Protective Effect of Indole-3-Pyruvate against Ultraviolet B-Induced Damage to Cultured HaCaT Keratinocytes and the Skin of Hairless Mice

Previous investigations demonstrated that pyruvate protects human keratinocytes against cell damage stemming from exposure to ultraviolet B (UVB) radiation. This study endeavoured to elucidate the protective capacity of aromatic pyruvates (e.g., phenylpyruvate (PPyr), 4-hydroxyphenylpyruvate (HPPyr), and indole-3-pyruvate (IPyr)) against UVB-induced injury to skin cells, both in vitro and in vivo. Cultured human HaCaT keratinocytes were irradiated with UVB light (60 mJ/cm2) and maintained with or without test compounds (1–25 mM). In addition, the dorsal skin of hairless mice (HR-1) was treated with test compounds (100 µmol) and exposed to UVB light (1 J/cm2) for two times. The ability of the test compounds to ameliorate UVB-induced cytotoxicity and inflammation was then assessed. Aromatic pyruvates reduced cytotoxicity in UVB-irradiated HaCaT keratinocytes, and also diminished the expression of interleukin 1β (IL-1β) and interleukin 6 (IL-6). IPyr was more efficacious than either PPyr or HPPyr. Furthermore, only IPyr inhibited cyclooxygenase-2 (Cox-2) expression at both the mRNA and the protein level in UVB-treated keratinocytes. Topical application of IPyr to the dorsal skin of hairless mice reduced the severity of UVB-induced skin lesions, the augmentation of dermal thickness, and transepithelial water loss. Overproduction of IL-1β and IL-6 in response to UVB radiation was also suppressed in vivo by the topical administration of IPyr. These data strongly suggest that IPyr might find utility as a UVB-blocking reagent in therapeutic strategies to lessen UVB-induced inflammatory skin damage.既往研究表明，丙酮酸（pyruvate）可保护人角质形成细胞免受紫外线B（UVB）辐射引发的细胞损伤。本研究旨在阐明芳香族丙酮酸类（例如苯丙酮酸（phenylpyruvate，PPyr）、4-羟基苯丙酮酸（4-hydroxyphenylpyruvate，HPPyr）以及吲哚-3-丙酮酸（indole-3-pyruvate，IPyr））在体外及体内模型中抵御UVB诱导的皮肤细胞损伤的保护能力。将培养的人HaCaT角质形成细胞以60 mJ/cm²的剂量进行UVB辐照，并分别在含或不含浓度为1~25 mM受试化合物的培养基中培养。此外，将无毛小鼠（HR-1）的背部皮肤涂抹100 μmol的受试化合物后，以1 J/cm²的UVB剂量进行两次辐照。随后评估受试化合物对UVB诱导的细胞毒性与炎症反应的改善作用。结果显示，芳香族丙酮酸类可降低UVB辐照后HaCaT角质形成细胞的细胞毒性，同时下调白细胞介素1β（interleukin 1β，IL-1β）与白细胞介素6（interleukin 6，IL-6）的表达水平，且IPyr的保护效果优于PPyr与HPPyr。此外，在经UVB处理的角质形成细胞中，仅IPyr可在mRNA与蛋白两个层面上抑制环氧合酶-2（cyclooxygenase-2，Cox-2）的表达。将IPyr局部涂抹于无毛小鼠背部皮肤，可减轻UVB诱导的皮肤损伤程度、真皮层增厚幅度及经表皮失水率（transepithelial water loss）；体内实验中，IPyr局部给药同样可抑制UVB辐射诱导的IL-1β与IL-6过度产生。上述实验结果充分表明，IPyr有望作为UVB阻断试剂，应用于减轻UVB诱导的炎症性皮肤损伤的治疗策略中。