An iron-regulated ferric reductase associated with the absorption of dietary iron.

The ability of intestinal mucosa to absorb dietary ferric iron is attributed to the presence of a brush-border membrane reductase activity that displays adaptive responses to iron status. We have isolated a complementary DNA, Dcytb (for duodenal cytochrome b), which encoded a putative plasma membrane di-heme protein in mouse duodenal mucosa. Dcytb shared between 45 and 50% similarity to the cytochrome b561 family of plasma membrane reductases, was highly expressed in the brush-border membrane of duodenal enterocytes, and induced ferric reductase activity when expressed in Xenopus oocytes and cultured cells. Duodenal expression levels of Dcytb messenger RNA and protein were regulated by changes in physiological modulators of iron absorption. Thus, Dcytb provides an important element in the iron absorption pathway.

CD44 as a Potential Screening Marker for Preliminary Differentiation Between Congenital Dyserythropoietic Anemia Type II and Hereditary Spherocytosis.

BACKGROUND: Bone marrow examination has been the confirmatory test for congenital dyserythropoietic anemia type II (CDAII). Occasional spherocytes on peripheral blood smear can confound the diagnosis. Since a screening test is still unavailable, we explored the feasibility of using flow cytometry as a preliminary screening method. METHODS: Thirteen monoclonal antibodies with specificities for eight erythrocyte membrane proteins were used in FACS analysis to probe the cellular features of red cells from CDAII, normal adults, hereditary spherocytosis (HS), and cord red cells. Confocal microscopy was performed on normal and CDAII to determine the overall distribution of CD44 and CD47. Their expression levels on cultured erythroblasts were also analyzed. RESULTS: The densely stained band 3 as seen in CDAII in gel electrophoresis was also obtained for Dantu phenotype. Likewise analysis of CDAII cases (n = 26) using the eosin-5'maleimide (EMA) binding test found 57% of patients giving results either positive or in the grey area for HS. Enhanced fluorescence of CD44 was detected in 96% of the CDAII patients, and anti-CD47 binding was also elevated to a lesser degree. Although RNA expressions of CD44 and CD47 in the cultured erythroblasts of normal controls and CDAII were similar, confocal microscopy revealed more CDAII red cells giving elevated fluorescence than normal red cells. CONCLUSIONS: A distinction between CDAII and HS can be made using the EMA Binding test and anti-CD44 binding. Confirmation of CDAII can subsequently be made based on clinical presentation together with either bone marrow examination or DNA sequencing of SEC23B. © 2016 International Clinical Cytometry Society.

Conformational analysis of pentapeptide sequences matching a proposed recognition motif for lysosomal degradation.

A selective pathway for the degradation of specific long-lived cytosolic proteins is activated in response to starvation in vivo or to serum withdrawal from cultured cells. It involves recognition of a targeting motif by a member of the hsp70 family. A 5-residue targeting motif has been proposed on the basis of sequence comparisons. We investigate whether there is any structural basis for this motif being the true recognition signal. We examine the conformations of four motif peptides in proteins that are either known to be serum regulated or are from related vertebrate species, and two equivalent peptides in bacterial proteins that closely resemble other regulated proteins. Our studies show that all the motif sequences are located near the ends of surface helices with one or more of the residues buried in the structure, yet it is known that members of the hsp70 family tend to interact with extended peptide chains. Furthermore, recognition by these proteins generally requires a specific ordering of key residues, yet the motif implies a largely order-independent sequence characterized by residue type only. We conclude that the proposed motif is unlikely to be the true targeting signal for lysosomal degradation unless additional factors apply.

Relationship between duodenal cytosolic aconitase activity and iron status in the mouse.

Cytosolic aconitase activity was assayed in duodenal mucosa from mice subjected to a variety of manipulations known to modulate duodenal iron status and duodenal iron absorption. No changes in cytosolic aconitase activity were observed 1 h after oral FeSO4 dosing or intramuscular desferrioxamine treatment. Three days of hypoxic exposure and two weeks treatment with intramuscular iron dextran also had no effect on cytosolic aconitase. Three weeks growth on an iron deficient diet significantly reduced cytosolic aconitase activity. In no situation was there any evidence for significant amounts of inactive aconitase which could be activated in vitro with FeSO4/cysteine. These data suggest that duodenal cytosolic aconitase is not sensitive to acute changes in mucosal iron levels and is generally much less sensitive to body iron status than is duodenal iron absorption. There is evidence that chronic iron depletion reduces cytosolic aconitase to a relatively small degree but generally activity is maintained, consistent with an important metabolic role for the enzyme.

Biochemical studies of the iron cores and polypeptide shells of haemosiderin isolated from patients with primary or secondary haemochromatosis.

Haemosiderin isolated from different iron-loading syndromes, primary haemochromatosis (PHC) and secondary haemochromatosis (SHC) biochemically exhibited differences in both their iron core and peptide composition. The rate of release of iron from PHC haemosiderin to oxalate was 3-fold greater than that from SHC haemosiderin. The major peptides separated by SDS-PAGE showed a major band at Mr 20,000 for PHC haemosiderin and at Mr 15,000 for SHC haemosiderin.

Plasma immunoreactive beta-melanocyte-stimulating hormone in chronic liver disease and fulminant hepatic failure.

Hyperpigmentation believed to be due to melanin, is a feature of chronic liver disease, especially primary biliary cirrhosis and hemochromatosis. Normal plasma concentrations of immunoreactive beta-melanocyte-stimulating hormone (beta-MSH) have been found in both these conditions; thus elevation of plasma beta-MSH plays no role in the pathogenesis of hepatic pigmentation. Normal levels are also found in hepatocellular failure, which supports the hypothesis that the kidney and not the liver is the site of metabolism of this hormone.

Hypogonadism and sexual dysfunction in hemochromatosis: the effects of cirrhosis and diabetes.

The contribution of diabetes and cirrhosis to sexual dysfunction and hypogonadism was evaluated by two-way analysis of variance in a group of 30 men with idiopathic hemochromatosis. The prevalence of severe sexual dysfunction was significantly higher in men with hemochromatosis than in a control group matched for prevalence of diabetes and age (P less than 0.001). In both controls and hemochromatosis patients the presence of diabetes was significantly associated with sexual dysfunction (P less than 0.005), but the more severe symptoms in the hemochromatosis patients were related to the additive effects of hypoandrogenism (P less than 0.01). Sexual dysfunction was a common early complaint in hemochromatosis patients, but these symptoms were frequently overlooked, leading to diagnostic delay. Mean testicular volume was a useful measure of gonadal status, being significantly correlated with indices of serum free testosterone (rs = 0.83; P less than 0.01) and LH (rs = 0.71; P less than 0.001). The presence of cirrhosis did not contribute significantly to symptomatology, but had an effect independent of and additive to hypogonadotropic hypogonadism in reducing serum free testosterone (P less than 0.02) and estradiol (P less than 0.002), an effect apparently mediated through central rather than testicular mechanisms. Hypoandrogenism was associated with an increase in serum sex hormone-binding globulin (SHBG) concentrations (P less than 0.005), but cirrhosis also had an independent effect in raising SHBG (P less than 0.005), which could not be accounted for by changes in circulating sex hormone concentrations. Thus, the evaluation of sexual dysfunction or hypogonadism in men with hemochromatosis requires consideration of the effects of both diabetes and cirrhosis. Because of the greater variance in SHBG some estimate of free testosterone rather than total testosterone is preferable.

A 6p22 reference map of leukocyte DNA: exclusion of rearrangement in four cases of atypical haemochromatosis.

We describe a 4 Mb reference map of the haemochromatosis gene region in leukocyte DNA from seven controls and four atypical haemochromatosis patients. Three patients had normal coding sequence for HFE, the candidate gene for genetic haemochromatosis (GH). The fourth patient had classical GH but was heterozygous for Cys282Tyr with otherwise normal coding sequence. The genomic DNA was mapped by pulsed-field gel electrophoresis (PFGE) using five rare-cutting enzymes. Seventeen probes including HFE were positioned on the map. Despite proximity to the highly polymorphic major histocompatibility complex (MHC), no polymorphism was observed in the control group with these telomeric probes. Furthermore, major rearrangement of the HFE region was excluded as a mutation contributing to iron overload in these atypical patients. Maps of cloned DNA are linked through genes and other probes to this reference map of the HFE region in uncloned genomic DNA.

Bleomycin-detectable iron in serum from leukaemic patients before and after chemotherapy. Therapeutic implications for treatment with oxidant-generating drugs.

Patients with acute myeloid leukaemia show elevated plasma iron and, in 2/6 cases studied, low-molecular-mass iron complexes capable of stimulating radical reactions were present in the plasma. Shortly after the onset of chemotherapy, there is a sharp rise in transferrin saturation and all patients studied showed low-molecular-mass iron in their plasma. It is proposed that such iron could interact with oxidants generated by certain drugs (e.g. adriamycin or daunorubicin) to facilitate tissue damage, and that some of the side-effects of chemotherapy might be ameliorated by careful co-administration of small doses of desferrioxamine.

Wash off liver cytology: a complementary diagnostic tool to liver biopsy.

Parenchymal and non-parenchymal cells were harvested by washing the liver tissue core and needle after percutaneous biopsy. The cytological material obtained was suitable for morphological analysis, including showing the presence of surface and cytoplasmic antigens using labelled antibody techniques. This technique provides a combined cytological and histological approach to the diagnosis of liver disease.

Metal ions catalytic for free radical reactions in the plasma of patients with fulminant hepatic failure.

We propose that the frequency and severity of multi-organ failure (MOF) in fulminant hepatic failure (FHF) involves free radical damage caused by the presence of circulating iron and copper ions, catalytic for free radical reactions. The presence of such metal ions is demonstrated by using the sensitive bleomycin and phenanthroline assays. Antioxidant therapy, e.g., using chelating agents that prevent metal ions from stimulating free radical reactions, may have benefit in the treatment of FHF and its consequences.

Hepatocellular carcinoma arising in the absence of cirrhosis in genetic haemochromatosis: three case reports and review of literature.

Genetic haemochromatosis constitutes a high risk factor for the development of hepatocellular carcinoma. It is widely accepted that venesection prevents the evolution of cirrhosis in haemochromatosis and indirectly protects against the development of hepatocellular carcinoma. Clinical, pathological and radiological data are presented on three patients who did not conform to the 'siderosis-cirrhosis-carcinoma' sequence and in whom prompt and adequate iron depletion did not prevent the development of cancer. This is the first report of hepatocellular carcinoma intervening in non-cirrhotic liver in two siblings with genetic haemochromatosis. The current literature on the subject is reviewed. The direct oncogenic role of iron remains to be elucidated. Hepatocellular carcinoma should be considered as a differential diagnosis in patients with non-cirrhotic genetic haemochromatosis who present with clinical deterioration during the course of an otherwise uneventful venesection programme.

The iron-chelating potential of silybin in patients with hereditary haemochromatosis.

Milk thistle contains silybin, which is a potential iron chelator. We aimed to determine whether silybin reduced iron absorption in patients with hereditary haemochromatosis. In this crossover study, on three separate occasions, 10 patients who were homozygous for the C282Y mutation in the HFE gene (and fully treated) consumed a vegetarian meal containing 13.9 mg iron with: 200 ml water; 200 ml water and 140 mg silybin (Legalon Forte); or 200 ml tea. Blood was drawn once before, then 0.5, 1, 2, 3 and 4 h after the meal. Consumption of silybin with a meal resulted in a reduction in the postprandial increase in serum iron (AUC±s.e.) compared with water (silybin 1726.6±346.8 versus water 2988.8±167; P<0.05) and tea (silybin 1726.6±346.8 versus tea 2099.3±223.3; P<0.05). In conclusion, silybin has the potential to reduce iron absorption, and this deserves further investigation, as silybin could be an adjunct in the treatment of haemochromatosis.

Chelation of transferrin iron by desferrioxamine in K562 cells. The partition of iron between ferrioxamine and ferritin.

In this study we have determined whether desferrioxamine can chelate iron delivered to human leukaemic cells by the transferrin endocytic cycle. The cellular uptake of desferrioxamine was investigated by an indirect method in which the conversion of repeated pulses of [59Fe]transferrin to [59Fe]ferrioxamine was determined at two concentrations of the drug. Maximum generation of [59Fe]ferrioxamine occurred in cells exposed to either 100 microM- or 500 microM-desferrioxamine after 40-60 min. Thereafter (up to 180 min) [59Fe]ferrioxamine levels remained steady with 20% of a 59Fe pulse partitioning to chelator at 100 microM and 50% at 500 microM. Of the cellular [59Fe]ferrioxamine loss 50% occurred within 90-120 min. In cells preloaded with desferrioxamine for 1 or 4 h the partitioning of iron during a 3 h incubation with [59Fe]transferrin was dependent upon the extracellular concentration of the chelator. Above 1 mM more than 80% of entering iron was converted to ferrioxamine and less than 5% partitioned to ferritin. Below this concentration (50-500 microM) a proportion of the iron became ferritin associated (7-41%). There was a linear increase in the total amount of intracellular [59Fe]ferrioxamine in accordance with cellular iron uptake showing that transferrin continued to cycle in the presence of high concentrations of desferrioxamine. The uptake of iron and generation of ferrioxamine were markedly reduced by 5 mM-methylamine, which prevented endosome acidification and uncoupling of iron from endocytosed transferrin.

Ferritin iron kinetics and protein turnover in K562 cells.

The binding, incorporation, and release of iron by ferritin were investigated in K562 cells using both pulse-chase and long term decay studies with 59Fe-transferrin as the labeled iron source. After a 20-min pulse of labeled transferrin, 60% of the 59Fe was bound by ferritin with the proportion increasing to 70% by 4 h. This initial binding was reduced to 35% when the cells were exposed to the chelator desferrioxamine (5 mM) for an additional 30 min. By 4 h the association of 59Fe with ferritin was unaffected by the presence of the chelator, and levels of 59Fe-ferritin were identical to those in control cells (70%). Between 4-10h there was a parallel decline in 59Fe-ferritin in both control and desferrioxamine-treated cells. When incoming iron was bound by ferritin it was, therefore, initially chelatable but with time progressed to a further, nonchelatable compartment. In turnover studies where ferritin was preloaded with 59Fe by overnight incubation, 50% of the label was released from the protein by 18 h, contrasting with a t 1/2 for cellular iron release of approximately 70 h. The half-time of 59Fe release from ferritin was accelerated to 11 h by the presence of desferrioxamine. The half-time for ferritin protein turnover determined by [35S]methionine labeling was approximately 12 h in the presence or absence of the chelator. Thus, when the reassociation of iron with ferritin was prevented by the exogenous chelator there was a concordant decay of both protein and iron moieties. The direct involvement of lysosomes in this turnover was demonstrated by the use of the inhibitors leupeptin and methylamine which stabilized both 59Fe (t 1/2 = 24 h) and 35S (t 1/2 = 25.6 h) labels. We conclude that in this cell type the predominant mechanism by which iron is released from ferritin is through the constitutive degradation of the protein by lysosomes.

Long term results of venesection therapy in idiopathic haemochromatosis.

Observations on the clinical effects of venesection therapy in 85 treated, as compared with 26 untreated, patients with idiopathic haemochromatosis showed decreased pigmentation and hepatomegaly together with a return to normal tests of liver function in half the patients who had abnormal tests at presentation. Control improved in 28 per cent of those patients with diabetes mellitus, although some patients developed it during the period of observation, despite venesection. Portal hypertension, testicular atrophy and arthropathy were not improved. In only 12 patients was there sufficient reaccumulation of iron after the initial course of venesection to merit further treatment. Rates of iron accumulation in these patients varied between 1-4 mg and 4-8 mg per day and chelatable iron levels were noted to be inappropriately high in relation to body iron stores during the early stages of the reaccumulation period. Life table data shows that the percentage survival five and ten years after diagnosis was 66 and 32 per cent respectively for the treated patients, and 18 and 6 per cent respectively for the untreated patients, both statistically highly significant differences (p less than 0-01). Possible clinical differences such as age of presentation, the presence of diabetes mellitus, cirrhosis, clinical hepatic failure and hepatoma between the treated and untreated groups that might otherwise have weighted survival in favour of the treated group were corrected by the use of covariant analysis. This gave mean log survival values of 4-15 and 2-88 for the treated and untreated patients respectively, equivalent to 63-4 months and 17-8 months, a highly significant difference (p less than 0-01). Ten patients, all of whom had cirrhosis at the time of diagnosis, died of malignant hepatoma between three and 15 years after completing venesection therapy. There was also a high rate of death from neoplasms in a variety of other sites--22 per cent in the venesected group, strikingly higher than that rate predicted for a similarly aged population using national cancer mortality rates.

A novel binding site for the native hepatic acute-phase protein alpha1-antitrypsin expressed on the human hepatoma cell line HepG 2 and intestinal cell line Caco 2.

AIMS/BACKGROUND: alpha1-antitrypsin (alpha1-AT) is a hepatic acute phase protein which predominantly inhibits neutrophil elastase. Besides this major function, we have also previously shown that alpha1-AT markedly increased H-ferritin mRNA expression and ferritin synthesis in the human hepatoma cell line HepG 2. These actions suggest that alpha1-AT might interact with HepG 2 cells via a specific cell surface binding site. METHODS AND RESULTS: Using radio-labelled native alpha1-AT, we observed saturable binding to HepG 2 cells with a dissociation constant (Kd) of 63.3+/-6.9 nM and a maximal density of binding sites (Bmax) of 0.34+/-0.05 pmol/10(6) cells equivalent to 195,800+/-29,200 sites/cell. The binding of [125I]alpha1-AT was time dependent with a calculated association rate constant of 9.22+/-1.84x10(4)xM(-1)xmin(-1). Binding was highly specific since other acute phase proteins or protease inhibitors failed to block binding. Although alpha1-AT-trypsin, alpha1-AT-elastase and the pentapeptide FVYLI, the minimal binding sequence for the SEC receptor, increased [125I]alpha1-AT binding, in long term experiments these complexes failed to influence the number of alpha1-AT binding sites. Specific, saturable binding of [125I]alpha1-AT was also found on the human intestinal epithelial Caco 2 cells, but not on fibroblast or leukaemic cell lines. CONCLUSION: These experiments demonstrate a specific, high affinity binding site for native alpha1-AT on HepG 2 and Caco 2 cells, cell lines derived from tissues involved in the acute phase response.