Iron- and inflammation-induced hepcidin gene expression in mice is not mediated by Kupffer cells in vivo

Hepcidin, a recently discovered iron regulatory peptide, is believed to inhibit the release of iron from absorptive enterocytes and macrophages. Liver hepcidin synthesis is induced in vivo by iron stores and inflammation. The molecular basis of the regulation of hepcidin gene expression by these effectors in hepatocytes is currently unknown, although there is strong evidence that indirect mechanisms are involved. The aims of this study were to gain insight into these mechanisms and to determine to what extent other liver cell types are responsible for transducing the signal by which hepcidin expression is regulated in mouse hepatocytes. For this, we depleted Kupffer cells by injection of liposome-encapsulated clodronate and then studied iron- and inflammation-induced hepcidin gene expression. In addition, we directly evaluated the role of the inflammatory cytokine interleukin 6 (IL-6) by using IL-6-deficient mice. Our results show that iron is able to induce hepcidin gene expression independently of Kupffer cells in the liver and circulating IL-6. In contrast, we show that hepcidin gene induction by inflammation is also independent of Kupffer cells, but involves, at least partly, IL-6. In conclusion, these results show that two independent regulatory pathways control hepcidin gene expression and suggest that hepatocytes play a key role in the regulation of hepcidin gene expression by sensing iron and inflammatory signals.     

Iron Uptake from Transferrin and Asialotransferrin by Hepatocytes from Chronically Alcohol-Fed Rats

Chronic alcohol intake is often associated with alterations to iron homeostasis and an increase in the serum levels of carbohydrate-deficient transferrin. As the liver is a major iron storage site and also synthesizes transferrin, the normal serum iron transport protein, the aim of this study was to test the hypothesis that these disturbances in iron homeostasis were caused by altered hepatocyte iron uptake from the abnormal transferrin. To achieve this, we have investigated iron uptake from both transferrin and asialotransferrin by hepatocytes from male Sprague-Dawley rats fed the De Carli and Lieber alcohol diet. Iron uptake from transferrin by hepatocytes from alcoholic rats was less than 60% that of control values, and in the presence of 50 mM ethanol decreased still further to 35% of the uptake by the corresponding control cells. Iron uptake from rat asialotransferrin was reduced in both groups when compared to that observed from normal transferrin; 13% by control cells and 39% by hepatocytes from alcohol-fed rats. Alcohol, however, had no further effect on asialotransferrin uptake by either hepatocytes from alcohol-fed rats, or their pair-fed controls. Transferrin binding to hepatocytes was also influenced by the alcohol diet. Although there was no difference in binding at 37 degrees C, cells from alcohol-fed rats bound 85% of this total at 4 degrees C, compared to 44% by control hepatocytes. Similar values were also obtained for hepatocyte binding of asialotransferrin; alcohol feeding resulted in an increase in binding at 4 degrees C to 73% from 58% with control cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gender-related variations in iron metabolism and liver diseases

The regulation of iron metabolism involves multiple organs including the duodenum, liver and bone marrow. The recent discoveries of novel iron-regulatory proteins have brought the liver to the forefront of iron homeostasis. The iron overload disorder, genetic hemochromatosis, is one of the most prevalent genetic diseases in individuals of Caucasian origin. Furthermore, patients with non-hemochromatotic liver diseases, such as alcoholic liver disease, chronic hepatitis C or nonalcoholic steatohepatitis, often exhibit elevated serum iron indices (ferritin, transferrin saturation) and mild to moderate hepatic iron overload. Clinical data indicate significant differences between men and women regarding liver injury in patients with alcoholic liver disease, chronic hepatitis C or nonalcoholic steatohepatitis. The penetrance of genetic hemochromatosis also varies between men and women. Hepcidin has been suggested to act as a modifier gene in genetic hemochromatosis. Hepcidin is a circulatory antimicrobial peptide synthesized by the liver. It plays a pivotal role in the regulation of iron homeostasis. Hepcidin has been shown to be regulated by iron, inflammation, oxidative stress, hypoxia, alcohol, hepatitis C and obesity. Sex and genetic background have also been shown to modulate hepcidin expression in mice. The role of gender in the regulation of human hepcidin gene expression in the liver is unknown. However, hepcidin may play a role in gender-based differences in iron metabolism and liver diseases. Better understanding of the mechanisms associated with gender-related differences in iron metabolism and chronic liver diseases may enable the development of new treatment strategies.     

Upregulation of hepcidin by interleukin-1beta in human hepatoma cell lines.

Anemia of chronic disease (ACD) is commonly observed in chronic inflammation, although its pathogenesis is poorly understood. Hepcidin is thought to be a key regulator in iron metabolism and has been implicated in ACD. Although the induction of hepcidin by an inflammatory cytokine interleukin-6 (IL-6) seems to have been confirmed, it is still controversial whether interleukin-1beta (IL-1beta), also known as an inflammatory cytokine, regulates hepcidin expression. We demonstrated that hepcidin mRNA was upregulated by IL-1beta in human hepatoma-derived HuH-7 cells, particularly at low concentrations of IL-1beta, while high concentrations of IL-6 were needed for the upregulation of hepcidin mRNA. Therefore, IL-1beta might be more important for the upregulation of hepcidin in physiological conditions than IL-6. Although IL-1beta induces IL-6 production in hepatocytes, our data indicate that the effect of IL-1beta on hepcidin expression is independent from that of IL-6. In conclusion, IL-1beta might have an important role in ACD.     

Hepatitis C virus-induced oxidative stress suppresses hepcidin expression through increased histone deacetylase activity

Chronic hepatitis C is characterized by iron accumulation in the liver, and excessive iron is hepatotoxic. However, the mechanism by which hepatitis C virus (HCV) regulates iron metabolism is poorly understood. Hepcidin plays a pivotal role as a negative regulator of iron absorption. The aim of the current study was to elucidate the mechanisms that govern hepcidin expression by HCV. Huh 7 cells, Huh7.5 cells, full-length HCV replicon cells established from Huh7.5 cells, and adenoviruses expressing HCV-core or HCV nonstructural proteins 3 through 5 (NS3-5) were used. Hepcidin expression was significantly lower in HCV replicon cells and in HCV core-expressing Huh7 cells. The expression was inversely correlated with the amount of reactive oxygen species (ROS) production. Anti-oxidants restored hepcidin expression in HCV replicon cells and Huh7 cells expressing HCV core. In HCV replicon cells, histone deacetylase (HDAC) activity was elevated at baseline and after exposure to hydrogen peroxide. Anti-oxidants reduced HDAC activity in a dose-dependent manner. HDAC inhibition increased hepcidin expression without affecting ROS production in HCV replicon cells. HCV-induced ROS stabilized the expression of two negative hepcidin regulators, HIF1alpha and HIF2alpha, and its expression was decreased by a HDAC inhibitor or an anti-oxidant. HCV-induced ROS also caused hypoacetylation of histones and inhibited binding of two positive regulators, C/EBPalpha and STAT3, to the hepcidin promoter, whereas anti-oxidant treatment of cells recovered C/EBPalpha and STAT3 binding to the hepcidin promoter. In addition, an HDAC inhibitor restored their binding to the hepcidin promoter via acetylation of histones. CONCLUSION: HCV-induced oxidative stress suppresses hepcidin expression through increased HDAC activity.     

Cytotoxicity of mononuclear cells and vulnerability of hepatocytes in alcoholic fatty liver of baboons

ABSTRACT— Mononuclear cell cytotoxicity against autologous, allogeneic and xenogeneic (rabbit) hepatocytes was investigated in nine baboons fed alcohol for 17–21 months and in nine pair-fed controls. All alcohol-fed animals developed fatty liver. Cytotoxicity of mononuclear cells was not observed when rabbit hepatocytes were used as target cells, but mononuclear cells of alcohol-fed baboons were cytotoxic against hepatocytes of both control animals and hepatocytes from alcohol-fed baboons, including the animals' own hepatocytes. Increased vulnerability of hepatocytes of alcohol-fed baboons was also demonstrated since mononuclear cells of both controls and alcohol-fed animals were more cytotoxic against hepatocytes of alcohol-fed baboons than against those of controls. Thus, autologous and heterologous hepatocytes are more sensitive in the baboon than rabbit hepatocytes in demonstrating cytotoxicity already at the stage of fatty liver. Two factors are contributory: mononuclear cells cytotoxicity and vulnerability of hepatocytes.     

Effect of Chronic Alcohol Feeding on Hepatic Iron Status and Ferritin Uptake by Rat Hepatocytes

Alcohol abuse is known to cause disturbances to iron homeostasis in man and is associated with elevated serum ferritin levels. We have previously shown that ethanol metabolism in the rat hepatocyte is associated with an immediate reduction in ferritin uptake by this cell. In this study we have examined the effect of pair-feeding the Lieber-DeCarli liquid alcohol diet on ferritin uptake by rat hepatocytes. Rat liver ferritin was radiolabeled with ⁵⁹Fe in vivo and isolated by conventional techniques. Rats were pair-fed the Lieber-DeCarli liquid alcoholic diet for 4–6 weeks. Hepatocytes, isolated from their livers by collagenase perfusion, were incubated with [⁵⁹Fe]ferritin in L-15 medium at 37°C and 4° to measure ferritin uptake and binding. The in vitro effect of ethanol on these hepatocytes was also studied. Ferritin and iron parameters were measured in the sera and hepatocytes of these animals and a comparable group of normal chowfed rats. The rate of ferritin uptake by hepatocytes from alcohol-fed rats was significantly faster than that of their pair-fed controls (0.743 ± 0.061 vs. 0.540 ± 0.042 ng/min/10⁶ cells, p < 0.05). However, the rats on Lieber-DeCarli control diet exhibited a lower hepatocyte ferritin uptake rate than chow-fed animals (79.3 ± 8.1% of the control values, p < 0.01). In vitro incubation of cells in 100 mm ethanol resulted in less inhibition of ferritin uptake by hepatocytes from alcoholic rats than from their pair-fed controls (11 ± 7.1% inhibition vs. 43.6 ± 10.7% for controls, p < 0.05). Receptor-mediated binding of ferritin to hepatocytes showed a 61% increase in saturable binding capacity for alcoholic rats (15,820 ± 4950 molecules/cell vs. 9798 ± 3622, p= 0.05). The presence of ethanol in the medium did not affect ferritin binding significantly. Although there was no significant difference in the serum iron values between all three groups, transferrin concentrations were markedly elevated in the alcohol-fed rats, resulting in a much lower transferrin iron saturation than for the control animals. Because the corresponding serum values for the diet controls were intermediate between those for the alcohol-fed rats and the chow-fed animals, these findings may reflect dietary restriction by the liquid diet, which is exacerbated by the addition of alcohol. These findings suggest that there is increased iron uptake by the hepatocyte following chronic alcohol administration, which may be due to the increased ferritin receptors. This is supported by the observation that this alcohol treatment also causes a depletion of serum ferritin. However, the decreased iron content in the alcohol-fed rats indicate that this may be due to a response to changes in iron homeostasis by the hepatocyte and/or redistribution in the body.     

Chronic ethanol consumption enhances interleukin-1-mediated signal transduction in rat liver and in cultured hepatocytes

BACKGROUND: Interleukin-1 (IL-1) is a central mediator of the inflammatory process. Increased serum levels of IL-1 have been reported in alcoholics with liver damage, but it remains unknown whether chronic ethanol intake, in the presence or absence of lipopolysaccharide (LPS), activates IL-1 release and signaling in the hepatocyte. METHODS: IL-1beta and IL-10 release, expression of their receptors (IL-1RI and IL-10R), and the IL-1RI signal transduction response were evaluated in livers and cultured hepatocytes from ethanol-fed or pair-fed rats exposed in vivo or in vitro to LPS, ethanol, or both. RESULTS: Chronic ethanol intake increased both the serum levels of IL-1beta and IL-10 and the expression of IL-1RI, but not of IL-10R, in the liver microsomal fraction. In vivo LPS administration potentiated the ethanol-induced release of plasma cytokines. It is interesting to note that ethanol, either given in a single dose or chronically fed, stimulated IL-1beta and IL-10 release from cultured hepatocytes. Stimulation of hepatocytes with IL-1beta caused a higher activation of IL-1-associated kinase, extracellular receptor-activated kinases 1 and 2, and nuclear factor-kappaB (NF-kappaB) in hepatocytes from alcohol-fed animals than from controls. Furthermore, in the absence of any stimulation, hepatocytes from alcohol-fed animals showed an activation of both kinases, as well as an increase in NF-kappaB binding. Our results suggest the participation of the extracellular signal-regulated kinase (ERK)1/2 pathway in ethanol-induced NF-kappaB activation, because treatment with PD-98059, an ERK1/2 inhibitor, partially suppressed IL-1beta-induced NF-kappaB expression. CONCLUSIONS: Chronic ethanol intake potentiates the action of the proinflammatory cytokine IL-1beta, enhancing the release and signaling response of IL-1beta in the hepatocyte, which in conjunction with other cytokines or LPS may exacerbate the inflammatory damage associated with alcoholic liver disease.     

Heat stress stimulates hepcidin mRNA expression and C/EBPα protein expression in aged rodent liver

Elevations in hepatic iron content occur with aging and physiological stressors, which may promote oxidative injury to the liver. Since dysregulation of the iron regulatory hormone, hepcidin, can cause iron accumulation, our goal was to characterize the regulation of hepcidin in young (6 mo) and old (24 mo) Fischer 344 rats exposed to environmental heat stress. Liver and blood samples were taken in the control condition and after heating. Hepcidin expression did not differ between young and old rats in the control condition, despite higher levels of hepatic iron and IL-6 mRNA in the latter. Following heat stress, pSTAT3 increased in both groups, but C/EBPα and hepcidin mRNA increased only in old rats. Despite this, serum iron decreased in both age groups 2 h after heat stress, suggesting hepcidin-independent hypoferremia in the young rats. The differential regulation of hepcidin between young and old rats after hyperthermia may be due to the enhanced expression of C/EBPα protein in old rats. These data support the concept of “inflammaging” and suggest that repeated exposures to stressors may contribute to the development of anemia in older individuals.     

An essential role for monocyte chemoattractant protein-1 in alcoholic liver injury: regulation of proinflammatory cytokines and hepatic steatosis in mice

The importance of chemokines in alcoholic liver injury has been implicated. The role of the chemokine, monocyte chemoattractant protein-1 (MCP-1), elevated in patients with alcoholic liver disease is not yet understood. Here, we evaluated the pathophysiological significance of MCP-1 and its receptor, chemokine (C-C motif) receptor 2 (CCR2), in alcoholic liver injury. The Leiber-DeCarli diet containing alcohol or isocaloric control diets were fed to wild-type (WT) and MCP-1-deficient knockout (KO) mice for 6 weeks. In vivo and in vitro assays were performed to study the role of MCP-1 in alcoholic liver injury. MCP-1 was increased in Kupffer cells (KCs) as well as hepatocytes of alcohol-fed mice. Alcohol feeding increased serum alanine aminotransferase in WT and CCR2KO, but not MCP-1KO, mice. Alcohol-induced liver steatosis and triglyceride were attenuated in alcohol-fed MCP-1KO, but high in CCR2KO mice, compared to WT, whereas serum endotoxin was high in alcohol-fed WT and MCP-1KO mice. Expression of liver proinflammatory cytokines tumor necrosis factor alpha, interleukin (IL)-1β, IL-6, KC/IL-8, intercellular adhesion molecule 1, and cluster of differentiation 68 was induced in alcohol-fed WT, but inhibited in MCP-1KO, mice independent of nuclear factor kappa light-chain enhancer of activated B cell activation in KCs. Oxidative stress, but not cytochrome P450 2E1, was prevented in chronic alcohol-fed MCP-1KO mice, compared to WT. Increased expression of peroxisome proliferator-activated receptor (PPAR)α and PPARγ was accompanied by nuclear translocation, DNA binding, and induction of fatty acid metabolism genes acyl coenzyme A oxidase and carnitine palmitoyltransferase 1A in livers of alcohol-fed MCP-1KO mice, compared to WT controls. In vitro assays uncovered an inhibitory effect of recombinant MCP-1 on PPARα messenger RNA and peroxisome proliferator response element binding in hepatocytes independent of CCR2. Conclusion: Deficiency of MCP-1 protects mice against alcoholic liver injury, independent of CCR2, by inhibition of proinflammatory cytokines and induction of genes related to fatty acid oxidation, linking chemokines to hepatic lipid metabolism.     

铁调蛋白在大鼠酒精性肝损伤中的保护作用及其机制

目的 研究铁调蛋白在酒精性肝损伤中的作用机制.方法 30只雄性wistar大鼠随机分为对照组、酒精组及铁调蛋白组,饲养6周后处死.检测血清ALT、AST、铁、总铁结合力(TIBC)、铁蛋白、丙二醛及铁调蛋白含量;肝组织行HE染色、普鲁士蓝铁染色及免疫组织化学染色,观察肝组织病理学改变.结果 (1)对照组、酒精组和铁调蛋白组的血清ALT值分别为(25.2±4.6)U/L、(37.9±14.3)U/L和(40.9±14.1)U/L,F=4.907,P＜0.05,差异有统计学意义;血清AST分别为(32.3±13.4)U/L、(55.0±18.6)U/L和(48.3±26.0)U/L,F=3.742,P＜0.05,差异有统计学意义.铁蛋白含量分别为(224.72±85.49)ng/ml、(345.59±124.75)ng/ml和(339.47±138.47)ng/ml,F=3.539,P＜0.05,差异有统计学意义.血清TIBC值分别为(147.30±31.98)μmol/L、(148.04±58.74)μmol/L和(143.28±37.38)μmol/L,F=1.209,P＞0.05,差异无统计学意义.血清铁含量分别为(55.64±13.32)μmol/L、(60.37±25.89)μmol/L和(49.77±17.64)μmol/L,F=0.651,P＞0.05,差异无统计学意义.血清丙二醛含量分别为(5.84±2.17)nmol/ml、(6.51±2.23)nmol/ml和(4.27±2.68)nmol/ml,F=2.782,P＞0.05,差异无统计学意义.血清铁调蛋白含量分别为(155.96±44.91)ng/ml、(124.11±31.98)ng/ml和(114.96±25.81)ng/ml,F=3.839,P＜0.05,差异有统计学意义.(2)组织学显示酒精组肝细胞明显脂肪变,铁调蛋白组肝细胞脂肪病变较酒精组有所改善.对照组、酒精组和铁调蛋白组每5个高倍视野(×400)的肝脏铁染颗粒数分别为(0.8±1.0)个、(1.2±1.6)个和(1.1±1.1)个,F=0.254,P＞0.05,差异无统计学意义.肝脏免疫组织化学每5个高倍视野(×400)阳性细胞数分别为(15.0±8.1)个、(6.6±4.2)个和(7.6±3.2)个,F=4.139,P＜0.05,差异有统计学意义.结论 酒精性肝病大鼠的铁调蛋白表达下降,伴铁代谢紊乱.补充铁调蛋白可以通过抑制脂质过氧化反应改善肝脏损伤.

Abstract：

Objective To study the mechanism of how iron-regulatory protein (hepcidin) affect iron overload in alcoholic liver disease (ALD). Methods Thirty male wistar rats were randomly divided into 3 groups:Lieber-Decarli liquid without alcohol group (control group), Lieber-Decarli liquid with alcohol (alcohol group) and hepcidin intraperitoneally injected group (hepcidin group), each rat was fed for 6 weeks. The Serum concentration of Alanine Aminotransferase (ALT), Aspartate Amino Transferase (AST), Iron, Total Iron Binding capacity (TIBC), Ferritin, Malonyl Dialdehyde (MDA) and Hepcidin were determined. Hepatic tissue was examined by hematoxylin and eosin staining, prussian blue iron staining and immunohistochemisty staining. Results (1) Serum concentration of ALT in control group, alcohol group and hepcidin group were (25.2 ± 4.6) U/L, (37.9 ± 14.3) U/L and (40.9 ± 14.1) U/L (F = 4.907, P ＜ 0.05), respectively. Serum AST among three groups were (32.3 ± 13.4) U/L, (55.0 ± 18.6) U/L and (48.3 ± 26.0) U/L (F = 3.742, P ＜ 0.05),respectively. The secretions of ferritin were (224.72 ± 85.49) ng/ml, (345.59 ± 124.75) ng/ml and (339.47 ±138.47) ng/ml (F = 3.539, P ＜ 0.05). The serum concentrations of TIBC were (147.30 ± 31.98) μ mol/L,(148.04 ± 58.74) μmol/L and (143.28 ± 37.38) μmol/L (F = 1.209, P ＞ 0.05), respectively. The serum concentrations of iron were (55.64 ± 13.32) μmol/L, (60.37 ± 25.89) μmol/L and (49.77 ± 17.64) μmol/L (F = 0.651, P ＞ 0.05), respectively. The serum concentration of MDA were (5.84 ± 2.17) nmol/ml, (6.51 ±2.23) nmol/ml and (4.27 ± 2.68) nmol/ml (F = 2.782, P ＞ 0.05), respectively. The serum concentration of Hepeidin were ( 155.96 ± 44.91 )ng/ml, (124.11 ± 31.98) ng/ml and ( 114.96 ± 25.81 ) ng/ml (F = 3.839, P ＜0.05), respectively. (2) Significant fat change observed in the liver of alcohol group. The positive granulationes of iron staining were (0.8 ± 1.0), (1.2 ± 1.6) and (1.1 ± 1.1) (F = 0.254, P ＞ 0.05), respectively. No differences found of liver iron express among the three groups. Intraperitoneal injection of hepcidin increased hepcidin expression in liver which was inhibited by alcohol (F= 4.139, P ＜ 0.05). Conclusion ALD rats with lower hepcidin expression in liver can result in iron metabolism disorder. Ectogenic hepcidin can protect liver against alcohol damage by inhibiting lipid peroxidation.     

Hepcidin,a putative mediator of anemia of inflammation,is a type II acute-phase protein

Hepcidin is a liver-made peptide proposed to be a central regulator of intestinal iron absorption and iron recycling by macrophages. In animal models, hepcidin is induced by inflammation and iron loading, but its regulation in humans has not been studied. We report that urinary excretion of hepcidin was greatly increased in patients with iron overload, infections, or inflammatory diseases. Hepcidin excretion correlated well with serum ferritin levels, which are regulated by similar pathologic stimuli. In vitro iron loading of primary human hepatocytes, however, unexpectedly down-regulated hepcidin mRNA, suggesting that in vivo regulation of hepcidin expression by iron stores involves complex indirect effects. Hepcidin mRNA was dramatically induced by interleukin-6 (IL-6) in vitro, but not by IL-1 or tumor necrosis factor alpha (TNF-alpha), demonstrating that human hepcidin is a type II acute-phase reactant. The linkage of hepcidin induction to inflammation in humans supports its proposed role as a key mediator of anemia of inflammation.