Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.6.5.2 (NQO1)
 6,196 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have previously identified that the predominant metabolic pathway for tanshinone IIa (TSA) in rat is the NAD(P)H:quinone oxidoreductase 1 (NQO1)-mediated quinone reduction and subsequent glucuronidation. The present study contributes to further research on its glucuronidation enzyme kinetics, the identification of human UDP-glucuronosyltransferase (UGT) isoforms, and the interaction potential with typical UGT substrates. A pair of regioisomers (M1 and M2) of reduced TSA glucuronides was found from human, rat, and mouse, whereas only M1 was found in dog liver S9 incubations. The overall glucuronidation clearance of TSA in human liver S9 was 11.8 +/- 0.8 microl/min/mg protein, 0.7-, 0.8-, and 3-fold of that in the mouse, rat, and dog, respectively. Using intrinsic clearance M2/M1 as a regioselective index, opposite regioselectivity was found between human (0.7) and mouse (1.3), whereas no significant regioselectivity was found in rat. In a sequential metabolism system, by applying human liver cytosol as an NQO1 donor combined with a screening panel of 12 recombinant human UGTs, multiple UGTs were found involved in the M1 formation, whereas only UGT1A9 and, to a very minor extent, UGT1A1 and UGT1A3 contributed to the M2 formation. Further enzyme kinetics, correlation, and chemical inhibition studies confirmed that UGT1A9 played a major role in both M1 and M2 formation. In addition, TSA presented a potent inhibitory effect on the glucuronidation of typical UGT1A9 substrates propofol and mycophenolic acid, with an IC(50) value of 8.4 +/- 1.8 and 8.9 +/- 1.9 microM, respectively. This study will help to guide future studies on characterizing the NQO1-mediated reduction and subsequent glucuronidation of other quinones.
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PMID:Regioselective glucuronidation of tanshinone iia after quinone reduction: identification of human UDP-glucuronosyltransferases, species differences, and interaction potential. 2038 56

Tanshinone I (TSI) is a lipophilic diterpene in Salvia miltiorrhiza with versatile pharmacological activities. However, metabolic pathway of TSI in human is unknown. In this study, we determined major metabolites of TSI using a preparation of human liver microsomes (HLMs) by HPLC-UV and Q-Trap mass spectrometer. A total of 6 metabolites were detected, which indicated the presence of hydroxylation, reduction as well as glucuronidation. Selective chemical inhibition and purified cytochrome P450 (CYP450) isoform screening experiments revealed that CYP2A6 was primarily responsible for TSI Phase I metabolism. Part of generated hydroxylated TSI was glucuronidated via several glucuronosyltransferase (UGT) isoforms including UGT1A1, UGT1A3, UGT1A7, UGT1A9, as well as extrahepatic expressed isoforms UGT1A8 and UGT1A10. TSI could be reduced to a relatively unstable hydroquinone intermediate by NAD(P)H: quinone oxidoreductase 1 (NQO1), and then immediately conjugated with glucuronic acid by a panel of UGTs, especially UGT1A9, UGT1A1 and UGT1A8. Additionally, NQO1 could also reduce hydroxylated TSI to a hydroquinone intermediate, which was immediately glucuronidated by UGT1A1. The study demonstrated that hydroxylation, reduction as well as glucuronidation were the major pathways for TSI biotransformation, and six metabolites generated by CYPs, NQO1 and UGTs were found in HLMs and S9 subcellular fractions.
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PMID:Metabolic characteristics of Tanshinone I in human liver microsomes and S9 subcellular fractions. 2935 26