Anti-inflammatory activity of myricetin-3-O-β-D-glucuronide and related compounds

Objective nod Design: The anti-inflammatory effect of myricetinglucuronide (MGL) was investigated and structurally-related compounds were compared to examine the structure/activity-relationship in carrageenan-induced rat paw edema. Materials nod Subjects: In vitro studies were performed using rat basophilic leukemia (RBL-1) cells, human polymorphonuclear leukocytes (PMNL), COX-I from ram seminal vesicle, COX-2 from sheep placenta and human venous blood. For the in vivo tests male Wistar rats were used, for the ex vivo test perfused rabbit ears. Treatment: 1-300 mu g/kg MGL or myricetinmethylglucuronate and 0.1-5 mg/kg other related compounds administered p.o, (carrageenan edema). 5, 50 and 150 mu g/kg MGL p.o, for 14 days (Freund's adjuvant arthritis), 5 and 50 mu g/kg p.o. for 6 days (ulceration). Methods: Anti-inflammatory effects were measured in carrageenan edema and in adjuvant arthritis. Incidence of gastric lesions was tested in an ulcerogenicity model in vivo. Influence on COX was determined in the perfused rabbit ear, in PMNL and in a test assay using COX-1 and COX-2. 5-LOX activity was studied using PMNL and RBL-1. The influence on platelet aggregation was evaluated measuring light transmission. Results: MGL exerted a marked and dose-dependent antiinflammatory effect in acute (carrageenan edema, ED50 15 mu g/kg, indomethacin ED50 10 mg/kg) and chronic (adjuvant arthritis, inhibition at 150 mu g/kg 18.1% left paw, 20.6% right paw, indomethacin 3 mg/kg 18.0% and 19.4%) models of inflammation. In the perfused rabbit ear 1 mu g MGL inhibited the release of PGI(2), PGD(2) and PGE(2) to the same extent as 1 mu g indomethacin. The inhibition of COX-1 in the intact cell system was IC50 = 0.5 mu M, that of indomethacin 0.0038 mu M. In the isolated enzyme preparations of COX-1 and COX-2 the IC50 was 10 mu M and 8 mu M, that of indomethacin 9.2mM and 2.4 mu M. In the RBL-1 and PMNL test assay the inhibition of 5-LOX was 0.1 mu M and 2.2 mu M. An orally administered dose of 50 mu g/kg/day induced no gastric ulcers in rats treated for 6 days. The investigations on carrageenan edema showed a close relationship between the structure of MGL and the anti-inflammatory effect. Conclusions: MGL is a COX-I, COX-2 and 5-LOX inhibitor. In view of the moderate in vitro activity and the very potent in vivo activity an additive mechanism must be involved. Small changes in the molecular structure lead to the loss or reduction of the anti-inflammatory activity.