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Six different commercial feeds used in weaning and postweaning of marine fish were analysed from the perspective of some of their main physico-chemical features and in vitro digestibility. While the range of particle sizes in dry state closely agreed to those claimed by the producing companies, dramatic changes were observed after suspension in water. Sedimentation rates measured in some of the feeds with higher particle sizes may be too high to ensure intake by young fish. The label claims of the products overestimate the amount of total protein but underestimate that of lipids. The analysis of amino acid profiles evidenced important differences in total amino acid composition between feeds of the same company but a great similitude in the profile of free amino acids (FAA). The evaluation of leaching evidenced that the fraction of FAA, which represented, This research was funded by project AGL2007-64450-CO2-02.

OBJECTIVES: For the treatment of septic arthritis in large animals, the local application of antibiotics as a slow release system may be an appropriate means to reach high local bioactivity and low systemic side effects and drug residues. In this study, doxycycline microspheres were developed and tested in vitro for their drug-release properties, suitability for intra-articular application and antimicrobial activity. METHODS: The development of a slow release system was achieved by microencapsulation of the drug into poly(lactide-co-glycolide) microspheres by a novel ultrasonic atomization method. Drug elution was evaluated from microspheres dispersed in elution medium at pre-defined time points by HPLC. Joint-tissue compatibility was tested on cultured bovine synoviocytes by evaluating the expression of pro-inflammatory cytokine mRNA and the production of nitric oxide (NO). Finally, the antimicrobial activity of the released antibiotic was assessed with gram-negative and gram-positive bacteria exposed to release medium sampled at days 1, 7 and 12 after microsphere suspension. RESULTS: An adequate size of the microspheres, sufficient stabilization of doxycycline in aqueous environment and drug release (25 mg microspheres in 4 mL medium) above MIC for bacteria usually isolated in bovine and equine joints were obtained over 15 days. Although the cytokine mRNA expression reflected the excellent tissue compatibility, the results with NO yielded contradictory results. Antimicrobial tests of the release medium proved to match perfectly the activity of non-encapsulated, free doxycycline as reported in the literature. CONCLUSIONS: The newly developed doxycycline delivery system achieved the target specifications and is ready for in vivo testing

The determination of in vitro release kinetics of peptides from poly(d,l-lactide-co-glycolide) (PLGA) microspheres generally requires optimization of the test conditions for a given formulation. This is particularly important when in vitro/in vivo correlation should be determined. Here, the somatostatin analogue vapreotide pamoate, an octapeptide, was microencapsulated into PLGA 50:50 by spray-drying. The solubility of this peptide and its in vitro release kinetics from the microspheres were studied in various test media. The solubility of vapreotide pamoate was approximately 20–40 μg/ml in 67 mM phosphate buffer saline (PBS) at pH 7.4, but increased to approximately 500–1000 μg/ml at a pH of 3.5. At low pH, the solubility increased with the buffer concentration (1–66 mM). Very importantly, proteins (aqueous bovine serum albumin (BSA) solution or human serum) appeared to solubilize the peptide pamoate, resulting in solubilities ranging from 900 to 6100 μg/ml. The release rate was also greatly affected by the medium composition. Typically, in PBS of pH 7.4, only 33±1% of the peptide were released within 4 days, whereas 53±2 and 61±0.9% were released in 1% BSA solution and serum, respectively. The type of medium was found critical for the estimation of the in vivo release. The in vivo release kinetics of vapreotide pamoate from PLGA microspheres following administration to rats were qualitatively in good agreement with those obtained in vitro using serum as release medium. Finally, sterilization by γ-irradiation had only a minor effect on the in vivo pharmacokinetics.

The determination of in vitro release kinetics of peptides from poly(d,l-lactide-co-glycolide) (PLGA) microspheres generally requires optimization of the test conditions for a given formulation. This is particularly important when in vitro/in vivo correlation should be determined. Here, the somatostatin analogue vapreotide pamoate, an octapeptide, was microencapsulated into PLGA 50:50 by spray-drying. The solubility of this peptide and its in vitro release kinetics from the microspheres were studied in various test media. The solubility of vapreotide pamoate was approximately 20–40 μg/ml in 67 mM phosphate buffer saline (PBS) at pH 7.4, but increased to approximately 500–1000 μg/ml at a pH of 3.5. At low pH, the solubility increased with the buffer concentration (1–66 mM). Very importantly, proteins (aqueous bovine serum albumin (BSA) solution or human serum) appeared to solubilize the peptide pamoate, resulting in solubilities ranging from 900 to 6100 μg/ml. The release rate was also greatly affected by the medium composition. Typically, in PBS of pH 7.4, only 33±1% of the peptide were released within 4 days, whereas 53±2 and 61±0.9% were released in 1% BSA solution and serum, respectively. The type of medium was found critical for the estimation of the in vivo release. The in vivo release kinetics of vapreotide pamoate from PLGA microspheres following administration to rats were qualitatively in good agreement with those obtained in vitro using serum as release medium. Finally, sterilization by γ-irradiation had only a minor effect on the in vivo pharmacokinetics.

The chemical conjugation or the physical embodiment of therapeutic agents in polymers offers great potential to improve the efficacy and safety of therapies and create novel therapeutic opportunities. This has led to numerous concepts regarding the formulation, the delivery and the targeting of therapeutics. Our current research portfolio in this field includes several projects. In all of them poly(lactide-co-glycolide), PLGA, varying in molecular weight and end-group modification, is used as a delivery platform. In this review we will firstly outline our concept of single-injection vaccines. Instead of the application of repeated booster doses, such vaccines are designed to deliver the antigen in a pulsed or sustained fashion, in such a way that protective humoral and cellular immunity can be achieved after a single injection. In the second polymer-based project we aim at the administration of insulin-like growth factor I (IGF-I), which bears great potential in tissue engineering, e.g. to enhance bone healing. Here we summarize on a PLGA microsphere system for the localized and controlled delivery of IGF-I in order to close bone defects after fracture, pathology or surgery. In a third project we use this polymeric platform for the design of antigen-encoding DNA vaccines designed to preferentially target the most potent antigen presenting cells, i.e. the dendritic cells. Two prime objectives are currently being studied, i) enhancement of phagocytosis of DNA-loaded PLGA microspheres by human-derived dendritic cells, and ii) release of intact plasmid DNA and concomitant transfection of dendritic cells once the PLGA microspheres were successfully phagocytosed.