Kazuhiko Aida

Intestinal absorption of dietary maize glucosylceramide in lymphatic duct cannulated rats

Sphingolipids are ubiquitous in all eukaryotic organisms. Various physiological functions of dietary sphingolipids, such as preventing colon cancer and improving the skin barrier function, have been recently reported. One of the common sphingolipids used as a foodstuff is glucosylceramide from plant sources, which is composed of sphingoid bases distinct from those of mammals. However, the fate of dietary sphingolipids derived from plants is still not understood. In this study, we investigated the absorption of maize glucosylceramide in the rat intestine using a lipid absorption assay of lymph from the thoracic duct. The free and complex forms of trans-4,cis-8-sphingadienine, the predominant sphingoid base of maize glucosylceramide, were found in the lymph after administration of maize glucosylceramide. This plant type of sphingoid base was detected in the ceramide fraction and N-palmitoyl-4,8-sphingadienine (C16:0-d18:2) and N-tricosanoyl-4,8-sphingadienine (C23:0-d18:2) were identified by LC-MS/MS. The cumulative recovery of 4t,8c-sphingadienine in the lymph was very low. These results indicate that dietary glucosylceramide originating from higher plants is slightly absorbed in the intestine and is incorporated into ceramide structures in the intestinal cells. However, it appears that the intact form of sphingoid bases is not reutilized well in the tissues.

Effect of dietary wine pomace extract and oleanolic acid on plasma lipids in rats fed high-fat diet and its DNA microarray analysis.

The aim of this study was to evaluate the concentration of oleanolic acids (OA) in pomace, a winemaking byproduct, and its influence on the levels of plasma lipids in rats fed a high-fat diet and on hepatic gene expression using DNA microarray analysis in vivo. HPLC analyses of pomace ethanol extract (PEE) revealed a high amount of OA ranging from 4 to 11 g/100 g. Male Sprague-Dawley rats were fed a normal-fat diet (NF group), a high-fat diet with 21% lard (HF group), a high-fat diet with 0.05% OA (OA group, 50 mg/kg/day), or a high-fat diet with 0.45% PEE (PEE group, 450 mg/kg/day). Plasma triacylglycerol and phospholipid concentrations were significantly lower in the OA and PEE groups than in the HF group. The microarray analysis of hepatic mRNA revealed reduced expression levels of lipogenic genes including acetyl-CoA carboxylase and glycerol-3-phosphate acyltransferase, probably resulting from the suppression of transcription factor Srebf1 expression. Gene expression of gluconeogensis and inflammatory cytokines was also down-regulated in the OA and PEE groups, suggesting that administration of OA or PEE could ameliorate obesity-induced insulin resistance, as well as prevent hyperlipidemia.

Dietary sphingolipids improve skin barrier functions via the upregulation of ceramide synthases in the epidermis

Sphingolipids are ubiquitous in eukaryotic organisms and are significant components in foods. It has been reported that treatment with sphingolipids prevents colon cancer, improves skin barrier function and suppresses inflammatory responses. However, the mechanisms for those effects of dietary sphingolipids are not well understood. In this study, to investigate the effects of dietary glucosylceramide (GluCer) and sphingomyelin (SM) on skin function, we characterized the recovery of skin barrier function and the change in sphingolipid metabolism‐related enzymes in the epidermis using a special Mg‐deficient diet–induced atopic dermatitis‐like skin and tape‐stripping damaged skin murine models. Our results show that dietary GluCer and SM accelerate the recoveries of damaged skin barrier functions. Correspondingly, dietary sphingolipids significantly upregulated the expression of ceramide synthases 3 and 4 in the epidermis of the atopic dermatitis‐like skin model (P < 0.05). In the case of cultured cells, the expression of ceramide synthases 2‐4 in normal human foreskin keratinocytes was significantly upregulated by treatment with 0.001–0.1 μm sphingoid bases (sphinganine, sphingosine and trans‐4,cis‐8‐sphingadienine) (P < 0.05). These results suggest that the effects of dietary sphingolipids might be due to the activation of ceramide synthesis in the skin, rather than the direct reutilization of dietary sphingolipids. Our findings provide a novel insight into the mechanisms of the skin barrier improving effect and a more comprehensive understanding of dietary sphingolipids.

Analysis of sphingolipid classes and their contents in meals.

Sphingolipids have attracted attention as physiologically functional lipids. We determined their class and content in Japanese meals that had been prepared by a nutritionist, mainly by using HPLC-ELSD. In all 12 meals tested, cerebroside and/or sphingomyelin were generally detected as the major sphingolipids. The total amounts of sphingolipids in typical high- and low-calorie meal samples over 2 days were 292 and 128 mg/day, and 81 and 45 mg/day, respectively.

Identification of Glucosylceramides Containing Sphingatrienine in Maize and Rice Using Ion Trap Mass Spectrometry

We characterized the glucosylceramide moieties from maize and rice using liquid chromatography-ion trap mass spectrometry. Glucosylceramides containing 4,8-sphingadienine (d18:2) acylated to hydroxy-fatty acids were detected as the predominant molecules both in maize and in rice. In addition, 4-hydroxy-8-sphingenine (t18:1) and sphingatrienine (d18:3) were found in maize and rice glucosylceramides, and in the case of rice, sphingenine (d18:1) was also detected. Glucosylceramides containing d18:3 were acylated to hydroxyl fatty acids (16–24 carbon atoms). Our results indicate the presence of the triene type of sphingoid base in higher plants.

Effects of Dietary Plant-Origin Glucosylceramide on Bowel Inflammation in DSS-Treated Mice

The effects of dietary plant-origin glucosylceramide (GlcCer) on symptoms similar to those of inflammatory bowel diseasewere investigated in dextran sulfate sodium salt (DSS)-treated mice. Dietary GlcCer suppressed decreases in body weight due to DSS administration. To determine its effects on the colon, we examined its surface under a microscope following toluidine blue staining. Dietary GlcCer decreased DSS-induced chorionic crypt injury and elevated myeloperoxidase levels. Moreover, dietary GlcCer significantly suppressed the production of cytokines by the intestinal mucosa. These results provide evidence for the suppression of DSS-induced inflammation by dietary GlcCer.

Effects of Dietary Plant-origin Glucosylceramide on Colon Cytokine Contents in DMH-treated Mice

In this study, the effects of dietary plant-origin glucosylceramide (GlcCer) on colon cytokine contents were investigated in 1,2-dimethylhydrazine (DMH)-treated mice, a model of colon cancer. DMH treatment induced the formation of aberrant crypt foci (ACF) and the production of inflammatory cytokines and chemokaines. Dietary GlcCer suppressed ACF formation and cytokine production in these mice. In particular, chemokine production was suppressed by dietary GlcCer. These GlcCer-related trends of suppression were similar to those observed in our previous study on dextran sulfate sodium salt (DSS)-treated mice. These results provide further evidence for the suppression of DMH-induced inflammation by dietary GlcCer.

Selective Absorption of Dietary Sphingoid Bases from the Intestine via Efflux by P-Glycoprotein in Rats

Various physiological functions of dietary sphingolipids, such as preventing inflammation and improving the skin barrier function, have been recently demonstrated. The sphingolipid most commonly used as a foodstuff is glucosylceramide from plant sources, which is composed of sphingoid bases that are distinctive from those found in mammals. Although the structure of sphingoid bases in higher plants is more complicated than the structure of those in mammals, the fate of dietary sphingolipids of plant origin is still not understood. In the present study, we investigated the absorption of 4,8-sphingadienine that originated from maize glucosylceramide in the rat intestine by using a lipid absorption assay of lymph collected from the thoracic duct. The cumulative recovery of 4,8-sphingadienine in the lymph was lower than that of sphingosine. Verapamil, a P-glycoprotein inhibitor, significantly increased the absorption of 4,8-sphingadienine but did not affect the absorption of sphingosine. Plant-derived sphingoid bases were detected in the ceramide fraction of lymph fluid by using liquid chromatography-mass spectrometry analysis. These results indicate that 4,8-sphingadienine that originates from the glucosylceramide of higher plants is poorly absorbed in the intestine because of efflux by P-glycoprotein and can be incorporated into a ceramide moiety, at least in part, in intestinal endothelial cells.

Effects of Plant Sphingolipids on Inflammatory Stress in Differentiated Caco-2 Cells

To determine the mechanism underlying the anti-inflammatory effects of plant sphingolipids, especially plant glucosylceramide (GlcCer), the effects of plant sphingolipids on inflammatory stress in differentiated Caco-2 cells were compared to those of a sphingolipid of animal origin, galactosylceramide (GalCer). Addition of GlcCer or GalCer suppressed cell injury caused lipopolysaccharide (LPS)- and TNF-α-induced inflammatory stress and induction of apoptosis in differentiated Caco-2 cells. There was no difference in the suppressive effect between GlcCer and GalCer. The inflammatory cytokines and chemokines induced by LPS were suppressed by GlcCer. GlcCer remained on the cell surface. The results of this study can be summarized as follows: 1) sphingolipids such as GlcCer have potent anti-inflammatory effects; 2) GlcCer suppresses LPS-induced production of cytokines and apoptosis; 3) sphingolipids may remain on the surface of cells, and 4) the chemical properties of sphingolipids may prevent the interaction between LPS and its receptor.