Hepatic lipid profiling of deer mice fed ethanol using ¹H and ³¹P NMR spectroscopy: a dose-dependent subchronic study

Dysregulated hepatic alcohol metabolism: a key factor involved in the pathogenesis of alcohol-associated liver disease

Alcohol use disorder is a major risk factor for alcohol-associated liver disease (ALD), characterized by reduced hepatic alcohol dehydrogenase (ADH) activity, increased body burden of alcohol, and its nonoxidative metabolism to fatty acid ethyl esters (FAEEs). However, the mechanism(s) underlying ALD remain unclear. This study investigated the metabolic basis and mechanism(s) of ALD in chronic ethanol (EtOH)-fed hepatic ADH1-deficient (ADH-) deer mice administered with a single dose of binge EtOH with/without FAEEs. Hepatic ADH- and ADH normal (ADH+) deer mice fed chronic EtOH daily for 3 mo, followed by a single dose of binge EtOH (3 g/kg·body wt) with/without FAEEs (100 mg/kg·body wt), 1 wk before euthanasia. Blood alcohol and acetaldehyde and liver injury markers in the plasma, hepatic FAEEs, lipids, and inflammatory markers were analyzed. Hepatic histology, ultrastructure, protein/mRNA expression of genes involved in alcohol metabolism and lipogenesis, cyclic adenosine monophosphate (cAMP), phosphodiesterase (PDE) activity, and AMP-activated protein kinase (AMPKα) signaling were assessed. Blood alcohol, hepatic lipids and FAEEs, inflammation, oxidative stress, and the expression of lipogenic proteins/genes were significantly increased in various chronic EtOH-fed groups of ADH- versus ADH+ deer mice. In addition, hepatic cAMP levels were reduced, whereas PDE activity and plasma transaminases were elevated. Binge EtOH with/without FAEEs did not significantly exacerbate the liver injury in chronic EtOH-fed ADH- as well as ADH+ deer mice. Overall, an increased body burden of EtOH and endogenously formed FAEEs due to hepatic ADH deficiency, along with dysregulated cAMP and AMPKα signaling, could be the determining factors for EtOH-induced liver injury leading to ALD.NEW & NOTEWORTHY Using hepatic alcohol dehydrogenase deficient (ADH-) deer mouse, which mimics the metabolic conditions observed in chronic alcoholics, we found significant hepatic injury along with degenerative changes in endoplasmic reticulum and mitochondria. Our findings suggest that an increased nonoxidative alcohol metabolism under hepatic alcohol dehydrogenase deficiency and associated hepatic lipid dysregulation and injury appear to be the key factors involved in the pathogenesis of alcohol-associated liver disease.

1H-NMR Lipidomics, Comparing Fatty Acids and Lipids in Cow, Goat, Almond, Cashew, Soy, and Coconut Milk Using NMR and Mass Spectrometry

Background/Objectives: Lipids are an important component of human nutrition. Conventional milk is obtained from animals, and dairy milk is consumed by many people worldwide. Recently, milk consumers have been increasingly shifting towards plant-based milk options. The aim of the study was the qualitative identification of lipid metabolites in animal- and plant-based milk, the identification and comparison of the fatty acids (FAs) of milk, and the qualitative identification of the lipid groups among the milk varieties. Methods: Milk samples were obtained from local grocery stores. Lipids were extracted using a modified Folch method and analyzed using nuclear magnetic resonance (NMR) metabolomics. Gas and liquid chromatography mass spectrometry methods (GC-MS and LC-MS) were used to identify the FAs and lipid groups. Lipid weights were compared and the NMR profiles of the lipids analyzed by multivariate statistical analysis. Principal component analysis was performed for the milk lipids obtained from the animal, and plant milk varieties. Results: Clustering of NMR data showed two main clusters: cow/almond/cashew and goat/soy/coconut. GC-MS analysis of the methylated fatty acids (FAs) showed the presence of 12:0, 14:0, 16:0, 16:1, 17:0, 18:0, 18:1, 18:2, 20:1, and 20:2 in all milk types, while FAs 19:0 and 20:4 were observed only in the dairy milk. LC-MS data showed common masses that may indicate the presence of mono- and diacyl glycerols and several lysophospholipids among the different types of milk. Conclusions: This study shows the advantage of using NMR, GC-MS, and LC-MS to differentiate the lipids among different milk types and compare them on one platform.

Emerging targets for therapy in ALD: Lessons from NASH

Alcohol-associated liver disease due to harmful alcohol use and NAFLD associated with metabolic syndrome are the 2 most common liver diseases worldwide. Control of respective risk factors is the cornerstone in the long-term management of these diseases. Furthermore, there are no effective therapies. Both diseases are characterized by metabolic derangements; thus, the focus of this review was to broaden our understanding of metabolic targets investigated in NAFLD, and how these can be applied to alcohol-associated liver disease. Conserved pathogenic pathways such as dysregulated lipid metabolism, cell death pathways including apoptosis and activation of innate immune cells, and stellate cells mediate both alcohol and NAFLDs, resulting in histological abnormalities of steatosis, inflammation, fibrosis, and cirrhosis. However, pathways such as gut microbiome changes, glucose metabolism and insulin resistance, inflammatory signaling, and microRNA abnormalities are distinct in these 2 diseases. In this review article, we describe conserved and distinct pathogenic pathways highlighting therapeutic targets that may be of potential in both diseases and those that are unique to each disease.

Quantitative Comparison of Avian and Mammalian Physiologies for Parameterization of Physiologically Based Kinetic Models

Physiologically based kinetic (PBK) models facilitate chemical risk assessment by predicting in vivo exposure while reducing the need for animal testing. PBK models for mammals have seen significant progress, which has yet to be achieved for avian systems. Here, we quantitatively compare physiological, metabolic and anatomical characteristics between birds and mammals, with the aim of facilitating bird PBK model development. For some characteristics, there is considerable complementarity between avian and mammalian species with identical values for the following: blood hemoglobin and hemoglobin concentrations per unit erythrocyte volume together with relative weights of the liver, heart, and lungs. There are also systematic differences for some major characteristics between avian and mammalian species including erythrocyte volume, plasma concentrations of albumin, total protein and triglyceride together with liver cell size and relative weights of the kidney, spleen, and ovary. There are also major differences between characteristics between sexually mature and sexually immature female birds. For example, the relative weights of the ovary and oviduct are greater in sexually mature females compared to immature birds as are the plasma concentrations of triglyceride and vitellogenin. Both these sets of differences reflect the genetic "blue print" inherited from ancestral archosaurs such as the production of large eggs with yolk filled oocytes surrounded by egg white proteins, membranes and a calciferous shell together with adaptions for flight in birds or ancestrally in flightless birds.

NMR spectroscopy of a single mammalian early stage embryo

The resolving power, chemical sensitivity and non-invasive nature of NMR have made it an established technique for in vivo studies of large organisms both for research and clinical applications. NMR would clearly be beneficial for analysis of entities at the microscopic scale of about 1 nL (the nanoliter scale), typical of early development of mammalian embryos, microtissues and organoids: the scale where the building blocks of complex organisms could be observed. However, the handling of such small samples (about 100 µm) and sensitivity issues have prevented a widespread adoption of NMR. In this article we show how these limitations can be overcome to obtain NMR spectra of a mammalian embryo in its early stage. To achieve this we employ ultra-compact micro-chip technologies in combination with 3D-printed micro-structures. Such device is packaged for use as plug & play sensor and it shows sufficient sensitivity to resolve NMR signals from individual bovine pre-implantation embryos. The embryos in this study are obtained through In Vitro Fertilization (IVF) techniques, transported cryopreserved to the NMR laboratory, and measured shortly after thawing. In less than 1 h these spherical samples of just 130-190 µm produce distinct spectral peaks, largely originating from lipids contained inside them. We further observe how the spectra vary from one sample to another despite their optical and morphological similarities, suggesting that the method can further develop into a non-invasive embryo assay for selection prior to embryo transfer.

Alcohol effects on hepatic lipid metabolism

Alcoholic liver disease (ALD) is the most prevalent type of chronic liver disease with significant morbidity and mortality worldwide. ALD begins with simple hepatic steatosis and progresses to alcoholic steatohepatitis, fibrosis, and cirrhosis. The severity of hepatic steatosis is highly associated with the development of later stages of ALD. This review explores the disturbances of alcohol-induced hepatic lipid metabolism through altered hepatic lipid uptake, de novo lipid synthesis, fatty acid oxidation, hepatic lipid export, and lipid droplet formation and catabolism. In addition, we review emerging data on the contributions of genetics and bioactive lipid metabolism in alcohol-induced hepatic lipid accumulation.

The hepatic lipidome: From basic science to clinical translation

The liver is the key organ involved in lipid metabolism and transport. Excessive lipid accumulation due to dysregulated lipid metabolism predisposes the liver to steatosis, cirrhosis, and hepatocellular carcinoma. Lipids are generally compartmentalized in specialized organelles called lipid droplets that enable cells to store and release lipids in a regulated manner. However, during flux-in and flux-out of droplets, lipids are converted into toxic species leading to lipid-mediated liver damage. Lipids are categorized into 'toxic' or 'healthy' lipids that are involved in liver disease pathogenesis or resolution, respectively. Lipidomic analysis have revealed unique lipid signature that correlates with the disease progression therefore being used for disease diagnosis. In this comprehensive review, we provide an overview on hepatic lipid homeostasis, lipid compartmentalization mechanisms and lipidomic profiles in different liver diseases. We further discuss promising therapeutics targeting the hepatic lipidome including pro-resolving lipids, liposomes, and small-molecule inhibitors for the treatment of liver diseases.

Linking Dysregulated AMPK Signaling and ER Stress in Ethanol-Induced Liver Injury in Hepatic Alcohol Dehydrogenase Deficient Deer Mice

Ethanol (EtOH) metabolism itself can be a predisposing factor for initiation of alcoholic liver disease (ALD). Therefore, a dose dependent study to evaluate liver injury was conducted in hepatic alcohol dehydrogenase (ADH) deficient (ADH⁻) and ADH normal (ADH⁺) deer mice fed 1%, 2% or 3.5% EtOH in the liquid diet daily for 2 months. Blood alcohol concentration (BAC), liver injury marker (alanine amino transferase (ALT)), hepatic lipids and cytochrome P450 2E1 (CYP2E1) activity were measured. Liver histology, endoplasmic reticulum (ER) stress, AMP-activated protein kinase (AMPK) signaling and cell death proteins were evaluated. Significantly increased BAC, plasma ALT, hepatic lipids and steatosis were found only in ADH⁻ deer mice fed 3.5% EtOH. Further, a significant ER stress and increased un-spliced X-box binding protein 1 were evident only in ADH⁻ deer mice fed 3.5% EtOH. Both strains fed 3.5% EtOH showed deactivation of AMPK, but increased acetyl Co-A carboxylase 1 and decreased carnitine palmitoyltransferase 1A favoring lipogenesis were found only in ADH⁻ deer mice fed 3.5% EtOH. Therefore, irrespective of CYP2E1 overexpression; EtOH dose and hepatic ADH deficiency contribute to EtOH-induced steatosis and liver injury, suggesting a linkage between ER stress, dysregulated hepatic lipid metabolism and AMPK signaling.

The Hepatic Lipidome: A Gateway to Understanding the Pathogenes is of Alcohol-Induced Fatty Liver

Chronic alcohol consumption can lead to the development of alcoholic fatty liver disease. The underlying pathogenic mechanisms however, have not been fully elucidated. Here, we review the current state of the art regarding the application of lipidomics to study alcohol's effect on hepatic lipids. It is clear that alcohol has a profound effect on the hepatic lipidome, with documented changes in the major lipid categories (i.e. fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterol lipids and prenol lipids). Alcohol's most striking effect is the marked change in the hepatic fatty acyl pool. This effect includes increased levels of 18-carbon fatty acyl chains incorporated into multiple lipid species, as well as a general shift toward increased unsaturation of fatty acyl moieties. In addition to our literature review, we also make several recommendations to consider when designing lipidomic studies into alcohol's effects. These recommendations include integration of lipidomic data with other measures of lipid metabolism, inclusion of multiple experimental time points, and presentation of quantitative data. We believe rigorous analysis of the hepatic lipidome can yield new insight into the pathogenesis of alcohol-induced fatty liver. While the existing literature has been largely descriptive, the field is poised to apply lipidomics to yield a new level of understanding on alcohol's effects on hepatic lipid metabolism.

Alcohol-Induced Hepatic Steatosis: A Comparative Study to Identify Possible Indicator(s) of Alcoholic Fatty Liver Disease

Background

Fatty liver is an early sign of both nonalcoholic and alcoholic fatty liver diseases. Ethanol feeding using a Lieber-DeCarli liquid diet (LD) model which contains 35% fat to rats or mice is a well-established model for alcoholic fatty liver. However, LD diet alone can also induce fatty liver and its differential metabolic profile may be able to differentiate steatosis induced by LD versus LD plus ethanol.

Purpose

We investigated the lipidomic differences in the livers of Sprague-Dawley (SD) rats fed a pellet diet (PD), LD and liquid ethanol diet (LED) for six weeks.

Study Design

Male Sprague Dawley rats were fed with nonalcoholic diets PD, LD or LED (ethanol in LD) for six weeks. Lipids were extracted and analyzed by nuclear magnetic resonance (NMR)- based metabolomics. The NMR data obtained was analyzed by multivariate Principal Component Analysis (PCA) and Spotfire DecisionSite 9.0 software to compare PD versus LD and LD versus LED groups.

Results

PCA of the NMR spectral data of livers of both comparisons showed a clear separation of PD from LD group and LD from LED group indicating differences in lipid profiles which corresponded with changes in total lipid weights. LD showed increases for cholesterol, esterified cholesterol, cholesterol acetate and triglycerides with decreases for fatty acyl chain, diallylic and allylic protons, while the LED showed increases in esterified cholesterol, cholesterol acetate, fatty acid methyl esters, allylic protons and some triglyceride protons with decreases in free cholesterol and phosphatidylcholine (PC).

Conclusion

Our data suggest that altered lipid signature or PC levels could be an indicator to differentiate between nonalcoholic versus alcoholic fatty liver.

Applications of nuclear magnetic resonance in lipid analyses: An emerging powerful tool for lipidomics studies

The role of lipids in cell, tissue, and organ physiology is crucial; as many diseases, including cancer, diabetes, neurodegenerative, and infectious diseases, are closely related to absorption and metabolism of lipids. Mass spectrometry (MS) based methods are the most developed powerful tools to study the synthetic pathways and metabolic networks of cellular lipids in biological systems; leading to the birth of an emerging subject lipidomics, which has been extensively reviewed. Nuclear magnetic resonance (NMR), another powerful analytical tool, which allows the visualization of single atoms and molecules, is receiving increasing attention in lipidomics analyses. However, very little work focusing on lipidomic studies using NMR has been critically reviewed. This paper presents a first comprehensive summary of application of ¹H, ¹³C &³¹P NMR in lipids and lipidomics analyses. The scientific basis, principles and characteristic diagnostic peaks assigned to specific atoms/molecular structures of lipids are presented. Applications of 2D NMR in mapping and monitoring of the components and their changes in complex lipids systems, as well as alteration of lipid profiling over disease development are also reviewed. The applications of NMR lipidomics in diseases diagnosis and food adulteration are exemplified.

Proteomic Profiling of Liver and Plasma in Chronic Ethanol Feeding Model of Hepatic Alcohol Dehydrogenase-Deficient Deer Mice

BACKGROUND

Chronic alcohol abuse, a major risk factor for such diseases as hepatitis and cirrhosis, impairs hepatic alcohol dehydrogenase (ADH; key ethanol [EtOH]-metabolizing enzyme). Therefore, differentially altered hepatic and plasma proteomes were identified in chronic EtOH feeding model of hepatic ADH-deficient (ADH^- ) deer mice to understand the metabolic basis of alcoholic liver disease (ALD).

METHODS

ADH^- deer mice were fed 3.5 g% EtOH via Lieber-DeCarli liquid diet daily for 3 months and histology of the liver assessed. Liver and plasma proteins were separated by 2-dimensional gel electrophoresis. The proteins differentially expressed were identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry.

RESULTS

Histology of the liver showed panlobular steatosis and infiltration of T lymphocytes. Using the criteria of ≥1.5 for fold change (p-value ≤0.05) with expectation value (E ≤10^-3 ) and protein score (≥64), 18 proteins in the livers and 5 in the plasma of EtOH-fed mice were differentially expressed and identified. Prolyl 4-hydroxylase, cytochrome b-5, endo A cytokeratin, ATP synthase, heat-shock 70 kD proteins, enoyl CoA hydratase, stress-70 protein, peroxiredoxin 1, and ornithine carbamoyl transferase were up-regulated in the livers. However, carbonic anhydrase 3, mitochondrial ATP synthase, aldolase 2, actin γ, laminin receptor, and carbamoyl phosphate synthase were down-regulated. Contrary to the increased expression of creatine kinase M-type, a decreased expression of serine protease inhibitor A3A precursor, sulfated glycoprotein-2 (clusterin), and apolipoprotein E isoforms were found in the plasma of EtOH group.

CONCLUSIONS

Chronic EtOH feeding in ADH^- deer mice causes steatosis and infiltration of T lymphocytes in the livers along with increased expression of proteins involved in endoplasmic reticulum (ER) stress, fibrosis, fatty acid β oxidation and biogenesis, and decreased expression of proteins involved in ATP synthesis, carbohydrate metabolism, in cell regulation and architecture. Reduced expression of various carrier proteins as found in the plasma of EtOH group has a biomarker potential.

Murine Models of Acute Alcoholic Hepatitis and Their Relevance to Human Disease

Alcohol-induced liver damage is a major burden for most societies, and murine studies can provide a means to better understand its pathogenesis and test new therapies. However, there are many models reported with widely differing phenotypes, not all of which fully regenerate the spectrum of human disease. Thus, it is important to understand the implications of these variations to efficiently model human disease. This review critically appraises key articles in the field, detailing the spectrum of liver damage seen in different models, and how they relate to the phenotype of disease seen in patients. A range of different methods of alcohol administration have been studied, ranging from ad libitum consumption of alcohol and water to modified diets (eg, Lieber deCarli liquid diet). Other feeding regimens have taken more invasive routes using intragastric feeding tubes to infuse alcohol directly into the stomach. Notably, models using wild-type mice generally produce a milder phenotype of liver damage than those using genetically modified mice, with the exception of the chronic binge-feeding model. We recommend panels of tests for consideration to standardize end points for the evaluation of the severity of liver damage-key for comparison of models of injury, testing of new therapies, and subsequent translation of findings into clinical practice.

Mycobacterial Lipidomics

Lipidomics is a distinct subspecialty of metabolomics concerned with hydrophobic molecules that organize into membranes. Most of the lipid classes present in Mycobacterium tuberculosis are found only in Actinobacteria and show extreme structural diversity. This article highlights the conceptual basis and the practical challenges associated with the mass spectrometry–based lipidomic study of M. tuberculosis to solve basic questions about the virulence of this lipid-laden organism.

Liver proteomics in progressive alcoholic steatosis

Fatty liver is an early stage of alcoholic and nonalcoholic liver disease (ALD and NALD) that progresses to steatohepatitis and other irreversible conditions. In this study, we identified proteins that were differentially expressed in the livers of rats fed 5% ethanol in a Lieber-DeCarli diet daily for 1 and 3 months by discovery proteomics (two-dimensional gel electrophoresis and mass spectrometry) and non-parametric modeling (Multivariate Adaptive Regression Splines). Hepatic fatty infiltration was significantly higher in ethanol-fed animals as compared to controls, and more pronounced at 3 months of ethanol feeding. Discovery proteomics identified changes in the expression of proteins involved in alcohol, lipid, and amino acid metabolism after ethanol feeding. At 1 and 3 months, 12 and 15 different proteins were differentially expressed. Of the identified proteins, down regulation of alcohol dehydrogenase (-1.6) at 1 month and up regulation of aldehyde dehydrogenase (2.1) at 3 months could be a protective/adaptive mechanism against ethanol toxicity. In addition, betaine-homocysteine S-methyltransferase 2 a protein responsible for methionine metabolism and previously implicated in fatty liver development was significantly up regulated (1.4) at ethanol-induced fatty liver stage (1 month) while peroxiredoxin-1 was down regulated (-1.5) at late fatty liver stage (3 months). Nonparametric analysis of the protein spots yielded fewer proteins and narrowed the list of possible markers and identified d-dopachrome tautomerase (-1.7, at 3 months) as a possible marker for ethanol-induced early steatohepatitis. The observed differential regulation of proteins have potential to serve as biomarker signature for the detection of steatosis and its progression to steatohepatitis once validated in plasma/serum.