Differential Rates of Glucuronidation for 7-Ethyl-10-Hydroxy-Camptothecin (Sn-38) Lactone and Carboxylate in Human and Rat Microsomes and Recombinant Udp-Glucuronosyltransferase Isoforms

Tallman, Melanie N.; Ritter, Joseph K.; Smith, Philip C.

doi:10.1124/dmd.104.003491

Cited by 28 publications

(28 citation statements)

References 24 publications

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“…Intestinal segments were defined as follows: duodenum, pyloric sphincter to ligament of Trietz; upper jejunum, upper half of remaining small intestine; lower jejunum-ileum, lower half of small intestine; and colon, cecum to rectum (Kararli, 1995). Intestinal scrapings and portions of excised kidneys and livers were homogenized, and the microsomes were isolated through differential ultracentrifugation (Tallman et al, 2005). Protein concentrations were determined using the Bradford assay with bovine serum albumin as the standard.…”

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confidence: 99%

Gender-Related Differences in Mycophenolate Mofetil-Induced Gastrointestinal Toxicity in Rats

Stern¹,

Tallman²,

Miles³

et al. 2006

Drug Metab Dispos

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ABSTRACT:Mycophenolate mofetil (MMF), the prodrug of mycophenolic acid (MPA), is included in current combination immunosuppressive regimens following organ transplant. Treatment with MMF often results in dose-limiting gastrointestinal (GI) side effects. The underlying mechanisms responsible for these side effects are not fully understood, but exposure of the intestinal epithelia to MPA during enterohepatic recycling may be involved. The present study demonstrated that female rats are more susceptible to MMF-induced GI toxicity than male rats. Female Sprague-Dawley rats treated chronically with an oral dose of 50 mg of MPA equivalents/kg/day experienced greater GI toxicity than male rats, as measured by diarrhea grade and weight loss. Intestinal microsomes harvested from the upper jejunum of female rats had approximately 3-fold lower MPA glucuronidation rates compared with male rats. In the remaining areas of the small and large intestine, there was also a trend toward decreased glucuronidation in the female rats. The area under the plasma concentration-time curve (AUC) for MPA following an oral dose of 50 mg of MPA equivalents/kg was roughly similar between genders, whereas the AUC for mycophenolic acid phenolic glucuronide (MPAG) was significantly lower in female rats. Female rats also excreted half of the biliary MPAG as male rats. The greater susceptibility of female rats to MMF-induced gastrointestinal toxicity, despite diminished intestinal MPA exposure via reduced biliary excretion of MPAG, may result from reduced protection of enterocytes by in situ glucuronidation. Likewise, susceptibility to MMF-induced GI toxicity in humans may also result from variable intestinal glucuronidation due to UDP glucuronosyltransferase polymorphisms or differential expression.

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confidence: 99%

Gender-Related Differences in Mycophenolate Mofetil-Induced Gastrointestinal Toxicity in Rats

Stern¹,

Tallman²,

Miles³

et al. 2006

Drug Metab Dispos

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“…Rat renal microsomes were prepared by differential centrifugation on study day 9, 24 h after the last dose administration (Tallman et al, 2005). Briefly, the kidney cortex was homogenized in 250 mM sucrose with EDTA (1 mM), dithiothreitol (0.1 mM), and phenylmethylsulfonyl fluoride (0.25 mM) and centrifuged at 10,000g for 20 min.…”

Section: Methodsmentioning

confidence: 99%

Androgen Regulation of Renal Uridine Diphosphoglucuronosyltransferase 1A1 in Rats: Fig. 1.

Stern

Tallman²,

Miles

et al. 2008

Drug Metab Dispos

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ABSTRACT:Many phase I and II enzymes are under hormonal regulation, resulting in sex-related expression patterns. This sex-related enzyme expression can result in differential metabolism of physiologically active endogenous substances, altered xenobiotic clearance, and differences in susceptibility to drug toxicities. Treatment of female Sprague-Dawley (SD) rats with 5 mg testosterone propionate/kg/day, 2 ml/kg s.c. for 8 days resulted in induction of renal uridine diphosphoglucuronosyltransferase (UGT) 1A1, as determined by immunoblot and probe substrate activity. Glucuronidation activity for mycophenolic acid, a substrate for rat UGT1A1, 1A6, and 1A7, was significantly elevated approximately 2-fold in renal microsomes from testosterone propionate-treated animals. Protein expression of rat UGT1A1 was also dramatically increased, whereas 1A6 and 1A7 remained unchanged as a result of treatment. Male SD rats were determined to express greater renal UGT1A1 than age-matched female rats. These data support the androgen regulation of rat renal UGT1A1.

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“…Irinotecan and SN-38G methyl ester were kindly provided by Dr. Robert Kelly (Pfizer, Inc., Kalamazoo, MI). Preparation and quantitation of SN-38 and SN-38G were described previously (Tallman et al, 2005). Reagents for microsomal experiments were purchased through Sigma-Aldrich (St. Louis, MO).…”

Section: Methodsmentioning

confidence: 99%

“…Intestines and colons from irinotecan-naive j/jAV and jϩAV (n ϭ 2 in each group) rats were extracted 7 days after adenovirus injection and used to make microsomes. The procedures followed to make microsomes from these organs were described previously (Tallman et al, 2005). Microsomal protein concentrations were determined by the Bradford method, using bovine albumin as a standard.…”

Section: Methodsmentioning

confidence: 99%

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The Contribution of Intestinal UDP-Glucuronosyltransferases in Modulating 7-Ethyl-10-hydroxy-camptothecin (SN-38)-Induced Gastrointestinal Toxicity in Rats

Tallman¹,

Miles²,

Kessler³

et al. 2006

J Pharmacol Exp Ther

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Life-threatening diarrhea afflicts a considerable percentage of patients treated with irinotecan, an anticancer agent with effects elicited through its active metabolite 7-ethyl-10-hydroxycamptothecin (SN-38). The primary detoxification pathway for SN-38 is glucuronidation. The purpose of this study was to evaluate the role that intestinal UDP-glucuronosyltransferases (UGTs) have from hepatic UGTs in modulating this diarrhea. To investigate this, Gunn rats devoid of UGT1A activity were injected with recombinant adenoviral vectors expressing UGT1A1, 1A6, and 1A7, resulting in reconstituted hepatic UGT expression comparable to a heterozygote. Hepatic microsome studies indicated that 4 to 7 days after adenoviral injection, transfected Gunn rats (j/jAV) had SN-38 glucuronide (SN-38G) formation rates three times higher than control heterozygote rats (jϩAV). The adenovirus did not impart any glucuronidating capacity to the intestine in j/jAV rats, whereas jϩAV rats possessed intestinal UGT function. After the administration of 20 mg/kg/day irinotecan i.p. to j/jAV rats 4 days after adenovirus injection, diarrhea ensued before the fourth irinotecan dose. jϩAV rats were spared the diarrhea, and the toxicity was mild compared with the j/jAV rats, as measured by diarrhea scores, weight loss, and histological assessments of the cecum and colon. The pharmacokinetics of irinotecan, SN-38, and SN-38G indicate that the systemic exposure of SN-38 and SN-38G was higher and lower, respectively, in j/jAV rats. Despite this, the biliary excretion of irinotecan and metabolites was similar. Because intestinal UGTs are the main discriminating factor between j/jAV and jϩAV rats, their presence seems to be critical for the gastrointestinal protection observed in jϩAV rats.The UDP-glucuronosyltransferases (UGTs) are a superfamily of metabolic enzymes that catalyze the transfer of UDP-glucuronic acid to endogenous and xenobiotic substrates. Glucuronidation is a detoxification mechanism from several standpoints. It decreases the apparent volume of distribution, increases the molecular weight, and increases substrate specificity for active transport by imparting a negative charge, which are all processes that facilitate substrate elimination from the body (Guillemette, 2003). Furthermore, in most cases, glucuronidation renders the substrate inactive with respect to its pharmacological or physiological target. A Wistar-derived rat model of UGT1A subfamily deficiency, the Gunn rat, has allowed tremendous insight into the importance of the UGT1A family in the metabolism and toxicity of substrates (Wells et al., 2004). The abolition of UGT1A glucuronidation in these rats stems from a frameshift mutation that yields a truncated, nonfunctional protein unable to bind UDP-glucuronic acid (Iyanagi et al., 1989).Although the primary organ of glucuronidation receiving most attention has been the liver, research on intestinal UGTs has shown their importance. Large differences in protein levels of the UGT1A family are not observed between these ...

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Differential Rates of Glucuronidation for 7-Ethyl-10-Hydroxy-Camptothecin (Sn-38) Lactone and Carboxylate in Human and Rat Microsomes and Recombinant Udp-Glucuronosyltransferase Isoforms

Cited by 28 publications

References 24 publications

Gender-Related Differences in Mycophenolate Mofetil-Induced Gastrointestinal Toxicity in Rats

Gender-Related Differences in Mycophenolate Mofetil-Induced Gastrointestinal Toxicity in Rats

Androgen Regulation of Renal Uridine Diphosphoglucuronosyltransferase 1A1 in Rats: Fig. 1.

The Contribution of Intestinal UDP-Glucuronosyltransferases in Modulating 7-Ethyl-10-hydroxy-camptothecin (SN-38)-Induced Gastrointestinal Toxicity in Rats

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