Nonalcoholic fatty liver disease (NAFLD) is a significant complication of obesity and is recognized as the hepatic manifestation of the metabolic syndrome. The process occurs in adults and children and is characterized by the presence of increased amounts of fat in the liver (steatosis). With inflammation, cell death and scarring (fibrosis), the process may result in end-stage liver disease, or be a precursor for hepatocellular carcinoma. Excess hepatic fat is now recognized as an independent marker for increased cardiovascular risk. Even though imaging studies and laboratory-based tests are accurate at detecting significant steatosis and/or advanced fibrosis, respectively, the diagnosis and characterization of NAFLD ultimately depend on histopathologic evaluation, as the parenchymal alterations that comprise the spectrum of injury in NAFLD include patterns as well as specific lesions. Histologic findings in children may differ from those in adults. In this Review, the histologic features that are diagnostic and discriminatory between steatosis and steatohepatitis, the significance of the distinction between steatosis and steatohepatitis, the types and locations of fibrosis, and the histologic variances between adult and pediatric NAFLD are discussed. Clinical advantages as well as potential drawbacks of liver biopsy are presented. Current pathophysiologic concepts relevant to histologic findings are discussed.

Pathology of nonalcoholic fatty liver disease.

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.

Animal models of nonalcoholic fatty liver disease/ nonalcoholic steatohepatitis

Results: The criteria macrovesicular steatosis, microvesicular steatosis, hepatocellular hypertrophy, inflammation and fibrosis were generally applicable to rodent NAFLD. The inter-observer reproducibility (evaluated using the Intraclass Correlation Coefficient) between the ten observers was high for the analysis of macrovesicular steatosis and microvesicular steatosis (ICC50.784 and 0.776, all p,0.001, respectively) and moderate for the analysis of hypertrophy and inflammation (ICC50.685 and 0.650, all p,0.001, respectively). The intra-observer reproducibility between the different observations of one observer was high for the analysis of macrovesicular steatosis, microvesicular steatosis and hypertrophy (ICC50.871, 0.871 and 0.896, all p,0.001, respectively) and very high for the analysis of inflammation (ICC50.931, p,0.001). Conclusions: We established a simple NAFLD scoring system with high reproducibility that is applicable for different rodent models and for all stages of NAFLD etiology. Background and aims: The recently developed histological scoring system for non-alcoholic fatty liver disease (NAFLD) by the NASH Clinical Research Network (NASH-CRN) has been widely used in clinical settings, but is increasingly employed in preclinical research as well. However, it has not been systematically analyzed whether the human scoring system can directly be converted to preclinical rodent models. To analyze this, we systematically compared human NAFLD liver pathology, using human liver biopsies, with liver pathology of several NAFLD mouse models. Based upon the features pertaining to mouse NAFLD, we aimed at establishing a modified generic scoring system that is applicable to broad spectrum of rodent models. Copyright: Methods: The histopathology of NAFLD was analyzed in several different mouse models of NAFLD to define generic criteria for histological assessment (preclinical scoring system). For validation of this scoring system, 36 slides of mouse livers, covering the whole spectrum of NAFLD, were blindly analyzed by ten observers. Additionally, the livers were blindly scored by one observer during two separate assessments longer than 3 months apart.

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Establishment of a General NAFLD Scoring System for Rodent Models and Comparison to Human Liver Pathology

miR-21 is one of the most highly expressed members of the small non-coding microRNA family in many mammalian cell types. Its expression is further enhanced in many diseased states including solid tumors, cardiac injury and inflamed tissue. Whilst the induction of miR-21 by inflammatory stimuli cells has been well documented in both hematopoietic cells of the immune system (particularly monocytes/macrophages but also dendritic and T-cells) and non-hematopoietic tumorigenic cells, the exact functional outcome of this elevated miR-21 is less obvious. Recent studies have confirmed a key role for miR-21 in the resolution of inflammation and in negatively regulating the proinflammatory response induced by many of the same stimuli that trigger miR-21 induction itself. In particular, miR-21 has emerged as a key mediator of the anti-inflammatory response in macrophages. This suggests that miR-21 inhibition in leukocytes will promote inflammation and may enhance current therapies for defective immune responses such as cancer, mycobacterial vaccines or Th2-associated allergic inflammation. At the same time, miR-21 has been shown to promote inflammatory mediators in non-hematopoietic cells resulting in neoplastic transformation. This review will focus on functional studies of miR-21 during inflammation which are complicated by the numerous molecular targets and processes that have emerged as miR-21 sensitive. It may be that the exact functional outcome of miR-21 is determined by multiple features including the cell type affected, the inducing signal, the transcriptomic profile of the cell, which ultimately affect the availability and ability to engage different target mRNAs and bring about its unique responses. Reviewing this data may illustrate that RNA-based oligonucleotide therapies for different diseases based upon miR-21 may have to target the unique and operative miRNA:mRNA interactions functionally active disease.

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Turning 21: Induction of miR-21 as a Key Switch in the Inflammatory Response.

Histological analysis of liver biopsies remains a standard against which other methods of assessment for the presence and amount of hepatic injury due to nonalcoholic fatty liver disease (NAFLD) are measured. Histological evaluation remains the sole method of distinguishing steatosis from advanced forms of NAFLD, i.e. nonalcoholic steatohepatitis (NASH) and fibrosis. Included in the lesions of NAFLD are steatosis, lobular and portal inflammation, hepatocyte injury in the forms of ballooning and apoptosis, and fibrosis. However, patterns of these lesions are as distinguishing as the lesions themselves. Liver injury in adults and children due to NAFLD may have different histological patterns. In this review, the rationale for liver biopsy, as well as the histopathological lesions, the microscopically observable patterns of injury, and the differential diagnoses of NAFLD and NASH are discussed.

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Histopathology of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD), a hepatic manifestation of metabolic syndrome, is the most common chronic liver disease, and the prevalence is rapidly increasing worldwide. Nonalcoholic steatohepatitis (NASH), the severe form of NAFLD, can progress to liver cirrhosis and hepatocellular carcinoma (HCC). Although noninvasive clinical scores and image-based diagnosis for NAFLD have improved, histopathological evaluation of biopsy specimens remains the gold standard for diagnosing NAFLD/NASH. Steatosis, lobular inflammation, and hepatocellular ballooning are all necessary components for the diagnosis of NASH; fibrosis is also typically observed. Other histopathological abnormalities commonly observed in NASH include hepatocellular glycogenated nuclei, lipogranulomas, and acidophil bodies. The characteristics of pediatric NAFLD/NASH differ from adult NAFLD/NASH. Specifically, steatosis and portal inflammation are more severe in pediatric NAFLD, while intralobular inflammation and perisinusoidal fibrosis are milder. Although interobserver agreement for evaluating the extent of steatosis and fibrosis is high, agreement is low for intralobular and portal inflammation. A recently reported histological variant of HCC, steatohepatitic HCC (SH-HCC), shows features that resemble non-neoplastic steatohepatitis, and is thought to be strongly associated with underlying NASH. In this report, we review the histopathological features of NAFLD/NASH.

Histopathology of nonalcoholic fatty liver disease/nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD)/nonalcoholic steatohepatitis (NASH) is considered to be a hepatic manifestation of metabolic syndrome, and its incidence is rapidly increasing worldwide. It is currently the most common chronic liver disease. NASH can progress to liver cirrhosis and hepatocellular carcinoma, and may result in liver-related death. Currently, the principal treatment for NAFLD/NASH is lifestyle modification by diet and exercise. However, pharmacological therapy is indispensable because obese patients with NAFLD often have difficulty maintaining improved lifestyles. The pathogenesis of NAFLD/NASH has not been completely elucidated. However, insulin resistance, inflammatory cytokines, and oxidative stress are thought to be important in the development and/or progression of the disease. Currently, insulin sensitizers (thiazolidinediones) and antioxidants (vitamin E) seem to be the most promising therapeutic agents for NAFLD/NASH, and lipid-lowering drugs, pentoxifylline, angiotensin receptor blockers, and n-3 polyunsaturated fatty acids also have promise. However, there is a lack of consensus regarding the most effective and appropriate pharmacotherapy for NAFLD/NASH. Animal experiments suggest that herbal medicines and natural products may be promising therapeutic agents for NAFLD/NASH, but their efficacy and safety are yet to be investigated in human studies. In this paper, we review the existing and potential pharmacological therapies for NAFLD/NASH.

Current pharmacological therapies for nonalcoholic fatty liver disease/nonalcoholic steatohepatitis.

Plexiform angiomyxoid myofibroblastic tumor of the stomach is a unique mesenchymal tumor that we first described in 2007. The tumor is very rare, and to date, only 18 cases confirmed by immunohistochemistry have been reported in the literature. The patients' ages ranged from 7 to 75 years (mean, 43 years), and the male-to-female ratio was approximately 1:1. Represen- tative clinical symptoms are ulceration, associated up- per gastrointestinal bleeding (hematemesis), and ane- mia. The tumors are located at the antrum in all cases, and grossly, the tumor is whitish to brownish or red- dish, and forms a lobulated submucosal or transmural mass. Microscopically, the tumor is characterized by a plexiform growth pattern, the proliferation of cytologi- cally bland spindle cells, and a myxoid stroma that is rich in small vessels and positive for Alcian blue stain. Immunohistochemically, the tumor cells are positive for α-smooth muscle actin and negative for KIT and CD34. Differential diagnoses include gastrointestinal stromal tumor and other mesenchymal tumors of the gastroin- testinal tract. Some authors proposed that this tumor should be designated as "plexiform fibromyxoma", but this designation might cause confusion. The tumor is probably benign and thus far, neither recurrence nor metastasis has been reported.

Yoshihisa Takahashi

Papers

Animal models of nonalcoholic fatty liver disease/ nonalcoholic steatohepatitis

Histopathology of nonalcoholic fatty liver disease/nonalcoholic steatohepatitis

Current pharmacological therapies for nonalcoholic fatty liver disease/nonalcoholic steatohepatitis.

Plexiform angiomyxoid myofibroblastic tumor of the stomach.

Histone acetyltransferase Hbo1: Catalytic activity, cellular abundance, and links to primary cancers