Abstract

A previous study identified certain low molecular anti-melanogenic peptides that share a common sequence with α-melanocyte stimulating hormone (MSH) and end with a glycinamide moiety. Glycinamide itself also showed anti-melanogenic activity in cell-based assays, but neither glycine nor acetyl glycinamide were active, which indicated a special structure and activity relationship. The aim of this study was to examine the skin depigmentation efficacy of glycinamide hydrochloride in human subjects. The primary skin irritation potential of glycinamide hydrochloride was evaluated by patch testing in 30 human subjects. The skin depigmentation efficacy of glycinamide hydrochloride was evaluated in a double-blinded clinical test in 21 human subjects. The test product and a control product were applied to designated sites on the right or left side of the face twice daily for eight weeks. Skin color parameters, i.e., the melanin index, the L* value (representing skin lightness), a* value (redness), and b* value (yellowness) were measured using instruments. The individual topology angle (ITAo, representing skin color) was calculated from L* and b values. The degree of skin pigmentation was visually assessed by two testers. The primary skin irritation test showed that a solution containing glycinamide hydrochloride up to 10% did not induce any adverse skin responses. In the efficacy test, the test product significantly reduced the melanin index, and increased L* value and ITAo after two weeks of application relative to the baseline value at the start of the test. It also significantly lowered the degree of pigmentation after 6 weeks of application, relative to the baseline value. Differences in the melanin index, L* value, ITAo and the degree of pigmentation between the test and control groups became statistically significant after six weeks or eight weeks of application. No signs of skin irritation were observed during the efficacy test. The present study suggests that glycinamide hydrochloride has great potential to be used in the control of skin hyperpigmentation.

Highlights

  • Human skin color is mainly determined by the content and distribution of various pigment substances, such as melanin, hemoglobin, and carotenoids [1]

  • Melanosomes supply melanin to surrounding keratinocytes and, as a result, melanin is distributed throughout the skin and expressed to produce various skin color [3]

  • We report the results of the first human skin application test of glycinamide, which is the smallest of the low molecular anti-melanogenic peptides

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Summary

Introduction

Human skin color is mainly determined by the content and distribution of various pigment substances, such as melanin, hemoglobin, and carotenoids [1]. Melanin is produced through a process in which an amino acid called L-tyrosine is metabolized in a series of enzymatic reactions. Melanosomes supply melanin to surrounding keratinocytes and, as a result, melanin is distributed throughout the skin and expressed to produce various skin color [3]. In addition to its effects on visual appearance of the skin, melanin plays an important role in protecting the body from the toxicity of ultraviolet (UV) rays [4]. The metabolism of melanin in skin has become an important research topic from both a physiological and aesthetic perspective [5,6]

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