Biomedical subjects

S Stolnik

Publications and source records attributed to S Stolnik.

16 recordsLinked to original sources

PubMed2001

The effect of surface coverage and conformation of poly(ethylene oxide) (PEO) chains of poloxamer 407 on the biological fate of model colloidal drug carriers.

Poloxamer 407 was adsorbed onto the surface of model colloidal drug carriers, polystyrene nanoparticles of 40, 70 and 137 nm in diameter, and the effect of the degree of surface coverage and the conformation of the poly(ethylene oxide) (PEO) chains on biological fate was studied. The relationship between the physicochemical and the biological properties of the nanoparticle systems was also investigated. The adsorbed layer of poloxamer 407 was characterised in terms of percentage surface coverage, thickness of the adsorbed layer and average surface area per PEO chain. Computer modelling of the adsorbed layer was performed (applying the self-consistent field technique), to obtain the structural information of the PEO chains in the layer. The in vitro interaction of the nanoparticles with different degrees of poloxamer 407 surface coverage with serum components and the in vivo biodistribution in the rat model were assessed. The results demonstrated that an increase in the surface coverage with poloxamer 407 resulted in an increased volume fraction of the PEO in the adsorbed layer, further extension of the PEO chains from the surface and closer packing of the chains at the surface. With regard to the interaction with the serum components, an increased surface coverage resulted in a reduction of the amount of serum proteins adsorbed, and, importantly, affected the type of proteins adsorbed. High molecular weight proteins were not adsorbed onto the nanoparticles with a surface coverage above approx. 25%. Following the intravenous administration to rats, even the nanoparticles with the lowest degree of surface coverage (approx. 5%) showed improved circulation profiles relative to the uncoated nanoparticles. The effect was more pronounced for the 40 nm nanoparticles. A further increase in the surface coverage to approx. 25% resulted in a significant increase in circulation time, as compared to uncoated and 5% coated systems, for all sizes of nanoparticles. Importantly, it was found that a long in vivo blood circulation time could be achieved for nanoparticles with a relatively low degree of surface coverage with PEO chains.

Adsorption↗

PubMed2001

Drug-polyionic block copolymer interactions for micelle formation: physicochemical characterisation.

While covalent attachment of small drug molecules to AB copolymers for the formation of polymeric micelles for drug delivery has been investigated, few studies have focused on non-covalent interactions. The aim of this study was therefore to explore the potential of non-covalent interactions between an AB copolymer, Poly(aspartic acid)-poly(ethylene glycol) (Pasp-PEG), with anionic pendant groups and diminazene aceturate, a small molecular weight cationic drug. Micelles were prepared by mixing solutions of Pasp-PEG and diminazene in 25 mM Tris-HCl buffer. At all Pasp-PEG concentrations studied, the micelles appeared to be water soluble with a unimodal size distribution and ranged in size from approximately 22 to 60 nm. The polyionic micelles also displayed similar and small absolute zeta potential values at various drug:monomer molar ratios which confirmed stabilisation by the PEG corona. The scattering intensity was maximal and remained unchanged, while particle size increased slightly at pH range from 3.4 to 7.2. At this pH range both the polymer and drug would be ionised and ionic interactions possible to drive micellar formation. An increase in size and scattering intensity with addition of NaCl to the micelles was attributed to dehydration of the PEG corona which may have led to aggregation of the micelles. The absence of micellar dissociation upon addition of salt was attributed to the dominance of hydrogen bonding between Pasp and diminazene aceturate, as assessed by isothermal titration microcalorimetry. Morphological evaluation of these constructs showed them to be discrete and fairly uniform in size and shape. This study was therefore successful in confirming the potential of non-covalent interactions using an AB copolymer to form polyionic micelles for drug delivery.

Drug Delivery Systems↗

PubMed2001

Copolymers of amine methacrylate with poly(ethylene glycol) as vectors for gene therapy.

A series of structurally related copolymers of tertiary amine methacrylate with poly(ethylene glycol) (PEG) were investigated for their potential to serve as vectors for gene therapy. The effects of copolymer structure on the complexation and transfection ability were assessed. The ability of the PEG-based copolymers and DMAEMA homopolymer to bind and condense DNA was confirmed by gel electrophoresis, ethidium bromide displacement and transmission electron microscopy. The presence of PEG in the copolymers had a beneficial effect on their ability to bind to DNA. Colloidally stable complexes were obtained for all the PEG-copolymer systems as shown by uniformly discrete spherical images from transmission electron microscopy and approximate diameters of 80-100 nm by dynamic light scattering studies. DMAEMA homopolymer, however, produced agglomerated particles, confirming the important role played by the PEG chains in producing compact stable DNA complexes. Assessment of the effect of ionic strength of the buffer on the complexation and dissociation of the complexes indicated the importance of both electrostatic and non-electrostatic interactions in the polymer-DNA complexation. In vitro transfection experiments showed that DMAEMA homopolymer gave the highest level of transfection comparable to a control poly-L-lysine (PLL) system. The PEG-based copolymers gave reduced levels of transfection, most likely due to the steric stabilization effect of a PEG corona.

DNA↗

PubMed2001

Polylactide-poly(ethylene glycol) micellar-like particles as potential drug carriers: production, colloidal properties and biological performance.

The micellar-like particle systems produced from poly-D,L-lactide-poly(ethylene glycol) (PLA-PEG) copolymers have been assessed using a range of physicochemical characterisation methods, followed by in vivo studies of their biodistribution after intravenous administration to the rat. The size of the PEG chain was kept constant at 5 or 2 kDa, while the PLA size increased within a series from 2 to 25 kDa. The results obtained reveal, that in an aqueous medium the copolymers assembled into micellar-like structures, with the PLA segments forming the core and the PEG segments the surrounding corona. The size of the PLA segments dominated the process of assembly of the molecules and the characteristics of the resultant micellar-like particles. The PLA-PEG micellar particles were found to be less dynamic than those obtained from conventional surfactants. Particles formed from the lower molecular weight PLA polymers allowed a level of chain mobility while the cores of the micellar particles formed from higher molecular weight PLA appeared to be solid-like in nature. The size of the micellar particles was dependent on the copolymer molecular weight and the z-average diameter increased from 25 to 76 nm as the molecular weight of the PLA moiety increased. This provides an ability to control the particle size by adjusting the molecular weight of the PLA moiety. Following intravenous administration to the rat model, micellar-like particles smaller than approximately 70 nm accumulated in the liver, despite the fact that the PEG corona provided an effective steric stabilization effect. Micellar-like particles with a diameter of more than approximately 70 nm exhibited prolonged systemic circulation and reduced liver uptake, although the steric stabilisation of these particles was shown to be less effective. These findings agree with recent observations from other research groups; that indicate a possibility that very small particulates can pass through the sinusoidal fenestrations in the liver and gain access to the parenchymal cells of the liver.

Animals↗

PubMed2000

Polymer chemical structure is a key determinant of physicochemical and colloidal properties of polymer-DNA complexes for gene delivery.

Polyplexes are now emerging as potentially useful vectors for gene therapy. To improve our understanding of how the chemical structure of the polymer affects the properties of these systems, a series of structurally related polymers, the linear poly(amidoamine)s (PAAs), have been examined for their abilities to form complexes with DNA. Structure-dependent differences in DNA binding are shown by gel electrophoretic retardation of DNA and thermal transition analyses. Two PAAs, NG28 and NG30, stand out as having high affinity DNA binding characteristics, similar to the model homopolypeptide, poly-L-lysine. In addition, differences in complex formation, particle size and surface charge are displayed for the different polymer-DNA systems. Electron microscopy studies showed that the polymers condensed DNA into similar unit structures but only complexes with NG30 did not undergo agglomeration. This was attributed to an excess of complexed polymer forming a shell of uncomplexed polymer chain segments around a condensed DNA-polymer core. The transfection activities of these polymer complexes differ greatly, and some of these differences can be explained in a multifactorial way by the physicochemical and colloidal properties. It is concluded that polymer chemical structure dictates the apparent affinity of DNA binding, and also several of the important colloidal characteristics of the resulting complexes.

Chloroquine↗

PubMed2000

Observation of DNA-polymer condensate formation in real time at a molecular level.

Dynamic real time assembly of toroidal and rod-like DNA condensates has been visualised using atomic force microscopy. Imaging has been conducted in an aqueous environment allowing the visualisation of hydrated, pegylated-polymer DNA condensates undergoing dynamic structural movement and conformational change. A major hurdle in the field of gene delivery is cellular transfection and the subsequent transfer of condensed genetic material to the cell nucleus. An increased understanding of the process of DNA condensation will aid the development and optimisation of gene delivery vectors.

Cations↗

PubMed2000

Defining the drug incorporation properties of PLA-PEG nanoparticles.

The drug incorporation and physicochemical properties of PLA-PEG micellar like nanoparticles were examined in this study using a model water soluble drug, procaine hydrochloride. Procaine hydrochloride was incorporated into nanoparticles made from a series of PLA-PEG copolymers with a fixed PEG block (5 kDa) and a varying PLA segment (3-110 kDa). The diameter of the PLA-nanoparticles increased from 27.7 to 174.6 nm, with an increase in the PLA molecular weight. However, drug incorporation efficiency remained similar throughout the series. Incorporation of drug into the smaller PLA-PEG nanoparticles made from 3:5, 15:5 and 30:5 copolymers did not influence the particle size, while an increase was observed for the larger systems comprising 75:5 and 110:5 copolymers. An increase in drug content for PLA-PEG 30:5 nanoparticles was achieved by increasing the theoretical loading (quantity of initially present drug). The size of these nanoparticles remained unchanged with the increasing drug content, supporting the proposed micellar type structure of the PLA-PEG 30:5 nanoparticles. The morphology of these systems remained unchanged both at low and high theoretical drug loadings. Formulation variables, such as an increase in the aqueous phase pH, replacement with the base form of the drug and inclusion of lauric acid in the formulation did not improve the incorporation efficiency of drug into PLA-PEG 30:5 nanoparticles. While poly(aspartic acid) as a complexation agent did not improve the drug incorporation efficiency of procaine hydrochloride, it did so for another water soluble drug diminazene aceturate. This may be attributed to a stronger interaction of diminazene aceturate with poly(aspartic acid) relative to procaine hydrochloride, as confirmed by thermodynamic analysis of isothermal titration calorimetric data. The drug incorporation and physicochemical characterisation data obtained in this study may be relevant in optimising the drug incorporation and delivery properties of these potential drug targeting carriers.

Anesthetics, Local↗

PubMed2000

Hydrogen bonding and electrostatic interaction contributions to the interaction of a cationic drug with polyaspartic acid.

PURPOSE: To determine the mechanism and identify forces of interaction between polyaspartic acid and diminazene (a model drug). Such knowledge is essential for the design of polymeric drug delivery systems that are based on molecular self-assembly into complexes or micellar type systems. METHODS: Complex formation was studied by isothermal titration microcalorimetry and the McGhee von Hippel model was applied to obtain K(obs), deltaH(obs), and n(obs). The calorimetry data were compared with both an optical density study and the amount of free/complexed drug. RESULTS: The diminazene-polyaspartic acid interaction is enthalpically driven, whereby one diminazene molecule interacts with two monomers of polyaspartic acid. The dependence of K(obs) on salt concentration reveals a contribution of electrostatic interactions. However, applying Manning's counter ion condensation theory shows that the major driving force for the complex formation is hydrogen bonding, with interfacial water molecules remaining buried within the complex. The modelling of the pH dependence of K(obs) and deltaH(obs) demonstrates that the ionization of carboxylic groups of polyaspartic acid is a prerequisite for the interaction. CONCLUSIONS: Complex formation between diminazene and polyaspartic acid is driven by both electrostatic interactions and hydrogen bonding, with the latter being the dominating force. Although electrostatic interactions are not the major driving force, ionization of the drug and polymer is essential for complex formation.

Cations↗

PubMed1999

PLGA nanoparticles prepared by nanoprecipitation: drug loading and release studies of a water soluble drug.

The nanoprecipitation technique for preparation of nanoparticles suffers the drawback of poor incorporation of water soluble drugs. The aim of this study was therefore to assess various formulation parameters to enhance the incorporation of a water soluble drug (procaine hydrochloride) into poly(dl-lactide-co-glycolide) (PLGA) nanoparticles prepared by this technique. Approaches investigated for drug incorporation efficiency enhancement included the influence of aqueous phase pH, replacement of procaine hydrochloride with procaine dihydrate and the inclusion of excipients: poly(dl-lactide) (PLA) oligomers, poly(methyl methacrylate-co-methacrylic acid) (PMMA-MA) or fatty acids into the formulation. The nanoparticles produced were submicron size (<210 nm) and of low polydispersity. It was found that an aqueous phase pH of 9.3, replacement of procaine hydrochloride with procaine dihydrate and the incorporation of PMMA-MA, lauric and caprylic acid into the formulation could enhance drug incorporation efficiency without the size, morphology and nanoparticle recovery being adversely influenced. For instance changing the aqueous phase pH from 5.8 to 9.3 increased nanoparticle recovery from 65.1 to 93.4%, drug content from 0.3 to 1.3% w/w and drug entrapment from 11.0 to 58.2%. However, the presence of high ratios of lauric acid and procaine dihydrate in the formulation adversely affected the morphology and size of the nanoparticles. Also, PLA oligomers were not considered a feasible approach since it decreased drug entrapment from 11.0 to 8.4% and nanoparticle recovery from 65.1 to 19.6%. Drug release from nanoparticles appears to consist of two components with an initial rapid release followed by a slower exponential stage. This study has demonstrated that formulation variables can be exploited in order to enhance the incorporation of a water soluble drug into PLGA nanoparticles by the nanoprecipitation technique.

Buffers↗

PubMed1999

Complex formation between the anionic polymer (PAA) and a cationic drug (procaine HCI): characterization by microcalorimetric studies.

PURPOSE: Due to the importance of drug-polymer interactions in, inter alia, drug loading/release, supramolecular assemblies and DNA delivery for gene therapy, the aim of this study was therefore to establish the mechanism of interaction between a model polymer (Polyacrylic acid, PAA) and a model drug (procaine HCl). METHODS: This was performed by studying the effect of salt (KCl) concentration on their heat released values using Isothermal Titration Microcalorimetry (ITM). The integrated released heat data were computer fitted to a one class binding model and the thermodynamic parameters (Kobs, deltaH, and N) were determined. RESULTS: As the KCl concentration was increased, Kobs decreased thus establishing the salt dependence of the interaction. The linear variation of deltaGobs with deltaSobs indicated that their interaction was entropically driven. The stoichiometry of the interaction was calculated to be one procaine molecule per monomer of PAA. Dissection of the total observed free energy at each KCI concentration indicated that the contribution of the non-electrostatic attractions to the interaction of PAA with procaine HCl was greater than those of the electrostatic attractions. CONCLUSIONS: We have shown that the interaction between PAA and procaine HCl is dependent upon the presence of counterions (monovalent ions) and is mainly entropically driven. The calculated stoichiometry indicated that one procaine HCl molecule neutralised one carboxylic acid group on PAA. Although electrostatic interactions were necessary for initiating complex formation, the non-electrostatic forces were dominant in stabilising the PAA-procaine HCl complex.

Acrylic Resins↗

PubMed1998

In vitro displacement by rat serum of adsorbed radiolabeled poloxamer and poloxamine copolymers from model and biodegradable nanospheres.

Poloxamer 407 and poloxamine 908 have been used by many research groups to modify the surface of both model latex and biodegradable nanospheres, thereby producing nanospheres that have shown reduced protein adsorption in vitro and extended circulation times in vivo. A potential limitation of such systems is the desorption of the copolymer coating layer. We describe a two-stage process to radiolabel poloxamer 407 and poloxamine 908 that has facilitated an investigation into this potential desorption, in vitro. The first stage of the labeling procedure involved the substitution of the terminal hydroxyl groups in each poly(ethylene oxide) (PEO) chain of poloxamer 407 and poloxamine 908 with an amino group. The aminated copolymers were then radiolabeled with 125Iodine Bolton-Hunter reagent. The efficiency of labeling was calculated to be approximately 20% for the tetramine poloxamine 908 and approximately 33% for the diamine poloxamer 407. Remaining free amino groups were then either acetylated, using acetic anhydride, or left in the free amino form. Covalent linkage of the radiolabel to the copolymer was confirmed by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. The stability of the link between radiolabel and copolymer to hydrolysis was also confirmed; <4% loss of radiolabel occurred from poloxamine 908 after incubation in phosphate-buffered saline (PBS) at 37 degrees C for 8 days. The radiolabeled copolymers (with the free amino groups acetylated) were then used in experiments that have given the first direct evidence that adsorbed copolymers can be displaced by serum proteins in significant amounts from the surface of model and biodegradable nanospheres. The displacement was highly dependent on copolymer-nanosphere compatibility, with up to 78% of 125I tetramine poloxamine 908 being displaced from poly(lactide-co-glycolide) (PLGA) nanospheres in 24 h, compared with 20% displacement of 125I tetramine poloxamine 908 in 24 h from polystyrene nanospheres. These results have direct implication for the future design of drug delivery systems based on coated nanospheres.

Animals↗

PubMed1998

Modification of the copolymers poloxamer 407 and poloxamine 908 can affect the physical and biological properties of surface modified nanospheres.

PURPOSE: To investigate the effects of the modification of the copolymers poloxamer 407 and poloxamine 908 on the physical and biological properties surface modified polystyrene nanospheres. METHODS: A method to modify poloxamer 407 and poloxamine 908, introducing a terminal amine group to each PEO chain has been developed. The aminated copolymers can be subsequently radiolabelled with Iodinated (I125) Bolton-Hunter reagent. The aminated copolymers were used to surface modify polystyrene nanospheres. The physical and biological properties of the coated nanospheres were studied using particle size, zeta potential, in vitro non-parenchymal cell uptake and in vivo biodistribution experiments. RESULTS: The presence of protonated amine groups in the modified copolymers significantly affected the physical and biological properties of the resulting nanospheres, although the effects were copolyme specific. The protonated surface amine groups in both copolymers reduced the negative zeta potential of the nanospheres. Acetylation of the copolymer's free amine groups resulted in the production of nanospheres with comparable physical properties to control unmodified copolymer coated nanospheres. In vivo, the protonated amine groups in the copolymers increased the removal of the nanospheres by the liver and spleen, although these effects were more pronounced with the modified poloxamer 407 coated nanospheres. Acetylation of the amine groups improved the blood circulation time of the nanospheres providing modified poloxamine 908 coated nanospheres with comparable biological properties to control poloxamine 908 coated nanospheres. Similarly, modified poloxamer 407 coated nanospheres had only slightly reduced circulation times in comparison to control nanospheres. CONCLUSIONS: The experiments have demonstrated the importance of copolymer structure on the biological properties of surface modified nanospheres. Modified copolymers, which possess comparable properties to their unmodified forms, could be used in nanosphere systems where antibody fragments can be attached to the copolymers, thereby producing nanospheres which target to specific body sites.

Animals↗

PubMed1997

Long circulating biodegradable poly(phosphazene) nanoparticles surface modified with poly(phosphazene)-poly(ethylene oxide) copolymer.

The biodistribution of biodegradable poly(organo phosphazene) nanoparticles surface modified by adsorption of a novel poly(organo phosphazene)-poly(ethylene oxide) copolymer with a 5000 M(W) PEO chain (PF-PEO[5000]), following intravenous administration in rats and rabbits, is described. The data are compared to the biodistribution of poly(organo phosphazene) and poly(lactide-co-glycolide) nanoparticles coated with a tetrafunctional copolymer of poly(ethylene oxide)-poly(propylene oxide) ethylenediamine, commercially available as Poloxamine 908. This copolymer has a PEO chain of the same size as the poly(organo phosphazene)-PEO derivative used. The results in the rat model reveal that poly(organo phosphazene) nanoparticles with a Poloxamine 908 coating were mainly captured by the liver, although a retardation in clearance from the systemic circulation was seen. In contrast, the poly(organo phosphazene) nanoparticles coated with PF-PEO(5000) showed a prolonged blood circulating profile, with only a small amount of the nanoparticles sequestered by the liver. This indicates the importance of the nature of both the anchoring group and the particle surface on the biological performances of the system. Study of the biodistribution of the PF-PEO(5000)-coated poly(organo phosphazene) nanoparticles in the rabbit model also indicated a prolonged systemic circulation lifetime and reduced liver uptake, whereby a significant amount of the administered nanoparticles was targeted to the bone marrow.

Animals↗

PubMed1997

The immune response to a model antigen associated with PLG microparticles prepared using different surfactants.

The effect of different surfactants on the surface characteristics of poly(D,L-lactideco-glycolide) microparticles prepared by the emulsification/solvent evaporation technique was investigated and the immune response to a protein antigen (OVA) associated with these microparticles was measured. Three surfactants--polyvinyl alcohol (PVA, a conventional stabilizer of PLG microparticles), the non-ionic surfactant, poly(oxyethylene glycerol mono-oleate) [Tagat] and Bile salts (a natural emulsifer)--were used to produce OVA-loaded PLG microparticles. Antigen was detected at the surface of all three types of OVA-loaded microparticles, in amounts in excess of 40% of the total protein load. The levels of specific serum IgG antibody elicited to OVA were significantly higher (P < 0.05) after a single subcutaneous administration of antigen associated with the Bile salts and Tagat formulations compared to the PVA formulation. A strong correlation was revealed between the levels of antibody measured and the magnitude of negative surface charge of the particulate carrier. The pattern of the IgG antibody response to OVA was similar in all three cases, indicating that the degradation rate of the PLG polymer determined the duration of the response. The results demonstrate the potential of using different surfactants to produce PLG microparticles with increased adjuvant activity.

Animals↗

PubMed1994

Surface modification of poly(lactide-co-glycolide) nanospheres by biodegradable poly(lactide)-poly(ethylene glycol) copolymers.

The modification of surface properties of biodegradable poly(lactide-co- glycolide) (PLGA) and model polystyrene nanospheres by poly(lactide)-poly(ethylene glycol) (PLA:PEG) copolymers has been assessed using a range of in vitro characterization methods followed by in vivo studies of the nanospheres biodistribution after intravenous injection into rats. Coating polymers with PLA:PEG ratio of 2:5 and 3:4 (PEG chains of 5000 and 2000 Da. respectively) were studied. The results reveal the formation of a PLA:PEG coating layer on the particle surface resulting in an increase in the surface hydrophilicity and decrease in the surface charge of the nanospheres. The effects of addition of electrolyte and changes in pH on stability of the nanosphere dispersions confirm that uncoated particles are electrostatically stabilized, while in the presence of the copolymers, steric repulsions are responsible for the stability. The PLA:PEG coating also prevented albumin adsorption onto the colloid surface. The evidence that this effect was observed for the PLA:PEG 3:4 coated nanospheres may indicate that a poly(ethylene glycol) chain of 2000 Da can provide an effective repulsive barrier to albumin adsorption. The in vivo results reveal that coating of PLGA nanospheres with PLA:PEG copolymers can alter the biodistribution in comparison to uncoated PLGA nanospheres. Coating of the model polystyrene nanospheres with PLA:PEG copolymers resulted in an initial high circulation level, but after 3 hours the organ deposition data showed values similar to uncoated polystyrene spheres. The difference in the biological behaviour of coated PLGA and polystyrene nanospheres may suggest a different stability of the adsorbed layers on these two systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMedDate not supplied

Microencapsulated monosialoganglioside GM1: physical properties and in vivo effects.

The prevention of the decrease of choline acetyltransferase (ChAT) enzymatic activity was achieved by applying GM1 in an animal model for studying retrograde degenerations of cholinergic neurons. Devascularizing lesions of the rat cortex led to a significant decrease in activity of ChAT in the nucleus basalis magnocellularis (NBM), but this decrease was effectively prevented by GM1 administration either centrally or locally in a microencapsulated form. Compared with the relatively large dose of GM1 which has to be given when the drug is administered. i.p. microencapsulated GM1 applied locally and directly over the lesioned cortical surface seems to be effective in much lower doses.

Animals↗