Structural insights into pH-responsive drug release of self-assembling human serum albumin-silk fibroin nanocapsules

Claudia Tallian, Alexandra Herrero-Rollett, Karina Stadler, Robert Vielnascher, Karin Wieland, Anna M. Weihs, Alessandro Pellis, Andreas H. Teuschl, Bernhard Lendl, Heinz Amenitsch, Georg M. Guebitz

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Inflammation processes are associated with significant decreases in tissue or lysosomal pH from 7.4 to 4, a fact that argues for the application of pH-responsive drug delivery systems. However, for their design and optimization a full understanding of the release mechanism is crucial. In this study we investigated the pH-depending drug release mechanism and the influence of silk fibroin (SF) concentration and SF degradation degree of human serum albumin (HSA)-SF nanocapsules. Sonochemically produced nanocapsules were investigated regarding particle size, colloidal stability, protein encapsulation, thermal stability and drug loading properties. Particles of the monodisperse phase showed average hydrodynamic radii between 438 and 888 nm as measured by DLS and AFM and a zeta potential of −11.12 ± 3.27 mV. Together with DSC results this indicated the successful production of stable nanocapsules. ATR-FTIR analysis demonstrated that SF had a positive effect on particle formation and stability due to induced beta-sheet formation and enhanced crosslinking. The pH-responsive release was found to depend on the SF concentration. In in-vitro release studies, HSA-SF nanocapsules composed of 50% SF showed an increased pH-responsive release for all tested model substances (Rhodamine B, Crystal Violet and Evans Blue) and methotrexate at the lowered pH of 4.5 to pH 5.4, while HSA capsules without SF did not show any pH-responsive drug release. Mechanistic studies using confocal laser scanning microscopy (CLSM) and small angle X-ray scattering (SAXS) analyses showed that increases in particle porosity and decreases in particle densities are directly linked to pH-responsive release properties. Therefore, the pH-responsive release mechanism was identified as diffusion controlled in a novel and unique approach by linking scattering results with in-vitro studies. Finally, cytotoxicity studies using the human monocytic THP-1 cell line indicated non-toxic behavior of the drug loaded nanocapsules when applied in a concentration of 62.5 µg mL−1. Based on the obtained release properties of HSA-SF nanocapsules formulations and the results of in-vitro MTT assays, formulations containing 50% SF showed the highest requirements arguing for future in vivo experiments and application in the treatment of inflammatory diseases.

Original languageEnglish
Pages (from-to)176-187
Number of pages12
JournalEuropean journal of pharmaceutics and biopharmaceutics
Volume133
DOIs
Publication statusPublished - 1 Dec 2018

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Keywords

  • Beta-sheet induction
  • Diffusion controlled release
  • HSA
  • pH-responsive drug release
  • Porod constant
  • Schulzsphere approximation
  • Silk
  • Small angle X-ray scattering
  • Sonochemistry

ASJC Scopus subject areas

  • Biotechnology
  • Pharmaceutical Science

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