Assessment of total and unbound cell-free heme in plasma of patients with sickle cell disease.

Intravascular hemolysis results in the release of cell-free hemoglobin and heme in plasma. In sickle cell disease, the fragility of the sickle red blood cell leads to chronic hemolysis, which can contribute to oxidative damage and activation of inflammatory pathways. The scavenger proteins haptoglobin and hemopexin provide pathways to remove hemoglobin and heme, respectively, from the circulation. Heme also intercalates in membranes of blood cells and endothelial cells in the vasculature and associates with other plasma components such as albumin and lipoproteins. Hemopexin has a much higher affinity and can strip heme from the other pools and detoxify plasma from cell-free circulatory heme. However, due to chronic hemolysis, hemopexin is depleted in individuals with sickle cell disease. Thus, cell-free unbound heme is expected to accumulate in plasma. We developed a methodology for the accurate quantification of the fraction of heme, which is pathologically relevant in sickle cell disease, that does not appear to be sequestered to a plasma compartment. Our data show significant variation in the concentration of unbound heme, and rather unexpectedly, the size of the unbound fraction does not correlate to the degree of hemolysis, as measured by the concentration of bound heme. Very high heme concentrations (>150 µM) were obtained in some plasma with unbound concentrations that were several fold lower than in plasma with much lower hemolysis (<50 µM). These findings underscore the long-term effects of chronic hemolysis on the blood components and of the disruption of the essential equilibrium between release of hemoproteins/heme in the circulation and adaptative response of the scavenging/removal mechanisms. Understanding the clinical implications of this loss of response may provide insights into diagnostic and therapeutic targets in patients with sickle cell disease.

Voxelotor for the treatment of sickle cell disease.

Introduction: The clinical manifestations of sickle cell disease (SCD) result from an inherited mutation in the beta-globin chain of hemoglobin (Hb) that causes Hb tetramers to polymerize when deoxygenated. The resulting erythrocyte deformation causes mechanical obstruction of blood flow by sickled cells, hemolysis, anemia and end-organ injury. While pain is the hallmark symptom of SCD, chronic organ injury as a result of anemia, inflammation and progressive vasculopathy play a major role in morbidity and mortality. Due to the complex pathophysiology of SCD, the need for an individualized, multi-modal pharmacologic approach is apparent. Until 2018, hydroxyurea was the only disease-modifying pharmacologic therapy approved for use in SCD. Since then, three new agents have been approved including voxelotor, the subject of this review.Areas covered: Published pre-clinical and clinical data are reviewed. Voxelotor is a first-in-class small-molecule agent that binds to Hb and increases oxygen affinity, preventing polymerization. Recent clinical trials have shown that it increases Hb concentration and reduces hemolysis in patients with SCD. This increase in Hb concentration may significantly impact morbidity and mortality from chronic organ injury.Expert opinion: The mechanism of action, published studies and current opinions on the clinical use of voxelotor in SCD are presented.

A pragmatic multi-institutional approach to understanding transplant-associated thrombotic microangiopathy after stem cell transplant.

Transplant-associated thrombotic microangiopathy (TA-TMA) is a severe complication of hematopoietic stem cell transplantation (HSCT). A single-center prospective screening study has shown that the incidence of TA-TMA is much higher than prior retrospective studies that did not systematically screen. These data have not been replicated in a multicenter study. Our objective was to determine the incidence and risk factors for TA-TMA and compare outcomes of pediatric HSCT patients with and without TA-TMA. Patients were prospectively screened for TA-TMA at participating centers using a simple to implement and inexpensive strategy from the start of the preparative regimen through day +100. TA-TMA was diagnosed if ≥4 of 7 laboratory/clinical markers diagnostic for TA-TMA were present concurrently or if tissue histology showed TA-TMA. A total of 614 patients (359 males; 58%) received prospective TA-TMA screening at 13 pediatric centers. TA-TMA was diagnosed in 98 patients (16%) at a median of 22 days (interquartile range, 14-44) posttransplant. Patients with TA-TMA had significantly increased bloodstream infections (38% [37/98] vs 21% [107/51], P ≤ .001), mean total hospitalization days (68; 95% confidence interval [CI], 63-74 vs 43; 95% CI, 41-45; P ≤ .001), and number of days spent in the intensive care unit (10.1; 95% CI, 6.4-14; vs 1.6; 95% CI, 1.1-2.2; P ≤ .001) in the first 100 days after HSCT compared with patients without TA-TMA. Overall survival was significantly higher in patients without TA-TMA (93%; 490/516) compared with patients with TA-TMA (78%; 76/98) (P ≤ .001). These data support the need for systematic screening for TA-TMA and demonstrate the feasibility and efficacy of an easy to implement strategy to do so.

Risk Factors for Transplant-Associated Thrombotic Microangiopathy after Autologous Hematopoietic Cell Transplant in High-Risk Neuroblastoma.

High-risk neuroblastoma has a poor prognosis, and research studies have shown that increasing the intensity of therapy improves outcomes. Autologous hematopoietic cell transplant (aHCT) as consolidation therapy confers a significant survival advantage but is accompanied by significant morbidity. Transplant-associated thrombotic microangiopathy (TA-TMA) is a life-threatening complication caused by endothelial injury that often leads to hemolytic anemia, microthrombotic platelet consumption, and renal injury. Here we investigated the incidence, potential risk factors, and sequelae of TA-TMA in patients with high-risk neuroblastoma. We conducted a retrospective chart review of all patients (n = 141) with neuroblastoma in our institutions who underwent aHCT from 2000 to 2017. Ten patients (7%) developed TA-TMA. The patients in the TA-TMA group were similar to the rest of the subjects in demographics, disease burden, prior therapies, renal function, and timing of transplant. The type of conditioning regimen was the only statistically significant pretransplant variable (P < .001). Six of 15 patients (40%) intended to receive tandem transplants (cyclophosphamide/thiotepa and then carboplatin/etoposide/melphalan (CEM)), 4 of 68 patients (6%) who received conditioning with single CEM, and none of the 56 patients who received busulfan/melphalan were diagnosed with TA-TMA. Patients with TA-TMA were more likely to require intensive care unit transfer, have a longer length of stay in the hospital, and experience a delay or change in their subsequent therapy. In our cohort overall, patients with a delay in therapy after transplant appeared to have a worse overall survival, although the difference was not statistically significant. Because of this high incidence and significant morbidity, we have implemented standardized screening for TA-TMA during and after transplant. We anticipate that screening will lead to earlier intervention and decreased severity of disease.

Venous thromboembolism in pediatric trauma patients: Ten-year experience and long-term follow-up in a tertiary care center.

BACKGROUND: Pediatric trauma patients are at high risk for development of venous thromboembolism (VTE). Our objective is to describe incidence, risk factors, and timing of development of VTE, anticoagulation complications, and long-term VTE outcomes in a critically injured pediatric population. PROCEDURE: We did a retrospective review of pediatric (0-17 years) trauma admissions to intensive care unit from 2005 to 2014. Our center employs VTE screening and prevention protocols for high-risk patients based on hypercoagulable history, age, injuries, and medical interventions. We collected demographics, VTE prevention measures, VTE incidence, therapeutic anticoagulant use, and outcomes including postthrombotic syndrome (PTS) and clot resolution. Analysis included Wilcoxon rank-sum, Fisher exact, and logistic regression modeling. RESULTS: Seven hundred fifty-three subjects were analyzed. No patients on chemical prophylaxis (21/753) developed VTE. Overall incidence of deep vein thrombosis (DVT) was 8.9%; pulmonary embolism (PE) was 0%. Time to diagnosis was median (interquartile range [IQR]) 10.5 (6.5-14.5) days, with 63% of clots being symptomatic. Risk factors for VTE development included severe traumatic brain injury (TBI), acute traumatic coagulopathy (defined by elevated admission international normalized ratio), age less than or equal to 3 or age 13 years or more, injury severity, and child abuse mechanism. At a median (IQR) follow-up of 13 (6-19) months, 52.1% had persistent clot and 15.8% had PTS. Therapeutic anticoagulation was not associated with clot resolution or prevention of PTS. CONCLUSION: TBI therapy is closely linked to the development of DVT. Coagulopathy on admission is associated with hypercoagulability in the postinjury period, suggesting a patient phenotype with systemic coagulation dysregulation. Treatment was not associated with improved VTE outcomes, suggesting that pediatric protocols should emphasize VTE prevention and prophylaxis strategies.

Unexpected Anemia and Reticulocytopenia in an Adolescent With Sickle Cell Anemia Receiving Chronic Transfusion Therapy.

In a patient with sickle cell disease receiving chronic transfusion, exacerbation of anemia with reticulocytopenia must prompt consideration of a delayed hemolytic transfusion reaction with hyperhemolysis, as further transfusion may worsen this condition; definitive diagnosis is sometimes difficult. Anemia evolving during parvovirus B19-induced erythroid hypoplasia (transient aplastic crisis) should be attenuated in chronic transfusion patients due to superior survival of transfused over endogenous red blood cells. A 16-year-old with sickle cell disease receiving chronic transfusion of modified intensity (goal to maintain hemoglobin S<50%) who developed symptomatic anemia with reticulocytopenia was later shown to have had transient aplastic crisis.