A randomized, controlled clinical trial established the efficacy and safety of short-term use of hydroxyurea in adult sickle cell anemia. To examine the risks and benefits of long-term hydroxyurea usage, patients in this trial were followed for 17.5 years during which they could start or stop hydroxyurea. The purpose of this follow-up was to search for adverse outcomes and estimate mortality. For each outcome and for mortality, exact 95% confidence intervals were calculated, or tests were conducted at a 5 0.05 level (P-value <0.05 for statistical significance). Although the death rate in the overall study cohort was high (43.1%; 4.4 per 100 person-years), mortality was reduced in individuals with long-term exposure to hydroxyurea. Survival curves demonstrated a significant reduction in deaths with long-term exposure. Twenty-four percent of deaths were due to pulmonary complications; 87.1% occurred in patients who never took hydroxyurea or took it for <5 years. Stroke, organ dysfunction, infection, and malignancy were similar in all groups. Our results, while no longer the product of a randomized study because of the ethical concerns of withholding an efficacious treatment, suggest that long-term use of hydroxyurea is safe and might decrease mortality. Am. J. Hematol. 85:403-408, 2010. V
We studied 47 patients with sickle-cell anemia to determine the effect of alpha-thalassemia on the severity of their hemolytic anemia. We diagnosed alpha-thalassemia objectively by using alpha-globin-gene mapping to detect alpha-globin-gene deletions, studying 25 subjects with the normal four alpha-globin-genes, 18 with three, and four with two. The mean hemoglobin, hematocrit, and absolute reticulocyte levels (+/- S.D.) were 7.9 +/- 0.9 g per deciliter (4.9 +/- 0.6 mmol per liter), 22.9 +/- 2.9 per cent, and 501,000 +/- 126,000 per cubic millimeter, respectively, in the non-thalassemic group; 9.8 +/- 1.6 g per deciliter (6.1 +/- 1.0 mmol per liter), 29.0 +/- 5.0 per cent, and 361,000 +/- 51,000 per cubic millimeter in the group with three alpha-globin genes; and 9.2 +/- 1.0 g per deciliter (5.7 +/- 0.6 mmol per liter), 27.5 +/- 3.0 per cent, and 100,000 +/- 15,000 per cubic millimeter in the group with two alpha-globin genes. Deletion of alpha-globin genes was also accompanied by a decreased mean corpuscular hemoglobin concentration (MCHC) in post-reticulocyte erythrocytes and by increased hemoglobin F levels. The decreased intraerythrocytic hemoglobin S concentration and elevated hemoglobin F levels associated with alpha-thalassemia appear to diminish the degree of hemolytic anemia found in sickle-cell disease.
In summary, we propose the following scheme (Figure 5) to describe the role of peroxidation in the pathophysiology of SCA. Sickle erythrocytes are more susceptible to peroxidation than are normal erythrocytes. This increased susceptibility to peroxidation is, in part, due to decreased blood vitamin E levels and abnormal membrane phospholipid organization induced by sickling. The peroxidative damage of sickle erythrocytes may accelerate or contribute to loss of cell deformability and to chronic hemolysis. Peroxidative damage can produce abnormal cellular properties, such as potassium leak and reduced filterability, and contribute to formation of ISCs. Increased red cell rigidity can initiate episodes of capillary obstruction, leading to vasoocclusive painful crises and to tissue infarction. Liver dysfunction as well as increased production of bilirubin secondary to hemolysis could result in bile sludging and decreased secretion of bile salts into the intestinal lumen. Reduced bile salt secretion leads to partial fat and vitamin E malabsorption. Vitamin E deficiency enhances red cell susceptibility to peroxidation and promotes a vicious cycle in SCA. Although we have not studied factors that might initiate peroxidative damage, sickle hemoglobin and excess body iron should be considered as potential sources. Our studies suggest that vitamin E supplementation to sickle-cell patients could be of clinical benefit.
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