Newest perspectives of glycopeptide antibiotics: biosynthetic cascades, novel derivatives, and new appealing antimicrobial applications.

Glycopeptide antibiotics (GPAs) are a family of non-ribosomal peptide natural products with polypeptide skeleton characteristics, which are considered the last resort for treating severe infections caused by multidrug-resistant Gram-positive pathogens. Over the past few years, an increasing prevalence of Gram-positive resistant strain "superbugs" has emerged. Therefore, more efforts are needed to study and modify the GPAs to overcome the challenge of superbugs. In this mini-review, we provide an overview of the complex biosynthetic gene clusters (BGCs), the ingenious crosslinking and tailoring modifications, the new GPA derivatives, the discoveries of new natural GPAs, and the new applications of GPAs in antivirus and anti-Gram-negative bacteria. With the development and interdisciplinary integration of synthetic biology, next-generation sequencing (NGS), and artificial intelligence (AI), more GPAs with new chemical structures and action mechanisms will constantly be emerging.

Microbial Transformation of Yakuchinone A and Cytotoxicity Evaluation of Its Metabolites.

Yakuchinone A (1) is a bioactive diarylheptanoid isolated from the dried fruits of Alpinia oxyphylla. Microbial transformation has been recognized as an efficient method to produce new biologically active derivatives from natural products. In the present study, microbial transformation of yakuchinone A was performed with the fungus Mucor hiemalis KCTC 26779, which led to the isolation of nine new metabolites (2, 3a, 3b, and 4-9). Their structures were elucidated as (3S)-oxyphyllacinol (2), (3S,7R)- and (3S,7S)-7-hydroxyoxyphyllacinol (3a and 3b), (3S)-oxyphyllacinol-4'-O-ß-d-glucopyranoside (4), (3S)-4″-hydroxyoxyphyllacinol (5), (3S)-3″-hydroxyoxyphyllacinol (6), (3S)-2″-hydroxyoxyphyllacinol (7), (3S)-2″-hydroxyoxyphyllacinol-2″-O-ß-d-glucopyranoside (8), and (3S)-oxyphyllacinol-3-O-ß-d-glucopyranoside (9) based on the comprehensive spectroscopic analyses and the application of modified Mosher's method. All compounds were evaluated for their cytotoxic activities against melanoma, as well as breast, lung, and colorectal cancer cell lines. Compound 9, which was O-glucosylated on the diarylheptanoid alkyl chain, exhibited the most selective cytotoxic activities against melanoma cell lines with the IC50 values ranging from 6.09 to 9.74 µM, indicating that it might be considered as a possible anti-cancer lead compound.

Biotransformation of (-)-α-Bisabolol by Absidia coerulea.

(-)-α-Bisabolol, a bioactive monocyclic sesquiterpene alcohol, has been used in pharmaceutical and cosmetic products with anti-inflammatory, antibacterial and skin-caring properties. However, the poor water solubility of (-)-α-bisabolol limits its pharmaceutical applications. It has been recognized that microbial transformation is a very useful approach to generate more polar metabolites. Fifteen microorganisms were screened for their ability to metabolize (-)-α-bisabolol in order to obtain its more polar derivatives, and the filamentous fungus Absidia coerulea was selected for scale-up fermentation. Seven new and four known metabolites were obtained from biotransformation of (-)-α-bisabolol (1), and all the metabolites exhibited higher aqueous solubility than that of the parent compound 1. The structures of newly formed metabolites were established as (1R,5R,7S)- and (1R,5S,7S)-5-hydroxy-α-bisabolol (2 and 3), (1R,5R,7S,10S)-5-hydroxybisabolol oxide B (4), (1R,7S,10S)-1-hydroxybisabolol oxide B (5), 12-hydroxy-α-bisabolol (7), (1S,3R,4S,7S)- and (1S,3S,4S,7S)-3,4-dihydroxy-α-bisabolol (8 and 10) on the basis of spectroscopic analyses. These compounds could also be used as reference standards for the detection and identification of the metabolic products of 1 in the mammalian system.

Microbial Transformation and Biological Activities of the Prenylated Aromatic Compounds from Broussonetia kazinoki.

Broussonetia kazinoki has been used as a traditional medicine for the treatment of burns and acne, and its extracts have been found to show tyrosinase inhibitory and anticancer activities. In this study, the tyrosinase inhibitory and cytotoxic activities of B. kazinoki were explored, leading to the isolation of kazinol C (1), kazinol E (2), kazinol F (3), broussonol N (4), and kazinol X (5), of which the compounds 4 and 5 have not been previously reported. Microbial transformation has been recognized as an efficient tool to generate more active metabolites. Microbial transformation of the major compounds 1 and 3 was conducted with Mucor hiemalis, where four glucosylated metabolites (6-9) were produced from 1, while one hydroxylated (10) and one glucosylated (11) metabolites were obtained from 3. Structures of the isolated metabolites were determined by extensive spectroscopic analyses. All compounds were evaluated for their tyrosinase inhibitory and cytotoxic activities. Compound 3 and its metabolites, kazinol Y (10) and kazinol F-4″-O-ß-d-glucopyranoside (11), exhibited the most potent tyrosinase inhibitory activities with the IC50 values ranging from 0.71 to 3.36 µM. Meanwhile, none of the metabolites, except for kazinol C-2',3″-di-O-ß-d-glucopyranoside (7), showed moderate cytotoxic activities (IC50 17.80 to 24.22 µM) against A375P, B16F10 and B16F1 cell lines.

Microbial Transformation of Broussochalcones A and B by Aspergillus niger.

Broussochalcones A (BCA, 1) and B (BCB, 2) are major bioactive constituents isolated from Broussonetia papyrifera, a polyphenol-rich plant belonging to the family Moraceae. Due to their low yields from natural sources, BCA (1) and BCB (2) were prepared synthetically by employing Claisen-Schmidt condensation, and these were used as substrates for microbial transformation to obtain novel derivatives. Microbial transformation of BCA (1) and BCB (2) with the endophytic fungus Aspergillus niger KCCM 60332 yielded 10 previously undescribed chalcones (1a-1e and 2a-2e). Their structures were established based on the spectroscopic methods. The cytotoxicity of BCA (1), BCB (2), and their metabolites (1a-1e and 2a-2e) was determined by human cancer cell lines A375P, A549, HT-29, MCF-7, and HepG2, with 1e shown to be most cytotoxic.

Microbial Conjugation Studies of Licochalcones and Xanthohumol.

Microbial conjugation studies of licochalcones (1-4) and xanthohumol (5) were performed by using the fungi Mucor hiemalis and Absidia coerulea. As a result, one new glucosylated metabolite was produced by M. hiemalis whereas four new and three known sulfated metabolites were obtained by transformation with A. coerulea. Chemical structures of all the metabolites were elucidated on the basis of 1D-, 2D-NMR and mass spectroscopic data analyses. These results could contribute to a better understanding of the metabolic fates of licochalcones and xanthohumol in mammalian systems. Although licochalcone A 4'-sulfate (7) showed less cytotoxic activity against human cancer cell lines compared to its substrate licochalcone A, its activity was fairly retained with the IC50 values in the range of 27.35-43.07 µM.

Biotransformation of the Phenolic Constituents from Licorice and Cytotoxicity Evaluation of Their Metabolites.

Biotransformation of four bioactive phenolic constituents from licorice, namely licoisoflavanone (1), glycyrrhisoflavone (2), echinatin (3), and isobavachalcone (4), was performed by the selected fungal strain Aspergillus niger KCCM 60332, leading to the isolation of seventeen metabolites (5-21). Structures of the isolated compounds were determined on the basis of extensive spectroscopic methods, twelve of which (5-7, 10-17 and 19) have been previously undescribed. A series of reactions including hydroxylation, hydrogenation, epoxidation, hydrolysis, reduction, cyclization, and alkylation was observed in the biotransformation process. All compounds were tested for their cytotoxic activities against three different human cancer cell lines including A375P, MCF-7, and HT-29. Compounds 1 and 12 exhibited most considerable cytotoxic activities against all the cell lines investigated, while compounds 2 and 4 were moderately cytotoxic. These findings will contribute to expanding the chemical diversity of phenolic compounds, and compounds 1 and 12 may serve as leads for the development of potential cancer chemopreventive agents.

Microbial Transformation of Prenylquercetins by Mucor hiemalis.

Quercetin, one of the most widely distributed flavonoids, has been found to show various biological activities including antioxidant, anticancer, and anti-inflammatory effects. It has been reported that bioactivity enhancement of flavonoids has often been closely associated with nuclear prenylation, as shown in 8-prenylquercetin and 5'-prenylquercetin. It has also been revealed in many studies that the biological activities of flavonoids could be improved after glucosylation. Three prenylated quercetins were prepared in this study, and microbial transformation was carried out in order to identify derivatives of prenylquercetins with increased water solubility and improved bioavailability. The fungus M. hiemalis was proved to be capable of converting prenylquercetins into more polar metabolites and was selected for preparative fermentation. Six novel glucosylated metabolites were obtained and their chemical structures were elucidated by NMR and mass spectrometric analyses. All the microbial metabolites showed improvement in water solubility.

Microbial Transformation of Licochalcones.

Microbial transformation of licochalcones B (1), C (2), D (3), and H (4) using the filamentous fungi Aspergillus niger and Mucor hiemalis was investigated. Fungal transformation of the licochalcones followed by chromatographic separations led to the isolation of ten new compounds 5-14, including one hydrogenated, three dihydroxylated, three expoxidized, and three glucosylated metabolites. Their structures were elucidated by combined analyses of UV, IR, MS, NMR, and CD spectroscopic data. Absolute configurations of the 2″,3″-diols in the three dihydroxylated metabolites were determined by ECD experiments according to the Snatzke's method. The trans-cis isomerization was observed for the metabolites 7, 11, 13, and 14 as evidenced by the analysis of their 1H-NMR spectra and HPLC chromatograms. This could be useful in better understanding of the trans-cis isomerization mechanism of retrochalcones. The fungal transformation described herein also provides an effective method to expand the structural diversity of retrochalcones for further biological studies.

Biotransformed Metabolites of the Hop Prenylflavanone Isoxanthohumol.

A metabolic conversion study on microbes is known as one of the most useful tools to predict the xenobiotic metabolism of organic compounds in mammalian systems. The microbial biotransformation of isoxanthohumol (1), a major hop prenylflavanone in beer, has resulted in the production of three diastereomeric pairs of oxygenated metabolites (2⁻7). The microbial metabolites of 1 were formed by epoxidation or hydroxylation of the prenyl group, and HPLC, NMR, and CD analyses revealed that all of the products were diastereomeric pairs composed of (2S)- and (2R)- isomers. The structures of these metabolic compounds were elucidated to be (2S,2"S)- and (2R,2"S)-4'-hydroxy-5-methoxy-7,8-(2,2-dimethyl-3-hydroxy-2,3-dihydro-4H-pyrano)-flavanones (2 and 3), (2S)- and (2R)-7,4'-dihydroxy-5-methoxy-8-(2,3-dihydroxy-3-methylbutyl)-flavanones (4 and 5) which were new oxygenated derivatives, along with (2R)- and (2S)-4'-hydroxy-5-methoxy-2"-(1-hydroxy-1-methylethyl)dihydrofuro[2,3-h]flavanones (6 and 7) on the basis of spectroscopic data. These results could contribute to understanding the metabolic fates of the major beer prenylflavanone isoxanthohumol that occur in mammalian system.

The Aggregated and Micellar Forms of ß-Casein Purified from Donkey and Bovine Milk Present Potential as Carriers for Bioactive Nutritional Compounds.

In recent years, there has been a growing interest in the pure casein fraction of milk protein, particularly ß-casein due to its physicochemical properties as well as its bio- and techno-functional properties. The utilization of self-assembled ß-caseins from bovine origin as nanocarriers for the delivery of nutraceutical compounds or drugs has increased dramatically. Concerning ß-caseins from other milk sources, the use of hypoallergenic donkey ß-caseins as a potential delivery vehicle for nutraceutical hydrophobic compounds is beginning to generate interest. The present review deals with casein micelles models, bovine and donkey ß-casein molecular structures, as well as their physical-chemical properties that account for their exploitation in nutraceutics and pharmaceutics. This review work suggests the possibility of developing delivery systems for hydrophobic bioactive compounds using ß-casein purified from hypoallergenic donkey milk, highlighting the potential of this protein as an innovative and promising vehicle for enhancing the enrichment and bioavailability of various bioactive substances in food products.

Improvement of the conjugation transfer of N. gerenzanensis based on the synergistic effect of quorum sensing and antibiotic interference.

Nonomuraea gerenzanensis (N. gerenzanensis) is known for its ability to biosynthesize A40926, the precursor of the glycopeptide antibiotic (GPA) Dalbavancin. However, challenges and uncertainties related to the genetic manipulation of the rare actinomycetes remain. In order to improve the conjugation transfer of N. gerenzanensis, the crucial factors affecting conjugal transfer were evaluated, including agar medium, mycelial state, donor-recipient ratio, magnesium ion concentration, and antibiotic coverage time firstly. Additionally, γ-butyrolactone (GBL) for quorum sensing (QS) and antibiotics targeting bacterial walls were applied to evaluate their effects on conjugation transfer. As a result, the optimal conditions of 5%TSB of liquid medium, 24 h of the period time, V0.1 of agar medium, 30 mM of magnesium ion, the ratio 10:1 of donor-to-recipient, and 27 h of the overlaying time of antibiotic were determined. Furthermore, the results showed that autoinducer GBL and GPA teicoplanin had a synergetic effect on the conjugation transfer of N. gerenzanensis at a working concentration of 60 µM and 0.5 µg mL-1, respectively. The highest conjugation efficiency could reach about 1.3 depending on the optimal process conditions and the interference of QS and antibiotics.

Inhibiting NF-κB-S100A11 signaling and targeting S100A11 for anticancer effects of demethylzeylasteral in human colon cancer.

Colon cancer is a common and deadly malignancy of the gastrointestinal tract. Targeting proteins that inhibit tumor proliferation could lead to innovative treatment strategies for this disease. Demethylzeylasteral, extracted naturally from Tripterygium wilfordii Hook. f., demonstrates incredible anti-colon cancer activity. However, the molecular mechanism behind this requires further investigation. This study aims to identify crucial targets and mechanisms of demethylzeylasteral in treating colon cancer, making it a promising candidate for anti-tumor therapy. Through gene knockout, overexpression techniques, and double Luciferase experiments, we confirmed that demethylzeylasteral reduces S100A11 expression in HT29 cells and in vivo tumor models to anti-colon cancer. By conducting Surface Plasmon Resonance, immunofluorescence staining, and confocal laser microscopy observations, we verified the direct interaction between demethylzeylasteral and S100A11, and explored the impact of S100A11's subcellular localization on cell proliferation. Demethylzeylasteral inhibited S100A11 expression and exhibited anti-cancer activity in both in vitro and in vivo colon cancer models. Conversely, overexpression of S100A11 hindered apoptosis induced by demethylzeylasteral. Additionally, we found that knockdown or overexpression of NF-κB respectively decreased or increased S100A11 expression, subsequently affecting cell proliferation. The dual Luciferase reporting experiment revealed that NF-κB is an upstream transcription factor regulating S100A11 expression. And Surface plasmon resonance confirmed that S100A11 can directly interact with demethylzeylasteral, this interaction limited the transport of S100A11 from the cytoplasm to nucleus, attenuation S100A11 mediated cell proliferation effect.

Microbial transformation of icariin and its derivatives.

Microbial transformation is an important tool to perform selective conversion of compounds to derivatives which are difficult to produce synthetically. In order to obtain icariside II and icaritin, the active components in Herba Epimedii in vivo, biotransformation studies using microbes as biocatalysts were carried out. Icariside II (2) and icaritin (3) were produced through biotransformation of icariin (1) using the fungi Hormoconis resinae and Mortierella ramanniana var. angulispora in 98% and 92% yields, respectively. In the subsequent transformation studies, 2 was deglycosylated to form 3 by Gliocladium deliquescens, whereas 3 was further converted to a novel compound icaritin-3-O-ß-d-glucopyranoside (4) and previously known icaritin-3,7-O-ß-d-diglucopyranoside (5) by Mucor hiemalis. Biological evaluation of these compounds using MTT assay exhibited potent cytotoxic activities against human cancer cell lines A549, A375P, and MCF-7, with icariin being the most active, indicating that glycosylation plays a role in the cytotoxic activity.

Line Graph or Scatter Plot? Automatic Selection of Methods for Visualizing Trends in Time Series.

Line graphs are usually considered to be the best choice for visualizing time series data, whereas sometimes also scatter plots are used for showing main trends. So far there are no guidelines that indicate which of these visualization methods better display trends in time series for a given canvas. Assuming that the main information in a time series is its overall trend, we propose an algorithm that automatically picks the visualization method that reveals this trend best. This is achieved by measuring the visual consistency between the trend curve represented by a LOESS fit and the trend described by a scatter plot or a line graph. To measure the consistency between our algorithm and user choices, we performed an empirical study with a series of controlled experiments that show a large correspondence. In a factor analysis we furthermore demonstrate that various visual and data factors have effects on the preference for a certain type of visualization.

A new flavonol glycoside from the aerial parts of Epimedium koreanum Nakai.

A new prenylated flavonol glycoside (1) was isolated from a 95% methanol extract of the dried and powdered aerial parts of Epimedium koreanum Nakai (Herba Epimedii), along with seven previously known flavonoids (2-8). The chemical structure of the new compound (1) was established to be 5-hydroxy-4'-methoxy-8-(2-hydroxy-3-methyl-3-butenyl)flavone 3-O-α-l-rhamnopyranosyl-7-O-ß-D-gluco pyranoside on the basis of spectroscopic methods. The antioxidant activities of these compounds were determined by the DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging assay and kaempferitrin (8) showed a high reactivity with DPPH.

Microbial transformation of the antimalarial sesquiterpene endoperoxide dihydroartemisinin.

Dihydroartemisinin (DHA, 1), a sesquiterpene endoperoxide derived from artemisinin, has shown potent antimalarial and anticancer activities. Microbial transformation of DHA by Absidia coerulea and Penicillium chrysogenum yielded one new (3) and four known metabolites (2, 4-6). The chemical structures of these compounds were identified as deoxydihydroartemisinin (2), 8α-hydroxydeoxyartemisinin (3), deoxyartemisinin (4), 9α-hydroxyartemethin-I (5) and 3α-hydroxydeoxydihydroartemisinin (6) using spectroscopic analyses. Among them, compounds 3 and 4 are artemisinin analogues, which were achieved by unusual oxidation at C-12 position. Biotransformation of DHA by microorganisms was an effective approach to obtain new derivatives of DHA.