Levels of endothelial, neutrophil and platelet-specific factors in sickle cell anemia patients during hydroxyurea therapy.

It has been shown that the clinical course of sickle cell (SS) patients can be ameliorated by administration of hydroxyurea (HU). Induction of hemoglobin F (HbF) is thought to be the mechanism responsible for clinical improvement in some patients. However, HU has a variable effect on HbF production and there exists no good correlation between the extent of HbF increase and clinical response. On the other hand, the degree of adherence of SS to vascular endothelium and neutrophil counts correlate well with clinical severity. Being a cytotoxic drug, used in myeloproliferative diseases, HU may alter proliferation among various cell lines. Moreover, HU has been reported to reduce red blood cell (RBC) adhesion receptor expression in young SS individuals and induces changes in endothelial cells in vitro. It should be conceived that in addition to its effects on HbF production, HU may change the clinical symptoms of SS patients by affecting the degree of adherence of different blood cells, by influencing the activity of endothelium as well as the activity of white blood cells (WBC) and platelets. To analyze whether several of the determinants of adhesion are modulated by HU treatment we studied the levels of endothelial activity (soluble vascular adhesion molecule-1, (sVCAM-1), interleukin-8 (IL-8), fibronectin, neutrophil activity (sL-selectin, sIL-6 receptor-alpha, myeloperoxidase) and platelet activity (von Willebrand factor) in relation to clinical symptoms, hematological data and HbF levels in 8 SS patients before and during 5 months of HU therapy. Steady state sVCAM-1 levels are increased compared to normal controls and a significant decrease is noted during HU treatment, suggesting a decrease in the interactions between RBC and vascular endothelium. The IL-8 levels are comparable to those in normal controls and remain unaffected by HU therapy. Intercurrent infection and crises reveal striking increases in IL-8 which are accompanied by leukocytosis, but otherwise the IL-8 levels do not correlate with hematological data. HU has no demonstrable effect on fibronectin or soluble neutrophil adhesion molecules, but the levels of myeloperoxidase decrease significantly while WBC counts do not, implying a reduction in neutrophil activity which may help attenuate the propagation phase of a vasoocclusive crisis.

Elevated IL-8 levels during sickle cell crisis.

The vaso-occlusive process (VOC) in sickle cell disease is of a complex nature. It involves intricate interactions between sickle red blood cells, endothelium and probably also leukocytes. As these interactions are regulated by cytokines, we analyzed the role of the potent neutrophil chemokine IL-8 by measuring serum levels in sickle cell patients during sickle cell crisis. These results were compared to nonsymptomatics and healthy controls. In patients having a vaso-occlusive crisis both HbSS and HbSC patients showed significantly enhanced serum IL-8 levels compared to healthy controls. Several of these patients showed extremely elevated serum IL-8 levels which were independent of the crisis inducing factor. Furthermore, a sickle cell patient with VOC as a complication of rhGM-CSF treatment similarly showed high IL-8 serum levels at crisis onset. Nonsymptomatic sickle cell patients serum IL-8 levels were comparable to healthy controls. These results implicate a role for IL-8 at or during (the initiation of) sickle cell crisis.

Cytokines and soluble adhesion molecules in sickle cell anemia patients during hydroxyurea therapy.

Hydroxyurea (HU) induces HbF production and can reduce painful crises in some patients with sickle cell anemia (SS). However, HbF induction alone cannot explain the beneficial effect of HU treatment as some patients experience clinical improvement while showing only minor increases in HbF. Other actions of HU, in particular its effects on vascular endothelium, adhesion molecule expression and cytokine production may also play a role in the final therapeutic outcome. In order to analyze these effects we studied the levels of interleukin-3 (IL-3), interleukin-6, granulocyte-macrophage colony-stimulating factor, erythropoietin, stem cell factor, soluble vascular adhesion molecule-1, soluble intercellular adhesion molecule-1, soluble E-selectin and soluble P-selectin in 7 SS patients before and during 5 months of HU treatment. Use of HU seems to have no detectable effect on soluble adhesion molecules, but the steady state levels of soluble vascular adhesion molecule-1 are enhanced in SS patients compared to normal controls. Of the cytokines studied, only IL-3 showed an increase during therapy, suggesting HU may induce early erythroid progenitors capable of producing HbF by a direct or indirect effect on IL-3 production. Remarkably, the steady state stem cell factor levels in sickle cell patients seemed to be decreased compared to healthy controls.

Hydroxyurea therapy in sickle cell anemia patients in Curaçao, The Netherlands Antilles.

We have treated 9 patients with sickle cell anemia (SS) with hydroxyurea (HU). All 9 patients carried 4 alpha-globin genes and the beta s-globin haplotypes 19/19 (Benin/Benin), except for 1 who had haplotype 19 together with type 3 (Benin/Senegal). Six patients received HU for 10 months and were again treated with the drug for 5 months after an interval of 1 year. One patient was given HU for 22 consecutive months. A record was kept of hematological and biochemical data, Hb F and G gamma levels, as well as possible clinical complications. Our data show that HU generally improves the hematological and biochemical values and the level of Hb F, and reduces painful crises in some patients. However, although the clinical symptoms improved in some patients during HU therapy, the older patients did not observe any changes in their general condition; the same is the case for the patient with haplotype 19/3. One patient also experienced life-threatening liver sequestration during treatment. We conclude that the selection of patients who may benefit from HU therapy needs further evaluation.

Pharmacological induction of foetal haemoglobin synthesis in sickle-cell disease.

In the present review the role and regulation of foetal haemoglobin (HbF) in sickle-cell disease as well as the clinical results of therapy aimed at augmenting HbF synthesis are briefly discussed. Enhanced levels of HbF have an inhibitory effect on sickling and ameliorate the clinical course of sickle-cell disease. This knowledge has incited a search for pharmacological agents capable of stimulating HbF production. Cytostatic drugs, in particular hydroxyurea, but also other agents such as erythropoietin, butyrate and its analogues have been shown to induce HbF production. The mechanisms of action and the clinical effects of these agents are summarized. Only hydroxyurea has shown significant clinical effects in terms of reduction of pain-crises, chest syndrome and transfusions in sickle-cell patients. However, not all patients experience clinical amelioration and it appears difficult to predict which patient will gain from hydroxyurea therapy. Further studies need to expand the clinical experience with hydroxyurea, other HbF-inducing agents and combinations of these drugs. Moreover, they will hopefully provide criteria to enable appropriate selection of those patients with sickle-cell anaemia who will benefit clinically from HbF stimulation, also taking into account the risks and costs of long-term pharmacological therapy.

Enhanced levels of soluble VCAM-1 in sickle cell patients and their specific increment during vasoocclusive crisis.

Adhesion of sickle erythrocytes to vascular endothelium plays a central role in sickle cell disease complications. Cytokines and adhesion molecules are critically involved in the regulation of these adhesive processes. To analyze their role, IL-6, GM-CSF, sVCAM-1, sICAM-1, sE-Selectin, and sP-Selectin serum levels were determined in sickle cell patients under basic conditions and during vasoocclusive crisis. In nonsymptomatic patients a high serum level of sVCAM-1 was observed compared to controls. In patients having vasoocclusive crisis sVCAM-1 levels increased even more and seemed to correlate with crisis evolution.

Isobutyramide therapy in patients with sickle cell anemia.

We have administered Isobutyramide as a suspension over a period of 3 months, from a starting dose of 50 mg/kg/day up to 150 mg/kg/day, to four adult sickle cell (SS) anemia patients. The maximum dose was maintained for 3 weeks. The blood counts remained stable and the Hb F levels decreased slightly. The G gamma levels increased at the end of the trial, suggesting activation of the G gamma gene at the highest dose of Isobutyramide. Three patients showed a stable rate of hemolysis, while in one patient, an increase of lactate dehydrogenase occurred. None of the patients experienced pain crisis or organ-specific crisis, but all four complained about mild epigastric burning and a bitter taste. After the first month of treatment one patient complained about intolerable epigastric discomfort which was relieved by Omeprazole. Another patient complained about increasing dyspepsia in the 12th week leading to the termination of the trial. Oral Isobutyramide administration does not qualify as an effective treatment of SS patients.