Objectives We designed a series of formulations of rhGH PK3/PLGA microspheres with different PK3/PLGA ratios to improve the stability and incomplete release of rhGH with the aim of achieving long-acting sustained-release rhGH microspheres. PK3 can undergo acid-catalyzed hydrolysis into low molecular weight hydrophilic compounds and release encapsulated drugs at an accelerated rate in acidic environments. PK3/PLGA microspheres effectively avoided the influence of the acidic environment produced by the degradation of PLGA on rhGH stability and solved the problem of difficult release of denaturated rhGH. The microspheres improved the poor mechanical properties of PK3 microspheres due to low molecular weights.
Methods We used a W/O/W double-emulsion technique to prepare rhGH microspheres. Briefly, 100 µL of 40 mg/mL rhGH was dissolved in 2 mL of acetone/methylene chloride solution (0.8:1.2) containing PK3/PLGA blends and homogenized at 6000 rpm for 120 s in an ice bath. The primary emulsion was injected into an aqueous solution containing 0.5% (w/v) PVA and 3% (w/v) NaCl and homogenized at 6000 rpm for 120 s. Microspheres were obtained by evaporating the organic solvents and centrifuging at 5000 rpm. We investigated the effects of different PK3/PLGA ratios (10:0, 8:2, 6:4, 5:5, 4:6, 2:8, 0:10) and the buffer pH value (pH 4.5, pH 7.4) on the in vitro release of rhGH microspheres. We studied the structural stability of rhGH in release medium and inside the microspheres.
Results Native PAGE results revealed the microspheres displaying enhanced structural stability of rhGH with a neutral microenvironment compared with PLGA microspheres. With an increase in PK3 ratios, the microspheres showed reduced incomplete release and increased total release of rhGH. When the PK3/PLGA ratios were above PK3-PLGA mass ratio 5:5, the mixing microspheres had a low balling rate and irregular form.
Conclusions The optimal ratio of PK3/PLGA was 3:7, producing significant rhGH stability and an in vitro release profile with less burst release and extended sustained release.
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