Search

The homozygous form of ß-thalassemia, the most common single gene disorder, is treated by red cell transfusion therapy. Following transfusion, the chelator, deferoximine, is administered to patients to remove excess iron. However, when this drug is given to young children, metaphyseal dysplasia and abnormalities of linear growth are frequently observed. To explore the notion that deferoximine mine interferes with endochondral growth by chelating zinc, we examined the effect of the drug on chondrocytes maintained in long-term culture. We found that deferoximine caused a dose-dependent inhibition of a wide range of functions including cell proliferation, protein synthesis (and possibly under-hydroxylation of type X collagen), and mineral deposition. Directly relevant to the mineralization process was the observation that the drug dramatically lowered the activity of alkaline phosphatase, a zinc-requiring enzyme. To test the hypothesis that enzyme inhibition was due to chelation of zinc by deferoximine, the cell culture medium was supplemented with excess zinc. However, this treatment did not overcome the deferoximine-dependent change in enzyme activity. We next examined the possibility that deferoximine, in the presence of ascorbate, could form a free radical system that would serve to inactivate the enzyme. Using alkaline phosphatase extracted from chick cartilage, we noted that the activity of the phosphatase was markedly reduced in the presence of deferoximine and ascorbate. These effects were consistant with the notion that deferoximine and ascorbate can act as a prooxidant couple. This conclusion was confirmed when we measured the oxidative activities of the system using nitroblue tetrazolium and cytochrome c. Indeed, we noted that deferoximine markedly activates the autocatalytic oxidation of ascorbate. We next investigated the possibility that the change in alkaline phosphatase activity was due to the formation of reactive oxygen radicals. Though oxygen radical scavengers and disproportionating agents did not change the activity of the enzyme, a-tocopherol provided complete protection. In conclusion, the deferoximine-ascorbate couple inactivates chondrocyte alkaline phosphatase probably by generation of free radicals. As free radicals can damage cartilage as well as other tissues, clinical regimens that are directed at elevating ascorbate levels in thalassemia need to be carefully reviewed.

Hemoglobin and DNA gene analyses were carried out in two Black Canadian families. In Family Q, both the parents and the brother were found to be heterozygotes for α-thalassemia-2 with the following α-genotypes: -α3.7/αα, -α4.2/αα and -α4.2/αα, respectively. In Family C, the mother was found to be a homozygote for α-thalassemia-2 with the α-genotype of -α3.7/-α3.7. In both families, the propositi were compound heterozygotes for α-thalassemia-2 with the α-genotype of -α3.7/-α4.2. Tne propositus in Family C was also a sickle cell trait carrier. The usefulness of DNA gene analyses in family studies of hemoglobinopathy was discussed.

Erythrocytes and progenitor-derived erythroblasts of sickle cell anemia patients from the Eastern Province of Saudi Arabia contain increased fetal hemoglobin and G gamma globin. A distinctive DNA polymorphism haplotype in the beta globin gene cluster (++- +-), tightly coupled to a C----T substitution at position -158 5' to the cap site of the G gamma globin gene, is strongly associated with sickle cell disease in this region. To determine whether the increased fetal hemoglobin production and/or elevated G gamma globin content are tightly linked to this haplotype, we studied 55 members of five Saudi families in which sickle cell disease is present. The results did not suggest a tight linkage of the haplotype to increased fetal hemoglobin production. On the other hand, several sickle trait family members heterozygous for the haplotype had normal fetal hemoglobin production in culture but elevated G gamma to A gamma ratios in peripheral blood. This observation suggests that in this genetic background increased expression of the G gamma globin gene may occur without a measurable increase in total fetal hemoglobin production. The family studies also clearly demonstrate that increased fetal hemoglobin production by erythroid progenitors is dependent on zygosity for the sickle gene in this population. These findings strongly suggest that other factors, such as the products of genes stimulated by hemolytic stress or other genetic determinants associated with the Saudi beta S chromosome, may interact with the -158 C----T substitution and influence gamma globin gene expression in this population.

1,2-Dimethyl-3-hydroxypyridin-4-one (CP020 or L1) is a novel oral iron chelator that has proved to be effective in animals and humans. A rapid, accurate, and sensitive high-performance liquid chromatography method is described for measuring L1in human plasma using a Hypercarb 7 μm column and monitoring the column eluent by ultraviolet absorption at 280 nm. CP020 and the internal standard (CP094) were extracted into dichloromethane (2x5 ml) from plasma at neutral pH [0.25 ml of plasma + 0.75 ml of 60 m M3-(N-morpholino)propanesulfonic acid buffer, pH 7.4]. The method proved to be linear (r2= 0.998) in the clinical range of 0.5–50 μg/ml when 0.25 ml of plasma was used, with the coefficient of variation less than 10 even at the lower concentration range.

The clinicopathologic effects of intravenously administered purified verocytotoxin 1 (VT1; Shiga-like toxin 1) in 2-kg male rabbits was studied. The 50% lethal dose was 0.2 micrograms of protein per kg of body weight (2 x 10(4) 50% cytotoxic doses per kg). The clinical features included nonbloody diarrhea and a progressive flaccid paresis, usually culminating in death. The histopathology was characterized by edema and hemorrhage in the mucosa and submucosa of the cecum and edema, hemorrhage, and neuronal necrosis in the brain and gray matter of the spinal cord. Thrombotic microangiopathy, the characteristic histopathologic renal lesion in the hemolytic-uremic syndrome, was also found to be the underlying lesion in verocytotoxemic rabbits. To determine the specific distribution of VT1 in rabbit tissues, purified 125I-labelled VT1 was administered intravenously to 20 rabbits (both immunologically naive and VT1-immune rabbits). The highest specific uptake of 125I-VT1 was in the spinal cord, brain, cecum, colon, and small bowel in unimmunized animals but in the liver, spleen, and lungs in immune animals. Immunofluorescent staining of cecal and spinal cord tissues after intravenous administration of VT1 showed evidence of specific vascular endothelial cell binding of the toxin. The striking correlation of the central nervous system and gastrointestinal localization of 125I-VT1 with the sites of known histopathology is consistent with direct toxin-mediated injury to these tissues, initiated by the specific binding of VT1 to the vascular endothelium. We conclude that the vascular damage induced by VT1 in affected rabbit tissues is similar to that seen in the kidneys and other tissues in patients with verocytotoxin-producing Escherichia coli-associated hemolytic-uremic syndrome. This suggests that although the rabbit model fails to replicate human hemolytic-uremic syndrome, it is useful for studying the pathogenesis of the vascular lesions in verocytotoxin-producing E. coli-associated diseases.

In this study, 50 thalassemia patients were tested using dualenergy X-ray absorptiometry (DEXA) and in vivo neutron activation analysis (IVNAA) to determine their bone mineral status. Both techniques were suitable for this purpose. Lower age was found to correspond to lower liver iron content and higher bone mineral content in the normal range. Patients undergoing treatment with transfusion had higher bone mineral content. Osteopenic patients had higher hepatic iron content than those with normal bone status. In the case of DEXA, bone mineral content (BMC) divided by height cubed was found to be a better indicator of bone mineral status than the BMD usually given. Liver density as determined by DEXA correlates well with hepatic iron

Although considered a mild disorder, beta thalassemia trait (uncomplicated by any other hematologic abnormality) has been reportedly associated with symptoms of anemia, while in other series hepatosplenomegaly has been reported as associated with this diagnosis. No controlled study has examined the symptoms and signs of individuals with beta thalassemia trait and compared these with age- and sex-matched normal individuals. We administered a questionnaire to 397 parents (67% females) of children with beta thalassemia major attending the National Thalassemia Centre in Kurunagala, Sri Lanka, and to 87 normal volunteers (90% females). All individuals underwent physical examination by the same investigator, as well as testing by automated cell counter (Coulter), and HPLC (Bio Rad). The mean age of the parents (33 years) and controls (29.5 years) was not significantly different. In parents with thalassemia trait, 20% of males and 42% of females complained of reduced exercise tolerance compared to 12.5% of males and 38% of females in the controls (P= NS). The questionnaire revealed that 41% of parents, and 36% of controls, complained of recurrent headache; 18% of parents, and 15% of controls, complained of lethargy (P=NS). A history of malaria infection was reported in 30% of parents with thalassemia trait, and in 24% of controls. Mean quality-of-life score, recorded formally by a linear analog scale, from 0 (poorest) to 10 (greatest) was 7.1 in parents and 7.2 in controls. Splenomegaly was detected in 6% of parents with beta thalassemia trait (mean spleen size 1.5 cm below the costal margin), and 5% of normal controls (mean spleen size 1 cm below the costal margin). These findings suggest that, by contrast to many reports in the older literature, in uncomplicated beta thalassemia trait there appears to be no symptoms or signs greater than those observed in a normal control population and that fatigue, lethargy, exercise intolerance, or splenomegaly in a patient with beta thalassemia trait should not be attributed to the underlying hemoglobinopathy.