Evaluation of the inhibition of mushroom tyrosinase and cellular tyrosinase activities of oxyresveratrol: comparison with mulberroside A

The inhibitory effects of oxyresveratrol, the aglycone of mulberroside A, on mushroom and cellular tyrosinase activities and melanin synthesis were evaluated. Mulberroside A and oxyresveratrol showed inhibitory activity against mushroom tyrosinase, with oxyresveratrol demonstrating a greater inhibitory effect than that of mulberroside A. Oxyresveratrol and mulberroside A strongly inhibited melanin production in Streptomyces bikiniensis and exhibited dose-dependent inhibition of tyrosinase activity and inhibition of melanin synthesis in B16F10 melanoma cells. However, the compounds exhibited nearly similar inhibitory effects on the activity of cellular tyrosinase and melanin synthesis in murine melanocytes. The inhibition of melanin synthesis by mulberroside A and oxyresveratrol was involved in suppressing the expression level of melanogenic enzymes, tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2). These results indicate that the inhibition rate of mushroom tyrosinase might not provide an accurate estimate of the inhibition rate of melanin synthesis in melanocytes.     

Evaluation of the inhibition of mushroom tyrosinase and cellular tyrosinase activities of oxyresveratrol: comparison with mulberroside A

The inhibitory effects of oxyresveratrol, the aglycone of mulberroside A, on mushroom and cellular tyrosinase activities and melanin synthesis were evaluated. Mulberroside A and oxyresveratrol showed inhibitory activity against mushroom tyrosinase, with oxyresveratrol demonstrating a greater inhibitory effect than that of mulberroside A. Oxyresveratrol and mulberroside A strongly inhibited melanin production in Streptomyces bikiniensis and exhibited dose-dependent inhibition of tyrosinase activity and inhibition of melanin synthesis in B16F10 melanoma cells. However, the compounds exhibited nearly similar inhibitory effects on the activity of cellular tyrosinase and melanin synthesis in murine melanocytes. The inhibition of melanin synthesis by mulberroside A and oxyresveratrol was involved in suppressing the expression level of melanogenic enzymes, tyrosinase, tyrosinase-related protein-1 (TRP-1), and tyrosinase-related protein-2 (TRP-2). These results indicate that the inhibition rate of mushroom tyrosinase might not provide an accurate estimate of the inhibition rate of melanin synthesis in melanocytes.     

Modification of Proteinase Inhibitor II in Adzuki Beans during Germination

We investigated the effects of compounds isolated from a methanolic extract of rose hips on melanin biosynthesis in B16 mouse melanoma cells and the possible mechanisms responsible for the inhibition of melanin biosynthesis. We found that, among the isolated compounds, quercetin was a particularly potent melanogenesis inhibitor. To reveal the mechanism for this inhibition, the effects on tyrosinase of B16 mouse melanoma were measured. Quercetin decreased the intracellular tyrosinase activity as well as the tyrosinase activity in a cell culture-free system. We also examined the cellular level of tyrosinase protein and found that quercetin dose-dependently inhibited tyrosinase protein expression. We consider from these results that the inhibition of melanogenesis by quercetin was due to the inhibition of both tyrosinase activity and of the protein expression.     

Tyrosinase inhibition and anti-melanin generation effect of cinnamamide analogues

Abnormal melanogenesis results in excessive production of melanin, leading to pigmentation disorders. As a key and rate-limiting enzyme for melanogenesis, tyrosinase has been considered an important target for developing therapeutic agents of pigment disorders. Despite having an (E)-β-phenyl-α,β-unsaturated carbonyl scaffold, which plays an important role in the potent inhibition of tyrosinase activity, cinnamic acids have not attracted attention as potential tyrosinase inhibitors, due to their low tyrosinase inhibitory activity and relatively high hydrophilicity. Given that cinnamic acids’ structure intrinsically features this (E)-scaffold and following our experience that minute changes in the chemical structure can powerfully affect tyrosinase activity, twenty less hydrophilic cinnamamide derivatives were designed as potential tyrosinase inhibitors and synthesised using a Horner-Wadsworth-Emmons reaction. Four of these cinnmamides (4, 9, 14, and 19) exhibited much stronger mushroom tyrosinase inhibition (over 90% inhibition) at 25 µM compared to kojic acid (20.57% inhibition); crucially, all four have a 2,4-dihydroxy group on the β-phenyl ring of the scaffold. A docking simulation using tyrosinase indicated that the four cinnamamides exceeded the binding affinity of kojic acid, and bound more strongly to the active site of tyrosinase. Based on the strength of their tyrosinase inhibition, these four cinnamamides were further evaluated in B16F10 melanoma cells. All four cinnamamides, without cytotoxicity, exhibited higher tyrosinase inhibitory activity (67.33 – 79.67% inhibition) at 25 μM than kojic acid (38.11% inhibition), with the following increasing inhibitory order: morpholino (9) = cyclopentylamino (14) < cyclohexylamino (19) < N-methylpiperazino (4) cinnamamides. Analysis of tyrosinase activity and melanin content in B16F10 cells showed that the four cinnamamides dose-dependently inhibited both cellular tyrosinase activity and melanin content and that their inhibitory activity at 25 μM was much better than that of kojic acid. The results of melanin content analysis well matched those of the cellular tyrosinase activity analysis, indicating that tyrosinase inhibition by the four cinnamamides is a major factor in the reduction of melanin production. These results imply that these four cinnamamides with a 2,4-dihydroxyphenyl group can act as excellent anti-melanogenic agents in the treatment of pigmentation disorders.     

Design,synthesis and anti-melanogenic effect of cinnamamide derivatives

Pigmentation disorders are attributed to excessive melanin which can be produced by tyrosinase. Therefore, tyrosinase is supposed to be a vital target for the treatment of disorders associated with overpigmentation. Based on our previous findings that an (E)-β-phenyl-α,β-unsaturated carbonyl scaffold can play a key role in the inhibition of tyrosinase activity, and the fact that cinnamic acid is a safe natural substance with a scaffolded structure, it was speculated that appropriate cinnamic acid derivatives may exhibit potent tyrosinase inhibitory activity. Thus, ten cinnamamides were designed, and synthesized by using a Horner-Emmons olefination as the key step. Cinnamamides 4 (93.72% inhibition), 9 (78.97% inhibition), and 10 (59.09% inhibition) with either a 2,4-dihydroxyphenyl, or 4-hydroxy-3-methoxyphenyl substituent showed much higher mushroom tyrosinase inhibition at 25?µM than kojic acid (18.81% inhibition), used as a positive control. Especially, the two cinnamamides 4 and 9 having a 2,4-dihydroxyphenyl group showed the strongest inhibition. Docking simulation with tyrosinase revealed that these three cinnamamides, 4, 9, and 10, bind to the active site of tyrosinase more strongly than kojic acid. Cell-based experiments carried out using B16F10 murine skin melanoma cells demonstrated that all three cinnamamides effectively inhibited cellular tyrosinase activity and melanin production in the cells without cytotoxicity. There was a close correlation between cellular tyrosinase activity and melanin content, indicating that the inhibitory effect of the three cinnamamides on melanin production is mainly attributed to their capability for cellular tyrosinase inhibition. These results imply that cinnamamides having the (E)-β-phenyl-α,β-unsaturated carbonyl scaffolds are promising candidates for skin-lighting agents.     

Enhancement of tyrosinase inhibition of the extract of Veratrum patulum using cellulase

Inhibitors of melanin biosynthesis were screened by using three different methods. The extract of Veratrum patulum contains hydroxystilbene compounds that are potent tyrosinase inhibitors. We evaluated the enzyme inhibitory property on the mushroom tyrosinase of hydroxystilbene compounds including resveratrol, oxyresveratrol, and their analogs. Biotransformation using cellulase of the whole extract brought about an increase in the inhibitory activity of the products on mushroom tyrosinase. The enhancement of tyrosinase inhibition is supposed to increase the concentration of aglycon, which has superior inhibitory activity to its glycoside. Eventually, melanin biosynthesis was inhibited by the enhanced tyrosinase inhibitory activity of the extract. This result indicated that deglycosylation of stilbene compounds has exerted more effective inhibition on the enzyme than that of the unprocessed plant extract.     

Inhibitory effect of dalbergioidin isolated from the trunk of Lespedeza cyrtobotrya on melanin biosynthesis

Tyrosinase is a key enzyme for melanin biosynthesis, and hyperpigmentation disorders are associated with abnormal accumulation of melanin pigments, which can be reduced by treatment with depigmenting agents. The methanol extract of Lespedeza cyrtobotrya MIQ showed inhibitory activity against mushroom tyrosinase. The active compound was purified from the methanol extract of L cyrtobotrya, followed by several chromatographic methods, and identified as dalbergioidin (DBG) by spectroscopic methods. The results showed that DBG exhibited tyrosinase inhibitory activity with an IC50 of 20 mM. The kinetic analysis tyrosinase inhibition revealed that DBG acted as noncompetitive inhibitor. In addition, DBG showed a melanin biosynthesis inhibition zone in the culture plate of Streptomyces bikiniensis that has commonly been used as an indicator organism. Furthermore, 27 mM DBG decreased more than 50% of melanin contents on the pigmentation using immortalized mouse melanocyte, melan-a cell.     

Tyrosinase inhibitory effect and inhibitory mechanism of tiliroside from raspberry

Tiliroside was found to inhibit both monophenolase and diphenolase activity of mushroom tyrosinase. The lag time of tyrosine oxidation catalyzed by mushroom tyrosinase was obviously lengthened; 0.337?mM of tiliroside resulted in the lag time extension from 46.7?s to 435.1?s. A kinetic analysis shown that tiliroside was a competitive inhibitor for monophenolase and diphenolase with K_i values of 0.052?mM and 0.26?mM, respectively. Furthermore, tiliroside showed 34.5% (p?<?0.05) inhibition of intracellular tyrosinase activity and 54.1% (p?<?0.05) inhibition of melanin production with low cytotoxicity on B16 mouse melanoma cells at 0.168?mM. In contrast, arbutin displayed 9.1% inhibition of cellular tyrosinase activity and 29.5% inhibition of melanin production at the same concentration. These results suggested that tiliroside was a potent tyrosinase inhibitor and might be used as a skin-whitening agent and pigmentation medicine.     

Skin whitening agents: medicinal chemistry perspective of tyrosinase inhibitors

Melanogenesis is a process to synthesize melanin, which is a primary responsible for the pigmentation of human skin, eye and hair. Although numerous enzymatic catalyzed and chemical reactions are involved in melanogenesis process, the enzymes such as tyrosinase and tyrosinase-related protein-1 (TRP-1) and TRP-2 played a major role in melanin synthesis. Specifically, tyrosinase is a key enzyme, which catalyzes a rate-limiting step of the melanin synthesis, and the downregulation of tyrosinase is the most prominent approach for the development of melanogenesis inhibitors. Therefore, numerous inhibitors that target tyrosinase have been developed in recent years. The review focuses on the recent discovery of tyrosinase inhibitors that are directly involved in the inhibition of tyrosinase catalytic activity and functionality from all sources, including laboratory synthetic methods, natural products, virtual screening and structure-based molecular docking studies.     

Structural requirement of phenylthiourea analogs for their inhibitory activity of melanogenesis and tyrosinase

Effect of a series of 1-phenylthioureas 1a-k and 1,3-disubstituted thioureas 2a-k were evaluated against melanin formation in melanoma B16 cell line and mushroom tyrosinase. Inhibitory activity of tyrosinase of 1-phenylthioureas 1a-k is parallel to their melanogenic inhibition. Thus, the melanogenic inhibition in melanoma B16 cells of 1-phenylthioureas could be the result of inhibition of tyrosinase. However, 1,3-diaryl or 1-phenyl-3-alkylthioureas, 2a-k, appears as melanogenic inhibitor without inhibition of tyrosinase. The molecular docking study of 1e and 2b to binding pocket of tyrosinase provided convincing explanation regarding the necessity of direct connection of planar phenyl to thiourea unit without N'-substitution of phenylthioureas 1 as tyrosinase inhibitor and 2 as non-tyrosinase inhibitor.     

New Thioureas and Related Substances Intended for Melanoma Targeting

Thiouracil and a few related drugs are known to be melanoma-seeking agents owing to specific incorporation into nascent melanin. The melanin-affinic properties are apparently due to binding to intermediates, preferably dopaquinone, produced in the melanin synthetic pathway by tyrosinase-catalysed oxidation of tyrosine. In the present paper, in vitro screening methods have been used for the identification of possible melanoma seekers according to the above principle. The binding of test substance to dopaquinone suppresses dopachrome formation by the withdrawal of dopaquinone from the reaction mixture, and the decrease in dopachrome concentration was monitored spectrophotometrically at 475 nm. In order to eliminate false results caused by tyrosinase inhibition, which also will decrease the dopachrome concentration, the oxygen consumption was followed potentiometrically. To avoid the effect of tyrosinase inhibition on dopachrome formation, additional experiments with autoxidation of L-dopa in the presence of test substance were performed. Of the 22 substances (mainly thioureylenes and thioamides) studied, 4,5,6-triamino-2(H)-pyrimidinehtionsulfate, trithiocyanuric acid, 2-thiouracil, 6-methyl-2-thiouracil, and 4-amino-2-mercaptopyrimidine most effectively decreased the dopachrome formation with no or little inhibition of tyrosinase activity. They should therefore be regarded as potential melanoma seekers. In a complementary autoradiographic study on the uptake of the potent tyrosinase inhibitor mercaptobenzothiazole (MBT) in B 16 melanoma, transplanted to mice, it was found that strong tyrosinase inhibition seems to decrease incorporation into melanin in vivo. MBT was partly accumulated in restricted areas of the tumor, which may be explained by the small molar dose injected.     

Inhibitory effects of N-(acryloyl)benzamide derivatives on tyrosinase and melanogenesis

Targeting of tyrosinase has proven to be the best means of identifying safe, efficacious, and potent tyrosinase inhibitors for whitening skin. We designed and synthesized ten NAB (N-(acryloyl)benzamide) derivatives (1a–1j) using the Horner-Wadsworth-Emmons olefination of diethyl (2-benzamido-2-oxoethyl)phosphonate and appropriate benzaldehydes. A mushroom tyrosinase inhibitory assay showed compounds 1a (36.71 ± 2.14% inhibition) and 1j (25.99 ± 2.77% inhibition) inhibited tyrosinase more than the other eight NAB derivatives and kojic acid (21.56 ± 2.93% inhibition), and docking studies indicated 1a (−6.9 kcal/mole) and 1j (−7.5 kcal/mole) had stronger binding affinities for tyrosinase than kojic acid (−5.7 kcal/mole). At a concentration of 25 μM, 1a and 1j were nontoxic in B16F10 melanoma cells and exhibited stronger tyrosinase inhibition (59.70% and 76.77%, respectively) than kojic acid (50.30% inhibition) or arbutin (41.78% inhibition at 400 μM). Similarly, in B16F10 melanoma cells, compounds 1a and 1j at 25 μM decreased total melanin content by 47.97% and 61.77%, respectively (kojic acid; 38.98%). Similarities between inhibitions of tyrosinase activity and melanin contents suggested the anti-melanogenic effects of 1a and 1j were due to tyrosinase inhibition. The excellent DPPH scavenging activity of 1j suggests it might enhance in vivo effect on melanin contents. The study suggests compound 1j offers a potential starting point for the development of safe, potent tyrosinase inhibitors.     

Selective cytotoxicity of hydroquinone for melanocyte-derived cells is mediated by tyrosinase activity but independent of melanin content

In previous studies we have shown melanotic melanomas to be exquisitely more sensitive to hydroquinone (HQ) inhibition than non-melanotic cell lines in vitro. Indeed, incorporation of [H3] Urd and [H3] Thd have been shown to be respectively 80 and 35 times more sensitive to HQ inhibition. The difference between the cell lines studied was their derivation, marked by their different melanin contents. The presence of melanin was proposed as a possible explanation of the differences. However, comparative experiments reported here demonstrate that amelanotic melanoma cell lines are equally susceptible to HQ inhibition. Thus, the action of HQ is apparently independent of the melanin content of the cell. Significantly, the tyrosinase levels in the melanomas and the amelanomas were found to be comparable and markedly different from that in the non-melanoma control cell lines. Thus, the results reported here support the hypothesis put forward by other workers that hydroquinone melanotoxicity is independent of cellular melanin content but requires the presence of active tyrosinase.     

Different susceptibilities of melanoma cells to retinoic acid-induced changes in melanotic expression

The effect of retinoic acid on murine B16 melanoma cell growth, tyrosinase activity and melanin synthesis was investigated. Retinoic acid inhibited the growth of B16F1, B16F10 and B16BL6 melanoma cells, but enhanced melanin synthesis only in the B16F1 cells. The B16F10 and B16BL6 cells exhibited retinoic acid-induced suppression of tyrosinase activity and melanin synthesis, which was most apparent in the B16F10 cell variant. For comparison, Cloudman S91 melanoma cells proved to be particularly sensitive to retinoic acid-induced growth inhibition and stimulation of the expression of their melanotic phenotype. These results suggest considerable heterogeneity in the B16 melanoma with respect to their response to retinoic acid.     

Modulation of melanogenesis by aloesin: a competitive inhibitor of tyrosinase

Aloesin, [2-acetonyl-8-beta-d-glucopyranosyl-7-hydroxy-5-methylchromone], a compound isolated from the Aloe plant, is shown in these studies to modulate melanogenesis via competitive inhibition of tyrosinase. Aloesin inhibits purified tyrosinase enzyme and specifically inhibits melanin production in vitro. Enzyme kinetics studies using normal human melanocyte cell lysates and cell-based melanin production demonstrated that aloesin is a competitive inhibitor of tyrosinase from mushroom, human and murine sources. Tyrosine hydroxylase and 3,4-dihydroxyphenylalanine (DOPA) oxidase activities of tyrosinase from normal human melanocyte cell lysates were inhibited by aloesin in a dose dependent manner. In a percutaneous absorption study a finite dose of aloesin penetrated the skin slowly and was recovered primarily in the surface wash. Aloesin shows promise as a pigmentation-altering agent for cosmetic or therapeutic applications.     

Inhibition of tyrosinase by green tea components

The pigment melanin in human skin is a major defense mechanism against ultraviolet light of the sun, but darkened skin color, which is the result of increased and redistributed epidermal melanin, could be a serious aesthetic problem. Epidemiologically, it is well known that the consumption of green tea may help prevent cancers in humans and also reduce several free radicals including peroxynitrite. In the present study, to assess the efficacy of the inhibition of mushroom tyrosinase (monophenol monooxygenase EC 1.14.18.1), ten kinds of Korean traditional teas were screened for their tyrosinase inhibitory activity. Green tea was the strongest inhibitor, and the major active constituents in the tea are (-)-epicatechin 3-O-gallate (ECG), (-)-gallocatechin 3-O-gallate (GCG), and (-)-epigallocatechin 3-O-gallate (EGCG). All are catechins with gallic acid group as an active site. The kinetic analysis for inhibition of tyrosinase revealed a competitive nature of GCG with this enzyme for the L-tyrosine binding at the active site of tyrosinase.     

Inhibition of tyrosinase by indole compounds and reaction products. Protection by albumin.

Tyrosinase activity decreases as the reaction proceeds and is inhibited by L-3,4-dihydroxyphenylalanine oxidation products. Indole and tryptophan inhibit tyrosinase reaction and bovine albumin protects against end-product(s) inhibition or inactivation. Since the same tyrosinase reaction products are indole compounds and some authors reported the binding of indole derivatives with albumin, it is here suggested that indole intermediates of melanin synthesis inhibit or inactivate tyrosinase.