Intestinal de novo phosphatidylcholine synthesis is required for dietary lipid absorption and metabolic homeostasis

Exploring the gut microbiota-hippocampus-metabolites axis dysregulation in sepsis mice

Background

Sepsis is commonly associated with a sudden impairment of brain function, thus leading to significant rates of illness and mortality. The objective of this research was to integrate microbiome and metabolome to reveal the mechanism of microbiota-hippocampus-metabolites axis dysfunction in a mouse model of sepsis.

Methods

A mouse model of sepsis was established via cecal ligation and puncture. The potential associations between the composition of the gut microbiota and metabolites in the hippocampus of mice with sepsis were investigated by combining 16S ribosomal RNA gene sequencing and ultra-high-performance liquid chromatography tandem mass spectrometry.

Results

A total of 140 differential metabolites were identified in the hippocampal tissues of mice with sepsis when compared to those of control mice. These differential metabolites in mice with sepsis were not only associated with autophagy and serotonergic synapse, but also involved in the metabolism and synthesis of numerous amino acids. At the phylum level, the abundance of Bacteroidota was increased, while that of Firmicutes (Bacillota) was decreased in mice with sepsis. At the genus level, the abundance of Alistipes was increased, while that of Lachnospiraceae_NK4A136_group was decreased in mice with sepsis. The Firmicutes (Bacillota)/Bacteroidota (F/B) ratio was decreased in mice with sepsis when compared to that of control mice. Furthermore, the F/B ratio was positively correlated with 5'-methylthioadenosine, PC (18:3(9Z,12Z,15Z)/18:0) and curdione, and negatively correlated with indoxylsulfuric acid, corticosterone, kynurenine and ornithine.

Conclusion

Analysis revealed a reduction in the F/B ratio in mice with sepsis, thus contributing to the disturbance of 5'-methylthioadenosine, curdione, PC (18:3(9Z,12Z,15Z)/18:0), corticosterone, ornithine, indoxylsulfuric acid and kynurenine; eventually, these changes led to hippocampus dysfunction. Our findings provide a new direction for the management of sepsis-induced hippocampus dysfunction.

Species differences in small intestinal exposure-related epithelial vacuolation in rats and dogs treated with a heteroaryldihydropyrimidine molecule

Small intestinal epithelial vacuolation induced by a heteroaryldihydropyrimidine compound (HAP-1) was observed in rats but not in dogs at termination in screening toxicity studies, despite the plasma exposure being higher in dogs. To understand the species differences, investigational studies with multiple time points following single dose (SD) and 7-day repeated dose (RD) were conducted in both species at doses resulting in comparable plasma exposures. In rats, epithelial vacuolation in the duodenum and jejunum were observed at all time points. In dogs, transient vacuolation was noted at 8 h post-SD (SD_8h) and 4 h post-RD (RD_4 h), but not at termination (RD_24 h). Special stains demonstrated lipid accumulation within enterocytes in both species and intracytoplasmic inclusion bodies in rats. Transmission electron microscopy identified these inclusion bodies as endoplasmic reticulum (ER) membranous structures. Transcriptomic analysis on jejunal mucosa at SD_8 h and RD_24 h revealed perturbations of lipid metabolism-related genes at SD_8 h in both species, but not at RD_24 h in dogs. ER stress-related gene changes at both time points were observed in rats only. Despite comparable HAP-1 plasma exposures, the duodenum and jejunum tissue concentrations of HAP-1 and acyl glucuronide metabolite were >5- and >30-fold higher in rats than in dogs, respectively. In vitro, similar cytotoxicity was observed in rat and dog duodenal organoids treated with HAP-1. In conclusion, HAP-1-induced intestinal epithelial vacuolation was related to lipid metabolism dysregulation in both species and ER-related injuries in rats only. The species differences were likely related to the difference in intestinal exposure to HAP-1 and its reactive metabolite.

Choline - a scoping review for Nordic Nutrition Recommendations 2023

Choline is an essential nutrient with metabolic roles as a methyl donor in one carbon metabolism and as a precursor for membrane phospholipids and the neurotransmitter acetylcholine. Choline content is particularly high in liver, eggs, and wheat germ, although it is present in a variety of foods. The main dietary sources of choline in the Nordic and Baltic countries are meat, dairy, eggs, and grain. A diet that is devoid of choline causes liver and muscle dysfunction within 3 weeks. Choline requirements are higher during pregnancy and lactation than in non-pregnant women. Although no randomized controlled trials are available, observational studies in human, supported by coherence from interventional studies with neurodevelopmental outcomes and experimental studies in animals, strongly suggest that sufficient intake of choline during pregnancy is necessary for normal brain development and function in the child. Observational studies suggested that adequate intake of choline could have positive effects on cognitive function in older people. However, prospective data are lacking, and no intervention studies are available in the elderly.

Effects of RIPC on the Metabolomical Profile during Lower Limb Digital Subtraction Angiography: A Randomized Controlled Trial

Remote ischemic preconditioning (RIPC) has demonstrated protective effects in patients with lower extremity arterial disease (LEAD) undergoing digital subtraction angiography (DSA) and/or percutaneous transluminal angioplasty (PTA). This study aimed to investigate the impact of RIPC on the metabolomical profile of LEAD patients undergoing these procedures and to elucidate its potential underlying mechanisms. A total of 100 LEAD patients were enrolled and randomly assigned to either the RIPC group (n = 46) or the sham group (n = 54). Blood samples were drawn before and 24 h after intervention. Targeted metabolomics analysis was performed using the AbsoluteIDQ p180 Kit, and changes in metabolite concentrations were compared between the groups. The RIPC group demonstrated significantly different dynamics in nine metabolites compared to the sham group, which generally showed a decrease in metabolite concentrations. The impacted metabolites included glutamate, taurine, the arginine-dimethyl-amide-to-arginine ratio, lysoPC a C24:0, lysoPC a C28:0, lysoPC a C26:1, PC aa C38:1, PC ae C30:2, and PC ae C44:3. RIPC exhibited a 'stabilization' effect, maintaining metabolite levels amidst ischemia-reperfusion injuries, suggesting its role in enhancing metabolic control. This may improve outcomes for LEAD patients. However, additional studies are needed to definitively establish causal relationships among these metabolic changes.

Biocoordination reactions in copper(II) ions and phosphocholine systems including pyrimidine nucleosides and nucleotides

The complexation reactions of phosphocholine and pyrimidine nucleosides as well as nucleotides with copper(II) ions were studied in the water system. Using potentiometric methods and computer calculations, the stability constants of the species were determined. Using spectroscopic methods such as UV-vis, EPR, ¹³C NMR, ³¹P NMR, FT-IR and CD, the coordination mode was established for complexes created in pH range 2.5-11.0. These studies will lead to a better understanding the role of copper(II) ions in living organisms and explain the interactions between them and the studied bioligands. The differences and similarities between nucleosides and nucleotides in the studied systems were also described, which testify to the significant influence of phosphate groups on the processes of metal ion complexation and interactions between ligands.

Polyunsaturated Fatty Acids (PUFAs): Sources, Digestion, Absorption, Application and Their Potential Adjunctive Effects on Visual Fatigue

When the eyes are exposed to the environment, they are easily affected by strong light stimulation and harmful substances. At the same time, prolonged use of the eyes or incorrect eye habits can cause visual fatigue, which mainly manifests as eye dryness, soreness, blurred vision, and various discomforts. The main reason for this is a decline in the function of the eye, especially the cornea and retina on the surface of the eye, which have the greatest impact on the normal function of the eye. Research has found that supplementation with appropriate foods or nutrients can effectively strengthen the eye against external and internal stimuli, thereby alleviating or avoiding visual fatigue. Among these, supplementation with polyunsaturated fatty acids has been found to be effective at protecting eye health and relieving visual fatigue. This article summarizes the sources of polyunsaturated fatty acids (including the main dietary sources and internal synthesis), the mechanisms of digestion and absorption of polyunsaturated fatty acids in the body and the safety of polyunsaturated fatty acid applications. It also reviews the mechanism of action of polyunsaturated fatty acids in aiding the relief of visual fatigue based on the mechanism of impaired function or structure of the ocular surface and fundus in the hope of providing some reference and insight into the development and application of polyunsaturated fatty acids in functional foods for the relief of visual fatigue.

Integrated Metabolomics and Lipidomics Analysis Reveals Lipid Metabolic Disorder in NCM460 Cells Caused by Aflatoxin B1 and Aflatoxin M1 Alone and in Combination

Aflatoxin B1 (AFB1) and aflatoxin M1 (AFM1) are universally found as environmental pollutants. AFB1 and AFM1 are group 1 human carcinogens. Previous sufficient toxicological data show that they pose a health risk. The intestine is vital for resistance to foreign pollutants. The enterotoxic mechanisms of AFB1 and AFM1 have not been clarified at the metabolism levels. In the present study, cytotoxicity evaluations of AFB1 and AFM1 were conducted in NCM 460 cells by obtaining their half-maximal inhibitory concentration (IC50). The toxic effects of 2.5 μM AFB1 and AFM1 were determined by comprehensive metabolomics and lipidomics analyses on NCM460 cells. A combination of AFB1 and AFM1 induced more extensive metabolic disturbances in NCM460 cells than either aflatoxin alone. AFB1 exerted a greater effect in the combination group. Metabolomics pathway analysis showed that glycerophospholipid metabolism, fatty acid degradation, and propanoate metabolism were dominant pathways that were interfered with by AFB1, AFM1, and AFB1+AFM1. Those results suggest that attention should be paid to lipid metabolism after AFB1 and AFM1 exposure. Further, lipidomics was used to explore the fluctuation of AFB1 and AFM1 in lipid metabolism. The 34 specific lipids that were differentially induced by AFB1 were mainly attributed to 14 species, of which cardiolipin (CL) and triacylglycerol (TAG) accounted for 41%. AFM1 mainly affected CL and phosphatidylglycerol, approximately 70% based on 11 specific lipids, while 30 specific lipids were found in AFB1+AFM1, mainly reflected in TAG up to 77%. This research found for the first time that the lipid metabolism disorder caused by AFB1 and AFM1 was one of the main causes contributing to enterotoxicity, which could provide new insights into the toxic mechanisms of AFB1 and AFM1 in animals and humans.

The role of phosphatidylcholine 34:1 in the occurrence, development and treatment of ulcerative colitis

Lipid homeostasis is considered to be related to intestinal metabolic balance, while its role in the pathogenesis and treatment of ulcerative colitis (UC) remains largely unexplored. The present study aimed to identify the target lipids related to the occurrence, development and treatment of UC by comparing the lipidomics of UC patients, mice and colonic organoids with the corresponding healthy controls. Here, multi-dimensional lipidomics based on LC-QTOF/MS, LC-MS/MS and iMScope systems were constructed and used to decipher the alteration of lipidomic profiles. The results indicated that UC patients and mice were often accompanied by dysregulation of lipid homeostasis, in which triglycerides and phosphatidylcholines were significantly reduced. Notably, phosphatidylcholine 34:1 (PC34:1) was characterized by high abundance and closely correlation with UC disease. Our results also revealed that down-regulation of PC synthase PCYT1α and Pemt caused by UC modeling was the main factor leading to the reduction of PC34:1, and exogenous PC34:1 could greatly enhance the fumarate level via inhibiting the transformation of glutamate to N-acetylglutamate, thus exerting an anti-UC effect. Collectively, our study not only supplies common technologies and strategies for exploring lipid metabolism in mammals, but also provides opportunities for the discovery of therapeutic agents and biomarkers of UC.

Palmitic acid induces intestinal lipid metabolism disorder, endoplasmic reticulum stress and inflammation by affecting phosphatidylethanolamine content in large yellow croaker Larimichthys crocea

In the 21^st century, intestinal homeostatic imbalance has emerged as a growing health challenge worldwide. Accumulating evidence reveals that excessive intake of saturated fatty acid (SFA) induces intestinal homeostatic imbalance. However, the potential molecular mechanism is still unclear. In the present study, we found that palm oil or palmitic acid (PA) treatment disturbed lipid metabolism homeostasis and triggered endoplasmic reticulum (ER) stress and inflammation in the intestine or intestinal cells of large yellow croaker (Larimichthys crocea). Interestingly, PA treatment significantly decreased phosphatidylethanolamine (PE) content in the intestinal cells. PE supplementation decreased triglyceride content in the intestinal cells induced by PA treatment by inhibiting fatty acid uptake and lipogenesis. PE supplementation suppressed ER stress. Meanwhile, PE supplementation alleviated inflammatory response through p38 MAPK-p65 pathway, reducing the damage of intestinal cells caused by PA treatment to some extent. Our work revealed that intestinal homeostatic imbalance caused by PA treatment was partly due to the decrease of PE content. PE consumption might be a nutritional strategy to regulate intestinal homeostasis in fish and even human beings.

Speciation Study on O-Phosphorylethanolamine and O-Phosphorylcholine: Acid–Base Behavior and Mg2+ Interaction

In the present study, the acid–base behavior of compounds constituting the headgroups of biomembranes, O-phosphorylethanolamine (PEA), and O-phosphorylcholine (PPC) was investigated by potentiometric titrations in NaCl aqueous solutions at different temperatures (15 ≤ t/°C ≤ 37) and ionic strength (0.15 ≤ I/mol L⁻¹ ≤ 1) values. The complexation properties and the speciation of these ligands with Mg²⁺ were defined under different temperatures (15 ≤ t/°C ≤ 37) and I = 0.15 mol L⁻¹. The results evidenced the formation of three species for PEA, namely, MLH₂, MLH, and ML and two species for PPC, namely, MLH and ML. ¹H-NMR titrations were performed on solutions containing ligand and metal–ligand solutions at t = 25°C and I = 0.15 mol L⁻¹. The estimated values of ligand protonation and complex formation constants and the speciation model are in accordance with the potentiometric data. The enthalpy changes were also determined at t = 25°C and I = 0.15 mol L⁻¹ by the dependence of formation constants on the temperature, confirming the electrostatic nature of the interactions. Matrix-assisted laser desorption mass spectrometry (MALDI-MS) was applied for the characterization of Mg²⁺-L systems (L = PEA or PCC). MS/MS spectra of free ligands and of Mg²⁺-L species were obtained. The observed fragmentation patterns of both Mg²⁺-L systems allowed elucidating the interaction mechanism that occurs via the phosphate group generating a four-membered cycle.

De novo phosphatidylcholine synthesis in the small intestinal epithelium is required for normal dietary lipid handling and maintenance of the mucosal barrier

Cytidine triphosphate:phosphocholine cytidylyltransferase-α (CTα) is the rate limiting enzyme in the major pathway for de novo phosphatidylcholine (PC) synthesis. When CTα is deleted specifically in intestinal epithelial cells of adult mice (CTα^IKO mice) fed a high-fat diet they present with weight loss, lipid malabsorption, and high postprandial GLP-1 levels. The current study aimed to characterize the changes that occur in the small intestines of CTα^IKO mice using transcriptomics and to determine whether intestinal function could be rescued in CTα^IKO mice. We found that impaired de novo PC synthesis in the gut is linked to lower abundance of transcripts related to lipid metabolism and higher abundance of transcripts related to ER stress and cell death, together with loss of goblet cells from the small intestinal epithelium. Furthermore, impaired movement of fatty acids from the intestinal lumen into enterocytes was observed in isolated intestinal sacs derived from CTα^IKO mice, a model that excludes factors such as bile, gastric emptying, the nervous system, and circulating hormones. Antibiotic treatment prevented acute weight loss and normalized jejunum TG concentrations after refeeding but did not prevent ER stress or loss of goblet cells in CTα^IKO mice. Dietary PC supplementation partially prevented loss of goblet cells but was unable to normalize jejunal TG concentrations after refeeding in CTα^IKO mice. High postprandial plasma GLP-1 levels were present in CTα^IKO mice regardless of antibiotic treatment, dietary PC content, or dietary fat content. Together, these data show that there is a specific requirement from de novo PC synthesis in maintaining small intestinal homeostasis, including dietary lipid uptake, normal hormone secretion, and barrier function.

Low production of 12α-hydroxylated bile acids prevents hepatic steatosis in Cyp2c70-/- mice by reducing fat absorption

Bile acids (BAs) play important roles in lipid homeostasis and BA signaling pathways serve as therapeutic targets for non-alcoholic fatty liver disease (NAFLD). Recently, we generated Cyp2c70^-/- mice with a human-like BA composition lacking mouse/rat-specific muricholic acids (MCAs) to accelerate translation from mice to humans. We employed this model to assess the consequences of a human-like BA pool on diet-induced obesity and NAFLD development. Male and female Cyp2c70^-/- mice and wild-type (WT) littermates were challenged with a 12-week Western-type high-fat diet (WTD) supplemented with 0.25% cholesterol. Cyp2c70-deficiency induced a hydrophobic BA pool with high abundances of chenodeoxycholic acid, particularly in females, due to sex-dependent suppression of sterol 12α-hydroxylase (Cyp8b1). Plasma transaminases were elevated and hepatic fibrosis was present in Cyp2c70^-/- mice, especially in females. Surprisingly, female Cyp2c70^-/- mice were resistant to WTD-induced obesity and hepatic steatosis while male Cyp2c70^-/- mice showed similar adiposity and moderately reduced steatosis compared to WT controls. Both intestinal cholesterol and fatty acid absorption were reduced in Cyp2c70^-/- mice, the latter more strongly in females, despite unaffected biliary BA secretion rates. Intriguingly, the biliary ratio 12α-/non-12α-hydroxylated BAs significantly correlated with fatty acid absorption and hepatic triglyceride content as well as with specific changes in gut microbiome composition. The hydrophobic human-like BA pool in Cyp2c70^-/- mice prevents WTD-induced obesity in female mice and NAFLD development in both genders, primarily due to impaired intestinal fat absorption. Our data point to a key role for 12α-hydroxylated BAs in control of intestinal fat absorption and modulation of gut microbiome composition.

Digestion and Absorption of Milk Phospholipids in Newborns and Adults

Milk polar lipids provide choline, ethanolamine, and polyunsaturated fatty acids, which are needed for the growth and plasticity of the tissues in a suckling child. They may also inhibit cholesterol absorption by interacting with cholesterol during micelle formation. They may also have beneficial luminal, mucosal, and metabolic effects in both the neonate and the adult. The milk fat globule membrane contains large proportions of sphingomyelin (SM), phosphatidylcholine (PC), and phosphatidylethanolamine (PE), and some phosphatidylserine (PS), phosphatidylinositol (PI), and glycosphingolipids. Large-scale technical procedures are available for the enrichment of milk fat globule membrane (MFGM) in milk replacement formulations and food additives. Pancreatic phospholipase A2 (PLA2) and mucosal phospholipase B digest glycero-phospholipids in the adult. In the neonate, where these enzymes may be poorly expressed, pancreatic lipase-related protein 2 probably has a more important role. Mucosal alkaline SM-ase and ceramidase catalyze the digestion of SM in both the neonate and the adult. In the mucosa, the sphingosine is converted into sphingosine-1-phosphate, which is both an intermediate in the conversion to palmitic acid and a signaling molecule. This reaction sequence also generates ethanolamine. Here, we summarize the pathways by which digestion and absorption may be linked to the biological effects of milk polar lipids. In addition to the inhibition of cholesterol absorption and the generation of lipid signals in the gut, the utilization of absorbed choline and ethanolamine for mucosal and hepatic phospholipid synthesis and the acylation of absorbed lyso-PC with polyunsaturated fatty acids to chylomicron and mucosal phospholipids are important.

Serum Metabolomics Reveals Underlying Mechanisms of Cholesterol-Lowering Effects of Oat Consumption: A Randomized Controlled Trial in a Mildly Hypercholesterolemic Population

INTRODUCTION

The purpose of this study is to examine the effects of oat supplementation on serum lipid in a population of adults with mild hypercholesterolemia and reveal the underlying mechanisms with serum untargeted metabolomics.

METHODS AND RESULTS

In this placebo-controlled trial, 62 participants from Nanjing, China, with mild elevations in cholesterol are randomly assigned to receive 80 g oats (containing 3 g beta-glucan) or rice daily for 45 days. Fasting blood samples are collected at the beginning, middle, and end of the trial. Compared with the rice group, oat consumption significantly decreases serum total cholesterol (TC) (-8.41%, p = 0.005), low-density lipoprotein cholesterol (LDL-c) (-13.93%, p = 0.001), and non high-density lipoprotein cholesterol (non-HDL-c) (-10.93%, p = 0.017) levels. There are no significant between-group differences in serum triglyceride (TG), apolipoprotein B (Apo B), glycated albumin, or fasting blood glucose levels. An orthogonal partial least squares discriminant analysis (OPLS-DA) suggests a clear separation in metabolic profiles between the groups after the intervention. Twenty-one metabolites in the oat group are significantly different from those in the rice group, among which 14 metabolites show a decreased trend. In comparison, seven metabolites show an increased trend. Correlations analysis from both groups indicate that most metabolites [e.g., sphinganine and phosphatidylcholine (PC)(20:5(5Z,8Z,11Z,14Z,17Z)/20:1(11Z))] have positive correlations with serum cholesterol levels. Kyoto Encyclopedia of Gene and Genomes pathway analysis suggests that oat consumption regulated glycerophospholipid, alanine, aspartate and glutamate, sphingolipid, and retinol metabolism.

CONCLUSION

Oat consumption has beneficial effects on serum lipids profiles. The underlying mechanisms involve glycerophospholipid, alanine, aspartate and glutamate, sphingolipid, and retinol metabolism in adults.

Emerging roles of bile acids in control of intestinal functions

PURPOSE OF REVIEW

Bile acids and their signalling pathways are increasingly recognized as potential therapeutic targets for several diseases. This review summarizes new insights in bile acid physiology, focussing on regulatory roles of bile acids in intestinal functions.

RECENT FINDINGS

Recent studies have highlighted the interactions between bile acids and gut microbiome: interfering with microbiome composition may be beneficial in treatment of liver and metabolic diseases by modulating bile acid composition, as different bile acid species have different signalling functions. In the intestine, bile acid receptors FXR, VDR and TGR5 are involved in control of barrier function, paracellular ion transport and hormone release. Specific microbial bile acid metabolites modulate immune responses of the host. In addition, new functions of bile acids in regulation of gastric emptying and satiation via brain-gut-liver axis have been discovered. Identification of Cyp2c70 as the enzyme responsible for generation of hydrophilic mouse/rat-specific muricholic acids has allowed the generation of murine models with a human-like bile acid composition.

SUMMARY

Specific bile acids act as important signalling molecules affecting whole body metabolism, specific transport processes and immunity in different segments of the intestinal tract. Their relevance for human (patho)physiology is emerging. Novel mouse models with human-like bile acid composition will aid to accelerate translational research.

Non-targeted metabolomic profiling of atrazine in Caenorhabditis elegans using UHPLC-QE Orbitrap/MS

The widespread use of the herbicides Atrazine (ATR) has been raised attention due to its ubiquitous occurrence in the environment. As an endocrine disruptor, ATR causes reproductive, immune, nervous system toxicity in biota. In this study, we aimed to investigate metabolic profile characteristics and potential metabolic biomarker that reflects specific damage in toxic effect after ATR exposure. Hence, a metabolomics study was performed to determine the significantly affected metabolites and the reproduction and locomotion of C. elegans were investigated. Mediation analysis was used to evaluate the mediating effect of metabolites on association between ATR exposure and toxic effect. ATR (≥0.04 mg/L) caused the significant dose dependent reduction of brood size and locomotion behavior, however, the body length and width were significantly decreased only in 40 mg/L group. These results suggesting that brood size, head thrashes and body bends are more sensitive indictor to assessment ATR toxicity in C. elegans. Meanwhile, metabolomics analysis revealed that ATR exposure can induce metabolic profiles significant alterations in C. elegans. We found that 9 metabolites significantly increased and 18 metabolites significantly decreased, such as phosphatidylcholine, GMP, CDP-choline, neopterin etc. Those alteration of metabolites were mainly involved in the pathways: glycerophospholipid metabolism, glycolysis/gluconeogenesis, folate biosynthesis, glycine, serine and threoninemetabolism, pyrimidine and purine metabolism. Overall, these changes are signs of possible oxidative stress and ATP synthesis disruption modification. Mediation analysis showed a significant indirect effect of ATR exposure on brood size, via 7,8-dihydroneopterin 2',3'-cyclic-p, and phosphatidylcholine might mediate association between ATR exposure and body bends, suggesting that 7,8-dihydroneopterin 2',3'-cyclic-p and phosphatidylcholine might be potentially specificity marker for brood size and body bend respectively. This preliminary analysis investigates metabolic characteristics in C. elegans after ATR exposure, helping to understand the pathways involved in the response to ATR exposure and provide potential biomarkers for the safety evaluation of ATR.

Two-Week Isocaloric Time-Restricted Feeding Decreases Liver Inflammation without Significant Weight Loss in Obese Mice with Non-Alcoholic Fatty Liver Disease

Prolonged, isocaloric, time-restricted feeding (TRF) protocols can promote weight loss, improve metabolic dysregulation, and mitigate non-alcoholic fatty liver disease (NAFLD). In addition, 3-day, severe caloric restriction can improve liver metabolism and glucose homeostasis prior to significant weight loss. Thus, we hypothesized that short-term, isocaloric TRF would improve NAFLD and characteristics of metabolic syndrome in diet-induced obese male mice. After 26 weeks of ad libitum access to western diet, mice either continued feeding ad libitum or were provided with access to the same quantity of western diet for 8 h daily, over the course of two weeks. Remarkably, this short-term TRF protocol modestly decreased liver tissue inflammation in the absence of changes in body weight or epidydimal fat mass. There were no changes in hepatic lipid accumulation or other characteristics of NAFLD. We observed no changes in liver lipid metabolism-related gene expression, despite increased plasma free fatty acids and decreased plasma triglycerides in the TRF group. However, liver Grp78 and Txnip expression were decreased with TRF suggesting hepatic endoplasmic reticulum (ER) stress and activation of inflammatory pathways may have been diminished. We conclude that two-week, isocaloric TRF can potentially decrease liver inflammation, without significant weight loss or reductions in hepatic steatosis, in obese mice with NAFLD.

Intestinal Phospholipid Disequilibrium Initiates an ER Stress Response That Drives Goblet Cell Necroptosis and Spontaneous Colitis in Mice

BACKGROUND & AIMS

Patients with ulcerative colitis have low concentrations of the major membrane lipid phosphatidylcholine (PC) in gastrointestinal mucus, suggesting that defects in colonic PC metabolism might be involved in the development of colitis. To determine the precise role that PC plays in colonic barrier function, we examined mice with intestinal epithelial cell (IEC)-specific deletion of the rate-limiting enzyme in the major pathway for PC synthesis: cytidine triphosphate:phosphocholine cytidylyltransferase-α (CTα^IKO mice).

METHODS

Colonic tissue of CTα^IKO mice and control mice was analyzed by histology, immunofluorescence, electron microscopy, quantitative polymerase chain reaction, Western blot, and thin-layer chromatography. Histopathologic colitis scores were assigned by a pathologist blinded to the experimental groupings. Intestinal permeability was assessed by fluorescein isothiocyanate-dextran gavage and fecal microbial composition was analyzed by sequencing 16s ribosomal RNA amplicons. Subsets of CTα^IKO mice and control mice were treated with dietary PC supplementation, antibiotics, or 4-phenylbutyrate.

RESULTS

Inducible loss of CTα in the intestinal epithelium reduced colonic PC concentrations and resulted in rapid and spontaneous colitis with 100% penetrance in adult mice. Colitis development in CTα^IKO mice was traced to a severe and unresolving endoplasmic reticulum stress response in IECs with altered membrane phospholipid composition. This endoplasmic reticulum stress response was linked to the necroptotic death of IECs, leading to excessive loss of goblet cells, formation of a thin mucus barrier, increased intestinal permeability, and infiltration of the epithelium by microbes.

CONCLUSIONS

Maintaining the PC content of IEC membranes protects against colitis development in mice, showing a crucial role for IEC phospholipid equilibrium in colonic homeostasis. SRA accession number: PRJNA562603.

Supplemental effects of dietary lysophospholipids in lactation diets on sow performance, milk composition, gut health, and gut-associated microbiome of offspring

Dietary lysophospholipids (LPL) would influence milk composition of sows, thus positively affect intestinal health of offspring. The objective of this study was to determine effects of dietary LPL fed to lactating sows on performance, milk characteristics, gut health, and gut-associated microbiome of offspring. Sixty pregnant sows were allotted to 2 treatments in a randomized complete block design with parity and BW as blocks on day 110 of gestation. Treatments were CON (no added LPL) and LPL (0.05% LPL; Lipidol-Ultra, Pathway Intermediates, Shrewsbury, UK). Sows were fed 2 kg/d from day 110 of gestation until farrowing and ad libitum after farrowing. Diets were formulated to meet NRC requirement for lactating sows. Colostrum and milk samples from 12 sows per treatment were collected to measure nutrients and immunoglobulins on days 1 and 18 of lactation, respectively. Twelve piglets per treatment (1 piglet per litter) were euthanized on day 18 to collect tissues to measure tumor necrosis factor-α, interleukin-8 (IL-8), malondialdehyde, protein carbonyl, IgA, histomorphology, crypt cell proliferation rate, and microbiota in the jejunum and colon. Data were analyzed using the MIXED procedure of SAS, and the mortality was analyzed using the GLIMMIX procedure of SAS. There was no difference in sow BW, parity, and litter size between treatments on day 0 of lactation. Sows fed LPL had increased (P < 0.05) litter BW gain (53.9 vs. 59.4 kg) and decreased piglet mortality (13.9% vs. 10.6%) on day 18 of lactation. Sows fed LPL had increased (P < 0.05) omega-6:omega-3 (22.1 vs. 23.7) and unsaturated:saturated (1.4 vs. 1.6) fatty acids ratios with increased oleic acid (29.1% vs. 31.4%) and tended to have increased (P = 0.092) IgG (1.14 vs. 1.94 g/L) and linoleic acid (17.7% vs. 18.7%) in the milk on day 18 of lactation. Piglets from sows fed LPL had increased (P < 0.05) IL-8 (184 vs. 245 pg/mg) and crypt cell proliferation rate (39.4% vs. 40.9%) and tended to have increased (P = 0.095) Firmicutes:Bacteroidetes ratio (1.0 vs. 3.5) in the jejunum. In conclusion, sows fed with LPL had milk with increased IgG, oleic acids, and linoleic acids without changes in BW and backfat during lactation. These changes could contribute to improved survivability and intestinal health of piglets by increasing IL-8 concentration, enhancing balance among gut-associated microbiome, and increasing enterocyte proliferation in the jejunum.

The marine compound and elongation factor 1A1 inhibitor, didemnin B, provides benefit in western diet-induced non-alcoholic fatty liver disease

Inhibition of eukaryotic elongation factor 1A1 (EEF1A1) with the marine compound didemnin B decreases lipotoxic HepG2 cell death in vitro and improves early stage non-alcoholic fatty liver disease (NAFLD) in young genetically obese mice. However, the effects of didemnin B on NAFLD in a model of long-term diet-induced obesity are not known. We investigated the effects of didemnin B on NAFLD severity and metabolic parameters in western diet-induced obese mice, and on the cell types that contribute to liver inflammation and fibrosis in vitro. Male 129S6 mice were fed either standard chow or western diet for 26 weeks, followed by intervention with didemnin B (50 μg/kg) or vehicle by intraperitoneal (i.p.) injection once every 3 days for 14 days. Didemnin B decreased liver and plasma triglycerides, improved oral glucose tolerance, and decreased NAFLD severity. Moreover, didemnin B moderately increased hepatic expression of genes involved in ER stress response (Perk, Chop), and fatty acid oxidation (Fgf21, Cpt1a). In vitro, didemnin B decreased THP-1 monocyte proliferation, disrupted THP-1 monocyte-macrophage differentiation, decreased THP-1 macrophage IL-1β secretion, and decreased hepatic stellate cell (HSteC) proliferation and collagen secretion under both basal and lipotoxic (high fatty acid) conditions. Thus, didemnin B improves hepatic steatosis, glucose tolerance, and blood lipids in obesity, in association with moderate, possibly hormetic, upregulation of pathways involved in cell stress response and energy balance in the liver. Furthermore, it decreases the activity of the cell types implicated in liver inflammation and fibrosis in vitro. These findings highlight the therapeutic potential of partial protein synthesis inhibition in the treatment of NAFLD.

Ezetimibe impairs transcellular lipid trafficking and induces large lipid droplet formation in intestinal absorptive epithelial cells

Ezetimibe inhibits Niemann-Pick C1-like 1 (NPC1L1) protein, which mediates intracellular cholesterol trafficking from the brush border membrane to the endoplasmic reticulum, where chylomicron assembly takes place in enterocytes or in the intestinal absorptive epithelial cells. Cholesterol is a minor lipid constituent of chylomicrons; however, whether or not a shortage of cholesterol attenuates chylomicron assembly is unknown. The aim of this study was to examine the effect of ezetimibe, a potent NPC1L1 inhibitor, on trans-epithelial lipid transport, and chylomicron assembly and secretion in enterocytes. Caco-2 cells, an absorptive epithelial model, grown onto culture inserts were given lipid micelles from the apical side, and chylomicron-like triacylglycerol-rich lipoprotein secreted basolaterally were analyzed after a 24-h incubation period in the presence of ezetimibe up to 50 μM. The secretion of lipoprotein and apolipoprotein B48 were reduced by adding ezetimibe (30% and 34%, respectively). Although ezetimibe allowed the cells to take up cholesterol normally, the esterification was abolished. Meanwhile, oleic acid esterification was unaffected. Moreover, ezetimibe activated sterol regulatory element-binding protein 2 by approximately 1.5-fold. These results suggest that ezetimibe limited cellular cholesterol mobilization required for lipoprotein assembly. In such conditions, large lipid droplet formation in Caco-2 cells and the enterocytes of mice were induced, implying that unprocessed triacylglycerol was sheltered in these compartments. Although ezetimibe did not reduce the post-prandial lipid surge appreciably in triolein-infused mice, the results of the present study indicated that pharmacological actions of ezetimibe may participate in a novel regulatory mechanism for the efficient chylomicron assembly and secretion.

Insufficient dietary choline aggravates disease severity in a mouse model of Citrobacter rodentium-induced colitis

Dietary choline, which is converted to phosphatidylcholine (PC) in intestinal enterocytes, may benefit inflammatory bowel disease patients who typically have reduced intestinal choline and PC. The present study investigated the effect of dietary choline supplementation on colitis severity and intestinal mucosal homoeostasis using a Citrobacter rodentium-induced colitis model. C57BL/6J mice were fed three isoenergetic diets differing in choline level: choline-deficient (CD), choline-sufficient (CS) and choline-excess (CE) for 3 weeks prior to infection with C. rodentium. The effect of dietary choline levels on the gut microbiota was also characterised in the absence of infection using 16S rRNA gene amplicon sequencing. At 7 d following infection, the levels of C. rodentium in CD mice were significantly greater than that in CS or CE groups (P < 0·05). CD mice exhibited greater damage to the surface epithelium and goblet cell loss than the CS or CE mice, which was consistent with elevated pro-inflammatory cytokine and chemokine levels in the colon. In addition, CD group exhibited decreased concentrations of PC in the colon after C. rodentium infection, although the decrease was not observed in the absence of challenge. Select genera, including Allobaculum and Turicibacter, were enriched in response to dietary choline deficiency; however, there was minimal impact on the total bacterial abundance or the overall structure of the gut microbiota. Our results suggest that insufficient dietary choline intake aggravates the severity of colitis and demonstrates an essential role of choline in maintaining intestinal homoeostasis.

Differential postprandial incorporation of 20:5n-3 and 22:6n-3 into individual plasma triacylglycerol and phosphatidylcholine molecular species in humans

The mechanisms by which digested fat is absorbed and transported in the circulation are well documented. However, it is uncertain whether the molecular species composition of dietary fats influences the molecular species composition of meal-derived lipids in blood. This may be important because enzymes that remove meal-derived fatty acids from the circulation exhibit differential activities towards individual lipid molecular species. To determine the effect of consuming oils with different molecular compositions on the incorporation of 20:5n-3 and 22:6n-3 into plasma lipid molecular species. Men and women (18-30 years) consumed standardised meals containing 20:5n-5 and 22:6n-3 (total 450 mg) provided by an oil from transgenic Camelina sativa (CSO) or a blended fish oil (BFO) which differed in the composition of 20:5n-3 and 22:6n-3 - containing molecular species. Blood was collected during the subsequent 8 h. Samples were analysed by liquid chromatography-mass spectrometry. The molecular species composition of the test oils was distinct from the composition of plasma triacylglycerol (TG) or phosphatidylcholine (PC) molecular species at baseline and at 1.5 or 6 h after the meal. The rank order by concentration of both plasma PC and TG molecular species at baseline was maintained during the postprandial period. 20:5n-3 and 22:6n-3 were incorporated preferentially into plasma PC compared to plasma TG. Together these findings suggest that the composition of dietary lipids undergoes extensive rearrangement after absorption, such that plasma TG and PC maintain their molecular species composition, which may facilitate lipase activities in blood and/or influence lipoprotein structural stability and function.

Phosphatidylcholine and its relation to apolipoproteins A-1 and B changes after Roux-en-Y gastric bypass: a cohort study

Background

Phosphatidylcholine (PC), the most abundant of the phospholipids, has several metabolic functions in organs such as the liver and the intestine, important structural- and signaling functions in biological membranes, and might have a role in the effects of Roux-en-Y gastric bypass (RYGB), an operation known to ameliorate metabolic diseases, including type 2 diabetes. We hypothesized that serum PC, as a reflection of phospholipid metabolism, changes after RYGB, and that changes are related to weight loss and possibly to changes in glucose metabolism (reflected in the HbA1c-level) as well as to changes in serum Apo A1, Apo B and Apo B/Apo A1 ratio.

Methods

In a cohort of 220 RYGB patients, we studied changes in serum PC after RYGB in relation to serum Apo A1 and Apo B, the main apolipoproteins in HDL- and LDL/VLDL-particles, respectively, up to 2 years following RYGB-surgery.

Results

Serum PC reached its lowest levels 3 months postoperatively to later rebound to preoperative levels 24 months after RYGB. No difference was seen between patients with or without type 2 diabetes. Serum Apo A1 showed a similar pattern whereas serum Apo B concentrations stayed low after the initial decrease after RYGB. As a result, the Apo B / Apo A1 ratio constantly decreased during follow-up. There was a strong positive correlation between PC and Apo A1, and between PC and Apo B, but none between Apo A1 and Apo B. After RYGB surgery, both PC and Apo A1, but not Apo B, correlated positively to weight loss. In relation to total cholesterol, the molar ratio between serum PC and plasma cholesterol increased steadily after RYGB.

Conclusions

We conclude that changes in PC and apolipoproteins after RYGB are highly dynamic, reflecting a large plasticity and capability of accommodating lipid metabolism including PC-, cholesterol- and apolipoprotein metabolism imposed by RYGB surgery, independent of glucose tolerance. We suggest that after RYGB and major weight loss, PC and Apo A1 might have a special role in the altered metabolism of lipoproteins.

Electronic supplementary material

The online version of this article (10.1186/s12944-019-1111-7) contains supplementary material, which is available to authorized users.

Improved quantitation of lipid classes using supercritical fluid chromatography with a charged aerosol detector

Quantitatively and rapidly analyzing lipids is necessary to elucidate their biological functions. Herein, we developed a quantitative method for various lipid classes using supercritical fluid chromatography (SFC) coupled with a charged aerosol detector (CAD), providing high-throughput data analysis to detect a large number of molecules in each lipid class as one peak. Applying the CAD was useful for analyzing lipid molecules in the same lipid class with a constant response under the same mobile phase composition. First, we optimized the washing method for the diethylamine column, achieving baseline separation of lipid classes while maintaining good peak shapes. In addition, the CAD conditions (organic solvent evaporation and numerical correction of the CAD data) were optimized to improve the signal-to-noise ratio. We used an internal standard (ceramide phosphoethanolamine d17:1-12:0), which did not coelute with the lipid classes and showed high extraction efficiency. Based on a quantitative analysis of HepG2 cells, the concentration of lipid classes detected by CAD was adequate compared with that obtained by triple-quadrupole MS (QqQMS) in a previous study because the deviations of the concentrations were 0.6- to 2.3-fold. These results also supported the quantitative performance of SFC-QqQMS developed in our previous report.

Substrate channeling in the glycerol-3-phosphate pathway regulates the synthesis, storage and secretion of glycerolipids

The successive acylation of glycerol-3-phosphate (G3P) by glycerol-3-phosphate acyltransferases and acylglycerol-3-phosphate acyltransferases produces phosphatidic acid (PA), a precursor for CDP-diacylglycerol-dependent phospholipid synthesis. PA is further dephosphorylated by LIPINs to produce diacylglycerol (DG), a substrate for the synthesis of triglyceride (TG) by DG acyltransferases and a precursor for phospholipid synthesis via the CDP-choline and CDP-ethanolamine (Kennedy) pathways. The channeling of fatty acids into TG for storage in lipid droplets and secretion in lipoproteins or phospholipids for membrane biogenesis is dependent on isoform expression, activity and localization of G3P pathway enzymes, as well as dietary and hormonal and tissue-specific factors. Here, we review the mechanisms that control partitioning of substrates into lipid products of the G3P pathway.

Pancreatic and mucosal enzymes in choline phospholipid digestion

The digestion of choline phospholipids is important for choline homeostasis, lipid signaling, postprandial lipid and energy metabolism, and interaction with intestinal bacteria. The digestion is mediated by the combined action of pancreatic and mucosal enzymes. In the proximal small intestine, hydrolysis of phosphatidylcholine (PC) to 1-lyso-PC and free fatty acid (FFA) by the pancreatic phospholipase A₂ IB coincides with the digestion of the dietary triacylglycerols by lipases, but part of the PC digestion is extended and must be mediated by other enzymes as the jejunoileal brush-border phospholipase B/lipase and mucosal secreted phospholipase A₂ X. Absorbed 1-lyso-PC is partitioned in the mucosal cells between degradation and reacylation into chyle PC. Reutilization of choline for hepatic bile PC synthesis, and the reacylation of 1-lyso-PC into chylomicron PC by the lyso-PC-acyl-CoA-acyltransferase 3 are important features of choline recycling and postprandial lipid metabolism. The role of mucosal enzymes is emphasized by sphingomyelin (SM) being sequentially hydrolyzed by brush-border alkaline sphingomyelinase (alk-SMase) and neutral ceramidase to sphingosine and FFA, which are well absorbed. Ceramide and sphingosine-1-phosphate are generated and are both metabolic intermediates and important lipid messengers. Alk-SMase has anti-inflammatory effects that counteract gut inflammation and tumorigenesis. These may be mediated by multiple mechanisms including generation of sphingolipid metabolites and suppression of autotaxin induction and lyso-phosphatidic acid formation. Here we summarize current knowledge on the roles of pancreatic and mucosal enzymes in PC and SM digestion, and its implications in intestinal and liver diseases, bacterial choline metabolism in the gut, and cholesterol absorption.

Lipin 2/3 phosphatidic acid phosphatases maintain phospholipid homeostasis to regulate chylomicron synthesis

The lipin phosphatidic acid phosphatase (PAP) enzymes are required for triacylglycerol (TAG) synthesis from glycerol 3-phosphate in most mammalian tissues. The 3 lipin proteins (lipin 1, lipin 2, and lipin 3) each have PAP activity, but have distinct tissue distributions, with lipin 1 being the predominant PAP enzyme in many metabolic tissues. One exception is the small intestine, which is unique in expressing exclusively lipin 2 and lipin 3. TAG synthesis in small intestinal enterocytes utilizes 2-monoacylglycerol and does not require the PAP reaction, making the role of lipin proteins in enterocytes unclear. Enterocyte TAGs are stored transiently as cytosolic lipid droplets or incorporated into lipoproteins (chylomicrons) for secretion. We determined that lipin enzymes are critical for chylomicron biogenesis, through regulation of membrane phospholipid composition and association of apolipoprotein B48 with nascent chylomicron particles. Lipin 2/3 deficiency caused phosphatidic acid accumulation and mammalian target of rapamycin complex 1 (mTORC1) activation, which were associated with enhanced protein levels of a key phospholipid biosynthetic enzyme (CTP:phosphocholine cytidylyltransferase α) and altered membrane phospholipid composition. Impaired chylomicron synthesis in lipin 2/3 deficiency could be rescued by normalizing phospholipid synthesis levels. These data implicate lipin 2/3 as a control point for enterocyte phospholipid homeostasis and chylomicron biogenesis.