Antivirulence Activity of a Dietary Phytochemical: Hibiscus Acid Isolated from Hibiscus sabdariffa L. Reduces the Virulence of Pseudomonas aeruginosa in a Mouse Infection Model.

Hibiscus sabdariffa L. (Hs) calyxes, rich in organic acids, are included in diets in different countries. In recent years, some phytochemicals have been shown to reduce bacterial virulence at sublethal concentrations by interfering with quorum sensing (QS) systems. Therefore, in this study the antivirulence properties of Hs calyxes and two γ-lactones (hibiscus acid [HA] and its methyl ester) in Pseudomonas aeruginosa were analyzed. Acetone and methanol extracts of Hs showed anti-QS activity by inhibiting violacein production (60% to 80% with 250 µg/mL). In molecular docking analysis, the γ-lactones registered a good binding score, which suggests strong interaction with the active site of LasR protein. To verify their effect in vitro, they were isolated from Hs and evaluated in six QS-regulated phenotypes, as well as in ExoU toxin that is released by the type III secretion system (T3SS). At 500 µg/mL they reduced alkaline protease (29-52%) and elastase (15-37%) activity, biofilm formation (∼75%), and swarming (50%), but there was no effect on pyocyanin production, hemolytic activity, or type III secretion. In a mouse abscess/necrosis model, HA at sublethal concentrations (15 and 31.2 µg/mL) affected infection establishment and prevented damage and systemic spread. In conclusion, HA is the first molecule identified with antivirulence properties in Hs with the potential to prevent infections caused by P. aeruginosa.

Sechium edule (Jacq.) Swartz, a New Cultivar with Antiproliferative Potential in a Human Cervical Cancer HeLa Cell Line.

The Sechium edule Perla Negra cultivar is a recently-obtained biological material whose progenitors are S. edule var. nigrum minor and S. edule var. amarus silvestrys, the latter of which has been reported to have antiproliferative activity against the HeLa P-388 and L-929 cancer cell lines. The present study aimed to determine if the methanolic extract of the fruit of the Perla Negra cultivar had the same biological activity. The methanolic extract was phytochemically characterized by thin layer chromatography (TLC) and column chromatography (CC), identifying the terpenes and flavonoids. The compounds identified via high performance liquid chromatography (HPLC) were Cucurbitacins B, D, E, and I for the terpene fractions, and Rutin, Phlorizidin, Myricetin, Quercetin, Naringenin, Phloretin, Apigenin, and Galangin for the flavonoid fractions). Biological activity was evaluated with different concentrations of the methanolic extract in the HeLa cell line and normal lymphocytes. The methanolic extract inhibited the proliferation of HeLa cells (IC50 1.85 µg·mL-1), but the lymphocytes were affected by the extract (IC50 30.04 µg·mL-1). Some fractions, and the pool of all of them, showed inhibition higher than 80% at a concentration of 2.11 µg·mL-1. Therefore, the biological effect shown by the methanolic extract of the Perla Negra has some specificity in inhibiting tumor cells and not normal cells; an unusual feature among molecules investigated as potential biomedical agents.

Fruit extract from a Sechium edule hybrid induce apoptosis in leukaemic cell lines but not in normal cells.

The antiproliferative potential of a crude extract from the chayote hybrid H-837-07-GISeM® and its potential for apoptosis induction were assessed in leukaemic cell lines and normal mouse bone marrow mononuclear cells (BM-MNCs). The extract strongly inhibited the proliferation of the P388, J774, and WEHI-3 cell lines (with an IC50 below 1.3 µg·mL(-1)), reduced cell viability, and induced apoptotic body production, phosphatidylserine translocation, and DNA fragmentation. However, the extract had no effect on BM-MNCs. We postulate that these properties make the extract a good candidate for an anti-tumour agent for clinical use.