Role of cytochrome P4501A2 in chemical carcinogenesis: implications for human variability in expression and enzyme activity

Investigation of smoking on the antiplatelet response to clopidogrel: Unravelling the smoker's paradox

The intricate relationship between smoking and the effects of the antiplatelet drug clopidogrel has been termed the "smoker's paradox". This paradox details the enhanced efficacy of clopidogrel in smokers compared to non-smokers. This review begins with an exploration of the proposed mechanisms of the smoker's paradox, particularly drawing attention to the induction of cytochrome P450 (CYP) isoenzymes via tobacco smoke, specifically the enzymes CYP1A2 and CYP2C19. Moreover, an investigation of the effects of genetic variability on the smoker's paradox was undertaken from both clinical and molecular perspectives, delving into the effects of ethnicity and genetic polymorphisms. The intriguing role of CYP1A2 genotypes and the response to clopidogrel in smoking and non-smoking populations was examined conferring insight into the individuality rather than universality of the smoker's paradox. CYP1A2 induction is hypothesised to elucidate the potency of smoking in exerting a counteracting effect in those taking clopidogrel who possess CYP2C19 loss of function polymorphisms. Furthermore, we assess the comparative efficacies of clopidogrel and other antiplatelet agents, namely prasugrel and ticagrelor. Studies indicated that prasugrel and ticagrelor provided a more consistent effect and further reduced platelet reactivity compared to clopidogrel within both smoking and non-smoking populations. Personalised dosing was another focus of the review considering patient comorbidities, genetic makeup, and smoking status with the objective of improving the antiplatelet response of those taking clopidogrel. In summation, this review provides insight into multiple areas of research concerning clopidogrel and the smoker's paradox taking into account proposed mechanisms, genetics, other antiplatelet agents, and personalised dosing.

Aflatoxin B1 induces infertility, fetal deformities, and potential therapies

Aflatoxin B1 (AFB1) is a subsidiary poisonous metabolite, archetypally spawned by Aspergillus flavus and A. parasiticus, which are often isolated in warm or tropical countries across the world. AFB1 is capable of disrupting the functioning of several reproductive endocrine glands by interrupting the enzymes and their substrates that are liable for the synthesis of various hormones in both males and females. In men, AFB1 is capable of hindering testicular development, testicular degeneration, and reduces reproductive capabilities. In women, a direct antagonistic interaction of AFB1 with steroid hormone receptors influencing gonadal hormone production of estrogen and progesterone was responsible for AFB1-associated infertility. AFB1 is potentially teratogenic and is responsible for the development of malformation in humans and animals. Soft-tissue anomalies such as internal hydrocephalus, microphthalmia, cardiac defects, augmented liver lobes, reproductive changes, immune modifications, behavioral changes and predisposition of animals and humans to neoplasm development are AFB1-associated anomalies. Substances such as esculin, selenium, gynandra extract, vitamins C and E, oltipraz, and CDDO-Im are potential therapies for AFB1. Thus, this review elucidates the pivotal pathogenic roles of AFB1 in infertility, fetal deformities, and potential therapies because AFB1 toxicity is a key problem globally.

Polymorphisms in the gene encoding CYP1A2 influence prostate cancer risk and progression

The role of the cytochrome P450 1A2 (CYP1A2) rs2472299, rs2470890 and rs11072508 polymorphisms in prostate cancer risk, disease progression and tumour development remains unclear. The potential associations of these three CYP1A2 polymorphisms and haplotypes with prostate cancer susceptibility and its clinicopathological characteristics were therefore investigated. The present case-control study consisted of 522 patients with prostate cancer and 554 healthy controls. High-resolution melting analysis was used to determine the CYP1A2 polymorphisms. No significant association in prostate cancer risk was seen for CYP1A2 rs2472299 and rs11072508. However, a significantly decreased risk of prostate cancer was found for CYP1A2 rs2470890 [odds ratio (OR), 0.67; P=0.02] in the recessive model. After analysis of the associations of clinical status and these three CYP1A2 polymorphisms, the CYP1A2 rs2470890 and rs11072508 polymorphisms showed a positive association with a higher Gleason score (rs2470890 OR, 1.36, P=0.04 in the allelic model; rs11072508 OR, 1.37, P=0.04 in the allelic model and OR, 1.60, P=0.03 in the dominant model). All three polymorphisms showed a significant positive association with pathological T stage in the additive, allelic and dominant genetic models (P<0.05). Haplotype analysis revealed that the most common haplotypes 'GTT' and 'ACC' were significantly associated with pathological T stages 3 and 4 (OR, 0.62; P=0.02 and OR, 1.54; P=0.03, respectively). A significant association was found between the 'GTT' haplotype and the Gleason score (OR, 0.71; P=0.03). In conclusion, these CYP1A2 polymorphisms and haplotypes have the potential to predict prostate cancer disease progression.

Interindividual Variability in Cytochrome P450 3A and 1A Activity Influences Sunitinib Metabolism and Bioactivation

Sunitinib is an orally administered tyrosine kinase inhibitor associated with idiosyncratic hepatotoxicity; however, the mechanisms of this toxicity remain unclear. We have previously shown that cytochromes P450 1A2 and 3A4 catalyze sunitinib metabolic activation via oxidative defluorination leading to a chemically reactive, potentially toxic quinoneimine, trapped as a glutathione (GSH) conjugate (M5). The goals of this study were to determine the impact of interindividual variability in P450 1A and 3A activity on sunitinib bioactivation to the reactive quinoneimine and sunitinib N-dealkylation to the primary active metabolite N-desethylsunitinib (M1). Experiments were conducted in vitro using single-donor human liver microsomes and human hepatocytes. Relative sunitinib metabolite levels were measured by liquid chromatography-tandem mass spectrometry. In human liver microsomes, the P450 3A inhibitor ketoconazole significantly reduced M1 formation compared to the control. The P450 1A2 inhibitor furafylline significantly reduced defluorosunitinib (M3) and M5 formation compared to the control but had minimal effect on M1. In CYP3A5-genotyped human liver microsomes from 12 individual donors, M1 formation was highly correlated with P450 3A activity measured by midazolam 1'-hydroxylation, and M3 and M5 formation was correlated with P450 1A2 activity estimated by phenacetin O-deethylation. M3 and M5 formation was also associated with P450 3A5-selective activity. In sandwich-cultured human hepatocytes, the P450 3A inducer rifampicin significantly increased M1 levels. P450 1A induction by omeprazole markedly increased M3 formation and the generation of a quinoneimine-cysteine conjugate (M6) identified as a downstream metabolite of M5. The nonselective P450 inhibitor 1-aminobenzotriazole reduced each of these metabolites (M1, M3, and M6). Collectively, these findings indicate that P450 3A activity is a key determinant of sunitinib N-dealkylation to the active metabolite M1, and P450 1A (and potentially 3A5) activity influences sunitinib bioactivation to the reactive quinoneimine metabolite. Accordingly, modulation of P450 activity due to genetic and/or nongenetic factors may impact the risk of sunitinib-associated toxicities.

Genetic Biomarkers of Metabolic Detoxification for Personalized Lifestyle Medicine

Metabolic detoxification (detox)—or biotransformation—is a physiological function that removes toxic substances from our body. Genetic variability and dietary factors may affect the function of detox enzymes, thus impacting the body’s sensitivity to toxic substances of endogenous and exogenous origin. From a genetic perspective, most of the current knowledge relies on observational studies in humans or experimental models in vivo and in vitro, with very limited proof of causality and clinical value. This review provides health practitioners with a list of single nucleotide polymorphisms (SNPs) located within genes involved in Phase I and Phase II detoxification reactions, for which evidence of clinical utility does exist. We have selected these SNPs based on their association with interindividual variability of detox metabolism in response to certain nutrients in the context of human clinical trials. In order to facilitate clinical interpretation and usage of these SNPs, we provide, for each of them, a strength of evidence score based on recent guidelines for genotype-based dietary advice. We also present the association of these SNPs with functional biomarkers of detox metabolism in a pragmatic clinical trial, the LIFEHOUSE study.

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.

How Can Drug Metabolism and Transporter Genetics Inform Psychotropic Prescribing?

Many genetic variants in drug metabolizing enzymes and transporters have been shown to be relevant for treating psychiatric disorders. Associations are strong enough to feature on drug labels and for prescribing guidelines based on such data. A range of commercial tests are available; however, there is variability in included genetic variants, methodology, and interpretation. We herein provide relevant background for understanding clinical associations with specific variants, other factors that are relevant to consider when interpreting such data (such as age, gender, drug-drug interactions), and summarize the data relevant to clinical utility of pharmacogenetic testing in psychiatry and the available prescribing guidelines. We also highlight areas for future research focus in this field.

CYP1A2 rs762551 polymorphism and risk for amyotrophic lateral sclerosis

BACKGROUND

Genetic variability is considered to confer susceptibility to amyotrophic lateral sclerosis (ALS). Oxidative stress is a significant contributor to ALS-related neurodegeneration, and it is regulated by cytochromes P450 (CYPs), such as CYP1A2; these are responsible for the oxidative metabolism of both exogenous and endogenous substrates in the brain, subsequently impacting ALS. The function of CYP1A2 is largely affected by genetic variability; however, the impact of CYP1A2 polymorphisms in ALS remains underinvestigated.

OBJECTIVE

This study aims to examine the possible association of ALS with the CYP1A2 rs762551 polymorphism, which codes for the high inducibility form of the enzyme.

METHODS

One hundred and fifty-five patients with sporadic ALS and 155 healthy controls were genotyped for the CYP1A2 rs762551. Statistical testing for the association of CYP1A2 rs762551 with risk for ALS was performed using SNPstats.

RESULTS

The CYP1A2 rs762551 C allele was associated with a decreased risk of ALS development. In the subgroup analysis according to the ALS site of onset, an association between CYP1A2 rs762551 and limb and bulbar onset of ALS was shown. Cox proportional-hazard regression analyses revealed a significant effect of the CYP1A2 rs762551 on the age of onset of ALS.

CONCLUSIONS

Based on our results, a primarily potential link between the CYP1A2 rs762551 polymorphism and ALS risk could exist.

Experimental Models to Define the Genetic Predisposition to Liver Cancer

Hepatocellular carcinoma (HCC) is a frequent human cancer and the most frequent liver tumor. The study of genetic mechanisms of the inherited predisposition to HCC, implicating gene-gene and gene-environment interaction, led to the discovery of multiple gene loci regulating the growth and multiplicity of liver preneoplastic and neoplastic lesions, thus uncovering the action of multiple genes and epistatic interactions in the regulation of the individual susceptibility to HCC. The comparative evaluation of the molecular pathways involved in HCC development in mouse and rat strains differently predisposed to HCC indicates that the genes responsible for HCC susceptibility control the amplification and/or overexpression of c-Myc, the expression of cell cycle regulatory genes, and the activity of Ras/Erk, AKT/mTOR, and of the pro-apoptotic Rassf1A/Nore1A and Dab2IP/Ask1 pathways, the methionine cycle, and DNA repair pathways in mice and rats. Comparative functional genetic studies, in rats and mice differently susceptible to HCC, showed that preneoplastic and neoplastic lesions of resistant mouse and rat strains cluster with human HCC with better prognosis, while the lesions of susceptible mouse and rats cluster with HCC with poorer prognosis, confirming the validity of the studies on the influence of the genetic predisposition to hepatocarinogenesis on HCC prognosis in mouse and rat models. Recently, the hydrodynamic gene transfection in mice provided new opportunities for the recognition of genes implicated in the molecular mechanisms involved in HCC pathogenesis and prognosis. This method appears to be highly promising to further study the genetic background of the predisposition to this cancer.

Expression, Localization, and Activity of the Aryl Hydrocarbon Receptor in the Human Placenta

The human placenta is an organ between the blood of the mother and the fetus, which is essential for fetal development. It also plays a role as a selective barrier against environmental pollutants that may bypass epithelial barriers and reach the placenta, with implications for the outcome of pregnancy. The aryl hydrocarbon receptor (AhR) is one of the most important environmental-sensor transcription factors and mediates the metabolism of a wide variety of xenobiotics. Nevertheless, the identification of dietary and endogenous ligands of AhR suggest that it may also fulfil physiological functions with which pollutants may interfere. Placental AhR expression and activity is largely unknown. We established the cartography of AhR expression at transcript and protein levels, its cellular distribution, and its transcriptional activity toward the expression of its main target genes. We studied the profile of AhR expression and activity during different pregnancy periods, during trophoblasts differentiation in vitro, and in a trophoblast cell line. Using diverse methods, such as cell fractionation and immunofluorescence microscopy, we found a constitutive nuclear localization of AhR in every placental model, in the absence of any voluntarily-added exogenous activator. Our data suggest an intrinsic activation of AhR due to the presence of endogenous placental ligands.

DFT investigation on the metabolic mechanisms of theophylline by cytochrome P450 monooxygenase

Theophylline, one of the most commonly used bronchodilators and respiratory stimulators for the treatment of acute and chronic asthmatic conditions, can cause permanent neurological damage through chronic or excessive ingestion. In this work, DFT calculation was performed to identify the metabolic mechanisms of theophylline by cytochrome P450 (CYP450) monooxygenase. Two main metabolic pathways were investigated, namely, N₁- (path A) and N₃- (path B) demethylations, which proceeded through N-methyl hydroxylation followed by the decomposition of the generated carbinolamine species. N-methyl hydroxylation involved a hydrogen atom transfer (HAT) mechanism, which can be generalized as the N-demethylation mechanism of xanthine derivatives. The energy gap between the low-spin double state (LS) and the high-spin quartet state (HS) was low (<1 kcal mol^-1), indicating a two-state reactivity (TSR) mechanism. The generated carbinolamine species preferred to decompose through the adjacent heteroatom (O₆ for path A and O₂ for path B) mediated mechanism. Path B was kinetically more feasible than path A attributed to its relatively lower activation energy. 1-Methylxanthine therefore was the energetically favorable metabolite of theophylline. The observations obtained in the work were in agreement with the experimental observation, which can offer important implications for further pharmacological and clinic studies.

Interference with mutagenic aflatoxin B1-induced checkpoints through antagonistic action of ochratoxin A in intestinal cancer cells: a molecular explanation on potential risk of crosstalk between carcinogens

Foodborne aflatoxin B₁ (AFB₁) and ochratoxin A (OTA) cause genotoxic injury and subsequent tumor formation. As a biomarker of oncogenic stimulation by genotoxic mycotoxins, p53-triggered Mdm2 was assessed in intestinal cancer cells. AFB₁ increased Mdm2 reporter expression in a dose-dependent manner. However, this was strongly antagonized by OTA treatment. As a positive transcription factor of Mdm2 expression, p53 levels were also increased by AFB₁ alone and reduced by OTA. With marginal cell death responses, AFB₁ induced p53-mediated S phase arrest and cell cycle-regulating target genes, which was completely suppressed by OTA. Although enterocyte-dominant CYP3A5 counteracted AFB₁-induced DNA damage, expression of CYP3A5 was decreased by OTA or AFB₁. Instead, OTA enhanced expression of another metabolic inactivating enzyme CYP3A4, attenuation of formation of AFB₁-DNA adduct and p53-mediated cell cycle checking responses to the mutagens. Finally, the growth of intestinal cancer cells exposed to the mycotoxin mixture significantly exceeded the expected growth calculated from that of cells treated with each mycotoxin. Although AFB₁-induced mutagen formation was decreased by OTA, interference with checkpoints through antagonistic action of OTA may contribute to the survival of tumor cells with deleterious mutations by genotoxic mycotoxins, potently increasing the risk of carcinogenesis.

Targeted metabolomic profiling indicates structure-based perturbations in serum phospholipids in children with acetaminophen overdose

Phospholipids are an important class of lipids that act as building blocks of biological cell membranes and participate in a variety of vital cellular functions including cell signaling. Previous studies have reported alterations in phosphatidylcholine (PC) and lysophosphatidylcholine (lysoPC) metabolism in acetaminophen (APAP)-treated animals or cell cultures. However, little is known about phospholipid perturbations in humans with APAP toxicity. In the current study, targeted metabolomic analysis of 180 different metabolites including 14 lysoPCs and 73 PCs was performed in serum samples from children and adolescents hospitalized for APAP overdose. Metabolite profiles in the overdose group were compared to those of healthy controls and hospitalized children receiving low dose APAP for treatment of pain or fever (therapeutic group). PCs and lysoPCs with very long chain fatty acids (VLCFAs) were significantly decreased in the overdose group, while those with comparatively shorter chain lengths were increased in the overdose group compared to the therapeutic and control groups. All ether linked PCs were decreased in the overdose group compared to the controls. LysoPC-C26:1 was highly reduced in the overdose group and could discriminate between the overdose and control groups with 100% sensitivity and specificity. The PCs and lysoPCs with VLCFAs showed significant associations with changes in clinical indicators of drug metabolism (APAP protein adducts) and liver injury (alanine aminotransferase, or ALT). Thus, a structure-dependent reduction in PCs and lysoPCs was observed in the APAP-overdose group, which may suggest a structure-activity relationship in inhibition of enzymes involved in phospholipid metabolism in APAP toxicity.

Root extract of water dropwort, Oenanthe javanica (Blume) DC, induces protein and gene expression of phase I carcinogen-metabolizing enzymes in HepG2 cells

Background

Cytochrome P450 (CYP) isoenzymes are an important phase I enzyme system. In the present study, we investigated the effects of Oenanthe javanica (Blume) DC on CYP1A1 and CYP1A2.

Findings

Whole plants were completely dried and then divided into leaves, stems, and roots for extraction. The human liver hepatocellular carcinoma cell line HepG2 was treated with ethanol extracts of these organs for 72 h and mRNA and protein expression levels were assessed. The root extract of O. javanica significantly elevated the expression of both CYP1A1 and CYP1A2 mRNAs (by 68 and 102 %, respectively). Similarly, the CYP1A1 and CYP1A2 protein levels were increased by the root extract (by 112 and 157 %, respectively). The effects of the root extract were much more pronounced than those of leaf and stem extracts. Subsequent GC–MS analysis revealed that the levels of major coumarin derivatives, xanthotoxin, bergapten, and isopimpinellin, were significantly higher in O. javanica root extracts than in leaf or stem extracts. Of note, 5 μM xanthotoxin (the most abundant furanocoumarin in O. javanica) induced the expression of CYP1A1 mRNA as well as CYP1A2 mRNA and protein, albeit the CYP1A1 protein level was elevated only at 10 μM xanthotoxin.

Conclusions

Although it is difficult to extrapolate such effects to metabolic outcomes because of the inherent limitations of in vitro experiments, it is important to note that dietary exposure to O. javanica may modulate phase I enzymes and thereby affect various xenobiotic metabolism.

Electronic supplementary material

The online version of this article (doi:10.1186/s40064-016-2078-8) contains supplementary material, which is available to authorized users.

Gene expression and immunochemical localization of major cytochrome P450 drug-metabolizing enzymes in bovine nasal olfactory and respiratory mucosa

Despite tremendous advancement in the characterization of nasal enzyme expression, knowledge of the role of the nasal mucosa in the metabolism of xenobiotics is still inadequate, primarily due to the limited availability of in vitro models for nasal metabolism screening studies. An extensive knowledge of the oxidative and conjugative metabolizing capacity of the cattle (Bos taurus) olfactory and respiratory mucosa can aid in efficient use of these tissues for pre-clinical investigations of the biotransformation and toxicity of therapeutic agents following nasal administration or inhalation. Cows are also exposed to a variety of airborne pollutants and pesticides during their lifetime, the metabolism of which can have profound toxicological and ecological consequences. The aim of the present study was to characterize cytochrome P450 (CYP) enzyme expression in the bovine nasal mucosa. Amplification of the specific genes through RT-PCR confirmed expression of several CYP enzymes in bovine hepatic and nasal tissues. The results demonstrate that bovine nasal olfactory and respiratory mucosal and liver tissues express similar populations, families, and distributions of CYP enzymes, as has been previously reported with other species, including humans. Bovine ex vivo tissues can serve as a readily available reference tissue to elucidate preclinical toxico-kinetic effects resulting from exposure to substances in the environment or following drug administration.

Four polymorphisms in the cytochrome P450 1A2 (CYP1A2) gene and lung cancer risk: a meta-analysis

BACKGROUND

Previous published data on the association between CYP1A2 rs762551, rs2069514, rs2069526, and rs2470890 polymorphisms and lung cancer risk have not allowed a definite conclusion. The present meta-analysis of the literature was performed to derive a more precise estimation of the relationship.

MATERIALS AND METHODS

8 publications covering 23 studies were selected for this meta-analysis, including 1,665 cases and 2,383 controls for CYP1A2 rs762551 (from 8 studies), 1,456 cases and 1,792 controls for CYP1A2 rs2069514 (from 7 studies), 657 cases and 984 controls for CYP1A2 rs2069526 (from 5 studies) and 691 cases and 968 controls for CYP1A2 rs2470890 (from 3 studies).

RESULTS

When all the eligible studies were pooled into the meta-analysis for the CYP1A2 rs762551 polymorphism, significantly increased lung cancer risk was observed in the dominant model (OR=1.21, 95 % CI=1.00-1.46). In the subgroup analysis by ethnicity, significantly increased risk of lung cancer was observed in Caucasians (dominant model: OR=1.29, 95%CI=1.11-1.51; recessive model: OR=1.33, 95%CI=1.01-1.75; additive model: OR=1.49, 95%CI=1.12-1.98). There was no evidence of significant association between lung cancer risk and CYP1A2 rs2069514, s2470890, and rs2069526 polymorphisms.

CONCLUSIONS

In summary, this meta-analysis indicates that the CYP1A2 rs762551 polymorphism is linked to an increased lung cancer risk in Caucasians. Moreover, our work also points out the importance of new studies for rs2069514 associations in lung cancer, where at least some of the covariates responsible for heterogeneity could be controlled, to obtain a more conclusive understanding about the function of the rs2069514 polymorphism in lung cancer development.

Association between the CYP1A2 polymorphisms and risk of cancer: a meta-analysis

The previously published data on the association between CYP1A2*1C (rs2069514) and CYP1A2*1F (rs762551) polymorphisms and cancer risk have remained controversial. Hence, we performed a meta-analysis to investigate the association between CYP1A2*1F and CYP1A2*1C polymorphisms and cancer risk under different inheritance models. Overall, significant association was observed between CYP1A2*1F and cancer risk when all the eligible studies were pooled into the meta-analysis (dominant model: OR 1.08, 95 % CI 1.02-1.15; heterozygous model: OR 1.06, 95 % CI 1.01-1.12; additive model: OR 1.07, 95 % CI 1.02-1.13). In the further stratified and sensitivity analyses, for CYP1A2*1F polymorphism, significantly increased lung cancer risk and significantly decreased bladder cancer risk were observed in Caucasians. For CYP1A2*1C polymorphism, no significant association was found in overall and all subgroup analyses. In summary, this meta-analysis suggests that CYP1A2*1F polymorphism is associated with lung cancer and bladder cancer risk in Caucasians.

Association between CYP1A2 and CYP1B1 polymorphisms and colorectal cancer risk: a meta-analysis

Background

The previous published data on the association between CYP1A2*F (rs762551), CYP1B1 Leu432Val (rs1056836), Asn453Ser (rs180040), and Arg48Gly (rs10012) polymorphisms and colorectal cancer risk remained controversial.

Methodology/Principal Findings

The purpose of this study is to evaluate the role of CYP1A2*F, CYP1B1 Leu432Val, Asn453Ser, and Arg48Gly genotypes in colorectal cancer susceptibility. We performed a meta-analysis on all the eligible studies that provided 5,817 cases and 6,544 controls for CYP1A2*F (from 13 studies), 9219 cases and 10406 controls for CYP1B1 Leu432Val (from 12 studies), 6840 cases and 7761 controls for CYP1B1 Asn453Ser (from 8 studies), and 4302 cases and 4791 controls for CYP1B1Arg48Gly (from 6 studies). Overall, no significant association was found between CYP1A2*F, CYP1B1 Leu432Val, Asn453Ser, and Arg48Gly and colorectal cancer risk when all the eligible studies were pooled into the meta-analysis. And in the subgroup by ethnicity and source of controls, no evidence of significant association was observed in any subgroup analysis.

Conclusions/Significance

In summary, this meta-analysis indicates that CYP1A2*F, CYP1B1 Leu432Val, Asn453Ser, and Arg48Gly polymorphisms do not support an association with colorectal cancer, and further studies are needed to investigate the association. In addition, our work also points out the importance of new studies for CYP1A2*F polymorphism in Asians, because high heterogeneity was found (dominant model: I² = 81.3%; heterozygote model: I² = 79.0).

Turpentine oil induced inflammation decreases absorption and increases distribution of phenacetin without altering its elimination process in rats

Plasma concentrations and pharmacokinetics of phenacetin, a CYP1A2 substrate were determined in normal and experimentally induced inflamed rats by turpentine oil to know the role of inflammation on the pharmacokinetics of phenacetin and formation of its active metabolite (paracetamol) by CYP1A2 in wistar albino rats, weighing about 200-250 g that were randomly divided into two groups consisting six in each group. Rats in group I (control) received phenacetin (150 mg kg(-1), PO) where as group II received phenacetin 12 h after induction of inflammation by turpentine oil (0.4 mL, i.m). Blood samples were collected from retro orbital plexus at pre-determined time intervals prior to and at 0.166, 0.33, 0.67, 1.5, 2, 4, 8 and 12 h post-administration of phenacetin. Plasma was separated and analyzed for phenacetin and its metabolite paracetamol by HPLC assay. Based on plasma concentrations of phenacetin and its metabolite paracetamol, the pharmacokinetic parameters were determined by compartmental methods. C(max) of phenacetin was significantly (p < 0.01) decreased to 19.50 ± 2.74 μg mL(-1) in inflamed conditions compared to 38.13 ± 2.20 μg mL(-1) obtained in normal rats. Except, for significant (p < 0.001) increase in volume of distribution at steady state (V(dss)) from 2.87 ± 0.37 to 8.03 ± 1.26 L kg(-1) and increased the rate of absorption with shorter absorption half-life (t(1/2ka)) for phenacetin in inflammation. None of the pharmacokinetic parameters of either phenacetin or its metabolite paracetamol were affected. It can be concluded that turpentine oil induced inflammation has no role on the activity of CYP1A2 in rats, as the plasma concentrations and pharmacokinetic parameters of paracetamol were found unaltered.

Curative Effects of ZHENG-Based Fuzheng-Huayu Tablet on Hepatitis B Caused Cirrhosis Related to CYP1A2 Genetic Polymorphism

Aim. To investigate the correlation of Fuzheng-Huayu tablet (FZHY) efficacy on chronic hepatitis B caused cirrhosis (HBC) and single nucleotide polymorphisms (SNPs) of CYP1A2. Methods. After 111 cases of HBC with 69 excess, 21 deficiency-excess, and 21 deficiency ZHENGs (ZHENG, also called traditional Chinese medicine syndrome) were treated by FZHY for 6 months, clinical symptoms, Child-Pugh score, and ZHENG score were observed. Three of the SNPs in CYP1A2 gene were detected and analyzed using SNaPshot assay. Results. In ZHENG efficacy between effective and invalid groups, there was significant difference (P < 0.001). The ZHENG deficiency was significantly correlated with FZHY efficacy (P < 0.05). AA genotype of CYP1A2-G2964A was significantly different with GG genotype (P < 0.05) between CYP1A2 Genotypes and FZHY efficacy on ZHENG. More importantly, GA plus AA genotype of CYP1A2-G2964A was significantly different with deficiency ZHENG (P < 0.05) between CYP1A2 genotypes and FZHY efficacy on ZHENG. Conclusion. FZHY improved ZHENG score of HBC, and these efficacies may relate to CYP1A2-G2964A sites. It was suggested that CYP1A2-G2964A locus is probably a risk factor for ZHENG-based FZHY efficacy in HBC.

Dietary aflatoxin B1 intake, genetic polymorphisms of CYP1A2, CYP2E1, EPHX1, GSTM1, and GSTT1, and gastric cancer risk in Korean

PURPOSE

We investigated the effects of aflatoxin B1 (AFB1) intake, genetic polymorphisms of AFB1 metabolic enzymes, and interactions between the polymorphisms and intake of AFB1 with regard to the risk of gastric cancer in Korean.

METHODS

The participants in the study included 477 gastric cancer patients and 477 age- and sex-matched control subjects. Direct interviews and a structured questionnaire were used to determine the level of exposure to AFB1, and the GoldenGate assay and multiplex polymerase chain reaction were used for genotypic analyses of the cytochrome P450 1A2 (CYP1A2), cytochrome P450 1E1, epoxide hydrolase 1, and glutathione S-transferase genes.

RESULTS

The probable daily intake of AFB1 was significantly higher among gastric cancer patients than among control subjects (cases vs. controls: 1.91 ± 0.87 vs. 1.65 ± 0.72 ng/kg bw/day, p < 0.0001), and increased AFB1 intake was significantly associated with an elevated risk of gastric cancer (odds ratio 1.94; 95 % confidence interval 1.43-2.63). However, genetic polymorphisms of AFB1 metabolic enzymes were not associated with gastric cancer, with the exception of CYP1A2. Moreover, there was no interaction between AFB1 intake and the genotypes of metabolic enzymes that affect gastric cancer risk.

CONCLUSIONS

Our results suggest that dietary AFB1 exposure might be associated with a risk of gastric cancer. However, the effect of AFB1 on gastric carcinogenesis may not be modulated by genetic polymorphisms of AFB1 metabolic enzymes.

quantitative assessment of the influence of cytochrome P450 1A2 gene polymorphism and colorectal cancer risk

Cytochrome P450 1A2 (CYP1A2) encodes a member of the cytochrome P450 superfamily of enzymes, which play a central role in activating and detoxifying many carcinogens and endogenous compounds thought to be involved in the development of colorectal cancer (CRC). The CYP1A2*C (rs2069514) and CYP1A2*F (rs762551) polymorphism are two of the most commonly studied polymorphisms of the gene for their association with risk of CRC, but the results are conflicting. To derive a more precise estimation of the relationship between CYP1A2 and genetic risk of CRC, we performed a comprehensive meta-analysis which included 7088 cases and 7568 controls from 12 published case-control studies. In a combined analysis, the summary per-allele odds ratio for CRC was 0.91 (95% CI: 0.83-1.00, P = 0.04), and 0.91 (95% CI: 0.68-1.22, P = 0.53), for CYP1A2 *F and *C allele, respectively. In the subgroup analysis by ethnicity, significant associations were found in Asians for CYP1A2*F and CYP1A2*C, while no significant associations were detected among Caucasian populations. Similar results were also observed using dominant genetic model. Potential sources of heterogeneity were explored by subgroup analysis and meta-regression. No significant heterogeneity was detected in most of comparisons. This meta-analysis suggests that the CYP1A2 *F and *C polymorphism is a protective factor against CRC among Asians.

Measurement of human cytochrome P4501A2 (CYP1A2) activity in vitro

Cytochrome P4501A2 (CYP1A2) is responsible for the metabolism of a diverse range of clinically used drugs and dietary and environmental chemicals (including many procarcinogens). CYP1A2 expression is influenced by numerous factors, and hence wide interindividual variability is a characteristic feature of this enzyme in humans. Phenacetin represents a convenient probe for the assessment of human CYP1A2 activity in vitro (hepatic microsomes and recombinant enzyme). It is a relatively high-turnover substrate that forms only one major primary metabolite, the O-deethylated derivative acetaminophen. Acetaminophen formation in incubations of phenacetin with a CYP1A2 source is readily measured by HPLC with UV detection. The assay has a low requirement for human liver microsomes or recombinant enzyme, and is both selective and sensitive without the requirement for a solvent extraction step. Overall assay reproducibility is excellent, with coefficients of variation <4%.

CYP1A2 rs762551 polymorphism contributes to cancer susceptibility: a meta-analysis from 19 case-control studies

BACKGROUND

Genetic polymorphism (rs762551A>C) in gene encoding cytochrome P450 1A2 (CYP1A2) has been shown to influence the inducibility of CYP1A2 expression and thus might be associated with risk of several types of human cancer. However, the results of previous studies on the associations of this polymorphism with risk of cancer are not all consistent. To clarify the potential contribution of CYP1A2 rs762551 to cancer risk, we performed a meta-analysis of the published case-control studies.

METHODS

We used PubMed, Embase, OVID, ScienceDirect, and Chinese National Knowledge Infrastructure databases to identify the related publications for this meta-analysis. The pooled odds ratio (OR) and 95% confidence interval (CI) were calculated using random effect model to evaluate the association of rs762551 with cancer risk. A χ(2)-based Q-test was used to examine the heterogeneity assumption and the funnel plot and Egger's test were used to examine the potential publication bias. The leave-one-out sensitivity analysis was conducted to determine whether our assumptions or decisions have a major effect on the results of the review.

RESULTS

Our analysis of 19 eligible case-control studies showed a significant association between rs762551C variant with risk of cancer in the genetic model of CC versus AA (OR = 1.30, 95% CI = 1.02-1.64) and the dominant model (OR = 1.19, 95% CI = 1.04-1.36). In subgroup analysis based on ethnicity, the rs762551CC genotype was associated with increased cancer risk (OR = 1.29, 95% CI = 1.27-1.63 in co-dominate model and OR = 1.17, 95% CI = 1.02-1.34 in dominant model in Caucasians, but not in Asians and the mixed population.

CONCLUSION

These results suggested that CYP1A2 rs762551 polymorphism is likely to be associated with susceptibility to cancer in Caucasians.

Interplay between smoking-induced genotoxicity and altered signaling in pancreatic carcinogenesis

Despite continuous research efforts directed at early diagnosis and treatment of pancreatic cancer (PC), the status of patients affected by this deadly malignancy remains dismal. Its notoriety with regard to lack of early diagnosis and resistance to the current chemotherapeutics is due to accumulating signaling abnormalities. Hoarding experimental and epidemiological evidences have established a direct correlation between cigarette smoking and PC risk. The cancer initiating/promoting nature of cigarette smoke can be attributed to its various constituents including nicotine, which is the major psychoactive component, and several other toxic constituents, such as nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, and polycyclic aromatic hydrocarbons. These predominant smoke-constituents initiate a series of oncogenic events facilitating epigenetic alterations, self-sufficiency in growth signals, evasion of apoptosis, sustained angiogenesis, and metastasis. A better understanding of the molecular mechanisms underpinning these events is crucial for the prevention and therapeutic intervention against PC. This review presents various interconnected signal transduction cascades, the smoking-mediated genotoxicity, and genetic polymorphisms influencing the susceptibility for smoking-mediated PC development by modulating pivotal biological aspects such as cell defense/tumor suppression, inflammation, DNA repair, as well as tobacco-carcinogen metabolization. Additionally, it provides a large perspective toward tumor biology and the therapeutic approaches against PC by targeting one or several steps of smoking-mediated signaling cascades.

Transcriptional ontogeny of the developing liver

Background

During embryogenesis the liver is derived from endodermal cells lining the digestive tract. These endodermal progenitor cells contribute to forming the parenchyma of a number of organs including the liver and pancreas. Early in organogenesis the fetal liver is populated by hematopoietic stem cells, the source for a number of blood cells including nucleated erythrocytes. A comprehensive analysis of the transcriptional changes that occur during the early stages of development to adulthood in the liver was carried out.

Results

We characterized gene expression changes in the developing mouse liver at gestational days (GD) 11.5, 12.5, 13.5, 14.5, 16.5, and 19 and in the neonate (postnatal day (PND) 7 and 32) compared to that in the adult liver (PND67) using full-genome microarrays. The fetal liver, and to a lesser extent the neonatal liver, exhibited dramatic differences in gene expression compared to adults. Canonical pathway analysis of the fetal liver signature demonstrated increases in functions important in cell replication and DNA fidelity whereas most metabolic pathways of intermediary metabolism were under expressed. Comparison of the dataset to a number of previously published microarray datasets revealed 1) a striking similarity between the fetal liver and that of the pancreas in both mice and humans, 2) a nucleated erythrocyte signature in the fetus and 3) under expression of most xenobiotic metabolism genes throughout development, with the exception of a number of transporters associated with either hematopoietic cells or cell proliferation in hepatocytes.

Conclusions

Overall, these findings reveal the complexity of gene expression changes during liver development and maturation, and provide a foundation to predict responses to chemical and drug exposure as a function of early life-stages.

Protective effect of boric acid against carbon tetrachloride-induced hepatotoxicity in mice

The protective effect of boric acid against liver damage was evaluated by its attenuation of carbon tetrachloride (CCl(4))-induced hepatotoxicity in mice. Male albino mice were treated intraperitoneally (i.p.) with boric acid (50, 100, and 200 mg/kg) or silymarin daily for 7 days and received 0.2% CCl(4) in olive oil (10 mL/kg, i.p.) on day 7. Results showed that administration of boric acid significantly reduced the elevation in serum levels of aspartate aminotransferase, alkaline phosphatase, alanine aminotransferase, and the level of malondialdehyde in the liver that were induced by CCl(4) in mice. Boric acid treatment significantly increased glutathione content, as well as the activities of superoxide dismutase and catalase in the liver. Boric acid treatment improved the catalytic activity of cytochrome P450 2E1 and maintained activation of nuclear factor kappa light-chain enhancer of activated B cell gene expression, with no effect on inducible nitric oxide synthase gene expression in the livers of mice. Histopathologically, clear decreases in the severity of CCl(4)-induced lesions were observed, particularly at high boric acid concentrations. Results suggest that boric acid exhibits potent hepatoprotective effects on CCl(4)-induced liver damage in mice, likely the result of both the increase in antioxidant-defense system activity and the inhibition of lipid peroxidation.

Metabolism and biomarkers of heterocyclic aromatic amines in molecular epidemiology studies: lessons learned from aromatic amines

Aromatic amines and heterocyclic aromatic amines (HAAs) are structurally related classes of carcinogens that are formed during the combustion of tobacco or during the high-temperature cooking of meats. Both classes of procarcinogens undergo metabolic activation by N-hydroxylation of the exocyclic amine group to produce a common proposed intermediate, the arylnitrenium ion, which is the critical metabolite implicated in toxicity and DNA damage. However, the biochemistry and chemical properties of these compounds are distinct, and different biomarkers of aromatic amines and HAAs have been developed for human biomonitoring studies. Hemoglobin adducts have been extensively used as biomarkers to monitor occupational and environmental exposures to a number of aromatic amines; however, HAAs do not form hemoglobin adducts at appreciable levels, and other biomarkers have been sought. A number of epidemiologic studies that have investigated dietary consumption of well-done meat in relation to various tumor sites reported a positive association between cancer risk and well-done meat consumption, although some studies have shown no associations between well-done meat and cancer risk. A major limiting factor in most epidemiological studies is the uncertainty in quantitative estimates of chronic exposure to HAAs, and thus, the association of HAAs formed in cooked meat and cancer risk has been difficult to establish. There is a critical need to establish long-term biomarkers of HAAs that can be implemented in molecular epidemioIogy studies. In this review, we highlight and contrast the biochemistry of several prototypical carcinogenic aromatic amines and HAAs to which humans are chronically exposed. The biochemical properties and the impact of polymorphisms of the major xenobiotic-metabolizing enzymes on the biological effects of these chemicals are examined. Lastly, the analytical approaches that have been successfully employed to biomonitor aromatic amines and HAAs, and emerging biomarkers of HAAs that may be implemented in molecular epidemiology studies are discussed.

Pharmacokinetics of caffeine in plasma and saliva, and the influence of caffeine abstinence on CYP1A2 metrics

OBJECTIVES

To investigate the utility of metrics of CYP1A2 activity using caffeine as a probe, and saliva and plasma sampling with or without a 24-h caffeine abstinence.

METHODS

This was a cross-over pharmacokinetic study in 30 healthy male subjects who received a single oral 100mg caffeine dose after 24-h caffeine abstinence or after maintaining their regular caffeine intake (no caffeine abstinence). Serial blood and saliva samples were collected simultaneously over 24h. Caffeine and paraxanthine concentrations were measured using a validated HPLC assay.

KEY FINDINGS

There was a strong correlation between the paraxanthine/caffeine AUC(0-24) ratio (reference metric) and the paraxanthine/caffeine concentration (C(t) ) ratio at 4h (C(4) ) in both saliva and plasma (r≥0.75). The paraxanthine/caffeine AUC(0-24) ratio in plasma and saliva did not differ between the 24-h caffeine abstinence and the no abstinence period (P>0.05). The optimal paraxanthine/caffeine C(t) that correlated with the plasma paraxanthine/caffeine AUC(0-24) ratio in the 24-h abstinence period was 2 and 4h (r=0.88) in plasma, and 4 and 6h in saliva (r=0.70), while it was the saliva 4h time-point in the no abstinence period (r=0.78).

CONCLUSIONS

The saliva paraxanthine/caffeine concentration ratio at 4h was a suitable metric to assess CYP1A2 activity after oral administration of caffeine without the need for 24-h caffeine abstinence.

Perspectives of breast cancer etiology: synergistic interaction between smoking and exogenous hormone use

To explore breast cancer etiology, literature was searched using Medline. We explored the 1) plausibility of smoking in breast carcinogenesis; 2) physiological properties, susceptibility windows, and exposure timing of breast cells; 3) role of exogenous hormones in breast carcinogenesis; 4) biological mechanism of synergistic interactions between smoking and exogenous hormones in breast carcinogenesis; and 5) evidence from epidemiologic studies and the fitted secular trend between smoking rate, exogenous hormone use, and breast cancer incidence in past decades. We deduced that exogenous hormone use per se is not a significant cause and its association with breast cancer is distorted by chronic exposure to environmental carcinogens, especially smoking. We hypothesize that smoking is one of the causes of breast cancer and that this causality is strengthened by synergistic interaction between smoking and exogenous hormone use. Physicians should be cautious of prescribing exogenous hormones for those with chronic exposure to environmental carcinogens to prevent breast cancer.

Effect of caffeine on SPECT myocardial perfusion imaging during regadenoson pharmacologic stress: rationale and design of a prospective, randomized, multicenter study

BACKGROUND

Caffeine attenuates the coronary hyperemic response to adenosine by competitive A₂(A) receptor blockade. This study aims to determine whether oral caffeine administration compromises diagnostic accuracy in patients undergoing vasodilator stress myocardial perfusion imaging (MPI) with regadenoson, a selective adenosine A(2A) agonist.

METHODS

This multicenter, randomized, double-blind, placebo-controlled, parallel-group study includes patients with suspected coronary artery disease who regularly consume caffeine. Each participant undergoes three SPECT MPI studies: a rest study on day 1 (MPI-1); a regadenoson stress study on day 3 (MPI-2), and a regadenoson stress study on day 5 with double-blind administration of oral caffeine 200 or 400 mg or placebo capsules (MPI-3; n = 90 per arm). Only participants with ≥ 1 reversible defect on the second MPI study undergo the subsequent stress MPI test. The primary endpoint is the difference in the number of reversible defects on the two stress tests using a 17-segment model. Pharmacokinetic/pharmacodynamic analyses will evaluate the effect of caffeine on the regadenoson exposure-response relationship. Safety will also be assessed.

CONCLUSION

The results of this study will show whether the consumption of caffeine equivalent to 2-4 cups of coffee prior to an MPI study with regadenoson affects the diagnostic validity of stress testing (ClinicalTrials.gov number, NCT00826280).

Pathway-Targeted Pharmacogenomics of CYP1A2 in Human Liver

The human drug metabolizing cytochrome P450 (CYP) 1A2, is one of the major P450 isoforms contributing by about 5–20% to the hepatic P450 pool and catalyzing oxidative biotransformation of up to 10% of clinically relevant drugs including clozapine and caffeine. CYP1A2 activity is interindividually highly variable and although twin studies have suggested a high heritability, underlying genetic factors are still unknown. Here we adopted a pathway-oriented approach using a large human liver bank (n = 150) to elucidate whether variants in candidate genes of constitutive, ligand-inducible, and pathophysiological inhibitory regulatory pathways may explain different hepatic CYP1A2 phenotypes. Samples were phenotyped for phenacetin O-deethylase activity, and the expression of CYP1A2 protein and mRNA was determined. CYP1A2 expression and function was increased in smokers and decreased in patients with inflammation and cholestasis. Of 169 SNPs in 17 candidate genes including the CYP1A locus, 136 non-redundant SNPs with minor allele frequency >5% were analyzed by univariate and multivariate methods. A total of 13 strong significant associations were identified, of which 10 SNPs in the ARNT, AhRR, HNF1α, IL1β, SRC-1, and VDR genes showed consistent changes for at least two phenotypes by univariate analysis. Multivariate linear modeling indicated that the polymorphisms and non-genetic factors together explained 42, 38, and 33% of CYP1A2 variation at activity, protein and mRNA levels, respectively. In conclusion, we identified novel trans-associations between regulatory genes and hepatic CYP1A2 function and expression, but additional genetic factors must be assumed to explain the full extent of CYP1A2 heritability.

Caffeine, selected metabolic gene variants, and risk for neural tube defects

BACKGROUND

Investigations of maternal caffeine intake and neural tube defects (NTDs) have not considered genetic influences. Caffeine metabolism gene effects were examined in the National Birth Defects Prevention Study.

METHODS

Average daily caffeine was summed from self-reported coffee, tea, soda, and chocolate intake for mothers of 768 NTD cases, and 4143 controls delivered from 1997 to 2002. A subset of 306 NTD and 669 control infants and their parents were genotyped for CYP1A2*1F, NAT2 481C>T, and NAT2 590G>A. CYP1A2*1F was classified by fast or slow oxidation status, and NAT2 variants were categorized into rapid or slow acetylation status. Case-control logistic regression analyses, family-based transmission/disequilibrium tests and log-linear analyses, and hybrid log-linear analyses were conducted to produce odds ratios (ORs) or relative risks (RRs) and 95% confidence intervals (CIs) for caffeine intake and maternal and infant gene variants, and to examine interaction effects.

RESULTS

NTDs were independently associated with infant slow NAT2 acetylator status (RR, 2.00; 95% CI, 1.10-3.64) and maternal CYP1A2*1F fast oxidation status (OR, 1.49; 95% CI, 1.10-2.03). Mothers who consumed caffeine, oxidized CYP1A2*1F quickly, and acetylized NAT2 slowly had a nonsignificantly elevated estimated risk for an NTD-affected pregnancy (OR, 3.10; 95% CI, 0.86-11.21). Multiplicative interaction effects were observed between maternal caffeine and infant CYP1A2*1F fast oxidizer status (p(interaction) = 0.03).

CONCLUSIONS

The association identified between maternal CYP1A2*1F fast oxidation status and NTDs should be examined further in the context of the other substrates of CYP1A2. Maternal caffeine and its metabolites may be associated with increased risk for NTD-affected pregnancies in genetically susceptible subgroups.

Classical twin design in modern pharmacogenomics studies

Response to medication is highly variable, unpredictable and, at times, may be fatal. All drugs are more effective in certain groups of the population while showing no or minimal benefit in other groups. Although the current data on the subject are piecemeal, anecdotal evidence suggests that, in line with other common multifactorial traits, a myriad of genomic as well as environmental factors underpin population variability in drug response. Pharmacogenomics is the study of how variations in the human genome affect the variability in response to medication. Efforts to personalize treatment based on results from pharmacogenomics studies have the potential to increase efficacy, lower the overall cost of treatment, and decrease the incidence of adverse drug reactions, and are one of the major challenges of the modern era. The classical twin design has traditionally been used to assess the relative contribution of genetic and environmental factors to population variation in common, complex phenotypes, including drug response. Twins are not commonly regarded as providing the optimal design in genomic studies. However, we argue that, through their precise ‘matching’ for confounding variables (age, sex, cohort and common environmental effects), their amenability to numerous nonclassical study designs (genome-wide association studies or the role of epigenetic factors), and the availability of large, established registries worldwide, the twin model represents a flexible study design for systems-biology studies of drug response in humans. In this review, we describe the ‘classical twin model’ and its application in traditional pharmacogenetics studies, discuss the value of the twin design in the modern systems biology era, and highlight the potential of existing twin registries in formulating future strategies in pharmacogenomics research. We argue that the usefulness of this design goes beyond its traditional applications. Moreover, the flexibility of the model in concert with the amenability of large, established registries of twins worldwide to the collecting of new phenotypes will mean that the study of identical and nonidentical twins will play a considerable role in shaping our understanding of the important factors that underpin population variability in common, complex phenotypes, including response to medication.

Lack of association of CYP1A2-164 A/C polymorphism with breast cancer susceptibility: a meta-analysis involving 17,600 subjects

Published data on the association between cytochrome P-450 1A2 (CYP1A2)-164 A/C polymorphism and breast cancer risk are inconclusive. To derive a more precise estimation of the relationship, a meta-analysis was performed. Medline, PubMed, Embase, and Web of Science were searched. Crude ORs with 95% CIs were used to assess the strength of association between CYP1A2-164 A/C polymorphism and breast cancer risk. The pooled ORs were performed for co-dominant model (AC versus AA, CC versus AA), dominant model (CC + AC versus AA), and recessive model (CC versus AA + AC), respectively. A total of 9 studies including 7,580 cases and 10,020 controls were involved in this meta-analysis. Overall, no significantly elevated breast cancer risk was found in all genetic models when all studies were pooled into the meta-analysis (AC versus AA: OR = 1.02, 95% CI = 0.92-1.13; CC versus AA: OR = 1.17, 95% CI = 0.83-1.64; dominant model: OR = 1.07, 95% CI = 0.93-1.23; and recessive model: OR = 1.13, 95% CI = 0.82-1.55). In the subgroup analysis by ethnicity or source of controls, there was still no significant association detected in all genetic models. In conclusion, upto date, there is still not enough evidence to indicate the association of CYP1A2-164 A/C polymorphism and breast cancer development.

CYP1A2, GSTM1, and GSTT1 polymorphisms and diet effects on CYP1A2 activity in a crossover feeding trial

Cytochrome P-450 1A2 (CYP1A2) is a biotransformation enzyme that activates several procarcinogens. CYP1A2 is induced by cruciferous and inhibited by apiaceous vegetable intake. Using a randomized, crossover feeding trial in humans, we investigated the dose effects of cruciferous vegetables and the effects of any interaction between cruciferous and apiaceous vegetables on CYP1A2 activity. We also investigated whether response varied by CYP1A2*1F, GSTM1, and GSTT1 genotypes (glutathione S-transferases that metabolize crucifer constituents) and whether CYP1A2 activity rebounds after apiaceous vegetables are removed from the diet. Participants (N = 73), recruited based on genotypes, consumed four diets for two weeks each: low-phytochemical diet (basal), basal plus single dose of cruciferous (1C), basal plus double dose of cruciferous (2C), and basal plus single dose of cruciferous and apiaceous vegetables (1C+A). CYP1A2 activity was determined by urine caffeine tests administered at baseline and the end of each feeding period. Compared with basal diet, the 1C diet increased CYP1A2 activity (P < 0.0001) and the 2C diet resulted in further increases (P < 0.0001), with men experiencing greater dose-response than women. The 1C+A diet decreased CYP1A2 activity compared with the 1C and 2C diets (P < 0.0001 for both). Although there was no overall effect of CYP1A2*1F or GSTM1-null/GSTT1-null genotypes or genotype-by-diet interactions, there were significant diet response differences within each genotype. Additionally, CYP1A2 activity recovered modestly one day after the removal of apiaceous vegetables. These results suggest complex interactions among dietary patterns, genetic variation, and modulation of biotransformation that may not be apparent in observational studies.

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.