Attenuation of acute and chronic liver injury in rats by iron-deficient diet

The Impact of the Combined Effect of Inhalation Anesthetics and Iron Dextran on Rats' Systemic Toxicity

Disruption of any stage of iron homeostasis, including uptake, utilization, efflux, and storage, can cause progressive damage to peripheral organs. The health hazards associated with occupational exposure to inhalation anesthetics (IA) in combination with chronic iron overload are not well documented. This study aimed to investigate changes in the concentration of essential metals in the peripheral organs of rats after iron overload in combination with IA. The aim was also to determine how iron overload in combination with IA affects tissue metal homeostasis, hepcidin-ferritin levels, and MMP levels according to physiological, functional, and tissue features. According to the obtained results, iron accumulation was most pronounced in the liver (19×), spleen (6.7×), lungs (3.1×), and kidneys (2.5×) compared to control. Iron accumulation is associated with elevated heavy metal levels and impaired essential metal concentrations due to oxidative stress (OS). Notably, the use of IA increases the iron overload toxicity, especially after Isoflurane exposure. The results show that the regulation of iron homeostasis is based on the interaction of hepcidin, ferritin, and other proteins regulated by inflammation, OS, free iron levels, erythropoiesis, and hypoxia. Long-term exposure to IA and iron leads to the development of numerous adaptation mechanisms in response to toxicity, OS, and inflammation. These adaptive mechanisms of iron regulation lead to the inhibition of MMP activity and reduction of oxidative stress, protecting the organism from possible damage.

Iron overload in alcoholic liver disease: underlying mechanisms, detrimental effects, and potential therapeutic targets

Alcoholic liver disease (ALD) is a global public health challenge due to the high incidence and lack of effective therapeutics. Evidence from animal studies and ALD patients has demonstrated that iron overload is a hallmark of ALD. Ethanol exposure can promote iron absorption by downregulating the hepcidin expression, which is probably mediated by inducing oxidative stress and promoting erythropoietin (EPO) production. In addition, ethanol may enhance iron uptake in hepatocytes by upregulating the expression of transferrin receptor (TfR). Iron overload in the liver can aggravate ethanol-elicited liver damage by potentiating oxidative stress via Fenton reaction, promoting activation of Kupffer cells (KCs) and hepatic stellate cells (HSCs), and inducing a recently discovered programmed iron-dependent cell death, ferroptosis. This article reviews the current knowledge of iron metabolism, regulators of iron homeostasis, the mechanism of ethanol-induced iron overload, detrimental effects of iron overload in the liver, and potential therapeutic targets.

The pivotal role of heme Oxygenase-1 in reversing the pathophysiology and systemic complications of NAFLD

The pathogenesis and molecular pathways involved in non-alcoholic fatty liver disease (NAFLD) are reviewed, as well as what is known about mitochondrial dysfunction that leads to heart disease and the progression to steatohepatitis and hepatic fibrosis. We focused our discussion on the role of the antioxidant gene heme oxygenase-1 (HO-1) and its nuclear coactivator, peroxisome proliferator-activated receptor-gamma coactivator (PGC1-α) in the regulation of mitochondrial biogenesis and function and potential therapeutic benefit for cardiac disease, NAFLD as well as the pharmacological effect they have on the chronic inflammatory state of obesity. The result is increased mitochondrial function and the conversion of white adipocyte tissue to beige adipose tissue ("browning of white adipose tissue") that leads to an improvement in signaling pathways and overall liver function. Improved mitochondrial biogenesis and function is essential to preventing the progression of hepatic steatosis to NASH and cirrhosis as well as preventing cardiovascular complications.

Dietary iron restriction leads to a reduction in hepatic fibrosis in a rat model of non-alcoholic steatohepatitis

Iron overload in the liver causes oxidative stress and inflammation, which result in organ dysfunction, making it a risk factor for non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma. We aimed to evaluate the effect of dietary iron restriction on disease progression in rats fed a choline-deficient L-amino acid-defined (CDAA) diet. Male F344 rats were fed a choline-sufficient amino acid-defined (control) diet, a CDAA diet or an iron-restricted CDAA diet for 4, 8 and 12 weeks. At each time point, hepatic iron levels, oxidative stress, inflammation and fibrosis were evaluated by immunohistochemistry. The iron-restricted CDAA diet significantly decreased serum iron levels for 12 weeks compared with the CDAA diet. Histological analysis confirmed that feeding with the CDAA diet induced hepatic iron overload and that this was associated with oxidative stress (number of 8-hydroxydeoxyguanosine-positive cells), inflammation (CD68 positive area) and fibrosis (Sirius Red positive area). Iron restriction with the CDAA diet significantly led to a reduction in the hepatic iron levels, oxidative stress, inflammation and fibrosis. Therefore, dietary iron restriction could be a useful therapeutic approach for NASH patients with hepatic iron overload.

Summary: We reveal that dietary iron restriction leads to a reduction in hepatic inflammation, oxidative stress and fibrosis in rats fed a choline-deficient L-amino acid-defined (CDAA) diet.

Iron-Induced Liver Injury: A Critical Reappraisal

Iron is implicated in the pathogenesis of a number of human liver diseases. Hereditary hemochromatosis is the classical example of a liver disease caused by iron, but iron is commonly believed to contribute to the progression of other forms of chronic liver disease such as hepatitis C infection and nonalcoholic fatty liver disease. In this review, we present data from cell culture experiments, animal models, and clinical studies that address the hepatotoxicity of iron. These data demonstrate that iron overload is only weakly fibrogenic in animal models and rarely causes serious liver damage in humans, calling into question the concept that iron overload is an important cause of hepatotoxicity. In situations where iron is pathogenic, iron-induced liver damage may be potentiated by coexisting inflammation, with the resulting hepatocyte necrosis an important factor driving the fibrogenic response. Based on the foregoing evidence that iron is less hepatotoxic than is generally assumed, claims that assign a causal role to iron in liver injury in either animal models or human liver disease should be carefully evaluated.

Effects of long-term exposures to low iron and branched-chain amino acid containing diets on aging skeletal muscle of Fisher 344 × Brown Norway rats

Aging skeletal muscle displays an altered iron status that may promote oxidative stress and sarcopenia. A diet containing low iron (LI) could reduce muscle iron status and attenuate age-related muscle atrophy. Supplemental branched-chain amino acids (BCAA) may also alleviate sarcopenia by promoting muscle protein synthesis and iron status improvement. This study examined individual and combined effects of LI and BCAA diets on anabolic signaling and iron status in skeletal muscle of aging rats. Twenty-nine-month-old male Fisher 344 × Brown Norway rats consumed the following control-base diets: control + regular iron (35 mg iron/kg) (CR; n = 11); control + LI (∼6 mg iron/kg) (CL; n = 11); 2×BCAA + regular iron (BR; n = 10); and 2×BCAA + LI (BL; n = 12) for 12 weeks. Although LI and/or 2×BCAA did not affect plantaris muscle mass, 2×BCAA groups showed lower muscle iron content than did CR and CL groups (P < 0.05). p70 ribosomal protein S6 kinase phosphorylation was greater in 2×BCAA and LI animals compared with CR animals (P < 0.05). Interactions between IRON and BCAA were observed for proteins indicative of mitochondrial biogenesis (peroxisome proliferator-activated receptor gamma coactivator 1 alpha) and oxidative capacity (cytochrome c oxidase subunit 2 and citrate synthase) (P < 0.05) wherein the combined diet (BL) negated potential benefits of individual diets. Antioxidant capacity, superoxide dismutase activity, and oxidative injury (3-nitrotyrosine, protein carbonyls, and 4-hydroxynonenal) were similar between groups. In conclusion, 12 weeks of LI and 2×BCAA diets showed significant impacts on increasing anabolic signaling as well as ameliorating iron status; however, these interventions did not affect muscle mass.

Iron depletion induces hepatic secretion of biliary lipids and glutathione in rats

Iron depletion (ID) has been shown to induce the liver expression of Cyp7a1, the rate-limiting enzyme initiating conversion of cholesterol to bile acids (BA), although the effect on bile acids metabolism and bile production is unknown. Therefore, we investigated changes in bile secretion and BA synthesis during diet-induced iron depletion (ID) in rats. ID increased bile flow along with augmented biliary excretion of bile acids, glutathione, cholesterol and phospholipids. Accordingly, we found transcriptional upregulation of the Cyp7a1, Cyp8b1, and Cyp27a1 BA synthetic enzymes, as well as induction of the Abcg5/8 cholesterol transporters in ID rat livers. In contrast, intravenous infusion of ³H-taurocholate failed to elicit any difference in biliary secretion of this compound in the ID rats. This corresponded with unchanged expression of canalicular rate-limiting transporters for BA as well as glutathione. We also observed that ID substantially changed the spectrum of BA in bile and decreased plasma concentrations of BA and cholesterol. Experiments with differentiated human hepatic HepaRG cells confirmed human CYP7A1 orthologue upregulation resulting from reduced iron concentrations. Results employing a luciferase reporter gene assay suggest that the transcriptional activation of the CYP7A1 promoter under ID conditions works independent of farnesoid X (FXR), pregnane X (PXR) and liver X (LXRα) receptors activation. It can be concluded that this study characterizes the molecular mechanisms of modified bile production as well as cholesterol as along with BA homeostasis during ID. We propose complex upregulation of BA synthesis, and biliary cholesterol secretion as the key factors affected by ID.

Genetic disruption of NRF2 promotes the development of necroinflammation and liver fibrosis in a mouse model of HFE-hereditary hemochromatosis

Background and Aims

In hereditary hemochromatosis, iron deposition in the liver parenchyma may lead to fibrosis, cirrhosis and hepatocellular carcinoma. Most cases are ascribed to a common mutation in the HFE gene, but the extent of clinical expression is greatly influenced by the combined action of yet unidentified genetic and/or environmental modifying factors. In mice, transcription factor NRF2 is a critical determinant of hepatocyte viability during exposure to acute dietary iron overload. We evaluated if the genetic disruption of Nrf2 would prompt the development of liver damage in Hfe^-/- mice (an established model of human HFE-hemochromatosis).

Methods

Wild-type, Nrf2^-/-, Hfe^-/- and double knockout (Hfe/Nrf2^-/-) female mice on C57BL/6 genetic background were sacrificed at the age of 6 (young), 12–18 (middle-aged) or 24 months (old) for evaluation of liver pathology.

Results

Despite the parenchymal iron accumulation, Hfe^-/- mice presented no liver injury. The combination of iron overload (Hfe^-/-) and defective antioxidant defences (Nrf2^-/-) increased the number of iron-related necroinflammatory lesions (sideronecrosis), possibly due to the accumulation of toxic oxidation products such as 4-hydroxy-2-nonenal-protein adducts. The engulfment of dead hepatocytes led to a gradual accumulation of iron within macrophages, featuring large aggregates. Myofibroblasts recruited towards the injury areas produced substantial amounts of collagen fibers involving the liver parenchyma of double-knockout animals with increased hepatic fibrosis in an age-dependent manner.

Conclusions

The genetic disruption of Nrf2 promotes the transition from iron accumulation (siderosis) to liver injury in Hfe^-/- mice, representing the first demonstration of spontaneous hepatic fibrosis in the long term in a mouse model of hereditary hemochromatosis displaying mildly elevated liver iron.

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Despite the parenchymal iron overload, single Hfe^-/- mice present no liver injury.

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Hfe and Nrf2 double knockout mice develop liver fibrosis with aging.

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Fibrosis is triggered by iron-related hepatocellular death (sideronecrosis).

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Nrf2 genetic disruption increases susceptibility to oxidative/electrophilic stress.

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NRF2 status is a potential determinant of liver injury in hemochromatosis.

Steatohepatitis is developed by a diet high in fat, sucrose, and cholesterol without increasing iron concentration in rat liver

Iron overload to the liver is known to be a pathogenesis of nonalcoholic steatohepatitis through oxidative stress. High-fat diets have been reported to increase iron concentration in livers that developed steatohepatitis in experimental animals. However, the effect of high-fat diets on hepatic iron concentration is controversial. We hypothesized that a diet high in lard, cholesterol, and sucrose (Western diet) leads to the development of steatohepatitis without increasing hepatic iron concentration. Rats were given either a control or the Western diet for 12 weeks. The Western diet increased triacylglycerol concentration and oxidative stress markers such as the concentration of thiobarbituric acid reactive substances and messenger RNA (mRNA) expression of heme oxygenase-1 in the liver. The Western diet also increased the mRNA expression of macrophage-1 antigen, cluster of differentiation (CD) 45, and CD68 in the liver, and nuclear factor κB level in liver nuclear fraction, suggesting the development of hepatic inflammation. Histological observation also indicated fatty liver and hepatic inflammation in the rats given the Western diet. In contrast, the Western diet decreased iron concentration in the liver. These results clearly indicated that the diet high in lard, cholesterol, and sucrose induces steatohepatitis without increasing hepatic iron concentration.

Iron Deficiency Impairs Intra-Hepatic Lymphocyte Mediated Immune Response

Hepatic expression of iron homeostasis genes and serum iron parameters predict the success of immunosuppression withdrawal following clinical liver transplantation, a phenomenon known as spontaneous operational tolerance. In experimental animal models, spontaneous liver allograft tolerance is established through a process that requires intra-hepatic lymphocyte activation and deletion. Our aim was to determine if changes in systemic iron status regulate intra-hepatic lymphocyte responses. We used a murine model of lymphocyte-mediated acute liver inflammation induced by Concanavalin A (ConA) injection employing mice fed with an iron-deficient (IrDef) or an iron-balanced diet (IrRepl). While the mild iron deficiency induced by the IrDef diet did not significantly modify the steady state immune cell repertoire and systemic cytokine levels, it significantly dampened inflammatory liver damage after ConA challenge. These findings were associated with a marked decrease in T cell and NKT cell activation following ConA injection in IrDef mice. The decreased liver injury observed in IrDef mice was independent from changes in the gut microflora, and was replicated employing an iron specific chelator that did not modify intra-hepatic hepcidin secretion. Furthermore, low-dose iron chelation markedly impaired the activation of isolated T cells in vitro. All together, these results suggest that small changes in iron homeostasis can have a major effect in the regulation of intra-hepatic lymphocyte mediated responses.

Hepatic fibrogenesis and transforming growth factor/Smad signaling activation in rats chronically exposed to low doses of lead

Lead is an important heavy metal pollutant in the environment. The nervous system, kidney and liver are the most susceptible organs to lead deposition, showing that this pollutant has no single target system. To examine the cellular and molecular mechanisms involved in their pathobiology of chronic lead at low-dose exposure in the liver, male Wistar rats were exposed to 0.06% lead acetate in drinking water every day for 4 months. At the end of the study, hepatic metal accumulation, morphology and function were examined. Immunochemical staining and Western blot analysis were performed to detect extracellular matrix proteins, α-smooth muscle actin and transforming growth factor (TGF)β1/Smad pathway expression. Results showed increased laminin, collagen IV and fibronectin, located at the perisinusoidal space. Phenotypic transformation of hepatic stellate cells into myofibroblast-like cells was evidenced at the ultrastructural level and a significant expression of α-smooth muscle actin in Disse’s space was observed. These findings were associated with a marked increase in TGFβ1/Smad2/3 signaling. Our data suggest that, chronically, exposure to low levels of lead could trigger the onset of a hepatic fibrogenic process through upregulated TGFβ1/Smad signaling.

Liver toxicity of thioacetamide is increased by hepatocellular iron overload

An increase in hepatic iron concentration might exacerbate liver injury. However, it is unknown whether hepatic iron overload may exacerbate acute liver injury from various toxins. Therefore, we evaluated how manipulations to increase hepatic iron concentration affected the extent of acute liver injury from thioacetamide. In this study, we used rats with either "normal" or increased hepatic iron concentration. Iron overload was induced by either providing excess iron in the diet or by injecting iron subcutaneously. Both routes of providing excess iron induced an increase in hepatic iron overload. Meanwhile, the subcutaneous route induced both hepatocellular and sinusoidal cell iron deposition; the oral route induced lesser degree of hepatic iron concentration and only hepatocellular iron overload. Thioacetamide administration to the rats with "normal" hepatic iron concentration induced hepatic cell necrosis and apoptosis associated with a remarkable increase in serum aminotransaminases and depletion of hepatic glutathione and other antioxidative indices. Thioacetamide administration to the iron-overloaded rats exacerbated the extent of liver injury only in the rats orally induced with iron overload. In the rats subcutaneously induced with iron overload, the extent of liver injury from thioacetamide was not different from that observed in the rats with "normal" iron overload. It was concluded that the outcome of thioacetamide-induced acute liver injury may depend on both the level of hepatic iron concentration and on the cellular distribution of iron. While isolated hepatocellular iron overload may exacerbate thioacetamide-induced acute liver injury, a combined hepatocellular and sinusoidal cell iron deposition, even at high hepatic iron concentration, had no such an effect.

Pathophysiology of NASH: perspectives for a targeted treatment

Non alcoholic steatohepatitis (NASH) is the more severe form of nonalcoholic fatty liver disease. In NASH, fatty liver, hepatic inflammation, hepatocyte injury and fibrogenesis are associated, and this condition may eventually lead to cirrhosis. Current treatment of NASH relies on the reduction of body weight and increase in physical activity, but there is no pharmacologic treatment approved as yet. Emerging data indicate that NASH progression results from parallel events originating from the liver as well as from the adipose tissue, the gut and the gastrointestinal tract. Thus, dysfunction of the adipose tissue through enhanced flow of free fatty acids and release of adipocytokines, and alterations in the gut microbiome generate proinflammatory signals that underlie NASH progression. Additional 'extrahepatic hits' include dietary factors and gastrointestinal hormones. Within the liver, hepatocyte apoptosis, ER stress and oxidative stress are key contributors to hepatocellular injury. In addition, lipotoxic mediators and danger signals activate Kupffer cells which initiate and perpetuate the inflammatory response by releasing inflammatory mediators that contribute to inflammatory cell recruitment and development of fibrosis. Inflammatory and fibrogenic mediators include chemokines, the cannabinoid system, the inflammasome and activation of pattern-recognition receptors. Here we review the major mechanisms leading to appearance and progression of NASH, focusing on both extrahepatic signals and local inflammatory mechanisms, in an effort to identify the most promising molecular targets for the treatment of this condition.

Pathophysiology of NASH: perspectives for a targeted treatment

Non alcoholic steatohepatitis (NASH) is the more severe form of nonalcoholic fatty liver disease. In NASH, fatty liver, hepatic inflammation, hepatocyte injury and fibrogenesis are associated, and this condition may eventually lead to cirrhosis. Current treatment of NASH relies on the reduction of body weight and increase in physical activity, but there is no pharmacologic treatment approved as yet. Emerging data indicate that NASH progression results from parallel events originating from the liver as well as from the adipose tissue, the gut and the gastrointestinal tract. Thus, dysfunction of the adipose tissue through enhanced flow of free fatty acids and release of adipocytokines, and alterations in the gut microbiome generate proinflammatory signals that underlie NASH progression. Additional 'extrahepatic hits' include dietary factors and gastrointestinal hormones. Within the liver, hepatocyte apoptosis, ER stress and oxidative stress are key contributors to hepatocellular injury. In addition, lipotoxic mediators and danger signals activate Kupffer cells which initiate and perpetuate the inflammatory response by releasing inflammatory mediators that contribute to inflammatory cell recruitment and development of fibrosis. Inflammatory and fibrogenic mediators include chemokines, the cannabinoid system, the inflammasome and activation of pattern-recognition receptors. Here we review the major mechanisms leading to appearance and progression of NASH, focusing on both extrahepatic signals and local inflammatory mechanisms, in an effort to identify the most promising molecular targets for the treatment of this condition.

Profibrotic effect of miR-33a with Akt activation in hepatic stellate cells

MicroRNAs (miRNAs) attract more attention in the pathophysiology of liver fibrosis and miR-33a has been previously demonstrated as involved in the regulation of cholesterol and lipid metabolism. Transforming growth factor-beta1 (TGF-β1) is generally accepted to be the main stimulating factor in the hepatic stellate cells (HSCs) activation, which plays an important role in hepatic fibrosis. However, the involvement and underlying mechanism of miR-33a and its role in TGF-β1-induced hepatic fibrogenesis remains unknown. Here, we investigate the role of miR-33a in the activation of immortalized human HSCs, Lx-2 cells. Our findings have shown that the expression of miR-33a with its host gene sterol regulatory element-binding protein 2 (SREBP2) was more highly expressed in activation of Lx-2 cells than in quiescent cells. The expression of miR-33a on TGF-β1-induced HSCs activation may be modulated via the activation of PI3K/Akt pathway. In addition, miR-33a significantly correlated with TGF-β1-induced expression of α1 (I) collagen (Col1A1) and α-SMA in HSCs. Bioinformatics analyses predict that peroxisome proliferator activated receptor-alpha (PPAR-α) is the potential target of miR-33a. We further found that anti-miR-33a significantly increases target gene PPAR-α mRNA and protein level, suggesting that miR-33a involved in HSCs function might be modulated by targeting PPAR-α. Finally, our results indicate that the expression of miR-33a increased with the progression of liver fibrosis. These results suggested that anti-miR-33a inhibit activation and extracellular matrix production, at least in part, via the activation of PI3K/Akt pathway and PPAR-α and anti sense of miR-33a may be a novel potential therapeutic approach for treating hepatic fibrosis in the future.

Effect of Nerium oleander (N.O.) leaves extract on serum hepcidin, total iron, and infiltration of ED1 positive cells in albino rat

To gain insight into the hepatohistological alterations in noninjured rat liver, Nerium oleander (N.O.) leaves extract was injected intramuscularly to induce an acute phase reaction (APR). Histopathological changes were studied after 3, 12, and 24 h time course of sterile muscle abscess. Tissue integrity and any infiltration of inflammatory cells in the liver were investigated by Hematoxylin and Eosin and ED1 peroxidase stainings. The administration of N.O. leaves extract (10 mL/kg) in H & E stained sections showed a general vacuolization of cytoplasm resulting loss of polarity with prominent nucleoli after 3 h of induction. At 12 h, eccentric nuclei were also observed in the sections. Marked infiltration of leucocytes with predominate macrophages was also found after 24 h as seen by ED1 positive staining. In the present study, a possible relationship between serum hepcidin and total iron level was also investigated in vivo. An early increase of hepcidin and total iron level (3 h) with a maximum at 12 h (P < 0.01; P < 0.001) was observed. These changes indicate that sterile muscle abscess may induce APR resulting in hepatic damage which is evident with the recruitment of inflammatory cells into the organ.

Gadolinium contrast agent-induced CD163+ ferroportin+ osteogenic cells in nephrogenic systemic fibrosis

Gadolinium-based contrast agents are linked to nephrogenic systemic fibrosis in patients with renal insufficiency. The pathology of nephrogenic systemic fibrosis is characterized by abnormal tissue repair: fibrosis and ectopic ossification. The mechanisms by which gadolinium could induce fibrosis and ossification are not known. We examined in vitro the effect of a gadolinium-based contrast agent on human peripheral blood mononuclear cells for phenotype and function relevant to the pathology of nephrogenic systemic fibrosis using immunofluorescence, flow cytometry, real-time PCR, and osteogenic assays. We also examined tissues from patients with nephrogenic systemic fibrosis, using IHC to identify the presence of cells with phenotype induced by gadolinium. Gadolinium contrast induced differentiation of human peripheral blood mononuclear cells into a unique cellular phenotype--CD163(+) cells expressing proteins involved in fibrosis and bone formation. These cells express fibroblast growth factor (FGF)23, osteoblast transcription factors Runt-related transcription factor 2, and osterix, and show an osteogenic phenotype in in vitro assays. We show in vivo the presence of CD163(+)/procollagen-1(+)/osteocalcin(+) cells in the fibrotic and calcified tissues of nephrogenic systemic fibrosis patients. Gadolinium contrast-induced CD163(+)/ferroportin(+)/FGF23(+) cells with osteogenic potential may play a role in systemic fibrosis and ectopic ossification in nephrogenic systemic fibrosis.

Dietary fat level affects tissue iron levels but not the iron regulatory gene HAMP in rats

Because dietary fats affect the regulation and use of body iron, we hypothesized that iron regulatory and transport genes may be affected by dietary fat. A model of early-stage I to II, nonalcoholic fatty liver was used in which rats were fed standard (35% energy from fat) or high-fat (71% energy from fat) liquid diets with normal iron content (STD/HF groups). In addition, intraperitoneal injections of iron dextran were given to iron-loaded (STD+/HF+ groups) and iron-deficient diets to STD-/HF- groups. Plasma osmolality, hemoglobin level, and mean corpuscular hemoglobin concentration were increased in all STD diet groups compared with all HF diet groups. Plasma iron and transferrin saturation were affected by an interaction between dietary fat and iron. They were high in the STD group (normal iron) compared with their respective HF group. Similarly, this group also showed a 4-fold increase in the messenger RNA expression of the hepatic hemochromatosis gene. Spleen iron was high in the iron-loaded STD+ group compared with all other groups. Hepatic iron and messenger RNA expression of peroxisome proliferator-activated receptor-γ, CCAAT/enhancer binding protein α, interleukin-6, and iron transport genes (transferrin receptor 2, divalent metal transporter 1 iron-responsive element, and divalent metal transporter 1 non-iron-responsive element) were increased, whereas tumor necrosis factor α was decreased in the HF diet groups. The expression of iron regulatory gene HAMP was not increased in the HF diet groups. Iron regulatory and transport genes involved in cellular and systemic iron homeostasis may be affected by the macronutrient composition of the diet.

Iron in fatty liver and in the metabolic syndrome: a promising therapeutic target

The dysmetabolic iron overload syndrome (DIOS) is now a frequent finding in the general population, as is detected in about one third of patients with nonalcoholic fatty liver disease (NAFLD) and the metabolic syndrome. The pathogenesis is related to altered regulation of iron transport associated with steatosis, insulin resistance, and subclinical inflammation, often in the presence of predisposing genetic factors. Evidence is accumulating that excessive body iron plays a causal role in insulin resistance through still undefined mechanisms that probably involve a reduced ability to burn carbohydrates and altered function of adipose tissue. Furthermore, DIOS may facilitate the evolution to type 2 diabetes by altering beta-cell function, the progression of cardiovascular disease by contributing to the recruitment and activation of macrophages within arterial lesions, and the natural history of liver disease by inducing oxidative stress in hepatocytes, activation of hepatic stellate cells, and malignant transformation by promotion of cell growth and DNA damage. Based on these premises, the association among DIOS, metabolic syndrome, and NAFLD is being investigated as a new risk factor to predict the development of overt cardiovascular and hepatic diseases, and possibly hepatocellular carcinoma, but most importantly, represents also a treatable condition. Indeed, iron depletion, most frequently achieved by phlebotomy, has been shown to decrease metabolic alterations and liver enzymes in controlled studies in NAFLD. Additional studies are warranted to evaluate the potential of iron reductive therapy on hard clinical outcomes in patients with DIOS.

Rescuing hepatocytes from iron-catalyzed oxidative stress using vitamins B1 and B6

In the following rescue experiments, iron-mediated hepatocyte oxidative stress cytotoxicity was found to be prevented if vitamin B1 or B6 was added 1h after treatment with iron. The role of iron in catalyzing Fenton-mediated oxidative damage has been implicated in iron overload genetic diseases, carcinogenesis (colon cancer), Alzheimer's disease and complications associated with the metabolic syndrome through the generation of reactive oxygen species (ROS). The objectives of this study were to interpret the cytotoxic mechanisms and intracellular targets of oxidative stress using "accelerated cytotoxicity mechanism screening" techniques (ACMS) and to evaluate the rescue strategies of vitamins B1 and B6. Significant cytoprotection by antioxidants or ROS scavengers indicated that iron-mediated cytotoxicity could be attributed to reactive oxygen species. Of the B6 vitamers, pyridoxal was best at rescuing hepatocytes from iron-catalyzed lipid peroxidation (LPO), protein oxidation, and DNA damage, while pyridoxamine manifested greatest protection against ROS-mediated damage. Thiamin (B1) decreased LPO, mitochondrial and protein damage and DNA oxidation. Together, these results indicate that added B1 and B6 vitamins protect against the multiple targets of iron-catalyzed oxidative damage in hepatocytes. This study provides insight into the search for multi-targeted natural therapies to slow or retard the progression of diseases associated with Fenton-mediated oxidative damage.

Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson's, Huntington's, Alzheimer's, prions, bactericides, chemical toxicology and others as examples

Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions.

Progress in developing rat models of hepatic encephalopathy

Hepatic encephalopathy is a serious complication of acute and chronic liver diseases and has a high mortality rate. The pathogenesis of hepatic encephalopathy remains unclear, and there is no means of prevention or effective cure for the disease. Therefore, there is an urgent need for the basic and clinical research of hepatic encephalopathy to elucidate its pathogenesis. The development of animal models is important for elucidating the pathogenesis of hepatic encephalopathy and providing new avenues for diagnosis and therapy of the disease. Among a variety of animal models, rat model is applied most widely for similarity to humans, repeatability, reliability, applicability, controllability, simplicity and economy. In this paper, we briefly review various rat models of hepatic encephalopathy that have different origins.

A human-type nonalcoholic steatohepatitis model with advanced fibrosis in rabbits

Nonalcoholic steatohepatitis (NASH) progresses to liver fibrosis and cirrhosis, which can lead to life-threatening liver failure and the development of hepatocellular carcinoma. The aim of the present study was to create a rabbit model of NASH with advanced fibrosis (almost cirrhosis) by feeding the animals a diet supplemented with 0.75% cholesterol and 12% corn oil. After 9 months of feeding with this diet, the rabbits showed high total cholesterol levels in serum and liver tissues in the absence of insulin resistance. The livers became whitish and nodular. In addition, the number of rabbit macrophage antigen-positive cells and the expression of mRNAs for inflammatory cytokines showed a significant increase. Moreover, fibrotic septa composed of collagens and alpha-smooth muscle actin-positive cells were found between the central and portal veins, indicating alteration of the parenchymal architecture. There was also a marked increase of mRNAs for transforming growth factor-beta1 and collagen 1A1. Comprehensive analysis of protein and gene expression revealed an imbalance of the antioxidant system and methionine metabolism. We also found that ezetimibe attenuated steatohepatitis in this model. In conclusion, the present rabbit model of NASH features advanced fibrosis that is close to cirrhosis and may be useful for analyzing the molecular mechanisms of human NASH. Ezetimibe blunted the development of NASH in this model, suggesting its potential clinical usefulness for human steatohepatitis.

Suppression of type I collagen production by microRNA-29b in cultured human stellate cells

MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression through imperfect base pairing with the 3' untranslated region (3'UTR) of target mRNA. We studied the regulation of alpha 1 (I) collagen (Col1A1) expression by miRNAs in human stellate cells, which are involved in liver fibrogenesis. Among miR-29b, -143, and -218, whose expressions were altered in response to transforming growth factor-beta1 or interferon-alpha stimulation, miR-29b was the most effective suppressor of type I collagen at the mRNA and protein level via its direct binding to Col1A1 3'UTR. miR-29b also had an effect on SP1 expression. These results suggested that miR-29b is involved in the regulation of type I collagen expression by interferon-alpha in hepatic stellate cells. It is anticipated that miR-29b will be used for the regulation of stellate cell activation and lead to antifibrotic therapy.

Cholestasis downregulate hepcidin expression through inhibiting IL-6-induced phosphorylation of signal transducer and activator of transcription 3 signaling

Hepcidin is downregulated during progressive cholestasis in biliary atresia, but the mechanism is unknown. To verify whether downregulation of hepcidin is specific to cholestasis irrespective of the patient's age, we first analyzed liver hepcidin mRNA and protein expression in adults with primary biliary cirrhosis (PBC) (n=4), non-cholestatic cirrhosis (n=19) and in controls (n=9). We evaluated the tyrosine phosphorylation of signal transducer and activator of transcription 3 (pSTAT3) expressions in the liver sections. A rat model of cholestasis by ligation of the extrahepatic bile duct (BDL) was created, and lipopolysaccharide (LPS)-induced cholangitis in cholestatic rats 2 weeks after BDL was also established to study the modulation of hepcidin by interleukin-6 (IL-6) and STAT3 signaling pathway in these models, using real-time quantitative reverse transcription-PCR, immunohistochemistry, western blotting and enzyme-linked immunosorbent assay (ELISA). An in vitro study of the effect of bile acids on hepcidin expression was carried out to re-confirm the in vivo findings. There was significantly lower hepcidin mRNA and pSTAT3 protein expression in cholestatic cirrhosis compared with non-cholestatic cirrhosis in adults. BDL caused significant decrease in hepcidin and gp130 mRNA expression compared with sham-operated group and normal control. Furthermore, there was significantly lower pSTAT3 protein expression and nuclear translocation in the cholestatic liver from the patients and the BDL rats, which was comparable to lower liver hepcidin mRNA and plasma hepcidin expression. Furthermore, BDL for 2 weeks attenuated the upregulation of hepcidin expression induced by LPS. Hydrophobic bile acid glycochenodeoxycholate inhibited IL-6-induced pSTAT3 expression in primary hepatocytes and resulted in the downregulation of hepcidin mRNA expression. In conclusion, the study shows that cholestasis or its important component-hydrophobic bile acids-can downregulate hepcidin expression through inhibiting IL-6-induced STAT3 phosphorylation and pSTAT3 protein nuclear translocation.