Evaluation of synthetic sphingolipid analogs as ligands for peroxisome proliferator-activated receptors

A Decrease in the Hardness of Feces with Added Glucosylceramide Extracted from Koji In Vitro-A Working Hypothesis of Health Benefits of Dietary Glucosylceramide

Skin barrier function, prevent colon cancer, head and neck cancer, and decrease liver cholesterol. However, the mechanism of action has not yet been elucidated. In this study, we propose a new working hypothesis regarding the health benefits and functions of glucosylceramide: decreased fecal hardness. This hypothesis was verified using an in vitro hardness test. The hardness of feces supplemented with glucosylceramide was significantly lower than that of the control. Based on these results, a new working hypothesis of dietary glucosylceramide was conceived: glucosylceramide passes through the small intestine, interacts with intestinal bacteria, increases the tolerance of these bacteria toward secondary bile acids, and decreases the hardness of feces, and these factors synergistically result in in vivo effects. This hypothesis forms the basis for further studies on the health benefits and functions of dietary glucosylceramides.

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.

Pseudoceramide stimulates peroxisome proliferator-activated receptor-α expression in a murine model of atopic dermatitis: molecular basis underlying the anti-inflammatory effect and the preventive effect against steroid-induced barrier impairment

Topical pseudoceramides are successfully used in skin barrier repair therapy for atopic dermatitis (AD) and demonstrated to reduce the adverse effects of topical glucocorticoids (GC). However, the molecular mechanisms involved are not fully understood. We investigated whether PC-9S (myristoyl/palmitoyloxostearamide/arachamide MEA, Neopharm, Daejeon, Korea), one of the synthetic pseudoceramides, could stimulate peroxisome proliferator-activated receptor (PPAR)α expression in a hapten [oxazolone (oxa)]-induced AD murine model (oxa-AD mice) and subsequently improved permeability barrier, reduced inflammation, and increased antimicrobial peptides (AMPs) expression. Normal hairless mice and oxa-AD mice were topically treated twice daily with either PC-9S-containing physiologic lipid mixture (PLM), vehicle (PLM), or PPARα agonist for 4 days. Topical PC-9S significantly increased PPARα expression in mouse epidermis in vivo and in oxa-AD mice skin comparable with PPARα agonist. Topical PC-9S-containing PLM significantly reduced basal trans-epidermal water loss (TEWL), surface pH, and mast cell infiltrates and prevented the decline of AMPs expression in oxa-AD mice, which were abrogated by PPARα antagonist. Then, oxa-AD mice were treated with super-potent topical GC twice daily for 4 days with or without PC-9S co-applications. Co-treatment with PC-9S-containing PLM suppressed GC-induced increase in basal TEWL, epidermal thinning, reduced loricrin expression, and impaired barrier recovery and these effects were attenuated by PPARα antagonist. Collectively, our findings suggest that pseudoceramide PC-9S-induced stimulation of PPARα expression provides a new mechanism by which pseudoceramides show anti-inflammatory property, improve the permeability and antimicrobial barrier function, and prevent the negative effects of topical GC.

Increased dihydroceramide/ceramide ratio mediated by defective expression of degs1 impairs adipocyte differentiation and function

Adipose tissue dysfunction is an important determinant of obesity-associated, lipid-induced metabolic complications. Ceramides are well-known mediators of lipid-induced insulin resistance in peripheral organs such as muscle. DEGS1 is the desaturase catalyzing the last step in the main ceramide biosynthetic pathway. Functional suppression of DEGS1 activity results in substantial changes in ceramide species likely to affect fundamental biological functions such as oxidative stress, cell survival, and proliferation. Here, we show that degs1 expression is specifically decreased in the adipose tissue of obese patients and murine models of genetic and nutritional obesity. Moreover, loss-of-function experiments using pharmacological or genetic ablation of DEGS1 in preadipocytes prevented adipogenesis and decreased lipid accumulation. This was associated with elevated oxidative stress, cellular death, and blockage of the cell cycle. These effects were coupled with increased dihydroceramide content. Finally, we validated in vivo that pharmacological inhibition of DEGS1 impairs adipocyte differentiation. These data identify DEGS1 as a new potential target to restore adipose tissue function and prevent obesity-associated metabolic disturbances.

CerS2 haploinsufficiency inhibits β-oxidation and confers susceptibility to diet-induced steatohepatitis and insulin resistance

Inhibition of ceramide synthesis prevents diabetes, steatosis, and cardiovascular disease in rodents. Six different ceramide synthases (CerS) that differ in tissue distribution and substrate specificity account for the diversity in acyl-chain composition of distinct ceramide species. Haploinsufficiency for ceramide synthase 2 (CerS2), the dominant isoform in the liver that preferentially makes very-long-chain (C22/C24/C24:1) ceramides, led to compensatory increases in long-chain C16-ceramides and conferred susceptibility to diet-induced steatohepatitis and insulin resistance. Mechanistic studies revealed that these metabolic effects were likely due to impaired β-oxidation resulting from inactivation of electron transport chain components. Inhibiting global ceramide synthesis negated the effects of CerS2 haploinsufficiency in vivo, and increasing C16-ceramides by overexpressing CerS6 recapitulated the phenotype in isolated, primary hepatocytes. Collectively, these studies reveal that altering sphingolipid acylation patterns impacts hepatic steatosis and insulin sensitivity and identify CerS6 as a possible therapeutic target for treating metabolic diseases associated with obesity.

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.

Microarray analysis of the intestinal host response in Giardia duodenalis assemblage E infected calves

Despite Giardia duodenalis being one of the most commonly found intestinal pathogens in humans and animals, little is known about the host-parasite interactions in its natural hosts. Therefore, the objective of this study was to investigate the intestinal response in calves following a G. duodenalis infection, using a bovine high-density oligo microarray to analyze global gene expression in the small intestine. The resulting microarray data suggested a decrease in inflammation, immune response, and immune cell migration in infected animals. These findings were examined in more detail by histological analyses combined with quantitative real-time PCR on a panel of cytokines. The transcription levels of IL-6, IL-8, IL-13, IL-17, and IFN-γ showed a trend of being downregulated in the jejunum of infected animals compared to the negative controls,.No immune cell recruitment could be seen after infection, and no intestinal pathologies, such as villus shortening or increased levels of apoptosis. Possible regulators of this intestinal response are the nuclear peroxisome proliferator-activated receptors alpha (PPARα), and gamma (PPARγ) and the enzyme adenosine deaminase (ADA), all for which an upregulated expression was found in the microarray and qRT-PCR analyses.

Metabolomics with LC-QTOF-MS permits the prediction of disease stage in aortic abdominal aneurysm based on plasma metabolic fingerprint

Abdominal aortic aneurysm (AAA) is a permanent and localized aortic dilation, defined as aortic diameter ≥3 cm. It is an asymptomatic but potentially fatal condition because progressive enlargement of the abdominal aorta is spontaneously evolving towards rupture.

Biomarkers may help to explain pathological processes of AAA expansion, and allow us to find novel therapeutic strategies or to determine the efficiency of current therapies. Metabolomics seems to be a good approach to find biomarkers of AAA. In this study, plasma samples of patients with large AAA, small AAA, and controls were fingerprinted with LC-QTOF-MS. Statistical analysis was used to compare metabolic fingerprints and select metabolites that showed a significant change. Results presented here reveal that LC-QTOF-MS based fingerprinting of plasma from AAA patients is a very good technique to distinguish small AAA, large AAA, and controls. With the use of validated PLS-DA models it was possible to classify patients according to the disease stage and predict properly the stage of additional AAA patients. Identified metabolites indicate a role for sphingolipids, lysophospholipids, cholesterol metabolites, and acylcarnitines in the development and progression of AAA. Moreover, guanidinosuccinic acid, which mimics nitric oxide in terms of its vasodilatory action, was found as a strong marker of large AAA.

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

Background

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that regulate lipid and glucose metabolism. PPARα is highly expressed in the liver and controls genes involved in lipid catabolism. We previously reported that synthetic sphingolipid analogs, part of which contains shorter-length fatty acid chains than natural sphingolipids, stimulated the transcriptional activities of PPARs. Sphingosine and dihydrosphingosine (DHS) are abundant sphingoid bases, and ceramide and dihydroceramide are major ceramide species in mammals. In contrast, phytosphingosine (PHS) and DHS are the main sphingoid bases in fungi. PHS and phytoceramide exist in particular tissues such as the epidermis in mammals, and involvement of ceramide species in PPARβ activation in cultured keratinocytes has been reported. The purpose of the present study is to investigate whether natural sphingolipids with C18 fatty acid and yeast-derived sphingoid bases activate PPARs as PPAR agonists.

Method

Lipids of brewer's yeast contain PHS- and DHS-based sphingolipids. To obtain the sphingoid bases, lipids were extracted from brewer's yeast and acid-hydrolyzed. The sphingoid base fraction was purified and quantified. To assess the effects of sphingolipids on PPAR activation, luciferase reporter assay was carried out. NIH/3T3 and human hepatoma (HepG2) cells were transfected with expression vectors for PPARs and retinoid × receptors, and PPAR responsive element reporter vector. When indicated, the PPAR/Gal4 chimera system was performed to enhance the credibility of experiments. Sphingolipids were added to the cells and the dual luciferase reporter assay was performed to determine the transcriptional activity of PPARs.

Results

We observed that phytoceramide increased the transcriptional activities of PPARs significantly, whereas ceramide and dihydroceramide did not change PPAR activities. Phytoceramide also increased transactivation of PPAR/Gal4 chimera receptors. Yeast-derived sphingoid base fraction, which contained PHS and DHS, or authentic PHS or DHS increased PPAR-dependent transcription. Additionally, phytoceramide stimulated PPARα activity in HepG2 hepatocytes, suggesting that phytoceramide activates genes regulated by PPARα.

Conclusions

Phytoceramide and yeast-derived sphingoid bases activate PPARs, whereas ceramide and dihydroceramide do not change the PPAR activity. The present findings suggest that phytoceramide acts as a PPAR ligand that would regulate PPAR-targeted genes.