Identification of a potent xanthine oxidase inhibitor from oxidation of caffeic acid

Abstract

Inhibitory activity of Fe-ion-catalyzed radical oxidation products from 22 types of phenolic compounds toward xanthine oxidase (XO) was investigated. Phenols are readily oxidizable compounds in nature and, thus, showed potent antioxidant activities. Among the phenols screened in this study, noticeable activity was observed in the oxidation product of caffeic acid, whereas almost no XO-inhibitory activity of caffeic acid was observed. Assay-guided purification of the oxidation product of caffeic acid afforded a highly potent XO inhibitor, with an IC50 value that was calculated to be 60 nmol L(-1), which indicated XO-inhibitory activity much stronger than that of allopurinol (IC50 = 1 μmol L(-1)), a potent XO inhibitor and excellent medicine for the treatment of gout. The chemical structure of this new XO inhibitor was investigated by one- and two-dimensional NMR and HR-ESI-MS analyses, and the unique tetracyclic structure was confirmed by synthesis starting from commercially available 1,2,4-trimethoxybenzene and 3,4-dimethoxylbenzoyl chloride.

Effect of propolis in gastric disorders: inhibition studies on the growth ofHelicobacter pyloriand production of its urease

“…Similarly, the P11 was distinguished from the other samples as it showed the greatest degree of urease inhibition. Similar to our results, a number of natural compounds, rich in polyphenolic agents, such as caffeic acid 28,29 , rutin 30 , as well as chestnut and oak honeys 13 and honey fractions 11 have been reported to inhibit H. pylori urease.…”

On the vasoprotective mechanisms underlying novel β-phosphorylated nitrones: Focus on free radical characterization, scavenging and NO-donation in a biological model of oxidative stress

“…Under these conditions, none of the tested compounds interfered with uric acid formation (not shown), whereas in this assay known xanthine oxidase inhibitors such as allopurinol and quercetin showed IC 50 values of 0.95 ± 0.07 µM and 3.50 ± 0.14 µM, respectively. Our results are in agreement with the reported weak activity of caffeic, gallic and sinapic acids (at concentrations up to 100 µM) toward xanthine oxidase [50]. and/or (ii) electron transfer from the phenolate groups [10,25,45], in the case of antioxidant-based PPNs.…”

“…Moreover, the β-phosphorylated secondary amine 7 ( Figure 5, inset) showed no activity (IC 50 > 40 mM) in the assay, further confirming that the nitrone function is an active site for scavenging. Finally, 2,6-Me-PPN 4q exhibited a poor scavenging effect (IC 50 ~ 350 µM) as a possible consequence of the slow rate of radical addition at the sterically-hindered nitrone site ( Figure 2B).…”

“…In parallel, however, only a modest LDH leakage was observed for all PPNs (5−25% of total baseline intracellular content) as concentrations causing cell death were applied. Under these conditions the calculated IC 50 values for the LDH assay are overestimated, showing an apparent increase of viability as compared to the above assays, giving false-positive results. It is thus possible that PPNs-induced membrane damage and/or necrosis is low compared to intracellular alterations or, more likely, that released LDH was degraded after 48 h incubation to reach undetectable levels.…”

“…To investigate the vascular relaxant potency of a subset of PPNs, we used endotheliumintact rat aortic rings precontracted with 5 × 10 -6 M of the α1-adrenoceptor agonist phenylephrine (PE) to similar levels. Concentration-response curves to endothelium-independent NO-donor SNP were recorded in the presence of nitrones (200 µM) in KH buffer with 0.1% DMSO as cosolvent, allowing quantification of the potency half maximal effective concentration (pEC 50 ) and relaxation efficacy (R max ).…”