Flavonoids differentially modulate liver X receptors activity-Structure-function relationship analysis.

Liver X receptors (LXRs) α (NR1H3) and ß (NR1H2) are nuclear receptors that have been involved in the regulation of many physiological processes, principally in the control of cholesterol homeostasis, as well as in the control of the cell death and proliferation balance. These receptors are thus promising therapeutic targets in various pathologies such as dyslipidemia, atherosclerosis, diabetes and/or cancers. These receptors are known to be activated by specific oxysterol compounds. The screening for LXR-specific ligands is a challenging process: indeed, these molecules should present a specificity towards each LXR-isoform. Because some natural products have significant effects in the regulation of the LXR-regulated homeostasis and are enriched in flavonoids, we have decided to test in cell culture the effects of 4 selected flavonoids (galangin, quercetin, apigenin and naringenin) on the modulation of LXR activity using double-hybrid experiments. In silico, molecular docking suggests specific binding pattern between agonistic and antagonistic molecules. Altogether, these results allow a better understanding of the ligand binding pocket of LXRα/ß. They also improve our knowledge about flavonoid mechanism of action, allowing the selection and development of better LXR selective ligands.

Ethanolic extract of Algerian propolis decreases androgen receptor transcriptional activity in cultured LNCaP cells.

Antiandrogens have a peculiar place in the treatment of metastatic prostate cancer by blocking the androgen receptor (AR). Unfortunately, aggressive tumors could rapidly develop into a castration resistant state. It is therefore essential to look for new molecules that are more effective, affecting not only the androgen signaling and with minimum undesirable effects. Natural products are an interesting source of new therapeutics, especially for cancer therapy as 70% of them have botanical origin. Based on an ethnobotany screening, we evaluated the effects of ethanolic extract of propolis (EEP) from Algeria on LNCaP cells. Results pointed out that EEP reduces the survival of LNCaP cells with an IC50 of 0.04 mg/ml, induces the apoptosis and blocks the cell cycle at G0/G1 phase. Interestingly, EEP decreased the accumulation of AR suggesting some anti-androgen activity. Indeed, secreted amount of the androgen target protein PSA was decreased when LNCaP cells were incubated with EEP, starting after 4 h of treatment. This anti-androgen activity was also shown on the androgen target genes Fkbp5 and Sgk1. Finally, the capacity of EEP to block AR functioning was demonstrated in transient transfections with human AR and the reporter gene ARE-tk-Luc. Propolis antagonizes the induction of the luciferase activity induced by the natural androgen DHT (10-8M) or the synthetic AR agonist R1881 (10-7M). Altogether, these results highlight the potential pharmacological effects of EEP in future treatments of prostate cancer.

Biological properties of propolis extracts: Something new from an ancient product.

Natural products are an interesting source of new therapeutics, especially for cancer therapy as 70% of them have botany origin. Propolis, a resinous mixture that honey bees collect and transform from tree buds, sap flows, or other botanical sources, has been used by ethnobotany and traditional practitioners as early in Egypt as 3000 BCE. Enriched in flavonoids, phenol acids and terpene derivatives, propolis has been widely used for its antibacterial, antifungal and anti-inflammatory properties. Even though it is a challenge to standardize propolis composition, chemical analyses have pointed out interesting molecules that also present anti-oxidant and anti-proliferative properties that are of interest in the field of anti-cancer therapy. This review describes the various geographical origins and compositions of propolis, and analyzes how the main compounds of propolis could modulate cell signaling. A focus is made on the putative use of propolis in prostate cancer.