Acute Vaso-occlusive Events Research Articles

Predicting Acute Chest Syndrome in Sickle Cell Disease Patients Hospitalized for Acute Vasoocclusive Events.

Acute painful vasoocclusive events (VOE) and acute chest syndrome (ACS) are the leading causes of hospitalization among patients with sickle cell disease (SCD). Although most patients with ACS are hospitalized explicitly for that reason, up to 36% of patients who were admitted for VOEs subsequently developed ACS, usually within several days of admission. Since ACS can be associated with hypoxemia and respiratory failure, leading to a need for blood transfusion and ventilatory support, the ability to predict which patients are at high risk for this serious complication might lead to better clinical outcomes. Using the results of standard-of-care blood testing obtained upon hospital admission, we present a novel model to predict the risk of developing ACS following hospitalization for a VOE. To generate this model, we retrospectively evaluated the records of 1,263 participants in the Cooperative Study of Sickle Cell Disease (CSSCD), with either sickle cell anemia (with or without co-incident alpha thalassemia) or HbSC disease, who were hospitalized for an acute VOE. During their hospitalization, 148 of these patients developed ACS, defined in the CSSCD as a new pulmonary infiltrate on a chest x-ray or evidence of pleuritic chest pain, with or without dyspnea; the remaining patients, who did not develop ACS, served as controls. Case patients were aged 7 to 55 years, with a mean age of 23 years; control patients were aged 5 to 72 years with a mean age of 24.5 years. Males were slightly more likely to develop ACS; 56% of case patients were male, compared with 46% of control patients (OR 1.5, 1.05–2.10). There was a significant difference in the distribution of SCD genotype, with fewer patients with HbSC disease and sickle cell anemia-alpha thalassemia in the control group (p=0.002). For each patient, we included in the model the hematocrit, hemoglobin concentration, mean corpuscular volume, reticulocyte count, white blood cell count with differential, and platelet count at hospital admission, along with their age, gender, and SCD genotype. Random Forest (RF) software, implemented in the R language, was used to create a set of 500 classification and regression trees using 80% of the subjects, and was then tested on the remaining 20%. For each test patient, each randomly generated decision tree classified the patient as high or low risk, and the consensus of the 500 tree forest was used to predict if the patient would develop ACS. This data driven approach produced a robust predictive model, while reducing analyst input and eliminating the need to identify important confounders a priori, as would be the case if attempting these analyses using stepwise logistic regression. The RF model correctly classified 95% of the patients for the development of ACS, with 67% sensitivity and 99% specificity. Neutrophil bands and platelet counts were identified by RF as the two most important predictors for the development of ACS, concordant with the potential roles of infection and infarction in its pathogenesis. With future validation, perhaps including prospective studies, this simple model, along with other predictors such as serum phospholipase A2 and studies of genetic modulators of this phenotype, could aid in identifying individuals who are at high risk for developing ACS. Ultimately, for patients hospitalized with VOEs, better identification of the risk of developing ACS might lead to more appropriate treatment with better clinical outcomes.

Preservation of spleen and brain function in children with sickle cell anemia treated with hydroxyurea

Chronic organ damage is an insidious process in patients with sickle cell anemia (SCA). Although hydroxyurea prevents acute vaso-occlusive events, its effects on the preservation of organ function remain undefined. We retrospectively reviewed our single institution experience with children with SCA treated with hydroxyurea for clinical disease severity, who had optional radionuclide liver-spleen (LS) and brain magnetic resonance imaging (MRI)/with angiography (MRA) performed before and during therapy. Studies were reviewed by pediatric radiologists blinded to treatment status. Demographic and laboratory predictors were modeled using logistic regression. A total of 43 children had spleen function measured both at baseline and on therapy. After a median of 2.6 years (range, 0.2-8.6 years) of hydroxyurea at maximum tolerated dose (MTD), six patients (14%) completely recovered splenic function and two (5%) had preserved splenic function. These eight children had a greater hemoglobin (Hb) concentration on hydroxyurea therapy than those without splenic function (9.1 vs. 8.6 gm/dl, P = 0.01). Of 25 children with brain MRI/MRA studies performed before initiating hydroxyurea and on therapy, 24 (96%) had no change in brain ischemic lesions compared with pre-treatment studies, after a median of 2.9 years of treatment. These retrospective data suggest that hydroxyurea at MTD possibly preserves spleen and brain function in children with SCA, and can even result in recovery of splenic function. Higher final Hb concentration during therapy is a significant laboratory predictor of improved splenic function.

ADAMTS13 Activity in Sickle Cell Disease: A Role in the Development of Clinical Vaso-Occlusion?.

Endothelial cell activation occurs continuously in sickle cell disease (SCD). As VWF and especially the ultra large VWF multimers, released from activated endothelial cells, can serve as bridging proteins between the vessel wall and sickle red blood cells, we determined ADAMTS13 (the vWF-cleaving protease) activity as well as VWF:Rcof and VWF:Ag levels in SCD. Fourteen sickle cell patients (13 HbSS, 1 HbSC; 39 samples collected) and 9 HbAA controls were included. VWF:Rcof and VWF:Ag were assessed by commercially available assays, ADAMTS13 activity was determined by quantitative immunoblotting of proteolysed VWF-substrate. VWF:Rcof and VWF:Ag levels were higher in patients, as compared to controls. ADAMTS13 activity ranged from 45–128% in asymptomatic patients, from 38–205 in patients during acute vaso-occlusive events (VOE) and from 43-75% in controls. The ratios of ADAMTS13 to vWF:Ag levels and activity were lower in patients (SCD asymptomatic: 0.44 [interquartile range 0.34–0.55], SCD acute VOE: 0.29 [0.21–0.43], HbAA: median 0.61 [0.33–1.23], Kruskar Wallis test p=0.003). The ADAMTS13 - VWF:Rcof and the ADATS13 - VWF:Ag ratios dropped during acute vaso-occlusive events in 3 of 6 patients. In patients from whom multiple samples were collected (n=4), ADAMTS13 activity and VWF:Ag levels (and to a lesser extent VWF:Rcof) were inversely related. One patient showed no change in ADAMTS13 activity despite strong increments in VWF:Ag and VWF:Rcof during vaso-occlusive pain crises prior to his death (pulmonary embolism). VWF:Ag levels at initial presentation of acute VOE were related to the duration of pain (rs=0.53, p=0.02), whereas the ratios of ADAMTS13 to VWF:Ag levels and ADAMTS13 to VWF:Rcof were inversely related hereto (rs=−0.67, p=0.002, rs=−0.53, p=0.02 respectively). These data demonstrate that ADAMTS13 activity is related to VWF:Ag levels and VWF:Rcof in SCD and that the role of ADAMTS13 and VWF in the pathophysiology of SCD deserves further evaluation.

In vitro induction of fetal hemoglobin in human erythroid progenitor cells.

Clinical heterogeneity among patients with sickle cell anemia (SCA) is influenced by the amount of fetal hemoglobin (HbF) within circulating erythrocytes. Current pharmacotherapy focuses on increasing HbF in order to reduce hemolysis and help prevent acute vaso-occlusive events. Hydroxyurea, a known S-phase-specific cytotoxic ribonucleotide reductase (RR) inhibitor, is an effective agent for HbF induction in patients with SCA, but the mechanisms by which hydroxyurea induces HbF in vivo have not been elucidated. We adapted an in vitro assay for HbF induction, growing burst-forming unit erythroid (BFU-E) colonies in methylcellulose from peripheral blood of children with SCA and extracting the hemoglobin for high-performance liquid chromatography analysis of HbF. Hydroxyurea and other known RR inhibitors, along with cytotoxic agents that are not RR inhibitors, were tested for the ability to induce HbF using this in vitro assay. Hydroxyurea decreased the number of BFU-E colonies that grew in culture and significantly increased HbF from 13.6%+/-6.2% to 25.4%+/-8.0% at 50 microM HU (p=0.012). Three other known RR inhibitors also significantly induced HbF: 4-methyl-5-amino-1-formylisoquinoline thiosemicarbazone (p=0.025), guanazole (p=0.008), and gemcitabine (p=0.028). Cytarabine and alkylating agents BCNU and 4-hydroperoxycyclophosphamide, which are cytotoxic agents but not RR inhibitors, reduced BFU-E colony number but did not significantly induce HbF. Hydroxyurea and other RR inhibitors significantly induce HbF in vitro in human erythroid progenitor cells. Inhibition of RR may be a critical mechanism by which hydroxyurea increases HbF in vivo in patients with SCA.

Pathophysiology of coronary thrombosis: Role of plaque rupture and plaque erosion

Coronary artery disease is the leading cause of death in much of the western world. Atherosclerotic plaques in the coronary arteries contribute to luminal obstruction leading to myocardial ischemia; however, abrupt coronary artery occlusion most frequently results from superimposition of a thrombus on a disrupted plaque, leading to the most serious clinical manifestations of coronary artery disease, ie, unstable angina, acute myocardial infarction, and sudden death. Plaque that have undergone disruption and, by inference, plaques at risk for disruption (vulnerable plaques), tend to demonstrate outward vessel remodeling, contain a large lipid core, thinned out fibrous cap, reduced collagen content, and increased inflammatory cell infiltration. Plaque stabilization through change in plaque composition may be responsible for reduced frequency of acute vaso-occlusive events observed with lipid and other risk-factor modifying interventions. Copyright 2002, Elsevier Science (USA). All rights reserved.

Sickle Cell Disease of Transgenic SAD Mice

Erythrocyte sickling on deoxygenation in vitro occurs in transgenic SAD mice, hemizygous for a modified human sickle hemoglobin, HbSAD [alpha 2 beta 2S(beta 6val)Antilles (beta 23 lle)D- Punjab (beta 121Gln)] (SAD-1, 19% HbSAD; beta-thal/SAD-1, 26% HbSAD). The present study examines the cellular defects in vivo and pathologic changes observed in SAD-1 mice at atmospheric oxygenation as well as the effect of acute hypoxia. The transgenic mice showed generalized congestion and microvascular occlusions, occasionally with thrombosis and infarctions of lung, kidneys, penis, and myocardium. The most prevalent chronic organ lesions were congestive splenomegaly (83% of animals) and renal glomerulopathy, which affected 75% of animals by 10 months of age. Further, SAD mice have a mean lifespan that was reduced by 40% when compared with nontransgenic littermates. Premature death of SAD mice was associated with acute vasoocclusive events or severe renal disease. SAD mice developed lethal vasoocclusive processes when exposed to reduced pO2 conditions, whereas control mice survived normally. The sensitivity to hypoxia appears to depend on the cellular level of HbSAD, because death occurred at pO2 of 42 mmHg for SAD mice and 49 mmHg for beta-thal/SAD. Administration of an antisickling agent that increases oxygen affinity (BW12C79) protected SAD and beta-thal/SAD mice from the lethal hypoxic stress. In conclusion, the transgenic SAD and beta-thal/SAD mice developed a pathophysiology that strongly resembles human sickle cell disease. Moreover, this animal model allows studies on the effect of antisickling agents.

Sickle cell disease of transgenic SAD mice

Erythrocyte sickling on deoxygenation in vitro occurs in transgenic SAD mice, hemizygous for a modified human sickle hemoglobin, HbSAD [alpha 2 beta 2S(beta 6val)Antilles (beta 23 lle)D- Punjab (beta 121Gln)] (SAD- 1, 19% HbSAD; beta-thal/SAD-1, 26% HbSAD). The present study examines the cellular defects in vivo and pathologic changes observed in SAD-1 mice at atmospheric oxygenation as well as the effect of acute hypoxia. The transgenic mice showed generalized congestion and microvascular occlusions, occasionally with thrombosis and infarctions of lung, kidneys, penis, and myocardium. The most prevalent chronic organ lesions were congestive splenomegaly (83% of animals) and renal glomerulopathy, which affected 75% of animals by 10 months of age. Further, SAD mice have a mean lifespan that was reduced by 40% when compared with nontransgenic littermates. Premature death of SAD mice was associated with acute vasoocclusive events or severe renal disease. SAD mice developed lethal vasoocclusive processes when exposed to reduced pO2 conditions, whereas control mice survived normally. The sensitivity to hypoxia appears to depend on the cellular level of HbSAD, because death occurred at pO2 of 42 mmHg for SAD mice and 49 mmHg for beta-thal/SAD. Administration of an antisickling agent that increases oxygen affinity (BW12C79) protected SAD and beta-thal/SAD mice from the lethal hypoxic stress. In conclusion, the transgenic SAD and beta-thal/SAD mice developed a pathophysiology that strongly resembles human sickle cell disease. Moreover, this animal model allows studies on the effect of antisickling agents.

Improvement of Microcirculation Abnormalities in Sickle Cell Patients upon Buflomedil Treatment

The efficacy of the vasoactive compound buflomedil on previously described microcirculation abnormalities observed in sickle cell disease (SCD) was investigated using bulbar conjunctival angioscopy (BCA) and laser doppler flux metering. Eleven sickle cell disease patients at steady state were studied in a double-blind randomized parallel-versus-placebo study (5 patients were given placebo and 6 patients received 600 mg buflomedil per day for 21 days after a washout period of 15 days). The blood flux score measured by BCA improved, indicating reduced entrapment of sickle red blood cells. There was a striking improvement of reactive alterations of vasomotion in the buflomedil group, particularly in postocclusive reactive hyperemia; the half return time was also significantly reduced. These results encourage further studies with buflomedil to investigate long-term effects of this compound in SCD, potential prevention of acute vasoocclusive events, and degenerative complications.