| |
| We have previously identified that the NQO1 mediated quinone reduction and subsequent glucuronidation is the predominant metabolic pathway for tanshinone IIa (TSA) in rats. The present study contributes to the further research on its glucuronidation enzyme kinetics, the identification of human UDP-glucuronosyltransferase (UGT) isoforms, and the interaction potentials. A pair of regioisomers of reduced TSA glucuronides was found from human, rats and mice, whereas only M1 was found in dog liver S9 incubations. The overall glucuronidations clearance of TSA in human liver S9 was 11.8±0.8μl/min/mg protein, 0.7, 0.8, and 3 fold of that in the mice, rats and dogs, respectively. Using CLint M2/M1 as a regioselective index, opposite regioselectivity was found between human (0.7) and mice (1.3), whereas no significant regioselectitvity was found in rats. In a sequential metabolism system by applying human liver cytosol as a NQO1 donor in combination with a panel of 12 recombinant human UGTs screen, multiple UGTs were found involved in the M1 formation, whereas only UGT1A9 and to a very minor extent of UGT1A1 and 1A3 contributed to the M2 formation. Further enzyme kinetics, correlation, and chemical inhibition studies confirmed that UGT1A9 played the major role for both M1 and M2 formations. In addition, TSA presented potent inhibitory effect on the glucuronidations of typical UGT1A9 substrates propofol and MPA, with an IC50 value at 8.4±1.8μM and 8.9±1.9μM respectively. This study would be helpful for guiding the future studies on characterizing the NQO1 mediated reduction and subsequent glucuronidations of other quinones. |
|
| Keywords:Tanshinone IIA;sequential metabolism;UDP-glucuronosyltransferase;species difference;regioselectivity |
|
