Human serum albumin as a probe for protein adsorption to nanoparticles: relevance to biodistribution

Bioinspired zwitterionic triblock copolymers designed for colloidal drug delivery: 1 - Synthesis and characterization

This study describes the synthesis and characterization of triblock copolymers composed of poly[2-(methacryloyloxy)ethyl phosphorylcholine]-block-poly(propylene glycol)-block-poly[2-(methacryloyloxy)ethyl phosphorylcholine] (PMPC-b-PPG-b-PMPC) intended for, but not limited to, applications in colloidal drug delivery. Atom transfer radical polymerization led to a library of well-defined PMPC-b-PPG-b-PMPC triblock copolymers with varying overall molecular weight (ranging from ∼5 to ∼25 kDa) and composition (weight fraction of the hydrophobic PPG block ranged from ∼10 to ∼50 wt%). The properties of the synthesized triblock copolymers were linked to the PPG to bioinspired PMPC block(s) ratio, where the more hydrophilic species showed adequate aqueous solubility, surface activity and biocompatibility (non-toxicity) in in vitro cell culture. Their amphiphilic nature makes them adsorb efficiently onto polymer nanoparticles, what improves colloidal stability under stress conditions and, furthermore, depletes proteins from unwanted adsorption to the underlying surface. The current findings strengthen our insights into structure-function relationships of PMPC-based coatings leading to protecting shells on relevant polymer nanoparticle formulations. PMPC-b-PPG-b-PMPC triblock copolymers composed of a hydrophobic PPG block of 2-4 kDa flanked by two hydrophilic PMPC blocks each of 5-10 kDa seem to be most promising to enhance colloidal drug delivery vehicles.

The Impact of Multiple Functional Layers in the Structure of Magnetic Nanoparticles and Their Influence on Albumin Interaction

In nanomedicine, hybrid nanomaterials stand out for providing new insights in both the diagnosis and treatment of several diseases. Once administered, engineered nanoparticles (NPs) interact with biological molecules, and the nature of this interaction might directly interfere with the biological fate and action of the NPs. In this work, we synthesized a hybrid magnetic nanostructure, with antibacterial and antitumoral potential applications, composed of a magnetite core covered by silver NPs, and coated with a modified chitosan polymer. As magnetite NPs readily oxidize to maghemite, we investigated the structural properties of the NPs after addition of the two successive layers using Mössbauer spectroscopy. Then, the structural characteristics of the NPs were correlated to their interaction with albumin, the major blood protein, to evidence the consequences of its binding on NP properties and protein retention. Thermodynamic parameters of the NPs–albumin interaction were determined. We observed that the more stable NPs (coated with modified chitosan) present a lower affinity for albumin in comparison to pure magnetite and magnetite/silver hybrid NPs. Surface properties were key players at the NP–biological interface. To the best of our knowledge, this is the first study that demonstrates a correlation between the structural properties of complex hybrid NPs and their interaction with albumin.

Polymeric matrix hydrophobicity governs saponin packing-density on nanoparticle surface and the subsequent biological interactions

This study investigated the loading behavior of Quillaja saponin as a model surface-active cargo on (NP) nanoparticles prepared with various hydrophobic polymers and using different organic solvents through emulsification/solvent evaporation, and the impact of NP surface hydrophobicity upon the cytotoxic and hemolytic properties of the loaded entity. A superficial monolayered arrangement of saponins on NP was established (R² > 0.9) for all NP, as the saponin loading values complied with the Langmuir adsorption isotherm over the entire concentration range. Next, based on the measurement of interfacial tension between formulation phases, and the subsequent use of Gibb's adsorption isotherm, the packing density (Г_exc) and loading of saponins on various nanospheres could be predicted with good correlation with the actual values (R² > 0.95). The results demonstrated that the hydrophobicity of the polymeric matrix was the major determinant of saponin packing density on the nanospheres. Finally, the impact of NP surface properties upon saponin biological interactions was investigated, where a linear correlation was found between the NP surface hydrophobicity and their hemolytic properties (R² ≅ 0.79), and cytotoxicity against two cancer cell lines (R² > 0.76). The surface hydrophobicity of the polymeric NP seemingly governed the NP-cell membrane binding, which in turn determined the amount of membrane-bound saponins per unit NP surface area. As the saponins exert their cytotoxicity mainly through strong permeabilization of the cell membrane, a higher amount of NP-membrane association governed by a more hydrophobic matrix can lead to higher levels of cytotoxicity. These findings highlight the importance of a detailed characterization of NP surface properties, particularly in case of surface-active cargos, for these dictate the side effects and biological interactions of the delivery system.

Isolation methods for particle protein corona complexes from protein-rich matrices

Background: Nanoparticles become rapidly encased by a protein layer when they are in contact with biological fluids. This protein shell is called a corona. The composition of the corona has a strong influence on the surface properties of the nanoparticles. It can affect their cellular interactions, uptake and signaling properties. For this reason, protein coronae are investigated frequently as an important part of particle characterization. Main body of the abstract: The protein corona can be analyzed by different methods, which have their individual advantages and challenges. The separation techniques to isolate corona-bound particles from the surrounding matrices include centrifugation, magnetism and chromatographic methods. Different organic matrices, such as blood, blood serum, plasma or different complex protein mixtures, are used and the approaches vary in parameters such as time, concentration and temperature. Depending on the investigated particle type, the choice of separation method can be crucial for the subsequent results. In addition, it is important to include suitable controls to avoid misinterpretation and false-positive or false-negative results, thus allowing the achievement of a valuable protein corona analysis result. Conclusion: Protein corona studies are an important part of particle characterization in biological matrices. This review gives a comparative overview about separation techniques, experimental parameters and challenges which occur during the investigation of the protein coronae of different particle types.

Peptide-MHC-based nanomedicines for autoimmunity function as T-cell receptor microclustering devices

We have shown that nanoparticles (NPs) can be used as ligand-multimerization platforms to activate specific cellular receptors in vivo. Nanoparticles coated with autoimmune disease-relevant peptide-major histocompatibility complexes (pMHC) blunted autoimmune responses by triggering the differentiation and expansion of antigen-specific regulatory T cells in vivo. Here, we define the engineering principles impacting biological activity, detail a synthesis process yielding safe and stable compounds, and visualize how these nanomedicines interact with cognate T cells. We find that the triggering properties of pMHC-NPs are a function of pMHC intermolecular distance and involve the sustained assembly of large antigen receptor microclusters on murine and human cognate T cells. These compounds show no off-target toxicity in zebrafish embryos, do not cause haematological, biochemical or histological abnormalities, and are rapidly captured by phagocytes or processed by the hepatobiliary system. This work lays the groundwork for the design of ligand-based NP formulations to re-program in vivo cellular responses using nanotechnology.

Poly(D, L-lactide-co-glycolide) nanoparticles as delivery agents for photodynamic therapy: enhancing singlet oxygen release and photototoxicity by surface PEG coating

Poly(D, L-lactide-co-glycolide) (PLGA) nanoparticles (NPs) are being considered as nanodelivery systems for photodynamic therapy. The physico-chemical and biological aspects of their use remain largely unknown. Herein we report the results of a study of PLGA NPs for the delivery of the model hydrophobic photosensitizer ZnTPP to HeLa cells. ZnTPP was encapsulated in PLGA with high efficiency and the NPs showed negative zeta potentials and diameters close to 110 nm. Poly(ethylene glycol) (PEG) coating, introduced to prevent opsonization and clearance by macrophages, decreased the size and zeta potential of the NPs by roughly a factor of two and improved their stability in the presence of serum proteins. Photophysical studies revealed two and three populations of ZnTPP and singlet oxygen in uncoated and PEGylated NPs, respectively. Singlet oxygen is confined within the NPs in bare PLGA while it is more easily released into the external medium after PEG coating, which contributes to a higher photocytotoxicity towards HeLa cells in vitro. PLGA NPs are internalized by endocytosis, deliver their cargo to lysosomes and induce cell death by apoptosis upon exposure to light. In conclusion, PLGA NPs coated with PEG show high potential as delivery systems for photodynamic applications.

Surface characterization and protein interaction of a series of model poly[acrylonitrile-co-(N-vinyl pyrrolidone)] nanocarriers for drug targeting

The surface properties of intravenously injected nanoparticles determine the acquired blood protein adsorption pattern and subsequently the organ distribution and cellular recognition. A series of poly[acrylonitrile-co-(N-vinyl pyrrolidone)] (PANcoNVP) model nanoparticles (133-181 nm) was synthesized, in which the surface properties were altered by changing the molar content of NVP (0-33.8 mol%) as the more hydrophilic repeating unit. The extent of achieved surface property variation was comprehensively characterized. The residual sodium dodecyl sulfate (SDS) content from the synthesis was in the range 0.3-1.6 μgml(-1), potentially contributing to the surface properties. Surface hydrophobicity was determined by Rose Bengal dye adsorption, hydrophobic interaction chromatography (HIC) and aqueous two-phase partitioning (TPP). Particle charge was quantified by zeta potential (ZP) measurements including ZP-pH profiles. The interaction with proteins was analyzed by ZP measurements in serum and by adsorption studies with single proteins. Compared to hydrophobic polystyrene model nanoparticles, all PANcoNVP particles were very hydrophilic. Differences in surface hydrophobicity could be detected, which did not linearly correlate with the systematically altered bulk composition of the PANcoNVP nanoparticles. This proves the high importance of a thorough surface characterization applying a full spectrum of methods, complementing predictions solely based on bulk polymer composition.

Protein Adsorption Patterns and Analysis on IV Nanoemulsions-The Key Factor Determining the Organ Distribution

Intravenous nanoemulsions have been on the market for parenteral nutrition since the 1950s; meanwhile, they have also been used successfully for IV drug delivery. To be well tolerable, the emulsions should avoid uptake by the MPS cells of the body; for drug delivery, they should be target-specific. The organ distribution is determined by the proteins adsorbing them after injection from the blood (protein adsorption pattern), typically analyzed by two-dimensional polyacrylamide gel electrophoresis, 2-D PAGE. The article reviews the 2-D PAGE method, the analytical problems to be faced and the knowledge available on how the composition of emulsions affects the protein adsorption patterns, e.g., the composition of the oil phase, stabilizer layer and drug incorporation into the interface or oil core. Data were re-evaluated and compared, and the implications for the in vivo distribution are discussed. Major results are that the interfacial composition of the stabilizer layer is the main determining factor and that this composition can be modulated by simple processes. Drug incorporation affects the pattern depending on the localization of the drug (oil core versus interface). The data situation regarding in vivo effects is very limited; mainly, it has to be referred to in the in vivo data of polymeric nanoparticles. As a conclusion, determination of the protein adsorption patterns can accelerate IV nanoemulsion formulation development regarding optimized organ distribution and related pharmacokinetics.

Multifunctional anticancer nanomedicine based on a magnetically responsive cyanoacrylate polymer

The therapeutic effect of antitumor molecules (efficacy and safety) is severely limited by their poor pharmacokinetic characteristics. Recently, the use of colloids has been proposed for the delivery of anticancer drugs to tumor cells, thereby providing a significant advance toward new treatments with improved specificity. In this respect, magnetically responsive nanopolymers are probably one of the most promising materials. In this contribution, we describe the basic steps to be followed in the development of such composite nanoplatforms. Starting from the formulation procedure, we detail the physicochemical engineering of these nanomedicines for combined antitumor activities (anticancer drug delivery plus hyperthermia effect). The key features determining drug incorporation to the nanomaterial are analyzed. Such stimuli-sensitive nanoparticles have promising properties (e.g., blood compatibility, hyperthermia, magnetic targeting capabilities, high drug loading, and little burst drug release), which could be used for efficient multifunctional anticancer therapy.

Nanoemulsion-templated multilayer nanocapsules for cyanine-type photosensitizer delivery to human breast carcinoma cells

There is great clinical interest in developing novel nanocarriers for hydrophobic cyanine dyes used as photosensitizing agents in photodynamic therapy (PDT). In the present study we have employed nanoemulsion-templated oil-core multilayer nanocapsules as robust nanocarriers for a cyanine-type photosensitizer IR-786. These nanoproducts were fabricated via layer-by-layer (LbL) adsorption of oppositely charged polyelectrolytes (PEs), i.e., anionic PSS and cationic PDADMAC on nanoemulsion liquid cores created by dicephalic or bulky saccharide-derived cationic surfactants. All nanocapsules, with different thicknesses of the PE shell and average size <200 nm (measured by DLS) demonstrated good capacity for IR-786 encapsulation. The nanocarriers were visualized by SEM and AFM and their photo-induced anticancer effect and cellular internalization in human breast carcinoma MCF-7/WT cells were determined. Biological response of the cell culture, expressed as dark and photocytotoxicity as well as fluorescence of drug molecules loaded in the multilayer vehicles, analyzed by the FACS and CLSM techniques, have indicated that the delivered IR-786 did not aggregate inside the cells and could, therefore, act as an effective third-generation photosensitizing agent. In vitro biological experiments demonstrated that the properties of studied nanostructures depended upon the PE type and the envelope thickness as well as on the surfactant architecture in the nanoemulsion-based templates employed for the nanocapsule fabrication. Similarity of results obtained for stored (three weeks in the dark at room temperature) and freshly-prepared nanocapsules, attests to viability of this stable, promising drug delivery system for poorly water-soluble cyanines useful in PDT.

Magnetic nanoparticles: preparation, physical properties, and applications in biomedicine

Finally, we have addressed some relevant findings on the importance of having well-defined synthetic strategies developed for the generation of MNPs, with a focus on particle formation mechanism and recent modifications made on the preparation of monodisperse samples of relatively large quantities not only with similar physical features, but also with similar crystallochemical characteristics. Then, different methodologies for the functionalization of the prepared MNPs together with the characterization techniques are explained. Theorical views on the magnetism of nanoparticles are considered.

Preparation and in vitro evaluation of doxorubicin-loaded Fe₃O₄ magnetic nanoparticles modified with biocompatible copolymers

BACKGROUND

Superparamagnetic iron oxide nanoparticles are attractive materials that have been widely used in medicine for drug delivery, diagnostic imaging, and therapeutic applications. In our study, superparamagnetic iron oxide nanoparticles and the anticancer drug, doxorubicin hydrochloride, were encapsulated into poly (D, L-lactic-co-glycolic acid) poly (ethylene glycol) (PLGA-PEG) nanoparticles for local treatment. The magnetic properties conferred by superparamagnetic iron oxide nanoparticles could help to maintain the nanoparticles in the joint with an external magnet.

METHODS

A series of PLGA:PEG triblock copolymers were synthesized by ring-opening polymerization of D, L-lactide and glycolide with different molecular weights of polyethylene glycol (PEG(2000), PEG(3000), and PEG(4000)) as an initiator. The bulk properties of these copolymers were characterized using (1)H nuclear magnetic resonance spectroscopy, gel permeation chromatography, Fourier transform infrared spectroscopy, and differential scanning calorimetry. In addition, the resulting particles were characterized by x-ray powder diffraction, scanning electron microscopy, and vibrating sample magnetometry.

RESULTS

The doxorubicin encapsulation amount was reduced for PLGA:PEG(2000) and PLGA:PEG(3000) triblock copolymers, but increased to a great extent for PLGA:PEG(4000) triblock copolymer. This is due to the increased water uptake capacity of the blended triblock copolymer, which encapsulated more doxorubicin molecules into a swollen copolymer matrix. The drug encapsulation efficiency achieved for Fe(3)O(4) magnetic nanoparticles modified with PLGA:PEG(2000), PLGA:PEG(3000), and PLGA:PEG(4000) copolymers was 69.5%, 73%, and 78%, respectively, and the release kinetics were controlled. The in vitro cytotoxicity test showed that the Fe(3)O(4)-PLGA:PEG(4000) magnetic nanoparticles had no cytotoxicity and were biocompatible.

CONCLUSION

There is potential for use of these nanoparticles for biomedical application. Future work includes in vivo investigation of the targeting capability and effectiveness of these nanoparticles in the treatment of lung cancer.

Superparamagnetic iron oxide nanoparticles (SPIONs): development, surface modification and applications in chemotherapy

At present, nanoparticles are used for various biomedical applications where they facilitate laboratory diagnostics and therapeutics. More specifically for drug delivery purposes, the use of nanoparticles is attracting increasing attention due to their unique capabilities and their negligible side effects not only in cancer therapy but also in the treatment of other ailments. Among all types of nanoparticles, biocompatible superparamagnetic iron oxide nanoparticles (SPIONs) with proper surface architecture and conjugated targeting ligands/proteins have attracted a great deal of attention for drug delivery applications. This review covers recent advances in the development of SPIONs together with their possibilities and limitations from fabrication to application in drug delivery. In addition, the state-of-the-art synthetic routes and surface modification of desired SPIONs for drug delivery purposes are described.

Enhanced passive pulmonary targeting and retention of PEGylated rigid microparticles in rats

The current study examines the passive pulmonary targeting efficacy and retention of 6μm polystyrene (PS) microparticles (MPs) covalently modified with different surface groups [amine (A-), carboxyl (C-) and sulfate (S-)] or single (PEG(1)-) and double (PEG(2)-) layers of α,ω-diamino poly(ethylene glycol) attached to C-MPs. The ζ-potential of A-MPs (-44.0mV), C-MPs (-54.3mV) and S-MPs (-49.6mV) in deionized water were similar; however PEGylation increased the ζ-potential for both PEG(1)-MPs (-18.3mV) and PEG(2)-MPs (11.5mV). The biodistribution and retention of intravenously administered MPs to male Sprague-Dawley rats was determined in homogenized tissue by fluorescence spectrophotometry. PEG(1)-MPs and PEG(2)-MPs demonstrated enhanced pulmonary retention in rats at 48h after injection when compared to unmodified A-MPs (59.6%, 35.9% and 17.0% of the administered dose, respectively). While unmodified MPs did not significantly differ in lung retention, PEGylation of MPs unexpectedly improved passive lung targeting and retention by modifying surface properties including charge and hydrophobicity but not size.

Potentiation of liposome-induced complement activation by surface-bound albumin

Large anionic multilamellar liposomes containing 71% membrane cholesterol (MLV) caused complement (C) activation in human serum in vitro, as reflected in significant rises in S protein-bound terminal complex (SC5b-9) and C3a-desarg levels. Increasing the albumin content in serum by 1-4 g/100 ml led to 50-100% further increase in MLV-induced C activation, while higher amounts of exogenous human serum albumin (HSA) gradually lost the capability to potentiate liposomal C activation. HSA alone had no influence on SC5b-9 formation at any level below 12%. Complement activation by liposomes and the potentiating effect of supplemental HSA were greatly reduced or eliminated in the absence of C1q or in the presence of 10 mM EGTA/2.5 mM Mg(2+), pointing to the involvement of the classical pathway. Potentiation of C activation by supplemental HSA was not unique to MLV-induced activation, as deposition of HSA on the membrane of "Centricon" ultrafiltration units also potentiated the C-activating effect of the polycarbonate membrane. Fatty acid (FA) or non-monomeric protein contamination in HSA were unlikely to be playing a role in the described effects, as 96% pure, FA-rich (Buminate) and 99% pure, FA-free HSA had identical effects on liposomal C activation. While highlighting a new modulatory mechanism on liposomal C activation, the above data raise the possibility that deposition of extravasated HSA at sites of tissue injury may serve a hitherto unrecognized proinflammatory function.

PEGylated PLGA nanoparticles as protein carriers: synthesis, preparation and biodistribution in rats

The aim of the present work was to assess the merits of PEGylated poly(lactic-co-glycolic acid) (PEG-PLGA) nanoparticles as protein and peptide drugs (PPD) carriers. PEG-PLGA copolymer, which could be used to prepare the stealth nanoparticles or long-circulating nanoparticles, was synthesized with methoxypolyethyleneglycol (MePEG) and PLGA. The structure of PEG-PLGA was confirmed with (1)H NMR and Fourier transform infrared (FTIR) spectrum, and molecular weight was determined by gel permeation chromatography (GPC). Bovine serum albumin (BSA), chosen as model protein, was encapsulated within the stealth nanoparticles with the double emulsion method. The particles were characterized in terms of size, zeta potential and in vitro release of the protein. The biological fate of the BSA-loaded nanoparticles following intravenous administration was determined over 24 h in rats. The experimental results showed that PEG-PLGA could be obtained by ring-opening polymerization of lactide and glycolide in the presence of MePEG. (1)H NMR and FTIR spectrum were consistent with the structure of PEG-PLGA copolymer. Molecular weight determined by GPC was 50800. The stealth nanoparticles loading BSA could be prepared by the double emulsion technique. The entrapment efficiency was 48.6%, particle size about 200 nm and zeta potential -16.1 mV. BSA release from the stealth nanoparticles showed an initial burst release and then sustained release. PEG-PLGA nanoparticles could extend half-life of BSA from 13.6 min of loaded in PLGA nanoparticles to 4.5 h and obviously change the protein biodistribution in rats compared with that of PLGA nanoparticles. Thus, PEG-PLGA nanoparticles could be an effective carrier for PPD delivery.

Microparticulate uptake mechanisms of in-vitro cell culture models of the respiratory epithelium

The objective of this study was to examine the uptake mechanisms of fluorescent polystyrene microspheres of various diameters and surface chemistry by two human cell lines derived from the respiratory epithelium, A549 and Calu-3. Briefly, A549 and Calu-3 cells were grown to confluence in 12-well cluster plates and the uptake of fluorescent microspheres by the cells was determined at various time points. The amount of microspheres internalized by the cells was determined by correcting for non-specific binding to the cell surface. The data showed that A549 cells appeared to have more phagocytic activity than Calu-3 cells. Albumin-coated microspheres as large as 3 microm diameter can be internalized by A549 cells. The amount of internalization by A549 cells observed for 0.5-microm diameter albumin-coated microspheres was approximately 10-times greater than that observed for 1-microm diameter spheres and approximately 100-times greater than values observed for 2- and 3-microm diameter beads. Transmission electron micrographs confirmed that the microspheres were internalized by the cells. Uptake experiments conducted with Calu-3 cells indicated that albumin-coated microspheres were neither bound nor internalized by the cells. The effect of microsphere surface chemistry on the uptake mechanism indicated that amidine microspheres were internalized more rapidly and to a greater extent by both A549 and Calu-3 cells than carboxylate microspheres and non-coated microspheres. This phenomenon is thought to be attributed to masking of the negative polystyrene core by the positive amidine functional group; this effect was less marked for the carboxylate microspheres. These results suggest that A549 and Calu-3 cells can internalize microspheres and that size and effective charge played an important role in the uptake process.

Influences of process parameters on nanoparticle preparation performed by a double emulsion pressure homogenization technique

The preparation of nanoparticles (NP) as an improved colloidal carrier system for proteins was investigated. Bovine serum albumin (BSA) was used as model drug. Owing to the high solubility of the protein in water, the double emulsion technique has been chosen as one of the most appropriate method. In order to both reaching submicron size as well as increasing the grade of monodispersity compared to previous preparation techniques, a microfluidizer as homogenization device was used. All experiments were performed using two biodegradable polymers, poly[D,L-lactic-co-glycolic acid] 50/50 (PLGA) and poly[epsilon-caprolactone] (PCL). The homogenization procedure has been optimized with regard to particle size and monodispersity by studying the influence of the homogenization time as well as the amount of polymer and surfactant in the external aqueous phase. The drug loading has been improved by varying the concentration of the protein in the inner aqueous phase. By increasing the protein concentration in the inner aqueous phase the polydispersity was slightly higher, while the particle size was not influenced significantly. The BSA encapsulation efficiency decreased with higher protein concentration in the inner aqueous phase. All release profiles were characterized by a initial burst effect, a higher release rate was obtained after 4 weeks for PLGA NP (60%) compared with PCL NP (47%).

Biodegradable monodispersed nanoparticles prepared by pressure homogenization-emulsification

The aim of the present work was to investigate the preparation of nanoparticles (NP) as potential drug carriers for proteins. The hydrophilic protein bovine serum albumin (BSA) was chosen as the model drug to be incorporated within NP. Owing to the high solubility of the protein in water, the double emulsion technique has been chosen as one of the most appropriate method. In order to reach submicron size we used a microfluidizer as a homogenization device with a view to obtaining NP with a very high grade of monodispersity. Two different biodegradable polymers, poly[D, L-lactic-co-glycolic acid] 50/50 (PLGA) and poly[epsilon-caprolactone] (PCL) has been used for the preparation of the NP. The drug loading has been optimized by varying the concentration of the protein in the inner aqueous phase, the polymer in the organic phase, the surfactant in the external aqueous phase, as well as the volume of the external aqueous phase. The BSA encapsulation efficiency was high (>80%) and release profiles were characterized by a substantial initial burst release for both PLGA and PCL NP. A higher release was obtained at the end of the dissolution study for PLGA NP (92%) compared with PCL NP (72%).

Activation of the mononuclear phagocyte system by poloxamine 908: its implications for targeted drug delivery

PURPOSE

To investigate the effect of poloxamine 908 on the MPS activity and the importance of its mode of presentation to the immune system.

METHODS

Solutions of endotoxin free poloxamine 908 were injected daily intravenously to rats, and the effect on the degree of sequestration by the liver of I125 labelled, poloxamine 908-coated 60 nm polystyrene particles was investigated by studying effect of dosing regimen(s) and assessment of opsonic activity.

RESULTS

After 3 or 4 days repeated dosing with poloxamine 908 (0.7 mg) in solution, the poloxamine 908-coated polystyrene particles (60 nm) were rapidly cleared from the circulation. The increase sequestration of the particles by the liver lasted for more than 7 days after last dosing with the poloxamine 908 solution. In subsequent studies, it was found that a single dose of poloxamine 908 (0.7 mg) in solution was sufficient to activate the MPS 4 days after the injection. The increased uptake was found not be mediated by a serum component, nor was it due to proliferation of the Kupffer cells in the liver.

CONCLUSIONS

The results provide evidence that a solution of endotoxin-free poloxamine 908 activates the MPS so that 4 days after injection otherwise long-term circulating poloxamine 908-coated particles are sequestered by the liver. This finding has implications for use of such coated systems in therapeutic situations.