Physalin H, physalin B, and isophysalin B suppress the quorum-sensing function of Staphylococcus aureus by binding to AgrA.

The virulence of Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), depends on the expression of toxins and virulence factors controlled by the quorum-sensing (QS) system, encoded on the virulence accessory gene regulator (agr) locus. The aim of this study was to identify a phytochemical that inhibits Agr-QS function and to elucidate its mechanism. We screened 577 compounds and identified physalin H, physalin B, and isophysalin B--phytochemicals belonging to physalins found in plants of the Solanaceae family--as novel Agr-QS modulators. Biological analyses and in vitro protein-DNA binding assays suggested that these physalins suppress gene expression related to the Agr-QS system by inhibiting binding of the key response regulator AgrA to the agr promoters, reducing the function of hemolytic toxins downstream of these genes in MRSA. Furthermore, although physalin F suppressed gene expression in the Agr-QS system, its anti-hemolytic activity was lower than that of physalins H, B, and isophysalin B. Conversely, five physalins isolated from the same plant with the ability to suppress Agr-QS did not reduce bacterial Agr-QS activity but inhibited AgrA binding to DNA in vitro. A docking simulation revealed that physalin interacts with the DNA-binding site of AgrA in three docking states. The carbonyl oxygens at C-1 and C-18 of physalins, which can suppress Agr-QS, were directed to residues N201 and R198 of AgrA, respectively, whereas these carbonyl oxygens of physalins, without Agr-QS suppression activity, were oriented in different directions. Next, 100-ns molecular dynamics simulations revealed that the hydrogen bond formed between the carbonyl oxygen at C-15 of physalins and L186 of AgrA functions as an anchor, sustaining the interaction between the carbonyl oxygen at C-1 of physalins and N201 of AgrA. Thus, these results suggest that physalin H, physalin B, and isophysalin B inhibit the interaction of AgrA with the agr promoters by binding to the DNA-binding site of AgrA, suppressing the Agr-QS function of S. aureus. Physalins that suppress the Agr-QS function are proposed as potential lead compounds in the anti-virulence strategy for MRSA infections.

Isolation of bioactive phytochemicals from Crinum asiaticum L. along with their cytotoxic and TRAIL-resistance abrogating prospect assessment.

Crinum asiaticum L. (Amaryllidaceae) is a perennial bulbous herb, locally utilized for possessing multifaceted pharmacological properties including anticancer, immune-stimulating, analgesic, antiviral, antimalarial, antibacterial and antifungal, in addition to its popularity as an aesthetic plant. Separation of MeOH extract of C. asiaticum leaves yielded three known compounds as cycloneolitsol (1), hippeastrine (2) and ß-sitosterol (3). Among these, compounds 1 and 2 were subjected to the cytotoxic assay and found that they induced mild effect against HCT116, Huh7 and DU145 cell lines with the IC50 values from 73.76 to 132.53 µM. When tested for TRAIL-resistance abrogating activity, 1 (100 µM) along with TRAIL (100 ng/mL) showed moderate activity in AGS cells producing 25 % more inhibition than the agent alone. Whereas 2 (20 and 30 µM) in combination with TRAIL (100 ng/mL) exhibited strong activity in abrogating TRAIL-resistance and caused 34 % and 36 % more inhibition in AGS cells, respectively. The in-silico studies of compound 2 revealed high docking hits with the TRAIL-associated anti-apoptotic proteins which give a justification for the regulatory interactions to induce such abrogating activity. It is still recommended to conduct further investigations to understand their exact molecular mechanism.

A new 1,2-diketone physalin isolated from Physalis minima and TRAIL-resistance overcoming activity of physalins.

A new 1,2-diketone physalin, physalin XII (1), and 13 known compounds were isolated from the methanol extract of Physalis minima whole plant collected in Thailand. Among them, five physalins (2-6) had tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-resistance overcoming activity, and physalin F (3) was the most active with an IC50 value of 0.39 µM against human gastric adenocarcinoma cell line AGS in the presence of TRAIL (100 ng/mL). An investigation of the TRAIL-resistance overcoming activity of physalins using western blot analysis showed that 3 promoted TRAIL-induced apoptosis by suppressing anti-apoptotic proteins c-FLIP and Bcl-2.

Two Bioactive Compounds, Uniformides A and B, Isolated from a Culture of Nocardia uniformis IFM0856T in the Presence of Animal Cells.

Two new peptides named uniformides A and B (1 and 2, respectively) were isolated from the cultured extracts of Nocardia uniformis IFM0856T in the presence of mouse macrophage-like cell line J774.1, in modified Czapek-Dox medium. These compounds were not produced in a culture containing only N. uniformis but in one that also included J774.1. Compounds 1 and 2 showed high cytotoxicity against J774.1 and suppressed the production of nitric oxide, IL-6, and IL-1ß by inhibiting the NF-κB pathway.

Thannilignan glucoside and 2-(ß-glucopyranosyl)-3-isoxazolin-5-one derivative, two new compounds isolated from Terminalia bellirica.

Two new compounds, thannilignan 9-O-ß-glucoside (1) and 2-(ß-glucopyranosyl)-3-isoxazolin-5-one derivative (2), and seven known compounds were isolated from the methanol extract of Terminalia bellirica leaves, collected in Bangladesh. The structures of the compounds were elucidated using spectroscopic analysis. Among these isolated compounds, corilagin (3) was cytotoxic against human gastric adenocarcinoma cell line AGS at an IC50 of 20.8 µM, and ß-D-glucopyranose 1,3,6-trigallate (4) exhibited the ability to overcome tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) resistance.

Isolation of Various Flavonoids with TRAIL Resistance-Overcoming Activity from Blumea lacera.

Eighteen compounds, including fourteen flavonoids (1-14), one steroid (15), two fatty acids (16,17), and one nitrogen-containing compound (18), were isolated from the methanol extract of the whole Blumea lacera plant collected in Thailand. Compounds 1-11 and 15-17 exhibited tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) resistance-overcoming activity. Among them, bonanzin (2) and cirsilineol (7) had particularly strong TRAIL resistance-overcoming activity, where the IC50 values against the human gastric adenocarcinoma cell line AGS in the presence of TRAIL (100 ng/mL) were 10.7 µM and 5.9 µM, respectively.