Olufolake Adisa

Extracellular hemin crisis triggers acute chest syndrome in sickle mice

The prevention and treatment of acute chest syndrome (ACS) is a major clinical concern in sickle cell disease (SCD). However, the mechanism underlying the pathogenesis of ACS remains elusive. We tested the hypothesis that the hemolysis byproduct hemin elicits events that induce ACS. Infusion of a low dose of hemin caused acute intravascular hemolysis and autoamplification of extracellular hemin in transgenic sickle mice, but not in sickle-trait littermates. The sickle mice developed multiple symptoms typical of ACS and succumbed rapidly. Pharmacologic inhibition of TLR4 and hemopexin replacement therapy prior to hemin infusion protected sickle mice from developing ACS. Replication of the ACS-like phenotype in nonsickle mice revealed that the mechanism of lung injury due to extracellular hemin is independent of SCD. Using genetic and bone marrow chimeric tools, we confirmed that TLR4 expressed in nonhematopoietic vascular tissues mediated this lethal type of acute lung injury. Respiratory failure was averted after the onset of ACS-like symptoms in sickle mice by treating them with recombinant hemopexin. Our results reveal a mechanism that helps to explain the pathogenesis of ACS, and we provide proof of principle for therapeutic strategies to prevent and treat this condition in mice.

Association between plasma free haem and incidence of vaso-occlusive episodes and acute chest syndrome in children with sickle cell disease.

We tested the hypothesis that extracellular haem is linked to the incidence of acute complications of sickle cell disease (SCD). Using multivariable regression analysis, higher plasma free haem, but not total plasma haem, was associated with increased odds of vaso‐occlusive crisis (VOC) [P = 0·028, odds ratio (OR); 2·05, 95% Confidence Interval (CI) = 1·08–3·89] and acute chest syndrome (ACS) [P = 0·016, OR; 2·56, CI = 1·19, 5·47], after adjusting for age and gender in children with SCD. These findings suggest that haem and factors that influence its concentration in plasma may be informative of the risk of VOC and ACS in SCD patients.

Alloimmunization to transfused HOD red blood cells is not increased in mice with sickle cell disease

BACKGROUND: Increased rates of red blood cell (RBC) alloimmunization in patients with sickle cell disease may be due to transfusion frequency, genetic predisposition, or immune dysregulation. To test the hypothesis that sickle cell pathophysiology influences RBC alloimmunization, we utilized two transgenic mouse models of sickle cell disease.

Global Gene Expression Profiling of Endothelium Exposed to Heme Reveals an Organ-Specific Induction of Cytoprotective Enzymes in Sickle Cell Disease

Background Sickle cell disease (SCD) is characterized by hemolysis, vaso-occlusion and ischemia reperfusion injury. These events cause endothelial dysfunction and vasculopathies in multiple systems. However, the lack of atherosclerotic lesions has led to the idea that there are adaptive mechanisms that protect the endothelium from major vascular insults in SCD patients. The molecular bases for this phenomenon are poorly defined. This study was designed to identify the global profile of genes induced by heme in the endothelium, and assess expression of the heme-inducible cytoprotective enzymes in major organs impacted by SCD. Methods and Findings Total RNA isolated from heme-treated endothelial monolayers was screened with the Affymetrix U133 Plus 2.0 chip, and the microarray data analyzed using multiple bioinformatics software. Hierarchical cluster analysis of significantly differentially expressed genes successfully segregated heme and vehicle-treated endothelium. Validation studies showed that the induction of cytoprotective enzymes by heme was influenced by the origin of endothelial cells, the duration of treatment, as well as the magnitude of induction of individual enzymes. In agreement with these heterogeneities, we found that induction of two major Nrf2-regulated cytoprotective enzymes, heme oxygenase-1 and NAD(P)H:quinone oxidoreductase-1 is organ-specific in two transgenic mouse models of SCD. This data was confirmed in the endothelium of post-mortem lung tissues of SCD patients. Conclusions Individual organ systems induce unique profiles of cytoprotective enzymes to neutralize heme in SCD. Understanding this heterogeneity may help to develop effective therapies to manage vasculopathies of individual systems.

Hydroxyurea effectiveness in children and adolescents with sickle cell anemia: A large retrospective, population-based cohort

The clinical efficacy of hydroxyurea in patients with sickle cell anemia (SCA) has been well established. However, data about its clinical effectiveness in practice is limited. We evaluated the clinical effectiveness of hydroxyurea in a large pediatric population using a retrospective cohort, pre‐post treatment study design to control for disease severity selection bias. The cohort included children with SCA (SS, Sβ0thalassemia) who received care at Childrens Healthcare of Atlanta (CHOA) and who initiated hydroxyurea in 2009‐2011. Children on chronic transfusions, or children with inadequate follow up data and/or children who had taken hydroxyurea in the 3 years prior were excluded. For each patient healthcare utilization, laboratory values, and clinical outcomes for the 2‐year period prior to hydroxyurea initiation were compared to those 2 years after initiation. Of 211 children with SCA who initiated hydroxyurea in 2009–2011, 134 met eligibility criteria. After initiation of hydroxyurea, rates of hospitalizations, pain encounters, and emergency department visits were reduced by 47% (<0.0001), 36% (P = 0.0001) and 43% (P < 0.0001), respectively. Average hemoglobin levels increased by 0.7 g/dl (P < 0.0001). Hydroxyurea effectiveness was similar across gender, insurance types and age, although there was a slightly greater reduction in hospitalizations in younger children. Am. J. Hematol. 92:77–81, 2017.

Inhaled corticosteroid use to prevent severe vaso-occlusive episode recurrence in children between 1 and 4 years of age with sickle cell disease: a multicenter feasibility trial

Julia E. Brittain , Ciprian Anea, Payal Desai, Jack Delaney, Adam McDonald, Stephen W. Looney, Nigel S. Key, Leslie V. Parise, Kenneth I. Ataga Vascular Biology Center, Augusta University, Augusta, Georgia Division of Hematology, Department of Medicine, The Ohio State University Division of Hematology and Oncology, Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina Department of Biostatistics and Epidemiology, Augusta University, Augusta, Georgia Department of Biochemistry & Biophysics, University of North Carolina, Chapel Hill, North Carolina

Sickle Cell Disease and Acute Chest Syndrome: Mechanisms and Pathogenenesis

Acute chest syndrome (ACS) is the major lung complication and leading cause of death in sickle cell disease (SCD). It is characterized by a rapid disease onset, pulmonary infiltration, hypoxemia, and several other clinical indications. Postmortem ACS lungs are characterized by histological evidence of alveolar capillary barrier disruption, fat emboli, and alveolar wall necrosis. Ischemia-reperfusion injury activation of invariant natural killer T lymphocytes is thought to heighten baseline pulmonary inflammation in SCD that may prime the lung for ACS development. Multiple factors, including hypoxia, infection, infarction, thrombosis, and fat emboli that are implicated in ACS pathogenesis are also associated with acute hemolysis. ACS is typically preceded by acute intravascular hemolysis, and the magnitude of anemia is linked to the severity of the lung injury. The heme hypothesis posits that the lung injury in ACS is caused by acute inflammation directly involving extracellular heme, a prototypical erythroid DAMP molecule released by hemolysis. In support of this model, the infusion of purified heme triggers a lethal acute lung injury in transgenic SCD mice that exhibit many of the characteristics of severe ACS. Additional experimental data indicate heme-induced ACS may involve vaso-occlusion and the release of neutrophil extracellular traps in the lung. Clinically, the risk of patients developing ACS is influenced by steady-state plasma concentrations of heme, and by polymorphisms in the gene encoding heme oxygenase-1, the rate-limiting heme degradation enzyme. Extracellular heme is therefore an ideal converging axis in the pathogenesis of ACS.

Are we missing the mark? Fever, respiratory symptoms, chest radiographs, and acute chest syndrome in sickle cell disease.

To the Editor: Acute chest syndrome (ACS) is defined as a new pulmonary infiltrate detected by chest radiography (CXR) associated with fever, respiratory symptoms, or chest pain [1,2]. It is the second most common cause of hospital admissions in SCD, and can lead to significant morbidity and mortality [2]. Evidence in the literature has established that clinical assessment alone is not a sensitive predictor of ACS [1,2]. Although these studies were performed nearly 20 years ago, they advocate for empiric CXR utilization all febrile children with SCD [1,2]. Since then, the incidence of ACS in febrile children has decreased from 27 to 17.4% (P < 0.001) [3], likely due in part to routine penicillin prophylaxis, expanded pneumococcal immunization coverage, and hydroxyurea use. National Institutes of Health (NIH) guidelines for febrile SCD patients were updated in 2014 recommending that patients with fever associated with shortness of breath, tachypnea, cough, and/or rales should undergo CXR to evaluate for ACS [4]. No systemic review of the literature was done regarding these SCD/fever guidelines, which utilized panel consensus expert opinion. Since there are discrepancies between the current NIH guidelines, many institutional clinical pathway recommendations and evidence from the literature, this study was undertaken to help identify febrile children with SCD requiring a CXR as part of their assessment. 2013 emergency department (ED) data were obtained by electronic medical record using ICD-9 codes linked to fever and SCD in children 2 months–18 years through a retrospective chart review at two urban tertiary-care campuses of Children’s Healthcare of Atlanta (CHOA). Demographics, past medical history, vital signs, review of systems (ROS), physical exam (PE) findings, CXR radiology interpretation, and ACS diagnosis were obtained by chart review; see “Supporting Information Methods” for details. Patient Demographics and Clinical Characteristics. A total of 356 patients with 609 ED encounters were evaluated. (see Supporting Information Fig. 1 for flowchart). Patient demographics are summarized in Supporting Information Table I. The mean age was 5.7 6 5 years. Half were female and the majority of patients (67%) had Hb-SS. Comparison of Patients with and without CXR Ordered. Patient demographics, clinical characteristics and risk factors for ordering of CXR are summarized in Supporting Information Table II. 379 CXRs were ordered from the 609 encounters (62%); see Supporting Information Methods/Results. Children with Negative Vs. Positive CXR (ACS). Supporting Information Table II summarizes demographics, clinical characteristics and risk factors for patients with ACS (n 5 66) compared to those with negative CXRs. Of encounters evaluated by CXR, the prevalence of ACS was 17.2% in our cohort. Risk factors for ACS as determined by univariate analysis include the presence of tachypnea, history of ACS, and abnormal ROS (presence of cough, wheeze, or chest pain). An abnormal lung exam was also more frequently found in children diagnosed with ACS. However, 62% of patients with ACS had a normal lung exam. Patients with ACS were also more frequently admitted to the hospital. Of all admitted patients, those with ACS more frequently utilized oxygen and BiPAP. However, there was no difference in age, gender, height of fever, asthma diagnosis, presence of rhinorrhea, congestion, grunting, or shortness of breath in children diagnosed with ACS compared to those with a negative CXR. Clinical characteristics involving patients discharged from the ED and <72-h ED returns are summarized in Supporting Information Methods/Results. One patient who was discharged without a CXR returned to the ED within 24 h with ACS. Risk Factors for ACS. Figure 1A summarizes multivariate logistic regression analysis, identifying history of ACS, cough, chest pain, and abnormal PE findings as independent risk factors associated with ACS, with an area under a receiver operating characteristics curve (AUC) of 0.7254, 95% CI [0.6612–0.7893]. Multivariate logistic regression was also applied to the 2014 NIH guidelines (Fig. 1A). There is a statistically significant difference in AUC between Emory/CHOA and the NIH risk stratification model, with NIH guidelines giving a lower AUC 5 0.6623, 95% CI [0.5946–0.7299] (P 5 0.04; Fig. 1B). Of the 66 CXRs found to be positive, no cases of ACS occurred in children who lacked all Emory/CHOA risk factors. Six out of 66 (9.1%) children with a positive CXR had a history of ACS alone and no other risk factors. Percentage of patients with ACS presenting with 0–4 risk factors is summarized in Supporting Information Table III. Of the 230 children with SCD and fever who were not evaluated by CXR, 112 (48.7%) had at least one of our identified independent risk factors for ACS. Subanalysis of Patient Encounters with Both Positive and Negative CXRs. Supporting Information Table IV summarizes data from 29 children who had multiple ED encounters with at least 1 positive and 1 negative CXR and were subsampled to perform a matched comparison. Our goal was to identify risk factors for ACS that might be helpful for the evaluating ED physician in order to identify children requiring a CXR as part of their fever workup. These data reveal both high and low ACS-risk models that include some unique features not previously described. The AUC for NIH-criteria risk factors when applied to our data set to identify ACS was only 0.6623. The Emory/CHOA model of a history of ACS, chest pain, cough, or abnormal physical exam findings appear to be better predictors of ACS with an AUC of 0.7254. There was a statistically significant difference between the 2 AUC, with our risk factors being more sensitive and specific than the current NIH guidelines to identify cases of ACS in this large cohort of children with SCD and fever. It may be useful to add “history of ACS” as one of the recommended criteria to obtain a CXR during a fever work-up. However, an AUC < 0.80 is still insufficient to accurately identify all ACS and is not an ideal prediction model. Although there are clinical signs and symptoms that identify ACS risk [1,2,5], the majority of patients will present early on with a normal lung exam, requiring a high level of suspicion given the morbidity and mortality associated with ACS. The results of this study mirror the findings of previous studies performed nearly 20 years ago that address this issue [1,2]. Despite recent advances in medicine, many children with SCD and fever still have few to no additional symptoms to suggest ACS when it is present. Clinical assessment alone is not reliable in identifying ACS, since 62% of children with ACS in our large cohort had a normal lung exam. Although the desire to decrease diagnostic radiation is an admirable goal [6], the SCD population may not be the ideal group in whom radiographs should be limited due to the high morbidity and mortality of ACS. Obtaining a CXR should be strongly considered in any child with SCD/fever and a history of ACS, chest pain or any respiratory symptoms, as missing ACS can lead to significant morbidity and mortality.

Alloimmunization to transfused HOD red blood cells is not increased in mice with sickle cell disease: ALLOIMMUNIZATION IN SICKLE CELL MICE

BACKGROUND: Increased rates of red blood cell (RBC) alloimmunization in patients with sickle cell disease may be due to transfusion frequency, genetic predisposition, or immune dysregulation. To test the hypothesis that sickle cell pathophysiology influences RBC alloimmunization, we utilized two transgenic mouse models of sickle cell disease.

Alloimmunization to transfused HOD RBCs is not increased in mice with sickle cell disease

BACKGROUND: Increased rates of red blood cell (RBC) alloimmunization in patients with sickle cell disease may be due to transfusion frequency, genetic predisposition, or immune dysregulation. To test the hypothesis that sickle cell pathophysiology influences RBC alloimmunization, we utilized two transgenic mouse models of sickle cell disease.