Branched Cell-Penetrating Peptides Improve Oral Insulin Delivery Through Intestinal Walls | Research

The takeaway

Branching cell-penetrating peptides into dimer and trimer forms significantly improved their ability to carry insulin across intestinal barriers, with dimeric penetramax confirmed as a potent carrier in animal studies.

Potency increased proportionally with branching degree
Branched penetratin and penetramax (dimers and trimers) significantly outperformed linear counterparts for intestinal insulin delivery, confirmed both in vitro and in vivo

What the researchers found

Branching cell-penetrating peptides (penetratin and penetramax) into dimer and trimer structures significantly increased their ability to enhance transepithelial permeation of insulin and other cargo molecules across Caco-2 cell monolayers. The enhancement correlated with the degree of branching — trimers outperformed dimers, which outperformed linear forms. The mechanism involved immediate and reversible effects on cell monolayer integrity and cytoskeletal alterations, consistent with paracellular transport. In vivo pharmacokinetic studies in rats confirmed that dimeric penetramax enhanced intestinal insulin delivery compared to linear penetramax.

Why it matters

Oral insulin has been a goal of diabetes research for decades, but the intestinal barrier has been the primary obstacle. Cell-penetrating peptides are among the most promising carriers, and this study shows that a simple structural modification — branching into dimers and trimers — dramatically increases their delivery potency. The reversibility of the effects on intestinal cells is also encouraging for safety.

The numbers in context

Dimer and trimer variants tested · Penetratin and penetramax peptides · Branching increased potency proportionally · Reversible effects on cell monolayers · In vivo confirmation with dimeric penetramax

How the study worked

Combined in vitro and in vivo study. Linear, dimer, and trimer versions of penetratin and penetramax were synthesized and tested using Caco-2 cell culture models for transepithelial permeation of insulin, dextran, mannitol, and metoprolol. Cell monolayer integrity and cytoskeletal changes were assessed. In vivo pharmacokinetic studies in rats evaluated dimeric penetramax as an insulin carrier, with histological assessment of intestinal tissue safety.

Who was studied

In vitro Caco-2 cell culture model and in vivo rat pharmacokinetic study for oral insulin delivery

What this study cannot tell us

Caco-2 cell models, while standard, do not fully replicate the complexity of the human intestine (mucus layer, immune cells, variable conditions). Only dimeric penetramax was tested in vivo, not the trimer variants. Long-term safety of repeated dosing with branched peptide carriers was not assessed. Specific blood glucose reduction data or bioavailability percentages are not provided in the abstract.

How to read the evidence

This is a preclinical study combining in vitro cell culture models with in vivo rat pharmacokinetic data. The mechanistic in vitro data is thorough and the in vivo confirmation is encouraging, but the technology has not been tested in humans and faces the typical translational challenges of oral peptide delivery systems.

When this study was published

Published in 2025, this is cutting-edge research in oral peptide delivery. The branching strategy for cell-penetrating peptides is a novel approach that could influence the design of future oral biologic formulations.

The bigger picture

Cell-penetrating peptides represent one of several approaches being pursued for oral macromolecular drug delivery, alongside nanoparticles, intestinal patches, and permeation enhancers. The branching strategy demonstrated here could potentially be applied to other peptide carriers and other biopharmaceutical cargos beyond insulin — including GLP-1 agonists, growth hormone, and monoclonal antibody fragments — expanding the toolkit for oral biologic delivery.

Questions still open

Would trimeric versions of penetramax show even greater insulin delivery in vivo than the dimer tested?
Is repeated daily dosing with branched cell-penetrating peptides safe for the intestinal epithelium over weeks or months?
Can this branching strategy be applied to other cell-penetrating peptide carriers to create a generalizable approach for oral biologic delivery?

Common questions

What are cell-penetrating peptides and how do they help with drug delivery?

Cell-penetrating peptides (CPPs) are short sequences of amino acids — typically 5 to 30 residues — that have the unusual ability to cross cell membranes and carry other molecules with them. When attached to drugs like insulin, they can help transport these large molecules across biological barriers that would normally block them, such as the intestinal wall. Penetratin, one of the peptides in this study, was originally discovered in a fruit fly protein.

What does 'branching' a peptide mean and why does it help?

Branching means connecting two (dimer) or three (trimer) copies of the peptide together in a tree-like structure rather than a single straight chain. This increases the peptide's interaction with cell membranes and its ability to temporarily open pathways between cells, allowing cargo like insulin to pass through more efficiently. Think of it like using multiple keys simultaneously to open a wider passage.

Read the original research

Branched penetratin and penetramax display enhanced intestinal insulin delivery potency compared to their linear counterparts.

Journal of controlled release : official journal of the Controlled Release Society, 380, 1031-1042

View on PubMed ↗Publisher’s paper ↗

Citation

Diedrichsen, Ragna Guldsmed; Mishra, Narendra Kumar; Fredholt, Freja; Heade, Joanne; Sørensen, Kasper Kildegaard; Jensen, Knud Jørgen; Nielsen, Hanne Mørck. (2025). Branched penetratin and penetramax display enhanced intestinal insulin delivery potency compared to their linear counterparts.. Journal of controlled release : official journal of the Controlled Release Society, 380, 1031-1042. https://doi.org/10.1016/j.jconrel.2025.02.044