Pulmonary hypertension associated with sickle cell disease: pathophysiology and rationale for treatment

Antibiotics for treating acute chest syndrome in people with sickle cell disease

BACKGROUND

The clinical presentation of acute chest syndrome is similar whether due to infectious or non-infectious causes, thus antibiotics are usually prescribed to treat all episodes. Many different pathogens, including bacteria, have been implicated as causative agents of acute chest syndrome. There is no standardized approach to antibiotic therapy and treatment is likely to vary from country to country. Thus, there is a need to identify the efficacy and safety of different antibiotic treatment approaches for people with sickle cell disease suffering from acute chest syndrome. This is an update of a Cochrane Review first published in 2007, and most recently updated in 2015.

OBJECTIVES

To determine whether an empirical antibiotic treatment approach (used alone or in combination):1. is effective for acute chest syndrome compared to placebo or standard treatment;2. is safe for acute chest syndrome compared to placebo or standard treatment;Further objectives are to determine whether there are important variations in efficacy and safety:3. for different treatment regimens,4. by participant age, or geographical location of the clinical trials.

SEARCH METHODS

We searched The Group's Haemoglobinopathies Trials Register, which comprises references identified from comprehensive electronic database searches and handsearching of relevant journals and abstract books of conference proceedings. We also searched the LILACS database (1982 to 23 October 2017), African Index Medicus (1982 to 23 October 2017) and trial registries (23 October 2017).Date of most recent search of the Haemoglobinopathies Trials Register: 10 July 2019.

SELECTION CRITERIA

We searched for published or unpublished randomised controlled trials.

DATA COLLECTION AND ANALYSIS

Each author intended to independently extract data and assess trial quality by standard Cochrane methodologies, but no eligible randomised controlled trials were identified.

MAIN RESULTS

For this update, we were unable to find any randomised controlled trials on antibiotic treatment approaches for acute chest syndrome in people with sickle cell disease.

AUTHORS' CONCLUSIONS

This update was unable to identify randomised controlled trials on efficacy and safety of the antibiotic treatment approaches for people with sickle cell disease suffering from acute chest syndrome. While randomised controlled trials are needed to establish the optimum antibiotic treatment for this condition, we do not envisage further trials of this intervention will be conducted, and hence the review will no longer be regularly updated.

New Nitric Oxide Donor NCX 1443: Therapeutic Effects on Pulmonary Hypertension in the SAD Mouse Model of Sickle Cell Disease

Nitric oxide (NO) donors may be useful for treating pulmonary hypertension (PH) complicating sickle cell disease (SCD), as endogenous NO is inactivated by hemoglobin released by intravascular hemolysis. Here, we investigated the effects of the new NO donor NCX1443 on PH in transgenic SAD mice, which exhibit mild SCD without severe hemolytic anemia. In SAD and wild-type (WT) mice, the pulmonary pressure response to acute hypoxia was similar and was abolished by 100 mg/kg NCX1443. The level of PH was also similar in SAD and WT mice exposed to chronic hypoxia (9% O2) alone or with SU5416 and was similarly reduced by daily NCX1443 gavage. Compared with WT mice, SAD mice exhibited higher levels of HO-1, endothelial NO synthase, and PDE5 but similar levels of lung cyclic guanosine monophosphate. Cultured pulmonary artery smooth muscle cells from SAD mice grew faster than those from WT mice and had higher PDE5 protein levels. Combining NCX1443 and a PDE5 inhibitor suppressed the growth rate difference between SAD and WT cells and induced a larger reduction in hypoxic PH severity in SAD than in WT mice. By amplifying endogenous protective mechanisms, NCX1443 in combination with PDE5 inhibition may prove useful for treating PH complicating SCD.

A modified noninvasive screening protocol for pulmonary hypertension in children with sickle cell disease-Who should be sent for invasive evaluation?

BACKGROUND

Invasive studies have shown that prevalence and severity of pulmonary hypertension (PH) in patients with sickle cell disease (SCD) tend to be overestimated if based exclusively on Doppler-derived tricuspid regurgitant velocity (TRV) as surrogate noninvasive marker with a cutoff ≥2.5 m/s.

OBJECTIVES

We aimed to better define a subgroup of pediatric SCD patients who should be sent for invasive evaluation of pulmonary artery pressure (PAP) based on a modified echocardiographic PH screening protocol that implements evidence from Doppler-catheter comparative studies.

STUDY DESIGN

Charts of 121 pediatric patients with stable SCD were reviewed regarding echocardiographically assessed risk for elevated PAP/PH and associated clinical characteristics. TRV cutoff was refined at ≥2.9 m/s to avoid overestimating the risk for PH. TRV was combined with additional echocardiographic parameters to avoid underestimating the PH risk.

RESULTS

Ninety-one patients qualified for analysis. Based on our modified echocardiographic protocol, 5.5% of patients qualified for at least moderate risk for elevated PAP (compatible with PH) as opposed to 20.9% if based exclusively on TRV ≥2.5 m/s. These patients were older, homozygous for hemoglobin S (HbSS), and more anemic. No subject had an echocardiographic risk constellation suggesting more than mild PH.

CONCLUSIONS

Our modified noninvasive screening protocol-if confirmed by invasive studies-may help to better identify a subgroup of pediatric SCD patients in whom evaluation by catheterization appears justified. Unlike estimates based on the conventional protocol, the size of the targeted subgroup compares favorably with catheterization-confirmed PH prevalence rates. Characteristics associated with an increased PH risk were also identified.

Antibiotics for treating acute chest syndrome in people with sickle cell disease

BACKGROUND

The clinical presentation of acute chest syndrome is similar whether due to infectious or non-infectious causes, thus antibiotics are usually prescribed to treat all episodes. Many different pathogens, including bacteria, have been implicated as causative agents of acute chest syndrome. There is no standardized approach to antibiotic therapy and treatment is likely to vary from country to country. Thus, there is a need to identify the efficacy and safety of different antibiotic treatment approaches for people with sickle cell disease suffering from acute chest syndrome. This is an update of a Cochrane review first published in 2007, and previously updated in 2013.

OBJECTIVES

To determine whether an empirical antibiotic treatment approach (used alone or in combination):1. is effective for acute chest syndrome compared to placebo or standard treatment;2. is safe for acute chest syndrome compared to placebo or standard treatment;Further objectives are to determine whether there are important variations in efficacy and safety:3. for different treatment regimens,4. by participant age, or geographical location of the clinical trials.

SEARCH METHODS

We searched The Group's Haemoglobinopathies Trials Register, which comprises references identified from comprehensive electronic database searches and handsearching of relevant journals and abstract books of conference proceedings. We also searched the LILACS database (1982 to 23 February 2015), African Index Medicus (1982 to 23 February 2015). and the World Health Organization International Clinical Trials Registry Platform Search Portal (23 February 2015).Date of most recent search of the Haemoglobinopathies Trials Register: 20 January 2015.

SELECTION CRITERIA

We searched for published or unpublished randomised controlled trials.

DATA COLLECTION AND ANALYSIS

Each author intended to independently extract data and assess trial quality by standard Cochrane Collaboration methodologies, but no eligible randomised controlled trials were identified.

MAIN RESULTS

For this update, we were unable to find any randomised controlled trials on antibiotic treatment approaches for acute chest syndrome in people with sickle cell disease.

AUTHORS' CONCLUSIONS

This update was unable to identify randomised controlled trials on efficacy and safety of the antibiotic treatment approaches for people with sickle cell disease suffering from acute chest syndrome. Randomised controlled trials are needed to establish the optimum antibiotic treatment for this condition.

MicroRNA 648 Targets ET-1 mRNA and is cotranscriptionally regulated with MICAL3 by PAX5

Pulmonary hypertension (PHT) is associated with high mortality in sickle cell anemia (SCA). Previously, we showed that elevated levels of placenta growth factor (PlGF) in SCA patients correlate with increased levels of the potent vasoconstrictor endothelin-1 (ET-1) and PHT. Moreover, PlGF induced the expression of ET-1 via hypoxia-inducible factor 1α. Here, we show a novel example of ET-1 posttranscriptional regulation by PlGF via action of microRNA 648 (miR-648), which is subject to transcriptional coregulation with its host gene, MICAL3 (microtubule-associated monooxygenase, calponin, and LIM domain containing 3gene). PlGF repressed expression of miR-648 in endothelial cells. Luciferase reporter assays using wild-type and mutant ET-1 3' untranslated region (UTR) constructs, and transfection of miR-648 mimics showed that miR-648 targets the 3' UTR of ET-1 mRNA. Since miR-648 is located in a 5'-proximal intron of MICAL3, we examined which of three potential promoters was responsible for its expression. The MICAL3 distal promoter (P1) was the predominant promoter used for transcription of pre-miR-648, and it was under positive control by PAX5 (paired box protein 5) transcription factor, as demonstrated by the loss and gain of function of PAX5 activity, and chromatin immunoprecipitation analysis. These studies provide a novel link wherein PlGF-mediated downregulation of PAX5 attenuates miR-648 expression leading to increased ET-1 levels that are known to induce PHT in SCA.

Evidence for the endothelin system as an emerging therapeutic target for the treatment of chronic pain

Many people worldwide suffer from pain and a portion of these sufferers are diagnosed with a chronic pain condition. The management of chronic pain continues to be a challenge, and despite taking prescribed medication for pain, patients continue to have pain of moderate severity. Current pain therapies are often inadequate, with side effects that limit medication adherence. There is a need to identify novel therapeutic targets for the management of chronic pain. One potential candidate for the treatment of chronic pain is therapies aimed at modulating the vasoactive peptide endothelin-1. In addition to vasoactive properties, endothelin-1 has been implicated in pain transmission in both humans and animal models of nociception. Endothelin-1 directly activates nociceptors and potentiates the effect of other algogens, including capsaicin, formalin, and arachidonic acid. In addition, endothelin-1 has been shown to be involved in inflammatory pain, cancer pain, neuropathic pain, diabetic neuropathy, and pain associated with sickle cell disease. Therefore, endothelin-1 may prove a novel therapeutic target for the relief of many types of chronic pain.

[Cardiopulmonary complications in sickle cell anemia]

Sickle cell anemia, considered the most prevalent genetic disease among African Americans, is a disease with autosomal recessive inheritance pattern, characterized by the production of hemoglobin S. This abnormal protein polymerizes and facilitates the formation of fibrillar aggregates that alters the erythrocyte morphology. The stiffness of the red blood cells hinders the adequate transit across microcirculation, leading to hemolysis and increased blood viscosity, which ease thrombogenesis and vascular occlusion, resulting in tissue ischemia and microinfarcts. This disease has a high rate of morbidity and mortality, especially in the first three years of life, when a rapid diagnosis and appropriate treatment are essential. Cardiovascular complications such as heart failure and pulmonary hypertension may develop independently, and each one contributes to increased mortality, being the combination of both risk factors, an important aggravating factor for prognosis and a determinant indicator of mortality.

Therapeutic approaches to limit hemolysis-driven endothelial dysfunction: scavenging free heme to preserve vasculature homeostasis

Hemolysis results in the release of hemoglobin and heme into the bloodstream and is associated with the development of several pathologic conditions of different etiology, including hemoglobinopathies, hemolytic anemias, bacterial infections, malaria, and trauma. In addition, hemolysis is associated with surgical procedures, hemodialysis, blood transfusion, and other conditions in which mechanical forces can lead to red blood cell rupture. Free plasma hemoglobin and heme are toxic for the vascular endothelium since heme iron promotes oxidative stress that causes endothelial activation responsible for vasoocclusive events and thrombus formation. Moreover, free hemoglobin scavenges nitric oxide, reducing its bioavailability, and heme favours ROS production, thus causing oxidative nitric oxide consumption. This results in the dysregulation of the endothelium vasodilator:vasoconstrictor balance, leading to severe vasoconstriction and hypertension. Thus, endothelial dysfunction and impairment of cardiovascular function represent a common feature of pathologic conditions associated with hemolysis. In this review, we discuss how hemoglobin/heme released following hemolysis may affect vascular function and summarise the therapeutic approaches available to limit hemolysis-driven endothelial dysfunction. Particular emphasis is put on recent data showing the beneficial effects obtained through the use of the plasma heme scavenger hemopexin in counteracting heme-mediated endothelial damage in mouse models of hemolytic diseases.

Antibiotics for treating acute chest syndrome in people with sickle cell disease

BACKGROUND

The clinical presentation of acute chest syndrome is similar whether due to infectious or non-infectious causes, thus antibiotics are usually prescribed to treat all episodes. Many different pathogens, including bacteria, have been implicated as causative agents of acute chest syndrome. There is no standardized approach to antibiotic therapy and treatment is likely to vary from country to country. Thus, there is a need to identify the efficacy and safety of different antibiotic treatment approaches for people with sickle cell disease suffering from acute chest syndrome.

OBJECTIVES

To determine whether an empirical antibiotic treatment approach (used alone or in combination): 1. is effective for acute chest syndrome compared to placebo or standard treatment; 2. is safe for acute chest syndrome compared to placebo or standard treatment;Further objectives are to determine whether there are important variations in efficacy and safety: 3. for different treatment regimens, 4. by participant age, or geographical location of the clinical trials.

SEARCH METHODS

We searched The Group's Haemoglobinopathies Trials Register, which comprises references identified from comprehensive electronic database searches and handsearching of relevant journals and abstract books of conference proceedings. We also searched the LILACS database (1982 to 19 October 2012), African Index Medicus (1982 to 3 November 2012). and the World Health Organization International Clinical Trials Registry Platform Search Portal (19 October 2012).Date of most recent search of the Haemoglobinopathies Trials Register: 29 October 2012.

SELECTION CRITERIA

We searched for published or unpublished randomised controlled trials.

DATA COLLECTION AND ANALYSIS

Each author intended to independently extract data and assess trial quality by standard Cochrane Collaboration methodologies, but no eligible randomised controlled trials were identified.

MAIN RESULTS

For this update, we were unable to find any randomised controlled trials on antibiotic treatment approaches for acute chest syndrome in people with sickle cell disease.

AUTHORS' CONCLUSIONS

This update was unable to identify randomised controlled trials on efficacy and safety of the antibiotic treatment approaches for people with sickle cell disease suffering from acute chest syndrome. Randomised controlled trials are needed to establish the optimum antibiotic treatment for this condition.

Atherosclerosis in sickle cell disease - a review

Acute, vaso-occlusive crises are the most common and earliest clinical manifestations of sickle cell disease. Recent thoughts about development of atherosclerosis as a result of this disease are presented. Current insights into the pathogenesis of atherosclerosis in sickle cell disease are reviewed, in particular the role of endothelial dysfunction, homocysteine and platelets. Common and uncommon sites of atherosclerosis are described. Radiological assessment and potential therapeutic agents to slow the progression of atherosclerosis are discussed. Finally, treatment of atherosclerosis in certain sites is evaluated and reviewed.

Pulmonary complications of sickle cell disease

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

High levels of placenta growth factor in sickle cell disease promote pulmonary hypertension

Pulmonary hypertension is associated with reduced nitric oxide bioavailability and early mortality in sickle cell disease (SCD). We previously demonstrated that placenta growth factor (PlGF), an angiogenic factor produced by erythroid cells, induces hypoxia-independent expression of the pulmonary vasoconstrictor endothelin-1 in pulmonary endothelial cells. Using a lentivirus vector, we simulated erythroid expression of PlGF in normal mice up to the levels seen in sickle mice. Consequently, endothelin-1 production increased, right ventricle pressures increased, and right ventricle hypertrophy and pulmonary changes occurred in the mice within 8 weeks. These findings were corroborated in 123 patients with SCD, in whom plasma PlGF levels were significantly associated with anemia, endothelin-1, and tricuspid regurgitant velocity; the latter is reflective of peak pulmonary artery pressure. These results illuminate a novel mechanistic pathway linking hemolysis and erythroid hyperplasia to increased PlGF, endothelin-1, and pulmonary hypertension in SCD, and suggest that strategies that block PlGF signaling may be therapeutically beneficial.

Investigational drugs in sickle cell anemia

Sickle cell anemia is one of the most common autosomal recessive diseases in the world. Patients with sickle cell anemia have variable penetrance and it is hard to predict the risk and timing of complications. It is characterized by a point mutation in the beta-globin gene (GAG --> GTG) and the production of hemoglobin S. The latter leads to decreased deformability of the red blood cells (RBCs) that adhere to endothelia cells culminating in vascular occlusion and its sequelae of tissue ischemia and organ damage. Moreover, sickled RBCs undergo intravascular hemolysis and accelerated erythropoesis. The hallmarks of this disease are shortened RBC survival and vaso-occlusive crises. For the past ten years, the pathophysiology of this disease has been better elucidated and has led to significant improvements in the standard of care. Vaso-occlusion is now understood to be a complex event that involves abnormal interactions between RBCs, leukocytes, endothelial cells and the coagulation pathways. The field of translational research in sickle cell anemia has expanded greatly and has led to new clinical trials with new therapeutic agents and strategies. In this paper, we review the drugs that are now being investigated in the treatment of sickle cell anemia.

Pathophisiology of sickle cell disease and new drugs for the treatment

A homozygous mutation in the gene for β globin, a subunit of adult hemoglobin A (HbA), is the proximate cause of sickle cell disease (SCD). Sickle hemoglobin (HbS) shows peculiar biochemical properties, which lead to polymerizing when deoxygenated. HbS polymerization is associated with a reduction in cell ion and water content (cell dehydration), increased red cell density which further accelerate HbS polymerization. Dense, dehydrated erythrocytes are likely to undergo instant polymerization in conditions of mild hypoxia due to their high HbS concentration, and HbS polymers may be formed under normal oxygen pressure. Pathophysiological studies have shown that the dense, dehydrated red cells may play a central role in acute and chronic clinical manifestations of sickle cell disease, in which intravascular sickling in capillaries and small vessels leads to vaso-occlusion and impaired blood flow in a variety of organs and tissue. The persistent membrane damage associated with HbS polymerization also favors the generation of distorted rigid cells and further contributes to vaso-occlusive crisis (VOCs) and cell destruction in the peripheral circulation. These damaged, dense sickle red cells also show a loss of phospholipid asymmetry with externalization of phosphatidylserine (PS), which is believed to play a significant role in promoting macrophage recognition with removal of erythrocytes (erythrophagocytosis). Vaso-occlusive events in the microcirculation result from a complex scenario involving the interactions between different cell types, including dense, dehydrated sickle cells, reticulocytes, abnormally activated endothelial cells, leukocytes, platelets and plasma factors such as cytokine and oxidized pro-inflammatory lipids. Hydroxycarbamide (hydroxyurea) is currently the only drug approved for chronic administration in adult patients with sickle cell disease to prevent acute painful crises and reduce the incidence of transfusion and acute chest crises. Here, we will focus on consolidated and experimental therapeutic strategies for the treatment of sickle cell disease, including:

agents which reduce or prevent sickle cell dehydration

agents which reduce sickle cell-endothelial adhesive events

nitric oxide (NO) or NO-related compounds

anti-oxidant agents

Correction of the abnormalities ranging from membrane cation transport pathways to red cell-endothelial adhesive events, might constitute new pharmacological targets for treating sickle cell disease.

Antibiotics for treating acute chest syndrome in people with sickle cell disease

BACKGROUND

The clinical presentation of acute chest syndrome is similar whether due to infectious or non-infectious causes, thus antibiotics are usually prescribed to treat all episodes. Many different bacteria have been implicated as causative agents of acute chest syndrome. There is no standardized approach to antibiotic therapy and treatment is likely to vary from country to country. Thus, there is a need to identify the efficacy and safety of different antibiotic treatment approaches for people with sickle cell disease suffering from acute chest syndrome.

OBJECTIVES

To determine whether an empirical antibiotic treatment approach (used either alone or in combination): (a) is effective in treating acute chest syndrome compared to placebo or standard treatment; (b) is safe in treating acute chest syndrome compared to placebo or standard treatment; (c) differs dependent on the regimen used in treating acute chest syndrome differ from each other with respect to efficacy and safety; and (d) varies between different age groups, regions or countries with respect to efficacy and safety.

SEARCH STRATEGY

We searched The Group's Haemoglobinopathies Trials Register, which comprises references identified from comprehensive electronic database searches and handsearching of relevant journals and abstract books of conference proceedings. We also searched the LILACS database (1982 to May 2006) and the website: http://www.clinicaltrials.gov (May 2006). Date of most recent search of the Haemoglobinopathies Trials Register: February 2007.

SELECTION CRITERIA

We searched for published or unpublished randomised controlled trials.

DATA COLLECTION AND ANALYSIS

Each author intended to independently extract data and assess trial quality by standard Cochrane Collaboration methodologies, but no eligible randomized controlled trials were identified.

MAIN RESULTS

We were unable to find any randomised controlled trials on antibiotic treatment approaches for acute chest syndrome in people with sickle cell disease.

AUTHORS' CONCLUSIONS

We were unable to identify randomised controlled trials on efficacy and safety of the antibiotic treatment approaches for people with sickle cell disease suffering from acute chest syndrome. Randomised controlled trials are needed to establish the optimum antibiotic treatment for this condition.