Functional analysis of UGT1A4^P24T and UGT1A4^L48V variant enzymes

Abstract

Aim: To investigate the effects of two nonsynonymous SNPs, UGT1A4*2 (rs#: 6755571, 70C>A, P24T) and UGT1A4*3 (rs#: 2011425, 142T>G, L48V), on the function of UGT1A4 against dihydrotestosterone (DHT), transandrosterone (t-AND), lamotrigine (LTG) and tamoxifen (TAM). Materials & methods: Detailed kinetic experiments were conducted with recombinant UGT1A4wild-type, UGT1A4P24T and UGT1A4L48V, which were overexpressed in HEK293 cell lines. The kinetic profiles and kinetic parameters (Km, Vmax and CLint) obtained with either UGT1A4P24T or UGT1A4L48V were compared with those obtained with the wild-type enzyme. The interaction of TAM on UG1A4-catalyzed DHT glucuronidation was also investigated with the three UGT1A4 polymorphic enzymes. Results: UGT1A4L48V had higher enzyme efficiency (CLint) compared with wild-type UGT1A4 on DHT glucuronidation; UGT1A4P24T and UGT1A4L48V had lower CLint than wild-type UGT1A4 for t-AND and LTG glucuronidation. The TAM CLint with UGT1A4P24T and UGT1A4L48V glucuronidation and the UGT1A4P24T-catalyzed DHT glucuronidation were, on the other hand, similar to those of the wild-type enzyme. With all three enzymes, TAM activated UGT1A4-catalyzed DHT glucuronidation in a concentration-dependent fashion. Conclusion: Decreased CLint of UGT1A4P24T and UGT1A4L48V on LTG glucuronidation may lead to interindividual variations in LTG metabolism in vivo. However, it is less likely that these polymorphisms would have impact on DHT and t-AND metabolism in vivo because these compounds are glucuronidated by multiple enzymes. Original submitted 31 May 2011; Revision submitted 19 July 2011

Model‐based lamotrigine clearance changes during pregnancy: clinical implication

“…9-11, 15, 16 Genotypic variations in the activity or induction of UGT1A4 could partly explain the varying degrees of enhanced oral CL between the two populations and may warrant further investigations. 16, 40-42 …”

Frequencies of UGT1A4*2 (P24T) and *3 (L48V) and their effects on serum concentrations of lamotrigine

“…Valproate (44) Enzyme inducer Carbamazepine (2), oxcarbazepine (5) Non-interacting co-medication (n) Antiepileptic drugs Levetiracetam (29), topiramate (8), zonisamide (6), pregabalin (5), clobazam (2), ethosuximide (1), gabapentin (1), rufinamide (1), retigabine (1), felbamate (1) Desogestrel (3), escitalopram (2), candesartan (2) Other drugs Thyroxine (2), simvastatin (2), acetylsalicylic acid (2) Ghotbi et al 2010;Gulcebi et al 2011;Haslemo et al 2012;Laverdiere et al 2011;Mori et al 2005;Zhou et al 2011). However, most of these studies were experimental, and clinical data are sparse.…”

Potential Role ofUGT1A4Promoter SNPs in Anastrozole Pharmacogenomics

“…Consistent with previous studies (Kamdem et al, 2010;Lazarus and Sun, 2010), we found no statistically significant association between these genetic variants and anastrozole glucuronidation formation rates. However, there are reports of an association of coding region SNPs with differential metabolic activity toward mutagenic amines and endogenous steroids, altering hepatic metabolism and detoxification (Ehmer et al, 2004;Benoit-Biancamano et al, 2009;Gulcebi et al, 2011;Zhou et al, 2011). More recently, functional SNPs in the promoter elements located in the 59-upstream region of UGT1A4 have been described (Saeki et al, 2005;Erichsen et al, 2008;Benoit-Biancamano et al, 2009;Menard et al, 2009).…”