Molecular Mechanisms of Leonurus Cardiaca L. Extract Activity in Prevention of Staphylococcal Endocarditis—Study on in Vitro and ex Vivo Models

Abstract

Better understanding the mechanisms of Leonurus cardiaca L. extract (LCE) activity is necessary to prepare recommendations for the use of LCE-based herbal products for preventive/supportive purposes in case of infective endocarditis (IE) and other staphylococcal invasive infections. The aim of the study was to analyze molecular mechanisms of LCE effect on Staphylococcus aureus and blood platelets in the context of their interactions playing a pivotal role in such disorders. Using atomic force microscopy, we demonstrated that adhesion forces of S. aureus were markedly reduced after exposure to LCE at subinhibitory concentrations. The effect resulted from the impact of LCE on S. aureus cell morphology and the composition of phospholipids and fatty acids in bacterial membranes (assessed by HPLC), which modulated their stabilization, hydrophobicity, and charge. Moreover, using FACS we showed also that LCE significantly reduced GP IIb/IIIa expression on blood platelets, thus the disruption of platelet-fibrinogen interactions seems to explain antiplatelet effect of LCE. The obtained results prove the usefulness of LCE in the prevention of S. aureus adhesion, platelet activation, and vegetations development, however, also pointed out the necessity of excluding the cationic antibiotics from the treatment of S. aureus-associated IE and other invasive diseases, when motherwort herb is used simultaneously as an addition to the daily diet.

An In Vitro Study of the Effect of Viburnum opulus Extracts on Key Processes in the Development of Staphylococcal Infections

“…Since the single-nucleotide polymorphisms in mprF correlated with the changes in the LYSYL-PG profile were demonstrated for clinical S. aureus strains exposed to daptomycin [ 64 ], the influence of V. opulus extracts on MprF activity could be a possible mechanism responsible for the inhibitory effect observed in our study. Although this hypothesis needs to be confirmed in future, V. opulus bark extracts, in contrast to the previously tested Leonurus cardiac extract [ 25 ], seem to have additional promise as preparations to prevent the activation of some mechanisms of staphylococcal resistance.…”

“…Their lipid composition is constantly being modified depending on the living conditions, such as temperature, osmolarity or pH [ 62 , 63 ]. There is no doubt that modifications to the membrane composition and, thus, cell surface stabilization, membrane-associated protein topology, surface hydrophobicity and charge, and finally bacterial cell resistance [ 62 , 63 , 64 ] play an important role in microbial adhesion and biofilm formation [ 25 ]. Moreover, SrtA is a membrane-localized enzyme, so these changes may also determine its expression and activity.…”

“…This reaction stabilizes the microbial membrane and modulates its charge, since anionic PG is converted to cationic LYSYL-PG. The described modification is recognized as one of the staphylococcal virulence factors that prevents membrane perturbation in the presence of cationic antimicrobials, such as antimicrobial peptides; thus, it is an important component of human and animal innate immunity or cationic antibiotics (e.g., daptomycin) [ 25 , 63 , 64 , 65 ]. In this study, we observed an increased content of PG but not LYSYL-PG in the membranes of staphylococci exposed to VBa and VBe, which may indicate the ability of these extracts to block a transformation of PG to LYSYL-PG.…”

“…Lipids from S. aureus cells were extracted according to our previous method [ 25 ] with modifications. The bacterial biomass was moved into 2 mL Eppendorf tubes containing glass beads, 0.33 mL methanol, and 0.66 mL chloroform.…”

“…Moreover, urine collected from volunteers following the consumption of cranberry powder was shown to possess the same effect, although this was clearly dose-dependent [ 24 ]. In our previous studies, promising data were provided that pointed to a limitation of S. aureus aggregation in the plasma, adhesion to abiotic or extracellular matrix protein-coated surfaces, and biofilm formation caused by polyphenol-rich Leonurus cardiaca extract [ 25 ]; phenolic and nonpolar fractions separated from Elaeagnus rhamnoides leaf, twig, and fruit extracts [ 26 ]; Pulmonaria officinalis extract [ 27 ]. Based on data in the literature, one of the most promising mechanisms of antistaphylococcal action is the inhibition of S. aureus sortase A (SrtA) activity, which may affect the expression of a wide range of staphylococcal adhesins.…”