N-containing sugars from Morus alba and their glycosidase inhibitory activities

Expression of Recombinant Human α-Glucosidase in HEK293 Cells

In mammals, intestinal α-glucosidase exists as a maltase-glucoamylase complex (MGAM) and a sucrase-isomaltase complex (SI). In this study, we transiently expressed human MGAM and SI in human embryonic kidney 293 (HEK293) cells. At pH 6.0 and 37 °C, the MGAM-expressing HEK293 cells extract (MGE) exhibited maltase, glucoamylase, and isomaltase activities but not sucrase activity, whereas the SI-expressing HEK293 cells extract (SIE) exhibited sucrase, isomaltase, and maltase activities but not glucoamylase activity. The apparent Km value of the MGE for maltose hydrolysis was 14-26% of that of the SIE for maltose, sucrose, and isomaltose hydrolysis. The respective apparent Vmax values of the MGE and SIE for sucrose and isomaltose hydrolysis were 0% and 6% and 10% and 42% of those for maltose hydrolysis. These results indicated that the maltase activities of MGAM and SI were higher than those of sucrase and isomaltase.

Effect of Powdered Morus australis Leaves on Arterial Stiffness Response after Sucrose Ingestion in Healthy Young Men: A Pilot Study

Acute arterial stiffening occurs during postprandial hyperglycemia. Such vascular responses are suggested to be averted by suppressing the postprandial glycemic response. We previously developed an α-glucosidase-inhibiting tea powder from the leaves of Morus australis (M. australis), a mulberry species distributed in the Ryukyu Islands, and demonstrated that this powder has an inhibitory effect on blood glucose elevation after sucrose ingestion. This study aimed to investigate the effect of powdered M. australis leaf intake on the arterial stiffness response after sucrose ingestion. In a randomized crossover design, 12 healthy young men completed two trials: with (mulberry [M] trial) and without (control [C] trial) intake of powdered M. australis leaves before ingestion of 75 g of sucrose. Blood glucose levels and brachial-ankle pulse wave velocity (baPWV), an index of systemic arterial stiffness, were measured at baseline and 30, 60, and 120 min after ingestion. Both trials caused a significant increase in blood glucose levels at 30 and 60 min after ingestion, with significantly lower values at 30 min after ingestion in the M trial than in the C trial. baPWV significantly increased at 60 min after ingestion in the C trial, but not in the M trial. These findings demonstrate that prior ingestion of powdered M. australis leaves can prevent the transient arterial stiffening after sucrose ingestion in healthy young men.

Efficient synthesis for each of the eight stereoisomers of the iminosugars lentiginosine and 1,4-dideoxy-1,4-imino-D-arabinitol (DAB)

Herein, we describe the efficient, diastereoselective syntheses of the iminosugars 1,4-dideoxy-1,4-imino-D-arabinitol (DAB) 1b, lentiginosine 3a, and the seven stereoisomers of each of these iminosugars starting from 4-benzoyl-6-deoxy-6-iodoglycopyranosides 47 with yields ranging from 38 % to 68 % for the DAB and isomers 1a-1h and from 44 % to 89 % for the lentiginosine and isomers 3a-3h. We also report the syntheses of the eight stereoisomers of the 4-benzoyl-6-deoxy-6-iodoglycopyranosides 47 from commercially available sugars. Key to the iminosugar syntheses is a single multistep reaction that converts the 4-benzoyl-6-deoxy-6-iodoglycopyranosides 47 to a vinyl pyrrolidine through a one-pot zinc mediated reductive elimination, followed by a reductive amination and finally an intramolecular nucleophilic substitution. Strategic selection of the amine utilized in the reductive amination and the functionalization of the intermediate carbon-carbon double bond provides access to a vast array of iminosugars.

Structures, activities, and putative biosynthetic pathways of characteristic polyphenolic compounds from Morus plants: A review

Morus plants played a pivotal role in ancient Chinese sericulture and silk production, which served as critical components of economy and culture. Besides, many parts of mulberry trees, including roots, leaves, stems, and fruits, hold various medicinal value, and have been utilized in traditional medicine for thousands of years. The chemical composition of mulberry has been reported in many literatures, while the characteristic compounds have not been systematically summarized. In this review, we focused on the polyphenolic compounds in mulberry, including flavonoids, 2-arylbenzofurans, and Diels-Alder (D-A) adducts, and summarized their structural features, structure-activity relationships, and potential biosynthetic pathways. The results revealed a characteristic class of 2'-hydroxylated flavonoids and stilbenes which played an important role in the biosynthesis of downstream 2-arylbenzofurans and D-A adducts in mulberry but had been overlooked by most studies. The prenylated modifications of different compounds were also discussed and their function as precursors of D-A adducts was emphasized. We also describe the effects of different modifications on biological activities. Besides, the chemical composition of Morus was most similar to that of Artocarpus in the Moraceae family in that they had almost identical characteristic compounds. Finally, a putative total biosynthetic pathway of D-A adducts in mulberry was proposed based on structure derivation and combination of verified reactions. This review contributes to the understanding of the biological activity and biosynthesis of the characteristic components of Morus plants.

Use of human Caco-2 cells and HPAE-PAD for α-glucosidase assay

To measure α-glucosidase activity, rat intestinal acetone powder is commonly used as a source of α-glucosidase, and the mutarotase-glucose oxidase (GOD) methods commonly used to quantitate glucose produced by enzymatic hydrolysis of the substrates. In this study, we compared human Caco-2 cell extracts with rat intestinal acetone powder extracts. We also compared high-performance anion-exchange chromatography with pulsed amperometric detection (HPAE-PAD) with the mutarotase-GOD method. The sensitivity of HPAE-PAD was higher than that of mutarotase-GOD. The glucose concentration quantified by HPAE-PAD was similar to that quantified using the mutarotase-GOD method. In the maltase reaction, 1-deoxynojirimycin (1-DNJ) exerted a more potent inhibitory effect on human enzymes than on rat enzymes. This order was reversed during the sucrase reaction. These results suggested that the combined use of Caco-2 cell extracts and HPAE-PAD is advantageous for use in α-glucosidase-related basic research.

Biosynthetic pathways and related genes regulation of bioactive ingredients in mulberry leaves

Mulberry leaves are served not only as fodder for silkworms but also as potential functional food, exhibiting nutritional and medical benefits due to the complex and diverse constituents, including alkaloids, flavonoids, phenolic acids, and benzofurans, which possess a wide range of biological activities, such as anti-diabete, anti-oxidant, anti-inflammatory, and so on. Nevertheless, compared with the well-studied phytochemistry and pharmacology of mulberry leaves, the current understanding of the biosynthesis mechanisms and regulatory mechanisms of active ingredients in mulberry leaves remain unclear. Natural resources of these active ingredients are limited owing to their low contents in mulberry leaves tissues and the long growth cycle of mulberry. Biosynthesis is emerging as an alternative means for accumulation of the desired high-value compounds, which can broaden channels for their large-scale green productions. Therefore, this review summarizes the recent research advance on the correlative key genes, enzyme biocatalytic reactions and biosynthetic pathways of valuable natural ingredients (i.e. alkaloids, flavonoids, phenolic acids, and benzofurans) in mulberry leaves, thereby offering important insights for their further biomanufacturing.

Effects and Mechanistic Role of Mulberry Leaves in Treating Diabetes and its Complications

Diabetes mellitus (DM) has become a surge burden worldwide owing to its high prevalence and range of associated complications such as coronary artery disease, blindness, stroke, and renal failure. Accordingly, the treatment and management of DM have become a research hotspot. Mulberry leaves (Morus alba L.) have been used in Traditional Chinese Medicine for a long time, with the first record of its use published in Shennong Bencao Jing (Shennong's Classic of Materia Medica). Mulberry leaves (MLs) are considered highly valuable medicinal food homologs that contain polysaccharides, flavonoids, alkaloids, and other bioactive substances. Modern pharmacological studies have shown that MLs have multiple bioactive effects, including hypolipidemic, hypoglycemic, antioxidation, and anti-inflammatory properties, with the ability to protect islet [Formula: see text]-cells, alleviate insulin resistance, and regulate intestinal flora. However, the pharmacological mechanisms of MLs in DM have not been fully elucidated. In this review, we summarize the botanical characterization, traditional use, chemical constituents, pharmacokinetics, and toxicology of MLs, and highlight the mechanisms involved in treating DM and its complications. This review can provide a valuable reference for the further development and utilization of MLs in the prevention and treatment of DM.

Evaluation of mulberry leaves’ hypoglycemic properties and hypoglycemic mechanisms

The effectiveness of herbal medicine in treating diabetes has grown in recent years, but the precise mechanism by which it does so is still unclear to both medical professionals and diabetics. In traditional Chinese medicine, mulberry leaf is used to treat inflammation, colds, and antiviral illnesses. Mulberry leaves are one of the herbs with many medicinal applications, and as mulberry leaf study grows, there is mounting evidence that these leaves also have potent anti-diabetic properties. The direct role of mulberry leaf as a natural remedy in the treatment of diabetes has been proven in several studies and clinical trials. However, because mulberry leaf is a more potent remedy for diabetes, a deeper understanding of how it works is required. The bioactive compounds flavonoids, alkaloids, polysaccharides, polyphenols, volatile oils, sterols, amino acids, and a variety of inorganic trace elements and vitamins, among others, have been found to be abundant in mulberry leaves. Among these compounds, flavonoids, alkaloids, polysaccharides, and polyphenols have a stronger link to diabetes. Of course, trace minerals and vitamins also contribute to blood sugar regulation. Inhibiting alpha glucosidase activity in the intestine, regulating lipid metabolism in the body, protecting pancreatic -cells, lowering insulin resistance, accelerating glucose uptake by target tissues, and improving oxidative stress levels in the body are some of the main therapeutic properties mentioned above. These mechanisms can effectively regulate blood glucose levels. The therapeutic effects of the bioactive compounds found in mulberry leaves on diabetes mellitus and their associated molecular mechanisms are the main topics of this paper’s overview of the state of the art in mulberry leaf research for the treatment of diabetes mellitus.

Combined Intake of Fish Oil and D-Fagomine Prevents High-Fat High-Sucrose Diet-Induced Prediabetes by Modulating Lipotoxicity and Protein Carbonylation in the Kidney

Obesity has been recognized as a major risk factor for chronic kidney disease, insulin resistance being an early common metabolic feature in patients suffering from this syndrome. This study aims to investigate the mechanism underlying the induction of kidney dysfunction and the concomitant onset of insulin resistance by long-term high-fat and sucrose diet feeding in Sprague Dawley rats. To achieve this goal, our study analyzed renal carbonylated protein patterns, ectopic lipid accumulation and fatty acid profiles and correlated them with biometrical and biochemical measurements and other body redox status parameters. Rats fed the obesogenic diet developed a prediabetic state and incipient kidney dysfunction manifested in increased plasma urea concentration and superior levels of renal fat deposition and protein carbonylation. An obesogenic diet increased renal fat by preferentially promoting the accumulation of saturated fat, arachidonic, and docosahexaenoic fatty acids while decreasing oleic acid. Renal lipotoxicity was accompanied by selectively higher carbonylation of proteins involved in the blood pH regulation, i.e., bicarbonate reclamation and synthesis, amino acid, and glucose metabolisms, directly related to the onset of insulin resistance. This study also tested the combination of antioxidant properties of fish oil with the anti-diabetic properties of buckwheat D-Fagomine to counteract diet-induced renal alterations. Results demonstrated that bioactive compounds combined attenuated lipotoxicity, induced more favorable lipid profiles and counteracted the excessive carbonylation of proteins associated with pH regulation in the kidneys, resulting in an inhibition of the progression of the prediabetes state and kidney disease.

Stable D-xylose ditriflate in divergent syntheses of dihydroxy prolines, pyrrolidines, tetrahydrofuran-2-carboxylic acids, and cyclic β-amino acids

Double nucleophilic displacement of D-xylo-ditriflate by amines, water and alkyl cyanoacetates, respectively, gave a series of bicyclic divergent intermediates for the synthesis of a wide range of highly functionalized targets, including hydroxylated prolines, pyrrolidines, furanoic acids, and cyclopentanes.

Metabolic Fate and Expectation of Health Benefits of [U-14C]-Sucrose Inhibited from Digestion Using Morus alba Leaf Extract

Morus alba leaf extract (MLE), a strong inhibitor of sucrase, suppresses blood glucose elevation following sucrose ingestion. To investigate that sucrose inhibited from digestion using MLE is utilized through gut microbiota, [U-¹⁴C]-sucrose solutions with or without MLE were administered orally to conventional and antibiotic-treated rats, and the excretion of ¹⁴CO₂ and H₂ produced by gut microbiota was measured for 24 h. After an administration of [U-¹⁴C]-sucrose to conventional rats, the unit excreted ¹⁴CO₂ peaked at 4 h, and the cumulative ¹⁴CO₂ excreted over 24 h was approximately 60% of the radioactivity administered. No H₂ was excreted. Following an administration of [U-¹⁴C]-sucrose and MLE in conventional rats, the unit excreted ¹⁴CO₂ peaked later, at 8 h, and was significantly lower (p<0.05). The cumulative ¹⁴CO₂ excreted over 24 h was equal in both groups, although there was a time lag of 2-3 h in rats given [U-¹⁴C]-sucrose and MLE. The amount of H₂ excreted by these rats peaked 8 h after administration. Following the administration of [U-¹⁴C]-sucrose and MLE to antibiotic-treated rats, the unit excreted ¹⁴CO₂ peaked lower, and the cumulative ¹⁴CO₂ excretion over 24 h was approximately 40%. In this group, H₂ was minimally excreted. H₂ and ¹⁴CO₂ produced by gut microbiota were excreted simultaneously. In conclusion, sucrose inhibited from digestion using MLE was fermented spontaneously by gut microbiota and was not excreted into feces. In addition, it confirmed that H₂ excretion could be used directly to indicate the degree of fermentation of nondigestible carbohydrates.

The chemistry and biology of natural ribomimetics and related compounds

Natural ribomimetics represent an important group of specialized metabolites with significant biological activities. Many of the activities, e.g., inhibition of seryl-tRNA synthetases, glycosidases, or ribosomes, are manifestations of their structural resemblance to ribose or related sugars, which play roles in the structural, physiological, and/or reproductive functions of living organisms. Recent studies on the biosynthesis and biological activities of some natural ribomimetics have expanded our understanding on how they are made in nature and why they have great potential as pharmaceutically relevant products. This review article highlights the discovery, biological activities, biosynthesis, and development of this intriguing class of natural products.

Calystegines Improve the Metabolic Activity of Human Adipose Derived Stromal Stem Cells (ASCs) under Hyperglycaemic Condition through the Reduction of Oxidative/ER Stress, Inflammation, and the Promotion of the AKT/PI3K/mTOR Pathway

Hyperglycaemia and its resulting glucotoxicity are among the most prominent hallmarks of diabetes mellitus (DM) development. Persistent hyperglycaemia further leads to oxidative stress via mitochondrial dysfunction and subsequent ER stress onset, while associated hyperlipidaemia triggers the adipose tissue to secrete pro-inflammatory cytokines. In this study, the effect of calystegines has been investigated in an experimental model of hyperglycaemia induced on human ASCs cells. Different cellular pathways including apoptosis, oxidative and ER stress, inflammation as well as Pi3K/AKT/mTOR metabolic-associated axis have been evaluated by means on RT-qPCR, western blot, and flow cytometry techniques. Treatment of HuASCs cells with calystegines strongly promoted the hyperglycaemic cells survival and significantly diminished oxidative stress, mitochondrial dynamics failure and ER stress, while improving the endogenous cellular antioxidant defenses. Interestingly, nortropane alkaloids efficiently prevented the hyperglycaemia-mediated inflammatory response, as evidenced by the regulation of the pro- and anti-inflammatory response in HuASCs cells. Finally, we evidenced that calystegines may exert their protective effect on HuASCs cells metabolic functions through the restoration of the defective PI3K/AKT/mTOR pathway. Overall, the present investigation demonstrated that calystegines possess important abilities to protect HuASCs against hyperglycaemia-induced cellular dysfunction, and it evidenced that the observed effects are associated to the promotion of PI3K/AKT/mTOR pathway.

Evaluation and development of a novel pre-treatment method for mulberry leaves to enhance their bioactivity via enzymatic degradation of GAL-DNJ to DNJ

Mulberry leaves are rich in 1-deoxynojirimycin (DNJ) and 2-O-α-D-galactopyranosyl-deoxynojirimycin (GAL-DNJ). Compared to DNJ, the bioactive potency of GAL-DNJ is low. We proposed that the conversion of GAL-DNJ into DNJ may improve its bioavailability. We evaluated this hypothesis and constructed a novel enzymatic-based method to induce the hydrolysis of GAL-DNJ to DNJ in order to improve the therapeutic potency of mulberry leaves.

Cyclisations and Strategies for Stereoselective Synthesis of Piperidine Iminosugars

This personal account focuses on synthesis of polyhydroxylated piperidines, a subset of compounds within the iminosugar family. Cyclisations to form the piperidine ring include reductive amination, substitution via amines, iminium ions and cyclic nitrones, transamidification (N-acyl transfer), addition to alkenes, ring contraction and expansion, photoinduced electron transfer, multicomponent Ugi reaction and ring closing metathesis. Enantiomerically pure piperidines are obtained from chiral pool precursors (e. g. sugars, amino acids, Garner's aldehyde) or asymmetric reactions (e. g. epoxidation, dihydroxylation, aminohydroxylation, aldol, biotransformation). Our laboratory have contributed cascades based on reductive amination from glycosyl azide precursors as well as Huisgen azide-alkene cycloaddition. The latter's combination with allylic azide rearrangement has given substituted piperidines, including those with quaternary centres adjacent to nitrogen.

Determination of 1-Deoxynojirimycin (1-DNJ) in Leaves of Italian or Italy-Adapted Cultivars of Mulberry (Morus sp.pl.) by HPLC-MS

Recently, 1-DNJ has been widely studied by scientists for its capacity to inhibit α-glucosidase and reduce postprandial blood glucose and fat accumulation. To the best of our knowledge, this is the first analytical determination of 1-DNJ in Morus sp.pl. leaves carried out on Italian crops, and it could be used as a reference to assess the quality of the plant material in comparison to Far Eastern Asia cultivations. The effects of two thermal treatments were compared to test the incidence of the drying process on the 1-DNJ extractability. In addition, two harvesting seasons in the same year (2017) and two subsequent harvesting years (2017-2018) were considered. The amount of 1-DNJ herein found was comparable to that reported in the scientific literature for Asian cultivations. The increase in 1-DNJ along the summer and the higher level of this compound in the apical leaves also complies with previous findings. However, a strong implication for the climatic conditions in the different years and a significant interaction between climate and genotypes suggest exploring very carefully the agronomic practices and selecting cultivars according to different environmental conditions with a view to standardize the 1-DNJ amount in leaves.

Inhibitory effect of Morus australis leaf extract and its component iminosugars on intestinal carbohydrate-digesting enzymes

α-Amylase and α-glucosidase are central enzymes involved in the digestion of carbohydrates. α-Glucosidase includes maltase-glucoamylase and sucrase-isomaltase. We have previously performed the kinetic analysis of the inhibitory effects of powdered or roasted Morus australis leaf extract and its component iminosugars, such as 1-deoxynojirimycin (1-DNJ), fagomine, and 2-O-α-d-galactopyranosyl deoxynojirimycin (GAL-DNJ) on the activity of maltase. In this study, we analyzed the inhibitory effects of the aforementioned compounds against α-amylase, glucoamylase, sucrase, and isomaltase. At pH 6.0 and 37 °C, each leaf extract sample inhibited glucoamylase, sucrase, and isomaltase but not α-amylase. 1-DNJ and fagomine showed weak α-amylase inhibitory activity while GAL-DNJ exhibited none. 1-DNJ showed a strong glucoamylase, sucrase, and isomaltase inhibitory potential. The inhibitory potential against these three enzymes was 18-500 and 1500-3000-fold higher in the case of 1-DNJ than that observed in the case of fagomine and GAL-DNJ, respectively. We also observed that the indigestible dextrin could considerably inhibit α-amylase. When the powdered M. australis leaf extract was blended with indigestible dextrin, the mixture inhibited α-amylase, as well as maltase, glucoamylase, sucrase, and isomaltase. These results suggest that the ingestion of the leaf extract blended with indigestible dextrin might have the potential to efficiently suppress the postprandial blood glucose level increase.

Kinetic analysis of inhibition of α-glucosidase by leaf powder from Morus australis and its component iminosugars

Abbreviations

1-DNJ: 1-deoxynojirimycin; GAL-DNJ: 2-O-α-D-galactopyranosyl-DNJ

Design and synthesis of 4,5-diphenyl-imidazol-1,2,3-triazole hybrids as new anti-diabetic agents: in vitro α-glucosidase inhibition, kinetic and docking studies

Fourteen novel 4,5-diphenyl-imidazol-1,2,3-triazole hybrids 8a-n were synthesized with good yields by performing click reaction between the 4,5-diphenyl-2-(prop-2-yn-1-ylthio)-1H-imidazole and various benzyl azides. The synthesized compounds 8a-n were evaluated against yeast α-glucosidase, and all these compounds exhibited excellent inhibitory activity (IC₅₀ values in the range of 85.6 ± 0.4-231.4 ± 1.0 μM), even much more potent than standard drug acarbose (IC₅₀ = 750.0 μM). Among them, 4,5-diphenyl-imidazol-1,2,3-triazoles possessing 2-chloro and 2-bromo-benzyl moieties (compounds 8g and 8i) demonstrated the most potent inhibitory activities toward α-glucosidase. The kinetic study of the compound 8g revealed that this compound inhibited α-glucosidase in a competitive mode. Furthermore, docking calculations of these compounds were performed to predict the interaction mode of the synthesized compounds in the active site of α-glucosidase. A novel series of 4,5-diphenyl-imidazol-1,2,3-triazole hybrids 8a-n was synthesized with good yields by performing click reaction between the 4,5-diphenyl-2-(prop-2-yn-1-ylthio)-1Himidazole and various benzyl azides. The synthesized compounds 8a-n were evaluated against yeast α-glucosidase and all these compounds exhibited excellent inhibitory activity (IC50 values in the range of 85.6 ± 0.4-231.4 ± 1.0 μM), even much more potent than standard drug acarbose (IC50 = 750.0 μM).

Anti-diabetic potential of plant alkaloids: Revisiting current findings and future perspectives

Diabetes mellitus (DM) is a chronic metabolic disease which causes millions of death all over the world each year, and its incidence is on increase. The most prevalent form, type 2 DM, is characterized by insulin resistance and β-cell dysfunction, whereas type 1 DM is due to insulin deficiency as a result of β-cell destruction. Various classes of synthetic drugs have been developed to regulate glucose homeostasis and combat the development of late-diabetic complications. However, several of these chemical agents are either sub-optimal in their effect and/or may have side effects. Biologically, alkaloids unveiled a wide range of therapeutic effects including anti-diabetic properties. The chemical backbones of these compounds have the potential to interact with a wide range of proteins involved in glucose homeostasis, and thus they have received increasing attention as reliable candidates for drug development. This review sets out to investigate the anti-diabetic potential of plant alkaloids (PAs), and therefore, scientific databases were comprehensively screened to highlight the biological activity of 78 PAs with a considerable anti-diabetic profile. There are not enough clinical data available for these phytochemicals to follow their fingerprint in human, but current studies generally recommending PAs as potent α-glucosidase inhibitors. Except for some classes of monoterpene alkaloids, other compounds showed similar features as well as the presently available anti-diabetic drugs such as amino sugars and other relevant drugs. Moreover, the evidence suggests that PAs have the potential to be used as alternative additives for the treatment of DM, however, further in vitro and in vivo studies are needed to validate these findings.

Functional Analysis of a Gene Cluster from Chitinophaga pinensis Involved in Biosynthesis of the Pyrrolidine Azasugar DAB-1

Azasugars, "nitrogen in the ring" analogues of monosaccharides, are known to be distributed in select plant, fungal. and bacterial species. We identify Chitinophaga pinensis DSM 2588 as the first bacterial source of the plant pyrrolidine azasugar 1,4-dideoxy-1,4-aminoarabinitol (DAB-1). Comparative sequence analyses identified C. pinensis as a putative azasugar producer, via observation of a three-gene cluster coding for putative aminotransferase, alcohol dehydrogenase, and sugar phosphatase enzymes, similar to the previously reported azasugar biosynthetic signature identified in Bacillus amyloliquefaciens FZB42. Multistep fractionation of C. pinensis culture media guided by a maltase inhibition assay yielded a component with a mass consistent with the structure of DAB-1. Heterologous expression of the three-gene cluster in E. coli, a non-azasugar producer, led to the isolation of nectrisine, a biosynthetic precursor to DAB-1, which displayed potent slow tight binding inhibition of maltase. Reduction of nectrisine with NaBH₄ removed the slow tight binding inhibition kinetics, and MS analysis provided evidence for the production of a compound matching that of the isolated DAB-1 from C. pinensis. ¹H NMR analysis of the nectrisine produced in E. coli after NaBD₄ reduction produced a spectrum consistent with DAB-1 deuterated at C-1, primarily at the pro-S position. These results support the idea that the azasugar three-gene cluster represents a general biosynthetic path leading to several different compounds, which may prove useful for the identification of other azasugar-producing organisms.

Identification of Bioactive Phytochemicals in Mulberries

Mulberries are consumed either freshly or as processed fruits and are traditionally used to tackle several diseases, especially type II diabetes. Here, we investigated the metabolite compositions of ripe fruits of both white (Morus alba) and black (Morus nigra) mulberries, using reversed-phase HPLC coupled to high resolution mass spectrometry (LC-MS), and related these to their in vitro antioxidant and α-glucosidase inhibitory activities. Based on accurate masses, fragmentation data, UV/Vis light absorbance spectra and retention times, 35 metabolites, mainly comprising phenolic compounds and amino sugar acids, were identified. While the antioxidant activity was highest in M. nigra, the α-glucosidase inhibitory activities were similar between species. Both bioactivities were mostly resistant to in vitro gastrointestinal digestion. To identify the bioactive compounds, we combined LC-MS with 96-well-format fractionation followed by testing the individual fractions for α-glucosidase inhibition, while compounds responsible for the antioxidant activity were identified using HPLC with an online antioxidant detection system. We thus determined iminosugars and phenolic compounds in both M. alba and M. nigra, and anthocyanins in M. nigra as being the key α-glucosidase inhibitors, while anthocyanins in M. nigra and both phenylpropanoids and flavonols in M. alba were identified as key antioxidants in their ripe berries.

Nutraceutical Properties of Mulberries Grown in Southern Italy (Apulia)

In this work, for the first time, were analyzed mulberry genotypes grown in Apulia (Southern Italy, Salento region) were analyzed. Two local varieties of Morus alba (cv. Legittimo nero and cv. Nello) and one of Morus nigra were characterized for content in simple sugars, organic acids, phenols, anthocyanins; fruit antioxidant activity (AA) was also evaluated by three different methods (2,2-Diphenyl-1-picrylhydrazyl, DPPH; 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid), ABTS; and Ferric reducing antioxidant potential, FRAP test). The results showed that the sugars amount ranged between 6.29 and 7.66 g/100 g fresh weight (FW) while the malic and citric acids content was low, at about 0.1–1 g/100 g FW. Mulberries are a good source of phenols which are present in higher values in M. nigra and M. alba cv. Legittimo nero (485 and 424 mg Gallic Acid Equivalent (GAE)/ 100 g FW, respectively). The high performance liquid chromatography/diode array detector/mass spectrometry (HPLC/DAD/MS) analysis identified 5 main anthocyanin compounds present in different concentrations in each variety of mulberry: cyanidin 3-sophoroside, cyanidin 3-glucoside, cyanidin 3-rutinoside, pelargonidin 3-glucoside, pelargonidin 3-rutinoside. The highest concentration of anthocyanins was determined in Morus alba Legittimo (about 300 mg/100 g FW) while the lowest content (about 25 mg/100 g FW) was measured in M. alba cv. Nello. Morus nigra showed a good AA in comparison with the different M. alba genotypes with all the used methods; its AA was equal to 33, 26 and 21 μmols Trolox/g FW when using DPPH, ABTS and FRAP tests, respectively. All genotypes showed an anti-inflammatory activity (measured by cyclooxygenase (COX) inhibitory assay) which was also compared with two commercial anti-inflammatory drugs. The data obtained support the high biological qualities of mulberry fruits and their diffusion in human nutrition.

Purification, characterization and in vitro and in vivo immune enhancement of polysaccharides from mulberry leaves

Mulberry leaf polysaccharide (MLP) was extracted and purified by DEAE-52 cellulose and Sephadex G-100 column chromatography to afford two major purified polysaccharides (MLP-1 and MLP-2). The purified polysaccharides were characterized, and their immune-enhancing properties were investigated. MLP-1 had a molecular weight of 9.31×104 Da and was composed of mannose, rhamnose, glucose, galactose, xylose, and arabinose in a molar ratio of 0.71:1.00:2.76:1.13:3.70:2.81. The molecular weight of MLP-2 was 2.22×106 Da, and its monosaccharide constituents were mannose, rhamnose, glucose, galactose, and arabinose in a molar ratio of 1.31:8.45:6.94:1.00:11.96. Infrared spectroscopy showed that each MLP had a typical absorption peak characteristic of sugars, and ultraviolet (UV) spectroscopy showed that neither MLP contained nucleic acid or protein components. Then, the abilities of these polysaccharides to stimulate spleen lymphocyte proliferation in mice in vitro were compared by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay. MLP-2 was more effective than MLP-1; therefore, MLP-2 was chosen for the study of its immune-enhancing effects in vivo. For the in vivo experiments, 14-day-old chickens immunized with Newcastle disease (ND) vaccine were orally administered MLP-2, and Astragalus polysaccharide (APS) was used as the control. Each chicken was orally administered 4 mg or 8 mg of MLP-2 for seven consecutive days starting three days before ND vaccine immunization. MLP-2 significantly improved the ND serum antibody titer and interleukin-2 (IL-2), interferon-γ (IFN-γ) and immunoglobulin A (sIgA) concentrations in tracheal and jejunal wash fluids, and increasing numbers of immune globulin A-positive (IgA+) cells in cecal tonsils and increased body weight. These results indicated that MLP-2 could significantly enhance immune activity and could therefore be utilized as an immunopotentiator drug candidate.

The Chemical Synthesis and Applications of Tropane Alkaloids

Tropanes are an important class of alkaloid natural products that are found in plants all over the world. These compounds can exhibit significant biological activity and are among the oldest known medicines. In the early 19th century, tropanes were isolated, characterized, and synthesized by notable chemical researchers. Their significant biological activities have inspired tremendous research efforts toward their synthesis and the elucidation of their pharmacological activity both in academia and in industry. In this chapter, which addresses the developments in this field since 1994, the focus is on the synthesis of these compounds, and several examples of sophisticated synthetic protocols involving both asymmetric and catalytic approaches are described. In addition, the structures of more than 100 new alkaloids are included as well as the applications and pharmacological properties of some tropane alkaloids.

Characterization of the PLP-dependent transaminase initiating azasugar biosynthesis

Biosynthesis of the azasugar 1-deoxynojirimycin (DNJ) critically involves a transamination in the first committed step. Here, we identify the azasugar biosynthetic cluster signature in Paenibacillus polymyxa SC2 (Ppo), homologous to that reported in Bacillus amyloliquefaciens FZB42 (Bam), and report the characterization of the aminotransferase GabT1 (named from Bam). GabT1 from Ppo exhibits a specific activity of 4.9 nmol/min/mg at 30°C (pH 7.5), a somewhat promiscuous amino donor selectivity, and curvilinear steady-state kinetics that do not reflect the predicted ping-pong behavior typical of aminotransferases. Analysis of the first half reaction with l-glutamate in the absence of the acceptor fructose 6-phosphate revealed that it was capable of catalyzing multiple turnovers of glutamate. Kinetic modeling of steady-state initial velocity data was consistent with a novel hybrid branching kinetic mechanism which included dissociation of PMP after the first half reaction to generate the apoenzyme which could bind PLP for another catalytic deamination event. Based on comparative sequence analyses, we identified an uncommon His-Val dyad in the PLP-binding pocket which we hypothesized was responsible for the unusual kinetics. Restoration of the conserved PLP-binding site motif via the mutant H119F restored classic ping-pong kinetic behavior.

Evaluation of the anti-hyperglycemic effect and safety of microorganism 1-deoxynojirimycin

1-Deoxynojirimycin (DNJ) is a potent α-glucosidase inhibitor and thus beneficial for prevention of diabetes. While we have succeeded in obtaining the culture supernatant extract (CSE) rich in DNJ from microorganism source, information regarding its anti-hyperglycemic effect and safety were still limited. Therefore, this study was aimed to evaluate the anti-hyperglycemic effect and safety of microorganism DNJ. Oral sucrose tolerance test was performed, and the result showed that CSE was able to significantly suppress the blood glucose elevation and suggested DNJ as the main active compound. To determine its safety, the absorption and excretion of microorganism DNJ were evaluated using 15N labeling method. Our findings investigated the recovery rate of 15N from DNJ reached 80% up to 48 hours after oral administration, suggesting its rapid excretion, suggesting the safety of DNJ. This study verified the functional properties and safety of DNJ from microorganisms, suggesting its potential use for functional purpose.

Novel pyridine-2,4,6-tricarbohydrazide thiourea compounds as small key organic molecules for the potential treatment of type-2 diabetes mellitus: In vitro studies against yeast α- and β-glucosidase and in silico molecular modeling

A range of novel pyridine-2,4,6-tricarbohydrazide thiourea compounds (4a-i) were synthesized in good to excellent yields (63-92%). The enzyme inhibitory potentials of these compounds were investigated against α- and β-glucosidases because these enzymes play a crucial role in treating type-2 diabetes mellitus (T2DM). As compared to the reference compound acarbose (IC₅₀ 38.22 ± 0.12 μM), compounds 4i (IC₅₀ 25.49 ± 0.67 μM), 4f (IC₅₀ 28.91 ± 0.43 μM), 4h (IC₅₀ 30.66 ± 0.52 μM), and 4e (IC₅₀ 35.01 ± 0.45 μM) delivered better inhibition against α-glucosidase and were quite inactive/completely inactive against β-glucosidase. The structure-activity relationship of these compounds was developed and elaborated with the help of molecular docking studies.

1-Deoxynojirimycin: Sources, Extraction, Analysis and Biological Functions

1-Deoxynojirimycin (DNJ), a natural polyhydroxylated piperidine alkaloid, is attracting growing attention due to its important biological functions. This paper introduces the discovery and origins of DNJ, its extraction, purification, and physiological functions in the treatment of diabetes. The mechanisms of DNJ in the inhibition of fat accumulation and tumor cell metastasis are also discussed. In addition, the prospects and challenges of DNJ for practical production are proposed. This work aims to provide technical advice on obtaining DNJ and a fuller understanding of its biological activities.

Effect of Lactic Acid Bacteria-Fermented Mulberry Leaf Extract on the Improvement of Intestinal Function in Rats

This study examined the laxative effects of mulberry leaf extract (MLE) fermented by lactic acid bacteria (LAB), which contains high levels of polyphenolic and flavonoid compounds, against loperamide-induced constipation in rats. Sprague-Dawley rats were divided into a normal group (N) and three experimental groups; loperamide treated group (C), loperamide and LAB-fermented MLE 300 mg/kg treated group (MLEL), and loperamide and LAB-fermented MLE 600 mg/kg treated group (MLEH). After 33 d, fecal pellet amount, fecal weight, water content of fecal, gastrointestinal transit time and length, and serum lipid profiles were measured. Constipation was induced via subcutaneous injection of loperamide (2.0 mg/kg b.w., twice a day) for the final 5 d of the experiment. After loperamide administration, the LAB-fermented MLE groups showed a significantly increase in the fecal pellets number, wet weight, and water content in rats compared with the C group. Moreover, increases in the intestinal length and viable Lactobacillus numbers in the feces were observed in the LAB-fermented MLE groups. The intestinal transit time was shorter in the LAB-fermented MLE groups than in the C group. In addition, the LAB-fermented MLE groups showed a significant decrease in triglyceride and total cholesterol levels and an increase in HDL-cholesterol level. These results indicated that oral administration of LAB-fermented MLE shows laxative effect in loperamide-induced constipated rats.

Accumulation of Flavonoid Glycosides and UFGT Gene Expression in Mulberry Leaves (Morus alba L.) before and after Frost

In order to determine the molecular mechanism underlying the influence of frost on chemical changes in mulberry leaves, the UFGT activity, expression level, and accumulation of flavonoid glycosides in mulberry leaves (Morus alba L.) were studied. The expression of UFGT gene was investigated by quantitative real-time PCR (qRT-PCR) and the UFGT activity, accumulation of flavonoid glycosides was studied by high performance liquid chromatography. Then, the correlation between the expression level of UFGT, the UFGT activity, and the flavonoid glycosides accumulation with temperature was explored. The accumulation of isoquercitrin and astragalin is significantly positively correlated with UFGT gene expression and UFGT activity. On the contrary, the average temperature was significantly negatively correlated with the level of UFGT gene expression and UFGT activity. The results show that after frost, low temperature can induce the expression of UFGT gene in mulberry leaves, resulting in the accumulation of flavonoid glycosides.

Potato plants with genetically engineered tropane alkaloid precursors

Solanum tuberosum tropinone reductase I reduced tropinone in vivo. Suppression of tropinone reductase II strongly reduced calystegines in sprouts. Overexpression of putrescine N -methyltransferase did not alter calystegine accumulation. Calystegines are hydroxylated alkaloids formed by the tropane alkaloid pathway. They accumulate in potato (Solanum tuberosum L., Solanaceae) roots and sprouting tubers. Calystegines inhibit various glycosidases in vitro due to their sugar-mimic structure, but functions of calystegines in plants are not understood. Enzymes participating in or competing with calystegine biosynthesis, including putrescine N-methyltransferase (PMT) and tropinone reductases (TRI and TRII), were altered in their activity in potato plants by RNA interference (RNAi) and by overexpression. The genetically altered potato plants were investigated for the accumulation of calystegines and for intermediates of their biosynthesis. An increase in N-methylputrescine provided by DsPMT expression was not sufficient to increase calystegine accumulation. Overexpression and gene knockdown of StTRI proved that S. tuberosum TRI is a functional tropinone reductase in vivo, but no influence on calystegine accumulation was observed. When StTRII expression was suppressed by RNAi, calystegine formation was severely compromised in the transformed plants. Under phytochamber and green house conditions, the StTRII RNAi plants did not show phenotypic alterations. Further investigation of calystegines function in potato plants under natural conditions is enabled by the calystegine deprived StTRII RNAi plants.