Hemolysis-associated hypercoagulability in sickle cell disease: the plot (and blood) thickens!

Vasculo-toxic and pro-inflammatory action of unbound haemoglobin, haem and iron in transfusion-dependent patients with haemolytic anaemias

Increasing evidence suggests that free haem and iron exert vasculo‐toxic and pro‐inflammatory effects by activating endothelial and immune cells. In the present retrospective study, we compared serum samples from transfusion‐dependent patients with β‐thalassaemia major and intermedia, hereditary spherocytosis and sickle cell disease (SCD). Haemolysis, transfusions and ineffective erythropoiesis contribute to haem and iron overload in haemolytic patients. In all cohorts we observed increased systemic haem and iron levels associated with scavenger depletion and toxic ‘free’ species formation. Endothelial dysfunction, oxidative stress and inflammation markers were significantly increased compared to healthy donors. In multivariable logistic regression analysis, oxidative stress markers remained significantly associated with both haem‐ and iron‐related parameters, while soluble vascular cell adhesion molecule 1 (sVCAM‐1), soluble endothelial selectin (sE‐selectin) and tumour necrosis factor α (TNFα) showed the strongest association with haem‐related parameters and soluble intercellular adhesion molecule 1 (sICAM‐1), sVCAM‐1, interleukin 6 (IL‐6) and vascular endothelial growth factor (VEGF) with iron‐related parameters. While hereditary spherocytosis was associated with the highest IL‐6 and TNFα levels, β‐thalassaemia major showed limited inflammation compared to SCD. The sVCAM1 increase was significantly lower in patients with SCD receiving exchange compared to simple transfusions. The present results support the involvement of free haem/iron species in the pathogenesis of vascular dysfunction and sterile inflammation in haemolytic diseases, irrespective of the underlying haemolytic mechanism, and highlight the potential therapeutic benefit of iron/haem scavenging therapies in these conditions.

Linking Labile Heme with Thrombosis

Thrombosis is one of the leading causes of death worldwide. As such, it also occurs as one of the major complications in hemolytic diseases, like hemolytic uremic syndrome, hemorrhage and sickle cell disease. Under these conditions, red blood cell lysis finally leads to the release of large amounts of labile heme into the vascular compartment. This, in turn, can trigger oxidative stress and proinflammatory reactions. Moreover, the heme-induced activation of the blood coagulation system was suggested as a mechanism for the initiation of thrombotic events under hemolytic conditions. Studies of heme infusion and subsequent thrombotic reactions support this assumption. Furthermore, several direct effects of heme on different cellular and protein components of the blood coagulation system were reported. However, these effects are controversially discussed or not yet fully understood. This review summarizes the existing reports on heme and its interference in coagulation processes, emphasizing the relevance of considering heme in the context of the treatment of thrombosis in patients with hemolytic disorders.

Enhanced Hypercoagulability in Sickle Cell Anaemia Patients with Chronic Leg Ulcers

Sickle Cell Anaemia (SCA) is associated with a hypercoagulable state resulting in a predisposition to venous thromboembolism. With improvements in the quality of care, more patients with SCA survive into adulthood with an associated increase in the frequency of end-organ damage and chronic complications such as chronic leg ulcers (CLUs). These ulcers rarely occur in the first decade of life and are recurrent, painful, and slow-to-heal. This study tested the hypothesis that coagulation is enhanced in SCA patients with CLU. 145 participants (50 SCA with CLU, 50 SCA without CLU, and 45 with haemoglobin AA) were assessed to determine their coagulation profile using selected tests of coagulation. The SCA with the CLU group had the lowest mean haemoglobin (Hb) concentration. SCA patients with and without CLUs had elevated mean platelet counts, shorter mean aPTT, and marginally prolonged mean PT  compared to HbAA patients. SCA with CLUs patients had a significantly shortened aPTT than those without CLUs (p = 0.035) and HbAA (p = 0.009). There were significant differences in the mean PT between SCA with CLUs patients and HbAA (p = 0.017); SCA without CLU and HbAA (p = 0.014). SCA with and without CLUs patients had higher mean D-dimer levels compared to HbAA. There was a negative correlation between Hb concentration and duration of CLU (r = -0.331, p = 0.021). In conclusion, our study demonstrates a heightened hypercoagulability in SCA patients with CLUs. We did not test for platelet activation, and it is not clear what role, if any, the enhanced hypercoagulability plays in the pathogenesis of CLUs in SCA. It will be useful to ascertain if antiplatelet agents or/and anticoagulants quicken the healing of CLUs in SCA patients.

Oral tetrahydrouridine and decitabine for non-cytotoxic epigenetic gene regulation in sickle cell disease: A randomized phase 1 study

BACKGROUND

Sickle cell disease (SCD), a congenital hemolytic anemia that exacts terrible global morbidity and mortality, is driven by polymerization of mutated sickle hemoglobin (HbS) in red blood cells (RBCs). Fetal hemoglobin (HbF) interferes with this polymerization, but HbF is epigenetically silenced from infancy onward by DNA methyltransferase 1 (DNMT1).

METHODS AND FINDINGS

To pharmacologically re-induce HbF by DNMT1 inhibition, this first-in-human clinical trial (NCT01685515) combined 2 small molecules-decitabine to deplete DNMT1 and tetrahydrouridine (THU) to inhibit cytidine deaminase (CDA), the enzyme that otherwise rapidly deaminates/inactivates decitabine, severely limiting its half-life, tissue distribution, and oral bioavailability. Oral decitabine doses, administered after oral THU 10 mg/kg, were escalated from a very low starting level (0.01, 0.02, 0.04, 0.08, or 0.16 mg/kg) to identify minimal doses active in depleting DNMT1 without cytotoxicity. Patients were SCD adults at risk of early death despite standard-of-care, randomized 3:2 to THU-decitabine versus placebo in 5 cohorts of 5 patients treated 2X/week for 8 weeks, with 4 weeks of follow-up. The primary endpoint was ≥ grade 3 non-hematologic toxicity. This endpoint was not triggered, and adverse events (AEs) were not significantly different in THU-decitabine-versus placebo-treated patients. At the decitabine 0.16 mg/kg dose, plasma concentrations peaked at approximately 50 nM (Cmax) and remained elevated for several hours. This dose decreased DNMT1 protein in peripheral blood mononuclear cells by >75% and repetitive element CpG methylation by approximately 10%, and increased HbF by 4%-9% (P < 0.001), doubling fetal hemoglobin-enriched red blood cells (F-cells) up to approximately 80% of total RBCs. Total hemoglobin increased by 1.2-1.9 g/dL (P = 0.01) as reticulocytes simultaneously decreased; that is, better quality and efficiency of HbF-enriched erythropoiesis elevated hemoglobin using fewer reticulocytes. Also indicating better RBC quality, biomarkers of hemolysis, thrombophilia, and inflammation (LDH, bilirubin, D-dimer, C-reactive protein [CRP]) improved. As expected with non-cytotoxic DNMT1-depletion, platelets increased and neutrophils concurrently decreased, but not to an extent requiring treatment holds. As an early phase study, limitations include small patient numbers at each dose level and narrow capacity to evaluate clinical benefits.

CONCLUSION

Administration of oral THU-decitabine to patients with SCD was safe in this study and, by targeting DNMT1, upregulated HbF in RBCs. Further studies should investigate clinical benefits and potential harms not identified to date.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01685515.

Examination of Reticulocytosis among Chronically Transfused Children with Sickle Cell Anemia

Sickle cell anemia (SCA) is an inherited hemolytic anemia with compensatory reticulocytosis. Recent studies have shown that increased levels of reticulocytosis during infancy are associated with increased hospitalizations for SCA sequelae as well as cerebrovascular pathologies. In this study, absolute reticulocyte counts (ARC) measured prior to transfusion were analysed among a cohort of 29 pediatric SCA patients receiving chronic transfusion therapy (CTT) for primary and secondary stroke prevention. A cross-sectional flow cytometric analysis of the reticulocyte phenotype was also performed. Mean duration of CTT was 3.1 ± 2.6 years. Fifteen subjects with magnetic resonance angiography (MRA) -vasculopathy had significantly higher mean ARC prior to initiating CTT compared to 14 subjects without MRA-vasculopathy (427.6 ± 109.0 K/μl vs. 324.8 ± 109.2 K/μl, p<0.05). No significant differences in hemoglobin or percentage sickle hemoglobin (HbS) were noted between the two groups at baseline. Reticulocyte phenotyping further demonstrated that the percentages of circulating immature [CD36(+), CD71(+)] reticulocytes positively correlated with ARC in both groups. During the first year of CTT, neither group had significant reductions in ARC. Among this group of children with SCA, cerebrovasculopathy on MRA at initiation of CTT was associated with increased reticulocytosis, which was not reduced after 12 months of transfusions.

Coagulation abnormalities of sickle cell disease: Relationship with clinical outcomes and the effect of disease modifying therapies

Sickle cell disease (SCD) is a hypercoagulable state. Patients exhibit increased platelet activation, high plasma levels of markers of thrombin generation, depletion of natural anticoagulant proteins, abnormal activation of the fibrinolytic system, and increased tissue factor expression, even in the non-crisis "steady state." Furthermore, SCD is characterized by an increased risk of thrombotic complications. The pathogenesis of coagulation activation in SCD appears to be multi-factorial, with contributions from ischemia-reperfusion injury and inflammation, hemolysis and nitric oxide deficiency, and increased sickle RBC phosphatidylserine expression. Recent studies in animal models suggest that activation of coagulation may contribute to the pathogenesis of SCD, but the data on the contribution of coagulation and platelet activation to SCD-related complications in humans are limited. Clinical trials of new generations of anticoagulants and antiplatelet agents, using a variety of clinical endpoints are warranted.

Mechanisms of hemolysis-associated platelet activation

BACKGROUND

Intravascular hemolysis occurs after blood transfusion, in hemolytic anemias, and in other conditions, and is associated with hypercoagulable states. Hemolysis has been shown to potently activate platelets in vitro and in vivo, and several mechanisms have been suggested to account for this, including: (i) direct activation by hemoglobin (Hb); (ii) increase in reactive oxygen species (ROS); (iii) scavenging of nitric oxide (NO) by released Hb; and (iv) release of intraerythrocytic ADP.

OBJECTIVE

To elucidate the mechanism of hemolysis-mediated platelet activation.

METHODS

We used flow cytometry to detect PAC-1 binding to activated platelets for in vitro experiments, and a Siemens' Advia 120 hematology system to assess platelet aggregation by using platelet counts from in vivo experiments in a rodent model.

RESULTS

We found that Hb did not directly activate platelets. However, ADP bound to Hb could cause platelet activation. Furthermore, platelet activation caused by shearing of red blood cells (RBCs) was reduced in the presence of apyrase, which metabolizes ADP to AMP. The use of ROS scavengers did not affect platelet activation. We also found that cell-free Hb enhanced platelet activation by abrogating the inhibitory effect of NO on platelet activation. In vivo infusions of ADP and purified (ADP-free) Hb, as well as hemolysate, resulted in platelet aggregation, as shown by decreased platelet counts.

CONCLUSION

Two primary mechanisms account for RBC hemolysis-associated platelet activation: ADP release, which activates platelets; and cell-free Hb release, which enhances platelet activation by lowering NO bioavailability.

Sickle cell disease: new opportunities and challenges in Africa

Sickle cell disease (SCD) is one of the most common genetic causes of illness and death in the world. This is a review of SCD in Africa, which bears the highest burden of disease. The first section provides an introduction to the molecular basis of SCD and the pathophysiological mechanism of selected clinical events. The second section discusses the epidemiology of the disease (prevalence, morbidity, and mortality), at global level and within Africa. The third section discusses the laboratory diagnosis and management of SCD, emphasizing strategies that been have proven to be effective in areas with limited resources. Throughout the review, specific activities that require evidence to guide healthcare in Africa, as well as strategic areas for further research, will be highlighted.

Dasatinib: a review of its use in the treatment of chronic myeloid leukaemia and Philadelphia chromosome-positive acute lymphoblastic leukaemia

Dasatinib (Sprycel®) is an orally administered small molecule inhibitor of multiple tyrosine kinases, including BCR-ABL and SRC family kinases, which is indicated for the treatment of adults with newly diagnosed chronic-phase chronic myeloid leukaemia (CML), CML (chronic-, accelerated- or blast-phase) with resistance or intolerance to prior therapy, including imatinib, or Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukaemia (ALL) with resistance or intolerance to prior therapy. Dasatinib is ≈325-fold more active than imatinib in inhibiting wild-type ABL kinase in vitro and is active against a wide variety of imatinib-resistant BCR-ABL mutants, except for T315I. This article reviews the efficacy and tolerability of dasatinib in the treatment of patients with newly diagnosed chronic-phase CML or imatinib-resistant or -intolerant CML or Ph+ ALL, as well as summarizing its pharmacological properties. In clinical trials, oral dasatinib was effective in achieving major or complete cytogenetic responses in both newly diagnosed and imatinib-resistant or -intolerant chronic-phase CML. Dasatinib was likewise effective in achieving major or overall haematological responses in imatinib-resistant or -intolerant, accelerated- or blast-phase CML, or Ph+ ALL. Responses were rapidly achieved within 1-3 months and were durable over 1-5 years of follow-up. The majority of adverse events with dasatinib were of mild to moderate severity. Fluid retention (including pleural effusion) was the most common adverse event. Haematological abnormalities were common and cytopenias were the most common grade 3/4 adverse events. Dasatinib 100 mg administered once daily was as effective as dasatinib 70 mg administered twice daily, and was better tolerated, being associated with lower incidences of pleural effusion and grade 3/4 thrombocytopenia, in particular. Dasatinib was more effective than high-dose imatinib in the treatment of patients with imatinib-resistant chronic-phase CML and was more effective than standard dosages of imatinib, as well as being associated with less frequent fluid retention, in patients with newly diagnosed chronic-phase CML. Dasatinib was generally equally effective in patients with or without BCR-ABL mutations at baseline. Therefore, oral dasatinib is a highly effective once-daily therapy for the first-line treatment of newly diagnosed patients with chronic-phase CML, as well as for the treatment of patients with imatinib-resistant or -intolerant chronic- and advanced-phase CML or Ph+ ALL.

Evaluation of the procoagulant activity of endogenous phospholipids in the platelet-free plasma of children with sickle cell disease using functional assays

BACKGROUND

The mechanisms of hypercoagulability in sickle cell disease (SCD) are poorly understood.

OBJECTIVE

We aimed to explore the procoagulant activity of endogenous phospholipids (ePL) in the platelet-free plasma of SCD children.

METHODS

A factor Xa clotting time (XACT), thrombin generation (TG) and a capture-based assay for the detection of procoagulant microparticles (PMP) were used. Forty three SCD children (35 SS, 6 SC and 2 Sβ+) were evaluated at steady-state and compared to 20 controls. Fourteen patients were also evaluated during vaso-occlusive crisis. TG was performed using 10 pM tissue factor without addition of exogenous phospholipids. A control condition was also performed using 10 pM tissue factor and 4 μM phospholipids. Percentages of the test/control conditions were calculated for the peak height (% peak), endogenous thrombin potential (% ETP) and velocity index (% VI).

RESULTS

XACT times were shorter, PMP levels, peak height and velocity index of thrombin generation were higher in SCD patients than controls. Lag time and ETP were not different between the two groups. % peak, % ETP and % VI were higher in patients than controls. Significant correlations were found between PMP levels and XACT, also between PMP levels and peak height, velocity index, ETP and their respective percentages to the control condition, but not with lag time. Double heterozygous patients showed intermediate values for XACT and TG parameters. No significant difference was observed when comparing patients at steady-state versus vaso-occlusive crisis.

CONCLUSION

High procoagulant activity of ePL was observed in the platelet-free plasma of SCD children, probably borne by procoagulant microparticles. This may contribute to a high hemostatic potential and predisposition to thrombotic complications in these patients.

A pilot study of subcutaneous decitabine in β-thalassemia intermedia

Ineffective erythropoiesis, the hallmark of β-thalassemia, is a result of α/non-α globin chain imbalance. One strategy to redress globin-chain imbalance is to induce γ-globin gene (HBG) expression. Repression of HBG in adult erythroid cells involves DNA methylation and other epigenetic changes. Therefore, the cytosine analog decitabine, which can deplete DNA methyltransferase 1 (DNMT1), can potentially activate HBG. In 5 patients with β-thalassemia intermedia, a dose and schedule of decitabine intended to deplete DNMT1 without causing significant cytotoxicity (0.2 mg/kg subcutaneous 2 times per week for 12 weeks) increased total hemoglobin from 7.88 ± 0.88 g/dL to 9.04 ± 0.77 g/dL (P = .004) and absolute fetal hemoglobin from 3.64 ± 1.13 g/dL to 4.29 ± 1.13 g/dL (P = .003). Significant favorable changes also occurred in indices of hemolysis and red blood cell densitometry. Consistent with a noncytotoxic, differentiation altering mechanism of action, the major side effect was an asymptomatic increase in platelet counts without erythrocyte micronucleus or VDJ recombination assay evidence of genotoxicity. This study was registered at www.clinicaltrials.gov as #NCT00661726.

Emerging drugs for chronic myeloid leukemia

IMPORTANCE OF THE FIELD

The deregulated tyrosine kinase activity of BCR-ABL has been demonstrated to be necessary and sufficient to maintain leukemia phenotype of chronic myeloid leukemia (CML) which, therefore, represents a unique model for the development of molecular targeted therapy and the first disease in which the tyrosine kinase inhibitors (TKIs) completely changed the therapeutical approach. The impressive results of TKIs in this model have been overshadowed by the development of clinical resistance.

AREAS COVERED IN THIS REVIEW

This review focuses on clinical results with imatinib therapy and second generation TKIs. Furthermore, a summary of the guidelines for the management of TKI resistant patients is provided together with a description of the new drugs in clinical or preclinical phases which are developing to overcome resistance.

WHAT THE READER WILL GAIN

Future perspective for the 'cure' of CML patients and new drugs designed for this purpose are suggested.

TAKE HOME MESSAGE

CML therapy has dramatically changed in the last few years due to the introduction of targeted therapy. Studies on new drugs targeting different pathways other than BCR-ABL are ongoing to improve the clinical results.

Once-Daily Dasatinib for Treatment of Patients with Chronic Myeloid Leukemia

Objective

To discuss the new dasatinib dosing regimen for the treatment of chronic phase chronic myelogenous leukemia (CP CML) in patients who failed or were intolerant to imatinib therapy.

Data Sources

Literature published between July 2008 and December 2008 was accessed via MEDLINE, the Proceedings of the American Society of Hematology, and the Proceedings of the American Society of Clinical Oncology using the key words chronic myelogenous leukemia, chronic myeloid leukemia, dasatinib, imatinib, nilotinib, pharmacokinetics, and regimen.

Study Selection And Data Extraction

Meeting abstracts and reports of major Phase 1–3 studies published in English are included.

Data Synthesis

Imatinib is the standard first-line therapy for CML; however, some patients develop resistance or are intolerant to the drug. Dasatinib was approved for the treatment of imatinib-resistant/intolerant patients with CML or Philadelphia chromosome–positive acute lymphoblastic leukemia at the dosage of 70 mg twice daily. A Phase 3 dose-optimization study was performed to compare this regimen with others, including dasatinib 100 mg once daily, in patients with CP CML. Results of this study showed that there was no significant difference in efficacy between these 2 regimens. The safety profile was improved in the 100-mg once-daily dasatinib arm with significantly reduced frequencies of grade 3–4 thrombocytopenia and all-grade pleural effusions. The number of patients who had to discontinue, reduce, or interrupt their dosage was also less among patients taking dasatinib 100 mg once daily.

Conclusions

Dasatinib 100 mg once daily has a more favorable risk to benefit assessment compared with the previous 70 mg twice-daily regimen and is now the recommended schedule for patients with CP CML.

Neither a nitric oxide donor nor potassium channel blockage inhibit RBC mechanical damage induced by a roller pump

Red blood cells (RBC) are exposed to various levels of shear stresses when they are exposed to artificial flow environments, such as extracorporeal flow circuits and hemodialysis equipment. This mechanical trauma affects RBC and the resulting effect is determined by the magnitude of shear forces and exposure time. It has been previously demonstrated that nitric oxide (NO) donors and potassium channel blockers could prevent the sub-hemolytic damage to RBC, when they are exposed to 120 Pa shear stress in a Couette shearing system. This study aimed at testing the effectiveness of NO donor sodium nitroprussid (SNP, 10^-4 M) and non-specific potassium channel blocker tetraethylammonium (TEA, 10^-7 M) in preventing the mechanical damage to RBC in a simple flow system including a roller pump and a glass capillary of 0.12 cm diameter. RBC suspensions were pumped through the capillary by the roller pump at a flow rate that maintains 200 mmHg hydrostatic pressure at the entrance of the capillary. An aliquot of 10 ml of RBC suspension of 0.4 L/L hematocrit was re-circulated through the capillary for 30 minutes. Plasma hemoglobin concentrations were found to be significantly increased (~7 folds compared to control aliquot which was not pumped through the system) and neither SNP nor TEA prevented this hemolysis. Alternatively, RBC deformability assessed by laser diffraction ektacytometry was not altered after 30 min of pumping and both SNP and TEA had no effect on this parameter. The results of this study indicated that, in contrast with the findings in RBC exposed to a well-defined magnitude of shear stress in a Couette shearing system, the mechanical damage induced by a roller pump could not be prevented by NO donor or potassium channel blocker.

Help me, Doctor! My D-dimer is raised

Although optimal strategy for management of patients with suspected venous thromboembolism depends on local expertise and cost, diagnostic algorithms including clinical assessment and D-dimer have been validated in several trials. However, a new paradigm shift is emerging, giving an extended role of D-dimer measurement in clinical practice. D-dimer is a useful biomarker to help determine initial anticoagulant therapy in patients with thrombosis. Emerging evidence also endorses a 'predictive' role for raised D-dimer levels, since its measurement provides prognostic indications for a variety of conditions, including venous thromboembolism, disseminated intravascular coagulation, cardiovascular disease, infectious diseases, and cancer. Additional investigation is needed to clarify whether raised D-dimer is an epiphenomenon or it is actively involved in pathophysiology. Further studies are also required to establish whether D-dimer testing, alone or combined with other prognostic indicators, can be used to identify patient candidates for further triage and treatment. Nevertheless, the hazard(s) associated with raised D-dimer in plasma requires re-emphasis in the teaching of post-graduates, junior doctors and medical students, including the most effective treatments to inhibit clot spread and decrease the probability of further significant thrombotic incidents even in the absence of any 'detectable' thrombosis.