Zinc supplementation reverses alcohol-induced steatosis in mice through reactivating hepatocyte nuclear factor-4alpha and peroxisome proliferator-activated receptor-alpha

New advances in molecular mechanisms and emerging therapeutic targets in alcoholic liver diseases

Alcoholic liver disease is a major health problem in the United States and worldwide. Chronic alcohol consumption can cause steatosis, inflammation, fibrosis, cirrhosis and even liver cancer. Significant progress has been made to understand key events and molecular players for the onset and progression of alcoholic liver disease from both experimental and clinical alcohol studies. No successful treatments are currently available for treating alcoholic liver disease; therefore, development of novel pathophysiological-targeted therapies is urgently needed. This review summarizes the recent progress on animal models used to study alcoholic liver disease and the detrimental factors that contribute to alcoholic liver disease pathogenesis including miRNAs, S-adenosylmethionine, Zinc deficiency, cytosolic lipin-1β, IRF3-mediated apoptosis, RIP3-mediated necrosis and hepcidin. In addition, we summarize emerging adaptive protective effects induced by alcohol to attenuate alcohol-induced liver pathogenesis including FoxO3, IL-22, autophagy and nuclear lipin-1α.

Dysregulation of hepatic zinc transporters in a mouse model of alcoholic liver disease

Zinc deficiency is a consistent phenomenon observed in patients with alcoholic liver disease, but the mechanisms have not been well defined. The objective of this study was to determine if alcohol alters hepatic zinc transporters in association with reduction of hepatic zinc levels and if oxidative stress mediates the alterations of zinc transporters. C57BL/6 mice were pair-fed with the Lieber-DeCarli control or ethanol diets for 2, 4, or 8 wk. Chronic alcohol exposure reduced hepatic zinc levels, but increased plasma and urine zinc levels, at all time points. Hepatic zinc finger proteins, peroxisome proliferator-activated receptor-α (PPAR-α) and hepatocyte nuclear factor 4α (HNF-4α), were downregulated in ethanol-fed mice. Four hepatic zinc transporter proteins showed significant alterations in ethanol-fed mice compared with the controls. ZIP5 and ZIP14 proteins were downregulated, while ZIP7 and ZnT7 proteins were upregulated, by ethanol exposure at all time points. Immunohistochemical staining demonstrated that chronic ethanol exposure upregulated cytochrome P-450 2E1 and caused 4-hydroxynonenal accumulation in the liver. For the in vitro study, murine FL-83B hepatocytes were treated with 5 μM 4-hydroxynonenal or 100 μM hydrogen peroxide for 72 h. The results from in vitro studies demonstrated that 4-hydroxynonenal treatment altered ZIP5 and ZIP7 protein abundance, and hydrogen peroxide treatment changed ZIP7, ZIP14, and ZnT7 protein abundance. These results suggest that chronic ethanol exposure alters hepatic zinc transporters via oxidative stress, which might account for ethanol-induced hepatic zinc deficiency.

Zinc and autophagy

Autophagy is a highly conserved degradative process through which cells overcome stressful conditions. Inasmuch as faulty autophagy has been associated with aging, neuronal degeneration disorders, diabetes, and fatty liver, autophagy is regarded as a potential therapeutic target. This review summarizes the present state of knowledge concerning the role of zinc in the regulation of autophagy, the role of autophagy in zinc metabolism, and the potential role of autophagy as a mediator of the protective effects of zinc. Data from in vitro studies consistently support the notion that zinc is critical for early and late autophagy. Studies have shown inhibition of early and late autophagy in cells cultured in medium treated with zinc chelators. Conversely, excess zinc added to the medium has shown to potentiate the stimulation of autophagy by tamoxifen, H2O2, ethanol and dopamine. The potential role of autophagy in zinc homeostasis has just begun to be investigated. Increasing evidence indicates that autophagy dysregulation causes significant changes in cellular zinc homeostasis. Autophagy may mediate the protective effect of zinc against lipid accumulation, apoptosis and inflammation by promoting degradation of lipid droplets, inflammasomes, p62/SQSTM1 and damaged mitochondria. Studies with humans and animal models are necessary to determine whether autophagy is influenced by zinc intake.

CMZ reversed chronic ethanol-induced disturbance of PPAR-α possibly by suppressing oxidative stress and PGC-1α acetylation, and activating the MAPK and GSK3β pathway

Background

Cytochrome P4502E1 (CYP2E1) has been suggested to play critical roles in the pathogenesis of alcoholic fatty liver (AFL), but the underlying mechanisms remains unclear. The current study was designed to evaluate whether CYP2E1 suppression by chlormethiazole (CMZ) could suppress AFL in mice, and to explore the underlying mechanisms.

Methods

Mice were treated with or without CMZ (50 mg/kg bw, i.p.) and subjected to liquid diet with or without ethanol (5%, w/v) for 4 weeks. Biochemical parameters were measured using commercial kits. The protein and mRNA levels were detected by western blot and qPCR, respectively. Histopathology and immunohistochemical assay were performed with routine methods.

Results

CYP2E1 inhibition by CMZ completely blocked AFL in mice, shown as the decline of the hepatic and serum triglyceride levels, and the fewer fat droplets in the liver sections. Chronic ethanol exposure led to significant decrease of the mRNA and protein levels of peroxisome proliferator-activated receptor α (PPAR-α), which was blocked by CMZ co-treatment. CMZ co-treatment suppressed ethanol-induced oxidative stress, overproduction of tumor necrosis α (TNF-α), and decrease of protein levels of the PPAR-α co-activators including p300 and deacetylated PGC1-α. Furthermore, CMZ co-treatment led to the activation of AMP-activated protein kinase (AMPK), mitogen-activated protein kinase (MAPK), and PI3K/Akt/GSK3β pathway. However, chronic ethanol-induced decline of acyl-CoA carboxylase (ACC) and fatty acid synthase (FAS) protein levels was partially restored by CMZ, while the activation of autophagy appeared to be suppressed by CMZ.

Conclusion

These results suggested that CMZ suppressed chronic ethanol-induced oxidative stress, TNF-α overproduction, decline of p300 protein level and deacetylation of PGC1-α, and activated AMPK, MAPK, and PI3K/Akt/GSK3β pathway, which might contribute to the activation of PPAR-α and account for the protection of CMZ against AFL.

Effects of rhaponticum carthamoides versus glycyrrhiza glabra and punica granatum extracts on metabolic syndrome signs in rats

Background

Rhaponticum cathamoides (RC) is an endemic wild Siberian herb with marked medicinal properties that are still poorly understood. The aim of this study is to investigate the therapeutic potential of RC extract (ERC) compared to the effects of Glycyrrhiza glabra (EGG) and Punica granatum extracts (EPG) in a rat model with high-fat diet-(HFD)-induced signs of metabolic syndrome; therefore, this study addresses a significant global public health problem.

Methods

Six-month-old male Wistar Albino Glaxo rats were subjected to eight weeks of a standard diet (SD), HFD, or HFD in which ERC, EGG, or EPG powders were incorporated at 300 mg/kg/day. The serum lipid profile, corticosterone and cytokine concentrations, glucose tolerance, systolic blood pressure, triacylglycerol accumulation, and PPARα DNA-binding activities in the liver samples were determined.

Results

In contrast to EGG and EPG, an ERC supplement significantly reduced the weight of epididymal tissue (19.0%, p < 0.01) and basal serum glucose level (19.4%, p < 0.05). ERC improved glucose intolerance as well as dyslipidemia more efficiently than EGG and EPG. EGG but not ERC or EPG supplementation decreased systolic blood pressure by 12.0% (p < 0.05). All of the tested extracts reduced serum IL6 and corticosterone levels induced by HFD. However, the lowering effects of ERC consumption on the serum TNF-α level and its restoring effect on the adrenal corticosterone level significantly exceeded the improvements induced by EGG and EPG. ERC intake also reduced triacylglycerol accumulation and increased the PPARα DNA-binding activity in the liver more significantly than EGG and EPG.

Conclusions

ERC powder supplementation improved glucose and lipid metabolism more significantly than EGG and EPG in rats fed on HFD, supporting the strategy of R. carthamoides use for safe relief of metabolic syndrome and its related disturbances such as inflammation, stress, and hepatic steatosis.

Identification of novel clinical factors associated with hepatic fat accumulation in extreme obesity

OBJECTIVES

The accumulation of lipids stored as excess triglycerides in the liver (steatosis) is highly prevalent in obesity and has been associated with several clinical characteristics, but most studies have been based on relatively small sample sizes using a limited set of variables. We sought to identify clinical factors associated with liver fat accumulation in a large cohort of patients with extreme obesity.

METHODS

We analyzed 2929 patients undergoing intraoperative liver biopsy during a primary bariatric surgery. Univariate and multivariate regression modeling was used to identify associations with over 200 clinical variables with the presence of any fat in the liver and with moderate to severe versus mild fat accumulation.

RESULTS

A total of 19 data elements were associated with the presence of liver fat and 11 with severity of liver fat including ALT and AST, plasma lipid, glucose, and iron metabolism variables, several medications and laboratory measures, and sleep apnea. The accuracy of a multiple logistic regression model for presence of liver fat was 81% and for severity of liver fat accumulation was 77%.

CONCLUSIONS

A limited set of clinical factors can be used to model hepatic fat accumulation with moderate accuracy and may provide potential mechanistic insights in the setting of extreme obesity.

Betaine attenuates hepatic steatosis by reducing methylation of the MTTP promoter and elevating genomic methylation in mice fed a high-fat diet

Aberrant DNA methylation contributes to the abnormality of hepatic gene expression, one of the main factors in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Betaine is a methyl donor and has been considered to be a lipotropic agent. However, whether betaine supplementation improves NAFLD via its effect on the DNA methylation of specific genes and the genome has not been explored. Male C57BL/6 mice were fed either a control diet or high-fat diet (HFD) supplemented with 0%, 1% and 2% betaine in water (wt/vol) for 12 weeks. Betaine supplementation ameliorated HFD-induced hepatic steatosis in a dose-dependent manner. HFD up-regulated FAS and ACOX messenger RNA (mRNA) expression and down-regulated PPARα, ApoB and MTTP mRNA expression; however, these alterations were reversed by betaine supplementation, except ApoB. MTTP mRNA expression was negatively correlated with the DNA methylation of its CpG sites at -184, -156, -63 and -60. Methylation of these CpG sites was lower in both the 1% and 2% betaine-supplemented groups than in the HFD group (averages; 25.55% and 14.33% vs. 30.13%). In addition, both 1% and 2% betaine supplementation significantly restored the methylation capacity [S-adenosylmethionine (SAM) concentration and SAM/S-adenosylhomocysteine ratios] and genomic methylation level, which had been decreased by HFD (0.37% and 0.47% vs. 0.25%). These results suggest that the regulation of aberrant DNA methylation by betaine might be a possible mechanism of the improvements in NAFLD upon betaine supplementation.

Increased plasma corticosterone contributes to the development of alcoholic fatty liver in mice

Ethanol ingestion increases endogenous glucocorticoid levels in both humans and rodents. The present study aimed to define a mechanistic link between the increased glucocorticoids and alcoholic fatty liver in mice. Plasma corticosterone levels were not affected in mice on a 2-wk ethanol diet regimen but significantly increased upon 4 wk of ethanol ingestion. Accordingly, hepatic triglyceride levels were not altered after 2 wk of ethanol ingestion but were elevated at 4 wk. Based on the observation that 2 wk of ethanol ingestion did not significantly increase endogenous corticosterone levels, we administered exogenous glucocorticoids along with the 2-wk ethanol treatment to determine whether the elevated glucocorticoid contributes to the development of alcoholic fatty liver. Mice were subjected to ethanol feeding for 2 wk with or without dexamethasone administration. Hepatic triglyceride contents were not affected by either ethanol or dexamethasone alone but were significantly increased by administration of both. Microarray and protein level analyses revealed two distinct changes in hepatic lipid metabolism in mice administered with both ethanol and dexamethasone: accelerated triglyceride synthesis by diacylglycerol O-acyltransferase 2 and suppressed fatty acid β-oxidation by long-chain acyl-CoA synthetase 1, carnitine palmitoyltransferase 1a, and acyl-CoA oxidase 1. A reduction of hepatic peroxisome proliferation activator receptor-α (PPAR-α) was associated with coadministration of ethanol and dexamethasone. These findings suggest that increased glucocorticoid levels may contribute to the development of alcoholic fatty liver, at least partially, through hepatic PPAR-α inactivation.

Alcoholism causes alveolar macrophage zinc deficiency and immune dysfunction

RATIONALE

Alcohol use disorders cause oxidative stress in the lower airways and increase susceptibility to pneumonia and lung injury. Currently, no therapeutic options exist to mitigate the pulmonary consequences of alcoholism.

OBJECTIVES

We recently determined in an animal model that alcohol ingestion impairs pulmonary zinc metabolism and causes alveolar macrophage immune dysfunction. The objective of this research is to determine the effects of alcoholism on zinc bioavailability and alveolar macrophage function in human subjects.

METHODS

We recruited otherwise healthy alcoholics (n = 17) and matched control subjects (n = 17) who underwent bronchoscopy for isolation of alveolar macrophages, which were analyzed for intracellular zinc, phagocytic function, and surface expression of granulocyte-macrophage colony-stimulating factor receptor; all three of these indices are decreased in experimental models.

MEASUREMENTS AND MAIN RESULTS

Alcoholic subjects had normal serum zinc, but significantly decreased alveolar macrophage intracellular zinc levels (adjusted means [SE], 718 [41] vs. 948 [25] RFU/cell; P < 0.0001); bacterial phagocytosis (adjusted means [SE], 1,027 [48] vs. 1,509 [76] RFU/cell; P < 0.0001); and expression of granulocyte-macrophage colony-stimulating factor receptor β subunit (adjusted means [SE], 1,471 [42] vs. 2,114 [35] RFU/cell; P < 0.0001]. Treating alveolar macrophages with zinc acetate and glutathione in vitro increased intracellular zinc levels and improved their phagocytic function.

CONCLUSIONS

These novel clinical findings provide evidence that alcohol abuse is associated with significant zinc deficiency and immune dysfunction within the alveolar space and suggest that dietary supplementation with zinc and glutathione precursors could enhance airway innate immunity and decrease the risk for pneumonia or lung injury in these vulnerable individuals.

Dietary zinc deficiency exaggerates ethanol-induced liver injury in mice: involvement of intrahepatic and extrahepatic factors

Clinical studies have demonstrated that alcoholics have a lower dietary zinc intake compared to health controls. The present study was undertaken to determine the interaction between dietary zinc deficiency and ethanol consumption in the pathogenesis of alcoholic liver disease. C57BL/6N mice were subjected to 8-week feeding of 4 experimental liquid diets: (1) zinc adequate diet, (2) zinc adequate diet plus ethanol, (3) zinc deficient diet, and (4) zinc deficient diet plus ethanol. Ethanol exposure with adequate dietary zinc resulted in liver damage as indicated by elevated plasma alanine aminotransferase level and increased hepatic lipid accumulation and inflammatory cell infiltration. Dietary zinc deficiency alone increased hepatic lipid contents, but did not induce hepatic inflammation. Dietary zinc deficiency showed synergistic effects on ethanol-induced liver damage. Dietary zinc deficiency exaggerated ethanol effects on hepatic genes related to lipid metabolism and inflammatory response. Dietary zinc deficiency worsened ethanol-induced imbalance between hepatic pro-oxidant and antioxidant enzymes and hepatic expression of cell death receptors. Dietary zinc deficiency exaggerated ethanol-induced reduction of plasma leptin, although it did not affect ethanol-induced reduction of white adipose tissue mass. Dietary zinc deficiency also deteriorated ethanol-induced gut permeability increase and plasma endotoxin elevation. These results demonstrate, for the first time, that dietary zinc deficiency is a risk factor in alcoholic liver disease, and multiple intrahepatic and extrahepatic factors may mediate the detrimental effects of zinc deficiency.

Binge ethanol-induced HDAC3 down-regulates Cpt1α expression leading to hepatic steatosis and injury

BACKGROUND

Recently, we have demonstrated that acute alcohol exposure due to binge drinking leads to hepatic steatosis with the deregulation of hepatic histone deacetylase (HDAC) expression. Various class I, II, and IV HDACs were down-regulated, whereas expression of HDAC3 was solely up-regulated. Hence, in the present work, we specifically examined the mechanistic role of HDAC3 in the development of hepatic steatosis occurring in response to binge alcohol administration.

METHODS

C57BL/6 mice were gavaged 3 times with ethanol (EtOH) at a dose of 4.5 g/kg. HDAC inhibitor, Trichostatin A (TSA) was simultaneously injected intraperitoneally at a dose of 1 mg/kg. Hepatic steatosis, injury, expression of HDAC3 and carnitine palmitoyltransferase 1α (CPT1α) were evaluated. HDAC3 and histone H3 acetylation levels at the Cpt1α promoter were analyzed by chromatin immunoprecipitation (ChIP).

RESULTS

The binge EtOH-mediated increase in HDAC3 was prevented by simultaneous administration of HDAC inhibitor, TSA, which markedly attenuated hepatic steatosis and injury. Importantly, HDAC3 inhibition was able to normalize the down-regulation of Cpt1α expression. Causal role of HDAC3 in the transcriptional repression of Cpt1α was demonstrated by increased HDAC3 binding at the thyroid receptor element site in the Cpt1α distal promoter region. Further, a resultant decrease in the transcriptionally permissive histone H3 lysine 9 acetylation in the proximal promoter region near the transcriptional start site was observed. Notably, TSA treatment reduced HDAC3 binding and increased H3K9 acetylation at Cpt1α promoter leading to increased Cpt1α expression. These molecular events resulted in attenuation of binge alcohol-induced hepatic steatosis.

CONCLUSIONS

These findings provide insights into potential epigenetic mechanisms underlying transcriptional regulation of Cpt1α in the hepatic steatosis occurring in response to binge EtOH administration.

Chronic alcohol exposure disturbs lipid homeostasis at the adipose tissue-liver axis in mice: analysis of triacylglycerols using high-resolution mass spectrometry in combination with in vivo metabolite deuterium labeling

A method of employing high-resolution mass spectrometry in combination with in vivo metabolite deuterium labeling was developed in this study to investigate the effects of alcohol exposure on lipid homeostasis at the white adipose tissue (WAT)-liver axis in a mouse model of alcoholic fatty liver. In order to differentiate the liver lipids synthesized from the fatty acids that were transported back from adipose tissue and the lipids synthesized from other sources of fatty acids, a two-stage mouse feeding experiment was performed to incorporate deuterium into metabolites. Hepatic lipids extracted from mouse liver, epididymal white adipose tissue (eWAT) and subcutaneous white adipose tissue (sWAT) were analyzed. It was found that 13 and 10 triacylglycerols (TGs) incorporated with a certain number of deuterium were significantly increased in alcohol induced fatty liver at two and four weeks of alcohol feeding periods, respectively. The concentration changes of these TGs ranged from 1.7 to 6.3-fold increase. A total of 14 deuterated TGs were significantly decreased in both eWAT and sWAT at the two and four weeks and the fold-change ranged from 0.19 to 0.77. The increase of deuterium incorporated TGs in alcohol-induced fatty liver and their decrease in both eWAT and sWAT indicate that alcohol exposure induces hepatic influx of fatty acids which are released from WATs. The results of time course analysis further indicate a mechanistic link between adipose fat loss and hepatic fat gain in alcoholic fatty liver.

Status of essential trace minerals and oxidative stress in viral hepatitis C patients with nonalcoholic fatty liver disease

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) may be an important factor leading to altered trace mineral homeostasis, thereby accelerating the progression of hepatitis C virus (HCV) infection. Our aim was to determine whether NAFLD influenced the status of certain essential trace minerals and oxidative stress in chronic HCV-infected patients.

DESIGN AND METHODS

Blood biochemical parameters were determined in a group of 30 healthy, non-obese, non-diabetic participants (CNL group), and hepatitis C patients without NAFLD (HCV group, n = 30) and with NAFLD (HCV-NAFLD group, n = 32).

RESULTS

Concentrations of thiobarbituric acid reactive substances (TBARS; a measure of oxidative stress), C-reactive protein (CRP), ferritin, aminotransferases, lipid profiles, and insulin metabolism were markedly abnormal in both patient groups than in CNL subjects. Compared to patients in the HCV group, those with HCV-NAFLD group had lower high-density lipoprotein concentrations, higher low-density lipoprotein and homeostasis model assessment-insulin resistance (HOMA-IR) values, disrupted antioxidant enzyme activities, and elevated TBARS concentrations, as well as decreased plasma concentrations of trace minerals zinc (Zn) and selenium (Se) and increased copper (Cu). The alterations in mineral homeostasis were also linked to TBARS, CRP, ferritin, lipoproteins, and HOMA-IR values in the HCV-NAFLD group.

CONCLUSIONS

There is a progressive deterioration in the homeostasis of minerals (Zn, Se, and Cu) in HCV-NAFLD patients, which may reflect greater oxidative stress and inflammation. These results suggest that the disturbance in mineral metabolism by NAFLD has an impact on the effectiveness of treatment for chronic HCV infection.

Preservation of hepatocyte nuclear factor-4α contributes to the beneficial effect of dietary medium chain triglyceride on alcohol-induced hepatic lipid dyshomeostasis in rats

BACKGROUND

Alcohol consumption is a major cause of fatty liver, and dietary saturated fats have been shown to protect against alcoholic fatty liver. This study investigated the mechanisms of how dietary saturated fat may modulate alcohol-induced hepatic lipid dyshomeostasis.

METHODS

Male Sprague Dawley rats were pair-fed with 3 isocaloric liquid diets, control, alcohol, and medium chain triglyceride (MCT)/alcohol, respectively, for 8 weeks. The control and alcohol diets were based on the Lieber-DeCarli liquid diet formula with 30% total calories derived from corn oil (rich in unsaturated long chain fatty acids). The corn oil was replaced by MCT, which consists of exclusive saturated fatty acids, in the MCT/alcohol diet. HepG2 cell culture was conducted to test the effects of unsaturated fatty acids on hepatocyte nuclear factor-4α (HNF4α) and the role of HNF4α in regulating hepatocyte lipid homeostasis.

RESULTS

Alcohol feeding caused significant lipid accumulation, which was attenuated by dietary MCT. The major effect of alcohol on hepatic gene expression is the up-regulation of CYP4A1, CD36, and GPAT3, and down-regulation of apolipoprotein B (ApoB). Dietary MCT further up-regulated CYP4A1 gene, normalized ApoB gene, and up-regulated MTTP and SCD1 genes. The protein level of HNF4α, a master transcription factor of the liver, was reduced by alcohol feeding, which was normalized by dietary MCT. Fatty acid profiling demonstrated that alcohol feeding dramatically increased hepatic unsaturated long chain fatty acyl species, particularly linoleic acid and oleic acid, which was attenuated by dietary MCT. Dietary MCT attenuated alcohol-reduced serum triglyceride level and modulated the fatty acid composition of the serum triglycerides. Cell culture study demonstrated polyunsaturated linoleic acid rather than monounsaturated oleic acid inactivated HNF4α in HepG2 cells. Knockdown of HNF4α caused lipid accumulation in HepG2 cells due to dysregulation of very low density lipoprotein secretion.

CONCLUSIONS

Results suggest that dietary MCT prevents alcohol-induced hepatic lipid accumulation, at least partially, through reducing hepatic polyunsaturated long chain fatty acids and preserving HNF4α.

A multimineral natural product from red marine algae reduces colon polyp formation in C57BL/6 mice

The goal of this study was to determine if a multimineral natural product derived from red marine algae could reduce colon polyp formation in mice on a high-fat diet. C57BL/6 mice were maintained for up to 18 mo either on a high-fat "Western-style" diet or on a low-fat diet (AIN 76A), with or without the multimineral-supplement. To summarize, colon polyps were detected in 22 of 70 mice (31%) on the high-fat diet but in only 2 of 70 mice (3%) receiving the mineral-supplemented high-fat diet (P < 0.0001). Colon polyps were detected in 16 of 70 mice (23%) in the low-fat group; not significantly different from high-fat group but significantly higher than the high-fat-supplemented group (P = 0.0006). This was in spite of the fact that the calcium level in the low-fat diet was comparable to the level of calcium in the high-fat diet containing the multimineral-product. Supplementation of the low-fat diet reduced the incidence to 8 of 70 mice (11% incidence). Taken together, these findings demonstrate that a multimineral natural product can protect mice on a high-fat diet against adenomatous polyp formation in the colon. These data suggest that increased calcium alone is insufficient to explain the lower incidence of colon polyps.

Deletion of angiotensin II type 1 receptor gene or scavenge of superoxide prevents chronic alcohol-induced aortic damage and remodelling

To investigate whether chronic alcohol consumption induces vascular injury via angiotensin II (Ang II) type 1 (AT1) receptor-dependent superoxide generation, male transgenic mice with knockout of AT1 gene (AT1-KO) and age-matched wild-type (WT) C57BL/6 mice were pair-fed a modified Lieber-DeCarli alcohol or isocaloric maltose dextrin control liquid diet for 2 months. Ethanol content (%, W/V) in the diet was 4.8 (34% of total calories) at initiation, and gradually increased up to 5.4 (38% of total calories). For some WT mice with and without alcohol treatment, superoxide dismutase mimetic (MnTMPyP) was given simultaneously by intraperitoneal injection at 5 mg/kg body weight daily for 2 months. At the end of studies, aortas were harvested for histopathological and immunohistochemical examination. Significant increases in the wall thickness and structural disarrangement of aorta were found in alcohol group, along with significant increases in aortic oxidative and/or nitrosative damage, expressions of NADPH oxidases (NOXs), inflammatory response, cell death and proliferation, and remodelling (fibrosis). However, these pathological changes were completely attenuated in alcohol-treated AT1-KO mice or in alcohol-treated WT mice that were also simultaneously treated with MnTMPyP for 2 months. These results suggest that chronic alcohol consumption may activate NOX via Ang II/AT1 receptor, to generate superoxide and associated peroxynitrite that in turn causes aortic nitrosative damage, inflammation, cell death and proliferation, and remodelling. Therefore, blocking Ang II/AT1 system or scavenging superoxide may become a potential preventive and/therapeutic approach to alcoholic vascular damage.

Deletion of angiotensin II type 1 receptor gene attenuates chronic alcohol-induced retinal ganglion cell death with preservation of VEGF expression

PURPOSE

To investigate how chronic alcohol consumption affects adult visual nervous system and whether renin-angiotensin system (RAS) is involved in this pathogenic process.

METHODS

Male transgenic mice with angiotensin II (Ang II) type 1 (AT1) receptor gene knockout (AT1-KO) and age-matched wild-type (WT) mice were pair-fed a modified Lieber-DeCarli alcohol or isocaloric maltose dextrin control liquid diet for 2 months. At the end of the study, retinas were harvested and subjected to histopathological and immunohistochemical examination.

RESULTS

We found that chronic alcohol consumption significantly increased retinal ganglion cell (RGC) apoptosis in the retina of WT mice, but not AT1-KO mice, detected by terminal deoxynucleotidyl-transferase-mediated dUTP-nick-end labeling staining and caspase 3 activation, along with an up-regulation of AT1 expression in RGC. At the same time, the phosphorylation of P53 in RGCs was significantly increased for both WT and AT1-KO mice exposed to alcohol, which could be significantly, although partially, prevented by AT1 gene deletion. We further examined the expression of vascular endothelial growth factor (VEGF) and CD31, and found that alcohol treatment significantly decreased the expression of VEGF and CD31 in RGCs of WT mice, but not AT1-KO mice.

CONCLUSION

Taken together, our study demonstrates that the induction of RGC apoptosis by chronic alcohol exposure may be related to p53-activation and VEGF depression, all which are partially dependent of AT1 receptor activation.

Reduced susceptibility of DNA methyltransferase 1 hypomorphic (Dnmt1N/+) mice to hepatic steatosis upon feeding liquid alcohol diet

BACKGROUND

Methylation at C-5 (5-mdC) of CpG base pairs, the most abundant epigenetic modification of DNA, is catalyzed by 3 essential DNA methyltransferases (Dnmt1, Dnmt3a and Dnmt3b). Aberrations in DNA methylation and Dnmts are linked to different diseases including cancer. However, their role in alcoholic liver disease (ALD) has not been elucidated.

METHODOLOGY/PRINCIPAL FINDINGS

Dnmt1 wild type (Dnmt1(+/+)) and hypomorphic (Dnmt1(N/+)) male mice that express reduced level of Dnmt1 were fed Lieber-DeCarli liquid diet containing ethanol for 6 weeks. Control mice were pair-fed calorie-matched alcohol-free liquid diet, and Dnmtase activity, 5-mdC content, gene expression profile and liver histopathology were evaluated. Ethanol feeding caused pronounced decrease in hepatic Dnmtase activity in Dnmt1(+/+) mice due to decrease in Dnmt1 and Dnmt3b protein levels and upregulation of miR-148 and miR-152 that target both Dnmt1 and Dnmt3b. Microarray and qPCR analysis showed that the genes involved in lipid, xenobiotic and glutathione metabolism, mitochondrial function and cell proliferation were dysregulated in the wild type mice fed alcohol. Surprisingly, Dnmt1(N/+) mice were less susceptible to alcoholic steatosis compared to Dnmt1(+/+) mice. Expression of several key genes involved in alcohol (Aldh3b1), lipid (Ppara, Lepr, Vldlr, Agpat9) and xenobiotic (Cyp39a1) metabolism, and oxidative stress (Mt-1, Fmo3) were significantly (P<0.05) altered in Dnmt1(N/+) mice relative to the wild type mice fed alcohol diet. However, CpG islands encompassing the promoter regions of Agpat9, Lepr, Mt1 and Ppara were methylation-free in both genotypes irrespective of the diet, suggesting that promoter methylation does not regulate their expression. Similarly, 5-mdC content of the liver genome, as measured by LC-MS/MS analysis, was not affected by alcohol diet in the wild type or hypomorphic mice.

CONCLUSIONS/SIGNIFICANCE

Although feeding alcohol diet reduced Dnmtase activity, the loss of one copy of Dnmt1 protected mice from alcoholic hepatosteatosis by dysregulating genes involved in lipid metabolism and oxidative stress.

Effects of cigarette smoke and ethanol intake on mouse oesophageal mucosa changes induced by dietary zinc deficiency and deoxycholic acid supplementation

The noxious effects of dietary zinc deficiency (ZD) and deoxycholic bile acid (DCA) supplementation in the oesophagus were investigated. The additional influence of cigarette smoke and ethanol intake on the changes in the oesophageal mucosa induced by dietary ZD plus DCA was also assessed. Male C57BL/6 mice were allocated into four groups: Group 1 was fed control diet and groups 2-4 were fed ZD plus DCA diet. After 5 weeks, groups 3 and 4 were exposed to 10% ethanol intake or cigarette smoke for 15 weeks, respectively. All animals were euthanized at the end of week 20, and the oesophagus, lung, liver and colon were collected and analysed by conventional morphology. Cell proliferation was assessed in the oesophageal mucosa by Ki-67 immunohistochemistry and cyclooxygenase 2 (COX-2) protein by Western blotting. Dietary ZD plus DCA treatment induced mild hyperkeratosis and hyperplasia, increased cell proliferation index and COX-2 protein expression in the oesophagus, and intranuclear inclusion, karyocytomegaly and microvesicular fatty change in the liver. Cigarette smoke increased COX-2 protein expression in oesophageal mucosa and irregular enlargement of alveolus and alveolar ductal air spaces, while ethanol enhanced liver damage induced by ZD plus DCA diet. These findings indicate that dietary ZD plus DCA treatment during 20 weeks induces a pattern of chemical oesophageal injury but not Barrett's-like lesions.

Leptin deficiency contributes to the pathogenesis of alcoholic fatty liver disease in mice

White adipose tissue (WAT) secretes adipokines, which critically regulate lipid metabolism. The present study investigated the effects of alcohol on adipokines and the mechanistic link between adipokine dysregulation and alcoholic fatty liver disease. Mice were fed alcohol for 2, 4, or 8 weeks to document changes in adipokines over time. Alcohol exposure reduced WAT mass and body weight in association with hepatic lipid accumulation. The plasma adiponectin concentration was increased at 2 weeks, but declined to normal at 4 and 8 weeks. Alcohol exposure suppressed leptin gene expression in WAT and reduced the plasma leptin concentration at all times measured. There is a highly positive correlation between plasma leptin concentration and WAT mass or body weight. To determine whether leptin deficiency mediates alcohol-induced hepatic lipid dyshomeostasis, mice were fed alcohol for 8 weeks with or without leptin administration for the last 2 weeks. Leptin administration normalized the plasma leptin concentration and reversed alcoholic fatty liver. Alcohol-perturbed genes involved in fatty acid β-oxidation, very low-density lipoprotein secretion, and transcriptional regulation were attenuated by leptin. Leptin also normalized alcohol-reduced phosphorylation levels of signal transducer Stat3 and adenosine monophosphate-activated protein kinase. These data demonstrated for the first time that leptin deficiency in association with WAT mass reduction contributes to the pathogenesis of alcoholic fatty liver disease.

Zinc supplementation during pregnancy protects against lipopolysaccharide-induced fetal growth restriction and demise through its anti-inflammatory effect

LPS is associated with adverse developmental outcomes, including preterm delivery, fetal death, teratogenicity, and intrauterine growth restriction (IUGR). Previous reports showed that zinc protected against LPS-induced teratogenicity. In the current study, we investigated the effects of zinc supplementation during pregnancy on LPS-induced preterm delivery, fetal death and IUGR. All pregnant mice except controls were i.p. injected with LPS (75 μg/kg) daily from gestational day (GD) 15 to GD17. Some pregnant mice were administered zinc sulfate through drinking water (75 mg elemental Zn per liter) throughout the pregnancy. As expected, an i.p. injection with LPS daily from GD15 to GD17 resulted in 36.4% (4/11) of dams delivered before GD18. In dams that completed the pregnancy, 63.2% of fetuses were dead. Moreover, LPS significantly reduced fetal weight and crown-rump length. Of interest, zinc supplementation during pregnancy protected mice from LPS-induced preterm delivery and fetal death. In addition, zinc supplementation significantly alleviated LPS-induced IUGR and skeletal development retardation. Further experiments showed that zinc supplementation significantly attenuated LPS-induced expression of placental inflammatory cytokines and cyclooxygenase-2. Zinc supplementation also significantly attenuated LPS-induced activation of NF-κB and MAPK signaling in mononuclear sinusoidal trophoblast giant cells of the labyrinth zone. It inhibited LPS-induced placental AKT phosphorylation as well. In conclusion, zinc supplementation during pregnancy protects against LPS-induced fetal growth restriction and demise through its anti-inflammatory effect.

A multi-mineral natural product inhibits liver tumor formation in C57BL/6 mice

C57BL/6 mice were maintained for up to 18 months on high-fat and low-fat diets with or without a multi-mineral supplement derived from the skeletal remains of the red marine algae Lithothamnion calcareum. Numerous grossly observable liver masses were visible in animals on the "western-style" high-fat diet sacrificed at 12 and 18 months. The majority of the masses were in male mice (20 out of 100 males versus 3 out of 100 females; p = 0.0002). There were more liver masses in animals on the high-fat diet than on the low-fat diet (15 out of 50 on high-fat versus 5 out of 50 on low-fat; p = 0.0254). The multi-mineral supplement reduced the number of liver masses in mice on both diets (3 out of 25 male mice in the low-fat diet group without the supplement versus 1 out of 25 mice with supplement; 12 of 25 male mice in the high-fat diet group without the supplement versus 3 of 25 mice with supplement [p = 0.0129]). Histological evaluation revealed a total of 17 neoplastic lesions (9 adenomas and 8 hepatocellular carcinomas), and 18 pre-neoplastic lesions. Out of eight hepatocellular carcinomas, seven were found in unsupplemented diet groups. Steatosis was widely observed in livers with and without grossly observable masses, but the multi-mineral supplement had no effect on the incidence of steatosis or its severity. Taken together, these findings suggest that a multi-mineral-rich natural product can protect mice against neoplastic and pre-neoplastic proliferative liver lesions that may develop in the face of steatosis.

Activation of peroxisome proliferator-activated receptor-γ by rosiglitazone improves lipid homeostasis at the adipose tissue-liver axis in ethanol-fed mice

The development of alcohol-induced fatty liver is associated with a reduction of white adipose tissue (WAT). Peroxisome proliferator-activated receptor (PPAR)-γ prominently distributes in the WAT and plays a crucial role in maintaining adiposity. The present study investigated the effects of PPAR-γ activation by rosiglitazone on lipid homeostasis at the adipose tissue-liver axis. Adult C57BL/6 male mice were pair fed liquid diet containing ethanol or isocaloric maltose dextrin for 8 wk with or without rosiglitazone supplementation to ethanol-fed mice for the last 3 wk. Ethanol exposure downregulated adipose PPAR-γ gene and reduced the WAT mass in association with induction of inflammation, which was attenuated by rosiglitazone. Ethanol exposure stimulated lipolysis but reduced fatty acid uptake capacity in association with dysregulation of lipid metabolism genes. Rosiglitazone normalized adipose gene expression and corrected ethanol-induced lipid dyshomeostasis. Ethanol exposure induced steatosis and upregulated inflammatory genes in the liver, which were attenuated by rosiglitazone. Hepatic peroxisomal fatty acid β-oxidation was suppressed by ethanol in associated with inhibition of acyl-coenzyme A oxidase 1. Rosiglitazone elevated plasma adiponectin level and normalized peroxisomal fatty acid β-oxidation rate. However, rosiglitazone did not affect ethanol-reduced very low-density lipoprotein secretion from the liver. These results demonstrated that activation of PPAR-γ by rosiglitazone reverses ethanol-induced adipose dysfunction and lipid dyshomeostasis at the WAT-liver axis, thereby abrogating alcoholic fatty liver.

Zinc and liver disease

Zinc is an essential trace element required for normal cell growth, development, and differentiation. It is involved in DNA synthesis, RNA transcription, and cell division and activation. It is a critical component in many zinc protein/enzymes, including critical zinc transcription factors. Zinc deficiency/altered metabolism is observed in many types of liver disease, including alcoholic liver disease (ALD) and viral liver disease. Some of the mechanisms for zinc deficiency/altered metabolism include decreased dietary intake, increased urinary excretion, activation of certain zinc transporters, and induction of hepatic metallothionein. Zinc deficiency may manifest itself in many ways in liver disease, including skin lesions, poor wound healing/liver regeneration, altered mental status, or altered immune function. Zinc supplementation has been documented to block/attenuate experimental ALD through multiple processes, including stabilization of gut-barrier function, decreasing endotoxemia, decreasing proinflammatory cytokine production, decreasing oxidative stress, and attenuating apoptotic hepatocyte death. Clinical trials in human liver disease are limited in size and quality, but it is clear that zinc supplementation reverses clinical signs of zinc deficiency in patients with liver disease. Some studies suggest improvement in liver function in both ALD and hepatitis C following zinc supplementation, and 1 study suggested improved fibrosis markers in hepatitis C patients. The dose of zinc used for treatment of liver disease is usually 50 mg of elemental zinc taken with a meal to decrease the potential side effect of nausea.

Chronic alcohol exposure stimulates adipose tissue lipolysis in mice: role of reverse triglyceride transport in the pathogenesis of alcoholic steatosis

Alcohol consumption induces liver steatosis; therefore, this study investigated the possible role of adipose tissue dysfunction in the pathogenesis of alcoholic steatosis. Mice were pair-fed an alcohol or control liquid diet for 8 weeks to evaluate the alcohol effects on lipid metabolism at the adipose tissue-liver axis. Chronic alcohol exposure reduced adipose tissue mass and adipocyte size. Fatty acid release from adipose tissue explants was significantly increased in alcohol-fed mice in association with the activation of adipose triglyceride lipase and hormone-sensitive lipase. Alcohol exposure induced insulin intolerance and inactivated adipose protein phosphatase 1 in association with the up-regulation of phosphatase and tensin homolog (PTEN) and suppressor of cytokine signaling 3 (SOCS3). Alcohol exposure up-regulated fatty acid transport proteins and caused lipid accumulation in the liver. To define the mechanistic link between adipose triglyceride loss and hepatic triglyceride gain, mice were first administered heavy water for 5 weeks to label adipose triglycerides with deuterium, and then pair-fed alcohol or control diet for 2 weeks. Deposition of deuterium-labeled adipose triglycerides in the liver was analyzed using Fourier transform ion cyclotron mass spectrometry. Alcohol exposure increased more than a dozen deuterium-labeled triglyceride molecules in the liver by up to 6.3-fold. These data demonstrate for the first time that adipose triglycerides due to alcohol-induced hyperlipolysis are reverse transported and deposited in the liver.

Restoration of C/EBPα in dedifferentiated liposarcoma induces G2/M cell cycle arrest and apoptosis

Well-differentiated liposarcoma (WDLS) and dedifferentiated liposarcoma (DDLS) represent the most common biological group of liposarcoma, and there is a pressing need to develop targeted therapies for patients with advanced disease. To identify potential therapeutic targets, we sought to identify differences in the adipogenic pathways between DDLS, WDLS, and normal adipose tissue. In a microarray analysis of DDLS (n = 84), WDLS (n = 79), and normal fat (n = 23), C/EBPα, a transcription factor involved in cell cycle regulation and differentiation, was underexpressed in DDLS when compared to both WDLS and normal fat (15.2- and 27.8-fold, respectively). In normal adipose-derived stem cells, C/EBPα expression was strongly induced when cells were cultured in differentiation media, but in three DDLS cell lines, this induction was nearly absent. We restored C/EBPα expression in one of the cell lines (DDLS8817) by transfection of an inducible C/EBPα expression vector. Inducing C/EBPα expression reduced proliferation and caused cells to accumulate in G2/M. Under differentiation conditions, the cell proliferation was reduced further, and 66% of the DDLS cells containing the inducible C/EBPα expression vector underwent apoptosis as demonstrated by annexin V staining. These cells in differentiation conditions expressed early adipocyte-specific mRNAs such as LPL and FABP4, but they failed to accumulate intracellular lipid droplets, a characteristic of mature adipocytes. These results demonstrate that loss of C/EBPα is an important factor in suppressing apoptosis and maintaining the dedifferentiated state in DDLS. Restoring C/EBPα may be a useful therapeutic approach for DDLS.

Alcoholic liver disease: pathogenesis and new therapeutic targets

Alcoholic liver disease (ALD) is a major cause of chronic liver disease worldwide and can lead to fibrosis and cirrhosis. The latest surveillance report published by the National Institute on Alcohol Abuse and Alcoholism showed that liver cirrhosis was the 12th leading cause of death in the United States, with a total of 29,925 deaths in 2007, 48% of which were alcohol related. The spectrum of ALD includes simple steatosis, alcoholic hepatitis, fibrosis, cirrhosis, and superimposed hepatocellular carcinoma. Early work on the pathogenesis of the disease focused on ethanol metabolism-associated oxidative stress and glutathione depletion, abnormal methionine metabolism, malnutrition, and production of endotoxins that activate Kupffer cells. We review findings from recent studies that have characterized specific intracellular signaling pathways, transcriptional factors, aspects of innate immunity, chemokines, epigenetic features, microRNAs, and stem cells that are associated with ALD, improving our understanding of its pathogenesis. Despite this progress, no targeted therapies are available. The cornerstone of treatment for alcoholic hepatitis remains as it was 40 years ago: abstinence, nutritional support, and corticosteroids. There is an urgent need to develop new pathophysiology-oriented therapies. Recent translational studies of human samples and animal models have identified promising therapeutic targets.

Redox balance in the pathogenesis of nonalcoholic fatty liver disease: mechanisms and therapeutic opportunities

Nonalcoholic fatty liver disease (NAFLD) is currently the most common liver disease in the world. It encompasses a histological spectrum, ranging from simple, nonprogressive steatosis to nonalcoholic steatohepatitis (NASH), which may progress to cirrhosis and hepatocellular carcinoma. While liver-related complications are confined to NASH, emerging evidence suggests both simple steatosis and NASH predispose to type 2 diabetes and cardiovascular disease. The pathogenesis of NAFLD is currently unknown, but accumulating data suggest that oxidative stress and altered redox balance play a crucial role in the pathogenesis of steatosis, steatohepatitis, and fibrosis. We will examine intracellular mechanisms, including mitochondrial dysfunction and impaired oxidative free fatty acid metabolism, leading to reactive oxygen species generation; additionally, the potential pathogenetic role of extracellular sources of reactive oxygen species in NAFLD, including increased myeloperoxidase activity and oxidized low density lipoprotein accumulation, will be reviewed. We will discuss how these mechanisms converge to determine the whole pathophysiological spectrum of NAFLD, including hepatocyte triglyceride accumulation, hepatocyte apoptosis, hepatic inflammation, hepatic stellate cell activation, and fibrogenesis. Finally, available animal and human data on treatment opportunities with older and newer antioxidant will be presented.

The nuclear receptor CAR modulates alcohol-induced liver injury

The constitutive androstane receptor (CAR) is a member of the nuclear receptor superfamily and a sensor and detoxifier of both xenobiotics and endobiotics. Recent studies also show that CAR participates in metabolism of glucose and lipid, and has an important role in fatty liver disease and diabetes. In this study, we investigate the roles of CAR in chronic and acute alcohol-induced liver injuries. The results showed that absence of CAR in rodents led to significantly increased susceptibility to chronic alcohol-induced liver injury, which was accompanied with elevated hepatocyte apoptosis and fat accumulation. However, pre-activation of CAR by a CAR agonist, TCPOBOP, strongly enhanced the hepatic toxicity by both chronic and acute alcohol infusion in wild-type, but not in CAR(-/-) mice. Gene expression analyses indicated that CAR pre-activation and alcohol infusion synergistically decreased the expression of enzymes that metabolize the alcohol in liver. These results support a role of CAR in modulating alcoholic liver injury and imply a risk of synergistic liver toxicity induced by alcohol and CAR activation.

Clinical characteristics of de novo nonalcoholic fatty liver disease following pancreaticoduodenectomy

BACKGROUND

Hepatic steatosis may develop after pancreatic resection, but its clinicopathological features remain unclear. We explored the clinical characteristics of newly appearing nonalcoholic fatty liver disease (NAFLD) after pancreaticoduodenectomy (PD), designated as de novo NAFLD after PD.

METHODS

Of 83 patients who underwent PD between 2001 and 2006, the patients with regular alcohol consumption after PD (n = 3), those who were unavailable for regular abdominal computed tomography follow-up (n = 12), and those who died within 6 months of PD (n = 8) were excluded from the study. In the remaining 60 patients, the prevalence and clinical features of de novo NAFLD after PD were examined.

RESULTS

NAFLD developed after PD in 14 (23%) patients in our cohort. Liver biopsy was performed in 8 patients and all showed typical steatohepatitis. Compared with the patients who had conventional nonalcoholic steatohepatitis (NASH), patients with post-PD de novo NASH demonstrated significant decreases in body mass index and lower levels of serum albumin, cholesterol, apolipoprotein B, and homeostasis model assessment for insulin resistance. Multivariate logistic regression analysis revealed that pancreatic head cancer was associated with an increased risk of developing NAFLD after PD (odds ratio 12.0, 95% confidence interval 2.0-71.4, P = 0.006). Increased dosage of oral pancreatic enzymes significantly ameliorated the steatosis, as well as leading to the recovery of body weight loss and resolution of the biochemical abnormalities.

CONCLUSIONS

De novo NAFLD/NASH after PD is characterized by non-obesity and lack of hyperlipidemia and insulin resistance and is associated with pancreatic exocrine insufficiency. In such patients, intensifying pancreatic enzyme supplementation may be useful.

Zinc and alcoholic liver disease

Zinc deficiency is one of the most consistent nutritional/biochemical observations in alcoholic liver disease (ALD). The objectives of our research are to determine how alcohol interferes with cellular zinc homeostasis and if zinc deficiency is a causal factor in the development of ALD. Metallothionein (MT) is a major protein responsible for cellular zinc homeostasis. MT-transgenic (MT-TG) mice with hepatic overexpression of MT and elevation of zinc level were resistant to ethanol-induced liver injury. MT-knockout (MT-KO) mice with a reduction of hepatic zinc were more susceptible to alcohol toxicity. However, zinc treatment also provided beneficial effects on alcohol hepatoxicity in MT-KO mice, suggesting a MT-independent action. Dietary zinc supplementation normalized hepatic zinc level and attenuated the pathological changes in the liver of mice chronically fed alcohol. Several mechanisms were involved in zinc action against alcoholic cytotoxicity. Zinc enhanced cellular antioxidant capacity and corrected alcohol metabolic switch from alcohol dehydrogenase to cytochrome P4502E1. Zinc attenuated cytokine production and TNF-α receptor- and Fas-mediated cell death pathways. Zinc restored activities of hepatocyte nuclear factor-4α (HNF-4α) and peroxisome proliferation activator-α (PPAR-α), and enhanced hepatic fatty acid β-oxidation and lipid secretion. Hepatoma cell cultures showed that zinc deprivation induces lipid accumulation via inactivating HNF-4α and PPAR-α. These results suggest that alcohol exposure interferes with hepatic zinc homeostasis, leading to cellular zinc deprivation. Inactivation of zinc proteins due to zinc release is likely an important molecular mechanism in the pathogenesis of ALD.

Dynamic transcriptomic profiles of zebrafish gills in response to zinc supplementation

Background

Dietary zinc supplementation may help to promote growth, boost the immune system, protect against diabetes, and aid recovery from diarrhoea. We exploited the zebrafish (Danio rerio) gill as a unique vertebrate ion transporting epithelium model to study the time-dependent regulatory networks of gene-expression leading to homeostatic control during zinc supplementation. This organ forms a conduit for zinc uptake whilst exhibiting conservation of zinc trafficking components.

Results

Fish were maintained with either zinc supplemented water (4.0 μM) and diet (2023 mg zinc kg^-1) or water and diet containing Zn²⁺ at 0.25 μM and 233 mg zinc kg^-1, respectively. Gill tissues were harvested at five time points (8 hours to 14 days) and transcriptome changes analysed in quintuplicate using a 16 K microarray with results anchored to gill Zn²⁺ influx and whole body nutrient composition (protein, carbohydrate, lipid, elements). The number of regulated genes increased up to day 7 but declined as the fish acclimated. In total 525 genes were regulated (having a fold-change more than 1.8 fold change and an adjusted P-value less than 0.1 which is controlling a 10% False discovery rate, FDR) by zinc supplementation, but little overlap was observed between genes regulated at successive time-points. Many genes displayed cyclic expression, typical for homeostatic control mechanisms. Annotation enrichment analysis revealed strong overrepresentation of "transcription factors", with specific association evident with "steroid hormone receptors". A suite of genes linked to "development" were also statistically overrepresented. More specifically, early regulation of genes was linked to a few key transcription factors (e.g. Mtf1, Jun, Stat1, Ppara, Gata3) and was followed by hedgehog and bone morphogenic protein signalling.

Conclusions

The results suggest that zinc supplementation reactivated developmental pathways in the gill and stimulated stem cell differentiation, a response likely reflecting gill remodelling in response to its altered environment. This provides insight to the role of zinc during cell differentiation and illustrates the critical nature of maintaining zinc status. The study also highlights the importance of temporal transcriptomics analysis in order resolve the discrete elements of biological processes, such as zinc acclimation.

Dynamic transcriptomic profiles of zebrafish gills in response to zinc depletion

BACKGROUND

Zinc deficiency is detrimental to organisms, highlighting its role as an essential micronutrient contributing to numerous biological processes. To investigate the underlying molecular events invoked by zinc depletion we performed a temporal analysis of transcriptome changes observed within the zebrafish gill. This tissue represents a model system for studying ion absorption across polarised epithelial cells as it provides a major pathway for fish to acquire zinc directly from water whilst sharing a conserved zinc transporting system with mammals.

RESULTS

Zebrafish were treated with either zinc-depleted (water = 2.61 μg L-1; diet = 26 mg kg-1) or zinc-adequate (water = 16.3 μg L-1; diet = 233 mg kg-1) conditions for two weeks. Gill samples were collected at five time points and transcriptome changes analysed in quintuplicate using a 16K oligonucleotide array. Of the genes represented the expression of a total of 333 transcripts showed differential regulation by zinc depletion (having a fold-change greater than 1.8 and an adjusted P-value less than 0.1, controlling for a 10% False Discovery Rate). Down-regulation was dominant at most time points and distinct sets of genes were regulated at different stages. Annotation enrichment analysis revealed that 'Developmental Process' was the most significantly overrepresented Biological Process GO term (P = 0.0006), involving 26% of all regulated genes. There was also significant bias for annotations relating to development, cell cycle, cell differentiation, gene regulation, butanoate metabolism, lysine degradation, protein tyrosin phosphatases, nucleobase, nucleoside and nucleotide metabolism, and cellular metabolic processes. Within these groupings genes associated with diabetes, bone/cartilage development, and ionocyte proliferation were especially notable. Network analysis of the temporal expression profile indicated that transcription factors foxl1, wt1, nr5a1, nr6a1, and especially, hnf4a may be key coordinators of the homeostatic response to zinc depletion.

CONCLUSIONS

The study revealed the complex regulatory pathways that allow the organism to subtly respond to the low-zinc condition. Many of the processes affected reflected a fundamental restructuring of the gill epithelium through reactivation of developmental programs leading to stem cell differentiation. The specific regulation of genes known to be involved in development of diabetes provides new molecular links between zinc deficiency and this disease. The present study demonstrates the importance of including the time-dimension in microarray studies.

Alterations in hepatic mRNA expression of phase II enzymes and xenobiotic transporters after targeted disruption of hepatocyte nuclear factor 4 alpha

Hepatocyte nuclear factor 4 alpha (HNF4a) is a liver-enriched master regulator of liver function. HNF4a is important in regulating hepatic expression of certain cytochrome P450s. The purpose of this study was to use mice lacking HNF4a expression in liver (HNF4a-HNull) to elucidate the role of HNF4a in regulating hepatic expression of phase II enzymes and transporters in mice. Compared with male wild-type mice, HNF4a-HNull male mouse livers had (1) markedly lower messenger RNAs (mRNAs) encoding the uptake transporters sodium taurocholate cotransporting polypeptide, organic anion transporting polypeptide (Oatp) 1a1, Oatp2b1, organic anion transporter 2, sodium phosphate cotransporter type 1, sulfate anion transporter 1, sodium-dependent vitamin C transporter 1, the phase II enzymes Uridine 5'-diphospho (UDP)-glucuronosyltransferase (Ugt) 2a3, Ugt2b1, Ugt3a1, Ugt3a2, sulfotransferase (Sult) 1a1, Sult1b1, Sult5a1, the efflux transporters multidrug resistance-associated protein (Mrp) 6, and multidrug and toxin extrusion 1; (2) moderately lower mRNAs encoding Oatp1b2, organic cation transporter (Oct) 1, Ugt1a5, Ugt1a9, glutathione S-transferase (Gst) m4, Gstm6, and breast cancer resistance protein; but (3) higher mRNAs encoding Oatp1a4, Octn2, Ugt1a1, Sult1e1, Sult2a2, Gsta4, Gstm1-m3, multidrug resistance protein (Mdr) 1a, Mrp3, and Mrp4. Hepatic signaling of nuclear factor E2-related factor 2 and pregnane X receptor appear to be activated in HNF4a-HNull mice. In conclusion, HNF4a deficiency markedly alters hepatic mRNA expression of a large number of phase II enzymes and transporters, probably because of the loss of HNF4a, which is a transactivator and a determinant of gender-specific expression and/or adaptive activation of signaling pathways important in hepatic regulation of these phase II enzymes and transporters.

Interleukin-22 treatment ameliorates alcoholic liver injury in a murine model of chronic-binge ethanol feeding: role of signal transducer and activator of transcription 3

Interleukin-22 (IL-22), a recently identified member of the IL-10 family of cytokines that is produced by Th17 and natural killer cells, plays an important role in controlling bacterial infection, homeostasis, and tissue repair. Here, we tested the effect of IL-22 on alcohol-induced liver injury in a murine model of chronic-binge ethanol feeding. Feeding male C57BL/6 mice with a Lieber-DeCarli diet containing 5% ethanol for 10 days, followed by a single dose of ethanol (5 g/kg body weight) by gavage, induces significant fatty liver and liver injury with peak serum levels of approximately 250 IU/L alanine aminotransferase and 420 IU/L aspartate aminotransferase 9 hours after gavage. Moreover, chronic-binge ethanol administration increases expression of hepatic and serum inflammatory cytokines and hepatic oxidative stress. Using this model, we demonstrate that treatment with IL-22 recombinant protein activates hepatic signal transducer and activator of transcription 3 (STAT3) and ameliorates alcoholic fatty liver, liver injury, and hepatic oxidative stress. Administration with IL-22 adenovirus also prevents alcohol-induced steatosis and liver injury. Deletion of STAT3 in hepatocytes abolishes the hepatoprotection provided by IL-22 in alcoholic liver injury. In addition, IL-22 treatment down-regulates the hepatic expression of fatty acid transport protein, but up-regulates several antioxidant, antiapoptotic, and antimicrobial genes. Finally, expression of IL-22 receptor 1 is up-regulated whereas IL-22 is undetectable in the livers from mice with chronic-binge ethanol feeding or patients with alcoholic hepatitis.

CONCLUSION

Chronic-binge ethanol feeding may be a useful model to study the early stages of alcoholic liver injury. IL-22 treatment could be a potential therapeutic option to ameliorate alcoholic liver disease, due to its antioxidant, antiapoptotic, antisteatotic, proliferative, and antimicrobial effects with the added benefit of potentially few side effects.

The plausibility of maternal nutritional status being a contributing factor to the risk for fetal alcohol spectrum disorders: the potential influence of zinc status as an example

There is increasing evidence that human pregnancy outcome can be significantly compromised by suboptimal maternal nutritional status. Poor diet results in a maternal-fetal environment in which the teratogenicity of other insults such as alcohol might be amplified. As an example, there is evidence that zinc (Zn) can interact with maternal alcohol exposure to influence the risk for fetal alcohol spectrum disorders (FASD). Studies with experimental animals have shown that the teratogenicity of alcohol is increased under conditions of Zn deficiency, whereas its teratogenicity is lessened when animals are given Zn-supplemented diets or Zn injections before the alcohol exposure. Alcohol can precipitate an acute-phase response, resulting in a subsequent increase in maternal liver metallothionein, which can sequester Zn and lead to decreased Zn transfer to the fetus. Importantly, the teratogenicity of acute alcohol exposure is reduced in metallothionein knockout mice, which can have improved Zn transfer to the conceptus relative to wild-type mice. Consistent with the above, Zn status has been reported to be low in alcoholic women at delivery. Preliminary data from two basic science and clinical nutritional studies that are ongoing as part of the international Collaborative Initiative on Fetal Alcohol Spectrum Disorders support the potential role of Zn, among other nutritional factors, relative to risk for FASD. Importantly, the nutrient levels being examined in these studies are relevant to general clinical populations and represent suboptimal levels rather than severe deficiencies. These data suggest that moderate deficiencies in single nutrients can act as permissive factors for FASD, and that adequate nutritional status or intervention through supplementation may provide protection from some of the adverse effects of prenatal alcohol exposure.

Anti-lipid peroxidation effects of taurine ganbo in rats with alcoholic liver disease

AIM: To observe the protective and therapeutic effects and anti-lipid peroxidation effects of taurine ganbo in rats with alcoholic liver disease.

METHODS: A rat model of alcoholic liver disease was established by intragastric infusion of alcohol. Seventy-five male Wistar rats were randomly divided into five groups: normal control group, model group, low-dose taurine ganbo group, middle-dose taurine ganbo group, and high-dose taurine ganbo group. The model group was given dehydrated alcohol (500 mL/L) once a day for 8 weeks. The three taurine ganbo groups were treated as the model group and additionally given taurine ganbo once a day for 8 weeks. The normal control group was given equal volumes of distilled water for the same duration. After treatment, all the rats were killed. Serum alanine aminotransferase (ALT), aspartate amino transferase (AST), triglyceride (TG), total cholesterol (T-CHO), glucose (GLU), and circulating IgG against malondialdehyde-modified human serum albumin (MDA-HSA) were measured. Hepatic pathological changes were observed.

RESULTS: The levels of serum ALT, AST, TG, T-CHO, and GLU were significantly higher in the model group than in the normal control group, the middle- and high-dose taurine ganbo groups (all P < 0.0). The levels of serum ALT, AST and GLU in the low-dose taurine ganbo group were lower than those in the model group (63.67 U/L ± 6.89 U/L vs 81.53 U/L ± 22.85 U/L, 131.2 U/L ± 11.63 U/L vs 156.47 U/L ± 32.23 U/L, and 6.38 mmol/L ± 0.66 mmol/L vs 6.86 mmol/L ± 0.67 mmol/L, respectively; all P < 0.01 or 0.05). The level of circulating IgG against MDA-HSA in the model group was higher than those in the normal control group and the middle- and high-dose taurine ganbo groups (all P < 0.01). Compared to the normal control group, the model group had a much heavier lipid accumulation (P < 0.01). The hepatic pathological changes were milder in the middle- and high-dose groups than in the model group (both P < 0.05).

CONCLUSION: Taurine ganbo can attenuate alcohol-mediated increase in serum ALT, AST, TG and T-CHO levels and exert anti-lipid peroxidation effects in rats with alcoholic liver disease.