Parenteral protein delivery systems using biodegradable polyesters of ABA block structure, containing hydrophobic poly(lactide-co-glycolide) A blocks and hydrophilic poly(ethylene oxide) B blocks

Recombinant human erythropoietin (rhEPO) loaded poly(lactide-co-glycolide) microspheres: influence of the encapsulation technique and polymer purity on microsphere characteristics

Recombinant human erythropoietin (EPO) and fluorescein isothiocyanate-labelled dextran (FITC-dextran) loaded biodegradable microspheres were prepared from poly(lactide-co-glycolide) (PLG) by a modified spray-drying technique. This microencapsulation method was compared with the water-in-oil-in-water (w/o/w) double-emulsion method. As expected, microsphere morphology, particle size and particle size distribution strongly depended on the production process. The spray-drying method was found to have a number of advantages compared to the w/o/w double-emulsion technique. The content of residual dichloromethane (DCM) in the final product was significantly lower in case of the microspheres prepared by spray-drying. Concerning EPO loaded microspheres, spray-drying yielded higher encapsulation efficiencies. Although the microspheres obtained by spray-drying are subjected to intensive mechanical and thermal stress during the preparation, the amount of aggregates of EPO in PLG microspheres were not increased compared to the w/o/w technique. Depending on the manufacturing method, addition of cyclic DL-lactide dimers (referred to as monomers in the following) affected the in vitro release profiles of EPO and FITC-dextran from PLG microspheres. Using differential scanning calorimetry it was shown that these low molecular weight substances only seem to be present inside the microspheres produced by spray-drying. DL-Lactide significantly reduced the initial burst release of both EPO and FITC-dextran. While the following release period of EPO was not affected by the DL-lactide content, a more linear FITC-dextran release pattern could be achieved. It can be concluded that the spray-drying technique provides a number of advantages compared to the w/o/w method. The modulation of protein release using low molecular weight additives is of particular interest for parenteral depot systems.

Labelling peptides with fluorescent probes for incorporation into degradable polymers

Two peptides, atrial natriuretic peptide (ANP) and salmon calcitonin (sCT) were conjugated with a fluorescent, amine-reactive probe 5-(and 6-)carboxytetramethylrhodamine,-succinimidylester (5-(6)-TAMRA-SE). The labelling reaction was followed by HPLC and found to be complete after 2 h. The labelled peptides were purified by gel filtration chromatography and characterised by [1H]NMR, UV/VIS and fluorescence spectroscopy. NMR-spectra confirmed the conjugation of dye to the peptides. Two absorption maxima between 500 and 600 nm were recorded in the UV/VIS-spectra. The fluorescence spectra were found to be pH-dependent, which allowed the measurement of pH in aqueous solution. The labelled peptides were encapsulated into poly(lactic acid) (PLA) microspheres using a double emulsion technique. Probe attachment permitted location of the peptides in the polymer.