PNPLA3 I148M polymorphism and progressive liver disease

PNPLA3 148M Carriers with Inflammatory Bowel Diseases Have Higher Susceptibility to Hepatic Steatosis and Higher Liver Enzymes

BACKGROUND

Inflammatory bowel diseases (IBD) are characterized by chronic relapsing inflammation of the gastrointestinal tract and encompass Crohn's disease and ulcerative colitis. IBD are often associated with extraintestinal manifestations affecting multiple organs including the liver. Increased levels of serum aminotransferases, possibly related to nonalcoholic fatty liver disease, constitute one of the most frequently described IBD-related liver diseases. The PNPLA3 I148M substitution is a major common genetic determinant of hepatic fat content and progression to chronic liver disease. The aim of this study was to investigate whether carriers of PNPLA3 148M allele with IBD have higher risk of liver steatosis and increase in transaminases levels.

METHODS

The PNPLA3 I148M (rs738409) genotype was performed by Taqman assays in 158 individuals from Southern Italy (namely, Catanzaro cohort) and in 207 individuals from Northern Italy (namely, Milan cohort) with a definite diagnosis of IBD. Demographic and clinical data and also alanine transaminase levels were collected for both cohorts. The Catanzaro cohort underwent liver evaluation by sonography and liver stiffness and controlled attenuation parameter measurements by transient elastography.

RESULTS

Here, we show for the first time that carriers of the PNPLA3 148M allele with IBD have a greater risk of hepatic steatosis (odds ratio, 2.9, and confidence interval, 1.1-7.8), higher controlled attenuation parameter values (P = 0.029), and increased circulating alanine transaminase (P = 0.035) in the Catanzaro cohort. We further confirm the higher alanine transaminase levels in the Milan cohort (P < 0.001).

CONCLUSIONS

Our results show that PNPLA3 148M carriers with IBD have higher susceptibility to hepatic steatosis and liver damage.

Treating liver fat and serum triglyceride levels in NAFLD, effects of PNPLA3 and TM6SF2 genotypes: Results from the WELCOME trial

BACKGROUND & AIMS

Genetic variation in both patatin-like phospholipase domain-containing protein-3 (PNPLA3) (I148M) and the transmembrane 6 superfamily member 2 protein (TM6SF2) (E167K) influences severity of liver disease, and serum triglyceride concentrations in non-alcoholic fatty liver disease (NAFLD), but whether either genotype influences the responses to treatments is uncertain.

METHODS

One hundred three patients with NAFLD were randomised to omega-3 fatty acids (DHA+EPA) or placebo for 15-18months in a double blind placebo controlled trial. Erythrocyte enrichment with DHA and EPA was measured by gas chromatography. PNPLA3 and TM6SF2 genotypes were measured by PCR technologies. Multivariable linear regression and analysis of covariance were undertaken to test the effect of genotypes on omega-3 fatty acid enrichment, end of study liver fat percentage and serum triglyceride concentrations. All models were adjusted for baseline measurements of each respective outcome.

RESULTS

Fifty-five men and 40 women (Genotypes PNPLA3 I148M, 148I/I=41, 148I/M=43, 148M/M=11; TM6SF2 E167K 167E/E=78, 167E/K+167K/K=17 participants) (mean ± SD age, 51 ± 11 years) completed the trial. Adjusting for baseline measurement, measured covariates and confounders, PNPLA3 148M/M variant was independently associated with percentage of DHA enrichment (B coefficient -1.02 (95% CI -1.97, -0.07), p=0.036) but not percentage of EPA enrichment (B coefficient -0.31 (95% CI -1.38, 0.75), p=0.56). This genotype was also independently associated with end of study liver fat percentage (B coefficient 9.5 (95% CI 2.53, 16.39), p=0.008), but not end of study triglyceride concentration (B coefficient -0.11 (95% CI -0.64, 0.42), p=0.68).

CONCLUSIONS

PNPLA3 148M/M variant influences the changes in liver fat and DHA tissue enrichment during the trial but not the change in serum triglyceride concentration.

A Meta-Analysis of the Association Between the I148M Variant of Patatin-Like Phospholipase Domain Containing 3 Gene and the Presence of Chronic Hepatitis C

CONTEXT

The objective of the current study was to evaluate the association between the I148M variant of patatin-like phospholipase domain-containing protein 3 (PNPLA3) and the presence of Chronic Hepatitis C (CHC) across different populations.

EVIDENCE ACQUISITION

This study was a meta-analysis of all relevant researches published in the literature from year 2000 to 2015. The odds ratios (ORs) of PNPLA3 allele distributions in CHC patients were analyzed and compared with healthy controls. The meta-analysis Revman 5.2 software was applied for investigating heterogeneity among individual studies and for summarizing all the studies. The meta-analysis was carried out according to the Cochrane Reviewers' Handbook recommendations. A total of 120 clinical trials or reports were retrieved, yet only five trials met the study selection criteria.

RESULTS

Five hospital-based case-control studies were included in the final analysis. The overall frequency of PNPLA3 gene polymorphisms was 20.4% (205/1005) in CHC and 10.23% (53/518) in controls. The summary odds ratio for the association of gene polymorphisms of PNPLA3 with the risk for CHC was determined as 2.20 (95% CI: 1.56 -3.11) and was statistically significant (P < 0.05).

CONCLUSIONS

The current meta-analysis showed an association between frequency of GG genotype of PNPLA3 and the risk of development of CHC in various populations throughout the world.

Stratification of Hepatocellular Carcinoma Patients Based on Acetate Utilization

Hepatocellular carcinoma (HCC) is a deadly form of liver cancer that is increasingly prevalent. We analyzed global gene expression profiling of 361 HCC tumors and 49 adjacent noncancerous liver samples by means of combinatorial network-based analysis. We investigated the correlation between transcriptome and proteome of HCC and reconstructed a functional genome-scale metabolic model (GEM) for HCC. We identified fundamental metabolic processes required for cell proliferation using the network centric view provided by the GEM. Our analysis revealed tight regulation of fatty acid biosynthesis (FAB) and highly significant deregulation of fatty acid oxidation in HCC. We predicted mitochondrial acetate as an emerging substrate for FAB through upregulation of mitochondrial acetyl-CoA synthetase (ACSS1) in HCC. We analyzed heterogeneous expression of ACSS1 and ACSS2 between HCC patients stratified by high and low ACSS1 and ACSS2 expression and revealed that ACSS1 is associated with tumor growth and malignancy under hypoxic conditions in human HCC.

Pathophysiology of lipid droplet proteins in liver diseases

Cytosolic lipid droplets (LDs) are present in most cell types, and consist of a core comprising neutral lipids, mainly triglycerides and sterol esters, surrounded by a monolayer of phospholipids. LDs are heterogeneous in their structure, chemical composition, and tissue distribution. LDs are coated by several proteins, including perilipins and other structural proteins, lipogenic enzymes, lipases and membrane-trafficking proteins. Five proteins of the perilipin (PLIN) family (PLIN1 (perilipin), PLIN2 (adipose differentiation-related protein), PLIN3 (tail-interacting protein of 47kDa), PLIN4 (S3-12), and PLIN5 (myocardial lipid droplet protein)), are associated with LD formation. More recently, the CIDE family of proteins, hypoxia-inducible protein 2 (HIG2), and patanin-like phospholipase domain-containing 3 (PNPLA3) have also gained attention in hepatic LD biology. Evidence suggests that LD proteins are involved in the pathophysiology of fatty liver diseases characterized by excessive lipid accumulation in hepatocytes. This review article will focus on how hepatic LDs and their associated proteins are involved in the pathogenesis of three chronic liver conditions: hepatitis C virus infection, non-alcoholic fatty liver disease, and alcoholic liver disease.

Statin use and non-alcoholic steatohepatitis in at risk individuals

BACKGROUND & AIMS

Excess hepatic free cholesterol contributes to the pathogenesis of non-alcoholic steatohepatitis, and statins reduce cholesterol synthesis. Aim of this study was to assess whether statin use is associated with histological liver damage related to steatohepatitis.

METHODS

The relationship between statin use, genetic risk factors, and liver damage was assessed in a multi-center cohort of 1201 European individuals, who underwent liver biopsy for suspected non-alcoholic steatohepatitis.

RESULTS

Statin use was recorded in 107 subjects, and was associated with protection from steatosis, NASH, and fibrosis stage F2-F4, in a dose-dependent manner (adjusted p<0.05 for all). In 100 treated patients matched 1:1 for modality of recruitment, gender, presence of IFG or type 2 diabetes, PNPLA3 I148M risk alleles, TM6SF2 E167K variant, age, and BMI, statin use remained associated with protection from steatosis (OR 0.09, 95% C.I. 0.01-0.32; p=0.004), steatohepatitis (OR 0.25, 95% C.I. 0.13-0.47; p<0.001), and fibrosis stage F2-F4 (OR 0.42, 95% C.I. 0.20-0.8; p=0.017). Results were confirmed in a second analysis, where individuals were matched within recruitment center (p<0.05 for all). The protective effect of statins on steatohepatitis was stronger in subjects not carrying the I148M PNPLA3 risk variant (p=0.02 for interaction), as statins were negatively associated with steatohepatitis in patients negative (p<0.001), but not in those positive for the I148M variant (p=n.s.).

CONCLUSIONS

Statin use was associated with protection towards the full spectrum of liver damage in individuals at risk of non-alcoholic steatohepatitis. However, the I148M PNPLA3 risk variant limited this beneficial effect.

PNPLA3 I148M Variant Influences Circulating Retinol in Adults with Nonalcoholic Fatty Liver Disease or Obesity

BACKGROUND

Retinol is a lipid-soluble essential nutrient that is stored as retinyl esters in lipid droplets of hepatic stellate cells. Patatin-like phospholipase domain-containing 3 (PNPLA3), through its retinyl-palmitate lipase activity, releases retinol from lipid droplets in hepatic stellate cells in vitro and ex vivo. We have shown that the genetic variant I148M (rs738409) reduces the PNPLA3 retinyl-palmitate lipase activity.

OBJECTIVE

The aim of the present genetic association study was to test whether overweight/obese carriers of the PNPLA3 148M mutant allele had lower circulating concentrations of retinol than individuals who are homozygous for the 148I allele.

METHODS

PNPLA3 I148M (rs738409) was genotyped by Taqman assay in 76 overweight/obese individuals [BMI (kg/m(2)) ≥25; mean ± SD age: 59.7 ± 11.4 y; male gender: 70%] with a histologic diagnosis of nonalcoholic fatty liver disease (NAFLD; namely the Milan NAFLD cohort) and in 413 obese men (BMI ≥30; mean ± SD age: 57.1 ± 4.9 y) from the α-Tocopherol, β-Carotene Cancer Prevention (ATBC) Study. Serum concentrations of retinol and α-tocopherol were measured by HPLC in both cohorts. β-Carotene concentrations in the ATBC study were measured by using HPLC.

RESULTS

The PNPLA3 148M mutant allele was associated with lower fasting circulating concentrations of retinol (β = -0.289, P = 0.03) in adults with NAFLD (Milan NAFLD cohort). The PNPLA3 148M mutant allele was also associated with lower fasting circulating concentrations of retinol in adults with a BMI ≥30 (ATBC study; β = -0.043, P = 0.04).

CONCLUSION

We showed for the first time, to our knowledge, that carriers of the PNPLA3 148M allele with either fatty liver plus obesity or obesity alone have lower fasting circulating retinol concentrations.

Influence of ethnicity on the distribution of genetic polymorphisms associated with risk of chronic liver disease in South American populations

BACKGROUND

The global burden of chronic liver disease is rising. Besides environmental, behavioral, viral and metabolic factors, genetic polymorphisms in patatin-like phospholipase-3 (PNPLA3) and vitamin D receptor (VDR) genes have been related to the development of chronic liver disease and progression towards liver cancer. Although their prevalence differs remarkably among ethnic groups, the frequency of these polymorphisms in South American populations -whose genetic background is highly admixed- has been poorly studied. Hence, the aim of this study was to characterize polymorphisms related to chronic liver disease and their association with the genetic ancestry of South American populations.

RESULTS

DNA samples from 258 healthy unrelated male volunteers were analyzed. The frequencies of G and C alleles of rs738409 polymorphism (PNPLA3 gene) were 74 % and 26 %, respectively; whereas the bAt (CCA) haplotype (VDR gene) was observed in 32.5 % of the samples. The GG genotype of PNPLA3 rs738409 and the bAt (CCA) haplotype -associated with an increased risk of chronic liver disease and progression towards liver cancer- were significantly more frequent among samples exhibiting maternal and paternal Native American haplogroups (63.7 % and 64.6 %), intermediate among admixed samples (45.1 % and 44.9 %; p = 0.03) and the lowest for Non-native American ancestry (30.1 % and 29.6 %; p = 0.001 and p = 0.0008).

CONCLUSIONS

These results suggest that individuals with Native American ancestry might have a high risk of chronic liver disorders and cancer. Furthermore, these data not only support the molecular evaluation of ancestry in multi-ethnic population studies, but also suggest that the characterization of these variants in South American populations may be useful for establishing public health policies aimed at high risk ethnic communities.

Genetic Factors in the Pathogenesis of Nonalcoholic Fatty Liver and Steatohepatitis

Liver fat accumulation generally related to systemic insulin resistance characterizes nonalcoholic fatty liver disease (NAFLD), which in the presence of nonalcoholic steatohepatitis (NASH) can progress towards cirrhosis and hepatocellular carcinoma. Due to the epidemic of obesity, NAFLD is now the most frequent liver disease in Western countries. Epidemiological, familial, and twin studies provide evidence for a strong genetic component of NAFLD susceptibility. Recently, genome-wide association studies led to the identification of the major inherited determinants of hepatic fat accumulation: patatin-like phospholipase domain-containing 3 (PNPLA3) I148M gene and transmembrane 6 superfamily member 2 (TM6SF2) E167K gene variants, involved in lipid droplets remodelling and very low-density lipoproteins secretion, are the major determinants of interindividual differences in liver steatosis, and susceptibility to progressive NASH. In this review, we aimed to provide an overview of recent insights into the genetics of hepatic fat accumulation and steatohepatitis.

Influence of the PNPLA3 rs738409 Polymorphism on Non-Alcoholic Fatty Liver Disease and Renal Function among Normal Weight Subjects

In normal weight subjects (body mass index < 25 kg/m2), non-alcoholic fatty liver disease (NAFLD) is likely to coexist with metabolic diseases. The patatin-like phospholipase 3 (PNPLA3) polymorphism rs738409 (c.444C>G) is associated with the risk of NAFLD and/or renal dysfunction; however, the influence of the weight status on the associations remains unknown. We aimed to clarify the associations of the PNPLA3 polymorphism with the risk of NAFLD and/or renal dysfunction, while also paying careful attention to the weight status of the subjects. Cross-sectional and retrospective longitudinal studies with 5.5 ± 1.1 years of follow-up were conducted in 740 and 393 Japanese participants (61.2 ± 10.5 and 67.5 ± 6.0 years), respectively, during a health screening program. Among 591 subjects who did not have a habitual alcohol intake and/or hepatitis B or C virus infections, the PNPLA3 G/G genotype was associated with the risk for NAFLD in normal weight subjects [odds ratio (95% CI): 3.06 (1.11-8.43), P < 0.05]. Among all subjects, carriers of the PNPLA3 G/G genotype with a normal weight had a lower eGFR than those of the C/C genotype [partial regression coefficient (SE): -3.26 (1.48), P < 0.05]. These associations were replicated in the longitudinal analyses. Among the overweight subjects, none of the genotypes were significantly associated in the cross-sectional and longitudinal analyses; however, the power of the analyses was small, especially in the analyses among overweight subjects. The findings of this study suggest that carriers of the PNPLA3 G/G genotype with a normal weight status should nevertheless be carefully monitored for the presence of NAFLD and/or renal dysfunction.

The 148 M allele of the PNPLA3 is associated with plasma irisin levels in a population sample of Caucasian children: The PANIC Study

BACKGROUND

There are no previous data on the association of PNPLA3 I148M polymorphism (rs738409) with circulating adipokines and myokines in children.

SUBJECTS/METHODS

Subjects were a population sample of 481 Caucasian children aged 6-8 years. We assessed circulating levels of irisin together with IL-6, TNF-α, leptin, high molecular weight (HMW)-adiponectin, alanine aminotransferase (ALT) and gamma-glutamyl transferase (GGT) while the subjects were stratified according to PNPLA3 I148M variants.

RESULTS

The PNPLA3 rs738409 polymorphism had a linear relationship with plasma levels of irisin after adjustment for age, sex and body height (p=0.007) but it was not associated with circulating levels of interleukin- 6 (IL-6), tumor-necrosis factor α (TNF-α), leptin or HMW-adiponectin.

CONCLUSION

PNPLA3 148M allele carriers had higher plasma levels of irisin than the non-carriers. This might be due to compensatory mechanism to limit early steatotic and inflammatory changes in the liver.

Understanding the pathophysiological mechanisms in the pediatric non-alcoholic fatty liver disease: The role of genetics

Classically, the non-alcoholic fatty liver disease (NAFLD) physiopathology and progression has been summarized in the two hits hypothesis. The first hit is represented by the action of hyperinsulinemia and insulin resistance, accompanying obesity, that leads to liver steatosis increasing the absolute non esterified fatty acids uptake in the liver and the esterification to form triacylglycerol. The oxidative stress is involved in the second hit leading to the progression to nonalcoholic steatohepatitis (NASH) because of its harmful action on steatosic hepatocytes. However, at the present time, the two hits hypothesis needs to be updated because of the discover of genetic polymorphisms involved both in the liver fat accumulation and progression to NASH that make more intriguing understanding the NAFLD pathophysiological mechanisms. In this editorial, we want to underline the role of PNPLA3 I148M, GPR120 R270H and TM6SF2 E167K in the pediatric NAFLD development because they add new pieces to the comprehension of the NAFLD pathophysiological puzzle. The PNPLA3 I148M polymorphism encodes for an abnormal protein which predisposes to intrahepatic triglycerides accumulation both for a loss-of-function of its triglyceride hydrolase activity and for a gain-of-function of its lipogenic activity.

Therefore, it is involved in the first hit, such as TM6SF2 E167K polymorphisms that lead to intrahepatic fat accumulation through a reduced very low density lipoprotein secretion. On the other hand, the GPR120 R270H variant, reducing the anti-inflammatory action of the GPR120 receptor expressed by Kuppfer cells, is involved in the second hit leading to the liver injury.

Strategies, models and biomarkers in experimental non-alcoholic fatty liver disease research

Non-alcoholic fatty liver disease encompasses a spectrum of liver diseases, including simple steatosis, steatohepatitis, liver fibrosis and cirrhosis and hepatocellular carcinoma. Non-alcoholic fatty liver disease is currently the most dominant chronic liver disease in Western countries due to the fact that hepatic steatosis is associated with insulin resistance, type 2 diabetes mellitus, obesity, metabolic syndrome and drug-induced injury. A variety of chemicals, mainly drugs, and diets is known to cause hepatic steatosis in humans and rodents. Experimental non-alcoholic fatty liver disease models rely on the application of a diet or the administration of drugs to laboratory animals or the exposure of hepatic cell lines to these drugs. More recently, genetically modified rodents or zebrafish have been introduced as non-alcoholic fatty liver disease models. Considerable interest now lies in the discovery and development of novel non-invasive biomarkers of non-alcoholic fatty liver disease, with specific focus on hepatic steatosis. Experimental diagnostic biomarkers of non-alcoholic fatty liver disease, such as (epi)genetic parameters and '-omics'-based read-outs are still in their infancy, but show great promise. In this paper, the array of tools and models for the study of liver steatosis is discussed. Furthermore, the current state-of-art regarding experimental biomarkers such as epigenetic, genetic, transcriptomic, proteomic and metabonomic biomarkers will be reviewed.

Calcium-independent phospholipases A2 and their roles in biological processes and diseases

Among the family of phospholipases A2 (PLA2s) are the Ca(2+)-independent PLA2s (iPLA2s) and they are designated group VI iPLA2s. In relation to secretory and cytosolic PLA2s, the iPLA2s are more recently described and details of their expression and roles in biological functions are rapidly emerging. The iPLA2s or patatin-like phospholipases (PNPLAs) are intracellular enzymes that do not require Ca(2+) for activity, and contain lipase (GXSXG) and nucleotide-binding (GXGXXG) consensus sequences. Though nine PNPLAs have been recognized, PNPLA8 (membrane-associated iPLA2γ) and PNPLA9 (cytosol-associated iPLA2β) are the most widely studied and understood. The iPLA2s manifest a variety of activities in addition to phospholipase, are ubiquitously expressed, and participate in a multitude of biological processes, including fat catabolism, cell differentiation, maintenance of mitochondrial integrity, phospholipid remodeling, cell proliferation, signal transduction, and cell death. As might be expected, increased or decreased expression of iPLA2s can have profound effects on the metabolic state, CNS function, cardiovascular performance, and cell survival; therefore, dysregulation of iPLA2s can be a critical factor in the development of many diseases. This review is aimed at providing a general framework of the current understanding of the iPLA2s and discussion of the potential mechanisms of action of the iPLA2s and related involved lipid mediators.

Composite prognostic models across the non-alcoholic fatty liver disease spectrum: Clinical application in developing countries

Heterogeneity in clinical presentation, histological severity, prognosis and therapeutic outcomes characteristic of non-alcoholic fatty liver disease (NAFLD) necessitates the development of scientifically sound classification schemes to assist clinicians in stratifying patients into meaningful prognostic subgroups. The need for replacement of invasive liver biopsies as the standard method whereby NAFLD is diagnosed, graded and staged with biomarkers of histological severity injury led to the development of composite prognostic models as potentially viable surrogate alternatives. In the present article, we review existing scoring systems used to (1) confirm the presence of undiagnosed hepatosteatosis; (2) distinguish between simple steatosis and NASH; and (3) predict advanced hepatic fibrosis, with particular emphasis on the role of NAFLD as an independent cardio-metabolic risk factor. In addition, the incorporation of functional genomic markers and application of emerging imaging technologies are discussed as a means to improve the diagnostic accuracy and predictive performance of promising composite models found to be most appropriate for widespread clinical adoption.

Insulin resistance in clinical and experimental alcoholic liver disease

Alcoholic liver disease (ALD) is the number one cause of liver failure worldwide; its management costs billions of healthcare dollars annually. Since the advent of the obesity epidemic, insulin resistance (IR) and diabetes have become common clinical findings in patients with ALD; and the development of IR predicts the progression from simple steatosis to cirrhosis in ALD patients. Both clinical and experimental data implicate the impairment of several mediators of insulin signaling in ALD, and experimental data suggest that insulin-sensitizing therapies improve liver histology. This review explores the contribution of impaired insulin signaling in ALD and summarizes the current understanding of the synergistic relationship between alcohol and nutrient excess in promoting hepatic inflammation and disease.

The UCP2 -866 G>A promoter region polymorphism is associated with nonalcoholic steatohepatitis

BACKGROUND & AIMS

Uncoupling protein 2 - UCP2 - regulates mitochondrial lipid fluxes and reactive oxygen species production by the respiratory chain. The -866 G>A UCP2 promoter region polymorphism has been linked to insulin resistance and lipid metabolism. The aim of this study was to assess whether the -866 G>A UCP2 polymorphism predisposes to nonalcoholic steatohepatitis in patients at risk, and the relationship with lipid metabolism and hepatic UCP2 expression.

METHODS

We considered 688 Italian patients who underwent liver biopsy for suspected NASH, and 232 healthy controls. The UCP2 -866 G>A polymorphism was determined by allele specific oligonucleotide probes, hepatic UCP2 mRNA levels by quantitative real-time PCR.

RESULTS

UCP2 A/A genotype was associated with a reduced risk of nonalcoholic steatohepatitis (Odds Ratio 0.49, 95% C.I. 0.26-0.90; P = 0.02; adjusted for age, sex, BMI, impaired fasting glucose or diabetes, PNPLA3 I148M alleles and recruitment centre). The A/A genotype was associated with reduced risk of steatosis grade G2-G3 and nonalcoholic steatohepatitis in patients without (P = 0.003 and P = 0.01 respectively), but not in those with (P = NS) impaired fasting glucose/diabetes. The UCP2 A/A genotype was associated with higher hepatic UCP2 mRNA levels (adjusted P = 0.008). Concerning the metabolic traits, the UCP2 A/A genotype was associated with higher total serum cholesterol levels (adjusted P = 0.03), but not with serum HDL, triglycerides or impaired fasting glucose/diabetes.

CONCLUSIONS

UCP2 -866 A/A genotype is associated with increased hepatic UCP2 expression and reduced risk of nonalcoholic steatohepatitis, particularly in subjects with normal fasting glucose.

PNPLA3 polymorphisms (rs738409) and non-alcoholic fatty liver disease risk and related phenotypes: a meta-analysis

BACKGROUND AND AIM

One single-nucleotide polymorphisms (SNPs) rs738409 in the patatin-like phospholipase domain-containing 3 gene (PNPLA3) has been implicated in susceptibility to non-alcoholic fatty liver disease (NAFLD) across different populations. One meta-analysis confirmed this association, but within it, only two Asian studies were included. This meta-analysis aimed to investigate the association in Asian population.

METHODS

All eligible case-control studies were identified by searching through PubMed and Chinese language databases (CNKI and WanFang) up to July 1, 2014. Pooled estimates (odds ratio [OR] and standardized mean difference) were used to assess the strength of associations in fixed or random-effects models.

RESULTS

A total of 12 studies with 4495 cases and 7431 controls were included. SNP rs738409 G allele was confirmed as a risk factor for NAFLD (G allele vs C allele: OR = 1.92, 95% confidence interval [95%CI]: 1.54-2.39). In addition, based on studies with certain clinical measurements data, G allele carriers were more likely to have higher level of serum alanine aminotransferase (ALT) (standard mean difference [SMD] = 7.03, 95% CI: 2.47-11.60), and higher fibrosis score (SMD = 0.39, 95% CI: 0.18-0.60).

CONCLUSION

This study provided evidence of SNP rs738409 G allele as a strong risk factor of NAFLD susceptibility and higher level of serum ALT in Asian population.

Recent advances in hemochromatosis: a 2015 update : a summary of proceedings of the 2014 conference held under the auspices of Hemochromatosis Australia

This review focuses on iron metabolism, the genetics of hemochromatosis, current treatment protocols and various screening methods. Even though the most common form of hereditary hemochromatosis, C282Y gene mutations in the HFE gene, has been extensively studied, novel mutations in both HFE and non-HFE genes have been implicated in this disease. These have important implications for the Asia-Pacific region. In overload, deposition of iron in various body tissues leads to toxic damage. Patients commonly present with non-specific symptoms of malaise and lethargy. Biochemical, imaging and genetic testing can be carried out to confirm diagnosis. Venesection forms the mainstay of treatment and at present cascade screening of affected families is recommended over population-level screening.

A concise review of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of the metabolic syndrome and the incidence of which is rising rapidly due to the increasing epidemic of obesity in both adults and children. The initial accumulation of fat followed by subsequent inflammation is central to the development of liver damage, and is critically influenced by host factors including age, gender, presence of diabetes, genetic polymorphisms and more recently by the gut microbiome. An increasing body of data suggest that NAFLD is also an independent risk factor of cardiovascular disease, which remains the commonest cause of mortality in such patients. This review focusses on the pathogenesis of NAFLD, and the evolution of new approaches to the management and treatment of NAFLD.

Pnpla3I148M knockin mice accumulate PNPLA3 on lipid droplets and develop hepatic steatosis

A sequence polymorphism (rs738409, I148M) in patatin-like phospholipid domain containing protein 3 (PNPLA3) is strongly associated with nonalcoholic fatty liver disease (NAFLD), but the mechanistic basis for this association remains enigmatic. Neither ablation nor overexpression of wild-type PNPLA3 affects liver fat content in mice, whereas hepatic overexpression of the human 148M transgene causes steatosis. To determine whether the 148M allele causes fat accumulation in the liver when expressed at physiological levels, we introduced a methionine codon at position 148 of the mouse Pnpla3 gene. Knockin mice had normal levels of hepatic fat on a chow diet, but when challenged with a high-sucrose diet their liver fat levels increased 2 to 3-fold compared to wild-type littermates without any associated changes in glucose homeostasis. The increased liver fat in the knockin mice was accompanied by a 40-fold increase in PNPLA3 on hepatic lipid droplets, with no increase in hepatic PNPLA3 messenger RNA (mRNA). Similar results were obtained when the catalytic dyad of PNPLA3 was inactivated by substituting the catalytic serine with alanine (S47A).

CONCLUSION

These data provide the first direct evidence that physiological expression of PNPLA3 148M variant causes NAFLD, and that the accumulation of catalytically inactive PNPLA3 on the surfaces of lipid droplets is associated with the accumulation of TG in the liver.

The rs738409 (I148M) variant of the PNPLA3 gene and cirrhosis: a meta-analysis

The human patatin-like phospholipase domain-containing-3 (PNPLA3) gene rs738409 C>G polymorphism is associated with several types of liver disease. The aim of this meta-analysis was to assess the risk of cirrhosis on the basis of rs738409 allele frequency and genotype. Medline, the Cochrane Library, EMBASE, and Google Scholar were searched for prospective and retrospective studies assessing the effect of the rs738409 polymorphism on liver cirrhosis. Seven studies, involving 2,023 patients with cirrhosis, were included. The G allele was associated with a significantly increased risk of cirrhosis versus the C allele [pooled odds ratio (OR) = 1.86, 95% confidence interval (CI) = 1.64-2.12, Z = 9.55, P < 0.001]. Both the GC and GG genotypes were associated with a significantly increased risk of cirrhosis versus the CC genotype (GC vs. CC: pooled OR = 1.73, 95% CI = 1.51-1.98, Z = 7.86, P < 0.001; GG vs. CC: pooled OR = 3.41, 95% CI = 2.77-4.18, Z = 11.65, P < 0.001). There was no evidence of publication bias. Our findings suggest that patients at risk for liver cirrhosis may benefit from PNPLA3 genotyping and thus more intensive monitoring if the rs738409 C>G polymorphism is identified.

Effect of excess body weight on the genetic susceptibility to cancer

Excess body weight and genetics play important roles in cancer susceptibility. Although several studies have reported on obesity and genetic variants as separate risk factors for cancer, very few studies have investigated the interaction between excess body weight and genetic variants in cancer susceptibility. In this review, we focus on the interplay between these 2 risk factors, which are a major determinant of the individual risk of cancer onset.

Obesity and the liver: nonalcoholic fatty liver disease

The increasing prevalence of nonalcoholic fatty liver disease (NAFLD) parallels the rise of obesity and its complications. NAFLD is a common cause of cirrhosis and a leading indication for liver transplant. Genetic susceptibility, dietary composition, and exercise habits influence the development of NAFLD, and insulin resistance results in widespread metabolic perturbations with a net effect of triglyceride accumulation in the liver. Some patients will develop hepatocyte cellular injury and fibrosis of the liver, which can progress to cirrhosis and require liver transplant. Treatments targeting the pathophysiological mechanisms of NAFLD exist, but carry some potential risk and are not universally effective. Weight loss and lifestyle changes remain the most effective and safest approach, but sustainable change is difficult for most patients to achieve. Future work will continue to focus on developing effective and safe interventions to prevent the development of advanced liver disease, whereas efforts in the public health domain continue to combat obesity.

Future therapy of portal hypertension in liver cirrhosis - a guess

In patients with chronic liver disease, portal hypertension is driven by progressive fibrosis and intrahepatic vasoconstriction. Interruption of the initiating and perpetuating etiology—mostly leading to necroinflammation—is possible for several underlying causes, such as autoimmune hepatitis, hepatitis B virus (HBV) infection, and most recently hepatitis C virus (HCV) infection. Thus, in the long run, lifestyle-related liver damage due to chronic alcoholism or morbid obesity will remain the main factor leading to portal hypertension. Both causes are probably more easily countered by socioeconomic measures than by individual approaches. If chronic liver injury supporting fibrogenesis and portal hypertension cannot be interrupted, a wide variety of tools are available to modulate and reduce intrahepatic resistance and therewith portal hypertension. Many of these have been evaluated in animal models. Also, some well-established drugs, which are used in humans for other indications (for example, statins), are promising if applied early and concomitantly to standard therapy. In the future, more individually tailored strategies must also be considered in line with the spectrum of portal hypertensive complications and risk factors defined by high-throughput analysis of the patient’s genome, transcriptome, metabolome, or microbiome.

Systematic review with meta-analysis: the I148M variant of patatin-like phospholipase domain-containing 3 gene (PNPLA3) is significantly associated with alcoholic liver cirrhosis

BACKGROUND

Several studies have reported an association between alcoholic liver cirrhosis (ALC) or other forms of alcoholic liver disease (ALD) and the genetic variant rs738409 (C>G) in adiponutrin/patatin-like phospholipase domain-containing 3 gene (PNPLA3).

AIM

To evaluate the influence of this variant on ALC and other forms of ALD.

METHODS

We performed a systematic review of previous studies on the relationship between rs738409 of PNPLA3 and ALD and meta-analysis was conducted in a random-effects model. Calculations of the odds ratios (ORs) and their confidence intervals (CIs), tests for heterogeneity and sensitivity analyses were performed.

RESULTS

Database search identified 11 previous studies available for inclusion with a total of 3495 patients with ALD (2087 with ALC) and 5038 controls (4007 healthy subjects and 1031 alcoholics without ALD). Patients with ALC compared to controls had a significantly higher prevalence of the G allele when comparing GG vs. CC (OR 4.30, 95% CI 3.25-5.69; P < 0.00001) or GC vs. CC genotypes (GC vs. CC: OR 1.91, 95% CI 1.67-2.17) or under a recessive or dominant model. Similar results were found when comparing separately patients with ALC vs. alcoholics without ALD or healthy subjects. An association of the G allele with ALD emerged when comparing ALD patients vs. alcoholics without ALD and/or healthy subjects although moderate to large heterogeneity was observed. Our data suggested an additive genetic model for this variant in ALD.

CONCLUSION

Our meta-analysis shows that the rs738409 variant of PNPLA3 is clearly associated with alcoholic liver cirrhosis.

Interaction between PNPLA3 I148M variant and age at infection in determining fibrosis progression in chronic hepatitis C

Background and Aims

The PNPLA3 I148M sequence variant favors hepatic lipid accumulation and confers susceptibility to hepatic fibrosis and hepatocellular carcinoma. The aim of this study was to estimate the effect size of homozygosity for the PNPLA3 I148M variant (148M/M) on the fibrosis progression rate (FPR) and the interaction with age at infection in chronic hepatitis C (CHC).

Methods

FPR was estimated in a prospective cohort of 247 CHC patients without alcohol intake and diabetes, with careful estimation of age at infection and determination of fibrosis stage by Ishak score.

Results

Older age at infection was the strongest determinant of FPR (p<0.0001). PNPLA3 148M/M was associated with faster FPR in individuals infected at older age (above the median, 21 years; −0.64±0.2, n = 8 vs. −0.95±0.3, n = 166 log₁₀ FPR respectively; p = 0.001; confirmed for lower age thresholds, p<0.05), but not in those infected at younger age (p = ns). The negative impact of PNPLA3 148M/M on fibrosis progression was more marked in subjects at risk of altered hepatic lipid metabolism (those with grade 2–3 steatosis, genotype 3, and overweight; p<0.05). At multivariate analysis, PNPLA3 148M/M was associated with FPR (incremental effect 0.08±0.03 log₁₀ fibrosis unit per year; p = 0.022), independently of several confounders, and there was a significant interaction between 148M/M and older age at infection (p = 0.025). The association between 148M/M and FPR remained significant even after adjustment for steatosis severity (p = 0.032).

Conclusions

We observed an interaction between homozygosity for the PNPLA3 I148M variant and age at infection in determining fibrosis progression in CHC patients.

Hepatic steatosis and PNPLA3 I148M variant are associated with serum Fetuin-A independently of insulin resistance

BACKGROUND & AIMS

Fetuin-A is a liver-derived peptide associated with insulin resistance. Aim of this cross-sectional study was to evaluate whether Fetuin-A is increased in patients with nonalcoholic fatty liver disease (NAFLD) vs. healthy subjects without metabolic abnormalities and the association with insulin resistance and liver damage. To investigate the causal relationship between fatty liver and Fetuin-A, we also analysed whether the inherited I148M PNPLA3 variant modulates Fetuin-A.

METHODS

In 137 patients with histological NAFLD, complete metabolic characterization, PNPLA3 genotype, and in 260 healthy subjects without metabolic alterations, Fetuin-A was measured by enzyme-linked immunoabsorbent assay.

RESULTS

Serum Fetuin-A was higher in NAFLD patients than in controls (P < 0·0001), independently of age, sex, BMI, insulin resistance, dyslipidemia, adiponectin, PNPLA3 I148M and ALT levels (OR 1·006 95% CI 1·003-1·11; P = 0·003). In NAFLD patients, Fetuin-A was associated with steatosis severity (P = 0·03) and metabolic syndrome features, but not with hepatic inflammation. At multivariate analysis, Fetuin-A levels were associated with BMI, triglycerides, hyperglycemia and PNPLA3 I148M (P = 0·034) independently also of age, sex and ALT levels. As PNPLA3 I148M is a strong and inherited determinant of liver fat without affecting insulin resistance and lipid levels, these data suggest that steatosis has a causal role in determining serum Fetuin-A levels.

CONCLUSIONS

Liver fat accumulation and the I148M variant of PNPLA3 are associated with serum Fetuin-A levels independently of insulin resistance. Fetuin-A may be implicated in the pathogenesis of metabolic complications associated with NAFLD.

Current status of fibrosis markers

PURPOSE OF REVIEW

Improved understanding of the pathophysiology of fibrosis and recent technological advances have resulted in the development of several serum biomarkers and imaging tools as noninvasive alternatives to biopsy. Most of these markers have been developed in chronic hepatitis C (CHC) and nonalcoholic fatty liver disease (NAFLD) patients. This review highlights some of the recent advances and potential clinical application of these modalities.

RECENT FINDINGS

Many noninvasive approaches initially developed for binary disease staging in CHC continue to be refined for diagnostic use in other chronic liver disease such as NAFLD. A combination of serum markers and imaging tools appears useful in reducing the need for biopsy for the diagnosis of cirrhosis, and providing functional assessment in advanced stage disease. Cytokeratin-18 fragments, controlled attenuation parameter (CAP), real-time elastography, and magnetic resonance imaging approaches appear promising for NAFLD, but require further validation.

SUMMARY

Current noninvasive tests of fibrosis provide good diagnostic and prognostic utility for advanced stage liver disease, and have been adapted into clinical practice for CHC. Reliable biomarkers for steatosis, nonalcoholic steatohepatitis, and assessment of fibrosis progression in chronic liver disease are still required. Continued advances in bioimaging and functional genomics will be important for quantitative assessment of fibrosis and future biomarker development.