Urease catalyzed high-density sodium alginate microspheres enable high oral bioavailability of macromolecular drugs

Destruction of insulin caused by the gastric microenvironment and rapid deactivation pose inevitable barriers to oral macromolecular absorption, especially for most peptide and protein drugs. In this study, we developed high-density sodium alginate microspheres composed of magnesium oxide and urease to address these challenges. These microspheres aim to anchor the gastric mucus layer and induce microenvironmental liquefaction, thereby enhancing gastric retention and the protection of insulin. The sedimentation test confirmed the capability of the Ins/Ur/MgO@SA microsphere to rapidly traverse the gastric juice under the influence of gravity. Additionally, the urease immobilized on the Ins/Ur/MgO@SA microspheres catalyzes the hydrolysis of urea in the gastric mucus and promotes the liquefaction of mucus, which is beneficial for microsphere retention. The inclusion of MgO particles and urease, acting as pH_M modifiers, helps in adjusting the local pH to avoid gastric acid-induced damage. Subsequently, an in vivo pharmacokinetic experiment verified that the relative bioavailability of the p.o. Ins/Ur/MgO@SA treated group was 15-fold higher than that of the p.o.insulin treated group. Meanwhile, satisfactory blood glucose level (BGL) reduction was observed in diabetic animals. In conclusion, Ins/Ur/MgO@SA microspheres demonstrate high biocompatibility as insulin carriers with prolonged drug release time and increased gastric retention properties, showing a far-reaching strategy for oral macromolecular drug delivery.