Tyrosinase inhibitory activity of flavonoids from Artocarpus heterophyllous

6,7-Bis-(2-methoxyethoxy)-4(3H)-quinazolinone as a novel inhibitor of tyrosinase and potential anti-browning agent of fresh-cut apples

6,7-Bis-(2-methoxyethoxy)-4(3H)-quinazolinone (BMEQ) was selected from quinazolinones for its strong tyrosinase inhibitory activity (IC50 = 160 ± 6 μM). It suppressed tyrosinase activity in a competitive way and quenched the fluorescence of the enzyme through a static mechanism. The binding of BMEQ to tyrosinase increased the hydrophobicity of the latter and facilitated non-radiative energy transfer between them. The formation of BMEQ-tyrosinase complex was driven by hydrogen bonds and hydrophobic interactions, and it loosened the basic framework structure of tyrosinase, affecting the conformation of the enzyme, and leading to a decrease in tyrosinase activity. In addition, the BMEQ postponed the oxidation of phenolics and flavonoids by inhibiting polyphenol oxidase (PPO) and peroxidase (POD), which resulted in the inhibition of the browning of fresh-cut apples. This study identified a novel tyrosinase inhibitor BMEQ and verified its potential application for improving the preservation of postharvest fruits.

Valorization of biomass polyphenols as potential tyrosinase inhibitors

Tyrosinases (TYRs; EC 1.14.18.1) catalyze two sequential oxidative reactions of the melanin biosynthesis pathway and play an important role in mammalian pigmentation and enzymatic browning of fruit and vegetables. Inhibition of TYR activity is therefore an attractive target for new drugs and/or food ingredients. In addition, increasing evidence suggests that TYR regulation could be a novel target for treatments of cancer and Parkinson's disease. Biomasses, notably industrial byproducts and biowaste, are good sustainable sources of phytochemicals that may be valorized into bioactive compounds including TYR inhibitors. This review presents potential applications of biomass-derived polyphenols targeting TYR inhibition. Insights into structure-activity relationships of several polyphenols and their glycosides are highlighted. Finally, some remarks and perspectives on research into new TYR inhibitors from biomass waste are provided.

Natural tyrosinase enzyme inhibitors: A path from melanin to melanoma and its reported pharmacological activities

The skin containing melanin pigment acts as a protective barrier and counteracts the UVR and other environmental stressors to maintain or restore disrupted cutaneous homeostasis. The production of melanin pigment is dependent on tyrosine levels. L-tyrosine and L-dihydroxyphenylalanine (L-DOPA) can serve both as a substrates and intermediates of melanin synthetic pathway and as inducers and positive regulators of melanogenesis. The biosynthesis of melanin is stimulated upon exposure to UVR, which can also stimulate local production of hormonal factors, which can stimulate melanoma development by altering the chemical properties of eu- and pheomelanin. The process of melanogenesis can be altered by several pathways. One involves activation of POMC, with the production of POMC peptides including MSH and ACTH, which increase intracellular cAMP levels, which activates the MITF, and helps to stimulate tyrosinase (TYR) expression and activity. Defects in OCA1 to 4 affects melanogenic activity via posttranslational modifications resulting in proteasomal degradation and reducing pigmentation. Further, altering, the MITF factor, helps to regulate the expression of MRGE in melanoma, and helps to increase the TYR glycosylation in ER. CRH stimulates POMC peptides that regulate melanogenesis and also by itself can stimulate melanogenesis. The POMC, P53, ACTH, MSH, MC1R, MITF, and 6-BH4 are found to be important regulators for pigmentation. Melanogenesis can affect melanoma behaviour and inhibit immune responses. Therefore, we reviewed natural products that would alter melanin production. Our special focus was on targeting melanin synthesis and TYR enzyme activity to inhibit melanogenesis as an adjuvant therapy of melanotic melanoma. Furthermore, this review also outlines the current updated pharmacological studies targeting the TYR enzyme from natural sources and its consequential effects on melanin production.

Pharmacognostical and Phytochemical Studies and Biological Activity of Curculigo latifolia Plant Organs for Natural Skin-Whitening Compound Candidate

Curculigo latifolia (family Amaryllidaceae) is used empirically for medicinal purposes. It is distributed throughout Asian countries, especially Indonesia. This study aimed at standardizing the C. latifolia plant, analyzing its phytochemical profile, and evaluating its pharmacological effects. The powder from each organ (root, stem, and leaves) was standardized organoleptically and microscopically. Samples were extracted by graded maceration using hexane, ethyl acetate, and ethanol. The extracts were determined for total phenolic content (TPC) and total flavonoid content (TFC). Antioxidant (radical scavenging and metal ion reduction) and antityrosinase activities were determined by spectrophotometric methods. Extracts were analysed for phytochemical profiles by LC-ESI-MS. The highest TPC and TFC were found in the ethanolic extract of the root organ (68.63 ± 2.97 mg GAE/g) and the ethyl acetate extract of the stem (14.33 ± 0.71 mg QE/g extract). High antioxidant activities were found in the ethanolic root extract (20.42 ± 0.33 µg/mL) and ethanolic stem extract (45.65 ± 0.77 µg/mL) by DPPH• and NO• assays, respectively. The ion reduction activity (by CUPRAC assay) was most significant in the ethyl acetate stem extract (390.42 ± 14.49 µmol GAEAC/g extract). Ethanolic root extract was the most active in inhibiting tyrosinase (IC50 value of 108.5 µg/mL). The correlation matrix between TPC and antioxidant activities showed a moderate to robust correlation, whereas the TPC and antityrosinase activity showed a robust correlation. The TFC and antioxidant or antityrosinase activities showed a weak to moderate correlation. The LC-ESI-MS data identified major phenols in the active extracts, including methyl 3-hydroxy-4-methoxy-benzoate, quercetin, 4-O-caffeoylquinic acid-1, and curculigoside. Overall, this study suggests that extracts from the C. latifolia plant offer potent antioxidant and antityrosinase activities, allowing them to be used as natural antioxidants and candidates for skin-lightening compounds.

Antioxidant Activity, Phenolic And Flavonoid Content of Passion Fruit Seed Oil

Passion fruit (Passiflora edulis Sims.) is a tropical plant that grows widely in South East Asian region, including on Sulawesi Island. The plant is important in the food sector and for medicinal purposes. The fruits of the Passion plant are made as a popular syrup beverage in Makassar produced by several companies. The production process results in an unusable seed containing potential natural oil. Passion Seed Oil (PSO) has several benefits in health and cosmetics. The oil contains chemically active compounds such as phenolic and flavonoids with antioxidant activities. This study was performed by comparison of several solvents acetone, ethyl acetate, chloroform, methanol, and n-hexane. The antioxidant activity, total phenolic and flavonoid content of all extracts were then examined by the researchers. The potential antioxidant activity of PSO was shown by a methanol extract of 71.67 µg/mL. The highest flavonoid content was ethyl acetate extract of 35.40 mg RE/g crude extract, and phenolic was acetone extract of 193.80 mg GAE/g crude extract.

Point-of-Care Portable 3D-Printed Multispectral Sensor for Real-Time Enzyme Activity Monitoring in Healthcare Applications

Absorbance spectroscopy finds many biomedical and physical applications ranging from studying the atomic and molecular details of the analyte to determination of unknown biological species and their concentration or activity in the samples. Commercially available laboratory-based spectrometers are usually bulky and require high power and laborious manual processing, making them unsuitable to be deployed in portable and space-constrained environments, thereby further limiting their utility for real-time on-site monitoring. To address these challenges, here we developed a portable 3D-printed multispectral spectrophotometer based on absorbance spectroscopy for real-time monitoring of enzyme molecular activity. Monitoring enzyme (such as tyrosinase) activity is critical, as it quantifies its reaction rate, which is dependent on many factors such as the enzyme and substrate concentrations, temperature, pH, and other regulators such as inhibitors and effectors. Tyrosinase is a critical enzyme responsible for melanin synthesis in living beings and exhibits enzymatic browning in fruits and vegetables. It finds various commercial applications in the fields of healthcare (skin pigmentation, wound healing, etc.), forensics, and food processing. Here, tyrosinase activity was monitored using a 3D-printed spectral sensor at different rates and compared against measurements obtained from laboratory instruments. The enzyme activity was also studied using kojic acid (i.e., a commonly employed commercial tyrosinase inhibitor) while varying its molar and volume concentrations to control the reaction rate at discrete activity levels. For tyrosinase activity monitoring, the fabricated device has shown significant correlation (R² = 0.9999) compared to measurements from the standard table-top spectrophotometer. We also provide a performance comparison between the 3D-printed and the laboratory spectrophotometer instruments by studying tyrosinase enzyme activity with and without the influence of an inhibitor. Such a device can be translated into various absorbance spectroscopy-based point-of-care biomedical and healthcare applications.

Strebluses E-H, four new stilbene-like derivatives from the stems of Streblus ilicifolius

Following bioactivity-guided isolation, four new stilbene-like derivatives, named Strebluses E-H, were isolated from the EtOAc-soluble fraction of the stems of Streblus ilicifolius (Moraceae). Their chemical structures were elucidated based on NMR spectroscopic data interpretation and optical rotation calculation. Streblus E possesses potent tyrosinase inhibitory activity with an IC₅₀ value of 0.1 μM. Oxy-tyrosinase has two bound Cu²⁺ ions and a peroxide group in the binding site, which has a role in the catalytic oxidation. Thus, a docking study of Streblus E with oxy-tyrosinase was performed to analyze the ligand-protein interactions. With in silico modelling, the S value and the ligand-protein interactions suggested that Streblus E showed lower binding affinity for oxy-tyrosinase than that of Streblus C.

Apigenin and its dermatological applications: A comprehensive review

Apigenin is one of the abundant flavonoids in fruits and vegetables of human diet with several demonstrated health benefits. The aim of the present study is to provide an overview of the current evidence regarding the effect of apigenin on different dermatological complications. Electronic databases including PubMed, Scopus, and Web of Science were searched to retrieve all papers assessing the dermatological effects of apigenin. Preclinical studies support beneficial effects of apigenin on UV-induced skin damage, vitiligo, dermatitis, wounds, skin aging, and some types of skin cancer. The compound mostly acts via inhibition of inflammation through suppression of pro-inflammatory cytokines and intracellular inflammatory mediators, as well as antioxidant properties such as improvement of endogenous antioxidant defense mechanisms. There are also some studies for the design and development of novel drug delivery systems for apigenin to improve its oral and topical bioavailability. Nevertheless, no clinical study has evaluated apigenin as a natural supplement for skin conditions. Considering the benefits of apigenin in preclinical models of dermatological disorders, as well as the acceptable safety of this compound, apigenin may be a future candidate to be used in dermatological disorders. Future clinical studies are needed to further confirm the safety and efficacy of apigenin in skin care products.

Tyrosinase Inhibitory Ability and In Vitro, In Vivo Acute Oral and In Silico Toxicity Evaluation of Extracts Obtained from Algerian Fir (Abiesnumidica de Lannoy ex CARRIERE) Needles

This study was designed to evaluate the tyrosinase inhibitory effect, in vitro, in vivo, and in silico toxicity of fractions isolated from A. numidica de Lannoy needles. The cytotoxicity of extracts was examined against Artemia salina larvae, while the toxicity of these extracts was tested by acute oral toxicity in mice; by administration of a dose of 2000 mg/kg b.w A. numidica leaves extracts. The blood samples were collected from the eye orbital sinus for further analysis of biochemical parameters. The absorption, distribution, metabolism, elimination, and toxicity (ADMET) properties were identified by the pkCSM web server. The data stated that ethyl acetate (EA) presented strong anti-tyrosinase apt. The results reported that ethyl acetate extract exhibited a strong inhibitory capacity against A. salina larvae with LD₅₀ of 75.004 µg/mL. The data also showed that no mortality occurred, and no toxicity symptoms were observed in mice. The biochemical parameters revealed that both extracts significantly affected the hepatic profile by increasing ALT, AST, and alkaline phosphatase. Histopathological tests also confirmed that both fractions were toxic at this concentration on hepatic and renal tissues, with necrosis observed. The toxicity of molecules in silico revealed no effect on all examined biomolecules.It can be concluded that this plant was toxic on the liver and renal profiles and tissues at the dose studied.

Molecular Action Mechanism of Coixol from Soft-Shelled Adlay on Tyrosinase: The Future of Cosmetics

Coix lacryma-jobi var. ma-yuen L. Gramineae is widely cultivated in Taiwan. Literature regarding the molecular action mechanism of coixol on tyrosinase and the application of coicis seed extracts to the processing of facial masks is still lacking. Solvent extractability analysis revealed that most of the polyphenolics in coicis seeds were water soluble (3.17 ± 0.12 to 3.63 ± 0.07 μg/mLGAE). In contrast, the methanolic extract contained the most flavonoids (0.06 ± 0.00~0.26 ± 0.03 μg/mL QE) and coixol (11.43 ± 0.13~12.83 ± 0.14 μg/mL), showing potent antioxidant capability. Additionally, the contents of coixenolide (176.77 ± 5.91 to 238.60 ± 0.21 μg/g), phytosterol (52.45 ± 2.05 to 58.23 ± 1.14 mg/g), and polysaccharides (3.42 ± 0.10 to 4.41 ± 0.10 mg/g) were rather high. The aqueous extract (10 μg/mL) and the ethanolic extract (1 mg/mL) showed no cytotoxicity to B16F10 melanocytes. More attractively, the ethanolic extract at 1 mg/mL caused 48.4% inhibition of tyrosinase activity in B16F10 melanocytes, and 50.7% on human tyrosinase (hTyr) fragment 369–377. Conclusively, the coicis seed extracts containing abundant nutraceuticals with promising anti-hTyr activity and moisturizing capability can serve as good ingredients for facial mask processing.

Insights on the Inhibitory Power of Flavonoids on Tyrosinase Activity: A Survey from 2016 to 2021

Tyrosinase is a multifunctional copper-containing oxidase enzyme that initiates melanin synthesis in humans. Excessive accumulation of melanin pigments or the overexpression of tyrosinase may result in skin-related disorders such as aging spots, wrinkles, melasma, freckles, lentigo, ephelides, nevus, browning and melanoma. Nature expresses itself through the plants as a source of phytochemicals with diverse biological properties. Among these bioactive compounds, flavonoids represent a huge natural class with different categories such as flavones, flavonols, isoflavones, flavan-3-ols, flavanones and chalcones that display antioxidant and tyrosinase inhibitor activities with a diversity of mechanistic approaches. In this review, we explore the role of novel or known flavonoids isolated from different plant species and their participation as tyrosinase inhibitors reported in the last five years from 2016 to 2021. We also discuss the mechanistic approaches through the different studies carried out on these compounds, including in vitro, in vivo and in silico computational research. Information was obtained from Google Scholar, PubMed, and Science Direct. We hope that the updated comprehensive data presented in this review will help researchers to develop new safe, efficacious, and effective drug or skin care products for the prevention of and/or protection against skin-aging disorders.

Antioxidant and tyrosinase inhibitory activities of traditional fermented Rosa from Dali Bai communities, Northwest Yunnan, China

Traditional fermented Rosa (TFR) is a typical food and medical product among the Dali Bai people, and its popularity is growing. A few studies have looked into TFR's medicinal advantages, linked germplasm resources, traditional processing procedures, and functional food qualities. Our goal was to look into Rosa's traditional processing, examine the dominant strains in TFR, and prove how these strains affected antioxidant and tyrosinase inhibitory activities. We used a snowball selection strategy to pick 371 informants for a semi-structured interview, supplemented with direct observations and sample collection. A microbial strain was isolated and identified from a TFR sample collected in the field. We synthesized TFR in the lab using the traditional way. Both of 2, 2-diphenyl-1 picrylhydrazyl (DPPH) free radical scavenging and tyrosinase inhibitory properties of the fermented solution of Rosa 'Dianhong' have been tested in this study. Altogether 15 species belonging to the genus Rosa, which are utilized in herbal medicine and fermented foods. Rosa 'Dianhong' was the Bai community's principal species with considerable cultural value and consumption. Raw Rosa petals included 15 major flavonoids and phenols, which were identified as TFR's active components. TFR-1 was discovered to be the dominating microbial strain in TFR, increasing total phenolic and flavonoid content in the fermented solution of Rosa 'Dianhong' by 0.45 mg GAE/ml and 0.60 mg RE/ml, respectively, after 30 days. TFR-1 also exhibited promising activity in terms of DPPH free radical scavenging and tyrosinase inhibition. TFR showed potent antioxidant and free-radical scavenger properties and is beneficial in skincare and nutrition, according to the findings. TFR's medicinal and edible properties suggest that it could be used as a cosmetic or nutraceutical product.

Green synthesis of magnesium nanoparticles mediated from Rosa floribunda charisma extract and its antioxidant, antiaging and antibiofilm activities

Flower based nanoparticles has gained a special attention as a new sustainable eco-friendly avenue. Rosa floribunda charisma belongs to modern roses with bright yellow, red flowers with marvellous rose scent. Different methods were used for the extraction of its floral scent such as hexane, microwave, and solid-phase micro-extraction. The latter was the most efficient method for the extraction of phenyl ethyl alcohol, the unique scent of roses. In the current study, magnesium nanoparticles (RcNps) have been synthesized using Rosa floribunda charisma petals that have privileges beyond chemical and physical routs. RcNps formation was confirmed using UV-Visible (UV-Vis) Spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), High Resolution-Transmission Electron Microscope (HR-TEM), Field Emission-Scanning Electron Microscope (FE-SEM), Energy dispersive X-ray (EDX), X-ray Diffractometer (XRD), and X-ray photoelectron spectroscopy (XPS). HR-TEM images detected the polyhedral shape of RcNps with a diverse size ranged within 35.25-55.14 nm. The resulting RcNps exhibited a high radical scavenging activity illustrated by inhibition of superoxide, nitric oxide, hydroxyl radical and xanthine oxidase by by IC50 values 26.2, 52.9, 31.9 and 15.9 µg/ml respectively as compared to ascorbic acid. Furthermore, RcNps at concentration of 100 µg/ml significantly reduced xanthine oxidase activity (15.9 ± 0.61 µg/ml) compared with ascorbic acid (12.80 ± 0.32 µg/ml) with p < 0.05. Moreover, RcNps showed an excellent antiaging activity demonstrated by inhibition of collagenase, elastase, hyaluronidase and tyrosinase enzymes in a dose-dependent manner with IC50 values of 58.7 ± 1.66 µg/ml, 82.5 ± 2.93 µg/ml, 191.4 ± 5.68 µg/ml and 158.6 ± 5.20 µg/ml as compared to EGCG respectively. RcNps also, exhibited a promising antibacterial activity against three skin pathogens delineate a significant threat to a public health, as Staphylococcus epidermidis, Streptococcus pyogenes, and Pseudomonas aeruginosa with MIC of 15.63, 7.81, 31.25 µg/ml as compared to ciprofloxacin (7.81, 3.9 and 15.63 µg/ml). Moreover, RcNps suppressed the formation of biofilms with minimum biofilm inhibitory concentrations 1.95, 1.95, 7.81 µg/ml against the fore mentioned strains, respectively. Overall, our findings indicate that Rosa floribunda nanoparticles could be used as a leading natural source in skin care cosmetic industry.

Effect of gamma irradiation on growth, proline content, bioactive compound changes, and biological activity of 5 popular Thai rice cultivars

Gamma irradiation is the technique used to induce plant mutation and it has affected both the physiological and biochemical compounds of the plant. Some new rice lines are also created through the gamma-irradiation technique. We investigated the effect of gamma irradiation on plant growth, volatile compounds, and the biological activity of gamma-irradiated rice extract compared to non-gamma-irradiated rice extract. The results reveal that the gamma-irradiated rice growth was related to the proline content, as the low gamma dose induced rice growth and proline accumulation in gamma-irradiated rice. We induced the bioactive compounds, including the flavonoid content and phenolic content of gamma-irradiated rice, through the low gamma irradiation dose at 60-100 Gy. Interestingly, bioactive compounds were stimulated by a gamma dose similar to that of the biological activity (antioxidant activity and enzyme inhibition) of gamma-irradiated rice. The results suggest that gamma-irradiated rice extract's biological activity was closely related to the flavonoid and phenolic content of rice. We also identified the variety of volatile compounds in gamma-irradiated rice and they were also reported for the biological activity. Our results can generate a new rice line that exhibits high plant growth and is rich with bioactive compounds such as flavonoid and phenolic compounds which are related to the improvement of human health.

Anti-Inflammatory Effects of Compounds from Cudrania tricuspidata in HaCaT Human Keratinocytes

The root bark of Cudrania tricuspidata has been reported to have anti-sclerotic, anti-inflammatory, antioxidant, neuroprotective, hepatoprotective, and cytotoxic activities. In the present study, the effect of 16 compounds from C. tricuspidata on tumor necrosis factor-α+interferon-γ-treated HaCaT cells were investigated. Among these 16 compounds, 11 decreased IL-6 production and 15 decreased IL-8 production. The six most effective compounds, namely, steppogenin (2), cudraflavone C (6), macluraxanthone B (12), 1,6,7-trihydroxy-2-(1,1-dimethyl-2-propenyl)-3- methoxyxanthone (13), cudraflavanone B (4), and cudratricusxanthone L (14), were selected for further experiments. These six compounds decreased the expression levels of chemokines, such as regulated on activation, normal T cell expressed and secreted (RANTES) and thymus and activation-regulated chemokine (TARC), and downregulated the protein expression levels of intercellular adhesion molecule-1. Compounds 2, 6, 12, 4, and 14 inhibited nuclear factor-kappa B p65 translocation to the nucleus; however, compound 13 showed no significant effects. In addition, extracellular signal regulatory kinase-1/2 phosphorylation was only inhibited by compound 14, whereas p38 phosphorylation was inhibited by compounds 13 and 4. Taken together, the compounds from C. tricuspidata showed potential to be further developed as therapeutic agents to suppress inflammation in skin cells.

Tyrosinase Inhibitors from the Stems of Streblus Ilicifolius

Two new stilbene derivatives, named strebluses C and D, were isolated from the EtOAc-soluble fraction of the stems of Streblus ilicifolius (Moraceae). Its absolute configuration was elucidated based on NMR spectroscopic data interpretation and optical rotation calculation. Streblus C possesses strong tyrosinase inhibitory activity with an IC₅₀ value of 0.01 μM. Docking studies of 1 and 2 with oxy-tyrosinase were carried out to analyze their interactions. The analysis of the docked poses confirmed that 1 showed better binding affinity for oxy-tyrosinase than that of 2.

Photoprotective and Inhibitory Activity of Tyrosinase in Extract and Fractions of Terminalia catappa L

BACKGROUND: Chronic exposure to ultraviolet (UV) radiation causes various skin damages. One of the most significant risks to skin occurrence is cancer and photoaging. Recent strategies for photoprotection have included incorporating natural sunscreens and antityrosinase. AIM: This study aimed to determine the sun protection factor (SPF) and inhibitory activity of tyrosinase of the extract and fractions of leaves of Terminalia catappa Linn. METHOD: The dried leaves were macerated with 96% ethanol and fractionated using n-hexane, ethyl acetate, and water. The extract and fractions were screened for their phytochemical profile, and tyrosinase inhibitory activity was evaluated and expressed as IC50. The photoprotective activity of extract and fractions were measured by a UV spectrophotometric. RESULTS: Among the tested samples, the ethyl acetate fraction showed ultraprotection on erythema transmission rate (%TE), sunblock on pigmentation transmission (%TP), and minimum protection on SPF. Ethyl acetate fraction showed the highest activity to inhibit tyrosinase (IC50 was 50.54±2.37 μg/mL). The phytochemical analysis of ethyl acetate fraction revealed the presence of phenolic and flavonoid compounds. CONCLUSION: This study’s findings revealed a higher tyrosinase inhibitor and sun protection capacity of ethyl acetate fraction of leaves of T. catappa and suitable to develop as a cosmetic agent.

Two new derivatives of 8-prenyl-5,7-dihydroxycoumarin from the stems of Streblus ilicifolius (S.Vidal) Corn

From the EtOAc-soluble extract of the stems of Streblus ilicifolius (Moraceae), two new secondary metabolites named strebluses A (1) and B (2) were isolated. Their chemical structures have been concluded based on the chemical derivatisation and the spectroscopic interpretation. All compounds have been tested for their tyrosinase inhibitory activity. They showed weaker inhibitory activity than that of kojic acid (IC₅₀, 44.6 µM).

Promotion effects of flavonoids on browning induced by enzymatic oxidation of tyrosinase: structure-activity relationship

Tyrosinase, widely distributed in nature, is a copper-containing polyphenol oxidase involved in the formation of melanin. Flavonoids are most often considered as tyrosinase inhibitors but have also been confirmed to be tyrosinase substrates. Four structure-related flavonoids including flavones (apigenin and luteolin) and flavonols (kaempferol and quercetin) are found to promote not inhibit browning induced by tyrosinase catalyzed oxidation both in model systems and in mushrooms under aerobic conditions. A comparison with enzymatic oxidation and autooxidation of flavonoids alone has helped to clarify why flavonoids function as a substrate rather than an inhibitor. Flavonoids almost do not affect the kinetics of melanin formation from enzymatic oxidation of l-dopa in excess. In addition, a new brown complex formed during the reaction of flavonoid quinone and dopaquinone is suggested to enhance the browning effects by competing with isomerization and autooxidation. Structure-activity relationships of the four flavonoids in melanin formation leading to browning induced by autooxidation and enzymatic oxidation confirm the enzymatic nature of the browning.

Decumbic anhydride from the stem barks of Swintonia floribunda (Anacardiaceae)

From an EtOAc-soluble fraction of the stem barks of Swintonia floribunda (Anacardiaceae), decumbic anhydride (1) and four known compounds 2-5 were isolated. Their chemical structures were elucidated based on the spectroscopic data interpretation. The GIAO-DFT calculation of ¹³C NMR chemical shifts was carried out to clarify the structure of 1. The absolute configuration of 1 was assigned based on the Cotton effects in its ECD spectrum. Compound 1 showed potent tyrosinase inhibitory activity with an IC₅₀ value of 52.2 μM.

A new lignan from the stems of Buchanania lucida Blume (Anacardiaceae)

From the EtOAc-soluble extract of the stems of Buchanania lucida, one new lignan, (+)-(8S,8'S)-5'-methoxy-4,4'-di-O-methylsecoisolariciresinol (1), together with five known compounds (2-6) were isolated. Their structures were elucidated on the basis of NMR spectroscopic interpretation. The absolute configuration of 1 was determined based on the Cotton effects in the ECD spectrum. In the tyrosinase inhibitory activity test, p-hydroxybenzoic acid (6) showed the strong effect, with an IC₅₀ value of 9.35 µM.

Neuroprotective and Anti-Inflammatory Effects of Kuwanon C from Cudrania tricuspidata Are Mediated by Heme Oxygenase-1 in HT22 Hippocampal Cells, RAW264.7 Macrophage, and BV2 Microglia

Heme oxygenase (HO)-1 is a detoxifying phase II enzyme that plays a role in both inflammatory and oxidative stress responses. Curdrania tricuspidata is widespread throughout East Asia and is used as a therapeutic agent in traditional medicine. We investigated whether treatment with sixteen flavonoid or xanthone compounds from C. tricuspidata could induce HO-1 expression in HT22 hippocampal cells, RAW264.7 macrophage, and BV2 microglia. In these compounds, kuwanon C showed the most remarkable HO-1 expression effects. In addition, treatment with kuwanon C reduced cytoplasmic nuclear erythroid 2-related factor (Nrf2) expression and increased Nrf2 expression in the nucleus. Significant inhibition of glutamate-induced oxidative injury and induction of reactive oxygen species (ROS) occurred when HT22 hippocampal cells were pretreated with kuwanon C. The levels of inflammatory mediator and cytokine, which increased following lipopolysaccharide (LPS) stimulation, were suppressed in RAW264.7 macrophage and BV2 microglia after kuwanon C pretreatment. Kuwanon C also attenuated p65 DNA binding and translocation into the nucleus in LPS-induced RAW264.7 and BV2 cells. The anti-inflammatory, anti-neuroinflammatory, and neuroprotective effects of kuwanon C were reversed when co-treatment with HO-1 inhibitor of tin protoporphyrin-IX (SnPP). These results suggest that the neuroprotective and anti-inflammatory effects of kuwanon C are regulated by HO-1 expression.

LC-ESI-QTOF-MS for the Profiling of the Metabolites and in Vitro Enzymes Inhibition Activity of Bryophyllum pinnatum and Oxalis corniculata Collected from Ramechhap District of Nepal

The objective of this study was to profile the chemical components and biological activity analysis of crude extract of Bryophyllum pinnatum and Oxalis corniculata. Results revealed that the analyzed plant materials encompass the high amount of total phenolic and flavonoids content and have significant antioxidant activities. Furthermore, methanol extracts are the potential source of α-amylase, α-glucosidase, lipase, tyrosinase and elastase inhibitors. High resolution mass spectrometry revealed the presence of diverse metabolites such as quercetin 3-O-α-L-rhamnopyranoside, myricetin 3-rhamnoside, bersaldegenin 1,3,5-orthoacetate, bryophyllin C, syringic acid, caffeic acid, p-coumaric acid, and quercetin in B. pinnatum and isoorientin, swertisin, apigenin 7,4'-diglucoside, vitexin, 4-hydroxybenzoic acid, vanillic acid, ethyl gallate, 3,3',4'-trihydroxy-5,7-dimethoxyflavone, and diosmetin-7-O-β-D-glucopyranoside in O. corniculata. Our finding suggested that these two plant species have high medicinal importance and are potential source of inhibitors for modern pharmaceuticals, nutraceuticals and cosmetics industries.

Natural and Bioinspired Phenolic Compounds as Tyrosinase Inhibitors for the Treatment of Skin Hyperpigmentation: Recent Advances

One of the most common approaches for control of skin pigmentation involves the inhibition of tyrosinase, a copper-containing enzyme which catalyzes the key steps of melanogenesis. This review focuses on the tyrosinase inhibition properties of a series of natural and synthetic, bioinspired phenolic compounds that have appeared in the literature in the last five years. Both mushroom and human tyrosinase inhibitors have been considered. Among the first class, flavonoids, in particular chalcones, occupy a prominent role as natural inhibitors, followed by hydroxystilbenes (mainly resveratrol derivatives). A series of more complex phenolic compounds from a variety of sources, first of all belonging to the Moraceae family, have also been described as potent tyrosinase inhibitors. As to the synthetic compounds, hydroxycinnamic acids and chalcones again appear as the most exploited scaffolds. Several inhibition mechanisms have been reported for the described inhibitors, pointing to copper chelating and/or hydrophobic moieties as key structural requirements to achieve good inhibition properties. Emerging trends in the search for novel skin depigmenting agents, including the development of assays that could distinguish between inhibitors and potentially toxic substrates of the enzyme as well as of formulations aimed at improving the bioavailability and hence the effectiveness of well-known inhibitors, have also been addressed.

Dynamic changes of secondary metabolites and tyrosinase activity of Malus pumila flowers

The dynamic changes of secondary metabolites and tyrosinase activity of Malus pumila flowers were investigated during blooming for full use of M. pumila flowers. Phlorizin, astragalin and afzelin were selected as the indicators to determine the optimum extraction conditions of M. pumila flowers by HPLC analysis and three-factor and three-level orthogonal design experiments. When the smashing mesh number was 40 mesh, the ultrasonic time was 30 min, the solid–liquid ratio was 1:120, and the centrifugal speed was 10,000 r/min, the total content of the three compounds was the highest. The total content of phlorizin, astragalin and afzelin increased firstly and then decreased, and the highest was on the third day (176.74 mg/g). At the same time, the tyrosinase activity of M. pumila flowers showed that it had an activation effect on tyrosinase during early blooming period, however it exhibited inhibitory effect during late blooming period.

Natural Tyrosinase Inhibitors: Role of Herbals in the Treatment of Hyperpigmentary Disorders

Cutaneous pigmentation plays critical role in determining the color of skin along with photo protection of skin from dreadful effects of ultraviolet radiations. Conversely, abnormal accumulation of melanin is responsible for hyper pigmentary disorders such as melasma, senile lentigines and freckles. Because of the visible nature of dermatologic diseases, they have a considerable psychosomatic effect on affected patients. Tyrosinase inhibitors are molecules that interrelate in some way with the enzyme to prevent it from working in the normal manner. Past many decades witnessed the quest for the development of natural tyrosinase inhibitors due to imperative role played by tyrosinase in the process of melanogenesis and fungi or fruit enzymatic browning. Mechanism of pigmentation is characterized by the intact process of the synthesis of specialized black pigment within melanosomes. Melanin is synthesized by a cascade of enzymatic and chemical reactions. For this reason, melanin production is mainly controlled by the expression and activation of tyrosinase. In the current article, we discussed tyrosinase inhibitors from the natural sources, which can be an essential constituent of cosmetics products and depigmenting agents for the treatment of hyperpigmentory disorders.

A new dimeric alkylresorcinol from the stem barks of Swintonia floribunda (Anacardiaceae)

From an EtOAc-soluble fraction of the stem barks of Swintonia floribunda (Anacardiaceae), one new dimeric alkylresorcinol named integracin E (1), together with 4 known compounds (2-5) were isolated. Their chemical structures were elucidated based on the spectroscopic data interpretation. The absolute configuration of 1 was determined by the specific rotation analysis of its acid-catalyzed hydrolysis product. Compound 1 showed potent tyrosinase inhibitory activity with an IC₅₀ value of 48.2 μM.

Artocarmins G-M, Prenylated 4-Chromenones from the Stems of Artocarpus rigida and Their Tyrosinase Inhibitory Activities

Phytochemical analysis of an EtOAc extract of the stems of Artocarpus rigida led to the identification of seven new prenylated 4-chromenones, artocarmins G-M (1-7), and nine known compounds (8-17). Their structures were identified based on physical data analysis. In the tyrosinase inhibitory activity test, norartocarpetin (8) displayed the strongest effect, with an IC₅₀ value of 0.023 μM.

Steppogenin Isolated from Cudrania tricuspidata Shows Antineuroinflammatory Effects via NF-κB and MAPK Pathways in LPS-Stimulated BV2 and Primary Rat Microglial Cells

Excessive microglial stimulation has been recognized in several neurodegenerative diseases, including Parkinson’s disease (PD), Alzheimer’s disease (AD), amyotropic lateral sclerosis (ALS), HIV-associated dementia (HAD), multiple sclerosis (MS), and stroke. When microglia are stimulated, they produce proinflammatory mediators and cytokines, including nitric oxide (NO) derived from inducible NO synthase (iNOS), prostaglandin E2 (PGE₂) derived from cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-12 (IL-12), and interleukin-6 (IL-6). These inflammatory reactions are related to the nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways. Therefore, the modulation of NF-κB and MAPK is vital to prevent microglial activation and confer resistance against neuronal injury. In this study, steppogenin (1) isolated from Cudrania tricuspidata suppressed the neuroinflammatory responses to lipopolysaccharide (LPS). Steppogenin (1) inhibited the production of proinflammatory mediators and cytokines in LPS-challenged BV2 and rat primary microglial cells. Moreover, western blot analysis and immunofluorescence revealed that the nuclear translocation of NF-κB was inhibited in LPS-induced BV2 and rat primary microglial cells. The LPS-stimulated activation of BV2 and rat primary microglial cells was inhibited by steppogenin (1) through the suppression of c-Jun NH2-terminal kinase (JNK) and p38 MAPK signaling. These results suggested that steppogenin (1) exerted antineuroinflammatory effects against acute neuroinflammation in BV2 and rat primary microglial cells by suppressing the activation of NF-κB and MAPK signaling and the production of proinflammatory mediators and cytokines.