Genetic determinants of susceptibility and severity in nonalcoholic fatty liver disease

Interplay between gut microbiome, host genetic and epigenetic modifications in MASLD and MASLD-related hepatocellular carcinoma

Metabolic dysfunction-associated steatotic liver disease (MASLD) encompasses a wide spectrum of liver injuries, ranging from hepatic steatosis, metabolic dysfunction-associated steatohepatitis (MASH), fibrosis, cirrhosis to MASLD-associated hepatocellular carcinoma (MASLD-HCC). Recent studies have highlighted the bidirectional impacts between host genetics/epigenetics and the gut microbial community. Host genetics influence the composition of gut microbiome, while the gut microbiota and their derived metabolites can induce host epigenetic modifications to affect the development of MASLD. The exploration of the intricate relationship between the gut microbiome and the genetic/epigenetic makeup of the host is anticipated to yield promising avenues for therapeutic interventions targeting MASLD and its associated conditions. In this review, we summarise the effects of gut microbiome, host genetics and epigenetic alterations in MASLD and MASLD-HCC. We further discuss research findings demonstrating the bidirectional impacts between gut microbiome and host genetics/epigenetics, emphasising the significance of this interconnection in MASLD prevention and treatment.

Insights into the Epidemiology, Pathogenesis, and Therapeutics of Nonalcoholic Fatty Liver Diseases

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease which affects ≈25% of the adult population worldwide, placing a tremendous burden on human health. The disease spectrum ranges from simple steatosis to steatohepatitis, fibrosis, and ultimately, cirrhosis and carcinoma, which are becoming leading reasons for liver transplantation. NAFLD is a complex multifactorial disease involving myriad genetic, metabolic, and environmental factors; it is closely associated with insulin resistance, metabolic syndrome, obesity, diabetes, and many other diseases. Over the past few decades, countless studies focusing on the investigation of noninvasive diagnosis, pathogenesis, and therapeutics have revealed different aspects of the mechanism and progression of NAFLD. However, effective pharmaceuticals are still in development. Here, the current epidemiology, diagnosis, animal models, pathogenesis, and treatment strategies for NAFLD are comprehensively reviewed, emphasizing the outstanding breakthroughs in the above fields and promising medications in and beyond phase II.

The Association between Angiotensin II Type 1 Receptor Gene A1166C Polymorphism and Non-alcoholic Fatty Liver Disease and Its Severity

BACKGROUND Genetic predisposition may have important role in pathogenesis of non-alcoholic fatty liver disease (NAFLD). Angiotensin II type I receptor (AGTR1) has been known to involve in the process of liver steatosis and fibrosis. This study aimed to investigate the association between AGTR1 A1166C polymorphism and NAFLD. METHODS A cross-sectional study was conducted during May 2014-May 2015 among healthy adults referring to our radiology clinic for abdominal sonography. AGTR1 A1166C polymorphism was evaluated in subjects with NAFLD and healthy individuals using allelic discrimination method. RESULTS 58 subjects with NAFLD were compared with 88 healthy individuals without NAFLD. The frequency of AA and CC genotypes of AGTR1 was significantly higher in patients with NAFLD compared with controls (p = 0.029 and 0.042, respectively). C allele was more detected in subjects with NAFLD compared with the healthy controls (OR: 2.1; 95% CI: 1.23-3.61, p = 0.006). CC genotype (OR: 10.62; 95% CI: 1.05-106.57, p = 0.045) and C allele (OR: 6.81; 95% CI: 1.42- 32.48, p = 0.016) were also predictors of severe fatty liver disease in our study population. CONCLUSION Our results provide the first evidence that AGTR1 gene A1166C polymorphism not only is associated with NAFLD and but also may predict its severity.

Association of MTTP gene variants with pediatric NAFLD: A candidate-gene-based analysis of single nucleotide variations in obese children

Objective

We used targeted next-generation sequencing to investigate whether genetic variants of lipid metabolism-related genes are associated with increased susceptibility to nonalcoholic fatty liver disease (NAFLD) in obese children.

Methods

A cohort of 100 obese children aged 6 to 18 years were divided into NAFLD and non-NAFLD groups and subjected to hepatic ultrasound, anthropometric, and biochemical analyses. We evaluated the association of genetic variants with NAFLD susceptibility by investigating the single nucleotide polymorphisms in each of 36 lipid-metabolism-related genes. The panel genes were assembled for target region sequencing. Correlations between single nucleotide variations, biochemical markers, and clinical phenotypes were analyzed.

Results

97 variants in the 36 target genes per child were uncovered. Twenty-six variants in 16 genes were more prevalent in NAFLD subjects than in in-house controls. The mutation rate of MTTP rs2306986 and SLC6A2 rs3743788 was significantly higher in NAFLD subjects than in non-NAFLD subjects (OR: 3.879; P = 0.004; OR: 6.667, P = 0.005). Logistic regression analysis indicated the MTTP variant rs2306986 was an independent risk factor for NAFLD (OR: 23.468, P = 0.044).

Conclusions

The results of this study, examining a cohort of obese children, suggest that the genetic variation at MTTP rs2306986 was associated with higher susceptibility to NAFLD. This may contribute to the altered lipid metabolism by disruption of assembly and secretion of lipoprotein, leading to reducing fat export from the involved hepatocytes.

Independent effects of diet and exercise training on fat oxidation in non-alcoholic fatty liver disease

AIM

To investigate the independent effects of 6-mo of dietary energy restriction or exercise training on whole-body and hepatic fat oxidation of patients with non-alcoholic fatty liver disease (NAFLD).

METHODS

Participants were randomised into either circuit exercise training (EX; n = 13; 3 h/wk without changes in dietary habits), or dietary energy restriction (ER) without changes in structured physical activity (ER; n = 8). Respiratory quotient (RQ) and whole-body fat oxidation rates (Fat_ox) were determined by indirect calorimetry under basal, insulin-stimulated and exercise conditions. Severity of disease and steatosis was determined by liver histology; hepatic Fat_ox was estimated from plasma β-hydroxybutyrate concentrations; cardiorespiratory fitness was expressed as VO_2peak. Complete-case analysis was performed (EX: n = 10; ER: n = 6).

RESULTS

Hepatic steatosis and NAFLD activity score decreased with ER but not with EX. β-hydroxybutyrate concentrations increased significantly in response to ER (0.08 ± 0.02 mmol/L vs 0.12 ± 0.04 mmol/L, P = 0.03) but remained unchanged in response to EX (0.10 ± 0.03 mmol/L vs 0.11 ± 0.07 mmol/L, P = 0.39). Basal RQ decreased (P = 0.05) in response to EX, while this change was not significant after ER (P = 0.38). VO_2peak (P < 0.001) and maximal Fat_ox during aerobic exercise (P = 0.03) improved with EX but not with ER (P > 0.05). The increase in β-hydroxybutyrate concentrations was correlated with the reduction in hepatic steatosis (r = -0.56, P = 0.04).

CONCLUSION

ER and EX lead to specific benefits on fat metabolism of patients with NAFLD. Increased hepatic Fat_ox in response to ER could be one mechanism through which the ER group achieved reduction in steatosis.

Contribution of Alcoholic and Nonalcoholic Fatty Liver Disease to the Burden of Liver-Related Morbidity and Mortality

Nonalcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) are common causes of chronic liver disease. NAFLD is associated with obesity and metabolic syndrome whereas ALD is associated with excessive alcohol consumption. Both diseases can progress to cirrhosis, hepatocellular carcinoma, and liver-related death. A higher proportion of patients with NAFLD die from cardiovascular disorders than patients with ALD, whereas a higher proportion of patients with ALD die from liver disease. NAFLD and ALD each are associated with significant morbidity, impairment to health-related quality of life, and economic costs to society.

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.

Status of hepatic DNA methylome predetermines and modulates the severity of non-alcoholic fatty liver injury in mice

Background

Nonalcoholic fatty liver disease (NAFLD) is a major health problem and a leading cause of chronic liver disease in the United States and Western countries. In humans, genetic factors greatly influence individual susceptibility to NAFLD; nonetheless, the effect of inter-individual differences in the normal liver epigenome with regard to the susceptibility to NAFLD has not been determined.

Results

In the present study, we investigated the association between the DNA methylation status in the livers of A/J and WSB/EiJ mice and the severity of NAFLD-associated liver injury. We demonstrate that A/J and WSB/EiJ mice, which are characterized by significant differences in the severity of liver injury induced by a choline- and folate-deficient (CFD) diet exhibit substantial differences in cytosine DNA methylation in their normal livers. Furthermore, feeding A/J and WSB/EiJ mice a CFD diet for 12 weeks resulted in different trends and changes in hepatic cytosine DNA methylation.

Conclusion

Our findings indicate a primary role of hepatic DNA methylation in the pathogenesis of NAFLD and suggest that individual variations in DNA methylation across the genome may be a factor determining and influencing the vulnerability to NAFLD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2617-2) contains supplementary material, which is available to authorized users.

Association of adiponectin gene variation with progression of nonalcoholic fatty liver disease: A 4-year follow-up survey

OBJECTIVE

To explore the role of tagging single nucleotide polymorphisms (tagSNPs) in the adiponectin gene in the natural course of nonalcoholic fatty liver disease (NAFLD).

METHODS

The participants were chosen from our previous survey containing 3543 individuals. Finally, a total of 696 participants who had been followed up for a median of 4 years were included. Each participant was administered with an interview, physical examination, blood tests and ultrasonic examination at both baseline and end-point. Polymerase chain reaction-restriction fragment length polymorphism was applied to determine seven tagSNPs in the adiponectin gene, namely, rs182052, rs16861205, rs822396, rs7627128, rs1501299, rs2241767 and rs3774261. Ordinal logistic regression was used to screen risk factors of NAFLD progression as well as the susceptibility to the disease. Haplotypes analyses were performed to confirm the results.

RESULTS

After adjusting for age and gender, rs1501299 (G276T), rs2241767 (A45G) and rs3774261 (A712G) were found to be risk factors of both susceptibility (OR 5.040, 7.471 and 3.546, respectively) and progression (OR 3.83, 3.51 and 3.30, respectively) to NAFLD. Nevertheless, rs182052, rs16861205, rs822396 and rs7627128 had no impact on them. These findings were confirmed by haplotype analysis.

CONCLUSION

The tagSNPs rs2241767, rs1501299 and rs3774261 in the adiponectin gene are risk factors for the individuals' susceptibility to and progression of NAFLD.

GWAS-Identified Common Variants With Nonalcoholic Fatty Liver Disease in Chinese Children

OBJECTIVES

Three genome-wide association studies were previously done for nonalcoholic fatty liver disease (NAFLD) among individuals of Western countries and identified several genetic variants associated with NAFLD. The study aimed to identify whether 7 GWAS-identified common variants (GCKR rs780094, PDGFA rs343064, FDFT1 rs2645424, COL13A1 rs1227756, EHBP1L1 rs6591182, NCAN rs2228603, and PNPLA3 rs738409) were associated with NAFLD in Chinese children.

METHODS

This case-control study recruited 1027 Chinese children of age 7 to 18 years, including 162 children with NAFLD and 865 children without NAFLD. Anthropometric measurements, alanine transaminase (ALT) detection, liver ultrasound examination, and genotyping of 7 variants were performed.

RESULTS

The G-allele of PNPLA3 rs738409 was associated with NAFLD (odds ratio [OR] 1.55, 95% confidence interval 1.13-2.11, P = 0.006) and moderate-to-severe steatosis (OR 3.77, 95% confidence interval 1.78-7.98, P = 0.001) adjusted for age, sex, and BMI standard deviation score. In addition, we found each G-allele of rs738409 increased ALT level by 1.09 IU/L (P = 0.011). Subjects carrying 10 or more risk alleles of 7 variants had an OR of 4.76 (P = 0.025) for NAFLD compared with subjects carrying 3 or fewer risk alleles.

CONCLUSIONS

The PNPLA3 rs738409 G-allele was associated with NAFLD and ALT level in Chinese children. It had stronger association with moderate-to-severe steatosis. Children carrying 10 or more risk alleles of 7 variants were susceptible for NAFLD.

Association between patatin-like phospholipase domain containing 3 gene (PNPLA3) polymorphisms and nonalcoholic fatty liver disease: a HuGE review and meta-analysis

We conducted a meta-analysis to assess the association between patatin-like phospholipase domain-containing 3 (PNPLA3) rs738409 polymorphism and nonalcoholic fatty liver disease (NAFLD) and its subtypes simple steatosis(SS) and nonalcoholic steatohepatitis (NASH). The study-specific odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using fixed-effects or random-effects models, with assessment for heterogeneity and publication bias. Twenty-three case-control studies involving 6071 NAFLD patients and 10366 controls were identified. The combined results showed a significant association between NAFLD risk and the rs738409 polymorphism in all genetic models (additive model: OR = 3.41, 95% CI = 2.57–4.52; P < 0.00001). In addition, evidence indicated that the rs738409 polymorphism was significantly associated with NASH in all genetic models (additive model: OR = 4.44, 95% CI = 3.39–5.82; P < 0.00001). The subgroup and sensitivity analyses showed that these changes were not influenced by the ethnicities and ages of subjects or by the source of controls. The rs738409 polymorphism was only significantly associated with risk of simple steatosis in the allele contrast and had no effect in the other genetic models. These findings suggest that the rs738409 polymorphism in PNPLA3 gene confers high cross-ethnicity risk for NAFLD and NASH development.

Systems biology for hepatologists

Medicine is expected to benefit from combining usual cellular and molecular studies with high-throughput methods (genomics, transcriptomics, proteomics, and metabolomics). These methods, collectively known as omics, permit the determination of thousands of molecules (variations within genes, RNAs, proteins, metabolites) within a tissue, cell, or biological fluid. The use of these methods is very demanding in terms of the design of the study, acquisition, storage, analysis, and interpretation of the data. When carried out properly, these studies can reveal new etiological pathways, help to identify patients at risk for disease, and predict the response to specific treatments. Here we review these omics methods and mention several applications in hepatology research.

Clinical differences between alcoholic liver disease and nonalcoholic fatty liver disease

Alcoholic liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD) are serious health problems worldwide. These two diseases have similar pathological spectra, ranging from simple hepatic steatosis to steatohepatitis, liver cirrhosis, and hepatocellular carcinoma. Although most subjects with excessive alcohol or food intake experience simple hepatic steatosis, a small percentage of individuals will develop progressive liver disease. Notably, both ALD and NAFLD are frequently accompanied by extrahepatic complications, including cardiovascular disease and malignancy. The survival of patients with ALD and NAFLD depends on various disease-associated conditions. This review delineates the clinical characteristics and outcomes of patients with ALD and NAFLD by comparing their epidemiology, the factors associated with disease susceptibility and progression, and the predictors and characteristics of outcomes. A comprehensive understanding of the characteristics and outcomes of ALD and NAFLD is imperative in the management of these chronic liver diseases.

Association of INSIG2 rs9308762 with ALT level independent of BMI

OBJECTIVES

An increasing number of people are at risk for developing nonalcoholic fatty liver disease (NAFLD). Because obesity is a risk factor for NAFLD, the common variants of obesity-susceptible genes may be associated with NAFLD. Our aim was to identify whether the obesity-susceptible gene variants (rs9939609, rs9930506, and rs4783819 in fat mass and obesity-associated gene (FTO); rs12970134 and rs17782313 in melanocortin-4 receptor gene (MC4R); and rs7566605, rs13428113, and rs9308762 in insulin-induced gene 2 [INSIG2]) were associated with NAFLD.

METHODS

The case-control study recruited 1027 Chinese children ages 7 to 18 years, including 162 children with NAFLD and 865 children without NAFLD. Anthropometric measurements, alanine transaminase (ALT) detection, liver ultrasound examination, and genotyping of 8 gene variants were performed.

RESULTS

The A-allele of FTO rs9939609 was associated with increased NAFLD risk (P = 0.029, odds ratio  1.43), but was not significant after being adjusted for body mass index (BMI) (P = 0.268). We also found an association between the 2 variants (rs12970134 in MC4R and rs9308762 in INSIG2) and ALT level. For rs12970134, each additional A-allele increased ALT level by 1.87 IU/L (P = 0.032). For rs9308762, the homozygotes of the C-allele had a higher ALT level than the T-allele carriers (β = 3.19, P = 0.007). After adjustment for BMI, the former association did not exist, whereas the latter reminded significant (P = 0.003).

CONCLUSIONS

The FTO rs9939609 A-allele increased risk of NAFLD and MC4R rs12970134 was associated with ALT level through an effect on BMI. The association between INSIG2 rs9308762 and ALT level was independent of BMI. The results provided evidence for identifying genetic factors of NAFLD and may be useful for risk assessment and personalized medicine of NAFLD.

A case-control study on the effect of metabolic gene polymorphisms, nutrition, and their interaction on the risk of non-alcoholic fatty liver disease

The oxidative stress is a key issue in the etiology of non-alcoholic fatty liver disease (NAFLD). The aim of our study was to evaluate the effect of metabolic gene polymorphisms involved in the oxidative stress (GSTT1, GSTM1, SULT1A1, CYP2E1, and 1A1), lifestyle and nutrition aspects, and their interaction, on the risk of NAFLD. We enrolled 294 cases and 359 controls, and collected demographics, anthropometric, lifestyle, and nutrition data. A subgroup of NAFLD provided additional data on nutrients and on physical activity engagement. Each patient provided a blood sample for DNA extraction and genotyping. Clinical and laboratory data were collected from cases. Multivariable analysis shows a significant protective effect of age, gender, and moderate drinking habits on the risk of NAFLD, while an increased risk for greater consumption of fruit and grilled meat or fish. Significant interactions were reported between alcohol consumption, fruit intake, grilled meat and fish, and selected genetic variants. From the subgroup analysis, a moderate/high consumption of fat and/or grilled meat/fish, and a high consumption of white meat increase the risk of NAFLD. Engaging any physical activity at least 1 time/week halves the risk of NAFLD. Besides confirming the beneficial effect of moderate alcohol intake and regular physical activity, and the increased risk associated with high fruit and fat intake, for the first time, we report a detrimental effect of grilled food on NAFLD risk. An effect modification by selected gene variants increases the risk in combination with fruit and grilled food intake.

Genetic architecture of human fibrotic diseases: disease risk and disease progression

Genetic studies of human diseases have identified multiple genetic risk loci for various fibrotic diseases. This has provided insights into the myriad of biological pathways potentially involved in disease pathogenesis. These discoveries suggest that alterations in immune responses, barrier function, metabolism and telomerase activity may be implicated in the genetic risks for fibrotic diseases. In addition to genetic disease-risks, the identification of genetic disease-modifiers associated with disease complications, severity or prognosis provides crucial insights into the biological processes implicated in disease progression. Understanding the biological processes driving disease progression may be critical to delineate more effective strategies for therapeutic interventions. This review provides an overview of current knowledge and gaps regarding genetic disease-risks and genetic disease-modifiers in human fibrotic diseases.

Whole-body substrate metabolism is associated with disease severity in patients with non-alcoholic fatty liver disease

OBJECTIVES

In non-alcoholic fatty liver disease (NAFLD), hepatic steatosis is intricately linked with a number of metabolic alterations. We studied substrate utilisation in NAFLD during basal, insulin-stimulated and exercise conditions, and correlated these outcomes with disease severity.

METHODS

20 patients with NAFLD (mean ± SD body mass index (BMI) 34.1 ± 6.7 kg/m(2)) and 15 healthy controls (BMI 23.4 ± 2.7 kg/m(2)) were assessed. Respiratory quotient (RQ), whole-body fat (Fat ox) and carbohydrate (CHO ox) oxidation rates were determined by indirect calorimetry in three conditions: basal (resting and fasted), insulin-stimulated (hyperinsulinaemic-euglycaemic clamp) and exercise (cycling at an intensity to elicit maximal Fat ox). Severity of disease and steatosis were determined by liver histology, hepatic Fat ox from plasma β-hydroxybutyrate concentrations, aerobic fitness expressed as VO2 peak, and visceral adipose tissue (VAT) measured by computed tomography.

RESULTS

Within the overweight/obese NAFLD cohort, basal RQ correlated positively with steatosis (r=0.57, p=0.01) and was higher (indicating smaller contribution of Fat ox to energy expenditure) in patients with NAFLD activity score (NAS) ≥ 5 vs <5 (p=0.008). Both results were independent of VAT, % body fat and BMI. Compared with the lean control group, patients with NAFLD had lower basal whole-body Fat ox (1.2 ± 0.3 vs 1.5 ± 0.4 mg/kg FFM/min, p=0.024) and lower basal hepatic Fat ox (ie, β-hydroxybutyrate, p=0.004). During exercise, they achieved lower maximal Fat ox (2.5 ± 1.4 vs. 5.8 ± 3.7 mg/kg FFM/min, p=0.002) and lower VO2 peak (p<0.001) than controls. Fat ox during exercise was not associated with disease severity (p=0.79).

CONCLUSIONS

Overweight/obese patients with NAFLD had reduced hepatic Fat ox and reduced whole-body Fat ox under basal and exercise conditions. There was an inverse relationship between ability to oxidise fat in basal conditions and histological features of NAFLD including severity of steatosis and NAS.

From NAFLD in clinical practice to answers from guidelines

This review of the literature consists of three sections. First, papers concerning non-alcoholic fatty liver disease (NAFLD) awareness among the general population, general practitioners, and liver and non-liver specialists were retrieved and analyzed to highlight the perception of disease, verify knowledge of current recommendations, and identify the main difficulties experienced in clinical practice. Next, position papers and clinical practice guidelines issued by International and National Hepatological Scientific Societies were identified and critically assessed in order to pinpoint the areas of convergence/difference. Finally, practical suggestions on NAFLD diagnosis and management in daily practice are provided and the open questions highlighted.

A 360-degree overview of paediatric NAFLD: recent insights

Non-alcoholic fatty liver disease (NAFLD) is a multi-faceted disorder, which ranges from simple steatosis to non-alcoholic steatohepatitis (NASH) with/without fibrosis. The effects of specific risk factors, such as obesity and sedentary lifestyle, on predisposing genetic settings eventually lead to the development of NAFLD in children. The complex interplay between genes and environment in NAFLD pathogenesis is sustained by multiple mechanisms that involve liver crosstalk with other organs and tissues, especially gut and adipose tissue. Unfortunately, natural history of paediatric NAFLD is lacking, and the etiopathogenesis is still in the process of being defined. Potential early predictors and suitable non-invasive diagnostic tools can be discovered based on the pathogenetic mechanisms and histological patterns. This will also help design novel treatments and a comprehensive and successful management strategy for patients. In this review, we discuss the recent advances made in genetics, etiopathogenesis, diagnosis, and therapeutic management of NAFLD, focusing especially on the obesity-related steatotic liver condition.

Therapeutic approaches to non-alcoholic fatty liver disease: past achievements and future challenges

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a leading cause of chronic liver injury and mortality in Western countries and China. However, as to date, there is no direct and effective therapy for this disease. The aim of this review is to analyze the key progress and challenges of main current therapeutic approaches in NAFLD.

DATA SOURCE

We carried out a PubMed search of English-language articles relevant to NAFLD therapy.

RESULTS

There are two major therapeutic strategies for NAFLD treatment: (1) lifestyle interventions (including weight reduction, dietary modification and physical exercise) and (2) pharmaceutical therapies. Lifestyle interventions, particularly chronic and moderate intensity exercise, are the most effective and recognized clinical therapies for NAFLD. For pharmaceutical therapies, although their effects and mechanisms have been extensively investigated in laboratory studies, they still need further tests and investigations in clinical human trials.

CONCLUSION

Future advancement of NAFLD therapy should focus on the mechanistic studies on cell based and animal models and human clinical trials of exercise, as well as the combination of lifestyle intervention and pharmaceutical therapy specifically targeting main signaling pathways related to lipid metabolism, oxidative stress and inflammation.

The C-681G polymorphism of the PPAR-γ gene is associated with susceptibility to non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is defined as excessive accumulation of fatty acid in the liver, a common disease in the world. The research of single nucleotide polymorphisms (SNPs) provides a new approach for managing NAFLD. SNPs may increase or decrease the functions of the target genes and their encoding proteins. Peroxisome proliferator-activated receptor (PPAR) plays a key role in modulating metabolism of hepatic triglycerides and consequently magnitude of NAFLD. In this study, we investigated the effect of three SNPs in the PPAR-γ gene i.e. rs10865710 (C-681G), rs7649970 (C-689T) and rs1801282 (C34G, also termed Pro12Ala) on susceptibility to NAFLD. The participants were selected from our epidemiological survey. Totally 169 participants were enrolled in NAFLD group, and 699 healthy subjects were included as controls. PCR-RFLP was applied to detect the SNPs. The G allele frequency of rs10865710 in NAFLD group (41.1%) was significantly higher than that (34.8%) in controls (p = 0.03). Differences in other two loci (rs7649970 and rs1801282) were not statistically significant between the two groups (p > 0.05). This result was confirmed by haplotype analysis. The GCC haplotype (a set of 3 adjacent SNPs in linkage disequilibrium, corresponding to the three alleles of above polymorphisms in order) was a risk factor for the susceptibility to NAFLD (p = 0.03). This study has revealed that the G allele of rs10865710 in the PPAR-γ gene is associated with the increased susceptibility to NAFLD. Our findings may provide novel diagnostic biomarkers and therapeutic targets for NAFLD.

The severity of histologic liver lesions is independent of body mass index in patients with nonalcoholic fatty liver disease

GOALS/BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is associated with obesity, but it may also be present in lean individuals. We evaluated the characteristics of NAFLD patients, focusing on those with normal body mass index (BMI).

STUDY

One hundred and sixty-two of 185 consecutive NAFLD patients were included. Demographic, clinical, somatometric, and laboratory characteristics were recorded. BMI<25 kg/m2 was considered to be normal.

RESULTS

Of the 162 patients, 12% had normal BMI. Patients with normal compared with those with increased BMI fulfilled more frequently no criterion of metabolic syndrome (43% vs. 2%; P<0.001) and had higher median alanine aminotransferase (92 vs. 62 IU/L; P=0.032) and aspartate aminotransferase levels (45 vs. 37 IU/L; P=0.036). Liver stiffness values by transient elastography were significantly lower in patients with normal than in those with increased BMI (5.0 ± 1.6 vs. 9.5 ± 8.7 kPa; P=0.003). In the 56 patients with liver biopsy, the prevalence of nonalcoholic steatohepatitis (50% vs. 68.8%; P=0.423) and the severity of inflammation and fibrosis did not significantly differ between cases with normal and those with increased BMI.

CONCLUSIONS

Approximately 1 of 8 NAFLD patients coming to a Greek tertiary liver center has normal BMI. On liver biopsy, normal BMI patients often have nonalcoholic steatohepatitis and histologic liver lesions of similar severity to the overweight or obese patients.

Does PPARγ2 gene Pro12Ala polymorphism affect nonalcoholic fatty liver disease risk? Evidence from a meta-analysis

Genetic factors can substantially contribute to the pathogenesis of nonalcoholic fatty liver disease (NAFLD). A missense Pro12Ala substitution in the PPARγ2 gene (rs1801282) has been studied in relation with NAFLD risk in different ethnic groups, but findings have been inconclusive. The aim of this was to evaluate the association between rs1801282 and NAFLD through meta-analysis of all relevant published evidence. A systematic search to find eligible studies was performed in Medline, HuGE Navigator, and SCOPUS databases. The strength of association was evaluated using odds ratios with 95% confidence intervals obtained from a random effect approach and under additive, dominant, co-dominant, recessive, and allelic contrast models. Seven studies comprising 1474 cases and 2259 controls met the eligibility criteria and included in the meta-analysis. Combined results did not indicate any predisposing or protective effect for rs1801282 under any of the assessed modes of inheritance. The rate of heterogeneity was generally high due to the inter-study variations in terms of age, gender, and ethnicity. Evidence from the current meta-analysis indicated that rs1801282 variants are not associated with NAFLD risk. Future large-scale studies are required to substantiate the present findings.

Strain-dependent dysregulation of one-carbon metabolism in male mice is associated with choline- and folate-deficient diet-induced liver injury

Dysregulation of one-carbon metabolism-related metabolic processes is a major contributor to the pathogenesis of nonalcoholic fatty liver disease (NAFLD). It is well established that genetic and gender-specific variations in one-carbon metabolism contribute to the vulnerability to NAFLD in humans. To examine the role of one-carbon metabolism dysregulation in the pathogenesis and individual susceptibility to NAFLD, we used a "population-based" mouse model where male mice from 7 inbred were fed a choline- and folate-deficient (CFD) diet for 12 wk. Strain-dependent down-regulation of several key one-carbon metabolism genes, including methionine adenosyltransferase 1α (Mat1a), cystathionine-β-synthase (Cbs), methylenetetrahydrofolate reductase (Mthfr), adenosyl-homocysteinase (Ahcy), and methylenetetrahydrofolate dehydrogenase 1 (Mthfd1), was observed. These changes were strongly associated with interstrain variability in liver injury (steatosis, necrosis, inflammation, and activation of fibrogenesis) and hyperhomocysteinemia. Mechanistically, the decreased expression of Mat1a, Ahcy, and Mthfd1 was linked to a reduced level and promoter binding of transcription factor CCAAT/enhancer binding protein β (CEBPβ), which directly regulates their transcription. The strain specificity of diet-induced dysregulation of one-carbon metabolism suggests that interstrain variation in the regulation of one-carbon metabolism may contribute to the differential vulnerability to NFLD and that correcting the imbalance may be considered as preventive and treatment strategies for NAFLD.

Alterations in the redox state and liver damage: hints from the EASL Basic School of Hepatology

The importance of a correct balance between oxidative and reductive events has been shown to have a paramount effect on cell function for quite a long time. However, in spite of this body of rapidly growing evidence, the implication of the alteration of the redox state in human disease has been so far much less appreciated. Liver diseases make no exception. Although not fully comprehensive, this article reports what discussed during an EASL Basic School held in 2012 in Trieste, Italy, where the effect of the alteration of the redox state was addressed in different experimental and human models. This translational approach resulted in further stressing the concept that this topic should be expanded in the future not only to better understand how oxidative stress may be linked to a liver damage but also, perhaps more important, how this may be the target for better, more focused treatments. In parallel, understanding how alteration of the redox balance may be associated with liver damage may help define sensitive and ideally early biomarkers of the disorder.

Relevance of CYP2E1 to non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) and its progression to steatohepatitis (NASH) and cirrhosis is a growing problem in most developed countries. Increased hepatic expression of CYP2E1, which carries out omega hydroxylation of fatty acids, was first shown in a mouse model of NASH and this was later also reported for human NASH, though not all studies agree with this finding and further larger studies are still needed. In view of its role in fatty acid metabolism which leads to increased levels of toxic lipid peroxides and its possible increased expression in NASH, CYP2E1 is an attractive candidate for a role as a genetic risk factor for both NAFLD generally including progression to NASH. Two studies have focused on the variant allele CYP2E1*5, which may be associated with increased CYP2E1 expression. Both reported increased frequencies of this allele in NASH patients, though statistical significance was not achieved because of small sample sizes. Some more indirect data also suggests a relationship between high CYP2E1 activity and progression to NASH. However, three recent genome-wide association studies on NAFLD have failed to find any evidence that single nucleotide polymorphisms in or adjacent to the CYP2E1 gene contribute to susceptibility. Further studies are needed to investigate a possible role in disease progression in addition to susceptibility and the possibility that statistical power in the existing studies was insufficient to detect a relatively small contribution to disease susceptibility.

Nonalcoholic fatty liver disease is associated with lower hepatic and erythrocyte ratios of phosphatidylcholine to phosphatidylethanolamine

Nonalcoholic fatty liver disease (NAFLD) is associated with altered hepatic lipid composition. Animal studies suggest that the hepatic ratio of phosphatidylcholine (PC) to phosphatidylethanolamine (PE) contributes to steatogenesis and inflammation. This ratio may be influenced by dysregulation of the PE N-methyltransferase (PEMT) pathway or by a low-choline diet. Alterations in the liver may also influence lipid composition in circulation such as in erythrocytes, which therefore may have utility as a biomarker of hepatic disease. Currently, no study has assessed both liver and erythrocyte PC/PE ratios in NAFLD. The aim of this study was to compare the PC/PE ratio in the liver and erythrocytes of patients with simple steatosis (SS) or nonalcoholic steatohepatitis (NASH) with that of healthy controls. PC and PE were measured by mass spectrometry in 28 patients with biopsy-proven NAFLD (14 SS, 14 NASH) and 9 healthy living liver donors as controls. The hepatic PC/PE ratio was lower in SS patients (median [range]) (1.23 [0.27-3.40]) and NASH patients (1.29 [0.77-3.22]) compared with controls (3.14 [2.20-3.73]); both p < 0.001) but it was not different between SS and NASH. PC was lower and PE higher in the liver of SS patients compared with controls, whereas in NASH patients only PE was higher. The PC/PE ratio in erythrocytes was also lower in SS and NASH patients compared with controls because of lower PC in both patient groups. PE in erythrocytes was not different among the groups. In conclusion, NAFLD patients have a lower PC/PE ratio in the liver and erythrocytes than do healthy controls, which may play a role in the pathogenesis. The underlying mechanisms require further investigation.

Prevalence and factors associated with nonalcoholic fatty liver disease in Shanghai work-units

Backgrounds

Nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease in Asians. However, data on prevalence and factors associated with NAFLD in Asians are lacking. The aim of this study is to investigate the prevalence of NAFLD in Shanghai employees to assess the relationship between NAFLD and age, gender, metabolic risk factors in this studied population.

Methods

We selected 7152 employees of Shanghai work-units. Each of them underwent detailed medical history-taking, physical examination, laboratory assessments and abdominal ultrasonography. The diagnosis of NAFLD was done according to established criteria. Receiver operating characteristics (ROC) curves were applied to detect areas under the ROC curves for each index. Nominal logistic regression analysis was used to estimate the odds ratio for risk factors of NAFLD.

Results

About 38.17% employees had NAFLD, more in men than in women. The prevalence of NAFLD increased with increasing age. In both genders, the prevalence of metabolic factors was higher in the NAFLD group. Body max index, waist circumference, weight-to-height ratio, blood pressure, blood glucose, total cholesterol, triglyceride, low density lipoprotein, high density lipoprotein and uric acid were found to have a diagnostic value for NAFLD. Body max index is a better index for diagnosing NAFLD. Uric acid is a new diagnosing index not inferior to lipid metabolic factors. Metabolic factors can increase the risk of NAFLD up to 1.5 ~ 3.8 times.

Conclusions

Older age, male gender, metabolic factors such as obesity, abdominal obesity, dyslipidemia, hypertension or type 2 diabetes are risk factors for NAFLD. Prevalence of NAFLD in Shanghai employees is high. Prevention is extremely important. Those achieve the critical point should have early intervention.

Non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the Western world. It is closely associated with metabolic syndrome. The alarming epidemics of diabetes and obesity have fueled an increasing prevalence of NAFLD, particularly among these high-risk groups. Histologically, NAFLD encompasses a disease spectrum ranging from simple steatosis to non-alcoholic steatohepatitis (NASH), which is characterized by hepatocyte injury, inflammation, and variable degrees of fibrosis on liver biopsy. Non-alcoholic steatohepatitis can progress to cirrhosis in a fraction of patients. There is currently little understanding of risk factors for disease progression and the disease pathogenesis has not been fully defined. Liver biopsy remains the gold standard for diagnosis. Weight loss, dietary modification, and the treatment of underlying metabolic syndrome remain the mainstays of therapy once the diagnosis is established. There are no well-established pharmacological agents for treatment of NASH, although this is a subject of ongoing research.

Interstrain differences in the severity of liver injury induced by a choline- and folate-deficient diet in mice are associated with dysregulation of genes involved in lipid metabolism

Nonalcoholic fatty liver disease (NAFLD) is a major health problem and a leading cause of chronic liver disease in the United States and developed countries. In humans, genetic factors greatly influence individual susceptibility to NAFLD. The goals of this study were to compare the magnitude of interindividual differences in the severity of liver injury induced by methyl-donor deficiency among individual inbred strains of mice and to investigate the underlying mechanisms associated with the variability. Feeding mice a choline- and folate-deficient diet for 12 wk caused liver injury similar to NAFLD. The magnitude of liver injury varied among the strains, with the order of sensitivity being A/J ≈ C57BL/6J ≈ C3H/HeJ < 129S1/SvImJ ≈ CAST/EiJ < PWK/PhJ < WSB/EiJ. The interstrain variability in severity of NAFLD liver damage was associated with dysregulation of genes involved in lipid metabolism, primarily with a down-regulation of the peroxisome proliferator receptor α (PPARα)-regulated lipid catabolic pathway genes. Markers of oxidative stress and oxidative stress-induced DNA damage were also elevated in the livers but were not correlated with severity of liver damage. These findings suggest that the PPARα-regulated metabolism network is one of the key mechanisms determining interstrain susceptibility and severity of NAFLD in mice.

The role of dietary fatty acids in the pathology of metabolic syndrome

Dysfunctional lipid metabolism is a key component in the development of metabolic syndrome, a very frequent condition characterized by dyslipidemia, insulin resistance, abdominal obesity and hypertension, which are related to an elevated risk for type 2 diabetes mellitus. The prevalence of metabolic syndrome is strongly associated with the severity of obesity; its physiopathology is related to both genetics and food intake habits, especially the consumption of a high-caloric, high-fat and high-carbohydrate diet. With the progress of scientific knowledge in the field of nutrigenomics, it was possible to elucidate how the majority of dietary fatty acids influence plasma lipid metabolism and also the genes expression involved in lipolysis and lipogenesis within hepatocytes and adipocytes. The aim of this review is to examine the relevant mechanistic aspects of dietary fatty acids related to blood lipids, adipose tissue metabolism, hepatic fat storage and inflammatory process, all of them closely related to the genesis of metabolic syndrome.

Nonalcoholic fatty liver disease: multimodal treatment options for a pathogenetically multiple-hit disease

Nonalcoholic fatty liver disease (NAFLD) has emerged as a significant public health problem. Besides the liver, NAFLD is also associated with increased cardiovascular and overall morbidity and mortality. NAFLD warrants intensive research, because no treatment has been established as yet. This may be partly attributed to the fact that the majority of the relative clinical trials have a monotherapeutic direction. However, the multifactorial pathogenesis of NAFLD may probably direct clinical trials to a combined therapeutic approach. The aim of this review is to provide a description of the multifactorial pathogenesis of NAFLD and type II diabetes mellitus-NAFLD interplay, and to summarize the therapeutic trials focusing on the combined NAFLD treatment, providing a link between the multiple-hit pathogenesis and the multimodal treatment of NAFLD patients. A diabetes-like therapeutic approach for NAFLD is finally proposed.

Inflammation and fibrogenesis in steatohepatitis

Nonalcoholic fatty liver disease consists of a range of disorders characterized by excess accumulation of triglyceride within the liver. Whereas simple steatosis is clinically benign, nonalcoholic steatohepatitis (NASH) often progresses to cirrhosis. Inflammation and fibrogenesis are closely inter-related and are major targets of NASH research. Experimental data have shown that inflammation in NASH is caused by insulin resistance, systemic lipotoxicity due to overnutrition, lipid metabolites, the production of proinflammatory cytokines and adipokines by visceral adipose tissue, gut-derived bacteria, and oxidative stress. In NASH-associated fibrosis, the principal cell type responsible for extracellular matrix production is recognized as the hepatic stellate cell. Although the fibrotic mechanisms underlying NASH are largely similar to those observed in other chronic liver diseases, the altered patterns of circulating adipokines, the generation of oxidative stress, and the hormonal profile associated with the metabolic syndrome might play unique roles in the fibrogenesis associated with the disease. Information on the basic pathogenesis of NASH with a focus on the generation of inflammation and fibrosis will be discussed.

Genetic factors associated with the presence and progression of nonalcoholic fatty liver disease: a narrative review

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the world. Whereas insulin resistance and obesity are considered major risk factors for the development and progression of NAFLD, the genetic underpinnings are unclear. Before 2008, candidate gene studies based on prior knowledge of pathophysiology of fatty liver yielded conflicting results. In 2008, Romeo et al. published the first genome wide association study and reported the strongest genetic signal for the presence of fatty liver (PNPLA3, patatin-like phospholipase domain containing 3; rs738409). Since then, two additional genome wide scans were published and identified 9 additional genetic variants. Whereas these results shed light into the understanding of the genetics of NAFLD, most of associations have not been replicated in independent samples and, therefore, remain undetermined the significance of these findings. This review aims to summarize the understanding of genetic epidemiology of NAFLD and highlights the gaps in knowledge.

Treatment of atherogenic liver based on the pathogenesis of nonalcoholic fatty liver disease: a novel approach to reduce cardiovascular risk?

Nonalcoholic fatty liver disease (NAFLD), which spans a spectrum of conditions ranging from simple steatosis to progressive nonalcoholic steatohepatitis (NASH), is the most common chronic liver disease and a relevant public health issue. The prevalence of NAFLD depends on adiposity, age, gender and ethnicity. The natural history of liver disease in those with NAFLD critically depends on liver histological changes. However, cardiovascular mortality is increased in NAFLD, particularly in middle-aged adults. Against such a background, this review consists of three sections. First, data on NAFLD as a novel mechanism of increased cardiovascular risk via hyperinsulinism, pro-thrombotic potential, and subclinical inflammation are summarized. Next, the role of atherogenic liver in the development of manifestations of oxidative stress and atherosclerosis is emphasized. Finally, whether and how treating NAFLD will mechanistically result in reduced cardiovascular risk through ameliorated metabolic syndrome is discussed.

Advances in understanding the role of PNPLA3 in the pathogenesis of non-alcoholic fatty liver disease

The incidence of non-alcoholic fatty liver disease (NAFLD) is rising worldwide. Investigation of genes involved in the pathogenesis of NAFLD is significant for replenishing treatment scheme and improving prognosis. Multiple studies have established a correlation between patatin-like phospholipase domain-containing 3 (PNPLA3) gene mutation and the pathogenesis of NAFLD, suggesting that PNPLA3 may affect lipid metabolism. However, the precise mechanism remains to be elucidated. Some researchers believed that PNPLA3 as a patatin-like protein might have triglyceride hydrolysis activity and therefore affect fat metabolism in the liver, while some others thought that PNPLA3 mutation might interfere with the lipid transfer process. In this paper, we give an overview of the PNPLA3 gene and its expression, and explore the correlation between PNPLA3 gene mutation and the pathogenesis of NAFLD.

Insulin resistance in nonalcoholic steatohepatitis: necessary but not sufficient - death of a dogma from analysis of therapeutic studies?

Studies on pathogenesis tend to blame insulin resistance as the chief pathogenic agent in the development and progression of nonalcoholic steatohepatitis (NASH). In this article, studies reporting histological changes induced by pharmacological therapy and nonpharmacological interventions in NASH are critically reviewed, assuming that analysis of morphological findings can provide further insight into the pathogenesis of NASH. PubMed database analysis provided 16 studies describing light microscopy in adults and three in children; ultrastructural analysis was conducted through electron microscopy in two human and four animal studies. Analysis of the data disclosed methodological issues, such as variable histological criteria, limited series, failure to stratify enrolled patients for their risk of progression and very few electron microscopy studies. Moreover, no particularly convincing 'proof-of-concept' study that might assist in understanding the pathogenesis of NASH was found. It is noteworthy that insulin sensitizers fail to treat NASH in all cases, do not reverse or even worsen mitochondrial abnormalities in NASH and, conversely, histological improvement of disease, at least in some patients, is observed with agents acting through mechanisms other than insulin sensitization, such as vitamin E. The finding that correction of insulin resistance may not be sufficient to successfully treat NASH in the majority of patients seems to conflict with studies on pathogenesis. This might imply that NASH is the shared end result of varying pathogenic mechanisms concurring to determine liver damage to a variable extent in the individual patients. If this hypothesis is true, we should try to tailor treatment to each subject.