Dietary sphingomyelin lowers hepatic lipid levels and inhibits intestinal cholesterol absorption in high-fat-fed mice

Advances in the composition, efficacy, and mimicking of human milk phospholipids

Phospholipids are the essential components of human milk, contributing to the enhancement of cognitive development, regulation of immune functions, and mitigation of elevated cholesterol levels. Infant formulas supplemented with phospholipids can change the composition, content, and globule membrane structure of milk lipids, improving their digestive properties and nutritional value. However, mimicking phospholipids in infant formulas is currently limited, and the supplemented standards of phospholipid species and amounts in infant formulas are unknown. Consequently, there is a significant difference between the phospholipids in infant formulas and those in human milk. This article reviews the recent progress in human milk phospholipid research, aiming to describe the composition, content, and positive effects of human milk phospholipids, as well as summarises the dietary sources of phospholipid supplementation and the current state of human milk phospholipid mimicking in infant formulas. This review provides clear directions for research on mimicking human milk phospholipids and evaluating the nutritional functions of phospholipids in infants.

Nutritional roles and therapeutic potentials of dietary sphingomyelin in brain diseases

Sphingolipids have recently gained interest as potential players in variety of diseases due to their import roles in human body particularly, the brain. As sphingomyelin is the most common type of sphingolipids, deficits in its distribution to brain cells may contribute to neurological anomalies. However, data is limited regarding the impact of different levels of dietary sphingomyelin intake on neural function especially if this approach can boost cognition and prevent neurological disorders. This review evaluates the effect of dietary sphingomyelin and its metabolites (ceramide and sphingosine-1-phosphate) in animal models and in humans, with a primary focus on its impact on brain health. Additionally, it proposes multiple neuroenhancing effects of sphingomyelin-rich diet. This presents an opportunity to stimulate further research that aims to determine the therapeutic value of dietary sphingomyelin in preventing, improving or slowing the progression of central nervous system disorders.

The Role of Lipids in the Regulation of Immune Responses

Lipid metabolism plays a major role in the regulation of the immune system. Exogenous (dietary and microbial-derived) and endogenous (non-microbial-derived) lipids play a direct role in regulating immune cell activation, differentiation and expansion, and inflammatory phenotypes. Understanding the complexities of lipid-immune interactions may have important implications for human health, as certain lipids or immune pathways may be beneficial in circumstances of acute infection yet detrimental in chronic inflammatory diseases. Further, there are key differences in the lipid effects between specific immune cell types and location (e.g., gut mucosal vs. systemic immune cells), suggesting that the immunomodulatory properties of lipids may be tissue-compartment-specific, although the direct effect of dietary lipids on the mucosal immune system warrants further investigation. Importantly, there is recent evidence to suggest that lipid-immune interactions are dependent on sex, metabolic status, and the gut microbiome in preclinical models. While the lipid-immune relationship has not been adequately established in/translated to humans, research is warranted to evaluate the differences in lipid-immune interactions across individuals and whether the optimization of lipid-immune interactions requires precision nutrition approaches to mitigate or manage disease. In this review, we discuss the mechanisms by which lipids regulate immune responses and the influence of dietary lipids on these processes, highlighting compelling areas for future research.

Changes in Choline Metabolites and Ceramides in Response to a DASH-Style Diet in Older Adults

This feeding trial evaluated the impact of the Dietary Approaches to Stop Hypertension diet on changes in plasma choline, choline metabolites, and ceramides in obese older adults; 28 adults consumed 3oz (n = 15) or 6oz (n = 13) of beef within a standardized DASH diet for 12 weeks. Plasma choline, betaine, methionine, dimethylglycine (DMG), phosphatidylcholine (PC), lysophosphotidylcholine (LPC), sphingomyelin, trimethylamine-N-oxide (TMAO), L-carnitine, ceramide, and triglycerides were measured in fasted blood samples. Plasma LPC, sphingomyelin, and ceramide species were also quantified. In response to the study diet, with beef intake groups combined, plasma choline decreased by 9.6% (p = 0.012); DMG decreased by 10% (p = 0.042); PC decreased by 51% (p < 0.001); total LPC increased by 281% (p < 0.001); TMAO increased by 26.5% (p < 0.001); total ceramide decreased by 22.1% (p < 0.001); and triglycerides decreased by 18% (p = 0.021). All 20 LPC species measured increased (p < 0.01) with LPC 16:0 having the greatest response. Sphingomyelin 16:0, 18:0, and 18:1 increased (all p < 0.001) by 10.4%, 22.5%, and 24%, respectively. In contrast, we observed that sphingomyelin 24:0 significantly decreased by 10%. Ceramide 22:0 and 24:0 decreased by 27.6% and 10.9% (p < 0.001), respectively, and ceramide 24:1 increased by 36.8% (p = 0.013). Changes in choline and choline metabolites were in association with anthropometric and cardiometabolic outcomes. These findings show the impact of the DASH diet on choline metabolism in older adults and demonstrate the influence of diet to modify circulating LPC, sphingomyelin, and ceramide species.

Novel Lipids to Regulate Obesity and Brain Function: Comparing Available Evidence and Insights from QSAR In Silico Models

Lipid molecules, such as policosanol, ergosterol, sphingomyelin, omega 3 rich phosphatidylcholine, α-tocopherol, and sodium butyrate, have emerged as novel additions to the portfolio of bioactive lipids. In this state-of-the-art review, we discuss these lipids, and their activity against obesity and mental or neurological disorders, with a focus on their proposed cellular targets and the ways in which they produce their beneficial effects. Furthermore, this available information is compared with that provided by in silico Absorption, Distribution, Metabolism, Excretion, and Toxicity (ADMET) models in order to understand the usefulness of these tools for the discovery of new bioactive compounds. Accordingly, it was possible to highlight how these lipids interact with various cellular targets related to the molecule transportation and absorption (e.g., α-tocopherol transfer protein for α-Tocopherol, ATP-binding cassette ABC transporters or Apolipoprotein E for sphingomyelins and phospholipids) or other processes, such as the regulation of gene expression (involving Sterol Regulatory Element-Binding Proteins for ergosterol or Peroxisome Proliferator-Activated Receptors in the case of policosanol) and inflammation (the regulation of interleukins by sodium butyrate). When comparing the literature with in silico Quantitative Structure-Activity Relationship (QSAR) models, it was observed that although they are useful for selecting bioactive molecules when compared in batch, the information they provide does not coincide when assessed individually. Our review highlights the importance of considering a broad range of lipids as potential bioactives and the need for accurate prediction of ADMET parameters in the discovery of new biomolecules. The information presented here provides a useful resource for researchers interested in developing new strategies for the treatment of obesity and mental or neurological disorders.

The Association of Dietary Cholesterol from Egg Consumption on Cardiovascular Diseases Risk Varies from Person to Person

The public and scientists remain skeptical about egg consumption, given that cardiovascular diseases (CVDs) are the leading causes of death in worldwide. This review mainly explained the recurrence of contradictory conclusions about relationships between egg consumption and CVD risk and discussed effects of egg cholesterol intake on cholesterol homeostasis. Factors including individual health status and cholesterol sensitivity, dietary pattern, region, and race should be distinguished when understanding generalized conclusions. Identified compensatory mechanisms in response to dietary cholesterol and the resulting balance in cholesterol biosynthesis, absorption, and efflux supported the view that moderate egg consumption had no substantial overall impacts on cholesterol homeostasis in healthy people. Excessive cholesterol intake is not recommended in individuals with distempered metabolism. More than cholesterol metabolism, impacts of egg consumption as a part of overall diet on CVD risk should be considered from aspects of nutrient intake, lipid metabolism, and energy supply in the future.

The nutritional functions of dietary sphingomyelin and its applications in food

Sphingolipids are common structural components of cell membranes and are crucial for cell functions in physiological and pathophysiological conditions. Sphingomyelin and its metabolites, such as sphingoid bases, ceramide, ceramide-1-phosphate, and sphingosine-1-phosphate, play signaling roles in the regulation of human health. The diverse structures of sphingolipids elicit various functions in cellular membranes and signal transduction, which may affect cell growth, differentiation, apoptosis, and maintain biological activities. As nutrients, dietary sphingomyelin and its metabolites have wide applications in the food and pharmaceutical industry. In this review, we summarized the distribution, classifications, structures, digestion, absorption and metabolic pathways of sphingolipids, and discussed the nutritional functioning of sphingomyelin in chronic metabolic diseases. The possible implications of dietary sphingomyelin in the modern food preparations including dairy products and infant formula, skin improvement, delivery system and oil organogels are also evaluated. The production of endogenous sphingomyelin is linked to pathological changes in obesity, diabetes, and atherosclerosis. However, dietary supplementations of sphingomyelin and its metabolites have been shown to maintain cholesterol homeostasis and lipid metabolism, and to prevent or treat these diseases. This seemly paradoxical phenomenon shows that dietary sphingomyelin and its metabolites are candidates for food additives and functional food development for the prevention and treatment of chronic metabolic diseases in humans.

Sphingolipids as Functional Food Components: Benefits in Skin Improvement and Disease Prevention

Sphingolipids are ubiquitous components in eukaryotic organisms and have attracted attention as physiologically functional lipids. Sphingolipids with diverse structures are present in foodstuffs as these structures depend on the biological species they are derived from, such as mammals, plants, and fungi. The physiological functions of dietary sphingolipids, especially those that improve skin barrier function, have recently been noted. In addition, the roles of dietary sphingolipids in the prevention of diseases, including cancer and metabolic syndrome, have been studied. However, the mechanisms underlying the health-improving effects of dietary sphingolipids, especially their metabolic fates, have not been elucidated. Here, we review dietary sphingolipids, including their chemical structures and contents in foodstuff; digestion, intestinal absorption, and metabolism; and nutraceutical functions, based on the available evidence and hypotheses. Further research is warranted to clearly define how dietary sphingolipids can influence human health.

Lipidomics Analysis of Outer Membrane Vesicles and Elucidation of the Inositol Phosphoceramide Biosynthetic Pathway in Bacteroides thetaiotaomicron

Approximately one-third of the human colonic microbiome is formed by bacteria from the genus Bacteroides. These bacteria produce a large amount of uniformly sized outer membrane vesicles (OMVs), which are equipped with hydrolytic enzymes that play a role in the degradation of diet- and host-derived glycans. In this work, we characterize the lipid composition of membranes and OMVs from Bacteroides thetaiotaomicron VPI-5482. Liquid chromatography-mass spectrometry (LC-MS) analysis indicated that OMVs carry sphingolipids, glycerophospholipids, and serine-dipeptide lipids. Sphingolipid species represent more than 50% of the total lipid content of OMVs. The most abundant sphingolipids in OMVs are ethanolamine phosphoceramide (EPC) and inositol phosphoceramide (IPC). Bioinformatics analysis allowed the identification of the BT1522-1526 operon putatively involved in IPC synthesis. Mutagenesis studies revealed that BT1522-1526 is essential for the synthesis of phosphatidylinositol (PI) and IPC, confirming the role of this operon in the biosynthesis of IPC. BT1522-1526 mutant strains lacking IPC produced OMVs that were indistinguishable from the wild-type strain, indicating that IPC sphingolipid species are not involved in OMV biogenesis. Given the known role of sphingolipids in immunomodulation, we suggest that OMVs may act as long-distance vehicles for the delivery of sphingolipids in the human gut. IMPORTANCE Sphingolipids are essential membrane lipid components found in eukaryotes that are also involved in cell signaling processes. Although rare in bacteria, sphingolipids are produced by members of the phylum Bacteroidetes, human gut commensals. Here, we determined that OMVs carry sphingolipids and other lipids of known signaling function. Our results demonstrate that the BT1522-1526 operon is required for IPC biosynthesis in B. thetaiotaomicron.

Dairy matrix: is the whole greater than the sum of the parts?

Dairy foods are a heterogeneous group of products that vary in physical state and structure; profile and amounts of essential nutrients, bioactive ingredients, and other constituents; the extent of alteration of these constituents by processing, whether they are fermented or aged; and addition of constituents during manufacture. The complexity of the dairy matrix is associated with a heterogeneous impact on health outcomes from increased, decreased, or neutral effects for specific dairy products and specific health outcomes. Researchers must become more nuanced and systematic in their study of the role of dairy products in health to develop meaningful dietary recommendations. This review of the evidence for the dairy matrix and health points out the dearth of randomized controlled trials and of mechanistic insights. The variable effects of dairy-product consumption on health suggest possibilities for personalized nutrition advice.

Dietary Sphingomyelin Metabolism and Roles in Gut Health and Cognitive Development

Sphingomyelin (SM) is a widely occurring sphingolipid that is a major plasma membrane constituent. Milk and dairy products are rich SM sources, and human milk has high SM content. Numerous studies have evaluated the roles of SM in maintaining cell membrane structure and cellular signal transduction. There has been a growing interest in exploring the role of dietary SM, especially from human milk, in imparting health benefits. This review focuses on recent publications regarding SM content in several dietary sources and dietary SM metabolism. SM digestion and absorption are slow and incomplete and mainly occur in the middle sections of the small intestine. This review also evaluates the effect of dietary SM on gut health and cognitive development. Studies indicate that SM may promote gut health by reducing intestinal cholesterol absorption in adults. However, there has been a lack of data supporting clinical trials. An association between milk SM and neural development is evident before childhood. Hence, additional studies and well-designed randomized controlled trials that incorporate dietary SM evaluation, SM metabolism, and its long-term functions on infants and children are required.

Milk polar lipids favorably alter circulating and intestinal ceramide and sphingomyelin species in postmenopausal women

BACKGROUND

High circulating levels of ceramides (Cer) and sphingomyelins (SM) are associated with cardiometabolic diseases. The consumption of whole fat dairy products, naturally containing such polar lipids (PL), is associated with health benefits, but the impact on sphingolipidome remains unknown.

METHODS

In a 4-week randomized controlled trial, 58 postmenopausal women daily consumed milk PL-enriched cream cheese (0, 3, or 5 g of milk PL). Postprandial metabolic explorations were performed before and after supplementation. Analyses included SM and Cer species in serum, chylomicrons, and feces. The ileal contents of 4 ileostomy patients were also explored after acute milk PL intake.

RESULTS

Milk PL decreased serum atherogenic C24:1 Cer, C16:1 SM, and C18:1 SM species (P_group < 0.05). Changes in serum C16+18 SM species were positively correlated with the reduction of cholesterol (r = 0.706), LDL-C (r = 0.666), and ApoB (r = 0.705) (P < 0.001). Milk PL decreased chylomicron content in total SM and C24:1 Cer (P_group < 0.001), parallel to a marked increase in total Cer in feces (P_group < 0.001). Milk PL modulated some specific SM and Cer species in both ileal efflux and feces, suggesting differential absorption and metabolization processes in the gut.

CONCLUSION

Milk PL supplementation decreased atherogenic SM and Cer species associated with the improvement of cardiovascular risk markers. Our findings bring insights on sphingolipid metabolism in the gut, especially Cer, as signaling molecules potentially participating in the beneficial effects of milk PL.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02099032, NCT02146339.

FUNDING

ANR-11-ALID-007-01; PHRCI-2014: VALOBAB, no. 14-007; CNIEL; GLN 2018-11-07; HCL (sponsor).

Lysolipids in Vascular Development, Biology, and Disease

Membrane phospholipid metabolism forms lysophospholipids, which possess unique biochemical and biophysical properties that influence membrane structure and dynamics. However, lysophospholipids also function as ligands for G-protein-coupled receptors that influence embryonic development, postnatal physiology, and disease. The 2 most well-studied species-lysophosphatidic acid and S1P (sphingosine 1-phosphate)-are particularly relevant to vascular development, physiology, and cardiovascular diseases. This review summarizes the role of lysophosphatidic acid and S1P in vascular developmental processes, endothelial cell biology, and their roles in cardiovascular disease processes. In addition, we also point out the apparent connections between lysophospholipid biology and the Wnt (int/wingless family) pathway, an evolutionarily conserved fundamental developmental signaling system. The discovery that components of the lysophospholipid signaling system are key genetic determinants of cardiovascular disease has warranted current and future research in this field. As pharmacological approaches to modulate lysophospholipid signaling have entered the clinical sphere, new findings in this field promise to influence novel therapeutic strategies in cardiovascular diseases.

Sphingolipids produced by gut bacteria enter host metabolic pathways impacting ceramide levels

Gut microbes are linked to host metabolism, but specific mechanisms remain to be uncovered. Ceramides, a type of sphingolipid (SL), have been implicated in the development of a range of metabolic disorders from insulin resistance (IR) to hepatic steatosis. SLs are obtained from the diet and generated by de novo synthesis in mammalian tissues. Another potential, but unexplored, source of mammalian SLs is production by Bacteroidetes, the dominant phylum of the gut microbiome. Genomes of Bacteroides spp. and their relatives encode serine palmitoyltransfease (SPT), allowing them to produce SLs. Here, we explore the contribution of SL-production by gut Bacteroides to host SL homeostasis. In human cell culture, bacterial SLs are processed by host SL-metabolic pathways. In mouse models, Bacteroides-derived lipids transfer to host epithelial tissue and the hepatic portal vein. Administration of B. thetaiotaomicron to mice, but not an SPT-deficient strain, reduces de novo SL production and increases liver ceramides. These results indicate that gut-derived bacterial SLs affect host lipid metabolism.

Sphingolipids in food and their critical roles in human health

Sphingolipids (SLs) are ubiquitous structural components of cell membranes and are essential for cell functions under physiological conditions or during disease progression. Abundant evidence supports that SLs and their metabolites, including ceramide (Cer), ceramide-1-phosphate (C1P), sphingosine (So), sphingosine-1-phosphate (S1P), are signaling molecules that regulate a diverse range of cellular processes and human health. However, there are limited reviews on the emerging roles of exogenous dietary SLs in human health. In this review, we discuss the ubiquitous presence of dietary SLs, highlighting their structures and contents in foodstuffs, particularly in sea foods. The digestion and metabolism of dietary SLs is also discussed. Focus is given to the roles of SLs in both the etiology and prevention of diseases, including bacterial infection, cancers, neurogenesis and neurodegenerative diseases, skin integrity, and metabolic syndrome (MetS). We propose that dietary SLs represent a "functional" constituent as emerging strategies for improving human health. Gaps in research that could be of future interest are also discussed.

Intestinal Availability and Metabolic Effects of Dietary Camelina Sphingolipids during the Metabolic Syndrome Onset in Mice

Sphingolipids appear as a promising class of components susceptible to prevent the onset of the metabolic syndrome (MetS). Gut availability and effects of Camelina sativa sphingolipids were investigated in a mouse model of dietary-induced MetS. Seed meals from two Camelina sativa lines enriched, respectively, in C24- and C16-NH_2^- glycosyl-inositol-phosphoryl-ceramides (NH₂GIPC) were used in hypercaloric diets. After 5 weeks on these two hypercaloric diets, two markers of the MetS were alleviated (adiposity and insulin resistance) as well as inflammation markers and colon barrier dysfunction. A more pronounced effect was observed with the C16-NH₂GIPC-enriched HC diet, in particular for colon barrier function. Despite a lower digestibility, C16-NH₂GIPC were more prevalent in the intestine wall. Sphingolipids provided as camelina meal can therefore counteract some deleterious effects of a hypercaloric diet in mice at the intestinal and systemic levels. Interestingly, these beneficial effects seem partly dependent on sphingolipid acyl chain length.

Dietary Egg Sphingomyelin Prevents Aortic Root Plaque Accumulation in Apolipoprotein-E Knockout Mice

Western-style diets have been linked with dyslipidemia and inflammation, two well-known risk factors associated with cardiovascular disease (CVD). Dietary sphingomyelin (SM) has been reported to modulate gut microbiota, and lower serum lipids and inflammation in mice on Western-style diets. However, few studies have examined if nutritionally-relevant intake of dietary SM can impact atherosclerosis progression. Thus, the aim of this study was to determine if incorporating 0.1% (w/w) egg SM (ESM) (equivalent to ~750 mg/day in humans) into a high-fat (45% kcal), cholesterol-enriched diet (HFD) could prevent atheroprogression in apoE^−/− mice (n = 15/group). We found that mice fed with the ESM-rich diet had significantly lower epididymal fat mass (−46%) and tended to have higher spleen weights (+15%). There were no significant differences in serum lipids between groups. However, ESM-fed mice had significantly lower alanine aminotransferase (ALT) activity. Additionally, ESM-fed mice displayed significantly less aortic root lipid accumulation (−31%) compared to controls. This improvement in atherosclerosis was paired with over a two-fold reduction in circulating serum amyloid A (SAA) in ESM-fed mice. Finally, there was also a modulation of the gut microbiota with ESM supplementation. ESM may have the potential to prevent atherosclerosis, however further research in the clinical setting is warranted.

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.

Long Noncoding RNAs: Advances in Lipid Metabolism

Long noncoding RNAs (lncRNAs) are an important group of pervasive noncoding RNAs (>200nt) proposed to be crucial regulators of numerous physiological and pathological processes. Through interactions with RNA, chromatin, and protein, lncRNAs modulate mRNA stability, chromatin structure, and the function of proteins (including transcription factors). In addition, to their well-known roles in the modulation of cell growth, apoptosis, neurological disease progression and cancer metastasis, these large molecules have also been identified as likely mediators of lipid metabolism. In particular, lncRNAs orchestrate adipogenesis; fatty acid, cholesterol, and phospholipid metabolism and transport; and the formation of high-density and low-density lipoproteins (HDLs and LDLs). LncRNAs also appear to target several transcription factors that play essential roles in the regulation of lipid metabolism, such as liver X receptors (LXRs), sterol regulatory element binding proteins (SREBPs), and peroxisome proliferator-activated receptor γ (PPARγ). Better understanding the regulatory roles of lncRNAs in dyslipidemia, atherosclerosis, and adipogenesis will reveal appropriate strategies to treat these diseases. In this review, we review recent progress in lncRNA-mediated regulation of lipid metabolism, as well as its role in the regulation of adipogenesis.

Flavonoids, Dairy Foods, and Cardiovascular and Metabolic Health: A Review of Emerging Biologic Pathways

A growing body of nutritional science highlights the complex mechanisms and pleiotropic pathways of cardiometabolic effects of different foods. Among these, some of the most exciting advances are occurring in the area of flavonoids, bioactive phytochemicals found in plant foods; and in the area of dairy, including milk, yogurt, and cheese. Many of the relevant ingredients and mechanistic pathways are now being clarified, shedding new light on both the ingredients and the pathways for how diet influences health and well-being. Flavonoids, for example, have effects on skeletal muscle, adipocytes, liver, and pancreas, and myocardial, renal, and immune cells, for instance, related to 5'-monophosphate-activated protein kinase phosphorylation, endothelial NO synthase activation, and suppression of NF-κB (nuclear factor-κB) and TLR4 (toll-like receptor 4). Effects of dairy are similarly complex and may be mediated by specific amino acids, medium-chain and odd-chain saturated fats, unsaturated fats, branched-chain fats, natural trans fats, probiotics, vitamin K1/K2, and calcium, as well as by processing such as fermentation and homogenization. These characteristics of dairy foods influence diverse pathways including related to mammalian target of rapamycin, silent information regulator transcript-1, angiotensin-converting enzyme, peroxisome proliferator-activated receptors, osteocalcin, matrix glutamate protein, hepatic de novo lipogenesis, hepatic and adipose fatty acid oxidation and inflammation, and gut microbiome interactions such as intestinal integrity and endotoxemia. The complexity of these emerging pathways and corresponding biological responses highlights the rapid advances in nutritional science and the continued need to generate robust empirical evidence on the mechanistic and clinical effects of specific foods.

Sphingolipids in host-microbial interactions

Sphingolipids, a lipid class characterized by a long-chain amino alcohol backbone, serve vital structural and signaling roles in eukaryotes. Though eukaryotes produce sphingolipids, this capacity is phylogenetically highly restricted in Bacteria. Intriguingly, bacterial species commonly associated in high abundance with eukaryotic hosts include sphingolipid producers, such as the Bacteroidetes in the mammalian gut. To date, a role for bacterial sphingolipids in immune system maturation has been described, but their fate and impact in host physiology and metabolism remain to be elucidated. The structural conservation of bacterial sphingolipids with those produced by their mammalian hosts offer clues about which aspects of mammalian biology may be modulated by these intriguing lipids.

Effect of long-term dietary sphingomyelin supplementation on atherosclerosis in mice

Sphingomyelin (SM) levels in the circulation correlate positively with atherosclerosis burden. SM is a ubiquitous component of human diets, but it is unclear if dietary SM increases circulating SM levels. Dietary choline increases atherosclerosis by raising circulating trimethylamine N-oxide (TMAO) levels in mice and humans. As SM has a choline head group, we ask in this study if dietary SM accelerates atherosclerotic lesion development by increasing circulating SM and TMAO levels. Three studies were performed: (Study 1) C57BL/6 mice were maintained on a high fat diet with or without SM supplementation for 4 weeks prior to quantification of serum TMAO and SM levels; (Study 2) atherosclerosis was studied in apoE^-/- mice after 16 weeks of a high fat diet without or with SM supplementation and (Study 3) apoE^-/- mice were maintained on a chow diet for 19 weeks without or with SM supplementation and antibiotic treatment prior to quantification of atherosclerotic lesions and serum TMAO and SM levels. SM consumption did not increase circulating SM levels or atherosclerosis in high fat-fed apoE^-/- mice. Serum TMAO levels in C57BL/6 mice were low and had no effect atherosclerosis lesion development. Dietary SM supplementation significantly reduced atherosclerotic lesion area in the aortic arch of chow-fed apoE^-/- mice. This study establishes that dietary SM does not affect circulating SM levels or increase atherosclerosis in high fat-fed apoE^-/- mice, but it is anti-atherogenic in chow-fed apoE^-/- mice.

Effect of whole milk compared with skimmed milk on fasting blood lipids in healthy adults: a 3-week randomized crossover study

BACKGROUND/OBJECTIVES

Dietary guidelines have for decades recommended choosing low-fat dairy products due to the high content of saturated fat in dairy known to increase blood concentration of LDL cholesterol. However, meta-analyses including observational studies show no association between overall dairy intake and risk of cardiovascular disease and even point to an inverse association with type 2 diabetes. The objective was to compare the effects of whole milk (3.5% fat) with skimmed milk (0.1% fat) on fasting serum blood lipids, insulin, and plasma glucose in healthy subjects.

SUBJECT/METHODS

A randomized, controlled 2 × 3-week crossover dietary intervention in 18 healthy adults randomly assigned to a sequence of treatments consisting of 0.5 L/d of whole milk and skimmed milk as part of their habitual diet. A total of 17 subjects completed the intervention.

RESULTS

Whole milk increased HDL cholesterol concentrations significantly compared to skimmed milk (P < 0.05). There were no significant differences between whole milk and skimmed milk in effects on total and LDL cholesterol, triacylglycerol, insulin, and glucose concentrations.

CONCLUSIONS

Intake of 0.5 L/d of whole milk did not adversely affect fasting blood lipids, glucose, or insulin compared to skimmed milk. Moreover, intake of whole milk increased HDL cholesterol concentration compared to skimmed milk. These findings suggest that if the higher energy content is taken into account, whole milk might be considered a part of a healthy diet among the normocholesterolemic population.

Dietary sphingolipids: potential for management of dyslipidemia and nonalcoholic fatty liver disease

The development of therapeutic approaches aimed at reducing inflammation, improving lipid metabolism, and preventing nonalcoholic fatty liver disease holds significant potential in the management of obesity-associated disease. In this review, the recent basic science and clinical research examining dietary sphingolipid intake and the prevention of dyslipidemia and nonalcoholic fatty liver disease is summarized. Dietary sphingolipids have been shown to dose-dependently reduce the acute intestinal absorption of cholesterol, triglycerides, and fatty acids in rodents. Overall, studies feeding dietary sphingolipids to rodents typically show reductions in serum lipids. Furthermore, these hypolipidemic effects are also observed in most human studies, although the magnitude of such effects is typically smaller. Dietary sphingolipids also appear useful in preventing hepatic lipid uptake and accumulation and have shown benefits in preventing hepatic steatosis in rodent models. Dietary sphingolipids may affect the gut-liver axis by preventing the translocation of gut bacteria-derived lipopolysaccharide and/or inhibiting its proinflammatory effects. Current evidence from preclinical studies indicates that dietary sphingolipids have lipid-lowering and anti-inflammatory properties, although their potential to prevent human chronic disease has not been fully explored. It will be important to determine if such effects seen in cell and animal models translate to humans. More research is warranted to define how dietary sphingolipids influence lipid metabolism and inflammation.

Milk fat globule membrane glycoproteins: Valuable ingredients for lactic acid bacteria encapsulation?

The membrane (Milk Fat Globule Membrane - MFGM) surrounding the milk fat globule is becoming increasingly studied for its use in food applications due to proven nutritional and technological properties. This review focuses first on current researches which have been led on the MFGM structure and composition and also on laboratory and industrial purification and isolation methods developed in the last few years. The nutritional, health benefits and techno-functional properties of the MFGM are then discussed. Finally, new techno-functional opportunities of MFGM glycoproteins as a possible ingredient for Lactic Acid Bacteria (LAB) encapsulation are detailed. The ability of MFGM to form liposomes entrapping bioactive compounds has been already demonstrated. One drawback is that liposomes are too small to be used for bacteria encapsulation. For the first time, this review points out the numerous advantages to use MFGM glycoproteins as a protecting, encapsulating matrix for bacteria and especially for LAB.

Loss of miR-141/200c ameliorates hepatic steatosis and inflammation by reprogramming multiple signaling pathways in NASH

Accumulation of lipid droplets and inflammatory cell infiltration is the hallmark of nonalcoholic steatohepatitis (NASH). The roles of noncoding RNAs in NASH are less known. We aim to elucidate the function of miR-141/200c in diet-induced NASH. WT and miR-141/200c-/- mice were fed a methionine and choline deficient (MCD) diet for 2 weeks to assess markers of steatosis, liver injury, and inflammation. Hepatic miR-141 and miR-200c RNA levels were highly induced in human patients with NASH fatty liver and in WT MCD mice. miR-141/200c-/- MCD mice had reduced liver weights and triglyceride (TG) levels, which was associated with increased microsomal TG transfer protein (MTTP) and PPARα but reduced SREBP1c and FAS expression. Inflammation was attenuated and F4/80 macrophage activation was suppressed in miR-141/200c-/- mice, as evidenced by decreased serum aminotransferases and IL-6 and reduced hepatic proinflammatory, neutrophil, and profibrotic genes. Treatment with LPS in BM-derived macrophages isolated from miR-200c/141-/- mice polarized macrophages toward the M2 antiinflammatory state by increasing Arg1 and IL-10 levels while decreasing the M1 marker iNOS. In addition, elevated phosphorylated AMPK (p-AMPK), p-AKT, and p-GSK3β and diminished TLR4 and p-mTOR/p-4EBP1 proteins were observed. Lipidomics and metabolomics revealed alterations of TG and phosphatidylcholine (PC) lipid species by miR-141/200c deficiency. In summary, miR-141/200c deficiency diminished NASH-associated hepatic steatosis and inflammation by reprogramming lipid and inflammation signaling pathways.

Dietary and Endogenous Sphingolipid Metabolism in Chronic Inflammation

Chronic inflammation is a common underlying factor in many major metabolic diseases afflicting Western societies. Sphingolipid metabolism is pivotal in the regulation of inflammatory signaling pathways. The regulation of sphingolipid metabolism is in turn influenced by inflammatory pathways. In this review, we provide an overview of sphingolipid metabolism in mammalian cells, including a description of sphingolipid structure, biosynthesis, turnover, and role in inflammatory signaling. Sphingolipid metabolites play distinct and complex roles in inflammatory signaling and will be discussed. We also review studies examining dietary sphingolipids and inflammation, derived from in vitro and rodent models, as well as human clinical trials. Dietary sphingolipids appear to influence inflammation-related chronic diseases through inhibiting intestinal lipid absorption, altering gut microbiota, activation of anti-inflammatory nuclear receptors, and neutralizing responses to inflammatory stimuli. The anti-inflammatory effects observed with consuming dietary sphingolipids are in contrast to the observation that most cellular sphingolipids play roles in augmenting inflammatory signaling. The relationship between dietary sphingolipids and low-grade chronic inflammation in metabolic disorders is complex and appears to depend on sphingolipid structure, digestion, and metabolic state of the organism. Further research is necessary to confirm the reported anti-inflammatory effects of dietary sphingolipids and delineate their impacts on endogenous sphingolipid metabolism.

Food Ingredients That Inhibit Cholesterol Absorption

Cholesterol is a vital component of the human body. It stabilizes cell membranes and is the precursor of bile acids, vitamin D and steroid hormones. However, cholesterol accumulation in the bloodstream (hypercholesterolemia) can cause atherosclerotic plaques within artery walls, leading to heart attacks and strokes. The efficiency of cholesterol absorption in the small intestine is of great interest because human and animal studies have linked cholesterol absorption with plasma concentration of total and low density lipoprotein cholesterol. Cholesterol absorption is highly regulated and influenced by particular compounds in the food supply. Therefore, it is desirable to learn more about natural food components that inhibit cholesterol absorption so that food ingredients and dietary supplements can be developed for consumers who wish to manage their plasma cholesterol levels by non-pharmacological means. Food components thus far identified as inhibitors of cholesterol absorption include phytosterols, soluble fibers, phospholipids, and stearic acid.

Whole dairy matrix or single nutrients in assessment of health effects: current evidence and knowledge gaps

Foods consist of a large number of different nutrients that are contained in a complex structure. The nature of the food structure and the nutrients therein (i.e., the food matrix) will determine the nutrient digestion and absorption, thereby altering the overall nutritional properties of the food. Thus, the food matrix may exhibit a different relation with health indicators compared to single nutrients studied in isolation. The evidence for a dairy matrix effect was presented and discussed by an expert panel at a closed workshop, and the following consensus was reached: 1) Current evidence does not support a positive association between intake of dairy products and risk of cardiovascular disease (i.e., stroke and coronary heart disease) and type 2 diabetes. In contrast, fermented dairy products, such as cheese and yogurt, generally show inverse associations. 2) Intervention studies have indicated that the metabolic effects of whole dairy may be different than those of single dairy constituents when considering the effects on body weight, cardiometabolic disease risk, and bone health. 3) Different dairy products seem to be distinctly linked to health effects and disease risk markers. 4) Different dairy structures and common processing methods may enhance interactions between nutrients in the dairy matrix, which may modify the metabolic effects of dairy consumption. 5) In conclusion, the nutritional values of dairy products should not be considered equivalent to their nutrient contents but, rather, be considered on the basis of the biofunctionality of the nutrients within dairy food structures. 6) Further research on the health effects of whole dairy foods is warranted alongside the more traditional approach of studying the health effects of single nutrients. Future diet assessments and recommendations should carefully consider the evidence of the effects of whole foods alongside the evidence of the effects of individual nutrients. Current knowledge gaps and recommendations for priorities in future research on dairy were identified and presented.

Sphingolipids and glycerophospholipids - The "ying and yang" of lipotoxicity in metabolic diseases

Sphingolipids in general and ceramides in particular, contribute to pathophysiological mechanisms by modifying signalling and metabolic pathways. Here, we present the available evidence for a bidirectional homeostatic crosstalk between sphingolipids and glycerophospholipids, whose dysregulation contributes to lipotoxicity induced metabolic stress. The initial evidence for this crosstalk originates from simulated models designed to investigate the biophysical properties of sphingolipids in plasma membrane representations. In this review, we reinterpret some of the original findings and conceptualise them as a sort of "ying/yang" interaction model of opposed/complementary forces, which is consistent with the current knowledge of lipid homeostasis and pathophysiology. We also propose that the dysregulation of the balance between sphingolipids and glycerophospholipids results in a lipotoxic insult relevant in the pathophysiology of common metabolic diseases, typically characterised by their increased ceramide/sphingosine pools.

The dietary effect of milk sphingomyelin on the lipid metabolism of obese/diabetic KK-A(y) mice and wild-type C57BL/6J mice

Purified milk sphingomyelin (SM) was obtained from lipid concentrated butter serum (LC-BS) by successive separations involving solvent fractionation, selective saponification, and silicic acid column chromatography. The SM obtained was given to obese/diabetic KK-A(y) mice and wild-type C57BL/6J mice. SM supplementation significantly increased fecal lipids paralleled with a decrease in non-HDL cholesterol levels in the serum and neutral lipids and in cholesterol levels in the livers of KK-A(y) mice. The reduction of liver lipid levels also resulted in a decrease in the total fatty acid content of the KK-A(y) mice livers, while n-3 fatty acids derived from the conversion of α-linolenic acid (18:3n-3) increased due to SM supplementation. In contrast to the KK-A(y) mice, little change in the serum and liver lipids was observed in wild-type C57BL/6J mice. The present study suggests that SM may be effective only in subjects with metabolic disorders.

Lipidomic investigation of eggs' yolk: Changes in lipid profile of eggs from different conditions

Eggs are one of the main foods eaten worldwide. Nutritionally they are one of the main sources of dietary lipids, impacting human health. Egg yolk lipid composition changes depending on different conditions associated with hens raising. Therefore, the purpose of our work was to use a lipidomic approach as a tool to evaluate if different diets (vegetable versus animal) and raising environments (free range versus indoor) interfere in the triacylglycerol (TAG) and phospholipid (PL) profiles of eggs' yolks and to use such differences to differentiate eggs according to their origin. To achieve that goal, total lipid extracts were obtained and then fractionated by solid-phase chromatography. TAGs fraction was analysed by ESI-MS and PLs fraction by HILIC-LC-MS/MS. TAG and five PL classes were identified, namely PC, LPC, PE, LPE and SM. Fatty acids (FA) esterified to the glycerol backbone of PL ranged between C16:0 and C22:6. On the other hand, FA esterified to TAG ranged from C14:0 to C20:0. Major differences on the PL profile were observed regarding eggs from free-range hens and fed with vegetable origin food and eggs from the remaining conditions, once the former presented higher levels of PC (O-34:0), PC (34:1) and PE (34:1). Eggs from hens fed with animal origin food contained PL and TAG molecular species richer in n-6 FA, according to GC-MS and to LC-MS/MS data. The lipidomic approach used herein proved to be promising in differentiating eggs from hens with different raising conditions.

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

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

Organization of lipids in milks, infant milk formulas and various dairy products: role of technological processes and potential impacts

The microstructure of milk fat in processed dairy products is poorly known despite its importance in their functional, sensorial and nutritional properties. However, for the last 10 years, several research groups including our laboratory have significantly contributed to increasing knowledge on the organization of lipids in situ in dairy products. This paper provides an overview of recent advances on the organization of lipids in the milk fat globule membrane using microscopy techniques (mainly confocal microscopy and atomic force microscopy). Also, this overview brings structural information about the organization of lipids in situ in commercialized milks, infant milk formulas and various dairy products (cream, butter, buttermilk, butter serum and cheeses). The main mechanical treatment used in the dairy industry, homogenization, decreases the size of milk fat globules, changes the architecture (composition and organization) of the fat/water interface and affects the interactions between lipid droplets and the protein network (concept of inert vs active fillers). The potential impacts of the organization of lipids and of the alteration of the milk fat globule membrane are discussed, and technological strategies are proposed, in priority to design biomimetic lipid droplets in infant milk formulas.

Effect of beta-3 adrenoceptor stimulation on the levels of ApoA-I, PPARα, and PPARγ in apolipoprotein E-deficient mice

The beta-3 adrenoceptor (β3-AR) protects against the progression of atherosclerosis. However, the specific mechanism of this antiatherosclerotic effect is still not clear. Thus, the aim of this study was to understand the antiatherosclerotic effects of β3-AR. Thirty-six male homozygous apolipoprotein E-deficient mice and wild-type C57BL/6J mice were randomized into 6 treatment groups: wild-type, atherosclerotic model, atorvastatin, low-dose β3-AR agonist, high-dose β3-AR agonist, and β3-AR antagonist groups. The serum lipids, aortic-free cholesterol (FC), and cholesteryl ester (CE) concentrations were measured at the end of the treatments. The mRNA expression levels of liver apolipoprotein A-I (apoA-I), peroxisome proliferator-activated receptor-α (PPARα), and peroxisome proliferator-activated receptor-γ (PPARγ) were detected by quantitative real-time PCR. Protein expression levels of apoA1, PPARα, and PPARγ in the liver were determined by western blot analysis. Treatment with β3-AR significantly increased the plasma levels of high-density lipoprotein cholesterol and apoA-I, whereas the levels of total cholesterol, triglycerides, and low-density lipoprotein cholesterol decreased. The β3-AR agonist treatment markedly decreased both the FC and the CE concentrations in the aorta compared with the atherosclerotic model mice. The β3-AR agonist increased the mRNA and protein expression levels of apoA-I, PPARα, and PPARγ in the liver. This study demonstrates that long-term β3-AR activation can regulate lipid metabolic disorders and reduces the aortic FC and the CE concentrations. These effects may be related to apoA-I, PPARα, and PPARγ.

Potential role of milk fat globule membrane in modulating plasma lipoproteins, gene expression, and cholesterol metabolism in humans: a randomized study

BACKGROUND

Butter is rich in saturated fat [saturated fatty acids (SFAs)] and can increase plasma low density lipoprotein (LDL) cholesterol, which is a major risk factor for cardiovascular disease. However, compared with other dairy foods, butter is low in milk fat globule membrane (MFGM) content, which encloses the fat. We hypothesized that different dairy foods may have distinct effects on plasma lipids because of a varying content of MFGM.

OBJECTIVE

We aimed to investigate whether the effects of milk fat on plasma lipids and cardiometabolic risk markers are modulated by the MFGM content.

DESIGN

The study was an 8-wk, single-blind, randomized, controlled isocaloric trial with 2 parallel groups including overweight men and women (n = 57 randomly assigned). For the intervention, subjects consumed 40 g milk fat/d as either whipping cream (MFGM diet) or butter oil (control diet). Intervention foods were matched for total fat, protein, carbohydrates, and calcium. Subjects were discouraged from consuming any other dairy products during the study. Plasma markers of cholesterol absorption and hepatic cholesterol metabolism were assessed together with global gene-expression analyses in peripheral blood mononuclear cells.

RESULTS

As expected, the control diet increased plasma lipids, whereas the MFGM diet did not [total cholesterol (±SD): +0.30 ± 0.49 compared with -0.04 ± 0.49 mmol/L, respectively (P = 0.024); LDL cholesterol: +0.36 ± 0.50 compared with +0.04 ± 0.36 mmol/L, respectively (P = 0.024); apolipoprotein B:apolipoprotein A-I ratio: +0.03 ± 0.09 compared with -0.05 ± 0.10 mmol/L, respectively (P = 0.007); and non-HDL cholesterol: +0.24 ± 0.49 compared with -0.14 ± 0.51 mmol/L, respectively (P = 0.013)]. HDL-cholesterol, triglyceride, sitosterol, lathosterol, campesterol, and proprotein convertase subtilisin/kexin type 9 plasma concentrations and fatty acid compositions did not differ between groups. Nineteen genes were differentially regulated between groups, and these genes were mostly correlated with lipid changes.

CONCLUSIONS

In contrast to milk fat without MFGM, milk fat enclosed by MFGM does not impair the lipoprotein profile. The mechanism is not clear although suppressed gene expression by MFGM correlated inversely with plasma lipids. The food matrix should be considered when evaluating cardiovascular aspects of different dairy foods. This trial was registered at clinicaltrials.gov as NCT01767077.

Metabolomics profiling to investigate the pharmacologic mechanisms of berberine for the treatment of high-fat diet-induced nonalcoholic steatohepatitis

Objective. Berberine has been used to treat nonalcoholic steatohepatitis (NASH), which has been addressed in many studies. In this study, we investigated the molecular pharmacology mechanisms of berberine using metabolomic techniques. Methods. Sprague-Dawley rats were randomly divided into three groups (10 rats in each group): (i) normal control group; (ii) high-fat diet- (HFD-) induced NASH model group; and (iii) HFD berberine-treated group (i.d. 200 mg/kg). The handling procedure lasted eight weeks. Then, UPLC-Q-TOF/MS techniques coupled with histopathology and biochemical analyses were adopted to explore the mechanisms of berberine on the protective effects against NASH. Key Findings. (i) According to conventional test results, berberine treatment plays a fighting role in HFD-induced NASH due to its beneficial effects against insulin resistance, inflammation, and lipid metabolism. (ii) Based on UPLC-Q-TOF/MS techniques, metabolic profiles that involved sphingomyelin (SM), phosphatidylcholine (PC), lysophosphatidylcholine (LysoPC), 13-hydroperoxy-9, 11-octadecadienoic acid (13-HpODE), eicosatrienoic acid, docosatrienoic acid, and eicosenoic acid could provide potential metabolic biomarkers to address the pharmacological mechanisms of berberine. Conclusions. The parts of molecular pharmacological mechanisms of berberine for NASH treatment are related to the regulation of metabolic disruption involving phospholipid and unsaturated fatty acids in rats with NASH.

Egg phospholipids and cardiovascular health

Eggs are a major source of phospholipids (PL) in the Western diet. Dietary PL have emerged as a potential source of bioactive lipids that may have widespread effects on pathways related to inflammation, cholesterol metabolism, and high-density lipoprotein (HDL) function. Based on pre-clinical studies, egg phosphatidylcholine (PC) and sphingomyelin appear to regulate cholesterol absorption and inflammation. In clinical studies, egg PL intake is associated with beneficial changes in biomarkers related to HDL reverse cholesterol transport. Recently, egg PC was shown to be a substrate for the generation of trimethylamine N-oxide (TMAO), a gut microbe-dependent metabolite associated with increased cardiovascular disease (CVD) risk. More research is warranted to examine potential serum TMAO responses with chronic egg ingestion and in different populations, such as diabetics. In this review, the recent basic science, clinical, and epidemiological findings examining egg PL intake and risk of CVD are summarized.

Alkaline sphingomyelinase (NPP7) promotes cholesterol absorption by affecting sphingomyelin levels in the gut: A study with NPP7 knockout mice

We previously showed that dietary sphingomyelin (SM) inhibited cholesterol absorption in animals. The key enzyme hydrolyzing SM in the gut is alkaline sphingomyelinase (alk-SMase, nucleotide pyrophosphatase/phosphodiesterase 7). Here using the fecal dual-isotope ratio method we compared cholesterol absorption in the wild-type (WT) and alk-SMase knockout (KO) mice. The animals were fed an emulsion containing [(14)C]cholesterol and [(3)H]sitosterol. The radioactivities in the lipids of the fecal samples collected 4, 8, and 24 h thereafter were determined, and the ratio of (14)C/(3)H was calculated. We found that the fecal [(14)C]cholesterol recovery in the KO mice was significantly higher than in the WT mice. A maximal 92% increase occurred 8 h after feeding. Recovery of [(3)H]sitosterol did not differ between the two groups. Accordingly, the (14)C-to-(3)H ratio of fecal lipids was 133% higher at 8 h and 75% higher at 24 h in the KO than in the WT mice. Decreased [(14)C]cholesterol was also found in the serum of the KO mice 4 h after feeding. Supplement of SM in the emulsion reduced the differences in fecal [(14)C]cholesterol recovery between the WT and KO mice because of a greater increase of [(14)C]cholesterol recovery in the WT mice. Without treatment, the KO mice had significantly higher SM levels in the intestinal content and feces, but not in the intestinal mucosa or serum. The expression of Niemann-Pick C1 like 1 protein in the small intestine was not changed. In conclusion, alk-SMase is a physiological factor promoting cholesterol absorption by reducing SM levels in the intestinal lumen.