Circulating triacylglycerol signatures and insulin sensitivity in NAFLD associated with the E167K variant in TM6SF2

PLD2 is a marker for MASLD-HCC with early-stage fibrosis: revealed by lipidomic and gene expression analysis

INTRODUCTION

Metabolic steatotic liver disease (MASLD) can progress to hepatocellular carcinoma (HCC). 25% of MASLD-HCCs occur in the absence of fibrosis.

OBJECTIVES

This study aimed to explore lipid metabolic pathways through "omics" and to identify biomarkers of MASLD-HCC based on the degree of fibrosis.

METHODS

Our cohort included 79 pairs of MASLD-HCC tumor tissues (TT) and adjacent non-tumor human liver tissues (NTT), which were divided into two groups according to fibrosis degree (F0F2 n = 45 and F3F4 n = 34). Lipidomic analysis (n = 52) using liquid chromatography high-resolution mass spectrometry (LC-HRMS/MS) and gene expression analysis (n = 79) using RT-qPCR were performed. For each group, TT was compared with NTT. Five healthy liver tissues were used as calibrators in gene expression analysis.

RESULTS

Using LC-HRMS/MS, 130 lipids were putatively annotated, 30 of which showed a significant difference between TT and NTT. In MASLD-HCC-F0F2, ceramide levels decreased. While sphingomyelin, most phosphatidylcholine and phosphatidylethanolamine species were increased. In contrast, in MASLD-HCC-F3F4, most lipid contents decreased. Based on lipidomic data, a panel of 18 genes related to lipid metabolism was analyzed. The expression of six genes, ACAT2, DGAT2, ACOX1, CHKA, PLD1, and PLD2, was exclusively upregulated in MASLD-HCC-F0F2. Taken together, these data support the existence of two MASLD-HCC lipid metabolic phenotypes, according to the degree of fibrosis.

CONCLUSION

In conclusion, our results allow: (1) discriminate two phenotypes of MASLD-HCC according to fibrosis level; (2) propose PLD as a potential drug target for MASLD-HCC-F0F2 patients, and suggest that PLD inhibitor could be evaluated in combination with immunotherapy treatment.

Molecular Regulation and Therapeutic Targeting of VLDL Production in Cardiometabolic Disease

There exists a complex relationship between steatotic liver disease (SLD) and atherosclerotic cardiovascular disease (CVD). CVD is a leading cause of morbidity and mortality among individuals with SLD, particularly those with metabolic dysfunction-associated SLD (MASLD), a significant proportion of whom also exhibit features of insulin resistance. Recent evidence supports an expanded role of very low-density lipoprotein (VLDL) in the pathogenesis of CVD in patients, both with and without associated metabolic dysfunction. VLDL represents the major vehicle for exporting neutral lipid from hepatocytes, with each particle containing one molecule of apolipoproteinB100 (APOB100). VLDL production becomes dysregulated under conditions characteristic of MASLD including steatosis and insulin resistance. Insulin resistance not only affects VLDL production but also mediates the pathogenesis of atherosclerotic CVD. VLDL assembly and secretion therefore represents an important pathway in the setting of cardiometabolic disease and offers several candidates for therapeutic targeting, particularly in metabolically complex patients with MASLD at increased risk of atherosclerotic CVD. Here we review the clinical significance as well as the translational and therapeutic potential of key regulatory steps impacting VLDL initiation, maturation, secretion, catabolism, and clearance.

Opportunities and barriers in omics-based biomarker discovery for steatotic liver diseases

The rising prevalence of liver diseases related to obesity and excessive use of alcohol is fuelling an increasing demand for accurate biomarkers aimed at community screening, diagnosis of steatohepatitis and significant fibrosis, monitoring, prognostication and prediction of treatment efficacy. Breakthroughs in omics methodologies and the power of bioinformatics have created an excellent opportunity to apply technological advances to clinical needs, for instance in the development of precision biomarkers for personalised medicine. Via omics technologies, biological processes from the genes to circulating protein, as well as the microbiome - including bacteria, viruses and fungi, can be investigated on an axis. However, there are important barriers to omics-based biomarker discovery and validation, including the use of semi-quantitative measurements from untargeted platforms, which may exhibit high analytical, inter- and intra-individual variance. Standardising methods and the need to validate them across diverse populations presents a challenge, partly due to disease complexity and the dynamic nature of biomarker expression at different disease stages. Lack of validity causes lost opportunities when studies fail to provide the knowledge needed for regulatory approvals, all of which contributes to a delayed translation of these discoveries into clinical practice. While no omics-based biomarkers have matured to clinical implementation, the extent of data generated has enabled the hypothesis-free discovery of a plethora of candidate biomarkers that warrant further validation. To explore the many opportunities of omics technologies, hepatologists need detailed knowledge of commonalities and differences between the various omics layers, and both the barriers to and advantages of these approaches.

Basic and translational evidence supporting the role of TM6SF2 in VLDL metabolism

PURPOSE OF REVIEW

Transmembrane 6 superfamily member 2 ( TM6SF2 ) gene was identified through exome-wide studies in 2014. A genetic variant from glutamic acid to lysine substitution at amino acid position 167 (NM_001001524.3:c.499G> A) (p.Gln167Lys/p.E167K, rs58542926) was discovered (p.E167K) to be highly associated with increased hepatic fat content and reduced levels of plasma triglycerides and LDL cholesterol. In this review, we focus on the discovery of TM6SF2 and its role in VLDL secretion pathways. Human data suggest TM6SF2 is linked to hepatic steatosis and cardiovascular disease (CVD), hence understanding its metabolic pathways is of high scientific interest.

RECENT FINDINGS

Since its discovery, completed research studies in cell, rodent and human models have defined the role of TM6SF2 and its links to human disease. TM6SF2 resides in the endoplasmic reticulum (ER) and the ER-Golgi interface and helps with the lipidation of nascent VLDL, the main carrier of triglycerides from the liver to the periphery. Consistent results from cells and rodents indicated that the secretion of triglycerides is reduced in carriers of the p.E167K variant or when hepatic TM6SF2 is deleted. However, data for secretion of APOB, the main protein of VLDL particles responsible for triglycerides transport, are inconsistent.

SUMMARY

The identification of genetic variants that are highly associated with human disease presentation should be followed by the validation and investigation into the pathways that regulate disease mechanisms. In this review, we highlight the role of TM6SF2 and its role in processing of liver triglycerides.

Exploring the impact of lipid droplets on the evolution and progress of hepatocarcinoma

Over the past 10 years, the biological role of lipid droplets (LDs) has gained significant attention in the context of both physiological and pathological conditions. Considerable progress has been made in elucidating key aspects of these organelles, yet much remains to be accomplished to fully comprehend the myriad functions they serve in the progression of hepatic tumors. Our current perception is that LDs are complex and active structures managed by a distinct set of cellular processes. This understanding represents a significant paradigm shift from earlier perspectives. In this review, we aim to recapitulate the function of LDs within the liver, highlighting their pivotal role in the pathogenesis of metabolic dysfunction-associated steatotic liver disease (MASLD) (Hsu and Loomba, 2024) and their contribution to the progression towards more advanced pathological stages up to hepatocellular carcinoma (HC) (Farese and Walther, 2009). We are aware of the molecular complexity and changes occurring in the neoplastic evolution of the liver. Our attempt, however, is to summarize the most important and recent roles of LDs across both healthy and all pathological liver states, up to hepatocarcinoma. For more detailed insights, we direct readers to some of the many excellent reviews already available in the literature (Gluchowski et al., 2017; Hu et al., 2020; Seebacher et al., 2020; Paul et al., 2022).

Hepatic glucose metabolism in the steatotic liver

The liver is central in regulating glucose homeostasis, being the major contributor to endogenous glucose production and the greatest reserve of glucose as glycogen. It is both a target and regulator of the action of glucoregulatory hormones. Hepatic metabolic functions are altered in and contribute to the highly prevalent steatotic liver disease (SLD), including metabolic dysfunction-associated SLD (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH). In this Review, we describe the dysregulation of hepatic glucose metabolism in MASLD and MASH and associated metabolic comorbidities, and how advances in techniques and models for the assessment of hepatic glucose fluxes in vivo have led to the identification of the mechanisms related to the alterations in glucose metabolism in MASLD and comorbidities. These fluxes can ultimately increase hepatic glucose production concomitantly with fat accumulation and alterations in the secretion and action of glucoregulatory hormones. No pharmacological treatment has yet been approved for MASLD or MASH, but some antihyperglycaemic drugs approved for treating type 2 diabetes have shown positive effects on hepatic glucose metabolism and hepatosteatosis. A deep understanding of how MASLD affects glucose metabolic fluxes and glucoregulatory hormones might assist in the early identification of at-risk individuals and the use or development of targeted therapies.

Management of cardiovascular risk in patients with metabolic dysfunction-associated steatotic liver disease

The novel term Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is proposed to replace non-alcoholic fatty liver disease (NAFLD) to highlight the close association with the metabolic syndrome. MASLD encompasses patients with liver steatosis and at least one of five cardiometabolic risk factors which implies that these patients are at increased risk of cardiovascular disease (CVD). Indeed, the prevalence of CVD in MASLD patients is increased and CVD is recognized as the most common cause of death in MASLD patients. We here present an update on the pathophysiology of CVD in MASLD, discuss the risk factors, and suggest screening for CVD in patients with MASLD. Currently, there is no FDA-approved pharmacological treatment for MASLD, and no specific treatment recommended for CVD in patients with MASLD. Thus, the treatment strategy is based on weight loss and a reduction and treatment of CVD risk factors. We recommend screening of MASLD patients for CVD using the SCORE2 system with guidance to specific treatment algorithms. In all patients with CVD risk factors, lifestyle intervention to induce weight loss through diet and exercise is recommended. Especially a Mediterranean diet may improve hyperlipidemia and if further treatment is needed, statins should be used as first-line treatment. Further, anti-hypertensive drugs should be used to treat hypertension. With the epidemic of obesity and type 2 diabetes mellitus (T2DM) the risk of MASLD and CVD is expected to increase, and preventive measures, screening, and effective treatments are highly needed to reduce morbidity and mortality in MASLD patients.

Unraveling the pathogenesis of non-alcoholic fatty liver diseases through genome-wide association studies

Non-alcoholic fatty liver disease (NAFLD) is a significant health burden around the world, affecting approximately 25% of the population. Recent advances in human genetic databases have allowed for the identification of various single nucleotide polymorphisms associated with NAFLD-related traits. Investigating the functions of these genetic factors provides insight into the pathogenesis of NAFLD and potentially identifies novel therapeutic targets for NAFLD. In this review, we summarized current research on genes with NAFLD-associated mutations, highlighting phospholipid remodeling and spatially clustered loci as common pathological and genetic features of these mutations. These features suggest a complex yet intriguing mechanism of dissociated steatosis and insulin resistance, which is observed in a subset of patients and may lead to more precise therapy against NAFLD in the future.

Effects of TM6SF2 rs58542926 polymorphism on hepatocellular lipids and insulin resistance in early type 2 diabetes

BACKGROUND AND AIMS

Increased hepatocellular lipid content (HCL) is linked to insulin resistance, risk of type 2 diabetes and related complications. Conversely, a single-nucleotide polymorphism (TM6SF2EK; rs58542926) in the transmembrane 6 superfamily member 2-gene has been associated with nonalcoholic fatty liver disease (NAFLD), but lower cardiovascular risk. This case-control study tested the role of this polymorphism for tissue-specific insulin sensitivity during early course of diabetes.

METHODS AND RESULTS

Males with recent-onset type 2 diabetes with (TM6SF2EK: n = 16) or without (TM6SF2EE: n = 16) the heterozygous TM6SF2-polymorphism of similar age and body mass index, underwent Botnia-clamps with [6,6-2H2]glucose to measure whole-body-, hepatic- and adipose tissue-insulin sensitivity. HCL was assessed with 1H-magnetic-resonance-spectroscopy. A subset of both groups (n = 24) was re-evaluated after 5 years. Despite doubled HCL, TM6SF2EK had similar hepatic- and adipose tissue-insulin sensitivity and 27% higher whole-body-insulin sensitivity than TM6SF2EE. After 5 years, whole-body-insulin sensitivity, HCL were similar between groups, while adipose tissue-insulin sensitivity decreased by 87% and 55% within both groups and circulating triacylglycerol increased in TM6SF2EE only.

CONCLUSIONS

The TM6SF2-polymorphism rs58542926 dissociates HCL from insulin resistance in recent-onset type 2 diabetes, which is attenuated by disease duration. This suggests that diabetes-related metabolic alterations dominate over effects of the TM6SF2-polymorphism during early course of diabetes and 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.

Concise review of lipidomics in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) encompasses simple liver steatosis, nonalcoholic steatohepatitis (NASH), and liver fibrosis that can progress to cirrhosis. NAFLD has become the principal cause of chronic liver disease in many parts of the world. Lipidomic studies, by allowing to determine concentrations of lipid classes and fatty acid composition of different lipid species, have been of great interest to help understand NAFLD pathophysiology and potentially identify novel biomarkers for diagnosis and prognosis. Indeed, lipidomic data give information on qualitative lipid abnormalities associated with NAFLD. The aim of our article was to create a comprehensive and more synthetic review of main results from lipidomic studies in NAFLD. Literature was searched for all human lipidomic studies evaluating plasma samples of individuals with NAFLD. Results were regrouped by the degree of liver damage, either simple steatosis, NASH or liver fibrosis, and presented by lipid categories. Overall, we summarized the main lipidomic abnormalities associated with NAFLD as follows: modification of free fatty acid distribution, increase in ceramides, reduced phosphatidylcholine / phosphatidylethanolamine ratio, and increase in eicosanoids. These lipid abnormalities are likely to promote NASH and liver fibrosis by inducing mitochondrial dysfunction, apoptosis, inflammation, oxidation, and endoplasmic reticulum stress. Although these lipidomic abnormalities are consistently reported in many studies, further research is needed to clarify whether they may be predictive for liver steatosis, NASH or liver fibrosis.

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.

Molecular Screening via Sanger Sequencing of the Genetic Variants in Non-Alcoholic Fatty Liver Disease Subjects in the Saudi Population: A Hospital-Based Study

Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases, along with steatosis and non-alcoholic steatohepatitis (NASH), and is associated with cirrhosis and hepatocellular carcinoma. Candidate gene and genome-wide association studies have validated the relationships between NAFLD, NASH, PNPLA3, TM6SF2, and HFE. The present study utilized five polymorphisms in three genes: PNPLA3 (I148M and K434E) TM6SF2 (E167K), and HFE (H63D and C282Y), based on undocumented case−control studies in the Saudi Arabian population. A total of 95 patients with NAFLD and 78 non-NAFLD subjects were recruited. Genomic DNA was isolated, and polymerase chain reaction and Sanger sequencing were performed using specific primers for the I148M, K434E, E167K, H63D, and C282Y. NAFLD subjects were older when compared to controls and showed the significant association (p = 0.0001). Non-significant association was found between gender (p = 0.26). However, both weight and BMI were found to be associated. Hardy−Weinberg equilibrium analysis confirmed that H63D, I148M, and K434E polymorphisms were associated. Genotype analysis showed only K434E variant was associated with NAFLD and non-NAFLD (OR-2.16; 95% CI: 1.08−4.31; p = 0.02). However, other polymorphisms performed with NAFLD and NASH were not associated (p > 0.05), and similar analysis was found when ANOVA was performed (p > 0.05). In conclusion, we confirmed that K434E polymorphism showed a positive association in the Saudi population.

Dissecting causal relationships between nonalcoholic fatty liver disease proxied by chronically elevated alanine transaminase levels and 34 extrahepatic diseases

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is prevalent worldwide and is associated with the risk of many extrahepatic diseases. However, whether NAFLD is a risk marker or a common cause of extrahepatic diseases is unclear.

METHODS

We searched PubMed to identify NAFLD-related extrahepatic diseases. Genetic instrumental variables (IVs) for NAFLD surrogated by chronically elevated alanine transaminase levels and eligible extrahepatic diseases were retrieved from the corresponding genome-wide association analysis. We proposed a procedure for Mendelian randomization (MR) analysis and performed validation analyses to dissect the association between NAFLD and extrahepatic diseases. The Bonferroni method was used to correct the bias of multiple testing.

RESULTS

In total, 34 extrahepatic diseases were included and 54 SNPs were used as IVs for NAFLD. The MR analysis gave a robust and significant (or suggestive) estimate for the association between NAFLD and 9 extrahepatic diseases: type 2 diabetes (odds ratio [OR] = 1.182, 95 % confidence interval [CI] 1.125-1.243, P = 5.40 × 10^-11), cholelithiasis (OR = 1.171, 95%CI 1.083-1.266, P = 7.47 × 10^-5), diabetic hypoglycemia (OR = 1.170, 95%CI 1.071-1.279, P = 5.14 × 10^-4), myocardial infarction (OR = 1.122, 95%CI 1.057-1.190, P = 1.46 × 10^-4), hypertension (OR = 1.060, 95%CI 1.029-1.093, P = 1.18 × 10^-4), coronary artery disease (OR = 1.052, 95%CI 1.010-1.097, P = 1.58 × 10^-2), heart failure (OR = 1.047, 95%CI 1.006-1.090, P = 2.44 × 10^-2), dementia (OR = 0.881, 95%CI 0.806-0.962, P = 5.01 × 10^-3), and pancreatic cancer (OR = 0.802, 95%CI 0.654-0.983, P = 3.32 × 10^-2). Validation analyses using IVs from biopsy-confirmed and imaging-determined NAFLD reported similar results to the main analysis. For the remaining 25 outcomes, no significant or definitive association was yielded in MR analysis.

CONCLUSIONS

Genetic evidence suggests putative causal relationships between NAFLD and a set of extrahepatic diseases, indicating that NAFLD deserves high priority in clinical practice.

Clinical outcome of non-alcoholic fatty liver disease: an 11-year follow-up study

OBJECTIVES

To clarify non-alcoholic fatty liver disease (NAFLD) prevalence, risk factors and clinical outcome in an exemplary Chinese population, a cohort of company employees was followed up for 11 years.

DESIGN

Retrospective cohort study.

SETTING

Between 2006 and 2016 in Ning bo, China.

PARTICIPANTS

13 032 company employees.

RESULTS

Over 11 years, the prevalence of NAFLD increased from 17.2% to 32.4% (men 20.5%-37% vs women 9.8%-22.2%). Male peak prevalence was between 40 and 60 years of age, whereas highest prevalence in women was at an age of 60 years and older. Logistic and Cox regression revealed 16 risk factors, including body mass index (BMI), albumin, white blood cell, triglycerides (TG), high-density lipoprotein, glutamyl transpeptidase, alanine transaminase, creatinine, urea acid, glucose, systolic blood pressure, diastolic blood pressure, blood sedimentation, haemoglobin, platelet and apolipoprotein B2 (p<0.05 for all factors). The area under the curve of these variables for NAFLD is 0.88. However, cause-effect analyses showed that only BMI, gender and TG directly contributed to NAFLD development. Over an 11-year follow-up period, 12.6%, 37.7% and 14.2% of male patients with NAFLD and 11.6%, 44.7% and 22.6% of female patients with NAFLD developed diabetes, hypertension and hyperuricaemia, respectively. Except one male patient who developed cirrhosis, no patients with NAFLD progressed into severe liver disease.

CONCLUSION

Diabetes, hypertension and hyperuricaemia are the main clinical outcomes of NAFLD. Eleven years of NAFLD are not sufficient to cause severe liver disease. Age and obesity are direct risk factors for NAFLD. BMI, gender and TG are three parameters directly reflecting the occurrence of NAFLD.

TM6SF2: A Novel Genetic Player in Nonalcoholic Fatty Liver and Cardiovascular Disease

Transmembrane 6 superfamily member 2 (TM6SF2) is located on chromosome 19 (19p12) and encodes for a protein of undetermined function. Genetic studies have reported the association between a nonsynonymous variant in TM6SF2 (E167K, rs58542926) with hepatic triglyceride content and its impact on the cardiovascular system. Clinical and epidemiological studies have confirmed the role of TM6SF2 in the development of nonalcoholic fatty liver disease (NAFLD). Recently, TM6SF2 was also shown to play an important role in promoting hepatic fibrosis and hepatocellular cancer in mouse models. This review aims to capture the physiological role of TM6SF2 in the regulation of lipid metabolism and its involvement in cardiometabolic diseases.

Research progress on the relationship between TM6SF2 rs58542926 polymorphism and non-alcoholic fatty liver disease

INTRODUCTION

nonalcoholic fatty liver disease is a common liver disease with a global average prevalence of about 25%. In addition to the incidence of NAFLD being related to obesity, diabetes, hyperlipidemia, etc., genetic factors also have an important impact on the incidence of NAFLD.

AREAS COVERED

Current experimental results and clinical studies show that the transmembrane 6 superfamily member 2 (TM6SF2) gene plays an important role in the pathogenesis of NAFLD. The research on genetic polymorphism of TM6SF2 gene mainly focuses on rs58542926 locus (rs58542926 c.449 C > T, p. Glu167Lys, E167K). The Mutations of this site might increase the risk of NAFLD in carriers.

EXPERT OPINION

The mutation of this site causes the disorder of triglyceride metabolism in the liver, which leads to the deposition of a large amount of lipids in the liver, and further induces the incidence of NAFLD. With the study of the mechanism of TM6SF2 gene polymorphism in the pathogenesis of NAFLD, it is helpful to understand the molecular mechanism of the pathogenesis of NAFLD, which has a great value for the treatment of NAFLD.

PNPLA3 is the dominant SNP linked to liver disease severity at time of first referral to a tertiary center

BACKGROUND

Single nucleotide polymorphisms (SNPs) in genes including PNPLA3, TM6SF2, HSD17B13 and SERPINA1 have been identified as risk modifiers of progression in chronic liver disease (CLD). However, it is unclear whether genotyping for these risk variants is useful in clinical routine.

METHODS

Liver disease severity was assessed by liver stiffness measurement (LSM) and by presence of clinical manifestations of advanced-chronic liver disease (ACLD) in 779 consecutive CLD patients at the time of referral to a tertiary center. The associations of risk variants with CLD severity were calculated individually and in a combined model using a polygenic risk-score.

RESULTS

Non-alcoholic fatty liver disease (NAFLD) was the most common etiology (n = 511, 65.6%), and ACLD was present in 217 (27.9%) patients. The PNPLA3-G-allele remained independently associated with higher LSM (adjusted-B: 2.508 [95%CI: 0.887-4.130], P = 0.002) or the presence of ACLD (aOR: 1.562 [95%CI: 1.097-2.226], P = 0.013). SERPINA1-Z-allele was also independently associated with LSM (adjusted-B: 4.558 [95%CI: 1.182-7.934], P = 0.008), while the other risk alleles did not attain statistical significance. Combining these risk alleles into a polygenic risk-score was significantly associated with LSM (adjusted-B: 0.948 [95%CI: 0.153-1.743], P = 0.020).

CONCLUSION

PNPLA3 risk-variants are linked to liver disease severity at the time of first referral to an outpatient hepatology clinic.

TM6SF2 rs58542926 is related to hepatic steatosis, fibrosis and serum lipids both in adults and children: A meta-analysis

BACKGROUND AND AIMS

Findings about the associations between transmembrane 6 superfamily member 2 (TM6SF2) rs58542926 and nonalcoholic fatty liver disease have not been consistently replicated, particularly in steatosis and fibrosis. The present study aimed to investigate the associations between the rs58542926T allele and the spectrum of NAFLD and its related metabolic phenotypes.

METHODS

Systematic literature research was performed to analyse the associations between rs58542926 and the spectrum of NAFLD and its related metabolic phenotypes. A random effects meta-analysis with a dominant genetic model was applied.

RESULTS

Data from 123,800 individuals across 44 studies were included in the current meta-analysis.rs58542926 T allele was associated with an increased risk of NAFLD in both adults (OR=1.62; 95% CI: 1.40, 1.86) and children (OR=2.87; 95% CI: 1.85, 4.46). Children had a stronger association with NAFLD (P=0.01). rs58542926 T allele was also positively associated with steatosis progression (mean difference=0.22; 95% CI: 0.05, 0.39) and fibrosis stage (OR=1.50; 95% CI: 1.20, 1.88) in adults. The TM6SF2 rs58542926 T allele was positively associated with ALT in both adults and children (both P<0.01) and only with higher AST in adults (P<0.01). The rs58542926 T allele was negatively associated with serum total cholesterol (TC), low-density lipoprotein (LDL), and triglycerides (TGs) in both adults and children (all P<0.01).The serum level of TG was much lower in adults than in children (P<0.01).

CONCLUSION

TM6SF2 rs58542926 is involved in the entire spectrum of NAFLD and its related metabolic phenotype, and differences in serum lipid levels were observed between adults and children.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42021288163.

Metabolomics and lipidomics in NAFLD: biomarkers and non-invasive diagnostic tests

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide and is often associated with aspects of metabolic syndrome. Despite its prevalence and the importance of early diagnosis, there is a lack of robustly validated biomarkers for diagnosis, prognosis and monitoring of disease progression in response to a given treatment. In this Review, we provide an overview of the contribution of metabolomics and lipidomics in clinical studies to identify biomarkers associated with NAFLD and nonalcoholic steatohepatitis (NASH). In addition, we highlight the key metabolic pathways in NAFLD and NASH that have been identified by metabolomics and lipidomics approaches and could potentially be used as biomarkers for non-invasive diagnostic tests. Overall, the studies demonstrated alterations in amino acid metabolism and several aspects of lipid metabolism including circulating fatty acids, triglycerides, phospholipids and bile acids. Although we report several studies that identified potential biomarkers, few have been validated.

Relationships among N,N-dimethylformamide exposure, CYP2E1 and TM6SF2 genes, and non-alcoholic fatty liver disease

OBJECTIVE

This study aimed to examine the relationships among N, N-dimethylformamide (DMF) exposure, cytochrome P4502E1 (CYP2E1) single nucleotide polymorphisms (SNPs) (rs2031920, rs3813867, rs6413432), transmembrane 6 superfamily member 2 (TM6SF2) SNP rs58542926 and non-alcoholic fatty liver disease (NAFLD).

METHODS

Baseline data were collected from participants who were then followed for 5 years in a prospective cohort study. The cohort initially consisted of 802 workers and ultimately included 660 people, all of whom underwent annual occupational health examinations from 2010 to 2015.

RESULTS

The above-threshold group (≥7.3 mg/m³ adjusted relative risk (RR)= 3.620, 95%CI 2.072-6.325) was significantly more likely to develop NAFLD than the below-threshold group (<7.3 mg/m³). The TM6SF2 SNP rs58542926 CT (adjusted RR=3.921, 95% CI 2.329-6.600, P = 0.000) and CT+TT (adjusted RR=4.385, 95% CI 2.639-7.287, P = 0.000) genotypes were risk factors for NAFLD, as compared with the TM6SF2 rs58542926 CC genotype. Each dose group (below-threshold group and above-threshold group) interacting with the genotype of TM6SF2 SNP rs58542926 had an adjusted RR from 7.764 (95% CI 3.272-18.420, P = 0.000) to 24.022 (95% CI 8.971-64.328, P = 0.000). The T allele of rs58542926 in the TM6SF2 gene may be a risk factor for susceptibility to DMF-induced NAFLD.

CONCLUSION

Polymorphisms of TM6SF2 SNP rs58542926 may play an important role in susceptibility to NAFLD after exposure to DMF.

Machine Learning-Based Identification of Potentially Novel Non-Alcoholic Fatty Liver Disease Biomarkers

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease that presents a great challenge for treatment and prevention.. This study aims to implement a machine learning approach that employs such datasets to identify potential biomarker targets. We developed a pipeline to identify potential biomarkers for NAFLD that includes five major processes, namely, a pre-processing step, a feature selection and a generation of a random forest model and, finally, a downstream feature analysis and a provision of a potential biological interpretation. The pre-processing step includes data normalising and variable extraction accompanied by appropriate annotations. A feature selection based on a differential gene expression analysis is then conducted to identify significant features and then employ them to generate a random forest model whose performance is assessed based on a receiver operating characteristic curve. Next, the features are subjected to a downstream analysis, such as univariate analysis, a pathway enrichment analysis, a network analysis and a generation of correlation plots, boxplots and heatmaps. Once the results are obtained, the biological interpretation and the literature validation is conducted over the identified features and results. We applied this pipeline to transcriptomics and lipidomic datasets and concluded that the C4BPA gene could play a role in the development of NAFLD. The activation of the complement pathway, due to the downregulation of the C4BPA gene, leads to an increase in triglyceride content, which might further render the lipid metabolism. This approach identified the C4BPA gene, an inhibitor of the complement pathway, as a potential biomarker for the development of NAFLD.

Main Risk Factors of Type 2 Diabetes Mellitus with Nonalcoholic Fatty Liver Disease and Hepatocellular Carcinoma

Type 2 diabetes mellitus (T2DM) with nonalcoholic fatty liver disease (NAFLD) is a pathological metabolic disease characterized by high ketone lipid based on abnormal lipid metabolism. Compared with patients with single T2DM or NAFLD, T2DM complicated with NAFLD has more complicated pathogenic factors and pathological processes. Hepatocellular carcinoma (HCC), the leading malignancy arising from cirrhosis, is the second most lethal cancer globally. The purpose of this study was to clarify the main risk factors of T2DM with NAFLD and HCC. There are many challenges in the diagnosis and treatment of T2DM patients with NAFLD and HCC. The current gold standard is to adjust treatment strategy, optimize metabolic control, and improve liver phenotype. It is necessary to identify further the risk factors driving the progression of T2DM with NAFLD and HCC and evaluate new therapeutic targets, in addition to exploring the syndromic forms of T2DM combined with NAFLD and providing a theoretical basis for early prevention, diagnosis, and treatment of the disease using traditional Chinese medicine (TCM).

Perturbation of TM6SF2 Expression Alters Lipid Metabolism in a Human Liver Cell Line

Non-alcoholic fatty liver disease (NAFLD) is caused by excess lipid accumulation in hepatocytes. Genome-wide association studies have identified a strong association of NAFLD with non-synonymous E167K amino acid mutation in the transmembrane 6 superfamily member 2 (TM6SF2) protein. The E167K mutation reduces TM6SF2 stability, and its carriers display increased hepatic lipids and lower serum triglycerides. However, the effects of TM6SF2 on hepatic lipid metabolism are not completely understood. We overexpressed wild-type or E167K variant of TM6SF2 or knocked down TM6SF2 expression in lipid-treated Huh-7 cells and used untargeted lipidomic analysis, RNAseq transcriptome analysis, and fluorescent imaging to determine changes in hepatic lipid metabolism. Both TM6SF2 knockdown and E167K overexpression increased hepatic lipid accumulation, while wild-type overexpression decreased acylglyceride levels. We also observed lipid chain remodeling for acylglycerides by TM6SF2 knockdown, leading to a relative increase in species with shorter, more saturated side chains. RNA-sequencing revealed differential expression of several lipid metabolizing genes, including genes belonging to AKR1 family and lipases, primarily in cells with TM6SF2 knockdown. Taken together, our data show that overexpression of TM6SF2 gene or its loss-of-function changes hepatic lipid species composition and expression of lipid metabolizing genes. Additionally, our data further confirms a loss-of-function effect for the E167K variant.

Lipid Droplet-Associated Factors, PNPLA3, TM6SF2, and HSD17B Proteins in Hepatopancreatobiliary Cancer

Simple Summary

Aberrant lipid synthesis and reprogrammed lipid metabolism are both associated with the development and progression of pancreatic and liver cancer. Most cells store fatty acids in the form of triacylglycerols in lipid droplets. Lipid droplets are intracellular organelles that not only store neutral lipids, but also play roles as molecular messengers and signaling factors. Some cancer cells accumulate massive amount of lipid droplets. Lipid droplets and lipid droplet-associated factors are further implicated to mediate proliferation, invasion, metastasis, as well as chemotherapy resistance in several types of cancer. This review dissected recent findings on the role of several lipid droplet-associated factors, patatin-like phospholipase domain-containing 3 (PNPLA3), Transmembrane 6 superfamily member 2 (TM6SF2), and 17β-hydroxysteroid dehydrogenase (HSD17B) 11 and 13 as well as their genetic variations in hepatopancreatobiliary diseases, especially cancer.

Abstract

Pancreatic and liver cancer are leading causes of cancer deaths, and by 2030, they are projected to become the second and the third deadliest cancer respectively. Cancer metabolism, especially lipid metabolism, plays an important role in progression and metastasis of many types of cancer, including pancreatic and liver cancer. Lipid droplets are intracellular organelles that store neutral lipids, but also act as molecular messengers, and signaling factors. It is becoming increasingly evident that alterations in the regulation of lipid droplets and their associated factors influence the risk of developing not only metabolic disease but also fibrosis and cancer. In the current review article, we summarized recent findings concerning the roles of lipid droplet-associated factors, patatin-like phospholipase domain-containing 3, Transmembrane 6 superfamily member 2, and 17β-hydroxysteroid dehydrogenase 11 and 13 as well as genetic variants in pancreatic and hepatic diseases. A better understanding of cancer type- and cell type-specific roles of lipid droplet-associated factors is important for establishing new therapeutic options in the future.

Scientific Advances in Diabetes: The Impact of the Innovative Medicines Initiative

Diabetes Mellitus is one of the World Health Organization's priority diseases under research by the first and second programmes of Innovative Medicines Initiative, with the acronyms IMI1 and IMI2, respectively. Up to October of 2019, 13 projects were funded by IMI for Diabetes & Metabolic disorders, namely SUMMIT, IMIDIA, DIRECT, StemBANCC, EMIF, EBiSC, INNODIA, RHAPSODY, BEAT-DKD, LITMUS, Hypo-RESOLVE, IM2PACT, and CARDIATEAM. In general, a total of €447 249 438 was spent by IMI in the area of Diabetes. In order to prompt a better integration of achievements between the different projects, we perform a literature review and used three data sources, namely the official project's websites, the contact with the project's coordinators and co-coordinator, and the CORDIS database. From the 662 citations identified, 185 were included. The data collected were integrated into the objectives proposed for the four IMI2 program research axes: (1) target and biomarker identification, (2) innovative clinical trials paradigms, (3) innovative medicines, and (4) patient-tailored adherence programmes. The IMI funded projects identified new biomarkers, medical and research tools, determinants of inter-individual variability, relevant pathways, clinical trial designs, clinical endpoints, therapeutic targets and concepts, pharmacologic agents, large-scale production strategies, and patient-centered predictive models for diabetes and its complications. Taking into account the scientific data produced, we provided a joint vision with strategies for integrating personalized medicine into healthcare practice. The major limitations of this article were the large gap of data in the libraries on the official project websites and even the Cordis database was not complete and up to date.

Interplay between Heart Disease and Metabolic Steatosis: A Contemporary Perspective

The liver-heart axis is a growing field of interest owing to rising evidence of complex bidirectional interplay between the two organs. Recent data suggest non-alcoholic fatty liver disease (NAFLD) has a significant, independent association with a wide spectrum of structural and functional cardiac diseases, and seems to worsen cardiovascular disease (CVD) prognosis. Conversely, the effect of cardiac disease on NAFLD is not well studied and data are mostly limited to cardiogenic liver disease. We believe it is important to further investigate the heart-liver relationship because of the tremendous global health and economic burden the two diseases pose, and the impact of such investigations on clinical decision making and management guidelines for both diseases. In this review, we summarize the current knowledge on NAFLD diagnosis, its systemic manifestations, and associations with CVD. More specifically, we review the pathophysiological mechanisms that govern the interplay between NAFLD and CVD and evaluate the relationship between different CVD treatments and NAFLD progression.

Non-Alcoholic Fatty Liver Disease in Obese Youth With Insulin Resistance and Type 2 Diabetes

Currently, Non-Alcoholic Fatty Liver Disease (NAFLD) is the most prevalent form of chronic liver disease in children and adolescents worldwide. Simultaneously to the epidemic spreading of childhood obesity, the rate of affected young has dramatically increased in the last decades with an estimated prevalence of NAFLD of 3%-10% in pediatric subjects in the world. The continuous improvement in NAFLD knowledge has significantly defined several risk factors associated to the natural history of this complex liver alteration. Among them, Insulin Resistance (IR) is certainly one of the main features. As well, not surprisingly, abnormal glucose tolerance (prediabetes and diabetes) is highly prevalent among children/adolescents with biopsy-proven NAFLD. In addition, other factors such as genetic, ethnicity, gender, age, puberty and lifestyle might affect the development and progression of hepatic alterations. However, available data are still lacking to confirm whether IR is a risk factor or a consequence of hepatic steatosis. There is also evidence that NAFLD is the hepatic manifestation of Metabolic Syndrome (MetS). In fact, NAFLD often coexist with central obesity, impaired glucose tolerance, dyslipidemia, and hypertension, which represent the main features of MetS. In this Review, main aspects of the natural history and risk factors of the disease are summarized in children and adolescents. In addition, the most relevant scientific evidence about the association between NAFLD and metabolic dysregulation, focusing on clinical, pathogenetic, and histological implication will be provided with some focuses on the main treatment options.

The Role of Hepatic Fat Accumulation in Glucose and Insulin Homeostasis-Dysregulation by the Liver

Accumulation of hepatic triacylglycerol (TG) is associated with obesity and metabolic syndrome, which are important pathogenic factors in the development of type 2 diabetes. In this narrative review, we summarize the effects of hepatic TG accumulation on hepatic glucose and insulin metabolism and the underlying molecular regulation in order to highlight the importance of hepatic TG accumulation for whole-body glucose metabolism. We find that liver fat accumulation is closely linked to impaired insulin-mediated suppression of hepatic glucose production and reduced hepatic insulin clearance. The resulting systemic hyperinsulinemia has a major impact on whole-body glucose metabolism and may be an important pathogenic step in the development of type 2 diabetes.

The PNPLA3-I148M Variant Confers an Antiatherogenic Lipid Profile in Insulin-resistant Patients

CONTEXT

The I148M (rs738409-G) variant in PNPLA3 increases liver fat content but may be protective against cardiovascular disease. Insulin resistance (IR) amplifies the effect of PNPLA3-I148M on liver fat.

OBJECTIVE

To study whether PNPLA3-I148M confers an antihyperlipidemic effect in insulin-resistant patients.

DESIGN

Cross-sectional study comparing the impact of PNPLA3-I148M on plasma lipids and lipoproteins in 2 cohorts, both divided into groups based on rs738409-G allele carrier status and median HOMA-IR.

SETTING

Tertiary referral center.

PATIENTS

A total of 298 obese patients who underwent a liver biopsy during bariatric surgery (bariatric cohort: age 49 ± 9 years, body mass index [BMI] 43.2 ± 6.8 kg/m2), and 345 less obese volunteers in whom liver fat was measured by proton magnetic resonance spectroscopy (nonbariatric cohort: age 45 ± 14 years, BMI 29.7 ± 5.7 kg/m2).

MAIN OUTCOME MEASURES

Nuclear magnetic resonance profiling of plasma lipids, lipoprotein particle subclasses and their composition.

RESULTS

In both cohorts, individuals carrying the PNPLA3-I148M variant had significantly higher liver fat content than noncarriers. In insulin-resistant and homozygous carriers, PNPLA3-I148M exerted a distinct antihyperlipidemic effect with decreased very-low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) particles and their constituents, and increased high-density lipoprotein particles and their constituents, compared with noncarriers. VLDL particles were smaller and LDL particles larger in PNPLA3-I148M carriers. These changes were geometrically opposite to those due to IR. PNPLA3-I148M did not have a measurable effect in patients with lower IR, and its effect was smaller albeit still significant in the less obese than in the obese cohort.

CONCLUSIONS

PNPLA3-I148M confers an antiatherogenic plasma lipid profile particularly in insulin-resistant individuals.

Insights into genetic variants associated with NASH-fibrosis from metabolite profiling

Several genetic discoveries robustly implicate five single-nucleotide variants in the progression of non-alcoholic fatty liver disease to non-alcoholic steatohepatitis and fibrosis (NASH-fibrosis), including a recently identified variant in MTARC1. To better understand these variants as potential therapeutic targets, we aimed to characterize their impact on metabolism using comprehensive metabolomics data from two population-based studies. A total of 9135 participants from the Fenland study and 9902 participants from the EPIC-Norfolk cohort were included in the study. We identified individuals with risk alleles associated with NASH-fibrosis: rs738409C>G in PNPLA3, rs58542926C>T in TM6SF2, rs641738C>T near MBOAT7, rs72613567TA>T in HSD17B13 and rs2642438A>G in MTARC1. Circulating levels of 1449 metabolites were measured using targeted and untargeted metabolomics. Associations between NASH-fibrosis variants and metabolites were assessed using linear regression. The specificity of variant-metabolite associations were compared to metabolite associations with ultrasound-defined steatosis, gene variants linked to liver fat (in GCKR, PPP1R3B and LYPLAL1) and gene variants linked to cirrhosis (in HFE and SERPINA1). Each NASH-fibrosis variant demonstrated a specific metabolite profile with little overlap (8/97 metabolites) comprising diverse aspects of lipid metabolism. Risk alleles in PNPLA3 and HSD17B13 were both associated with higher 3-methylglutarylcarnitine and three variants were associated with lower lysophosphatidylcholine C14:0. The risk allele in MTARC1 was associated with higher levels of sphingomyelins. There was no overlap with metabolites that associated with HFE or SERPINA1 variants. Our results suggest a link between the NASH-protective variant in MTARC1 to the metabolism of sphingomyelins and identify distinct molecular patterns associated with each of the NASH-fibrosis variants under investigation.

Effects of TM6SF2 E167K on hepatic lipid and very low-density lipoprotein metabolism in humans

Nonalcoholic fatty liver disease (NAFLD) is characterized by hepatic lipid accumulation. The transmembrane 6 superfamily member 2 (TM6SF2) E167K genetic variant associates with NAFLD and with reduced plasma triglyceride levels in humans. However, the molecular mechanisms underlying these associations remain unclear. We hypothesized that TM6SF2 E167K affects hepatic very low-density lipoprotein (VLDL) secretion and studied the kinetics of apolipoprotein B100 (apoB100) and triglyceride metabolism in VLDL in homozygous subjects. In 10 homozygote TM6SF2 E167K carriers and 10 matched controls, we employed stable-isotope tracer and compartmental modeling techniques to determine apoB100 and triglyceride kinetics in the 2 major VLDL subfractions: large triglyceride-rich VLDL₁ and smaller, less triglyceride-rich VLDL₂. VLDL₁-apoB100 production was markedly reduced in homozygote TM6SF2 E167K carriers compared with controls. Likewise, VLDL₁-triglyceride production was 35% lower in the TM6SF2 E167K carriers. In contrast, the direct production rates for VLDL₂-apoB100 and triglyceride were not different between carriers and controls. In conclusion, the TM6SF2 E167K genetic variant was linked to a specific reduction in hepatic secretion of large triglyceride-rich VLDL₁. The impaired secretion of VLDL₁ explains the reduced plasma triglyceride concentration and provides a basis for understanding the lower risk of cardiovascular disease associated with the TM6SF2 E167K genetic variant.

NAFLD, and cardiovascular and cardiac diseases: Factors influencing risk, prediction and treatment

BACKGROUND AND AIM

Non-alcoholic fatty liver disease (NAFLD), affecting up to around 30% of the world's adult population, causes considerable liver-related and extrahepatic morbidity and mortality. Strong evidence indicates that NAFLD (especially its more severe forms) is associated with a greater risk of all-cause mortality, and the predominant cause of mortality in this patient population is cardiovascular disease (CVD). This narrative review aims to discuss the strong association between NAFLD and increased risk of cardiovascular, cardiac and arrhythmic complications. Also discussed are the putative mechanisms linking NAFLD to CVD and other cardiac/arrhythmic complications, with a brief summary of CVD risk prediction/stratification and management of the increased CVD risk observed in patients with NAFLD.

RESULTS

NAFLD is associated with an increased risk of CVD events and other cardiac complications (left ventricular hypertrophy, valvular calcification, certain arrhythmias) independently of traditional CVD risk factors. The magnitude of risk of CVD and other cardiac/arrhythmic complications parallels the severity of NAFLD (especially liver fibrosis severity). There are most likely multiple underlying mechanisms through which NAFLD may increase risk of CVD and cardiac/arrhythmic complications. Indeed, NAFLD exacerbates hepatic and systemic insulin resistance, promotes atherogenic dyslipidaemia, induces hypertension, and triggers synthesis of proatherogenic, procoagulant and proinflammatory mediators that may contribute to the development of CVD and other cardiac/arrhythmic complications.

CONCLUSION

Careful assessment of CVD risk is mandatory in patients with NAFLD for primary prevention of CVD, together with pharmacological treatment for coexisting CVD risk factors.

Significance of Simple Steatosis: An Update on the Clinical and Molecular Evidence

Non-alcoholic fatty liver disease (NAFLD) is defined clinicopathologically by the accumulation of lipids in >5% of hepatocytes and the exclusion of secondary causes of fat accumulation. NAFLD encompasses a wide spectrum of liver damage, extending from simple steatosis or non-alcoholic fatty liver (NAFL) to non-alcoholic steatohepatitis (NASH)—the latter is characterized by inflammation and hepatocyte ballooning degeneration, in addition to the steatosis, with or without fibrosis. NAFLD is now the most common cause of chronic liver disease in Western countries and affects around one quarter of the general population. It is a multisystem disorder, which is associated with an increased risk of type 2 diabetes mellitus as well as liver- and cardiovascular-related mortality. Although earlier studies had suggested that NAFL is benign (i.e., non-progressive), cumulative evidence challenges this dogma, and recent data suggest that nearly 25% of those with NAFL may develop fibrosis. Importantly, NAFLD patients are more susceptible to the toxic effects of alcohol, drugs, and other insults to the liver. This is likely due to the functional impairment of steatotic hepatocytes, which is virtually undetectable by current clinical tests. This review provides an overview of the current evidence on the clinical significance of NAFL and discusses the molecular basis for NAFL development and progression.

Hepatic lipid droplets: A balancing act between energy storage and metabolic dysfunction in NAFLD

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is defined by the abundance of lipid droplets (LDs) in hepatocytes. While historically considered simply depots for energy storage, LDs are increasingly recognized to impact a wide range of biological processes that influence cellular metabolism, signaling, and function. While progress has been made toward understanding the factors leading to LD accumulation (i.e. steatosis) and its progression to advanced stages of NAFLD and/or systemic metabolic dysfunction, much remains to be resolved.

SCOPE OF REVIEW

This review covers many facets of LD biology. We provide a brief overview of the major pathways of lipid accretion and degradation that contribute to steatosis and how they are altered in NAFLD. The major focus is on the relationship between LDs and cell function and the detailed mechanisms that couple or uncouple steatosis from the severity and progression of NAFLD and systemic comorbidities. The importance of specific lipids and proteins within or on LDs as key components that determine whether LD accumulation is linked to cellular and metabolic dysfunction is presented. We discuss emerging areas of LD biology and future research directions that are needed to advance our understanding of the role of LDs in NAFLD etiology.

MAJOR CONCLUSIONS

Impairments in LD breakdown appear to contribute to disease progression, but inefficient incorporation of fatty acids (FAs) into LD-containing triacylglycerol (TAG) and the consequential changes in FA partitioning also affect NAFLD etiology. Increased LD abundance in hepatocytes does not necessarily equate to cellular dysfunction. While LD accumulation is the prerequisite step for most NAFLD cases, the protein and lipid composition of LDs are critical factors in determining the progression from simple steatosis. Further defining the detailed molecular mechanisms linking LDs to metabolic dysfunction is important for designing effective therapeutic approaches targeting NAFLD and its comorbidities.

Application of Metabolomics in Diagnosis and Treatment of Chronic Liver Diseases

Chronic liver disease represents stepwise destruction of the liver parenchyma after chronic liver injury, which is often difficult to be diagnosed accurately. Thus, the development of specific biomarkers of chronic liver disease is important. Metabolomics is a powerful tool for biomarker exploration, which enables the exploration of disease pathogenesis or drug action mechanisms at the global metabolic level. The metabolomics workflow generally includes collection, preparation, and analysis of samples, and data processing and bioinformatics. A metabolomics study can simultaneously detect the dysfunctions in the glucose, lipid, amino-acid, and nucleotide metabolisms. Hence, it facilitates the obtaining of a better understanding of the pathogenesis of chronic liver disease and its diagnosis. Many effective drugs could reverse the change of comprehensive biochemical phenotypes induced by chronic liver disease. They can even potentially restore the normal metabolic signatures of patients. Increasingly more researchers have begun to apply metabolomics technologies to diagnose chronic liver disease and investigate the mechanism of action of effective drugs or the variations in drug responses. We are convinced that deepening the understanding of the metabolic alterations could extend their use as powerful biomarkers, promoting the more effective clinical diagnosis and treatment of chronic liver disease in the future.

Circulating lipidomic alterations in obese and non-obese subjects with non-alcoholic fatty liver disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) affects obese and non-obese individuals. However, mechanisms underlying non-obese non-alcoholic steatohepatitis (NASH) remain unclear.

AIMS

To attempt to identify metabolic perturbations associated with non-obese and obese NAFLD using a lipidomics approach.

METHODS

A cross-sectional analysis of 361 subjects with biopsy-proven NAFLD (157 NAFL and 138 NASH) and healthy controls (n = 66) was performed. Individuals were categorised as obese or non-obese based on the Asian cut-off for body mass index. Circulating lipidomic profiling of sera was performed based on the histological severity of NAFLD. Circulating lipidomic alterations were validated with an independent validation set (154 NAFLD subjects [93 NAFL and 61 NASH] and 21 healthy controls).

RESULTS

Saturated sphingomyelin (SM) species were significantly associated with visceral adiposity in non-obese NAFLD (SM d38:0; P < 0.001) but not in obese NAFLD. Additionally, SM levels were significantly associated with systemic and adipose tissue insulin resistance (SM d38:0; P = 0.002 and <0.001, respectively). Five potential lipid metabolites for non-obese subjects and seven potential lipids for obese subjects were selected to predict NAFLD and NASH. These lipid combinations showed good diagnostic performance for non-obese (area under the curve [AUC] for NAFLD/NASH = 0.916/0.813) and obese (AUC for NAFLD/NASH = 0.967/0.812) subjects. Moreover, distinctly altered patterns of diacylglycerol (DAG), triacylglycerol (TAG) and SM levels were confirmed in the validation set depending on the histological severity of NAFLD.

CONCLUSION

Non-obese and obese NAFLD subjects exhibit unique circulating lipidomic signatures, including DAGs, TAGs and SMs. These lipid combinations may be useful biomarkers for non-obese and obese NAFLD patients.

Dysregulated lipid metabolism links NAFLD to cardiovascular disease

Background

Non-alcoholic fatty liver disease (NAFLD) is rapidly becoming a global health problem. Cardiovascular diseases (CVD) are the most common cause of mortality in NAFLD patients. NAFLD and CVD share several common risk factors including obesity, insulin resistance, and type 2 diabetes (T2D). Atherogenic dyslipidemia, characterized by plasma hypertriglyceridemia, increased small dense low-density lipoprotein (LDL) particles, and decreased high-density lipoprotein cholesterol (HDL-C) levels, is often observed in NAFLD patients.

Scope of review

In this review, we highlight recent epidemiological studies evaluating the link between NAFLD and CVD risk. We further focus on recent mechanistic insights into the links between NAFLD and altered lipoprotein metabolism. We also discuss current therapeutic strategies for NAFLD and their potential impact on NAFLD-associated CVD risk.

Major conclusions

Alterations in hepatic lipid and lipoprotein metabolism are major contributing factors to the increased CVD risk in NAFLD patients, and many promising NASH therapies in development also improve dyslipidemia in clinical trials.

Human and molecular genetics shed lights on fatty liver disease and diabetes conundrum

The causal role of abdominal overweight/obesity, insulin resistance and type 2 diabetes (T2D) on the risk of fatty liver disease (FLD) has robustly been proven. A consensus of experts has recently proposed the novel definition of 'metabolic dysfunction-associated fatty liver disease, MAFLD' instead of 'nonalcoholic fatty liver disease, NAFLD', emphasizing the central role of dysmetabolism in the disease pathogenesis. Conversely, a direct and independent contribution of FLD per se on risk of developing T2D is still a controversial topic. When dealing with FLD as a potential risk factor for T2D, it is straightforward to think of hepatic insulin resistance as the most relevant underlying mechanism. Emerging evidence supports genetic determinants of FLD (eg PNPLA3, TM6SF2, MBOAT7, GCKR, HSD17B13) as determinants of insulin resistance and T2D. However, recent studies highlighted that the key molecular mechanism of dysmetabolism is not fat accumulation per se but the degree of hepatic fibrosis (excess liver fat content-lipotoxicity), leading to reduced insulin clearance, insulin resistance and T2D. A consequence of these findings is that drugs that will ameliorate liver fat accumulation and fibrosis in principle may also exert a beneficial effect on insulin resistance and risk of T2D in individuals with FLD. Finally, initial findings show that these genetic factors might be directly implicated in modulating pancreatic beta-cell function, although future studies are needed to fully understand this relationship.

Nonalcoholic fatty liver disease and type 2 diabetes: pathophysiological mechanisms shared between the two faces of the same coin

The pathophysiological mechanisms underlying the close relationship between nonalcoholic fatty liver disease (NAFLD) and type 2 diabetes mellitus (T2DM) are multiple, complex and only partially known. The purpose of this paper was to review the current knowledge of these mechanisms in a unified manner. Subjects with NAFLD and T2DM have established insulin resistance (IR), which exacerbates the two comorbidities. IR worsens NAFLD by increasing the accumulation of free fatty acids (FFAs) in the liver. This occurs due to an increase in the influx of FFAs from peripheral adipose tissue by the activation of hormone-sensitive lipase. In addition, there is de novo increased lipogenesis, a transcription factor, the sterols regulatory element-binding transcription factor 1c (SREBP-1c), which activates the expression of several genes strongly promotes lipogenesis by the liver and facilitate storage of triglycerides. Lipids accumulation in the liver induces a chronic stress in the endoplasmic reticulum of the hepatocytes. Genome-wide association studies have identified genetic variants associated with NAFLD severity, but unrelated to IR. In particular, the alteration of patatin-like phospholipase domain-containing protein 3 contributes to the susceptibility to NAFLD. Furthermore, the lipotoxicity of ceramides and diacylglycerol, well known in T2DM, triggers a chronic inflammatory process favoring the progression from hepatic steatosis to steatohepatitis. Reactive oxygen species produced by mitochondrial dysfunction trigger both liver inflammation and beta-cells damage, promoting the progression of both NAFLD and T2DM. The close association between NAFLD and T2DM is bidirectional, as T2DM may trigger both NAFLD onset and its progression, but NAFLD itself may contribute to the development of IR and T2DM. Future studies on the mechanisms will have to deepen the knowledge of the interaction between the two pathologies and should allow the identification of new therapeutic targets for the treatment of NAFLD, currently substantially absent.

Noninvasive Evaluation of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent liver diseases and can progress to advanced fibrosis and end-stage liver disease. Thus, intensive research has been performed to develop noninvasive methods for the diagnosis of nonalcoholic steatohepatitis (NASH) and fibrosis. Currently, no single noninvasive tool covers all of the stages of pathologies and conditions of NAFLD, and the cost and feasibility of known techniques are also important issues. Blood biomarkers for NAFLD may be useful to select subjects who need ultrasonography (US) screening for NAFLD, and noninvasive tools for assessing fibrosis may be helpful to exclude the probability of significant fibrosis and to predict advanced fibrosis, thus guiding the decision of whether to perform liver biopsy in patients with NAFLD. Among various methods, magnetic resonance-based methods have been shown to perform better than other methods in assessing steatosis as well as in detecting hepatic fibrosis. Many genetic markers are associated with the development and progression of NAFLD. Further well-designed studies are needed to determine which biomarker panels, imaging studies, genetic marker panels, or combinations thereof perform well for diagnosing NAFLD, differentiating NASH and fibrosis, and following-up NAFLD, respectively.

Oxidative Stress Management in Chronic Liver Diseases and Hepatocellular Carcinoma

Chronic viral hepatitis B and C and non-alcoholic fatty liver disease (NAFLD) have been widely acknowledged to be the leading causes of liver cirrhosis and hepatocellular carcinoma. As anti-viral treatment progresses, the impact of NAFLD is increasing. NAFLD can coexist with chronic viral hepatitis and exacerbate its progression. Oxidative stress has been recognized as a chronic liver disease progression-related and cancer-initiating stress response. However, there are still many unresolved issues concerning oxidative stress, such as the correlation between the natural history of the disease and promising treatment protocols. Recent findings indicate that oxidative stress is also an anti-cancer response that is necessary to kill cancer cells. Oxidative stress might therefore be a cancer-initiating response that should be down regulated in the pre-cancerous stage in patients with risk factors for cancer, while it is an anti-cancer cell response that should not be down regulated in the post-cancerous stage, especially in patients using anti-cancer agents. Antioxidant nutrients should be administered carefully according to the patients’ disease status. In this review, we will highlight these paradoxical effects of oxidative stress in chronic liver diseases, pre- and post-carcinogenesis.

Interaction of TM6SF2 E167K and PNPLA3 I148M variants in NAFLD in northeast China

INTRODUCTION AND AIM

This study aimed to confirm the association of the transmembrane 6 superfamily member 2 (TM6SF2) E167K variant with non-alcoholic fatty liver disease (NAFLD) and the degree of steatosis, as well as the additive effect of body mass index (BMI) or the patatin-like phospholipase domain-containing protein 3 (PNPLA3) I148M and TM6SF2 E167K variants in NAFLD.

MATERIALS AND METHODS

A total of 158 NAFLD patients and 158 matched controls were recruited. Steatosis was classified as mild, moderate and severe by FibroScan. Associations between the TM6SF2 E167K variant and NAFLD as well as clinical parameters were evaluated.

RESULTS

Although the frequency of the T allele was low in the Chinese population (MAF=7.4%), there was still a significant association between the E167K variant and NAFLD (odds ratio=3.379, 95% confidence interval: 1.500-7.612, P=0.003). In particular, the TM6SF2 genotype was also associated with the degree of steatosis (P=0.023). The TM6SF2 variant was associated with increased alanine aminotransferase (ALT) but no other clinical parameters, such as aspartate aminotransferase (AST), alkaline phosphatase (ALP) and lipids. Notably, we also found that an additive effect of the TM6SF2 E167K and PNPLA3 I148M variants in NAFLD. Furthermore, we did not identify an association between the TM6SF2 E167K variant and NAFLD in the non-obese population.

CONCLUSION

The TM6SF2 E167K variant was associated with NAFLD in northeast China, and there was an interaction between the PNPLA3 I148M and TMS6F2 E167K variants in NAFLD.

Toward Genetic Prediction of Nonalcoholic Fatty Liver Disease Trajectories: PNPLA3 and Beyond

Nonalcoholic fatty liver disease (NAFLD) is on the verge of becoming the leading cause of liver disease. NAFLD develops at the interface between environmental factors and inherited predisposition. Genome-wide association studies, followed by exome-wide analyses, led to identification of genetic risk variants (eg, PNPLA3, TM6SF2, and SERPINA1) and key pathways involved in fatty liver disease pathobiology. Functional studies improved our understanding of these genetic factors and the molecular mechanisms underlying the trajectories from fat accumulation to fibrosis, cirrhosis, and cancer over time. Here, we summarize key NAFLD risk genes and illustrate their interactions in a 3-dimensional "risk space." Although NAFLD genomics sometimes appears to be "lost in translation," we envision clinical utility in trial design, outcome prediction, and NAFLD surveillance.

Assessment of Genetic Aspects of Non-alcoholic Fatty Liver and Premature Cardiovascular Events

Recent evidence has demonstrated a strong interplay and multifaceted relationship between non-alcoholic fatty liver disease (NAFLD) and cardiovascular disease (CVD). CVD is the major cause of death in patients with NAFLD. NAFLD also has strong associations with diabetes and metabolic syndrome. In this comprehensive review, we aimed to overview the primary environmental and genetic risk factors of NAFLD, and CVD and also focus on the genetic aspects of these two disorders. NAFLD and CVD are both heterogeneous diseases with common genetic and molecular pathways. We have searched for the latest published articles regarding this matter and tried to provide an overview of recent insights into the genetic aspects of NAFLD and CVD. The common genetic and molecular pathways involved in NAFLD and CVD are insulin resistance (IR), subclinical inflammation, oxidative stress, and atherogenic dyslipidemia. According to an investigation, the exact associations between genomic characteristics of NAFLD and CVD and casual relationships are not fully determined. Different gene polymorphisms have been identified as the genetic components of the NAFLDCVD association. Some of the most documented ones of these gene polymorphisms are patatin-like phospholipase domain-containing protein 3 (PNPLA3), transmembrane 6 superfamily member 2 (TM6SF2), hydroxysteroid 17-beta dehydrogenase 13 (HSD17B13), adiponectin-encoding gene (ADIPOQ), apolipoprotein C3 (APOC3), peroxisome proliferator-activated receptors (PPAR), leptin receptor (LEPR), sterol regulatory element-binding proteins (SREBP), tumor necrosis factor-alpha (TNF-α), microsomal triglyceride transfer protein (MTTP), manganese superoxide dismutase (MnSOD), membrane-bound O-acyltransferase domain-containing 7 (MBOAT7), and mutation in DYRK1B that substitutes cysteine for arginine at position 102 in kinase-like domain. Further cohort studies with a significant sample size using advanced genomic assessments and next-generation sequencing techniques are needed to shed more light on genetic associations between NAFLD and CVD.

The European medical information framework: A novel ecosystem for sharing healthcare data across Europe

INTRODUCTION

The European medical information framework (EMIF) was an Innovative Medicines Initiative project jointly supported by the European Union and the European Federation of Pharmaceutical Industries and Associations, that generated a common technology and governance framework to identify, assess and (re)use healthcare data, to facilitate real-world data research. The objectives of EMIF included providing a unified platform to support a wide range of studies within two verification programmes-Alzheimer's disease (EMIF-AD), and metabolic consequences of obesity (EMIF-MET).

METHODS

The EMIF platform was built around two main data-types: electronic health record data and research cohort data, and the platform architecture composed of a set of tools designed to enable data discovery and characterisation. This included the EMIF catalogue, which allowed users to find relevant data sources, including the data-types collected. Data harmonisation via a common data model were central to the project especially for population data sources. EMIF also developed an ethical code of practice to ensure data protection, patient confidentiality and compliance with the European Data Protection Directive, and GDPR.

RESULTS

Currently 18 population-based disease agnostic and 60 cohort-based Alzheimer's data partners from across 14 countries are contained within the catalogue, and this will continue to expand. The work conducted in EMIF-AD and EMIF-MET includes standardizing cohorts, summarising baseline characteristics of patients, developing diagnostic algorithms, epidemiological studies, identifying and validating novel biomarkers and selecting potential patient samples for pharmacological intervention.

CONCLUSIONS

EMIF was designed to provide a sustainable model as demonstrated by the sustainability plans for EMIF-AD. Although network-wide studies using EMIF were not conducted during this project to evaluate its sustainability, learning from EMIF will be used in the follow-on IMI-2 project, European Health Data and Evidence Network (EHDEN). Furthermore, EMIF has facilitated collaborations between partners and continues to promote a wider adoption of principles, technology and architecture through some of its continued work.

Genetic Risk Factors and Disease Modifiers of Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease is strongly associated with obesity and the metabolic syndrome, but genetic factors also contribute to disease susceptibility. Human genetic studies have identified several common genetic variants contributing to nonalcoholic fatty liver disease initiation and progression. These findings have provided new insights into the pathogenesis of nonalcoholic fatty liver disease and opened up new avenues for the development of therapeutic interventions. In this review, we summarize the current state of knowledge about the genetic determinants of nonalcoholic fatty liver disease, focusing on the most robustly validated genetic risk factors and on recently discovered modifiers of disease progression.

Independent and joint correlation of PNPLA3 I148M and TM6SF2 E167K variants with the risk of coronary heart disease in patients with non-alcoholic fatty liver disease

Background

CHD is reported to be the primary cause of death in patients with NAFLD. Genetic susceptibility genes contribute to the developmental risk of NAFLD or CHD. Whether the genetic factors could affect the risk of CHD in NAFLD patients is not clear. The aim of this study was to investigate the association of PNPLA3 I148M and TM6SF2 E167K variants with the risk of CHD in NAFLD patients in Chinese Han population.

Patients and methods

PNPLA3 I148M and TM6SF2 E167K variants were genotyped in a cohort of 189 patients with NAFLD and CHD, as well as 242 patients with NAFLD and 242 healthy controls by gene sequencing. Additionally, serum lipids profiles were determined by standard clinical laboratory methods.

Results

The minor allele frequency of PNPLA3 I148M and TM6SF2 E167K were 0.39 and 0.06 in this cohort, respectively. The distributions of PNPLA3 I148M genotypes and alleles were significant different in NAFLD group vs controls and in NAFLD+CHD group vs NAFLD group (all P <  0.05). NAFLD patients who carry the CG + GG genotype suffered the relative lower risk of CHD than CC genotype carriers (OR = 0.6, 95%CI: 0.40–0.90, P = 0.01). In addition, PNPLA3 I148M and TM6SF2 E167K possess the joint correlation with the decreased risk of CHD in NAFLD patients with the increased number of risk alleles. Besides, PNPLA3 I148M and TM6SF2 E167K variants associated with the decreased serum lipid levels in overall series.

Conclusions

There was a joint protective correlation of PNPLA3 I148M and TM6SF2 E167K variants with the developmental risk of CHD in NAFLD patients. PNPLA3 I148M and TM6SF2 E167K variants might correlated with the decreased risk of CHD in NAFLD patients by associated with the reduced serum lipid levels.

Hepatocellular Carcinoma in Non Alcoholic Fatty Liver Disease

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a global epidemic involving 20-40% of the general population. NAFLD is rapidly becoming the leading cause of hepatocellular carcinoma (HCC) worldwide. Knowledge about NAFLD-HCC peculiar features is needed to understand this emerging disease better.

OBJECTIVE

To review the current literature about the epidemiological, pathogenic and clinical features characterising the NAFLD and distinguishing it from HCC of other etiologies.

METHODS

A systematic review of the literature (PubMed and Medline) using the following string ("Non-alcoholic Fatty Liver Disease"[Mesh] and "Carcinoma, Hepatocellular"[Mesh]). Particular relevance was given to papers published in the last five years as well as previously published manuscript very relevant to this topic according to the experience of the authors.

RESULTS

A total of 244 original papers in humans in English literature were analysed. Inherent difficulties in the identification of high-risk subjects and the possibility of occurrence in non-cirrhotic livers are peculiar characteristics of NAFLD-HCC hampering surveillance programs. The consequently delayed diagnosis limits access to surgical procedures and impacts on survival. After correction for tumour burden, however, the survival is not different from that of viral HCC, suggesting that NAFLD-HCC is not intrinsically a more aggressive malignancy.

CONCLUSION

A great deal of effort is needed to improve the clinical outcome of NAFLD-HCC, especially in terms of prevention, surveillance protocols, and identification of drug modifying the natural history of the underlying liver disease. The outcome of these efforts will significantly impact global HCC-related costs and mortality.