Search

Iron homeostasis is tightly regulated, as cells work to conserve this essential but potentially toxic metal. The translation of many iron proteins is controlled by the binding of two cytoplasmic proteins, iron regulatory protein 1 and 2 (IRP1 and IRP2) to stem loop structures, known as iron-responsive elements (IREs), found in the untranslated regions of their mRNAs. In short, when iron is depleted, IRP1 or IRP2 bind IREs; this decreases the synthesis of proteins involved in iron storage and mitochondrial metabolism (e.g. ferritin and mitochondrial aconitase) and increases the synthesis of those involved in iron uptake (e.g. transferrin receptor). It is likely that more iron-containing proteins have IREs and that other IRPs may exist. One obvious place to search is in Complex I of the mitochondrial respiratory chain, which contains at least 6 iron-sulfur (Fe-S) subunits. Interestingly, in idiopathic Parkinson's disease, iron homeostasis is altered, and Complex I activity is diminished. These findings led us to investigate whether iron status affects the Fe-S subunits of Complex I. We found that the protein levels of the 75-kDa subunit of Complex I were modulated by levels of iron in the cell, whereas mRNA levels were minimally changed. Isolation of a clone of the 75-kDa Fe-S subunit with a more complete 5'-untranslated region sequence revealed a novel IRE-like stem loop sequence. RNA-protein gel shift assays demonstrated that a specific cytoplasmic protein bound the novel IRE and that the binding of the protein was affected by iron status. Western blot analysis and supershift assays showed that this cytosolic protein is neither IRP1 nor IRP2. In addition, ferritin IRE was able to compete for binding with this putative IRP. These results suggest that the 75-kDa Fe-S subunit of mitochondrial Complex I may be regulated by a novel IRE-IRP system.

In vivo bone lead measurements with 109Cd-based K-shell X-ray fluorescence (XRF) have been used to assess long-term lead exposure in adults. Tibia lead levels were measured in 210 children (106 boys, 104 girls) of 11-12(1/2) years of age in a lead smelter town and in a control (nonexposed) town. Tibia lead levels, methodological uncertainties, and models of some of the factors influencing them are presented. 109Cd-based K-shell XRF tibia lead methodological uncertainty in children is comparable to that in adults., (Copyright 2001 Academic Press.)

A primary rat choroidal epithelial cell culture system was developed to investigate mechanisms of heavy metal toxicity on the blood-cerebrospinal fluid (CSF) barrier. Epithelial cells were dissociated from choroidal tissue by pronase digestion and cultured in standard DMEM culture media supplemented with 10% fetal bovine serum and 10 ng epithelial growth factor per ml. The procedure yielded 2-5 x 10(4) cells from pooled plexuses of three to four rats, and a viability of 77-85%. The cultures displayed a dominant polygonal type of epithelial cells, with a population doubling time of 2-3 d. The cultures were of distinct choroidal epithelial origins. For example, immunocytochemical studies using monospecific rabbit anti-rat TTR polyclonal antibody revealed a strong positive stain of transthyretin (TTR), a thyroxine transport protein exclusively produced by the choroidal epithelia. Also, reverse-transcriptase polymerase chain reaction (PCR) confirmed the presence of specific TTR mRNA in the cultures. The cultures were further adapted to grow on a freely permeable membrane sandwiched between two culture chambers. The formation of an impermeable confluent monolayer occurred within 5 d after seeding and was verified by the presence of a steady electrical resistance across the membrane (80 +/- 10 ohm per cm2). The epithelial barriers appeared to actively transport [125I]-thyroxine from the basal to apical chamber. These results suggest that this primary cell culture system possesses typical choroidal epithelial characteristics and appears to be a suitable model for in vitro mechanistic investigations of blood-CSF barrier.

We are prospectively examining the relation between environmental lead exposure and pregnancy outcome in cohorts of women exposed to a wide range of air lead concentrations. Titova Mitrovica, Yugoslavia, is the site of a large lead smelter, refinery, and battery factory. At midpregnancy, 602 women in T. Mitrovica and 900 women in Pristina, a non-lead-exposed control town, were interviewed. Blood was obtained for blood lead (PbB), hemoglobin, erythrocyte protoporphyrin, and serum ferritin measurements. Women were seen again at delivery, at which time maternal and umbilical cord blood samples were obtained. While many demographic and social characteristics were similar across the two towns, women in Pristina were more likely to report employment outside the home, cigarette smoking, and alcohol use during pregnancy. As expected, PbB levels were substantially higher in the smelter town. At midpregnancy, PbB geometric means were 17.1 micrograms/dL in T. Mitrovica and 5.1 micrograms/dL in Pristina; 86% of the pregnant women in T. Mitrovica, compared to 3.4% of those in Pristina, had PbB levels greater than 10 micrograms/dL. Within T. Mitrovica, distance between the home and the smelter was the most important predictor of PbB at mid-pregnancy and delivery. Husband's employment in the lead industry was associated with a significant increase in maternal PbB levels independent of place of residence. Higher maternal serum ferritin concentrations were associated with lower PbB levels, suggesting that dietary iron inhibits lead absorption. Overall, the placenta was a poor barrier to lead; the relationship between maternal PbB and umbilical cord PbB was linear across a wide range of PbB levels.

In an attempt to understand the variability of the hematologic response to oral sodium cyanate, iron metabolism was studied in a group of 39 patients with sickel cell disease. Eleven of the 39 patients were found to have no stainable iron in the marrow despite the fact that patients with sickle cell disease are generally considered to have hemosiderosis. The mean per cent saturation and total iron-binding capacity were in the low-normal range in sickle cell patients whether or not stainable iron was present in the bone marrow aspirate. Serum ferritin concentrations, on the other hand, were found to be high in both groups (greater than 500 mu g/liter) when compared to controls (60 mu g/liter). The high serum ferritin levels denoted significant total-body iron deposition which may be unavailable for normal metabolic processes. One patient with no stainable iron in the bone marrow aspirate did respond to iron therapy alone with an increase in hemoglobin concentration. Serum ceruloplasmin levels were also found to be high in sickle cell disease patients. The ability to respond to oral cyanate therapy was correlated with the amount of stainable iron in the bone marrow aspirate. These studies emphasize the necessity of a reevaluation of iron metabolism in the pathophysiology and treatment of sickle cell disease.

The relationships among hemoglobin concentration (Hb), red cell 2,3-diphosphoglycerate (2,3-DPG), and p50 were studied in 20 chronically hypertransfused patients with thalassemia major. In the nontransfused control group, which included normal individuals as well as patients with sickle cell disease or iron deficiency anemia, the Hb correlated inversely with both 2,3-DPG concentration and p50, as is well established. In contrast, however, prior to transfusion, at the nadir of Hb, patients with thalassemia major had inappropriately low 2,3-DPG concentrations and p50s. These findings occurred in all patients, regardless of whether they had received packed, leukocyte-poor, or frozen-thawed red cells. The hypothesis that the time of blood storage was a factor was excluded by repeatedly transfusing one patient with packed red cells administered within 4 hr of collection in CPDA-1. A second hypothesis, that red cell function might be impaired by the iron-overloaded thalassemic environment, was excluded by studying a newly diagnosed, newly transfused patient with aplastic anemia. In both cases, the same inability to appropriately increase 2,3-DPG and p50 as the Hb fell during the intertransfusion interval was noticed. These data suggest that red cells of chronically transfused patients are unable to adapt to the decline in Hb that occurs during the intertransfusion interval.

Our previous cross-sectional study of patients with thalassemia major suggested progressive lung changes characterized by low total lung capacity, hypoxemia, and elevated transfer factor for carbon monoxide. We reevaluated nine of the patients for three reasons: to determine the relationship of the previous findings to the immediate effects of blood transfusion; to assess the longitudinal progression of the lung changes; and to evaluate the effect of splenectomy on lung volume changes in these patients, all of whom underwent splenectomy in the interval between the two studies. We found that during the 5- to 6-yr period between studies total lung capacity had decreased significantly (p less than 0.05) from a mean 86% predicted to a mean 79% predicted. However, vital capacity increased significantly (p less than 0.05) from a mean 81% predicted to 88% with no significant change in functional residual capacity. There was no significant immediate effect of transfusion on total lung capacity, vital capacity, or functional residual capacity. However, the diffusion constant for carbon monoxide increased significantly (p less than 0.005) immediately following transfusion and there was a positive correlation between the increase and the amount of blood transfused (r = 0.74, p less than 0.05). Arterial oxygen saturation was below 95% in five of eight patients and increased significantly with transfusion (p less than 0.05). We conclude: 1) thalassemia major and/or its treatment is associated with hypoxemia and a progressive reduction in total lung capacity. 2) Despite the progressive reduction in total lung capacity, splenectomy in patients with thalassemia major increases expiratory reserve volume and thereby increases vital capacity.

We have developed a rapid and simple method for the isolation of relatively young cells from ordinary fresh or previously frozen blood units, using the IBM-2991 Blood Cell Processor. Based on in vitro measurements of red cell pyruvate kinase activity, the resolution of the method is excellent, comparable to that of the stractan discontinuous gradient system. In splenectomized patients with thalassemia major, the administration of the "youngest" 50% of blood units yielded 51Cr survival times of 40 and 42 days for fresh packed red cells and 41 and 43 days for previously frozen red cells.