Controlled drug release from gels using surfactant aggregates. II. Vesicles formed from mixtures of amphiphilic drugs and oppositely charged surfactants

Amphiphilic Ionic Liquids Capable to Formulate Organized Systems in an Aqueous Solution, Designed by a Combination of Traditional Surfactants and Commercial Drugs

The present review describes the state of the art in the conversion of pharmaceutically active ingredients (API) in amphiphilic Ionic Liquids (ILs) as alternative drug delivery systems. In particular, we focus our attention on the compounds generated by ionic exchange and without original counterions which generate different systems in comparison with the simple mixtures. In water, these new amphiphiles show similar or even better properties as surfactants in comparison with their precursors. Cations such as 1-alkyl-3-methyl-imidazolium and anions such as dioctyl sulfosuccinate or sodium dodecyl sulfate appear as the amphiphilic components most studied. In conclusion, this work shows interesting information on several promissory compounds and they appear as an interesting challenge to extend the application of ILs in the medical field.

Formation of Drug-Participating Catanionic Aggregates for Extended Delivery of Non-Steroidal Anti-Inflammatory Drugs from Contact Lenses

This paper focuses on extending drug release duration from contact lenses by incorporating catanionic aggregates. The aggregates consist of a long-chain cationic surfactant, i.e., cetalkonium chloride (CKC), and an oppositely charged anti-inflammatory amphiphilic drug. We studied three non-steroidal anti-inflammatory (NSAID) drugs with different octanol–water partition coefficients; diclofenac sodium (DFNa), flurbiprofen sodium (FBNa), and naproxen sodium (NPNa). Confirmation of catanionic aggregate formation in solution was determined by steady and dynamic shear rheology measurements. We observed the increased viscosity, shear thinning, and viscoelastic behavior characteristic of wormlike micelles; the rheological data are reasonably well described using a Maxwellian fluid model with a single relaxation time. In vitro release experiments demonstrated that the extension in the drug release time is dependent on the ability of a drug to form viscoelastic catanionic aggregates. Such aggregates retard the diffusive transport of drug molecules from the contact lenses. Our study revealed that the release kinetics depends on the CKC concentration and the alkyl chain length of the cationic surfactant. We demonstrated that more hydrophobic drugs such as diclofenac sodium show a more extended release than less hydrophobic drugs such as naproxen sodium.

Investigating structure-dependent diffusion in hydrogels using spatially resolved NMR spectroscopy

HYPOTHESIS

Incorporation of the drug-loaded surfactant micelles into polymer hydrogels is a common method used to achieve controlled drug delivery. The characterization of the diffusion processes in drug delivery systems is critical in order to tune the drug loading and release.

EXPERIMENTS

We present a simple and efficient NMR protocol to investigate the transport of the surfactant molecules in hydrogels on micro- and macroscale under non-equilibrium conditions. Our experimental protocol is based on a combination of ¹H 1D NMR chemical shift imaging and slice-selective diffusion experiments, which enables determination of the mutual and self-diffusion coefficients of the surfactant in the non-equilibrium hydrogel-based system within the same short time frame.

FINDINGS

Our results show that the self-diffusion coefficient of the positively charged surfactant in the hydrogel (D_s^gel) decreases with the increasing surfactant concentration until it reaches a plateau value of 6.6±0.5×10^-11m²s^-1. The surfactant self-diffusion in the solution (D_s^sln) remains constant over the experiment with an average value of 6.7±0.3×10^-11m²s^-1. The surfactant mutual diffusion coefficient obtained from 1D chemical shift imaging in this hydrogel system (D_m) is 7.7±0.5×10^-11m²s^-1. Correlation of the localized D_s to the 1D chemical shift images gives insight into the structure-dependent diffusional behavior of surfactant molecules in the hydrogel. This NMR protocol will be of great value in studies of concentration dependent structures on the interfaces between two immiscible liquids.

Nanoformulated water-soluble paclitaxel to enhance drug efficacy and reduce hemolysis side effect

Surgery, chemotherapy, and radiotherapy are the three top cancer treatment modalities. Paclitaxel (PTX) is one of the most widely used chemotherapy drugs. However, its clinical applications have been significantly limited due to: (i) serious hemolysis effect of currently available commercial paclitaxel formulations and (ii) its water insolubility. An easy way to deliver paclitaxel by a new nanocarrier system using pluronic copolymers of P123/F68 and Sorbitan monopalmitate (Span 40) was reported in our previous research article. The characterization of the formulation and analysis of drug release and cellular uptake were also presented. In this article, we reported discoveries of our follow-up in vivo antitumor and in vitro hemolytic study discoveries. The experimental results showed that the nanoformulated PTX achieved much better tumor suppression performance while reducing hemolysis side effects. This newly formulated drug can significantly improve patient outcomes in cancer chemotherapy.

Ex vivo skin permeation and retention studies on chitosan-ibuprofen-gellan ternary nanogel prepared by in situ ionic gelation technique--a tool for controlled transdermal delivery of ibuprofen

The chemical potentials of drug-polymer electrostatic interaction have been utilized to develop a novel ternary chitosan-ibuprofen-gellan nanogel as controlled transdermal delivery tool for ibuprofen. The ternary nanogels were prepared by a combination of electrostatic nanoassembly and ionic gelation techniques. The electrostatic and hydrophobic interactions as well as hydrogen bonding between ibuprofen and chitosan were confirmed with FTIR, while DSC, TGA and SEM confirmed the physical state, thermal and morphological characteristics, respectively. The ex vivo delivery of ibuprofen onto and across the skin was evaluated based on system specific drug release parameters such as steady state permeation rate, permeability coefficient, permeability enhancement ratio, skin/gel partition coefficient, diffusion coefficient, lag time and release rate constant and mechanisms of release were determined using mathematical models. Interaction between ibuprofen and chitosan produced new spherical eutectic nanoconjugates with remarkable decrease in particle size of ibuprofen from 4580 (length-to-breadth aspect ratio) to a minimum of 14.15 nm (324-times), and thermally stable amorphous characteristics. The nanogels exhibited significant elastic and pseudoplastic characteristics dictated by the concentration of chitosan with maximum swelling capacity of 775% w/w at 6.55 mM chitosan compared with 281.16 and 506.50% for plain gellan and control ibuprofen hydrogel, respectively. Chitosan enhanced the skin penetration, permeability and the rate of transdermal release of ibuprofen by a factor of 4, dictated by the extent of ibuprofen-chitosan ionic interaction and its concentration. The major mechanism of ibuprofen release through the pig skin was drug diffusion however drug partition and matrix erosion also occurred. It was evident that ternary nanogels are novel formulations with potential application in controlled transdermal delivery of ibuprofen.

Surfactant behavior of ionic liquids involving a drug: from molecular interactions to self-assembly

Aggregates formed in an aqueous medium by three ionic liquids CnMImIbu made up of 1-alkyl-3-methyl-imidazolium cation (n = 4, 6, 8) and ibuprofenate anion are investigated. Dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), (1)H nuclear magnetic resonance measurements, and atom-scale molecular dynamics simulations are used to shed light on the main interactions governing the formation of the aggregates and their composition. At high concentration, mixed micelles are formed with a composition that depends on the imidazolium alkyl chain length. For the shortest alkyl chain, micelles are mainly composed of ibuprofenate anions with some imidazolium cations intercalated between the anions. Upon increasing the alkyl chain length, the composition of the aggregates gets enriched in imidazolium cations and aggregates of stoichiometric composition are obtained. Attractive interactions between these aggregates led to the formation of larger aggregates. As suggested by molecular simulations, these larger aggregates might constitute the early stage of phase separation. Transitions from micelles to vesicles or ribbons are observed due to dilution effects and changes in the chemical composition of the aggregates. We also show that aggregation can be probed using simple microscopic quantities such as radial distribution functions and average solvation numbers.

Micellar transitions in catanionic ionic liquid–ibuprofen aqueous mixtures; effects of composition and dilution

Interactions between 1-dodecyl-3-methylimidazolium chloride and ibuprofen molecules in aqueous solution form catanionic mixtures, with morphologies of mixed micelles dependent on solution composition.

Agarose drug delivery systems upgraded by surfactants inclusion: critical role of the pore architecture

Anionic or non-ionic surfactants have been introduced in agarose-based hydrogels aiming to tailor the release of drugs with different solubility. The release of a hydrophilic model drug, Theophylline, shows the predictable release enhancement that varies depending on the surfactant. However, when the hydrophobic Tolbutamide is considered, an unexpected retarded release is observed. This effect can be explained not only considering the interactions established between the drug loaded micelles and agarose but also to the alteration of the freeze-dried hydrogels microstructure. It has been observed that the modification of the porosity percentage as well as the pore size distribution during the lyophilization plays a critical role in the different phenomena that take place as soon as desiccated hydrogel is rehydrated. The possibility of tailoring the pore architecture as a function of the surfactant nature and percentage can be applied from drug control release to the widespread and growing applications of materials based on hydrogel matrices.

Surfactants modify the release from tablets made of hydrophobically modified poly (acrylic acid)

Many novel pharmaceutically active substances are characterized by a high hydrophobicity and a low water solubility, which present challenges for their delivery as drugs. Tablets made from cross-linked hydrophobically modified poly (acrylic acid) (CLHMPAA), commercially available as Pemulen™, have previously shown promising abilities to control the release of hydrophobic model substances. This study further investigates the possibility to use CLHMPAA in tablet formulations using ibuprofen as a model substance. Furthermore, surfactants were added to the dissolution medium in order to simulate the presence of bile salts in the intestine.

The release of ibuprofen is strongly affected by the presence of surfactant and/or buffer in the dissolution medium, which affect both the behaviour of CLHMPAA and the swelling of the gel layer that surrounds the disintegrating tablets. Two mechanisms of tablet disintegration were observed under shear, namely conventional dissolution of a soluble tablet matrix and erosion of swollen insoluble gel particles from the tablet. The effects of surfactant in the surrounding medium can be circumvented by addition of surfactant to the tablet. With added surfactant, tablets that may be insusceptible to the differences in bile salt level between fasted or fed states have been produced, thus addressing a central problem in controlled delivery of hydrophobic drugs. In other words CLHMPAA is a potential candidate to be used in tablet formulations for controlled release with poorly soluble drugs.

The nanostructure of surfactant-DNA complexes with different arrangements

The nanostructure of DNA with different cationic surfactant has been studied in order to elucidate the detailed arrangement concerning the position of DNA and surfactant domains in the complexes. Also, the orientation of the DNA cylinders in the thin films of the complexes was investigated. Attention was directed on the preparation methods of the complexes and to how the different surfactant structure affects the compaction of the DNA. The cationic surfactant-DNA complexes were investigated by X-ray scattering, polarized light microscopy and elemental microanalysis. It was observed that the molecular organization of the complexes between DNA and cationic surfactant corresponds to a hexagonal structure with different packing arrangements. The nanostructure of the complexes depends on the hydrophobic/hydrophilic balance of the cationic surfactant. In particular the use of arginine derived surfactants, with a large polar head group able to interact not only by electrostatics but also by hydrogen bonding, allows for the formation of more compact structures. The results suggest that the smaller the lattice parameter the more compact and stable is the complex implying slower DNA release.

Liposomes containing bile salts as novel ocular delivery systems for tacrolimus (FK506): in vitro characterization and improved corneal permeation

The objective of this study was to investigate the potential of liposomes containing bile salts as an ophthalmic delivery system for tacrolimus to improve corneal permeability. Liposomes containing bile salts, including sodium taurocholate, sodium deoxycholate, and sodium glycocholate, were produced by the thin-film dispersion method with a particle size of approximately 100 nm and an entrapment efficiency of more than 90%. Less than 5% tacrolimus was released from conventional liposomes and from liposomes containing sodium taurocholate, sodium deoxycholate, or sodium glycocholate over 12 hours. The cellular uptake of conventional liposomes was significantly higher than that of liposomes containing bile salts. However, liposomes containing bile salts exerted a 3–4-fold increase of tacrolimus in ex vivo corneal transport of tacrolimus compared with conventional liposomes. When rabbit eyes were treated with a DiI perchlorate-loaded liposome suspension, liposomes containing bile salts showed fast and sustained penetration across the cornea. Unfortunately, liposomes containing sodium deoxycholate caused toxicity or irritation to both spontaneously derived human corneal epithelial cells and the rabbit cornea. Therefore, liposomes containing sodium taurocholate and sodium glycocholate are potential carriers in ocular drug delivery systems, given their low toxicity and vastly improved permeability.

Phospholipid bilayer-perturbing properties underlying lysis induced by pH-sensitive cationic lysine-based surfactants in biomembranes

Amino acid-based surfactants constitute an important class of natural surface-active biomolecules with an unpredictable number of industrial applications. To gain a better mechanistic understanding of surfactant-induced membrane destabilization, we assessed the phospholipid bilayer-perturbing properties of new cationic lysine-based surfactants. We used erythrocytes as biomembrane models to study the hemolytic activity of surfactants and their effects on cells' osmotic resistance and morphology, as well as on membrane fluidity and membrane protein profile with varying pH. The antihemolytic capacity of amphiphiles correlated negatively with the length of the alkyl chain. Anisotropy measurements showed that the pH-sensitive surfactants, with the positive charge on the α-amino group of lysine, significantly increased membrane fluidity at acidic conditions. SDS-PAGE analysis revealed that surfactants induced significant degradation of membrane proteins in hypo-osmotic medium and at pH 5.4. By scanning electron microscopy examinations, we corroborated the interaction of surfactants with lipid bilayer. We found that varying the surfactant chemical structure is a way to modulate the positioning of the molecule inside bilayer and, thus, the overall effect on the membrane. Our work showed that pH-sensitive lysine-based surfactants significantly disturb the lipid bilayer of biomembranes especially at acidic conditions, which suggests that these compounds are promising as a new class of multifunctional bioactive excipients for active intracellular drug delivery.

Nanostructuring biosynthetic hydrogels for tissue engineering: a cellular and structural analysis

The nanostructuring of hydrogel scaffolds used in tissue engineering provides the ability to control cellular fate and tissue morphogenesis through cell-matrix interactions. Here we describe a method to provide nanostructure to a biosynthetic hydrogel scaffold made from crosslinked poly(ethylene glycol)-fibrinogen conjugates (PEG-fibrinogen), by modifying them with the block-copolymer Pluronic® F127. The copolymeric additive self-assembled into micelles at certain concentrations and temperatures, thereby creating nanostructures within the crosslinked hydrogel. Small-angle X-ray scattering (SAXS) and transmission electron microscopy at cryogenic temperature were used to detect Pluronic® F127 micelles embedded within the crosslinked PEG-fibrinogen hydrogels. The density and order of the micelles within the hydrogel matrix increased as the relative Pluronic® F127 concentration was raised. The transient stability of the micelles within the hydrogel network was analyzed using time-dependent swelling and Pluronic® F127 release measurements. These characterizations revealed that most of the Pluronic® F127 molecules diffuse out of the hydrogels after 4 days in aqueous buffer and SAXS analysis confirmed a significant change in the structure and interactions of the micelles during this time. Cell culture experiments evaluating the three-dimensional fibroblast morphology within the matrix indicated a strong correlation between cell spreading and the hydrogel's characteristic mesh size. The present research thereby provides a more quantitative understanding of how structural features in an encapsulating hydrogel environment can affect cell morphogenesis towards tissue regeneration.

Gel formulations containing catanionic vesicles composed of alprenolol and SDS: effects of drug release and skin penetration on aggregate structure

To fully utilize the extended contact time of gel formulations a novel formulation with drug containing catanionic aggregates offering prolonged drug release and skin penetration were investigated. This study aimed to further explore the drug release process from catanionic vesicles in gels. Catanionic vesicles were formed from alprenolol and sodium dodecyl sulphate. Physical gels composed of catanionic vesicles and a SoftCAT polymer were used as well as covalent Carbopol gels. Drug release was measured in vitro using a modified USP paddle method and the skin penetration was studied using dermatomized pig ear skin mounted in horizontal Ussing chambers. The aggregate structure was visualized with cryo-TEM during the drug release and skin penetration process. The study results show that catanionic vesicles are present in the formulations throughout the drug release process and during the clinically relevant skin application time. Hence, the decreased skin penetration rate stems from the prolonged release of drug substance from the gels. The rheological investigation shows that the gel structure of the physically cross-linked gels is maintained even as the drug substance is released and the gel volume is decreased. These findings indicate that the applicability of formulations like these is a future possibility.

Comparative sensitivity of tumor and non-tumor cell lines as a reliable approach for in vitro cytotoxicity screening of lysine-based surfactants with potential pharmaceutical applications

Surfactants are used as additives in topical pharmaceuticals and drug delivery systems. The biocompatibility of amino acid-based surfactants makes them highly suitable for use in these fields, but tests are needed to evaluate their potential toxicity. Here we addressed the sensitivity of tumor (HeLa, MCF-7) and non-tumor (3T3, 3T6, HaCaT, NCTC 2544) cell lines to the toxic effects of lysine-based surfactants by means of two in vitro endpoints (MTT and NRU). This comparative assay may serve as a reliable approach for predictive toxicity screening of chemicals prior to pharmaceutical applications. After 24-h of cell exposure to surfactants, differing toxic responses were observed. NCTC 2544 and 3T6 cell lines were the most sensitive, while both tumor cells and 3T3 fibroblasts were more resistant to the cytotoxic effects of surfactants. IC(50)-values revealed that cytotoxicity was detected earlier by MTT assay than by NRU assay, regardless of the compound or cell line. The overall results showed that surfactants with organic counterions were less cytotoxic than those with inorganic counterions. Our findings highlight the relevance of the correct choice and combination of cell lines and bioassays in toxicity studies for a safe and reliable screen of chemicals with potential interest in pharmaceutical industry.

Novel gel formulations with catanionic aggregates enable prolonged drug release and reduced skin permeation

Objectives

The aim of this study was to investigate skin permeation rates of a drug substance when applied in novel gel formulations with catanionic aggregates.

Methods

Reference gel without catanionic aggregates was compared with formulations with catanionic aggregates composed of tetracaine and either sodium dodecyl sulphate (SDS) or capric acid. Carbomer and SoftCAT were used to compare the effect of different gel types to elucidate if physically cross-linked, ‘self-destructing’ systems had benefits compared with classical, covalently cross-linked, gels.

Key findings

The rheological investigation showed that the interactions between the SoftCAT polymer and tetracaine/SDS aggregates were stronger than when the tetracaine/capric acid aggregates were used. The skin permeation was measured ex vivo in horizontal Ussing chambers and the permeation of tetracaine was significantly lower when formulations with tetracaine/SDS aggregates were applied (P < 0.001), but not statistically different from the reference when capric acid was used.

Conclusions

No morphological differences could be distinguished between the skin samples exposed to the different formulations or the reference. Skin permeation was compared with silicone sheet permeation and the results indicated that silicone sheets could be used as a model of skin when using these formulations.

Pharmaceutical applications for catanionic mixtures

Mixtures of oppositely charged surfactants, so called catanionic mixtures, are a growing area of research. These mixtures have been shown to form several different types of surfactant aggregates, such as micelles of various forms and sizes, and lamellar structures, such as vesicles. In this review, a short introduction to the field of catanionic mixtures is presented and the pharmaceutical possibilities offered by such mixtures are reviewed. There are several interesting ideas on how to apply catanionic mixtures to improve the delivery of, for example, drug compounds and DNA, or for HIV treatment.

Reversal of Compromised Bonding in Bleached Enamel Using Antioxidant Gel

Dental bond strength is significantly reduced when bonding is performed immediately after bleaching treatments. It has also been reported that the application of an antioxidant after bleaching treatment improves the adhesive bond strength of oxidized enamel tissue. The application of an antioxidant in gel form by the patient makes the application process easier and shortens time spent in the clinic.

Diffusion of camptothecin immobilized with cationic surfactant into agarose hydrogel containing anionic carrageenan

Camptothecin (CPT) is a hydrophobic antitumor drug. Controlled release of CPT from hydrogel has not been satisfactorily achieved because of its poor compatibility and weak interaction with a hydrophilic hydrogel matrix. A new approach has been attempted in this work to solve these problems. In our approach, CPT was first solubilized in a micellar solution of cetyltrimethylammonium bromide (CTAB), a cationic surfactant. It was found that the solubility of CPT could be enhanced by CTAB (10 mM) to 0.17 mg/mL, which is 127 times higher than that in pure water, providing a great feasibility of drug loading. The micellar drug solution of CTAB-CPT was subsequently used to prepare agarose hydrogels containing a small content (<or= 0.3 wt %) of kappa-carrageenan, an anionic water-soluble polysaccharide. The release of CPT from so fabricated hydrogel-surfactant systems has been investigated by varying the content of kappa-carrageenan in the hydrogel. It was observed that the presence of kappa-carrageenan in the hydrogel system resulted in a significant decrease in the release rate of the drug. This effect was ascribed to the ionic interaction between the positively charged surfactant micelles and the negatively charged kappa-carrageenan. The release profiles were fitted to two mathematic models of diffusion and the diffusion coefficients of the drug were obtained as a function of kappa-carrageenan content.

Hemolysis and antihemolysis induced by amino acid-based surfactants

Surfactants have the special ability to interact with the lipid bilayer of cell membranes. The red blood cell is one of the most used cellular membrane models to study the mechanisms underlying surfactant-induced osmotic cell resistance. To increase our knowledge regarding the mechanisms of surfactant membrane interaction, we studied the action of five lysine-derivative anionic and three arginine-derivative cationic amino acid-based surfactants on hypotonic hemolysis. Results showed two different antihemolytic behaviors among amino acid-based surfactants, both related to the maximal protective concentration. How the physico-chemical properties and structure of these compounds determine the protection against hypotonic hemolysis is discussed in detail. We found a good correlation between the CMC and the concentrations resulting in maximum protection against hypotonic hemolysis for the cationic surfactants, but no correlation for the anionic surfactants. In the case of lysine derivative surfactants, which only differ in their counterions, the counterion is implicated in the differences in the antihemolytic potency and the hemolytic activities of this.

Disturbance of erythrocyte lipid bilayer by amino acid-based surfactants

In an attempt to increase our knowledge regarding the mechanisms of surfactant membrane interaction, we studied the action of several anionic and cationic amino acid-based surfactants on membrane fluidity using fluorescence anisotropy. Anisotropy measurements demonstrated that almost all of the surfactants studied disturbed the external region of the erythrocyte membrane without affecting the core of the bilayer. How the physico-chemical properties and structure of these compounds affect dynamics of the lipid bilayer is discussed in detail.

Polymer-surfactant and protein-surfactant interactions

The phase behavior and some physicochemical properties of homopolymers (HP) and hydrophobically modified (HMP) polymers, as well as of polyelectrolytes (PE) and proteins (PR), in the presence of aqueous surfactants, or their mixtures, are discussed. Mixing the above components gives rise to the formation of organized phases, whose properties are controlled by polymer and/or surfactant content, temperature, pH, and ionic strength. Depending on the nature, concentration, and net charge of both solutes, molecular solutions, polymer-surfactant complexes, adsorption onto micelles and vesicles, gels, liquid crystalline phases, and precipitates are observed. Such rich polymorphic behavior is the result of a complex balance between electrostatic, excluded volume, van der Waals, and other contributions to overall system stability. It is also modulated by the molecular details and architecture of both the polymer and the surfactant. Different experimental methods allow investigation of the above systems and getting information on the nature of polymer-surfactant interactions (PSI). Surface adsorption and thermodynamic methods, together with investigation of the phase diagrams, give information on the forces controlling PSI and on the existence of different phases. Conductivity, QELS and viscosity allow estimating the size and shape of polymer-surfactant (protein-surfactant) complexes. Optical microscopy, cryo-TEM, AFM, NMR, fluorescence, and relaxation methods give more information on the above systems. Use of the above mixtures in controlling gelation, surface covering, preparing dielectric layers, and drug release is suggested.

The biological properties of lysine-derived surfactants

We examine the effects of aquatic toxicity on Daphnia magna, the antimicrobial activity of new anionic lysine-derivative surfactants, and the influence of different-sized counterions associated with the surfactants. Surfactants with Tris and Lithium had less of a toxic effect on Daphnia, while all surfactants proved highly active against yeasts and the gram-negative bacteria Bordetella bronchiseptica. Counterion size was found to have no effect on aquatic toxicity or antimicrobial activity.

Catanionic mixtures involving a drug: A rather general concept that can be utilized for prolonged drug release from gels

The aim of this work was to study at what extent mixtures of drug substances and oppositely charged surfactants form catanionic aggregates and to apply these as a means of obtaining prolonged drug release from a gel. The properties of traditional catanionic mixtures are relatively well known, but only recently we found that not only traditional surfactants form these mixtures, but also structurally more complex surface active drug compounds. In this study, several different compositions of catanionic mixtures were studied visually, by cryogenic transmission electron microscopy (cryo-TEM) and rheologically using a Bohlin VOR Rheometer. Some of the catanionic vesicle and micelle phases were incorporated in and released from gels using the USP paddle method. The drug compounds investigated were lidocaine, ibuprofen, naproxen, alprenolol, propranolol, and orphenadrine. Of the six drug molecules used in this study, five, both positively and negatively charged, were capable of forming catanionic vesicles and/or micelles with oppositely charged surfactants. The drug release studies show that catanionic drug surfactant mixtures are beneficial for obtaining prolonged release from gels, as the drug release using catanionic vesicles and micelles was prolonged between 10 and 100 times compared to the release of pure drug substance from the gel.

Niosomes as carriers for tretinoin. III. A study into the in vitro cutaneous delivery of vesicle-incorporated tretinoin

The influence of drug thermodynamic activity and niosome composition, size, lamellarity and charge on the (trans)dermal delivery of tretinoin (TRA) was studied. For this purpose, tretinoin was incorporated at saturated and unsaturated concentrations in both multilamellar (MLV) and unilamellar (UV) vesicular formulations using two different commercial mixtures of alkyl polyglucosides: octyl-decyl polyglucoside and decyl polyglucoside. Positively and negatively charged vesicular formulations were prepared using either stearylamine or dicetylphosphate as a charge inducer. Niosomes made with polyoxyethylene (4) lauryl ether and liposomes made with soy phosphatidylcholine were also prepared and studied. Vesicular formulations were characterised by transmission electron microscopy and optical and light polarized microscopy for vesicle formation and morphology, and by dynamic laser light scattering for size distribution. The effect of the vesicular incorporation of tretinoin on its (trans)dermal delivery through the newborn pig skin was also investigated in vitro using Franz cells, in comparison with a commercial formulation of the drug (RetinA). The amount of tretinoin delivered through and accumulated in the several skin layers was detected by HPLC. Overall, obtained results showed that tretinoin cutaneous delivery is strongly affected by vesicle composition and thermodynamic activity of the drug. In particular, small, negatively charged niosomal formulations, which are saturated with tretinoin, have shown to give higher cutaneous drug retention than both liposomes and commercial formulation. Moreover, interactions between skin and vesicles seem to depend on physico-chemical properties of the main component of the vesicular bilayer.

Potential irritation of lysine derivative surfactants by hemolysis and HaCaT cell viability

Surfactants represent one of the most common constituents in topical pharmaceutical and cosmetic applications or cleansers. Since adverse skin and ocular reactions can be caused by them, it is important to evaluate damaging effects. Amino acid-based surfactants deserve particular attention because of their low toxicity and environmental friendly properties. New lysine derivative surfactants associated with heavy and light counterions were tested. The ocular irritancy was assessed by hemolysis, and photohemolysis was employed to evaluate their phototoxicity. Cytotoxicity on HaCaT cells was determined by neutral red uptake and MTT assay to predict skin irritation. All lysine derivative surfactants were less hemolytic and thus less eye-irritating than the commercial surfactants used as model irritants. No phototoxic effects were found. All surfactants presented cytotoxic effects as demonstrated by decrease of neutral red uptake and reduction of MTT salt, with clear concentration-effect profiles. However, the rates of cytotoxicity on HaCaT for the new surfactants suggested that they were less cytotoxic and then, less skin-irritating than the reference ones; surfactants with heavy counterions were the less cytotoxic. The anionic surfactants investigated in the present work may constitute a promising class of surfactants given their low irritancy potential for pharmaceutical and cosmetic preparations.

Electrodynamic Investigations of Ion Transport and Structural Properties in Drug-Containing Gels: Dielectric Spectroscopy and Transient Current Measurements on Catanionic Carbopol Systems

The aim of this study is to show the potential of using electrodynamic methods as characterization tools in the controlled drug release process, on complex drug release systems. The two formulations under study were a Carbopol gel containing diphenhydramine and an identical gel also containing the surfactant sodium dodecyl sulfate which forms catanionic vesicles with the diphenhydramine. The average diffusion coefficients were calculated from both the dielectric spectroscopy and the transient current measurements. Comparing the herein-obtained diffusion coefficients with those obtained in another study using a traditional USP technique for the same system, the values are virtually the same. The two electrodynamic methods proved to be potentially valuable tools for obtaining information about the concentration and the motion of the drug molecules inside the gel. The transient current measurements are particularly interesting in this case, as the method gives information not only on an average level, but also of the different charged moieties separately. Interestingly, it seems that the methods also are applicable for obtaining information about the mesh size in the gel.