In this study, the influence of guelder rose (Viburnum opulus) fruit fresh juice (FJ) and a phenolic-rich fraction (PRF) isolated from juice on mice insulinoma MIN6 cells activities was investigated. Extracts were able to decrease intracellular oxidative stress at the highest non-cytotoxic concentrations. They induced glucagon-like peptide-1 (GLP-1) secretion in the presence of an elevated glucose concentration, and they inhibited in vitro activity of the dipeptidyl peptidase-4 (DPP4) enzyme. Nonetheless, inhibition of glucose-stimulated insulin secretion was detected, which was accompanied by a decrease of cellular membrane fluidity and hyperpolarization effect. In addition, the increase of free fatty acid uptake and accumulation of lipid droplets in MIN6 cells were observed. Elevated extract concentrations induced cell apoptosis through the intrinsic mitochondrial pathway with activation of initiatory caspase-9 and downstream caspases-3/7. The fluorescence-quenching studies indicated that PRF extract has binding affinity to human serum albumin, which is one of the factors determining drug bioavailability. Taken together, despite the cytoprotective activity against generated intracellular oxidative stress, V. opulus revealed potential toxic effects as well as decreased insulin secretion from MIN6 cells. These findings are relevant in understanding V. opulus limitations in developing diet supplements designed for the prevention and treatment of postprandial glucose elevation.
Structure-related biological activities of flavanones are still considered largely unexplored. Since they exhibit various medicinal activities, it is intriguing to enter deeper into their chemical structures, electronic transitions or interactions with some biomolecules in order to find properties that allow us to better understand their effects. Little information is available on biological activity of flavanone and its monohydroxy derivatives in relation to their physicochemical properties as spectral profiles, existence of protonated/deprotonated species under pH changes or interaction with Calf Thymus DNA. We devoted this work to research demonstrating differences in the physicochemical properties of the four flavanones: flavanone, 2′-hydroxyflavanone, 6-hydroxyflavanone and 7-hydroxyflavanone and linking them to their biological activity. Potentiometric titration, UV–Vis spectroscopy were used to investigate influence of pH on acid–base and spectral profiles and to propose the mode of interaction with DNA. Cyclic voltammetry was applied to evaluate antioxidant potentiality and additionally, theoretical DFT(B3LYP) method to disclose electronic structure and properties of the compounds. Molecular geometries, proton affinities and pKa values have been determined. According to computational and cyclic voltammetry results we could predict higher antioxidant activity of 6-hydroxyflavanone with respect to other compounds. The values of Kb intrinsic binding constants of the flavanones indicated weak interactions with DNA. Structure–activity relationships observed for antioxidant activity and DNA interactions suggest that 6-hydroxyflavanone can protect DNA against oxidative damage most effectively than flavanone, 2′-hydroxyflavanone or 7-hydroxyflavanone.
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