UDP-glucuronosyltransferase UGT1A7 induced in rat small intestinal mucosa by oral administration of 2-naphthoflavone

MALDI Mass Spectrometry Imaging for Evaluation of Therapeutics in Colorectal Tumor Organoids

Patient-derived colorectal tumor organoids (CTOs) closely recapitulate the complex morphological, phenotypic, and genetic features observed in in vivo tumors. Therefore, evaluation of drug distribution and metabolism in this model system can provide valuable information to predict the clinical outcome of a therapeutic response in individual patients. In this report, we applied matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to examine the spatial distribution of the drug irinotecan and its metabolites in CTOs from two patients. Irinotecan is a prodrug and is often prescribed as part of therapeutic regimes for patients with advanced colorectal cancer. Irinotecan shows a time-dependent and concentration-dependent permeability and metabolism in the CTOs. More interestingly, the active metabolite SN-38 does not co-localize well with the parent drug irinotecan and the inactive metabolite SN-38G. The phenotypic effect of irinotecan metabolism was also confirmed by a viability study showing significantly reduced proliferation in the drug treated CTOs. MALDI-MSI can be used to investigate various pharmaceutical compounds in CTOs derived from different patients. By analyzing multiple CTOs from a patient, this method could be used to predict patient-specific drug responses and help to improve personalized dosing regimens. Graphical Abstract ᅟ.

Effects of β-Naphthoflavone on Ugt1a6 and Ugt1a7 Expression in Rat Brain

Uridine 5'-diphosphate-glucuronosyltransferase (UGT) catalyzes a major phase II reaction in a drug-metabolizing enzyme system. Although the UGT1A subfamily is expressed mainly in the liver, it is also expressed in the brain. The purpose of the present study was to elucidate the effect of β-naphthoflavone (BNF), one of the major inducers of drug-metabolizing enzymes, on Ugt1a6 and Ugt1a7 mRNA expression and their glucuronidation in the rat brain. Eight-week-old male Sprague-Dawley rats were treated intraperitoneally with BNF (80 mg/kg), once daily for 7 d. Ugt1a6 and Ugt1a7 mRNA expression increased in the cerebellum and hippocampus (Ugt1a6: 2.1- and 2.3-fold, respectively; Ugt1a7: 1.7- and 2.8-fold, respectively); acetaminophen glucuronidation also increased in the same regions by 4.1- and 2.7-fold, respectively. BNF induced Ugt1a6 and Ugt1a7 mRNA expression and their glucuronidation, and the degree of induction differed among 9 regions. BNF also upregulated CYP1A1, CYP1A2, and CYP1B1 mRNAs in the rat brain. Since the aryl hydrocarbon receptor signaling pathway was activated by BNF, it is indicated that Ugt1a6 and Ugt1a7 were induced via AhR in the rat brain. This study clarified that Ugt1a6 and Ugt1a7 mRNA expression and their enzyme activities were altered by BNF, suggesting that these changes may lead to alteration in the pharmacokinetics of UGT substrate in rat brain.

The UDP-glucuronosyltransferases of the blood-brain barrier: their role in drug metabolism and detoxication

UDP-glucuronosyltransferases (UGTs) form a multigenic family of membrane-bound enzymes expressed in various tissues, including brain. They catalyze the formation of β-D-glucuronides from structurally unrelated substances (drugs, other xenobiotics, as well as endogenous compounds) by the linkage of glucuronic acid from the high energy donor, UDP-α-D-glucuronic acid. In brain, UGTs actively participate to the overall protection of the tissue against the intrusion of potentially harmful lipophilic substances that are metabolized as hydrophilic glucuronides. These metabolites are generally inactive, except for important pharmacologically glucuronides such as morphine-6-glucuronide. UGTs are mainly expressed in endothelial cells and astrocytes of the blood brain barrier (BBB). They are also associated to brain interfaces devoid of BBB, such as circumventricular organ, pineal gland, pituitary gland and neuro-olfactory tissues. Beside their key-role as a detoxication barrier, UGTs play a role in the steady-state of endogenous compounds, like steroids or dopamine (DA) that participate to the function of the brain. UGT isoforms of family 1A, 2A, 2B and 3A are expressed in brain tissues to various levels and are known to present distinct but overlapping substrate specificity. The importance of these enzyme species with regard to the formation of toxic, pharmacologically or physiologically relevant glucuronides in the brain will be discussed.

ELOVL2 overexpression enhances triacylglycerol synthesis in 3T3-L1 and F442A cells

Elongation of very long-chain fatty acids (ELOVL) members were overexpressed in two preadipocyte cell lines, ELOVL2 and ELOVL3 in 3T3-L1 cells, and ELOVL1-3 in F442A cells. Cells overexpressing ELOVL2, whose preferred substrates are arachidonic acid (AA, C20:4n-6) and eicosapentaenoic acid (EPA, C20:5n-3), showed an enhanced triacylglycerol (TAG) synthesis and subsequent accumulation of lipid droplets. Incorporation of fatty acid (FA) but not of glucose into TAG was enhanced by ELOVL2-overexpression. Two lipogenic genes encoding diacylglycerol acyltransferase-2 (DGAT2) and fatty acid-binding protein-4 (FABP4, aP2) were induced in ELOVL2-overexpressing cells, whereas no such effect was seen on the fatty acid synthase (FAS) gene.

Induction of Rat UDP-Glucuronosyltransferases in Liver and Duodenum by Microsomal Enzyme Inducers That Activate Various Transcriptional Pathways

Microsomal enzyme inducers (MEIs) up-regulate phase I biotransformation enzymes, most notably cytochromes P450. Transcriptional up-regulation by MEIs occurs through at least three nuclear receptor mechanisms: constitutive androstane receptor (CAR; CYP2B inducers), pregnane X receptor (PXR; CYP3A inducers), and peroxisome proliferator-activated receptor alpha (PPARalpha; CYP4A inducers). Other mechanisms include transcription factors aryl hydrocarbon receptor (AhR; CYP1A inducers), and nuclear factor erythroid 2 (NF-E2)-related factor 2 (Nrf2; NADPH-quinone oxidoreductase inducers). UDP-glucuronosyltransferases (UGTs) are phase II biotransformation enzymes that are predominantly expressed in liver and intestine. MEIs increase UGT activity; however, transcriptional regulation of individual UGT isoforms is not completely understood. The purpose of this study was to examine inducibility of individual UGT isoforms and potential mechanisms of transcriptional regulation in rat liver and duodenum. UGT mRNA levels were assessed in liver and duodenum of rats treated with MEIs that activate various transcriptional pathways. All four CAR activators induced UGT2B1 in liver, but not duodenum. UGT1A1, 1A5, 1A6, and 2B12 were induced by at least two CAR activators in liver only. Two PXR ligands induced UGT1A2, but only in duodenum. Two PPARalpha ligands induced UGT1A1 and 1A3 in liver only. AhR ligands induced UGT1A6 and 1A7 in liver, but not duodenum. Nrf2 activators increased UGT2B3 and 2B12 in both liver and duodenum, and UGT1A6, 1A7, and 2B1 in liver only. In summary, only UGT1A2 and 1A8 were not inducible in liver by MEIs. MEIs differentially regulate hepatic expression of individual UGT isoforms, although no one transcriptional pathway dominated. In duodenum, MEIs had minimal effects on UGT expression.

Characterization of Rat Intestinal Microsomal UDP-Glucuronosyltransferase Activity toward Mycophenolic Acid

Mycophenolic acid (MPA) is the active immunosuppressive metabolite of the anti-organ rejection drug mycophenolate mofetil (MMF) and is implicated in the gastrointestinal toxicity associated with MMF therapy. Intestinal UDP-glucuronosyltransferases (UGT) have been proposed to provide intrinsic resistance against MMF-induced gastrointestinal toxicity by converting MPA to the inactive MPA 7-O-glucuronide. Using an optimized intestinal microsome preparation method that stabilized the intestinal MPA UGT activity, the MPA UGT activity of male Sprague-Dawley rat intestinal microsomes was characterized. A longitudinal gradient similar to that described for other phenolic compounds was observed, with the activity decreasing from the duodenum to the distal small intestine and colon. The catalytic efficiency of MPA glucuronidation decreased from the proximal to distal intestine as a result of decreasing Vmax and increasing Km. The finding that homozygous Gunn rats lack detectable intestinal MPA UGT activity indicates exclusive roles of UGT1A1, UGT1A6, and/or UGT1A7. Quantitative immunoblotting revealed a parallel between the MPA UGT activity and the content of UGT1A7-like immunoreactivity (18.7 and 7.3 microg/mg for duodenum and colon, respectively). In contrast, the lesser MPA-metabolizing UGT, UGT1A1 and UGT1A6, were lower in abundance (1.6-2.1 and 1.7-2.9 microg/mg, respectively), and their patterns of longitudinal distribution were distinct from the MPA UGT activity. These data suggest a dominant role of a UGT1A7-like enzyme, presumably UGT1A7 itself, in the catalysis of rat intestinal MPA glucuronidation. Studies are ongoing to investigate the relationship between intestinal UGT1A enzymes and susceptibility to MMF-induced gastrointestinal toxicity.

ANALYSIS OF SUBSTRATE SPECIFICITIES AND TISSUE EXPRESSION OF RAT UDP-GLUCURONOSYLTRANSFERASES UGT1A7 AND UGT1A8

The UGT1 complex codes for a subfamily of homologous "1A7-like" UDP-glucuronosyltransferases (UGTs), including UGT1A7 and UGT1A8. Little information is available regarding either the substrate specificities or regulation of the UGT1A7-like forms from rats. We compared the activities and tissue expression of UGT1A7 and UGT1A8, which exhibit 77% identity in their amino terminal sequence. UGT1A7 shows broad specificity, catalyzing the glucuronidation of 31 of 40 randomly selected substrates (100 muM) at rates >0.1 nmol/mg/min. UGT1A7 substrates included both planar and nonplanar compounds, mono- and polycyclic aromatics, and compounds with bulky side chain ring substitutions. UGT1A8 exhibited a narrower substrate specificity that completely overlapped with UGT1A7. UGT1A8 was most active toward the 1-OH, 4-OH, 5-OH, 6-OH, 7-OH, 10-OH, 11-OH, and 12-OH derivatives of benzo[a]pyrene. Other effective UGT1A8 substrates (>0.1 nmol/mg/min) included 9-OH-benzo[a]pyrene, 1-naphthol, 4-methylumbelliferone, 7-hydroxycoumarin, chrysin, quercetin, 4-nitrophenol, and estriol. In general, substrates preferred by UGT1A8 were polyaromatic planar structures with nonbulky substituents and a superimposable 1-naphtho ring structure. Studies of the tissue expression of the UGT1A7 and 1A8 mRNAs using RNase protection analysis suggested that each is expressed in liver and kidney of control rats. A major difference is the higher expression of UGT1A7 mRNA in intestine. These studies suggest complementary functions of the UGT1A7 and UGT1A8 forms in xenobiotic metabolism. Further studies are necessary to determine whether their relative contributions change as a function of development, hormonal status, or exposure to inducing agents.

Glucuronidation and the UDP-glucuronosyltransferases in health and disease

This article is an updated report of a symposium held at the June 2000 annual meeting of the American Society for Pharmacology and Experimental Therapeutics in Boston. The symposium was sponsored by the ASPET Divisions for Drug Metabolism and Molecular Pharmacology. The report covers research from the authors' laboratories on the structure and regulation of UDP-glucuronosyltransferase (UGT) genes, glucuronidation of xenobiotics and endobiotics, the toxicological relevance of UGTs, the role of UGT polymorphisms in cancer susceptibility, and gene therapy for UGT deficiencies.

High glucuronidation activity of environmental estrogens in the carp (Cyprinus carpino) intestine

Many adverse effects on carp reproductive organs have been reported to be caused by exposure to environmental estrogens, such as nonylphenol and bisphenol A, which contaminate the aquatic environment. The glucuronidation activities of xenoestrogens (bisphenol A and diethylstilbestrol) and phytoestrogens (coumestrol, genistein and biochanin A), but not nonylphenol and octylphenol, were observed in microsomes prepared from carp organs. The highest levels of glucuronidation of environmental estrogens, for which the optimum temperature was 25-30 degrees C, were observed in the intestinal microsomes of 2-year-old carp. These activities in carp intestine increased developmentally, and the maximum levels corresponded to 5-10 % of that in rat liver microsomes. However, the glucuronidation of phytoestrogen by carp intestinal microsomes corresponded to that of rat liver microsomes. Only bisphenol A-glucuronide was excreted from the everted intestine, indicating that bisphenol A is metabolized in the carp intestine mainly as glucuronide. These results suggest that glucuronidation by carp intestine plays an important role for the detoxification of xenoestrogens and phytoestrogens, except for nonylphenol and octylphenol.

High expression of 92 kDa type IV collagenase (matrix metalloproteinase-9) in canine mammary adenocarcinoma

The 92 kDa type VI collagenase (matrix metalloproteinase-9 (MMP-9)) activities on zymography assay were found to be 1-6 times higher in benign tumor breast tissues of 12 canines and 4-26 times higher in adenocarcinoma breast tissues of nine canines than that of control tissues, respectively. A full-length canine MMP-9 cDNA was cloned from the adenocarcinoma tissue by reverse transcription-PCR and 5'- and 3'-RACE. The isolated cDNA contained an open reading frame coding for a polypeptide of 704 amino acids. The predicted protein sequence displayed extensive similarity to that of known MMP-9s and contained a putative signal sequence, a propeptide, an active site with three zinc-binding histidine residues, a calcium-binding domain, a hemopexin region, and three key cysteine residues. Western blotting using MMP-9-specific antibodies prepared against the peptide corresponding to Arg(642)-Asp(704) of canine MMP-9 and Northern blotting using a MMP-9-specific cDNA fragment as a probe confirmed that MMP-9 (the 92 kDa protein band) was highly expressed in canine mammary adenocarcinoma tissues. Higher levels of MMP-9 activity were found in the sera of canines with mammary adenocarcinoma. The results indicated that MMP-9 plays an important role in the progression of a canine mammary tumor and that assay of serum MMP-9 is helpful for early diagnosis as progress of adenocarcinoma.

Roles of glucuronidation and UDP-glucuronosyltransferases in xenobiotic bioactivation reactions

Glucuronide conjugates represent one of the major types of naturally occurring phase 2 metabolites of xenobiotics and endobiotics. The process underlying their formation, glucuronidation, is normally considered detoxifying, because glucuronides usually possess less intrinsic biological or chemical activity than their parent aglycones and they are rapid excreted. However, a number of glucuronide conjugates are known that are active and may contribute to pharmacological activities or toxicities associated with their parent compounds. These include two classes of glucuronides with electrophilic chemical reactivity (N-O-glucuronides of hydroxamic acids and acyl glucuronides of carboxylic acids) and several types of glucuronides that impart biological effects through non-covalent interactions (morphine 6-O-glucuronide, retinoid glucuronides, and D-ring glucuronides of estrogens). Glucuronides may thus contribute to clinically significant effects, including environmental arylamine-induced carcinogenesis, drug hypersensitivity and other toxicities associated with carboxylic acid drugs, morphine analgesia, and cholestasis from estrogens. This review summarizes the rat and human UDP-glucuronosyltransferases that may be involved in the formation of bioactive glucuronides, including their substrate- and tissue-specificity and genetic and environmental influences on their activity. This knowledge may be useful for enhancing the therapeutic efficacy and minimizing the risk of adverse effects associated with xenobiotics that undergo bioactivating glucuronidation reactions.

Involvement of hepatocyte nuclear factor 1 in the regulation of the UDP-glucuronosyltransferase 1A7 (UGT1A7) gene in rat hepatocytes

UDP-glucuronosyltransferase 1A7 (UGT1A7) is a major UGT contributing to the glucuronidation of xenobiotic phenols in rats. Its expression in rat liver is tightly regulated, with low constitutive and high inducible expression in response to aryl hydrocarbon receptor ligands and oltipraz. Previously, we reported the absence of 3-methylcholanthrene- or oltipraz-responsive elements in the 1.6-kbp region flanking the UGT1A7 promoter. However, potential binding sites were noted for several liver-enriched transcription factors. Here we show that deletion of the hepatic nuclear factor (HNF)3, HNF4, and CCAAT-enhancer binding protein-like binding sites had no effect on the expression of a UGT1A7 reporter plasmid, p(-965/+56)1A7-Luc, in primary rat hepatocytes. The full activity of the promoter was contained in the region between bases -157 and +76. Two sites of binding by rat liver nuclear proteins were detected in this region by DNase footprinting. PR-1 corresponded to the HNF1-like binding site between bases -52 and -38, whereas PR-2 was located between -30 to -6. Gel retardation studies supported the presence of HNF1alpha in the PR-1 DNA-liver nuclear protein complex. Mutation of PR-1 inhibited binding in the gel shift assay, prevented activation by overexpressed HNF1 in human embryonic kidney cells, and reduced by >80% the maximal luciferase activities expressed from basal and 3-methylcholanthrene-responsive UGT1A7 gene reporter constructs in primary rat hepatocytes. These data provide evidence for an important stimulatory role of HNF1 in promoting UGT1A7 gene expression in rat liver.

Distribution and inducibility by 3-methylcholanthrene of family 1 UDP-glucuronosyltransferases in the rat gastrointestinal tract

UDP-Glucuronosyltransferases (UGT) catalyze the glucuronidation of a broad spectrum of endobiotic and xenobiotic substrates. The resulting glucuronides are more hydrophilic, facilitating renal and biliary excretion. Apart from hepatic glucuronidation, high rates of gastrointestinal glucuronidation have been observed. The aim of this study was to characterize the expression of family 1 UGTs (UGT1A) in liver, kidney, and all parts of the rat gastrointestinal tract by reverse transcription polymerase reaction (RT-PCR), Northern blot, and xenobiotic induction experiments. RT-PCR experiments were performed with primers specific for all known rat UGT1A mRNAs. UGT1A1, UGT1A6, and UGT1A7 were expressed in liver, kidney, and the gastrointestinal tract. UGT1A5 transcripts were detected in liver, but not in kidney or gastrointestinal tissue. In contrast, UGT1A2 and UGT1A3 were not expressed in liver or kidney, but were detected in intestine. Low levels of UGT1A3 were detectable in duodenum and jejunum. UGT1A2 was abundantly expressed in the small intestine; expression levels in the stomach and the large intestine were low. Quantitative evaluation of RNA levels by Northern blot revealed expression in gradients, with highest UGT1A mRNA levels in duodenum and decreasing levels in the small and large intestine. Only UGT1A6 was expressed at high levels in the rectum. Rats treated with 3-methylcholanthrene (3-MC) displayed a 10-fold induction of hepatic UGT1A6 and UGT1A7 mRNAs. In gastric tissues and in intestine, induction was 4-fold and 2-fold, respectively. In contrast to the constitutive expression of UGT1A7 in kidney, UGT1A6 was inducible in the liver. Effects of 3-MC on UGT1A1 expression revealed downregulation in the liver and highly variable effects in duodenum and stomach. This study demonstrates tissue-specific expression and tissue-specific induction patterns in rat liver, kidney, and gastrointestinal tract, which may represent the physiological basis of tissue-specific glucuronidation in rats.

1-Naphthol beta-D-glucuronide formed intraluminally in rat small intestine mucosa and absorbed into the colon

UDP-glucuronosyltransferase expressed in the rat intestinal epithelial cells is important as the first barrier against chemicals. The distribution of 1-naphthol and its glucuronide formed in rat intestine was estimated by using everted intestine. Roughly 60% of the 1-naphthol added to the mucosal fluid was absorbed into the mucosa of the small intestine and colon within 30 min. Approximately 66% of the 1-naphthol absorbed in the proximal intestine was secreted intraluminally as a glucuronide, and a minimal 9% was transported into the serosal fluid as a glucuronide. In the distal intestine, approximately 34% was secreted intraluminally and 30% was transported into the serosal fluid as a glucuronide. The greatest amount of the glucuronide (37% of the absorbed 1-naphthol) was transported into the serosal fluid, whereas a minimal 7% was secreted intraluminally in the colon. In marked contrast, the colon was found to transport 1-naphthol-glucuronide from the mucosal fluid into the serosal fluid at an approximately 8-fold higher rate than that of the small intestine. These results suggest that, in the small intestine, phenolic xenobiotics are mostly glucuronidated and secreted intraluminally and that the resulting glucuronide is absorbed and transported into the serosal side of the colon.

Small intestinal UDP-glucuronosyltransferase sheUGT1A07: partial purification and cDNA cloning from sheep small intestine

A phenol UDPglucuronosyltransferase (UGT) was partially purified, and the cDNA encoding the isoform was cloned and sequenced from sheep small intestine. The purified preparation containing a one major band (57 kDa) and one minor band (50 kDa) revealed high activities toward xenobiotics such as 1-naphthol (1-NA), 4-nitrophenol, and 4-methylumbelliferone. The preparation, however, had only little activity toward 4-hydroxybiphenyl and no activity toward bilirubin, suggesting that the preparation contains UGT1 isoforms. The NH2-terminal amino acid sequence of the major band was determined to be Gly-Lys-Leu-Leu-Val-Val-Pro-Met-Asp-Gly-Ser. A full-length UGT cDNA was obtained by reverse transcription-polymerase chain reaction with the degenerated 5'-primer from the NH2-terminal amino acid sequence of the purified major one and rapid amplification of cDNA ends from sheep small intestine. The cloned cDNA named sheUGT1A07 by amino acid similarity has a NH2-terminus sequence identical to that of the purified major one. Another phenol UGT cDNA named sheUGT1A6 was also cloned from sheep liver. sheUGT1A6 was expressed mainly in the liver, whereas sheUGT1A07 mRNA was expressed almost only in the alimentary organs, suggesting that sheUGT1A6 plays a role as a general drug metabolizing UGT isoform in the liver and sheUGT1A07 plays important role in the xenobiotics glucuronidation in the sheep small intestine.