The Mechanism of Melanocytes-Specific Cytotoxicity Induced by Phenol Compounds Having a Prooxidant Effect, relating to the Appearance of Leukoderma

Abstract

Specific phenol compounds including rhododendrol (RD), a skin-brightening ingredient in cosmetics, are reported to induce leukoderma, inducing a social problem, and the elucidation of mechanism of leukoderma is strongly demanded. This study investigated the relationship among the cytotoxicities of six phenol compounds on B16F10 melanoma cells and HaCaT keratinocytes and generated reactive oxygen species (ROS). As a result, the cytotoxicity of RD on B16F10 cells was higher than that on HaCaT cells, and RD significantly increased intracellular ROS and hydrogen peroxide (H2O2) levels in B16F10 cells. Furthermore, although raspberry ketone (RK), RD derivative, also increased intracellular ROS in B16F10 cells, increase in ROS was suppressed by disodium dihydrogen ethylenediaminetetraacetate dehydrate (EDTA). The amounts of increased ROS with RK in HaCaT cells without melanocyte were further increased by tyrosinase. Therefore, tyrosinase, a metalloprotein having copper, was speculated to be one of causative agents allowing phenol compounds to work as a prooxidant. Hydroxyl radical was generated by adding a mixture of tyrosinase and H2O2 to RD, and the amount of the radical was further increased by UVB, indicating that RD cytotoxicity was caused by intracellularly increased ROS, which possibly related to phenol induced prooxidants.

Generation of hydroxyl radicals and singlet oxygen during oxidation of rhododendrol and rhododendrol-catechol

“…As previously reported, hydrogen peroxide is produced during tyrosinase-catalyzed rhododendrol and rhododendrol-catechol oxidations. (13) We also confirmed the hydrogen peroxide generation by measuring the increase in dissolved oxygen concentration by the addition of catalase. The hydrogen peroxide generated in the oxidation of rhododendrol and rhododendrol-catechol may cause hydroxyl radical generation.…”

“…The generation of hydroxyl radicals was observed in a mixture of rhododendrol, tyrosinase, and hydrogen peroxide, and the generation was enhanced by irradiation with 1,000 J/m 2 UV-B (ultraviolet light with 280–315 nm-wavelength). (13) Further, ROS generation was detected during rhododendrol oxidation by tyrosinase. (14) Hence, in addition to hydrogen peroxide, hydroxyl radicals and singlet oxygen ( 1 O 2 ) are strong candidates for the onset of leukoderma caused by rhododendrol.…”

Kanamycin induces free radicals formation in melanocytes: An important factor for aminoglycosides ototoxicity

“…Catalase is the main enzyme responsible for the degradation of hydrogen peroxide in melanocytes . When H 2 O 2 is not effectively eliminated, levels of reactive hydroxyl radicals may increase due to iron‐catalyzed Fenton reaction . Moreover, in pigmented cells melanin can act as a free radicals scavenger and may possess the superoxide dismutase activity …”

4‐(4‐Hydroxyphenyl)‐2‐butanol (rhododendrol)‐induced melanocyte cytotoxicity is enhanced by UVB exposure through generation of oxidative stress

“…To clarify the pathogenesis of RD‐induced leukoderma, we investigated the effect of UVR in NHEMs treated with RD, as a potential additional factor enhancing RD‐induced melanocyte cytotoxicity. Recent reports indicated that UVB exposure influences RD‐induced melanocyte cytotoxicity . Nagata et al showed that UVB irradiation amplifies RD‐induced cytotoxicity in B16F10 melanoma cells and increases the generation of hydroxyl radicals by a mixture of tyrosinase and H 2 O 2 .…”

“…Recent reports indicated that UVB exposure influences RD‐induced melanocyte cytotoxicity . Nagata et al showed that UVB irradiation amplifies RD‐induced cytotoxicity in B16F10 melanoma cells and increases the generation of hydroxyl radicals by a mixture of tyrosinase and H 2 O 2 . Lee et al have shown that UVB irradiation enhances RD‐induced cytotoxicity and induces apoptosis in NHEMs.…”