Our current understanding of skin aging is that it has extrinsic components, such as ultraviolet light exposure, and an intrinsic component due to oxidative metabolism (Fig. 1). Skin aging has been hypothesized to be analogous to an extensive, chronic wound that the body loses its ability to repair over time, leading to the development of rhytides and skin elastosis. This is accompanied by a reduction of up to 20 percent in total dermal collagen,¹ in particular Type 1 collagen, which is the primary provider of skin support and structure. The result is a relative excess of Type 3 collagen, which has less structural value than Type 1 collagen and is not considered to play a significant role in healthy adult skin. Antioxidant stores also become depleted in aging skin. In the May edition (available online at PracticalDermatology.com), I discussed the use of three key topical anti-aging actives—growth factors, antioxidants and retinoids—for skin rejuvenation. 2 In this article, I will discuss more strategies for selecting topically applied peptides, and for combining them with growth factors, antioxidants, and retinoids, starting with Strategy 4.

Strategy 4: Pick Proven Peptides
Peptides comprise a diverse group of compounds. The general rationale for their topical use is to mimic the action of naturally occurring proteins or protein fragments. Peptide activity, unlike antioxidant activity, is difficult to assay, thus clinical studies may be the most convincing way of demonstrating the in vivo activity and efficacy of a specific topical peptide formulation.

The best characterized collagen-mimetic peptide for skin rejuvenation is palmitoyl oligopeptide (Pal- GHK), which comprises a short chain of amino acids (glycine-histidine-lysine, abbreviated to GHK) connected to palmitic acid. The GHK chain is a Type 1 collagen fragment that serves as a biological indicator of degraded collagen. Peptides are inherently unstable, and the palmitoyl side chain, which is hydrophobic, increases the peptide's stability and enhances skin penetration. The aim of applying Pal-GHK topically is to mimic collagen degradation and trigger a feedback loop that stimulates fibroblasts to produce new collagen and other extracellular matrix (ECM) components. Newer collagenmimetic peptides include Pal-KTTKS (Pal-pentapeptide-3), commonly known as Matrixyl, which is considered to be more potent than Pal-GHK. The amino acid sequence, KTTKS, is a pentapeptide fragment of procollagen that is formed during collagen breakdown. Addition of the hydrophobic palmitoyl side chain allows the peptide to penetrate the skin and signal fibroblasts to produce extracellular matrix.^3,4

Neuropeptides such as acetyl hexapeptide (Argireline) are applied topically with the intent that they will bind to the neuromuscular junction and block muscle contractions. Acetyl hexapeptide mimics the N-terminal of SNAP-25, the neuromuscular junction protein that is cleaved by botulinum neurotoxin A (BoNT-A) products such as Dysport and Botox. While there is no objective evidence to substantiate claims that topical neuropeptides are an alternative to injected BoNT-A, there may be some modest inhibition of neurotransmitter release and muscle contraction.⁵

Topical copper peptide products are actually better categorized as antioxidants rather than as peptides, since the peptide component serves merely as a delivery agent, and the activity lies in the copper component, which is antioxidant. The aim of a topical copper peptide product is to normalize collagen synthesis in wounds by inducing the degradation of large collagen aggregates and promoting the synthesis of normal collagen. The copper component may also promote the synthesis of elastin, proteoglycans, glycosaminoglycans and other components of the ECM.

Strategy 5: Know When to Lump and When to Split
It is beneficial to combine topical growth factors, antioxidants, and peptides in a single formulation to promote patient compliance. The multiple functions of these anti-aging actives enhance overall product efficacy, and there is also the potential for synergistic enhancement of activity via protein signaling and chaperoning. Interactions between growth factors in a physiologically balanced, highly concentrated mixture may optimize product efficacy and stability and provide necessary feedback control loops. The stability of such a combination formulation must be demonstrated through appropriate assays and clinical evaluation (Fig. 2).

However, it may be a sounder strategy to keep retinoids separate, since they are reactive molecules and tend to degrade readily in combination formulations. A solo retinoid product can be applied in tandem with a combination formulation containing growth factors, antioxidants, and peptides.

Strategy 6: Consider the Whole Formulation
As discussed previously,2 the most physiologically relevant determinant of antioxidant activity may be to measure protection of the skin from UV induced erythema. Test skin sites that are either untreated or treated with a topical antioxidant formulation are exposed to UVA and UVB radiation supplied by an artificial source that has a UV range comparable to that of natural sunlight.3 Diminution or blockage of reactive oxygen species by the topical antioxidant formulation will manifest as a reduction in UV-induced erythema in skin treated with the formulation, compared to untreated skin. This methodology can be modified to also study the effects of antioxidants on hyperpigmentation.

A recent pilot study of 11 subjects showed up to 50 percent reduction in UV-induced erythema in skin treated twice daily for 10 days with a topical product containing a combination of growth factors, antioxidants, and peptides, compared to untreated skin6 (Figs. 3 and 4).

In vitro assays and study data for individual components of a skin rejuvenation formulation are of value in elucidating the mechanism of action, but what matters ultimately are patient results from the whole product. Skin biopsies with measurement of Grenz zone thickness are the best indicator of in vivo collagen synthesis (Fig. 5). Additional data may be provided by skin surface impressions and topography, by cutometry and by clinical evaluation—which is best performed by physicians who are blinded to the study methodology (Figs. 6-9).

It is worth keeping in mind the value to an overall skin rejuvenation strategy of adding adjunctive ingredients to optimize skin barrier function, either as a component of an antiaging formulation or as separately applied products. Two topically applied prescription products that I find helpful in this regard are a skin barrier repair cream containing glycyrrhetinic acid, hyaluronic acid and shea butter (Atopiclair, Graceway) and a skin barrier emulsion that contains physiologic ratios of ceramide, cholesterol, and free fatty acids. (EpiCeram, Promius Pharma).

Dr. Sundaram has served as an Advisor, Clinical Investigatorand/or Consultant for Graceway Pharmaceuticals, Johnson & Johnson, Promius Pharma and SkinMedica. She has no stocks, shares, or other financial interests in these or any other pharmaceutical companies.

1. Schwartz E, Cruickshank FA, Christensen CC, Perlish JS, Lebwohl M. Collagen alterations in chronically sun-damaged human skin. Photochem Photobiol. 1993 Dec;58(6):841-4.
2. Sundaram H. Six Strategies for Scientific Skincare Part 1. Pract. Dermatol. 2010; 7(5):30-32.
3. Robinson LR, Fitzgerald NC, Doughty DG, Dawes NC, Berge CA, Bissett DL. Topical palmitoyl pentapeptide provides improvement in photoaged human facial skin. Int J Cosmet Sci. 2005 Jun;27(3):155-60.
4. Kaczvinsky JR, Griffiths CE, Schnicker MS, Li J. Efficacy of anti-aging products for periorbital wrinkles as measured by 3-D imaging. J Cosmet Dermatol. 2009 Sep;8(3):228-33.
5. Blanes-Mira C, Clemente J, Jodas G, Gil A, Fernández-Ballester G, Ponsati B, Gutierrez L, Pérez-Payá E, Ferrer-Montiel A. A synthetic hexapeptide (Argireline) with antiwrinkle activity. Int J Cosmet Sci. 2002 Oct;24(5):303- 10.
6. Sundaram H et al. Topically applied physiologically balanced growth factors: a new paradigm of skin rejuvenation. J Drugs Dermatol 2009;8(5) Supplement.