Sickle red cell-endothelium interactions

Heterogeneous red blood cell adhesion and deformability in sickle cell disease

We present a microfluidic approach that allows simultaneous interrogation of RBC properties in physiological flow conditions at a single cell level. With this method, we studied healthy hemoglobin A (HbA) and homozygous sickle hemoglobin (HbS) containing RBCs using whole blood samples from twelve subjects. We report that HbS-containing RBCs are heterogeneous in terms of adhesion and deformability in flow.

Clinical biomarkers in sickle cell disease

Sickle cell disease (SCD) is a hereditary blood disorder caused by a single gene. Various blood and urine biomarkers have been identified in SCD which are associated with laboratory and medical history. Biomarkers have been proven helpful in identifying different interconnected disease-causing mechanisms of SCD, including hypercoagulability, hemolysis, inflammation, oxidative stress, vasculopathy, reperfusion injury and reduced vasodilatory responses in endothelium, to name just a few. However, there exists a need to establish a panel of validated blood and urine biomarkers in SCD. This paper reviews the current contribution of biochemical markers associated with clinical manifestation and identification of sub-phenotypes in SCD.

Quantitative intravital two-photon excitation microscopy reveals absence of pulmonary vaso-occlusion in unchallenged Sickle Cell Disease mice

Sickle cell disease (SCD) is a genetic disorder that leads to red blood cell (RBC) sickling, hemolysis and the upregulation of adhesion molecules on sickle RBCs. Chronic hemolysis in SCD results in a hyper-inflammatory state characterized by activation of circulating leukocytes, platelets and endothelial cells even in the absence of a crisis. A crisis in SCD is often triggered by an inflammatory stimulus and can lead to the acute chest syndrome (ACS), which is a type of lung injury and a leading cause of mortality among SCD patients. Although it is believed that pulmonary vaso-occlusion could be the phenomenon contributing to the development of ACS, the role of vaso-occlusion in ACS remains elusive. Intravital imaging of the cremaster microcirculation in SCD mice has been instrumental in establishing the role of neutrophil-RBC-endothelium interactions in systemic vaso-occlusion; however, such studies, although warranted, have never been done in the pulmonary microcirculation of SCD mice. Here, we show that two-photon excitation fluorescence microscopy can be used to perform quantitative analysis of neutrophil and RBC trafficking in the pulmonary microcirculation of SCD mice. We provide the experimental approach that enables microscopic observations under physiological conditions and use it to show that RBC and neutrophil trafficking is comparable in SCD and control mice in the absence of an inflammatory stimulus. The intravital imaging scheme proposed in this study can be useful in elucidating the cellular and molecular mechanism of pulmonary vaso-occlusion in SCD mice following an inflammatory stimulus.

Phase 1 study of the E-selectin inhibitor GMI 1070 in patients with sickle cell anemia

BACKGROUND

Sickle cell anemia is an inherited disorder of hemoglobin that leads to a variety of acute and chronic complications. Abnormal cellular adhesion, mediated in part by selectins, has been implicated in the pathophysiology of the vaso-occlusion seen in sickle cell anemia, and selectin inhibition was able to restore blood flow in a mouse model of sickle cell disease.

METHODS

We performed a Phase 1 study of the selectin inhibitor GMI 1070 in patients with sickle cell anemia. Fifteen patients who were clinically stable received GMI 1070 in two infusions.

RESULTS

The drug was well tolerated without significant adverse events. There was a modest increase in total peripheral white blood cell count without clinical symptoms. Plasma concentrations were well-described by a two-compartment model with an elimination T1/2 of 7.7 hours and CLr of 19.6 mL/hour/kg. Computer-assisted intravital microscopy showed transient increases in red blood cell velocity in 3 of the 4 patients studied.

CONCLUSIONS

GMI 1070 was safe in stable patients with sickle cell anemia, and there was suggestion of increased blood flow in a subset of patients. At some time points between 4 and 48 hours after treatment with GMI 1070, there were significant decreases in biomarkers of endothelial activation (sE-selectin, sP-selectin, sICAM), leukocyte activation (MAC-1, LFA-1, PM aggregates) and the coagulation cascade (tissue factor, thrombin-antithrombin complexes). Development of GMI 1070 for the treatment of acute vaso-occlusive crisis is ongoing.

TRIAL REGISTRATION

ClinicalTrials.gov NCT00911495.

Trauma-hemorrhagic shock induces a CD36-dependent RBC endothelial-adhesive phenotype

OBJECTIVE

Microvascular dysfunction is a key element in the development of the multiple organ dysfunction syndrome. Although the mechanisms for this response are unclear, RBC adhesion to endothelium may initiate intravascular occlusion leading to ischemic tissue injury. Thus, we tested the hypothesis that trauma-hemorrhage induces RBC-endothelial cell adhesion.

DESIGN

Prospective in vivo and in vitro animal study and analysis of patient blood samples.

SETTING

University research laboratory and hospital emergency and trauma units.

INTERVENTION

We initially assayed RBC adhesion to endothelial cells in vitro using RBCs obtained from rats subjected to trauma-hemorrhagic shock or sham shock as well as from severely injured trauma patients. Subsequently, we measured the role of putative RBCs and endothelial cell receptors in the increased RBC-endothelial cell adhesive response.

MAIN RESULTS

In both rats and humans, trauma-hemorrhagic shock increased RBC adhesion to endothelium as well as increasing several putative RBC surface adhesion molecules including CD36. The critical factor leading to RBC-endothelial cell adhesion was increased surface RBC CD36 expression. Adhesion of trauma-hemorrhagic shock RBCs was mediated, at least in part, by the binding of RBC CD36 to its cognate endothelial receptors (αVβ3 and VCAM-1). Gut-derived factors carried in the intestinal lymphatics triggered these trauma-hemorrhagic shock-induced RBC changes because 1) preventing trauma-hemorrhagic shock intestinal lymph from reaching the systemic circulation abrogated the RBC effects, 2) in vitro incubation of naïve whole blood with trauma-hemorrhagic shock lymph replicated the in vivo trauma-hemorrhagic shock-induced RBC changes while 3) injection of trauma-hemorrhagic shock lymph into naïve animals recreated the RBC changes observed after actual trauma-hemorrhagic shock.

CONCLUSIONS

1) Trauma-hemorrhagic shock induces rapid RBC adhesion to endothelial cells in patients and animals. 2) Increased RBC CD36 expression characterizes the RBC-adhesive phenotype. 3) The RBC phenotypic and functional changes were induced by gut-derived humoral factors. These novel findings may explain the microvascular dysfunction occurring after trauma-hemorrhagic shock, sepsis, and other stress states.

Influence of the Clinical Status on Stress Reticulocytes, CD 36 and CD 49d of SSFA 2 Homozygous Sickle Cell Patients Followed in Abidjan

Background and Objectives. Interactions between sickle cells involving CD 49d, CD36, and the vascular endothelium may initiate vasoocclusion leading to acute painful episodes and multiple organ failure. Materials and Methods. We selected 60 SS patients who had never been treated by hydroxyurea. We performed a total blood count. We identified with immunophenotyping by flow cytometry total reticulocytes their distribution according to the degree of maturity (mature, intermediate, very immature) and CD 36(+) and CD 49d(+) antigens. Stress reticulocytes corresponded to the sum of intermediate and immature cells. Results. Subjects in crisis had more total reticulocytes and very immature reticulocytes than subjects in stationary phase (P < 0.05). During the crisis, total CD 36(+) reticulocytes (214 870 ± 107 584/ μ L versus 148 878 ± 115 024/ μ L; P < 0.05) and the very immature CD 36(+) reticulocytes (28.9 ± 7.9% versus 23.0 ± 6.4%; P < 0.05) increased. The clinical status had no impact on CD 49d(+) reticulocytes. Conclusion. The rates of stress reticulocytes in general and those expressing CD 49d and CD 36 were very high. The clinical status had an influence on CD 36(+) reticulocytes. The expression of adhesion molecules is only one of the parameters involved in sickle cell disease crisis.

Vaso-occlusion in sickle cell disease: pathophysiology and novel targeted therapies

Recurrent and unpredictable episodes of vaso-occlusion are the hallmark of sickle cell disease. Symptomatic management and prevention of these events using the fetal hemoglobin-reactivating agent hydroxyurea are currently the mainstay of treatment. Discoveries over the past 2 decades have highlighted the important contributions of various cellular and soluble participants in the vaso-occlusive cascade. The role of these elements and the opportunities for therapeutic intervention are summarized in this review.

Sickle erythrocytes target cytotoxics to hypoxic tumor microvessels and potentiate a tumoricidal response

Resistance of hypoxic solid tumor niches to chemotherapy and radiotherapy remains a major scientific challenge that calls for conceptually new approaches. Here we exploit a hitherto unrecognized ability of sickled erythrocytes (SSRBCs) but not normal RBCs (NLRBCs) to selectively target hypoxic tumor vascular microenviroment and induce diffuse vaso-occlusion. Within minutes after injection SSRBCs, but not NLRBCs, home and adhere to hypoxic 4T1 tumor vasculature with hemoglobin saturation levels at or below 10% that are distributed over 70% of the tumor space. The bound SSRBCs thereupon form microaggregates that obstruct/occlude up to 88% of tumor microvessels. Importantly, SSRBCs, but not normal RBCs, combined with exogenous prooxidant zinc protoporphyrin (ZnPP) induce a potent tumoricidal response via a mutual potentiating mechanism. In a clonogenic tumor cell survival assay, SSRBC surrogate hemin, along with H(2)O(2) and ZnPP demonstrate a similar mutual potentiation and tumoricidal effect. In contrast to existing treatments directed only to the hypoxic tumor cell, the present approach targets the hypoxic tumor vascular environment and induces injury to both tumor microvessels and tumor cells using intrinsic SSRBC-derived oxidants and locally generated ROS. Thus, the SSRBC appears to be a potent new tool for treatment of hypoxic solid tumors, which are notable for their resistance to existing cancer treatments.

Vaso-occlusion in sickle cell disease: pathophysiology and novel targeted therapies

Recurrent and unpredictable episodes of vaso-occlusion are the hallmark of sickle cell disease. Symptomatic management and prevention of these events using the fetal hemoglobin-reactivating agent hydroxyurea are currently the mainstay of treatment. Discoveries over the past 2 decades have highlighted the important contributions of various cellular and soluble participants in the vaso-occlusive cascade. The role of these elements and the opportunities for therapeutic intervention are summarized in this review.

Effect of omega-3 (n-3) fatty acid supplementation in patients with sickle cell anemia: randomized, double-blind, placebo-controlled trial

BACKGROUND

Blood cell aggregation and adherence to vascular endothelium and inflammation play a central role in vaso-occlusive crisis in sickle cell disease. The antiaggregatory, antiadhesive, antiinflammatory, and vasodilatory omega-3 (n-3) fatty acids (DHA and EPA) are significantly reduced in patients with the disease.

OBJECTIVE

The aim was to investigate the therapeutic potential of omega-3 fatty acids for patients with homozygous sickle cell disease in a randomized, placebo-controlled, double-blind trial.

DESIGN

One hundred forty patients recruited from a single center in Sudan were randomly assigned and received, daily, 1 (age 2-4 y), 2 (age 5-10 y), 3 (age 11-16 y), or 4 (age ≥17 y) omega-3 capsules containing 277.8 mg DHA and 39.0 mg EPA or placebo for 1 y. Of these patients, 128 were followed up and the data were obtained. The primary and secondary endpoints-rates of clinical vaso-occlusive crisis and hemolytic events, blood transfusion rate, school attendance, and blood count-were analyzed by intention-to-treat analysis (n = 140).

RESULTS

Omega-3 treatment reduced the median rate of clinical vaso-occlusive events (0 compared with 1.0 per year, P < 0.0001), severe anemia (3.2% compared with 16.4%; P < 0.05), blood transfusion (4.5% compared with 16.4%; P < 0.05), white blood cell count (14.4 ± 3.3 compared with 15.6 ± 4.0 ×10(3)/μL; P < 0.05), and the OR of the inability to attend school at least once during the study period because of illness related to the disease to 0.4 (95% CI: 0.2, 0.9; P < 0.05).

CONCLUSION

The findings of this trial, which need to be verified in a large multicenter study, suggest that omega-3 fatty acids can be an effective, safe, and affordable therapy for sickle cell anemia. This trial was registered with Current Controlled Trials as ISRCTN80844630.

In vitro modeling of the microvascular occlusion and thrombosis that occur in hematologic diseases using microfluidic technology

In hematologic diseases, such as sickle cell disease (SCD) and hemolytic uremic syndrome (HUS), pathological biophysical interactions among blood cells, endothelial cells, and soluble factors lead to microvascular occlusion and thrombosis. Here, we report an in vitro "endothelialized" microfluidic microvasculature model that recapitulates and integrates this ensemble of pathophysiological processes. Under controlled flow conditions, the model enabled quantitative investigation of how biophysical alterations in hematologic disease collectively lead to microvascular occlusion and thrombosis. Using blood samples from patients with SCD, we investigated how the drug hydroxyurea quantitatively affects microvascular obstruction in SCD, an unresolved issue pivotal to understanding its clinical efficacy in such patients. In addition, we demonstrated that our microsystem can function as an in vitro model of HUS and showed that shear stress influences microvascular thrombosis/obstruction and the efficacy of the drug eptifibatide, which decreases platelet aggregation, in the context of HUS. These experiments establish the versatility and clinical relevance of our microvasculature-on-a-chip model as a biophysical assay of hematologic pathophysiology as well as a drug discovery platform.

Sickle cell biomechanics

As the predominant cell type in blood, red blood cells (RBCs) and their biomechanical properties largely determine the rheological and hemodynamic behavior of blood in normal and disease states. In sickle cell disease (SCD), mechanically fragile, poorly deformable RBCs contribute to impaired blood flow and other pathophysiological aspects of the disease. The major underlying cause of this altered blood rheology and hemodynamics is hemoglobin S (HbS) polymerization and RBC sickling under deoxygenated conditions. This review discusses the characterization of the biomechanical properties of sickle RBCs and sickle blood as well as their implications toward a better understanding of the pathophysiology of the disease.

Neutrophil microdomains: linking heterocellular interactions with vascular injury

PURPOSE OF REVIEW

Neutrophil infiltration is an important feature in inflammatory scenarios. Before these cells infiltrate tissues, however, they contribute to crucial intravascular events in which neutrophil microdomains mediate heterotypic interactions with endothelial cells, red blood cells and/or platelets. In vascular diseases, this can result in exacerbated neutrophil activation, subsequent vascular injury and obstruction of microcirculatory blood flow. This review discusses recent advances in elucidating these neutrophil domains and their associated functions in cell adhesion.

RECENT FINDINGS

Neutrophil recruitment is mediated by sequential interactions with the endothelium, termed rolling, adhesion and extravasation. Evidence points to novel signaling pathways induced during the rolling phase resulting in the transition to leukocyte adhesion, which appear to contribute to chemokine mediated activation. In addition, specific neutrophil microdomains are important for interactions with other hematopoietic cells inducing reductions in microvascular flow and injury.

SUMMARY

Neutrophils integrate signals received from the endothelium to act as linkers between the vessel wall and a variety of vascular components (i.e. endothelial cells, platelets, red blood cells) in acute and chronic inflammatory conditions to mediate interactions that can result in vascular injury and vasoocclusion.

Transfusion of sickle cells may be a therapeutic option for patients suffering metastatic disease

Red blood cells from patients with sickle cell disease will sickle under conditions of hypoxemia and acidosis which is a similar milieu found in malignant tumors. While control of tumor angiogenesis has long been a goal of cancer therapy, selective occlusion of tumor blood supply may be achieved by transfusion of sickle cells into patients who suffer metastatic cancer. Although this potential therapy has not been previously reported in the medical literature, the concept may have been elusive to medical mainstream thinking because it requires transfusion of diseased cells. For this therapy to be effective, other environmental factors may need to be manipulated such inducing mild hypoxemia or hypercarbia (respiratory acidosis) to induce red cell sickling. Preliminary evidence supportive of this therapeutic approach to cancer treatment is provided by case evidence that sickle cell occlusion of a malignant brain tumor (glioma) produced tumor necrosis. Also sickle cells have been successfully transfused into primates. Furthermore, donor blood is crossmatched and transfused into patients suffering from sickle cell disease regularly in clinics and this procedure is associated with acceptable morbidity. Most importantly, animal models of sickle cell disease and cancer currently exist, and this theory could be tried with available technologies including ultrasound detection of vaso-occlusion. While the proposed therapy may not cure metastatic cancer, this treatment could prove useful for decreasing the size and perhaps the pain from metastatic tumor burden. Therefore, it is hypothesized that ABO Rh compatible crossmatched sickle cells transfused into patients who suffer metastatic cancer under controlled conditions of blood oxygenation and pH will selectively produce vaso-occlusive infarcts in malignant tumors and be a useful therapy. The author hopes for further investigations.

Human platelet alloantigens (HPA) 1, HPA2, HPA3, HPA4, and HPA5 polymorphisms in sickle cell anemia patients with vaso-occlusive crisis

OBJECTIVES

Vaso-occlusive crisis (VOC) is a significant cause of morbidity and mortality in sickle cell anemia (SCA) patients. Insofar as polymorphism in human platelet alloantigen (HPA) exhibit a prothrombotic nature, we hypothesized that specific HPA polymorphic variants are associated with VOC. We investigated the distribution of HPA1, HPA2, HPA3, HPA4, and HPA5 alleles genotypes among VOC and non-VOC control SCA patients.

PATIENTS/METHODS

This was a case-control study. Study subjects comprised SCA patients with (VOC group; n = 127) or without (Steady-state group; n = 130) VOC events. HPA genotyping was done by PCR-SSP.

RESULTS

Significantly higher frequencies of HPA-2b, HPA-3b, and HPA-5b alleles, and marked enrichment of HPA-3b/3b, HPA-5a/5b, and HPA-5b/5b genotypes, were seen in VOC than in control SCA patients. Taking homozygous wild-type genotypes as reference, univariate analysis identified HPA-3a/3b, HPA-3b/3b, and HPA-5b/5b to be associated with VOC. Multivariate analysis confirmed the independent association of only HPA-3a/3b and HPA-3b/3b genotypes with VOC. HPA-3 genotypes were significantly correlated with VOC frequency, type, and medication, and requirement for hospitalization. While both HPA 3a/3b (P = 0.002; OR = 2.94; 95% CI = 1.49-5.77) and 3b/3b (P = 0.006; OR = 3.16; 95% CI = 1.40-7.17) genotypes were associated with need for hospitalization, only HPA-3b/3b was associated with VOC frequency, type (localized vs. generalized), and medication (narcotics vs. NSAIDs).

CONCLUSION

This confirms the association of HPA polymorphisms with SCA VOC, of which HPA-3 appears to be independent genetic risk factors for SCA VOC.

Hemoglobin disorders and endothelial cell interactions

Endothelial damage and inflammation make a significant contribution to the pathophysiology of sickle cell disease (SCD) and the beta-thalassemia syndromes. Endothelial dysfunction and ensuing vasculopathy are implicated in pulmonary hypertension in the hemoglobinopathies and endothelial activation and endothelial-blood cell adhesion, accompanied by inflammatory processes and oxidative stress, are imperative to the vaso-occlusive process in SCD. Herein, we discuss the role that the endothelium plays in all of these processes and the effect that genetic modifiers and hydroxyurea therapy may have upon endothelial interactions. Therapies targeting the endothelium and endothelial interactions may represent a promising approach for treating these diseases.

Delayed hemolytic transfusion reaction in sickle cell disease patients: evidence of an emerging syndrome with suicidal red blood cell death

BACKGROUND

Delayed hemolytic transfusion reaction (DHTR) is a life-threatening complication in sickle cell disease (SCD) characterized by recurrence of disease complications, recipient red blood cell (RBC) destruction, and frequently no detectable antibody. Phosphatidylserine (PS) exposure signs suicidal RBC death or eryptosis and is involved in vasoocclusive crisis (VOC).

STUDY DESIGN AND METHODS

Transfusion was monitored in 48 SCD patients for up to 20 days. PS exposure was evaluated in vivo on patient RBCs (PS-RBCs) at five time points and in vitro after incubation of donor RBCs with pretransfusion plasma.

RESULTS

Three VOC patients displayed DHTR with recurrent SCD features and no detectable antibody in two cases. In vitro, PS-RBC percentage was significantly increased by incubating donor RBCs with pretransfusion plasma samples from DHTR patients with no detectable antibody. No such increase was observed with samples from other patients. This result indicates that donor RBCs may be damaged by the environment of SCD patients, increasing the physiologic clearance of apoptotic RBCs. In vivo, PS-RBC percentage increased in all three cases after destruction of transfused RBCs, indicating that DHTR induces PS-RBCs and, possibly, subsequent VOC and autologous RBC destruction.

CONCLUSION

This study clearly demonstrates that DHTR can occur in the absence of detectable antibody. In these cases, a mechanism of excessive eryptosis is proposed.