Haplotype analysis of UDP-glucuronocyltransferase 2B7 gene (UGT2B7) polymorphisms in healthy Japanese subjects

Pharmacogenetic Variants and Plasma Concentrations of Antiseizure Drugs: A Systematic Review and Meta-Analysis

Importance

Precise estimation of a patient's drug metabolism capacity is important for antiseizure dose personalization.

Objective

To quantify the differences in plasma concentrations for antiseizure drugs associated with variants of genes encoding drug metabolizing enzymes.

Data Sources

PubMed, Clinicaltrialsregister.eu, ClinicalTrials.gov, International Clinical Trials Registry Platform, and CENTRAL databases were screened for studies from January 1, 1990, to September 30, 2023, without language restrictions.

Study Selection

Two reviewers performed independent study screening and assessed the following inclusion criteria: appropriate genotyping was performed, genotype-based categorization into subgroups was possible, and each subgroup contained at least 3 participants.

Data Extraction and Synthesis

The Meta-analysis of Observational Studies in Epidemiology (MOOSE) guidelines were followed for data extraction and subsequent quality, validity, and risk-of-bias assessments. The results from the included studies were pooled with random-effect meta-analysis.

Main Outcomes and Measures

Plasma concentrations of antiseizure drugs were quantified with the dose-normalized area under the concentration-time curve, the dose-normalized steady state concentration, or the concentrations after a single dose at standardized dose and sampling time. The ratio of the means was calculated by dividing the mean drug plasma concentrations of carriers and noncarriers of the pharmacogenetic variant.

Results

Data from 98 studies involving 12 543 adult participants treated with phenytoin, valproate, lamotrigine, or carbamazepine were analyzed. Studies were mainly conducted within East Asian (69 studies) or White or European (15 studies) cohorts. Significant increases of plasma concentrations compared with the reference subgroup were observed for phenytoin, by 46% (95% CI, 33%-61%) in CYP2C9 intermediate metabolizers, 20% (95% CI, 17%-30%) in CYP2C19 intermediate metabolizers, and 39% (95% CI, 24%-56%) in CYP2C19 poor metabolizers; for valproate, by 12% (95% CI, 4%-20%) in CYP2C9 intermediate metabolizers, 12% (95% CI, 2%-24%) in CYP2C19 intermediate metabolizers, and 20% (95% CI, 2%-41%) in CYP2C19 poor metabolizers; and for carbamazepine, by 12% (95% CI, 3%-22%) in CYP3A5 poor metabolizers.

Conclusions and Relevance

This systematic review and meta-analysis found that CYP2C9 and CYP2C19 genotypes encoding low enzymatic capacity were associated with a clinically relevant increase in phenytoin plasma concentrations, several pharmacogenetic variants were associated with statistically significant but only marginally clinically relevant changes in valproate and carbamazepine plasma concentrations, and numerous pharmacogenetic variants were not associated with statistically significant differences in plasma concentrations of antiseizure drugs.

Breast cancer resistance protein polymorphism ABCG2 c.421C>A (rs2231142) moderates the effect of valproate on lamotrigine trough concentrations in adults with epilepsy

BACKGROUND

Valproate inhibits clearance of lamotrigine and greatly increases its concentrations. We assessed whether this effect was moderated by a polymorphism (ABCG2 c.421C>A) of the breast cancer resistance protein.

METHODS

In two consecutive independent studies in adults with epilepsy on lamotrigine monotherapy or cotreated with valproate: (i) Exposure to valproate was considered treatment, (ii) dose-adjusted lamotrigine troughs at steady state were the outcome, and (iii) ABCG2 c.421C>A genotype (wild-type [wt] homozygosity or variant carriage) was the tested moderator. We used entropy balancing (primary analysis) and exact/optimal full matching (secondary analysis) to control for confounding, including polymorphisms (and linked polymorphisms) suggested to affect exposure to lamotrigine (UGT1A4*3 c.142T>G, rs2011425; UGT2B7-161C>T, rs7668258; ABCB1 1236C>T, rs1128503) to generate frequentist and Bayesian estimates of valproate effects (geometric means ratios [GMR]).

RESULTS

The two studies yielded consistent results (replicated); hence, we analyzed combined data (total N = 471, 140 treated, 331 controls, 378 ABCG2 c.421C>A wt subjects, 93 variant carriers). Primary analysis: in variant carriers, valproate effect (GMR) on lamotrigine (treated, n = 21 vs. controls, n = 72) was around 60% higher than in wt subjects (treated, n = 119 vs. controls, n = 259)-ratio of GMRs 1.61 (95%CI 1.23-2.11) (frequentist) and 1.63 (95%CrI 1.26-2.10) (Bayes). Similar differences in valproate effects between variant carriers and wt subjects were found in the secondary analysis (valproate troughs up to 364 μmol/L vs. no valproate; or valproate ≥364 μmol/L vs. no valproate). Susceptibility of the estimates to unmeasured confounding was low.

CONCLUSION

Data suggest that polymorphism rs2231142 moderates the effect of valproate on exposure to lamotrigine.

Properties of Dietary Flavone Glycosides, Aglycones, and Metabolites on the Catalysis of Human Endoplasmic Reticulum Uridine Diphosphate Glucuronosyltransferase 2B7 (UGT2B7)

Flavone glycosides, their aglycones, and metabolites are the major phytochemicals in dietary intake. However, there are still many unknowns about the cellular utilization and active sites of these natural products. Uridine diphosphate glucuronosyltransferases (UGTs) in the endoplasmic reticulum have gene polymorphism distribution in the population and widely mediate the absorption and metabolism of endogenous and exogenous compounds by catalyzing the covalent addition of glucuronic acid and various lipophilic chemicals. Firstly, we found that rutin, a typical flavone O-glycoside, has a stronger UGT2B7 binding effect than its metabolites. After testing a larger number of flavonoids with different aglycones, their aglycones, and metabolites, we demonstrated that typical dietary flavone O-glycosides generally have high binding affinities towards UGT2B7 protein, but the flavone C-glycosides and the phenolic acid metabolites of flavones had no significant effect on this. With the disposition of 4-methylumbelliferone examined by HPLC assay, we determined that 10 μM rutin and nicotifiorin could significantly inhibit the activity of recombinant UGT2B7 protein, which is stronger than isovitexin, vitexin, 3-hydroxyphenylacetic acid and 3,4-dihydroxyphenylacetic acid. In addition, in vitro experiments showed that in normal and doxorubicin-induced lipid composition, both flavone O-glycosides rutin and flavone C-glycosides isovitexin at 10 μM had no significant effect on the expression of UGT1A1, UGT2B4, UGT2B7, and UGT2B15 genes for 24 h exposure. The obtained results enrich the regulatory properties of dietary flavone glycosides, aglycones, and metabolites towards the catalysis of UGTs and will contribute to the establishment of a precise nutritional intervention system based on lipid bilayers and theories of nutrients on endoplasmic reticulum and mitochondria communication.

Bearing variant alleles at uridine glucuronosyltransferase polymorphisms UGT2B7 -161C > T (rs7668258) or UGT1A4*3 c.142 T > G (rs2011425) has no relevant consequences for lamotrigine troughs in adults with epilepsy

PURPOSE

To estimate whether epilepsy patients with variant UGT2B7 -161C > T (rs7668258) or UGT1A4*3 c.142 T > G (rs2011425) alleles differ from their wild-type (wt) peers in exposure to lamotrigine.

METHODS

Consecutive adults on lamotrigine monotherapy or lamotrigine + valproate co-treatment undergoing routine therapeutic drug monitoring, otherwise generally healthy and free of interacting drugs, were genotyped for UGT2B7 -161C > T and UGT1A4*3 c.142 T > G. Heterozygous, variant homozygous, or combined heterozygous/variant homozygous subjects were compared to their wt controls for dose-adjusted lamotrigine troughs with adjustment for age, sex, body weight, rs7668258/rs2011425, polymorphisms of efflux transporter proteins ABCG2 c.421C > A (rs2231142) and ABCB1 1236C > T (rs1128503), and level of exposure to valproate using covariate entropy balancing.

RESULTS

Of the 471 included patients, 328 (69.6%) were on monotherapy and 143 were co-treated with valproate. Dose-adjusted lamotrigine troughs in UGT2B7 -161C > T heterozygous (CT, n = 237) or variant homozygous (TT, n = 115) subjects were closely similar to those in their wt controls (CC, n = 119): geometric means ratios (GMRs) (frequentist and Bayes) 1.00 (95%CI 0.86-1.16) and 1.00 (95%CrI 0.83-1.22) for CT vs. CC; and 0.97 (0.81-1.17) and 0.97 (0.80-1.20) for TT vs. CC subjects. Lamotrigine troughs were also closely similar in UGT1A4*3 c.142 T > G variant carriers (n = 106: 102 TG + 4 GG subjects) and wt controls (TT, n = 365): GMR = 0.95 (0.81-1.12) frequentist, 0.96 (0.80-1.16) Bayes. GMRs for variant carriers vs. wt controls were around unity also at different levels of exposure to valproate.

CONCLUSION

Dose-adjusted lamotrigine troughs in epilepsy patients with variant UGT2B7 -161C > T or UGT1A4*3 c.142 T > G alleles are equivalent to those in their respective wt peers.

Significance of UGT1A6, UGT1A9, and UGT2B7 genetic variants and their mRNA expression in the clinical outcome of renal cell carcinoma

UDP-glucuronosyltransferase (UGT) metabolizes a number of endogenous and exogenous substrates. Renal cells express high amounts of UGT; however, the significance of UGT in patients with renal cell carcinoma (RCC) remains unknown. In this study, we profile the mRNA expression of UGT subtypes (UGT1A6, UGT1A9, and UGT2B7) and their genetic variants in the kidney tissue of 125 Japanese patients with RCC (Okayama University Hospital, Japan). In addition, we elucidate the association between the UGT variants and UGT mRNA expression levels and clinical outcomes in these patients. The three representative genetic variants, namely, UGT1A6 541A > G, UGT1A9 i399C > T, and UGT2B7-161C > T, were genotyped, and their mRNA expression levels in each tissue were determined. We found that the mRNA expression of the three UGTs (UGT1A6, UGT1A9, and UGT2B7) are significantly downregulated in RCC tissues. Moreover, in patients with RCC, the UGT2B7-161C > T variant and high UGT2B7 mRNA expression are significantly correlated with preferable cancer-specific survival (CSS) and overall survival (OS), respectively. As such, the UGT2B7-161C > T variant and UGT2B7 mRNA expression level were identified as significant independent prognostic factors of CSS and CSS/OS, respectively. Taken together, these findings indicate that UGT2B7 has a role in RCC progression and may, therefore, represent a potential prognostic biomarker for patients with RCC.

Effects of genetic polymorphism of drug-metabolizing enzymes on the plasma concentrations of antiepileptic drugs in Chinese population

As a chronic brain disease, epilepsy affects ~50 million people worldwide. The traditional antiepileptic drugs (AEDs) are widely applied but showing various problems. Although the new AEDs have partially solved the problems of traditional AEDs, the current clinical application of traditional AEDs are not completely replaced by new drugs, particularly due to the large individual differences in drug plasma concentrations and narrow therapeutic windows among patients. Therefore, it is still clinically important to continue to treat patients using traditional AEDs with individualized therapeutic plans. To date, our understanding of the molecular and genetic mechanisms regulating plasma concentrations of AEDs has advanced rapidly, expanding the knowledge on the effects of genetic polymorphisms of genes encoding drug-metabolizing enzymes on the plasma concentrations of AEDs. It is increasingly imperative to summarize and conceptualize the clinical significance of recent studies on individualized therapeutic regimens. In this review, we extensively summarize the critical effects of genetic polymorphisms of genes encoding drug-metabolizing enzymes on the plasma concentrations of several commonly used AEDs as well as the clinical significance of testing genotypes related to drug metabolism on individualized drug dosage. Our review provides solid experimental evidence and clinical guidance for the therapeutic applications of these AEDs.

Identifying complex gene-gene interactions: a mixed kernel omnibus testing approach

Genes do not function independently; rather, they interact with each other to fulfill their joint tasks. Identification of gene-gene interactions has been critically important in elucidating the molecular mechanisms responsible for the variation of a phenotype. Regression models are commonly used to model the interaction between two genes with a linear product term. The interaction effect of two genes can be linear or nonlinear, depending on the true nature of the data. When nonlinear interactions exist, the linear interaction model may not be able to detect such interactions; hence, it suffers from substantial power loss. While the true interaction mechanism (linear or nonlinear) is generally unknown in practice, it is critical to develop statistical methods that can be flexible to capture the underlying interaction mechanism without assuming a specific model assumption. In this study, we develop a mixed kernel function which combines both linear and Gaussian kernels with different weights to capture the linear or nonlinear interaction of two genes. Instead of optimizing the weight function, we propose a grid search strategy and use a Cauchy transformation of the P-values obtained under different weights to aggregate the P-values. We further extend the two-gene interaction model to a high-dimensional setup using a de-biased LASSO algorithm. Extensive simulation studies are conducted to verify the performance of the proposed method. Application to two case studies further demonstrates the utility of the model. Our method provides a flexible and computationally efficient tool for disentangling complex gene-gene interactions associated with complex traits.

Associations between UGT2B7 polymorphisms and cancer susceptibility: A meta-analysis

BACKGROUND

UGT2B7 was recently acknowledged as a new critical enzyme involved in biotransformation of a variety of carcinogens, whose function was reported to be significantly associated with its encoding gene (UGT2B7) polymorphisms. However, results regarding the associations between single nucleotide polymorphisms (SNPs) of UGT2B7 and cancer risk still remained controversial. Therefore, a meta-analysis was conducted to further elucidate the role of UGT2B7 SNPs on cancer susceptibilities.

METHODS

PubMed, EMBASE, Cochrane library, Chinese National Knowledge Infrastructure (CNKI), Technology of Chongqing (VIP) and Wan Fang Database were searched for eligible studies until March 2019. All analysis was carried out using the Review Manager 5.3 software. Subgroup analyses were performed by cancer types, ethnicity or source of controls.

RESULTS

13 studies with a total of 7688 cancer cases and 11,281 controls were included in this meta-analysis. The results showed that UGT2B7 rs7439366 increased the colorectal cancer risk in dominant model (OR = 0.76, 95% CI = 0.61-0.95, P = 0.02). However, as for the rs7435335 and rs12233719, we did not find their associations with cancer risk in all genetic models. In addition, the rs7441774 was found to be associated with breast cancer risk and significantly reduced papillary thyroid cancer risk in rs3924194 was also observed. Nevertheless, these findings remained to be further proven in future studies since these 2 SNPs were only respectively involved in 1 study.

CONCLUSION

This meta-analysis confirmed the association of UGT2B7 rs7439366 with colorectal cancer risk, which may be a potential promising biomarker for prediction of colorectal cancer risk.

Association between UGT2B7 gene polymorphisms and fentanyl sensitivity in patients undergoing painful orthognathic surgery

Background

Fentanyl is often used instead of morphine for the treatment of pain because it has fewer side effects. The metabolism of morphine by glucuronidation is known to be influenced by polymorphisms of the UGT2B7 gene. Some metabolic products of fentanyl are reportedly metabolized by glucuronate conjugation. The genes that are involved in the metabolic pathway of fentanyl may also influence fentanyl sensitivity. We analyzed associations between fentanyl sensitivity and polymorphisms of the UGT2B7 gene to clarify the hereditary determinants of individual differences in fentanyl sensitivity.

Results

This study examined whether single-nucleotide polymorphisms (SNPs) of the UGT2B7 gene affect cold pain sensitivity and the analgesic effects of fentanyl, evaluated by a standardized pain test and fentanyl requirements in healthy Japanese subjects who underwent uniform surgical procedures. The rs7439366 SNP of UGT2B7 is reportedly associated with the metabolism and analgesic effects of morphine. We found that this SNP is also associated with the analgesic effects of fentanyl in the cold pressor-induced pain test. It suggested that the C allele of the rs7439366 SNP may enhance analgesic efficacy. Two SNPs of UGT2B7, rs4587017 and rs1002849, were also found to be novel SNPs that may influence the analgesic effects of fentanyl in the cold pressor-induced pain test.

Conclusions

Fentanyl sensitivity for cold pressor-induced pain was associated with the rs7439366, rs4587017, and rs1002849 SNPs of the UGT2B7 gene. Our findings may provide valuable information for achieving satisfactory pain control and open to new avenues for personalized pain treatment.

Correlations between UGT2B7∗2 gene polymorphisms and plasma concentrations of carbamazepine and valproic acid in epilepsy patients

PURPOSE

The study aims to detect the polymorphisms in uridine diphosphate glucuronyl transferase (UGT) 2B7∗2 and investigate the corresponding effects on the blood concentrations of valproic acid (VPA) and carbamazepine (CBZ).

METHODS

A chemiluminescence immunoassay analyzer was used to detect the plasma concentrations of VPA or CBZ in patients. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was used to analyze UGT2B7∗2 gene polymorphisms.

RESULTS

A total of 117 patients were enrolled under the VPA group, out of which 84 patients were aged 6years or older. Comparison of the blood concentrations of VPA showed significant differences among patients with the three standard genotypes (mutant, heterozygous, and wild-type) based on one-way ANOVA (F=4.386, p=0.016). In addition, comparison of the blood concentrations among the three genotypes in the CBZ group (78 patients) showed no significant differences based on analysis using ANOVA (F=0.897, p=0.412).

CONCLUSION

The UGT2B7∗2 gene polymorphisms significantly affect the standard blood concentrations of VPA, but not CBZ.

OPRM1 and ABCB1 Polymorphisms and Their Effect on Postoperative Pain Relief With Piritramide

Genetic factors may contribute to the differential response to opioids. The aim of this study was to evaluate the association between polymorphisms of µ1-opioid receptor gene OPRM1 (rs1799971), and P-glycoprotein transporter gene ABCB1 (rs1045642, rs2032582), and piritramide efficacy under postoperative patient-controlled analgesia (PCA). In 51 patients, OPRM1 variant was associated with decreased efficacy in early postoperative period evidenced by sum of pain intensity difference in the 0-6 h postoperative period (SPID0-6), (F=3.27, p=0.029). Mean (SD) SPID0-6 was observed in the 118AA genotype 22.9 (6.1) mm, which was significantly higher from the 118GG genotype 10.0 (4.4) mm, p=0.006. The lowest cumulative dose was recorded in 118AA genotype 19.1 (9.8) mg, which was significantly less than in the 118GG genotype group 36.6 (6.1) mg, p=0.017. Opioid–induced adverse effects were observed in 11, 30, and 100 % of patients in 118AA, 118AG, and 118GG genotype groups, respectively (p<0.05). Piritramide efficacy and safety was not significantly affected by ABCB1 (rs1045642, rs2032582) polymorphisms. Variant OPRM1 118G allele is associated with decreased acute postoperative pain relief after piritramide. Decreased efficacy leads to higher drug consumption under PCA settings, which however, does not fully compensate insufficient pain relief, but increases incidence of adverse effects.

Influence of valproic acid concentration and polymorphism of UGT1A4*3, UGT2B7 -161C > T and UGT2B7*2 on serum concentration of lamotrigine in Chinese epileptic children

PURPOSE

To investigate the impact of valproic acid (VPA) and genetic polymorphism of the major metabolizing enzyme (UGT1A4, UGT2B7) of lamotrigine (LTG) and VPA on LTG concentration in Chinese epileptic children.

METHODS

Three single nucleotide polymorphisms (UGT1A4*3, UGT2B7 -161C > T and UGT2B7*2) were analyzed by polymerase chain reaction-restriction fragment length polymorphism or direct DNA sequencing. The concentrations of LTG and VPA were measured by high-performance liquid chromatography (HPLC) and fluorescence polarization immunoassay, respectively. The adjusted concentration of LTG was defined as the concentration-to-dose-ratio (CDRLTG). Data analysis was performed using IBM SPSS Statistics 21.0.

RESULTS

A total of 56 patients treated with LTG as monotherapy and 158 patients treated with LTG plus VPA were included in this study. In the polytherapy group, LTG concentration showed a good linear relationship with gender, age, daily LTG dose, VPA concentration, and UGT1A4*3 polymorphism, but had no relationship with the polymorphism of UGT2B7 -161C > T or UGT2B7*2. Moreover, LTG concentration and CDRLTG for the UGT1A4*3 were higher compared to UGT1A4*1 (LTG: 7.24 ± 3.51 vs 5.26 ± 3.27 μg/mL, p = 0.001; CDRLTG: 2.75 ± 1.02 vs 2.14 ± 0.96 μg/mL per mg/kg, p < 0.001, respectively). In the monotherapy group, there was no statistical difference between UGT1A4*3 and UGT1A4*1 in LTG concentration or CDRLTG. The patients in the polytherapy group were divided into two subgroups according to VPA concentration (lower/higher: 10-50/50-125 μg/mL). CDRLTG values of the patients carrying the UGT1A4*3 genotype were higher compared to UGT1A4*1*1 (2.86 ± 1.03 vs 2.22 ± 0.94 μg/mL per mg/kg, p = 0.001) only when the VPA concentration was higher.

CONCLUSIONS

UGT1A4*3 polymorphism had an effect on LTG concentration only with VPA co-administration, and the effect was remarkable when VPA concentration was higher.

Influence of uridine diphosphate glucuronosyltransferase 2B7 -161C>T polymorphism on the concentration of valproic acid in pediatric epilepsy patients

BACKGROUND

Valproic acid (VPA) is widely used to treat various types of epilepsy. Interindividual variability in VPA pharmacokinetics may arise from genetic polymorphisms of VPA-metabolizing enzymes. This study aimed to examine the relationships between plasma VPA concentrations and the -161C>T single nucleotide polymorphism in uridine diphosphate glucuronosyltransferase (UGT) 2B7 genes in pediatric epilepsy patients.

METHODS

This study included 78 pediatric epilepsy patients carrying the cytochrome P450 (CYP) 2C9*1/*1 genotype and who were not treated with the enzyme inducers (phenytoin, phenobarbital, and carbamazepine), lamotrigine, and/or topiramate. CYP2C9*3 and UGT2B7 -161C>T polymorphisms were identified using methods based on polymerase chain reaction-restriction fragment length polymorphism. Blood samples were drawn from each patient under steady-state conditions, and plasma VPA concentrations were measured.

RESULTS

Significant differences in adjusted plasma VPA concentrations were observed between carriers of CC, CT, and TT genotypes in the UGT2B7 -161C>T polymorphism (P = 0.039). Patients with the CC genotype had lower adjusted plasma VPA concentrations than those with CT or TT genotype (P = 0.028).

CONCLUSIONS

These data suggest that the UGT2B7 -161C>T polymorphism in pediatric epilepsy patients carrying the CYP2C9*1/*1 genotype affects VPA concentration.

OPRM1 A118G Gene Variant and Postoperative Opioid Requirement

Background:

Although a number of studies have investigated the association of the OPRM1 A118G polymorphism with pain response, a consensus has not yet been reached.

Methods:

The authors searched PubMed, EMBASE, and the Cochrane Library to identify gene-association studies that explored the impact of the OPRM1 A118G polymorphism on postoperative opioid requirements through July 2013. Two evaluators independently reviewed and selected articles on the basis of prespecified selection criteria. The authors primarily investigated the standardized mean difference (SMD) of required amounts of opioids between AA homozygotes and G-allele carriers. The authors also performed subgroup analyses for race, opioid use, and type of surgery. Potential bias was assessed using the Egger’s test with a trim and fill procedure.

Results:

Three hundred forty-six articles were retrieved from databases, and 18 studies involving 4,607 participants were included in the final analyses. In a random-effect meta-analysis, G-allele carriers required a higher mean opioid dose than AA homozygotes (SMD, −0.18; P = 0.003). Although there was no evidence of publication bias, heterogeneity was present among studies (I2 = 66.8%). In the subgroup meta-analyses, significance remained robust in Asian patients (SMD, −0.21; P = 0.001), morphine users (SMD, −0.29; P &lt;0.001), and patients who received surgery for a viscus (SMD, −0.20; P = 0.008).

Conclusions:

The OPRM1 A118G polymorphism was associated with interindividual variability in postoperative response to opioids. In a subpopulation, identifying OPRM1 A118G polymorphism may provide valuable information regarding the individual analgesic doses that are required to achieve satisfactory pain control.

Polymorphisms and haplotypes of the UDP-glucuronosyltransferase 2B7 gene promoter

Identification of functional polymorphisms in the UDP-glucuronosyltransferase 2B7 (UGT2B7) gene predicting interpatient variability in the glucuronidation of drugs that are primarily metabolized by UGT2B7 has been the subject of many studies. These studies have shown linkage disequilibrium (LD) covering the region from -2 kb to 16 kb of the UGT2B7 gene. We identified three novel single-nucleotide polymorphisms (SNPs) and extended this LD in the 5'-upstream direction to cover an additional nine prevalent polymorphisms in the distal -2600- to -4000-base pair (bp) promoter. We further showed complete LD between these distal promoter SNPs and the SNP (802C>T) in exon 2 in a panel of 26 livers. Because of this LD, we showed that all of the 23 prevalent polymorphisms in the 4-kb UGT2B7 promoter are linked together, defining two major haplotypes (i.e., I and II). The addition of the minor allele of a rare polymorphism and allele exchanges between haplotypes I and II generated subhaplotypes of I and II. We demonstrated a higher promoter activity of haplotype II over haplotype I, and this higher activity was abolished by an A-to-G change at a single SNP (-900A>G). This mutation changed a consensus activating protein-1 (AP-1) site (TGAGTCA) as occurred in haplotype II to a mutated AP-1 site (TGAGTCG) as occurred in haplotype I. Finally, we showed that the previously reported Alu element resides exclusively in haplotype I and is a highly conserved CG-rich Alu Y element.

Pharmacogenomics of opioids and perioperative pain management

Inadequate pain relief and adverse effects from analgesics remain common in children and adults during the perioperative period. Opioids are the most commonly used analgesics in children and adults to treat perioperative pain. Narrow therapeutic index and a large interpatient variability in response to opioids are clinically significant, with inadequate pain relief at one end of the spectrum and serious side effects, such as respiratory depression and excessive sedation due to relative overdosing, at the other end. Personalizing analgesia during the perioperative period attempts to maximize pain relief while minimizing adverse events from therapy. While various factors influence response to treatment among surgical patients, age, sex, race and pharmacogenetic differences appear to play major roles in predicting outcome. Genetic factors include a subset of genes that modulate the proteins involved in pain perception, pain pathway, analgesic metabolism (pharmacokinetics), transport and receptor signaling (pharmacodynamics). While results from adult genetic studies can provide direction for pediatric studies, they have limited direct applicability, as children's genetic predispositions to analgesic response may be influenced by developmental and behavioral components, altered sensitivity to analgesics and variation in gene-expression patterns. We have reviewed the available evidence on improving and personalizing pain management with opioids and the significance of individualizing analgesia, in order to maximize analgesic effect with minimal adverse effects with opioids. While the early evidence on individual genotype associations with pain, analgesia and opioid adverse outcome are promising, the large amount of conflicting data in the literature suggests that there is a need for larger and more robust studies with appropriate population stratification and consideration of nongenetic and other genetic risk factors. Although the clinical evidence and the prospect of being able to provide point-of-care genotyping to enable clinicians to deliver personalized analgesia for individual patients is still not available, positioning our research to identify all possible major genetic and nongenetic risk factors of an individual patient, advancing less expensive point-of-care genotyping technology and developing easy-to-use personalized clinical decision algorithms will help us to improve current clinical and economic outcomes associated with pain and opioid pain management.

Influence of concomitant antiepileptic drugs on plasma lamotrigine concentration in adult Japanese epilepsy patients

Lamotrigine (LTG) is an antiepileptic drug (AED) that was approved in Japan in 2008. We evaluated the influence of AEDs that induce hepatic enzymes (including phenytoin (PHT), phenobarbital (PB), carbamazepine (CBZ)), valproic acid (VPA), and various combinations of these drugs, on plasma LTG concentration in adult Japanese epilepsy patients. A total of 621 patients (mean age 34.4±11.8 years) were evaluated retrospectively. We calculated the concentration to dose ratio (CD ratio) for LTG with different AED regimens, and employed multiple regression analysis to determine factors influencing the LTG concentration. There was a linear correlation between the dose and concentration of LTG in patients treated with LTG (group I), LTG+VPA (group II), LTG+inducers (group III), or LTG+VPA+inducers (group IV). The mean CD ratio of patients on LTG monotherapy was 1.43±0.4 (μg/mL)/(mg/kg). When LTG was combined with VPA, the CD ratio increased about 2.2-fold, but there was no significant correlation between the CD ratio and VPA concentration. The mean CD ratios calculated in patients receiving LTG+PHT, LTG+PB, and LTG+CBZ were 0.56, 0.84, and 0.91, respectively. Addition of PHT significantly reduced the CD ratio in a concentration-dependent manner, in comparison with PB and CBZ (p<0.005 and p<0.001, respectively). Stepwise multiple regression analysis showed that the coefficient of determination of groups I, II, III, and IV were 0.94, 0.94, 0.90, and 0.91, respectively. In the clinical setting, these findings can help to estimate LTG concentrations and predict the inducing or inhibiting effects of concomitant AEDs.

Functional impact and prevalence of polymorphisms involved in the hepatic glucuronidation of valproic acid

Metabolism of valproic acid, a widely used drug, is only partially understood. It is mainly metabolized through glucuronidation and acts as a substrate for various UDP-glucuronosyltransferases (UGTs). UGTs metabolizing valproic acid in the liver are UGT1A3, UGT1A4, UGT1A6, UGT1A9 and UGT2B7, with UGT1A6 and UGT2B7 being the most prominent. Polymorphisms in genes expressing these enzymes may have clinical consequences, regarding dosing, blood levels of the drug and adverse reactions. Not all genes are well studied and studies, where they exist, report conflicting results. Prevalence of polymorphisms and various haplotypes is also of great importance, as it may suggest different therapeutic approaches in various populations. Presented here is a review of currently known polymorphisms, their functional impact, when known, and their prevalence in different populations, highlighting the current state of understanding and areas where there is a lack of data and suggesting new perspectives for further research.

Worldwide variation in human drug-metabolism enzyme genes CYP2B6 and UGT2B7: implications for HIV/AIDS treatment

AIM

Hepatic enzymes, CYP2B6 and UGT2B7 play a major role in the metabolism of the widely used antiretroviral drugs efavirenz, nevirapine and zidovudine. In the present study, we provide a view of UGT2B7 haplotype structure, and quantify the genetic diversity and differentiation at both CYP2B6 and UGT2B7 genes on a worldwide scale.

MATERIALS & METHODS

We genotyped one intronic and three promoter SNPs, and together with three nonsynonymous SNPs, inferred UGT2B7 alleles in north American (n = 326), west African (n = 133) and Papua New Guinean (n = 142) populations. We also included genotype data for five CYP2B6 and six UGT2B7 SNPs from an additional 12 worldwide populations (n = 629) analyzed in the 1000 Genomes Project.

RESULTS

We observed significant differences in certain SNP and allele frequencies of CYP2B6 and UGT2B7 among worldwide populations. Diversity values were higher for UGT2B7 than for CYP2B6, although there was more diversity between populations for CYP2B6. For both genes, most of the genetic variation was observed among individuals within populations, with the Papua New Guinean population showing the highest pairwise differentiation values for CYP2B6, and the Asian and European populations showing higher pairwise differentiation values for UGT2B7.

CONCLUSION

These new genetic distinctions provide additional insights for investigating differences in antiretroviral pharmacokinetics and therapy outcomes among ethnically and geographically diverse populations.

Hydrophilic interaction LC–MS/MS analysis of opioids in urine: significance of glucuronide metabolites

Background: In clinical laboratories, a large proportion of the toxicology workload is drug confirmations. Our GC–MS method for opioid confirmation detects total codeine, morphine, hydrocodone, hydromorphone, oxycodone and oxymorphone. The objective of this study was to develop a LC–MS/MS assay measuring the above drugs and glucuronide metabolites. In addition, to determine if measuring free drug only would lead to false negative results. Results: In 85 patient urines, 43% were positive for morphine glucuronide, but not morphine, 48% were positive for hydromorphone glucuronide, but not hydromorphone, 33% were positive for codeine glucuronide, but not codeine, and 44% were positive for oxymorphone glucuronide, but not oxymorphone. Conclusion: We developed an LC–MS/MS assay capable of detecting codeine, morphine, hydrocodone, hydromorphone, oxycodone, oxymorphone and glucuronide metabolites. Detection of free drug only led to false negative confirmations.

Genetic variations in UDP-glucuronosyltransferase 2B7 gene (UGT2B7) in a Korean population

Glucuronidation by UDP-glucuronosyltransferase 2B7 (UGT2B7) has been identified as an important pathway for the elimination of its substrate drugs in humans. Alterations in UGT2B7 function or expression may influence individual variations in drug responses. In an effort to screen for UGT2B7 single nucleotide polymorphisms (SNPs) in Koreans, the UGT2B7 gene was directly sequenced in 50 normal subjects. A total of 19 genetic variations were found: seven in exons, eight in introns, and four in the 5'-untranslated region. The order of the frequency distribution of UGT2B7 variations was: -900A>G, -327G>A, -161C>T, 10539A>G, 10711G>C and 10806T>A (40%); 2099T>A, 2100C>T, 2283A>G and 2316A>G (39%); 12029T>A (37%); 10928C>A (33%); 10541G>A (28%); 10897insA (24%); 372A>G (13%) and 211G>T (12%), as well as other minor alleles with less than 10% frequency. Nineteen variations were used to characterize linkage disequilibrium (LD) structures at the UGT2B7 locus. Eight tagging SNPs in UGT2B7 were determined. Identification of UGT2B7 SNPs with LD and the tagging SNPs lays the foundation for investigating UGT2B7-related genotype/phenotype association studies for Koreans as well as other populations.

Opioid switching and rotation in primary care: implementation and clinical utility

BACKGROUND

Opioid therapy is the standard treatment for moderate-to-severe cancer pain and is becoming a more frequent treatment for moderate-to-severe chronic noncancer pain. Response to opioids varies significantly between patients and even within the individual patient at different stages of treatment. Finding an opioid at a dose that provides adequate long-term analgesia with minimal adverse effects can be difficult. Opioid switching and opioid rotation, at different stages of therapy, represent two clinical strategies used to optimize opioid response for patients with moderate-to-severe pain.

OBJECTIVES

Review the theoretical and clinical evidence supporting the concepts of opioid switching and rotation, outline the conditions under which these practices should be considered, and briefly suggest practical steps for their implementation.

SCOPE

Clinical literature, clinical practice and guideline databases, and professional society websites were searched for articles or reports describing opioid switching or opioid rotation in chronic pain therapy; variability in patient response to opioid therapy; physiologic, pharmacologic, and genetic factors that affect clinical response to opioids; and practical approaches to maximizing analgesia and minimizing adverse effects in opioid therapy. It is outside the scope of this review to evaluate the pharmacoeconomic aspects that affect changes in opioid therapy.

FINDINGS

The variability in de novo clinical response to opioids likely represents the interaction of the varying properties of the individual opioids with the variability in individual patient biology. This interaction forms the rationale for opioid switching and explains its clinical utility. As with opioid switching, success with opioid rotation is related to the myriad of factors determining an individual patient's response to a specific opioid. However, the benefits of opioid rotation also derive from a partial reversal of tolerance at the mu-opioid receptor and the response of different micro-opioid receptor subtypes to the different opioids.

Single nucleotide polymorphism discovery and functional assessment of variation in the UDP-glucuronosyltransferase 2B7 gene

OBJECTIVE

UDP-glucuronosyltransferase 2B7 (UGT2B7) plays a central role in the liver-mediated biotransformation of endogenous and exogenous compounds. The genetic basis of interindividual variability in UGT2B7 function is unknown. This study aimed to discover novel gene variants of functional significance.

METHODS

Caucasian human livers (n=54) were used. UGT2B7 was resequenced in 12 samples [(six highest and six lowest for the formation of morphine-3-glucuronide (M3G)]. Haplotype-tagging single nucleotide polymorphisms were genotyped in the entire sample set. Samples were phenotyped for mRNA expression.

RESULTS

10 haplotype-tagging single nucleotide polymorphisms were identified and their haplotypes were inferred. Haplotype 4 (-45597G; -6682_-6683A; 372A; IVS1+9_IVS1+10A; IVS1+829T; IVS1+985G; IVS1+999C; IVS1+1250G; 801T; IVS4+185C) (frequency of 0.12) was associated with an increase in enzyme activity and gene expression. The 1/4 and 4/6 diplotypes had higher M3G formation compared with 1/1 (P<0.05) and 2/3 (P<0.01) diplotypes. Diplotypes containing haplotype 4 resulted in a significant 45% average increase in the formation of M3G compared with diplotypes without haplotype 4 (P=0.002). There was also an association between haplotype 4 and increased mRNA expression. IVS1+985A>G, 735A>G, and 1062C>T are the putative functional variants of haplotype 4. We also identified two mRNA splicing variants (UGT2B7_v2 and UGT2B7_v3) splicing out exon 1, 4, 5, and 6 but sharing exons 2 and 3 with the involvement of additional 5' exons. UGT2B7_v2 was detected in all livers tested, but UGT2B7_v3 was present at much lower levels compared with UGT2B7_v2. The UGT2B7 reference sequence mRNA is now named UGT2B7_v1.

CONCLUSION

UGT2B7 haplotype 4 is functional and its effects on the biotransformation of UGT2B7 substrates should be tested in controlled clinical trials. Biochemical studies should investigate the functional role of the newly discovered mRNA splicing variants.

Association of SLC22A4/5 polymorphisms with steroid responsiveness of inflammatory bowel disease in Japan

PURPOSE

We investigated the association between steroid responsiveness and single nucleotide polymorphisms of SLC22A4/A5 located within inflammatory bowel disease 5 locus. Our goal is personalized steroid therapy adjusted to match individual variations in drug responsiveness in each inflammatory bowel disease patient.

METHODS

Unrelated Japanese cohorts of 94 patients with Crohn's, 94 patients with ulcerative colitis, and 257 healthy control subjects were consecutively enrolled in this study. Genotyping and haplotype analysis focusing on steroid responsiveness was performed by using 15 single nucleotide polymorphisms.

RESULTS

The G allele of -368T > G in SLC22A5, in which strong linkage disequilibrium was observed and the limited diversity of three haplotypes was estimated, was significantly associated with steroid resistance in Japanese patients with Crohn's disease (P = 0.016). Haplotype analysis between -446C > T and -368T > G in the SLC22A5 promoter region showed that the CG allele appeared to be a risk haplotype for steroid resistance (CG: odds ratio, 4.13; 95 percent confidence interval, 1.41-12.1; P = 0.016).

CONCLUSIONS

This extensive linkage disequilibrium may form a general risk haplotype for steroid resistance in Crohn's disease in Japanese. Further analyses of the pharmacogenomics of steroid responsiveness are warranted to achieve the goal of individualized steroid therapy against inflammatory bowel disease.

Pharmacogenetics of Opioids

Opioids are used for acute and chronic pain and dependency. They have a narrow therapeutic index and large interpatient variability in response. Genetic factors regulating their pharmacokinetics (metabolizing enzymes, transporters) and pharmacodynamics (receptors and signal transduction elements) are contributors to such variability. The polymorphic CYP2D6 regulates the O-demethylation of codeine and other weak opioids to more potent metabolites with poor metabolizers having reduced antinociception in some cases. Some opioids are P-glycoprotein substrates, whereas, ABCB1 genotypes inconsistently influence opioid pharmacodynamics and dosage requirements. Single-nucleotide polymorphisms in the mu opioid receptor gene are associated with increasing morphine, but not methadone dosage requirements and altered efficacy of mu opioid agonists and antagonists. As knowledge regarding the interplay between genes affecting opioid pharmacokinetics including cerebral kinetics and pharmacodynamics increases, our understanding of the role of pharmacogenomics in mediating interpatient variability in efficacy and side effects to this important class of drugs will be better informed. Opioid drugs as a group have withstood the test of time in their ability to attenuate acute and chronic pain. Since the isolation of morphine in the early 1800s by Friedrich Sertürner, a large number of opioid drugs beginning with modification of the 4,5-epoxymorphinan ring structure were developed in order to improve their therapeutic margin, including reducing dependence and tolerance, ultimately without success.

Prevalence of UGT1A9 and UGT2B7 nonsynonymous single nucleotide polymorphisms in West African, Papua New Guinean, and North American populations

OBJECTIVE

UDP-glucuronosyltransferases (UGTs) UGT1A9 and UGT2B7 are involved in the metabolism of antimalarial dihydroartemisinin and antiretroviral zidovudine. Our aim was to analyze the prevalence of UGT1A9 (chromosome 2) and UGT2B7 (chromosome 4) nonsynonymous single nucleotide polymorphisms (SNPs) in West African (WA), Papua New Guinean (PNG), and North American (NA) populations.

METHODS

Using a post-PCR ligation detection reaction-fluorescent microsphere assay, frequencies of UGT1A9 (8G > A, 98T > C, 766G > A) and UGT2B7 (211G > T, 802C > T, 1192G > A) SNPs were determined in WA (n = 133, 5 countries), PNG (n = 153), and NA (n = 350, 4 ethnic groups) individuals.

RESULTS

The UGT1A9 variant alleles were not common in the study populations. None of the SNPs were present in WA and PNG. Among NA, all 3 SNPs were present (1% each) in Asian-Americans, while 98T > C was present only in Caucasian-Americans (1%) and Hispanic-Americans (1%). Regarding UGT2B7 SNPs, the prevalence of 802C > T was 21% in WA, 28% in PNG, and 28-52% in NA. The SNP 211G > T was present only in Asian-Americans (9%) and Hispanic-Americans (2%), while 1192G > A was not present in any of the subjects. No significant linkage was observed at UGT1A9, UGT2B7, and between both the loci in any of the study populations.

CONCLUSIONS

Taken together, the UGT1A9-UGT2B7 polymorphism profile in WA and PNG populations is similar to African-Americans, but different from Asian-Americans. It is important to determine if these differences, along with previously reported differences in cytochrome P450 2B6 allele frequencies, are associated with altered metabolism/effectiveness of artemisinin drugs.