Metabolism of Rofecoxib in Vitro Using Human Liver Subcellular Fractions

Slaughter, Donald; Takenaga, Norihiro; Lü, Ping; Assang, Carol; Walsh, Deborah J.; Arison, Byron H.; Cui, Donghui; Halpin, Rita A.; Geer, Leslie A.; Vyas, Kamlesh P.; Baillie, Thomas A.

doi:10.1124/dmd.31.11.1398

Cited by 27 publications

(20 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Rofecoxib has previously been suggested to have a relatively low propensity to interact with drugs metabolized by P450 enzymes (Merck & Co., 2002;Slaughter et al, 2003). However, the inhibition of CYP1A2 by rofecoxib is clinically relevant as documented by the clinical studies with tizanidine, theophylline, and warfarin (Schwartz et al, 2000;Bachmann et al, 2003;Backman et al, 2006b).…”

Section: Discussionmentioning

confidence: 89%

“…However, rofecoxib is mainly reduced to different 3,4-dihydrohydroxy acid derivatives in vivo (Fig. 1), and P450 enzymes have been suggested to play only a minor role in its metabolism (Merck & Co., 2002;Slaughter et al, 2003). In vitro, CYP1A2 and CYP3A4 have catalyzed the 5-hydroxylation of rofecoxib, but the contributions of non-P450-mediated pathways to the total metabolism of rofecoxib have been greater .…”

Section: Discussionmentioning

confidence: 99%

“…1) (Merck & Co., 2002;Slaughter et al, 2003). In human liver microsomal incubations, rofecoxib has been found to be metabolized to 5-hydroxyrofecoxib by several P450 enzymes, CYP1A2 and CYP3A4 having the greatest contributions .…”

mentioning

confidence: 99%

See 2 more Smart Citations

Rofecoxib Is a Potent, Metabolism-Dependent Inhibitor of CYP1A2: Implications for in Vitro Prediction of Drug Interactions

Karjalainen¹,

Neuvonen²,

Backman³

2006

Drug Metab Dispos

View full text Add to dashboard Cite

ABSTRACT:Rofecoxib was recently found to greatly increase plasma concentrations of the CYP1A2 substrate drug tizanidine in humans, but there are no published in vitro studies on the CYP1A2-inhibiting effects of rofecoxib. Our objective was to investigate whether rofecoxib is a direct-acting or metabolism-dependent inhibitor of CYP1A2 in vitro. The effect of rofecoxib on the O-deethylation of phenacetin (20 M) was studied using human liver microsomes. The effect of preincubation time on the inhibitory potential of rofecoxib was also studied, and the inhibitor concentration that supports half the maximal rate of inactivation (K I ) and the maximal rate of inactivation (k inact ) were determined. Rofecoxib is a cyclooxygenase-2-selective nonsteroidal anti-inflammatory drug, which was recently withdrawn, possibly temporarily, from clinical use because of its cardiovascular side effects. Previous studies have shown that rofecoxib moderately increases plasma concentrations and effects of theophylline (Bachmann et al., 2003) and the R-isomer of warfarin (Schwartz et al., 2000). Quite recently, rofecoxib in therapeutic doses of 25 mg per day was found to increase more than 10-fold the plasma concentrations of the CYP1A2 substrate tizanidine in humans (Backman et al., 2006b). The effects on tizanidine pharmacokinetics suggest that rofecoxib can be a relatively potent inhibitor of CYP1A2. However, hitherto, there have been no published in vitro studies on the effect of rofecoxib on CYP1A2 activity, nor has the type of CYP1A2 inhibition by rofecoxib been clarified.Rofecoxib itself is extensively metabolized via complex oxidative, reductive, and back-reduction pathways (Fig. 1) (Merck & Co., 2002;Slaughter et al., 2003). In human liver microsomal incubations, rofecoxib has been found to be metabolized to 5-hydroxyrofecoxib by several P450 enzymes, CYP1A2 and CYP3A4 having the greatest contributions . In liver S9 fractions, the metabolite profile of rofecoxib has been more complex, including the formation of both 5-hydroxyrofecoxib and different 3,4-dihydrohydroxy acid derivatives; the latter are considered to represent the major pathways in vivo (Halpin et al., 2002). Thus, it has been suggested that P450 enzymes play a minor role in rofecoxib's metabolism. However, in our recent study, the plasma concentrations of rofecoxib correlated to the plasma caffeine-paraxanthine ratio in vivo, suggesting a role for CYP1A2 in the metabolism of rofecoxib (Backman et al., 2006b). Our purpose, in the current study, was to explore in vitro the CYP1A2-inhibitory potency of rofecoxib and to elucidate the type of possible CYP1A2 inhibition. Materials and Methods Chemicals and Microsomes. Rofecoxib (Sequoia Research ProductsLimited, Pangbourne, UK), phenacetin, acetaminophen, ␤-NADPH (SigmaAldrich, St. Louis, MO), methanol, acetonitrile, and ethyl acetate (Rathburn Chemicals Ltd., Walkerburn, Scotland) were used in this study. Other chemicals were obtained from Merck (Darmstadt, Germany). Pooled human liver microsomes were obtained from BD ...

show abstract

Section: Discussionmentioning

confidence: 89%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Rofecoxib Is a Potent, Metabolism-Dependent Inhibitor of CYP1A2: Implications for in Vitro Prediction of Drug Interactions

Karjalainen¹,

Neuvonen²,

Backman³

2006

Drug Metab Dispos

View full text Add to dashboard Cite

show abstract

“…In rats after administration of rofecoxib, the main components in plasma were reported to be unchanged rofecoxib, 5-hydroxyrofecoxib that was partially produced from the parent by some isoforms of cytochrome P450, and its glucuronide (5-hydroxyrofecoxib-O-␤-D-glucuronide) (Halpin et al, 2000, Slaughter et al, 2003. Among them, the glucuronide was thought to be chemically inactive, so we hypothesized that either rofecoxib or 5-hydroxyrofecoxib or both were bound to the elastin.…”

Section: Discussionmentioning

confidence: 99%

Mechanism for Covalent Binding of Rofecoxib to Elastin of Rat Aorta

Oitate¹,

Hirota²,

Takahashi³

et al. 2006

J Pharmacol Exp Ther

View full text Add to dashboard Cite

We have previously reported that oral administration of [14 C]rofecoxib to rats resulted in the long retention of radioactivity by the aorta as a consequence of covalent binding to elastin. Treatment of rats with ␣-phenyl-␣-propylbenzeneacetic acid 2-[diethylamino]-ethyl ester hydrochloride (SKF-525A), a cytochrome P450 inhibitor, significantly decreased the systemic exposure of 5-hydroxyrofecoxib, one of the main metabolites of rofecoxib, whereas there was no statistically significant change in the retention of radioactivity from [14 C]rofecoxib in the aorta. On the other hand, the aortic retention of radioactivity closely correlated to the systemic exposure of unchanged rofecoxib in the dose range between 2 and 10 mg/kg. A covalent binding study of [14 C]rofecoxib in vitro using rat aorta homogenate in the presence of D-penicillamine, hydralazine, ␤-aminopropionitrile, and sodium borohydride suggested that the aldehyde group of allysine in elastin was relevant to the covalent binding. In a model reaction using benzaldehyde, rofecoxib but not 5-hydroxyrofecoxib reacted with the aldehyde group of benzaldehyde in a manner of condensation reaction under a physiological pH condition. A histopathological examination using an electron microscope demonstrated that multiple oral administration of rofecoxib to rats caused marked degradation of the elastic fiber system of the aorta. These results suggested that rofecoxib as such is reactive in vivo, undergoing a condensation reaction with allysine, thereby preventing the formation of cross-linkages in elastin, i.e., desmosine and isodesmosine, and causing the degradation of the elastic fibers.

show abstract

“…In vitro data obtained with different subcellular fractions indicate that metabolism of rofecoxib is complex and involves oxidation (5-hydroxylation), hydration, and reduction (Slaughter et al, 2003). The latter two reactions require cytosol, and only the formation of 5-hydroxy rofecoxib in human liver microsomes is catalyzed by P450s (CYP3A4, ϳ60%; CYP1A2, ϳ30%).…”

Section: Rodriguesmentioning

confidence: 99%

IMPACT OFCYP2C9GENOTYPE ON PHARMACOKINETICS: ARE ALL CYCLOOXYGENASE INHIBITORS THE SAME?: TABLE 1

Rodrigues¹

2005

Drug Metab Dispos

103

View full text Add to dashboard Cite

ABSTRACT:The market withdrawals of rofecoxib (Vioxx) and valdecoxib (Bextra) have focused considerable attention on the side effect profiles of cyclooxygenase (COX) inhibitors. As a result, attempts will be made to identify risk factors in the hope that physicians might be able to ensure patient safety. At first glance, CYP2C9 genotype might be considered a risk factor because many COX inhibitors are CYP2C9 substrates in vitro. This observation has led some to hypothesize that a reduction in clearance, in subjects expressing variant forms of the enzyme (e.g., CYP2C9*1/*3 or CYP2C9*3/*3 genotype), will lead to increased exposure and a greater risk of cardiovascular or gastrointestinal side effects. For any drug, however, one has to consider all clearance pathways. Therefore, a number of COX inhibitors were surveyed and it was determined that CYP2C9 plays a relatively minor role in the overall clearance (<20% of the dose) of sulindac, naproxen, ketoprofen, diclofenac, rofecoxib, and etoricoxib. CYP2C9 genotype would have no clinically meaningful impact on the pharmacokinetics of these drugs. In contrast, CYP2C9 genotype is expected to impact the clearance of ibuprofen, indomethacin, flurbiprofen, celecoxib, valdecoxib, lornoxicam, tenoxicam, meloxicam, and piroxicam. However, even when CYP2C9 is a major determinant of clearance, it is necessary to consider CYP2C8 genotype (e.g., ibuprofen) and, possibly, CYP3A4 activity (e.g., celecoxib, valdecoxib, and meloxicam) also.Events surrounding the market withdrawal of rofecoxib (Vioxx), a potent and selective COX-2 inhibitor, have raised concerns about the safety of other COX-2 selective inhibitors such as etoricoxib (Arcoxia), celecoxib (Celebrex), lumiracoxib (Prexige), and valdecoxib (Bextra) (Mukherjee et al., 2002;Bing, 2003;Couzin, 2004;Davies and Jamali, 2004;Fitzgerald, 2004;Kim and Reicin, 2004;Ray et al., 2004;Scheen, 2004;Bannwarth, 2005;Berenbaum, 2005). Such concerns finally resulted in the withdrawal of valdecoxib about seven months after the withdrawal of rofecoxib (Lenzer, 2005;Young, 2005). Nonselective COX inhibitors (NSAIDs) like naproxen, diclofenac, and ibuprofen have also come under scrutiny from regulators, physicians, and patient safety advocacy groups (McGettigan and Henry, 2000;Meagher, 2003).At the present time, it is thought that the CV and GI side effects of COX inhibitors are related to their mechanism of action. This involves the inhibition of COX, a hemeprotein that exists in two forms (COX-1 and COX-2). COX-1 is expressed constitutively in most tissues, whereas the expression of COX-2 can be induced by growth factors, cytokines, and vasoactive peptides such as endothelin. In response to cell damage, therefore, COX-2 is inducible by proinflammatory mediators and plays a role in the generation of prostaglandin E 2 , a major mediator of inflammatory response. On the other hand, the products of COX-1 are cytoprotective in GI epithelium, and selective inhibition of COX-2 is anticipated to reduce inflammation, and modulate pain, without the GI...

show abstract

Metabolism of Rofecoxib in Vitro Using Human Liver Subcellular Fractions

Cited by 27 publications

References 27 publications

Rofecoxib Is a Potent, Metabolism-Dependent Inhibitor of CYP1A2: Implications for in Vitro Prediction of Drug Interactions

Rofecoxib Is a Potent, Metabolism-Dependent Inhibitor of CYP1A2: Implications for in Vitro Prediction of Drug Interactions

Mechanism for Covalent Binding of Rofecoxib to Elastin of Rat Aorta

IMPACT OFCYP2C9GENOTYPE ON PHARMACOKINETICS: ARE ALL CYCLOOXYGENASE INHIBITORS THE SAME?: TABLE 1

Contact Info

Product

Resources

About