Small keratin peptides (under 3 kDa) successfully delivered insulin into intestinal cells without causing toxicity, opening a potential path for oral drug delivery.
8–19 amino acid fragmentsThe most effective keratin peptide fragments for cell penetration were 8–19 amino acids long, small enough to mimic cell-penetrating peptides
What the researchers found
Keratin peptides under 3 kDa (KEP1) showed the highest cell-penetrating ability at a concentration of 2 mg/mL. They delivered fluorescein-labeled insulin (FITC-INS) into Caco2 intestinal cells without covalent bonding, meaning the keratin peptides and insulin were simply mixed together.
The most effective keratin fragments were 8-19 amino acids long and included hydrophobic peptides (like RVVIEPSPVVV), PPII amphipathic peptides (like PPPVVVTFP), and cysteine-rich peptides (like LCAPTPCGPTPL). Uptake was energy-dependent and primarily used macropinocytosis. The peptides' rich hydrophobic residues and disulfide bonds contributed to their cell-penetrating ability.
Why it matters
Oral insulin delivery remains one of the holy grails of drug delivery. If keratin peptides can carry insulin across intestinal cell barriers, it could open a path toward oral insulin or oral delivery of other peptide drugs. Keratin is biocompatible, biodegradable, low-toxicity, and available from natural sources (hair, wool, feathers), making it a practical carrier material.
The numbers in context
- KEP1 (under 3 kDa): highest cell penetration at 2 mg/mL
- Most effective fragments: 8-19 amino acids long
- Uptake mechanism: energy-dependent macropinocytosis
- Key sequences identified: RVVIEPSPVVV, PPPVVVTFP, LCAPTPCGPTPL
- No covalent bonding needed between carrier and cargo
How the study worked
Researchers fractionated keratin into different molecular weight groups and tested each fraction's ability to enter Caco2 cells (a standard model for intestinal absorption). They used fluorescein-labeled insulin as a cargo molecule. They identified the most effective peptide sequences through further fractionation and analysis. Uptake mechanisms were studied using inhibitors of different cellular uptake pathways.
Who was studied
In vitro study using Caco2 human intestinal cells and fluorescein-labeled insulin
What this study cannot tell us
This was tested in Caco2 cells (intestinal cell line in a dish), not in a living organism. Cell culture uptake does not guarantee oral bioavailability in humans because the gut has mucus layers, enzymes, and other barriers not present in cell culture. The insulin was labeled with fluorescein for tracking, which may affect its behavior. No biological activity of the delivered insulin was confirmed.
How to read the evidence
Rated preliminary: in vitro study in Caco2 cells (a standard intestinal model) showing proof of concept. Far from clinical application.
When this study was published
Published in 2024. Oral drug delivery research using biological carriers is an active and growing field.
The bigger picture
Oral insulin delivery is a holy grail of drug delivery. If keratin peptides can carry insulin across the intestinal barrier, it could eventually eliminate the need for insulin injections — transforming daily life for millions of diabetic patients.
Questions still open
- Will keratin peptides protect insulin from stomach acid?
- Can this approach achieve therapeutic insulin levels in the blood?
- How does it compare to other oral delivery systems?
Common questions
What are keratin peptides?
Could this lead to oral insulin?
Read the original research
Enhanced Delivery of Biomolecules into Caco2 Cells Based on the Cell-Penetrating Ability of Keratin Peptides.
ACS applied materials & interfaces, 16(42), 56815-56825
Citation
Qin, Xiaojie; Guo, Yujie; Li, Ruilin; Bitter, Johannes H; Scott, Elinor L; Zhang, Chunhui. (2024). Enhanced Delivery of Biomolecules into Caco2 Cells Based on the Cell-Penetrating Ability of Keratin Peptides.. ACS applied materials & interfaces, 16(42), 56815-56825. https://doi.org/10.1021/acsami.4c13236