Sickle cell disease: role of reactive oxygen and nitrogen metabolites

Enhanced vasoconstriction in sickle cell disease is dependent on ETA receptor activation

Sickle cell disease (SCD) carries a significant risk for poor vascular health and vascular dysfunction. High levels of vascular reactive oxygen species (ROS) as well as elevated plasma endothelin-1 (ET-1), a potent vasoconstrictor with actions via the ETA receptor, are both common phenotypes in SCD. Alpha-1 adrenergic receptor activation is a major mediator of stress-induced vasoconstriction. However, the mechanism of the SCD enhanced vasoconstrictive response is unknown. We hypothesized that SCD induces enhanced alpha-1 adrenergic mediated vasoconstriction through the ET-1/ETA receptor pathway in arterial tissues. Utilizing humanized SCD (HbSS) and genetic control (HbAA) mice, alpha-1a, but not alpha-1b or alpha-1d, receptor expression was significantly greater in aortic tissue from HbSS mice compared to HbAA mice. Significantly enhanced vasoconstriction in aortic and carotid arterial segments were observed from HbSS mice compared with HbAA mice. Treatment with ambrisentan, a selective ETA receptor antagonist, and a ROS scavenger normalized the aortic vasoconstrictive response in HbSS mice. In a randomized translational study, patients with SCD were treated with placebo or ambrisentan for 3 months, with the treatment group showing an increase in the percent brachial arterial diameter. Taken together, these data suggest that the ETA receptor pathway interaction with the adrenergic receptor pathway contributes to enhanced aortic vasoconstriction in SCD. Findings indicate the potential of ETA antagonism as a therapeutic avenue for improving vascular health in SCD.

Prevalence of metabolic syndrome in sickle cell disease patients: A cross-sectional study at a tertiary hospital in Nepal

Background

Sickle cell disease (SCD) is the most common hemoglobinopathy caused by an autosomal recessive genetic disorder leading to increased morbidity and mortality rates. SCD is prevalent in the Tharu community in the lowland (Terai) region of Nepal. Prevalence of metabolic syndrome among adults with SCD is poorly studied.

Methodology

This prospective cross-sectional study was conducted at Seti Provincial Hospital in Dhangadhi, Nepal, among 140 adolescents and adults with SCD, aged 15-60 years. Anthropometric and laboratory data were collected using an assisted questionnaire, and the SPSS software version 23 was used for data analysis. Descriptive and inferential statistics were used to summarize the presence of metabolic syndrome and were stratified in separate analyses by age and sex. National Cholesterol Education Program-Adult Treatment Panel III criteria were used to define metabolic syndrome.

Aim

This cross-sectional study aimed to assess the prevalence of metabolic syndrome among SCD patients with SCD registered at the Seti Provincial Hospital in Dhangadhi, Nepal.

Results

The prevalence of metabolic syndrome in the study participants was 7.8%. Our study revealed 5% of the patients overweight, and 1.4% obese. In this study, the mean triglyceride level was 118.5 mg/dL, and the mean high-density lipoprotein (HDL) level was 36.2 mg/dL (men) and 36.7 mg/dL (women). This study found that the mean fasting blood glucose level was 88.6 gm/dL. Similarly, 3.5% of patients had increased systolic blood pressure, and 7.8% had raised diastolic blood pressure. Study shows that changes in triglyceride level (p = 0.013), waist circumference, and HDL level (p = 0.0001 and 0.0048, respectively) are significantly associated with smoking or alcohol consumption; however, change in blood pressure (p = 0.013) and fasting blood sugar level (p = 0.086) are not associated with smoking or alcohol consumption.

Conclusion

Study concluded that though a lower proportion of SCD patients met the criteria for metabolic syndrome than in studies conducted in developed countries, it is crucial to consider metabolic syndrome while managing patients with SCD. Nevertheless, the authors advocate a more comprehensive study to draw significant conclusions.

Red Blood Cells as Therapeutic Target to Treat Sickle Cell Disease

Significance: Sickle cell disease (SCD) is the most common inherited diathesis affecting mostly underserved populations globally. SCD is characterized by chronic pain and fatigue, severe acute painful crises requiring hospitalization and opioids, strokes, multiorgan damage, and a shortened life span. Symptoms may appear shortly after birth, and, in less developed countries, most children with SCD die before attaining age 5. Hematopoietic stem cell transplant and gene therapy offer a curative therapeutic approach, but, due to many challenges, are limited in their availability and effectiveness for a majority of persons with SCD. A critical unmet need is to develop safe and effective novel targeted therapies. A wide array of drugs currently undergoing clinical investigation hold promise for an expanded pharmacological armamentarium against SCD. Recent Advances: Hydroxyurea, the most widely used intervention for SCD management, has improved the survival in the Western world and more recently, voxelotor (R-state-stabilizer), l-glutamine, and crizanlizumab (anti-P-selectin antibody) have been approved by the Food and Drug Administration (FDA) for use in SCD. The recent FDA approval emphasizes the need to revisit the advances in understanding the core pathophysiology of SCD to accelerate novel evidence-based strategies to treat SCD. The biomechanical breakdown of erythrocytesis, the core pathophysiology of SCD, is associated with intrinsic factors, including the composition of hemoglobin, membrane integrity, cellular volume, hydration, andoxidative stress. Critical Issues and Future Directions: In this context, this review focuses on advances in emerging nongenetic interventions directed toward the therapeutic targets intrinsic to sickle red blood cells (RBCs), which can prevent impaired rheology of RBCs to impede disease progression and reduce the sequelae of comorbidities, including pain, vasculopathy, and organ damage. In addition, given the intricate pathophysiology of the disease, it is unlikely that a single pharmacotherapeutic intervention will comprehensively ameliorate the multifaceted complications associated with SCD. However, the availability of multiple drug options affords the opportunity for individualized therapeutic regimens tailored to specific SCD-related complications. Furthermore, it opens avenues for combination drug therapy, capitalizing on distinct mechanisms of action and profiles of adverse effects.

Clinical and laboratory differences between pediatric hospitalized patients with sickle cell disease infected or not by SARS-CoV-2

OBJECTIVE

The aim of this study was to identify clinical and complete blood count differences between pediatric hospitalized patients with sickle cell disease infected or not by SARS-CoV-2 and compare the complete blood count of patients with sickle cell disease infected by SARS-CoV-2 before hospitalization and on admission.

METHODS

This study was a single-center prospective cohort. Data were collected from medical records of pediatric inpatients with sickle cell disease under 18 years old infected or not with SARS-CoV-2 from the first visit to the hospital until discharge and from the last medical appointment. All patients were tested for SARS-CoV-2 by the real-time reverse transcription polymerase chain reaction.

RESULTS

Among 57 pediatric patients with sickle cell disease hospitalized from March to November 2020 in a Brazilian academic hospital, 11 (19.3%) had a positive result for SARS-CoV-2. Patients infected by SARS-CoV-2 had a higher prevalence of comorbidities than the ones who were not infected (63.6 vs. 30.4%; p=0.046). During hospital stay, no clinical or complete blood count differences between groups were found. There was a decrease in eosinophil count on hospital admission in patients with sickle cell disease infected by SARS-CoV-2 (p=0.008).

CONCLUSIONS

Pediatric hospitalized patients with sickle cell disease infected by SARS-CoV-2 had more comorbidities and had a decrease in eosinophil count between hospital admission and the last medical appointment.

Redox Balance in β-Thalassemia and Sickle Cell Disease: A Love and Hate Relationship

β-thalassemia and sickle cell disease (SCD) are inherited hemoglobinopathies that result in both quantitative and qualitative variations in the β-globin chain. These in turn lead to instability in the generated hemoglobin (Hb) or to a globin chain imbalance that affects the oxidative environment both intracellularly and extracellularly. While oxidative stress is not among the primary etiologies of β-thalassemia and SCD, it plays a significant role in the pathogenesis of these diseases. Different mechanisms exist behind the development of oxidative stress; the result of which is cytotoxicity, causing the oxidation of cellular components that can eventually lead to cell death and organ damage. In this review, we summarize the mechanisms of oxidative stress development in β-thalassemia and SCD and describe the current and potential antioxidant therapeutic strategies. Finally, we discuss the role of targeted therapy in achieving an optimal redox balance.

Anti-inflammatory cytokines in sickle cell disease

Sickle cell disease (SCD) is a well-studied monogenetic disease with an established chronic inflammatory component. The paradigm shift towards inflammation has made the pathophysiology of SCD even more complex. Studies have shown that an imbalance between the pro-inflammatory and anti-inflammatory cytokines in SCD exists; however, the reports are skewed toward the pro-inflammatory mediators. We enumerate recent in vitro and in vivo studies on anti-inflammatory cytokines in SCD patients, and discuss the biology of anti-inflammatory cytokines including the already reported IL-2, TGF-β, and IL-10 as well as the recently discovered IL-27, IL-35 and IL-37. This review will improve the understanding of the pathophysiology of SCD and aid in the search of new therapeutic options for patients with SCD.

Testosterone Deficiency in Sickle Cell Disease: Recognition and Remediation

Hypogonadism is common in men with sickle cell disease (SCD) with prevalence rates as high as 25%. Testicular failure (primary hypogonadism) is established as the principal cause for this hormonal abnormality, although secondary hypogonadism and compensated hypogonadism have also been observed. The underlying mechanism for primary hypogonadism was elucidated in a mouse model of SCD, and involves increased NADPH oxidase-derived oxidative stress in the testis, which reduces protein expression of a steroidogenic acute regulatory protein and cholesterol transport to the mitochondria in Leydig cells. In all men including those with SCD, hypogonadism affects physical growth and development, cognition and mental health, sexual function, as well as fertility. However, it is not understood whether declines in physical, psychological, and social domains of health in SCD patients are related to low testosterone, or are consequences of other abnormalities of SCD. Priapism is one of only a few complications of SCD that has been studied in the context of hypogonadism. In this pathologic condition of prolonged penile erection in the absence of sexual excitement or stimulation, hypogonadism exacerbates already impaired endothelial nitric oxide synthase/cGMP/phosphodiesterase-5 molecular signaling in the penis. While exogenous testosterone alleviates priapism, it disadvantageously decreases intratesticular testosterone production. In contrast to treatment with exogenous testosterone, a novel approach is to target the mechanisms of testosterone deficiency in the SCD testis to drive endogenous testosterone production, which potentially decreases further oxidative stress and damage in the testis, and preserves sperm quality. Stimulation of translocator protein within the transduceosome of the testis of SCD mice reverses both hypogonadism and priapism, without affecting intratesticular testosterone production and consequently fertility. Ongoing research is needed to define and develop therapies that restore endogenous testosterone production in a physiologic, mechanism-specific fashion without affecting fertility in SCD men.

The Role of RBC Oxidative Stress in Sickle Cell Disease: From the Molecular Basis to Pathologic Implications

Sickle cell disease (SCD) is an inherited monogenic disorder and the most common severe hemoglobinopathy in the world. SCD is characterized by a point mutation in the β-globin gene, which results in hemoglobin (Hb) S production, leading to a variety of mechanistic and phenotypic changes within the sickle red blood cell (RBC). In SCD, the sickle RBCs are the root cause of the disease and they are a primary source of oxidative stress since sickle RBC redox state is compromised due to an imbalance between prooxidants and antioxidants. This imbalance in redox state is a result of a continuous production of reactive oxygen species (ROS) within the sickle RBC caused by the constant endogenous Hb autoxidation and NADPH oxidase activation, as well as by a deficiency in the antioxidant defense system. Accumulation of non-neutralized ROS within the sickle RBCs affects RBC membrane structure and function, leading to membrane integrity deficiency, low deformability, phosphatidylserine exposure, and release of micro-vesicles. These oxidative stress-associated RBC phenotypic modifications consequently evoke a myriad of physiological changes involved in multi-system manifestations. Thus, RBC oxidative stress in SCD can ultimately instigate major processes involved in organ damage. The critical role of the sickle RBC ROS production and its regulation in SCD pathophysiology are discussed here.

Relationship of oxidative stress and antioxidant response with vaso-occlusive crisis in sickle cell anaemia

BACKGROUND

Though sickle cell anaemia (SCA) is known to promote oxidative stress, there is paucity of information on the relationship between oxidative stress and vaso-occlusive crisis (VOC).

OBJECTIVE

This study was undertaken to evaluate the relationship of oxidative stress and antioxidant response with VOC in SCA.

METHODS

A cross-sectional case-control study was carried out at University of Nigeria Teaching Hospital (UNTH), Ituku-Ozalla, Enugu Nigeria involving 116 individuals which included 36 SCA subject, 40 sickle cell carriers (AS) and 40 healthy individuals (AA). Baseline information as well as the frequency of VOC was obtained from the participants and anaemia as well as oxidative stress and antioxidant indices were assessed in blood.

RESULTS

Anaemia was prevalent (88.9 %) in SCA individuals compared to AS (52.5%) and AA (47.5 %) individuals. Nitric oxide scavenging (NOS) and superoxide dismutase (SOD) activities as well as glutathione level were significantly (p<0.005) lower while catalase activity was higher in SCA individuals compared to controls (AA and AS). Higher malondialdehyde (MDA) level was associated with very severe VOC while low level of NOS activity was associated with severe VOC in SCA individuals.

CONCLUSION

Sickle cell anaemia exhibited oxidative stress and alteration in the levels of antioxidant indices which was possibly associated with vaso-occlusive crisis.

Sickle Cell Disease: Role of Oxidative Stress and Antioxidant Therapy

Sickle cell disease (SCD) is the most common hereditary disorder of hemoglobin (Hb), which affects approximately a million people worldwide. It is characterized by a single nucleotide substitution in the β-globin gene, leading to the production of abnormal sickle hemoglobin (HbS) with multi-system consequences. HbS polymerization is the primary event in SCD. Repeated polymerization and depolymerization of Hb causes oxidative stress that plays a key role in the pathophysiology of hemolysis, vessel occlusion and the following organ damage in sickle cell patients. For this reason, reactive oxidizing species and the (end)-products of their oxidative reactions have been proposed as markers of both tissue pro-oxidant status and disease severity. Although more studies are needed to clarify their role, antioxidant agents have been shown to be effective in reducing pathological consequences of the disease by preventing oxidative damage in SCD, i.e., by decreasing the oxidant formation or repairing the induced damage. An improved understanding of oxidative stress will lead to targeted antioxidant therapies that should prevent or delay the development of organ complications in this patient population.

In utero Therapy for the Treatment of Sickle Cell Disease: Taking Advantage of the Fetal Immune System

Sickle Cell Disease (SCD) is an autosomal recessive disorder resulting from a β-globin gene missense mutation and is among the most prevalent severe monogenic disorders worldwide. Haematopoietic stem cell transplantation remains the only curative option for the disease, as most management options focus solely on symptom control. Progress in prenatal diagnosis and fetal therapeutic intervention raises the possibility of in utero treatment. SCD can be diagnosed prenatally in high-risk patients using chorionic villus sampling. Among the possible prenatal treatments, in utero stem cell transplantation (IUSCT) shows the most promise. IUSCT is a non-myeloablative, non-immunosuppressive alternative conferring various unique advantages and may also offer safer postnatal management. Fetal immunologic immaturity could allow engraftment of allogeneic cells before fetal immune system maturation, donor-specific tolerance and lifelong chimerism. In this review, we will discuss SCD, screening and current treatments. We will present the therapeutic rationale for IUSCT, examine the early experimental work and initial human experience, as well as consider primary barriers of clinically implementing IUSCT and the promising approaches to address them.

Targeting AnxA1/Formyl Peptide Receptor 2 Pathway Affords Protection against Pathological Thrombo-Inflammation

Stroke is a leading cause of death and disability globally and is associated with a number of co-morbidities including sepsis and sickle cell disease (SCD). Despite thrombo-inflammation underlying these co-morbidities, its pathogenesis remains complicated and drug discovery programs aimed at reducing and resolving the detrimental effects remain a major therapeutic challenge. The objective of this study was to assess whether the anti-inflammatory pro-resolving protein Annexin A1 (AnxA1) was able to reduce inflammation-induced thrombosis and suppress platelet activation and thrombus formation in the cerebral microvasculature. Using two distinct models of pathological thrombo-inflammation (lipopolysaccharide (LPS) and sickle transgenic mice (STM)), thrombosis was induced in the murine brain using photoactivation (light/dye) coupled with intravital microscopy. The heightened inflammation-induced microvascular thrombosis present in these two distinct thrombo-inflammatory models was inhibited significantly by the administration of AnxA1 mimetic peptide AnxA1_Ac2-26 (an effect more pronounced in the SCD model vs. the endotoxin model) and mediated by the key resolution receptor, Fpr2/ALX. Furthermore, AnxA1_Ac2-26 treatment was able to hamper platelet aggregation by reducing platelet stimulation and aggregation (by moderating α_IIbβ₃ and P-selectin). These findings suggest that targeting the AnxA1/Fpr2/ALX pathway represents an attractive novel treatment strategy for resolving thrombo-inflammation, counteracting e.g., stroke in high-risk patient cohorts.

Naphthalene Toxicity in a Three-Year-Old Child Complicated by Severe Hemolytic Anemia and Mild Methemoglobinemia: A Case Report

BACKGROUND

Exposure to naphthalene, which is widely used in mothballs, does not usually produce adverse effects. However, naphthalene can be toxic, especially in individuals with underlying conditions such as glucose-6-phosphate-dehydrogenase (G6PD) deficiency.

CASE REPORT

A 3-year-old boy was brought to our Emergency Department after accidentally ingesting naphthalene mothballs 3 days prior to presentation. Laboratory investigations revealed that he had severe hemolytic anemia and mild methemoglobinemia (6%), which were treated with ascorbic acid and N-acetylcysteine. The patient tested positive for G6PD deficiency after stabilization and completion of his treatment. All provided treatments were administered empirically; test results were available only after the patient was discharged. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: Naphthalene exposure is a common pediatric presentation with various complications that can occur in certain high-risk individuals, such as those with G6PD deficiency. Emergency physicians should be aware of this to anticipate and be able to treat worsening toxicity.

Evolutionary History and Activity of RNase H1-Like Proteins in Arabidopsis thaliana

RNase H1 is an endonuclease specific toward the RNA strand of RNA:DNA hybrids. Members of this protein family are present in most living organisms and are essential for removing RNA that base pairs with DNA. It prevents detrimental effects of RNA:DNA hybrids and is involved in several biological processes. Arabidopsis thaliana has been previously shown to contain three genes encoding RNase H1 proteins that localize to three distinct cellular compartments. We show that these genes originate from two gene duplication events. One occurred in the common ancestor of dicots and produced nuclear and organellar RNase H1 paralogs. Second duplication occurred in the common ancestor of Brassicaceae and produced mitochondrial- and plastid-localized proteins. These proteins have the canonical RNase H1 activity, which requires at least four ribonucleotides for endonucleolytic digestion. Analysis of mutants in the RNase H1 genes revealed that the nuclear RNH1A and mitochondrial RNH1B are dispensable for development under normal growth conditions. However, the presence of at least one organellar RNase H1 (RNH1B or RNH1C) is required for embryonic development. The plastid-localized RNH1C affects plastid DNA copy number and sensitivity to replicative stress. Our results present the evolutionary history of RNH1 proteins in A. thaliana, demonstrate their canonical RNase H1 activity and indicate their role in early embryonic development.

MEK1/2 as a Therapeutic Target in Sickle Cell Disease

Identification of novel therapeutic targets has improved diagnostics and treatment of many diseases. Many innovative treatment strategies have been developed based on the newly identified biomarkers and key molecules. Most of the research focused on ways to manipulate signaling pathways by activating or suppressing them, validate new therapeutic targets for treatment, and epigenetic treatment of diseases. With the identification of aberrations in multiple growth pathways, the focus then shifted to the small molecules involved in these pathways for targeted therapy. In this communication/short review, we highlight the importance of identification of abnormal activation of the mitogen-activated protein kinase (MAPK), ERK1/2, and its upstream mediator MEK1/2, in erythrocytes in patients with sickle cell disease (SCD) critical for the adhesive interactions of these cells with the endothelium, and leukocytes promoting circulatory obstruction leading to tissue ischemia and infraction. We also discuss how targeting this signaling cascade with MEK1/2 inhibitors can reverse acute vasoocclusive crises in SCD.

Thalassemia and Moyamoya syndrome: unfurling an intriguing association

INTRODUCTION

Moyamoya angiopathy (MMA) is a rare cerebrovascular disease with progressive bilateral narrowing of intracranial parts of the internal carotid artery and proximal parts of the anterior and middle cerebral artery resulting in recurrent hemodynamic ischemic attacks, strokes and hemorrhages. If associated with other diseases, it is called Moyamoya syndrome (MMS). Until now, MMS has rarely been described with thalassemia.

METHODS

Of the 75 cases of MMA collected in our Indian center in the last 3 years, 4 new patients with the rare cooccurence of thalassemia and MMS were found. Thalassemia cases were confirmed by hemoglobin electrophoresis and MMA was diagnosed on the basis of MR angiography. Other known secondary causes of MMA were ruled out by relevant investigations. Thirteen previously reported cases of thalassemia and MMA were retrieved by literature search in PubMed and Google Scholar using the keywords "Moyamoya" AND "thalassemia". Subsequently all the data were analyzed and compared by using descriptive statistics.

RESULTS

Analysis of our 4 cases and those 13 found in the literature showed early childhood diagnosis of thalassemia and in most cases later manifestation of MMS in the age of 14.5 + 10.72 years (mean + SD) in our cases and with 10.97 + 6.47 years in previous cases. While 9 out of the former 13 and 3 of our 4 cases showed obvious infarcts in brain imaging, 1 case with HbE-β-thalassemia presented with intracerebral hemorrhage. Hemiplegia/hemiparesis was present among all of our 4 cases, while it was present in 69.23% cases of the previous 13 reports. Neither transfusion dependence nor the history of splenectomy was found to be associated with MMA development.

CONCLUSION

These four new cases of MMS in thalassemia enlarged our knowledge about MMS in patients with thalassemia. MMS is a relevant complication in patients with thalassemia and early detection is essential to avoid disability.

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.

Vaso-occlusive crisis in sickle cell disease: current paradigm on pain management

This narrative review aims to highlight the current paradigm on pain management in sickle cell vaso-occlusive crisis. It specifically examines the pathophysiologic mechanisms of sickle cell pain as well as the pharmacologic and nonpharmacologic methods of pain management. Recurrent painful episodes constitute the major morbidity in sickle cell disease (SCD). While adolescents and young adults experience mostly acute episodic nociceptive pain, it is now recognized that a significant number of adult patients develop chronic neuropathic and centralized pain. In fact, current evidence points to an age-dependent increase in the frequency of SCD patients with chronic pain. Management of disease-related pain should be based on its pathophysiologic mechanisms instead of using recommendations from other non-SCD pain syndromes. Pain management in vaso-occlusive crisis is complex and requires multiple interventions such as pharmacologic, nonpharmacologic, and preventive therapeutic interventions. Pharmacologic treatment involves the use of non-opioid and opioid analgesics, and adjuvants - either singly or in combination - depending on the severity of pain. The basic approach is to treat SCD pain symptomatically with escalating doses of non-opioid and opioid analgesics. Given the moderate-to-severe nature of the pain usually experienced in this form of SCD crisis, opioids form the bedrock of pharmacologic treatment. Multimodal analgesia and structured, individualized analgesic regimen appear more effective in achieving better treatment outcomes. Although the current evidence is still limited on the supportive role of cognitive behavioral therapy in pain management, this nonpharmacologic approach is reportedly effective, but needs further exploration as a possible adjunct in analgesia.

Neuronal transient receptor potential (TRP) channels and noxious sensory detection in sickle cell disease

Pain is the leading cause for hospitalization in patients with sickle cell disease (SCD). While the characteristics of SCD pain can vary widely between patients and between phases of the disease (e.g. vasoocclusive crisis pain vs. chronic pain), similar neuronal mechanisms likely underlie the various aspects of nociceptive processing. In the peripheral nervous system, small unmyelinated C fibers and lightly-myelinated Aδ fibers detect and transmit noxious stimuli. Both classes of neurons express members of the transient receptor potential (TRP) family, a group of ligand gated ion-channels that are activated by thermal, chemical, and mechanical stimuli. Promiscuous TRP channel family members are activated by a wide range of stimuli, many of which are dysregulated in patients with SCD and transgenic SCD mouse models. In 2011, our lab published the first report of TRP channel contributions to rodent SCD pain. Since that time, additional basic and clinical research efforts have investigated the genetic and biochemical status of TRP channels in SCD, placing particular focus on TRPV1. This review will discuss these advances and highlight the clinical SCD presentations that have not yet been studied, but which may be mediated by TRP channel activity.

Microfluidics for investigating vaso-occlusions in sickle cell disease

SCD stems from amutation in the beta globin gene. Upon deoxygenation, hemoglobin polymerizes and triggers RBC remodeling. This phenomenon is central to SCD pathogenesis as individuals suffering from the disease are plagued by painful vaso-occlusive crises episodes. These episodes are the result of a combination of processes including inflammation, thrombosis, and blood cell adhesion to the vascular wall which leads to blockages within the vasculature termed vaso-occlusions. Vaso-occlusive episodes deprive tissues of oxygen and are a major contributor to SCD-related complications; unfortunately, the complex mechanisms that contribute to vaso-occlusions are not well understood. Vaso-occlusions can occur in post-capillary venules; hence, the microvasculature is a prime target for SCD therapies. Traditional in vitro systems poorly recapitulate architectural and dynamic flow properties of in vivo systems. However, microfluidic devices can capture features of the native vasculature such as cellular composition, flow, geometry, and ECM presentation. This review, although not comprehensive, highlights microfluidic approaches that aim to improve our current understanding of the pathophysiological mechanisms surrounding SCD. Microfluidic platforms can aid in identifying factors that may contribute to disease severity and can serve as suitable test beds for novel treatment strategies which may improve patient outcomes.

Left Ventricular Structural and Functional Changes in Children With β-Thalassemia and Sickle Cell Disease: Relationship to Sleep-disordered Breathing

Cardiovascular complications are well recognized in β-thalassemia and sickle cell disease (SCD). The objective of this study was to evaluate left ventricular (LV) structural and functional changes and their relationship to sleep-disordered breathing (SDB) in children with β-thalassemia and SCD. One hundred patients recruited from the hematology clinic were subjected to Pittsburgh Sleep Quality Index score; 26 patients had positive score (Pittsburgh Sleep Quality Index ≥5) (15 β-thalassemia major and 11 SCD) and were compared with 25 age-matched and sex-matched controls. All underwent polysomnography and tissue Doppler echocardiography. SDB was detected in 73% of thalassemia patients (all had increased LV mass index [LVMI], diastolic dysfunction [increased E/Em], and 53% had pulmonary hypertension [tricuspid valve resurgence (TR) velocity ≥2.5 m/s]) and in 46% of SCD patients ( all had increased LVMI, 81.8% had pulmonary hypertension, and 76% had diastolic dysfunction). Sleep O2 saturation of β-thalassemia patients negatively correlated with TR velocity and LVMI (P=0.027, 0.015), and lower asleep O2 saturation was associated with increased E/Em. In SCD patients, sleep and awake O2 saturation negatively correlated with TR velocity and E/Em (P=0.024 and 0.041), and lower sleep O2 saturation was associated with increased LV diameter (P=0.021). SDB is common and associated with LV structural and functional changes in β-thalassemia and SCD.

Sickle cell disease

Sickle cell disease (SCD) is a group of inherited disorders caused by mutations in HBB, which encodes haemoglobin subunit β. The incidence is estimated to be between 300,000 and 400,000 neonates globally each year, the majority in sub-Saharan Africa. Haemoglobin molecules that include mutant sickle β-globin subunits can polymerize; erythrocytes that contain mostly haemoglobin polymers assume a sickled form and are prone to haemolysis. Other pathophysiological mechanisms that contribute to the SCD phenotype are vaso-occlusion and activation of the immune system. SCD is characterized by a remarkable phenotypic complexity. Common acute complications are acute pain events, acute chest syndrome and stroke; chronic complications (including chronic kidney disease) can damage all organs. Hydroxycarbamide, blood transfusions and haematopoietic stem cell transplantation can reduce the severity of the disease. Early diagnosis is crucial to improve survival, and universal newborn screening programmes have been implemented in some countries but are challenging in low-income, high-burden settings.

An Investigation of the Antioxidant Capacity in Extracts from Moringa oleifera Plants Grown in Jamaica

Moringa oleifera trees grow well in Jamaica and their parts are popularly used locally for various purposes and ailments. Antioxidant activities in Moringa oleifera samples from different parts of the world have different ranges. This study was initiated to determine the antioxidant activity of Moringa oleifera grown in Jamaica. Dried and milled Moringa oleifera leaves were extracted with ethanol/water (4:1) followed by a series of liquid–liquid extractions. The antioxidant capacities of all fractions were tested using a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. IC₅₀ values (the amount of antioxidant needed to reduce 50% of DPPH) were then determined and values for the extracts ranged from 177 to 4458 μg/mL. Extracts prepared using polar solvents had significantly higher antioxidant capacities than others and may have clinical applications in any disease characterized by a chronic state of oxidative stress, such as sickle cell anemia. Further work will involve the assessment of these extracts in a sickle cell model of oxidative stress.

Oxidative pathways in the sickle cell and beyond

Polymerization of deoxy sickle cell hemoglobin (HbS) is well recognized as the primary event that triggers the classic cycles of sickling/unsickling of patients red blood cells (RBCs). RBCs are also subjected to continuous endogenous and exogenous oxidative onslaughts resulting in hemolytic rate increases which contribute to the evolution of vasculopathies associated with this disease. Compared to steady-state conditions, the occurrences of vaso-occlusive crises increase the levels of both RBC-derived microparticles as well as extracellular Hb in circulation. Common byproduct resulting from free Hb oxidation and from Hb-laden microparticles is heme (now recognized as damage associated molecular pattern (DAMP) molecule) which has been shown to initiate inflammatory responses. This review provides new insights into the interplay between microparticles, free Hb and heme focusing on Hb's pseudoperoxidative activity that drives RBC's cytosolic, membrane changes as well as oxidative toxicity towards the vascular system. Emerging antioxidative strategies that include the use of protein and heme scavengers in controlling Hb oxidative pathways are discussed.

Brain neurochemical and hemodynamic findings in the NY1DD mouse model of mild sickle cell disease

To characterize the cerebral profile associated with sickle cell disease (SCD), we used in vivo proton MRI and MRS to quantify hemodynamics and neurochemicals in the thalamus of NY1DD mice, a mild model of SCD, and compared them with wild-type (WT) control mice. Compared with WT mice, NY1DD mice at steady state had elevated cerebral blood flow (CBF) and concentrations of N-acetylaspartate (NAA), glutamate (Glu), alanine, total creatine and N-acetylaspartylglutamate. Concentrations of glutathione (GSH) at steady state showed a negative correlation with BOLD signal change in response to 100% oxygen, a marker for oxidative stress, and mean diffusivity assessed using diffusion-tensor imaging, a marker for edematous inflammation. In NY1DD mice, elevated basal CBF was correlated negatively with [NAA], but positively with concentration of glutamine ([Gln]). Immediately after experimental hypoxia (at reoxygenation after 18 hours of 8% O₂ ), concentrations of NAA, Glu, GSH, Gln and taurine (Tau) increased only in NY1DD mice. [NAA], [Glu], [GSH] and [Tau] all returned to baseline levels two weeks after the hypoxic episode. The altered neurochemical profile in the NY1DD mouse model of SCD at steady state and following experimental hypoxia/reoxygenation suggests a state of chronic oxidative stress leading to compensatory cerebral metabolic adjustments.

Intravascular hemolysis and the pathophysiology of sickle cell disease

Hemolysis is a fundamental feature of sickle cell anemia that contributes to its pathophysiology and phenotypic variability. Decompartmentalized hemoglobin, arginase 1, asymmetric dimethylarginine, and adenine nucleotides are all products of hemolysis that promote vasomotor dysfunction, proliferative vasculopathy, and a multitude of clinical complications of pulmonary and systemic vasculopathy, including pulmonary hypertension, leg ulcers, priapism, chronic kidney disease, and large-artery ischemic stroke. Nitric oxide (NO) is inactivated by cell-free hemoglobin in a dioxygenation reaction that also oxidizes hemoglobin to methemoglobin, a non-oxygen-binding form of hemoglobin that readily loses heme. Circulating hemoglobin and heme represent erythrocytic danger-associated molecular pattern (eDAMP) molecules, which activate the innate immune system and endothelium to an inflammatory, proadhesive state that promotes sickle vaso-occlusion and acute lung injury in murine models of sickle cell disease. Intravascular hemolysis can impair NO bioavailability and cause oxidative stress, altering redox balance and amplifying physiological processes that govern blood flow, hemostasis, inflammation, and angiogenesis. These pathological responses promote regional vasoconstriction and subsequent blood vessel remodeling. Thus, intravascular hemolysis represents an intrinsic mechanism for human vascular disease that manifests clinical complications in sickle cell disease and other chronic hereditary or acquired hemolytic anemias.

Red blood cell deformability is reduced in homozygous sickle cell disease patients with leg ulcers

Previous reports differ as to whether a decreased elongation index (EI), a proxy for red blood cell (RBC) deformability, is associated with leg ulcers (LU) in people with homozygous sickle cell disease (SCD). We sought to determine whether erythrocyte deformability (ED) and haematological indices were associated with the presence of LU in patients with SCD. The study design was cross-sectional. Twenty-seven patients with LU and 23 with no history of ulceration were recruited into the study. A laser assisted rotational red cell analyzer was used in the determination of the EI. Haematological indices were determined using a CELL-DYN Ruby haematology analyzer. Data were normally distributed and presented as means±SD. Two-sample t-test was used to test for associations between haemorheological variables in SCD patients with and without LU. Statistical significance was taken as p < 0.05. The EI was significantly lower in the group with ulcers (0.30±0.07 vs. 0.35±0.07, p = 0.02). Haematological indices were comparable in patients with and without LU. Erythrocyte deformability, but not haematological indices, was associated with LU in patients with SCD.

Efficient Quantitative Analysis of Carboxyalkylpyrrole Ethanolamine Phospholipids: Elevated Levels in Sickle Cell Disease Blood

γ-Hydroxy-α,β-unsaturated aldehydes, generated by oxidative damage of polyunsaturated phospholipids, form pyrrole derivatives that incorporate the ethanolamine phospholipid (EP) amino group such as 2-pentylpyrrole (PP)-EP and 2-(ω-carboxyalkyl)pyrrole (CAP)-EP derivatives: 2-(ω-carboxyethyl)pyrrole (CEP)-EP, 2-(ω-carboxypropyl)pyrrole (CPP)-EP, and 2-(ω-carboxyheptyl)pyrrole (CHP)-EP. Because EPs occur in vivo in various forms, a complex mixture of pyrrole-modified EPs with different molecular weights is expected to be generated. To provide a sensitive index of oxidative stress, all of the differences in mass related to the glycerophospholipid moieties were removed by releasing a single CAP-ethanolamine (ETN) or PP-ETN from each mixture by treatment with phospholipase D. Accurate quantization was achieved using the corresponding ethanolamine-d4 pyrroles as internal standards. The product mixture obtained by phospholipolysis of total blood phospholipids from sickle cell disease (SCD) patients was analyzed by LC-MS/MS. The method was applied to measure CAP-EP and PP-EP levels in blood plasma from clinical monitoring of SCD patients. We found uniformly elevated blood levels of CEP-EP (63.9 ± 9.7 nM) similar to mean levels in blood from age-related macular degeneration (AMD) patients (56.3 ± 37.1 nM), and 2-fold lower levels (27.6 ± 3.6 nM, n = 5) were detected in plasma from SCD patients hospitalized to treat a sickle cell crisis, although mean levels remain higher than those (12.1 ± 10.5 nM) detected in blood from healthy controls. Plasma levels of CPP-EPs from SCD clinic patients were 4-fold higher than those of SCD patients hospitalized to treat a sickle cell crisis (45.1 ± 10.9 nM, n = 5 versus 10.9 ± 3.4 nM, n = 6; p < 0.002). PP-EP concentration in plasma from SCD clinic patients is nearly 4.8-fold higher than its level in plasma samples from SCD patients hospitalized to treat a sickle cell crisis (7.06 ± 4.05 vs 1.48 ± 0.92 nM; p < 0.05). Because CAP-EPs promote angiogenesis and platelet activation, the elevated levels present in SCD blood can contribute to the hypercoaguability and vaso-occlusive events that are critical pathophysiologic features of SCD.

Inheritance of the Bantu/Benin haplotype causes less severe hemolytic and oxidative stress in sickle cell anemia patients treated with hydroxycarbamide

Beta S-globin gene cluster haplotypes (β(S)-haplotypes) can modulate the response to hydroxycarbamide (HC) treatment in sickle cell anemia (SCA) patients. In Brazil, the most common haplotypes are Bantu and Benin, and both confer a poor prognosis for patients when untreated with HC. We evaluated oxidative and hemolytic biomarkers in 48 SCA patients undergoing HC treatment separated in three subgroups: Bantu/Bantu, Bantu/Benin and Benin/Benin haplotype. On the basis of reduced haptoglobin (HP) levels, patients with Bantu/Bantu haplotypes had 3.0% higher hemolysis degree when compared with those with Bantu/Benin haplotypes (P=0.01). The Benin/Benin patients had 53.6% greater lipid peroxidation index than the Bantu/Bantu patients (P=0.01) because of evaluated thiobarbituric acid reactive species levels. The Bantu/Benin subgroup had intermediate levels of hemolytic and oxidative stress markers compared with the homozygous subgroups. Through strict inclusion criteria adopted, as well as consolidated and well-described hemolytic and the oxidative parameters evaluated, we suggest a haplotype-interaction response to HC treatment mediated by a 'balance' between the genetic factors of each haplotype studied.

Association of erythrocytes antioxidant enzymes and their cofactors with markers of oxidative stress in patients with sickle cell anemia

BACKGROUND

Sickle cell anemia (SCA) is an inherited blood disease with known complications as a result of certain pathophysiological dysfunctions. It has been suggested that an increase in oxidative stress contributes to the incidence of these changes.

OBJECTIVES

This study investigated the oxidant/antioxidant status of patients with SCA, and evaluated the effect of SCA on antioxidant enzymes and their cofactors.

METHODS

The study included 42 patients with SCA (in steady state), and a control group of 50 age-matched individuals without SCA. Serum malondialdehyde (MDA), copper, zinc, ferritin and iron levels, red blood cell (RBC) superoxide dismutase (SOD) and catalase levels were measured for the SCA and control groups.

RESULTS

Significantly lower levels of antioxidant enzymes (RBC SOD and catalase) and higher serum MDA levels (biomarker of oxidative stress) were found in SCA patients compared to the control group (all p < 0.001). Increased levels of serum ferritin, iron and copper and decreased zinc concentrations were also found in the SCA patients compared to the control group (all p < 0.001). In the SCA group, there were significant negative correlations between MDA levels and RBC SOD, RBC catalase, and serum zinc levels (p < 0.01), while a significant positive correlation between MDA with serum copper and iron levels (p < 0.01) was observed.

CONCLUSION

SCA is associated with alterations in markers of oxidative stress including an increased MDA level, decreased antioxidant enzyme levels, and altered levels of enzyme cofactors (zinc, copper, and iron). This suggests that these antioxidant enzymes could be used as effective therapeutic targets for the treatment of this disease and supplementation of patients with substances with antioxidant properties may reduce the complications of this disease.

Does physical activity increase or decrease the risk of sickle cell disease complications?

Sickle cell disease (SCD) is the most common inherited disease in the world. Red blood cell sickling, blood cell-endothelium adhesion, blood rheology abnormalities, intravascular haemolysis, and increased oxidative stress and inflammation contribute to the pathophysiology of SCD. Because acute intense exercise may alter these pathophysiological mechanisms, physical activity is usually contra-indicated in patients with SCD. However, recent studies in sickle-cell trait carriers and in a SCD mice model show that regular physical activity could decrease oxidative stress and inflammation, limit blood rheology alterations and increase nitric oxide metabolism. Therefore, supervised habitual physical activity may benefit patients with SCD. This article reviews the literature on the effects of acute and chronic exercise on the biological responses and clinical outcomes of patients with SCD.

The Effect of a Selective Inhibitor of Phosphodiesterase-9 on Oxidative Stress, Inflammation and Cytotoxicity in Neutrophils from Patients with Sickle Cell Anaemia

The aim of the study was to investigate the possible anti-inflammatory and antioxidant effects of BAY 73-6691 on neutrophils from SCA patients. This study included 35 patients with a molecular diagnosis of SCA, whose neutrophils were isolated and treated with BAY 73-6691 at the concentrations 100, 10, 1.0 and 0.1 μg/mL. LDH release and MTT assays were performed to verify cell viability. To evaluate oxidative stress, the following parameters were determined by spectrophotometric assays: NO and malondialdehyde (MDA) levels and activity of catalase, superoxide dismutase (SOD) and glutathione peroxidase (GPx). As inflammatory markers, myeloperoxidase (MPO) levels were evaluated by colorimetric assay and TNF-α by enzyme immunoassay. The results showed that neutrophils from SCA patients not treated with hydroxyurea (HU) had significantly lower NO levels and catalase and SOD activity, as well as significantly higher MDA, MPO and TNF-α levels when compared with neutrophils from SCA patients treated with HU and neutrophils from control group. Treatment of SCA neutrophils with BAY 73-6691 resulted in 94%, 200% and 168% increase in NOx levels, SOD and catalase activity, respectively. In addition, there was a reduction of approximately 46% and 45% in TNF-α and MPO levels, respectively. In SCAHU neutrophils, there was a 30% and 44% increase in NOx levels and SOD activity, respectively, and a 28% and 37% decrease in TNF-α and MPO levels, respectively. However, these effects were observed at cytotoxic doses only. The results of this study are original and demonstrate that inhibition of phosphodiesterase-9 in neutrophils from SCA patients with BAY 73-6691 was able to increase the NO bioavailability and attenuate oxidative stress and inflammation in neutrophils from patients not treated with HU.

Nitrergic Mechanisms for Management of Recurrent Priapism

INTRODUCTION

Priapism is a condition involving prolonged penile erection unrelated to sexual interest or desire. The ischemic type, including its recurrent variant, is often associated with both physical and psychological complications. As such, management is of critical importance. Ideal therapies for recurrent priapism should address its underlying pathophysiology.

AIM

To review the available literature on priapism management approaches particularly related to nitrergic mechanisms.

METHODS

A literature review of the pathophysiology and management of priapism was performed using PubMed.

MAIN OUTCOME MEASURE

Publications pertaining to mechanisms of the molecular pathophysiology of priapism.

RESULTS

Nitrergic mechanisms are characterized as major players in the molecular pathophysiology of priapism. PDE5 inhibitors represent an available therapeutic option with demonstrated ability in attenuating these underlying nitrergic derangements. Several additional signaling pathways have been found to play a role in the molecular pathophysiology of priapism and have also been associated with these nitrergic mechanisms.

CONCLUSION

An increasing understanding of the molecular pathophysiology of priapism has led to the discovery of new potential targets. Several mechanism-based therapeutic approaches may become available in the future.

Mechanism of testosterone deficiency in the transgenic sickle cell mouse

Testosterone deficiency is associated with sickle cell disease (SCD), but its underlying mechanism is not known. We investigated the possible occurrence and mechanism of testosterone deficiency in a mouse model of human SCD. Transgenic sickle male mice (Sickle) exhibited decreased serum and intratesticular testosterone and increased luteinizing hormone (LH) levels compared with wild type (WT) mice, indicating primary hypogonadism in Sickle mice. LH-, dbcAMP-, and pregnenolone- (but not 22-hydroxycholesterol)- stimulated testosterone production by Leydig cells isolated from the Sickle mouse testis was decreased compared to that of WT mice, implying defective Leydig cell steroidogenesis. There also was reduced protein expression of steroidogenic acute regulatory protein (STAR), but not cholesterol side-chain cleavage enzyme (P450scc), in the Sickle mouse testis. These data suggest that the capacity of P450scc to support testosterone production may be limited by the supply of cholesterol to the mitochondria in Sickle mice. The sickle mouse testis exhibited upregulated NADPH oxidase subunit gp91phox and increased oxidative stress, measured as 4-hydroxy-2-nonenal, and unchanged protein expression of an antioxidant glutathione peroxidase-1. Mice heterozygous for the human sickle globin (Hemi) exhibited intermediate hypogonadal changes between those of WT and Sickle mice. These results demonstrate that testosterone deficiency occurs in Sickle mice, mimicking the human condition. The defects in the Leydig cell steroidogenic pathway in Sickle mice, mainly due to reduced availability of cholesterol for testosterone production, may be related to NADPH oxidase-derived oxidative stress. Our findings suggest that targeting testicular oxidative stress or steroidogenesis mechanisms in SCD offers a potential treatment for improving phenotypic changes associated with testosterone deficiency in this disease.

How I treat priapism

Priapism is a disorder of persistent penile erection unrelated to sexual interest or desire. This pathologic condition, specifically the ischemic variant, is often associated with devastating complications, notably erectile dysfunction. Because priapism demonstrates high prevalence in patients with hematologic disorders, most commonly sickle cell disease (SCD), there is significant concern for its sequelae in this affected population. Thus, timely diagnosis and management are critical for the prevention or at least reduction of cavernosal tissue ischemia and potential damage consequent to each episode. Current guidelines and management strategies focus primarily on reactive treatments. However, an increasing understanding of the molecular pathophysiology of SCD-associated priapism has led to the identification of new potential therapeutic targets. Future agents are being developed and explored for use in the prevention of priapism.

Erectile dysfunction after sickle cell disease-associated recurrent ischemic priapism: profile and risk factors

INTRODUCTION

Risk factors associated with erectile dysfunction (ED) that results from recurrent ischemic priapism (RIP) in sickle cell disease (SCD) are incompletely defined.

AIM

This study aims to determine and compare ED risk factors associated with SCD and non-SCD-related "minor" RIP, defined as having ≥2 episodes of ischemic priapism within the past 6 months, with the majority (>75%) of episodes lasting <5 hours.

METHODS

We performed a retrospective study of RIP in SCD and non-SCD patients presenting from June 2004 to March 2014 using the International Index of Erectile Function (IIEF), IIEF-5, and priapism-specific questionnaires.

MAIN OUTCOME MEASURES

Prevalence rates and risk factor correlations for ED associated with RIP.

RESULTS

The study was comprised of 59 patients (40 SCD [mean age 28.2 ± 8.9 years] and 19 non-SCD [15 idiopathic and four drug-related etiologies] [mean age 32.6 ± 11.7 years]). Nineteen of 40 (47.5%) SCD patients vs. four of 19 (21.1%) non-SCD patients (39% overall) had ED (IIEF <26 or IIEF-5 <22) (P = 0.052). SCD patients had a longer mean time-length with RIP than non-SCD patients (P = 0.004). Thirty of 40 (75%) SCD patients vs. 10 of 19 (52.6%) non-SCD patients (P = 0.14) had "very minor" RIP (episodes regularly lasting ≤2 hours). Twenty-eight of 40 (70%) SCD patients vs. 14 of 19 (73.7%) non-SCD patients had weekly or more frequent episodes (P = 1). Of all patients with very minor RIP, ED was found among 14 of 30 (46.7%) SCD patients vs. none of 10 (0%) non-SCD patients (P = 0.008). Using logistic regression analysis, the odds ratio for developing ED was 4.7 for SCD patients, when controlling for RIP variables (95% confidence interval: 1.1-21.0).

CONCLUSIONS

ED is associated with RIP, occurring in nearly 40% of affected individuals overall. SCD patients are more likely to experience ED in the setting of "very minor" RIP episodes and are five times more likely to develop ED compared with non-SCD patients.

Triterpenoid inducers of Nrf2 signaling as potential therapeutic agents in sickle cell disease: a review

Sickle cell disease (SCD) is an inherited disorder of hemoglobin in which the abnormal hemoglobin S polymerizes when deoxygenated. This polymerization of hemoglobin S not only results in hemolysis and vasoocclusion but also precipitates inflammation, oxidative stress and chronic organ dysfunction. Oxidative stress is increasingly recognized as an important intermediate in these pathophysiological processes and is therefore an important target for therapeutic intervention. The transcription factor nuclear erythroid derived-2 related factor 2 (Nrf2) controls the expression of anti-oxidant enzymes and is emerging as a protein whose function can be exploited with therapeutic intent. This review article is focused on triterpenoids that activate Nrf2, and their potential for reducing oxidative stress in SCD as an approach to prevent organ dysfunction associated with this disease. A brief overview of oxidative stress in the clinical context of SCD is accompanied by a discussion of several pathophysiological mechanisms contributing to oxidative stress. Finally, these mechanisms are then related to current management strategies in SCD that are either utilized currently or under evaluation. The article concludes with a perspective on the potential of the various therapeutic interventions to reduce oxidative stress and morbidity associated with SCD.

Oxidant-antioxidant status in Egyptian children with sickle cell anemia: a single center based study

OBJECTIVE

the present study was conducted to investigate the oxidant-antioxidant status in Egyptian children with sickle cell anemia.

METHODS

the serum levels of total antioxidant capacity (TAO), paraoxonase (PON), vitamin E, nitrite, and malondialdehyde (MDA) were measured in 40 steady state children with homozygous sickle cell anemia (24 males and 16 females) and 20 apparently healthy age- and gender-matched controls.

RESULTS

mean serum TAO, PON, vitamin E, and nitrite levels were significantly lower in the group with sickle cell anemia, whereas mean serum MDA was significantly higher in these children compared to controls. No significant differences in mean levels of TAO, PON, nitrite, vitamin E, and MDA were found in sickle cell anemia patients receiving hydroxyurea when compared with those not receiving hydroxyurea. A significant negative correlation between serum nitrite and the occurrence of vaso-occlusive crises (VOC) was observed (r=-0.3, p=0.04). PON level was found to be positively correlated with patients' weight and BMI (r=-0.4, p=0.01; r=-0.7, p<0.001, respectively), but not with frequency of VOC. The area under the curve of serum nitrite in predicting occurrence of VOC was 0.782, versus 0.701 for PON, and 0.650 for TAO (p=0.006). Serum MDA was not correlated with nitrite, PON, TAO, or vitamin E levels. No significant correlations were detected between serum nitrite and hemoglobin or antioxidant enzymes.

CONCLUSION

children with sickle cell anemia have chronic oxidative stress that may result in increased VOC, and decreased serum nitrite may be associated with increases in VOC frequency. A novel finding in this study is the decrease in PON level in these patients, which is an interesting subject for further research.

Microvascular oxygen consumption during sickle cell pain crisis

Sickle cell disease is an inherited blood disorder characterized by chronic hemolytic anemia and episodic vaso-occlusive pain crises. Vaso-occlusion occurs when deoxygenated hemoglobin S polymerizes and erythrocytes sickle and adhere in the microvasculature, a process dependent on the concentration of hemoglobin S and the rate of deoxygenation, among other factors. We measured oxygen consumption in the thenar eminence during brachial artery occlusion in sickle cell patients and healthy individuals. Microvascular oxygen consumption was greater in sickle cell patients than in healthy individuals (median [interquartile range]; sickle cell: 0.91 [0.75-1.07] vs healthy: 0.75 [0.62-0.94] -ΔHbO2/min, P < .05) and was elevated further during acute pain crisis (crisis: 1.10 [0.78-1.30] vs recovered: 0.88 [0.76-1.03] -ΔHbO2/min, P < .05). Increased microvascular oxygen consumption during pain crisis could affect the local oxygen saturation of hemoglobin when oxygen delivery is limiting. Identifying the mechanisms of elevated oxygen consumption during pain crisis might lead to the development of new therapeutic interventions. This trial was registered at www.clinicaltrials.gov as #NCT01568710.

Does erythropoietin have a role in the treatment of β-hemoglobinopathies?

This review presents the indications and contraindications (pros and cons) for the potential use of erythropoietin (Epo) as a treatment in β-thalassemia and sickle cell anemia (SCA). Its high cost and route of administration (by injection) are obvious obstacles, especially in underdeveloped countries, where thalassemia is prevalent. We believe that from the data summarized in this review, the time has come to define, by studying in vitro and in vivo models, as well as by controlled clinical trials, the rationale for treating patients with various forms of thalassemia and SCA with Epo alone or in combination with other medications.

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.