Hepatic gene expression profile associated with non-alcoholic steatohepatitis protection by S-nitroso-N-acetylcysteine in ob/ob mice

HbA1c may contribute to the development of non-alcoholic fatty liver disease even at normal-range levels

Previous clinical studies highlighted nonalcoholic fatty liver disease (NAFLD) as a hepatic facet of metabolic syndrome, which progresses toward Type 2 diabetes along with an elevation of HbA1c in the blood. Longitudinal observations were performed in a cohort of 2811 participants with no liver disease at inception. The rate of the conversion into NAFLD was 15.7% (440/2811), with a steady increase in prevalence observed in sub-cohorts with increasing HbA1c levels. Moreover, regression analysis indicated that HbA1c levels serve as the risk factors for NAFLD after multiple adjustments (odds ratio: 1.58, P-value < 0.004). When HbA1c-related molecular networks were investigated using natural language programming algorithms, multiple genetic/small molecular (SM) pathways were highlighted as connectors between the HbA1c levels and the development of NAFLD, including ones for nitric oxide, hypoxia and receptor for advanced glycation end products (RAGE). Our results suggest that increased levels of HbA1c may contribute to the progression of NAFLD either directly, by stimulating RAGE or indirectly, through the promotion of hypoxia and suppression of the release of NO. Further studies are needed to test the impact of HbA1c on the development of the chronic liver disease.

N-Acetyl Cysteine Targets Hepatic Lipid Accumulation to Curb Oxidative Stress and Inflammation in NAFLD: A Comprehensive Analysis of the Literature

Impaired adipose tissue function and insulin resistance remain instrumental in promoting hepatic lipid accumulation in conditions of metabolic syndrome. In fact, enhanced lipid accumulation together with oxidative stress and an abnormal inflammatory response underpin the development and severity of non-alcoholic fatty liver disease (NAFLD). There are currently no specific protective drugs against NAFLD, and effective interventions involving regular exercise and healthy diets have proved difficult to achieve and maintain. Alternatively, due to its antioxidant and anti-inflammatory properties, there has been growing interest in understanding the therapeutic effects of N-acetyl cysteine (NAC) against metabolic complications, including NAFLD. Here, reviewed evidence suggests that NAC blocks hepatic lipid accumulation in preclinical models of NAFLD. This is in part through the effective regulation of a fatty acid scavenger molecule (CD36) and transcriptional factors such as sterol regulatory element-binding protein (SREBP)-1c/-2 and peroxisome proliferator-activated receptor gamma (PPARγ). Importantly, NAC appears effective in improving liver function by reducing pro-inflammatory markers such as interleukin (IL)-6 IL-1β, tumour necrosis factor alpha (TNF-α) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). This was primarily through the attenuation of lipid peroxidation and enhancements in intracellular response antioxidants, particularly glutathione. Very few clinical studies support the beneficial effects of NAC against NAFLD-related complications, thus well-organized randomized clinical trials are still necessary to confirm its therapeutic potential.

Long term N-acetylcysteine administration rescues liver steatosis via endoplasmic reticulum stress with unfolded protein response in mice

Background

Fat accumulation in the liver contributes to the development of non-alcoholic fatty liver disease (NAFLD). N-acetylcysteine (NAC) is an antioxidant, acting both directly and indirectly via upregulation of cellular antioxidants. We examined the mechanisms of liver steatosis after 12 months high fat (HF) diet and tested the ability of NAC to rescue liver steatosis.

Methods

Seven-week-old C57BL/6 (B6) male mice were administered HF diet for 12 months (HF group). Two other groups received HF diet for 12 months accompanied by NAC for 12 months (HFD + NAC(1–12)) or 6 months (HFD + NAC(1–6)). The control group was fed regular diet for 12 months (CD group).

Results

Liver steatosis was more pronounced in the HF group than in the CD group after 12 month feeding. NAC intake for 6 or 12 months decreased liver steatosis in comparison with HF diet (p < 0.05). Furthermore, NAC treatment also reduced cellular apoptosis and caspase-3 expression. In the unfolded protein response (UPR) pathway, the expression of ECHS1, HSP60, and HSP70 was decreased in the HFD group (p < 0.05) and rescued by NAC therapy. With regards to the endoplasmic reticulum (ER) stress, Phospho-PERK (p-PERK) and ATF4 expression was decreased in the HF group, and only the HFD + NAC(1–12), but not HFD + NAC(1–6) group, showed significant improvement.

Conclusion

HF diet for 12 months induces significant liver steatosis via altered ER stress and UPR pathway activity, as well as liver apoptosis. NAC treatment rescues the liver steatosis and apoptosis induced by HF diet.

S-nitroso-N-acetylcysteine attenuates liver fibrosis in experimental nonalcoholic steatohepatitis

S-Nitroso-N-acetylcysteine (SNAC) is a water soluble primary S-nitrosothiol capable of transferring and releasing nitric oxide and inducing several biochemical activities, including modulation of hepatic stellate cell activation. In this study, we evaluated the antifibrotic activity of SNAC in an animal model of nonalcoholic steatohepatitis (NASH) induced in Sprague-Dawley rats fed with a choline-deficient, high trans fat diet and exposed to diethylnitrosamine for 8 weeks. The rats were divided into three groups: SNAC, which received oral SNAC solution daily; NASH, which received the vehicle; and control, which received standard diet and vehicle. Genes related to fibrosis (matrix metalloproteinases [MMP]-13, -9, and -2), transforming growth factor β-1 [TGFβ-1], collagen-1α, and tissue inhibitors of metalloproteinase [TIMP-1 and -2] and oxidative stress (heat-shock proteins [HSP]-60 and -90) were evaluated. SNAC led to a 34.4% reduction in the collagen occupied area associated with upregulation of MMP-13 and -9 and downregulation of HSP-60, TIMP-2, TGFβ-1, and collagen-1α. These results indicate that oral SNAC administration may represent a potential antifibrotic treatment for NASH.

S-Nitroso-N-acetylcysteine induces de-differentiation of activated hepatic stellate cells and promotes antifibrotic effects in vitro

Nitric oxide (NO) has been shown to act as a potent antifibrogenic agent by decreasing myofibroblast differentiation. S-Nitroso-N-acetylcysteine (SNAC), a NO donor, attenuates liver fibrosis in rats, but the cellular and molecular mechanisms on liver myofibroblast-like phenotype still remain unknown. Here, we investigate the antifibrotic effects of SNAC on hepatic stellate cells, the major fibrogenic cell type in the liver. A murine GRX cell line was incubated with SNAC (100μM) or vehicle (control group) for 72h. Cell viability was measured by MTT colorimetric assay and the conversion of myofibroblast into quiescent fat-storing cell phenotype was evaluated by Oil-Red-O staining. TGFβ-1, TIMP-1, and MMP-13 levels were measure in the supernatant by ELISA. Profibrogenic- and fibrolytic-related gene expression was quantified using real-time qPCR. SNAC induced phenotype conversion of myofibroblast-like phenotype into quiescent cells. SNAC decreased gene and protein expression of TGFβ-1 and MMP-2 compared to control groups. Besides, SNAC down-regulated profibrogenic molecules and up-regulated MMP-13 gene expression, which plays a key role in the degradation of interstitial collagen in liver fibrosis. In conclusion, these findings demonstrate that SNAC efficiently can modulate the activation and functionality of murine hepatic stellate cells and could be considered as an antifibrotic treatment to human liver fibrosis.

Transcriptional profile of genes involved in oxidative stress and antioxidant defense in a dietary murine model of steatohepatitis

Oxidative stress is a core abnormality responsible for disease progression in nonalcoholic steatohepatitis (NASH). However, the relevant pathways that contribute to oxidative damage in vivo remain poorly understood. Here we explore the gene-expression patterns related to oxidative stress, antioxidant defense, and reactive oxygen metabolism in an established dietary murine model of NASH. C57BL/6 mice were placed on either a methionine- and choline-deficient (MCD) or a control (CTL) diet for 6 weeks. Hepatic oxidative damage and the development of NASH were monitored by biochemical and histologic indices. Analysis of 84 oxidative stress-related genes was performed by real-time reverse transcription polymerase chain reaction (PCR) in the livers of the two groups of mice. Mice on the MCD diet showed increased ALT, histologic features of NASH, and oxidative liver damage with increases in 4-hydroxynonenal and 3-nitrotyrosine. Of the genes analyzed, the GPx family were most significantly upregulated, whereas SCD1 was most significantly downregulated. Other genes that were significantly upregulated included Fmo2 and peroxiredoxins, whereas genes downregulated included Catalase and Serpinb1b. Our data demonstrate that oxidative stress-related genes are differentially expressed in the livers of mice with diet-induced NASH. These findings have important implications for NASH pathogenesis and the development of novel therapeutic strategies for patients with this condition.

S-nitroso-N-acetylcysteine: a promising drug for early ischemia/reperfusion injury in rat liver

BACKGROUND/AIMS

Ischemia-reperfusion (I/R) injury is among the major causes of poor graft function early after liver transplantation that adversely influences patient survival. A variety of mediators have been implicated in the pathogenesis of I/R vascular injury, including nitric oxide (NO). Because of the beneficial effects of NO during preconditioning and reperfusion, strategies to prevent or ameliorate I/R injury through the stimulation of hepatic NO production are an area of significant clinical interest. We evaluated the role of S-nitroso-N-acetylcysteine (SNAC) as an NO donor in the prevention of liver I/R injury in an animal model.

METHODS

Adult male Wistar rats were randomly assigned to 3 experimental groups containing 5 animals each: the University of Wisconsin (UW) solution group; SNAC solution group; and SNAC-containing UW solution (SNAC+UW) group. Aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) were determined in samples of the cold storage solution at 2, 4, and 6 hours of preservation. After 6 hours of cold storage, We applied a 15-minute reperfusion period. Thereafter, the reperfusion was interrupted with blood samples obtained to measure AST, ALT, LDH, and thiobarbituric acid reactive substances (TBARS). Hepatic fragments were processed for histologic analysis, and to determine of TBARS, catalase, and glutathione levels.

RESULTS

During cold preservation, AST and LDH were significantly lower among the SNAC than the UW group or the SNAC+UW group (P = .004 and P = .03, respectively). ALT was comparable among the groups (P = .3). After reperfusion, serum levels of AST, ALT, and LDH, as well as of hepatic TBARS and catalase showed no differences among the groups. Glutathione concentration was lower in the SNAC and SNAC+UW group (P < .001) compared with the UW group. We did not observe histologic signs of preservation injury.

CONCLUSION

The SNAC solution showed a greater protective effect to preserve rat livers during cold storage, but it was comparable with UW.

S-nitroso-N-acetylcysteine ameliorates ischemia-reperfusion injury in the steatotic liver

BACKGROUND

Steatosis is currently the most common chronic liver disease and it can aggravate ischemia-reperfusion (IR) lesions. We hypothesized that S-nitroso-N-acetylcysteine (SNAC), an NO donor component, can ameliorate cell damage from IR injury. In this paper, we report the effect of SNAC on liver IR in rats with normal livers compared to those with steatotic livers.

METHODS

Thirty-four rats were divided into five groups: I (n=8), IR in normal liver; II (n=8), IR in normal liver with SNAC; III (n=9), IR in steatotic liver; IV (n=9), IR in steatotic liver with SNAC; and V (n=10), SHAN. Liver steatosis was achieved by administration of a protein-free diet. A SNAC solution was infused intraperitoneally for one hour, beginning 30 min. after partial (70%) liver ischemia. The volume of solution infused was 1 ml/100 g body weight. The animals were sacrificed four hours after reperfusion, and the liver and lung were removed for analysis. We assessed hepatic histology, mitochondrial respiration, oxidative stress (MDA), and pulmonary myeloperoxidase.

RESULTS

All groups showed significant alterations compared with the group that received SHAN. The results from the steatotic SNAC group revealed a significant improvement in liver mitochondrial respiration and oxidative stress compared to the steatotic group without SNAC. No difference in myeloperoxidase was observed. Histological analysis revealed no difference between the non-steatotic groups. However, the SNAC groups showed less intraparenchymal hemorrhage than groups without SNAC (p=0.02).

CONCLUSION

This study suggests that SNAC effectively protects against IR injury in the steatotic liver but not in the normal liver.

Intake of trans fatty acids causes nonalcoholic steatohepatitis and reduces adipose tissue fat content

We investigated the effects of dietary trans fatty acids, PUFA, and SFA on body and liver fat content, liver histology, and mRNA of enzymes involved in fatty acid metabolism. LDL receptor knockout weaning male mice were fed for 16 wk with diets containing 40% energy as either trans fatty acids (TRANS), PUFA, or SFA. Afterwards, subcutaneous and epididymal fat were weighed and histological markers of nonalcoholic fatty liver disease (NAFLD) were assessed according to the Histological Scoring System for NAFLD. PPARalpha, PPARgamma, microsomal triglyceride transfer protein (MTP), carnitine palmitoyl transferase 1 (CPT-1), and sterol regulatory element binding protein-1c (SREBP-1c) mRNA were measured by quantitative RT-PCR. Food intake was similar in the 3 groups, although mice fed the TRANS diet gained less weight than those receiving the PUFA diet. Compared with the PUFA- and SFA-fed mice, TRANS-fed mice had greater plasma total cholesterol (TC) and triglyceride (TG) concentrations, less epididymal and subcutaneous fat, larger livers with nonalcoholic steatohepatitis (NASH)-like lesions, and greater liver TC and TG concentrations. Macrosteatosis in TRANS-fed mice was associated with a higher homeostasis model assessment of insulin resistance (HOMA(IR)) index and upregulated mRNA related to hepatic fatty acid synthesis (SREBP-1c and PPARgamma) and to downregulated MTP mRNA. Diet consumption did not alter hepatic mRNA related to fatty acid oxidation (PPARalpha and CPT-1). In conclusion, compared with PUFA- and SFA-fed mice, TRANS-fed mice had less adiposity, impaired glucose tolerance characterized by greater HOMA(IR) index, and NASH-like lesions due to greater hepatic lipogenesis. These results demonstrate the role of trans fatty acid intake on the development of key features of metabolic syndrome.

Nonalcoholic steatohepatitis, animal models, and biomarkers: what is new?

Nonalcoholic fatty liver disease (NAFLD) is a clinicopathological term that encompasses a spectrum of abnormalities ranging from simple triglyceride accumulation in the hepatocytes (hepatic steatosis) to hepatic steatosis with inflammation (steatohepatitis, also known as nonalcoholic steatohepatitis or NASH). NASH can also progress to cirrhosis and hepatocellular carcinoma (HCC). Steatohepatitis has been estimated to affect around 5% of the total population and 20% of those who are overweight. The mechanisms leading to NASH and its progression to cirrhosis and HCC remain unclear, but it is a condition typically associated with obesity, insulin resistance, diabetes, and hypertriglyceridemia. This point corroborates the need for animal models and molecular markers that allow us to understand the mechanisms underlying this disease. Nowadays, there are numerous mice models to study abnormal liver function such as steatosis, NASH, and hepatocellular carcinoma. The study of the established animal models has provided many clues in the pathogenesis of steatosis and steatohepatitis, although these remain incompletely understood and no mice model completely fulfills the clinical features observed in humans. In addition, there is a lack of accurate sensitive diagnostic tests that do not involve invasive procedures. Current laboratory tests include some biochemical analysis, but their utility for diagnosing NASH is still poor. For that reason, a great effort is being made toward the identification and validation of novel biomarkers to assess NASH using high-throughput analysis based on genomics, proteomics, and metabolomics. The most recent discoveries and their validation will be discussed.

Mitochondrial dysfunction and oxidative stress in the pathogenesis of alcohol- and obesity-induced fatty liver diseases

Fatty liver disease associated with chronic alcohol consumption or obesity/type 2 diabetes has emerged as a serious public health problem. Steatosis, accumulation of triglyceride in hepatocytes, is now recognized as a critical "first-hit" in the pathogenesis of liver disease. It is proposed that steatosis "primes" the liver to progress to more severe liver pathologies when individuals are exposed to subsequent metabolic and/or environmental stressors or "second-hits." Genetic risk factors can also influence the susceptibility to and severity of fatty liver disease. Furthermore, oxidative stress, disrupted nitric oxide (NO) signaling, and mitochondrial dysfunction are proposed to be key molecular events that accelerate or worsen steatosis and initiate progression to steatohepatitis and fibrosis. This review article will discuss the following topics regarding the pathobiology and molecular mechanisms responsible for fatty liver disease: (1) the "two-hit" or "multi-hit" hypothesis, (2) the role of mitochondrial bioenergetic defects and oxidant stress, (3) the interplay between NO and mitochondria in fatty liver disease, (4) genetic risk factors and oxidative stress-responsive genes, and (5) the feasibility of antioxidants for treatment.

Modulation of hepatic microsomal triglyceride transfer protein (MTP) induced by S-nitroso-N-acetylcysteine in ob/ob mice

We evaluated the effects of a potent NO donor, S-nitroso-N-acetylcysteine (SNAC), on microsomal triglyceride transfer protein (MTP) expression in ob/ob mice. NAFLD was induced in male ob/ob mice using a methionine-choline deficient diet (MCD) concomitantly with oral SNAC fed solution (n=5) or vehicle (control; n=5) by gavage daily for 4 weeks. Livers were collected for histology and for assessing MTP by RT-qPCR, Western blot, immunohistochemistry and immunogold electron microscopy analyses. Histological analysis showed diffuse macro and microvesicular steatosis, moderate hepatocellular ballooning and moderate inflammatory infiltrate in ob/ob mice fed the MCD diet. With SNAC, mice showed a marked reduction in liver steatosis (p<0.01), in parenchymal inflammation (p=0.02) and in MTP protein immunoexpression in zone III (p=0.05). Moreover, SNAC caused reduction of MTP protein in Western blot analysis (p<0.05). In contrast, MTP mRNA content was significantly higher (p<0.05) in mice receiving SNAC. Immuno-electron microscopy showed MTP localized in the rough endoplasmic reticulum of hepatocytes in both treated and untreated groups. However with SNAC treatment, MTP was also observed surrounding fat globules. Histological improvement mediated by a nitric oxide donor is associated with significantly altered expression and distribution of MTP in this animal model of fatty liver disease. Further studies are in progress to examine possible mechanisms and to develop SNAC as a possible therapy for human fatty liver disease.