Identification of Resveratrol as Bioactive Compound of Propolis from Western Romania and Characterization of Phenolic Profile and Antioxidant Activity of Ethanolic Extracts.

The present study aimed to assess the phenolic content of eight ethanolic propolis samples (P1-P8) harvested from different regions of Western Romania and their antioxidant activity. The mean value of total phenolic content was 214 ± 48 mg gallic acid equivalents (GAE)/g propolis. All extracts contained kaempferol (514.02 ± 114.80 µg/mL), quercetin (124.64 ± 95.86 µg/mL), rosmarinic acid (58.03 ± 20.08 µg/mL), and resveratrol (48.59 ± 59.52 µg/mL) assessed by LC-MS. The antioxidant activity was evaluated using 2 methods: (i) DPPH (2,2-diphenyl-1-picrylhydrazyl) assay using ascorbic acid as standard antioxidant and (ii) FOX (Ferrous iron xylenol orange OXidation) assay using catalase as hydrogen peroxide (H2O2) scavenger. The DPPH radical scavenging activity was determined for all samples applied in 6 concentrations (10, 5, 3, 1.5, 0.5 and 0.3 mg/mL). IC50 varied from 0.0700 to 0.9320 mg/mL (IC50 of ascorbic acid = 0.0757 mg/mL). The % of H2O2 inhibition in FOX assay was assessed for P1, P2, P3, P4 and P8 applied in 2 concentrations (5 and 0.5 mg/mL). A significant H2O2% inhibition was obtained for these samples for the lowest concentration. We firstly report the presence of resveratrol as bioactive compound in Western Romanian propolis. The principal component analysis revealed clustering of the propolis samples according to the polyphenolic profile similarity.

Quercetin exerts an inhibitory effect on cellular bioenergetics of the B164A5 murine melanoma cell line.

Modulation of mitochondrial bioenergetics and glycolysis in malignancies has recently emerged a potential chemotherapeutic strategy since numerous malignant cells have overcome inhibition of the glycolytic pathway by increasing mitochondrial ATP production. Quercetin is a flavonoid with antioxidant, antiangiogenic, and chemoprotective properties but the mitochondrial effects are less characterized. The present study was purported to assess the effects of quercetin on the bioenergetic profile of B164A5 murine melanoma cell line. The oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) were measured at 24, 48, and 72 h of treatment of B164A5 murine melanoma cells with increasing concentrations (25, 50, 100, and 150 µM) of quercetin using the extracellular flux analyzer Seahorse XF24e (Seahorse Agilent). Analysis of mitochondrial function was performed in the presence of the classic modulators of the electron transport chain: oligomycin, FCCP, and rotenone. 72-h treatment with quercetin induced a dose-dependent decrease of all OCR parameters (basal respiration, proton leak, ATP turnover, maximal respiration, reserve capacity) as well as of ECAR. At variance, 48-h treatment induced a decrease of OCR and ECAR when quercetin was applied at 50, 100, and 150 µM, while the 24-h treatment induced a decrease of bioenergetic parameters only for the highest concentrations (100 and 150 µM) of the compound. Our data clearly demonstrated that quercetin elicited dose-dependent inhibitory effect on examined parameters of cellular bioenergetics that was most potent at 72 h of treatment. Thereby quercetin, modulating both glycolytic and mitochondrial pathways for ATP production, might be an efficient approach in killing cancer cells.