Zoe Diana Draelos, MD, answers questions about the function of peptides in skin care.
Peptides are composed of various numbers of amino acids. A dipeptide consists of 2 amino acids, a tripeptide consists of 3 amino acids, and a tetrapeptide consists of 4 amino acids. Not only is the number of amino acids important, but also the order in which the amino acids are arranged. For example, glycyl-histidyl-lysine is thought to stimulate collagen synthesis in fibroblasts, whereas glycyl-lysyl-histidine is thought to stimulate lipolysis in adipocytes. Nevertheless, the function of a peptide in skin care is to transmit a biochemical message from one body area to another body area, providing for communication of a physiologic change.
The 2 most frequently used antioxidant peptides in skin care are glutathione (β-glutamyl-cysteinyl-glycine) and carnosine (γ-alanyl-L-histidine). Glutathione is a tripeptide abbreviated GSH. Because the level of glutathione decreases with age, the topical use of the antioxidant peptide is thought to possess antiaging properties, despite limited evidence of clinical benefit topically.
Carnosine is a well-known scavenger of reactive oxygen species in the cell membrane, preventing the oxidation of free fatty acids. It can also inhibit the formation of skin advanced glycation end products by preventing the nonenzymatic binding of sugars to proteins. Over time, carnosine is degraded to β-alanine and histamine. β-Alanine is thought to stimulate the biosynthesis of nucleic acids and collagen. Thus, both the peptide and its breakdown products are thought to be biologically active.
The idea that a peptide applied to either a wound bed or intact skin could stimulate collagen production is compelling. These fragmented macromolecules are known as matrikines. Matrikines recycle breakdown fragments of larger molecules, such as collagen, to trigger repair activity. For example, the most widely used matrikine peptide in skin care is the pentapeptide Pal-KTTKS, composed of palmitic acid, lysine, threonine, threonine, lysine and serine, also known as palmitoyl pentapeptide-4. This is the name that will be found on the ingredient disclosure list when this peptide is used. This pentapeptide is the shortest type 1 procollagen fragment capable of stimulating fibroblast collagen synthesis in a petri dish. It was discovered by serially cleaving collagen and putting the fragments on fibroblast cell cultures to see which cultures produced more collagen.
It can be challenging to fully understand the true benefit of tissue repair peptides and peptides in general. Due to expense, peptides are used in a concentration of parts per million. It is thought that because they are modifying a biologic process, a small amount will produce sufficient results to see appearance improvement. However, it is not possible to apply pure peptide to the skin in such low concentrations. The peptide must be delivered in some type of vehicle, usually a moisturizer, to spread the active ingredient over the skin surface. This means that it can be hard to separate the moisturizing vehicle benefit from the peptide benefit. Vehicle controlled studies are the best way to determine the added benefit of the peptide, but they are seldomly performed.