Potentiation effects by usnic acid in combination with antibiotics on clinical multi-drug resistant isolates of methicillin-resistant Staphylococcus aureus (MRSA)

Inhibition of penicillin-binding protein 2a (PBP2a) in methicillin resistant Staphylococcus aureus (MRSA) by combination of oxacillin and a bioactive compound from Ramalinaroesleri

Lichens are known to be useful and important in ethanopharmacology since ages and still possess substantial interest in alternative medical practices around the world. The intent of this investigation was to evaluate and to understand the antibacterial potential of usnic acid which was isolated from Himalyan fruticose lichen Ramalina roesleri. Usnic acid is predicted for its pharmaceutical properties through in -silico studies. Binding efficiency of usnic acid with Penicillin binding protein-PBP2a, a protein which is responsible for conferring resistance in Staphylococcus aureus was accessed using in-silico interaction assays comparing with oxacillin and ceftaroline. Further, the validation of in-silico modelling was checked by determining the antibacterial potential of usnic acid against methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates. In total, 28 clinical isolates collected from hospitals/medical students were included in the study and the anti-Staphylococcal activity was determined using agar plate dilution method followed by time-kill kinetics and synergistic studies. The scanning electron microscopic (SEM) pictures were obtained to show the cell wall disruption of MRSA by usnic acid. Docking results clearly indicated the enhanced binding potential of usnic acid (Glide XP G Score: 10.968; Glide energy -64.869) with PBP2a which is better than the energy range of reference compound, oxacillin (Glide XP G Score: 6.596; Glide energy -53.285) and roughly comparable to the co-crystallized ligand ceftaroline (Glide XP G Score: 12.20; Glide energy -70.322). Cefteroline is known to be more active against MRSA compared to oxacillin. The minimum inhibitory concentrations (MICs) of usnic acid against the clinical isolates of MRSA and reference strain (NCTC-6571) were in the range of 32-128 μg/ml. The high affinity of usnic acid to bind with PBP2a which is demonstrated via in-silico studies is further confirmed by the impressive inhibitory activity of usnic acid on MRSA clinical isolates.

A New Depsidone from Teloschistes flavicans and the Antileukemic Activity

Lichens produce a variety of secondary metabolites that could be potential sources of pharmaceutically useful chemicals. However, only a limited number of lichen metabolites have been investigated for their biological significance. The objective of this study was to identify the potential compounds responsible for the antileukemic activity of lichen Teloschistes flavicans. Among three fractions (n-hexane, EtOAc, and MeOH-H₂O), the ethyl acetate (EtOAc) fraction of T. flavicans methanolic extract showed the strongest inhibition in the HL-60 cell line. Additionally, the EtOAc fraction was further purified to obtain a new depsidone, 2,7-dichloro-3,8-dimethoxy-1,6,9-trimethyl-11H-dibenzo[b,e][1,4]dioxepin-11-one, named as flavicansone, along with rhizonic acid, parietin, and vicanicin. Flavicansone demonstrated the most significant inhibitory action against cell proliferation among the four isolated compounds.

Synergistic Effect of a Pleuromutilin Derivative with Tetracycline against Streptococcus suis In Vitro and in the Neutropenic Thigh Infection Model

Tetracycline (TET) has been widely used in the treatment of Streptococcus suis (S. suis) infection. However, it was found that the efficacy of many antibiotics in S. suis decreased significantly, especially tetracycline. In this study, GML-12 (a novel pleuromutilin derivative) was used in combination with TET against 12 S. suis isolates. In the checkerboard assay, the TET/GML-12 combination exhibited synergistic and additive effects against S. suis isolates (n = 12). In vitro time-killing assays and in vivo therapeutic experiments were used to confirm the synergistic effect of the TET/GML-12 combination against S. suis strains screened based on an FICI ≤ 0.5. In time-killing assays, the TET/GML-12 combination showed a synergistic effect or an additive effect against three isolates with a bacterial reduction of over 2.4-log10 CFU/mL compared with the most active monotherapy. Additionally, the TET/GML-12 combination displayed potent antimicrobial activity against four isolates in a mouse thigh infection model. These results suggest that the TET/GML-12 combination may be a potential therapeutic strategy for S. suis infection.

Synergistic effects of hormone therapy drugs and usnic acid on hormone receptor-positive breast and prostate cancer cells

The aim of this study was to investigate the combined effects of usnic acid (UA) and Tamoxifen (Tam) or Enzalutamide (Enz) on hormone receptor-positive breast and prostate cancer (BC and PC), respectively. The antiproliferative and apoptotic effects of Tam or Enz alone and in combination with UA on MCF7 and LNCaP cancer cells were detected. The results of the WST-1 assay indicated that UA was a promising anticancer compound that significantly enhanced the effectiveness of hormone therapy drugs compared with each drug alone (combination index < 1). In addition, the combination of UA with Tam or Enz remarkably induced more cell cycle arrest at the G0/G1 phase and apoptosis than only drug-treated cells (P < 0.01). Consequently, our findings suggest that the combination of UA with Tam or Enz may be a potential therapeutic approach for the treatment of BC and PC and further studies are required to exploit the potential mechanisms of synergistic effects.

Biosynthesis of Ag and Cu NPs by secondary metabolites of usnic acid and thymol with biological macromolecules aggregation and antibacterial activities against multi drug resistant (MDR) bacteria

Thymol and usnic acid as the important secondary metabolites of respectively Artemisia haussknechtii and Protoparmeliopsis muralis were used for reduction and stabilizing of AgNO₃ and CuSO₄ in metal nanoparticles (MNPs) biosynthesis process. Antibacterial effects of prepared Ag-thymol (ATNPs), Ag-usnic acid (AUNPs), Cu-thymol (CTNPs), and Cu-usnic acid (CUNPs) on multi drug resistant (MDR) bacteria including methicillin-resistant Staphylococcus aureus (MRSA) (gram positive), Acinetobacter baumannii (A52), and Klebsiella pneumonia (K38) (gram negative) were compared with thymol, usnic acid, AgNO₃, CuSO₄, and tetracycline. Results of this study showed higher antibacterial activities of usnic acid, CUNPs, and CTNPs with MIC/MBC values (20, 40, and 40 μg/mL, respectively) than ATNPs and AUNPs against MRSA bacteria. Leakage of macromolecules involving nucleic acids and proteins from bacteria under stress of MNPs, thymol, and usnic acid proved significant antibacterial activities of usnic acid, and Cu NPs. In addition, SEM images illustrated different patterns of aggregation in biofilms resulted from interactions of these antibacterial agents with bacterial macromolecules. Totally, this investigation illustrated new green method of Ag and Cu NPs biosynthesis with suitable antibacterial properties.