Evaluation of liver fatty acid oxidation in the leptin-deficient obese mouse

Novel insights into metabolic-associated steatotic liver disease preclinical models

Metabolic-associated steatotic liver disease (MASLD) encompasses a wide spectrum of metabolic conditions associated with an excess of fat accumulation in the liver, ranging from simple hepatic steatosis to cirrhosis and hepatocellular carcinoma. Finding appropriate tools to study its development and progression is essential to address essential unmet therapeutic and staging needs. This review discusses advantages and shortcomings of different dietary, chemical and genetic factors that can be used to mimic this disease and its progression in mice from a hepatic and metabolic point of view. Also, this review will highlight some additional factors and considerations that could have a strong impact on the outcomes of our model to end up providing recommendations and a checklist to facilitate the selection of the appropriate MASLD preclinical model based on clinical aims.

Liver fibrosis: Pathophysiology and clinical implications

Liver fibrosis is a clinically significant finding that has major impacts on patient morbidity and mortality. The mechanism of fibrosis involves many different cellular pathways, but the major cell type involved appears to be hepatic stellate cells. Many liver diseases, including Hepatitis B, C, and fatty liver disease cause ongoing hepatocellular damage leading to liver fibrosis. No matter the cause of liver disease, liver-related mortality increases exponentially with increasing fibrosis. The progression to cirrhosis brings more dramatic mortality and higher incidence of hepatocellular carcinoma. Fibrosis can also affect outcomes following liver transplantation in adult and pediatric patients and require retransplantation. Drugs exist to treat Hepatitis B and C that reverse fibrosis in patients with those viral diseases, but there are currently no therapies to directly treat liver fibrosis. Several mouse models of chronic liver diseases have been successfully reversed using novel drug targets with current therapies focusing mostly on prevention of myofibroblast activation. Further research in these areas could lead to development of drugs to treat fibrosis, which will have invaluable impact on patient survival. This article is categorized under: Metabolic Diseases > Molecular and Cellular Physiology.

Fatty Acids and Effects on In Vitro and In Vivo Models of Liver Steatosis

BACKGROUND

Fatty liver, or steatosis, is a condition of excess accumulation of lipids, mainly under form of triglycerides (TG), in the liver, and it is the hallmark of non-alcoholic fatty liver disease (NAFLD). NAFLD is the most common liver disorder world-wide and it has frequently been associated with obesity, hyperlipidemia and insulin resistance. Free fatty acids (FA) are the major mediators of hepatic steatosis; patients with NAFLD have elevated levels of circulating FA that correlate with disease severity.

METHODS

Steatosis is a reversible condition that can be resolved with changed behaviors, or that can progress towards more severe liver damages such as steatohepatitis (NASH), fibrosis and cirrhosis. In NAFLD, FA of exogenous or endogenous origin accumulate in the hepatocytes and trigger liver damages. Excess TG are stored in cytosolic lipid droplets (LDs) that are dynamic organelles acting as hubs for lipid metabolism.

RESULTS

In the first part of this review, we briefly reassumed the main classes of FA and their chemical classification as a function of the presence and number of double bonds, their metabolic pathways and effects on human health. Then, we summarized the main genetic and diet-induced animal models of NAFLD, as well as the cellular models of NAFLD.

CONCLUSIONS

In recent years, both the diet-induced animal models of NAFLD as well as the cellular models of NAFLD have found ever more application to investigate the mechanisms involved in NAFLD, and we referred to their advantages and disadvantages.

Aged garlic extract ameliorates fatty liver and insulin resistance and improves the gut microbiota profile in a mouse model of insulin resistance

Aged garlic extract (AGE) produced by the aging process has various beneficial pharmacological effects. In this study, the effects of AGE on fatty liver, insulin resistance and intestinal microbiota were compared between ddY-H mice, an insulin resistance mouse, and ddY-L mice, normal mice. Mice were fed an AGE-supplemented diet (4% w/w) for 7 weeks. The administration of AGE had no effect on the body weight and dietary intake of both types of mice. In the ddY-H mice, the serum levels of glucose and insulin were increased and glucose tolerance was impaired; however, the administration of AGE ameliorated these abnormal conditions. AGE did not have these effects in ddY-L mice. Triglyceride (TG) accumulation in the liver and fat absorption from the digestive tract were increased in the ddY-H mice; however, the administration of AGE reduced this increase. On the other hand, AGE exerted no such effects in the ddY-L mice. In addition, the gut microbiota has been shown to be closely associated with obesity, diabetes, dyslipidemia and non-alcoholic fatty liver disease in human and animal models. The bacterial composition of the gut microbiota in the feces of the ddY-H mice did not differ from that of the ddY-L mice at 5 weeks of age; however, it was altered in the mice at 9 and 12 weeks of age even when the mice were fed a standard diet. In the ddY-H mice, the relative presence of Lactobacillales was increased, while that of Bifidobacterium, Clostridium cluster XVIII and Prevotella was decreased. The alteration of the bacterial composition in the ddY-H mice was reversed by the administration of AGE; however, this effect of AGE was not observed in the ddY-L mice. On the whole, the findings of this study indicate that AGE improves abnormal fat accumulation and insulin resistance, and also alters the intestinal flora in ddY-H mice, suggesting the possibility that these effects of AGE may be related.

Dynamic Contrast-Enhanced MRI of OATP Dysfunction in Diabetes

Diabetes is associated with hepatic metabolic dysfunction predisposing patients to drug-induced liver injury. Mouse models of type 2 diabetes (T2D) have dramatically reduced expression of organic anion transporting polypeptide (OATP)1A1, a transporter expressed in hepatocytes and in the kidneys. The effects of diabetes on OATP1B2 expression are less studied and less consistent. OATP1A1 and OATP1B2 both transport endogenous substrates such as bile acids and hormone conjugates as well as numerous drugs including gadoxetate disodium (Gd-EOB-DTPA). As master pharmacokinetic regulators, the altered expression of OATPs in diabetes could have a profound and clinically significant influence on drug therapies. Here, we report a method to noninvasively measure OATP activity in T2D mice by quantifying the transport of hepatobiliary-specific gadolinium-based contrast agents (GBCAs) within the liver and kidneys using dynamic contrast-enhanced MRI (DCE-MRI). By comparing GBCA uptake in control and OATP knockout mice, we confirmed liver clearance of the hepatobiliary-specific GBCAs, Gd-EOB-DTPA, and gadobenate dimeglumine, primarily though OATP transporters. Then, we measured a reduction in the hepatic uptake of these hepatobiliary GBCAs in T2D ob/ob mice, which mirrored significant reductions in the mRNA and protein expression of OATP1A1 and OATP1B2. As these GBCAs are U.S. Food and Drug Administration-approved agents and DCE-MRI is a standard clinical protocol, studies to determine OATP1B1/1B3 deficiencies in human individuals with diabetes can be easily envisioned.

Advancing the understanding of NAFLD to hepatocellular carcinoma development: From experimental models to humans

Nonalcoholic fatty liver disease (NAFLD) has recently been recognized as an important etiology contributing to the increased incidence of hepatocellular carcinoma (HCC). NAFLD, characterized by fat accumulation in the liver, is affecting at least one-third of the global population. The more aggressive form, nonalcoholic steatohepatitis (NASH), is characterized by hepatocyte necrosis and inflammation. The development of effective approaches for disease prevention and/or treatment heavily relies on deep understanding of the mechanisms underlying NAFLD to HCC development. However, this has been largely hampered by the lack of robust experimental models that recapitulate the full disease spectrum. This review will comprehensively describe the current in vitro and mouse models for studying NAFLD/NASH/HCC, and further emphasize their applications and possible future improvement for better understanding the molecular mechanisms involved in the cascade of NAFLD to HCC progression.

Animal models of NAFLD from the pathologist's point of view

Fatty liver disease is a multifactorial world-wide health problem resulting from a complex interplay between liver, adipose tissue and intestine and initiated by alcohol abuse, overeating, various types of intoxication, adverse drug reactions and genetic or acquired metabolic defects. Depending on etiology fatty liver disease is commonly categorized as alcoholic or non-alcoholic. Both types may progress from simple steatosis to the necro-inflammatory lesion of alcoholic (ASH) and non-alcoholic steatohepatitis (NASH), respectively, and finally to cirrhosis and hepatocellular carcinoma. Animal models are helpful to clarify aspects of pathogenesis and progression. Generally, they are classified as nutritional (dietary), toxin-induced and genetic, respectively, or represent a combination of these factors. Numerous reviews are dealing with NASH animal models designed to imitate as closely as possible the metabolic situation associated with human disease. This review focuses on currently used mouse models of NASH with particular emphasis on liver morphology. Despite metabolic similarities most models (except those with chemically or genetically induced porphyria or keratin 18-deficiency) fail to develop the morphologic key features of NASH, namely hepatocyte ballooning and formation of histologically and immunohistochemically well-defined Mallory-Denk-Bodies (MDBs). Although MDBs are not universally detectable in ballooned hepatocytes in NASH their experimental reproduction and analysis may, however, significantly contribute to our understanding of important pathogenic aspects of NASH despite the obvious differences in etiology.

Animal Models of Nonalcoholic Steatohepatitis: Eat, Delete, and Inflame

With the obesity epidemic, nonalcoholic fatty liver disease (NAFLD) has become a public health problem with increasing prevalence. The mechanism of disease progression remains obscure and effective therapy is lacking. Therefore, there is a need to understand the pathogenic mechanisms responsible for disease development and progression in order to develop innovative therapies. To accomplish this goal, experimental animal models that recapitulate the human disease are necessary, especially, since causative mechanistic studies of NAFLD are more difficult or unethical to perform in humans. A large number of studies regarding the pathophysiology and treatment of nonalcoholic steatohepatitis (NASH) have been undertaken in mice to model human NAFLD and NASH. This review discusses the known dietary, genetic, and inflammation-based animal models of NASH described in recent years, with a focus on the major advances made in this field.

How Useful Are Monogenic Rodent Models for the Study of Human Non-Alcoholic Fatty Liver Disease?

Improving understanding of the genetic basis of human non-alcoholic fatty liver disease (NAFLD) has the potential to facilitate risk stratification of affected patients, permit personalized treatment, and inform development of new therapeutic strategies. Animal models have been widely used to interrogate the pathophysiology of, and genetic predisposition to, NAFLD. Nevertheless, considerable interspecies differences in intermediary metabolism potentially limit the extent to which results can be extrapolated to humans. For example, human genome-wide association studies have identified polymorphisms in PNPLA3 and TM6SF2 as the two most prevalent determinants of susceptibility to NAFLD and its inflammatory component (NASH), but animal models of these mutations have had only variable success in recapitulating this link. In this review, we critically appraise selected murine monogenic models of NAFLD, NASH, and hepatocellular carcinoma (HCC) with a focus on how closely they mirror human disease.

Nonalcoholic Steatohepatitis: A Search for Factual Animal Models

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic steatosis, which occurs in the absence of alcohol abuse. NAFLD can evolve into progressive liver injury and fibrosis in the form of nonalcoholic steatohepatitis (NASH). Several animal models have been developed to attempt to represent the morphological, biochemical, and clinical features of human NASH. The actual review presents a critical analysis of the most commonly used experimental models of NAFLD/NASH development. These models can be classified into genetic, nutritional, and a combination of genetic and nutritional factors. The main genetic models are ob/ob and db/db mutant mice and Zucker rats. The principal nutritional models employ methionine- and choline-deficient, high-fat, high-cholesterol and high-cholate, cafeteria, and high-fructose diets. Currently, associations between high-fructose and various compositions of high-fat diets have been widely studied. Previous studies have encountered significant difficulties in developing animal models capable of reproducing human NASH. Some models produce consistent morphological findings, but the induction method differs significantly compared with the pathophysiology of human NASH. Other models precisely represent the clinical and etiological contexts of this disease but fail to provide accurate histopathological representations mainly in the progression from steatosis to liver fibrosis.

Fast food diet with CCl4 micro-dose induced hepatic-fibrosis--a novel animal model

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is defined as a spectrum of conditions ranging from hepatocellular steatosis to steatohepatitis and fibrosis, progressing to cirrhosis, which occur in the absence of excessive alcohol use. Several animal models capture aspects of NAFLD but are limited either in their representation of the disease stages or use for development of therapeutics due to the extended periods of time required to develop full histological features.

METHODS

Here, we report the development of a novel rat model for NAFLD that addresses some of these limitations. We used a fast food diet (FFD) and a CCl4 micro dose (0.5 ml/kg B.wt) for 8 weeks in Wistar rats. Serological analyses, gene expression profiling and liver histology studies were conducted to investigate the development of steatosis, steatohepatitis and fibrosis in the FFD-CCl4 model when compared to the individual effects of a FFD or a micro dose of CCl4 in rats.

RESULTS

The serum biochemical profile of the FFD-CCl4 model showed an increase in liver injury and fibrosis. This was also accompanied by a significant increase in liver triglycerides (TG), inflammation and oxidative stress. Importantly, we observed extensive fibrosis confirmed by: i) increased gene expression of fibrosis markers and, ii) moderate to severe collagen deposition seen as perisinusoidal and bridging fibrosis using H&E, Trichome and Sirius Red staining.

CONCLUSIONS

In summary, we find that the FFD-CCl4 rat model developed NAFLD histological features including, steatosis, inflammation and fibrosis in 8 weeks showing promise as a model that can be used to develop NAFLD therapeutics and liver anti-fibrotics.

Rapid improvement of hepatic steatosis after initiation of leptin substitution in a leptin-deficient girl

BACKGROUND

Leptin deficiency is associated with severe obesity and metabolic disturbances. Increased liver fat content has been reported in only one case beforehand, even though hepatic steatosis is a typical comorbidity of common obesity. It is also frequent in patients with lipodystrophy where it resolves under leptin therapy.

SUBJECT AND METHODS

In 2010, we reported a leptin-deficient patient with a novel homozygous mutation in the leptin gene and severe hepatic steatosis. We have now studied serum changes and changes in liver fat content during the substitution with recombinant methionyl human leptin.

RESULTS

After 23 weeks of leptin substitution, elevated transaminases, total cholesterol and low-density lipoprotein levels normalized. After 62 weeks, homeostasis model assessment of insulin resistance improved from 10.7 to 6.0 and body fat mass dropped from 50.2 to 37.8%. Liver fat content was drastically reduced from 49.7 to 9.4%. The first changes in liver fat content were detectable after 3 days of therapy.

CONCLUSION

Our patient showed a remarkable reduction of liver fat content during the treatment with recombinant methionyl human leptin. These changes occurred rapidly after initiation of the substitution, which implies that leptin has a direct effect on hepatic lipid metabolism in humans as it is seen in rodents.

Experimental liver fibrosis research: update on animal models, legal issues and translational aspects

Liver fibrosis is defined as excessive extracellular matrix deposition and is based on complex interactions between matrix-producing hepatic stellate cells and an abundance of liver-resident and infiltrating cells. Investigation of these processes requires in vitro and in vivo experimental work in animals. However, the use of animals in translational research will be increasingly challenged, at least in countries of the European Union, because of the adoption of new animal welfare rules in 2013. These rules will create an urgent need for optimized standard operating procedures regarding animal experimentation and improved international communication in the liver fibrosis community. This review gives an update on current animal models, techniques and underlying pathomechanisms with the aim of fostering a critical discussion of the limitations and potential of up-to-date animal experimentation. We discuss potential complications in experimental liver fibrosis and provide examples of how the findings of studies in which these models are used can be translated to human disease and therapy. In this review, we want to motivate the international community to design more standardized animal models which might help to address the legally requested replacement, refinement and reduction of animals in fibrosis research.

In vitro and in vivo models of non-alcoholic fatty liver disease (NAFLD)

By now, non-alcoholic fatty liver disease (NAFLD) is considered to be among the most common liver diseases world-wide. NAFLD encompasses a broad spectrum of pathological conditions ranging from simple steatosis to steatohepatitis, fibrosis and finally even cirrhosis; however, only a minority of patients progress to end-stages of the disease, and the course of the disease progression to the later stages seems to be slow, developing progressively over several years. Key risk factors including overweight, insulin resistance, a sedentary life-style and an altered dietary pattern, as well as genetic factors and disturbances of the intestinal barrier function have been identified in recent years. Despite intense research efforts that lead to the identification of these risk factors, knowledge about disease initiation and molecular mechanisms involved in progression is still limited. This review summarizes diet-induced and genetic animal models, as well as cell culture models commonly used in recent years to add to the understanding of the mechanisms involved in NAFLD, also referring to their advantages and disadvantages.

Nitric oxide regulates mitochondrial fatty acid metabolism through reversible protein S-nitrosylation

Cysteine S-nitrosylation is a posttranslational modification by which nitric oxide regulates protein function and signaling. Studies of individual proteins have elucidated specific functional roles for S-nitrosylation, but knowledge of the extent of endogenous S-nitrosylation, the sites that are nitrosylated, and the regulatory consequences of S-nitrosylation remains limited. We used mass spectrometry-based methodologies to identify 1011 S-nitrosocysteine residues in 647 proteins in various mouse tissues. We uncovered selective S-nitrosylation of enzymes participating in glycolysis, gluconeogenesis, tricarboxylic acid cycle, and oxidative phosphorylation, indicating that this posttranslational modification may regulate metabolism and mitochondrial bioenergetics. S-nitrosylation of the liver enzyme VLCAD [very long chain acyl-coenzyme A (CoA) dehydrogenase] at Cys(238), which was absent in mice lacking endothelial nitric oxide synthase, improved its catalytic efficiency. These data implicate protein S-nitrosylation in the regulation of β-oxidation of fatty acids in mitochondria.

High fat diets and pathology in the guinea pig. Atherosclerosis or liver damage?

Animal models have been widely used to investigate the relationship between diet and atherosclerosis and also to study disease etiology and possible interventions. Guinea pigs have been suggested to be a more "realistic" model for atherosclerosis due to their many similarities to humans. However, few published studies actually reported observations of characteristic atherosclerotic lesions and even fewer of advanced lesions. Studies, by our group, of guinea pigs fed on a high-fat diet revealed similar observations, with indications primarily of fatty streaks but little evidence of atherosclerotic plaques. This review discusses the feasibility of the guinea pig as a model for dietary-induced atherosclerosis. As it stands, current evidence raises doubt as to whether guinea pigs could serve as a realistic model for atherosclerosis. However, our own data and the literature suggest that they could be useful models for studying lipoprotein metabolism, non-alcoholic fatty liver disease, and dietary interventions which may help regulate these conditions.

Animal models of nonalcoholic fatty liver disease/nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is a condition in which excess fat accumulates in the liver of a patient without a history of alcohol abuse. Nonalcoholic steatohepatitis (NASH), a severe form of NAFLD, can progress to liver cirrhosis and hepatocellular carcinoma. NAFLD is regarded as a hepatic manifestation of metabolic syndrome and incidence has been increasing worldwide in line with the increased prevalence of obesity, type 2 diabetes, and hyperlipemia. Animal models of NAFLD/NASH give crucial information, not only in elucidating pathogenesis of NAFLD/NASH but also in examining therapeutic effects of various agents. An ideal model of NAFLD/NASH should correctly reflect both hepatic histopathology and pathophysiology of human NAFLD/NASH. Animal models of NAFLD/NASH are divided into genetic, dietary, and combination models. In this paper, we review commonly used animal models of NAFLD/NASH referring to their advantages and disadvantages.

Genetically modified mouse models for the study of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is associated with obesity, insulin resistance, and type 2 diabetes. NAFLD represents a large spectrum of diseases ranging from (1) fatty liver (hepatic steatosis); (2) steatosis with inflammation and necrosis; to (3) cirrhosis. The animal models to study NAFLD/nonalcoholic steatohepatitis (NASH) are extremely useful, as there are still many events to be elucidated in the pathology of NASH. The study of the established animal models has provided many clues in the pathogenesis of steatosis and steatohepatitis, but these remain incompletely understood. The different mouse models can be classified in two large groups. The first one includes genetically modified (transgenic or knockout) mice that spontaneously develop liver disease, and the second one includes mice that acquire the disease after dietary or pharmacological manipulation. Although the molecular mechanism leading to the development of hepatic steatosis in the pathogenesis of NAFLD is complex, genetically modified animal models may be a key for the treatment of NAFLD. Ideal animal models for NASH should closely resemble the pathological characteristics observed in humans. To date, no single animal model has encompassed the full spectrum of human disease progression, but they can imitate particular characteristics of human disease. Therefore, it is important that the researchers choose the appropriate animal model. This review discusses various genetically modified animal models developed and used in research on NAFLD.

Animal models of cutaneous and hepatic fibrosis

Fibrosis occurs as a part of normal wound healing. However, excessive or dysregulated fibrosis can lead to severe organ dysfunction and is a feature of a variety of diseases. Due to its insidious onset, fibrosis tends to go undetected in its early stages. This is in part why these diseases remain so poorly understood. Animal models have provided a means to examine these early stages and to isolate and understand the effect of perturbations in signaling pathways, chemokines, and cytokines. Here, we summarize recent progress in the understanding of the molecular pathogenesis of fibrosis, both its initiation and its maintenance phases, from animal models of fibrosis in the skin and liver. Due to these organs' properties, modeling fibrosis in them poses unique challenges. Elegant solutions have therefore been developed for modeling fibrosis in each, and now, great potential for animal models to contribute to our understanding appears scientifically imminent.

Alcoholic liver disease and exacerbation by malnutrition and infections: what animal models are currently available?

Alcoholic liver disease remains a frequent and serious problem for increasing numbers of patients. Research has expanded our molecular understanding of the cellular basis of disease progression; however, translation into therapy is still hampered by a lack of suitable animal models for alcoholic liver disease, as well as from consequences of related liver damage due to malnutrition, hepatitis C virus infection, or abuse of other substances. Many patients with liver disease do not simply consume too much alcohol; they also suffer from comorbidities such as obesity or viral hepatitis, and/or may be addicted to other drugs besides alcohol. This review will summarize the currently available animal models to study liver disease due to either single causes or combinations of liver toxic substances/infections and alcohol.

Mice lacking angiotensin-converting enzyme have increased energy expenditure, with reduced fat mass and improved glucose clearance

In addition to its role in the storage of fat, adipose tissue acts as an endocrine organ, and it contains a functional renin-angiotensin system (RAS). Angiotensin-converting enzyme (ACE) plays a key role in the RAS by converting angiotensin I to the bioactive peptide angiotensin II (Ang II). In the present study, the effect of targeting the RAS in body energy homeostasis and glucose tolerance was determined in homozygous mice in which the gene for ACE had been deleted (ACE(-/-)) and compared with wild-type littermates. Compared with wild-type littermates, ACE(-/-) mice had lower body weight and a lower proportion of body fat, especially in the abdomen. ACE(-/-) mice had greater fed-state total energy expenditure (TEE) and resting energy expenditure (REE) than wild-type littermates. There were pronounced increases in gene expression of enzymes related to lipolysis and fatty acid oxidation (lipoprotein lipase, carnitine palmitoyl transferase, long-chain acetyl CoA dehydrogenase) in the liver of ACE(-/-) mice and also lower plasma leptin. In contrast, no differences were detected in daily food intake, activity, fed-state plasma lipids, or proportion of fat excreted in fecal matter. In conclusion, the reduction in ACE activity is associated with a decreased accumulation of body fat, especially in abdominal fat depots. The decreased body fat in ACE(-/-) mice is independent of food intake and appears to be due to a high energy expenditure related to increased metabolism of fatty acids in the liver, with the additional effect of increased glucose tolerance.

Non-alcoholic fatty liver disease: further expression of the metabolic syndrome

Non-alcoholic fatty liver disease has been associated with metabolic disorders, including central obesity, dyslipidemia, hypertension and hyperglycemia. Metabolic syndrome, obesity, and insulin resistance are major risk factors in the pathogenesis of non-alcoholic fatty liver disease. Non-alcoholic fatty liver disease refers to a wide spectrum of liver damage, ranging from simple steatosis to non-alcoholic steatohepatitis, advanced fibrosis and cirrhosis.

Mouse models in non-alcoholic fatty liver disease and steatohepatitis research

Non-alcoholic fatty liver disease (NAFLD) represents a histological spectrum of liver disease associated with obesity, diabetes and insulin resistance that extends from isolated steatosis to steatohepatitis and cirrhosis. As well as being a potential cause of progressive liver disease in its own right, steatosis has been shown to be an important cofactor in the pathogenesis of many other liver diseases. Animal models of NAFLD may be divided into two broad categories: those caused by genetic mutation and those with an acquired phenotype produced by dietary or pharmacological manipulation. The literature contains numerous different mouse models that exhibit histological evidence of hepatic steatosis or, more variably, steatohepatitis; however, few replicate the entire human phenotype. The genetic leptin-deficient (ob/ob) or leptin-resistant (db/db) mouse and the dietary methionine/choline-deficient model are used in the majority of published research. More recently, targeted gene disruption and the use of supra-nutritional diets to induce NAFLD have gained greater prominence as researchers have attempted to bridge the phenotype gap between the available models and the human disease. Using the physiological processes that underlie the pathogenesis and progression of NAFLD as a framework, we review the literature describing currently available mouse models of NAFLD, highlight the strengths and weaknesses of established models and describe the key findings that have furthered the understanding of disease pathogenesis.

Hepatic gene expression profiles in a long-term high-fat diet-induced obesity mouse model

To understand the molecular mechanisms underlying alterations in the pathophysiologic status of dietary obesity, we examined hepatic genes differentially expressed in a long-term high-fat intake-induced obesity mouse model. C57BL/6J male mice were fed with two kinds of diets for 12 weeks; a low-fat diet (LFD), a high-fat diet (HFD; n=8), and the expression levels of approximately 10,000 transcripts in liver tissues from the two groups were assessed using cDNA microarray analysis. Twelve-week feeding with the HFD resulted in significant increase in body weight, visceral fat accumulation and circulating cholesterol concentration, compared with the LFD group. The cDNA microarray analysis revealed marked differences in the expressions of 97 hepatic genes. These genes were categorized into seven groups:metabolism; defense, stress, and inflammation responses; signal transduction, apoptosis, and cell cycle; transcription regulation; protein synthesis and modification; transport; and cellular adhesion, cytoskeleton and trafficking. The expression of genes involved in fatty acid catabolism and ketone body synthesis, such as acyl-CoA oxidase1 (Acox1) and HMG-CoA lyase (Hmgcl), was significantly increased, and expression of genes involved in lipogenesis and cholesterol synthesis, such as acetyl-CoA synthetase2 (Acs2), fatty acid synthase (Fasn), and squalene epoxidase (Sqle), was drastically decreased in the HFD group. Interestingly, the genes implicated in defense and stress responses, such as glutathione S-transferases (GSTs) and heat shock proteins (Hsps), were also highly represented in the HFD group. Besides, a number of previously unappreciated regulatory molecules were changed by the HFD. These results revealed a transcriptional adaptation to long-term HFD and provided interesting information about the molecules involved in the development and maintenance of the obesity phenotype in vivo.