College of Pharmacy, Freie Universität Berlin, Kelchstrasse 31, 12169 Berlin, Germany.
College of Pharmacy, Freie Universität Berlin, Kelchstrasse 31, 12169 Berlin, Germany; Pensatech Pharma GmbH, Kelchstrasse 31, 12169 Berlin, Germany.
Int J Pharm. 2018 Mar 1;538(1-2):139-146. doi: 10.1016/j.ijpharm.2018.01.026. Epub 2018 Jan 31.
The objectives of this study were to assess the feasibility of hot melt extrusion (HME) for the preparation of PLGA-based ovalbumin-loaded implants as well as to characterize and improve protein release from the implants. Ovalbumin (OVA) was stable during extrusion, which was attributed to a protective effect of the biodegradable matrix. OVA release was characterized by a low burst, a slow release up to day 21, which plateaued thereafter resulting in incomplete release for all evaluated protein loadings. Release incompleteness was accompanied by the formation of an insoluble residual mass. Further characterization of this mass indicated that it consisted of non-covalent protein aggregates and polymer, where ovalbumin was ionically bound as the pH inside the degrading matrix decreased below the pI of the protein. Although higher protein release was obtained with the inclusion of weak bases because of their neutralizing effect, OVA aggregation and release incompleteness were not fully avoided. With the use of shellac, a well-known enteric and biocompatible polymer, as protective excipient, a distinct late release phase occurred and release completeness was increased to more than 75% cumulative release. Shellac apparently protected the protein against the acidic microclimate due to its low solubility at low pH. Protected OVA was thus released once the pH increased due to a declining PLGA-oligomer formation. The result was a triphasic release profile consisting of an initial burst, a slow diffusion phase over about 7 weeks, and an erosion-controlled dissolution phase over the next 3 weeks. An acid-labile protein like OVA was thus feasibly protected from interactions with PLGA and its degradation products, resulting in a controlled delivery of more than 85% of the original payload.
本研究的目的是评估熔融挤出（HME）制备基于 PLGA 的卵清蛋白负载植入物的可行性，以及表征和改善植入物中蛋白质的释放。在挤出过程中卵清蛋白（OVA）是稳定的，这归因于可生物降解基质的保护作用。OVA 释放的特点是突释低、直至第 21 天缓慢释放，此后达到平台期，导致所有评估的蛋白载量均不完全释放。释放不完全伴随着不溶性残余物的形成。对这种残余物的进一步表征表明，它由非共价的蛋白质聚集体和聚合物组成，其中卵清蛋白作为降解基质内的 pH 降低到蛋白质的等电点以下时通过离子键结合。尽管由于弱碱的中和作用，蛋白质的释放量更高，但卵清蛋白的聚集和释放不完全仍然没有完全避免。使用虫胶作为一种众所周知的肠溶和生物相容的聚合物作为保护赋形剂，会出现明显的后期释放阶段，并且使释放完全度提高到超过 75%的累积释放度。虫胶显然由于其在低 pH 下的低溶解度而保护了蛋白质免受酸性微环境的影响。因此，一旦由于 PLGA-低聚物形成减少而导致 pH 增加，就会释放出受保护的 OVA。结果是形成了一个三相释放曲线，包括初始突释、大约 7 周的缓慢扩散相和接下来 3 周的侵蚀控制溶解相。像 OVA 这样的酸不稳定蛋白因此可以防止与 PLGA 及其降解产物相互作用，从而实现超过 85%的原始载药量的控制释放。
