Catechol ortho-quinones: the electrophilic compounds that form depurinating DNA adducts and could initiate cancer and other diseases

A novel source of biologically active compounds - The leaves of Serbian herbaceous peonies

In order to gain further insight into how various extraction techniques (maceration, microwave-, and ultrasound-assisted extractions) affect the chemical profile and biological activities of leaf extracts from Paeonia tenuifolia L., Paeonia peregrina Mill., and Paeonia officinalis L., this research was performed. The targeted chemical characterization of the extracts was achieved using the Ultra-High-Performance-Liquid-Chromatography-Linear-Trap-Mass-Spectrometry OrbiTrap instrumental technique, while Fourier Transform Infrared Spectroscopy was conducted to investigate the structural properties of the examined leaf extracts. According to the results, the species P. officinalis, Božurna locality as the origin of the plant material, and microwave-assisted extraction produced the maximum polyphenol yield, (491.9 ± 2.7 mg gallic acid equivalent (GAE)/mL). The ethanolic extracts exhibited moderate antioxidant activity as evaluated by DPPH (2,2-diphenyl-1-picrylhydrazyl) and phosphomolybdenum tests. With MIC values of 0.125 mg/mL, the leaf extracts produced by ultrasound-assisted extraction and maceration (Deliblato sands and Bogovo gumno) had the best antibacterial activity against Pseudomonas aeruginosa and Salmonella Typhimurium. Ultrasound-assisted extraction has proven to produce the most effective antimicrobial agents. Inhibitory potential towards glucosidase, amylase, cholinesterases, and tyrosinase was evaluated in enzyme inhibition assays and molecular docking simulations. Results show that leaves of P. tenuifolia L. obtained by ultrasound-assisted extraction had the highest acetylcholinesterase and butyrylcholinesterase inhibitory activity. Namely, the complexity of the polyphenol structures, the extraction method, the used locality, and the different mechanisms of the reactions between bioactives from leaf extracts and other components (free radicals, microorganisms, and enzymes) are the main factors that influence the results of the antioxidant tests, as well as the antibacterial and enzyme-inhibitory activities of the extracts. Hydroxymethyl-phenyl pentosyl-hexoside and acetyl-hydroxyphenyl-hexoside were the first time identified in the leaf extract of the Paeonia species. Due to their proven biological activities and the confirmed existence of bioactive compounds, leaf extracts may find use in foodstuffs, functional foods, and pharmaceutical products.

Engineering non-conservative substrate recognition sites of extradiol dioxygenase: Computation guided design to diversify and accelerate degradation of aromatic compounds

Extradiol dioxygenases (EDOs) catalyzing meta-cleavage of catecholic compounds promise an effective way to detoxify aromatic pollutants. This work reported a novel scenario to engineer our recently identified Type I EDO from Tcu3516 for a broader substrate scope and enhanced activity, which was based on 2,3-dihydroxybiphenyl (2,3-DHB)-liganded molecular docking of Tcu3516 and multiple sequence alignment with other 22 Type I EDOs. 11 non-conservative residues of Tcu3516 within 6 Å distance to the 2,3-DHB ligand center were selected as potential hotspots and subjected to semi-rational design using 6 catecholic analogues as substrates; the mutants V186L and V212N returned with progressive evolution in substrate scope and catalytic activity. Both mutants were combined with D285A for construction of double mutants and final triple mutant V186L/V212N/D285A. Except for 2,3-DHB (the mutant V186L/D285A gave the best catalytic performance), the triple mutant prevailed all other 5 catecholic compounds for their degradation; affording the catalytic efficiency kcat/Km value increase by 10-30 folds, protein Tm (structural rigidity) increase by 15 °C and the half-life time enhancement by 10 times compared to the wild type Tcu3516. The molecular dynamic simulation suggested that a stabler core and a more flexible entrance are likely accounting for enhanced catalytic activity and stability of enzymes.

Dopamine oxidation promoted by human telomeric DNA models in the presence of a Cu(II) terpyridine chelate

We found that under oxidative stress conditions, the coexistence of human telomeric DNA (HT-DNA) and a copper-terpyridine metallodrug can accelerate dopamine oxidation. The unwinding of HT-DNA from a duplex to cytosine-rich (C-rich) and guanine-rich (G-rich) single strands promotes dopamine oxidation in a general order of C-rich > G-rich > duplex. Along with dopamine oxidation, HT-DNA also undergoes severe damage.

Piperazine amides with desirable solubility, physicochemical and drug-like properties: Synthesis and evaluation of the anti-Trypanosoma cruzi activity

The absence of effective chronic treatment, expansion to non-endemic countries and the significant burden in public health have stimulated the search for novel therapeutic options to treat Chagas disease, a protozoan disease caused by Trypanosoma cruzi. Despite current efforts, no new drug candidates were approved in clinical trials in the past five decades. Considering this, our group has focused on the expansion of a series (LINS03) with low micromolar activity against amastigotes, considering the optimization of pharmacokinetic properties through increasing drug-likeness and solubility. In this work, we report a new set of 13 compounds with modifications in both the arylpiperazine and the aromatic region linked by an amide group. Five analogues showed activity against intracellular amastigotes (IC₅₀ 17.8 to 35.9 µM) and no relevant cytotoxicity to mammalian cells (CC₅₀ > 200 µM). Principal component analysis (PCA) was performed to identify structural features associated to improved activity. The data revealed that polarity, hydrogen bonding ability and flexibility were key properties that influenced the antiparasitic activity. In silico drug-likeness assessments indicated that compounds with the 4-methoxycinammyl (especially compound 2b) had the most prominent balance between properties and activity in the series, as confirmed by SAR analysis.

Functionalized Sulfur-Containing Heterocyclic Analogs Induce Sub-G1 Arrest and Apoptotic Cell Death of Laryngeal Carcinoma In Vitro

In this study, we speculate that the hydroxyl-containing benzo[b]thiophene analogs, 1-(3-hydroxybenzo[b]thiophen-2-yl) ethanone (BP) and 1-(3-hydroxybenzo[b]thiophen-2-yl) propan-1-one hydrate (EP), might possess antiproliferative activity against cancer cells. Hydroxyl-containing BP and EP show selectivity towards laryngeal cancer cells (HEp2), with IC₅₀ values of 27.02 ± 1.23 and 35.26 ± 2.15 µM, respectively. The hydroxyl group present in the third position is responsible for the anticancer activity and is completely abrogated when the hydroxyl group is masked. BP and EP enhance the antioxidant enzyme activity and reduce the ROS production, which are correlated with the antiproliferative effect in HEp-2 cells. An increase in the BAX/BCL-2 ratio occurs during the BP and EP treatment and activates the caspase cascade, resulting in apoptosis stimulation. It also arrests the cells in the Sub-G1 phase, indicating the induction of apoptosis. The molecular docking and simulation studies predicted a strong interaction between BP and the CYP1A2 protein, which could aid in combinational therapy by enhancing the bioavailability of the drugs. BP and EP possess an antioxidant property with low antiproliferative effects (~5.18 µg/mL and ~7.8 µg/mL) as a standalone drug, therefore, they can be combined with other drugs for effective chemotherapy that might trigger the effect of pro-oxidant drug on healthy cells.

Anti-Melanogenic Potential of Natural and Synthetic Substances: Application in Zebrafish Model

Melanogenesis is a biosynthetic pathway for the formation of the pigment melanin in human skin. A key enzyme in the process of pigmentation through melanin is tyrosinase, which catalyzes the first and only limiting step in melanogenesis. Since the discovery of its methanogenic properties, tyrosinase has been the focus of research related to the anti-melanogenesis. In addition to developing more effective and commercially safe inhibitors, more studies are required to better understand the mechanisms involved in the skin depigmentation process. However, in vivo assays are necessary to develop and validate new drugs or molecules for this purpose, and to accomplish this, zebrafish has been identified as a model organism for in vivo application. In addition, such model would allow tracking and studying the depigmenting activity of many bioactive compounds, important to genetics, medicinal chemistry and even the cosmetic industry. Studies have shown the similarity between human and zebrafish genomes, encouraging their use as a model to understand the mechanism of action of a tested compound. Interestingly, zebrafish skin shares many similarities with human skin, suggesting that this model organism is suitable for studying melanogenesis inhibitors. Accordingly, several bioactive compounds reported herein for this model are compared in terms of their molecular structure and possible mode of action in zebrafish embryos. In particular, this article described the main metabolites of Trichoderma fungi, in addition to substances from natural and synthetic sources.

Increasing the antioxidant capacity of ceria nanoparticles with catechol-grafted poly(ethylene glycol)

Ceria nanoparticles are remarkable antioxidants due to their large cerium(III) content and the possibility of recovering cerium(III) from cerium(IV) after reaction. Here we increase the cerium(III) content of colloidally stable nanoparticles (e.g., nanocrystals) using a reactive polymeric surface coating. Catechol-grafted poly(ethylene glycols) (PEG) polymers of varying lengths and architectures yield materials that are non-aggregating in a variety of aqueous media. Cerium(IV) on the ceria surface both binds and oxidizes the catechol functionality, generating a dark-red colour emblematic of surface-oxidized catechols with a concomitant increase in cerium(III) revealed by X-ray photoemission spectroscopy (XPS). The extent of ceria reduction depends sensitively on the architecture of the coating polymer; small and compact polymer chains pack with high density at the nanoparticle surface yielding the most cerium(III). Nanoparticles with increased surface reduction, quantified by the intensity of their optical absorption and thermogravimetric measures of polymer grafting densities, were more potent antioxidants as measured by a standard TEAC antioxidant assay. For the same core composition nanoparticle antioxidant capacities could be increased over an order of magnitude by tailoring the length and architecture of the reactive surface coatings.

DNA Damage and Oxidative Stress of Tobacco Smoke Condensate in Human Bladder Epithelial Cells

Smoking is a major risk factor for bladder cancer (BC), with up to 50% of BC cases being attributed to smoking. There are 70 known carcinogens in tobacco smoke; however, the principal chemicals responsible for BC remain uncertain. The aromatic amines 4-aminobiphenyl (4-ABP) and 2-naphthylamine (2-NA) are implicated in BC pathogenesis of smokers on the basis of the elevated BC risk in factory workers exposed to these chemicals. However, 4-ABP and 2-NA only occur at several nanograms per cigarette and may be insufficient to induce BC. In contrast, other genotoxicants, including acrolein, occur at 1000-fold or higher levels in tobacco smoke. There is limited data on the toxicological effects of tobacco smoke in human bladder cells. We have assessed the cytotoxicity, oxidative stress, and DNA damage of tobacco smoke condensate (TSC) in human RT4 bladder cells. TSC was fractionated by liquid-liquid extraction into an acid-neutral fraction (NF), containing polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs, phenols, and aldehydes, and a basic fraction (BF) containing aromatic amines, heterocyclic aromatic amines, and N-nitroso compounds. The TSC and NF induced a time- and concentration-dependent cytotoxicity associated with oxidative stress, lipid peroxide formation, glutathione (GSH) depletion, and apurinic/apyrimidinic (AP) site formation, while the BF showed weak effects. LC/MS-based metabolomic approaches showed that TSC and NF altered GSH biosynthesis pathways and induced more than 40 GSH conjugates. GSH conjugates of several hydroquinones were among the most abundant conjugates. RT4 cell treatment with synthetic hydroquinones and cresol mixtures at levels present in tobacco smoke accounted for most of the TSC-induced cytotoxicity and the AP sites formed. GSH conjugates of acrolein, methyl vinyl ketone, and crotonaldehyde levels also increased owing to TSC-induced oxidative stress. Thus, TSC is a potent toxicant and DNA-damaging agent, inducing deleterious effects in human bladder cells at concentrations of <1% of a cigarette in cell culture media.

Assessing the Morphological and Behavioral Toxicity of Catechol Using Larval Zebrafish

Catechol is a ubiquitous chemical used in the manufacturing of fragrances, pharmaceuticals and flavorants. Environmental exposure occurs in a variety of ways through industrial processes, during pyrolysis and in effluent, yet despite its prevalence, there is limited information regarding its toxicity. While the genotoxicity and gastric carcinogenicity of catechol have been described in depth, toxicological studies have potentially overlooked a number of other effects relevant to humans. Here, we have made use of a general and behavioral larval zebrafish toxicity assay to describe previously unknown catechol-based toxicological phenomena. Behavioral testing revealed catechol-induced hypoactivity at concentrations an order of magnitude lower than observable endpoints. Catechol exposure also resulted in punctate melanocytes with concomitant decreases in the expression of pigment production and regulation markers mitfa, mc1r and tyr. Because catechol is converted into a number of toxic metabolites by tyrosinase, an enzyme found almost exclusively in melanocytes, an evaluation of the effects of catechol on these cells is critical to evaluating the safety of this chemical. This work provides insights into the toxic nature of catechol and highlights the benefits of the zebrafish larval testing platform in being able to dissect multiple aspects of toxicity with one model.

Polymerases and DNA Repair in Neurons: Implications in Neuronal Survival and Neurodegenerative Diseases

Most of the neurodegenerative diseases and aging are associated with reactive oxygen species (ROS) or other intracellular damaging agents that challenge the genome integrity of the neurons. As most of the mature neurons stay in G0/G1 phase, replication-uncoupled DNA repair pathways including BER, NER, SSBR, and NHEJ, are pivotal, efficient, and economic mechanisms to maintain genomic stability without reactivating cell cycle. In these progresses, polymerases are prominent, not only because they are responsible for both sensing and repairing damages, but also for their more diversified roles depending on the cell cycle phase and damage types. In this review, we summarized recent knowledge on the structural and biochemical properties of distinct polymerases, including DNA and RNA polymerases, which are known to be expressed and active in nervous system; the biological relevance of these polymerases and their interactors with neuronal degeneration would be most graphically illustrated by the neurological abnormalities observed in patients with hereditary diseases associated with defects in DNA repair; furthermore, the vicious cycle of the trinucleotide repeat (TNR) and impaired DNA repair pathway is also discussed. Unraveling the mechanisms and contextual basis of the role of the polymerases in DNA damage response and repair will promote our understanding about how long-lived postmitotic cells cope with DNA lesions, and why disrupted DNA repair contributes to disease origin, despite the diversity of mutations in genes. This knowledge may lead to new insight into the development of targeted intervention for neurodegenerative diseases.

In silico ADMET, molecular docking and molecular simulation-based study of glabridin’s natural and semisynthetic derivatives as potential tyrosinase inhibitors

Hyper-pigmentation conditions may develop due to erroneous melanogenesis cascade which leads to excess melanin production. Recently, inhibition of tyrosinase is the main focus of investigation as it majorly contributes to melanin production. This inhibition property can be exploited in medicine, agriculture, and in cosmetics. Present study aims to find a natural and safe alternative molecule as tyrosinase inhibitor. In this study, human tyrosinase enzyme was modelled due to unavailability of its crystal structure to look into the degree of efficacy of glabridin and its 15 derivatives as tyrosinase inhibitor. Docking was performed by Autodock Vina at the catalytic core enzyme. Glabridin effects on melanoma cell lines was also elucidated by analysing cytotoxicity and effect on melanin production. Computational ADME analysis was done by SwissADME. Molecular dynamic simulation was also performed to further evaluate the interaction profile of these molecules and kojic acid (positive inhibitor) with respect to apo protein. Notably, four derivatives 5′-formylglabridin, glabridin dimer, 5′-prenyl glabridin and R-glabridin exhibited better binding affinity than glabridin. Glabridin effectively inhibited melanin production in a dose dependent manner. Among these, 5′-formylglabridin displayed highest binding affinity with docking score − 9.2 kcal/mol. Molecular properties and bioactivity analysis by Molinspiration web server and by SwissADME also presented these molecules as potential drug candidates. The study explores the understanding for the development of suitable tyrosinase inhibitor/s for the prevention of hyperpigmentation. However, a detailed in vivo study is required for glabridin derivatives to suggest these molecules as anti-melanogenic compound.

A new thermophilic extradiol dioxygenase promises biodegradation of catecholic pollutants

Extradiol dioxygenases (EDOs) catalyze the meta cleavage of catechol into 2-hydroxymuconaldehyde, a critical step in the degradation of aromatic compounds in the environment. In the present work, a novel thermophilic extradiol dioxygenase from Thermomonospora curvata DSM43183 was cloned, expressed, and characterized by phylogenetic and biochemical analyses. This enzyme exhibited excellent thermo-tolerance, displaying optimal activity at 50 °C, remaining >40% activity at 70 °C. Structural modeling and molecular docking demonstrated that both active center and pocket-construction loops locate at the C-terminal domain. Site-specific mutants D285A, H205V, F301V based on a rational design were obtained to widen the entrance of substrates; resulting in significantly improved catalytic performance for all the 3 mutants. Compared to the wild-type, the mutant D285A showed remarkably improved activities with respect to the 3,4-dihydroxyphenylacetic acid, catechol, and 3-chlorocatechol, by 17.7, 6.9, and 3.7-fold, respectively. The results thus verified the effectiveness of modeling guided design; and confirmed that the C-terminal loop structure indeed plays a decisive role in determining catalytic ring-opening efficiency and substrate specificity of the enzyme. This study provided a novel thermostable dioxygenase with a broad substrate promiscuity for detoxifying environmental pollutants and provided a new thinking for further enzyme engineering of EDOs.

Neuroprotective Properties of Quinone Reductase 2 Inhibitor M-11, a 2-Mercaptobenzimidazole Derivative

The ability of NQO2 to increase the production of free radicals under enhanced generation of quinone derivatives of catecholamines is considered to be a component of neurodegenerative disease pathogenesis. The present study aimed to investigate the neuroprotective mechanisms of original NQO2 inhibitor M-11 (2-[2-(3-oxomorpholin-4-il)-ethylthio]-5-ethoxybenzimidazole hydrochloride) in a cellular damage model using NQO2 endogenous substrate adrenochrome (125 µM) and co-substrate BNAH (100 µM). The effects of M-11 (10-100 µM) on the reactive oxygen species (ROS) generation, apoptosis and lesion of nuclear DNA were evaluated using flow cytometry and single-cell gel electrophoresis assay (comet assay). Results were compared with S29434, the reference inhibitor of NQO2. It was found that treatment of HT-22 cells with M-11 results in a decline of ROS production triggered by incubation of cells with NQO2 substrate and co-substrate. Pre-incubation of HT-22 cells with compounds M-11 or S29434 results in a decrease of DNA damage and late apoptotic cell percentage reduction. The obtained results provide a rationale for further development of the M-11 compound as a potential neuroprotective agent.

A Classification Model to Identify Direct-Acting Mutagenic Polycyclic Aromatic Hydrocarbon Transformation Products

Polycyclic aromatic hydrocarbons (PAHs) are a complex group of environmental contaminants, many having long environmental half-lives. As these compounds degrade, the changes in their structure can result in a substantial increase in mutagenicity compared to the parent compound. Over time, each individual PAH can potentially degrade into several thousand unique transformation products, creating a complex, constantly evolving set of intermediates. Microbial degradation is the primary mechanism of their transformation and ultimate removal from the environment, and this process can result in mutagenic activation similar to the metabolic activation that can occur in multicellular organisms. The diversity of the potential intermediate structures in PAH-contaminated environments renders hazard assessment difficult for both remediation professionals and regulators. A mixture of structural and energetic descriptors has proven effective in existing studies for classifying which PAH transformation products will be mutagenic. However, most existing studies of environmental PAH mutagens primarily focus on nitrogenated derivatives, which are prevalent in the atmosphere and not as relevant in soil. Additionally, PAH products commonly found in the environment can range from as large as five rings to as small as a single ring, requiring a broadly inclusive methodology to comprehensively evaluate mutagenic potential. We developed a combination of supervised and unsupervised machine learning methods to predict environmentally induced PAH mutagenicity with improved performance over currently available tools. K-means clustering with principal component analysis allows us to identify molecular clusters that we hypothesize to have similar mechanisms of action. Recursive feature elimination identifies the most influential descriptors. The cluster-specific regression outperforms available classifiers in predicting direct-acting mutagens resulting from the microbial biodegradation of PAHs and provides direction for future studies evaluating the environmental hazards resulting from PAH biodegradation.

Interactions of the antioxidant enzymes NAD(P)H: Quinone oxidoreductase 1 (NQO1) and NRH: Quinone oxidoreductase 2 (NQO2) with pharmacological agents, endogenous biochemicals and environmental contaminants

NAD(P)H

Quinone Oxidoreductase 1 (NQO1) is an antioxidant enzyme that catalyzes the two-electron reduction of several different classes of quinone-like compounds (quinones, quinone imines, nitroaromatics, and azo dyes). One-electron reduction of quinone or quinone-like metabolites is considered to generate semiquinones to initiate redox cycling that is responsible for the generation of reactive oxygen species and oxidative stress and may contribute to the initiation of adverse drug reactions and adverse health effects. On the other hand, the two-electron reduction of quinoid compounds appears important for drug activation (bioreductive activation) via chemical rearrangement or autoxidation. Two-electron reduction decreases quinone levels and opportunities for the generation of reactive species that can deplete intracellular thiol pools. Also, studies have shown that induction or depletion (knockout) of NQO1 were associated with decreased or increased susceptibilities to oxidative stress, respectively. Moreover, another member of the quinone reductase family, NRH: Quinone Oxidoreductase 2 (NQO2), has a significant functional and structural similarity with NQO1. The activity of both antioxidant enzymes, NQO1 and NQO2, becomes critically important when other detoxification pathways are exhausted. Therefore, this article summarizes the interactions of NQO1 and NQO2 with different pharmacological agents, endogenous biochemicals, and environmental contaminants that would be useful in the development of therapeutic approaches to reduce the adverse drug reactions as well as protection against quinone-induced oxidative damage. Also, future directions and areas of further study for NQO1 and NQO2 are discussed.

Naturally occurring and synthetic peptides: Efficient tyrosinase inhibitors

Tyrosinase is a copper-containing enzyme involved in the biosynthesis of melanin pigment, which is the most important photo protective agent against skin photo carcinogenesis. Excess production of melanin causes hyperpigmentation leading to undesired browning in human skin, fruits, and vegetable as well as plant-derived foods. Moreover, the role of tyrosinase in the onset and progression of various diseases such as cancers, Alzheimer's, and Parkinson diseases has been well documented in the literature. In this respect, tyrosinase inhibitors have been in the center of attention particularly as the efficient skin whitening agents. Among a wide range of compounds possessing anti-tyrosinase activity, peptides both natural and synthetic derivatives have attracted attention due to high potency and safety.

SAR and QSAR research on tyrosinase inhibitors using machine learning methods

Tyrosinase is a key rate-limiting enzyme in the process of melanin synthesis, which is closely related to human pigmentation disorders. Tyrosinase inhibitors can down-regulate tyrosinase to effectively reduce melanin synthesis. In this work, we conducted structure-activity relationship (SAR) study on 1097 diverse mushroom tyrosinase inhibitors. We applied five kinds of machine learning methods to develop 15 classification models. Model 5B built by fully connected neural networks and ECFP4 fingerprints achieved the highest prediction accuracy of 91.36% and Matthews correlation coefficient (MCC) of 0.81 on the test set. The applicability domains (AD) of classification models were defined by d S T D - P R O method. Moreover, we clustered the 1097 inhibitors into eight subsets by K-Means to figure out inhibitors' structural features. In addition, 10 quantitative structure-activity relationship (QSAR) models were constructed by four machine learning methods based on 813 inhibitors. Model 6 J, the best QSAR model, was developed by fully connected neural networks with 50 RDKit descriptors. It resulted in a coefficient of determination (r ²) of 0.770 and a root mean squared error (RMSE) of 0.482 on the test set. The AD of Model 6 J was visualized by Williams plot. The models built in this study can be obtained from the authors.

Copper-assisted oxidation of catechols into quinone derivatives

Catechols are ubiquitous substances often acting as antioxidants, thus of importance in a variety of biological processes. The Fenton and Haber–Weiss processes are thought to transform these molecules into aggressive reactive oxygen species (ROS), a source of oxidative stress and possibly inducing degenerative diseases. Here, using model conditions (ultrahigh vacuum and single crystals), we unveil another process capable of converting catechols into ROSs, namely an intramolecular redox reaction catalysed by a Cu surface. We focus on a tri-catechol, the hexahydroxytriphenylene molecule, and show that this antioxidant is thereby transformed into a semiquinone, as an intermediate product, and then into an even stronger oxidant, a quinone, as final product. We argue that the transformations occur via two intramolecular redox reactions: since the Cu surface cannot oxidise the molecules, the starting catechol and the semiquinone forms each are, at the same time, self-oxidised and self-reduced. Thanks to these reactions, the quinone and semiquinone are able to interact with the substrate by readily accepting electrons donated by the substrate. Our combined experimental surface science and ab initio analysis highlights the key role played by metal nanoparticles in the development of degenerative diseases.

An antioxidant catechol transforms following intramolecular redox reactions into highly reactive oxygen species, a semiquinone and a quinone, on copper.

Jeju Magma-Seawater Inhibits α-MSH-Induced Melanogenesis via CaMKKβ-AMPK Signaling Pathways in B16F10 Melanoma Cells

Melanin protects skin from ultraviolet radiation, toxic drugs, and chemicals. Its synthesis is sophisticatedly regulated by multiple mechanisms, including transcriptional and enzymatic controls. However, uncontrolled excessive production of melanin can cause serious dermatological disorders, such as freckles, melasma, solar lentigo, and cancer. Moreover, melanogenesis disorders are also linked to neurodegenerative diseases. Therefore, there is a huge demand for safer and more potent inhibitors of melanogenesis. In the present study, we report novel inhibitory effects of Jeju magma-seawater (JMS) on melanogenesis induced by α-melanocyte stimulating hormone (α-MSH) in B16F10 melanoma cells. JMS is the abundant underground seawater found in Jeju Island, a volcanic island of Korea. Research into the physiological effects of JMS is rapidly increasing due to its high contents of various minerals that are essential to human health. However, little is known about the effects of JMS on melanogenesis. Here, we demonstrate that JMS safely and effectively inhibits α-MSH-induced melanogenesis via the CaMKKβ (calcium/calmodulin-dependent protein kinase β)-AMPK (5′ adenosine monophosphate-activated protein kinase) signaling pathway. We further demonstrate that AMPK inhibits the signaling pathways of protein kinase A and MAPKs (mitogen-activated protein kinase), which are critical for melanogenesis-related gene expression. Our results highlight the potential of JMS as a novel therapeutic agent for ameliorating skin pigmentation-related disorders.

Chemical Reactivities of ortho-Quinones Produced in Living Organisms: Fate of Quinonoid Products Formed by Tyrosinase and Phenoloxidase Action on Phenols and Catechols

Tyrosinase catalyzes the oxidation of phenols and catechols (o-diphenols) to o-quinones. The reactivities of o-quinones thus generated are responsible for oxidative browning of plant products, sclerotization of insect cuticle, defense reaction in arthropods, tunichrome biochemistry in tunicates, production of mussel glue, and most importantly melanin biosynthesis in all organisms. These reactions also form a set of major reactions that are of nonenzymatic origin in nature. In this review, we summarized the chemical fates of o-quinones. Many of the reactions of o-quinones proceed extremely fast with a half-life of less than a second. As a result, the corresponding quinone production can only be detected through rapid scanning spectrophotometry. Michael-1,6-addition with thiols, intramolecular cyclization reaction with side chain amino groups, and the redox regeneration to original catechol represent some of the fast reactions exhibited by o-quinones, while, nucleophilic addition of carboxyl group, alcoholic group, and water are mostly slow reactions. A variety of catecholamines also exhibit side chain desaturation through tautomeric quinone methide formation. Therefore, quinone methide tautomers also play a pivotal role in the fate of numerous o-quinones. Armed with such wide and dangerous reactivity, o-quinones are capable of modifying the structure of important cellular components especially proteins and DNA and causing severe cytotoxicity and carcinogenic effects. The reactivities of different o-quinones involved in these processes along with special emphasis on mechanism of melanogenesis are discussed.

Nordihydroguaiaretic Acid: From Herbal Medicine to Clinical Development for Cancer and Chronic Diseases

Nordihydroguaiaretic acid (NDGA) is a phenolic lignan obtained from Larrea tridentata, the creosote bush found in Mexico and USA deserts, that has been used in traditional medicine for the treatment of numerous diseases such as cancer, renal, cardiovascular, immunological, and neurological disorders, and even aging. NDGA presents two catechol rings that confer a very potent antioxidant activity by scavenging oxygen free radicals and this may explain part of its therapeutic action. Additional effects include inhibition of lipoxygenases (LOXs) and activation of signaling pathways that impinge on the transcription factor Nuclear Factor Erythroid 2-related Factor (NRF2). On the other hand, the oxidation of the catechols to the corresponding quinones my elicit alterations in proteins and DNA that raise safety concerns. This review describes the current knowledge on NDGA, its targets and side effects, and its synthetic analogs as promising therapeutic agents, highlighting their mechanism of action and clinical projection towards therapy of neurodegenerative, liver, and kidney disease, as well as cancer.

Hydroethanolic extract from Endopleura uchi (Huber) Cuatrecasas and its marker bergenin: Toxicological and pharmacokinetic studies in silico and in vivo on zebrafish

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E. uchi stem bark hydroethanolic extract in zebrafish.

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Evaluating the in silico pharmacokinetic and toxicological parameters.

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Behavioral, biochemical and histopathological changes was dose dependent.

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In silico bergenin and its metabolites showed high intestinal absorption.

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Bergenin inhibited CYP2C9, CYP3A4 and CYP2C19.

Endopleura uchi, is used for the treatment of inflammatory disease and related to the female reproductive tract. The aim of this study was to evaluate the acute toxicity of the Endopleura uchi stem bark hydroethanolic extract (EEu) in zebrafish, emphasizing the histopathological and biochemical parameters, as well as evaluating the in silico pharmacokinetic and toxicological parameters of the phytochemical/pharmacological marker, bergenin, as their metabolites. The animals were orally treated with EEu at a single dose of 75 mg/kg, 500 mg/kg, 1000 mg/kg and 3000 mg/kg. the oral LD₅₀ of the EEu higher to the dose of 3000 mg/kg. Behavioral, biochemical and histopathological changes were dose dependent. In silico pharmacokinetic predictions for bergenin and its metabolites showed moderate absorption in high human intestinal absorption (HIA) and Caco-2 models, reduced plasma protein binding, by low brain tissue binding and no P-glycoprotein (P-Gp) inhibition. Their metabolism is defined by the CYP450 enzyme, in addition to bergenin inhibition of CYP2C9, CYP3A4 and CYP2C19. In the bergenin and its metabolites in silico toxicity test it have been shown to cause carcinogenicity and a greater involvement of the bergenin with the CYP enzymes in the I and II hepatic and renal metabolism’s phases was observed. It is possible to suggest that the histopathological damages are involved with the interaction of this major compound and its metabolites at the level of the cellular-biochemical mechanisms which involve the absorption, metabolization and excretion of these possible prodrug and drug.

Novel tyrosinase inhibitory peptide with free radical scavenging ability

Tyrosinase is a key enzyme involved in melanin synthesis. Therefore, various tyrosinase inhibitors have been screened by researchers in recent years. In the present study, we discovered a novel tyrosinase inhibitor, a peptide ECGYF (named EF-5), with free radical scavenging ability. The effect of tyrosinase inhibition by EF-5 was stronger than that of arbutin and glutathione, when analyzed both in vitro (IC50: 0.46 mM) and in vivo. The UV-Vis absorption and circular dichroism spectroscopies indicated that EF-5 interacted with tyrosinase in a different way as that of glutathione. The results of molecular docking showed that the binding between EF-5 and tyrosinase was determined majorly by hydrogen bonds and hydrophobic interactions. EF-5 had also retained its ability to scavenge both hydroxyl and superoxide radicals in vitro and was found to be nontoxic to cells, as revealed by the MTT assay. These features suggested that the EF-5 peptide may serve as a safe and effective alternative as a tyrosinase inhibitor.

Synthesis of N-arylindazole-3-carboxamide and N-benzoylindazole derivatives and their evaluation against α-MSH-stimulated melanogenesis

We have designed and synthesized twenty-six N-arylindazole-3-carboxamide (3a-p) and N-benzoylindazole (6a-j) derivatives to discover with excellent inhibition activities of α-MSH-stimulated melanogenesis. In the bio evaluation studies of these compounds, we discovered eighteen compounds, out of twenty-six exhibited more potent inhibition than the positive control arbutin. From the SAR studies, we identified 3k and 6g as lead compounds which displayed almost 5 and 9 times more potent inhibition of α-MSH-stimulated melanogenesis respectively than the reference arbutin. It is also evident the presence of electron withdrawing group at para position (R³) for the compounds (3a-p) and presence of +M group at ortho position (R⁵) for the compounds (6a-j) were crucial for their excellent inhibition activities of α-MSH-stimulated melanogenesis.

Antioxidant, anti-tyrosinase and anti-melanogenic effects of (E)-2,3-diphenylacrylic acid derivatives

During our continued search for strong skin whitening agents over the past ten years, we have investigated the efficacies of many tyrosinase inhibitors containing a common (E)-β-phenyl-α,β-unsaturated carbonyl scaffold, which we found to be essential for the effective inhibition of mushroom and mammalian tyrosinases. In this study, we explored the tyrosinase inhibitory effects of 2,3-diphenylacrylic acid (2,3-DPA) derivatives, which also possess the (E)-β-phenyl-α,β-unsaturated carbonyl motif. We synthesized fourteen (E)-2,3-DPA derivatives 1a-1n and one (Z)-2,3-DPA-derivative 1l' using a Perkin reaction with phenylacetic acid and appropriate substituted benzaldehydes. In our mushroom tyrosinase assay, 1c showed higher tyrosinase inhibitory activity (76.43 ± 3.53%, IC₅₀ = 20.04 ± 1.91 µM) with than the other 2,3-DPA derivatives or kojic acid (21.56 ± 2.93%, IC₅₀ = 30.64 ± 1.27 μM). Our mushroom tyrosinase inhibitory results were supported by our docking study, which showed compound 1c (-7.2 kcal/mole) exhibited stronger binding affinity for mushroom tyrosinase than kojic acid (-5.7 kcal/mole). In B16F10 melanoma cells (a murine cell-line), 1c showed no cytotoxic effect up to a concentration of 25 μM and exhibited greater tyrosinase inhibitory activity (68.83%) than kojic acid (49.39%). In these cells, arbutin (a well-known tyrosinase inhibitor used as the positive control) only inhibited tyrosinase by 42.67% even at a concentration of 400 μM. Furthermore, at 25 µM, 1c reduced melanin contents in B16F10 melanoma cells by 24.3% more than kojic acid (62.77% vs. 38.52%). These results indicate 1c is a promising candidate treatment for pigmentation-related diseases and potential skin whitening agents.

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.

DNA-Stabilized Silver Nanoclusters as Specific, Ratiometric Fluorescent Dopamine Sensors

Neurotransmitters are small molecules that orchestrate complex patterns of brain activity. Unfortunately, there exist few sensors capable of directly detecting individual neurotransmitters. Those sensors that do exist are either unspecific or fail to capture the temporal or spatial dynamics of neurotransmitter release. DNA-stabilized silver nanoclusters (DNA-AgNCs) are a new class of biocompatible, fluorescent nanostructures that have recently been shown to offer promise as biosensors. In this work, we identify two different DNA sequences that form dopamine-sensitive nanoclusters. We demonstrate that each sequence supports two distinct DNA-AgNCs capable of providing specific, ratiometric fluorescent sensing of dopamine concentration in vitro. DNA-Ag nanoclusters therefore offer a novel, low-cost approach to quantification of dopamine, creating the potential for real-time monitoring in vivo.

Removal of catechol from water by modified dolomite: performance, spectroscopy, and mechanism

Dolomite was treated at 800 °C (D800), characterized, and used in the adsorptive removal of catechol (1,2-dihydroxybenzene) from aqueous solutions. The performances of the D800 sample, named dolomitic solid, were compared with those of the raw material. A bibliographic review shows that the data on the adsorption of phenolic compounds by dolomites are non-existent. Kinetic data, equilibrium isotherms, thermodynamic parameters, and pH influence were reported. Special attention was paid to the spectroscopic study, before and after adsorption. The purpose was to understand the mechanism of catechol uptake on dolomitic materials. Kinetics follows the pseudo-second order model. The Redlich-Peterson isotherm provides the best correlation of our isotherms. Affinity follows the sequence: D800 ≫ raw dolomite. The process is spontaneous at low temperatures and exothermic. After catechol adsorption, the shape of the band in the 3,600-3,000 cm^-1 range and its red shift towards 3,429 cm^-1 reflect a deep involvement of OH groups both of D800 and catechol, which confirm hydrogen bonding via their respective OH. On this basis, a schematic illustration was proposed. The understanding of the phenolic compound-dolomitic solid interactions constitutes a fundamental approach to developing the application of these materials in wastewater treatment.

Mass spectrometry investigation of DNA adduct formation from bisphenol A quinone metabolite and MCF-7 cell DNA

Bisphenol A (BPA) is a widely used additive in the plastic industry and has been reported to have genotoxicity. A hypothesis that BPA may enhance breast cancer risk through the formation of its metabolic intermediate or DNA adduct has been proposed. In this study, breast cancer cell MCF-7 was cultured and the cellular DNA was extracted from the cells. The adducts of bisphenol A 3,4-quinone (BPAQ) with 2'-deoxyguanosine (dG), calf thymus DNA and MCF-7 cell DNA were investigated. DNA adducts were characterized by using electrospray ionization Orbitrap high-resolution mass spectrometry and tandem mass spectrometry. The BPA-DNA adducts of BPAQ with dG, calf thymus and MCF-7 cell DNA were identified as 3-hydroxy-bisphenol A-N7-guanine (3-OH-BPA-N7Gua). The MS/MS fragmentation pathway of 3-OH-BPA-N7Gua was proposed based on obtained accurate mass data. BPA quinone metabolites can react with MCF-7 cell DNA in vitro. The findings provide evidence that BPA might covalently bind to DNA in MCF-7 cells mediated by quinone metabolites, which may increase our understanding of health risk associated with BPA exposure.

Synthesis and Biological Evaluation of S-Substituted Perhalo-2-nitrobuta-1,3-dienes as Novel Xanthine Oxidase, Tyrosinase, Elastase, and Neuraminidase Inhibitors

S-substituted perhalo-2-nitrobuta-1,3-dienes 3a, b were synthesized by the reaction of polyhalo-2-nitrobuta-1,3-dienes 1a, b with allyl mercaptan. 1-(2,3-Dibromopropanethio)-4-bromo-1,3,4-trichloro-2-nitrobuta-1,3-diene 4 was obtained from the addition of bromine to S-substituted polyhalo-2-nitrobuta-1,3-diene 3b in carbon tetrachloride. Sulfoxides 5a, b, and 6 were obtained from the reaction of thiosubstituted polyhalonitrobutadienes 3a, b, and 4 with m-CPBA in CHCl3. The structures of the new compounds were determined by spectroscopic data (FTIR, 1H NMR, 13C NMR, MS). These compounds exhibited antixanthine oxidase, antityrosinase, antielastase, and antineuraminidase activities.

Thiopurine Drugs Repositioned as Tyrosinase Inhibitors

Drug repositioning is the application of the existing drugs to new uses and has the potential to reduce the time and cost required for the typical drug discovery process. In this study, we repositioned thiopurine drugs used for the treatment of acute leukaemia as new tyrosinase inhibitors. Tyrosinase catalyses two successive oxidations in melanin biosynthesis: the conversions of tyrosine to dihydroxyphenylalanine (DOPA) and DOPA to dopaquinone. Continuous efforts are underway to discover small molecule inhibitors of tyrosinase for therapeutic and cosmetic purposes. Structure-based virtual screening predicted inhibitor candidates from the US Food and Drug Administration (FDA)-approved drugs. Enzyme assays confirmed the thiopurine leukaemia drug, thioguanine, as a tyrosinase inhibitor with the inhibitory constant of 52 μM. Two other thiopurine drugs, mercaptopurine and azathioprine, were also evaluated for their tyrosinase inhibition; mercaptopurine caused stronger inhibition than thioguanine did, whereas azathioprine was a poor inhibitor. The inhibitory constant of mercaptopurine (16 μM) was comparable to that of the well-known inhibitor kojic acid (13 μM). The cell-based assay using B16F10 melanoma cells confirmed that the compounds inhibit mammalian tyrosinase. Particularly, 50 μM thioguanine reduced the melanin content by 57%, without apparent cytotoxicity. Cheminformatics showed that the thiopurine drugs shared little chemical similarity with the known tyrosinase inhibitors.

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.

N-Acetylcysteine Prevents the Increase in Spontaneous Oxidation of Dopamine During Monoamine Oxidase Inhibition in PC12 Cells

The catecholaldehyde hypothesis for the pathogenesis of Parkinson's disease proposes that the deaminated dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL) is toxic to nigrostriatal dopaminergic neurons. Inhibiting monoamine oxidase (MAO) should therefore slow the disease progression; however, MAO inhibition increases spontaneous oxidation of dopamine, as indicated by increased 5-S-cysteinyl-dopamine (Cys-DA) levels, and the oxidation products may also be toxic. This study examined whether N-acetylcysteine (NAC), a precursor of the anti-oxidant glutathione, attenuates the increase in Cys-DA production during MAO inhibition. Rat pheochromocytoma PC12 cells were incubated with NAC, the MAO-B inhibitor selegiline, or both. Selegiline decreased DOPAL and increased Cys-DA levels (p < 0.0001 each). Co-incubation of NAC at pharmacologically relevant concentrations (1-10 µM) with selegiline (1 µM) attenuated or prevented the Cys-DA response to selegiline, without interfering with the selegiline-induced decrease in DOPAL production or inhibiting tyrosine hydroxylation. NAC therefore mitigates the increase in spontaneous oxidation of dopamine during MAO inhibition.

Transformation of halobenzoquinones with the presence of amino acids in water: Products, pathways and toxicity

The transformation and detoxification of halobenzoquinones (HBQs), a class of emerging disinfection byproducts (DBPs), was studied in the presence of amino acids (AAs). The reaction activity of three HBQs with AAs generally ranked as 2-chlorobenzoquinone (CBQ) < 2,6-dichlorobezoquinone (DCBQ) < tetrachloroquinone (TCBQ), consistent with their halogenation degree and the calculated electron affinity (EA) results. According to mass spectrometry and density functional theory (DFT) calculations, AAs can easily covalently incorporate into HBQs via nucleophilic addition (CBQ and DCBQ) or substitution (TCBQ) through CNC or CSC linkages. Hydroxylation, nucleophilic reaction and decarboxylation were proposed to be the three major reaction pathways for HBQs transformation with AAs. HBQs firstly underwent the spontaneous hydrolysis, resulting in OH-HBQs formation. Then, nucleophilic addition/substitution of AAs occurred on HBQs and OH-HBQs to produce AA-HBQs/AA-HBQs-OH adducts. These adducts were subsequently oxidized into their corresponding decarboxylated forms. Based on the results of Luminous bacterium Q67 acute toxicity test, the toxicity of HBQs solution greatly decreased with AAs presented. The toxicity change was well explained by the lowest unoccupied molecular orbital energy (E_LUMO) of formed products. Notably, the step that AAs nucleophilic bonded with HBQs led to the highest rise of E_LUMO, which should be the most effective pathway for HBQs detoxification. This study shows that binding with amino nitrogen compounds should be an important process for HBQs transformation and detoxification, which helps to better understand the fate of this typical DBP in surface water.

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.

Genotoxicity of ortho-quinones: reactive oxygen species versus covalent modification

o-Quinones are formed metabolically from natural and synthetic estrogens as well as upon exposure to polycyclic aromatic hydrocarbons (PAH) and contribute to estrogen and PAH carcinogenesis by genotoxic mechanisms. These mechanisms include the production of reactive oxygen species to produce DNA strand breaks and oxidatively damaged nucleobases; and the formation of covalent depurinating and stable DNA adducts. Unrepaired DNA-lesions can lead to mutation in critical growth control genes and cellular transformation. The genotoxicity of the o-quinones is exacerbated by nuclear translocation of estrogen o-quinones by the estrogen receptor and by the nuclear translocation of PAH o-quinones by the aryl hydrocarbon receptor. The properties of o-quinones, their formation and detoxication mechanisms, quinone-mediated DNA lesions and their mutagenic properties support an important role in hormonal and chemical carcinogenesis.

Critical depurinating DNA adducts: Estrogen adducts in the etiology and prevention of cancer and dopamine adducts in the etiology and prevention of Parkinson's disease

Endogenous estrogens become carcinogens when dangerous metabolites, the catechol estrogen quinones, are formed. In particular, the catechol estrogen-3,4-quinones can react with DNA to produce an excess of specific depurinating estrogen-DNA adducts. Loss of these adducts leaves apurinic sites in the DNA, generating subsequent cancer-initiating mutations. Unbalanced estrogen metabolism yields excessive catechol estrogen-3,4-quinones, increasing formation of depurinating estrogen-DNA adducts and the risk of initiating cancer. Evidence for this mechanism of cancer initiation comes from various types of studies. High levels of depurinating estrogen-DNA adducts have been observed in women with breast, ovarian or thyroid cancer, as well as in men with prostate cancer or non-Hodgkin lymphoma. Observation of high levels of depurinating estrogen-DNA adducts in high risk women before the presence of breast cancer indicates that adduct formation is a critical factor in breast cancer initiation. Formation of analogous depurinating dopamine-DNA adducts is hypothesized to initiate Parkinson's disease by affecting dopaminergic neurons. Two dietary supplements, N-acetylcysteine and resveratrol complement each other in reducing formation of catechol estrogen-3,4-quinones and inhibiting formation of estrogen-DNA adducts in cultured human and mouse breast epithelial cells. They also inhibit malignant transformation of these cells. In addition, formation of adducts was reduced in women who followed a Healthy Breast Protocol that includes N-acetylcysteine and resveratrol. When initiation of cancer is blocked, promotion, progression and development of the disease cannot occur. These results suggest that reducing formation of depurinating estrogen-DNA adducts can reduce the risk of developing a variety of types of human cancer.

Silkworm Sericin: Properties and Biomedical Applications

Silk sericin is a natural polymer produced by silkworm, Bombyx mori, which surrounds and keeps together two fibroin filaments in silk thread used in the cocoon. The recovery and reuse of sericin usually discarded by the textile industry not only minimizes environmental issues but also has a high scientific and commercial value. The physicochemical properties of the molecule are responsible for numerous applications in biomedicine and are influenced by the extraction method and silkworm lineage, which can lead to variations in molecular weight and amino acid concentration of sericin. The presence of highly hydrophobic amino acids and its antioxidant potential make it possible for sericin to be applied in the food and cosmetic industry. The moisturizing power allows indications as a therapeutic agent for wound healing, stimulating cell proliferation, protection against ultraviolet radiation, and formulating creams and shampoos. The antioxidant activity associated with low digestibility of sericin that expands the application in the medical field, such as antitumour, antimicrobial and anti-inflammatory agent, anticoagulant, acts in colon health, improving constipation and protects the body from obesity through improved plasma lipid profile. In addition, the properties of sericin allow its application as a culture medium and cryopreservation, in tissue engineering and for drug delivery, demonstrating its effective use, as an important biomaterial.

Downregulation of melanogenesis: drug discovery and therapeutic options

Melanin, primarily responsible in humans for hair, eye and skin pigmentation, is produced by melanocytes through a process called melanogenesis. However, the abnormal accumulation of melanin causes dermatological problems such as café-au-lait macules ephelides (freckles), solar lentigo (age spots) and melasma, as well as cancer and vitiligo. Hence the regulation of melanogenesis is very important for treating hyperpigmentary disorders. Numerous antimelanogenic agents that target tyrosinase activity and/or stability, melanosome maturation, transfer and trafficking, or melanogenesis-related signaling pathways have been developed. This article reviews recent advances in research and development of human tyrosinase and melanogenesis-related signaling pathway inhibitors. Attempts have been made to provide a complete description of the mechanism of action of inhibitors on various melanogenesis signaling pathways.

Genetic polymorphisms in APE1 Asp148Glu(rs3136820) as a modifier of the background levels of abasic sites in human leukocytes derived from breast cancer patients and controls

BACKGROUND

Apurinic/apyrimidinic (abasic/AP) sites are among the most common endogenous DNA lesions. AP sites, if not repaired, could result in genomic instability as well as chromosome aberrations. Information regarding the direct assay of the number of abasic sites in human leukocytes and its association with risk of breast cancer has not been reported.

METHODS

In this study, we investigated the association between certain risk factors for breast cancer and the background levels of AP sites in leukocytes derived from 148 Taiwanese women with breast cancer and 140 cancer-free controls. The risk factors studied include age, body mass index (BMI), and polymorphisms of apurinic/apyrimidinic endonuclease (APE1) [APE1 Asp148Glu(rs3136820)].

RESULTS

Mean levels of AP sites were estimated to be 23.3 and 50.3 per 10⁶ nucleotides in controls and breast cancer patients, respectively (~twofold, p < 0.001). In subjects with age <50 or BMI < 27 (kg/m²), the levels of AP sites in breast cancer patients were ~2-3-fold greater than those of controls (p < 0.05). Additionally, results from the AP site 3'-cleavage assay indicated that the AP sites detected in both controls and patients were likely to be oxidant-mediated 5'-cleaved AP sites (~61-64 %). The number of AP sites in breast cancer patients was ~twofold greater in subjects with Asp/Glu + Glu/Glugenotypes than those with Asp/Asp genotype (p < 0.001).

CONCLUSIONS

We confirmed that cumulative body burden of AP sites is a significant predictor of the risk of developing breast cancer and that genetic predisposition and environment factors may modulate the induction of oxidative DNA lesions in breast cancer patients.