Serum-mediated recognition of liposomes by phagocytic cells of the reticuloendothelial system - The concept of tissue specificity

Factors controlling nanoparticle pharmacokinetics: an integrated analysis and perspective

Intravenously injected nanoparticulate drug carriers provide a wide range of unique opportunities for site-specific targeting of therapeutic agents to many areas within the vasculature and beyond. Pharmacokinetics and biodistribution of these carriers are controlled by a complex array of interrelated core and interfacial physicochemical and biological factors. Pertinent to realizing therapeutic goals, definitive maps that establish the interdependency of nanoparticle size, shape, and surface characteristics in relation to interfacial forces, biodistribution, controlled drug release, excretion, and adverse effects must be outlined. These concepts are critically evaluated and an integrated perspective is provided on the basis of the recent application of nanoscience approaches to nanocarrier design and engineering. The future of this exciting field is bright; some regulatory-approved products are already on the market and many are in late-phase clinical trials. With concomitant advances in extensive computational knowledge of the genomics and epigenomics of interindividual variations in drug responses, the boundaries toward development of personalized nanomedicines can be pushed further.

Stability of Self-Assembled Polymeric Micelles in Serum

The stability of polymeric nanoparticles in serum is critical to their use in drug delivery where dilution after intravenous injection often results in nanoparticle disassembly and drug unloading; however, few investigate this in biologically relevant media. To gain greater insight into nanoparticle stability in blood, the stability of self-assembled polymeric micelles of poly(d,l-lactide-co-2-methyl-2-carboxytrimethylene carbonate)-g-poly(ethylene glycol), P(LA-co-TMCC)-g-PEG, were tested in both serum and individual serum protein solutions. By encapsulating Förster resonance energy transfer pairs and following their release by fluorescence, these micelles demonstrated excellent thermodynamic and kinetic stability in the presence of serum. Further analyses by fast protein liquid chromatography and dynamic light scattering confirmed these data. Moreover, these micelles are compatible with red blood cells, as shown by a hemolysis assay. The stability and compatibility demonstrated in blood suggest that these micelles may be stable in vivo, which is critical for intravenous drug delivery applications. This comprehensive approach to understanding micelle stability and compatibility is broadly applicable.

An in vitro assay based on surface plasmon resonance to predict the in vivo circulation kinetics of liposomes

The adsorption of blood proteins onto liposomes and other colloidal particles is an important process influencing the circulation time. Proteins adsorbed to the surface of liposomes can mediate recognition of the liposomes by macrophages of the reticuloendothelial system (RES) facilitating their clearance from the circulation. Coating liposomes with poly(ethylene glycol) (PEG) decreases the blood clearance considerably, most likely due to reduced protein adsorption and/or liposome aggregation. By using the relation between clearance and protein binding, the present study introduces an in vitro assay measuring interactions of liposomes with proteins to predict their blood clearance in vivo. Such assay is valuable since it limits time and costs, and importantly reduces the number of animals required for pharmacokinetic investigations of new formulations. In the current study, Surface Plasmon Resonance (SPR) and fluorescence Single Particle Tracking (fSPT) were used to study liposome-protein interactions and blood induced liposome aggregation in vitro. By means of SPR the interactions between proteins and liposomes coated with PEG of different molecular weights and at different densities (PEG(2000) in 2.5%, 5% and 7%; PEG(5000) in 0.5%, 1.5% and 2.5%), were measured for several plasma proteins: human serum albumin (HSA), apolipoprotein E (ApoE), α2-macroglobulin (α2-M), β2-glycoprotein (β2-G) and fibronectin (Fn). Liposomes coated with PEG interacted less with all proteins, an effect which increased with the PEG surface density. In parallel, fSPT analysis showed that the exposure of liposomes to full blood did not change the liposome size, indicating that aggregation is not a strong attributive factor in the clearance of these liposomes. In addition, the SPR measurements of the interactions between liposomes and proteins were correlated with the blood clearance of the liposomes. For each protein, the degree of protein-liposome interaction as determined by SPR showed a moderate to strong positive correlation with the clearance of the liposome type.

Opsonization, biodistribution, cellular uptake and apoptosis study of PEGylated PBCA nanoparticle as potential drug delivery carrier

PURPOSE

For nanocarrier-based targeted delivery systems, preventing phagocytosis for prolong circulation half life is a crucial task. PEGylated poly(n-butylcyano acrylate) (PBCA) NP has proven a promising approach for drug delivery, but an easy and reliable method of PEGylation of PBCA has faced a major bottleneck.

METHODS

PEGylated PBCA NPs containing docetaxel (DTX) by modified anionic polymerization reaction in aqueous acidic media containing amine functional PEG were made as an single step PEGylation method. In vitro colloidal stability studies using salt aggregation method and antiopsonization property of prepared NPs using mouse macrophage cell line RAW264 were performed. In vitro performance of anticancer activity of prepared formulations was checked on MCF7 cell line. NPs were radiolabeled with 99mTc and intravenously administered to study blood clearance and biodistribution in mice model.

RESULTS

These formulations very effectively prevented phagocytosis and found excellent carrier for drug delivery purpose. In vivo studies display long circulation half life of PBCA-PEG20 NP in comparison to other formulations tested.

CONCLUSIONS

The PEGylated PBCA formulation can work as a novel tool for drug delivery which can prevent RES uptake and prolong circulation half life.

Liposome-encapsulated neuropeptides for site-specific microinjection

This paper describes an experimental approach based on nanotechnology for assessing the chronic actions of short-lived neuropeptides at specific sites of the brain. This methodology combines the advantages of two different techniques: the microinjection of a suspension of peptide-containing liposomes into a specific site of the brain, and the use of liposomes as a local and sustained release nanosystem of the peptide.

Phase I and pharmacokinetic studies of CYT-6091, a novel PEGylated colloidal gold-rhTNF nanomedicine

PURPOSE

A novel nanomedicine, CYT-6091, constructed by simultaneously binding recombinant human tumor necrosis factor alpha (rhTNF) and thiolyated polyethylene glycol to the surface of 27-nm colloidal gold particles, was tested in a phase I dose escalation clinical trial in advanced stage cancer patients.

EXPERIMENTAL DESIGN

CYT-6091, whose dosing was based on the amount of rhTNF in the nanomedicine, was injected intravenously, and 1 cycle of treatment consisted of 2 treatments administered 14 days apart.

RESULTS

Doses from 50 μg/m(2) to 600 μg/m(2) were well tolerated, and no maximum tolerated dose (MTD) was reached, as the highest dose exceeded the target dosage of 1-mg rhTNF per treatment, exceeding the previous MTD for native rhTNF by 3-fold. The first 2 patients on the study, each receiving 50 μg/m(2), did not receive any prophylactic antipyretics or H2 blockade. A predicted, yet controllable fever occurred in these patients, so all subsequently treated patients received prophylactic antipyretics and H2 blockers. However, even at the highest dose rhTNF's dose-limiting toxic effect of hypotension was not seen. Using electron microscopy to visualize nanoparticles of gold in patient biopsies of tumor and healthy tissue showed that patient biopsies taken 24 hours after treatment had nanoparticles of gold in tumor tissue.

CONCLUSIONS

These data indicate that rhTNF formulated as CYT-6091 may be administered systemically at doses of rhTNF that were previously shown to be toxic and that CYT-6091 may target to tumors. Future clinical studies will focus on combining CYT-6091 with approved chemotherapies for the systemic treatment of nonresectable cancers.

Nanomedicine Faces Barriers

Targeted nanoparticles have the potential to improve drug delivery efficiencies by more than two orders of magnitude, from the ~ 0.1% which is common today. Most pharmacologically agents on the market today are small drug molecules, which diffuse across the body’s blood-tissue barriers and distribute not only into the lesion, but into almost all organs. Drug actions in the non-lesion organs are an inescapable part of the drug delivery principle, causing “side-effects” which limit the maximally tolerable doses and result in inadequate therapy of many lesions. Nanoparticles only cross barriers by design, so side-effects are not built into their mode of operation. Delivery rates of almost 90% have been reported. This review examines the significance of these statements and checks how far they need qualification. What type of targeting is required? Is a single targeting sufficient? What new types of clinical challenge, such as immunogenicity, might attend the use of targeted nanoparticles?

Strategies in the design of nanoparticles for therapeutic applications

Engineered nanoparticles have the potential to revolutionize the diagnosis and treatment of many diseases; for example, by allowing the targeted delivery of a drug to particular subsets of cells. However, so far, such nanoparticles have not proved capable of surmounting all of the biological barriers required to achieve this goal. Nevertheless, advances in nanoparticle engineering, as well as advances in understanding the importance of nanoparticle characteristics such as size, shape and surface properties for biological interactions, are creating new opportunities for the development of nanoparticles for therapeutic applications. This Review focuses on recent progress important for the rational design of such nanoparticles and discusses the challenges to realizing the potential of nanoparticles.

Liposomal simvastatin attenuates neointimal hyperplasia in rats

Monocytes, macrophages, and inflammation play a key role in the process of neointimal proliferation and restenosis. The present study evaluated whether systemic and transient depletion of monocytes could be obtained by a single intravenous (IV) injection of simvastatin liposomes, for the inhibition of neointima formation. Balloon-injured carotid artery rats (n = 30) were randomly assigned to treatment groups of free simvastatin, simvastatin in liposomes (3 mg/kg), and saline (control). Stenosis and neointima to media ratio (N/M) were determined 14 days following single IV injection at the time of injury by morphometric analysis. Depletion of circulating monocytes was determined by flow cytometry analyzes of blood specimens. Inhibition of RAW264.7, J774, and THP-1 proliferation by simvastatin-loaded liposomes and free simvastatin was determined by the 3-(4, 5-dimethylthiazolyl-2)-2, 5- diphenyltetrazolium bromide assay. Simvastatin liposomes were successfully formulated and were found to be 1.5-2 times more potent than the free drug in suppressing the proliferation of monocytes/macrophages in cell cultures of RAW 264.7, J774, and THP-1. IV injection of liposomal simvastatin to carotid-injured rats (3 mg/kg, n = 4) resulted in a transient depletion of circulating monocytes, significantly more prolonged than that observed following treatment with free simvastatin. Administration to balloon-injured rats suppressed neointimal growth. N/M at 14 days was 1.56 +/- 0.16 and 0.90 +/- 0.12, control and simvastatin liposomes, respectively. One single systemic administration of liposomal simvastatin at the time of injury significantly suppresses neointimal formation in the rat model of restenosis, mediated via a partial and transient depletion of circulating monocytes.

Modified hydrolysis kinetics of the active lactone moiety of 10-hydroxycamptothecin by liposomal encapsulation

The key structural requirement for the antitumor activity of 10-hydroxycamptothecin (HCPT) is the intact lactone moiety which is always instability and suffered from pH-dependent hydrolysis. The aim of this study was to evaluate the protection effects of liposomal encapsulation on the labile lactone ring. Mono-modal dispersed quasi-spherical liposomes with mean diameter of 145 nm and high drug entrapment efficiency of 90% were obtained under optimal conditions. The in vitro hydrolysis kinetics behaviors of lactone were studied in varied pH buffers. Compared to that of free HCPT in solution formulation, both the hydrolysis half-life and observed equilibrium constant of liposomal HCPT were increased significantly along with the decreased apparent hydrolysis rate constant. The plasma pharmacokinetics was studied by assessing the lactone stability versus time profiles in vivo following intravenous administration of free and liposomal HCPT. The liposomal encapsulation led to a twofold increase in the AUC values and significant decrease in the plasma clearance of lactone (P < 0.05). There was a good correlation between in vitro and in vivo stability of HCPT-lactone. These results suggested a potential application of the novel liposome formulation for the stable delivery system of HCPT.

In vitro macrophage uptake and in vivo biodistribution of PLA-PEG nanoparticles loaded with hemoglobin as blood substitutes: effect of PEG content

The aim of the present work is to investigate the effect of PEG content in copolymer on physicochemical properties, in vitro macrophage uptake, in vivo pharmacokinetics and biodistribution of poly(lactic acid) (PLA)-poly(ethylene glycol) (PEG) hemoglobin (Hb)-loaded nanoparticles (HbP) used as blood substitutes. The HbP were prepared from PLA and PLA-PEG copolymer of varying PEG contents (5, 10, and 20 wt%) by a modified w/o/w method and characterized with regard to their morphology, size, surface charge, drug loading, surface hydrophilicity, and PEG coating efficiency. The in vitro macrophage uptake, in vivo pharmacokinetics, and biodistribution following intravenous administration in mice of HbP labeled with 6-coumarin, were evaluated. The HbP prepared were all in the range of 100-200 nm with highest encapsulation efficiency 87.89%, surface charge -10 to -33 mV, static contact angle from 54.25 degrees to 68.27 degrees , and PEG coating efficiency higher than 80%. Compared with PLA HbP, PEGylation could notably avoid the macrophage uptake of HbP, in particular when the PEG content was 10 wt%, a minimum uptake (6.76%) was achieved after 1 h cultivation. In vivo, besides plasma, the major cumulative organ was the liver. All PLA-PEG HbP exhibited dramatically prolonged blood circulation and reduced liver accumulation, compared with the corresponding PLA HbP. The PEG content in copolymer affected significantly the survival time in blood. Optimum PEG coating (10 wt%) appeared to exist leading to the most prolonged blood circulation of PLA-PEG HbP, with a half-life of 34.3 h, much longer than that obtained by others (24.2 h). These results demonstrated that PEG 10 wt% modified PLA HbP with suitable size, surface charge, and surface hydrophilicity, has a promising potential as long-circulating oxygen carriers with desirable biocompatibility and biofunctionality.

Polyethylene glycol-complexed cationic liposome for enhanced cellular uptake and anticancer activity

Liposomes as one of the efficient drug carriers have some shortcomings such as their relatively short blood circulation time, fast clearance from human body by reticuloendothelial system (RES) and limited intracellular uptake to target cells. In this study, polyethylene glycol (PEG)-complexed cationic liposomes (PCL) were prepared by ionic complex of cationically charged liposomes with carboxylated polyethylene glycol (mPEG-COOH). The cationic liposomes had approximately 98.6+/-1.0 nm of mean particle diameter and 45.5+/-1.1 mV of zeta potential value. While, the PCL had 110.1+/-1.2 nm of mean particle diameter and 18.4+/-0.8 mV of zeta potential value as a result of the ionic complex of mPEG-COOH with cationic liposomes. Loading efficiency of model drug, doxorubicin, into cationic liposomes or PCL was about 96.0+/-0.7%. Results of intracellular uptake evaluated by flow cytometry and fluorescence microscopy studies showed higher intracellular uptake of PCL than that of Doxil. In addition, in vitro cytotoxicity of PCL was comparable to cationic liposomes. In pharmacokinetic study in rats, PCL showed slightly lower plasma level of DOX than that of Doxil. In vivo antitumor activity of DOX-loaded PCL was comparable to that of Doxil against human SKOV-3 ovarian adenocarcinoma xenograft rat model. Consequently, the PCL, of which surface was complexed with PEG by ionic complex may be applicable as drug delivery carriers for increasing therapeutic efficacy of anticancer drugs.

In vitro assessments of nanomaterial toxicity

Nanotechnology has grown from a scientific interest to a major industry with both commodity and specialty nanomaterial exposure to global populations and ecosystems. Sub-micron materials are currently used in a wide variety of consumer products and in clinical trials as drug delivery carriers and imaging agents. Due to the expected growth in this field and the increasing public exposure to nanomaterials, both from intentional administration and inadvertent contact, improved characterization and reliable toxicity screening tools are required for new and existing nanomaterials. This review discusses current methodologies used to assess nanomaterial physicochemical properties and their in vitro effects. Current methods lack the desired sensitivity, reliability, correlation and sophistication to provide more than limited, often equivocal, pieces of the overall nanomaterial performance parameter space, particularly in realistic physiological or environmental models containing cells, proteins and solutes. Therefore, improved physicochemical nanomaterial assays are needed to provide accurate exposure risk assessments and genuine predictions of in vivo behavior and therapeutic value. Simpler model nanomaterial systems in buffer do not accurately duplicate this complexity or predict in vivo behavior. A diverse portfolio of complementary material characterization tools and bioassays are required to validate nanomaterial properties in physiology.

Nanoparticle interaction with plasma proteins as it relates to particle biodistribution, biocompatibility and therapeutic efficacy

Proteins bind the surfaces of nanoparticles, and biological materials in general, immediately upon introduction of the materials into a physiological environment. The further biological response of the body is influenced by the nanoparticle-protein complex. The nanoparticle's composition and surface chemistry dictate the extent and specificity of protein binding. Protein binding is one of the key elements that affects biodistribution of the nanoparticles throughout the body. Here we review recent research on nanoparticle physicochemical properties important for protein binding, techniques for isolation and identification of nanoparticle-bound proteins, and how these proteins can influence particle biodistribution and biocompatibility. Understanding the nanoparticle-protein complex is necessary for control and manipulation of protein binding, and allows for improved engineering of nanoparticles with favorable bioavailability and biodistribution.

In vivo pharmacokinetics, tissue distribution and underlying mechanisms of various PEI(-PEG)/siRNA complexes

BACKGROUND

RNA interference (RNAi) represents a novel therapeutic strategy allowing the knockdown of any pathologically relevant target gene. Since it relies on the action of small interfering RNAs (siRNAs), the in vivo delivery of siRNAs is instrumental. Polyethylenimines (PEIs) and PEGylated PEIs have been shown previously to complex siRNAs, thus mediating siRNA protection against nucleolytic degradation, cellular uptake and intracellular release.

PURPOSE

The present study determines in vivo pharmacokinetics, tissue distribution/efficacy of siRNA delivery and adverse effects of a broad panel of PEI(-PEG)-based siRNA complexes. The aim is to systematically evaluate the effects of different degrees and patterns of PEGylation in PEI-PEG copolymers on the in vivo behavior of PEI(-PEG)/siRNA complexes in mice.

RESULTS

Upon i.v. injection of radioactively labeled, PEI(-PEG) complexed siRNAs, marked differences in the pharmacokinetics and biodistribution of the complexes are observed, with the fate of the PEI(-PEG)/siRNA complexes being mainly dependent on the degree of uptake in liver, spleen, lung and kidney. Thus, the role of these tissues is investigated in greater detail using representative PEI(-PEG)/siRNA complexes. The induction of erythrocyte aggregation and hemorrhage is dependent on the degree and pattern of PEGylation as well as on the PEI/siRNA (N/P) ratio, and represents one important effect in the lung. Furthermore, siRNA uptake in liver and spleen, but not in lung or kidney, is mediated by macrophage and is dependent on macrophage activity. In the kidney PEI(-PEG)/siRNA uptake is mostly passive and reflects the total stability of the complexes.

CONCLUSION

Liver, lung, spleen and kidney are the major players determining the in vivo biodistribution of PEI(-PEG)/siRNA complexes. Beyond their physicochemical and in vitro bioactivity characteristics, PEI(-PEG)/siRNA complexes show marked differences in vivo which can be explained by distinct effects in different tissues. Based on these data, our study also identifies which PEGylated PEIs are promising tools for in vivo siRNA delivery in future therapeutic studies and which major determinants require further investigation.

Equivalence-by-design: targeting in vivo drug delivery profile

In the United States (U.S.), drug products are considered therapeutically equivalent if they meet regulatory criteria of pharmaceutical equivalence and bioequivalence. These requirements can be traced back to 1977 when the U.S. Food and Drug Administration (FDA) published the regulations on bioavailability and bioequivalence. Over the years, to keep up with the advancement in science and technology, the FDA has been constantly updating the regulatory approaches to assessing and ensuring equivalence. In view of the recent growth in novel pharmaceutical dosage forms and delivery systems, this paper examines the current framework for documentation of therapeutic equivalence and explores the opportunities of further advancing equivalence methods for complex drug products. It is proposed that equivalence may be established by matching the in vivo drug delivery profile (iDDP) between drug products in comparison. This can be achieved by characterizing the iDDP of the reference formulation with application of an equivalence-by-design approach for pharmaceutical development. Critical variables can be identified to serve as in vitro markers or biomarkers for mapping the desired drug delivery profile in vivo. A multidisciplinary approach may be necessary to develop these markers for characterization of iDDPs.

Preparation of alendronate liposomes for enhanced stability and bioactivity: in vitro and in vivo characterization

Liposomes containing bisphosphonates have been shown to deplete circulating monocytes and reduce experimental restenosis. However, acceptable shelf life was not achieved, and the disruption extent and rate of the vesicles in the circulation has not been examined. Designing an optimal liposomal formulation in general, and for an anti-inflammatory effect in particular, requires careful consideration of the factors that contribute to their in vitro stability and integrity in the blood after injection. An improved liposomal alendronate formulation was prepared by a modified thin lipid film hydration technique followed by extrusion, resulting in relatively smaller size vesicles, narrow size distribution, and low drug to lipid ratio in comparison to the reverse phase evaporation method. In order to rule out premature leakage of the drug, the integrity of the vesicles was examined by means of size-exclusion chromatography in vitro and in vivo, with subsequent analysis of size, drug (fractions of encapsulated and free) and lipid concentrations. Vesicles were found to be stable in serum, with 15 +/- 3% leakage of the drug after 10 min in rabbit's circulation, and intact liposomes were detected in the circulation 24 h following administration. It is concluded that the new formulation results in increased stability (2.5 years) as determined by the insignificant changes in vesicle size, drug leakage, lipid and drug stability, in vitro bioactivity (macrophages inhibition), as well as in vivo in depleting circulating monocytes and inhibition of restenosis in rabbits. Our in vitro stability results regarding dilution in serum paralleled in vivo data. Thus, in vitro assessment may provide a valuable tool in assessing in vivo integrity of liposomal formulations.

Time-dependent changes in opsonin amount associated on nanoparticles alter their hepatic uptake characteristics

The relationship between the time-dependent change in serum proteins adsorbed on nanoparticles and their disposition to the liver was investigated by employing lecithin-coated polystyrene nanosphere with a size of 50 nm (LNS-50) as a model nanoparticle in rats. The total amount of proteins adsorbed on LNS-50 increased and the qualitative profile of serum proteins adsorbed on LNS-50 changed during the incubation with serum up to 360 min. The liver perfusion study indicated that the hepatic uptake of LNS-50 incubated with serum for 360 min was significantly larger than those of LNS-50 incubated for shorter period. It was suggested that the increase in the hepatic uptake of LNS-50 with the increase in incubation time would be ascribed mainly to the increase in the opsonin-mediated uptake by Kupffer cells. Semi-quantification of major opsonins, complement C3 (C3) and immunoglobulin G (IgG), and in vitro uptake study in primary cultured Kupffer cells demonstrated that the increase in C3 and IgG amounts adsorbed on LNS-50 was directly reflected in the increased disposition of LNS-50 to Kupffer cells. These results indicate that the amounts of opsonins associated on nanoparticles would change over time and this process would be substantially reflected in the alteration of their hepatic disposition characteristics.

The in vitro kinetics of the interactions between PEG-ylated magnetic-fluid-loaded liposomes and macrophages

Binding and uptake kinetics of magnetic-fluid-loaded liposomes (MFL) by endocytotic cells were investigated in vitro on the model cell-line J774. MFL consisted of unilamellar phosphatidylcholine vesicles (mean hydrodynamic diameter close to 200nm) encapsulating 8-nm nanocrystals of maghemite (gamma-Fe(2)O(3)) and sterically stabilized by introducing 5mol% of distearylphosphatidylcholine poly(ethylene glycol)(2,000) (DSPE-PEG(2,000)) in the vesicle bilayer. The association processes with living macrophages were followed at two levels. On one hand, the lipid vesicles were imaged by confocal fluorescence microscopy. For this purpose 1mol% of rhodamine-marked phosphatidylethanolamine was added to the liposome composition. On the other hand, the iron oxide particles associated with cells were independently quantified by magnetophoresis. All the experiments were similarly performed with PEG-ylated or conventional MFL to point out the role of polymer coating. The results showed cell association with both types of liposomes resulting from binding followed by endocytosis. Steric stabilization by PEG chains reduced binding efficiency limiting the amount of MFL internalized by the macrophages. In contrast, PEG coating did not change the kinetics of endocytosis which exhibited the same first-order rate constant for both conventional and PEG-ylated liposomes. Moreover, lipids and iron oxide particle uptakes were perfectly correlated, indicating that MFL vesicle structure and encapsulation rate were preserved upon cell penetration.

Ligand-receptor binding on nanoparticle-stabilized liposome surfaces

We explore the access of receptor (streptavidin) to liposome-immobilized ligand (biotin) in cases where the liposomes are stabilized against fusion by allowing nanoparticles to adsorb. It is found that receptor binding persists over that range of nanoparticle surface coverage where liposome fusion and large-scale aggregation are prevented. This indicates that liposome outer surfaces, in the presence of stabilizers, remain biofunctionalizable, and may have bearing on explaining the long circulation time of stabilized liposomes as drug delivery vehicles.

A novel approach based on nanotechnology for investigating the chronic actions of short-lived peptides in specific sites of the brain

This review presents a novel experimental approach for investigating the chronic actions of short-lived peptides in specific sites of the brain. This method combines the advantages of three different techniques: liposome encapsulation, site-specific microinjection and telemetry. First, liposomes can be designed to remain located at the injection site for a long period of time, where they protect encapsulated peptide from rapid degradation and act as a sustained-release system. Secondly, microinjection allows the administration of peptides in specific sites of the brain with minimal side effects. Finally, using telemetry, it is possible to register physiological parameters and their circadian variations in undisturbed free-moving animals for several days. Angiotensin-(1-7) and angiotensin II were used as peptide models, in order to validate the proposed method. Following the unilateral microinjection of the liposome-encapsulated peptides into the rostral ventrolateral medulla (RVLM) of Wistar rats, long-lasting cardiovascular actions were elicited, for several days. Importantly, new physiological actions of angiotensin-(1-7) at the RVLM were unmasked: modulation of the circadian rhythms of blood pressure and heart rate. It is felt that this method can be applied to a wide variety of short-lived bioactive peptides and should encounter numerous applications in the field of neurosciences.

Macrophage uptake of core-shell nanoparticles surface modified with poly(ethylene glycol)

The in vitro uptake of core-shell nanoparticles encapsulated in a bio-macromolecular nanoshell assembled from multilayered polyelectrolytes was studied. Sulfate modified fluorescent polystyrene nanobeads (diameter 200 nm) were used as a solid core upon which charged multilayers of poly-l-lysine, chitosan, and heparin sulfate are electrostatically deposited utilizing a layer-by-layer (LbL) self-assembly process. The nanoshell composed of the multilayered polyelectrolytes was modified with poly(ethylene glycol) (PEG) of varying molecular weights (either MW 2000, 5000, or 20 000 Da) to form a hydrophilic and long-circulating nanoparticle. The assembly of the nanoshell was confirmed by zeta potential, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The reversal in charge upon the deposition of alternating polyelectrolytes was observed by zeta potential measurements. The nanometer thickness of the nanoshell was confirmed by TEM. The presence of the (C-C-O)(n)() backbone in PEG at the surface of the nanoshell was confirmed by the increase in (C-O,N) peak area concentrations compared to (C-C) peak area, and these results were gathered from XPS. In vitro studies between suspension macrophages and core-shell nanoparticles were performed to determine how the hydrophilicity and the charge on the nanoshell can promote or reduce uptake. Results showed that after 24 h uptake was decreased 3-fold when PEGs of 2000 and 20 000 Da were chemisorbed to the nanoshell, as opposed to a nanoshell with either a positive or highly negative charge. Confocal microscopy aided in verifying that core-shell nanoparticles were internalized within the cell cytoplasm and were not attached to the cell surface. Protein adhesion studies with bovine serum albumin were performed to determine the relationship between surface charge and opsonization of core-shell nanoparticles. It was found that a hydrophilic surface with a low negative charge reduced protein adsorption and uptake. The in vitro uptake of macrophages and protein adsorption onto core-shell nanoparticles formed using layer-by-layer assembly has not been previously studied.

Water-soluble quantum dots for biomedical applications

Semiconductor nanocrystals are 1-10nm inorganic particles with unique size-dependent optical and electrical properties due to quantum confinement (so they are also called quantum dots). Quantum dots are new types of fluorescent materials for biological labeling with high quantum efficiency, long-term photostability, narrow emission, and continuous absorption spectra. Here, we discuss the recent development in making water-soluble quantum dots and related cytotoxicity for biomedical applications.

Parameters influencing the stealthiness of colloidal drug delivery systems

Over the last few decades, colloidal drug delivery systems (CDDS) such as nano-structures have been developed in order to improve the efficiency and the specificity of drug action. Their small size permits them to be injected intravenously in order to reach target tissues. However, it is known that they can be rapidly removed from blood circulation by the immune system. CDDS are removed via the complement system and via the cells of the mononuclear phagocyte system (MPS), after their recognition by opsonins and/or receptors present at the cell surface. This recognition is dependent on the physicochemical characteristics of the CDDS. In this study, we will focus on parameters influencing the interactions of opsonins and the macrophage plasma membrane with the surface of CDDS, whereby parameters of the polymer coating become necessary to provide good protection.

Improved targeting of antimony to the bone marrow of dogs using liposomes of reduced size

A novel liposomal formulation of meglumine antimoniate (MA), consisting of vesicles of reduced size, has been evaluated in dogs with visceral leishmaniasis to determine its pharmacokinetics as well as the impact of vesicle size on the targeting of antimony to the bone marrow. Encapsulation of MA in liposomes was achieved through freeze-drying of empty liposomes in the presence of sucrose and rehydration with a solution of MA. The resulting formulation, with a mean vesicle diameter of about 400 nm, was given to mongrel dogs with visceral leishmaniasis as an i.v. bolus injection at 4.2 mgSb/kg of body weight. The pharmacokinetics of antimony were assessed in the blood and in organs of the mononuclear phagocyte system and compared to those achieved with the free drug and the drug encapsulated in large sized liposomes (mean diameter of 1200 nm). The targeting of antimony to the bone marrow was improved (approximately three-fold) with the novel liposomal formulation, when compared to the formulation of MA in large sized liposomes. This study provides the first direct experimental evidence that passive targeting of liposomes to the bone marrow of dogs is improved by the reduction of vesicle size from the micron to the nanometer scale.

A Nanoparticle-Based Model Delivery System To Guide the Rational Design of Gene Delivery to the Liver. 1. Synthesis and Characterization

Nonviral gene delivery systems are amenable to forming colloidal particles with a wide range of physicochemical properties that include size, surface charge, and density and type of ligand presented. However, it is not known how to best design these particles without having a set of physicochemical design constraints that have been optimized for the intended gene delivery application. Here, a nanoparticle-based model delivery system is developed that can mimic the surface properties of nonviral gene delivery particles, and this model system is used to define design constraints that should be applied to next generation gene delivery particles. As a test case, a well-defined nanoparticle-based system is developed to guide the rational design of gene delivery to hepatocytes in the liver. The synthetic scheme utilizes monodisperse polystyrene particles and provides for variation of mean particle size and particle size distribution through variation in reaction conditions. The nanoparticles are PEGylated to provide stability in serum and also incorporate targeting ligands, e.g., galactose, at tunable densities. Four nanoparticles are synthesized from uniformly sized polystyrene beads specifically for the purpose of identifying design constraints to guide next generation gene delivery to the liver. These four nanoparticles are Gal-50 and Gal-140, that are galactosylated 50 and 140 nm nanoparticles, and MeO-50 and MeO-140, that are methoxy-terminated 50 and 140 nm nanoparticles. All four particles have the same surface charge, and Gal-50 and Gal-140 have the same surface galactose density. The availability of galactose ligands to receptor binding is demonstrated here by agglutination with RCA120.

Uptake of phosphatidylserine-containing liposomes by liver sinusoidal endothelial cells in the serum-free perfused rat liver

We studied the kinetics of hepatic uptake of liposomes during serum-free recirculating perfusion of rat livers. Liposomes consisted of phosphatidylcholine, cholesterol and phosphatidylserine in a 6:4:0 or a 3:4:3 molar ratio and were radiolabelled with [3H]cholesteryl oleyl ether. The negatively charged liposomes were taken up to a 10-fold higher extent than the neutral ones. Hepatic uptake of fluorescently labelled liposomes was examined by fluorescence microscopy. The neutral liposomes displayed a typical Kupffer cell distribution pattern, in addition to weak diffuse staining of the parenchyma, while the negatively charged liposomes showed a characteristic sinusoidal lining pattern, consistent with an endothelial localization. In addition, scattered Kupffer cell staining was distinguished as well as diffuse parenchymal fluorescence. The mainly endothelial localisation of the negatively charged liposomes was confirmed by determining radioactivity in endothelial and Kupffer cells isolated following a 1-h perfusion. Perfusion in the presence of polyinosinic acid, an inhibitor of scavenger receptor activity, reduced the rate of uptake of the negatively charged liposomes twofold, indicating the involvement of this receptor in the elimination mechanism. These results are compatible with earlier in vitro studies on liposome uptake by isolated endothelial cells and Kupffer cells, which showed that in the absence of serum also endothelial cells in situ are able to take up massive amounts of negatively charged liposomes. The present results emphasize that the high in vitro endothelial cell uptake in the absence of serum from earlier observations was not an artifact induced by the cell isolation procedure.

Influence of serum protein on polycarbonate-based copolymer micelles as a delivery system for a hydrophobic anti-cancer agent

A new micelle system formed from methoxy (polyethylene glycol)-b-poly (5-benzyloxy-trimethylene carbonate; MePEG-b-PBTMC 5000-b-4800) was investigated as a delivery system for the hydrophobic anti-cancer agent, ellipticine. The ellipticine was loaded into the MePEG-b-PBTMC micelles with a loading efficiency of 95% using a high-pressure extrusion technique. The ellipticine-loaded micelles have a spherical morphology and an average diameter of 96 nm. The anti-cancer activity of ellipticine was confirmed to be retained following formulation in the MePEG-b-PBTMC micelles. The extent of protein adsorption to the MePEG-b-PBTMC micelles was investigated by transmission electron microscopy, dynamic light scattering and gel filtration chromatography. Overall, the amount of protein both loosely and tightly associated with the micelles was found to be minimal and insignificant. The partitioning properties of ellipticine between an aqueous medium containing protein and the MePEG-b-PBTMC micelles were examined over a range of protein concentrations. Under physiologically relevant conditions, it was found that 61% of the drug remained within the micelle fraction while 39% was in the protein-containing aqueous phase. In addition, the in vitro drug release profile of ellipticine from the micelles was fit using a modified Higuchi model and found to be accelerated in the presence of protein. These studies demonstrate that although there are no significant interactions between micelle and protein, the properties of the micelle as a delivery vehicle may be strongly influenced by protein-drug interactions.

Fibronectin conformational changes induced by adsorption to liposomes

One of the major drawbacks of drug delivery techniques that utilize liposomes as carriers is that they are often cleared from the body before they can deliver their therapeutic cargo. It is well known that serum proteins can adsorb to these drug delivery vehicles and influence their uptake by phagocytic cells. For this reason, protein adsorption to liposomes has been extensively quantified, and strategies have been developed to minimize protein adsorption to improve drug delivery. However, the conformation of proteins on surfaces can play an even greater role in controlling cell behavior than the quantity of adsorbed protein. We have therefore used fluorescence resonance energy transfer (FRET) to measure changes in the structure of fibronectin (Fn)--a key serum protein involved in phagocytosis--upon interaction with phosphatidylcholine (PC) liposomes. Our experiments reveal that fibronectin opens up from its inactive, compact conformation upon interaction with gel phase PC liposomes. We also used FRET to estimate a physiologically relevant dissociation constant, KD=1.1 nM, for the interaction. Conformational changes in serum proteins may result in the exposure of otherwise concealed recognition sites and therefore influence the interaction of liposomes with phagocytic cells.

Colloidal gold: a novel nanoparticle vector for tumor directed drug delivery

Colloidal gold, a sol comprised of nanoparticles of Au(0), has been used as a therapeutic for the treatment of cancer as well as an indicator for immunodiagnostics. However, the use of these gold nanoparticles for in vivo drug delivery has never been described. This communication outlines the development of a colloidal gold (cAu) nanoparticle vector that targets the delivery of tumor necrosis factor (TNF) to a solid tumor growing in mice. The optimal vector, designated PT-cAu-TNF, consists of molecules of thiol-derivatized PEG (PT) and recombinant human TNF that are directly bound onto the surface of the gold nanoparticles. Following intravenous administration, PT-cAu-TNF rapidly accumulates in MC-38 colon carcinoma tumors and shows little to no accumulation in the livers, spleens (i.e., the RES) or other healthy organs of the animals. The tumor accumulation was evidenced by a marked change in the color of the tumor as it acquired the bright red/purple color of the colloidal gold sol and was coincident with the active and tumor-specific sequestration of TNF. Finally, PT-cAu-TNF was less toxic and more effective in reducing tumor burden than native TNF since maximal antitumor responses were achieved at lower doses of drug.

Pegylated polystyrene particles as a model system for artificial cells

Pegylated polystyrene particles (PS-PEG) were prepared as a model system for artificial cells, by modification of carboxyl polystyrene particles (PS-COOH) with homo- and hetero-bifunctional polyethylene glycols (PEG, MW 1500, 3400, and 5000) containing an amino end group for immobilization and an amino, hydroxyl, or methoxy end group that is exposed at the surface after immobilization. Protein adsorption from human plasma dilutions (85 v %) onto PS-PEG with a PEG surface concentration higher than 40 pmol/cm2 was reduced up to 90-95% compared with protein adsorption onto PS-COOH with a final protein surface concentration of approximately 30 ng/cm2. Two-dimensional gel electrophoresis analyses showed that 30% of the total amount of adsorbed proteins onto PS-PEG are dysopsonins (i.e., nonadhesive proteins like albumin and apolipoproteins). For PS-COOH, <15% of the amount of adsorbed proteins are dysopsonins. In addition, the generation of terminal complement compound (TCC) by PS-PEG particles with a PEG surface concentration lower than approximately 55 pmol/cm2 is not significant. The low protein adsorption, the relatively high percentage of adsorbed dysopsonins, and the low level of complement activation may prevent the uptake of PS-PEG by the mononuclear phagocytic system (MPS) in vivo. Moreover, PS-PEG (PEG surface concentration > approximately 35 pmol/cm2) shows minimal interaction with cultured human umbilical vein endothelial cells (HUVEC), which mimics the endothelial lining of the blood vessel wall.

Effect of the physicochemical properties of initially injected liposomes on the clearance of subsequently injected PEGylated liposomes in mice

Using mice as a model, we recently reported that the long-circulating properties of polyethylene glycol (PEG) (M.W. 2000)-modified liposomes (mPEG(2000)-liposomes) disappeared when they were intravenously injected at certain intervals [referred to as the "accelerated blood clearance (ABC) phenomenon"]. Herein, we report on a study of issue of whether physicochemical properties of a prior dose of liposomes such as degree of PEGylation, PEG chain length, lipid dose, surface charge, size, play a role in inducing this phenomenon. The injection of conventional liposomes (without a PEG-coating) significantly induced the phenomenon. The PEGylation of conventional liposomes attenuated the induction of the phenomenon somewhat with increasing molar content of PEG derivative and PEG chain length. These findings clearly suggest that the PEGylation of liposomes are not the major cause of the ABC phenomenon but, rather, played a role in preventing it. In addition, increasing the lipid dose in a prior dose of mPEG(2000)-liposomes (0-25 micromol/kg) increased the induction of the phenomenon in a sigmoid manner. The surface charge and size of the liposomes were not critical for the induction of the phenomenon, although generally these serve as determinants in the biodistribution of liposomes. The results reported here clearly indicate that the physicochemical properties of a prior dose of liposomes strongly affect the pharmacokinetic behavior of a subsequent injection of mPEG(2000)-liposomes: The extent of PEGylation and the lipid dose had an effect, but the surface charge and size did not. The results reported herein have a considerable impact on the design and engineering of liposomal formulations for use in multiple drug therapy as well as in therapy that involves the use of liposomal drugs.

Rational design and engineering of delivery systems for therapeutics: biomedical exercises in colloid and surface science

Engineering delivery systems of therapeutic agents has grown into an independent field, transcending the scope of traditional disciplines and capturing the interest of both academic and industrial research. At the same time, the acceleration in the discovery of new therapeutic moieties (chemical, biological, genetic and radiological) has led to an increasing demand for delivery systems capable of protecting, transporting, and selectively depositing those therapeutic agents to desired sites. The vast majority of delivery systems physically reside in the colloidal domain, while their surface properties and interfacial interactions with the biological milieu critically determine the pharmacological profiles of the delivered therapeutic agents. Interestingly though, the colloidal and surface properties of delivery systems are commonly overlooked in view of the predominant attention placed on the therapeutic effectiveness achieved. Moreover, the development and evaluation of novel delivery systems towards clinical use is often progressed by serendipity rather than a systematic design process, often leading to failure. The present article will attempt to illustrate the colloid and interfacial perspective of a delivery event, as well as exemplify the vast opportunities offered by treating, analysing and manipulating delivery systems as colloidal systems. Exploring and defining the colloid and surface nature of the interactions taking place between the biological moieties in the body and an administered delivery vehicle will allow for the rational engineering of effective delivery systems. A design scheme is also proposed on the way in which the engineering of advanced delivery systems should be practiced towards their transformation from laboratory inventions to clinically viable therapeutics. Lastly, three case studies are presented, demonstrating how rational manipulation of the colloidal and surface properties of delivery systems can lead to newly engineered systems relevant to chemotherapy, gene therapy and radiotherapy.