alpha-Arbutin: Skin Lightening Efficacy, Mechanism of Action and Safety

Arbutin is a compound with a structure in which one molecule of D-glucose is bound to hydroquinone. D-glucose exists in α, β, or γ-anomeric form in aqueous solution, with β-anomer being a dominant form. β-Arbutin in which the β-anomer of D-glucose is bound to hydroquinone is mainly found in plants, such as wheat, pear, and bearberry. alpha-Arbutin is a compound of hydroquinone and the α-anomer of D-glucose. It has been about 30 years since arbutin was studied in earnest to use as a hydroquinone alternative for skin lightening purposes. This article will discuss the skin lightening efficacy, mechanism of action and safety of alpha-Arbutin.[1]

Antimelanogenic Effects

The antimelanogenic effects of α-arbutin were reported by Sugimoto et al [2]. They showed that α-arbutin decreased melanin content and TYR activity in cultured human melanoma cells, at a concentration below 1.0 mM, without significant effects on cell growth and TYR mRNA level. They further showed that treatment of the human skin model with α-arbutin (250 μg per tissue) reduced melanin content to a 40% level of the control, without causing cell death.

Mechanism of Action

The generally agreed view on the mechanism by which alpha-Arbutin inhibits the melanin synthesis in cells is that it inhibits the catalytic activity of already expressed TYR (tyrosinase) or irreversibly inactivates it rather than suppressing the new synthesis of TYR. Many studies reported that arbutin did not affect mRNA and protein expression of TYR in the concentration range where it inhibited cellular melanin synthesis. There are only a few reports that arbutin reduced the protein level of intracellular TYR.

alpha-Arbutin is structurally similar to L-tyrosine and can bind to the active site of TYR, thereby acting as a competitive inhibitor. In addition, arbutin can irreversibly inactivate TYR by binding to the enzyme in the form of Emet when diphenol substrates are deficient. Of course, there is a possibility that arbutin may act as a substrate for TYR in the form of Eoxy when diphenol substrates are present. The last mechanism may not be excluded, because arbutin has been shown to increase cellular melanin synthesis at certain conditions. However, most studies support the mechanism by which arbutin inhibits the catalytic activity of TYR or causes its irreversible inactivation, thereby preventing the synthesis of melanin in cells.

Side Effects

Alpha-arbutin have the possibility to produce hydroquinone in the manufacturing process of raw materials, the manufacturing and storage process of cosmetic products, and the human use of the products. Whether they are chemically synthesized, extracted from plants, or produced by biological conversion processes, it is an important goal to achieve high purity in the final raw materials. The formulation is important to stabilize alpha-arbutin in the final products. It should be remembered that exposure to microorganisms or UVR during storage and use of the product has the potential to generate hydroquinone. Since dermatitis or allergic dermatitis has been observed in certain people using arbutin-containing cosmetic products, if any side effects are observed while using the product, one must discontinue use immediately and consult a doctor.

References

[1] Boo, Y.C. Arbutin as a Skin Depigmenting Agent with Antimelanogenic and Antioxidant Properties. Antioxidants 2021, 10, 1129.

[2] Sugimoto, K.; Nishimura, T.; Nomura, K.; Sugimoto, K.; Kuriki, T. Inhibitory effects of alpha-arbutin on melanin synthesis in cultured human melanoma cells and a three-dimensional human skin model. Biol. Pharm. Bull. 2004, 27, 510–514. 

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