Binding and distribution of water molecules in DPPC bilayers doped with ß-sitosteryl sulfate.

We have comparatively studied the behavior of water molecules associated with the DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) bilayers in the presence and absence of ß-sitosteryl sulfate (PSO4) with the help of differential scanning calorimetry (DSC) and SAXS (small-angle x-ray scattering) techniques. The DSC heating endotherms were analyzed to understand the intermolecular interactions between water molecules and the lipid headgroups. The strongly bound, weakly bound, and free water (SB-Water, WB-Water, and FW-Water, respectively) were thus identified in the bilayers and the impact of incorporating PSO4 was evaluated. The SAXS data provided the supporting evidence for the impact of PSO4 on the intake of water into the bilayer. Regardless of the presence or absence of PSO4, the SB-Water existed in the system as the non-freezable fraction. On the other hand, the WB-Water and FW-Water fractions, both of which are freezable, exhibited freezing and melting behaviors that differed from each other significantly. The enthalpies of fusion of the WB-Water, which differed from that of the FW-Water, also varied with the mole fractions of PSO4. PSO4 enhanced the fraction of WB -water in the bilayer while at the same time reducing the fractions of SB-Water and FW-Water. The optimum retainability and the ease of release of the available water makes this system efficient for maintaining skin homeostasis if used in cosmetic and pharmaceutical formulations.

Impact of Doping a Phytosteryl Sulfate on the Properties of Liposomes Made of Saturated and Unsaturated Phosphatidylcholines.

The size, dispersibility, and fluidity of DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine), POPC (1-palmitoy-2-oleoyl-sn-glycero-3-phosphocholine), and DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) liposomes doped with ß-sitosteryl sulfate (PSO4) were comparatively studied. In all three types of liposomes, PSO4 reduced sizes and enhanced the negative values of the ζ-potential. However, the effect on sizes quantitatively differed in the three cases in a manner dependent on their phase behaviors. PSO4 rigidified each type of membrane in its liquid crystalline phase and fluidized the gel phase. It enhanced the glucose trapping efficiency (TE) of both DPPC and DOPC liposomes. The TE of DPPC first increased with the increasing concentration of PSO4, then decreased gradually. On the other hand, in the case of DOPC, the TE increased significantly upon addition of PSO4, then remained nearly constant. Though the exact dependence of TE on the PSO4 concentration differed in the two cases, its effect, in each case, was more than the effect of ß-sitosterol (POH). The ability of PSO4 for reducing the size and enhancing dispersibility and TE of liposomes can be useful for preparing cosmetics and pharmaceutical formulations.

Phase Behavior of the Bilayers Containing Hydrogenated Soy Lecithin and ß-Sitosteryl Sulfate.

The phase behaviors of systems containing saturated phosphatidylcholine (PC) and plant steroids can be important for designing new alternative delivery methods. In our previous studies, we found that even a small amount of ß-sitosteryl sulfate (PSO4) significantly affects the phase behavior, hydration properties, and liposomal properties of pure saturated phosphatidylcholines [Kafle, A.; Colloids Surf., B 2018, 161, 59-66; Kafle, A.; J. Oleo Sci. 2018, 67 (12), 1511-1519]. In the current paper, we are reporting the phase behavior of a more complex system consisting of hydrogenated soy lecithin (HLC), which is useful as a carrier in drug delivery systems or in cosmetics, and PSO4. HLC, which is composed of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidic acid (PA), and lysophosphatidylcholine (LPC), demonstrated a versatile phase behavior. The PC component of HLC was found to separate from the PE and PA components as a result of nonideal mixing. At room temperature, these two domains represented two distinct gel phases denoted Lß1 and Lß2. The Lß1 phase selectively underwent transition into the liquid crystalline phase (Lα) at a lower temperature than Lß2. Upon addition of PSO4, at room temperature, the PC fraction gradually converted into the liquid-ordered (Lo) phase, while the (PE + PA) fraction remained unaffected. When heated above 60 °C, the whole material converted into the liquid crystalline phase. The observed fluidizing effect of PSO4 on HLC can find applications in preparing vehicles for moisture or drugs in cosmetic and pharmaceutical formulations.

Effects of ß-Sitosteryl Sulfate on the Properties of DPPC Liposomes.

The effect of ß-sitosteryl sulfate (PSO4) on the liposomal size, stability, fluidity, and dispersibility of DPPC liposomes prepared by vortex mixing, bath-sonication, and probe-sonication has been studied. PSO4 significantly decreases the particle size of the multilamellar liposomes (MLVs). The sizes of the vortexmixed and the bath-sonicated liposomes vary as a function of PSO4 concentration. On the other hand, PSO4 has only little effect on the particle sizes of probe sonicated liposomes. In some cases, the liposomal stability at higher PSO4 concentrations depends on the preparation method. PSO4 improves the dispersibility of the DPPC liposomes and enhances their hydration. It also increases the fluidity of the liposomes prepared by each method. Our results suggest that liposomes consisting of DPPC and PSO4 can be suitable as a cosmetic or pharmaceutical ingredient for the effective delivery of the active components into the body.

Effects of ß-Sitosteryl Sulfate on the Hydration Behavior of Dipalmitoylphosphatidylcholine.

We investigated the hydration behavior of dipalmitoylphosphatidylcholine (DPPC) bilayers containing sodium ß-sitosteryl sulfate (PSO4). PSO4 was found to enhance hydration in the headgroup region of DPPC bilayers. Therefore, with the incorporation of PSO4 into DPPC membranes, the amount of water required to reach the fully hydrated state was enhanced as indicated by the constant values of the main phase transition temperature (Tm) and the bilayer repeat distance (d). For example, with the addition of 20 mol% of PSO4, the saturation point was shifted to ~70 wt% water compared to ~40 wt% for pure DPPC and 47 wt% for DPPC-cholesterol. The effectiveness of PSO4 in fluidizing the membrane and enhancing its hydration state can be useful in the pharmaceutical and cosmetic industries.

Effects of ß-Sitosteryl Sulfate on the Phase Behavior and Hydration Properties of Distearoylphosphatidylcholine: a Comparison with Dipalmitoylphosphatidylcholine.

We have studied the phase behavior of distearoylphosphatidylcholine (DSPC) in the presence of sodium ß-sitosteryl sulfate (PSO4). PSO4 was found to induce sterol-rich and sterol-poor domains in the DSPC membrane. These two domains constitute a fluid, liquid ordered (Lo) phase and a gel (Lß) phase. PSO4 was less miscible in DSPC than in a dipalmitoylphosphatidylcholine (DPPC) membrane, as evidenced by its tendency to separate from the bilayer at a concentration of 50 mol%. This lack of miscibility was attributed to the greater van der Waals forces between the PC hydrocarbon chains. In addition to affecting the phase behavior, PSO4 also enhanced the hydration of the membrane. Despite its weaker interaction with DSPC compared to DPPC, its tendency to fluidize this phospholipid and enhance its hydration can be useful in formulating cosmetics and pharmaceutical products.

Effects of sodium ß-sitosteryl sulfate on the phase behavior of dipalmitoylphosphatidylcholine.

We have studied the phase behavior of dipalmitoylphosphatidylcholine (DPPC) containing sodium ß-sitosteryl sulfate (PSO4). PSO4 was found to lower the phase transition temperature of DPPC to a higher degree than cholesterol or ß-sitosterol. It also gave rise to the formation of a modulated (ripple) phase (Pß) at low to moderate concentrations. At concentrations greater than 25 mol%, it completely changed the membrane into a fluid phase. This shows that PSO4 is capable of disordering the hydrocarbon chains of PC efficiently. The characteristics of PSO4 for fluidizing the membrane can be useful for the pharmaceutical and cosmetics industries.

Detection of superoxide anion radical in a stratum corneum intercellular lipid model using an electrochemical sensor.

A stratum corneum intercellular lipid model was prepared in a quasi-non-aqueous system. It was found that the detection of the superoxide anion radical (O2⁻•) generated in the lipid model by ultraviolet (UV) irradiation was possible using an electrochemical O2⁻• sensor. The use of an electron spin resonance-spin trap method confirmed that the reactive oxygen species generated in the lipid model by UV irradiation was O2⁻•; the presence of a hydroxyl radical (•OH) was also proven. In addition, a reduction in the electric current in the O2⁻• sensor was observed in lipid models containing added antioxidants such as d-α-tocopherol and ß-carotene. Moreover, there was a correlation between the degree of oxidative degradation of the lipid, which was determined by the thiobarbituric acid method, and the electric current due to the O2⁻• detected using the O2⁻• sensor.