Regulation of pigmentation by substrate elasticity in normal human melanocytes and melanotic MNT1 human melanoma cells

The elasticity of the cellular microenvironment is a key regulator of cellular physiology in many cell types. To investigate the effects of substrate stiffness on the pigmentation process, we cultured normal human melanocytes (NHM) and MNT1 melanoma cells on laminin‐coated polydimethylsiloxane (PDMS) substrates of different stiffness. The dendricity of NHM and MNT1 cells was reduced as the substrate stiffness decreased, and the degree of melanosome transfer from NHM or MNT1 cells to normal human keratinocytes was decreased on softer substrates with the reduced dendricity. Gene and protein expressions of MITF, tyrosinase, TRP2, and gp100/PMEL17 exhibited a consistent decreasing trend with the decreasing stiffness. Because the stiffness sensing is mediated by focal adhesion complex through integrin receptors, we checked laminin specific integrin alpha 6 and p‐FAK for MNT1 cells to observe that the substrate adhesion was weakened as the substrate stiffness decreased. Weaker adhesion on a softer substrate was accompanied by dynamic shape changes in MNT1 cells with higher speed and larger scattering. Dendritic MNT1 cells cultured on a stiffer substrate exhibited lower migration with smaller root mean squared displacement. These results demonstrate the possibility that skin pigmentation can be influenced by mechanical properties of the cellular microenvironment and can increase when the skin becomes stiff.     

驱白艾力勒思亚散乙醇提取物对小鼠B16黑素瘤细胞增殖及黑素生成的影响

目的研究维药复方驱白艾力勒思亚散(QBALLSYS)乙醇提取物对小鼠B16黑素瘤细胞增殖、黑素合成以及酪氨酸酶活性的影响。方法以MTT法测定培养的B16黑素瘤细胞的增殖活性;氢氧化钠法测定黑素生成量;体外氧化多巴反应方法测定酪氨酸酶活性。结果与空白对照组相比,驱白艾力勒思亚散乙醇提取物对B16黑素瘤细胞的增殖活性、黑素生成量、酪氨酸酶活性均有显著性作用(P<0.05或P<0.01)。驱白艾力勒思亚散乙醇提取物对小鼠B16黑素瘤细胞的增殖活性有上调作用,对细胞黑素生成以及酪氨酸酶的活性均有不同程度的促进作用。结论驱白艾力勒思亚散的乙醇提取物具有促进黑素细胞增殖和合成黑素的作用。     

The effect of niacinamide on reducing cutaneous pigmentation and suppression of melanosome transfer

BACKGROUND: Cutaneous hyperpigmentation occurs in multiple conditions. In addition, many Asian women desire a lighter skin colour. Thus, there is a need for the development of skin lightening agents. Niacinamide is a possible candidate. OBJECTIVES: To investigate the effects of niacinamide on melanogenesis in vitro and on facial hyperpigmentation and skin colour in vivo in Japanese women. METHODS: Melanin production was measured in a purified mushroom tyrosinase assay, cultured melanocytes, a keratinocyte/melanocyte coculture model, and a pigmented reconstructed epidermis (PREP) model. The clinical trials included 18 subjects with hyperpigmentation who used 5% niacinamide moisturizer and vehicle moisturizer in a paired design, and 120 subjects with facial tanning who were assigned to two of three treatments: vehicle, sunscreen and 2% niacinamide + sunscreen. Changes in facial hyperpigmentation and skin colour were objectively quantified by computer analysis and visual grading of high-resolution digital images of the face. RESULTS: Niacinamide had no effect on the catalytic activity of mushroom tyrosinase or on melanogenesis in cultured melanocytes. However, niacinamide gave 35-68% inhibition of melanosome transfer in the coculture model and reduced cutaneous pigmentation in the PREP model. In the clinical studies, niacinamide significantly decreased hyperpigmentation and increased skin lightness compared with vehicle alone after 4 weeks of use. CONCLUSIONS: The data suggest niacinamide is an effective skin lightening compound that works by inhibiting melanosome transfer from melanocytes to keratinocytes.     

验方祛斑汤含药血清对A375人黑素瘤细胞黑素合成的影响

目的用血清药理学方法研允验方祛斑汤对A375人黑素瘤细胞株细胞增殖、酪氨酸酶活性和黑素合成的影响，并探讨本方治疗黄褐斑的作用机制。方法用四甲基偶氮唑蓝法（MTT）测定验方祛斑汤对细胞增殖的影响，酶学方法测定其封酪氨酸酶活性的影响，475nm比色法测定其对黑素含量的影响。结果验方祛斑汤含药血清封体外培养的A375人黑素瘤细胞具有抑制细胞增殖，降低酪氨酸酶活性和黑素含量作用。结论验方祛斑汤能抑制黑素细胞黑素合成，这可能是其治疗黄褐斑的作用机制之一。     

9‐cis retinoic acid is the ALDH1A1 product that stimulates melanogenesis

Aldehyde dehydrogenase 1A1 (ALDH1A1), an enzyme that catalyses the conversion of lipid aldehydes to lipid carboxylic acids, plays pleiotropic roles in UV‐radiation resistance, melanogenesis and stem cell maintenance. In this study, a combination of RNAi and pharmacologic approaches were used to determine which ALDH1A1 substrates and products regulate melanogenesis. Initial studies revealed that neither the UV‐induced lipid aldehyde 4‐hydroxy‐2‐nonenal nor the ALDH1A1 product all‐trans retinoic acid appreciably induced melanogenesis. In contrast, both the ALDH1A1 substrate 9‐cis retinal and its corresponding product 9‐cis retinoic acid potently induced the accumulation of MITF mRNA, Tyrosinase mRNA and melanin. ALDH1A1 depletion inhibited the ability of 9‐cis retinal but not 9‐cis retinoic acid to stimulate melanogenesis, indicating that ALDH1A1 regulates melanogenesis by catalysing the conversion of 9‐cis retinal to 9‐cis retinoic acid. The addition of potent ALDH1A inhibitors (cyanamide or Angeli's salt) suppressed Tyrosinase and MITF mRNA accumulation in vitro and also melanin accumulation in skin equivalents, suggesting that 9‐cis retinoids regulate melanogenesis in the intact epidermis. Taken together, these studies not only identify cyanamide as a potential novel treatment for hyperpigmentary disorders, but also identify 9‐cis retinoic acid as a pigment stimulatory agent that may have clinical utility in the treatment of hypopigmentary disorders, such as vitiligo.