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Peptides are short proteins containing less than 50 amino acids. They are formed by a chemical bond called “peptide bond”. Peptides are ubiquitous in all living systems and are signaling molecules, which are involved in the control of critical biological functions such as growth, differentiation, chemotaxis, and immunity. Small chain of peptides, in specific sequence may be able to initiate some biologic process to stimulate repair, whereas other peptides may inhibit processes that accelerate the damage of the skin.
Peptides have a broad range of potential clinical benefits as drugs and active cosmetics. By now several peptides, peptide derivatives and peptidomimetics of over 50 products are on the market as drugs and of over 30 products as cosmetic ingredients. Many researchers have concentrated in the last decade on the development of therapeutic agents based on peptides. The reason for this interest arises from the continuous discovery of new, highly potent, biologically active peptides. Although there have been more researches aiming to the development of potent drugs using peptide as lead compound, peptides exclusively in cosmetic point of view will be discussed here.
Since a number of bioactive peptides such as palmitoyl pentapeptide-4, acetyl hexapeptide-8 and copper peptides gained much popularities and success in the cosmetic market, many efforts have been dedicated in the last few years in the development of more active and multifunctional peptides. Peptides have several and characteristic advantages over other synthetic or natural cosmetic ingredients. The most important advantage of using peptides is their high activity and specificity. Peptides exclusively bind to their specific molecular target and process their regulatory signals. Peptides are less accumulated in tissues and therefore have low toxicity in general. They also offer a biological and chemical diversity, which is also easy to investigate from the therapeutic point of view.
Although many peptides have been found biologically potent in in vitro test, most of them failed to give clear clinical efficacy. The reason for this inconsistency may come from several factors that have been regarded as major limitation in the use of peptides as topical ingredients. Firstly and most importantly, peptides show in general very short half-life and are cleared very quickly from the body. Human skin contains various enzymes that recognize peptides and quickly degrade them into amino acids. Therefore, it is very difficult for these peptides to reach their target cells. Secondly, many bioactive peptides are high molecular weight compounds and usually contain several hydrophilic amino acids that make peptides overall more polar. This character makes peptides difficult to penetrate through the hydrophobic skin layer.
To overcome the short half-life and low bioavailability, several technologies have been investigated. Among them, peptide backbone modifications such as introducing unnatural amino acids or D-forms of amino acids, and peptide bond modification have been most frequently applied. In some cases, conjugation with a fatty acid or PEG-derivative represents good ways to enhance peptide stability. Attaching a fatty acid to a peptide may not only result in increased half-life and bioavailability but can also lead to increased permeability and more specificity. For example, pentapeptide-4 (KTTKS), N-terminal fragment of collagen type I, has been modified by conjugating its N-terminal with palmitic acid to increase its stability and penetration into skin.
Another disadvantage to overcome is the challenging and costly synthesis. Peptides are known to be highly expensive materials to be used in cosmetics. There have been tremendous advances in peptide synthesis techniques and ways to approach. With about 50 years of experience in synthetic organic chemistry, our peptide chemists have been devoted to the synthesis of various peptides in cost effective ways. We believe peptides are no more expensive materials to be applied easily and in near future, peptides will be one of the most popular active ingredients in the market.
The use of bioactive peptides continues to be an area of interest. We believe this technology is still in its infancy and that enhanced efficacy will be achieved through better sophistication in peptide design, validation of mechanisms of action and clinical efficacy.