Inhibitory effects of macelignan isolated from Myristica fragrans HOUTT. on melanin biosynthesis

The aim of this study was to investigate the in vitro inhibitory effects of macelignan isolated from Myristica fragrans HOUTT. on melanogenesis and its related enzymes such as tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2) in melan-a murine melanocytes. The IC50 values of macelignan for melanogenesis and tyrosinase were 13 microM and 30 microM, respectively, while those of arbutin as a positive control were 990 microM and 660 microM, respectively. In Western blot analysis, macelignan also significantly decreased tyrosinase, TRP-1, and TRP-2 protein expression. These results indicate that macelignan effectively inhibits melanin biosynthesis and thus could be employed as a new skin-whitening agent.     

Identification of quinolines that inhibit melanogenesis by altering tyrosinase family trafficking

A series of quinolines, including chloroquine and quinine, were identified as potent pigmentation inhibitors through screening a compound library in murine melanocytes. Structure-activity relationship analysis indicated that 4-substituted amino groups with a tertiary amine side chain, such as chloroquine, were associated with robust inhibitory activity. In contrast to many previously identified pigmentation inhibitors, these newly identified inhibitors had no effect on either the level or the enzymatic activity of tyrosinase, the rate-limiting enzyme in melanin production. Rather, our results showed that these quinolines inhibited melanogenesis by disrupting the intracellular trafficking of tyrosinase-related proteins and lysosome-associated membrane protein 1 (Lamp-1). In treated melanocytes, tyrosinase and tyrosinase-related protein 1 accumulated in Lamp-1-positive perinuclear organelles instead of melanosomes, thus preventing melanogenesis. The depigmenting abilities of chloroquine and quinine salicylate were assessed in a human skin equivalent model (MelanoDerm). Both compounds were considerably more effective than arbutin, a widely used lightening agent. Our results indicate that quinolines may be useful agents for "cosmeceutical" skin lightening and treatment of hyperpigmentation disorders.     

Gentamicin affects melanogenesis in normal human melanocytes

Background: Aminoglycoside antibiotics, including gentamicin, despite their ability to induce adverse effects on pigmented tissues, remain valuable and sometimes indispensable for the treatment of various infections. It is known that gentamicin binds to melanin biopolymers, but the relation between this drug affinity to melanin and its toxicity is not well documented. The aim of this work was to examine the impact of gentamicin on viability and melanogenesis in HEMa-LP (light pigmented) and HEMn-DP (dark pigmented) normal human melanocytes.

Methodology/principal findings: The effect of gentamicin on cell viability was determined by 4-[3-(4-iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1) assay; melanin content and tyrosinase activity were measured spectrophotometrically. It has been demonstrated that gentamicin induces concentration-dependent loss in melanocytes viability. The application of antibiotic in concentration of 10?mM causes higher reduction in viability of the light pigmented melanocytes (by about 74%) when compared with the dark pigmented ones (by about 62%). The value of the concentration of a drug that produces loss in cell viability by 50% (EC₅₀) for both cell lines was found to be ～7.5?mM. It has been shown that gentamicin causes inhibition of tyrosinase activity and reduces melanin content in light pigmented melanocytes significantly more than in the dark pigmented cells.

Conclusion/significance: We have found that gentamicin modulates melanization process in melanocytes in vitro, what may explain the potential role of melanin biopolymer in the mechanisms of undesirable toxic effects of this drug in vivo, as a result of its accumulation in pigmented tissues. We have also stated that the melanogenesis process in light pigmented melanocytes is more sensitive to the inhibitory effect of gentamicin than in the dark pigmented cells.     

Phloridzin-induced melanogenesis is mediated by the cAMP signaling pathway

Melanogenesis is a physiological process that results in the synthesis of melanin pigments, which play a crucial protective role in protection against skin photocarcinogenesis. Phloridzin is a phloretin 2′-glucoside that is found in many parts of the apple tree that reportedly increases tyrosinase activity and melanin contents through inhibition of protein kinase C (PKC) activity in B16 melanoma cells. In this study, we attempted to accurately determine the effects and mechanisms of action of phloridzin on melanogenesis. Specifically, we observed that phloridzin-induced a dose-dependent increase in tyrosinase activity and melanin contents, and that these changes were accompanied by an increase in the levels of tyrosinase and the tyrosinase-related proteins, TRP-1 and TRP-2. Furthermore, the cAMP-dependent protein kinase A (PKA) inhibitor H89 impaired the response of the tyrosinase activity and melanin synthesis to phloridzin. Additionally, phloridzin stimulated cAMP production and phosphorylation of the cAMP-response element binding protein (CREB). Taken together, the results of this study indicate that phloridzin increases tyrosinase gene expression through the cAMP signaling pathway, thereby leading to the stimulation of melanogenesis.     

Additive effects of heat and p38 mapk inhibitor treatment on melanin synthesis

It has been reported that the activation of extracellular signal-regulated kinase (ERK) reduces melanin synthesis. Recently, we also found that heat treatment induces ERK activation and inhibits melanogenesis in Mel-Ab cells (a mouse melanocyte cell line). In addition, it was reported that p38 MAPK (mitogen-activated protein kinase) inhibition blocks melanogenesis. Thus, we investigated the effects of heat and of the p38 MAPK inhibitor, SB203580, on melanogenesis. In this study, we found that heat treatment activates ERK and reduces melanin production in human melanocytes, and that this is accompanied by a reduction in tyrosinase activity. To regulate the ERK and p38 MAPK pathways simultaneously, we combined heat treatment and SB203580 and measured melanin synthesis. The results obtained showed that heat treatment and SB203580 reduced melanin synthesis more effectively than heat or SB203580 alone. We conclude that ERK activation and p38 MAPK inhibition can work in an additive manner to decrease melanogenesis.     

Modulation of melanogenesis and antioxidant defense system in melanocytes by amikacin

Amikacin is principally used to treat infections caused by microorganisms resistant to other aminoglycosides. Ototoxicity is one of the side effects of amikacin, but the causative mechanism of damage to the ear has not been fully established. Thus, the aim of this work was to examine the impact of amikacin on the melanogenesis and antioxidant defense system in cultured human normal melanocytes (HEMa-LP). Amikacin induced the concentration – dependent loss in melanocytes viability. The value of EC₅₀ was determined to be ～7.5 mM. The analyzed antibiotic inhibited melanin biosynthesis in concentration-dependent manner. Increasing the amikacin concentration also resulted in a decrease in cellular tyrosinase activity. To study the antioxidant defense system in melanocytes, the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) in cells exposed to amikacin were determined. Significant changes in cellular antioxidant enzymes activities were observed. Modulation of melanogenesis and the antioxidant status of melanocytes resulting from the use of amikacin in vitro may explain a potential role of melanin and melanocytes in the mechanisms of aminoglycosides ototoxic effects in vivo.     

Inhibition of melanogenesis by selina-4(14),7(11)-dien-8-one isolated from Atractylodis Rhizoma Alba

To develop effective skin-lightening agents, we tested medicinal herbal extracts for their melanogenic-inhibitory activities. We isolated a sesquiterpenoid compound from the extract of Atractylodis Rhizoma Alba using the bioactivity-guided fractionation and identified it as selina-4(14),7(11)-dien-8-one (compound 1) with spectroscopic methods. Compound 1 dramatically reduced melanin synthesis of melan-a cells without any apparent cytotoxicity. Compound 1 did not inhibit cell-free tyrosinase activity but decreased tyrosinase activity in melanocytes. These effects were attributed to reduced expression of melanogenic enzymes such as tyrosinase, tyrosinase-related protein 1 (TRP-1), and tyrosinase-related protein 2 (TRP-2). These results suggest that compound 1 may be an effective skin-lightening agent that regulates expression of melanogenic enzymes.     

Effect of Tunisian <Emphasis Type="Italic">Capparis spinosa</Emphasis> L. extract on melanogenesis in B16 murine melanoma cells

The effect of Tunisian Capparis spinosa L. aromatic plant extract on melanogenesis regulation in B16 murine melanoma cells was investigated. B16 cells were treated with 0.0005, 0.005, and 0.05% (w/v) C. spinosa extract after which the melanin content and cell viability were measured. To clarify the mechanism behind melanogenesis regulation, the expression of tyrosinase was determined. Results showed that the extract had a significant stimulative effect on melanogenesis in B16 cells in a dose-dependent manner without cytotoxicity. Western blot analysis showed that expression of tyrosinase in cells treated with 0.03% (w/v) C. spinosa extract increased by 12.5- and 20-fold after 24 and 48 h of incubation, respectively, compared with untreated cells. HPLC analysis of the extract revealed the presence of 1% quercetin, a known melanogenesis stimulator, indicating that our findings may be attributed to quercetin; however, other compounds present in the extract may also have an effect on the overall ability of the extract to stimulate melanogenesis. We report here that Tunisian C. spinosa leaf extract can stimulate melanogenesis in a dose-dependent manner without cytotoxicity by increasing tyrosinase protein expression and has the potential to be used as a possible tanning agent or as a treatment for hair depigmentation.     

Curcumin-like diarylpentanoid analogues as melanogenesis inhibitors

Anti-melanogenesis screening of 47 synthesized curcumin-like diarylpentanoid analogues was performed to show that some had a potent inhibitory effect on the melanogenesis in B16 melanoma cells. Their actions were considered to be mostly due to tyrosinase inhibition, tyrosinase expression inhibition, and melanin pigment degradation. The structure–activity relationships of those curcumin-like diarylpentanoid analogues which inhibited the melanogenesis and tyrosinase activity were also discussed. Of those compounds assayed, (2E,6E)-2,6-bis(2,5-dimethoxybenzylidene)cyclohexanone showed the most potent anti-melanogenesis effect, the mechanism of which is considered to be the degradation of the melanin pigment in B16 melanoma cells, affecting neither the tyrosinase activity nor tyrosinase expression.     

Temperature regulates melanin synthesis in melanocytes

Temperature change is one of the major environmental factors that influence the human skin. However, the relationship between temperature and melanogenesis has received little attention. In the present study, we investigated the effects of temperature change on melanogenesis in a mouse melanocyte cell line (Mel-Ab), and primary cultured human melanocytes. We found that Mel-Ab cells cultured at low temperatures (31 and 34 degrees C) produce less melanin than cells at 37 degrees C. These results were confirmed by experiments upon human melanocytes, demonstrating that the hypopigmenting effect of low temperatures is not cell type dependent. The observed melanin production was found to be accompanied by tyrosinase activity at each temperature, indicating that tyrosinase activity is regulated by temperature. We further examined whether the incubation period at low temperatures plays an important role in the regulation of melanogenesis. Short exposures to 27 degrees C for 1 h or 3 h did not affect tyrosinase activity or melanin synthesis, whereas long exposures to 31 degrees C for 2 days or 6 days significantly reduced tyrosinase activity and melanin synthesis in a duration-dependent manner. Our results suggest that exposure to low temperature and the duration of this exposure are important regulators of melanogenesis.     

Hesperetin induces melanin production in adult human epidermal melanocytes

One of the major sources of flavonoids for humans are citrus fruits, hesperidin being the predominant flavonoid. Hesperetin (HSP), the aglycon of hesperidin, has been reported to provide health benefits such as antioxidant, anti-inflammatory and anticarcinogenic effects. However, the effect of HSP on skin pigmentation is not clear. Some authors have found that HSP induces melanogenesis in murine B16-F10 melanoma cells, which, if extrapolated to in vivo conditions, might protect skin against photodamage. Since the effect of HSP on normal melanocytes could be different to that observed on melanoma cells, the described effect of HSP on murine melanoma cells has been compared to the effect obtained using normal human melanocytes. HSP concentrations of 25 and 50 µM induced melanin synthesis and tyrosinase activity in human melanocytes in a concentration-dependent manner. Compared to control melanocytes, 25 µM HSP increased melanin production and tyrosinase activity 1.4-fold (p < 0.01) and 1.1-fold (p < 0.01), respectively, and the corresponding increases in the case of 50 µM HSP were 1.9-fold (p < 0.001) and 1.3-fold (p < 0.001). Therefore, HSP could be considered a valuable photoprotective substance if its capacity to increase melanin production in human melanocyte cultures could be reproduced on human skin.