Stabilization of Glucagon by Trehalose Glycopolymer Nanogels
Abstract
Glucagon is a peptide hormone used for the treatment of hypoglycemia; however, its clinical potential is limited by its insolubility and instability in solution. Herein, the encapsulation, stabilization, and release of glucagon by trehalose glycopolymer nanogels are reported. Methacrylate-functionalized trehalose is copolymerized with pyridyl disulfide ethyl methacrylate using free radical polymerization conditions to form trehalose glycopolymers with thiol-reactive handles. Glucagon is chemically modified to contain two thiol groups and is subsequently utilized as the cross-linker to form redox-responsive trehalose nanogels with greater than 80% conjugation yield. Nanogel formation and subsequent glucagon stabilization are characterized using polyacrylamide gel electrophoresis, dynamic light scattering, and transmission electron microscopy. It is determined that the solution stability of the glucagon increased from less than 24 h to at least three weeks in the nanogel form. Additionally, in vitro activity of the synthesized glucagon analog and released glucagon is investigated, demonstrating that the glucagon remains active after modification. It is anticipated that these glucagon–nanogel conjugates will be useful as a stabilizing glucagon formulation, allowing for cargo release under mild reducing conditions.
Conclusion
The use of a modified glucagon to assemble and cross-link PDSMA-co-TrMA polymers into nanogels without the need for any additional reagents or cross-linkers is described. Nanogels were obtained with conjugation efficiency greater than 80%. Moreover, glucagon–nanogel conjugates exhibited superior stability in solution to aggregation compared to unencapsulated glucagon with the additional benefit of being soluble at both acidic and neutral pH. Glucagon release was observed under mild reducing conditions, suggesting that this encapsulation strategy may be a useful delivery vehicle. In addition to presenting a stabilizing nanogel system, we also synthesized a modified glucagon compound with a reactive functional handle. This modified glucagon was found to retain bioactivity both when conjugated and upon release, suggesting it may be a promising candidate for further study.
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