The Impact of Dietary Sphingolipids on Intestinal Microbiota and Gastrointestinal Immune Homeostasis

The large surfaces of gastrointestinal (GI) organs are well adapted to their diverse tasks of selective nutritional uptake and defense against the external environment. To maintain a functional balance, a vast number of immune cells is located within the mucosa. A strictly regulated immune response is required to impede constant inflammation and to maintain barrier function. An increasing prevalence of GI diseases has been reported in Western societies over the past decades. This surge in GI disorders has been linked to dietary changes followed by an imbalance of the gut microbiome, leading to a chronic, low grade inflammation of the gut epithelium. To counteract the increasing health care costs associated with diseases, it is paramount to understand the mechanisms driving immuno-nutrition, the associations between nutritional compounds, the commensal gut microbiota, and the host immune response. Dietary compounds such as lipids, play a central role in GI barrier function. Bioactive sphingolipids (SLs), e.g. sphingomyelin (SM), sphingosine (Sph), ceramide (Cer), sphingosine-1- phosphate (S1P) and ceramide-1-phosphate (C1P) may derive from dietary SLs ingested through the diet. They are not only integral components of cell membranes, they additionally modulate cell trafficking and are precursors for mediators and second messenger molecules. By regulating intracellular calcium levels, cell motility, cell proliferation and apoptosis, SL metabolites have been described to influence GI immune homeostasis positively and detrimentally. Furthermore, dietary SLs are suggested to induce a shift in the gut microbiota. Modes of action range from competing with the commensal bacteria for intestinal cell attachment to prevention from pathogen invasion by regulating innate and immediate defense mechanisms. SL metabolites can also be produced by gut microorganisms, directly impacting host metabolic pathways. This review aims to summarize recent findings on SL signaling and functional variations of dietary SLs. We highlight novel insights in SL homeostasis and SL impact on GI barrier function, which is directly linked to changes of the intestinal microbiota. Knowledge gaps in current literature will be discussed to address questions relevant for understanding the pivotal role of dietary SLs on chronic, low grade inflammation and to define a balanced and healthy diet for disease prevention and treatment.

RIPK3 Contributes to Lyso-Gb3-Induced Podocyte Death

Fabry disease is a lysosomal storage disease with an X-linked heritage caused by absent or decreased activity of lysosomal enzymes named alpha-galactosidase A (α-gal A). Among the various manifestations of Fabry disease, Fabry nephropathy significantly affects patients' morbidity and mortality. The cellular mechanisms of kidney damage have not been elusively described. Necroptosis is one of the programmed necrotic cell death pathways and is known to play many important roles in kidney injury. We investigated whether RIPK3, a protein phosphokinase with an important role in necroptosis, played a crucial role in the pathogenesis of Fabry nephropathy both in vitro and in vivo. The cell viability of podocytes decreased after lyso-Gb3 treatment in a dose-dependent manner, with increasing RIPK3 expression. Increased reactive oxygen species (ROS) generation after lyso-Gb3 treatment, which was alleviated by GSK'872 (a RIPK3 inhibitor), suggested a role of oxidative stress via a RIPK3-dependent pathway. Cytoskeleton rearrangement induced by lyso-Gb3 was normalized by the RIPK3 inhibitor. When mice were injected with lyso-Gb3, increased urine albuminuria, decreased podocyte counts in the glomeruli, and effaced foot processes were observed. Our results showed that lyso-Gb3 initiated albuminuria, a clinical manifestation of Fabry nephropathy, by podocyte loss and subsequent foot process effacement. These findings suggest a novel pathway in Fabry nephropathy.

Alterations of endogenous sphingolipid metabolism in cardiometabolic diseases: Towards novel therapeutic approaches

The increasing prevalence of obesity and metabolic diseases is a worldwide public health concern, and the advent of new analytical technologies has made it possible to highlight the involvement of some molecules, such as sphingolipids (SL), in their pathophysiology. SL are constituents of cell membranes, lipoproteins and lipid droplets (LD), and are now considered as bioactive molecules. Indeed, growing evidence suggests that SL, characterized by diverse families and species, could represent one of the main regulators of lipid metabolism. There is an increasing amount of data reporting that plasma SL profile is altered in metabolic diseases. However, less is known about SL metabolism dysfunction in cells and tissues and how it may impact the lipoprotein metabolism, its functionality and composition. In cardiometabolic pathologies, the link between serum SL concentrations and alterations of their metabolism in various organs and LD is still unclear. Pharmacological approaches have been developed in order to activate or inhibit specific key enzymes of the SL metabolism, and to positively modulate SL profile or related metabolic pathways. Nevertheless, little is known about the long-term impact of such approaches in humans and the current literature still focuses on the decomposition of the different parts of this complex system rather than performing an integrated analysis of the whole SL metabolism. In addition, since SL can be provided from exogenous sources, it is also of interest to evaluate their impact on the homeostasis of endogenous SL metabolism, which could be beneficial in prevention or treatment of obesity and related metabolic disorders.

Milk fat components with potential anticancer activity-a review

During many years, the milk fat has been unfairly undervalued due to its association with higher levels of cardiovascular diseases, dyslipidaemia or obesity, among others. However, currently, this relationship is being re-evaluated because some of the dairy lipid components have been attributed potential health benefits. Due to this, and based on the increasing incidence of cancer in our society, this review work aims to discuss the state of the art concerning scientific evidence of milk lipid components and reported anticancer properties. Results from the in vitro and in vivo experiments suggest that specific fatty acids (FA) (as butyric acid and conjugated linoleic acid (CLA), among others), phospholipids and sphingolipids from milk globule membrane are potential anticarcinogenic agents. However, their mechanism of action remains still unclear due to limited and inconsistent findings in human studies.

New sphingolipids from the root of Isatis indigotica and their cytotoxic activity

Two new sphingolipids were isolated from the 95% EtOH extract of traditional Chinese medicinal plant Isatis indigotica. Their structures were elucidated as (2S,3R)-3-hydroxymethyl-N-(2'-hydroxynonacosanoyl)-trideca-9E-sphingenine(1) and 1-O-beta-D-glucopyranosyl-(2S,3R)-3-hydroxymethyl-N-(2'-hydroxynonacosanoyl)-trideca-9E-sphingenine(2) on the basis of spectroscopic data. Their cytotoxic effects were evaluated by using MTT method.

Dietary sphingolipids lower plasma cholesterol and triacylglycerol and prevent liver steatosis in APOE*3Leiden mice

BACKGROUND

The prevalence of dyslipidemia and obesity resulting from excess energy intake and physical inactivity is increasing. The liver plays a pivotal role in systemic lipid homeostasis. Effective, natural dietary interventions that lower plasma lipids and promote liver health are needed.

OBJECTIVE

Our goal was to determine the effect of dietary sphingolipids on plasma lipids and liver steatosis.

DESIGN

APOE*3Leiden mice were fed a Western-type diet supplemented with different sphingolipids. Body cholesterol and triacylglycerol metabolism as well as hepatic lipid concentrations and lipid-related gene expression were determined.

RESULTS

Dietary sphingolipids dose-dependently lowered both plasma cholesterol and triacylglycerol in APOE*3Leiden mice; 1% phytosphingosine (PS) reduced plasma cholesterol and triacylglycerol by 57% and 58%, respectively. PS decreased the absorption of dietary cholesterol and free fatty acids by 50% and 40%, respectively, whereas intestinal triacylglycerol lipolysis was not affected. PS increased hepatic VLDL-triacylglycerol production by 20%, whereas plasma lipolysis was not affected. PS increased the hepatic uptake of VLDL remnants by 60%. Hepatic messenger RNA concentrations indicated enhanced hepatic lipid synthesis and VLDL and LDL uptake. The net result of these changes was a strong decrease in plasma cholesterol and triacylglycerol. The livers of 1% PS-fed mice were less pale, 22% lighter, and contained 61% less cholesteryl ester and 56% less triacylglycerol than livers of control mice. Furthermore, markers of liver inflammation (serum amyloid A) and liver damage (alanine aminotransferase) decreased by 74% and 79%, respectively, in PS-fed mice.

CONCLUSION

Sphingolipids lower plasma cholesterol and triacylglycerol and protect the liver from fat- and cholesterol-induced steatosis.

Mucosal immunization against hepatitis A: antibody responses are enhanced by co-administration of synthetic oligodeoxynucleotides and a novel cationic lipid

Hepatitis A caused by hepatitis A virus (HAV) transmitted by the fecal-oral route, results in considerable morbidity and economic loss. Mucosal immunization can be more effective than conventional injection at inducing both local and systemic immunity to HAV. Here we show that co-administration of killed HAV with synthetic oligodeoxynucleotides (ODNs) containing CpG sequences, and a novel polycationic sphingolipid (CCS)/cholesterol liposomal delivery system, markedly enhances the HAV-specific antibody response at the intestinal interface, particularly when delivered intrarectally or intranasally, to Balb/c mice at low HAV doses. A mucosally delivered, antigen-sparing HAV vaccine that is easily administered without specialized equipment or personnel, is an attractive alternative for facilitating mass immunization in hepatitis A outbreaks.

Inhibitory effect of dietary monoglucosylceramide 1-O-beta-glucosyl-N-2'-hydroxyarachidoyl-4,8-sphingadienine on two different categories of colon preneoplastic lesions induced by 1,2-dimethylhydrazine in F344 rats

Sphingolipids display a wide spectrum of biological activities, including cell growth, differentiation and apoptosis. However, precise mechanisms by which these compounds exert anticancer or cancer-preventive effects are not known. In the present study, we evaluated the preventive efficacy of enriched dietary monoglucosylceramide 1-O-beta-glucosyl-N-2'-hydroxyarachidoyl-4,8-sphingadienine (G(1)CM) on 1,2-dimethylhydrazine (DMH)-induced aberrant crypt foci (ACF) and beta-catenin-accumulated crypt (BCAC) formation in F344 rats during initiation stage. We also examined whether G(1)CM affects cell proliferation and apoptosis in these lesions. Pure G(1)CM was isolated from rice bran. Forty-two rats were divided randomly into five experimental groups. Rats in groups 1-3 were given subcutaneous injections of DMH (40 mg/kg body weight) once a week for 2 weeks. One week before the first injection of DMH, rats in groups 2 and 3 were fed a diet containing 200 and 1,000 p.p.m. G(1)CM, respectively, for 5 weeks. Rats in group 4 were fed a diet containing 1,000 p.p.m. G(1)CM. Rats in group 5 were given the basal diet alone and served as untreated controls. The experiment was terminated 5 weeks after the start. Dietary G(1)CM at both doses (groups 2 and 3) significantly inhibited the induction of ACF and BCAC (P<0.001) when compared to group 1 treated with DMH alone. In groups 2 and 3, the proliferating cell nuclear antigen labeling indices of epithelial cells in ACF and BCAC were also lower than in group 1 (P<0.0001 for ACF, P<0.05 for BCAC). These results, that dietary G(1)CM has possible chemopreventive effects in the present short-term colon carcinogenesis bioassays, suggest that longer exposure may cause suppression of tumor development.

The effect of dietary sphingolipids on plasma sphingomyelin metabolism and atherosclerosis

Sphingomyelin (SM) plays a very important role in cell membrane formation and plasma lipoprotein metabolism. All these functions may have an impact on atherosclerotic development. To investigate the relationship between SM metabolism and atherosclerosis, we utilized a sphingolipid-rich diet to feed LDL receptor gene knockout (LDLr KO) mice and studied lipid metabolism and atherosclerosis in the mice. After 3 months of a sphingolipid-rich diet, we found a significant increase in SM, cholesterol, and SM/phosphatidylcholine (PC) ratio (50%, P<0.001; 62%, P<0.01; and 45%, P<0.01, respectively), compared to chow fed diet. HDL-lipids were not significantly altered. Non-HDL-SM, non-HDL-C, and non-HDL-SM/non-HDL-PC ratio were significantly increased (115%, P<0.001; 106%, P<0.001; and 106%, P<0.01, respectively). FPLC confirmed the results. SDS-PAGE showed an increase of apoB48 and apoB100, but no changes of apoAI. Moreover, we found that an SM-rich diet significantly increased atherosclerotic lesion area in both root assay and en face assay, compared to chow diet (58,210+/-15,300 microm(2) vs. 9670+/-2370 microm(2), P<0.001; 5.9+/-3.1% vs. 1.1+/-0.9%, P<0.001). These results indicate that the enrichment of sphingolipids in diet has proatherogenic properties.

Dietary soy sphingolipids suppress tumorigenesis and gene expression in 1,2-dimethylhydrazine-treated CF1 mice and ApcMin/+ mice

Dietary supplementation with milk sphingolipids inhibits colon tumorigenesis in CF1 mice treated with a colon carcinogen [1,2-dimethylhydrazine (DMH)] and in multiple intestinal neoplasia (Min) mice, which develop intestinal tumors spontaneously. Plant sphingolipids differ structurally from those of mammals [soy glucosylceramide (GlcCer) consists predominantly of a 4,8-sphingadiene backbone and alpha-hydroxy-palmitic acid], which might affect their bioactivity. Soy GlcCer was added to the AIN-76A diet (which contains <0.005% sphingolipid) to investigate whether it would also suppress tumorigenesis in these mouse models. Soy GlcCer reduced colonic cell proliferation in the upper half of the crypts in mice treated with DMH by 50 and 56% (P < 0.05) at 0.025 and 0.1% of the diet (wt/wt), respectively, and reduced the number of aberrant colonic crypt foci (an early marker of colon carcinogenesis) by 38 and 52% (P < 0.05). Min mice fed diets containing 0.025 and 0.1% (wt/wt) soy GlcCer developed 22 and 37% fewer adenomas (P < 0.05), respectively. The effects of dietary sphingolipids on gene expression in the intestinal mucosal cells of Min mice were analyzed using Affymetrix GeneChip microarrays. Soy GlcCer affected the expression of 96 genes by > or = 2-fold in a dose-dependent manner, increasing 32 and decreasing 64. Decreases in the mRNA expression of two transcription factors associated with cancer, hypoxia-induced factor 1 alpha (HIF1 alpha) and transcription factor 4 (TCF4), were confirmed by quantitative RT-PCR. In conclusion, soy GlcCer suppressed colon tumorigenesis in two mouse models; hence, plant sphingolipids warrant further investigation as inhibitors of colon cancer. Because soy contains relatively high amounts of GlcCer, sphingolipids may partially account for the anticancer benefits attributed to soy-based foods.

Damage to the gills, skin and other tissues by lysenin and the coelomic fluid of the earthworm Eisenia foetida in two teleosts, Tanichthys albonubes and Oreochromis mossambicus

Lysenin is a 33-kDa protein found in the coelomic fluid (CF) of the earthworm Eisenia foetida. Purified lysenin binds specifically to sphingomyelin (SM). In the present studies, we found that the white cloud mountain minnow Tanichthys albonubes and the Mozambique tilapia Oreochromis mossambicus died in solutions of lysenin (at concentrations above 2.5 microg/ml) and CF (0.6%, v/v) within 2 h. The gills of both species of fish were damaged similarly by lysenin and by CF. Most gill lamellae became irregularly bent or curled, with swelling of the epithelial cells of the lamellae. Red blood cells in the lamellar vascular sinuses, in the central venous sinuses, and in the blood vessels of the entire body became swollen and lysed, choking the sinuses. Epithelial cells in the skin were also damaged. When fish of both species were treated with lysenin or CF that had been incubated with SM-liposomes, they did not die. Their behavior remained normal and there was no damage to any cells or tissues. These findings suggest that SM might be involved in the lethal effects of lysenin and CF. It is likely that purified lysenin and lysenin in CF bound to SM in the cell membranes of the tissues mentioned above, damaging the cells. The presence of SM in the gills and skin was confirmed, supporting this hypothesis. The damage to gills and hemolysis might have resulted in lethal respiratory problems. Damage to the skin might disturb the exchange of ions through the skin, hastening death. Damage by lysenin and CF to epithelial cells of the cornea and the wall of the oral cavity was also recognized, but there was no such damage to the intestine.

Dietary sphingolipids in colorectal cancer prevention

Sphingolipids are widespread membrane components that are found in all eukaryotic cells. They consist of a long chain sphingoid-base, usually sphingosine, which is acylated at the 2-amino position, forming a ceramide. All together, sphingolipids may represent the most structurally diverse category of lipids in nature. There is no known nutritional requirement for sphingolipids. Nonetheless, studies with experimental animals have shown that consumption of sphingolipids inhibits colon carcinogenesis, reduces serum low-density lipoprotein cholesterol and elevates high-density lipoproteins, which suggest that they are 'functional' components of food. In animal models (CF1 mice) sphingomyelin supplementation reduces the number of aberrant colonic crypt foci by approximately 70% and, with longer feeding, reduces the number of colonic adenocarcinomas. A possible mechanism of action of sphingolipids in suppressing colon carcinogenesis is that exogenously supplied sphingolipids bypass a sphingolipid signalling defect that is important in cancer (for example, a loss of cellular sphingomyelin turnover to produce ceramide and sphingosine). Indirect evidence suggests that sphingolipids can inhibit colon cancer in humans: sphingosine and ceramide induce apoptosis in a human adenocarcinoma cell line and feeding sphingolipids to Min mice reduces the number of colon tumours.

Modulation of intracellular beta-catenin localization and intestinal tumorigenesis in vivo and in vitro by sphingolipids

Sphingolipid consumption suppresses colon carcinogenesis, but the specific genetic defect(s) that can be bypassed by these dietary components are not known. Colon tumors often have defect(s) in the adenomatous polyposis coli (APC)/beta-catenin regulatory system. Therefore, C57Bl/6J(Min/+) mice with a truncated APC gene product were fed diets supplemented with ceramide, sphingomyelin, glucosylceramide, lactosylceramide, and ganglioside G(D3) (a composition similar in amount and type to that of dairy products) to determine whether tumorigenesis caused by this category of genetic defect is suppressed. Sphingolipid feeding reduced the number of tumors in all regions of the intestine, and caused a marked redistribution of beta-catenin from a diffuse (cytosolic plus membrane) pattern to a more "normal" localization at mainly intercellular junctions between intestinal epithelial cells. The major digestion product of complex sphingolipids is sphingosine, and treatment of two human colon cancer cell lines in culture (SW480 and T84) with sphingosine reduced cytosolic and nuclear beta-catenin, inhibited growth, and induced cell death. Ceramides, particularly long-chain ceramides, also had effects. Thus, dietary sphingolipids, presumably via their digestion products, bypass or correct defect(s) in the APC/beta-catenin regulatory pathway. This may be at least one mechanism whereby dietary sphingolipids inhibit colon carcinogenesis, and might have implications for dietary intervention in human familial adenomatous polyposis and colon cancer.

Importance of sphingolipids and inhibitors of sphingolipid metabolism as components of animal diets

Sphingolipids are highly bioactive compounds that participate in the regulation of cell growth, differentiation, diverse cell functions, and apoptosis. They are present in both plant and animal foods in appreciable amounts, but little is known about their nutritional significance. Recent studies have shown that feeding sphingomyelin to female CF1 mice treated with a colon carcinogen (1,2-dimethylhydrazine) reduced the number of aberrant colonic crypt foci; longer-term feeding also affected the appearance of colonic adenocarcinomas. Therefore, dietary sphingolipids should be considered in studies of the relationships between diet and cancer. Sphingolipids have also surfaced as important factors in understanding the mechanism of action of a recently discovered family of mycotoxins, termed fumonisins. Fumonisins are produced by fungi commonly found on maize and a few related foods, and their consumption can result in equine leukoencephalomalacia, porcine pulmonary edema and a number of other diseases of veterinary animals and, perhaps, humans. A cellular target of fumonisins is the enzyme ceramide synthase, and disruption of sphingolipid metabolism by fumonisins has been established by studies with both cells in culture and animals that have consumed these toxic mycotoxins. These findings underscore the ways in which sphingolipids and agents that affect sphingolipid utilization should be given consideration in selecting animal diets for nutritional and toxicological studies.

Oral administration of semisynthetic sphingolipids promotes recovery of striatal dopamine concentrations in a murine model of parkinsonism

The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) administered to young C57/B16J black mice caused a striatal dopamine depletion that could be at least partially reversed by chronic intraperitoneal administration of GM1 ganglioside. The present study shows that the semisynthetic sphingolipids LIGA 4 (II3Neu-5-AcGgOse4-2-d-erythro-1,3-dihydroxy-2-acetamide-4-t rans-octadacene) and LIGA 20 (II3Neu-5-AcGgOse4-2-d-erythro-1,3-dihydroxy-2-chloro-acetam ide-4- trans-octadacene) are also effective in at least partially reversing MPTP-induced striatal dopamine depletions in mice after oral administration. These results suggest that semisynthetic ganglioside derivatives may be superior to the parent GM1 ganglioside for human clinical use.

Farber bodies found in murine phagocytes after injection of ceramides and related sphingolipids

Mice were injected subcutaneously with a single dose of sphingolipids. The sphingolipids tested were: ceramide with alpha-hydroxy fatty acids, ceramide with non-hydroxy fatty acids, glucocerebroside, sphingomyelin, and galactocerebroside. Lipids without sphingolipids served as a control. The mice were sacrificed 1, 2, 3, 4, 5 and 7 days after injection. Three mice were used for each experiment. The subcutaneous tissue at the injected area, the liver and the spleen were studied histologically. At 1-3 days after injection, numerous cytoplasmic inclusion bodies were observed in the macrophages and fibroblasts in the subcutaneous tissue, but not in the liver or the spleen. Ultrastructural studies of the inclusion bodies indicated that the sphingolipids taken up by the phagocytes retained their respective original shape during the 1-3 day stage. At days 4 and 5, the number of the inclusion bodies decreased, but they contained Farber bodies, i.e. curvilinear bodies 12 to 25 nm wide and up to 120 nm long. The mice with galactocerebroside were an exception, with parallel leaflets structures, but without the Farber bodies.