Distinguishing NASH Histological Severity Using a Multiplatform Metabolomics Approach

Increased hepatic putrescine levels as a new potential factor related to the progression of metabolic dysfunction-associated steatotic liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a chronic liver condition that often progresses to more advanced stages, such as metabolic dysfunction-associated steatohepatitis (MASH). MASH is characterized by inflammation and hepatocellular ballooning, in addition to hepatic steatosis. Despite the relatively high incidence of MASH in the population and its potential detrimental effects on human health, this liver disease is still not fully understood from a pathophysiological perspective. Deregulation of polyamine levels has been detected in various pathological conditions, including neurodegenerative diseases, inflammation, and cancer. However, the role of the polyamine pathway in chronic liver disorders such as MASLD has not been explored. In this study, we measured the expression of liver ornithine decarboxylase (ODC1), the rate-limiting enzyme responsible for the production of putrescine, and the hepatic levels of putrescine, in a preclinical model of MASH as well as in liver biopsies of patients with obesity undergoing bariatric surgery. Our findings reveal that expression of ODC1 and the levels of putrescine, but not spermidine nor spermine, are elevated in hepatic tissue of both diet-induced MASH mice and patients with biopsy-proven MASH compared with control mice and patients without MASH, respectively. Furthermore, we found that the levels of putrescine were positively associated with higher aspartate aminotransferase concentrations in serum and an increased SAF score (steatosis, activity, fibrosis). Additionally, in in vitro assays using human HepG2 cells, we demonstrate that elevated levels of putrescine exacerbate the cellular response to palmitic acid, leading to decreased cell viability and increased release of CK-18. Our results support an association between the expression of ODC1 and the progression of MASLD, which could have translational relevance in understanding the onset of this disease. © 2024 The Pathological Society of Great Britain and Ireland.

A methionine-choline-deficient diet induces nonalcoholic steatohepatitis and alters the lipidome, metabolome, and gut microbiome profile in the C57BL/6J mouse

The methionine-choline-deficient (MCD) diet-induced non-alcoholic steatohepatitis (NASH) in mice is a well-established model. Our study aims to elucidate the factors influencing liver pathology in the MCD mouse model by examining physiological, biochemical, and molecular changes using histology, molecular techniques, and OMICS approaches (lipidomics, metabolomics, and metagenomics). Male C57BL/6J mice were fed a standard chow diet, a methionine-choline-sufficient (MCS) diet, or an MCD diet for 10 weeks. The MCD diet resulted in reduced body weight and fat mass, along with decreased plasma triglyceride, cholesterol, glucose, and insulin levels. However, it notably induced steatosis, inflammation, and alterations in gene expression associated with lipogenesis, inflammation, fibrosis, and the synthesis of apolipoproteins, sphingolipids, ceramides, and carboxylesterases. Lipid analysis revealed significant changes in plasma and tissues: most ceramide non-hydroxy-sphingosine lipids significantly decreased in the liver and plasma but increased in the adipose tissue of MCD diet-fed animals. Oxidized glycerophospholipids mostly increased in the liver but decreased in the adipose tissue of the MCD diet-fed group. The gut microbiome of the MCD diet-fed group showed an increase in Firmicutes and a decrease in Bacteroidetes and Actinobacteria. Metabolomic profiling demonstrated that the MCD diet significantly altered amino acid biosynthesis, metabolism, and nucleic acid metabolism pathways in plasma, liver, fecal, and cecal samples. LC-MS data indicated higher total plasma bile acid intensity and reduced fecal glycohyodeoxycholic acid intensity in the MCD diet group. This study demonstrates that although the MCD diet induces hepatic steatosis, the mechanisms underlying NASH in this model differ from those in human NASH pathology.

Gut microbiota dysbiosis links chronic apical periodontitis to liver fibrosis in nonalcoholic fatty liver disease: Insights from a mouse model

AIM

In this study, we investigated the systemic implications of chronic apical periodontitis (CAP). CAP may contribute to the nonalcoholic fatty liver disease (NAFLD) progression through the gut microbiota and its metabolites, which are related to the degree of fibrosis.

METHODOLOGY

Sixteen 7-week-old male apolipoprotein E knockout (apoE-/-) mice were randomly divided into two groups: the CAP and Con groups. A CAP model was established by sealing the first- and second-maxillary molars with bacterium-containing cotton balls. Apical lesions were evaluated by micro-CT. Histological evaluations of NAFLD were performed using second harmonic generation/two-photon excitation fluorescence (SHG/TPEF) assays. Additionally, we comprehensively analyzed the gut microbiota using 16S rRNA gene sequencing and explored metabolic profiles by liquid chromatography-mass spectrometry (LC-MS). Immunofluorescence analysis was used to examine the impact of CAP on tight junction proteins and mucin expression. Transcriptome assays have elucidated gene expression alterations in liver tissues.

RESULTS

Micro-CT scans revealed an evident periapical bone loss in the CAP group, and the total collagen percentage was increased (Con, 0.0361 ± 0.00510%, CAP, 0.0589 ± 0.00731%, p < .05). 16S rRNA sequencing revealed reduced diversity and distinct taxonomic enrichment in the CAP group. Metabolomic assessments revealed that differentially enriched metabolites, including D-galactosamine, were enriched and that 16-hydroxyhexadecanoic acid and 3-methylindole were depleted in the CAP group. Immunofluorescence analyses revealed disruptions in tight junction proteins and mucin production, indicating intestinal barrier integrity disruption. Liver transcriptome analysis revealed upregulation of Lpin-1 expression in the CAP group.

CONCLUSION

This study provides comprehensive evidence of the systemic effects of CAP on liver fibrosis in NAFLD patients by elucidating alterations in the gut microbiota composition and metabolism.

Naringenin prevents non-alcoholic steatohepatitis by modulating the host metabolome and intestinal microbiome in MCD diet-fed mice

Non-alcoholic steatohepatitis (NASH) is a severe inflammatory phase of the non-alcoholic fatty liver disease (NAFLD) spectrum and can progress to advanced stages of NAFLD if left untreated. This study uses multi-omics data to elucidate the underlying mechanism of naringenin's reported benefit in alleviating (NASH). Male mice were fed a NASH-inducing (methionine-choline-deficient) MCD diet with or without naringenin supplementation for 6 weeks. Naringenin prevented NASH-induced histopathological liver damage and reversed the abnormal levels of hepatic triglyceride (TG)/total cholesterol (TC), serum TG/TC, serum alanine aminotransferase/aspartate transaminase, and hepatic malondialdehyde and glutathione. Importantly, naringenin intervention significantly modulated the relative abundance of gut microbiota and the host metabolomic profile. We detected more than 700 metabolites in the serum and found that the gut genus levels of Anaeroplasma and the [Eubacterium] nodatum group were closely associated with xanthine, 2-picoline, and securinine, respectively. Tuzzerella alterations showed the highest number of associations with host endogenous metabolites such as FAHFA (8:0/10:0), FFA (20:2), carnitine C8:1, tridecanedioic acid, securinine, acetylvaline, DL-O-tyrosine, and Phe-Asn. This study indicates that the interplay between host serum metabolites and gut microbiota may contribute to the therapeutic effect of naringenin against NASH.

sTREM2 is a plasma biomarker for human NASH and promotes hepatocyte lipid accumulation

BACKGROUND

Pathogenetic mechanisms of the progression of NAFL to advanced NASH coupled with potential noninvasive biomarkers and novel therapeutic targets are active areas of investigation. The recent finding that increased plasma levels of a protein shed by myeloid cells -soluble Triggering Receptor Expressed on Myeloid cells 2 (sTREM2) -may be a biomarker for NASH has received much interest. We aimed to test sTREM2 as a biomarker for human NASH and investigate the role of sTREM2 in the pathogenesis of NASH.

METHODS

We conducted studies in both humans (comparing patients with NASH vs. NAFL) and in mice (comparing different mouse models of NASH) involving measurements of TREM2 gene and protein expression levels in the liver as well as circulating sTREM2 levels in plasma. We investigated the pathogenetic role of sTREM2 in hepatic steatosis using primary hepatocytes and bone marrow derived macrophages.

RESULTS

RNA sequencing analysis of livers from patients with NASH or NAFL as well as livers from 2 mouse models of NASH revealed elevated TREM2 expression in patients/mice with NASH as compared with NAFL. Plasma levels of sTREM2 were significantly higher in a well-characterized cohort of patients with biopsy-proven NASH versus NAFL (area under receiver-operating curve 0.807). Mechanistic studies revealed that cocultures of primary hepatocytes and macrophages with an impaired ability to shed sTREM2 resulted in reduced hepatocyte lipid droplet formation on palmitate stimulation, an effect that was counteracted by the addition of exogenous sTREM2 chimeric protein. Conversely, exogenous sTREM2 chimeric protein increased lipid droplet formation, triglyceride content, and expression of the lipid transporter CD36 in hepatocytes. Furthermore, inhibition of CD36 markedly attenuated sTREM2-induced lipid droplet formation in mouse primary hepatocytes.

CONCLUSIONS

Elevated levels of sTREM2 due to TREM2 shedding may directly contribute to the pathogenesis of NAFLD by promoting hepatocyte lipid accumulation, as well as serving as a biomarker for distinguishing patients with NASH versus NAFL. Further investigation of sTREM2 as a clinically useful diagnostic biomarker and of the therapeutic effects of targeting sTREM2 in NASH is warranted.

Exploring the underlying mechanisms of Ashitaba in the management of non-alcoholic fatty liver disease by integrating the analysis of transcriptomics and metabolomics

Ashitaba seems to improve glucose intolerance and decrease triglyceride (TG) and total cholesterol (TC), which contribute to the development of non-alcoholic fatty liver disease (NAFLD). However, it remains to be explored the mechanism of Ashitaba in managing NAFLD. We determined the impact of Ashitaba on NAFLD, particularly its underlying mechanisms at the bioinformatic level. The established NAFLD mouse model was treated with or without Ashitaba, and the underlying mechanism was explored using transcriptomics paired with metabolomics. Ashitaba reduced obesity and liver steatosis in NAFLD mice. It identified 429 differentially expressed genes (DEGs) and verified 45 differential metabolites, especially those that alleviate NAFLD via the FXR signaling pathway. Our data may provide insight into the therapeutic impact of Ashitaba in the management of NAFLD and may be useful in clinical interventions for NAFLD.

Metabolic role of the hepatic valine/3-hydroxyisobutyrate (3-HIB) pathway in fatty liver disease

BACKGROUND

The valine (branched-chain amino acid) metabolite 3-hydroxyisobutyrate (3-HIB), produced by 3-Hydroxyisobutyryl-CoA Hydrolase (HIBCH), is associated with insulin resistance and type 2 diabetes, but implicated tissues and cellular mechanisms are poorly understood. We hypothesized that HIBCH and 3-HIB regulate hepatic lipid accumulation.

METHODS

HIBCH mRNA in human liver biopsies ("Liver cohort") and plasma 3-HIB ("CARBFUNC" cohort) were correlated with fatty liver and metabolic markers. Human Huh7 hepatocytes were supplemented with fatty acids (FAs) to induce lipid accumulation. Following HIBCH overexpression, siRNA knockdown, inhibition of PDK4 (a marker of FA β-oxidation) or 3-HIB supplementation, we performed RNA-seq, Western blotting, targeted metabolite analyses and functional assays.

FINDINGS

We identify a regulatory feedback loop between the valine/3-HIB pathway and PDK4 that shapes hepatic FA metabolism and metabolic health and responds to 3-HIB treatment of hepatocytes. HIBCH overexpression increased 3-HIB release and FA uptake, while knockdown increased cellular respiration and decreased reactive oxygen species (ROS) associated with metabolic shifts via PDK4 upregulation. Treatment with PDK4 inhibitor lowered 3-HIB release and increased FA uptake, while increasing HIBCH mRNA. Implicating this regulatory loop in fatty liver, human cohorts show positive correlations of liver fat with hepatic HIBCH and PDK4 expression (Liver cohort) and plasma 3-HIB (CARBFUNC cohort). Hepatocyte 3-HIB supplementation lowered HIBCH expression and FA uptake and increased cellular respiration and ROS.

INTERPRETATION

These data implicate the hepatic valine/3-HIB pathway in mechanisms of fatty liver, reflected in increased plasma 3-HIB concentrations, and present possible targets for therapeutic intervention.

FUNDING

Funding was provided by the Research Council of Norway (263124/F20), the University of Bergen, the Western Norway Health Authorities, Novo Nordisk Scandinavia AS, the Trond Mohn Foundation and the Norwegian Diabetes Association.

Restoring polyamine levels by supplementation of spermidine modulates hepatic immune landscape in murine model of NASH

AIMS

To determine if changes in polyamines metabolism occur during non-alcoholic steatohepatitis (NASH) in human patients and mice, as well as to assess systemic and liver-specific effects of spermidine administration into mice suffering from advanced NASH.

MATERIALS AND METHODS

Human fecal samples were collected from 50 healthy and 50 NASH patients. For the preclinical studies C57Bl6/N male mice fed GAN or NIH-31 diet for 6 months were ordered from Taconic and liver biopsy was performed. Based on severity of liver fibrosis, body composition and body weight, the mice from both dietary groups were randomized into another two groups: half receiving 3 mM spermidine in drinking water, half normal water for subsequent 12 weeks. Body weight was measured weekly and glucose tolerance and body composition were assessed at the end. Blood and organs were collected during necropsy, and intrahepatic immune cells were isolated for flow cytometry analysis.

RESULTS

Metabolomic analysis of human and murine feces confirmed that levels of polyamines decreased along NASH progression. Administration of exogenous spermidine to the mice from both dietary groups did not affect body weight, body composition or adiposity. Moreover, incidence of macroscopic hepatic lesions was higher in NASH mice receiving spermidine. On the other hand, spermidine normalized numbers of Kupffer cells in the livers of mice suffering from NASH, although these beneficial effects did not translate into improved liver steatosis or fibrosis severity.

CONCLUSION

Levels of polyamines decrease during NASH in mice and human patients but spermidine administration does not improve advanced NASH.

Spermidine suppresses the activation of hepatic stellate cells to cure liver fibrosis through autophagy activator MAP1S

BACKGROUND AND AIMS

Liver diseases present a wide range of fibrosis, from fatty liver with no inflammation to steatohepatitis with varying degrees of fibrosis, to established cirrhosis leading to HCC. In a multivariate analysis, serum levels of spermidine were chosen as the top metabolite from 237 metabolites and its levels were drastically reduced along with progression to advanced steatohepatitis. Our previous studies that showed spermidine supplementation helps mice prevent liver fibrosis through MAP1S have prompted us to explore the possibility that spermidine can alleviate or cure already developed liver fibrosis.

METHODS

We collected tissue samples from patients with liver fibrosis to measure the levels of MAP1S. We treated wild-type and MAP1S knockout mice with CCl₄ -induced liver fibrosis with spermidine and isolated HSCs in culture to test the effects of spermidine on HSC activation and liver fibrosis.

RESULTS

Patients with increasing degrees of liver fibrosis had reduced levels of MAP1S. Supplementing spermidine in mice that had already developed liver fibrosis after 1 month of CCl₄ induction for an additional 3 months resulted in significant reductions in levels of ECM proteins and a remarkable improvement in liver fibrosis through MAP1S. Spermidine also suppressed HSC activation by reducing ECM proteins at both the mRNA and protein levels, and increasing the number of lipid droplets in stellate cells.

CONCLUSIONS

Spermidine supplementation is a potentially clinically meaningful approach to treating and curing liver fibrosis, preventing cirrhosis and HCC in patients.

Sex dimorphism and metabolic profiles in management of metabolic-associated fatty liver disease

Metabolic-associated fatty liver disease (MAFLD) refers to the build-up of fat in the liver associated with metabolic dysfunction and has been estimated to affect a quarter of the population worldwide. Although metabolism is highly influenced by the effects of sex hormones, studies of sex differences in the incidence and progression of MAFLD are scarce. Metabolomics represents a powerful approach to studying these differences and identifying potential biomarkers and putative mechanisms. First, metabolomics makes it possible to obtain the molecular phenotype of the individual at a given time. Second, metabolomics may be a helpful tool for classifying patients according to the severity of the disease and obtaining diagnostic biomarkers. Some studies demonstrate associations between circulating metabolites and early and established MAFLD, but little is known about how metabolites relate to and encompass sex differences in disease progression and risk management. In this review, we will discuss the epidemiological metabolomic studies for sex differences in the development and progression of MAFLD, the role of metabolic profiles in understanding mechanisms and identifying sex-dependent biomarkers, and how this evidence may help in the future management of the disease.

Metabolic Pathway Analysis: Advantages and Pitfalls for the Functional Interpretation of Metabolomics and Lipidomics Data

Over the past decades, pathway analysis has become one of the most commonly used approaches for the functional interpretation of metabolomics data. Although the approach is widely used, it is not well standardized and the impact of different methodologies on the functional outcome is not well understood. Using four publicly available datasets, we investigated two main aspects of topological pathway analysis, namely the consideration of non-human native enzymatic reactions (e.g., from microbiota) and the interconnectivity of individual pathways. The exclusion of non-human native reactions led to detached and poorly represented reaction networks and to loss of information. The consideration of connectivity between pathways led to better emphasis of certain central metabolites in the network; however, it occasionally overemphasized the hub compounds. We proposed and examined a penalization scheme to diminish the effect of such compounds in the pathway evaluation. In order to compare and assess the results between different methodologies, we also performed over-representation analysis of the same datasets. We believe that our findings will raise awareness on both the capabilities and shortcomings of the currently used pathway analysis practices in metabolomics. Additionally, it will provide insights on various methodologies and strategies that should be considered for the analysis and interpretation of metabolomics data.

Lipidized PrRP Analog Exhibits Strong Anti-Obesity and Antidiabetic Properties in Old WKY Rats with Obesity and Glucose Intolerance

Prolactin-releasing peptide (PrRP) is an anorexigenic neuropeptide that has potential for the treatment of obesity and its complications. Recently, we designed a palmitoylated PrRP31 analog (palm¹¹-PrRP31) that is more stable than the natural peptide and able to act centrally after peripheral administration. This analog acted as an anti-obesity and glucose-lowering agent, attenuating lipogenesis in rats and mice with high-fat (HF) diet-induced obesity. In Wistar Kyoto (WKY) rats fed a HF diet for 52 weeks, we explored glucose intolerance, but also prediabetes, liver steatosis and insulin resistance-related changes, as well as neuroinflammation in the brain. A potential beneficial effect of 6 weeks of treatment with palm¹¹-PrRP31 and liraglutide as comparator was investigated. Liver lipid profiles, as well as urinary and plasma metabolomic profiles, were measured by lipidomics and metabolomics, respectively. Old obese WKY rats showed robust glucose intolerance that was attenuated by palm¹¹-PrRP31, but not by liraglutide treatment. On the contrary, liraglutide had a beneficial effect on insulin resistance parameters. Despite obesity and prediabetes, WKY rats did not develop steatosis owing to HF diet feeding, even though liver lipogenesis was enhanced. Plasma triglycerides and cholesterol were not increased by HFD feeding, which points to unincreased lipid transport from the liver. The liver lipid profile was significantly altered by a HF diet that remained unaffected by palm¹¹-PrRP31 or liraglutide treatment. The HF-diet-fed WKY rats revealed astrogliosis in the brain cortex and hippocampus, which was attenuated by treatment. In conclusion, this study suggested multiple beneficial anti-obesity-related effects of palm¹¹-PrRP31 and liraglutide in both the periphery and brain.

Nanomaterial-induced toxicity in pathophysiological models representative of individuals with pre-existing medical conditions

The integration of nanomaterials (NMs) into an ever-expanding number of daily used products has proven to be highly desirable in numerous industries and applications. Unfortunately, the same "nano" specific physicochemical properties, which make these materials attractive, may also contribute to hazards for individuals exposed to these materials. In 2021, it was estimated that 7 out of 10 deaths globally were accredited to chronic diseases, such as chronic liver disease, asthma, and cardiovascular-related illnesses. Crucially, it is also understood that a significant proportion of global populace numbering in the billions are currently living with a range of chronic undiagnosed health conditions. Due to the significant number of individuals affected, it is important that people suffering from chronic disease also be considered and incorporated in NM hazard assessment strategies. This review examined and analyzed the literature that focused on NM-induced adverse health effects in models which are representative of individuals exhibiting pre-existing medical conditions with focus on the pulmonary, cardiovascular, hepatic, gastrointestinal, and central nervous systems. The overall objective of this review was to outline available data, highlighting the important role of pre-existing disease in NM-induced toxicity with the aim of establishing a weight of evidence approach to inform the public on the potential hazards posed by NMs in both healthy and compromised persons in general population.

The interplay between nonalcoholic fatty liver disease and atherosclerotic cardiovascular disease

Therapeutic approaches that lower circulating low-density lipoprotein (LDL)-cholesterol significantly reduced the burden of cardiovascular disease over the last decades. However, the persistent rise in the obesity epidemic is beginning to reverse this decline. Alongside obesity, the incidence of nonalcoholic fatty liver disease (NAFLD) has substantially increased in the last three decades. Currently, approximately one third of world population is affected by NAFLD. Notably, the presence of NAFLD and particularly its more severe form, nonalcoholic steatohepatitis (NASH), serves as an independent risk factor for atherosclerotic cardiovascular disease (ASCVD), thus, raising interest in the relationship between these two diseases. Importantly, ASCVD is the major cause of death in patients with NASH independent of traditional risk factors. Nevertheless, the pathophysiology linking NAFLD/NASH with ASCVD remains poorly understood. While dyslipidemia is a common risk factor underlying both diseases, therapies that lower circulating LDL-cholesterol are largely ineffective against NASH. While there are no approved pharmacological therapies for NASH, some of the most advanced drug candidates exacerbate atherogenic dyslipidemia, raising concerns regarding their adverse cardiovascular consequences. In this review, we address current gaps in our understanding of the mechanisms linking NAFLD/NASH and ASCVD, explore strategies to simultaneously model these diseases, evaluate emerging biomarkers that may be useful to diagnose the presence of both diseases, and discuss investigational approaches and ongoing clinical trials that potentially target both diseases.

Plasma Metabolomic and Lipidomic Profiling of Metabolic Dysfunction-Associated Fatty Liver Disease in Humans Using an Untargeted Multiplatform Approach

Metabolic dysfunction-associated fatty liver disease (MAFLD) is a complex disorder that is implicated in dysregulations in multiple biological pathways, orchestrated by interactions between genetic predisposition, metabolic syndromes and environmental factors. The limited knowledge of its pathogenesis is one of the bottlenecks in the development of prognostic and therapeutic options for MAFLD. Moreover, the extent to which metabolic pathways are altered due to ongoing hepatic steatosis, inflammation and fibrosis and subsequent liver damage remains unclear. To uncover potential MAFLD pathogenesis in humans, we employed an untargeted nuclear magnetic resonance (NMR) spectroscopy- and high-resolution mass spectrometry (HRMS)-based multiplatform approach combined with a computational multiblock omics framework to characterize the plasma metabolomes and lipidomes of obese patients without (n = 19) or with liver biopsy confirmed MAFLD (n = 63). Metabolite features associated with MAFLD were identified using a metabolome-wide association study pipeline that tested for the relationships between feature responses and MAFLD. A metabolic pathway enrichment analysis revealed 16 pathways associated with MAFLD and highlighted pathway changes, including amino acid metabolism, bile acid metabolism, carnitine shuttle, fatty acid metabolism, glycerophospholipid metabolism, arachidonic acid metabolism and steroid metabolism. These results suggested that there were alterations in energy metabolism, specifically amino acid and lipid metabolism, and pointed to the pathways being implicated in alerted liver function, mitochondrial dysfunctions and immune system disorders, which have previously been linked to MAFLD in human and animal studies. Together, this study revealed specific metabolic alterations associated with MAFLD and supported the idea that MAFLD is fundamentally a metabolism-related disorder, thereby providing new perspectives for diagnostic and therapeutic strategies.

Systematic Review of NMR-Based Metabolomics Practices in Human Disease Research

Nuclear magnetic resonance (NMR) spectroscopy is one of the principal analytical techniques for metabolomics. It has the advantages of minimal sample preparation and high reproducibility, making it an ideal technique for generating large amounts of metabolomics data for biobanks and large-scale studies. Metabolomics is a popular “omics” technology and has established itself as a comprehensive exploratory biomarker tool; however, it has yet to reach its collaborative potential in data collation due to the lack of standardisation of the metabolomics workflow seen across small-scale studies. This systematic review compiles the different NMR metabolomics methods used for serum, plasma, and urine studies, from sample collection to data analysis, that were most popularly employed over a two-year period in 2019 and 2020. It also outlines how these methods influence the raw data and the downstream interpretations, and the importance of reporting for reproducibility and result validation. This review can act as a valuable summary of NMR metabolomic workflows that are actively used in human biofluid research and will help guide the workflow choice for future research.

Application of metabolomics in the diagnosis of non-alcoholic fatty liver disease and the treatment of traditional Chinese medicine

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease around the world, and it often coexists with insulin resistance-related diseases including obesity, diabetes, hyperlipidemia, and hypertension, which seriously threatens human health. Better prevention and treatment strategies are required to improve the impact of NAFLD. Although needle biopsy is an effective tool for diagnosing NAFLD, this method is invasive and difficult to perform. Therefore, it is very important to develop more efficient approaches for the early diagnosis of NAFLD. Traditional Chinese medicine (TCM) can play a certain role in improving symptoms and protecting target organs, and its mechanism of action needs to be further studied. Metabolomics, the study of all metabolites that is thought to be most closely associated with the patients’ characters, can provide useful clinically biomarkers that can be applied to NAFLD and may open up new methods for diagnosis. Metabolomics technology is consistent with the overall concept of TCM, and it can also be used as a potential mechanism to explain the effects of TCM by measuring biomarkers by metabolomics. Based on PubMed/MEDLINE and other databases, this paper retrieved relevant literature NAFLD and TCM intervention in NAFLD using metabolomics technology in the past 5 years were searched, and the specific metabolites associated with the development of NAFLD and the potential mechanism of Chinese medicine on improving symptoms were summarized.

Multiomics technologies: role in disease biomarker discoveries and therapeutics

 

Medical research has been revolutionized after the publication of the full human genome. This was the major landmark that paved the way for understanding the biological functions of different macro and micro molecules. With the advent of different high-throughput technologies, biomedical research was further revolutionized. These technologies constitute genomics, transcriptomics, proteomics, metabolomics, etc. Collectively, these high-throughputs are referred to as multi-omics technologies. In the biomedical field, these omics technologies act as efficient and effective tools for disease diagnosis, management, monitoring, treatment and discovery of certain novel disease biomarkers. Genotyping arrays and other transcriptomic studies have helped us to elucidate the gene expression patterns in different biological states, i.e. healthy and diseased states. Further omics technologies such as proteomics and metabolomics have an important role in predicting the role of different biological molecules in an organism. It is because of these high throughput omics technologies that we have been able to fully understand the role of different genes, proteins, metabolites and biological pathways in a diseased condition. To understand a complex biological process, it is important to apply an integrative approach that analyses the multi-omics data in order to highlight the possible interrelationships of the involved biomolecules and their functions. Furthermore, these omics technologies offer an important opportunity to understand the information that underlies disease. In the current review, we will discuss the importance of omics technologies as promising tools to understand the role of different biomolecules in diseases such as cancer, cardiovascular diseases, neurodegenerative diseases and diabetes.

SUMMARY POINTS

Clinical Phenotyping and the Application of Precision Medicine in MAFLD

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A pilot study optimizing metabolomic and lipidomic acquisition in serum for biomarker discovery in nonalcoholic fatty liver disease

Background

The worldwide prevalence of non-alcoholic fatty liver disease (NAFLD) has stimulated work to identify biomarkers and develop effective treatments. Metabolomics is an emerging tool that has been widely applied to discover biomarkers and simultaneously uncover pathological mechanisms. Here, we aim to optimize metabolomic acquisition with the goal of obtaining a systemic metabolic profile to unravel the potential link between dysregulated metabolism and NAFLD.

Methods

We analyzed serum samples collected from healthy subjects (n = 8) and NAFLD patients (n = 8) via an integrative analytical workflow using two orthogonal separation modes with T3 and amide columns and two ionization polarity modes on a UPLC-ESI-Q/TOF. Data dependent acquisition was employed for data acquisition. Differentially expressed metabolites and lipids were identified by comparing the collected metabolic and lipidomic profiles between the healthy subjects and NAFLD patients.

Results

The integrative LC-MS/MS analytical workflow employed here features an improved coverage of metabolites and lipids, which leads to the identification of 20 potential biomarkers of NAFLD, including lipids, acylcarnitines, and organic acids.

Conclusions

This pilot study has identified potential biomarkers for NAFLD and revealed corresponding dysregulated metabolic pathways related to NAFLD's occurrence and progression, establishing a molecular basis for NAFLD diagnosis and therapeutic intervention.

Aqueous Metabolite Trends for the Progression of Nonalcoholic Fatty Liver Disease in Female Bariatric Surgery Patients by Targeted 1H-NMR Metabolomics

Determining biomarkers and better characterizing the biochemical progression of nonalcoholic fatty liver disease (NAFLD) remains a clinical challenge. A targeted ¹H-NMR study of serum, combined with clinical variables, detected and localized biomarkers to stages of NAFLD in morbidly obese females. Pre-surgery serum samples from 100 middle-aged, morbidly obese female subjects, grouped on gold-standard liver wedge biopsies (non-NAFLD; steatosis; and fibrosis) were collected, extracted, and analyzed in aqueous (D₂O) buffer (¹H, 600 MHz). Profiled concentrations were subjected to exploratory statistical analysis. Metabolites varying significantly between the non-NAFLD and steatosis groups included the ketone bodies 3-hydroxybutyrate (↓; p = 0.035) and acetone (↓; p = 0.012), and also alanine (↑; p = 0.004) and a putative pyruvate signal (↑; p = 0.003). In contrast, the steatosis and fibrosis groups were characterized by 2-hydroxyisovalerate (↑; p = 0.023), betaine (↓; p = 0.008), hypoxanthine (↓; p = 0.003), taurine (↓; p = 0.001), 2-hydroxybutyrate (↑; p = 0.045), 3-hydroxyisobutyrate (↑; p = 0.046), and increasing medium chain fatty acids. Exploratory classification models with and without clinical variables exhibited overall success rates ca. 75–85%. In the study conditions, inhibition of fatty acid oxidation and disruption of the hepatic urea cycle are supported as early features of NAFLD that continue in fibrosis. In fibrosis, markers support inflammation, hepatocyte damage, and decreased liver function. Complementarity of NMR concentrations and clinical information in classification models is shown. A broader hypothesis that standard-of-care sera can yield metabolomic information is supported.

Spermidine Supplementation Protects the Liver Endothelium from Liver Damage in Mice

Chronic liver diseases are multifactorial and the need to develop effective therapies is high. Recent studies have shown the potential of ameliorating liver disease progression through protection of the liver endothelium. Polyamine spermidine (SPD) is a caloric restriction mimetic with autophagy-enhancing properties capable of prolonging lifespan and with a proven beneficial effect in cardiovascular disease in mice and humans. We evaluated the use of dietary supplementation with SPD in two models of liver disease (CCl4 and CDAAH diet). We analyzed the effect of SPD on endothelial dysfunction in vitro and in vivo. C57BL/6J mice were supplemented with SPD in the drinking water prior and concomitantly with CCl4 and CDAAH treatments. Endothelial autophagy deficient (Atg7endo) mice were also evaluated. Liver tissue was used to evaluate the impact of SPD prophylaxis on liver damage, endothelial dysfunction, oxidative stress, mitochondrial status, inflammation and liver fibrosis. SPD improved the endothelial response to oxidative injury in vitro and improved the liver endothelial phenotype and protected against liver injury in vivo. SPD reduced the overall liver oxidative stress and improved mitochondrial fitness. The absence of benefits in the Atg7endo mice suggests an autophagy-dependent effect of SPD. This study suggests SPD diet supplementation in early phases of disease protects the liver endothelium from oxidative stress and may be an attractive approach to modify the chronic liver disease course and halt fibrosis progression.

Particulate and drug-induced toxicity assessed in novel quadruple cell human primary hepatic disease models of steatosis and pre-fibrotic NASH

In an effort to replace, reduce and refine animal experimentation, there is an unmet need to advance current in vitro models that offer features with physiological relevance and enhanced predictivity of in vivo toxicological output. Hepatic toxicology is key following chemical, drug and nanomaterials (NMs) exposure, as the liver is vital in metabolic detoxification of chemicals as well as being a major site of xenobiotic accumulation (i.e., low solubility particulates). With the ever-increasing production of NMs, there is a necessity to evaluate the probability of consequential adverse effects, not only in health but also in clinically asymptomatic liver, as part of risk stratification strategies. In this study, two unique disease initiation and maintenance protocols were developed and utilised to mimic steatosis and pre-fibrotic NASH in scaffold-free 3D liver microtissues (MT) composed of primary human hepatocytes, hepatic stellate cells, Kupffer cells and sinusoidal endothelial cells. The characterized diseased MT were utilized for the toxicological assessment of a panel of xenobiotics. Highlights from the study included: 1. Clear experimental evidence for the pre-existing liver disease is important in the augmentation of xenobiotic-induced hepatotoxicity and 2. NMs are able to activate stellate cells. The data demonstrated that pre-existing disease is vital in the intensification of xenobiotic-induced liver damage. Therefore, it is imperative that all stages of the wide spectrum of liver disease are incorporated in risk assessment strategies. This is of significant consequence, as a substantial number of the general population suffer from sub-clinical liver injury without any apparent or diagnosed manifestations.

Multi-omics profiling: the way towards precision medicine in metabolic diseases

Metabolic diseases including type 2 diabetes mellitus (T2DM), non-alcoholic fatty liver disease (NAFLD), and metabolic syndrome (MetS) are alarming health burdens around the world, while therapies for these diseases are far from satisfying as their etiologies are not completely clear yet. T2DM, NAFLD, and MetS are all complex and multifactorial metabolic disorders based on the interactions between genetics and environment. Omics studies such as genetics, transcriptomics, epigenetics, proteomics, and metabolomics are all promising approaches in accurately characterizing these diseases. And the most effective treatments for individuals can be achieved via omics pathways, which is the theme of precision medicine. In this review, we summarized the multi-omics studies of T2DM, NAFLD, and MetS in recent years, provided a theoretical basis for their pathogenesis and the effective prevention and treatment, and highlighted the biomarkers and future strategies for precision medicine.

The Role of the Transsulfuration Pathway in Non-Alcoholic Fatty Liver Disease

The prevalence of non-alcoholic fatty liver disease (NAFLD) is increasing and approximately 25% of the global population may have NAFLD. NAFLD is associated with obesity and metabolic syndrome, but its pathophysiology is complex and only partly understood. The transsulfuration pathway (TSP) is a metabolic pathway regulating homocysteine and cysteine metabolism and is vital in controlling sulfur balance in the organism. Precise control of this pathway is critical for maintenance of optimal cellular function. The TSP is closely linked to other pathways such as the folate and methionine cycles, hydrogen sulfide (H₂S) and glutathione (GSH) production. Impaired activity of the TSP will cause an increase in homocysteine and a decrease in cysteine levels. Homocysteine will also be increased due to impairment of the folate and methionine cycles. The key enzymes of the TSP, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE), are highly expressed in the liver and deficient CBS and CSE expression causes hepatic steatosis, inflammation, and fibrosis in animal models. A causative link between the TSP and NAFLD has not been established. However, dysfunctions in the TSP and related pathways, in terms of enzyme expression and the plasma levels of the metabolites (e.g., homocysteine, cystathionine, and cysteine), have been reported in NAFLD and liver cirrhosis in both animal models and humans. Further investigation of the TSP in relation to NAFLD may reveal mechanisms involved in the development and progression of NAFLD.

Protein and amino acids in nonalcoholic fatty liver disease

PURPOSE OF REVIEW

In this review, the latest evidence on the influence of dietary protein and plasma amino acids in the pathogenesis of nonalcoholic fatty liver disease (NAFLD) is discussed.

RECENT FINDINGS

Increasing protein consumption during weight loss and maintenance may help reduce liver fat content. Conversely, high protein intake characteristic of the unhealthy Western diet is associated with increased NAFLD prevalence and severity. Plasma concentration of several amino acids, including branched-chain (BCAA) and aromatic amino acids (AAA), is altered in NAFLD. Excess amino acid availability contributes to intrahepatic fat accumulation and may reflect poor dietary habits and dysregulation of amino acid metabolic processing in both liver and peripheral tissues. Specific amino acid patterns, characterized by increased BCAA, AAA, alanine, glutamate, lysine levels, and decreased glycine and serine levels, may be used for early detection of NAFLD and noninvasive assessment of its histological severity.

SUMMARY

Mechanistic studies in NAFLD have been mostly focused on carbohydrate and fat metabolism, while little is known about the influence of protein and amino acids. Moreover, intervention and observational studies on the relation between protein intake and NAFLD yielded conflicting results. Filling the current knowledge gaps would help define the optimal diet composition for NAFLD prevention and management. Furthermore, metabolomics studies may provide insight into the pathogenesis of NAFLD, identify useful diagnostic and prognostic biomarkers, and unravel novel pharmacological targets and treatment options.

Glutamate-Serine-Glycine Index: A Novel Potential Biomarker in Pediatric Non-Alcoholic Fatty Liver Disease

Preliminary evidence suggests that the glutamate-serine-glycine (GSG) index, which combines three amino acids involved in glutathione synthesis, may be used as a potential biomarker of non-alcoholic fatty liver disease (NAFLD). We investigated whether the GSG index is associated with NAFLD in youth, independent of other risk factors. Intrahepatic fat content (HFF%) and abdominal fat distribution were measured by magnetic resonance imaging (MRI) in a multiethnic cohort of obese adolescents, including Caucasians, African Americans, and Hispanics. NAFLD was defined as HFF% ≥ 5.5%. Plasma amino acids were measured by mass spectrometry. The GSG index was calculated as glutamate/(serine + glycine). The GSG index was higher in NAFLD patients (p = 0.03) and positively correlated with HFF% (r = 0.26, p = 0.02), alanine aminotransferase (r = 0.39, p = 0.0006), and aspartate aminotransferase (r = 0.26, p = 0.03). Adolescents with a high GSG index had a twofold higher prevalence of NAFLD than those with a low GSG index, despite similar adiposity, abdominal fat distribution, and liver insulin resistance. NAFLD prevalence remained significantly different between groups after adjustment for age, sex, race/ethnicity, and body mass index (OR 3.07, 95% confidence interval 1.09-8.61, p = 0.03). This study demonstrates the ability of the GSG index to detect NAFLD in at-risk pediatric populations with different genetically determined susceptibilities to intrahepatic fat accumulation, independent of traditional risk factors.