Analogues of N-hydroxycinnamoylphenalkylamides as inhibitors of human melanocyte-tyrosinase

Leucoderma in Buffaloes (Bubalus bubalis) in the Amazon Biome

Leucoderma is a condition that affects the skin and hair of animals, causing depigmentation and acromotrichia. In buffaloes, this condition results in significant economic losses for the production chain due to its impact on the leather trade. This study aimed to investigate the epidemiological and clinicopathological aspects of leucoderma in buffaloes in the Amazon biome and describe the prophylactic treatment to control the disease. The study included 40 buffaloes, 16 males and 24 females, aged between 1 and 10 years, and were of the Murrah, Jafarabadi, Mediterranean, and Murrah × Mediterranean crossbreed breeds. The animals were raised without mineral supplementation. The clinical signs observed in the animals included acromotrichia and depigmentation, with varying degrees and distribution of skin lesions. Histological examination of the epidermis showed interrupted melanin production, mild dermal fibrosis, mild perivascular mononuclear inflammatory infiltrate, and pigmentary incontinence. None of the animals had the genotype for albinism. After 120 days of mineral supplementation based on the use of copper sulfate, the clinical signs of leucoderma regressed. There was no predisposition by breed, sex, or age for the occurrence of the disease. The regression of skin lesions after proper mineral supplementation suggests that copper deficiency may be considered an important factor for the occurrence of leucoderma in buffaloes in the Amazon biome.

Methoxy-Substituted Tyramine Derivatives Synthesis, Computational Studies and Tyrosinase Inhibitory Kinetics

Targeting tyrosinase for melanogenesis disorders is an established strategy. Hydroxyl-substituted benzoic and cinnamic acid scaffolds were incorporated into new chemotypes that displayed in vitro inhibitory effects against mushroom and human tyrosinase for the purpose of identifying anti-melanogenic ingredients. The most active compound 2-((4-methoxyphenethyl)amino)-2-oxoethyl (E)-3-(2,4-dihydroxyphenyl) acrylate (Ph9), inhibited mushroom tyrosinase with an IC₅₀ of 0.059 nM, while 2-((4-methoxyphenethyl)amino)-2-oxoethyl cinnamate (Ph6) had an IC₅₀ of 2.1 nM compared to the positive control, kojic acid IC₅₀ 16700 nM. Results of human tyrosinase inhibitory activity in A375 human melanoma cells showed that compound (Ph9) and Ph6 exhibited 94.6% and 92.2% inhibitory activity respectively while the positive control kojic acid showed 72.9% inhibition. Enzyme kinetics reflected a mixed type of inhibition for inhibitor Ph9 (K_i 0.093 nM) and non-competitive inhibition for Ph6 (K_i 2.3 nM) revealed from Lineweaver–Burk plots. In silico docking studies with mushroom tyrosinase (PDB ID:2Y9X) predicted possible binding modes in the catalytic site for these active compounds. Ph9 displayed no PAINS (pan-assay interference compounds) alerts. Our results showed that compound Ph9 is a potential candidate for further development of tyrosinase inhibitors.

Antioxidant, Pancreatic Lipase Inhibitory, and Tyrosinase Inhibitory Activities of Extracts of the Invasive Plant Spartina anglica (Cord-Grass)

Since 2016, the invasive halophyte Spartina anglica has been colonizing mudflats along the western coast of South Korea. In order to minimize costs on S. anglica expansion management and waste-treatment of collected biomass, the potential application of the collected biomass of S. anglica was investigated. Ethanolic extracts and subfractions thereof (hexanes, methylene chloride, ethyl acetate, 1-butanol, and water-soluble) of the aerial and belowground parts of S. anglica showed free radical-scavenging [2,2-diphenyl-1-picrylhydrazyl (DPPH), and 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS)], tyrosinase inhibitory, and pancreatic lipase inhibitory activities. An ethyl acetate fraction derived from aerial parts (EA-a) showed the most potent radical-scavenging and pancreatic lipase inhibitory activities, whereas tyrosinase inhibition was mainly observed in the methylene chloride soluble fractions (MC-bg) and other lipophilic fractions (ethyl acetate and hexanes layers) obtained from belowground parts. The major EA-a compound isolated and identified was 1,3-di-O-trans-feruloyl quinic acid (1) based on spectroscopic analysis, whereas the two major MC-bg compounds were identified as p-hydroxybenzaldehyde (2) and N-trans-feruloyltyramine (3). Compounds 1 and 3 scavenged both DPPH and ABTS radicals, whereas 1 and 2 inhibited pancreatic lipase activity. These results indicate that extracts and fractions of S. anglica have antioxidant, anti-obesity, and whitening properties with potential pharmaceutical, cosmeceutical, and functional food applications.

Tyramine-derived hydroxycinnamic acid amides in plant foods: sources, synthesis, health effects and potential applications in food industry

Tyramine-derived hydroxycinnamic acid amines (HCAAT) are naturally occurring group of secondary metabolites present in various plant genera, such as Allium, Cannabis, Lycium, Polyganotum and Solanum. It belongs to the neutral, water-insoluble compounds and plays a role in plant growth, development and defence mechanism. The past two decades have seen a shift in the study of HCAAT from its role in plants to its potent biological activities. This review highlights the sources, roles in plants, biosynthetic pathways, metabolic engineering and chemical synthesis of HCAAT. The biological properties of HCAAT remain the focus in this paper, including antioxidant, anti-inflammatory, anti-cancer, anti-diabetic, anti-melanogenesis and neuroprotective properties. The effects of food processing and technology on HCAAT are also discussed. Given the current research gap, this review proposes future directions on the study of HCAAT, as well as its potential applications in food and pharmaceutical industry.

Molecular modification approach on kojic acid derivatives as antioxidants related to ascorbic acid

A hypothetical study by using molecular modeling for antioxidant capacity of kojic acid derivatives was performed using quantum chemistry calculations by DFT/B3LYP/6-311++G(3d,2p). Four modification approaches were considered namely simplification, functional modifications, ring regioisomerism, and hydroxylation. Molecular orbitals, single-electron transfers, hydrogen atom transfers, and spin density distributions were used for antioxidant prediction. In accordance with HOMO, LUMO, Gap, ionization potential, bond dissociation energy, and stabilization energy, the molecular simplifications of kojic acid show that enol moiety is more important for antioxidant capacity than alcohol group. Few molecular modifications on alcohol or enol position were more potent than kojic acid. The π conjugation system among ether, alkene, and hydroxyl moieties can be involved on resonance effects of better compounds. A different performance was observed on alcohol molecular modifications when compared to enol position. All lactone derivatives were more potent than kojic acid on both mechanisms, and their hydroxylated derivatives were more potent than ascorbic acid. In conclusion, the ring regioisomers and its hydroxylated derivatives have better antioxidant capacity than kojic acid. Graphical Abstract The theoretical study using molecular modeling for antioxidant capacity prediction of kojic acid was more related to enol moiety than alcohol. The regioisomerism and hybrid derivatives show that the lactone derivatives increase antioxidant capacity more than the pyrone derivatives.

Phenolamides: Plant specialized metabolites with a wide range of promising pharmacological and health-promoting interests

Phenolamides constitute a family of metabolites, widely represented in the plant kingdom, that can be found in all plant organs with a predominance in flowers and pollen grains. They represent a large and structurally diverse family, resulting from the association of phenolic acids with aliphatic or aromatic amines. Initially revealed as active compounds in several medicinal plant extracts, phenolamides have been extensively studied for their health-promoting and pharmacological properties. Indeed, phenolamides have been shown to exhibit antioxidant, anti-inflammatory, anti-cancer and antimicrobial properties, but also protective effects against metabolic syndrome and neurodegenerative diseases. The purpose of this review is to summarise this large body of literature, including in vitro and in vivo studies, by describing the diversity of their biological properties and our actual knowledge of the molecular mechanisms behind them. With regard to their considerable pharmacological interest, the question of industrial production is also tackled through chemical and biological syntheses in engineered microorganisms. The diversity of biological activities already described, together with the active discovery of the broad structural diversity of this metabolite family, make phenolamides a promising source of new active compounds on which future studies should be focused.

New class of alkynyl glycoside analogues as tyrosinase inhibitors

A new series of alkynyl glycoside analogues were designed and synthesized from cheap and a commercially available sugar by introduction of various alkynyl and alkyl groups at C-1 and C-6 positions of the sugar ring. The inhibitory abilities of alkynyl glycosides were investigated in vitro on mushroom tyrosinase for the catalysis of l-Tyrosine and l-DOPA as substrates and comparing with arbutin and kojic acid. Non-terminal alkyne compound 2d showed excellent tyrosinase inhibitory activity (IC₅₀ 54.0 μM) against l-Tyrosine comparable to arbutin (IC₅₀ 1.46 mM) while 2b exhibited potent activities (IC₅₀ 34.3 μM) against L-DOPA higher than kojic acid (IC₅₀ 0.11 mM) and arbutin (IC₅₀ 13.3 mM). Kinetic studies revealed that compound 2d was a non-competitive inhibitor with the best Ki value of 21 μM and formed an irreversible receptor complex with mushroom tyrosinase. The SARs results showed that the type of alkyne and alkyl groups at position C-6 on sugar and the stereoisomer played an important role in determining their inhibitory activities. The potent activity of alkynyl glycosides identified in this study highlight the importance of this scaffold and these compounds are very modestly potent to the development of new class for tyrosinase inhibitor.

Hydroxycinnamic acid derivatives isolated from hempseed and their effects on central nervous system enzymes

New neuroprotective treatments of natural origin are being investigated. Both, plant extracts and isolated compounds have shown bioactive effects. Hempseed is known for its composition of fatty acids, proteins, fibre, vitamins, as well as a large number of phytochemical compounds. After a defatting process of the seeds, hydroxycinnamic acids and its amine derivatives are the majoritarian compounds in an ethyl acetate fraction (EAF). In the present study, we investigated in vitro effect on neuronal enzymes: MAO-A, MAO-B, tyrosinase and acetylcholinesterase. Besides, the effect of EAF on striatal biogenic amines in mice was evaluated. Both, EAF and isolated compounds (N-trans-caffeoyltyramine and N-trans-coumaroyltyramine), showed inhibitory action on MAO-A, MAO-B and tyrosinase. Furthermore, an increasing of biogenic amines was observed in the corpus striatum of the mice, after administration of EAF. These findings show that EAF and the hydroxycinnamic acid derivatives may represent a potential treatment in degenerative neuronal diseases.

In search for potential antidiabetic compounds from natural sources: docking, synthesis and biological screening of small molecules from Lycium spp. (Goji)

Current clinical antidiabetic drugs, like rosiglitazone 1, have been implicated in some serious side effects like edema, weight gain, and heart failure, making it necessary to find alternative agents. Partial agonists of peroxisome-proliferator activated receptor-gamma (PPARγ) were determined to possess improved insulin sensitivity without undeseirable side-effects when compared to full agonists of PPARγ, like rosiglitazone 1. The traditional Chinese medicine (TCM) plants, Goji (Lycium barbarum and Lycium chinense) are widely used for treating symptoms related to various diseases including diabetes and hypertension. Twenty-seven reported compounds from Goji were docked into both partial- and full-agonist binding sites of PPARγ. Amongst the docked compounds, phenylethylamide-based phytochemicals (5–9) (termed as tyramine-derivatives, TDs) were found to possess good docking scores and binding poses with favorable interactions. Synthesis of 24 TDs, including three naturally occuring amides (6, 8, 9) were synthesized and tested for PPARγ gene induction with cell-based assay. Three compounds showed similar or higher fold induction than the positive control, rosiglitazone. Among these three active TDs, trans-N-feruloyloctopamine (9) and tyramine derivatives-enriched extract (TEE) (21%) of the root bark of L. chinense were further studied in vivo using db/db mice. However, both TEE as well as 9 did not show significant antidiabetic properties in db/db mice. In vivo results suggest that the proposed antidiabetic property of Lycium species may not be due to tyramine derivatives alone. Further studies of tyramine derivatives or enriched extract(s) for other bioactivities like hypocholesterolemic activities, and studies of novel isolated compounds from Goji will enable a more complete understanding of their bioactivities.

Synthesis, computational molecular docking analysis and effectiveness on tyrosinase inhibition of kojic acid derivatives

Tyrosinase inhibitors have become increasingly important as whitening agents and for the treatment of pigmentary disorders. In this study, the synthesis of kojic acid derivatives having 2-substituted-3-hydroxy-6-hyroxymethyl/chloromethyl/methyl/morpholinomethylpiperidinyl- methyl/pyrrolidinylmethyl-4H-pyran-4-one structure (compounds 1-30) with inhibitory effects on tyrosinase enzyme were described. One-pot Mannich reaction was carried out by using kojic acid/chlorokojic acid/allomaltol and substituted benzylpiperazine derivatives in presence of formaline. Subsequently, cyclic amine (morpholine, piperidine and pyrrolidine) derivatives of the 6th-position of chlorokojic acid were obtained with nucleophilic substitutions in basic medium. The structures of new compounds were identified by FT-IR, ¹H- and ¹³C NMR, ESI-MS and elemental analysis data. The potential mushroom tyrosinase inhibitory activity of the compounds were evaluated by the spectrophotometric method using l-DOPA as a substrate and kojic acid as the control agent. The potential inhibitory activity was also investigated in silico using molecular docking simulation method. Tyrosinase inhibitory action was significantly more efficacious for several compounds (IC₅₀: 86.2-362.1 µM) than kojic acid (IC₅₀: 418.2). Compound 3 bearing 3,4-dichlorobenzyl piperazine moiety was proven to have the highest inhibitory activity. The results of docking studies showed that according to the predicted conformation of compound 3 in the enzyme binding site, hydroxymethyl group provides a metal complex with copper ions and enzyme. Thus, this interaction explain the high inhibitory activities of the compounds 1, 3 and 4 possessing hydroxymethyl substituent supporting the mushroom assay results with docking studies. In accordance with the results, it is suggested that Mannich bases of kojic acid bearing substituted benzyl piperazine groups (compounds 1, 3, 4, 11, 13, 14, 23, 24, 28, and 29) could be promising antityrosinase agents. Additionally, considering the relationship between tyrosinase inhibitory activity results and molecular docking, a new tyrosinase inhibition mechanism can be proposed.

Novel Piperazine Amides of Cinnamic Acid Derivatives as Tyrosinase Inhibitors

Background:

A series of novel cinnamic acid piperazine amide derivatives has been designed and synthesized, and their biological activities were also evaluated as potential tyrosinase inhibitors.

Methods:

Compounds 9, 11 and 17 showed the most potent biological activity (IC50 = 66.5, 61.1 and 66 µM, respectively). In silico docking simulation was performed to position compound 11 into the Agaricus bisporus mushroom tyrosinase’s active site to determine the putative binding interactions.

Results and Conclusion:

The results indicated that compound 11 could serve as a promising lead compound for further development of potent tyrosinase inhibitors.

Design, Synthesis of N-phenethyl Cinnamide Derivatives and Their Biological Activities for the Treatment of Alzheimer's Disease: Antioxidant, Beta-amyloid Disaggregating and Rescue Effects on Memory Loss

Gx-50 is a bioactive compound for the treatment of Alzheimer’s disease (AD) found in Sichuan pepper (Zanthoxylum bungeanum). In order to find a stronger anti-AD lead compound, 20 gx-50 (1–20) analogs have been designed and synthesized, and their molecular structures were determined based on nuclear magnetic resonance (NMR) and mass spectrometry (MS) analysis, as well as comparison with literature data. Compounds 1–20 were evaluated for their anti-AD potential by using DPPH radical scavenging assay for considering their anti-oxidant activity, thioflavin T (ThT) fluorescence assay for considering the inhibitory or disaggregate potency of Aβ, and transgenic Drosophila model assay for evaluating their rescue effect on memory loss. Finally, compound 13 was determined as a promising anti-AD candidate.

Inhibitors of Melanogenesis: An Updated Review

Melanins are pigment molecules that determine the skin, eye, and hair color of the human subject to its amount, quality, and distribution. Melanocytes synthesize melanin and provide epidermal protection from various stimuli, such as harmful ultraviolet radiation, through the complex process called melanogenesis. However, serious dermatological problems occur when there is excessive production of melanin in different parts of the human body. These include freckles, melasma, senile lentigo, pigmented acne scars, and cancer. Therefore, controlling the production of melanin is an important approach for the treatment of pigmentation related disorderes. In this Perspective, we focus on the inhibitors of melanogenesis that directly/indirectly target a key enzyme tyrosinase as well as its associated signaling pathways.

Synthesis of avenanthramides using engineered Escherichia coli

Background

Hydroxycinnamoyl anthranilates, also known as avenanthramides (avns), are a group of phenolic alkaloids with anti-inflammatory, antioxidant, anti-itch, anti-irritant, and antiatherogenic activities. Some avenanthramides (avn A–H and avn K) are conjugates of hydroxycinnamic acids (HC), including p-coumaric acid, caffeic acid, and ferulic acid, and anthranilate derivatives, including anthranilate, 4-hydroxyanthranilate, and 5-hydroxyanthranilate. Avns are primarily found in oat grain, in which they were originally designated as phytoalexins. Knowledge of the avns biosynthesis pathway has now made it possible to synthesize avns through a genetic engineering strategy, which would help to further elucidate their properties and exploit their beneficial biological activities. The aim of the present study was to synthesize natural avns in Escherichia coli to serve as a valuable resource.

Results

We synthesized nine avns in E. coli. We first synthesized avn D from glucose in E. coli harboring tyrosine ammonia lyase (TAL), 4-coumarate:coenzyme A ligase (4CL), anthranilate N-hydroxycinnamoyl/benzoyltransferase (HCBT), and anthranilate synthase (trpEG). A trpD deletion mutant was used to increase the amount of anthranilate in E. coli. After optimizing the incubation temperature and cell density, approximately 317.2 mg/L of avn D was synthesized. Avn E and avn F were then synthesized from avn D, using either E. coli harboring HpaBC and SOMT9 or E. coli harboring HapBC alone, respectively. Avn A and avn G were synthesized by feeding 5-hydroxyanthranilate or 4-hydroxyanthranilate to E. coli harboring TAL, 4CL, and HCBT. Avn B, avn C, avn H, and avn K were synthesized from avn A or avn G, using the same approach employed for the synthesis of avn E and avn F from avn D.

Conclusions

Using different HCs, nine avns were synthesized, three of which (avn D, avn E, and avn F) were synthesized from glucose in E. coli. These diverse avns provide a strategy to synthesize both natural and unnatural avns, setting a foundation for exploring the biological activities of diverse avns.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0896-9) contains supplementary material, which is available to authorized users.

Recent development of signaling pathways inhibitors of melanogenesis

Human skin, eye and hair color rely on the production of melanin, depending on its quantity, quality, and distribution, Melanin plays a monumental role in protecting the skin against the harmful effect of ultraviolet radiation and oxidative stress from various environmental pollutants. However, an excessive production of melanin causes serious dermatological problems such as freckles, solar lentigo (age spots), melasma, as well as cancer. Hence, the regulation of melanin production is important for controlling the hyper-pigmentation. Melanogenesis, a biosynthetic pathway to produce melanin pigment in melanocyte, involves a series of intricate enzymatic and chemical catalyzed reactions. Several extrinsic factors include ultraviolet radiation and chemical drugs, and intrinsic factors include molecules secreted by surrounding keratinocytes or melanocytes, and fibroblasts, all of which regulate melanogenesis. This article reviews recent advances in the development of melanogenesis inhibitors that directly/indirectly target melanogenesis-related signaling pathways. Efforts have been made to provide a description of the mechanism of action of inhibitors on various melanogenesis signaling pathways.

Study on the design, synthesis and structure-activity relationships of new thiosemicarbazone compounds as tyrosinase inhibitors

52 Structure-based thiosemicarbazone compounds bearing various substituted-lipophilic part, including substituted-benzaldehyde, substituted-phenylalkan-1-one and their biphenyl-type thiosemicarbazone analogs, were designed, synthesized and evaluated as new tyrosinase inhibitors. The results demonstrated that 22 compounds have potent inhibitory activities against tyrosinase with the IC₅₀ value of lower than 1.0 μM. On the basis of the obtained experimental data, the structure-activity relationships (SARs) were rationally derived. Besides, the inhibition mechanism and the inhibitory kinetics of selected compounds 3d and 6e were investigated, revealing that such type of compounds were belonged to the reversible and competitive tyrosinase inhibitors. To verify the safety of these developed thiosemicarbazone compounds, four randomly selected compounds 3d, 4e, 6a and 9a were also tested in 293T cell line for the evaluation of the cytotoxicity. Interestingly, all these compounds almost did not perform any toxicity to 293T cells even at a high concentration of 1000 μmol/L. Taken together, these results suggested that such compounds could serve as the highly efficient and more safe candidates for the treatment of tyrosinase-related disorders.

Synthesis and biological evaluation of caffeic acid derivatives as potent inhibitors of α-MSH-stimulated melanogenesis

We have disclosed our effort to develop caffeic acid derivatives as potent and non-toxic inhibitors of α-MSH-stimulated melanogenesis to treat pigmentation disorders and skin medication including a cosmetic skin-whitening agent. The SAR studies revealed that cyclohexyl ester and secondary amide derivatives of caffeic acid showed significant inhibitory activities.

N-(4-methoxyphenyl) caffeamide-induced melanogenesis inhibition mechanisms

Background

The derivative of caffeamide exhibits antioxidant and antityrosinase activity. The activity and mechanism of N-(4-methoxyphenyl) caffeamide (K36E) on melanogenesis was investigated.

Methods

B16F0 cells were treated with various concentrations of K36E; the melanin contents and related signal transduction were studied. Western blotting assay was applied to determine the protein expression, and spectrophotometry was performed to identify the tyrosinase activity and melanin content.

Results

Our results indicated that K36E reduced α-melanocyte-stimulating hormone (α-MSH)-induced melanin content and tyrosinase activity in B16F0 cells. In addition, K36E inhibited the expression of phospho-cyclic adenosine monophosphate (cAMP)-response element-binding protein, microphthalmia-associated transcription factor (MITF), tyrosinase, and tyrosinase-related protein-1 (TRP-1). K36E activated the phosphorylation of protein kinase B (AKT) and glycogen synthase kinase 3 beta (GSK3β), leading to the inhibition of MITF transcription activity. K36E attenuated α-MSH induced cAMP pathways, contributing to hypopigmentation.

Conclusions

K36E regulated melanin synthesis through reducing the expression of downstream proteins including p-CREB, p-AKT, p-GSK3β, tyrosinase, and TRP-1, and activated the transcription factor, MITF. K36E may have the potential to be developed as a skin whitening agent.

Inhibitory Kinetics of Azachalcones and their Oximes on Mushroom Tyrosinase: A Facile Solid-state Synthesis

A solid-state-based mechanochemical process was used to synthesize novel azachalcones and their oximes as tyrosinase inhibitors. Their inhibitory activities on mushroom tyrosinase using l-3,4-dihydroxyphenylalanine as a substrate were investigated. Two of the novel oxime derivatives synthesized were seen to be more potent than the positive control, kojic acid. Both the compounds 1b and 2b inhibited the diphenolase activity of tyrosinase in a dose-dependent manner with their IC50 values of 15.3 and 12.7 μm, respectively. The kinetic analysis showed that their inhibition mechanism was reversible. Both the novel oxime compounds displayed competitive inhibition with their Ki values of 5.1 and 2.5 μm, respectively. This method minimizes waste disposal problems and provides a simple, efficient, and benign method for the synthesis of novel tyrosinase inhibitors for use as skin-whitening agents or as anti-browning food additives.

Synthesis and biological evaluation of piperic acid amides as free radical scavengers and α-glucosidase inhibitors

A series of piperic acid amides (4-24, 29, 30) were synthesized and their 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging and α-glucosidase inhibitory activities were evaluated. Among the synthesized compounds, the amides 11, 13 and 15, which contain o-methoxyphenol, catechol or 5-hydroxyindole moieties, showed potent DPPH free radical scavenging activity (11: EC50 140 µM; 13: EC50 28 µM; 15: EC50 20 µM). The amides 10, 18 and 23 showed higher inhibitory activity of α-glucosidase (10: IC50 21 µM; 18: IC50 21 µM; 23: IC50 12 µM). These data suggest that the hydrophobicity of the conjugated amines is an important determinant of α-glucosidase inhibitory activity. In addition, the amides 13 and 15 showed both potent DPPH free radical scavenging activity and α-glucosidase inhibitory activity (13: IC50 46 µM; 15: IC50 46 µM). This is the first report identifying the DPPH free radical scavenging and α-glucosidase inhibitory activities of piperic acid amides and suggests that these amides may serve as lead compounds for the development of novel α-glucosidase inhibitors with antioxidant activity.

Bacterial synthesis of N-hydroxycinnamoyl phenethylamines and tyramines

Background

Hydroxycinnamic acids (HCAs) including cinnamic acid, p-coumaric acid, caffeic acid, and ferulic acid, are C6–C3 phenolic compounds that are synthesized via the phenylpropanoid pathway. HCAs serve as precursors for the synthesis of lignins, flavonoids, anthocyanins, stilbenes and other phenolic compounds. HCAs can also be conjugated with diverse compounds including quinic acid, hydroxyl acids, and amines. Hydroxycinnamoyl (HC) amine conjugates such as N-HC tyramines and N-HC phenethylamines have been considered as potential starting materials to develop antiviral and anticancer drugs.

Results

We synthesized N-HC tyramines and N-HC phenethylamines using three different approaches in Escherichia coli. Five N-HC phenethylamines and eight N-HC tyramines were synthesized by feeding HCAs and phenethylamine or tyramine to E. coli harboring 4CL (encoding 4-coumarate CoA:ligase) and either SHT (encoding phenethylamine N-HC transferase) or THT (encoding tyramine N-HC transferase). Also, N-(p-coumaroyl) phenethylamine and N-(p-coumaroyl) tyramine were synthesized from p-coumaric acid using E. coli harboring an additional gene, PDC (encoding phenylalanine decarboxylase) or TDC (encoding tyrosine decarboxylase). Finally, we synthesized N-(p-coumaroyl) phenethylamine and N-(p-coumaroyl) tyramine from glucose by reconstructing the metabolic pathways for their synthesis in E. coli. Productivity was maximized by optimizing the cell concentration and incubation temperature.

Conclusions

We reconstructed the metabolic pathways for synthesis of N-HC tyramines and N-HC phenethylamines by expressing several genes including 4CL, TST or SHT, PDC or TDC, and TAL (encoding tyrosine ammonia lyase) and engineering the shikimate metabolic pathway to increase endogenous tyrosine concentration in E. coli. Approximately 101.9 mg/L N-(p-coumaroyl) phenethylamine and 495.4 mg/L N-(p-coumaroyl) tyramine were synthesized from p-coumaric acid. Furthermore, 152.5 mg/L N-(p-coumaroyl) phenethylamine and 94.7 mg/L N-(p-coumaroyl) tyramine were synthesized from glucose.

Survey of phytochemical composition and biological effects of three extracts from a wild plant (Cotoneaster nummularia Fisch. et Mey.): a potential source for functional food ingredients and drug formulations

This study was focused on the analysis of the phenolic content, antioxidant, antibacterial, anti-cholinesterase, anti-tyrosinase, anti-amylase and anti-glucosidase activity of three solvent extracts from Cotoneaster nummularia. Moreover, water extract was tested in terms of mutagenic/anti-mutagenic effects. The antioxidant activities of these extracts were evaluated by DPPH, ABTS, O₂, metal chelating, phosphomolybdenum, β-carotene/linoleic acid, ferric and cupric reducing power assays. Enzyme inhibitory activities were also examined with colorimetric methods. Generally, methanol and water extracts exhibited excellent biological activities. These extracts were rich in phenolic and flavonoid content. Furthermore, Cotoneaster extracts indicated appreciable antibacterial properties against human pathogen strains. HPLC analysis showed that ferulic acid, chlorogenic acid, (-) – epicatechin and (+)-catechin were the major phenolics in extracts tested. These data offer that these extracts from C. nummularia may be considered as a potential source of biological agents for developing functional foods or drug formulations.

Kinetics of mushroom tyrosinase and melanogenesis inhibition by N-acetyl-pentapeptides

We investigated the kinetics of 4N-acetyl-pentapeptides, Ac-P1, Ac-P2, Ac-P3, and Ac-P4, regarding inhibition of mushroom tyrosinase activity. The peptides sequences of Ac-P1, Ac-P2, Ac-P3, and Ac-P4 were Ac-RSRFK, Ac-KSRFR, Ac-KSSFR, and Ac-RSRFS, respectively. The 4N-acetyl-pentapeptides were able to reduce the oxidation of l-DOPA by tyrosinase in a dose-dependent manner. Of the 4N-acetyl-pentapeptides, only Ac-P4 exhibited lag time (80 s) at a concentration of 0.5 mg/mL. The tyrosinase inhibitory effects of Ac-P4 (IC₅₀ 0.29 mg/mL) were more effective than those of Ac-P1, Ac-P2, and Ac-P3, in which IC₅₀s were 0.75 mg/mL, 0.78 mg/mL, and 0.81 mg/mL, respectively. Kinetic analysis demonstrated that all 4N-acetyl-pentapeptides were mixed-type tyrosinase inhibitors. Furthermore, 0.1 mg/mL of Ac-P4 exhibited significant melanogenesis inhibition on B16F10 melanoma cells and was more effective than kojic acid. The melanogenesis inhibition of Ac-P4 was dose-dependent and did not induce any cytotoxicity on B16F10 melanoma cells.

Identification of Sake Extract as a New Anti-melanogenic Ingredient by in vitro and Clinical Trials

Overproduction of melanin is the cause of skin hyperpigmentation, which is related to several skin diseases and cosmetic concerns. Sake is a Japanese alcoholic beverage produced from rice and water by fermentation, but is little known for its effect on melanogenesis. To identify the effect of sake extract on melanin synthesis, a melanin assay was performed in melan-A murine melanocytes. Sake extract treatment significantly inhibited melanin production in a dose-dependent manner, and tyrosinase, the rate-limiting enzyme of melanogenesis, decreased significantly at the protein level. Further investigations were performed with multiple assay systems; a sake extract reduced melanin production in melan-A/SP-1 murine cell co-culture, and also in MelanoDermTM, a skin equivalent model of human keratinocytes-melanocytes. Finally, subjects were treated with a formula containing the sake extract. Topical application of the sake extract product improved skin lightness (L*) significantly within 7 days. We identified sake extract as a new anti-melanogenic ingredient through in vitro and in vivo experiments. These results suggest that a sake extract can be used to improve skin hyperpigmentation.

Design and synthesis of hydroxypyridinone-L-phenylalanine conjugates as potential tyrosinase inhibitors

A range of hydroxypyridinone-L-phenylalanine conjugates were synthesized starting from kojic acid. Their tyrosinase activity was determined, and it was found that one of the compounds ((S)-(5-(benzyloxy)-1-octyl-4-oxo-1,4-dihydropyridin-2-yl)methyl 2-amino-3-phenylpropanoate, 5e) showed potent inhibitory effect against mushroom tyrosinase, the IC50 values for monophenolase and diphenolase activities being 12.6 and 4.0 μM, respectively. It was also demonstrated that these conjugates are mixed-type inhibitors, suggesting they could bind to both the free enzyme and the enzyme-substrate complexes. MTT assay indicated that 5e was nontoxic to three cell lines. This compound may find applications in food preservation and cosmetics.

Development of microemulsion of a potent anti-tyrosinase essential oil of an edible plant

The aim of this study is to develop a microemulsion product from a plant essential oil having the highest anti-tyrosinase activity. The in vitro anti-tyrosinase activity of six essential oils extracted from six edible plants was compared. The oil of Cymbopogon citratus demonstrated the highest activity which was significantly nontoxic to normal human cells. The GC-MS data indicated that geranial and neral are the major compounds in the oil. The phase diagram composed of C. citrates oil, water, and surfactant mixture was conducted by a titration method. Ethyl alcohol was found to be the most suitable cosurfactant for the C. citrates oil microemulsion. The results revealed that the amount of oil and water played an important role in microemulsion conductivity and type. The most desirable o/w type of C. citratus oil microemulsion was found to be composed of 20% oil, 30% water, and 50% surfactant mixture of a 2:1 weight ratio of Tween 20 and ethyl alcohol.

Cinnamoylphenethyl Amides from Polygonum hyrcanicum Possess Anti-Trypanosomal Activity

A methanolic extract from aerial parts of Polygonum hyrcanicum (Polygonaceae) showed high activity against Trypanosoma brucei rhodesiense (IC50=3.7 μg/mL). Bioassay-guided fractionation of the extract resulted in isolation of cinnamoylphenethyl amides, including N-trans-caffeoyltyramine (1), N-trans-p-coumaroyltyramine (7), and N-trans-feruloyltyramine (8) as the main active constituents (IC50s ranging from 2.2 to 13.3 μM). Some structurally related, but less active compounds, such as cannabisin B (2), tyrosol (3), p-coumaric acid (4), ferulic acid (5), and N-cis-feruloyltyramine (6) were also identified, along with N-trans-3,4-dimethoxycinnamoyldopamine (9). Cytotoxicity of the active compounds in L6 cells was determined, and selectivity indices (SI) of 7.9 to 33.4 were calculated.

Kojic acid-induced IL-6 production in human keratinocytes plays a role in its anti-melanogenic activity in skin

BACKGROUND

Kojic acid is a fungal metabolite widely used in medicinal and cosmetic formulations as a skin-lightening agent based on its de-pigmenting activity. Although in human clinical studies kojic acid has been shown to be effective in the treatment of hyper-pigmentation disorders such as melasma, the reasons for its apparent lack of anti-melanogenic activity in cultured mammalian melanocytes are unclear.

OBJECTIVES

This study was aimed to elucidate pharmacological mechanisms of the in vivo anti-melanogenic activity of kojic acid in human skin.

METHODS

A primary human melanocyte and keratinocyte co-culture system was used to evaluate whether kojic-acid-induced changes in keratinocytes were associated with anti-melanogenic activities in melanocytes. The cytokine secretion profiles in response to kojic acid were analyzed.

RESULTS

Kojic acid increased interleukin (IL)-6 and IL-8 production in melanocyte/keratinocyte co-cultures; however, IL-6 directly inhibited melanogenesis whereas IL-8 did not. In melanocyte monocultures, kojic acid did not increase IL-6 production whereas in keratinocyte monocultures it significantly up-regulated IL-6 gene and protein expression. Therefore, the up-regulation of IL-6 in melanocyte/keratinocyte co-cultures seems to be originated from kojic acid-induced changes in keratinocytes. Anti-IL-6 antibody treatment antagonized the anti-melanogenic effect of kojic acid on the co-cultures.

CONCLUSIONS

The pharmacological mechanism of kojic acid to explain clinically effective anti-melanogenic activity on hyper-pigmented skin is associated with the kojic acid-induced IL-6 production in keratinocytes. The cross-talk between melanocytes and keratinocytes should be determined in future studies on the pharmacological mechanisms of clinically effective dermatological drugs acting on the epidermis.

Molecular docking studies of a phlorotannin, dieckol isolated from Ecklonia cava with tyrosinase inhibitory activity

In this study, the phlorotannin dieckol, which was isolated from the brown alga Ecklonia cava, was examined for its inhibitory effects on melanin synthesis. Tyrosinase inhibitors are important agents for cosmetic products. We therefore examined the inhibitory effects of dieckol on mushroom tyrosinase and melanin synthesis, and analyzed its binding modes using the crystal structure of Bacillus megaterium tyrosinase (PDB ID: 3NM8). Dieckol inhibited mushroom tyrosinase with an IC(50) of 20μM and was more effective as a cellular tyrosinase having melanin reducing activities than the commercial inhibitor, arbutin, in B16F10 melanoma cells, and without apparent cytotoxicity. It was found that dieckol behaved as a non-competitive inhibitor with l-tyrosine substrates. For further insight, we predicted the 3D structure of tyrosinase and used a docking algorithm to simulate binding between tyrosinase and dieckol. These molecular modeling studies were successful (calculated binding energy value: -126.12kcal/mol), and indicated that dieckol interacts with His208, Met215, and Gly46. These results suggest that dieckol has great potential to be further developed as a pharmaceutical or cosmetic agent for use in dermatological disorders associated with melanin.