Rapid screening and evaluation of XOD inhibitors and O2 (*-) scavenger from total flavonoids of Ginkgo biloba Leaves by LC-MS and multi-mode microplate reader.

Superoxide anion radical scavenger and xanthine oxidase inhibitor plays an important function in the treatment of several relevant human diseases. In the present study, the 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 G. biloba leaves. As a result, four compounds (quercetin, apigenin, kaempferol and isorhamnetin) are screened as xanthine oxidase inhibitors by ultrafiltration LC-MS, and the IC50 values of the screened flavonoids were lower than allopurinol. Lineweaver-Burk plot results indicated that kaempferol was competitive xanthine oxidase inhibitors, other flavonoids were all anticompetitive inhibitors. Four flavonoids, named 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 superoxide anion radical scavenger and xanthine oxidase inhibitor from complex mixture system is feasible and efficient.