Tissue factor-positive monocytes in children with sickle cell disease: correlation with biomarkers of haemolysis.

Tissue Factor (TF) initiates thrombin generation, and whole blood TF (WBTF) is elevated in sickle cell disease (SCD). We sought to identify the presence of TF-positive monocytes in SCD and their relationship with the other coagulation markers including WBTF, microparticle-associated TF, thrombin-antithrombin (TAT) complexes and D-dimer. Whether major SCD-related pathobiological processes, including haemolysis, inflammation and endothelial activation, contribute to the coagulation abnormalities was also studied. The cohort comprised children with SCD (18 HbSS, 12 HbSC, mean age 3·6 years). We demonstrated elevated levels of TF-positive monocytes in HbSS, which correlated with WBTF, TAT and D-dimer (P = 0·02 to P = 0·0003). While TF-positive monocytes, WBTF, TAT and D-dimer correlated with several biomarkers of haemolysis, inflammation and endothelial activation in univariate analyses, in multiple regression models the haemolytic markers (reticulocytes and lactate dehydrogenase) contributed exclusively to the association with all four coagulant markers evaluated. The demonstration that haemolysis is the predominant operative pathology in the associated perturbations of coagulation in HbSS at a young age provides additional evidence for the early use of therapeutic agents, such as hydroxycarbamide to reduce the haemolytic component of this disease.

Tapered oral dexamethasone for the acute chest syndrome of sickle cell disease.

Tapered oral dexamethasone for acute chest syndrome (ACS) in sickle cell anaemia was studied using a novel ACS assessment tool and investigational biomarkers. Twelve participants were randomized (mean age 17·3 years) before early study termination. Dexamethasone decreased duration of hospitalization for ACS by 20·8 h compared to placebo (P = 0·024). Rebound pain occurred in both groups (3 dexamethasone versus 1 placebo). Overall, dexamethasone decreased the leucocyte activation biomarker, sL-selectin; however, participants with rebound pain had higher sL-selectin within 24 h of treatment (dexamethasone or placebo). This ACS assessment tool was feasibly applied, and sL-selectin is a promising biomarker of ACS therapy.

Relationship of Omega-3 fatty acids DHA and EPA with the inflammatory biomarker hs-CRP in children with sickle cell anemia.

BACKGROUND: Inflammation and vaso-occlusion play key roles in Sickle Cell Disease (SCD) pathophysiology. Lipoxygenase products of the omega-3 fatty acids (O3FAs), docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids, are potent anti-inflammatory mediators modulating pain. O3FAs decrease episodes of vaso-occlusion in SCD. METHODS: We assessed erythrocyte fatty acid composition in two major cell membrane phospholipids, phosphatidylcholine and phosphatidylethanolamine, in children with SCD HbSS-disease (n = 38) and age/race-matched HbAA-controls (n = 18). Ratio of pro-inflammatory arachidonic acid (AA) to anti-inflammatory DHA and EPA (FA-Ratio), and its relationship to hs-CRP were evaluated. RESULTS: FA-Ratios were increased in both phosphatidylcholine and phosphatidylethanolamine in HbSS compared to controls. Correlations were noted in HbSS subjects between hs-CRP and FA-Ratios (p = 0.011). FA-Ratios increased with age (p = 0.0007) due to an increase in pro-inflammatory AA with a concomitant decrease in anti-inflammatory DHA. CONCLUSIONS: Findings demonstrate relative deficiencies in HbSS of the anti-inflammatory precursor fatty acids DHA and EPA, which correlates positively with hs-CRP.

Ambulatory hypertension in a pediatric cohort of sickle cell disease.

Hypertension is an established risk factor for subsequent cardiovascular and renal disease in children as well as adults. Sickle cell disease (SCD) is a genetic disorder associated with chronic hemolytic anemia with the major manifestation of vaso-occlusive crises. Although this disease entity involves most organ systems causing vascular and pulmonary injury, little is known about blood pressure (BP) levels or prevalence of hypertension in children with SCD. A cross-sectional study was conducted on 56 children with SCD (54 with hemoglobin SS disease; 2 with hemoglobin Sß0 thalassemia; 29 females). Study participants underwent 24-hour ambulatory BP monitoring (ABPM). Serum creatinine and cystatin C were obtained to assess estimated glomerular filtration rate with age-based formulas. A random urine sample was obtained to estimate urine osmolality and urine albumin to creatinine ratio. Mean age range was 11.9 (±4.5) years. Seventeen participants (30%) met criteria for hypertension based on ABPM. Of the 17 participants classified with hypertension, three had office hypertension with ambulatory hypertension, and 14 had masked hypertension detected on ABPM. Another 28 participants (50%) had some abnormal ABPM parameters in the form of either prehypertension and/or lack of normal nocturnal dipping status. The prevalence of confirmed hypertension, largely manifest by masked hypertension, is high in children, as young as 6 years of age with SCD. Early identification of hypertension in SCD children can confer benefit as it is an important modifiable risk factor for progression of cardiovascular and renal disease.

Sickle-cell disease.

With the global scope of sickle-cell disease, knowledge of the countless clinical presentations and treatment of this disorder need to be familiar to generalists, haematologists, internists, and paediatricians alike. Additionally, an underlying grasp of sickle-cell pathophysiology, which has rapidly accrued new knowledge in areas related to erythrocyte and extra-erythrocyte events, is crucial to an understanding of the complexity of this molecular disease with protean manifestations. We highlight studies from past decades related to such translational research as the use of hydroxyurea in treatment, as well as the therapeutic promise of red-cell ion-channel blockers, and antiadhesion and anti-inflammatory therapy. The novel role of nitric oxide in sickle-cell pathophysiology and the range of its potential use in treatment are also reviewed. Understanding of disease as the result of a continuing interaction between basic scientists and clinical researchers is best exemplified by this entity.

Hypoxaemia in sickle cell disease: biomarker modulation and relevance to pathophysiology.

BACKGROUND: Nocturnal oxyhaemoglobin desaturation might have a role in CNS complications related to sickle cell disease, and rates of painful crises. We attempted to examine the biological relations, and describe the haematological risk factors for oxyhaemoglobin desaturation. METHODS: The study population included children with sickle cell disease and controls. Cellular activation was assessed by measurement of soluble vascular cell adhesion molecule 1, P-selectin, L-selectin, and leukotriene B4. Erythrocyte-endothelial adhesion and routine haematological variables were assessed. Oxygen saturation (SaO2) was measured by pulse oximetry while children were awake and asleep. Children with a mean sleeping SaO2 of < or =93% were identified as hypoxaemic. Children were divided into four groups: controls (ten children), HbSC (nine, all normoxic), HbSS normoxic (13), and HbSS hypoxaemic (15). FINDINGS: Among haematological variables, sleeping SaO2 correlated only with packed-cell volume (r=0.7; p<0.0001). Inverse relations were noted between sleeping SaO2 and adhesion (-0.45; p<0.01), and markers of white-cell (-0.51; p<0.01), platelet (-0.61; p<0.001), and endothelial activation (-0.46; p<0.01). In the HbSS group who had sleeping hypoxaemia, waking SaO2 measurements showed continuing hypoxaemia, with similar correlation between SaO2 and cell activation markers. INTERPRETATION: Our adhesion-related findings suggest a potential mechanism for the increased occurrence of clinical vaso-occlusive crises in individuals with sickle cell disease who have oxyhaemoglobin desaturation. Release of cellular mediators in hypoxaemia, and the relation between anaemia and oxyhaemoglobin desaturation, suggest that risk factors for stroke, including anaemia, might have a role in CNS-vasculopathy through hypoxia-mediated pathways. Further more, hypoxaemia in the older child also occurs during the day; such mild untreated hypoxia could lead to an increased risk of vaso-occlusive episodes.

Role of erythrocyte phosphatidylserine in sickle red cell-endothelial adhesion.

Phosphatidlyserine (PS) exposure on the erythrocyte surface endows the cell with the propensity of adhering to vascular endothelium. Because individuals with sickle cell disease (SCD) manifest loss of erythrocyte membrane asymmetry with PS exposure, we have assessed the contribution of this marker to the process of sickle erythrocyte-microendothelial adhesion. Assays for plasma-induced adhesion were conducted on unactivated endothelium, in the absence of immobilized ligands, such that PS was compared to the erythrocyte adhesion receptor CD36. Blocking studies with erythrocytes pretreated with annexin V (to cloak PS) or anti-CD36 or both revealed an inhibitory effect on adhesion of 36% +/- 10% and 23% +/- 8% with blocking of both sites suggestive of an additive effect. We next evaluated 87 blood samples from patients with SCD and grouped them into 4 categories based on adhesion marker (CD36 and PS) levels. Results revealed a striking correlation between erythrocyte PS positivity and adhesion. Analyses of the individual patient data demonstrated a positive correlation between PS and adhesion (R = 0.52, P <.000 001), whereas none was noted between adhesion and CD36 (R = 0.2, P >.07). The effect of PS on adhesion appears to be related to the quantitative differences in erythrocyte markers in SCD, with PS the predominant marker when compared to CD36 both in the total erythrocyte population, and when the adherence-prone erythrocyte, the CD71(+) stress reticulocyte, was evaluated. Our study signals the entrance of an important new contributor to the field of sickle erythrocyte-endothelial adhesion. The implications of erythrocyte PS exposure in relation to the vascular pathology of SCD need to be assessed.

Eicosanoids in sickle cell disease: potential relevance of neutrophil leukotriene B4 to disease pathophysiology.

Neutrophil activation with the release of intracellular granule contents has been observed in sickle cell disease (SCD). Because leukotriene B(4) (LTB(4)), a 5-lipoxygenase metabolite of arachidonic acid in neutrophils, is a chemoattractant and enhances neutrophil adhesion to endothelium, we assessed plasma levels of this metabolite in controls (n = 9) and individuals with SCD, SS genotype, both in basal "steady state" (n = 37) and during episodes of vaso-occlusion (n = 10) and acute chest syndrome (n = 5). Thirteen patients with SCD, SC genotype, in steady state were also studied. Although no significant differences were noted between the control (136 +/- 32 fmol/mL) and SC genotype (177 +/- 83 fmol/mL, P >.15), LTB(4) levels were markedly increased in patients with SS genotype in basal steady state (207 +/- 64 fmol/mL, P <.003) compared with those in controls. Values were further increased during vaso-occlusion (264 +/- 94 fmol/mL) and acute chest syndrome (363 +/- 124 fmol/mL). These levels were significantly different from measurements taken during steady state (P <.04 and P <.0001, respectively). No correlation was noted between LTB(4) level and total white cell or neutrophil count. Additionally, the significant correlation noted in SCD between increased levels of plasma LTB(4) and soluble L-selectin (P <.03) reflects neutrophil activation. We also observed an effect of LTB(4) on red cell-endothelial adhesion at concentrations that appear clinically relevant (1-10 pmol/mL) with concomitant up-regulation of mRNA for the endothelial vitronectin receptor. These properties of LTB(4) are relevant to disease pathophysiology, providing further evidence of the contribution of the neutrophil to the proinflammatory and proadhesive phenotype in SCD.