Abstract-Certain representatives from the large natural compound class known as coumarins are known to inhibit the enzyme xanthine oxidase (XO) and are capable of absorbing reactive oxygen species (ROS) produced by XO and other enzymes. These dual properties make coumarins a promising scaffold for the development of agents against reperfusion injuries, which are caused to a large extent by ROS and occur once blood circulation has been restored after ischemic events. A selection of eighteen coumarins was tested for XO inhibition and radical scavenging activities in cell-free assays. The most effective XO inhibitors carried a hydroxyl group in the C7 position of the coumarin scaffold whereas the best radical scavengers were coumarins with two hydroxyl groups in neighboring positions at the phenyl ring. Molecular docking confirmed the essential role of hydroxyl groups for effective enzyme/inhibitor interactions. The coumarins were further investigated in cell-based assays that determined their ability to reduce oxidative stress. As anticipated, the in vivo test results showed that the most effective compounds were those that were both potent XO inhibitors and good radical scavengers, thereby illustrating the potential of coumarins with dual activities for future development.

Bisphenols (BPs) are a class of small organic compounds with widespread industrial applications. Previous studies have identified several BPs that interfere with the activity of the ion-translocating enzyme sarco/endoplasmic reticulum calcium ATPase (SERCA). In order to define the molecular determinants of BP-mediated SERCA inhibition, we conducted enzyme activity assays with rabbit SERCA to determine the inhibitory potencies of 27 commercially available BPs, which were the basis for structure-activity relationships. The most potent BPs inhibited SERCA at low micromolar concentrations and carried at their two phenyl rings multiple non-polar substituents, such as small alkyl groups or halides. Furthermore, the presence of methyl groups or a cyclohexyl group at the central carbon atom connecting the two phenyl moieties correlated with good potencies. For a characterization and visualization of inhibitor/enzyme interactions, molecular docking was performed, which suggested that hydrogen bonding with Asp254 and hydrophobic interactions were the major driving forces for BP binding to SERCA. Calcium imaging studies with a selection of BPs showed that these inhibitors were able to increase intracellular calcium levels in living human cells, a behavior consistent with that of a SERCA inhibitor.

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