Rheological properties of a two phase lipid monolayer at the air/water interface: effect of the composition of the mixture

Many biologically relevant monolayers show coexistence of discrete domains of a long-range ordered condensed phase dispersed in a continuous, disordered, liquid-expanded phase. In this work, we determined the viscous and elastic components of the compressibility modulus and the shear viscosity of monolayers exhibiting phase coexistence with the aim at elucidating the contribution of each phase to the observed monolayer mechanical properties. To this purpose, mixed monolayers with different proportions of distearoylphosphatidylcholine (DSPC) and dimyristoylphosphatidylcholine (DMPC) were prepared and their rheological properties were analyzed. The relationship between the phase diagram of the mixture at 10 mN m(-1) and the rheological properties was studied. We found that the monolayer shear viscosity is highly dependent on the presence of domains and on the domain density. In turn, the monolayer compressibility is only influenced by the presence of domains for high domain densities. For monolayers that look homogeneous on the micrometer scale (DSPC amount lower that 23 mol %), all the analyzed rheological properties remain similar to those observed for pure DMPC monolayers, indicating that in this proportion range the DSPC molecules contribute as DMPC to the surface rheology in spite of having hydrocarbon chains four carbons longer.

A comparative clinical study investigating the efficacy of a dentifrice containing 8% strontium acetate and 1040 ppm fluoride in a silica base and a control dentifrice containing 1450 ppm fluoride in a silica base to provide immediate relief of dentin hypersensitivity

OBJECTIVE

The objective of this clinical study was to evaluate and compare the efficacy of a dentifrice containing 8% strontium acetate and 1040 ppm fluoride (from sodium fluoride) in a silica base (test dentifrice) to a control dentifrice containing 1450 ppm fluoride (from sodium fluoride) in a silica base, to reduce dentin hypersensitivity immediately after a single dab-on self-application, and after subsequent twice-daily brushing for three days.

METHODS

This was a randomized, examiner-blind, two-arm parallel group, three-day clinical study with seventy-nine subjects, stratified based on baseline tooth sensitivity. Tooth sensitivity was determined through subject responses to both evaporative (Schiff and Visual Analogue Scale [VAS]) and tactile stimuli (Yeaple probe), prior to and immediately after subjects self-applied a single pea-sized amount of either the test or control dentifrice to qualifying sensitive teeth, massaging the toothpaste onto the sensitive area for one minute. Tooth sensitivity was further assessed in response to the same stimuli after subjects brushed twice daily for an additional three days. Subject assessments were performed by the same examiner throughout the study.

RESULTS

Seventy-nine subjects completed this clinical study. Both subject groups exhibited reductions in dentin hypersensitivity directly after a single dab-on application. These reductions were significant across all measures for the test dentifrice. Between-treatment analyses showed the test dentifrice to be significantly better at relieving subjects' sensitivity across all measures (Schiff p = 0.0003, tactile p = 0.0003, and VAS p = 0.0077) compared to the control. After the additional three days of twice-daily brushing, between-treatment analyses showed the test dentifrice to be significantly better at relieving subjects' sensitivity across all measures (Schiff p = 0.0102, tactile p = 0.0493, and VAS p = 0.0067) than the control dentifrice.

CONCLUSION

The 8% strontium acetate, 1040 ppm fluoride dentifrice provided significant within-treatment reductions in dentin hypersensitivity for all measures at both time points (immediate and three-day brushing). Compared to the control dentifrice, significant between-treatment reductions in sensitivity were observed after a single dab-on application for all measures, and following the additional twice-daily brushing for three days in favor of the 8% strontium acetate, 1040 ppm fluoride dentifrice.

Development of an in situ methodology for the clinical evaluation of dentine hypersensitivity occlusion ingredients

OBJECTIVE

The aim of these clinical studies was to evaluate an in situ dentine tubule occlusion model, and to determine the occluding effect from novel occluding agents on patent dentine tubules compared to a positive control (8% strontium acetate--Sensodyne Mint) and negative control (a non-occluding agent) after four days of brushing treatment.

METHODS

These two in situ clinical studies were of single-center, randomized, crossover, single-blind design. Healthy participants wore two lower intra-oral appliances retaining four dentine samples for four treatment days for each period of the study. Samples were power-brushed each day with the test product. Assessment utilized surface topological analysis with a replica-based methodology under scanning electron microscopy (SEM).

RESULTS

Both clinical trials demonstrated that the positive control (8% strontium acetate) occluded dentine tubules significantly better (p = 0.0007; p < 0.0009) than the negative controls in the two studies, respectively. The experimental occluding agents demonstrated varying degrees of success for occluding effect compared to the controls.

CONCLUSION

The methodology clearly demonstrates that this in situ clinical model can robustly and reproducibly detect the dentine tubular occlusive effects of positive and negative controls in the treatment of dentine hypersensitivity brushed on the dentine surface. Using this methodology, new occlusion agents for the relief of dentine hypersensitivity can be assessed for occlusive effects on dentine.

A comparative clinical study evaluating stain removal efficacy of a new sensitivity whitening dentifrice compared to commercially available whitening dentifrices

OBJECTIVE

To assess the extrinsic stain removal efficacy of a new sensitivity dentifrice containing sodium tripolyphosphate (STP) to marketed whitening toothpastes after six weeks of product use.

METHODS

This was a single-center, double-blind, stratified, six-week clinical study comparing the reduction in stain area and intensity of Sensodyne Extra Whitening to Crest Maximum Strength Sensitivity Protection Whitening plus Scope and Colgate Tartar Control Plus Whitening Mint dentifrice, as measured by MacPherson's Modification of the Lobene Stain Index (MMLSI) in a forced stain model.

RESULTS

Two-hundred and ninety-five subjects completed the study. Tooth stain MMSLI scores showed significant differences between Sensodyne and Crest dentifrices in favor of Sensodyne for all surface sites (p = 0.014), and individually for facial (p = 0.023), lingual (p = 0.027), and interproximal (p = 0.014) surfaces. No significant statistical differences between Sensodyne and Colgate dentifrices were observed for any of the surfaces.

CONCLUSION

Results from this stain removal clinical study demonstrate significant extrinsic stain removal efficacy for all dentifrices relative to baseline. Significant differences between the two marketed sensitivity whitening dentifrices were demonstrated in favor of the new Sensodyne Sensitivity Whitening dentifrice.

Externally applied electric fields on immiscible lipid monolayers: repulsion between condensed domains precludes domain migration

Lipid and protein molecules anisotropically oriented at a hydrocarbon-aqueous interface configure a dynamic array of self-organized molecular dipoles. Electrostatic fields applied to lipid monolayers have been shown to induce in-plane migration of domains or phase separation in a homogeneous system. In this work, we have investigated the effect of externally applied electrostatic fields on different lipid monolayers exhibiting surface immiscibility. In the monolayers studied, lipids in the condensed state segregate in discontinuous round-shaped domains, with the lipid in the liquid-expanded state forming the continuous phase. The use of fluorescent probes with selective phase partitioning allows analyzing by epifluorescence microscopy the migrations of the domains under the influence of inhomogeneous electric fields applied to the surface. Our observations indicate that a positive potential applied to an electrode placed over the monolayer promotes a repulsion of the domains until a steady state is reached, indicating the presence of a force opposed to the externally applied electric force. The experimental results were modeled by considering that the opposing force is generated by the dipole-dipole repulsion between the domains.

Protein-mediated surface structuring in biomembranes

The lipids and proteins of biomembranes exhibit highly dissimilar conformations, geometrical shapes, amphipathicity, and thermodynamic properties which constrain their two-dimensional molecular packing, electrostatics, and interaction preferences. This causes inevitable development of large local tensions that frequently relax into phase or compositional immiscibility along lateral and transverse planes of the membrane. On the other hand, these effects constitute the very codes that mediate molecular and structural changes determining and controlling the possibilities for enzymatic activity, apposition and recombination in biomembranes. The presence of proteins constitutes a major perturbing factor for the membrane sculpturing both in terms of its surface topography and dynamics. We will focus on some results from our group within this context and summarize some recent evidence for the active involvement of extrinsic (myelin basic protein), integral (Folch-Lees proteolipid protein) and amphitropic (c-Fos and c-Jun) proteins, as well as a membrane-active amphitropic phosphohydrolytic enzyme (neutral sphingomyelinase), in the process of lateral segregation and dynamics of phase domains, sculpturing of the surface topography, and the bi-directional modulation of the membrane biochemical reactivity.

Properties of galactocerebroside layers transferred to glassy carbon electrodes: effect of an applied electric field

Galactocerebroside films deposited onto glassy carbon electrodes have been previously studied through the electrochemical response of a redox couple present in solution. Those experiments indicated that the film is inhomogeneous and that there are lipid-free places. In this work, we present experimental results indicating that those bare regions are formed when the electrode is introduced in an aqueous solution, and that the size and/or amount of uncovered domains increase when negative potentials are applied to the film. The experimental techniques employed for these findings are epifluorescence microscopy and ellipsometry.

The Folch-Lees proteolipid induces phase coexistence and transverse reorganization of lateral domains in myelin monolayers

Solvent solubilized myelin membranes spread as monomolecular layers at the air-water interface show a heterogeneous pattern at all surface pressures. In order to asses the role of myelin protein and lipid components in the surface structuring we compared the topography, as seen by Brewster angle microscopy (BAM) and epifluorescence microscopy, of monolayers made from mixtures containing all myelin lipids (except gangliosides) and variable proportions of Folch-Lees proteolipid protein (PLP, the major protein component of myelin). The presence of the single PLP, in the absence of the other myelin proteins, can reproduce the surface pattern of the whole myelin extract films in a concentration-dependant manner. Moreover, a threshold mole fraction of PLP is necessary to induce the lipid-protein component reorganization leading to the appearance of a rigid (gray) phase, acting as a surface skeleton, at low surface pressures and of fractal clusters at high surface pressures. The average size of those clusters is also dependent on the PLP content in the monolayer and on the time elapsed from the moment of film spreading, as they apparently result from an irreversible lateral aggregation process. The transverse rearrangement of the monolayer occurring under compression was different in films with the highest and lowest PLP mole fractions tested.

Safety evaluation of a novel whitening gel, containing 6% hydrogen peroxide and a commercially available whitening gel containing 18% carbamide peroxide in an exaggerated use clinical study

OBJECTIVES

The aim of this study was to compare the effect on oral soft tissue of a self-applied tooth whitening gel containing 6% hydrogen peroxide (Xtra White) with a marketed paint-on whitening gel containing 18% carbamide peroxide (Colgate Simply White) after 2-weeks of using products four times daily.

METHODS

A 2-week, examiner-blind, stratified, parallel design clinical trial was conducted. Twenty subjects were divided into two groups, balanced according to age and gender. Subjects followed a 2-week, twice-daily regimen of brushing with standard fluoride toothpaste and applied gel product to facial aspects of six upper and six lower incisors/canines, twice in succession with 30 min between applications. Soft tissue examinations were performed on Day 1, before the first application of the test products, and on Day 2, 5, 8 and 15.

RESULTS

During the 2-week treatment period, twelve adverse reactions were recorded as potentially attributable to the study products, evenly split between the two test groups. All reports were mild in symptoms and resolved without the need of medical intervention. None of the subjects experiencing an adverse event requested to be withdrawn from the study.

CONCLUSIONS

Under the exaggerated use conditions of this test, there was no evidence to suggest that either of the whitening gels produced irritation that was building or developing during the course of the study. It is concluded that both products are safe for their intended use.

Clinical evaluation of a novel whitening gel, containing 6% hydrogen peroxide and a standard fluoride toothpaste

OBJECTIVES

The aim of this study was to determine the effect on tooth colour (after 1 and 2 weeks use) of a self-applied tooth-whitening gel containing 6% hydrogen peroxide using a novel applicator, compared to a standard fluoride toothpaste.

METHODS

A 2-week, examiner-blind, stratified, parallel design clinical trial was conducted. Efficacy was measured by comparing the Vita shade scores recorded at baseline and after 1 and 2 weeks of product application. To qualify for the study, subjects were required to have at least one upper incisor/canine tooth measuring Vita shade A3 or darker. All upper incisors/canines of qualifying subjects were evaluated for change in Vita shade irrespective of their level of whiteness at baseline, allowing for the whitening gel to be tested on the full range of Vita tooth shades. One hundred and seventeen subjects were divided into two groups, balanced according to their darkest tooth shade. One group followed a 2-week, twice-daily regimen of brushing with toothpaste followed by the application of the hydrogen peroxide whitening gel. The other group brushed twice daily with toothpaste for 2 weeks.

RESULTS

Subjects using the whitening gel showed a statistically significant improvement, (p<0.05) in mean tooth shade score of 0.75 and 1.02 units after 1 and 2 weeks, compared to baseline. These improvements from baseline were significantly greater than those observed for the toothpaste only group (0.14 and 0.35 units change after 1 and 2 weeks).

CONCLUSIONS

The self-applied tooth-whitening gel containing 6% hydrogen peroxide has been shown to significantly improve the whiteness of teeth after 1 and 2 weeks of product use, compared to the baseline and the toothpaste only group.

Evaluation of a whitening gel designed to accelerate whitening

A clinical trial was conducted with 25 subjects to evaluate the effects and safety of Zoom! Take-Home whitening gel, a 6% hydrogen peroxide gel for vital tooth bleaching. Tooth bleaching was accomplished using a tray system overnight for 6 nights. Over the 6 nights, a significant change (from darker to lighter) was seen in tooth shades as demonstrated by 3 assessment methods: VITA Shade Value Oriented Guide, Trubyte Bioform Color Ordered Shade Guide scoring system, and the Chroma Meter CR-321 assessments. VITA Shade scores showed a mean change of -6.49 shades (P = .0001) from baseline to day 4 and a -7.72 shades (P = .0001) from baseline to day 7. The Trubyte scores showed a mean change of -9.31 shades (P = .0001) from baseline to day 4 and a -10.77 shades (P = .0001) from baseline to day 7. The Chroma Meter was used to measure tooth color. Analysis of Chroma Meter data showed a significant change in color (delta E), 13.82 mean score change (P = .0001) from baseline to day 4 and a 7.25 mean score change (P = .0001) from baseline to day 7. At day 4 minor tooth sensitivity was reported, and all tooth sensitivity resolved within a few days after treatment.

Clinical study to compare two in-office (chairside) whitening systems

The objective of this clinical study was to compare the whitening/bleaching efficacy of two marketed in-office whitening systems: Discus Dental Zoom! Chairside System (25% hydrogen peroxide whitening gel) and Opalescence Xtra Boost Kit (38% hydrogen peroxide whitening gel), using the Vita Shade Guide and chromameter measurements. The study was an examiner-blind, parallel group, randomized and controlled clinical trial conducted in a dental setting. All subjects signed a study consent form prior to admission and were given Crest Regular Toothpaste and an Oral-B 40 straight-handle toothbrush to use during the study. Subjects received a supragingival prophylaxis followed by a screening eligibility Vita Shade assessment from which 22 subjects were selected. At baseline, all six maxillary anterior teeth were assessed with the Vita Shade Guide. Chromameter measurements were taken on either the right maxillary central or left maxillary central (tooth No. 8 or tooth No. 9). Subjects were assigned to one of two treatment groups, and had three applications of their assigned product. Following completion of the treatment phase, and on post-treatment Days 2 and 7, a visual examination of the condition of the oral soft tissues, together with a Vita Shade assessment on maxillary anterior teeth, a chromameter reading and a questionnaire regarding tooth sensitivity were completed. At the termination of the study, the statistical analysis of the Vita Shade scores indicated that both products significantly (p < 0.0001) lightened the color of the teeth. The average improvement was between 6 and 9 shade changes. Additionally, the Zoom! Chairside System was significantly better than the Opalescense Xtra Boost Kit at all time points: post-treatment (p < 0.0001); Day 2 (p < 0.004); Day 7 (p < 0.003). This difference was between 1 and 2 shade changes. The chromameter readings showed a significant difference in the overall color change (delta E) to a lighter color for both the Zoom! Chairside System and the Opalescence Xtra Boost Kit. Using delta E, the Zoom! Chairside System was directionally better than the Opalescense Xtra Boost Kit at Day 2 (p < 0.08), and significantly better at Day 7 (p < 0.025). Analysis of the composite parameters of delta E (L*, a*, b*) showed that no differences could be detected in the a* (redness) parameter. Changes were observed in the L* (brightness) and b* (yellow) parameters which paralleled the delta E differences. There were no significant differences in induced sensitivity between whitening systems at any time point.

Concerted modulation by myelin basic protein and sulfatide of the activity of phospholipase A2 against phospholipid monolayers

The effect of myelin basic protein (MBP) on the activity of phospholipase A2 (PLA2, EC 3.1.1.4) against monolayers of dilauroylphosphatidylcholine (dlPC) or dilauroylphosphatidic acid (dlPA) containing different proportions of sulfatide (Sulf) and galactocerebroside (GalCer) was investigated. MBP was introduced into the interface by direct spreading as an initial constitutive component of the lipid-protein film or by adsorption and penetration from the subphase into the preformed lipid monolayers. The effect of MBP on PLA2 activity depends on the type of phospholipid and on the proportion of MBP at the interface. At a low mole fraction of MBP, homogeneously mixed lipid-protein monolayers are formed, and the PLA2 activity against dlPC is only slightly modified while the degradation of dlPA is markedly inhibited. This is probably due to favorable charge-charge interactions between dlPA and MBP that interfere with the enzyme action. The PLA2 activity against either phospholipid is increased when the mole fraction of MBP exceeds the proportion at which immiscible surface domains are formed. GalCer has little effect on the modulation by MBP of the phospholipase activity. The effect of Sulf depends on its proportions in relation to MBP. The individual effects of both components balance each other, and a finely tuned modulation is regulated by the interactions of MBP with Sulf or with the phospholipid.

Synthesis and antimicrobial evaluation of new phenoxyacetamide derivatives

New N-(5-methylisoxazol-3-yl)-2 or 3 or 4-(phenoxyacetamido)benzamides 6a-t were synthesized and tested for their in vitro antimicrobial activity against gram positive (Staphylococcus aureus ATCC 25923) and gram negative (Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853) bacteria as well as fungi (Candida albicans ATCC 10231, Candida tropicalis ATCC 13803 and Cryptococcus neoformans ATCC 90112). Compounds 6 were devoid of antibacterial as well as antifungal activities at maximum tested concentrations of 50 micrograms/ml for bacteria and 100 micrograms/ml for yeast.

The amphiphilic character of glycogenin

This study describes for the first time the amphiphilicity of the protein moiety of proteoglycogen. Glycogenin but not proteoglycogen associates to phospholipid vesicles and forms by itself stable Gibbs and Langmuir monolayers at the air-buffer interface. The adsorption free energy (-6.7 kcal/mol) and the glycogenin collapse pressure (47 mN/m) are indicative of its high surface activity which can thermodynamically drive and retain the protein at the membrane interface to a maximum equilibrium adsorption surface pressure of 21 mN/m. The marked surface activity of glycogenin is further enhanced by its thermodynamically favorable penetration into zwitterionic and anionic phospholipids with a high cut-off surface pressure point above 30 mN/m. The strong association to phospholipid vesicles and the marked surface activity of glycogenin correspond to a high amphiphilic character which supports its spontaneous association to membrane interfaces, in which the de novo biosynthesis of glycogen was proposed to initiate.

Transduction to self-assembly of molecular geometry and local interactions in mixtures of ceramides and ganglioside GM1

In mixed monolayers with ganglioside GM1, ceramide induces a non-ideal increase of the monolayer collapse pressure, a reduction of the mean molecular area and a decrease of the surface potential per molecule at all surface pressures. The critical packing parameter and van der Waals interaction energy calculated from monolayer data predict the transduction of changes from the molecular to the supramolecular level, such as formation of bilayers and possible subsequent facilitation of non-bilayer structures as the ceramide concentration increases, along with a greater thermal stability of the lipid structures. In agreement with the expectations from monolayer data, calorimetry, dynamic light scattering and electron microscopy data reveal the actual presence of phases with high phase-transition temperatures; at about 5 mol% ceramide in the mixture, the aggregates change their topology from micelles to multilamellar vesicles of increasing size and finally to long, thin tubules as the amount of ceramide in the system increases.

Synthesis and pharmacological study of ethyl 1-methyl-5-(substituted 3,4-dihydro-4-oxoquinazolin-3-yl)-1H-pyrazole-4-acetates

Several new ethyl 1-methyl-5-(substituted 3,4-dihydro-4-oxoquinazolin-3-yl)-1H-pyrazole-4-acetates 2, substituted at 2 and, alternatively at, 6, 7 or 8 positions of the quinazolinone nucleus, were synthesised. The compounds were screened for their analgesic and antiinflammatory activities, acute toxicity and ulcerogenic effect. Substitution in the benzene moiety of the quinazolinone ring did not show any advantage for the analgesic activity, whereas it improved in some cases the antiinflammatory activity. Some compounds showed appreciable antiinflammatory activity and, at the same time, very low ulcerogenic index.

Phenylamides of 1-phenyl (or methyl)-5-benzamidopyrazole-4-carboxylic acid as vratizolin analogs with analgesic and antiinflammatory activities

A number of phenylamides of 5-benzamidopyrazole-4-carboxylic acid were prepared in 50-80% yields from 1-phenyl (or methyl)-6-phenylpyrazolo[3,4-d]1,3-oxazin-4(1H)-ones and aniline derivatives. All the compounds were tested for their analgesic and antiinflammatory activities, as well as for their ulcerogenic potential and acute toxicity. Some derivatives, when compared to phenylbutazone, proved more active in the tests for analgesic and antiexudative activities, but less active in the carrageenin paw oedema test. The compounds proved to posses marginal or no ulcerogenic effect, as well as low systemic toxicity.

c-Fos is surface active and interacts differentially with phospholipid monolayers

The transcription factor c-Fos forms stable Gibbs and Langmuir monolayers at the air-buffer interface. Its marked surface activity is enhanced by penetration into phospholipid films above the protein's own maximum adsorption surface pressure to a lipid-free interface. The protein-phospholipid stabilizing interactions at the interface depend on the lipid polar head group and the increases of lateral surface pressure generated are comparable to those of membrane-active proteins. The surface activity of c-Fos is strong enough to thermodynamically drive and retain c-Fos at the membrane interface where it may exert direct or indirect effects.