Impaired Heme Research Articles

Heme synthesis in sideroblastic anaemias.

The underlying biochemical abnormalities common to all forms of sideroblastic anaemia appear to be associated with impaired heme synthesis in erythroid precursors. Present knowledge on the specific enzymatic defects of heme synthesis, which are thought to be the basis for the ring sideroblast abnormality, is presented in this review. Different forms of sideroblastic anaemia have different enzyme defects, but some of them might be secondary due to inhibition by mitochondrial iron overload. Some drugs and toxins may suppress heme synthesis and cause a reversible sideroblastic anaemia. Recent experimental studies have also provided detailed biochemical explanations for cases responding to pyridoxine therapy. Leukaemic transformation, which occurs in some cases of idiopathic sideroblastic anaemia, is not predictable on the basis of any abnormality of heme synthesis, but further impairment of heme synthesis seems to accompany the leukaemic development in such patients. So far, no association between the chromosomal aberrations and the defects of heme synthetic enzymes has been found.

Coproporphyrinogen oxidase activity and porphyrin concentrations in peripheral red blood cells in hereditary sideroblastic anaemia.

The activity of coproporphyrinogen oxidase and the concentrations of coproporphyrin and protoporphyrin (measured by HPLC) in peripheral red blood cells were established in 2 families with different types of hereditary sideroblastic anaemia. 2 males and 4 females were members of a family with an X-chromosome-linked and pyridoxine-responsive HSA, and 3 females were members of another family where the mode of inheritance is not clear and where pyridoxine did not produce a haematological response. Coproporphyrinogen oxidase activity was normal in 8 of 9 patients and slightly decreased only in 1 patient. All patients had normal red cell coproporphyrin concentrations, but red cell protoporphyrin concentration was decreased in 4 patients. These findings indicate that in vivo haem synthesis was not impaired at the step of coproporphyrinogen oxidase, hence enzymatic defects in earlier steps of haem synthesis are more evident. Earlier suggestions of impaired haem synthesis at this level, based on observed increased concentrations of coproporphyrin in peripheral red blood cells might be explained by the use of unspecific methods.

The effect of iron substrate on mitochondrial haem synthesis in copper deficiency.

Studies of iron utilization and haem synthesis were carried out with hepatic mitochondria obtained from copper-deficient and pair-fed control rats. Ferric chloride can be used as Fe substrate for mitochondrial haem synthesis in the presence of succinate. Utilization is further enhanced by the addition of FMN. Ferritin does not support haem synthesis in the presence of succinate alone, but does support haem synthesis when FMN is added. Mitochondrial haem synthesis is impaired in Cu deficiency when either FeCl3 or homologous ferritin is used as Fe substrate. The results of the present study suggest that impaired haem synthesis in Cu deficiency occurs at a step following the chemical reduction of Fe substrate.

Pregnancy in the marfan syndrome.

The early stages of many neurodegenerative diseases and age-related degeneration are characterized by neurite damage and compromised synaptic function that precede neuronal cell death. We investigated the signaling mechanisms underlying neurite degeneration using cortical neuron cultures. Inhibition of heme synthesis caused neurite damage, without neuronal death, and was mediated by reduced NMDA receptor (NMDAR) expression and phosphorylation. The signaling toward the degenerative phenotype involved suppression of the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway, and electrophysiological recording showed that the neurodegeneration is accompanied by reduced NMDAR current and Ca²⁺ influx, as well as reduced voltage-gated sodium currents, consistent with compromised neurite integrity. Rescue from the degenerative phenotype by heme replacement was dependent on restoration of NR2B subunit phosphorylation and expression of NMDAR currents with higher Ca²⁺ permeability, consistent with triggering prosurvival ERK1/2 signaling to maintain and extend neurites. This study demonstrated a new mechanism of neurodegeneration in which impaired heme synthesis led to NMDAR signaling dysfunction, suppression of the prosurvival ERK1/2 pathway, and progressive fragmentation of neuronal projections.

Fluorescence Methods in the Diagnosis and Management of Diseases of Tetrapyrrole Metabolism

Under appropriate conditions fluorescent porphyrins and bilirubin present in blood and other body fluids can be examined spectrofluorometrically without prior extraction. Uses of such direct fluorescence spectroscopy of porphyrins and bilirubin in studies and diagnoses of diseases associated with abnormal or impaired heme synthesis and metabolism are reviewed. The method of "front-face" fluorometry which allows quantitative assays of fluorescent porphyrins and bilirubin in small undiluted blood specimens is described.

Vitamin B6 metabolism in idiopathic sideroblastic anaemia and related disorders.

Patients with idiopathic anaemias associated with abnormal sideroblasts were defined according to morphologic and ferrokinetic criteria and the haematologic and biochemical effects of vitamin B6 therapy were evaluated. While all patients presented similar clinical pictures, peripheral blood changes and bone marrow abnormalities, two distinct groups were identified by sideroblast morphology and ferrokinetics. Patients with more than 5% true ring sideroblasts in the marrow (IRSA) uniformly had marked ineffective erythropoiesis, while those with abnormal sideroblasts but few true ring forms were hypoproliferative. Measurements of red cell pyridoxine kinase (PnK) and intracellular pyridoxal 5-phosphate availability (PLP) as assessed by the activity of the PLP-dependent enzyme asparate aminotransferase (EGOT), revealed slightly decreased PnK levels in IRSA subjects but normal intracellular PLP activities in both groups. Furthermore, when treated with pyridoxine, all patients showed increases in both red cell PnK and EGOT activities which were similar to those seen in normal subjects. Treatment with PLP also effectively increased erythrocyte vitamin B6 activity. Even so, neither pyridoxine nor intramuscular PLP improved erythropoiesis as determined by serial haematocrits, reticulocyte counts and erythron iron turnover measurements.However, since both therapies increased red cell protoporphyrin levels and the excretion of urinary coproporphyrin in a number of subjects, the possibility that impaired haem synthesis in the sideroblastic anaemias is associated with abnormal vitamin B6 metabolism at the level of the mitochondrion must still be considered.

Lead and cadmium absorption among children near a nonferrous metal plant: A follow-up study of a test case

During a first survey (1974) increased lead absorption accompanied by impaired heme biosynthesis was found among children (11 yr) attending schools situated at less than 1 km (subgroup A) and 2.5 km (subgroup B) from a lead smelter. Eighteen months after major improvements had been introduced in the factory to reduce its lead emission, a second survey (1976) was carried out in the same schools (lead smelter and rural area) on other groups of children which were comparable with those of the first survey. The continuous air monitoring revealed for the lead smelter area a considerable decrease in airborne lead. The median values dropped from 3.2 to 1.2 μg Pb/m 3 at less than 1 km and from 1.6 to 0.5–0.8 μg Pb/m 3 at 1.5 km from the plant; in the rural area it remained unchanged at 0.3 μg Pb/m 3. In order to evaluate the efficiency of the technological improvements we assessed the lead and cadmium exposure of the children by measuring lead concentration in blood (PbB) and urine (PbU), erythrocyte δ-aminolevulinic acid dehydratase (ALAD) activity, free erythrocyte porphyrin (FEP) concentration, δ-aminolevulinic acid excretion in urine (ALAU), and cadmium concentration in blood (CdB) and urine (CdU). Subgroups A and B exhibited higher PbB and CdU levels, and lower ALAD activity than the rural group; but PbU, CdB, FEP, and ALAD were significantly increased only in subgroup A. Compared with the results of the first survey, a significant tendency to a normalization of PbB was found at 2.5 km, but at less than 1 km the biological parameters (particularly PbB, ALAD, FEP) did not improve. The PbB percentile distribution in subgroup B lies now under the tentative PbB percentile distribution proposed in the PbB Directive of the Commission of the European Communities (CEC): that of subgroup A, however, is still above that of the CEC proposal. Taking into account the higher degree of vulnerability to lead exposure as compared to adults a more restrictive PbB percentile distribution has been proposed for children. Two hypotheses have been put forward to explain the lack of significant improvements in the biological parameters of the children living at less than 1 km from the lead smelter. Ingestion of dust and dirt (probably due to hand contamination) from their surroundings in the course of their normal everyday activity may represent, in addition to air, a supplementary cause of increased lead accumulation in these children. Indeed, dust and dirt samples collected on the school playgrounds at less than 1 km from the factory contained (mean ± SD) 3541 ± 1310 and 5466 ± 831 μg Pb/g, whereas at 2.5 km and in the rural area it only amounted to 397 ± 33 and 152 ± 41 μg Pb/g, respectively. The alternative explanation is that a continuous resuspension of dust and dirt particles from the highly contaminated soil around the lead smelter may maintain a very high airborne lead concentration at the breathing height of the children. In addition to a lasting reduction of lead emission from the plant, the remedial actions should also take into consideration these two possibilities.

Rapid Diagnosis of Iron Deficiency by Measurement of Free Erythrocyte Porphyrins and Hemoglobin: The FEP/Hemoglobin Ratio

The concentration of free erythrocyte prophyrins (FEP) and of hemoglobin can be measured on blood samples spotted on filter paper. The FEP/hemoglobin ratio in iron deficiency increases exponentially with a decrease of both transferrin saturation and hemoglobin level. The FEP/hemoglobin is an indicator of imparied heme synthesis. In small children an elevation of the FEP/hemoglobin ratio is a better indicator of iron-deficiency anemia than low transferrin saturation. The FEP/hemoglobin ratio is normal in thalassemia trait and renal anemia but it may be elevated in sickle-cell anemia. Measurement of FEP and hemoglobin on filter paper provides a useful diagnostic tool for the diagnosis of iron deficiency, of anemia, and (in populations at risk) of leas intoxication.

The ability of exogenous heme to restore globin synthesis in reticulocytes with impaired heme formation

The addition of isonicotinic acid hydrazide (INH) or cycloheximide decreases the incorporation of 75Se-methionine and 14C-labeled aminoacids into globin. 10 −4M hemin added to the incubation mixture removes the inhibition of globin synthesis caused by INH but is without effect on the synthesis of globin inhibited by cycloheximide.

Hemoglobin Gun Hill: An Unstable Protein Associated with Chronic Hemolysis

AbstractA new unstable hemoglobin variant, hemoglobin Gun Hill, is reported. Two members of a Caucasian family were found to be heterozygous for the abnormal hemoglobin. Evidence of mild chronic hemolysis was found in both individuals.Heinz-Ehrlich bodies were absent from the peripheral blood of the patients with hemoglobin Gun Hill, but Heinz-like inclusions were readily produced in their red cells upon in vitro incubation with the redox dyes brilliant cresyl blue or new methylene blue. Precipitation of hemoglobin occurred when solutions of hemoglobin Gun Hill were exposed to the dyes or were heated to 50 C. Previous studies have shown that there is a deletion of five amino acids in the β chains of hemoglobin Gun Hill. This results in impaired heme binding, and the abnormal molecule lacks half the expected number of heme groups. These structural alterations are probably responsible for the instability of the abnormal hemoglobin.Studies of the relative rates of synthesis of hemoglobins A and Gun Hill, using in vitro and in vivo technics, indicated an increased turnover rate for the variant protein. The evidence also suggested that hemoglobin Gun Hill is synthesized more rapidly than hemoglobin A.

Effect of Hæmin Supplementation on Porphyrin Accumulation and Catalase Synthesis during Anaerobic Growth of Staphylococcus

GROWTH of some facultatively anaerobic micro-organisms under anaerobic rather than aerobic conditions leads to an impaired synthesis of haem compounds1–3. This is accompanied by a large accumulation of coproporphyrin in cultures of Bacillus cereus1 and by a diminished synthesis of catalase in cells of Saccharomyces cerevisiae4. Previous work in this laboratory has revealed that Staphylococcus epidermidis also exhibits an impaired haem synthesis during anaerobic growth, which results in an inability to reduce nitrate under these conditions5,6. Results reported in this communication indicate that the accumulation of coproporphyrin and the decreased catalase synthesis which occur during anaerobic growth of one strain, of S. epidermidis are markedly affected by the addition of haemin to the growth medium.