Pharmacokinetic and pharmacodynamic profiles of recombinant human erythropoietin-loaded poly(lactic-co-glycolic acid) microspheres in rats.

AIM: To characterize the pharmacokinetic and pharmacodynamic profiles of the recombinant human erythropoietin (rhEPO)-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres in rats. METHODS: The rhEPO-loaded microspheres were prepared using a solid-in-oil-in-water emulsion method. Pharmacokinetics and pharmacodynamics of the rhEPO-loaded microspheres were evaluated in male Sprague-Dawley rats. The serum rhEPO level was determined with ELISA. The level of anti-rhEPO antibody in the serum was measured to assess the immunogenicity of rhEPO released from the microspheres. RESULTS: rhEPO was almost completely released from the PLGA microspheres in vitro, following zero-order release kinetics over approximately 30 d. After intramuscular injection (10,000 or 30,000 IU rhEPO/kg) in the rats, the serum rhEPO concentration reached maximum levels on d 1, then decreased gradually and was maintained at nearly steady levels for approximately 4 weeks. Furthermore, the release of rhEPO from the PLGA microspheres was found to be controlled mainly by a dissolution/diffusion mechanism. A good linear correlation (R(2)=0.98) was obtained between the in vitro and in vivo release data. A single intramuscular injection of the rhEPO-loaded PLGA microspheres (10,000 or 30,000 IU rhEPO/kg) in the rats resulted in elevated hemoglobin and red blood cell concentrations for more than 28 d. Moreover, the immunogenicity of rhEPO released from the PLGA microspheres was comparable with that of the unencapsulated rhEPO. CONCLUSION: The results prove the feasibility of using the PLGA-based microspheres to deliver rhEPO for approximately 1 month.

[Effect of NaCl in outer water phase on the characteristics of BSA-loaded PLGA sustained-release microspheres fabricated by a solid-in-oil-in-water emulsion technique].

The aim of this study is to investigate the critical factor affecting the properties of PLGA microspheres fabricated by a solid-in-oil-in-water (S/O/W) emulsion technique with BSA as a model protein. Prior to encapsulation, the BSA microparticles were fabricated by a modified freezing-induced phase separation method. The microparticles were subsequently encapsulated into PLGA microspheres by S/O/W emulsion method, then Motic BA200 biological microscope, confocal laser scanning microscope, scanning electron microscope were used to observe the structure of S/O/W emulsion and PLGA microspheres. The protein content extracted or released from BSA microspheres was measured by Bradford protein assay method. It was found that NaCl added in the outer aqueous phase effectively suppressed material exchange between the inner and outer phase of S/O/W emulsion. Then, the structure and permeability of obtained microspheres were influenced. As a result, with the increase of NaCl concentration in the outer aqueous phase, the encapsulation efficiency of microspheres significantly increased from 60% to more than 85%, the burst release of microspheres reduced from 70% to 20%, and the particle size decreased from 103 microm to 62 microm. Furthermore, the rehydration of encapsulated protein was also retarded and then integrity of BSA was successfully protected during encapsulation process. In vitro release test showed that BSA released from PLGA microspheres in a sustained manner for more than 30 days.

Stabilization and encapsulation of a staphylokinase variant (K35R) into poly(lactic-co-glycolic acid) microspheres.

The aim of this study is to prepare poly(lactic-co-glycolic acid) (PLGA) microspheres containing a staphylokinase variant K35R (DGR) with purpose of preserving the protein stability during both encapsulation and drug release. DGR-loaded microspheres are fabricated using a double-emulsion solvent extraction technique. Prior to encapsulation, the effect of ultrasonication emulsification of DGR solutions with methylene chloride on protein recovery was investigated. Moderate ultrasonic treatment of aqueous DGR/dichloromethane mixtures caused approximately 84% DGR aggregation. Polyvinyl alcohol (PVA) added into aqueous DGR solutions significantly improved DGR recovery to >90%. The effects of co-encapsulated PVA and NaCl in the external aqueous phase on the characteristics of the microspheres were investigated. When 2% PVA was co-encapsulated and 2.5% NaCl was added to the external water phase, DGR encapsulation efficiency was significantly increased from 7.1% to 78.1% and DGR was distributed uniformly throughout the microspheres. In vitro release test showed that DGR was released from PLGA microspheres in a sustained manner over 15 days. A large amount of released DGR was inactive in the absence of co-encapsulated PVA. On the contrary, when 2% PVA was co-encapsulated, the released DGR was almost completely intact within 9 days. In conclusion, PLGA microspheres can be an effective carrier for DGR and form a promising depot system.

Preparation and characterization of PLGA microspheres containing a staphylokinase variant (K35R).

AIM: To produce poly (lactic-co-glycolic acid) (PLGA) microspheres, containing a staphylokinase variant (K35R, DGR) with reduced immunogenecity and antiplatelet aggregation activities, which allowed the preservation of protein stability during both particle processing and drug release. METHODS: DGR-loaded microspheres were fabricated using a double emulsion-solvent evaporation technique. The effects of preparative parameters, such as stirring rate, polymer concentration, and the excipients of both internal and external aqueous phase (W2), on DGR encapsulation efficiency and microsphere characteristics were investigated. In vitro and in vivo release of DGR were conducted and the cause for instability of DGR during release was also investigated. RESULTS: Moderate ultrasonic treatment of aqueous DGR/dichloromethane mixtures caused approximately. Eighty four per cent DGR denaturation. However, the activity recovery of DGR almost amounted to 100% when 2% polyvinyl alcohol (PVA) was addled into the aqueous phase. It was found that NaCl in the external water phase significantly increased DGR encapsulation efficiency. Furthermore, NaCl in the external water phase played a role in determining size and surface morphology of microsphere. In vitro release test showed a burst release of DGR from microspheres, followed by sustained release of 50% total activity over 15 days. In vivo experiments showed that DGR released from microspheres sustained 5 days. Denaturation of DGR within microspheres might be resulted from acidic microclimate. CONCLUSION: The stability of DGR was effectively protected during microencapsulation and a relatively high encapsulation efficiency of DGR was obtained. PLGA microspheres could be an effective carrier for DGR.

[FTIR characterization of the secondary structure of a staphylokinase variant (K35R) encapsulated within PLGA microspheres].

The secondary structure of a staphylokinase variant (K35R, DGR) encapsulated in poly (lactic-co-glycolic acid) (PLGA) microspheres was quantitatively examined by Fourier transform infrared (FTIR) spectroscopy. Resolution enhancement technique and Fourier deconvolution were combined with band with curve-fitting procedures to quantitate the spectral information from the amide I bands. Nine component bands were found under the broad, nearly featureless amide I bands and assigned to alpha-helix, beta-sheet, turn and irregular (random) structures. The changes of bands at 1 651 and 1 623 cm(-1) after encapsulation were discussed.