Monitoring the acute phase response to vaso-occlusive crisis in sickle cell disease

A randomized, placebo-controlled, double-blind trial of canakinumab in children and young adults with sickle cell anemia

Excessive intravascular release of lysed cellular contents from damaged red blood cells (RBCs) in patients with sickle cell anemia (SCA) can activate the inflammasome, a multiprotein oligomer promoting maturation and secretion of pro-inflammatory cytokines, including interleukin 1-beta (IL-1b). We hypothesized that IL-1b blockade by canakinumab in patients with SCA would reduce markers of inflammation and clinical disease activity. In this randomized, double-blind, multi-center phase 2a study, patients aged 8-20 years old with SCA (HbSS or HbSb0thalassemia), history of acute pain episodes and elevated hsCRP >1.0 mg/L at screening were randomized 1:1 to received 6 monthly treatments with 300 mg s.c. canakinumab or placebo. Measured outcomes at baseline and weeks 4, 8, 12, 16, 20 and 24 included electronic patient-reported outcomes, hospitalization rate and adverse events (AEs) and serious AEs (SAEs). All but one of the 49 enrolled patients were receiving stable background hydroxyurea therapy. Although the primary objective (pre-specified reduction of pain) was not met, compared to placebo-arm patients, canakinumab-treated patients had reductions in markers of inflammation, occurrence of SCA-related AE and SAE, and number and duration of hospitalizations, as well as trends for improvement in pain intensity, fatigue and absences from school or work. Post-hoc analysis revealed treatment effects on weight, restricted to pediatric patients. Canakinumab was well tolerated with no treatment-related SAEs and no new safety signal. These findings demonstrate that the inflammation associated with SCA can be reduced by selective IL-1b blockade by canakinumab with potential for therapeutic benefits. This trial was registered at www.clinicaltrials.gov as NCT02961218.

The Role of RBC Oxidative Stress in Sickle Cell Disease: From the Molecular Basis to Pathologic Implications

Sickle cell disease (SCD) is an inherited monogenic disorder and the most common severe hemoglobinopathy in the world. SCD is characterized by a point mutation in the β-globin gene, which results in hemoglobin (Hb) S production, leading to a variety of mechanistic and phenotypic changes within the sickle red blood cell (RBC). In SCD, the sickle RBCs are the root cause of the disease and they are a primary source of oxidative stress since sickle RBC redox state is compromised due to an imbalance between prooxidants and antioxidants. This imbalance in redox state is a result of a continuous production of reactive oxygen species (ROS) within the sickle RBC caused by the constant endogenous Hb autoxidation and NADPH oxidase activation, as well as by a deficiency in the antioxidant defense system. Accumulation of non-neutralized ROS within the sickle RBCs affects RBC membrane structure and function, leading to membrane integrity deficiency, low deformability, phosphatidylserine exposure, and release of micro-vesicles. These oxidative stress-associated RBC phenotypic modifications consequently evoke a myriad of physiological changes involved in multi-system manifestations. Thus, RBC oxidative stress in SCD can ultimately instigate major processes involved in organ damage. The critical role of the sickle RBC ROS production and its regulation in SCD pathophysiology are discussed here.

Azithromycin Reduces Markers of Vascular Damage in Pediatric Patients With Sickle Cell Disease

Background

Immunomodulatory effects of macrolides in chronic inflammation are well known. In this study, we tested our hypothesis that azithromycin (AZT) can decrease inflammation in pediatric patients with sickle cell disease (SCD).

Methods

The use of AZT as an anti-inflammatory agent was evaluated in double-blind, placebo-controlled, cross-over study for 8 weeks of treatment with 8 weeks of washout. Blood samples were collected before (PRE) and after (POST) each 8-week treatment period. Repeated measures analysis of variance (ANOVA) with post hoc multiple comparison procedures and Chi-square test were used for statistical analysis of the data. Complete blood count, distribution of the lymphocyte subsets, and plasma levels of markers of vascular damage were analyzed.

Results

A significant decrease in the number of leucocytes and granulocytes was observed in AZT group following treatment. An opposite dynamic was observed in placebo group; numbers of granulocytes significantly increased at POST interval. All markers of vascular damage were reduced in AZT group at POST interval with overall significance (P = 0.026). The most prominent significant changes were observed in levels of myeloid-related protein 8/14 (MRP8/14), lipocalin A (NGAL), matrix metalloproteinases (MMP) 9, and insulin-like growth factor-binding protein (IGFBP) 4. Plasma level of C-reactive protein (CRP) was significantly decreased in AZT group as well.

Conclusions

Data suggested that AZT may be beneficial in management of microvascular injury in SCD.

Altered HDL particle in sickle cell disease: decreased cholesterol content is associated with hemolysis, whereas decreased Apolipoprotein A1 is linked to inflammation

Background

Hypocholesterolemia is the most frequently encountered lipid abnormality in sickle cell disease (SCD). We enrolled pediatric patients to determine the relationships between lipid profile and parameters of hemolysis, oxidative stress and chronic inflammation in SCD.

Methods

The study involved 35 pediatric SCD patients and 19 healthy controls. Patients were crisis-free and had not received transfusions for the last 3 months. Total cholesterol, triglyceride, HDL-C, LDL-C, VLDL-C, apolipoprotein A1, apolipoprotein B, LCAT, LDH, bilirubin, haptoglobin, iron, ferritin, hemin, serum amyloid A (SAA), myeloperoxidase (MPO), uric acid, ALT and GGT levels were evaluated in patients’ blood.

Results

Patients had hypocholesterolemia depicted by lower levels of total cholesterol, HDL-C, LDL-C, as well as Apolipoprotein A1 and Apolipoprotein B compared to controls. The chronic hemolysis of SCD was evident in patients by higher LDH and bilirubin and almost undetectable haptoglobin levels. Hemin levels (as a measure of oxidized heme) were significantly increased in patients with SCD. Inflammation markers, SAA and MPO, were significantly increased in the patients as well. There were negative correlations between HDL-C and LDH, and Apo A1 and SAA. Hemin was positively correlated to MPO.

Conclusion

Hemolysis was associated with decreased HDL –C, and Inflammation was linked to decreased apolipoprotein A1 levels in our SCD patients. Therefore, we suggest that the HDL particle is altered during the course of the disease. The altered HDL in SCD may become dysfunctional and result with a slowing down of the reverse cholesterol transport.

Inhaled steroids associated with decreased macrophage markers in nonasthmatic individuals with sickle cell disease in a randomized trial

Inhaled mometasone was shown to improve pain scores and decrease soluble vascular cell adhesion molecule (sVCAM) concentration in a randomized controlled trial of nonasthmatic patients with sickle cell disease. We sought to explore potential changes in systemic inflammation as a mechanism underlying this effect. Serum samples from 41 trial participants (15 placebo- and 26 mometasone-treated) were analyzed using a 92 inflammatory marker panel at baseline and after 8 weeks of mometasone therapy. Individual marker analysis and correlation analysis were conducted. Adjusted for age, the mometasone-treated group decreased the concentration of CXCL9, CXCL11, CD40, IL-10, and IL-18 relative to placebo-treated participants. Hierarchical clustering and correlation analysis identified additional evidence for a decrease in cytokines linking to macrophage signaling and migration. There was no statistically significant change in markers of asthma and allergy, indicating that the improvement was unlikely mediated by modulation of occult reactive airway disease. This analysis of inflammatory markers suggests that decrease in macrophage activity may be involved in the mediation of the clinical benefit seen with use of inhaled mometasone in nonasthmatic patients with sickle cell disease.Trial registration: clinicaltrials.gov identifier: NCT02061202.

Erythrocyte Aggregation and Blood Viscosity is Similar in Homozygous Sickle Cell Disease Patients with and without Leg Ulcers

Background  There is no consensus regarding the role of red blood cell (RBC) aggregation in the pathogenesis of leg ulcers (LUs) in sickle cell disease (SCD). Objectives  We sought to evaluate whether the cross-sectional determination of RBC aggregation and hematological indices were associated with the presence of LU in homozygous SCD. Methods  Twenty-seven patients with LU and 23 with no history of ulceration were recruited into the study. A laser-assisted rotational red cell analyzer (LoRRca) was used in the determination of the aggregation index (AI), aggregation half-time ( t_1/2 ), and the RBC aggregate strength (AMP). Hematological indices were determined using a CELL-DYN Ruby analyzer. Whole blood viscosity (WBV) and plasma viscosity (PV) were measured using a Vilastic bioprofiler. The data were presented as means ± standard deviation or median, interquartile range. Two-sample t -test was used to test for associations between the AIs, WBV, and PV in patients with and without LU. Statistical significance was taken as p  < 0.05. All analyses were conducted using Stata/SE v . 12.1 (StataCorp, College Station, TX). Results  The AI was comparable in the group with and without ulcers (68.6, 16.7 versus 67.7, 16.9; p  = 0.74); t_1/2 (1.7, 1.3 versus 1.8, 1.3; p  = 0.71); AMP (18.8, 14.5 versus 19.1, 13.3; p  = 0.84), WBV (3.8, 1.2 versus 3.8, 0.7; p  = 0.77); and the PV (1.3, 0.08 versus 1.4, 0.1; p  = 0.31) and were also not statistically different between the groups of participants. Conclusion  RBC aggregation and aggregate strength are not associated with leg ulceration in SCD.

Serum IL-6, IL-10, and TNFα levels in pediatric sickle cell disease patients during vasoocclusive crisis and steady state condition

Vaso-occlusive crisis (VOC) is a significant complication of sickle cell disease (SCD), and altered production of pro-inflammatory and anti-inflammatory molecules contributed to its pathogenesis. In view of the association of chronic inflammation with VOC onset, and given the capacity of interleukin (IL)-10 as anti-inflammatory, and IL-6, and TNFα as pro-inflammatory cytokines, we tested the association of altered IL-10, IL-6, and TNFα secretion with VOC pathogenesis and its severity. Study subjects comprised 147 SCD patients with active VOC (VOC Group), and 63 pain-free SCD patients for at least 9 months before blood collection (Steady-state Group). Serum cytokine concentrations were determined by ELISA. IL-10 levels were significantly reduced, while IL-6 levels were increased in VOC compared to Steady-state groups; serum TNFα levels were comparable between both groups. There was enrichment of low IL-10, but high IL-6 and TNFα quartiles in VOC Group, which translated into increased VOC risk. In contrast, high IL-10, but low IL-6 and TNFα quartiles were seen in Steady-state Group. Correlation analysis demonstrated significant association between reduced IL-10 levels and the frequency, type, severity, and duration of VOC and requirement for hydroxyurea treatment, while IL-6 correlated with duration of VOC episodes. Our data support strong association of reduced IL-10 and increased IL-6 levels with VOC, and their modulation of VOC-related parameters.

Dietary supplementation with docosahexanoic acid (DHA) increases red blood cell membrane flexibility in mice with sickle cell disease

Humans and mice with sickle cell disease (SCD) have rigid red blood cells (RBCs). Omega-3 fatty acids, such as docosahexanoic acid (DHA), may influence RBC deformability via incorporation into the RBC membrane. In this study, sickle cell (SS) mice were fed natural ingredient rodent diets supplemented with 3% DHA (DHA diet) or a control diet matched in total fat (CTRL diet). After 8weeks of feeding, we examined the RBCs for: 1) stiffness, as measured by atomic force microscopy; 2) deformability, as measured by ektacytometry; and 3) percent irreversibly sickled RBCs on peripheral blood smears. Using atomic force microscopy, it is found that stiffness is increased and deformability decreased in RBCs from SS mice fed CTRL diet compared to wild-type mice. In contrast, RBCs from SS mice fed DHA diet had markedly decreased stiffness and increased deformability compared to RBCs from SS mice fed CTRL diet. Furthermore, examination of peripheral blood smears revealed less irreversibly sickled RBCs in SS mice fed DHA diet as compared to CTRL diet. In summary, our findings indicate that DHA supplementation improves RBC flexibility and reduces irreversibly sickled cells by 40% in SS mice. These results point to potential therapeutic benefits of dietary omega-3 fatty acids in SCD.

Ischemia-reperfusion injury in sickle cell anemia: relationship to acute chest syndrome, endothelial dysfunction, arterial vasculopathy, and inflammatory pain

Ischemia-reperfusion (I/R) physiology, also called reperfusion injury, instigates vascular and tissue injury in human disease states. This review describes why sickle cell anemia should be conceptualized in this fashion and how I/R physiology explains the genesis of characteristic aspects of vascular pathobiology and clinical disease in sickle cell anemia. The nature of I/R and its relevance to sickle cell anemia are discussed, with an emphasis on the acute chest syndrome, endothelial dysfunction with aberrant vasoregulation, circle of Willis vasculopathy, and inflammatory pain. Viewing sickle disease from this perspective elucidates defining pathophysiology and identifies a host of novel potential therapeutic targets.

C-reactive Protein and Disease Outcome in Nigerian Sickle Cell Disease Patients

Background:

Evidence suggests that sickle cell disease (SCD) is associated with a chronic inflammatory state. C-reactive protein (CRP) is known to modulate inflammation. Its role in the chronic inflammation of SCD may make it valuable as a therapeutic target.

Aim:

The aim was to determine CRP levels in SCD subjects in asymptomatic steady state (ASS) and crisis and correlate these with severity scores in the ASS.

Subjects and Methods:

We measured the level of CRP in 30 hemoglobin SS (HbSS) individuals in ASS and seven in crisis. As controls, we measured CRP in 50 individuals each who were hemoglobin AS and hemoglobin AA respectively, using enzyme linked immunoabsorbent assay based commercially available kits from East Wing Diagnostic Limited Full blood count (white blood cell [WBC]) was done for the ASS HbSS individuals using a cell counter and their disease severity calculated by an objective scoring method.

Results:

Our results showed that ASS HbSS individuals had significantly higher CRP levels compared with the controls. The HbSS individuals in crisis also had a significantly higher level of CRP compared to the ASS HbSS individuals. Disease severity and WBC were found to be negatively correlated with CRP levels (P = 0.17; and 0.73, respectively).

Conclusion:

Our results suggest that increased levels of CRP in ASS HbSS individuals may play a protective role in SCD leading to better disease outcome, and may have value as a therapeutic target.

An Intervention to Decrease Stigma in Young Adults With Sickle Cell Disease

Young adults with sickle cell disease (SCD) are often stigmatized when they seek care for pain. The purpose of this pilot study was to test an intervention to decrease health-related stigma during care-seeking. Young adults with SCD ages 18 to 35 years ( n = 90) were randomized to either the care-seeking intervention (CSI) or an attention control group that participated in life review interviews. The two groups were compared by t tests and longitudinal data analyses on the change from baseline to the last time point in total health-related stigma and health-related stigma by doctors. Findings suggest that the CSI was associated with significant increased awareness of perceived total stigma and stigma by doctors compared with the attention control group. These findings are promising in terms of lessons learned from a pilot intervention that focused on the role communication skills play in decreasing health-related stigma in young adults with SCD.

Serum copeptin and cortisol do not accurately predict sickle cell anaemia vaso-occlusive crisis as C-reactive protein

OBJECTIVE

This study assessed the diagnostic performance and prognostic properties of C-reactive protein (CRP), copeptin and cortisol in individuals with sickle cell anaemia (SCA).

DESIGN

Prospective case-control study.

METHODS

Sixty consecutive SCA subjects (18-40 years) comprising 30 subjects in the steady state and 30 subjects in vaso-occlusive crisis (VOC) were recruited into this study. Thirty (30) apparently healthy individuals with HbAA genotype served as controls. ELISA was used for the determination of serum levels of copeptin, CRP and cortisol. Data obtained were statistically analyzed using the Student's t-test and Mann Whitney U as appropriate and P<0.05 was considered significant.

RESULTS

SCA subjects in VOC had significantly lower copeptin level and significantly higher CRP level compared with controls. However, serum levels of copeptin, cortisol and CRP were significantly higher in SCA subjects in VOC compared with SCA subjects in steady state. Furthermore, CRP had the widest Area under the ROC curve (AUROC) than copeptin and cortisol. No significant difference was observed in the levels of copeptin, CRP and cortisol when SCA subjects in VOC who were hospitalized for less ≤ 5 days were compared with subjects who had longer stays.

CONCLUSION

It could be concluded that C-reactive protein has a superior diagnostic performance for vaso-occlusive crisis in individuals with sickle cell anaemia and that C-reactive protein, cortisol and copeptin are not good prognostic markers in SCA subjects in vaso-occlusive crisis.

Care seeking for pain in young adults with sickle cell disease

In individuals with sickle cell disease (SCD), recognizing the cues to an acute pain episode and responding appropriately are important. The purpose of this mixed-methods pilot study is to identify preliminary factors that influence care seeking for pain in young adults with SCD. Responses were received from 69 young adults with SCD, age 18-35 years. The majority of respondents (88%) wait until the pain intensity is an average of 8.7 (± 1.2) on a scale of 1 to 10 before seeking care. Prominent themes influencing care seeking for pain include: trying to treat pain at home, avoiding the emergency department because of past treatment experiences, the desire to avoid admission to the hospital, and the importance of time in the lives of the young adults with SCD. Young adults with SCD need additional support from family and healthcare providers in order to make timely, appropriate decisions regarding care seeking.

Utility of plasma transferrin receptor, ferritin and inflammatory markers in children with sickle cell disease

BACKGROUND

Soluble transferrin receptor (sTfR) is generally unaffected by inflammatory status, whereas ferritin increases along with acute-phase proteins. The utility of these iron biomarkers in relation to inflammatory markers in children with sickle cell disease (SCD) with differing grades of severity is unclear.

OBJECTIVES

To describe iron biomarker profiles and inflammatory responses in relation to disease severity in children with SCD.

METHODS

This cross-sectional study describes plasma levels of sTfR, ferritin, C-reactive protein (CRP) and serum amyloid A (SAA) among 102 Yemeni children with SCD in relation to clinical profiles and disease severity.

RESULTS

Median (IQR) sTfR was 58·5 mg/L (38-81), and concentration was positively correlated with reticulocyte count (r = +0·31, P = 0·002) and splenic enlargement (r = +0·20, P = 0·04), and was negatively correlated with Hb (r = -0·28, P = 0·004). Subcategories of children in a steady state were identified using ferritin and CRP cut-off values to discriminate iron status. In children in a steady state, the prevalence of iron deficiency was 25%, iron repletion 48% and marginal or normal status 27%. Ferritin concentration correlated positively with Hb and 23% of iron-deficient children had severe anaemia. CRP and SAA were increased in the steady state and were higher with acute disease complications (P<0·05 and <0·001, respectively). There was no association between sTfR or sTfR-ferritin index and inflammatory markers or disease severity score.

CONCLUSION

In SCD, elevated sTfR is related to hypererythropoietic activity and does not correlate with inflammatory status or disease severity. Iron deficiency prevalence was estimated to be 25%. A classification of iron status is proposed.

Leukotriene pathway in sickle cell disease: a potential target for directed therapy

Sickle cell disease (SCD) is characterized by recurrent episodes of vaso-occlusion, resulting in tissue ischemia and end-organ damage. Inflammation is critical to the pathogenesis of vaso-occlusion and has been associated with SCD-related morbidity and mortality. Despite the impact of inflammation, no directed anti-inflammatory therapies for the treatment or prevention of vaso-occlusive events currently exist. Among individuals with SCD, asthma is a comorbid inflammatory condition that increases the risk of pain episodes, acute chest syndrome and death. Inflammation associated with asthma could augment the proinflammatory state of SCD, increasing episodes of vaso-occlusion. Leukotrienes are inflammatory mediators that play a prominent role in the pathogenesis of asthma and have been associated with SCD-related morbidity. Targeting inflammatory mediators, such as leukotrienes, is a promising approach for the development of novel therapies for the treatment of SCD. This review will examine the relationship between inflammation and vaso-occlusion, with particular focus on the leukotriene pathway.

Lactate dehydrogenase and severity of pain in children with sickle cell disease

OBJECTIVES

This prospective study was carried out to assess lactate dehydrogenase (LDH) as a biochemical marker during acute painful episode and steady state in children with sickle cell disease (SCD).

DESIGN AND METHODS

A prospective descriptive study has been carried out on children and adolescents with SCD and pain during a vaso-occlusive episode. A total of 76 patients aged 1-18 years were included. Assessment of pain was done using the suitable pain assessment tool (visual analogue scales, Oucher scale) for school and preschool children. Complete blood count, liver function tests, LDH and C-reactive protein assay were performed on all patients during acute painful episode and steady state.

RESULTS

LDH has been found to increase significantly during acute painful episode compared with steady state (p < 0.01). There is also a significant positive correlation between LDH level and severity of pain (p < 0.05). In addition, C-reactive protein level was found to be significantly elevated during acute painful episode (p < 0.01) and its level correlates significantly with severity of pain (p = 0.01).

CONCLUSION

From this study it can be concluded that LDH is a significant biochemical marker for the severity of pain during a vaso-occlusive episode in SCD.

The proteome of sickle cell disease: insights from exploratory proteomic profiling

The expanding realm of exploratory proteomics has added a unique dimension to the study of the complex pathophysiology involved in sickle cell disease. A review of proteomic studies published on sickle cell erythrocytes and plasma shows trends of upregulation of antioxidant proteins, an increase in cytoskeletal defects, an increase in protein repair and turnover components, a decrease in lipid raft proteins and apolipoprotein dysregulation. Many of these findings are consistent with the pathophysiology of sickle cell disease, including high oxidant burden, resulting in damage to cytoskeletal and other proteins, and erythrocyte rigidity. More unexpected findings, such as a decrease in lipid raft components and apolipoprotein dysregulation, offer previously unexplored targets for future investigation and potential therapeutic intervention. Exploratory proteomic profiling is a valuable source of hypothesis generation for the cellular and molecular pathophysiology of sickle cell disease.

Health-related stigma in young adults with sickle cell disease

Health-related stigma is increasingly becoming a major public health issue that is receiving more attention. Young adults with sickle cell disease (SCD) are at risk for health-related stigmatization due to the many challenges of the disease. SCD includes the lifelong challenges of managing the chronic illness while accessing and navigating the health care system. The burdens of the disease can affect all aspects of the lives of individuals with SCD to include physiological, psychological, and social well-being. Although others may be involved in the process of stigmatization, the purpose of this paper was to support the need to develop patient-oriented interventions to prevent and treat health-related stigma in young adults with SCD, as these individuals may face health-related stigma throughout their lives, but especially immediately after transitioning from pediatric to adult care. Additionally, the Revised Theory of Self-Care Management for Sickle Cell Disease is offered as a framework from which theory-based interventions can be derived.

Apolipoprotein A-I and serum amyloid A plasma levels are biomarkers of acute painful episodes in patients with sickle cell disease

BACKGROUND

Acute painful episodes are the clinical hallmark of sickle cell disease and have been linked to morbidity and mortality in the sickle cell population.

DESIGN AND METHODS

We undertook exploratory proteomic studies on paired plasma samples collected from a cohort of 26 adult sickle cell patients during steady state and on the first day of an acute painful episode. We screened for changes in abundance of specific protein peaks via surface-enhanced laser desorption/ionization time of flight mass spectrometry (SELDI-TOF MS), and confirmed the identify of candidate protein peaks by specific immunoassays.

RESULTS

The levels of hemoglobin, hematocrit, total protein, and albumin were lower and the levels of lactate dehydrogenase and absolute reticulocytes higher during acute painful episodes than during the steady state. Surface-enhanced laser desorption/ionization time of flight mass spectrometry spectral analysis consistently showed a mass-to-charge peak at 11.7 kDa with elevated intensities during acute painful episodes, which correlated significantly with the serum amyloid A immunoassay. Serum amyloid A levels were significantly elevated during acute painful episodes, especially in four patients with marked end-organ complications of such episodes. A second, recurring peak, less abundant during acute painful episodes, was present at 28.1 kDa; this peak was correlated significantly with immunoassay measurements of apolipoprotein A1.

CONCLUSIONS

On the average, plasma serum amyloid A rises and apolipoprotein AI falls during acute painful episodes. The serum amyloid A/apolipoprotein AI ratio increased in 81% of the patients during acute painful episodes, potentially making it a useful objective marker of such episodes. We propose that these protein alterations, known to contribute to endothelial dysfunction in other settings, might do likewise acutely in acute painful episodes and present a new target for therapeutic intervention in sickle cell disease. (ClincalTrials.gov Identifier: NCT00081523).

Histopathology of experimentally induced asthma in a murine model of sickle cell disease

Asthma is a comorbid condition associated with increased rates of pain, acute chest syndrome, and premature death in human sickle cell disease (SCD). We developed an experimental asthma model in SCD and control mice expressing either normal human or murine hemoglobin to determine its effect on mortality and lung pathology. To induce lung inflammation, experimental mice were sensitized to ovalbumin (OVA) by subcutaneous OVA implantation (Sen), allowed 2 weeks to recover, and then divided into 2 groups, each receiving over a subsequent 10-day period the same dosage of aerosolized OVA but 2 different levels of exposure: 15 minutes (LoSen) and 30 minutes (HiSen). During recovery, 10% of SCD mice died compared with no deaths in control mice. An additional 30% of HiSen SCD mice died during aerosolization compared with 10% in LoSen SCD. Histologic indices of lung inflammation (eg, eosinophil recruitment, airway and vessel wall thickening, and immunoreactive TGFbeta and fsp-1) and bronchial alveolar lavage fluid eosinophil peroxidase activity differentially increased in sensitized mice compared with unsensitized mice. Our findings indicate SCD mice with experimentally induced asthma are more susceptible to death and pulmonary inflammation compared with control mice, suggesting that asthma contributes significantly to morbidity and mortality in SCD.

C-reactive protein and interleukin-6 are decreased in transgenic sickle cell mice fed a high protein diet

Sickle cell disease is associated with hypermetabolism and a consequent shortage of substrates for normal growth and healthy immune response. The protein:energy ratio is a major determinant of dietary adequacy; the requirement for optimal growth of control mice is 20% of energy from dietary protein. This study investigated the efficacy of increased dietary protein for improving weight gain and reducing inflammation in the Berkeley sickle cell mouse model (S). The study examined the effect of diet on weight gain and circulating levels of 2 inflammatory proteins, C-reactive protein (CRP), and cytokine interleukin-6 (IL-6). Male C57BL/6 (C) control (n = 8) and S mice (n = 8) were randomized at weaning to 40 d of isoenergetic diets containing 20% (normal) and 35% (high) of energy from protein (C20, C35, S20, S35), replacing dextrin. Rate of weight gain was calculated and plasma CRP and IL-6 concentrations determined by ELISA. Liver mRNA expression of these proteins was measured by real-time PCR and L-arginase by colorimetric assay. S35 mice tended to gain weight more rapidly than S20 mice (P = 0.06) and more rapidly than C35 mice (P < 0.01). Circulating CRP and IL-6 levels were also lower in S35 mice than in S20 mice (P < 0.05), as was liver CRP mRNA expression (P < 0.01). These results demonstrate that introducing a high protein diet at weaning attenuates the steady-state inflammation in this S mouse model. Dietary L-arginine availability was investigated as a possible mechanism for increased nitric oxide production and consequent reduced inflammation.

Renal amyloidosis in a child with sickle cell anemia

The kidney is frequently affected in patients with sickle cell syndrome, i.e., homozygous and heterozygous patients, with a consequently large spectrum of renal abnormalities that may range from minimal functional changes to chronic renal failure. Here, we present a 13-year-old boy with sickle cell anemia (SCA) (HbSS) who was referred to our unit with nephrotic syndrome. Renal biopsy revealed AA type amyloidosis on the basis of light microscopic findings, indicating Congo red staining and immunohistochemistry. He had neither a family history of familial Mediterranean fever (FMF) nor any complaint of recurrent abdominal pain, arthritis, and fever, but frequent painful vaso-occlusive crises. The patient was found to have no MEFV gene (Mediterranean feVer) mutations either. Painful episodic attacks might provoke recurrent acute inflammation, leading to repeated stimulation of acute phase responses and cause secondary amyloidosis. To our knowledge, this boy is the first case of SCA complicated by renal amyloidosis observed in childhood.

Proinflammatory cytokines and the hypermetabolism of children with sickle cell disease

Sickle cell anemia (HbSS) includes chronic inflammation, but the origin is unclear. We hypothesized that in stable HbSS patients the inflammation was associated with hypermetabolism. We compared selected hypermetabolic and key immunomodulator indicators in HbSS versus control children and examined associations between measures of hypermetabolism and inflammation. Twelve fasting asymptomatic HbSS children 6-12 years and 9 controls matched for age, gender and fat mass (FM) were studied. Proportional reticulocyte count (retic%) and resting energy expenditure (REE) represented hypermetabolism, and C-reactive protein (CRP) indicated inflammation. Proinflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6), chemokine monocyte chemoattractant protein-1 (MCP-1), and energy balance cytokine leptin were measured. Methods were indirect calorimetry, enzyme-linked immunosorbent assay, and radioimmunoassay. Statistical analysis included simple correlation and regression analysis. REE (51 +/- 6 vs. 43 +/- 12 kcal/kg per fat-free mass (FFM), mean +/- SD), retic% (12 +/- 4 vs. 0.7 +/- 0.3%), CRP (5 +/- 3 vs. 0.3 +/- 0.4 mg/liter), and IL-6 (71 +/- 40 vs. 20 +/- 7 pg/ml) were significantly higher for HbSS than controls (P < 0.05). Conversely, leptin (0.1 +/- 0.1 vs. 2 +/- 1 microg/liter per kgFM) and MCP-1 (34 +/- 5 vs. 41 +/- 4 pg/ml) were significantly lower for the HbSS subjects (P < 0.01). TNF-alpha was not significantly different. There were no significant associations between REE or retic% and any cytokine measured. However, CRP was significantly associated with REE in HbSS (r = 0.8, P = 0.003) and an important predictor of REE/FFM. We provide new evidence for low circulating levels of inflammatory chemokine MCP-1 in stable HbSS children, confirm mostly low cytokine levels, inflammation, and hypermetabolism and demonstrate association of hypermetabolism with inflammation via CRP but not via cytokines.

Microvascular blood flow and stasis in transgenic sickle mice: utility of a dorsal skin fold chamber for intravital microscopy

Vascular inflammation, secondary to ischemia-reperfusion injury, may play an essential role in vaso-occlusion in sickle cell disease (SCD). To investigate this hypothesis, dorsal skin fold chambers (DSFCs) were implanted on normal and transgenic sickle mice expressing human alpha and beta(s)/beta(s-Antilles) globin chains. Microvessels in the DSFC were visualized by intravital microscopy at baseline in ambient air and after exposure to hypoxia-reoxygenation. The mean venule diameter decreased 9% (P < 0.01) in sickle mice after hypoxia-reoxygenation but remained constant in normal mice. The mean RBC velocity and wall shear rate decreased 55% (P < 0.001) in sickle but not normal mice after hypoxia-reoxygenation. None of the venules in normal mice became static at any time during hypoxia-reoxygenation; however, after 1 hr of hypoxia and 1 hr of reoxygenation, 11.9% of the venules in sickle mice became static (P < 0.001). After 1 hr of hypoxia and 4 hr of reoxygenation, most of the stasis had resolved; only 3.6% of the subcutaneous venules in sickle mice remained static (P = 0.01). All of the venules were flowing again after 24 hr of reoxygenation. Vascular stasis could not be induced in the subcutaneous venules of sickle mice by tumor necrosis factor alpha (TNF-alpha). Leukocyte rolling flux and firm adhesion, manifestations of vascular inflammation, were significantly higher at baseline in sickle mice compared to normal (P < 0.01) and increased 3-fold in sickle (P < 0.01), but not in normal mice, after hypoxia-reoxygenation. Plugs of adherent leukocytes were seen at bifurcations at the beginning of static venules. Misshapen RBCs were also seen in subcutaneous venules.

Sickle cell crisis and endothelin antagonists

Sickle cell crisis may be more complex than a vaso-occlusive event in response to hypoxia. Endothelin-1 (ET-1) is a potent vasoconstrictor and mitogen secreted in response to hypoxia. ET-1 contributes to the vaso-occlusion and inflammation in sickle cell crisis. ET-1 antagonists may be useful in the prevention and treatment of crisis.

Transgenic sickle mice have vascular inflammation

Inflammation may play an essential role in vaso-occlusion in sickle cell disease. Sickle patients have high white counts and elevated levels of serum C-reactive protein (CRP), cytokines, and adhesion molecules. In addition, circulating endothelial cells, leukocytes, and platelets are activated. We examined 4 transgenic mouse models expressing human alpha- and sickle beta-globin genes to determine if they mimic the inflammatory response seen in patients. These mouse models are designated NY-S, Berk-S(Antilles), NY-S/S(Antilles) (NY-S x Berk-S(Antilles)), and Berk-S. The mean white counts were elevated 1.4- to 2.1-fold (P </=.01) in the Berk-S(Antilles), NY-S/S(Antilles), and Berk-S mice, but not in the NY-S mice compared with controls. Serum amyloid P-component (SAP), an acute-phase response protein with 60% to 70% sequence homology to CRP, was elevated 8.5- to 12.1-fold (P </=.001) in transgenic sickle mice. Similarly, serum interleukin-6 (IL-6) was elevated 1.6- to 1.9-fold (P </=.05). Western blots, confirming immunohistochemical staining, showed vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM), and platelet-endothelial cell adhesion molecule (PECAM) were up-regulated 3- to 5-fold (P </=.05) in the lungs of sickle mice. Ribonuclease protection assays (RPAs) demonstrated VCAM mRNA also was elevated in sickle mice 1.2- to 1.4-fold (P </=.01). Nuclear factor kappaB (NF-kappaB), a transcription factor critical for the inflammatory response, was elevated 1.9-fold (P </=.006) in NY-S sickle mouse lungs. We conclude that transgenic sickle mice are good models to study vascular inflammation and the potential benefit of anti-inflammatory therapies to prevent vaso-occlusion in sickle cell disease.

Activated monocytes in sickle cell disease: potential role in the activation of vascular endothelium and vaso-occlusion

Sickle cell anemia is characterized by painful vaso-occlusive crises. It is hypothesized that monocytes are activated in sickle cell disease and can enhance vaso-occlusion by activating endothelium. To test this hypothesis, human umbilical vein endothelial cells (HUVEC) and human microvascular endothelial cells (MVEC) with sickle and normal mononuclear leukocytes were incubated, and endothelial activation was measured. Endothelial cells incubated with sickle mononuclear leukocytes were more activated than those incubated with normal mononuclear leukocytes, as judged by the increased endothelial expression of adhesion molecules and tissue factor and the adhesion of polymorphonuclear leukocytes (PMNL). Monocytes, not lymphocytes or platelets, were the mononuclear cells responsible for activating endothelial cells. Sickle monocytes triggered endothelial nuclear factor-kappa B (NF-κB) nuclear translocation. Cell-to-cell contact of monocytes and endothelium enhanced, but was not required for, activation. Antibodies to tumor necrosis factor-alpha (TNF-α) and interleukin-1-beta (IL-1β) blocked activation of the endothelium by monocytes. Peripheral blood monocytes from patients with sickle cell disease had 34% more IL-1β (P = .002) and 139% more TNF-α (P = .002) per cell than normal monocytes. Sixty percent of sickle monocytes expressed the adhesion molecule ligand CD11b on their surfaces compared with only 20% of normal monocytes (P = .002). Serum C-reactive protein, a marker of systemic inflammation, was increased 12-fold in sickle serum than in normal serum (P = .003). These results demonstrate that sickle monocytes are activated and can, in turn, activate endothelial cells. It is speculated that vascular inflammation, marked by activated monocytes and endothelium, plays a significant role in the pathophysiology of vaso-occlusion in sickle cell anemia.

Activated monocytes in sickle cell disease: potential role in the activation of vascular endothelium and vaso-occlusion

Sickle cell anemia is characterized by painful vaso-occlusive crises. It is hypothesized that monocytes are activated in sickle cell disease and can enhance vaso-occlusion by activating endothelium. To test this hypothesis, human umbilical vein endothelial cells (HUVEC) and human microvascular endothelial cells (MVEC) with sickle and normal mononuclear leukocytes were incubated, and endothelial activation was measured. Endothelial cells incubated with sickle mononuclear leukocytes were more activated than those incubated with normal mononuclear leukocytes, as judged by the increased endothelial expression of adhesion molecules and tissue factor and the adhesion of polymorphonuclear leukocytes (PMNL). Monocytes, not lymphocytes or platelets, were the mononuclear cells responsible for activating endothelial cells. Sickle monocytes triggered endothelial nuclear factor-kappa B (NF-κB) nuclear translocation. Cell-to-cell contact of monocytes and endothelium enhanced, but was not required for, activation. Antibodies to tumor necrosis factor-alpha (TNF-α) and interleukin-1-beta (IL-1β) blocked activation of the endothelium by monocytes. Peripheral blood monocytes from patients with sickle cell disease had 34% more IL-1β (P = .002) and 139% more TNF-α (P = .002) per cell than normal monocytes. Sixty percent of sickle monocytes expressed the adhesion molecule ligand CD11b on their surfaces compared with only 20% of normal monocytes (P = .002). Serum C-reactive protein, a marker of systemic inflammation, was increased 12-fold in sickle serum than in normal serum (P = .003). These results demonstrate that sickle monocytes are activated and can, in turn, activate endothelial cells. It is speculated that vascular inflammation, marked by activated monocytes and endothelium, plays a significant role in the pathophysiology of vaso-occlusion in sickle cell anemia.

Tumor necrosis factor-alpha is undetectable in the plasma of SS patients with elevated Hb F

Steady-state sickle cell disease (SCD) patients may have increased plasma levels of acute phase reactants and pro-inflammatory cytokines because of subclinical inflammation. We have estimated TNF-alpha levels in the plasma and in supernatants following peripheral blood mononuclear cell (PBMC) activation with phytohemagglutinin (PHA) in a group of Kuwaiti SCD patients using ELISA. The group consisted of 28 SS, 8 Sbeta-thal, and 2 SD patients all in steady state; 5 SS patients were studied during 7 episodes of painful crisis. The subjects were aged 2 to 16 years, with a mean of 7.3 +/- 3.5 years. The beta(S)-globin gene cluster haplotype, alpha-tha1 status, and spleen function were determined in the SS group using standard techniques. Most (82%) were homozygous for the Saudi Arabia/India haplotype and had elevated Hb F levels ranging from 15% to 35%. There were 24 controls (Hb AA or AS), of whom 14 were healthy and 10 were acutely ill at the time of the study. None of the children with SCD (either in steady state or crisis) had detectable plasma TNF-alpha, but four controls (3 acutely ill and one healthy) had levels ranging from 61.7 to 249.8 pg/mL. Following PHA stimulation most subjects responded with high levels of TNF-alpha, with the median level among the steady-state SS patients being significantly higher than that in the controls (both the acutely ill or healthy). It therefore appears that because of the mild disease among our Arab SS children, TNF-alpha is not detectable in their plasma in steady state; these children, however, had a significantly higher response than controls following PBMC activation.

Sequential nitric oxide measurements during the emergency department treatment of acute vasoocclusive sickle cell crisis

This prospective study was designed to examine the relationship between serial serum nitric oxide (NO) levels and pain during the emergency department (ED) treatment of acute vasoocclusive sickle cell crisis (SCC). 102 patient visits, age > or =18 years of age, presenting to the ED with uncomplicated, typical SCC pain had serum NO levels obtained at 2-hr intervals during treatment of pain and were measured using an NO-specific chemiluminesence technique. Pain was measured prior to each NO measurement using a 10 cm visual analog scale (VAS), and subjects were divided into a persistent pain group and an improved pain group. Patients with persistent pain had significantly low initial NO levels (11.51 microM +/- 2.8, P < 0.05) while those with pain improvement had higher initial NO levels (18.1 microM +/- 3.08, P < 0.05). There was no significant correlation between changes in NO and changes in pain scores. These results suggest that the initial NO level may serve as a marker for the severity of tissue ischemia. Sequential NO levels do not appear useful in predicting the course of SCC.

Acute phase proteins and interleukins in steady state sickle cell disease

To identify a possible acute phase response during the steady state of sickle cell disease, we estimated the serum alterations of acute phase proteins, beta2-microglobulin (beta2M), kappa and lambda light chains, interleukins (ILs) and tumor necrosis factor-alpha (TNFalpha) in 21 patients. Increased concentrations of C-reactive protein (CRP) were found in 5 patients, alpha-1-acid-glycoprotein (AGP) in 3, alpha-1-antitrypsin (AAT) in 8, ceruloplasmin (CER) in 2, alpha-2-macroglobulin (AMG) in 14 and decreased haptoglobin (HPT) and transferrin (TFR) in 11 and 9, respectively. Increased beta2M was found in 10 patients and kappa and lambda light chains in 11. IL-1beta, IL-2, IL-4, IL-10 and TNFalpha were not detected in any of the patients. However, significantly increased values of IL-6 and sIL-2r were found. This study has demonstrated increased serum levels of some of the acute phase proteins in patients during the steady state of sickle cell disease. This may be a result of a subclinical vaso-occlusion which in turn leads to a covert inflammatory response. Cytokines, and in particular IL-6, produced after this response, seem to be responsible for the high levels of acute phase proteins in the steady state of this disease.

Increased circulating levels of soluble HLA class I heterodimers in patients with sickle cell disease

This study examined the presence of a persistent state of low-grade inflammation in sickle cell anemia patients by measuring circulating sHLA-I heterodimers and C-reactive protein during the steady state and after recent crises. Thirty-nine pediatric sickle hemoglobinopathy patients were studied during the steady state and 11 patients were evaluated within 1 month of a painful crisis. A disease severity score was generated for each patient, and soluble HLA-I (sHLA-I) and C-reactive protein levels were determined. Soluble HLA-I was significantly elevated in 55% of the steady-state group and in 36% of the recent-crisis group. The percentage of patients with elevated sHLA-I differed in the various disease subgroups in the steady state: 46% of Hb SS patients, 70% of Hb SC patients, 75% of Hb S beta-thal patients, and 20% of Hb SSF patients. Steady-state and recent-crisis sHLA-I levels were not significantly different. C-reactive protein levels were elevated in 11% of steady-state patients and in 9% of recent-crisis patients. Soluble HLA-I levels did not correlate with C-reactive protein levels or disease severity score, age, hemoglobin, reticulocyte count, platelet count, or white cell count. These results show that the majority of sickle hemoglobinopathy patients have elevated sHLA-I levels during the steady state and after recent crisis, suggesting the presence of chronic inflammation during the steady state.

New concepts in the immunology of sickle cell disease

OBJECTIVE

Our objective is to review the role of adhesion molecules, cytokines, and inflammation in the abnormal adherence of sickle red blood cells to vascular endothelia in the pathogenesis of vascular complication in patients with sickle cell anemia.

DATA SOURCES

The MEDLINE database was used to review the hematologic, immunologic, and allergy literature in English with respect to the adhesion molecules involved in sickle hematopoiesis and vascular complications.

STUDY SELECTION

Studies selected for review were those that identified the adhesion molecules involved in reticulocyte-endothelial adhesion and the influence that cytokines, infections, and atopy have upon the expression of these molecules.

RESULTS

In sickle cell disease, a constant low level of inflammation caused by abnormal adhesion of sickle erythrocytes to endothelial cells in the microvasculature produces low-level tissue ischemia. Allergic and infectious inflammations are likely to lead to increased sickle erythrocyte trapping in the microvascular endothelia which progresses to vessel obstruction, end organ ischemic damage, and dysfunction.

CONCLUSION

The identification of underlying immune defects that predispose patients to infections and inflammation needs to be emphasized. Anti-inflammatory medications, anti-adhesion molecule monoclonal antibodies, and adhesion molecule binding-site analogs may have a future in the treatment of the acute vascular complications of sickle cell disease.