle cell disease (SCD) affects millions worldwide, yet there are few therapeutic options. To develop effective treatments, preclinical models that recapitulate human physiology and SCD pathophysiology are needed. SCD arises from a single Glu-to-Val substitution at position 6 in the β subunit of hemoglobin (Hb), promoting Hb polymerization and subsequent disease. Sheep share important physiological and developmental characteristics with humans, including the same developmental pattern of fetal to adult Hb switching. Herein, we investigated whether introducing the SCD mutation into the sheep β-globin locus would recapitulate SCD's complex pathophysiology by generating high quality SWISS-MODEL sheep Hb structures and performing MD simulations of normal/sickle human (huHbA/huHbS) and sheep (shHbB/shHbS) Hb, establishing how accurately shHbS mimics huHbS behavior. shHbS, like huHbS, remained stable with low RMSD, while huHbA and shHbB had higher and fluctuating RMSD. shHbB and shHbS also behaved identically to huHbA and huHbS with respect to β2-Glu6 and β1-Asp73 (β1-Asn72 in sheep) solvent interactions. These data demonstrate that introducing the single SCD-causing Glu-to-Val substitution into sheep β-globin causes alterations consistent with the Hb polymerization that drives RBC sickling, supporting the development of a SCD sheep model to pave the way for alternative cures for this debilitating, globally impactful disease.

Targeted modification of furan-2-carboxaldehydes into Michael acceptor analogs yielded long-acting hemoglobin modulators with dual antisickling activities

Sickle cell disease (SCD) is the most common genetic disorder, affecting millions of people worldwide. Aromatic aldehydes, which increase the oxygen affinity of human hemoglobin to prevent polymerization of sickle hemoglobin and inhibit red blood cell (RBC) sickling, have been the subject of keen interest for the development of effective treatment against SCD. However, the aldehyde functional group metabolic instability has severly hampered their development, except for voxelotor, which was approved in 2019 for SCD treatment. To improve the metabolic stability of aromatic aldehydes, we designed and synthesized novel molecules by incorporating Michael acceptor reactive centers into the previously clinically studied aromatic aldehyde, 5-hydroxymethylfurfural (5-HMF). Eight such derivatives, referred to as MMA compounds were synthesized and studied for their functional and biological activities. Unlike 5-HMF, which forms Schiff-base interaction with αVal1 nitrogen of hemoglobin, the MMA compounds covalently interacted with βCys93, as evidenced by reverse-phase HPLC and disulfide exchange reaction, explaining their RBC sickling inhibitory activities, which at 2 mM and 5 mM, range from 0% to 21% and 9% to 64%, respectively. Additionally, the MMA compounds showed a second mechanism of sickling inhibition (12%-41% and 13%-62% at 2 mM and 5 mM, respectively) by directly destabilizing the sickle hemoglobin polymer. In vitro studies demonstrated sustained pharmacologic activities of the compounds compared to 5-HMF. These findings hold promise for advancing SCD therapeutics.

Ellagic Acid Exerts Dual Action to Curb the Pathophysiological Manifestations of Sickle Cell Disease and Attenuate the Hydroxyurea-Induced Myelosuppression in Berkeley Mice

The use of adjuvant therapy is an attractive approach to manage sickle cell disease (SCD) symptomatically. The present study aimed to investigate the potential of ellagic acid as an adjuvant therapy with hydroxyurea (HU), a key drug for SCD with myelosuppressive toxic effects. A panel of experiments was performed using SCD patient's blood (ex vivo) and transgenic mice model of SCD (in vivo). Ellagic acid exhibited the following beneficial pharmacological actions: (a) potent anti-sickling, polymerization inhibitory, and inherent non-hemolytic activity; (b) pronounced action to abrogate HU-induced neutropenia and to improve key hematological parameters during SCD (RBC, Hb, platelet levels); (c) considerable action to foster vascular tone (L-proline); (d) marked attenuating effect against oxidative stress (nitrotyrosine, hypoxanthine, MDA, GSH); (e) substantial inhibitory role against inflammation (analgesic activity and regulation of hemin, TNF-α, IL-1β, NF-κB/IκBα); (f) remarkable outcome of declining vaso-occlusive crisis (P-selectin, ERK1/2); (g) notable shielding deed against elevated biochemical marker for organ toxicity (creatinine); (h) noticeably prevented histopathological alterations of the spleen. Additionally, the pharmacokinetic study results of HU in the presence and absence of ellagic acid using a mouse model demonstrate that ellagic acid could be safely co-administered with HU. Overall findings suggest that ellagic acid is a promising candidate for adjuvant therapy in SCD based on its own significant ability against SCD and potentiating capability of HU action via targeting improvement at the various stages of pathophysiological complications during SCD and minimizing HU-induced toxicological manifestations.

X-ray crystallography and sickle cell disease drug discovery-a tribute to Donald Abraham

X-ray crystallography and structure-based drug discovery have played a major role in the discovery of antisickling agents that target hemoglobin (Hb) for the treatment of sickle cell disease (SCD). Sickle cell disease, the most common inherited hematologic disorder, occurs as a result of a single point mutation of βGlu6 in normal human adult hemoglobin (HbA) to βVal6 in sickle hemoglobin (HbS). The disease is characterized by polymerization of HbS and sickling of red blood cells (RBCs), leading to several secondary pathophysiologies, including but not limited to vaso-occlusion, hemolytic anemia, oxidative stress, inflammation, stroke, pain crisis, and organ damage. Despite the fact that SCD was the first disease to have its molecular basis established, the development of therapies was for a very long time a challenge and took several decades to find therapeutic agents. The determination of the crystal structure of Hb by Max Perutz in the early 60s, and the pioneering X-ray crystallography research by Donald J. Abraham in the early 80s, which resulted in the first structures of Hb in complex with small molecule allosteric effectors of Hb, gave much hope that structure-based drug discovery (SBDD) could be used to accelerate development of antisickling drugs that target the primary pathophysiology of hypoxia-induced HbS polymerization to treat SCD. This article, which is dedicated to Donald J. Abraham, briefly reviews structural biology, X-ray crystallography and structure-based drug discovery from the perspective of Hb. The review also presents the impact of X-ray crystallography in SCD drug development using Hb as a target, emphasizing the major and important contributions by Don Abraham in this field.

Design, Synthesis, and Investigation of Novel Nitric Oxide (NO)-Releasing Aromatic Aldehyde as Drug Candidates for the Treatment of Sickle Cell Disease

Sickle cell disease (SCD) is caused by a single-point mutation, and the ensuing deoxygenation-induced polymerization of sickle hemoglobin (HbS), and reduction in bioavailability of vascular nitric oxide (NO), contribute to the pathogenesis of the disease. In a proof-of-concept study, we successfully incorporated nitrate ester groups onto two previously studied potent antisickling aromatic aldehydes, TD7 and VZHE039, to form TD7-NO and VZHE039-NO hybrids, respectively. These compounds are stable in buffer but demonstrated the expected release of NO in whole blood in vitro and in mice. The more promising VZHE039-NO retained the functional and antisickling activities of the parent VZHE039 molecule. Moreover, VZHE039-NO, unlike VZHE039, significantly attenuated RBC adhesion to laminin, suggesting this compound has potential in vivo RBC anti-adhesion properties relevant to vaso-occlusive events. Crystallographic studies show that, as with VZHE039, VZHE039-NO also binds to liganded Hb to make similar protein interactions. The knowledge gained during these investigations provides a unique opportunity to generate a superior candidate drug in SCD with enhanced benefits.

Metabolic Reprogramming in Sickle Cell Diseases: Pathophysiology and Drug Discovery Opportunities

Sickle cell disease (SCD) is a genetic disorder that affects millions of individuals worldwide. Chronic anemia, hemolysis, and vasculopathy are associated with SCD, and their role has been well characterized. These symptoms stem from hemoglobin (Hb) polymerization, which is the primary event in the molecular pathogenesis of SCD and contributes to erythrocyte or red blood cell (RBC) sickling, stiffness, and vaso-occlusion. The disease is caused by a mutation at the sixth position of the β-globin gene, coding for sickle Hb (HbS) instead of normal adult Hb (HbA), which under hypoxic conditions polymerizes into rigid fibers to distort the shapes of the RBCs. Only a few therapies are available, with the universal effectiveness of recently approved therapies still being monitored. In this review, we first focus on how sickle RBCs have altered metabolism and then highlight how this understanding reveals potential targets involved in the pathogenesis of the disease, which can be leveraged to create novel therapeutics for SCD.

Design, Synthesis, and Antisickling Investigation of a Nitric Oxide-Releasing Prodrug of 5HMF for the Treatment of Sickle Cell Disease

5-hydroxyfurfural (5HMF), an allosteric effector of hemoglobin (Hb) with an ability to increase Hb affinity for oxygen has been studied extensively for its antisickling effect in vitro and in vivo, and in humans for the treatment of sickle cell disease (SCD). One of the downstream pathophysiologies of SCD is nitric oxide (NO) deficiency, therefore increasing NO (bio)availability is known to mitigate the severity of SCD symptoms. We report the synthesis of an NO-releasing prodrug of 5HMF (5HMF-NO), which in vivo, is expected to be bio-transformed into 5HMF and NO, with concomitant therapeutic activities. In vitro studies showed that when incubated with whole blood, 5HMF-NO releases NO, as anticipated. When incubated with sickle blood, 5HMF-NO formed Schiff base adduct with Hb, increased Hb affinity for oxygen, and prevented hypoxia-induced erythrocyte sickling, which at 1 mM concentration were 16%, 10% and 27%, respectively, compared to 21%, 18% and 21% for 5HMF. Crystal structures of 5HMF-NO with Hb showed 5HMF-NO bound to unliganded (deoxygenated) Hb, while the hydrolyzed product, 5HMF bound to liganded (carbonmonoxy-ligated) Hb. Our findings from this proof-of-concept study suggest that the incorporation of NO donor group to 5HMF and analogous molecules could be a novel beneficial strategy to treat SCD and warrants further detailed in vivo studies.

Altered Ca2+ Homeostasis in Red Blood Cells of Polycythemia Vera Patients Following Disturbed Organelle Sorting during Terminal Erythropoiesis

Over 95% of Polycythemia Vera (PV) patients carry the V617F mutation in the tyrosine kinase Janus kinase 2 (JAK2), resulting in uncontrolled erythroid proliferation and a high risk of thrombosis. Using mass spectrometry, we analyzed the RBC membrane proteome and showed elevated levels of multiple Ca2+ binding proteins as well as endoplasmic-reticulum-residing proteins in PV RBC membranes compared with RBC membranes from healthy individuals. In this study, we investigated the impact of JAK2V617F on (1) calcium homeostasis and RBC ion channel activity and (2) protein expression and sorting during terminal erythroid differentiation. Our data from automated patch-clamp show modified calcium homeostasis in PV RBCs and cell lines expressing JAK2V617F, with a functional impact on the activity of the Gárdos channel that could contribute to cellular dehydration. We show that JAK2V617F could play a role in organelle retention during the enucleation step of erythroid differentiation, resulting in modified whole cell proteome in reticulocytes and RBCs in PV patients. Given the central role that calcium plays in the regulation of signaling pathways, our study opens new perspectives to exploring the relationship between JAK2V617F, calcium homeostasis, and cellular abnormalities in myeloproliferative neoplasms, including cellular interactions in the bloodstream in relation to thrombotic events.

Improving the Solubility and Oral Bioavailability of a Novel Aromatic Aldehyde Antisickling Agent (PP10) for the Treatment of Sickle Cell Disease

BACKGROUND

Aromatic aldehydes, with their ability to increase the oxygen affinity of sickle hemoglobin, have become important therapeutic agents for sickle cell disease (SCD). One such compound, voxelotor, was recently approved for SCD treatment. Methyl 6-((2-formyl-3-hydroxyphenoxy)methyl) picolinate (PP10) is another promising aromatic aldehyde, recently reported by our group. Like voxelotor, PP10 exhibits O2-dependent antisickling activity, but, unlike voxelotor, PP10 shows unique O2-independent antisickling effect. PP10, however, has limited solubility. This study therefore aimed to develop oral and parenteral formulations to improve PP10 solubility and bioavailability.

METHODS

Oral drug tablets with 2-hydroxypropyl beta cyclodextrin (HP-β-CD), polyvinylpyrrolidone, or Eudragit L100-55 PP10-binary system, and an intravenous (IV) formulation with d-α-tocopherol polyethylene glycol 1000 succinate (TPGS) or HP-β-CD, were developed. The pharmacokinetic behavior of the formulations was studied in Sprague-Dawley rats. PP10, a methylester, and its acid metabolite were also studied in vitro with sickle whole blood to determine their effect on Hb modification, Hb oxygen affinity, and sickle red blood cell inhibition.

RESULTS

Aqueous solubility of PP10 was enhanced ~5 times with the HP-β-CD binary system, while the TPGS aqueous micelle formulation was superior, with a drug concentration of 0.502 ± 0.01 mg/mL and a particle size of 26 ± 3 nm. The oral tablets showed relative and absolute bioavailabilities of 173.4% and 106.34%, respectively. The acid form of PP10 appeared to dominate in vivo, although both PP10 forms demonstrated pharmacologic effect.

CONCLUSION

Oral and IV formulations of PP10 were successfully developed using HP-β-CD binary system and TPGS aqueous micelles, respectively, resulting in significantly improved solubility and bioavailability.

An Investigation of Structure-Activity Relationships of Azolylacryloyl Derivatives Yielded Potent and Long-Acting Hemoglobin Modulators for Reversing Erythrocyte Sickling

Aromatic aldehydes that bind to sickle hemoglobin (HbS) to increase the protein oxygen affinity and/or directly inhibit HbS polymer formation to prevent the pathological hypoxia-induced HbS polymerization and the subsequent erythrocyte sickling have for several years been studied for the treatment of sickle cell disease (SCD). With the exception of Voxelotor, which was recently approved by the U.S. Food and Drug Administration (FDA) to treat the disease, several other promising antisickling aromatic aldehydes have not fared well in the clinic because of metabolic instability of the aldehyde moiety, which is critical for the pharmacologic activity of these compounds. Over the years, our group has rationally developed analogs of aromatic aldehydes that incorporate a stable Michael addition reactive center that we hypothesized would form covalent interactions with Hb to increase the protein affinity for oxygen and prevent erythrocyte sickling. Although, these compounds have proven to be metabolically stable, unfortunately they showed weak to no antisickling activity. In this study, through additional targeted modifications of our lead Michael addition compounds, we have discovered other novel antisickling agents. These compounds, designated MMA, bind to the α-globin and/or β-globin to increase Hb affinity for oxygen and concomitantly inhibit erythrocyte sickling with significantly enhanced and sustained pharmacologic activities in vitro.

Hemoglobin: Structure, Function and Allostery

This chapter reviews how allosteric (heterotrophic) effectors and natural mutations impact hemoglobin (Hb) primary physiological function of oxygen binding and transport. First, an introduction about the structure of Hb is provided, including the ensemble of tense and relaxed Hb states and the dynamic equilibrium of Hb multistate. This is followed by a brief review of Hb variants with altered Hb structure and oxygen binding properties. Finally, a review of different endogenous and exogenous allosteric effectors of Hb is presented with particular emphasis on the atomic interactions of synthetic ligands with altered allosteric function of Hb that could potentially be harnessed for the treatment of diseases.

Serum Potassium, Sodium, and Chloride Levels in Sickle Cell Disease Patients and Healthy Controls: A Case-Control Study at Korle-Bu Teaching Hospital, Accra

The activity of Na⁺-K⁺ ATPase is altered in sickle cell disease (SCD), which affects serum electrolyte levels. This alteration is associated with several complications in sickle cell patients. This study evaluated the serum levels of sodium, potassium, and chloride in patients with SCD. The study was a case-control cross-sectional study involving 120 SCD patients in the steady state and 48 ‘healthy’ controls. The SCD patients were made up of 69 HbSS patients and 41 HbSC patients. Serum electrolyte levels (Na⁺, K⁺, and Cl⁻) were measured using a Flame Atomic Absorption Spectrometer (Variant 240FS; Varian Australia Pty Ltd). Serum sodium levels were significantly lower in the sickle cell patients, compared with their ‘healthy’ counterparts (P = .0001). Although the study found significantly higher serum levels of potassium in the SCD patients (P = .0001), there was no significant difference in serum chloride levels between patients with SCD and the controls (P = .098). Serum sodium and chloride levels were not significantly different in both HbSS and HbSC patients (P = .197 and P = .553, respectively). The level of serum potassium in the HbSS patients was, however, significantly higher compared with those with the HbSC genotype (P = .0001). There is higher efflux of K⁺ from the intracellular into the extracellular space in HbSS patients, which may lead to red cell membrane dysfunction and associated complications.

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.

Red Blood Cell and Serum Magnesium Levels Among Children and Adolescents With Sickle Cell Anemia

Patients with sickle cell anemia (SCA) can acquire many biochemical abnormalities, including altered magnesium levels. However, the roles of magnesium in the pathogenesis and management of SCA need to be determined. The aim of this work was to evaluate magnesium levels among pediatric patients with SCA in Basra, Iraq. The study employed a case-control design and examined 87 patients with SCA (3-15 years old) who had attended the Basra Center for Hereditary Blood Diseases while in a steady state and 90 apparently healthy control subjects. Complete blood count, red blood cell (RBC), and serum magnesium, calcium, potassium, sodium, zinc, and copper levels were measured in all subjects. The results revealed significantly lower RBC and serum magnesium levels among the patients with SCA (3.62 ± 0.42 and 1.35 ± 0.19 mg/dL, respectively) than those among the control subjects (4.47 ± 0.55 and 1.87 ± 0.27 mg/dL, respectively). In addition, compared to the control subjects, the patients with SCA had significantly lower serum levels of potassium, sodium, and zinc; significantly higher serum levels of copper; and significantly higher Ca/Mg and Na/Mg ratios. Among the SCA patients, the RBC magnesium level was significantly negatively associated with the frequencies of vaso-occlusive crises (r = - 0.423, P < 0.001) and disease-related hospitalization (r = - 0.225, P < 0.05). To conclude, the RBC magnesium level, but not the serum magnesium level, is significantly associated with vaso-occlusive crises and hospitalization. Therefore, screening and management of low RBC magnesium levels in SCA patients are required.

Adenotonsillar Hypertrophy in Pre-School Children with Sickle Cell Disease and Diagnostic Accuracy of the Sleep Disturbance Scale for Children

Introduction  Adenotonsillar hypertrophy is more common in children with sickle cell disease, and can lead to sleep-disordered breathing.

Objectives  To determine the frequency of adenotonsillar hypertrophy in pre-school children with sickle cell disease and assess the diagnostic accuracy of the sleep-disordered breathing subscale in the Sleep Disturbance Scale for Children.

Method  Observational study with a group of 48 children with sickle cell disease and a control group of 35 children without the disease. The children underwent oropharingoscopy and video nasal endoscopy. The parents and/or guardians answered the questions of the subscale.

Results  Adenotonsillar hypertrophy was observed in 25% of the children in the study group, and in 20% of the children in the control group, with no statistical difference between the groups. The subscale score ranged from 3 to 11 in both groups. There was a statistical significance in the study group. The average was 4.79 (standard deviation [SD] ± 2.50), with 4.19 (SD ± 1.72) among the children without adenotonsillar hypertrophy, and 6.5 (SD ± 3.40) among the children with adenotonsillar hypertrophy. There was also a statistical significance in the control group. The average was 5.23 (SD ± 2.81), with 4.44 (SD ± 2.2) among the children without adenotonsillar hypertrophy, and 7.87 (SD ± 2.89) among the children with adenotonsillar hypertrophy.

Conclusion  Adenotonsillar hypertrophy was not associated with sickle cell disease in pre-school children. The subscale of sleep-disordered breathing in the Sleep Disturbance Scale for Children was a useful tool for the diagnostic suspicion of adenotonsillar hypertrophy in children in this age group.

From Erythroblasts to Mature Red Blood Cells: Organelle Clearance in Mammals

Erythropoiesis occurs mostly in bone marrow and ends in blood stream. Mature red blood cells are generated from multipotent hematopoietic stem cells, through a complex maturation process involving several morphological changes to produce a highly functional specialized cells. In mammals, terminal steps involved expulsion of the nucleus from erythroblasts that leads to the formation of reticulocytes. In order to produce mature biconcave red blood cells, organelles and ribosomes are selectively eliminated from reticulocytes as well as the plasma membrane undergoes remodeling. The mechanisms involved in these last maturation steps are still under investigation. Enucleation involves dramatic chromatin condensation and establishment of the nuclear polarity, which is driven by a rearrangement of actin cytoskeleton and the clathrin-dependent generation of vacuoles at the nuclear-cytoplasmic junction. This process is favored by interaction between the erythroblasts and macrophages at the erythroblastic island. Mitochondria are eliminated by mitophagy. This is a macroautophagy pathway consisting in the engulfment of mitochondria into a double-membrane structure called autophagosome before degradation. Several mice knock-out models were developed to identify mitophagy-involved proteins during erythropoiesis, but whole mechanisms are not completely determined. Less is known concerning the clearance of other organelles, such as smooth and rough ER, Golgi apparatus and ribosomes. Understanding the modulators of organelles clearance in erythropoiesis may elucidate the pathogenesis of different dyserythropoietic diseases such as myelodysplastic syndrome, leukemia and anemia.

Design, Synthesis, and Biological Evaluation of Ester and Ether Derivatives of Antisickling Agent 5-HMF for the Treatment of Sickle Cell Disease

Candidate drugs to counter intracellular polymerization of deoxygenated sickle hemoglobin (Hb S) continue to represent a promising approach to mitigating the primary cause of the pathophysiology associated with sickle cell disease (SCD). One such compound is the naturally occurring antisickling agent, 5-hydroxymethyl-2-furfural (5-HMF), which has been studied in the clinic for the treatment of SCD. As part of our efforts to develop novel efficacious drugs with improved pharmacologic properties, we structurally modified 5-HMF into 12 ether and ester derivatives. The choice of 5-HMF as a pharmacophore was influenced by a combination of its demonstrated attractive hemoglobin modifying and antisickling properties, well-known safety profiles, and its reported nontoxic major metabolites. The derivatives were investigated for their time- and/or dose-dependent effects on important antisickling parameters, such as modification of hemoglobin, corresponding changes in oxygen affinity, and inhibition of red blood cell sickling. The novel test compounds bound and modified Hb and concomitantly increased the protein affinity for oxygen. Five of the derivatives exhibited 1.5- to 4.0-fold higher antisickling effects than 5-HMF. The binding mode of the compounds with Hb was confirmed by X-ray crystallography and, in part, helps explain their observed biochemical properties. Our findings, in addition to the potential therapeutic application, provide valuable insights and potential guidance for further modifications of these (and similar) compounds to enhance their pharmacologic properties.

Hydroxyurea therapy in adult Nigerian sickle cell disease: a monocentric survey on pattern of use, clinical effects and patient's compliance

BACKGROUND

The clinical prospects of hydroxyurea therapy in the management of sickle cell disease (SCD) require evaluation in the Nigerian setting to develop indigenous guidelines. This survey examines the pattern of hydroxyurea therapy, its clinico-haematologic benefits and safety profile in Nigerian SCD subjects.

METHODS

A cross sectional pilot survey was carried out among 60 adult SCD subjects over 3 months. Data on clinical phenotypes, relevant haematological parameters and details of hydroxyurea therapy were obtained using a structured questionnaire through an interview process and case file review.

RESULTS

The median age was 30 years. Thirty-four (56.7%) of the subjects are aware of hydroxyurea therapy in SCD. Twenty-four (40%) SCD patients had previously used hydroxyurea. Only 4 subjects were fully compliant. Reasons for non-compliance included poor knowledge and lack of funds. In particular, hydroxyurea reduced leucocyte count and increased mean red cell volume (MCV) in compliant subjects.

CONCLUSION

Hydroxyurea use is low among Nigerian SCD subjects despite its proven efficacy/clinical prospects in the developed nations. Large scale multicenter studies and clinical trials are needed to form a basis for developing standard local treatment protocol for its use.

Aryloxyalkanoic Acids as Non-Covalent Modifiers of the Allosteric Properties of Hemoglobin

Hemoglobin (Hb) modifiers that stereospecifically inhibit sickle hemoglobin polymer formation and/or allosterically increase Hb affinity for oxygen have been shown to prevent the primary pathophysiology of sickle cell disease (SCD), specifically, Hb polymerization and red blood cell sickling. Several such compounds are currently being clinically studied for the treatment of SCD. Based on the previously reported non-covalent Hb binding characteristics of substituted aryloxyalkanoic acids that exhibited antisickling properties, we designed, synthesized and evaluated 18 new compounds (KAUS II series) for enhanced antisickling activities. Surprisingly, select test compounds showed no antisickling effects or promoted erythrocyte sickling. Additionally, the compounds showed no significant effect on Hb oxygen affinity (or in some cases, even decreased the affinity for oxygen). The X-ray structure of deoxygenated Hb in complex with a prototype compound, KAUS-23, revealed that the effector bound in the central water cavity of the protein, providing atomic level explanations for the observed functional and biological activities. Although the structural modification did not lead to the anticipated biological effects, the findings provide important direction for designing candidate antisickling agents, as well as a framework for novel Hb allosteric effectors that conversely, decrease the protein affinity for oxygen for potential therapeutic use for hypoxic- and/or ischemic-related diseases.

Crystal structure of carbonmonoxy sickle hemoglobin in R-state conformation

The fundamental pathophysiology of sickle cell disease is predicated by the polymerization of deoxygenated (T-state) sickle hemoglobin (Hb S) into fibers that distort red blood cells into the characteristic sickle shape. The crystal structure of deoxygenated Hb S (DeoxyHb S) and other studies suggest that the polymer is initiated by a primary interaction between the mutation βVal6 from one Hb S molecule, and a hydrophobic acceptor pocket formed by the residues βAla70, βPhe85 and βLeu88 of an adjacent located Hb S molecule. On the contrary, oxygenated or liganded Hb S does not polymerize or incorporate in the polymer. In this paper we present the crystal structure of carbonmonoxy-ligated sickle Hb (COHb S) in the quaternary classical R-state at 1.76Å. The overall structure and the pathological donor and acceptor environments of COHb S are similar to those of the isomorphous CO-ligated R-state normal Hb (COHb A), but differ significantly from DeoxyHb S as expected. More importantly, the packing of COHb S molecules does not show the typical pathological interaction between βVal6 and the βAla70, βPhe85 and βLeu88 hydrophobic acceptor pocket observed in DeoxyHb S crystal. The structural analysis of COHb S, COHb A and DeoxyHb S provides atomic level insight into why liganded hemoglobin does not form a polymer.

Low-molecular-weight heparins for managing vaso-occlusive crises in people with sickle cell disease

BACKGROUND

Sickle cell disease is one of the most common and severe genetic disorders in the world. It can be broadly divided into two distinct clinical phenotypes characterized by either haemolysis or vaso-occlusion. Pain is the most prominent symptom of vaso-occlusion, and hypercoagulability is a well-established pathogenic phenomenon in people with sickle cell disease. Low-molecular-weight heparins might control this hypercoagulable state through their anticoagulant effect. This is an update of a previously published version of this review.

OBJECTIVES

To assess the effects of low-molecular-weight heparins for managing vaso-occlusive crises in people with sickle cell disease.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Haemoglobinopathies Trials Register comprising references identified from comprehensive electronic database searches. We also searched abstract books of conference proceedings and several online trials registries for ongoing trials.Date of the last search of the Cochrane Cystic Fibrosis and Genetic Disorders Group Haemoglobinopathies Trials Register: 28 September 2015.

SELECTION CRITERIA

Randomised controlled clinical trials and controlled clinical trials that assessed the effects of low-molecular-weight heparins in the management of vaso-occlusive crises in people with sickle cell disease.

DATA COLLECTION AND ANALYSIS

Study selection, data extraction, assessment of risk of bias and analyses were carried out independently by the two review authors.

MAIN RESULTS

Two studies comprising 287 participants were included. One study (with an overall unclear to high risk of bias) involved 253 participants and the quality of the evidence for most outcomes was very low. This study, reported that pain severity at day two and day three was lower in the tinzaparin group than in the placebo group (P < 0.01, analysis of variance (ANOVA)) and additionally at day 4 (P < 0.05 (ANOVA)). Thus tinzaparin resulted in more rapid resolution of pain, as measured with a numerical pain scale. The mean difference in duration of painful crises was statistically significant at -1.78 days in favour of the tinzaparin group (95% confidence interval -1.94 to -1.62). Participants treated with tinzaparin had statistically significantly fewer hospitalisation days than participants in the group treated with placebo, with a mean difference of -4.98 days (95% confidence interval -5.48 to -4.48). Two minor bleeding events were reported as adverse events in the tinzaparin group, and none were reported in the placebo group. The second study (unclear risk of bias) including 34 participants and was a conference abstract with limited data and only addressed one of the predefined outcomes of the review; i.e. pain intensity. After one day pain intensity reduced more, as reported on a visual analogue scale, in the dalteparin group than in the placebo group, mean difference -1.30 (95% confidence interval -1.60 to -1.00), with the quality of evidence rated very low. The most important reasons for downgrading the quality of evidence were serious risk of bias and imprecision (due to low sample size or low occurrence of events).

AUTHORS' CONCLUSIONS

Based on the results of two studies, evidence is incomplete to support or refute the effectiveness of low-molecular-weight heparins in people with sickle cell disease. Vaso-occlusive crises are extremely debilitating for sufferers of sickle cell disease; therefore well-designed placebo-controlled studies with other types of low-molecular-weight heparins, and in participants with different genotypes of sickle cell disease, still need to be carried out to confirm or dismiss the results of this single study.

Hemopexin therapy reverts heme-induced proinflammatory phenotypic switching of macrophages in a mouse model of sickle cell disease

Hemolytic diseases, such as sickle cell anemia and thalassemia, are characterized by enhanced release of hemoglobin and heme into the circulation, heme-iron loading of reticulo-endothelial system macrophages, and chronic inflammation. Here we show that in addition to activating the vascular endothelium, hemoglobin and heme excess alters the macrophage phenotype in sickle cell disease. We demonstrate that exposure of cultured macrophages to hemolytic aged red blood cells, heme, or iron causes their functional phenotypic change toward a proinflammatory state. In addition, hemolysis and macrophage heme/iron accumulation in a mouse model of sickle disease trigger similar proinflammatory phenotypic alterations in hepatic macrophages. On the mechanistic level, this critically depends on reactive oxygen species production and activation of the Toll-like receptor 4 signaling pathway. We further demonstrate that the heme scavenger hemopexin protects reticulo-endothelial macrophages from heme overload in heme-loaded Hx-null mice and reduces production of cytokines and reactive oxygen species. Importantly, in sickle mice, the administration of human exogenous hemopexin attenuates the inflammatory phenotype of macrophages. Taken together, our data suggest that therapeutic administration of hemopexin is beneficial to counteract heme-driven macrophage-mediated inflammation and its pathophysiologic consequences in sickle cell disease.

Design, Synthesis, and Investigation of Novel Nitric Oxide (NO)-Releasing Prodrugs as Drug Candidates for the Treatment of Ischemic Disorders: Insights into NO-Releasing Prodrug Biotransformation and Hemoglobin-NO Biochemistry

We have developed novel nitric oxide (NO)-releasing prodrugs of efaproxiral (RSR13) for their potential therapeutic applications in a variety of diseases with underlying ischemia. RSR13 is an allosteric effector of hemoglobin (Hb) that decreases the protein's affinity for oxygen, thereby increasing tissue oxygenation. NO, because of its vasodilatory property, in the form of ester prodrugs has been found to be useful in managing several cardiovascular diseases by increasing blood flow and oxygenation in ischemic tissues. We synthesized three NO-donor ester derivatives of RSR13 (DD-1, DD-2, and DD-3) by attaching the NO-releasing moieties nitrooxyethyl, nitrooxypropyl, and 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate, respectively, to the carboxylate of RSR13. In vitro studies demonstrated that the compounds released NO in a time-dependent manner upon being incubated with l-cysteine (1.8-9.3%) or human serum (2.3-52.5%) and also reduced the affinity of Hb for oxygen in whole blood (ΔP50 of 4.9-21.7 mmHg vs ΔP50 of 25.4-32.1 mmHg for RSR13). Crystallographic studies showed RSR13, the hydrolysis product of the reaction between DD-1 and deoxygenated Hb, bound to the central water cavity of Hb. Also, the hydrolysis product, NO, was observed exclusively bound to the two α hemes, the first such HbNO structure to be reported, capturing the previously proposed physiological bis-ligated nitrosylHb species. Finally, nitrate was observed bound to βHis97. Ultraperformance liquid chromatography-mass spectrometry analysis of the compounds incubated with matrices used for the various studies demonstrated the presence of the predicted reaction products. Our findings, beyond the potential therapeutic application, provide valuable insights into the biotransformation of NO-releasing prodrugs and their mechanism of action and into hemoglobin-NO biochemistry at the molecular level.

Bacterial Infections Following Splenectomy for Malignant and Nonmalignant Hematologic Diseases

Splenectomy, while often necessary in otherwise healthy patients after major trauma, finds its primary indication for patients with underlying malignant or nonmalignant hematologic diseases. Indications of splenectomy for hematologic diseases have been reducing in the last few years, due to improved diagnostic and therapeutic tools. In high-income countries, there is a clear decrease over calendar time in the incidence of all indication splenectomy except nonmalignant hematologic diseases. However, splenectomy, even if with different modalities including laparoscopic splenectomy and partial splenectomy, continue to be a current surgical practice both in nonmalignant hematologic diseases, such as Immune Thrombocytopenic Purpura (ITP), Autoimmune Hemolytic Anemia (AIHA), Congenital Hemolytic Anemia such as Spherocytosis, Sickle Cell Anemia and Thalassemia and Malignant Hematological Disease, such as lymphoma. Today millions of people in the world are splenectomized. Splenectomy, independently of its cause, induces an early and late increase in the incidence of venous thromboembolism and infections. Infections remain the most dangerous complication of splenectomy. After splenectomy, the levels of antibody are preserved but there is a loss of memory B cells against pneumococcus and tetanus, and the loss of marginal zone monocytes deputed to immunological defense from capsulated bacteria. Commonly, the infections strictly correlated to the absence of the spleen or a decreased or absent splenic function are due to encapsulated bacteria that are the most virulent pathogens in this set of patients. Vaccination with polysaccharide and conjugate vaccines again Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis should be performed before the splenectomy. This practice reduces but does not eliminate the occurrence of overwhelming infections due to capsulated bacteria. At present, most of infections found in splenectomized patients are due to Gram-negative (G-) bacteria. The underlying disease is the most important factor in determining the frequency and severity of infections. So, splenectomy for malignant diseases has the major risk of infections.

Identification of a novel class of covalent modifiers of hemoglobin as potential antisickling agents

Aromatic aldehydes and ethacrynic acid (ECA) exhibit antipolymerization properties that are beneficial for sickle cell disease therapy. Based on the ECA pharmacophore and its atomic interaction with hemoglobin, we designed and synthesized several compounds - designated as KAUS (imidazolylacryloyl derivatives) - that we hypothesized would bind covalently to βCys93 of hemoglobin and inhibit sickling. The compounds surprisingly showed weak allosteric and antisickling properties. X-ray studies of hemoglobin in complex with representative KAUS compounds revealed an unanticipated mode of Michael addition between the β-unsaturated carbon and the N-terminal αVal1 nitrogen at the α-cleft of hemoglobin, with no observable interaction with βCys93. Interestingly, the compounds exhibited almost no reactivity with the free amino acids, L-Val, L-His and L-Lys, but showed some reactivity with both glutathione and L-Cys. Our findings provide a molecular level explanation for the compounds biological activities and an important framework for targeted modifications that would yield novel potent antisickling agents.

Management of sickle cell disease: a review for physician education in Nigeria (sub-saharan Africa)

Sickle cell disease (SCD) predominates in sub-Saharan Africa, East Mediterranean areas, Middle East, and India. Nigeria, being the most populous black nation in the world, bears its greatest burden in sub-Saharan Africa. The last few decades have witnessed remarkable scientific progress in the understanding of the complex pathophysiology of the disease. Improved clinical insights have heralded development and establishment of disease modifying interventions such as chronic blood transfusions, hydroxyurea therapy, and haemopoietic stem cell transplantation. Coupled with parallel improvements in general supportive, symptomatic, and preventive measures, current evidence reveals remarkable appreciation in quality of life among affected individuals in developed nations. Currently, in Nigeria and other West African states, treatment and control of SCD are largely suboptimal. Improved knowledge regarding SCD phenotypes and its comprehensive care among Nigerian physicians will enhance quality of care for affected persons. This paper therefore provides a review on the aetiopathogenesis, clinical manifestations, and management of SCD in Nigeria, with a focus on its local patterns and peculiarities. Established treatment guidelines as appropriate in the Nigerian setting are proffered, as well as recommendations for improving care of affected persons.