Pathology of nonalcoholic fatty liver disease

Inflammation in nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) describes a range of disorders characterized by excess accumulation of triglyceride within the liver. While simple steatosis may be clinically stable, nonalcoholic steatohepatitis (NASH) can be progressive. Inflammation is believed to be the driving force behind NASH and the progression to fibrosis and subsequent cirrhosis. This article will review and interpret the current literature in an attempt to expand our understanding of the environmental and genetic causes of inflammation and its effects in NAFLD.

Liver fibrosis in paediatric liver diseases

Numerous paediatric liver diseases from different origins may be complicated by development of liver fibrosis and progression to cirrhosis. Although fibrogenesis, which represents a major driving force for the development of liver fibrosis, has common tracts whatever the aetiology, liver fibrosis has different histopathological patterns in paediatric liver disease. In these diseases management choices may depend upon the stage of liver fibrosis. Thus, the accurate estimation of histological pattern of liver fibrosis is important for the prevention of the subsequent complications. Liver biopsy has long been considered as a gold standard diagnostic method for assessing liver fibrosis. However, due to its several disadvantages, in the last decades alternative and accurate non-invasive means to estimate fibrosis are developed. In this review, we characterised the most frequent histological patterns of liver fibrosis in paediatric liver diseases. Furthermore, we describe use of liver biopsy in diagnosis and staging of liver fibrosis, list the alternative non-invasive techniques that have an emerging role in the assessment of liver fibrosis, and propose a management algorithm.

Relationship between nonalcoholic fatty liver disease and metabolic syndrome

OBJECTIVE

The aim of this study was to investigate the prevalence of nonalcoholic fatty liver disease (NAFLD) and metabolic syndrome (MS) in subjects who underwent a routine health checkup. We intended to establish a clinical association between NAFLD and MS as well as to compare the diagnostic criteria of MS based on the definitions set forth by the International Diabetes Federation (IDF), the US National Cholesterol Education Program Adult Treatment Panel III (2001) (NCEP/ATP-III) and the Metabolic Syndrome Study Group of Chinese Diabetes Society (CDS).

METHODS

Weight, height, waist circumference, hip circumference, percentage of body fat, blood pressure and ultrasound of liver were performed on subjects undergoing routine health checkup. Serum triglyceride, total cholesterol, high density lipoprotein cholesterol and fasting plasma glucose level were measured.

RESULTS

A total of 2394 subjects were included in this analysis and 437 had NAFLD. The prevalence of MS in the whole sample according to IDF, NCEP/ATP-III and CDS definitions was 11.11%, 8.48% and 5.30%, respectively. The total degree of agreement between IDF, NCEP/ATP-III and CDS definition was 87.76%. The prevalence of MS in NAFLD subjects is much higher than that in non-NAFLD subjects. The prevalence of NAFLD in MS subjects is also much higher than that in non-MS subjects.

CONCLUSION

The prevalence of MS varied depending on the diagnostic criteria used. NAFLD was strongly associated with the MS, although it remains unknown whether NAFLD is a cause or effect of MS.

Drug-induced toxicity on mitochondria and lipid metabolism: mechanistic diversity and deleterious consequences for the liver

Numerous investigations have shown that mitochondrial dysfunction is a major mechanism of drug-induced liver injury, which involves the parent drug or a reactive metabolite generated through cytochromes P450. Depending of their nature and their severity, the mitochondrial alterations are able to induce mild to fulminant hepatic cytolysis and steatosis (lipid accumulation), which can have different clinical and pathological features. Microvesicular steatosis, a potentially severe liver lesion usually associated with liver failure and profound hypoglycemia, is due to a major inhibition of mitochondrial fatty acid oxidation (FAO). Macrovacuolar steatosis, a relatively benign liver lesion in the short term, can be induced not only by a moderate reduction of mitochondrial FAO but also by an increased hepatic de novo lipid synthesis and a decreased secretion of VLDL-associated triglycerides. Moreover, recent investigations suggest that some drugs could favor lipid deposition in the liver through primary alterations of white adipose tissue (WAT) homeostasis. If the treatment is not interrupted, steatosis can evolve toward steatohepatitis, which is characterized not only by lipid accumulation but also by necroinflammation and fibrosis. Although the mechanisms involved in this aggravation are not fully characterized, it appears that overproduction of reactive oxygen species by the damaged mitochondria could play a salient role. Numerous factors could favor drug-induced mitochondrial and metabolic toxicity, such as the structure of the parent molecule, genetic predispositions (in particular those involving mitochondrial enzymes), alcohol intoxication, hepatitis virus C infection, and obesity. In obese and diabetic patients, some drugs may induce acute liver injury more frequently while others may worsen the pre-existent steatosis (or steatohepatitis).

Growth hormone-dependent pathogenesis of human hepatic steatosis in a novel mouse model bearing a human hepatocyte-repopulated liver

Clinical studies have shown a close association between nonalcoholic fatty liver disease and adult-onset GH deficiency, but the relevant molecular mechanisms are still unclear. No mouse model has been suitable to study the etiological relationship of human nonalcoholic fatty liver disease and human adult-onset GH deficiency under conditions similar to the human liver in vivo. We generated human (h-)hepatocyte chimeric mice with livers that were predominantly repopulated with h-hepatocytes in a h-GH-deficient state. The chimeric mouse liver was mostly repopulated with h-hepatocytes about 50 d after transplantation and spontaneously became fatty in the h-hepatocyte regions after about 70 d. Infusion of the chimeric mouse with h-GH drastically decreased steatosis, showing the direct cause of h-GH deficiency in the generation of hepatic steatosis. Using microarray profiles aided by real-time quantitative RT-PCR, comparison between h-hepatocytes from h-GH-untreated and -treated mice identified 14 GH-up-regulated and four GH-down-regulated genes, including IGF-I, SOCS2, NNMT, IGFLS, P4AH1, SLC16A1, SRD5A1, FADS1, and AKR1B10, respectively. These GH-up- and -down-regulated genes were expressed in the chimeric mouse liver at lower and higher levels than in human livers, respectively. Treatment of the chimeric mice with h-GH ameliorated their altered expression. h-Hepatocytes were separated from chimeric mouse livers for testing in vitro effects of h-GH or h-IGF-I on gene expression, and results showed that GH directly regulated the expression of IGF-I, SOCS2, NNMT, IGFALS, P4AH1, FADS1, and AKR1B10. In conclusion, the chimeric mouse is a novel h-GH-deficient animal model for studying in vivo h-GH-dependent human liver dysfunctions.

A circadian rhythm orchestrated by histone deacetylase 3 controls hepatic lipid metabolism

Disruption of the circadian clock exacerbates metabolic diseases, including obesity and diabetes. We show that histone deacetylase 3 (HDAC3) recruitment to the genome displays a circadian rhythm in mouse liver. Histone acetylation is inversely related to HDAC3 binding, and this rhythm is lost when HDAC3 is absent. Although amounts of HDAC3 are constant, its genomic recruitment in liver corresponds to the expression pattern of the circadian nuclear receptor Rev-erbα. Rev-erbα colocalizes with HDAC3 near genes regulating lipid metabolism, and deletion of HDAC3 or Rev-erbα in mouse liver causes hepatic steatosis. Thus, genomic recruitment of HDAC3 by Rev-erbα directs a circadian rhythm of histone acetylation and gene expression required for normal hepatic lipid homeostasis.

Fate and complex pathogenic effects of dioxins and polychlorinated biphenyls in obese subjects before and after drastic weight loss

BACKGROUND

In humans, persistent organic pollutants (POPs) are stored primarily in adipose tissue. Their total body burden and their contribution to obesity-associated diseases remain unclear.

OBJECTIVES

We characterized POP total body burden and their redistribution in obese individuals before and after drastic weight loss and compared these values with a variety of molecular, biological, and clinical parameters.

METHODS

Seventy-one obese subjects were enrolled and underwent bariatric surgery. Blood and adipose tissue samples were obtained at different times from these individuals as well as from 18 lean women.

RESULTS

POP content (17 dioxins/furans and 18 polychlorinated biphenyl congeners) in different adipose tissue territories was similar, allowing us to assess total POP body burden from a single biopsy. Total POP body burden was 2 to 3 times higher in obese than in lean individuals. We also found increased expression of some POP target genes in obese adipose tissue. Drastic weight loss led to increased serum POPs and, within 6-12 months, to a significant 15% decrease in total polychlorinated biphenyl body burden. Importantly, serum POP levels were positively correlated with liver toxicity markers and lipid parameters, independently of age and body mass index.

CONCLUSIONS

POP content in adipose tissue and serum correlate with biological markers of obesity-related dysfunctions. Drastic weight loss leads to a redistribution of POPs and to a moderate decrease of their total body burden.

Endoplasmic reticulum stress is a mediator of posttransplant injury in severely steatotic liver allografts

Hepatic steatosis continues to present a major challenge in liver transplantation. These organs have been shown to have increased susceptibility to cold ischemia/reperfusion (CIR) injury in comparison with otherwise comparable lean livers; the mechanisms governing this increased susceptibility to CIR injury are not fully understood. Endoplasmic reticulum (ER) stress is an important link between hepatic steatosis, insulin resistance, and metabolic syndrome. In this study, we investigated ER stress signaling and blockade in the mediation of CIR injury in severely steatotic rodent allografts. Steatotic allografts from genetically leptin-resistant rodents had increased ER stress responses and increased markers of hepatocellular injury after liver transplantation into strain-matched lean recipients. ER stress response components were reduced by the chemical chaperone taurine-conjugated ursodeoxycholic acid (TUDCA), and this resulted in an improvement in the allograft injury. TUDCA treatment decreased nuclear factor kappa B activation and the proinflammatory cytokines interleukin-6 and interleukin-1β. However, the predominant response was decreased expression of the ER stress cell death mediator [CCAAT/enhancer-binding protein homologous protein (CHOP)]. Furthermore, activation of inflammation-associated caspase-11 was decreased, and this linked ER stress/CHOP to proinflammatory cytokine production after steatotic liver transplantation. These data confirm ER stress in steatotic allografts and implicate this as a mediating mechanism of inflammation and hepatocyte death in the steatotic liver allograft.

Carnosic acid prevents obesity and hepatic steatosis in ob/ob mice

AIM

  Carnosic acid (CA) inhibits adipogenesis in vitro. The present study evaluated the therapeutic effects of CA in ob/ob mice.

METHODS

  The experimental animals were given a standard chow diet with or without CA for 5 weeks. Bodyweight gain and food intake were measured during this period. Magnetic resonance imaging analysis, histological examination, serum chemistry analysis and intraperitoneal glucose tolerance test (IPGTT) were all performed.

RESULTS

  The mice fed CA experienced significant weight loss and reduced visceral adiposity, in addition to significantly reduced serum triglyceride (TG) and cholesterol levels. Importantly, CA had a dramatic effect on the liver by reducing the hepatic TG content, thus decreasing serum alanine aminotransferase levels. In addition, IPGTT revealed that CA significantly improved glucose tolerance.

CONCLUSION

  These data suggest that CA is a novel therapeutic agent for obesity-related non-alcoholic fatty liver disease.

Effects of interventions on intra- and interobserver agreement on interpretation of nonalcoholic fatty liver disease histology

Accurate and reproducible interpretation of nonalcoholic fatty liver disease (NAFLD) histology has significant clinical and research-related implications. We evaluated the impact of 2 interventions ([1] review of illustrative histologic images of NAFLD with the study pathologists; [2] use of a scoring sheet with written diagnostic criteria for different NAFLD phenotypes) on intra- and interobserver agreement on interpretation of NAFLD histology. Before and after the interventions, 2 pathologists twice read 65 liver biopsies done for evaluation of suspected NAFLD. The intra- and interobserver agreement was highest on assessment of steatosis and fibrosis. The interventions significantly improved the intraobserver agreement only on assessment of hepatocellular ballooning. The interobserver agreement was only fair on assessment of lobular inflammation, ballooning, and diagnostic classification and did not improve after the interventions. Methods to improve interobserver agreement on assessment of lobular inflammation and ballooning are needed and would likely increase pathologists' agreement on NAFLD diagnostic classification.

[Revascularization of the isolated popliteal segment]

An alternative to crural reconstruction of obliterations of the popliteal vascular axis and an angiographically ascertained isolated popliteal segment is a bypass to the isolated popliteal segment. A patency rate of 82.7% was found 1 year after bypass; after 3 years the patency totaled 76%, and after 4 years the cumulative patency rate amounted to 59%. A comparison of these results with those of crural reconstruction (a patency rate of no more than 60% after 3 years) proved the superiority of the bypass.