Evidence for a functional genetic polymorphism of the human mercaptopyruvate sulfurtransferase (MPST), a cyanide detoxification enzyme

Mercaptopyruvate sulfurtransferase (MPST) plays a central role in both cysteine degradation and cyanide detoxification. Moreover, deficiency in MPST activity has been suggested to be responsible for a rare inheritable disorder known as mercaptolactate-cysteine disulfiduria (MCDU). To date, no mutation of the human MPST gene has been reported. We developed a screening strategy to search for mutations in the MPST gene of 50 unrelated French individuals. Two intronic polymorphisms (IVS1-110C>G and IVS2+39C>T) and a nonsense mutation (Tyr(85)Stop) were identified and their functional consequences were assessed in vivo by measurement of erythrocyte MPST activity and/or in vitro using heterologous expression or transient transfection assay. The nonsense mutation likely leads to the synthesis of a severely truncated protein without enzymatic activity, as supported by our in vitro data. This work constitutes the first report of the existence of a functional genetic polymorphism affecting MPST and should be of great help to investigate certain disorders such as MCDU.

Identification by single-strand conformational polymorphism analysis of known and new mutations of the CYP3A5 gene in a French population

The cytochrome P450 3A5 (CYP3A5) has been shown to be highly involved in the metabolism of many therapeutic agents. To date, several polymorphisms affecting the CYP3A5 gene have been identified but few studies have shown a complete description of the variability of the CYP3A5 in the French population. Therefore, the extent of CYP3A5 genetic polymorphism was investigated in a French population of 114 patients. The screening of the coding region with their intron-exon boundaries and the proximal flanking regions was performed using a PCR-SSCP strategy. Eighteen polymorphisms were identified, including four new mutations. They correspond to -19 T>C upstream of the exon 1, 7360 T>C in intron 4, 12991 T>C in intron 5 and 29788 delG in exon 12. We also identified 13 alleles including six new alleles. As expected, the most frequent allelic variant is CYP3A5*3, with a frequency of 87% of all alleles. These data confirmed that CYP3A5 gene is highly polymorphic. Furthermore, it will be now interesting to evaluate the impact of this polymorphism on the pharmacokinetic parameters of different drugs.

Evidence for a functional genetic polymorphism of the human retinoic acid–metabolizing enzyme CYP26A1, an enzyme that may be involved in spina bifida

BACKGROUND

CYP26A1, together with CYP26B1 and CYP26C1, are key enzymes of all-trans retinoic acid (RA) inactivation and their specific and restricted expression in developing embryos participate in the fine tuning RA levels. As RA is a critical regulator of gene expression during embryonic development, the imbalance between the synthesis and degradation of RA during embryogenesis could contribute to malformations and developmental defects.

METHODS

A PCR-single strand conformation polymorphism (PCR-SSCP) strategy was developed to screen for CYP26A1 sequence variations that could affect the enzyme expression and/or activity and applied to DNA samples from 80 unrelated Caucasians, comprising 40 French healthy volunteers and 40 Italian patients with spina bifida. The consequence of the 1-bp deletion identified in the coding sequence was investigated by an in vitro functional assay using COS-7 cells.

RESULTS

A total of 7 polymorphisms were identified, comprising 1 nucleotide deletion in the coding sequence (g.3116delT) that results in a frameshift and consequently in the creation of a premature stop codon. The g.3116delT mutation is of particular interest because it was identified in a patient with spina bifida and likely encodes a truncated protein with no enzymatic activity, as demonstrated by our preliminary in vitro data.

CONCLUSIONS

Despite the fact that our findings could not show any evidence that the CYP26A1 genetic polymorphism has implications in the pathogenesis of spina bifida, this work represents the first description of a functional genetic polymorphism affecting the coding sequence of the human CYP26A1 gene.

[Xenobiotic-metabolizing polymorphic enzymes. An opportunity for individualized drug treatment]

Interindividual variability in drug responses can complicate patient management. This variability is partly due to genetic factors that affect pharmacokinetic and pharmacodynamic behavior Pharmacogenetics is a discipline focusing on the molecular mechanisms underlying drug responses. Its overriding goal is to optimize drug treatments, in terms of both their efficacy and their safety. Polymorphisms of genes that encode drug-metabolizing enzymes, transporter molecules and receptors have a well-documented impact on the distribution and effects of many medications. This review examines the scope of pharmacogenetics, the molecular bases of interindividual variations in drug responses, and the methods used to assess the individual risk of drug failure or toxicity. Pharmacogenetic approaches have already entered the clinical arena, resulting in significant improvements in patient management. Clinical validation of new pharmacogenetic tests and the development of new efficient genotyping technologies should rapidly lead to patient-tailored therapy.

Functional analysis of CYP2D6.31 variant: Homology modeling suggests possible disruption of redox partner interaction by Arg440His substitution

Cytochrome P450 2D6 (CYP2D6) is an important human drug-metabolizing enzyme that exhibits a marked genetic polymorphism. Numerous CYP2D6 alleles have been characterized at a functional level, although the consequences for expression and/or catalytic activity of a substantial number of rare variants remain to be investigated. One such allele, CYP2D6*31, is characterized by mutations encoding three amino acid substitutions: Arg296Cys, Arg440His and Ser486Thr. The identification of this allele in an individual with an apparent in vivo poor metabolizer phenotype prompted us to analyze the functional consequence of these substitutions on enzyme activity using yeast as a heterologous expression system. We demonstrated that the Arg440His substitution, alone or in combination with Arg296Cys and/or Ser486Thr, altered the respective kinetic parameters [Km (microM) and kcat (min(-1))] of debrisoquine 4-hydroxylation (wild-type, 25; 0.92; variants, 43-68; 0.05-0.11) and dextromethorphan O-demethylation (wild-type, 1; 4.72; variants, 12-23; 0.64-1.43), such that their specificity constants (kcat/Km) were decreased by more than 95% compared to those observed with the wild-type enzyme. The rates of oxidation of rac-metoprolol at single substrate concentrations of 40 and 400 microM were also markedly decreased by approximately 90% with each CYP2D6 variant containing the Arg440His substitution. These in vitro data confirm that the CYP2D6*31 allele encodes an enzyme with a severely impaired but residual catalytic activity and, furthermore, that the Arg440His exchange alone is the inactivating mutation. A homology model of CYP2D6 based on the crystal structure of rabbit CYP2C5 locates Arg440 on the proximal surface of the protein. Docking the structure of the FMN domain of human cytochrome P450 reductase to the CYP2D6 model suggests that Arg440 is a key member of a cluster of basic amino acid residues important for reductase binding.

Identification and functional analysis of two rare allelic variants of the thiopurine S-methyltransferase gene, TPMT*16 and TPMT*19

Human thiopurine S-methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs. TPMT is genetically polymorphic and is associated with large interindividual variations in thiopurine drug toxicity and therapeutic efficacy. During routine genotyping of patients with Crohn's disease, one novel missense mutation, 365A>C (TPMT*19, Lys(122)Thr), and a recently described missense mutation, 488G>A (TPMT*16, Arg(163)His), were identified in a Caucasian and a Moroccan patient, respectively. Using a heterologous yeast expression system, kinetic parameters (K(m) and V(max)) of the two variants with respect to 6-thioguanine S-methylation were determined and compared with those obtained with the wild-type enzyme. The Lys(122)Thr exchange did not significantly decrease the intrinsic clearance value (V(max)/K(m)) of the variant enzyme. In contrast, the Arg(163)His substitution significantly decreased the intrinsic clearance value by three-fold. The Arg(163) is located in a highly conserved region of the human TPMT protein and, as such, the Arg(163)His substitution is expected to result in a marked reduction of enzyme activity, as confirmed by the in vitro data. Phenotyping by measurement of red blood cell TPMT activity indicated that the patient heterozygous for the Lys(122)Thr mutation had normal TPMT activity, whereas the patient heterozygous for the Arg(163)His mutation was an intermediate methylator, which demonstrated a positive correlation between TPMT phenotyping and the in vitro data. The identification of a novel non-functional allele of the TPMT gene improves our knowledge of the genetic basis of interindividual variability in TPMT activity. These data further enhance the efficiency of genotyping methods to predict patients at risk of an inadequate response to thiopurine therapy.

Human CYP4F12 genetic polymorphism: identification and functional characterization of seven variant allozymes

The human cytochrome CYP4F12 has been shown to be metabolically active toward inflammatory mediators and exogenous compounds such as antihistaminic drugs. We recently identified a genetic polymorphism within the promoter region, associated with a decreased level of enzyme expression. In the present study, we report the further identification of single nucleotide polymorphisms in the coding sequence of the CYP4F12 gene. A polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) analysis of DNA samples from 53 unrelated French Caucasians, allowed the identification of ten mutations, comprising seven missense mutations, 31C>T (Leu11Phe), 38C>T (Pro13Leu), 47C>T (Met16Thr), 4759G>A (Asp76Asn), 4801G>A (Val90Leu), 8896C>T (Arg188Cys) and 23545G>A (Gly522Ser). Their functional impact toward ebastine hydroxylation was evaluated using heterologous expression in Saccharomyces cerevisiae cells of site-directed mutated cDNA variants. Five out seven variants did not exhibit any significant difference in CYP4F12 catalytic activity, whereas two variants, Val90Ile and Arg188Cys, displayed significant changes in their Michaelis-Menten (Km, Vm) parameters. These data on CYP4F12 genetic polymorphism provide tools for further studies of association with pathological processes involving an inflammatory component and with variations in anti-histaminic drug response.

Clomipramine, fluoxetine and CYP2D6 metabolic capacity in depressed patients

Cytochrome P450-2D6 may be involved in the metabolism of many drugs such as psychotropic drugs and its genetic polymorphism is responsible for inter-individual differences in the therapeutic effect and toxicity of these drugs. Moreover with the same genetic basis, CYP2D6 metabolic capacity variations are observed. Different factors of variation may be involved, among them the prescribed drugs. The aim of this study was to compare the influence of two types of antidepressants, tricyclic (clomipramine) and serotonergic specific recapture inhibitor (SSRI) (fluoxetine), on the CYP2D6 metabolic capacity of depressed inpatients. The CYP2D6 phenotype (dextromethorphan test) was determined in 56 genotyped (PCR-SSCP) depressed caucasian inpatients with a heterozygous genotype. Forty-five subjects were treated with clomipramine and eleven received fluoxetine. The dextromethorphan metabolic ratio (MR) median was significantly higher in the fluoxetine group (0.255) than in the clomipramine group (0.083, p < 0.014). In this study, fluoxetine involved a greater decrease of CYP2D6 metabolic capacity than clomipramine. Clinical implications and the possible connection between a decreased CYP2D6 activity and adverse drug effects were discussed. Caution should be taken when drugs with a low therapeutic index must be coprescribed in such patients.

Functional characterization of genetic polymorphisms identified in the human cytochrome P450 4F12 (CYP4F12) promoter region

The human cytochrome CYP4F12 has been shown to be active toward inflammatory mediators and exogenous compounds such as antihistaminic drugs. In the present study, we report the first investigation of polymorphisms in the human CYP4F12 gene. A screening for sequence variations in the 5'-flanking region was performed by a Polymerase Chain Reaction-Single Strand Conformational Polymorphism (PCR-SSCP) strategy, using DNA samples from 53 unrelated French individuals of Caucasian origin. Several polymorphisms were identified, comprising a large deletion located in intron 1 (CYP4F12*v1), two isolated substitutions -402G>A (CYP4F12*v3) and -188 T>C (CYP4F12*v4) and nine combined mutations, -474T>C, -279A>C, -224A>G, -173G>A, -145C>G, -140T>C, -126T>C, -56T>C, and -21T>G (CYP4F12*v2). Considering the nature and location of the polymorphisms characterizing the CYP4F12*v1 and *v2, the functional relevance of those two allelic variants was further examined by transfecting different cell lines with constructs of the related region of the CYP4F12/luciferase reporter gene. Both alleles lead to a significant decrease of CYP4F12 gene expression in HepG2 cell line and, therefore, are likely to determine interindividual differences in CYP4F12 gene expression.

Nonresponse to clozapine and ultrarapid CYP1A2 activity: clinical data and analysis of CYP1A2 gene

Clozapine (CLO), an atypical antipsychotic, depends mainly on cytochrome P450 1A2 (CYP1A2) for its metabolic clearance. Four patients treated with CLO, who were smokers, were nonresponders and had low plasma levels while receiving usual doses. Their plasma levels to dose ratios of CLO (median; range, 0.34; 0.22 to 0.40 ng x day/mL x mg) were significantly lower than ratios calculated from another study with 29 patients (0.75; 0.22 to 2.83 ng x day/mL x mg; P < 0.01). These patients were confirmed as being CYP1A2 ultrarapid metabolizers by the caffeine phenotyping test (median systemic caffeine plasma clearance; range, 3.85; 3.33 to 4.17 mL/min/kg) when compared with previous studies (0.3 to 3.33 mL/min/kg). The sequencing of the entire CYP1A2 gene from genomic DNA of these patients suggests that the -164C > A mutation (CYP1A2*1F) in intron 1, which confers a high inducibility of CYP1A2 in smokers, is the most likely explanation for their ultrarapid CYP1A2 activity. A marked (2 patients) or a moderate (2 patients) improvement of the clinical state of the patients occurred after the increase of CLO blood levels above the therapeutic threshold by the increase of CLO doses to very high values (ie, up to 1400 mg/d) or by the introduction of fluvoxamine, a potent CYP1A2 inhibitor, at low dosage (50 to 100 mg/d). Due to the high frequency of smokers among patients with schizophrenia and to the high frequency of the -164C > A polymorphism, CYP1A2 genotyping could have important clinical implications for the treatment of patients with CLO.

Genetic polymorphism of the human cytochrome CYP2A13 in a French population: implication in lung cancer susceptibility

The human cytochrome CYP2A13, which is mainly expressed in the respiratory tract, has been shown to be highly efficient in vitro in the metabolism of tobacco-smoke carcinogens and procarcinogens such as 4-methylnitroso-1-(3-pyridyl)-1-butanone (NNK). In order to investigate the extent of CYP2A13 genetic polymorphism in a French Caucasian population of 102 individuals, a screening for sequence variations in the 5'-untranslated and protein encoding regions of its gene was performed using a polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) strategy. Six polymorphisms in the coding region were identified, including two rare missense mutations (C474G or Asp158Glu, G967T or Val323Leu) and one nonsense mutation (Arg101Stop). This deleterious mutation, the most frequent (5%) in our population, presumably encodes a severely truncated protein. The influence of the nonsense mutation in lung cancer susceptibility was examined by PCR-SSCP using peripheral blood DNA from 204 cases of lung cancer and 201 controls. The CYP2A13*7 allele, which harbours the C301T mutation, was present in 2.0% of controls and 3.4% of cases. However, multivariate analysis showed an elevated risk for small cell lung cancer in subjects heterozygous for the null allele (odds ratio OR=9.9; 95% confidence interval CI=1.9-52.2). This increased risk was not linked to other histological types of lung cancer.

First report of a genetic polymorphism of the cytochrome P450 3A43 (CYP3A43) gene: identification of a loss-of-function variant

In the present study, we report the first investigation of polymorphisms in the human CYP3A43 gene. A screening for sequence variations in the 5'-flanking and protein coding regions of the CYP3A43 gene was performed by a Polymerase Chain Reaction - Single Strand Conformational Polymorphism (PCR-SSCP) strategy, using DNA samples from 48 unrelated French individuals. Three polymorphisms in the coding region were identified, comprising two nucleotide substitutions, one silent (c.1047C>T) and one missense mutation (c.1018C>G/P340A), and a frame shift mutation (c.74delA), leading to a premature stop codon and, presumably, to a severely truncated protein. In order to evaluate the extent of the frame shift mutation in a larger population, 352 individuals were further genotyped. Thirty-four samples (4.83%) were found to be heterozygous and one homozygous (0.14%) for the nucleotide deletion, which suggests that, although the potential significance of this polymorphism remains to be further evaluated, some individuals are deficient for CYP3A43 activity.

Polymorphisms in the CYP 2D6 gene: association with plasma concentrations of fluoxetine and paroxetine

Most antidepressants are metabolized by cytochrome P450 (CYP) 2D6, and it is well known that there may be significant interindividual variation in the capacity to metabolize xenobiotics. About 7 to 10% of whites are poor metabolisers (PM), and, on the contrary, about 5% are ultrarapid metabolizers (UM), inducing very different rates in the transformation of antidepressants extensively metabolized by CYP 2D6. CYP 2D6 polymorphism can be a potential risk factor for the development of side effects or a reason for the poor efficacy of the treatment. Various probe drugs may be used for phenotyping CYP 2D6, but genotyping is now available using leukocyte DNA and is independent of concomitant drug use. In this study, we used PCR-based methods for the identification of CYP 2D6 genotypes in 49 patients receiving standard doses of fluoxetine or paroxetine and found that plasma concentration of the antidepressant drugs was significantly correlated with genetic status. In one patient who displayed CYP 2D6 gene duplication (UM), paroxetine plasma concentration was extremely low. In PM fluoxetine-treated patients, drug plasma concentration was significantly higher than that seen in extensive metabolizers.

N-Acetyltransferase 2 Acetylation Polymorphism: Prevalence of Slow Acetylators Does Not Differ between Atopic Dermatitis Patients and Healthy Subjects

The genetic polymorphism of human N-acetyltransferase 2 (NAT2) divides the human population into groups with rapid, intermediate and slow acetylator status. Slow acetylator status has been considered a predisposing factor for allergic diseases, lupus erythematosus, toxic epidermal necrolysis or Stevens-Johnson syndrome. The aim of this study was to investigate whether Caucasian patients suffering from atopic dermatitis differed from healthy individuals with regard to the genotype and phenotype of NAT2. Twenty unrelated healthy Caucasian volunteers (9 females and 11 males, aged from 22 to 59 years) and twenty unrelated Caucasian patients suffering from atopic dermatitis (9 females and 11 males, aged between 20 and 54 years) participated in this study. For each one, the NAT2 genotype was determined by polymerase chain reaction with DNA extracted from peripheral blood, using specific primers for the wild-type allele (wt) and the 3 most frequent mutated alleles of NAT2 (C481-->T, G590-->A and G857-->A). The NAT2 phenotype was evaluated with dapsone as a test substrate using high-pressure liquid chromatography. Statistical analysis was performed using the chi(2) test. Phenotype and genotype were distributed as follows: (1) of the healthy subjects, 60% were rapid acetylators (RA) and 40% were slow acetylators (SA); 10% of the RA and 15% of the SA were homozygous, 50% of the RA and 25% of the SA were heterozygous; (2) of the patients, 55% were RA, 40% were SA and 5% were intermediate acetylators (IA); 10% of the RA and 10% of the SA were homozygous, 45% of the RA and 35% of the SA were heterozygous. No significant statistical difference was found between the two groups for genotypes (p = 0.75) or phenotypes (p = 0.60). The phenotyping and genotyping results of healthy subjects were comparable to those found in previous studies. The absence of a significant statistical difference between healthy subjects and atopic dermatitis patients is in contrast to the results of previous studies. Some authors considered that allergic patients are mostly SAs. This could be explained by the fact that we only considered patients suffering from atopic dermatitis whereas, in other studies, patients suffered from different (one or several associated) allergic diseases. NAT2 polymorphism does not differ between patients suffering from atopic dermatitis and healthy subjects. The importance attributed to the SA status, which was previously considered a predisposing factor for allergic diseases such as atopic dermatitis, should be reviewed.

In vitro characterization of four novel non-functional variants of the thiopurine S-methyltransferase

Human thiopurine S-methyltransferase (TPMT) is an enzyme responsible for the detoxification of widely used thiopurine drugs such as azathioprine (Aza). Its activity is inversely related to the risk of developing severe hematopoietic toxicity in certain patients treated with standard doses of thiopurines. DNA samples from four leucopenic patients treated with Aza were screened by PCR-SSCP analysis for mutations in the 10 exons of the TPMT gene. Four missense mutations comprising two novel mutations, A83T (TPMT*13, Glu(28)Val) and C374T (TPMT*12, Ser(125)Leu), and two previously described mutations, G430C (TPMT*10, Gly(144)Arg) and T681G (TPMT*7, His(227)Gln) were identified. Using a recombinant yeast expression system, kinetic parameters (K(m) and V(max)) of 6-thioguanine S-methylation of the four TPMT variants were determined and compared to those obtained with wild-type TPMT. This functional analysis suggests that these rare allelic variants are defective TPMT alleles. The His(227)Gln variant retained only 10% of the intrinsic clearance value (V(max)/K(m) ratio) of the wild-type enzyme. The Ser(125)Leu and Gly(144)Arg variants were associated with a significant decrease in intrinsic clearance values, retaining about 30% of the wild-type enzyme, whereas the Glu(28)Val variant produced a more modest decrease (57% of the wild-type enzyme). The data suggest that the sporadic contribution of the rare Glu(28)Val, Ser(125)Leu, Gly(144)Arg, and His(227)Gln variants may account for the occurrence of altered metabolism of TPMT substrates. These findings improve our knowledge of the genetic basis of interindividual variability in TPMT activity and would enhance the efficiency of genotyping methods to predict patients at risk of inadequate responses to thiopurine therapy.

Identification of a novel splice-site mutation in the CYP1A2 gene

AIMS

To identify the molecular basis for a low CYP1A2 metabolic status, as determined by a caffeine phenotyping test, in a 71-year-old, nonsmoking, Caucasian woman who presented with very high clozapine concentrations despite being administered a standard dose of the drug.

METHODS

The nucleotide sequence of the 7 exons, exon-intron boundaries and 5'-flanking region of the CYP1A2 gene was analysed by direct sequencing.

RESULTS

Only one heterozygous point mutation was identified in the donor splice site of intron 6 (3534G > A) of CYP1A2. This mutation could cause abnormal RNA splicing and therefore lead to a truncated nonfunctional enzyme. No other carrier of this mutation was identified in a population of 100 unrelated healthy Caucasians.

CONCLUSIONS

This is the first report of a splice-site mutation affecting the CYP1A2 gene. This polymorphism is a likely explanation for the low CYP1A2 activity associated with high clozapine concentrations in this patient.

Sequence analysis, frequency and ethnic distribution of VNTR polymorphism in the 5'-untranslated region of the human prostacyclin synthase gene (CYP8A1)

The prostacyclin synthase enzyme (CYP8A1, EC 5.3.99.4) is the unique member of family 8 in the cytochrome P450 superfamily. Inheritable interindividual differences in prostacyclin production may be implicated in the pathogenesis of human vascular diseases. Recently, we functionally characterized a variable number of tandem repeat (VNTR) polymorphism in the 5'-proximal regulatory region of CYP8A1. In this study, we extended the CYP8A1 VNTR polymorphism analysis using a panel of DNA samples from distinct ethnic populations: Tunisians, Gaboneses and French Caucasians. A total of nine VNTR were detected, three of which represent new variants in the CYP8A1 promoter region. Differences among the three ethnic panels in the frequency of the VNTR variants were observed. This study represents the first multi-population-based analysis of the frequency and distribution of VNTR polymorphism affecting the CYP8A1 promoter.

Genetic polymorphism of the human cytochrome P450 CYP4B1: evidence for a non-functional allelic variant

In the present study, we report the first systematic investigation of polymorphism in the human CYP4B1 gene. Using a strategy based on single-strand conformation polymorphism analysis of PCR products (PCR-SSCP), we analyzed the twelve exons of the gene, as well as their 5'- and 3'- proximal flanking sequences, in DNA samples from 190 French Caucasians. In addition to the wild-type CYP4B1* allele (CYP4B1*1), four variants, namely CYP4B1*2, *3, *4 and *5, were characterized. The CYP4B1*3, *4 and *5 alleles encode missense mutations Arg173Trp, Ser322Gly and Met331Ile, respectively. The fourth variant, CYP4B1*2, harbors three missense mutations (Met331Ile, Arg340Cys and Arg375Cys) and a double nucleotide deletion (AT881-882del) that causes a frameshift and premature stop codon in the second third of the coding sequence of the gene. This latter mutation can be assumed to lead to the synthesis of a severely truncated protein and, therefore, probably contributes to interindividual variability of CYP4B1 expression and enzymatic activity. In order to investigate the extent of the CYP4B1*2 allele in a large population, a rapid genotyping test, based on restriction analysis of PCR products, was developed and applied to 2082 French Caucasians. Forty-two subjects were found homozygous for the AT881-882 deletion, which suggests that about 2% of individuals should be unable to develop metabolic reactions mediated by CYP4B1. Given the relatively high frequency and the functional consequences of the CYP4B1*2 allele, associations between CYP4B1 polymorphism and certain pathological processes should be considered.

Effect of interferon alpha-ribavirin bitherapy on cytochrome P450 1A2 and 2D6 and N-acetyltransferase-2 activities in patients with chronic active hepatitis C

BACKGROUND

Interferon alpha (IFN-alpha) is thought to be responsible for cytochrome P450 (CYP)-dependent drug interactions mediated by a decrease in CYP activities.

OBJECTIVES

The objectives are to determine whether IFN-alpha and ribavirin can alter pretreatment CYP1A2, CYP2D6, CYP3A4 and N-acetyltransferase-2 activities after 1 month of treatment.

METHODS

Enzymatic activities were determined among 14 patients with chronic active hepatitis C before IFN-alpha (3. 10(6) U, 3 times a week) and ribavirin introduction and after 1 month of treatment. During both study periods, subjects received 80 mg dextromethorphan and 140 mg caffeine (1,3,7-trimethylxanthine [137X]). CYP3A4, CYP2D6, and NAT2 activities were assessed by use of urinary metabolic ratios of 3-methoxymorphinan/dextromethorphan, dextrorphan/dextromethorphan, and 5-acetylamino-6-formylamino-3-methyluracil (AFMU)/1-methylxanthine(1X). The plasma paraxanthine/caffeine ratio was used to measure CYP1A2 activity.

RESULTS

CYP3A4 and CYP2D6 activities tended to increase after 1 month of antiviral therapy, but the change did not reach statistical significance. CYP1A2 and NAT2 activities were not significantly modified after 1 month of antiviral treatment. Pretreatment activities were significantly lower than those previously observed in healthy volunteers for CYP2D6 (mean +/- SD, 148 +/- 139 versus 759 +/- 692; P =.0008) and CYP3A4 (0.18 +/- 0.06 versus 0.52 +/- 0.72; P =.0006). This difference was no longer statistically significant after 1 month of treatment, because CYP2D6 and CYP3A4 activities improved in 7 patients.

CONCLUSION

In patients with chronic hepatitis C, pretreatment CYP3A4 and CYP2D6 activities were significantly lower than those observed in healthy volunteers. These differences disappeared after 1 month of antiviral treatment because of the restoration of these CYP activities in about half of the patients.

In-vitro analysis of the contribution of CYP2D6.35 to ultra-rapid metabolism

From 10 to 30% of CYP2D6 ultra-rapid metabolizers of Caucasian origin harbor alleles with duplicated or amplified functional CYP2D6 genes. Recently, the CYP2D6*35 allele has been reported to be more frequent in ultra-rapid metabolizing subjects than in extensive metabolizers, suggesting a possible role of this variant in CYP2D6 duplication-negative ultra-rapid metabolizing subjects. In this study, we examined the functional consequences of the Val11Met, Arg296Cys and Ser486Thr amino acid substitutions associated with the CYP2D6*35 on the expression and catalytic activity of the variant enzyme, heterologously expressed in yeast. Our results indicate that the functional activity and level of expression of recombinant CYP2D6.35 are comparable with those of the wild-type enzyme, thus precluding the hypothesis that the high level of enzyme activity in CYP2D6 duplication-negative ultra-rapid metabolizing subjects is a consequence of the expression of a more catalytically effective CYP2D6.35 enzyme.

Cytochrome P450 2D6 genotype and methadone steady-state concentrations

A genetic polymorphism of cytochrome P450 2D6 has been described with the existence of poor (zero functional genes), extensive (one or two functional genes), and ultrarapid metabolizers (three or more functional genes). The authors measured the steady-state trough (R)- (i.e., the active enantiomer), (S)-, and (R,S)-methadone plasma levels in opiate-dependent patients receiving methadone maintenance treatment (MMT) and genotyped them for cytochrome P4502D6. The patients' medical records were reviewed to assess the outcome of the MMT with regard to the absence of illicit opiate consumption and to the absence of withdrawal complaints in ultrarapid and poor metabolizers. Of 256 patients included, 18 were found to be poor metabolizers, 228 to be extensive metabolizers, and 10 to be ultrarapid metabolizers. Significant differences were found between genotypes for (R)- (p = 0.024), (S)- (p = 0.033), and (R,S)-methadone (p = 0.026) concentrations to dose-to-weight ratios. For (R)-methadone, a significant difference was found between ultrarapid metabolizers and poor metabolizers (p = 0.009), with the median value in the former group being only 54% of the median value in the latter group. These results confirm the involvement of cytochrome P450 2D6 in methadone metabolism. Although the difference was nonsignificant (p = 0.103), 13 (72%) of the 18 poor metabolizers and only 4 (40%) of the 10 ultrarapid metabolizers were considered successful in their treatment. More studies are needed to examine the influence of the ultrarapid metabolizer status on the outcome of the MMT.

Characterization of new mutations in the coding sequence and 5'-untranslated region of the human prostacylcin synthase gene (CYP8A1)

Inheritable interindividual differences in prostacyclin production may be implicated in the pathogenesis of several human vascular diseases. Using a polymerase chain reaction/single-strand conformation polymorphism strategy, we screened for mutations in the gene encoding cytochrome P450 prostacyclin synthase (CYP8A1). DNA samples from healthy French volunteers (n = 130) of Caucasian origin were examined. Five mutations, comprising two previously reported silent mutations and three novel rare missense mutations (P38L, S118R, and R379S), were identified in the coding sequence of the gene. In the 5'-proximal region, we also found a variable number of tandem repeats (VNTR) polymorphism that consisted of four different alleles with 4-6 tandem repeats of a 9-bp unit containing a putative Spl transcriptional factor binding site. One of these (R6), a frequent allele (23.6% of alleles tested) harboring six repeats, is novel, whereas the other three are known. In vitro analysis of the effect of each VNTR allele on promoter activity of a reporter gene was performed by a transient transfection assay. Data confirmed the modulator effect of the VNTR polymorphism on reporter gene transcription. Furthermore, the data demonstrate that allele R6 has the most potent inducing effects in the A549 cell line and, after IL-6 stimulation, in human pulmonary artery endothelial cells. Overall, the data demonstrate that CYP8A1 is polymorphic in Caucasians, and that a polymorphism affecting the 5'-proximal region may result in interindividual differences in CYP8A1 transcriptional regulation in vivo. Additional factors, such as the presence of inflammatory mediators, may be required to modulate transcription of the CYP8A1 gene.

Identification of genetic variants in the human thromboxane synthase gene (CYP5A1)

Thromboxane synthase (CYP5A1) catalyzes the conversion of prostaglandin H2 to thromboxane A2, a potent mediator of platelet aggregation, vasoconstriction and bronchoconstriction. It has been implicated in the patho-physiological process of a variety of diseases, such as atherosclerosis, myocardial infarction, stroke and asthma. On the basis of the hypothesis that variations of the CYP5A1 gene may play an important role in human diseases, we performed a screening for variations in the human CYP5A1 gene sequence. We examined genomic DNA from 200 individuals, for mutations in the promoter region, the protein encoding sequences and the 3'-untranslated region of the CYP5A1. Eleven polymorphisms have been identified in the CYP5A1 gene including eight missense mutations R61H, D161E, N246S, L357V, Q417E, E450K, T451N and R466Q. This is the first report of genetic variants in the human CYP5A1 altering the protein sequence. The effect of these variants on the metabolic activity of CYP5A1 remains to be further evaluated.

Detection of known and new mutations in the thiopurine S-methyltransferase gene by single-strand conformation polymorphism analysis

To detect mutations in the thiopurine S-methyltransferase gene (TPMT), we have developed a strategy based on single-strand conformation polymorphism (SSCP) analysis of the gene amplified by polymerase chain reaction (PCR). The sensitivity of the method was first evaluated by analyzing DNA samples from five individuals, including two high methylators (HMs), two intermediate methylators (IMs), and one deficient methylator (DM). TPMT alleles and mutations in each of these individuals had previously been characterized by conventional PCR-based assays and direct sequencing analysis. All mutations were associated with particular shifts in the electrophoretic mobility of DNA fragments, allowing their identification. We further tested the efficiency of the strategy to detect new TPMT mutations. For this purpose, additional DNAs from 15 IMs and 15 HMs were submitted to PCR-SSCP analysis. A total of 7 alleles were characterized, including two new alleles. The first one, termed TPMT*1A, harbors a single mutation C-->T at nucleotide -178 in exon 1 and was detected in a HM subject. The second one, termed TPMT*7, was characterized by a T-->G transversion at nucleotide 681 in exon 10. This allele should be a nonfunctional allele of the TPMT gene since it was observed in combination with a wild-type allele in an intermediate methylator. We conclude that the PCR-SSCP strategy we developed could be advantageously used to fully characterize the extent of allelic variation at the TPMT gene locus in populations and thus to improve our understanding of the genetic polymorphism of TPMT activity, which has considerable consequences for the toxicity and efficacy of therapeutically important and widely used drugs.

Genotypic analysis of thiopurine S-methyltransferase in patients with Crohn's disease and severe myelosuppression during azathioprine therapy

BACKGROUND & AIMS

Myelosuppression in patients with Crohn's disease (CD) treated with azathioprine has been attributed to low activity of thiopurine S-methyltransferase (TPMT). Allelic variants of the TPMT gene responsible for changes in the enzyme activity have been characterized. We investigated the distribution of mutant alleles associated with TPMT deficiency in patients with CD and myelosuppression during azathioprine/6-mercaptopurine therapy.

METHODS

Forty-one patients with CD were included. They developed leukopenia or thrombocytopenia during azathioprine or 6-mercaptopurine treatment. Polymerase chain reaction-based methods were used to search for mutations associated with TPMT deficiency.

RESULTS

Four patients (10%) had 2 mutant alleles associated with TPMT deficiency, 7 (17%) had 1 mutant allele, and 30 (73%) had no known TPMT mutation. The delay between administration of the drug and occurrence of bone marrow toxicity was less than 1.5 months in the 4 patients with 2 mutant alleles, and ranged from 1 to 18 months in patients with 1 mutant allele and from 0.5 to 87 months in patients with normal genotype.

CONCLUSIONS

Twenty-seven percent of patients with CD and myelosuppression during azathioprine therapy had mutant alleles of the TPMT gene associated with enzyme deficiency. Myelosuppression is more often caused by other factors. Continued monitoring of blood cell counts remains mandatory in patients treated with azathioprine.

Molecular analysis of the N-acetyltransferase 1 gene (NAT1*) using polymerase chain reaction-restriction fragment-single strand conformation polymorphism assay

One major interest to analyse the extent of N-acetyltransferase 1 (NAT1*) allelic variation in the human population stems to a great extent from the possible association of interindividual differences in the metabolism of aromatic amines with certain chemically induced diseases, including cancer. Considering the increasing number of mutations in the NAT1 gene that are detected, NAT1* genotyping using conventional polymerase chain reaction (PCR) restriction fragment length polymorphism (RFLP) or allele-specific amplification assays has become complicated. We developed a rapid and powerful strategy allowing the full characterization of NAT1* alleles. This method, based on single-strand conformation polymorphism analysis of a unique PCR product encompassing the entire intronless NAT1*-coding region along with additional flanking segments in the 5' and 3' untranslated regions, was then applied to DNA samples from 270 individuals. Nine NAT1* allelic variants, including two novel (NAT1*28 and NAT1*29), and 15 different genotypes were identified. This approach could be advantageously used in epidemiological studies to provide more definite data on suspected associations between NAT1* genotype and certain pathological processes.

Thiopurine methyltransferase activity and its relationship to the occurrence of rejection episodes in paediatric renal transplant recipients treated with azathioprine

AIMS

Azathioprine is a prodrug commonly used in combination therapy to prevent allograft rejection after renal transplantation. After conversion to 6-mercaptopurine, the drug is metabolized into 6-thioguanine nucleotides (6-TGN) and catabolized by thiopurine methyltransferase (TPMT), an enzyme under monogenic control. The aim of this study was to evaluate the inter- and intraindividual variability of red blood cell thiopurine methyltransferase and 6-TGN concentrations and their relationship to the clinical effects of azathioprine in paediatric patients.

METHODS

In the present study, the inter- and intraindividual variations in red blood cell TPMT activity and 6-TGN concentrations and their relationship to the actions of azathioprine were evaluated during the first year after renal transplantation in 22 paediatric patients.

RESULTS

6-TGN concentration reached steady-state values after 6 months and correlated negatively with TPMT activity (P=0.004). Initial TPMT activity (median: 20.8 nmol h-1 ml-1, range 7.8-34.6) and 6-TGN concentration at steady-state (median: 80 pmol 8 x 10(8-1) cells, range not detected to 366) were not related to the occurrence of rejection episodes during the period of the study. In contrast, TPMT activity and the percentage difference in TPMT activity from the day of transplantation determined at month 1 were higher in the patients with rejection episodes by comparison with those that did not reject during the first 3 months or the first year following transplantation (P<0.005).

CONCLUSIONS

We report a relationship between TPMT activity and occurrence of rejection in paediatric kidney transplant patients undergoing azathioprine therapy. These data suggest a link between high red blood cell TPMT activity and poor clinical outcome probably caused by rapid azathioprine catabolism.

Drug extrapyramidal side effects. CYP2D6 genotypes and phenotypes

OBJECTIVE

Among Caucasians, a lack of cytochrome P450 enzyme CYP2D6 is observed in 5-10% of individuals, named poor metabolizers (PMs). A consequence may be an impaired metabolism of many drugs such as most of the psychotropic drugs with an increased risk of drug side effects. This enzyme is also involved in the metabolism of endogenous compounds, including neurotransmitters such as dopamine and dopamine-related neurotransmitters which play a role in the mechanism of action of extrapyramidal drug side effects. The present study investigates whether patients who have developed and those who have not developed extrapyramidal drug side effects differ in their CYP2D6 genotypes and phenotypes.

METHODS

The CP2D6 genotype (method involving restriction length fragment polymorphism and polymerase chain reaction-single strand conformation polymorphism) was determined in 65 drug-treated in-patients, and the CYP2D6 phenotype (with dextromethorphan probe) in 62 of them. Two groups were constituted, one with 22 patients who had developed extrapyramidal drug side effects, and the second with 43 patients without such side effects.

RESULTS

In the whole population, there was an over-representation of PM phenotypes--more marked in the first group than the second (45% vs 14%). Concerning the genotypes, we observed that the percentage of functional alleles (with extensive metabolic capacity) was higher in group 2, whereas the percentage of nonfunctional alleles (without metabolic activity) was higher in group 1; this frequency difference was only marginally significant (chi 2 5.95; P < 0.0509; degrees of freedom = 2). Consequently, there was a higher percentage of genotypes with no (extensive) functional alleles in the group of patients suffering from extrapyramidal side effects than in the other group (P < 0.00001).

CONCLUSION

CYP2D6-impaired metabolic capacity may be a contributory factor in extrapyramidal drug side effects.

Citalopram: an interaction study with clomipramine in a patient heterozygous for CYP2D6 genotype

A pharmacokinetic interaction between the selective serotonin reuptake inhibitor citalopram and a tricyclic antidepressant, clomipramine, was noted in a patient treated for major depression and obsessive-compulsive disorder. After the addition of citalopram, a desmethylclomipramine plasma level increase and an 8-hydroacy-desmethylclomipramine plasma level decrease were observed. The CYP2D6 phenotype, determined when the patient received the antidepressant comedication, characterized a poor metabolizer status (dextromethorphan metabolic ratio >0.3), despite a heterozygous genotype containing a wild-type allele with extensive metabolic capacity and a mutant non-functional allele (CYP2D6*1A/CYP2D6*4A). This case seems to be one of the first descriptions of the clinical relevance of a CYP2D6 heterozygous genotype in a patient treated with antidepressant.

Characterization of a variable number tandem repeat region in the thiopurine S-methyltransferase gene promoter

Characterization of the genetic polymorphism of thiopurine S-methyltransferase enzyme (TPMT; EC 2.1.1.67) is required because of its clinical importance for patients exposed to thiopurine drugs. A number of point mutations have already been characterized in exons and introns of the TPMT gene. Here we report the identification of a polymorphic locus within the promoter region of the gene. This polymorphism was detected by polymerase chain reaction - single strand conformation polymorphism analysis of DNA samples from 54 unrelated European individuals. A total of five alleles with length variations were distinguished through the 5'-flanking region involved in the TPMT gene expression. Sequence analysis revealed that these variations were due to a variable number of tandem repeats (VNTR), ranging from four to eight repeats. Each repeat consists of 17 or 18 bp units and contains putative binding sites for transcription factors. The most frequent alleles harbour four or five tandem repeats, a heterozygosity rate of 0.44 was calculated, and a stable Mendelian inheritance of alleles was demonstrated. Analysis of the effect of each VNTR allele on promoter activity of a reporter gene was further performed in various cell lines by transient transfection assay. A modulatory effect of VNTR alleles was observed in vitro, but the repeat polymorphism did not display a significative role in TPMT gene regulation in vivo. Further studies need to be carried out to support the hypothesis that VNTR may contribute to the large interindividual variations of TPMT activity.

CYP2D6 polymorphism and Parkinson's disease susceptibility

Following the recent identification of multiple novel mutations and alleles of the cytochrome P450 CYP2D6 gene which cause decreased, increased, or absent enzyme activity, we re-examined the controversial hypothesis of a role of the CYP2D6 polymorphism in Parkinson's disease (PD) susceptibility. For this purpose, a strategy based on PCR-SSCP and RFLP analyses allowing the detection of all known CYP2D6 alleles was performed in DNA from 109 patients with sporadic PD. This strategy was also applied to DNA from 68 members of PD families including 18 affected and 50 unaffected members. Seventeen mutations occurring alone or in various combination on 14 alleles of CYP2D6 have been identified in patients with sporadic PD. Moreover, 12 mutations and nine alleles of the gene have been characterized in members of PD families. No significant difference was observed when the distribution of mutations and alleles of CYP2D6 was compared between the PD patients and 514 control subjects previously analyzed using the same strategy. There was also no difference in the distribution of phenotypes predicted from genotypes between both groups. In addition, when the distribution of CYP2D6 genotypes was compared, no difference between affected and unaffected members of PD families was observed. These data indicate that CYP2D6 polymorphism is not a susceptibility factor to PD.

Genotypic and phenotypic analysis of the polymorphic thiopurine S-methyltransferase gene (TPMT) in a European population

1. Characterization of allelic variants of the TPMT gene (TPMT) responsible for changes in TPMT activity, and elucidation of the mechanism by which these alleles act, are required because of the clinical importance of this polymorphism for patients receiving thiopurine drugs. 2. We defined the mutational and allelic spectrum of TPMT in a group of 191 Europeans. Using PCR-SSCP, we screened for mutation the entire coding sequence, the exon-intron boundaries, the promoter region and the 3'-flanking region of the gene. Six mutations were detected throughout the ten exons and seven TPMT alleles were characterized. Four of them, TPMT*2, *3A, *3C and *7, harbouring the known mutations, G238C, G460A, A719G or T681G, were nonfunctional and accounted for 0.5, 5.7, 0.8 and 0.3% of the allele totality, respectively. 3. Within the promoter region, six alleles corresponding to a variable number of tandem repeats (VNTR), were identified. VNTR*V4 and *V5a which harbour four or five repeats of a 17-18 bp unit, were the most frequent (55% and 34%, respectively). The other VNTR alleles, having from five to eight repeats, were rarer. 4. The TPMT phenotype was correctly predicted by genotyping for 87% of individuals. A clear negative correlation between the total number of repeats from both alleles and the TPMT activity level was observed, indicating that VNTRs contribute to interindividual variations of TPMT activity. Therefore, additional analysis of the promoter region of TPMT can improve the phenotype prediction rate by genotyping.

[Treatment of discoid lupus erythematosus with sulfasalazine: 11 cases]

INTRODUCTION

Antimalaria agents and thalidomide are two reference drugs for discoid lupus erythematosus. In non-responders or after secondary resistance or contraindications, there are a number of alternative therapeutics which are less effective and more toxic. We therefore conducted an open study in patients with discoid lupus erythematosus treated with sulfasalazine.

PATIENTS AND METHODS

Seven men and four women (mean age 40 years) with severe discoid lupus erythematosus (mean duration of disease 14 years) were treated with sulfasalazine (2 g/d). This treatment was initiated after a previous failure or contraindication of antimalarial drugs or thalidomide. The acetylation phenotype was predicted in all patients with N-acetyltransferase 2 genotyping. Genome DNA was tested for mutations causing an N-acetyltransferase deficiency. Homozygous individuals or those with heterozygous composites for the tested mutations were predicted slow acetylators and those with a homozygous or heterozygous genotype for an allele carrying a normal sequence at the mutation sites were predicted rapid acetylators.

RESULTS

We had 7 complete responses, 1 partial response and 3 failures. Mean delay to efficacy was 7 weeks, longer for lesions involving the scalp (4 to 5 months). Six of the 8 responders were given sulfasalazine exclusively. The effect was suspensive and dose-dependent; the minimal effective dose was 1.5 g/d. Excepting light sensitization requiring discontinuation, there were no clinically significant side effects. Neutropenia occurred in one patient and moderate and transient live enzyme movements did not require treatment withdrawal. The only immunoallergic side effect (light sensitization) observed occurred in a slow acetylator. All responders except one were rapid acetylators.

DISCUSSION

Salazosulfapyridine, or sulfasalazine, is composed of a derivative of 5-aminosalicylic acid and a sulfamide fraction, sulfapyridine. It is only marginally used in dermatology except for psoriasis. Its efficacy in chronic lupus erythematosus has been reported in one case. We confirmed the role of this compound in the treatment of chronic lupus erythematosus. The rare observations of induced lupus and development of antinuclear antibodies are not a contraindication, but require close regular clinical and biological surveillance. The potential risk is that possible hypersensitivity could lead to reserving sulfasalazine for severe resistant chronic lupus erythematosus after failure with antimalarials and thalidomide. Nevertheless, our study demonstrates that the slow acetylator phenotype predicts immunoallergic events, as observed by other authors, and would be a factor predicting nonresponse. If these results are confirmed by other studies, it would be possible to propose sulfasalazine as a treatment for discoid lupus erythematosus in rapid acetylators.

Genetic analysis of the cytochrome P450 CYP2D6 polymorphism in patients with systemic lupus erythematosus

Previous reports of an association between the polymorphic cytochrome P450 CYP2D6 and systemic lupus erythematosus are conflicting. Following the elucidation of the molecular basis of the CYP2D6 genetic polymorphism, we re-examined the hypothesis of an association of this gene with a susceptibility to system lupus erythematosus by analysing the complete CYP2D6 coding sequence. For this purpose, we studies the occurrence of 16 mutations in genomic DNA from 69 systemic lupus erythematosus patients and a large control group using a previously described polymerase chain reaction-single strand confirmation polymorphism analysis. In addition, we studied the occurrence of 11 alleles and 21 genotypes in the same individuals by the combined use of restriction fragment length polymorphism and allele-specific polymerase chain reaction followed by polymerase chain reaction-single strand confirmation polymorphism analysis. No significant differences in the distribution of overall genotypes and predicted phenotypes were observed between system lupus erythematosus patients and controls. The only new finding of our study is the higher frequency of one non functional allele, namely the CYP2D6*4A, in systemic lupus erythematosus versus control individuals (P = 0.007). This increased frequency was not statistically significant in multiple comparison analysis and was not related to any specific clinical features of systemic lupus erythematosus. These results suggest that CYP2D6 genotype as well as CYP2D6 phenotype are not determinant of susceptibility to systemic lupus erythematosus but the presence of the inactive CYP2D6*4A allele may be a contributory factor.

Cytochrome P450 CYP2D6 gene polymorphism and lung cancer susceptibility in Caucasians

Many studies have been performed in an attempt to establish a link between the polymorphism of the cytochrome P450 CYP2D6 gene and the incidence of lung cancer. Nevertheless, whether or not this genetic polymorphism has a role in the development of the disease remains unclear. Recently, new advances in our knowledge of the CYP2D6 gene and its locus (CYP2D) have been achieved. In particular, CYP2D6 was found to be highly polymorphic and multiple novel mutations and allelic variants of the gene have been identified. In addition, a number of CYP2D rearrangements, including those with amplification of the gene, have been demonstrated. Taking this new information into account, we have reconsidered the potential influence of CYP2D6 polymorphism in lung cancer susceptibility by performing a comparative analysis of the overall mutational spectrum of CYP2D6 and of the rearrangements of CYP2D in 249 patients with lung cancer and in 265 control individuals matched on age, sex, hospital and residence area. For this purpose, a strategy based on SSCP analysis of the entire coding sequence of CYP2D6 and on RFLP analysis of the gene locus was carried out in DNA samples from each individual. Forty mutations occurring in various combinations on 42 alleles of the gene and 82 different genotypes were identified. No significant difference in the distribution of the mutations, alleles or genotypes was observed between the two groups, except a particular genotype (CYP2D6*1A/*2), which was more common in the sub-group of moderate smokers (< 30 pack-years) suffering from small cell carcinoma (Odds Ratio (OR) 3.6, 95% CI 1.1-11.9). When the phenotype was predicted according to genotype, only a trend toward a higher frequency of ultrarapid metabolizers in patients was obtained. In spite of a complete analysis of the CYP2D6 gene and its locus, this case-control study provides elements against an influence of the CYP2D6 polymorphism on lung cancer susceptibility.

Evidence for CYP2D6 expression in human lung

The cytochrome P450 CYP2D6 gene (CYP2D6) expression was examined in samples from human bronchial mucosa and lung parenchyma using reverse transcription-polymerase chain reaction (RT-PCR) and immunochemistry. Except specimen from a patient previously genotyped as homozygous for a complete deletion of the gene, all tissue samples were positive. When compared to that in the liver, the mean level of CYP2D6 mRNA was 3-fold lower in bronchial mucosa and 6-fold lower in lung parenchyma. To our knowledge, these data demonstrate for the first time the presence of CYP2D6 protein in human lung. They also indicate that the gene is nonuniformly distributed within this organ. The possibility that CYP2D6 has a role in lung carcinogenesis by locally activating inhaled chemicals should therefore be considered.

Polymorphism of the cytochrome P450 CYP2D6 gene in a European population: characterization of 48 mutations and 53 alleles, their frequencies and evolution

The polymorphic cytochrome P450 CYP2D6 is involved in the metabolism of various drugs of wide therapeutic use and is a presumed susceptibility factor for certain environmentally-induced diseases. Our aim was to define the mutations and alleles of the CYP2D6 gene and to evaluate their frequencies in the European population. Using polymerase chain reaction-single strand conformation polymorphism analysis, 672 unrelated subjects were screened for mutations in the 9 exons of the gene and their exon-intron boundaries. A total of 48 point mutations were identified, of which 29 were novel. Mutations 1749 G-->C, 2938 C-->T and 4268 G-->C represented 52.6%, 34.3% and 52.9% of the mutations in the total population, respectively. Of the eight detrimental mutations detected, the 1934 G-->A, the 1795 Tdel and the 2637 Adel accounted for 65.8%, 6.2% and 4.8% respectively, within the poor metabolizer subgroup. Fifty-three different alleles were characterized from the mutation pattern and by allele-specific sequencing. They are derived from three major alleles, namely the wild-type CYP2D6*1A, the functional CYP2D6*2 and the null CYP2D6*4A. Five allelic variants (CYP2D6*1A, *2, *2B, *4A and *5) account for about 87% of all alleles, while the remaining alleles occur with a frequency of 0.1%-2.7%. These data provide a solid basis for future epidemiological, clinical as well as interethnic studies of the CYP2D6 polymorphism and highlight that the described single strand conformation polymorphism method can be successfully used in designing such studies.

NAT2 genotyping and efficacy of sulfasalazine in patients with chronic discoid lupus erythematosus

Sulfasalazine is an effective agent for chronic discoid lupus erythematosus (CDLE) but the response to treatment is considerably variable between patients and is also unpredictable. The reason for this might relate to differences in metabolism of the drug which is extensively acetylated by the polymorphic enzyme N-acetyltransferase 2 (NAT2). To test this possibility, the N-acetylation phenotype of eleven patients with CDLE and treated by standard doses of sulfasalazine was retrospectively determined by genotyping. A clear-cut difference in the outcome of treatment was observed according to whether the patients were slow acetylators (SA) or rapid acetylators (RA). Eight out of 11 patients responded to treatment with a complete or marked remission of the disease. Seven of them were RA. The three other patients who did not respond at all to the drug were SA. In addition, SA seem to be more prone to toxic events. These findings strongly suggest that the genetic polymorphism of NAT2 is responsible for differences in the response to sulfasalazine in patients with CDLE. Therefore, candidates for sulfasalazine therapy should be genotyped to identify those patients who might benefit from the drug.

Influence of a mutation reducing the catalytic activity of the cytochrome P450 CYP2D6 on lung cancer susceptibility

The possible association between lung cancer and the CYP2D6*9 mutant allele, which reduces the catalytic activity of cytochrome P450 CYP2D6, was examined by PCR-SSCP using peripheral blood DNA from 249 cases of lung cancer and 265 controls, with detailed data on smoking. The CYP2D6*9 mutant allele was present in 4.9% of controls and 6% of cases. Adjusted for age, hospital and smoking, the odds ratio (OR) of lung cancer associated with the presence of the CYP2D6*9 mutant allele was 1.2 [95% confidence interval (CI) 0.5-2.9]. According to histological type, adenocarcinoma and small cell carcinoma were not associated with the presence of the CYP2D6*9 mutant allele and a non-significant higher occurrence of the mutant allele was observed for squamous cell carcinoma (OR 1.74, 95% CI 0.6-4.8). Moreover, no associations were observed upon stratification by number of pack-years of cigarette smoking. These results do not confirm an earlier report that this CYP2D6*9 mutant allele may be an additional risk factor for the development of lung cancer.

Nomenclature for human CYP2D6 alleles

To standardize CYP2D6 allele nomenclature, and to conform with international human gene nomenclature guidelines, an alternative to the current arbitrary system is described. Based on recommendations for human genome nomenclature, we propose that alleles be designated by CYP2D6 followed by an asterisk and a combination of roman letters and arabic numerals distinct for each allele with the number specifying the key mutation and, where appropriate, a letter specifying additional mutations. Criteria for classification as a separate allele and protein nomenclature are also presented.