Minireview: Peptide analogs and short sequence oligopeptides as modulators of skin pigmentation.

Short sequence amino acids or oligopeptides have recently garnered attention for use as treatments for a myriad of dermatologic disorders due to their ability to effect and modulate various biological processes in the epidermis and dermis, rendering them promising candidates as medical and cosmeceutical therapeutics. Major advantages include their relative ease of synthesis and multitude of modifications that can be applied to enhance potency, affinity, specificity, hydrophilicity or hydrophobicity and cytotoxicity. Given the photoprotective effects of eumelanin on skin, there has been substantial interest in developing agents, particularly α-MSH analogs, that can induce 'sunless tanning' helping reduce risk of melanoma and non-melanoma skin cancer. In this mini review, we present some of the recent and leading peptide modulators of melanogenesis with relevant clinical data and medical indications. Short sequence oligopeptides with tyrosinase inhibitory activity that can significantly reduce hyperpigmentation, as well α-MSH analogs that can enhance eumelanogenesis, are currently being clinically tested for treatment of erythropoietic protoporphyria, polymorphous light eruption, solar urticaria, actinic keratosis, and "sunless tanning". Success in developing such products can help reduce the incidence of skin cancer, one that surpasses that of all other human cancers combined.

Novel pentapeptide activators of mammalian and mushroom tyrosinase.

Melanoma incidence continues to rise due to intentional exposure to ultraviolet radiation (UVR) from sunlight and indoor tanning beds. Eumelanin exhibits photoprotective effects; thus, agents that induce its synthesis offer a means for sunless tanning without UVR damage. Herein, we report the development of two pentapeptides, P9 and P10, capable of enhancing melanin synthesis in B16 melanoma cells by activating mushroom and mouse tyrosinases without any effect on cell viability or proliferation. P9 and P10 significantly increased melanin content in a dose-dependent manner comparable to the positive controls, IBMX, scoparone, and α-MSH. However, unlike IBMX and scoparone, but similar to α-MSH, P9 and P10 were able to reverse 6BH4-dependent tyrosinase inhibition. We hypothesize that P9 and P10 allosterically activate tyrosinase and consequently enhance epidermal melanin synthesis. P9 and P10 may offer an alternative to tanning bed use and non-photoprotective tanning products. Moreover, sustained increase of melanin content in skin has the potential to reduce symptoms of photosensitivity disorders such as erythropoietic protoporphyria (EPP), solar urticaria (SU) and polymorphic light eruption (PLE), which lack fully effective treatments and result in significant morbidity.

Minimally invasive bipolar fractional radiofrequency treatment upregulates anti-senescence pathways.

BACKGROUND: The sirtuin gene family has been implicated in various anti-senescence pathways. Its connection, if any, with the skin wound healing response has yet to be elucidated. OBJECTIVE: The goal of our study was to better understand the effects of FRF treatment on the sirtuin anti-senescence pathway in skin. METHODS: Human abdominal skin was treated with FRF, and then harvested at 0, 2, 14, and 28 days post-treatment to assess for temporal changes in gene expression levels. RESULTS: Decreased levels of SIRT1, 3, 5, and 7 were observed immediately post-FRF treatment. By Day 2, SIRT1, 6, and 7 expressions increased 50-100%. SIRT6 and 7 expression continued to increase through Day 28. Expression levels of apoptosis genes FoxO3 and p53 decreased, while Bax levels increased by Day 28. CONCLUSIONS: Our results raise the possibility that sirtuin activity may be used as an accurate corollary to clinical improvement in skin quality.

Potent low toxicity inhibition of human melanogenesis by novel indole-containing octapeptides.

BACKGROUND: Abnormal production and accumulation of melanin are characteristics of a number of skin disorders, including postinflammatory hyperpigmentation and melasma. Our objective was to develop and validate novel oligopeptides with potent inhibitory activity against mushroom and human tyrosinase with minimal toxicity toward melanocytes, keratinocytes, and fibroblasts. METHODS: A library of short sequence oligopeptides was docked against the crystal structure of mushroom tyrosinase to screen for favorable binding free energies and direct interaction with the catalytic pocket. The inhibitory activity of the octapeptides and hydroquinone (HQ) was assessed using mushroom and human tyrosinase and melanin content via human primary melanocytes. Effects on cell viability and proliferation were determined using the MTT assay and cytotoxicity via trypan blue exclusion. RESULTS: Octapeptides P16-18 outperformed HQ, the benchmark of hypopigmenting agents, in all tested categories. Prolonged incubation of human keratinocytes, fibroblasts, or melanocytes with 30-3000µM HQ led to 8- to 65-fold greater cell death than with octapeptides. After 6d of incubation with 30µM HQ, we observed 70±3% and 60±2% cell death in melanocytes and fibroblasts, respectively, versus minimal toxicity up to an octapeptide concentration of 3mM. CONCLUSION: Octapeptides P16-18 are potent competitive tyrosinase inhibitors with minimal toxicity toward the major cell types of human skin. GENERAL SIGNIFICANCE: The findings in our study suggest that all three novel octapeptides may serve as safe and efficacious replacements of HQ for the treatment of pigmentary disorders.

Bipolar fractional radiofrequency treatment induces neoelastogenesis and neocollagenesis.

BACKGROUND: We recently introduced Renesis, a novel minimally invasive radiofrequency (RF) device, for the treatment of human skin. The wound healing response post-fractional RF (FRF) treatment was examined in human subjects. STUDY DESIGN: The FRF system delivered RF energy directly within the dermis via 5 micro-needle electrode pairs. Tissue temperature was held at 72 degrees C for 4 seconds using an intelligent feedback system. The wound healing response was evaluated histologically and by RT-PCR up to 10 weeks post-RF treatment. Neoelastogenesis and the role of heat shock proteins (HSPs) were assessed by immunohistochemistry. RESULTS: FRF treatment generated a RF thermal zone (RFTZ) pattern in the reticular dermis that consisted of zones of denatured collagen separated by zones of spared dermis. RFTZs were observed through day 28 post-treatment but were replaced by new dermal tissue by 10 weeks. HSP72 expression rapidly diminished after day 2 while HSP47 expression increased progressively through 10 weeks. Reticular dermal volume, cellularity, hyaluronic acid, and elastin content increased. RT-PCR studies revealed an immediate increase in IL-1beta, TNF-alpha, and MMP-13 while MMP-1, HSP72, HSP47, and TGF-beta levels increased by 2 days. We also observed a marked induction of tropoelastin, fibrillin, as well as procollagens 1 and 3 by 28 days post-treatment. CONCLUSION: Our study revealed a vigorous wound healing response is initiated post-treatment, with progressive increase in inflammatory cell infiltration from day 2 through 10 weeks. An active dermal remodeling process driven by the collagen chaperone HSP47 led to complete replacement of RFTZs with new collagen by 10 weeks post-treatment. Furthermore, using both immunohistochemical and PCR studies, we successfully demonstrated for the first time evidence of profound neoelastogenesis following RF treatment of human skin. The combination of neoelastogenesis and neocollagenesis induced by treatment with the FRF system may provide a reliable treatment option for skin laxity and/or rhytids.