Iron overload promotes Cyclin D1 expression and alters cell cycle in mouse hepatocytes

Dynamic chromatin accessibility during nutritional iron overload reveals a BMP6-independent induction of cell cycle genes

Iron is essential to organism physiology as it participates in numerous biological processes including oxygen transport, respiration and erythropoiesis. Although iron is critical to physiology, excess iron is toxic to cells and tissues due to generation of reactive oxygen species. Therefore, well-kept iron homeostasis is a mainstay of proper cell and organ function. Iron overload disorders, caused by nutritional or genetic factors, contribute to many pathologies such as diabetes, non-alcoholic steatohepatitis and hepatocellular carcinoma. The liver is not only vulnerable to the effects of iron overload, it is also the major organ controlling iron homeostasis. During iron overload, Bone Morphogenic Protein (BMP) levels increase and initiate a hepatic response aimed at lowering iron levels. The transcriptional effects of iron overload are not well-characterized and the underlining enhancer regulation is uncharted. Here, we profiled the liver's transcriptome and chromatin accessibility following nutritional iron overload. We found marked changes in gene expression and enhancer accessibility following iron overload. Surprisingly, 16% of genes induced following iron overload participate in propagating the cell cycle. Induction of cell cycle genes was independent of BMP. Genome-wide enhancer landscape profiling revealed hundreds of enhancers with altered activity following iron overload. Characterization of transcription factor motifs and footprints in iron-regulated enhancers showed a role for the Activator Protein 1 (AP-1) transcription factor in promoting cell cycle-related transcription. In summary, we found that the transcriptional program at play during iron overload is bifurcated in which BMP signaling controls iron homeostasis genes while an AP-1-driven program controls cell cycle genes.

CHIR99021 Maintenance of the Cell Stemness by Regulating Cellular Iron Metabolism

CHIR99021 is an aminopyrimidine derivative, which can efficiently inhibit the activity of glycogen synthesis kinase 3α (GSK-3α) and GSK-3β. As an essential component of stem cell culture medium, it plays an important role in maintaining cell stemness. However, the mechanism of its role is not fully understood. In the present study, we first found that removal of CHIR99021 from embryonic stem cell culture medium reduced iron storage in mouse embryonic stem cells (mESCs). CHIR99021-treated Neuro-2a cells led to an upregulation of ferritin expression and an increase in intracellular iron levels, along with GSK3β inhibition and Wnt/GSK-3β/β-catenin pathway activation. In addition, iron treatment activated the classical Wnt pathway by affecting the expression of β-catenin in the Neuro-2a cells. Our data link the role of iron in the maintenance of cell stemness via the Wnt/GSK-3β/β-catenin signaling pathway, and identify intermediate molecules, including Steap1, Bola2, and Kdm6bos, which may mediate the upregulation of ferritin expression by CHIR99021. These findings reveal novel mechanisms of the maintenance of cell stemness and differentiation and provide a theoretical basis for the development of new strategies in stem cell treatment in disease.

Polyploidization of Hepatocytes: Insights into the Pathogenesis of Liver Diseases

Polyploidization is a process by which cells are induced to possess more than two sets of chromosomes. Although polyploidization is not frequent in mammals, it is closely associated with development and differentiation of specific tissues and organs. The liver is one of the mammalian organs that displays ploidy dynamics in physiological homeostasis during its development. The ratio of polyploid hepatocytes increases significantly in response to hepatic injury from aging, viral infection, iron overload, surgical resection, or metabolic overload, such as that from non-alcoholic fatty liver diseases (NAFLDs). One of the unique features of NAFLD is the marked heterogeneity of hepatocyte nuclear size, which is strongly associated with an adverse liver-related outcome, such as hepatocellular carcinoma, liver transplantation, and liver-related death. Thus, hepatic polyploidization has been suggested as a potential driver in the progression of NAFLDs that are involved in the control of the multiple pathogenicity of the diseases. However, the importance of polyploidy in diverse pathophysiological contexts remains elusive. Recently, several studies reported successful improvement of symptoms of NAFLDs by reducing pathological polyploidy or by controlling cell cycle progression in animal models, suggesting that better understanding the mechanisms of pathological hepatic polyploidy may provide insights into the treatment of hepatic disorders.

Polyploidy control in hepatic health and disease

A balanced increase in DNA content (ploidy) is observed in some human cell types, including bone-resorbing osteoclasts, platelet-producing megakaryocytes, cardiomyocytes or hepatocytes. The impact of increased hepatocyte ploidy on normal physiology and diverse liver pathologies is still poorly understood. Recent findings suggest swift genetic adaptation to hepatotoxic stress and the protection from malignant transformation as beneficial effects. Herein, we discuss the molecular mechanisms regulating hepatocyte polyploidisation and its implication for different liver diseases and hepatocellular carcinoma. We report on centrosomes' role in limiting polyploidy by activating the p53 signalling network (via the PIDDosome multiprotein complex) and we discuss the role of this pathway in liver disease. Increased hepatocyte ploidy is a hallmark of hepatic inflammation and may play a protective role against liver cancer. Our evolving understanding of hepatocyte ploidy is discussed from the perspective of its potential clinical application for risk stratification, prognosis, and novel therapeutic strategies in liver disease and hepatocellular carcinoma.

Iron: Key player in cancer and cell cycle?

BACKGROUND

Iron is an essential element for growth and metabolic activities of all living organisms but remains in its oxyhydroxide ferric ion form in the surrounding. Unavailability of iron in soluble ferrous form led to development of specific pathways and machinery in different organisms to make it available for use and maintain its homeostasis. Iron homeostasis is essential as under different circumstances iron in excess as well as deprivation leads to different pathological conditions in human.

OBJECTIVE

This review highlights the current findings related to iron excess as well as deprivation with regards to cellular proliferation.

CONCLUSIONS

Iron excess is extensively associated with different types of cancers viz. colorectal cancer, breast cancer etc. by producing an oxidative stressed condition and alteration of immune system. Ironically its deprivation also results in anaemic conditions and leads to cell cycle arrest at different phases with mechanism yet to be explored. Iron deprivation arrests cell cycle at G1/S and in some cases at G2/M checkpoints resulting in growth arrest. However, in some cases iron overload arrests cell cycle at G1 phase by blocking certain signalling pathways. Certain natural and synthetic iron chelators are being explored from few decades to combat diseases caused by alteration in iron homeostasis.

Myricitrin pretreatment ameliorates mouse liver ischemia reperfusion injury

BACKGROUND

Myricitrin has been reported to exert protective effects on liver diseases, but the protective effects of myricitrin against liver ischemia reperfusion (I/R) injury and the underlying mechanisms remain unexplored. This study aimed to investigate the effects of myricitrin on liver I/R injury and elucidate the underlying mechanisms.

METHODS

Mice were pretreated with myricitrin before liver I/R injury modeling. The mice were pretreated with either myricitrin or vehicle prior to liver ischemia. Some mice were further pretreated with the PI3K inhibitor LY294002. Liver tissues and blood samples were collected after 6 h of reperfusion. The degree of liver damage was determined by the serum levels of alanine aminotransferase (ALT), aspartate transaminase (AST), and lactic dehydrogenase (LDH) and histological examinations. The tumour necrosis factor-α (TNF-α), interleukin--1β (IL-1β), IL-4 and IL-10 expression levels were assessed by qRT-PCR and enzyme-linked immunosorbent assays (ELISAs). Serum superoxide dismutase (SOD) activity, catalase (CAT) activity, and contents of malondialdehyde (MDA), glutathione (GSH) and nitric oxide (NO) contents were measured. Western blotting and caspase-3 activity were conducted to determine the effect of myricitrin on apoptosis. The expression levels of proliferation related genes (Cyclin D1 and Cyclin E1) were determined by qRT-PCR and western-blotting. The expression of p-Akt, p-mTOR and p-eNOS in liver tissue were investigated by western-blotting.

RESULTS

Myricitrin not only significantly decreased the ALT, AST and LDH levels but also reduced the necrotic areas in the liver tissue compared with liver I/R injury group. In addition, myricitrin pretreatment alleviated liver injury by inhibiting the inflammatory response and suppressing oxidative stress. Western blotting and caspase-3 activity revealed that myricitrin inhibited liver I/R induced-apoptosis. Myricitrin promoted hepatocyte proliferation following liver I/R injury by upregulating the expression levels of Cyclin D1 and Cyclin E1. Further experiments indicated that the myricitrin pretreatment increased nitric oxide (NO) production by activating the PI3K/Akt signaling pathway. However, myricitrin triggered the hepatocyte proliferation and NO synthase activation was blocked by LY294002.

CONCLUSION

These results demonstrate that myricitrin alleviates liver I/R injury by suppressing oxidative stress, the inflammatory response, and apoptosis, improving liver proliferation and upregulating p-eNOS expression.

Consequences of parenteral iron-dextran loading investigated in minipigs. A new model of transfusional iron overload

Patients with blood transfusion-dependent anemias develop transfusional iron overload (TIO), which may cause cardiosiderosis. In patients with an ineffective erythropoiesis, such as thalassemia major, common transfusion regimes aim at suppression of erythropoiesis and of enteral iron loading. Recent data suggest that maintaining residual, ineffective erythropoiesis may protect from cardiosiderosis. We investigated the common consequences of TIO, including cardiosiderosis, in a minipig model of iron overload with normal erythropoiesis. TIO was mimicked by long-term, weekly iron-dextran injections. Iron-dextran loading for around one year induced very high liver iron concentrations, but extrahepatic iron loading, and iron-induced toxicities were mild and did not include fibrosis. Iron deposits were primarily in reticuloendothelial cells, and parenchymal cardiac iron loading was mild. Compared to non-thalassemic patients with TIO, comparable cardiosiderosis in minipigs required about 4-fold greater body iron loads. It is suggested that this resistance against extrahepatic iron loading and toxicity in minipigs may at least in part be explained by a protective effect of the normal erythropoiesis, and additionally by a larger total iron storage capacity of RES than in patients with TIO. Parenteral iron-dextran loading of minipigs is a promising and feasible large-animal model of iron overload, that may mimic TIO in non-thalassemic patients.

Adipose-Derived Stem Cell Transplantation Attenuates Inflammation and Promotes Liver Regeneration after Ischemia-Reperfusion and Hemihepatectomy in Swine

Aim

To study the anti-inflammatory and liver regenerative effects of adipose-derived mesenchymal stem cells (ADSCs) on a porcine model of ischemia-reperfusion (IR) and hemihepatectomy.

Methods

Eighteen healthy Bama miniature pigs were randomly divided into the sham-operated (sham), untreated IR injury (IRI), and ADSC-transplanted (ADSC) groups. Hepatic IR was established by laparoscopic hemihepatectomy. ADSCs were transplanted directly into the liver parenchyma after the surgery. Hepatic inflammation and liver regeneration were evaluated by histopathological examination and assessment of relevant cytokines and other factors.

Results

ADSC transplantation successfully ameliorated the IRI-induced histopathological damage and the high levels of pro-inflammatory cytokines like IL-1β, IL-6, and TNF-α. In addition, the ADSCs enhanced the expression of the anti-inflammatory IL-10, regenerative factors including HGF, Cyclin D1, and proliferating cell nuclear antigen (PCNA), and angiogenic factors like VEGF, ANG-1, and ANG-2.

Conclusions

ADSCs attenuated the hepatic IRI-induced inflammatory response and promoted liver regeneration.

Linking Cancer Metabolic Dysfunction and Genetic Instability through the Lens of Iron Metabolism

Iron (Fe) is an essential element that plays a fundamental role in a wide range of cellular functions, including cellular proliferation, DNA synthesis, as well as DNA damage and repair. Because of these connections, iron has been strongly implicated in cancer development. Cancer cells frequently have changes in the expression of iron regulatory proteins. For example, cancer cells frequently upregulate transferrin (increasing uptake of iron) and down regulate ferroportin (decreasing efflux of intracellular iron). These changes increase the steady-state level of intracellular redox active iron, known as the labile iron pool (LIP). The LIP typically contains approximately 2% intracellular iron, which primarily exists as ferrous iron (Fe²⁺). The LIP can readily contribute to oxidative distress within the cell through Fe²⁺-dioxygen and Fenton chemistries, generating the highly reactive hydroxyl radical (HO^•). Due to the reactive nature of the LIP, it can contribute to increased DNA damage. Mitochondrial dysfunction in cancer cells results in increased steady-state levels of hydrogen peroxide and superoxide along with other downstream reactive oxygen species. The increased presence of H₂O₂ and O₂^•- can increase the LIP, contributing to increased mitochondrial uptake of iron as well as genetic instability. Thus, iron metabolism and labile iron pools may play a central role connecting the genetic mutational theories of cancer to the metabolic theories of cancer.

Cell cycle and transmembrane mitochondrial potential analysis after treatment with chromium(iii), iron(iii), molybdenum(iii) or nickel(ii) and their mixtures

The aim of this study was to examine the effect of chromium(iii), iron(iii), molybdenum(iii) and nickel(ii) and their combinations on the cell cycle and mitochondrial transmembrane potential (MTP) in BALB/3T3 and HepG2 cells. A statistically significant dose related decrease of the percentage of cells in the G0/G1 and S phases was observed. However, a statistically significant dose related increase of the percentage of cells in the G2/M phase after exposure to chromium(iii), nickel(ii) or molybdenum(iii) at 200-1000 μM concentrations in both cell lines was observed. Moreover, an increase of the percentage of cells in the subG1 phase was observed. In both cell lines a statistically significant dose related decrease of the percentage of cells in the G2/M phase after exposure to iron(iii) at 200-1000 μM concentrations was observed. However, a statistically significant dose related increase of the percentage of cells in the G0/G1 phase after exposure to iron(iii) at 200-1000 μM concentrations was observed. A concentration dependent statistically significant decrease in the level of the MTP was observed in both cell lines after exposure to chromium(iii), iron(iii), nickel(ii) and molybdenum(iii). The results obtained from both cell lines show that HepG2 cells are more sensitive when compared to BALB/3T3 cells. Additions of Cr(iii) at 200 μM plus Fe(iii) at 1000 μM showed a synergistic effect on the cell cycle and MTP. In the case of Cr(iii) at 200 μM plus Mo(iii) at 1000 μM, an antagonistic effect was observed in both analyses. In the case of Cr(iii) at 1000 μM plus Mo(iii), Ni(ii) and Fe(iii) at 200 μM, no changes in the percentage of cells in all phases were observed in both cell lines in both analyses.

When should iron supplementation in dialysis patients be avoided, minimized or withdrawn?

Parenteral iron is used to restore the body's iron pool before and during erythropoiesis-stimulating agent (ESA) therapy; together these agents form the backbone of anemia management in end-stage renal disease (ESRD) patients undergoing hemodialysis. ESRD patients receiving chronic intravenous iron products, which exceed their blood loss are exposed to an increased risk of positive iron balance. Measurement of the liver iron concentration (LIC) reflects total body iron stores in patients with secondary hemosiderosis and genetic hemochromatosis. Recent studies of LIC in hemodialysis patients, measured by quantitative MRI and magnetic susceptometry, have demonstrated a high risk of iron overload in dialysis patients treated with IV iron products at doses advocated by current anemia management guidelines for dialysis patients. Liver iron overload causes increased production of hepcidin and elevated plasma levels, which can activate macrophages of atherosclerotic plaques. This mechanism may explain the results of 3 long-term epidemiological studies which showed the association of excessive IV iron doses with increased risk of cardiovascular morbidity and mortality among hemodialysis patients. A more physiological approach of iron therapy in ESRD is needed. Peritoneal dialysis patients, hemodialysis patients infected with hepatitis C virus, and hemodialysis patients with ferritin above 1000 μg/L without a concomitant inflammatory state, all require specific and cautious iron management. Two recent studies have shown that most hemodialysis patients will benefit from lower maintenance IV iron dosages; their results are applicable to American hemodialysis patients. Novel pharmacometric and economic approaches to iron therapy and anemia management are emerging which are designed to lessen the potential side effects of excessive IV iron while maintaining hemoglobin stability without an increase in ESA dosing.

Impact of iatrogenic iron overload on the course of hepatitis C in the dialysis population: A plea for caution

About 2.5% of the world population, corresponding to about 177 million individuals, are infected by hepatitis C virus (HCV), a small, single-stranded RNA virus. The prevalence of HCV infection among dialysis patients in Japan, Europe, and North America during the 2012 to 2015 period was found to be 8.7% in the DOPPS study. Nosocomial HCV spread in hemodialysis facilities still occurs. Increased hepatic tissue iron has been shown to play a deleterious role in the course of hepatitis C, favor development of fibrosis and cirrhosis and possibly increase the risk of liver cancer in the general population. Regular loss of blood in the hemodialysis circuit, in routine blood sampling for laboratory tests (for uremia monitoring), and in gut due to uremic enteropathy, invariably results in iron deficiency for which patients are commonly treated with intravenous (IV) iron preparations. Data on the effects of IV iron in hemodialysis patients with hepatitis C are limited (2 studies) and strongly suggest that parenteral iron may contribute to hepatocellular injury. Iatrogenic iron overload is extremely prevalent among hemodialysis population worldwide. Iron overload and toxicity has emerged as one of the most controversial topic in the management of anemia in dialysis patients. Given the known impact of iron in promoting growth and virulence of HCV and the associated liver disease, it is necessary to use iron therapy cautiously and closely monitor plasma markers of iron metabolism and liver iron stores non-invasively by means of MRI to avoid iron overload in this vulnerable population.

TGFbeta Induces Binucleation/Polyploidization in Hepatocytes through a Src-Dependent Cytokinesis Failure

In all mammals, the adult liver shows binucleated as well as mononucleated polyploid hepatocytes. The hepatic polyploidization starts after birth with an extensive hepatocyte binucleation and generates hepatocytes of several ploidy classes. While the functional significance of hepatocyte polyploidy is becoming clearer, how it is triggered and maintained needs to be clarified. Aim of this study was to identify a major inducer of hepatocyte binucleation/polyploidization and the cellular and molecular mechanisms involved. We found that, among several cytokines analyzed, known to be involved in early liver development and/or mass control, TGFbeta1 was capable to induce, together with the expected morphological changes, binucleation in hepatocytes in culture. Most importantly, the pharmacological inhibition of TGFbeta signaling in healthy mice during weaning, when the physiological binucleation occurs, induced a significant decrease of hepatocyte binucleation rate, without affecting cell proliferation and hepatic index. The TGFbeta-induced hepatocyte binucleation resulted from a cytokinesis failure, as assessed by video microscopy, and is associated with a delocalization of the cytokinesis regulator RhoA-GTPase from the mid-body of dividing cells. The use of specific chemical inhibitors demonstrated that the observed events are Src-dependent. Finally, the restoration of a fully epithelial phenotype by TGFbeta withdrawal gave rise to a cell progeny capable to maintain the polyploid state. In conclusion, we identified TGFbeta as a major inducer of hepatocyte binucleation both in vitro and in vivo, thus ascribing a novel role to this pleiotropic cytokine. The production of binucleated/tetraploid hepatocytes is due to a cytokinesis failure controlled by the molecular axis TGFbeta/Src/RhoA.

Oxidative stress promotes pathologic polyploidization in nonalcoholic fatty liver disease

Polyploidization is one of the most dramatic changes that can occur in the genome. In the liver, physiological polyploidization events occur during both liver development and throughout adult life. Here, we determined that a pathological polyploidization takes place in nonalcoholic fatty liver disease (NAFLD), a widespread hepatic metabolic disorder that is believed to be a risk factor for hepatocellular carcinoma (HCC). In murine models of NAFLD, the parenchyma of fatty livers displayed alterations of the polyploidization process, including the presence of a large proportion of highly polyploid mononuclear cells, which are rarely observed in normal hepatic parenchyma. Biopsies from patients with nonalcoholic steatohepatitis (NASH) revealed the presence of alterations in hepatocyte ploidy compared with tissue from control individuals. Hepatocytes from NAFLD mice revealed that progression through the S/G2 phases of the cell cycle was inefficient. This alteration was associated with activation of a G2/M DNA damage checkpoint, which prevented activation of the cyclin B1/CDK1 complex. Furthermore, we determined that oxidative stress promotes the appearance of highly polyploid cells, and antioxidant-treated NAFLD hepatocytes resumed normal cell division and returned to a physiological state of polyploidy. Collectively, these findings indicate that oxidative stress promotes pathological polyploidization and suggest that this is an early event in NAFLD that may contribute to HCC development.

Biodistribution and predictive hepatic gene expression of intravenous iron sucrose

INTRODUCTION

We have examined iron biodistribution and hepatic gene expression in rats following administration of the generic Iron Sucrose Azad (ISA) or the reference iron sucrose drug Venofer®.

METHODS

ISA and Venofer® were administered intravenously to normal, non-anemic, male rats at 15 mg/kg (a supra-therapeutic dose-level). To evaluate biodistribution, tissue iron levels were determined over 28 days for plasma, liver, spleen, bone marrow, heart, kidney, lung and stomach using a validated ICP-MS method. Hepatic gene expression was evaluated by microarray analysis of mRNA from samples taken 24 h after drug administration.

RESULTS

Iron concentration/time profiles for plasma and tissues were quantitatively similar for ISA and Venofer. Following administration, circulating iron levels briefly exceeded transferrin binding capacity and there was a transient increase in hepatic iron. Bone marrow iron levels remained elevated throughout the study. No increases in tissue iron levels were observed in the heart, stomach or lungs. Spleen iron levels increased over the course of the study in treated and control rats. Small, transient increases were recorded in the kidneys of treated rats. The effects of ISA and Venofer® on hepatic gene transcription were similar. Principal components analysis showed that there was no systematic effect of either treatment on transcriptional profiles. Only a small number of genes showed significant modulation of expression. No transcriptional pattern matches with toxicity pathways were found in the ToxFX database for either treatment. No modulation of key genes in apoptosis, inflammation or oxidative stress pathways was detected.

DISCUSSION

These findings demonstrated that the biodistribution of administered iron is essentially similar for Iron Sucrose Azad and Venofer®, that iron sucrose partitions predominantly into the liver, spleen and bone marrow, and that hepatic gene expression studies did not provide any evidence of toxicity in animals treated at a supra-therapeutic dose-level.

Dietary iron overload induces visceral adipose tissue insulin resistance

Increased iron stores associated with elevated levels of the iron hormone hepcidin are a frequent feature of the metabolic syndrome. The aim of this study was to assess the effect of dietary iron supplementation on insulin resistance and the role of hepcidin in C57Bl/6 male mice fed a standard or iron-enriched diet for 16 weeks. Iron supplementation increased hepatic iron and serum hepcidin fivefold and led to a 40% increase in fasting glucose due to insulin resistance, as confirmed by the insulin tolerance test, and to threefold higher levels of triglycerides. Iron supplemented mice had lower visceral adipose tissue mass estimated by epididymal fat pad, associated with iron accumulation in adipocytes. Decreased insulin signaling, evaluated by the phospho-Akt/Akt ratio, was detected in the visceral adipose tissue of iron overloaded mice, and gene expression analysis of visceral adipose tissue showed that an iron-enriched diet up-regulated iron-responsive genes and adipokines, favoring insulin resistance, whereas lipoprotein lipase was down-regulated. This resulted in hyperresistinemia and increased visceral adipose tissue expression of suppressor of cytokine signaling-3 (Socs3), a target of resistin and hepcidin implicated in insulin resistance. Acute hepcidin administration down-regulated lipoprotein lipase and up-regulated Socs3 in visceral adipose tissue. In conclusion, we characterized a model of dysmetabolic iron overload syndrome in which an iron-enriched diet induces insulin resistance and hypertriglyceridemia and affects visceral adipose tissue metabolism by a mechanism involving hepcidin up-regulation.

Aneuploidy, polyploidy and ploidy reversal in the liver

Polyploidy has been described in the liver for over 100 years. The frequency of polyploid hepatocytes varies by age and species, but up to 90% of mouse hepatocytes and approximately 50% of human hepatocytes are polyploid. In addition to alterations in the entire complement of chromosomes, variations in chromosome copy number have been recently described. Aneuploidy in the liver is pervasive, affecting 60% of hepatocytes in mice and 30-90% of hepatocytes in humans. Polyploidy and aneuploidy in the liver are closely linked, and the ploidy conveyor model describes this relationship. Diploid hepatocytes undergo failed cytokinesis to generate polyploid cells. Proliferating polyploid hepatocytes, which form multipolar spindles during cell division, generate reduced ploidy progeny (e.g., diploid hepatocytes from tetraploids or octaploids) and/or aneuploid daughters. New evidence suggests that random hepatic aneuploidy can promote adaptation to liver injury. For instance, in response to chronic liver damage, subsets of aneuploid hepatocytes that are differentially resistant to the injury remain healthy, regenerate the liver and restore function. Future work is required to elucidate the mechanisms regulating dynamic chromosome changes in the liver and to understand how these processes impact normal and abnormal liver function.

Elevated hepatic iron activates NF-E2-related factor 2-regulated pathway in a dietary iron overload mouse model

Hepatic iron overload has been associated classically with the genetic disorder hereditary hemochromatosis. More recently, it has become apparent that mild-to-moderate degrees of elevated hepatic iron stores observed in other liver diseases also have clinical relevance. The goal was to use a mouse model of dietary hepatic iron overload and isobaric tag for relative and absolute quantitation proteomics to identify, at a global level, differentially expressed proteins in livers from mice fed a control or 3,5,5-trimethyl-hexanoyl-ferrocene (TMHF) supplemented diet for 4 weeks. The expression of 74 proteins was altered by ≥ ±1.5-fold, showing that the effects of iron on the liver proteome were extensive. The top canonical pathway altered by TMHF treatment was the NF-E2-related factor 2 (NRF2-)-mediated oxidative stress response. Because of the long-standing association of elevated hepatic iron with oxidative stress, the remainder of the study was focused on NRF2. TMHF treatment upregulated 25 phase I/II and antioxidant proteins previously categorized as NRF2 target gene products. Immunoblot analyses showed that TMHF treatment increased the levels of glutathione S-transferase (GST) M1, GSTM4, glutamate-cysteine ligase (GCL) catalytic subunit, GCL modifier subunit, glutathione synthetase, glutathione reductase, heme oxygenase 1, epoxide hydrolase 1, and NAD(P)H dehydrogenase quinone 1. Immunofluorescence, carried out to determine the cellular localization of NRF2, showed that NRF2 was detected in the nucleus of hepatocytes from TMHF-treated mice and not from control mice. We conclude that elevated hepatic iron in a mouse model activates NRF2, a key regulator of the cellular response to oxidative stress.

Overexpression of active Aurora-C kinase results in cell transformation and tumour formation

Aurora kinases belong to a conserved family of serine/threonine kinases key regulators of cell cycle progression. Aurora-A and Aurora-B are expressed in somatic cells and involved mainly in mitosis while Aurora-C is expressed during spermatogenesis and oogenesis and is involved in meiosis. Aurora-C is hardly detectable in normal somatic cells. However all three kinases are overexpressed in many cancer lines. Aurora-A possesses an oncogenic activity while Aurora-B does not. Here we investigated whether Aurora-C possesses such an oncogenic activity. We report that overexpression of Aurora-C induces abnormal cell division resulting in centrosome amplification and multinucleation in both transiently transfected cells and in stable cell lines. Only stable NIH3T3 cell clones overexpressing active Aurora-C formed foci of colonies when grown on soft agar, indicating that a gain of Aurora-C activity is sufficient to transform cells. Furthermore, we reported that NIH-3T3 stable cell lines overexpressing Aurora-C induced tumour formation when injected into nude mice, demonstrating the oncogenic activity of enzymatically active Aurora kinase C. Interestingly enough tumor aggressiveness was positively correlated with the quantity of active kinase, making Aurora-C a potential anti-cancer therapeutic target.

3,5,5-trimethyl-hexanoyl-ferrocene diet protects mice from moderate transient acetaminophen-induced hepatotoxicity

Acetaminophen (APAP) overdose is the most frequent cause of adult acute liver failure. Susceptibility or resistance to APAP toxicity is most likely accounted for by the interplay of several factors. One factor important in multiple different chronic liver diseases that may play a role in APAP toxicity is elevated hepatic iron. Hereditary hemochromatosis is traditionally associated with hepatic iron overload. However, varying degrees of elevated hepatic iron stores observed in chronic hepatitis C and B, alcoholic liver disease and nonalcoholic fatty liver disease also have clinical relevance. We employed an animal model in which mice are fed a 3,5,5-trimethyl-hexanoyl-ferrocene (TMHF)-supplemented diet to evaluate the effect of elevated hepatic iron on APAP hepatotoxicity. Three hundred milligrams per kilogram APAP was chosen because this dosage induces hepatotoxicity but is not lethal. Since both excess iron and APAP induce oxidative stress and mitochondrial dysfunction, we hypothesized that the TMHF diet would enhance APAP hepatotoxicity. The results were the opposite. Centrilobular vacuolation/necrosis, APAP adducts, nitrotyrosine adducts, and a spike in serum alanine aminotransferase, which were observed in control mice treated with APAP, were not observed in TMHF-fed mice treated with APAP. Further analysis showed that the levels of CYP2E1 and CYP1A2 were not significantly different in TMHF-treated compared with control mice. However, the magnitude of depletion of glutathione following APAP treatment was considerably less in TMHF-treated mice than in mice fed a control diet. We conclude that a TMHF diet protects mice from moderate transient APAP-induced hepatotoxicity prior to the formation of APAP adducts, and one contributing mechanism is reduction in glutathione depletion.

Natural and synthetic STAT3 inhibitors reduce hepcidin expression in differentiated mouse hepatocytes expressing the active phosphorylated STAT3 form

During the inflammatory process, hepcidin overexpression favours the development of anaemia of chronic diseases which represents the second most common form of anaemia worldwide. The identification of therapeutic agents decreasing hepcidin expression is therefore an important goal. The aim of this study was to target the STAT3 signalling involved in the development of increased hepcidin expression related to chronic inflammation. In a co-culture model associating mouse hepatocytes and rat liver epithelial cells, the mRNA levels of hepcidin1, albumin, aldolase B, Cyp3a4, Stat3, Smad4 and iron regulatory genes were measured by real-time PCR. STAT3 and phosphorylated SMAD1/5/8 proteins were analysed by Western blot. At variance of hepatocyte pure culture, co-culture provided high levels of hepcidin1 mRNA, reaching 400% of the freshly isolated hepatocyte values after 6 days of culture. Hepcidin expression was associated with the maintenance of hepatocyte phenotype, STAT3 phosphorylation and functional BMP/SMAD pathway. Stat3 siRNAs inhibited the hepcidin1 mRNA expression. STAT3 inhibitors, including curcumin, AG490 and a peptide (PpYLKTK), reduced hepcidin1 mRNA expression even when cells were additionally exposed to IL-6. Hepcidin1 mRNA was expressed at high levels by hepatocytes in the co-culture model, and STAT3 pathway activation was controlled through STAT3 inhibitors. Such inhibitors could be useful to prevent anaemia related to hepcidin overexpression during chronic inflammation.

Elevated hepatic iron: a confounding factor in chronic hepatitis C

Historically, iron overload in the liver has been associated with the genetic disorders hereditary hemochromatosis and thalassemia and with unusual dietary habits. More recently, elevated hepatic iron levels also have been observed in chronic hepatitis C virus (HCV) infection. Iron overload in the liver causes many changes including induction of oxidative stress, damage to lysosomes and mitochondria, altered oxidant defense systems and stimulation of hepatocyte proliferation. Chronic HCV infection causes numerous pathogenic changes in the liver including induction of endoplasmic reticulum stress, the unfolded protein response, oxidative stress, mitochondrial dysfunction and altered growth control. Understanding the molecular and cellular changes that could occur in a liver which has elevated hepatic iron levels and in which HCV replication and gene expression are ongoing has clinical relevance and represents an area of research in need of further investigation.

Microarray analysis of liver gene expression in iron overloaded patients with sickle cell anemia and beta-thalassemia

Chronic transfusion therapy is used clinically to supply healthy erythrocytes for patients with sickle cell anemia (SCA) or beta-thalassemia major (TM). Despite the benefits of red blood cell transfusions, chronic transfusions lead to iron accumulation in key tissues such as the heart, liver, and endocrine glands. Transfusion-acquired iron overload is recognized as a cause of morbidity and mortality among patients receiving chronic transfusions. At present, there is little understanding of molecular events that occur during transfusional iron loading and the reasons for the large inter-individual variation observed clinically in transfusion-acquired iron accumulation. To address these issues, we examined whether any liver-expressed genes in SCA or TM patients with transfusional iron overload were associated with the degree of iron accumulation. Specifically, we performed microarray analysis on liver biopsy specimens comparing SCA patients with mild or severe iron overload and also compared SCA with TM patients. Fifteen candidate genes were identified with significantly differential expression between the high and low liver iron concentrations. SCA patients and 20 candidate genes were detected between the SCA and TM patient comparison. Subsequent quantitative PCR experiments validated 12 candidate genes; with GSTM1, eIF5a, SULF2, NTS, and HO-1 being particularly good prospects as genes that might affect the degree of iron accumulation. Future work will determine the baseline expression of these genes prior to transfusional iron overload and elucidate the full impact of these genes on the inter-individual variation observed clinically in transfusion-acquired iron accumulation.

Hepatic iron overload and hepatocellular carcinoma

The liver is the main storage site for iron in the body. Excess accumulation of iron in the liver has been well-documented in two human diseases, hereditary hemochromatosis and dietary iron overload in the African. Hepatic iron overload in these conditions often results in fibrosis and cirrhosis and may be complicated by the development of hepatocellular carcinoma. Malignant transformation usually occurs in the presence of cirrhosis, suggesting that free iron-induced chronic necroinflammatory hepatic disease plays a role in the hepatocarcinogenesis. However, the supervention of hepatocellular carcinoma in the absence of cirrhosis raises the possibility that ionic iron may also be directly hepatocarcinogenic. Support for this possibility is provided by a recently described animal model of dietary iron overload in which iron-free preneoplastic nodules and hepatocellular carcinoma developed in the absence of fibrosis or cirrhosis. The mechanisms by which iron induces malignant transformation have yet to be fully characterized but the most important appears to be the generation of oxidative stress. Free iron generates reactive oxygen intermediates that disrupt the redox balance of the cells and cause chronic oxidative stress. Oxidative stress leads to lipid peroxidation of unsaturated fatty acids in membranes of cells and organelles. Cytotoxic by-products of lipid peroxidation, such as malondialdehyde and 4-hydroxy-2'-nonenal, are produced and these impair cellular function and protein synthesis and damage DNA. Deoxyguanosine residues in DNA are also hydroxylated by reactive oxygen intermediates to form 8-hydroxy-2'-deoxyguanosine, a major promutagenic adduct that causes G:C to T:A transversions and DNA unwinding and strand breaks. Free iron also induces immunologic abnormalities that may decrease immune surveillance for malignant transformation.

Transcripts of ceruloplasmin but not hepcidin, both major iron metabolism genes, exhibit a decreasing pattern along the portocentral axis of mouse liver

BACKGROUND/AIMS

During iron overload of dietary origin, iron accumulates predominantly in periportal hepatocytes. A gradient in the basal and normal transcriptional control of genes involved in iron metabolism along the portocentral axis of liver lobules could explain this feature. Therefore, we aimed at characterizing, by quantitative RT-PCR, the expression of iron metabolism genes in adult C57BL/6 mouse hepatocytes regarding lobular localisation, with special emphasis to cell ploidy, considering its possible relationship with lobular zonation.

METHODS

We used two methods to analyse separately periportal and perivenous liver cells: 1) a selective liver zonal destruction by digitonin prior to a classical collagenase dissociation, and 2) laser capture microdissection. We also developed a method to separate viable 4N and 8N polyploid hepatocytes by flow cytometer.

RESULTS

Transcripts of ceruloplasmin, involved in iron efflux, were overexpressed in periportal areas and the result was confirmed by in situ hybridization study. By contrast, hepcidin 1, hemojuvelin, ferroportin, transferrin receptor 2, hfe and L-ferritin mRNAs were not differentially expressed according to either lobular zonation or polyploidisation level.

CONCLUSIONS

At variance with glutamine or urea metabolism, iron metabolism is not featured by a metabolic zonation lying only on a basal transcriptional control. The preferential periportal expression of ceruloplasmin raises the issue of its special role in iron overload disorders involving a defect in cellular iron export.

Physiopathologie et génétique de l'hémochromatose HFE de type 1

Hereditary type 1 HFE hemochromatosis is associated with homozygosity for the p.Cys282Tyr mutation of the HFE gene (C282Y mutation). The p.Cys282Tyr mutation of the HFE gene leads to an abnormal reduction in hepatic expression of hepcidin, a protein that appears to control the release of iron from enterocytes and macrophages towards plasma. Abnormally low hepcidin levels promote an increase in the bioavailability of plasma iron, characterized by elevated transferrin saturation and the appearance of non transferrin bound iron. This nontransferrin-bound iron is avidly taken up by the liver, heart, and pancreas, the principal target organs for systemic iron overload. The variable penetrance of this disease is related to environmental and genetic factors. Among the genetic factors, mutations of some newly identified genes may aggravate the phenotype of iron overload associated with homozygosity for the p.Cys282Tyr mutation of the HFE gene; these new genes include those of hemojuvelin (HJV), transferrin receptor 2 (TfR2), and hepcidin (HAMP).

Review article: the genetic basis of haemochromatosis

BACKGROUND

Since the seminal discovery of the HFE gene a decade ago, considerable further progress in unravelling the genetic basis of haemochromatosis has been made. Novel genes and iron overload phenotypes have been described with potential insights into the molecular pathophysiology of human iron metabolism.

AIM

To review recent key advances in the field of inherited iron overload and assess their impact on clinical practice and on our understanding of iron regulation.

METHODS

A PubMed search was undertaken predominantly using 'haemochromatosis', 'HFE', 'hepcidin' and 'ferroportin'. Illustrative cases were sought.

RESULTS

The impact of HFE mutation analysis on the management of haemochromatosis is significant and allows early accurate diagnosis. HFE is also implicated in the siderosis associated with other liver pathologies. Non-HFE genes underpinning other forms of haemochromatosis are now recognized and genotype-phenotype interactions result in a spectrum of disease. These novel gene products interact with HFE in a common pathway for iron homeostasis.

CONCLUSIONS

Further identification of non-HFE genes associated with iron homeostasis will enhance our diagnostic certainty of primary haemochromatosis and may explain the variable expression seen in HFE-related disease. Improving our understanding of the mechanisms of iron regulation may lead to novel therapeutic strategies for the management of iron overload.

Dietary iron overload in the African and hepatocellular carcinoma

Dietary iron overload occurs commonly in parts of sub-Saharan Africa. It results from the consumption of large volumes of traditional beer that is home-brewed in iron pots or drums and consequently has a high iron content. The liver becomes iron overloaded and may develop portal fibrosis or, less often, cirrhosis. A genetic predisposition to the condition has been suggested, but no putative gene has yet been identified. Although originally believed not to cause hepatocellular carcinoma, recent case-control studies have shown African Blacks with dietary iron overload to be at increased risk for the tumour and a causal association has been confirmed in an animal model. The mechanisms of iron-induced malignant transformation are yet to be fully characterised, but the close association between cirrhosis and hepatocellular carcinoma in patients with hereditary haemochromatosis and the lesser association in those with dietary iron overload, suggests that chronic necroinflammatory hepatic disease contributes to the malignant transformation. Increased hepatic iron may, however, also be directly carcinogenic. Probable mechanisms include the generation of reactive oxygen intermediates and the resultant chronic oxidative stress that damages hepatocytes and proteins, causes lipid peroxidation, and induces strand breaks, DNA unwinding, and mutations in tumour-suppressor genes and critical DNA repair genes.

Efficacy and safety of 6-month iron reduction therapy in patients with hepatitis C virus-related cirrhosis: a pilot study

BACKGROUND

Iron reduction therapy (IRT) has been recognized as beneficial for chronic hepatitis C patients. However, its efficacy for hepatitis C virus-related liver cirrhosis (LC-C) has not been elucidated. We evaluated the efficacy and safety of IRT for LC-C patients.

METHODS

Twenty-two LC-C patients were treated with biweekly phlebotomy and low iron diet for 6 months, in addition to regular hepatoprotective therapy. Nineteen sex- and age-matched patients who refused to receive IRT were used as controls. The efficacy of IRT was evaluated on the basis of biochemical parameters.

RESULTS

Of 22 patients receiving IRT, 19 completed the 6-month treatment. IRT significantly reduced serum levels of aspartate aminotransferase (from 89 to 57 U/L; P = 0.003), alanine aminotransferase (from 101 to 54 U/L; P < 0.001), and alpha-fetoprotein (from 28 to 12 ng/mL; P = 0.003). These changes were not observed in the controls. Two patients whose serum albumin concentrations were less than 3.6 g/dL at the beginning of IRT withdrew from IRT because of the new appearance of ascites.

CONCLUSIONS

IRT improved the serum levels of aminotransferases and alpha-fetoprotein in LC-C patients and was generally safe; however, IRT should be performed in patients who maintain serum albumin concentrations of more than 3.6 g/dL.