Bioassay Guided Isolation and Docking Studies of a Potential β-Lactamase Inhibitor from Clutia myricoides

Isolation of quinic acid from dropped Citrus reticulata Blanco fruits: its derivatization, antibacterial potential, docking studies, and ADMET profiling

Citrus reticulata dropped fruits are generally discarded as waste, causing environmental pollution and losses to farmers. In the present study, column chromatography has been used to isolate quinic acid (1,3,4,5-tetrahydroxycyclohexane-1-carboxylic acid) from the ethyl acetate fraction of a methanol extract of citrus fruits dropped in April. Quinic acid is a ubiquitous plant metabolite found in various plants and microorganisms. It is an important precursor in the biosynthesis of aromatic natural compounds. It was further derivatized into 3,4-o-isopropylidenequinic acid 1,5-lactone (QA1), 1,3,4,5-tetraacetoxycyclohexylaceticanhydride (QA2), and cyclohexane-1,2,3,5-tetraone (QA3). These compounds were further tested for their antibacterial potential against the foodborne pathogens Staphylococcus aureus, Bacillus spp., Yersinia enterocolitica, and Escherichia coli. QA1 exhibited maximum antibacterial potential (minimum inhibitory concentration; 80-120 μg/mL). QA1 revealed synergistic behavior with streptomycin against all the tested bacterial strains having a fractional inhibitory concentration index ranging from 0.29 to 0.37. It also caused a significant increase in cell constituent release in all the tested bacteria compared to the control, along with prominent biofilm reduction. The results obtained were further checked with computational studies that revealed the best docking score of QA1 (-6.30 kcal/mol, -5.8 kcal/mol, and -4.70 kcal/mol) against β-lactamase, DNA gyrase, and transpeptidase, respectively. The absorption, distribution, metabolism, excretion, and toxicity (ADMET) analysis revealed that the drug-like properties of QA1 had an ideal toxicity profile, making it a suitable candidate for the development of antimicrobial drugs.

Drug Discovery in the Field of β-Lactams: An Academic Perspective

β-Lactams are the most widely prescribed class of antibiotics that inhibit penicillin-binding proteins (PBPs), particularly transpeptidases that function in peptidoglycan synthesis. A major mechanism of antibiotic resistance is the production of β-lactamase enzymes, which are capable of hydrolyzing β-lactam antibiotics. There have been many efforts to counter increasing bacterial resistance against β-lactams. These studies have mainly focused on three areas: discovering novel inhibitors against β-lactamases, developing new β-lactams less susceptible to existing resistance mechanisms, and identifying non-β-lactam inhibitors against cell wall transpeptidases. Drug discovery in the β-lactam field has afforded a range of research opportunities for academia. In this review, we summarize the recent new findings on both β-lactamases and cell wall transpeptidases because these two groups of enzymes are evolutionarily and functionally connected. Many efforts to develop new β-lactams have aimed to inhibit both transpeptidases and β-lactamases, while several promising novel β-lactamase inhibitors have shown the potential to be further developed into transpeptidase inhibitors. In addition, the drug discovery progress against each group of enzymes is presented in three aspects: understanding the targets, screening methodology, and new inhibitor chemotypes. This is to offer insights into not only the advancement in this field but also the challenges, opportunities, and resources for future research. In particular, cyclic boronate compounds are now capable of inhibiting all classes of β-lactamases, while the diazabicyclooctane (DBO) series of small molecules has led to not only new β-lactamase inhibitors but potentially a new class of antibiotics by directly targeting PBPs. With the cautiously optimistic successes of a number of new β-lactamase inhibitor chemotypes and many questions remaining to be answered about the structure and function of cell wall transpeptidases, non-β-lactam transpeptidase inhibitors may usher in the next exciting phase of drug discovery in this field.

Compounds Related to Saudin and Three New Series of Diterpenoids from Clutia lanceolata

Clutia lanceolata is a medicinal plant native to Ethiopia and sub-Saharan Africa and to the Arabian Peninsula. It is used traditionally in Saudi Arabia for the treatment of diabetes. Previous phytochemical analysis of this species has been limited to the identification of methylthiocoumarins. Further work has led to isolation of 19 new diterpenoids in three structural classes. Their structures were established by HRMS and by a range of NMR techniques (1H, 13C, COSY, NOESY, HSQC, HMBC), with confirmation for some examples by X-ray crystallography. NOESY and 1H-1H NMR coupling constants gave the relative stereochemical configurations and conformational information, with absolute configurations being established through X-ray crystallography. One example closely related to the known hypoglycemic compound saudin (found in C. richardiana and also in C. lanceolata) and one with a different core tetracycle were found to enhance strongly the glucose-triggered release of insulin from murine pancreatic islets. Biosynthetic proposals for the three groups of new diterpenoids by alternative cyclization of a common precursor are put forward. Lanceolide P (16) is proposed as a lead compound for further development for the treatment of diabetes.

Neolamarckia cadamba (Roxb.) Bosser (Rubiaceae) extracts: promising prospects for anticancer and antibacterial potential through in vitro and in silico studies

Neolamarckia cadamba is an Indian traditional medicinal plant having various therapeutic potentials. In the present study, we did solvent-based extraction of Neolamarckia cadamba leaves. The extracted samples were screened against liver cancer cell line (HepG2) and bacteria (Escherichia coli). MTT cytotoxic assay was performed for in vitro analysis of extracted samples against the HepG2 cell lines and the normal human prostate PNT2 cell line. Chloroform extract of Neolamarckia cadamba leaves showed better activity with IC50 value 69 μg/ml. DH5α strain of Escherichia coli (E. coli) was cultured in Luria Bertani (LB) broth media and minimum inhibitory concentration (MIC) and Minimum bactericidal concentration (MBC) were calculated. Solvent extract chloroform showed better activity in MTT analysis and antibacterial screening and it was taken for characterization of phytocomposition by Fourier transform infrared (FTIR) and gas chromatography mass spectrometry (GC-MS). The identified phytoconstituents were docked with potential targets of liver cancer and E. coli. The phytochemical 1-(5-Hydroxy-6-hydroxymethyl-tetrahydropyran-2-yl)-5-methyl-1H-pyrimidine-2,4-dione shows highest docking score against the targets PDGFRA (PDB ID: 6JOL) and Beta-ketoacyl synthase 1(PDB ID: 1FJ4) and their stability was further confirmed by molecular dynamics simulation studies.

Antibacterial sensitizers from natural plants: A powerful weapon against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a drug-resistant bacterium that can cause a range of infections with high morbidity and mortality, including pneumonia, etc. Therefore, development of new drugs or therapeutic strategies against MRSA is urgently needed. Increasing evidence has shown that combining antibiotics with "antibacterial sensitizers" which itself has no effect on MRSA, is highly effective against MRSA. Many studies showed the development of antibacterial sensitizers from natural plants may be a promising strategy against MRSA because of their low side effects, low toxicity and multi-acting target. In our paper, we first reviewed the resistance mechanisms of MRSA including "Resistance to Beta-Lactams", "Resistance to Glycopeptide antibiotics", "Resistance to Macrolides, Aminoglycosides, and Oxazolidinones" etc. Moreover, we summarized the possible targets for antibacterial sensitizers against MRSA. Furthermore, we reviewed the synergy effects of active monomeric compounds from natural plants combined with antibiotics against MRSA and their corresponding mechanisms over the last two decades. This review provides a novel approach to overcome antibiotic resistance in MRSA.

Innovative next-generation therapies in combating multi-drug-resistant and multi-virulent Escherichia coli isolates: insights from in vitro, in vivo, and molecular docking studies

Despite notable advances in vaccine and antimicrobial therapies, treatment failure has been increasingly reported worldwide. Of note, multi-drug-resistant (MDR) Escherichia coli (E. coli) strains have a considerable share in the evolution of this crisis. So, current practice guidelines are directed towards complementary and alternative therapies. Therefore, we evaluated the antibacterial and antivirulence activities of curcumin, thymol, and eugenol essential oils (EOs) as well as EOs-EOs and EOs-antibiotics interactions on MDR and multi-virulent E. coli isolates. Unfortunately, MDR E. coli could be isolated with a prevalence rate of 95.6% (86/90). Additionally, the majority of our isolates harbored both fimH (95.6%) and ompA (91.1%) genes, and half of them (45/90) were multi-virulent. Interestingly, all the tested EOs, especially curcumin, exhibited inhibitory activities against all MDR and multi-virulent E. coli isolates. The addition of thymol enhanced the antibacterial activities of curcumin and eugenol. Moreover, the activities of piperacillin/tazobactam and imipenem were increased by adding any one of the tested EOs. Regarding the antivirulence activities of the tested EOs, the cell surfaces of treated E. coli isolates under transmission electron microscope (TEM) were uneven. The cells appeared damaged and lost their appendages. Furthermore, EOs strongly reduced the transcription of ompA and fimH genes. The antibacterial and antivirulence activities of the used EOs were confirmed by in silico and mice protection assays. Hereby, we introduced the promising uses of curcumin, thymol, and eugenol oils as complementary and alternative therapies for combating MDR and multi-virulent E. coli isolates. KEY POINTS: • Our promising results confirmed that we were right for renewed interest of EOs. • The EOs, especially curcumin, can be used to prevent treatment failure. • We supposed a new pharmaceutical formulation of antibiotic powders dissolved in EOs.

Four New Anthraquinones with Histone Deacetylase Inhibitory Activity from Ventilago denticulata Roots

Chromatographic separation of the crude extracts from the roots of Ventilago denticulata led to the isolation of four new anthraquinones, ventilanones L–O (1–4), together with eight known anthraquinones (5–12). Their structures were elucidated by spectroscopic methods (UV, IR, ¹H NMR, ¹³C NMR, and 2D NMR) and mass spectrometry (MS), as well as comparison of their spectroscopic data with those reported in the literature. HDACs inhibitory activity evaluation resulted that compound 2 exhibited moderate antiproliferative activity against HeLa and A549 cell lines but nontoxic to normal cell. Molecular docking indicated the phenolic functionality of 2 plays crucial interactions with class II HDAC4 enzyme.

Repurposing of antidiabetics as Serratia marcescens virulence inhibitors

BACKGROUND

Serratia marcescens becomes an apparent nosocomial pathogen and causes a variety of infections. S. marcescens possess various virulence factors that are regulated by intercellular communication system quorum sensing (QS). Targeting bacterial virulence is a proposed strategy to overcome bacterial resistance. Sitagliptin anti-QS activity has been demonstrated previously and we aimed in this study to investigate the effects of antidiabetic drugs vildagliptin and metformin compared to sitagliptin on S. marcescens pathogenesis.

METHODS

We assessed the effects of tested drugs in subinhibitory concentrations phenotypically on the virulence factors and genotypically on the virulence encoding genes' expressions. The protection of tested drugs on S. marcescens pathogenesis was performed in vivo. Molecular docking study has been conducted to evaluate the interference capabilities of tested drugs to the SmaR QS receptor.

RESULTS

Vildagliptin reduced the expression of virulence encoding genes but did not show in vitro or in vivo anti-virulence activities. Metformin reduced the expression of virulence encoding genes and inhibited bacterial virulence in vitro but did not show in vivo protection. Sitagliptin significantly inhibited virulence factors in vitro, reduced the expression of virulence factors and protected mice from S. marcescens. Docking study revealed that sitagliptin is more active than metformin and fully binds to SmaR receptor, whereas vildagliptin had single interaction to SmaR.

CONCLUSION

The downregulation of virulence genes was not enough to show anti-virulence activities. Hindering of QS receptors may play a crucial role in diminishing bacterial virulence.

seco-Labdanes: A Study of Terpenoid Structural Diversity Resulting from Biosynthetic C-C Bond Cleavage

The cleavage of a C-C bond is a complexity generating process, which complements oxidation and cyclisation events in the biosynthesis of terpenoids. This process leads to increased structural diversity in a cluster of related secondary metabolites by modification of the parent carbocyclic core. In this review, we highlight the diversifying effect of C-C bond cleavage by examining the literature related to seco-labdanes-a class of diterpenoids arising from such C-C bond cleavage events.

Repurposing Anti-diabetic Drugs to Cripple Quorum Sensing in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a significant human pathogen, it possesses almost all of the known antimicrobial resistance mechanisms. Quorum sensing (QS) is an intercellular communication system that orchestrates bacterial virulence and its targeting is an effective approach to diminish its pathogenesis. Repurposing of drugs is an advantageous strategy, in this study we aimed to repurpose the anti-diabetic drugs sitagliptin, metformin and vildagliptin as anti-QS in P. aeruginosa. The effects of sub-inhibitory concentrations of the tested drugs on the expression of QS-encoding genes and QS-regulated virulence factors were assessed. The protective activity of tested drugs on P. aeruginosa pathogenesis was evaluated in vivo on mice. In silico analysis was performed to evaluate the interference capabilities of the tested drugs on QS-receptors. Although the three drugs reduced the expression of QS-encoding genes, only sitagliptin inhibited the P. aeruginosa virulence in vitro and protected mice from it. In contrast, metformin showed significant in vitro anti-QS activities but failed to protect mice from P. aeruginosa. Vildagliptin did not show any in vitro or in vivo efficacy. Sitagliptin is a promising anti-QS agent because of its chemical nature that hindered QS-receptors. Moreover, it gives an insight to consider their similar chemical structures as anti-QS agents or even design new chemically similar anti-QS pharmacophores.