Interplay between coagulation and vascular inflammation in sickle cell disease

Sickle cell disease is the most common inherited haematological disorder that leads to the irreversible damage of multiple organs. Although sickling of red blood cells and vaso‐occlusion are central to the pathophysiology of sickle cell disease, the importance of haemolytic anaemia and vasculopathy has been recently recognized. A hypercoagulable state is another prominent feature of sickle cell disease and is mediated by activation of both intrinsic and extrinsic coagulation pathways. Growing evidence demonstrates that coagulation may not only contribute to the thrombotic complications, but also to vascular inflammation associated with this disease. This article summarizes the role of vascular inflammation and coagulation activation, discusses potential mechanisms responsible for activation of coagulation and reviews recent data demonstrating the crosstalk between coagulation and vascular inflammation in sickle cell disease.     

Hydroxyurea therapy requires HbF induction for clinical benefit in a sickle cell mouse model

Hydroxyurea has proven clinical efficacy in patients with sickle cell disease. Potential mechanisms for the beneficial effects include fetal hemoglobin induction and the reduction of cell adhesive properties, inflammation and hypercoagulability. Using a murine model of sickle cell disease in which fetal hemoglobin induction does not occur, we evaluated whether hydroxyurea administration would still yield improvements in hematologic parameters and reduce end-organ damage. Animals given a maximally tolerated dose of hydroxyurea that resulted in significant reductions in the neutrophil and platelet counts showed no improvement in hemolytic anemia and end-organ damage compared to control mice. In contrast, animals having high levels of fetal hemoglobin due to gene transfer with a γ-globin lentiviral vector showed correction of anemia and organ damage. These data suggest that induction of fetal hemoglobin by hydroxyurea is an essential mechanism for its clinical benefits.     

Increased levels of soluble ICAM-1 in the plasma of sickle cell patients are reversed by hydroxyurea

Increased adhesive events between the blood vessel endothelium and red and white cells play a central role in the initiation of vasoocclusive crisis in sickle cell disease (SCD). Soluble VCAM-1 levels are increased in the plasma of sickle cell patients and may be reduced during hydroxyurea (HU) therapy. Reports regarding any changes in soluble ICAM-1 (sICAM-1) levels in sickle cell patients, however, are conflicting, and as yet no beneficial effect of HU upon levels has been observed. Thus, we sought to thoroughly investigate changes in sICAM-1 levels in SCD patients and the effect of HU therapy (20-30 mg/kg/day). Plasma sVCAM-1 levels were significantly higher in steady-state SCD patients than in normal controls (766 +/- 86 ng/mL vs. 325 +/- 38 ng/mL, respectively, P < 0.0001). sVCAM-1 levels were decreased in patients on HU therapy (543 +/- 69 ng/mL) compared to those not taking HU; however, this difference was not significant. Plasma sICAM-1 levels were significantly increased in steady-state SCD patients compared to normal individuals (285 +/- 20 ng/mL vs. 202 +/- 16 ng/mL, respectively, P = 0.002), and HU therapy significantly reduced sICAM-1 levels in patients (217 +/- 12, P = 0.027) to levels approaching those of healthy individuals. sVCAM-1 levels inversely correlated with fetal hemoglobin levels in SCD patients, while a nonsignificant inverse trend was observed between sICAM-1 levels and fetal hemoglobin. In conclusion, plasma sICAM-1 levels were significantly increased in SCD patients, and this increase was reversed by hydroxyurea therapy, possibly reflecting reduced endothelial activation in patients taking HU. Such an event may benefit patients by reducing adhesive interactions between white cells and the endothelium.     

The endothelial biology of sickle cell disease: inflammation and a chronic vasculopathy

A single amino acid substitution in hemoglobin comprises the molecular basis for sickle cell anemia, but evolution of the corresponding clinical disease is extraordinarily complicated and likely involves multiple pathogenic factors. Sickle disease is fundamentally an inflammatory state, with activation of the endothelium, probably through proximate effects of reperfusion injury physiology and chronic molestation by adherent red cells and white cells. The disease also involves enhanced angiogenic propensity, activation of coagulation, disordered vasoregulation, and a component of chronic vasculopathy. Sickle cell anemia is truly an endothelial disease, and it is likely that genetic differences in endothelial function help govern its astonishing phenotypic diversity.     

Hydroxyurea therapy for sickle cell disease in community-based practices: a survey of Florida and North Carolina hematologists/oncologists

Little is known about patterns of hydroxyurea (HU) use by community-based hematologist/oncologists (H/Os) for the treatment of sickle cell disease (SCD). Determination of these practice patterns pertaining to adult SCD patients was the focus of this study. A self-administered survey was mailed to H/Os in two southeastern states. Replies were received from 70% of eligible physicians. This study focuses on responses from 184 community H/Os and a comparison group of 30 university-based/affiliated H/Os providing ongoing care for at least 3 SCD patients/month. The majority of community H/O respondents saw less than 3 SCD patients/month. HU was prescribed by more than half (55%) of community H/Os in at least 10% of their patients. The most common reasons cited for prescribing HU include frequent painful crises (76%), chronic pain with frequent narcotic use (58%), and acute chest syndrome (43%). Although the majority of community H/Os care for few patients with SCD, the reported indications for HU were consistent with currently accepted recommendations. However, community H/Os reported acute chest syndrome, stroke, and pulmonary hypertension as indications for HU less often than the academic H/O group. Barriers to wider use of HU include physician concerns about carcinogenic potential, doubts about HU effectiveness, perceived patient apprehension about adverse effects, concern about lack of contraceptive use, and patient compliance. Further resources should focus on updating physicians on recently published material supporting the effectiveness of HU in symptomatic SCD as well as providing management guidelines to optimize the use of HU.     

Adherent leukocytes capture sickle erythrocytes in an in vitro flow model of vaso-occlusion

Recent in vivo studies suggest that adherent leukocytes bind RBCs and contribute to the microvascular pathology that characterizes sickle cell disease (SCD). A parallel-plate flow assay was used: to investigate the capture of RBCs by adherent neutrophils, monocytes, and T-lymphocytes; to examine whether RBC capture is elevated in patients with SCD; and to determine whether hydroxyurea (HU) therapy affects these interactions. Four measures of cell-cell adhesion were used: adhesion of leukocytes to TNF-alpha-treated human umbilical vein endothelial cells (HUVECs), percent of adherent leukocytes that captured RBCs, number of RBCs captured per interacting leukocyte, and duration of RBC capture. Leukocyte subpopulations from sickle patients were more adherent to activated ECs and captured more RBCs per interacting leukocyte than the corresponding subpopulations from healthy controls. While HU did not affect leukocyte adhesion to activated ECs, it reduced the proportion of adherent leukocytes that captured RBCs, as well as the number of RBCs captured per neutrophil. T-lymphocytes demonstrated elevated adhesion in all measures, and may be the leukocyte subpopulation whose behavior is most altered in SCD. Our findings suggest that neutrophils, monocytes, and T-lymphocytes could all be involved in adhesive interactions with autologous RBCs in patients with SCD.     

The effect of non-steroidal anti-inflammatory drugs on the endothelial function of patients with osteoarthritis in short term

Objective: Our primary aim was to test whether non‐steroid anti‐inflammatory drug (NSAID) use may account for endothelial dysfunction (ED) in the acute period. Additionally, we also aimed to compare the effect of diclofenac and naproxen on endothelial function. Methods: Forty patients with osteoarthritis (OA) were included in the study. Subjects currently receiving NSAIDs were asked to discontinue their anti‐inflammatory medications (for at least 5 days) before the study. After the wash‐out period, all subjects underwent vascular ultrasound measurements. Following baseline vascular imaging, patients were randomly assigned in a 1 : 1 ratio to receive either diclofenac (75 mg twice daily, n = 20), or naproxen (500 mg twice daily, n = 20) for 7 days. Endothelial function was evaluated by using the flow‐mediated dilatation (FMD) method, at baseline, and after 1 week of NSAID treatment. Results: There were 40 OA patients (4 male, 36 female). The median age of the patients was 60 ± 14 years. There were equal numbers of subjects in each treatment group. Age, sex distribution, body mass index, serum lipids, erythrocyte sedimentation rate, C‐reactive protein and fasting glucose levels were similar between the diclofenac and naproxen groups (P > 0.05). The brachial artery diameter (BAD), endothelium‐dependent vasodilatation (FMD%) and nitroglycerin‐induced endothelium‐independent vasodilatation (NTG%) values were not different between pretreatment and on the seventh day in the NSAID treatment groups (P > 0.05). Subgroup analysis also showed similar values of BAD, FMD%, and NTG% between naproxen and diclofenac groups (P > 0.05). Conclusion: Our results suggest that nonselective cyclo‐oxygenase antagonists naproxen and diclofenac have no effect on endothelial function during short‐term use.     

Effects of hydroxyurea in a population of Brazilian patients with sickle cell anemia

Fetal hemoglobin (HbF) inhibits the polymerization of sickle hemoglobin, modulating the clinical features of sickle cell anemia (SCA). Hydroxyurea (HU) therapy can increase the HbF level, although its production can be influenced by genetic determinants. Twenty-two Brazilian SCA patients were evaluated over 5 years before and after HU use. We analyzed (1) betaS haplotype; (2) patient characteristics; and (3) toxicity. No differences between age, sex, and HU response were observed. We found 40.9% of homozygous for Bantu haplotype, and, in contrasting to other trials, we observed HbF level increase in this group (3.84-9.08 g/dL, P=0.003). Adverse effects were rare. Labyrinthitis was observed in 2 (9.10%) patients after HU use, although this complication had not been described before.     

Characterization of a mouse model of sickle cell trait: parallels to human trait and a novel finding of cutaneous sensitization

Sickle cell trait (SCT) has classically been categorized as a benign condition except in rare cases or upon exposure to severe physical conditions. However, several lines of evidence indicate that individuals with SCT are not always asymptomatic, and additional physiological changes and risks may remain unexplored. Here, we utilized mice harbouring one copy of normal human β globin and one copy of sickle human β globin as a model of SCT to assess haematological, histopathological and somatosensory outcomes. We observed that SCT mice displayed renal and hepatic vascular congestion after exposure to hypoxia. Further, we observed that SCT mice displayed increased cold aversion as well as mechanical and heat sensitivity, though to a lesser degree than homozygous sickle cell disease mice. Notably, mechanical hypersensitivity increased following hypoxia and reoxygenation. Overall our findings suggest that SCT is not entirely benign, and further assessment of pain and cutaneous sensitization is warranted both in animal models and in clinical populations.     

Renal protection by atorvastatin in a murine model of sickle cell nephropathy

Recent studies have demonstrated pleiotropic effects of statins in various mouse models of kidney disease. In this study, Townes humanized sickle cell mice were treated for 8 weeks with atorvastatin at a dose of 10 mg/kg/day starting at 10 weeks of age. Treatment with atorvastatin significantly reduced albuminuria, and improved both urine concentrating ability and glomerular filtration rate. Atorvastatin also decreased markers of kidney injury and endothelial activation, and ameliorated oxidant stress in renal tissues and peripheral macrophages. Atorvastatin downregulated the expression of mRNA levels of the NADPH oxidases, Cybb (also termed Nox2) and Nox4, which are major sources of oxidant stress in the kidney. These findings highlight the pleiotropic effects of atorvastatin and suggest that it may provide beneficial effects in sickle cell nephropathy.     

Mitral valve prolapse in sickle cell disease: Manifestation of a generalized connective tissue disorder

Previous studies have shown an association of sickle cell disease with generalized connective tissue disorders such as pscudoxanthoma elasticum. We recently documented an unexpectedly high prevalence of mitral valve prolapse, a connective tissue disorder, in sickle cell discase. To investigate this association, skin biopsies were analyzed from 32 sickle cell disease patients, 11 of whom had mitral prolapse. Total and type III collagen, collagen solubility, and uronic acid were not different between the patients with or without mitral prolapse (p > 0.05). Computerized morphometric quantitation of the volume fraction of elastic fibers was greater in sickle cell disease patients than in 10 normals (3.1 ± 0.1 mean ± SEM vs 2.0 ± 0.3%; p < 0.01) but less than in three patients with pseudoxanthoma elasticum (9.7 0.6%; p < 0.001). Desmosine radioimmunoassay (an index of elastic fibers) was greater in sickle cell disease patients with mitral prolapse than those without (239.3 ± 9.3 vs 171.7 ± 25.4 ng/mg wet weight; p < 0.02). Histopathologic grading showed a similar trend (p = 0.07). The combined probabilities of these three independent tests of elastic fiber quantity showed an increased elastic fiber concentration in mitral prolapse patients compared to those without mitral prolapse (p < 0.02). Thus, there is no evidence for a specific collagen defect; rather, sickle cell disease appears to be associated with a spectrum of elastic tissue disorders, a feature that could predispose to mitral valve prolapse.     

Elevated plasma levels and platelet-associated expression of the pro-thrombotic and pro-inflammatory protein, TNFSF14 (LIGHT), in sickle cell disease

Chronic vascular inflammation and endothelial activation may initiate vaso‐occlusion in sickle cell disease (SCD). TNFSF14 (CD258; LIGHT), a recently‐identified pro‐thrombotic and pro‐inflammatory tumour necrosis factor (TNF)‐superfamily cytokine, has a potent activating effect on endothelial cells. We evaluated whether TNFSF14 production is altered in SCD and whether platelets contribute to this production. TNFSF14 was measured in platelet‐free plasma from healthy‐control individuals (CON), steady‐state sickle cell anaemia (SCA), SCA on hydroxycarbamide therapy (SCAHC) and haemoglobin SC (HbSC) patients. Mean plasma TNFSF14 was significantly increased in SCA, SCAHC and HbSC, compared to CON individuals. In SCA/SCAHC patients, plasma TNFSF14, showed no correlation with haematological variables, but was significantly correlated with serum lactate dehydrogenase and inflammatory markers (CD40LG , IL8 and ICAM1). Platelet‐membrane TNFSF14 expression was significantly augmented on SCA platelets, and correlated with platelet activation; furthermore, measurement of platelet TNFSF14 release indicated that platelets may be a major source of circulating TNFSF14 in SCA. Interestingly, high plasma TNFSF14 was significantly associated with elevated tricuspid regurgitant velocity (≥2·5 m/s) in a population of SCA/SCAHC patients. The pro‐inflammatory and atherogenic cytokine, TNFSF14, could contribute to endothelial activation and inflammation in SCA; future investigations may confirm whether this protein contributes to major clinical complications of the disease, such as pulmonary hypertension, and represents a potential therapeutic target.     

Temporal relationship of asthma to acute chest syndrome in sickle cell disease

Acute chest syndrome (ACS) is an important cause of mortality and morbidity in children with sickle cell disease (SCD). An association between asthma and ACS has been reported. Our aims were to determine whether asthma was more common in SCD children than controls and the relationship of the timing of the SCD children's first ACS episode to a diagnosis of asthma. One hundred and sixty-five SCD children median age 8.2 (range 0.3-17.3) years and 151 similar ethnic origin and aged controls were prospectively recruited into the study and a detailed history was taken from all of the children to determine if they were taking anti-asthma medication. The medical records of the SCD children were examined to assess whether they had an ACS episode, the age this episode occurred and when any diagnosis of asthma had been made. A similar proportion of the SCD children and controls were taking anti-asthma medication (7% and 9%). Thirty-three SCD children had at least one ACS episode. More of the children who had an ACS compared to those who had not were taking anti-asthma medication (P = 0.02). The ACS children had been diagnosed as asthmatic at a median of 3.5 (range 0.5-7) years prior to their first ACS episode. In conclusion, these results suggest asthma exacerbations may predispose to ACS episodes.     

血管周围脂肪组织在动脉粥样硬化炎症发展中的作用

动脉粥样硬化被认为是一个多细胞、多因子参与的慢性炎症性疾病,血管外层在其中发挥了重要作用。血管周围脂肪组织在肥胖、炎症等病理状态下,会通过脂肪细胞表型转化进而释放脂肪因子及炎症因子并调节各类炎症细胞,“从外向内”调控血管的免疫反应,进一步调控动脉粥样硬化。对血管周围脂肪组织进行干预可能是防治动脉粥样硬化的新策略。