Bakuchiol inhibits Pseudomonas aeruginosa's quorum sensing-dependent biofilm formation by selectively inhibiting its transcriptional activator protein LasR

In the present study, we characterized Bakuchiol (Bak) as a new potent quorum sensing (QS) inhibitor against Pseudomonas aeruginosa biofilm formation. Upon extensive in vitro investigations, Bak was found to suppress the P. aeruginosa biofilm formation (75.5 % inhibition) and its associated virulence factor e.g., pyocyanin and rhamnolipids (% of inhibition = 71.5 % and 66.9 %, respectively). Upon LuxR-type receptors assay, Bak was found to selectively inhibit P. aeruginosa's LasR in a dose-dependent manner. Further in-depth molecular investigations (e.g., sedimentation velocity and thermal shift assays) revealed that Bak destabilized LasR upon binding and disrupted its functioning quaternary structure (i.e., the functioning dimeric form). The subsequent modeling and molecular dynamics (MD) simulations explained in more molecular detail how Bak interacts with LasR and how it can induce its dimeric form disruption. In conclusion, our study identified Bak as a potent and specific LasR antagonist that should be widely used as a chemical probe of QS in P. aeruginosa, offering new insights into LasR antagonism processes. The new findings shed light on the cryptic world of LuxR-type QS in this important opportunistic pathogen.

Norlobaridone Inhibits Quorum Sensing-Dependent Biofilm Formation and Some Virulence Factors in Pseudomonas aeruginosa by Disrupting Its Transcriptional Activator Protein LasR Dimerization

In the present study, norlobaridone (NBD) was isolated from Parmotrema and then evaluated as a new potent quorum sensing (QS) inhibitor against Pseudomonas aeruginosa biofilm development. This phenolic natural product was found to reduce P. aeruginosa biofilm formation (64.6% inhibition) and its related virulence factors, such as pyocyanin and rhamnolipids (% inhibition = 61.1% and 55%, respectively). In vitro assays inhibitory effects against a number of known LuxR-type receptors revealed that NBD was able to specifically block P. aeruginosa's LasR in a dose-dependent manner. Further molecular studies (e.g., sedimentation velocity and thermal shift assays) demonstrated that NBD destabilized LasR upon binding and damaged its functional quaternary structure (i.e., the functional dimeric form). The use of modelling and molecular dynamics (MD) simulations also allowed us to further understand its interaction with LasR, and how this can disrupt its dimeric form. Finally, our findings show that NBD is a powerful and specific LasR antagonist that should be widely employed as a chemical probe in QS of P. aeruginosa, providing new insights into LasR antagonism processes. The new discoveries shed light on the mysterious world of LuxR-type QS in this key opportunistic pathogen.

Bacterial virulence factors: a target for heterocyclic compounds to combat bacterial resistance

Antibiotic resistance is one of the most important challenges of the 21st century. However, the growing understanding of bacterial pathogenesis and cell-to-cell communication has revealed many potential strategies for the discovery of drugs that can be used for the treatment of bacterial infections. Interfering with bacterial virulence and/or quorum sensing could be a particularly interesting approach, because it is believed to exert less selective pressure on the bacterial resistance than with traditional strategies, geared toward killing bacteria or preventing their growth. Here, we discuss the mechanism of bacterial virulence, presenting promising strategies and recently synthesized heterocyclic compounds to combat future bacterial infections.

Design and synthesis of 1,2,4-triazolo[1,5-a]pyrimidine derivatives as PDE 4B inhibitors endowed with bronchodilator activity

A series of 1,2,4-triazolo[1,5-a]pyrimidine derivatives was designed, synthesized, and screened for their phosphodiesterase (PDE 4B) inhibitory activity and bronchodilation ability. Compound 7e showed 41.80% PDE 4B inhibition at 10 µM. Eight compounds were screened for their bronchodilator activity, where compounds 7f and 7e elicited promising bronchodilator activity with EC₅₀ values of 18.6 and 57.1 µM, respectively, compared to theophylline (EC₅₀  = 425 µM). Molecular docking at the PDE 4B active site revealed a binding mode and docking scores comparable to those of a reference ligand, consistent with their PDE 4B inhibition activity.