PXR Polymorphisms Research Articles

Association of polymorphism of CYP3A4, ABCB1, ABCC2, ABCG2, NFKB1, POR, and PXR with the concentration of cyclosporin A in allogeneic haematopoietic stem cell transplantation recipients

Cyclosporin a (CsA) was characterized by a narrow therapeutic window and high interindividual pharmacokinetic variability. In this study, we aimed to identify the association of CYP3A4, ABCB1, ABCC2, ABCG2, NFKB1, POR, and PXR polymorphisms with CsA concentrations in patients with allogeneic haematopoietic cell transplantation (allo-HSCT) based on the route of administration. A total of 40 allo-HSCT recipients receiving CsA were genotyped for CYP3A4, ABCB1, ABCC2, ABCG2, NFKB1, POR, and PXR polymorphisms. The correlation between polymorphisms and CsA concentration was analysed. The CsA dose-adjusted trough concentration (Cssmin/D) of oral or intravenous administration was significantly different (p < 0.001). For CsA Cssmin/D of intravenous administration, CYP3A4 rs2246709 (p = 0.015), ABCC2 rs717620 (p = 0.024), ABCG2 rs2231142 (p = 0.042), PXR rs3732359 (p = 0.008), PXR rs3814058 (p = 0.028) and PXR rs6785049 (p < 0.001) had a significant effect on CsA Cssmin/D. For CsA Cssmin/D of oral administration, ABCC2 rs717620 (p = 0.009) and ABCG2 rs2231142 (p = 0.011) had a significant effect on CsA Cssmin/D. These results illustrated that the CYP3A4, ABCC2, ABCG2, and PXR genotypes were closely correlated with CsA Cssmin/D, suggesting these SNPs were suitable for determining the appropriate dose of CsA.

Variability of voriconazole concentrations in patients with hematopoietic stem cell transplantation and hematological malignancies: influence of loading dose, procalcitonin, and pregnane X receptor polymorphisms.

Voriconazole (VCZ) displays highly variable pharmacokinetics affecting treatment efficacy and safety. We aimed to identify the factors affecting VCZ steady-state trough concentration (Cssmin) to provide evidence for optimizing VCZ treatment regimens. A total of 510 Cssmin of 172 patients with hematopoietic stem cell transplantation and hematologic malignancies and their clinical characteristics and genotypes of FMO, POR, and PXR were included in this study. In univariate analysis, the standard loading dose of VCZ significantly increased the Cssmin of VCZ (P < 0.001). The Cssmin of VCZ was significantly correlated with patients' total bilirubin (TB) (P < 0.001) and procalcitonin (PCT) (P < 0.001). FMO3 rs2266780 (P = 0.025), POR rs10954732 (P = 0.015), PXR rs2461817 (P = 0.010), PXR rs7643645 (P = 0.003), PXR rs3732359 (P = 0.014), PXR rs3814057 (P = 0.005), and PXR rs6785049 (P = 0.013) have a significant effect on Cssmin of VCZ. Loading dose, TB, PCT level, and PXRrs3814057 polymorphism were independent influencing factors of VCZ Cssmin in the analysis of multivariate linear regression. And loading dose, PCT, and PXR rs3814057 had significant effects on the probability of the therapeutic window of VCZ. The high variability of VCZ Cssmin may be partially explained by loading dose, liver function, inflammation, and PXR polymorphisms. This study suggests the VCZ standard loading dose regimen significantly increased Cssmin and probability of the therapeutic window providing treatment benefits. Patients in the high PCT group may be more likely to exceed 5.5μg/mL, thus suffering from VCZ toxicity.

PXR polymorphisms have impact on the clinical efficacy of clopidogrel in patients undergoing percutaneous coronary intervention

BackgroundsClopidogrel is widely used in Coronary Heart Disease (CHD) patients undergoing percutaneous coronary intervention (PCI) to prevent thrombotic events. However, clopidogrel response variability (CRV) may affect the patients' clinical outcomes. The current data have shown that genetic factors play an important role in CRV. The aim of this research is to investigate the association of pregnane X receptor (PXR, also called NR1I2) genetic polymorphisms with the clinical efficacy of clopidogrel in patients undergoing PCI. MethodsA total of 384 patients undergoing PCI were recruited and treated with dual antiplatelet therapy (DAPT) for 12 months. The plasma concentration of clopidogrel carboxylic acid metabolites (CLPM) was measured by High Performance Liquid Chromatography (HPLC). The maximum aggregation rate (MAR) of platelet were measured by PL-11 analyzer. PXR genetic polymorphisms were determined by Sequenom MassArray system. The clinical outcomes were observed by readmission, outpatient and calling back interview within 12 months after PCI. ResultsAmong all 384 patients, a total of 153 patients were occurred with major adverse cardiovascular events (MACE), 29 patients were occurred with bleeding events, the other patients had a favorable prognosis. The polymprphisms of PXR rs3814057A > C [OR(95%CI): 0.71(0.527–0.957), P = 0.024], rs3814058T > C [OR (95%CI): 1.395(1.034–1.883), P = 0.029] and rs6785049 A > G [OR(95%CI): 0.724 (0.535–0.979), P = 0.036] were significantly associated with MACE. The haplotype h1 (GCC) was associated with a higher risk of MACE [OR (95%CI): 1.385 (1.028–1.866), P = 0.031]. Whereas, the haplotype h2 (AAT) was associated with a lower risk of MACE [OR (95%CI): 0.711(0.525–0.962), P = 0.027]. ConclusionsThe genotypes and haplotypes of PXR rs3814057, rs3814058 and rs6785049 have impact on the MACE in clopidogrel treated patients after PCI.

Treatment response to unboosted atazanavir in combination with tenofovir disoproxil fumarate and lamivudine in human immunodeficiency virus-1-infected patients who have achieved virological suppression: A therapeutic drug monitoring and pharmacogenetic study

Treatment response to switch regimens containing unboosted atazanavir and tenofovir disoproxil fumarate (TDF)/lamivudine guided by therapeutic drug monitoring in human immunodeficiency virus-infected patients is rarely investigated. Consecutive patients with plasma human immunodeficiency virus RNA load<200copies/mL switching to unboosted atazanavir plus zidovudine-lamivudine (coformulated), abacavir-lamivudine (coformulated), or TDF/lamivudine>3months were included for determinations of treatment response, plasma atazanavir concentrations, and single-nucleotide polymorphisms of MDR1, PXR, and UGT1A1 genes from 2010 to 2014. Treatment failure was defined as either discontinuation of atazanavir for any reason or plasma viral load ≥200copies/mL within 96weeks. During the study period, 128 patients switched to unboosted atazanavir with TDF/lamivudine (TDF group) and 186 patients switched to unboosted atazanavir with two other nucleoside reverse-transcriptase inhibitors (non-TDF group). There were no statistically significant differences in the distributions of single-nucleotide polymorphisms of MDR1 (2677 and 3435), PXR genotypes (63396), and UGT1A1*28 between the two groups. Recommended plasma atazanavir concentrations were achieved in 83.5% and 64.9% of the TDF group and non-TDF group, respectively (p<0.01). After a median follow-up duration of 96.0weeks, treatment failure occurred in 19 (14.9%) and 34 (18.3%) patients in the TDF group and non-TDF group, respectively (p=0.60). Low-level viremia (40-200 copies/mL) before switch (adjusted hazard ratio, 2.12; 95% confidence interval, 1.12-4.01) and without therapeutic drug monitoring (adjusted hazard ratio, 2.08; 95% confidence interval, 1.16-3.73) were risk factors for treatment failure. Switch to unboosted atazanavir with TDF/lamivudine achieves a similar treatment response to that with two other nucleoside reverse-transcriptase inhibitors in patients achieving virological suppression with the guidance of therapeutic drug monitoring.

Functional variants inPXRare associated with colorectal cancer susceptibility in Chinese populations

BackgroundAs an important member of the steroid nuclear receptor family, recent research has suggested that PXR may play important roles in the development of multiple cancers. However, no well-designed studies has been conducted to investigate the associations between genetic polymorphisms of PXR and colorectal cancer (CRC) risk in Chinese populations. Materials and methodsWe performed a hospital-based case–control analysis to assess two genetic polymorphisms in the 3′-untranslated regions (3′-UTR) via allele-specific MALDI-TOF mass spectrometry assay and evaluated the associations between two polymorphisms and risk of CRC. ResultsThe PXR rs3814058C>T polymorphism was significantly associated with a higher risk of CRC (P<10–3), and the CT/TT variant genotypes had an increased CRC risk (adjusted odds ratio=1.54, 95% confidence interval=1.27–1.83) comparing CC genotype. In stratified analyses, rs3814058CT+TT genotypes was associated with increased risk among alcohol consumers (P=0.002). In vitro experiments indicated that the rs3814058C to rs3814058T transition gained a new binding of the microRNA hsa-miR-129-5p and decreased the PXR expression. ConclusionsOur data suggest that the functional polymorphism rs3814058C>T in 3′-UTR of PXR may be a functional biomarker to predict risk of CRC.

GW26-e1255 Genetic Polymorphisms of PXR and POR are Associated with Increased Warfarin Maintenance Dose in Han Chinese

GW26-e1255 Genetic Polymorphisms of PXR and POR are Associated with Increased Warfarin Maintenance Dose in Han Chinese

PXR polymorphisms and their impact on pharmacokinetics/pharmacodynamics of repaglinide in healthy Chinese volunteers

CYP3A4 is the main isoform of cytochrome P450 oxidases involved in the metabolism of approximately 60 % drugs, and its expression level is highly variable in human subjects. CYP3A4 is regulated by many transcription factors, among which the pregnane X receptor/steroid and xenobiotic receptor (PXR/SXR, NR1I2) have been identified as the most critical. Genetic polymorphisms (such as SNPs) in PXR may affect the expression level of CYP3A4. Although numerous SNPs have been identified in PXR and have appeared to affect PXR function, their impact on the expression of CYP3A4 in human subjects has not been well studied. Thus, a clinical study in healthy Chinese subjects was conducted to investigate the impact of PXR polymorphisms on repaglinide (an endogenous marker for CYP3A4 activity) pharmacokinetics used alone or in combination with a PXR inducer, flucloxacillin. Two SNPs, -298A>G and 11193T>C, were identified as the tag SNPs to represent the overall genetic polymorphic profile of PXR. To evaluate the potential functional change of these two SNPs, 24 healthy subjects were recruited in a pharmacokinetics/pharmacodynamics study of repaglinide with or without flucloxacillin. The pharmacokinetic parameters including AUC and T1/2 were significantly different among the PXR genotype groups. The SNPs of -298G/G and 11193C/C were found to be associated with a lower PXR activity resulting in reduction of CYP3A4 activity in vivo. After administration of flucloxacillin, a significant drug-drug interaction was observed. The clearance of repagnilide was significantly increased by concomitant flucloxacillin in a genotype dependent manner. The subjects with SNPs of -298G/G and 11193C/C appeared to be less sensitive to flucloxacillin. Our study results demonstrated for the first time the impact of genetic polymorphisms of PXR on the PK and PD of repaglinide, and showed that subjects with genotype of -298G/G and 11193C/C in PXR has a decreased elimination rate of 3A4/2C8. Furthermore, flucloxacillin was able to induce 3A4/2C8 expression mediated by PXR in a genotype dependent manner.

Genetic Variability of PXR in Saudi Arabians

Polymorphisms in the PXR gene play important roles in influencing the efficacy and toxicity of a large number of endogenous and exogenous substrates. Because of ethnic specificity, several studies have been directed toward the determination of PXR polymorphisms in various populations. In the current study, we determined the genotype and allele frequencies of 19 coding and regulatory polymorphisms in the PXR gene in Saudi Arabians by direct sequencing. Our results show that the frequencies of the regulatory PXR SNPs in Saudi Arabians differ from those in other ethnic groups, and the results endorse the commonly seen ethnic pattern of a paucity of the PXR coding SNPs.

Influence of MDR1 C1236T polymorphism on lopinavir plasma concentration and virological response in HIV-1-infected children

BackgroundVariability in MDR1 and PXR has been associated with differences in drug plasma levels and response to antiretroviral therapy. We investigated whether polymorphisms in MDR1 (T-129C, C1236T and C3435T) and PXR (C63396T) affect lopinavir plasma concentration and the virological or immunological response to HAART in HIV-1-infected children. MethodsGenotypes were identified in 100 blood donors and 38 HIV-1-infected children. All children received HAART with lopinavir boosted with ritonavir (LPV/r) at the time of LPV plasma level quantification, before (Ctrough) and between 1 and 2h after (Cpost-dose) the administration of the next dose of drug. CD4+ T-cell counts and plasma viral load were analyzed before and after the initiation of LPV/r. ResultsMDR1 1236T, MDR1 3435T and PXR 63396T alleles showed a frequency of ~50% while the MDR1 -129C allele only reached 5%. Children heterozygotes 1236CT showed a significantly lower LPV Cpost-dose than homozygotes 1236TT (median Cpost-dose=3.04μg/ml and 6.50μg/ml, respectively; p=0.016). Children heterozygotes 1236CT also had a lower decrease of viral load after 36weeks of LPV/r exposure compared with homozygotes 1236CC (median viral load changes=−0.50log10 copies/ml and −2.08log10 copies/ml, respectively; p=0.047). No effect on the immunological response was observed for polymorphisms of MDR1 or PXR. ConclusionsOur results suggest that the MDR1 C1236T SNP significantly reduces LPV plasma concentration affecting the virological response to HAART. Heterozygotes 1236CT might have an altered level of P-gp expression/activity in enterocytes and CD4+ T lymphocytes that limits the absorption of LPV leading to an impaired virological suppression.

PXR Polymorphisms Interacted With CYP2B6 Polymorphisms on Methadone Metabolites

Tsai, Hui-Ju MPH, PhD; Wang, Sheng-Chang MD, MS; Tian, Jia-Ni MS; Chang, Tsung-Kai MS; Ho, Ing-Kang PhD; Hsiao, Chin-Fu PhD; Chen, Chia-Hui MD; Tan, Happy Kuy-Lok MD; Lin, Linen MD; Wu, Chi-Shin MD, MS; Su, Lien-Wen MD; Huang, Chieh-Liang MD; Yang, Yi-Hong MD; Liu, Ming-Lun MD; Lin, Keh-Ming MD, MPH; Liu, Yu-Li PhD Author Information

PXR Polymorphisms Interacted With CYP2B6 Polymorphisms on Methadone Metabolites

PXR Polymorphisms Interacted With CYP2B6 Polymorphisms on Methadone Metabolites

PXR and CAR single nucleotide polymorphisms influence plasma efavirenz levels in South African HIV/AIDS patients

BackgroundThis study investigated variation in NR1I2 and NR1I3 and its effect on plasma efavirenz levels in HIV/AIDS patients. Variability in plasma drug levels has largely led research on identifying causative variants in drug metabolising enzyme (DME) genes, with little focus on the nuclear receptor genes NR1I2 and NR1I3, coding for PXR and CAR, respectively, that are involved in regulating DMEs.Methods464 Bantu-speaking South Africans comprising of HIV/AIDS patients on efavirenz-based treatment (n=301) and 163 healthy subjects were genotyped for 6 SNPs in NR1I2 and NR1I3. 32 of the 301 patients had their DNA binding domains (DBDs) in NR1I2 and NR1I3 sequenced.ResultsSignificantly decreased efavirenz plasma concentrations were observed in patients carrying the NR1I3 rs3003596C/C and T/C genotypes (P=0.015 and P=0.010, respectively). Sequencing resulted in the discovery of a further 13 SNPs, 3 of which are novel variants in the DBD of NR1I2. There were significant differences in the distribution of NR1I2 and NR1I3 SNPs between South Africans when compared to Caucasian, Asian and Yoruba population groups.ConclusionFor the realisation of personalised medicine, PXR and CAR genetic variation should be taken into consideration because of their involvement in the regulation of DMEs.

Expression, localization and polymorphisms of the nuclear receptor PXR in Barrett's esophagus and esophageal adenocarcinoma

BackgroundThe continuous exposure of esophageal epithelium to refluxate may induce ectopic expression of bile-responsive genes and contribute to the development of Barrett's esophagus (BE) and esophageal adenocarcinoma. In normal physiology of the gut and liver, the nuclear receptor Pregnane × Receptor (PXR) is an important factor in the detoxification of xenobiotics and bile acid homeostasis. This study aimed to investigate the expression and genetic variation of PXR in reflux esophagitis (RE), Barrett's esophagus (BE) and esophageal adenocarcinoma.MethodsPXR mRNA levels and protein expression were determined in biopsies from patients with adenocarcinoma, BE, or RE, and healthy controls. Esophageal cell lines were stimulated with lithocholic acid and rifampicin. PXR polymorphisms 25385C/T, 7635A/G, and 8055C/T were genotyped in 249 BE patients, 233 RE patients, and 201 controls matched for age and gender.ResultsPXR mRNA levels were significantly higher in adenocarcinoma tissue and columnar Barrett's epithelium, compared to squamous epithelium of these BE patients (P < 0.001), and RE patients (P = 0.003). Immunohistochemical staining of PXR showed predominantly cytoplasmic expression in BE tissue, whereas nuclear expression was found in adenocarcinoma tissue. In cell lines, stimulation with lithocholic acid did not increase PXR mRNA levels, but did induce nuclear translocation of PXR protein. Genotyping of the PXR 7635A/G polymorphism revealed that the G allele was significantly more prevalent in BE than in RE or controls (P = 0.037).ConclusionsPXR expresses in BE and adenocarcinoma tissue, and showed nuclear localization in adenocarcinoma tissue. Upon stimulation with lithocholic acid, PXR translocates to the nuclei of OE19 adenocarcinoma cells. Together with the observed association of a PXR polymorphism and BE, this data implies that PXR may have a function in prediction and treatment of esophageal disease.

Frequency of genetic polymorphisms of PXR gene in the Brazilian population

INTRODUCTION:PXR polymorphisms have been implicated in modulating CYP3A4 and PXR expression, potentially accounting for interindividual differences in drug metabolism. The prevalence of PXR polymorphisms varies among ethnic groups and data on the allelic distribution in the highly mixed Brazilian population is lacking. The aim of this study was to analyze genetic variations in the PXR gene in Brazilians and to compare the results to other ethnic groups.METHODS:DNA samples from 117 healthy Brazilians underwent PCR amplification and sequencing.RESULTS:Eleven polymorphisms were identified, 3 of which are highly associated with differences in CYP3A4 expression. We also identified 1 new synonymous variant in 1.3% of the alleles. Among the functional polymorphisms, –25913 C>T and –6994T>C occurred at a higher frequency compared to the African alleles (p < 0.05) but at a lower frequency compared to Caucasian alleles. The 8055 C>T allele was found at a similar frequency to those described in Caucasians and Africans (p > 0.05).CONCLUSION:We observed that functional variants of the PXR were frequent in our sample of the Brazilian population. Our results suggest that PXR gene variants may be of interest in pharmacogenetic studies involving Brazilians.

Polymorphisms in NFkB, PXR, LXR and risk of colorectal cancer in a prospective study of Danes

BackgroundTranscription factors and nuclear receptors constitute a link between exposure to heterocyclic amines and polycyclic aromatic hydrocarbons from meat and tobacco smoke and colorectal cancer (CRC) risk. The aim of this study was to investigate if polymorphisms in nuclear factor kappa-B, pregnane X receptor, and liver X receptor were associated with risk of CRC, and to investigate possible interactions with lifestyle factors such as smoking, meat consumption, and NSAID use.MethodsThe polymorphisms nuclear factor kappa-B (NFkB, NFKB1) -94 insertion/deletion ATTG (rs28362491), pregnane X receptor (PXR, NR1I2) A-24381C (rs1523127), C8055T (rs2276707), A7635G (rs6785049), liver X receptor (LXR-β, NR1H3) C-rs1405655T, T-rs2695121C were assessed together with lifestyle factors in a nested case-cohort study of 378 CRC cases and 756 random participants from the Danish prospective Diet, Cancer and Health study of 57,053 persons.ResultsCarriers of NFkB -94deletion were at 1.45-fold higher risk of CRC than homozygous carriers of the insertion allele (incidence rate ratio (IRR) = 1.45, 95% confidence interval (95% CI): 1.10-1.92). There was interaction between this polymorphism and intake of red and processed meat in relation to CRC risk. Carriers of NFkB -94deletion were at 3% increased risk pr 25 gram meat per day (95% CI: 0.98-1.09) whereas homozygous carriers of the insertion were not at increased risk (p for interaction = 0.03). PXR and LXR polymorphisms were not associated with CRC risk. There was no interaction between use of nonsteroid antiinflammatory drugs (NSAID) or smoking status and NFkB, PXR or LXR polymorphisms.ConclusionsA polymorphism in NFkB was associated with CRC risk and there was interaction between this polymorphism and meat intake in relation to CRC risk. This study suggests a role for NFkB in CRC aetiology.

Polymorphisms in genes of the steroid receptor superfamily modify postmenopausal breast cancer risk associated with menopausal hormone therapy

Menopausal hormone therapy (HT) is associated with increased breast cancer risk among postmenopausal women. Nuclear receptors are involved in steroid hormone- and xenobiotic-mediated signal transduction playing a crucial role in regulating gene expression. Therefore, variations within these genes may influence HT-associated breast cancer risk. We investigated 3,149 postmenopausal breast cancer patients and 5,489 controls from 2 German population-based case-control studies. Thirty-three polymorphisms selected on the basis of known or putative functional relevance located in ESR1, ESR2, PGR, PXR and AR were genotyped. Conditional logistic regression was used to assess multiplicative statistical interaction between polymorphisms and duration of estrogen-progestagen therapy and of estrogen monotherapy with regard to breast cancer risk assuming log-additive and codominant modes of inheritance. We observed an increased risk for women carrying short AR_(CAG) alleles of <22 repeats associated with combined estrogen-progestagen therapy compared with those with long alleles (> or =22 repeats) (p(interaction) = 0.03). Additionally, risk associated with combination therapy use was significantly modified by 2 PXR polymorphisms with reduction of risk effects in carriers of the minor PXR_rs6785049_G and PXR_rs1054191_A alleles (p(interaction) = 0.04 and 0.05, respectively). Variants in both ESR1 and ESR2 modified risk associated with estrogen monotherapy use. Higher risk were observed in homozygotes for the major ESR1_rs910416_T allele (p(interaction) < 0.01) and in homozygotes for the minor ESR2_rs1271572_T, major ESR2_rs4986938_G and minor ESR2_rs928554_G alleles (p(interaction) = 0.02, 0.05, 0.02, respectively). Risk effect modification by ESR1_rs910416 and AR_(CAG)n polymorphisms remained significant after correction for multiple testing. We conclude that genetic variants in nuclear receptor genes may modify HT-associated postmenopausal breast cancer risk.

The influence of common gene variants of the xenobiotic receptor (PXR) in genetic susceptibility to intrahepatic cholestasis of pregnancy

The xenobiotic nuclear pregnane X receptor is implicated in many physiological pathways and diseases, including bile acid detoxification and cholestasis. Aim To estimate the contribution of common gene variants of the xenobiotic receptor (pregnane X receptor, PXR) to genetic susceptibility to intrahepatic cholestasis of pregnancy. A total of 101 intrahepatic cholestasis of pregnancy patients and 171 healthy pregnant women in the third trimester of their pregnancies were included. Four tag single nucleotide polymorphisms (SNPs) (rs12488820 C/T, rs2472671 C/T, rs2461823 A/G, and rs1054191 A/G) encompassing 36 kb in chromosome 3, with a minor allele frequency > or =0.10 and representing 33 polymorphic sites were genotyped. Besides these, three additional SNPs (rs3814057, rs6785049, and rs7643645) were included because they showed previous evidence of functionality. Genotypic test for single SNPs showed that rs2461823 genotypes were significantly associated with intrahepatic cholestasis of pregnancy (P < 0.0069), OR per G allele: 1.44, 95% CI: 1.01-2.05, P < 0.042. The Cochran-Armitage test for trend and the allelic test showed a significant association with disease status (P < 0.04 and 0.03 respectively), G being the risk allele. A positive association between rs2461823 and ALT, AST, and bilirubin concentrations was observed. Neonate birth weight adjusted by the Capurro index was significantly associated with rs2461823 (P < 0.05); the proportion of the total variation attributed to rs2461823 genotypes was 7.8%. Common PXR polymorphisms may contribute to the genetic susceptibility to intrahepatic cholestasis of pregnancy.

PXR: A Xenobiotic Receptor of Diverse Function Implicated in Pharmacogenetics

The pregnane X receptor (PXR; NR1I2), a member of the nuclear receptor superfamily, regulates the expression of drug-metabolic enzymes and transporters involved in the responses of mammals to their chemical environment. The same enzyme and transporter systems are also involved in the homeostasis of numerous endogenous chemicals. The regulatory function of PXR is implicated in normal physiology and diseases, such as drug-drug interactions, hepatic steatosis, vitamin D homeostasis, bile acids homeostasis, steroid hormones homeostasis and inflammatory bowel diseases. As such, any genetic variations of this receptor could potentially have widespread effects on the disposition of xenobiotics and endobiotics. Knowledge concerning the genetic polymorphisms of PXR may help to understand the variations in human drug response and ensure safe drug use. The correlation of PXR genetic polymorphisms with several disease conditions also suggests that this receptor may represent a valid therapeutic for hepato-intestinal disorders such as inflammatory bowel disease and primary sclerosing cholangitis.

Role of the PXR gene locus in inflammatory bowel diseases

The pregnane X receptor gene (PXR/NR1I2) has been recently associated with an increased risk for inflammatory bowel disease (IBD), although a subsequent case-control study failed to replicate the original association in an independent population. This nuclear receptor regulates genes involved in the detoxification process in the liver and intestine, like ABCB1/MDR1. PXR expression was significantly reduced in the colon of patients with ulcerative colitis (UC), but remained unaffected in Crohn's disease (CD) patients. Considering previous results, we aimed at investigating the impact of this locus on IBD predisposition in the Spanish population. Three PXR polymorphisms, including the 1 more strongly correlated with IBD risk in the initial study at -25385C/T (rs3814055) and the 6 haplotypes conformed by them, were analyzed in 365 UC and 331 CD patients and compared with 550 ethnically matched controls. The overall haplotypic distribution showed a significant difference between UC and CD patients (P = 0.05; chi(2) = 10.84). Among UC patients a significant difference was seen between those with extensive colitis and controls (P = 0.004; chi(2) = 17.04), mainly due to the presence of a risk haplotype (rs3814055*T//rs6784598*C//rs2276707*C: P = 0.001; odds ratio [OR] = 1.66, 95% confidence interval [CI] 1.20-2.30). Patients with extensive UC carrying the -25385T allele showed increased susceptibility compared with left-sided colitis patients and with healthy subjects. In patients with extensive UC a significantly different distribution of genotypes of the MDR1 G/A change located in intron 3 (rs3789243) was observed between carriers/noncarriers of the -25385T risk allele (P = 0.005). Our data seem to support the association of the PXR locus with extensive UC and the interaction between PXR and MDR1 genes.

Fexofenadine and midazolam disposition in relation to genetic polymorphisms of CYP3A, PXR and P‐glycoprotein (PGP)

Clinical Pharmacology &amp; Therapeutics (2003) 73, P19–P19; doi: