Involvement of Human UGT2B7 and 2B15 in Rofecoxib Metabolism

Abstract

ABSTRACT:O-Glucuronidation of 5-hydroxyrofecoxib is the major biotransformation pathway of rofecoxib in human, rat, and dog. The glucuronide conjugate is also involved in the reversible metabolism of rofecoxib in rat and human. Atypical bimodal phenomena were observed in their plasma concentration-time curves with a large variability among different human subjects. It is unclear which family members of human UDP-glucuronosyltransferases (UGT) are involved in the formation of the glucuronide. O-Glucuronidation ) and is marketed by Merck as an anti-inflammatory drug (VIOXX) for the treatment of arthritis and pain Prasitet al., 1999). The absorption, distribution, metabolism, and excretion of rofecoxib in rat, dog, and human have been reported (Halpin et al., 2000(Halpin et al., , 2002. Rofecoxib was extensively metabolized with the major metabolites as 5-hydroxyrofecoxib and its O-glucuronide conjugate. In the rat, an unusual feature of the plasma concentration versus time profile for rofecoxib following oral administration was the presence of a distinct second C max . Similar phenomena were also observed in human pharmacokinetic profiles with a large variability among different subjects. It was suggested that the atypical bimodal phenomena in plasma concentration-time curves were due to reversible metabolism of 5-hydroxyrofecoxib to rofecoxib (Baillie et al., 2001). The 5-hydroxyrofecoxib was metabolized to its glucuronide conjugate and excreted in bile. The glucuronide metabolite was deconjugated in the lower gastrointestinal tract, resulting in 5-hydroxyrofecoxib. Reduction of the 5-hydroxyrofecoxib formed a hydroxyacid that cyclized spontaneously to regenerate rofecoxib, which was reabsorbed and entered the systemic circulation. The second C max was due to reabsorption of rofecoxib formed from 5-hydroxyrofecoxib glucuronide in the lower gastrointestinal tract.Since O-glucuronidation of 5-hydroxyrofecoxib plays a major role in biotransformation and reabsorbtion of rofecoxib in human, it is interesting to identify human UGT enzymes responsible for the glucuronidation of 5-hydroxyrofecoxib. To date no human UGT isoform responsible for the glucuronidation of 5-hydroxyrofecoxib has been reported. The primary goal of the present investigation was to determine which human UGT isoforms are responsible for the glucuronidation of 5-hydroxyrofecoxib and to understand the mechanism of high variability in pharmacokinetic patterns in human subjects. 5-Hydroxyrofecoxib was incubated with human liver microsomes and eight cDNA expressed human UGT isoforms from 1A and 2B subfamilies that are involved in xenobiotic metabolism (Mackenzie et al., 1997;Jedlitschky et al., 1999). The incubated samples were analyzed by LC-MS coupled with UV detection. For active UGT isoforms, kinetic parameters were determined and compared with those determined for human liver microsomes in an attempt to better explain the variation in clearance of the compound.

AMIDE N-GLUCURONIDATION OF MAXIPOST CATALYZED BY UDP-GLUCURONOSYLTRANSFERASE 2B7 IN HUMANS

“…Glucuronidation of BMS-204352 at the amide nitrogen represents a newly identified glucuronidation reaction by UGT2B7. UGT2B7 has been demonstrated to conjugate many drugs including morphine (Coffman et al, 1997), zidovudine (Barbier et al, 2000), epirubicin (Innocenti et al, 2001), estrogens and retinoic acid (Czernik et al, 2000), diclofenac (King et al, 2001), and rofecoxib (Zhang et al, 2003b). These reactions represent glucuronidations by UGT2B7 at nucleophilic functional groups of oxygen (carboxylic acid, phenol, and primary and secondary alcohols).…”

UDP-Glucuronosyltransferase (UGT) 2B15 Pharmacogenetics: UGT2B15 D85Y Genotype and Gender Are Major Determinants of Oxazepam Glucuronidation by Human Liver

“…Although we have shown that the D85Y polymorphism affects oxazepam glucuronidation, it is not yet apparent whether other clinically important substrates of UGT2B15, such as E-4-hydroxytamoxifen (Nishiyama et al, 2002) and 5-hydroxyrofecoxib (Zhang et al, 2003) will be affected to a similar degree. Indeed, our previous work using recombinant D85 and Y85 variants indicates that the magnitude of the effect could be substrate dependent in that a greater than 10-fold difference between variants was observed for naringenin glucuronidation, compared with a 5-fold difference for oxazepam glucuronidation, whereas there was less than a 2-fold difference for dihydrotestosterone glucuronidation (Court et al, 2002).…”

“…Pharmaceutical substrates of UGT2B15 that have been identified include oxazepam, E-4-hydroxytamoxifen, 5-hydroxyrofecoxib, eugenol, 8-hydroxyquinoline, phenolphthalein, 4Ј-hydroxyphenytoin, and nandrolone (Green et al, 1994;Court et al, 2002;Nishiyama et al, 2002;Kuuranne et al, 2003;Zhang et al, 2003). Oxazepam, a commonly used 1,4-benzodiazepine anxiolytic drug, is of considerable interest because it is cleared primarily by glucuronidation and has been used extensively as an in vivo probe of drug glucuronidation in people (Greenblatt et al, 1980(Greenblatt et al, , 1984Greenblatt, 1981;Sonne, 1993).…”

Inhibition screening method of microsomal UGTs using the cocktail approach

“…According to the literature, the UGT 2B15 isoform could be investigated with bisphenol A (Hanioka et al, 2008), HMMA (Shoda et al, 2009) or 5-hydroxyrofecoxib (Zhang et al, 2003). The latter substrate was not assessed because of its light sensitivity.…”