Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0039730 (thalassemia)
 10,305 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Since 1996, the identification of the HFE gene has enabled DNA testing for hereditary haemochromatosis (HH). The range of DNA testing available includes: (1) diagnostic, (2) predictive (also called presymptomatic testing) and (3) screening. Access to DNA testing has been facilitated by an Australian Medicare rebate, the first available for genetic disorders. Despite the availability of HFE DNA testing in HH, it remains necessary to interpret results in the context of the clinical picture. Traditional markers based on phenotype (transferrin ferritinsaturation, and liver biopsy) are still required in some circumstances. We report our experience with HFE DNA testing using a semi-automated approach, which allows multiplexing for the two common mutations (C282Y and H63D). Screening a cohort of beta-thalassaemia major and sickle cell anaemia patients of predominantly Mediterranean origin showed that these individuals do not have the common C282Y mutation. This excluded C282Y as a factor in the pathogenesis of iron overload in these haemoglobinopathies. It also showed that the C282Y mutation is of limited value when investigating HH in certain ethnic groups. An Australian family studied illustrated the relative contribution of C282Y and H63D in iron overload. A recently reported third mutation (S65C) in the HFE gene was detected in a low frequency in the populations tested.
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PMID:DNA testing for haemochromatosis: diagnostic, predictive and screening implications. 1118 24

The expanding indications for transfusions in patients with sickle cell disease raise the issues of appropriate measurement of body iron burden and optimal timing of iron chelation therapy. In this study, we obtained 42 biopsy specimens from 20 patients with sickle cell disease (mean age, 15.7 years) who received transfusions. In 12 patients whose mean age was 11.3 years at the time of liver biopsy, hepatic iron concentration was measured to provide information about the rate of iron accumulation in sickle cell disease, as well as to guide the initiation of chelating therapy. Mean hepatic iron concentration after an average of 15.4 transfusions administered over 21 months was 9.4 +/- 1.2 mg/g liver, dry weight, which did not correlate significantly with determinations of serum transferrin or ferritin levels. On Initial liver biopsy, hepatic portal fibrosis was noted in 4 of 12 patients. Twenty-nine biopsies in 16 patients were performed after variable periods of treatment with deferoxamine. These 16 patients had received a mean of 38.5 transfusions over 4 years. Hepatic iron was 14.1 +/- 1.9 mg/g of liver, dry weight, Indicating poor control of body iron in many patients. Cirrhosis was reported in one of 29 and portal fibrosis in 10 biopsy specimens. Hepatic iron concentration in patients in whom fibrosis was observed varied from 8.9 to 37.7 mg/g of liver, dry weight. These data show that after 1 to 2 years of conventional transfusions, variable tissue iron concentrations and tissue damage are observed in patients with sickle cell disease. In some patients, iron chelation therapy may not be appropriate after 1 year of transfusions; in others, therapy is clearly indicated by this time to prevent tissue injury. The data also suggest that patients with sickle cell disease develop increased portal fibrosis at the thresholds previously described in young patients with thalassemia (approximately 7 mg/g of liver, dry weight).
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PMID:Progression of iron overload in sickle cell disease. 1120 62

Determination of the reticulocyte hemoglobin content (CHr) provides an early measure of functional iron deficiency because reticulocytes are the earliest erythrocytes released into blood and circulate for only 1 to 2 days. The CHr in 78 patients undergoing bone marrow examination was measured to assess its clinical utility for the diagnosis of iron deficiency. Twenty-eight patients were iron deficient, based on the lack of stainable iron in the aspirate. The diagnostic power of CHr is limited in patients with high mean cellular volume (MCV) or red cell disorders such as thalassemia. However, when patients with MCV more than 100 fL are excluded, receiver operator curve analysis of CHr, ferritin, transferrin saturation, and MCV demonstrates that CHr has the highest overall sensitivity and specificity of these peripheral blood tests for predicting the absence of bone marrow iron stores.
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PMID:Clinical utility of the reticulocyte hemoglobin content in the diagnosis of iron deficiency. 1248 40

Mycobacterium avium growth in cultured human macrophages is influenced by serum lipids, transferrin and iron levels. Iron-saturated transferrin enhances M. avium growth, whereas apotransferrin inhibits mycobacterial replication. The ability of iron chelators to mimic the effects of transferrin on intracellular and extracellular M. avium growth was examined. Smooth, transparent, AIDS patient derived M. avium 7497 scrovar 4 was used to infect 7-day cultured human macrophages. Growth was measured by determining the colony-forming units (CFU) after infected macrophages were lysed 0 to 7 days after infection. The new iron chelating drug deferiprone (1,2-dimethyl-3-hydroxypyrid-4-one or L1, CAS 30652-11-0), 1-ethyl-2-methyl-3-hydroxypyrid-4-one (L1NEt), 1-propyl-2-methyl-3-hydroxypyrid-4-one (L1NPr), 1-allyl-2-methyl-3-hyproxypyrid-4-one (L1NAll), and 3,4-dihydroxycinnamic acid enhanced intracellular and extracellular mycobacterial replication at concentrations of 0.1-2.5 micrograms/ml. 2-Pyridinecarboxaldehyde-2-quinolylhydrazone (PCQH) inhibited intracellular replication from 0.1-1.0 microgram/ml. Most, but not all of the PCQH-induced intracellular inhibition could be eliminated using iron at concentrations greater than 1.0 microgram/ml. Iron also suppressed the effects of PCQH on extracellular M. avium replication. These results indicate that iron chelators may have variable effects at different concentrations and can significantly alter both intracellular and extracellular M. avium replication. It is suggested that at low concentrations deferiprone and other aketohydroxypyridine chelators could enhance the growth of M. avium but at high concentrations may function as adjunct therapy with other antimicrobials against infections with M. avium. These findings are important for therapeutic considerations and dose protocol design in relation to the new iron chelating drug deferiprone, which is currently used in thalassaemia and other iron loaded patients, some of whom are suffering from AIDS.
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PMID:Effects on Mycobacterium avium replication in normal human macrophages by deferiprone (L1) and other iron chelators. Possible implications on toxicity. 1183 74

Eighty multi-transfused beta-thalassemics--40 of them on regular transfusion (RT) (every 3-4 weeks) and 40 irregularly transfused (IT)-and 20 age- and-sex-matched controls were evaluated for serum erythropoietin (sEpo) and soluble serum transferrin receptors (sTfr) as indicators of erythropoietic activity. All subjects were studied for pre-transfusion hemoglobin (Hb), reticulocytic index (RI), serum ferritin, sEpo and sTfr. Results showed that the mean RI, sEpo and sTfr values were significantly higher in the IT group (2.8; 80 mU/ml; and 19 microg/ml, respectively) compared to the RT group (1.2; 35.2 mU/ml; and 13.9 microg/ml, respectively) and controls (1.1; 22.6 mU/ml; and 7 microg/ml, respectively) (p < 0.05); while only the mean sTfr value was significantly higher in the RT group compared to controls. The mean pre-transfusion Hb was significantly lower in the IT group (8 g/dl) compared to both the RT group (9.3 g/dl) and controls (12.5 g/dl) (p < 0.05); while the RT group level was significantly lower than controls. There was an inverse correlation between Hb level on one hand and sEpo (r = 0.324,p < 0.05), sTfr (r = -0.651, p < 0.05) and RI (r = -0.451, p < 0.05) on the other. In summary, sEpo, sTfr and RI could be used as accurate and reliable indicators of successful erythroid marrow suppression and for the determination of optimal pre-transfusion Hb level in thalassemia on an individual basis, with sTfr being the most sensitive indicator.
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PMID:Evaluation of serum soluble transferrin receptors and erythropoietin levels as indicators for erythropoietic activity among multi-transfused beta-thalassemic patients. 1186 34

Iron, to be redox cycling active, has to be released from its macromolecular complexes (ferritin, transferrin, hemoproteins, etc.). Iron is released from hemoglobin or its derivatives in a nonprotein-bound, desferrioxamine-chelatable form (DCI) in a number of conditions in which the erythrocytes are subjected to oxidative stress. Such conditions can be related to toxicological events (haemolytic drugs) or to physiological situations (erythrocyte ageing, reproduced in a model of prolonged aerobic incubation), but can also result from more subtle circumstances in which a state of ischemia-reperfusion is imposed on erythrocytes (e.g., childbirth). The released iron could play a central role in oxidation of membrane proteins and senescent cell antigen (SCA) formation, one of the major pathways for erythrocyte removal. Iron chelators able to enter cells (such as ferrozine, quercetin, and fluor-benzoil-pyridoxal hydrazone) prevent both membrane protein oxidation and SCA formation. The increased release of iron observed in beta-thalassemia patients and newborns (particularly premature babies) suggests that fetal hemoglobin is more prone to release iron than adult hemoglobin. In newborns the release of iron in erythrocytes is correlated with plasma nonprotein-bound iron and may contribute to its appearance.
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PMID:Iron release, oxidative stress and erythrocyte ageing. 1190 91

Iron is an essential mineral for normal cellular physiology, but an excess can result in cell injury. Iron in low-molecular-weight forms may play a catalytic role in the initiation of free radical reactions. The resulting oxyradicals have the potential to damage cellular lipids, nucleic acids, proteins, and carbohydrates; the result is wide-ranging impairment in cellular function and integrity. The rate of free radical production must overwhelm the cytoprotective defenses of cells before injury occurs. There is substantial evidence that iron overload in experimental animals can result in oxidative damage to lipids in vivo, once the concentration of iron exceeds a threshold level. In the liver, this lipid peroxidation is associated with impairment of membrane-dependent functions of mitochondria and lysosomes. Iron overload impairs hepatic mitochondrial respiration primarily through a decrease in cytochrome C oxidase activity, and hepatocellular calcium homeostasis may be compromised through damage to mitochondrial and microsomal calcium sequestration. DNA has also been reported to be a target of iron-induced damage, and this may have consequences in regard to malignant transformation. Mitochondrial respiratory enzymes and plasma membrane enzymes such as sodium-potassium-adenosine triphosphatase (Na(+) + K(+)-ATPase) may be key targets of damage by non-transferrin-bound iron in cardiac myocytes. Levels of some antioxidants are decreased during iron overload, a finding suggestive of ongoing oxidative stress. Reduced cellular levels of ATP, lysosomal fragility, impaired cellular calcium homeostasis, and damage to DNA all may contribute to cellular injury in iron overload. Evidence is accumulating that free-radical production is increased in patients with iron overload. Iron-loaded patients have elevated plasma levels of thiobarbituric acid reactants and increased hepatic levels of aldehyde-protein adducts, indicating lipid peroxidation. Hepatic DNA of iron-loaded patients shows evidence of damage, including mutations of the tumor suppressor gene p53. Although phlebotomy therapy is effective in removing excess iron in hereditary hemochromatosis, chelation therapy is required in the treatment of many patients who have combined secondary and transfusional iron overload due to disorders in erythropoiesis. In patients with beta-thalassemia who undergo regular transfusions, deferoxamine treatment has been shown to be effective in preventing iron-induced tissue injury and in prolonging life expectancy. The use of the oral chelator deferiprone remains controversial, and work is continuing on the development of new orally effective iron chelators.
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PMID:Iron toxicity and chelation therapy. 1241 32

Both desferrioxamine (DFO) and chloroquine can significantly reduce hepatic iron in experimental animals with iron overload by chelating iron from the low-molecular-weight pool or decreasing iron uptake by the transferrin-transferrin receptor cycle, respectively. However, no previous studies have investigated whether combination therapy of these two drugs would further decrease the tissue iron overload as well as iron-induced toxicity. Chloroquine administration, 15 mg/kg, 5x/week, to rats during the iron loading regime, 10 mg/kg, 3x/week for 4 weeks, significantly decreased both hepatic (54%) and macrophage iron content (24%). However when administered in combination with desferrioxamine, 10 mg/kg, 3x/week for 2 weeks at the cessation of iron loading, no further reduction of hepatic iron content was noted while the iron content of the macrophages significantly increased, possibly indicating the flux of ferrioxamine through these cells. Further studies are warranted to investigate the speciation of iron within these macrophages. Macrophages isolated from chloroquine-treated iron loaded rats showed a reduction in latent NFkappaB activation and a significant increase in lipopolysaccharide-stimulated nitrite release by comparison to these parameters in iron loaded macrophages. Co-administration of chloroquine and desferrioxamine normalised the latent activity of NFkappaB to that of control macrophages as well as increasing LPS-stimulated NO release towards control values. However, DFO alone did not have any significant effect upon either of these parameters. Such results may have important relevance for the reduced immune function of iron loaded macrophages isolated from thalassaemia patients receiving chelation therapy and their propensity to increased infection.
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PMID:Changes in function of iron-loaded alveolar macrophages after in vivo administration of desferrioxamine and/or chloroquine. 1262 Jun 71

Our understanding of how iron transverses the intestinal epithelium has improved greatly in recent years, although the mechanism by which body iron demands regulate this process remains poorly understood. By critically examining the earlier literature in this field and considering it in combination with recent advances we have formulated a model explaining how iron absorption could be regulated by body iron requirements. In particular, this analysis suggests that signals to alter absorption exert a direct effect on mature enterocytes rather than influencing the intestinal crypt cells. We propose that the liver plays a central role in the maintenance of iron homeostasis by regulating the expression of hepcidin in response to changes in the ratio of diferric transferrin in the circulation to the level of transferrin receptor 1. Such changes are detected by transferrin receptor 2 and the HFE/transferrin receptor 1 complex. Circulating hepcidin then directly influences the expression of Ireg1 in the mature villus enterocytes of the duodenum, thereby regulating iron absorption in response to body iron requirements. In this manner, the body can rapidly and appropriately respond to changes in iron demands by adjusting the release of iron from the duodenal enterocytes and, possibly, the macrophages of the reticuloendothelial system. This model can explain the regulation of iron absorption under normal conditions and also the inappropriate absorption seen in pathological states such as hemochromatosis and thalassemia.
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PMID:The orchestration of body iron intake: how and where do enterocytes receive their cues? 1273 47

Plasma non-transferrin-bound-iron (NTBI) is believed to be responsible for catalyzing the formation of reactive radicals in the circulation of iron overloaded subjects, resulting in accumulation of oxidation products. We assessed the redox active component of NTBI in the plasma of healthy and beta-thalassemic patients. The labile plasma iron (LPI) was determined with the fluorogenic dihydrorhodamine 123 by monitoring the generation of reactive radicals prompted by ascorbate but blocked by iron chelators. The assay was LPI specific since it was generated by physiologic concentrations of ascorbate, involved no sample manipulation, and was blocked by iron chelators that bind iron selectively. LPI, essentially absent from sera of healthy individuals, was present in those of beta-thalassemia patients at levels (1-16 microM) that correlated significantly with those of NTBI measured as mobilizer-dependent chelatable iron or desferrioxamine chelatable iron. Oral treatment of patients with deferiprone (L1) raised plasma NTBI due to iron mobilization but did not lead to LPI appearance, indicating that L1-chelated iron in plasma was not redox active. Moreover, oral L1 treatment eliminated LPI in patients. The approach enabled the assessment of LPI susceptibility to in vivo or in vitro chelation and the potential of LPI to cause tissue damage, as found in iron overload conditions.
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PMID:Labile plasma iron in iron overload: redox activity and susceptibility to chelation. 1280 56


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