Conjugation of Desmethylnaproxen in the Rat—A Novel Acyl Glucuronide-Sulfate Diconjugate as a Major Biliary Metabolite

115

ABSTRACT:Studies have shown that in the rat, bisphenol A (BPA) is metabolized and eliminated primarily as a monoglucuronide, a metabolite without estrogenic activity. The purpose of this study was to determine the extent of monoglucuronide formation in monolayers of hepatocytes from rats, mice, and humans. Noncytotoxic concentrations of BPA (10, 20, and 35 M; 1.0 Ci), as assessed by lactate dehydrogenase leakage, were incubated with isolated hepatocytes for 0-6 h. Media were collected and analyzed for metabolites by radiochemical high performance liquid chromatography and liquid chromatography-tandem mass spectrometry. The metabolites identified include a monoglucuronide (major metabolite), a sulfate conjugate, and a glucuronide/sulfate diconjugate (minor metabolites). In hepatocytes of male Fischer-344 rats, the predominate metabolite was the diconjugate (glucuronide/sulfate). Under these conditions, the extent of metabolism by 3 h was similar in all species tested because all BPA was converted to conjugates by 3 h. Initial rates of metabolism in hepatocytes followed the order of mice > rats > humans. However, when extrapolated to the whole liver (i.e., cells per liver), the hepatic capacity for BPA glucuronidation is predicted to be humans > rats > mice. This research was supported in part by The Society of Plastics Industry Inc., and Southwest Environmental Health Science Center (ES 06694).Bisphenol A (BPA 1 ) is used in the production of polycarbonates, epoxy resins, phenolic resins, and diacrylates. Polycarbonates, one of the most widely used plastics, accounts for 60% of the total production of BPA (Perez et al., 1998). Epoxy-based resins are used in a variety of consumer products that include decorative floor manufacture, lacquer coatings in cans, dental composites and sealants, and as additives in the production of vinyl and acrylic resins. Trace amounts of BPA monomer have been reported to leach out of polycarbonate and epoxy resins (Brotons et al., 1995). Such leaching may result in the potential exposure of humans to trace amounts of BPA.Exposure to BPA is of interest, because it is known to possess weak estrogenic activity (Dodds and Lawson, 1936). In vitro it displaces estradiol from both the ␣ and ␤ estrogen receptor and exhibits weak estrogenic activity (Krishnan et al., 1993, Kuiper et al., 1997. The binding of BPA to the estrogen receptor has been reported to be 10,000 times less than that of 17␤-estradiol (Gaido et al., 1997). Following oral exposure, BPA undergoes its first pass metabolism in the intestine and/or liver, which greatly limits its systemic bioavailability (Pottenger et al., 2000;Upmeier et al., 2000). In vitro data show that BPA is rapidly conjugated with glucuronic acid by hepatic rat microsomes (Yokota et al., 1999). Recent results obtained using rat hepatocytes (HC) or perfused liver confirm the extensive formation of a BPA monoglucuronide (Nakagawa and Tayama, 2000;Inoue et al., 2001) and correlate with in vivo findings that demonstrated the BPA-glucuronide to be the major me...

Section: Discussionmentioning

confidence: 99%

Metabolism of Bisphenol A in Primary Cultured Hepatocytes from Mice, Rats, and Humans

Pritchett

Kuester²,

Sipes³

2002

115

“…Fenselau and Johnson (1980) and Niemeijer et al (1991) reported that the O bond to the aromatic ring is not readily broken in the mass spectrometric analysis of phenols or phenol derivatives. The m/z 193 ion is considered to be the deprotonated glucuronic acid ion produced by cleaving the carboxyl group C-O bond, as reported by Jaggi et al (2002) and Plumb et al (2007) on the acyl O-glucuronides of desmethylnaproxen and ibuprofen. Given the mass spectrometric analysis and the fact that G2 is alkali-labile, this strongly suggests that G2 is the acyl O-glucuronide of T-5224.…”

Section: Discussionmentioning

confidence: 99%

Metabolism of the c-Fos/Activator Protein-1 Inhibitor T-5224 by Multiple Human UDP-Glucuronosyltransferase Isoforms

Uchihashi

Fukumoto²,

Onoda³

et al. 2011

ABSTRACT:We developed 3-{5-[4-(cyclopentyloxy)-2-hydroxybenzoyl]-2-[(3-hydroxy-1,2-benzisoxazol-6-yl)methoxy]phenyl} propionic acid (T-5224) as a novel inhibitor of the c-Fos/activator protein-1 for rheumatoid arthritis therapy. We predicted the metabolism of T-5224 in humans by using human liver microsomes (HLM), human intestinal microsomes (HIM), recombinant human cytochrome P450 (P450), and UDP-glucuronosyltransferases (UGTs). T-5224 was converted to its acyl O-glucuronide (G2) by UGT1A1 and UGT1A3 and to its hydroxyl O-glucuronide (G3) by several UGTs, but it was not metabolized by the P450s. A comparison of the intrinsic clearances (CL int ) between HLM and HIM suggested that the glucuronidation of T-5224 occurs predominantly in the liver. UGT1A1 showed a higher k cat /K m value than UGT1A3 for G2 formation, but a lower k cat /K m value than UGT1A3 for G3 formation. A high correlation was observed between G2 formation activity and UGT1A1-specific activity (␤-estradiol 3-glucuronidation) in seven individual HLM. A high correlation was also observed between G2 formation activity and UGT1A1 content in the HLM. These results strongly suggest that UGT1A1 is responsible for G2 formation in human liver. In contrast, no such correlation was observed with G3 formation, suggesting that multiple UGT isoforms, including UGT1A1 and UGT1A3, are involved in G3 formation. G2 is also observed in rat and monkey liver microsomes as a major metabolite of T-5224, suggesting that G2 is not a human-specific metabolite. In this study, we obtained useful information on the metabolism of T-5224 for its clinical use.

“…Naproxen, a nonsteroidal anti-inflammatory agent, undergoes oxidative dealkylation to form 6-O-desmethyl naproxen. An acyl glucuronide-sulfate conjugate of this primary metabolite of naproxen was identified as a major biliary metabolite in male Sprague-Dawley rats (Jaggi et al, 2002). Efavirenz, a non-nucleoside reverse-transcriptase inhibitor of HIV-1, has also been shown to form a glucuronide-sulfate diconjugate in rat urine and bile (Mutlib et al, 1999).…”

Section: Glucuronide-sulfate Diconjugatesmentioning

confidence: 99%

Unusual Glucuronides

Argikar¹

2012

ABSTRACT:Glucuronidation reaction is catalyzed by mammalian uridine diphosphoglucuronosyl transferases by using uridine diphosphoglucuronic acid as a cosubstrate. Conjugation of glucuronic acid to nucleophilic functional groups in chemical entities results in formation of glucuronides. As anticipated, a number of nucleophilic functional groups such as hydroxyl, phenolic, acyl, primary secondary and tertiary amino, etc. in a diverse set of chemical compounds are known to form the corresponding glucuronides. Glucuronides have been reported to be formed at carbon atoms, selenium atoms, and upon N-carbamoylation of primary and secondary amino groups. Glucuronides are also believed to be the end products of metabolism. However, there are examples where glucuronidation results in further oxidative or conjugative biotransformation reactions. The objective of this review is to highlight unusual glucuronide conjugates. Diglucuronide conjugates reported in the literature fall under two distinct categories. Use of prefixes such as "bis" versus "di" has been previously proposed for separating the two types of diglucuronides. In spite of this, literature reports for diconjugative glucuronide metabolites reflect interchangeable use of "bisglucuronides" and "diglucuronides." Furthermore, the application of such prefixes does not adhere to recommendations of International Union of Pure and Applied Chemistry nomenclature for substituent groups. Therefore, an effort is made in this review to document the historic reports for diglucuronides into two distinct types for sake of clarity and to allow differentiation between the two types of diconjugative metabolites. Overall, this commentary centers on unusual glucuronide metabolites that result from conjugation at uncommon functional groups, glucuronides undergoing ensuing oxidative or conjugative metabolic transformations. Structural and mechanistic aspects are also discussed.