Fluorescence polarization order parameters and phase transitions in lipids and lipoproteins

Positive effects of hypoxic preconditioning of the extracellular matrix and stromal vascular fraction from adipose tissue

Background

Numerous approaches have been developed to decelerate the aging process of facial skin. Synthetic fillers and cell-enriched fat grafts are the main procedures employed to fill wrinkles.

Objective

The aim of this study was to evaluate the in vitro and in vivo safety and efficiency of a new process developed by SYMBIOKEN: the AmeaCell, which facilitates the extraction of the stromal vascular fraction (SVF) and the associated hypoxia pre-conditioned matrix to promote fat graft survival.

Methods

The AmeaCell device allows the extraction from adipose tissue of SVF and pre-conditioned MatriCS and promotes a hypoxic environment. Experiments were carried out on human cells and then in mice.

Results

Characterization of cells and MatriCS showed that after their extraction using the new process developed by SYMBIOKEN, the extracted cells expressed stem-cell markers. The presence of characteristic proteins and lipid fractions found in the adipose matrix were confirmed in MatriCS. Cobalt chloride treatment of the matrix using the AmeaCell device induced modifications in the matrix composition with a decrease in laminin and without collagen modification, both of which promote adhesion and differentiation of SVF or adipose-derived stromal cells. The combination of MatriCS and SVF (1 × 106 and 5 × 106, respectively) is safe and efficient to fill winkles induced by UVB irradiation. The cross-talk between MatriCS and SVF can act a durable filler compared to the filling performed using cells or matrix or fat alone, which need to be replaced frequently.

Conclusion

These results indicate that the combination of MatriCS and SVF is safe and effective as a biological filler for achieving skin rejuvenation and wrinkle filling.

Self-Organisation, Thermotropic and Lyotropic Properties of Glycolipids Related to their Biological Implications

Glycolipids are amphiphilic molecules which bear an oligo- or polysaccharide as hydrophilic head group and hydrocarbon chains in varying numbers and lengths as hydrophobic part. They play an important role in life science as well as in material science. Their biological and physiological functions are quite diverse, ranging from mediators of cell-cell recognition processes, constituents of membrane domains or as membrane-forming units. Glycolipids form an exceptional class of liquid-crystal mesophases due to the fact that their self-organisation obeys more complex rules as compared to classical monophilic liquid-crystals. Like other amphiphiles, the supra-molecular structures formed by glycolipids are driven by their chemical structure; however, the details of this process are still hardly understood. Based on the synthesis of specific glycolipids with a clearly defined chemical structure, e.g., type and length of the sugar head group, acyl chain linkage, substitution pattern, hydrocarbon chain lengths and saturation, combined with a profound physico-chemical characterisation of the formed mesophases, the principles of the organisation in different aggregate structures of the glycolipids can be obtained. The importance of the observed and formed phases and their properties are discussed with respect to their biological and physiological relevance. The presented data describe briefly the strategies used for the synthesis of the used glycolipids. The main focus, however, lies on the thermotropic as well as lyotropic characterisation of the self-organised structures and formed phases based on physico-chemical and biophysical methods linked to their potential biological implications and relevance.

EPR spin label study of walnut oil effects on phosphatidylcholine membranes

Effects of walnut oil (WO) on dynamic and thermodynamic properties of 0-50 wt% cholesterol (CH) containing dimyristoylphosphatidylcholine (DMPC) and 10 wt% CH containing dipalmitoylphosphatidylcholine (DPPC) membrane dispersions were studied by electron paramagnetic resonance (EPR), using 5-doxyl stearic acid (5-DSA) and 16-doxyl stearic acid (16-DSA). Incorporation of 10 wt% WO alone decreased the phase transition temperature and created depth-dependent effects at the gel phase. The order increased close to the head region and decreased in the hydrocarbon core of the DMPC bilayer. For DPPC, the order decreased both close to head region and in the hydrocarbon core. Ten weight percent WO did not have considerable effect at the fluid phase for both DMPC and DPPC. Incorporation of 40 wt% WO into DMPC created an abrupt decrease in the maximum hyperfine splitting values after 305 K. The effect of 10 wt% WO in CH containing DMPC dispersions was dependent on the CH concentration. An increase and a decrease in the order were observed at low and high CH concentrations, respectively. Incorporation of WO created different effects on fluidity of 10 wt% CH containing DMPC and DPPC dispersions. Close to the head group region, the order in DMPC increased both in the gel and fluid phases; but for DPPC, an opposite effect was observed in both of the phases. In the hydrocarbon core of the bilayer, addition of 10 wt% WO into 10 wt% CH containing DMPC decreased the order in the gel phase and WO did not affect the order in the fluid phase. For DPPC, WO effects were observed to alter with temperature. In the studied temperature range, order parameters, diffusion constants and effective tilt angles were obtained from simulations of the spectra using Microscopic Order Macroscopic Disorder (MOMD) and Vary Anisotropic Reorientation (VAR) models. For 16-DSA, spectra were also simulated using two domains with EPRSIM.

Identification of peptides that neutralize bacterial endotoxins using beta-hairpin conformationally restricted libraries

Bacterial endotoxins are the major mediator of septic shock; therefore, endotoxin-neutralizing molecules could have biomedical applications. The septic shock cascade relies in a series of molecular recognition processes. The large contact-surface described for the interacting macromolecules, in most cases, prevents the identification of small molecules that could modulate such recognition events. Here we report on a beta-hairpin conformationally restricted combinatorial library that has been generated and screened towards the identification of new peptides that neutralize bacterial endotoxins. Starting with a de novo designed linear peptide that shows a beta-hairpin structure population of around 30%, (Ramirez-Alvarado, M., Blanco, F. J. and Serrano, L. Nat. Struc. Biol., 7, 604-612 (1996)), we selected four positions to build up a combinatorial library of 20(4) sequences. Deconvolution of the library reduced such a sequence complexity to 8 defined sequences. The newly identified peptides have a biological activity equivalent to that reported for peptides derived from natural endotoxin-binding proteins.

Phases and phase transitions of the phosphatidylcholines

LIPIDAT (http://www.lipidat.chemistry.ohio-state.edu) is an Internet accessible, computerized relational database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior and molecular structures. Here, a review of the data subset referring to phosphatidylcholines is presented together with an analysis of these data. This subset represents ca. 60% of all LIPIDAT records. It includes data collected over a 43-year period and consists of 12,208 records obtained from 1573 articles in 106 different journals. An analysis of the data in the subset identifies trends in phosphatidylcholine phase behavior reflecting changes in lipid chain length, unsaturation (number, isomeric type and position of double bonds), asymmetry and branching, type of chain-glycerol linkage (ester, ether, amide), position of chain attachment to the glycerol backbone (1,2- vs. 1,3-) and head group modification. Also included is a summary of the data concerning the effect of pressure, pH, stereochemical purity, and different additives such as salts, saccharides, amino acids and alcohols, on phosphatidylcholine phase behavior. Information on the phase behavior of biologically derived phosphatidylcholines is also presented. This review includes 651 references.

Effect of lovastatin on lipoprotein fluidity in patients with hypercholesterolaemia

Lovastatin was administered to six hypercholesterolaemic patients (mean plasma cholesterol 450 mg dl-1). Plasma lipoproteins (VLDL, LDL, and HDL) were separated before and following 7 and 12 weeks treatment with lovastatin. Fluidity was quantified by fluorescence polarization measurements using 1,6-diphenyl 1,3,5 hexatriene (DPH) as the fluorescent probe. Lovastatin treatment resulted in a significant reduction of total plasma cholesterol, LDL cholesterol and VLDL cholesterol (-41%, -44%, -68%, respectively). Fluidity measurements showed significant (p < 0.01) increase in LDL fluidity by 11% and 21% after 7 and 12 weeks of lovastatin treatment, whereas, VLDL fluidity was increased by 27% after 12 weeks of therapy. HDL fluidity was not altered. These alterations in the fluidity of the atherogenic lipoproteins (LDL and VLDL) in hypercholesterolaemic patients may prove to be of significance in reducing the risk of atherosclerosis.

Fluidity changes and chemical composition of lipoproteins in type IIa hyperlipoproteinemia

The chemical composition and the physical properties of lipoproteins (VLDL, LDL and HDL) were studied in two groups of patients: 14 healthy normolipidemic subjects and 15 type IIa familial hypercholesterolemic patients. The steady-state fluorescence anisotropy rs was estimated in lipoproteins by the fluorescence depolarization of two fluorescent probes: the DPH (1,6-diphenyl-1,3,5-hexatriene) and the TMA-DPH (1,4-trimethylammonium phenyl-6-1,3,5-hexatriene). A structured order parameter S was calculated from the DPH fluorescence anisotropy. The flow activation energies were calculated for LDL and HDL from both groups from the Arrhenius plots (log r DPH versus 1/T). By using TNBS (trinitrobenzene sulfonic acid) as a distance control quencher, the two probes were located in the outer shell of LDL. In HDL, TMA-DPH remained at the surface of the particles, while DPH was more deeply embedded in the lipid core. There was no difference in the physico-chemical properties of VLDL between the two groups studied. DPH fluorescence anisotropies were significantly increased in LDL and HDL from the hypercholesterolemic group compared to the control particles (P less than 0.05 and P less than 0.01, respectively). In LDL this modification of the fluorescence anisotropy can be related to a change in the lipid composition of particles. LDL from hypercholesterolemic patients contained significantly less triacylglycerol (P less than 0.01) and more cholesteryl ester (N.S.). Their cholesteryl ester to triacylglycerol ratio was significantly higher. In HDL, there was no difference in chemical composition between the two groups. The increase in DPH fluorescence anisotropy can be related to the presence of smaller particles in HDL from HC group. No difference was noted in the TMA-DPH fluorescence anisotropy at 37 degrees C in the LDL from the two groups. In contrast, TMA-DPH fluorescence anisotropy in HDL from hypercholesterolemic group was significantly higher than in control HDL. The flow activation energy of DPH was also significantly higher in both LDL and HDL from the hypercholesterolemic group than in control group particles. In both LDL and HDL from the control group, DPH fluorescence anisotropy was negatively correlated with TG/protein and TG/PL ratios and positively correlated with the CE/TG ratio. No correlation was observed between lipid composition and DPH fluorescence anisotropy values in hypercholesterolemic particles. The modification in fluidity parameters, especially the increase in the flow activation energies in LDL and HDL from hypercholesterolemic patients, could lead to a restriction of cholesterol movements in these particles. From a physiological point of view, this could represent a loss of functional capacity.

A fluorescent sterol probe study of human serum low-density lipoproteins

The fluorescent sterol probe, ergosta-5,7,9,(11),22-tetraen-3 beta-ol (dehydroergosterol), was utilized as a cholesterol analog to label human serum low-density lipoproteins (LDL). Quenching of dehydroergosterol fluorescence by KI indicated that most of the fluorophore was either buried within the outer phospholipid monolayer of LDL or within the neutral lipid core of LDL. The steady-state anisotropy of dehydroergosterol in LDL detected the cholesteric core phase transition near 30 degrees C. Fluorescence lifetime decays for dehydroergosterol contained two components, both below and above the cholesteric phase transition, with the major lifetime component near 1 ns. Neither lifetime component underwent a detectable change in duration at the core phase transition temperature. Time-correlated fluorescence anisotropy decays of dehydroergosterol indicated a single rotational correlation time near 1.7 ns, which was unaffected by the core phase transition. Time-correlated anisotropy decays also suggested hindered rotation of dehydroergosterol in LDL. These results indicate that unesterified cholesterol is primarily located in the outer phospholipid monolayer of LDL, with the majority of cholesterol not in direct contact with the aqueous phase.

Dietary linoleate increases fluidity and influences chemical composition of plasma low density lipoprotein in adult men

Dietary linoleate was effective to increase LDL fluidity in adult men but did not significantly influence VLDL or HDL fluidities. Lipoproteins were isolated ultracentrifugally from plasma of sixteen healthy, free living male volunteers consuming controlled diets formulated from typical U.S.A. foods to have 35 energy % fat with 10 g (diet L) or 30 g (diet H) linoleate per day, 30-50 g saturated fatty acids/day and the balance mainly monounsaturated fatty acids. Calculated cholesterol intakes were 500 mg/day at each calorie level. Changes in LDL fluidity were detected as differences in diphenylhexatriene (DPH) fluorescence polarization upon crossover between the two controlled diets. Thermotropic measurement of DPH fluorescence anisotropy and compositional analyses indicated that LDL and HDL fluidities were dependent upon phospholipid and triacylglycerol concentrations, respectively, and were modulated by the presence of cholesteryl esters. Fatty acid analyses of the major lipid classes of the isolated lipoproteins indicated that changes, upon diet crossover, in DPH fluorescence anisotropy, were a linear function of the incremental change in LDL phospholipid linoleate. The fluorescent probe described an environment corresponding to the fatty acyl moieties of the phospholipids on the LDL periphery, which composition is apparently under dietary control. It is suggested that the diet induced fluidity changes may affect the conformation of the apoprotein moiety on the LDL surface and thus the potential for LDL interaction with cellular LDL receptors.

Influence of saturated and unsaturated fats on platelet fatty acids in cholesterol-fed rabbits

Feeding natural fats varying in contents of palmitate (16:0), stearate (18:0), oleate (18:1), and linoleate (18:2) to rabbits resulted in modulation of platelet phospholipid fatty acyl composition. Rabbits were fed high fat semipurified diets containing 2% corn oil (CO) + 18% CO, cocoa butter (CB) or milkfat (M) for periods of up to 300 d. Platelet phospholipid linoleate contents corresponded to diet levels with 18:2 highest in CO-fed rabbits and following the sequence CO greater than CB greater than M. Stearate was highest in CB-fed rabbits, corresponding to high 18:0 levels in CB, but palmitate levels were not affected by diet. Both CB and M-fed rabbits were higher than CO-fed rabbits in oleate. Though CO is highest in 18:2, the accepted 20:4 precursor, arachidonate was highest in M-fed rabbits. Adding cholesterol (0.2%) to the diets did not affect platelet phospholipid fatty acyl composition except to elevate 20:4 in M-fed rabbits. CO-fed rabbits showed uniquely high levels of tetracosadienoate (24:2). Fatty acyl composition data were essentially constant between 200 and 300 d on diet. Phospholipid fatty acyl unsaturation was apparently homeostatically controlled as mole percent unsaturate to saturate ratios were independent of diet. The observed homeostasis resulted in minimal diet influences on platelet membrane fluidity and ADP or collagen stimulated platelet aggregation. Platelet fluidity, determined by fluorescence polarization, was a function of oleate and linoleate contents of the cells. Cholesterol feeding generally lowered platelet fluidity and altered the dependence of fluidity on fatty acyl composition.

Acyl chain interactions and the modulation of phase changes in glycerolipids

Fluorescence polarization measurements with 1,6-diphenyl-1,3,5-hexatriene and differential scanning calorimetry (DSC) were used to monitor phase transitions and order in the liquid state in sonicated dispersions of mono-, di- and triacylglycerols. Residual order in melted glycerolipids was indicated when the structural order parameter, S, assumed non-zero values at temperatures, t greater than or equal to tf, the DSC-determined fusion temperature. Residual order was observed with cis unsaturated di- and triacylglycerols but not with corresponding trans unsaturated or with saturated compounds. The reduced fluidity was attributed to adjacent binding of fatty acids to the glycerol molecule and the resulting interactions between fatty acyl moieties and packing effects. Lipids were considered as in an isotropic liquid or highly fluid state when diphenylhexatriene fluorescence anisotropy, rs, was equal to or less than 0.08, corresponding to S = 0. Temperatures, t0.08, for transition from the fluid state upon cooling were noted when rs = 0.08, and delta t = t0.08-tf was then taken as a measure of residual order. Tri-, 1,2-di and 1,3-dioleoylglycerol delta t values were 75, 60.9 and 13.6 degrees C, respectively. Tri-, 1,3-di- and monolinoleoylglycerol delta t values were 86, 30 and 41 degrees C, respectively. Restrictions in mobility when observed are attributable to interactions between adjacent acyl chains. Double bond location in the hydrocarbon chain affected ordering in the liquid state as simple triacylglycerol esters of cis 18:1 delta 6, trans 18:1 delta 6 and cis 24:1 delta 15 exhibited t = 37, 14 and 18 degrees C, respectively.

Lipid solvation of the aqueous form of the myelin proteolipid apoprotein: evidence and characterization of two lipid populations by fluorescence polarization, differential calorimetry, and sucrose gradient centrifugation

The interaction between dipalmitoylphosphatidylcholine (DPPC) and the aqueous form of the myelin proteolipid apoprotein (PLA) has been investigated. Lyophilization was found to be an efficient and nonperturbing method for membrane reconstitution. Mixtures of different lipid/protein ratios were analyzed by means of differential calorimetry, fluorescence polarization, and sucrose gradient centrifugation. The presence of two coexisting lipid populations, termed "bulk" and "interacting" lipids, was demonstrated by these three techniques. By differential calorimetry, 23 DPPC molecules per molecule of protein (30 kDa) were shown to be excluded from the lipid phase transition. By fluorescence polarization, we detected above the phase-transition temperature a large perturbation of the lipid acyl chain dynamics induced by the aqueous form of PLA. Increasing the protein content above 35% by weight within the recombinants caused drastic changes in both delta H values and the fluorescence anisotropy parameter, which could stem from protein aggregation.

Influence of age and sex on composition and lipid fluidity in miniature swine plasma lipoproteins

Age- and sex-related differences were observed in the plasma cholesterol level, the plasma concentrations of certain lipoprotein components, and the HDL lipid phase fluidity in miniature swine from post-weaning (6 weeks) through puberty (6 months), maturity (2-6 years), and old age (10-12 years). Age effects were more dominant in the males, with VLDL protein; LDL protein, triacylglycerol, and phospholipid; and HDL triacylglycerol, phospholipid, cholesterol, and polyunsaturated fatty acids showing statistically significant negative correlations with age. These effects were not observed in females. HDL cholesterol was positively correlated with age in females. Total plasma cholesterol decreased with age in males only, but plasma triacylglycerol was not influenced by age in either sex. Higher concentrations of all lipoprotein lipids were observed in the female minipigs regardless of age. HDL lipids became less fluid with age in the males alone suggesting a physical chemical basis for the lower incidence of heart disease among females. The more fluid HDL circulating in the female may be more capable of mobilizing peripheral tissue cholesterol for catabolism thus protecting her from developing atherosclerotic lesions.