INTRODUCTION

In dermatology, there are often many ways to accomplish any particular goal. One method to reverse cutaneous signs of aging is through the use of prescription retinoids, such as tretinoin or tazarotene. However, these substances are irritating to the skin, resulting in the peeling and stinging characteristic of barrier damage. In recent years, the trend in cosmeceuticals has been for products that improve the appearance of aging skin without the irritation of topical retinoids. This has resulted in the popularity of peptides, which have demonstrated cosmeceutical effects both in vitro and in vivo that could result in clinical aging skin improvement. This chapter discusses the current use of cosmeceutical peptides to aid the practicing dermatologist in understanding the science behind these new ingredients and how to utilize them for cutaneous antiaging treatment.

TERMINOLOGY AND DEFINITIONS

Peptides are short chains of amino acid sequences that make up larger proteins. There are three main categories of peptides currently being used in cosmeceutical products (Box 17.1). This increase in peptide technology has arisen because of the technology to synthesize fragments that mimic peptide sequences in collagen and elastin with the ability to stimulate production of new collagen and elastin. Other peptides are currently available that function primarily as carriers of cofactors for important enzymatic steps in collagen production. Peptide fragments also exist that are able to modulate neurotransmitter release. Since some wrinkling of the skin is caused by collagen breakdown, while other wrinkles are caused by hyperkinetic facial muscle movement, peptides that have actions to inhibit or reverse these actions could have clinical antiaging cosmeceutical benefits.

INDICATIONS AND BIOLOGIC ACTIVITY

Clinically, photoaged skin has wrinkles that are coarse, while the wrinkles of naturally aged skin are much finer. Both of these wrinkles are due, in part, to the loss of collagen in the skin. Chronologically aged skin shows decreased production of new collagen, as well as increased proteolytic activity resulting in increased collagen degradation. Aging fibroblasts show decreased synthesis of mRNA for type I collagen, which is the major collagen in the skin. Also, in skin cell cultures, aging fibroblasts proliferate at a slower rate than fetal fibroblasts. Therefore, natural aging is at least partly the result of the limited replicative capacity of dermal fibroblasts, as well as the overexpression of proteolytic activity of matrix metalloproteinase-1 (MMP-1, interstitial collagenase).

Additionally, both photoaged and naturally aged human skin have lower procollagen type I mRNA and protein compared to younger skin. The balance between collagen synthesis and collagen breakdown appears to be different in the same individual from photoaged to naturally aged skin. While both show greater MMP activity, it is even higher in the skin aged from ultraviolet (UV) radiation exposure. The precocious elastosis seen in actinically damaged skin is also at least partially responsible for the difference in the appearance of the sun-induced versus age-induced wrinkling. The elastotic degeneration of sun-damaged skin may be due to chronic injury to fibroblasts that results in thicker elastotic fibers with accentuated microfibril dense masses. In the photoaged skin, both mRNA and protein production are reduced when compared to sun-protected skin of the same individual. UV radiation is well known to stimulate MMP-1, which in turn damages and degrades collagen. It is likely that the degraded and damaged collagen has further deleterious effects on dermal fibroblast function after repeated injury. Thus, there is a need for cosmeceuticals capable of either increasing collagen regeneration or preventing its further demise. Peptides and proteins for antiaging purposes were developed with this end in mind.

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