Skincare Science Updates

Some of the most promising skincare ingredients are backed by solid research. Here’s a look at recent developments.

Tyrosinase Inhibitors. The most obvious way to determine whether a new compound is a tyrosinase inhibitor would be to replicate human tyrosinase (HTyr) in vitro, but this has proven to be exceedingly difficult. Industry was forced to turn to a non-human model, with mushroom tyrosinase (MTyr) being the most widely adopted. Extracted from the common species Agaricus Bisporus, MTyr has three important characteristics for its use as a substitute for HTyr: it is plentiful, cheap, and its chemical and 3D structures are thought to roughly resemble those of its human counterpart. In addition, compounds that inhibit mushroom tyrosinase could have utility both as a whitening agent for humans and to reduce browning due to the natural aging or large-scale handling of fruits and vegetables.

The use of MTyr has its limitations. Indeed, many compounds that show inhibitory activity against MTyr fail to reproduce similar efficacy in vivo. This could be related to properties of the enzymes, which are notably different. For example, the optimal temperature for MTyr activity is 40 degrees Celsius, while HTyr operates best at 50 degrees C, and MTyr operates most efficiently at a more acidic pH than HTyr. Scientists are turning to big data and bioinformatics to replace MTyr with more reliable and applicable HTyr models.

One of these is the tyrosinase in B. Megatarium. Using homologous modeling (predicting the 3D structure of an unknown protein using known proteins that are assumed similar to the unknown protein) to predict the structure of HTyr, scientists found that this bacterial tyrosinase had a high similarity (33.5%) to the assumed HTyr. Using docking simulations and molecular dynamic calculations of various known tyrosinase inhibitors to MTyr, B. Megatarium tyrosinase, and HTyr, the histamine binding residues responsible for the enzyme/inhibitor interaction were completely different in all three. Thus, while the bacteria-derived tyrosinase exhibited higher similarity to HTyr, the modeling showed that it likely is not sufficient to replicate HTyr function.

A more compelling answer may involve the novel production of a truncated HTyr, where primarily the catalytic (active) domain is produced in vitro by HEK 293 cells, a cell line derived from human kidney epithelial cells. Instead of relying on mammalian or fungal models, now scientists have a true comparative to analyze current (assumed) tyrosinase inhibitors and screen for new ones. A recent study (Mann et al, 2019) utilized this truncated HTyr in a high-throughput screen utilizing 50,000 compounds, with the goal of understanding the “structural motifs in small-molecule compounds that efficiently inhibit HTyr.”

Included in this compound library were numerous well-known lightening compounds, such as hydroquinone, kojic acid, resorcinol derivatives, and arbutin. The results are enlightening. Comparing Ki values (Ki is the inhibitor constant, a measure of inhibition potency, or the concentration required to produce half-maximum inhibition), the three resorcinol derivatives had Ki values between 9.1 and 39; kojic acid’s value was 145; and hydroquinone’s value was not determined (ie, unmeasurable).

Exosomes. Wound healing is divided into five stages: inflammatory, epithelialization, wound contraction, collagen deposition, and remodeling. Intercellular communication is essential in wound healing as it requires a coordinated effort by keratinocytes, fibroblasts, macrophages, and inflammatory cells. Exosomes from macrophages promote wound healing by stimulating angiogenesis and cell proliferation. These macrophage-derived exosomes cause conversion of M1 macrophages to M2 macrophages, resulting in enhanced fibroblast migration, collagen production, and endothelial cell tube formation. ADSC exosomes loaded in an alginate-based hydrogel that functions as a scaffolding was shown to provide continuous release of bioactive materials into the wound site in animals. This dressing promoted wound closure, collagen synthesis, and angiogenesis. In addition, exosomes may help minimize scar formation. Zhang et al demonstrated that human MSC exosomes promoted wound healing while reducing scar widths.

Skin pigmentation is a coordinated effort between melanocytes and keratinocytes. Both cell types can secrete exosomes and can take up exosomes from each other. It is known that keratinocyte-derived exosomes contain miRNA and other soluble factors that are involved in pigment modulation. Co-culture of melanocytes from human foreskin and exosomes derived from keratinocytes promotes melanocyte proliferation and tyrosinase activity. In contrast, murine keratinocyte exosomes that over-express miR-330-5p significantly decrease production of melanin and expression of tyrosinase in melanocytes. Interestingly, the miRNA profile of keratinocyte exosomes is altered by UVB exposure. Exosomes isolated from UVB-irradiated keratinocytes contained miR-3196 that increases the melanin content of human melanocytes suggesting that altered exosomes may play a role in UV-induced skin pigmentation. Further studies on the role of exosomes in the cross talk between melanocytes and keratinocytes may provide new ways to modulate pigment production.

Recent studies suggest that exosomes may be useful in alopecia. Dermal papillae cell (DPC) exosomes injected into hair follicles at different stages accelerated the onset of anagen, delayed catagen, lengthened hair shafts and resulted in larger bulge regions in mice. 3D cultured human DPC exosomes promoted DPCs and outer root sheath viability, increased expression of insulin-like growth factor (IGF) 1, keratinocyte growth factor, and hepatocyte growth factor. They also facilitated hair shaft elongation of cultured human hair follicles and induced anagen from telogen and prolonged anagen in mice. Accordingly, dermal papillae cell exosomes hold promise for prevention and treatment of hair loss.

Exosomes are also of interest for skin rejuvenation. Exosomes from 3D cultured human dermal fibroblasts (HDF) were delivered by needle-free injection into the skin of photoaged nude mice. HDF exosomes increased procollagen 1 and decreased MMP-1 by down-regulating TNF-α and increasing TGF-Β. The HDF exosomes also resulted in a greater increase in dermal collagen deposition when compared to bone marrow stem cell derived exosomes. Pluripotent stem cells in culture produced exosomes that mitigated changes seen in senescent human fibroblasts. These exosomes reduced expression of beta galactosidase, MMP 1, MMP 3, and restored collagen type I mRNA expression. Human ADSC exosomes injected subcutaneously into photoaged skin of rats markedly decreased epidermal thickness and increased the dermal thickness of photoaged skin in 7 days. There was an increase in mRNA expression of type I collagen while type III collagen, MMP 1 and MMP 3 was decreased.

Niacinamide. The anti-aging benefits of niacinamide are due in part to its ability to increase intracellular NAD and NADP, whose reduced forms (NDAH and NDAPH) function as antioxidants. Topical niacinamide increases collagen production, inhibits deposition of excessive glycosaminoglycans, and prevents protein glycation. Glycation results in the crosslinking of collagen and elastin molecules making them stiff and ridge, changing the viscoelastic properties of the skin. Glycated proteins are also responsible for sallowness seen in actinically damaged skin. In a double-blind, placebo-controlled, split-face clinical trial, 50 subjects used either a 5% niacinamide moisturizer or placebo twice daily for 12 weeks. Subjects in the test group saw an improvement in fine lines and wrinkles, hyperpigmented spots, texture, red blotchiness, and sallowness compared to control. The niacinamide moisturizer was well tolerated.

Niacinamide is an effective skin lightening agent that combats hyperpigmentation by preventing the transfer of melanosomes to epidermal keratinocytes and interfering with cell signaling pathways between keratinocytes and melanocytes. Due to its unique mechanism of action, niacinamide is helpful when used in combination with other skin lightening ingredients.

Excerpted from Practical Dermatology magazine. For more: PracticalDermatology.com/SkincareSummit. Drs. Farris and Lain are co-founders of the Science of Skincare Summit, to be held October 28-30 in Austin, TX. scienceofskincaresummit.com

1. Seo SY, Sharma VK, Sharma N. Mushroom tyrosinase: recent prospects. J Agric Food Chem. 2003 May 7;51(10):2837-53.

2. Mann T, Gerwat W, Batzer J, Eggers K, Scherner C, Wenck H, Stäb F, Hearing VJ, Röhm KH, Kolbe L. Inhibition of Human Tyrosinase Requires Molecular Motifs Distinctively Different from Mushroom Tyrosinase. J Invest Dermatol. 2018 Jul;138(7):1601-1608.

3. Nokinsee D, Shank L, Lee VS, Nimmanpipug P. Estimation of Inhibitory Effect against Tyrosinase Activity through Homology Modeling and Molecular Docking. Enzyme Res. 2015;2015:262364.