How Cell-Penetrating Peptides Interact With Membranes: Implications for Oral Insulin Delivery | Research

The takeaway

Three carrier peptides used for oral insulin delivery each interacted differently with model cell membranes — penetratin caused irreversible clustering while its analogues were reversible — but none disrupted the membranes, supporting their safety for drug delivery.

No membrane disruption
All three cell-penetrating peptides interacted with liposome membranes without breaking them — a key safety requirement for oral drug delivery

What the researchers found

All three cell-penetrating peptides — penetratin, shuffle, and penetramax — adsorbed to lipid bilayer surfaces and induced liposome clustering at specific peptide-to-lipid ratios. However, the nature of their interactions differed significantly: penetratin caused irreversible clustering, penetramax caused partly reversible clustering, and shuffle caused fully reversible clustering.

Shuffle and penetramax additionally caused liposome shape deformation, while penetratin did not. Importantly, none of the peptides disrupted liposome integrity under any tested conditions, meaning they interact with membranes without destroying them — a critical requirement for safe drug delivery applications.

Why it matters

Oral delivery of peptide drugs like insulin could eliminate the need for daily injections for millions of diabetes patients. Understanding exactly how carrier peptides interact with gut cell membranes — without damaging them — is essential for designing safe and effective oral peptide delivery systems. The reversibility differences between these peptides could influence which is best suited for clinical use.

How the study worked

Peptide-liposome interactions were studied using small-angle neutron scattering (SANS) and fluorescence lifetime imaging microscopy (FLIM). Liposomes served as model cell membranes. The three carrier peptides (penetratin, shuffle, and penetramax) were tested at various peptide-to-lipid ratios to characterize membrane adsorption, clustering behavior, reversibility, and structural integrity.

What this study cannot tell us

Liposomes are simplified models that do not capture the full complexity of living cell membranes, which contain proteins, sugars, and asymmetric lipid compositions. The study did not assess whether the observed membrane interactions translate to actual drug transport across biological barriers. In vivo conditions including enzymes, mucus, and pH changes in the gut were not modeled.

How to read the evidence

This is a biophysical laboratory study using model membrane systems (liposomes). While the techniques are sophisticated (SANS, FLIM), the findings are mechanistic and have not been validated in biological tissue or in vivo models.

When this study was published

Published in 2023, this study reflects the current state of biophysical research into peptide-based drug delivery and uses advanced techniques to address a long-standing question in the oral peptide delivery field.

The bigger picture

Oral delivery of peptide therapeutics is one of the biggest challenges in pharmaceutical science. Cell-penetrating peptides represent one of the most promising strategies for enabling oral bioavailability of drugs like insulin. This biophysical study provides the mechanistic foundation needed to rationally design and optimize carrier peptide sequences for this purpose, moving beyond trial-and-error approaches.

Questions still open

Does the reversibility of membrane clustering correlate with better drug delivery efficiency or safety in living tissue?
Which of these carrier peptides — penetratin, shuffle, or penetramax — is most effective at transporting insulin across real intestinal epithelium?
Can the sequence modifications that make shuffle and penetramax reversible be further optimized for clinical oral peptide delivery?

Common questions

Why can't you just take insulin as a pill?

Insulin is a peptide that gets destroyed by stomach acid and digestive enzymes before it can be absorbed. Even if it survives digestion, it's too large to easily cross the gut lining into the bloodstream. Carrier peptides like those in this study can potentially shuttle insulin across the gut barrier by interacting with cell membranes in a way that allows the drug to pass through without damaging the cells.

What makes these three carrier peptides different from each other?

Penetratin is the original cell-penetrating peptide, while shuffle and penetramax are modified versions with rearranged amino acid sequences. Despite their similarities, they interact with membranes quite differently: penetratin sticks permanently to membranes, shuffle's effects are fully reversible, and penetramax falls in between. These differences could determine which is safest and most effective for carrying drugs across biological barriers.

Read the original research

Carrier peptide interactions with liposome membranes induce reversible clustering by surface adsorption and shape deformation.

Journal of colloid and interface science, 650(Pt B), 1821-1832

View on PubMed ↗Publisher’s paper ↗

Citation

Diedrichsen, Ragna Guldsmed; Vetri, Valeria; Prévost, Sylvain; Foderà, Vito; Nielsen, Hanne Mørck. (2023). Carrier peptide interactions with liposome membranes induce reversible clustering by surface adsorption and shape deformation.. Journal of colloid and interface science, 650(Pt B), 1821-1832. https://doi.org/10.1016/j.jcis.2023.07.078