Thierry Verrecchia

Non-stealth(poly(lactic acid/albumin))and stealth(poly(lactic acid-polyethylene glycol))nanoparticles as injectable drug carriers

Abstract Stealth liposomes and, today, stealth nanoparticles, constitute a new generation of parenteral therapeutic systems. PLA/ abumin nanoparticles are of particular interest because they constitute fully biodegradable and well tolerated colloidal suspensions. Solvent evaporation and microfluidisation did not damage the albumin molecules; therefore, PLA/albumin nanoparticles are no more immunogenic than native albumin in solution. However, rapid albumin exchanges on the nanoparticle surface probably does not prevent C3-complement binding and phagocytosis by the liver Kupffer cells. Because of their possible intracellular accumulation and toxicity, PLA/albumin nanoparticles are presumably limited to subcutaneous or intramuscular administration. Poly( d,l -lactide)-poly (ethylene glycol) (PLA-PEG) is a new biodegradable hydrophobic dibloc copolymer. The oriented PEG layer, coating the nanoparticle surface, dramatically increases the plasma half-life of the colloidal carrier (‘stealth nanoparticles’ ). In this way, the PLAPEG nanoparticle half-life is about 6 h instead of a few minutes as for PLA/ albumin or PLA/poloxamer 188-coated nanoparticles. The plasma clearance of a water-insoluble hydrophobic drug encapsulated in stealth nanoparticles and administered intravenously, decreases very significantly in comparison with non-stealth nanoparticles. PLAPEG nanoparticles can be considered as a sustained release parenteral (intravenous) dosage form.

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 Mies 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.

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.

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.

Simultaneous use of size-exclusion chromatography and photon correlation spectroscopy for the characterization of poly(lactic acid) nanoparticles

Abstract Fetuin-coated poly(lactic acid) particles of size range 50–200 nm were prepared by an emulsion, microfluidization and solvent evaporation method. The separation of 14 C-labelled particles made with 125 I-labelled protein by size-exclusion chromatography (SEC) was followed by the measurement in each collected fraction, of the average diameter of the particles by photon correlation spectroscopy, absorbance and concentrations by radioactivity counting. In one experiment, this showed that the dependence of the specific turbidity of the particles on their diameter correlated well with Mies theory. A first approximation of the particle size distribution could also be obtained together with the separation capacities of Sepharose CL-2B and Sephacryl S1000, in addition to the, amount of bound protein per unit surface area of the particles. Thus, the simultaneous use of size-exclusion chromatography and photon correlation spectroscopy was found to be a powerful tool that needed neither column dispersion function analysis nor any column standardization.