Naturally occurring Diels-Alder-type adducts from Morus nigra as potent inhibitors of Mycobacterium tuberculosis protein tyrosine phosphatase B

Enrichment of deoxynojirimycin in mulberry using cation exchange resin: Adsorption/desorption characteristics and process optimization

Deoxynojirimycin (DNJ) is an α-glucosidase inhibitor with high food values. However, the complex and costly enrichment processes have greatly prevented its application. Herein, this study aimed to propose a simple and efficient enrichment process for DNJ from Morus alba L. extracts using cation exchange resins. The LSI and D113 resins were chosen due to their excellent adsorption and desorption properties. The adsorption characteristics agreed with the pseudo-first-order kinetic model and the Langmuir isotherm model. This adsorption was chemisorption, spontaneous, endothermic and entropy-driven. Furthermore, the concentration and pH of the extracts, desorption solvent, breakthrough and elution curves, sample loading and elution rate were investigated to optimize the enrichment process by resin column chromatography. The results also showed that the purity of DNJ was improved to 44.00 % with a total recovery of 78.21 % using the LSI-D113 combination strategy. This research demonstrated the industrial feasibility of DNJ enrichment using cation exchange resins.

Toward Mycobacterium tuberculosis Virulence Inhibition: Beyond Cell Wall

Mycobacterium tuberculosis (Mtb) is one of the most successful bacterial pathogens in human history. Even in the antibiotic era, Mtb is widespread and causes millions of new cases of tuberculosis each year. The ability to disrupt the host's innate and adaptive immunity, as well as natural persistence, complicates disease control. Tuberculosis traditional therapy involves the long-term use of several antibiotics. Treatment failures are often associated with the development of resistance to one or more drugs. The development of medicines that act on new targets will expand treatment options for tuberculosis caused by multidrug-resistant or extensively drug-resistant Mtb. Therefore, the development of drugs that target virulence factors is an attractive strategy. Such medicines do not have a direct bacteriostatic or bactericidal effect, but can disarm the pathogen so that the host immune system becomes able to eliminate it. Although cell wall-associated targets are being actively studied for anti-TB drug development, other virulence factors important for adaptation and host interaction are also worth comprehensive analysis. In this review, specific Mtb virulence factors (such as secreted phosphatases, regulatory systems, and the ESX-1 secretion system) are identified as promising targets for novel anti-virulence drug development. Additionally, models for the search of virulence inhibitors are discussed, such as virtual screening in silico, in vitro enzyme inhibition assay, the use of recombinant Mtb strains with reporter constructs, phenotypic analysis using in vitro cell infection models and specific environments.

Combating Tuberculosis via Restoring the Host Immune Capacity by Targeting M. tb Kinases and Phosphatases

Mycobacterium tuberculosis (M. tb) is a remarkably versatile pathogen that possesses a unique ability to counteract the host's defence mechanisms to control the infection. Several mycobacterial protein kinases and phosphatases were found to play a key role in impeding phagosome maturation in macrophages and accordingly blocking the phagosome-lysosome fusion, therefore allowing the bacteria to survive. During phagocytosis, both M. tb and the host's phagocytic cells develop mechanisms to fight each other, resulting in pathogen elimination or survival. In this respect, M. tb uses a phosphorylation-based signal transduction mechanism, whereby it senses extracellular signals from the host and initiates the appropriate adaptation responses. Indeed, the ability of M. tb to exist in different states in the host (persistent quiescent state or actively replicating mode) is mainly mediated through protein phosphorylation/dephosphorylation signalling. The M. tb regulatory and defensive responses coordinate different aspects of the bacilli's physiology, for instance, cell wall components, metabolic activity, virulence, and growth. Herein, we will discuss the implication of M. tb kinases and phosphatases in hijacking the host immune system, perpetuating the infection. In addition, the role of PknG, MPtpA, MPtpB, and SapM inhibitors in resetting the host immune system will be highlighted.

Chemistry, bioactivities, structure-activity relationship, biosynthesis and metabolism of prenylated flavonoids in Moraceae plants

Plants from Moraceae are globally popular as they represent a valuable resource with wide applications in food, health-care products, and other fields. Prenylated flavonoids are important active components in Moraceae. These compounds share a flavonoid skeleton with prenylated side chain, mostly in the form of single or multiple isoprenyl substituents and benzodimethylfuran structures. So far, nearly 400 prenylated flavonoids have been found in Moraceae, especially a large number of Diels-Alder adducts, which are characteristic components of this family. Due to their distinctive structures, diverse pharmacological properties and interesting synthesis processes, these compounds have attracted considerable attention from scientists. Herein, we review the advances in the structural characteristics, bioactivities, structure-activity relationships, biosynthesis strategies and in vivo metabolism of prenylated flavonoids in Moraceae plants, aiming at strengthening research efforts and utilization toward the great untapped potential of these unique constituents in human health.

Specific Antimicrobial Activities Revealed by Comparative Evaluation of Selected Gemmotherapy Extracts

Nowadays, unprecedented health challenges are urging novel solutions to address antimicrobial resistance as multidrug-resistant strains of bacteria, yeasts and moulds are emerging. Such microorganisms can cause food and feed spoilage, food poisoning and even more severe diseases, resulting in human death. In order to overcome this phenomenon, it is essential to identify novel antimicrobials that are naturally occurring, biologically effective and increasingly safe for human use. The development of gemmotherapy extracts (GTEs) using plant parts such as buds and young shoots has emerged as a novel approach to treat/prevent human conditions due to their associated antidiabetic, anti-inflammatory and/or antimicrobial properties that all require careful evaluations. Seven GTEs obtained from plant species like the olive (Olea europaea L.), almond (Prunus amygdalus L.), black mulberry (Morus nigra L.), walnut (Juglans regia L.), blackberry (Rubus fruticosus L.), blackcurrant (Ribes nigrum L.) and bilberry (Vaccinium myrtillus L.) were tested for their antimicrobial efficiency via agar diffusion and microbroth dilution methods. The antimicrobial activity was assessed for eight bacterial (Bacillus cereus, Staphylococcus aureus, Salmonella enterica subsp. enterica, Proteus vulgaris, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa and Listeria monocytogenes), five moulds (Aspergillus flavus, Aspergillus niger, Aspergillus ochraceus, Penicillium citrinum, Penicillium expansum) and one yeast strain (Saccharomyces cerevisiae). The agar diffusion method revealed the blackberry GTE as the most effective since it inhibited the growth of three bacterial, four moulds and one yeast species, having considered the total number of affected microorganism species. Next to the blackberry, the olive GTE appeared to be the second most efficient, suppressing five bacterial strains but no moulds or yeasts. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were then determined for each GTE and the microorganisms tested. Noticeably, the olive GTE appeared to feature the strongest bacteriostatic and bactericidal outcome, displaying specificity for S. aureus, E. faecalis and L. monocytogenes. The other GTEs, such as blueberry, walnut, black mulberry and almond (the list indicates relative strength), were more effective at suppressing microbial growth than inducing microbial death. However, some species specificities were also evident, while the blackcurrant GTE had no significant antimicrobial activity. Having seen the antimicrobial properties of the analysed GTEs, especially the olive and black mulberry GTEs, these could be envisioned as potential antimicrobials that might enhance antibiotic therapies efficiency, while the blackberry GTE would act as an antifungal agent. Some of the GTE mixtures analysed have shown interesting antimicrobial synergies, and all the antimicrobial effects observed argue for extending these studies to include pathological microorganisms.

Pyrazole Scaffold: Potential PTP1B Inhibitors for Diabetes Treatment

BACKGROUND

The overexpression of the Protein Tyrosine Phosphatase 1B (PTP1B), a key role in the development of insulin resistance, diabetes (T2DM) and obesity, seems to have a substantial impact as a negative regulator of the insulin and leptin signaling pathways. Therefore, inhibiting PTP1B is a prospective therapeutic approach for the treatment of diabetes and obesity. However, the pyrazole scaffold is expected to be of significant pharmaceutical interest due to its broad spectrum of pharmacological actions. This study aims to focus on the significance of pyrazole scaffold in medicinal chemistry, the impact of PTP1B in diabetes and the therapeutic approach of pyrazole scaffold to treat T2DM.

METHODS

A comprehensive analysis of the published literature in several pharmaceutical and medical databases, such as the Web of Science (WoS), PubMed, ResearchGate, ScienceDirect etc., were indeed successfully completed and classified accordingly.

RESULTS

As reviewed, the various derivatives of the pyrazole scaffold exhibited prominent PTP1B inhibitory activity. The result showed that derivatives of oxadiazole and dibenzyl amine, chloro substituents, 1, 3-diaryl pyrazole derivatives with rhodanine-3-alkanoic acid groups, naphthalene and also 1, 3, 5-triazine-1H-pyrazole-triazolothiadiazole derivatives, octyl and tetradecyl derivative, indole- and N-phenylpyrazole-glycyrrhetinic acid derivatives with trifluoromethyl group, 2,3-pyrazole ring-substituted-4,4-dimethyl lithocholic acid derivatives with 4- fluoro phenyl substituted and additional benzene ring in the pyrazole scaffold significantly inhibits PTP1B. In silico study observed that pyrazole scaffold interacted with amino acid residues like TYR46, ASP48, PHE182, TYR46, ALA217 and ILE219.

CONCLUSION

Diabetes is a metabolic disorder that elevates the risk of mortality and severe complications. PTP1B is a crucial component in the management of diabetes and obesity. As a result, PTP1B is a promising therapeutic target for the treatment of T2DM and obesity in humans. We concluded that the pyrazole scaffold has prominent inhibitory potential against PTP1B.

Integrative Omic Analysis Reveals the Dynamic Change in Phenylpropanoid Metabolism in Morus alba under Different Stress

Morus alba is used as a traditional Chinese medicine due to its various biological activities. Phenylpropanoid metabolism is one of the most important pathways in Morus alba to produce secondary metabolites and response to stress. From the general phenylpropanoid pathway, there are two metabolic branches in M. alba, including flavonoid and lignin biosynthesis, which also play roles in response to stress. However, the dynamic changes between flavonoid and lignin biosynthesis under Botrytis cinerea infection and UV-B stress in M. alba were unclear. To explore the different regulation mode of flavonoid and lignin biosynthesis in M. alba leaves' response to biotic and abiotic stress, a combined proteomic and metabolomic study of M. alba leaves under UV-B stress and B. cinerea infection was performed. The results showed that most of the proteins involved in the lignin and flavonoid biosynthesis pathway were increased under either UV-B stress or B. cinerea infection in M. alba. This was also confirmed by enzyme assays and metabolomics analysis. Additionally, the abundance of proteins involved in the biosynthesis of jasmonic acid was increased after B. cinerea infection. This suggests that both flavonoid and lignin biosynthesis participate in the responses to abiotic and biotic stress in M. alba, but they might be regulated by different hormone signaling.

Selection of Natural Compounds with HMGA-Interfering Activities and Cancer Cell Cytotoxicity

HMGA proteins are intrinsically disordered (ID) chromatin architectural factors characterized by three DNA binding domains (AT-hooks) that allow them to bind into the DNA minor groove of AT-rich stretches. HMGA are functionally involved in regulating transcription, RNA processing, DNA repair, and chromatin remodeling and dynamics. These proteins are highly expressed and play essential functions during embryonic development. They are almost undetectable in adult tissues but are re-expressed at high levels in all cancers where they are involved in neoplastic transformation and cancer progression. We focused on identifying new small molecules capable of binding into the minor groove of AT-rich DNA sequences that could compete with HMGA for DNA binding and, thus, potentially interfere with their activities. Here, a docking-based virtual screening of a unique high diversity in-house library composed of around 1000 individual natural products identified 16 natural compounds as potential minor groove binders that could inhibit the interaction between HMGA and DNA. To verify the ability of these selected compounds to compete with HMGA proteins, we screened them using electrophoretic mobility shift assays. We identified Sorocein C, a Diels-Alder (D-A)-type adducts, isolated from Sorocea ilicifolia and Sorocea bonplandii with an HMGA/DNA-displacing activity and compared its activity with that of two structurally related compounds, Sorocein A and Sorocein B. All these compounds showed a cytotoxicity effect on cancer cells, suggesting that the Sorocein-structural family may provide new and yet unexplored chemotypes for the development of minor groove binders to be evaluated as anticancer agents.

Exploring the role of secretory proteins in the human infectious diseases diagnosis and therapeutics

Secretory proteins are playing important role during the host-pathogen interaction to develop the infection or protection into the cell. Pathogens developing infectious disease to human being are taken up by host macrophages or number of immune cells, play an important role in physiological, developmental and immunological function. At the same time, infectious agents are also secreting various proteins to neutralize the resistance caused by host cells and also helping the pathogens to develop the infection. Secretory proteins (secretome) are only developed at the time of host-pathogen interaction, therefore they become very important to develop the targeted and potential therapeutic strategies. Pathogen specific secretory proteins released during interaction with host cell provide opportunity to develop point of care and rapid diagnostic kits. Proteins secreted by pathogens at the time of interaction with host cell have also been found as immunogenic in nature and numbers of vaccines have been developed to control the spread of human infectious diseases. This chapter highlights the importance of secretory proteins in the development of diagnostic and therapeutic strategies to fight against human infectious diseases.

Identification of Small Molecular Chaperones Binding P23H Mutant Opsin through an In Silico Structure-Based Approach

N-terminal P23H opsin mutation accounts for most of retinitis pigmentosa (RP) cases. P23H functions and folding can be rescued by small chaperone ligands, which contributes to validate mutant opsin as a suitable target for pharmacological treatment of RP. However, the lack of structural details on P23H mutant opsin strongly impairs drug design, and new chemotypes of effective chaperones of P23H opsin are in high demand. Here, a computational-boosted workflow combining homology modeling with molecular dynamics (MD) simulations and virtual screening was used to select putative P23H opsin chaperones among different libraries through a structure-based approach. In vitro studies corroborated the reliability of the structural model generated in this work and identified a number of novel chemotypes of safe and effective chaperones able to promote P23H opsin trafficking to the outer cell membrane.

Synthesis, Biosynthesis, and Biological Activity of Diels-Alder Adducts from Morus Genus: An Update

The plants of the Moraceae family are producers of a great variety of polyphenolic natural products. Among these, the Diels-Alder type adducts (DAAs) are endowed with a unique cyclohexene scaffold, since they are biosynthesized from [4+2] cycloaddition of different polyphenolic precursors such as chalcones and dehydroprenyl polyphenols. To date, more than 150 DAAs have been isolated and characterized from Moraceous and related plants. The main source of DAAs is the mulberry root bark, also known as "Sang-Bai-Pi" in Traditional Chinese Medicine, but they have also been isolated from root bark, stem barks, roots, stems or twigs, leaves, and callus cultures of Moraceous and other related plants. Since 1980, many biological activities of DAAs have been identified, including anti-HIV, antimicrobial, anti-inflammatory, and anticancer ones. For these reasons, natural DAAs have been intensively investigated, and a lot of efforts have been made to study their biosynthesis and to establish practical synthetic access. In this review, we summarized all the updated knowledge on biosynthesis, chemoenzymatic synthesis, racemic and enantioselective total synthesis, and biological activity of natural DAAs from Moraceous and related plants.

Rapid Screening of Nonalkaloid α-Glucosidase Inhibitors from a Mulberry Twig Extract Using Enzyme-Functionalized Magnetic Nanoparticles Coupled with UPLC-MS/MS

Mulberry twigs are an important source of α-glucosidase inhibitors. To date, research studies on α-glucosidase in mulberry twigs have mainly focused on alkaloids such as 1-deoxynojirimycin (DNJ). Preliminary studies have shown that there may be more active nonalkaloid α-glucosidase inhibitors in mulberry twigs. In this study, we immobilized α-glucosidase on Fe₃O₄@SiO₂ for the first time and rapidly screened four nonalkaloid α-glucosidase inhibitors (kuwanon G, kuwanon C, kuwanon H, and morusin) using ligand fishing technology with ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) from the mulberry twig extract of Jialing 20, the excellent artificial triploid variety of mulberry cultivated extensively in Southwest China. The half maximal inhibitory concentrations (IC₅₀) of kuwanon H and kuwanon G were 2.82 ± 0.68 and 2.83 ± 0.31 μM, respectively, with better inhibition activity than that of DNJ (with an IC₅₀ of 7.04 ± 0.82 μM). Meanwhile, the molecular docking results showed that the action sites of these two isopentenyl flavonoids on α-glucosidase were different from that of DNJ. In brief, this work is beneficial to discovering new α-glucosidase inhibitors from mulberry twigs quickly and accurately and provides a theoretical basis for the mulberry twig extract as a functional food or a natural hypoglycemic drug source, as well as a reference for directional breeding of mulberry, which greatly improves the exploitation and utilization value of mulberry twigs as an agricultural byproduct in the fields of agricultural production, functional food, and natural medicine.

Mulberry Diels-Alder-type adducts: isolation, structure, bioactivity, and synthesis

Mulberry Diels-Alder-type adducts (MDAAs) are unique phenolic natural products biosynthetically derived from the intermolecular [4 + 2]-cycloaddition of dienophiles (mainly chalcones) and dehydroprenylphenol dienes, which are exclusively distributed in moraceous plants. A total of 166 MDAAs with diverse skeletons have been isolated and identified since 1980. Structurally, the classic MDAAs characterized by the chalcone-skeleton dienophiles can be divided into eight groups (Types A - H), while others with non-chalcone dienophiles or some variations of classic MDAAs are non-classic MDAAs (Type I). These compounds have attracted significant attention of natural products and synthetic chemists due to their complex architectures, remarkable biological activities, and synthetic challenges. The present review provides a comprehensive summary of the structural properties, bioactivities, and syntheses of MDAAs. Cited references were collected between 1980 and 2021 from the SciFinder, Web of Science, and China National Knowledge Internet (CNKI).

Targeting protein tyrosine phosphatases for the development of antivirulence agents: Yersinia spp. and Mycobacterium tuberculosis as prototypes

Protein phosphorylation mediated by protein kinases and phosphatases has a central regulatory function in many cellular processes in eukaryotes and prokaryotes. As a result, several diseases caused by imbalance in phosphorylation levels are known, especially due to protein tyrosine phosphatases (PTPs) activity, an important family of signaling enzymes. Furthermore, over the last decades several studies have shown the main role of PTPs in pathogenic bacteria: they are associated with growth, cell division, cell wall biosynthesis, biofilm formation, metabolic processes, as well as virulence factor. In this way, PTPs have ascended as targets for antibacterial drug design, particularly in view of the antibiotic resistance in pathogenic bacteria, which demands novel therapeutics strategies. Targeting secreted PTPs is an antivirulence strategy to combat the emergence of antimicrobial resistance (AMR). This review focuses on the recent advances in understanding the role of PTPs and the approaches to target them, with an emphasis in Yersinia spp. and Mycobacterium tuberculosis pathogenesis.

Inhibition Mechanism of Components Isolated from Morus alba Branches on Diabetes and Diabetic Complications via Experimental and Molecular Docking Analyses

Previously, we reported the anti-diabetic effect of Morus alba root bark and the compounds therein. In our continuous study of other parts of this plant, the ability of the branch of Morus alba to inhibit α-glucosidase, protein tyrosine phosphatase 1B (PTP1B), and advanced glycation end products (AGEs) formation was evaluated. Moreover, there are no previous studies that have performed enzyme kinetics and molecular docking analyses, along with assessments of peroxynitrite (ONOO⁻) inhibitory activities. Since the Morus alba branch exhibited favorable inhibitory effects, repeated column chromatography was performed to obtain eight compounds, including four flavonoids (1, 3, 6, 8), one arylbenzofuran (2), one stilbene (5), one Diels–Alder-type adduct (7), and one sterol (4). Among them, compounds 1–3 and 5–7 were mixed-type inhibitors of α-glucosidase, sharing the same catalytic residues with acarbose and the same allosteric sites with (Z)-3-bytylidenephthalide. On the other hand, kuwanon C (1) and oxyresveratrol (5) interacted with residues of the allosteric site (α3 and α6 helices) of PTP1B, indicating their use as non-competitive inhibitors. Interestingly, kuwanon G (7) directly bound the catalytic site, or interrupted the binding between the substrate and the active site, as a mixed-type inhibitor. Moreover, most of the compounds exhibited greater activity against AGE formation and ONOO⁻ than positive controls. The IC₅₀ values required to inhibit ONOO⁻ using compounds 1, 3, 5, 6, and 7 were reported for the first time, and range from 1.08 to 12.92 μM. Based on the structure–activity relationship, the presence of hydroxyl, resorcinol, and prenyl moieties was important in the prevention of diabetes’ pathological mechanisms, and these findings have been further supported by molecular docking analysis. These computational and experimental results will be useful in the development of therapeutic candidates to prevent/treat diabetes and its complications.

Phytochemical Composition of Different Botanical Parts of Morus Species, Health Benefits and Application in Food Industry

In recent years, mulberry has acquired a special importance due to its phytochemical composition and its beneficial effects on human health, including antioxidant, anticancer, antidiabetic and immunomodulatory effects. Botanical parts of Morus sp. (fruits, leaves, twigs, roots) are considered a rich source of secondary metabolites. The aim of our study was to highlight the phytochemical profile of each of the botanical parts of Morus tree, their health benefits and applications in food industry with an updated review of literature. Black and white mulberries are characterized in terms of predominant phenolic compounds in correlation with their medical applications. In addition to anthocyanins (mainly cyanidin-3-O-glucoside), black mulberry fruits also contain flavonols and phenolic acids. The leaves are a rich source of flavonols, including quercetin and kaempferol in the glycosylated forms and chlorogenic acid as predominant phenolic acids. Mulberry bark roots and twigs are a source of prenylated flavonoids, predominantly morusin. In this context, the exploitation of mulberry in food industry is reviewed in this paper, in terms of developing novel, functional food with multiple health-promoting effects.

UPLC-MS/MS Profiling, Antioxidant, α-Glucosidase Inhibitory, Cholinesterase Inhibitory, and Cardiovascular Protection Potentials of Jialing 20 (Morus multicaulis Perr.) Mulberry Branch Extract

As a by-product in the sericulture industry, mulberry branches are not currently utilized effectively. Jialing 20 is an artificial triploids mulberry that widely cultivated in southwest China. In this study, the chemical composition of the Jialing 20 mulberry branch extract (MBE) was first analyzed by UPLC-MS/MS, and 42 components, including alkaloids, flavonoids, and coumarins, were obtained. Then, the antioxidant activities, hypoglycemic effect, Alzheimer’s disease inhibition, and cardiovascular protection of MBE were also evaluated in vitro. The IC₅₀ values for the scavenging DPPH and ABTS radicals were, respectively, 31.23 ± 0.57 μg/mL and 8.88 ± 0.36 μg/mL (IC₅₀ values of positive Vc were, respectively, 4.41 ± 0.19 μg/mL and 8.79 ± 0.41 μg/mL). The IC₅₀ value for inhibiting α-glucosidase was 1.90 ± 0.05 μg/mL (IC₅₀ value of positive acarbose was 0.03 μg/mL). The IC₅₀ values for inhibiting acetylcholinesterase and butyrylcholinesterase were, respectively, 179.47 ± 0.38 μg/mL and 101.82 ± 3.37 μg/mL (IC₅₀ values of positive berberine were, respectively, 1.27 ± 0.03 μg/mL and 57.41 ± 0.21 μg/mL). MBE (10 μg/mL and 40 μg/mL) significantly increased the survival rate of oxidized low-density lipoprotein- (ox-LDL) induced human umbilical vein endothelial cells (HUVECs) and significantly decreased the intracellular reactive oxygen species. These results suggest that the extracts of Jialing 20 mulberry branches could be used as a functional food additive.

Natural products against key Mycobacterium tuberculosis enzymatic targets: Emerging opportunities for drug discovery

For centuries, natural products (NPs) have served as powerful therapeutics against a variety of human ailments. Nowadays, they still represent invaluable resources for the treatment of many diseases, including bacterial infections. After nearly three decades since the World Health Organization's (WHO) declaration of tuberculosis (TB) as a global health emergency, Mycobacterium tuberculosis (Mtb) continues to claim millions of lives, remaining among the leading causes of death worldwide. In the last years, several efforts have been devoted to shortening and improving treatment outcomes, and to overcoming the increasing resistance phenomenon. Nature has always provided a virtually unlimited source of bioactive molecules, which have inspired the development of new drugs. NPs are characterized by an exceptional chemical and structural diversity, the result of millennia of evolutionary responses to various stimuli. Thanks to their favorable structural features and their enzymatic origin, they are naturally prone to bind proteins and exhibit bioactivities. Furthermore, their worldwide distribution and ease of accessibility has contributed to promote investigations on their activity. Overall, these characteristics make NPs excellent models for the design of novel therapeutics. This review offers a critical and comprehensive overview of the most promising NPs, isolated from plants, fungi, marine species, and bacteria, endowed with inhibitory properties against traditional and emerging mycobacterial enzymatic targets. A selection of 86 compounds is here discussed, with a special emphasis on their biological activity, structure-activity relationships, and mechanism of action. Our study corroborates the antimycobacterial potential of NPs, substantiating their relevance in future drug discovery and development efforts.

A unique high-diversity natural product collection as a reservoir of new therapeutic leads

We review the successful application of computer-aided methods to screen a unique and high-diversity in house collection library composed of around 1000 individual natural products.

Identification of fusarielin M as a novel inhibitor of Mycobacterium tuberculosis protein tyrosine phosphatase B (MptpB)

The secreted Mycobacterium tuberculosis (Mtb) protein tyrosine phosphatase B (MptpB) is an essential virulence factor required for the intracellular survival of Mtb within host macrophages. MptpB has become a promising target for the development of novel anti-tuberculosis (TB) drugs. In this study, two new fusarielins, fusarielins M (1) and N (2), and a biogenetically related known compound, fusarielin G (3) were isolated from the marine-derived fungus Fusarium graminearum SYSU-MS5127. Their inhibitory effects on MptpB were evaluated. Among these compounds, fusarielin M substantially inhibited MptpB with a half-maximal inhibitory concentration (IC₅₀) of 1.05 ± 0.08 μM, and an inhibition constant (K_i) of 1.03 ± 0.39 μM. Surface plasmon resonance analysis was used to characterize the interaction between fusarielin M and MptpB in vitro. Fusarielin M also exhibited cellular activity in blocking MptpB-mediated Erk1/2 and p38 inactivation in macrophages. Importantly, fusarielin M (20 μM) substantially reduced intracellular mycobacterial growth within macrophages, causing a 62% reduction in the bacterial burden. The binding mode of fusarielin M was further explored via molecular docking which suggested that fusarielin M binds to the active site of MptpB, forming a hydrogen bond with the side chain of Asp165; this is unique in the P-loop of MptpB compared to conventional human PTPs. The contact between fusarielin M and Asp165 in the catalytic loop provides a potential basis for inhibitor selectivity. Therefore, fusarielin M shows great potential as an anti-TB drug candidate.

The antidiabetic drug lobeglitazone has the potential to inhibit PTP1B activity

Protein tyrosine phosphatase 1B (PTP1B) is considered a potential therapeutic target for the treatment of type 2 diabetes mellitus (T2DM), since this enzyme plays a significant role to down-regulate insulin and leptin signalling and its over expression has been implicated in the development of insulin resistance, T2DM and obesity. Some thiazolidinediones (TZD) derivatives have been reported as promising PTP1B inhibitors with anti hyperglycemic effects. Recently, lobeglitazone, a new TZD, was described as an antidiabetic drug that targets the PPAR-γ (peroxisome γ proliferator-activated receptor) pathway, but no information on its effects on PTP1B have been reported to date. We investigated the effects of lobeglitazone on PTP1B activity in vitro. Surprisingly, lobeglitazone led to moderate inhibition on PTP1B (IC₅₀ 42.8 ± 3.8 µM) activity and to a non-competitive reversible mechanism of action. As lobeglitazone inhibits PTP1B activity in vitro, we speculate that it could also target PTP1B signalling pathway in vivo and thus contribute to potentiate its antidiabetic effects.

Natural Flavones from Morus alba against Methicillin-Resistant Staphylococcus aureus via Targeting the Proton Motive Force and Membrane Permeability

The emergence and rapid spread of methicillin-resistant Staphylococcus aureus (MRSA) critically requires alternative therapeutic options. New antibacterial drugs and strategies are urgently needed to combat MRSA-associated infections. Here, we investigated the antibacterial activity of flavones from Morus alba and the potential mode of action against MRSA. Kuwanon G, kuwanon H, mulberrin, and morusin displayed high efficiency in killing diverse MRSA isolates. On the basis of structure-activity analysis, the cyclohexene-phenyl ketones and isopentenyl groups were critical to increase the membrane permeability and to dissipate the proton motive force. Meanwhile, mechanistic studies further showed that kuwanon G displayed rapid bactericidal activity in vitrowith difficulty in developing drug resistance. Kuwanon G targeted phosphatidylglycerol and cardiolipin in the cytoplasmic membrane through the formation of hydrogen bonds and electrostatic interactions. Additionally, kuwanon G promoted wound healing in a mouse model of MRSA skin infection. In summary, these results indicate that flavones are promising lead compounds to treat MRSA-associated infections through disrupting the proton motive force and membrane permeability.

Kinase Targets for Mycolic Acid Biosynthesis in Mycobacterium tuberculosis

BACKGROUND

Mycolic acids (MAs) are the characteristic, integral building blocks for the mycomembrane belonging to the insidious bacterial pathogen Mycobacterium tuberculosis (M.tb). These C60-C90 long α-alkyl-β-hydroxylated fatty acids provide protection to the tubercle bacilli against the outside threats, thus allowing its survival, virulence and resistance to the current antibacterial agents. In the post-genomic era, progress has been made towards understanding the crucial enzymatic machineries involved in the biosynthesis of MAs in M.tb. However, gaps still remain in the exact role of the phosphorylation and dephosphorylation of regulatory mechanisms within these systems. To date, a total of 11 serine-threonine protein kinases (STPKs) are found in M.tb. Most enzymes implicated in the MAs synthesis were found to be phosphorylated in vitro and/or in vivo. For instance, phosphorylation of KasA, KasB, mtFabH, InhA, MabA, and FadD32 downregulated their enzymatic activity, while phosphorylation of VirS increased its enzymatic activity. These observations suggest that the kinases and phosphatases system could play a role in M.tb adaptive responses and survival mechanisms in the human host. As the mycobacterial STPKs do not share a high sequence homology to the human's, there have been some early drug discovery efforts towards developing potent and selective inhibitors.

OBJECTIVE

Recent updates to the kinases and phosphatases involved in the regulation of MAs biosynthesis will be presented in this mini-review, including their known small molecule inhibitors.

CONCLUSION

Mycobacterial kinases and phosphatases involved in the MAs regulation may serve as a useful avenue for antitubercular therapy.

Dual-targeting GroEL/ES chaperonin and protein tyrosine phosphatase B (PtpB) inhibitors: A polypharmacology strategy for treating Mycobacterium tuberculosis infections

Current treatments for Mycobacterium tuberculosis infections require long and complicated regimens that can lead to patient non-compliance, increasing incidences of antibiotic-resistant strains, and lack of efficacy against latent stages of disease. Thus, new therapeutics are needed to improve tuberculosis standard of care. One strategy is to target protein homeostasis pathways by inhibiting molecular chaperones such as GroEL/ES (HSP60/10) chaperonin systems. M. tuberculosis has two GroEL homologs: GroEL1 is not essential but is important for cytokine-dependent granuloma formation, while GroEL2 is essential for survival and likely functions as the canonical housekeeping chaperonin for folding proteins. Another strategy is to target the protein tyrosine phosphatase B (PtpB) virulence factor that M. tuberculosis secretes into host cells to help evade immune responses. In the present study, we have identified a series of GroEL/ES inhibitors that inhibit M. tuberculosis growth in liquid culture and biochemical function of PtpB in vitro. With further optimization, such dual-targeting GroEL/ES and PtpB inhibitors could be effective against all stages of tuberculosis - actively replicating bacteria, bacteria evading host cell immune responses, and granuloma formation in latent disease - which would be a significant advance to augment current therapeutics that primarily target actively replicating bacteria.

Pharmacological Properties of Morus nigra L. (Black Mulberry) as A Promising Nutraceutical Resource

Mulberry plants belonging to the Moraceae family have been grown for the purpose of being the nutrient source for silk worm and raw materials for the preparation of jams, marmalades, vinegars, juices, wines, and cosmetics. Morus nigra L. (black mulberry) is native to Southwestern Asia, and it has been used as a traditional herbal medicine for animals and humans. In this article, recent research progress on various biological and pharmacological properties of extracts, fractions, and isolated active constituents from different parts of M. nigra are reviewed. M. nigra exhibited a wide-spectrum of biological and pharmacological therapeutic effects including antinociceptive, anti-inflammatory, antimicrobial, anti-melanogenic, antidiabetic, anti-obesity, anti-hyperlipidemic, and anticancer activities. M. nigra also showed protective effects against various human organs and systems, mainly based on its antioxidant capacity. These findings strongly suggest that M. nigra can be used as a promising nutraceutical resource to control and prevent various chronic diseases.