Circulating triacylglycerol signatures in nonalcoholic fatty liver disease associated with the I148M variant in PNPLA3 and with obesity

The association between platelet-related parameters and nonalcoholic fatty liver disease in a metabolically healthy nonobese population

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease characterized by subclinical inflammation and is related to obesity and metabolic syndrome (MS), but it is also frequently observed in nonobese populations. We aimed to evaluate the relationship between the white blood cell count-to-mean platelet volume ratio (WBC/MPV), platelet-to-lymphocyte count ratio (PLR) and lymphocyte-monocyte ratio (LMR) in association with NAFLD, considering the presence of obesity and MS. Additionally, we aimed to investigate whether these parameters exhibited similar correlations in metabolic dysfunction-associated steatotic liver disease (MASLD) as observed in NAFLD. This cross-sectional study included subjects who underwent a comprehensive health evaluation, including blood tests and abdominal ultrasonography. Subgroup analyses were conducted based on obesity and MS. Out of a total 5929 subjects (3271 males, mean age 49.7 ± 10.6 years), 2253 (38.0%) had NAFLD. WBC/MPV was significantly higher, and PLR was significantly lower in subjects with NAFLD. In the analysis restricted to the nonobese (BMI < 25 kg/m2) population without MS, both WBC/MPV and PLR were independently associated with NAFLD: WBC/MPV (adjusted OR 3.366; 95% CI 2.238-5.066) and PLR (adjusted OR 0.997; 95% CI 0.996-0.999). When assessing the risk of NAFLD based on the WBC/MPV and PLR quartiles, the adjusted OR and 95% CI for the lowest quartile compared to the highest were 2.055 (95% CI 1.626-2.602) for WBC/MPV and 0.660 (95% CI 0.523-0.832) for PLR in the nonobese, metabolically healthy group. The levels of WBC/MPV and PLR were independently associated with NAFLD. Furthermore, in MASLD, an association with WBC/MPV, PLR and LMR was identified, similar to the results observed in NAFLD, even after adjusting for confounding variables. In conclusion, the present study demonstrated a significant association between NAFLD and platelet-related parameters, especially in nonobese, metabolically healthy subjects.

Familial clustering of nonalcoholic fatty liver disease in first-degree relatives of adults with lean nonalcoholic fatty liver disease

BACKGROUND AND AIMS

The heritability of nonalcoholic fatty liver disease (NAFLD) in lean individuals is undetermined. This familial aggregation study aimed to evaluate familial linkage for NAFLD and the risk of NAFLD among first-degree relatives of probands with lean NAFLD.

METHODS

This study prospectively recruited cohorts of probands with lean NAFLD, probands with obese NAFLD, and lean probands with non-NAFLD and their respective first-degree relatives. A total of 257 participants were evaluated for liver steatosis, defined by the controlled attenuation parameter ≥288 dB/m2 , metabolic characteristics, and the PNPLA3, TM6SF2, and MBOAT7 polymorphisms.

RESULTS

The prevalence of NAFLD in first-degree relatives of lean NAFLD probands (39.9%) was similar to that in the obese NAFLD group (36.9%) and was significantly higher than in lean persons without NAFLD (19.1%). First-degree relatives of probands with NAFLD who were male, and had central obesity, hypertriglyceridaemia, insulin resistance, and the PNPLA3 rs738409C>G allele had a significantly higher prevalence of NAFLD. After multivariable adjustment for gender, metabolic characteristics, and the PNPLA3 rs738409C>G allele, first-degree relatives of probands with lean NAFLD (odds ratio [OR], 5.13; 95% CI, 1.77-14.86) and obese NAFLD (OR, 3.20; 95% CI, 1.14-8.99) exhibited an increased risk of NAFLD compared with those of lean controls without NAFLD.

CONCLUSIONS

Our well-phenotype cohorts revealed familial clustering of NAFLD and higher risks of NAFLD in first-degree relatives of probands with lean or obese NAFLD. The findings encourage clinicians caring for NAFLD patients to be more vigilant for NAFLD in their family members.

Metabolic Syndrome and Its Association with Nonalcoholic Steatohepatitis

The relationship between insulin resistance, metabolic syndrome (MetS), and nonalcoholic fatty liver disease (NAFLD) is complicated. Although insulin resistance is almost universal in people with NAFLD and MetS, NAFLD may be present without features of MetS and vice versa. While NAFLD has a strong correlation with cardiometabolic risk factors, these are not intrinsic components of this condition. Taken together, our knowledge gaps call for caution regarding the common assertion that NAFLD is the hepatic manifestation of the MetS, and for defining NAFLD in broad terms as a "metabolic dysfunction" based on a diverse and poorly understood constellation of cardiometabolic features.

PNPLA3 rs738409 risk genotype decouples TyG index from HOMA2-IR and intrahepatic lipid content

BACKGROUND

Recent reports suggested a different predictive value for TyG index compared to HOMA-IR in coronary artery calcification (CAC) and other atherosclerotic outcomes, despite that both indices are proposed as surrogate markers of insulin resistance. We hypothesized a key role for liver pathology as an explanation and therefore assessed the relationship among the two indices and the intrahepatic lipid content stratified by PNPLA3 rs738409 genotypes as a known non-alcoholic fatty liver disease (NAFLD) genetic risk.

METHODS

Thirty-nine women from a prior GDM-genetic study were recalled with PNPLA3 rs738409 CC and GG genotypes for metabolic phenotyping and to assess hepatic triglyceride content (HTGC). 75 g OGTT was performed, fasting lipid, glucose, insulin levels and calculated insulin resistance indices (TyG and HOMA2-IR) were used. HTGC was measured by MR based methods. Mann-Whitney-U, χ² and for the correlation analysis Spearman rank order tests were applied.

RESULTS

The PNPLA3 rs738409 genotype had a significant effect on the direct correlation between the HOMA2-IR and TyG index: the correlation (R = 0.52, p = 0.0054) found in the CC group was completely abolished in those with the GG (NAFLD) risk genotype. In addition, the HOMA2-IR correlated with HTGC in the entire study population (R = 0.69, p < 0.0001) and also separately in both genotypes (CC R = 0.62, p = 0.0006, GG: R = 0.74, p = 0.0058). In contrast, the correlation between TyG index and HTGC was only significant in rs738409 CC genotype group (R = 0.42, p = 0.0284) but not in GG group. A similar pattern was observed in the correlation between TG and HTGC (CC: R = 0.41, p = 0.0335), when the components of the TyG index were separately assessed.

CONCLUSIONS

PNPLA3 rs738409 risk genotype completely decoupled the direct correlation between two surrogate markers of insulin resistance: TyG and HOMA2-IR confirming our hypothesis. The liver lipid content increased in parallel with the HOMA2-IR independent of genotype, in contrast to the TyG index where the risk genotype abolished the correlation. This phenomenon seems to be related to the nature of hepatic fat accumulation and to the different concepts establishing the two insulin resistance markers.

Concise review of lipidomics in nonalcoholic fatty liver disease

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

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

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

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

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

Modeling PNPLA3-Associated NAFLD Using Human-Induced Pluripotent Stem Cells

BACKGROUND AND AIMS

NAFLD is a growing public health burden. However, the pathogenesis of NAFLD has not yet been fully elucidated, and the importance of genetic factors has only recently been appreciated. Genomic studies have revealed a strong association between NAFLD progression and the I148M variant in patatin-like phospholipase domain-containing protein 3 (PNPLA3). Nonetheless, very little is known about the mechanisms by which this gene and its variants can influence disease development. To investigate these mechanisms, we have developed an in vitro model that takes advantage of the unique properties of human-induced pluripotent stem cells (hiPSCs) and the CRISPR/CAS9 gene editing technology.

APPROACH AND RESULTS

We used isogenic hiPSC lines with either a knockout (PNPLA3^KO ) of the PNPLA3 gene or with the I148M variant (PNPLA3^I148M ) to model PNPLA3-associated NAFLD. The resulting hiPSCs were differentiated into hepatocytes, treated with either unsaturated or saturated free fatty acids to induce NAFLD-like phenotypes, and characterized by various functional, transcriptomic, and lipidomic assays. PNPLA3^KO hepatocytes showed higher lipid accumulation as well as an altered pattern of response to lipid-induced stress. Interestingly, loss of PNPLA3 also caused a reduction in xenobiotic metabolism and predisposed PNPLA3^KO cells to be more susceptible to ethanol-induced and methotrexate-induced toxicity. The PNPLA3^I148M cells exhibited an intermediate phenotype between the wild-type and PNPLA3^KO cells.

CONCLUSIONS

Together, these results indicate that the I148M variant induces a loss of function predisposing to steatosis and increased susceptibility to hepatotoxins.

Genome-wide association study of serum liver enzymes implicates diverse metabolic and liver pathology

Serum liver enzyme concentrations are the most frequently-used laboratory markers of liver disease, a major cause of mortality. We conduct a meta-analysis of genome-wide association studies of liver enzymes from UK BioBank and BioBank Japan. We identified 160 previously-unreported independent alanine aminotransferase, 190 aspartate aminotransferase, and 199 alkaline phosphatase genome-wide significant associations, with some affecting multiple different enzymes. Associated variants implicate genes that demonstrate diverse liver cell type expression and promote a range of metabolic and liver diseases. These findings provide insight into the pathophysiology of liver and other metabolic diseases that are associated with serum liver enzyme concentrations.

Serum liver enzymes are used as markers of liver disease, their concentration influenced in part by genetic factors. Here the authors meta-analyse genome-wide association studies on the UK Biobank and BioBank Japan to evaluate the association of three liver enzymes with liver and other metabolic diseases.

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

BACKGROUND

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSION

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

Review article: the emerging role of genetics in precision medicine for patients with non-alcoholic steatohepatitis

BACKGROUND

Non-alcoholic steatohepatitis (NASH) is a severe form of non-alcoholic fatty liver disease (NAFLD) characterised by liver fat accumulation, inflammation and progressive fibrosis. Emerging data indicate that genetic susceptibility increases risks of NAFLD, NASH and NASH-related cirrhosis.

AIMS

To review NASH genetics and discuss the potential for precision medicine approaches to treatment.

METHOD

PubMed search and inclusion of relevant literature.

RESULTS

Single-nucleotide polymorphisms in PNPLA3, TM6SF2, GCKR, MBOAT7 and HSD17B13 are clearly associated with NASH development or progression. These genetic variants are common and have moderate-to-large effect sizes for development of NAFLD, NASH and hepatocellular carcinoma (HCC). The genes play roles in lipid remodelling in lipid droplets, hepatic very low-density lipoprotein (VLDL) secretion and de novo lipogenesis. The PNPLA3 I148M variant (rs738409) has large effects, with approximately twofold increased odds of NAFLD and threefold increased odds of NASH and HCC per allele. Obesity interacts with PNPLA3 I148M to elevate liver fat content and increase rates of NASH. Although the isoleucine-to-methionine substitution at amino acid position 148 of the PNPLA3 enzyme inactivates its lipid remodelling activity, the effect of PNPLA3 I148M results from trans-repression of another lipase (ATGL/PNPLA2) by sequestration of a shared cofactor (CGI-58/ABHD5), leading to decreased hepatic lipolysis and VLDL secretion. In homozygous Pnpla3 I148M knock-in rodent models of NAFLD, targeted PNPLA3 mRNA knockdown reduces hepatic steatosis, inflammation and fibrosis.

CONCLUSION

The emerging genetic and molecular understanding of NASH paves the way for novel interventions, including precision medicines that can modulate the activity of specific genes associated with NASH.

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

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

Genetic variants that associate with cirrhosis have pleiotropic effects on human traits

BACKGROUND AND AIMS

Cirrhosis is characterized by extensive fibrosis of the liver and is a major cause of liver-related mortality. Cirrhosis is partially heritable but genetic contributions to cirrhosis have not been systemically explored. Here, we carry out association analyses with cirrhosis in two large biobanks and determine the effects of cirrhosis associated variants on multiple human disease/traits.

METHODS

We carried out a genome-wide association analysis of cirrhosis as a diagnosis in UK BioBank (UKBB; 1088 cases vs. 407 873 controls) and then tested top-associating loci for replication with cirrhosis in a hospital-based cohort from the Michigan Genomics Initiative (MGI; 875 cases of cirrhosis vs. 30 346 controls). For replicating variants or variants previously associated with cirrhosis that also affected cirrhosis in UKBB or MGI, we determined single nucleotide polymorphism effects on all other diagnoses in UKBB (PheWAS), common metabolic traits/diseases and serum/plasma metabolites.

RESULTS

Unbiased genome-wide association study identified variants in/near PNPLA3 and HFE, and candidate variant analysis identified variants in/near TM6SF2, MBOAT7, SERPINA1, HSD17B13, STAT4 and IFNL4 that reproducibly affected cirrhosis. Most affected liver enzyme concentrations and/or aspartate transaminase-to-platelet ratio index. PheWAS, metabolic trait and serum/plasma metabolite association analyses revealed effects of these variants on lipid, inflammatory and other processes including new effects on many human diseases and traits.

CONCLUSIONS

We identified eight loci that reproducibly associate with population-based cirrhosis and define their diverse effects on human diseases and traits.

Obesity genetics and cardiometabolic health: Potential for risk prediction

The increasing burden of obesity worldwide and its effect on cardiovascular disease (CVD) risk is an opportunity for evaluation of preventive approaches. Both obesity and CVD have a genetic background and polymorphisms within genes which enhance expression of variant proteins that influence CVD in obesity. Genome-based prediction may therefore be a feasible strategy, but the identification of genetically driven risk factors for CVD manifesting as clinically recognized phenotypes is a major challenge. Clusters of such risk factors include hyperglycaemia, hypertension, ectopic liver fat, and inflammation. All involve multiple genetic pathways having complex interactions with variable environmental influences. The factors that make significant contributions to CVD risk include altered carbohydrate homeostasis, ectopic deposition of fat in muscle and liver, and inflammation, with contributions from the gut microbiome. A futuristic model depends on harnessing the predictive power of plausible genetic variants, phenotype reversibility, and effective therapeutic choices based on genotype-phenotype interactions. Inverting disease phenotypes into ideal cardiovascular health metrics could improve genetic and epigenetic assessment, and form the basis of a future model for risk detection and early intervention.

Current Progress of Lipid Analysis in Metabolic Diseases by Mass Spectrometry Methods

BACKGROUND

Obesity, insulin resistance, diabetes, and metabolic syndrome are associated with lipid alterations, and they affect the risk of long-term cardiovascular disease. A reliable analytical instrument to detect changes in the composition or structures of lipids and the tools allowing to connect changes in a specific group of lipids with a specific disease and its progress, is constantly lacking. Lipidomics is a new field of medicine based on the research and identification of lipids and lipid metabolites present in human organism. The primary aim of lipidomics is to search for new biomarkers of different diseases, mainly civilization diseases.

OBJECTIVE

We aimed to review studies reporting the application of mass spectrometry for lipid analysis in metabolic diseases.

METHOD

Following an extensive search of peer-reviewed articles on the mass spectrometry analysis of lipids the literature has been discussed in this review article.

RESULTS

The lipid group contains around 1.7 million species; they are totally different, in terms of the length of aliphatic chain, amount of rings, additional functional groups. Some of them are so complex that their complex analyses are a challenge for analysts. Their qualitative and quantitative analysis of is based mainly on mass spectrometry.

CONCLUSION

Mass spectrometry techniques are excellent tools for lipid profiling in complex biological samples and the combination with multivariate statistical analysis enables the identification of potential diagnostic biomarkers.

Human Multilineage 3D Spheroids as a Model of Liver Steatosis and Fibrosis

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disorder in western countries. Despite the high prevalence of NAFLD, the underlying biology of the disease progression is not clear, and there are no approved drugs to treat non-alcoholic steatohepatitis (NASH), the most advanced form of the disease. Thus, there is an urgent need for developing advanced in vitro human cellular systems to study disease mechanisms and drug responses. We attempted to create an organoid system genetically predisposed to NAFLD and to induce steatosis and fibrosis in it by adding free fatty acids. We used multilineage 3D spheroids composed by hepatocytes (HepG2) and hepatic stellate cells (LX-2) with a physiological ratio (24:1). HepG2 and LX-2 cells are homozygotes for the PNPLA3 I148M sequence variant, the strongest genetic determinant of NAFLD. We demonstrate that hepatic stellate cells facilitate the compactness of 3D spheroids. Then, we show that the spheroids develop accumulations of fat and collagen upon exposure to free fatty acids. Finally, this accumulation was rescued by incubating spheroids with liraglutide or elafibranor, drugs that are in clinical trials for the treatment of NASH. In conclusion, we have established a simple, easy to handle, in vitro model of genetically induced NAFLD consisting of multilineage 3D spheroids. This tool may be used to understand molecular mechanisms involved in the early stages of fibrogenesis induced by lipid accumulation. Moreover, it may be used to identify new compounds to treat NASH using high-throughput drug screening.

NAFLD risk alleles in PNPLA3, TM6SF2, GCKR and LYPLAL1 show divergent metabolic effects

Fatty liver has been associated with unfavourable metabolic changes in circulation. To provide insights in fatty liver-related metabolic deviations, we compared metabolic association profile of fatty liver versus metabolic association profiles of genotypes increasing the risk of non-alcoholic fatty liver disease (NAFLD). The cross-sectional associations of ultrasound-ascertained fatty liver with 123 metabolic measures were determined in 1810 (N_{fatty liver} = 338) individuals aged 34–49 years from The Cardiovascular Risk in Young Finns Study. The association profiles of NAFLD-risk alleles in PNPLA3, TM6SF2, GCKR, and LYPLAL1 with the corresponding metabolic measures were obtained from a publicly available metabolomics GWAS including up to 24 925 Europeans. The risk alleles showed different metabolic effects: PNPLA3 rs738409-G, the strongest genetic NAFLD risk factor, did not associate with metabolic changes. Metabolic effects of GCKR rs1260326-T were comparable in many respects to the fatty liver associations. Metabolic effects of LYPLAL1 rs12137855-C were similar, but statistically less robust, to the effects of GCKR rs1260326-T. TM6SF2 rs58542926-T displayed opposite metabolic effects when compared with the fatty liver associations. The metabolic effects of the risk alleles highlight heterogeneity of the molecular pathways leading to fatty liver and suggest that the fatty liver-related changes in the circulating lipids and metabolites may vary depending on the underlying pathophysiological mechanism. Despite the robust cross-sectional associations on population level, the present results showing neutral or cardioprotective metabolic effects for some of the NAFLD risk alleles advocate that hepatic lipid accumulation by itself may not increase the level of circulating lipids or other metabolites.

Methyl donor supplementation suppresses the progression of liver lipid accumulation while modifying the plasma triacylglycerol lipidome in periparturient Holstein dairy cows

Co-supplementation of methyl donors may lower hepatic lipid content in transition cows. To define the ability of methyl donor supplementation (MDS) to reduce hepatic lipid content and modify the plasma lipidome, 30 multiparous Holstein cows (2.04 ± 0.69 lactations; 689 ± 58 kg of body weight; 3.48 ± 0.10 units of body condition score) were fed a ration with or without rumen-protected methyl donors (22 g/d of Met, 10 g/d of choline chloride, 3 g/d of betaine, 96 mg/d of riboflavin, and 1.4 mg/d of vitamin B₁₂) from d -28 before expected calving through d 14 postpartum. Cows were randomly enrolled based on predefined selection criteria (body condition score and parity). Base diets without MDS were formulated for gestation (15.4% crude protein with a predicted Lys-to-Met ratio of 3.25; 1.44 Mcal of net energy for lactation/kg of dry matter) and lactation (16.6% crude protein with a predicted Lys-to-Met ratio of 3.36; 1.64 Mcal of net energy for lactation/kg of dry matter). Blood sampling occurred from d -28 relative to expected calving through d 14 postpartum. Liver tissue was biopsied at d -28 relative to expected calving and on d 5 and 14 postpartum. In addition to routine analyses, serum AA concentrations on d 10 and 12 were quantified using mass spectrometry. Plasma triacylglycerol (TAG) and cholesteryl esters (CE) were qualitatively measured using time-of-flight mass spectrometry. Data were analyzed using a mixed model with repeated measures. Dry matter intake and milk yield were not modified by MDS. The transition from d -28 relative to expected parturition to d 14 postpartum was characterized by increased plasma fatty acid (0.15 to 0.71 mmol/L) and β-hydroxybutyrate (0.34 to 0.43 mmol/L) levels and liver lipid content (3.91 to 9.16%). Methyl donor supplementation increased the serum Met level by 26% and decreased the serum Lys-to-Met ratio by 21% on d 10 and 12, respectively. Moreover, the increase in hepatic lipid content from d 5 through 14 postpartum was suppressed with MDS relative to control (3.57 vs. -0.29%). Dietary MDS modified the TAG and CE lipidome. For example, MDS increased plasma TAG 46:3 (carbon number:double bond) by 116% relative to control cows on d 5 postpartum. Moreover, MDS tended to increase plasma CE 34:6. In contrast, MDS lowered plasma TAG 54:8 by 39% relative to control cows on d 5 postpartum. We concluded that in the absence of gains in dry matter intake and milk and milk protein yields, dietary MDS slows the progression of hepatic lipid accumulation and modifies the plasma TAG lipidome in transition cows.

PNPLA3 rs139051 is associated with phospholipid metabolite profile and hepatic inflammation in nonalcoholic fatty liver disease

AIM

To investigate the effect of PNPLA3 polymorphisms on serum lipidomics and pathological characteristics in nonalcoholic fatty liver disease (NAFLD).

METHODS

Thirty-four biopsy-proven NAFLD patients from Northern, Central, and Southern China were subjected to stratification by genotyping their single nucleotide polymorphisms (SNPs) in PNPLA3. Ultra performance liquid chromatographytandem mass spectrometry was then employed to characterize the effects of PNPLA3 SNPs on serum lipidomics. In succession, correlation analysis revealed the association of PNPLA3-related lipid profile and hepatic pathological characteristics on a basis of steatosis, activity, and fibrosis assessment. The variant-based scoring of hepatocyte steatosis, ballooning, lobular inflammation, and liver fibrosis was finally performed so as to uncover the actions of lipidomics-affecting PNPLA3 SNPs in NAFLD-specific pathological alterations.

RESULTS

PNPLA3 SNPs (rs139051, rs738408, rs738409, rs 2072906, rs2294918, rs2294919, and rs4823173) demonstrated extensive association with the serum lipidomics, especially phospholipid metabolites [lysophosphatidylcholine (LPC), lysophosphatidylcholine plasmalogen (LPCO), lysophosphatdylethanolamine (LPE), phosphatidylcholine (PC), choline plasmalogen (PCO), phosphatidylethanolamine (PE), ethanolamine plasmalogen (PEO)], of NAFLD patients. PNPLA3 rs139051 (A/A genotype) and rs2294918 (G/G genotype) dominated the up-regulatory effect on phospholipids of LPCs (LPC 17:0, LPC 18:0, LPC 20:0, LPC 20:1, LPC 20:2) and LPCOs (LPC O-16:1, LPC O-18:1). Moreover, subjects with high-level LPCs/LPCOs were predisposed to low-grade lobular inflammation of NAFLD (rho: -0.407 to -0.585, P < 0.05-0.001). The significant correlation of PNPLA3 rs139051 and inflammation grading [A/A vs A/G + G/G: 0.50 (0.00, 1.75) vs 1.50 (1.00, 2.00), P < 0.05] further demonstrated its pathological role based on the modulation of phospholipid metabolite profile.

CONCLUSION

The A/A genotype at PNPLA3 rs139051 exerts an up-regulatory effect on serum phospholipids of LPCs and LPCOs, which are associated with low-grade lobular inflammation of NAFLD.

Dissociation of Fatty Liver and Insulin Resistance in I148M PNPLA3 Carriers: Differences in Diacylglycerol (DAG) FA18:1 Lipid Species as a Possible Explanation

Fatty liver is tightly associated with insulin resistance and the development of type 2 diabetes. I148M variant in patatin-like phospholipase domain-containing protein 3 (PNPLA3) gene is associated with high liver fat but normal insulin sensitivity. The underlying mechanism of the disassociation between high liver fat but normal insulin sensitivity remains obscure. We investigated the effect of I148M variant on hepatic lipidome of subjects with or without fatty liver, using the Lipidyzer method. Liver samples of four groups of subjects consisting of normal liver fat with wild-type PNPLA3 allele (group 1); normal liver fat with variant PNPLA3 allele (group 2); high liver fat with wild-type PNPLA3 allele (group 3); high liver fat with variant PNPLA3 allele (group 4); were analyzed. When high liver fat to normal liver fat groups were compared, wild-type carriers (group 3 vs. group 1) showed similar lipid changes compared to I148M PNPLA3 carriers (group 4 vs. group 2). On the other hand, in wild-type carriers, increased liver fat significantly elevated the proportion of specific DAGs (diacylglycerols), mostly DAG (FA18:1) which, however, remained unchanged in I148M PNPLA3 carriers. Since DAG (FA18:1) has been implicated in hepatic insulin resistance, the unaltered proportion of DAG (FA18:1) in I148M PNPLA3 carriers with fatty liver may explain the normal insulin sensitivity in these subjects.

Combination of PNPLA3 and TLL1 polymorphism can predict advanced fibrosis in Japanese patients with nonalcoholic fatty liver disease

BACKGROUND

Hepatic fibrosis is an independent risk factor for mortality and liver-related events in patients with nonalcoholic fatty liver disease (NAFLD). PNPLA3 rs738409 has been associated with fibrosis in viral and non-viral hepatitis. TLL1 rs17047200 also has been associated with developing hepatocellular carcinoma probably via hepatic fibrogenesis. We estimated the impact of these genetic polymorphisms on hepatic fibrosis in Japanese patients with NAFLD.

METHODS

We analyzed the association between these genetic variants and the backgrounds of 817 individuals who received health checkups (health check cohort) from 2012 to 2014. Then, we investigated the relationship between genetic variants and liver histology in 258 consecutive patients with biopsy-proven NAFLD in Japan (NAFLD cohort) from 2012 to 2017 (UMIN000027399).

RESULTS

The prevalence of PNPLA3 CG/GG in the NAFLD cohort was higher than that in the health check cohort (p < 0.001). The prevalence of patients with advanced fibrosis (stages 3-4) was higher for PNPLA3 genotype CG/GG than CC (p = 0.048) and for TLL1 genotype AT/TT than AA (p = 0.044). The high-risk group which had at least two risk alleles of these variants was more likely to have advanced fibrosis (p = 0.004). Multivariate analysis identified body mass index [odds ratio (OR) 1.123, serum AST (OR 1.037, p = 0.004], serum albumin (OR 0.247, p = 0.032), and genetic high risk (OR 2.632, p = 0.026) as predictors of advanced fibrosis.

CONCLUSIONS

In Japanese patients with NAFLD, individuals with risk alleles of PNPLA3 and TLL1 may have a risk of advanced fibrosis.

Nonalcoholic Fatty Liver Disease and Metabolic Syndrome

Nonalcoholic fatty liver disease (NAFLD) and metabolic syndrome (MS) are highly prevalent, affecting approximately one-third of the US population. The relationship between NAFLD and MS is complex and may be bidirectionally associated. NAFLD is strongly associated with MS, the components of which include abdominal obesity, hyperglycemia, hypertension, and dyslipidemia. NAFLD associated with certain genetic factors such as the PNPLA3 G allele variant is not accompanied by insulin resistance and MS. Lifestyle modification, including diet and physical activity targeting visceral adiposity, remains the standard of care for patients with NAFLD and MS.

Fatty liver without a large “belly”: Magnified review of non-alcoholic fatty liver disease in non-obese patients

Nonalcoholic fatty liver disease (NAFLD) is well described as a common cause of chronic liver disease, mostly in the obese population. It refers to a spectrum of chronic liver disease that starts with simple steatosis than progresses to nonalcoholic steatohepatitis and cirrhosis in patients without significant alcohol consumption. NAFLD in the non-obese population has been increasingly reported and studied recently. The pathogenesis of nonobese NAFLD is poorly understood and is related to genetic predisposition, most notably patatin-like phospholipase domain-containing 33 G allele polymorphism that leads to intrahepatic triglyceride accumulation and insulin resistance. Non-obese NAFLD is associated with components of metabolic syndrome and, especially, visceral obesity which seems to be an important etiological factor in this group. Dietary factors and, specifically, a high fructose diet seem to play a role. Cardiovascular events remain the main cause of mortality and morbidity in NAFLD, including in the non-obese population. There is not enough data regarding treatment in non-obese NAFLD patients, but similar to NAFLD in obese subjects, lifestyle changes that include dietary modification, physical activity, and weight loss remain the mainstay of treatment.

Clinical and Metabolic Characterization of Lean Caucasian Subjects With Non-alcoholic Fatty Liver

OBJECTIVES

Non-alcoholic fatty liver disease (NAFLD) is closely linked to obesity; however, 5-8% of lean subjects also have evidence of NAFLD. We aimed to investigate clinical, genetic, metabolic and lifestyle characteristics in lean Caucasian subjects with NAFLD.

METHODS

Data from 187 subjects allocated to one of the three groups according to body mass index (BMI) and hepatic steatosis on ultrasound were obtained: lean healthy (BMI≤25 kg/m², no steatosis, N=71), lean NAFLD (BMI≤25 kg/m², steatosis, N=55), obese NAFLD (BMI≥30 kg/m², steatosis; N=61). All subjects received a detailed clinical and laboratory examination including oral glucose tolerance test. The serum metabolome was assessed using the Metabolomics AbsoluteIDQ p180 kit (BIOCRATES Life Sciences). Genotyping for single-nucleotide polymorphisms (SNPs) associated with NAFLD was performed.

RESULTS

Lean NAFLD subjects had fasting insulin concentrations similar to lean healthy subjects but had markedly impaired glucose tolerance. Lean NAFLD subjects had a higher rate of the mutant PNPLA3 CG/GG variant compared to lean controls (P=0.007). Serum adiponectin concentrations were decreased in both NAFLD groups compared to controls (P<0.001 for both groups) The metabolomics study revealed a potential role for various lysophosphatidylcholines (lyso-PC C18:0, lyso-PC C17:0) and phosphatidylcholines (PCaa C36:3; false discovery rate (FDR)-corrected P-value<0.001) as well as lysine, tyrosine, and valine (FDR<0.001).

CONCLUSIONS

Lean subjects with evidence of NAFLD have clinically relevant impaired glucose tolerance, low adiponectin concentrations and a distinct metabolite profile with an increased rate of PNPLA3 risk allele carriage.

Nonalcoholic fatty liver disease: cause or consequence of type 2 diabetes?

Growing epidemiological evidence suggests that nonalcoholic fatty liver disease (NAFLD) is an early predictor of and determinant for the development of type 2 diabetes and other features of the metabolic syndrome. This finding may have important clinical implications for the diagnosis, prevention and treatment of type 2 diabetes and its chronic complications. However, given the complex and bi-directional relationships between NAFLD, insulin resistance and chronic hyperglycaemia, it is extremely difficult to distinguish whether NAFLD is a cause or a consequence of insulin resistance and type 2 diabetes. Indeed, at the molecular level, hepatic lipogenesis and hepatic glucose production depend on differentially regulated branches of the insulin signalling pathway. Furthermore, genetic studies suggest that excess hepatic fat is associated with progressive liver disease, but does not always increase the risk of incident type 2 diabetes. Here, we will briefly review the epidemiological, pathophysiological and molecular evidence linking NAFLD to the development of type 2 diabetes. We will also discuss some recent genetic and therapeutic advances that seem to challenge a causal role of NAFLD in the pathogenesis type 2 diabetes, and propose a working hypothesis to explain this apparent conundrum. In conclusion, progressive liver disease and type 2 diabetes are divergent though inter-related consequences of insulin resistance and the metabolic syndrome.

The intersection of nonalcoholic fatty liver disease and obesity

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide and recently emerged as the most rapidly increasing indication for liver transplant. Although obesity is a risk factor for NAFLD, overlap between these two entities is incompletely understood. We highlight recent insights into the pathogenesis of human NAFLD in relation to obesity and discuss advances in the diagnosis and treatment of NAFLD.

Influence of Ethnicity on the Accuracy of Non-Invasive Scores Predicting Non-Alcoholic Fatty Liver Disease

OBJECTIVES

Presence of non-alcoholic fatty liver disease (NAFLD) can predict risks for diabetes, cardiovascular disease and advanced liver disease in the general population. We aimed to establish a non-invasive score for prediction of NAFLD in Han Chinese, the largest ethnic group in the world, and detect whether ethnicity influences the accuracy of such a score.

METHODS

Liver fat content (LFAT) was measured by quantitative ultrasound in 3548 subjects in the Shanghai Changfeng Community and a Chinese score was created using multivariate logistic regression analyses. This new score was internally validated in Chinese and externally in Finns. Its diagnostic performance was compared to the NAFLD liver fat score, fatty liver index (FLI) and hepatic steatosis index (HSI) developed in Finns, Italians and Koreans. We also analyzed how obesity related to LFAT measured by 1H-MRS in 79 Finns and 118 Chinese with type 2 diabetes (T2D).

RESULTS

The metabolic syndrome and T2D, fasting serum insulin, body mass index (BMI) and AST/ALT ratio were independent predictors of NAFLD in Chinese. The AUROC in the Chinese validation cohort was 0.76 (0.73-0.78) and in Finns 0.73 (0.68-0.78) (p<0.0001). 43%, 27%, 32% and 42% of Chinese had NAFLD when determined by the Chinese score, NAFLD liver fat score (p<0.001 vs. Chinese score), FLI (p<0.001) and HSI (NS). For any given BMI and waist circumference, the Chinese had a markedly higher LFAT than the Finns.

CONCLUSION

The predictors of NAFLD in Han Chinese are as in Europids but the Chinese have more LFAT for any given degree of obesity than Europids. Ethnicity needs to be considered when NAFLD is predicted using risk scores.

Genetics of nonalcoholic fatty liver disease

Epidemiological, familial, and twin studies indicate that non-alcoholic fatty liver disease, now the leading cause of liver damage in developed countries, has a strong heritability. The common I148M variant of PNPLA3 impairing hepatocellular lipid droplets remodeling is the major genetic determinant of hepatic fat content. The I148M variant has a strong impact on the full spectrum of liver damage related to fatty liver, encompassing non-alcoholic steatohepatitis, advanced fibrosis, and hepatocellular carcinoma, and influences the response to therapeutic approaches. Common variants in GCKR enhance de novo hepatic lipogenesis in response to glucose and liver inflammation. Furthermore, the low-frequency E167K variant of TM6SF2 and rare mutations in APOB, which impair very low-density lipoproteins secretion, predispose to progressive fatty liver.

CONCLUSIONS

These and other recent findings reviewed here indicate that impaired lipid handling by hepatocytes has a major role in the pathogenesis of non-alcoholic fatty liver disease by triggering inflammation, fibrogenesis, and carcinogenesis. These discoveries have provided potential novel biomarkers for clinical use and have revealed intriguing therapeutic targets.

Compounds of the sphingomyelin-ceramide-glycosphingolipid pathways as secondary messenger molecules: new targets for novel therapies for fatty liver disease and insulin resistance

The compounds of sphingomyelin-ceramide-glycosphingolipid pathways have been studied as potential secondary messenger molecules in various systems, along with liver function and insulin resistance. Secondary messenger molecules act directly or indirectly to affect cell organelles and intercellular interactions. Their potential role in the pathogenesis of steatohepatitis and diabetes has been suggested. Data samples collected from patients with Gaucher's disease, who had high levels of glucocerebroside, support a role for compounds from these pathways as a messenger molecules in the pathogenesis of fatty liver disease and diabetes. The present review summarizes some of the recent data on the role of glycosphingolipid molecules as messenger molecules in various physiological and pathological conditions, more specifically including insulin resistance and fatty liver disease.

Non-alcoholic fatty liver disease and risk of type 2 diabetes

Non-alcoholic fatty liver disease (NAFLD) covers a spectrum of liver disease from simple steatosis to non-alcoholic steatohepatitis (NASH) and cirrhosis. NAFLD is commonly associated with features of the metabolic/insulin resistance syndrome ('Metabolic/Obese NAFLD') and may therefore predict type 2 diabetes (T2DM). For this review, we searched for prospective studies examining whether NAFLD predicts T2DM, and if so, whether this occurs independently of factors such as age and obesity. These studies included NAFLD diagnosed by ultrasonography (n = 6) or liver enzymes (n = 14). All ultrasonography studies found NAFLD to predict the risk of T2DM independently of age, and in 4 out of 6 studies NAFLD was also a predictor independently of BMI. NAFLD was a predictor of T2DM in all 14 studies where NAFLD was diagnosed by liver enzymes. In 12 of these studies, ALT or AST or GGT were significant predictors of T2DM risk, independently of age and BMI. NAFLD, however, is heterogeneous and may also be caused by common genetic variants. The I148M variant in PNPLA3 and the E167K variant in TM6SF2 are both associated with increased liver fat content, but not features of the metabolic/insulin resistance syndrome. These genetic forms of NAFLD predict NASH and cirrhosis but not T2DM. Taken together these data imply that 'Metabolic/Obese NAFLD' predicts T2DM independently of age and obesity and support the role of hepatic insulin resistance in the pathogenesis of this disease.

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.

The Impact of PNPLA3 rs738409 Genetic Polymorphism and Weight Gain ≥10 kg after Age 20 on Non-Alcoholic Fatty Liver Disease in Non-Obese Japanese Individuals

Non-alcoholic fatty liver disease (NAFLD) in non-obese individuals is inadequately elucidated. We aim to investigate the impact of known genetic polymorphisms on NAFLD and the interaction between genetic risks and weight gain on NAFLD in obese and non-obese Japanese individuals. A total of 1164 participants who received health checkups were included. Participants with excessive alcohol consumption, with viral hepatitis or other inappropriate cases were excluded. Fatty liver was diagnosed by ultrasonography. Participants with a body mass index (BMI) of <18.5 kg/m2, 18.5-22.9 kg/m2, 23.0-24.9 kg/m2 and ≥25 kg/m2 were classified underweight, normal weight, overweight and obese, respectively. Self-administered questionnaire for lifestyle was assessed and a total of 8 previously reported genetic polymorphisms were chosen and examined. In all, 824 subjects were enrolled. The overall prevalence of NAFLD was 33.0%: 0% in underweight, 15.3% in normal weight, 41.1% in overweight and 71.7% in obese individuals. The prevalence of NAFLD is more affected by the G allele of patatin-like phospholipase domain-containing protein 3 (PNPLA3) rs738409 in normal weight (odds ratio (OR) 3.52; 95%-CI: 1.42-8.71; P = 0.0063) and in overweight individuals (OR 2.60; 95%-CI: 1.14-5.91; P = 0.0225) than in obese individuals (not significant). Moreover, the G allele of PNPLA3 rs738409 and weight gain ≥10 kg after age 20 had a joint effect on the risk of NAFLD in the normal weight (OR 12.00; 95% CI: 3.71-38.79; P = 3.3×10-5) and the overweight individuals (OR 13.40; 95% CI: 2.92-61.36; P = 0.0008). The G allele of PNPLA3 rs738409 is a prominent risk factor for NAFLD and the interaction between the PNPLA3 rs738409 and weight gain ≥10 kg after age 20 plays a crucial role in the pathogenesis of NAFLD, especially in non-obese Japanese individuals.

Adipose Tissue Dysfunction and Altered Systemic Amino Acid Metabolism Are Associated with Non-Alcoholic Fatty Liver Disease

Background

Fatty liver is a major cause of obesity-related morbidity and mortality. The aim of this study was to identify early metabolic alterations associated with liver fat accumulation in 50- to 55-year-old men (n = 49) and women (n = 52) with and without NAFLD.

Methods

Hepatic fat content was measured using proton magnetic resonance spectroscopy (¹H MRS). Serum samples were analyzed using a nuclear magnetic resonance (NMR) metabolomics platform. Global gene expression profiles of adipose tissues and skeletal muscle were analyzed using Affymetrix microarrays and quantitative PCR. Muscle protein expression was analyzed by Western blot.

Results

Increased branched-chain amino acid (BCAA), aromatic amino acid (AAA) and orosomucoid were associated with liver fat accumulation already in its early stage, independent of sex, obesity or insulin resistance (p<0.05 for all). Significant down-regulation of BCAA catabolism and fatty acid and energy metabolism was observed in the adipose tissue of the NAFLD group (p<0.001for all), whereas no aberrant gene expression in the skeletal muscle was found. Reduced BCAA catabolic activity was inversely associated with serum BCAA and liver fat content (p<0.05 for all).

Conclusions

Liver fat accumulation, already in its early stage, is associated with increased serum branched-chain and aromatic amino acids. The observed associations of decreased BCAA catabolism activity, mitochondrial energy metabolism and serum BCAA concentration with liver fat content suggest that adipose tissue dysfunction may have a key role in the systemic nature of NAFLD pathogenesis.

Fasting enriches liver triacylglycerol with n-3 polyunsaturated fatty acids: implications for understanding the adipose-liver axis in serum docosahexaenoic acid regulation

We investigated the effect of short-term fasting on coordinate changes in the fatty acid composition of adipose triacylglycerol (TAG), serum non-esterified fatty acids (NEFA), liver TAG, and serum TAG and phospholipids in mice fed ad libitum or fasted for 16 h overnight. In contrast to previous reports under conditions of maximal lipolysis, adipose tissue TAG was not preferentially depleted of n-3 PUFA or any specific fatty acids, nor were there any striking changes in the serum NEFA composition. Short-term fasting did, however, increase the hepatic proportion of n-3 PUFA, and almost all individual species of n-3 PUFA showed relative and absolute increases. The relative proportion of n-6 PUFA in liver TAG also increased but to a lesser extent, resulting in a significant decrease in the n-6:n-3 PUFA ratio (from 14.3 ± 2.54 to 9.6 ± 1.20), while the proportion of MUFA decreased significantly and SFA proportion did not change. Examination of genes involved in PUFA synthesis suggested that hepatic changes in the elongation and desaturation of precursor lipids could not explain this effect. Rather, an increase in the expression of fatty acid transporters specific for 22:6n-3 and other long-chain n-3 and n-6 PUFA likely mediated the observed hepatic enrichment. Analysis of serum phospholipids indicated a specific increase in the concentration of 22:6n-3 and 16:0, suggesting increased specific synthesis of DHA-enriched phospholipid by the liver for recirculation. Given the importance of blood phospholipid in distributing DHA to neural tissue, these findings have implications for understanding the adipose-liver-brain axis in n-3 PUFA metabolism.

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.

Pathophysiology of diabetic dyslipidaemia: where are we?

Cardiovascular disease is a major cause of morbidity and mortality in patients with type 2 diabetes mellitus, with a two- to fourfold increase in cardiovascular disease risk compared with non-diabetic individuals. Abnormalities in lipid metabolism that are observed in the context of type 2 diabetes are among the major factors contributing to an increased cardiovascular risk. Diabetic dyslipidaemia includes not only quantitative lipoprotein abnormalities, but also qualitative and kinetic abnormalities that, together, result in a shift towards a more atherogenic lipid profile. The primary quantitative lipoprotein abnormalities are increased triacylglycerol (triglyceride) levels and decreased HDL-cholesterol levels. Qualitative lipoprotein abnormalities include an increase in large, very low-density lipoprotein subfraction 1 (VLDL1) and small, dense LDLs, as well as increased triacylglycerol content of LDL and HDL, glycation of apolipoproteins and increased susceptibility of LDL to oxidation. The main kinetic abnormalities are increased VLDL1 production, decreased VLDL catabolism and increased HDL catabolism. In addition, even though LDL-cholesterol levels are typically normal in patients with type 2 diabetes, LDL particles show reduced turnover, which is potentially atherogenic. Although the pathophysiology of diabetic dyslipidaemia is not fully understood, the insulin resistance and relative insulin deficiency observed in patients with type 2 diabetes are likely to contribute to these lipid changes, as insulin plays an important role in regulating lipid metabolism. In addition, some adipocytokines, such as adiponectin or retinol-binding protein 4, may also contribute to the development of dyslipidaemia in patients with type 2 diabetes.

PNPLA3 rs738409 I748M is associated with steatohepatitis in 434 non-obese subjects with hepatitis C

BACKGROUND

The PNPLA3/Adiponutrin rs738409 C/G single nucleotide polymorphism is associated with the severity of steatosis, steatohepatitis and fibrosis in patients with non-alcoholic fatty liver disease, as well as the severity of steatosis and fibrosis in patients with chronic hepatitis C (CHC).

AIM

To test in genotype 1(G1)-CHC patients, the putative association between the PNPLA3 variant and histological features of steatohepatitis, as well as their impact on the severity of fibrosis.

METHODS

Four hundred and thirty-four consecutively biopsied Caucasian G1-CHC patients were genotyped for PNPLA3 rs738409, its effect evaluated by using an additive model. Histological features of steatohepatitis in CHC were assessed using the Bedossa classification. Hepatic expression of PNPLA3 mRNA was evaluated in 63 patients.

RESULTS

The prevalence of steatohepatitis increased from 16.5% in patients with PNPLA3 CC, to 23.2% in CG and 29.2% in the GG genotype (P = 0.02). By multiple logistic regression, PNPLA3 genotype (OR 1.54, 95% CI 1.03-2.30, P = 0.03), together with age (OR 1.03, 95% CI 1.00-1.05, P = 0.02), BMI ≥ 30 (OR 2.06, 95% CI 1.04-4.10, P = 0.03) and homoeostasis model assessment (HOMA, OR 1.18, 95% CI 1.04-1.32, P = 0.006) were independently linked to steatohepatitis. When stratifying for obesity, PNPLA3 was associated with NASH in non-obese patients only (12.0% in CC vs. 18.3% in CG vs. 27.3% in GG, P = 0.01), including after correction for metabolic confounders (OR 2.06, 95% CI 1.26-3.36, P = 0.004). We showed an independent association between steatohepatitis (OR 2.05, 95% CI 1.05-4.02, P = 0.003) and severe fibrosis. Higher liver PNPLA3 mRNA was associated both with the severity of steatosis (adjusted P = 0.03) and steatohepatitis after adjusting for gender, age, BMI and HOMA (P = 0.002).

CONCLUSION

In patients with genotype 1 hepatitis C, the PNPLA3 G variant is associated with a higher risk of steatosis severity and steatohepatitis, particularly among non-obese subjects.

Circulating phospholipid profiling identifies portal contribution to NASH signature in obesity

BACKGROUND & AIMS

Non-alcoholic steatohepatitis (NASH) is characterized by steatosis, lobular inflammation, hepatocyte ballooning with fibrosis in severe cases, and high prevalence in obesity. We aimed at defining NASH signature in morbid obesity by mass spectrometry-based lipidomic analysis.

METHODS

We analyzed systemic blood before and 12 months after bariatric surgery, along with portal blood and adipose tissue lipid efflux collected from obese women at the time of surgery (9 structural classes, 150 species).

RESULTS

Increased concentrations of several glycerophosphocholines (PC), glycerophosphoethanolamines (PE), glycerophosphoinositols (PI), glycerophosphoglycerols (PG), lyso-glycerophosphocholines (LPC), and ceramides (Cer) were detected in systemic circulation of NASH subjects. Post-surgery weight loss (12 months) improved the levels of liver enzymes, as well as several lipids, but most PG and Cer species remained elevated. Analysis of lipids from hepatic portal system at the time of surgery revealed limited lipid alterations compared to systemic circulation, but PG and PE classes were found significantly increased in NASH subjects. We evaluated the contribution of visceral adipose tissue to lipid alterations in portal circulation by measuring adipose tissue lipid efflux ex vivo, and observed only minor alterations in NASH subjects. Interestingly, integration of clinical and lipidomic data (portal and systemic) led us to define a NASH signature in which lipids and clinical parameters are equal contributors.

CONCLUSIONS

Circulatory (portal and systemic) phospholipid profiling and clinical data defines NASH signature in morbid obesity. We report weak contribution of visceral adipose tissue to NASH-related portal lipid alterations, suggesting possible contribution from other organs draining into hepatic portal system.

NAFLD: a multisystem disease

Non-alcoholic fatty liver disease (NAFLD) is the most common cause of chronic liver disease in Western countries that is predicted to become also the most frequent indication for liver transplantation by 2030. Over the last decade, it has been shown that the clinical burden of NAFLD is not only confined to liver-related morbidity and mortality, but there is now growing evidence that NAFLD is a multisystem disease, affecting extra-hepatic organs and regulatory pathways. For example, NAFLD increases risk of type 2 diabetes mellitus (T2DM), cardiovascular (CVD) and cardiac diseases, and chronic kidney disease (CKD). Although the primary liver pathology in NAFLD affects hepatic structure and function to cause morbidity and mortality from cirrhosis, liver failure and hepatocellular carcinoma, the majority of deaths among NAFLD patients are attributable to CVD. This narrative review focuses on the rapidly expanding body of clinical evidence that supports the concept of NAFLD as a multisystem disease. The review discusses the factors involved in the progression of liver disease in NAFLD and the factors linking NAFLD with other extra-hepatic chronic diseases, such as T2DM, CVD, cardiac diseases and CKD. The review will not discuss NAFLD treatments as these are discussed elsewhere in this issue of the Journal. For this review, PubMed was searched for articles using the keywords "non-alcoholic fatty liver disease" or "fatty liver" combined with "diabetes", "cardiovascular (or cardiac) disease", "cardiovascular mortality" or "chronic kidney disease" between 1990 and 2014. Articles published in languages other than English were excluded.

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

BACKGROUND & AIMS

The Glu167Lys (E167K) variant in the transmembrane 6 superfamily member 2 protein (TM6SF2) was recently shown to influence liver fat (LFAT) content. We aimed at studying how this variant influences circulating triacylglycerol (TAG) signatures and whether it influences hepatic or adipose tissue insulin sensitivity.

METHODS

We genotyped 300 Finnish subjects for the E167K (rs58542926) variant in TM6SF2 and for the I148M (rs738409) variant in the patatin-like phospholipase domain-containing protein 3 (PNPLA3) in whom LFAT was measured using 1H-MRS and circulating lipids by UPLC-MS. We compared the plasma lipidome between E167K carriers (TM6SF2EK/KK) and non-carriers (TM6SF2EE), and between three groups of NAFLD: (i) carriers of the E167K but not of the I148M variant in PNPLA3 ('TM6SF2 NAFLD'), (ii) carriers of the I148M but not of the E167K variant ('PNPLA3 NAFLD'), and (iii) non-carriers of either risk allele ('Non-risk NAFLD'). Hepatic and adipose tissue insulin sensitivities were measured using the euglycemic hyperinsulinemic clamp technique combined with infusion of [3-3H]glucose in 111 subjects.

RESULTS

The LFAT content was 34% higher in the TM6SF2EK/KK (13.07±1.57%) than in the TM6SF2EE group (9.77±0.58%, p=0.013). The effect of insulin on glucose production and lipolysis were significantly higher in the TM6SF2EK/KK than in the TM6SF2EE group. Comparison of the three NAFLD groups with similar LFATs showed that both the 'TM6SF2 NAFLD' and 'PNPLA3 NAFLD' had significantly lower triglyceride levels and were characterized by lower levels of most common TAGs compared to the 'Non-risk NAFLD' group.

CONCLUSIONS

We conclude that the E167K variant in TM6SF2 is associated with a distinct subtype of NAFLD, characterized by preserved insulin sensitivity with regard to lipolysis, hepatic glucose production and lack of hypertriglyceridemia despite a clearly increased LFAT content.

Isoleucine-to-methionine substitution at residue 148 variant of PNPLA3 gene and metabolic outcomes in gestational diabetes

BACKGROUND

A single nucleotide polymorphism (SNP) of the patatin-like phospholipase-3 (PNPLA3)/adiponutrin gene (rs738409 C>G) is strongly associated with nonalcoholic fatty liver disease; to our knowledge, no data are available on the impact of this PNPLA3 SNP on liver and metabolic outcomes during pregnancy in patients with gestational diabetes (GD).

OBJECTIVE

We evaluated the impact of the PNPLA3 rs738409 SNP on liver enzymes, metabolic indexes, and maternal and neonatal outcomes in 200 GD patients enrolled in a lifestyle intervention.

DESIGN

In a randomized trial with a 2 × 2 factorial design, exercise significantly improved maternal and neonatal outcomes in GD patients. Effects of the G allele on metabolic and liver indexes and maternal and neonatal outcomes were evaluated in these patients.

RESULTS

At the end of the trial, fasting insulin and homeostasis model assessment of insulin resistance (HOMA-IR) values were significantly lower and liver enzymes significantly higher in PNPLA3 G-allele carriers. In a multiple regression model, the G allele was associated directly with aspartate aminotransferase (β = 2.60; 95% CI: 0.99, 4.20), alanine aminotransferase (β = 3.70; 95% CI: 1.78, 5.62), and γ-glutamyl transferase (β = 3.70; 95% CI: 0.80, 6.60) and inversely with insulin (β = -2.01; 95% CI: -3.24, -0.78) and HOMA-IR (β = -0.39; -0.64, -0.14) values at the end of the trial. In a multiple logistic regression model, the G allele was associated directly with risk of developing liver enzyme elevation during pregnancy (OR: 4.21; 95% CI: 1.78, 9.97) and inversely with the birth of large-for-gestational-age newborns (OR: 0.19; 95% CI: 0.06, 0.62). No diet × genotype or exercise × genotype interaction was shown.

CONCLUSION

The PNPLA3 SNP rs738409 G allele was associated with risk of mildly elevated transaminases in GD independent of a lifestyle intervention and despite a significant reduction in insulin resistance and risk of macrosomic offspring. This trial was registered at clinicaltrials.gov as NCT01506310.

Whole-body and hepatic insulin resistance in obese children

Background

Insulin resistance may be assessed as whole body or hepatic.

Objective

To study factors associated with both types of insulin resistance.

Methods

Cross-sectional study of 182 obese children. Somatometric measurements were registered, and the following three adiposity indexes were compared: BMI, waist-to-height ratio and visceral adiposity. Whole-body insulin resistance was evaluated using HOMA-IR, with 2.5 as the cut-off point. Hepatic insulin resistance was considered for IGFBP-1 level quartiles 1 to 3 (<6.67 ng/ml). We determined metabolite and hormone levels and performed a liver ultrasound.

Results

The majority, 73.1%, of obese children had whole-body insulin resistance and hepatic insulin resistance, while 7% did not have either type. HOMA-IR was negatively associated with IGFBP-1 and positively associated with BMI, triglycerides, leptin and mother's BMI. Girls had increased HOMA-IR. IGFBP-1 was negatively associated with waist-to-height ratio, age, leptin, HOMA-IR and IGF-I. We did not find HOMA-IR or IGFBP-1 associated with fatty liver.

Conclusion

In school-aged children, BMI is the best metric to predict whole-body insulin resistance, and waist-to-height ratio is the best predictor of hepatic insulin resistance, indicating that central obesity is important for hepatic insulin resistance. The reciprocal negative association of IGFBP-1 and HOMA-IR may represent a strong interaction of the physiological processes of both whole-body and hepatic insulin resistance.

Non-alcoholic fatty liver disease as a cause and a consequence of metabolic syndrome

Metabolic syndrome is a cluster of metabolic abnormalities that identifies people at risk of diabetes and cardiovascular disease, whereas non-alcoholic fatty liver disease (NAFLD) is defined as a disorder with excess fat in the liver due to non-alcoholic causes. Two key components of metabolic syndrome, glucose and triglycerides, are overproduced by the fatty liver. The liver is therefore a key determinant of metabolic abnormalities. The prevalence of both metabolic syndrome and NAFLD increases with obesity. Other acquired causes for both disorders include excessive intake of simple sugars and physical inactivity. Both disorders predict type 2 diabetes, cardiovascular disease, non-alcoholic steatohepatitis (NASH), and hepatocellular carcinoma. Because metabolic syndrome can be defined in many different ways, NAFLD might be a more direct predictor of these diseases. Half of people with NAFLD carry at least one variant (G) allele at rs738409 in the PNPLA3 gene, which is associated with high liver fat content. Steatosis in PNPLA3-associated NAFLD is not accompanied by features of metabolic syndrome. All forms of NAFLD increase the risk of NASH, cirrhosis, and hepatocellular carcinoma.

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.