Eriodictyol and thymonin act as GPR35 agonists.

Although herbs and spices have been used in traditional medicine for more than a century owing to their health benefits, the associated underlying mechanism is still not clear. Since the G protein-coupled receptor 35 (GPR35) has been linked to exert various antioxidant and anti-inflammatory effects, we screened 19 different herbs and spices for possible GPR35 agonist(s) to understand the GPR35-dependent functions of herbs and spices. Among the screened extracts, the ethyl acetate extract of thyme exhibited a remarkable GPR35 agonistic activity. Activity-guided separations allowed us to identify 2 polyphenolic phytochemicals, eriodictyol and thymonin, acting as GPR35 agonists. Both eriodictyol and thymonin showed a potent and specific agonist activity toward GPR35 with half maximal effective concentration values of 5.48 and 8.41 µm, respectively. These findings indicate that these phytochemicals may have beneficial health effects upon GPR35 activation.

Mechanistic Differences in the Inhibition of NF-κB by Turmeric and Its Curcuminoid Constituents.

Turmeric extract, a mixture of curcumin and its demethoxy (DMC) and bisdemethoxy (BDMC) isomers, is used as an anti-inflammatory preparation in traditional Asian medicine. Curcumin is considered to be the major bioactive compound in turmeric but less is known about the relative anti-inflammatory potency and mechanism of the other components, their mixture, or the reduced in vivo metabolites. We quantified inhibition of the NF-κB pathway in cells, adduction to a peptide mimicking IκB kinase ß, and the role of cellular glutathione as a scavenger of electrophilic curcuminoid oxidation products, suggested to be the active metabolites. Turmeric extracts (IC50 14.5 ± 2.9 µM), DMC (IC50 12.1 ± 7.2 µM), and BDMC (IC50 8.3 ± 1.6 µM), but not reduced curcumin, inhibited NF-κB similar to curcumin (IC50 18.2 ± 3.9 µM). Peptide adduction was formed with turmeric and DMC but not with BDMC, and this correlated with their oxidative degradation. Inhibition of glutathione biosynthesis enhanced the activity of DMC but not BDMC in the cellular assay. These findings suggest that NF-κB inhibition by curcumin and DMC involves their oxidation to reactive electrophiles, whereas BDMC does not require oxidation. Because it has not been established whether curcumin undergoes oxidative transformation in vivo, oxidation-independent BDMC may be a promising alternative to test in clinical trials.

Toll-like receptors as a target of food-derived anti-inflammatory compounds.

Toll-like receptors (TLRs) play a key role in linking pathogen recognition with the induction of innate immunity. They have been implicated in the pathogenesis of chronic inflammatory diseases, representing potential targets for prevention/treatment. Vegetable-rich diets are associated with the reduced risk of several inflammatory disorders. In the present study, based on an extensive screening of vegetable extracts for TLR-inhibiting activity in HEK293 cells co-expressing TLR with the NF-κB reporter gene, we found cabbage and onion extracts to be the richest sources of a TLR signaling inhibitor. To identify the active substances, we performed activity-guiding separation of the principal inhibitors and identified 3-methylsulfinylpropyl isothiocyanate (iberin) from the cabbage and quercetin and quercetin 4'-O-ß-glucoside from the onion, among which iberin showed the most potent inhibitory effect. It was revealed that iberin specifically acted on the dimerization step of TLRs in the TLR signaling pathway. To gain insight into the inhibitory mechanism of TLR dimerization, we developed a novel probe combining an isothiocyanate-reactive group and an alkyne functionality for click chemistry and detected the probe bound to the TLRs in living cells, suggesting that iberin disrupts dimerization of the TLRs via covalent binding. Furthermore, we designed a variety of iberin analogues and found that the inhibition potency was influenced by the oxidation state of the sulfur. Modeling studies of the iberin analogues showed that the oxidation state of sulfur might influence the global shape of the isothiocyanates. These findings establish the TLR dimerization step as a target of food-derived anti-inflammatory compounds.