Search for an association between the human CYP1A2 genotype and CYP1A2 metabolic phenotype

Protocol for the CoNoR Study: A prospective multi-step study of the potential added benefit of two novel assessment tools in colorectal liver metastases technical resectability decision-making

INTRODUCTION

Liver resection is the only curative treatment for colorectal liver metastases (CLM). Resectability decision-making is therefore a key determinant of outcomes. Wide variation has been demonstrated in resectability decision-making, despite the existence of criteria. This paper summarises a study protocol to evaluate the potential added value of two novel assessment tools in assessing CLM technical resectability: the Hepatica preoperative MR scan (MR-based volumetry, Couinaud segmentation, liver tissue characteristics and operative planning tool) and the LiMAx test (hepatic functional capacity).

METHODS AND ANALYSIS

This study uses a systematic multistep approach, whereby three preparatory workstreams aid the design of the final international case-based scenario survey:Workstream 1: systematic literature review of published resectability criteria.Workstream 2: international hepatopancreatobiliary (HPB) interviews.Workstream 3: international HPB questionnaire.Workstream 4: international HPB case-based scenario survey.The primary outcome measures are change in resectability decision-making and change in planned operative strategy, resulting from the novel test results. Secondary outcome measures are variability in CLM resectability decision-making and opinions on the role for novel tools.

ETHICS AND DISSEMINATION

The study protocol has been approved by a National Health Service Research Ethics Committee and registered with the Health Research Authority. Dissemination will be via international and national conferences. Manuscripts will be published.

REGISTRATION DETAILS

The CoNoR Study is registered with ClinicalTrials.gov (registration number NCT04270851). The systematic review is registered on the PROSPERO database (registration number CRD42019136748).

Correlation between assessment of cytochrome P450 1A2 activity and enzyme activity scores, and their relation to clozapine exposure

AIMS

Cytochrome P450 1A2 (CYP1A2) is involved in the metabolism of antipsychotic drugs such as clozapine and olanzapine. Personalization of these treatments requires an accurate estimation of CYP1A2 activity. In this study, we aimed (1) to evaluate the correlation between activity score (AS), covariate-corrected activity score (CCS) and the phenotype of CYP1A2 using a caffeine test probe and (2) to investigate their relationship with dose-adjusted clozapine concentrations in a subgroup of the cohort.

METHODS

A multicentric, retrospective and observational study was carried out in the French university hospitals of Marseille and Tours. CYP1A2 activity was calculated by the paraxanthine/caffeine (17X/137X) ratio determined 4 h after an oral intake of 100 mg caffeine. AS was calculated according to the CYP1A2*1F alleles. CCS was calculated according to the CYP1A2*1F alleles, smoking status and the presence of concomitant inhibitors.

RESULTS

As expected, among the 89 patients included, the 17X/137X ratio was significantly higher in patients who smoked. We found a significant but modest correlation between the 17X/137X ratio and CCS (R²  = 0.3, P = 1.74 × 10^-8 ) but none between the 17X/137X ratio and AS (R²  = -0.007, P = 0.52). AS was not correlated with dose-adjusted clozapine levels, contrary to CCS (R²  = 0.19, P = 0.016) and especially the 17X/137X ratio (R²  = 0.42, P = 1.7 × 10^-5 ).

CONCLUSIONS

Correlation with clozapine concentrations showed the advantage of the 17X/137X ratio over the CCS in clozapine dose optimization. CYP1A2 activity, especially when determined by the caffeine probe, may be used to personalize clozapine dosing for patients experiencing treatment failure.

Pharmacokinetics of Caffeine: A Systematic Analysis of Reported Data for Application in Metabolic Phenotyping and Liver Function Testing

Caffeine is by far the most ubiquitous psychostimulant worldwide found in tea, coffee, cocoa, energy drinks, and many other beverages and food. Caffeine is almost exclusively metabolized in the liver by the cytochrome P-450 enzyme system to the main product paraxanthine and the additional products theobromine and theophylline. Besides its stimulating properties, two important applications of caffeine are metabolic phenotyping of cytochrome P450 1A2 (CYP1A2) and liver function testing. An open challenge in this context is to identify underlying causes of the large inter-individual variability in caffeine pharmacokinetics. Data is urgently needed to understand and quantify confounding factors such as lifestyle (e.g., smoking), the effects of drug-caffeine interactions (e.g., medication metabolized via CYP1A2), and the effect of disease. Here we report the first integrative and systematic analysis of data on caffeine pharmacokinetics from 141 publications and provide a comprehensive high-quality data set on the pharmacokinetics of caffeine, caffeine metabolites, and their metabolic ratios in human adults. The data set is enriched by meta-data on the characteristics of studied patient cohorts and subjects (e.g., age, body weight, smoking status, health status), the applied interventions (e.g., dosing, substance, route of application), measured pharmacokinetic time-courses, and pharmacokinetic parameters (e.g., clearance, half-life, area under the curve). We demonstrate via multiple applications how the data set can be used to solidify existing knowledge and gain new insights relevant for metabolic phenotyping and liver function testing based on caffeine. Specifically, we analyzed 1) the alteration of caffeine pharmacokinetics with smoking and use of oral contraceptives; 2) drug-drug interactions with caffeine as possible confounding factors of caffeine pharmacokinetics or source of adverse effects; 3) alteration of caffeine pharmacokinetics in disease; and 4) the applicability of caffeine as a salivary test substance by comparison of plasma and saliva data. In conclusion, our data set and analyses provide important resources which could enable more accurate caffeine-based metabolic phenotyping and liver function testing.

Drug-Drug Interactions Involving Intestinal and Hepatic CYP1A Enzymes

Cytochrome P450 (CYP) 1A enzymes are considerably expressed in the human intestine and liver and involved in the biotransformation of about 10% of marketed drugs. Despite this doubtless clinical relevance, CYP1A1 and CYP1A2 are still somewhat underestimated in terms of unwanted side effects and drug–drug interactions of their respective substrates. In contrast to this, many frequently prescribed drugs that are subjected to extensive CYP1A-mediated metabolism show a narrow therapeutic index and serious adverse drug reactions. Consequently, those drugs are vulnerable to any kind of inhibition or induction in the expression and function of CYP1A. However, available in vitro data are not necessarily predictive for the occurrence of clinically relevant drug–drug interactions. Thus, this review aims to provide an up-to-date summary on the expression, regulation, function, and drug–drug interactions of CYP1A enzymes in humans.

Prospective study of change in liver function and fat in patients with colorectal liver metastases undergoing preoperative chemotherapy: protocol for the CLiFF Study

INTRODUCTION

Preoperative chemotherapy in patients undergoing resection for colorectal liver metastases (CLM) improves oncological outcomes. However, chemotherapy-associated liver injury (occurring in two patterns: vascular and fat deposition) is a real clinical concern prior to hepatic resection. After major liver resection, regeneration of the residual liver is a prerequisite for recovery and avoidance of liver failure, but this regenerative capacity may be hindered by chemotherapy. Thus, there is a need to predict for this serious complication. Over the past two decades, several tests and derived indices have been developed, which have failed to achieve clinical utility, mainly as they were indirect measurements of liver function. Here, we will use a novel test of liver function (the liver maximum capacity (LiMAx) test), and measure liver fat using MRI.

METHODS AND ANALYSIS

This prospective study will assess changes in liver function longitudinally, measured by the LiMAx test, and liver fat, measured by advanced MRI using both MR spectroscopy and the modified Dixon method, in up to 35 patients undergoing preoperative chemotherapy for CLM. The primary outcomes will be the changes in liver function and fat compared with baseline prechemotherapy measurements. Secondary outcome measures include: routinely measured liver function blood tests, anthropometric measurements, postoperative histology and digital quantification of fat, postoperative complications and mortality and quality of life.

ETHICS AND DISSEMINATION

The study was approved by a National Health Service Research Ethics Committee and registered with the Health Research Authority. Dissemination will be via international and national conferences and the National Institute for Health Research network. Manuscripts will be published.

TRIAL REGISTRATION NUMBER

This study is registered online at www.clinicaltrials.gov (registration number NCT03562234).

A Randomised, Placebo-Controlled, Crossover Study Investigating the Optimal Timing of a Caffeine-Containing Supplement for Exercise Performance

BACKGROUND

Pre-exercise supplements containing low doses of caffeine improve endurance exercise performance, but the most efficacious time for consumption before intense endurance exercise remains unclear, as does the contribution of caffeine metabolism.

METHODS

This study assessed the timing of a commercially available supplement containing 200 mg of caffeine, 1600 mg of β-alanine and 1000 mg of quercetin [Beachbody Performance Energize, Beachbody LLC, USA] on exercise performance, perception of effort and plasma caffeine metabolites. Thirteen cyclists (V̇O_2max 64.5 ± 1.4 ml kg^- 1 min^- 1 (± SEM)) completed four experimental visits consisting of 30 min of steady-state exercise on a cycle ergometer at 83 ± 1% V̇O_2max followed by a 15-min time trial, with perceived exertion measured regularly. On three of the visits, participants consumed caffeine either 35 min before steady-state exercise (PRE), at the onset of steady-state (ONS) or immediately before the time trial (DUR) phases, with a placebo consumed at the other two time points (i.e. three drinks per visit). The other visit (PLA) consisted of consuming the placebo supplement at all three time points. The placebo was taste-, colour- and calorie-matched.

RESULTS

Total work performed during the time trial in PRE was 5% greater than PLA (3.53 ± 0.14 vs. 3.36 ± 0.13 kJ kg^- 1 body mass; P = 0.0025), but not ONS (3.44 ± 0.13 kJ kg^- 1; P = 0.3619) or DUR (3.39 ± 0.13 kJ kg^- 1; P = 0.925), which were similar to PLA. Perceived exertion was lowest during steady-state exercise in the PRE condition (P < 0.05), which coincided with elevated plasma paraxanthine in PRE only (P < 0.05).

CONCLUSION

In summary, ingestion of a pre-exercise supplement containing 200 mg caffeine 35 min before exercise appeared optimal for improved performance in a subsequent fatiguing time trial, possibly by reducing the perception of effort. Whether this was due to increased circulating paraxanthine requires further investigation.

TRIAL REGISTRATION

ClinicalTrials.Gov, NCT02985606 ; 10/26/2016.

Effects of short-term saffron (Crocus sativus L.) intake on the in vivo activities of xenobiotic metabolizing enzymes in healthy volunteers

Crocus sativus L., a perennial plant grown mainly around the Mediterranean and Iran, has many medicinal properties including anti-inflammatory, anti-depressive and cancer preventing properties. Aqueous herbal extracts may affect the activity of Phase I and II enzymes involved in xenobiotic metabolism. The present study was designed to determine whether C. sativus infusion alters the activity of CYP1A2, CYP2A6, XO and NAT2 enzymes in humans. Thirty-four healthy volunteers consumed infusion prepared from C. sativus stigmata for six days. Enzyme phenotyping was assessed in saliva and urine using caffeine metabolite ratios as follows: CYP1A2: 17X/137Χ (saliva) and CYP1A2: (AFMU+1U+1X)/17U, CYP2A6: 17U/(17U + 17X), XO: 1U/(1U+1X) and NAT2: AFMU/(AFMU+1U+1X) (urine). Following C. sativus intake, CYP1A2 index was reduced by ∼13.7% in saliva (before: 0.51 ± 0.22, after: 0.44 ± 0.14; p = 0.002) and ∼6.0% in urine (before: 3.81 ± 1.20, after: 3.58 ± 0.92; p = 0.054). CYP1A2 index was significantly reduced only in males (saliva, before: 0.65 ± 0.22, after: 0.51 ± 0.16; p = 0.0001; urine, before: 4.53 ± 1.19, after: 4.03 ± 0.87; p = 0.017) suggesting sexual dimorphism in CYP1A2 inhibition. There was no effect of C. sativus intake on CYP2A6, XO or NAT2 indices. Short-term consumption of C. sativus infusion is unlikely to result in significant herb-drug interactions involving the enzymes studied, with the exception of potential herb-CYP1A2 substrate interaction in males.

Personalized medicine: going to the dogs?

Interindividual variation in drug response occurs in canine patients just as it does in human patients. Although canine pharmacogenetics still lags behind human pharmacogenetics, significant life-saving discoveries in the field have been made over the last 20 years, but much remains to be done. This article summarizes the available published data about the presence and impact of genetic polymorphisms on canine drug transporters, drug-metabolizing enzymes, drug receptors/targets, and plasma protein binding while comparing them to their human counterparts when applicable. In addition, precision medicine in cancer treatment as an application of canine pharmacogenetics and pertinent considerations for canine pharmacogenetics testing is reviewed. The field is poised to transition from single pharmacogene-based studies, pharmacogenetics, to pharmacogenomic-based studies to enhance our understanding of interindividual variation of drug response in dogs. Advances made in the field of canine pharmacogenetics will not only improve the health and well-being of dogs and dog breeds, but may provide insight into individual drug efficacy and toxicity in human patients as well.

In vitro analysis of factors influencing CYP1A2 expression as potential determinants of interindividual variation

Individual differences in drug metabolism contribute to interindividual variation that characterizes responses to drugs and risk in exposure to foreign chemicals. Large individual differences are found in expression levels of CYP1A2, a major drug-metabolizing enzyme. Underlying causes for this variation are not well understood. Several factors, including tobacco smoking, consumption of cruciferous vegetables, and sex, have been associated with modulating CYP1A2 expression. To understand factors regulating expression of CYP1A2 in establishing a causal relationship, this study examined effects of cigarette smoke condensate (CSC), indole-3-carbinol (I3C), and 17β-estradiol (estradiol) on CYP1A2 expression in in vitro systems using human liver and lung cells. Treatment with CSC (2-25 μg/mL) significantly increased levels of CYP1A2 in six cell lines examined, in a concentration- and time-dependent manner. Fold changes in expression levels relative to controls varied among cell lines. CYP1A2 enzymatic activity also increased with CSC exposure. Treatment of H1299 and HepB3 cells with dietary agent I3C (50 and 100 μmol/L) increased CYP1A2 expression. In human cell lines H1299 and H1395, treatment with estradiol (10 and 100 nmol/L) significantly reduced expression of CYP1A2. Using ChIP assays, effects of CSC on histone modifications were analyzed. Increases in H3K4me3 and H4K16ac were observed at several segments in the CYP1A2 gene, whereas H3K27me3 decreased, following CSC treatment. These results suggest that CYP1A2 expression is affected epigenetically by CSC. Additional studies will be needed to further establish regulatory mechanisms underlying effects of various environmental, dietary, and endogenous factors on CYP1A2 expression in better predicting individual variation.

Determination of Human Hepatic CYP2C8 and CYP1A2 Age-Dependent Expression to Support Human Health Risk Assessment for Early Ages

Predicting age-specific metabolism is important for evaluating age-related drug and chemical sensitivity. Multiple cytochrome P450s and carboxylesterase enzymes are responsible for human pyrethroid metabolism. Complete ontogeny data for each enzyme are needed to support in vitro to in vivo extrapolation (IVIVE). This study was designed to determine age-dependent human hepatic CYP2C8 expression, for which only limited ontogeny data are available, and to further define CYP1A2 ontogeny. CYP2C8 and 1A2 protein levels were measured by quantitative Western blotting using liver microsomal samples prepared from 222 subjects with ages ranging from 8 weeks gestation to 18 years after birth. The median CYP2C8 expression was significantly greater among samples from subjects older than 35 postnatal days (n = 122) compared with fetal samples and those from very young infants (fetal to 35 days postnatal, n = 100) (0.00 vs. 13.38 pmol/mg microsomal protein; p < 0.0001). In contrast, the median CYP1A2 expression was significantly greater after 15 months postnatal age (n = 55) than in fetal and younger postnatal samples (fetal to 15 months postnatal, n = 167) (0.0167 vs. 2.354 pmol/mg microsomal protein; p < 0.0001). CYP2C8, but not CYP1A2, protein levels significantly correlated with those of CYP2C9, CYP2C19, and CYP3A4 (p < 0.001), consistent with CYP2C8 and CYP1A2 ontogeny probably being controlled by different mechanisms. This study provides key data for the physiologically based pharmacokinetic model-based prediction of age-dependent pyrethroid metabolism, which will be used for IVIVE to support pyrethroid risk assessment for early life stages.

CYP1A2--a novel genetic marker for early aromatase inhibitor response in the treatment of breast cancer patients

Background

Endocrine resistance is a major obstacle to optimal treatment effect in breast cancer. Some genetic markers have been proposed to predict response to aromatase inhibitors (AIs) but the data is insufficient. The aim of the study was to find new genetic treatment predictive markers of AIs.

Methods

The ongoing population-based BC-blood study in Lund, Sweden includes women with primary breast cancer. This paper is based on AI-treated patients with estrogen receptor positive tumors who underwent breast cancer surgery in 2002–2008. First, an exploratory analysis of 1931 SNPs in 227 genes involved in absorption, distribution, metabolism, and elimination of multiple medications, using DMET™ chips, was conducted in a subset of the cohort with last follow-up in December 31^st 2011 (13 cases, 11 controls). Second, selected SNPs from the first analysis were re-analyzed concerning risk for early breast cancer events in the extended cohort of 201 AI-treated with last follow-up in June 30^th 2014. Clinical data were obtained from medical records and population registries.

Results

Only CYP1A2 rs762551 C-allele was significantly associated with increased risk for early events in the 24 patients (P = 0.0007) and in the extended cohort, adjusted Hazard ratio (HR) 2.22 (95 % CI 1.03–4.80). However, the main prognostic impact was found within five years, adjusted HR 7.88 (95 % CI 2.13–29.19). The impact of the CYP1A2 rs762551 C-allele was modified by a functional polymorphism in the regulator gene AhR Arg554Lys (G > A). Compared to patients who were homozygous for the major allele in both genes (CYP1A2 A/A and AhR G/G), a 9-fold risk for early events was found in patients who had at least one minor allele in both genes, adjusted HR 8.95 (95 % CI 2.55–31.35), whereas patients with at least one minor allele in either but not both genes had a 3-fold risk for early events, adjusted HR 2.81 (95 % CI 1.07–7.33). The impact of CYP1A2 rs762551 C-allele was also modified by the CYP19A1 rs4646 C/C, adjusted HR 3.39 (95 % CI 1.60–7.16) for this combination. This association was strongest within the first five years, adjusted HR 10.42 (95 % CI 3.45–31.51).

Conclusion

CYP1A2 rs762551 was identified as a new potential predictive marker for early breast cancer events in AI-treated breast cancer patients. Moreover, combined genotypes of CYP1A2 rs762551 and CYP19A1 rs4646 or AhR Arg554Lys could further improve prediction of early AI-treatment response. If confirmed, these results may provide a way to more personalized medicine.

Caffeine Cytochrome P450 1A2 Metabolic Phenotype Does Not Predict the Metabolism of Heterocyclic Aromatic Amines in Humans

2-Amino-1-methylimidazo[4,5-b]pyridine (PhIP) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) are carcinogenic heterocyclic aromatic amines (HAAs) formed in well-done cooked meats. Chemicals that induce cytochrome P450 (P450) 1A2, a major enzyme involved in the bioactivation of HAAs, also form in cooked meat. Therefore, well-done cooked meat may pose an increase in cancer risk because it contains both inducers of P450 1A2 and procarcinogenic HAAs. We examined the influence of components in meat to modulate P450 1A2 activity and the metabolism of PhIP and MeIQx in volunteers during a 4 week feeding study of well-done cooked beef. The mean P450 1A2 activity, assessed by caffeine metabolic phenotyping, ranged from 6.3 to 7.1 before the feeding study commenced and from 9.6 to 10.4 during the meat feeding period: the difference in means was significant (P < 0.001). Unaltered PhIP, MeIQx, and their P450 1A2 metabolites, N(2)-(β-1-glucosiduronyl)-2-(hydroxyamino)-1-methyl-6-phenylimidazo[4,5-b]pyridine (HON-PhIP-N(2)-Gl); N3-(β-1-glucosiduronyl)-2-(hydroxyamino)-1-methyl-6-phenylimidazo[4,5-b]pyridine (HON-PhIP-N3-Gl); 2-amino-3-methylimidazo-[4,5-f]quinoxaline-8-carboxylic acid (IQx-8-COOH); and 2-amino-8-(hydroxymethyl)-3-methylimidazo[4,5-f]quinoxaline (8-CH2OH-IQx) were measured in urine during days 2, 14, and 28 of the meat diet. Significant correlations were observed on these days between the levels of the unaltered HAAs and their oxidized metabolites, when expressed as percent of dose ingested or as metabolic ratios. However, there was no statistically significant correlation between the caffeine P450 1A2 phenotype and any urinary HAA biomarker. Although the P450 1A2 activity varied by greater than 20-fold among the subjects, there was a large intraindividual variation of the P450 1A2 phenotype and inconsistent responses to inducers of P450 1A2. The coefficient of variation of the P450 1A2 phenotype within-individual ranged between 1 to 112% (median = 40%) during the entire course of the study. The caffeine metabolic phenotype for P450 1A2 was a poor predictor of oxidative urinary metabolites of PhIP and MeIQx and may not be a reliable measure to assess the role of HAAs in cancer risk.

Activity of cytochrome P450 1A2 in relation to hepatic iron accumulation in transfusion-dependent β-thalassaemia major patients

BACKGROUND

Cytochrome P450 1A2 (CYP1A2) is a cytochrome enzyme with a pivotal role in hepatic drug metabolism. Data from CYP1A2((-/-)) mouse suggest that CYP1A2 plays a role in aspects of hepatic iron toxicity. The aim of this study was to assess the activity of CYP1A2 in relation to hepatic iron load in patients with transfusion-dependent β-thalassaemia major.

METHODS

The (13) C-methacetin continuous breath test was performed on 30 consecutive patients with transfusion-dependent β-thalassaemia major. CYP1A2 activity was measured by the rate at which the (13) C substrate is metabolized and exhaled expressed as percentage dose recovery (PDR) per hour. CYP1A2 activity was correlated with clinical and laboratory parameters and hepatic iron accumulation by T2* magnetic resonance imaging (T2*MRI).

RESULTS

Cytochrome P450 1A2 activity in patients with transfusion-dependent β- thalassaemia major was positivity correlated with plasma ferritin levels. No correlation was found with age, duration and amount of red blood cell transfusion and type of iron chelation therapy. Low CYP1A2 activity was negatively associated with hepatic iron accumulation (T2*MRI ≤ 6.3 ms); adjusted odds ratio (OR; 95% CI) for hepatic iron accumulation in patients with low CYP1A2 activity was 0.047 (0.003-0.72; P = 0.021). Of the six patients with decreased activity of CYP1A2, five had no hepatic iron accumulation and one had mild hepatic iron accumulation by T2*MRI.

CONCLUSION

Activity of CYP1A2 is associated with hepatic iron accumulation in patients with transfusion-depended β-thalassaemia major. Further studies are needed to assess the exact role of CYP1A2 in iron metabolism in human.

New perspectives in the assessment of future remnant liver

In order to achieve microscopic radical resection margins and thus better survival, surgical treatment of hepatic tumors has become more aggressive in the last decades, resulting in an increased rate of complex and extended liver resections. Postoperative outcomes mainly depend on the size and quality of the future remnant liver (FRL). Liver resection, when performed in the absence of sufficient FRL, inevitably leads to postresection liver failure. The current gold standard in the preoperative assessment of the FRL is computed tomography volumetry. In addition to the volume of the liver remnant after resection, postoperative function of the liver remnant is directly related to the quality of liver parenchyma. The latter is mainly influenced by underlying diseases such as cirrhosis and steatosis, which are often inaccurately defined until microscopic examination after the resection. Postresection liver failure remains a point of major concern that calls for accurate methods of preoperative FRL assessment. A wide spectrum of tests has become available in the past years, attesting to the fact that the ideal methodology has yet to be defined. The aim of this review is to discuss the current modalities available and new perspectives in the assessment of FRL in patients scheduled for major liver resection.

Age-related changes in mRNA levels of hepatic transporters, cytochrome P450 and UDP-glucuronosyltransferase in female rats

Hepatic transporters and metabolic enzymes affect drug pharmacokinetics. Limited information exists on the alteration in mRNA levels of hepatic transporters and metabolic enzymes with aging. We examined the effects of aging on the mRNA levels of representative hepatic drug transporters and metabolic enzymes by analyzing their levels in 10-, 30- and 50-week-old male and female rats. Levels of mRNA of drug transporters including multidrug resistance protein (Mdr)1a, multidrug resistance-associated protein (Mrp)2, breast cancer resistance protein (Bcrp) and organic anion-transporting polypeptide (Oatp)1a1, and the metabolic enzymes cytochrome P450 (CYP)3A1, CYP3A2 and UDP-glucuronosyltransferase (UGT)1A1 were analyzed using real-time reverse transcriptase polymerase chain reaction. The mRNA levels of transporters in male rats did not decrease with age, while the mRNA levels of Bcrp and Oatp1a1 in female rats decreased with age. The mRNA levels of CYP3A1 and CYP3A2 in male rats were higher than those in female rats. The mRNA levels of metabolic enzymes decreased with age in female but not male rats. In particular, the mRNA levels of UGT1A1 in 10-week-old female rats were higher than those in male rats. mRNA expression of hepatic transporters and metabolic enzymes are more susceptible to aging in female than male rats. The age-related decreases in the mRNA levels of Bcrp, Oatp1a1, CYP3A1 and CYP3A2 in female rats may affect the metabolism and transport of substrates. This study showed that aging affected the mRNA expression of hepatic transporters and metabolic enzymes in rats.

Genetic polymorphism of cytochrome P450 (CYP) 1A1, CYP1A2, and CYP2E1 genes modulate susceptibility to gastric cancer in patients with Helicobacter pylori infection

BACKGROUND

Activity of cytochrome P450 (CYP), a polymorphic carcinogen-activating enzyme, is exaggerated following Helicobacter pylori infection. We studied the role of CYP2E1, CYP1A2 (rs762551), and CYP1A1 (rs4646903) polymorphisms in association with H. pylori infection in gastric carcinogenesis.

METHODS

Genotyping of CYP2E1 (96-bp insertion), CYP1A2 (164A to C), and CYP1A1 (3801C to T) was carried out in 88, 76, 53, and 170 patients with gastric cancer (GC), functional dyspepsia (FD), peptic ulcer (PU), and healthy controls (HC), respectively. Serum IgG antibody (all subjects), rapid urease test, and histology (GC, FD, and PU patients) were used to test for H. pylori.

RESULTS

CYP2E1 gene polymorphism was more common among patients with GC than HC and PU [48/88 (54.5 %) vs. 67/170 (39.4 %); OR 1.9, 95 % CI 1.1-3.2, p = 0.016) and [PU 18/53 (34 %); OR 2.3 (1-4.7), p = 0.02]. CYP1A2 CC or CT genotypes was lower among patients with GC than HC [50/88 (56.8 %) vs. 120/170 (70.6 %); OR 0.54 (0.31-0.92), p = 0.023]. CYP1A1 polymorphism and CYP1A1-CYP1A2 haplotypes were comparable among different groups. CYP2E1 was also more common in patients with GC than HC and PU in the absence of H. pylori [33/60 (55 %) vs. 19/52 (36.5 %); OR 4 (1.5-11.4), p = 0.007 and PU 7/22 (31.8 %); OR 3.4 (1-11.6), p = 0.05]. CYP1A1 (CT + TT) was more common in patients with GC than PU in presence of H. pylori [17/26 (65.4 %) vs. 11/29 (38 %); OR 3.0 (1.03-9.3), p = 0.045].

CONCLUSIONS

The presence of CYP2E1 (96-bp insertion) is associated with increased risk of GC even in absence of H. pylori. CYP1A2 CC or CT is associated with reduced risk of GC.

Genetic risk prediction: individualized variability in susceptibility to toxicants

Genetic risk prediction uses genetic data to individualize prediction of outcome or effect from a known harmful toxicant. Several examples of toxicogenetics (usually binary traits) are discussed, reflecting largely Mendelian traits before the Human Genome Project began in 1990. Numerous complexities of the genome and what constitutes "a gene" have emerged during these past two decades. Examples of toxicogenomics (continuous outcomes, gradients) are examined. Most xenobiotic-induced environmental diseases resemble human complex diseases or other multifactorial traits such as height; these traits result from hundreds of low-effect genes. Consequently, uncovering an association between a trait and a genetic variant in a large cohort can provide important information about underlying biology; however, screening for a specific variant in an individual worker or patient has poor predictive value and little clinical utility. Individualized risk assessment for toxicants that cause environmental diseases, although a lofty goal, remains to be achieved.

Functional characterization of eight human CYP1A2 variants: the role of cytochrome b5

BACKGROUND

Interindividual variability in cytochrome P450 (CYP)-mediated xenobiotic metabolism is extensive. CYP metabolism requires two electrons, which can be donated by NADPH cytochrome P450 oxidoreductase (CYPOR) and/or cytochrome b5 (b5). Although substantial number of studies have reported on the function and effect of b5 in CYP-mediated catalysis, its mode of action is still not fully understood.

OBJECTIVE

The aim of this work was to examine the effect of b5 on the activities of eight natural-occurring variants of human CYP1A2, namely, T83M, S212C, S298R, G299S, I314V, I386F, C406Y, and R456H.

MATERIALS AND METHODS

An approach, as used in our former study was applied, coexpressing these polymorphic CYP1A2 variants separately with CYPOR and b5 in the bacterial cell model BTC-CYP. For each variant, 16 different activity parameters were measured, using eight different substrates. This heterogeneous data set was merged with the one of our former study (i.e. without b5) and a multivariate analysis was carried out.

RESULTS

This analysis indicated that b5 seems to have the ability to affect CYP1A2 variants to behave more like the wild-type variant. This was especially the case for variant I386F, for which the presence of b5 was crucial to show activity. Variants T83M and C406Y showed considerably different activity-profiles when in the presence of b5. Furthermore, our data seem to implicate CYP1A2 residue G299 in its interaction with CYPOR and/or b5.

CONCLUSION

Results indicate the ability of b5 to affect CYP1A2 variants to behave more like the wild-type variant, attenuating detrimental effects of structural mutations of these variants, seemingly through extensive allosteric effects.

Gene-environment interactions of selected pharmacogenes in arterial hypertension

Hypertension affects approximately 1 billion people worldwide. Owing to population aging, hypertension-related cardiovascular burden is expected to rise in the near future. In addition to genetic variants influencing the blood pressure response to antihypertensive drugs, several genes encoding for drug-metabolizing or -transporting enzymes have been associated with blood pressure and/or hypertension in humans (e.g., ACE, CYP1A2, CYP3A5, ABCB1 and MTHFR) regardless of drug treatment. These genes are also involved in the metabolism and transport of endogenous substances and their effects may be modified by selected environmental factors, such as diet or lifestyle. However, little is currently known on the complex interplay between environmental factors, endogenous factors, genetic variants and drugs on blood pressure control. This review will discuss the respective role of population-based primary prevention and personalized medicine for arterial hypertension, taking a pharmacogenomics' perspective focusing on selected pharmacogenes.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Haplotypes in the 5'-untranslated region of the CYP1A2 gene are inversely associated with lung cancer risk but do not correlate with caffeine metabolism

In this study, we analyzed the influence of CYP1A2 genetic variation and enzyme activity on lung cancer risk in a high-incidence area. A total of 95 lung cancer patients and 196 controls were genotyped for the -3860G/A, -3113A/G, -2467T/delT, -739T/G, and -163C/A polymorphisms in the 5'-untranslated region of the gene. In addition, a subset of 70 patients and 115 controls were phenotyped by high-performance liquid chromatography determination of the caffeine metabolic ratio (CMR). The -2467T/delT polymorphism and the CYP1A2*1V haplotype (-163C>A, -2467T>delT) were inversely associated with lung cancer risk (odds ratio [OR] = 0.47 [0.2-0.9]; P = 0.02 and OR = 0.13 [0.02-1.0]; P = 0.04; respectively). In addition, the CYP*1A/*1V and *1F (-163C>A)/*1D (-163C>A, -2467T>delT) diplotypes were absent in the patients group, whereas accounting for 7.1% (P = 0.017) and 5.6% (P = 0.037) of controls, respectively. Mean CMR was significantly higher in patients than in controls (10.50 ± 17.31 vs. 6.52 ± 6.26, P = 0.01) but regression analyses did not yield significant ORs for the association with lung cancer risk. Similarly, no significant correlations were found between any genetic variant and enzyme activity. Several CYP1A2 haplotypes and diplotypes containing the -2467delT variant were associated with lower lung cancer risk; however, they did not correlate with significant changes in CYP1A2 metabolic activity toward caffeine.

Cytochrome P450 enzymes in drug metabolism: regulation of gene expression, enzyme activities, and impact of genetic variation

Cytochromes P450 (CYP) are a major source of variability in drug pharmacokinetics and response. Of 57 putatively functional human CYPs only about a dozen enzymes, belonging to the CYP1, 2, and 3 families, are responsible for the biotransformation of most foreign substances including 70-80% of all drugs in clinical use. The highest expressed forms in liver are CYPs 3A4, 2C9, 2C8, 2E1, and 1A2, while 2A6, 2D6, 2B6, 2C19 and 3A5 are less abundant and CYPs 2J2, 1A1, and 1B1 are mainly expressed extrahepatically. Expression of each CYP is influenced by a unique combination of mechanisms and factors including genetic polymorphisms, induction by xenobiotics, regulation by cytokines, hormones and during disease states, as well as sex, age, and others. Multiallelic genetic polymorphisms, which strongly depend on ethnicity, play a major role for the function of CYPs 2D6, 2C19, 2C9, 2B6, 3A5 and 2A6, and lead to distinct pharmacogenetic phenotypes termed as poor, intermediate, extensive, and ultrarapid metabolizers. For these CYPs, the evidence for clinical significance regarding adverse drug reactions (ADRs), drug efficacy and dose requirement is rapidly growing. Polymorphisms in CYPs 1A1, 1A2, 2C8, 2E1, 2J2, and 3A4 are generally less predictive, but new data on CYP3A4 show that predictive variants exist and that additional variants in regulatory genes or in NADPH:cytochrome P450 oxidoreductase (POR) can have an influence. Here we review the recent progress on drug metabolism activity profiles, interindividual variability and regulation of expression, and the functional and clinical impact of genetic variation in drug metabolizing P450s.

Influence of environmental and genetic factors on CYP1A2 activity in individuals of South Asian and European ancestry

The drug-metabolizing enzyme CYP1A2 contributes to the metabolism of a number of commonly used medicines and displays wide interindividual variability. The aim of this study was to investigate CYP1A2 activity in a population of South Asian ancestry and compare it with a population of European ancestry. CYP1A2 activity was determined using the 4 h paraxanthine/caffeine saliva concentration ratio following a 100-mg oral dose of caffeine in healthy individuals of South Asian (n = 166) and European (n = 166) ancestry. Participants were surveyed for extrinsic ethnic factors and genotyped for polymorphisms in CYP1A2 and related genes. Significantly lower CYP1A2 activity was observed in South Asian participants (median: 0.42; range: 0.10-1.06) as compared with European participants (0.54; 0.12-1.64) (P < 0.01). Multiple linear regression indicated that 41% of the variability in CYP1A2 activity could be explained by the diet, lifestyle, and genetic factors studied.

Association study of 27 annotated genes for clozapine pharmacogenetics: validation of preexisting studies and identification of a new candidate gene, ABCB1, for treatment response

OBJECTIVE

Pharmacogenetic studies on clozapine (CLZ) have provided meaningful insights but have shown redundancies owing to wide interindividual variability and insufficient replication. The present study was designed to validate hitherto suggested candidate genes on CLZ pharmacokinetics and pharmacodynamics and explore new markers through an integrative study.

METHODS

Based on a literature review, a total of 127 variations in 27 candidate genes were selected and analyzed. Ninety-six schizophrenic patients of Korean ethnicity with constant CLZ dosing were recruited, and information on body weight and smoking habits was gathered, as well as plasma drug levels and treatment responses.

RESULTS

Among the pharmacokinetic-related single nucleotide polymorphisms, rs2069521 and rs2069522 in CYP1A2 for CLZ/(dose/weight) and norclozapine/(dose/weight) and rs1135840 in CYP2D6 for norclozapine/CLZ showed borderline associations that were insignificant after correction for multiple testing. Regarding treatment response, significant associations were exhibited in rs7787082 and rs10248420 of ABCB1 (P = 0.0005 and P = 0.0013, respectively) even after correction, and the rs7787082 G and rs10248420 A alleles in ABCB1 were more frequently observed in nonresponders. We also observed a trend in the associations of rs13064530 in HRH1 and rs4938013 in DRD2/ANKK1 with treatment response.

CONCLUSIONS

We could not convincingly replicate most of the previous studies, a result that is possibly due to modest association between the suggested genes. Rather, we found a new candidate gene, ABCB1, for treatment response, which may provide a hypothesis on the relationship between the blood-brain distribution of CLZ and its clinical efficacy.

Top Three Pharmacogenomics and Personalized Medicine Applications at the Nexus of Renal Pathophysiology and Cardiovascular Medicine

Pharmacogenomics is a field with origins in the study of monogenic variations in drug metabolism in the 1950s. Perhaps because of these historical underpinnings, there has been an intensive investigation of 'hepatic pharmacogenes' such as CYP450s and liver drug metabolism using pharmacogenomics approaches over the past five decades. Surprisingly, kidney pathophysiology, attendant diseases and treatment outcomes have been vastly under-studied and under-theorized despite their central importance in maintenance of health, susceptibility to disease and rational personalized therapeutics. Indeed, chronic kidney disease (CKD) represents an increasing public health burden worldwide, both in developed and developing countries. Patients with CKD suffer from high cardiovascular morbidity and mortality, which is mainly attributable to cardiovascular events before reaching end-stage renal disease. In this paper, we focus our analyses on renal function before end-stage renal disease, as seen through the lens of pharmacogenomics and human genomic variation. We herein synthesize the recent evidence linking selected Very Important Pharmacogenes (VIP) to renal function, blood pressure and salt-sensitivity in humans, and ways in which these insights might inform rational personalized therapeutics. Notably, we highlight and present the rationale for three applications that we consider as important and actionable therapeutic and preventive focus areas in renal pharmacogenomics: 1) ACE inhibitors, as a confirmed application, 2) VDR agonists, as a promising application, and 3) moderate dietary salt intake, as a suggested novel application. Additionally, we emphasize the putative contributions of gene-environment interactions, discuss the implications of these findings to treat and prevent hypertension and CKD. Finally, we conclude with a strategic agenda and vision required to accelerate advances in this under-studied field of renal pharmacogenomics with vast significance for global public health.

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.

Cytochrome P4501A2 phenotype and bladder cancer risk: The Shanghai bladder cancer study

Cytochrome P450 1A2 (CYP1A2) is hypothesized to catalyze the activation of arylamines, known human bladder carcinogens present in cigarette smoke. The relationship between CYP1A2 phenotype and bladder cancer risk was examined in a case-control study involving 519 patients and 514 controls in Shanghai, China. Both CYP1A2 and N-acetyltransferase 2 (NAT2) phenotypic status were determined by a caffeine-based urinary assay. Our study showed that among smokers at urine collection, patients with bladder cancer had statistically significantly higher CYP1A2 phenotype scores compared to control subjects (p = 0.001). The odds ratios (95% confidence intervals) of bladder cancer for the second, third and fourth quartiles of the CYP1A2 score were 1.31 (0.53-3.28), 2.04 (0.90-4.60) and 2.82 (1.32-6.05), respectively, relative to the lowest quartile (p for trend = 0.003). NAT2 slow acetylation phenotype was associated with a statistically significant 40% increased risk of bladder cancer, and the relationship was independent of subjects' smoking status. Subjects possessing the NAT2 slow acetylation phenotype and the highest tertile of CYP1A2 scores showed the highest risk for bladder cancer. Their odds ratios (95% confidence intervals) was 2.13 (1.24-3.68) relative to their counterparts possessing the NAT2 rapid acetylation phenotype and the lowest tertile of CYP1A2 scores. The findings of our study demonstrate that CYP1A2 phenotype may be an important contributing factor in the development of smoking-related bladder cancer in humans.

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

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

Genetic variation in the bioactivation pathway for polycyclic hydrocarbons and heterocyclic amines in relation to risk of colorectal neoplasia

Animal work implicates chemical carcinogens, such as polycyclic aromatic hydrocarbons (PAHs) and heterocyclic aromatic amines (HAAs) as contributing to the development of colorectal cancer (CRC). The epidemiologic evidence, however, remains inconsistent possibly due to intra-individual variation in bioactivation of these compounds. We conducted a case-control study of colorectal adenoma (914 cases, 1185 controls) and CRC (496 cases, 607 controls) among Japanese Americans, European Americans and Native Hawaiians to investigate the association of genetic variation in the PAH and HAA bioactivation pathway (CYP1A1, CYP1A2, CYP1B1, AHR and ARNT) identified through sequencing with risk of colorectal neoplasia, as well as their interactions with smoking and intakes of red meat and HAAs. The A allele for ARNT rs12410394 was significantly inversely associated with CRC [odds ratios (ORs) and 95% confidence intervals (CIs) for GG, AG and AA genotypes: 1.00, 0.66 (0.48-0.89), 0.54 (0.37-0.78), P(trend) = 0.0008] after multiple comparison adjustment. CYP1A2 rs11072508 was marginally significantly associated with CRC, where each copy of the T allele was associated with reduced risk (OR: 0.72, 95% CI: 0.58-0.88, P(trend) = 0.0017). No heterogeneity of genetic effects across racial/ethnic groups was detected. In addition, no significant interaction was observed after adjusting for multiple testing between genetic variants and pack-years of smoking, intake of red meat or HAAs (PhIP, MeIQx, Di-MeIQx or total HAAs) or NAT2 genotype (Rapid versus Slow or Intermediate). This study suggests that the genomic region around ARNT rs12410394 may harbor variants associated with CRC.

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.

In utero and lactational exposure to a complex mixture of polychlorinated biphenyls: toxicity in pups dependent on the Cyp1a2 and Ahr genotypes

Polychlorinated biphenyls (PCBs) are persistent toxic pollutants occurring as complex mixtures in the environment. Humans are known genetically to have > 60-fold differences in hepatic cytochrome P450 1A2 (CYP1A2) levels and > 12-fold differences in aryl hydrocarbon receptor (AHR) affinity, both of which could affect PCB pharmacokinetics. Thus, we compared Ahr(b1)_Cyp1a2(+/+) high-affinity AHR wild-type, Ahr(d)_Cyp1a2(+/+) poor affinity AHR wild-type, Ahr(b1)_Cyp1a2(-/-) knockout, and Ahr(d)_Cyp1a2(-/-) knockout mouse lines. We chose a mixture of three coplanar and five noncoplanar PCBs to reproduce that seen in human tissues, breast milk, and the food supply. The mixture was given by gavage to the mother on gestational day 10.5 (GD10.5) and postnatal day 5 (PND5); tissues were collected from pups and mothers at GD11.5, GD18.5, PND6, PND13, and PND28. Ahr(b1)_Cyp1a2(-/-) pups showed lower weight at birth and slower rate of growth postnatally. Absence of CYP1A2 resulted in significant splenic atrophy at PND13 and PND28. Presence of high-affinity AHR enhanced thymic atrophy and liver hypertrophy in the pups. Concentrations of each congener were analyzed at all time points: maximal noncoplanar congener levels in maternal tissues were observed from GD18 until PND6, whereas the highest levels in pups were found between PND6 and PND28. Coplanar PCB concentrations were generally higher in Ahr(d)-containing pup tissues; these findings are consistent with earlier studies demonstrating the crucial importance of AHR-mediated inducible CYP1 in the gastrointestinal tract as a means of detoxication of oral planar polycyclic aromatic hydrocarbons.

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

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

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.

CYP2B6 (c.516G-->T) and CYP2A6 (*9B and/or *17) polymorphisms are independent predictors of efavirenz plasma concentrations in HIV-infected patients

AIMS

Interindividual variability in efavirenz pharmacokinetics is not entirely explained by the well-recognized CYP2B6 516G-->T single nucleotide polymorphism. The aim of this study was to determine whether polymorphisms in the CYP2A6 gene can be used to enhance the predictability of efavirenz concentrations in human immunodeficiency virus (HIV)-infected native African patients.

METHODS

Mid-dose efavirenz plasma concentrations were determined at 4 and 8 weeks following initiation of antiretroviral therapy in 65 HIV-infected Ghanaian patients. Selected CYP2B6 and CYP2A6 genotypes were determined by commercial 5'-nuclease assays. Relationships between averaged 4- and 8-week mid-dose efavirenz concentrations, demographic variables and genotypes were evaluated by univariate and multivariate statistical approaches including gene-gene interactions.

RESULTS

CYP2B6 c.516G-->T, CYP2B6 c.983T-->C, CYP2A6*9B and CYP2A6*17 allele frequencies were 45, 4, 5 and 12%, respectively. Rifampicin therapy, gender, age and body mass index had no significant influence on efavirenz mid-dose concentrations. Median efavirenz concentrations were more than five times higher (P < 0.001) in patients with CYP2B6 c.516TT genotype compared with GG and GT genotypes. Although none of the CYP2A6 genotypes was associated with altered efavirenz concentrations individually, CYP2A6*9B and/or CYP2A6*17 carriers showed a 1.8 times higher median efavirenz concentration (P= 0.017) compared with noncarriers. Multiple linear regression analysis indicated that the CYP2B6 c.516G-->T polymorphism and CYP2A6 slow-metabolizing variants accounted for as much as 36 and 12% of the total variance in efavirenz concentrations, respectively.

CONCLUSIONS

Our findings support previous work showing efavirenz oxidation by CYP2A6, and suggest that both CYP2A6 and CYP2B6 genotyping may be useful for predicting efavirenz plasma concentrations.

Prediction of postoperative outcome after hepatectomy with a new bedside test for maximal liver function capacity

OBJECTIVE

To validate the LiMAx test, a new bedside test for the determination of maximal liver function capacity based on C-methacetin kinetics. To investigate the diagnostic performance of different liver function tests and scores including the LiMAx test for the prediction of postoperative outcome after hepatectomy.

SUMMARY BACKGROUND DATA

Liver failure is a major cause of mortality after hepatectomy. Preoperative prediction of residual liver function has been limited so far.

METHODS

Sixty-four patients undergoing hepatectomy were analyzed in a prospective observational study. Volumetric analysis of the liver was carried out using preoperative computed tomography and intraoperative measurements. Perioperative factors associated with morbidity and mortality were analyzed. Cutoff values of the LiMAx test were evaluated by receiver operating characteristic.

RESULTS

Residual LiMAx demonstrated an excellent linear correlation with residual liver volume (r = 0.94, P < 0.001) after hepatectomy. The multivariate analysis revealed LiMAx on postoperative day 1 as the only predictor of liver failure (P = 0.003) and mortality (P = 0.004). AUROC for the prediction of liver failure and liver failure related death by the LiMAx test was both 0.99. Preoperative volume/function analysis combining CT volumetry and LiMAx allowed an accurate calculation of the remnant liver function capacity prior to surgery (r = 0.85, P < 0.001).

CONCLUSIONS

Residual liver function is the major factor influencing the outcome of patients after hepatectomy and can be predicted preoperatively by a combination of LiMAx and CT volumetry.

Use of physiologically based biokinetic (PBBK) modeling to study estragole bioactivation and detoxification in humans as compared with male rats

The extent of bioactivation of the herbal constituent estragole to its ultimate carcinogenic metabolite 1′-sulfooxyestragole depends on the relative levels of bioactivation and detoxification pathways. The present study investigated the kinetics of the metabolic reactions of both estragole and its proximate carcinogenic metabolite 1′-hydroxyestragole in humans in incubations with relevant tissue fractions. Based on the kinetic data obtained a physiologically based biokinetic (PBBK) model for estragole in human was defined to predict the relative extent of bioactivation and detoxification at different dose levels of estragole. The outcomes of the model were subsequently compared with those previously predicted by a PBBK model for estragole in male rat to evaluate the occurrence of species differences in metabolic activation. The results obtained reveal that formation of 1′-oxoestragole, which represents a minor metabolic route for 1′-hydroxyestragole in rat, is the main detoxification pathway of 1′-hydroxyestragole in humans. Due to a high level of this 1′-hydroxyestragole oxidation pathway in human liver, the predicted species differences in formation of 1′-sulfooxyestragole remain relatively low, with the predicted formation of 1′-sulfooxyestragole being twofold higher in human compared with male rat, even though the formation of its precursor 1′-hydroxyestragole was predicted to be fourfold higher in human. Overall, it is concluded that in spite of significant differences in the relative extent of different metabolic pathways between human and male rat there is a minor influence of species differences on the ultimate overall bioactivation of estragole to 1′-sulfooxyestragole.

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.

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.