SolEmuls-novel technology for the formulation of i.v. emulsions with poorly soluble drugs

Intravenously injectable o/w emulsions of drugs being poorly soluble in water and simultaneously in oils need to be produced by locating the drug in the interfacial lecithin layer, e.g. amphotericin B. For achieving this, up to now organic solvents were required. The objective was to develop a solvent-free production method for such emulsions. Drug and the pre-formed parenteral emulsion Lipofundin were mixed and subjected to high pressure homogenisation. Drug powder and emulsions were characterised regarding size and physical stability by photon correlation spectroscopy (PCS), laser diffractometry (LD) and zeta potential measurements. Drug incorporation was studied using light microscopy, electron microscopy (EM) and a centrifugation test to separate non-dissolved drug. Amphotericin B and carbamazepine were used as model drugs. The high streaming velocities lead to accelerated drug dissolution and partitioning into the interfacial layer (so-called "solubilisation by emulsification", SolEmuls Technology). The interfacial layer could incorporate (solubilise) a certain amount of drug, revealed by EM pictures. Exceeding this concentration, hybrid dispersions were formed consisting of drug-loaded oil droplets and drug nanocrystals of similar size (approximately 200 nm). Both dispersion types are i.v. injectable opening the opportunity to deliver the drug in a concentrated form at desired low injection volume, e.g. 10 mg/ml.

Solid lipid nanoparticles for parenteral drug delivery

This review describes the use of nanoparticles based on solid lipids for the parenteral application of drugs. Firstly, different types of nanoparticles based on solid lipids such as "solid lipid nanoparticles" (SLN), "nanostructured lipid carriers" (NLC) and "lipid drug conjugate" (LDC) nanoparticles are introduced and structural differences are pointed out. Different production methods including the suitability for large scale production are described. Stability issues and drug incorporation mechanisms into the particles are discussed. In the second part, the biological activity of parenterally applied SLN and biopharmaceutical aspects such as pharmacokinetic profiles as well as toxicity aspects are reviewed.

Influence of surfactants on the physical stability of solid lipid nanoparticle (SLN) formulations

The choice of surfactant or surfactant mixtures at suitable concentrations contributes to the stability of solid lipid nanoparticles (SLN). In this study, it was found that 1.5% TegoCare 450 was the most effective stabilizer for the Witepsol E85 SLN dispersion compared to Tween 80, Tyloxapol and Pluronic F68 according to the data obtained from differential scanning calorimetry (DSC), zeta potential (ZP) measurements and particle size analysis.

Formulation of intravenous carbamazepine emulsions by SolEmuls technology

Oil in water (O/W) emulsions for parenteral nutrition can be employed as intravenous (i.v.) carriers for drugs that are poorly soluble in water and in oil by localising the drug in the interfacial lecithin layer, e.g. Amphotericin B emulsions. By now, the emulsion production required organic solvents. SolEmuls technology localises the drug in the interfacial layer by a solvent-free high-pressure homogenisation process. SolEmuls was applied to produce Carbamazepine emulsions at increasing drug concentrations from 0.5 to 10mg/ml. Drug powder and Lipofundin emulsion were mixed and homogenised at 1500bar. Characterisation of emulsions and short-term stability were performed by photon correlation spectroscopy (PCS) and laser diffractometry. Drug incorporation (absence of non-dissolved drug crystals) was investigated by light microscopy and a centrifugation test. The emulsions were physically stable and complete drug dissolution is possible up to 3mg/ml. Up to 10mg/ml drug hybrid dispersions of emulsion droplets and ultrafine nanocrystals were obtained. Both, emulsions and hybrid dispersions are suitable as i.v. injectables regarding size and stability.

Interaction of bronchoalveolar lavage fluid with polyplexes and lipoplexes: analysing the role of proteins and glycoproteins

BACKGROUND

Plasmid DNA complexed with cationic lipids (lipoplexes) or cationic polymers (polyplexes) has been used for gene transfer into the lung. Topical gene administration of lipoplexes or polyplexes into the lung after intratracheal instillation or aerosolisation could cause interaction of the complexes with extracellular substances of the airway surface liquid (ASL). These extracellular interactions might be causal for the observed inefficient transfection rate in vivo after topical administration. Therefore, we studied the impact of bronchoalveolar lavage fluid (BALF) on reporter gene expression mediated by non-viral gene vectors. BALF was considered as a model system to mimic possible interactions of the gene vectors with the ASL.

METHODS

BALF was taken from 15 patients who underwent diagnostic bronchoscopy. Lipoplexes and polyplexes were incubated with increasing concentrations of BALF and major components of the BALF such as albumin, mucin and alpha(1)-glycoprotein, as a representative of glycosylated proteins. As cationic polymers, we tested dendrimers (fractured PAMAM) and polyethylenimine 25 kDa (PEI) and, as cationic liposomes, we used Lipofect-AMINE. The effect of BALF on polyplexes and lipoplexes was analysed by transfection experiments, fluorescence-quenching assay, 2-D-gel electrophoresis, SDS-PAGE, DNAse protection assay, size and zeta-potential measurements.

RESULTS

BALF inhibited polyplex- and lipoplex-mediated gene transfer. Analysing components of BALF, we found that dendrimer-mediated gene transfer was not inhibited by any specific component. PEI-mediated gene transfer was dose-dependently inhibited by alpha(1)-glycoprotein, slightly inhibited by mucin, but not inhibited in the presence of albumin. Lipoplex-mediated gene transfer was inhibited by mucin at higher concentrations and by albumin, but not by alpha(1)-glycoprotein. 2-D-gel electrophoresis revealed that proteins of the BALF were adsorbed more intensively to lipoplexes than to polyplexes. In addition, mucin and alpha(1)-glycoprotein also adsorbed more intensively to lipoplexes than to polyplexes. Adsorption of BALF components led to a decrease in the positive zeta-potential of lipoplexes and led to a negative zeta-potential of polyplexes. Complement cleavage fragment C3 beta, and in the case of lipoplexes also the C3 alpha fragment, were found among the proteins opsonised on gene vectors.

CONCLUSIONS

Our study shows that BALF contains inhibitory components for non-viral gene transfer. We could not detect a specific inhibitory component, but inhibition was most likely due to the change in the surface charge of the gene vectors. Interestingly, there is evidence for complement activation when the route of pulmonary gene vector administration is chosen. Consequently, shielding of gene vectors to circumvent interaction with the ASL environment should be a focus for pulmonary administration in the future.

Solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) in cosmetic and dermatological preparations

Solid lipid nanoparticles (SLN) were developed at the beginning of the 1990 s as an alternative carrier system to emulsions, liposomes and polymeric nanoparticles. The paper reviews advantages-also potential limitations-of SLN for the use in topical cosmetic and pharmaceutical formulations. Features discussed include stabilisation of incorporated compounds, controlled release, occlusivity, film formation on skin including in vivo effects on the skin. As a novel type of lipid nanoparticles with solid matrix, the nanostructured lipid carriers (NLC) are presented, the structural specialties described and improvements discussed, for example, increase in loading capacity, physical and chemical long-term stability, triggered release and potentially supersaturated topical formulations. For both SLN and NLC, the technologies to produce the final topical formulation are described, especially the production of highly concentrated lipid nanoparticle dispersions >30-80% lipid content. Production issues also include clinical batch production, large scale production and regulatory aspects (e. g. status of excipients or proof of physical stability).

Nanostructured lipid matrices for improved microencapsulation of drugs

At the beginning of the nineties solid lipid nanoparticles (SLN) have been introduced as a novel nanoparticulate delivery system produced from solid lipids. Potential problems associated with SLN such as limited drug loading capacity, adjustment of drug release profile and potential drug expulsion during storage are avoided or minimised by the new generation, the nanostructured lipid carriers (NLC). NLC are produced by mixing solid lipids with spatially incompatible lipids leading to special structures of the lipid matrix, i.e. three types of NLC: (I) the imperfect structured type, (II) the structureless type and (III) the multiple type. A special preparation process-applicable to NLC but also SLN-allows the production of highly concentrated particle dispersions (>30-95%). Potential applications as drug delivery system are described.

Solid lipid nanoparticles as carrier for sunscreens: in vitro release and in vivo skin penetration

The aim of this study was the comparison of two different formulations (solid lipid nanoparticles (SLN) and conventional o/w emulsion) as carrier systems for the molecular sunscreen oxybenzone. The influence of the carrier on the rate of release was studied in vitro with a membrane-free model. The release rate could be decreased by up to 50% with the SLN formulation. Further in vitro measurements with static Franz diffusion cells were performed. In vivo, penetration of oxybenzone into stratum corneum on the forearm was investigated by the tape stripping method. It was shown that the rate of release is strongly dependent upon the formulation and could be decreased by 30-60% in SLN formulations. In all test models, oxybenzone was released and penetrated into human skin more quickly and to a greater extent from the emulsions. The rate of release also depends upon the total concentration of oxybenzone in the formulation. In vitro-in vivo correlations could be made qualitatively.

Buparvaquone mucoadhesive nanosuspension: preparation, optimisation and long-term stability

The poorly soluble drug buparvaquone is used in experimental clinics against the gastrointestinal persisting parasite Cryptosporidium parvum. It was produced as nanosuspension by high pressure homogenisation. Main advantages of nanosuspensions (amongst others) are their increase of saturation solubility and dissolution velocity, improving the bioavailability of drugs. The buparvaquone nanosuspension had a bulk population of about 600 nm (analysed by photon correlation spectroscopy (PCS)). The additional analysis performed with laser diffraction showed that only a very small content of microparticles occurred, which is, for the special features of nanosuspensions, negligible because they were still below 3 microm. Another feature of nanosuspensions is the adhesion properties to surfaces, e.g. mucosa. To further increase the adhesion time of the buparvaquone nanosuspension to C. parvum, the nanosuspension was formulated with hydrogels made from mucoadhesive polymers, e.g. different types of Carbopol and chitosan. Only a small increase of the particle size of the bulk population occurred directly after the incorporation of buparvaquone nanosuspension into the hydrogels. The nanosuspension/hydrogel systems were physically long-term stable over a period of 6 months as indicated by the unchanged particle sizes.

Semisolid SLN dispersions for topical application: influence of formulation and production parameters on viscoelastic properties

Aqueous solid lipid nanoparticle (SLN) dispersions with a high lipid content up to 35% and viscous to semisolid consistency were produced by a high pressure homogenization process. Despite their high lipid content and viscosity these dispersions preserved their colloidal size range. The SLN dispersions were compared to nanoemulsions and microparticle dispersions with regard to particle size, viscoelastic properties and formation of a semisolid gel structure. Viscoelastic measurements including oscillation stress sweep tests and oscillation frequency sweep tests demonstrated that the existence of a solid particle matrix with a particle size in the nanometer range is a prerequisite to form a semisolid dispersion having the appropriate consistency for topical application. Striking differences were observed between solid lipid micro- and nanodispersions of the same composition. Particle size reduction resulted in an 80-fold increase of the elastic modulus. Particle size distribution, the physical state of the dispersed lipid phase and the emulsifier concentration have been identified as further key factors for the viscoelastic properties and gel structure of the lipid nanodispersions. By conducting oscillation measurements it was possible to relate the stability of lipid dispersions to specific rheological parameters therefore providing a sensitive tool in stability assessment. Changing the production process from a 40 ml batch to a 2 l batch turned out to have an influence on the colloidal structures of semisolid SLN dispersions. Consistency increased but particle size and ratio of elastic to viscous properties stayed in the same range.

Physiological and genetic characteristics of two bacterial strains utilizing phenoxypropionate and phenoxyacetate herbicides

Two strains, Rhodoferax sp. P230 and Delftia (Comamonas) acidovorans MCI, have previously been shown to carry activities for the degradation of the two enantiomers of (RS)-2-(2,4-dichlorophenoxy-)propionate (dichlorprop) and (RS)-2-(4-chloro-2-methylphenoxy-)propionate (mecoprop) and, in addition, are capable of degrading phenoxyacetate derivatives 2.4-dichlorophenoxyacetate (2,4-D) and 4-chloro-2-methylphenoxyacetate (MCPA). Metabolism of the herbicides is initiated by alpha-ketoglutarate-dependent dioxygenases for both enantiomers of the phenoxypropionate herbicides and for 2,4-D. These activities were constitutively expressed for both enantiomers of dichlorprop in strain MC1 and for the Renantiomer in strain P230. Enzyme activities for the complete degradation of phenoxyacetate and phenoxypropionate herbicides were induced during incubation on either of these herbicides. Strain MC1 has about threefold higher activities for the degradation of dichlorprop and for growth on this substrate (mumax = 0.15 h(-1)) than strain P230; the maximum growth rate on 2,4-D amounts to 0.045 h(-1) with strain MC1. Dichlorprop is utilized faster than mecoprop and the R-enantiomers are cleaved with higher rates than the S-enantiomers. The degradation of the chlorophenolic intermediates seems to proceed via the modified ortho cleavage pathway as indicated by activities of the respective enzymes. The enzymatic results were supported by genetic investigations by which the presence of the genes tfdB (encoding a dichlorophenol hydroxylase), tfdC (encoding a chlorocatechol 1,2-dioxygenase) and tfdD (encoding a chloromuconate cycloisomerase) could be demonstrated in both strains by PCR after application of respective primers. The presence of the tfdA gene (encoding a 2,4-D/alpha-ketoglutarate dioxygenase) was only shown for strain P230 but was lacking in strain MC1. Sequence analysis of the tfd gene fragments revealed high homology to the degradative genes of other proteobacterial strains degrading chloroaromatic compounds. Strain MC1 carries a plasmid of about 120 kb which apparently harbors herbicide degradative genes as concluded from deletion mutants which have lost 2,4-D[phenoxalkanoate]/alpha-ketoglutarate dioxygenase activities for cleavage of the R- and S-enantiomer, and of 2,4-D. For strain P230, no plasmid could be demonstrated; the activity was stably conserved in this strain during growth under nonselective conditions.

Effect of lipid matrix and size of solid lipid nanoparticles (SLN) on the viability and cytokine production of macrophages

Solid lipid nanoparticles (SLN) interact with mononuclear cells following intravenous injection. Little is known about the interaction of SLN with these cells, including cytotoxic effects and a possible up-regulation of pro-inflammatory cytokines. Therefore, we investigated the influence of lipid matrix, concentration, and size of SLN on murine peritoneal macrophages (mphi). mphi were incubated with SLN consisting of different lipid matrices and coated with the same surfactant. Cytotoxicity as assessed by MTT test was found to be concentration-dependent and was dramatically influenced by the lipid matrix. Marked cytotoxic effects were observed when cells were incubated with SLN consisting of stearic acid (STE) or dimethyl-dioctadecylammonium bromide (DDA) at concentrations of 0.01%, whereas SLN consisting of triglycerides, cetylpalmitate or paraffin did not exert major cytotoxic effects at the same concentrations. Cytotoxic effects were most likely caused by products of enzymatic degradation including free stearic acid. Analysis of cytokine production by mphi following incubation with SLN revealed concentration-dependent decreases in IL-6 production. These decreases seemed to be associated with cytotoxic effects. IL-12 and TNF-alpha production was neither detected in supernatants of mphi treated with SLN at any concentration nor in those of untreated cells. The size of SLN did neither affect cytotoxicity of SLN nor resulted in induction or digression of cytokine production by mphi. In conclusion, results of the present study revealed that the nature of the lipid matrix and the concentration of SLN dramatically impact cytotoxicity of SLN on mononuclear cells. Lipid matrices of SLN should therefore be carefully chosen and tested for later intravenous use.

Differences in the coalescence kinetics of fat emulsions in dependence on the amount of fat and age

The destabilizing effect of calcium ions on emulsions was studied as a function of the age of the emulsions and the degree of emulsion dilution (2%, 0.2% an 0.02% fat). Particle size measurements were performed both in the Coulter counter and a laser diffraction device equipped with PIDS technology. The data of both instruments showed a good correlation. zeta-Potential was determined by laser doppler anemometrie. The physical stability of the emulsions in 6 mmolar Calcium Chloride decreased with increasing dilution--despite the diminished rate of collision in diluted systems. In addition, and increased electrolyte sensitivity was observed with increasing age of the emulsions--despite enhanced electrostatic stabilization by an increased zeta-potential. Both effects were attributed to an increased binding of calcium ions per surface area of the droplets, i.e. increased ratio calcium ions to surface by dilution and increased binding by the increased charge of aged emulsions.

Jet nebulization of PEI/DNA polyplexes: physical stability and in vitro gene delivery efficiency

BACKGROUND

Aerosol drug delivery currently represents the most acceptable and convenient delivery system for repeated drug application to the lungs. Although polyethyleneimine (PEI) has recently been demonstrated to mediate gene transfer successfully to mouse lungs via aerosol delivery, the effect of the jet nebulization process on the properties of PEI/DNA polyplexes has not yet been examined.

METHODS

PEI/DNA polyplexes were generated in several commonly used solvents, such as distilled water, HEPES buffered saline (HBS), and 5% glucose. The complex parameters, such as particle size, zeta potential, DNA integrity, and transfection efficiency, were examined before and after jet nebulization.

RESULTS

The complex parameters and the transfection efficiency were influenced by the solvent that was used for complex formulation and by the nebulization process itself. When polyplexes were formulated in HBS, the particle size, zeta potential, and DNA concentration were affected by the nebulization process and the transfection efficiency decreased dramatically. Polyplexes formulated in 5% glucose were less susceptible to the nebulization process, as indicated by only minor changes of the zeta potential and particle size when compared with HBS. The resulting transfecion efficiency was very low both before and after nebulization. Polyplexes formulated in distilled water had the most resistant behavior with the nebulization process. Zeta potential, particle size, and DNA integrity were influenced least of all by nebulization.

CONCLUSION

As a result, the transfection efficiency of PEI/DNA complexes remained constant throughout the nebulization process only when formulated in distilled water. These data suggest that distilled water represents the most appropriate solvent for polyplex formulation when delivered by jet nebulization.

Cationic solid-lipid nanoparticles can efficiently bind and transfect plasmid DNA

The suitability of cationically modified solid-lipid nanoparticles (SLN) as a novel transfection agent was investigated. SLN were produced by hot homogenisation using either Compritol ATO 888 or paraffin as matrix lipid, a mixture of Tween 80 and Span 85 as tenside and either EQ1 (N,N-di-(beta-steaorylethyl)-N,N-dimethylammonium chloride) or cetylpyridinium chloride as charge carrier. The resulting particles were approximately 100 nm in size and showed zeta potentials around +40 mV at pH 7.4. DNA binding was tested by agarose gel electrophoresis. The resulting SLN-DNA complexes were further characterised by AFM and zeta potential measurements. Only the SLN batch SII-13, composed of 4% Compritol, 4% Tween/Span and 1% EQ1, was able to form stable complexes with DNA. Typical complexes were 300 to 800 nm in size. Cytotoxicity and transfection efficiency was tested in vitro on Cos-1 cells. Cationic SLN produced by modification with EQ1 were well tolerated, with LD50 values >3 mg/ml in the LDH release assay and >0.6 mg/ml in the WST-1 assay. Further, SLN-DNA complexes containing between 10 and 200 weight equivalents of SII-13 (matrix lipid) efficiently transfected the galactosidase expression plasmid pCMVbeta in the absence and presence of the endosomolytic agent chloroquine.

Expression of the 2,4-D degradative pathway of pJP4 in an alkaliphilic, moderately halophilic soda lake isolate, Halomonas sp. EF43

The broad host range plasmid pJP4, which carries genes for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D), 2-methyl-4-chlorophenoxyacetic acid, and 3-chlorobenzoic acid, was used in conjugation experiments with mixed cultures enriched from water and sediment samples from an alkaline pond in the area of Szegedi Fehértó, a soda lake in south Hungary. pJP4-encoded mercury resistance was used as a selection marker. One of the transconjugants, the alkaliphilic, moderately halophilic strain EF43, stably maintained the plasmid and was able to degrade 2,4-D and 3-chlorobenzoate under alkaline conditions in the presence of an additional carbon source such as pyruvate, benzoate, or alpha-ketoglutarate, indicating that the degradative genes of pJP4 were expressed in this strain. However, it was unable to grow on these chloroaromatic substrates when the substrate was the sole source of carbon and energy. Chemostat cultivation experiments revealed that the 2,4-D degradation rate during growth on benzoate or pyruvate was limited by the low activity of chlorocatechol-degrading enzymes, particularly chloromuconate cycloisomerase. Strain EF43 was identified as Halomonas sp. on the basis of 16S rRNA sequencing and additional taxonomic studies. 16S rRNA sequence analysis revealed that strain EF43 is closely related to typical soda lake isolates belonging to the genus Halomonas.

Comparison of protein adsorption patterns onto differently charged hydrophilic superparamagnetic iron oxide particles obtained in vitro and ex vivo

Protein adsorption patterns of superparamagnetic iron oxides (SPIO) were evaluated by two-dimensional electrophoresis (2-DE) after in vitro incubation of the particles in plasma or serum. SPIO particles having positive (MKK 1211), negative (MKA 1211), or neutral (MKG 1411) charge were used. Protein adsorption patterns of different charged SPIO particles acquired in vitro and recollected 5 min after intravenous injection into rats (ex vivo) were compared. For the uncharged MKG 1411 particles, the differences of protein adsorption patterns were negligible and only minor differences were found for the negatively charged MKA 1211 and positively charged MKK 1211 particles. A good correlation between in vitro and ex vivo data could be shown. For the evaluation of protein adsorption patterns of SPIO particles determining organ distribution and allowing estimation of site-specific delivery (drug targeting), the currently used protocol for 2-DE analysis could be confirmed.

Solid lipid nanoparticles (SLN)--a novel carrier for UV blockers

The formulation of safe sunscreen products is of high importance due to their increasing use because of the diminishing ozone layer. Solid lipid nanoparticles (SLN) are introduced as the new generation of carriers for cosmetics, especially for UV blockers for the use on human skin and/or hair and production thereof is described. The crystalline cetylpalmitate SLN particles have the ability of reflecting and scattering UV radiation on their own thus leading to photoprotection without the need for molecular sunscreens. An in vitro assay showed that a placebo cetyl palmitate SLN formulation is twice to three times as potent in absorbing UV radiation as a conventional emulsion. Incorporation of sunscreens into SLN lead to a synergistic photoprotection, i.e. higher than the additive effect of UV scattering caused by the SLN and UV absorption by the sunscreen. The photoprotective effect after incorporation of the molecular sunscreen 2-hydroxy-4-methoxybenzophenone (Eusolex 4360) into the SLN dispersion was observed to be increased threefold compared to a reference emulsion. Further, film formation on the skin was investigated by scanning electron microscopy, showing particle fusion due to water evaporation and formation of a dense film.

Atovaquone nanosuspensions show excellent therapeutic effect in a new murine model of reactivated toxoplasmosis

Immunocompromised patients are at risk of developing toxoplasma encephalitis (TE). Standard therapy regimens (including sulfadiazine plus pyrimethamine) are hampered by severe side effects. While atovaquone has potent in vitro activity against Toxoplasma gondii, it is poorly absorbed after oral administration and shows poor therapeutic efficacy against TE. To overcome the low absorption of atovaquone, we prepared atovaquone nanosuspensions (ANSs) for intravenous (i.v.) administration. At concentrations higher than 1.0 microg/ml, ANS did not exert cytotoxicity and was as effective as free atovaquone (i.e., atovaquone suspended in medium) against T. gondii in freshly isolated peritoneal macrophages. In a new murine model of TE that closely mimics reactivated toxoplasmosis in immunocompromised hosts, using mice with a targeted mutation in the gene encoding the interferon consensus sequence binding protein, i.v.-administered ANS doses of 10.0 mg/kg of body weight protected the animals against development of TE and death. Atovaquone was detectable in the sera, brains, livers, and lungs of mice by high-performance liquid chromatography. Development of TE and mortality in mice treated with 1.0- or 0.1-mg/kg i.v. doses of ANS did not differ from that in mice treated orally with 100 mg of atovaquone/kg. In conclusion, i.v. ANSs may prove to be an effective treatment alternative for patients with TE.

Electrolyte- and pH-stabilities of aqueous solid lipid nanoparticle (SLN) dispersions in artificial gastrointestinal media

The influence of artificial gastrointestinal (GI) media on the physical stability of solid lipid nanoparticle (SLN) formulations consisting of different lipids and various surfactants/stabilizers has been investigated in vitro, with respect to ionic strength and pH. Laser diffractometry and zeta potential measurements were the techniques applied. Some SLN formulations already showed aggregation/particle growth in the presence of electrolytes at neutral pH. Other lipid nanodispersions remained physically stable with respect to the influence of electrolytes, but were pH-sensitive. It was possible to produce SLN that were GIT (gastrointestinal tract) stable by an optimized stabilizer composition. There is no optimal surfactant mixture for stabilization of any lipid, e.g. SLN consisting of the lipid Cutina CP showed GIT stability in combination with the stabilizer sugar ester S1670, whereas the stabilization with the surfactant mixture Tween 80/Span 85 was not effective. Vice versa, the emulsifier Pluronic F68 stabilized the lipid Compritol ATO 888 but not the lipid Imwitor 900 sufficiently to avoid aggregation of the SLN dispersion in artificial GI media. The stabilizing properties depend obviously on the specific interactions of the lipid matrix with the emulsifier, e.g. anchoring of the stabilizer on the lipid surface and density on the surface.

Evaluation of desorption of proteins adsorbed to hydrophilic surfaces by two-dimensional electrophoresis

The evaluation of the plasma protein adsorption patterns of superparamagnetic iron oxide (SPIO) particles is of high interest concerning their in vivo fate and is carried out by two-dimensional electrophoresis (2-DE). The sample preparation is of great importance, especially the removal of the adsorbed proteins (desorption) from the particle surface for subsequent analysis by 2-DE. The removal is carried out by a desorption solution. In this study, negatively and positively charged SPIO model particles were under investigation concerning the desorption of proteins adsorbed on their surfaces. Firstly, the desorption process was determined quantitatively using the Bradford protein assay. Secondly, the removable or nonremovable protein species, from particles surface were under investigation by 2-DE. Looking at the desorption in a quantitative manner with the Bradford assay, the desorption efficacy from negatively charged particles was about 90%. In the case of the positively charged particles, the desorption efficacy seemed to be reduced, approximately 34% of the proteins remained on the surface. Comparing the protein patterns of the particles evaluated by 2-DE in the desorption solution and the proteins remaining on the particles, they confirmed the results from the protein quantification. After desorption, the IgG gamma-chains were found to be the dominant protein fraction remaining on the negatively charged particles. On the positively charged particles, many more protein species were found after desorption. The more basic the protein fragments, the more ineffective was the desorption from the positively charged model particle, and vice versa. Nevertheless, all protein spots were found qualitatively in the desorption solution, especially when the desorption solutions still containing the particles were used for the 2-DE analysis. In conclusion, 2-DE could be confirmed as the "gold standard" for determining the plasma protein adsorption patterns of nanoparticulate systems.

Production of aqueous shellac dispersions by high pressure homogenisation

The use of shellac for coating purposes in pharmacy, food and nutriceutical industry generally involves the use of organic solvents. An aqueous shellac dispersion has been developed by applying high pressure homogenisation. Shellac was dissolved in alkaline solution, precipitated by HCl addition and the obtained suspension homogenised at 1500 bar applying 20 cycles. The volume diameter 50% was 2 microm, a distinct fraction of particles was in the nanometer range. This surfactant-free shellac dispersion with 20% solid content proved to be physically stable and showed good film forming properties.

Surfactant, but not the size of solid lipid nanoparticles (SLN) influences viability and cytokine production of macrophages

After intravenous (i.v.) injection, solid lipid nanoparticles (SLN) interact with mononuclear cells. Murine peritoneal macrophages were incubated with SLN formulations consisting of Dynasan 114 coated with different surfactants. The present study was performed to examine the impact of surfactants, which are important surface defining components of SLN, on viability and cytokine production by macrophages. Cytotoxicity, as assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) test, was strongly influenced by the surfactant used being marked with cetylpyridinium chloride- (CPC-) coated SLN at a concentration of 0.001% and further increased at SLN concentrations of 0.01 and 0.1%. All other SLN formulations -- containing Poloxamine 908 (P908), Poloxamer 407 (P407), Poloxamer 188 (P188), Solutol HS15 (HS15), Tween 80 (T80), Lipoid S75 (S75), sodium cholate (SC), or sodium dodecylsulfate (SDS) -- when used at the same concentrations reduced cell viability only slightly. None of the SLN formulations tested induced cytokine production but a concentration-dependent decrease of IL-6 production was observed, which appeared to be associated with cytotoxic effects. IL-12 and TNF-alpha were detected neither in supernatants of macrophages treated with SLN at any concentration nor in those of untreated cells. In contrast to the type of surfactant, the size of SLN was found neither to affect cytotoxicity of SLN nor to result in induction or digression of cytokine production by macrophages. In conclusion, testing the effects of surfactants on SLN on activity of macrophages is a prerequisite prior to in vivo use of SLN.

Formulation and in vitro-in vivo evaluation of piribedil solid lipid micro- and nanoparticles

Modification of the dissolution rate and, thus, the enhancement of the bioavailability of a dopaminergic drug, piribedil, which has a low aqueous solubility and short elimination half-life have been the aim in this study. Preparations of micron and submicron particles using solid lipid carriers have been performed for this purpose. For the avoidance of solvent residues resulting from the preparation technique, cold and hot homogenization methods have been used to prepare solid lipid particles. After obtaining an appropriate particle size, piribedil loading and preparation yield by the use of those two methods, various formulations have been prepared with different lipid, drug and surfactant materials. The factors mentioned were found to affect properties of the particles, and the release rate was found to be the fastest in acidic medium. Suspensions of pure piribedil and a formulation, selected according to the results obtained from in vitro dissolution and particle size experiments, were compared using tremor tests in mice. The same suspensions were applied perorally to rabbits and bioavailability of the solid lipid particle was found to be higher than the pure piribedil. After an in vitro-in vivo evaluation of piribedil solid lipid particles developed for Parkinson's disease therapy, it has been determined that release rate could be controlled and piribedil bioavailability could be improved.

Nanosuspensions as particulate drug formulations in therapy. Rationale for development and what we can expect for the future

An increasing number of newly developed drugs are poorly soluble; in many cases drugs are poorly soluble in both aqueous and organic media excluding the traditional approaches of overcoming such solubility factors and resulting in bioavailability problems. An alternative and promising approach is the production of drug nanoparticles (i.e. nanosuspensions) to overcome these problems. The major advantages of this technology are its general applicability to most drugs and its simplicity. In this article, the production of nanoparticles on a laboratory scale is presented, special features such as increased saturation solubility and dissolution velocity are discussed, and special applications are highlighted, for example, mucoadhesive nanosuspensions for oral delivery and surface-modified drug nanoparticles for site-specific delivery to the brain. The possibilities of large scale production -- the prerequisite for the introduction of a delivery system to the market -- are also discussed.

Preparation of semisolid drug carriers for topical application based on solid lipid nanoparticles

Aqueous dispersions of solid lipid nanoparticles (SLN) show some interesting features in topical drug delivery. However, to get a semisolid carrier having the appropriate consistency for topical application, the liquid SLN dispersions have to be incorporated in convenient topical dosage forms like hydrogels or creams. This is a time-consuming production process with several disadvantages. A new one-step production process delivering a semisolid topical formulation including SLN is presented avoiding these disadvantages. The semisolid SLN dispersions were produced by high-pressure homogenization using an APV Lab 40 homogenizer. The resulting dispersions were characterized concerning their particle size and rheological properties. Despite the high lipid content of the SLN dispersions, they retained their colloidal particle size. Viscoelastic measurements proved the existence of a gel-like structure with a prevailing elastic component.

The role of plasma proteins in brain targeting: species dependent protein adsorption patterns on brain-specific lipid drug conjugate (LDC) nanoparticles

The in vivo organ distribution of particulate drug carriers is decisively influenced by the interaction with plasma proteins after i.v. administration. Serum protein adsorption on lipid drug conjugate nanoparticles, a new carrier system for i.v. application, was investigated by 2-dimensional electrophoresis (2-DE). The particles were surface-modified to target them to the brain. To assess the protein adsorption pattern after i.v. injection in mice prior to in vivo studies, the particles were incubated in mouse serum. Incubation in human serum was carried out in parallel to investigate similarities or differences in the protein patterns obtained from men and mice. Distinct differences were found. Particles incubated in human serum showed preferential adsorption of apolipoproteins A-I, A-IV and E. Previously, preferential adsorption of ApoE was reported as one important factor for targeting of Tween(R)80 modified polybutylcyanoacrylate nanoparticles to the brain. Preferential adsorption of ApoA-I and A-IV took place after incubation in mouse serum, adsorption of ApoE could not be clearly confirmed. In vivo localization of the LDC nanoparticles at the blood-brain barrier and diffusion of the marker Nile Red into the brain could be shown by confocal laser-scanning microscopy. Differences of the obtained adsorption patterns are discussed with regard to their relevance for correlations of in vitro and in vivo data obtained from different species.

Production and characterisation of mucoadhesive nanosuspensions for the formulation of bupravaquone

Bupravaquone is a new naphthoquinone antibiotic against Cryptosporidium parvum and other parasites. It has attracted interest for the treatment of C. parvum infections, because of the lack of a drug in the treatment of mostly AIDS patients. The bioavailability of bupravaquone is limited when given orally. To overcome the problem of the high elimination rate caused by diarrhoea, typical for C. parvum infections, bupravaquone was formulated as a mucoadhesive nanosuspension, i.e. combining the properties of mucoadhesive drug delivery systems, in this case hydro gels, with nanosuspensions. In this study different polymers/hydro gels were employed to create a prolonged retention time for the drug in the infected gastrointestinal tract (GIT). The second step to improve the bioavailability of bupravaquone was the formulation as nanosuspension. Therefore various concentrations of bupravaquone with different surfactants were tested. The production of these nanosuspensions was carried out by high pressure homogenisation. In addition to the classical stepwise production, about a new one step production method is described.

Production and characterisation of highly concentrated nanosuspensions by high pressure homogenisation

Nanosuspensions produced by high-pressure homogenisation are a solution for the formulation of poorly soluble drugs with bioavailability problems. The typical solid concentration of the nanosuspensions is 10%. However, to transfer the nanosuspensions to a dry product (e.g. granulation, tablets, pellets), a higher solid content is required to remove less water. Nanosuspensions with 20 and 30% solid content were produced, the effect of surfactant concentration assessed and their quality (size data) compared with the lower standard concentrations of 1-10% solid.

Two-time window and multiangle photon correlation spectroscopy size and zeta potential analysis--highly sensitive rapid assay for dispersion stability

Polysaccharide-stabilized iron oxide particles are highly potent contrast agents in magnetic resonance imaging. After intravenous injection, the size of these small or ultrasmall particles strongly influences their distribution in the body. Knowledge about the uniformity of particle size distribution within this particle size range is not accessible by laser diffraction (lower edge of detection range), and photon correlation spectroscopy (PCS) data only yield insufficient information, the so-called polydispersity index. A combination of two-time window and multiangle analysis makes detailed characterization of particle size distribution and particle aggregation feasible, which was shown using five different iron oxide dispersions. Additional particle charge characterization yielded conclusions about the type of stabilization present in the dispersion - electrostatic or steric stabilization. Thus, this thorough particle size and charge analysis is a tool for quick detection of broad particle distributions or aggregates.

'Stealth' corona-core nanoparticles surface modified by polyethylene glycol (PEG): influences of the corona (PEG chain length and surface density) and of the core composition on phagocytic uptake and plasma protein adsorption

Nanoparticles possessing poly(ethylene glycol) (PEG) chains on their surface have been described as blood persistent drug delivery system with potential applications for intravenous drug administration. Considering the importance of protein interactions with injected colloidal dug carriers with regard to their in vivo fate, we analysed plasma protein adsorption onto biodegradable PEG-coated poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA) and poly(varepsilon-caprolactone) (PCL) nanoparticles employing two-dimensional gel electrophoresis (2-D PAGE). A series of corona/core nanoparticles of sizes 160-270 nm were prepared from diblock PEG-PLA, PEG-PLGA and PEG-PCL and from PEG-PLA:PLA blends. The PEG Mw was varied from 2000-20000 g/mole and the particles were prepared using different PEG contents. It was thus possible to study the influence of the PEG corona thickness and density, as well as the influence of the nature of the core (PLA, PLGA or PCL), on the competitive plasma protein adsorption, zeta potential and particle uptake by polymorphonuclear (PMN) cells. 2-D PAGE studies showed that plasma protein adsorption on PEG-coated PLA nanospheres strongly depends on the PEG molecular weight (Mw) (i.e. PEG chain length at the particle surface) as well as on the PEG content in the particles (i.e. PEG chain density at the surface of the particles). Whatever the thickness or the density of the corona, the qualitative composition of the plasma protein adsorption patterns was very similar, showing that adsorption was governed by interaction with a PLA surface protected more or less by PEG chains. The main spots on the gels were albumin, fibrinogen, IgG, Ig light chains, and the apolipoproteins apoA-I and apoE. For particles made of PEG-PLA45K with different PEG Mw, a maximal reduction in protein adsorption was found for a PEG Mw of 5000 g/mole. For nanospheres differing in their PEG content from 0.5 to 20 wt %, a PEG content between 2 and 5 wt % was determined as a threshold value for optimal protein resistance. When increasing the PEG content in the nanoparticles above 5 wt % no further reduction in protein adsorption was achieved. Phagocytosis by PMN studied using chemiluminescence and zeta potential data agreed well with these findings: the same PEG surface density threshold was found to ensure simultaneously efficient steric stabilization and to avoid the uptake by PMN cells. Supposing all the PEG chains migrate to the surface, this would correspond to a distance of about 1.5 nm between two terminally attached PEG chains in the covering 'brush'. Particles from PEG5K-PLA45K, PEG5K-PLGA45K and PEG5K-PCL45K copolymers enabled to study the influence of the core on plasma protein adsorption, all other parameters (corona thickness and density) being kept constant. Adsorption patterns were in good qualitative agreement with each other. Only a few protein species were exclusively present just on one type of nanoparticle. However, the extent of proteins adsorbed differed in a large extent from one particle to another. In vivo studies could help elucidating the role of the type and amount of proteins adsorbed on the fate of the nanoparticles after intraveinous administration, as a function of the nature of their core. These results could be useful in the design of long circulating intravenously injectable biodegradable drug carriers endowed with protein resistant properties and low phagocytic uptake.

Effect of solid lipid nanoparticles (SLN) on cytokine production and the viability of murine peritoneal macrophages

The purpose of this study was to investigate possible immunomodulatory and cytotoxic effects of solid lipid nanoparticles (SLN) on murine peritoneal macrophages. Immunomodulatory effects of SLN composed of either a lipid- (glycerol-behenate) or a wax (cetylpalmitate) matrix stabilized by the surfactant Poloxamer 188 were analysed by detection of proinflammatory and down-regulatory cytokines in supernatants of thioglycollate-elicited peritoneal macrophages using enzyme-linked immunosorbent assay (ELISA). Cytotoxicity of SLN was assessed using the ITT test. Incubation of macrophages with either SLN at low concentrations did not increase production of interleukin (IL)-6, IL-12, and tumour necrosis factor (TNF)-alpha. At higher SLN concentrations, a concentration-dependent decrease in IL-6 secretion was observed compared to background production of IL-6 by untreated macrophages. IL-12 and TNF-alpha production was neither detected in supernatants of macrophages treated with SLN at any concentration nor in those of untreated cells. The decrease in IL-6 secretion was paralleled by concentration-dependent cytotoxicity of SLN on these cells. In contrast, incubation with polystyrene reference particles neither resulted in decreased IL-6 production nor in a loss of viability. SLN-treated macrophages were found to up-regulate their cytokine production following stimulation with Pansorbin, despite the concentration-dependent cytotoxicity induced by SLN. Down-regulatory effects on SLN-treated macrophages by IL-10 were not observed. In conclusion, incubation of SLN with murine peritoneal macrophages did not induce the production of proinflammatory and down-regulatory cytokines. At high concentrations of SLN, cytotoxic effects on these cells were observed. Cytotoxicity appears to be the main cause of decreased cytokine production by these cells.

Analysis of plasma protein adsorption onto polystyrene particles by two-dimensional electrophoresis: comparison of sample application and isoelectric focusing techniques

Two-dimensional electrophoresis (2-DE) was previously established for analysis of plasma protein adsorption patterns on particulate carriers for intravenous drug targeting. This study addresses a possible effect of polymeric particles on protein separation in the first dimension, e.g., hindrance of protein entry into the gel or interaction of particles with the gel matrix. Polystyrene beads of mean diameter 100, 200 and 1000 nm were used as model carriers. Two different separation techniques were performed in the first dimension of 2-DE to study possible interactions of the beads with the different gel matrices, i.e., carrier ampholytes (CA) and immobilized pH gradients (IPGs). Comparison of gels obtained from samples including the particles from samples separated from the polystyrene beads showed no noteworthy differences. Therefore, a negative effect of the particles can be excluded, and particle separation from the sample is not necessary. Another goal of this study was the transfer of analytical protocols for isoelectric focusing from CA to IPGs with regard to enhanced reproducibility, faster sample processing, and easier handling. Transfer from CA to IPGs was carried out successfully and showed improved resolution of basic proteins. In contrast to that, lower amounts of a few high molecular mass proteins were detected, especially when sample application cups were employed. A qualitative change in the obtained protein pattern was not observed. Increased entry of high molecular weight proteins was achieved by in-sample rehydration instead of using sample cups.

In vivo gene delivery to the lung using polyethylenimine and fractured polyamidoamine dendrimers

BACKGROUND

Gene transfer into the airways could be of importance for the treatment of chronic lung diseases such as cystic fibrosis. In the past few years several attempts have been made to effectively deliver DNA to the lung using different viral and non-viral vector systems. Viral vectors and cationic lipids have been tested intensively but the properties of cationic polymers such as polyethylenimine (PEI) 25 kDa and fractured polyamidoamine dendrimers to deliver DNA to the airways have not been studied. Surfactant preparations have been shown to influence pulmonary adenoviral and naked plasmid DNA mediated gene transfer in vivo. We investigated the gene delivery efficiency of branched PEI 25 kDa and fractured dendrimers to the murine lung in vivo and also examined the effect of surfactant on PEI 25 kDa mediated gene transfer to the lung.

METHODS

Cationic polymer/DNA complexes were prepared in 25 mM HEPES buffer (pH = 7.4) or double distilled water and administered to the lungs of BALB/c mice via cannula intubation. The trachea, left and right lung, heart, liver and esophagus were examined for luciferase activity. Inflammation was assessed by performing standard histology.

RESULTS

PEI/DNA complexes showed a high level of luciferase gene expression in the lung. Complexes formed in double distilled water exhibited higher gene expression than complexes formed in 25 mM HEPES buffer (pH 7.4). The optimal N/P ratio was found to be N/P = 10 in double distilled water. Luciferase activity was only detected in the lung and decreased rapidly in a time-dependent manner. The addition of a natural surfactant preparation, Alveofact, slightly reduced gene transfer of branched PEI 25 kDa. Luciferase gene expression obtained by using fractured dendrimers was very low.

CONCLUSION

The present study demonstrates that PEI 25 kDa, but not polyamidoamine dendrimers, effectively mediates transient gene transfer to the murine lung after intratracheal intubation. In conclusion, branched PEI 25 kDa was found to be an effective vector for pulmonary gene delivery in vivo, being superior to fractured dendrimers.