DeoxyArbutin and Its Derivatives Inhibit Tyrosinase Activity and Melanin Synthesis Without Inducing Reactive Oxygen Species or Apoptosis
October 2012 | Volume 11 | Issue 10 | Original Article | e28 | Copyright © 2012
Safety is a major concern in developing commercial skin-lightening agents. Here, we report the modulating effects of deoxyArbutin (dA) and its second-generation derivatives—deoxyFuran (dF), 2-fluorodeoxyArbutin (fdA), and thiodeoxyArbutin (tdA)—on tyrosinase, and consequently, on melanization. Results demonstrate that dA and its derivatives inhibit tyrosine hydroxylase and dopa oxidase activity of tyrosinase. The inhibition is dose-dependent, thereby inhibiting melanin synthesis in intact melanocytes, when used at concentrations that retain 95% viability of the treated cells in culture. Herein we demonstrate that dA, and its second-generation derivatives dF, fdA, and tdA, exhibit dose-dependent reductions in melanocyte cell number, primarily due to inhibition of proliferation rather than initiation of apoptosis as exemplified by hydroquinone (HQ), ie, cytostatic as opposed to cytotoxic. Human and murine melanocytes with functional mutations in either tyrosinase or tyrosinase-related protein 1 (Tyrp1) are less sensitive to the cytostatic effects of dA and its derivatives. Minimal amounts of reactive oxygen species (ROS) were generated upon treatment with dA and its derivatives, in contrast to a dramatic amount of ROS induced by HQ. This increase in ROS subsequently induced the expression of the endogenous antioxidant catalase in treated melanocytes. Treatment with exogenous antioxidants provided protection for melanocytes treated with HQ, but not dA and its derivatives, suggesting that HQ exerts more oxidative stress. These studies demonstrate that dA and its derivatives are relatively safe tyrosinase inhibitors for skin lightening or for ameliorating hyperpigmented lesions.
J Drugs Dermatol. 2012;11(10):e28-e34.
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Hyperpigmentary disorders of the skin such as melasma, age spots, and solar lentigines result from excessive epidermal melanin synthesized by cutaneous melanocytes.1 Thus, the unique biochemical pathway of melanogenesis provides a mechanism for developing pharmacologic regulators of pigmentation. Since its introduction for clinical use in 1961, hydroquinone (HQ) has been a successful tyrosinase inhibitor for treating hyperpigmentation.2 However, HQ can be metabolized by tyrosinase into toxic oxidation products, causing oxidative damage to the cell and inducing melanocyte death.3 As an alternative, deoxyArbutin (dA) and its second-generation derivatives, deoxyFuran (dF), 2-fluorodeoxyArbutin (fdA), and thiodeoxyArbutin (tdA), are considered to be promising skin-lightening agents because they inhibit melanogenesis at lower concentrations compared with HQ.4 We have compared toxicity profiles of dA and its derivatives with that of HQ, aiming to develop an effective therapeutic tyrosinase inhibitor that simultaneously exhibits minimal cytotoxicity.
Phenolic/catecholic derivatives that are structurally similar to the melanin precursor tyrosine can exhibit melanocyte-specific cytotoxicity by interacting with melanogenic enzymes to produce reactive quinones and reactive oxygen species (ROS).5 The reactive quinones undergo intracellular covalent binding with crucial nucleophilic thiol groups in proteins essential for cell survival.6 ROS generation can induce oxidative stress, ultimately inducing apoptosis.7 For cellular protection, oxidative stress induced by phenolic compounds can also trigger activation of an intricate arsenal of antioxidants. These antioxidants (superoxide dismutase [SOD], catalase, glutathione peroxidase, and thioredoxin) serve to scavenge and/or detoxify reactive oxygen intermediates or block free-radical chain reactions (tocopherol) to prevent cell death.8 Catalase is one of the primary defense molecules against oxidative stress. Cellular expression levels of catalase may be a useful marker of both acute and chronic oxidative stress9 because of its ability to neutralize hydrogen peroxide and thus lower ROS concentrations.