Mimosine Dipeptide Enantiomsers: Improved Inhibitors against Melanogenesis and Cyclooxygenase

Catechol-mimicking transition-state analogues as non-oxidizable inhibitors of tyrosinases

Tyrosinases are copper-containing metalloenzymes involved in several processes in both mammals, insects, bacteria, fungi and plants. Their phenol oxidation properties are especially responsible for human melanogenesis, potentially leading to abnormal pigmentation, and for postharvest vegetable tissue browning. Thus, targeting tyrosinases attracts interest for applications both in dermocosmetic and agrofood fields. However, a large part of the literature about tyrosinase inhibitors is dedicated to the report of copper-interacting phenolic compounds, that are more likely alternative substrates leading to undesirable toxic quinones production. To circumvent this issue, the use of catechol-mimicking copper-chelating groups that are analogues of the tyrosinase oxidation transition state appears as a valuable strategy. Relying on several non-oxidizable pyridinone, pyrone or tropolone moieties, innovative inhibitors were developed, especially within the past decade, and the best reported analogues reached IC50 values in the nanomolar range. Herein, we review the design, the activity against several tyrosinases, and the proposed binding modes of reported catechol-mimicking, non-oxidizable molecules, in light of recent structural data.

Whole Genome Resequencing Reveals Selection Signals Related to Wool Color in Sheep

Wool color is controlled by a variety of genes. Although the gene regulation of some wool colors has been studied in relative depth, there may still be unknown genetic variants and control genes for some colors or different breeds of wool that need to be identified and recognized by whole genome resequencing. Therefore, we used whole genome resequencing data to compare and analyze sheep populations of different breeds by population differentiation index and nucleotide diversity ratios (Fst and θπ ratio) as well as extended haplotype purity between populations (XP-EHH) to reveal selection signals related to wool coloration in sheep. Screening in the non-white wool color group (G1 vs. G2) yielded 365 candidate genes, among which PDE4B, GMDS, GATA1, RCOR1, MAPK4, SLC36A1, and PPP3CA were associated with the formation of non-white wool; an enrichment analysis of the candidate genes yielded 21 significant GO terms and 49 significant KEGG pathways (p < 0.05), among which 17 GO terms and 21 KEGG pathways were associated with the formation of non-white wool. Screening in the white wool color group (G2 vs. G1) yielded 214 candidate genes, including ABCD4, VSX2, ITCH, NNT, POLA1, IGF1R, HOXA10, and DAO, which were associated with the formation of white wool; an enrichment analysis of the candidate genes revealed 9 significant GO-enriched pathways and 19 significant KEGG pathways (p < 0.05), including 5 GO terms and 12 KEGG pathways associated with the formation of white wool. In addition to furthering our understanding of wool color genetics, this research is important for breeding purposes.

Anserine/Carnosine-Rich Extract from Thai Native Chicken Suppresses Melanogenesis via Activation of ERK Signaling Pathway

Skin hyperpigmentation is an aesthetic problem that leads to psychosocial issues. Thus, skin whitening agents from agro- and poultry-industrial co-products are considered high economic value ingredients of interest for sustainable application. Therefore, this study aimed to determine the cosmeceutical potential of anserine/carnosine-rich chicken extract (ACCE) from the Thai native chicken Pradu Hang Dam Mor Kor 55 (PD) meat. The chemical composition was identified and quantified using the HPLC-UV method. Then, the antioxidation potential of the extract was compared to that of L-anserine and L-carnosine, using 1,1-diphenyl-2-picrylhydrazyl assay and shikonin-induced production of reactive oxygen species in CCD-986Sk cell models, and the anti-melanogenesis effect in the MNT-1 melanoma cell line model was investigated. Furthermore, related mechanisms were identified using colorimetric tyrosinase assay and the Western blot technique. The ACCE was composed of L-anserine and L-carnosine as two major constituents. In a dose-dependent manner, ACCE, L-anserine, and L-carnosine manifested significant antioxidation potential and significant reduction of melanin production. Activation of the extracellular signal-regulated kinase (ERK) signaling pathway and inhibition of tyrosinase activity of ACCE were demonstrated as the mechanisms of the anti-melanogenesis effect. In conclusion, ACCE has been revealed as a potential cosmeceutical agent due to its antioxidation and anti-melanogenic activity in association with L-anserine and L-carnosine composition and biomolecular regulating ability. Therefore, further studies and development should be considered to support the utilization of anserine/carnosine-rich chicken extract in the cosmetic industry for economic value creation and sustainability.

Amino Acid Based Antimicrobial Agents - Synthesis and Properties

Structures of several dozen of known antibacterial, antifungal or antiprotozoal agents are based on the amino acid scaffold. In most of them, the amino acid skeleton is of a crucial importance for their antimicrobial activity, since very often they are structural analogs of amino acid intermediates of different microbial biosynthetic pathways. Particularly, some aminophosphonate or aminoboronate analogs of protein amino acids are effective enzyme inhibitors, as structural mimics of tetrahedral transition state intermediates. Synthesis of amino acid antimicrobials is a particular challenge, especially in terms of the need for enantioselective methods, including the asymmetric synthesis. All these issues are addressed in this review, summing up the current state‐of‐the‐art and presenting perspectives fur further progress.

Potency of bisresorcinol from Heliciopsis terminalis on skin aging: in vitro bioactivities and molecular interactions

Background

A bisresorcinol was isolated as the main constituent of Heliciopsis terminalis’s trunk (Proteaceae). Recently, resorcinol is applied as an active whitening agent in various cosmetic products. Because of the structural mimic to resorcinol, benefits of the bisresorcinol as an aging-enzyme antagonist were demonstrated in this study.

Methods

The bisresorcinol was purified from the crude ethanolic extract of H. terminalis’s trunk by solvent extraction and preparative chromatography, respectively. Inhibitory activity on collagenase, elastase, and tyrosinase of the compound was investigated by using a different spectroscopic technique. Molecular docking was carried out to predict possible interactions of the substance around the enzyme active sites.

Results

The IC₅₀ values on collagenase of the bisresorcinol and caffeic acid were 156.7 ± 0.7 and 308.9 ± 1.6 µmole L⁻¹, respectively. For elastase activity, the IC₅₀ of 33.2 ± 0.5 and 34.3 ± 0.3 µmole L⁻¹ was respectively determined for the bisresorcinol and ursolic acid. The bisresorcinol was inhibitory to tyrosinase by exhibiting the IC₅₀ of 22.8 µmole L⁻¹, and that of 78.4 µmole L⁻¹ was present for β-arbutin. The bisresorcinol bound to collagenase, elastase, and tyrosinase with the respective binding energies of −5.89, −5.69, and −6.57 kcal mol⁻¹. These binding energies were in the same ranges of tested inhibitors. The aromatic phenol groups in the structure were responsible for principle as well as supporting binding interactions with enzymes. Hydrogen binding due to hydroxyl groups and π-related attractive forces from an aromatic ring(s) provided binding versatility to bisresorcinol.

Conclusion

The bisresorcinol purified from H. terminalis might be useful for inclusion in cosmetic products as an aging-enzyme antagonist.

Synthesis and Mass Spectrometry Analysis of Mimosine-Containing Peptides

Non-proteinogenic amino acids are widely explored group of compounds due to their chemical properties and great potential of application in the combinatorial chemistry, medicinal investigation etc. Therefore the synthetic methods of their incorporation to the peptide chain are required. l-Mimosine, (S)-α-amino-β-(3-hydoxy-4-oxo-1,4-dihydropyridin-1-yl)-propanoic acid), is a plant amino acid, known to induce apoptosis in human pancreatic cancer xenografts. Here we present our investigations on the synthesis of mimosine-containing peptide and their ESI-MS/MS analysis. We successfully applied Fmoc-protected mimosine a with a free hydroxy ketone group for efficient peptide synthesis in the presence of HATU as a coupling reagent without the formation of side products. Additionally the tandem mass spectrometry analysis revealed the characteristic loss of the heterocyclic ring from mimosine residue side chain. The described method allows insertion of mimosine residue at any endo-position within a peptide sequence. The obtained results may be useful in the synthesis and mass spectrometry analysis of various mimosine-containing peptides.

Metal self-assembly mimosine peptides with enhanced antimicrobial activity: towards a new generation of multitasking chelating agents

Mimosine is a non-protein amino acid that can be used as a building block in peptides with metal coordination ability.

Discovery of new depigmenting compounds and their efficacy to treat hyperpigmentation: Evidence from in vitro study

Human skin pigmentation is a result of constitutive and facultative pigmentation. Facultative pigmentation is frequently stimulated by UV radiation, pharmacologic drugs, and hormones whereby leads to the development of abnormal skin hyperpigmentation. To date, many state-of-art depigmenting compounds have been studied using in vitro model to treat hyperpigmentation problems for cosmetic dermatological applications; little attention has been made to compare the effectiveness of these depigmenting compounds and their mode of actions. In this present article, new and recent depigmenting compounds, their melanogenic pathway targets, and modes of action are reviewed. This article compares the effectiveness of these new depigmenting compounds to modulate several melanogenesis-regulatory enzymes and proteins such as tyrosinase (TYR), TYR-related protein-1 (TRP1), TYR-related protein-2 (TRP2), microphthalmia-associated transcription factor (MITF), extracellular signal-regulated kinase (ERK) and N-terminal kinases (JNK) and mitogen-activated protein kinase p38 (p38 MAPK). Other evidences from in vitro assays such as inhibition on melanosomal transfer, proteasomes, nitric oxide, and inflammation-induced melanogenesis are also highlighted. This article also reviews analytical techniques in different assays performed using in vitro model as well as their advantages and limitations. This article also provides an insight on recent finding and re-examination of some protocols as well as their effectiveness and reliability in the evaluation of depigmenting compounds. Evidence and support from related patents are also incorporated in this present article to give an overview on current patented technology, latest trends, and intellectual values of some depigmenting compounds and protocols, which are rarely highlighted in the literatures.

1,2,3-Triazolyl ester of Ketorolac: A "Click Chemistry"-based highly potent PAK1-blocking cancer-killer

An old anti-inflammatory/analgesic drug called Toradol is a racemic form of Ketorolac (50% R-form and 50% S-form) that blocks the oncogenic RAC-PAK1-COX-2 (cyclooxygenase-2) signaling, through the direct inhibition of RAC by the R-form and of COX-2 by the S-form, eventually down-regulating the production of prostaglandins. However, due to its COOH moiety which is clearly repulsive to negatively-charged phospholipid-based plasma membrane, its cell-permeability is rather poor (the IC₅₀ against the growth of human cancer cells such as A549 is around 13 μM). In an attempt to boost its anti-cancer activity, hopefully by increasing its cell-permeability through abolishing the negative charge, yet keeping its water-solubility, here we synthesized a 1,2,3-triazolyl ester of Toradol through "Click Chemistry". The resultant water-soluble "azo" derivative called "15K" was found to be over 500 times more potent than Toradol with the IC₅₀ around 24 nM against the PAK1-dependent growth of A549 cancer cells, inactivating PAK1 in cell culture with the apparent IC₅₀ around 65 nM, and inhibiting COX-2 in vitro with the IC₅₀ around 6 nM. Furthermore, the Click Chemistry boosts the anti-cancer activity of Ketorolac by 5000 times against the PAK1-independent growth of B16F10 melanoma cells. Using a multi-drug-resistant (MDR) cancer cell line (EMT6), we found that the esterization of Ketorolac boosts its cell-permeability by at least 10 folds. Thus, the Click Chemistry dramatically boosts the anti-cancer activity of Ketorolac, at least in three ways: increasing its cell-permeability, the anti-PAK1 activity of R-form and anti-COX-2 activity of S-form. The resultant "15K" is so far among the most potent PAK1-blockers, and therefore would be potentially useful for the therapy of many different PAK1-dependent diseases/disorders such as cancers.

Resistance to ursolic acid-induced apoptosis through involvement of melanogenesis and COX-2/PGE2 pathways in human M4Beu melanoma cancer cells

Melanoma is one of the most aggressive forms of cancer with a continuously growing incidence worldwide and is usually resistant to chemotherapy agents, which is due in part to a strong resistance to apoptosis. Previously, we had showed that B16-F0 murine melanoma cells undergoing apoptosis are able to delay their own death induced by ursolic acid (UA), a natural pentacyclic triterpenoid compound. We had demonstrated that tyrosinase and TRP-1 up-regulation in apoptotic cells and the subsequent production of melanin were implicated in an apoptosis resistance mechanism. Several resistance mechanisms to apoptosis have been characterized in melanoma such as hyperactivation of DNA repair mechanisms, drug efflux systems, and reinforcement of survival signals (PI3K/Akt, NF-κB and Raf/MAPK pathways). Otherwise, other mechanisms of apoptosis resistance involving different proteins, such as cyclooxygenase-2 (COX-2), have been described in many cancer types. By using a strategy of specific inhibition of each ways, we suggested that there was an interaction between melanogenesis and COX-2/PGE2 pathway. This was characterized by analyzing the COX-2 expression and activity, the expression of tyrosinase and melanin production. Furthermore, we showed that anti-proliferative and proapoptotic effects of UA were mediated through modulation of multiple signaling pathways including Akt and ERK-1/2 proteins. Our study not only uncovers underlying molecular mechanisms of UA action in human melanoma cancer cells but also suggest its great potential as an adjuvant in treatment and cancer prevention.

The Chemistry and Biological Activities of Mimosine: A Review

Mimosine [β-[N-(3-hydroxy-4-oxypyridyl)]-α-aminopropionic acid] is a non-protein amino acid found in the members of Mimosoideae family. There are a considerable number of reports available on the chemistry, methods for estimation, biosynthesis, regulation, and degradation of this secondary metabolite. On the other hand, over the past years of active research, mimosine has been found to have various biological activities such as anti-cancer, antiinflammation, anti-fibrosis, anti-influenza, anti-virus, herbicidal and insecticidal activities, and others. Mimosine is a leading compound of interest for use in the development of RAC/CDC42-activated kinase 1 (PAK1)-specific inhibitors for the treatment of various diseases/disorders, because PAK1 is not essential for the growth of normal cells. Interestingly, the new roles of mimosine in malignant glioma treatment, regenerative dentistry, and phytoremediation are being emerged. These identified properties indicate an exciting future for this amino acid. The present review is focused on the chemistry and recognized biological activities of mimosine in an attempt to draw a link between these two characteristics. Copyright © 2016 John Wiley & Sons, Ltd.