Recent progress in the oral delivery of therapeutic peptides and proteins: Overview of pharmaceutical strategies to overcome absorption hurdles

Objective: This review aims to critically examine and summarize the innovations and mechanisms involved in oral delivery of peptide and protein drugs. Significance: Proteins and peptides have secured a place as excellent therapeutic moieties on account of their high selectivity and efficacy. However due to oral absorption limitations, current formulations are mostly delivered parenterally. Oral delivery of peptides and proteins can be considered the need of the hour due to the immense benefits of this route. Methods: Comprehensive literature search was undertaken, spanning the early development to the current state of the art, using online search tools (PubMed, Google Scholar, ScienceDirect and Scopus). Results: Research in oral delivery of proteins and peptides has a long and rich history and the development of biologics has encouraged additional research effort in recent decades. Enzyme hydrolysis and inadequate permeation into intestinal mucosa are the major causes that result in limited oral absorption of biologics. Pharmaceutical and technological strategies including use of absorption enhancers, enzyme inhibition, chemical modification (PEGlyation, pro-drug approach, peptidomimetics, glycosylation), particulate delivery (polymeric nanoparticles, liposomes, micelles, microspheres), site-specific delivery in the GIT, membrane transporters, novel approaches (self-nanoemulsifying drug delivery systems, Eligen technology, peptelligence, self-assembling bubble carrier approach, luminal unfolding microneedle injector, microneedles) and lymphatic targeting, are discussed. Limitations of these strategies and future innovations for improving oral bioavailability of protein and peptide drugs are also discussed. Conclusion: This review underlines the application of oral route for peptide and protein delivery, which can direct the formulation scientist for better exploitation of this route.