Quercetin as a tyrosinase inhibitor: Inhibitory activity, conformational change and mechanism

The mechanism of resveratrol stabilization and degradation by synergistic interactions between constituent proteins of whey protein

Whey protein isolate (WPI) is mainly composed of β-lactoglobulin (β-LG), α-lactalbumin (α-LA) and bovine serum albumin (BSA). The aim of this study was to compare and analyze the influence of WPI and its three main constituent proteins, as well as proportionally reconstituted WPI (R-WPI) on resveratrol. It was found that the storage stability of resveratrol was protected by WPI, not affected by R-WPI, but reduced by individual whey proteins at 45°C for 30 days. The rank of accelerated degradation of resveratrol by individual whey proteins was BSA > α-LA > β-LG. The antioxidant activity, localization of resveratrol and oxidation of carrier proteins were determined by ABTS, H2O2 assay, synchronous fluorescence, carbonyl and circular dichroism. The non-covalent interactions and disulfide bonds between constituent proteins improved the antioxidant activity of the R-WPI-resveratrol complex, the oxidation stability of the carrier and the solvent shielding effect on resveratrol, which synergistically inhibited the degradation of resveratrol in R-WPI system. The results gave insight into elucidating the interaction mechanism of resveratrol with protein carriers.

Natural products and derivatives for breast cancer treatment: From drug discovery to molecular mechanism

BACKGROUND

Breast cancer stands as the most common malignancy among women globally and a leading cause of cancer-related mortality. Conventional treatments, such as surgery, hormone therapy, radiotherapy, chemotherapy, and small-molecule targeted therapy, often fall short of addressing the complexity and heterogeneity of certain breast cancer subtypes, leading to drug resistance and metastatic progression. Thus, the search for novel therapeutic targets and agents is imperative. Given their low toxicity and abundant variety, natural products and their derivatives are increasingly considered valuable sources for small-molecule anticancer drugs.

PURPOSE

This review aims to elucidate the pharmacological impacts and underlying mechanisms of active compounds found in select natural products and their derivatives, primarily focusing on breast cancer treatment. It intends to underscore the potential of these substances in combating breast cancer and guide future research directions for the development of natural product-based therapeutics.

METHODS

We conducted comprehensive searches in electronic databases such as PubMed, Web of Science, and Scopus until October 2023, using keywords such as 'breast cancer', 'natural products', 'derivatives', 'mechanism', 'signaling pathways', and various keyword combinations.

RESULTS

The review presents a spectrum of phytochemicals, including but not limited to flavonoids, polyphenols, and alkaloids, and examines their actions in various animal and cellular models of breast cancer. The anticancer effects of these natural products and derivatives are manifested through diverse mechanisms, including induction of cell death via apoptosis and autophagy, and suppression of tumor angiogenesis.

CONCLUSION

An increasing array of natural products and their derivatives are proving effective against breast cancer. Future therapeutic strategies can benefit from strategic enhancement of the anticancer properties of natural compounds, optimization for targeted action, improved bioavailability, and minimized side effects. The forthcoming research on natural products should prioritize these facets to maximize their therapeutic potential.

Elucidating the substance basis and pharmacological mechanism of Fufang Qiling granules in modulating xanthine oxidase for intervention in hyperuricemia

ETHNOPHARMACOLOGICAL RELEVANCE

Fufang Qiling granules (FQG), derived from the traditional Qiling Decoction with a longstanding clinical history, is utilized for the treatment of hyperuricemia (HUA). FQG is formulated with a combination of seven Chinese herbs based on the principles of traditional Chinese medicine (TCM) theories. Clinical evidence indicates that FQG exhibits favorable therapeutic effects in reducing uric acid (UA) levels and attenuating renal damage.

AIM OF THIS STUDY

To elucidate the potential active components and pharmacological mechanism of FQG in the treatment of HUA, and to provide an experimental basis for the development of efficient and low-toxicity TCM for HUA treatment.

MATERIALS AND METHODS

A HUA rat model induced by potassium oxonate and adenine was established to initially evaluate the hypouricemic effects of FQG. Chemical analyses were conducted using an ultra-high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). Network pharmacology was used to investigate the active components and mechanism of FQG in the treatment of HUA. Potential Xanthine oxidase (XOD) inhibitors were screened from FQG based on ultrafiltration liquid chromatography and mass spectrometry (UF-LC-MS). Molecular docking, surface plasmon resonance (SPR) and circular dichroism (CD) spectroscopy were applied to validate the interactions between the active components and XOD.

RESULTS

In comparison to the model group, treatment with FQG significantly decreased serum UA, serum creatinine (CREA), serum blood urea nitrogen (BUN), and liver XOD activity. Additionally, the FQG administration notably ameliorated HUA-induced renal injury in rats. Through the pharmacodynamics of the HUA rat models and network pharmacology, it was found that XOD was a key pathway enzyme in UA metabolism. 18 XOD inhibitors were screened from FQG by UF-LC-MS, and 11 compounds with strong affinity were verified by SPR, molecular docking and CD spectroscopy.

CONCLUSION

In summary, flavonoids, organic acids and saponins may be the active components in FQG that alleviate HUA. The primary mechanism of FQG involves inhibiting XOD enzyme activity in the plasma to reduce UA production, alleviating renal tubular epithelial cell necrosis, tubulointerstitial injury, fibrosis, and urate deposition, ultimately exerting a therapeutic effect on HUA.

Metabolomics and network pharmacology reveal the mechanism of Castanopsis honey against Streptococcus pyogenes

Streptococcus pyogenes (GAS) is one of the most virulent and infectious bacteria, severely threatening health and lives of people worldwide. Honey has been proven to have effective capability against GAS, but the underlying metabolites and mechanisms are still unclear. In this study, the Castanopsis honey (CH) showed significant antibacterial ability compared to other seven kinds of honey and artificial honey. Furthermore, the antibacterial metabolites and their targets in CH were screened by combined method of metabolomics, network pharmacology, and molecular docking. The results suggested that the activities of two antioxidant enzymes, glutathione peroxidase and tyrosyl tRNA synthetase identified as the primary targets, were significantly inhibited by CH, which significantly increased the level of oxidative stress in GAS. The results revealed a possibly novel mechanism regulating the oxidative stress and inhibits the growth in bacteria, providing strong experimental evidence to support the further development of CH as a novel antibacterial agent.

Discovery of novel 1,2,4-triazole tethered β-hydroxy sulfides as bacterial tyrosinase inhibitors: synthesis and biophysical evaluation through in vitro and in silico approaches

In this study, a series of 1,2,4-triazole-tethered β-hydroxy sulfide scaffolds 11a-h was synthesized in good to remarkable yields (69-90%) through the thiolysis of oxiranes by the thiols in aqueous basic catalytic conditions. The synthesized 1,2,4-triazole-tethered β-hydroxy sulfides were screened against bacterial tyrosinase enzyme, and Gram-positive and Gram-negative bacterial cultures i.e., (S. aureus) Staphylococcus aureus & (E. coli) Escherichia coli. Among the synthesized derivatives, the molecules 11a (IC50 = 7.67 ± 1.00 μM), 11c (IC50 = 4.52 ± 0.09 μM), 11d (IC50 = 6.60 ± 1.25 μM), and 11f (IC50 = 5.93 ± 0.50 μM) displayed the better tyrosinase inhibitory activity in comparison to reference drugs ascorbic acid (IC50 = 11.5 ± 1.00 μM) and kojic acid (IC50 = 30.34 ± 0.75 μM). The molecule benzofuran-triazol-propan-2-ol 11c proved to be the most potent bacterial tyrosinase inhibitory agent with a minimum IC50 of 4.52 ± 0.09 μM, as compared to other synthesized counterparts and both standards (kojic acid and ascorbic acid). The compound diphenyl-triazol-propan-2-ol 11a and benzofuran-triazole-propan-2-ol 11c showed comparable anti-bacterial chemotherapeutic efficacy with minimum inhibitory concentrations (MIC = 2.0 ± 2.25 mg mL-1 and 2.5 ± 0.00 mg mL-1, respectively) against S. aureus bacterial strain in comparison with standard antibiotic penicillin (MIC = 2.2 ± 1.15 mg mL-1). Furthermore, among the synthesized derivatives, only compound 11c demonstrated better anti-bacterial activity (MIC = 10 ± 0.40 mg mL-1) against E. coli, which was slightly less than the standard antibiotic i.e., penicillin (MIC = 2.4 ± 1.00 mg mL-1). The compound 11c demonstrated a better binding score (-7.08 kcal mol-1) than ascorbic acid (-5.59 kcal mol-1) and kojic acid (-5.78 kcal mol-1). Molecular docking studies also validate the in vitro anti-tyrosinase assay results; therefore, the molecule 11c can be the lead bacterial tyrosinase inhibitor as well as the antibacterial agent against both types of bacterial strains after suitable structural modifications.

Unraveling the binding interactions between two Pt(II) complexes of aliphatic glycine derivatives with human serum albumin: A comprehensive computational and multi-spectral investigation

This article delves into the interaction between HSA protein and synthesized platinum complexes, with formula: [Pt(Propyl-NH2)2(Propylglycine)]NO3 and [Pt(Tertpentyl-NH2)2(Tertpentylglycine)]NO3, through a range of methods, including spectroscopic (UV-visible, fluorescence, synchronous fluorescence and CD) analysis and computational modeling (molecular docking and MD simulation). The binding constants, the number of binding sites, and thermodynamic parameters were obtained at 25 to 37 °C. The study found that both complexes could bind with HSA (moderate affinity for Tertpentyl and strong affinity for Propyl derivatives) and occupied one binding site in HSA (validated with, Stern-Volmer, Job-plots, and molecular docking investigations) located in subdomain IIA. The binding mechanisms of both mentioned Pt(II) agents were different, with the Propyl derivative predominantly using van der Waals forces and hydrogen bond interactions with a static quenching mechanism and the Tertpentyl derivative mainly utilizing hydrophobic force with a dynamic quenching mechanism. However, the two ligands affected protein differently; the Tertpentyl complex did not significantly alter the protein structure upon binding, as evidenced by synchronous fluorescence spectroscopy (SFS), CD spectroscopy, and MD analysis. The outcome helps in understanding the binding mechanisms and structural modifications induced by the ligands, which could aid in the innovation of more effective and stable Pt(II)-based drugs.

Pulp or Peel? Comparative Analysis of the Phytochemical Content and Selected Cosmetic-Related Properties of Annona cherimola L., Diospyros kaki Thumb., Cydonia oblonga Mill. and Fortunella margarita Swingle Pulp and Peel Extracts

Fruit peels might be a valuable source of active ingredients for cosmetics, leading to more sustainable usage of plant by-products. The aim of the study was to evaluate the phytochemical content and selected biological properties of hydroglycolic extracts from peels and pulps of Annona cherimola, Diospyros kaki, Cydonia oblonga, and Fortunella margarita as potential cosmetic ingredients. Peel and pulp extracts were compared for their antiradical activity (using DPPH and ABTS radical scavenging assays), skin-lightening potential (tyrosinase inhibitory assay), sun protection factor (SPF), and cytotoxicity toward human fibroblast, keratinocyte, and melanoma cell lines. The total content of polyphenols and/or flavonoids was significantly higher in peel than in pulp extracts, and the composition of particular active compounds was also markedly different. The HPLC-MS fingerprinting revealed the presence of catechin, epicatechin and rutoside in the peel of D. kaki, whereas kaempferol glucoside and procyanidin A were present only in the pulp. In A. cherimola, catechin, epicatechin and rutoside were identified only in the peel of the fruit, whereas procyanidins were traced only in the pulp extracts. Quercetin and luteolinidin were found to be characteristic compounds of F. margarita peel extract. Naringenin and hesperidin were found only in the pulp of F. margarita. The most significant compositional variety between the peel and pulp extracts was observed for C. oblonga: Peel extracts contained a higher number of active components (e.g., vicenin-2, kaempferol rutinoside, or kaempferol galactoside) than pulp extract. The radical scavenging potential of peel extracts was higher than of the pulp extracts. D. kaki and F. margarita peel and pulp extracts inhibited mushroom and murine tyrosinases at comparable levels. The C. oblonga pulp extract was a more potent mushroom tyrosinase inhibitor than the peel extract. Peel extract of A. cherimola inhibited mushroom tyrosinase but activated the murine enzyme. F. margarita pulp and peel extracts showed the highest in vitro SPF. A. cherimola, D. kaki, and F. margarita extracts were not cytotoxic for fibroblasts and keratinocytes up to a concentration of 2% (v/v) and the peel extracts were cytotoxic for A375 melanoma cells. To summarize, peel extracts from all analyzed fruit showed comparable or better cosmetic-related properties than pulp extracts and might be considered multifunctional active ingredients of skin lightening, anti-aging, and protective cosmetics.

Evaluation of Bioactive Effects of Five Plant Extracts with Different Phenolic Compositions against Different Therapeutic Targets

Plant extracts rich in phenolic compounds have been reported to exert different bioactive properties. Despite the fact that there are plant extracts with completely different phenolic compositions, many of them have been reported to have similar beneficial properties. Thus, the structure-bioactivity relationship mechanisms are not yet known in detail for specific classes of phenolic compounds. In this context, this work aims to demonstrate the relationship of extracts with different phenolic compositions versus different bioactive targets. For this purpose, five plant matrices (Theobroma cacao, Hibiscus sabdariffa, Silybum marianum, Lippia citriodora, and Olea europaea) were selected to cover different phenolic compositions, which were confirmed by the phytochemical characterization analysis performed by HPLC-ESI-qTOF-MS. The bioactive targets evaluated were the antioxidant potential, the free radical scavenging potential, and the inhibitory capacity of different enzymes involved in inflammatory processes, skin aging, and neuroprotection. The results showed that despite the different phenolic compositions of the five matrices, they all showed a bioactive positive effect in most of the evaluated assays. In particular, matrices with very different phenolic contents, such as T. cacao and S. marianum, exerted a similar inhibitory power in enzymes involved in inflammatory processes and skin aging. It should also be noted that H. sabdariffa and T. cacao extracts had a low phenolic content but nevertheless stood out for their bioactive antioxidant and anti-radical capacity. Hence, this research highlights the shared bioactive properties among phenolic compounds found in diverse matrices. The abundance of different phenolic compound families highlights their elevated bioactivity against diverse biological targets.

Preparation, Characterization, and Antioxidant Activities of Extracts from Amygdalus persica L. Flowers

A novel water-soluble Amygdalus persica L. flowers polysaccharide (APL) was successfully isolated and purified from Amygdalus persica L. flowers by hot water extraction. Its chemical components and structure were analyzed by IR, GC-MS, and HPLC. APL consisted of rhamnose, arabinose, mannose and glucose in a molar ratio of 0.17:0.034:1.0:0.17 with an average molecular weight of approximately 208.53 kDa and 15.19 kDa. The antioxidant activity of APL was evaluated through radical scavenging assays using 1,1-diphenyl-2-picrylhydrazyl (DPPH), 3-ethylbenzthiazoline-6-sulfonic acid (ABTS), Hydroxyl radical scavenging, Superoxide radical scavenging, and the reducing power activity was also determined in vitro. Besides, in vivo antioxidant experiment, zebrafish (Danio rerio) embryos were treated with different concentrations of APL and then exposed to LPS to induce oxidative stress. Treatment with APL at 50 or 100 µg/mL significantly reduced LPS-induced oxidative stress in the zebrafish, demonstrating the strong antioxidant activity of APL. Moreover, the effect of APL on zebrafish depigmentation was tested by analyzing the tyrosinase activity and melanin content of zebrafish embryos. APL showed a potential reduction in the total melanin content and tyrosinase activity after treatment. This work provided important information for developing a potential natural antioxidant in the field of cosmetics and food.

Phytochemical characterization and biological activities of Inula viscosa L. Aiton: a promising plant from Turkey

The methanol extract of Inula viscosa (IVM) was investigated for its antioxidant potential using the DPPH and ABTS radical scavenging as well as iron chelating assays (ICA). The total phenol (TPC) and flavonoid contents (TFC) of IVM were determined using the Folin-Ciocalteu and aluminum trichloride methods, respectively. Antimicrobial activity of different concentrations of I. viscosa methanol extract was investigated by disc diffusion and broth microdilution method. The IVM extract was found to be containing TPC (236.78 ± 7.63 mg GAE/g) and TFC (94.36 ± 1.86 mg QE/g). Antioxidant activity IC50 values for the DPPH, ABTS and ICA assays were found to be 277.7 ± 3.68, 2.44 ± 0.02, and 222.1 ± 0.71 µg/mL, respectively. The MIC values of the IVM on the tested microorganisms ranged from 0.48 to 7.81 mg/mL. Furthermore, IVM extract was demonstrated 18.32 ± 1.37%, 23.06 ± 1.05%, 4.72 ± 0.13%, 15.13 ± 0.37% and 37.64 ± 4.02% inhibition against tyrosinase, α-amylase, α-glucosidase, AChE and BChE, respectively. In the results of LC-MS/MS analysis, acacetin, quercetin, chlorogenic acid and protocatechuic acid were determined as most dominant compounds. These findings suggested that this plant may be a natural resource for creating novel medicinal compounds.

Inhibition Effect of Okanin Toward Human Cytochrome P450 3A4 and 2D6 with Multi-spectroscopic Studies and Molecular Docking

Okanin, a major flavonoid of a popular herb tea, Coreopsis tinctoria Nutt., showed strong inhibition on CYP3A4 and CYP2D6. The strong interaction between okanin and CYPs were determined by enzyme kinetics, multispectral technique and molecular docking. The inhibition type of two enzymes, CYP3A4 and CYP2D6, by okanin are mixed and non-competitive inhibition type, respectively. The IC50 values and the binding constant of okanin to CYP3A4 can be deduced that the interaction was stronger than that of CYP2D6. The Conformations of CYP3A4 and CYP2D6 were changed by okanin. The evidence from fluorescence measurement along with molecular docking verified that these two CYPs were bound with okanin by hydrogen bonds and hydrophobic forces. Our investigation suggested that okanin may lead to interactions between herb and drug by inhibiting CYP3A4 and CYP2D6 activities, thus its consumption should be taken with caution.

Ferulic acid ameliorates hyperuricemia by regulating xanthine oxidase

Hyperuricemia is characterized by elevated uric acid (UA) level in the body. The xanthine oxidase (XO) inhibitory ability is an important way to evaluate the anti-hyperuricemia effect of natural products. Ferulic acid (FA) is a phenolic acid compound, and it is a free radical scavenger with many physiological functions. The aim of this study was to investigate the structure-activity relationship, potential mechanism and interaction of FA as XO's inhibitor. In the cell experiment, using 1.25 mM adenosine to incubate for 24 h under the optimal conditions (37 °C, pH = 7.2) can increase the UA production by 1.34 folds. PCR analysis showed that FA could reduce the mRNA expression level of XO. FA inhibited XO in a mixed mode (IC50 = 13.25 μM). The fluorescence quenching of XO by FA occurs through a static mechanism, with an inhibition constant of Ki = 9.527 × 10-5 mol L-1 and an apparent coefficient of α = 1.768. The enthalpy and entropy changes were found as -267.79 KJ mol-1 and - 860.85 KJ mol-1, indicating that both hydrogen binding and hydrophobic are involved in the interaction of this polyphenolic natural compound with XO. Thus, FA supplementation may be a potential therapeutic strategy to improve hyperuricemia by reducing UA production.

Investigation on the inhibition mechanism and binding behavior of paeonol to tyrosinase and its anti-browning property by multi-spectroscopic and molecular docking methods

Paeonol, as one effective tyrosinase inhibitor, had been used as food preservative and clinical medication for skin disorders. In this study, the inhibition mechanism and binding behavior of paeonol to tyrosinase and its anti-browning property were investigated using multi-spectroscopic and molecular docking methods. Activity assay and kinetic results confirmed paeonol as a reversible mixed-type tyrosinase inhibitor. Results of the mechanistic studies were clarified using fluorescence quenching, synchronous fluorescence, CD spectra and 3D fluorescence, and showed that the binding of paeonol to tyrosinase might change the chromophore microenvironment and conformation of tyrosinase to inhibit enzyme catalytic activity. Molecular docking results revealed the detailed binding between paeonol and tyrosinase. Moreover, paeonol could prevent the browning of fresh-cut apples, as well as inhibiting PPO and POD activities and increasing APX activity. All above findings established a reliable basis for the inhibitory mechanism of paeonol against tyrosinase and therefore contributed to its application in anti-browning.

Beyond traditional methods: Unveiling the skin whitening properties of Rhein-Embedded PROTACs

Proteolysis Targeting Chimeras (PROTAC) technology has emerged as a promising approach for targeted protein degradation. In this study, we focused on tyrosinase (TYR), a key enzyme involved in melanin synthesis and pigmentation. For this target, we designed and synthesized a series of PROTACs (D3-D9), employing Rhein as the target protein-ligand. Through some experimental tests, we made a significant discovery. Preliminary experimental results show that the most promising compound (D6) demonstrated the ability to degrade MITF and inhibit the expression and TYR in B16-F10 cells, effectively suppressing melanogenesis in zebrafish. Notably, at equivalent concentrations, the whitening effect of D6 surpassed that of its precursor Rhein and was even comparable to that of the well-established whitening agent, β-arbutin. Validating experiments further revealed that the action of D6 was reliant on the E3 ligand, indicating its capacity to degrade TYR and MITF through the ubiquitination pathway. Whether D6 acts directly on TYR or MITF needs to be further explored. These compelling results underscore the tremendous whitening potential of D6, suggesting its suitability as a valuable lead for whitening agents and its potential to expand the range of whitening cosmetic products.

Exploring the effect of a series of flavonoids on tyrosinase using integrated enzyme kinetics, multispectroscopic, and molecular modelling analyses

The control of food browning can be achieved by inhibiting tyrosinase (TY) activity, but current studies on the interaction of flavonoids as potent inhibitors with TY are inadequate. Herein, the effect of a library of flavonoids on TY was investigated using enzyme kinetics, multispectroscopic methods, and molecular modelling. Some flavonoids including 4, 8, 10, 17, 18, 28, 30, 33, and 34 exhibited potent TY inhibitory activity, with compound 10 demonstrating reversible inhibition in a mixed-competitive manner. Ultraviolet-visible spectral changes confirmed the formation of flavonoid-TY complexes. Fluorescence quenching analysis suggested effective intrinsic fluorescence quenching by flavonoids through static quenching with the ground-state complex formation. Synchronous fluorescence spectra showed the microenvironment change around the fluorophores induced by flavonoids. ANS-binding fluorescence assay indicated TY's surface hydrophobicity change by flavonoids and highlighted the change in secondary structure conformation, which was further confirmed by Fourier-transform infrared spectra. Molecular modelling results helped visualize the preferred binding conformation at the active site of TY, and demonstrated the important role of hydrophobic interaction and hydrogen bonding in stabilizing the flavonoid-TY complexes. These findings prove that diverse flavonoid structures distinctly impact their binding behavior on TY and contribute to understanding flavonoids' potential as TY inhibitors in controlling food browning.

Isolation and structure elucidation of antioxidant compounds from stem and root barks of Daphne giraldii

Two new compounds, aphegiractin A1/A2 (1a/1b), and seven known compounds were isolated by phytochemical work on EtOAc-soluble ingredients extracted from stem and root barks of Daphne giraldii. Their structures were established based on extensive spectroscopic methods, including HRESIMS, CD experiments, 1D and 2D NMR. All compounds were evaluated for their antioxidant activity to DPPH, ABTS radical scavenging activity and inhibitory activity on tyrosinase. Of these compounds, compound 3 exhibited significant antioxidant activities.

Assessment of in vitro anti-skin aging activities of Phyllanthus indofischeri Bennet extracts for dermatological and aesthetic applications

Giant Indian Gooseberry (GIG) or Phyllanthus indofischeri Bennet are commercially cultivated and commonly used herbs in Traditional medicine, especially in Thailand. The aim of this study was to assess the potential of the GIG extracts in anti-aging activities to be a dermatological application. The juice, meat residues, and seeds of GIG collected from Sra Kaeo Province, Thailand, were extracted by the Boiling method (B) and the Maceration process (M) by using 95% ethanol as a solvent. The GIG extracts gave the total phenolic, total flavonoid contents and quercetin contents, as well as exhibited anti-oxidative activities. The GIG-R-B extract inhibited tyrosinase activity and had the highest anti-melanogenesis activity on B16F10 cells at 31.63 ± 0.70%. The GIG-S-B, GIG-S-M, and GIG-R-M extracts demonstrated the highest collagen biosynthesis, which was comparable to vitamin C (p < 0.05), whereas the GIG-R-B extracts gave the highest stimulation of anti-aging genes (SIRT1 and FOXO1). All extracts at the concentration of 0.1 mg/mL showed no cytotoxicity on human skin fibroblasts. Therefore, the GIG-S-B extract was discovered to be a promising natural anti-aging agent for dermatological health and aesthetic applications that can be further developed in cosmetic, functional food and food supplement industries.

The Potential of Mangifera indica L. Peel Extract to Be Revalued in Cosmetic Applications

The constant growth of the cosmetic industry, together with the scientific evidence of the beneficial properties of phytochemicals, has generated great interest in the incorporation of bioactive extracts in cosmetic formulations. This study aims to evaluate the bioactive potential of a mango peel extract for its incorporation into cosmetic formulations. For this purpose, several assays were conducted: phytochemical characterization; total phenolic content (TPC) and antioxidant potential; free-radical scavenging capacity; and skin aging-related enzyme inhibition. In addition, the extract was incorporated into a gel formulation, and a preliminary stability study was conducted where the accelerated (temperature ramp, centrifugation, and heating/cooling cycles) and long-term (storage in light and dark for three months) stability of the mango peel formulations were evaluated. The characterization results showed the annotation of 71 compounds, gallotannins being the most representative group. In addition, the mango peel extract was shown to be effective against the •NO radical with an IC50 of 7.5 mg/L and against the hyaluronidase and xanthine oxidase enzymes with IC50 of 27 mg/L and 2 mg/L, respectively. The formulations incorporating the extract were stable during the stability study. The results demonstrate that mango peel extract can be a by-product to be revalorized as a promising cosmetic ingredient.

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.

Novel kojic acid-1,2,4-triazine hybrids as anti-tyrosinase agents: Synthesis, biological evaluation, mode of action, and anti-browning studies

A class of new kojic acid hybrids (7a-7o) bearing a 1,2,4-triazine moiety were prepared, and their inhibitory activities and mechanism on tyrosinase were investigated. All derivatives showed good to excellent anti-tyrosinase activity with IC₅₀ values ranging from 0.34 ± 0.06 μM to 8.44 ± 0.73 μM. In kinetic study, compound 7m was a mixed-type inhibitor with K_i and K_is of 0.73 and 1.27 μM, respectively. The interaction mechanism toward tyrosinase of compound 7m was further elaborated in combination with molecular docking and various spectral techniques. The results showed that compound 7m could change the secondary structure of tyrosinase to reduce its catalytic activity. Anti-browning assays demonstrated that 7m inhibited the browning of bananas effectively during storage. What's more, 7m was found to have low cytotoxicity in vitro. In conclusion, compound 7m has the potential to be applied as an anti-browning agent.

Effects of Water-Ethanol Extracts from Four Sphagnum Species on Gene Expression of Selected Enzymes in Normal Human Dermal Fibroblasts and Their Antioxidant Properties

Mosses (Bryophyta), particularly species of the genus Sphagnum, which have been used for centuries for the treatment of skin diseases and damage, are still not explored enough in terms of their use in cosmetics. The purpose of this study was to determine the antioxidant properties of water-ethanol extracts from four selected species of the genus Sphagnum (S. girgenshonii Russow, S. magellanicum Brid., S. palustre L., and S. squarrosum Crome) and their impact on the expression of genes encoding key enzymes for the functioning of the skin. In this study, the effects of Sphagnum extracts on the expression of genes encoding tyrosinase, collagenase, elastase, hyaluronidase and hyaluronic acid synthase in human dermal fibroblasts were determined for the first time in vitro. The extracts inhibited tyrosinase gene expression and showed antioxidant activity. The experiment showed an increase in the expression of some genes encoding collagenase (MMP1) or hyaluronidase (HYAL2, HYAL3 and HYAL4) and a decrease in the hyaluronan synthase (HAS1, HAS2 and HAS3) genes expression by the tested extracts. The obtained results suggest that using extracts from the tested Sphagnum species in anti-aging cosmetics does not seem beneficial. Further studies are needed to clarify their impact on the skin.

Hydroxypropyl-β-Cyclodextrin-Based Helichrysum italicum Extracts: Antioxidant and Cosmeceutical Activity and Biocompatibility

Two Helichrysum italicum extracts, OPT-1 (rich in phenolic acids) and OPT-2 (rich in total phenols and flavonoids), were prepared using hydroxypropyl-β-cyclodextrin (HP-β-CD)-assisted extraction. The prepared extracts were rich in phenolic compounds, including flavonoids and phenolic acids. GC-MS analysis of the extracts identified neryl acetate, neo-intermedeol, β-selinene, γ-curcumene, italidione I, and nerol as the main volatile components of the extracts, as well as plant sterols, γ-sitosterol, campesterol, and stigmasterol. The antioxidant (DPPH radical scavenging, reducing power, and a carotene linoleic acid assay) and cosmeceutical (anti-hyaluronidase, anti-tyrosinase, anti-lipoxygenase, ovalbumin anti-coagulation, and a UV-absorption assay) activity of the extracts in most of the assays was better than the activity of the applied positive controls. Especially low were the IC50 values of the extracts in the anti-hyaluronidase (14.31 ± 0.29 μL extract/mL and 19.82 ± 1.53 μL extract/mL for OPT-1 and OPT-2, respectively) and the anti-lipoxygenase (0.96 ± 0.11 μL extract/mL and 1.07 ± 0.01 μL extract/mL for OPT-1 and OPT-2, respectively) assays. The extracts were non-toxic to HaCaT cells in concentrations of up to 62.5 µL extract/mL assuring their status as excellent candidates for cosmeceutical product development appropriate for direct use in cosmetic products without solvent evaporation.

Penta-O-galloyl-β-d-glucose inhibits the formation of advanced glycation end-products (AGEs): A mechanistic investigation

Penta-O-galloyl-β-d-glucose (PGG) was prepared from tannic acid methanolysis products based on HSCCC, and its protective effects and mechanism on the glucose-induced glycation were investigated for the first time. PGG was confirmed to exhibit strong anti-AGEs effects in bovine serum albumin (BSA)-glucose (Glu) and BSA-methylglyoxal (MGO) glycation systems. It was showed that PGG could inhibit the AGEs formation by blocking glycated intermediates (fructosamine and α-dicarbonyl compounds), eliminating radicals, and chelating metal-ions. In-depth mechanism analysis proved that PGG could prevent BSA from glycation by hindering the accumulation of amyloid fibrils, stabilizing the BSA secondary structures, and binding the partial glycation sites. Furthermore, PGG exhibited a prominent trapping capacities on the reactive intermediate MGO by generating PGG-mono-MGO adduct. This research indicated that PGG could be an effective agent to block Glu/MGO-triggered glycation and offered new insights into PGG as a functional ingredient in food materials for preventing diabetic syndrome.

Oxidation of baicalein by tyrosinase and by o-quinones

Baicalein (5,6,7-trihydroxyflavone) has been previously described as an inhibitor of tyrosinase (Guo et al. Int. J. Biol. Macromol. 118 (2018) 57-68). However, long before this article was published this flavonoid had been shown to be a substrate of this enzyme and a catecholic cofactor partially abolishing the lag-phase during oxidation of l-tyrosine. Other compounds with a 1,2,3-triphenol moiety, such as pyrogallol, gallic acid and its esters are also oxidized by tyrosinase. Gallic acid was also shown to reduce tyrosinase-generated o-quinones. We have demonstrated that baicalein is also rapidly oxidized by o-quinones generated from catechols by tyrosinase or by treatment with sodium periodate. Smaller changes of absorbance at 475 nm during oxidation of l-dopa by tyrosinase in the presence of baicalein do not result from enzyme inhibition but from reduction of dopaquinone by baicalein. This reaction prevents formation of dopachrome giving an effect of inhibition, which is only apparent. The actual reaction rates did not decrease but increased in the presence of baicalein, which we demonstrated by measurements of oxygen consumption.

Pharmacological activities and effective substances of the component-based Chinese medicine of Ginkgo biloba leaves based on serum pharmacochemistry, metabonomics and network pharmacology

As a potential drug candidate for the treatment of hypertension and complications, it is speculated that the component-based Chinese medicine of Ginkgo biloba leaves (GBCCM) which mainly composed of flavonoid aglycones (FAs) and terpene lactones (TLs) may have different pharmacological effects at different doses or ratios. Taking the normal mice as the study object, metabonomics was conducted by giving different doses of GBCCM. Based on the components of GBCCM absorbed into the blood, the network pharmacological prediction was carried out. By integrating the results of metabonomics and network pharmacology, predict the possible pharmacological effects of GBCCM and conduct experimental verification. It was found that eight of the 19 compounds in GBCCM could be absorbed into the blood. GBCCM mainly affected the signal pathways of unsaturated fatty acid, pyruvate, bile acid, melanin and stem cells. It was speculated that GBCCM might have activities such as lowering blood pressure, regulating stem cell proliferation and melanogenesis. By establishing the models of mushroom tyrosinase, rat bone marrow mesenchymal stem cells (BMSCs) and spontaneously hypertensive rats (SHRs), we found that FAs and TLs showed synergistic effect in hypertension and tyrosinase models, and the optimal ratio was 3:2 (4.4 mg/kg) and 1:1 (0.4 mg/ml), respectively. As effective substances, FAs significantly promoted the proliferation of rat BMSCs on the third and fifth days at the concentration of 0.2 μg/ml (p &lt; 0.05). GBCCM showed a variety of pharmacological effects at different doses and ratios, which provided an important reference for the druggability of GBCCM.

New Insights into the Inhibition of Hesperetin on Polyphenol Oxidase: Inhibitory Kinetics, Binding Characteristics, Conformational Change and Computational Simulation

The inhibitory activity of hesperetin on polyphenol oxidase (PPO) and their interaction characteristics were investigated using multiple spectroscopic methods and computational simulation. Hesperetin, a mixed inhibitor, reversibly inhibited PPO activity, and its half-maximum inhibitory concentration (IC₅₀) values on monophenolase and diphenolase were 80.8 ± 1.4 μM and 776.0 ± 15.5 μM, respectively. Multivariate curve resolution-alternate least squares (MCR-ALS) analysis suggested PPO interacted with hesperetin and formed PPO-hesperetin complex. Hesperetin statically quenched PPO's endogenous fluorescence, and hydrophobic interactions mainly drove their binding. Hesperetin affected the polarity of the microenvironment around the Trp residues in PPO, but had no effect on that around Tyr residues. Circular dichroism (CD) results showed that hesperetin increased α-helix content and decreased β-fold and random coil contents, thus tightening PPO's structure. Molecular docking showed that hesperetin entered the hydrophobic cavity of PPO, bound near the dinuclear copper active center, interacted with Val283, Phe264, His85, Asn260, Val248, and His263 via hydrophobic interactions, formed hydrogen bonds with Met280, His89, and His259 residues and also interacted with Phe292, His61, Phe90, Glu256, His244, Asn260, Phe264, and Gly281 via van der Waals forces. The molecular dynamics simulation results also demonstrated that the addition of hesperetin reduced the stability and hydrophobicity of PPO and increased PPO's structural denseness. Thus, the inhibition of hesperetin on PPO may be because hesperetin bound near the active center of PPO, interacted with the surrounding residues, occupied the binding site for substrate, and induced the changes in PPO's secondary structure, thus inhibiting the catalytic activity of PPO. This study may provide novel views for the inhibition of hesperetin on PPO and theoretical guidance for developing flavonoids as new and efficient PPO inhibitors.

Quercetin 3-O-Galactoside Isolated from Limonium tetragonum Inhibits Melanogenesis by Regulating PKA/MITF Signaling and ERK Activation

Quercetin 3-O-galactoside (Q3G) is a common dietary flavanol that has been shown to possess several bioactivities, including anti-melanogenesis. However, how Q3G exerts its anti-melanogenic effect has not been studied. The current study, therefore aimed to investigate the anti-melanogenesis potential of Q3G and elucidate the underlying action mechanism in α-melanocyte-stimulating hormone (α-MSH)-induced hyperpigmentation model of B16F10 murine melanoma cells. Results showed that α-MSH stimulation significantly increased tyrosinase (TYR) and melanin production, which were significantly downregulated by Q3G treatment. The treatment with Q3G suppressed the transcriptional and protein expressions of melanogenesis-related enzymes TYR, tyrosinase related protein-1 (TRP-1), and TRP-2, along with the melanogenic transcription factor microphthalmia-associated transcription factor (MITF) in B16F10 cells. It was shown that Q3G downregulated MITF expression and suppressed its transcriptional activity by inhibiting the cAMP-dependent protein kinase A (PKA)-mediated activation of CREB and GSK3β. In addition, MAPK-regulated MITF activation signaling was also involved in the inhibition of melanin production by Q3G. The results suggest that the anti-melanogenic properties of Q3G rationalize further studies in vivo to confirm its action mechanism and consequent utilization as a cosmetic ingredient against hyperpigmentation.

Complex plant protein prepared from rice protein and pea protein: Improve the thermal stability of betanin

Betanin (BN) is a kind of edible natural red pigment with a variety of biological activities, but the thermal instability of BN has critically restricted its application in food industry. In this study, complex plant protein (RP-PP) was constructed by rice protein (RP) and pea protein (PP) to study the thermal protection effect and protective mechanism on BN. Thermal degradation results indicated RP-PP significantly improved thermal protection effect, and the degradation rate of BN was decreased from 93.74 % to 56.48 % after heating at 80 ℃ for 60 min. The main interaction between RP-PP and BN was hydrophobic force based on the result of fluorescence spectroscopy, FTIR and molecular docking. In addition, a porous network structure of RP-PP was observed by SEM, and the pore structure gradually decreased at the presence of BN, which speculated BN was trapped in it. TEM observation showed that RP-PP gradually aggregated with the increasing BN concentration, leading to a significant increase in particle size and the formation of network structure. The BN acted as a bridge to the surrounding proteins in the aggregated complex and was encapsulated within it. The interaction and encapsulation may be the key reasons for the improved thermal stability of BN.

Metabolite Profile of Athrixia phylicoides DC. (Bush Tea) and Determination of Inhibitory Mechanism against Tyrosinase Enzyme from Mushroom

Athrixia phylicoides DC. (Bush tea) is a shrub harvested in the north-eastern mountain regions of South Africa and belongs to the Asteraceae family. Generally, A. phylicoides is consumed as a hot tea beverage for its associated health benefits. The use of bush tea extracts for beauty enhancement has not been investigated even though several ethnobotanical reports have indicated its usage against skin imperfections. Therefore, the aim of the study was to assess plant metabolites of A. phylicoides for their inhibition of tyrosinase from mushroom and determine their inhibitory mechanism. Methanolic extracts (80% v/v) of A. phylicoides were evaluated using a tyrosinase-based TLC (thin-layer chromatography) autography technique. The inhibitory mechanism of active metabolites against the enzyme was determined using Lineweaver–Burk plots. Quercetin and an unknown metabolite with a retention factor (Rf) value of 0.73 inhibited melanogenesis. However, the IC50 value for Quercetin was reported as 51.07 ± 2.43 µg/mL higher than that of kojic acid of 5.22 ± 1.44 µg/mL. Chlorogenic acid was reported to have a similar Rf value as kojic acid, suggesting similarities in polarity and affinity towards the adsorbent material. However, chlorogenic acid with an IC50 value of 15.25 ± 1.18 µg/mL and an inhibitory strength of 2.92 could not inhibit melanogenesis with a similar intensity as kojic acid. The inhibitory mechanism for A. phylicoides extract was reported to be mixed inhibition (competitive/uncompetitive). The IC50 value for A. phylicoides was recorded as 20.65 ± 0.14 µg/mL with an inhibitory strength of 3.96. These results suggest that A. phylicoides extracts could be used against dark spots associated with scarring and ageing through modulation of tyrosinase activity.

Flavonoids as tyrosinase inhibitors in in silico and in vitro models: basic framework of SAR using a statistical modelling approach

Flavonoids are widely distributed in plants and constitute the most common polyphenolic phytoconstituents in the human diet. In this study, the in vitro inhibitory activity of 44 different flavonoids (1-44) against mushroom tyrosinase was studied, and an in silico study and type of inhibition for the most active compounds were evaluated too. Tyrosinase inhibitors block melanogenesis and take part in melanin production or distribution leading to pigmentation diseases. The in vitro study showed that quercetin was a competitive inhibitor (IC50=44.38 ± 0.13 µM) and achieved higher antityrosinase activity than the control inhibitor kojic acid. The in silico results highlight the importance of the flavonoid core with a hydroxyl at C7 as a strong contributor of interference with tyrosinase activity. According to the developed statistical model, the activity of molecules depends on hydroxylation at C3 and methylation at C8, C7, and C3 in the benzo-γ-pyrane ring of the flavonoids.

Action mechanisms of two key xanthine oxidase inhibitors in tea polyphenols and their combined effect with allopurinol

BACKGROUND

Tea polyphenols have been reported to have the effect of lowering uric acid. However, there are few studies on the inhibitory effects and molecular mechanisms of specific catechins on the urate-metabolizing enzyme xanthine oxidase (XO). In this research, multiple spectroscopic methods and computer simulations were used to determine the inhibitory ability and mechanisms of epigallocatechin gallate (EGCG) and gallocatechin gallate (GCG) on XO.

RESULTS

Herein, EGCG and GCG reversibly inhibited XO activity in a mixed manner, with IC₅₀ values of 40.50 ± 0.32 and 33.60 ± 0.53 μmol L^-1 , and also decreased the superoxide anion radical (O₂ ^- ) of the catalytic system by reducing the XO molecule and inhibiting the formation of uric acid. The combination of EGCG or GCG with allopurinol showed synergistic inhibition on XO. The binding of EGCG or GCG to XO with moderate affinity formed a stable complex by hydrogen bonds and van der Waals forces. The presence of EGCG and GCG made the structure of XO more stable and compact. The two inhibitors bound to the vicinity of flavin adenine dinucleotide (FAD) in XO, hindering the entry of substrate; thus the activity of XO was suppressed.

CONCLUSION

Both EGCG and GCG are excellent natural XO inhibitors, and inhibited the activity of XO by occupying the channel of the substrate to enter the active center and interfering with the dual substrate reaction catalyzed by XO. These findings provide a scientific basis for the application of catechins in dietary supplements and medicines with lowering uric acid effects. © 2022 Society of Chemical Industry.

Modulation of the lipophilicity and molecular size of thiosemicarbazone inhibitors to regulate tyrosinase activity

A group of 5-methylsalicylaldehyde thiosemicarbazone derivatives (HMTs) bearing different lipophilic and steric substituents attached at the 3-position of cresol ring were synthesized and investigated as mushroom tyrosinase (TYR) inhibitors. The ability of HMTs to inhibit the diphenolase activity of TYR was evaluated with L-DOPA as substrate by determining IC₅₀ values in relation to their structure modifications. HMTs displayed distinct inhibitory competencies towards TYR activity with IC₅₀ values in the range of 1.02-143.56 μM. A close correlation between their inhibition potency and both lipophilicity and molecular size was observed. The inhibitory effect of the hydroxyethyl-containing derivatives was much higher than the hydroxyethyl-free ones overall. Among them, HMT-NBO exhibited the most potent effect with IC₅₀ of 5.85 μM, which was nearly 25-fold and 3.8-fold lower than its parent HMT-NBE and the control kojic acid, respectively. The hydroxyethyl clearly benefited the improvement of the inhibitory competences and acted as a regulating group of lipophilicity of the inhibitors. The kinetic analyses showed that HMTs were reversible and mixed type inhibitors against mushroom TYR. The inhibition mechanism was studied by means of fluorescence spectroscopy, FT-IR, ESI-MS and molecular docking analysis. The results indicated that the observed inhibitory effect of HMTs was accomplished by acting on the amino acid residues rather than by chelating the centre copper ions of TYR. Each of HMTs can insert the hydrophobic pocket and interact with the residues of TYR through Van der Waals forces and hydrogen bonds, with additional electrostatic interactions for HMT-NEE and HMT-NEO further strengthening the affinity. Meanwhile, the inhibitors were observed to bind with L-DOPA or/and L-DOPAquinone forming 1:1 stoichiometric complexes, probably exerting indirect inhibition against TYR activity.

Bioactivities and phenolic composition of Limonium boitardii Maire and L. cercinense Brullo & Erben (Plumbaginaceae): two Tunisian strict endemic plants

Limonium genus is traditionally used in North Africa for disease treatment and in cosmetic. This study investigates for the first time the antioxidant, anti-inflammatory and enzyme inhibitory activities of two Tunisian endemic plants, L. boitardii and L. cercinense. Analysis of phenolic compounds was carried out by using RP-HPLC. Total phenolic and flavonoid contents, antioxidant activity (antiradical, reducing and total antioxidant activities), tyrosinase and α-glucosidase, collagenase inhibition activities were determined. Inhibiting of NO release in LPS-stimulated macrophages was assessed. L. cercinense exhibited strong antioxidant and anti-inflammatory effects. In the tyrosinase and α-glucosidase inhibitor activity tests, the two species were highly active, especially L. cercinense. High total phenolic and flavonoid contents were recorded in L. cercinense and myricitrin, myricetin, myricetin 3-O-β-D-galatopyranoside, luteolin 7-O-glucoside and rutin were the main phenolics in both species. The results obtained render L. boitardii and L. cercinense as valuable new natural sources for cosmetic and pharmacological applications.

Preparation of Fluorescently Labeled Chitosan-Quercetin Drug-Loaded Nanoparticles with Excellent Antibacterial Properties

In recent years, quercetin plays an increasingly important role in the medical field. However, the absorption and effect of quercetin as a drug in vivo are limited due to its extremely poor solubility in water. In addition, chitosan nanoparticles can deliver poorly soluble drugs as drug delivery carriers. Herein, chitosan nanoparticles were prepared by oxidative degradation and ionic cross-linking technology to study the drug loading properties of quercetin. On the other hand, the application of chitosan for fluorescent materials can improve the biocompatibility of fluorescent materials and increase the adsorption of fluorescent materials. Fluorescently labeled chitosan nanoparticles, especially chitosan microsphere fluorescent probes prepared using the abundant amino groups on chitosan chains to react with fluorescein isothiocyanate (FTIC), have been widely used as fluorescent probes in biomarkers and medical diagnostics. Therefore, chitosan–quercetin (CS–QT) drug-loaded nanoparticles are labeled with FITC, and the drug-loaded rate, encapsulation efficiency, and antioxidant properties were investigated. The drug-loaded rate of the sample reaches 8.39%, the encapsulation rate reaches 83.65%, and exhibits good antioxidant capacity. The fluorescence aperture of the obtained sample was consistent with the inhibition zone, which could realize the visualization of the antibacterial performance of the sample. The fluorescent-labeled nano-system exhibit superior antibacterial properties, which provide a strategy for observing the release and function of drugs.

Recent insights into oxidative metabolism of quercetin: catabolic profiles, degradation pathways, catalyzing metalloenzymes and molecular mechanisms

Quercetin is the most abundant polyphenolic flavonoid (flavonol subclass) in vegetal foods and medicinal plants. This dietary chemopreventive agent has drawn significant interest for its multiple beneficial health effects ("polypharmacology") largely associated with the well-documented antioxidant properties. However, controversies exist in the literature due to its dual anti-/pro-oxidant character, poor stability/bioavailability but multifaceted bioactivities, leaving much confusion as to its exact roles in vivo. Increasing evidence indicates that a prior oxidation of quercetin to generate an array of chemical diverse products with redox-active/electrophilic moieties is emerging as a new linkage to its versatile actions. The present review aims to provide a comprehensive overview of the oxidative conversion of quercetin by systematically analyzing the current quercetin-related knowledge, with a particular focus on the complete spectrum of metabolite products, the enzymes involved in the catabolism and the underlying molecular mechanisms. Herein we review and compare the oxidation pathways, protein structures and catalytic patterns of the related metalloenzymes (phenol oxidases, heme enzymes and specially quercetinases), aiming for a deeper mechanistic understanding of the unusual biotransformation behaviors of quercetin and its seemingly controversial biological functions.

Nomilin from Yuzu Seed Has In Vitro Antioxidant Activity and Downregulates Melanogenesis in B16F10 Melanoma Cells through the PKA/CREB Signaling Pathway

Yuzu (Citrus junos) is a citrus plant native to Asian countries, including Korea, Japan, and China. Yuzu peel and seed contain abundant vitamin C, citric acid, and polyphenols. Although the antioxidative and antimelanogenic activities of other citrus fruits and yuzu extract have been reported, the tyrosinase inhibitory activity of the limonoid aglycone contained in yuzu seed extract is unknown. We separated yuzu seeds into the husk, shell, and meal and evaluated antioxidant activity of each. The limonoid glucoside fraction of the husk identified nomilin, a novel tyrosinase inhibitor. We performed tyrosinase inhibitory activity and noncompetitive inhibition assays and docking studies to determine nomilin binding sites. Furthermore, we evaluated the antioxidative mechanism and antimelanogenic activity of nomilin in B16F10 melanoma cells. The concentration of nomilin that did not show toxicity was <100 µg/mL. Nomilin suppressed protein expression of TYR, TRP-1, TRP-2, and microphthalmia-associated transcription factor (MITF) in a concentration-dependent manner. Nomilin significantly reduced the levels of p-CREB and p-PKA at the protein level and decreased the levels of skin-whitening-related factors MITF, tyrosinase, TRP-1, and TRP-2 at the mRNA level in a concentration-dependent manner. Thus, nomilin from yuzu seed husk can be used as a skin-whitening agent in cosmetics.

The inhibitory kinetics and mechanism of quercetin-3-O-rhamnoside and chlorogenic acid derived from Smilax china L. EtOAc fraction on xanthine oxidase

Smilax china L. showed various biological activities mainly due to its phenolic components; however, the mechanism of isolated phenolic fraction against xanthine oxidase (XO) has not been investigated. Quercetin-3-O-rhamnoside (QORh) and chlorogenic acid (CGA) extracted from Smilax china L. ethyl acetate fraction was analyzed for its XO inhibitory kinetics and mechanism using multispectroscopic methods and molecular docking techniques. QORh and CGA reversibly inhibited XO activity in competitive and non-competitive modes, respectively. The bioactive compounds bound with XO were dominated mainly by hydrogen bonds and van der Waals forces to form QORh-XO, and CGA-XO complexes with one affinity binding site. The synchronous fluorescence, circular dichroism, three-dimensional (3D) fluorescence, and Fourier transform infrared spectra exhibited that XO binding with QORh or CGA leads to the secondary and tertiary structural variation of the protein. Additionally, molecular docking further revealed that QORh binds to the active site of XO and forms hydrogen coupling with amino acid residues. The results showed that QORh and CGA had inhibitory activity on XO, which might be further used to modify the bioactive compounds and improve their efficacy to treat gout.

Bridging the Chemical Profiles and Biological Effects of Spathodea campanulata Extracts: A New Contribution on the Road from Natural Treasure to Pharmacy Shelves

Spathodea campanulata is an important medicinal plant with traditional uses in the tropical zone. In the current work, we aimed to determine the chemical profiles and biological effects of extracts (methanolic and infusion (water)) from the leaves and stem bark of S. campanulata. The chemical components of the tested extracts were identified using LC-ESI-QTOF-MS. Biological effects were tested in terms of antioxidant (radical scavenging, reducing power, and metal chelating), enzyme inhibitory (cholinesterase, amylase, glucosidase, and tyrosinase), antineoplastic, and antiviral activities. Fifty-seven components were identified in the tested extracts, including iridoids, flavonoids, and phenolic acids as the main constituents. In general, the leaves-MeOH extract was the most active in the antioxidant assays (DPPH, ABTS, CUPRAC, FRAP, metal chelating, and phosphomolybdenum). Antineoplastic effects were tested in normal (VERO cell line) and cancer cell lines (FaDu, HeLa, and RKO). The leaf infusion, as well as the extracts obtained from stem bark, showed antineoplastic activity (CC₅₀ 119.03–222.07 µg/mL). Antiviral effects were tested against HHV-1 and CVB3, and the leaf methanolic extract (500 µg/mL) exerted antiviral activity towards HHV-1, inhibiting the viral-induced cytopathic effect and reducing the viral infectious titre by 5.11 log and viral load by 1.45 log. In addition, molecular docking was performed to understand the interactions between selected chemical components and viral targets (HSV-1 DNA polymerase, HSV-1 protease, and HSV-1 thymidine kinase). The results presented suggest that S. campanulata may be a bright spot in moving from natural sources to industrial applications, including novel drugs, cosmeceuticals, and nutraceuticals.

Bamboo Lignin Fractions with In Vitro Tyrosinase Inhibition Activity Downregulate Melanogenesis in B16F10 Cells via PKA/CREB Signaling Pathway

Cosmetic ingredients originating from natural resources have garnered considerable attention, and the demand for whitening ingredients is increasing, particularly in Asian countries. Lignin is a natural phenolic biopolymer significantly effective as a natural sunscreen, as its ultraviolet protection efficacy ranges from 250 to 400 nm. However, using different types of lignin as cosmetic ingredients is difficult owing to the heterogeneity of lignin and the lack of in vitro and in vivo safety and efficacy data. Thus, steam-exploded lignin (SEL) was prepared from bamboo, fractionated via successive organic solvent extraction, and sequentially fractionated using ethyl acetate, methanol, and acetone to investigate its potential as a natural whitening material. Gel permeation chromatography showed that the molecular weight of acetone-soluble and acetone-insoluble SEL fractions were the lowest and the highest, respectively. Monomer structures of the four lignin fractions were elucidated using 1H, 13C, and 2D heteronuclear single quantum coherence nuclear magnetic resonance and pyrolysis gas chromatography/mass spectrometry. The antioxidant and tyrosinase inhibition activities of the four fractions were compared. The methanol-soluble SEL fraction (SEL-F2) showed the highest antioxidant activity (except 2,2-diphenyl-1-picrylhydrazyl scavenging activity), and the enzyme inhibition kinetics were confirmed. In this study, the expression pattern of the anti-melanogenic-related proteins by SEL-F2 was confirmed for the first time via the protein kinase A (PKA)/cAMP-response element-binding (CREB) protein signaling pathway in B16F10 melanoma cells. Thus, SEL may serve as a valuable cosmetic whitening ingredient.

Exploring the binding mechanism of ferulic acid and ovalbumin: insights from spectroscopy, molecular docking and dynamics simulation

BACKGROUND

Ferulic acid (FA), a phenolic acid widely occurring in nature, has attracted extensive attention because of its biological activity. Ovalbumin (OVA) is a commonly used carrier protein. The mechanism of FA binding with OVA was investigated by utilizing a variety of spectral analyses, accompanied by computer simulation.

RESULTS

It was discovered that the fluorescence quenching mechanism of OVA by FA was a static mode as a result of the formation of an FA-OVA complex, which was verified by the concentration distributions and pure spectrum of the constituents decomposed from the high overlap spectrum signals using multivariate curve resolution-alternate least squares algorithm. Hydrogen bonds and Van der Waals forces drove the formation of FA-OVA complex with a binding constant of 1.69 × 10⁴  L mol^-1 . The presence of FA induced the loose structure of OVA with an attenuation of α-helix content and improved the thermal stability of OVA. Computer docking indicated that FA interacted with the amino acid residues Arg84, Asn88, Leu101 and Ser103 of OVA through hydrogen bonds. Molecular dynamics simulation proved that the combination of FA with OVA boosted the conformational stability of OVA and hydrogen bonds brought a crucial part in stabilizing the structure of the complex.

CONCLUSIONS

The study may supply the theoretical basis for the design of FA transport system using OVA as carrier protein to improve the instability and low bioavailability of FA. © 2021 Society of Chemical Industry.

Comparing the effect of benzoic acid and cinnamic acid hydroxyl derivatives on polyphenol oxidase: activity, action mechanism, and molecular docking

BACKGROUND

Polyphenol oxidase (PPO) is considered to have a key role in the food industry because it initiates enzymatic browning in the processing and storage of fruit and vegetables. Increasing numbers of benzoic and cinnamic acid derivatives have been found to be efficient inhibitors of polyphenol oxidase, but a comparison study on activity and action mechanism is lacking. In this study, 18 benzoic acid and cinnamic acid hydroxy derivatives were selected and investigated.

RESULTS

Three substrates, four activators and 11 inhibitors were identified from benzoic and cinnamic acid derivatives. 2,4-Dihydroxycinnamic acid and benzoic acid showed the strongest inhibitory effect on PPO, with IC₅₀ of 0.092 and1.425 mmol L^-1 , respectively. Benzoic acid reversibly inhibited PPO in a competitive manner, while 2,4-dihydroxycinnamic acid showed a mixed-type inhibition. Both of them showed that static-type fluorescence quenching and electrostatic interaction were the main driving force in the bonding process. Compared with benzoic acid, 2,4-dihydroxycinnamic acid more easily formed hydrogen bonds in the active site of PPO, making the interaction more stable.

CONCLUSION

Comparative analysis showed that the inhibition effect of cinnamic acid hydroxyl derivatives on PPO was stronger than that of benzoic acid derivatives. Benzoic acid and 2,4-dihydroxycinnamic acid were the strongest inhibitors. PPO inhibitors identified from benzoic and cinnamic acid derivatives are expected to be promising inhibitors for controlling fruit and vegetable browning. © 2021 Society of Chemical Industry.