Formation of bilayer membrane and niosomes by double-tailed polyglyceryl-type nonionic surfactant

Vesicle formation of single-tailed amphiphilic alkyltrimethylammonium bromides in water induced by dehydration-rehydration

We recently found that rough glass surfaces (RGSs) can in situ mediate the micelle-to-vesicle transition in single-component solutions of simple single-tailed amphiphiles (STAs), but only result in a relatively small number of vesicles coexisting with a large number of micelles. In the current work, a dehydration-rehydration (DHRH) method was used to induce the formation of vesicles in the single-component aqueous solutions of alkyltrimethylammonium bromides (C_nTABs, n = 12, 14, and 16), a kind of typical cationic STAs. That is, a C_nTAB micelle solution dropped on smooth glass surfaces (SGSs) was first dried, and the dried C_nTAB aggregates were then rehydrated in a monomer solution of C_nTAB. A large population of vesicles and even pure vesicle (or vesicle-dominated) systems were obtained, indicating that the DHRH process could more effectively induce the formation of STA vesicles than RGS in situ mediation. The so-obtained vesicles were characterized using DLS, FF-/cryo-TEM, AFM, SAXS, and fluorescence techniques, and their stability was determined. In addition, the effects of the conditions of DHRH and the chain length of C_nTABs on the vesicle formation were examined. It was demonstrated that the vesicles can be formed as long as the concentrations of C_nTABs in the rehydrated systems are higher than their critical micelle concentrations. The size and wall thickness of vesicles increase with an increase in chain length. A possible mechanism for the DHRH-induced vesicle formation is proposed: bilayer sheets are formed on SGSs during dehydration, and then detached from the SGSs to form vesicles during rehydration. A highly interdigitated structure of alkyl chains between two leaflets was identified in the bilayers, which probably is the origin of the formation and stability of STA vesicles.

Formulation of Bicelles Based on Lecithin-Nonionic Surfactant Mixtures

Bicelles have been intensively studied for use as drug delivery carriers and in biological studies, but their preparation with low-cost materials and via a simple process would allow their use for other purposes as well. Herein, bicelles were prepared through a semi-spontaneous method using a mixture of hydrogenated soybean lecithin (SL) and a nonionic surfactant, polyoxyethylene cholesteryl ether (ChEO₁₀), and then we investigated the effect of composition and temperature on the structure of bicelles, which is important to design tailored systems. As the fraction of ChEO₁₀ (X_C) was increased, a bimodal particle size distribution with a small particle size of several tens of nanometers and a large particle size of several hundred nanometers was obtained, and only small particles were observed when X_C ≥ 0.6, suggesting the formation of significant structure transition (liposomes to bicelles). The small-angle neutron scattering (SANS) spectrum for these particles fitted a core-shell bicelle model, providing further evidence of bicelle formation. A transition from a monomodal to a bimodal size distribution occurred as the temperature was increased, with this transition taking place at lower temperatures when higher SL-ChEO₁₀ concentrations were used. SANS showed that this temperature-dependent size change was reversible, suggesting the SL-ChEO₁₀ bicelles were stable against temperature, hence making them suitable for several applications.

Thermodynamically stable vesicle formation of biodegradable double mPEG-tailed amphiphiles with sulfonate head group

The development of efficient, biodegradable and biocompatible surfactants has become a pressing need because of adverse effects of surface-active compounds on the aquatic environment and human health. Cleavable surfactants containing a labile functional group have the ability to eliminate some of these problems. Consequently, PEGylated amphiphiles have found widespread applications in pharmaceutics, household purposes, and drug delivery. Herein we report synthesis and characterization of two novel amphiphiles which to our knowledge are the first examples of double PEG-tailed amphiphiles with an anionic head group. Considering their chemical structure, they are expected to be biodegradable, biocompatible, milder and less irritant than conventional surfactants. The solution behavior of these newly developed amphiphiles was thoroughly investigated in aqueous buffer (pH 7.0) at 25 °C. The surface activity of the compounds in aqueous buffer was studied by surface tension measurements. The self-assembly properties were investigated by various techniques such as fluorescence and NMR spectroscopy, dynamic light scattering, transmission electron microscopy, atomic force microscopy, and isothermal titration calorimetry. Both molecules were found to be surface active in water and exhibit spontaneous vesicle formation in the absence of any additives at room temperature. As in the cases of conventional surfactants, the self-assembly is driven by the hydrophobic effect. The vesicles produced in aqueous media were shown to encapsulate hydrophobic dyes and exhibit structural transitions upon addition of salts. The sensitivity of the vesicles to change in environments qualifies them for potential use in drug delivery.

Spontaneous vesicle formation by biodegradable novel double mPEG-tailed amphiphiles.

What dominates the interfacial properties of extended surfactants: Amphipathicity or surfactant shape?

HYPOTHESIS

The properties of conventional surfactants (c-surfactants) are generally accepted to be amphipathicity-dominated, but extended surfactants (e-surfactants) are additionally polypropylene oxide (PPO)-dependent; this additional property makes us wonder how an intramolecular PPO spacer would be "extended" at various interfaces and what is responsible for the excellent all-round properties of e-surfactants.

EXPERIMENTS

A series of novel sodium medium alkyl chain PPO-b-PEO sulfates (2-ethylhexyl polypropylene oxide-block-polyethylene oxide sulfates, C₈P_pE_eS) were designed, synthesized and structurally identified. Tensiometry was applied to estimate the surfactant shape at the air/water surface. Surface tension, interfacial tension, emulsifying power, electrolyte tolerance, adsorption onto oil sands and thermal hydrolysis stability were measured to evaluate the effect of the PPO coil on the interfacial and micellar properties of the e-surfactants.

FINDINGS

On the basis of obtaining greater values for e-surfactants than c-surfactants for both surface area (a_m) per surfactant molecule and the corresponding shape factor (S), we were surprised to find that e-surfactants form a rugby ball shape not only at the air/water surface but also at the oil/water interface; this result is potentially explained by the PPO spacer coiling and collapsing to produce dense packing at the monolayer adsorption, which is rationally borrowed by other interfaces. Many positive or negative correlations were observed between the interfacial/micellar properties of C₈P_pE_eS and a_m values, which seems that the surfactant shape dominants the properties of the e-surfactants. In fact, the properties of C₈P_pE_eS are dominated by the dynamic amphipathicity and assisted by the rugby ball shape of the molecules because of both being driven by the dynamic biphasic affinity of the PPO coil in response to the external environment; these findings provide soft interfacial materials specially adapted for surfactant flooding.

Comparative Study of Conventional/Ethoxylated/Extended n-Alkylsulfate Surfactants

A series of novel anionic e-surfactants n-C _cP _pS was molecular designed and synthesized from long-chain fatty alcohols by polypropoxylation and sulfation followed by neutralization. Excellent all-round performance of extended surfactants (e-surfactants) interests us how a simple polypropylene oxide (PPO) spacer has great effects on properties. By a comparative study of conventional/ethoxylated/extended n-alkylsulfate surfactants, we were surprised to find that e-surfactants are in an obvious rugby shape at the air/water surface according to molecular surface area ( a_m), and it comes down to the intramolecular PPO spacer coiling and surface-induced collapse. On the basis of the interfacial properties of the e-surfactants, it is found that the PPO spacer can provide both hydrophilic and lipophilic contributions to an e-surfactant molecule. The synergism between PPO spacers and alkyl chains indicates that a certain PPO spacer can adjust the contributions in view of different alkyl chain lengths. Therefore, it is both the rugby-shaped molecular geometry of e-surfactants and the dynamic amphipathicity of a PPO spacer that makes e-surfactants behave with excellent interfacial and solution properties for household cleaning. Therefore, this work gives us a hint that the molecular geometry of surfactants plays a vital role in interfacial and solution properties similar to molecular amphipathicity.

Synthesis of Nitrogen Containing Biocompatible Non-ionic Surfactants and Investigation for Their Self-Assembly Based Nano-Scale Vesicles

Nonionic surfactants are increasingly interesting because of the solubility and release of drugs. Here, a synthesis of four nonionic nitrogen-containing surfactants is reported. In the synthesis, sulfonamide was reacted with alkyl halides of different lipophilicity. The synthesized nonionic surfactants were characterized by 1H NMR and mass spectroscopy. Their critical micelle concentration (CMC) was determined with a UV spectrophotometer. The self-assembly of surfactants to form drug-loaded, niosomal vesicles with Simvastatin as model drug was investigated. The resulting niosoaml vesicles were characterized by atomic force microscope (AFM), zeta-sizer, and UV spectrophotometer for shape, size, polydispersity index, zeta potential, and drug inclusion efficiency. Their biocompatibility has been determined by blood hemolysis and cell toxicity tests. The synthesized surfactants showed low CMC values and were able to form nano-sized round niosomal vesicles with a homogeneous population and surface negativity. Depending on the lipophilicity, they absorbed an increased amount of drug. The biocompatibility studies show that the surfactants are hemocompatible and non-toxic. The results of the study confirm that the synthesized nonionic surfactants are suitable for the solubilization and release of hydrophobic drugs as efficient novel biocompatible carriers.

Hemolytic and cellular toxicology of a sulfanilamide-based nonionic surfactant: a niosomal carrier for hydrophobic drugs

Biocompatible surfactants are of diverse pharmaceutical interest due to their ability to self-assemble into nano-particulate systems which can be used for single-step drug loading, based upon the hydrophobic-hydrophobic interaction between a hydrophobic drug and the lipophilic part of a surfactant molecule. However, surfactants are associated with cytotoxicity and hemolysis due to their amphiphilic interaction with cellular membranes. This study reports a novel membrane-compatible surfactant, synthesized from sulfanilamide and its self-micellization into niosomes. The surfactant was synthesized in a single step reaction via the introduction of an alkyl chain in the sulfanilamide moiety by conjugation with deconyl chloride. The synthesized surfactant (S-SDC) was characterized by ¹H and ¹³C NMR, mass spectrometry and single crystal XRD. The S-SDC niosomes were explored for drug delivery with clarithromycin as a model drug. The biocompatibility of the surfactant was investigated through hemolysis and cytotoxicity. The surfactant presented a very low critical micellar concentration (CMC) of 0.04 mM and entrapped 65% of the drug which was released in a sustained manner, over 12 h, at acidic and physiological pH. The vesicles were spherical in shape with 234 ± 3.61 nm mean diameter and a narrow size distribution. Niosomes were hemocompatible and nontoxic to cellular membrane. The results suggested the sulfanilamide based surfactant can be applied as a novel and cell membrane compatible niosomal drug delivery vehicle.

Cholesterol-Induced Formation of Liquid Ordered Phase-Like Structures in Non-Phospholipid Systems

The formation of liquid ordered (L_o) phase-like structures in stearyltrimethylammonium chloride/cholesterol/1,3-butanediol/water and hepta(oxyethylen) octadecyl ether/cholesterol/1,3-butanediol/water systems was investigated. Differential scanning calorimetry and X-ray scattering measurements confirmed that L_o phase-like structures were formed in both surfactant/cholesterol systems, similar to the lysophospholipid/cholesterol system. It was revealed that the concentration of cholesterol at which only L_o phase-like structures are formed increases in the order stearyltrimethylammonium chloride < lysophospholipid < hepta(oxyethylen) octadecyl ether. In addition, for both surfactants, the interlayer spacing, d, was larger for L_o phase-like structures than for α-gel structures. These results suggest that the ionicity and structure of the hydrophilic group of each surfactant play important roles.

One-step formulation of nonionic surfactant bicelles (NSBs) by a double-tailed polyglycerol-type nonionic surfactant

Bicelles are generally formed by phospholipid-based systems and are useful for various applications, such as nanocarriers or membrane protein crystallization. The same disc-like assemblies, nonionic surfactant bicelles (NSBs), can also be formed using nonionic amphiphiles, but this has not been reported extensively. We report a novel NSB system that employs the double-tailed nonionic amphiphile, polyglyceryl dialkyl ether (C₁₂C_mG_n), which has two alkyl chains and a polyglyceryl group. A symmetric-tail molecule, C₁₂C₁₂G_13.8, formed vesicles, whereas an asymmetric-tail molecule, C₁₂C₁₄G_15.5, formed NSBs through a simple one-step process using ultrasonication. The 1 wt% aqueous solution of C₁₂C₁₄G_15.5 was in a two-phase equilibrium of a lamellar phase and a water phase. Transparent dispersion was obtained through ultrasonication treatment. The size distribution in the dispersion was obtained by dynamic light scattering (DLS), resulting in a narrow distribution of around 20 nm in diameter. A negatively-stained transmission electron microscopy (TEM) image showed oblong and spherical shapes, which are typically observed in bicelle-forming systems. A small angle neutron scattering (SANS) measurement well proved bicelle formation by fitting a core-shell bicelle form factor model. The disc thickness and diameter were in agreement with the values obtained by DLS and TEM, respectively. A larger shell thickness at the rim part than at the flat disc part suggested that NSB aggregates have inhomogeneous molecular distribution. Similar to phospholipid systems, the bicelle-forming C₁₂C₁₄G_15.5 system produced a defective lamellar phase formation at high surfactant concentrations, whereas a general lamellar phase was formed in the vesicle-forming C₁₂C₁₂G_13.8 system.

Retinal gene delivery enhancement by lycopene incorporation into cationic niosomes based on DOTMA and polysorbate 60

The present study aimed to evaluate the incorporation of the natural lipid lycopene into niosome formulations based on cationic lipid DOTMA and polysorbate 60 non-ionic surfactant to analyze the potential application of this novel formulation to deliver genetic material into the rat retina. Both niosomes with and without lycopene were prepared by the reverse phase evaporation method and physicochemically characterized in terms of size, zeta potential, polydispersity index and capacity to condense, release and protect the DNA against enzymatic digestion. In vitro experiments were performed in ARPE-19 cells after complexion of niosomes with pCMS-EGFP plasmid at appropriate cationic lipid/DNA ratios. At 18/1 mass ratio, nioplexes containing lycopene had nanometric size, positive zeta potential, low polydispersity and were able to condense, release and protect DNA. Percentage of transfected cell was around 35% without compromising cell viability. The internalization pathways studies revealed a preference to caveolae mediated endocytosis and macropinocytosis, which could circumvent lysosomal degradation. Both subretinal and intravitreal administrations to the rat retina showed that nioplexes were able to transfect efficiently the outer segments of the retina, which offer reasonable hope for the treatment of many inherited retinal diseases by a safe non-viral vector formulation after the less invasive intravitreal administration.

Cholesterol-dependent thermotropic behavior and organization of neuronal membranes

The composition of neuronal membranes is unique with diverse lipid composition due to evolutionary requirement. The organization and dynamics of neuronal membranes are crucial for efficient functioning of neuronal receptors. We have previously established hippocampal membranes as a convenient natural source for exploring lipid-protein interactions, and organization of neuronal receptors. Keeping in mind the pathophysiological role of neuronal cholesterol, in this work, we used differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS) to explore thermotropic phase behavior and organization (thickness) of hippocampal membranes under conditions of varying cholesterol content. Our results show that the apparent phase transition temperature of hippocampal membranes displays characteristic linear dependence on membrane cholesterol content. These results are in contrast to earlier results with binary lipid mixtures containing cholesterol where phase transition temperature was found to be not significantly dependent on cholesterol concentration. Interestingly, SAXS data showed that hippocampal membrane thickness remained more or less invariant, irrespective of cholesterol content. We believe that these results constitute one of the early reports on the thermotropic phase behavior and organizational characterization of hippocampal membranes under varying cholesterol content. These results could have implications in the functioning of neuronal receptors in healthy and diseased states.

Development of a biocompatible creatinine-based niosomal delivery system for enhanced oral bioavailability of clarithromycin

CONTEXT

Nonionic surfactant vesicles have gained increasing scientific attention for hydrophobic drugs delivery due to their biocompatibility, stability and low cost.

OBJECTIVE

The aim of the present study was to synthesize and evaluate a novel creatinine-based nonionic surfactant in terms of its ability to generate biocompatible niosomal system for the delivery of Clarithromycin.

MATERIALS AND METHODS

The surfactant was synthesized by reacting creatinine with lauroyl chloride followed by characterization using ¹HNMR and MS. The drug-loaded niosomal vesicles of the surfactant were characterized for drug encapsulation efficiency (EE) using LC-MS, vesicle size using dynamic light scattering (DLS) and vesicle shape using atomic force microscopy (AFM). The surfactant was also investigated for blood hemolysis, in vitro cytotoxicity against different cell lines and in vivo acute toxicity in mice. Furthermore, the in vivo bioavailability of Clarithromycin encapsulated in the novel niosomal formulation was investigated using rabbits and quantified through validated LC-MS/MS method.

RESULTS AND DISCUSSION

Findings showed that vesicles were able to entrap up to 67.82 ± 1.27% of the drug, and were rounded in shape with a size around 202.73 ± 5.30 nm and low polydispersity. The surfactant caused negligible blood hemolysis, very low cytotoxicity and was found to be safe up to 2500 mg/kg body weight using mice. The niosomal formulation showed twofold enhanced oral bioavailability of Clarithromycin as compared to commercial formulations of the drug.

CONCLUSION

The study has shown that the creatinine-based niosomes developed in our laboratory were biocompatible, safe and increased the oral bioavailability of the model hydrophobic Clarithromycin using experimental animals.