Reduction in the appearance of facial hyperpigmentation by topical N‐undecyl‐10‐enoyl‐l‐phenylalanine and its combination with niacinamide

Objectives N‐undecyl‐10‐enoyl‐l ‐phenylalanine (Sepiwhite^®, N‐undecylenoyl phenylalanine), a reported alpha‐melanocyte‐stimulating hormone (MSH) receptor antagonist, has been observed to reduce melanin production in cultured melanocytes. In other testing, niacinamide has been found to inhibit melanosome transfer in cultured cells and to reduce the appearance of hyperpigmented spots in clinical studies. Since these two agents function by different mechanisms, we conducted two studies to determine if their combination is more effective than niacinamide alone in reducing facial hyperpigmentation. Methods  Two double‐blind, 10‐week (2‐week washout + 8‐week treatment), left‐right randomized, split‐face clinical studies were conducted. In one, two groups of Japanese women applied one of two pairs of test emulsion formulations: a vehicle control and a 5% niacinamide formulation (n= 40), or a 5% niacinamide and a 5% niacinamide plus 1%N‐undecylenoyl phenylalanine formulation (n = 40). Each formulation was applied to the randomly assigned side of the face. In the second study, Caucasian women applied one of three emulsions: vehicle control, 5% niacinamide formulation, or combination 5% niacinamide plus 1%N‐undecylenoyl‐phenylalanine formulation to the randomly assigned side of the face (n = ～60 treatment sites per formulation). In both studies, hyperpigmented spots were evaluated at weeks 4 and 8 by quantitative image analysis. Results  In both studies, the combination formulation was significantly more effective than the vehicle and the 5% niacinamide formulation in reducing the appearance of hyperpigmentation after 8 weeks. Conclusions  The combination of 5% niacinamide and 1%N‐undecylenoyl phenylalanine is an effective anti‐aging technology for use on facial skin.     

N‐Acetylcysteine in psychodermatological disorders

Treatment of psychodermatological conditions, particularly body‐focused repetitive behavior disorders, is often unsatisfactory. Various psychopharmacological and non‐pharmacological treatments have been used to ameliorate the symptoms of these disorders. N‐Acetylcysteine (NAC) is a newer modality in the treatment of these disorders. This short review focuses on pharmacology, mode of action, and use of NAC in common body‐focused repetitive disorders such as trichotillomania, skin‐picking disorders, and onychotillomania (nail biting). Current research and literature review have been evaluated and will be discussed.     

In vitro and in vivo evidence of tyrosinase inhibitory activity of a synthesized (Z)‐5‐(3‐hydroxy‐4‐methoxybenzylidene)‐2‐thioxothiazolidin‐4‐one (5‐HMT)

Tyrosinase is a key enzyme that catalyses the initial rate‐limiting steps of melanin synthesis. Due to its critical role in melanogenesis, various attempts were made to find potent tyrosinase inhibitors although many were not safe and effective in vivo. We evaluated tyrosinase inhibitory activity of six compounds. Among them, (Z)‐5‐(3‐hydroxy‐4‐methoxybenzylidene)‐2‐thioxothiazolidin‐4‐one (5‐HMT) had the greatest inhibitory effect and potency as the IC₅₀ value of 5‐HMT was lower than that of kojic acid, widely‐known tyrosinase inhibitor. Based on in silico docking simulation, 5‐HMT had a greater binding affinity than kojic acid with a different binding conformation in the tyrosinase catalytic site. Furthermore, its skin depigmentation effect was confirmed in vivo as 5‐HMT topical treatment significantly reduced UVB‐induced melanogenesis in HRM2 hairless mice. In conclusion, our study demonstrated that 5‐HMT has a greater binding affinity and inhibitory effect on tyrosinase and may be a potential candidate for a therapeutic agent for preventing melanogenesis.     

1‐(2‐Hydroxyethyl)‐2‐imidazolidinone,a heparanase and matrix metalloproteinase inhibitor,improves epidermal basement membrane structure and epidermal barrier function

Daily exposure to sunlight is known to affect the structure and function of the epidermal basement membrane (BM), as well as epidermal differentiation and epidermal barrier function. The aim of this study is to clarify whether the inhibition of BM‐degrading enzymes such as heparanase and matrix metalloproteinase 9 (MMP‐9) can improve the epidermal barrier function of facial skin, which is exposed to the sun on a daily basis. 1‐(2‐hydroxyethyl)‐2‐imidazolidinone (HEI) was synthesized as an inhibitor of both heparanase and MMP‐9. HEI inhibited not only the BM damage at the DEJ but also epidermal proliferation, differentiation, water contents and transepidermal water loss abnormalities resulting from ultraviolet B (UVB). This was determined in this study by the use of UVB‐induced human cultured skins as compared with the control without HEI. Moreover, topical application of HEI improved epidermal barrier function by increasing water content and decreasing transepidermal water loss in daily sun‐exposed facial skin as compared with non‐treated skins. These results suggest that the inhibition of both heparanase and MMP‐9 is an effective way to care for regularly sun‐exposed facial skin by protecting the BM from damage.