Transcriptional Enhancement of UDP-Glucuronosyltransferase Form 1A2 (UGT1A2) by Nuclear Factor I-A (NFI-A) in Rat Hepatocytes

In cultured primary hepatocytes UDP-glucuronosyltransferase form 1A2 (UGT1A2) mRNA level is 80 times higher than that found in rat liver. We previously identified an enhancer sequence in the UGT1A2 promoter, and designated it as culture-associated expression responsive enhancer module (CEREM). Affinity chromatography with DNA fragments containing CEREM allowed enrichment of nuclear factor I (NFI) proteins from cultured hepatocytes. The NFI family is encoded by four distinct genes, NFI-A, NFI-B, NFI-C, and NFI-X. Immunoblot analysis with isoform-specific antibodies showed that NFI-A1 existed as a major component in rat liver and cultured hepatocytes. By contrast, NFI-C1 was present in rat liver but disappeared immediately upon cultivation of hepatocytes. Only trace amounts of NFI-B and NFI-X were detectable in rat liver and cultured hepatocytes. NFI-A1 elevated expression of the reporter gene that is under the control of CEREM, while NFI-C1 had an inhibitory effect. Co-expression of a constant amount of NFI-A1 with an increasing amount of NFI-C1 led to a concentration-dependent decrease in the expression of the CEREM-controlled reporter gene mediated by NFI-A1. Activation of UGT1A2 expression by NFI-A1 is suppressed by the coexistence of NFI-C1 in the liver, and culture-associated expression of UGT1A2 is triggered by the rapid disappearance of NFI-C1 in cultured hepatocytes.

Irinotecan Therapy in a 12-year-old Girl with Recurrent Brain Stem Glioma and without Functional Polymorphisms in UGT1A1 Activity: Case Report

A 10-year-old girl was diagnosed with astrocytoma grade 2. Immuno-chemo-radiotherapy (interferon, ranimustine, and radiation), second-line chemotherapy (carboplatin and etoposide, 7 cycles) and third-line chemotherapy (ifosfamide, carboplatin, and etoposide) was given to treat progressive disease. Finally, irinotecan therapy was initiated and led to dramatic clinical improvement. Irinotecan is metabolized by carboxylesterase to form an active SN-38, which is further conjugated and detoxified by UDP-glucuronosyltransferase (UGT) to yield its beta-glucuronide. The polymorphic UGT isoenzyme, UGT1A1 has genetic variants which decrease in SN-38 glucuronidating capacity and could help predict irinotecan-associated toxicity. The patient suffered excessive toxicity with low-dose irinotecan although no functional polymorphism in UGT1A1 was identified. We suggest that irinotecan offers an effective treatment option for children with recurrent brain stem glioma and other genetic variants except UGT1A1 may be a risk factor for irinotecan-induced toxicity.

Differential UGT1A1 Induction by Chrysin in Primary Human Hepatocytes and HepG2 Cells

Chrysin, a dietary flavonoid, has been shown to markedly induce UGT1A1 expression and activity in HepG2 and Caco-2 cell lines; thus, it has been suggested to have clinical utility in the treatment of UGT1A1-mediated deficiencies, such as unconjugated hyperbilirubinemia or the prevention of 7-ethyl-10-hydroxycamptothecin (SN-38) toxicity. However, little is known about its induction potential in a more physiologically relevant model system, such as primary hepatocyte culture. In this study, induction of UGT1A1 expression (mRNA, protein, and activity) was investigated in primary human hepatocyte cultures after treatment with chrysin and other prototypical inducers. Endogenous nuclear receptor-mediated UGT1A1 induction was studied using transient transfection reporter assays in primary human hepatocytes and HepG2 cells. Results indicated that induction of UGT1A1 expression was minimal in human hepatocytes treated with chrysin compared with that in HepG2 cells (1.2-versus 11-fold, respectively). Subsequent experiments to determine whether the differential response was due to its metabolic stability revealed strikingly different elimination rate constants between the two cell systems (half-life of 13 min in human hepatocytes versus 122 min in HepG2 cell suspensions). Further study demonstrated that UGT1A1 mRNA expression could be induced in human hepatocyte cultures by either increasing the chrysin dosing frequency or by modulating chrysin metabolism, suggesting that the differential induction observed in hepatocytes and HepG2 cells was due to differences in the metabolic clearance of chrysin. In conclusion, this study suggests that the metabolic stability of chrysin likely would limit its ability to induce UGT1A1 in vivo.

A phase I pharmacologic and pharmacogenetic trial of sequential 24-hour infusion of irinotecan followed by leucovorin and a 48-hour infusion of fluorouracil in adult patients with solid tumors

PURPOSE

In preclinical studies, sequential exposure to irinotecan (CPT-11) then fluorouracil (5-FU) is superior to concurrent exposure or the reverse sequence; a 24-hour infusion of CPT-11 may be better tolerated than shorter infusions.

EXPERIMENTAL DESIGN

CPT-11 was first given at four levels (70-140 mg/m(2)/24 hours), followed by leucovorin 500 mg/m(2)/0.5 hours and 5-FU 2,000 mg/m(2)/48 hours on days 1 and 15 of a 4-week cycle. 5-FU was then increased in three cohorts up to 3,900 mg/m(2)/48 hours.

RESULTS

Two patients had dose-limiting toxicity during cycle 1 at 140/3,900 of CPT-11/5-FU (2-week delay for neutrophil recovery; grade 3 nausea despite antiemetics); one of six patients at 140/3,120 had dose-limiting toxicity (grade 3 diarrhea, grade 4 neutropenia). Four of 22 patients with colorectal cancer had partial responses, two of which had prior bolus CPT-11/5-FU. The mean 5-FU plasma concentration was 5.1 micromol/L at 3,900 mg/m(2)/48 hours. The end of infusion CPT-11 plasma concentration averaged 519 nmol/L at 140 mg/m(2)/24 hours. Patients with UDP-glucuronosyltransferase (UGT1A1; TA)6/6 promoter genotype had a lower ratio of free to glucuronide form of SN-38 than in patients with >/=1 (TA)7 allele. Thymidylate synthase genotypes for the 28-base promoter repeat were 2/2 (13%), 2/3 (74%), 3/3 (13%); all four responders had a 2/3 genotype.

CONCLUSIONS

Doses (mg/m(2)) of CPT-11 140/24 hours, leucovorin 500/0.5 hours and 5-FU 3,120/48 hours were well tolerated.

Three vertebrate hyaluronan synthases are expressed during mouse development in distinct spatial and temporal patterns

We have used in situ hybridization to study the expression of the vertebrate hyaluronan synthase (Has) gene family members, designated Has1, Has2, and Has3, during mouse development. At embryonic day (E) 7.5, Has1 and Has2 are expressed throughout the gastrulating embryo. After E8.5, Has1 expression disappears, but Has2 continues to be strongly, albeit transiently, expressed in numerous tissues, including the branchial arches and craniofacial structures such as the palatal shelves and lens pit. Has2 is also expressed during cardiac, skeletal, and tail development. Has3 transcripts are first detected at E10.5 in the maxillary and mandibular components of the first branchial arch. Notably, Has3 expression in the developing teeth, vibrissae hair follicles, nasal cavity, and inner ear complements the expression pattern of Has2. Our results indicate that, whereas Has2 is exclusively expressed in some tissues, its expression pattern overlaps and/or complements that of Has1 and Has3 in others.

Human UDP-Glucuronosyltransferase 1A5: Identification, Expression, and Activity

The human UDP-glucuronosyltransferase (UGT) subfamily 1A includes nine genes. The expression of all the UGT1A isoforms, apart from UGT1A5, has been reported previously. We have now detected a low basal level of UGT1A5 expression in cultured human hepatocytes, and treatment with rifampicin or 3-methylcholanthrene increased the level of UGT1A5 mRNA. Low-level UGT1A5 expression was also found in HepG2 and Caco-2 cells as well as human liver. Furthermore, UGT1A5 expression has been detected in various segments of the intestine from human donors, revealing high interindividual variability in its level and distribution along the intestine. Full-length UGT1A5 cDNA was isolated from Caco-2 cells that had been transfected with the pregnane X receptor and treated with rifampicin. Recombinant UGT1A5, expressed in baculovirus-infected insect cells, exhibited very low rates of 4-methylumbelliferone and scopoletin glucuronidation, whereas 1-hydroxypyrene was a much better substrate for it. UGT1A5 did not glucuronidate 4-aminobiphenyl, a good substrate for the highly homologous enzymes UGT1A4 and UGT1A3. However, replacing the first 110 amino acids of UGT1A5, a region that may be involved in substrate binding, with the counterpart segment from UGT1A4 did not increase the 4-aminobiphenyl glucuronidation activity. Collectively, this work demonstrates for the first time that the human UGT1A5 is expressed in several tissues, is inducible, and is catalytically active.

Association of genetic variation in tamoxifen-metabolizing enzymes with overall survival and recurrence of disease in breast cancer patients

Tamoxifen has been a mainstay of adjuvant therapy for breast cancer for many years. We sought to determine if genetic variability in the tamoxifen metabolic pathway influenced overall survival in breast cancer patients treated with tamoxifen. We examined functional polymorphisms in CYP2D6, the P450 catalyzing the formation of active tamoxifen metabolites, and UGT2B15, a Phase II enzyme facilitating the elimination of active metabolite in a retrospective study of breast cancer patients. We also examined whether the combination of variant alleles in SULT1A1 and UGT2B15 had more of an impact on overall survival in tamoxifen-treated patients than when the genes were examined separately. We conducted a retrospective study using archived paraffin blocks for DNA extraction and data from pathology reports and hospital tumor registry data for information on clinical characteristics, treatment, and outcomes (162 patients receiving tamoxifen and 175 who did not). Genotypes for CYP2D6 and UGT2B15 were obtained and Cox proportional hazards modeling was performed. After adjusting for age, race, stage of disease at diagnosis, and hormone receptor status, we found no significant association between CYP2D6 genotype and overall survival in either group of breast cancer patients. Tamoxifen-treated patients with UGT2B15 high activity genotypes had increased risk of recurrence and poorer survival. When UGT2B15 and SULT1A1 'at-risk' alleles were combined, women with two variant alleles had significantly greater risk of recurrence and poorer survival than those with common alleles. These studies indicate that genetic variation in Phase II conjugating enzymes can influence the efficacy of tamoxifen therapy for breast cancer.

Optimization of conditions for clinical human hepatocyte infusion

Cytotoxicity and apoptosis are common problems in the isolation and storage of human hepatocytes. In vitro environments of hepatocytes during cell infusion may be critical to reducing cellular damage and enhancing cell viability. We examined the effects of donor liver histology (40-50% steatosis vs. normal), incubation time, temperature, and three solutions for infusion on banked primary human hepatocytes, by studying: trypan blue exclusion, AST release, LDH release, MTT assay, detection of DNA ladder, and a hepatocyte proliferation assay. In addition, the microstructure functions of the endoplasmic reticulum and mitochondria of the intact hepatocytes were determined by measuring correlates of UGT 1A1 and cytochrome P-450 3A (CYP3A4) activity. In general, hepatocyte viability decreased significantly within 60 min after thawing. Cells suspended in 5% dextrose lactated Ringers solution (D5LR) maintained greater cell viability. Hepatocytes from normal liver donors showed less AST and LDH enzyme leak in comparison with cells from fatty liver donors. Mild hypothermic temperature (32 degrees C) inhibited cellular damage that otherwise significantly increased at 60 min. Hepatocytes did not proliferate until 12 h from thaw, regardless of supernatant or conditions of suspension. CYP3A4 activity and a marker for UGT 1A1 activity in hepatocytes from normal donor livers were higher than those from steatotic donor livers. These findings suggest that hepatocytes suspended for infusion after isolation from normal liver donors have normal biological functions and less cellular damage/necrosis in contrast with those isolated from fatty liver donors. These damages are inhibited significantly by maintaining hepatocytes at a mild hypothermic temperature (32 degrees C). D5LR alone maintained the best cell viability for up to 60 min. Media of D5LR + adenosine and HMM were able to partially inhibit hepatocyte apoptosis in hepatocytes from steatotic livers.

The influence of uridine diphosphate glucuronosyl transferase 1A promoter polymorphisms, beta-globin gene haplotype, co-inherited alpha-thalassemia trait and Hb F on steady-state serum bilirubin levels in sickle cell anemia

PURPOSE

Homozygosity for the (AT)7 allele of uridine diphosphate glucuronosyl transferase 1A (UGT1A1) gene polymorphism is associated with increased bilirubin levels in sickle cell anemia (SCA). In the present study, in addition to UGT1A1 promoter genotype, serum bilirubin level was related to other genetic modifiers -beta(S)-globin gene haplotype, Hb F, co-inherited alpha-thal trait, age and gender.

METHODS

The patients were randomly selected from the sickle cell clinic, Medical College of Georgia. UGT1A1 promoter polymorphisms were determined using automated sequencing. Other investigations were with standard techniques.

RESULTS

There were 67 SCA patients (41 males and 26 females), aged 2-44 yr (mean of 20.6 +/- 10.7). Ten (14.9%) patients were homozygous for the (AT)6 UGT1A1 allele, 35 (52.2%) were heterozygous for (AT)6 and (AT)7 alleles while 22 (32.8%) were homozygous for (AT)7. Serum bilirubin was significantly higher in the homozygous (AT)7 group (3.7 +/- 1.5, 3.8 +/- 2.3 and 5.6 +/- 2.4 mg/dL, respectively). It was also significantly higher in males than females and in patients aged >10 yr. There was a significant negative linear correlation (r = -0.304, P = 0.016) of serum bilirubin with Hb F. The beta-globin haplotype and co-existing alpha-thal trait did not have any significant influence on serum bilirubin levels. Patients on hydroxyurea were older, had lower Hb F, but higher mean serum bilirubin. The latter also was signifcantly higher among those with UGT1A1 (AT)7 homozygosity.

CONCLUSIONS

Apart from UGT1A1 (AT)7 homozygosity, Hb F, age and gender are the other factors that significantly influence serum bilirubin level in SCA.

Genetic rearrangements on the Chlorovirus genome that switch between hyaluronan synthesis and chitin synthesis

Chlorella viruses or chloroviruses form polysaccharide fibers on the cell wall of host Chlorella cells after infection. Such polysaccharides are either hyaluronan synthesized by virus-encoded hyaluronan synthase (HAS) or chitin synthesized by viral chitin synthase (CHS). Some chloroviruses synthesize both hyaluronan (HA) and chitin simultaneously. To understand the relationship between "HA-synthesizing" and "chitin-synthesizing" viruses, we characterized the CVK2 genomic regions, one flanking chs and the other corresponding to PBCV-1 has and found that on CVK2 DNA, a single ORF (PBCV-1 A330R) was replaced with a 5 kbp region containing chs, ugdh2 (the second gene for UDP-glucose dehydrogenase) and two other ORFs, and that has was replaced with another chs gene. In some chloroviruses, ugdh was lost. These results suggest that chlorovirus types changed from "has viruses" to "chs viruses" or from "chs viruses" to "has viruses" by exchanging the genes.

Clinical response to morphine in cancer patients and genetic variation in candidate genes

Morphine is the analgesic of choice for moderate to severe cancer pain; however, 10-30% of patients do not tolerate morphine. This study evaluated genetic variation in the mu-opioid receptor, betaarrestin2, stat6 and uridine diphosphate-glucuronysltransferase 2B7 (UGT2B7) genes, in patients who responded to morphine vs those who were switched to alternative opioids. We prospectively recruited and genotyped 162 Caucasian patients (117 controls, 39 switchers). Switchers, were more likely to carry the common allele at 1182 G/A, 5864 G/A, 8622T/C and 11143 G/A in the betaarrestin2 gene (P = 0.021, 0.043, 0.013, 0.043, respectively). Switchers had increased carriage of the T allele (-1714 C/T) and a significant difference in the allelic frequency at 9065 C/T (chi(2) = 3.86, P = 0.049) in the stat6 gene. No differences were seen in genotype or allele frequencies of SNPs in the mu-opioid receptor gene or UGT2B7 gene. This study presents novel data suggesting that variation in genes involved in mu-opioid receptor signalling influence clinical response to morphine.

Transfection assays with allele-specific constructs: functional analysis of UDP-glucuronosyltransferase variants

Adverse drug reactions (ADRs) are a major clinical problem. A rapidly growing body of evidence suggests that genetic factors, at least in part, determine individual susceptibility to ADRs. A large number of pharmacogenetic studies have identified a number of polymorphisms as predictors of drug efficacy and/or adverse events. These candidate markers should be investigated further to ascertain the underlying mechanism of action, for example, changes in the kinetic parameters of an enzyme, or transcriptional activity of a promoter region. In this chapter, we describe a transient transfection assay for the functional characterization of naturally occurring variants of UDP-glucuronosyltransferase (UGT) 1A1. This phase II drug metabolizing enzyme is involved in the glucuronidation of SN-38, an active metabolite of the anti-cancer drug irinotecan. Single-nucleotide polymorphisms of the UGT1A1 gene have been correlated to irinotecan-induced ADRs. Variant UGT1A1s are heterologously expressed in COS-1 cells and characterized in terms of the level of protein expression and enzyme kinetics.

Single Hepatic Venous Injection of Liver-Specific Naked Plasmid Vector Expressing Human UGT1A1 Leads to Long-Term Correction of Hyperbilirubinemia and Prevention of Chronic Bilirubin Toxicity in Gunn Rats

Previously, we have demonstrated that hepatic venous injection of pcDNA3hUGT1A1 expressing human bilirubin glucuronosyl transferase 1A1 (hUGT1A1) under the control of the cytomegalovirus promoter results in excretion of bilirubin glucuronides in bile and significant decrease in serum bilirubin for at least 2 weeks in the Gunn rat, an animal model of Crigler-Najjar syndrome type I. In this study we compared repeat delivery of pcDNA3hUGT1A1 with single injection of pBShUGT1A1 expressing hUGT1A1 under liver-specific regulatory control, for treatment of hyperbilirubinemia in the Gunn rat. Although repeat injections of pcDNA3hUGT1A1 consistently reduced serum bilirubin levels, the effect did not exceed 2 weeks; hUGT1A1 was detectable in livers only for 2 weeks, despite the presence of vector and transcript for at least 1 month. In contrast, injection of pBShUGT1A1 resulted in persistence of vector, transcript, and recombinant protein and sustained correction of hyperbilirubinemia for at least 8 months; furthermore, renal tubular damage, the principal manifestation of chronic bilirubin toxicity in the Gunn rat, was prevented. Sera from animals treated with pBShUGT1A1 consistently contained anti-hUGT1A1 antibodies, but a significant increase in the number of hepatic CD4(+) and CD8(+) cells was seen only in the pcDNA3hUGT1A1 group; thus liver-specific expression of hUGT1A1 may attenuate immune response. Our results provide further evidence of the feasibility of long-term correction of hepatic enzyme deficiencies with plasmid vectors optimized for expression in the liver.

Genetic variability and clinical efficacy of morphine

The individual variability of opioid pharmacology suggests that the patients' genetic disposition influences the response to opioids. Given the complexity of morphine pharmacology, variability may be caused by several genes. We review data which shows that variability in genes coding the enzyme metabolizing morphine (UGT2B7 gene), mu-opioid receptors (OPRM gene) and blood-brain barrier (BBB) transport of morphine by multidrug resistance transporters (MDR1 gene) influences the clinical efficacy of morphine. Furthermore, variability in an enzyme degrading catecholamines (COMT gene) alters the efficacy of morphine demonstrating that genetic variability in non-opioid systems may indirectly influence the clinical efficacy from morphine. Thus, results obtained so far strongly argue that opioid efficacy is partly related to inborn properties caused by genetic variability.

Successful gene therapy of the Gunn rat by in vivo neonatal hepatic gene transfer using murine oncoretroviral vectors

Crigler-Najjar type 1 disease (CN1) is a rare inherited metabolic disease characterized by complete absence of hepatic UDP-glucuronosyl transferase (UGT1), resulting in high levels of unconjugated bilirubin. CN1 is an attractive candidate disease for gene therapy. Here we show that in vivo neonatal hepatocyte transduction using recombinant oncoretroviral vectors results in long-term and complete phenotype correction in Gunn rats, a model for CN1. Two-day-old newborn Gunn rats were injected via the temporal vein with 200 microL UGT1 or control beta-galactosidase retroviral vectors. In UGT1-injected animals, bilirubinemia was normal at 6 weeks (3 micromol/L) and remained in the normal range (i.e., <10 micromol/L) for more than 34 weeks. In contrast, in beta-galactosidase-injected animals as well as in noninjected controls, bilirubinemia remained at a high level (i.e., >100 micromol/L) during the whole experimental follow-up. Large amounts of bilirubin monoglucuronides and diglucuronides were present in the bile of treated animals. Finally, polymerase chain reaction and reverse transcription polymerase chain reaction analysis as well as Western blot confirmed the presence and expression of UGT1 almost exclusively in the liver. The estimated proportion of transduced hepatocytes was in the range of 5% to 10%. In conclusion, complete and permanent correction of hyperbilirubinemia in newborn Gunn rats using retroviral vectors can be obtained, paving the way for future gene therapy for CN1.

UGT1A1 polymorphisms are important determinants of dietary carcinogen detoxification in the liver

PhIP (2-amino-1-methyl-6-phenylimidazo[4,5-f]pyridine), the most abundant heterocyclic amine in diet, is involved in the etiology of cancer. PhIP and its carcinogenic metabolite N-hydroxy-PhIP (N-OH-PhIP) are extensively conjugated by UDP-glucuronosyltransferase (UGTs) with wide variability. This study aimed to determine the genetic influence of UGTs on the hepatic detoxification of this carcinogen. The formation of N-OH-PhIP glucuronides was studied in 48 human liver samples by mass spectrometry. Liver samples were genotyped for common polymorphisms and correlated with UGT protein levels and N-OH-PhIP glucuronidation activities. The formation of four different N-OH-PhIP glucuronide metabolites was observed in all livers. The major metabolite was N-OH-PhIP-N(2)-glucuronide (N(2)G), which is the primary metabolite found in human urine, and showed a high interindividual variability (up to 28-fold). Using an heterologous expression system, the bilirubin-conjugating UGT1A1 enzyme was identified among all known UGTs (n = 16) as the predominant enzyme involved. The significant correlation between UGT1A1 protein content and formation of N(2)G (Rs = 0.87; P < .0001) suggests a critical role for UGT1A1 in the hepatic metabolism of this carcinogen. UGT1A1 expression was strongly determined by the presence of the common promoter polymorphisms, UGT1A1*28 (TATA box polymorphism) (P = .0031), -3156G/A (P = .0006) and -3279G/T (P = .0017), and rates of N(2)G were indeed correlated with these polymorphisms (P < .05), whether analyzed individually or in combination (haplotypes). In conclusion, UGT1A1 polymorphisms modulate the hepatic metabolism of the carcinogenic intermediate of PhIP and may determine the level of its exposure and potentially influence the risk of cancer through dietary exposure to HCAs.

UDP-glucuronosyltransferase 1A7 genetic polymorphisms are associated with hepatocellular carcinoma risk and onset age

OBJECTIVES

It has been demonstrated that the UDP-glucuronosyltransferase (UGT) 1A7*3 allele is a risk factor for hepatocellular carcinoma (HCC) in German and Japanese populations. In this study, therefore, we evaluated the association between UGT1A7 genetic polymorphisms and HCC risk in southern Taiwan, where hepatitis B virus (HBV) and hepatitis C virus (HCV) infections are endemic.

METHODS

The 217 HCC patients and 291 controls enrolled in this case-control study were genotyped for UGT1A7 polymorphisms using polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

Univariate logistic regression analysis revealed that presence of UGT1A7*2 and *3 alleles was associated with HCC risk [odds ratio (OR) = 1.50, 95% confidence interval (CI): 1.04 approximately 2.16 and OR = 1.73, 95% CI: 1.19 approximately 2.52, respectively]. Multiple logistic regression analysis demonstrated that significant independent risk factors for HCC were male gender (OR = 2.53, 95% CI: 1.42 approximately 4.52), HBV infection (OR = 13.73, 95% CI: 8.04 approximately 23.46), HCV infection (OR = 83.93, 95% CI: 37.01 approximately 190.32), and low-activity UGT1A7 genotype [high/low (H/L) genotype: OR = 1.93, 95% CI: 1.12 approximately 3.32; low/low (L/L) genotype: OR = 3.06, 95% CI: 1.50 approximately 6.24]. For male HCC patients, significantly earlier onset age was observed for those bearing the UGT1A7 low-activity genotype as opposed to those with the high-activity analogue (median age: 50 vs 59 yr; p < 0.05).

CONCLUSIONS

An inverse dose-response relationship was demonstrated between the detoxifying activity of the UGT1A7 genotypes and HCC. Of the male HCC patients, median onset age for those carrying an UGT1A7 low-activity genotype was 9 yr lower than those bearing the high-activity variant.

DECREASE IN SERUM THYROXINE LEVEL BY PHENOBARBITAL IN RATS IS NOT NECESSARILY DEPENDENT ON INCREASE IN HEPATIC UDP-GLUCURONOSYLTRANSFERASE

We have previously reported that there is a poor correlation between increase in the levels of UDP-glucuronosyltransferases, UGT1A1 and UGT1A6, and decrease in the levels of serum total thyroxine (T4) and free T4 in phenobarbital (PB)-treated rats, although the PB-induced decrease in rats is generally thought to occur through induction of the UDP-glucuronosyltransferase (T4-UDP-GT: UGT1A1 and UGT1A6). In the present study, to clarify a relationship between the decrease in serum T4 level and the increase in the T4-UDP-GT activity by PB in rats, we examined the relationship using Gunn rats, a mutant strain of Wistar rats deficient in UGT1A isoforms. Levels of serum total T4, free T4, and total triiodothyronine (T3) were markedly decreased not only in Wistar rats but also in Gunn rats 1 day after the final administration of PB (80 mg/kg i.p., once daily for 4 days), and no significant difference in magnitude of the decrease between Wistar and Gunn rats was observed. On the other hand, the level and activity of T4-UDP-GT were significantly increased by treatment with PB in Wistar rats but not in Gunn rats. Furthermore, significant decrease in the activity of hepatic type I iodothyronine deiodinase, which mediates the deiodination of T4 and T3, by PB treatment was observed in both Wistar and Gunn rats. In addition, no significant change in the level of serum thyroid-stimulating hormone, the activity of hepatic sulfotransferase, and the binding of [125I]T4 to serum transthyretin and albumin by PB treatment was observed in either Wistar or Gunn rats. In conclusion, the present results demonstrate that the decrease in serum total T4 level by PB in Gunn rats is not dependent on the increase in hepatic T4-UDP-GT activity and suggest that even in Wistar rats, the PB-induced decrease in serum T4 level does not occur only through increase in hepatic T4-UDP-GT.

METABOLISM OF N-HYDROXYGUANIDINES (N-HYDROXYDEBRISOQUINE) IN HUMAN AND PORCINE HEPATOCYTES: REDUCTION AND FORMATION OF GLUCURONIDES

The biotransformation of N-hydroxydebrisoquine, a model substrate for N-hydroxyguanidines, was studied in vitro with cultured and characterized porcine and human hepatocytes. The objective of the present work was to compare the N-oxidative and N-reductive metabolism of this compound using a monolayer culture system with previously described microsomal studies and to investigate the phase 2 metabolism, in particular, the glucuronidation of this class of compounds. At the same time, the suitability of pig hepatocytes as a model system for the human metabolism could be investigated. Two glucuronides of the parent compound N-hydroxydebrisoquine were analyzed. For the first time, one of these phase 2 metabolites could be identified as an O-glucuronide of an N-hydroxyguanidine by comparing it to a synthesized authentic compound. The involvement of certain human UDP-glucuronosyltransferases (UGTs) was evaluated by incubating the substrate with eight human hepatic recombinant UGT enzymes. Metabolites were determined by a newly developed LC-MS (liquid chromatography/mass spectrometry) analysis using electrospray ionization (ESI). The known microsomal reduction of the N-hydroxylated compound was also demonstrated with hepatocytes. The N-hydroxylation of the corresponding reduced compound (debrisoquine), which was previously described with microsomes, could not be detected in hepatocytes. There was no qualitative difference in the formation of the described derivatives by human and porcine hepatocytes. All phase 2 metabolites identified in hepatocyte culture were also formed by glucuronosyltransferases. In culture, the N-reduction of the N-hydroxylated substrate is the dominating reaction, indicating a predominance of N-reduction in vivo.

Severe irinotecan-induced toxicities in a patient with uridine diphosphate glucuronosyltransferase 1A1 polymorphism

Irinotecan is an analogue of camptothecin, a topoisomerase I inhibitor, that has an important role in the management of advanced colorectal cancer. It is approved as first-line therapy in combination with 5-fluorouracil and leucovorin or as monotherapy in the second-line setting. Its clinical use has been associated with variability in terms of pharmacokinetic behavior and toxicities, especially myelosuppression and diarrhea. Irinotecan is metabolized to the active compound SN-38; it is now known that the metabolism of irinotecan and the inactivation of SN-38 by glucuronidation are mediated by genetic differences, which contributes to the variability. In this article, a case is presented that illustrates this, and there is a brief discussion of the clinical pharmacology of irinotecan and some of the genetic variations that affect its cellular metabolism.

Genetic factors related to unconjugated hyperbilirubinemia amongst adults

Some variations in the UDP-glucuronosyltransferase 1A1 (UGT1A1) gene are involved in the development of unconjugated hyperbilirubinemia. We hypothesize that other genetic factors may also be associated with this disease. A total of 227 adults with normal routine haematology and liver function (apart from bilirubin testing for which they revealed bilirubin > or = 25.7 micromol/l and unconjugated bilirubin/total bilirubin > or = 80%), and 235 sex- and age-matched controls, were recruited. All subjects were analysed for UGT1A1, glucose-6-phosphate dehydrogenase (G6PD) and organic anion transporter polypeptide 2 (OATP2) genotypes using polymerase chain reaction-restriction fragment length polymorphism. The results indicated that G6PD deficiency, variant UGT1A1 gene and variant OATP2 gene were risk factors for hyperbilirubinemia. The odds ratios (OR) (with 95% confidence interval) were 220.83 (34.68-1406.30), 73.61 (17.01-318.63), 45.15 (11.19-182.22), 15.46 (4.35-54.99) and 6.51 (1.83-23.09), respectively, for individuals featuring the common UGT1A1/OATP2 haplotypes homozygous/heterozygous, compound heterozygous/heterozygous, compound heterozygous/wild-type, heterozygous/heterozygous and heterozygous/wild-type variations amongst subjects with normal G6PD activity. Amongst the subjects with G6PD deficiency, the OR was 159.00 (24.57-1028.94) for individuals carrying variations in both UGT1A1 and OATP2 genes. The UGT1A1/OATP2 haplotypes homozygous/wild-type, homozygous/compound heterozygous and homozygous/homozygous for G6PD normal and variant/wild-type for G6PD deficient individuals were only observed in the case group, and not in the control group. Amongst hyperbilirubinemic adults, bilirubin values tended to parallel variation status of their haplotypes. Adults featuring certain haplotypes in UGT1A1, OATP2 and G6PD genes face a high risk of developing unconjugated hyperbilirubinemia.

Genetic polymorphism in the phenobarbital-responsive enhancer module of the UDP-glucuronosyltransferase 1A1 gene and irinotecan toxicity

Genetic polymorphism of the UDP-glucuronosyltransferase (UGT) 1A1 gene is associated with the decreased glucuronidation activity of an active metabolite of irinotecan, SN-38, and UGT1A1*28 has been shown as a predictive factor for irinotecan toxicity. The phenobarbital-responsive enhancer module (PBREM) of the UGT1A1 promoter region has been reportedly associated with the transcriptional activity of the gene. We investigated whether the polymorphism of PBREM (T-3279G) would affect inter-patient variations in sensitivity to irinotecan toxicity. The study population comprised 119 cancer patients who had received irinotecan. We reviewed their clinical records, including patient characteristics, and observed their toxicity levels following irinotecan infusion. Genotyping was performed by sequencing analyses. Logistic regression analyses were performed to assess the relationship between genotypes and irinotecan toxicity. We identified the homozygotes of the reference allele for T-3279G in 68 patients, the heterozygotes in 37, and the homozygotes for the variant in 14. Logistic regression analysis indicated a significant association between the homozygotes for T-3279G and the severe toxicity (odds ratio 5.80; 95% confidence interval 1.67-20.1). However, multivariate analysis, including the data of UGT1A1*28 polymorphism, revealed a diminution of the association due to a highly significant linkage disequilibrium between these polymorphisms. Our results suggest that a highly significant linkage disequilibrium exists between T-3279G and UGT1A1*28 polymorphisms, and that the variants of T-3279G and UGT1A1*28 cooperatively decrease transcriptional activity of the UGT1A1 promoter. The determination of T-3279G and UGT1A1*28 genotypes might be clinically useful in predicting severe irinotecan toxicity in cancer patients.

Antisense-Mediated Suppression of Hyaluronan Synthase 2 Inhibits the Tumorigenesis and Progression of Breast Cancer

The progression of several cancers is correlated with the increased synthesis of the glycosaminoglycan, hyaluronan. Hyaluronan is synthesized at the plasma membrane by various isoforms of hyaluronan synthases (HAS). The importance of HAS2 expression in highly invasive breast cancer was characterized by the antisense inhibition of HAS2 (ASHAS2). The effect of HAS2 inhibition on cell proliferation, migration, hyaluronan metabolism, and receptor status was characterized in vitro, whereas the effect on tumorigenicity and metastasis was established in vivo. HAS2 inhibition resulted in a 24-hour lag in proliferation that was concomitant to transient arrest of 79% of the cell population in G0-G1. Inhibition of HAS2 did not alter the expression of the other HAS isoforms, whereas hyaluronidase (HYAL2) and the hyaluronan receptor, CD44, were significantly down-regulated. ASHAS2 cells accumulated greater amounts of high molecular weight hyaluronan (>10,000 kDa) in the culture medium, whereas mock and parental cells liberated less hyaluronan of three distinct molecular weights (100, 400, and 3,000 kDa). The inhibition of HAS2 in the highly invasive MDA-MB-231 breast cancer cell line inhibited the initiation and progression of primary and secondary tumor formation following s.c. and intracardiac inoculation into nude mice, whereas controls readily established both primary and secondary tumors. The lack of primary and secondary tumor formation was manifested by increased survival times where ASHAS2 animals survived 172% longer than the control animals. Collectively, these unique results strongly implicate the central role of HAS2 in the initiation and progression of breast cancer, potentially highlighting the co-dependency between HAS2, CD44, and HYAL2 expression.

Plasma membrane residence of hyaluronan synthase is coupled to its enzymatic activity

Hyaluronan is a multifunctional glycosaminoglycan up to 10(7) Da molecular mass produced by the integral membrane glycosyltransferase, hyaluronan synthase (HAS). When expressed in keratinocytes, N-terminally tagged green fluorescent protein-HAS2 and -HAS3 isoenzymes were found to travel through endoplasmic reticulum (ER), Golgi, plasma membrane, and endocytic vesicles. A distinct enrichment of plasma membrane HAS was found in cell protrusions. The total turnover time of HAS3 was 4-5 h as judged by the green fluorescent protein signal decay and hyaluronan synthesis inhibition in cycloheximide-treated cells. The transfer from ER to Golgi took about 1 h, and the dwell time on the plasma membrane was less than 2 h in experiments with a relief and introduction, respectively, of brefeldin A. Constructs of HAS3 with 16- and 45-amino-acid C-terminal deletions mostly stayed within the ER, whereas a D216A missense mutant was localized within the Golgi complex but not the plasma membrane. Both types of mutations were almost or completely inactive, similar to the wild type enzyme that had its entry to the plasma membrane experimentally blocked by brefeldin A. Inhibition of hyaluronan synthesis by UDP-glucuronic acid starvation using 4-methyl-umbelliferone also prevented HAS access to the plasma membrane. The results demonstrate that 1) a latent pool of HAS exists within the ER-Golgi pathway; 2) this pool can be rapidly mobilized and activated by insertion into the plasma membrane; and 3) inhibition of HAS activity through mutation or substrate starvation results in exclusion of HAS from the plasma membrane.

Long-term correction of hyperbilirubinemia in the Gunn rat by repeated intravenous delivery of naked plasmid DNA into muscle

We evaluated nonviral gene delivery into skeletal muscle via femoral artery and great saphenous vein for correction of hyperbilirubinemia in the Gunn rat, the animal model of Crigler-Najjar syndrome type I. A single injection of pDNA expressing hUGT1A1 under the CMV promoter resulted in excretion of bilirubin glucuronides in bile and a significant decrease in serum bilirubin for at least 2 or 4 weeks, respectively. Loss of metabolic effect was associated with a decrease in recombinant protein in muscle, while pDNA and transcript were detectable 4 weeks after gene delivery. Monthly intravenous gene delivery maintained metabolic correction for at least 5 months. Fibrosis around vessels in the arterial group limited the number of successful repeat gene transfer sessions to 3. Animals expressing hUGT1A1 developed anti-hUGT1A1 antibodies and lymphocytic infiltrate in muscle. Immunosuppression abrogated antibody response, ameliorated lymphocytic inflammation, and enhanced metabolic correction but did not prevent a decrease in the amount of recombinant protein. In conclusion, repeated intravenous delivery of pDNA into muscle enables long-term correction of hyperbilirubinemia in the Gunn rat. The procedure is safe and simple, with great clinical potential. Further studies are needed to explain the mechanisms of loss and improve the stability of recombinant hUGT1A1 in muscle.