Irreversibly sickled erythrocytes in sickle cell anemia: a quantitative reappraisal

Irreversibly sickled cells (ISCs), considered by some to be of major pathophysiologic significance, have been reported to comprise between 5-50% of the total red cell population in patients with homozygous sickle cell anemia. Since the deformation of erythrocytes containing sickle hemoglobin is highly dependent on the concentration of hemoglobin in the deoxy conformation, any method established to enumerate the true ISC count requires the hemoglobin to be in the full oxy or liganded conformation. Because the oxygen dissociation curve for sickle erythrocytes is significantly shifted to the right, extremely high partial pressures of oxygen are required to approach full saturation. On the other hand, fully liganding the hemoglobin in the oxy conformation with carbon monoxide (CO) can be readily accomplished. We found that there is a significant reduction in the average number of sickled forms in the peripheral blood of sickle cell anemia patients after incubation in CO (to a value of 6.5 +/- 3.5%) when compared to conventional methods for ISC preparations. These results suggest that fully liganded erythrocytes should be used in quantitating ISCs in studies of the pathophysiology of this disease, especially since ISCs are likely to affect rheology differently from reversibly sickling cells.     

Fetal characteristics of erythrocytes in sickle cell anemia: an immunofluorescence study of individual cells.

In a group of disease states that includes sickle cell anemia (SS disease), two fetal erythrocyte markers, Hb F and i antigen, persist into adulthood. Using the technique of single-cell immunofluorescence, we determined the expression of l-i antigens and the presence of Hb F within populations of erythrocytes. Subjects tested included normal adults, normal newborns, patients with SS disease, and individuals with sickle cell trait. We classified erythrocytes reacting to anti-i as i cells and those reacting to anti-l as l cells, a terminology analogous to that used to identify erythrocytes containing increased amounts of Hb F as F cells. The expression of l and i antigens within populations of both normal and SS erythrocytes was found to be heterogeneous. The proporations of both i cells and l cells in all SS patients studied exceeded those found in normal adults, and an overall stronger-than-normal reactivity of individual SS cells to the two antibodies was observed. Proportions of F cells showed no correlation with proportions of i cells; and with double fluroescence staining for both Hb F and i, a significant proportion of each total SS red cell population was found to carry only one or the other marker. These findings confirm and clarify on a cellular level our previous demonstration, by means of quantitative hemagglutination, that there is increased expression of both l and i by whole populations of SS erythrocytes. In addition, we provide here new information on the expression of l and i within populations of normal human erythrocytes.     

Exercise-induced cardiac dysfunction in sickle cell anemia. A radionuclide study

Cardiac performance was studied by radionuclide angiography at rest and during exercise in 22 adolescents with sickle cell (SC) anemia and the results were compared with those in 12 control subjects. At rest, cardiac contractility was normal; cardiac output and end-diastolic volume were increased. At maximal exercise, heart rate, cardiac output response, and work capacity were reduced; the reduction was related to the degree of anemia. Left ventricular end-diastolic volume decreased with exercise most markedly in patients with ischemic exercise electrocardiograms. An abnormal ejection fraction response to exercise occurred in 4 patients; electrocardiographic signs of ischemia developed in all 4, and wall motion abnormalities in 2. Those patients who had electrocardiographic signs of ischemia had a significantly lower heart rate, ejection fraction, and cardiac output response to exercise, and a lower hematocrit level than subjects with normal results on exercise electrocardiography. The increase in cardiac output was not sufficient to maintain a normal level of exercise. The decrease in end-diastolic volume suggests that diastolic function was abnormal during exercise. Cardiac dysfunction was manifested by an abnormal ejection fraction response, wall motion abnormalities, and incomplete left ventricular filling during exercise.     

Bone marrow transplantation in a young child with sickle cell anemia

Bone marrow transplantation (BMT) is the only curative therapy available for hemoglobinopathies. BMT was performed on a young child with sickle cell anemia (SCA) after approximately 9 months of transfuslon therapy following her initial stroke. The patient received a matched sibling donor (sickle trait) BMT. The conditioning regimen consisted of busulfan 4 mg/kg/day × 4, cyclophosphamide 50 mg/kg/day × 4. Graft vs. host disease prophylaxis was daily cyclosporine for 6 months. There were no significant complications during BMT. Engraftment occurred on day + 17 and the patient was transfusion independent since day +45. Pre-BMT cerebral arteriography showed multiple stenotic cerebral vessels and a moya-moya pattern. Perfusion MRI demonstrated reduced capillary perfusion. Approximately 170 days after BMT the patient experienced episodes of transient left-sided weakness and speech problems. Neuroimaging revealed progression of large vessel pathology by angiography despite significant improvement in cortical perfusion (MR perfusion scan). Molecular analysis by PCR and DNA fingerprinting confirmed absence of mixed mosaicism. Rheologic evaluation showed normal corrected bulk viscosity. It is possible that progression of large vessel pathology and return of clinical symptoms in the face of normal rheologic parameters may be due to worsening of the already damaged cerebral vessels by the BMT conditioning regimen. Further evaluations of patients with SCA undergoing BMT after a stroke are needed to answer this question. © 1995 Wiley-Liss, Inc.     

Thinking beyond sickling to better understand pain in sickle cell disease

Painful vaso‐occlusive crises (VOCs) are the hallmark of sickle cell disease (SCD); however, many patients experience frequent daily pain that does not follow the pattern of typical VOCs. This pain of variable severity, also referred as persistent pain in the SCD literature, contributes to significant morbidity and poor quality of life and often fails to respond adequately to standard SCD therapies. In this article, we briefly describe types of pain encountered in SCD with a special emphasis on persistent pain. We discuss altered pain processing as a potential contributing mechanism, which may lead to development and maintenance of persistent pain. We describe the advances in the non‐SCD pain field that may help improve the understanding of SCD pain. We highlight the need for further investigation in this area because some of these patients with persistent pain may benefit from receiving adjuvant mechanism‐based therapies used successfully in other non‐SCD chronic pain conditions.     

Cardiac function in sickle cell anemia

Although ventricular dysfunction is suspected to underlie congestive heart failure in sickle cell anemia (SCA), ejection indexes of left ventricular (LV) pump performance have been found to be normal. The increased preload and decreased afterload of SCA increases the ejection phase indexes and might obscure true LV dysfunction. Therefore, the preload and afterload independent end-systolic stress-volume index was compared in 11 patients with SCA and in 11 normal volunteers. End-systolic pressure and echocardiographic LV dimensions were determined during rest, leg raise, hand-grip and amyl nitrite inhalation. Systemic vascular resistance (afterload) was decreased to 1,033 ± 314 dynes s cm⁻⁵ (mean ± standard deviation) in SCA from 1,701 ± 314 dynes s cm⁻⁵ in normal subjects. End-diastolic volume index (preload) was increased to 102 ± 24 ml/m² in SCA from 66 ± 10 ml/m² in normal subjects. Cardiac index was increased to 4.7 ± 1.1 liters/min/m² in SCA from 2.8 ± 0.8 liters/ min/m² in normal subjects. Ejection fractions were similar: 0.59 ± 0.09 in SCA versus 0.62 ± 0.07 in normal subjects. However, in patients with SCA, the ratio of resting end-systolic stress-volume index was decreased (1.5 ± 0.5 in SCA versus 2.8 ± 0.6 in normal subjects) and the slope of the end-systolic stress versus end-systolic volume index relation was decreased (2.7 ± 1.3 in SCA versus 4.4 ± 1.8 in normal subjects), suggesting LV dysfunction in those patients. Thus, LV muscle contractile performance is depressed in SCA. Increased preload and decreased afterload compensate for the LV dysfunction and maintain a normal ejection fraction and high cardiac output.     

Fetal hemoglobin in sickle cell anemia

Fetal hemoglobin (HbF) is the major genetic modulator of the hematologic and clinical features of sickle cell disease, an effect mediated by its exclusion from the sickle hemoglobin polymer. Fetal hemoglobin genes are genetically regulated, and the level of HbF and its distribution among sickle erythrocytes is highly variable. Some patients with sickle cell disease have exceptionally high levels of HbF that are associated with the Senegal and Saudi-Indian haplotype of the HBB-like gene cluster; some patients with different haplotypes can have similarly high HbF. In these patients, high HbF is associated with generally milder but not asymptomatic disease. Studying these persons might provide additional insights into HbF gene regulation. HbF appears to benefit some complications of disease more than others. This might be related to the premature destruction of erythrocytes that do not contain HbF, even though the total HbF concentration is high. Recent insights into HbF regulation have spurred new efforts to induce high HbF levels in sickle cell disease beyond those achievable with the current limited repertory of HbF inducers.