Mechanistic Evaluation of Lipopolysaccharide-Alexidine Interaction Using Spectroscopic and in Silico Approaches

The membrane-active polyaminoisoprenyl compound NV716 re-sensitizes Pseudomonas aeruginosa to antibiotics and reduces bacterial virulence

Pseudomonas aeruginosa is intrinsically resistant to many antibiotics due to the impermeability of its outer membrane and to the constitutive expression of efflux pumps. Here, we show that the polyaminoisoprenyl compound NV716 at sub-MIC concentrations re-sensitizes P. aeruginosa to abandoned antibiotics by binding to the lipopolysaccharides (LPS) of the outer membrane, permeabilizing this membrane and increasing antibiotic accumulation inside the bacteria. It also prevents selection of resistance to antibiotics and increases their activity against biofilms. No stable resistance could be selected to NV716-itself after serial passages with subinhibitory concentrations, but the transcriptome of the resulting daughter cells shows an upregulation of genes involved in the synthesis of lipid A and LPS, and a downregulation of quorum sensing-related genes. Accordingly, NV716 also reduces motility, virulence factors production, and biofilm formation. NV716 shows a unique and highly promising profile of activity when used alone or in combination with antibiotics against P. aeruginosa, combining in a single molecule anti-virulence and potentiator effects. Additional work is required to more thoroughly understand the various functions of NV716.

The polyaminoisoprenyl compound NV716 re-sensitizes Pseudomonas aeruginosa to antibiotics through permeabilizing the outer membrane and increases the activity of antibiotics on biofilms.

Phosphatase inhibitors BVT-948 and alexidine dihydrochloride inhibit sexual development of the malaria parasite Plasmodium berghei

Background

With the emergence of resistance to front-line antimalarials, there is an urgent need to develop new medicines, including those targeting sexual development. This study aimed to assess the activity of a panel of phosphatase inhibitors against the sexual development of Plasmodium berghei and evaluate their potential as transmission-blocking agents.

Methods

Twenty-five compounds were screened for transmission-blocking activity in vitro using the P. berghei ookinete culture assay. The inhibitory effects on male gametogenesis, gamete-ookinete, and zygote-ookinete formation were evaluated. The transmission-blocking activity of two compounds was evaluated using an in vivo mosquito feeding assay. Their cytotoxic effects were assessed on the human cell line HepG2.

Results

Twelve compounds inhibited P. berghei ookinete formation with an IC₅₀ < 10 μM. Two compounds, BVT-948 and alexidine dihydrochloride, significantly inhibited different developmental stages from gametogenesis through ookinete maturation. They also showed a substantial in vivo transmission-blocking activity by the mosquito feeding assay.

Conclusions

Some phosphatase inhibitors effectively inhibited Plasmodium sexual development and exhibited evident transmission-blocking activity, suggesting that phosphatases are valid targets for antimalarial development.

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BVT-948 and alexidine·2HCl inhibit sexual developmental stages of Plasmodium.

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BVT-948 and alexidine·2HCl show a substantial transmission-blocking activity.

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BVT-948 and alexidine·2HCl show a relatively low cytotoxicity to HepG2 cells.

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Phosphatases are valid targets for antimalarial development.

Fighting Against Bacterial Lipopolysaccharide-Caused Infections through Molecular Dynamics Simulations: A Review

Lipopolysaccharide (LPS) is the primary component of the outer leaflet of Gram-negative bacterial outer membranes. LPS elicits an overwhelming immune response during infection, which can lead to life-threatening sepsis or septic shock for which no suitable treatment is available so far. As a result of the worldwide expanding multidrug-resistant bacteria, the occurrence and frequency of sepsis are expected to increase; thus, there is an urge to develop novel strategies for treating bacterial infections. In this regard, gaining an in-depth understanding about the ability of LPS to both stimulate the host immune system and interact with several molecules is crucial for fighting against LPS-caused infections and allowing for the rational design of novel antisepsis drugs, vaccines and LPS sequestration and detection methods. Molecular dynamics (MD) simulations, which are understood as being a computational microscope, have proven to be of significant value to understand LPS-related phenomena, driving and optimizing experimental research studies. In this work, a comprehensive review on the methods that can be combined with MD simulations, recently applied in LPS research, is provided. We focus especially on both enhanced sampling methods, which enable the exploration of more complex systems and access to larger time scales, and free energy calculation approaches. Thereby, apart from outlining several strategies for surmounting LPS-caused infections, this work reports the current state-of-the-art of the methods applied with MD simulations for moving a step forward in the development of such strategies.

Biguanides: Species with versatile therapeutic applications

Biguanides are compounds in which two guanidine moieties are fused to form a highly conjugated system. Biguanides are highly basic and hence they are available as salts mostly hydrochloride salts, these cationic species have been found to exhibit many therapeutic properties. This review covers the research and development carried out on biguanides and accounts the various therapeutic applications of drugs containing biguanide group-such as antimalarial, antidiabetic, antiviral, anticancer, antibacterial, antifungal, anti-tubercular, antifilarial, anti-HIV, as well as other biological activities. The aim of this review is to compile all the medicinal chemistry applications of this class of compounds so as to pave way for the accelerated efforts in finding the drug action mechanisms associated with this class of compounds. Importance has been given to the organic chemistry of these biguanide derivatives also.

A Single Step in vitro Bioassay Mimicking TLR4-LPS Pathway and the Role of MD2 and CD14 Coreceptors

Acute systemic Gram-negative bacterial infections are accompanied by release of lipopolysaccharide (LPS) endotoxins into the bloodstream and an innate immune host response via the well-known toll like receptor 4 (TLR4) pathway. In this, LPS associates non-covalently with TLR4 to form an activated heterodimer (LPS/MD2/TLR4)₂ complex in vivo, assisted by a coreceptor CD14. This complexation process has been illustrated ex vivo using indirect methods such as cytokine, interleukin, TNF-α measurements and by direct demonstration of sequential binding events on a surface using advanced optics. We are the first ones to carry out homogeneous self-assembly of LPS-rTLR4-MD2 conjugates in vitro in a single step, and further demonstrate the role of CD14 as a catalyst during this process. The assay comprises of LPS, MD2, CD14, and recombinant TLR4-conjugated magnetic particles co-incubated in a buffer at room temperature. The complexes are removed by magnetic separation and the extent of binding is estimated by quantifying the unbound biomolecules in the supernatant using standard biophysical techniques. Our results show that rTLR4-MD2-LPS complexes form in an hour and follow a 1:1:1 stoichiometry, in agreement with the in vivo/ex vivo studies. The assay is also highly specific; addition of known LPS-binding ligands decreased the LPS-rTLR4 complexation, allowing its use as a rapid tool for molecular inhibitor screening.

Selective Labeling and Growth Inhibition of Pseudomonas aeruginosa by Aminoguanidine Carbon Dots

Pseudomonas aeruginosa is a highly virulent bacterium, particularly associated with the spread of multidrug resistance. Here we show that carbon dots (C-dots), synthesized from aminoguanidine and citric acid precursors, can selectively stain and inhibit the growth of P. aeruginosa strains. The aminoguanidine-C-dots were shown both to target P. aeruginosa bacterial cells and also to inhibit biofilm formation by the bacteria. Mechanistic analysis points to interactions between aminoguanidine residues on the C-dots' surface and P. aeruginosa lipopolysaccharide moieties as the likely determinants for both antibacterial and labeling activities. Indeed, the application of biomimetic membrane assays reveals that LPS-promoted insertion and bilayer permeation constitute the primary factors in the anti- P. aeruginosa effect of the aminoguanidine-C-dots. The aminoguanidine C-dots are easy to prepare in large quantities and are inexpensive and biocompatible and thus may be employed as a useful vehicle for selective staining and antibacterial activity against P. aeruginosa.