Genetic polymorphism in the 5'-flanking region of human CYP1A2 gene: effect on the CYP1A2 inducibility in humans

CYP1A2*1C, CYP2E1*5B, and GSTM1 polymorphisms are predictors of risk and poor outcome in head and neck squamous cell carcinoma patients

Head and neck squamous cell carcinoma (HNSCC) is associated with environmental factors, especially tobacco and alcohol consumption. Most of the carcinogens present in tobacco smoke are converted into DNA-reactive metabolites by cytochrome P450 (CYPs) enzymes and detoxification of these substances is performed by glutathione S-transferases (GSTs). It has been suggested that genetic alterations, such as polymorphisms, play an important role in tumorigenesis and HNSCC progression. The aim of this study was to investigate CYP1A1, CYP1A2, CYP2E1, GSTM1, and GSTT1 polymorphisms as risk factors in HNSCC and their association with clinicopathologic data. The patients comprised 153 individuals with HNSCC (cases) and 145 with no current or previous diagnosis of cancer (controls). Genotyping of the single nucleotide polymorphisms (SNPs) of the CYP1A1, CYP1A2, and CYP2E1 genes was performed by PCR-RFLP and the GSTM1 and GSTT1 copy number polymorphisms (CNPs) were analyzed by PCR-multiplex. As expected, a significant difference was detected for tobacco and alcohol consumption between cases and controls (P<0.001). It was observed that the CYP1A2*1D (OR=16.24) variant and GSTM1 null alleles (OR=0.02) confer increased risk of HNSCC development (P<0.001). In addition, head and neck cancer alcohol consumers were more frequently associated with the CYP2E1*5B variant allele than control alcohol users (P<0.0001, OR=190.6). The CYP1A2*1C polymorphism was associated with tumor recurrence (log-rank test, P=0.0161). The CYP2E1*5B and GSTM1 null alleles were significantly associated with advanced clinical stages (T3+T4; P=0.022 and P=0.028, respectively). Overall, the findings suggested that the genetic polymorphisms studied are predictors of risk and are also associated with tumor recurrence, since they are important for determining the parameters associated with tumor progression and poor outcomes in HNSCC.

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.

The impact of NAT2 acetylator genotype on mutagenesis and DNA adducts from 2-amino-9H-pyrido[2,3-b]indole

2-amino-9H-pyrido[2,3-b]indole (AalphaC) is a carcinogenic heterocyclic aromatic amine (HAA) that is produced in high quantities in tobacco smoke and that also forms in charred meats. The bioactivation of AalphaC occurs by cytochrome P450-mediated (P450 1A2) N-oxidation of the exocyclic amine group, to form 2-hydroxyamino-9H-pyrido[2,3-b]indole (HONH-AalphaC). The HONH-AalphaC metabolite can then undergo further activation by phase II enzymes to form the penultimate ester species, which bind to DNA. Some epidemiological studies suggest a role for NAT2 genetic polymorphisms in human susceptibilities to various cancers from tobacco smoke and from consumption of well-done meats, where the exposures to AalphaC can be substantial. In this investigation, we have measured the genotoxicity of AalphaC in nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells stably transfected with human P450 1A2 and either the NAT2*4 (rapid, wild-type acetylator) or the NAT2*5B (the most common slow acetylator) allele, to determine the role of NAT2 phenotype in the biological effects of AalphaC. Mutations at the hypoxanthine phosphoribosyl transferase (hprt) locus were induced in a dose-dependent manner by AalphaC and were found to be highest in cells transfected with P450 1A2 and NAT2*4, followed by cells transfected with P450 1A2 and NAT2*5B. The level of formation of the deoxyguanosine (dG) adduct N-(deoxyguanosin-8-yl)-2-amino-9H-pyrido[2,3-b]indole (dG-C8-AalphaC) paralleled the mutagenic potency in these cell lines. However, AalphaC did not form DNA adducts or induce mutations in untransfected CHO cells or in cells only expressing P450 1A2. These findings clearly demonstrate that NAT2 genetic polymorphism plays a major role in the genotoxic potency of AalphaC.

CYP1A2 genetic polymorphisms and adenocarcinoma lung cancer risk in the Tunisian population

AIMS

In this study, the effects of four single nucleotide polymorphisms (SNPs), -3860G>A, -2467delT, -739T>G and -163C>A, of CYP1A2 gene on lung cancer were evaluated in Tunisian population.

MAIN METHODS

Four polymorphisms of CYP1A2 gene were analysed in 109 healthy smokers and in 101 lung cancer cases, including 63 with squamous cell carcinoma (SCC) and 41 with adenocarcinoma (AD). The genotyping for the SNPs -3860 G>A, -2467delT, -739T>G and -163C>A was performed by polymerase chain reaction (PCR)-restriction fragment length polymorphism analysis.

KEY FINDINGS

The results showed that smokers with CYP1A2 gene polymorphisms were associated with an increased risk for the development of lung AD. There was however no significant increased risk of developing lung SCC in smokers having CYP1A2 gene polymorphisms. An increased risk of developing AD was observed in smokers who are carriers of at least one copy of -3680A or -739G giving a significant odds ratio (OR) of 6.02 (CI=2.91-12.9) and 3.01 (CI=1.54-5.98), respectively.

SIGNIFICANCE

These genotyping data are consistent with the hypothesis that tobacco-specific-N-nitrosamines (TSN) such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are major contributors to the development of lung AD and that CYP1A2 gene product plays an important role in the metabolic activation of NNK. This study suggests that SNPs of CYP1A2 could be considered as promising biomarkers in the aetiology of lung AD in smokers.

Aromatic DNA adducts and polymorphisms in metabolic genes in healthy adults: findings from the EPIC-Spain cohort

Aromatic compounds such as polycyclic aromatic hydrocarbons, arylamines and heterocyclic amines require metabolic activation to form metabolites able to bind to DNA, a process mediated by polymorphic enzymes. We measured aromatic DNA adducts in white blood cells by the (32)P-post-labelling assay in a sample of 296 healthy adults (147 men and 149 women) from five regions of Spain. We also analyzed functional polymorphisms in the metabolic genes CYP1A1, CYP1A2, EPHX1, GSTM1, GSTT1, NAT2 and SULT1A1. A significant increased level of DNA aromatic adducts was found related to the fast oxidation-hydrolysis phenotype defined by the polymorphism I462V in CYP1A1, the allele A in IVS1-154C>A of CYP1A2 and the combination Tyrosine-Arginine for Y113H and H139R of EPHX1. Geometric means (adducts per 10(-9) normal nucleotides) were 2.17, 4.04 and 6.30 for slow, normal and fast phenotypes, respectively (P-trend = 0.01). Slow acetylation by NAT2 was associated with a significant decrease in adduct level; subjects with slow alleles *5A and *7A/B had in average 1.56 x 10(-9)adducts, as compared with 5.60 for those with normal NAT2 activity (P-value = 0.01). No association was seen with polymorphisms of other metabolic genes such as GSTM1, GSTT1 or SULT1A1. We concluded that the metabolic pathways of oxidation, hydrolysis and acetylation are relevant to the formation of bulky DNA adducts. This could suggest a potential involvement of aromatic compounds in the formation of such adducts; however, given lack of specificity of the post-labeling assay, a firm conclusion cannot be drawn.

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.

Comparison of CYP1A2 and NAT2 phenotypes between black and white smokers

The lower incidence rate of transitional cell carcinoma of the urinary bladder in blacks than in whites may be due to racial differences in the catalytic activity of enzymes that metabolize carcinogenic arylamines in tobacco smoke. To examine this, we compared cytochrome P4501A2 (CYP1A2) and N-acetyltransferase-2 activities (NAT2) in black and white smokers using urinary caffeine metabolites as a probe for enzyme activity in a community-based study of 165 black and 183 white cigarette smokers. The paraxanthine (1,7-dimethylxanthine, 17X)/caffeine (trimethylxanthine, 137X) ratio or [17X+1,7-dimethyluric acid (17U)]/137X ratio was used as an indicator of CYP1A2 activity. The 5-acetyl-amino-6-formylamino-3-methyluracil (AFMU)/1-methylxanthine (1X) ratio indicated NAT2 activity. The odds ratio for the slow NAT2 phenotype associated with black race was 0.4; 95% confidence intervals 0.2-0.7. The putative combined low risk phenotype (slow CYP1A2/rapid NAT2) was more common in blacks than in whites (25% vs. 15%, P<0.02). There were no significant racial differences in slow and rapid CYP1A2 phenotypes, and in the combined slow NAT2/rapid CYP1A2 phenotype. Age, education, cigarette smoking amount, body mass index, GSTM1 and GSTM3 genotypes were unrelated to CYP1A2 and NAT2 activity. Intake of cruciferous vegetables (primarily broccoli), red meat, carrots, grapefruit and onions predicted CYP1A2 activity either for all subjects or in race-specific analyses. Carrot and grapefruit consumption was related to NAT2 activity. Collectively, these results indicated that phenotypic differences in NAT2 alone or in combination with CYP1A2 might help explain the higher incidence rates of transitional cell bladder cancer in whites.

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.

Identification of the novel canine CYP1A2 1117 C>T SNP causing protein deletion

The pharmacokinetics of YM-64227 (4-cyclohexyl-1-ethyl-7-methylpyrido[2,3-d]-pyrimidine-2-(1H)-one), a novel and selective phosphodiesterase type 4 inhibitor, was characterized in beagle dogs. Based on the plasma parent drug to major hydroxylated metabolite ratio, 21 dogs were phenotyped as 16 extensive metabolizers (EM) and five poor metabolizers (PM). Nucleotide sequences of CYPs 1A2, 2B11, 2C21, 2D15, 2E1 and 3A12 were investigated in the EM and PM dogs. A CYP1A2 1117 C>T single nucleotide polymorphism was found, which resulted in an amino acid change from an Arg codon to a stop codon at position 373. All dogs phenotyped as PM were T/T homozygous, whereas EMs were C/C homozygous and C/T heterozygous. In Western blotting of liver microsomes, CYP1A protein expression was detected in the C/C and C/T types, but not in the T/T type. Of 65 dogs genotyped using genome DNA, the frequencies of the C and T alleles were 0.61 and 0.39, respectively, suggesting approximately 15% of the dogs would not express the CYP1A2 protein. The findings provide a coherent explanation for the inter-individual variability in the pharmacokinetics of CYP1A2 substrate drugs in dogs.

Functional pharmacogenetics/genomics of human cytochromes P450 involved in drug biotransformation

We investigated the elimination routes for the 200 drugs that are sold most often by prescription count in the United States. The majority (78%) of the hepatically cleared drugs were found to be subject to oxidative metabolism via cytochromes P450 of the families 1, 2 and 3, with major contributions from CYP3A4/5 (37% of drugs) followed by CYP2C9 (17%), CYP2D6 (15%), CYP2C19 (10%), CYP1A2 (9%), CYP2C8 (6%), and CYP2B6 (4%). Clinically well-established polymorphic CYPs (i.e., CYP2C9, CYP2C19, and CYP2D6) were involved in the metabolism of approximately half of those drugs, including (in particular) NSAIDs metabolized mainly by CYP2C9, proton-pump inhibitors metabolized by CYP2C19, and beta blockers and several antipsychotics and antidepressants metabolized by CYP2D6. In this review, we provide an up-to-date summary of the functional polymorphisms and aspects of the functional genomics of the major human drug-metabolizing cytochrome P450s, as well as their clinical significance.

Sex-specific differences in CYP450 isoforms in humans

BACKGROUND

The activity of various CYP isoforms is critical for maintaining the clinical effectiveness of many medications. Therefore, determining the sex-dependent activity of clinically relevant CYP families is highly important for optimal therapeutic effectiveness.

OBJECTIVE

This review examined the sex-dependent activity of CYP3A, CYP1A2, CYP2D6, CYP2C9, CYP2C19 and CYP2E1.

METHODS

This review searched for studies performed in humans and hormonal status was not a limiting factor.

RESULTS/CONCLUSIONS

The current evidence suggests that CYP2E1 and CYP1A2 activity is higher in males than females, while CYP3A, one of the most clinically relevant CYP isoforms, appears to have greater activity in females. Overall, more studies are needed to fully support these conclusions as there are many factors that influence drug metabolism and thus it is very difficult to isolate gender as a sole modulator of CYP activity.

Drug safety assurance through clinical genotyping: near-term considerations for a system-wide implementation of personalized medicine

The rationale and overall system-wide behavior of a clinical genotyping information system (both DNA analysis and data management) requires a near-term, scalable approach, which is emerging in the focused implementation of pharmacogenomics and drug safety assurance. The challenges to implementing a successful clinical genotyping system are described, as are how the benefits of a focused, near-term system for drug safety assessment and assurance overcome the logistical and operational challenges that perpetually hinder the development of a societal-scale clinical genotyping system. This rationale is based on the premise that a focused application domain for clinical genotyping, specifically drug safety assurance, provides a transition paradigm for both professionals and consumers of healthcare, thereby facilitating the movement of genotyping from bench to bedside and paving the way for the adoption of prognostic and diagnostic applications in clinical genomics.

Genetic determinants in the metabolism of bladder carcinogens in relation to risk of bladder cancer

Genetically determined factors that alter the metabolism of tobacco carcinogens can influence an individual's susceptibility to bladder cancer. The associations between the genotypes of glutathione S-transferase (GST) M1, GSTP1, GSTT1 and N-acetyltransferase (NAT) 1 and the phenotypes of NAT2 and cytochrome P450 (CYP) 1A2 and bladder cancer risk were examined in a case-control study involving 731 bladder cancer patients and 740 control subjects in Los Angeles County, California. Individual null/low-activity genotypes of GSTM1, GSTT1 and GSTP1 were associated with a 19-48% increase in odds ratio (OR) of bladder cancer. The strongest association was noted for GSTM1 [OR for the null genotype = 1.48, 95% confidence interval (CI) = 1.19-1.83]. When the three GST genes were examined together, there was a monotonic, statistically significant association between increasing number of null/low-activity genotypes and risk (P for trend = 0.002). OR (95% CI) for one and two or more null/low-activity GST genotypes was 1.42 (1.12-1.81) and 1.71 (1.25-2.34), respectively, relative to the absence of null/low-activity GST genotype. NAT2 slow acetylation was associated with doubled risk of bladder cancer among individuals with known high exposures to carcinogenic arylamines (OR = 2.03, 95% CI = 1.12-3.69, P = 0.02). The effect of NAT2 slow acetylation was even stronger in the presence of two or more null/low-activity GST genotypes. There were no associations between bladder cancer risk and NAT1 genotype or CYP1A2 phenotype.

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.

Antipsychotic-induced tardive dyskinesia and polymorphic variations in COMT, DRD2, CYP1A2 and MnSOD genes: a meta-analysis of pharmacogenetic interactions

Despite accumulating evidence pointing to a genetic basis for tardive dyskinesia, results to date have been inconsistent owing to limited statistical power and limitations in molecular genetic methodology. A Medline, EMBASE and PsychINFO search for literature published between 1976 and June 2007 was performed, yielding 20 studies from which data were extracted for calculation of pooled estimates using meta-analytic techniques. Evidence from pooled data for genetic association with tardive dyskinesia (TD) showed (1) in COMT(val158met), using Val-Val homozygotes as reference category, a protective effect for Val-Met heterozygotes (OR=0.63, 95% CI: 0.46-0.86, P=0.004) and Met carriers (OR=0.66, 95% CI: 0.49-0.88, P=0.005); (2) in Taq1A in DRD2, using the A1 variant as reference category, a risk-increasing effect for the A2 variant (OR=1.30, 95% CI: 1.03-1.65, P=0.026), and A2-A2 homozygotes using A1-A1 as reference category (OR=1.80, 95% CI: 1.03-3.15, P=0.037); (3) in MnSOD Ala-9Val, using Ala-Ala homozygotes as reference category, a protective effect for Ala-Val (OR=0.37, 95% CI: 0.17-0.79, P=0.009) and for Val carriers (OR=0.49, 95% CI: 0.24-1.00, P=0.047). These analyses suggest multiple genetic influences on TD, indicative of pharmacogenetic interactions. Although associations are small, the effects underlying them may be subject to interactions with other loci that, when identified, may have acceptable predictive power. Future genetic research will take advantage of new genomic knowledge. Molecular Psychiatry (2008) 13, 544-556; doi:10.1038/sj.mp.4002142; published online 8 January 2008.

Biomonitoring of complex occupational exposures to carcinogens: the case of sewage workers in Paris

Background

Sewage workers provide an essential service in the protection of public and environmental health. However, they are exposed to varied mixtures of chemicals; some are known or suspected to be genotoxics or carcinogens. Thus, trying to relate adverse outcomes to single toxicant is inappropriate. We aim to investigate if sewage workers are at increased carcinogenic risk as evaluated by biomarkers of exposure and early biological effects.

Methods/design

This cross sectional study will compare exposed sewage workers to non-exposed office workers. Both are voluntaries from Paris municipality, males, aged (20–60) years, non-smokers since at least six months, with no history of chronic or recent illness, and have similar socioeconomic status. After at least 3 days of consecutive work, blood sample and a 24-hour urine will be collected. A caffeine test will be performed, by administering coffee and collecting urines three hours after. Subjects will fill in self-administered questionnaires; one covering the professional and lifestyle habits while the a second one is alimentary. The blood sample will be used to assess DNA adducts in peripheral lymphocytes. The 24-hour urine to assess urinary 8-oxo-7, 8-dihydro-2'-deoxy-Guanosine (8-oxo-dG), and the in vitro genotoxicity tests (comet and micronucleus) using HeLa S3 or HepG2 cells. In parallel, occupational air sampling will be conducted for some Polycyclic Aromatic Hydrocarbons and Volatile Organic Compounds. A weekly sampling chronology at the offices of occupational medicine in Paris city during the regular medical visits will be followed. This protocol has been accepted by the French Est III Ethical Comitee with the number 2007-A00685-48.

Discussion

Biomarkers of exposure and of early biological effects may help overcome the limitations of environmental exposure assessment in very complex occupational or environmental settings.

Variant CYP2C9 Alleles and Warfarin Concentrations in Patients Receiving Low-Dose Versus Average-Dose Warfarin Therapy

This study compared the frequency of variant cytochrome P450 2C9 ( CYP2C9) alleles and warfarin S/R concentration ratio in patients who required low-dose (<2.5 mg/day) and average-dose (5 ± 0.5 mg/day) warfarin. Patients who achieved a therapeutic international normalized ratio were recruited from the Atlanta Veterans Affairs Medical Center anticoagulation clinic. CYP2C9*2 and *3 alleles were determined by validated Taqman allelic discrimination assays. Warfarin S and R concentrations were determined by chiral capillary electrochromatography with electrospray ionization mass spectrometry. At least 1 variant allele was found in 66.7% and 22.2% of patients in the low-dose and average-dose groups, respectively ( P = .001, χ2). The warfarin S/R concentration ratio was 0.665 (range, 0.162-3.58) and 0.452 (range, 0.159-2.36) for patients receiving low-dose and average-dose therapy, respectively ( P = .097). A warfarin requirement of <2.5 mg/day and an elevated warfarin S/R concentration ratio were each associated with a higher frequency of variant CYP2C9 alleles.

From human genetics and genomics to pharmacogenetics and pharmacogenomics: past lessons, future directions

A brief history of human genetics and genomics is provided, comparing recent progress in those fields with that in pharmacogenetics and pharmacogenomics, which are subsets of genetics and genomics, respectively. Sequencing of the entire human genome, the mapping of common haplotypes of single-nucleotide polymorphisms (SNPs), and cost-effective genotyping technologies leading to genome-wide association (GWA) studies - have combined convincingly in the past several years to demonstrate the requirements needed to separate true associations from the plethora of false positives. While research in human genetics has moved from monogenic to oligogenic to complex diseases, its pharmacogenetics branch has followed, usually a few years behind. The continuous discoveries, even today, of new surprises about our genome cause us to question reviews declaring that "personalized medicine is almost here" or that "individualized drug therapy will soon be a reality." As summarized herein, numerous reasons exist to show that an "unequivocal genotype" or even an "unequivocal phenotype" is virtually impossible to achieve in current limited-size studies of human populations. This problem (of insufficiently stringent criteria) leads to a decrease in statistical power and, consequently, equivocal interpretation of most genotype-phenotype association studies. It remains unclear whether personalized medicine or individualized drug therapy will ever be achievable by means of DNA testing alone.

[Review of sick house syndrome]

'Sick house syndrome' (SHS) is a health issue that closely resembles sick building syndrome (SBS) that had occurred in European countries. The aim of this review is to clarify the characteristics of SHS by reviewing previous reports rigorously. We propose the definition of SHS as "health impairments caused by indoor air pollution, regardless of the place, causative substance, or pathogenesis". Cases of SBS are reported to occur predominantly in offices and sometimes schools, whereas those of SHS are usually found in general dwellings. In many cases, SHS is caused by biologically and/or chemically polluted indoor air. Physical factors might affect the impairments of SHS in some cases. It is considered that symptoms of SHS develop through toxic, allergic and/or some unknown mechanisms. Psychological mechanisms might also affect the development of SHS. It is still unclear whether SBS and SHS are very close or identical clinical entities, mostly because a general agreement on a diagnostic standard for SHS has not been established. Previous research gradually clarified the etiology of SHS. Further advances in research, diagnosis, and treatment of SHS are warranted with the following measures. Firstly, a clinical diagnostic standard including both subjective and objective findings must be established. Secondly, a standard procedure for assessing indoor air contamination should be established. Lastly, as previous research indicated multiple causative factors for SHS, an interdisciplinary approach is needed to obtain the grand picture of the syndrome.

Functional polymorphisms of the cytochrome P450 1A2 (CYP1A2) gene and prolonged QTc interval in schizophrenia

CYP1A2 is an important inducible enzyme involved in the metabolism of antipsychotics. This study examined two functional polymorphisms in the gene as potential markers in predicting prolongation of QTc interval in patients treated with antipsychotics. QT intervals were measured by 12-lead electrocardiography (ECG) for patients with a DSM-IV diagnosis of schizophrenia. Genomic DNA extracted from venous blood were genotyped for the two polymorphisms by PCR-RFLP. Statistically significant result for CYP1A2(*)1F was noted for all patients receiving chlorpromazine equivalent doses of above 300 mg and also for a further subgroup on antipsychotics known to be CYP1A2 substrates (p=0.007, mean QTc in ms for A/A: 395.5+/-15.1, A/C: 425.7+/-25.1, C/C: 427.3+/-20.7). For CYP1A2(*)1C, there was no statistically significant association between genotypes and mean QTc interval. Overall, there was a trend of those with the C allele of the CYP1A2(*)1F polymorphism having longer QTc intervals. The results of this study suggest that the CYP1A2(*)1F polymorphism may contribute to the risk of developing prolonged QT-interval in patients who are treated with higher doses of antipsychotics.

Caffeine intake and small-for-gestational-age birth: modifying effects of xenobiotic-metabolising genes and smoking

The relationship between caffeine consumption and small-for-gestational-age (SGA) birth remains uncertain. However, factors that can influence caffeine metabolism, such as genetic polymorphisms, have not been considered, while other similar factors such as smoking and ethnicity have not always been fully accounted for in the interpretation of results. A case-control study was carried out comprising 493 cases and 472 controls. Cases were newborns whose birthweight was below the 10th percentile according to gestational age and sex, based on national norms, and controls were at or above the 10th percentile. Caffeine consumption from beverages was estimated for each pregnancy trimester. Maternal and newborn variants in the CYP1A2 and CYP2E1 genes involved in the metabolism of caffeine were determined. Contrasting consumption >or=300 mg/day with a lower level, or using caffeiwne as a continuous measure, while adjusting for smoking and nausea, showed no increased risk for SGA. However, when stratifying for cigarette smoking, caffeine odds ratios (for the continuous and dichotomous measures) in the first trimester were statistically heterogeneous, suggesting a greater risk among non-smokers. Using birthweight as the outcome and caffeine as a continuous measure, a small 38 g [95% confidence interval -68, -8] decrement for every 100 mg of daily caffeine was observed in the third trimester. The studied polymorphisms did not modify the effect of caffeine. Caffeine consumption is unlikely to be a major risk factor for SGA or low birthweight in pregnant women.

Metabolic differences between Asian and Caucasian patients on clozapine treatment

OBJECTIVE

To establish if there are ethnic differences in the various metabolic disturbances that are common with clozapine treatment.

METHOD

Forty subjects (20 Asians and 20 Caucasians) with a diagnosis of schizophrenia were recruited for the study. Clozapine blood levels as well as fasting blood glucose, lipid levels, and liver function tests were established. Other clinical parameters such as blood pressure and Body Mass Index (BMI) were recorded for each patient.

RESULTS

The mean clozapine dose was significantly higher in the Caucasian subjects (432.5+/-194.7 mg) as compared to the Asian subjects (175.6+/-106.9 mg) (p<0.001) while the mean weight-corrected dose for Asian patients was lower (3.0+/-1.9 and 5.0+/-2.1 mg/kg, respectively, p=0.005). There were, however, no ethnic differences in the mean plasma clozapine concentration (415.3+/-185.8 ng/ml in Caucasians and 417.1+/-290.8 ng/ml in Asians). BMI were significantly higher in Caucasians, as were the number of subjects with hypertension; levels of hepatic enzymes were higher in the Asian group.

CONCLUSIONS

Not only are there pharmacokinetic differences between Asian and Caucasian patients receiving clozapine, but there may also be differential emergence of certain metabolic abnormalities like hypertension and weight gain in these two ethnic groups. However, the effects of life style including diet and exercise cannot be excluded.

Comparisons of CYP1A2 genetic polymorphisms, enzyme activity and the genotype-phenotype relationship in Swedes and Koreans

OBJECTIVES

To investigate the CYP1A2 genotype-phenotype relationship and to compare CYP1A2 genetic polymorphisms and enzyme activity in terms of the effect of smoking and oral contraceptive (OC) use in Swedes and Koreans.

METHODS

CYP1A2 enzyme activity was determined in 194 and 150 healthy Swedish and Korean subjects, respectively, on the basis of the 4-h plasma paraxanthine/caffeine (17X/137X) ratio determined using high-performance liquid chromatography. Genotyping for the -3860G>A, -2467delT, -739 T>G, -729 C>T, -163C>A and -3113A>G polymorphisms was performed by PCR-restriction fragment length polymorphism analysis.

RESULTS

The mean 17X/137X ratio was 1.54-fold higher in Swedes than in Koreans (mean difference: 0.16; 95% CI of the mean difference: 0.12, 0.20; p < 0.0001). Smokers had a significantly higher 17X/137X ratio (higher CYP1A2 activity) than non-smokers, while Swedish OC users had a significantly lower 17X/137X ratio than non-users (mean difference: 0.31, 95% CI of the mean difference: 0.23, 0.39; p < 0.0001). No effect of gender differences on enzyme activity was observed. Four known (CYP1A2*1A, *1D, *1F, and *1L) and two novel haplotypes (CYP1A2*1V and CYP1A2*1W) were found. CYP1A2*1K was rare in Swedes and absent in Koreans. No significant genotype-phenotype relationship was observed, with the exception of CYP1A2*1F in Swedish smokers, where it was associated with higher enzyme inducibility (p = 0.02). Koreans displayed a significantly lower mean 17X/137X ratio than Swedes having the same CYP1A2 genotype, smoking habit and OC use.

CONCLUSIONS

We found significant differences in CYP1A2 enzyme activity between Swedes and Koreans that could not be explained by environmental factors or the CYP1A2 haplotypes examined, despite differences in allele frequencies. None of the investigated CYP1A2 haplotypes are critical in inducing variations in enzyme activity, with the exception of CYP1A2*1F.

Polymorphism of selected enzymes involved in detoxification and biotransformation in relation to lung cancer

Available data indicate that there are significant differences in individual susceptibility to lung cancer within the human population. It is believed to be underlie by inherited genetic predispositions related to the genetic polymorphism of several enzymes involved in the detoxification and xenobiotic metabolism. In this review, we collect and discuss the evidence reported up to date on the association between lung cancer and genetic polymorphism of cytochromes P450, N-acetyltransferase, glutathione S-transferases, microsomal epoxide hydrolase, NAD(P)H:quinone oxidoreductase, myeloperoxidase and glutathione peroxidase. All these genes might appear to be candidates for lung cancer susceptibility genes, nevertheless, the present state of the art still offers only a limited explanation of the link between such polymorphisms and increased risk of lung cancer.

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.

Association between polymorphisms of biotransformation and DNA-repair genes and risk of colorectal cancer in Taiwan

The relationship between diet and colorectal cancer has been previously demonstrated and supported with strong epidemiological evidence. The role of genetic polymorphisms has, however, been less well elaborated upon. We conducted a hospital-based case-control study including 727 cases and 736 healthy controls to evaluate the associations of the polymorphic phase-I and -II biotransformations (CYP1A1, CYP1A2, GSTM1, GSTT1, GSTP1, NAT1 and NAT2) and DNA-repair enzymes (XRCC1, XRCC3 and XPD) with the risk of contracting colorectal cancer. We found that men featuring the CYP1A1*2C G/G genotype, the GSTT1 null genotype and XPD 751 with the Gln allele were associated with an elevated risk of colorectal cancer than were men who did not exhibit such genetic features. Multivariate logistic regression analysis revealed that individuals featuring more than two high-risk genotypes increased the colorectal-cancer risk 3.1-fold (OR = 3.1, 95% CI = 1.8-5.2). For women, subjects featuring the CYP1A1*2C G/G genotype and the XRCC3 Thr/Thr genotype faced a 3.1-fold greater risk (95% CI = 1.3-7.0) of colorectal cancer when compared to those featuring the CYP1A1*2C A allele and the XRCC3 Met allele. Taken together, this study suggests that polymorphisms of genes involved in biotransformation and DNA repair could modulate colorectal-cancer risk in Taiwan.

Dietary phytoestrogen intake is associated with reduced colorectal cancer risk

Evidence suggests dietary phytoestrogens may reduce the risk of certain hormonal cancers (e.g. breast and prostate). There is a paucity of data regarding phytoestrogens and colorectal cancer risk. Phytoestrogens are plant compounds with estrogen-like activities. Main classes include isoflavones (found in legumes such as soy) and lignans (found in grains, seeds, nuts, fruits, and vegetables). Although isoflavones have dominated phytoestrogen cancer research, lignans may be more relevant to North American diets. Food questionnaires and analytic databases have recently been modified to incorporate some lignan information. We conducted a case-control study to evaluate the association between phytoestrogen intake and colorectal cancer risk. Colorectal cancer cases were diagnosed in 1997-2000, aged 20-74 y, identified through the population-based Ontario Cancer Registry, and recruited by the Ontario Familial Colorectal Cancer Registry. Controls were a sex and age-group matched random sample of the population of Ontario. Epidemiologic and food frequency questionnaires were completed by 1095 cases and 1890 control subjects. Multivariate logistic regression analysis was used to obtain adjusted odds ratio (OR) estimates. Dietary lignan intake was associated with a significant reduction in colorectal cancer risk [OR (T3 vs. T1) = 0.73; 95% CI: 0.56, 0.94], as was isoflavone intake [OR (T3 vs. T1) = 0.71; 95% CI: 0.58, 0.86]. We evaluated interactions between polymorphic genes that encode enzymes possibly involved in metabolism of phytoestrogens (CYPs, catechol O-methyl transferase, GSTs, and UGTs) and found no significant effect modification with respect to phytoestrogen intake. This finding that phytoestrogen intake may reduce colorectal cancer risk is important, because dietary intake is potentially modifiable.

Caffeine N3-demethylation (CYP1A2) in a population with an increased exposure to polychlorinated biphenyls

OBJECTIVE

To investigate the CYP1A2 phenotype distribution in a population with an increased exposure to polychlorinated biphenyls (PCBs) that would likely induce an increased activity of this enzyme. Further, to investigate the effect of sex, smoking, and oral contraceptive use on the CYP1A2 activity.

METHODS

In 305 randomly selected Faroese residents aged 18-60 years, the CYP1A2 activity was determined following oral intake of a caffeine dose and subsequent determination of the urinary metabolites and calculation of the caffeine metabolic ratio (CMR). PCB exposure was assessed by measuring the serum concentration of major congeners.

RESULTS

The CYP1A2 phenotype distribution was unimodal. The CMR was significantly higher both in smoking men and in smoking women, independent of oral contraceptive use, as compared with non-smokers. Among non-smokers, the CMR was significantly higher in women not using oral contraceptives than in those using oral contraceptives; a similar difference could not be established among smokers. The CMR appeared higher in men than in women, but stratified analyses confirmed a significant sex-related difference only among smokers not using oral contraceptives. Overall, the mean CMR in Faroese was significantly higher compared with the mean CMR in Danish historical controls. No association was found with PCB exposure and individual PCB congeners, except for one of three dioxin-like congeners, in confounder-adjusted multiple regression analyses.

CONCLUSION

The CYP1A2 phenotype in Faroese residents was unimodally distributed and showed the inducing effect of smoking and the inhibiting effect of use of oral contraceptives, but a sex-related difference was not apparent after confounder adjustment. There was no statistically significant association between CMR and PCB exposure.

Single nucleotide polymorphisms: early diagnosis and risk assessment in genitourinary malignancy

Genetic screening for malignancy has been limited to high-risk individuals with a strong hereditary predisposition to cancer. With the cloning of the human genome, it has become apparent that genetic anomalies are not limited to high-risk individuals; more than 10 million genetic variants exist. Because the vast majority of these genetic variants have no functional significance, current efforts are focused on identification of which impact cancer development and/or progression. Here, we review the rationale for studying polymorphic variants in urologic malignancies, prior studies in the field, and future avenues of research.

Effect of Caffeine Intake 12 or 24 Hours Prior to Melatonin Intake and CYP1A2*1F Polymorphism on CYP1A2 Phenotyping by Melatonin

Earlier evidence suggests that melatonin is almost exclusively metabolised by CYP1A2 and could serve as a probe drug for CYP1A2 phenotyping. However, caffeine inhibits the metabolism of melatonin by CYP1A2 and dietary caffeine could be a potential confounder for the measurement of CYP1A2 activity with melatonin. We undertook a 3-phase cross-over study in 12 healthy volunteers to examine whether caffeine (200 mg single dose), taken 12 hr or 24 hr prior to melatonin intake, would affect the results of CYP1A2 phenotyping results as assessed by a spot sample melatonin concentration 1.5 hr after intake of 6 mg of melatonin orally. In addition we examined the influence of the CYP1A2*1F polymorphism on the phenotyping results by combining the present material with another 12 persons from a previous study. Caffeine, co-administered 12 or 24 hr prior to melatonin intake, did not have any significant effect on the 1.5 hr melatonin concentration (P=0.086 for ANOVA), but in two volunteers about 4 times increase in melatonin concentration was observed after caffeine intake 12 hr (but not 24 hr) before phenotyping with melatonin. Also, individuals homozygous for the CYP1A2*1A allele had clearly higher 1.5 hr melatonin concentration compared with the *1F/*1F or the *1F/*1A genotypes. Abstinence from caffeine for 24 hr prior to melatonin intake should be enough to overcome the possible confounding effect of caffeine on the CYP1A2 phenotyping with melatonin. Also, melatonin may be a sensitive probe to detect phenotypic differences with regard to CYP1A2*1F polymorphism. Melatonin might be, thus, advantageous for CYP1A2 phenotyping compared to the standard probe caffeine.

Genetic susceptibility to Tardive Dyskinesia in chronic schizophrenia subjects: V. Association of CYP1A2 1545 C>T polymorphism

Tardive dyskinesia (TD) is an iatrogenic disorder observed in approximately 20-30% of schizophrenia patients on long-term treatment with typical antipsychotic drugs. CYP1A2 is involved in the metabolism of atypical antipsychotic drugs such as clozapine and olanzapine. It is not directly involved in the metabolism of typical antipsychotic drugs, but gains importance when the schizophrenia patients are under long-term chronic treatment, acting as a low-affinity high-capacity metabolizing enzyme. In this study, we have completely sequenced the coding region to ascertain the presence of common coding polymorphisms and their role if any in susceptibility to TD and schizophrenia. Four previously reported polymorphisms, CYP1A2*1F (intron A), rs2472304 & rs3743484 (intron D) and rs2470890 (CYP1A2 1545 C>T) in exon 7 were identified. We further investigated whether the CYP1A2 1545 C>T polymorphism has any role to play in susceptibility to TD and in schizophrenia per se. Association of this single nucleotide polymorphism with TD (P=0.03) and schizophrenia (P=0.04) was observed, but was rendered insignificant after corrections for multiple comparisons.

Role of the aryl hydrocarbon receptor in drug metabolism

The aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor that regulates the transcription of certain key enzymes involved in the metabolism of xenobiotic substances including some drugs. The AhR can be activated by a wide range of classes of compounds (e.g. polycyclic aromatic hydrocarbons, benzimidazoles and flavonoids), and interacts with a number of other proteins, including nuclear hormone receptors such as the oestrogen and androgen receptors. Activation of the AhR antagonises the oestrogen receptor and can lead to modulation of its transcriptional activity; thus, activating the AhR may serve as a target for breast cancer therapy. Disruption of normal signalling by drug interactions with the AhR or downstream components of this pathway could result in adverse effects, such as the bioactivation of procarcinogens or the disruption of normal homeostasis. The cytochrome P450s CYP1A1, -1B1, -1A2 and -2S1 are regulated by the AhR, and they are all involved in the metabolism of endogenous substrates as well as xenobiotics. Polymorphisms in the AhR, or polymorphisms in enzymes regulated by the AhR, may cause variations in response to certain drugs in different individuals; this needs to be taken into consideration when administering drugs that interact with this pathway.

Xenobiotic-metabolizing enzymes involved in activation and detoxification of carcinogenic polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental carcinogens and metabolized by a variety of xenobiotic-metabolizing enzymes such as cytochrome P450 (P450 or CYP), epoxide hydrolase, glutathione transferase, UDP-glucuronosyltransferase, sulfotransferase, NAD(P)H quinone oxidoreductase 1, and aldo-keto reductase. These enzymes mainly participate in the conversion of PAHs to more polar and water-soluble metabolites, and the resultant metabolites are readily excreted from the body. However, during the course of metabolism, a variety of unstable and reactive intermediates of PAHs are formed, and these metabolites attack DNA, causing cell toxicity and transformation. P450s and epoxide hydrolase convert PAHs to proximate carcinogenic metabolites, PAH-diols, and these products are further metabolized by P450s to ultimate carcinogenic metabolites, PAH diol-epoxides, or by aldo-keto reductase to reactive PAH o-quinones. PAHs are also activated by P450 and peroxidases to reactive radical cations that bind covalently to DNA. The oxygenated and reactive metabolites of PAHs are usually converted to more polar and detoxified products by phase II enzymes. Inter-individual differences exist in levels of expression and catalytic activities of a variety of enzymes that activate and/or detoxify PAHs in various organs of humans and these phenomena are thought to be critical in understanding the basis of individual differences in response to PAHs. Factors affecting such variations include induction and inhibition of enzymes by diverse chemicals and, more importantly, genetic polymorphisms of enzymes in humans.

Coffee and health: a review of recent human research

Coffee is a complex mixture of chemicals that provides significant amounts of chlorogenic acid and caffeine. Unfiltered coffee is a significant source of cafestol and kahweol, which are diterpenes that have been implicated in the cholesterol-raising effects of coffee. The results of epidemiological research suggest that coffee consumption may help prevent several chronic diseases, including type 2 diabetes mellitus, Parkinson's disease and liver disease (cirrhosis and hepatocellular carcinoma). Most prospective cohort studies have not found coffee consumption to be associated with significantly increased cardiovascular disease risk. However, coffee consumption is associated with increases in several cardiovascular disease risk factors, including blood pressure and plasma homocysteine. At present, there is little evidence that coffee consumption increases the risk of cancer. For adults consuming moderate amounts of coffee (3-4 cups/d providing 300-400 mg/d of caffeine), there is little evidence of health risks and some evidence of health benefits. However, some groups, including people with hypertension, children, adolescents, and the elderly, may be more vulnerable to the adverse effects of caffeine. In addition, currently available evidence suggests that it may be prudent for pregnant women to limit coffee consumption to 3 cups/d providing no more than 300 mg/d of caffeine to exclude any increased probability of spontaneous abortion or impaired fetal growth.

Association of CYP1A2 genetic polymorphisms with hepatocellular carcinoma susceptibility: a case-control study in a high-risk region of China

OBJECTIVES

Aflatoxin B1 exposure is one of the major risk factors for hepatocellular carcinoma (HCC). CYP1A2 is a cytochrome P450 isoenzyme that plays an important role in the bioactivation of AFB1 to its carcinogenic metabolite. The study was designed to assess whether genetic polymorphisms in CYP1A2 are associated with HCC susceptibility in a high-risk region.

METHODS

A case-control study of 431 HCC cases and 550 cancer-free controls recruited from an HCC endemic region in China was carried out. Three single nucleotide polymorphisms, namely -3860G > A (CYP1A2*1C), -3113G > A, and 5347T > C (CYP1A2*1B) were genotyped by polymerase chain reaction-restriction fragment length polymorphism methods.

RESULTS

Homozygous carriers of the major haplotype -3860G/-3113G/5347C were associated with increased HCC susceptibility in the overall population (odds ratio [OR] = 1.65, 95% confidence interval [CI]: 1.11-2.46, P = 0.014), in HBsAg seronegative individuals (OR = 2.69, 95% CI: 1.43-5.06, P = 0.002), and in heavy smokers (OR = 2.14, 95% CI: 1.21-3.80, P=0.009). In addition, individuals carrying at least one CYP1A2*1C allele showed significantly decreased HCC risk (OR = 0.49, 95% CI: Q0.27-0.86, P = 0.013) in the HBsAg seronegative subpopulation. Furthermore, as compared with HBsAg seropositive patients, wild-type homozygotes of the CYP1A2*1C polymorphism were significantly over-represented in HBsAg seronegative patients (P = 0.024). No significant association between CYP1A2 genetic polymorphisms and HCC risk was observed in either HBsAg seropositive individuals or non-smokers.

CONCLUSIONS

CYP1A2 genetic polymorphisms are associated with HCC susceptibility in smokers and HBsAg seronegative individuals in the Fusui endemic region.

Caffeine metabolites in umbilical cord blood, cytochrome P-450 1A2 activity, and intrauterine growth restriction

Studies investigating antenatal caffeine consumption and reproductive outcomes show conflicting results, and most studies have used maternal self-reported caffeine consumption to estimate fetal exposure. This study (n=1,606) was specifically designed to test the association of caffeine and its primary metabolites in umbilical cord blood with intrauterine growth restriction (IUGR). Pregnant women were recruited from 56 obstetric practices and 15 clinics affiliated with six hospitals in Connecticut and Massachusetts between September 1996 and January 2000. In an adjusted model including caffeine only, levels in all quartiles were associated with reduced risk of IUGR. In adjusted analyses including paraxanthine and caffeine, serum paraxanthine levels in the highest quartile were associated with increased risk of IUGR (adjusted odds ratio=3.29, 95% confidence interval: 1.17, 9.22); caffeine remained protective. These conflicting findings suggest that cytochrome P-450 1A2 (CYP1A2) metabolic activity may be associated with IUGR, so the ratio of paraxanthine to caffeine was then modeled. The likelihood of IUGR increased 21% for every one standard deviation change in the ratio (adjusted odds ratio=1.21, 95% confidence interval: 1.07, 1.37), suggesting that CYP1A2 activity, and not the absolute levels of paraxanthine, influences fetal growth. No associations were observed between caffeine or any metabolites and preterm delivery.

Increased clozapine plasma concentrations and side effects induced by smoking cessation in 2 CYP1A2 genotyped patients

Clozapine, an atypical antipsychotic, depends mainly on cytochrome P4501A2 (CYP1A2) for its metabolic clearance. CYP1A2 is inducible by smoking, and lower plasma concentrations of clozapine are measured in smokers than in nonsmokers. Case reports have been published on the effects of discontinuing smoking in patients receiving clozapine, which might lead to elevated plasma concentrations and severe side effects. We present 2 cases on the consequences of smoking cessation in patients receiving this drug. In the first patient, smoking cessation resulted, within 2 weeks, in severe sedation and fatigue, with an approximately 3-fold increase of plasma clozapine concentrations. In the second patient, a very high plasma concentration of clozapine (3004 ng/mL) was measured 6 days following a 16-day stay in a general hospital, during which smoking was prohibited. In the latter patient, the replacement of omeprazole, a strong CYP1A2 inducer, by pantoprazole, a weaker CYP1A2 inducer, could have contributed, in addition to smoking cessation, to the observed strong increase of plasma clozapine concentrations. Genotyping of the 2 patients revealed that they were carriers of the AA genotype for the -164C>A polymorphism (CYP1A2*1F) in intron 1 of CYP1A2 gene, which has previously been shown to confer a high inducibility of CYP1A2 by smoking. Thus, at the initiation of clozapine treatment, smoking patients should be informed that, if they decide to stop smoking, they are encouraged to do so but must inform their prescriber beforehand. Also, because of the increased use of no-smoking policies in many hospitals, studies examining the consequences of such policies on the pharmacokinetics/pharmacodynamics of drugs metabolized by CYP1A2, taking into account different CYP1A2 genotypes, are needed.

Population-based case–control study of AhR (aryl hydrocarbon receptor) and CYP1A2 polymorphisms and breast cancer risk

The aryl hydrocarbon receptor (AhR) is a key regulator of the transcriptional expression for the cytochrome P450 1 (CYP1) genes. CYP1A2 is one of the major CYP1 enzymes that catalyse 2-hydroxylation of estrogen, a hormone that plays a critical role in the etiology of breast cancer. In this study, we investigated whether two common polymorphisms in these two genes, CYP1A2*1F and AhR Lys554Arg, were associated with breast cancer risk in 1090 cases and 1183 controls, a subset of the population-based case-control study, the Shanghai Breast Cancer Study. Caffeine tests were performed in vivo in a subset of 236 study subjects to investigate the relationship of these two polymorphisms with CYP1A2 activity. For the AhR gene, the A (Lys) allele was associated with a decreased risk of breast cancer. Using the genotype GG as reference, odds ratios of 0.82 [95% confidence interval (CI)=0.69-0.99] for the AG genotype and 0.76 (95% CI=0.58-1.01) for the AA genotype (P for trend=0.018) were obtained. However, no association was observed between CYP1A2 genotypes and breast cancer risk, although the CYP1A2*1F polymorphism was found to be related to CYP1A2 activity. The geometric mean values for the caffeine metabolites ratio were 2.90, 2.30, and 1.95 for CC, AC, and AA genotypes, respectively (P for trend=0.024). In conclusion, the results from our study suggest that the AhR Lys554Arg polymorphism may be a genetic susceptibility factor for breast cancer, whereas CYP1A2*1F, which is a potentially functional single nucleotide polymorphism, may not be related to breast cancer risk.

Assay for the simultaneous detection of the *1C and *1F alleles of the CYP1A2 gene by real-time polymerase chain reaction and melting curve analysis

Pharmacogenetic variation is an important factor in the therapeutic outcome of many drug treatments. The cytochrome P450 isoform CYP1A2 is involved in the metabolism of a number of antipsychotic drugs. Variable expression of this enzyme may result in idiosyncratic drug responses, including adverse reactions. A number of DNA sequence polymorphisms have been identified in the CYP1A2 gene. Of these, two alleles, CYP1A2*1C and CYP1A2*1F, have been linked to changes in gene expression among smokers. In addition, these polymorphisms have been linked to susceptibility to tardive dyskinesia in some patient populations receiving antipsychotic drug therapy. Here, we present a rapid and robust method for simultaneously genotyping the CYP1A2*1C and *1F alleles using fluorescent hybridization probes and a widely available real-time polymerase chain reaction platform. Such an assay would offer the opportunity to routinely establish the CYP1A2 genotype of a patient prior to commencing drug therapy.

Association of CYP2D6 and CYP1A2 gene polymorphism with tardive dyskinesia in Chinese schizophrenic patients

AIM

To investigate the possible association of the CYP2D6 gene C100T polymorphism and the CYP1A2 gene C163A polymorphism with tardive dyskinesia (TD) in Chinese patients with schizophrenia.

METHODS

The recruited schizophrenic patients were assessed with the Abnormal Involuntary Movement Scale (AIMS), and divided into groups with TD (n=91) and without TD (n=91) according to the AIMS score. Polymorphisms of the CYP2D6 and CYP1A2 genes were determined by polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP).

RESULTS

No allele frequencies deviated from Hardy-Weinberg equilibrium. No significant differences in genotypes frequencies of the CYP2D6 C100T polymorphism were observed between patients with TD and without TD (Chi2=4.078, P>0.05), but patients with TD had a significant excess of the T allele compared with those without TD (Chi2=4.28, P<0.05). Moreover, the frequency of the CYP1A2 C allele in patients with TD was significantly higher than that in those without TD (Chi2=6.38, P<0.05). An association between TD and the CYP2D6 100T and CYP1A2 163C alleles was observed. Additionally, there were no differences in the mean AIMS scores among different genotypes in TD patients as a group or in smokers. The results of logistic regression analysis demonstrated that mean age and duration of illness were risk factors for TD, but not sex, cumulative exposure to neuroleptic drugs in years, CYP2D6 or CYP1A2 genotype.

CONCLUSION

The C100T polymorphism of the CYP2D6 gene and the C163A polymorphism of the CYP1A2 gene may be associated with neuroleptic drug-induced tardive dyskinesia in Chinese patients with schizophrenia. However, genetic factors have a weaker association with susceptibility to TD compared with mean age and duration of illness.

Variable therapeutic response in asthma: a genetic perspective

Asthma is a complex clinical syndrome with multiple genetic and environmental factors contributing to its phenotypic expression. This etiological heterogeneity adds to the complexity when addressing variation in the response to antiasthma treatment. There is regular progress in the field of asthma pharmacogenetics in determining the efficacy and potential for adverse effects of the asthma medication from a patient's genetic background. This reveals that a clinically relevant variability in response to the asthma medications may be due to genetic determinants, and refers to the polymorphisms in the genes encoding either the drug targets, or the molecular component of the downstream signal transduction pathways responsible for drug actions. The major classes of asthma therapy, β-agonists, leukotriene antagonists and inhaled corticosteroids, demonstrate wide interindividual variability. The statistical issues, such as population stratification, sample size and statistical power, are crucial factors for the identification of significant biological marker(s) for patient's response. The aim of this review is to discuss the scientific rationale and outline the genetic impact on the variability in response to different asthma medications. In conclusion, despite of new developments and recent studies in asthma pharmacogenetics, significant gaps in knowledge still remain, and several replicate studies are needed in different populations to derive firm conclusions that may help to bring pharmacotyping into clinical practice.

Therapeutic Drug Monitoring and Pharmacogenetic Tests as Tools in Pharmacovigilance

Therapeutic drug monitoring (TDM) and pharmacogenetic tests play a major role in minimising adverse drug reactions and enhancing optimal therapeutic response. The response to medication varies greatly between individuals, according to genetic constitution, age, sex, co-morbidities, environmental factors including diet and lifestyle (e.g. smoking and alcohol intake), and drug-related factors such as pharmacokinetic or pharmacodynamic drug-drug interactions. Most adverse drug reactions are type A reactions, i.e. plasma-level dependent, and represent one of the major causes of hospitalisation, in some cases leading to death. However, they may be avoidable to some extent if pharmacokinetic and pharmacogenetic factors are taken into consideration. This article provides a review of the literature and describes how to apply and interpret TDM and certain pharmacogenetic tests and is illustrated by case reports. An algorithm on the use of TDM and pharmacogenetic tests to help characterise adverse drug reactions is also presented. Although, in the scientific community, differences in drug response are increasingly recognised, there is an urgent need to translate this knowledge into clinical recommendations. Databases on drug-drug interactions and the impact of pharmacogenetic polymorphisms and adverse drug reaction information systems will be helpful to guide clinicians in individualised treatment choices.

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.

Influence of the genetic polymorphism in the 5′-noncoding region of the CYP1A2 gene on CYP1A2 phenotype and urinary mutagenicity in smokers

The functional significance of genetic polymorphisms on tobacco smoke-induced CYP1A2 activity was examined. The influence of three polymorphisms of the cytochrome P450 1A2 gene (CYP1A2) (-3860 G-->A (allele *1C), -2467 T-->delT (allele *1D), -163C-->A (allele *1F)), located in the 5'-noncoding promoter region of the gene, on CYP1A2 activity (measured as caffeine metabolic ratio, CMR), was studied in Caucasian current smokers (n=95). Tobacco smoke intake was calculated from the number of cigarettes/day. Also, studied was the influence of these CYP1A2 genotypes on smoking-associated urinary mutagenicity, detected in Salmonella typhimurium strain YG1024 with S9 mix, considering the urinary excretion of nicotine plus its metabolites as an internal indicator of tobacco smoke exposure. Smokers with at least one of the variant alleles CYP1A2 -3860A and -2467 delT showed a significantly increased CYP1A2 CMR (-3860 G/A versus G/G, p<0.05; -2467 delT/delT versus T/delT and T/T, p<0.01). Multiple regression analysis showed that the increase in CYP1A2 CMR (ln values) was again significantly related to the presence of CYP1A2 variants -2467delT and also to variant -163A (p<0.05), but moderately to -3860A (p=0.084). No influence of the number of cigarettes smoked per day by each subject was found. Heavy smokers (n=48, with urinary nicotine plus its metabolites>or=0.69 mg/mmol creatinine) with variant allele -2467delT or -163A had significantly increased urinary mutagenicity (p<0.01 and <0.05). CYP1A2 genetic polymorphisms are shown to influence the CYP1A2 phenotype in smokers, -2467 T-->delT having the main effect. This information is of interest for future studies assessing the possible role of tobacco smoke-inducible CYP1A2 genotypes as individual susceptibility factors in exposure to carcinogens.