Sex hormones differentially regulate isoforms of UDP-glucuronosyltransferase

Central metabolism as a potential origin of sex differences in morphine antinociception but not induction of antinociceptive tolerance in mice

BACKGROUND AND PURPOSE

In rodents, morphine antinociception is influenced by sex. However, conflicting results have been reported regarding the interaction between sex and morphine antinociceptive tolerance. Morphine is metabolised in the liver and brain into morphine-3-glucuronide (M3G). Sex differences in morphine metabolism and differential metabolic adaptations during tolerance development might contribute to behavioural discrepancies. This article investigates the differences in peripheral and central morphine metabolism after acute and chronic morphine treatment in male and female mice.

EXPERIMENTAL APPROACH

Sex differences in morphine antinociception and tolerance were assessed using the tail-immersion test. After acute and chronic morphine treatment, morphine and M3G metabolic kinetics in the blood were evaluated using LC-MS/MS. They were also quantified in several CNS regions. Finally, the blood-brain barrier (BBB) permeability of M3G was assessed in male and female mice.

KEY RESULTS

This study demonstrated that female mice showed weaker morphine antinociception and faster induction of tolerance than males. Additionally, female mice showed higher levels of M3G in the blood and in several pain-related CNS regions than male mice, whereas lower levels of morphine were observed in these regions. M3G brain/blood ratios after injection of M3G indicated no sex differences in M3G BBB permeability, and these ratios were lower than those obtained after injection of morphine.

CONCLUSION

These differences are attributable mainly to morphine central metabolism, which differed between males and females in pain-related CNS regions, consistent with weaker morphine antinociceptive effects in females. However, the role of morphine metabolism in antinociceptive tolerance seemed limited.

LINKED ARTICLES

This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Sex-dependent influences of morphine and its metabolites on pain sensitivity in the rat

Preclinical studies report that the effective dose for morphine is approximately 2-fold higher in females than males. Following systemic administration, morphine is metabolized via Phase II glucuronidation in the liver and brain into two active metabolites: morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G), each possessing distinct pharmacological profiles. M6G binds to μ opioid receptors and acts as a potent analgesic. In contrast, M3G binds to toll-like receptor 4 (TLR4), initiating a neuroinflammatory response that directly opposes the analgesic effects of morphine and M6G. M3G serum concentrations are 2-fold higher in females than males, however, sex-specific effects of morphine metabolites on analgesia and glial activation in vivo remain unknown. The present studies test the hypothesis that increased M3G, and subsequent TLR4-mediated activation of glia, is a primary mechanism driving the attenuated response to morphine in females. We demonstrate that intra-PAG M6G results in a greater analgesic response in females than morphine alone. M6G analgesia was reversed with co-administration of (-)-naloxone, but not (+)-naloxone, suggesting that this effect is μ opioid receptor mediated. In contrast, intra-PAG administration of M3G significantly attenuated the analgesic effects of systemic morphine in males only, increasing the 50% effective dose of morphine two-fold (5.0 vs 10.3mg/kg) and eliminating the previously observed sex difference. An increase in IL-1β, IL-6 and TNF was observed in females following intra-PAG morphine or M6G. In males, only IL-1β levels increased following morphine. Changes in cytokine levels following M3G were limited to TNF in females. Together, these data implicate sex differences in morphine metabolism, specifically M3G, as a contributing factor in the attenuated response to morphine observed in females.

Hormonal regulation of hepatic drug biotransformation and transport systems

The human body is constantly exposed to many xenobiotics including environmental pollutants, food additives, therapeutic drugs, etc. The liver is considered the primary site for drug metabolism and elimination pathways, consisting in uptake, phase I and II reactions, and efflux processes, usually acting in this same order. Modulation of biotransformation and disposition of drugs of clinical application has important therapeutic and toxicological implications. We here provide a compilation and analysis of relevant, more recent literature reporting hormonal regulation of hepatic drug biotransformation and transport systems. We provide additional information on the effect of hormones that tentatively explain differences between sexes. A brief discussion on discrepancies between experimental models and species, as well as a link between gender-related differences and the hormonal mechanism explaining such differences, is also presented. Finally, we include a comment on the pathophysiological, toxicological, and pharmacological relevance of these regulations.

UGT1A and UGT2B genetic variation alters nicotine and nitrosamine glucuronidation in european and african american smokers

BACKGROUND

Identifying sources of variation in the nicotine and nitrosamine metabolic inactivation pathways is important to understanding the relationship between smoking and cancer risk. Numerous UGT1A and UGT2B enzymes are implicated in nicotine and nitrosamine metabolism in vitro; however, little is known about their roles in vivo.

METHODS

Within UGT1A1, UGT1A4, UGT1A9, UGT2B7, UGT2B10, and UGT2B17, 47 variants were genotyped, including UGT2B10*2 and UGT2B17*2. The association between variation in these UGTs and glucuronidation activity within European and African American current smokers (n = 128), quantified as urinary ratios of the glucuronide over unconjugated compound for nicotine, cotinine, trans-3'-hydroxycotinine, and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), was investigated in regression models assuming a dominant effect of variant alleles.

RESULTS

Correcting for multiple testing, three UGT2B10 variants were associated with cotinine glucuronidation, rs2331559 and rs11726322 in European Americans and rs835309 in African Americans (P ≤ 0.0002). Additional variants predominantly in UGT2B10 were nominally associated with nicotine (P = 0.008-0.04) and cotinine (P = <0.001-0.02) glucuronidation in both ethnicities in addition to UGT2B10*2 in European Americans (P = 0.01, P < 0.001). UGT2B17*2 (P = 0.03) in European Americans and UGT2B7 variants (P = 0.02-0.04) in African Americans were nominally associated with 3HC glucuronidation. UGT1A (P = 0.007-0.01), UGT2B10 (P = 0.02), and UGT2B7 (P = 0.02-0.03) variants in African Americans were nominally associated with NNAL glucuronidation.

CONCLUSIONS

Findings from this initial in vivo study support a role for multiple UGTs in the glucuronidation of tobacco-related compounds in vivo, in particular UGT2B10 and cotinine glucuronidation.

IMPACT

Findings also provide insight into ethnic differences in glucuronidation activity, which could be contributing to ethnic disparities in the risk for smoking-related cancers. Cancer Epidemiol Biomarkers Prev; 24(1); 94-104. ©2014 AACR.

Ovariectomy lowers urine levels of unconjugated (+)-catechin, (–)-epicatechin, and their methylated metabolites in rats fed grape seed extract

Steroid hormones modulate expression of enzymes that metabolize xenobiotics, including dietary supplements. Half of the human population undergoes menopause, yet the effect of this age-related loss of ovarian steroid hormones on the metabolism of dietary supplements has yet to be determined. Grape seed extract (GSE) is a dietary supplement comprised of monomeric and oligomeric catechins and has health benefits in models of age-related diseases. We hypothesized that surgically-induced loss of ovarian hormones would increase methylation, glucuronidation, and/or sulfation of the grape seed polyphenols (+)-catechin and (–)-epicatechin. Fourteen-week-old spontaneously hypertensive rats (SHRs) were ovariectomized (OVX) or sham-OVX. At 17 weeks of age, SHRs were gavaged with vehicle (water) or GSE (300 mg/kg body weight) once daily for 6 days. Urinary excretion of (+)-catechin, (–)-epicatechin, and their metabolites was analyzed by liquid chromatography-mass spectrometry. Although total urinary output of (+)-catechin, (–)-epicatechin, and their methylated metabolites was unaffected by OVX, the amounts of (+)-catechin, (–)-epicatechin and their methylated metabolites that were not conjugated with glucuronic acid or sulfate were lowered by OVX. Specifically, urine from OVX SHRs administered GSE contained 30% higher proportions (91.8% vs. 62.3%) of glucuronidated (+)-catechin and (–)-epicatechin and glucuronidated methyl (+)-catechin and methyl (–)-epicatechin than urine from sham-OVX SHRs. However, there were no differences in urinary levels of total methylated or sulfated catechins in OVX SHRs. This is the first quantitative characterization of metabolites of grape seed polyphenols in a model of menopause; it indicates that ovariectomy causes either an increase in expression and/or activity of select uridine 5′-diphospho-glucuronosyltransferase(s).

Regulation of uterine AHR battery gene expression by 17β-Estradiol is predominantly mediated by estrogen receptor α

The aryl hydrocarbon receptor (AHR) is known to mediate the cellular response to numerous xenobiotics including dioxin. Surprisingly AHR knockout mice provide evidence for the involvement of the AHR signalling cascade in estrogen regulated physiological functions of the female reproductive system. Several studies already aimed to investigate the impact of the AHR mediated xenobiotic response pathway on estrogen receptor (ER) signalling, whereas on contrary availability of data describing the effect of 17β-Estradiol (E2) on the AHR signalling cascade is rather limited. In this study we observed an inhibitory effect of E2 treatment on uterine Ahr, Arnt, Arnt2, Ahrr, Cyp1a1, Ugt1 and Nfe2l2 gene expression in ovariectomized Wistar rats, whereas Cyp1b1, Nqo1 and Gsta2 displayed an increased transcription. The usage of the ER selective agonists, 16α-LE(2) (ERα selective) and 8β-VE(2) (ERβ selective), enabled us to distinguish between ER subtype specific responses. On mRNA level the observed changes in gene expression were mainly mediated by ERα except for the expression of Nqo1. In most cases the activation of ERβ caused effects opposite to the ones observed following activation of ERα. Despite the significant changes in AHR mRNA levels immunohistochemical staining uterine tissue section did not reveal changes of the AHR protein level. Taken together our results validate, support and extend the hypothesis of uterine crosstalk between AHR and ER signalling pathways. Furthermore they give an insight into how the AHR and its related genes may participate in E2 dependent uterine physiological processes and provide another potential mechanism of action for xenoestrogens.

Constraints-based stoichiometric analysis of hypoxic stress on steroidogenesis in fathead minnows, Pimephales promelas

In this study, an in silico genome-scale metabolic model of steroidogenesis was used to investigate the effects of hypoxic stress on steroid hormone productions in fish. Adult female fathead minnows (Pimephales promelas) were exposed to hypoxia for 7 days with fish sub-sampled on days 1, 3 and 7 of exposure. At each time point, selected steroid enzyme gene expressions and steroid hormone productions were quantified in ovaries. Fold changes in steroid enzyme gene expressions were used to qualitatively scale transcript enzyme reaction constraints (akin to the range of an enzyme’s catalytic activity) in the in silico model. Subsequently, in silico predicted steroid hormone productions were qualitatively compared with experimental results. Key findings were as follows. (1) In silico gene deletion analysis identified highly conserved ‘essential’ genes required for steroid hormone productions. These agreed well (75%) with literature-published genes downregulated in vertebrates (fish and mammal) exposed to hypoxia. (2) Quantification of steroid hormones produced ex vivo from ovaries showed a significant reduction for 17β-estradiol and 17α,20β-dihydroxypregnenone production after 24 h (day 1) of exposure. This lowered 17β-estradiol production was concomitant with downregulation of cyp19a1a gene expression in ovaries. In silico predictions showed agreement with experimentation by predicting effects on estrogen (17β-estradiol and estrone) production. (3) Stochastic sampling of in silico reactions indicated that cholesterol uptake and catalysis to pregnenolone along with estrogen methyltransferase and glucuronidation reactions were also impacted by hypoxia. Taken together, this in silico analysis introduces a powerful model for pathway analysis that can lend insights on the effects of various stressor scenarios on metabolic functions.

Sex differences in UDP-glucuronosyltransferase 2B17 expression and activity

UDP-glucuronosyltransferases (UGTs) are enzymes involved in the metabolism of steroid hormones, carcinogens, cancer chemotherapy agents, and addictive agents from cigarettes. Because the UGT2B family of genes has been linked to hormonal regulation in human cell lines in vitro, we hypothesized that there may be sex-related differences in the expression and activity of these genes in human tissues. To evaluate whether there are sex differences in UGT2B expression and activity, we examined 103 normal human liver specimens for UGT2B expression by real-time polymerase chain reaction and in vitro glucuronidation activities in human liver microsomes (HLM). Men exhibited an approximately 4-fold higher level of expression of UGT2B17 than women (p = 0.007). Consistent with the increased expression of UGT2B17 in men, HLM from men also had a higher level of glucuronidation activity than HLM from women against three UGT2B17 substrates: 3-fold higher for 17-dihydroexemestane (p = 0.002); 3-fold higher for 3-hydroxycotinine (p < 0.001); and 1.5-fold higher for suberoylanilide hydroxamic acid (p = 0.014). When we stratified by UGT2B17 gene deletion genotype, similar patterns were observed for all three substrates, with HLM from men with the UGT2B17 (+/+) or (+/0) genotypes exhibiting significantly higher levels of glucuronidation activity against all three substrates compared with HLM from women. These data suggest that men have a higher amount of UGT2B17 glucuronidation activity then women. This sex difference in UGT2B17 gene expression and corresponding protein activity could potentially result in different levels of carcinogen detoxification or drug elimination in men versus women.

Central insulin sensitivity in male and female juvenile rats

The incidence of juvenile obesity is increasing at an alarming rate. In adults, central insulin administration decreases hypothalamic orexigenic neuropeptides, food intake and body weight more effectively in males than females. Mechanisms regulating energy balance in juvenile animals are inherently different from those in adults due to differences in growth rates and hormonal milieu. Therefore, we sought to determine if central insulin treatment in juvenile rats (4 wk) would have similar sex-dependent effects on food intake as those reported in adult rats. Twenty-four hour food intake was measured following icv saline or insulin (0.01 or 0.1 U) prior to the onset of dark phase of the light cycle. An additional set of animals was used to assess the effects of central insulin on hypothalamic orexigenic (NPY, AgRP) and anorexigenic (POMC) neuropeptide mRNA expression. In both males and females, insulin reduced meal size initially (first 4 h) and later decreased meal frequency (4-24 h) to reduce cumulative food intake. Consistent with this, central insulin decreased hypothalamic NPY and AgRP and increased POMC mRNA expression. In contrast to adult studies, there were no demonstrated sex differences. These studies indicate that juvenile females and males are equally sensitive to central insulin anorexigenic effects, perhaps due to a lack of circulating gonadal hormones. The anorexigenic responsiveness of both genders suggests a potential pharmacologic approach to childhood obesity.

Mechanism of gender-divergent UDP-glucuronosyltransferase mRNA expression in mouse liver and kidney

UDP-glucuronosyltransferases (UGTs) catalyze the addition of glucuronic acid to endo- and xenobiotics, increasing hydrophilicity and enhancing elimination. Gender-divergent glucuronidation rates are observed in humans and rats, and gender differences in UGT mRNA levels have been observed in rodents. The purpose of this study was to establish the hormonal regulation of gender-dependent Ugt mRNA expression in mouse liver and kidney. Therefore, three mouse models were used to characterize the involvement of sex hormones and gender-specific growth hormone (GH) secretion patterns, including 1) hypophysectomized mice treated with male- or female-pattern GH, testosterone, or 17beta-estradiol; 2) GH releasing hormone receptor-deficient little (lit/lit) mice treated with male- or female-pattern GH; and 3) gonadectomized mice treated with testosterone or 17beta-estradiol. Messenger RNA expression of mouse Ugt isozymes was determined by the branched DNA assay. In C57BL/6 mice, male-predominant expression of Ugt2b1 and Ugt2b38 was observed in liver and kidney, respectively. Female-predominant expression was observed for Ugt1a1 and Ugt1a5 in liver and Ugt1a2 in kidney. In liver, regulation of Ugt1a1 and Ugt1a5 expression was attributed to repression of Ugt mRNA by male-pattern GH secretion. Conversely, regulation of Ugt2b1 expression in liver was attributed to male-pattern GH secretion. In kidney, regulation of Ugt2b38 expression was attributed to inductive effects by testosterone. Conversely, Ugt1a2 expression in kidney was negatively regulated by testosterone. In conclusion, gender differences in mouse Ugt mRNA expression were influenced by male-pattern GH secretion in liver, whereas gender differences were regulated by the effects of androgens in kidney.

Tissue- and gender-specific mRNA expression of UDP-glucuronosyltransferases (UGTs) in mice

UDP-glucuronosyltransferases (UGTs) catalyze phase II biotransformation reactions in which lipophilic substrates are conjugated with glucuronic acid to increase water solubility and enhance excretion. Currently, little information regarding tissue- or gender-specific expression of mouse UGTs is available. Mice are increasingly popular models in biomedical research, and therefore, thorough characterization of murine drug metabolism is desired. The purpose of the present study was to determine both tissue- and gender-specific UGT gene expression profiles in mice. RNA from 14 tissues was isolated from male and female C57BL/6 mice and UGT expression was determined by the branched DNA signal amplification assay. UGTs highly expressed in mouse liver include Ugt1a1, Ugt1a5, Ugt1a6, Ugt1a9, Ugt2a3, Ugt2b1, Ugt2b5/37/38, Ugt2b34, Ugt2b35, and Ugt2b36. Several isoforms were expressed in the gastrointestinal (GI) tract, including Ugt1a6, Ugt1a7c, Ugt2a3, Ugt2b34, and Ugt2b35. In kidney, Ugt1a2, Ugt1a7c, Ugt2b5/37/38, Ugt2b35, and Ugt3a1/2 were expressed. UGT expression was also observed in other tissues: lung (Ugt1a6), brain (Ugt2b35), testis and ovary (Ugt1a6 and Ugt2b35), and nasal epithelia (Ugt2a1/2). Male-predominant expression was observed for Ugt2b1 in liver, Ugt2b5/37/38 in kidney, and Ugt1a6 in lung. Female-predominant expression was observed for Ugt1a1 and Ugt1a5 in liver, Ugt1a2 in kidney, Ugt2b35 in brain, and Ugt2a1/2 in nasal epithelia. UDP-glucose pyrophosphorylase was highly expressed in liver, kidney, and GI tract, whereas UDP-glucose dehydrogenase was highly expressed in the GI tract. In conclusion, marked differences in tissue- and gender-specific expression patterns of UGTs exist in mice, potentially influencing drug metabolism and pharmacokinetics.

Follicle-stimulating hormone, testosterone, and hypoxia differentially regulate UDP-glucuronosyltransferase 1 isoforms expression in rat sertoli and peritubular myoid cells

Uridine diphosphoglucuronosyltransferases (UGTs) are detoxifying enzymes responsible for the metabolism of endogenous and xenobiotics compounds. UGT isoforms are widely distributed in rat tissues showing a constitutive and inducible gene expression. However, little information is available concerning UGTs expression in testis. The UGT1A1, UGT1A2, and UGT1B1 mRNAs expression in whole rat testis, in Sertoli and peritubular myoid cells in basal conditions, and after hormonal and hypoxic stimulation were investigated by reverse transcriptase-polymerase chain reaction (RT-PCR). Constitutive expression of each UGT1 isoform was present in rat testis with higher levels of UGT1A2. UGT transcripts were also detected in Sertoli and peritubular myoid cells. After FSH stimulation, Sertoli cells showed an increase in UGT1B1 mRNA expression, whereas the levels of UGT1A1 and UGT1A2 resulted unmodified. The main effect induced by testosterone was a decrease of UGT1B1 mRNA expression in peritubular myoid cells, whereas in Sertoli cells an increase in UGT1A1 and UGT1B1 was observed. In hypoxic conditions, a reduction in UGTs mRNA levels was detected in both cell types. These findings suggest that rat UGT1 isoforms are regulated in testis by hormonal and environmental factors. Thus, it was speculated that alterations in UGTs expression and/or activity may be involved in the pathogenesis of testis injury.

Dependency of cyclosporine tissue distribution and metabolism on the age and gender of rats after a single intravenous dose

In a previous study we demonstrated the dependency of cyclosporine (CyA) pharmacokinetics on the age and gender of Wistar rats given 10 mg/kg intravenously. The present study has been conducted under the same experimental conditions (10 mg/kg as a single intravenous dose) to identify the mechanisms behind such differences. On the one hand, drug distribution was studied by measuring the CyA levels in blood, liver, kidney, spleen, adipose tissue, skin and muscle at 48 h post-treatment by using a specific fluorescence polarization immunoassay (m-FPIA, Abbott Laboratories). Drug blood and tissue levels in male rats were significantly higher than the female counterparts except for adipose tissue where the concentrations were 2-fold higher in females. In males, the highest CyA concentrations were observed in the liver, followed in rank order by kidney and spleen, fat, skin, muscle, then blood. On the contrary, females showed the highest drug levels in fat, followed by liver, kidney, spleen, skin, muscle and blood. Age exerted a significant influence on CyA tissue levels in males but no effect was observed in females. The potential differences in drug metabolism were established by measuring (HPLC) the amounts of CyA and its metabolites accumulated in faeces after hepatic biotransformation and biliary excretion. The amounts of circulating metabolites in blood as well as those accumulated and excreted in the liver and urine were also estimated by using specific (m-FPIA) and non-specific fluorescence polarization immunoassay (p-FPIA, Abbott Laboratories), respectively. The analysis of faeces revealed that AM9 was the major identified metabolite with females excreting lower amounts of unchanged CyA than males. In addition, the comparison of the AUC values corresponding to parent CyA and total CyA derivatives suggested that blood concentrations of CyA metabolites were higher in females indicating higher biotransformation rates. Therefore, both CyA distribution and metabolism are responsible for the sex-associated differences in drug pharmacokinetics previously found in rats.

Conjugation of 1-naphthol in primary cell cultures of rat ovarian cells

The present study concerns conjugation of 1-naphthol in primary cultures of rat ovarian cells. Two phase II enzymes catalyzing conjugation, i.e. phenol sulfotransferase (P-SULT) and phenol UDP-glucuronosyltransferase (P-UGT), were measured using 1-naphthol as substrate. The rates of conjugation by the different cell types of the rat ovary were the same at low concentrations and short incubation times. However, after 20 h of incubation the rate of conjugation in cells isolated from ovaries enriched in corpora lutea (CL) exceeded the rate in cells isolated from ovaries enriched in preovulatory follicles. In addition, when the granulosa cells were removed from the preovulatory follicles, the rate of conjugation was 1.7-fold higher, i.e. in the theca/stroma cells. When the cells were incubated with 1-[14C]naphthol and conjugates were subsequently separated by thin-layer chromatography, naphthyl glucuronide was the only conjugate observed. Pentachlorophenol (PCP), a commonly used inhibitor of P-SULT, inhibited 1-naphthol conjugation 50% in cell cultures, as well as in microsomal preparations. alpha-Naphthoflavone (ANF) and ellipticine (ELP), both cytochrome P450 (CYP) inhibitors, affected the conjugation of 1-naphthol in different ways; ANF did not affect P-UGT activity in microsomal preparations, but inhibited 1-naphthol conjugation in cell cultures by as much as 90%. On the other hand, ELP inhibited the conjugation of 1-naphthol up to 99% in the cell cultures, but only 75% in microsomal fractions. Testosterone (TST) and estradiol inhibited this activity approximately equal 50% in both of these experimental systems. Clomiphene citrate (CLF), a drug used to induce ovulation and demonstrating both estrogenic and antiestrogenic effects, did not influence the conjugation of 1-naphthol significantly in the cell cultures. The present findings demonstrate that P-UGT is by far the major enzyme conjugating 1-naphthol in the rat ovary and that commonly used inhibitors of P-SULT and CYPs also inhibit P-UGT activity, either directly or via other mechanisms.

Morphine regulation of a novel uridine diphosphate glucuronosyl-transferase in guinea pig pups following in utero exposure

The uridine diphosphate glucuronosyltransferases (UGTs) catalyze conjugation reactions between various substrates and glucuronic acid, UDPGA (uridine diphosphate glucuronic acid), within the endoplasmic reticulum. Conjugation with UDPGA (glucuronidation) is an important pathway in the elimination, detoxification, and activation of compounds including steroid hormones, xenobiotics, and quaternary ammonium substrates. The guinea pig, which has a placental structure and a glucuronidation profile for morphine that are similar to the human, serves as a good small animal model to study the ontogeny of UGTs and the effect of in utero exposure to morphine on UGTs. We examined type 2 UGTs expressed in the guinea pig using amplification and cloning of partial cDNAs from liver RNA. Sequence analysis revealed a novel UGT2 (subsequently named UGT2A3),(2) that has a 64% amino acid sequence similarity to a known UGT2.(3) Full-length cDNAs were isolated from a guinea pig liver cDNA library. Tissue distribution of UGT2A3 using Northern blot analysis showed expression of three distinct size UGT2A3 mRNAs with unique expression in liver and small intestine. UGT2A3 mRNA is expressed at high levels in liver and lower levels in kidney and small intestine. In utero exposure to chronic intermittent morphine resulted in the up regulation of mRNA in 7-day-old female pups' liver and kidney as determined by quantitative RT-PCR analysis. The conjugation profile for UGT2A3 using stable expression in CHO cells and thin-layer chromatography demonstrated active conjugation of phenolic substrates. Regulation of UGTs by in utero morphine exposure may play an important role in fetal development.

The effect of hormones on the expression of five isoforms of UDP-glucuronosyltransferase in primary cultures of rat hepatocytes

PURPOSE

To investigate the direct effects of sex hormones, growth hormone, thyroid hormones and dexamethasone on the regulation of UDP-glucuronosyltransferase (UGT).

METHODS

Rat hepatocytes were cultured on matrigel and treated with various hormones. Northern blot analysis was carried out using cDNA probes to family 1 and family 2 isoforms.

RESULTS

Treatment with 10(-5) M testosterone increased the mRNA levels of UGT 2B1 by 29% and UGT2B3 by 32%. Incubation of growth hormone (10 mU) with hepatocytes suppressed the expression of UGT2B1 and UGT2B3 by 17% and 38%, respectively. T3 administration resulted in a time and dose-dependent effect on the expression of UGT 1 isoforms, with increased UGT1A6 by 70%, and decreased UGT1A1 by 38% and UGT1A5 by 35%. All UGT isoforms except UGT 1A6 studied in this assay were up-regulated by dexamethasone, but to different degrees. The regulation of UGT1A1 and UGT2B1 by dexamethasone was dose and time dependent, and the induction of dexamethasone in the expression of UGT1A1 and UGT2B1 was blocked by cycloheximide but not dichloro-1-D-ribofuranosylbenzimidazole.

CONCLUSIONS

This study demonstrates that multiple hormones take part in the regulation of UGT mRNA expression in the rat and individual genes can be differentially modulated.