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PubMed2004

Altered de novo sphingolipid biosynthesis is involved in the serum deprivation-induced cell death in LLC-PK1 cells.

Fumonisin B1, a specific inhibitor of ceramide synthase, and ISPI (Myriocin), a serine palmitoyltransferase inhibitor, modulate the de novo sphingolipid biosynthesis pathway. This study was conducted to determine whether serum deprivation-induced cell death is regulated by de novo sphingolipid biosynthesis in pig kidney LLC-PK1 cells. Serum withdrawal from the culture medium produced cell death in LLC-PK1 cells. Fumonisin B1 at concentrations ranging from 5 M to 30 M delayed until 48 h this cell death resulting from the absence of fetal bovine serum (FBS) in cell culture. Pretreatment of cultured cells with fumonisin B1 in the presence of serum for 24 h increased by approximately 70% this cytoprotective activity of fumonisin B1 against serum deprivation-induced cell death. Serum deprivation increased sphingolipid biosynthesis threefold compared to 5% serum-enriched culture. Fumonisin B1 at 5-30 M lowered the content of total complex sphingolipids to levels of 50% and 77% of the content in serum-enriched culture, although the concentration of intracellular free sphinganine was elevated. ISP1 alone at greater than 1 nM concentration reduced total complex sphingolipid content to values in LLC-PK1 cells grown in the presence of 5% FBS. The results suggest that the de novo complex sphingolipid biosynthesis modulated by either fumonisin B1 or ISP1 may regulate serum deprivation-induced cell death in LLC-PK1 cells.

Animals↗
PubMed1992

Increases in serum sphingosine and sphinganine and decreases in complex sphingolipids in ponies given feed containing fumonisins, mycotoxins produced by Fusarium moniliforme.

Consumption of food contaminated with Fusarium moniliforme causes leucoencephalomalacia and hepatotoxicity in horses, pulmonary edema in pigs and liver cancer in rats, and has been correlated with esophageal cancer in humans. The causative agents are thought to be a family of compounds called fumonisins, which have recently been shown to be potent inhibitors of sphingosine (sphinganine) N-acyltransferase. Because inhibition at this step blocks the formation of complex sphingolipids while leading to accumulation of sphinganine, we hypothesized that exposure of animals to fumonisin-contaminated feed might be detected by analyses of serum sphingolipids. Within days of giving ponies feed contaminated with 15 to 44 micrograms/g fumonisin B1, there was an increase in the amount of free sphinganine (and sometimes sphingosine) and a reduction in complex sphingolipids. Free sphinganine and sphingosine decreased when ponies consumed less of the contaminated feed, and increased again when they consumed more fumonisin. When toxicosis was evident as indicated by other serum markers, complex sphingolipids as well as free sphingosine and sphinganine were elevated, probably due to loss of sphingolipids from dying cells. These findings establish that consumption of fumonisin-contaminated feed disrupts sphingolipid metabolism. Because the changes in sphinganine and sphingosine were seen before liver enzymes were noticeably elevated, they may be an early marker of exposure to fumonisins.

Animal Feed↗
PubMed2004

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.

1,2-Dimethylhydrazine↗
PubMed2006

The essential nature of sphingolipids in plants as revealed by the functional identification and characterization of the Arabidopsis LCB1 subunit of serine palmitoyltransferase.

Serine palmitoyltransferase (SPT) catalyzes the first step of sphingolipid biosynthesis. In yeast and mammalian cells, SPT is a heterodimer that consists of LCB1 and LCB2 subunits, which together form the active site of this enzyme. We show that the predicted gene for Arabidopsis thaliana LCB1 encodes a genuine subunit of SPT that rescues the sphingolipid long-chain base auxotrophy of Saccharomyces cerevisiae SPT mutants when coexpressed with Arabidopsis LCB2. In addition, homozygous T-DNA insertion mutants for At LCB1 were not recoverable, but viability was restored by complementation with the wild-type At LCB1 gene. Furthermore, partial RNA interference (RNAi) suppression of At LCB1 expression was accompanied by a marked reduction in plant size that resulted primarily from reduced cell expansion. Sphingolipid content on a weight basis was not changed significantly in the RNAi suppression plants, suggesting that plants compensate for the downregulation of sphingolipid synthesis by reduced growth. At LCB1 RNAi suppression plants also displayed altered leaf morphology and increases in relative amounts of saturated sphingolipid long-chain bases. These results demonstrate that plant SPT is a heteromeric enzyme and that sphingolipids are essential components of plant cells and contribute to growth and development.

Amino Acid Sequence↗
PubMed2004

Sphingolipid-free Leishmania are defective in membrane trafficking, differentiation and infectivity.

Sphingolipids are structural components of the eukaryotic plasma membrane that are involved, together with cholesterol, in the formation of lipid microdomains (rafts). Additionally, sphingolipid metabolites have been shown to modulate a wide variety of cellular events, including differentiation and apoptosis. To investigate the role of de novo sphingolipid biosynthesis in Leishmania, we have focused on serine palmitoyltransferase (SPT), which catalyses the first, rate-limiting step in the synthetic pathway. Genetic ablation of one SPT subunit, LmLCB2, yields viable null parasites that can no longer synthesize ceramide and sphingolipids de novo. Unexpectedly, LmLCB2 expression (and sphingolipid biosynthesis) is stage regulated in Leishmania, being undetectable in intramacrophage parasites. As expected from this observation, the LmLCB2 null mutants maintain infectivity in vivo. However, they are compromised in their ability to form infective extracellular parasites, correlating with a defect in association of the virulence factor, leishmanolysin or GP63, with lipid rafts during exocytosis and an observed relocalization of a second virulence factor, lipophosphogycan, during differentiation. Thus, de novo sphingolipid biosynthesis is critical for membrane trafficking events in extracellular Leishmania but has at best a minor role in intracellular pathogenesis.

Acyltransferases↗
PubMed2006

Distribution and dynamic changes of sphingolipids in blood in response to platelet activation.

BACKGROUND: Sphingolipids are signaling molecules in a range of biological processes. While sphingosine-1-phosphate (S1P) is thought to be abundantly stored in platelets and released upon stimulation, knowledge about the distribution and function of other sphingolipids in blood is lacking. OBJECTIVES: To analyze the sphingolipid content of blood components with special emphasis on dynamic changes in platelets. METHODS: Blood components from mice and humans were prepared by gradient centrifugation and analyzed by liquid chromatography-mass spectrometry. Additionally, murine platelets were activated in vitro and in vivo. RESULTS: Isolated non-activated platelets of mice were devoid of S1P, but instead contained dihydrosphingosine-1-phosphate (dhS1P), along with a high concentration of ceramide. Activation of platelets in vitro led to a loss of dhS1P and an increase in sphingosine, accompanied by a reduction of ceramide content. Platelet activation in vivo led to an immediate and continuous rise of dhS1P in plasma, while S1P remained stable. The sphingolipid distribution of human blood was markedly different from mice. Human platelets contained dhS1P in addition to S1P. CONCLUSIONS: Mouse platelets contain dhS1P instead of S1P. Platelet activation causes loss of dhS1P and breakdown of ceramide, implying ceramidase activation. Release of dhS1P from activated platelets might be a novel signaling pathway. Finally, the sphingolipid composition of mouse and human blood shows large differences, which must be considered when studying sphingolipid biology.

Animals↗
PubMed2005

Functional analysis of CaIPT1, a sphingolipid biosynthetic gene involved in multidrug resistance and morphogenesis of Candida albicans.

In the present study we describe the isolation and functional analysis of a sphingolipid biosynthetic gene, IPT1, of Candida albicans. The functional consequence of the disruption of both alleles of IPT1 was confirmed by mass analysis of its sphingolipid composition. The disruption of both alleles or a single allele of IPT1 did not lead to any change in growth phenotype or total sphingolipid, ergosterol, or phospholipid content of the mutant cells. The loss of mannosyl diinositol diphosphoceramide [M(IP)(2)C] in the ipt1 disruptant, however, resulted in increased sensitivity to drugs like 4-nitroquinoline oxide, terbinafine, o-phenanthroline, fluconazole, itraconazole, and ketoconazole. The increase in drug susceptibilities of ipt1 cells was linked to an altered sphingolipid composition, which appeared to be due to the impaired functionality of Cdr1p, a major drug efflux pump of C. albicans that belongs to the ATP binding cassette superfamily. Our confocal and Western blotting results demonstrated that surface localization of green fluorescent protein-tagged Cdr1p was affected in ipt1 disruptant cells. Poor surface localization of Cdr1p resulted in an impaired ability to efflux fluconazole and rhodamine 6G. The effect of mannosyl inositol phosphoceramide accumulation in the ipt1 mutant and the absence of M(IP)(2)C from the ipt1 mutant on the efflux of drug substrates was very selective. The efflux of methotrexate, a specific substrate of CaMdr1p, another major efflux pump of major facilitator superfamily, remained unaffected in ipt1 mutant cells. Interestingly, changes in sphingolipid composition affected the ability of mutant cells to form proper hyphae in various media. Taken together, our results demonstrate that an altered composition of sphingolipid, which is among the major constituents of membrane rafts, affects the drug susceptibilities and morphogenesis of C. albicans.

Antifungal Agents↗
PubMedDate not supplied

Sphingolipid signaling in epidermal homeostasis. Current knowledge and new therapeutic approaches in dermatology.

In the present review we have attempted to give an overview of the role of sphingolipids in skin homoeostasis. Sphingolipid metabolites are emerging as potent second messengers in diverse cellular signaling pathways. In the skin little is known about sphingolipids in signaling events. In various cell populations it has been shown that different sphingolipid metabolites have opposing effects on the biological outcome of a stimulus. Therefore, the term 'sphingolipid rheostat' has been established and has also been shown to exist in skin-derived cell populations. In many cells ceramide is a mediator of proliferation inhibition and apoptosis, whereas sphingosine-1-phosphate acts more like a growth factor and reverses ceramide effects. In keratinocytes extracellular and intracellular ceramides play important roles. Extracellular ceramides are necessary for the water retention capacity and for maintaining the permeability barrier of the skin. Intracellular ceramides cause differentiation of keratinocytes. Until now less is known about the effect of other sphingolipid metabolites in the skin.

Animals↗
PubMed2006

Sphingolipids in anticancer therapy.

Sphingolipids constitute a broad class of compounds with many biological functions. The sphingolipid metabolites ceramide and sphingosine are potent apoptosis inducers and produce cell cycle arrest, whereas sphingosine-1-phosphate promotes cellular growth and differentiation. Herein, the effects of sphingolipids and their analogs on diverse signaling pathways implicated in the apoptotic process are highlighted. The relatively simple chemical structure of these compounds has led to several strategies for their total synthesis. Those methods have contributed to the development and biological study of several analogs that present diverse degree of modification from the original structure. This article catalogues many of the recently developed synthetic analogs that act on diverse aspects of sphingolipid metabolism. A description of known enzyme inhibitors of the sphigolipids pathway is also given. Finally, diverse new sphingolipid-like antitumor agents isolated from marine sources are presented. This contribution opens the way for future development of new sphingolipid analogs that might be useful in cancer chemotherapy.

Antineoplastic Agents↗
PubMedDate not supplied

Fusion of Semliki Forest virus with cholesterol-containing liposomes at low pH: a specific requirement for sphingolipids.

Semliki Forest virus (SFV) utilizes a membrane fusion strategy to introduce its genome into the host cell. After binding to cell-surface receptors, virus particles are internalized through receptor-mediated endocytosis and directed to the endosomal cell compartment. Subsequently, triggered by the acid pH in the lumen of the endosomes, the viral envelope fuses with the endosomal membrane. As a result of this fusion reaction the viral RNA gains access to the cell cytosol. Low-pH-induced fusion of SFV, in model systems as well as in cells, has been demonstrated previously to be strictly dependent on the presence of cholesterol in the target membrane. In this paper, we show that fusion of SFV with cholesterol-containing liposomes depends on sphingomyelin (SM) or other sphingolipids in the target membrane, ceramide representing the sphingolipid minimally required for mediating the process. The action of the sphingolipid is confined to the actual fusion event, cholesterol being necessary and sufficient for low-pH-dependent binding of the virus to target membranes. The 3-hydroxyl group on the sphingosine backbone plays a key role in the SFV fusion reaction, since 3-deoxy-sphingomyelin does not support the process. This, and the remarkably low levels of sphingolipid required for half-maximal fusion (1-2 mol%), suggest that the sphingolipid does not play a structural role in SFV fusion, but rather acts as a cofactor, possibly through activation of the viral fusion protein. Domain formation between cholesterol and sphingolipid, although it may facilitate SFV fusion, is unlikely to play a crucial role in the process.

Animals↗
PubMed2001

Regulation of sphingolipid and glycosphingolipid metabolism in extrahepatic tissues by endotoxin.

The host response to infection and inflammation is associated with multiple alterations in lipid metabolism. We have shown that endotoxin [lipopolysaccharide (LPS)] stimulates hepatic sphingolipid synthesis and increases ceramide and glucosylceramide (GlcCer) content in circulating lipoproteins in Syrian hamsters. LPS also increases the activity and mRNA levels of serine palmitoyltransferase (SPT) and GlcCer synthase, the committed enzymes in sphingolipid and glycosphingolipid (GSL) synthesis, respectively, in the liver. To determine whether sphingolipid and GSL metabolism are regulated in other tissues during the host response to infection, we examined the effect of LPS on the regulation of SPT and GlcCer synthase in extrahepatic tissues in Syrian hamsters. LPS significantly increased SPT activity in spleen and kidney after 16 h of treatment, but had no effect on SPT activity in lung and brain, suggesting that the effect of LPS on sphingolipid metabolism is tissue specific. LPS also increased SPT mRNA levels in spleen and kidney by approximately 3-fold, suggesting that the increase in SPT activity is due to an increase in SPT mRNA expression. LPS significantly increased GlcCer synthase activity in spleen and kidney, and produced 4- and 15-fold increases in GlcCer synthase mRNA levels in spleen and kidney, respectively. LPS treatment increased GlcCer content by 1.3-fold in spleen and by 6.2-fold in kidney. LPS also increased the content of ceramide trihexoside by 1.7-fold in spleen. These results suggest that LPS regulates sphingolipid and GSL metabolism in spleen and kidney. An increase in GSL metabolites in spleen and kidney during the host response to infection and inflammation may be required for modulation of immune responses and regulation of cell growth. -- Memon, R. A., W. M. Holleran, Y. Uchida, A. H. Moser, C. Grunfeld, and K. R. Feingold. Regulation of sphingolipid and glycosphingolipid metabolism in extrahepatic tissues by endotoxin. J. Lipid Res. 2001. 42: 452--459.

Acyltransferases↗
PubMed2003

Metabolomic profiling of sphingolipids in human glioma cell lines by liquid chromatography tandem mass spectrometry.

Sphingolipids participate in membrane structure and signaling in neuronal cells, and an emerging strategy for control of gliomas is to inhibit growth and/or induce apoptosis using ceramide and ceramide analogs. Nonetheless, some sphingolipids (ceramides and sphingosine) induce and others (sphingosine 1-phosphate) inhibit apoptosis; therefore, when testing putative anti-cancer agents, it is critical to obtain precise knowledge of the types and quantities of not only the test compounds, but also their effects on endogenous species. Combination of liquid chromatography and tandem mass spectrometry affords a "metabolomic" profile of all of the intermediates of ceramide biosynthesis (3-ketosphinganine, sphinganine and dihydroceramides) and the direct products of ceramide metabolism (sphingomyelins and monohexosylceramides as well as sphingosine and sphingosine 1-phosphate). This method has been applied to four human glioma cell lines (LN18, LN229, LN319 and T98G), and differences in the amounts and types of sphingolipids were found. For example, LN229 and LN319 have approximately twice the sphingosine 1-phosphate of LN18 and T98G; LN229 and LN319 have more monohexosylceramides than lactosylceramides, whereas the opposite is the case for LN18 and T98G; and the fatty acyl chain distributions of the sphingolipids differ among the cell lines. The ability to obtain this type of "metabolomic" profile allows studies of how anti-cancer agents (especially sphingolipids and sphingolipid analogs) affect the amounts of these bioactive species, and may lead to a better understanding of the abnormal phenotypes of gliomas.

Astrocytoma↗
PubMed1993

Fumonisin B1 inhibits sphingosine (sphinganine) N-acyltransferase and de novo sphingolipid biosynthesis in cultured neurons in situ.

Fumonisins, mycotoxins produced by Fusarium moniliforme and a number of other fungi, cause neuronal degeneration, liver and renal toxicity, cancer, and other injury to animals. Recent work with rat hepatocytes (Wang, E., Norred, W. P., Bacon, C. W., Riley, R. T., and Merrill, A. H., Jr. (1991) J. Biol. Chem. 266, 14486-14490) found that fumonisins block sphingosine biosynthesis by inhibiting the conversion of sphinganine to dihydroceramides, which precedes introduction of the 4,5-trans-double bond of sphingosine. The current study utilized mouse cerebellar neurons in culture to evaluate how this affects the distribution of newly synthesized ceramides among different complex sphingolipids. Fumonisin B1 inhibited ceramide synthase in mouse brain microsomes with a competitive-like kinetic behavior with respect to both sphinganine and stearoyl-CoA. Fumonisin B1 inhibited sphingolipid biosynthesis in cultured cerebellar neurons in situ as reflected by accumulation of free sphinganine, a reduction in the mass of total sphingolipids, reductions in the incorporation of [14C]serine into glucosylceramide, lactosylceramide, sphingomyelin, and gangliosides (GM1, GD3, GD1a, GD1b, GT1b, and GQ1b), and inhibition of the incorporation of [14C]galactose and [3H]sphinganine into complex sphingolipids. Dose-response studies revealed that the labeling of sphingomyelin (IC50 of 0.7 microM) was more sensitive to inhibition by fumonisin B1 than was glycolipid formation (IC50 of approximately 7 microM) in these cells. A similar effect was seen when beta-fluoroalanine was added to inhibit the activity of serine palmitoyltransferase, the first enzyme of the pathway. The inhibition of complex sphingolipid synthesis was reversible, and nearly normal labeling profiles were obtained 48 h after removing the mycotoxin. These studies establish that fumonisin B1 inhibits de novo sphingolipid biosynthesis by neuronal cells and, moreover, that limiting ceramide synthesis differentially affects the formation of sphingomyelin versus glycosphingolipids.

Acyltransferases↗
PubMed1993

Differential metabolism and trafficking of sphingolipids in differentiated versus undifferentiated HT29 cells.

Trafficking and metabolism of sphingolipids were examined in undifferentiated (G+) and differentiated (G+ reversed) HT29 human colon adenocarcinoma cell lines. Metabolic experiments employing a fluorescently labeled sphingolipid precursor, 6-[N-(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]hexanoylceramide++ + (C6-NBD-ceramide) revealed that both qualitative and quantitative differences exist in sphingolipid synthesis between the 2 cell lines. One of the C6-NBD-sphingolipids synthesized in G+ cells is not found in the G+ reversed cells. Furthermore, the ratio of the 2 main products, C6-NBD-glucosylceramide and C6-NBD-sphingomyelin, differs: in G+ cells glucosylceramide is by far the main product, whereas G+ reversed cells synthesize C6-NBD-sphingomyelin in slight excess. Once established, these ratios of sphingolipids are quickly restored metabolically when distortion of the ratio is caused by experimental manipulation. This indicates that they represent a true metabolic equilibrium situation of the 2 sphingolipids in these cells, while the distinct ratios are mainly determined by the NBD-lipid pool in the plasma membrane. Preferential synthesis and transfer of glucosylceramide from its site of synthesis to the cell surface do not occur when the plasma membrane pool of glucosylceramide is selectively removed. This suggests that instantaneous replenishment via specific signalling is probably not involved as a mechanism in re-establishing perturbed lipid pools. In conjunction with observations on distinct lipid trafficking pathways of glucosylceramide in G+ and G+ reversed cells, the present metabolic studies emphasize a relation between the expression of this glycolipid and the state of differentiation of HT29 cells.

4-Chloro-7-nitrobenzofurazan↗
PubMed1992

Fumonisin inhibition of de novo sphingolipid biosynthesis and cytotoxicity are correlated in LLC-PK1 cells.

Fumonisins are a group of structurally related compounds produced by Fusarium moniliforme. Recently, it has been shown that fumonisins B1 and B2 are the first naturally occurring inhibitors of sphingosine and sphinganine N-acyltransferase (ceramide synthase) in rat primary hepatocytes (Wang et al. J. Biol. Chem. 266, 14, 486-14, 490, 1991). These enzymes are key components in the pathways for de novo sphingolipid biosynthesis and sphingolipid turnover. The results of the present study show that fumonisins B1 and B2 inhibit proliferation and are cytotoxic to LLC-PK1 cells. Concentrations of fumonisin B1 and B2 between 10 and 35 microM inhibited cell proliferation, whereas higher concentrations (greater than 35 microM) killed cells. Inhibition of cell proliferation and cell death were preceded by a lag period of at least 24 hr during which cells appeared to be functioning normally. Cells exposed to fumonisin B1 exhibited normal growth kinetics and morphology soon after fumonisin B1 was removed; thus, the effects of fumonisin B1 were reversible. The EC50 for alterations in sphingolipid biosynthesis was 10 to 15 microM. Inhibition of de novo sphingolipid biosynthesis occurred before inhibition of cell proliferation or cytotoxicity, and the dose response for the decrease in the [3H]sphingosine to [3H]sphinganine ratio at 7 hr closely paralleled the dose response for effects on proliferation and cytotoxicity at 3-5 days. In addition, the level of free sphinganine, and to a lesser extent sphingosine, increased in fumonisin-treated cells in a dose-dependent manner. During the 24-hr lag period preceding inhibition of cell proliferation, the free sphinganine content increased by 12,800% in cells exposed to 35 microM fumonisin B1. Whereas a mechanistic relationship between the inhibition of de novo sphingolipid biosynthesis and inhibition of proliferation and cell death has not been demonstrated, the results of this study support the hypothesis that inhibition of de novo sphingolipid biosynthesis is an early event in the toxicity of fumonisins to LLC-PK1 cells.

Acyltransferases↗
PubMed1994

Membrane fusion of Semliki Forest virus requires sphingolipids in the target membrane.

Enveloped animal viruses, such as Semliki Forest virus (SFV), utilize a membrane fusion strategy to deposit their genome into the cytosol of the host cell. SFV enters cells through receptor-mediated endocytosis, fusion of the viral envelope occurring subsequently from within acidic endosomes. Fusion of SFV has been demonstrated before to be strictly dependent on the presence of cholesterol in the target membrane. Here, utilizing a variety of membrane fusion assays, including an on-line fluorescence assay involving pyrene-labeled virus, we demonstrate that low-pH-induced fusion of SFV with cholesterol-containing liposomal model membranes requires the presence of sphingomyelin or other sphingolipids in the target membrane. The minimal molecular characteristics essential for supporting SFV fusion are encompassed by a ceramide. The action of the sphingolipids is confined to the actual fusion event, cholesterol being necessary and sufficient for low-pH-dependent binding of the virus to target membranes. Complex formation of the sphingolipids with cholesterol is unlikely to be important for the induction of SFV--liposome fusion, as sphingolipids that do not interact appreciably with cholesterol, such as galactosylceramide, effectively support the process. The remarkably low levels of sphingomyelin required for half-maximal fusion (1-2 mole%) suggest that sphingolipids do not play a structural role in the SFV fusion process, but rather act as a cofactor, possibly activating the viral fusion protein in a specific manner.

Acids↗
PubMed2002

Identification of a novel role for sphingolipid signaling in TNF alpha and ischemic preconditioning mediated cardioprotection.

TNF alpha administration mimics ischemic preconditioning and neutralizing antibodies to TNF alpha and IL-1 beta abolish exercise-induced preconditioning. However, the pharmacology of TNF alpha's cardioprotective effects and associated downstream signaling events has not been delineated. We evaluated the temporal and dose specific requirements of TNF alpha to function as a preconditioning mimetic. Furthermore we postulated that the preconditioning effect of TNF alpha might be orchestrated via sphingolipid signaling. The cardioprotective effect of TNF alpha and the role of sphingolipid signaling were assessed using a classical preconditioning protocol in the isolated perfused rat heart with the measurement of infarct size and contractile function modulation in response to index ischemia and reperfusion. Recombinant TNF alpha at an optimal dose of 0.5 ng/ml mimicked ischemic preconditioning by reducing infarct size by 60%v non-preconditioned ischemia-reperfusion controls (P<0.01). The infarct sparing effect of TNF alpha required a wash-out period prior to the index ischemic-reperfusion. Moreover, the classic ischemic preconditioning antagonist such as 5-hydroxydecanoate abolished TNF alpha preconditioning. An inhibitor of the sphingolipid signaling pathway, N-oleoylethanolamine (NOE, 1 microm) attenuated ischemic and TNF alpha preconditioning. Likewise, cell-permeable C(2)-ceramide and sphingosine 1-phosphate (sphingolipid signaling intermediates) both reproduced the preconditioning cardioprotective phenotype. Finally, TNF alpha and ceramide conferred preconditioning-like cardioprotection against post-ischemic contractile dysfunction and this cardioprotective effect was attenuated by NOE. In contrast, NOE did not reverse ischemic preconditioning enhanced post-ischemic contractile function. In conclusion, TNF alpha activates preconditioning-like tolerance against infarction and contractile dysfunction. This cardioprotection is mediated, in part, via activation of novel sphingolipid signaling intermediates.

Animals↗
PubMed2006

Simultaneous production of sphingolipids and ethanol by Kluyveromyces thermotolerans.

Kluyveromyces thermotolerans strain NBRC 1674 was selected for the simultaneous production of sphingolipids and ethanol from beet molasses. The strain gradually synthesized ethanol with fermentation periods and attained a level slightly higher than that of the strain of Saccharomyces cerevisiae usually used for ethanol production. The sphingolipids accumulated in the cells were composed of almost equal amounts of free ceramides and glucosylceramides. The sphingoid bases and fatty acids of the two sphingolipids differed from each other and changed under aerobic and anaerobic growth conditions. Oxygen limitation may cause accumulation of sphinganine by inhibiting sphingolipid desaturases and enhance its proportion in both the sphingolipids.

Anaerobiosis↗