Comparative study of the antioxidant and anti-inflammatory effects of the natural coumarins 1,2-benzopyrone, umbelliferone and esculetin: in silico, in vitro and in vivo analyses.

The aim of this work was to compare the anti-inflammatory and antioxidant effects of three natural coumarins: 1,2-benzopyrone, umbelliferone and esculetin. The antioxidant capacity of coumarins was evaluated using both chemical and biological in vitro assays. Chemical assays included DPPH and ABTS∙+ radical scavenging as well as ferric ion reducing ability power (FRAP) assay. Inhibition of mitochondrial ROS generation and lipid peroxidation in brain homogenates were used as biological in vitro assays. The experimental method of carrageenan-induced pleurisy in rats was used for the in vivo investigation of the anti-inflammatory activity. In silico molecular docking analysis was undertaken to predict the affinity of COX-2 to the coumarins. Considering the antioxidant capacity, esculetin was the most efficient one as revealed by all employed assays. Particularly, the mitochondrial ROS generation was totally abolished by the compound at low concentrations (IC50 = 0.57 µM). As for the anti-inflammatory effects, the COX-2 enzyme presented good affinities to the three coumarins, as revealed by the molecular docking analyses. However, considering the in vivo anti-inflammatory effects, 1,2-benzopyrone was the most efficient one in counteracting pleural inflammation and it potentiated the anti-inflammatory actions of dexamethasone. Umbelliferone and esculetin treatments failed to reduce the volume of pleural exudate. Overall, therefore, our results support the notion that this class of plant secondary metabolites displays promising effects in the prevention and/or treatment of inflammation and other diseases associated with oxidative stress, although the singularities regarding the type of the inflammatory process and pharmacokinetics must be taken into account.

Inhibition of O-acetylserine (thiol) lyase as a promising new mechanism of action for herbicides.

Enzymes of the sulfur assimilation pathway of plants have been identified as potential targets for herbicide development, given their crucial role in synthesizing amino acids, coenzymes, and various sulfated compounds. In this pathway, O-acetylserine (thiol) lyase (OAS-TL; EC 2.5.1.47) catalyzes the synthesis of L-cysteine through the incorporation of sulfate into O-acetylserine (OAS). This study used an in silico approach to select seven inhibitors for OAS-TL. The in silico experiments revealed that S-benzyl-L-cysteine (SBC) had a better docking score (-7.0 kcal mol-1) than the substrate OAS (-6.6 kcal mol-1), indicating its suitable interaction with the active site of the enzyme. In vitro experiments showed that SBC is a non-competitive inhibitor of OAS-TL from Arabidopsis thaliana expressed heterologously in Escherichia coli, with a Kic of 4.29 mM and a Kiu of 5.12 mM. When added to the nutrient solution, SBC inhibited the growth of maize and morning glory weed plants due to the reduction of L-cysteine synthesis. Remarkably, morning glory was more sensitive than maize. As proof of its mechanism of action, L-cysteine supplementation to the nutrient solution mitigated the inhibitory effect of SBC on the growth of morning glory. Taken together, our data suggest that reduced L-cysteine synthesis is the primary cause of growth inhibition in maize and morning glory plants exposed to SBC. Furthermore, our findings indicate that inhibiting OAS-TL could potentially be a novel approach for herbicidal action.