Hydroxyurea-induced denaturation of normal and sickle cell hemoglobins in vitro

An experimental erythrocyte rigidity index (Ri) and its correlations with Transcranial Doppler velocities (TAMMV), Gosling Pulsatility Index PI, hematocrit, hemoglobin concentration and red cell distribution width (RDW)

Brain artery velocities (Time-Averaged Maximum Mean Velocity, TAMMV) by Transcranial Doppler (TCD), hematocrit, hemoglobin, Red blood cell (RBC) Distribution Width (RDW) and RBC rigidity index (Ri), when reported together with their correlations, provide a accurate and useful diagnostic picture than blood viscosity measurements alone. Additionally, our study included a sixth parameter provided by TCD, the Gosling Pulsatility Index PI, which is an indicator of CBF (Cerebral Blood Flow) resistance. All these parameters are routine in Hematology except for values of Ri. The rigidity (Ri) of the RBC is the main rheological characteristic of the blood of Sickle Cell Anemia (SCA) patients and several pathologies. However, its quantification depends on many commercial and experimental techniques, none disseminated and predominant around the World. The difference in absorbance values of the blood, during the process of sedimentation in a microwell of a Microplate Reader, is a straightforward way of semi-quantifying the RBC rigidity Ri, since the fraction of irreversibly sickled red blood cells does not form rouleaux. Erythrocyte Rigidity Index (Ri) was calculated using initial absorbance A_initial (6 s) and final A_final (540 s), Ri = 1 / (Ai-Af). The Ri of 119 patients (2–17 y / o, M & F) SCA, SCC (Sickle Cell/hemoglobin C), SCD (Sickle Cell/hemoglobin D), Sβ0thal (Sickle Cell/hemoglobin Beta Zero Thalassemia) and 71 blood donors (20–65 y / o, M & F) were measured in our laboratory while the five parameters (TAMMV and PI by TCD, Hct, Hb and RDW) were obtained from medical records. The in vitro addition of hydroxyurea (HU, 50mg /dl, n = 51 patients, and n = 8 healthy donors) in the samples decreased the rouleaux adhesion strength of both donor and patients’ blood samples, leading to extraordinarily high Ri values. The correlation between the studied parameters was especially significant for the direct relationships between Ri, TAMMV, and PI.

Widespread Natural Occurrence of Hydroxyurea in Animals

Here we report the widespread natural occurrence of a known antibiotic and antineoplastic compound, hydroxyurea in animals from many taxonomic groups.

Hydroxyurea occurs in all the organisms we have examined including invertebrates (molluscs and crustaceans), fishes from several major groups, amphibians and mammals. The species with highest concentrations was an elasmobranch (sharks, skates and rays), the little skate Leucoraja erinacea with levels up to 250 μM, high enough to have antiviral, antimicrobial and antineoplastic effects based on in vitro studies. Embryos of L. erinacea showed increasing levels of hydroxyurea with development, indicating the capacity for hydroxyurea synthesis. Certain tissues of other organisms (e.g. skin of the frog (64 μM), intestine of lobster (138 μM) gills of the surf clam (100 μM)) had levels high enough to have antiviral effects based on in vitro studies. Hydroxyurea is widely used clinically in the treatment of certain human cancers, sickle cell anemia, psoriasis, myeloproliferative diseases, and has been investigated as a potential treatment of HIV infection and its presence at high levels in tissues of elasmobranchs and other organisms suggests a novel mechanism for fighting disease that may explain the disease resistance of some groups. In light of the known production of nitric oxide from exogenously applied hydroxyurea, endogenous hydoxyurea may play a hitherto unknown role in nitric oxide dynamics.

Hydroxyurea: The drug of choice for polycythemia vera and essential thrombocythemia

Hydroxyurea is an old drug that is often used to control essential thrombocythemia and polycythemia vera in patients with high-risk disease. It is usually well tolerated and cheap and has been proven effective in many studies for the prevention of thrombohemorrhagic complications associated with these disorders. However, many clinicians are reluctant to use it because of the perceived risk of progression to acute leukemia. Several recent, large studies have given this drug a new lease on life. Relevant results from these studies are discussed, and the risk of leukemia is placed in perspective to demonstrate that hydroxyurea remains the drug of choice in patients with either of these disorders.

Hydroxyurea-induced hemolytic anemia in a patient with essential thrombocythemia

Hydroxyurea (HU) has been used in patients with essential thrombocythemia (ET) to reduce the frequency and severity of thrombotic complications of the disease. It acts by causing bone marrow depression, resulting in a decrease in platelet and leukocyte counts and in anemia with megaloblastosis. Herein we report a case of an 80-year-old man with ET who developed severe hemolytic anemia requiring multiple packed RBC transfusions while being treated with HU. The hemolysis persisted until discontinuation of the drug. This case suggests hemolysis as a potential side effect of HU and raises the clinical concern that not all HU-induced anemia is secondary to erythropoiesis depression. With the increasing use of HU in the management of ET, hemoglobinopathy, and other diseases, the importance of monitoring for hemolysis must be further emphasized in these patients.

Effect of hydroxyurea on G gamma chain fetal hemoglobin synthesis by sickle-cell disease patients

Hydroxyurea is used for sickle-cell disease patients in order to increase fetal hemoglobin synthesis and consequently decrease the severity of pain episodes. Fetal hemoglobin, which is formed by gamma-globin chains A and G, is present in a constant composition throughout fetal development: about 75% of Ggamma and 25% of Agamma. In contrast, adult red cells contain about 40% of Ggamma and 60% of Agamma. In the present study, we analyzed the effect of hydroxyurea induction on the gamma chain composition of fetal hemoglobin in 31 sickle-cell disease patients treated with hydroxyurea. The control group was composed of 30 sickle-cell disease patients not treated with hydroxyurea in clinical steady state. The patients were older than 13 years and were not matched for age. All patients were seen at Hemocentro/UNICAMP and Boldrini Infantile Center, Campinas, SP, Brazil. The levels of total hemoglobin were significantly higher in patients treated with hydroxyurea (mean +/- SD, 9.6+/-2.16 g/dl) than in untreated patients (8.07+/-0.91 g/dl). Fetal hemoglobin levels were also higher in treated patients (14.16+/-8.31%) than in untreated patients (8.8+/-4.09%), as was the Ggamma/Agamma ratio (1.45+/-0.78 vs 0.98+/-0.4, P < 0.005). The increase in the Ggamma/Agamma ratio in patients treated with hydroxyurea suggests the prevalence of a pattern of fetal hemoglobin synthesis, whereas patients not treated with hydroxyurea maintain the adult pattern of fetal hemoglobin synthesis. Because no correlation was observed between the Ggamma/Agamma ratio and total hemoglobin or fetal hemoglobin levels, the increase in Ggamma chain synthesis may not imply a higher production of hemoglobin.

Clinical and hematological responses to hydroxyurea in Sicilian patients with Hb S/beta-thalassemia

Although, several reports have detailed that hydroxyurea can ameliorate the clinical course of adult and pediatric patients with sickle cell anemia (Hb S or beta(S)), few clinical studies have been carried out in patients with beta(S)/beta-thalassemia. In a two-year clinical study, we evaluated the efficacy of hydroxyurea in a group of 22 adult Sicilian patients with beta(S)/beta-thalassemia with severe phenotypes. Among the 20 patients evaluated during 2 years of treatment, we observed a very good clinical response with a 93% reduction of the annual number of crises (median 7 versus 0.5 crises per year; P < 0.001) and of days in hospital (mean 22+/- 21.9 versus 1.2 +/- 2.3; P < 0.001), a significant increase in Hb F (7.5 +/- 5.3% versus 25.2 +/- 5.2%; P < 0.001) and in MCV (73.1 +/- 4.8 fL versus 96.4 +/- 7.2 fL; P < 0.001), and no significant modifications in Hb (9.6 +/- 1.3 g/dL versus 10.0 +/- 1.5 g/dL; P > 0.05) and in WBC (11.4 +/- 3.9 x 10(9)/L versus 10.2 +/- 3.9 x 10(9)/L; P > 0.05). Twelve patients had no crises from the first month of treatment; 16 patients showed a 2-3-fold increase over baseline in Hb F. During the study no severe complications and no important side effects of hydroxyurea were observed. Our data suggest that hydroxyurea efficacy in patients with beta(S)/beta-thalassemial may be greater than that described in patients with sickle cell disease. This pattern and durability of response will need to be confirmed in a larger, randomized, clinical trial.