Involvement of nitric oxide in cerebroside-induced defense responses and taxol production in Taxus yunnanensis suspension cells

This work was to characterize the generation of nitric oxide (NO) in Taxus yunnanensis cells induced by a fungal-derived cerebroside and the signal role of NO in the elicitation of plant defense responses and taxol production. (2S,2'R,3R,3'E,4E,8E)-1-O-beta-D-glucopyranosyl-2-N-(2'-hydroxy-3'-octadecenoyl)-3-hydroxy-9-methyl-4,8-sphingadienine at 10 microg/ml induced a rapid and dose-dependent NO production in the Taxus cell culture, reaching a maximum within 5 h of the treatment. The NO donor sodium nitroprusside (SNP) potentiated cerebroside-induced H(2)O(2) production and cell death. Inhibition of nitric oxide synthase activity by phenylene-1,3-bis(ethane-2-isothiourea) dihydrobromide or scavenging NO by 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide partially blocked the cerebroside-induced H(2)O(2) production and cell death. Moreover, NO enhanced cerebroside-induced activation of phenylalanine ammonium-lyase and accumulation of taxol in cell cultures. These results are suggestive of a role for NO as a new signal component for activating the cerebroside-induced defense responses and secondary metabolism activities of plant cells.

Structure and biological functions of fungal cerebrosides

Ceramide monohexosides (CMHs, cerebrosides) are glycosphingolipids composed of a hydrophobic ceramide linked to one sugar unit. In fungal cells, CMHs are very conserved molecules consisting of a ceramide moiety containing 9-methyl-4,8-sphingadienine in amidic linkage to 2-hydroxyoctadecanoic or 2-hydroxyhexadecanoic acids, and a carbohydrate portion consisting of one residue of glucose or galactose. 9-Methyl 4,8-sphingadienine-containing ceramides are usually glycosylated to form fungal cerebrosides, but the recent description of a ceramide dihexoside (CDH) presenting phytosphingosine in Magnaporthe grisea suggests the existence of alternative pathways of ceramide glycosylation in fungal cells. Along with their unique structural characteristics, fungal CMHs have a peculiar subcellular distribution and striking biological properties. In Pseudallescheria boydii, Candida albicans, Cryptococcus neoformans, Aspergillus nidulans, A. fumigatus, and Schizophyllum commune, CMHs are apparently involved in morphological transitions and fungal growth. The elucidation of structural and functional aspects of fungal cerebrosides may therefore contribute to the design of new antifungal agents inhibiting growth and differentiation of pathogenic species.

[Study of ceramide monohexoside in ovarian cell line COC1/DDP resistant to cisplantin]

OBJECTIVE

To investigate the effect of ceramide monohexoside (CMH) on resistance to cisplatin and apoptosis in ovarian cell line COC1/DDP, and to provide new ideals and clues to seek new effective methods for studying the mechanism and reversing the resistance in ovarian cell line as well.

METHODS

COC1 cells and COC1/DDP cells (before and after the treatment of mifepristone) were collected and neutral glycosphingolipids (N-GSLs) of the cells was isolated and purified, changes of CMH content were analyzed by high performance thin layer chromatography (HPTLC). The COC1/DDP cells were divided into three groups, one treated by cisplatin, one treated by mifepristone, the other treated by cisplatin and mifepristone. The survival rate of cells in three groups were evaluated by the methyl thiazolyl tetrazolium (MTT) assay, DNA ladders were presented by DNA gel electrophoresis, the forms of cells were observed by transmission electron microscope (TEM).

RESULTS

The levels of CMH were (37.1 +/- 3.3)% in COC1/DDP, higher than that in COC1 (14.1 +/- 1.4)% (P < 0.001). After treating by 1.25, 5 micro mol/L mifepristone, the CMH were (26.6 +/- 2.6)% (P < 0.05) and (17.5 +/- 0.7)% (P < 0.001), respectively. Mifepristone had no effect on the viability of COC1/DDP cell below a concentration of 5 micro mol/L. But when mifepristone of 1.25 or 5 micro mol/L combined with cisplatin at a concentration of 0.1, 0.25, 0.5, 1.25, 2.5 micro g/ml, the inhibition rate of COC1/DDP cell is higher than that of COC1/DDP cells only treated by cisplatin at the concentration of 0.1 to 2.5 micro g/ml (P < 0.001). The combined treatment elicited DNA fragmentation, however, neither cisplatin of 1.25 micro g/ml nor mifepristone of 5 micro mol/L alone could potentiate DNA fragmentation. After the combined treatment, the COC1/DDP cells produced apoptosis body.

CONCLUSIONS

CMH is related with resistance to cisplantin in ovarian cell line COC1/DDP. When CMH of COC1/DDP cells was inhibited by mifepristone, the cells were sensitive to cisplatin and apoptosis was elicited.

Human antibodies against a purified glucosylceramide from Cryptococcus neoformans inhibit cell budding and fungal growth

A major ceramide monohexoside (CMH) was purified from lipidic extracts of Cryptococcus neoformans. This molecule was analyzed by high-performance thin-layer chromatography (HPTLC), gas chromatography coupled with mass spectrometry, and fast atom bombardment-mass spectrometry. The cryptococcal CMH is a beta-glucosylceramide, with the carbohydrate residue attached to 9-methyl-4,8-sphingadienine in amidic linkage to 2-hydroxyoctadecanoic acid. Sera from patients with cryptococcosis and a few other mycoses reacted with the cryptococcal CMH. Specific antibodies were purified from patients' sera by immunoadsorption on the purified glycolipid followed by protein G affinity chromatography. The purified antibodies to CMH (mainly immunoglobulin G1) bound to different strains and serological types of C. neoformans, as shown by flow cytofluorimetry and immunofluorescence labeling. Transmission electron microscopy of yeasts labeled with immunogold-antibodies to CMH and immunostaining of isolated cell wall lipid extracts separated by HPTLC showed that the cryptococcal CMH predominantly localizes to the fungal cell wall. Confocal microscopy revealed that the beta-glucosylceramide accumulates mostly at the budding sites of dividing cells with a more disperse distribution at the cell surface of nondividing cells. The increased density of sphingolipid molecules seems to correlate with thickening of the cell wall, hence with its biosynthesis. The addition of human antibodies to CMH to cryptococcal cultures of both acapsular and encapsulated strains of C. neoformans inhibited cell budding and cell growth. This process was complement-independent and reversible upon removal of the antibodies. The present data suggest that the cryptococcal beta-glucosylceramide is a fungal antigen that plays a role on the cell wall synthesis and yeast budding and that antibodies raised against this component are inhibitory in vitro.

Modulation of GABA(A) receptors and inhibitory synaptic currents by the endogenous CNS sleep regulator cis-9,10-octadecenoamide (cOA)

1. Cis-9,10-octadecenoamide (cOA) accumulates in the CSF of sleep-deprived cats and may represent a novel signalling molecule. Synthetic cOA has been shown to induce physiological sleep when injected into laboratory rats. Here we assess the cellular mode of action of cOA in vitro. 2. In all rat cultured cortical neurones (pyramidal cells) examined, the synthetic brain lipid (3.2-64 microM) enhanced the responses to subsaturating GABA concentrations (up to circa 2x) in a concentration-dependent manner (EC50, circa 15 microM). 3. (20 microM) cOA significantly enhanced the affinity of exogenous GABA for its receptor without changing the Hill slope or the maximal response. These effects were not voltage-dependent or secondary to shifts in E(Cl). 4. In the absence of GABA, cOA directly evoked small inhibitory currents in a subpopulation (<7%) of sensitive cells. 5. 20 microM cOA reversibly enhanced the duration of spontaneous inhibitory post synaptic currents (circa 2 fold) without significantly altering their amplitude. 6. At 32-64 microM, cOA reversibly reduced the incidence and amplitude of both inhibitory post synaptic currents (i.p.s.cs) and excitatory post synaptic currents (e.p.s.cs) in the cultured neuronal circuits in common with other depressant drugs acting at the GABA(A) receptor. 7. 32 microM Oleic acid did not modulate exogenous GABA currents or synaptic activity suggesting that cOAs actions are mediated through a specific receptor. 8. A specific, protein-dependent interaction with GABA(A) receptors was confirmed in Xenopus oocytes. Recombinant human receptors were modulated by 10 microM cOA (and diazepam) only when a gamma2 subunit was co-expressed with alpha1beta2: the cOA response was not sensitive to the specific benzodiazepine antagonist flumazenil (1 microM). 9. cOA may represent an endogenous ligand for allosteric modulatory sites on isoforms of GABA(A) receptors which are crucial for the regulation of arousal and have recently been implicated in the circadian control of physiological sleep.

Brain lipids that induce sleep are novel modulators of 5-hydroxytrypamine receptors

Amide derivatives of fatty acids were recently isolated from cerebrospinal fluid of sleep-deprived animals and found to induce sleep in rats. To determine which brain receptors might be sensitive to these novel neuromodulators, we tested them on a range of receptors expressed in Xenopus oocytes. cis-9,10-Octadecenamide (ODA) markedly potentiated the action of 5-hydroxytryptamine (5-HT) on 5-HT2A and 5-HT2C receptors, but this action was not shared by related compounds such as oleic acid and trans-9,10-octacenamide. ODA was active at concentrations as low as 1 nM. The saturated analog, octadecanamide, inhibited rather than potentiated 5-HT2C responses. ODA had either no effect or only weak effects on other receptors, including muscarinic cholinergic, metabotropic glutamate, GABA(A), N-methyl-D-asparate, or alpha-amino-3-hydroxy-5-methyl-4-isoxozolepropionic acid receptors. Modulation of 5-HT2 receptors by ODA and related lipids may represent a novel mechanism for regulation of receptors that activate G proteins and thereby play a role in alertness, sleep, and mood as well as disturbances of these states.

Sphingolipids and glycerolipids. I. Chemical structures and ionophoretic activities of soya-cerebrosides I and II from soybean

Two glycosphingolipids named soya-cerebrosides I and II were isolated from soybean, the seeds of Glycine max Merrill (Leguminosae), and their chemical structures have been elucidated on the basis of physicochemical evidence and several chemical degradation reactions. By using a newly constructed liquid membrane-type apparatus (W-08) for measurement of ion-transport and ion-binding activities and by employing a method using human erythrocyte membranes for measurement of ion-permeability, it has been found that soya-cerebroside II exhibits ionophoretic activity for Ca2+ ion.

Glycolipids and transmembrane signaling: antibodies to galactocerebroside cause an influx of calcium in oligodendrocytes

This is the first study to provide evidence that one function for the surface glycolipid galactocerebroside (GalC) is participation in the opening of Ca2+ channels in oligodendroglia in culture. This glycolipid is a unique differentiation marker for myelin-producing cells; antibodies to GalC have been shown to markedly alter oligodendroglial morphology via disruption of microtubules (Dyer, C. A., and J. A. Benjamins. 1988. J. Neurosci. 8:4307-4318). This study demonstrates that extracellular EGTA blocks anti-GalC-induced disassembly of microtubules in oligodendroglial membrane sheets, demonstrating that an influx of extracellular Ca2+ mediates the cytoskeletal changes. The Ca2+ influx was examined directly by loading oligodendroglia with the fluorescent dye Indo-1 in defined medium, and measuring changes in Ca2+ in individual cells with a laser cytometer. Upon addition of anti-GalC IgG, a marked sustained increase in intracellular Ca2+ occurred in 80% of the oligodendroglia observed. EGTA blocked the increase, indicating the increase is due to an influx of extracellular Ca2+, and not due to release from intracellular stores. The effect is specific, since Ca2+ levels remain normal in oligodendroglia treated with nonimmune IgG; astrocytes do not respond to the anti-GalC. The Ca2+ response in oligodendrocytes is dependent on concentration of antibody and GalC on the oligodendroglial membrane surface. The Ca2+ influx is not mediated by voltage-sensitive Ca2+ channels: it is not blocked by cadmium, and depolarization with K+ does not mimic the response. The kinetics of the response suggest that second messenger-mediated opening of Ca2+ channels is involved.

Antigenic structure of Clostridium botulinum type B neurotoxin and its interaction with gangliosides, cerebroside, and free fatty acids

A fragment distinct from the heavy and light chains was obtained by treatment of Clostridium botulinum type B neurotoxin with chymotrypsin. Enzyme-linked immunosorbent assay and immunoblotting analysis with monoclonal antibodies showed that the fragment consisted of the light chain and part of the heavy chain (H-1 fragment) linked together by a disulfide bond. Monoclonal antibodies reacting to the heavy chain but not to the fragment were thought to recognize the epitopes on the remaining portion (H-2 fragment) of the heavy chain, being easily digested by chymotrypsin. Thus, the antigenic structure of type B neurotoxin resembles those of type A and E neurotoxins. The chymotrypsin-induced fragment bound to cerebroside and free fatty acids but not to gangliosides. The manner of binding of type B neurotoxin to gangliosides and free fatty acids was different from those of type A and E neurotoxins. Such differences in the reactivities to lipids may be related to the finding that each neurotoxin binds to a type-specific site on the neural membrane.

Structure and function of urodele myelin lacking alpha-hydroxy fatty acid-containing galactosphingolipids: slow nerve conduction and unusual myelin thickness

Myelin of several Caudata (Urodela) species appears to be unique in the fact that it lacks hydroxycerebrosides and hydroxysulfatides although it contains their non-hydroxy counterparts. Comparison of the nerve conduction velocities in the Urodeles Necturus (salamander) and Notophthalmus (newt) with that in a reptile, Anolis (chameleon) which contains hydroxycerebrosides and -sulfatides indicated that the values were significantly reduced in the urodeles. Furthermore, urodele myelin thickness remained uniformly the same regardless of the size of the nerve fiber. Despite these differences the myelins appeared structurally similar. Electron microscopic and X-ray diffraction studies did not disclose any structural difference between the two orders. A teased fiber technique established that the ratio of internodal distance and fiber diameter in urodele nerves was essentially similar to that in Anolis. These findings suggest that the absence of hydroxycerebroside and -sulfatide may be related to the reduction in nerve conduction velocity and unusual myelin thickness in the urodele nervous system.

Structure of biologically active and inactive cerebrosides prepared from Schizophyllum commune

A cerebroside fraction prepared from the mycelia of Schizophyllum commune was further fractionated into five components (I-V) by reverse-phase high-performance liquid chromatography. Fruiting-inducing activity was found in I-IV but not in V. By gas-liquid chromatography-mass spectrometry and nuclear magnetic resonance analyses it was shown that these fractions contained: I, a mixture of N-2'-hydroxypentadecanoyl-1-O-glucosyl-nonadecasphingadienine++ + and N-2'-hydroxyhexadecanoyl-1-O-glucosyl-sphingadienine; II, (4E,8E)-N-D-2'-hydroxyhexadecanoyl-1-O-beta-D-glucopyr anosyl-9-methyl-4,8- sphingadienine (Kawai and Ikeda. 1983. Biochim. Biophys. Acta. 754: 243-248); III, N-2'-hydroxyheptadecanoyl-1-O-glucosyl-nonadecasphingadienine++ +; IV, N-2'-hydroxyoctadecanoyl-1-O-glucosyl-nonadecasphinadienine; V, (4E,8E)-N-2'-hydroxytetracosanoyl-1-O-beta-glucopyrano syl-9-methyl-4,8- sphingadienine. The only structural difference observed between biologically active and inactive cerebrosides was the chain length of acyl moiety; the cerebroside having an acyl chain of 24 carbon atoms was inactive.

[Cerebrosides as one of the factors regulating the functional state of the blood-vascular wall system]

During 4 months rats were given intraperitoneal injections of cerebrosides in a dose of 5 mg/kg bw. The measurements were taken of the arterial blood pressure and the function of blood cells. It has been demonstrated that as compared to the control, the experimental animals showed a significant elevation of the blood pressure, hyperaggregation of platelets and red cells, an increase in the ability of platelets to adhesion. It has been also disclosed that there was a decrease in the time of the occurrence of muscle fatigue and death under stress induced by forced dynamic work. The data obtained are of interest in the aspect of investigating the role played by glycolipids in the pathogenesis of cardiovascular diseases.

Galactocerebroside-phospholipid interactions in bilayer membranes

Differential scanning calorimetry (DSC) and x-ray diffraction have been used to study the interaction of hydrated N-palmitoylgalactosylsphingosine (NPGS) and dipalmitoylphosphatidylcholine (DPPC). For mixtures containing less than 23 mol% NPGS, complete miscibility of NPGS into hydrated DPPC bilayers is observed in both the bilayer gel and liquid-crystal phases. X-ray diffraction data demonstrate insignificant differences in the DPPC-bilayer gel-phase parameters on incorporation of up to 23 mol% NPGS. At greater than 23 mol% NPGS, additional high-temperature transitions occur, indicating phase separation of cerebroside. For these cerebroside concentrations, at 20 degrees C, x-ray diffraction shows two lamellar phases, hydrated DPPC-NPGS gel bilayers (d = 64 A) containing 23 mol% NPGS, and NPGS "crystal" bilayers (d = 55 A). On heating to temperatures greater than 45 degrees C, the mixed DPPC-NPGS bilayer phase undergoes chain melting, and on further increasing the temperature progressively more NPGS is incorporated into the liquid-crystal DPPC-NPGS bilayer phase. At temperatures greater than 82 degrees C (the transition temperature of hydrated NPGS), complete lipid miscibility is observed at all DPPC/NPGS molar ratios.

Differential uptake of liposomes varying in size and lipid composition by parenchymal and kupffer cells of mouse liver

Using liposomes differing in size and lipid composition, we have studied the uptake characteristics of the liver parenchymal and Kupffer cells. Desferal labeled with iron-59 was chosen as a radiomarker for the liposomal content, because Desferal in its free form does not cross cellular membranes. At various time intervals after an intravenous injection of liposomes into mice, the liver was perfused with collagenase, and the cells were separated in a Percoll gradient. It was found that large multilamellar liposomes (diameter of about 0.5 micron) were mainly taken up by the Kupffer cells. For these large liposomes, the rate of uptake by Kupffer cells was rapid, with maximum uptake at around 2 hours after liposome injection. Unexpectedly, small unilamellar liposomes (diameter of about 0.08 micron) were less effectively taken up by Kupffer cells, and the rate of uptake was slow, with a maximum uptake at about 10 hours after liposome injection. In contrast, parenchymal cells were more effective in taking up small liposomes and the uptake of large liposomes was negligible. In addition, liposomes made with a galactolipid as part of the lipid constituents appeared to have higher affinity to parenchymal cells than liposomes made without the galactolipid. These findings should be of importance in designing suitable liposomes for drug targeting.