Tripeptide-10 Citrulline (Decorinyl)

Tripeptide-10 Citrulline, commercially known as Decorinyl (trade name from Lipotrue SL), is a synthetic tripeptide (Asp-Lys-Citrulline) designed to mimic the active site of decorin — a small leucine-rich proteoglycan that plays a fundamental role in collagen fibril assembly and organization in the extracellular matrix.

Decorin is named for its function: it "decorates" collagen fibrils by binding to their surface and regulating the lateral fusion of collagen molecules during fibril assembly. Decorin's core protein contains a leucine-rich repeat (LRR) domain that interacts with specific sites on collagen type I and II fibrils. This interaction: 1. Controls collagen fibril diameter (decorin-deficient mice have abnormally large, irregular collagen fibrils) 2. Regulates fibril spacing in the ECM 3. Influences the mechanical properties of connective tissues

**Scar tissue and fibrosis connection:** In normal wound healing and in scarring (particularly hypertrophic scars and keloids), the collagen deposited during repair is often disorganized — fibers are thicker, randomly oriented, and packed in a "whorled" pattern rather than the basket-weave arrangement of normal dermis. Decorin expression is reduced in scar tissue and fibrotic lesions, and this reduced decorin is believed to contribute to the abnormal collagen architecture.

Tripeptide-10 Citrulline is designed to bind to collagen fibrils at the decorin interaction site, partially substituting for decorin's organizing function. In vitro studies show that it promotes more uniform collagen fibril diameter and organization in fibroblast-collagen gel models. In formulation with other ECM-supporting ingredients, it is used in anti-scar and post-procedure skin care.

The citrulline residue (an unusual amino acid not incorporated in proteins by the ribosome) is proposed to improve the peptide's skin penetration and bioavailability due to its unique chemical properties compared to arginine.