Down-regulation of tyrosinase expression by acetylsalicylic acid in murine B16 melanoma

Acetylsalicylic acid (aspirin; ASA) is widely used as an analgesic/antipyretic drug. ASA exhibits a wide range of biological effects, including preventative effects against heart attack, stroke, and the development of some types of cancer. However, the effects of ASA on melanogenesis are not well known. Therefore, we investigated the effect of ASA on melanin production using B16 murine melanoma cells and demonstrated a new biological effect of ASA. In the presence of alpha-melanocyte stimulating hormone (alpha-MSH), B16 melanoma cells are stimulated to enhance melanin synthesis. ASA (2 mM) inhibited alpha-MSH-enhanced melanin synthesis in melanoma more strongly than other well-known anti-melanogenic agents such as arbutin (2 mM) and kojic acid (200 microM). Interestingly, ASA did not inhibit the catalytic activity of mushroom tyrosinase (concentration range 0.5-4.0 mM). To clarify the target of ASA action in melanogenesis, we performed Western blotting for tyrosinase, which is a key melanogenic enzyme. ASA inhibited tyrosinase expression in a dose-dependent manner. Therefore, the depigmenting effect of ASA might be due to inhibition of tyrosinase expression or enhancement of tyrosinase degradation. This study suggests that ASA is a candidate anti-melanogenic agent and it might be effective in hyperpigmentation disorders.     

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.     

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.     

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.     

Hypo-pigmenting effect of sesquiterpenes from Inula britannica in B16 melanoma cells

During the course of screens to identify anti-melanogenic agents from natural resources, we found that the methanol extract of the dried flower of Inula britannica L. inhibited melanin synthesis in cultured melanoma cells stimulated with 3-isobutyl-1-methylxanthine (IBMX). A bioassay-guided isolation of the chloroform fraction of the I. britannica using an in vitro melanogenesis inhibition assay led to the isolation of sesquiterpenes, 1-O-acetylbritannilactone (1), britannilactone (2) and neobritannilactone B (3). Compounds 1 and 2 significantly reduced melanin production in a dose-dependent manner with IC₅₀ values of 13.3 and 15.5 μM, respectively, whereas compound 3 was found to be cytotoxic. Compound 1 also inhibited the tyrosinase activity only in cell based-systems. Western blot analysis indicated that compound 1 inhibited melanogenesis by activating extracellular signal-regulated kinase (ERK) and Akt signaling and also inhibiting cAMP related binding protein, which regulates its downstream pathway, including tyrosinase, tyrosinase related protein-1 and TRP-2. These results demonstrated that compound 1, a major sesquiterpene from the flowers of I. britannica, exhibited anti-melanogenic activity by suppression of tyrosinase expression via ERK and Akt signaling. Taken together, our results suggest that these compounds may act as potent natural skin-lightening agents.     

N-trans-feruloyltyramine as a melanin biosynthesis inhibitor

In this study, we examined the effect of N-trans-feruloyltyramine (FA) on melanogenesis in mouse B16 melanoma cells. Melanogenesis was inhibited by FA in a dose-dependent manner. FA exhibited a greater potency than kojic acid as a standard inhibitor of melanogenesis. Moreover, treatment of B16 melanoma cells with FA was found to cause marked decreases in the expression levels of tyrosinase. FA-induced downregulation of tyrosinase resulted in suppression of melanin biosynthesis in murine B16 melanoma cells.     

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.     

杏仁油对黑色素瘤细胞B16细胞增殖及黑素合成的影响

目的探讨杏仁油对小鼠黑色素瘤细胞B16增殖及黑素合成的影响。方法采用MTT法测定杏仁油对小鼠黑色素瘤细胞B16增殖的影响,L-dopa氧化法测定酪氨酸酶活性,NaOH裂解法测定黑素合成。结果杏仁油浓度在0.1～100μg/mL时对小鼠黑色素瘤细胞B16增殖无影响(P>0.05),对酪氨酸酶活性和黑素含量均呈浓度依赖性抑制,均具有显著性抑制作用(P<0.05)。结论杏仁油对黑色素瘤细胞B16酪氨酸酶活性和黑素生成有较强的剂量相关性抑制作用。     

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.     

Piperlonguminine from Piper longum with inhibitory effects on alpha-melanocyte-stimulating hormone-induced melanogenesis in melanoma B16 cells

Skin hyperpigmentations such as melasma, freckles and senile lentigines can be subjectively treated by depigmenting agents. In our ongoing study to find melanogenesis inhibitors from natural sources, Piper longum L (fruits, Piperaceae) was discovered to have an inhibitory effect on alpha-melanocyte-stimulating hormone (alpha-MSH)-induced melanogenesis in melanoma B16 cells. Piperlonguminine has been identified as the melanogenesis inhibitor from P. longum by activity-guided extraction and isolation. The compound showed dose-dependent inhibitory effects with 85.1 +/- 4.9% inhibition at 25 microM, 62.1 +/- 6.1% at 12.5 microM, 36.4 +/- 4.6% at 6.3 microM and 18.4 +/- 5.1% at 3.1 microM on alpha-MSH-induced melanogenesis, showing an IC50 value of 9.6 microM. As a positive control, kojic acid exhibited an IC50 value of 44.6 microM on the melanogenesis. As to the mode of action, piperlonguminine showed an inhibitory effect on alpha-MSH-induced tyrosinase synthesis, documented by Western immunoblot analysis. However, piperlonguminine did not show an inhibitory effect on tyrosinase activity or a direct depigmenting effect of melanin.