Background: Exosome, a type of extracellular vesicles, can associate with A␤ in vitro. Results: Intracerebrally injected exosomes trapped A␤ on surface glycosphingolipids and transported it into microglia in AD mouse brains, resulting in reductions in A␤ pathology. Conclusion: Exogenous exosomes act as potent scavengers for A␤ in mouse brains. Significance: The findings provide a novel therapeutic approach for AD.

a b s t r a c tElevated amyloid-b peptide (Ab) in brain contributes to Alzheimer's disease (AD) pathogenesis. We demonstrated the presence of exosome-associated Ab in the cerebrospinal fluid (CSF) of cynomolgus monkeys and APP transgenic mice. The levels of exosome-associated Ab notably decreased in the CSF of aging animals. We also determined that neuronal exosomes, but not glial exosomes, had abundant glycosphingolipids and could capture Ab. Infusion of neuronal exosomes into brains of APP transgenic mice decreased Ab and amyloid depositions, similarly to what reported previously on neuroblastoma-derived exosomes. These findings highlight the role of neuronal exosomes in Ab clearance, and suggest that their downregulation might relate to Ab accumulation and, ultimately, the development of AD pathology.

Objective:Recent studies indicate that sphingolipids, sphingomyelin (SM) and ceramide (Cer) are associated with the development of metabolic syndrome. However, detailed profiles of serum sphingolipids in the pathogenesis of this syndrome are lacking. Here we have investigated the relationship between the molecular species of sphingolipids in serum and the clinical features of metabolic syndrome, such as obesity, insulin resistance, fatty liver disease and atherogenic dyslipidemia.Subjects:We collected serum from obese (body mass index, BMI⩾35, n=12) and control (BMI=20−22, n=11) volunteers (18−27 years old), measured the levels of molecular species of SM and Cer in the serum by liquid chromatography-mass spectrometry and analyzed the parameters for insulin resistance, liver function and lipid metabolism by biochemical blood test.Results:The SM C18:0 and C24:0 levels were higher, and the C20:0 and C22:0 levels tended to be higher in the obese group than in the control group. SM C18:0, C20:0, C22:0 and C24:0 significantly correlated with the parameters for obesity, insulin resistance, liver function and lipid metabolism, respectively. In addition, some Cer species tended to correlate with these parameters. However, SM species containing unsaturated acyl chains and most of the Cer species were not associated with these parameters.Conclusions:The present results demonstrate that the high levels of serum SM species with distinct saturated acyl chains (C18:0, C20:0, C22:0 and C24:0) closely correlate with the parameters of obesity, insulin resistance, liver function and lipid metabolism, suggesting that these SM species are associated with the development of metabolic syndrome and serve as novel biomarkers of metabolic syndrome and its associated diseases.

Sea cucumber is a health-beneficial food, and contains a variety of physiologically active substances including glycosphingolipids. We show here the sphingoid base composition of cerebrosides prepared from sea cucumber and the cytotoxicity against human colon cancer cell lines. The composition of sphingoid bases prepared from sea cucumber was different from that of mammals, and the major constituents estimated from mass spectra had a branched C17-19 alkyl chain with 1-3 double bonds. The viability of DLD-1, WiDr and Caco-2 cells treated with sea cucumber sphingoid bases was reduced in a dose-dependent manner and was similar to that of cells treated with sphingosine. The sphingoid bases induced such a morphological change as condensed chromatin fragments and increased the caspase-3 activity, indicating that the sphingoid bases reduced the cell viability by causing apoptosis in these cells. Sphingolipids of sea cucumber might therefore serve as bioactive dietary components to suppress colon cancer.

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.

Carotenoids have been demonstrated to possess antioxidative and anti-inflammatory effects. However, there is no report that the effects of carotenoids on degranulation of mast cell is critical for type I allergy. In this study, we focused on the effect of carotenoids on antigen-induced degranulation of mast cells. Fucoxanthin, astaxanthin, zeaxanthin, and ␤-carotene significantly inhibited the antigen-induced release of ␤-hexosaminidase in rat basophilic leukemia 2H3 cells and mouse bone marrow-derived mast cells. Those carotenoids also inhibited antigen-induced aggregation of the high affinity IgE receptor (Fc⑀RI), which is the most upstream of the degranulating signals of mast cells. Furthermore, carotenoids inhibited Fc⑀RI-mediated intracellular signaling, such as phosphorylation of Lyn kinase and Fyn kinase. It suggests that the inhibitory effect of carotenoids on the degranulation of mast cells were mainly due to suppressing the aggregation of Fc⑀RI followed by intracellular signaling. In addition, those carotenoids inhibited antigen-induced translocation of Fc⑀RI to lipid rafts, which are known as platforms of the aggregation of Fc⑀RI. We assume that carotenoids may modulate the function of lipid rafts and inhibit the translocation of Fc⑀RI to lipid rafts. This is the first report that focused on the aggregation of Fc⑀RI to investigate the mechanism of the inhibitory effects on the degranulation of mast cells and evaluated the functional activity of carotenoids associated with lipid rafts.Mast cells play pivotal roles in inflammation and immediatetype allergic reactions by secreting biologically active substances including histamine, eicosanoids, proteolytic enzymes, cytokines, and chemokines. The antigen-induced aggregation of the high affinity IgE receptor (Fc⑀RI) 2 expressed on the cell surface triggers the degranulation of mast cells. Fc⑀RI has a tetrameric structure comprised of an IgE binding ␣-chain, a ␤-chain, and a disulfide-linked ␥-chain dimer (1). The aggregation of Fc⑀RI by means of multivalent antigen-IgE complexes activates cytosolic Src protein-tyrosine kinases, such as Fyn and Lyn, which then regulate the activation of mast cells (2). Fyn kinase plays a key role in mast cell degranulation and in cytokine production by regulating Gab2 and phosphatidylinositol 3-kinase (3). Phosphorylated Lyn activates immunoreceptor tyrosine-based activation motifs of the ␤-and ␥-chains, and the phosphorylated immunoreceptor tyrosine-based activation motifs of the ␥-chain phosphorylate Syk kinase. Thereafter, a number of other signaling and adaptor molecules, such as phospholipase C␥ and protein kinase C (PKC), are phosphorylated (4). Phospholipase C␥ catalyzes the generation both of inositol 1,4,5-trisphosphate and diacylglycerol. Inositol 1,4,5-trisphosphate is an inducer of intracellular Ca 2ϩ mobilization, which is critical for degranulation, and diacylglycerol is an activator of PKC (5). Activated PKC is translocated from the cytosol to the plasma membrane fraction. PKC regulates many functions of ma...

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Lipid transfer proteins mediate inter-organelle transport of membrane lipids at organelle contact sites in cells, playing fundamental roles in the lipidome and membrane biogenesis in eukaryotes. We previously developed a ceramide-mimetic compound as a potent inhibitor of the ceramide transport protein CERT. Here we develop CERT inhibitors with structures unrelated to ceramide. To this aim, we identify a seed compound with no ceramide-like structure but with the capability of forming a hydrogen-bonding network in the ceramidebinding START domain, by virtual screening of~3 × 10 6 compounds. We also establish a surface plasmon resonance-based system to directly determine the affinity of compounds for the START domain. Then, we subject the seed compound to a series of in silico docking simulations, efficient chemical synthesis, affinity analysis, protein-ligand co-crystallography, and various in vivo assays. This strategy allows us to obtain ceramide-unrelated compounds that potently inhibited the function of CERT in human cultured cells.