Phytoceramide and sphingoid bases derived from brewer's yeast Saccharomyces pastorianus activate peroxisome proliferator-activated receptors

The two-way immunotoxicity in native fish induced by exudates of Microcystis aeruginosa: Immunostimulation and immunosuppression

Secondary metabolites of cyanobacterial blooms have caused serious risks to aquatic animals. The immune system is an important barrier for fish against pollutants in aquatic systems. The immunetoxic mechanism of the exudates of Microcystis aeruginosa (MaE) on fish was lacking due to the complex components of MaE. In this project, Sinocyclocheilus grahami was used as the model to study the immunotoxic effects of MaE and PHS (one of the main components of the MaE) in fish. The immunosuppression effects of MaE are mainly in, decreased head-kindey index, damaged tissue structure of head-kidney and downregulated NF-κB, IL-1β. PHS induce immunostimulation via, increasing spleen index, apparently increasing leucocytes, increasing the IgM and lysozyme levels in serum and skin mucus, upregulating protease in skin mucus, increasing pro-immunologic factors (IL-1β, IL-6, IL-8, IL-10, TNF-α and NF-κB), probably activating the TLRs/NF-κB, MAPK, FoxO1 and PPARγ signaling pathways. Therefore, our research identified potential data gaps that how the exudates of cyanobacteria induces immunostimulation and immunosuppression from immune organs level to skin mucus to blood cells to inflammatory factors to potential molecular initiating event of MaE and PHS. Further research is needed to obtain a deeper view of the molecular mechanisms involved in MaE and PHS immunotoxicity and its consequences in long-time exposures.

Ceramides Increase Fatty Acid Utilization in Intestinal Progenitors to Enhance Stemness and Increase Tumor Risk

BACKGROUND & AIMS

Cancers of the alimentary tract, including esophageal adenocarcinomas, colorectal cancers, and cancers of the gastric cardia, are common comorbidities of obesity. Prolonged, excessive delivery of macronutrients to the cells lining the gut can increase one's risk for these cancers by inducing imbalances in the rate of intestinal stem cell proliferation vs differentiation, which can produce polyps and other aberrant growths. We investigated whether ceramides, which are sphingolipids that serve as a signal of nutritional excess, alter stem cell behaviors to influence cancer risk.

METHODS

We profiled sphingolipids and sphingolipid-synthesizing enzymes in human adenomas and tumors. Thereafter, we manipulated expression of sphingolipid-producing enzymes, including serine palmitoyltransferase (SPT), in intestinal progenitors of mice, cultured organoids, and Drosophila to discern whether sphingolipids altered stem cell proliferation and metabolism.

RESULTS

SPT, which diverts dietary fatty acids and amino acids into the biosynthetic pathway that produces ceramides and other sphingolipids, is a critical modulator of intestinal stem cell homeostasis. SPT and other enzymes in the sphingolipid biosynthesis pathway are up-regulated in human intestinal adenomas. They produce ceramides, which serve as prostemness signals that stimulate peroxisome-proliferator activated receptor-α and induce fatty acid binding protein-1. These actions lead to increased lipid utilization and enhanced proliferation of intestinal progenitors.

CONCLUSIONS

Ceramides serve as critical links between dietary macronutrients, epithelial regeneration, and cancer risk.

Serum Metabolic Profile in Schizophrenia Patients With Antipsychotic-Induced Constipation and Its relationship With Gut Microbiome

BACKGROUND AND HYPOTHESIS

Antipsychotics (APs), the cornerstone of schizophrenia treatment, confer a relatively high risk of constipation. However, the mechanisms underpinning AP-induced constipation are poorly understood. Thus, we hypothesized that (1) schizophrenia patients with AP-induced constipation have distinct metabolic patterns; (2) there is more than one mechanism at play in producing this adverse drug effect; and (3) AP-associated changes in the gut microbiome are related to the altered metabolic profiles.

STUDY DESIGN

Eighty-eight schizophrenia patients, including 44 with constipation (C) and 44 matched patients without constipation (NC), were enrolled in this study. Constipation was diagnosed by Rome IV criteria for constipation and colonic transit time using radiopaque markers (ROMs) while severity was evaluated with the Bristol Stool Form Scale (BSS) and Constipation Assessment Scale (CAS). Fasting blood samples were drawn from all participants and were subjected to non-targeted liquid chromatography-mass spectrometry (LC-MS) metabolomic analysis.

STUDY RESULTS

Eleven metabolites were significantly altered in AP-induced constipation which primarily disturbed sphingolipid metabolism, choline metabolism, and sphingolipid signaling pathway (P value < .05, FDR < 0.05). In the C group, changes in the gut bacteria showed a certain degree of correlation with 2 of the significantly altered serum metabolites and were associated with alterations in choline metabolism.

CONCLUSIONS

Our findings indicated that there were disturbances in distinct metabolic pathways that were associated with AP-induced constipation. In addition, this study presents evidence of a link between alterations in the gut microbiome and host metabolism which provides additional mechanistic insights on AP-induced constipation.

Implications of endocrine-disrupting chemicals on polycystic ovarian syndrome: A comprehensive review

Polycystic ovarian syndrome (PCOS) is a complex multifactorial disorder of unknown pathogenesis in which genetic and environmental factors contribute synergistically to its phenotypic expressions. Endocrine-disrupting chemicals (EDCs), a group of widespread pollutants freely available in the environment and consumer products, can interfere with normal endocrine signals. Extensive evidence has shown that EDCs, environmental contributors to PCOS, can frequently induce ovarian and metabolic abnormalities at low doses. The current research on environmental EDCs suggests that there may be link between EDC exposure and PCOS, which calls for more human bio-monitoring of EDCs using highly sophisticated analytical techniques for the identification and quantification and to discover the underlying pathophysiology of the disease. This review briefly elaborated on the general etiology of PCOS and listed various epidemiological and experimental data from human and animal studies correlating EDCs and PCOS. This review also provides insights into various analytical tools and sample preparation techniques for biomonitoring studies for PCOS risk assessment. Furthermore, we highlight the role of metabolomics in disease-specific biomarker discovery and its use in clinical practice. It also suggests the way forward to integrate biomonitoring studies and metabolomics to underpin the role of EDCs in PCOS pathophysiology.

Structural Elucidation of Irish Ale Bioactive Polar Lipids with Antithrombotic Properties

The structures of bioactive polar lipids (PLs) of Irish ale with potent antithrombotic and cardioprotective properties were elucidated. Ale PL was fractionated by preparative thin layer chromatography (TLC) into subclasses, and their antithrombotic effect was assessed against human platelet aggregation induced by the pro-inflammatory mediator, platelet-activating factor (PAF). The fatty acid content and the overall structures of ale PL were elucidated by liquid chromatography mass spectrometry (LC-MS). Phosphatidylcholines (PC) and molecules of the sphingomyelin (SM) family exhibited the strongest anti-PAF effects, followed by phosphatidylethanolamines (PE). PC contained higher amounts of omega-3 polyunsaturated fatty acids (n-3 PUFA) and thus the lowest n-6/n-3 ratio. Bioactive diacyl and alkyl-acyl PC and PE molecules bearing n-3 PUFA at their sn-2 position, especially docosahexaenoic acid (DHA) and α-linolenic acid (ALA) but mostly oleic acid (OA), were identified in both PC and PE subclasses. Eicosapentaenoic acid (EPA) was present only in bioactive PC molecules and not in PE, explaining the lower anti-PAF effects of PE. Bioactive sphingolipid and glycolipid molecules with reported anti-inflammatory and anti-tumour properties, such as specific ceramides and glucosylcerebrosides with sphingosine, phytosphingosine and dihydrosphingosine bases but also specific monogalactodiglycerides and SM species bearing ALA at their sn-2 position, were identified in the SM subclass, providing a rational for its strong bioactivities against the PAF pathway. Further studies are required on the health benefits of bioactive PL from beer and brewery by-products.

Mammalian sphingoid bases: Biophysical, physiological and pathological properties

Sphingoid bases encompass a group of long chain amino alcohols which form the essential structure of sphingolipids. Over the last years, these amphiphilic molecules were moving more and more into the focus of biomedical research due to their role as bioactive molecules. In fact, free sphingoid bases interact with specific receptors and target molecules and have been associated with numerous biological and physiological processes. In addition, they can modulate the biophysical properties of biological membranes. Several human diseases are related to pathological changes in the structure and metabolism of sphingoid bases. Yet, the mechanisms underlying their biological and pathophysiological actions remain elusive. Within this review, we aimed to summarize the current knowledge on the biochemical and biophysical properties of the most common sphingoid bases and to discuss their importance in health and disease.

Phytosphingosine Increases Biosynthesis of Phytoceramide by Uniquely Stimulating the Expression of Dihydroceramide C4-desaturase (DES2) in Cultured Human Keratinocytes

Ceramide NP is known to be the most abundant class of 12 ceramide (CER) families that form a permeability barrier in the human skin barrier. However, not many studies have been reported on the regulation of the biosynthesis of ceramide NP. Recently, it has been reported that phytosphingosine (PHS) treatment in the cultured keratinocytes (KC) notably increased the content of ceramide NP. However, the mechanism behind the PHS-induced enhancement of ceramide NP has not been elucidated. In this study, we investigated the effects of PHS on the expression of several essential genes for the biosynthesis of CER. Also, we determined the molecular mechanism behind the unique enhancement of ceramide NP upon treatment of PHS in the cultured KC. The expressions of all of the three genes (SPT, ceramide synthase 3 [CERS3], and ELOVL4) and their respective proteins were markedly increased in PHS-treated KC. In addition, the expression of the dihydroceramide C4-desaturase (DES2) responsible for conversion of dihydroceramide into ceramide NP was uniquely enhanced only by PHS treatment. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed that more than 20-fold increase of ceramide NP by PHS was observed while no significant enhancement of ceramide NS and NDS was observed. This study demonstrates that PHS plays a fundamental role in strengthening the epidermal permeability barrier by stimulating the overall processes of biosynthesis of all classes of CER in epidermis. The dramatic increase of ceramide NP upon PHS treatment seemed to be the outcome of transformation of dihydroceramide and/or ceramide NS by C4-hydroxylase activity.

Mammalian sphingoid bases: Biophysical, physiological and pathological properties

Sphingoid bases encompass a group of long chain amino alcohols which form the essential structure of sphingolipids. Over the last years, these amphiphilic molecules were moving more and more into the focus of biomedical research due to their role as bioactive molecules. In fact, free sphingoid bases interact with specific receptors and target molecules, and have been associated with numerous biological and physiological processes. In addition, they can modulate the biophysical properties of biological membranes. Several human diseases are related to pathological changes in the structure and metabolism of sphingoid bases. Yet, the mechanisms underlying their biological and pathophysiological actions remain elusive. Within this review, we aimed to summarize the current knowledge on the biochemical and biophysical properties of the most common sphingoid bases and to discuss their importance in health and disease.

Follicular dynamics of glycerophospholipid and sphingolipid metabolisms in polycystic ovary syndrome patients

Polycystic ovary syndrome (PCOS) is a common heterogeneous disease, affecting up to 5-10% women at reproductive age. Although PCOS patients could produce morphologically normal metaphase II oocytes undergoing assisted reproductive techniques (ART), oocyte developmental competence and embryo development have been impaired in following in-vitro fertilization (IVF) steps. Follicular fluid (FF) provides a variety of information in oocyte environment when oocytes grow. In the present work, based on ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS), the metabolic signatures of PCOS FF have been compared with healthy women using untargeted metabolomics approach. Significant abundance differences of a series of glycerolipid, glycerophospholipids, sphingolipids, and carboxylic acids have been discovered. Among them, reduced levels of phosphatidylglycerolphosphate (PGP) and a triglyceride (TG) were highly related to the lower fertilization rate in PCOS; increased abundance of lysoPE and decreased amount of PC were significantly correlated with LH/FSH (ratio of luteinizing hormone to follicle stimulating hormone). Some metabolites, including decreased sphingolipids, glycerophospholipids, and fluctuated fatty acyls, also performed close relationship with other ART and clinical results. We concluded that dysfunctions in the metabolism of glycerolipid, glycerophospholipid, sphingolipid, and glycosphingolipid biosynthesis in PCOS patients' follicles play a non-ignorable role in declining the 2 pronuclei (PN) fertilization rate during IVF procedure.

SWATHHM-Based Metabolomics of Follicular Fluid in Patients Shows That Progesterone Adversely Affects Oocyte Quality

Objective

We reveal the relationship between progesterone level in follicular fluid and oocyte quality based on sequential window acquisition of all theoretical fragment-ion spectra (SWATH™), a powerful high-resolution mass spectrometric data independent acquisition technique.

Method

Follicular fluid samples were collected from 22 subjects (the level of progesterone > 1.5 ng/mL) of progesterone group, as well as from 22 subjects (the level of progesterone < 1.5 ng/mL) of control group, and analyzed using UPLC-Q-TOF. All methods were performed in accordance with ISO 9001:2008. Novel SWATH acquisition mode on an ultra-high performance liquid chromatography coupled with hybrid triple quadrupole time-of-flight mass spectrometry (with resolving power 20,000–40,000) was investigated for the analysis of human follicular fluid. The principal component variable grouping detects intersample variable correlation and groups variables with similar profiles which simplifies interpretation and highlights related ions and fragments. It can also extract product ion spectra from the data collected by fragmenting a wide precursor ion window.

Results

Follicular fluid from the two groups differed with respect to five metabolites. Follicular fluid from the progesterone group contained elevated levels of 8-hydroxyguanosine and 4-hydroxynonenal and reduced levels of ATP, estradiol, and L-carnitine. The increased progesterone level on the day of HCG injection could negatively impact oocyte quality, thus reducing the pregnancy rate of IVF patients.

Potential Applications of Phyto-Derived Ceramides in Improving Epidermal Barrier Function

The outer most layer of the skin, the stratum corneum, consists of corneocytes which are coated by a cornified envelope and embedded in a lipid matrix of ordered lamellar structure. It is responsible for the skin barrier function. Ceramides (CERs) are the backbone of the intercellular lipid membranes. Skin diseases such as atopic dermatitis and psoriasis and aged skin are characterized by dysfunctional skin barrier and dryness which are associated with reduced levels of CERs. Previously, the effectiveness of supplementation of synthetic and animal-based CERs in replenishing the depleted natural skin CERs and restoring the skin barrier function have been investigated. Recently, however, the barrier function improving effect of plant-derived CERs has attracted much attention. Phyto-derived CERs (phytoCERs) are preferable due to their assumed higher safety as they are mostly isolated from dietary sources. The beneficial effects of phytoCER-based oral dietary supplements for skin hydration and skin barrier reinforcement have been indicated in several studies involving animal models as well as human subjects. Ingestible dietary supplements containing phytoCERs are also widely available on the market. Nonetheless, little effort has been made to investigate the potential cosmetic applications of topically administered phytoCERs. Therefore, summarizing the foregoing investigations and identifying the gap in the scientific data on plant-derived CERs intended for skin-health benefits are of paramount importance. In this review, an attempt is made to synthesize the information available in the literature regarding the effects of phytoCER-based oral dietary supplements on skin hydration and barrier function with the underlying mechanisms.

Phytosphingosine, sphingosine and dihydrosphingosine ceramides in model skin lipid membranes: permeability and biophysics

Ceramides based on phytosphingosine, sphingosine and dihydrosphingosine are essential constituents of the skin lipid barrier that protects the body from excessive water loss. The roles of the individual ceramide subclasses in regulating skin permeability and the reasons for C4-hydroxylation of these sphingolipids are not completely understood. We investigated the chain length-dependent effects of dihydroceramides, sphingosine ceramides (with C4-unsaturation) and phytoceramides (with C4-hydroxyl) on the permeability, lipid organization and thermotropic behavior of model stratum corneum lipid membranes composed of ceramide/lignoceric acid/cholesterol/cholesteryl sulfate. Phytoceramides with very long C24 acyl chains increased the permeability of the model lipid membranes compared to dihydroceramides or sphingosine ceramides with the same chain lengths. Either unsaturation or C4-hydroxylation of dihydroceramides induced chain length-dependent increases in membrane permeability. Infrared spectroscopy showed that C4-hydroxylation of the sphingoid base decreased the relative ratio of orthorhombic chain packing in the membrane and lowered the miscibility of C24 phytoceramide with lignoceric acid. The phase separation in phytoceramide membranes was confirmed by X-ray diffraction. In contrast, phytoceramides formed strong hydrogen bonds and highly thermostable domains. Thus, the large heterogeneity in ceramide structures and in their aggregation mechanisms may confer resistance towards the heterogeneous external stressors that are constantly faced by the skin barrier.

Effects of Asterias amurensis-derived Sphingoid Bases on the de novo Ceramide Synthesis in Cultured Normal Human Epidermal Keratinocytes

Asterias amurensis starfish provide several bioactive species in addition to being fishery waste. Glucosyl ceramides (GlcCers) were extracted from the viscera of these starfish and were isolated by silica gel column chromatography. Degraded GlcCers generated A. amurensis sphingoid bases (ASBs) that mainly consisted of the triene-type bases d18:3 and 9-methyl-d18:3. The effect of these bases on ceramide synthesis and content were analyzed using normal human epidermal keratinocytes (NHEKs). The bases significantly enhanced the de novo ceramide synthesis and gene expression in NHEKs for proteins, such as serine-palmitoyltransferase and ceramide synthase. Total ceramide, GlcCer, and sphingomyelin contents increased dramatically upon ASB treatment. In particular, GlcCer bearing very-long-chain fatty acids (≥C28) exhibited a significant content increase. These ASB-induced enhancements on de novo ceramide synthesis were only observed in undifferentiated NHEKs. This stimulation of the de novo sphingolipid synthesis may improve skin barrier functions.

An integrative view of microbiome-host interactions in inflammatory bowel diseases

The intestinal microbiota, which is composed of bacteria, viruses, and micro-eukaryotes, acts as an accessory organ system with distinct functions along the intestinal tract that are critical for health. This review focuses on how the microbiota drives intestinal disease through alterations in microbial community architecture, disruption of the mucosal barrier, modulation of innate and adaptive immunity, and dysfunction of the enteric nervous system. Inflammatory bowel disease is used as a model system to understand these microbial-driven pathologies, but the knowledge gained in this space is extended to less-well-studied intestinal diseases that may also have an important microbial component, including environmental enteropathy and chronic colitis-associated colorectal cancer.

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.

New long chain bases in lipophosphonoglycan of Acanthamoeba castellanii

The polymer called lipophosphonoglycan (LPG) was isolated from Acanthamoeba castellanii membranes after exhaustive delipidation and butanol extraction. A novel extremely long phytosphingosine was revealed in glycoinositolphosphosphingolipid (GIPSL). All data obtained by gas-liquid chromatography coupled with MS analyses of products liberated during acid methanolysis and products of sodium metaperiodate and permanganate-periodate oxidations showed an unusual pattern of long chain bases (LCB) with branched bases (anteiso-C₂₄, anteiso-C₂₅, anteiso-C₂₆, iso-C₂₆, anteiso-C₂₇, and anteiso-C28) and normal ones (C₂₄, C₂₅, C₂₆, C₂₇). The phytosphingosines with hexa-, hepta-, and octacosanoic chains have not been detected in Acanthamoeba cells up to now. Also, the isomer configuration of long chain bases in LPG of A. castellanii was not defined in earlier reports. In the GC-MS chromatograms, the component forming a peak corresponding to anteiso-C₂₅ phytosphingosine was the most abundant and constituted more than 50 % of all LCB.

Administration of glucosylceramide ameliorated the memory impairment in aged mice

The function and the role of glucosylceramide have not been well studied in the central nervous system. This study was aimed to investigate the possible roles of glucosylceramide in memory function in aged mice. Glucosylceramide (50 mg/kg, p.o.) showed memory enhancing activity after 3-month treatment in the aged mice (C56BL/6, 18–20 months old) through Y-maze, novel objective test, and Morris water maze test. Long-term treatment of glucosylceramide decreased the expression of iNOS and COX-2 in the brain of aged mice. The LPS-induced mRNA level of iNOS, COX-2, IL-1β, and TNF-α was reduced by the acute treatment with glucosylceramide in adult mice. These results suggest that glucosylceramide plays an important role in anti-inflammatory and memory enhancement, and it could be a potential new therapeutic agent for the treatment of neurodegenerative diseases such as Alzheimer's disease.

Improved high-fat diet-induced glucose intolerance by an oral administration of phytosphingosine

We have previously reported that phytoceramide and phytosphingosine (PHS) stimulated the transcriptional activity of peroxisome proliferator-activated receptor γ (PPARγ) in cells. PPARγ is a therapeutic target for type 2 diabetes. We found in this study that an oral administration of PHS improved diet-induced glucose intolerance in mice. Since PHS is highly expressed in yeast, PHS in fermented foods may improve diabetes.

Oral intake of beet extract provides protection against skin barrier impairment in hairless mice

The epidermis acts as a functional barrier against the external environment. Disturbances in the function of this barrier cause water loss and increase the chances of penetration by various irritable stimuli, leading to skin diseases such as dry skin, atopic dermatitis, and psoriasis. Ceramides are a critical natural element of the protective epidermal barrier. The aim of this study was to evaluate whether the oral intake of beet (Beta vulgaris) extract, a natural product rich in glucosylceramide (GlcCer), may prevent disturbance in skin barrier function. When HR-1 hairless mice were fed a special diet (HR-AD), transepidermal water loss (TEWL) from the dorsal skin increased, with a compensatory increase in water intake after 5 weeks. Mice fed with HR-AD had dry skin with erythema and showed increased scratching behaviour. Histological examinations revealed a remarkable increase in the thickness of the skin at 8 weeks. Supplemental addition of beet extract, which contained GlcCer at a final concentration of 0.1%, significantly prevented an increase TEWL, water intake, cumulative scratching time, and epidermal thickness at 8 weeks. These results indicate that oral intake of beet extract shows potential for preventing skin diseases associated with impaired skin barrier function.

4,8-Sphingadienine and 4-hydroxy-8-sphingenine activate ceramide production in the skin

Background

Ingestion of glucosylceramide improves transepidermal water loss (TEWL) from the skin, but the underlying mechanism by which a small amount of dietary glucosylceramide can vastly improve skin conditions remains unclear. In a previous report, glucosylceramides were shown to be digested to sphingoids, which were shown to be absorbed through the intestinal epithelium. Based on these observations, we hypothesized that sphingoids are the key molecules facilitating endogenous ceramide production. In this study, we assessed the effect of 4,8-sphingadienine (d18:2) and 4-hydroxy-8-sphingenine (t18:1), derived from konjac glucosylceramide, on stimulating ceramide production.

Methods

Konjac glucosylceramide acidolysis was performed using hydrochloric acid; the resulting d18:2 and t18:1 were fractionated by column chromatography. Real-time quantitative RT-PCR was performed to assess the effect of d18:2 and t18:1 on gene expression in normal human epidermal keratinocytes, while their effect on the nuclear receptor, peroxisome proliferator-activated receptor (PPAR)γ, was measured using a receptor-cofactor assay system. The effect of d18:2 and t18:1 on stimulating ceramide production was evaluated using HPTLC analysis in a 3-dimensional human skin model.

Results

We noted the upregulation of genes related to de novo ceramide synthesis as well as of those encoding the elongases of very long-chain fatty acids by d18:2 and t18:1, but not by glucosylceramide and 4-sphingenine. Both these sphingoids also facilitated the expression of PPARβ/δ and PPARγ; moreover, they also demonstrated ligand activity for PPARγ. These results indicated that d18:2 and t18:1 promote the differentiation of keratinocytes. Analysis of the lipids within the 3-dimensional human skin model indicated that treatment with d18:2 and t18:1 not only upregulated gene expression but also increased ceramide production.

Conclusions

The sphingoids d18:2 and t18:1 activated genes related to de novo ceramide synthesis and increased ceramide production, whereas glucosylceramide and 4-sphingenine could not. These results suggest that the effect of dietary glucosylceramides on the skin is mediated by d18:2 and t18:1.