Dietary green and white teas suppress UDP-glucuronosyltransferase UGT2B17 mediated testosterone glucuronidation

The anabolic steroid testosterone can be used by athletes to enhance athletic performance and muscle growth. UDP-glucuronosyltransferase (UGT2B17) is the key enzyme involved in the glucuronidation of testosterone to testosterone glucuronide, which also serves as a marker for the testosterone/epitestosterone (T/E) ratio used to detect testosterone abuse in sport. Inhibitors of testosterone glucuronidation could have an impact on circulating testosterone levels, thus aiding performance, as well as potentially affecting the urinary T/E ratio and therefore masking testosterone abuse. Previous reports have revealed that non-steroidal, anti-inflammatory drugs, diclofenac and ibuprofen, inhibit the UGT2B17 enzyme. The aim of this study is to analyse dietary tea samples for inhibition of testosterone glucuronidation and, where inhibition is present, to identify the active compounds. Analysis of testosterone glucuronidation was conducted by performing UGT2B17 assays with detection of un-glucuronidated testosterone using high performance liquid chromatography. The results from this study showed that testosterone glucuronidation was inhibited by the green and white tea extracts, along with specific catechin compounds, notably: epicatechin, epigallocatechin gallate (EGCG) and catechin gallate. The IC50 inhibition value for EGCG was determined, using a Dixon plot, to be 64 μM, equalling the most active NSAID inhibitor diclofenac. Thus, common foodstuffs and their constituents, for the first time, have been identified as inhibitors of a key enzyme involved in testosterone glucuronidation. Whilst these common compounds are not substrates of the UGT2B17 enzyme, we showed that they inhibit testosterone glucuronidation which may have implications on current doping control in sport.     

Identification of UGT2B9*2 and UGT2B33 isolated from female rhesus monkey liver

Two UDP-glucuronosyltransferases (UGT2B9(*)2 and UGT2B33) have been isolated from female rhesus monkey liver. Microsomal preparations of the cell lines expressing the UGTs catalyzed the glucuronidation of the general substrate 7-hydroxy-4-(trifluoromethyl)coumarin in addition to selected estrogens (beta-estradiol and estriol) and opioids (morphine, naloxone, and naltrexone). UGT2B9(*)2 displayed highest efficiency for beta-estradiol-17-glucuronide production and did not catalyze the glucuronidation of naltrexone. UGT2B33 displayed highest efficiency for estriol and did not catalyze the glucuronidation of beta-estradiol. UGT2B9(*)2 was found also to catalyze the glucuronidation of 4-hydroxyestrone, 16-epiestriol, and hyodeoxycholic acid, while UGT2B33 was capable of conjugating 4-hydroxyestrone, androsterone, diclofenac, and hyodeoxycholic acid. Three glucocorticoids (cortisone, cortisol, and corticosterone) were not substrates for glucuronidation by liver or kidney microsomes or any expressed UGTs. Our current data suggest the use of beta-estradiol-3-glucuronidation, beta-estradiol-17-glucuronidation, and estriol-17-glucuronidation to assay UGT1A01, UGT2B9(*)2, and UGT2B33 activity in rhesus liver microsomes, respectively.     

Carboxyl nonsteroidal anti-inflammatory drugs are efficiently glucuronidated by microsomes of the human gastrointestinal tract

Limited studies have been carried out on the biotransformation of carboxyl nonsteroidal anti-inflammatory drugs (NSAIDs) in the liver. However, the role of the intestine in NSAID metabolism has not been investigated. In this report, the contribution of UDP-glucuronosyltransferases (UGTs) in the human gastrointestinal (GI) tract from five donors to the glucuronidation of the NSAIDs, RS-ketoprofen, S-naproxen, RS- and S-etodolac, was investigated. UGT activity and, for some donors, mRNA levels were evaluated. All NSAIDs were glucuronidated throughout the GI tract; however, glucuronidation was low in stomach and duodenum as compared to the remainder of the intestine. RT-PCR analysis demonstrated that the UGT1A isoforms, UGT1A3, 1A8, and 1A10, and UGT2B7 were expressed in the GI tract. Human recombinant UGT1A3, 1A9, 1A10 and 2B7 were actively involved in the glucuronidation of all NSAIDs while UGT1A7 and the intestine-specific UGT1A8 had no glucuronidating activity towards those compounds. Despite interindividual variations in both the levels of mRNA and the distribution of activity through the intestine, UGTs in the GI tract may contribute significantly to the first pass metabolism of orally administered NSAIDs.     

Biotransformation of Bisphenol AF to Its Major Glucuronide Metabolite Reduces Estrogenic Activity

Bisphenol AF (BPAF), an endocrine disrupting chemical, can induce estrogenic activity through binding to estrogen receptor (ER). However, the metabolism of BPAF in vivo and the estrogenic activity of its metabolites remain unknown. In the present study, we identified four metabolites including BPAF diglucuronide, BPAF glucuronide (BPAF-G), BPAF glucuronide dehydrated and BPAF sulfate in the urine of Sprague-Dawley (SD) rats. BPAF-G was further characterized by nuclear magnetic resonance (NMR). After treatment with a single dose of BPAF, BPAF was metabolized rapidly to BPAF-G, as detected in the plasma of SD rats. Biotransformation of BPAF to BPAF-G was confirmed with human liver microsomes (HLM), and V_max of glucuronidation for HLM was 11.6 nmol/min/mg. We also found that BPAF glucuronidation could be mediated through several human recombinant UDP-glucuronosyltransferases (UGTs) including UGT1A1, UGT1A3, UGT1A8, UGT1A9, UGT2B4, UGT2B7, UGT2B15 and UGT2B17, among which UGT2B7 showed the highest efficiency of glucuronidation. To explain the biological function of BPAF biotransformation, the estrogenic activities of BPAF and BPAF-G were evaluated in ER-positive breast cancer T47D and MCF7 cells. BPAF significantly stimulates ER-regulated gene expression and cell proliferation at the dose of 100 nM and 1 μM in breast cancer cells. However, BPAF-G did not show any induction of estrogenic activity at the same dosages, implying that formation of BPAF-G is a potential host defense mechanism against BPAF. Based on our study, biotransformation of BPAF to BPAF-G can eliminate BPAF-induced estrogenic activity, which is therefore considered as reducing the potential threat to human beings.     

Expression of UDP-glucuronosyltransferases (UGTs) 2B7 and 1A6 in the human brain and identification of 5-hydroxytryptamine as a substrate

The extrahepatic expression of UDP-glucuronosyltransferases (UGTs) is important in the detoxification of a number of endogenous and exogenous compounds, including 5-hydroxytryptamine and morphine. Studies were designed to investigate the extrahepatic expression of human UGTs using RT-PCR techniques and to determine the UGTs involved in the glucuronidation of 5-hydroxytryptamine. Human UGT2B7 expression was found in the human liver, kidney, pancreas, and brain, while UGT1A6 expression is found in the liver, kidney, and brain. This is the first observation of UGTs present in the human central nervous system. Using glucuronidation assays, a significant amount of 5-hydroxytryptamine glucuronide was found to be catalyzed by UGT1A6. These studies suggest that UGT2B7 may play an important role in the overall contribution of morphine analgesia by serving to generate the potent morphine-6-O-glucuronide in situ. UGT1A6 could play an important role in the glucuronidation of 5-hydroxytryptamine in vivo, therefore terminating the actions of the neurotransmitter.     

Glucuronidation of linoleic acid diols by human microsomal and recombinant UDP-glucuronosyltransferases: identification of UGT2B7 as the major isoform involved

Recent reports suggest that linoleic acid (LA) epoxides and diols are associated with important physiological, pharmacological, and pathological events in vivo. We have shown recently that LA-diols are excellent substrates for human liver microsomal UDP-glucuronosyltransferases (UGTs); however, it is not known if other human tissues glucuronidate LA-diols or which UGT isozyme(s) is involved. The present studies with human intestinal microsomes indicate that glucuronidation of LA-diols occurs throughout the gastrointestinal tract, with the highest activity in the small intestine. LA-diols yielded exclusively hydroxyl-linked glucuronides, whereas LA yielded the carboxyl-linked glucuronide. Studies with human recombinant UGTs demonstrated that only UGT2B7 glucuronidated LA and LA-diols. Kinetic analysis with UGT2B7 yielded apparent K(m) values in the range of 40-70 microM and V(max) values from 4.5 to 5.4 nmol/mg x min. These studies indicate that LA and LA-diols are excellent substrates for intestinal UGTs and provide the first evidence for UGT2B7 being the major isoform involved.     

Glucuronidation of the steroid enantiomers ent-17β-estradiol, ent-androsterone and ent-etiocholanolone by the human UDP-glucuronosyltransferases

Steroids enantiomers are interesting compounds for detailed exploration of drug metabolizing enzymes, such as the UDP-glucuronosyltransferases (UGTs). We have now studied the glucuronidation of the enantiomers of estradiol, androsterone and etiocholanolone by the 19 human UGTs of subfamilies 1A, 2A and 2B. The results reveal that the pattern of human UGTs of subfamily 2B that glucuronidate ent-17β-estradiol, particularly 2B15 and 2B17, resembles the glucuronidation of epiestradiol (17α-estradiol) rather than 17β-estradiol, the main physiological estrogen. The UGTs of subfamilies 1A and 2A exhibit higher degree of regioselectivity than enantioselectivity in the conjugation of these estradiols, regardless of whether the activity is primarily toward the non-chiral site, 3-OH (UGT1A1, UGT1A3, UGT1A7, UGT1A8 and, above all, UGT1A10), or the 17-OH (UGT1A4). In the cases of etiocholanolone and androsterone, glucuronidation of the ent-androgens, like the conjugation of the natural androgens, is mainly catalyzed by UGTs of subfamilies 2A and 2B. Nevertheless, the glucuronidation of ent-etiocholanolone and ent-androsterone by both UGT2B7 and UGT2B17 differs considerably from their respective activity toward the corresponding endogenous androgens, whereas UGT2A1-catalyzed conjugation is much less affected by the stereochemistry differences. Kinetic analyses reveal that the K(m) value of UGT2A1 for ent-estradiol is much higher than the corresponding value in the other two high activity enzymes, UGT1A10 and UGT2B7. Taken together, the results highlight large enantioselectivity differences between individual UGTs, particularly those of subfamily 2B.     

Glucuronidation of the soyabean isoflavones genistein and daidzein by human liver is related to levels of UGT1A1 and UGT1A9 activity and alters isoflavone response in the MCF-7 human breast cancer cell line

The soyabean isoflavones genistein and daidzein, which may protect against some cancers, cardiovascular disease and bone mineral loss, undergo substantial Phase 2 metabolism, predominantly glucuronidation. We observed a correlation between rates of metabolism of marker substrates of specific UGTs and rates of glucuronidation of genistein and daidzein in vitro by a panel of human liver microsomes, demonstrating that UGT1A1 and UGT1A9, but not UGT1A4, make a major contribution to the metabolism of these isoflavones by human liver. These findings were substantiated by observations that recombinant human UGT1A1 and UGT1A9, but not UGT1A4, catalysed the production of the major glucuronides of both genistein and daidzein in vitro. Recombinant human UGT1A8 also metabolised both genistein and daidzein, whereas UGT1A6 was specific to genistein and UGTs 2B7 and 2B15 were inactive, or only marginally active, with either isoflavone as substrate. The intestinal isoform UGT1A10 metabolised either both isoflavones or genistein only, depending on the commercial supplier of the recombinant enzyme, possibly as a result of a difference in amino acid sequence, which we were unable to confirm. Daidzein (16 microM) increased cell death in the MCF-7 human breast cancer cell line and this effect was reversed by glucuronidation. In view of a well-characterised functional polymorphism in UGT1A1, these observations may have implications for inter-individual variability in the potential health-beneficial effects of isoflavone consumption.     

Glucuronidation of haloperidol by rat liver microsomes: involvement of family 2 UDP-glucuronosyltransferases

The purposes of this study were to develop a HPLC method to assay for haloperidol glucuronide (HALG); to apply this assay method to the in vitro determination of haloperidol (HAL) UDP-glucuronosyltransferase (UGT) enzyme kinetics in rat liver microsomes (RLM); and to identify the UGT isoforms catalyzing glucuronidation of HAL in rats. Incubation of Brij-activated RLM with HAL and UDP-glucuronic acid (UDPGA) in TRIS pH 7.4 buffer resulted in the formation of a single peak in the HPLC chromatogram at 270 nm. The identity of this peak was confirmed to be that of HALG by 1) β-glucuronidase hydrolysis; 2) incubation without UDPGA; 3) UV spectral analysis; and 4) LC/MS/MS to yield the expected mass of 552.1. Enzyme kinetic studies using single enzyme Michaelis-Menton model showed an apparent V_max = 271.9 ± 10.1 pmoles min⁻¹ mg protein⁻¹ and K_m = 61 ± 7.2 μM. Glucuronidation activity in homozygous Gunn (j/j) rats was approximately 80% as compared to Sprague-Dawley RLM. HALG formation was approximately doubled in PB-induced RLM. There was no increase in glucuronidation activities in 3MC-induced RLM. The Gunn rat and the PB-induced RLM data suggest predominant but not exclusive involvement of the UGT2B family in the formation of HALG. Because the UGTs exhibit overlapping substrate specificities and most substrates are glucuronidated by more than one isoform, inhibition studies with UGT2B1 substrate probe testosterone and the UGT2B12 substrate probe borneol were conducted. UGT2B1 and UGT2B12 exhibited 40% and 90% inhibition of HAL glucuronidation, respectively. Thus, UGT2B12 and UGT 2B1 isoforms are responsible for catalyzing HAL glucuronidation in rats. Our HPLC assay provides a specific and sensitive technique for the measurement of in vitro HAL-UGT activity.     

4-hydroxyretinoic acid, a novel substrate for human liver microsomal UDP-glucuronosyltransferase(s) and recombinant UGT2B7

It is suggested that formation of more polar metabolites of all-trans-retinoic acid (atRA) via oxidative pathways limits its biological activity. In this report, we investigated the biotransformation of oxidized products of atRA via glucuronidation. For this purpose, we synthesized 4-hydroxy-RA (4-OH-RA) in radioactive and nonradioactive form, 4-hydroxy-retinyl acetate (4-OH-RAc), and 5,6-epoxy-RA, all of which are major products of atRA oxidation. Glucuronidation of these retinoids by human liver microsomes and human recombinant UDP-glucuronosyltransferases (UGTs) was characterized and compared with the glucuronidation of atRA. The human liver microsomes glucuronidated 4-OH-RA and 4-OH-RAc with 6- and 3-fold higher activity than atRA, respectively. Analysis of the glucuronidation products showed that the hydroxyl-linked glucuronides of 4-OH-RA and 4-OH-RAc were the major products, as opposed to the formation of the carboxyl-linked glucuronide with atRA, 4-oxo-RA, and 5,6-epoxy-RA. We have also determined that human recombinant UGT2B7 can glucuronidate atRA, 4-OH-RA, and 4-OH-RAc with activities similar to those found in human liver microsomes. We therefore postulate that this human isoenzyme, which is expressed in human liver, kidney, and intestine, plays a key role in the biological fate of atRA. We also propose that atRA induces its own oxidative metabolism via a cytochrome P450 (CYP26) and is further biotransformed into glucuronides via UGT-mediated pathways.     

Molecular and functional characterization of microsomal UDP-glucuronic acid uptake by members of the nucleotide sugar transporter (NST) family

Transport of the co-substrate UDPGA (UDP-glucuronic acid) into the lumen of the endoplasmic reticulum is an essential step in glucuronidation reactions due to the intraluminal location of the catalytic site of the enzyme UGT (UDP-glucuronosyltransferase). In the present study, we have characterized the function of several NSTs (nucleotide sugar transporters) and UGTs as potential carriers of UDPGA for glucuronidation reactions. UDPGlcNAc (UDP-N-acetylglucosamine)-dependent UDPGA uptake was found both in rat liver microsomes and in microsomes prepared from the rat hepatoma cell line H4IIE. The latency of UGT activity in microsomes derived from rat liver and V79 cells expressing UGT1A6 correlated well with mannose-6-phosphatase latency, confirming the UGT in the recombinant cells retained a physiology similar to rat liver microsomes. In the present study, four cDNAs coding for NSTs were obtained; two were previously reported (UGTrel1 and UGTrel7) and two newly identified (huYEA4 and huYEA4S). Localization of NSTs within the human genome sequence revealed that huYEA4S is an alternatively spliced form of huYEA4. All the cloned NSTs were stably expressed in V79 (Chinese hamster fibroblast) cells, and were able to transport UDPGA after preloading of isolated microsomal vesicles with UDPGlcNAc. The highest uptake was seen with UGTrel7, which displayed a V(max) approx. 1% of rat liver microsomes. Treatment of H4IIE cells with beta-naphthoflavone induced UGT protein expression but did not affect the rate of UDPGA uptake. Furthermore, microsomes from UGT1-deficient Gunn rat liver showed UDPGA uptake similar to those from control rats. These data show that NSTs can act as UDPGA transporters for glucuronidation reactions, and indicate that UGTs of the 1A family do not function as UDPGA carriers in microsomes. The cell line H4IIE is a useful model for the study of UDPGA transporters for glucuronidation reactions.     

Anti-Cancer Drugs Elicit Re-Expression of UDP-Glucuronosyltransferases in Melanoma Cells

The UDP-glucuronosyltransferase (UGT) family of enzymes plays a vital role in the detoxification of carcinogens as well as clearance of anti-cancer drugs. In humans, 19 UGT family members have been identified and are expressed in a tissue specific manner throughout the body. However, the UGTs have not been previously characterized in melanocytes or melanoma. In the present study, UGT2B7, UGT2B10, and UGT2B15 were identified as being normally expressed in human melanocytes. The same three UGT family members were also expressed in the primary melanoma cell line WM115. No UGT expression was detected in another primary melanoma cell line, WM3211, or in any metastatic melanoma cell line examined. These results suggest that UGT expression is lost during melanoma progression. Treatment of WM3211 or metastatic melanoma cell lines with anti-cancer agents (including vemurafenib) induced expression of UGT2B7, UGT2B10 and UGT2B15 demonstrating that melanoma cells retain the ability to re-express these same three UGTs. The corresponding increase in glucuronidation activity in melanoma cells following anti-cancer treatment was also observed. Furthermore, knockdown of UGT2B7 in WM115 cells sensitized these cells to treatment by adriamycin and epirubicin indicating that UGT2B7 is involved in resistance to these drugs. However, knockdown of UGT2B7 had no effect on temozolomide toxicity. Taken together, these results clearly demonstrate a role for UGTs in melanoma etiology. Since the UGTs are drug metabolism enzymes, we propose that re-expression of the UGTs constitutes a previously unsuspected mechanism for intratumoral drug resistance in melanoma.     

Glucuronidation of carboxylic acid containing compounds by UDP-glucuronosyltransferase isoforms

Glucuronide conjugation of xenobiotics containing a carboxylic acid moiety represents an important metabolic pathway for these compounds in humans. Several human UDP-glucuronosyltransferases (UGTs) have been shown to catalyze the formation of acyl-glucuronides, including UGT2B7, UGT1A3, and UGT1A9. In this study, recombinant expressed UGT isoforms were investigated with many structurally related carboxylic acid analogues, and the UGT rank order for catalyzing the glucuronidation of carboxylic acids was UGT2B7?UGT1A3 approximately UGT1A9. Despite being a poor substrate with UGT1A3, coumarin-3-carboxylic acid was not a substrate for any other UGT isoform tested in this study, suggesting that it could be a specific substrate for UGT1A3. Interestingly, UGT1A7 and UGT1A10 also react with several carboxylic acid aglycones. Kinetic analysis showed that UGT2B7 exhibits much higher glucuronidation efficiency (Vmax/Km) with ibuprofen, ketoprofen, and others, compared to UGT1A3. These data indicate that UGT2B7 could be the major isoform involved in the glucuronidation of carboxylic acid compounds in humans.     

UDP-glucuronosyltransferase 2B15 (UGT2B15) and UGT2B17 enzymes are major determinants of the androgen response in prostate cancer LNCaP cells

Uridine diphosphate-glucuronosyltransferase 2 (UGT2)B15 and B17 enzymes conjugate dihydrotestosterone (DHT) and its metabolites androstane-3alpha, 17beta-diol (3alpha-DIOL) and androsterone (ADT). The presence of UGT2B15/B17 in the epithelial cells of the human prostate has been clearly demonstrated, and significant 3alpha-DIOL glucuronide and ADT-glucuronide concentrations have been detected in this tissue. The human androgen-dependent cancer cell line, LNCaP, expresses UGT2B15 and -B17 and is also capable of conjugating androgens. To assess the impact of these two genes in the inactivation of androgens in LNCaP cells, their expression was inhibited using RNA interference. The efficient inhibitory effects of a UGT2B15/B17 small interfering RNA (siRNA) probe was established by the 70% reduction of these UGT mRNA levels, which was further confirmed at the protein levels. The glucuronidation of dihydrotestosterone (DHT), 3alpha-DIOL, and ADT by LNCaP cell homogenates was reduced by more than 75% in UGT2B15/B17 siRNA-transfected LNCaP cells when compared with cells transfected with a non-target probe. In UGT2B15/B17-deficient LNCaP cells, we observe a stronger response to DHT than in control cells, as determined by cell proliferation and expression of eight known androgen-sensitive genes. As expected, the amounts of DHT in cell culture media from control cells were significantly lower than that from UGT2B15/B17 siRNA-treated cells, which was caused by a higher conversion to its corresponding glucuronide derivative. Taken together these data support the idea that UGT2B15 and -B17 are critical enzymes for the local inactivation of androgens and that glucuronidation is a major determinant of androgen action in prostate cells.     

Glucuronidation of arachidonic and linoleic acid metabolites by human UDP-glucuronosyltransferases

Arachidonic acids (AA) and linoleic acids (LAs) are metabolized, in several tissues, to hydroxylated metabolites that are important mediators of many physiological and pathophysiological processes. The conjugation of leukotriene B4 (LTB4), 5-hydroxyeicosatetraenoic acid (HETE), 12-HETE, 15-HETE, and 13-hydroxyoctadecadienoic acid (HODE) by the human UDP-glucuronosyltransferase (UGT) enzymes was investigated. All substrates tested were efficiently conjugated by human liver microsomes to polar derivatives containing the glucuronyl moiety as assessed by mass spectrometry. The screening analyses with stably expressed UGT enzymes in HK293 showed that glucuronidation of LTB4 was observed with UGT1A1, UGT1A3, UGT1A8, and UGT2B7, whereas UGT1A1, UGT1A3, UGT1A4, and UGT1A9 also conjugated most of the HETEs and 13-HODE. LA and AA metabolites also appear to be good substrates for the UGT2B subfamily members, especially for UGT2B4 and UGT2B7 that conjugate all HETE and 13-HODE. Interestingly, UGT2B10 and UGT2B11, which are considered as orphan enzymes since no conjugation activity has so far been demonstrated with these enzymes, conjugated 12-HETE, 15-HETE, and 13-HODE. In summary, our data showed that several members of UGT1A and UGT2B families are capable of converting LA and AA metabolites into glucuronide derivatives, which is considered an irreversible step to inactivation and elimination of endogenous substances from the body.     

Identification of human UDP-glucuronosyltransferase isoform(s) responsible for the C-glucuronidation of phenylbutazone

Glucuronidation is a major metabolic pathway in the biotransformation of many xenobiotics and endogeneous compounds. There have been many studies on the formation of O-, N- or S-glucuronides and identification of the UDP-glucuronosyltransferase (UGT) isoforms responsible for the formation of these glucuronides. However, there is no information available on which UGT isoform(s) catalyzes C-glucuronidation. In the present study, 16 human UGTs (UGTs 1A1, 1A3, 1A4, 1A5, 1A6, 1A7, 1A8, 1A9, 1A10, 2B4, 2B7, 2B10, 2B11, 2B15, 2B17 and 2B28) were cloned and expressed in baculovirus-infected insect cells and investigated to determine their C-glucuronidating activity toward phenylbutazone (PB). Among the UGT isoforms investigated, only UGT1A9 catalyzed PB C-glucuronidation. Human liver and kidney microsomes, which are well known to express UGT1A9, had C-glucuronidating activity toward PB. However, the jejunum, which did not express UGT1A9, had no C-glucuronidating activity. These results demonstrate for the first time that PB C-glucuronidation is catalyzed by only UGT1A9.     

Activators of the farnesoid X receptor negatively regulate androgen glucuronidation in human prostate cancer LNCAP cells

Androgens are major regulators of prostate cell growth and physiology. In the human prostate, androgens are inactivated in the form of hydrophilic glucuronide conjugates. These metabolites are formed by the two human UGT2B15 [UGT (UDP-glucuronosyltransferase) 2B15] and UGT2B17 enzymes. The FXR (farnesoid X receptor) is a bile acid sensor controlling hepatic and/or intestinal cholesterol, lipid and glucose metabolism. In the present study, we report the expression of FXR in normal and cancer prostate epithelial cells, and we demonstrate that its activation by chenodeoxycholic acid or GW4064 negatively interferes with the levels of UGT2B15 and UGT2B17 mRNA and protein in prostate cancer LNCaP cells. FXR activation also causes a drastic reduction of androgen glucuronidation in these cells. These results point out activators of FXR as negative regulators of androgen-conjugating UGT expression in the prostate. Finally, the androgen metabolite androsterone, which is also an activator of FXR, dose-dependently reduces the glucuronidation of androgens catalysed by UGT2B15 and UGT2B17 in an FXR-dependent manner in LNCaP cells. In conclusion, the present study identifies for the first time the activators of FXR as important regulators of androgen metabolism in human prostate cancer cells.