Design, development and optimization of methacrylic acid-based pH-responsive hydrogels for the oral delivery of model protein therapeutics

Protein therapeutics have tremendous potential to treat a variety of debilitating diseases, however, due to their large size and low stability, their administration has been limited to injections. An orally delivered carrier capable of protecting the protein during its transit through the gastrointestinal tract could potentially overcome the limits of protein stability, improve oral bioavailability, and provide a more patient tolerated means of protein administration. A pH-responsive hydrogel system composed of methacrylic acid, N-vinyl pyrrolidone, and poly(ethylene glycol), designated as P((MAA-co-NVP)-g-EG), was developed. The effects of crosslinking lengths and density and incorporation of poly(ethylene glycol) tethers on swelling behavior and loading capability of protein therapeutics were evaluated. It was shown that P((MAA-co-NVP-g-EG) swelled to a greater extent than P(MAA-co-NVP) in equilibrium studies at neutral pH and showed a faster rate of swelling in dynamic conditions. Mesh sizes ranged from 400-650 Å, which was deemed sufficient for drug loading and release. Three therapeutic proteins were evaluated for their loading capability: insulin, porcine growth hormone (pGH), and ovalbumin. The weight loading efficiencies of the proteins were optimized by varying pH and ionic strength and ranged from 8-9% for insulin, 6-7% for pGH, and 4-5% for ovalbumin. There was no discernible effect of crosslinking density and length on loading. The incorporation of PEG tethers showed a significant improvement in loading of human GH, increasing weight-loading efficiencies from 4.5 to 6.4%. When exposed to simulated gastrointestinal conditions, the loaded microparticles released ~10% of their hGH payload at intestinal pH. The hydrogels were also evaluated for their safety in vitro and in vivo. No cytotoxicity was observed in two model intestinal cell lines at dosages less than 2.5 mg/mL. When exposed to C57Bl/6 mice at 66.7 mg/kg dose, the hydrogels triggered no inflammatory response and no deleterious effects on organ function after acute and long-term administration. In model intestinal epithelial layers, both P((MAA-co-NVP)-g-EG) and P(MAA-co-NVP) hydrogels significantly improved transport of hGH over hGH alone. In vivo studies performed in Sprague Dawley rats confirmed that hGH-loaded hydrogels yielded hGH bioavailabilities ranging from 0.46-4.8%. Therefore, these pH-responsive hydrogels show great promise for oral protein delivery.