Adaptation of mitochondrial metabolism in liver cirrhosis. Different strategies to maintain a vital function

The gut–microbiota–brain changes across the liver disease spectrum

Gut microbiota dysbiosis plays a significant role in the progression of liver disease, and no effective drugs are available for the full spectrum. In this study, we aimed to explore the dynamic changes of gut microbiota along the liver disease spectrum, together with the changes in cognition and brain metabolism. Sprague–Dawley rats were divided into four groups reflecting different stages of liver disease: control diet (NC); high-fat, high-cholesterol diet (HFHC), emulating non-alcoholic steatohepatitis; control diet + thioacetamide (NC + TAA), simulating acute liver failure; and high-fat, high-cholesterol diet + thioacetamide (HFHC + TAA) to assess the effect of the superimposed damages. The diet was administered for 14 weeks and the thioacetamide was administrated (100 mg/kg day) intraperitoneally over 3 days. Our results showed changes in plasma biochemistry and liver damage across the spectrum. Differences in gut microbiota at the compositional level were found among the experimental groups. Members of the Enterobacteriaceae family were most abundant in HFHC and HFHC + TAA groups, and Akkermansiaceae in the NC + TAA group, albeit lactobacilli genus being dominant in the NC group. Moreover, harm to the liver affected the diversity and bacterial community structure, with a loss of rare species. Indeed, the superimposed damage group (HFHC + TAA) suffered a loss of both rare and abundant species. Behavioral evaluation has shown that HFHC, NC + TAA, and HFHC + TAA displayed a worsened execution when discriminating the new object. Also, NC + TAA and HFHC + TAA were not capable of recognizing the changes in place of the object. Furthermore, working memory was affected in HFHC and HFHC + TAA groups, whereas the NC + TAA group displayed a significant delay in the acquisition. Brain oxidative metabolism changes were observed in the prefrontal, retrosplenial, and perirhinal cortices, as well as the amygdala and mammillary bodies. Besides, groups administered with thioacetamide presented an increased oxidative metabolic activity in the adrenal glands. These results highlight the importance of cross-comparison along the liver spectrum to understand the different gut–microbiota–brain changes. Furthermore, our data point out specific gut microbiota targets to design more effective treatments, though the liver–gut–brain axis focused on specific stages of liver disease.

Lack of the Lysosomal Membrane Protein, GLMP, in Mice Results in Metabolic Dysregulation in Liver

Ablation of glycosylated lysosomal membrane protein (GLMP, formerly known as NCU-G1) has been shown to cause chronic liver injury which progresses into liver fibrosis in mice. Both lysosomal dysfunction and chronic liver injury can cause metabolic dysregulation. Glmp^gt/gt mice (formerly known as Ncu-g1^gt/gtmice) were studied between 3 weeks and 9 months of age. Body weight gain and feed efficiency of Glmp^gt/gt mice were comparable to wild type siblings, only at the age of 9 months the Glmp^gt/gt siblings had significantly reduced body weight. Reduced size of epididymal fat pads was accompanied by hepatosplenomegaly in Glmp^gt/gt mice. Blood analysis revealed reduced levels of blood glucose, circulating triacylglycerol and non-esterified fatty acids in Glmp^gt/gt mice. Increased flux of glucose, increased de novo lipogenesis and lipid accumulation were detected in Glmp^gt/gt primary hepatocytes, as well as elevated triacylglycerol levels in Glmp^gt/gt liver homogenates, compared to hepatocytes and liver from wild type mice. Gene expression analysis showed an increased expression of genes involved in fatty acid uptake and lipogenesis in Glmp^gt/gt liver compared to wild type. Our findings are in agreement with the metabolic alterations observed in other mouse models lacking lysosomal proteins, and with alterations characteristic for advanced chronic liver injury.

A switch in the source of ATP production and a loss in capacity to perform glycolysis are hallmarks of hepatocyte failure in advance liver disease

BACKGROUND & AIMS

The cause of hepatic failure in the terminal stages of chronic injury is unknown. Cellular metabolic adaptations in response to the microenvironment have been implicated in cellular breakdown.

METHODS

To address the role of energy metabolism in this process we studied mitochondrial number, respiration, and functional reserve, as well as cellular adenosine-5'-triphosphate (ATP) production, glycolytic flux, and expression of glycolysis related genes in isolated hepatocytes from early and terminal stages of cirrhosis using a model that produces hepatic failure from irreversible cirrhosis in rats. To study the clinical relevance of energy metabolism in terminal stages of chronic liver failure, we analyzed glycolysis and energy metabolism related gene expression in liver tissue from patients at different stages of chronic liver failure according to Child-Pugh classification. Additionally, to determine whether the expression of these genes in early-stage cirrhosis (Child-Pugh Class A) is related to patient outcome, we performed network analysis of publicly available microarray data obtained from biopsies of 216 patients with hepatitis C-related Child-Pugh A cirrhosis who were prospectively followed up for a median of 10years.

RESULTS

In the early phase of cirrhosis, mitochondrial function and ATP generation are maintained by increasing energy production from glycolytic flux as production from oxidative phosphorylation falls. At the terminal stage of hepatic injury, mitochondria respiration and ATP production are significantly compromised, as the hepatocytes are unable to sustain the increased demand for high levels of ATP generation from glycolysis. This impairment corresponds to a decrease in glucose-6-phosphatase catalytic subunit and phosphoglucomutase 1. Similar decreased gene expression was observed in liver tissue from patients at different stages of chronic liver injury. Further, unbiased network analysis of microarray data revealed that expression of these genes was down regulated in the group of patients with poor outcome.

CONCLUSIONS

An adaptive metabolic shift, from generating energy predominantly from oxidative phosphorylation to glycolysis, allows maintenance of energy homeostasis during early stages of liver injury, but leads to hepatocyte dysfunction during terminal stages of chronic liver disease because hepatocytes are unable to sustain high levels of energy production from glycolysis.

Diet, nutrients, phytochemicals, and cancer metastasis suppressor genes

The major factor in the morbidity and mortality of cancer patients is metastasis. There exists a relative lack of specific therapeutic approaches to control metastasis, and this is a fruitful area for investigation. A healthy diet and lifestyle not only can inhibit tumorigenesis but also can have a major impact on cancer progression and survival. Many chemicals found in edible plants are known to inhibit metastatic progression of cancer. While the mechanisms underlying antimetastatic activity of some phytochemicals are being delineated, the impact of diet, dietary components, and various phytochemicals on metastasis suppressor genes is underexplored. Epigenetic regulation of metastasis suppressor genes promises to be a potentially important mechanism by which dietary components can impact cancer metastasis since many dietary constituents are known to modulate gene expression. The review addresses this area of research as well as the current state of knowledge regarding the impact of diet, dietary components, and phytochemicals on metastasis suppressor genes.

Identification of novel mechanisms of silymarin on the carbon tetrachloride-induced liver fibrosis in mice by nuclear factor-κB bioluminescent imaging-guided transcriptomic analysis

In this study, we applied bioluminescent imaging-guided transcriptomic analysis to evaluate and identify the therapeutic potentials and novel mechanisms of silymarin on carbon tetrachloride (CCl(4))-induced liver fibrosis. Transgenic mice, carrying the luciferase genes driven by nuclear factor-κB (NF-κB), were given with CCl(4) and/or silymarin. In vivo NF-κB activity was evaluated by bioluminescent imaging, liver fibrosis was judged by Sirius red staining and immunohistochemistry, and gene expression profiles of silymarin-treated livers were analyzed by DNA microarray. CCl(4) enhanced the NF-κB-dependent hepatic luminescence and induced hepatic fibrosis, while silymarin reduced the CCl(4)-induced hepatic luminescence and improved CCl(4)-induced liver fibrosis. Microarray analysis showed that silymarin altered the transforming growth factor-β-mediated pathways, which play pivotal roles in the progression of liver fibrosis. Moreover, we newly identified that silymarin downregulated the expression levels of cytoskeleton organization genes and mitochondrion electron-transfer chain genes, such as cytochrome c oxidase Cox6a2, Cox7a1, and Cox8b genes. In conclusion, the correlation of NF-κB-dependent luminescence and liver fibrosis suggested the feasibility of NF-κB bioluminescent imaging for the evaluation of liver fibrosis progression and therapeutic potentials. Moreover, our findings suggested that silymarin might exhibit anti-fibrotic effects in vivo via altering the expression of genes involved in cytoskeleton organization and mitochondrion electron-transfer chain.

Evidence for the role of oxidative stress in the acetylation of histone H3 by ethanol in rat hepatocytes

The relationship between ethanol-induced oxidative stress and acetylation of histone H3 at lysine 9 (H3AcK9) remains unknown and was therefore investigated in primary cultures of rat hepatocytes. Cells were treated with ethanol, and a select group of pharmacological agents and the status of H3AcK9 and reactive oxygen species (ROS) were monitored. Pretreatment of hepatocytes with N-acetyl cystein (ROS reducer), or dietary antioxidants (quercetin, reserveratrol), or NADPH (reduced nicotinamide adenine dinucleotide phosphate) oxidase inhibitor apocynin, significantly reduced ethanol (50 mM, 24 h) induced increases in ROS and H3AcK9. In contrast, l-buthionine sulfoximine (ROS inducer) and inhibitor of mitochondrial complexes I (rotenone) and III (antimycin) increased ethanol-induced H3AcK9 (P<.01). Oxidative stress also affected ethanol-induced alcohol dehydrogenase 1 mRNA expression. These results demonstrate for the first time that oxidative stress is involved in the ethanol-induced histone H3 acetylation in hepatocytes.

Keratin mutation predisposes to mouse liver fibrosis and unmasks differential effects of the carbon tetrachloride and thioacetamide models

BACKGROUND & AIMS

Keratins 8 and 18 (K8/K18) are important hepatoprotective proteins. Animals expressing K8/K18 mutants show a marked susceptibility to acute/subacute liver injury. K8/K18 variants predispose to human end-stage liver disease and associate with fibrosis progression during chronic hepatitis C infection. We sought direct evidence for a keratin mutation-related predisposition to liver fibrosis using transgenic mouse models because the relationship between keratin mutations and cirrhosis is based primarily on human association studies.

METHODS

Mouse hepatofibrosis was induced by carbon tetrachloride (CCl(4)) or thioacetamide. Nontransgenic mice, or mice that over express either human Arg89-to-Cys (R89C mice) or wild-type K18 (WT mice) were used. The extent of fibrosis was evaluated by quantitative real-time reverse-transcription polymerase chain reaction of fibrosis-related genes, liver hydroxyproline measurement, and Picro-Sirius red staining and collagen immunofluorescence staining.

RESULTS

Compared with control animals, CCl(4) led to similar liver fibrosis but increased injury in K18 R89C mice. In contrast, thioacetamide caused more severe liver injury and fibrosis in K18 R89C as compared with WT and nontransgenic mice and resulted in increased messenger RNA levels of collagen, tissue inhibitor of metalloproteinase 1, matrix metalloproteinase 2, and matrix metalloproteinase 13. Analysis in nontransgenic mice showed that thioacetamide and CCl(4) have dramatically different molecular expression responses involving cytoskeletal and chaperone proteins.

CONCLUSIONS

Over expression of K18 R89C predisposes transgenic mice to thioacetamide- but not CCl(4)-induced liver fibrosis. Differences in the keratin mutation-associated fibrosis response among the 2 models raise the hypothesis that keratin variants may preferentially predispose to fibrosis in unique human liver diseases. Findings herein highlight distinct differences in the 2 widely used fibrosis models.

Effects of vitamin A deficiency on mitochondrial function in rat liver and heart

The aim of this study was to investigate comparative effects of vitamin A deficiency on respiratory activity and structural integrity in liver and heart mitochondria. Male rats were fed a liquid control diet (control rats) or a liquid vitamin A-deficient diet (vitamin A-deficient rats) for 50 days. One group of vitamin-A deficient rats was refed a control diet for 15 days (vitamin A-recovered rats). To assess the respiratory function of mitochondria the contents of coenzyme Q (ubiquinone, CoQ), cytochrome c and the activities of the whole electron transport chain and of each of its respiratory complexes were evaluated. Chronic vitamin A deficiency promoted a significant increase in the endogenous coenzyme Q content in liver and heart mitochondria when compared with control values. Vitamin A deficiency induced a decrease in the activity of complex I (NADH–CoQ reductase) and complex II (succinate–CoQ reductase) and in the levels of complex I and cytochrome c in heart mitochondria. However, NADH and succinate oxidation rates were maintained at the control levels due to an increase in the CoQ content in accordance with the kinetic behaviour of CoQ as an homogeneous pool. On the contrary, the high CoQ content did not affect the electron-transfer rate in liver mitochondria, whose integrity was preserved from the deleterious effects of the vitamin A deficiency. Ultrastuctural assessment of liver and heart showed that vitamin A deficiency did not induce appreciable alterations in the morphology of their mitochondria. After refeeding the control diet, serum retinol, liver and heart CoQ content and the activity of complex I and complex II in heart mitochondria returned to normality. However, the activities of both whole electron transfer chain and complex I in liver were increased over the control values. The interrelationships between physiological antioxidants in biological membranes and the beneficial effects of their administration in mitochondrial diseases are discussed.

Oxidative stress in the development of liver cirrhosis: a comparison of two different experimental models

BACKGROUND/AIMS

Oxidative stress has been implicated in liver cirrhosis. Carbon tetrachloride and thioacetamide are the most widely used models to develop cirrhosis in rats and the present study compares oxidative stress in the liver induced by these compounds at different stages of cirrhosis development.

METHODS

Twice-weekly intragastric or intraperitoneal administration of carbon tetrachloride or thioacetamide, respectively, produced liver cirrhosis after 3 months. Histology, serum markers and hepatic hydroxy proline content confirmed the cirrhosis.

RESULTS

An increase in oxidative stress parameters was seen in mitochondria, peroxisomes and microsomes from the liver after carbon tetrachloride or thioacetamide treatment. Oxidative stress was more severe in carbon tetrachloride treated animals than thioacetamide. Mild oxidative stress was evident at 1 and 2 months of treatment and a significant increase was seen by 3 months of treatment with either compound. By this time, frank liver cirrhosis was also observed.

CONCLUSIONS

These results suggest that evidence of oxygen free radicals is also found early in the development of fibrosis and cirrhosis in both models.

Cellular and molecular events leading to mitochondrial toxicity of 1-(2-deoxy-2-fluoro-1-beta-D-arabinofuranosyl)-5-iodouracil in human liver cells

We have explored the mechanism(s) related to FIAU-induced liver toxicity, particularly focusing on its effect on mitochondrial function in a human hepatoma cell line-HepG2. The potential role of FMAU and FAU, metabolites detected in FIAU-treated patients were also ascertained. FIAU and FMAU inhibited cell growth and were effectively phosphorylated. A substantial increase in lactic acid production in medium of cells incubated with 1-10 microM FIAU or FMAU was consistent with mitochondrial dysfunction. Slot blot analysis demonstrated that a two week exposure to 10 microM FIAU or FMAU was not associated with a decrease in total mitochondrial (mt) DNA content. However, FIAU and FMAU were incorporated into nuclear and mtDNA and relative values suggest that both compounds incorporate at a much higher rate into mtDNA. Electron micrographs of cells incubated with 10 microM FIAU or FMAU revealed the presence of enlarged mitochondria with higher cristae density and lipid vesicles. In conclusion, these data suggest that despite the lack of inhibition of mtDNA content, incorporation of FIAU and FMAU into mtDNA of HepG2 cells leads to marked mitochondrial dysfunction as evidenced by disturbance in cellular energy metabolism and detection of micro- and macrovesicular steatosis.

Alterations in mitochondrial function and morphology in chronic liver disease: pathogenesis and potential for therapeutic intervention

Studies assessing mitochondrial function and structure in livers from humans or experimental animals with chronic liver disease, including liver cirrhosis, revealed a variety of alterations in comparison with normal subjects or control animals. Depending on the etiology of chronic liver disease, the function of the electron transport chain and/or ATP synthesis was found to be impaired, leading to decreased oxidative metabolism of various substrates and to impaired recovery of the hepatic energy state after a metabolic insult. Changes in mitochondrial structure include megamitochondria with reduced cristae, dilatation of mitochondrial cristae and crystalloid inclusions in the mitochondrial matrix. The most important strategies to maintain an adequate mitochondrial function per liver are mitochondrial proliferation and increases in the activity of critical enzymes or in the content of cofactors per mitochondrion. Possibilities to assess hepatic mitochondrial function and to treat mitochondrial dysfunction in patients with chronic liver disease are discussed.