Sequence variability and candidate gene analysis in two cancer patients with complex clinical outcomes during morphine therapy

Contribution of Japanese scientists to drug metabolism and disposition

Japanese researchers have played a pivotal role in advancing the field of drug metabolism and disposition, as demonstrated by their substantial contributions to the journal Drug Metabolism and Disposition (DMD) over the past 5 decades. This review highlights the historical and ongoing impact of Japanese scientists on DMD, celebrating their achievements in elucidating drug metabolism, membrane transport, pharmacokinetics, and toxicology. From the discovery of cytochrome P450 by Tsuneo Omura and Ryo Sato in 1962 to subsequent advances in drug transport research, Japan has maintained a leading position in the field. A geographical analysis of DMD publications reveals a notable increase in contributions from Japan during the 1980s, ranking second globally and maintaining this position through the 2000s. However, recent years have seen a slight decline in output, likely influenced by the COVID-19 pandemic and increased online journals as well as structural changes within academia and industry. Importantly, this trend is not unique to Japan. To sustain excellence and innovation in this field, it is crucial to strengthen funding for absorption, distribution, metabolism, excretion, and toxicity research and promote collaborations between academia, industry, and regulatory agencies. By prioritizing the translation of fundamental discoveries into drug development and clinical applications, scientists in this area can further advance global efforts toward achieving optimal drug efficacy and safety. This review underscores the enduring contributions of Japanese researchers to DMD and calls for renewed efforts to drive innovation and progress in this vital area of science. SIGNIFICANCE STATEMENT: Over the past 5 decades, Japanese scientists have made significant contributions to Drug Metabolism and Disposition through groundbreaking discoveries and advancements in the study of drug-metabolizing enzymes, transporters, pharmacokinetics analysis, and related areas. These contributions continue to shape the field, offering a foundation for future innovation in this area. We hope that the next generation of Japanese scientists will further solidify their global leadership in this area to advance drug development and proper pharmacotherapy.

In vitro inhibitory effects of selumetinib on activity of human UDP-glucuronosyltransferases and prediction of in vivo drug-drug interactions

Selumetinib is an oral, effective, and selective tyrosine kinase inhibitor targeting mitogen-activated protein kinase 1 and 2 (MEK1/2), which is clinically active in multiple tumor types, such as neurofibromatosis type 1 (NF1), melanoma, gliomas and non-small cell lung cancer (NSCLC). The purpose of this article was to assess the effects of selumetinib on the activities of twelve human UDP-glucosyltransferases (UGTs) including UGT1A1, 1A3, 1A4, 1A6, 1A7, 1A8, 1A9, 1A10, 2B4, 2B7, 2B15, and 2B17, and its potential for inducing clinical drug-drug interactions (DDIs). The results demonstrated that selumetinib potently inhibited the activity of UGT2B7 through the mechanism of mixed inhibition with the inhibition constant value of 5.79 ± 0.65 μM. Furthermore, the plasma concentration of UGT2B7 substrate as the co-administered drug was predicted to be increased by at least 84 % when patients took selumetinib 75 mg twice daily, suggesting a high potential to induce clinical DDIs. Selumetinib exhibited weak inhibitory effects on other human UGTs and was unlikely to trigger off UGTs-mediated DDIs except for UGT2B7. Therefore, the combination of selumetinib with the substrate drug of UGT2B7 requires additional attention to avoid adverse events in clinical treatment.

Reviewing pharmacogenetics to advance precision medicine for opioids

BACKGROUND

Adequate opioid prescribing is critical for therapeutic success of pain management. Despite the widespread use of opioids, optimized opioid therapy remains unresolved with risk of accidental lethal overdosing. With the emergence of accumulating evidence linking genetic variation to opioid response, pharmacogenetic based treatment recommendations have been proposed.

OBJECTIVE

The aim of this review is to evaluate pharmacogenetic evidence and provide an overview on genes involved in the pharmacokinetics and pharmacodynamics of opioids.

METHODS

For this review, a systematic literature search of published articles was used in PubMed®, with no language restriction and between the time period of January 2000 to December 2020. We reviewed randomized clinical studies, study cohorts and case reports that investigated the influence of genetic variants on selected opioid pharmacokinetics and pharmacodynamics. In addition, we reviewed current CPIC clinical recommendations for pharmacogenetic testing.

RESULTS

Results of this review indicate consistent evidence supporting the association between selected genetic variants of CYP2D6 for opioid metabolism. CPIC guidelines include recommendations that indicate the avoidance of tramadol use, in addition to codeine, in CYP2D6 poor metabolizers and ultrarapid metabolizers, and to monitor intermediate metabolizers for less-than-optimal response. While there is consistent evidence for OPRM1 suggesting increased postoperative morphine dosing requirements in A118G G-allele carriers, the clinical relevance remains limited.

CONCLUSION

There is emerging evidence of clinical relevance of CYP2D6 and, to a lesser extent, OPRM1 polymorphism in personalized opioid drug dosing. As a result, first clinics have started to implement pharmacogenetic guidelines for CYP2D6 and codeine.

Association between sex hormones regulation-related SNP rs12233719 and lung cancer risk among never-smoking Chinese women

BACKGROUND

The mechanism of rapidly increased non-small cell lung cancer (NSCLC) among never-smoking Chinese women has not been elucidated. Ovarian sex steroid hormones have been suggested to counteract lung cancer development, and sex hormone-binding globulin (SHBG) is essential in sex hormones regulation. This study aims to exploring single nucleotide polymorphisms (SNPs) in genomic regions associated with SHBG concentrations that contributed to never-smoking female NSCLC.

METHODS

Candidate genes were selected by a genome-wide association (GWAS) meta-analysis and gene expression profiles of never-smoking NSCLC of Chinese women. The candidate SNPs limited to common minor allele frequency (MAF), missense variant, ethnic heterogeneous distribution, and SNPs were genotyped using the TaqMan method. A two-stage case-control design was adopted for exploration and validation of associations between candidate SNPs and risk of NSCLC. All participants were never-smoking Chinese women. Chi-square test and multivariate logistic regression were applied.

RESULTS

Beginning with 12 genomic regions associated with circulating SHBG concentrations and gene expression profiles from never-smoking NSCLC in Chinese women, candidate SNP rs12233719 and rs7439366 both located in candidate gene UGT₂ B_7, which may be related to circulating SHBG concentrations and cancer risk, were identified. A two-stage case-control study was conducted in Shenyang and Tianjin represented as the training stage and validation stage, respectively. Under the dominant model, compared to individuals with the wild G/G genotype, the adjusted OR of those with the T allele was 1.58 (95% CI: 1.15-2.16) in Chinese Shenyang training set, and was 1.49 (95% CI: 1.02-2.18) in Chinese Tianjin validation set, both accompanied with a significant trend relationship consistently. UGT2B7 was upregulated in female NSCLC patients' tumor tissues and was associated with a poor prognosis in NSCLC.

CONCLUSION

Our findings indicated that a sex hormones regulation-related SNP rs12233719 was associated with never-smoking female lung cancer risk, which might partially explain NSCLC-susceptibility in Chinese women.

Effects of CYP3A5 and UGT2B7 variants on steady-state carbamazepine concentrations in Chinese epileptic patients

Carbamazepine (CBZ) is a widely used antiepileptic drug with large interindividual variability in serum concentrations. Previous studies found that CYP3A5*3 (rs776746), UGT2B7*2 (802C>T), and UGT2B7*3 (211G>T) variants could change the enzymes' activity, which may influence drug concentrations. Our study aims to investigate whether these variants affect steady-state CBZ concentrations in Chinese epileptic patients. In our study, 62 epileptic patients who received CBZ as monotherapy were monitored for steady-state CBZ concentrations. We used polymerase chain reaction (PCR)-based Sanger sequencing to assess the variants CYP3A5*3, UGT2B7*2, and UGT2B7*3. The results showed a positive correlation between dose and CBZ serum concentration in all patients and in patients with 3 different variants (all P < .05). After CBZ concentrations were normalized by the dose administered, negative correlations between dose-normalized CBZ concentrations and CBZ doses were observed in all patients, and in CYP3A5*3 and UGT2B7*3 patients (all P < .05), but not in UGT2B7*2 patients (P = .1080). UGT2B7*2 patients exhibited lower dose-normalized CBZ concentrations and larger CBZ dose requirements than UGT2B7*1/*1 patients (P = .0139, P = .032, respectively). There were no differences between UGT2B7*3, UGT2B7*1/*1 and CYP3A5*3, and CYP3A5*1/*1 patients with regard to steady-state CBZ concentration, dose-normalized concentration, required CBZ dose, and body weight-normalized dose (all P > .05). Moreover, a significant difference in body weight-normalized CBZ dose between UGT2B7 GC and TT haplotype patients was observed (P = .0154). In conclusion, our study found that the UGT2B7*2 variant, but not the CYP3A5*3 or UGT2B7*3 variant, could affect steady-state CBZ concentrations in epileptic patients.

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.

Population pharmacokinetics and Bayesian estimation of mycophenolic acid concentrations in Chinese adult renal transplant recipients

Mycophenolate mofetil (MMF) is an important immunosuppressant used in renal transplantation, and mycophenolic acid (MPA) is the active component released from the ester prodrug MMF. The objective of this study was to investigate the population pharmacokinetics of mycophenolic acid (MPA) following oral administration of MMF in Chinese adult renal transplant recipients and to identify factors that explain MPA pharmacokinetic variability. Pharmacokinetic data for MPA and covariate information were retrospectively collected from 118 patients (79 patients were assigned to the group for building the population pharmacokinetic model, while 39 patients were assigned to the validation group). Population pharmacokinetic data analysis was performed using the NONMEM software. The pharmacokinetics of MPA was best described by a two-compartment model with a first-order absorption rate with no lag time. Body weight and serum creatinine level were positively correlated with apparent clearance (CL/F). The polymorphism in uridine diphosphate glucuronosyltransferase gene, UGT2B7, significantly explained the interindividual variability in the initial volume of distribution (V₁/F). The estimated population parameters (and interindividual variability) were CL/F 18.3 L/h (34.2%) and V₁/F 27.9 L (21.3%). The interoccasion variability was 13.7%. These population pharmacokinetic data have significant clinical value for the individualization of MMF therapy in Chinese adult renal transplant patients.

Association of UGT2B7 and UGT1A4 Polymorphisms with Serum Concentration of Antiepileptic Drugs in Children

Background

This study aimed to analyze the relationship of UGT2B7 and UGT1A4 polymorphisms with metabolism of valproic acid (VPA) and lamotrigine (LTG) in epileptic children.

Material/Methods

We administered VPA (102) and LTG (102) to 204 children with epilepsy. Blood samples were collected before the morning dose. Serum concentration of LTG was measured by high-performance liquid chromatography (HPLC). Serum VPA concentration was tested by fluorescence polarization immunoassay. UGT2B7 A268G, C802T, and G211T polymorphisms, as well as UGT1A4 L48V polymorphism, were assayed by direct automated DNA sequencing after PCR. Evaluation of efficacy was conducted using the Engel method.

Results

The adjusted serum concentration of VPA was 4.26 μg/mL per mg/kg and LTG was 1.56 μg/mL per mg/kg. Multiple linear regression analysis revealed that VPA or LTG adjusted concentration showed a good linear relation with sex and age. UGT2B7 A268G and C802T polymorphisms were demonstrated to affect the serum concentration of VPA (F=3.147, P=0.047; F=22.754, P=0.000). UGT1A4 L48V polymorphism was not related with the serum concentration of LTG (F=5.328, P=0.006). In the efficacy analysis, we found that C802T polymorphism exerted strong effects on efficacy of VPA (χ²=9.265, P=0.010). L48V polymorphism also showed effects on efficacy of LTG (χ²=17.397, P=0.001).

Conclusions

UGT2B7, UGT1A4 polymorphisms play crucial roles in metabolism of VPA and LTG.

µ-opioid receptor gene variant OPRM1 118 A>G: a summary of its molecular and clinical consequences for pain

The human µ-opioid receptor variant 118 A>G (rs1799971) has become one of the most analyzed genetic variants in the pain field. At the molecular level, the variant reduces opioid receptor signaling efficiency and expression, the latter probably via a genetic-epigenetic interaction. In experimental settings, the variant was reproducibly associated with decreased effects of exogenous opioids. However, this translates into very small clinical effects (meta-analysis of 14 studies: Cohen's d = 0.096; p = 0.008), consisting of slightly higher opioid dosing requirements in peri- and post-operative settings. An effect can neither be maintained for chronic analgesic therapy nor for opioid side effects. It seems unlikely that further studies will reveal larger effect sizes and, therefore, further analyses appear unwarranted. Thus, due to its small effect size, the SNP is without major clinical relevance as a solitary variant, but should be regarded as a part of complex genotypes underlying pain and analgesia.

Influence of UGT2B7, OPRM1 and ABCB1 gene polymorphisms on postoperative morphine consumption

Therapeutic modulation of pain with morphine and other opioids is associated with significant variation in both effects and adverse effects in individual patients. Many factors including gene polymorphisms have been shown to contribute to the interindividual variability in the response to opioids. The aim of this study was to investigate the significance of UGT2B7, OPRM1 and ABCB1 polymorphisms for interindividual variability in morphine-induced analgesia in patients undergoing hysterectomy. The frequency of these polymorphisms was also investigated in forensic autopsies as morphine is also a very commonly abused drug. Blood samples were collected from 40 patients following abdominal hysterectomy, 24 hr after initiation of analgesia through a patient-controlled analgesia (PCA) pump. Samples were genotyped and analysed for morphine and its metabolites. We also genotyped approximately 200 autopsies found positive for morphine in routine forensic analysis. Patients homozygous for UGT2B7 802C needed significantly lower dose of morphine for pain relief. The same trend was observed for patients homozygous for ABCB1 1236T and 3435T, as well as to OPRM1 118A. The dose of morphine in patients included in this study was significantly related to variation in UGT2B7 T802C. Age was significantly related to both dose and concentration of morphine in blood. Regression analysis showed that 30% of differences in variation in morphine dose could be explained by SNPs in these genes. The genotype distribution was similar between the forensic cases and the patients. However, the mean concentration of morphine was higher in forensic cases compared to patients. We conclude that gene polymorphisms contribute significantly to the variation in morphine concentrations observed in individual patients.

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.

Life-threatening adverse events following therapeutic opioid administration in adults: is pharmacogenetic analysis useful?

BACKGROUND

Systemic approaches are needed to understand how variations in the genes associated with opioid pharmacokinetics and response can be used to predict patient outcome. The application of pharmacogenetic analysis to two cases of life-threatening opioid-induced respiratory depression is presented. The usefulness of genotyping in the context of these cases is discussed.

METHODS

A panel of 20 functional candidate polymorphisms in genes involved in the opioid biotransformation pathway (CYP2D6, UGT2B7, ABCB1, OPRM1, COMT) were genotyped in these two patients using commercially available genotyping assays.

RESULTS

In case 1, the patient experienced adverse outcomes when administered codeine and morphine, but not hydromorphone. Genetic test results suggested that this differential response may be due to an inherent propensity to generate active metabolites from both codeine and morphine. These active metabolites are not generated with hydromorphone. In case 2, the patient experienced severe respiratory depression during postoperative recovery following standard doses of morphine. The patient was found to carry genetic variations that result in decreased morphine efflux transporter activity at the blood-brain barrier and increased sensitivity to opioids.

CONCLUSIONS

Knowledge of the relative contribution of pharmacogenetic biomarkers and their influence on opioid response are continually evolving. Pharmacogenetic analysis, together with clinical history, has the potential to provide mechanistic insight into severe respiratory depressive events in patients who receive opioids at therapeutic doses.

Opioid therapy pharmacogenomics for noncancer pain: efficacy, adverse events, and costs

Chronic non-cancer pain is a debilitating condition associated with high individual and societal costs. While opioid treatment for pain has been available for centuries, it is associated with high variability in outcome, and a considerable proportion of patients is unable to attain relief from symptoms while suffering adverse events and developing medication dependence. We performed a review of the efficacy of pharmacogenomic markers and their abilities to predict adverse events, dependence, and associated economic costs, focusing on two genes: OPRM1 and CYP2D6. Data sources were articles indexed by PubMed on or before August 6, 2013. Articles were first selected after review of their titles and abstracts, and full papers were read to confirm eligibility. Initially, fifty-two articles were identified. Of these, 17 were relevant to biological actions of pharmacogenomic markers and their effect on therapeutic efficacy, 16 to adverse events, 15 to opioid dependence, and eight to economic costs. In conclusion, increasing costs of opioid therapy have made the advances in pharmacogenomics an attractive solution to personalize care with unclear repercussions related to the impact on costs, morbidity, and outcomes. This intersection of pharmacoeconomics and pharmacogenomics presents a unique platform to further examine current advances in clinical medicine and their utility in cost-effective treatment of chronic pain.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) metabolism-related enzymes gene polymorphisms, NNK metabolites levels and urothelial carcinoma

Gene polymorphisms of the 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) metabolism-related enzymes-cytochrome P450 (CYP) monooxygenase 2A13 (CYP2A13) and UDP-glucuronosyltransferases (UGT)-2B7 could contribute to the levels of NNK-related metabolites in urine, thereby increasing the susceptibility to urothelial carcinoma (UC). Therefore, our study aimed to evaluate the roles of two gene polymorphisms (CYP2A13 and UGT2B7) of NNK metabolism-related enzymes in the carcinogenesis of UC in Taiwan. A hospital-based pilot case-control study was conducted. There were 121 UC cases and 121 age- and sex-matched healthy participants recruited from March 2007 to April 2009. Urine samples were analyzed for NNK-related metabolites using the liquid chromatography-tandem mass spectrometry method. Genotyping was conducted using a polymerase chain reaction-restriction fragment length polymorphism technique. ANCOVA and multivariate logistic regression were applied for data analyses. In healthy controls, former smokers had significantly higher total NNAL and higher NNAL-Gluc than never smokers or current smokers. Subjects carrying the UGT2B7 268 His/Tyr or Tyr/Tyr genotype had significantly lower total NNAL than those carrying His/His genotype. However, no association was seen between gene polymorphisms of CYP2A13 and UGT2B7 and UC risk after adjustment for age and sex. Significant dose -response associations between total NNAL, free NNAL, the ratios of free NNAL/total NNAL and NNAL-Gluc/total NNAL and UC risk were observed. In the future, large-scale studies will be required to verify the association between the single nucleotide polymorphisms of NNK metabolism-related enzymes and UC risk.

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.

Pilot study examining the frequency of several gene polymorphisms involved in morphine pharmacodynamics and pharmacokinetics in a morbidly obese population

Morbidly obese patients are at significantly elevated risk of postsurgery complications and merit closer monitoring by health care professionals after bariatric surgery. It is now recognized that genetic factors influence individual patient's response to drug used in anesthesia and analgesia. Among the many drug administered by anesthetists, we focused in this pilot study on morphine, since morphine patient-controlled anesthesia in obese patients undergoing gastric bypass surgery is frequently prescribed. We examined the allelic frequency of three polymorphisms involved in morphine pharmacodynamics and pharmacokinetics in patients with body mass index (BMI) >40. One hundred and nine morbidly obese patients (BMI = 49.1 ± 7.7 kg/m²) were genotyped for three polymorphisms c.A118G of mu opioid receptor (OPRM1), c.C3435T of the P-glycoprotein gene (ABCB1), and p.Val158Met of catechol-O-methyltransferase gene (COMT). Allelic frequencies were 118G-0.22, C3435-0.55, and 158Met-0.5 in our whole population and 0.23, 0.5, and 0.47 in Caucasian population. Allelic frequencies did not differ according to gender. Mean BMI did no differ according to the allelic variant. OPRM1118G allele was more frequent in our population than in most previously described European populations. Since the concept of "personalized medicine" promises to individualize therapeutics and optimize medical treatment in term of efficacy and safety, especially when prescribing drugs with a narrow therapeutic index such as morphine, further clinical studies examining the clinical consequences of the OPRM1 c.A118G polymorphism in patients undergoing gastric bypass surgery are needed.

Association of polymorphisms in EPHX1, UGT2B7, ABCB1, ABCC2, SCN1A and SCN2A genes with carbamazepine therapy optimization

AIM

Carbamazepine (CBZ) is one of the most widely used antiepileptic drugs. The aim of the present study is to investigate the impacts of polymorphisms in genes related to pharmacokinetic and pharmacodynamic pathways of CBZ on the large interindividual variability in dosages and concentrations.

METHODS & RESULTS

Genetic polymorphisms in the candidate genes were detected in 234 epileptic patients under maintenance CBZ monotherapy by real-time PCR and PCR-RFLP. Results of statistical analysis demonstrated that carriers of the variant SCN1A IVS5-91G>A and EPHX1 c.337T>C allele tended to require higher CBZ dosages and lower ln(concentration-dose ratios) than noncarriers (p < 0.0001) and the homozygous carriers also seemed to require higher CBZ dosages and lower ln(concentration-dose ratios) (p < 0.0001). In addition, the multiple regression model of concentration-dose ratio of CBZ also revealed that genetic variants in SCN1A, EPHX1 and UGT2B7 genes interactively affect the concentration-dose ratio of CBZ (adjusted r(2) = 55%).

CONCLUSION

The present study identified genetic factors associated with CBZ therapy optimization and provided useful information for individualized CBZ therapy in epileptic patients. Further studies in larger populations are needed to confirm our results.

Pharmacogenomics of the human µ-opioid receptor

The µ-opioid receptor is a primary target for clinically important opioid analgesics, including morphine, fentanyl and methadone. Many genetic variations have been identified in the human µ-opioid receptor MOP gene (OPRM1), and their implications have been reported in the effects of opioid drugs and susceptibility to drug dependence. Interestingly, agonistic and antagonistic opioid effects are inversely associated with the A118G polymorphism genotype. The A118G polymorphism may also be associated with substance dependence and susceptibility to other disorders, including epilepsy and schizophrenia. The IVS1+A21573G, IVS1-T17286C, and TAA+A5359G polymorphisms in the OPRM1 gene may be associated with alcohol, opioid and tobacco dependence, respectively. However, some studies have failed to confirm the correlations between the polymorphisms and opioid effects and substance dependence. Further studies are needed to elucidate the molecular mechanisms underlying the effects of OPRM1 polymorphisms.

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.

Activation of morphine glucuronidation by fatty acyl-CoAs and its plasticity: a comparative study in humans and rodents including chimeric mice carrying human liver

The formation of morphine-3-glucuronide (M-3-G, pharmacologically inactive) and morphine-6-glucuronide (M-6-G, active metabolite) by liver microsomes from humans and rodents, including chimeric mice carrying human liver, was evaluated in the presence of fatty acyl-CoAs. Medium- to long-chain fatty acyl-CoAs, including oleoyl-CoAs, at a physiologic level (around 15 microM) markedly enhanced M-3-G formation catalyzed by rat liver microsomes. A separate experiment indicated that 15 microM oleoyl-CoA enhanced (14)C-UDP-glucuronic acid (UDPGA) uptake by microsomes. The activation by acyl-CoAs disappeared or was greatly reduced by either pre-treating microsomes with detergent or freezing/thawing the rat liver before preparation. Many of the microsomes prepared from frozen human livers (N=14) resisted oleoyl-CoA-mediated activation of UDP-glucuronosyltransferase (UGT) activity, including M-6-G formation, which is highly specific to humans. In sharp contrast, the activity of M-6-G and M-3-G formation in freshly-prepared hepatic microsomes from chimeric mice with humanized liver was potently activated by oleoyl-CoA. Thus, acyl-CoAs activate morphine glucuronidation mediated by human as well as rat UGTs. This activation is assumed to be due to the acyl-CoA-facilitated transportation of UDPGA, and microsomes need to maintain the intact conditions required for the activation. The function of UGT appears to be dynamically changed depending on the cellular acyl-CoA level in many species.

Modulation of UDP-glucuronosyltransferase activity by endogenous compounds

Glucuronidation is one of the major pathways of metabolism of endo- and xenobiotics. UDP-Glucuronosyltransferase (UGT)-catalyzed glucuronidation accounts for up to 35% of phase II reactions. The expression and function of UGT is modulated by gene regulation, post-translational modifications and protein-protein association. Many studies have focused on drug-drug interactions involving UGT, and there are a number of reports describing the inhibition of UGT by xenobiotics. However, studies about the role of endogenous compounds as an inhibitor or activator of UGT are limited, and it is important to understand any change in the function and regulation of UGT by endogenous compounds. Recent studies in our laboratory have shown that fatty acyl-CoAs are endogenous activators of UGT, although fatty acyl-CoAs had been considered as inhibitors of UGT. Further, we have also suggested that adenine and related compounds are endogenous allosteric inhibitors of UGT. In this review, we summarize the endogenous modulators of UGT and discuss their relevance to UGT function.

Association of UGT2B7 and ABCB1 genotypes with morphine-induced adverse drug reactions in Japanese patients with cancer

PURPOSE

To investigate the effects of genetic polymorphisms on morphine-induced adverse events in cancer patients.

METHODS

We examined the relation of morphine-related adverse events to polymorphisms in UDP-glucuronosyltransferase (UGT) 2B7, ATP-binding cassette, sub-family B, number 1 (ABCB1), and μ-opioid receptor 1 genes in 32 Japanese cancer patients receiving oral controlled-release morphine sulfate tablets.

RESULTS

The T/T genotype at 1236 or TT/TT diplotype at 2677 and 3435 in ABCB1 was associated with significantly lower frequency of fatigue (grades 1-3) (P = 0.012 or 0.011, Fisher’s exact test). The UGT2B7*2 genotype was associated with the frequency of nausea (grades 1-3) (P = 0.023). The frequency of nausea was higher in patients without UGT2B7*2 allele than others. The diplotype at 2677 and 3435 in ABCB1 was associated with the frequency of vomiting (grades 1-3) (P = 0.011). No patient whose diplotype was consisted of no GC allele at 2677 and 3435 suffered from vomiting.

CONCLUSION

Our findings suggest that pharmacogenetics can be used to predict the risk of morphine-induced adverse events.

Meta-analysis of the relevance of the OPRM1 118A>G genetic variant for pain treatment

Regard of functional pharmacogenetic polymorphisms may further the success of pain therapy by adopting individualized approaches. The mu-opioid receptor gene (OPRM1) 118A>G polymorphism is a promising candidate for both opioid effects and pain because of both biological reasonability and apparent experimental and clinical evidence. We analyzed its importance for pain therapy using a meta-analytic approach to studies relating it to opioid pain therapy. Data from suitable studies selected from hits of a PubMed search for "OPRM1" were independently extracted by two authors. The meta-analysis included phenotypes by OPRM1 genotype (opioid dosing, pain, and side effects), publication year, diagnostic status, proportion of male study participants, and whether genotype frequencies agreed with Hardy-Weinberg equilibrium. We found no consistent association between OPRM1 118A>G genotypes and most of the phenotypes in a heterogeneous set of eight clinical studies. Only weak evidence of an association with less nausea (effect size, Cohen's d=-0.21, p=0.037) and of increased opioid dosage requirements (d=0.56, p=0.018) in homozygous carriers of the G allele was obtained. This indicates that despite initially promising results, available evidence of the clinical relevance of the OPRM1 118A>G polymorphism does not withhold a meta-analysis. This discourages basing personalized therapeutic concepts of pain therapy on OPRM1 118A>G genotyping at the present state of evidence.

Pharmacogenetic insights into codeine analgesia: implications to pediatric codeine use

Codeine has been used medicinally since the 1800s as an analgesic and antitussive agent. Although very few studies have methodically examined the safety of codeine use in the pediatric age group, it is nonetheless commonly prescribed to children and breastfeeding mothers. Empirical evidence over the last century has suggested variability in the efficacy of codeine, and recent genomic advancements have shed important light on the mechanisms leading to such variability. Aside from evaluating the role of genetic variability in drug-metabolizing enzymes, receptors and transporters, the development of the blood–brain-barrier and the ontogeny of drug-metabolizing enzymes must also be considered in newborns and young children.

PhRMA white paper on ADME pharmacogenomics

Pharmacogenomic (PGx) research on the absorption, distribution, metabolism, and excretion (ADME) properties of drugs has begun to have impact for both drug development and utilization. To provide a cross-industry perspective on the utility of ADME PGx, the Pharmaceutical Research and Manufacturers of America (PhRMA) conducted a survey of major pharmaceutical companies on their PGx practices and applications during 2003-2005. This white paper summarizes and interprets the results of the survey, highlights the contributions and applications of PGx by industrial scientists as reflected by original research publications, and discusses changes in drug labels that improve drug utilization by inclusion of PGx information. In addition, the paper includes a brief review on the clinically relevant genetic variants of drug-metabolizing enzymes and transporters most relevant to the pharmaceutical industry.

Variable response to opioid treatment: any genetic predictors within sight?

The aim of this literature review is to summarize and discuss the available evidence for a relationship between polymorphisms in human genes and variability in opioid analgesia and side effects among patients treated for moderate or severe pain. The evidence supporting a role of certain alleles, genotypes or haplotypes in modulation of opioid analgesia is derived from a limited number of studies, a limited number of genes and a limited number of opioids. Although several interesting candidates have emerged as potentially relevant factors, only for one polymorphism, the prevalent 118A>G of the micro-opioid receptor, the accumulated evidence is sufficient to suggest a clinically relevant effect for an opioid used for moderate or severe pain. Still the data are valid only at the group level and cannot be used to predict treatment outcome in individual patients. Only a few of the symptoms often seen as opioid adverse effects in palliative care, such as nausea, vomiting, constipation and sedation, have been associated with genetic variants in various genes, but the results have been based on case reports, healthy volunteers or post-operative patients. So far, there is no clear evidence that genetic markers can be used to predict opioid efficacy or adverse effects in palliative care patients. This reflects the general lack of studies performed in the context of palliative care, the lack of sufficiently scaled studies and the lack of international standards for the assessment of subjective symptoms.

Pruritus in primary biliary cirrhosis: pathogenesis and therapy

Pruritus is a symptom experienced by patients who have primary biliary cirrhosis. It seems to result from pruritogens that (as a result of cholestasis) accumulate in plasma and other tissues, and which lead to altered neurotrasnmission. Administration of medications that change opioid neurotransmission (ie, opiate antagonists) results in relief of pruritus and its behavioral manifestation, scratching. Through unknown mechanisms, other centrally acting medications, including antidepressants, may have ameliorating effects on the pruritus of cholestasis. Stimulating endogenous detoxification pathways in the liver may also lead to the amelioration of pruritus. The removal of pruritogens through administration of nonabsorbable resins, nasobiliary drainage, biliary diversion, plasmapheresis, and various dialysis procedures is reported to decrease pruritus in liver disease, although the substances that are presumably removed are unknown.

Genetic mutations that prevent pain: implications for future pain medication

Part of the interindividual variability in pain therapy has been associated with genetic polymorphisms. Several genetic variants prevent or at least decrease pain in their carriers as compared with carriers of the respective wild-type or common alleles by impeding the generation, transmission and processing of nociceptive information or by increasing the local availability of active analgesics or their pharmacodynamic effects. Complete prevention of pain has so far been seen in six distinct rare hereditary syndromes, namely the ‘channelopathy-associated insensitivity to pain’, caused by 13 currently identified variants in the SCN9A gene coding for the α-subunit of the voltage-gated sodium channel, and five maladies belonging to the hereditary sensory and autonomic neuropathy (HSAN) I–V syndromes, caused by various mutations in several genes. Reduced pain in the average population has been associated with frequent variants in the µ-opioid receptor gene (OPRM1), catechol-O-methyltransferase gene (COMT), guanosine triphosphate cyclohydrolase 1/dopa-responsive dystonia gene (GCH1), transient receptor potential cation channel, subfamily V, member 1 gene (TRPV1) or the melanocortin-1 receptor gene (MC1R). Duplications/amplifications of the cytochrome P450 2D6 (CYP2D6) gene leading to increased enzyme function may cause intense opioid effects of codeine up to toxicity. The COMT V158M variant has been associated with decreased morphine requirements for analgesia. Inactivating MC1R variants have been associated with increased opioid analgesia of the µ-opioid receptor agonist morphine-6-glucuronide and, in women only, of κ-opioid agonists. Finally, variants in the P-glycoprotein gene (ABCB1) conferring decreased transporter function have been associated with increased respiratory depressive effects of fentanyl. In summary, a finite number of genetic variants that prevent pain by decreasing nociception or increasing analgesia have been identified. Given the complex biological and psychological nature of pain, we will see in the near future how much of the interindividual variance in pain and analgesia is due to identifiable genetic causes, and to what extent genetics enters clinical pain therapy.

Mechanisms of Opioid-Induced Tolerance and Hyperalgesia

Opioid tolerance and opioid-induced hyperalgesia are conditions that negatively affect pain management. Tolerance is defined as a state of adaptation in which exposure to a drug induces changes that result in a decrease of the drug's effects over time. Opioid-induced hyperalgesia occurs when prolonged administration of opioids results in a paradoxic increase in atypical pain that appears to be unrelated to the original nociceptive stimulus. Complex intracellular neural mechanisms, including opioid receptor desensitization and down-regulation, are believed to be major mechanisms underlying opioid tolerance. Pain facilitatory mechanisms in the central nervous system are known to contribute to opioid-induced hyperalgesia. Recent research indicates that there may be overlap in the two conditions. This article reviews known and hypothesized pathophysiologic mechanisms surrounding these phenomena and the clinical implications for pain management nurses.

Development of the Handy Bio-Strand and its application to genotyping of OPRM1 (A118G)

We previously developed a three-dimensional microarray system, the Bio-Strand, which exhibits advantages in automated DNA analysis in combination with our Magtration Technology. In the current study, we have developed a compact system for the Bio-Strand, the Handy Bio-Strand, which consists of several tools for the preparation of Bio-Strand Tip, hybridization, and detection. Using the Handy Bio-Strand, we performed single nucleotide polymorphism (SNP) genotyping of OPRM1 (A118G) by allele-specific oligonucleotide competitive hybridization (ASOCH). DNA fragments containing SNP sites were amplified from genomic DNA by PCR and then were fixed on a microporous nylon thread. Thus, prepared Bio-Strand Tip was hybridized with allele-specific Cy5 probes (<15mer), on which the SNP site was designed to be located in the center. By optimizing the amount of competitors, the selectivity of Cy5 probes increased without a drastic signal decrease. OPRM1 (A118G) genotypes of 23 human genomes prepared from whole blood samples were determined by ASOCH using the Handy Bio-Strand. The results were perfectly consistent with those determined by PCR direct sequencing. ASOCH using the Handy Bio-Strand would be a very simple and reliable method for SNP genotyping for small laboratories and hospitals.

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.

Parental history of chronic pain may be associated with impairments in endogenous opioid analgesic systems

A family history of chronic pain has previously been linked to increased incidence of spontaneous acute pain and risk for chronic pain. Mechanisms underlying these associations are unknown, although similar effects on both acute and chronic pain suggest that central endogenous analgesic system differences may be relevant. This study tested whether a positive parental chronic pain history (PH+) was associated with impaired endogenous opioid analgesic responses to acute pain. Seventy-three chronic low back pain patients (LBP) and 46 pain-free controls received opioid blockade (8mg naloxone i.v.) and placebo blockade (saline) in randomized, counterbalanced order in separate sessions. During each, subjects participated in a 1-min finger pressure pain task followed by an ischemic forearm pain task, providing pain intensity ratings during and immediately following each task. To assess opioid analgesic function, blockade effects were derived by subtracting placebo from blockade condition pain responses. Placebo condition analyses indicated that both PH+ subjects and LBP subjects reported greater acute pain sensitivity than respective comparison groups (p's<.05). Multivariate analyses indicated that, beyond any influence of current chronic pain status, PH+ subjects failed to exhibit any endogenous opioid analgesia to acute ischemic pain, whereas PH- subjects elicited effective opioid analgesia (p<.05). A significant multivariate PHxSubject Type interaction (p<.05) indicated that opioid analgesic impairments were most prominent in PH+ LBP subjects. Similar analyses for finger pressure pain blockade effects were nonsignificant (p>.10). The possible heritability of endogenous opioid analgesic dysfunction observed in individuals with a positive parental chronic pain history remains to be investigated.