IGF-1 is degraded within minutes in the gut, but co-administration with casein protein significantly protects it from breakdown, suggesting a strategy for oral peptide delivery.
2-minute half-lifeIGF-1 was degraded with a half-life of just 2 minutes in the duodenum and ileum of fasted rats
What the researchers found
IGF-1 had a half-life of only 2 minutes in the duodenum and ileum, but casein protein significantly protected it from degradation in the gut.
Why it matters
This study addresses one of the biggest challenges in peptide therapeutics — oral bioavailability — and identified casein as a practical protective agent for gut-delivered peptides.
How the study worked
Researchers injected radiolabeled IGF-1 into ligated gut segments of fasted adult rats and measured its survival using three different assays (TCA precipitation, antibody binding, and receptor binding).
What this study cannot tell us
Animal study using ligated gut segments, which don't fully represent normal gut transit. The 8.6 ng dose is much smaller than therapeutic doses. Protection by casein may vary with different peptides.
How to read the evidence
Moderate animal evidence with rigorous methodology using three independent assays. Directly relevant to peptide delivery challenges but not yet tested in humans.
When this study was published
Published in 1995, this study remains relevant to ongoing research into oral peptide delivery strategies.
The bigger picture
Oral delivery of peptide therapeutics remains a major pharmaceutical challenge. This study's finding that a common milk protein can protect peptides from gut degradation opened a practical avenue for improving oral peptide bioavailability.
Questions still open
- Could casein-based formulations make oral peptide therapeutics viable?
- Does this protective effect extend to other peptides beyond IGF-1?
Common questions
Why can't most peptides be taken orally?
How does casein protect peptides?
Read the original research
Degradation of IGF-I in the adult rat gastrointestinal tract is limited by a specific antiserum or the dietary protein casein.
The Journal of endocrinology, 146(2), 215-25
Citation
Xian, C J; Shoubridge, C A; Read, L C. (1995). Degradation of IGF-I in the adult rat gastrointestinal tract is limited by a specific antiserum or the dietary protein casein.. The Journal of endocrinology, 146(2), 215-25.