Peroral administration of 14C-poly(D,L-lactic acid) nanoparticles coated with human serum albumin or polyvinyl alcohol to guinea pigs.

Biodegradable 14C-poly(D,L-lactic acid) (PLA50) nanoparticles coated either with a readily digestible protein albumin or with a non-digestible coating agent, polyvinyl alcohol (PVA), were prepared by the solvent evaporation technique. The nanoparticles were administered perorally to guinea pigs to evaluate the gastro-intestinal degradation of their PLA50 matrix. In the case of PLA50 nanoparticles coated with digestible albumin, substantial gastro-intestinal degradation of the PLA50 matrix occurred, leading to the passage of considerable amount (> or =45%) of water-soluble products across the gastrointestinal barrier. When a non-digestible coating agent like PVA was used, the degradation of the PLA50 matrix in the gastro-intestinal tract was at least two times lower (> or =19%). The results show that it is possible to control the in vivo degradation of PLA50 nanoparticles using appropriate coating agents. The present investigations showed a good correlation between previously observed in vitro results and the in vivo findings.

Interactions of poly(lactic acid) and poly(lactic acid-co-ethylene oxide) nanoparticles with the plasma factors of the coagulation system.

When surfactant-stabilized biodegradable poly(lactic acid) (PLA) particles are injected into rats, the rate of clearance from blood is fast. The rate can be strongly reduced by using particles made from diblock copolymers of PLA and poly(ethylene oxide) (PLA-PEO), resulting in an increased duration of contact with the components of the coagulation system. Thus, possible adverse effects such as activation of the coagulation cascade could occur. In this paper, the interactions of surfactant-stabilized PLA and PLA-PEO nanoparticle suspensions with the plasma factors of the coagulation system are presented. PLA suspensions stabilized by sodium cholate (PLA-Ch) interact with thrombin, factor V and calcium ions. Formation of complexes and aggregates is induced by addition of calcium ions to PLA-Ch suspensions in the presence or in the absence of plasma. On the contrary, PLA-PEO suspensions are remarkably inert towards the coagulation factors and calcium ions, even when cholate is present. Steric repulsion owing to the high surface density of PEO is sufficient to avoid strong interations with the proteins and formation of aggregates between particles.

Effect of PEO surface density on long-circulating PLA-PEO nanoparticles which are very low complement activators.

The rapid uptake of injected nanoparticles by cells of the mononuclear phagocytes system (MPS) is a major obstacle when a long blood circulation time is needed. Whereas nanoparticles made from PLA and stabilized by surfactants (PLA-F68) are rapidly phagocytized, the rate of phagocytosis is strongly reduced in case of nanoparticles made from a diblock copolymer (PLA-PEO). Because of the role of the complement system in opsonization, this difference of phagocytosis was hypothesized to be related to this system. An important complement consumption was obtained in 5 min in the presence of PLA-F68 particles. In the presence of a higher surface area of PLA-PEO particles possessing a high PEO surface density, the consumption remained very low. When the average PEO surface density was decreased on such particles below a given threshold, a fast and strong complement consumption occurred again. These experimental data support the concept of steric repulsion towards proteins, by surfaces covered with terminally attached PEO chains and emphasize the prime importance of PEO surface density in such an effect. The major, but probably not exclusive, role of complement as an opsonin capable of inducing a fast phagocytosis by MPS should be taken into account concerning the in vitro evaluation of nanoparticles as candidates for a long blood circulation.

Degradation of poly(D,L-lactic acid) nanoparticles coated with albumin in model digestive fluids (USP XXII).

Entirely biodegradable poly(D, L-lactic acid) (PLA50) nanoparticles coated with albumin were prepared by the solvent evaporation technique. Their degradative properties were investigated in simulated gastric and intestinal fluids (USP XXII). The degradation of the albumin coating was monitored by HPLC, whereas PLA50 degradation was determined by size exclusion chromatography (SEC) as well as by the detection of lactate in bulk solution by enzymatic assay. As expected, the coating effect of albumin, a readily digestible protein, rapidly disappeared in both gastric and intestinal media, thus exposing albumin-free PLA50 cores to hydrolytic processes. In pepsin-rich simulated gastric fluid, no degradation of the PLA50 core was observed over 8 h incubation time. In contrast, in pancreatin-rich simulated intestinal fluid, the PLA50 nanoparticles were rapidly converted into lactate. The results showed that the PLA50 degradation was mainly due to an enzymatic cleavage process. Further experiments showed the involvement of lipases in the degradation of the PLA50 core in simulated intestinal fluid.

Stealth Me.PEG-PLA nanoparticles avoid uptake by the mononuclear phagocytes system.

Nanoparticles were prepared from methoxy poly(ethylene glycol)poly(d,l-lactic acid) block copolymers (Me.PEG-PLA) or blends of Me.PEG-PLA and PLA by the precipitation-solvent diffusion method. These nanoparticles, labeled by introducing [14C]PLA in the formulation, were shown to be more slowly captured by cultured THP-1 monocytes than F68-coated PLA nanoparticles, in a PEG chain-length-dependent manner. In vivo, the half-life in plasma of the Me.PEG-PLA nanoparticles that were intravenously administered to rats is increased by a factor 180 compared with the F68-coated PLA nanoparticles. This mononuclear phagocytes system avoidance was explained according to a conformation model in which the PEG density at the surface of the particles is a key parameter.

Adsorption/desorption of human serum albumin at the surface of poly(lactic acid) nanoparticles prepared by a solvent evaporation process.

Biocompatible and biodegradable nanoparticles of poly(lactic acid) (100% L-lactic units = PLA) were prepared by an emulsion, microfluidization, and solvent evaporation method using human serum albumin (HSA) as a surface agent. A radiolabeling technique was employed to quantify the serum albumin bound to the nanoparticles and to measure its desorption kinetics in various media at 22 degrees C and 37 degrees C (phosphate buffer pH 7.4, serum albumin 40 g/L in phosphate buffer pH 7.4 and fetal calf serum). The amount of serum albumin bound to the nanoparticles was found to be a linear function of 1/D (where D is the nanoparticle mean diameter) and was related to the total developed area of the nanoparticles. The adsorption/desorption behavior of serum albumin at the surface of the nanoparticles suggested a multilayer adsorption model. Moreover, a part of the serum albumin molecules was irreversibly bound regardless of the incubation conditions. Consequently, the classical Langmuirian theories of equilibria could not be applied.

Body distribution of fully biodegradable [14C]-poly(lactic acid) nanoparticles coated with albumin after parenteral administration to rats.

Fully biodegradable polylactic acid (PLA) nanoparticles (90-250 nm) coated with human serum albumin (HSA) were prepared by high-pressure emulsification and solvent evaporation, using the protein as surfactant. A new analytical tool was developed, based on Mie's law and size exclusion chromatography, to establish that, after evaporation of the solvent, the protein saturates the surface of the nanoparticles, masking the PLA core. According to this technique, no HSA is encapsulated in the polymer matrix. A radiolabelled [14C]-PLA50 was synthesized to follow the fate of this new drug carrier after i.v. administration to rats. The time necessary to clear the albumin-coated nanoparticles from the plasma was significantly longer than for the uncoated ones but not extended enough to target cells other than mononuclear phagocytes. As deduced from whole-body autoradiography and quantitative distribution experiments, the 14C-labelled polymer is rapidly captured by liver, bone marrow, lymph nodes, spleen and peritoneal macrophages. Nanoparticle degradation was addressed following 14C excretion. The elimination of the 14C was quick on the first day (30% of the administered dose) but then slowed down. In fact, if the metabolism of the PLA proceeds to lactic acid which is rapidly converted into CO2 via the Krebs cycle (80% of the total excretion was fulfilled by the lungs), anabolism from the lactic acid may also have taken place leading to long-lasting radioactive remnants, by incorporation of 14C into endogenous compounds.

In vitro and in vivo degradation of poly(D,L lactide/glycolide) type microspheres made by solvent evaporation method.

Microspheres of different poly(alpha-hydroxy acids) were prepared by solvent evaporation to study the effects of gamma-sterilization on stability and to establish the degradation process in vitro and in vivo. gamma-Irradiation dramatically decreases polymer molecular weight and this degradation continues on storage. gamma-Irradiation modifies the controlled release pattern of cisplatin-loaded microspheres. After embolization of rat livers by microspheres, a histological study of the inflammatory response was made, along with gel permeation chromatography analysis of degrading polymers. The degradation rate of the polymers increased with the glycolic unit content in the lactic chains. Scanning electron microscopy of microsphere degradation in vitro correlated with the former observations.

Biodegradable microparticles for delivery of polypeptides and proteins.

Interest in the immobilization of polypeptides has caused various workers to develop methods for fabricating polypeptide-loaded microparticles from biodegradable polymers. A range of physical phenomena is used to form these microparticles. Thus far, all of the processes utilize a solvent or solvent combination. Selection of these solvents in such a manner that particles free of potentially harmful residual or entrapped material can be produced has not been discussed, but should receive full attention.

Formation and characterization of cisplatin loaded poly(d,l-lactide) microspheres for chemoembolization.

Cisplatin, a slightly water soluble anticancer drug, has been incorporated into biodegradable poly(d,l-lactide) microspheres using the solvent evaporation process. The optimal experimental conditions to produce spherical and separate drug-loaded particles (45% cisplatin) were as follows: the dispersing phase was a mixture of 0.05% methylcellulose and 4% polyvinyl alcohol (8 mPa-s grade); and the optimal poly(d,l-lactide) concentration in the organic phase was found to be greater than or equal to 7.16%. Microscopic studies showed that increasing the drug content in the microspheres produced the appearance of rod-like crystals at the microparticle surface. In addition, the cisplatin crystals were found homogeneously distributed in the polymer matrix, even at a high drug content. Increased viscosities of the organic phase enhanced the mean microsphere size, while increasing the emulsifier concentration in the aqueous phase decreased the average particle size. The drug incorporation efficiency was markedly improved after saturation of the dispersing phase with cisplatin. It was also noted that the amount of drug incorporated increased with increasing mean microsphere diameter. The methylene chloride content entrapped within the microspheres was found to depend upon the microsphere size distribution and the cisplatin content. An increase of the microsphere system porosity, by the addition of 10% cyclohexane in the organic phase, caused a reduction in the residual methylene chloride content. Finally, the in vitro release kinetics of cisplatin were influenced by the drug loading.