Species and tissue differences in serotonin glucuronidation

Drug Metabolism and Disposition

Katoh

Kondo

et al. 2015

UDP-glucuronosyltransferase (UGT), a phase II drug-metabolizing enzyme, is expressed in the brain and can catalyze glucuronidation of endogenous and exogenous substrates in the brain. Thus, changes in UGT1A expression could affect homeostasis and drug efficacy. Phenobarbital (PB), a typical inducer of drug-metabolizing enzymes, has been reported to induce oxidative stress and epigenetic changes, which could alter UGT expression in the brain. Here, we aimed to clarify the effects of PB on Ugt1a6 and Ugt1a7 gene expression in rat brains. Sprague-Dawley rats were treated intraperitoneally with PB (80 mg/kg), once daily for 7 days. Ugt1a6 and Ugt1a7 mRNA expression levels were increased in the striatum and thalamus (Ugt1a6, 3.0-and 2.9-fold, respectively; Ugt1a7, 2.6-and 2.6-fold, respectively). Acetaminophen glucuronidation was also increased in the medulla oblongata and thalamus by 1.8-and 1.2-fold, respectively. The induction rates within different brain regions were correlated with Ugt1a6 and Ugt1a7 mRNA expression, and the degree of induction also correlated with that of NF-E2-related factor-2 mRNA. Measurement of oxidative stress markers suggested that PB induced oxidative stress in brain regions in which Ugt1a6 and Ugt1a7 mRNAs were increased. Moreover, histone modifications were altered by PB treatment, resulting in increased histone H3 lysine 4 trimethylation in the striatum and thalamus and decreased histone H3 lysine 9 trimethylation in the thalamus. These results suggested that oxidative stress and histone modifications may promote transcriptional activation of Ugt1a6 and Ugt1a7 genes. In summary, Ugt1a6 and Ugt1a7 mRNA levels were increased by PB treatment, which may alter pharmacokinetics in the brain.

Section: Methodsmentioning

confidence: 99%

Effects of Phenobarbital on Expression of UDP-Glucuronosyltransferase 1a6 and 1a7 in Rat Brain

Drug Metabolism and Disposition

Katoh

Kondo

et al. 2015

“…Pooled rat microsomes from brain regions (n=8) and livers (n=3) were prepared as described previously. 21) β-Estradiol 3-Glucuronidation in Rat Brain Regions β-Estradiol 3-glucuronide levels were determined using a method described previously 22) with slight modifications. The incubation mixture contained 50 mM Tris (hydroxymethyl) aminomethane-HCl (pH 7.4), 5 mM MgCl 2 , 25 µg/mL alamethicin, 3 mM uridine 5′-diphosphoglucuronic acid, 5 µM β-estradiol, and microsomal proteins (brain: 0.5 mg/mL or liver: 0.01 mg/mL).…”

Section: Methodsmentioning

confidence: 99%

“…Bilirubin (5-50 µM), serotonin (1-10 mM), and APAP (1-10 mM) were glucuronidated mainly by Ugt1a1, 23) Ugt1a6, 21) and Ugt1a6 and Ugt1a7, 24) respectively, which were used as the Ugt inhibitors. β-Estradiol 3-glucuronidation was analyzed in the presence of each Ugt inhibitor.…”

Section: Kinetic Analysis Of β-Estradiol 3-glucuronidation In Rat Cermentioning

confidence: 99%

Characterization of β-Estradiol 3-Glucuronidation in Rat Brain

Asai

Biological & Pharmaceutical Bulletin

Onouchi

et al. 2017

Self Cite

β-Estradiol is conjugated by uridine 5′-diphosphate-glucuronosyltransferase (UGT) 1A to 3-glucuronide in the human liver. UGT1A has been found in the brain; therefore, UGT1A may be involved in β-estradiol 3-glucuronidation in the brain. In the present study, we aimed to characterize the β-estradiol 3-glucuronidation reaction in the rat brain. β-Estradiol 3-glucuronidation was detected in eight rat brain regions (cerebellum, frontal cortex, parietal cortex, piriform cortex, hippocampus, medulla oblongata, striatum, and thalamus). β-Estradiol 3-glucuronidation in the cerebellum was fitted to the Hill equation (S 50 8.0 µM, n 1.1). In inhibition experiments, β-estradiol 3-glucuronidation was inhibited to 73.6% in the cerebellum by 50 µM bilirubin, whereas it was reduced to 20.5% with 5 µM bilirubin in the liver. Unlike in the liver, Ugt1a1 may not be the main isoform catalyzing this glucuronidation in the brain. Serotonin and acetaminophen at 10 mM inhibited glucuronidation to 1.17 and 25.5%, respectively, in the cerebellum. In induction experiments, the administration of β-naphthoflavone, carbamazepine, and phenobarbital did not increase β-estradiol 3-glucuronidation in the brain except for phenobarbital in the striatum. In addition, β-estradiol 3-glucuronidation was not correlated with serotonin or acetaminophen glucuronidation in the brain, suggesting that Ugt1a6 and Ugt1a7 are not major isoforms of β-estradiol 3-glucuronidation in the rat brain. In the present study, although we were unable to identify the isoform responsible for β-estradiol 3-glucuronidation, we confirmed that β-estradiol could be metabolized to glucuronide in the brain under a different metabolic profile from that in the liver.

“…The liver, small intestine, and kidney were removed from 8-week-old male Sprague-Dawley rats or C57BL/6N mice (Japan SLC, Hamamatsu, Japan). Pooled rat and mouse (n=5 each) liver, small intestine, and kidney microsomes were prepared as described previously, 12) and were stored at −80°C until used. Protein concentration was measured using the Lowry method with a Bio-Rad protein assay kit (Bio-Rad, Hercules, CA, U.S.A.).…”

Section: Methodsmentioning

confidence: 99%

“…Numerous studies have evaluated the in vivo effects of E2 using experimental animal models such as rats and mice, and many researchers have attempted to extrapolate the animal data to humans. [9][10][11] Since species differences in the kinetics of serotonin 12) and propofol glucuronidation 13) have been reported between human and rodents, it would be expedient to clarify whether similar differences occur in E17G formation.…”

mentioning

confidence: 99%

Species and Tissue Differences in β-Estradiol 17-Glucuronidation

Asai

Biological & Pharmaceutical Bulletin

Kondo

et al. 2017

Self Cite

Uridine 5′-diphosphate-glucuronosyltransferase (UGT) is expressed in the liver and extrahepatic tissues. One of the major metabolic pathways of β-estradiol (E2) is glucuronidation at the 17-hydroxy position by UGTs. This study was performed to determine E2 17-glucuronidation kinetics in human and rodent liver, small intestine, and kidney microsomes and to clarify the species and tissue differences. In the human liver and small intestine, Eadie-Hofstee plots exhibited biphasic kinetics, suggesting that E2 17-glucuronide (E17G) formation was catalyzed by more than two UGT isoforms in both tissues. The K m values for E17G formation by the high-affinity enzymes in the human liver and small intestine were 1.79 and 1.12 µM, respectively, and corresponding values for the low-affinity enzymes were 3.72 and 11.36 µM, respectively. Meanwhile, E17G formation in the human kidney was fitted to the Hill equation (S 50 1.73 µM, n 1.63), implying that the UGT isoform catalyzing E17G formation in the kidney differed from that in the liver and small intestine. The maximum clearance for E17G formation in the human kidney was higher than the intrinsic clearance in the liver. E17G formation in the rat liver and kidney exhibited biphasic kinetics, whereas that in the small intestine was fitted to the Hill equation. In mice, all 3 tissues exhibited biphasic kinetics. In conclusion, we reported species and tissue differences in E2 17-glucuronidation, which occurred not only in the human liver but also in the extrahepatic tissues particularly the kidney.