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Biomedical subjects

R H Müller

Publications and source records attributed to R H Müller.

At least 73 records · Page 4Linked to original sources
PubMed2000

Nanoparticles with decreasing surface hydrophobicities: influence on plasma protein adsorption.

The rapid uptake of i.v. injected nanoparticles by cells of the mononuclear phagocytic system (MPS) is a major obstacle for a long blood circulation time and a drug targeting to sites other than the MPS. The adsorption of proteins on the particles surface after i.v. administration depends on their surface characteristics and is regarded as key factor for the in vivo organ distribution. The objective of this study is to investigate changes in the plasma protein adsorption patterns in the course of surface hydrophobicity variation. Latex particles with decreasing surface hydrophobicity were synthesized as model colloidal carriers. Physicochemical characterization had been performed and considerable differences in the protein adsorption patterns on the particles could be detected by using two-dimensional polyacrylamide gel electrophoresis (2-D PAGE). Correlations between physicochemical characteristics and the protein adsorption patterns have been found and are discussed.

Adsorption↗
PubMed2000

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.

Ferric Compounds↗
PubMed2000

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.

Acrylic Resins↗
PubMed2000

Solid lipid nanoparticles (SLN) for controlled drug delivery - a review of the state of the art.

Solid lipid nanoparticles (SLN) introduced in 1991 represent an alternative carrier system to traditional colloidal carriers, such as emulsions, liposomes and polymeric micro- and nanoparticles. SLN combine advantages of the traditional systems but avoid some of their major disadvantages. This paper reviews the present state of the art regarding production techniques for SLN, drug incorporation, loading capacity and drug release, especially focusing on drug release mechanisms. Relevant issues for the introduction of SLN to the pharmaceutical market, such as status of excipients, toxicity/tolerability aspects and sterilization and long-term stability including industrial large scale production are also discussed. The potential of SLN to be exploited for the different administration routes is highlighted. References of the most relevant literature published by various research groups around the world are provided.

Animals↗
PubMed2000

Adsorption kinetics of plasma proteins on oil-in-water emulsions for parenteral nutrition.

The plasma protein adsorption patterns on colloidal drug carriers are regarded as an important factor for their in vivo fate. In this study the adsorption kinetics on oil-in-water emulsions were determined and compared to the adsorption kinetics on polystyrene particles. In addition, the adsorption kinetics on the same systems after surface-modification with a hydrophilic polymer were also investigated. The protein adsorption was determined by means of two dimensional polyacrylamide gel electrophoresis (2D-PAGE). The determination of the plasma protein adsorption kinetics was carried out using different concentrations of human plasma in the incubation medium to prolong the residence time of the more abundant plasma proteins on the surface. Proteins which are likely to be displaced in a split second are thus accessible to analysis. The oil-in-water emulsion showed a distinctly different adsorption behavior from the one previously described for solid surfaces, where initially adsorbed proteins are displaced by others, having a higher affinity to the surface ('Vroman effect'). No competitive protein adsorption could be observed on the emulsions. Moreover, the predominantly adsorbed apolipoproteins A-I, A-IV, C-II and C-III increase in amount with increasing plasma concentration. The knowledge of the adsorption kinetics of colloidal carriers might be helpful for a better understanding of the in vivo behavior of such systems and for the transfer of principles already known from other carrier systems to the controlled development of emulsions for site specific drug delivery.

Adsorption↗
PubMed2000

The influence of alkali fatty acids on the properties and the stability of parenteral O/W emulsions modified with solutol HS 15.

Arachis oil based parenteral O/W emulsions were prepared using soya bean phosphatidylcholine (SPC) and different combinations of co-emulsifiers containing polyethylene glycol fatty acid esters (Solutol HS 15) and alkali fatty acids (sodium laurate, sodium stearate). The parameters measured were droplet size (both by photon correlation spectroscopy and laser diffractometry), pH and zeta potential. All emulsions were subjected to autoclaving. The addition of polyethylene glycol 12-hydroxy stearate (Solutol HS 15) led to a significant decrease of mean oil droplet size. For long-term stability the amount added turned out to be the most important factor. With increased amounts of Solutol HS 15 the packing density of the emulsifier layer and the zeta potential decreased leading to instability. The optimum load of Solutol HS 15 was found to be 15 micromol/ml. Alkali fatty acids markedly improved the physical stability of the emulsions. Improved stability properties conferred to emulsions by alkali fatty acids could be attributed to the zeta potential increase even in the presence of Solutol HS 15. Consequently a mixed emulsifier film was established in which the ionized fatty acids determined the interface charge. In addition to this a strengthening of the molecular interactions occurring between phospholipid and Solutol HS 15 emulsifier in the presence of ionized fatty acids at the O/W interface can be assumed (L. Rydhag, The importance of the phase behaviour of phospholipids for emulsion stability, Fette Seifen Anstrichm. 81 (1979) 168-173). Different co-emulsifier mixtures were shown to have a pronounced impact on the plasma protein adsorption onto emulsion droplets.

Adsorption↗
PubMed2000

Preparation of a clofazimine nanosuspension for intravenous use and evaluation of its therapeutic efficacy in murine Mycobacterium avium infection.

Clofazimine nanosuspensions were produced by high pressure homogenization and the formulation was optimized for lyophilization. Characterization of the product by photon correlation spectroscopy, laser diffraction and Coulter counter analysis showed that the clofazimine nanosuspensions were suitable for iv injection with a particle size permitting passive targeting to the reticuloendothelial system. Following iv administration to mice of either the nanocrystalline or a control liposomal formulation at a dose of 20 mg clofazimine/kg bodyweight, drug concentrations in livers, spleens and lungs reached comparably high concentrations, well in excess of the MIC for most Mycobacterium avium strains. When C57BL/6 mice were experimentally infected with M. avium strain TMC 724, nanocrystalline clofazimine was as effective as liposomal clofazimine in reducing bacterial loads in the liver, spleen and lungs of infected mice. Nanocrystalline suspensions of poorly soluble drugs such as riminophenazines are easy to prepare and to lyophilize for extended storage and represent a promising new drug formulation for intravenous therapy of mycobacterial infections.

Animals↗
PubMed2000

A theoretical study on the metabolic requirements resulting from alpha-ketoglutarate-dependent cleavage of phenoxyalkanoates.

The etherolytic cleavage of phenoxyalkanoic acids in various bacteria is catalyzed by an alpha-ketoglutarate-dependent dioxygenase. In this reaction, the electron acceptor is oxidatively decarboxylated to succinate, whereas the proper substrate is cleaved by forming the oxidized alkanoic acid and the phenolic intermediate. The necessity of regenerating alpha-ketoglutarate and the consequences for the overall metabolism were investigated in a theoretical study. It was found that the dioxygenase mechanism is accompanied by a significant loss of carbon amounting to up to 62.5% in the assimilatory branch, thus defining the upper limit of carbon conversion efficiency. This loss in carbon is almost compensated for in comparison to a monooxygenase-catalyzed initial step when the dissimilatory efforts of the entire metabolism are included: the yield coefficients become similar. The alpha-ketoglutarate-dependent dioxygenase mechanism has more drastic consequences for microorganisms which are restricted in their metabolism to the first step of phenoxyalkanoate degradation by excreting the phenolic intermediate as a dead-end product. In the case of phenoxyacetate derivatives, the cleavage reaction would quickly cease due to the exhaustion of alpha-ketoglutarate and no growth would be possible. With the cleavage products of phenoxypropionate and phenoxybutyrate herbicides, i.e., pyruvate and succinate(semialdehyde), respectively, as the possible products, the regeneration of alpha-ketoglutarate will be guaranteed for stoichiometric reasons. However, the maintenance of the cleavage reaction ought to be restricted due to physiological factors owing to the involvement of other metabolic reactions in the pool of metabolites. These effects are discussed in terms of a putative recalcitrance of these compounds.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1999

An investigation into the distribution of lecithins in nanosuspension systems using low frequency dielectric spectroscopy.

A range of nanosuspensions comprising a model drug (RMKP 22) with varying concentrations of Phospholipon 90 were prepared using high pressure homogenization and analyzed using low frequency dielectric spectroscopy as a novel means of characterizing the distribution of Phospholipon 90 within the suspensions. A corresponding range of aqueous Phospholipon 90 suspensions were also studied for the purpose of comparison. The dielectric responses were interpreted using a modification of the Maxwell-Wagner approach, whereby the systems were considered to comprise a high frequency response corresponding to the bulk layer serially connected to a lower frequency response corresponding to an electrode barrier layer. The low frequency responses of both the Phospholipon 90 dispersions and the nanosuspensions were found to be essentially independent of phospholipid concentration, indicating the presence of a barrier layer covering the electrode surfaces. In contrast, the high frequency (bulk) loss response was found to increase with Phospholipon 90 concentration for the surfactant suspensions while a maximum in response was seen with Phospholipon 90 concentration for the nanosuspensions; this behaviour was attributed to the presence of impurities within the phospholipids. Based on this investigation, a model is proposed with which the dielectric response may be related to the surface coverage of the suspended drug particles.

Chemistry, Pharmaceutical↗
PubMed1999

Enzymatic degradation of SLN-effect of surfactant and surfactant mixtures.

Solid lipid nanoparticles (SLN) show different degradation velocities by the lipolytic enzyme pancreatic lipase as a function of their composition (lipid matrix, stabilizing surfactant). In combination with pancreatic colipase a degradation assay has been developed for studying the degradation behavior. As a measure to follow the degradation the formed free fatty acids have been analyzed using an enzymatic test. In the studies SLN degradation showed dependencies in relation to the length of the fatty acid chains in the triglycerides and the surfactants used for SLN production. The longer the fatty acid chains in the glycerides, the slower the degradation. The influence of surfactants can be degradation accelerating (e.g. cholic acid sodium salt) or a hindering, degradation slowing down effect due to steric stabilization (e.g. Poloxamer 407). As a second steric stabilizer, Tween 80 has been used and the results showed a less pronounced effect on hindering the degradation process than for Poloxamer 407. This result seems to be correlated to the number of ethyleneoxide chains in the molecule. The longer the ethyleneoxide chains are in the molecule, the more hindered is the anchoring of the lipase/colipase complex and consequently the degradation of the SLN. The result can be used to adjust degradation of SLN and consequently drug release in a controlled way.

Biodegradation, Environmental↗
PubMed1999

Visualization of in vitro protein-rejecting properties of PEGylated stealth polycyanoacrylate nanoparticles.

The in vitro protein-rejecting properties of PEG-coated polyalkylcyanoacrylate (PACA) nanoparticles were for the first time visualized after freeze-fracture of the nanoparticles pre-incubated with fibrinogen as a model blood protein. The reduced protein association to the nanoparticles was evidenced also by two-dimensional PAGE after incubation of the nanoparticles with human plasma. In vivo experiments showed the 'stealth' long-circulating properties of the PEGylated nanoparticles after intravenous administration to mice. Thus, the images obtained after nanoparticle-protein incubation were predictive of the behavior observed in vivo. In conclusion, freeze-fracture analysis represents a novel and original qualitative approach to investigate the interactions between proteins and particulate systems.

Adsorption↗
PubMed1999

Complement activation by model drug carriers for intravenous application: determination by two-dimensional electrophoresis.

The interactions of intravenously injected drug carriers with blood proteins are considered as an important factor for the fate of the particles after their administration. Protein adsorption on latex particles applied as model for intravenous drug carriers was analysed using two-dimensional electrophoresis (2-DE). The particles were incubated in citrated plasma, serum and heat-inactivated serum, respectively. Incubation in the various media resulted in clear differences in the protein adsorption patterns. Two characteristic protein spots were determined to be enriched on the 2-DE gels only after incubation of the particles in serum. Employing N-terminal microsequencing these protein spots were identified to be fragments of the complement protein C3. Enrichment of these particular spots was most likely a result of complement activation by the particles. Mechanism of C3 binding to the particle surface and subsequent inactivation by cleavage are discussed in order to explain the results. It could be demonstrated that 2-DE analysis provides the possibility to distinguish between adsorption and covalent attachment of C3 to particulate surfaces. The findings indicate that complement activation was caused by covalent binding of the C3 component C3b to the particles' surface. The influence of the incubation medium on the in vitro protein adsorption of particulate drug carriers has to be considered when a correlation between the protein adsorption pattern and the in vivo behaviour of the particles is approached.

Adsorption↗
PubMed1999

HPLC determination of clofazimine in tissues and serum of mice after intravenous administration of nanocrystalline or liposomal formulations.

A simple HPLC method is described for the determination of clofazimine in mouse tissues and in serum. The main application of the method was the determination of the drug in mouse tissues after i.v. administration of nanocrystalline suspensions or liposomal encapsulated clofazimine. Tissues were extracted with a 10-fold (w/v) volume of an extraction solution consisting of methanol/glacial acetic acid 9:1 (v/v). Serum proteins were precipitated with a 2-fold volume of acetonitrile. Isocratic chromatography was performed using an anion exchange column (Nucleosil 100-5 SA, Macherey & Nagel) for separation. The mobile phase was a mixture of acetonitrile and 0.1 mol/l aqueous phosphoric acid (75:25, v/v), adjusted to pH 2.9 with sodium hydroxide solution. Absorption of the eluate was monitored at 495 nm. The assay was precise, simple to perform and fast. Recovery from tissues was > or = 98%, from nanoparticles > or = 98%, and from liposomes > or = 96%. No interference was observed in extracts from mouse liver, spleen, lungs and human serum.

Animals↗
PubMed1999

Correlation between long-term stability of solid lipid nanoparticles (SLN) and crystallinity of the lipid phase.

Aqueous dispersions of solid lipid nanoparticles (SLN) are usually physically stable for more than 3 years. However, in some systems gelation occurred leading to solid gels due to an unknown mechanism. To elucidate this mechanism, Compritol SLN were stored at different temperatures, varying light exposure, in different packing materials and stressed by shear forces in short-term tests and a long-term study of 3 years. The SLN were analyzed by differential scanning calorimetry and sizing techniques. After production by hot homogenization of the melted lipid, the Compritol SLN crystallize in a mixture of stable beta' with unstable polymorphs (alpha, sub alpha). The destabilizing factors light, temperature and shear forces cause a distinct increase in the recrystallization index by transformation of the lipid to the beta' modification being accompanied by gel formation. Physically stable SLN remain as a mixture of modifications, increase in crystallinity index during storage is slow and crystallization occurs mainly in unstable modifications. From this, stabilization of physically critical SLN dispersions seems possible by inhibition of the transformation of the lipid to the stable modification.

Calorimetry, Differential Scanning↗
PubMed1999

Comamonas acidovorans strain MC1: a new isolate capable of degrading the chiral herbicides dichlorprop and mecoprop and the herbicides 2,4-D and MCPA.

A gram-negative prototrophic bacterial species, strain MC1, was isolated from the vicinity of herbicide-contaminated building rubble and identified by 16S rDNA sequence analysis, its physiological properties, GC content, and fatty acid composition as Comamonas acidovorans. This strain displays activity for the productive degradation of the two enantiomers of dichlorprop [(RS)-2-(2,4-dichlorophenoxy-)propionate; (RS)-2,4-DP] and mecoprop [(RS)-2-(4-chloro-2-methyl-) phenoxypropionate; (RS)-MCPP] in addition phenoxyacetate herbicides, i.e. 2,4-dichlorophenoxyacetate (2,4-D) and 4-chloro-2-methylphenoxyacetate (MCPA), and various chlorophenols were utilized. Rates amounted to 1.2 mmoles/h g dry mass (2,4-D) and 2.7 mmoles/h g dry mass [(RS)-2,4-DP]. Degradation of (RS)-2,4-DP was not inhibited up to concentrations of 500 mg/l, nor of 2,4-D up to 200 mg/l. The optimum pH value of (RS)-2,4-DP degradation was around 8. The application of respective primers for PCR amplification revealed the presence of tfdB and tfdC genes.

2,4-Dichlorophenoxyacetic Acid↗
PubMed1999

High resolution size determination of 20 nm colloidal gold particles by SedFFF.

PURPOSE: Assessment of lower size limit of Sedimentation Field-Flow Fractionation (SedFFF), specifically to evaluate if the method is suitable to determine the size and size distribution of 20 nm colloidal gold particles with high resolution. METHODS: Sedimentation Field-Flow Fractionation was used to determine the size of the colloidal particles. Due to the high density of gold it was possible to extend the lower size limit of SedFFF well below 20 nm. The size distribution of a gold colloid was obtained from the peak broadening caused by the polydispersity of the sample. The peak broadening due to instrumental imperfections was determined. For comparison purpose the particles were also sized using SEM and PCS. RESULTS: The mean diameter of the particles was determined to be (20.87+/-0.05) nm, the standard deviation in size being 1.04 nm (about 5%). SEM could confirm that the particles are about 20 nm in diameter. A sizing with PCS was not possible. The particles have a strong tendency to aggregate and PCS yields a diameter that is much too large. CONCLUSIONS: At optimized analytical parameters Sedimentation Field-Flow Fractionation is an effective method to measure the size of gold particles as small as 15 nm with an accuracy of about 0.1 nm. The polydispersity of the sample can easily be determined.

Chemical Fractionation↗
PubMed1998

Plasma protein adsorption on biodegradable microspheres consisting of poly(D,L-lactide-co-glycolide), poly(L-lactide) or ABA triblock copolymers containing poly(oxyethylene). Influence of production method and polymer composition.

Biodegradable particulate systems have been considered as parenteral drug delivery systems. The adsorption of plasma proteins on micro- and nanoparticles is determined by the surface properties and may, in turn, strongly influence the biocompatibility and biodistribution of both carriers. In the present study the influence of the polymer composition and the production method of microspheres on the in vitro plasma protein adsorption were investigated using two-dimensional electrophoresis (2-DE). Microparticles were prepared from poly(l-lactide) (l-PLA), poly(d,l-lactide-co-glycolide) (PLGA), and ABA triblock copolymers containing hydrophilic poly(oxyethylene) (B-blocks) domains connected to hydrophobic polyesters (A-blocks). Two different microencapsulation methods were employed, namely the w/o/w emulsion solvent evaporation method and the spray-drying technique. It could be demonstrated that the polymer composition and, especially, the encapsulation technique, influenced the interactions with plasma proteins significantly. For example, the percentages of several apolipoproteins in the plasma protein adsorption patterns of spray-dried PLGA- and l-PLA-particles were distinctly higher when compared to the adsorption patterns of the particles produced by the w/o/w-technique. Some adsorbed proteins were found to be characteristic or even specific for particles produced by the same method or consisting of identical polymers. Polyvinyl alcohol used as stabilizer in the w/o/w-technique may decisively influence the surface properties relevant for protein adsorption. The plasma protein adsorption on particles composed of ABA copolymers was drastically reduced when compared to microspheres made from pure polyesters. The adsorption patterns of ABA-particles were dominated by albumin. The plasma protein adsorption patterns detected on the different microspheres are likely to affect their in vivo performance as parenteral drug delivery systems.

Adsorption↗