Mechanisms regulating body distribution of nanospheres conditioned with pluronic and tetronic block co-polymers

Influence of the Hydrophobicity of Pluronic Micelles Encapsulating Curcumin on the Membrane Permeability and Enhancement of Photoinduced Antibacterial Activity

Apart from its well-known activity as an antimicrobial agent, Curcumin (CURC) has recently started to arouse interest as a photosensitizer in the photodynamic therapy of bacterial infections. The aim of the present study was to evidence the influence of the encapsulation of Curcumin into polymeric micelles on the efficiency of photoinduced microbial inhibition. The influence of the hydrophobicity of the selected Pluronics (P84, P123, and F127) on the encapsulation, stability, and antimicrobial efficiency of CURC-loaded micelles was investigated. In addition, the size, morphology, and drug-loading capacity of the micellar drug delivery systems have been characterized. The influence of the presence of micellar aggregates and unassociated molecules of various Pluronics on the membrane permeability was investigated on both normal and resistant microbial strains of E. coli, S. aureus, and C. albicans. The antimicrobial efficiency on the common pathogens was assessed for CURC-loaded polymeric micelles in dark conditions and activated by blue laser light (470 nm). Significant results in the reduction of the microorganism’s growth were found in cultures of C. albicans, even at very low concentrations of surfactants and Curcumin. Unlike the membrane permeabilization effect of the monomeric solution of Pluronics, reported in the case of tumoral cells, a limited permeabilization effect was found on the studied microorganisms. Encapsulation of the Curcumin in Pluronic P84 and P123 at very low, nontoxic concentrations for photosensitizer and drug-carrier, produced CURC-loaded micelles that prove to be effective in the light-activated inhibition of resistant species of Gram-positive bacteria and fungi.

Immobilization of PR4A3 enzyme in pluronic F127 polymeric micelles against colorectal adenocarcinoma cells and increase of in vitro bioavailability

Traditional therapy for malignant neoplasms involving surgical procedures, radiotherapy and chemotherapy aims to kill neoplastic cells, but also affects normal cells. Therefore, exogenous proteases are the target of studies in cancer therapy, as they have been shown to be effective in suppressing tumors and reducing metastases. Pluronic F127 (F127) is a copolymer of amphiphilic blocks that has shown significant potential for drug administration, as it is capable of incorporating hydrophobic drugs and self-assembling in micrometers of nanometric size. This study investigated the effects of immobilization of the alkaline protease PR4A3 with pluronic F127 micelles on the enzyme-induced cytotoxicity. Protease immobilization was demonstrated through UV-visible and circular dichroism (CD) spectroscopies, as the enzyme interacts with the polymeric micelle of Pluronic F127 without changing its secondary structure. In addition, the immobilized form of the enzyme showed greater bioavailability after passing through the simulated gastrointestinal transit. Cell viability was assessed using the tetrazoic methylthiazole (MTT) assay. The results open perspectives for new research and development for PR4A3 in the treatment of colorectal carcinoma.

A Role for Nanoparticles in Treating Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the main causes of disability in children and young adults, as well as a significant concern for elderly individuals. Depending on the severity, TBI can have a long-term impact on the quality of life for survivors of all ages. The primary brain injury can result in severe disability or fatality, and secondary brain damage can increase the complexities in cellular, inflammatory, neurochemical, and metabolic changes in the brain, which can last decades post-injury. Thus, survival from a TBI is often accompanied by lifelong disabilities. Despite the significant morbidity, mortality, and economic loss, there are still no effective treatment options demonstrating an improved outcome in a large multi-center Phase III trial, which can be partially attributed to poor target engagement of delivered therapeutics. Thus, there is a significant unmet need to develop more effective delivery strategies to overcome the biological barriers that would otherwise inhibit transport of materials into the brain to prevent the secondary long-term damage associated with TBI. The complex pathology of TBI involving the blood-brain barrier (BBB) has limited the development of effective therapeutics and diagnostics. Therefore, it is of great importance to develop novel strategies to target the BBB. The leaky BBB caused by a TBI may provide opportunities for therapeutic delivery via nanoparticles (NP). The focus of this review is to provide a survey of NP-based strategies employed in preclinical models of TBI and to provide insights for improved NP based diagnostic or treatment approaches. Both passive and active delivery of various NPs for TBI are discussed. Finally, potential therapeutic targets where improved NP-mediated delivery could increase target engagement are identified with the overall goal of providing insight into open opportunities for NP researchers to begin research in TBI.

Delivery of doxorubicin-loaded PLGA nanoparticles into U87 human glioblastoma cells

The paramount problem in the therapy of brain tumors is the inability of most drugs to cross the blood-brain barrier. PLGA nanoparticles overcoated with poloxamer 188 could overcome this problem and enabled a high anti-tumoral effect against the very aggressive intracranial 101.8 glioblastoma in rats that closely resembles human grade IV glioblastomas. The basis for the transport of these particles across the blood-brain barrier appears to be adsorption of blood apolipoproteins (ApoE or ApoA-I) on the nanoparticle surface caused by the poloxamer 188-coating, followed by receptor-mediated transcytosis of the nanoparticles. The objective of the present study is the elucidation of the mechanism by which the poloxamer 188-coated nanoparticles then enter the brain tumor cells. Their intracellular fate, therefore, was investigated using the U87 human glioma cell line. The main mechanism of the PLGA nanoparticle internalization by U87 cells was clathrin-mediated endocytosis. Within 1h free doxorubicin was released from late endosomes and could reach its target site, i.e. the DNA in the nuclei without degradation, whereas the PLGA nanoparticles, which were labeled with Cy5.5, still were observed in the endo-lysosomal compartment. These results demonstrate that the underlying mechanism of action in the brain cells is by diffusive doxorubicin release from the nanoparticles rather than by their intracellular degradation.

Superparamagnetic iron oxide nanoparticles dispersed in Pluronic F127 hydrogel: potential uses in topical applications

The present study is focused on the synthesis and characterization of nitric oxide (NO)-releasing superparamagnetic iron oxide nanoparticles, and their incorporation in Pluronic F127 hydrogel with great potential for topical applications.

Long-Circulating Polymeric Nanovectors for Tumor-Selective Gene Delivery

Significant advances in the understanding of the genetic abnormalities that lead to the development, progression, and metastasis of neoplastic diseases has raised the promise of gene therapy as an approach to medical intervention. Most of the clinical protocols that have been approved in the United States for gene therapy have used the viral vectors because of the high efficiency of gene transfer. Conventional means of gene delivery using viral vectors, however, has undesirable side effects such as insertion of mutational viral gene into the host genome and development of replication competent viruses. Among non-viral gene delivery methods, polymeric nanoparticles are increasingly becoming popular as vectors of choice. The major limitation of these nanoparticles is poor transfection efficiency at the target site after systemic administration due to uptake by the cells of reticuloendothelial system (RES). In order to reduce the uptake by the cells of the RES and improve blood circulation time, these nanoparticles are coated with hydrophilic polymers such as poly(ethylene glycol) (PEG). This article reviews the use of such hydrophilic polymers employed for improving the circulation time of the nanocarriers. The mechanism of polymer coating and factors affecting the circulation time of these nanocarriers will be discussed. In addition to the long circulating property, modifications to improve the target specificity of the particles and the limitations of steric protection will be analyzed.

Droplet sorting based on the number of encapsulated particles using a solenoid valve

Droplet microfluidics provides a high-throughput platform for screening subjects and conditions involved in biology. Droplets with encapsulated beads and cells have been increasingly used for studying molecular and cellular biology. Droplet sorting is needed to isolate and analyze the subject of interest during such screening. The vast majority of current sorting techniques use fluorescence intensity emitted by each droplet as the only criterion. However, due to the randomness and imperfections in the encapsulation process, typically a mixed population of droplets with an uneven number of encapsulated particles results and is used for screening. Thus droplet sorting based on the number of encapsulated particles becomes necessary for isolating or enriching droplets with a specific occupancy. In this work, we developed a fluorescence-activated microfluidic droplet sorter that integrated a simple deflection mechanism based on the use of a solenoid valve and a sophisticated signal processing system with a microcontroller as the core. By passing droplets through a narrow interrogation channel, the encapsulated particles were detected individually. The microcontroller conducted the computation to determine the number of encapsulated particles in each droplet and made the sorting decision accordingly that led to actuation of the solenoid valve. We tested both fluorescent beads and stained cells and our results showed high efficiency and accuracy for sorting and enrichment.

The necessity for the coating of perfluorodecalin-filled poly(lactide-co-glycolide) microcapsules in the presence of physiological cholate concentrations: Tetronic-908 as an exemplary polymeric surfactant

Recently, we demonstrated that biodegradable poly(lactide-co-glycolide) (PLGA) micro- and nanocapsules with a liquid content of perfluorodecalin are principally useful for the development of artificial oxygen carriers. In order to solve a decisive and well-known problem with PLGA microcapsules, i.e. the spontaneous agglomeration of the capsules after depletion of the emulsifying agent (i.e. cholate), coating with the ABA block copolymer, Tetronic-908 was studied. After Tetronic-908 treatment at concentrations that were harmless to cultured cells, the clustering of the microcapsules was prevented, the adsorption of opsonins was decreased and the attachment to cells was inhibited, but the oxygen transport capacity of PLGA microcapsules was even increased. The present data clearly show that perfluorodecalin-filled PLGA microcapsules must be coated before decreasing the emulsifying agent cholate to physiological concentrations, in order to develop a solution that has the capabilities to function as a potential artificial oxygen carrier suspension.

Biodistribution of encapsulated indocyanine green in healthy mice

Indocyanine green (ICG) is a fluorescent probe used in various optically mediated diagnostic and therapeutic applications. However, utility of ICG remains limited by its unstable optical properties and nonspecific localization. We have encapsulated ICG within electrostatically assembled mesocapsules (MCs) to explore its potential for targeted optical imaging and therapy. In this study, we investigate how the surface coating and size of the MCs influences ICG's biodistribution in vivo. ICG was administered intravenously to Swiss Webster mice as a free solution or encapsulated within either 100 nm diameter MCs coated with dextran; 500 nm diameter MCs coated with dextran; or 100 nm diameter MCs coated with 10 nm ferromagnetic iron oxide nanoparticles, themselves coated with polyethylene glycol. ICG was extracted from harvested blood and organs at various times and its amount quantified with fluorescence measurements. MCs containing ICG accumulated in organs of the reticuloendothelial system, namely, the liver and spleen, as well as the lungs. The circulation kinetics of ICG appeared unaffected by encapsulation; however, the deposition within organs other than the liver suggests a different biodistribution mechanism. Results suggest that the capsules' coating influences their biodistribution to a greater extent than their size. The MC encapsulation system allows for delivery of ICG to organs other than the liver, enabling the potential development of new optical imaging and therapeutic strategies.

Distribution of fluorescent microspheres in vascular space and parenchymal organs of intact nude rats

PURPOSE

To assess kinetics of elimination of different sized microspheres (MS) from the blood pool and tendency of their distribution in parenchymal organs of intact nude rats.

MATERIALS AND METHODS

A mixture of 1 microm and 3 microm MS in phosphate-buffered saline was injected intravenously into eight rats under intraperitoneal anaesthesia. Blood samples were collected before, just after and in 2, 5 and 10 min after MS injection. Dynamics of MS elimination from blood pool was evaluated with flow cytometry. After euthanasia, histological sections were prepared and distributions of MS through the liver, spleen, kidney and lung were analysed with fluorescence microscopy and flow cytometry.

RESULTS

The number of microspheres registered in the intravascular space showed a marked exponential decrease over time independent of MS size. Different amounts and proportions of 1 microm and 3 microm MS were revealed in lung, liver, spleen and kidneys of the rats. Most of 1 microm MS were localised in liver and spleen. In contrast, 3 microm MS were detected predominantly in lung.

CONCLUSION

1 microm and 3 microm MS may be assumed as free circulating particles only for a short period of time after injection. Their elimination kinetics seems to be tightly linked to specific tissue properties such a pulmonary vasoconstriction and phagocytosis.

Preparation and body distribution of freeze-dried powder of ursolic acid phospholipid nanoparticles

Ursolic acid (UA) is a poor soluble natural triterpenoid. It has a wide variety of antitumor activities. We extracted it from Crataegus pinnatifida for the first time. To achieve a high bioavailability, targeting effect, stability, and an intravenous (i.v.) administration, the UA phospholipid nanopowders (UA-PL-NP) were prepared, characterized, and evaluated. With soybean phospholipid as the carrier and poloxamer 188 as emulsifier, the UA nanoparticle suspension was prepared by solvent emulsification-evaporation and ultrasonic dispersion. The UA-PL-NP was obtained by freeze drying. The body distribution in mice was studied after i.v. administration of UA-PL-NP and an UA control solution (UA-Sol). The entrapment efficiency (EE) and UA concentration in vitro and in vivo were analyzed by high-performance liquid chromatography (HPLC). The results showed that the UA-PL-NP had an average diameter of 273.8 nm with a zeta potential of -23.2 mV. The EE was up to 86.0%, and the drug loading (DL) was 12.8%. After i.v. administration of UA-PL-NP with low, middle and high doses, UA concentration in the livers of mice obviously increased during tested period and was highest in tested organs at 4 h. The AUC(0-12) ratio of UA-PL-NP in liver to that in plasma was much higher than that of UA-Sol, and the liver AUC(0-12) ratio of UA-PL-NP to UA-Sol was 8.6. These results indicate the UA-PL-NP have a good targeting to the liver after i.v. administration. Therefore, the UA-PL-NP is demonstrated to be available as an i.v. and liver targeting system for lipophilic antitumor triterpenoids.

Anion effects on electrostatic charging of sterically stabilized, water insoluble drug particles

Water-insoluble suspensions of itraconazole and budesonide were sterically stabilized using nonionic polymers (poloxamer 188 or polysorbate 80) and probed for polymer-anion interactions by measuring changes in particle zeta potential. Anions comprising a range of functionalities and aqueous solubilities were examined. Results showed that the more hydrophobic anions partitioned to the particle interface, and a simple model for predicting anion adsorption was developed from their calculated properties. Anions with a calculated Klopman water solubility less than 10 microM or a calculated log P>3.5 were adsorbed to the particle-polymer interface effectively increasing the overall particle charge. Anions of similar hydrophobicities with sulfonate or sulfate functionalities showed a much higher degree of particle charging compared with their carboxylate and phosphonate analogs at pH 9.5. In addition, the electrostatic charging of particles occurred at lower solution concentrations of sulfonate derivatives. These results suggest that the relative basicity of the oxoanion functionality may influence protonation or ion-pairing phenomena of the anions when adsorbed at the particle-polymer interface. Cetyltetramethylammonium bromide (CTAB) produced a positively charged particle consistent with the model developed for anion adsorption. Particle charging of sterically stabilized drug suspensions appeared largely independent of drug and polymer type. Anion hydrophobicity (solubility) and headgroup functionality dictated the observed charging behavior.

Preparation and Characterization of Solid Lipid Nanoparticles Containing Silibinin

The study describes the development of stealth solid lipid nanoparticles (SLNs) as colloidal carriers for silibinin, a drug with very low solubility. Stealth SLNs were constituted mainly of bioacceptable and biodegradable lipids, such as stearic acid and surfactant Brij 78 (polyoxyethylene 20 stearyl ether) and can incorporate amounts of silibinin up to 7.55%. Stealth-loaded SLNs were in the nanometer size range. Thermal analysis (differential scanning calorimetry) showed that silibinin was dispersed in the stealth SLNs at an amorphous state. Release of silibinin from stealth SLNs was very slow. Stealth SLNs were stable without precipitation of silibinin on storage conditions and can be proposed for their parenteral administration.

Lung-targeting delivery of dexamethasone acetate loaded solid lipid nanoparticles

The objective of the present study was to develop a novel solid lipid nanoparticle (SLN) for the lung-targeting delivery of dexamethasone acetate (DXM) by intravenous administration. DXM loaded SLN colloidal suspensions were prepared by the high pressure homogenization method. The mean particle size, drug loading capacity and drug entrapment efficiency (EE%) of SLNs were investigated. In vitro drug release was also determined. The biodistribution and lung-targeting efficiency of DXM-SLNs and DXM-solutions (DXM-sol) in mice after intravenous administration were studied using reversed-phase high-performance liquid chromatography (HPLC). The results (expressed as mean +/- SD) showed that the DXM-SLNs had an average diameter of 552 +/- 6.5 nm with a drug loading capacity of 8.79 +/- 0.04% and an entrapment efficiency of 92.1 +/- 0.41%. The in vitro drug release profile showed that the initial burst release of DXM from DXM-SLNs was about 68% during the first 2 h, and then the remaining drug was released gradually over the following 48 hours. The biodistribution of DXM-SLNs in mice was significantly different from that of DXM-sol. The concentration of DXM in the lung reached a maximum level at 0.5 h post DXM-SLNs injection. A 17.8-fold larger area under the curve of DXM-SLNs was achieved compared to that of DXM-sol. These results indicate that SLN may be promising lung-targeting drug carrier for lipophilic drugs such as DXM.

Chemotherapy of brain tumour using doxorubicin bound to surfactant-coated poly(butyl cyanoacrylate) nanoparticles: revisiting the role of surfactants

Poly(butyl cyanoacrylate) nanoparticles coated with poloxamer 188 (Pluronic) F68) and also, as shown previously, polysorbate 80 (Tween 80) considerably enhance the anti-tumour effect of doxorubicin against an intracranial glioblastoma in rats. The investigation of plasma protein adsorption on the surface of the drug-loaded nanoparticles by two-dimensional electrophoresis (2-D PAGE) revealed that both surfactants, besides other plasma components, induced a considerable adsorption of apolipoprotein A-I (ApoA-I). It is hypothesized that delivery of doxorubicin to the brain by means of nanoparticles may be augmented by the interaction of apolipoprotein A-I that is anchored on the surface of the nanoparticles with the scavenger receptor class B type I (SR-BI) located at the blood-brain barrier. This is the first study that shows a correlation between the adsorption of apolipoprotein A-I on the nanoparticle surface and the delivery of the drug across the blood-brain barrier.

Coating of DNA/Poly(l-lysine) Complexes by Covalent Attachment of Poly[N-(2-hydroxypropyl)methacrylamide]

N-(2-Hydroxypropyl)methacrylamide (HPMA) copolymers (pHPMA) containing 4-nitrophenyl ester (ONp) or thiazolidine-2-thione (TT) reactive groups in side chains and telechelic/semitelechelic pHPMA with TT groups were designed as highly hydrophilic biocompatible polymers suitable for chemical coating of polyelectrolyte-based DNA-containing nanoparticles bearing amino groups on the surface. The course of the coating reaction carried out in aqueous solution was evaluated on model self-assembling polyelectrolyte DNA/poly(L-lysine) (DNA/PLL) complexes either by monitoring the amount of residual polymer reactive groups by UV spectroscopy or by monitoring changes in the weight-average molecular weight and hydrodynamic size of the complexes using light scattering methods. Physicochemical stability of the coated complexes in buffered saline solution was also investigated. Contrary to uncoated particles, the coated complexes showed remarkable stability to aggregate in 0.15 M NaCl. Coating with pHPMA had practically no effect on the size distribution of the most stable complexes prepared by complexation of DNA with high-molecular-weight PLL (M(w) = 134 000) as shown by dynamic light scattering. The coating reaction was faster and more efficient with multivalent HPMA copolymers containing TT reactive groups than that with HPMA copolymers containing ONp groups.

Body distribution and in situ evading of phagocytic uptake by macrophages of long-circulating poly (ethylene glycol) cyanoacrylate-co-n-hexadecyl cyanoacrylate nanoparticles

AIM

To investigate the body distribution in mice of [14C]-labeled poly methoxyethyleneglycol cyanoacrylate-co-n-hexadecyl cyanoacrylate (PEG-PHDCA) nanoparticles and in situ evading of phagocytic uptake by mouse peritoneal macrophages.

METHODS

PEG-PHDCA copolymers were synthesized by condensation of methoxypolyethylene glycol cyanoacetate with [14C]-hexadecyl-cyanoacetate. [14C]-nanoparticles were prepared using the nanoprecipitation/solvent diffusion method, while fluorescent nanoparticles were prepared by incorporating rhodamine B. In situ phagocytic uptake was evaluated by flow cytometry. Body distribution in mice was evaluated by determining radioactivity in tissues using a scintillation method.

RESULTS

Phagocytic uptake by macrophages can be efficiently evaded by fluorescent PEG-PHDCA nanoparticles. After 48 h, 31% of the radioactivity of the stealth [14C]-PEG-PHDCA nanoparticles after iv injection was still found in blood, whereas non-stealth PHDCA nanoparticles were cleaned up from the bloodstream in a short time. The distribution of stealth PEG-PHDCA nanoparticles and non-stealth PHDCA nanoparticals in mice was poor in lung, kidney, and brain, and a little higher in hearts. Lymphatic accumulation was unusually high for both stealth and non-stealth nanoparticles, typical of lymphatic capture. The accumulation of stealth PEG-PHDCA nanoparticles in the spleen was 1.7 times as much as that of non-stealth PHDCA (P< 0.01). But the accumulation of stealth PEG-PHDCA nanoparticles in the liver was 0.8 times as much as that of non-stealth PHDCA (P< 0.05).

CONCLUSION

PEGylation leads to long-circulation of nanoparticles in the bloodstream, and splenotropic accumulation opens up the potential for further development of spleen-targeted drug delivery.

In vitro evaluation of PLA nanoparticles containing a lipophilic drug in water-soluble or insoluble form

Cloricromene (AD6), an anti-ischemic drug, is rapidly metabolised into a stable and active metabolite (cloricromene acid, AD6-acid) poorly soluble in water and less lipophilic than cloricromene. The aim of this study was to evaluate which of the two forms has more possibility to be efficiently encapsulated in nanoparticles based on poly(D,L-lactide) and prepared using the nanoprecipitation method. Increasing the theoretical loading of AD6, an increase in drug actual loading and in the mean particle size occurred, while no formation of nanoparticles was observed when the highest theoretical loading (50 mg) was employed. Changing the pH of the aqueous phase the drug content dramatically increased. However, at a pH value of 11 a more rapid hydrolysis of AD6 occurred. When AD6-acid was embedded in the nanoparticles, suitable results concerning both drug content and encapsulation efficiency were achieved. A good control in the release of AD6 from the AD6-loaded nanoparticles was observed while the liberation of AD6-acid from the AD6-acid-loaded nanoparticles was faster than the dissolution of the AD6-acid free. These results confirm that the most easy encapsulable form in nanoparticles is AD6-acid probably owing to its poor water solubility. Further studies will be carried out in order to evaluate if the increase in the liberation of AD6-acid by nanoencapsulation may have outcomes in its bioavaibility in vivo.

Enhanced brain targeting by synthesis of 3',5'-dioctanoyl-5-fluoro-2'-deoxyuridine and incorporation into solid lipid nanoparticles

To overcome the limited access of the drug 5-fluoro-2'-deoxyuridine (FUdR) to the brain, 3',5'-dioctanoyl-5-fluoro-2'-deoxyuridine (DO-FUdR) was synthesized and incorporated into solid lipid nanoparticles (DO-FUdR-SLN). DO-FUdR-SLN were prepared by a thin-layer ultrasonication technique and a central composite design (CCD) was applied to optimize the formulation. The median particle size of DO-FUdR-SLN was 76 nm with drug loading of 29.02% and entrapment efficiency of 96.62%. The in vitro drug release was studied by a bulk-equilibrium reverse dialysis bag technique in phosphate-buffered saline (pH 7.4) containing 0.3% pancreatic enzyme at 37 degrees C. The concentrations of FUdR in various organs were determined by reversed-phase high-performance liquid chromatography after intravenous administration of DO-FUdR-SLN, DO-FUdR or FUdR. The brain area under the concentration-time curve of DO-FUdR-SLN and DO-FUdR were 10.97- and 5.32-fold higher than that of FUdR, respectively. These results indicated that DO-FUdR-SLN had a good brain targeting efficiency in vivo. SLN can improve the ability of the drug to penetrate through the blood-brain barrier and is a promising drug targeting system for the treatment of central nervous system disorders.

Quantification and localization of PEGylated polycyanoacrylate nanoparticles in brain and spinal cord during experimental allergic encephalomyelitis in the rat

Under healthy conditions, the blood-brain barrier (BBB) limits the passage of solutes and cells from the blood to the CNS. During neurological diseases, BBB permeability increases dramatically and it has been hypothesized that drug carrier systems such as polymeric nanoparticles could cross the BBB and penetrate into the CNS. PEGylated polyalkylcyanoacrylate nanoparticles (long-circulating carrier) are one such system and have been investigated during experimental allergic encephalomyelitis (EAE). Brain and spinal cord concentrations of [(14)C]-radiolabelled PEGylated polyalkylcyanoacrylate nanoparticles were compared with another blood long-circulating carrier (poloxamine 908-coated polyalkylcyanoacrylate nanoparticles) and with conventional non-long-circulating polyalkylcyanoacrylate nanoparticles. The microscopic localization of fluorescent nanoparticles in the CNS was also investigated in order to further understand the mechanism by which the particles penetrate the BBB. The results demonstrate that the concentration of PEGylated nanoparticles in the CNS, especially in white matter, is greatly increased in comparison to conventional non-PEGylated nanoparticles. In addition, this increase was significantly higher in pathological situations where BBB permeability is augmented and/or macrophages have infiltrated. Passive diffusion and macrophage uptake in inflammatory lesions seems to be the mechanism underlying such particles' brain penetration. Based on their long-circulating properties in blood and on their surface characteristics that allow cell interactions, PEGylated nanoparticles penetrated into CNS to a larger extent than all the other formulations tested. Thus, PEGylated polycyanoacrylate nanoparticles are proposed here as a new brain delivery system for neuroinflammatory diseases.

Steric stabilization of poly-L-Lysine/DNA complexes by the covalent attachment of semitelechelic poly[N-(2-hydroxypropyl)methacrylamide]

The concept of steric stabilization was utilized for self-assembling polyelectrolyte poly-L-lysine/DNA (pLL/DNA) complexes using covalent attachment of semitelechelic poly[N-(2-hydroxypropyl)methacrylamide] (pHPMA). We have examined the effect of coating of the complexes with pHPMA on their physicochemical stability, phagocytic uptake in vitro, and biodistribution in vivo. The coated complexes showed stability against aggregation in 0.15 M NaCl and reduced binding of albumin, chosen as a model for the study of the interactions of the complexes with plasma proteins. The presence of coating pHPMA had no effect on the morphology of the complexes as shown by transmission electron microscopy. However, results of the study of polyelectrolyte exchange reactions with heparin and pLL suggested decreased stability of the coated complexes in these types of reactions compared to uncoated pLL/DNA complexes. Coated complexes showed decreased phagocytic capture by mouse peritoneal macrophages in vitro. Decreased phagocytosis in vitro, however, did not correlate with results of in vivo study in mice showing no reduction in the liver uptake and no increase in the circulation times in the blood. We propose that the rapid plasma elimination of coated pLL/DNA complexes is a result of binding serum proteins and also of their low stability toward polyelectrolyte exchange reactions as a consequence of their equilibrium nature.

Comparative pharmacokinetics, tissue distributions, and effects on renal function of novel polymeric formulations of amphotericin B and amphotericin B-deoxycholate in rats

The pharmacokinetic profiles of a traditional formulation of amphotericin B (Fungizone) and novel nanosphere and mixed micelle delivery systems developed for amphotericin B were compared and described. Six groups of male Wistar rats received intravenous injections of the different formulations. Plasma and tissue samples were obtained at 11 different times after dosing, with three animals used each time. The amphotericin B concentrations in plasma and tissues were analyzed by high-performance liquid chromatography. The plasma drug concentration-time profiles were best described by a two-compartment model. Models that described the observed single or double peak disposition kinetics in kidney, liver, and spleen were also developed. Parameter estimates from those models show that components of the formulation such as poloxamer 188, which is present in all new formulations, seem to play an important role in the rate of drug uptake by the tissues; in general, the levels of amphotericin B in tissues were increased after the administration of the new formulations compared with those after the administration of Fungizone. The increment in the baseline plasma creatinine level was used as an index of renal function. All formulations increased this baseline value, but the novel formulations exhibited fewer renal effects than Fungizone did. However, a direct relationship between drug exposure in the kidneys and development of renal damage could not be found.

Re-establishing the long circulatory behaviour of poloxamine-coated particles after repeated intravenous administration: applications in cancer drug delivery and imaging

In accordance with earlier observations, a single intravenous injection of long circulatory poloxamine-908-coated polystyrene particles to rats dramatically affected the circulation half-life and body distribution of a second dose when administered 10 days later. Both liver and spleen macrophages recognised and cleared from the blood the majority of the second dose of poloxamine-908-coated particles. The second dose of poloxamine-908-coated particles, however, regained their long circulatory behaviour when administered 1-3 h after a bolus intravenous injection of 30 mg free poloxamine-908 or poloxamer-407 (in saline)/150 g body weight. When the interval between free copolymer and particle administration was increased to 24 h then macrophage-rich organs were able to extract poloxamine-coated beads from the blood. In contrast to poloxamine-908 and poloxamer-407, prior administration of poloxamer-188 and polyethyleneglycol-20000 also failed to restore the long circulatory behaviour of the second dose of poloxamine-908-coated particles. These observations are of interest in experimental drug delivery, particularly in experimental cancer therapy (diagnostic imaging and drug delivery), involving multiple injections of poloxamine-based long circulating nanosized vehicles.

Effect of albumin and polyanion on the structure of DNA complexes with polycation containing hydrophilic nonionic block

Self-assembling systems based on ionic complexes of DNA with block copolymer of N-(2-hydroxypropyl)methacrylamide with 2-(trimethylammonio)ethyl methacrylate were studied as systems suitable for gene delivery. In this study, the influence of albumin and polyanion on parameters of the DNA polyelectrolyte complexes in aqueous solutions was investigated. Static and dynamic light-scattering methods were used as a main tool for characterizing these interactions. It was found that albumin is not able to release free DNA, but it can rather bind to the complexes forming ternary DNA-polycation-albumin complexes with increased hydrodynamic radii of about 10 nm. Polyanion tested, sodium poly(styrenesulfonate), was able to release free DNA in the presence of a low-molecular-weight electrolyte. In the absence of a low-molecular-weight electrolyte, only formation of ternary complexes and no DNA release was observed. The in vivo biodistribution analysis of DNA complexes showed no effect of the presence of hydrophilic nonionic poly(HPMA) on the circulatory time or organ distribution. The interaction of DNA complexes with albumin and other plasma proteins was suggested to be a major reason for the short circulatory times.

Body distribution in mice of intravenously injected camptothecin solid lipid nanoparticles and targeting effect on brain

The objective of the present study was to investigate the specific drug targeting of anticarcinogenic drugs, such as camptothecin (CA), after intravenous (i.v.) injection by incorporation into solid lipid nanoparticles (SLN). A CA loaded SLN suspension consisted of 0.1% (w/w) camptothecin, 2.0% (w/w) stearic acid, 1.5% (w/w) soybean lecithin and 0.5% (w/w) polyoxyethylene-polyoxypropylene copolymer (Poloxamer 188) was prepared by high pressure homogenization. In vitro drug release was investigated in pH 7.4 phosphate-buffered saline at 37 degrees C. The concentrations of camptothecin in various organs were determined using reversed-phase high-performance liquid chromatography with a fluorescence detector after i.v. administration of CA-SLN and a camptothecin control solution (CA-Sol). The results showed that the CA-SLN had an average diameter 196.8 nm with a Zeta potential of -69.3 mV and in vitro drug release was achieved for up to a week. In tested organs, the AUC/dose and the mean residence times (MRT) of CA-SLN were much higher than those of CA-Sol, especially in brain, heart and reticuloendothelial cells containing organs. The brain AUC ratio of CA-SLN to CA-Sol was the highest among the tested organs. These results indicate that SLN are a promising sustained release and drug targeting system for lipophilic antitumour drugs, and may also allow a reduction in dosage and a decrease in systemic toxicity.

Microparticles of novel branched copolymers of lactic acid and amino acids: preparation and characterization

The preparation and characterization of microparticles produced from a new class of functionalized, biodegradable, comblike graft copolymers is presented. The copolymers are polyester-polyamino acid hybrids, composed of a poly(L-lactic acid-co-L-lysine) (PLAL) backbone, and poly(L-lysine), poly(D,L-alanine) or poly(L-aspartic acid) side chains extending from the lysine residues of PLAL. The microparticles have been characterized with regard to their surface properties, morphology, and size. Thus, electron spectroscopy for chemical analysis data and results of Zeta potential measurements suggest that the polyamino acid side chains tend to concentrate at the surface of the particles. Also, analyses by environmental scanning electron microscopy and confocal scanning laser microscopy indicate that particles carrying poly(lysine) chains have an unusual porous structure, most probably due to the combined effects of the amphiphilic, polyelectrolyte, and chemical nature of the composing copolymer, as well as of the particular preparation technique employed. The capabilities of the microparticles to serve as carriers in controlled drug release and delivery devices were demonstrated by encapsulation and release of rhodamine B, a low molecular weight drug model.

Polymer-coated long-circulating microparticulate pharmaceuticals

The field of long-circulating microparticulate drug carriers is reviewed. The protective effect of certain polymers including poly(ethylene glycol) on nanoparticulate carriers (liposomes, nanoparticles, micelles) is considered in terms of statistical behaviour of macromolecules in solution. Using liposomes as an example, the mechanism is discussed assuming that surface-grafted chains of flexible and hydrophilic polymers form dense 'conformational clouds' preventing other macromolecules from interaction with the surface even at low concentrations of the protecting polymer. The scale of the protective effect is interpreted as the balance between the energy of the hydrophobic anchor interaction with the liposome membrane core or with the particle surface and the energy of the polymer chain free motion in solution. The possibility of using protecting polymers other than poly(ethylene glycol) is analysed, and examples of such polymers are given, based on polymer-coated liposome biodistribution data. General requirements for protecting polymers are formulated. Sterically protected nanoparticles and micelles are considered, and differences in steric protection of liposomes and particles are discussed. The problem of the preparation of drug carriers combining longevity and targetability is analysed. The biological consequences of steric protection of drug carriers with surface-grafted polymers are discussed, and possible clinical applications for long-circulating pharmaceutical carriers are considered.

Prolonging the circulation time and modifying the body distribution of intravenously injected polystyrene nanospheres by prior intravenous administration of poloxamine-908. A 'hepatic-blockade' event or manipulation of nanosphere surface in vivo?

Intravenously injected uncoated small (60 nm) and large (250 nm) size model polystyrene particles (which are cleared rapidly from the blood by macrophages of the reticuloendothelial system) can be converted to long-circulatory and splenotropic particles in vivo, respectively, if such particles are injected shortly (up to 3 h) after an appropriate dose of the block polymer non-ionic surfactant, poloxamine-908. Evidence indicates that small and large size polystyrene beads can acquire a coating of poloxamine-908 and/or poloxamine-protein complexes in vivo. The adsorption of such complexes on to the bead surface could explain their altered body distribution since small and large size polystyrene beads that were precoated with poloxamine-908 exhibit similar biodistribution following i.v. injection.

Preparation of surface-modified albumin nanospheres

Surface-modified human serum albumin (HSA) nanospheres with a size of around 100 nm in diameter were prepared from poly(amidoamine)-poly(ethylene glycol) copolymer grafted human serum albumin (HSA-PAA-PEG) and poly(thioetheramido acid)-poly(ethylene glycol) copolymer grafted human serum albumin (HSA-PTAAC-PEG). The nanospheres were produced using a pH-coacervation method and cross-linked with glutaraldehyde. The cross-linking efficiency was affected by the type of albumin conjugate used. The zeta potential of the surface-modified nanospheres was significantly lower than that of unmodified particles. The existence of a hydrated steric barrier surrounding the nanospheres was confirmed by electrolyte- and pH-induced flocculation tests. The surface-modified nanospheres showed a reduced plasma protein adsorption on the particle surface compared with unmodified particles.