Sickle cell disease: from membrane pathophysiology to novel therapies for prevention of erythrocyte dehydration

Sickle cell anemia is characterized by the presence of dense dehydrated erythrocytes that have lost most of their K content. Due to the unique dependence of Hb S polymerization on intracellular Hb S concentration, preventing this dehydration should markedly reduce polymerization. The erythrocyte intermediate conductance Ca-activated K channel (hSK4 or KCNN4), first described by Gardos, has been shown to be a major pathway for sickle cell dehydration. Studies with the imidazole antimycotic clotrimazole have shown reduction of sickle cell dehydration in vivo in a small number of patients with sickle cell disease; dose-limiting gastrointestinal and liver toxicities were observed. Based on the chemical structure of clotrimazole metabolites, a novel Gardos channel inhibitor, ICA-17043, has been developed. It has shown substantial activity both in vitro and in vivo in transgenic sickle mice. ICA-17043 is currently in phase 2 human trials. Another potential therapeutic target is the K-Cl cotransport. When sickle erythrocytes are exposed to relatively acidic conditions, they undergo cell shrinkage via activation of this pathway. K-Cl cotransport can be blocked by increasing the abnormally low erythrocyte Mg content of sickle erythrocytes. Oral Mg supplementation has been shown to reduce sickle cell dehydration in vivo in transgenic sickle mice and in patients in two separate clinical trials. Oral Mg pidolate is being tested in clinical trials in homozygous sickle cell disease and in Hb S/HbC (SC) disease, either as a single agent or in combination with hydroxyurea. The ongoing trials will determine the clinical effectiveness of therapies aimed at preventing sickle erythrocyte dehydration.     

Resolution of chronic hepatic sequestration in a patient with homozygous sickle cell disease receiving hydroxyurea

Hepatic sequestration is an uncommon complication in patients with homozygous sickle cell disease. Although transfusion therapy has been effective for the acute condition, no definitive treatment of chronic hepatic sequestration has been identified. We describe a 17-year-old male patient with hemoglobin SS and chronic hepatic sequestration who was treated with long-term (60 months) hydroxyurea. After 36 months of HU therapy, the patient had both an excellent hematologic response and a resolution of hepatic sequestration, as evidenced by disappearance of clinical hepatomegaly, normalization of liver volume on serial computed tomography scans, as well as decreased sinusoidal dilatation and congestion and red blood cell sickling on liver biopsy. The findings in this case suggest that hydroxyurea may benefit patients who have unusual complications of sickle cell disease, such as chronic erythrocyte sickling in the liver.     

Liver biopsy results in patients with sickle cell disease on chronic transfusions: poor correlation with ferritin levels

Background:

Chronic transfusions are effective in preventing stroke and other complications of sickle cell disease. The aim of this study was to determine whether serum ferritin levels correlated with liver iron content in sickle cell patients on chronic transfusion.

Procedure:

Forty‐four liver biopsy specimens from 38 patients with homozygous sickle cell anemia (HbSS) and one patient with sickle thalassemia receiving chronic transfusions were studied. Five patients underwent a second liver biopsy for follow up. Three ferritin measurements were used to calculate a mean for each patient. The association between serum ferritin levels and liver iron quantitation was measured using the Spearman rank correlation, and sensitivity and specificity were determined for selected threshold values of serum ferritin.

Results:

Serum ferritin levels ranged from 515 to 6076 ng/ml, liver iron concentration ranged from 1.8 to 67.97 mg/g dry weight. The amount of iron per gram liver dry weight was moderately correlated with serum ferritin values (r = 0.46). The correlation of duration of transfusion with serum ferritin (r = 0.40) and with liver iron content (r = 0.41) also indicated moderate correlation. Liver biopsy results led to changes in the management after 29/44 (66%) of the biopsies. Serum ferritin ≥2500 ng/ml predicted high liver iron content (≥7 mg/g), with a sensitivity of 62.5% and a specificity of 77.8%.

Conclusion:

We found a poor correlation between serum ferritin levels and liver iron content (LIC). Despite being on chelation therapy, many patients on chronic transfusion had high levels of liver iron. Measurement of LIC is highly recommended in these patients. Pediatr Blood Cancer 2008;50:62–65. © 2007 Wiley‐Liss, Inc.     

Cholelithiasis in children with sickle cell disease.

A group of 47 children with homozygous sickle cell disease ranging in age from 2 to 18 years was studied for the prevalence of gallstones. All of these patients had oral cholecystogram and cholecystosonogram. Eight of the 47 patients (17%) had gallstones both on oral cholecystography and on cholecystosonography. These eight patients had a history of recurrent abdominal pain usually localized to the right upper quadrant. All were admitted on several occasions for sickle cell abdominal crises and four of these were admitted for acute hepatic crisis. These patients have undergone elective cholecystectomy and gallstones were found in every patient. The patients have been followed up from seven to 17 months after cholecystectomy and none have had abdominal symptoms or required hospitalization for abdominal crises.     

Prevention of sickle cell crises with multiple phlebotomies]

OBJECTIVES: Sickle cell disease patients suffering from frequent painful crises were submitted to phlebotomies in order to reduce hospitalization days due to pain, through hemoglobin (Hb) level reduction and iron deficiency in patients with an hemoglobin level equal to or above 9.5 g/dL. PATIENTS: Seven sickle cell disease patients (four SC, three SS), aged four to 24 years, were submitted to sequential phlebotomies during periods from 18 months to four years. METHODS: The number of hospitalization days for crises was considered. The volumes and frequencies of phlebotomies were adjusted according to the patients ages, the hemoglobin concentrations and the serum ferritin levels. RESULTS: One hundred and forty-four hospitalization days were recorded in the seven patients in the year preceding the treatment. During the study period, the annual numbers of hospitalization days were respectively 20, five, six and one. Mean hemoglobin concentration was 10.7 g/dL before phlebotomies and 8.8 to 9.2 g/dL during the four years of treatment. Mean corpuscular volume, mean corpuscular hemoglobin concentration and serum ferritin were also reduced. The volume of phlebotomies was 116 to 39 mL/kg/year according to the patients. COMMENTS AND CONCLUSION: The striking decrease of the number of hospitalization days for all the patients suggests a closed relationship between therapy and clinical improvement. The mechanism of this effect is probably multifactorial: a) the concentration of Hb level is known to influence the blood viscosity and its decrease always improved rheology in sickle cell disease patients; b) the mean corpuscular hemoglobin concentration is a critical factor concerning the HbS molecule polymerization in sickle cell disease, and its slight reduction may have an important biological effect. We observed these two biological modifications in our patients and suggest that they mediate the clinical effects. The iron deficiency induced by phlebotomies has no evident deleterious consequence either on height and weight in the children or on intellectual performance in any patients.     

Newborn screening for sickle cell disease: effect on mortality

Newborn screening for sickle cell disease has been recommended as a method of decreasing patient mortality. However, its effectiveness in accomplishing this has not been reliably measured. To help determine the effectiveness, 10 years of experience in newborn screening have been summarized. The effects of early patient enrollment in a comprehensive treatment program on long-term morbidity and mortality are reported. From 1975 to 1985, 84,663 newborns were screened regardless of race or ethnic background. Bart's hemoglobin was present in 5%, hemoglobin AS in 2.6%, and hemoglobin AC in 0.75%. Excluding Bart's, approximately 3.6% of all newborns were carriers for hemoglobinopathy. Sickle cell disease occurred in 1:951 births (58 hemoglobin SS, 25 hemoglobin FSC, three hemoglobin S-beta +-thalassemia, and three hemoglobin S-beta O-thalassemia). In addition, one in every 4,233 newborns had a clinically significant thalassemia syndrome (eight hemoglobin FE, ten hemoglobin F only, two hemoglobin H). Compared with other newborn screening programs in California, (congenital hypothyroidism, 1:3,849; phenylketonuria 1:22,474, galactosemia 1:74,103), hemoglobinopathies are the most prevalent congenital disease. Eighty-one newborns with sickle cell disease were followed for 7.2 years. Patients experienced 513 hospitalizations, including 13 episodes of sepsis with or without meningitis and ten acute sequestration crises. The overall mortality rate for patients with sickle cell anemia diagnosed in the newborn period was 1.8%. In comparison, the clinical course of 64 patients with sickle cell anemia diagnosed after 3 months of age and followed for an average of 9.4 years was analyzed. Five of these patients died. In two of these, sickle cell anemia was diagnosed at the time of the death.(ABSTRACT TRUNCATED AT 250 WORDS)     

Splenic function in sickle cell disease in the Eastern Province of Saudi Arabia

The sickle cell disease that occurs in the Eastern Province of Saudi Arabia is reported to be clinically benign. It is biochemically characterized by high levels of fetal hemoglobin. Twenty-four Saudi patients with sickle cell disease were compared with 22 American patients. As a group, the Saudi patients were less anemic and had less hemolysis, microcytic RBC, and much higher levels of Hb F. Splenic function was assessed by enumeration of pocked RBC. Seventeen Saudi patients had low numbers of Pk RBC, indicating normal or nearly normal splenic function, whereas all American patients had markedly decreased splenic function and high numbers of Pk RBC. Low levels of Pk RBC were strongly associated with high levels of Hb F. The genetic basis of the milder sickle cell disease in Saudi Arabia has not been elucidated, but may involve multiple genetic factors. Although the sickle cell disease in Arab patients of eastern Saudi Arabia is often less severe than that in America, it is far from "benign," and some patients have severe clinical courses similar to those in patients in the West.     

Chemotherapy to increase fetal hemoglobin in patients with sickle cell anemia

The obvious beneficial effects of hemoglobin F on sickling have motivated numerous investigators to increase this type of hemoglobin artificially in patients with sickle cell anemia. Various chemotherapeutic agents including 5-azacytidine, hydroxyurea, and cytosine arabinoside, have been used successfully in patients. All of these drugs can increase the level of hemoglobin F in sickle cell anemia (SS) patients, but the kinetics and magnitude of the responses are highly individual and variable. The mechanism or mechanisms responsible for the increased synthesis of hemoglobin F remain unknown. Further controlled studies in a limited number of patients with severe sickle cell disease will be necessary in order to work out a rational, safe treatment program suitable for wider use.     

Lamellation of the diploe in the skulls of patients with sickle cell anaemia.

This study describes the radiological and pathological findings in a necropsy series of 70 skulls of Nigerian patients with sickle cell gene, and 70 controls matched for sex and age with no sickle cell gene. 6 (35%) of the 17 patients with sickle anaemia, or 17% of 35 patients with sickle cell gene excluding the trait, all under age 10 years, were shown to have bone trabeculae within the diploe arranged in stripes parallel to the curvature of the cranial tables on radiography. Histological examination of the skulls with curvilinear stripes showed long trabeculae of bone within the diploe similarly arranged in parallel rows but joint at variable intervals by short bridges of bone. The radiolucent areas between trabeculae corresponded to areas of marrow hyperplasia. A skull radiograph in an African child presenting with this radiological sign should raise the suspicion of sickel cell disease.     

Sickle cell anemia in two White American children: essential laboratory criteria for diagnosis.

A number of hematologic disorders share diagnostic and clinical features of sickle cell anemia but have significantly different genetic implications and prognosis. Because of these differences, the establishment of a precise diagnosis is essential for the child in whom any form of sickle cell disease is identified. To illustrate the requirements for a definitive laboratory diagnosis of sickle cell anemia, this report presents the approach to establishing this diagnosis in two white American patients. From a review of the literature, these patients appear to be the only white Americans with sickle cell anemia in whom the diagnosis has been unequivocally established.     

Nesidioblastosis in sickle cell disease

Although the endocrine pancreas appears to play an important role in the pathophysiology of sickle cell disease, very little is known about the morphologic changes in this tissue. Our study was initiated to delineate the microscopic features of the endocrine pancreas in a large autopsy series of sickle cell hemoglobinopathies. From more than 650 cases archived at the Centralized Pathology Unit for Sickle Cell Disease (Mobile, AL), 224 autopsy cases were identified for review of clinical and gross autopsy findings and/or for microscopic studies, including histochemical stains (trichrome, reticulin, iron), and immunohistochemical stains (insulin, glucagon, somatostatin, and pancreatic polypeptide). The gross examinations were recorded as unremarkable in 65% of the autopsies. In childhood and adolescence (< or = 18 years), pancreas weights (50.76 +/- 5.16SE gm) were significantly greater (p < 0.0001) than age-matched controls (30.42 +/- 3.59SE gm). In adulthood, pancreas weights (108.34 +/- 5.29SE gm) were not significantly different from controls (110 gm). Microscopic findings included vascular congestion (48%), edema (65%), siderosis (31%), and nesidioblastosis (76%), which included islet cell dispersion (53%), hyperplasia (23%), and hypertrophy (25%). Analysis by age groups suggested that islet cell dispersion/hyperplasia persists unchanged, whereas diameters of compact islets tend to increase with age. These findings may be related to local tissue hypoxia and/or increased metabolic energy needs in sickle cell disease.     

STEM CELL TRANSPLANTATION FOR SICKLE CELL DISEASE: CAN WE REDUCE THE TOXICITY?

Since the genetic basis of sickle cell anemia was discovered over 50 years ago, many therapies have been developed for the treatment of this disorder. Hematopoietic cell transplantation offers curative potential, but it is associated with a 5-10% risk of dying. Patients who undergo allografting but develop stable donor-host hematopoietic chimerism appear to experience a significant clinical benefit. Our paper discusses the risks and benefits of hematopoietic cell transplantation in patients with sickle cell disease and summarizes the outcome of 147 patients who received allografts for sickle cell disease. We also review the development of new approaches to establish stable mixed chimerism after transplantation for sickle cell disease.     

Pain,quality of life,and coping in sickle cell disease.

This study examined the frequency and severity of sickle related pain, its impact on quality of life, and methods of coping for 25 children with sickle cell disease, aged 6-16 years. Subjects were matched with non-affected peers and asked to complete the Central Middlesex Hospital Children''s Health Diary for four weeks. Results indicated that sickle pain occurred on average one in 14 days, and total summary pain scores indicated significantly greater pain than for controls. Children with sickle cell disease could discriminate sickle pain and did not adopt sick role responses to ordinary childhood ailments. Nearly all sickle pain was dealt with at home. Sickle pain resulted in over seven times increased risk of not attending school and was highly disruptive of social and recreational activities. Careful assessment of sickle pain in the home environment is an essential part of a community focused pain management service, which effectively supports children''s resilience and improves their quality of life.     

Activity of the alternative complement pathway after splenectomy: comparison to activity in sickle cell disease and hypogammaglobulinemia.

Patients with sickle cell disease and individuals who have undergone splenectomy share defects of certain host defense mechanisms and a predisposition to severe pyogenic bacterial infections. Since patients with sickle cell disease can have deficient activity of the alternative complement pathway, we have tested such activity in sera from splenectomized children and adults. A new kinetic hemolytic assay has been used, and we have compared results to those obtained with sera from patients with sickle cell disease or hypogammaglobulinemia. Sera from six of 58 splenectomized individuals (10%) had defective function of the alternative pathway, compared to 10 of 62 sera from patients with sickle cell disease (16%) and 10 of 18 sera from hypogammaglobulinemic patients (56%). Deficiency of antibody, a rate-influencing component of alternative pathway activity in this system, appears responsible for deficient activity in the hypogammaglobulinemic sera. The molecular basis for the deficiency found in sickle cell disease or after splenectomy is not clear. Defective function of the alternative complement pathway could contribute to the increased predisposition to bacterial infection that exists in these three patient groups.     

IRON DEFICIENCY IN SICKLE CELL DISEASE

Abstract. Nagaraj Rao, J. and Sur, A. M. (Department of Paediatrics, Medical College and Hospital, Nagpur, India). Iron deficiency in sickle cell disease. Acta Paediatr Scand, 69:337, 1980.—Iron studies were performed on 25 children with homozygous sickle cell disease. The majority (80%) of patients had never been transfused. Surprisingly, the results showed that all had low serum iron and low transferrin saturation. Three children had no marrow iron stores while the rest had diminished amounts of iron. This may be an important finding in view of recent efforts at fortifying common salt with iron. The exact effects of iron deficiency on sickle cell disease are not known and a controlled trial is called for.     

Diverse manifestations of acute sickle cell hepatopathy in pediatric patients with sickle cell disease: A case series

The hepatic complications of sickle cell disease (SCD) are associated with increased morbidity and mortality in adults; children usually survive but may suffer significant sequelae. Few diagnostic tools differentiate the various hepatic manifestations of SCD. Why patients exhibit one hepatic pathology versus another is unclear. We report four pediatric patients with hemoglobin SS disease with diverse manifestations of acute hepatic involvement including acute sickle hepatic crisis, hepatic sequestration, sickle cell intrahepatic cholestasis, and a non‐SCD cause of hepatopathy in a patient with viral hepatitis. These complications require a systematic approach to extensive evaluation and coordinated multidisciplinary care.     

Echocardiographic aspects in pediatric patients with sickle cell disease]

BACKGROUND: Cardiovascular involvement is not well studied in children with sickle cell disease. The aim of this study was to evaluate the echocardiographic parameters of children with sickle cell disease. PATIENTS AND METHODS: We performed a transversal and case-control study including 80 subjects of six months to 16 years of age divided into four groups of 20 children each: heterozygous sickle cell disease, homozygous sickle cell anemia, anemia of other causes than sickle cell, and healthy children. All children had a complete physical examination, biological screening including hemogram and hemoglobin electrophoresis, chest x-ray, electrocardiogram, and Doppler echocardiogram. Data were compared using the chi 2 method and the Student's t-test. RESULTS: The mean age was 8.5 years and the sex-ratio was 1. Echocardiographic abnormalities were observed in seven patients with anemia unrelated to sickle cell, 15 children with heterozygous anemia and all the homozygous patients. The main abnormalities were: left ventricular enlargement (ten homozygous patients, one heterozygous subject, five of the patients with another cause of anemia), increased contractility of the heart (18 homozygous patients, seven heterozygous patients, five in the anemia group) and mild to moderate mitral or tricuspid regurgitation (12 homozygous, five heterozygous and five patients in the anemia group). One homozygous child had a dilated and hypokinetic cardiomyopathy with pulmonary hypertension. The parameters of left ventricular systolic function and left heart chamber dimensions were lower in the control group (P < 0.04). DISCUSSION: This study shows the frequency of heart chamber dilatation with left ventricular hyperkinesis usually described in the literature. The lack of case of chronic cor pulmonale may be due to the young age of our patients. One case of dilated and hypokinetic cardiomyopathy suggests that other causes than anemia should be considered, particularly myocardial ischemia, which could not be demonstrated because of our limited investigative methods. CONCLUSION: These results emphasize the frequency of the heart involvement in sickle cell disease, particularly in the homozygous type, and point out the importance of the cardiologic screening of these patients.     

Acute liver failure due to T cell lymphoma without hepatic infiltration

Hepatomegaly and alterations in hepatic function are common to all patients with sickle-cell disease. In these patients, hepatic sickling is a manifestation of severe intrahepatic vaso-oclusive crises, even at levels of 25 % HbS and hematocrits of more than 45-50 %, which in 10 % of cases can lead to acute hepatic failure (AHF). AHF can be due to a variety of causes, including hematologic malignancies, but T cell lymphoma, which is usually secondary to diffuse hepatic infiltration and ischemia, is an exceptional cause, although other mechanisms can be involved. Cytokines released by lymphomas have recently been implicated as a cause of AHF.We describe a black girl with sickle cell disease, who developed AHF due to T cell lymphoma without lymphomatous infiltration of the liver. The only mechanism found to explain the clinical findings was release of cytokines by lymphoma. In patients with AHF of unknown etiology we propose early liver biopsy, because prognosis depends on the presence or absence of hepatic tumour infiltration. If AHF develops in a patient with diagnosed malignant disease, cytokine release may be the cause of AHF. Consequently, early diagnosis of the underlying disease and provision of liver support, as well as direct removal of inflammatory mediators from the circulation by exchange transfusion or other methods, should be the main priorities.     

Acute splenic sequestration in female children with sickle cell disease in the North of Jordan

The objective of this study was to evaluate the rate of acute splenic sequestration (ASSC) in patients with sickle beta-thalassaemia and sickle cell anaemia, the risk of recurrence in those who survive the first episode, and the relationship between ASSC episodes and subsequent hypersplenism. All patients with confirmed diagnosis of sickle cell disease at a tertiary referral teaching hospital, between January 1994 and December 2002 were interviewed and had their medical records reviewed. Seventy-seven patients with sickle cell disease were identified. Their ages ranged between 2 and 18 years (mean, 10.1 years). There were 35 females and 38 males. Thirty-seven (50.6%) had sickle beta-thalassaemia, and 36 (49.4%) had homozygous sickle cell anaemia. Of these, 26 had high level of Hb F and 11 had normal level of fetal haemoglobin (Hb F). Twenty-one patients (28%) had 63 episodes of acute splenic sequestration. Thirty-seven episodes were experienced by 12 patients with sickle beta-thalassaemia; of these 11 were major attacks with one fatality. Twenty-six episodes were experienced by nine patients with sickle cell anaemia. Splenomegaly and hypersplenism were greater in the acute splenic sequestration group than in the rest of the sickle cell anaemia patients, and the differences were extremely significant. ASSC was found in nine siblings of sickle beta-thalassaemia group, while none were found in the sickle cell anaemia group. The mean age of the first episode was significantly higher in sickle beta-thalassaemia, with significant differences in the levels of Hb F, Hb S, size of spleen and severity of crisis between both groups. In the sickle cell anaemia group the only significant difference between patients with and these without acute splenic sequestration was the difference in the size of spleen. In this study, the rate of ASSC in the sickle beta-thalassaemia patients was 32%, in contrast to 25% in the sickle cell anaemia patients. The risk of recurrence was about 70% in those who survived their first episodes. There was a close relationship between ASSC and subsequent hypersplenism. Important predictable factors for ASSC in sickle beta-thalassaemia patients were the presence of splenomegaly of more than 5 cm below the costal margin, history of acute splenic sequestration in siblings and high Hb F. Most of first episodes in sickle cell anaemia occur under the age of 2 years, while in sickle beta-thalassaemia the majority of patients have their first crisis at the age of > or =3.5 years.