Light-scattering Changes Research Articles

Simultaneous absolute measures of glabrous skin hemodynamic and light-scattering change in response to formalin injection in rats

Subcutaneous injection of formalin is a well-known model to study the nature of inflammatory pain. One of the cardinal signs of inflammation is redness, as a result of increased blood perfusion. We used an optical technology, light reflectance spectroscopy, to noninvasively obtain absolute measures of cutaneous hemodynamic components, including the concentrations of oxy- ([HbO]), deoxy- ([Hb]), total-hemoglobin ([HbT]), oxygen saturation (SO 2), and the reduced light-scattering coefficient (μs’). The objective is to assess the effect of formalin-induced skin inflammation on the aforementioned parameters. Six rats were injected with formalin (50 μl, 3%) into left hind paw under pentobarbital anesthesia. Our results indicate prolonged increases in [HbO], [HbT], and SO 2 post injection only in the ipsilateral side. No statistically significant changes in [Hb] and μ s ’ occurred in either side. The arterial blood influx tends to be the major attribute of local hyperemia during inflammation. Thereby, [HbO] appears to be superior to [Hb] in measuring inflammation. In conclusion, the needle-probe-based light reflectance can be a feasible means to obtaining absolute measures of skin hemodynamic and light-scattering parameters when studying inflammatory pain.

Reticulocyte population data in different erythropoietic states

AimsTo assess changes in reticulocyte impedance volume, conductivity and light scatter (reticulocyte population data or RPD) obtained with the volume, conductivity and laser light scatter (VCS) technology in healthy subjects...

Detection of TiO2 nanoparticles in cells by flow cytometry

Evaluation of the potential hazard of man-made nanomaterials has been hampered by a limited ability to observe and measure nanoparticles in cells. In this study, different concentrations of TiO(2) nanoparticles were suspended in cell culture medium. The suspension was then sonicated and characterized by dynamic light scattering and microscopy. Cultured human-derived retinal pigment epithelial cells (ARPE-19) were incubated with TiO(2) nanoparticles at 0, 0.1, 0.3, 1, 3, 10, and 30 microg/ml for 24 hours. Cellular reactions to nanoparticles were evaluated using flow cytometry and dark field microscopy. A FACSCalibur flow cytometer was used to measure changes in light scatter after nanoparticle incubation. Both the side scatter and forward scatter changed substantially in response to the TiO(2). From 0.1 to 30 microg/ml TiO(2), the side scatter increased sequentially while the forward scatter decreased, presumably due to substantial light reflection by the TiO(2) particles. Based on the parameters of morphology and the calcein-AM/propidium iodide viability assay, TiO(2) concentrations below 30 microg/ml TiO(2) caused minimal cytotoxicity. Microscopic analysis was done on the same cells using an E-800 Nikon microscope containing a xenon light source and special dark field objectives. At the lowest concentrations of TiO(2) (0.1-0.3 microg/ml), the flow cytometer could detect as few as 5-10 nanoparticles per cell due to intense light scattering by TiO(2). Rings of concentrated nanoparticles were observed around the nuclei in the vicinity of the endoplasmic reticulum at higher concentrations. These data suggest that the uptake of nanoparticles within cells can be monitored with flow cytometry and confirmed by dark field microscopy. This approach may help fulfill a critical need for the scientific community to assess the relationship between nanoparticle dose and cellular toxicity Such experiments could potentially be performed more quickly and easily using the flow cytometer to measure both nanoparticle uptake and cellular health.

Multi-parameter flow cytometry as a tool to monitor heterotrophic microalgal batch fermentations for oil production towards biodiesel

Multi-parameter flow cytometry was used to monitor cell intrinsic light scatter, viability, and lipid content of Chlorella protothecoides cells grown in shake flasks. Changes in the right angle light scatter (RALS) and forward angle light scatter (FALS) were detected during the microalgal growth, which were attributed to the different microalgal cell cycle stages. The proportion of cells not stained with PI (cells with intact cytoplasmic membrane) was high (> 90%) during the microalgal growth, even in the latter stationary phase, suggesting that the microalgal cells built-up storage materials which allowed them to survive under nutrient starvation, maintaining their cytoplasmic membranes intact. A high correlation between the Nile Red fluorescence intensity measured by flow cytometry and total lipid content assayed by the traditional lipid extraction method was found for this microalga, making this method a suitable and quick technique for the screening of microalgal strains for lipid production, optimization of biofuel production bioprocesses, and scale-up studies. The highest oil content (∼28% w/w dry cell weight, estimated by flow cytometry) was observed in the latter stationary phase. In addition, C. protothecoides oil also depicted the adequate fatty acid methyl ester composition for biodiesel purposes at this growth phase, suggesting that the microalgal oil produced during the latter stationary phase could be an adequate substitute for diesel fuel. Medium growth optimization for enhancement of microalgal oil production is now in progress, using the multi-parameter approach.

Gold Nanoparticle Based Plasmon Resonance Light-Scattering Method as a New Approach for Glycogen−Biomacromolecule Interactions

A model was developed for the interactions between glycogen and biomacromolecules by gold nanoparticle plasmon resonance light-scattering method. The interactions between glycogen and biomacromolecules can alter the aggregation status of gold nanoparticles, which produced intensity changes in plasmon resonance light-scattering. This is a sensitive method to study the interactions between glycogen and biomacromolecules from nano- to micromolar level. And it is also a simple method that measurement can be carried out with a common fluorospectrometer using label-free gold nanoparticles as the transducer.

The Role of Varnishes in Modifying Light Reflection from Rough Surfaces - A Study of Changes in Light Scattering Caused by Variations in Varnish Topography and Development of a Drying Model

To obtain a better understanding of the variations in the appearance of paintings brought about by different varnishes, their ability to form an optically smooth film over rough surfaces was studied using laser scanning confocal microscopy and stylus profi lometry, as well as gloss and distinctness-of-image gloss measurements. Two different varnishes, one made with a low molecular weight resin and having low viscosity, and another, made with a polymer of high molecular weight and having high viscosity, were applied over glass plates that had been given surface roughness in the micrometer range. Measurement of the topography showed that the polymeric resin eliminated mid-to-high spatial frequency roughness of the ground glass but did not eliminate roughness of lower spatial frequencies. The results are discussed in terms of the surface state of the varnish, using concepts such as root-mean-square roughness, total integrated scattering and the power spectral density. These observations indicate that both varnishes reduce the wide-angle light scattering by the rough substrates, but only the varnish made with the low molecular weight resin reduces the small-angle scattering about the specular refl ection. This suggests that the smoothness of the varnished surface depends both on the molecular weight of the resin and on the spatial frequencies of the surface roughness of the surface beneath it. A model for the drying of varnishes is presented that takes the spatial frequency dependence into account.

Determination of membrane permeability to water from osmotically induced light-scattering changes of membrane vesicles: Analysis of the method

The kinetics of osmotically induced changes in vesicular volume and internal solute concentration were analyzed for membrane vesicles containing fixed quantity of impermeable osmoticum in the lumen. The kinetic curves of the concentration and volume changes were shown to be dissimilar. The average durations of these two processes may differ by several tens of percents, depending on the extent and polarity of the initially imposed osmotic gradient. For vesicles containing identical solutes in the internal and external solutions, the problem is analyzed of how the concentration and volume changes are manifested in changes of the effective scattering cross-section of the vesicle. The light scattering changes, directed oppositely to volume changes, were found to coincide roughly with the kinetics of volume changes. The analysis shows that calculations of water permeability coefficient should be based on average duration of volume changes rather than the duration of concentration changes. The replacement in calculations of the first parameter with the second one may result in overestimation of water permeability by a factor of 1.5. This might be relevant to the reported discrepancies in water permeability values determined by the osmotic and isotope methods. Although the allowance for 1.5-fold overestimation cannot fully account for the differences observed, it significantly lowers the discrepancy between these estimates in some cases. The opposite signs of light scattering and volume changes originate from the presence of two components in the optical path of the vesicle, i.e., the membrane and the lumenal solution.

Determination of the rate of K + movement through potassium channels in isolated rat heart and liver mitochondria

Both ATP-regulated (mitoK ATP) and large conductance calcium-activated (mitoBK Ca) potassium channels have been proposed to regulate mitochondrial K + influx and matrix volume and to mediate cardiac ischaemic preconditioning (IP). However, the specificity of the pharmacological agents used in these studies and the mechanisms underlying their effects on IP remain controversial. Here we used increasing concentrations of K +-ionophore (valinomycin) to stimulate respiration by rat liver and heart mitochondria in the presence of the K +/H + exchanger nigericin. This allowed rates of valinomycin-induced K + influx to be determined whilst parallel measurements of light scattering (A 520) and matrix volume ( 3H 2O and [ 14C]-sucrose) enabled rates of K + influx to be correlated with increases in matrix volume. Light scattering readily detected an increase in K + influx of < 5 nmol K + min − 1 per mg protein corresponding to < 2% mitochondrial matrix volume increase. In agreement with earlier data no light-scattering changes were observed in response to any mitoK ATP channel openers or blockers. However, the mitoBK Ca opener NS1619 (10–50 µM) did decrease light scattering slightly, but this was also seen in K +-free medium and was accompanied by uncoupling. Contrary to prediction, the mitoBK Ca blocker paxilline (10–50 µM) decreased rather than increased light scattering, and it also slightly uncoupled respiration. Our data argue against the presence of significant activities of either the mitoK ATP or the mitoBK Ca channel in rat liver and heart mitochondria and provide further evidence that preconditioning induced by pharmacological openers of these channels is more likely to involve alternative mechanisms.

Scattered Light and Visual Function in a Randomized Trial of Deep Lamellar Endothelial Keratoplasty and Penetrating Keratoplasty

To compare vision, intraocular forward light scatter and corneal backscatter between deep lamellar endothelial keratoplasty (DLEK) and penetrating keratoplasty (PK) for endothelial dysfunction. A randomized clinical trial. Thirteen eyes (12 patients) were randomized to DLEK with a 9 mm scleral incision, and 15 eyes (14 patients) were randomized to PK. The primary outcome was high-contrast best spectacle-corrected visual acuity (BSCVA) at 12 months after surgery; intraocular forward light scatter and corneal backscatter were measured at one, three, six, and 12 months after surgery. BSCVA at 12 months was 0.34 +/- 0.16 logMAR (logarithm of the minimum angle of resolution) for DLEK and 0.25 +/- 0.21 logMAR for PK (P = .23; minimum detectable difference at 12 months was 0.23 logMAR). The change in postoperative forward light scatter after DLEK correlated with the change in BSCVA (r = -0.66; P < .001; n = 11). Corneal backscatter was higher after DLEK than after PK at three and six months in the anterior third (P < or = .005), at one through 12 months in the middle third (P < .001), and at one through six months in the posterior third (P < or = .02) of the cornea. Backscatter after DLEK did not return to normal through 12 months (P < .001). BSCVA was similar at one year after DLEK and PK. Improvement in BSCVA after DLEK correlated with decreasing forward light scatter. Increased backscatter after DLEK originated not only from the posterior cornea (interface) but also from the host cornea, which might limit visual outcomes after posterior lamellar keratoplasty.

Irradiation‐Induced Enhancement of Pc 4 Fluorescence and Changes in Light Scattering are Potential Dosimeters for Pc 4‐PDT†

Phthalocyanine 4 (Pc 4) is a promising photosensitizer currently in clinical trials. Photobiological responses to Pc 4 photodynamic therapy (Pc 4-PDT) have been characterized extensively, but relatively little has been done to evaluate dose metrics for this sensitizer. We describe an irradiation-induced increase in fluorescence in tumor cell monolayers. This increase is due solely to enhanced fluorescence from Pc 4, as confirmed by confocal spectroscopy. In EMT6 cells incubated with 250 nM Pc 4 for 24 h, the maximum increase in fluorescence is approximately 3.7-fold above baseline levels. This increase occurs over a range of fluences, 0.05-0.6 J cm(-2), where clonogenic survival decreases by 3 orders of magnitude. Light scattering measurements performed on similarly treated EMT6 cells in suspension suggested a Pc 4-PDT-mediated mitochondrial swelling of approximately 13% at 0.6 J cm(-2), where fluorescence enhancement saturates under these treatment conditions. Fluorescence imaging and light scattering experiments performed at a five-fold lower Pc 4 incubation concentration revealed a reduced fluorescence enhancement at a five-fold higher fluence, which produced comparable mitochondrial swelling. Taken together, these data suggest that Pc 4 is initially aggregated at high local concentration in mitochondria and that irradiation relaxes the quenching of Pc 4 fluorescence through a mechanism that may involve mitochondrial swelling.

GABA-induced intracellular Ca 2+ elevation in the embryonic chick brainstem slice

We examined the intracellular Ca 2+ ([Ca 2+] i) elevation evoked by GABA in an 8-day embryonic chick brainstem slice using a Ca imaging technique with Ca green-1 AM. When small quantities of GABA were pressure-ejected on the surface of the slice, the [Ca 2+] i elevation was clearly detected. The GABA-induced [Ca 2+] i elevation was eliminated in a Ca 2+-free solution, whereas the previously reported GABA-induced light-scattering change was independent of extracellular Ca 2+. Although, micro-application of glycine or glutamate also induced [Ca 2+] i elevation, these changes were smaller than that by GABA. These results suggest that the GABA-induced [Ca 2+] i elevation is due to Ca 2+ entry resulting from membrane depolarization and may play an important role in the development of the central nervous system (CNS).

Non‐destructive Visible/NIR Spectroscopy for Differentiation of Fresh and Frozen‐thawed Fish

ABSTRACTNondestructive visible/near‐infrared (NIR) spectroscopy was evaluated to investigate whether fish has been frozen‐thawed. Fresh or frozen‐thawed red sea bream Pagrus major (n= 108) were scanned using a NIRSystems 6500 spectrophotometer equipped with a surface interactance fiber‐optic accessory then discriminated by soft independent modeling of class analogy (SIMCA) and linear discriminant analysis (LDA) based on principal component analysis (PCA) scores. The major effect of freeze‐thawing treatment involves a gross change in total reflectance after freezing and thawing; this arises from changes in light scatter presumably arising from alterations in the physical structure of at least the surface layer of fish. Untreated original absorbance spectra achieved much better (100%) classification accuracy for the prediction samples while the same figures for multiplicative scatter correction (MSC) treated spectra are considerably worse, indicating that scattering is the major information that makes classification work. No incorrect type of classification at all and also there are no samples classified to both groups either. This faster technique has the potential to differentiate fresh and frozen‐thawed fish and could be applied for online or at‐line processing control.

A Selective, Slow Binding Inhibitor of Factor VIIa Binds to a Nonstandard Active Site Conformation and Attenuates Thrombus Formation in Vivo

The serine protease factor VIIa (FVIIa) in complex with its cellular cofactor tissue factor (TF) initiates the blood coagulation reactions. TF.FVIIa is also implicated in thrombosis-related disorders and constitutes an appealing therapeutic target for treatment of cardiovascular diseases. To this end, we generated the FVIIa active site inhibitor G17905, which displayed great potency toward TF.FVIIa (Ki = 0.35 +/- 0.11 nM). G17905 did not appreciably inhibit 12 of the 14 examined trypsin-like serine proteases, consistent with its TF.FVIIa-specific activity in clotting assays. The crystal structure of the FVIIa.G17905 complex provides insight into the molecular basis of the high selectivity. It shows that, compared with other serine proteases, FVIIa is uniquely equipped to accommodate conformational disturbances in the Gln217-Gly219 region caused by the ortho-hydroxy group of the inhibitor's aminobenzamidine moiety located in the S1 recognition pocket. Moreover, the structure revealed a novel, nonstandard conformation of FVIIa active site in the region of the oxyanion hole, a "flipped" Lys192-Gly193 peptide bond. Macromolecular substrate activation assays demonstrated that G17905 is a noncompetitive, slow-binding inhibitor. Nevertheless, G17905 effectively inhibited thrombus formation in a baboon arterio-venous shunt model, reducing platelet and fibrin deposition by approximately 70% at 0.4 mg/kg + 0.1 mg/kg/min infusion. Therefore, the in vitro potency of G17905, characterized by slow binding kinetics, correlated with efficacious antithrombotic activity in vivo.

Measurements of Ocular Aberrations and Light Scatter in Healthy Subjects

To report and validate an optical imaging system that provides measurements of higher order ocular aberrations and light scatter in human eyes. An optical imaging system has been established that provides for combined measurements of ocular aberrations and light scatter. A laser beam was expanded and focused to a point on the retina by the optics of the eye. Wavefront sensing was performed with a Shack-Hartmann aberrometer to determine the wavefront aberration function and calculate the point spread function, giving information on ocular aberrations. A cylindrical lens was placed in the path of the incident laser beam path, and the line spread function was derived from the laser slit, giving information on combined ocular aberrations and light scatter. A relative index for ocular light scatter was determined by subtracting the area under the two line spread functions. Measurements were performed in one eye of 20 normal healthy subjects. The subjects' ages ranged between 21 and 78 years, and the average for all the eyes was 43 +/- 17 years (mean +/- SD). Higher order ocular aberrations were correlated with subjects' ages (r = 0.6; p = 0.01; N = 20). Combined higher order ocular aberrations and light scatter were correlated with age (r = 0.7; p = 0.0002; N = 20). Light scatter was correlated with age (r = 0.6; p = 0.002; N = 20). A method was established to measure age-related changes in ocular higher order aberrations and light scatter. Differentiating the contribution of ocular aberrations and light scatter to the retinal image quality has potential value for anticipating the outcome of procedures that attempt to compensate for ocular aberrations and for providing information on factors that degrade the optical performance of the eye in health and disease.

Mast cells generate intracellular reactive oxygen species that are involved in Ag mediated degranulation. Evidence for the lack of involvement of endogenous nitric oxide

Rationale Reactive oxygen species (ROS) and nitric oxide (NO) have an inhibitory effect on Ag mediated mast cell degranulation but there is controversy over whether mast cells themselves can produce these immunoregulatory molecules. We investigated the intracellular generation of ROS/NO in mast cells and examined the effect of such production on degranulation. Methods Mast cells were purified from OVA-sensitized BN rats and cultured overnight with inhibitors of ROS/NO. Following a 1 h incubation with the intracellular probes DCF (ROS nonspecific) or DAF-2 (NO specific), cells were stimulated with either OVA or LPS/IFN-γ and fluorescence monitored over the next 24-48 h by flow cytometry. Peritoneal macrophages were used as a positive control. Degranulation was monitored by release of incorporated serotonin and changes in light side scatter. Results Mast cells generated intracellular ROS following OVA challenge and this was accompanied by degranulation. Both ROS production and degranulation were inhibited by the flavoenzyme inhibitor DPI but not by the intracellular superoxide dismutase scavenger MnTmPyP. Challenge of mast cells with OVA or LPS + IFN-γ over a wide range of time periods failed to generate intracellular NO whereas peritoneal macrophages generated NO readily in response to LPS + IFN-γ.o:p> Conclusions Rat peritoneal mast cells generate intracellular ROS but not NO and a non-superoxide intracellular ROS product facilitates Ag-induced mast cell degranulation.

Automated quantitation of peripheral blood neutrophil activation in patients with myocardial ischaemia

Background: Coronary ischaemic syndromes are associated with neutrophil activation. The Bayer automated haematology analysers can detect increased light scatter of neutrophil populations, which correlates with neutrophil activation. We aimed to assess the role of an automated analyser in detecting systemic neutrophil activation in peripheral blood samples of patients with coronary ischaemia. Methods: A prospective cross-sectional study was undertaken in 18 patients with chronic stable angina, 9 with unstable angina and 26 normal control subjects. Whole blood samples were taken to assess neutrophil count and light scatter, and serum samples were taken from some patients for assessment of Troponin T, C-reactive protein (CRP) and myeloperoxidase (MPO). In addition, whole blood was stimulated in vitro with interleukin (IL)-8 and N-formyl-methionyl-leucyl-phenylalanine (fMLP) to assess changes in neutrophil light scatter detected by the analyser. Results: Neutrophil light scatter was increased in patients with chronic stable and unstable angina compared to normal control subjects (normal subjects 74.1 (73.3, 75.0) (mean arbitrary units (95% confidence intervals, (CI)) vs. 78.6 (76.9, 80.3) in the chronic stable angina group P<0.001 and 77.1 (75.3, 79.0) in the unstable angina group P<0.007). In vitro stimulation of whole blood produced comparable increases in neutrophil light scatter when morphological changes in neutrophils were demonstrable under electron microscopy. Conclusions: Automated measurement of neutrophil activation by light scatter is possible using the Advia 120 analyser and is superior to a neutrophil count in discriminating groups with angina. This technique may be useful in monitoring disease activity and progression in coronary artery disease and in guiding the use of anti-inflammatory therapies.

Light Scattering Changes in Isolated Brain Mitochondria during Anoxia - Magnesium Effect on Morphological Changes and Respiration -

Under pathological conditions, morphological changes of the cells and tissues may differ from those of normal conditions, which can be reflected by changes in light scattering (LS). Consequently, LS has been recognized as a potential non-invasive tool for optical diagnosis of living tissue. This paper aimed to identify the basic properties of LS of isolated brain mitochondria in vitro under normoxic and anoxic conditions in the presence and absence of Mg2+. An increase in LS was observed during anoxia in both the presence and absence of Mg2+. In both cases, the changes in LS initiated by anoxia and reoxygenation started concomitantly with the reduction of heme aa3. The rates of LS changes were slower than those of heme aa3, particularly in the presence of Mg2+. Mg2+ inhibited the morphological responses of mitochondria caused by the addition of ADP and ATP, and significantly reduced the oxygen consumption rate in state 4. These results are due to modulation of the K+/H+ antiporter affected by Mg2+. In addition, the mitochondria were well coupled, although the basal level of LS fell after addition of Mg2+. Therefore, the observed responses of mitochondria at anoxia were physiological and independent of the presence or absence of Mg2+. The relationship between LS and redox state of cytochrome c oxidase, an anoxic indicator, provides a basis to assess the tissue conditions in vivo.

Protection by rapid chemical preconditioning of stressed hippocampal slice: a study of cellular swelling using optical scatter imaging

It has been demonstrated that anoxic preconditioning protects against a subsequent ‘lethal’ injury in the hippocampal slice. The goal of this paper was to test the hypothesis that chemical preconditioning could help reduce the cellular swelling observed in excitotoxically injured hippocampal slices. The control slice was given a 10-min insult of 100 μM N-methyl- d-aspartate (NMDA) to simulate ischemic injury, followed by 30-min perfusion of standard Ringers solution. Cellular swelling was observed with a microscope designed to image light scatter changes resulting from cellular swelling. After the control NMDA injury, the average peak scatter change for CA1, CA3 and DG regions was 31.0±3.4, 22.4±4.8 and 27.6±4.6%, respectively. The peak scatter change of the overall slice was 26.0±3.6%. The experimental slices were preconditioned by three short 100 μM NMDA insults of 15 s each separated by 10 min of standard Ringers solution perfusion. The slices then received 10 min of ‘lethal’ injury by 100 μM NMDA. It was observed that the overall scatter signal, as a measure of cellular swelling, was reduced by 8.0% ( P<0.05, n=11) after preconditioning. A regional heterogeneity in the responses was also observed. Cellular swelling in CA1, CA3 and DG were reduced by 9.8% ( P<0.001, n=11), 9.2% ( P<0.005, n=11) and 7.7% ( P<0.05, n=11), respectively, when compared to the control. This study presents experimental evidence that short episodes of preconditioning may protect against acute cellular swelling under ischemic conditions.

Dodecyl maltoside as a solubilizing agent of stratum corneum lipid liposomes

The lytic interactions of the nonionic surfactant dodecyl maltoside (DM) with liposomes formed by a mixture of lipids modeling the stratum corneum (SC) lipid composition were investigated. To this end, the surfactant to lipid molar ratios (Re) and the normalized bilayer/aqueous phase partition coefficients (K) were determined by monitoring the changes in the static light-scattering (SLS) of the system during solubilization. The fact that the free surfactant concentration was always similar to its critical micelle concentration indicates that the liposome solubilization was mainly ruled by formation of mixed micelles. In addition, the linear dependence established between the level of SLS and Re indicates a progressive incorporation of DM in the liposomes as well as the progressive formation of mixed micelles. DM showed in all cases lower bilayer activity (higher Re values) and greater affinity with vesicles (higher K values) than those reported for its interaction with phosphatidylcholine (PC) liposomes. Thus, whereas the SC lipid liposomes were more resistant to the action of this surfactant, its degree of partitioning into SC bilayers was higher throughout the solubilization process than that exhibited in PC vesicles. Comparison of the present Re values with those reported for the lytic interaction of dodecyl glucoside (DG) with SC liposomes reveals that in the case of DM the bilayer activity was more than three times higher than that for DG in spite of the identical alkyl chain length.

Influence of the hydrophobic tail of alkyl glucosides on their ability to solubilize stratum corneum lipid liposomes

The lytic interactions of a series of alkyl glucosides (alkyl chain lengths ranging from C8 to C12) with liposomes formed by a mixture of lipids modeling the stratum corneum (SC) lipid composition were investigated. The surfactant-to-lipid molar ratios (Re) and the normalized bilayer/aqueous phase partition coefficients (K) were determined by monitoring the changes in the static light-scattering (SLS) of the system during solubilization. The fact that the free surfactant concentrations were always similar to their critical micelle concentrations indicates that the liposome solubilization was mainly ruled by the formation of mixed micelles. At the two interaction levels studied (100 and 0% SLS) the nonyl glucoside showed the highest ability to saturate and to solubilize liposomes (lowest Re values), whereas the dodecyl glucoside showed the highest degree of partitioning into liposomes or affinity with these structures (highest K values). Comparison of the data for octyl glucoside with that reported for the interaction of this surfactant with phosphatidylcholine (PC) liposomes shows that whereas the SC lipid liposomes were more resistant to the action of this surfactant (higher Re values), its degree of partitioning into SC bilayers was both in the saturation and solubilization of liposomes similar to that exhibited in PC vesicles (similar K values).