Novel chemical modifications of the KTTKS peptide (Matrixyl®) produced potent plasmin inhibitors that were non-toxic to skin cells, though collagen-boosting effects lacked a clear dose-response pattern.
0% cytotoxicityNone of the novel KTTKS analogues were toxic to cultured fibroblasts, supporting their safety profile for potential skincare use.
What the researchers found
A series of novel KTTKS analogues — modified versions of the collagen-derived pentapeptide used in Matrixyl® skincare — were synthesized and tested for protease inhibition, cytotoxicity, and collagen stimulation in fibroblast cultures.
The palmitoyl-modified peptides were the most potent plasmin inhibitors, regardless of whether they were in acid or amide form. Swapping lysine for arginine in the sequences had no measurable biological effect. None of the synthesized analogues were cytotoxic to fibroblasts, and three of them promoted fibroblast cell growth. However, those three growth-promoting peptides did not show a clear concentration-dependent relationship in collagen or DNA biosynthesis assays.
Why it matters
KTTKS (marketed as Matrixyl®) is one of the most widely used peptides in anti-aging skincare. This study explored whether chemical modifications to the KTTKS backbone could improve its stability or biological activity. The finding that palmitoyl versions were strong plasmin inhibitors is notable because plasmin breaks down extracellular matrix proteins — blocking it could theoretically help preserve collagen in skin. The lack of cytotoxicity across all analogues is reassuring for potential topical applications.
How the study worked
Researchers designed and synthesized a series of pentapeptides based on the KTTKS sequence, modifying them with acetyl, lipoyl, or palmitoyl groups. They tested each analogue's ability to inhibit six proteases (urokinase, thrombin, trypsin, plasmin, t-PA, and kallikrein). Cytotoxicity was assessed on cultured fibroblasts, and selected peptides were further tested for their effects on collagen and DNA biosynthesis.
Who was studied
Cultured fibroblast cells (in vitro)
What this study cannot tell us
This was an in vitro study using cultured fibroblasts, so results may not translate to intact human skin. The peptides that promoted cell growth did not show dose-response relationships in collagen/DNA synthesis assays, making it hard to determine optimal concentrations. No skin penetration or in vivo testing was performed.
How to read the evidence
This is a preliminary in vitro study using cultured cells. While it demonstrates basic safety and biological activity, no animal or human testing was conducted, placing it at the earliest stage of evidence.
When this study was published
Published in 2019. The findings remain relevant to ongoing cosmetic peptide development, though newer analogues may have been developed since.
The bigger picture
As the cosmetic peptide market grows, researchers are looking for ways to improve on first-generation ingredients like Matrixyl®. This study adds to a growing body of work exploring how chemical modifications can enhance peptide stability and biological activity. The plasmin-inhibiting properties of the palmitoyl analogues suggest a dual mechanism — not just stimulating new collagen production, but also protecting existing collagen from enzymatic breakdown.
Questions still open
- Would these modified KTTKS analogues penetrate human skin effectively in a topical formulation?
- Why did the growth-promoting peptides fail to show dose-dependent collagen synthesis, and could different concentrations or exposure times change the outcome?
- Could combining plasmin inhibition with collagen stimulation in one peptide offer meaningful anti-aging benefits in vivo?
Common questions
What is KTTKS and why is it used in skincare?
Did this study prove these new peptides work better than regular Matrixyl?
Read the original research
The Effects of a Novel Series of KTTKS Analogues on Cytotoxicity and Proteolytic Activity.
Molecules (Basel, Switzerland), 24(20)
Citation
Tałałaj, Urszula; Uścinowicz, Paulina; Bruzgo, Irena; Surażyński, Arkadiusz; Zaręba, Ilona; Markowska, Agnieszka. (2019). The Effects of a Novel Series of KTTKS Analogues on Cytotoxicity and Proteolytic Activity.. Molecules (Basel, Switzerland), 24(20). https://doi.org/10.3390/molecules24203698