UGT2B17 Deletion Polymorphism Research Articles

Abstract P6-13-05: Association between the UGT2B17 gene deletion, exemestane metabolites and vasomotor QOL in women participating on the MAP3 prevention trial

Abstract Background: The aromatase inhibitor Exemestane (EXE) reduces the risk of breast cancer in postmenopausal women. However, participants have varied responses to EXE treatment in terms of efficacy and toxicity, possibly due to differences in EXE metabolism. One of the main elimination pathways for EXE is through glucuronidation by UGT2B17. Aims: This project examined the relationship between the UGT2B17 gene deletion, EXE metabolites and menopause-related quality of life (QOL) in postmenopausal women. Hypothesis: Glucuronidation of the main EXE metabolite, 17-dihydroexemestane (17-DHE), is reduced in women with the UGT2B17 double gene deletion, leading to increased circulating 17-DHE and potential toxicity. Methods: This study included 3576 women nested within the CCTG MAP.3 trial, who were allocated to EXE or placebo treatment groups. Genotyping analysis was conducted with baseline blood cell DNA using real-time PCR and allelic discrimination. Women who were homozygous null were considered “exposed”. In addition to EXE, EXE metabolites including 17-DHE and glucuronidated 17-DHE (17 DHE-Gluc) were analyzed from serum by UPLC/MS. Ratios of the main metabolites (17-DHE/EXE) and glucuronidated metabolites (17-DHE-Gluc/17-DHE) were standardized, using an autoscaling method. Metabolite levels that were below the detection limit were replaced by “half the detection limit for that metabolite”. Women had the outcome if they experienced a clinically meaningful (>10%) worsening in vasomotor QOL from baseline within the first year. Modified Poisson regression models were used to calculate the relative risks for both the (1) UGT2B17 gene deletion and (2) metabolite ratios and vasomotor QOL. Results: Ten percent of participants exhibited the homozygous UGT2B17 deletion genotype. There was no significant relationship between the UGT2B17 deletion polymorphism and worsened vasomotor QOL (RR= 1.04, 95% CI: 0.93, 1.17), adjusted for age, race and treatment. Among women with no vasomotor symptoms at baseline but extremely bothersome symptoms at follow-up (incident vasomotor symptoms), there was a suggestive but non-significant protective effect of the UGT2B17 deletion (RR=0.61, 95% CI: 0.32-1.19). This effect was more extreme in the placebo arm (RR=0.20) than in the EXE arm (RR=0.78; p-interaction=0.17). Among women on EXE, levels of EXE and 17-DHE were not different between UGT2B17 genotypes, but levels of 17-DHE-Gluc were significantly lower for the UGT2B17 deletion genotype (p=<0.0001). An increasing ratio of 17-DHE-Gluc/17-DHE [per standard deviation (SD) increase] had a borderline protective effect against worsened vasomotor QOL (RR=0.94, p=0.049), adjusted for age and race. In contrast, an increasing ratio of 17-DHE /EXE (per SD increase) was associated with a small but significant increased risk of worsened vasomotor QOL (RR=1.02, p=0.01). The effect observed for the 17-DHE/EXE ratio was stronger for very bothersome incident vasomotor symptoms at follow-up, but this did not reach statistical significance [17-DHE/EXE (per SD increase): RR=1.36, p=0.12]. Conclusion: EXE metabolite levels could potentially be used as a biomarker for extreme vasomotor QOL changes in breast cancer chemoprevention settings using EXE. Citation Format: Richardson H, Knight B, Chen G, Luo S, Massey T, Goss PE, Lazarus P. Association between the UGT2B17 gene deletion, exemestane metabolites and vasomotor QOL in women participating on the MAP3 prevention trial [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-13-05.

UGT2B17 deletion polymorphism and exemestane-induced toxicity.

e12534Background: Genetic polymorphisms in drug metabolizing enzymes can have significant impact on drug toxicity and/or efficacy. Exemestane (Exe), a steroidal aromatase inhibitor, is extensively ...

Dose-dependent testosterone sensitivity of the steroidal passport and GC-C-IRMS analysis in relation to the UGT2B17 deletion polymorphism.

The newly implemented Steroid Module of the Athlete Biological Passport has improved doping tests for steroids. A biomarker included in this passport is the urinary testosterone glucuronide to epitestosterone glucuronide (T/E) ratio, a ratio greatly affected by a deletion polymorphism in UGT2B17. Suspect urine doping tests are further analyzed with gas chromatography-combustion-isotope ratio mass spectrometry (GC-C-IRMS) to determine the origin of the androgen. In this study, we investigated the sensitivity of the steroidal module and the IRMS analysis, in subjects administered with three doses of testosterone enanthate (500, 250, and 125 mg), in relation to the UGT2B17 polymorphism. All subjects carrying the UGT2B17 enzyme reached the traditionally used threshold, a T/E ratio of 4, after all three administered doses, whereas none of the subjects devoid of this enzyme reached a T/E of 4. On the other hand, using the athlete biological passport and IRMS analysis, all three doses could be detected to a high degree of sensitivity. The concentrations of all steroids included in the steroidal module were dose dependently increased, except for epitestosterone which decreased independent of dose. The decrease in epitestosterone was significantly associated with circulatory levels of testosterone post dose (rs =0.60 and p=0.007). In conclusion, these results demonstrate that administration of a single dose of 125-500 mg testosterone enanthate could be detected using the athlete biological passport, together with IRMS. Since IRMS is sensitive to testosterone doping independent of UGT2B17 genotype, also very small changes in the steroidal passport should be investigated with IRMS.

Meta-analysis reveals a lack of association between UGT2B17 deletion polymorphism and tumor susceptibility.

PurposeUGT2B17 is a vital member of the UGT2 family and functions as a detoxification enzyme which catalyzes the glucuronidation of lipophilic compounds. Accumulating evidences implicates that it may contribute to the susceptibility of tumor risk. Identification of a UGT2B17 deletion polymorphism has attracted studies to evaluate the association between the UGT2B17 deletion polymorphism and tumor risk in diverse populations. However, the available results are conflicting.MethodsA meta-analysis based on 14 studies from 10 publications including 5,732 cases and 5,112 controls was performed. Published literature from PubMed, EMBASE and Web of Science was pooled and the crude odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to estimate the strength of the associations.ResultsConclusively, our results indicate that individuals with a UGT2B17 deletion polymorphism were associated with tumor risks (OR = 1.29, 95% CI = 1.03–1.63, P<0.001) in a recessive model. However, after excluding two studies for their heterogeneity, the result then demonstrated that the UGT2B17 deletion polymorphism was not associated with tumor risks (OR = 1.118, 95%CI = 0.938–1.332, P>0.1). A subgroup analysis based on tumor type, sex or race did not show significant results.ConclusionThese results suggest that the UGT2B17 deletion polymorphism is not associated with tumor risks.

Testosterone challenge and androgen receptor activity in relation to UGT2B17 genotypes

We investigated the androgen receptor (AR) bioluminescense response in serum and urine before and after testosterone challenge in different genotypes of the UGT2B17 enzyme, which catalyses testosterone glucuronidation. The androgen receptor activity was determined using a yeast-based bioluminescence assay. The androgens were analysed using LC-MS/MS, and the individuals were genotyped for UGT2B17 deletion polymorphism using real-time polymerase chain reaction. The serum concentrations of testosterone and dihydrotestosterone (DHT) were markedly elevated on days 2 and 4 and were still above baseline on day 15 after a dose of 500mg testosterone enanthate. The androgenic activity in serum increased in parallel and correlated with the hormone concentrations and remained above baseline on day 15. The urinary androgenic activity increased 4-5-fold and was closely related to the unconjugated testosterone and independent of the UGT2B17 genotype. The AR assay may serve as a complement to the urinary testosterone/epitestosterone (T/E) doping test, because this is profoundly influenced by the UGT2B17 deletion polymorphism. It may also be useful for detection of other illicit androgens in sports, or in the society, or for monitoring and diagnostics of androgen-related disorders.

Implication of Human UGT2B7, 2B15, and 2B17 in 19-Norandrosterone Metabolism

Nandrolone (19-nortestosterone) is an anabolic androgenic steroid commonly abused for doping purposes. Nandrolone is mainly metabolized in the liver into 19-norandrosterone prior to glucuronidation and excretion through urine over an extended period of time. Several UGTs (i.e., UGT2B7, UGT2B15, and UGT2B17) are thought to be the major enzymes responsible for conjugation of androgens in human. An in vitro study using recombinant enzymes expressed in insect cells showed that UGT1A4 and UGT2B7 are the two main enzymes responsible of 19-norandrosterone glucuronidation. However, the identity of the enzyme involved in nandrolone metabolism in vivo together with their relative contribution and regulation remain unknown. Inhibition assays using human liver microsomes (HLM) incubated with 19-norandrosterone and selective inhibitors confirmed that UGT2B7 and UGT2B15 are involved in 19-norandrosterone glucuronidation, since the presence of the specific UGT2B7 and UGT2B15 inhibitors gemfibrozil and valproic acid inhibited the 19-norandrosterone glucuronidation by 35 and 45%, respectively. HLM were genotyped for UGT2B15 D85Y, UGT2B7 H268Y, and the UGT2B17 deletion polymorphism. The glucuronidation activity on 19-norandrosterone was significantly higher in UGT2B15 DD than in the other UGT2B15 genotypes (p < 0.05). Moreover, human liver cancer HepG2 cells were exposed to androgens to determine if the transcriptional activity of the genes of interest was affected. Only UGT2B7 mRNA expression was significantly increased (1.8-folds) after incubation with nandrolone decanoate. These results show that the UGT2B7 and UGT2B15 are involved in 19-norandrosterone glucuronidation and that the UGT2B15 polymorphism (D85Y) is the only UGT genetic variation that influences the glucuronidation activity. This could partly explain the inter-individual variation in 19-norandrosterone excretion.

UGT2B17 Genotype and the Pharmacokinetic Serum Profile of Testosterone during Substitution Therapy with Testosterone Undecanoate. A Retrospective Experience from 207 Men with Hypogonadism

Background: Testosterone (T) is mainly excreted in the urine as testosterone glucuronide (TG). This glucuronidation is partly dependent on the UGT2B17 genotype, and TG excretion is therefore lower in men having the UGT2B17 deletion. However, the possible influence of UGT2B17 genotype on serum T during androgen therapy is unknown. We retrospectively investigated the possible association between the UGT2B17 gene polymorphism and serum T levels in hypogonadal men during Testosterone undecanoate (TU) substitution therapy.Subjects and Methods: Two hundred and seven patients treated with TU (Nebido®) were genotyped by quantitative polymerase chain reaction for the UGT2B17 deletion polymorphism. All were given 1000 mg TU per injection at 0, 6, and 18 weeks. Blood samples were taken 2 and 6 weeks after the first and second injection, prior to the third injection, and after 2–3 years of treatment. We analyzed for the levels of T, luteinizing hormone (LH), sex-hormone-binding globulin, estradiol, prostate specific antigen, hematocrit, hemoglobin, and total cholesterol.Results: The UGT2B17 genotype frequency was: ins/ins: 42%, ins/del: 44%, and del/del: 14%. During the initial 18 weeks of TU treatment, large intra- and inter-individual variations in serum T levels were observed. Large peaks in T levels, ranging from 6.7 to 69.5 nmol/l, were noted 2 weeks after injections, regardless of the genotype. T levels did not differ between the three genotypes prior to the third injection, but the del/del group had significantly lower levels of LH. At follow-up after 2–3 years, the injection interval or daily T dosage was not dependent on the UGT2B17 genotype.Conclusion: In conclusion, we found large intra- and inter-individual variations in serum T during standard TU treatment regimen in hypogonadal men. Only subtle differences in serum T and LH were noted according to UGT2B17 genotype, which however suggest that the UGT2B17 genotype exert modest influence on the pharmacokinetic profile of T after TU treatment.

Tissue Distribution and Relative Gene Expression of UDP-Glucuronosyltransferases (2B7, 2B15, 2B17) in the Human Fetus

UDP-glucuronosyltransferases (UGTs) catalyze phase II conjugation reactions and play an important role in the inactivation and elimination of several drugs. It is well known that the UGT activity in fetal livers is low compared with the UGT activity in adult livers. In this study the mRNA expression levels of the three human subfamilies, 2B7, 2B15, and 2B17, were determined in 20 adult and 60 fetal liver tissue specimens. The expression profile in fetal kidneys (N = 43), adrenals (N = 46), and lungs (N = 37) was also determined. All fetal and adult samples were genotyped for the UGT2B17 deletion polymorphism. Adult liver contained 13-36 times higher levels of UGT2B mRNAs as compared with fetal livers. UGT2B7 was most abundant in fetal lungs and kidneys, whereas UGT2B15 and UGT2B17 were predominant in the liver. There was a significant correlation between UGT2B7 expression levels in lungs and kidneys, whereas for the other UGT2Bs no correlation between the different tissues was observed. Fetuses expressing two UGT2B17 alleles (ins/ins) displayed significantly higher levels of UGT2B17 mRNA compared to ins/del fetuses in lungs, whereas in the other tissues no gene dose-effect was observed.

Doping and Genetic Testing: Sex Difference in UGT2B15 Expression, Testosterone Glucuronidation Activity and Urinary Testosterone/ Epitestosterone Glucuronide Ratio

Doping with testosterone is conventionally detected by urinary assay of the testosterone/epitestosterone (T/E) glucuronide ratio. This ratio is strongly associated with a deletion polymorphism in the UDP-glucuronosyltransferase (UGT) 2B17 gene. The metabolism of certain UGT specific drugs has been shown to be different in men and women. The objective of this study was to evaluate the impact of gender as well as human genetic variation on testosterone metabolism and the T/E ratio. We also carried out legal and policy analysis of the extant regulatory documents with a view to assess their preparedness for the introduction of genetic testing to the field of doping, and interpretation of doping related tests in the future. Testosterone glucuronidation rate was measured in female and male liver microsomes and analyzed with HPLC. UGT2B15 mRNA was measured in human liver samples using real-time PCR. Elite athletes participating in different endurance sports were genotyped for the UGT2B17 deletion polymorphism and compared with their urinary T/E ratio. The testosterone glucuronidation rate was 1.7 times higher in male than in female liver microsomes (p <0.05). Male del/del livers had significantly higher expression of UGT2B15 compared to female del/del livers (p <0.05). Men, but not women, seem to compensate for their lack of UGT2B17 activity with increased UGT2B15 expression. The T/E ratios in males, but not in females, are strongly associated with the UGT2B17 ins/ins and ins/del genotype (p <0.05).The results presented herein directly inform the ways in which doping tests may have to be designed and interpreted in the future so as to take into account host (athletes’) individual characteristics and gene-by-gender interactions. Additionally we suggest that the current legal and policy frameworks are in need of substantive amendment if the field of doping testing is to benefit from advances in genomics technologies and personalized medicine. Keywords: Androgens, doping and genetic testing convergence, sex difference, legal and technology policy analysis, sports medicine, T/E ratio, testosterone, UGT2B17

Bioavailability of testosterone enanthate dependent on genetic variation in the phosphodiesterase 7B but not on the uridine 5′-diphospho-glucuronosyltransferase (UGT2B17) gene.

To study the disposition of serum testosterone and seven of its metabolites before and after 2 days of an intramuscular dose (500 mg) of testosterone enanthate in relation to the phosphodiesterase (PDE7B) and the uridine 5'-diphospho-glucuronosyltransferase (UGT2B17) genotypes. Patients were genotyped for UGT2B17 deletion polymorphism and single nucleotide polymorphisms in the PDE7B gene. The involvement of PDE7B in hydrolysis of enanthate was assessed in human liver homogenates. Genetic variation in the PDE7B gene was found to be associated with the serum level of testosterone. Individuals homozygous for PDE7B rs7774640 G allele had a smaller increase (2.5-fold) in the serum testosterone levels compared with carriers of the A allele (3.9-fold, P=0.0006). In addition, genetic variation in the PDE7B gene significantly influences the testosterone/epitestosterone ratio, a biomarker of testosterone doping. Our in-vitro incubation studies confirmed that PDE7B serves as a catalyst of the hydrolysis of testosterone enanthate. The UGT2B17 deletion polymorphism did not show any significant association with serum testosterone levels or the other androgen metabolites investigated. We have shown that PDE7B is involved in the hydrolysis of testosterone enanthate and that genetic variation in the PDE7B gene is a determinant of the systemic levels of testosterone after administration of testosterone enanthate. It is reasonable to believe that the genetic variation in testosterone bioavailability may be correlated to varying effects of this androgen, whether it is used for replacement therapy or abused in doping. Thus our results may be important to consider in doping test programmes and in therapeutics with androgens and other esterified drugs.

Characterization of 17-dihydroexemestane glucuronidation: potential role of the UGT2B17 deletion in exemestane pharmacogenetics.

Exemestane is a third-generation aromatase inhibitor used in the treatment of breast cancer in postmenopausal women. Reduction to form 17-dihydroexemestane and subsequent glucuronidation to exemestane-17-O-glucuronide is a major pathway for exemestane metabolism. The goal of this study was to analyze 17-dihydroexemestane anti-aromatase activity, characterize the 17-dihydroexemestane glucuronidation pathway, and determine whether the functional polymorphisms in active UGTs could play a role in altered 17-dihydroexemestane glucuronidation. Homogenates from a HEK293 aromatase-overexpressing cell line (HEK293-aro) were used to examine exemestane versus 17-dihydroexemestane anti-aromatase activities. UGT-overexpressing cell lines and a panel (n=110) of human liver microsome (HLM) were screened for glucuronidation activity against 17-dihydroexemestane. UGT2B17 genotyping and liver mRNA expression were performed by real-time PCR. The inhibition of estrone formation from androst-4-ene-3,17-dione in HEK293-aro cell homogenates was similar for 17-dihydroexemestane (IC(50)=2.3±0.83 μmol/l) and exemestane (IC(50)=1.4±0.42 μmol/l). UGTs 2B17 and 1A4 were high-expression hepatic UGTs that exhibited activity against 17-dihydroexemestane, with UGT2B17 exhibiting a 17-fold higher V(max)/K(M) than UGT1A4. The rate of exemestane-17-O-glucuronide formation was shown to be significantly (P<0.001) decreased (14-fold) in HLMs exhibiting the UGT2B17(*2/*2) deletion genotype versus wild-type UGT2B17(*1/*1) HLMs; a 36-fold lower V(max)/K(M) (P=0.023) was observed in UGT2B17(*2/*2) versus UGT2B17(*1/*1) HLMs. A significant (P<0.0001, R(2)=0.72) correlation was observed between HLM exemestane-17-O-glucuronide formation and liver UGT2B17 expression. These data suggest that 17-dihydroexemestane is an active metabolite of exemestane and that the UGT2B17 deletion polymorphism could play an important role in determining levels of excretion of 17-dihydroexemestane and overall exemestane metabolism.

The Uridine Diphosphate Glucuronosyltransferase 2B15 D85Y and 2B17 Deletion Polymorphisms Predict the Glucuronidation Pattern of Androgens and Fat Mass in Men

Previous in vitro studies have demonstrated that the UDP glucuronosyltransferase (UGT)2B15 and UGT2B17 glucuronidate androgens and their metabolites. Our objective was to determine in vivo whether the UGT2B15 D85Y and the UGT2B17 deletion polymorphisms predict androgen glucuronidation and body composition. Two population-based cohorts including young adult (n = 1068; age = 18.9 yr) and elderly (n = 1001; age = 75.3 yr) men were included in the study. Serum and urine levels of testosterone (T) and dihydrotestosterone (DHT) were measured by gas chromatography-mass spectrometry, and serum levels of the major glucuronidated androgen metabolites androstane-3alpha,17beta-diol(androstanediol)-3-glucuronide, androstanediol-17-glucuronide, and androsterone-glucuronide were measured by liquid chromatography-tandem mass spectrometry. Body composition was measured by dual-energy x-ray absorptiometry. Both the UGT2B15 D85Y and the UGT2B17 deletion polymorphisms were associated with serum levels of androstanediol-17-glucuronide (P < 0.001) but not with levels of androstanediol-3-glucuronide or androsterone-glucuronide in both cohorts. Glucuronidation of T and DHT was associated with the UGT2B17 deletion but not with the UGT2B15 D85Y polymorphism, suggested by strong associations between the deletion polymorphism and urine levels of these two hormones. Both polymorphisms were associated with several different measures of fat mass (P < 0.01). The UGT2B17 deletion polymorphism was associated with insulin sensitivity (P < 0.05) as indicated by the homeostasis model assessment index. The UGT2B15 D85Y and the UGT2B17 deletion polymorphisms are both predictors of the glucuronidation pattern of androgens/androgen metabolites. Our findings indicate that UGT2B17 is involved in 17-glucuronidation of mainly T but also of DHT and androstanediol and that UGT2B15 is involved in the 17-glucuronidation of androstanediol. Furthermore, these two polymorphisms are predictors of fat mass in men.

Deletion polymorphism of the UGT2B17 gene is associated with increased risk for prostate cancer and correlated to gene expression in the prostate

Metabolism of androgens includes glucuronidation, the major pathway of steroid elimination in several steroid target tissues. Glucuronidation is catalysed by UDP-glucuronosyltransferases (UGTs). UGT2B17 has been shown to be particularly active against androgens and is highly abundant in the prostate. Recently, we discovered that deletion of the UGT2B17 gene is associated with low or undetectable urinary testosterone levels. Here, we determined the phenotypic outcome of the deletion by quantifying the UGT2B17 mRNA expression in normal prostate tissues in individuals with different genotypes. Additionally, the frequency of UGT2B17 deletion polymorphism was studied in a Swedish population-based case-control study including 176 patients diagnosed with prostate cancer and 161 controls. We found that the individuals homozygous for the insertion allele expressed 30 times more UGT2B17 mRNA in prostate tissue than the heterozygotes. Carriers of the deletion allele had a significantly increased risk of prostate cancer (OR=2.07; 95% CI=1.32-3.25). In conclusion, these results show the UGT2B17 deletion polymorphism is associated with prostate cancer risk.

The UGT2B17 gene deletion polymorphism and risk of prostate cancer : A case–control study in Caucasians

Background: UDP-glucuronosyltransferase (UGT) 2B17 is a phase II metabolizing enzyme that mediates the glucuronidation of C 19 steroids. A deletion polymorphism in the UGT2B17 gene is associated with a substantial reduction in glucuronidation activity in vitro. Methods: We examined the association between the UGT2B17 deletion polymorphism and the risk of incident prostate cancer in a population-based study from central Arkansas that included 411 Caucasian cases and 397 Caucasian controls. We developed a novel high-throughput procedure that uses real-time PCR and allelic discrimination for genotyping analysis. Results: The prevalence of the UGT2B17 deletion [(0/0)] was 12% in the controls, which was consistent with previous population estimates and with Hardy Weinberg equilibrium. There was no association between the UGT2B17 deletion polymorphism and prostate cancer risk in unconditional logistic regression analysis. Compared to the wild-type group (+/+), the adjusted odds ratio (OR) was 0.89 (95% CI = 0.55–1.45) for the homozygous deletion (0/0), and the OR was 0.99 (95% CI = 0.73–1.35) for the heterozygote group (+/0). Conclusion: These findings show that the UGT2B17 deletion polymorphism is not associated with prostate cancer risk in Caucasians.

Large Differences in Testosterone Excretion in Korean and Swedish Men Are Strongly Associated with a UDP-Glucuronosyl Transferase 2B17 Polymorphism

The reproductive endocrinology in Asians and Caucasians is of great interest in view of large differences in prostate cancer rate and sensitivity to pharmacological male contraception. In addition, interpretation of certain antidoping tests is confounded by interethnic variation in androgen disposition. Uridine diphosphoglucuronosyl transferases have a key role in the homeostasis and metabolism of androgens. Recently a deletion polymorphism was detected in the UGT2B17 gene. The objective of the study was to evaluate the contribution of the UGT2B17 deletion polymorphism to the interindividual and interethnic variation of androgen metabolism and excretion. Urine from 122 Swedish and 74 Korean healthy men was analyzed for several androgen glucuronides including testosterone. The distribution of the natural logarithms of urinary testosterone concentrations showed a distinct bimodal pattern in both groups, suggesting a monogenic inheritance. When the UGT2B17 genotypes were compared with urinary testosterone levels, all of the individuals of the UGT2B17 homozygous deletion/deletion genotype had no or negligible amounts of urinary testosterone. The deletion/deletion genotype was seven times more common in the Korean (66.7%) than the Swedish population (9.3%). In addition, the Swedes had significantly higher levels of serum testosterone, compared with the Koreans. Our results show that the UGT2B17 polymorphism is strongly associated with the bimodal distribution of the testosterone excretion and also with the large differences in testosterone excretion between Koreans and Swedes.

Genotype–phenotype correlation between the polymorphic UGT2B17 gene deletion and NNAL glucuronidation activities in human liver microsomes

The nicotine-derived tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), is one of the most potent and abundant procarcinogens found in tobacco and tobacco smoke, and glucuronidation of its major metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), is an important mechanism for NNK detoxification. In cigarette smokers and tobacco chewers, there is a wide variation in the urinary levels of the ratio of NNAL to NNAL glucuronide (NNAL-Gluc). To determine whether genetic variation plays a potential role in this inter-individual variability, NNAL-glucuronidating activities were analysed in a series of human liver microsomal specimens and compared with UGT2B17 deletion genotypes in the same subjects. Assays performed in vitro demonstrated that over-expressed UGT2B17 exhibits high O-glucuronidating activity against NNAL. When stratifying subjects by UGT2B17 genotype, a significant or near-significant decrease in NNAL-O-Gluc formation was observed in liver microsomes from individuals who were either heterozygous [(+/0), P=0.07] or homozygous [(0/0), P=0.016] for the UGT2B17 deletion compared to liver microsomes from individuals with intact UGT2B17 alleles [(+/+)]. There was a significant (P<0.01) association between the level of liver microsomal NNAL-O-glucuronide formation and increasing numbers of the UGT2B17 null alleles in the liver microsomal specimens examined in this study, and a significant decrease in NNAL-O-Gluc formation was observed when comparing liver microsomes from individuals who had at least one UGT2B17 allele deleted [(+/0)+(0/0)] versus microsomes from UGT2B17 (+/+) subjects (P=0.004). When stratifying by the median value of NNAL-O-Gluc formation activity, a significantly (P=0.015) higher number of subjects with liver microsomes having low NNAL-O-Gluc formation activity contained the UGT2B17 null genotype compared to subjects with liver microsomes exhibiting high NNAL-O-Gluc formation activity. When stratifying by UGT2B7/UGT2B17 haplotypes, the association between the level of liver microsomal NNAL-O-glucuronide formation and increasing numbers of the UGT2B17 null allele was at the level of statistical significance for subjects with the UGT2B7 (*1/*2) (P=0.05) or UGT2B7 (*2/*2) (P<0.02) genotypes. These data suggest that the UGT2B17 deletion polymorphism is associated with a reduced rate of NNAL detoxification in vivo and may increase individual susceptibility to tobacco-related cancers.

Characterization of a common deletion polymorphism of the UGT2B17 gene linked to UGT2B15

Members of the human UDP-glucuronosyltransferase 2B family are located in a cluster on chromosome 4q13 and code for enzymes whose gene products are responsible for the normal catabolism of steroid hormones. Two members of this family, UGT2B15 and UGT2B17, share over 95% sequence identity. However, UGT2B17 exhibits broader substrate specificity due to a single amino acid difference. Using gene-specific primers to explore the genomic organization of these two genes, it was determined that UGT2B17 is absent in some human DNA samples. The gene-specific primers demonstrated the presence or absence of a 150 kb genomic interval spanning the entire UGT2B17 gene, revealing that UGT2B17 is present in the human genome as a deletion polymorphism linked to UGT2B15. Furthermore, it is shown that the UGT2B17 deletion polymorphism shows Mendelian segregation and allele frequencies that differ between African Americans and Caucasians.