Significance of genetic polymorphisms in patients with nonalcoholic fatty liver disease

Because of recent advances in genetic research such as genome-wide association studies, the underlying genetic mechanisms of nonalcoholic fatty liver disease (NAFLD) pathophysiology have been elucidated. Here, we present a review of the current literature on the impact of genetic polymorphisms in patients with NAFLD. These genetic polymorphisms, which regulate lipid metabolism, glucose metabolism, and the renin-angiotensin system, are involved in NAFLD onset, steatosis, inflammation, fibrosis, and hepatocellular carcinoma (HCC). Among these genetic polymorphisms, many studies and meta-analyses have demonstrated that position 148 (rs738409 C/G) of the patatin-like phospholipase domain-containing protein (PNPLA3) is a genetic factor associated with NAFLD pathophysiological features, such as hepatic fat level, hepatic inflammation, fibrosis, and HCC. However, the impact of genetic polymorphisms on NAFLD pathophysiology appears to differ among ethnic groups. Therefore, further studies with larger sample sizes are needed for each ethnic group.     

The genetics of nonalcoholic fatty liver disease

The increasing prevalence of obesity in Western countries has led to a significant increase of nonalcoholic fatty liver disease (NAFLD) over the past decades. Being part of the metabolic syndrome, NAFLD is thought to be the most frequent cause of elevated liver enzymes in the United States affecting up to one third of the population. NAFLD is also proposed to be the major cause for cryptogenic cirrhosis and hepatocellular cancer of unknown etiology, and thus, represents one of the most important problems for hepatologists in the future. However, the natural course of NAFLD is highly variable and is influenced by both environmental and genetic factors. Polymorphisms in specific genes have been proposed to increase the risk of fibrosis in patients with NAFLD. The present review article summarizes currently available data from genotype-phenotype studies and defines candidate genes that deserve future investigation.     

非酒精性脂肪性肝病的诊断

有关非酒精性脂肪性肝病(NAFLD)的诊断,不同的国家或地区某些指标有一定的差别,国内目前普遍采用哑太地区NAFLD诊疗指南[1]和2006年中华医学会肝病学分会脂肪肝和酒精性肝病学组制定的NAFLD诊疗指南(以下简称中国指南)[2].这些指南对规范NAFLD的研究具有重要的指导意义,但有些内容还需要进一步明确或商榷.现结合近年的国内外研究进展和临床体会,就NAFLD临床诊断的相关问题作一简述.     

Mitochondria in nonalcoholic fatty liver disease

Nonalcoholic fatty liver (NAFL) is associated with fundamental issues of fat metabolism and insulin resistance. These abnormalities have been linked to impairment of ATP homeostasis, and a growing body of literature has reported mitochondrial abnormalities in various forms of hepatic steatosis. The changes are evident as structural abnormalities, including greatly increased size and the development of crystalline inclusions, and are usually regarded as pathologic, reflecting either a protective or degenerative response to injury. Although the relationships between structural changes,decreased mitochondrial function, and disease states are becoming clearer, the molecular basis for the perturbations is not well understood.Oxidative damage is the most likely causative process and may result in alterations of mitochondrial DNA (mtDNA), stimulated apoptotic pathways, and increased propensity for necrosis.Overall mitochondrial health likely depends on multiple factors including the integrity of the mtDNA, the composition of cellular lipids, lipoprotein trafficking, the balance of pro- and antioxidant factors, and the metabolic demands placed on the liver. Mitochondrial dysfunction may play a role in numerous clinical conditions associated with NAFL, such as hepatocellular carcinoma, lipodystrophy,age-related insulin resistance, gut dysmotility, cryptogenic cirrhosis, a mild form of gaze palsy, and possibly other more severe neurodegenerative diseases. The prominent role of mitochondrial dysfunction in NAFL provides a new and exciting paradigm in which to view this disorder, its complications, and potential dietary and pharmacologic intervention.     

Biomarkers in nonalcoholic fatty liver disease

BACKGROUND:

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver condition characterized by insulin resistance, type 2 diabetes and fat accumulation in the liver that may cause hepatic inflammation and progressive scarring leading to nonalcoholic steatohepatitis (NASH) and irreversible liver damage (cirrhosis). As a result, there has been increased recognition of the need to assess and closely monitor individuals for risk factors of components of NAFLD and NASH, as well as the severity of these conditions using biomarkers.

AIM:

To review the biomarkers used to diagnose and define the severity of NAFLD and NASH.

METHODS:

A comprehensive PubMed and Google Scholar literature search was performed using the terms “non-alcoholic fatty liver disease”, “non-alcoholic steatohepatitis”, as well as the name of each biomarker known to be used. Articles indexed between 2004 and 2014 were used. Each author read the publications separately and the results were discussed.

RESULTS:

Biomarkers offer a potential prognostic or diagnostic indicator for disease manifestation, progression or both. Serum biomarkers, including total cholesterol, triglycerides, insulin resistance and C-peptide, have been used for many years. Emerging biomarkers, such as apolipoprotein A1, apolipoprotein B, leptin, adiponectin, free fatty acids, ghrelin and tumour necrosis factor-alpha, have been proposed as tools that could provide valuable complementary information to that obtained from traditional biomarkers. Moreover, markers of cell death and mitochondrial dysfunction (cytokeratins) represent powerful predictors of risk. For biomarkers to be clinically useful in accurately diagnosing and treating disorders, age-specific reference intervals that account for differences in sex and ethnic origin are a necessity.

CONCLUSIONS:

The present review attempts to provide a comprehensive analysis of the emerging risk biomarkers of NAFLD and NASH, and to use the clinical significance and analytical considerations of each biomarker pointing out sentinel features of disease progression.     

Leptin in nonalcoholic fatty liver disease

Background: Non-alcoholic fatty liver disease (NAFLD) is a prevalent condition associated with obesity and insulin resistance (IR). Leptin plays a key role in the control of energy balance, and insulin sensitivity. In this study, we aimed to examine whether serum leptin levels correlate with insulin resistance, oxidative stress parameters and the severity of histological changes in NAFLD. Methods: Fifty-two patients (M/F: 28/24) with no alcohol intake and biopsy-proven diagnosis of NAFLD were studied. Serum leptin levels were measured by radioimmunoassay. HOMA (homeostasis model assessment) IR index was calculated. Comparisons between the patients with NAFLD and non-alcoholic steatohepatitis (NASH) were performed using the Student’s t test. Multivariate regression analysis and the area under the receiver operating characteristic (ROC) curve were used to identify the independent predictors for NASH. Results: We found no association between serum leptin, fasting insulin levels, and oxidative stress parameters. ROC curve and multiple regression analysis revealed no association between the severity of histological changes and serum leptin levels. During six months followed-up period only NASH group with elevated leptin levels had significant reductions of ALT and AST values (p = 0.03, and 0.005, respectively). Conclusion: Our findings show a preventive effect of leptin against progressive liver injury in NAFLD.     

The genetic epidemiology of nonalcoholic fatty liver disease: toward a personalized medicine

The understanding of the genetic bases of complex diseases such as nonalcoholic fatty liver disease opens new opportunities and challenges. This article explores new tools designed toward moving genomic data into clinical medicine, providing putative answers to more practical questions.     

The epidemiology of nonalcoholic fatty liver disease in adults

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease that has been shown to progress to cirrhosis and hepatocellular carcinoma. This article reviews the prevalence of NAFLD and the factors associated this disorder, and with the more advanced stages of NAFLD, including nonalcoholic steatohepatitis (NASH) and fibrosis. In the general population, the estimated prevalence ranges from 3% to 24%, with most estimates in the 6% to 14% range. NAFLD is extremely common among patients undergoing bariatric surgery, ranging from 84% to 96%. In these patients, 25% to 55% have NASH, 34% to 47% have fibrosis, and 2% to 12% have bridging fibrosis or cirrhosis. NAFLD appears to be most strongly associated with obesity, and insulin resistance states including diabetes and with other features of the metabolic syndrome, such as high triglycerides and low HDL. It appears to be more common in men, and it increases with increasing age and after menopause. Some data suggest that Mexican Americans are more likely to have NAFLD and blacks are less likely compared with non-Hispanic whites. More advanced stages of NAFLD are associated with older age, higher body mass index, diabetes, hypertension, high triglycerides, and/or insulin resistance. An AST/ALT ratio greater >1 may also indicate more severe disease. Although hepatocellular carcinoma can occur in the setting of NAFLD, the risk factors for hepatocellular carcinoma in the setting of NAFLD have not been established. More prospective studies are needed to determine the true risk factors for the development and progression of NAFLD to help identify patients at highest risk who might benefit from treatment trials.     

The histologic spectrum of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) represents a range of histologic lesions in the liver that occur in individuals who do not consume alcohol in quantities that generally are considered to be harmful. The histologic spectrum of NAFLD includes isolated predominantly macrovesicular steatosis alone at one end and steatohepatitis at the other. Nonalcoholic steatohepatitis can progress to cirrhosis and now also is considered to be a precursor of cryptogenic cirrhosis. This article provides an understanding of the histologic features of NAFLD and the potential pitfalls in the histologic assessment of this condition.     

非酒精性脂肪性肝病动物模型研究进展*

目的 非酒精性脂肪性肝病(NAFLD)发病率逐年增加,并可能发展成为终末期肝病。目前,仍缺乏针对该病的治疗药物,建立动物模型研究很有必要。尽管已有多种不同种类的疾病模型,但仍没有一种能真正反映人类整个疾病谱的代表性的NAFLD模型。本文对目前应用的NAFLD模型进行了综述,重点介绍动物模型、2D细胞模型和3D肝脏模型及其优缺点。     

非酒精性脂肪性肝病研究进展

非酒精性脂肪性肝病(NAFLD)的相关研究进展日益显示出肝脏脂肪沉积在促发胰岛素抵抗和糖脂代谢异常方面的重要地位.作为一个代谢性疾病的早期可逆性干预治疗靶位,NAFLD越来越受到国内外内分泌代谢和消化领域专家的重视,对其研究也不断深入拓展.本综述结合NAFLD的最新研究进展,从代谢的角度阐述对NAFLD的新认识和新概念,介绍我国最新NAFLD诊疗共识的特点以及国内外在NAFLD诊断和治疗方面取得的最新成果.在此基础上,预测NAFLD研究领域的进一步探索发展方向.     

Circulating microRNAs in nonalcoholic fatty liver disease

Liver biopsy is currently recognized as the most accurate method for diagnosing and staging nonalcoholic fatty liver disease (NAFLD). However, this procedure is typically performed when disease has progressed to clinically significant stages, thereby limiting early diagnosis of patients who are at high risk for development of liver- and cardiovascular-related morbidity and mortality. Recently, microRNAs (miRNAs), short, noncoding RNAs that regulate gene expression, have been associated with histological features of NAFLD and are readily detected in the circulation. As such, miRNAs are emerging as potentially useful noninvasive markers with which to follow the progression of NAFLD. In this article, we present the evidence linking circulating miRNAs with NAFLD and discuss the potential value of circulating miRNA profiles in the development of improved methods for NAFLD diagnosis and clinical monitoring of disease progression.     

Genes and nonalcoholic fatty liver disease

Whereas most individuals with nonalcoholic fatty liver disease (NAFLD) will have steatosis, only a minority will ever develop progressive disease. Family studies and interethnic variations in susceptibility suggest that genetic factors may be important in determining disease risk. Although no genetic associations with advanced NAFLD have been replicated in large studies, preliminary data suggest that polymorphisms in the genes encoding microsomal triglyceride transfer protein, superoxide dismutase 2, the CD14 endotoxin receptor, tumor necrosis factor-α, transforming growth factor-β, and angiotensinogen may be associated with steatohepatitis and/or fibrosis. With the advent of high-throughput gene analyses and the reduced cost of whole genomewide scans, it seems likely that genes contributing to inherited susceptibility to this common disease will be identified in the near future.     

Treatment of nonalcoholic fatty liver disease

Opinion statement Nonalcoholic fatty liver disease (NAFLD) is very common in the United States, and in some patients it may lead to cirrhosis, liver failure, and liver cancer. NAFLD encompasses a spectrum of liver injury, ranging from steatosis to steatohepatitis, advanced fibrosis, and cirrhosis. Nonalcoholic steatohepatitis (NASH), an advanced form of NAFLD, histologically comprises steatosis, balloon degeneration, inflammation, and fibrosis in varying degrees. It is generally believed that simple steatosis is benign with minimal risk of progression, whereas NASH is progressive and can lead to cirrhosis. The commonly associated risk factors for NAFLD include obesity, hyperlipidemia, and diabetes mellitus. The pathogenesis of NAFLD and NASH is not fully known; however, current evidence suggests that insulin resistance and lipid peroxidation play a role in the pathogenesis of this condition. Currently, there are no proven effective therapies available for the treatment of NASH. Although there are numerous studies that have explored various treatments for NASH, these generally consist of small numbers of patients with suboptimal endpoints. Treatment strategies for NAFLD and NASH can be broadly divided into 1) treatment or control of underlying risk factors such as hyperlipidemia, diabetes mellitus, and obesity; and 2) specific pharmacologic therapy such as insulin sensitizers, antioxidants, or cytoprotective agents. Newer thiazolidinediones, such as rosiglitazone and pioglitazone, have shown promise in the treatment of NASH in pilot studies. However, these agents should not be used in clinical practice until their efficacy and safety are firmly established in larger studies. Despite encouraging initial studies, the recently completed multicenter, randomized, controlled trial failed to show any efficacy for ursodeoxycholic acid in the treatment of NASH. Other agents, such as vitamin E, betaine, probucol, and atorvastatin, have been explored as therapeutic agents for NASH. However, none of these studies have shown convincingly their utility in the treatment of NASH. Attempts to identify optimal therapy for patients with NASH are being vigorously pursued by the research community and important advances are expected within next several years. Until then, subjects should be advised to avoid alcohol, lose weight, and exercise regularly, and meticulous attention should be paid to the control of their risk factors such as diabetes and hyperlipidemia.     

Update on nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease is now recognized as the most common liver disease in the United States, with a prevalence of approximately 5% in the general population and up to 25% to 75% in patients with obesity and type II diabetes mellitus. Nonalcoholic fatty liver disease is a clinicopathologic syndrome with a wide spectrum of histologic abnormalities and clinical outcomes. Hepatic steatosis has a benign clinical course. In contrast, nonalcoholic steatohepatitis (NASH) may progress to cirrhosis and liver-related death in 25% and 10% of patients, respectively. Cases occur most commonly in obese, middle-aged women with diabetes. However, NASH may also occur in children and normal-weight men with normal glucose and lipid metabolism. The pathophysiology involves two steps. The first is insulin resistance, which causes steatosis. The second is oxidative stress, which produces lipid peroxidation and activates inflammatory cytokines resulting in NASH. Liver biopsy provides prognostic information and identifies NASH patients who may benefit from therapy. Treatment consists of managing the comorbidities: obesity, diabetes, and hyperlipidemia. Although antioxidant therapy with vitamin E is often used, ursodeoxycholic acid is the only drug that has shown benefit and is the most promising of the drugs currently being investigated. Future therapies will depend on a greater understanding of the pathophysiology and should focus on diminishing fibrosis.     

Treatment strategies in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is an increasingly recognized health problem. Increased fat accumulation in the liver is observed in 20-30% of the population in the Western world, and in approximately 10% of this cohort it is associated with nonalcoholic steatohepatitis, which is characterized by inflammation and fibrosis. Disease presentation of NAFLD ranges from asymptomatic disease to cirrhosis with the complication of liver failure and hepatocellular carcinoma. NAFLD is suspected on the basis of various clinical aspects (an elevated alanine aminotransferase concentration, presence of obesity and diabetes) that alone are not sufficient to establish diagnosis or prognosis. The major diagnostic procedure is liver biopsy, which allows assessment of liver injury. In most cases, NAFLD is associated with insulin resistance, which is therefore the target of most current NAFLD treatment modalities. Various treatment strategies such as weight loss and/or exercise, thiazolidinediones, metformin, lipid-lowering agents and antioxidants have been studied. So far, no single intervention has convincingly improved liver histology. It is recommended that patients at high risk of developing advanced liver disease, and who are not part of controlled studies, should receive nutritional counseling and take physical exercise to achieve moderate weight loss and improve insulin sensitivity.