Protease Degradation of Peptides
The digestive tract is designed to cut proteins into amino acids, and it does not distinguish a therapeutic peptide from a meal. Pepsin, pancreatic proteases and brush-border peptidases degrade most unprotected peptides within minutes, which is the first reason nearly all peptide therapeutics are injected.
The enzymes involved
In the stomach, pepsin cleaves at hydrophobic and aromatic residues. In the intestinal lumen, trypsin, chymotrypsin, elastase and carboxypeptidases from the pancreas cut at specific residue types. At the epithelium, brush-border enzymes such as aminopeptidase N and dipeptidyl peptidase IV, plus gamma-glutamyl transferase for glutathione, trim what remains. Short linear peptides without protective modifications are the most vulnerable. Together these enzymes can reduce an unprotected peptide dose to fragments before most of it reaches the absorptive surface.
How the field responds
Medicinal chemists modify the peptide itself: D-amino acids, N-methylation, cyclization and fatty acid side chains, as used in semaglutide. Formulators add protease inhibitors such as aprotinin or soybean trypsin inhibitor, acidifiers such as citric acid to suppress pH-dependent proteases, and enteric coatings. These approaches improve stability but still leave permeability as the rate-limiting step. Even the best combinations of these strategies deliver only a small fraction of the dose intact and absorbed.
Peptides this affects
Every peptide in our compound library faces this barrier when taken by mouth, from the small tripeptides glutathione and GHK-Cu to incretin analogs, BPC-157 and thymosin fragments. Size, sequence and modifications change how fast each is cut, so protease stability is measured per compound rather than assumed. Regulatory status also varies widely across these peptides, from approved drugs to unapproved research compounds, and each profile states it plainly. Stability is tested per sequence.
Key facts
- Luminal and brush-border proteases are a primary barrier to oral peptide delivery (Drucker 2020, Nat Rev Drug Discov)
- Semaglutide's fatty acid side chain and Aib substitution protect against DPP-4 and support albumin binding (Lau et al. 2015, J Med Chem)
- Native GLP-1 is inactivated by DPP-4 with a plasma half-life of about 2 minutes (Deacon et al. 1995, Diabetes)
- Gamma-glutamyl transferase on cell surfaces initiates glutathione breakdown (Wu et al. 2004, J Nutr)
How our delivery technology applies
Protease shielding is where layered encapsulation is most mechanistically direct. Dense biopolymer layers can physically exclude enzymes of 20 to 35 kDa while the peptide remains inside, and layers can co-load local protease inhibitors or acidifiers. Protection is measured as intact peptide recovered after sequential simulated gastric and intestinal digestion. Shielding does not solve permeability, so both are reported.
Propose a peptide for our protease-shielding screen.
Related reading
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