A multi-ethnic study of a PNPLA3 gene variant and its association with disease severity in non-alcoholic fatty liver disease

Integrating genetic and socioeconomic data to predict the progression of nonalcoholic fatty liver disease

OBJECTIVES

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease globally, with an estimated prevalence exceeding 25%. Variants in the PNPLA3 and HSD17B13 genes have been a focus of investigations surrounding the etiology and progression of NAFLD and are believed to contribute to a greater burden of disease experienced by Hispanic Americans. However, little is known about socioeconomic factors influencing NAFLD progression or its increased prevalence among Hispanics.

MATERIALS AND METHODS

We cross-sectionally analyzed 264 patients to assess the role of genetic and socioeconomic variables in the development of advanced liver fibrosis in individuals at risk for NAFLD.

RESULTS

Adjusting for age, sex, body mass index, and PNPLA3 genotype, lacking a college degree was associated with 3.3 times higher odds of advanced fibrosis (95% confidence interval [CI]: 1.21-8.76, p = 0.019), an effect comparable to that of possessing the major PNPLA3 risk variant. Notably, the effect of PNPLA3 genotype on advanced fibrosis was attenuated to nonsignificance following adjustment for education and other socioeconomic markers. The effect of the protective HSD17B13 variant, moreover, diminished after adjustment for education (odds ratio [OR]: 0.39 [95% CI: 0.13-1.16, p = 0.092]), while lower education continued to predict advanced fibrosis following multivariable adjustment with an OR of 8.0 (95% CI: 1.91-33.86, p = 0.005).

DISCUSSION

Adjusting for education attenuated the effects of genotype and Hispanic ethnicity on liver fibrosis, suggesting that social factors-rather than genes or ethnicity-may be driving disease severity within some populations. Findings reveal the importance of including socioenvironmental controls when considering the role of genetics or ethnicity in complex disease.

Genotypic variation in CYP2E1, GCKR, and PNPLA3 among nonalcoholic steatohepatitis patients of Turkish origin

BACKGROUND

This study examines genetic variations in CYP2E1 (rs6413432, rs3813867), GCKR (rs780094, rs1260326), and PNPLA3 (rs738409) among Turkish patients to assess their influence on nonalcoholic steatohepatitis.

METHODS

Allele and genotype frequencies were compared between 245 NASH patients and 120 healthy controls using SNP genotyping via polymerase chain reaction-restriction fragment length polymorphism. Additionally, the deviation of the observed genotype frequencies from Hardy-Weinberg proportion was examined.

RESULTS

No significant differences were found in the allelic and genotypic distributions of rs6413432, rs3813867, and rs780094 between NASH patients and healthy controls. However, significant disparities were noted for rs1260326 and rs738409. Gender and age-specific distributions showed no notable differences. The only observed deviation from Hardy-Weinberg proportion was in the genotype frequency of rs738409.

CONCLUSIONS

Variants in GCKR (rs1260326) and PNPLA3 (rs738409) are significantly associated with increased NASH risk in the Turkish population, with the rs738409 variant potentially playing a more prominent role in NASH development.

Relevance of PNPLA3, TM6SF2, HSD17B13, and GCKR Variants to MASLD Severity in an Egyptian Population

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as non-alcoholic fatty liver disease (NAFLD), is a frequent clinical condition globally. Single nucleotide polymorphisms (SNPs) associated with NAFLD have been proposed in the literature and based on bioinformatic screening. The association between NAFLD and genetic variants in Egyptians is still unclear. Hence, we sought to investigate the association of some genetic variants with NAFLD in Egyptians. Egyptians have been categorized into either the MASLD group (n = 205) or the healthy control group (n = 187). The severity of hepatic steatosis and liver fibrosis was assessed by a Fibroscan device. TaqMan-based genotyping assays were employed to explore the association of selected SNPs with MASLD. PNPLA3 rs738409 C>G variant is associated with the presence of MASLD with liver fibrosis, the severity of both hepatic steatosis and liver fibrosis, increased systolic and diastolic blood pressure and increased alanine aminotransferase (all p < 0.05), while the TM6SF2 rs58542926 C>T, HSD17B13 rs9992651 G>A, and GCKR rs1260326 T>C variants were not (all p > 0.05). The TM6SF2 rs58542926 T allele is associated with increased fasting blood glucose and a decreased waist circumference. The GCKR rs1260326 C allele is associated with decreased aspartate transaminase and diastolic blood pressure (all p < 0.05). Only after adjusting for the risk factors (age, sex, BMI, WC, HDL, TG, diabetes mellitus, and hypertension) F2 liver fibrosis score is negatively correlated with the HSD17B13 rs9992651 GA genotype. This study offers evidence for the association of the PNPLA3 rs738409 C>G variant with MASLD among Egyptians and for the association of the PNPLA3 rs738409 G allele, the TM6SF2 rs58542926 T allele, and the GCKR rs1260326 C allele with some parameters of cardiometabolic criteria.

Coagulation Dysfunctions in Non-Alcoholic Fatty Liver Disease-Oxidative Stress and Inflammation Relevance

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases. Its incidence is progressively rising and it is possibly becoming a worldwide epidemic. NAFLD encompasses a spectrum of diseases accounting for the chronic accumulation of fat within the hepatocytes due to various causes, excluding excessive alcohol consumption. In this study, we aimed to focus on finding evidence regarding the implications of oxidative stress and inflammatory processes that form the multifaceted pathophysiological tableau in relation to thrombotic events that co-occur in NAFLD and associated chronic liver diseases. Recent evidence on the pathophysiology of NAFLD suggests that a complex pattern of multidirectional components, such as prooxidative, proinflammatory, and prothrombotic components, better explains the multiple factors that promote the mechanisms underlying the fatty acid excess and subsequent processes. As there is extensive evidence on the multi-component nature of NAFLD pathophysiology, further studies could address the complex interactions that underlie the development and progression of the disease. Therefore, this study aimed to describe possible pathophysiological mechanisms connecting the molecular impairments with the various clinical manifestations, focusing especially on the interactions among oxidative stress, inflammation, and coagulation dysfunctions. Thus, we described the possible bidirectional modulation among coagulation homeostasis, oxidative stress, and inflammation that occurs in the various stages of NAFLD.

Genetic Predictors of Comorbid Course of COVID-19 and MAFLD: A Comprehensive Analysis

Metabolic-associated fatty liver disease (MAFLD) and its potential impact on the severity of COVID-19 have gained significant attention during the pandemic. This review aimed to explore the genetic determinants associated with MAFLD, previously recognized as non-alcoholic fatty liver disease (NAFLD), and their potential influence on COVID-19 outcomes. Various genetic polymorphisms, including PNPLA3 (rs738409), GCKR (rs780094), TM6SF2 (rs58542926), and LYPLAL1 (rs12137855), have been investigated in relation to MAFLD susceptibility and progression. Genome-wide association studies and meta-analyses have revealed associations between these genetic variants and MAFLD risk, as well as their effects on lipid metabolism, glucose regulation, and liver function. Furthermore, emerging evidence suggests a possible connection between these MAFLD-associated polymorphisms and the severity of COVID-19. Studies exploring the association between indicated genetic variants and COVID-19 outcomes have shown conflicting results. Some studies observed a potential protective effect of certain variants against severe COVID-19, while others reported no significant associations. This review highlights the importance of understanding the genetic determinants of MAFLD and its potential implications for COVID-19 outcomes. Further research is needed to elucidate the precise mechanisms linking these genetic variants to disease severity and to develop gene profiling tools for the early prediction of COVID-19 outcomes. If confirmed as determinants of disease severity, these genetic polymorphisms could aid in the identification of high-risk individuals and in improving the management of COVID-19.

Comparison between obese and non-obese nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum of liver conditions that are characterized by excess accumulation of fat in the liver, and is diagnosed after exclusion of significant alcohol intake and other causes of chronic liver disease. In the majority of cases, NAFLD is associated with overnutrition and obesity, although it may be also found in lean or non-obese individuals. It has been estimated that 19.2% of NAFLD patients are lean and 40.8% are non-obese. The proportion of patients with more severe liver disease and the incidence of all-cause mortality, liver-related mortality, and cardiovascular mortality among non-obese and obese NAFLD patients varies across studies and may be confounded by selection bias, underestimation of alcohol intake, and unaccounted weight changes over time. Genetic factors may have a greater effect towards the development of NAFLD in lean or non-obese individuals, but the effect may be less pronounced in the presence of strong environmental factors, such as poor dietary choices and a sedentary lifestyle, as body mass index increases in the obese state. Overall, non-invasive tests, such as the Fibrosis-4 index, NAFLD fibrosis score, and liver stiffness measurement, perform better in lean or non-obese patients compared to obese patients. Lifestyle intervention works in non-obese patients, and less amount of weight loss may be required to achieve similar results compared to obese patients. Pharmacological therapy in non-obese NAFLD patients may require special consideration and a different approach compared to obese patients.

Genetic Polymorphisms and Diversity in Nonalcoholic Fatty Liver Disease (NAFLD): A Mini Review

Nonalcoholic fatty liver disease (NAFLD) is a common liver disease with a wide spectrum of liver conditions ranging from hepatic steatosis to nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and hepatocellular carcinoma. The prevalence of NAFLD varies across populations, and different ethnicities have specific risks for the disease. NAFLD is a multi-factorial disease where the genetics, metabolic, and environmental factors interplay and modulate the disease's development and progression. Several genetic polymorphisms have been identified and are associated with the disease risk. This mini-review discussed the NAFLD's genetic polymorphisms and focusing on the differences in the findings between the populations (diversity), including of those reports that did not show any significant association. The challenges of genetic diversity are also summarized. Understanding the genetic contribution of NAFLD will allow for better diagnosis and management explicitly tailored for the various populations.

Epidemiologic, Genetic, Pathogenic, Metabolic, Epigenetic Aspects Involved in NASH-HCC: Current Therapeutic Strategies

Hepatocellular carcinoma (HCC) is the most common primary liver cancer and is the sixth most frequent cancer in the world, being the third cause of cancer-related deaths. Nonalcoholic steatohepatitis (NASH) is characterized by fatty infiltration, oxidative stress and necroinflammation of the liver, with or without fibrosis, which can progress to advanced liver fibrosis, cirrhosis and HCC. Obesity, metabolic syndrome, insulin resistance, and diabetes exacerbates the course of NASH, which elevate the risk of HCC. The growing prevalence of obesity are related with increasing incidence of NASH, which may play a growing role in HCC epidemiology worldwide. In addition, HCC initiation and progression is driven by reprogramming of metabolism, which indicates growing appreciation of metabolism in the pathogenesis of this disease. Although no specific preventive pharmacological treatments have recommended for NASH, dietary restriction and exercise are recommended. This review focuses on the molecular connections between HCC and NASH, including genetic and risk factors, highlighting the metabolic reprogramming and aberrant epigenetic alterations in the development of HCC in NASH. Current therapeutic aspects of NASH/HCC are also reviewed.

Epidemiological trends of gastrointestinal and liver diseases in Malaysia: A single-center observational study

BACKGROUND AND AIM

The spectrum of gastrointestinal (GI) and liver diseases is recognized to have a geographical variation, which may be due to environmental or genetic differences. We aimed to explore this further in a specialist clinic serving a multi-ethnic Asian urban population.

METHODS

A retrospective analysis of outpatient data from this institution's electronic medical records was conducted between January and June 2019. Clinical diagnoses of GI and liver diseases and associated demographic information were collected.

RESULTS

Data from 3676 adult patients (median age 62 years, female 51.1%) were available for analysis. The frequency of luminal GI, liver and pancreato-biliary diseases were 34.2%, 63.2%, and 2.6%, respectively. Among luminal GI diseases, 38.6% were functional gastrointestinal disorders and 61.4% had an organic cause. A higher proportion of patients of Indian ethnicity were diagnosed with IBD compared with other ethnic groups (India 21.9%, Malay 16.5%, Chinese 12.2%, P = 0.001). Among liver diseases, the most common etiologies were HBV (44.4%) and NAFLD (39.3%). Cirrhosis and/or hepatocellular carcinoma were present in 18% of liver diseases, with NAFLD as the most frequent etiology. Among patients with NAFLD, a higher proportion of ethnic Malays and Indians were evident (Malay 53.8% vs Chinese 28.7% vs Indian 61.1%, P < 0.001). In contrast, a greater proportion of ethnic Chinese were diagnosed with HBV compared with other ethnic groups (Malay 30.9% vs Chinese 57.5% vs Indian 8.4%, P < 0.001).

CONCLUSION

The spectrum of GI and liver diseases has a peculiar epidemiology, particularly with reference to the ethnic predilection of certain diseases.

The genetic interactions between non-alcoholic fatty liver disease and cardiovascular diseases

The ongoing debate on whether non-alcoholic fatty liver disease (NAFLD) is an active contributor or an innocent bystander in the development of cardiovascular disease (CVD) has sparked interests in understanding the common mediators between the two biologically distinct entities. This comprehensive review identifies and curates genetic studies of NAFLD overlapping with CVD, and describes the colinear as well as opposing correlations between genetic associations for the two diseases. Here, CVD described in relation to NAFLD are coronary artery disease, cardiomyopathy and atrial fibrillation. Unique findings of this review included certain NAFLD susceptibility genes that possessed cardioprotective properties. Moreover, the complex interactions of genetic and environmental risk factors shed light on the disparity in genetic influence on NAFLD and its incident CVD. This serves to unravel NAFLD-mediated pathways in order to reduce CVD events, and helps identify targeted treatment strategies, develop polygenic risk scores to improve risk prediction and personalise disease prevention.

Hepatic patatin-like phospholipase domain-containing 3 levels are increased in I148M risk allele carriers and correlate with NAFLD in humans

In nonalcoholic fatty liver disease (NAFLD) the patatin‐like phospholipase domain‐containing 3 (PNPLA3) rs738409 variant is a contributor. In mice, the Pnpla3 148M variant accumulates on lipid droplets and probably leads to sequestration of a lipase cofactor leading to impaired mobilization of triglycerides. To advance our understanding of the localization and abundance of PNPLA3 protein in humans, we used liver biopsies from patients with NAFLD to investigate the link to NAFLD and the PNPLA3 148M genotype. We experimentally qualified an antibody against human PNPLA3. Hepatic PNPLA3 protein fractional area and localization were determined by immunohistochemistry in biopsies from a well‐characterized NAFLD cohort of 67 patients. Potential differences in hepatic PNPLA3 protein levels among patients related to degree of steatosis, lobular inflammation, ballooning, and fibrosis, and PNPLA3 I148M gene variants were assessed. Immunohistochemistry staining in biopsies from patients with NAFLD showed that hepatic PNPLA3 protein was predominantly localized to the membranes of small and large lipid droplets in hepatocytes. PNPLA3 protein levels correlated strongly with steatosis grade (p = 0.000027) and were also significantly higher in patients with lobular inflammation (p = 0.009), ballooning (p = 0.022), and significant fibrosis (stage 2–4, p = 0.014). In addition, PNPLA3 levels were higher in PNPLA3 rs738409 148M (CG, GG) risk allele carriers compared to 148I (CC) nonrisk allele carriers (p = 0.0029). Conclusion: PNPLA3 protein levels were associated with increased hepatic lipid content and disease severity in patients with NAFLD and were higher in PNPLA3 rs738409 (148M) risk allele carriers. Our hypothesis that increased hepatic levels of PNPLA3 may be part of the pathophysiological mechanism of NAFLD is supported.

The National Consensus statement on the management of adult patients with non-alcoholic fatty liver disease and main comorbidities

The National Consensus was prepared with the participation of the National Medical Association for the Study of the Multimorbidity, Russian Scientific Liver Society, Russian Association of Endocrinologists, Russian Association of Gerontologists and Geriatricians, National Society for Preventive Cardiology, Professional Foundation for the Promotion of Medicine Fund PROFMEDFORUM. The aim of the multidisciplinary consensus is a detailed analysis of the course of non-alcoholic fatty liver disease (NAFLD) and the main associated conditions. The definition of NAFLD is given, its prevalence is described, methods for diagnosing its components such as steatosis, inflammation and fibrosis are described. The association of NAFLD with a number of cardio-metabolic diseases (arterial hypertension, atherosclerosis, thrombotic complications, type 2 diabetes mellitus (T2DM), obesity, dyslipidemia, etc.), chronic kidney disease (CKD) and the risk of developing hepatocellular cancer (HCC) were analyzed. The review of non-drug methods of treatment of NAFLD and modern opportunities of pharmacotherapy are presented. The possibilities of new molecules in the treatment of NAFLD are considered: agonists of nuclear receptors, antagonists of pro-inflammatory molecules, etc. The positive properties and disadvantages of currently used drugs (vitamin E, thiazolidinediones, etc.) are described. Special attention is paid to the multi-target ursodeoxycholic acid (UDCA) molecule in the complex treatment of NAFLD as a multifactorial disease. Its anti-inflammatory, anti-oxidant and cytoprotective properties, the ability to reduce steatosis an independent risk factor for the development of cardiovascular pathology, reduce inflammation and hepatic fibrosis through the modulation of autophagy are considered. The ability of UDCA to influence glucose and lipid homeostasis and to have an anticarcinogenic effect has been demonstrated. The Consensus statement has advanced provisions for practitioners to optimize the diagnosis and treatment of NAFLD and related common pathogenetic links of cardio-metabolic diseases.

Heterogeneity of non-alcoholic fatty liver disease: Implications for clinical practice and research activity

Non-alcoholic fatty liver disease (NAFLD) is a heterogeneous condition with a wide spectrum of clinical presentations and natural history and disease severity. There is also substantial inter-individual variation and variable response to a different therapy. This heterogeneity of NAFLD is in turn influenced by various factors primarily demographic/dietary factors, metabolic status, gut microbiome, genetic predisposition together with epigenetic factors. The differential impact of these factors over a variable period of time influences the clinical phenotype and natural history. Failure to address heterogeneity partly explains the sub-optimal response to current and emerging therapies for fatty liver disease. Consequently, leading experts across the globe have recently suggested a change in nomenclature of NAFLD to metabolic-associated fatty liver disease (MAFLD) which can better reflect current knowledge of heterogeneity and does not exclude concomitant factors for fatty liver disease (e.g. alcohol, viral hepatitis, etc.). Precise identification of disease phenotypes is likely to facilitate clinical trial recruitment and expedite translational research for the development of novel and effective therapies for NAFLD/MAFLD.

Research progress, challenges and perspectives on PNPLA3 and its variants in Liver Diseases

The human patatin-like phospholipase domain-containing 3 gene (PNPLA3) is highly expressed in liver and adipose tissue and encodes a transmembrane polypeptide chain containing 481 amino acids. The I148M variant of PNPLA3 is a single nucleotide polymorphism, which is related to a variety of liver and cardiovascular diseases and their complications (such as non-alcoholic fatty liver disease, liver fibrosis, coronary artery disease). This review mainly describes the pathophysiological effects of PNPLA3 and its variants, and their roles in the progression of liver disease and its complications.

Poor Outcomes of Cirrhosis due to Nonalcoholic Steatohepatitis Compared With Hepatitis B After Decompensation With Ascites

INTRODUCTION

Decompensation with ascites portends a poor prognosis in cirrhosis. The aim of this study was to compare the outcomes of patients with nonalcoholic steatohepatitis (NASH) with hepatitis B virus (HBV) cirrhosis after decompensation with ascites.

METHODS

We conducted a retrospective study to evaluate the outcomes of patients with NASH and HBV cirrhosis who were admitted to hospital for first-onset ascites from January 1, 2004, to June 30, 2015. They were followed up until death, liver transplantation, or loss to follow up.

RESULTS

Patients with NASH had lower median (interquartile range) Model for End-Stage Liver Disease score (11 [9-14] vs 14 [11-17], P < 0.001). Over 60 months, patients with NASH cirrhosis had higher cumulative incidence of dilutional hyponatremia (P < 0.001) and refractory ascites (P = 0.028). They also had higher cumulative incidence of cirrhosis-related deaths and liver transplantation compared with HBV cirrhosis (65.7%; [95% confidence interval (CI) 53.6-75.4] vs 42.5% [95% CI 32.4-55.2], P = 0.008). Multivariable competing risk analysis showed that NASH (subdistribution hazard ratio [sHR] 1.88 [95% CI 1.14-3.11], P = 0.014), non-Chinese ethnicity (sHR 1.63 [95% CI 1.06-2.50], P = 0.027), history of hepatocellular carcinoma (sHR 1.76 [95% CI 1.05-2.95], P = 0.033), estimated glomerular filtration rate <60 mL/min/1.73 m2 (sHR 1.70 [95% CI 1.09-2.65], P = 0.020), and Model for End-Stage Liver Disease score ≥15 (sHR 3.26 [95% CI 2.11-5.05], P < 0.001) were independent predictors of poor transplant-free survival.

DISCUSSION

Patients with decompensated cirrhosis due to NASH had much poorer prognosis compared with HBV with more complications and greater healthcare resource utilization. Greater awareness is necessary for early diagnosis of NASH before decompensation.

Association between PNPLA3 rs738409 polymorphism and nonalcoholic fatty liver disease: a systematic review and meta-analysis

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a common disorder that is known to be the leading cause of chronic liver disease worldwide. This study aims to systematically review and meta-analyze the association between PNPLA3 rs738409 polymorphism and non-alcoholic fatty liver.

METHODS

Following a systematic review and meta-analysis method, articles without any time limitation, were extracted from SID, MagIran, IranDoc, Scopus, Embase, Web of Science (WoS), PubMed and ScienceDirect international databases. Random effects model was used for analysis, and heterogeneity of studies was investigated considering the I² index and using Comprehensive Meta-Analysis software.

RESULTS

The odds ratio of CC genotype in patients with non-alcoholic fatty liver demonstrates the protective effect of CC genotype with the ratio of 0.52, whereas CG genotype presents an increasing effect of CG genotype with the ratio of 0.19, and GG genotype also showed an increasing effect of GG genotype with the ratio of 1.05. Moreover, CG + GG genotypes as a single group demostrated an odds rartio of 0.88.

CONCLUSION

This meta-analysis highlights that people with CC genotype has 52% lower chance of developing non-alcoholic fatty liver disease, and those with CG genotype had 19% higher risk of developing non-alcoholic fatty liver. Those with GG genotype were 105% more likely to develop non-alcoholic fatty liver than others. Moreover, those present in a population with CG + GG genotypes were 88% more likely to have non-alcoholic fatty liver disease.

Modest alcohol intake not associated with significant hepatic steatosis or more severe liver disease among patients with diabetes mellitus

BACKGROUND

The effect of modest alcohol intake on prevalence of significant hepatic steatosis and severity of liver disease in patients with type 2 diabetes mellitus (T2DM) is unclear.

METHODS

This is a cross-sectional study on T2DM patients. Modest alcohol intake was defined as alcohol intake ≤ 21 units/week in men and ≤ 14 units/week in women. Significant hepatic steatosis was diagnosed on the basis of controlled attenuation parameter > 263 dB/m, while advanced fibrosis was diagnosed on the basis of liver stiffness measurement ≥ 9.6 kPa using M probe or ≥ 9.3 kPa using XL probe. Patients with liver stiffness measurement ≥ 8.0 kPa were offered liver biopsy.

RESULTS

Five hundred fifty-seven patients underwent transient elastography, and 71 patients underwent liver biopsy. The prevalence of modest drinking was 16.5%. Modest drinking was equally prevalent among ethnic Indians and Chinese at 22.9% and 23.3%, respectively, but uncommon among ethnic Malays at 1.7%. Modest drinkers were more likely to be male, smoked, and had significantly lower glycated hemoglobin, total cholesterol, low-density lipoprotein cholesterol, alkaline phosphatase, and platelet count. There was no significant difference in the prevalence of significant hepatic steatosis or advanced fibrosis based on transient elastography and steatohepatitis or advanced fibrosis between modest drinkers and nondrinkers. The prevalence of significant hepatic steatosis was higher among ethnic Malays and Indians compared with ethnic Chinese, but the Chinese did not have a lower prevalence of more severe liver disease.

CONCLUSION

Modest alcohol intake is not associated with higher prevalence of significant hepatic steatosis or more severe liver disease among patients with T2DM.

Loss-of-function HSD17B13 variants, non-alcoholic steatohepatitis and adverse liver outcomes: Results from a multi-ethnic Asian cohort

Background/Aims

17β-hydroxysteroid dehydrogenase 13 (HSD17B13) variants were recently reported to have significantly lower odds of non-alcoholic fatty liver disease (NAFLD). This is a two-part study that aimed to evaluate the association of HSD17B13 variants with NAFLD and its histological severity, and to identify the association of the variants with clinical outcomes in a cohort of biopsy-proven NAFLD patients.

Methods

Consecutive biopsy-proven NAFLD patients and controls without fatty liver were recruited for this study between 2009 and 2014. Genotyping for HSD17B13 variants was performed using rhAmp assays. A total of 165 patients with NAFLD were monitored up until August 2019. Clinical outcomes were recorded.

Results

HSD17B13 rs72613567 TA allele and rs6834314 G allele were associated with lower odds of non-alcoholic steatohepatitis (NASH) in the overall cohort and among ethnic Chinese, but not among ethnic Malays or Indians (P<0.05). During a mean follow-up of 89 months, 32 patients (19.4%) experienced at least one clinical outcome (cardiovascular events, n=22; liver-related complications, n=6; extra-hepatic malignancy, n=5; and mortality, n=6). The rs72613567 homozygous TA allele and the rs6834314 homozygous G allele were independently associated with a lower incidence of liver-related complications (hazard ratio [HR], 0.004; 95% confidence interval [CI], 0.00–0.64; P=0.033 and HR, 0.01; 95% CI, 0.00–0.97; P=0.048, respectively) and were associated with lower grade of hepatocyte ballooning among the ethnic Chinese.

Conclusion

HSD17B13 rs72613567 and rs6834314 variants were inversely associated with NAFLD and NASH, and were associated with lower incidence of adverse liver outcomes in a cohort of multi-ethnic Asian patients with NAFLD.

Nonalcoholic Fatty Liver Disease: A Global Perspective

The prevalence of nonalcoholic fatty liver disease (NAFLD) has been increasing over the years and is now as high in Asia as in the Western world, so much so that it should no longer be considered a Western disease. In fact, China is expected to have the largest increase in the number of NAFLD cases in the coming years. The increase in prevalence of NAFLD in Asia lags behind that of the Western world; thus, there will be a lag in more severe liver disease in Asia despite a similar prevalence of the disease. NAFLD is more prevalent among patients with diabetes mellitus, which is also an important risk factor for more severe liver disease. Patients with diabetes mellitus thus represent an important target for screening for NAFLD and more severe liver disease. Although the PNPLA3 gene polymorphism is the most studied in NAFLD, it is increasingly clear that the cumulative effect of multiple genes likely predisposes to NAFLD and more severe liver disease in the different ethnic groups, and polygenic risk scores are emerging. Lean NAFLD has been largely reported in Asia but is increasingly recognized worldwide. Multiple risk factors have been identified for the disease that manifests in metabolically unhealthy normal weight individuals; however, it responds to lifestyle intervention, similar to the disease in obese individuals. Lastly, the newer term "metabolic dysfunction-associated fatty liver disease" provides a more accurate reflection of the disease, giving more focus to clinicians and researchers in tackling this increasingly common and challenging disease.

Allele HLA-DQB1*06 reduces fibrosis score in patients with non-alcoholic fatty liver disease

AIM

Human leukocyte antigen (HLA) regions were highlighted as important genetic markers for various liver diseases by hepatology-related genome-wide association studies. Replication studies in non-alcoholic fatty liver disease (NAFLD) are limited and none has investigated the association of HLA alleles with non-alcoholic steatohepatitis (NASH) and other histological characteristics. In the current study, we examined the association of HLA-DQA1 and HLA-DQB1 alleles with NAFLD spectrum and its histological characteristics.

METHODS

Consecutive biopsy-proven NAFLD patients (n = 191) and healthy controls (n = 188) were enrolled and genotyped for HLA-DQA1 and HLA-DQB1 alleles using the sequence-specific oligonucleotide-polymerase chain reaction method.

RESULTS

No association was found between the HLA alleles and NAFLD or NASH in a case-control setting. Nevertheless, among NAFLD patients, the frequency of HLA-DQB1*06 allele was significantly the lowest in NASH with significant fibrosis (10.4%) and approximately similar for NASH without significant fibrosis (22.9%) and NAFL (22.5%) (P = 0.004). It is noteworthy that the association remains significant after correction for multiple comparisons (P_c  = 0.04). Multivariate analysis revealed that HLA-DQB1*06 allele is also associated with fibrosis score (P = 0.001); the result remains significant after correction for multiple comparisons.

CONCLUSION

These findings suggest that HLA-DQB1*06 is associated with lower fibrosis score in NAFLD patients.

Epidemiology of non-alcoholic fatty liver disease in Asia

The growing burden of non-alcoholic fatty liver disease (NAFLD) parallels the increasing prevalence of obesity in Asia. The overall prevalence of NAFLD in Asia is now estimated to be 29.6% and may have surpassed that in Western populations. NAFLD increases with increasing age and is closely associated with metabolic syndrome. Ethnic differences exist in the prevalence of NAFLD, but the underlying factors are unclear. There were initial concerns about lean NAFLD being associated with more severe liver disease and increased mortality, but subsequent studies suggested otherwise. Only some NAFLD patients progress to develop advanced liver fibrosis and cirrhosis, while the liver status remains unchanged in the majority; fibrosis stage is the most important predictor of disease-specific mortality in NAFLD. Surveillance for hepatocellular carcinoma (HCC) remains a challenge due to undiagnosed cirrhosis and the development of HCC in non-cirrhotic NAFLD patients. Diabetes mellitus shares a bidirectional relationship with NAFLD; NAFLD is highly prevalent among patients with diabetes mellitus, and diabetes mellitus is associated with more severe NAFLD. Chronic hepatitis B (CHB) is a major cause of chronic liver disease in Asia; NAFLD and CHB are increasingly observed together because of the increasing prevalence of NAFLD. Despite studies reporting favorable virologic outcome in CHB patients with NAFLD, NAFLD has been found to be independently associated with fibrosis progression and poorer prognosis in CHB patients. Therefore, NAFLD in CHB patients should be given more attention.

The effect of PNPLA3 polymorphism as gain in function mutation in the pathogenesis of non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is often associated with metabolic syndrome (type 2 diabetes, hypertension, hypertriglyceridemia, insulin resistance, and obesity). NAFLD is multi-factorial in pathogenesis with some genetic predisposition. The variant patatin-like phospholipase domain-containing protein 3 (PNPLA3) is known to be an independent risk factor for hepatocellular cancer (HCC). The aim of this study was to investigate the role of PNPLA3 polymorphism as the risk factor for NAFLD.

METHODOLOGY

Patients had histological, ultrasonographic, biopsy evidence of NAFLD (n=248) and 81 controls were studied for PNPLA3 polymorphism. PNPLA3 genotyping was done from peripheral blood DNA by real-time polymerase chain reaction (RT-PCR).

RESULTS

PNPLA3 genotyping of the groups NAFLD (CC [n = 76], CG [n = 83], GG [n = 89]) and control (CC [n= 42], CG [n = 22], GG [n = 17]) was determined. In the patient group, the G allele was 261 (52.63%) and the C allele was 235 (47.37%), whereas in the control group, the G allele was 56 (34.54%) and the C allele was 106 (65.43%). In our study, 53 out of 174 women had GG allele and 54 out of 155 men had GG allele.

CONCLUSION

The findings suggest that there is a predominant relationship between men with PNPLA3 I148M variant with NAFLD in women. Patients with NAFLD carrying PNPLA3 rs738409 G>C variant are at higher risk of NAFLD.

Association of rs780094 polymorphism of glucokinase regulatory protein with non-alcoholic fatty liver disease

OBJECTIVE

GCK rs780094 polymorphism is a single nucleotide polymorphism that has been associated with obesity, type II diabetes and dyslipidemia in some populations, conditions that highly related to NAFL etiology. The present study aimed to evaluate the relationship between NAFLD and rs780094 polymorphism in patients with NAFLD in Tabriz city, northwest of Iran. The rs780094 polymorphism was determined in 74 patients with NAFLD by PCR-RFLP technique. Demographic information was collected using a questionnaire and biochemical analysis was performed using standard laboratory methods.

RESULTS

There was a significant difference between case and control subjects for alanine aminotransferase, aspartate aminotransferase, HDL-C and triglycerides (P < 0.05). Analysis by PCR-RFLP method revealed that there were no significant differences between NAFLD and healthy subjects for rs780094 polymorphism in the study population. The results of this study indicated that rs780094 polymorphism is not associated with NAFLD in subjects from Tabriz city.

PNPLA3-A Potential Therapeutic Target for Personalized Treatment of Chronic Liver Disease

Patatin-like phospholipase domain-containing protein 3 (PNPLA3) is a lipid droplet-associated protein that has been shown to have hydrolase activity toward triglycerides and retinyl esters. The first evidence of PNPLA3 being associated with fatty liver disease was revealed by a genome-wide association study (GWAS) of Hispanic, African American, and European American individuals in the Dallas Heart Study back in 2008. Since then, numerous GWAS reports have shown that PNPLA3 rs738409[G] (148M) variant is associated with hepatic triglyceride accumulation (steatosis), inflammation, fibrosis, cirrhosis, and even hepatocellular carcinoma regardless of etiologies including alcohol- or obesity-related and others. The frequency of PNPLA3(148M) variant ranges from 17% in African Americans, 23% in European Americans, to 49% in Hispanics in the Dallas Heart Study. Due to high prevalence of obesity and alcohol consumption in modern societies, the PNPLA3(148M) gene variant and environment interaction poses a serious concern for public health, especially chronic liver diseases including alcohol-related liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD). Therefore, PNPLA3(148M) variant is a potential therapeutic target for chronic liver disease in the rs738409 allele carriers. Currently, there is no approved drug specifically targeting the PNPLA3(148M) variant yet. With additional mechanistic studies, novel therapeutic strategies are expected to be developed for the treatment of the PNPLA3(148M) variant-associated chronic liver diseases in the near future.

Epidemiological differences of common liver conditions between Asia and the West

Liver diseases form a heterogenous group of acute and chronic disorders of varying etiologies. Not only do they result in significant morbidity and mortality, but they also lead to a marked reduction in quality of life, together with a high socioeconomic burden globally. A better understanding of their global distribution is necessary to curb the massive health-care and socioeconomic burden that they entail. Notable differences and similarities have been described between common liver disease conditions occurring in Asia and the West (Europe and North America), giving rise to the need for an updated collective appraisal of this subject. In this review, the epidemiological differences of common liver conditions, specifically acute liver failure, drug-induced liver injury, acute-on-chronic liver failure, hepatocellular carcinoma, and non-alcoholic fatty liver disease, between Asia and the West are discussed.

High frequency of the PNPLA3 rs738409 [G] single-nucleotide polymorphism in Hmong individuals as a potential basis for a predisposition to chronic liver disease

BACKGROUND

An exploratory study was performed to determine the prevalence of the patatin-like phospholipase domain-containing protein 3 (PNPLA3) rs78409 [G] allele among the Hmong as a risk factor for nonalcoholic fatty liver disease (NAFLD). NAFLD/nonalcoholic steatohepatitis is the world's most common chronic liver disease and is expected to replace viral hepatitis as the leading cause of cirrhosis and potential precursor to hepatocellular carcinoma (HCC). Of all populations in California, the Hmong experience the highest risk of death from HCC and the highest prevalence of metabolic syndrome risk factors among Asians that predispose them to NAFLD. Here a genetic explanation was sought for the high rates of chronic liver disease among the Hmong. The literature pointed to the PNPLA3 rs738409 [G] allele as a potential genetic culprit.

METHODS

Cell-free DNA was isolated from 26 serum samples previously collected in community settings. Quantitative polymerase chain reaction-based single-nucleotide polymorphism (SNP) genotyping was performed with a validated TaqMan SNP genotyping assay, and results were analyzed with TaqMan Genotyper software.

RESULTS

The PNPLA3 rs738409 [C>G] variant occurred at a frequency of 0.46 (12 of 26; 95% confidence interval, 0.27-0.67). This carrier rate would rank the Hmong as the third highest population in the 1000 Genomes Project.

CONCLUSIONS

Although this small sample size limits the generalizability, the high frequency rates of this allele along with the presence of metabolic syndrome risk factors warrant further studies into the etiology of NAFLD among the Hmong. Cancer 2018;124:1583-9. © 2018 American Cancer Society.

Quantitative digital pathology reveals association of cell-specific PNPLA3 transcription with NAFLD disease activity

Background & Aims

The I148M variant (rs738409) in patatin-like phospholipase domain-containing protein 3 (PNPLA3) is by far the most important genetic determinant of non-alcoholic fatty liver disease (NAFLD). However, in the context of NAFLD, the transcriptional regulation of PNPLA3 in human liver cells is not known. In this study, we aimed to define the relationship between PNPLA3 transcription and disease characteristics of human NAFLD.

Methods

The abundance of PNPLA3 and collagen 1α (COL1α) transcripts was quantified in situ at single-cell resolution using RNAscope® in 87 patients with NAFLD. We examined the association of PNPLA3 and COL1α transcript levels with NAFLD disease severity, defined by histology.

Results

While the majority of PNPLA3 transcripts were found in hepatocytes, approximately 7% of PNPLA3-positive cells co-express COL1α, representing activated myofibroblasts. There is no association between the rs738409 genotype and the level of PNPLA3 transcript. The overall PNPLA3 transcript abundance is lower in zone 1 hepatocytes, patients with higher body mass index, and those with advanced liver fibrosis. The negative association between the PNPLA3 transcript levels and liver fibrosis is largely driven by COL1α-positive cells. A significant proportion of PNPLA3 mRNA is seen in the nucleus. The cytoplasmic-to-nuclear PNPLA3 mRNA ratio is inversely associated with NAFLD disease activity.

Conclusions

PNPLA3 transcript abundance and nuclear-to-cytoplasmic translocation are negatively associated with hepatic steatosis and NAFLD disease activity, while its abundance in activated myofibroblasts is inversely associated with the stage of liver fibrosis.

Lay summary

A genetic variant in patatin-like phospholipase domain-containing protein 3 (or PNPLA3) is the most important genetic determinant of non-alcoholic fatty liver disease (NAFLD). However, it is not known how transcriptional regulation of the PNPLA3 gene contributes to the disease characteristics of human NAFLD. Herein, we show that the mRNA levels of PNPLA3, particularly in the cytoplasm, are negatively associated with the severity of NAFLD in humans.

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Relationships between PNPLA3 transcription and the severity of human non-alcoholic fatty liver disease was unknown.

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PNPLA3 transcript abundance is negatively associated with hepatic steatosis and non-alcoholic fatty liver disease activity.

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Nuclear-to-cytoplasmic translocation of PNPLA3 is also negatively associated with non-alcoholic fatty liver disease severity.

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PNPLA3 transcript abundance in activated myofibroblasts is inversely associated with the stage of liver fibrosis.

Association between PNPLA3 rs738409 polymorphism and nonalcoholic fatty liver disease (NAFLD) susceptibility and severity: A meta-analysis

OBJECTIVE

This meta-analysis is to investigate the relationship between the patatin-like phospholipase domain containing 3 (PNPLA3) rs738409 polymorphism and the susceptibility and severity of nonalcoholic fatty liver disease (NAFLD).

METHODS

Chinese Journal Full-text Database, Wanfang Database, VIP Database, and PubMed Database were subjected to case-control study retrieving, from January 2008 to December 2014. Following key words were used: fatty liver, PNPLA3, and rs738409 gene or variants or polymorphism or alleles. Meta-analysis was performed based on the retrieved articles.

RESULTS

In total 65 studies were first retrieved according to the key words, and finally 21 studies with 14,266 subjects were included. Meta-analysis showed that PNPLA3 rs738409 polymorphism exerted strong influence not only on fatty liver but also on the histological injury. PNPLA3 rs738409 [G] allele was a risk factor for NAFLD (GG vs CC, OR = 4.01, 95% CI 2.93-5.49; GC vs CC, OR = 1.88, 95% CI 1.58-2.24). PNPLA3 gene variant was significantly associated with the increased serum alanine aminotransferase (ALT) levels (GG vs CC, standardized mean difference  = 0.47, 95% CI 0.14-0.81). In addition, nonalcoholic steatohepatitis (NASH) was more frequently observed in G allele carriers (GG vs CC, OR = 3.24, 95% CI 2.79-3.76; GC vs CC, OR = 2.14, 95% CI 1.43-3.19).

CONCLUSION

PNPLA3 rs738409 polymorphism is not only a factor significantly associated with the susceptibility of NAFLD, but also related to the susceptibility of aggressive diseases.

Association between non-alcoholic fatty liver disease evaluated by transient elastography with extracranial carotid atherosclerosis in a multiethnic Asian community

Background and Aim

There is not much data on the association between non‐alcoholic fatty liver disease (NAFLD) and advanced fibrosis assessed using Fibroscan with carotid intima‐media thickness (CIMT) in the general population. The objective of this study was to evaluate the association between NAFLD and advanced fibrosis, as diagnosed by Fibroscan, with an increased CIMT in the Malaysian population.

Methods

A cross‐sectional study of government officers and their family members attending a health screening at a public healthcare facility was conducted. All subjects underwent clinical evaluation, biochemical testing, anthropometry, ultrasound carotid Doppler, and Fibroscan examination.

Results

Data for 251 subjects were analyzed (mean age 47.1 ± 12.4 years, 74.1% male). Prevalence of NAFLD and advanced fibrosis were 57.4 and 17.5%, respectively. Independent factors associated with NAFLD were waist circumference (odds ratio [OR] = 1.077, 95% confidence interval [CI] 1.038–1.118, P < 0.001) and serum alanine aminotransferase (ALT) (OR = 1.039, 95% CI 1.005–1.074, P = 0.024). Independent factors associated with advanced fibrosis were male gender (OR = 4.847, 95% CI 1.369–17.155, P = 0.014) and serum aspartate aminotransferase (AST) (OR = 1.057, 95% CI 1.003–1.113, P = 0.036). Prevalence of increased CIMT was 29.0%. Independent factor associated with increased CIMT was older age (OR = 1.146, 95% CI 1.067–1.231, P < 0.001). Of the subjects, 34.5% with NAFLD had increased CIMT compared to 19.1% of the subjects without NAFLD (P = 0.063). Advanced fibrosis was not associated with increased CIMT.

Conclusions

Prevalence of NAFLD, advanced liver fibrosis, and increased CIMT were high. NAFLD and advanced liver fibrosis appeared not to be associated with increased CIMT. However, a larger sample size is needed to demonstrate whether there is any association.

PNPLA3 rs738409 Polymorphism Predicts Development and Severity of Hepatic Steatosis but Not Metabolic Syndrome in Celiac Disease

Metabolic syndrome (MS) and hepatic steatosis (HS) have been described in patients with celiac disease (CD) after starting a gluten-free diet (GFD), but data on predictive factors for these conditions are scarce. Recently, the patatin-like phospholipase domain-containing protein 3 (PNPLA3) rs738409 has been identified as a key factor for HS development in the general population. The aim of the study was to evaluate the role of PNPLA3 rs738409 in the development of MS and HS in CD patients after starting GFD. Between June 2014 and September 2016, we consecutively enrolled CD patients with HS, while those without steatosis served as a control group. All patients underwent anthropometric and serologic investigations, ultrasonography (US) to assess the degree and severity of HS, and genotyping of the PNPLA3 rs738409 polymorphism. Finally, 370 subjects were enrolled (136 with and 234 without HS). At genotyping assays, the CC genotype was found in 194 subjects (52.4%), the CG genotype in 138 subjects (37.3%), and the GG genotype in 38 subjects (10.2%). At binary logistic regression, only CG and GG alleles were predictive for the development of HS (odds ratio (OR) 1.97; p < 0.01 for CG and OR 6.9; p < 0.001 for GG). Body mass index (BMI) (OR 3.8; p < 0.001) and waist circumference (OR 2.8; p = 0.03) at CD diagnosis were the only independent factors for the development of MS. Intergroup comparisons showed that the severe grade of HS was more frequently observed in GG than in CC carriers (74% vs. 11.3%, p < 0.001, OR 21.8). PNPLA3 CG and GG carriers with CD have a higher susceptibility to hepatic steatosis, but not to metabolic syndrome. Moreover, patients with GG alleles display more severe forms of HS based on ultrasound.

Risk Factors for the Development of Nonalcoholic Fatty Liver Disease/Nonalcoholic Steatohepatitis, Including Genetics

Nonalcoholic fatty liver disease is emerging as the most common cause of chronic liver disease worldwide. This trend is, in part, secondary, to the growing incidence of obesity, type 2 diabetes, and metabolic syndrome. Other risk factors include age, gender, race/ethnicity, genetic predisposition, and polycystic ovarian disease. With the introduction of genome-wide association studies, genetic mutations contributing to inherited susceptibility to steatosis have been identified, which hold keys to future improvement in diagnosis and management. This article expands on the aforementioned risk factors and summarizes the current available data on genetic and environmental factors associated with this common entity.

Risk estimation model for nonalcoholic fatty liver disease in the Japanese using multiple genetic markers

The genetic factors affecting the natural history of nonalcoholic fatty liver disease (NAFLD), including the development of nonalcoholic steatohepatitis (NASH) and NASH-derived hepatocellular carcinoma (NASH-HCC), are still unknown. In the current study, we sought to identify genetic factors related to the development of NAFLD, NASH, and NASH-HCC, and to establish risk-estimation models for them. For these purposes, 936 histologically proven NAFLD patients were recruited, and genome-wide association (GWA) studies were conducted for 902, including 476 NASH and 58 NASH-HCC patients, against 7,672 general-population controls. Risk estimations for NAFLD and NASH were then performed using the SNPs identified as having significant associations in the GWA studies. We found that rs2896019 in PNPLA3 [p = 2.3x10^-31, OR (95%CI) = 1.85 (1.67–2.05)], rs1260326 in GCKR [p = 9.6x10^-10, OR (95%CI) = 1.38(1.25–1.53)], and rs4808199 in GATAD2A [p = 2.3x10^-8, OR (95%CI) = 1.37 (1.23–1.53)] were significantly associated with NAFLD. Notably, the number of risk alleles in PNPLA3 and GATAD2A was much higher in Matteoni type 4 (NASH) patients than in type 1, type 2, and type 3 NAFLD patients. In addition, we newly identified rs17007417 in DYSF [p = 5.2x10^-7, OR (95%CI) = 2.74 (1.84–4.06)] as a SNP associated with NASH-HCC. Rs641738 in TMC4, which showed association with NAFLD in patients of European descent, was not replicated in our study (p = 0.73), although the complicated LD pattern in the region suggests the necessity for further investigation. The genetic variants of PNPLA3, GCKR, and GATAD2A were then used to estimate the risk for NAFLD. The obtained Polygenic Risk Scores showed that the risk for NAFLD increased with the accumulation of risk alleles [AUC (95%CI) = 0.65 (0.63–0.67)]. Conclusions: We demonstrated that NASH is genetically and clinically different from the other NAFLD subgroups. We also established risk-estimation models for NAFLD and NASH using multiple genetic markers. These models can be used to improve the accuracy of NAFLD diagnosis and to guide treatment decisions for patients.

Genetic variants in COL13A1, ADIPOQ and SAMM50, in addition to the PNPLA3 gene, confer susceptibility to elevated transaminase levels in an admixed Mexican population

Non-alcoholic fatty liver disease (NAFLD) is the accumulation of extra fat in liver cells not caused by alcohol. Elevated transaminase levels are common indicators of liver disease, including NAFLD. Previously, we demonstrated that PNPLA3 (rs738409), LYPLAL1 (rs12137855), PPP1R3B (rs4240624), and GCKR (rs780094) are associated with elevated transaminase levels in overweight/obese Mexican adults. We investigated the association between 288 SNPs identified in genome-wide association studies and risk of elevated transaminase levels in an admixed Mexican-Mestizo sample of 178 cases of NAFLD and 454 healthy controls. The rs2896019, rs12483959, and rs3810622 SNPs in PNPLA3 and rs1227756 in COL13A1 were associated with elevated alanine aminotransferase (ALT, ≥40IU/L). A polygenic risk score (PRS) based on six SNPs in the ADIPOQ, COL13A1, PNPLA3, and SAMM50 genes was also associated with elevated ALT. Individuals carrying 9-12 risk alleles had 65.8% and 48.5% higher ALT and aspartate aminotransferase (AST) levels, respectively, than those with 1-4 risk alleles. The PRS showed the greatest risk of elevated ALT levels, with a higher level of significance than the individual variants. Our findings suggest a significant association between variants in COL13A1, ADIPOQ, SAMM50, and PNPLA3, and risk of NAFLD/elevated transaminase levels in Mexican adults with an admixed ancestry. This is the first study to examine high-density single nucleotide screening for genetic variations in a Mexican-Mestizo population. The extent of the effect of these variations on the development and progression of NAFLD in Latino populations requires further analysis.

Pathogenesis of NASH: How Metabolic Complications of Overnutrition Favour Lipotoxicity and Pro-Inflammatory Fatty Liver Disease

Overnutrition, usually with obesity and genetic predisposition, lead to insulin resistance, which is an invariable accompaniment of nonalcoholic fatty liver disease (NAFLD). The associated metabolic abnormalities, pre- or established diabetes, hypertension and atherogenic dyslipidemia (clustered as metabolic syndrome) tend to be worse for nonalcoholic steatohepatitis (NASH), revealing it as part of a continuum of metabolic pathogenesis. The origins of hepatocellular injury and lobular inflammation which distinguish NASH from simple steatosis have intrigued investigators, but it is now widely accepted that NASH results from liver lipotoxicity. The key issue is not the quantity of liver fat but the type(s) of lipid molecules that accumulate, and how they are "packaged" to avoid subcellular injury. Possible lipotoxic mediators include free (unesterified) cholesterol, saturated free fatty acids, diacylglycerols, lysophosphatidyl-choline, sphingolipids and ceramide. Lipid droplets are intracellular storage organelles for non-structural lipid whose regulation is influenced by genetic polymorphisms, such as PNPLA3. Cells unable to sequester chemically reactive lipid molecules undergo mitochondrial injury, endoplasmic reticulum (ER) stress and autophagy, all processes of interest for NASH pathogenesis. Lipotoxicity kills hepatocytes by apoptosis, a highly regulated, non-inflammatory form of cell death, but also by necrosis, necroptosis and pyroptosis; the latter involve mitochondrial injury, oxidative stress, activation of c-Jun N-terminal kinase (JNK) and release of danger-associated molecular patterns (DAMPs). DAMPs stimulate innate immunity by binding pattern recognition receptors, such as Toll-like receptor 4 (TLR4) and the NOD-like receptor protein 3 (NLRP3) inflammasome, which release a cascade of pro-inflammatory chemokines and cytokines. Thus, lipotoxic hepatocellular injury attracts inflammatory cells, particularly activated macrophages which surround ballooned hepatocytes as crown-like structures. In both experimental and human NASH, livers contain cholesterol crystals which are a second signal for NLRP3 activation; this causes interleukin (IL)-1β and IL18 secretion to attract and activate macrophages and neutrophils. Injured hepatocytes also liberate plasma membrane-derived extracellular vesicles; these have been shown to circulate in NASH and to be pro-inflammatory. The way metabolic dysfunction leads to lipotoxicity, innate immune responses and the resultant pattern of cellular inflammation in the liver are likely also relevant to hepatic fibrogenesis and hepatocarcinogenesis. Pinpointing the key molecules involved pharmacologically should eventually lead to effective pharmacotherapy against NASH.

PNPLA3 expression and its impact on the liver: current perspectives

A single-nucleotide polymorphism occurring in the sequence of the human patatin-like phospholipase domain-containing 3 gene (PNPLA3), known as I148M variant, is one of the best characterized and deeply investigated variants in several clinical scenarios, because of its tight correlation with increased risk for developing hepatic steatosis and more aggressive part of the disease spectrum, such as nonalcoholic steatohepatitis, advanced fibrosis and cirrhosis. Further, the I148M variant is positively associated with alcoholic liver diseases, chronic hepatitis C-related cirrhosis and hepatocellular carcinoma. The native gene encodes for a protein that has not yet a fully defined role in liver lipid metabolism and, according to recent observations, seems to be divergently regulated among distinct liver cells type, such as hepatic stellate cells. Therefore, the aim of this review is to collect the latest data regarding PNPLA3 expression in human liver and to analyze the impact of its genetic variant in human hepatic pathologies. Moreover, a description of the current biochemical and metabolic data pertaining to PNPLA3 function in both animal models and in vitro studies is summarized to allow a better understanding of the relevant pathophysiological role of this enzyme in the progression of hepatic diseases.

Association of single nucleotide polymorphism at PNPLA3 with fatty liver, steatohepatitis, and cirrhosis of liver

BACKGROUND/PURPOSE

The aim of this study was to determine the association of single nucleotide polymorphism (SNP) in patatin-like phospholipase domain-containing 3 (PNPLA3) at I148 with histological severity of non-alcoholic fatty liver disease (NAFLD).

METHODS

Patients were selected for the study if they had histological evidence of NAFLD and clinical evidence of non-alcoholic steatohepatits (NASH) cirrhosis. We included 50 NASH cirrhosis, 99 patients of NAFLD including 36 non-NASH fatty liver (NNFL) along with 63 NASH and 75 healthy controls. PNPLA3 genotyping was done by real-time PCR using a Taqman assay for rs738409.

RESULTS

CC, CG, and GG frequencies were 45 (60.0%)/27 (36.0%)/3 (4.0%) in healthy control, 19 (52.8%)/14 (38.9%)/ 3 (8.3%) in NNFL, 18 (28.6%)/29 (46.0%)/16 (25.4%) in NASH, and 7 (14.6%), 25 (52.1%), 16 (33.3%) in cirrhosis. The frequency of G allele was significantly higher (62.6%) in NAFLD than in healthy control. The GG genotype had 20.25 times odds of NAFLD. The GG genotype had 6.53 times odds of having NASH. HOMA-IR > 1.6 had 3.81 times odds of having NASH. Regression analysis revealed that G allele odds of having cirrhosis was 3.9 times compared to C. The G allele was also significantly associated with steatosis, lobular inflammation, NAFLD activity score, and fibrosis.

CONCLUSION

PNPLA3 genotype showed an association with NAFLD, NASH, fibrosis, and cirrhosis.

Nonalcoholic fatty liver disease in Asia: emerging perspectives

As in the West, nonalcoholic fatty liver disease (NAFLD) is the commonest chronic liver disease in Asia, with a prevalence higher than 40 % in some countries. The risk factors for NAFLD development are similar to those in Western countries, including increased body mass index, diabetes, insulin resistance, and metabolic syndrome. NAFLD in Asians is associated with different extrahepatic manifestations involving the cardiovascular, gastrointestinal, and renal systems. A considerable proportion of Asians with NAFLD are described as having "lean" NAFLD. Present in approximately 20 % of the Asian population, lean NAFLD is closely linked with insulin resistance, diabetes, and other metabolic complications, but its association with disease progression to nonalcoholic steatohepatitis and cirrhosis remains to be defined. There is emerging evidence of the interactions of NAFLD with hepatitis B virus and hepatitis C virus infection in Asia. Unlike in Western countries, NAFLD constitutes only a minority of cirrhosis and hepatocellular carcinoma cases in Asia. Possible explanations are the lower prevalence of obesity and the overwhelming problem of viral hepatitis in Asia. With aging of the obesity cohort in Asia, NAFLD-related liver complications are expected to increase.

PNPLA3 as a Genetic Determinant of Risk for and Severity of Non-alcoholic Fatty Liver Disease Spectrum

Background and Aims:Patatin-like phospholipase domain protein 3 (PNPLA3) polymorphisms (rs738409 C>G) are associated with non-alcoholic fatty liver disease (NAFLD). We performed a systematic review and meta-analysis to examine the association of PNPLA3 polymorphisms with the spectrum and severity of this disease. Methods: Studies evaluating the association between the PNPLA3 polymorphism spectrum (fatty liver, steatohepatitis, cirrhosis, and hepatocellular carcinoma) and NAFLD were included. Pooled data are reported as odds ratios (ORs) with 95% confidence intervals. Results: Of 393 potentially relevant studies, 35 on NAFLD were included in the analysis. Compared to healthy controls, the pooled ORs for rs738409 CG and GG compared to CC among patients with non-alcoholic fatty liver (NAFL) were 1.46 (1.16-1.85) and 2.76 (2.30-3.13), and were 1.75 (1.24-2.46) and 4.44 (2.92-6.76) among patients with non-alcoholic steatohepatitis respectively. The respective ORs for CG and GG compared to the CC genotype were 2.35 (0.90-6.13) and 5.05 (1.47-17.29) when comparing non-alcoholic hepatocellular carcinoma to NAFL patients. Among the NAFLD patients, the ORs for G allele frequency when comparing steatosis grade 2-3 to grade 0-1 NAFL, when comparing the NAFLD activity score of ≥ 4 to score ≤ 3, when comparing NASH to NAFLD, when comparing the presence of lobular inflammation to absence, and when comparing the presence of hepatocyte ballooning to absence were 2.33 (1.43-3.80), 1.80 (1.36-2.37), 1.66 (1.42-1.94), 1.58 (1.19-2.10), and 2.63 (1.87-3.69) respectively. Subgroup analysis based on ethnicity showed similar results. Conclusions:PNPLA3 polymorphisms have strong association with the risk for and severity of NAFLDs. PNPLA3 polymorphism plays an evolving role in diagnosis and treatment decisions in patients with NAFLD.

The role of mitochondrial genomics in patients with non-alcoholic steatohepatitis (NASH)

Background

Visceral obesity and metabolic syndrome are commonly associated with non-alcoholic fatty liver disease (NAFLD). The progression of steatosis to NASH depends on a number of metabolic and patient-related factors. The mechanisms of genetic predisposition towards the development of NASH and related fibrosis remain unclear. In this study, our aim was to utilize mitotyping and identify mitochondrial haplotypes that may be associated with NAFLD.

Methods

We examined mitochondrial haplotypes along with patatin-like phospholipase domain containing 3 (PNPLA3) rs738409 genotype to determine their association with NAFLD phenotypes. Whole blood samples were obtained from 341 patients (BMI > 35) undergoing weight reduction surgery after written consent. Liver biopsies were centrally reviewed by a single pathologist based on predetermined pathologic protocol (41.9 % Non-NASH NAFLD, 30.4 % NASH, 27.5 % controls). A 1,122 bp of the mitochondrial control loop was sequenced for each sample and classified into haplogroups.

Results

The presence of haplogroup L exhibits protection against the development of NASH and pericellular fibrosis. The alleles of PNPLA3 locus showed differential distribution in cohorts with NAFLD, NASH and pericellular fibrosis. Heterozygosity at this locus is independently associated with higher risk of having NASH and pericellular fibrosis.

Conclusion

Mitochondrial genetics play an important role in NASH probably by modulation of oxidative stress and the efficiency of oxidative phosphorylation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-016-0324-0) contains supplementary material, which is available to authorized users.

PNPLA3 Expression Is Related to Liver Steatosis in Morbidly Obese Women with Non-Alcoholic Fatty Liver Disease

Recent reports suggest a role for the Patatin-like phospholipase domain-containing protein 3 (PNPLA3) in the pathology of non-alcoholic fatty liver disease (NAFLD). Lipid deposition in the liver seems to be a critical process in the pathogenesis of NAFLD. The aim of the present work was to evaluate the association between the liver PNPLA3 expression, key genes of lipid metabolism, and the presence of NAFLD in morbidly obese women. We used real-time polymerase chain reaction (PCR) analysis to analyze the hepatic expression of PNPLA3 and lipid metabolism-related genes in 55 morbidly obese subjects with normal liver histology (NL, n = 18), simple steatosis (SS, n = 20), and non-alcoholic steatohepatitis (NASH, n = 17). Liver biopsies were collected during bariatric surgery. We observed that liver PNPLA3 expression was increased in NAFLD than in NL. It was also upregulated in SS than in NL. Interestingly, we found that the expression of PNPLA3 was significantly higher in severe than mild SS group. In addition, the expression of the transcription factors LXRα, PPARα, and SREBP2 was positively correlated with PNPLA3 liver expression. Regarding rs738409 polymorphism, GG genotype was positive correlated with the presence of NASH. In conclusion, our results show that PNPLA3 could be related to lipid accumulation in liver, mainly in the development and progression of simple steatosis.

TM6SF2 E167K Variant, a Novel Genetic Susceptibility Variant, Contributing to Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is one of the most common causes of liver dysfunction worldwide, and its prevalence is highly associated with genetic susceptibility. The transmembrane 6 superfamily member 2 (TM6SF2) E167K variant represents a general genetic determinant of hepatic triglyceride content and lobular inflammation, and its presence appears to be directly involved in the pathogenesis and development of NAFLD. Although this variant appears to be a novel powerful modifier in the development of NAFLD, whether it is associated with an increased risk of NAFLD-related liver fibrosis and hepatocellular carcinoma (HCC) remains to be determined. The aim of this review is to describe the functions of the TM6SF2 E167K variant and its association with NAFLD, with particular emphasis on the underlying mechanisms of its role in the development and progression of NAFLD. Additionally, the links between the TM6SF2 E167K variant and NAFLD-related liver fibrosis and HCC will be discussed.

Hepatocyte X-box binding protein 1 deficiency increases liver injury in mice fed a high-fat/sugar diet

Fatty liver is associated with endoplasmic reticulum stress and activation of the hepatic unfolded protein response (UPR). Reduced hepatic expression of the UPR regulator X-box binding protein 1 spliced (XBP1s) is associated with human nonalcoholic steatohepatitis (NASH), and feeding mice a high-fat diet with fructose/sucrose causes progressive, fibrosing steatohepatitis. This study examines the role of XBP1 in nonalcoholic fatty liver injury and fatty acid-induced cell injury. Hepatocyte-specific Xbp1-deficient (Xbp1(-/-)) mice were fed a high-fat/sugar (HFS) diet for up to 16 wk. HFS-fed Xbp1(-/-) mice exhibited higher serum alanine aminotransferase levels compared with Xbp1(fl/fl) controls. RNA sequencing and Gene Ontogeny pathway analysis of hepatic mRNA revealed that apoptotic process, inflammatory response, and extracellular matrix structural constituent pathways had enhanced activation in HFS-fed Xbp1(-/-) mice. Liver histology demonstrated enhanced injury and fibrosis but less steatosis in the HFS-fed Xbp1(-/-) mice. Hepatic Col1a1 and Tgfβ1 gene expression, as well as Chop and phosphorylated JNK (p-JNK), were increased in Xbp1(-/-) compared with Xbp1(fl/fl) mice after HFS feeding. In vitro, stable XBP1-knockdown Huh7 cells (Huh7-KD) and scramble control cells (Huh7-SCR) were generated and treated with palmitic acid (PA) for 24 h. PA-treated Huh7-KD cells had increased cytotoxicity measured by lactate dehydrogenase release, apoptotic nuclei, and caspase3/7 activity assays compared with Huh7-SCR cells. CHOP and p-JNK expression was also increased in Huh7-KD cells following PA treatment. In conclusion, loss of XBP1 enhances injury in both in vivo and in vitro models of fatty liver injury. We speculate that hepatic XBP1 plays an important protective role in pathogenesis of NASH.

Vitamin E reduces liver stiffness in nonalcoholic fatty liver disease

AIM: To evaluate the efficacy of vitamin E treatment on liver stiffness in nonalcoholic fatty liver disease (NAFLD).

METHODS: Thirty-eight NAFLD patients were administered vitamin E for > 1 year. The doses of vitamin E were 150, 300, or 600 mg; three times per day after each meal. Responses were assessed by liver enzyme levels [aspartate aminotransferase (AST), alanine aminotranferease (ALT), and γ-glutamyl transpeptidase (γ-GTP)], noninvasive scoring systems of hepatic fibrosis-4 [FIB-4 index and aspartate aminotransferase-to-platelet index (APRI)], and liver stiffness [velocity of shear wave (Vs)] measured by acoustic radiation force impulse elastography. Vs measurements were performed at baseline and 12 mo after baseline. The patients were genotyped for the patatin-like phospholipase domain containing 3 (PNPLA3) polymorphisms and then divided into either the CC/CG or GG group to examine each group’s responses to vitamin E treatment.

RESULTS: We found marked differences in the platelet count, serum albumin levels, alkaline phosphatase levels, FIB-4 index, APRI, and Vs at baseline depending on the PNPLA3 polymorphism. AST, ALT, and γ-GTP levels (all P < 0.001); FIB-4 index (P = 0.035); APRI (P < 0.001); and Vs (P < 0.001) significantly decreased from baseline to 12 mo in the analysis of all patients. In the subset analyses of PNPLA3 genotypes, AST levels (P = 0.011), ALT levels (P < 0.001), γ-GTP levels (P = 0.005), APRI (P = 0.036), and Vs (P = 0.029) in genotype GG patients significantly improved, and AST and ALT levels (both P < 0.001), γ-GTP levels (P = 0.003), FIB-4 index (P = 0.017), and APRI (P < 0.001) in genotype CC/CG patients.

CONCLUSION: One year of vitamin E treatment improved noninvasive fibrosis scores and liver stiffness in NAFLD patients. The responses were similar between different PNPLA3 genotypes.

Molecular mechanisms of fatty liver in obesity

Nonalcoholic fatty liver disease (NAFLD) covers a spectrum of liver disorders ranging from simple steatosis to advanced pathologies, including nonalcoholic steatohepatitis and cirrhosis. NAFLD significantly contributes to morbidity and mortality in developed societies. Insulin resistance associated with central obesity is the major cause of hepatic steatosis, which is characterized by excessive accumulation of triglyceride-rich lipid droplets in the liver. Accumulating evidence supports that dysregulation of adipose lipolysis and liver de novo lipogenesis (DNL) plays a key role in driving hepatic steatosis. In this work, we reviewed the molecular mechanisms responsible for enhanced adipose lipolysis and increased hepatic DNL that lead to hepatic lipid accumulation in the context of obesity. Delineation of these mechanisms holds promise for developing novel avenues against NAFLD.

The SRE Motif in the Human PNPLA3 Promoter (-97 to -88 bp) Mediates Transactivational Effects of SREBP-1c

Patatin-like phospholipase domain containing 3 (PNPLA3) is a non-secreted protein primarily expressed in liver and adipose tissue. Recently, numerous genetic studies have shown that PNPLA3 is a major susceptibility gene for nonalcoholic fatty liver disease (NAFLD). However, the mechanism involved in transcriptional regulation of the PNPLA3 gene remains unknown. We performed a detailed analysis of the human PNPLA3 gene promoter and identified two novel cis-acting elements (SRE and NFY binding motifs) located at -97/-88 and -26/-22 bp, respectively. Overexpression of SREBP-1c in HepG2 cells significantly increased PNPLA3 promoter activity. Mutation of either of the putative SRE or NFY binding motifs blocked the transactivation effects of SREBP-1c on the promoter. Overexpression of SREBP-1c and NFY together increased PNPLA3 promoter activity twice as much as that of SREBP-1c or NFY expression alone. This result suggests that SREBP-1c and NFY synergistically transactivate the human PNPLA3 gene. The ability of SREBP-1c and NFY to bind these cis-elements was confirmed using gel shift analysis. Putative SRE and NFY motifs also mediated synergistic insulin-induced transactivation of the PNPLA3 promoter in HepG2 cells. Additionally, the ability of SREBP-1c to bind to the PNPLA3 promoter was increased by insulin in a dose-dependent manner. Moreover, the treatment of HepG2 cells with the PI3K inhibitor LY294002 led to reduced insulin promoter-activating ability accompanied by a decrease in PNPLA3 and SREBP-1c protein expression. These results demonstrate that SREBP-1c is a direct activator of the human PNPLA3 gene and insulin transactivates the PNPLA3 gene via the PI3K-SREBP-1c/NFY pathway in HepG2 cells.

Targeted-bisulfite sequence analysis of the methylation of CpG islands in genes encoding PNPLA3, SAMM50, and PARVB of patients with non-alcoholic fatty liver disease

BACKGROUND & AIMS

The pathogenesis of non-alcoholic fatty liver disease (NAFLD) is affected by epigenetic factors as well as by genetic variation.

METHODS

We performed targeted-bisulfite sequencing to determine the levels of DNA methylation of 4 CpG islands (CpG99, CpG71, CpG26, and CpG101) in the regulatory regions of PNPLA3, SAMM50, PARVB variant 1, and PARVB variant 2, respectively. We compared the levels of methylation of DNA in the livers of the first and second sets of patients with mild (fibrosis stages 0 and 1) or advanced (fibrosis stages 2 to 4) NAFLD and in those of patients with mild (F0 to F2) or advanced (F3 and F4) chronic hepatitis C infection. The hepatic mRNA levels of PNPLA3, SAMM50, and PARVB were measured using qPCR.

RESULTS

CpG26, which resides in the regulatory region of PARVB variant 1, was markedly hypomethylated in the livers of patients with advanced NAFLD. Conversely, CpG99 in the regulatory region of PNPLA3 was substantially hypermethylated in these patients. These differences in DNA methylation were replicated in a second set of patients with NAFLD or chronic hepatitis C. PNPLA3 mRNA levels in the liver of the same section of a biopsy specimen used for genomic DNA preparation were lower in patients with advanced NAFLD compared with those with mild NAFLD and correlated inversely with CpG99 methylation in liver DNA. Moreover, the levels of CpG99 methylation and PNPLA3 mRNA were affected by the rs738409 genotype.

CONCLUSIONS

Hypomethylation of CpG26 and hypermethylation of CpG99 may contribute to the severity of fibrosis in patients with NAFLD or chronic hepatitis C infection.