A novel in vitro release technique for peptide containing biodegradable microspheres

Area of Science:

• Biomaterials Science
• Drug Delivery Systems
• Pharmacokinetics

Background:

• Poly(d,l-lactide-co-glycolide) (PLGA) microspheres are widely used for controlled peptide release.
• Accurate in vitro release testing is crucial for predicting in vivo performance.
• Existing in vitro methods may not fully capture the complex release kinetics influenced by pH and drug properties.

Purpose of the Study:

• To develop and validate a dialysis in vitro release technique for peptide-loaded PLGA microspheres.
• To ensure the developed technique correlates with in vivo release data.
• To evaluate the influence of pH on peptide solubility, stability, and microsphere properties.

Main Methods:

• Orntide acetate (a luteinizing hormone-releasing hormone analogue) loaded PLGA microspheres were prepared.
• In vitro release studies were conducted using a conventional extraction method and a novel dialysis method in phosphate buffer (PB) and acetate buffer (AB).
• Physicochemical characterization included drug content, particle size, morphology, polymer mass loss, hydration, and peptide adsorption. In vivo studies in rats assessed serum Orntide and testosterone levels.

Main Results:

• Orntide acetate solubility and stability were significantly pH-dependent, with higher solubility and stability in AB (pH 4.0) compared to PB (pH 7.4).
• The dialysis method in AB showed a higher overall release rate and better correlation with in vivo data compared to the conventional method in PB.
• Microsphere mass loss, hydration, and peptide adsorption were also influenced by buffer pH, with faster mass loss and lower adsorption in AB.

Conclusions:

• The pH of the buffer system critically affects peptide solubility, stability, and PLGA microsphere characteristics.
• The developed dialysis in vitro release technique in acetate buffer provides a more reliable prediction of in vivo peptide release from PLGA microspheres.
• This optimized in vitro method can aid in the development of effective long-acting injectable peptide formulations.