Injectable system for spatio-temporally controlled delivery of hypoxia-induced angiogenic signalling

• Published in: Journal of controlled release 2012-08, Vol.161 (3), p.852-860
• Main Authors: Hadjipanayi, E., Cheema, U., Hopfner, U., Bauer, A., Machens, H.G., Schilling, A.F.
• Format: Article
• Language: English
• Subjects: angiogenesis; Angiogenic factor; bioactive properties; Biological and medical sciences; collagen; Collagen Type I - administration & dosage; Drug Delivery Systems; Fibroblast Growth Factors - administration & dosage; Fibroblast Growth Factors - metabolism; General pharmacology; Human Umbilical Vein Endothelial Cells; Humans; Hydrogels; Hypoxia; Hypoxia - metabolism; Hypoxia-Inducible Factor 1, alpha Subunit - administration & dosage; Hypoxia-Inducible Factor 1, alpha Subunit - metabolism; Injectable delivery; Injections; interleukin-8; Interleukin-8 - administration & dosage; Interleukin-8 - metabolism; Medical sciences; Neovascularization, Physiologic; oxygen; Pharmaceutical technology. Pharmaceutical industry; Pharmacology. Drug treatments; phase transition; Signal Transduction; Spatio-temporal control; temperature; tissues; Vascular Endothelial Growth Factor A - administration & dosage; Vascular Endothelial Growth Factor A - metabolism; vascular endothelial growth factors
• ISSN: 0168-3659; 1873-4995
• DOI: 10.1016/j.jconrel.2012.04.048

While chronically ischaemic tissues are continuously exposed to hypoxia, the primary angiogenic stimulus, they fail to appropriately respond to it, as hypoxia-regulated angiogenic factor production gradually undergoes down-regulation, thus hindering adaptive angiogenesis. We have previously reported on two strategies for delivering on demand hypoxia-induced signalling (HIS) in vivo, namely, implanting living or non-viable hypoxic cell-matrix depots that actively produce factors or act as carriers of factors trapped within the matrix during in vitro pre-conditioning, respectively. This study aims to improve this approach through the development of a novel, injectable system for delivering cell-free matrix HIS-carriers. 3D spiral collagen constructs, comprising an inner cellular and outer acellular compartment, were cultured under hypoxia (5% O2). Cell-produced angiogenic factors (e.g. VEGF, FGF, PLGF, IL-8) were trapped within the nano-porous matrix of the acellular compartment as they radially diffused through it. The acellular matrix was mechanically fragmented into micro-fractions and added into a low temperature (5°C) thermo-responsive type I collagen solution, which underwent a collagen concentration-dependent solution-to-gel phase transition at 37°C. Levels of VEGF and IL-8, delivered from matrix fractions into media by diffusion through collagen sol–gel, were up-regulated by day 4 of hypoxic culture, peaked at day 8, and gradually declined towards the baseline by day 20, while FGF levels were stable over this period. Factors captured within matrix fractions were bioactive after 3months freeze storage, as shown by their ability to induce tubule formation in an in vitro angiogenesis assay. This system provides a minimally invasive, and repeatable, method for localised delivery of time-specific, cell-free HIS factor mixtures, as a tool for physiological induction of spatio-temporally controlled angiogenesis. System for exposing cells to hypoxia to upregulate expression of angiogenic factor proteins, which can be time-dependently captured within an acellular nano-porous matrix. Factor-loaded matrix is subsequently fragmented and added to sol–gel delivery vehicle. [Display omitted]