Discovery of antibacterial active components from the root barks of Sophora flavescens and evaluation of their antibacterial in vitro and infected wound healing activity in vivo.

ETHNOPHARMACOLOGICAL RELEVANCE: The development of novel antibacterial agents is a critical challenge facing the global healthcare system. Although the traditional Chinese herb Sophora flavescens (S. flavescens) is widely used to treat diseases such as dysentery, eczema, and vaginal infections, its specific active components and antibacterial mechanisms have not yet been systematically elucidated.

AIM OF THE STUDY: To elucidate the antimicrobial mechanisms of S. flavescens and its active ingredients against pathogenic microorganisms, systematic in vitro and in vivo studies are required.

MATERIALS AND METHODS: The antimicrobial activities of extracts from the bark (BSF), xylem (XSF) and phloem (PSF) of S. flavescens were assessed using the broth microdilution method on microdilution plates. The major components of BSF were identified using NMR. Cytotoxic and hemolytic activities of Sophoraflavanone G (SFG) were assessed using MTT assay and fresh mouse erythrocyte assay, respectively. Bactericidal kinetics were evaluated using the agar plate coating method. The effect of compounds on biofilm formation was determined using crystal violet staining. Transcriptomics was performed to investigate the potential antibacterial mechanism. Scanning electron microscope (SEM) and laser scanning confocal microscopy (LSCM) and propidium (PI) staining were employed to observe the disruption of bacterial cell membranes. Leakage of proteins and nucleic acids was determined using Bradford assay and ultramicro fluorescence spectrophotometry. The efficacy and safety were assessed using a mouse model of whole skin infection in vivo.

RESULTS: The active components of the roots of S. flavescens were identified by NMR, revealing that BSF served as its antibacterial active site, containing mainly prenylated flavonoids. All nine compounds obtained exhibited potent antibacterial activities. Further investigations revealed that SFG exhibited low hemolytic activity, low cytotoxicity and rapid bactericidal effects. Transcriptome analysis revealed that SFG can affect the expression of genes related to bacterial cell wall and cell membrane synthesis, transmembrane transport of substances, and carbohydrate and amino acid metabolism. Preliminary mechanistic studies showed that SFG disrupts the integrity of the bacterial cell membrane, leading to the leakage of intracellular proteins and nucleic acids, and induces the generation of abundant reactive oxygen species within the cells, triggering oxidative stress, inactivating bacterial metabolism, and ultimately causing bacterial lysis and death. In vivo pharmacodynamic results demonstrated that SFG has good antibacterial and anti-inflammatory effects, can promote wound healing at the infection site, and exhibits good biocompatibility.

CONCLUSIONS: This study confirmed that BSF and its isolated bioactive compounds exhibit significant antibacterial activity and possess the potential to be developed into novel antibiotics. Subsequent studies will be extended to a broader range of Gram-negative bacteria and other pathogens to comprehensively elucidate its antimicrobial spectrum.