Differential gene expression profiles in the steatosis/fibrosis model of rat liver by chronic administration of carbon tetrachloride

Comparative analysis of the expression profiles of genes related to the Gadd45α signaling pathway in four kinds of liver diseases

Gadd45α (growth arrest and DNA damage inducible alpha) is a member of a group of genes whose transcript levels are increased following stressful conditions that lead to growth arrest and treatment with agents that lead to DNA damage. Gadd45α is upregulated in liver cirrhosis (LC), hepatic cancer (HC), acute liver failure (AHF) and non-alcoholic fatty liver disease(NAFLD). Here, we investigated the essential differences in the Gadd45α signaling pathway in these diseases at the transcriptional level. The results showed that 44, 46, 71 and 27 genes significant changes in these diseases, and the H-cluster showed that the expression of the Gadd45α signaling-related genes was significantly different in the four liver diseases. DAVID functional analysis showed that the Gadd45α signaling pathway-related genes were mainly involved in cell adhesion and migration, cell proliferation, apoptosis, stress and inflammatory responses, etc. Ingenuity pathway analysis (IPA) software was used to predict the functions of the Gadd45α signaling-related genes, and the results indicated that there were significant changes in cell differentiation, DNA damage repair, autophagy, apoptosis and necrosis. Gadd45α signaling pathway is involved in four kinds of liver disease and regulates a variety of activities via P38 MAPK, NF-κB, mTOR/STAT3, P21, PCNA, PI3K/Akt and other signaling pathways. Modulation of Gadd45α may be exploited to prevent the progression of liver disease, and to identify specific treatments for different stages of liver disease. In summary, the Gadd45α signaling pathway is involved in four kinds of liver disease and regulates a variety of physiological activities through various signaling pathways.

Dietary chia seeds (Salvia hispanica) improve acute dyslipidemia and steatohepatitis in rats

Chia seeds (Salvia hispanica L.) are rich in omega fatty acids. Dyslipidemia and steatohepatitis are diseases that require effective treatments in obese and non-obese patients. The aim was to evaluate the effect of chia intake on acute tyloxapol (TI)-induced dyslipidemia, on acute carbon tetrachloride (TC)-induced steatohepatitis, and on mixed damage (TC+TI) in non-obese rats. Four experimental groups were fed for 4 weeks a diet with established rodent food (DE), and four groups were fed a diet with 15% added chia (DC). Plasma samples were analyzed for total cholesterol, triglycerides, glucose, biochemical liver damage markers, and tumor necrosis factor-α (TNF-α). Liver samples were used to quantify glycogen, catalase, lipid peroxidation, and TNF-α. A histopathological analysis was performed. DC intake partially or totally prevented steatohepatitis, and reduced lipids in the dyslipidemic groups. The hypolipidemic and hepatoprotective effects of chia may be correlated to its high content of α-linolenic acid (omega-3) and phenolics. PRACTICAL APPLICATIONS: Metabolic syndrome is associated with non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH), which are currently the most common causes of chronic liver disease, cirrhosis, and hepatocellular carcinoma (HCC) worldwide. Dyslipidemia is a significant risk factor for NAFLD and NASH. Non-obese patients may have NAFLD or NASH. Metabolic syndrome and dyslipidemia are more strongly associated with NAFLD in non-obese than in obese patients. This is the first study evaluating the hypolipidemic and hepatoprotective effects of chia seed intake on acute dyslipidemia and/or steatohepatitis caused by the individual or combined administration of the inducers tyloxapol and carbon tetrachloride, respectively, in non-obese rats. The pharmacological effects of dietary chia are correlated to its high content of omega-3 and omega-6 (1:1), protein, dietary fiber, and phenolics. The results suggest that inclusion of chia in diets of non-obese patients with dyslipidemia and/or NAFLD/NASH may improve their health state and preventing cirrhosis or HCC.

Metabolic network-based predictions of toxicant-induced metabolite changes in the laboratory rat

In order to provide timely treatment for organ damage initiated by therapeutic drugs or exposure to environmental toxicants, we first need to identify markers that provide an early diagnosis of potential adverse effects before permanent damage occurs. Specifically, the liver, as a primary organ prone to toxicants-induced injuries, lacks diagnostic markers that are specific and sensitive to the early onset of injury. Here, to identify plasma metabolites as markers of early toxicant-induced injury, we used a constraint-based modeling approach with a genome-scale network reconstruction of rat liver metabolism to incorporate perturbations of gene expression induced by acetaminophen, a known hepatotoxicant. A comparison of the model results against the global metabolic profiling data revealed that our approach satisfactorily predicted altered plasma metabolite levels as early as 5 h after exposure to 2 g/kg of acetaminophen, and that 10 h after treatment the predictions significantly improved when we integrated measured central carbon fluxes. Our approach is solely driven by gene expression and physiological boundary conditions, and does not rely on any toxicant-specific model component. As such, it provides a mechanistic model that serves as a first step in identifying a list of putative plasma metabolites that could change due to toxicant-induced perturbations.

Oxaloacetate Ameliorates Chemical Liver Injury via Oxidative Stress Reduction and Enhancement of Bioenergetic Fluxes

Chemical injury is partly due to free radical lipid peroxidation, which can induce oxidative stress and produce a large number of reactive oxygen species (ROS). Oxaloacetic acid is an important intermediary in the tricarboxylic acid cycle (TCA cycle) and participates in metabolism and energy production. In our study, we found that oxaloacetate (OA) effectively alleviated liver injury which was induced by hydrogen peroxide (H₂O₂) in vitro and carbon tetrachloride (CCl₄) in vivo. OA scavenged ROS, prevented oxidative damage and maintained the normal structure of mitochondria. We further confirmed that OA increased adenosine triphosphate (ATP) by promoting the TCA production cycle and oxidative phosphorylation (OXPHOS). Finally, OA inhibited the mitogen-activated protein kinase (MAPK) and apoptotic pathways by suppressing tumor necrosis factor-α (TNF-α). Our findings reveal a mechanism for OA ameliorating chemical liver injury and suggest a possible implementation for preventing the chemical liver injury.

Herbal Supplement Ameliorates Cardiac Hypertrophy in Rats with CCl(4)-Induced Liver Cirrhosis

We used the carbon tetrachloride (CCl(4)) induced liver cirrhosis model to test the molecular mechanism of action involved in cirrhosis-associated cardiac hypertrophy and the effectiveness of Ocimum gratissimum extract (OGE) and silymarin against cardiac hypertrophy. We treated male wistar rats with CCl(4) and either OGE (0.02 g/kg B.W. or 0.04 g/kg B.W.) or silymarin (0.2 g/kg B.W.). Cardiac eccentric hypertrophy was induced by CCl(4) along with cirrhosis and increased expression of cardiac hypertrophy related genes NFAT, TAGA4, and NBP, and the interleukin-6 (IL-6) signaling pathway related genes MEK5, ERK5, JAK, and STAT3. OGE or silymarin co-treatment attenuated CCl(4)-induced cardiac abnormalities, and lowered expression of genes which were elevated by this hepatotoxin. Our results suggest that the IL-6 signaling pathway may be related to CCl(4)-induced cardiac hypertrophy. OGE and silymarin were able to lower liver fibrosis, which reduces the chance of cardiac hypertrophy perhaps by lowering the expressions of IL-6 signaling pathway related genes. We conclude that treatment of cirrhosis using herbal supplements is a viable option for protecting cardiac tissues against cirrhosis-related cardiac hypertrophy.

Hepatoprotective effect and its possible mechanism of Coptidis rhizoma aqueous extract on carbon tetrachloride-induced chronic liver hepatotoxicity in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Coptidis rhizoma is traditionally used for heat-clearing and toxic-scavenging and it belongs to liver meridian in Chinese medicine practice. Clinically, Coptidis rhizoma can be used for hepatic and biliary disorders, yet details in the therapies of liver diseases and underlying mechanism(s) remain unclear. Our previous study demonstrated that Coptidis rhizoma aqueous extract (CRAE) against CCl(4)-induced acute liver damage was related to antioxidant property. In the present study, the protection of CRAE on chronic liver damage induced by carbon tetrachloride (CCl(4)) in rats and its related mechanism were explored.

MATERIALS AND METHODS

The CCl(4)-induced chronic liver damage model was established, and CRAE's protective effect was examined. Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activity, serum and liver superoxide dismutase (SOD) activity were then measured. The histological changes were observed under microscopy and then computed in numerical score. The normal or damaged cells were isolated and related signaling pathway was evaluated.

RESULT

Serum AST and ALT activities were significantly decreased in rats treated with different doses of CRAE, indicating its protective effect against CCl(4)-induced chronic liver damage. Observation on serum SOD activity revealed that CRAE might act as an anti-oxidant agent against CCl(4)-induced chronic oxide stress. Histological study supported these observations. Erk1/2 inhibition may take part into CRAE's effect on preventing hepatocyte from apoptosis when exposed to oxidative stress.

CONCLUSION

CRAE showed protective effect against CCl(4)-induced chronic liver damage in rats and its potential as an agent in the treatment of chronic liver diseases by protecting hepatocyte from injury.

In vivo biodistribution and biological impact of injected carbon nanotubes using magnetic resonance techniques

Background:

Single-walled carbon nanotubes (SWCNT) hold promise for applications as contrast agents and target delivery carriers in the field of nanomedicine. When administered in vivo, their biodistribution and pharmacological profile needs to be fully characterized. The tissue distribution of carbon nanotubes and their potential impact on metabolism depend on their shape, coating, and metallic impurities. Because standard radiolabeled or fluorescently-labeled pharmaceuticals are not well suited for long-term in vivo follow-up of carbon nanotubes, alternative methods are required.

Methods:

In this study, noninvasive in vivo magnetic resonance imaging (MRI) investigations combined with high-resolution magic angle spinning (HR-MAS), Raman spectroscopy, iron assays, and histological analysis ex vivo were proposed and applied to assess the biodistribution and biological impact of intravenously injected pristine (raw and purified) and functionalized SWCNT in a 2-week longitudinal study. Iron impurities allowed raw detection of SWCNT in vivo by susceptibility-weighted MRI.

Results:

A transitional accumulation in the spleen and liver was observed by MRI. Raman spectroscopy, iron assays, and histological findings confirmed the MRI readouts. Moreover, no acute toxicological effect on the liver metabolic profile was observed using the HR-MAS technique, as confirmed by quantitative real-time polymerase chain reaction analysis.

Conclusion:

This study illustrates the potential of noninvasive MRI protocols for longitudinal assessment of the biodistribution of SWCNT with associated intrinsic metal impurities. The same approach can be used for any other magnetically-labeled nanoparticles.

Enhancement of P-glycoprotein expression by hepatocyte transplantation in carbon tetrachloride-induced rat liver

The multidrug resistance protein P-glycoprotein (P-gp) is physiologically expressed at the bile canalicular membrane of the liver, where it participates in the biliary excretion of various lipophilic drugs. Chronic exposure to carbon tetrachloride (CCI(4)) is known to induce hepatic fibrosis resulting in hepatotoxicity. This study focuses on the effects of CCI(4) and hepatic transplantation (HT) on the P-gp expressions in rat liver. Male SD rats were treated with CCI(4) to induce liver damage for 3, 7, 14, 21, and 28 days, respectively. Immunohistochemistry revealed that P-gp was widely distributed in the liver and was spread from the cytoplasm to cell membrane of the rat liver. Western blot showed remarkable increase of P-gp expression in 3 days CCI(4)-treated rats, whereas, a continuous decrease in the P-gp expression was seen in 7, 14, 21, and 28 days CCI(4)-treated rats. After HT with cells from the normal rat liver, the level of P-gp increased comparing with those from the sham operation. Blood biochemistry showed decreased levels of serum alanine transaminase, aspartate transaminase, and alkaline phosphatase and increased serum levels of triglyceride and total protein, which indicated the improved function of the liver damaged by CCI(4). These results illustrate the variation of the expression of P-gp in CCI(4)-induced hepatic damage and an increase of P-gp level after HT in the toxic liver induced by CCI(4). We hypothesized that P-gp may play a protective role in the process of liver injury. HT can be beneficial to ameliorate the rat liver functional damage induced by CCI(4).

Animal models of non-alcoholic fatty liver disease: recent advances

Nonalcoholic fatty liver disease (NAFLD) refers to a wide spectrum of disorders that range from simple steatosis to steatohepatitis, advanced fibrosis, and cirrhosis. NAFLD is associated strongly with the components of metabolic syndrome, such as obesity, diabetes and insulin resistance. To date, the pathogenesis of NAFLD has not been well elucidated, and few effective therapeutic approaches for NAFLD are available. The development of animal models of NAFLD can enhance our understanding of its pathogenesis. In this article, we will review the recent advances in animal models currently available for studying NAFLD.

In vitro assay for drug-induced hepatosteatosis using rat primary hepatocytes, a fluorescent lipid analog and gene expression analysis

To evaluate new drugs' potential for hepatosteatosis, we developed a cell-based assay using a fluorescent fatty acid analog: BODIPY558/568 C12. Rat primary hepatocytes were exposed to positive reference compounds [cyclosporine A (CsA), clofibrate (CFR), tetracycline (TC), valproic acid (VPA), carbon tetrachloride (CCl4), tamoxifen (TMX)] in the presence of BODIPY558/568 C12. The formation of fluorscecent particles or lipid droplets in the cytoplasm was confirmed by confocal laser scanning microscopy and electron microscopy respectively. The accumulation of BODIPY558/568 C12 was measured by fluorometry and high content imaging method. All positive reference compounds increased fluorescent particles in number and fluorescence intensity. High content imaging was more sensitive and selective method than fluorometry to detect fluorescent particles. Gene expression analysis of the hepatocytes showed two patterns: genes related to lipid metabolism/synthesis were down-regulated by oxidative stress inducing compounds: CsA, TC and TMX, and up-regulated by peroxisome proliferator-activated receptor-alpha agonists: CFR and VPA. From these findings, we concluded that the cell-based assay developed in this study is an appropriate method to predict drugs' potential for hepatosteatosis, and gene expression analysis is useful to profile the mechanism of the hepatosteatosis.

TNFalpha-dependent hepatic steatosis and liver degeneration caused by mutation of zebrafish S-adenosylhomocysteine hydrolase

Hepatic steatosis and liver degeneration are prominent features of the zebrafish ducttrip (dtp) mutant phenotype. Positional cloning identified a causative mutation in the gene encoding S-adenosylhomocysteine hydrolase (Ahcy). Reduced Ahcy activity in dtp mutants led to elevated levels of S-adenosylhomocysteine (SAH) and, to a lesser degree, of its metabolic precursor S-adenosylmethionine (SAM). Elevated SAH in dtp larvae was associated with mitochondrial defects and increased expression of tnfa and pparg, an ortholog of the mammalian lipogenic gene. Antisense knockdown of tnfa rescued hepatic steatosis and liver degeneration in dtp larvae, whereas the overexpression of tnfa and the hepatic phenotype were unchanged in dtp larvae reared under germ-free conditions. These data identify an essential role for tnfa in the mutant phenotype and suggest a direct link between SAH-induced methylation defects and TNF expression in human liver disorders associated with elevated TNFalpha. Although heterozygous dtp larvae had no discernible phenotype, hepatic steatosis was present in heterozygous adult dtp fish and in wild-type adult fish treated with an Ahcy inhibitor. These data argue that AHCY polymorphisms and AHCY inhibitors, which have shown promise in treating autoimmunity and other disorders, may be a risk factor for steatosis, particularly in patients with diabetes, obesity and liver disorders such as hepatitis C infection. Supporting this idea, hepatic injury and steatosis have been noted in patients with recently discovered AHCY mutations.

Toxicogenomic biomarkers for liver toxicity

Toxicogenomics (TGx) is a widely used technique in the preclinical stage of drug development to investigate the molecular mechanisms of toxicity. A number of candidate TGx biomarkers have now been identified and are utilized for both assessing and predicting toxicities. Further accumulation of novel TGx biomarkers will lead to more efficient, appropriate and cost effective drug risk assessment, reinforcing the paradigm of the conventional toxicology system with a more profound understanding of the molecular mechanisms of drug-induced toxicity. In this paper, we overview some practical strategies as well as obstacles for identifying and utilizing TGx biomarkers based on microarray analysis. Since clinical hepatotoxicity is one of the major causes of drug development attrition, the liver has been the best documented target organ for TGx studies to date, and we therefore focused on information from liver TGx studies. In this review, we summarize the current resources in the literature in regard to TGx studies of the liver, from which toxicologists could extract potential TGx biomarker gene sets for better hepatotoxicity risk assessment.

Preventive effect of pioglitazone against nonalcoholic fatty liver disease in Sprague-Dawley rats and its mechanism

AIM: To explore the prevention effect and mechanism of pioglitazone (PIO) on nonalcoholic fatty liver disease (NAFLD) in rats.

METHODS: Seventy two Sprague-Dawley rats were randomly divided into three groups: normal diet group (NG), high fat diet group (HG) and PIO group (PIOG), with 24 rats in every group. PIOG were fed with high fat diet and PIO for eight weeks. IR was tested by euglycemic-hyperinsulinemic clamp; TG, ALT, AST, FFAs, FINS and TNF-α were tested by biochemistry automatic analyzer or RIA; mRNA expression of peroxisome proliferator-activated receptor (PPARγ) was detected using RT-PCR. The expression of PPARγ and c-Jun amino-terminal kinase 1 (JNK1) were detected by Western blot.

RESULTS: The glucose infusion rate (GIR) decreased and JNK1 increased in HG rats in a time-dependent manner from 1st to 8th week (P < 0.05). Compared with NG, at the end of 8th week, the hepatic steatosis was significant in HG group. The weight, liver index, serum levels of TG, ALT, AST, FFAs, FINS and TNF-α increased, while IR was aggravated. Meanwhile, the JNK1 protein expression in liver tissue was up-regulated, while expression of PPARγ was decreased (TG: 1.23 ± 0.08 vs 0.62 ± 0.12; ALT: 92.80 ± 7.09 vs 51.34 ± 8.12; AST: 153.22 ± 20.65 vs 119.26 ± 13.61; FFAs: 511.94 ± 24.88 vs 335.31 ± 15.71; FINS: 41.23 ± 1.84 vs 22.65 ± 2.25; TNF-α: 1.02 ± 0.12 vs 0.34 ± 0.07, all P < 0.05). In PIOG, all the indexes were improved, but didn't completely return to the same as those of NG group.

CONCLUSION: PIO could prevent NAFLD induced by a high-fat diet and other IR-related diseases.

An abnormal gene expression of the beta-adrenergic system contributes to the pathogenesis of cardiomyopathy in cirrhotic rats

Decreased cardiac contractility and beta-adrenergic responsiveness have been observed in cirrhotic cardiomyopathy, but their molecular mechanisms remain unclear. To study beta-adrenergic-stimulated contractility and beta-adrenergic gene expression patterns, 20 Wistar Kyoto rats were treated with carbon tetrachloride to induce cirrhosis and 20 rats were used as controls. Left ventricular contractility was recorded in electrically driven isolated hearts perfused at constant flow with isoproterenol (10(-10) to 10(-6) M). A cardiac gene expression profile was obtained using a microarray for the myocyte adrenergic pathway. The cardiac contractility maximal response to isoproterenol was significantly reduced in cirrhotic rats in comparison to control rats, whereas the half-maximal effective concentration was not different. In cirrhotic rats, cardiac gene expression analysis showed a significant overexpression of G protein alpha-inhibiting subunit 2 (Galpha(i2)), cyclic nucleotide phosphodiesterase (PDE2a), regulator of G-protein signaling 2 (RGS2), and down-expression of adenylate cyclase (Adcy3). These results indicate that overexpression of Galpha(i2), PDE2a, and RGS2 down-regulates the beta-adrenergic signaling pathway, thus contributing to the pathogenesis of cirrhotic cardiomyopathy.

Gene expression profiles of murine fatty liver induced by the administration of valproic acid

Valproic acid (VPA) has been used as anticonvulsants, however, it induces hepatotoxicity such as microvesicular steatosis and necrosis in the liver. To explore the mechanisms of VPA-induced steatosis, we profiled the gene expression patterns of the mouse liver that were altered by treatment with VPA using microarray analysis. VPA was orally administered as a single dose of 100 mg/kg (low-dose) or 1000 mg/kg (high-dose) to ICR mice and the animals were killed at 6, 24, or 72 h after treatment. Serum alanine aminotransferase and aspartate aminotransferase levels were not significantly altered in the experimental animals. However, symptoms of steatosis were observed at 72 h with low-dose and at 24 h and 72 h with high-dose. After microarray data analysis, 1910 genes were selected by two-way ANOVA (P<0.05) as VPA-responsive genes. Hierarchical clustering revealed that gene expression changes depended on the time rather than the dose of VPA treatment. Gene profiling data showed striking changes in the expression of genes associated with lipid, fatty acid, and steroid metabolism, oncogenesis, signal transduction, and development. Functional categorization of 1156 characteristically up- and down-regulated genes (cutoff >1.5-fold) revealed that 60 genes were involved in lipid metabolism that was interconnected with biological pathways for biosynthesis of triglyceride and cholesterol, catabolism of fatty acid, and lipid transport. This gene expression profile may be associated with the known steatogenic hepatotoxicity of VPA and it may provide useful information for prediction of hepatotoxicity of unknown chemicals or new drug candidates through pattern recognition.