Enzymatic synthesis of apigenin glucosides by glucosyltransferase (YjiC) from Bacillus licheniformis DSM 13

Biosynthesis of Apigenin Glucosides in Engineered Corynebacterium glutamicum

Glucosylation is a well-known approach to improve the solubility, pharmacological, and biological properties of flavonoids, making flavonoid glucosides a target for large-scale biosynthesis. However, the low yield of products coupled with the requirement of expensive UDP-sugars limits the application of enzymatic systems for large-scale. C. glutamicum is a Gram-positive and generally regarded as safe (GRAS) bacteria frequently employed for the large-scale production of amino acids and bio-fuels. Due to the versatility of its cell factory system and its non-endotoxin producing properties, it has become an attractive system for the industrial-scale biosynthesis of alternate products. Here, we explored the cell factory of C. glutamicum for efficient glucosylation of flavonoids using apigenin as a model flavonoid, with the heterologous expression of a promiscuous glycosyltransferase, YdhE from Bacillus licheniformis and the endogenous overexpression of C. glutamicum genes galU1 encoding UDP-glucose pyrophosphorylase and pgm encoding phosphoglucomutase involved in the synthesis of UDP-glucose to create a C. glutamicum cell factory system capable of efficiently glucosylation apigenin with a high yield of glucosides production. Consequently, the production of various apigenin glucosides was controlled under different temperatures yielding almost 4.2 mM of APG1(apigenin-4'-O-β-glucoside) at 25°C, and 0.6 mM of APG2 (apigenin-7-O-β-glucoside), 1.7 mM of APG3 (apigenin-4',7-O-β-diglucoside) and 2.1 mM of APG4 (apigenin-4',5-O-β-diglucoside) after 40 h of incubation with the supplementation of 5 mM of apigenin and 37°C. The cost-effective developed system could be used to modify a wide range of plant secondary metabolites with increased pharmacokinetic activities on a large scale without the use of expensive UDP-sugars.

Exploring the Role of Apigenin in Neuroinflammation: Insights and Implications

Neuroinflammation, a hallmark of various central nervous system disorders, is often associated with oxidative stress and neuronal or oligodendrocyte cell death. It is therefore very interesting to target neuroinflammation pharmacologically. One therapeutic option is the use of nutraceuticals, particularly apigenin. Apigenin is present in plants: vegetables (parsley, celery, onions), fruits (oranges), herbs (chamomile, thyme, oregano, basil), and some beverages (tea, beer, and wine). This review explores the potential of apigenin as an anti-inflammatory agent across diverse neurological conditions (multiple sclerosis, Parkinson's disease, Alzheimer's disease), cancer, cardiovascular diseases, cognitive and memory disorders, and toxicity related to trace metals and other chemicals. Drawing upon major studies, we summarize apigenin's multifaceted effects and underlying mechanisms in neuroinflammation. Our review underscores apigenin's therapeutic promise and calls for further investigation into its clinical applications.

Investigation on production and reaction conditions of sucrose synthase based glucosylation cascade towards flavonoid modification

Enzyme-based glycosylation is of great interest in the context of natural products decoration. Yet, its industrial application is hindered by optimisation difficulties and hard-to-standardise productivities. In this study, five sugar nucleotide-dependent glucosyltransferases from different origins (bacterial, plant and fungal) were coupled with soy sucrose synthase (GmSuSy) to create a set of diverse cascade biocatalysts for flavonoid glucosylation, which evaluation brought new insights into the field. Investigations into co-expression conditions and reaction settings enabled to define optimal induction temperature (25 °C) and uridine diphosphate (UDP) concentration (0.5 mM) for all tested pairs of enzymes. Moreover, the influence of pH and substrate concentration on the monoglucosylated product distribution was detected and analysed. The utilisation of crude protein extracts as a cost-effective source of catalysts unveiled their glycosidase activity against flavonoid glucosides, resulting in decreased productivity, which, to our knowledge, has not previously been discussed in such a context. Additionally, examination of the commercially available EziG immobilisation resins showed that selection of suitable carrier for solid catalyst production can be problematic and not only enzyme's but also reagent's properties have to be considered. Flavonoids, due to their complexation and hydrophobic properties, can adsorb on different types of surfaces, including divalent metal ions required for IMAC based immobilisation, necessitating detailed examination of the resins while the catalysis design.

Anti-influenza drug screening and inhibition of apigetrin on influenza A virus replication via TLR4 and autophagy pathways

Activation of Toll-like receptor (TLR) 4 plays important roles in the influenzaA virus (IAV) infection. To explore TLR4 inhibitors, 161 traditional Chinese medicines (TCMs) were screened. Further, we screened out Ixeris sonchifolia Hance, and its active compound, Apigetrin (apigenin-7-O-glucoside). Antiviral activity of Apigetrin was determined by plaque assay. We also further investigated the influence of Apigetrin on immune signaling pathways including TLRs, MAPK, NF-κB and autophagy pathways. The in-vitro results showed that the extract and its several ingredients could significantly inhibit IAV replication. Apigetrin significantly improved IAV-induced oxidative stress, inhibited the IAV-induced cytokine storm by suppressing the excessive activation of TLR3/4/7, JNK/p38 MAPK and NF-κB. Apigetrin decreased autophagosome accumulation and promoted degradation of IAV protein. Interestingly, Apigetrin antiviral activity was reversed by using H2O2 and the agonists of TLR4, JNK/p38, NF-κB and autophagy. Most important, the in-vitro effective concentration is higher than the reported plasma concentration. The in-vivo test showed that Apigetrin significantly increased the average survival time, reduced the lung edema and IAV replication. In conclusion, we have found that Ixeris sonchifolia Hance and its several ingredients can inhibit IAV infection, and the mechanisms of action of Apigetrin against IAV is by regulating TLR4 and autophagy signaling pathways.

Diversification of phenolic glucosides by two UDP-glucosyltransferases featuring complementary regioselectivity

BACKGROUND

Glucoside natural products have been showing great medicinal values and potentials. However, the production of glucosides by plant extraction, chemical synthesis, and traditional biotransformation is insufficient to meet the fast-growing pharmaceutical demands. Microbial synthetic biology offers promising strategies for synthesis and diversification of plant glycosides.

RESULTS

In this study, the two efficient UDP-glucosyltransferases (UGTs) (UGT85A1 and RrUGT3) of plant origin, that are capable of recognizing phenolic aglycons, are characterized in vitro. The two UGTs show complementary regioselectivity towards the alcoholic and phenolic hydroxyl groups on phenolic substrates. By combining a developed alkylphenol bio-oxidation system and these UGTs, twenty-four phenolic glucosides are enzymatically synthesized from readily accessible alkylphenol substrates. Based on the bio-oxidation and glycosylation systems, a number of microbial cell factories are constructed and applied to biotransformation, giving rise to a variety of plant and plant-like O-glucosides. Remarkably, several unnatural O-glucosides prepared by the two UGTs demonstrate better prolyl endopeptidase inhibitory and/or anti-inflammatory activities than those of the clinically used glucosidic drugs including gastrodin, salidroside and helicid. Furthermore, the two UGTs are also able to catalyze the formation of N- and S-glucosidic bonds to produce N- and S-glucosides.

CONCLUSIONS

Two highly efficient UGTs, UGT85A1 and RrUGT3, with distinct regioselectivity were characterized in this study. A group of plant and plant-like glucosides were efficiently synthesized by cell-based biotransformation using a developed alkylphenol bio-oxidation system and these two UGTs. Many of the O-glucosides exhibited better PEP inhibitory or anti-inflammatory activities than plant-origin glucoside drugs, showing significant potentials for new glucosidic drug development.

Novel Biotransformation of Maslinic Acid to MA-2-O-β-D-Glucoside by UDP-Glycosyltransferases from Bacillus subtilis

Maslinic acid (MA) is a pentacyclic triterpenoid which originates from olive and other plants. Though MA possesses multiple biological activities, it has limitations due to its poor water solubility. YojK, YjiC, and UGT109A3 UDP-glycosyltransferases (UGTs) from Bacillus subtilis (B. subtilis) were utilized to catalyze the conjugation of MA with UDP-Glucose to generate a new MA glycosylation product, MA-2-O-β-D-glucoside (MA-2-O-β-D-Glu). The experimental results indicated that the resultant water solubility of MA-2-O-β-D-Glu is 1.69 times higher than that of MA. In addition, the recombinant YojK showed maximum activity at 40 °C with a pH range of 8.0−10.0, while the recombinant YjiC showed maximum activity at 45 °C with a pH of 8.0, and the recombinant UGT109A3 showed maximum activity at 40 °C with a pH of 8.0. Mg2+ is an important factor for efficient catalysis by three recombinant glycosyltransferases. The chemical conversion rate of the recombinant YojK, YjiC, and UGT109A3 is nearly 100% at their optimum pH, temperature, and metal ions. Furthermore, eight essential residues of three UGTs for MA glycosylation modification were further determined by molecular docking and site-directed mutagenesis. Thus, efficient glycosylation modification improves the water solubility of MA and provides a new potential method for the glycosylation modification of other pentacyclic triterpenoids.

Glycosylation of Methylflavonoids in the Cultures of Entomopathogenic Filamentous Fungi as a Tool for Obtaining New Biologically Active Compounds

Flavonoid compounds are secondary plant metabolites with numerous biological activities; they naturally occur mainly in the form of glycosides. The glucosyl moiety attached to the flavonoid core makes them more stable and water-soluble. The methyl derivatives of flavonoids also show increased stability and intestinal absorption. Our study showed that such flavonoids can be obtained by combined chemical and biotechnological methods with entomopathogenic filamentous fungi as glycosylation biocatalysts. In the current paper, two flavonoids, i.e., 2′-hydroxy-4-methylchalcone and 4′-methylflavone, have been synthesized and biotransformed in the cultures of two strains of entomopathogenic filamentous fungi Isaria fumosorosea KCH J2 and Beauveria bassiana KCH J1.5. Biotransformation of 2′-hydroxy-4-methylchalcone resulted in the formation of two dihydrochalcone glucopyranoside derivatives in the culture of I. fumosorosea KCH J2 and chalcone glucopyranoside derivative in the case of B. bassiana KCH J1.5. 4′-Methylflavone was transformed in the culture of I. fumosorosea KCH J2 into four products, i.e., 4′-hydroxymethylflavone, flavone 4′-methylene-O-β-d-(4″-O-methyl)-glucopyranoside, flavone 4′-carboxylic acid, and 4′-methylflavone 3-O-β-d-(4″-O-methyl)-glucopyranoside. 4′-Methylflavone was not efficiently biotransformed in the culture of B. bassiana KCH J1.5. The computer-aided simulations based on the chemical structures of the obtained compounds showed their improved physicochemical properties and antimicrobial, anticarcinogenic, hepatoprotective, and cardioprotective potential.

Dietary biomolecules as promising regenerative agents for peripheral nerve injury: An emerging nutraceutical-based therapeutic approach

Peripheral nerve damage is a debilitating condition that can result in partial or complete functional loss as a result of axonal degeneration, as well as lifelong dependence. Many therapies have been imbued with a plethora of positive features while posing little risks. It is worth noting that these biomolecules work by activating several intrinsic pathways that are known to be important in peripheral nerve regeneration. Although the underlying mechanism is used for accurate and speedy functional recovery, none of them are without side effects. As a result, it is believed that effective therapy is currently lacking. The dietary biomolecules-based intervention, among other ways, is appealing, safe, and effective. Upregulation of transcription factors, neurotrophic factors, and growth factors such as NGF, GDNF, BDNF, and CTNF may occur as a result of these substances' dietary intake. Upregulation of the signaling pathways ERK, JNK, p38, and PKA has also been seen, which aids in axonal regeneration. Although several mechanistic approaches to understanding their involvement have been suggested, more work is needed to reveal the amazing properties of these biomolecules. We have discussed in this article that how different dietary biomolecules can help with functional recovery and regeneration after an injury. PRACTICAL APPLICATIONS: Based on the information known to date, we may conclude that treatment techniques for peripheral nerve injury have downsides, such as complications, donor shortages, adverse effects, unaffordability, and a lack of precision in efficacy. These difficulties cast doubt on their efficacy and raise severe concerns about the prescription. In this situation, the need for safe and effective therapeutic techniques is unavoidable, and dietary biomolecules appear to be a safe, cost-efficient, and effective way to promote nerve regeneration following an injury. The information on these biomolecules has been summarized here. Upregulation of transcription factors, neurotrophic factors, and growth factors, such as NGF, GDNF, BDNF, and CTNF, as well as the ERK, JNK, p38, and PKA, signaling pathways, may stimulate axonal regeneration.

Flavonoids, the Family of Plant-derived Antioxidants making inroads into Novel Therapeutic Design against IR-induced Oxidative Stress in Parkinson's Disease

Background:

Ionizing radiation from telluric sources is unceasingly an unprotected pitfall to humans. Thus, the foremost contributors to human exposure are global and medical radiations. Various evidences assembled during preceding years reveal the pertinent role of ionizing radiation-induced oxidative stress in the progression of neurodegenerative insults, such as Parkinson’s disease, which have been contributing to increased proliferation and generation of reactive oxygen species.

Objective:

This review delineates the role of ionizing radiation-induced oxidative stress in Parkinson’s disease and proposes novel therapeutic interventions of flavonoid family, offering effective management and slowing down the progression of Parkinson’s disease.

Methods:

Published papers were searched in MEDLINE, PubMed, etc., published to date for in-depth database collection.

Results:

The oxidative damage may harm the non-targeted cells. It can also modulate the functions of the central nervous system, such as protein misfolding, mitochondria dysfunction, increased levels of oxidized lipids, and dopaminergic cell death, which accelerate the progression of Parkinson’s disease at the molecular, cellular, or tissue levels. In Parkinson’s disease, reactive oxygen species exacerbate the production of nitric oxides and superoxides by activated microglia, rendering death of dopaminergic neuronal cell through different mechanisms.

Conclusion:

Rising interest has extensively engrossed in the clinical trial designs based on the plant-derived family of antioxidants. They are known to exert multifarious impact on neuroprotection via directly suppressing ionizing radiation-induced oxidative stress and reactive oxygen species production or indirectly increasing the dopamine levels and activating the glial cells.

Electrospray ionisation mass spectrometric behaviour of flavonoid 5-O-glucosides and their positional isomers detected in the extracts from the bark of Prunus cerasus L. and Prunus avium L

INTRODUCTION

Literature data concerning the electrospray ionisation mass spectrometry (ESI-MS) behaviour of flavonoid 5-O-glycosides are poor and sometimes disputable. Therefore, we decided to analyse the compounds of this kind present in the bark of Prunus cerasus and Prunus avium by using high-performance liquid chromatography HPLC/ESI-MS.

OBJECTIVE

The aim of this study is to obtain the comprehensive information about the ESI-MS(+/-) behaviour of flavonoid 5-O-glucosides, to compare their behaviour with that of their positional isomers, to confirm that the known susceptibility of flavonoid 5-O-glucosides to hydrolysis may be successfully used for their identification.

METHOD

The bark from Prunus trees was extracted with pure methanol or, in order to perform hydrolysis and extraction simultaneously, with 5% methanolic solution of hydrochloric acid. The HPLC-ESI-MS analyses were performed using a Waters model 2690 HPLC pump and Waters/Micromass ZQ2000 mass spectrometer.

RESULTS

Flavonoid 5-O-glycosides were completely hydrolysed under the acid conditions used, in contrast to their positional isomers. In positive ion mode, at low cone voltage, flavonoid 5-O-glycosides yield abundant Y₀ ⁺ aglycone ions, in contrast to their positional isomers. In the negative ion mode, flavonoid 5-O-glycosides do not yield [Y₀ - H]^-· fragment ions, in contrast to their positional isomers. When aglycone contains only two hydroxyl groups, the flavonoid 5-O-glycosides can be detected in negative ion mode, whereas their positional isomers do not yield [M - H]^- ions.

CONCLUSION

It has been demonstrated that the susceptibility to hydrolysis of the analysed compounds, the abundances of respective fragment ions formed, and their ESI(-) response allow unambiguous identification of flavonoid 5-O-glycosides and their differentiation from their positional isomers.

Flavonoids and Polyphenolic Compounds as Potential Talented Agents for the Treatment of Alzheimer's Disease and their Antioxidant Activities

Aging is a normal human cycle and the most important risk factor for neurodegenerative diseases. Alternations in cells due to aging contribute to loss of the nutrient-sensing, cell function, increased oxidative stress, loss of the homeostasis cell, genomic instability, the build-up of malfunctioning proteins, weakened cellular defenses, and a telomere split. Disturbance of these essential cellular processes in neuronal cells can lead to life threats including Alzheimer's disease (AD), Huntington's disease (HD), Lewy's disease, etc. The most common cause of death in the elderly population is AD. Specific therapeutic molecules were created to alleviate AD's social, economic, and health burden. In clinical practice, almost every chemical compound was found to relieve symptoms only in palliative treatment. The reason behind these perfect medicines is that the current medicines are not effective in targeting the cause of this disease. In this paper, we explored the potential role of flavonoid and polyphenolic compounds, which could be the most effective preventative anti-Alzheimer's strategy.

Apigenin as Tumor Suppressor in Cancers: Biotherapeutic Activity, Nanodelivery, and Mechanisms With Emphasis on Pancreatic Cancer

Pancreatic cancer is the most lethal malignancy of the gastrointestinal tract. Due to its propensity for early local and distant spread, affected patients possess extremely poor prognosis. Currently applied treatments are not effective enough to eradicate all cancer cells, and minimize their migration. Besides, these treatments are associated with adverse effects on normal cells and organs. These therapies are not able to increase the overall survival rate of patients; hence, finding novel adjuvants or alternatives is so essential. Up to now, medicinal herbs were utilized for therapeutic goals. Herbal-based medicine, as traditional biotherapeutics, were employed for cancer treatment. Of them, apigenin, as a bioactive flavonoid that possesses numerous biological properties (e.g., anti-inflammatory and anti-oxidant effects), has shown substantial anticancer activity. It seems that apigenin is capable of suppressing the proliferation of cancer cells via the induction of cell cycle arrest and apoptosis. Besides, apigenin inhibits metastasis via down-regulation of matrix metalloproteinases and the Akt signaling pathway. In pancreatic cancer cells, apigenin sensitizes cells in chemotherapy, and affects molecular pathways such as the hypoxia inducible factor (HIF), vascular endothelial growth factor (VEGF), and glucose transporter-1 (GLUT-1). Herein, the biotherapeutic activity of apigenin and its mechanisms toward cancer cells are presented in the current review to shed some light on anti-tumor activity of apigenin in different cancers, with an emphasis on pancreatic cancer.

Entomopathogenic Filamentous Fungi as Biocatalysts in Glycosylation of Methylflavonoids

Flavonoids are known for their numerous biological activities; however, their pharmacological application is limited by poor bioavailability. Glycosides are usually more stable and more soluble in water and in this form, flavonoids are present in nature. Likewise, the presence of the methyl group in the flavonoid skeleton results in facilitated absorption and greater bioavailability. Entomopathogenic filamentous fungi are effective in the biotransformation of flavonoids; they are known especially for efficient glycosylation. In the current study we used strains of Beauveria bassiana KCH J1.5 and Isaria fumosorosea KCH J2 to biotransform flavonoids with a single methyl group. 2′-Hydroxy-5′-methylchalcone was biotransformed by both strains into 2′-hydroxy-5′-methylchalcone 3-O-β-D-(4″-O-methyl)-glucopyranoside. In the culture of B. bassiana KCH J1.5 four products were obtained from 6-methylflavanone: 4′-hydroxy-6-methylflavanone 3′-O-β-D-(4″-O-methyl)-glucopyranoside; 4′-hydroxyflavanone 6-methylene-O-β-D-(4″-O-methyl)-glucopyranoside; 6-hydroxymethylflavanone 3′-O-β-D-(4″-O-methyl)-glucopyranoside and 4′-hydroxy-6-hydroxymethylflavanone 3′-O-β-D-(4″-O-methyl)-glucopyranoside. Biotransformation with I. fumosorosea KCH J2 as a biocatalyst resulted in the formation of 6-methylflavanone 4′-O-β-D-(4″-O-methyl)-glucopyranoside and 2-phenyl-6-methylchromane 4-O-β-D-(4″-O-methyl)-glucopyranoside. All of these flavonoids can be used in biological activity tests and can be useful in studies concerning structure—bioactivity relationships.

Enzymatic Monoglucosylation of Rubusoside and the Structure-Sweetness/Taste Relationship of Monoglucosyl Derivatives

Monoglucosylation of rubusoside not only could increase its structural diversity but may also improve its taste. To biosynthesize the monoglucosyl rubusosides, a series of glycosyltransferases and glycosynthases were screened to identify the enzymes capable of specifically glycosylating the hydroxyl groups of the 13-O-β-d-glucosyl and 19-COO-β-d-glucosyl moieties. After structural characterization, the effect of structure on sweetness and taste was established based on these rubusoside-derived analogues, including two first characterized compounds. β-Monoglucosylation of two 2-hydroxyl groups, as well as α-monoglucosylations of the 4- and 6-hydroxyl groups of the 13-glucosyl moiety, could significantly increase the relative sweetness of rubusoside to 140 while maintaining or improving the taste quality. In contrast, monoglucosylations of other hydroxyl groups in our study usually decreased the taste quality of the rubusoside. Additionally, the possibility of a negative influence of these monoglucosylated derivatives on the function of islets was preliminarily excluded, which should facilitate the development of rubusoside-derived sweeteners.

An Ambidextrous Polyphenol Glycosyltransferase PaGT2 from Phytolacca americana

The glycosylation of small hydrophobic compounds is catalyzed by uridine diphosphate glycosyltransferases (UGTs). Because glycosylation is an invaluable tool for improving the stability and water solubility of hydrophobic compounds, UGTs have attracted attention for their application in the food, cosmetics, and pharmaceutical industries. However, the ability of UGTs to accept and glycosylate a wide range of substrates is not clearly understood due to the existence of a large number of UGTs. PaGT2, a UGT from Phytolacca americana, can regioselectively glycosylate piceatannol but has low activity toward other stilbenoids. To elucidate the substrate specificity and catalytic mechanism, we determined the crystal structures of PaGT2 with and without substrates and performed molecular docking studies. The structures have revealed key residues involved in substrate recognition and suggest the presence of a nonconserved catalytic residue (His81) in addition to the highly conserved catalytic histidine in UGTs (His18). The role of the identified residues in substrate recognition and catalysis is elucidated with the mutational assay. Additionally, the structure-guided mutation of Cys142 to other residues, Ala, Phe, and Gln, allows PaGT2 to glycosylate resveratrol with high regioselectivity, which is negligibly glycosylated by the wild-type enzyme. These results provide a basis for tailoring an efficient glycosyltransferase.

Enzymatic Synthesis of Anabolic Steroid Glycosides by Glucosyltransferase from Terribacillus sp. PAMC 23288

The application of steroids has steadily increased thanks to their therapeutic effects. However, alternatives are required due their severe side effects; thus, studies on the activities of steroid derivatives are underway. Sugar derivatives of nandrolone, which is used to treat breast cancer, as well as cortisone and prednisone, which reduce inflammation, pain, and edema, are unknown. We linked O-glucose to nandrolone and testosterone using UDP-glucosyltransferase (UGT-1) and, then, tested their bioactivities in vitro. Analysis by NMR showed that the derivatives were 17β-nandrolone β-D-glucose and 17β-testosterone β-D-glucose, respectively. The viability was higher and cytotoxicity was evident in PC12 cells incubated with rotenone and, testosterone derivatives, compared to the controls. SH-SY5Y cells incubated with H₂O₂ and nandrolone derivatives remained viable and cytotoxicity was attenuated. Both derivatives enhanced neuronal protective effects and increased the amounts of cellular ATP.

Efficient Biocatalytic Preparation of Rebaudioside KA: Highly Selective Glycosylation Coupled with UDPG Regeneration

Rebaudioside KA is a diterpene natural sweetener isolated in a trace amount from the leaves of Stevia rebaudiana. Selective glycosylation of rubusoside, a natural product abundantly presented in various plants, is a feasible approach for the biosynthesis of rebaudioside KA. In this study, bacterial glycosyltransferase OleD was identified to selectively transfer glucose from UDPG to 2′-hydroxyl group with a β-1,2 linkage at 19-COO-β-D-glucosyl moiety of rubusoside for the biosynthesis of rebaudioside KA. To eliminate the use of UDPG and improve the productivity, a UDPG regeneration system was constructed as an engineered Escherichia coli strain to couple with the glycosyltransferase. Finally, rubusoside at 22.5 g/L (35.0 mM) was completely converted to rebaudioside KA by the whole cells without exogenous addition of UDPG. This study provides an efficient and scalable method for highly selective biosynthesis of rebaudioside KA.

OleD Loki as a Catalyst for Hydroxamate Glycosylation

Herein we describe the ability of the permissive glycosyltransferase (GT) OleD Loki to convert a diverse set of >15 histone deacetylase (HDAC) inhibitors (HDACis) into their corresponding hydroxamate glycosyl esters. Representative glycosyl esters were subsequently evaluated in assays for cancer cell line cytotoxicity, chemical and enzymatic stability, and axolotl embryo tail regeneration. Computational substrate docking models were predictive of enzyme-catalyzed turnover and suggest certain HDACis may form unproductive, potentially inhibitory, complexes with GTs.

A Review on Flavonoid Apigenin: Dietary Intake, ADME, Antimicrobial Effects, and Interactions with Human Gut Microbiota

Apigenin is a flavonoid of low toxicity and multiple beneficial bioactivities. Published reviews all focused on the findings using eukaryotic cells, animal models, or epidemiological studies covering the pharmacokinetics, cancer chemoprevention, and drug interactions of apigenin; however, no review is available on the antimicrobial effects of apigenin. Research proves that dietary apigenin passes through the upper gastrointestinal tract and reaches the colon after consumption. For that reason, it is worthwhile to study the potential interactions between apigenin and human gut microbiota. This review summarizes studies on antimicrobial effects of apigenin as well as what has been reported on apigenin and human gut microbiota. Various levels of effectiveness have been reported on apigenin's antibacterial, antifungal, and antiparasitic capability. It has been shown that apigenin or its glycosides are degraded into smaller metabolites by certain gut bacteria which can regulate the human body after absorption. How apigenin contributes to the structural and functional changes in human gut microbiota as well as the bioactivities of apigenin bacterial metabolites are worth further investigation.

Enzyme-Catalyzed Glycosylation of Curcumin and Its Analogues by Glycosyltransferases from Bacillus subtilis ATCC 6633

Curcumin is a naturally occurring polyphenolic compound that is commonly used in both medicine and food additives, but its low aqueous solubility and poor bioavailability hinder further clinical applications. For assessing the effect of the glycosylation of curcumin on its aqueous solubility, two glycosyltransferase genes (BsGT1 and BsGT2) were cloned from the genome of the strain Bacillus subtilis ATCC 6633 and over-expressed in Escherichia coli. Then, the two glycosyltransferases were purified, and their glycosylation capacity toward curcumin and its two analogues was verified. The results showed that both BsGT1 and BsGT2 could convert curcumin and its two analogues into their glucosidic derivatives. Then, the structures of the derivatives were characterized as curcumin 4′-O-β-D-glucoside and two new curcumin analogue monoglucosides namely, curcumoid-O-α-D-glucoside (2a) and 3-pentadienone-O-α-D-glucoside (3a) by nuclear magnetic resonance (NMR) spectroscopy. Subsequently, the dissolvability of curcumin 4′-O-β-D-glucoside was measured to be 18.78 mg/L, while its aglycone could not be determined. Furthermore, the optimal catalyzing conditions and kinetic parameters of BsGT1 and BsGT2 toward curcumin were determined, which showed that the Kcat value of BsGT1 was about 2.6-fold higher than that of BsGT2, indicating that curcumin is more favored for BsGT2. Our findings effectively apply the enzymatic approach to obtain glucoside derivatives with enhanced solubility.

Biotransformation into 11α-hydroxyprogesterone glucosides by glucosyltransferase

Recently, studies on the steroidal hormone activity in the brain have attracted attention, and the influences of the varied glucosides and their artificial derivatives have been discussed; additionally, it has been suggested that glucosides are the synthetic precursors of glucuronide as a label molecule. However, glucosides are formed with 11α-hydroxyprogesterone (1), which is important as a blood pressure regulator, but anti-androgen activity remains unknown. Using UDP-glucosyltransferase, glucoside synthesis was successful in linking β-d-glucopyranose and β-d-laminaribiose to 11α oxygen of 1 at a high conversion ratio, and full assignment structure was analyzed for the two glucosides by high-resolution quadrupole-time flight electrospray ionization-mass spectrometry, 1D (¹H and ¹³C) NMR and 2D (COSY, ROESY, HSQC-DEPT and HMQC) NMR. Furthermore, the bioactivity of 1 and two 11α-hydroxyprogesterone glucosides [11α-(β-d-glucopyranosyl)oxyprogesterone, 2, and 11α-(β-d-laminaribiosyl)oxyprogesterone, 3] was tested in vitro. On rotenone-induced PC12 cells, the two 11α-hydroxyprogesterone glucosides (2 and 3) showed superior neuroprotective effects and increased cellular ATP levels compared with those of 1.

Enzymatic Synthesis of Unnatural Ginsenosides Using a Promiscuous UDP-Glucosyltransferase from Bacillus subtilis

Glycosylation, which is catalyzed by UDP-glycosyltransferases (UGTs), is an important biological modification for the structural and functional diversity of ginsenosides. In this study, the promiscuous UGT109A1 from Bacillus subtilis was used to synthesize unnatural ginsenosides from natural ginsenosides. UGT109A1 was heterologously expressed in Escherichia coli and then purified by Ni-NTA affinity chromatography. Ginsenosides Re, Rf, Rh1, and R1 were selected as the substrates to produce the corresponding derivatives by the recombinant UGT109A1. The results showed that UGT109A1 could transfer a glucosyl moiety to C3-OH of ginsenosides Re and R1, and C3-OH and C12-OH of ginsenosides Rf and Rh1, respectively, to produce unnatural ginsenosides 3,20-di-O-β-d-glucopyranosyl-6-O-[α-l-rhamnopyrano-(1→2)-β-d-glucopyranosyl]-dammar-24-ene-3β,6α,12β,20S-tetraol (1), 3,20-di-O-β-d-glucopyranosyl-6-O-[β-d-xylopyranosyl-(1→2)-β-d-glucopyranosyl]-dammar-24-ene-3β,6α,12β,20S-tetraol (6), 3-O-β-d-glucopyranosyl-6-O-[β-d-glucopyranosyl-(1→2)-β-d-glucopyranosyl]-dammar-24-ene-3β,6α,12β,20S-tetraol (3), 3,12-di-O-β-d-glucopyranosyl-6-O-[β-d-glucopyranosyl-(1→2)-β-d-glucopyranosyl]-dammar-24-ene-3β,6α,12β,20S-tetraol (2), 3,6-di-O-β-d-glucopyranosyl-dammar-24-ene-3β,6α,12β,20S-tetraol (5), and 3,6,12-tri-O-β-d-glucopyranosyl-dammar-24-ene-3β,6α,12β,20S-tetraol (4). Among the above products, 1, 2, 3, and 6 are new compounds. The maximal activity of UGT109A1 was achieved at the temperature of 40 °C, in the pH range of 8.0⁻10.0. The activity of UGT109A1 was considerably enhanced by Mg2+, Mn2+, and Ca2+, but was obviously reduced by Cu2+, Co2+, and Zn2+. The study demonstrated that UGT109A1 was effective in producing a series of unnatural ginsenosides through enzymatic reactions, which could pave a way to generate promising leads for new drug discovery.

Effects of Apigenin and Apigenin- Loaded Nanogel on Induction of Apoptosis in Human Chronic Myeloid Leukemia Cells

Background:

Diet plays an important role in cancer prevention. Apigenin, a flavonoid with thechemical formula C15H10O5 , is abundantly present in vegetables. Vegetarian foods containing flavonoids are rich sources of bioactive compounds. Flavonoids have been utilized in herbal treatment. Nanogels are drug delivery systems based on polymers and are used in tissue engineering and for drug delivery. This study was conducted to compare the effects of apigenin and a nanodrug on the viability of the K562 cell line of chronic myeloid leukemia at different durations under laboratory conditions.

Materials and Methods:

Chitosan was first dissolved in 1% acetic acid, and ethylene dichloride EDC and NHS were added to the solution. Then, the nanodrug was prepared by loading apigenin into stearate–chitosan nanogel (scs nanogel), and its physical and morphological characteristics were evaluated by TEM, DLS, and FTIR. Trypan blue staining, MTT assay, and flow cytometry were used to analyze the effects of various concentrations of apigenin and apigenin-loaded chitosan–stearate nanogel (APG–SCS) at 24, 48, and 72 h after they were applied to the K562 cell line.

Results:

The diameter of the nanodrug particles was measured using DLS and confirmed by TEM. The K562 cells treated with APG–SCS and with apigenin exhibited significant differences compared with the control (P < 0.05). Apoptosis was detected by flow cytometry.

Conclusion:

This study showed that the toxic effects of apigenin and the nanodrug improved with increasing concentrations and exposure durations compared to those in the control.The toxic effect of apigenin loaded into the stearate-chitosan nanogel was greater than apigenin, and the toxic effects of both materials were greater compared to the control under laboratory conditions.

Role of Plant-Derived Flavonoids and Their Mechanism in Attenuation of Alzheimer's and Parkinson's Diseases: An Update of Recent Data

Neurodegeneration is a progressive loss of neuronal cells in certain regions of the brain. Most of the neurodegenerative disorders (NDDs) share the communal characteristic such as damage or reduction of various cell types typically including astrocytes and microglial activity. Several compounds are being trialed to treat NDDs but they possess solitary symptomatic advantages along with copious side effects. The finding of more enthralling and captivating compounds to suspend and standstill the pathology of NDDs will be considered as a hallmark of present times. Phytochemicals possess the potential to alternate the synthetic line of therapy against NDDs. The present review explores the potential efficacy of plant-derived flavonoids against most common NDDs including Alzheimer's disease (AD) and Parkinson's disease (PD). Flavonoids are biologically active phytochemicals which possess potential pharmacological effects, including antiviral, anti-allergic, antiplatelet, anti-inflammatory, anti-tumor, anti-apoptotic and anti-oxidant effects and are able to attenuate the pathology of various NDDs through down-regulating the nitric oxide (NO) production, by reducing the tumor necrosis factor-α (TNF-α), by reducing the excitotoxicity of superoxide as well as acting as tyrosine kinase (TK) and monoamine oxidase (MAO) inhibiting enzyme.

Biosynthesis of flavone C-glucosides in engineered Escherichia coli

Two plant-originated C-glucosyltransferases (CGTs) UGT708D1 from Glycine max and GtUF6CGT1 from Gentiana triflora were accessed for glucosylation of selected flavones chrysin and luteolin. Uridine diphosphate (UDP)-glucose pool was enhanced in Escherichia coli cell cytosol by introducing heterologous UDP-glucose biosynthetic genes, i.e., glucokinase (glk), phosphoglucomutase (pgm2), and glucose 1-phosphate uridylyltransferase (galU), along with glucose facilitator diffusion protein from (glf) from different organisms, in a multi-monocistronic vector with individual T7 promoter, ribosome binding site, and terminator for each gene. The C-glucosylated products were analyzed by high-performance liquid chromatography-photodiode array, high-resolution quadruple time-of-flight electrospray ionization mass spectrometry, and one-dimensional nuclear magnetic resonance analyses. Fed-batch shake flask culture showed 8% (7 mg/L; 16 μM) and 11% (9 mg/L; 22 μM) conversion of chrysin to chrysin 6-C-β-D-glucoside with UGT708D1 and GtUF6CGT1, respectively. Moreover, the bioengineered E. coli strains with exogenous UDP-glucose biosynthetic genes and glucose facilitator diffusion protein enhanced the production of chrysin 6-C-β-D-glucoside by approximately 1.4-fold, thus producing 10 mg/L (12%, 24 μM) and 14 mg/L (17%, 34 μM) by UGT708D1 and GtUF6CGT1, respectively, without supplementation of additional UDP-glucose in the medium. The biotransformation was further elevated when the bioengineered strain was scaled up in lab-scale fermentor at 3 L volume. HPLC analysis of fermentation broth extract revealed 50% (42 mg/L, 100 μM) conversion of chrysin to chrysin 6-C-β-D-glucoside at 48 h upon supplementation of 200 μM of chrysin. The maximum conversion of luteolin was 38% (34 mg/L, 76 μM) in 50-mL shake flask fermentation at 48 h. C-glucosylated derivative of chrysin was found to be more soluble and more stable to high temperature, different pH range, and β-glucosidase enzyme, than O-glucosylated derivative of chrysin.

Engineering co-culture system for production of apigetrin in Escherichia coli

Microbial cells have extensively been utilized to produce value-added bioactive compounds. Based on advancement in protein engineering, DNA recombinant technology, genome engineering, and metabolic remodeling, the microbes can be re-engineered to produce industrially and medicinally important platform chemicals. The emergence of co-culture system which reduces the metabolic burden and allows parallel optimization of the engineered pathway in a modular fashion restricting the formation of undesired byproducts has become an alternative way to synthesize and produce bioactive compounds. In this study, we present genetically engineered E. coli-based co-culture system to the de novo synthesis of apigetrin (APG), an apigenin-7-O-β-D-glucopyranoside of apigenin. The culture system consists of an upstream module including 4-coumarate: CoA ligase (4CL), chalcone synthase, chalcone flavanone isomerase (CHS, CHI), and flavone synthase I (FNSI) to synthesize apigenin (API) from p-coumaric acid (PCA). Whereas, the downstream system contains a metabolizing module to enhance the production of UDP-glucose and expression of glycosyltransferase (PaGT3) to convert API into APG. To accomplish this improvement in titer, the initial inoculum ratio of strains for making the co-culture system, temperature, and media component was optimized. Following large-scale production, a yield of 38.5 µM (16.6 mg/L) of APG was achieved. In overall, this study provided an efficient tool to synthesize bioactive compounds in microbial cells.

Glycosylation of 6-methylflavone by the strain Isaria fumosorosea KCH J2

Entomopathogenic fungi are known for their ability to carry out glycosylation of flavonoids, which usually results in the improvement of their stability and bioavailability. In this study we used a newly isolated strain of the entomopathogenic filamentous fungus Isaria fumosorosea KCH J2 as a biocatalyst. Our aim was to evaluate its ability to carry out the biotransformation of flavonoids and to obtain new flavonoid derivatives. The fungus was isolated from a spider's carcass and molecularly identified using analysis of the ITS1-ITS2 rDNA sequence. As a result of biotransformation of 6-methylflavone two new products were obtained: 6-methylflavone 8-O-β-D-(4"-O-methyl)-glucopyranoside and 6-methylflavone 4'-O-β-D-(4"-O-methyl)-glucopyranoside. Chemical structures of the products were determined based on spectroscopic methods (1H NMR, 13C NMR, COSY, HMBC, HSQC). Our research allowed us to discover a new species of filamentous fungus capable of carrying out glycosylation reactions and proved that I. fumosorosea KCH J2 is an effective biocatalyst for glycosylation of flavonoid compounds. For the first time we describe biotransformations of 6-methylflavone and the attachment of the sugar unit to the flavonoid substrate having no hydroxyl group. The possibility of using flavonoid aglycones is often limited by their low bioavailability due to poor solubility in water. The incorporation of a sugar unit improves the physical properties of tested compounds and thus increases the chance of using them as pharmaceuticals.

Enzymatic biosynthesis of novel neobavaisoflavone glucosides via Bacillus UDP-glycosyltransferase

The present study was designed to perform structural modifications of of neobavaisoflavone (NBIF), using an in vitro enzymatic glycosylation reaction, in order to improve its water-solubility. Two novel glucosides of NBIF were obtained from an enzymatic glycosylation by UDP-glycosyltransferase. The glycosylated products were elucidated by LC-MS, HR-ESI-MS, and NMR analysis. The HPLC peaks were integrated and the concentrations in sample solutions were calculated. The MTT assay was used to detect the cytotoxic activity of compounds in cancer cell lines. Based on the spectroscopic analyses, the two novel glucosides were identified as neobavaisoflavone-4'-O-β-D-glucopyranoside (1) and neobavaisoflavone-4', 7-di-O-β-D-glucopyranoside (2). Additionally, the water-solubilities of compounds 1 and 2 were approximately 175.1- and 4 031.9-fold higher than that of the substrate, respectively. Among the test compounds, only NBIF exhibited weak cytotoxicity against four human cancer cell lines, with IC₅₀ values ranging from 63.47 to 72.81 µmol·L^-1. These results suggest that in vitro enzymatic glycosylation is a powerful approach to structural modification, improving water-solubility.

Synthesis of umbelliferone derivatives in Escherichia coli and their biological activities

BACKGROUND

Umbelliferone, also known as 7-hydroxycoumarin, is a phenolic metabolite found in many familiar plants. Its derivatives have been shown to have various pharmacological and chemo-preventive effects on human health. A uridine diphosphate glycosyltransferase YjiC from Bacillus licheniformis DSM 13, a cytochrome P450BM3 (CYP450 BM3) variant namely mutant 13 (M13) from Bacillus megaterium, and an O-methyltransferase from Streptomyces avermitilis (SaOMT2) were used for modifications of umbelliferone.

RESULTS

Three umbelliferone derivatives (esculetin, skimmin, and herniarin) were generated through enzymatic and whole cell catalysis. To improve the efficiencies of biotransformation, different media, incubation time and concentration of substrate were optimized and the production was scaled up using a 3-L fermentor. The maximum yields of esculetin, skimmin, and herniarin were 337.10 μM (67.62%), 995.43 μM (99.54%), and 37.13 μM (37.13%), respectively. The water solubility of esculetin and skimmin were 1.28-folds and 3.98-folds as high as umbelliferone, respectively, whereas herniarin was 1.89-folds less soluble than umbelliferone. Moreover, the antibacterial and anticancer activities of herniarin showed higher than umbelliferone, esculetin and skimmin.

CONCLUSIONS

This study proves that both native and engineered enzymes could be employed for the production of precious compounds via whole cell biocatalysis. We successfully produced three molecules herniarin, esculetin and skimmin in practical amounts and their antibacterial and anticancer properties were accessed. One of the newly synthesized molecules the present research suggests that the combinatorial biosynthesis of different biosynthetic enzymes could rapidly promote to a novel secondary metabolite.

Genome-wide identification and characterization of macrolide glycosyltransferases from a marine-derived Bacillus strain and their phylogenetic distribution

Clarifying glycosyltrasferases (GTs) function is of significance for the development of GT inhibitors as drugs, and the use of GTs to glycodiversify small molecules in the search of drug leads. While many Actinomyces natural-product GTs had been functionally characterized, our understanding towards Bacillus natural-product GTs is so far very limited. Herein, genome-wide identification of macrolide GT genes from marine-derived Bacillus methylotrophicus B-9987 revealed the presence of three macrolide GT genes bmmGT1-3. While bmmGT1 was previously revealed to be involved in the biosynthesis of trans-acyltransferase (AT) polyketides compounds macrolactins (MLNs) and bacillaenes (BAEs), the functions of bmmGT2 and bmmGT3 were probed, demonstrating that they are capable to biochemically catalyze glycosylation of MLNs and BAEs as well but interestingly with different regioselectivity, affording four new MLNs analogs. Notably, further genome mining revealed that the orthologs of these three macrolide GT genes showed a regular distribution in the subtilis- and the cereus-clade Bacillus strains; interestingly, bmmGT1 orthologs only occurred in the subtilis-clade Bacillus, and they were also found in the genomes of Streptomyces strains, suggesting their close phylogenetic relationship. These results provide the first significant insight into the important roles of Bacillus macrolide GTs in the biology of the species.

Recent developments in the enzymatic O-glycosylation of flavonoids

The glycosylation of bioactive compounds, such as flavonoids, is of particular relevance, as it modulates many of their pharmacokinetic parameters. This article reviews the literature between 2010 and the end of 2015 that deals with the enzymatic O-glycosylation of this class of compounds. Enzymes of glycosyltransferase family 1 remain the biocatalysts of choice for glycodiversification of flavonoids, in spite of relatively low yields. Transfers of 14 different sugars, in addition to glucose, were reported. Several Escherichia coli strains were metabolically engineered to enable a (more efficient) synthesis of the required donor during in vivo glycosylations. For the transfer of glucose, enzymes of glycoside hydrolase families 13 and 70 were successfully assayed with several flavonoids. The number of acceptor substrates and of regiospecificities characterized so far is smaller than for glycosyltransferases. However, their glycosyl donors are much cheaper and yields are considerably higher. A few success stories of enzyme engineering were reported. These improved the catalytic efficiency as well as donor, acceptor, or product ranges. Currently, the development of appropriate high-throughput screening systems appears to be the major bottleneck for this powerful technology.