Quinone reductase (QR) inducers from Andrographis paniculata and identification of molecular target of andrographolide

In the present study, it was demonstrated that the petroleum extract of Andrographis paniculata (AP) had quinone reductase (QR) inducing activity, which might be attributed to the modification of key cysteine residues in Keap1 by Michael addition acceptors (MAAs) in it. To screen MAAs in AP, glutathione (GSH) was employed, and a LC/MS/MS method was implied. Three compounds, andrographoside, andrographolide, 14-deoxy-14,15-dehydroandrographolide were revealed could well conjugated with GSH. Then, andrographolide along with 4 new and 14 known compounds were isolated to conduct QR induction evaluation, and the CD (the concentration required to double the activity of QR) value of andrographolide is 1.43 mu M. The QR induce activity of andrographolide might be attributed to its targeting multiple cysteine residues in Keap1, therefore, the alkylation of Keap1 by andrographolide was further studied and the result showed that four cysteine residues: Cys77, Cys151, Cys273 and Cys368 were alkylated, which indicated that Keap1 is a potential target for the QR induce activity of andrographolide. (C) 2012 Elsevier B.V. All rights reserved.