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PubMed2006

Proteomic analysis of iron overload in human hepatoma cells.

Iron-mediated organ damage is common in patients with iron overload diseases, namely, hereditary hemochromatosis. Massive iron deposition in parenchymal organs, particularly in the liver, causes organ dysfunction, fibrosis, cirrhosis, and also hepatocellular carcinoma. To obtain deeper insight into the poorly understood and complex cellular response to iron overload and consequent oxidative stress, we studied iron overload in liver-derived HepG2 cells. Human hepatoma HepG2 cells were exposed to a high concentration of iron for 3 days, and protein expression changes initiated by the iron overload were studied by two-dimensional electrophoresis and mass spectrometry. From a total of 1,060 spots observed, 21 spots were differentially expressed by iron overload. We identified 19 of them; 11 identified proteins were upregulated, whereas 8 identified proteins showed a decline in response to iron overload. The differentially expressed proteins are involved in iron storage, stress response and protection against oxidative stress, protein folding, energy metabolism, gene expression, cell cycle regulation, and other processes. Many of these molecules have not been previously suggested to be involved in the response to iron overload and the consequent oxidative stress.

Aldehyde Dehydrogenase↗
PubMed2005

Hepatic expression of hemochromatosis genes in two mouse strains after phlebotomy and iron overload.

BACKGROUND AND OBJECTIVES: Iron homeostasis is tightly regulated in mammals according to the needs of erythropoiesis and the iron stores present. This regulation is disrupted in hereditary hemochromatosis (HH), a genetic disorder characterized by increased intestinal iron absorption, leading to iron overload. The genes coding for HFE, transferrin receptor 2 (TFR2), ferroportin (SLC40A1 or FPN1), hepcidin (HEPC) and hemojuvelin (HJV or RGMC) are responsible for different types of genetic iron overload. All these genes are highly expressed in the liver and their protein products are likely components of a single hepcidin-related pathway. In order to gain insights into the molecular relationship among the HH proteins we evaluated the hepatic expression of HH genes in conditions of iron restriction or overload. DESIGN AND METHODS: Data were obtained after phlebotomy, to activate the erythroid regulators and following parenteral iron dextran loading, to activate the store regulators, in two mice strains (C57BL/6 and DBA/2). HH genes and proteins expression were analyzed by quantitative real time polymerase chain reaction and by Western blotting, respectively. RESULTS: Hepc RNA was reduced after phlebotomy and increased in iron overload. A statistically significant reduction of hepatic Fpn1 RNA expression was observed after phlebotomy; this effect was more evident in the DBA/2 strain. Fpn1 increased in C57BL/6 mice, but not in the DBA/2 ones in parenteral iron loading. Fpn1 protein did not change substantially in either condition. Hfe, Rgmc and Tfr2 expression was not influenced by phlebotomy. In parenteral iron overload, Tfr2 gene and protein expression decreased concomitant to the increase in Hepc, while Hfe RNA remained constant. INTERPRETATION AND CONCLUSIONS: Our results indicate that regulation of hepatic Fpn1 differs from that reported for duodenal Fpn1. Furthermore, taken the differences in gene expression in dietary overload (increased Hfe but not Tfr2), distinct roles are suggested for Hfe and Tfr2 in Hepc activation.

Animals↗
PubMed2002

Hereditary haemochromatosis: a realistic approach to prevention of iron overload disease in the population.

Iron overload in body tissues can cause complications such as cirrhosis, cardiomyopathy, diabetes, hypogonadism and arthritis. In populations of northern European descent, most iron overload is due to hereditary haemochromatosis (HHC), a genetic condition that causes increased iron absorption. HHC can be treated or prevented by regular phlebotomy treatments. Some experts have called for population screening for HHC, so that early phlebotomy treatment can be initiated. Two screening tests are available: measurement of the serum iron transferrin saturation (Tf%) and genetic testing for HFE mutations. However, both methods have low positive predictive values. Current data suggest that most people at risk are unlikely to develop clinical symptoms and that the population prevalence of clinical complications of HHC is low, arguing against population screening. Two other prevention strategies are available. (1) Health provider education, to heighten awareness of HHC as an explanation for symptoms and signs seen in early iron overload including unexplained fatigue, joint pain, palpitations, abdominal pain, elevated liver function tests, hepatomegaly and elevated serum ferritin. (2) Family-based testing after a diagnosis of HHC, to ensure that relatives are evaluated for evidence of iron overload. More research is also needed to identify the factors that increase risk for disease in persons with excess iron uptake, to determine whether moderate iron overload is a health risk and to evaluate the causes of iron overload other than HHC.

Family Health↗
PubMed2001

Expression of the duodenal iron transporters divalent-metal transporter 1 and ferroportin 1 in iron deficiency and iron overload.

BACKGROUND & AIMS: Imbalances of iron homeostasis are accompanied by alterations of intestinal iron absorption. The identification of divalent-metal transporter 1 (DMT1) and ferroportin 1 (FP1) has improved our understanding of transmembrane iron trafficking. To gain insight into the regulatory properties of these transporters in the duodenum, we studied their expression in patients with hereditary hemochromatosis (HFE-associated and non-HFE-associated), secondary iron overload, and iron deficiency. METHODS: DMT1, FP1 messenger RNA (mRNA), and protein expression were analyzed in duodenal biopsy specimens from patients by means of TaqMan real-time polymerase chain reaction, Western blotting technique, and immunohistochemistry. RESULTS: DMT1 and FP1 mRNA levels are positively correlated with each other in all patient groups (P < 0.001). Moreover, DMT1 and FP1 mRNA levels were significantly increased in patients with iron deficiency, HFE and non-HFE hemochromatosis, whereas they were unchanged in patients with secondary iron overload. Alterations in DMT1 and FP1 mRNA levels were paralleled by comparable changes in the duodenal expression of these proteins. In patients with normal iron status or iron deficiency, significant negative correlations between DMT1, FP1 mRNA, and serum iron parameters were found, which were absent in subjects with primary hemochromatosis. CONCLUSIONS: DMT1 and FP1 are centrally involved in iron uptake/transfer in the duodenum and in the adaptive changes of iron homeostasis to iron deficiency and overload.

Adult↗
PubMed2000

Characterization of hepatic iron overload following dietary administration of dicyclopentadienyl iron (Ferrocene) to mice: cellular, biochemical, and molecular aspects.

A unique organic form of iron (dicyclopentadienyl iron; ferrocene) has been used to further elucidate specific hepatic histopathologic, biochemical, and molecular parameters associated with dietary iron overload. Male C57BL/6Ibg mice fed a diet containing 0.04-0.2% w/w ferrocene for 115 days displayed severe hepatic siderosis of hepatocytes accompanied by a 15-fold induction of nonheme iron content compared to control mice receiving a diet with normal amounts of iron. The ferrocene treatment led to significant increases in hepatocellular necrosis as measured by plasma alanine aminotransferase activity. Histological assessment of hepatic fibrosis revealed mild increases in collagen deposition localized with accumulations of hemosiderin primarily in centrilobular hepatocytes. Hepatic fibrosis was confirmed by measurement of hepatic hydroxyproline content that was increased 4-fold in ferrocene-fed animals compared to control animals not ingesting ferrocene. Hepatic siderosis was accompanied by significant increases in hepatic malondialdehyde content suggesting the ferrocene-induced iron burden initiated lipid peroxidation in vivo. Expression of the heavy-chain isoform of ferritin mRNA and protein measured in liver after ferrocene feeding was increased approximately 8- and 2-fold, respectively, compared to the appropriate controls. These results, using an organic form of iron fed to genetically well-characterized inbred mice, provide new additional insight into the specific molecular and biochemical events that occur in association with histopathologic changes initiated by iron-induced liver injury. These data support the hypothesis that peroxidation of cellular membrane lipids is an important mechanism involved in the toxicity of excess hepatic iron and possibly the initiation of liver fibrogenesis. The results presented here also provide novel in vivo evidence documenting the cellular modulation of ferritin in response to the toxic effects of hepatic iron overloading and iron-mediated oxidative stress.

Alanine Transaminase↗
PubMed1995

HLA-linked hemochromatosis and other forms of iron overload.

Inherited forms of iron overload are common. HLA-linked hemochromatosis and possibly African iron overload are associated with a significant risk of developing hepatocellular carcinoma. Early diagnosis and treatment, before substantial iron overloading occurs, reduces morbidity and mortality. HLA-linked hemochromatosis is easily diagnosed, and routine screening in European-derived populations may be appropriate.

Africa↗
PubMedDate not supplied

Can defects in transferrin receptor 2 and hereditary hemochromatosis genes account for iron overload in HbH disease?

Iron overload was found to be the major cause of disability in Chinese HbH disease patients although they were not on regular blood transfusion. The transferrin receptor 2 (TFR2) and hereditary hemochromatosis (HFE) genes were examined to see if inheritance of these gene defects may be a possible cause of iron overload in 45 HbH patients. A novel intronic (IVS6 (+6) T-->A) mutation of the TFR2 gene was identified in one patient, and six others were found to carry a known missense mutation (exon 5, I238M) that was also present in one normal control subject. One HbH patient and one normal control carried the H63D mutation of the HFE gene. Since only eight out of 45 iron-overloaded HbH patients carry a defect in the TFR2 or HFE gene in the heterozygote state and their iron loading status was comparable to the matched controls without such defects, it would appear that the accumulation of excess iron in HbH disease is more likely a result of increase dietary absorption secondary to ineffective erythropoiesis.

Alleles↗
PubMed2002

[Mutations in the HFE gene (C282Y, H63D, S65C) in alcoholic patients with finding of iron overload].

INTRODUCTION: The pathogenesis of iron overload in alcoholic individuals is not fully elucidated. The frequency of mutations in hereditary hemochromatosis (HFE) is high in this population. Heterozygotes show data of iron overload similar to those in alcoholic individuals. OBJECTIVE: To analyze whether iron excess among alcoholic individuals is associated with mutations in C282Y, H63D or S65C in the HFE gene. Patients and methods. Thirty-two active alcoholic individuals (29 males and 3 females, age range 30-67 years) with data of iron overload (increased serum ferritin with or without saturation of increased transferrin) were studied. In all individuals, mutations C282Y, H63D and S65C were investigated. From 16 cases, liver histology was available. Data on iron overload were compared between patients with and without mutations. RESULTS: Twenty-two patients (68.8%) did not show any mutation, one (3.1%) was heterozygous for C282Y, three (9.4%) were homozygous for H63D, four (12.5%) were heterozygous for H63D, and two patients (6.3%) were heterozygous for C282Y/H63D. None of the patients was homozygous for C282Y or presented mutation in S65C. Transferrin saturation, serum ferritin and liver iron index were similar among with and without mutations. Three patients (9.3%) were diagnosed of hemochromatosis. One of them was homozygous for H63D, other patient was heterozygous for the combined C282Y/H63D, and in the remaining patient none of the mutations was found. CONCLUSIONS: In our setting, iron overload among alcoholic individuals seems to be independent of the presence of mutations C282Y, H63D and S65C in the HFE gene.

Adult↗
PubMed1994

Resistance of rat kidney mitochondrial membranes to oxidation induced by acute iron overload.

The effect of iron-overload on rat kidney was studied after a single injection of iron-dextran. Total iron content in kidney and isolated kidney mitochondria was markedly elevated over control values. To assess mitochondrial damage by iron overload, succinate-cytochrome c reductase and NADH-cytochrome c reductase activities as well as the rate of succinate-dependent hydrogen peroxide generation were measured. None of these activities were significantly affected by acute iron overload. The net content and the rate of TBARS (thiobarbituric acid reactive species) formation in kidney homogenates from iron-treated rats was significantly higher than that of control animals. Total superoxide dismutase activity in the homogenates from iron overloaded kidney was decreased by 26%, as compared to controls. Catalase, glutathione peroxidase, and Mn-superoxide dismutase activities were not affected by the treatment. The content of alpha-tocopherol was consistently decreased in whole kidney homogenates (-31%), mitochondria from kidney medulla (-31%) and cortex (-34%), from iron-overloaded rats. Our data suggest that iron dextran treatment does not affect kidney integrity, even though increases in lipid peroxidation occur. Vitamin E appears to be effective in controlling iron-dextran dependent radical generation in kidney.

Animals↗
PubMed1999

Premalignant lesions and hepatocellular carcinoma in a non-cirrhotic alcoholic patient with iron overload and normal transferrin saturation.

A 66-year-old white man had a hepatic resection for a 6-cm well-differentiated hepatocellular carcinoma which had developed in a non-cirrhotic liver. The only risk factors found were heavy drinking, smoking and heterozygosity for the C282Y mutation of the HFE gene. The liver was mildly fibrotic and overloaded with iron. It also contained numerous iron-free hepatocellular lesions from <1 to 10 mm, suggesting a premalignant change. These lesions were of three types: (i) iron-free foci, (ii) hyperplastic nodules and (iii) dysplastic nodules with severe dysplasia or even foci of well-differentiated grade I hepatocellular carcinoma. This observation suggests the possibility of malignant transformation of the liver in the newly-described syndrome of iron overload and normal transferrin saturation. It also illustrates the multistep process of carcinogenesis in the non-cirrhotic liver.

Aged↗
PubMed1999

Immunological analysis of beta-thalassemic mouse intestinal proteins reveals up-regulation of sucrase-isomaltase in response to iron overload.

Maintenance of iron homeostasis must balance the demand for iron due to heme synthesis, which is driven by hematopoiesis, and the restricted intestinal uptake of iron, which otherwise limits absorption of this toxic element. The consequences of perturbed iron homeostasis are witnessed in inherited forms of beta-thalassemia in which erythroid hyperplasia results in enhanced intestinal iron absorption despite tissue iron overload. To gain a better understanding of intestinal factors that are induced when iron homeostasis is disrupted, a panel of monoclonal antibodies that recognize intestinal microvillous membrane proteins of the beta-thalassemic Hbbd(th3)/Hbbd(th3) mouse was established. The monoclonal antibodies were screened by differential Western blotting against normal and beta-thalassemic mouse intestine to identify antigens modulated in the disease state. Here we report the initial characterization of one immunoreactive species that is up-regulated in beta-thalassemic mouse intestine and the tentative identification of this antigen as sucrase-isomaltase. Studies in Caco-2 cells revealed the rather unexpected finding that expression of this intestinal hydrolase is increased in response to iron toxicity.

Animals↗
PubMed1991

Hepatic iron overload: quantitative MR imaging.

Iron deposits demonstrate characteristically shortened T2 relaxation times. Several previously published studies reported poor correlation between the in vivo hepatic 1/T2 measurements made by means of midfield magnetic resonance (MR) units and the hepatic iron content of iron-overloaded patients. In this study, the authors assessed the use of in vivo 1/T2 measurements obtained by means of MR imaging at 0.5 T using short echo times (13.4 and 30 msec) and single-echo-sequences as well as computed tomographic (CT) attenuation as a measure of liver iron concentration in 10 severely iron-overloaded patients with beta-thalassemia major. The iron concentrations in surgical wedge biopsy samples of the liver, which varied between 3 and 9 mg/g of wet weight (normal, less than or equal to 0.5 mg/g), correlated well (r = .93, P less than or equal to .0001) with the preoperative in vivo hepatic 1/T2 measurements. The CT attenuation did not correlate with liver iron concentration. Quantitative MR imaging is a readily available noninvasive method for the assessment of hepatic iron concentration in iron-overloaded patients, reducing the need for needle biopsies of the liver.

Adolescent↗
PubMed1994

Potentiation of iron accumulation in cardiac myocytes during the treatment of iron overload in gerbils with the hydroxypyridinone iron chelator CP94.

Gerbils administered iron dextran are the only animal species which have been shown to develop hemochromatosis of the liver and heart in the same manner as transfusion dependent homozygous thalassemics. The iron chelating hydroxypyridinone, CP94, has been administered prophylactically to iron overloaded gerbils in a dosing regime which favors the formation of bidentate chelated iron, to examine the possibility of additional toxicity being caused to the liver and heart by the bidentate chelated iron complex. Hepatic iron accumulation was inhibited by CP94 administration for up to 6 weeks, but not after 20 weeks. Iron accumulation in the heart was increased significantly after 6 and 20 weeks of chelator treatment. Pathological changes in both organs were markedly more severe after 20 weeks in chelator treated animals. There was a higher incidence of cardiofibrosis and more extensive liver fibrosis in iron overloaded, chelator treated animals after 20 weeks.

Animals↗
PubMed1989

Inherited iron overload.

Several inherited forms of iron overload have been described. It is now accepted that HC, usually regarded as a disease of adult life, is an inherited disorder, hence all first degree relatives must be presumed to be at increased risk of developing iron overload and the diagnosis is now frequently made in young relatives. The combination of serum iron, transferrin saturation and serum ferritin determination will detect iron overload in an early, precirrhotic stage. Liver biopsy and the determination of hepatic iron concentration provide the definitive proof. Where HC is recognized sufficiently early to permit adequate removal of iron before cirrhosis has developed, the prognosis is excellent. Thus haemochromatosis as a clinical disease should be preventable in a large proportion of patients. Severe iron overload has been described in juveniles and also in neonates. These conditions are familial but whether they are HLA-related has not been determined. Cardiac and endocrine disorders are frequently the presenting manifestations of parenchymal iron overload in the young and, at least in neonates, the condition is usually fatal in early infancy. It is not possible at present, to say whether these rare juvenile and neonatal forms of haemochromatosis are related to the much more common adult form. Identification of the gene for HC may assist in answering this question.

Adolescent↗
PubMed1988

Hyperlactataemia, hyperkalemia and heart block in acute iron overload: the fatal role of the hepatic iron-incorporation rate in rats on ferric citrate infusions.

An animal model is presented that provides constant and controllable conditions for approaching gradually, and within reasonable time, different stages of iron overload and, probably, an iron-induced mitochondrial disorder. Thirty-five rats were infused with ferric citrate, sodium citrate and saline at constant rates for 6-24 h. In the 200-3200 micrograms Fe h-1 loading range, the iron-incorporation capacity of the liver was not saturable and the fractional iron uptake by the liver remained at approximately 30% even at a loading rate of 3200 micrograms Fe h-1. Up to a loading rate of 200 micrograms Fe h-1, iron storage was not associated with toxic effects. Beyond this loading rate, however, the liver was no longer able to prevent a massive plasma iron increase on one side and hyperlactataemia on the other. These signs most probably represent hepatocellular decompensation with respect to a critical iron-storage rate. The product of plasma iron x exposition time was significantly correlated with increased plasma lactate levels (r = 0.89, P less than 0.005), whereas increased plasma iron levels per se were not. Hyperlactataemia was associated with hyperkalaemia and progressive cardiac conduction defects leading to cardiac arrest at lactate concentration of 9.1 +/- 4.3 mmol l-1. The hypothesis is discussed that toxicity in acute iron overload may entirely be due to hepatocellular (mitochondrial) damage, and not to multiple organ iron overload.

Animals↗