Inflammation and fibrogenesis in steatohepatitis

Nonalcoholic fatty liver disease consists of a range of disorders characterized by excess accumulation of triglyceride within the liver. Whereas simple steatosis is clinically benign, nonalcoholic steatohepatitis (NASH) often progresses to cirrhosis. Inflammation and fibrogenesis are closely inter-related and are major targets of NASH research. Experimental data have shown that inflammation in NASH is caused by insulin resistance, systemic lipotoxicity due to overnutrition, lipid metabolites, the production of proinflammatory cytokines and adipokines by visceral adipose tissue, gut-derived bacteria, and oxidative stress. In NASH-associated fibrosis, the principal cell type responsible for extracellular matrix production is recognized as the hepatic stellate cell. Although the fibrotic mechanisms underlying NASH are largely similar to those observed in other chronic liver diseases, the altered patterns of circulating adipokines, the generation of oxidative stress, and the hormonal profile associated with the metabolic syndrome might play unique roles in the fibrogenesis associated with the disease. Information on the basic pathogenesis of NASH with a focus on the generation of inflammation and fibrosis will be discussed.     

Heme oxygenase-1 levels and oxidative stress-related parameters in non-alcoholic fatty liver disease patients

BACKGROUND/AIMS: Non-alcoholic steatohepatitis (NASH) is a disorder that is histologically characterized by macrovesicular steatosis and lobular hepatitis with necrosis or ballooning degeneration and fibrosis. NASH can range from a benign condition to end-stage liver disease. The mechanisms promoting transition from steatosis to NASH appear to involve multiple cellular adaptations to the oxidative stress occurring when fatty acid metabolism is altered. We evaluated the relationship between lipid peroxidation and other oxidative stress biomarkers with changes in expression of heme oxygenase-1 (HO-1) in human hepatic steatosis ranging from simple steatosis to NASH. METHODS: HO-1 expression, lipid peroxidation, ferritin and GSH levels were assayed from liver biopsies obtained from 60 subjects: 35 with NASH, 15 with simple steatosis and 10 controls. RESULTS: The HO-1 expression was significantly increased in NASH patients and the increase reflected the severity of the disease. A significant correlation was observed between the increased levels of HO-1 and ferritin, and between the increased levels of HO-1 and lipid peroxidation. Moreover, NASH patients with lower levels of GSH exhibited higher expression of HO-1. CONCLUSIONS: The induction of HO-1 is an adaptive response against oxidative damage elicited by lipid peroxidation and it may be critical in the progression of the disease.     

Lipidomics in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD), the most common chronic liver disorder in Western countries, comprises steatosis to nonalcoholic steatohepatitis (NASH), with the latter having the potential to progress to cirrhosis. The transition from isolated steatosis to NASH is still poorly understood, but lipidomics approach revealed that the hepatic lipidome is extensively altered in the setting of steatosis and steatohepatitis and these alterations correlate with disease progression. Recent data suggest that both quantity and quality of the accumulated lipids are involved in pathogenesis of NAFLD. Changes in glycerophospholipid, sphingolipid, and fatty acid composition have been described in both liver biopsies and plasma of patients with NAFLD, implicating that specific lipid species are involved in oxidative stress, inflammation, and cell death. In this article, we summarize the findings of main human lipidomics studies in NAFLD and delineate the currently available information on the pathogenetic role of each lipid class in lipotoxicity and disease progression.     

Are oxidative stress mechanisms the common denominator in the progression from hepatic steatosis towards non‐alcoholic steatohepatitis (NASH)?

Non‐alcoholic fatty liver disease (NAFLD) is not a single disease entity, rather it describes a spectrum of liver conditions that range from fatty liver (steatosis) to more severe steatosis coupled with marked inflammation and fibrosis [non‐alcoholic steatohepatitis (NASH)] to severe liver disease such as cirrhosis and possibly hepatocellular carcinoma. Obesity, notably abdominal obesity, is a common risk factor for NAFLD. The pathogenesis from steatosis to NASH is poorly understood, and the ‘two hit’ model, as suggested nearly two decades ago, provides a feasible starting point for characterization of underlying mechanisms. This review will examine the oxidative stress factors (‘triggers’) which have been implicated as a ‘second hit’ in the development of primary NASH. It would be reasonable to assume that multiple, rather than single, pro‐oxidative intracellular and extracellular triggers act in conjunction promoting oxidative stress that drives the development of NASH. It is likely that the common denominator of these pro‐oxidative triggers is mitochondrial dysfunction. Understanding the contribution of each of these ‘triggers’ is an essential step in starting to understand and elucidate the mechanisms responsible for progression from steatosis to NASH, thus enabling the development of therapeutic targeting to prevent NASH development and progression.     

Galectin-3 and IL-33/ST2 axis roles and interplay in dietinduced steatohepatitis

Immune reactivity and chronic low-grade inflammation(metaflammation) play an important role in the pathogenesis of obesity-associated metabolic disorders, including type 2 diabetes and nonalcoholic fatty liver disease(NAFLD), a spectrum of diseases that include liver steatosis, nonalcoholic steatohepatitis(NASH), fibrosis, and cirrhosis. Increased adiposity and insulin resistance contribute to the progression from hepatic steatosis to NASH and fibrosis through the development of proinflammatory and profibrotic processes in the liver, including increased hepatic infiltration of innate and adaptive immune cells, altered balance of cytokines and chemokines, increased reactive oxygen species generation and hepatocellular death. Experimental models of dietary-induced NAFLD/NASH in mice on different genetic backgrounds or knockout mice with different immune reactivity are used for elucidating the pathogenesis of NASH and liver fibrosis. Galectin-3(Gal-3), a unique chimera-type β-galactoside-binding protein of the galectin family has a regulatory role in immunometabolism and fibrogenesis. Mice deficient in Gal-3 develop pronounced adiposity, hyperglycemia and hepatic steatosis, as well as attenuated liver inflammation and fibrosis when fed an obesogenic high-fat diet. Interleukin(IL)-33, a member of the IL-1 cytokine family, mediates its effects through the ST receptor, which is present on immune and nonimmune cells and participates in immunometabolic and fibrotic disorders. Recent evidence, including our own data, suggests a protective role for the IL-33/IL-33R(ST2) signaling pathway in obesity, adipose tissue inflammation and atherosclerosis, but a profibrotic role in NASH development. The link between Gal-3 and soluble ST2 in myocardial fibrosis and heart failure progression has been demonstrated and we have recently shown that Gal-3 and the IL-33/ST2 pathway interact and both have a profibrotic role in diet-induced NASH. This review discusses the current evidence on the roles of Gal-3 and the IL-33/ST2 pathway and their interplay in obesity-associated hepatic inflammation and fibrogenesis that may be of interest in the development of therapeutic interventions to prevent and/or reverse obesity-associated hepatic inflammation and fibrosis.     

The latest idea in NAFLD/NASH pathogenesis

Nonalcoholic fatty liver disease (NAFLD) is a metabolic disorder characterized by fatty accumulation in the liver without alcohol consumption. NAFLD ranges from simple steatosis to nonalcoholic steatohepatitis (NASH), which may progress to end-stage liver disease. The prevalence of NAFLD is rising because of an increasing prevalence of obesity and metabolic syndrome. The progression of these diseases is considered to be related to metabolic syndrome, which is characterized by obesity, glucose impairment, dyslipidemia, hypertension, and adipocytokine impairment. In addition, the pathogenesis of NAFLD/NASH is considered to be multifactorial and complex and is influenced by lifestyle habits, nutritional factors, and genetics. In particular, the PNPLA3 gene has been recently recognized as the most important functional gene polymorphism in the progression of NASH. Disruption in hepatic lipid metabolism is closely related to the development of fatty liver. Accumulation of excess triglycerides (TGs) induces hepatic steatosis. However, TG accumulation itself is not harmful to hepatocytes and may instead act as a protective mechanism against free fatty acid (FFA)-induced lipotoxicity. Excess FFAs also contribute to hepatotoxicity in NAFLD/NASH because oxidation of FFAs in hepatic microsomes generates excessive oxidative stress. Oxidative stress is considered one of the most important pathogenic factors in the development of NASH. Mitochondrial abnormalities, which are frequently observed in NASH-affected livers, are associated with impaired electron transport and result in further oxidative stress formation. The aims of this review are to assess the mechanisms of lipid metabolism and hepatic steatosis, the background of the disease, and the potential molecular mechanisms involved.     

Growth hormone reverses nonalcoholic steatohepatitis in a patient with adult growth hormone deficiency

BACKGROUND AND AIMS: Nonalcoholic steatohepatitis (NASH) is an emerging progressive hepatic disease and demonstrates steatosis, inflammation, and fibrosis. Insulin resistance is a common feature in the development of NASH. Molecular pathogenesis of NASH consists of 2 steps: triglyceride accumulation in hepatocytes with insulin resistance and an enhanced oxidative stress caused by reactive oxygen species. Interestingly, NASH demonstrates a striking similarity to the pathologic conditions observed in adult growth hormone deficiency (AGHD). AGHD is characterized by decreased lean body mass, increased visceral adiposity, abnormal lipid profile, and insulin resistance. Moreover, liver dysfunctions with hyperlipidemia and nonalcoholic fatty liver disease (NAFLD) are frequently observed in patients with AGHD, and it is accompanied by metabolic syndrome. METHODS: We studied a case diagnosed as NASH with hyperlipidemia in AGHD. The effect of GH-replacement therapy on the patient was analyzed. RESULTS: Six months of GH-replacement therapy in the patient drastically ameliorated NASH and the abnormal lipid profile concomitant with a marked reduction in oxidative stress. CONCLUSIONS: These results suggest that GH plays an essential role in the metabolic and redox regulation in the liver.     

Angiotensin II-induced non-alcoholic fatty liver disease is mediated by oxidative stress in transgenic TG(mRen2)27(Ren2) rats

BACKGROUND/AIMS: Non-alcoholic fatty liver disease (NAFLD) is a common health problem and includes a spectrum of hepatic steatosis, steatohepatitis and fibrosis. The renin-angiotensin system (RAS) plays a vital role in blood pressure regulation and appears to promote hepatic fibrogenesis. We hypothesized that increased RAS activity causes NAFLD due to increased hepatic oxidative stress. METHODS: We employed the transgenic TG(mRen2)27(Ren2) hypertensive rat, harboring the mouse renin gene with elevated tissue Angiotensin II (Ang II). RESULTS: Compared with normotensive Sprague-Dawley (SD) control rats, Ren2 developed significant hepatic steatosis by 9 weeks of age that progressed to marked steatohepatitis and fibrosis by 12 weeks. These changes were associated with increased levels of hepatic reactive oxygen species (ROS) and lipid peroxidation. Accordingly, 9-week-old Ren2 rats were treated for 3 weeks with valsartan, an angiotensin type 1 receptor blocker, or tempol, a superoxide dismutase/catalase mimetic. Hepatic indices for oxidative stress, steatosis, inflammation and fibrosis were markedly attenuated by both valsartan and tempol treatment. CONCLUSIONS: This study suggests that Ang II causes development and progression of NAFLD in the transgenic Ren2 rat model by increasing hepatic ROS. Our findings also support a potential role of RAS in prevention and treatment of NAFLD.     

Potential role of chitotriosidase gene in nonalcoholic fatty liver disease evolution

BACKGROUND: Nonalcoholic steatohepatitis (NASH) is a liver disease characterized by steatosis and periportal and lobular inflammation. The molecular mechanisms involved in the anomalous behavior of liver cells have only partially been disclosed. Human Chitotriosidase (Chit) is a member of the chitinase family that it is mainly synthesized by activated macrophages. We investigated chitotriosidase gene expression in Kupffer cells to determine the potential implication of this enzyme in the inflammation and in the progression from uncomplicated steatosis to steatohepatitis with progressive fibrosis. METHODS: Seventy-five liver biopsies from 40 subjects with NASH, 20 with simple steatosis, and 15 controls were used to detect CHIT expression, tumor necrosis factor-alpha (TNF-alpha), alpha-smooth muscle actin (alpha-SMA), and lipid peroxidation. RESULTS: CHIT was expressed exclusively by Kupffer cells. The levels of CHIT expression were significantly higher in NASH patients than in simple steatosis patients and in the control group. In addition, we found that CHIT over-expression influenced hepatic stellate cells activation, as demonstrated by the significant correlation between CHIT and alpha-SMA expression in NASH patients. A significant correlation was observed also between CHIT, TNF-alpha and lipid peroxidation in both NASH and simple steatosis. CONCLUSION: These results suggest that CHIT over-produced by Kupffer cells may contribute to the progression of hepatic fibrosis.     

Lipid-induced oxidative stress causes steatohepatitis in mice fed an atherogenic diet

Recently, nonalcoholic steatohepatitis (NASH) was found to be correlated with cardiovascular disease events independently of the metabolic syndrome. The aim of this study was to investigate whether an atherogenic (Ath) diet induces the pathology of steatohepatitis necessary for the diagnosis of human NASH and how cholesterol and triglyceride alter the hepatic gene expression profiles responsible for oxidative stress. We investigated the liver pathology and plasma and hepatic lipids of mice fed the Ath diet. The hepatic gene expression profile was examined with microarrays and real-time polymerase chain reactions. The Ath diet induced dyslipidemia, lipid peroxidation, and stellate cell activation in the liver and finally caused precirrhotic steatohepatitis after 24 weeks. Cellular ballooning, a necessary histological feature defining human NASH, was observed in contrast to existing animal models. The addition of a high-fat component to the Ath diet caused hepatic insulin resistance and further accelerated the pathology of steatohepatitis. A global gene expression analysis revealed that the Ath diet up-regulated the hepatic expression levels of genes for fatty acid synthesis, oxidative stress, inflammation, and fibrogenesis, which were further accelerated by the addition of a high-fat component. Conversely, the high-fat component down-regulated the hepatic gene expression of antioxidant enzymes and might have increased oxidative stress. CONCLUSION: The Ath diet induces oxidative stress and steatohepatitis with cellular ballooning. The high-fat component induces insulin resistance, down-regulates genes for antioxidant enzymes, and further aggravates the steatohepatitis. This model suggests the critical role of lipids in causing oxidative stress and insulin resistance leading to steatohepatitis.     

From the metabolic syndrome to NAFLD or vice versa?

The metabolic syndrome encompasses metabolic and cardiovascular risk factors which predict diabetes and cardiovascular disease (CVD) better than any of its individual components. Nonalcoholic fatty liver disease (NAFLD) comprises a disease spectrum which includes variable degrees of simple steatosis (nonalcoholic fatty liver, NAFL), nonalcoholic steatohepatitis (NASH) and cirrhosis. NAFLD is the hepatic manifestation of the metabolic syndrome, with insulin resistance as the main pathogenetic mechanism. Recent data indicate that hyperinsulinemia is probably the consequence rather than cause of NAFLD and NAFLD can be considered an independent predictor of cardiovascular disease. Serum free fatty acids derived from lipolysis of visceral adipose tissue are the main source of hepatic triglycerides in NAFLD, although hepatic de novo lipogenesis and dietary fat supply contribute to the pathogenesis of NAFLD. Approximately 10–25% NAFLD patients develop NASH, the evolutive form of hepatic steatosis. Presumably in a genetically predisposed environment, this increased lipid overload overwhelms the oxidative capacity and reactive oxygen species are generated, leading to lipid peroxidation, cytokine induction, chemoattraction of inflammatory cells, hepatic stellate cell activation and finally fibrogenesis with extracellular matrix deposition. No currently available therapies for NAFLD and NASH exist. Recently nuclear receptors have emerged as key regulators of lipid and carbohydrate metabolism for which specific pharmacological ligands are available, making them attractive therapeutic targets for NAFLD and NASH.     

Non-alcoholic steatohepatitis: review of a growing medical problem

Non-alcoholic steatohepatitis (NASH) is a metabolic liver disorder that is seen in 2-6% of the general population. It manifests itself by elevated liver enzymes, frequently without symptoms. The histological findings include steatosis, inflammation, fibrosis, and cirrhosis. Three case reports are presented to illustrate features of NASH. A two-hit model has been proposed in the pathogenesis of NASH. The first hit is hepatic steatosis. A hypercaloric diet with high levels of carbohydrates and saturated fatty acids results in elevated plasma free fatty acids (FFA) and expands the adipose tissue. Insulin resistance develops and augments steatosis. Oxidation of FFA yields toxic free radicals, resulting in lipid peroxidation. They cause the second hits: increased oxidative stress on hepatocytes and induction of pro-inflammatory cytokines. When the antioxidant capacities of the liver are insufficient, mitochondrial dysfunction and tumor necrosis factor alpha (TNF-alpha) cause inflammation and fibrosis. Treatment consists of life style modifications, particularly weight loss and exercise. Many drugs have been tried in the treatment of NASH. The insulin-sensitizing drugs metformin, rosiglitazone, and pioglitazone, and the antioxidant vitamin E show promising results. Further investigation of therapeutic options is needed to direct the choice of therapy in the future.     

Pathophysiological mechanisms involved in non-alcoholic steatohepatitis and novel potential therapeutic targets

Non-alcoholic fatty liver disease (NAFLD) is a major health care problem and represents the hepatic expression of the metabolic syndrome. NAFLD is classified as non-alcoholic fatty liver (NAFL) or simple steatosis, and non-alcoholic steatohepatitis (NASH). NASH is characterized by the presence of steatosis and inflammation with or without fibrosis. The physiopathology of NAFL and NASH and their progression to cirrhosis involve several parallel and interrelated mechanisms, such as, insulin resistance (IR), lipotoxicity, inflammation, oxidative stress, and recently the gut-liver axis interaction has been described. Incretin-based therapies could play a role in the treatment of NAFLD. Glucagon-like peptide-1 (GLP-1) is an intestinal mucosa-derived hormone which is secreted into the bloodstream in response to nutrient ingestion; it favors glucose-stimulated insulin secretion, inhibition of postprandial glucagon secretion and delayed gastric emptying. It also promotes weight loss and is involved in lipid metabolism. Once secreted, GLP-1 is quickly degraded by dipeptidyl peptidase-4 (DPP-4). Therefore, DPP-4 inhibitors are able to extend the activity of GLP-1. Currently, GLP-1 agonists and DPP-4 inhibitors represent attractive options for the treatment of NAFLD and NASH. The modulation of lipid and glucose metabolism through nuclear receptors, such as the farsenoid X receptor, also constitutes an attractive therapeutic target. Obeticholic acid is a potent activator of the farnesoid X nuclear receptor and reduces liver fat content and fibrosis in animal models. Ursodeoxycholic acid (UDCA) is a hydrophilic bile acid with immunomodulatory, anti-inflammatory, antiapoptotic, antioxidant and anti-fibrotic properties. UDCA can improve IR and modulate lipid metabolism through its interaction with nuclear receptors such as, TGR5, farnesoid X receptor-α, or the small heterodimeric partner. Finally, pharmacologic modulation of the gut microbiota could have a role in the therapy of NAFLD and NASH. Probiotics prevent bacterial translocation and epithelial invasion, inhibit mucosal adherence by bacteria, and stimulate host immunity. In animal models, probiotics prevent obesity, decrease transaminase levels, and improve IR and liver histology in NASH.     

Nonalcoholic steatohepatitis and the metabolic syndrome

Nonalcoholic fatty liver disease (NAFLD) is a major form of chronic liver disease in adults and children. It is one of the consequences of the current obesity epidemic, and can progress to nonalcoholic steatohepatitis (NASH), characterized by steatosis, inflammation, and progressive fibrosis, ultimately leading to cirrhosis and end-stage liver disease. The factors implicated in this progression are poorly understood. NASH is closely associated with obesity and the metabolic syndrome. Recent studies emphasize the role of insulin resistance, oxidative stress, lipid peroxidation, and cytokine release in the development of NASH. This review summarizes the current knowledge on the etiology and pathomechanism of NASH and the role of the metabolic syndrome in NASH development.     

The potential role of genes in nonalcoholic fatty liver disease

Although most people with obesity and type 2 diabetes will have steatosis, only a minority will ever develop nonalcoholic steatohepatitis (NASH), fibrosis, and cirrhosis. Family studies suggest that genetic factors are important in disease progression, although dissecting genetic factors playing a role in NASH and fibrosis from those influencing the development established risk factors is difficult.Several approaches can be used to look for genetic factors playing a role in nonalcoholic fatty liver disease (NAFLD). In the future, genome-wide single nucleotide polymorphism (SNP) scanning of cases and controls may become feasible. To date, however,studies have relied on candidate gene, case control, allele association methodology. Recent, and as yet preliminary, studies have reported associations between steatosis severity, NASH, and fibrosis with genes whose products are involved in lipid metabolism,oxidative stress, and endotoxin-cytokine interactions. If confirmed,these associations will enhance understanding of disease pathogenesis,and accordingly, the ability to design effective therapies.     

Bezafibrate prevents hepatic stellate cell activation and fibrogenesis in a murine steatohepatitis model,and suppresses fibrogenic response induced by transforming growth factor‐β1 in a cultured stellate cell line

Aim: The aim of this study was to investigate the preventive actions of bezafibrate against non‐alcoholic steatohepatitis (NASH), the activation of hepatic stellate cells (HSC), and fibrogenesis by using a model of NASH and an in vitro model. Methods: Male KK‐A^y/TaJcl (KK‐A^y) mice were fed a methionine and choline‐deficient (MCD) diet or a MCD diet containing bezafibrate or pioglitazone for 7 weeks, after which biochemical parameters, pathological changes, and hepatic mRNA levels were assessed. An in vitro HSC model was designed by using a previously described RI‐T cell line stimulated by transforming growth factor‐β1 (TGF‐β1). Results: MCD diet‐fed KK‐A^y mice developed hepatic steatosis, oxidative stress, inflammation, and hepatic fibrosis. Bezafibrate markedly decreased the hepatic content of triglyceride accumulation of fatty droplets within hepatocytes, and increased the expression of hepatic fatty acid β‐oxidative genes in MCD diet‐fed KK‐A^y mice. Bezafibrate markedly inhibited the increases in the plasma alanine aminotransferase level and hepatic content of thiobarbituric acid‐reactive substances in this model. Moreover, it dramatically reduced hepatic inflammatory changes and fibrosis concomitantly with marked reductions in the mRNA levels for inflammatory cytokine, chemokine, and profibrogenic genes. Importantly, both bezafibrate and pioglitazone markedly reduced the mRNA levels of profibrogenic and fibrogenic genes in TGF‐β1‐stimulated cells. Conclusion: Bezafibrate improved hepatic steatosis and potently prevented inflammation, oxidative stress, HSC activation, and fibrogenesis in the liver. Moreover, this study was the first to demonstrate that bezafibrate directly inhibits hepatic fibrogenic response induced by TGF‐β1 in vitro. Hence bezafibrate may be a new therapeutic strategy against NASH and hepatic fibrosis.     

Lipid peroxidation, stellate cell activation and hepatic fibrogenesis in a rat model of chronic steatohepatitis

BACKGROUND/AIMS: We explored the involvement of cell types, cytokines and lipid peroxidation in a rat dietary model of fibrosing steatohepatitis. METHODS: Male rats were fed a high fat diet deficient in methionine and choline (MCD) for up to 17 weeks. Whole liver, hepatocytes and non-parenchymal cells were analysed for reduced glutathione (GSH) levels, products of lipid peroxidation (thiobarbituric acid reactive substances, TBARS), liver injury, and fibrosis. RESULTS: MCD diet-fed rats developed hepatic steatosis at week 2 and focal necroinflammatory change by week 5, while pericellular fibrosis evolved and progressed between weeks 12 and 17. Collagen alpha(1)(1) gene expression was upregulated by week 5 and increased fivefold by week 17. Stellate cells were the unique source of collagen gene expression. TIMP-1 and -2 were increased at week 12. Livers of MCD diet-fed rats exhibited lowered levels of GSH and elevated TBARS. Hepatocytes were the source of lipid peroxidation, and mRNA levels for TGFbeta1 were increased only in this cell type. CONCLUSIONS: The MCD model of 'fibrosing steatohepatitis' replicates the histologic features of human steatohepatitis, and the sequence of steatosis, inflammatory cell injury and fibrogenesis. The temporal sequence is consistent with a concept for involvement of oxidative injury in inflammatory recruitment and pathogenesis of hepatic fibrogenesis.     

The ins and outs of mitochondrial dysfunction in NASH

Rich diet and lack of exercise are causing a surge in obesity, insulin resistance and steatosis, which can evolve into steatohepatitis. Steatosis and nonalcoholic steatohepatitis (NASH) can also be induced by drugs such as amiodarone, tamoxifen and some antiretroviral drugs. There is growing evidence that mitochondrial dysfunction, and more specifically respiratory chain deficiency, plays a role in the pathophysiology of NASH whatever its initial cause. In contrast, the B-oxidation of fatty acids can be either increased (as in insulin resistance-associated NASH) or decreased (as in drug-induced NASH). However, in both circumstances, the generation of reactive oxygen species (ROS) by the damaged respiratory chain is augmented, as components of this chain are over-reduced by electrons, which then abnormally react with oxygen to form increased amounts of ROS. Concomitantly, ROS oxidize fat deposits to release lipid peroxidation products that have detrimental effects on hepatocytes and other hepatic cells. In hepatocytes, ROS and lipid peroxidation products further impair the respiratory chain, either directly or indirectly through oxidative damage to the mitochondrial genome. This, in turn, leads to the generation of more ROS and a vicious cycle ensues. Mitochondrial dysfunction can also lead to apoptosis or necrosis depending on the energy status of the cell. ROS and lipid peroxidation products also activate stellate cells, thus resulting in fibrosis. Finally, ROS and lipid peroxidation increase the generation of several cytokines (TNF-alpha, TGF-B, Fas ligand) that play sundry roles in the pathogenesis of NASH. Recent investigations have shown that some genetic polymorphisms can significantly increase the risk of steatohepatitis and that several drugs can prevent or even reverse NASH. For the next decade, reducing the incidence of NASH will be a major challenge for hepatologists.     

Inhibiting triglyceride synthesis improves hepatic steatosis but exacerbates liver damage and fibrosis in obese mice with nonalcoholic steatohepatitis

In the early stages of nonalcoholic fatty liver disease (NAFLD), triglycerides accumulate in hepatocytes. Diacylglycerol acyltransferase 2 (DGAT2) catalyzes the final step in hepatocyte triglyceride biosynthesis. DGAT2 antisense oligonucleotide (ASO) treatment improved hepatic steatosis dramatically in a previous study of obese mice. According to the 2-hit hypothesis for progression of NAFLD, hepatic steatosis is a risk factor for nonalcoholic steatohepatitis (NASH) and fibrosis. To evaluate this hypothesis, we inhibited DGAT2 in a mouse model of NASH induced by a diet deficient in methionine and choline (MCD). Six-week-old genetically obese and diabetic male db/db mice were fed either the control or the MCD diet for 4 or 8 weeks. The MCD diet group was treated with either 25 mg/kg DGAT2 ASO or saline intraperitoneally twice weekly. Hepatic steatosis, injury, fibrosis, markers of lipid peroxidation/oxidant stress, and systemic insulin sensitivity were evaluated. Hepatic steatosis, necroinflammation, and fibrosis were increased in saline-treated MCD diet-fed mice compared to controls. Treating MCD diet-fed mice with DGAT2 ASO for 4 and 8 weeks decreased hepatic steatosis, but increased hepatic free fatty acids, cytochrome P4502E1, markers of lipid peroxidation/oxidant stress, lobular necroinflammation, and fibrosis. Progression of liver damage occurred despite reduced hepatic expression of tumor necrosis factor alpha, increased serum adiponectin, and striking improvement in systemic insulin sensitivity. CONCLUSION: Results from this mouse model would suggest accumulation of triglycerides may be a protective mechanism to prevent progressive liver damage in NAFLD.