E. Santucci

Lidocaine-loaded non-ionic surfactant vesicles: characterization and in vitro permeation studies.

Our research on topical application of lidocaine-loaded non-ionic surfactant vesicles (NSVs) was prompted by the great interest on new delivery systems for local anaesthetics. This study is focused on a novel formulation of NSVs entrapping lidocaine in the form of a free base (LID) and a hydrochloride (LIDHCl). NSVs were prepared from polyoxyethylene sorbitan monolaurate (Tween20) and cholesterol. The effect of vesicle composition and environmental pH condition (8.6-5.5) on drug encapsulation efficiency (e.e.) was investigated. Experimental strategies involved: freeze-fracture, microscopy technique, dynamic light scattering, permeation through Silastic and mouse abdominal skin, in vitro release kinetics of vesicle-entrapped drugs, fluorescence quenching analyses. Diffusion experiments showed that the flux of charged lidocaine through Silastic membrane was possible only after the vesicle encapsulation. Permeation through mouse abdominal skin of LIDHCl loaded vesicles showed a higher flux and a shorter lag time with respect to classical liposome formulations, while LID permeation rate was quite similar for NSV and liposome formulations. Vesicles were also prepared in the presence of dicetylphosphate (DCP) and N-cetylpyridinium chloride (CP) to obtain negatively and positively charged vesicles respectively, but in this case the e.e. of the drug was negligible. The possible reason of the remarkable lower e.e. observed with charged vesicles was investigated by means of fluorescence quenching experiments.

Preparation and properties of new unilamellar non-ionic/ionic surfactant vesicles

Abstract Non-ionic surfactant vesicles (NSVs) were prepared from polysorbate 20 and cholesterol by means of two different methods: by direct sonication of an aqueous dispersion of the various components (bulk) or by solubilization of the components, evaporation of the organic solvent to form a film inside the vessel used for the preparation and then by sonication (film). The influence of the preparation technique on the properties of the obtained structures was studied. Vesicles with bigger dimensions and higher entrapment efficiency were obtained when sonication was carried out after the film formation. Vesicle formation in the presence of ionic surfactants was investigated in order to evaluate the effect of charged components on vesicle dimensions, entrapment efficiency and stability. Dimethyldioctadecylammonium bromide (DDOA) and cetylpyridinium chloride (CPy) were used to introduce a positive charge in the vesicle structure, while dicetylphosphate (DCP) was used for a negative charge. Better resistance to osmotic stress and higher entrapment efficiency values were obtained with vesicles containing DCP and CPy.

Structural and rheological characterization of Scleroglucan/borax hydrogel for drug delivery

The polysaccharide Scleroglucan, one of the most rigid polymers found in nature, can form a chemical/physical gel, in the presence of borax. The obtained hydrogel was loaded with three different model molecules (Theophylline, Vitamin B12 and Myoglobin) and then, after freeze-drying, was used as a matrix for tablets. The release profiles of the substances from the dosage forms were evaluated; the matrix appeared capable to modulate the diffusion of the chosen molecules, and different diffusion rates were observed, according to the different radii of the tested molecules. Interestingly, in the dissolution medium the matrix undergoes an anisotropic swelling taking place only in the axial direction, while a negligible radial variation occurs. The water uptake of the matrix occurs according to a Fickian process. Samples at two different polymer concentrations (0.7 and 2.3%, w/v) were characterized in terms of rheological and mechanical parameters and the properties were interpreted in terms of the molecular structure obtained by conformational analysis. The flow curves acquired in the viscoelasticity interval, show the effect of the borate ion in improving the resistance of the gel in comparison to the polymer alone. The evaluation of the moduli indicates that the system is viscoelastic, with an appreciable liquid component that increases as the polymer concentration decreases. Also the cohesion of the gel is higher in comparison to the Scleroglucan and is strongly dependent on temperature. The combination of experimental and theoretical conformational analysis approaches, allowed us to propose a model for the structure of the macromolecular network and to give an explanation to the anomalous swelling that was observed. It came out that the polymer can built up a channel structure, mediated via borax ion interaction, that can accommodate guest molecules of different size.

Novel hydrogel system from scleroglucan: synthesis and characterization

New hydrogels obtained by a crosslinking reaction between the polycarboxylated derivative of scleroglucan (sclerox) and 1, 6-hexanedibromide have been prepared and characterized. Different ratios between the alkane dihalide and sclerox yielded products with appreciably different properties. Water uptake by the hydrogel with a low degree of crosslinking was remarkably affected by ionic strength. The diffusion of a model molecule (theophylline) through the swelled crosslinked polymers was studied and the theoretical analysis leading to the calculation of permeability coefficients in different environmental conditions is reported. Tablets prepared with one of the new hydrogels behaved as swellable monolithic systems suitable for sustained drug release.

Gellan for the formulation of sustained delivery beads

Gellan beads containing a model molecule, clay, and in most cases oil and a surfactant were prepared. The release from the obtained beads was studied in vitro with different techniques and the effects of the presence of varying amounts of oil in the formulation was investigated. The behaviour of gellan was compared with that of alginate in the same experimental conditions. The results indicate that gellan is suitable for the formulation of sustained release beads and that, for the tested preparations, the presence of oil results in a marked reduction in delivery rate. From release experiments, carried out with the various formulations and with different concentrations of the substances used as models, it can be suggested that the swelling of the matrix seems to be the most likely factor responsible for the overall rate of delivery.

Effect of cholesterol on the formation and hydration behavior of solid-supported niosomal membranes.

The effect of cholesterol on the formation and hydration behavior of solid-supported polysorbate 20 (Tween 20)/cholesterol self-assemblies was investigated by means of in situ energy-dispersive X-ray diffraction in a wide range of relative humidity (0.4 < RH < 1). At low hydration, Tween 20 and cholesterol were found to demix, with the latter molecules forming crystallites with a pseudobilayer structure (d approximately = 34 A). Water adsorption promoted the progressive solubilization of cholesterol crystallites. When in the presence of enough cholesterol, the formation of niosomal bilayer membranes rich in Tween 20 occurred (RH approximately = 0.985). Upon further hydration, two distinct regimes associated with remarkable changes in the niosomal membrane structure were identified. In the first regime (0.985 < RH < 0.988), the swelling of the lamellar d spacing was due to the enlargement of the membrane thickness. In the second regime, the structure of Tween 20/cholesterol membranes was quite insensitive to hydration, and the thickness of the intermembrane water layer increased substantially. Remarkably, the curve of the calculated number of waters per surfactant molecule showed a distinct break at RH approximately 0.988, suggesting that the observed structural change in niosomal membranes was most likely due to the completion of the filling of the Tween 20 hydration shell. At full hydration, niosomal membranes exhibited the same lamellar d spacing of niosomes vesicles in aqueous solution. The process completely reversed upon dehydration.

Gellan in sustained release formulations: preparation of gel capsules and release studies

The ability of gellan to form gels in the presence of calcium ions enabled us to prepare capsules by gelation of this polysaccharide around a core containing starch, calcium chloride and a model drug. Release from the dried capsules was studied in vitro by means of the rotating basket technique (USP) in different environmental conditions (distilled water, pH = 2.0, pH = 6.8) and the effects of the presence of increasing amounts of drug in the formulation were also investigated. The behaviour of the gellan capsules was compared with that of beads prepared with the same polysaccharide but containing different additives. Results obtained indicate that gellan is suitable for the formulation of sustained release capsules and that solvent uptake by the dried capsules is most likely the main factor capable of affecting the rate of delivery from the tested preparations.

Span and Tween neutral and pH-sensitive vesicles: Characterization and in vitro skin permeation

The aim of this work was the preparation, characterization, and comparison of novel pH-sensitive nonphospholipid vesicles (niosomes) from two nonionic surfactants, with different hydrophilic-lipophilic balance values (Tween®20-TW20 = 16.7 and Span®60-SP60 = 4.7). Surfactants were mixed with cholesterol (CHOL) and its derivative, cholesteryl hemisuccinate (CHEMS), as a pH-sensitive molecule. Vesicles were characterized by dynamic light scattering, in order to evaluate their dimensions and vesicle stability, by ζ-potential measurements and by means of electronic microscopy after freeze-fracture. Ibuprofen (IBU) was used as the model drug, and high-performance liquid chromatography analyses were performed to evaluate drug-entrapment efficiency and release in a neutral, acidic environment. The influence of the vesicle composition on skin accumulation and transdermal permeation of IBU across excised hairless rat skin was investigated by using vertical Gummer diffusion cells. When niosomes with SP60 and CHEMS were prepared, there was a statistically significant increase of skin permeation of IBU, while TW20 niosomes did not show statistically significant differences in Papp values without the influence of the vesicle size and charge.

Maleic- and fumaric-diamides of (O,O-diacetyl)-L-Dopa-methylester as anti-Parkinson prodrugs in liposomal formulation

The maleic and fumaric diamides preparation of (O,O-diacetyl)-L-Dopa-methylester [(+)-4, (+)-5] are reported; they were synthesized in order to attenuate marked fluctuations of L-DOPA (LD) plasma levels and to overcome the problem of low bioavailability of LD. The new compounds were characterized evaluating solubility, chemical stability, apparent partition coefficient (log P) and comparing neostriatum dopamine (DA) levels in freely moving rats after i.p. administration of prodrugs [(+)-4, (+)-5] with prodrugs in liposomal formulations [(+)-4 Lip, (+)-5 Lip]. All the new compounds showed chemical stability in aqueous buffer solutions (pH 1.3 and 7.4). A relatively slow release of LD in human plasma was observed. Among the studied products, prodrug was able to induce sustained delivery of DA in rat striatal dialysate with respect to equimolar i.p admistration of LD. Furthermore, neostriatum DA concentration after administration of the synthesized prodrugs vs. prodrugs in liposomal formulations was compared (+)-4 Lip, (+)-5 Lip). The results suggest that cis dimeric prodrug (+)-4 and (+)-4 Lip can improve the release of DA in rat brain and demonstrate the potential of these formulations for controlled delivery of antiparkinson agents.

Potential dopamine prodrug-loaded liposomes: preparation, characterization, and in vitro stability studies

Dopamine delivery to the central nervous system (CNS) undergoes the permeability limitations of the blood-brain barrier (BBB). Condensation of dopamine with neutral amino acids could afford potential prodrugs able to interact with the BBB endogenous transporters and easily enter the brain. To improve the bioavailability of the dopamine prodrug, 2-amino-N-[2-(3,4-dihydroxy-phenyl)-ethyl]-3-phenyl-propionamide (DOPH), it was encapsulated in unilamellar liposomes of dimiristoylphosphatidylcholine (DMPC) and cholesterol. Vesicles were characterized by dynamic light scattering in order to evaluate their dimensions and vesicle stability, by zeta-potential measurements, by means of electronic microscopy after freeze-fracture and differential scanning calorimetry. The influence of vesicle composition on DOPH chemical and enzymatic stability was also evaluated. The formulated liposome suspensions were found to be stable, monodisperse systems with a negative zeta potential. From the obtained results, it is possible to conclude that, in studied samples, DOPH inclusion in liposomes offers the possibility of preventing photodegradation and of enhancing in vitro plasma stability. These studies suggest the potential of these formulations as a method to prevent DOPH chemical degradation and enzymatic metabolism.