Flavonols interrupt internalized bacteria hijacking cellular responses via suppressing oxidative stress induced cellular apoptotic death.

Internalized bacteria evolve multiple means to hijack cellular responses and survive in epithelial cells for causing persistent infections. Conventional antibiotics targeting bacteria alone often fall short in eradicating such infections, prompting the exploration of host-directed therapies as promising alternatives. Nevertheless, the potential molecular targets of these host-directed interventions remain unclear. Herein, we present evidence that three flavonols (myricetin, kaempferol, and quercetin) exhibit host-directed antibacterial activity in combating internalized bacteria. Firstly, flavonol treatments downregulated 1-fold changes of MBC compared to MBC and reduced about 80% intracellular colonization of internalized S. aureus and S. pneumoniae in lung epithelial cells. Furthermore, the combined approach using network pharmacology and transcriptomics were utilized to identify potential targets of these flavonols, revealing their ability to inhibit apoptotic cell death. Moreover, flavonol treatments were found to decrease reactive oxygen species (ROS) production and recover the decrease of mitochondrial membrane potential (ΔΨm) caused by internalized bacteria, thereby attenuating apoptotic cell death triggered by bacterial internalization. These beneficial effects of flavonols are likely attributed to their high phenolic hydroxyl group content, with myricetin, possessing the greatest number of phenolic hydroxyl groups, exhibiting the most pronounced impact. Finally, further mechanistic research has revealed that flavonols mitigate apoptotic cell death through the modulation of PI3K/Bcl-2 and caspase-9/caspase-3 cascades in vitro and in vivo. These findings collectively not only highlight the host-directing antibacterial properties of flavonols but also emphasize their potential in combating persistent infections initiated by internalized bacteria.