Sustained-release of erythropoietin using a novel injectable thermosensitive hydrogel: in vitro studies, biological activity, and efficacy in rats

In the current study erythropoietin (EPO) loaded trimethyl chitosan/tripolyphosphate nanoparticles-embedded in a thermosensitive hydrogel was prepared. The influence of the main experimental factors on the properties of EPO-loaded nanoparticles were evaluated using a two-factors central composite design and the optimized formulation was then freeze dried. Sodium dodecyl sulfate-page and circular dichroismspectroscopy were used to confirm the structural stability of EPO following encapsulation and freeze drying. Rheological properties, and the release rate of EPO from the hydrogel were examined. Mean particle size, zeta potential, and entrapment efficiency of the optimized EPO-loaded nanoparticles were confirmed 151.5 ± 16 nm, 11.5 ± 1.8 mV, and 78.5 ± 5.9%, respectively. The hydrogel containing nanoparticles existed as a solution at room temperature converted to a semisolid upon increasing the temperature to 35 ± 1.2 °C and demonstrated controlled release of EPO for more than 10 days. The stability of EPO in the hydrogel system was further investigated using in vivo biological activity assay and the result revealed relative potency of 0.85 as calibrated with standard EPO. Finally, a single injection of the EPO-loaded nanoparticles-embedded in the hydrogel administered to Sprague-Dawley rats resulted in elevated reticulocytes for about 20 days compared to control group received blank hydrogel.