Nonalcoholic fatty liver disease – current status and future directions

Nonalcoholic fatty liver disease (NAFLD) has emerged as the most common chronic liver disease worldwide with a reported prevalence ranging 6–33%, depending on the studied populations. It encompasses a spectrum of liver manifestations ranging from simple steatosis (also known as nonalcoholic fatty liver, NAFL) to nonalcoholic steatohepatitis (NASH), fibrosis and cirrhosis, which may ultimately progress to hepatocellular carcinoma. NAFLD is strongly associated with the components of metabolic syndrome, mainly obesity and type 2 diabetes mellitus. NAFLD patients are at increased risk of liver‐related as well as cardiovascular mortality. Current paradigm suggests a benign course for NAFL whereas NASH is considered to be the progressive phenotype. Although previously under‐recognized accumulating evidence suggests that NAFL may also progress, suggesting a higher number of patients at risk than previously appreciated. Liver biopsy remains the gold standard for definitive diagnosis, but the majority of patients can be diagnosed accurately by noninvasive methods. Approved therapies for NAFLD are still lacking and lifestyle modifications aiming at weight loss remain the mainstay of NAFLD treatment. Intensive research could identify insulin resistance, lipotoxicity and dysbiosis of the gut microbiota as major pathophysiological mechanisms, leading to the development of promising targeted therapies which are currently investigated in clinical trials. In this review we summarized the current knowledge of NAFLD epidemiology, natural history, diagnosis, pathogenesis and treatment and considered future directions.     

Liver steatosis,but not fibrosis,is associated with insulin resistance in nonalcoholic fatty liver disease

Background To address the hypothesis that liver steatosis causes systemic insulin resistance, we sought to determine the liver histological feature that most strongly contributes to insulin resistance in patients with nonalcoholic fatty liver disease (NAFLD). Methods Liver biopsy specimens were obtained from 131 patients with clinically suspected NAFLD. The stage, grade of nonalcoholic steatohepatitis (NASH), and level of steatosis were scored and analyzed in relation to the homeostasis model assessment of insulin resistance (HOMA-IR) and the metabolic clearance rate (MCR), measured using the glucose clamp method. Results In the univariate analysis, the degree of hepatic steatosis (r = 0.458, P < 0.001), stage (r = 0.360, P < 0.001), and grade (r = 0.349, P < 0.01) of NASH were significantly correlated with the HOMA-IR. Multiple regression analysis adjusting for age, sex, body mass index, and each histological score showed that steatosis was significantly and independently associated with HOMA-IR (coefficient = 1.42, P < 0.001), but not with the stage (coefficient = 0.33, P = 0.307) or grade (coefficient = 0.67, P = 0.134) of NASH. Similar independent relationships were observed between steatosis and MCR, but the relationship was weaker (coefficient = −0.98, P = 0.076). Conclusions Steatosis of the liver, but not the stage or the grade of NASH, is associated with insulin resistance in patients with NAFLD.     

Methylenetetrahydrofolate Reductase C677T Mutation and Nonalcoholic Fatty Liver Disease

A mutation in the methylenetetrahydrofolate reductase (MTHFR) gene is known as one of the causes of hyperhomocyteinemia. The oxidation products of homocysteine can initiate lipid peroxidation, which has a central role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). We aimed to assess the possible role of the MTHFR C677T mutation in the progression of simple steatosis to an advanced form of NAFLD. Thirty-four patients with NAFLD diagnosed by histologic analysis and 282 healthy controls were included in the study. The discrimination of nonalcoholic steatohepatitis (NASH) from another NAFLD was made by NAFLD activity score (NAS), and a NAS≥5 was considered NASH. Patients with either NASH or nonalcoholic fatty liver (NAFL) and controls were evaluated for frequency of the MTHFR C677T mutation. The frequency of the MTHFR C677T mutation was 53.5% (CT, 44.7%; TT, 8.9%) in controls and 41.5% (CT, 37.7%; TT, 3.8%) in patients (odds ratio [OR], 0.62; 95% confidence interval [CI], 0.34–1.12). There was no statistical difference in the frequency of this genotype between patients with NAFL and those with NASH (36% [CT, 28%; TT, 8%] vs 46.4% [CT, 46.4; TT, 0%]; OR, 0.65; 95% CI, 0.22–1.96). According to this study, the MTHFR C677T mutation does not seem to be a risk factor for the progression of NAFL to NASH.     

Progression from Nonalcoholic Fatty Liver to Nonalcoholic Steatohepatitis Cirrhosis Confirmed by Liver Histology after 14 Years

A 44-year-old patient progressed from nonalcoholic fatty liver (NAFL) to nonalcoholic steatohepatitis (NASH) cirrhosis. She was diagnosed with NAFL via a liver biopsy. At 56 years old, she was diagnosed with NASH stage 3 via a second liver biopsy. One year later, she was diagnosed with NASH cirrhosis via a third liver biopsy. This is the first study to report the gradual deterioration of liver histology shown via three liver biopsies and fibrosis markers in a patient who progressed from NAFL to NASH cirrhosis. Following menopause, it is necessary to be aware of the rapid development of liver fibrosis.     

Effects of bariatric surgery on nonalcoholic fatty liver disease: preliminary findings after 2 years

Background and Aim: Although nonalcoholic fatty liver disease (NAFLD) is very common among morbidly obese patients, the effect of weight loss after bariatric surgery on inflammation and fibrosis related to NAFLD is still a matter of debate. The aim of this study was to evaluate the impact of Roux‐en‐Y gastric bypass (RYGB) surgery on NAFLD with a follow up of 2 years. Methods: Eighteen consecutive NAFLD patients with body mass index >40 kg/m² undergoing gastroplasty with RYGB were enrolled, and wedge liver biopsy was obtained at the operation. After 2 years, these patients underwent percutaneous liver biopsy. Results: At baseline, 67% of patients had nonalcoholic steatohepatitis (NASH) and 33% had steatosis, according to the NASH Clinical Research Network Scoring System (NAS) for biopsy. Cirrhosis was present in 5.5% of the patients with NASH. After a mean excess weight loss of 60%, steatosis disappeared in 84% and fibrosis disappeared in 75% of the patients. Hepatocellular ballooning disappeared in 50%. A slight lobular inflammatory infiltrate remained in 81%, apparently unrelated to fatty degeneration. As liver biochemical variables had been found within normal limits in 92.3% of patients at initial biopsy, no difference was found 2 years later. Lipid profile and blood sugar plasma concentration were closer to normal in all patients after 2 years (P < 0.05). Conclusions: Aspects of NAFLD including steatohepatitis improved significantly with massive weight loss at 2 years after RYGB surgery. No patient in this series had progression of hepatic fibrosis.     

细胞因子在非酒精性脂肪性肝炎发病机制中的作用

随着非酒精性脂肪性肝病发病率的逐年上升及其对健康的危害,包括3种类型:单纯性脂肪肝、脂肪性肝炎和脂肪性肝硬化已受到越来越多的重视,而非酒精性脂肪性肝炎是由单纯性脂肪肝发展为脂肪性肝硬化的必经阶段,了解其发病机制,探讨具有多种生物学效应的细胞因子在非酒精性脂肪性肝炎中的作用,对于弄清其发病机制的多样性有着深刻的意义。     

Noninvasive evaluation of nonalcoholic fatty liver disease: Current evidence and practice

With the increasing number of individuals with diabetes and obesity,nonalcoholic fatty liver disease(NAFLD) is becoming increasingly prevalent,affecting one-quarter of adults worldwide. The spectrum of NAFLD ranges from simple steatosis or nonalcoholic fatty liver(NAFL) to nonalcoholic steatohepatitis(NASH). NAFLD, especially NASH, may progress to fibrosis, leading to cirrhosis and hepatocellular carcinoma. NAFLD can impose a severe economic burden,and patients with NAFLD-related terminal or deteriorative liver diseases have become one of the main groups receiving liver transplantation. The increasing prevalence of NAFLD and the severe outcomes of NASH make it necessary to use effective methods to identify NAFLD. Although recognized as the gold standard, biopsy is limited by its sampling bias, poor acceptability, and severe complications, such as mortality, bleeding, and pain. Therefore, noninvasive methods are urgently needed to avoid biopsy for diagnosing NAFLD. This review discusses the current noninvasive methods for assessing NAFLD,including steatosis, NASH, and NAFLD-related fibrosis, and explores the advantages and disadvantages of measurement tools. In addition, we analyze potential noninvasive biomarkers for tracking disease processes and monitoring treatment effects, and explore effective algorithms consisting of imaging and nonimaging biomarkers for diagnosing advanced fibrosis and reducing unnecessary biopsies in clinical practice.     

Nonalcoholic fatty liver disease and steatohepatitis in people living with HIV

ABSTRACT

Introduction: The burden of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) is increasing worldwide. This phenomenon poses a potentially dangerous risk of rise in mortalities caused by cirrhosis and liver cancer. Owing to a complex combination of factors, NAFLD and NASH arise in a majority of people living with HIV (PLWH), but accurate estimates of prevalence differ, depending on sample selection, type of analysis, and data interpretation. The wide range of diagnostic tools used to assess liver steatosis and lack of control groups in many studies further contributes to current difficulties in properly assessing prevalence of these conditions.

Areas covered: Thoroughly scrutinizing the current literature, we compared the prevalence of NAFLD and NASH in PLWH to rates found in the general population. We highlighted strengths and limitations of the studies, in order to determine the effective impact of these medical conditions in PLWH.

Expert opinion: The prevalence and progression of NAFLD in human immunodeficiency virus (HIV) infection are reported to be widely variable. HIV infection itself and antiretroviral treatment have been demonstrated to play a role in the development of NAFLD. Larger and more effective studies are needed to evaluate the effects of NASH in PLWH and its progression.     

Non-invasive diagnosis of nonalcoholic fatty liver and nonalcoholic steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the USA and many other parts of the world. Its prevalence continues to rise; currently affecting about one in four adults and 10% of children in the USA. NAFLD represents a wide spectrum of conditions ranging from fatty liver, which in general follows a benign, no-progressive clinical course, to nonalcoholic steatohepatitis (NASH), a more serious form of NAFLD that may progress to cirrhosis and end-stage liver disease. Currently, the diagnosis of NASH requires an invasive liver biopsy with drawbacks of sampling and interpretation error. Clinical risk factors for NASH include diabetes and the metabolic syndrome; however, these are not sufficiently predictive of the condition by themselves. Routine liver enzyme levels are not reliable; however, novel plasma hepatocyte cell death markers either alone or in combination with clinical risk factors are potential non-invasive diagnostic tools for the future. This review provides a concise overview of the role non-invasive diagnostic tools for the differentiation of fatty liver from NASH as well as for the determination of presence and extent of fibrosis.     

血管内皮生长因子与非酒精性脂肪性肝病

非酒精性脂肪性肝病（NAFLD）是影响公共健康的全球性疾病,其病理变化可向非酒精性单纯性脂肪肝（NAFL）、脂肪性肝炎（NASH）甚至脂肪性肝硬化（FLC）发展。虽然NAFLD的这些病理进展机制尚未明确,但仍有一些实验研究提示了可能的诱发机制。其中血管内皮生长因子（VEGF）在促进NAFLD肝脏炎症、肝纤维化中发挥着重要的作用。本文就VEGF与NAFLD关系的研究进展予以综述。     

长链非编码RNA EXOC7在非酒精性脂肪性肝病中的表达及临床意义

目的 观察非酒精性脂肪性肝病(NAFLD)患者血清及肝穿刺组织中长链非编码RNA(lncRNA)EXOC7的表达及临床意义。方法 选取2013年1月1日-2018年12月31日于西南医科大学附属医院住院行肝穿刺并经影像学及组织病理学诊断为NAFLD的患者120例,其中非酒精性单纯性脂肪肝(NAFL)47例,非酒精性脂肪性肝炎(NASH)73例。另选取同期体检的50例无脂肪变性和脂肪性肝炎的其他肝病患者作为对照组。采用Real-time PCR法检测lncRNA EXOC7在肝组织及血清中的表达。计量资料两组间比较采用t检验;多组间比较采用方差分析,进一步两两比较采用SNK-q检验。计数资料两组间比较采用χ2检验。采用Pearson相关分析lncRNA EXOC7表达与临床各生化指标的关系。绘制受试者工作特征曲线(ROC曲线)并分析lncRNA EXOC7的临床诊断价值。结果 与对照组相比,NAFL和NASH患者的组织及血清中lncRNA EXOC7表达显著增高(P值均<0.05),且其表达水平随着肝脏脂肪变性及炎症程度的加重而提升(F=19.96,P<0.05)。相关性分析结果显示,lncRNA EXOC7表达与TG、LDL-C呈正相关(r值分别为0.785、0.847,P值均<0.001);而与HDL-C、胰岛素敏感指数呈负相关(r值分别为-0.726、-0.709,P值均<0.001)。lncRNA EXOC7诊断NAFLD的ROC曲线下面积为0.812(95%可信区间:0.599~0.915,P<0.001),敏感度为85.42%,特异度为81.17%。结论 lncRNA EXOC7在NAFLD患者中高表达,并随脂肪变性及炎症程度的加重而升高,提示lncRNA EXOC7可能是NAFLD防治的潜在新靶点。     

无创诊断和评估非酒精性脂肪性肝炎研究进展*

非酒精性脂肪性肝病（NAFLD）主要包括单纯性脂肪肝（NAFL)、非酒精性脂肪性肝炎（NASH）、相关肝硬化和肝细胞癌。相对于NAFL,NASH更易发展为肝硬化和肝癌,故早期诊断并对其干预尤为重要。近年来,多项无创诊断方法的出现致力于替代肝脏穿刺活检,主要包括血清学和影像学检查等,本文就无创性诊断和评估NASH作一综述。     

A lipidomic analysis of nonalcoholic fatty liver disease

The spectrum of nonalcoholic fatty liver disease (NAFLD) includes a nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH). The specific types and amounts of lipids that accumulate in NAFLD are not fully defined. The free fatty acid (FFA), diacylglycerol (DAG), triacylglycerol (TAG), free cholesterol (FC), cholesterol ester, and phospholipid contents in normal livers were quantified and compared to those of NAFL and NASH, and the distribution of fatty acids within these classes was compared across these groups. Hepatic lipids were quantified by capillary gas chromatography. The mean (nmol/g of tissue) DAG (normal/NAFL/NASH: 1922 versus 4947 versus 3304) and TAG (13,609 versus 128,585 versus 104,036) increased significantly in NAFLD, but FFA remained unaltered (5533 versus 5929 versus 6115). There was a stepwise increase in the mean TAG/DAG ratio from normal livers to NAFL to NASH (7 versus 26 versus 31, P < 0.001). There was also a similar stepwise increment in hepatic FC (7539 versus 10,383 versus 12,863, P < 0.05 for NASH). The total phosphatidylcholine (PC) decreased in both NAFL and NASH. The FC/PC ratio increased progressively (0.34 versus 0.69 versus 0.71, P < 0.008 for both). Although the levels for linoleic acid (18:2n-6) and alpha-linolenic acid (18:3n-3) remained unaltered, there was a decrease in arachidonic acid (20:4n-6) in FFA, TAG, and PC (P < 0.05 for all) in NASH. Eicosapentanoic acid (20:5n-3) and docosahexanoic acid (22:6n-3) were decreased in TAG in NASH. The n-6:n-3 FFA ratio increased in NASH (P < 0.05). CONCLUSIONS: NAFLD is associated with numerous changes in the lipid composition of the liver. The potential implications are discussed.     

Nonalcoholic fatty liver disease from a primary care perspective

Nonalcoholic fatty liver disease (NAFLD) affects up to one-third of the US population. Approximately one-fifth of patients with NAFLD have nonalcoholic steatohepatitis (NASH), characterized by hepatocyte damage and inflammation with or without fibrosis. NASH leads to greater risk of liver-related complications and liver-related mortality, with the poorest outcomes seen in patients with advanced fibrosis. NASH is also associated with other metabolic comorbidities and conveys an increased risk of adverse cardiovascular outcomes and extrahepatic cancers. Despite its high prevalence, NAFLD is frequently underdiagnosed. This is a significant concern, given that early diagnosis of NAFLD is a key step in preventing progression to NASH. In this review, we describe the clinical impact of NASH from the perspective of both the clinician and the patient. In addition, we provide practical guidance on the diagnosis and management of NASH for primary care providers, who play a pivotal role in the frontline care of patients with NASH, and we use case studies to illustrate real-world scenarios encountered in the primary care setting.     

Endocannabinoid receptor CB2 in nonalcoholic fatty liver disease.

BACKGROUND AND AIM: Fatty infiltration and fibrosis are major issues in chronic liver disease. Recent reports suggest a role for the endocannabinoid system in these processes. AIM: To characterize localization and expression of CB2 in normal liver and nonalcoholic fatty liver. METHODS: We studied 64 liver biopsies: eight were considered normal; 56 had a diagnosis of nonalcoholic fatty liver disease (NAFLD); 32 with nonalcoholic steatosis and 24 nonalcoholic steatohepatitis (NASH). CB2 immunolocalization was studied in 38 samples in paraffin blocks using immunohistochemistry, and a computerized semiquantitative analysis was carried out. CB2 mRNA expression was assessed through RT-PCR in 26 frozen liver samples and the ratio CB2/beta-actin was used to evaluate differences between groups. Statistical analysis was performed with central tendency measures and the Mann-Whitney U-test. We considered as significant differences those with a P-value <0.05. RESULTS: Neither parenchymal nor nonparenchymal cells in normal liver tissue react towards anti-CB2 antibodies. All the samples from patients with steatosis and nonalcoholic steatohepatitis showed hepatocellular immunoreactivity. Cholangiocytes were positive only in the NAFLD group. Normal liver tissue showed a normalized CB2/beta-actin ratio of 0.001+/-0.01, steatosis 6.52+/-17.3 (P=0.05 vs normal) and NASH 6.49+/-12.2 (P=0.06 vs normal and P=0.6 vs steatosis). CONCLUSION: CB2 receptors are expressed by hepatocytes in nonalcoholic fatty liver disease but not in normal liver.     

Pharmacotherapy of nonalcoholic steatohepatitis: Reflections on the existing evidence

Pharmacotherapy for nonalcoholic fatty liver disease (NAFLD) has not yet been approved by the US Food and Drug Administration. Over the past decade, a large number of clinical studies have explored the safety and efficacy of different drugs in treating nonalcoholic steatohepatitis (NASH), including diet pills, antioxidants, insulin sensitizers, lipid‐lowering agents, anti‐inflammatory cytokines, cytoprotective agents and intestinal probiotics. Based on the evidence from randomized controlled trials a number of academic groups have developed guidelines for the diagnosis and management of NAFLD and NASH. In this article, we discussed the current situation of NASH pharmacotherapy.     

Crosstalk between nonalcoholic fatty liver disease and cardiometabolic syndrome

Nonalcoholic fatty liver disease (NAFLD) is a chronic condition characterized by fat accumulation combined with low‐grade inflammation in the liver. A large body of clinical and experimental data shows that increased flux of free fatty acids from increased visceral adipose tissue and de novo lipogenesis can lead to NAFLD and insulin resistance. Thus, individuals with obesity, insulin resistance, and dyslipidaemia are at the greatest risk of developing NAFLD. Conversely, NAFLD is a phenotype of cardiometabolic syndrome. Notably, researchers have discovered a close association between NAFLD and impaired glucose metabolism and focused on the role of NAFLD in the development of type 2 diabetes. Moreover, recent studies provide substantial evidence for an association between NAFLD and atherosclerosis and cardiometabolic disorders. Even if NAFLD can progress into severe liver disorders including nonalcoholic steatohepatitis (NASH) and cirrhosis, the majority of subjects with NAFLD die from cardiovascular disease eventually. In this review, we propose a potential pathological link between NAFLD/NASH and cardiometabolic syndrome. The potential factors that can play a pivotal role in this link, such as inflammation, insulin resistance, alteration in lipid metabolism, oxidative stress, genetic predisposition, and gut microbiota are discussed.     

Sampling variability of liver biopsy in nonalcoholic fatty liver disease

BACKGROUND & AIMS: In nonalcoholic fatty liver disease (NAFLD), the distinction between steatosis and steatohepatitis (NASH) and the assessment of the severity of the disease rely on liver histology alone. The aim of this study was to assess the sampling error of liver biopsy and its impact on the diagnosis and staging of NASH. METHODS: Fifty-one patients with NAFLD underwent percutaneous liver biopsy with 2 samples collected. The agreement between paired biopsy specimens was assessed by the percentage of discordant results and by the kappa reliability test. RESULTS: No features displayed high agreement; substantial agreement was only seen for steatosis grade; moderate agreement for hepatocyte ballooning and perisinusoidal fibrosis; fair agreement for Mallory bodies; acidophilic bodies and lobular inflammation displayed only slight agreement. Overall, the discordance rate for the presence of hepatocyte ballooning was 18%, and ballooning would have been missed in 24% of patients had only 1 biopsy been performed. The negative predictive value of a single biopsy for the diagnosis of NASH was at best 0.74. Discordance of 1 stage or more was 41%. Six of 17 patients with bridging fibrosis (35%) on 1 sample had only mild or no fibrosis on the other and therefore could have been under staged with only 1 biopsy. Intraobserver variability was systematically lower than sampling variability and therefore could not account for most of the sampling error. CONCLUSIONS: Histologic lesions of NASH are unevenly distributed throughout the liver parenchyma; therefore, sampling error of liver biopsy can result in substantial misdiagnosis and staging inaccuracies.     

Expression and activity of the cytochrome P450 2E1 in patients with nonalcoholic steatosis and steatohepatitis.

BACKGROUND/AIMS: Nonalcoholic steatohepatitis (NASH) and nonalcoholic fatty liver (NAFL) have a different prognosis and should be dealt with differently. The pathogenesis of NASH implicates the overexpression of cytochrome P450 2E1 (CYP2E1). We investigated whether the noninvasive determination of CYP2E1 activity could replace a liver biopsy in order to differentiate NASH from NAFL. METHOD: Forty patients referred for suspicion of NASH underwent liver biopsy. In these patients, CYP2E1 activity was determined noninvasively by the 6-hydroxychlorzoxazone/chlorzoxazone (CHZ) ratio (CHZ test). Expression of CYP2E1 on liver slides was assessed by immunohistochemistry, and immunostaining for smooth muscle actin was used to assess the activation of hepatic stellate cells (HSC). RESULTS: Thirty patients with NASH were compared with 10 subjects with NAFL. No statistically significant difference could be identified for the clinical and biochemical parameters between the two groups. In the histology, steatosis was more important in NASH than in NAFL (P<0.0001). There was no difference either in the activity (CHZ test) or in the expression of CYP2E1 (immunohistochemistry) between patients with NASH and patients with NAFL. The degree of HSC activation was also comparable between the two groups. A positive and significant correlation was found between the activity of CYP2E1 and body mass index (P<0.001) as well as with the degree of steatosis (P=0.008). CONCLUSION: For patients suspected to have NASH, noninvasive tests including the determination of the CYP2E1 activity are unable to distinguish them from patients with steatosis.     

Non-alcoholic fatty liver disease and type 2 diabetes mellitus: The liver disease of our age?

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease that might affect up to one-third of the adult population in industrialised countries. NAFLD incorporates histologically and clinically different non-alcoholic entities; fatty liver (NAFL, steatosis hepatis) and steatohepatitis (NASH-characterised by hepatocyte ballooning and lobular inflammation ± fibrosis) might progress to cirrhosis and rarely to hepatocellular cancer. NAFL increasingly affects children (paediatric prevalence is 4.2%-9.6%). Type 2 diabetes mellitus (T2DM), insulin resistance (IR), obesity, metabolic syndrome and NAFLD are particularly closely related. Increased hepatic lipid storage is an early abnormality in insulin resistant women with a history of gestational diabetes mellitus. The accumulation of triacylglycerols in hepatocytes is predominantly derived from the plasma nonesterified fatty acid pool supplied largely by the adipose tissue. A few NAFLD susceptibility gene variants are associated with progressive liver disease, IR, T2DM and a higher risk for hepatocellular carcinoma. Although not approved, pharmacological approaches might be considered in NASH patients.