Journal article
UDP glucuronosyltransferase (UGT) 1A6 pharmacogenetics: II. Functional impact of the three most common nonsynonymous UGT1A6 polymorphisms (S7A, T181A, and R184S)
The Journal of pharmacology and experimental therapeutics, Vol.313(3), pp.1340-1346
06/2005
Handle:
https://hdl.handle.net/2376/107748
PMID: 15761113
Abstract
The objective of this study was to use recombinant enzymes and human liver microsomes (HLMs) to comprehensively evaluate the functional impact of the three most common nonsynonymous polymorphisms (S7A, T181A, and R184S) identified in the human UDP glucuronosyltransferase (UGT) 1A6 gene. In addition to the known allozymes, other possible amino acid variants were expressed in human embryonic kidney (HEK)293 cells to enable structure-function analysis. Initial studies using different substrates (serotonin, 5-hydroxytryptophol, 4-nitrophenol, acetaminophen, and valproic acid) showed similar results with 2-fold higher glucuronidation by UGT1A6(*)2 (S7A/T181A/R184S) compared with UGT1A6(*)1 (reference), and intermediate activities for other variants. Enzyme kinetic analyses with the UGT1A6-specific substrate (serotonin) showed 50% lower K(m) values for all R184S variants and 2-fold higher V(max) values for both S7A/T181A variants compared with UGT1A6(*)1. Furthermore, intrinsic clearance (V(max)/K(m)) values were highest for the UGT1A6(*)2 allozyme (2.3-fold over UGT1A6(*)1), resulting from additive effects of higher enzyme affinity and activity. As expected, K(m) values of (*)1/(*)1 genotyped HLMs (5.4 +/- 0.2 mM) were similar to recombinant UGT1A6(*)1 (5.8 +/- 0.6 mM). Conversely, (*)2/(*)2 HLMs showed higher K(m) values (7.0 +/- 0.3 mM) rather than the lower K(m) values displayed by recombinant UGT1A6(*)2 (3.6 +/- 0.3 mM), suggesting that this allozyme may display different enzyme kinetic behavior in HLMs compared with HEK293 cells. At best, these polymorphisms were predicted to account for 15 to 20% of the observed 13-fold variability in glucuronidation of UGT1A6 substrates by HLMs, indicating that there are likely other genetic or environmental factors responsible for the majority of this variation.
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Details
- Title
- UDP glucuronosyltransferase (UGT) 1A6 pharmacogenetics: II. Functional impact of the three most common nonsynonymous UGT1A6 polymorphisms (S7A, T181A, and R184S)
- Creators
- Soundararajan Krishnaswamy - Molecular Pharmacogenetics Laboratory, Department of Pharmacology and Experimental Therapeutics, Tufts University, Boston, MA 02111, USAQin HaoAbdul Al-RohaimiLeah M HesseLisa L von MoltkeDavid J GreenblattMichael H Court
- Publication Details
- The Journal of pharmacology and experimental therapeutics, Vol.313(3), pp.1340-1346
- Academic Unit
- Veterinary Clinical Sciences, Department of
- Publisher
- United States
- Grant note
- DK-58496 / NIDDK NIH HHS GM-61834 / NIGMS NIH HHS DA-05258 / NIDA NIH HHS AG-17880 / NIA NIH HHS RR-00054 / NCRR NIH HHS AT-01381 / NCCIH NIH HHS DA-13209 / NIDA NIH HHS MH-58435 / NIMH NIH HHS AI-058784 / NIAID NIH HHS
- Identifiers
- 99900547588501842
- Language
- English
- Resource Type
- Journal article