A population and family study of CYP1A2 using caffeine urinary metabolites

Simultaneous quantitation of serum caffeine and its metabolites by ultra-high-performance liquid chromatography-tandem mass spectrometry for CYP1A2 activity prediction in premature infants

Caffeine (CA) is accepted as a probe of cytochrome P450 1A2 enzyme (CYP1A2) activity and is commonly used in premature infants with great inter-individual variability of metabolism. To evaluate the change characteristics of CYP1A2 activity in premature infants, an ultra-high-performance liquid chromatography-tandem mass spectrometry method was developed and optimized for the simultaneous quantitation of serum CA and its major metabolites, including paraxanthine (PX), theophylline (TP) and theobromine (TB), in premature infants. A C₁₈ column and gradient elution with 0.1% formic acid in methanol and 0.1% formic acid in water at a flow rate of 0.3 mL/min were used for compound separation. The mass spectrometer monitored the transitions of CA (m/z 195.0 → 138.0), CA-d9 (m/z 204.0 → 144.1), PX (m/z 181.0 → 124.1), TP (m/z 181.0 → 123.9) and TB (m/z 181.0 → 138.0) using multiple reaction monitoring in positive ion mode. CYP1A2 activity was evaluated by serum molar concentration ratios of CA and its metabolites. The results showed that CYP1A2 has a significant positive correlation with the clearance of CA, and was affected by current weight and CYP1A2*1C. The results suggested that the serum concentration ratios of CA metabolites could be used to predict the changes in CYP1A2 enzyme activity in premature infants.

Sex Differences in Response to Triptans: A Systematic Review and Meta-analysis

OBJECTIVE

To examine the effect of sex on clinical response to triptans in migraine and to determine whether these differences are related to pharmacokinetics of triptans in men and women, we performed a systematic review and meta-analysis.

METHODS

We searched clinical trials distinguishing clinical response to or pharmacokinetic parameters of triptans between sexes in PubMed, MEDLINE, Cochrane Library, Embase, and Web of Science up to Dec 12, 2019. Analysis was based on data extracted from published reports. Male-to-female pooled risk ratios (RR) were calculated for clinical outcomes and pooled ratio of means (RoM) for pharmacokinetic outcomes using random-effects models.

RESULTS

Of 1,188 publications on clinical trials with triptans, 244 were identified with sex-related search terms. Only 19 publications presented sex-specific results, comprising n = 2,280 men and n = 13,899 women. No sex differences were revealed for 2-hour headache and pain-free responses, but men had a lower risk for headache recurrence (male-to-female RR 0.64, 95% confidence interval [CI]: 0.55-0.76, Q = 0.81) and adverse events (RR 0.82, 95% CI: 0.72-0.93, Q = 4.93). Men had lower drug exposure with lower area under the curve (RoM 0.69, 95% CI: 0.60-0.81, Q = 18.06) and peak drug concentration (RoM 0.72, 95% CI: 0.64-0.82, Q = 8.24) than women.

CONCLUSIONS

Remarkably few publications about sex differences in triptan response are available. The limited number of eligible studies show sex differences in adverse event frequency, which may be partly because of drug exposure differences. This higher drug exposure in women is not reflected in different response rates. Despite higher exposure, women have higher headache recurrence rates possibly because of longer attack duration related to sex hormonal changes.

Altered activity of xenobiotic detoxifying enzymes at menopause - A cross-sectional study

Xenobiotic metabolism at menopause is an under-investigated topic, albeit women spend one-third of their life in the postmenopausal period. The present study examined the effect of menopause on the in vivo activities of CYP1A2, CYP2A6, xanthine oxidase (XO) and N-acetyltransferase-2 (NAT2) xenobiotic metabolizing enzymes. Enzyme activity was determined in 152 non-smoking volunteers following oral intake of a single dose of 200 mg caffeine and subsequent determination of caffeine metabolite ratios (CMRs) in a 6-h urine sample as follows: CYP1A2: (AFMU+1U+1X)/17U, CYP2A6: 17U/(17U + 17X), XO: 1U/(1U+1X) and NAT2: AFMU/(AFMU+1U+1X). CMRs among groups were analyzed using one-way ANOVA. Significantly lower CYP1A2 and higher CYP2A6 CMRs were observed in postmenopausal compared to premenopausal women and age-matched men. These changes could be attributed to menopause rather than chronological aging since an age-related effect was not observed in premenopausal women or men of any age group. XO CMRs were higher in postmenopausal women and men>50 compared to premenopausal women and men<50, respectively, suggesting an age-related increase in XO activity. No significant alterations were discerned in NAT2 CMRs, in either slow- or rapid-acetylators, indicating that menopause exerts minimal modulation of xenobiotics metabolized by this enzyme. This study provides evidence that the transition to menopause induces significant alterations in xenobiotic-metabolizing enzymes independent of chronological aging suggesting altered metabolism of pharmaceutical and environmental agents.

New insights of CYP1A in endogenous metabolism: a focus on single nucleotide polymorphisms and diseases

Cytochrome P450 1A (CYP1A), one of the major CYP subfamily in humans, not only metabolizes xenobiotics including clinical drugs and pollutants in the environment, but also mediates the biotransformation of important endogenous substances. In particular, some single nucleotide polymorphisms (SNPs) for CYP1A genes may affect the metabolic ability of endogenous substances, leading to some physiological or pathological changes in humans. This review first summarizes the metabolism of endogenous substances by CYP1A, and then introduces the research progress of CYP1A SNPs, especially the research related to human diseases. Finally, the relationship between SNPs and diseases is discussed. In addition, potential animal models for CYP1A gene editing are summarized. In conclusion, CYP1A plays an important role in maintaining the health in the body.

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.

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

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

Polymorphism of human cytochrome P450 enzymes and its clinical impact

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

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

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

Enhancer elements in the mouse CYP1A2 gene: A comparative sequencing among different inbred mouse strains

CYP1A2 expression is constitutively high in mouse liver and is well known for metabolizing several drugs and many procarcinogens to reactive intermediates that can cause toxicity or cancer. In the present study, the basal level of hepatic CYP1A2 activity was shown to vary among different inbred mouse strains. The highest methoxyresorufin-O-demethylase activity (261+/-52pmol/mgprotein/min) was registered in CC57BR and the lowest (82+/-11pmol/mgprotein/min) in C3H/a. We have tested the hypothesis that possible polymorphisms in regulatory elements in the 5'-upstream region of the mouse CYP1A2 gene could cause the differences in CYP1A2 enzyme activity among different inbred strains. We have performed a study on the CYP1A2 gene by sequencing the regulatory region from -4675 to -4204 where two enhancer elements were recently identified. The absence of mutation prescribing the phenotype in the CYP1A2 gene was found. The region studied seems to be a highly conserved in mice and not to be associated with interstrain differences in constitutive CYP1A2 enzyme activity.

Estrogen-metabolizing gene polymorphisms in the assessment of female hormone-dependent cancer risk

Allelic variants of cytochrome P450: CYP1A1, CYP1A2, CYP19 (Aromatase) and II-phase enzyme Sulfotransferase (SULT1A1) genes are associated with a high risk of hormone-dependent cancers. We estimated a frequency of these allelic variants in the female Caucasian population of the Novosibirsk region of Russia and their association with the elevated risk of ovarian and endometrial cancer. A DNA bank of gynecologic oncology patients, patients with benign gynecologic diseases and healthy women was created, and the following single nucleotide polymorphisms (SNPs) were examined: CYP1A1 M1 polymorphism, that is, T264 --> C transition in the 3'-noncoding region; CYP1A2*1F polymorphism, that is, C734 --> A transversion in CYP1A2 gene; C --> T transition (Arg264Cys) in exon 7 of CYP19; SULT1A1*2 polymorphism, that is, G638 --> A transition (Arg213His) in SULT1A1 gene. A positive correlation of C allele of CYP1A2*1F and G allele of SULT1A1*2 with hormone-dependent cancers in women was found. Thus, these genes are appropriate candidates for studying the contribution of genetic factors to endocrine disorder and environmentally determined diseases susceptibility. In contrast, no association of CYP19 and CYP1A1 polymorphisms with increased cancer risk was revealed.

A preliminary study of the effect of fluoxetine treatment on the 2:16-alpha-hydroxyestrone ratio in young women

Cytochrome P450 isoenzymes are known to contribute to estrone metabolism. The authors hypothesized that fluoxetine, a known inhibitor of multiple P450 isoenzymes including 3A4, 2C9, and 2D6, would affect estrone metabolism, altering the 2-hydroxyestrone:16-alpha-hydroxyestrone (2OHE1:16OHE1) ratio. In this preliminary study, four of eight recruited women with regular menstrual cycles, aged 21-37 years, completed a 24-hour urine collection prior to initiation of fluoxetine therapy and after at least 5 weeks of antidepressant treatment. In three of the four women who were nonsmokers, the 2OHE1:16OHE1 ratio was significantly higher after 5 weeks of fluoxetine therapy (pretreatment, 2.08 +/- 0.11; posttreatment, 3.50 +/- 0.46; paired Student's t-test P = 4.72, P = 0.021).

The interindividual differences in the 3-demthylation of caffeine alias CYP1A2 is determined by both genetic and environmental factors

This study investigated the role of genetic factors (CYP1A2) in caffeine metabolism. The CYP1A2 activity was determined in 378 Danish twins following oral intake of a single dose of 200 mg caffeine and subsequent determination of the caffeine ratio (AFMU+1MU+1MX)/17DMU in a 6-h urine sample. The mean (+/- SD) caffeine ratio was 5.9 +/- 3.4. The caffeine ratio was statistically significantly higher in men compared to women, in smoking men and women compared to non-smoking persons of the same gender and in women not taking oral contraceptives compared with women on oral contraceptives. Thus, we confirmed that CYP1A2 is more active in men than in women, that it is induced by smoking and inhibited by oral contraceptives. In the subsequent analysis of heritability, we included 49 monozygotic twin pairs and 34 same gender dizygotic twin pairs concordant for non-smoking and non-use of oral contraceptives. The intraclass correlation coefficient was 0.798 (95% confidence interval, 0.696-0.900) and 0.394 (95% confidence interval, 0.109-0.680) in the monozygotic and dizygotic twins, respectively. The correlation was statistically significantly higher (P = 0.0015) in the former compared with the latter. A biometrical model for the caffeine ratio including only additive genetic factors and unique environmental factors was the overall best fitting model. Estimates based on this model gave a heritability estimate of 0.725 (95% confidence interval 0.577-0.822). Unique environmental effects seem to account for the remainder 0.275 (95% confidence interval, 0.178-0.423). Our study shows that the CYP1A2 activity is mainly governed by genetic factors.

Pharmacokinetic aspects of treating infections in the intensive care unit: focus on drug interactions

Pharmacokinetic interactions involving anti-infective drugs may be important in the intensive care unit (ICU). Although some interactions involve absorption or distribution, the most clinically relevant interactions during anti-infective treatment involve the elimination phase. Cytochrome P450 (CYP) 1A2, 2C9, 2C19, 2D6 and 3A4 are the major isoforms responsible for oxidative metabolism of drugs. Macrolides (especially troleandomycin and erythromycin versus CYP3A4), fluoroquinolones (especially enoxacin, ciprofloxacin and norfloxacin versus CYP1A2) and azole antifungals (especially fluconazole versus CYP2C9 and CYP2C19, and ketoconazole and itraconazole versus CYP3A4) are all inhibitors of CYP-mediated metabolism and may therefore be responsible for toxicity of other coadministered drugs by decreasing their clearance. On the other hand, rifampicin is a nonspecific inducer of CYP-mediated metabolism (especially of CYP2C9, CYP2C19 and CYP3A4) and may therefore cause therapeutic failure of other coadministered drugs by increasing their clearance. Drugs frequently used in the ICU that are at risk of clinically relevant pharrmacokinetic interactions with anti-infective agents include some benzodiazepines (especially midazolam and triazolam), immunosuppressive agents (cyclosporin, tacrolimus), antiasthmatic agents (theophylline), opioid analgesics (alfentanil), anticonvulsants (phenytoin, carbamazepine), calcium antagonists (verapamil, nifedipine, felodipine) and anticoagulants (warfarin). Some lipophilic anti-infective agents inhibit (clarithromycin, itraconazole) or induce (rifampicin) the transmembrane transporter P-glycoprotein, which promotes excretion from renal tubular and intestinal cells. This results in a decrease or increase, respectively, in the clearance of P-glycoprotein substrates at the renal level and an increase or decrease, respectively, of their oral bioavailability at the intestinal level. Hydrophilic anti-infective agents are often eliminated unchanged by renal glomerular filtration and tubular secretion, and are therefore involved in competition for excretion. Beta-lactams are known to compete with other drugs for renal tubular secretion mediated by the organic anion transport system, but this is frequently not of major concern, given their wide therapeutic index. However, there is a risk of nephrotoxicity and neurotoxicity with some cephalosporins and carbapenems. Therapeutic failure with these hydrophilic compounds may be due to haemodynamically active coadministered drugs, such as dopamine, dobutamine and furosemide, which increase their renal clearance by means of enhanced cardiac output and/or renal blood flow. Therefore, coadministration of some drugs should be avoided, or at least careful therapeutic drug monitoring should be performed when available. Monitoring may be especially helpful when there is some coexisting pathophysiological condition affecting drug disposition, for example malabsorption or marked instability of the systemic circulation or of renal or hepatic function.

Association between CYP1A2 polymorphism and susceptibility to porphyria cutanea tarda

Individuals with the most common form of the porphyrias, porphyria cutanea tarda (PCT), are believed to be genetically predisposed to development of clinically overt disease through mutations and polymorphisms in genes associated with known precipitating factors. In this study, we have examined a group of Danish patients with PCT for the presence of the C/A polymorphism in intron 1 of CYP1A2. The results demonstrate that the frequency of the highly inducible A/A genotype is increased in both familial and sporadic PCT. This suggests that inheritance of this genotype is a susceptibility factor in development of PCT.

Clinically significant pharmacokinetic interactions between dietary caffeine and medications

Caffeine from dietary sources (mainly coffee, tea and soft drinks) is the most frequently and widely consumed CNS stimulant in the world today. Because of its enormous popularity, the consumption of caffeine is generally thought to be safe and long term caffeine intake may be disregarded as a medical problem. However, it is clear that this compound has many of the features usually associated with a drug of abuse. Furthermore, physicians should be aware of the possible contribution of dietary caffeine to the presenting signs and symptoms of patients. The toxic effects of caffeine are extensions of their pharmacological effects. The most serious caffeine-related CNS effects include seizures and delirium. Other symptoms affecting the cardiovascular system range from moderate increases in heart rate to more severe cardiac arrhythmia. Although tolerance develops to many of the pharmacological effects of caffeine, tolerance may be overwhelmed by the nonlinear accumulation of caffeine when its metabolism becomes saturated. This might occur with high levels of consumption or as the result of a pharmacokinetic interaction between caffeine and over-the-counter or prescription medications. The polycyclic aromatic hydrocarbon-inducible cytochrome P450 (CYP) 1A2 participates in the metabolism of caffeine as well as of a number of clinically important drugs. A number of drugs, including certain selective serotonin reuptake inhibitors (particularly fluvoxamine), antiarrhythmics (mexiletine), antipsychotics (clozapine), psoralens, idrocilamide and phenylpropanolamine, bronchodilators (furafylline and theophylline) and quinolones (enoxacin), have been reported to be potent inhibitors of this isoenzyme. This has important clinical implications, since drugs that are metabolised by, or bind to, the same CYP enzyme have a high potential for pharmacokinetic interactions due to inhibition of drug metabolism. Thus, pharmacokinetic interactions at the CYP1A2 enzyme level may cause toxic effects during concomitant administration of caffeine and certain drugs used for cardiovascular, CNS (an excessive dietary intake of caffeine has also been observed in psychiatric patients), gastrointestinal, infectious, respiratory and skin disorders. Unless a lack of interaction has already been demonstrated for the potentially interacting drug, dietary caffeine intake should be considered when planning, or assessing response to, drug therapy. Some of the reported interactions of caffeine, irrespective of clinical relevance, might inadvertently cause athletes to exceed the urinary caffeine concentration limit set by sports authorities at 12 mg/L. Finally, caffeine is a useful and reliable probe drug for the assessment of CYP1A2 activity, which is of considerable interest for metabolic studies in human populations.

Evaluation of caffeine as an in vivo probe for CYP1A2 using measurements in plasma, saliva, and urine

Twenty-five healthy volunteers were given 100 mg caffeine orally and several estimates of cytochrome P450 1A2 (CYP1A2) activity were evaluated. The validation was performed by correlation of different parameters in plasma, saliva, and urine to two measures of caffeine clearance, CL(oral) and CL(137X-->17X) that served as standards of reference. Two subjects were excluded because of noncompliance with a caffeine-free diet. In the remaining 23 subjects, both plasma and saliva total clearances of caffeine were highly correlated with each other (r(s) = 0.97, p < 0.0001). The ratio 17X/137X restricted to one sampling point taken 4 hours after dose, showed a high correlation (r(s)) with CL(oral) and CL(137X-->17X) in plasma (0.84/0.83) and saliva (0.82/0.77) (p < 0.0001 for all the correlation values) where 17X is 1,7-dimethylxanthine (paraxanthine) and 137X is 1,3,7-trimethylxanthine (caffeine). Additionally, the ratio (AFMU + 1U + 1X + 17U + 17X)/137X in a 0-24 hours urine sampling showed the highest correlation with CL(137X-->17X) (r(s) = 0.85, p < 0.001) where AFMU is 5-acetylamino-6-formylamino-3-methyluracil, 1U is 1-methyluracil, 1X is 1-methylxanthine, and 17U is 1,7-dimethyluric acid. The major estimates of CYP1A2 activity were significantly less in nonsmoking females, and this probably was related to the use of oral contraceptives in this subpopulation. In summary, among caffeine-based approaches for CYP1A2, the authors recommend either plasma or saliva 17X/137X ratio and the urinary (AFMU + 1U + 1X + 17U + 17X)/137X ratio during a sampling interval of at least 8 hours, starting at time zero since caffeine intake. These indices are simple, reliable, and relatively inexpensive estimates of CYP1A2 activity to be used in the study of human populations.

Monitoring of cytochrome P-450 1A activity by determination of the urinary pattern of caffeine metabolites in Wistar and hyperbilirubinemic Gunn rats

Various studies suggest that induction of cytochrome P-450 1A (CYP1A) might be a valuable therapeutic modality for reducing the hyperbilirubinemia of infants with Crigler-Najjar syndrome type I (CNS-I), a severe form of congenital jaundice. To evaluate inducers of CYP1A as possible tools in the treatment of hyperbilirubinemia, a novel assay was established, based on the analysis of the urinary pattern of caffeine metabolites in rats. Wistar rats received [1-Me-(14)C]-caffeine (10 mg/kg i.p.), before and 48h after administration of the potent CYP1A inducer 5,6-benzoflavone (BNF) (80 mg/kg, i.p.). A substantial increase in the fractions of the terminal caffeine metabolites 1-methyluric acid (1-U), 1-methylxanthine (1-X), and a concomitant decrease in the caffeine demethylation product 1,7-dimethylxanthine (1,7-X) was observed after application of BNF. The ratio of the caffeine metabolites (1-U+1-X)/1,7-X may serve as an index of CYP1A activity in rats in vivo. Hyperbilirubinemic, homozygous (jj) Gunn rats are an accepted model for human CNS-I. In male jj Gunn rats treated with BNF or with indole-3-carbinol (I3C, 80 mg/kg, oral gavage), the inducing effect of BNF and 13C on CYP1A activity was confirmed by the urinary pattern of caffeine metabolites, and was parallelled by a decrease in plasma bilirubin levels. These data demonstrate the usefulness of the established caffeine assay for the evaluation of inducers of CYP1A as tools for reducing hyperbilirubinemia and further confirm the potential value of I3C in the treatment of CNS-I.

The effect of NAT2 genotype and gender on the metabolism of caffeine in nonsmoking subjects

AIMS

To establish whether gender or N-acetyltransferase 2 (NAT2) genotype influence the urinary 17 U+17X/137X ratio after dosing with caffeine.

METHODS

Ninety-two nonsmoking individuals underwent caffeine phenotyping. NAT2 genotype was determined by the polymerase chain reaction followed by a restriction digest (PCR-RFLP).

RESULTS

The median ratio for urinary 17 U+17X/137X was 6.7 (range 1.45-18. 65). 55% of subjects were slow acetylators. Gender did not affect the metabolic ratio or NAT2 genotype. Mean 17 U+17X/137X ratio differed between fast (6.75) and slow (8.69) acetylators (95% CI for the difference, 0.32-3.56).

CONCLUSIONS

The findings are further evidence that the 17 U+17X/137X urinary ratio is not a robust measure of CYP1A2 activity. A possible mechanism by which the ratio might be influenced by NAT2 genotype is suggested.

Variation in induced CYP1A1 levels: relationship to CYP1A1, Ah receptor and GSTM1 polymorphisms

The genotypic basis of interindividual variation in levels of induced CYP1A1 activity has been investigated by screening both the CYP1A1 gene and the Ah receptor gene (AhR) for both previously described and novel polymorphisms. A 103-fold level of interindividual variation in induced CYPlA1 activity [ethoxyresorufin O-deethylase (EROD)] was observed in lymphocytes from a group of 30 Caucasian volunteers. High levels of induced EROD activity did not correlate with the presence of CYP1A1*2 or CYP1A1*4 alleles or with the GSTM1 null genotype. Novel CYP1A1 alleles with the base substitutions C4151T, G-469A and C-459T respectively, were detected by screening the coding exons and approximately 1 kb of upstream sequence in 20 individuals by single-strand conformational polymorphism (SSCP) analysis but none of the three novel alleles appeared to be associated with high induced CYP1A1 activity in the study group. Screening of the 11 exons of the AhR gene by SSCP analysis confirmed the existence of the previously described G1721A polymorphism in a Caucasian population and a novel allele (G1768A which results in the amino acid substitution V5701) was also detected. The novel allele was very rare in Caucasians though more common in African-Americans. Individuals with at least one copy of the G1721A AhR variant allele showed a significantly higher level of induced CYP1A1 activity compared with individuals negative for the polymorphism (P = 0.0001). A similar finding was obtained for induced CYP1A1 protein levels determined by immunoblotting. Levels of induced CYP1A1 activity were also found to show a sex difference with women showing a significantly lower induced activity compared with men. We conclude that genotypes for the G1721A AhR polymorphism and gender appear to be determinants of levels of induced CYP1A1 activity and that interindividual variation in levels of induced CYP1A1 activity appears to be associated more with regulatory factors than polymorphism in the CYP1A1 gene.

Phenotypic polymorphism and gender-related differences of CYP1A2 activity in a Chinese population

AIMS

To investigate the distribution characteristics of CYP1A2 in a Chinese population, and to examine gender-related differences in CYP1A2 activity.

METHODS

Two hundred and twenty-nine healthy subjects, 120 men and 109 women, were enrolled in this study. CYP1A2 activity was measured by plasma paraxanthine/caffeine (1,7X/1,3,7X) ratio 6 h after administration of 300 mg caffeine. The concentrations of paraxanthine and caffeine in plasma were detected by h.p.l.c.

RESULTS

A 16-fold variation of CYP1A2 activity (range 0. 09 to 1.46) was shown in this study. The coefficient of variation (CV %) of CYP1A2 activity was 62.9%. Non-normal distribution of CYP1A2 activity was indicated by the Shapiro-Wilk test (P<0.001). Probit plots of CYP1A2 activity revealed a bimodal distribution with breakpoint of 1,7X/1,3,7X ratio of 0.12. The percentage of poor metabolizers (PMs) was 5.24% (95% CI: 2.35% approximately 8.13%) in this Chinese population. Residual analysis of the data also supported bimodality (P<0.01). The CYP1A2 activity of men was higher than that of women (median: 0.33 vs 0.23, P<0.001). A probit plot of CYP1A2 activity in men was shifted to the left compared with that in women. Based on phenotype, the gender-related difference was observed in extensive metabolizers (EMs) (P<0.001), but not in PMs (P >0.1). In addition, there was no sex-related difference in the incidence of PMs (P >0.1).

CONCLUSIONS

There is a phenotypic polymorphism in CYP1A2 activity in this Chinese population, and CYP1A2 activity is higher in men than that in women.

Functional significance of a C-->A polymorphism in intron 1 of the cytochrome P450 CYP1A2 gene tested with caffeine

AIMS

The cytochrome P450 enzyme CYP1A2 metabolises several drugs and carcinogens. We wanted to determine how much of the variability of CYP1A2 activity is explained by a newly discovered gene polymorphism in intron 1.

METHODS

A single nucleotide polymorphism in intron 1 of the CYP1A2 gene at position 734 downstream of the first transcribed nucleotide was identified by DNA sequence analysis. The functional significance of this C/A polymorphism was assessed in 185 healthy Caucasian non-smokers and in 51 smokers by genotyping and phenotyping using caffeine (100 mg oral dose).

RESULTS

Out of the total sample, 46% were homozygous for the variant A, 44% were heterozygous, and 10% were homozygous for the variant C. The ratio of 1,7-dimethylxanthine (17X) plus 1,7-dimethyluric acid divided by caffeine in 0-5 h urine samples from 185 non-smokers did not differ significantly between the three CYP1A2 genotypes. In the 51 smokers, analysis of variance revealed significant differences in the 5 h plasma 17X/caffeine ratios between the genotypes (P=0.008, F-test). The mean ratio was 1.37 in carriers of the A/A genotype, 0.88 in heterozygotes and 0.82 in carriers of C/C. The mean difference between the A/A and C/A groups was 0.48 (95% confidence interval 0. 15-0.81; P=0.01).

CONCLUSIONS

The A/A genotype, which may represent a CYP1A2 high inducibility genotype, may either be a direct cause of increased CYP1A2 activity, or be genetically linked to polymorphisms conferring high inducibility. Further studies are needed to define the role of this polymorphism on the pharmacokinetics of drugs metabolised by CYP1A2 and in the activation of carcinogens.

The pharmacodynamics and pharmacokinetics of the 5HT1B/1D-agonist zolmitriptan in healthy young and elderly men and women

OBJECTIVE

Zolmitriptan is a selective 5HT1B/1D-agonist for the treatment of migraine. In this study we investigated the cardiovascular and central nervous system effects and the pharmacokinetics of zolmitriptan in young and elderly adults.

METHODS

Twelve young adult and 12 elderly volunteers received single doses of 5, 10, and 15 mg zolmitriptan during a randomized, double-blind, placebo-controlled study. Blood pressure, heart rate, ECG, and central nervous system effects were monitored, and pharmacokinetic parameters of zolmitriptan and its metabolites calculated.

RESULTS

Zolmitriptan did not affect heart rate and had little effect on systolic blood pressure in the young adults. In the elderly, mean peak supine systolic blood pressure values were 9 to 16 mm Hg higher after zolmitriptan than after placebo. Mean peak diastolic pressure was 6 to 10 mm Hg higher in both age groups. These changes were transient. Postural changes in blood pressure were unaffected. There was a dose-related increase in sedation, but the magnitude of the effects was small. Mean observed peak plasma concentration (Cmax) and area under the plasma concentration-time profile [AUC(0-infinity)] for zolmitriptan and its active N-desmethyl metabolite were similar in both age groups but higher in young women than in young men. Metabolite/parent ratios probably the result of greater first-pass metabolism in young men. Zolmitriptan half-life was 2.8 to 3.6 hours in the elderly compared with 2.7 to 2.9 hours in young adults. Mean Cmax and AUC(0-infinity) for the inactive, N-oxide, and the indole acetic acid metabolites were higher in the elderly, associated with lower renal clearance.

CONCLUSIONS

Zolmitriptan was well tolerated, with an effect of age on its effects on blood pressure and the pharmacokinetics of its metabolites. The data suggest no need for dose adjustment for age. In young subjects, concentrations were higher in women than in men, but the differences were insufficient to justify dosage adjustment.

Impact of long-term ethanol consumption on CYP1A2 activity

Ethanol is a well-known inducer of CYP2E1; whether or not it is an inducer of other cytochromes has not been investigated systematically. The aim of our study was to evaluate the impact of ethanol consumption on the activity of CYP1A2, which has been shown to be influenced by drugs (inhibited or induced). We evaluated CYP1A2 activity by the ratio of the molar urinary concentrations of the three end products of paraxanthine demethylation of caffeine to the molar concentration of a paraxanthine 8-hydroxylation product. This urinary metabolite ratio has previously been shown to correlate with caffeine clearance. The caffeine metabolites were measured in urine collected during the 3 hours after oral administration of 200 mg caffeine. The caffeine test was performed in 12 smokers (> 25 cigarettes/day) and 12 nonsmokers, all of whom were alcoholic inpatients (daily intake > 100 mg absolute ethanol), within the first 3 days of their hospital stay and after 14 days of abstinence from ethanol. In alcoholic patients who were smokers the molar urinary concentration ratio was 3.14 +/- 0.97 before withdrawal and 4.01 +/- 0.92 after 14 days of abstinence from ethanol. In contrast, in alcoholic patients who were nonsmokers it was 2.62 +/- 0.95 and 2.18 +/- 0.96 before and after withdrawal, respectively. In volunteers who were smokers the molar urinary concentration ratio was 5.02 +/- 1.51, whereas in volunteers who were nonsmokers it was 3.22 +/- 1.46. Our results confirm the well-known induction of CYP1A2 activity by tobacco smoking and show that this induction is masked by long-term ethanol consumption.

Interpatient variability: genetic predisposition and other genetic factors

Polymorphisms and other genetic factors related to enzymes metabolizing drugs and xenobiotic chemicals are well known. This article focuses on selected molecular mechanisms and introduces some of the clinical implications arising from genetically determined interpatient variability or expression in some of these enzymes. Selected are the polymorphic enzymes of cytochromes P-450 (CYP) as examples of phase I enzymes and methyl transferases, n-acetyl transferases, and glutathione-s-transferases as examples of phase II enzymes. The polymorphism surrounding arylhydrocarbon hydroxylase induction is briefly described. Phase I enzymatic reactions are predominantly oxidative, whereas phase II reactions often couple with the byproducts of phase I. Overall, in poor metabolizers, whether phase I or phase II, there is limited metabolism in most patients unless another major metabolic pathway involving other enzymes exists. Drug metabolism also depends on whether the parent compound is a prodrug that forms an active metabolite, and poor metabolizers under this condition will form only trace amounts of an active compound. Therefore, the clinical significance of genetic polymorphisms and other genetic factors may be related to substrate, metabolite, or the major elimination pathway.

Influence of oral contraceptive use and cigarette smoking, alone and together, on antipyrine pharmacokinetics

The pharmacokinetics of antipyrine following a single 1-g intravenous dose was determined in 63 healthy women. Subjects were divided into 4 groups as follows: 1) cigarette smokers using low-dose oral contraceptives (n = 15); 2) nonsmokers using low-dose oral contraceptives (n = 12); 3) cigarette smokers not using oral contraceptives (n = 10); and 4) controls, neither cigarette smokers nor oral contraceptive users. Plasma antipyrine concentrations during 24 to 48 hours after dosage were measured by high-performance liquid chromatography. Mean kinetic variables in the nonsmoking, non-oral contraceptive using control group were: volume of distribution, 37.7 L; elimination half-life, 13.2 hours; and clearance, 34.4 mL/min. In cigarette smoking, non-oral contraceptive users versus controls, elimination half-life was reduced (8.0 vs. 13.2 hours, P < 0.05) and clearance increased (56.0 vs. 34.4 mL/min, P < 0.05). In nonsmoker oral contraceptive users, the reverse was true (elimination half-life was significantly increased: 16.6 vs. 13.2 hours, P < 0.05; and clearance was significantly decreased: 24.8 vs. 34.4 mL/min, P < 0.05). In smokers who were using oral contraceptives, values were not significantly different from controls (elimination half-life, 11.2 hours; clearance, 39.5 mL/min). Volume of distribution did not differ among the four groups. Thus the opposing effects on antipyrine clearance of the induction of metabolism by cigarette smoking and the inhibition due to low dose oral contraceptive use in effect negate each other when combined in humans.

Omeprazole and lansoprazole are not inducers of cytochrome P4501A2 under conventional therapeutic conditions

OBJECTIVES

Claims that substituted benzimidazole molecules induce cytochromes P4501A2 are still controversial. This study was undertaken to evaluate their inducing potency under conventional therapeutic conditions.

METHODS

Twelve healthy non-smoking young volunteers were given 20 mg omeprazole or 30 mg lansoprazole daily, in random order, for 2 weeks, separated by a 3 week wash-out period. We evaluated the CYP1A2 activity by the ratio of the molar urinary concentrations (CUM ratio) of the three end products of the paraxanthine demethylation of caffeine over the molar concentration of a paraxanthine 8-hydroxylation product.

RESULTS

This urinary metabolite ratio has previously been shown to be correlated with caffeine clearance. There was slight but non-significant enhancement of the CUM ratio after 2 weeks of treatment with omeprazole (3.62 (1.58) on Day 15 vs 3.09 (1.43) on Day 1), and after lansoprazole (4.26 (2.3) vs 3.65 (2.36)). Similarly, one week of treatment did not significantly alter the CUM ratio after omeprazole or lansoprazole (3.11 (1.58) and 3.28 (1.59), respectively on Day 8).

CONCLUSION

The results show that both omeprazole and lansoprazole in the daily recommended therapeutic doses of 20 mg and 30 mg, respectively, have no influence on the metabolism of caffeine, and therefore no influence on cytochrome CYP1A2 activity.