Table 2.

Overview of peptide modifications and delivery systems associated with their site of action.

Goal of modification	Peptide
Stomach
Increased Stability	PEG, d-amino acids, nanoparticles, SLN
Small intestine
Increased Stability	Cyclization, PEG, lipidization, d-amino acids, polymer matrices, nanoparticles, esterification, N-acetylation
Enzyme Inhibitors	Soybean trypsin inhibitor, aprotinin, puromycin, bacitracin
Absorption Enhancers	Chitosans, fatty acids, lectins, ZOT, CPP, liposomes, nanoemulsions, mucoadhesive polymers, nanoparticles, SLN
Circulation
Increased Stability	PEG, hyperglycosylation, liposomes, nanoparticles
Targeting	Antibody CPP

CPP: Cell-penetrating peptide; SLN: Solid lipid nanoparticle; ZOT: Zonula occludens toxin.