438 research outputs found

    Anti-Pseudomonas aeruginosa activity of natural antimicrobial peptides when used alone or in combination with antibiotics

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    The World Health Organization has recently published a list of 12 drug-resistant bacteria that posed a significant threat to human health, and Pseudomonas aeruginosa (P. aeruginosa) was among them. In China, P. aeruginosa is a common pathogen in hospital acquired pneumonia, accounting for 16.9–22.0%. It is a ubiquitous opportunistic pathogen that can infect individuals with weakened immune systems, leading to hospital-acquired acute and systemic infections. The excessive use of antibiotics has led to the development of various mechanisms in P. aeruginosa to resist conventional drugs. Thus, there is an emergence of multidrug-resistant strains, posing a major challenge to conventional antibiotics and therapeutic approaches. Antimicrobial peptides are an integral component of host defense and have been found in many living organisms. Most antimicrobial peptides are characterized by negligible host toxicity and low resistance rates, making them become promising for use as antimicrobial products. This review particularly focuses on summarizing the inhibitory activity of natural antimicrobial peptides against P. aeruginosa planktonic cells and biofilms, as well as the drug interactions when these peptides used in combination with conventional antibiotics. Moreover, the underlying mechanism of these antimicrobial peptides against P. aeruginosa strains was mainly related to destroy the membrane structure through interacting with LPS or increasing ROS levels, or targeting cellular components, leaded to cell lysis. Hopefully, this analysis will provide valuable experimental data on developing novel compounds to combat P. aeruginosa

    Biosynthese und Funktion von Naturstoffen aus Mortierella alpina

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    In dieser Arbeit wurde anhand des Modellorganismus Mortierella alpina gezeigt, dass basale Pilze wohl zu ausgedehnter Naturstoffbiosyntese befähigt sind. So konnte für die Biosynthese der Malpinine, der Malpicycline, der Malpibaldine sowie das Calpinactam jeweils eine zugehörige Nicht-ribosomale Peptidsynthetase (NRPSen) identifziert werden. Bei den jeweils zugrundeliegenden Biosynthesegenen malA, mpbA, calA und mpcA handelt es sich um pilzliche Gene, die jedoch bakteriellen Ursprungs sind und durch horizontalen Gentransfer auf M. alpina übertragen worden sind. Zusätzlich wurde die biologische Funktion sowie mögliche pharmazeutische Anwendungsmöglichkeiten untersucht

    Natural Products as Kinase Inhibitors: Total Synthesis, in Vitro Kinase Activity, in Vivo Toxicology in Zebrafish Embryos and in Silico Docking

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    Despite significant progress in developing small molecule kinase inhibitors, most human kinases still lack high-quality selective inhibitors that might be employed as chemical probes to study their biological function and pharmacology. Natural products (NPs) and their synthetic derivates might give avenues to overcome this frequently encountered challenge as they demonstrated to target a wide range of kinases, including all subfamilies of the known kinome. Nonetheless, isolating these NPs from their sources necessitates massive harvesting, which is fraught with difficulties and triggers enormous harm to the ecology. Moreover, the challenges encountered while extracting these NPs from their sources are constantly present and have few viable solutions. Considering these aspects, total synthesis and semisynthesis have been employed to replicate the most intriguing compounds of living nature in laboratories to obtain larger quantities for extended studies. The present work outlined the attempts to perform the first total syntheses and to evaluate the biological activity of naturally occurring potent anti-cancer compounds: Depsipeptide PM181110, Eudistomidin C, and Fusarithioamide A. Efforts to achieve the first total syntheses of these natural compounds have been based on highly convergent and unified approaches. Depsipeptide PM181110 is a bicyclic depsipeptide featuring four stereogenic centres whose attempts to perform its first total synthesis were undertaken by synthesizing its diastereomers 3R,9R,14R,17R, and 3R,9S,14R,17R. Similarly, for Eudistomidin C and Fusarithioamide A having known stereochemistry, the attempts to perform their syntheses were made starting from enantiomerically pure reagents. The synthesized compounds BSc5484, BSc5517 and the analogues were subjected to biological activity tests afterwards. Accordingly, a kinase inhibitory activity test was performed, followed by an in vivo toxicology assay in wild-type and gold-type zebrafish embryos Danio rerio. As a result, the assayed compounds displayed moderate to good inhibition of the kinases with an apparent selectivity profile and toxicity in zebrafish embryos illustrated by the observed phenotypes. Finally, an in silico experiment revealed that BSc5484 and BSc5485 might bind as type IV inhibitors, while BSc5517 demonstrated a better binding affinity to human Haspin kinase compared to the known b-carboline inhibitor Harmine across the panel of the tested kinases. This work thus provides the first directed tools about the potential of naturally derived compounds as inhibitors of disease-causing proteins that are key players in numerous forms of cancer and other illnesses. Consequently, establishing depsipeptide and b-carboline-based compounds as therapeutic leads is crucial and will provide a powerful tool to further elucidate their biological function through targeted structural variations

    Antibacterial Activity of Nanoparticle Biosynthesis by Bacteria

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    الخلفية: لا تزال العدوى البكتيرية هي السبب الأكثر شيوعًا للمرض والوفاة في العالم. وفقًا لتقرير منظمة الصحة العالمية، تشكل مقاومة البكتيريا للمضادات الحيوية تهديدًا خطيرًا للصحة العامة العالمية. في السنوات الأخيرة، زاد استخدام الجسيمات النانوية  كبديل للمضادات الحيوية.    النتائج: نظرًا لنشاط الجسيمات النانوية المضاد للبكتيريا المتأصل، فإن الجسيمات النانوية المعدنية وأكسيد المعادن هي أكثر المواد النانوية الواعدة للتطبيقات البيولوجية. على الرغم من أن للجسيمات النانوية خصائص مضادة للبكتيريا مثيرة للاهتمام، إلا أن استخدامها في التطبيقات الطبية مقيد حاليًا بسبب عدم وجود فهم واضح للآليات الكامنة وراء عملها.  الخلاصة: كان التركيز الرئيسي لهذه المراجعة على التفاعلات بين البكتيريا والقدرات المضادة للبكتيريا للجسيمات النانوية. ملامسة الغشاء، إطلاق الكاتيون، أكسدة الجزيئات الحيوية، إنتاج أنواع الأكسجين التفاعلية، وأنواع الأكسجين التفاعلية هي بعض الطرق التي  يمكن للبكتريا ان تقتل بها نفسها. يعد فحص كيفية تأثير الجسيمات النانوية   على أنماط تنظيم الجينات والبروتينات (النسخية والبروتينية) امرا بالغ الاهمية.   Background: The world's most common cause of illness and death is still bacterial infections. According to a World Health Organization report, bacterial resistance to antibiotics poses a serious threat to global public health. In recent years, the use of nanoparticles (NPs) as an antibiotic alternative has increased. Results: Due to the nanoparticles' inherent antibacterial activity, metal and metal oxide nanoparticles are the most promising nanomaterials for biological applications. Although nanoparticles have intriguing antibacterial properties, their use in medical applications is currently restricted due to the lack of clear understanding of the mechanisms underlying their action. Conclusion: The main focus of this review  was the interactions between bacteria and the antibacterial capabilities of nanoparticles. Membrane contact, cation release, biomolecule oxidation, production of reactive oxygen species, and reactive oxygen species are  some ways bacteria can kill themselves.  Examining how NP affects gene and protein regulation patterns (transcriptomic and proteomic) is crucial

    Membrane Effects of Antimicrobial Peptides

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    Antimicrobial resistance is becoming an increasing challenge that threatens the human health system. The overuse of antibiotics has led to an acceleration in the emergence of antibiotic-resistant bacteria, the result of bacterial adaption to evolutionary pressure when they encounter antibiotics. Thus, bacteria constantly evolve resistance genes in order to survive, which makes it hard if not impossible to find an effective antibiotic that does not induce any antibiotic resistance at all. Chemical modification has helped to extend the useful lifetime of clinically used antibiotics that encountered resistance. Yet, this likely only postpones the inevitable clinical failure of a whole class of antibiotics in the future. Hence, it is important to discover new antibiotics and study their modes of action. This thesis is centered on studying the mode of action (MoA) of antimicrobial peptides (AMPs). These AMPs form a large family of peptides that have broad spectrum antibiotic activity against bacteria including antibiotic-resistant bacteria. They are regarded as potential candidates to tackle the rising antimicrobial resistant problem. Chapter 1 introduces the bacterial cell wall synthesis pathway and its central precursor Lipid II as well as the family of lantibiotics, a large family of post-translationally modified AMPs. Those AMPS have the potential to tackle the antibiotic-resistant bacteria problem. In Chapter 2, we briefly describe the regulation of intracellular pH homeostasis, ion homeostasis and ATP synthesis, three interrelated phenomena, in bacteria. The intracellular proton gradient (∆pH), electrical potential (∆ψ) and ATP synthesis/hydrolysis are actively or passively regulated by bacteria when under outside stresses such as antibiotic treatment. This is especially relevant for AMPs that target the bacterial membrane as the membrane plays a central role in all these processes. Monitoring the changes of ∆pH, ∆ψ and ATP level thus provides important insight into the MoAs of these AMPs. Chapter 3 introduces epilancin 15X and the first steps to unravel its mode of action. Here, 5 probes are used to study the membrane effects of epilancin 15X and to compare these to those caused by nisin and the chemical variant of teixobactin, [R4L10]-teixobactin, in the gram-positive bacteria Staphylococcus simulans, Micrococcus flavus and Bacillus megaterium. Chapter 4 is zooming in on the mode of action of epilancin 15X and the possible involvement of Lipid II. Clear interaction between epilancin 15X and Lipid II was observed by antagonism-based experiments. However, epilancin’s interaction with Lipid II did not lead to membrane effects. While it remained uncertain if Lipid II is the target of epilancin 15X, depolarization assays did point to the involvement of a target within a polyisoprene-based biosynthesis pathway, as clear effects could be observed on the activity of epilancin 15X by compounds that acted specifically on these pathways. Yet, unfortunately, the exact target of epilancin 15X remains obscure so far. Chapter 5 studies the mode of action of brevibacillins. They belong to a novel class of non-ribosomally produced lipo-tridecapeptides and exhibit activity towards antimicrobial resistant pathogens. Binding to Lipid II and membrane permeabilization were thus considered as 2 independent modes of action of brevibacillins

    Some bis (3-(4-nitrophenyl)acrylamide derivatives: Synthesis, characterization, DFT, antioxidant, antimicrobial properties, molecular docking and molecular dynamics simulation studies

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    Alzheimer's disease, which is a progressive neurologic disorder, is the most common form of dementia. Although there are various treatment options for Alzheimer’s disease, there is no definite treatment for this disease yet. In this study it was aimed to investigate the treatment potentials of three bis(3-(4-nitrophenyl)acrylamide) derivatives, two of which are known and one is new, for Alzheimer's disease. The study consists of three parts; in the first part of the study, synthesis and characterization studies of the investigated compounds were carried out. In the characterization of the compounds, IR, 1H-NMR, 13C-NMR, LC-MS and elemental analysis techniques were used. In the second part of the study, the compounds were investigated computationally with the assistance of various computational techniques including density functional theory (DFT) calculations, molecular docking and molecular dynamics simulations. In this part, binding free energy calculations were also performed on the investigated compounds. Results of computational studies showed that synthesized compounds interacted with AChE effectively and can be promising structures as AChE inhibitors. In the last part of the study, antioxidant and antimicrobial properties of the compounds were investigated. Antioxidant activities were determined by DPPH˙ and ABTS˙⁺ radical scavenging methods. According to the DPPH˙ test, the most active compound was found to be 2, while the most active compound was found to be 3 according to the ABTS⁺ test, showing that these methods for antioxidant assay were not significantly correlated with each other. On the other hand, the results of the antimicrobial activity tests showed that compound 3 was the most active compound, which exhibited both antioxidant and antimicrobial activity

    Novel ruthenium metal-based complexes as antimicrobial agents

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    Antimicrobial resistance (AMR) is becoming increasingly prevalent amongst clinically significant bacteria. The World Health Organization (WHO) has declared AMR as one of the greatest public health threats facing humanity. There has been a sharp decline in the number of new clinically approved antibiotics, with most new antibiotics being based on pre-existing antibiotic scaffolds. As a result, there is an urgent need for new novel ways to treat infections caused by AMR bacteria. There has been an increased focus on Ruthenium (Ru) complexes acting as antimicrobial agents. This is in part due to their biological compatibility, multiple oxidation states and bonding configuration allowing for specific geometries that are ideally suited for biological applications. This study evaluated the antimicrobial activity of 12 repurposed Ru complexes. Preliminary screening against a diverse selection of clinically significant bacteria identified Ru complexes 1 (C22H23Cl3N2SRu) and 7 ([Ru(NH3)6]Cl3) as potential lead candidates with the Ru complexes acted as bactericidal agents against S. aureus USA300 JE2 and P. aeruginosa PAO1 respectively. Eukaryotic cytotoxicity testing against HeLa and HEK 293T cell lines demonstrated Ru complex 7 exhibited no significant cytotoxic effects against both cell lines (p>0.05), whilst Ru complex 1 was significantly cytotoxic (p<0.05). S. aureus USA300 JE2 and E. coli EC958 were able to tolerate an 11-fold increase in MIC after long term incrementally increasing concentrations of Ru complex 1. Comparative genome analysis of S. aureus USA300 JE2 showed long term exposure to Ru complex 1 increased the rate of mutagenesis and led to 17 de novo mutations being identified within eight genes. Furthermore, significant gene expression changes in clpP, katA and norA were reported in S. aureus USA300 JE2 after exposure to Ru complex 1, indicating Ru complex 1 affected a wide array of cellular functions. The mechanisms of action for antimicrobials Ru complex 1 and 7 were investigated. Ru complex 1 displayed no significant outer membrane or inner membrane permeabilising effects, whilst Ru complex 7 caused no significant outer membrane permeabilising but did stimulate elevated depolarisation of the inner membrane in a number of bacterial species. Scanning electron microscopy confirm that both complexes appeared not to be directly targeting the outer membrane as no cellular morphological changes were observed. Cellular metal uptake studies using Ru complexes 1 and 7 showed elevated intracellular concentrations in S. aureus USA300 JE2 and P. aeruginosa PAO1 respectively compared to the exposure concentrations. Electrophoretic mobility shift assays (EMSA) and competitive binding assays showed that intracellular concentrations of Ru complexes 1 and 7 had a significant impact on DNA mobility and displacement of SYTO 9 from the SYTO 9/DNA complex. Exposure to Ru complexes 1 and 7 caused elevated but not significant levels of reactive oxygen species generation (ROS) in S. aureus USA300 JE2, P. aeruginosa PAO1 and E. coli EC958 The results of the thesis demonstrate the potential to use mononuclear Ru complexes as antimicrobial agents. Notably, the potent antimicrobial activity of Ru complex 7 against P. aeruginosa PAO1, coupled with low levels of cytotoxicity make this an ideal candidate for further in vivo investigation

    Development of teixobactin analogues containing hydrophobic, non-proteogenic amino acids that are highly potent against multidrug-resistant bacteria and biofilms.

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    Teixobactin is a cyclic undecadepsipeptide that has shown excellent potency against multidrug-resistant pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE). In this article, we present the design, synthesis, and antibacterial evaluations of 16 different teixobactin analogues. These simplified analogues contain commercially available hydrophobic, non-proteogenic amino acid residues instead of synthetically challenging expensive L-allo-enduracididine amino acid residue at position 10 together with different combinations of arginines at positions 3, 4 and 9. The new teixobactin analogues showed potent antibacterial activity against a broad panel of Gram-positive bacteria, including MRSA and VRE strains. Our work also presents the first demonstration of the potent antibiofilm activity of teixobactin analogoues against Staphylococcus species associated with serious chronic infections. Our results suggest that the use of hydrophobic, non-proteogenic amino acids at position 10 in combination with arginine at positions 3, 4 and 9 holds the key to synthesising a new generation of highly potent teixobactin analogues to tackle resistant bacterial infections and biofilms

    Exploring the selectivity and engineering potential of an NRPS condensation domain involved in the biosynthesis of the thermophilic siderophore fuscachelin

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    In nonribosomal peptide synthesis, condensation (C) domains are key catalytic domains that most commonly link carrier protein bound substrates to form peptides or depsipeptides. While adenylation domains have been well characterized due to their role in the selection of monomers and hence as gate keepers in nonribosomal peptide biosynthesis, C-domains have been the subject of debate as they do not have apparent “A-domain like” side chain selectivity for their acceptor substrates. To probe the selectivity and specificity of C-domains, here we report our biochemical and structural characterization of the C3-domain from the biosynthesis of the siderophore fusachelin. Our results show that this C-domain is not broadly flexible for monomers bearing significantly alternated side chains or backbones, which suggests there can be a need to consider C-domain specificity for acceptor substrates when undertaking NRPS engineering