Thermotropic and structural evaluation of the interaction of natural sphingomyelins with cholesterol

Abstract

The structural transitions in aqueous dispersions of egg-sphingomyelin and bovine brain-sphingomyelin and sphingomyelin co-dispersed with different proportions of cholesterol were compared during temperature scans between 20 degrees and 50 degrees Celsius using small-angle and wide-angle X-ray scattering techniques. The Bragg reflections observed in the small-angle scattering region from pure phospholipids and codispersions of sphingomyelin:cholesterol in molar ratios 80:20 and 50:50 could all be deconvolved using peak fitting methods into two coexisting lamellar structures. Electron density profiles through the unit cell normal to the bilayer plane were calculated to derive bilayer and water layer thicknesses of coexisting structures at 20 degrees and 50 degrees Celsius. Codispersions of sphingomyelin:cholesterol in a molar ratio 60:40 consisted of an apparently homogeneous bilayer structure designated as liquid-ordered phase. Curve fitting analysis of the wide-angle scattering bands were applied to correlate changes in packing arrangements of hydrocarbon in the hydrophobic domain of the bilayer with changes in enthalpy recorded by differential scanning calorimetry. At 20 degrees Celsius the wide-angle scattering bands of both pure sphingomyelins and codispersions of sphingomyelin and cholesterol could be deconvolved into two symmetric components. A sharp component located at a d-spacing of 0.42 nm was assigned to a gel phase in which the hydrocarbon chains are oriented perpendicular to the bilayer plane. A broader symmetric band centered at d-spacings in the region of 0.44 nm was assigned as disordered hydrocarbon in dispersions of pure sphingomyelin and as liquid-ordered phase in codispersions of sphingomyelin and cholesterol. It is concluded from the peak fitting analysis that cholesterol is excluded from gel phases of egg and brain sphingomyelins at 20 degrees Celsius. The gel phases coexist with liquid-ordered phase comprised of egg-sphingomyelin and 27 mol% cholesterol and brain-sphingomyelin and 33 mol% cholesterol, respectively. Correlation of the disappearance of gel phase during heating scans and the enthalpy change recorded by calorimetry in codispersions of sphingomyelin and cholesterol leads to the conclusion that a major contribution to the broadened phase transition endotherm originates from dilution of the cholesterol-rich liquid-ordered phase by mobilization of sphingomyelin from the melting gel phase.

Comparison of the liquid-ordered bilayer phases containing cholesterol or 7-dehydrocholesterol in modeling Smith-Lemli-Opitz syndrome

“…As a consequence, it was pointed out in the same study that the raft-altered structure resulted in a hyperallergic response of mast cells prepared from Dhcr7 Ϫ / Ϫ mice ( 19 ). More specifi cally, mast cells derived from 7-DHC reductase knockout mice show a high cytokine production can be readily related to earlier studies of sphingomyelin/ cholesterol binary mixtures ( 27,31 ). The present study illustrates how subtle differences in the structure of the sterol nucleus may cause membrane lipid dysfunctions that "cascade" to create major consequences, such as SLO syndrome.…”

“…The organic solvent was subsequently evaporated in SpeedVac equipment (SPD111V, Savant, Thermo Fisher, Illkirch, France). The dry lipids were hydrated with an equal weight of water and heated repeatedly above 45°C, a temperature cycling which was found effi cient to fully hydrate a control of pure SM ( 26,27 ). Simultaneous small-and wide-angle X-ray scattering intensities were recorded during thermal scans between 20° and 50°C on beamline 2.1 of the Daresbury SRS as described elsewhere ( 27 ).…”

“…After correcting the raw data by subtracting the background scattering from both water and the sample cell, each of the Bragg peaks were fi tted by a Gaussian/Lorentzian (Voigt) distribution using PeakFit 4.12 (Systat Software). The protocol has been recently described in ( 27,29 ).…”

Gel Formulation Containing Mixed Surfactant and Lipids Associating with Carboplatin

“…This is in contrast to the anticipated ordering effect reported by cholesterol in other systems [71]. Cholesterol has been shown to decrease the thermal sensitivity of a gel by decreasing the distance between polar head groups [72], and such interactions could deter the mechanic properties of a gel. It is the fluctuating traits that allow for the flexibility of gel to swell in an aqueous environment [63].…”

The unfavorable lipid environment reduced caveolin-1 expression in apical membranes from human preeclamptic placentas

“…Cho and SM have both hydrogen-bond donor and acceptor groups that together with the Cho flat and extended hydrophobic structure promote the tight packing of SM and Cho into the liquid-ordered arrangement [53]. Thus, SM and Cho, are relevant in determining lipid conformational order and packing [31][32][33].…”