Rapid screening and evaluation of XOD inhibitors and O2 •- scavenger from total flavonoids of Ginkgo biloba leaves by LC-MS and multimode microplate reader.

Superoxide anion radical scavenger and xanthine oxidase inhibitor play an important role in the treatment of several relevant human diseases. In the present study, ultrafiltration liquid chromatography-mass spectrometry coupled to microplate reader was applied to screen and identify superoxide anion radical scavengers and xanthine oxidase inhibitors from total flavonoids of Ginkgo biloba leaves. As a result, four compounds (quercetin, apigenin, kaempferol and isorhamnetin) were screened as xanthine oxidase inhibitors by ultrafiltration LC-MS, and the 50% scavenging concentration values of the screened flavonoids were lower than those for allopurinol. Lineweaver-Burk plot results indicated that kaempferol was a competitive xanthine oxidase inhibitor; the other flavonoids were all anticompetitive inhibitors. Four flavonoids-rutin, quercetin, kaempferol and isorhamnetin-were screened as superoxide anion radical scavengers by LC-MS. The results demonstrate that the method for screening and evaluation of superoxide anion radical scavenger and xanthine oxidase inhibitor from a complex mixture system is feasible and efficient.