Polymorphism of cytochrome P-450 in humans

Safety profile of Pertuzumab with Trastuzumab and Docetaxel in patients from Asia with human epidermal growth factor receptor 2-positive metastatic breast cancer: results from the phase III trial CLEOPATRA

INTRODUCTION

We report detailed safety analyses by geographic region from the phase III study CLEOPATRA with pertuzumab, trastuzumab, and docetaxel in patients with human epidermal growth factor receptor 2 (HER2)-positive first-line metastatic breast cancer.

PATIENTS AND METHODS

Patients received pertuzumab/placebo at 840 mg in cycle 1 and 420 mg in subsequent cycles, and trastuzumab at 8 mg/kg in cycle 1 and 6 mg/kg in subsequent cycles; docetaxel was initiated at 75 mg/m(2). All study drugs were given intravenously, 3 times weekly.

RESULTS

Docetaxel dose reductions below 75 mg/m(2) were more common in patients from Asia (47.0%) than other regions (13.4%); docetaxel dose escalations to 100 mg/m(2) were less frequent in Asia (2.4%) than other regions (18.7%). Rates of edema (26.1% and 5.4% for Asia and other regions, respectively), myalgia (42.3%, 14.7%), nail disorder (39.9%, 15.1%), febrile neutropenia (18.6%, 7.1%), upper respiratory tract infection (25.7%, 10.2%), decreased appetite (47.0%, 19.1%), and rash (44.3%, 22.0%) were at least twice as high in Asia as in other regions. Adverse events did not result in a reduction in the median number of study treatment cycles administered in patients from Asia. Efficacy analyses per region showed hazard ratios similar to those of the whole intention-to-treat (ITT) population for progression-free survival (ITT: 0.63; Asia: 0.68; other regions: 0.61) and overall survival (ITT: 0.66; Asia: 0.64; other regions: 0.66).

CONCLUSION

Despite a higher proportion of docetaxel dose reductions in patients from Asia, survival benefits were comparable between regions. The benefit-risk profile of pertuzumab, trastuzumab, and docetaxel supports this regimen as the first-line therapy for patients with HER2-positive metastatic breast cancer from all geographic regions.

Characterisation of the metabolites of 1,8-cineole transferred into human milk: concentrations and ratio of enantiomers

1,8-Cineole is a widely distributed odorant that also shows physiological effects, but whose human metabolism has hitherto not been extensively investigated. The aim of the present study was, thus, to characterise the metabolites of 1,8-cineole, identified previously in human milk, after the oral intake of 100 mg of this substance. Special emphasis was placed on the enantiomeric composition of the metabolites since these data may provide important insights into potential biotransformation pathways, as well as potential biological activities of these substances, for example on the breastfed child. The volatile fraction of the human milk samples was therefore isolated via Solvent Assisted Flavour Evaporation (SAFE) and subjected to gas chromatography-mass spectrometry (GC-MS). The absolute concentrations of each metabolite were determined by matrix calibration with an internal standard, and the ratios of enantiomers were analysed on chiral capillaries. The concentrations varied over a broad range, from traces in the upper ng/kg region up to 40 µg/kg milk, with the exception of the main metabolite α2-hydroxy-1,8-cineole that showed concentrations of 100-250 µg/kg. Also, large inter- and intra-individual variations were recorded for the enantiomers, with nearly enantiomerically pure α2-hydroxy- and 3-oxo-1,8-cineole, while all other metabolites showed ratios of ~30:70 to 80:20.

CYP1A1, CYP3A5 and CYP3A7 polymorphisms and testicular cancer susceptibility

Testicular cancer (TC) incidence is increasing worldwide, but the aetiology remains largely unknown. An unbalanced level of oestrogens and androgens in utero is hypothesized to influence TC risk. Polymorphisms in genes encoding cytochrome P450 (CYP) enzymes involved in metabolism of reproductive hormones, such as CYP1A1, CYP3A5 and CYP3A7, may contribute to variability of an individual's susceptibility to TC. The aim of this case-control study was to investigate possible associations between different CYP genotypes and TC, as well as histological type of TC. The study comprised 652 TC cases and 199 controls of Norwegian Caucasian origin. Genotyping of the CYP1A1*2A (MspI), CYP1A1*2C (I462V), CYP1A1*4 (T461N), CYP3A5*3C (A6986G) and CYP3A7*2 (T409R) polymorphisms was performed using TaqMan allelic discrimination or sequencing. The CYP1A1*2A allele was associated with 44% reduced risk of TC with each polymorphic allele [odds ratio (OR) = 0.56, 95% confidence interval (CI) = 0.40-0.78, p(trend) = 0.001], whereas the CYP1A1*2C allele was associated with 56% reduced risk of TC with each polymorphic allele (OR = 0.44, 95% CI = 0.25-0.75, p(trend) = 0.003). The decreased risk per allele was significant for seminomas (OR = 0.46, 95% CI, 0.31-0.70, p(trend) < 0.001 and OR = 0.31, 95% CI = 0.14-0.66, p(trend) = 0.002, respectively), but only borderline significant for non-seminomas (OR = 0.65, 95% CI = 0.45-0.95, p(trend) = 0.027 and OR = 0.55, 95% CI = 0.30-1.01, p(trend) = 0.052, respectively). There were no statistically significant differences in the distribution of the CYP3A5*3C and CYP3A7*2 polymorphic alleles between TC cases and controls. This study suggests that polymorphisms in the CYP1A1 gene may contribute to variability of individual susceptibility to TC.

Drug metabolism enzyme expression and activity in primary cultures of human proximal tubular cells

We previously catalogued expression and activity of organic anion and cation, amino acid, and peptide transporters in primary cultures of human proximal tubular (hPT) cells to establish them as a cellular model to study drug transport in the human kidney [Lash, L.H., Putt, D.A., Cai, H., 2006. Membrane transport function in primary cultures of human proximal tubular cells. Toxicology 228, 200-218]. Here, we extend our analysis to drug metabolism enzymes. Expression of 11 cytochrome P450 (CYP) enzymes was determined with specific antibodies. CYP1B1, CYP3A4, and CYP4A11 were the only CYP enzymes readily detected in total cell extracts. These same CYP enzymes, as well as CYP3A5 and possibly CYP2D6, were detected in microsomes from confluent hPT cells, although expression levels varied among kidney samples. In agreement with Western blot data, only activity of CYP3A4/5 was detected among the enzyme activities measured. Expression of all three glutathione S-transferases (GSTs) known to be found in hPT cells, GSTA, GSTP, and GSTT, was readily detected. Variable expression of three sulfotransferases (SULTs), SULT1A3, SULT1E, and SULT2A1, and three UDP-glucuronosyltransferases (UGTs), UGT1A1, UGT1A6, and UGT2B7, was also detected. When examined over the course of cell growth to confluence, expression of all enzymes was generally maintained at readily measurable levels, although they were often lower than in fresh tissue. These results indicate that primary cultures of hPT cells possess significant capacity to metabolize many classes of drugs, and can be used as an effective model to study drug metabolism.

Biochemical applications of ultrathin films of enzymes, polyions and DNA

This feature article summarizes recent applications of ultrathin films of enzymes and DNA assembled layer-by-layer (LbL). Using examples mainly from our own research, we focus on systems developed for biocatalysis and biosensors for toxicity screening. Enzyme-poly(L-lysine) (PLL) films, especially when stabilized by crosslinking, can be used for biocatalysis at unprecedented high temperatures or in acidic or basic solutions on electrodes or sub-micron sized beads. Such films have bright prospects for chiral synthesis and biofuel cells. Excellent bioactivity and retention of enzyme structure in these films facilitates their use in detailed kinetic studies. Biosensors and arrays employing DNA-enzyme films show great promise in predicting genotoxicity of new drug and chemical product candidates. These devices combine metabolic biocatalysis, reactive metabolite-DNA reactions, and DNA damage detection. Catalytic voltammetry or electrochemiluminescence (ECL) can be used for high throughput arrays utilizing multiple LbL "spots" of DNA, enzyme and metallopolymer. DNA-enzyme films can also be used to produce nucleobase adduct toxicity biomarkers for detection by LC-MS. These approaches provide valuable high throughput tools for drug and chemical product development and toxicity prediction.

The Urinary Disposition of Intravenously Administered 11-Nor-9-carboxy-delta-9-Tetrahydrocannabinol in Humans

The objective of this study was to investigate the fraction of an administered dose of 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THCCOOH) that is actually excreted into urine and to determine its urinary half-life independent of the parent compound. Ten healthy, male marijuana nonusers who were enrolled in the study were administered a single dose of 5 mg THCCOOH by the intravenous route. Urine specimens were collected up to 96 hours after administration. Samples were extracted before and after alkaline hydrolysis. The concentration of unconjugated and total THCCOOH was determined using gas chromatography-mass spectrometry. Most of the THCCOOH found in urine was conjugated, with only 0.14 +/- 0.08% of the dose present as unconjugated THCCOOH. The amount of conjugated THCCOOH ranged from 149.3 to 559.8 (mean +/- SD, 342.8 +/- 117.3) microg, representing a recovery of 3% to 11% of the administered dose. The measured amounts of total THCCOOH were low and highly varied among individuals. Renal excretion does not appear to be the preferred elimination pathway for THCCOOH. Urinary elimination half-life of unconjugated and conjugated THCCOOH ranged from 9.0 to 27.4 (mean +/- SD, 17.3 +/- 5.3) hours and from 10.7 to 27.6 (mean +/- SD, 16.0 +/- 5.0) hours, respectively. Although preliminary in nature, the actual urinary elimination half-life of THCCOOH appears to be significantly shorter than its apparent or terminal half-life reported from single or multiple dosing of delta-9-tetrahydrocannabinol (THC).

Inter-individual variation in the metabolic activation of the antimalarial biguanides

The aryl-biguanides proguanil and chlorproguanil were developed as part of a collaborative programme between ICI and the Liverpool School of Tropical Medicine during the 1940s. The compounds were characterized by their absence of host toxicity. However, the rapid development of parasite resistance to the actions of these drugs and the development of the 4-aminoquinoline, chloroquine, severely limited their use. The subsequent widespread development of parasite resistance to chloroquine, together with the observations that the magnitude of dihydrofolate reductase inhibitor resistance (the site of action of the biguanides) developed to pyrimethamine is not directly correlated with biguanide resistance(1,2). has resulted in renewed interest in these drugs. In particular, proguanil is now the drug of choice for malaria prophylaxis, in combination with chloroquine; used in combination with a suitable sulphonamide, it may be of value in malaria therapy.

The cyp2e1-humanized transgenic mouse: role of cyp2e1 in acetaminophen hepatotoxicity

The cytochrome P450 (P450) CYP2E1 enzyme metabolizes and activates a wide array of toxicological substrates, including alcohols, the widely used analgesic acetaminophen, acetone, benzene, halothane, and carcinogens such as azoxymethane and dimethylhydrazine. Most studies on the biochemical and pharmacological actions of CYP2E1 are derived from studies with rodents, rabbits, and cultured hepatocytes; therefore, extrapolation of the results to humans can be difficult. Creating "humanized" mice by introducing the human CYP2E1 gene into Cyp2e1-null mice can circumvent this disadvantage. A transgenic mouse line expressing the human CYP2E1 gene was established. Western blot and high-performance liquid chromatography/mass spectrometry analyses revealed human CYP2E1 protein expression and enzymatic activity in the liver of CYP2E1-humanized mice. Treatment of mice with the CYP2E1 inducer acetone demonstrated that human CYP2E1 was inducible in this transgenic model. The response to the CYP2E1 substrate acetaminophen was explored in the CYP2E1-humanized mice. Hepatotoxicity, resulting from the CYP2E1-mediated activation of acetaminophen, was demonstrated in the livers of CYP2E1-humanized mice by elevated serum alanine aminotransferase levels, increased hepatocyte necrosis, and decreased P450 levels. These data establish that in this humanized mouse model, human CYP2E1 is functional and can metabolize and activate different CYP2E1 substrates such as chlorzoxazone, p-nitrophenol, acetaminophen, and acetone. CYP2E1-humanized mice will be of great value for delineating the role of human CYP2E1 in ethanol-induced oxidative stress and alcoholic liver damage. They will also function as an important in vivo tool for predicting drug metabolism and disposition and drug-drug interactions of chemicals that are substrates for human CYP2E1.

Epoxidation of styrene by human cyt P450 1A2 by thin film electrolysis and peroxide activation compared to solution reactions

Films of human cytochrome P450 1A2 (cyt P450 1A2) and polystyrene sulfonate were constructed on carbon cloth electrodes using layer-by-layer alternate absorption and evaluated for electrochemical- and H(2)O(2)-driven enzyme-catalyzed oxidation of styrene to styrene oxide. At -0.6 V vs. saturated calomel reference electrode in an electrochemical cell, epoxidation of styrene was mediated by initial catalytic reduction of dioxygen to H(2)O(2) which activates the enzyme for the catalytic oxidation. Slightly larger turnover rates for cyt P450 1A2 were found for the electrolytic and H(2)O(2) (10 mM) driven reactions compared to conventional enzymatic reactions using cyt P450s, reductases, and electron donors for cytochromes P450 1A2. Cyt P450(cam) gave comparable turnover rates in film electrolysis and solution reactions. Results demonstrate that cyt P450 1A2 catalyzes styrene epoxidation faster than cyt P450(cam), and suggests the usefulness of this thin-film electrolytic method for relative turnover rate studies of cyt P450s.

The cytochrome P-450 isoenzyme CYP2E1 in the biological processing of industrial chemicals: consequences for occupational and environmental medicine

The importance of the isoform CYP2E1 of the human cytochrome P-450 superfamily of enzymes for occupational and environmental medicine is derived from its unique substrate spectrum that includes a number of highly important high-production chemicals, such as aliphatic and aromatic hydrocarbons, solvents and industrial monomers (i.a. alkanes, alkenes, aromatic and halogenated hydrocarbons). Many polymorphic genes, such as CYP2E1, show considerable differences in allelic distribution between different human populations. The polymorphic nature of the human CYP2E1 gene is significant for inter-individual differences in toxicity of its substrates. Since the substrate spectrum of CYP2E1 includes many compounds of basic relevance to industrial toxicology, a rationale for metabolic interactions of different CYP2E1 substrates is provided. In-depth research into the inter-individual phenotypic differences of human CYP2E1 enzyme activities was enabled by the recognition that the 6-hydroxylation of the drug chlorzoxazone is mediated by CYP2E1. Studies on CYP2E1 phenotyping have pointed to inter-individual variations in enzyme activities. There are consistent ethnic differences in CYP2E1 enzyme expression, mostly demonstrated between European and Japanese populations, which point to a major impact of genetic factors. The most frequently studied genetic polymorphisms are the restriction fragment length polymorphisms PstI/ RsaI (mutant allele: CYP2E1*5B) located in the 5'-flanking region of the gene, as well as the DraI polymorphism (mutant allele: CYP2E1*6) located in intron 6. These polymorphisms are partly related, as they form the common allele designated CYP2E1*5A. Striking inter-ethnic differences between Europeans and Asians appear with respect to the frequencies of the CYP2E1*5A allele (only approximately 5% of Europeans are heterozygous, but 37% of Asians are, whilst 6% of Asians are homozygous). Available studies indicate a wide variation in human CYP2E1 expression, which are very likely based on complex gene-environment interactions. Major inter-ethnic differences are apparent on the genotyping and the phenotyping levels. Selected cases are presented where inter-ethnic variations of CYP2E1 may provide likely explanations for unexplained findings concerning industrial chemicals that are CYP2E1 substrates. Possible consequences of differential inter-individual and inter-ethnic susceptibilities are related to individual expressions of clinical symptoms of chemical toxicity, to results of biological monitoring of exposed workers, and to the interpretation of results of epidemiological or molecular-epidemiological studies.

Impact of incorporating the 2C5 crystal structure into comparative models of cytochrome P450 2D6

Cytochrome P450 2D6 (CYP2D6) metabolizes approximately one third of the drugs in current clinical use. To gain insight into its structure and function, we have produced four different sets of comparative models of 2D6: one based on the structures of P450s from four different microorganisms (P450 terp, P450 eryF, P450 cam, and P450 BM3), another on the only mammalian P450 (2C5) structure available, and the other two based on alternative amino acid sequence alignments of 2D6 with all five of these structures. Principal component analysis suggests that inclusion of the 2C5 crystal structure has a profound effect on the modeling process, altering the general topology of the active site, and that the models produced differ significantly from all of the templates. The four models of 2D6 were also used in conjunction with molecular docking to produce complexes with the substrates codeine and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP); this identified Glu 216 [in the F-helix; substrate recognition site (SRS) 2] as a key determinant in the binding of the basic moiety of the substrate. Our studies suggest that both Asp 301 and Glu 216 are required for metabolism of basic substrates. Furthermore, they suggest that Asp 301 (I-helix, SRS-4), a residue thought from mutagenesis studies to bind directly to the basic moiety of substrates, may play a key role in positioning the B'-C loop (SRS-1) and that the loss of activity on mutating Asp 301 may therefore be the result of an indirect effect (movement of the B'-C loop) on replacing this residue.

Identification and cross-species comparisons of CYP2F subfamily genes in mammals

The cytochrome P450 2F (CYP2F) subfamily genes are currently known only from cDNA sequences in human, mouse, rat and goat. Compared to other divisions of the CYP2 gene family, the CYP2F subfamily is unusual in having few genes per species and in being selectively expressed in lung tissues. Sequencing genomic DNAs from human and gorilla has allowed us to determine the number of CYP2F subfamily loci in these species, the sources of known human transcripts, and the functional status of CYP2F loci in both primates. This information will make accurate genotyping of the functional and medically significant CYP2F1 gene possible in humans. Comparisons across multiple species show that the sequences of CYP2F subfamily genes are very conserved in mammals for intronic as well as exonic DNA.

Drug interactions with cisapride: clinical implications

Cisapride, a prokinetic agent, has been used for the treatment of a number of gastrointestinal disorders, particularly gastro-oesophageal reflux disease in adults and children. Since 1993, 341 cases of ventricular arrhythmias, including 80 deaths, have been reported to the US Food and Drug Administration. Marketing of the drug has now been discontinued in the US; however, it is still available under a limited-access protocol. Knowledge of the risk factors for cisapride-associated arrhythmias will be essential for its continued use in those patients who meet the eligibility criteria. This review summarises the published literature on the pharmacokinetic and pharmacodynamic interactions of cisapride with concomitantly administered drugs, providing clinicians with practical recommendations for avoiding these potentially fatal events. Pharmacokinetic interactions with cisapride involve inhibition of cytochrome P450 (CYP) 3A4, the primary mode of elimination of cisapride, thereby increasing plasma concentrations of the drug. The macrolide antibacterials clarithromycin, erythromycin and troleandomycin are inhibitors of CYP3A4 and should not be used in conjunction with cisapride. Azithromycin is an alternative. Similarly, azole antifungal agents such as fluconazole, itraconazole and ketoconazole are CYP3A4 inhibitors and their concomitant use with cisapride should be avoided. Of the antidepressants nefazodone and fluvoxamine should be avoided with cisapride. Data with fluoxetine is controversial, we favour the avoidance of its use. Citalopram, paroxetine and sertraline are alternatives. The HIV protease inhibitors amprenavir, indinavir, nelfinavir, ritonavir and saquinavir inhibit CYP3A4. Clinical experience with cisapride is lacking but avoidance with all protease inhibitors is recommended, although saquinavir is thought to have clinically insignificant effects on CYP3A4. Delavirdine is also a CYP3A4 inhibitor and should be avoided with cisapride. We also recommend avoiding coadministration of cisapride with amiodarone, cimetidine (alternatives are famotidine, nizatidine, ranitidine or one of the proton pump inhibitors), diltiazem and verapamil (the dihydropyridine calcium antagonists are alternatives), grapefruit juice, isoniazid, metronidazole, quinine, quinupristin/dalfopristin and zileuton (montelukast is an alternative). Pharmacodynamic interactions with cisapride involve drugs that have the potential to have additive effects on the QT interval. We do not recommend use of cisapride with class Ia and III antiarrhythmic drugs or with adenosine, bepridil, cyclobenzaprine, droperidol, haloperidol, nifedipine (immediate release), phenothiazine antipsychotics, tricyclic and tetracyclic antidepressants or vasopressin. Vigilance is advised if anthracyclines, cotrimoxazole (trimethoprim-sulfamethoxazole), enflurane, halothane, isoflurane, pentamidine or probucol are used with cisapride. In addition, uncorrected electrolyte disturbances induced by diuretics may increase the risk of torsade de pointes. Patients receiving cisapride should be promptly treated for electrolyte disturbances.

Certain clinically-utilized antibiotics enhance the behavioural effects of cocaine

Abstract Cytochrome P-450s (CYPs) belonging to subfamilies 2B and 3A are the major CYPs involved in the N -demethylation of cocaine in the rat. However, the effects of inhibitors of these enzymes on the behavioural actions of cocaine are unknown. Hence, the effects of the CYP 3A inhibitors troleandomycin and erythromycin, and the CYP 2B (and 3A) inhibitor chloramphenicol, were examined on the locomotor activating effects of cocaine (20 mg/kg i.p.). Troleandomycin, chloramphenicol and erythromycin all potentiated the locomotor activating effects of cocaine, although the effect was only statistically significant for the first two drugs. Since variation exists in the human population with respect to the catalytic activity of CYP 3A isozymes, which are the principal cocaine N -demethylators in humans, inhibition of CYP 3A by troleandomycin in the rat may be useful as a model of the human cocaine "poor metabolizer" phenotype.

Two compounds commonly used for phospholipase C inhibition activate the nuclear estrogen receptors

The aminosteroid U73122 is generally used as a specific inhibitor of phosphoinositide specific phospholipase C (PLC) and typically, the structurally related compound U73343 is used as control, since it lacks PLC inhibitory activity. We have found that both compounds possess strong estrogenic activity and that this activity is mediated by the estrogen receptors (ER) alpha and beta. Although no direct evidence for binding of U73122 and U73343 to the ER could be provided, the estrogenic activity of the aminosteroids requires an intact ER hormone binding pocket. Given the chemical structure of the two aminosteroids, they may be converted to an estrogenic derivative by chemical degradation or an enzymatic metabolization reaction. Our data indicate that additional care should be taken in the interpretation of the effects of U73122 in cells expressing ER.

Quantitation of cytochrome P450 mRNAs in patients with suspected liver diseases as assessed by reverse transcriptase-polymerase chain reaction

The cytochrome P450 system (CYP) is vital for the oxidation and detoxification of numerous drugs and other xenobiotics in the liver. Many of the CYP enzymes are polymorphically expressed and may be induced or inhibited by xenobiotics including drugs and alcohol. The measurement of gene expression is thus important in studies of the mechanisms of interaction with and function of the CYP system. We have developed a quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method for the study of the mRNA expression of three CYP enzymes--2E1, 1A2, and 3A4--in snap-frozen percutaneous liver biopsy samples. The method was made quantitative by the introduction of a recombinant RNA internal standard that contains a transcript of the beta-globin gene and sequences specific for the studied CYP enzymes. The method allows the analysis of mRNA expression of several enzymes in as little as 5 mg of liver tissue. Liver tissue specimens from 19 patients with suspected liver disease were analyzed for CYP-specific mRNA expression. The mean mRNA concentrations for CYP1A2, 2E1, and 3A4 were 0.16, 0.74, and 0.32 amol of specific mRNA per nanogram of poly (A+) mRNA, respectively, but a large interindividual variation was observed. CYP3A7 primers were included in the internal standard. However, because of low expression it was not possible to quantitate the enzyme. This quantitative RT-PCR method is of value for studies of the mechanisms of variation and interactions with the members of the CYP enzyme family in healthy and diseased liver and other organs.

The actions of the H2-blocker cimetidine on the toxicity and biotransformation of the phosphorothioate insecticide parathion

Parathion, like most organophosphorus insecticides currently in use, must undergo cytochrome P450(P450)-dependent activation in order to exert its acute mammalian toxicity (cholinergic crisis). Since P450 isoforms play such an important role in mediating the toxicity of parathion and related insecticides, factors which significantly alter P450 activities, such as exposure to certain xenobiotics, can also be expected to affect the toxicity of these potentially hazardous insecticides. Cimetidine is a H2-histamine antagonist that has been shown to inhibit several P450-isoforms. In addition, administration of cimetidine has been reported to result in clinically significant pharmacokinetic interactions with a wide variety of drugs. In the present study coexposure to cimetidine and parathion resulted in a moderate increase in the toxicity of this pesticide. However, coexposure to cimetidine and paraoxon did not alter the toxicity of the organophosphate, indicating that cimetidine likely affected P450-dependent formation of paraoxon from parathion. In vitro incubations of mouse hepatic microsomes demonstrated that, in addition to reducing the velocity of P450-dependent metabolism of parathion, cimetidine increased the proportion of paraoxon formed (activation). and decreased the proportion of p-nitrophenol formed (detoxification). Since parathion is not eliminated significantly by other routes in the mouse, the bulk of parathion in vivo was metabolized by P450 (although more slowly) in the presence of cimetidine, leading to a greater amount of paraoxon produced, and therefore greater toxicity. Incubations with individual P450 isoforms suggested that cimetidine could act by inhibition of P450 isoforms that detoxify parathion to a greater degree than cimetidine-resistant isoforms, and/or cimetidine could alter the proportions of detoxification versus activation of certain individual isoforms.

Time-dependent expression of cytochrome P450 genes in primary cultures of well-differentiated human hepatocytes

We sought to establish an in vitro system to study the regulation of highly differentiated hepatocellular functions, and specifically the time-dependent expression of four cytochrome P450 (P450) genes at the messenger RNA (mRNA) and protein levels. When seeded onto matrigel, hepatocytes could be maintained for 8 days in media that were free of serum and hormones (except for insulin). Cells retained a spherical phenotype; they secreted albumin and not alpha-fetoprotein; and the cellular RNA/DNA ratio rose progressively in culture. The isolation procedure and the duration of culture affected expression of specific P450s differently. CYP1A2, CYP2C9, and CYP2E1 mRNAs were not altered by cell isolation, and levels of CYP1A2 and CYP2C9 mRNA were also maintained for 8 days in culture, whereas CYP2E1 mRNA declined to 9% of values in fresh hepatocytes by day 8. CYP3A4 mRNA content was considerably decreased in freshly isolated hepatocytes compared with normal liver, and expression of this gene during the course of culture was more variable than that of the other P450s. Use of Williams' E medium considerably enhanced accumulation of CYP3A4 mRNA, compared with modified Waymouth 752/1 medium, but had a detrimental effect on levels of the other P450 mRNAs. Despite high levels of expression at the mRNA level, the microsomal protein contents of CYP1A2, CYP2C9, CYP2E1, and CYP3A4 declined progressively during the course of culture; this decline was most rapid for CYP3A4. These results confirm the potential of primary cultures of well-differentiated human hepatocytes for studies of P450 gene regulation in humans, but they also demonstrate that culture conditions are variables that must be carefully controlled when examining liver-specific gene expression in vitro. In particular, time in culture may variably affect expression of P450 enzyme changes at both the mRNA and protein levels.

Genetic polymorphisms in human drug-metabolizing enzymes: potential uses of reverse genetics to identify genes of toxicological relevance

The human mind was engaged with fundamental questions on the nature of heredity long before the study of genetics became a scientific discipline. Many traits, such as height, eye color, blood pressure, or cancer susceptibility, have been known to run in families, although the genes or combination of genes that underlie these observable characteristics remain unknown in most cases. Differences in susceptibility to environmental agents in humans are likewise determined by variations in genetic background--genetic polymorphisms. In this article, we review the current status of studies on human polymorphisms in drug-metabolizing enzymes and discuss various approaches to the analysis of genetic polymorphisms. We expect that in the near future, novel methods in genetic analysis of human populations will be likely to play a key role in the identification of genes of toxicological relevance.

Inhibition of tolbutamide 4-methylhydroxylation by a series of non-steroidal anti-inflammatory drugs in V79-NH cells expressing human cytochrome P4502C10

1. To study the role of cytochrome P4502C10 in the metabolism of the non-steroidal antiinflammatory drugs (NSAIDs) diclofenac, phenylbutazone, fenoprofen, ibuprofen, flurbiprofen, ketoprofen and naproxen, a cell line was developed stably expressing CYP2C10 cDNA. A retroviral vector construct, containing a human CYP2C10 cDNA, was transfected in V79-NH Chinese hamster lung cells by calcium phosphate co-precipitation. Sublines stably expressing human cytochrome P450 cDNA were established by selection with the neomycin analogue G418. 2. Enzymatic activity of CYP2C10 was detected by 4-methylhydroxylation of tolbutamide. This activity was inhibited to background levels by preincubation with the CYP2C9/10 inhibitor sulphaphenazole. 3. Preincubations with the NSAIDs ketoprofen, phenylbutazone, flurbiprofen and diclofenac (all 250 microM) caused a decrease in 4-methylhydroxylation of tolbutamide (500 microM), significantly different from control values (p < 0.05). Inhibition of this activity was not seen in preincubations with the NSAIDs fenoprofen, ibuprofen and naproxen (250 microM). 4. The V79-NH CYP2C10 cell line we have developed has been shown to be a useful tool to predict drug-drug interactions.

Ethnic-related differences in coumarin 7-hydroxylation activities catalyzed by cytochrome P4502A6 in liver microsomes of Japanese and Caucasian populations

1. Interethnic differences in cytochrome P4502A6 (CYP2A6) levels and coumarin 7-hydroxylation activities were determined in liver microsomes of 30 Japanese and 30 Caucasians. 2. Although CYP2A6 levels and coumarin 7-hydroxylation activities varied very significantly in the 60 human samples examined, both CYP2A6 levels and coumarin 7hydroxylation activities were found to be higher in Caucasian than Japanese population. 3. Interestingly, eight of the 30 Japanese examined showed very low or undetectable levels of coumarin 7-hydroxylation activities as well as of CYP2A6 in liver microsomes. All of the Caucasians, however, had significant CYP2A6 levels and variable 7-hydroxylation activities. 4. Kinetic analvsis of coumarin 7-hydroxylation activities in liver microsomes of various human samples suggested that although there were 260-fold differences in Vmax's in 10 human samples examined, the Km's were very similar (2.1 + or - 107 mu M); a value consistent with that obtained (1.2 mu M) with purified CYP2A6 in reconstituted system. 5. The results suggest that CYP2A6 is actually involved in the 7-hydroxylation of coumarin in human liver microsomes, and that interethnic differences in coumarin 7-hydroxylation activities in Japanese and Caucasian population may be ascribed to the differences in expression of CYP2A6 protein.

In vitro interaction of the antipsychotic agent olanzapine with human cytochromes P450 CYP2C9, CYP2C19, CYP2D6 and CYP3A

1. The ability of olanzapine to inhibit the metabolism of marker catalytic activities for the cytochromes P450 CYP3A, CYP2D6, CYP2C9, and CYP2C19 was examined. This inhibitory capability was compared with that obtained with clozapine and known inhibitory compounds for the same cytochromes P450. 2. Olanzapine, clozapine, and ketoconazole were all found to non-competitively inhibit 1'-hydroxy midazolam formation, form selective for CYP3A, yielding Ki values of 491, 99 and 0.11 microM, respectively. The 1'-hydroxylation of bufuralol, form selective for CYP2D6, was competitively inhibited by olanzapine (Ki = 89 microM), clozapine (Ki = 19 microM), and quinidine (Ki = 0.03 microM). Tolbutamide metabolism to 4-hydroxy tolbutamide, form selective for CYP2C9, was competitively inhibited by clozapine and phenytoin (Ki of 31 microM and 17 microM, respectively). Olanzapine non-competitively inhibited tolbutamide metabolism with a Ki of 715 microM. The marker catalytic activity for CYP2C19 mediated metabolism, 4'-hydroxy S-mephenytoin formation, was competitively inhibited by clozapine (Ki = 69 microM) and omeprazole (Ki = 4.1 microM). Non-competitive inhibition of CYP2C19 mediated metabolism was seen with olanzapine with a Ki of 920 microM. 3. The calculated percent inhibition by olanzapine of substrates metabolized by CYP3A, CYP2D6, CYP2C9, and CYP2C19 was modeled assuming a total plasma concentration in the therapeutic range (0.2 microM). Total olanzapine vs unbound olanzapine was used to model the worst case (most conservative) situation. In all cases, the calculated percent inhibition of these cytochromes P450 by olanzapine was < 0.3%, suggesting that there would be little in vivo inhibition of the metabolism of substrates of these enzymes when co-administered with olanzapine.

Can grapefruit juice influence ethinylestradiol bioavailability?

The effects of grapefruit juice on the bioavailability of 17 alpha-ethinylestradiol (EE2) after a single oral administration of 50 micrograms EE2 have been investigated. The pharmacokinetics of EE2 were studied in an open, randomized, cross-over study in which 13 healthy volunteers were administered the drug with herbal tea or grapefruit juice (naringin, 887 mg/ml). In contrast to herbal tea, grapefruit juice increased the peak plasma concentration (Cmax) significantly to 137% (mean; range 64% to 214%, p = 0.0088) and increased the area under plasma concentration-time curve from 0 to 8 hours (AUC0-8) to 128% (mean; range 81% to 180%, p = 0.0186). This study shows that grapefruit juice increases the bioavailable amount of EE2. A possible explanation may be that grapefruit juice inhibits the metabolic degradation of EE2. Whether the increased bioavailability of EE2 following grapefruit juice administration is of clinical importance should be investigated in long-term studies.

Flavonoids in grapefruit juice inhibit the in vitro hepatic metabolism of 17 beta-estradiol

Naringenin, quercetin and kaempferol, which may be found in glycoside form in natural compounds such as grapefruit, are potent inhibitors of cytochrome P-450 metabolism. The influence of these flavonoids on the metabolism of 17 beta-estradiol was investigated in a microsome preparation from human liver. The flavonoids were added in concentrations of 10, 50, 100, 250 and 500 mumol/l to the microsome preparation. The metabolism of 17 beta-estradiol was concentration dependently inhibited by all the flavonoids tested. Addition of the flavonoids to the microsome preparation did not influence estrone formation, while a potent inhibition of estriol formation was observed. At the highest concentrations tested of the respective flavonoid, there was approximately 75-85% inhibition of estriol formation. However, naringenin was a less potent inhibitor of 17 beta-estradiol metabolism as compared to quercetin and kaempferol. The most likely mechanism of action of the flavonoids on 17 beta-estradiol metabolism is inhibition of the cytochrome P-450 IIIA4 enzyme, which catalyzes the reversible hydroxylation of 17 beta-estradiol into estrone and further into estriol. These hydroxylation processes represent the predominant steps of the hepatic metabolic conversion of endogenous as well as exogenous 17 beta-estradiol. This interaction would be expected to inhibit the first-pass metabolism of 17 beta-estradiol, and this has recently been demonstrated after oral administration of 17 beta-estradiol to women.

Metabolism of capsaicinoids: evidence for aliphatic hydroxylation and its pharmacological implications

A new metabolic oxidation pathway of capsaicin (N-[(4-hydroxy-3-methoxyphenyl)-methyl]-8-methyl-(E)-6 -nonenamide), a major pungent and pharmacologically active principle of hot peppers, was investigated. Incubation of capsaicin with phenobarbital-induced rat liver postmitochondrial supernatant enriched with NADPH-generating system produced N-(4,5-dihydroxy-3-methoxybenzyl)-(E)-6 -nonenylamide and a more polar metabolite. The latter metabolite was spectrophotometrically and chromatographically identical to authentic omega-hydroxycapsaicin. This new metabolite was also detected in the urine of rabbits given capsaicin by gastric intubation. Other analogs of capsaicin, such as dihydrocapsaicin and nonivamide, also formed similar metabolites via aliphatic hydroxylation. When tested for antinociceptive activity as well as pungency, the above polar metabolites were found to be inactive while their parent compounds exhibited strong sensory effects. Capsaicin interacted irreversibly with heptic drug metabolizing enzymes, thereby inhibiting their activity as indicated by prolongation of pentobarbital sleeping time in rats. Such inhibition of drug metabolism was not observed with omega-hydroxycapsaicin. These findings suggest that metabolism of capsaicinoids via hydroxylation of their side chains plays an important role in the detoxification of these pharmacologically active substances.

Inhibition of 17 beta-estradiol metabolism by grapefruit juice in ovariectomized women

In an open, randomized, cross-over study the concentrations of 17 beta-estradiol and estrone in serum were measured over 192 hours in 8 ovariectomized women after a single oral dose intake of 2 mg micronized 17 beta-estradiol. The subjects were studied with and without grapefruit juice intake containing the three natural flavonoids, naringenin, quercetin and kaempherol, which are found as glycosides in citrus fruit. These flavonoids interact with the metabolism of drugs such as 17 beta-estradiol and other steroids that are extensively metabolised through the P-450NF (P-450 IIIA4) enzyme or closely related P-450 systems. After administration of grapefruit juice, peak estrone (between 2-6 hours after tablet intake) concentrations increased significantly. The AUC0-48 and AUC0-192 for estrone but not 17 beta-estradiol, resulting from a single administration of micronized 17 beta-estradiol, were significantly altered. Combined measured estrogens (i.e. 17 beta-estradiol and estrone) also increased significantly. The relationship between the AUCs for 17 beta-estradiol and estrone was not altered by juice intake indicating that a metabolic step after estrone, i.e. further A and/or D ring conversion was inhibited. This study demonstrates that grapefruit juice may alter the metabolic degradation of estrogens, and increase the bioavailable amounts of 17 beta-estradiol and its metabolite estrone, presumably by affecting the oxidative degradation of estrogens. This food interaction may be one factor behind the interindividual variability in 17 beta-estradiol, estrone and estriol serum concentrations after exogenous administration of 17 beta-estradiol to patients.

Isolation and purification of three glucuronides of antipyrine. Proposal for an original analytical method for quantitation of sulpho- and glucuroconjugated metabolites

The determination of the concentrations of antipyrine metabolites in biological fluids is hampered by the difficulty in obtaining pure conjugated compounds to be used as standards. Most authors have proposed determination of total forms by high performance liquid chromatography (HPLC) after deconjugation of these metabolites using chemical or enzymatic hydrolysis. Up to now there is no satisfactory hydrolysis method for the study of all antipyrine metabolites. The situation is further complicated by the fact that the deconjugated metabolites are highly unstable whichever technique is being used. Because of the lack of stability of all these molecules it has been necessary to isolate the glucuroconjugated compounds from urine. We describe a method which allows us to obtain highly purified glucuroconjugated metabolites of antipyrine. Sulphoconjugated compounds have been synthesized previously. We are thus able to propose a chromatographic procedure which allows us to determine simultaneously all stable phase I and phase II metabolites of antipyrine in biological fluids without any step of extraction. This analytical technique allows us to study the activity of the different isoenzymes implicated in the metabolism of antipyrine.

Comparison of levels of cytochromes P-450, CYP1A2, CYP2E1, and their related monooxygenase activities in human surgical liver samples

Hepatic microsomal cytochromes P-450 CYP1A2, and CYP2E1 contents and catalytic activities have been simultaneously investigated in 42 patients undergoing diagnostic liver biopsy. CYP1A2 contents, measured by Western blotting, were correlated with methoxyresorufin-O-demethylation and ethoxyresorufin-O-deethylation (r = 0.65 and r = 0.66, p < 0.001, respectively). CYP2E1 contents were correlated with 1-butanol oxidation and 6-hydroxylation of chlorzoxazone (r = 0.75 for both, p < 0.001). CYP1A2 catalytic activities varied by 30- to 40-fold, whereas CYP2E1 activities varied by 6- to 20-fold. In our study, these variations were not related to liver diseases or cancer of the digestive tract nor to alcohol drinking or smoking habits, because patients were alcohol- and tobacco-free for 1 month before the study. Other environmental factors, diet habits, and/or genetic factors could explain the large interindividual variations observed.

Immunochemical specificity of placental NADPH cytochrome c (P-450) reductase in neoplastic and non-neoplastic human tissue

NADPH cytochrome c (P-450) reductase was purified from human placental microsomes using a combination of affinity and gel filtration chromatography. Affinity chromatography using agarose-hexane-adenosine 2'5 diphosphate resulted in two protein bands being detected by SDS-PAGE of approximate MwS 68 and 75 kDa. Fractions containing the two proteins were pooled, and then resolved using Sephacryl S-200. Both of the purified proteins displayed enzyme activity, measured by their ability to reduce cytochrome c. The 75 kDa protein obtained was used to immunize three female New Zealand white rabbits. The IgG fraction was partly purified from rabbit sera which suppressed placental microsomal NADPH cytochrome c reductase activity by > 80% using 33% ammonium sulphate. The procured antibody suppressed androstenedione aromatase activity in microsomal preparations of human placental and breast adipose tissue, and NADPH cytochrome c reductase activity in prostate (benign and malignant), MDA-MB-231 breast cancer cells, breast adipose, Hep G2 hepatoma cells and placental microsomal preparations. The extent of NADPH cytochrome c reductase inhibition varied in the order of malignant prostate < benign prostate < MDA < breast adipose < Hep G2 < placenta. The results suggest that human placental NADPH cytochrome c (P-450) reductase shares common antigenic epitopes pertinent to its capability of reducing cytochrome c in all of the above-mentioned tissues. In attempting to associate possible changes in NADPH cytochrome c reductase activity imposed by neoplasia to the obtained immunochemical cross reactivity and enzyme activity results, it was noted that microsomes obtained from MDA cells exhibited enzyme activity significantly less than that of breast adipose microsomes (1.6 and 8.1 nmol/min/mg protein, respectively) and by comparison showed 6% less homology towards the placental antibody. The results obtained for benign and malignant prostate showed no significant difference between the neoplastic states as adjudged by enzyme activity and immunochemical assays.

Endogenous and exogenous factors modifying the activity of human liver cytochrome P-450 enzymes

Cytochrome P-450 dependent monooxygenases play a dual role for xenobiotic metabolism. On one hand they initiate the primary rate limiting step for the elimination of a bulk of drugs and organic chemicals. On the other hand they catalyze the formation of toxic metabolites from chemical carcinogens and many other toxic chemicals. Numerous studies have shown that their activity in animals is subject to the influence of various modifying factors, such as strain, species, sex, age, diurnal rhythm and the effect of enzyme inducers. Less is known about the influence of these factors on human cytochrome P-450 enzymes. Here we report the results of an extended study on human liver cytochrome P-450 performed with liver biopsies of 178 individuals taken for diagnostic purposes. The enzymatic activity was determined by the aldrin epoxidase assay indicating a variety of enzymes inducible by phenobarbital and by glucocorticoid and androgenic hormones. The frequency histogram of individual aldrin epoxidase activities showed a unimodal distribution and a variation factor of 100 between maximal and minimal activity. Individuals with severe liver diseases, such as cirrhosis and fatty liver, exhibited a 50% loss of enzyme activity. Age and sex did not significantly influence the enzyme activity. No significant correlation was observable between the rate of aldrin epoxidation and debrisoquine 4-hydroxylation, a prototype of a genetically controlled cytochrome P-450 reaction. We assume that the broad interindividual variation of epoxidase activities is more likely due to the influence of exogenous and endogenous inducers rather than to a genetic polymorphism.(ABSTRACT TRUNCATED AT 250 WORDS)

Immobilized metal affinity chromatography as a means of fractionating microsomal cytochrome P-450 isozymes

Fractionation of microsomal cytochrome P-450s is usually done by chromatography on ion-exchange resins and hydroxyapatite. The resolution of the great number of similar P-450 isozymes, however, requires additional methods based on different separation parameters. For this purpose immobilized-metal affinity chromatography (IMAC) was applied to the separation of P-450 isozymes. The method in its application to rat liver microsomes is described in detail. For method optimization and for the reproducibility of analytical fractionations a completely automatic fast protein liquid chromatographic system especially designed for IMAC is presented. Optimization is done with respect to the choice of the immobilized metal ion and the elution conditions. The chromatographic resolution is markedly enhanced by using segmented vs. linear gradients. The efficiency of P-450 resolution is demonstrated by sodium dodecyl sulphate polyacrylamide gel electrophoresis and immunoblotting, verifying the different retention behaviours of the isozymes. However, for all the isozymes analysed so far, reactivity with one particular polyclonal antibody is observed with more than two IMAC fractions of a single run. This may be explained in part by the occurrence of isozymic forms distinguishable by the pattern of chymotryptic peptides. Hence IMAC appears to be suitable for the separation of closely related isozyme forms.

Omeprazole drug interaction studies

This review examines the literature on drug interactions with omeprazole. Different mechanisms have been proposed as potential causes for such interactions. First, the absorption of some drugs might be altered due to the decreased intragastric acidity resulting from omeprazole treatment. There was no effect of omeprazole on the absorption of amoxycillin, bacampicillin and alcohol, while the amount of digoxin and nifedipine absorbed was increased by 10 and 21%, respectively, both increases probably being of no clinical significance. Secondly, the metabolism of high clearance drugs might be altered by changes in liver blood flow, although that is not affected by omeprazole, as indicated by the unchanged elimination of indocyanine green. In addition, the clearance of intravenously administered lidocaine (lignocaine) [a high clearance drug] was unaffected by omeprazole, further indicating that the latter does not alter liver blood flow. Thirdly, since omeprazole is a substituted benzimidazole, it might have the potential to interfere with the metabolism of other drugs by altering the activity of drug metabolising enzymes in the cytochrome P450 system, through either induction or inhibition. There is no indication of induction of this enzyme system in any interaction study with omeprazole. As regards inhibition, on the other hand, there is now considerable information available which indicates that omeprazole has the potential to partly inhibit the metabolism of drugs metabolised to a great extent by the cytochrome P450 enzyme subfamily IIC (diazepam, phenytoin), but not of those metabolised by subfamilies IA (caffeine, theophylline), IID (metoprolol, propranolol) and IIIA (cyclosporin, lidocaine, quinidine). Since relatively few drugs are metabolised mainly by IIC compared with IID and IIIA, the potential for omeprazole to interfere with the metabolism of other drugs appears to be limited.

Effects of troleandomycin and josamycin on thyroid hormone and steroid serum levels, liver function tests and microsomal monooxygenases in healthy volunteers: a double blind placebo-controlled study

Serum TSH levels are moderately but significantly (P ANOVA: 0.05) decreased by troleandomycin (T; 1 g bid over a 10-day period) compared with josamycin (J) (same doses) and placebo (P) in healthy volunteers. T also significantly increases serum estradiol concentration (P ANOVA: 0.03). This effect may be related to a T-induced inhibition of some P450 monooxygenase isoenzymes and more specifically P 450 NF, determined in our study by a decrease in urinary excretion of 6-beta-hydroxy-cortisol. Troleandomycin and josamycin both show poor upper GI tolerance. Liver enzymes (SGOT, SGPT, alkaline phosphatase and gGT) are significantly altered by T compared with J and P (P ANOVA: 0.007, 0.001, 0.09 and 0.04 respectively). After J, liver function tests are very close to control values (placebo). Liver enzymes are significantly more altered by T than by J (P 0.004, 0.001 and 0.06 for SGOT, SGPT and gGT respectively). Using 6 volunteers in a latin-square designed study, some established effects of oral macrolides were confirmed (poor upper GI tolerance; liver toxicity of T). Some other effects of T were also elicited, which were either unknown (decrease in serum TSH) or expected but which had not previously been assessed in man (increase in serum estradiol; decreased urinary excretion of 6-beta-hydroxy-cortisol).

Phenothiazine-associated apnea in two siblings

A two-month-old white girl presented to our facility with increasing lethargy and new onset apnea and bradycardia following a week of upper respiratory tract infection symptoms. The patient had been receiving a cough syrup containing promethazine hydrochloride during the previous five days, which was temporally correlated with the onset of lethargy and apneic episodes. Upon further investigation, it was discovered that the patient's older sibling also may have experienced phenothiazine-associated apnea after receiving a combination of meperidine hydrochloride, promethazine hydrochloride, and chlorpromazine as a premedication prior to an endoscopic examination. In addition to the presentation of these cases, the literature pertaining to phenothiazine-associated apnea is reviewed.

Drug disposition and switch process: an attractive hypothesis

Two cases of bipolar psychosis presented a rapid manic switch following administration of tricyclic antidepressants. In both cases the oxidation capacity was genetically deficient. The role of oxidation deficit is discussed in the pathogenesis of switch process and preventive measures are considered.

A liquid chromatographic method for determination of theophylline in serum and capillary blood--a comparison

A simple, fast and reliable liquid chromatographic method for the determination of theophylline in serum and capillary blood after a solid phase extraction is described for therapeutic drug monitoring. The employment of capillary blood permits the determination of an individual drug profile and other pharmacokinetic studies in neonates and infants. There were no differences in venous- and capillary-blood levels but these values compared poorly with those in serum. An adjustment of the results by correction of the different volumes of serum and blood by haematocrit was unsuccessful. Differences in the binding of theophylline to erythrocytes could be an explanation for the differences in serum at blood levels of theophylline.

The determination of antipyrine elimination in saliva by liquid chromatography

A simple, fast and reliable liquid chromatographic method for the determination of antipyrine in saliva is described. The elimination of antipyrine is a good indicator for general evaluation of the liver function for dispositional purposes for example in occupational and environmental medicine. The described LC method was compared with a more extensive photometric procedure. The results obtained from both methods show very good correlation. Only one measurement is necessary to determine the antipyrine clearance. Furthermore the antipyrine dosage can be minimized, because of the sensitivity of the HPLC-method.

Genetic polymorphism of sparteine/debrisoquine oxidation: a reappraisal

Polymorphic oxidation of the sparteine/debrisoquine-type has been shown to account for much of the interindividual variation in the metabolism, pharmacokinetics and pharmacodynamics of an increasing number of drugs, including some antiarrhythmic, antidepressant and beta-adrenoceptor antagonist agents. Impaired hydroxylation of these drugs results from the absence of the enzyme cytochrome P450IID6 in the livers of poor metabolisers, who constitute 6% to 10% of Caucasian populations. The clinical importance of the phenomenon has to be explored further and for most sparteine/debrisoquine-related substrates there is a need for controlled prospective studies to define the consequences to the patient of impaired or enhanced drug oxidation.

Heterogeneity of vascular muscarinic receptors

Muscarinic receptors mediate diverse effects on the vasculature. Recently, a consensus has been arrived at with regard to muscarinic receptor classification (Levine & Birdsall, 1989). As a result, it may now be possible to clarify the role of each subtype in the responses of vascular tissues to muscarinic agonists. It is apparent that vascular muscarinic receptors form a heterogeneous population. M1 receptors contract canine venous tissue, whilst M3 receptors contract porcine and bovine coronary arteries. M3 receptors also mediate EDRF-dependent relaxant responses in the majority of tissues studied to date. M2 receptors elicit relaxations by a decrease in sympathetic outflow in canine femoral vein, rabbit ear artery and rat portal vein. These conclusions are primarily derived from functional estimations of equilibrium dissociation constants, since comparable radioligand binding data are both scarce and contradictory. It is concluded that all three major subtypes of receptors are present in the vasculature. However, the limited selectivity of the available antagonists, the lack of extensive use of such compounds and the unavailability of selective agonists clearly indicate the need for more definitive studies to be undertaken.

Metronidazole and antipyrine as probes for the study of foreign compound metabolism

The aim of the present work was to develop a tool for the study of the enzyme activities relevant for the biotransformation of foreign compounds, their elimination and/or activation to toxic substances. The activity of an enzyme may be assessed by the rate of metabolism of a preferably specific probe or model compound. The cytochrome P450'ies, the key enzymes for the elimination and/or activation of most foreign compounds, exist in multiple forms with variable substrate specificity and regulation. Some cytochrome P450'ies are under genetic control, whereas the activity of others is mainly regulated by the influence from factors in the environment. Only some of the cytochrome P450'ies are relevant for the formation of harmful metabolites. Thus, the activity of as many cytochrome P450 forms as possible should be assessable, preferably simultaneously. The present work evaluated metronidazole in a cocktail with antipyrine as a tool for the study of the regulation of foreign compound metabolism in the liver. The cytochrome P450 catalyzed metabolism of metronidazole and antipyrine was studied in humans and in isolated rat hepatocytes. In humans the influence of dose, route of administration, enzyme induction and inhibition and liver disease was investigated. Rats of either sex were studied with and without pretreatment with specific enzyme inducers and incubations included specific enzyme inhibitors. Evidence was provided that the oxidative formation of the five major metabolites, two from metronidazole and three from antipyrine, depends on different cytochrome P450'ies. In humans it was demonstrated that the clearance of metronidazole and antipyrine could be determined from the same saliva sample collected 16-24 hours after their oral administration and so could the clearance for formation of each metabolite if urine was collected for 48 hours. Thus, with the cocktail of metronidazole and antipyrine and simple non-invasive sampling the activity of five different cytochrome P450'ies can be assessed in vivo. In addition, metronidazole may also be used for assessment of the glucuronidation capacity although this is a minor pathway in man. Because the variation within subjects is much less than between them, the cocktail test is particularly suited for paired designs with measurements before and after an environmental change and the subjects serving as their own control. The metronidazole/antipyrine cocktail may have many applications in the study of the regulation of foreign compound metabolism in man and in animals, in vivo and in vitro.