Single nucleotide polymorphisms and haplotypes of CYP1A2 in a Japanese population

Letter to the FDA Proposing Major Changes in the US Clozapine Package Insert Supported by Clozapine Experts Worldwide. Part I: A Review of the Pharmacokinetic Literature and Proposed Changes

PURPOSE/BACKGROUND

Clozapine was approved in the United States (US) using 1989 regulations and knowledge. After 30 years, many sections of the US package insert (PI) are outdated.

METHODS

We comprehensively reviewed the literature to propose PI updates. We present the information in 2 articles. In Part I, we focus on basic pharmacology based on 407 relevant articles. Part II focuses on clinical aspects and pharmacovigilance.

FINDINGS/RESULTS

Based on more recent expectations of Food and Drug Administration regulations, we reviewed clozapine basic pharmacology including the following: 1) clearance, 2) pharmacokinetics and pharmacodynamics, and 3) monitoring tools. We identified 9 major problems in the basic pharmacological sections of the PI including the following: 1) in vivo studies indicate that clozapine is dependent on CYP1A2 for its metabolism, 2) the minor role of CYP2D6 in clozapine metabolism requires removing the PI recommendation to lower clozapine doses in CYP2D6 poor metabolizers, 3) in nontoxic concentrations CYP3A4 has a minor role in clozapine metabolism and potent CYP3A4 inhibitors lack clinically relevant effects, 4) several drug-drug interactions need to be updated based on recent literature, 5) systemic inflammation may decrease clozapine metabolism and increase the risk of clozapine intoxication, 6) obesity may decrease clozapine metabolism, 7) patients of Asian and Indigenous American ancestry need lower clozapine doses, 8) personalized titration and c-reactive protein monitoring should be considered until prospective studies are available, and 9) the half-life section needs to be modified to acknowledge that single dosing at night is frequent in the US.

IMPLICATIONS/CONCLUSIONS

An improvement in the US clozapine PI may lead to improvement in PIs worldwide.

Molecular Insights of Drug Resistance in Epilepsy: Multi-omics Unveil

Epilepsy is a devastating neurological disorder mainly associated with impaired synchronic discharge that leads to sensory, motor, and psychomotor impairments. Till now, about 30 anti-seizure medications (ASMs) have been approved for the management of epilepsy, yet one-third of individuals still have uncontrollable epilepsy and develop resistance. Drug resistance epilepsy (DRE) is defined as the condition where two ASMs fail to control the seizure in epileptic patients. The leading cause of the resistance was the extended use of ASMs. According to various studies, alterations in some genes and their expressions, along with specific metabolic impairments, are suggested to be associated with ASMs resistance and DRE pathophysiology. Several factors aid in the pathophysiology of DRE, such as alterations in protein-encoding genes such as neurotransmitter receptors, drug transporters, ion channels, and drug targets. Furthermore, the altered metabolite levels of metabolites implicated in neurotransmitter signaling, energetic pathways, oxidative stress, and neuroinflammatory signaling differentiate the epileptic patient from the DRE patient. Various DRE biomarkers can be identified using the "integrated omics approach," which includes the study of genomics, transcriptomics, and metabolomics. The current review has been compiled to understand the pathophysiological mechanisms of DRE by focusing on genomics, transcriptomics, and metabolomics. An effort has also been made to identify the therapeutic targets based on identifying significant markers by a multi-omics approach. This has the potential to develop novel therapeutic interventions in the future.

Dutch Pharmacogenetics Working Group (DPWG) guideline for the gene-drug interaction between CYP2D6, CYP3A4 and CYP1A2 and antipsychotics

The Dutch Pharmacogenetics Working Group (DPWG) aims to facilitate pharmacogenetics implementation in clinical practice by developing evidence-based guidelines to optimize pharmacotherapy. A guideline describing the gene-drug interaction between the genes CYP2D6, CYP3A4 and CYP1A2 and antipsychotics is presented here. The DPWG identified gene-drug interactions that require therapy adjustments when respective genotype is known for CYP2D6 with aripiprazole, brexpiprazole, haloperidol, pimozide, risperidone and zuclopenthixol, and for CYP3A4 with quetiapine. Evidence-based dose recommendations were obtained based on a systematic review of published literature. Reduction of the normal dose is recommended for aripiprazole, brexpiprazole, haloperidol, pimozide, risperidone and zuclopenthixol for CYP2D6-predicted PMs, and for pimozide and zuclopenthixol also for CYP2D6 IMs. For CYP2D6 UMs, a dose increase or an alternative drug is recommended for haloperidol and an alternative drug or titration of the dose for risperidone. In addition, in case of no or limited clinical effect, a dose increase is recommended for zuclopenthixol for CYP2D6 UMs. Even though evidence is limited, the DPWG recommends choosing an alternative drug to treat symptoms of depression or a dose reduction for other indications for quetiapine and CYP3A4 PMs. No therapy adjustments are recommended for the other CYP2D6 and CYP3A4 predicted phenotypes. In addition, no action is required for the gene-drug combinations CYP2D6 and clozapine, flupentixol, olanzapine or quetiapine and also not for CYP1A2 and clozapine or olanzapine. For identified gene-drug interactions requiring therapy adjustments, genotyping of CYP2D6 or CYP3A4 prior to treatment should not be considered for all patients, but on an individual patient basis only.

Reflections on the Lack of Consideration of Ethnic Ancestry to Stratify Clozapine Dosing

This review article argues against trusting standard clozapine references, including the US package insert, because they do not include advances in the sciences of pharmacokinetics and pharmacovigilance and ignore the effects of ethnic ancestry on therapeutic dosing. The minimum therapeutic dose leading to the minimum therapeutic concentration of 350 ng/mL in serum/plasma can be used to compare individuals/groups with treatment-resistant schizophrenia. The US clozapine package insert recommends targeting doses of 300-450 mg/day and, subsequently, increments of up to 100 mg with a maximum dose of 900 mg/day. Ethnic ancestry is defined by DNA ancestry group. Asians (people with ancestry ranging from Pakistan to Japan) and Indigenous Americans are similar in clozapine dosing; their average clozapine minimum therapeutic dose ranged from 166 mg/day (female non-smokers) to 270 mg/day (male smokers). For those with European ancestry, average clozapine minimum therapeutic doses ranged from 236 mg/day (female non-smokers) to 368 mg/day (male smokers). Based on limited studies, Black (African sub-Saharan ancestry) patients may be treated with typical US doses (300-600 mg/day), assuming no poor metabolism (PM) status. Ancestry's impact on clozapine lethality in four countries is discussed (two countries with highly homogenous populations, Denmark and Japan, and two countries with increasingly heterogenous populations due to immigration, Australia and the UK). An international guideline with 104 authors from 50 countries/regions was recently published, providing 6 personalized clozapine titration schedules for adult inpatients (3 ancestry groups and PM/non-PM schedules) and recommending c-reactive protein monitoring at baseline and weekly for 4 weeks.

Effects of Pharmacogenomic Testing in Clinical Pain Management: Retrospective Study

BACKGROUND

The availability of pharmacogenomic (PGx) methods to determine the right drug and dosage for individualized patient treatment has increased over the past decade. Adoption of the resulting PGx reports in a clinical setting and monitoring of clinical outcomes is a challenging and long-term commitment.

OBJECTIVE

This study summarizes an extended PGx deep sequencing panel intended for medication dosing and prescription guidance newly adopted in a pain management clinic. The primary outcome of this retrospective study reports the number of cases and types of drugs covered, for which PGx data appears to have assisted in optimal drug prescription and dosing.

METHODS

A PGx panel is described, encompassing 23 genes and 141 single-nucleotide polymorphisms or indels, combined with PGx dosing guidance and drug-gene interaction (DGI) and drug-drug interaction (DDI) reporting to prevent adverse drug reactions (ADRs). During a 2-year period, patients (N=171) were monitored in a pain management clinic. Urine toxicology, PGx reports, and progress notes were studied retrospectively for changes in prescription regimens before and after the PGx report was made available to the provider. An additional algorithm provided DGIs and DDIs to prevent ADRs.

RESULTS

Among patient PGx reports with medication lists provided (n=146), 57.5% (n=84) showed one or more moderate and 5.5% (n=8) at least one serious PGx interaction. A total of 96 (65.8%) patients showed at least one moderate and 15.1% (n=22) one or more serious DGIs or DDIs. A significant number of active changes in prescriptions based on the 102 PGx/DGI/DDI report results provided was observed for 85 (83.3%) patients for which a specific drug was either discontinued or switched within the defined drug classes of the report, or a new drug was added.

CONCLUSIONS

Preventative action was observed for all serious interactions, and only moderate interactions were tolerated for the lack of other alternatives. This study demonstrates the application of an extended PGx panel combined with a customized informational report to prevent ADRs and improve patient care.

Correction: An International Adult Guideline for Making Clozapine Titration Safer by Using Six Ancestry-Based Personalized Dosing Titrations, CRP, and Clozapine Levels

This international guideline proposes improving clozapine package inserts worldwide by using ancestry-based dosing and titration. Adverse drug reaction (ADR) databases suggest that clozapine is the third most toxic drug in the United States (US), and it produces four times higher worldwide pneumonia mortality than that by agranulocytosis or myocarditis. For trough steady-state clozapine serum concentrations, the therapeutic reference range is narrow, from 350 to 600 ng/mL with the potential for toxicity and ADRs as concentrations increase. Clozapine is mainly metabolized by CYP1A2 (female non-smokers, the lowest dose; male smokers, the highest dose). Poor metabolizer status through phenotypic conversion is associated with co-prescription of inhibitors (including oral contraceptives and valproate), obesity, or inflammation with C-reactive protein (CRP) elevations. The Asian population (Pakistan to Japan) or the Americas’ original inhabitants have lower CYP1A2 activity and require lower clozapine doses to reach concentrations of 350 ng/mL. In the US, daily doses of 300–600 mg/day are recommended. Slow personalized titration may prevent early ADRs (including syncope, myocarditis, and pneumonia). This guideline defines six personalized titration schedules for inpatients: 1) ancestry from Asia or the original people from the Americas with lower metabolism (obesity or valproate) needing minimum therapeutic dosages of 75–150 mg/day, 2) ancestry from Asia or the original people from the Americas with average metabolism needing 175–300 mg/day, 3) European/Western Asian ancestry with lower metabolism (obesity or valproate) needing 100–200 mg/day, 4) European/Western Asian ancestry with average metabolism needing 250–400 mg/day, 5) in the US with ancestries other than from Asia or the original people from the Americas with lower clozapine metabolism (obesity or valproate) needing 150–300 mg/day, and 6) in the US with ancestries other than from Asia or the original people from the Americas with average clozapine metabolism needing 300–600 mg/day. Baseline and weekly CRP monitoring for at least four weeks is required to identify any inflammation, including inflammation secondary to clozapine rapid titration.

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.

CYP1A2 mRNA Expression Rather than Genetic Variants Indicate Hepatic CYP1A2 Activity

CYP1A2, one of the most abundant hepatic cytochrome P450 enzymes, is involved in metabolism of several drugs and carcinogenic compounds. Data on the significance of CYP1A2 genetic polymorphisms in enzyme activity are highly inconsistent; therefore, the impact of CYP1A2 genetic variants (−3860G>A, −2467delT, −739T>G, −163C>A, 2159G>A) on mRNA expression and phenacetin O-dealkylation selective for CYP1A2 was investigated in human liver tissues and in psychiatric patients belonging to Caucasian populations. CYP1A2*1F, considered to be associated with high CYP1A2 inducibility, is generally identified by the presence of −163C>A polymorphism; however, we demonstrated that −163C>A existed in several haplotypes (CYP1A2*1F, CYP1A2*1L, CYP1A2*1M, CYP1A2*1V, CYP1A2*1W), and consequently, CYP1A2*1F was a much rarer allelic variant (0.4%) than reported in Caucasian populations. Of note, −163C>A polymorphism was found to result in an increase of neither mRNA nor the activity of CYP1A2. Moreover, hepatic CYP1A2 activity was associated with hepatic or leukocyte mRNA expression rather than genetic polymorphisms of CYP1A2. Consideration of non-genetic phenoconverting factors (co-medication with CYP1A2-specific inhibitors/inducers, tobacco smoking and non-specific factors, including amoxicillin+clavulanic acid therapy or chronic alcohol consumption) did not much improve genotype−phenotype estimation. In conclusion, CYP1A2-genotyping is inappropriate for the prediction of CYP1A2 function; however, CYP1A2 mRNA expression in leukocytes can inform about patients’ CYP1A2-metabolizing capacity.

Functional Characterization of 21 Rare Allelic CYP1A2 Variants Identified in a Population of 4773 Japanese Individuals by Assessing Phenacetin O-Deethylation

Cytochrome P450 1A2 (CYP1A2), which accounts for approximately 13% of the total hepatic cytochrome content, catalyzes the metabolic reactions of approximately 9% of frequently used drugs, including theophylline and olanzapine. Substantial inter-individual differences in enzymatic activity have been observed among patients, which could be caused by genetic polymorphisms. Therefore, we functionally characterized 21 novel CYP1A2 variants identified in 4773 Japanese individuals by determining the kinetic parameters of phenacetin O-deethylation. Our results showed that most of the evaluated variants exhibited decreased or no enzymatic activity, which may be attributed to potential structural alterations. Notably, the Leu98Gln, Gly233Arg, Ser380del Gly454Asp, and Arg457Trp variants did not exhibit quantifiable enzymatic activity. Additionally, three-dimensional (3D) docking analyses were performed to further understand the underlying mechanisms behind variant pharmacokinetics. Our data further suggest that despite mutations occurring on the protein surface, accumulating interactions could result in the impairment of protein function through the destabilization of binding regions and changes in protein folding. Therefore, our findings provide additional information regarding rare CYP1A2 genetic variants and how their underlying effects could clarify discrepancies noted in previous phenotypical studies. This would allow the improvement of personalized therapeutics and highlight the importance of identifying and characterizing rare variants.

Metabolism and Mechanism of Human Cytochrome P450 Enzyme 1A2

Human cytochrome P450 enzyme 1A2 (CYP1A2) is one of the most important cytochrome P450 (CYP) enzymes in the liver, accounting for 13% to 15% of hepatic CYP enzymes. CYP1A2 metabolises many clinical drugs, such as phenacetin, caffeine, clozapine, tacrine, propranolol, and mexiletine. CYP1A2 also metabolises certain precarcinogens such as aflatoxins, mycotoxins, nitrosamines, and endogenous substances such as steroids. The regulation of CYP1A2 is influenced by many factors. The transcription of CYP1A2 involves not only the aromatic hydrocarbon receptor pathway but also many additional transcription factors, and CYP1A2 expression may be affected by transcription coactivators and compression factors. Degradation of CYP1A2 mRNA and protein, alternative splicing, RNA stability, regulatory microRNAs, and DNA methylation are also known to affect the regulation of CYP1A2. Many factors can lead to changes in the activity of CYP1A2. Smoking, polycyclic aromatic hydrocarbon ingestion, and certain drugs (e.g., omeprazole) increase its activity, while many clinical drugs such as theophylline, fluvoxamine, quinolone antibiotics, verapamil, cimetidine, and oral contraceptives can inhibit CYP1A2 activity. Here, we review the drugs metabolised by CYP1A2, the metabolic mechanism of CYP1A2, and various factors that influence CYP1A2 metabolism. The metabolic mechanism of CYP1A2 is of great significance in the development of personalised medicine and CYP1A2 target-based drugs.

The Influence of Caffeine Expectancies on Sport, Exercise, and Cognitive Performance

Caffeine (CAF) is widely consumed across sport and exercise for its reputed ergogenic properties, including central nervous stimulation and enhanced muscular force development. However, expectancy and the related psychological permutations that are associated with oral CAF ingestion are generally not considered in most experimental designs and these could be important in understanding if/how CAF elicits an ergogenic effect. The present paper reviews 17 intervention studies across sport, exercise, and cognitive performance. All explore CAF expectancies, in conjunction with/without CAF pharmacology. Thirteen out of 17 studies indicated expectancy effects of varying magnitudes across a range of exercise tasks and cognitive skills inclusive off but not limited to; endurance capacity, weightlifting performance, simple reaction time and memory. Factors, such as motivation, belief, and habitual CAF consumption habits influenced the response. In many instances, these effects were comparable to CAF pharmacology. Given these findings and the lack of consistency in the experimental design, future research acknowledging factors, such as habitual CAF consumption habits, habituated expectations, and the importance of subjective post-hoc analysis will help to advance knowledge within this area.

Investigation of the major cytochrome P450 1A2 genetic variant in a healthy Tibetan population in China

The cytochrome P450 (CYP) 1A2 gene is involved in the metabolism of several carcinogens and clinically important drugs, generating a high potential for pharmacokinetic interactions. Since no data are available for Tibetan aborigines, the present study aimed to investigate the distribution of variant CYP1A2 alleles in a population living in Tibetan region of China. Genotyping analyses of CYP1A2 were conducted in 96 unrelated, healthy volunteers of Tibetan ancestry using direct sequencing assays. A total of 14 different CYP1A2 polymorphisms, including two novel variants (1690G>A and 2896C>T) in the intron region and a novel non-synonymous one (795G>C, Gln265His) were detected. CYP1A2*1A (6.77%), CYP1A2*1B (58.33%) and CYP1A2*1F (14.58%) were the most frequent defective alleles identified in the sample. The frequencies of the prevalent genotypes CYP1A2*1A/*1B, *1B/*1B, *1B/*1F were 13.54%, 16.67% and 29.17%, respectively. In addition, the novel non-synonymous variant 795G>C (Gln265His) was predicted to be benign by PolyPhen-2 and SIFT tools. The present study provides useful information on the pattern of CYP1A2 polymorphisms in Chinese Tibetan population. The current results may have potential benefits for the development of personalized medicine in the Tibetan population.

Impaired dacarbazine activation and 7-ethoxyresorufin deethylation in vitro by polymorphic variants of CYP1A1 and CYP1A2: implications for cancer therapy

OBJECTIVES

To extend our understanding of how interindividual variability mediates the efficacy of cancer treatment.

MATERIALS AND METHODS

The kinetics of dacarbazine (DTIC) N-demethylation by the most frequent polymorphic variants of CYP1A1 (T461N, I462V) and CYP1A2 (F186L, D348N, I386F, R431W, R456H) were characterized, along with kinetic parameters for the O-deethylation of the prototypic CYP1A substrate 7-ethoxyresorufin, using recombinant protein expression and high-performance liquid chromatographic techniques.

RESULTS

A reduction of ∼30% in the catalytic efficiencies (measured as in-vitro intrinsic clearance, CLint) was observed for DTIC N-demethylation by the two CYP1A1 variants relative to wild type. Although a modest increase in the CLint value for DTIC N-demethylation was observed for the CYP1A2 D348N variant relative to the wild type, the CLint for the F186L variant was reduced and the I386F, R431W, and R456H variants all showed loss of catalytic function.

CONCLUSION

Comparison of the kinetic data for DTIC N-demethylation and 7-ethoxyresorufin O-deethylation indicated that alterations in the kinetic parameters (Km, Vmax, CLint) observed with each of the CYP1A1 and CYP1A2 polymorphic variants were substrate dependent. These data indicate that cancer patients treated with DTIC who possess any of the CYP1A1-T461N and I462V variants or the CYP1A2-F186L, D348N, I386F, R431W, and R456H variants are likely to have decreased prodrug activation, and hence may respond less favorably to DTIC treatment compared with individuals with wild-type CYP1A alleles.

Relationship between metabolic phenotypes and genotypes of CYP1A2 and CYP2A6 in the Nigerian population

BACKGROUND

CYP1A2 and CYP2A6 are polymorphic drug-metabolising enzymes that are also implicated in the activation of procarcinogens in humans. Some of their alleles and haplotypes, often varied in prevalence across populations, are thought to influence activity despite the known contribution of environmental factors. This study assessed the potential influence of some genetic variants of CYP1A2 and CYP2A6 on metabolic phenotypes in Nigerians.

METHODS

Genomic DNA was extracted from blood samples of 100 healthy, unrelated subjects for whom CYP1A2 and CYP2A6 phenotypes had previously been determined, alongside an additional 80 other individuals for whom phenotype data were unavailable. The samples were screened for CYP1A2 (*1C,*1D,*1E,*1F, *3,*4,*6,*7) and CYP2A6 (*9,*11,*17) alleles using the Sequenom MassARRAY platform for some alleles and direct Sanger sequencing for others. The genetic data acquired were subsequently analysed for haplotypes and assessed for concordance with phenotypes.

RESULTS

All five CYP1A2 haplotypes (CYP1A2*1F, 1J, 1N, 1L, 1W) identified in the Nigerian population were not significantly predictive of metabolic phenotypes. Heterozygous CYP1A2*1J carriers and homozygous CYP1A2*1W carriers showed statistically insignificant decrease in CYP1A2 activity. The CYP2A6*9/*17 genotype was, however, significantly associated with the CYP2A6-poor metabolic phenotype, whereas CYP2A6*9 or CYP2A6*17 alone did not show any such association. CYP2A6*11 was not detected in the population.

CONCLUSIONS

Our findings suggest that CYP1A2 alleles or haplotypes were not predictive of metabolic phenotypes in the Nigerian population. Carriers of CYP2A6*9/*17 genotype are likely to be poor metabolisers of CYP2A6 substrates and may experience adverse reactions or poor efficacy while using drugs metabolised mainly by CYP2A6.

Associations between Rs4244285 and Rs762551 gene polymorphisms and age-related macular degeneration

BACKGROUND

Age-related macular degeneration is the leading cause of blindness in elderly individuals in developed countries. The etiology and pathophysiology of age-related macular degeneration have not been elucidated yet. Knowing that the main pathological change of age-related macular degeneration is formation of drusen containing about 40% of lipids, there have been attempts to find associations between age-related macular degeneration and genes controlling lipid metabolism.

PURPOSE

To determine the frequency of CYP2C19 (G681A) Rs4244285 and CYP1A2 (-163C>A) Rs762551 genotypes in patients with age-related macular degeneration.

METHODS

The study enrolled 150 patients with early age-related macular degeneration and 296 age- and gender-matched healthy controls. The genotyping of Rs4244285 and Rs762551 was carried out by using the real-time polymerase chain reaction method.

RESULTS

The CYP1A2 (-163C>A) Rs762551 C/C genotype was more frequently detected in patients with age-related macular degeneration than in the control group (32.7% vs. 21.6%, p = 0.011) and was associated with an increased risk of developing early age-related macular degeneration (OR = 1.759, 95% CI: 1.133-2.729; p = 0.012). The CYP1A2 (-163C>A) Rs762551 C/A genotype was more frequently documented in the control group compared with patients with age-related macular degeneration (46.3% vs. 30.7%, p = 0.002) and was associated with a decreased risk of having age-related macular degeneration (OR = 0.580. 95% CI: 0.362-0.929, p = 0.023) in the co-dominant model.

CONCLUSION

The study showed that the CYP1A2 (-163C>A) Rs762551 C/C genotype was associated with an increased risk of age-related macular degeneration.

The Impact of CYP1A2 and CYP2E1 Genes Polymorphism on Theophylline Response

Theophylline is a medicine with narrow therapeutic index. This implies that a small change in dosage would cause side effects. Theophylline is metabolized by CYP1A2 and CYP2E1. The aim of this review is to know the impact of CYP1A2 and CYP2E1 genes polymorphism on theophylline response. The review was done by searching literature in Pubmed and Science Direct databases with keywords 'polymorphism', 'pharmacogenetic', 'CYP1A2', 'CYP2E1' and 'theophylline'. There were 5 research articles from Pubmed and 65 articles (21 research articles, 23 review articles and 21 book chapters) from Science Direct. The exclusion criteria were - articles discussing about polymorphism but not CYP1A2 or CYP2E1, the ones with a mention of theophylline but not about its metabolism, articles on CYP1A2 and/or 2E1 polymorphism but not on the effect on theophylline. Thus, 33 articles were reviewed due to their suitability. The review discusses the influence of polymorphism of CYP1A2 and CYP2E1 genes on theophylline response.

Genetic polymorphism analysis of the drug-metabolizing enzyme CYP1A2 in a Uyghur Chinese population: a pilot study

1. CYP1A2 is a highly polymorphic gene and CYP1A2 enzyme results in broad inter-individual variability in response to certain pharmacotherapies, while little is known about the genetic variation of CYP1A2 in Uyghur Chinese population. The aim of the present study was to screen Uyghur volunteers for CYP1A2 genetic polymorphisms. 2. We used DNA sequencing to investigate promoter, exons, introns, and 3' UTR of the CYP1A2 gene in 96 unrelated healthy Uyghur individuals. We also used SIFT (Sorting Intolerant From Tolerant) and PolyPhen-2 (Polymorphism Phenotyping v2) to predict the protein function of the novel non-synonymous mutation in CYP1A2 coding regions. 3. We identified 20 different CYP1A2 polymorphisms in the Uyghur Chinese population, including two novel variants (119A > G and 2410G > A). Variant 119A > G was predicted to be probably damaging on protein function by PolyPhen-2, by contrast, 2410G > A was identified as benign. The allele frequencies of CYP1A2*1A, *1B, *1F, *1G, *1J, *1M, *4, and *9 were 23.4%, 53.1%, 3.7%, 2.6%, 2.6%, 13.5%, 0.5%, and 0.5%, respectively. The frequency of *1F, a putative high inducibility allele, was higher in our sample population compared with that in the Caucasian population (p < 0.05). The most common genotype combinations were *1A/*1B (46.9%) and *1B/*1M (27.1%). 4. Our results provide basic information on CYP1A2 polymorphisms in Uyghur individuals and suggest that the enzymatic activities of CYP1A2 may differ among the diverse ethnic populations of the world.

Effect of Cytochrome b5 Content on the Activity of Polymorphic CYP1A2, 2B6, and 2E1 in Human Liver Microsomes

Human cytochrome b5 (Cyt b5) plays important roles in cytochrome P450 (CYP)-mediated drug metabolism. However, the expression level of Cyt b5 in normal human liver remains largely unknown. The effect of Cyt b5 on overall CYP activity in human liver microsomes (HLM) has rarely been reported and the relationship between Cyt b5 and the activity of polymorphic CYP has not been systematically investigated. In this study, we found that the median value of Cyt b5 protein was 270.01 pmol/mg from 123 HLM samples, and 12- and 19-fold individual variation was observed in Cyt b5 mRNA and protein levels, respectively. Gender and smoking clearly influenced Cyt b5 content. In addition, we found that Cyt b5 protein levels significantly correlated with the overall activity of CYP1A2, 2B6, and 2E1 in HLM. However, when the CYP activities were sorted by single nucleotide polymorphisms (SNP), the effect of Cyt b5 protein on the kinetic parameters varied greatly. There were significant correlations between Cyt b5 content and V_max and CL_int of CYP1A2 wild-types (3860GG, 2159GG, and 5347CC) as well as homozygous mutants (163AA and 3113GG). In contrast to V_max and CL_int, the K_m of CYP2B6 516GG and 785AA genotypes was inversely associated with Cyt b5 content. Correlations between Cyt b5 content and V_max and CL_int of CYP2E1 -1293GG, -1293GC, 7632TT, 7632TA, -333TT, and -352AA genotypes were also observed. In conclusion, Cyt b5 expression levels varied considerably in the Chinese cohort from this study. Cyt b5 had significant impact on the overall activity of CYP1A2, 2B6, and 2E1 in HLM and the effects of Cyt b5 protein on polymorphic CYP1A2, 2B6, and 2E1 activity were SNP-dependent. These findings suggest that Cyt b5 plays an important role in CYP-mediated activities in HLM and may possibly be a contributing factor for the individual variation observed in CYP enzyme activities.

Functional characterization of 20 allelic variants of CYP1A2

Genetic variations in cytochrome P450 1A2 (CYP1A2) are associated with interindividual variability in the metabolism and efficacy of many medications. Twenty CYP1A2 variants harboring amino acid substitutions were analyzed for functional changes in enzymatic activity. Recombinant CYP1A2 variant proteins were heterologously expressed in COS-7 cells. Enzyme kinetic analyses were performed with two representative CYP1A2 substrates, phenacetin and 7-ethoxyresorufin. Among the 20 CYP1A2 allelic variants, CYP1A2*4, CYP1A2*6, CYP1A2*8, CYP1A2*15, CYP1A2*16, and CYP1A2*21 were inactive toward both substrates. CYP1A2*11 showed markedly reduced activity, but the changes in Km were different between the substrates. CYP1A2*14 and CYP1A2*20 exhibited increased activity compared to the wild-type enzyme, CYP1A2*1. This comprehensive in vitro assessment provided insight into the specific metabolic activities of CYP1A2 proteins encoded by variant alleles, which may to be valuable when interpreting the results of in vivo studies.

Functional Significance of Cytochrome P450 1A2 Allelic Variants, P450 1A2*8, *15, and *16 (R456H, P42R, and R377Q)

P450 1A2 is responsible for the metabolism of clinically important drugs and the metabolic activation of environmental chemicals. Genetic variations of P450 1A2 can influence its ability to perform these functions, and thus, this study aimed to characterize the functional significance of three P450 1A2 allelic variants containing nonsynonymous single nucleotide polymorphisms (P450 1A2*8, R456H; *15, P42R; *16, R377Q). Variants containing these SNPs were constructed and the recombinant enzymes were expressed and purified in Escherichia coli. Only the P42R variant displayed the typical CO-binding spectrum indicating a P450 holoenzyme with an expression level of ∼ 170 nmol per liter culture, but no P450 spectra were observed for the two other variants. Western blot analysis revealed that the level of expression for the P42R variant was lower than that of the wild type, however the expression of variants R456H and R377Q was not detected. Enzyme kinetic analyses indicated that the P42R mutation in P450 1A2 resulted in significant changes in catalytic activities. The P42R variant displayed an increased catalytic turnover numbers (k_cat) in both of methoxyresorufin O-demethylation and phenacetin O-deethylation. In the case of phenacetin O-deethylation analysis, the overall catalytic efficiency (k_cat/K_m) increased up to 2.5 fold with a slight increase of its K_m value. This study indicated that the substitution P42R in the N-terminal proline-rich region of P450 contributed to the improvement of catalytic activity albeit the reduction of P450 structural stability or the decrease of substrate affinity. Characterization of these polymorphisms should be carefully examined in terms of the metabolism of many clinical drugs and environmental chemicals.

Genetic polymorphisms in promoter and intronic regions of CYP1A2 gene in Roma and Hungarian population samples

The purpose of this study was to determine the interethnic differences of four CYP1A2 drug metabolizing enzyme variants. A total of 404 Roma and 396 Hungarian healthy subjects were genotyped for -163C>A, -729C>T, -2467delT and -3860G>A variants of CYP1A2 by RT-PCR and PCR-RFLP technique. The -3860A and -729T allele were not detectable in Roma samples, while in Hungarian samples were present with 2.02% and 0.25% prevalence, respectively. There was a 1.5-fold difference in presence of homozygous -163AA genotype between Hungarian and Roma samples (49.5% vs. 31.9%, p<0.001). The -163A allele frequency was 68.6% in Hungarians and 56.9% in Romas (p=0.025). The -2467delT allele frequency was 6.81% in Roma group and 5.81% in Hungarians. The most frequent allelic constellation was -3860G/-2467T/-729C/-163A in both populations. In conclusion, Hungarians have markedly elevated chance for rapid metabolism of CYP1A2 substrates, intensified procarcinogen activation and increased risk for cancers.

Increased genetic diversity of ADME genes in African Americans compared with their putative ancestral source populations and implications for pharmacogenomics

BACKGROUND

African Americans have been treated as a representative population for African ancestry for many purposes, including pharmacogenomic studies. However, the contribution of European ancestry is expected to result in considerable differences in the genetic architecture of African American individuals compared with an African genome. In particular, the genetic admixture influences the genomic diversity of drug metabolism-related genes, and may cause high heterogeneity of drug responses in admixed populations such as African Americans.

RESULTS

The genomic ancestry information of African-American (ASW) samples was obtained from data of the 1000 Genomes Project, and local ancestral components were also extracted for 32 core genes and 252 extended genes, which are associated with drug absorption, distribution, metabolism, and excretion (ADME) genes. As expected, the global genetic diversity pattern in ASW was determined by the contributions of its putative ancestral source populations, and the whole profiles of ADME genes in ASW are much closer to those in YRI than in CEU. However, we observed much higher diversity in some functionally important ADME genes in ASW than either CEU or YRI, which could be a result of either genetic drift or natural selection, and we identified some signatures of the latter. We analyzed the clinically relevant polymorphic alleles and haplotypes, and found that 28 functional mutations (including 3 missense, 3 splice, and 22 regulator sites) exhibited significantly higher differentiation between the three populations.

CONCLUSIONS

Analysis of the genetic diversity of ADME genes showed differentiation between admixed population and its ancestral source populations. In particular, the different genetic diversity between ASW and YRI indicated that the ethnic differences in pharmacogenomic studies are broadly existed despite that African ancestry is dominant in Africans Americans. This study should advance our understanding of the genetic basis of the drug response heterogeneity between populations, especially in the case of population admixture, and have significant implications for evaluating potential inter-population heterogeneity in drug treatment effects.

Considering CYP1A2 phenotype and genotype for optimizing the dose of olanzapine in the management of schizophrenia

INTRODUCTION

Schizophrenia, a mental disorder, is a debilitating condition which typically strikes young people in their early 20's. Antipsychotic medications are widely prescribed for the treatment of schizophrenia however a balancing act is necessary to provide the correct dose to each patient. It is suggested that a large number of patients discontinue antipsychotic pharmacotherapy because the treatments provided do not always reduce the positive symptoms of the disease, while many have adverse effects on the patients. This implies that neither the incorrect drug nor the optimal dosage for that patient is achieved.

AREAS COVERED

The current review investigates variability in response to olanzapine with a specific focus on the common intrinsic and extrinsic factors that influence both olanzapine and CYP1A2 activity. Furthermore, the authors discuss the utilization of phenotyping and genotyping of CYP1A2 and their potential utility in clinical practice for olanzapine dosing regimens. The authors also consider the potential of pharmacometrics compared to pharmacogenomics as a tool to personalize medicine.

EXPERT OPINION

Careful consideration must be given to the impact of a genetic variant on the disposition of a drug prior to implementing genetic 'tests' to determine response. CYP1A2 phenotypic assessment can yield important information regarding the disposition of olanzapine; however, it relies on the accuracy of the metric and the minimal impact of other metabolic pathways. The application of pharmacometrics provides an effective method to establish covariates that significantly influence olanzapine disposition which can incorporate phenotype and/or genotype.

Association between CYP1A2 gene single nucleotide polymorphisms and clinical responses to clozapine in patients with treatment-resistant schizophrenia

OBJECTIVES

Despite clozapine's superior clinical efficacy in treatment-resistant schizophrenia (TRS), its adverse effects, need for periodic leukocyte monitoring, cost and variable clinical outcomes mandate a clinical need to predict its treatment response. Although cytochrome P450 1A2 (CYP1A2) is the principal determinant of metabolism of clozapine, the role of CYP1A2 gene in the clinical response to clozapine is uncertain. Hence, we investigated its association with treatment responses and adverse events of clozapine in TRS.

METHODS

We evaluated four single nucleotide polymorphisms (SNP) in the CYP1A2 gene, clinical responses and serum clozapine levels in 101 consecutive patients with TRS on stable doses of clozapine. We defined clozapine response a priori and investigated allelic and genotypic associations. We assessed the socio-demographic and clinical profiles, premorbid adjustment, traumatic life events, cognition and disability of the participants, using standard assessment schedules for appropriate multivariate analyses.

RESULTS

Our results revealed that CYP1A2 gene SNP (*1C, *1D, *1E and *1F) were not associated with clozapine treatment response, adverse effects, serum clozapine levels or with disability (p values > 0.10).

CONCLUSION

As CYP1A2 gene SNP do not help to predict the clinical response to clozapine, routine screening for them prior to start clozapine is currently unwarranted. We suggest future longitudinal genome-wide association studies investigating clinical and pharmacogenetic variables together.

Association between common CYP1A2 polymorphisms and theophylline metabolism in non-smoking healthy volunteers

This study was designed to investigate the impact of cytochrome P450 (CYP) 1A2 polymorphisms on theophylline metabolism in a non-smoking healthy male Chinese population. Four polymorphisms CYP1A2 1C (G-3860A), G-3113A, CYP1A2 1F (C-163A) and CYP1A2 1B (C-5347T) were screened in 238 unrelated male volunteers. Then, a single oral 200-mg dose of theophylline was administered to 37 volunteers, who were selected from 238 volunteers based on the CYP1A2 genotype. CYP1A2 activities were evaluated by plasma 1,7-dimethylxanthine/caffeine ratios (17X/137X) after administration of 100-mg caffeine. The plasma concentrations of theophylline, 17X and 137X were determined by high-performance liquid chromatography. The activity of CYP1A2 was lower in volunteers with the -3113 AA genotype compared with those with the -3113 AG genotype (0.35 ± 0.04 versus 0.48 ± 0.07, p = 0.016) or the -3113 GG genotype (0.35 ± 0.04 versus 0.58 ± 0.22, p = 0.037). CYP1A2 1F polymorphisms were associated with increased CYP1A2 activity in volunteers with -3860G/-3113G/5347C homozygosity (0.66 ± 0.24 versus 0.46 ± 0.05, p = 0.034). However, theophylline metabolism showed no difference among volunteers carrying different haplotype pairs. CYP1A2 genetic polymorphisms influenced CYP1A2 enzyme activity as measured by caffeine, but CYP1A2 gene polymorphisms appeared to have limited influence on theophylline metabolism in our study.

Polymorphisms of cytochrome p450 genes in three ethnic groups from Russia

OBJECTIVE

To determine the prevalence of the most common allelic variants of CYP1A1, CYP1A2, CYP1B1, CYP2C9, CYP2E1, CYP2F1, CYP2J2 and CYP2S1 in a representative sample of the three ethnic groups (Russians, Tatars and Bashkirs) from Republic of Bashkortostan (Russia), and compare the results with existing data published for other populations.

MATERIAL AND METHODS

CYPs genotypes were determined in 742 DNA samples of healthy unrelated individuals representative of three ethnic groups. The CYPs gene polymorphisms were examined using the PCR-RLFP method.

RESULTS

Analysis of the CYP1A1 (rs1048943, rs4646903), CYP1A2 (rs762551), CYP2E1 (rs2031920) allele, genotype and haplotype frequencies revealed significant differences among healthy residents of the Republic of Bashkortostan of different ethnicities. Distribution of allele and genotype frequencies of CYP1A2 (rs35694136), CYP1B1 (rs1056836), CYP2C9 (rs1799853, rs1057910), CYP2F1 (rs11399890), CYP2J2 (rs890293), CYP2S1 (rs34971233, rs338583) genes were similar in Russians, Tatars, and Bashkirs. Analysis of the CYPs genes allele frequency distribution patterns among the ethnic groups from the Republic of Bashkortostan in comparison with the different populations worldwide was conducted.

CONCLUSION

The peculiarities of the allele frequency distribution of CYPs genes in the ethnic groups of the Republic of Bashkortostan should be taken into consideration in association and pharmacogenetic studies. The results of the present investigation will be of great help in elucidating the genetic background of drug response, susceptibility to cancer and complex diseases, as well as in determining the toxic potentials of environmental pollutants in our region.

Polymorphic metabolism by functional alterations of human cytochrome P450 enzymes

The study of cytochrome P450 pharmacogenomics is of particular interest because of its promise in the development of rational means to optimize drug therapy with respect to patient's genotype to ensure maximum efficacy with minimal adverse effects. Drug metabolizing P450 enzymes are polymorphic and are the main phase I enzymes responsible for the metabolism of clinical drugs. Therefore, polymorphisms in the P450s have the most impact on the fate of clinical drugs in phase I metabolism since almost 80% of drugs in use today are metabolized by these enzymes. Predictive genotyping for P450 enzymes for a more effective therapy will be routine for specific drugs in the future. In this review, we discuss the current knowledge of polymorphic metabolism by functional alterations in nonsynonymous SNPs of P450 1A2, 2A6, 2C8, 2C9, 2C19, 2D6, and 3A4 enzymes.

The effect of CYP1A2 gene polymorphisms on Theophylline metabolism and chronic obstructive pulmonary disease in Turkish patients

Cytochrome P450 (CYP) 1A2 gene polymorphisms are thought to be involved in the metabolism of theophylline (TP). We aimed to investigate the effect of CYP1A2*1C, CYP1A2*1D, CYP1A2*1E, and CYP1A2*1F polymorphisms of the CYP1A2 on TP metabolism by PCR-RFLP in 100 Turkish patients with chronic obstructive pulmonary disease (COPD) receiving TP. One hundred and one healthy volunteers were included as control group. The genotype frequencies of the CYP1A2*1D and CYP1A2*1F were found to be significantly different in the patients compared to the controls. The "T" allele at -2467 delT and the "C" allele at -163 C > A in the CYP1A2 displayed association with a significantly increased risk for COPD. "T" allele at - 2467 delT was also associated with a high risk of disease severity in COPD. In conclusion, our data suggest that genetic alterations in CYP1A2 may play a role both in the pharmacogenetics of TP and in the development of COPD.

Effects of cigarette smoking and cytochrome P450 2D6 genotype on fluvoxamine concentration in plasma of Japanese patients

Fluvoxamine is a selective serotonin reuptake inhibitor widely used in the treatment of depression and other psychiatric diseases. The aim of this study was to assess the clinical impact of cigarette smoking on plasma fluvoxamine concentration in Japanese patients, and evaluate whether the cytochrome P450 (CYP) 1A2 and CYP2D6 genotypes have effects on that concentration. Thirty-two Japanese patients receiving fluvoxamine were enrolled. They were maintained on the same daily dose of fluvoxamine (mean + or - S.D., 109.4 + or - 66.2 mg/d) for at least 4 weeks to obtain the steady-state plasma concentration. The steady-state plasma concentration-to-dose (C/D) ratio of fluvoxamine in patients who smoked (n = 6, 11.8 + or - 6.5 ng/ml/dose) was significantly lower than that in non-smoker patients (n = 26, 22.8 + or - 11.2 ng/ml/dose). There was no significant difference for the C/D ratio of fluvoxamine in patients with CYP1A2 -3860G/G, -3860G/A, and -3860A/A between non-smokers and smokers. Among non-smoker patients, the C/D ratios of fluvoxamine in those with one and two mutated alleles of CYP2D6 were 1.6- and 1.4-fold higher, respectively, than those with no mutated alleles, though the differences among those three genotype groups were not significant. Furthermore, stepwise multiple regression analysis revealed that cigarette smoking and daily dose had significant positive correlations with the plasma concentration of fluvoxamine. Our findings suggest that cigarette smoking has a significant impact on the steady-state plasma concentration of fluvoxamine in Japanese patients.

Structure, function, regulation and polymorphism and the clinical significance of human cytochrome P450 1A2

Human CYP1A2 is one of the major CYPs in human liver and metabolizes a number of clinical drugs (e.g., clozapine, tacrine, tizanidine, and theophylline; n > 110), a number of procarcinogens (e.g., benzo[a]pyrene and aromatic amines), and several important endogenous compounds (e.g., steroids). CYP1A2 is subject to reversible and/or irreversible inhibition by a number of drugs, natural substances, and other compounds. The CYP1A gene cluster has been mapped on to chromosome 15q24.1, with close link between CYP1A1 and 1A2 sharing a common 5'-flanking region. The human CYP1A2 gene spans almost 7.8 kb comprising seven exons and six introns and codes a 515-residue protein with a molecular mass of 58,294 Da. The recently resolved CYP1A2 structure has a relatively compact, planar active site cavity that is highly adapted for the size and shape of its substrates. The architecture of the active site of 1A2 is characterized by multiple residues on helices F and I that constitutes two parallel substrate binding platforms on either side of the cavity. A large interindividual variability in the expression and activity of CYP1A2 has been observed, which is largely caused by genetic, epigenetic and environmental factors (e.g., smoking). CYP1A2 is primarily regulated by the aromatic hydrocarbon receptor (AhR) and CYP1A2 is induced through AhR-mediated transactivation following ligand binding and nuclear translocation. Induction or inhibition of CYP1A2 may provide partial explanation for some clinical drug interactions. To date, more than 15 variant alleles and a series of subvariants of the CYP1A2 gene have been identified and some of them have been associated with altered drug clearance and response and disease susceptibility. Further studies are warranted to explore the clinical and toxicological significance of altered CYP1A2 expression and activity caused by genetic, epigenetic, and environmental factors.

Polymorphism of human cytochrome P450 enzymes and its clinical impact

Pharmacogenetics is the study of how interindividual variations in the DNA sequence of specific genes affect drug response. This article highlights current pharmacogenetic knowledge on important human drug-metabolizing cytochrome P450s (CYPs) to understand the large interindividual variability in drug clearance and responses in clinical practice. The human CYP superfamily contains 57 functional genes and 58 pseudogenes, with members of the 1, 2, and 3 families playing an important role in the metabolism of therapeutic drugs, other xenobiotics, and some endogenous compounds. Polymorphisms in the CYP family may have had the most impact on the fate of therapeutic drugs. CYP2D6, 2C19, and 2C9 polymorphisms account for the most frequent variations in phase I metabolism of drugs, since almost 80% of drugs in use today are metabolized by these enzymes. Approximately 5-14% of Caucasians, 0-5% Africans, and 0-1% of Asians lack CYP2D6 activity, and these individuals are known as poor metabolizers. CYP2C9 is another clinically significant enzyme that demonstrates multiple genetic variants with a potentially functional impact on the efficacy and adverse effects of drugs that are mainly eliminated by this enzyme. Studies into the CYP2C9 polymorphism have highlighted the importance of the CYP2C9*2 and *3 alleles. Extensive polymorphism also occurs in other CYP genes, such as CYP1A1, 2A6, 2A13, 2C8, 3A4, and 3A5. Since several of these CYPs (e.g., CYP1A1 and 1A2) play a role in the bioactivation of many procarcinogens, polymorphisms of these enzymes may contribute to the variable susceptibility to carcinogenesis. The distribution of the common variant alleles of CYP genes varies among different ethnic populations. Pharmacogenetics has the potential to achieve optimal quality use of medicines, and to improve the efficacy and safety of both prospective and currently available drugs. Further studies are warranted to explore the gene-dose, gene-concentration, and gene-response relationships for these important drug-metabolizing CYPs.

Insights into the substrate specificity, inhibitors, regulation, and polymorphisms and the clinical impact of human cytochrome P450 1A2

Human CYP1A2 is one of the major CYPs in human liver and metabolizes a variety of clinically important drugs (e.g., clozapine, tacrine, tizanidine, and theophylline), a number of procarcinogens (e.g. benzo[a]pyrene and aflatoxin B(1)), and several important endogenous compounds (e.g. steroids and arachidonic acids). Like many of other CYPs, CYP1A2 is subject to induction and inhibition by a number of compounds, which may provide an explanation for some drug interactions observed in clinical practice. A large interindividual variability in the expression and activity of CYP1A2 and elimination of drugs that are mainly metabolized by CYP1A2 has been observed, which is largely caused by genetic (e.g., SNPs) and epigenetic (e.g., DNA methylation) and environmental factors (e.g., smoking and comedication). CYP1A2 is primarily regulated by the aromatic hydrocarbon receptor (AhR) and CYP1A2 is induced through AhR-mediated transactivation following ligand binding and nuclear translocation. To date, more than 15 variant alleles and a series of subvariants of the CYP1A2 gene have been identified and some of they have been associated with altered drug clearance and response to drug therapy. For example, lack of response to clozapine therapy due to low plasma drug levels has been reported in smokers harboring the -163A/A genotype; there is an association between CYP1A2*1F (-163C>A) allele and the risk for leflunomide-induced host toxicity. The *1F allele is associated with increased enzyme inducibility whereas *1C causes reduced inducibility. Further studies are warranted to explore the clinical and toxicological significance of altered CYP1A2 expression and activity caused by genetic, epigenetic, and environmental factors.

Influence of genetic polymorphisms, smoking, gender and age on CYP1A2 activity in a Turkish population

Aims: To study the variation in CYP1A2 activity in relation to smoking, gender, age and CYP1A2 polymorphisms. Materials & methods: CYP1A2 activity was determined by plasma paraxanthine:caffeine ratio (17X:137X) 4 h after the intake of a standardized cup of coffee in 146 Turkish healthy volunteers. Seven CYP1A2 polymorphisms (-3860G>A, -3113G>A, -2467del/T, -739T>G, -729C>T, -163C>A and 5347T>C) were analyzed. Results: The 17X:137X ratios were increased in smokers (p < 0.0001) and tended to be higher in men both among nonsmokers (p = 0.051) and smokers (p = 0.064). Age-related differences were observed only among nonsmoking women (p = 0.024). The -163C>A polymorphism correlated with 17X:137X ratios only in smokers (p = 0.006). Furthermore, increased 17X:137X ratios were observed in CYP1A2 haplotype H4 (-3860G, -3113G, -2467del, -739T, -729C, -163A and 5347T) carriers in the overall study population (p = 0.026). Multiple regression analyses including smoking, gender, -163C>A genotype and age revealed a significant influence of smoking (p < 0.0001) and gender (p = 0.002) in the overall study population. However, in nonsmokers only the influence of gender remained significant (p = 0.021), while in smokers the influence of the -163C>A genotype held the statistical significance (p = 0.019). The influence of haplotype H4 remained significant (p = 0.028) in the overall study population in similar analyses. Conclusion: Smoking has the strongest impact on CYP1A2 activity, while gender and haplotype H4 showed marginal effects. The influence of the -163C>A polymorphism on CYP1A2 activity in smokers suggests an effect on the inducibility of the enzyme.

Polymorphisms of cytochrome P450 1A2 and N-acetyltransferase genes, meat consumption, and risk of colorectal cancer

PURPOSE

Polymorphic cytochrome P-450 1A2, N-acetyltransferase 1, and 2 are important enzymes involved in the biotransformation of aromatic and heterocyclic amines known as carcinogens for colorectal cancer. A hospital-based study was designed to investigate the association between colorectal cancer and cytochrome P-450 1A2, N-acetyltransferase 1, and N-acetyltransferase 2, with the interaction of meat consumption.

METHODS

We genotyped these polymorphisms for 727 colorectal cancer cases and 736 healthy controls. Information on sociodemographic characteristics and diet were ascertained using a structured questionnaire.

RESULTS

The colorectal cancer risk was significantly increased in rapid N-acetyltransferase 1 carriers with high white meat consumption (almost every day) compared to those carrying the slow N-acetyltransferase 1 genotype with low white meat consumption (less than once a week, odds ratio, 3.00; 95 percent confidence interval, 1.83-4.92). Furthermore, a gene-gene interaction between cytochrome P-450 1A2*1C and N-acetyltransferase 1 was found and modulated by white meat consumption.

CONCLUSIONS

N-acetyltransferase 1 might compete with cytochrome P-450 1A2*1C to increase the colorectal cancer risk in intermediate white meat consumers, whereas the rapid N-acetyltransferase 1 genotype may exert a harmful effect on individuals with high carcinogen exposure.

Variation in CYP1A2 activity and its clinical implications: influence of environmental factors and genetic polymorphisms

CYP1A2 is involved in the metabolism of several widely used drugs and endogenous compounds, and in the activation of procarcinogens. Both genetic and environmental factors influence the activity of this enzyme. The current knowledge regarding factors influencing the activity of CYP1A2 is summarized in this review. Substrates, inhibitors and inducers of CYP1A2 activity, as well as phenotyping probes, are discussed. The functional significance and clinical importance of CYP1A2 gene polymorphisms are reviewed and interethnic differences in the distribution of CYP1A2 variant alleles and haplotypes are summarized. Finally, future perspectives for the possible clinical applications of CYP1A2 genotyping are discussed.

CYP1A2 polymorphism (C > A at position −163) in Ovambos, Koreans and Mongolians

Cytochrome P450 1A2 (CYP1A2) plays an important role in metabolizing drugs and xenobiotics, and is a possible participant in the development of several human diseases. Recent studies have shown that genetic polymorphism of -163 C > A single nucleotide mutation of CYP1A2 increases the risk of myocardial infarction and modulates CYP1A2 activity. In this study, we investigated the frequency of the -163 C > A mutation in Ovambos (n = 177), Koreans (n = 250) and Mongolians (n = 153) and compared our results with other studies. Detection of this single nucleotide polymorphism was by polymerase chain reaction-restriction fragment length polymorphism analysis (PCR-RFLP). The frequencies of mutation (CYP1A2*-163A) in the Ovambos, Koreans and Mongolians were 0.46, 0.32 and 0.21, respectively. Ovambos showed a relatively higher frequency of mutation, similar to that of Tanzanians, while the Mongolians showed the lowest frequency of all study groups, including those from previous studies. This study is the first to investigate the distribution of the CYP1A2 (-163 C > A single nucleotide polymorphism) mutant allele in Ovambo, Korean and Mongolian populations.

New cytochrome P450 2D6*56 allele identified by genotype/phenotype analysis of cryopreserved human hepatocytes

Genotype/phenotype analysis with human hepatocytes has identified a new inactive CYP2D6 allele, CYP2D6*56. Cryopreserved human hepatocytes from 51 livers were evaluated for CYP2D6 activity with dextromethorphan as the probe substrate. Hepatocyte lots that lacked CYP2D6 activity were further evaluated for CYP2D6 expression and known genetic variations, including CYP2D6*2, *3, *4, *5, *6, *7, *8, *9, *10, *11, *14, *15, *17, *18, *19, *20, *25, *26, *29, *30, *35, *40, *41, *43, and various multiple copy CYP2D6 alleles (*1xn, *2xn, and *4xn) by the AmpliChip CYP450 prototype microarray (Roche Molecular Systems, Inc., Branchburg, NJ). Two discrepancies were uncovered between the CYP2D6 genotype and activity by this approach. In one sample, a previously unreported 3201C 224 T transition in exon 7 resulted in Arg344(CGA) being replaced by a stop codon (TGA), resulting in a CYP2D6 enzyme lacking the terminal 153 amino acids. This allele was given the designation of CYP2D6*56 and the GenBank accession number DQ282162. The lack of CYP2D6 activity in cryopreserved hepatocytes and microsomes found in the second sample, despite a normal level of CYP2D6 expression and a genotype (*10/*1) predictive of normal CYP2D6 activity, was attributed to enzyme inactivation by an unknown metabolite. The identification and characterization of the CYP2D6*56 allele indicates that commercial cryopreserved human hepatocytes may provide a valuable means to rapidly identify genetic variations with functional relevance. This integrated approach of identifying alleles and examining allele relationships to gene expression and function could be of tremendous value to understanding the mechanism responsible for functional differences in gene variation. The commercial availability of human cryopreserved hepatocytes also makes this potential readily available to any who are interested in it, not just those with access to private liver banks.

Phenotype-genotype analysis of CYP1A2 in Japanese patients receiving oral theophylline therapy

OBJECTIVE

To clarify the association between the cytochrome P450 (CYP) 1A2 genotype with the CYP1A2 phenotype and to search for the CYP1A2*1K haplotype, which has been shown to decrease CYP1A2 inducibility and/or other functional polymorphisms in Japanese.

METHODS

Two polymorphisms, CYP1A2*1C and CYP1A2*1F, were genotyped in 126 patients receiving oral slow-release theophylline (TP) therapy and in 224 healthy volunteers. The CYP1A2 phenotype was assessed by the plasma [1-methyluric acid (1U)+3-methylxanthine (3X)]/TP ratio in the patients. The volunteers were given 150 mg caffeine, and the urine [1X+1U+5-acetylamino-6-amino-3-methyluracil (AAMU)]/17U ratio was used for CYP1A2 phenotyping. CYP1A2 intron 1 and six exons (exon 2-exon 7) were sequenced in the patients whose (1U+3X)/TP ratios were below the mean-2SD of those of all patients, and intron 1 was also sequenced in an additional 20 healthy volunteers exhibiting putative low CYP1A2 activities.

RESULTS

The individual (1U+3X)/TP ratios ranged from 0.007 to 0.21 (a 30-fold difference) in the patients, and the (1X+1U+AAMU)/17U ratios ranged from 1.6 to 112 (a 70-fold difference) in the healthy volunteers. The CYP1A2 activities were not significantly influenced by CYP1A2*1C or CYP1A2*1F. We found no functional polymorphisms by a sequencing analysis.

CONCLUSION

These results suggest that the CYP1A2*1C and CYP1A2*1F genotypes are not crucial factors for the variability of CYP1A2 activity and that the CYP1A2*1K haplotype is either nil or only shows a very low frequency in Japanese.

Functional analysis of three CYP1A2 variants found in a Japanese population

Human cytochrome P450 1A2 (CYP1A2) catalyzes the metabolism of many important drugs and environmental chemicals. We previously reported three naturally occurring genetic polymorphisms (125C>G, Pro42Arg, CYP1A2*15; 1130G>A, Arg377Gln, *16; and 1367G>A, Arg456His, *8) found in a Japanese population. In this study, these variant enzymes were expressed in Chinese hamster V79 cells, and their mRNA and protein expression levels as well as catalytic activities were determined. All three variant enzymes showed reduced protein expression levels (66% for Pro42Arg and approximately 30% for Arg377Gln and Arg456His) compared with that of the wild type (WT) without any change in mRNA expression levels. Kinetic analysis for 7-ethoxyresorufin O-deethylation revealed that V(max) and V(max)/K(m) of all three variants were less than 3 and 1% of the WT, respectively, although the K(m) value was significantly increased only in the Arg377Gln variant (approximately a 9-fold increase). Markedly reduced activities of the three variants were also observed for phenacetin O-deethylation. In the reduced CO difference spectral analysis using recombinant proteins produced in the Sf21/baculovirus system, the peak at 450 nm seen in the WT protein was hardly observed in the three variants, suggesting marked reductions in their hemoprotein formation. These results suggest that Pro42, Arg377, and Arg456 are critical amino acids for the production of catalytically active CYP1A2 holoenzyme.

Rapid genotyping for relevant CYP1A2 alleles by pyrosequencing

OBJECTIVE

To develop a rapid and reliable screening method for identifying the relevant cytochrome P450 (CYP) 1A2 alleles CYP1A2*1D (-2467Tdel), *1F (-163A>C), and *1K (-739T>G, -729C>T, -163A>C) that are in linkage disequilibrium with the functionally relevant CYP1A2 polymorphisms and therefore are considered to be predictive for the CYP1A2 phenotype.

METHODS

CYP1A2 single nucleotide polymorphisms (SNPs) -2467Tdel, -739T>G, -729C>T, and -163A>C were screened for in 495 healthy Caucasian volunteers using newly developed pyrosequencing duplex and simplex assays. Conventional sequencing of randomly selected samples served as quality control.

RESULTS

Frequencies were 7.9% for CYP1A2*1D, 31.8% for *1F, and 0.4% for *1K. The observed distribution of homozygous and heterozygous carriers of the alleles corresponded to the predicted one according to the Hardy-Weinberg law. It also corresponded to reported allelic frequencies from Caucasians but differed significantly from the distribution seen in other ethnicities. The most frequent haplotype was -2467T/-739T/-729C/-163A (allelic frequency 61.6%), followed by -2467T/-739T/-729C/-163C (30.5%), -2467Tdel/-739T/-729C/-163A (5.1%), -2467Tdel/-739G/-729C/-163A (1.2%), and -2467Tdel/-739T/-729C/-163C (1.1%). Complete linkage disequilibrium (value of D' nearly 1) existed between -2467Tdel, -739T>G, and -729C>T and between -729T>G and -163A>C.

CONCLUSIONS

Pyrosequencing facilitates rapid and reliable detection of those CYP1A2 alleles that, based on current knowledge, can be considered predictive for the CYP1A2 phenotype.