6-Benzylaminopurine stimulates melanogenesis via cAMP-independent activation of protein kinase A

Melanogenesis is a physiological process that results in the synthesis of melanin pigments, which play a crucial protective role against skin photocarcinogenesis. The present study was designed to determine the effects of 6-benzylaminopurine (6-BAP) on melanogenesis and elucidate the molecular events of melanogenesis induced by 6-BAP. To elucidate the pigmenting effect of 6-BAP and its mechanism, several experiments were performed in B16 melanoma cells. Melanin content, tyrosinase activity, cAMP production, and Western blots for proteins which are involved in melanogenesis were introduced in this study. Melanin content and tyrosinase activity increased in response to treatment with 6-BAP in a concentration-dependent manner. The tyrosinase, TRP-1, TRP-2 and MITF protein levels were found to increase significantly in response to 6-BAP in a time-dependent manner. In addition, Western blot analysis revealed that 6-BAP increased the phosphorylated level of CRE-binding protein. The increased melanin synthesis that was induced by treatment with 6-BAP treatment was reduced significantly in response to co-treatment with H-89 [a protein kinase A (PKA) inhibitor], whereas co-treatment with SB203580 (a p38 MAPK inhibitor) and Ro-32-0432 (a PKC inhibitor) did not attenuate the increase in melanin content levels that was induced by 6-BAP. In a cAMP production assay, 6-BAP did not increase the intracellular cAMP level. These findings suggest that 6-BAP activates PKA via a cAMP-independent pathway and subsequently stimulates melanogenesis by up-regulating MITF and tyrosinase expression.     

p-Coumaric acid, a constituent of Sasa quelpaertensis Nakai, inhibits cellular melanogenesis stimulated by alpha-melanocyte stimulating hormone

Background   Recent study has demonstrated that Sasa quelpaertensis (Korean name, Jeju-Joritdae) extracts inhibit cellular melanogenesis implicating potential use in the control of skin pigmentation.
Objectives   The purpose of the present study was to elucidate the active constituents of this plant inhibiting melanogenesis and the associated mechanism.
Methods   The effect of the plant-derived materials on melanin production and/or tyrosinase expression was examined in murine melanoma B16/F10 cells and neonatal human melanocytes.
Results   When tested in melanoma B16/F10 cells treated with the α-melanocyte stimulating hormone (α-MSH), the aqueous ethanol extract of S . quelpaertensis culm inhibited the cellular melanogenesis more effectively than its leaf extract. A major active compound was isolated from the culm extract by solvent fractionation and column chromatography, and identified to be p -coumaric acid by spectroscopic and chromatographic analyses. The compound ( p -coumaric acid) inhibited α-MSH-stimulated cellular melanogenesis more effectively than arbutin or other structurally similar compounds including 3-(4-hydroxyphenyl) propionic acid, cinnamic acid and caffeic acid. It also attenuated α-MSH-dependent increase of tyrosinase protein. The antimelanogenic effect of p -coumaric acid was also verified in neonatal human melanocytes.
Conclusions   The present study identified p -coumaric acid as a main constituent of S . quelpaertensis inhibiting cellular melanogenesis. Because of its structural similarity, p -coumaric acid may interfere with l -tyrosine action in the control of tyrosinase expression in response to α-MSH.     

枸杞多糖通过调控α-MSH蛋白的表达抑制UVA诱导的细胞黑色素生成

 目的 探究枸杞多糖（LBP）对UVA诱导细胞黑色素生成的影响。 方法 用不同浓度LBP(0、20、50、100、200、300、400、500 μg/mL)处理HaCaT细胞和HEM细胞，采用CCK8法检测对细胞增殖的影响，筛选出适宜浓度的LBP进行后续实验。使用300 μg/mL LBP、20 μM N-1A处理被30 J/cm2 UVA照射的HaCaT细胞和HEM细胞，多巴氧化法测定细胞中tyrosinase活性、NaOH裂解法测定黑色素含量。通过酶联免疫吸附试验（ELISA）检测 LBP对细胞内α-MSH蛋白表达的调控，应用Western blot检测细胞黑色素生成相关蛋白MITF、tyrosinase、TRP1和TRP2的表达水平。 结果 CCK8实验结果提示，当LBP浓度等于300 μg/mL时，HaCaT细胞和HEM细胞的增殖无明显变化（t=1.89、0.07，P=0.107、0.947）。相较于UVA组， LBP在体外可以明显抑制UVA诱导的HEM细胞中tyrosinase活性（t=33.19，P=0.001）以及减低黑色素含量（t=7.13，P=0.019）；ELISA结果提示，UVA照射可以促进HaCaT细胞和HEM细胞的α-MSH蛋白分泌（t=-3.79、-3.41，P=0.043、0.046）， LBP能够抑制HaCaT细胞和HEM细胞中α-MSH的蛋白表达水平（t=3.75、3.41，P=0.044、0.048）；Western blot结果显示， LBP可显著下调UVA诱导的黑色素生成相关蛋白MITF、tyrosinase、TRP1和TRP2的表达。 结论 LBP可显著抑制UVA诱导的细胞黑色素生成，其机制可能通过调控HaCaT细胞和HEM细胞中α-MSH蛋白水平实现。     

siRNA-mediated knock-down of COX-2 in melanocytes suppresses melanogenesis

Cyclooxygenase-2 (COX-2) is an enzyme induced in response to multiple mitogenic and inflammatory stimuli, including UV light. UV-induced COX-2 expression induces production of prostaglandin E2 (PGE2) in keratinocytes, which mediates inflammation and cell proliferation. Until recently, studies regarding COX-2 and PGE2 in the skin have focused on keratinocytes and skin cancer and the effect of PGs produced by keratinocytes on melanocytes. However, the effects of COX-2 itself or COX-2 inhibitors on melanogenesis are not well known. Therefore, to establish the role of COX-2 in melanogenesis, we investigated the effects of knock-down of COX-2 in melanocytes on melanin production and the expression of melanogenic molecules through silencing of COX-2 expression with COX-2 short interfering RNA (siRNA). COX-2 knock-down in melanocytes decreased the expressions of tyrosinase, TRP-1, TRP-2, gp100 and MITF and also reduced tyrosinase enzyme activity. Furthermore, COX-2 siRNA-transfected melanocytes showed markedly reduced alpha-melanocyte stimulating hormone (α-MSH)-induced melanin production. In addition, α-MSH-induced COX-2 expression in both scrambled siRNA-transfected and COX-2 siRNA-transfected melanocytes was greater than α-MSH-untreated cells. Our results suggest that COX-2 might be a candidate target for the development of anti-melanogenic agents and α-MSH-induced pigmentation could be closely associated with COX-2 expression. COX-2 inhibitors might therefore be of particular use in whitening cosmetics for hyperpigmentation disorders such as melasma, postinflammatory hyperpigmentation and solar lentigo.     

墨旱莲乙醇提取物动物致色素作用和对小鼠B16黑素瘤细胞黑素生成的影响

目的选择离体实验中对黑色素合成的关键酶—酪氨酸酶(tyrosinase,TYR)有激活作用的墨旱莲(旱莲草),研究其动物致色素作用和对小鼠B16黑素瘤细胞黑素生成及相关基因犤TYR、TYR相关蛋白(TRP-1/2)mRNA犦表达的影响。方法以棕色豚鼠为动物模型,用Schmorl法染色,计数含黑素的细胞;用多巴(DOPA)-氧化酶染色,计算每100个基底细胞中DOPA阳性细胞数。培养的小鼠B16黑素瘤细胞以四甲基偶氮唑盐比色(MTT)法、氢氧化钠(NaOH)法和体外氧化DOPA反应方法分别测定细胞的增殖活性、黑素生成量及TYR活性;逆转录-聚合酶链反应(RT-PCR)测定TYR及其TRP-1/2基因的表达。结果墨旱莲乙醇提取物可使豚鼠表皮基底层中含黑素颗粒细胞增多,使豚鼠表皮内DOPA阳性细胞增多(P<0.05);具有促进小鼠B16黑素瘤细胞黑素合成及TYR活性作用(P<0.05),对细胞TYR基因有上调作用,而对TRP-1/2mRNA的表达无明显作用。结论墨旱莲乙醇提取物具有促进黑素合成及上调酪氨酸酶基因表达的作用,对白癜风色素恢复有较好应用和开发的前景。     

The expression of melanogenic proteins in Korean skin after ultraviolet irradiation

For proper melanin production, several specific enzymes such as tyrosinase, tyrosinase-related protein 1 (TRP-1) and dopachrome tautomerase are required. Their expressions are increased after exposure to UVB. However, it is not known how long tyrosinase and TRP-1 activities continue after UV irradiation in vivo. The purpose of this study is to measure the changes in expressions of tyrosinase, TRP1, and MITF after exposure to UV on skin in a Korean population. We established an immunohistochemical staining protocol for specimens which were obtained from UV-irradiated skin in five healthy Korean males on the 2nd, 5th, 7th, 28th, and 56th days after UV irradiation. Tyrosinase, TRP-1, and MITF expressions increased until 7 days after UV irradiation and then dropped to the basal constitutive level 4 and 8 weeks later. Interestingly, tyrosinase increased prior to TRP-1. This study reveals the time-sequence of melanin-synthesized enzymes and provides important information for the clinical evaluation of the effectiveness of whitening agents.     

女贞子对培养的黑素细胞酪氨酸酶活性和黑素合成的影响

目的 研究女贞子单体酪醇和齐墩果酸对人黑素细胞的增殖、酪氨酸酶活性及黑素合成的影响。方法 采用MTT法测定细胞增殖情况,多巴氧化法测定酪氨酸酶活性,氢氧化钠裂解法测定黑素含量,半定量RT-PCR检测药物对黑素细胞酪氨酸酶和酪氨酸酶相关蛋白-1 mRNA表达的影响。结果 加入酪醇72h后,各组黑素细胞的酪氨酸酶活性和合成黑素能力明显增强,且呈浓度依赖性;酪氨酸酶和酪氨酸酶相关蛋白-1 mRNA表达量分别比空白对照增加39.10%和99.26%;齐墩果酸也能明显激活酪氨酸酶(P<0.01),促进黑素合成(P<0.05),并使黑素细胞酪氨酸酶和酪氨酸酶相关蛋白-1mRNA表达量分别比加入无水乙醇的对照增加31.88%和17.73%。结论 酪醇和齐墩果酸可能通过上调酪氨酸酶和酪氨酸酶相关蛋白-1 mRNA的表达而增强正常人黑素细胞的黑素合成和酪氨酸酶活性:两者可能是女贞子中影响黑素细胞生物学活性的主要成分。