Effect of N-dodecyl-N,N-dimethylamine N-oxide on unilamellar liposomes (original) (raw)
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Physico?chemical modifications of liposome structures through interaction with surfactantsy
International Journal of Cosmetic Science, 1992
The liposome-surfactant interaction has been studied in this paper through the disrupting effect caused by surfactant molecules on large unilamellar vesicles prepared by reverse-phase evaporation. This process leads, in the end, to the rupture of such structures and to the solubilization of the phospholipidic components, via mixed surfactant-phospholipid micelle formation. This phenomenon is described by a three-stage model and characterized by two parameters: the highest surfactantlphospholipid ratio that can exist in a vesicle (Re=,) and the lowest surfactant/phospholipid ratio required to keep the lipid and surfactant in the form of mixed micelles (Resol). These parameters have been determined by spectrophotometry and 31P NMR spectroscopy, obtaining results in a good agreement with both techniques. The surfactants tested have been: sodium dodecyl sulfate (SDS), sodium laurylether sulfate (SLES), N-hexadecyl-trimethylammonium bromide (HTAB), octylphenol series (8-20 EO) and alkylbetaines (C-10, C-12 and C-14). Different Re,, and Re,, values have been obtained for each of the surfactants. This has permitted a study of the solubilizing capacity versus the phospholipidic bilayer of the different surfactants as a function of their structure. RCsumC L'interaction liposome-tensioactif a t t t ttudite moyennant I'effet cause par les molecules des tensioactifs sur des vtsicules grandes et unilamellaires prtpartes par la mtthode d'tvaporation en phase reverse. Le procts a m h e finalement ri la rupture des liposomes et A la solubilisation des composants phospholipidiques par la formation de micelles mixtes tensioactif-phospholipide. Ce phtnomtne est dtcrit par un modtle en trois ttages et caracttrist par deux paramttres: la plus haute relation tensioactif-phospholipide qui peut exister dans une vtsicule (Re=,) et la plus basse relation tensioactif-phospholipide requise pour solubiliser le lipide en micelles mixtes (ReWl). Ces paramttres ont t t t dttermints par spectrophotometrie et spectroscopie de RMN de P3', obtenant de rtsultats concordants avec les deux techniques. Les tensioactifs essayts ont t t t les suivants: dodecyl sulphate de sodium (SDS), laurylether sulphate de sodium (SLES), bromure de N-hexadecyltrimethylammonium (HTAB), une serie d'octylphenols (8-20 EO) et alkylbetaines (C-10, C-12 and C-14). On a obtenu difftrents valeurs de Re,, et de Re,, pour chacun des tensioactifs essayts. Ce fait a permis I'ttude de la capacite de solubilisation des difftrents tensioactifs face a des liposomes en fonction de la structure de ces tensioactifs.
Mechanism of mixed liposome solubilization in the presence of sodium dodecyl sulfate
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2001
Structural transformations of vesicles to micelles that take place during the interaction of sodium dodecyl sulfate (SOS) with individual and mixed vesicles of phosphatidyl choline (PC) and phosphatidic acid (FA), have been studied by monitoring changes in optical density and in the concentration of free SOS monomer in the respective systems. Incorporation of the surfactant monomers (SOS) in the bilayers was found to result in an initial increase in concentration of the mixed vesicles up to its saturation. Subsequently a progressive relaxation of these structures together with a simultaneous fonnation of mixed micelles was found to occur. The breakup of bilayer and the fonnation of mixed micelles were completely dependent on the structure of the individual phospholipid. The solubilization of the anionic phosphatidic acid vesicle was very fast in the presence of SOS, due to its simple structure and its compatibility with the SOS molecule. But solubilization of the zwitter ionic phosphatidyl choline vesicle was very complicated in the presence of SOS, possibly due to its complex structure and the zwitterionic nature. On the other hand, solubilization of the mixed vesicle (mixed liposome) and fonnation of mixed micelle was found to be relatively easier. This may be attributed to one of the phospholipid component preferentially coming out first through interaction with SOS, thereby making the overall system unstable and enhancing the micellization processes. 0 200 I Elsevier Science B. V. All rights reserved. studying solubilization of cell membranes [4-7] and surfactants interactions with such biosystems as skin. The interaction of surfactants with liposomes eventually leads to the rupture of its vesicle structure resulting in the solubilization of phospholipid components. In general, there is agreement that growth of vesicles occurs in the initial stages, followed by the formation of a number'of complex lipid-surfactant aggregates associated with the vesicle to micelle transformations. The interactions of sodium dodecyl sulfate (SDS) with
Solubilization of phosphatidylcholine liposomes by the amphoteric surfactant dodecyl betaine
Chemistry and Physics of Lipids, 1998
The interaction of the amphoteric surfactant N-dodecyl-N,N-dimethylbetaine (C 12 -Bet) with phosphatidylcholine (PC) liposomes was investigated. Permeability alterations were detected as a change in 5(6)-carboxyfluorescein (CF) released from the interior of vesicles and bilayer solubilization as a decrease in the static light-scattering (SLS) of the system. At sublytic level a initial maximum in the bilayer/water partitioning (K) followed by an abrupt decrease of this parameter occurred as the surfactant to lipid molar ratio (Re) rose. At lytic level a direct dependence was established between both parameters. The fact that the free surfactant concentration at sublytic and lytic levels showed values lower than and similar to its critical micelle concentration indicates that permeability alterations and solubilization were determined, respectively, by the action of surfactant monomer and by the formation of mixed micelles. A direct correlation occurred in the initial interaction steps (up to 50% CF release) between the growth of vesicles their fluidity and Re. A similar direct dependence was established during solubilization (up to 30% SLS) between the fall in both the surfactant-lipid aggregate size, the SLS of the system and Re. This surfactant showed higher capacity to solubilize PC liposomes than that reported by the commonly used non-ionic surfactants octyl glucoside and Triton X-100 and by the anionic one sodium dodecyl sulfate.
Archives of Biochemistry and Biophysics, 1999
The vesicle-to-micelle structural transitions that occurred in the interaction of sodium dodecyl sulfate with phosphatidylcholine vesicles were studied at the equilibrium by means of dynamic light scattering (at different scattering angles) and freeze-fracture electron microscopy techniques. The incorporation of surfactant monomers in the bilayers resulted in an initial contraction of the mixed vesicles formed up to their saturation (size reduction of about 10%). Then, a progressive relaxation of these structures (growth from 170 to 225 nm) and a simultaneous formation of mixed micelles (particles of about 6 nm) occurred. Hence, in this interval "relaxed mixed vesicles" and mixed micelles coexisted in different proportions without formation of intermediate complex aggregates (bimodal size distribution curves). Freeze-fracture electron microscopy showed a direct formation of mixed micelles within the bilayer and their subsequent separation from the vesicle surface without formation of complex intermediate aggregates. This simple process progressed up to the complete vesicle solubilization.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1999
The interaction of a series of alkyl sulfates (alkyl chain lengths C-10 (C 10 -SO 4 ), C-12 (C 12 -SO 4 ) and C-14 (C 14 -SO 4 )) with liposomes modeling the stratum corneum (SC) lipid composition (40% ceramides, 25% cholesterol, 25% palmitic acid and 10% cholesteryl sulfate) was investigated. The surfactant/lipid molar ratios (Re) and the bilayer/aqueous phase partition coefficients (K) were determined by monitoring the changes in the static light scattering of the system during solubilization. The fact that the free concentration for each surfactant tested was always similar to its critical micelle concentration (in the experimental working medium) indicates that the liposome solubilization was mainly ruled by the formation of mixed micelles. The K parameter progressively rose as the surfactant CMC decreased or its alkyl chain length increased, whereas the Re showed a minimum for C 12 -SO 4 . Thus, although the maximum ability to saturate or solubilize SC liposomes corresponded to the C 12 -SO 4 , the C 14 -SO 4 showed the highest degree of partitioning into liposomes or affinity with these bilayer structures. The overall balance of these two tendencies shows that the C 14 -SO 4 and the C 12 -SO 4 had, respectively the highest power to saturate and solubilize SC liposomes in terms of total surfactant amount needed to produce these effects. Different trends in the interaction of these surfactants with SC liposomes were observed when comparing the Re and K parameters with those reported for PC ones. Whereas SC liposomes were more resistant to the surfactant action, the affinity of these surfactants with these bilayer structures was higher in all cases. , bilayer/aqueous phase surfactant partition coefficient for liposome saturation; K sol , bilayer/aqueous phase surfactant partition coefficient for liposome solubilization; PA, palmitic acid; PI, polydispersity index; PIPES, piperazine-1,4 bis(2-ethanesulphonic acid); r 2 , regression coefficient; Re, effective surfactant/lipid molar ratio; Re sat , effective surfactant/lipid molar ratio for liposome saturation; Re sol , effective surfactant/lipid molar ratio for liposome solubilization; S b , surfactant concentration in the bilayers; SC, stratum corneum; SLS, static light-scattering; S w , surfactant concentration in the aqueous medium; S w,sat , surfactant concentration in the aqueous medium for liposome saturation; S w,sol , surfactant concentration in the aqueous medium for liposome solubilization; TLC-FID, thin-layer chromatography/flame ionization detection system.
ABSTRACT: Surfactant?liposome interactions have been previously studied through different methods and techniques. We present here a classical physical chemistry study on liposome solutions added to destabilizing agents at concentrations well above the solubilizationconcentration, whichenableustodraw useful andinterestingconclusions about the mechanism of surfactant-induced liposomal breakdown by simply exploiting the kinetics and the reaction order of the liposomal content release. In such excess of surfactant, the mechanism of surfactant-induced rupture of the liposomes has been demonstrated to be different from that proposed for low surfactant concentrations. Thus, depending on the surfactant concentration, two prevailing processes have been evidenced:(i)acooperativemechanismthatimpliestheassemblyofacriticalnumberof surfactantmoleculestotriggertheformationofachannelandthereforethereleaseofthe liposomal content and (ii) a mechanism driven by direct interaction of the surfactant molecules with the lipids that causes the complete solubilization of the liposomes. The former mechanism occurs at low surfactant concentrations, whereas the latter occurs at higher concentrations and above the CMC of the surfactants. The effect of different guests embedded into the liposomal bilayer on the mechanism of surfactant-induced liposomal breakdown has been compared by using the second-order rate constants measured for the liposome breakdown process.
Surfactant-induced release of liposomal contents. A survey of methods and results
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1988
A systematic approach to the phenomenon of surfactant-dependent release of liposomal contents has been attempted. A variety of methods have been comparatively studied. The influence of the size of the entrapped molecule, nature of the surfactant, composition of bilayers and sonication of liposomes have been considered separately. In order to compare different results, a parameter has been defined, R50, as the phospholipid/surfactant mole ratio producing 50% release of the entrapped solute. This parameter appears to be, to a large extent, independent of time and liposome concentration. Surfactant-induced release of liposomal contents does not occur as a result of breakdown of phospholipid bilayers, but is rather a different phenomenon, occurring at detergent concentrations substantially lower (2-5 times) than solubilization. The required amount of surfactant appears to increase with the size of the entrapped solute. R50 depends clearly on the nature of the soluble amphiphile, but there is no obvious relationship with its critical micellar concentration. Liberation of vesicle content also depends on bilayer composition: phospholipids have various effects on the stability of the membrane, while the hydrophobic peptide, gramicidin A, appears to have little influence. Cholesterol is interesting, since at equimolar proportions with phosphatidylcholine, it decreases the stability of bilayer towards Triton X-100, while increasing it in the presence of cholate. Sonication also exerts an influence on the surfactant-dependent release of vesicle contents; it appears to decrease the bilayer stability, so that lower detergent concentrations are required to liberate the entrapped solutes. Finally, it should be noted that, although the decrease in self-quenching of 6-carboxyfluorescein is a convenient method for the study of solute liberation, glucose release, as detected by enzymatic methods, may be more reliable for accurate measurements.
Interactions of Novel, Nonhemolytic Surfactants with Phospholipid Vesicles
Langmuir, 2007
PEG-12-acyloxystearates constitute a novel class of pharmaceutical solubilizers and are synthesized from polyethylene glycol and 12-hydroxystearic acid, which has been esterified with a second acyl chain. The hemolytic activity of these surfactants decreases drastically with increasing pendant acyloxy chain length, and surfactants with an acyloxy chain of 14 carbon atoms or more are essentially nonhemolytic. In this paper, the interactions of PEG-12-acyloxystearates (acyloxy chain lengths ranging from 8 to 16 carbon atoms) with phosphatidylcholine vesicles, used as a model system for erythrocyte membranes, were studied in search of an explanation for the large variations in hemolytic activity. Surfactant-induced alterations of membrane permeability were investigated by studying the leakage of vesicle-entrapped calcein. It was found that all of the surfactants within the series interact with the vesicle membranes and cause slow leakage at elevated surfactant concentrations, but with large variations in leakage kinetics. The initial leakage rate decreases rapidly with increasing pendant acyloxy chain length. After prolonged incubation, on the other hand, the leakage is not a simple function of acyloxy chain length. The effect of the surfactants on membrane integrity was also investigated by turbidity measurements and cryo-transmission electron microscopy. At a surfactant/lipid molar ratio of 0.4, the vesicle membranes are saturated with surfactant. When the surfactant/lipid molar ratio is further increased, the vesicle membranes are progressively solubilized into mixed micelles. The rate of this process decreases strongly with increasing acyloxy chain length. When comparing the results of the different experiments, it can be concluded that there is no membrane permeabilization below saturation of the vesicle membranes. The large variations in the kinetics suggest that several steps are involved in the mechanism of leakage induced by PEG-12-acyloxystearates and that their relative rates vary with acyloxy chain length. The slow kinetics may in part be explained by the low critical micelle concentrations (CMCs) exhibited by the surfactants. The CMCs were found to be in the range of 0.003-0.025 µM.
Characterization of the solubilization of lipid bilayers by surfactants
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1985
This communication addresses the state of aggregation of lipid-detergent mixed dispersions Analysis of recently published data suggest that for any given detergent-lipid mixture the most important factor m determining the type of aggregates (mixed vesicles or mixed micelles) and the size of the aggregate is the detergent to lipid molar ratio in these aggregates, herein denoted the effective ratio, R e. For mixed bilayers this effective ratio has been previously shown to be a function of the lipid and detergent concentrations and of an equilibrium partition coefficient, K, which describes the distribution of the detergent between the bilayers and the aqueous phase. We show that, similar to mixed bilayers, the size of mixed micelles is also a function of the effective ratio, but for these dispersions the distribution of detergent between the mixed micelles and the aqueous medium obeys a much higher partition coefficient. In practical terms, the detergent concentration in the mixed micelles is equal to the difference between the total detergent concentration and the critical micelle concentration (cmc) Thus, the effective ratio is equal to this difference divided by the lipid concentration Transformation of mixed bilayers to mixed micelles, commonly denoted solubilization, occurs when the surfactant to lipid effective ratio reaches a critical value. Experimental evaluation of this critical ratio can be based on the linear dependence of detergent concentration, required for solubilization, on the lipid concentration. According to the 'equilibrium partition model', the dependence of the 'solubilizing detergent concentration' on the lipid concentration intersects with the lipid axis at -1/K, while the slope of this dependence is the critical effective ratio. On the other hand, assuming that when solubilization occurs the detergent concentration in the aqueous phase is approximately equal to the critical micelle concentration, implies that the above dependence intersects with the detergent axis at the critical micelle concentration, while its slope, again, is equal to the critical effective ratio. Analysis of existing data suggests that within experimental error both these distinctively different approaches are valid, indicating that the critical effective ratio at which solubilization occurs is approximately equal to the product of the critical micelle concentration and the distribution coefficient K Since the nature of detergent affects K and the critical micelle concentration in opposite directions, the critical ('solubilizing') effective ratio depends upon the nature of detergent less than any of these two factors Abbreviations and symbols PC phosphatldvlchohne, L total hp~d concentration, D r, total detergent concentration, O h detergent concentration m bdayer, D~, detergent concentration tn dqueous medium, cmc, critical mlcelle concentratton, K = Db/LD~ I, R~ = Db/L, D~-m` and D~, m~ the detergent concentratlons (total and m the bdayer respechvely) when D,, = cmc, D~-and D~,, the detergent concentrations (total and Jn the bdayer, respectively) when solublhzatlon occurs R~ m'= D~rnt/L R~=D~/L, AD t AD W and AD h the detergent concentrations (total and m the water and bdayer, respecuvely) that should be added to dlsperstons m which Dw = cmc to solubfltze the hplds, K'=ADb/LAD,~, RH mean hydrodynamic radius of vesicles or mlcelles 0005-2736/85/$03 30 " 1985 Elsevier Science Pubhshers B V (Biomedical Dwlslon)
Mechanisms of Solubilization of Mixed Liposomes: Preferential Dissolution of Liposome Components
Industrial & Engineering Chemistry Research, 2005
The mechanism of vesicle-to-micelle transformation due to the interactions with sodium dodecylsulfate (SDS) has been studied by monitoring changes in the optical density, surface tension, SDS monomer concentrations, pyrene fluorescence, and mass spectrometry. Two inflection points appeared on the optical density as well as effective hydrodynamic diameter curves. Based on the results of the surface tension and SDS monomer measurements, the first inflection point is attributed to the saturation of bilayers by SDS monomers and the onset of liposome solubilization processes. The second inflection point corresponds to the onset of complete disruption of bilayers and the critical micelle concentration of the mixed systems. The fluorescence results show the core of the mixed micelles to be more hydrophobic than that of the SDS micelles, suggesting that liposome solubilization is a micellization process. From the individual phospholipid liposome solubilization studies, it was found that phosphatidic acid (PA) molecules are more susceptible toward SDS. Interestingly, it has been detected from the mass spectra that the disruption of liposome bilayers is a preferential dissolution process. It is proposed that, at low SDS concentration, PA molecules preferentially exit first from the mixed liposome bilayers (1:1 PA/phosphatidylcholine), causing liposome solubilization. In contrast, at high SDS concentrations, the breakdown of liposome takes place instantaneously.