Characterization of water-in-oil microemulsion for oral delivery of earthworm fibrinolytic enzyme

Earthworm fibrinolytic enzyme (EFE-d, Mr 24177), a water-soluble protein, is clinically used for the management of cardiovascular diseases. However, this protein drug has a very low oral bioavailability because of its low oil/water partitioning, low membrane permeability and unstable nature in harsh gastric juice. This study explored the possibility of absorption and efficacy enhancement for EFE-d through the delivery of the water-in-oil (w/o) microemulsions. The w/o microemulsion consisting of Labrafac CC, Labrasol, Plurol Oleique CC 497 and saline (54/18/18/10, % w/w) was developed and characterized, including conductivity, viscosity, particle size and in vitro membrane permeability. The w/o microemulsion and the control solution of EFE-d were administered intraduodenally (or orally) to rats. The w/o microemulsion possessed a higher intestinal membrane permeability in vitro as well as a higher absorption and efficacy in vivo, when compared to control solution. The intraduodenal bioavailability of EFE-d for microemulsions was 208-fold higher than that of control solution and the absolute bioavailability was 17.55%. Meanwhile, there was no tissue damage of the intestinal mucosa found after oral multiple-dose administration of the EFE-d microemulsion to rats. These findings indicated that the w/o microemulsion may represent a safe and effective oral delivery system for hydrophilic bioactivity macromolecules.