Searching of new enantiomerically pure chiral derivatives of xanthones (CDXs) with potential pharmacological properties, particularly those with anti-inflammatory activity, has remained an area of interest of our group. Herein, we describe in silico studies and in vitro inhibitory assays of cyclooxygenases (COX-1 and COX-2) for different enantiomeric pairs of CDXs. The evaluation of the inhibitory activities was performed by using the COX Inhibitor Screening Assay Kit. Docking simulations between the small molecules (CDXs; known ligands and decoys) and the enzyme targets were undertaken with AutoDock Vina embedded in PyRx—Virtual Screening Tool software. All the CDXs evaluated exhibited COX-1 and COX-2 inhibition potential as predicted. Considering that the (S)-(−)-enantiomer of the nonsteroidal anti-inflammatory drug ketoprofen preferentially binds to albumin, resulting in lower free plasma concentration than (R)-(+)-enantiomer, protein binding affinity for CDXs was also evaluated by spectrofluorimetry as well as in in silico. For some CDXs enantioselectivity was observed.
Background and Aims The addition of oenological tannins during winemaking is a longstanding technological practice. To assist such a practice, knowledge of their antioxidant properties is an asset for understanding their role in redox processes occurring in wine. Hence, the aim of this work was to assess the antioxidant profile of oenological tannins from several botanical sources, which are usually applied at different winemaking steps. Methods and Results Several antioxidant assays, including the ability to reduce copper(II) assay (CUPRAC), the scavenging capacity against 2,2′‐azinobis‐(3‐ethylbenzothiazoline‐6‐sulfonate) (ABTS) and 2,2‐diphenyl‐1‐picrylhydrazyl radicals (DPPH), and the peroxyl radical scavenging capacity (oxygen radical absorbance capacity assay, ORAC) were applied. The concentration of phenolic substances and the ability to chelate iron(II) (ICA) were also determined. A significant correlation was obtained between the concentration of phenolic substances and the copper(II) reducing antioxidant capacity (R = 0.89), and the 2,2′‐azinobis‐(3‐ethylbenzothiazoline‐6‐sulfonate) (R = 0.86) and 2,2‐diphenyl‐1‐picrylhydrazyl (R = 0.86) assays. No such correlation was observed (R = 0.15) with the oxygen radical absorbance capacity assay. Conclusions The highest radical scavenging capacity was attained for oenological tannins composed of gallotannins, while those containing ellagic acid were able to chelate iron(II) strongly, preventing the oxidative damage mediated by Fenton‐based reactions. Condensed tannins demonstrated a significant ability to scavenge peroxyl radicals, which represents a powerful antioxidant mechanism to prevent lipid peroxidation. Significance of the Study The chemical antioxidant profile of oenological tannins displayed in radar charts provides valuable information for winemakers and manufacturers of oenological tannins.
The analysis and interpretation of data retrieved from Oxygen Radical Absorbance Capacity (ORAC) assays represent a challenging task. ORAC indexes originate from different mathematical approaches often lacking correct elucidation of kinetic features concerning radical scavenging reactions by antioxidant compounds. In this work, the expression of ORAC values as area under fluorescein (FL) decay curves (AUC) and lag time are critically compared. This multi-parametric analysis showed the extension of radical scavenging reactions beyond the lag time period for caffeic acid, gallic acid, reduced glutathione and quercetin, extending their antioxidant protection of FL. Ethanol delayed the reaction of both FL and antioxidant compounds with free radical species generated from 2,2′-azobis(2-amidinopropane) dihydrochloride thermolysis. Trolox equivalent values, commonly used to express ORAC values, were more affected by the differences in radical scavenging kinetics between the reference and the tested antioxidant compounds when calculated from AUC than from lag time. These findings stressed the importance of choosing calibrator compounds presenting ORAC kinetics similar to samples to prevent biased estimation of the antioxidant capacity. Additionally, the framework proposed here provides a sustainable analytical method for the evaluation of antioxidant capacity, with an AGREE score of 0.73.
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