Novel Vanillin-based hybrids inhibit quorum sensing and silences phenotypical expressions in Pseudomonas aeruginosa

Tailored multilayer nanoparticles against resistant P. aeruginosa by disrupting the thickened mucus, dense biofilm and hyperinflammation

Therapeutic challenges of chronic pulmonary infections caused by multidrug-resistant Pseudomonas aeruginosa (MDRP. aeruginosa) biofilms due to significantly enhanced antibiotic resistance. This resistance is driven by reduced outer membrane permeability, biofilm barriers, and excessive secretion of virulence factors. Thickened mucus in the airways exacerbates the problem by impeding antibiotic penetration, providing a breeding ground for biofilms, consequently aggravating infection. Moreover, biofilms recruit numerous immune cells, resulting in chronic inflammation and lung tissue damage. In turn, damaged airway further facilitates bacterial colonization and elevated mucus production. To thoroughly disintegrate the stubborn triad of "thickened mucus & dense biofilm & excessive inflammation" and address drug resistance, tailored multilayer nanoparticles (NPVC/PBIP NPs) were developed. NPVC/PBIP NPs were engineered through self-assembly of vanillin-chitosan amphiphilic polymer loading polymyxin B-linoleic acid ion pairs in. Then polyaspartic acid and N-acetylcysteine-ε-poly-l-lysine were coated by layer-by-layer on the surface of vanillin-chitosan NPs via electrostatic interactions. As expected, the NAC units on NPVC/PBIP NPs effectively thinned human clinical sputum and porcine sputum, resulting in rapid sputum penetration followed by biofilm permeation. NPVC/PBIP NPs achieved over 99 % eradication of mature biofilms in vitro. Furthermore, they effectively inhibited virulence factors production and bacteria re-adhesion (biofilm reformation) while exhibiting superior anti-inflammatory and antioxidant activities. In a chronic pulmonary infection model, NPVC/PBIP NPs remarkably thinned airway mucus, reduced bacterial burden by 99.7 %, alleviated inflammatory cell infiltration, and minimized lung tissue damage. In summary, the NPVC/PBIP NPs represent a novel and promising strategy to manage MDRP. aeruginosa biofilms associated infections by disintegrating the stubborn triad of "thickened mucus & dense biofilm & excessive inflammation".

Characterization of natural product inhibitors of quorum sensing reveals competitive inhibition of Pseudomonas aeruginosa RhlR by ortho-vanillin

Quorum sensing (QS) is a cell-cell signaling system that enables bacteria to coordinate population density-dependent changes in behavior. This chemical communication pathway is mediated by diffusible N-acyl L-homoserine lactone signals and cytoplasmic signal-responsive LuxR-type receptors in Gram-negative bacteria. As many common pathogenic bacteria use QS to regulate virulence, there is significant interest in disrupting QS as a potential therapeutic strategy. Prior studies have implicated the natural products salicylic acid, cinnamaldehyde, and other related benzaldehyde derivatives as inhibitors of QS in the opportunistic pathogen Pseudomonas aeruginosa, yet we lack an understanding of the mechanisms by which these compounds function. Herein, we evaluate the activity of a set of benzaldehyde derivatives using heterologous reporters of the P. aeruginosa LasR and RhlR QS signal receptors. We find that most tested benzaldehyde derivatives can antagonize LasR or RhlR reporter activation at micromolar concentrations, although certain molecules also cause mild growth defects and nonspecific reporter antagonism. Notably, several compounds showed promising RhlR or LasR-specific inhibitory activities over a range of concentrations below that causing toxicity. ortho-Vanillin, a previously untested compound, was the most promising within this set. Competition experiments against the native ligands for LasR and RhlR revealed that ortho-vanillin can interact competitively with RhlR but not with LasR. Overall, these studies expand our understanding of benzaldehyde activities in the LasR and RhlR receptors and reveal potentially promising effects of ortho-vanillin as a small molecule QS modulator against RhlR.

IMPORTANCE

Quorum sensing (QS) regulates many aspects of bacterial pathogenesis and has attracted much interest as a target for anti-virulence therapies over the past 30 years, for example, antagonists of the LasR and RhlR QS receptors in Pseudomonas aeruginosa. Potent and selective QS inhibitors remain relatively scarce. However, natural products have provided a bounty of chemical scaffolds with anti-QS activities, but their molecular mechanisms are poorly characterized. The current study serves to fill this void by examining the activity of an important and wide-spread class of natural product QS modulators, benzaldehydes, and related derivatives, in LasR and RhlR. We demonstrate that ortho-vanillin can act as a competitive inhibitor of RhlR, a receptor that has emerged and may supplant LasR in certain settings as a target for P. aeruginosa QS control. The results and insights provided herein will advance the design of chemical tools to study QS with improved activities and selectivities.

Characterization of natural product inhibitors of quorum sensing in Pseudomonas aeruginosa reveals competitive inhibition of RhlR by ortho-vanillin

Quorum sensing (QS) is a cell-cell signaling system that enables bacteria to coordinate population density-dependent changes in behavior. This chemical communication pathway is mediated by diffusible N-acyl L-homoserine lactone signals and cytoplasmic signal-responsive LuxR-type receptors in Gram-negative bacteria. As many common pathogenic bacteria use QS to regulate virulence, there is significant interest in disrupting QS as a potential therapeutic strategy. Prior studies have implicated the natural products salicylic acid, cinnamaldehyde and other related benzaldehyde derivatives as inhibitors of QS in the opportunistic pathogen Pseudomonas aeruginosa, yet we lack an understanding of the mechanisms by which these compounds function. Herein, we evaluate the activity of a set of benzaldehyde derivatives using heterologous reporters of the P. aeruginosa LasR and RhlR QS signal receptors. We find that most tested benzaldehyde derivatives can antagonize LasR or RhlR reporter activation at micromolar concentrations, although certain molecules also caused mild growth defects and nonspecific reporter antagonism. Notably, several compounds showed promising RhlR or LasR specific inhibitory activities over a range of concentrations below that causing toxicity. Ortho-Vanillin, a previously untested compound, was the most promising within this set. Competition experiments against the native ligands for LasR and RhlR revealed that ortho-vanillin can interact competitively with RhlR but not with LasR. Overall, these studies expand our understanding of benzaldehyde activities in the LasR and RhlR receptors and reveal potentially promising effects of ortho-vanillin as a small molecule QS modulator against RhlR.