Postprandial Plasma Lipidomics Reveal Specific Alteration of Hepatic-derived Diacylglycerols in Nonalcoholic Fatty Liver Disease

Impact of High-Fat Diet-induced Metabolic Dysfunction-associated Steatotic Liver Disease on Heart, Kidney, and Skeletal Muscle Metabolomes in Wild-Type Mice

Background: Metabolic dysfunction-associated steatotic liver disease (MASLD) can be recapitulated in mice fed a high-fat diet. The development of MASLD and the diet per se can both perturb metabolism in key extrahepatic tissues such as the heart, kidney, and skeletal muscle. To date, these alterations have not been well described in this animal model of diet-induced MASLD. Methodology: Male C57BL/6J mice were fed either standard (SC, n = 12) or high-fat chow (HF, n = 11) for 18 weeks. Metabolites were extracted from the heart, kidney, and skeletal muscle and analyzed by 1H nuclear magnetic resonance (NMR) spectroscopy, along with multivariate and univariate statistical analyses. Results: Kidney metabolite profiles exhibited the largest differences between HF and SC diets, followed by those of skeletal muscle and then the heart. Some alterations were common across all tissues, namely decreased trimethylamine and elevated levels of linoleic acid and polyunsaturated fatty acids in HF compared to SC (p < 0.05 for all three metabolites). Overall, the metabolite variations were consistent with shifts in carbohydrate and lipid substrate selection for oxidation, increased tissue stress in the heart and kidneys, and altered choline metabolism. These findings may serve as additional important descriptors of MASLD onset and progression.

Microenvironmental arginine restriction sensitizes pancreatic cancers to polyunsaturated fatty acids by suppression of lipid synthesis

Nutrient limitation is a characteristic feature of poorly perfused tumors. In contrast to well-perfused tissues, nutrient deficits in tumors perturb cellular metabolic activity, which imposes metabolic constraints on cancer cells. The metabolic constraints created by the tumor microenvironment can lead to vulnerabilities in cancers. Identifying the metabolic constraints of the tumor microenvironment and the vulnerabilities that arise in cancers can provide new insight into tumor biology and identify promising antineoplastic targets. To identify how the microenvironment constrains the metabolism of pancreatic tumors, we challenged pancreatic cancer cells with microenvironmental nutrient levels and analyzed changes in cell metabolism. We found that arginine limitation in pancreatic tumors perturbs saturated and monounsaturated fatty acid synthesis by suppressing the lipogenic transcription factor SREBP1. Synthesis of these fatty acids is critical for maintaining a balance of saturated, monounsaturated, and polyunsaturated fatty acids in cellular membranes. As a consequence of microenvironmental constraints on fatty acid synthesis, pancreatic cancer cells and tumors are unable to maintain lipid homeostasis when exposed to polyunsaturated fatty acids, leading to cell death by ferroptosis. In sum, arginine restriction in the tumor microenvironment constrains lipid metabolism in pancreatic cancers, which renders these tumors vulnerable to polyunsaturated-enriched fat sources.

Untargeted lipidomic analysis of metabolic dysfunction-associated steatohepatitis in women with morbid obesity

Metabolic Dysfunction-Associated Steatohepatitis (MASH) represents the severe condition of Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD). Currently, there is a need to identify non-invasive biomarkers for an accurate diagnosis of MASH. Previously, omics studies identified alterations in lipid metabolites involved in MASLD. However, these studies require validation in other cohorts. In this sense, our aim was to perform lipidomics to identify the circulating lipid metabolite profile of MASH. We assessed a liquid chromatography coupled to a mass spectrometer-based untargeted lipidomic assay in serum samples of 216 women with morbid obesity that were stratified according to their hepatic diagnosis into Normal Liver (NL, n =  44), Simple Steatosis (SS, n =  66) and MASH (n =  106). First, we identified a profile of lipid metabolites that are increased in MASLD, composed of ceramides, triacylglycerols (TAG) and some phospholipids. Then, we identified that patients with SS have a characteristic profile of increased levels of ceramides, diacylglycerols DG (36:2) and DG (36:4), some TAG and a few phospholipids such as PC (32:1), PE (38:3), PE (40:6), PI (32:0) and PI (32:1). Later, in MASH patients, we found increased levels of ceramides, deoxycholic acid, a set of TAG, and some phospholipids such as PC, PE, PI and LPI; while we found decreased levels of the DG (36:0). Finally, we have reported a panel of lipid metabolites that might be used to differentiate patients with MASH from SS patients, made up of increased levels of 9-HODE some PC and PE, the LPI (16:0) and decreased levels of DG (36:0). To conclude, our investigation has suggested a lipid metabolite profile associated with MASLD and MASH. Specifically, a set of lipid metabolites seems to be discriminatory in MASH subjects compared to SS individuals. Thus, this panel of lipid metabolites could be used as a non-invasive diagnostic tool.

Lipid metabolism in MASLD and MASH: From mechanism to the clinic

Metabolic dysfunction-associated steatotic liver disease/steatohepatitis (MASLD/MASH) is recognised as a metabolic disease characterised by excess intrahepatic lipid accumulation due to lipid overflow and synthesis, alongside impaired oxidation and/or export of these lipids. But where do these lipids come from? The main pathways related to hepatic lipid accumulation are de novo lipogenesis and excess fatty acid transport to the liver (due to increased lipolysis, adipose tissue insulin resistance, as well as excess dietary fatty acid intake, in particular of saturated fatty acids). Not only triglycerides but also other lipids are secreted by the liver and are associated with a worse histological profile in MASH, as shown by lipidomics. Herein, we review the role of lipid metabolism in MASLD/MASH and discuss the impact of weight loss (diet, bariatric surgery, GLP-1RAs) or other pharmacological treatments (PPAR or THRβ agonists) on hepatic lipid metabolism, lipidomics, and the resolution of MASH.

Lipoprotein Lipidomics as a Frontier in Non-Alcoholic Fatty Liver Disease Biomarker Discovery

Non-alcoholic fatty liver disease (NAFLD) is a progressive liver disease characterized by the build-up of fat in the liver of individuals in the absence of alcohol consumption. This condition has become a burden in modern societies aggravated by the lack of appropriate predictive biomarkers (other than liver biopsy). To better understand this disease and to find appropriate biomarkers, a new technology has emerged in the last two decades with the ability to explore the unmapped role of lipids in this disease: lipidomics. This technology, based on the combination of chromatography and mass spectrometry, has been extensively used to explore the lipid metabolism of NAFLD. In this review, we aim to summarize the knowledge gained through lipidomics assays exploring tissues, plasma, and lipoproteins from individuals with NAFLD. Our goal is to identify common features and active pathways that could facilitate the finding of a reliable biomarker from this field. The most frequent observation was a variable decrease (1-9%) in polyunsaturated fatty acids in phospholipids and non-esterified fatty acids in NAFLD patients, both in plasma and liver. Additionally, a reduction in phosphatidylcholines is a common feature in the liver. Due to the scarcity of studies, further research is needed to properly detect lipoprotein, plasma, and tissue lipid signatures of NAFLD etiologies, and NAFLD subtypes, and to define the relevance of this technology in disease management strategies in the push toward personalized medicine.

Navigating the Link Between Non-alcoholic Fatty Liver Disease/Non-alcoholic Steatohepatitis and Cardiometabolic Syndrome

The global prevalence of non-alcoholic fatty liver disease (NAFLD) is nearly 25% and is increasing rapidly. The spectrum of liver damage in NAFLD ranges from simple steatosis to non-alcoholic steatohepatitis, characterised by the presence of lobular inflammation and hepatocyte ballooning degeneration, with or without fibrosis, which can further develop into cirrhosis and hepatocellular carcinoma. Not only is NAFLD a progressive liver disease, but numerous pieces of evidence also point to extrahepatic consequences. Accumulating evidence suggests that patients with NAFLD are also at increased risk of cardiovascular disease (CVD); in fact, CVDs are the most common cause of mortality in patients with NAFLD. Obesity, type 2 diabetes and higher levels of LDL are common risk factors in both NAFLD and CVD; however, how NAFLD affects the development and progression of CVD remains elusive. In this review, we comprehensively summarise current data on the key extrahepatic manifestations of NAFLD, emphasising the possible link between NAFLD and CVD, including the role of proprotein convertase substilisin/kenin type 9, extracellular vesicles, microbiota, and genetic factors.

Autophagy and the unfolded protein response shape the non-alcoholic fatty liver landscape: decoding the labyrinth

The incidence of nonalcoholic fatty liver disease (NAFLD) is on the rise, mirroring a global surge in diabetes and metabolic syndrome, as its major leading causes. NAFLD represents a spectrum of liver disorders, ranging from nonalcoholic fatty liver (NAFL) to nonalcoholic steatohepatitis (NASH), which can potentially progress to cirrhosis and hepatocellular carcinoma (HCC). Mechanistically, we know the unfolded protein response (UPR) as a protective cellular mechanism, being triggered under circumstances of endoplasmic reticulum (ER) stress. The hepatic UPR is turned on in a broad spectrum of liver diseases, including NAFLD. Recent data also defines molecular mechanisms that may underlie the existing correlation between UPR activation and NAFLD. More interestingly, subsequent studies have demonstrated an additional mechanism, i.e. autophagy, to be involved in hepatic steatosis, and thus NAFLD pathogenesis, principally by regulating the insulin sensitivity, hepatocellular injury, innate immunity, fibrosis, and carcinogenesis. All these findings suggest possible mechanistic roles for autophagy in the progression of NAFLD and its complications. Both UPR and autophagy are dynamic and interconnected fluxes that act as protective responses to minimize the harmful effects of hepatic lipid accumulation, as well as the ER stress during NAFLD. The functions of UPR and autophagy in the liver, together with findings of decreased hepatic autophagy in correlation with conditions that predispose to NAFLD, such as obesity and aging, suggest that autophagy and UPR, alone or combined, may be novel therapeutic targets against the disease. In this review, we discuss the current evidence on the interplay between autophagy and the UPR in connection to the NAFLD pathogenesis.

[Risk analysis of serum chemical residues for metabolic associated fatty liver disease based on exposome-lipidome wide association study]

Metabolic associated fatty liver disease (MAFLD) is a common liver disease with a prevalence of up to 25%; it not only adversely affects human health but also aggravates the economic burden of society. An increasing number of studies have suggested that the occurrence of chronic noncommunicable diseases is affected by both environmental exposures and genetic factors. Research has also shown that environmental pollution may increase the risk of MAFLD and promote its occurrence and development. However, the relationship between these concepts, as well as the underlying exposure effects and mechanism, remains incompletely understood. Lipidomics, a branch of metabolomics that studies lipid disorders, can help researchers investigate abnormal lipid metabolites in various disease states. Lipidome-exposome wide association studies are a promising paradigm for investigating the health effects of cumulative environmental exposures on biological responses, and could provide new ideas for determining the associations between metabolic and lipid changes and disease risk caused by chemical-pollutant exposure. Hence, in this study, targeted exposomics and nontargeted lipidomics studies based on ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) and ultra-high performance liquid chromatography-high resolution mass spectrometry (UHPLC-HRMS) were used to characterize exogenous chemical pollutants and endogenous lipid metabolites in the sera of patients with MAFLD and healthy subjects. The results demonstrated that fipronil sulfone, malathion dicarboxylic acid, and monocyclohexyl phthalate may be positively associated with the disease risk of patients diagnosed as simple fatty liver disease (hereafter referred to as MAFLD(0)). Moreover, fipronil sulfone, acesulfame potassium, perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluoroundecanoic acid (PFUnDA), 4-hydroxybenzophenone, and 3,5-di-tert-butyl-4-hydroxybenzoic acid (DBPOB) may be positively associated with the disease risk of patients diagnosed as fatty liver complicated by single or multiple metabolic disorders. Association analysis was carried out to explore the lipid metabolites induced by chemical residues. Triglyceride (TG) and diglyceride (DG) were significantly increased in MAFLD and MAFLD(0). The numbers of carbons of significantly changed DGs and TGs were mainly in the ranges of 32-40 and 35-60, respectively, and both were mainly characterized by changes in polyunsaturated lipids. Most of the lipid-effect markers were positively correlated with chemical residues and associated with increased disease risk. Our research provides a scientific basis for studies on the association and mechanism between serum chemical-pollutant residues and disease outcomes.

Inter-organ crosstalk during development and progression of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is characterized by tissue-specific insulin resistance and pancreatic β-cell dysfunction, which result from the interplay of local abnormalities within different tissues and systemic dysregulation of tissue crosstalk. The main local mechanisms comprise metabolic (lipid) signalling, altered mitochondrial metabolism with oxidative stress, endoplasmic reticulum stress and local inflammation. While the role of endocrine dysregulation in T2DM pathogenesis is well established, other forms of inter-organ crosstalk deserve closer investigation to better understand the multifactorial transition from normoglycaemia to hyperglycaemia. This narrative Review addresses the impact of certain tissue-specific messenger systems, such as metabolites, peptides and proteins and microRNAs, their secretion patterns and possible alternative transport mechanisms, such as extracellular vesicles (exosomes). The focus is on the effects of these messengers on distant organs during the development of T2DM and progression to its complications. Starting from the adipose tissue as a major organ relevant to T2DM pathophysiology, the discussion is expanded to other key tissues, such as skeletal muscle, liver, the endocrine pancreas and the intestine. Subsequently, this Review also sheds light on the potential of multimarker panels derived from these biomarkers and related multi-omics for the prediction of risk and progression of T2DM, novel diabetes mellitus subtypes and/or endotypes and T2DM-related complications.

Comparative Lipidomics and Metabolomics Reveal the Underlying Mechanisms of Taurine in the Alleviation of Nonalcoholic Fatty Liver Disease Using the Aged Laying Hen Model

SCOPE

Aged laying hen is recently suggested as a more attractive animal model than rodent for studying nonalcoholic fatty liver disease (NAFLD) of humans. This study aims to reveal effects and metabolic regulation mechanisms of taurine alleviating NAFLD by using the aged laying hen model.

METHODS AND RESULTS

Liver histomorphology and biochemical indices show 0.02% taurine effectively alleviated fat deposition and liver damage. Comparative liver lipidomics and gene expressions analyses reveal taurine promoted lipolysis, fatty acids oxidation, lipids transport, and reduced oxidative stress in liver. Furthermore, comparative serum metabolomics screen six core metabolites negatively correlated with NAFLD, including linoleic acid, gamma-linolenic acid, pantothenate, L-methionine, 2-methylbutyroylcarnitine, L-carnitine; and two core metabolites positively correlated with NAFLD, including lysophosphatidylcholine (14:0/0:0) and lysophosphatidylcholine (16:0/0:0). Metabolic pathway analysis reveals taurine mainly regulated linoleic acid metabolism, cysteine and methionine metabolism, carnitine metabolism, pantothenic acid and coenzyme A biosynthesis metabolism, and glycerophospholipid metabolism to up-adjust levels of six negatively correlated metabolites and down-adjust two positively correlated metabolites for alleviating NAFLD of aged hens.

CONCLUSION

This study firstly reveals underlying metabolic mechanisms of taurine alleviating NAFLD using the aged hen model, thereby laying the foundation for taurine's application in the prevention of NAFLD in both human and poultry.

Divergent pathways of liver fat accumulation, oxidation, and secretion in lipodystrophy versus obesity-associated NAFLD

BACKGROUND AND AIMS

Fatty liver is common in obesity as well as in partial lipodystrophy (PL) syndromes, characterized by deficient adipose tissue. Insulin resistance is key to fatty liver pathogenesis in both entities. We aimed to compare the contributions of insulin resistance and adipose tissue to hepatic steatosis in PL and non-syndromic, obesity-associated non-alcoholic fatty liver disease (NS-NAFLD).

METHODS

In a cross-sectional comparison of people with NS-NAFLD (N = 73) and PL (N = 27), liver fat was measured by FibroScan® controlled attenuation parameter (CAP) and insulin resistance by HOMA-IR, Adipo-IR, and NMR-based LP-IR.

RESULTS

Insulin resistance was greater in PL versus NS-NAFLD by HOMA-IR (p = 0.005), Adipo-IR (p = 0.01) and LP-IR (p = 0.05) while liver fat was comparable (304 vs. 324 dB/m, p = 0.12). Liver fat correlated with HOMA-IR in both groups, but CAP values were lower by 32 dB/m in PL compared with NS-NAFLD for any given HOMA-IR. In contrast, Adipo-IR and LP-IR correlated with CAP only in the NS-NAFLD group, suggesting different pathways for fat accumulation. Plasma free fatty acids, reflecting substrate input from the adipose tissue, were comparable between groups. However, the levels of β-hydroxybutyrate, a marker of β-oxidation, and large triglyceride-rich lipoprotein particles, a marker of VLDL secretion, were both higher in PL (p < 0.001 for both).

CONCLUSION

Liver fat content was comparable in subjects with PL-associated NAFLD and NS-NAFLD, despite worse insulin resistance in partial lipodystrophy. Our data demonstrate higher triglyceride oxidation and export in PL, suggesting a compensatory shift of fat from liver storage into the circulation that does not occur in NS-NAFLD.

Lipidomics in pathogenesis, progression and treatment of nonalcoholic steatohepatitis (NASH): Recent advances

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease affecting up to 30% of the general adult population. NAFLD encompasses a histological spectrum ranging from pure steatosis to non-alcoholic steatohepatitis (NASH). NASH can progress to cirrhosis and is becoming the most common indication for liver transplantation, as a result of increasing disease prevalence and of the absence of approved treatments. Lipidomic readouts of liver blood and urine samples from experimental models and from NASH patients disclosed an abnormal lipid composition and metabolism. Collectively, these changes impair organelle function and promote cell damage, necro-inflammation and fibrosis, a condition termed lipotoxicity. We will discuss the lipid species and metabolic pathways leading to NASH development and progression to cirrhosis, as well as and those species that can contribute to inflammation resolution and fibrosis regression. We will also focus on emerging lipid-based therapeutic opportunities, including specialized proresolving lipid molecules and macrovesicles contributing to cell-to-cell communication and NASH pathophysiology.

Chewing the fat: How lipidomics is changing our understanding of human health and disease in 2022

Lipids are biological molecules that play vital roles in all living organisms. They perform many cellular functions, such as 1) forming cellular and subcellular membranes, 2) storing and using energy, and 3) serving as chemical messengers during intra- and inter-cellular signal transduction. The large-scale study of the pathways and networks of cellular lipids in biological systems is called "lipidomics" and is one of the fastest-growing omics technologies of the last two decades. With state-of-the-art mass spectrometry instrumentation and sophisticated data handling, clinical studies show how human lipid composition changes in health and disease, thereby making it a valuable medium to collect for clinical applications, such as disease diagnostics, therapeutic decision-making, and drug development. This review gives a comprehensive overview of current workflows used in clinical research, from sample collection and preparation to data and clinical interpretations. This is followed by an appraisal of applications in 2022 and a perspective on the exciting future of clinical lipidomics.

Metabolomics analysis of the serum metabolic signature of nonalcoholic fatty liver disease combined with prediabetes model rats after the intervention of Lycium barbarum polysaccharides combined with aerobic activity

Metabolic disorders accompany nonalcoholic fatty liver disease (NAFLD), associated with prediabetes. Lycium barbarum polysaccharides (LBP) seem to be a potential prebiotic, and aerobic exercise has shown protective effects on NAFLD with prediabetes. However, their combined effects on NAFLD and prediabetes remain unclear. This study investigated the effects of LBP and aerobic exercise alone, and their combined effects on the metabolomics of serum, and explored the potential mechanisms utilizing a high-fat diet-induced rat model of NAFLD and prediabetes. It provided the metabolic basis for the pathogenesis and early diagnosis of prediabetes complicated with NAFLD. Untargeted metabolomics profiling was performed using ultra-high-performance liquid chromatography coupled with quadrupole Orbitrap mass spectrometry to analyze the changes in overall metabolites in each group of samples. An orthogonal partial least squares-discriminant analysis model with variable importance on projection >1 and p < 0.05 were used as the screening criteria to screen the significant differential metabolites and analyze the expression changes and functional pathways. Different intervention treatments showed clear discrimination by univariate and multivariate analyses. The model group had a high relative level of expression of lipids. Comparison between the two groups showed steroids with high expression after LBP and aerobic exercise treatment separately and alkaloids and fatty acyls with high expression after aerobic exercise and the combination intervention, respectively. Comparison of the five groups showed some of the metabolites to be differently expressed after the intervention improved lipid and fatty acid metabolism. The three types of intervention had sound effects on the changes in liver index for the diseases studied. Furthermore, the combination treatment may be a better choice for disease prevention and treatment than a single treatment. Our analysis of metabolomics confirmed that the different treatments had significant regulatory effects on the metabolic pathways. Our findings strongly support the possibility that aerobic exercise combined with LBP can be regarded as a potential therapeutic method for NAFLD in prediabetics.

Lipidomics in nutrition research

PURPOSE OF REVIEW

This review focuses on the recent findings from lipidomics studies as related to nutrition and health research.

RECENT FINDINGS

Several lipidomics studies have investigated malnutrition, including both under- and overnutrition. Focus has been both on the early-life nutrition as well as on the impact of overfeeding later in life. Multiple studies have investigated the impact of different macronutrients in lipidome on human health, demonstrating that overfeeding with saturated fat is metabolically more harmful than overfeeding with polyunsaturated fat or carbohydrate-rich food. Diet rich in saturated fat increases the lipotoxic lipids, such as ceramides and saturated fatty-acyl-containing triacylglycerols, increasing also the low-density lipoprotein aggregation rate. In contrast, diet rich in polyunsaturated fatty acids, such as n-3 fatty acids, decreases the triacylglycerol levels, although some individuals are poor responders to n-3 supplementation.

SUMMARY

The results highlight the benefits of lipidomics in clinical nutrition research, also providing an opportunity for personalized nutrition. An area of increasing interest is the interplay of diet, gut microbiome, and metabolome, and how they together impact individuals' responses to nutritional challenges.