Cholesteryl sulfate-phosphatidylcholine interactions

Impact of Doping a Phytosteryl Sulfate on the Properties of Liposomes Made of Saturated and Unsaturated Phosphatidylcholines

The size, dispersibility, and fluidity of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine), POPC (1-palmitoy-2-oleoyl-sn-glycero-3-phosphocholine), and DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) liposomes doped with β-sitosteryl sulfate (PSO₄) were comparatively studied. In all three types of liposomes, PSO₄ reduced sizes and enhanced the negative values of the ζ-potential. However, the effect on sizes quantitatively differed in the three cases in a manner dependent on their phase behaviors. PSO₄ rigidified each type of membrane in its liquid crystalline phase and fluidized the gel phase. It enhanced the glucose trapping efficiency (TE) of both DPPC and DOPC liposomes. The TE of DPPC first increased with the increasing concentration of PSO₄, then decreased gradually. On the other hand, in the case of DOPC, the TE increased significantly upon addition of PSO₄, then remained nearly constant. Though the exact dependence of TE on the PSO₄ concentration differed in the two cases, its effect, in each case, was more than the effect of β-sitosterol (POH). The ability of PSO₄ for reducing the size and enhancing dispersibility and TE of liposomes can be useful for preparing cosmetics and pharmaceutical formulations.

Effects of β-Sitosteryl Sulfate on the Properties of DPPC Liposomes

The effect of β-sitosteryl sulfate (PSO₄) on the liposomal size, stability, fluidity, and dispersibility of DPPC liposomes prepared by vortex mixing, bath-sonication, and probe-sonication has been studied. PSO₄ significantly decreases the particle size of the multilamellar liposomes (MLVs). The sizes of the vortexmixed and the bath-sonicated liposomes vary as a function of PSO₄ concentration. On the other hand, PSO₄ has only little effect on the particle sizes of probe sonicated liposomes. In some cases, the liposomal stability at higher PSO₄ concentrations depends on the preparation method. PSO₄ improves the dispersibility of the DPPC liposomes and enhances their hydration. It also increases the fluidity of the liposomes prepared by each method. Our results suggest that liposomes consisting of DPPC and PSO₄ can be suitable as a cosmetic or pharmaceutical ingredient for the effective delivery of the active components into the body.

Water Permeability across Symmetric and Asymmetric Droplet Interface Bilayers: Interaction of Cholesterol Sulfate with DPhPC

Cellular membranes employ a variety of strategies for controlling the flow of small molecules into the cytoplasmic space, including incorporation of sterols for modulation of permeability and maintenance of lipid asymmetry to provide both sides of the membrane with differing biophysical properties. The specific case of cholesterol asymmetry, especially, is known to have profound effects in neurological cellular systems. Synthetic membrane models that can readily determine valuable physical parameters, such as water transport rates, for sterol-containing membranes of defined lipid composition remain in demand. We report the use of the droplet interface bilayer (DIB), composed of adherent aqueous droplets surrounded by a lipid monolayer and immersed in a hydrophobic medium, for measurement of water permeability across the membrane, with rapid visualization and ease of experimental setup. We studied droplet bilayer membranes composed of the prototypical synthetic membrane lipid (i.e., the archaeal lipid DPhPC) as well as of symmetric and asymmetric DIBs formed by DPhPC and sodium cholesterol sulfate (S-Chol). The presence of S-Chol in DPhPC in symmetric DIB reduced the passive water permeability rate (P(f)) at all concentrations and increased the activation energy (E(a)) to 17-18 kcal/mol. When only one side of the DIB contains S-Chol (asymmetric DIB), an E(a) of 14-15 kcal/mol was obtained, a value intermediate that of pure lipid and symmetrical DIB containing lipid and S-Chol. Our data are consistent with a capability for regulation of water transport by one leaflet independent of the other. The engineering of our various systems is believed to have implications for garnering detailed knowledge regarding the transport of small moieties across bilayers in a wide variety of lipid systems.

Studying interfacial reactions of cholesterol sulfate in an unsaturated phosphatidylglycerol layer with ozone using field induced droplet ionization mass spectrometry

Field-induced droplet ionization (FIDI) is a recently developed ionization technique that can transfer ions from the surface of microliter droplets to the gas phase intact. The air-liquid interfacial reactions of cholesterol sulfate (CholSO(4)) in a 1-palmitoyl-2-oleoyl-sn-phosphatidylglycerol (POPG) surfactant layer with ozone (O(3)) are investigated using field-induced droplet ionization mass spectrometry (FIDI-MS). Time-resolved studies of interfacial ozonolysis of CholSO(4) reveal that water plays an important role in forming oxygenated products. An epoxide derivative is observed as a major product of CholSO(4) oxidation in the FIDI-MS spectrum after exposure of the droplet to O(3) for 5 s. The abundance of the epoxide product then decreases with continued O(3) exposure as the finite number of water molecules at the air-liquid interface becomes exhausted. Competitive oxidation of CholSO(4) and POPG is observed when they are present together in a lipid surfactant layer at the air-liquid interface. Competitive reactions of CholSO(4) and POPG with O(3) suggest that CholSO(4) is present with POPG as a well-mixed interfacial layer. Compared with CholSO(4) and POPG alone, the overall ozonolysis rates of both CholSO(4) and POPG are reduced in a mixed layer, suggesting the double bonds of both molecules are shielded by additional hydrocarbons from one another. Molecular dynamics simulations of a monolayer comprising POPG and CholSO(4) correlate well with experimental observations and provide a detailed picture of the interactions between CholSO(4), lipids, and water molecules in the interfacial region.

Phase Behavior of Palmitic Acid/Cholesterol/Cholesterol Sulfate Mixtures and Properties of the Derived Liposomes

The phase behavior of mixtures formed by palmitic acid (PA), cholesterol (Chol), and sodium cholesteryl sulfate (Schol) has been characterized by differential scanning calorimetry and infrared and 2H NMR spectroscopy. It is reported that it is possible to form, with PA/sterol mixtures, fluid lamellar phases where the sterol content is very high (a sterol mole fraction of 0.7). As a consequence of the rigidifying ability of the sterols, the PA acyl chains are very ordered. The stability of these self-assembled bilayers is found to be pH-dependent. This property can be controlled by the Chol/Schol molar ratio, and it is proposed that this parameter modulates the balance between the intermolecular interactions between the constituting species. A phase-composition diagram summarizing the behavior of these mixtures as a function of pH, at room temperature, is presented. It is also shown that it is possible to produce large unilamellar vesicles (LUVs) from these mixtures, using standard extrusion techniques. The resulting LUVs display a very limited passive release of the entrapped material. In addition, these LUVs constitute a versatile vector for pH-triggered release.

Cholesterol sulfate and Ca(2+) modulate the mixing properties of lipids in stratum corneum model mixtures

The influence of cholesterol sulfate (CS) and calcium on the phase behavior of lipid mixtures mimicking the stratum corneum (SC) lipids was examined using vibrational spectroscopy. Raman microspectrocopy showed that equimolar mixtures of ceramide, palmitic acid, and cholesterol underwent a phase transition in which, at low temperatures, lipids formed mainly a mosaic of microcrystalline phase-separated domains, and above 45 degrees C, a more fluid and disordered phase in which the three lipid species were more miscible. In the presence of Ca(2+), there was the formation of fatty acid-Ca(2+) complexes that led to domains stable on heating. Consequently, these lipid mixtures remained heterogeneous, and the fatty acid molecules were not extensively involved in the formation of the fluid lipid phase, which included mainly ceramide and cholesterol. However, the presence of CS displaced the association site of Ca(2+) ions and inhibited the formation of domains formed by the fatty acid molecules complexed with Ca(2+) ions. This work reveals that CS and Ca(2+) modulate the lipid mixing properties and the lipid order in SC lipid models. The balance in the equilibria involving Ca(2+), CS, and fatty acids is proposed to have an impact on the organization and the function of the epidermis.

Sterolsulphate sulphohydrolase from human placenta microsomes--30 kDa molecular weight form of cholesterol sulphate sulphohydrolase

The cholesterol sulphate sulphohydrolase (CHS-ase) exhibiting molecular weight of 30 kDa was purified from human placenta microsomes. The microsomal proteins were extracted with 0.5% Triton X-100. The DEAE-cellulose chromatography of the solubilized microsomal proteins, performed at pH 7.6 allowed to separate two enzymatically active fractions. One of them was associated with the protein fraction unbound by DEAE-cellulose, the other was tightly bound by ion exchanger. The 30 kDa cholesterol sulphate sulphohydrolase was purified to homogenity from the protein fraction tightly bound by DEAE-cellulose. The highly purified enzyme preparation (specific activity 385 nmol min(-1)mg(-1) of protein) exhibited optimal activity at pH 6.4, the K(m) was established to be 6.7 x 10(-6)M, the pI value was 7.4. The 30 kDa cholesterol sulphate sulphohydrolase, in contrast to the CHS-ase form originated from the protein fraction unbound by DEAE-cellulose, was not sensitive to alkaline phosphatase treatment and phosphohydrolase inhibitors. The effects of steroids, -SH reacting agents and sulphohydrolase inhibitors on the enzyme activity were tested.

Cholesterol versus cholesterol sulfate: effects on properties of phospholipid bilayers containing docosahexaenoic acid

The important omega-3 fatty acid docosahexaenoic acid (DHA) is present at high concentration in some membranes that also contain the unusual sterol cholesterol sulfate (CS). The association between these lipids and their effect on membrane structure is presented here. Differential scanning calorimetry (DSC), MC540 fluorescence, erythritol permeability, pressure/area isotherms on lipid monolayers and molecular modeling are used to compare the effect of CS and cholesterol on model phospholipid membranes. By DSC, CS decreases the main phase transition temperature and broadens the transitions of dipalmitolyphosphatidylcholine (DPPC), 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (18:0,18:1 PC) and 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (18:0,22:6 PC) to a much larger extent than does cholesterol. In addition CS produces a three-component transition in 18:0,18:1 PC bilayers that is not seen with cholesterol. In a mixed phospholipid bilayer composed of 18:0,18:1 PC/18:0,22:6 PC (1:1, mol/mol), CS at 2.5 membrane mol% or more induces lateral phase separation while cholesterol does not. CS decreases lipid packing density and increases permeability of 18:0,18:1 PC and 18:0,22:6 PC bilayers to a much larger extent than cholesterol. CS disrupts oleic acid-containing bilayers more than those containing DHA. Molecular modeling confirms that the anionic sulfate moiety on CS renders this sterol more polar than cholesterol with the consequence that CS likely resides higher (extends further into the aqueous environment) in the bilayer. CS can therefore be preferentially accommodated into DHA-enriched bilayers where its tetracyclic ring system may fit into the delta 4 pocket of DHA, a location excluded to cholesterol. It is proposed that CS may in part replace the membrane function of cholesterol in DHA-rich membranes.

Interaction of dehydroepiandrosterone with phospholipid membranes: an infrared spectroscopy investigation

The interaction between dehydroepiandrosterone (DHEA) and its sulfate metabolite (DHEA-S) with deuterated dimirystoylphosphatidylcholine (DMPC-d54) was investigated by FTIR spectroscopy. DHEA, as cholesterol, induces some conformational order in the liquid-crystalline phase of DMPC-d54. Attenuated total reflectance (ATR) measurements performed on oriented DMPC-d54/steroids samples have shown that in the gel phase, the acyl chains of DMPC-d54 become more normal to the bilayer surface in the presence of DHEA or cholesterol. On the other hand, DHEA-S increases the number of gauche conformers along the hydrocarbon chains of DMPC-d54. No evidence for the presence of hydrogen bond was found between both steroids and the 13C labeled carbonyl group of hydrated DMPC.

The thickness of cholesterol sulfate-containing membranes depends upon hydration

The ordering of 30 mol % cholesterol (CH) or cholesterol sulfate (CS) on chain deuterated dimyristoylphosphatidylcholine (DMPC) was investigated by 2H-NMR for different hydrations. It is found that: (i) hydration has merely no influence on chain order (chain length) for DMPC-cholesterol systems, (ii) in CS-containing mixtures chain order (length) is greater at low hydration (DMPC-to-water molar ratio, Ri, of 11.3) than in excess water (Ri approximately 500) and (iii) at low hydration the ordering is about the same for CS or CH-containing systems whereas it is not at high hydration. DMPC-CS bilayer thickness is therefore very sensitive to hydration.

Enhanced arachidonic acid and calcium metabolism in cholesteryl sulfate-enriched rat platelets

We previously found that cholesteryl sulfate (CS), a minor lipid constituent, is present in blood platelets and might influence platelet aggregation. In this study, we investigated whether CS modifies platelet arachidonic acid and calcium metabolism. In CS-loaded rat platelets, we found a potentiation of the arachidonate-induced aggregation, an increase in the thrombin-induced release of radiolabeled arachidonate preincorporated into platelet phospholipids and an increased formation of cyclooxygenase and lipoxygenase products. In addition, the calcium uptake in non-stimulated as well as in thrombin-stimulated CS-loaded platelets was enhanced. The above-mentioned effects were never observed with cholesterol, cholesteryl acetate, estrone and estrone sulfate. Although the precise determinants for the platelet CS concentration are not presently known, our findings might suggest a new role for CS as a modulator of the activity of these cells.

Occurrence and biological effects of cholesteryl sulfate on blood platelets

Although the exact function of cholesteryl sulfate (CS) is unknown, it is present in low concentration in lipoproteins, in red blood cells and spermatozoa. In the present study, we investigated whether CS is present in blood platelets and its possible biological involvement in platelet function. Extensively washed platelets were prepared from rat and human blood. After lipid extraction and thin layer chromatography (TLC) on silica gel, a compound with the same mobility as authentic CS was isolated and identified by two different methods: (1) without hydrolysis, negative ion fast atom bombardment combined with tandem mass spectrometry (MS/MS); (2) after acidic hydrolysis, identification of cholesterol (Chol) by TLC and gas chromatography-MS. CS concentrations measured using beta-sitosteryl sulfate as internal standard in normal rat or human platelets were in the range of 164-512 pmol/10(9) platelets. This represented less than 1% of cell Chol. Biological effects of CS on platelet function were studied in vitro. CS incubated with rat platelets either as methanol solution or as albumin-bound complex potentiated the ADP- or thrombin-induced aggregation and serotonin secretion. The results of platelet sterol analysis indicated that CS was incorporated into platelet membrane and did not significantly change the platelet cholesterol composition. The potentiating effect of CS on platelet-induced aggregation and secretion was not obtained with cholesterol, cholesteryl acetate or estrone. In contrast, an inhibitory effect of estrone sulfate was observed. These results indicate that both the sulfate group and the cholesterol moiety are involved in the pro-aggregant property of CS. In addition, platelet mediators seem to be implicated in the mechanism since the thrombin-induced production of thromboxane B2, the stable end-product of arachidonic acid metabolism, was also enhanced in the presence of CS. These results suggest a new role for CS which may be involved in the modulation of platelet function.

Interaction of calcium and cholesterol sulphate induces membrane destabilization and fusion: implications for the acrosome reaction

Cholesterol sulphate is a potent stabilizer of membrane bilayer structure in both dielaidoylphosphatidylethanolamine and egg phosphatidylethanolamine model membranes, however, the addition of calcium abolishes this bilayer stabilization. Calcium also induces fusion and leakage of egg phosphatidylethanolamine large unilamellar vesicles containing cholesterol sulphate, but has no effect on fusion or leakage of egg phosphatidylcholine large unilamellar vesicles containing cholesterol sulphate. With egg phosphatidylethanoiamine liposomes, the initial rate, and extent of fusion, at constant calcium concentration, vary inversely with the mol percentage of cholesterol sulphate present in the vesicle membrane. The interaction of calcium and cholesterol sulphate, which causes membrane destabilization and fusion in phosphatidylethanolamine containing model systems, may play a role in the acrosome reaction in human sperm.

Lack of correlation between steroid sulfatase activities and lipid content in uterus and liver microsomes of guinea pigs

Lipid content and steroid sulfatase activities were determined in liver and uterus microsomes of non-pregnant guinea pigs. The results were compared with values obtained in pregnant and cortisol-treated animals. Steroid sulfatase activities were always higher in pregnant animals, and we supposed that the increase in circulating cortisol in pregnant guinea pigs before parturition has an influence on the membrane-bound sulfatase activities. Sulfatase activities were identical in cortisol-treated and untreated non-pregnant females, although cortisol induced changes in microsomal lipid composition. These results lead us to three conclusions: in intact female guinea pigs, cortisol induces variations in the lipid content of uterus and liver microsomes, especially in the cholesteryl sulfate to phospholipid ratios; the variations of the lipid composition in pregnant animals do not appear to be cortisol-dependent; membrane-bound steroid sulfatase activities are not directly influenced by the lipid composition of microsomes.