Pharmacokinetics and metabolism of ifosfamide in relation to DNA damage assessed by the COMET assay in children with cancer.

The degree of damage to DNA following ifosfamide (IFO) treatment may be linked to the therapeutic efficacy. The pharmacokinetics and metabolism of IFO were studied in 19 paediatric patients, mostly with rhabdomyosarcoma or Ewings sarcoma. Ifosfamide was dosed either as a continuous infusion or as fractionated doses over 2 or 3 days.

Genetic polymorphism of manganese superoxide dismutase (MnSOD) and breast cancer susceptibility.

Within mitochondria, manganese superoxide dismutase (MnSOD) provides a major defence against oxidative damage by reactive oxygen species (ROS). An alanine-9valine (Ala-9Val) polymorphism in the mitochondrial targeting sequence of MnSOD has been described and has recently been associated with risk of human breast cancer. Our present case-control study was performed to explore the association between MnSOD genetic polymorphism and individual susceptibility to breast cancer.

N-acetyltransferase (NAT2) polymorphism and breast cancer susceptibility: a lack of association in a case-control study of Turkish population.

Increased exposure to environmental carcinogens, including several aromatic and heterocyclic amines (HAs), is suspected to be one factor contributing to incidence of breast cancer. The N-acetyltransferase 2 (NAT2) acetylation polymorphism have been associated with a number of drug-induced toxicities and cancer in various tissues, resulting from decreased capacity to activate/deactivate several aromatic amine, hydrazine drugs, as well as HA carcinogens. Ethnic differences exist in NAT2 genotype frequencies, which maybe a factor in cancer incidence.

Cytochrome P450 CYP1B1 and catechol O-methyltransferase (COMT) genetic polymorphisms and breast cancer susceptibility in a Turkish population.

Epidemiological studies indicate that most risk factors for breast cancer are related to reproductive and hormonal factors. Estrogen has been proposed to trigger breast cancer development via an initiating mechanism involving its metabolite, catechol estrogen (CE). Because of the important role of cytochrome P450 1B1 ( CYP1B1) and catechol O-methyltransferase ( COMT) in mammary estrogen and carcinogen metabolism, we examined the CYP1B1 and COMT genes to determine whether genetic variations could account for inter-individual differences in breast cancer.

Catechol-O-methyltransferase (COMT) genetic polymorphism in a Turkish population.

Catechol-O-methyltransferase (COMT) inactivates neurotransmitters, catechol hormones and drugs such as levodopa and methyldopa. A low activity allele has been demonstrated at codon 108/158 of the soluble and membrane-bound COMT, respectively, whereby a G to A transition results in a valine to methionine substitution. Ethnic and inter-individual differences in red blood cell COMT activity have been observed in the different populations studied so far.

Determination of coumarin metabolism in Turkish population.

Cytochrome P450 2A6 is an important human hepatic P450 which activates precarcinogens and oxidizes some drug constituents such as coumarin, halothane, and the major nicotine C-oxidase. Genetic polymorphism exists in the CYP2A6 gene. CYP2A6*1 (wild type) is responsible for the 7-hydroxylation of coumarin.

The effect of fluconazole on cyclophosphamide metabolism in children.

Fluconazole is increasingly used in children receiving chemotherapy. Many of these patients are being treated with cyclophosphamide, which must undergo hepatic metabolism to produce active alkylating species. As a consequence of the cytochrome P-450 inhibitory properties of fluconazole, a potential interaction exists between these two agents that could influence the therapeutic effect of cyclophosphamide.

Lack of association between the dopamine D2 receptor gene allele DRD2*A1 and cigarette smoking in a United Kingdom population.

The dopamine D2 receptor gene contains a TaqI repeat fragment length polymorphism creating two alleles DRD2*A1 and DRD2*A2. It has been previously suggested that the lesser allele, DRD2*A1, is more prevalent in individuals who are susceptible to impulsive/addictive/compulsive behaviour, for example, alcoholics, polysubstance abusers and tobacco smokers. We genotyped a series of 104 smokers and 117 non smokers and compared the allele frequencies between the groups.

Variability of coumarin 7- and 3-hydroxylation in a Jordanian population is suggestive of a functional polymorphism in cytochrome P450 CYP2A6.

Objective: To determine the variability of coumarin 7- and 3-hydroxylation in a human population and to evaluate the evidence for the existence of genetic polymorphism in these pathways. 7-Hydroxylation of coumarin is considered to be a detoxication pathway, whilst 3-hydroxylation, which predominates in rats, leads to hepatotoxicity in the rat. Coumarin metabolic phenotypes could aid in refining the risk evaluation for humans of dietary and environmental exposure to coumarin and for the chronic use of coumarin in high doses as a drug to treat lymphoedema and certain cancers.

A single amino acid substitution (Leu160His) in cytochrome P450 CYP2A6 causes switching from 7-hydroxylation to 3-hydroxylation of coumarin.

Human populations are thought to metabolize coumarin almost exclusively by 7-hydroxylation. We have identified an individual who is homozygous for a single amino acid substitution (Leu160His) in the cytochrome P450 CYP2A6 arising from the variant CYP2A6*2 allele. On administration of coumarin (2 mg orally) no detectable 7-hydroxycoumarin was excreted in the 0-8-hr urine, rather, approximately 50% of the dose was eliminated as 2-hydroxyphenylacetic acid, the end-product of coumarin 3-hydroxylation.

Trimethylamine N-oxidation in Turkish women with bacterial vaginosis.

Bacterial vaginosis (BV) is the most common cause of vaginal discharge in women of child-bearing age. A common symptom of this condition is a fishy-smelling vaginal discharge. Trimethylamine (TMA) is the substance which is primarily responsible for this distinctive odour.

Automated gas chromatographic assay for amlodipine in plasma and gingival crevicular fluid.

This paper describes an automated capillary gas chromatographic method for the determination of amlodipine in plasma, and in sub-microlitre volumes of gingival crevicular fluid (GCF), in order to assess if amlodipine is present in GCF under conditions of gingival overgrowth, as has been shown for nifedipine, another dihydropyridine drug. Liquid-liquid extraction followed by derivatisation was employed to isolate amlodipine and render it suitable for gas chromatography. Amlodipine was analysed in plasma and GCF of four patients undergoing amlodipine therapy for cardiovascular disorders, three of whom had significant gingival overgrowth.

A genetic polymorphism in coumarin 7-hydroxylation: sequence of the human CYP2A genes and identification of variant CYP2A6 alleles.

A group of human cytochrome P450 genes encompassing the CYP2A, CYP2B, and CYP2F subfamilies were cloned and assembled into a 350-kb contig localized on the long arm of chromosome 19. Three complete CYP2A genes--CYP2A6, CYP2A7, and CYP2A13--plus two pseudogenes truncated after exon 5, were identified and sequenced. A variant CYP2A6 allele that differed from the corresponding CYP2A6 and CYP2A7 cDNAs previously sequenced was found and was designated CYP2A6v2.

The N-oxidation of trimethylamine in a Jordanian population.

The ability to oxidise trimethylamine (TMA) to trimethylamine N-oxide (TMAO) is distributed polymorphically within a British white population with the majority of individuals excreting greater than 90% of total urinary TMA as TMAO. The opposite extreme is characterised by a rare inborn error of TMA N-oxidation known as the fish-odour syndrome. However there is a lack of information regarding inter-individual variability in the N-oxidation of TMA in other ethnic groups.

Genotyping for polymorphisms in xenobiotic metabolism as a predictor of disease susceptibility.

Polymorphisms in many xenobiotic metabolizing enzymes occur leading to variation in the level of enzyme expression in vivo. Enzymes showing such polymorphisms include the cytochrome P450 enzymes CYP1A1, CYP1A2, CYP2A6, CYP2D6, and CYP2E1 and the phase two metabolism enzymes glutathione S-transferase MI (GSTMI) and arylamine N-acetyltransferase 2 (NAT2). In the past, these polymorphisms have been studied by phenotyping using in vivo administration of probe drugs.

Identification of the major human hepatic cytochrome P450 involved in activation and N-dechloroethylation of ifosfamide.

Two NADPH-dependent metabolic routes for the anticancer drug ifosfamide, 4-hydroxylation (activation) and N-dechloroethylation (a detoxication pathway), were studied in human liver microsomes to identify the cytochrome P450 enzymes involved. Naringenin, a grapefruit aglycone and an inhibitor of cytochrome P450 3A4 (CYP3A4)-catalysed reactions, was found to inhibit ifosfamide activation and N-dechloroethylation by human liver microsomes. IC50 for both reactions was of the order of 70 microM.

Metabolic polymorphisms.

Polymorphisms have been detected in a variety of xenobiotic-metabolizing enzymes at both the phenotypic and genotypic level. In the case of four enzymes, the cytochrome P450 CYP2D6, glutathione S-transferase mu, N-acetyltransferase 2 and serum cholinesterase, the majority of mutations which give rise to a defective phenotype have now been identified. Another group of enzymes show definite polymorphism at the phenotypic level but the exact genetic mechanisms responsible are not yet clear.

The pharmacogenetics of chemical carcinogenesis.

The human body is endowed with a large number of xenobiotic chemical metabolizing enzymes, a significant proportion of which are polymorphic and thus render one individual at greater or lesser risk than another of chemically-induced disease. All examples of genetic polymorphism of chemical metabolizing enzymes have been reviewed in relation to their potential to activate and detoxicate procarcinogens and promutagens. Many examples are cited whereby phenotype can act as a carcinogenic risk factor.

The role of individual human cytochromes P450 in drug metabolism and clinical response.

Recent advances in the study of human cytochromes P450 by protein purification, molecular cloning techniques and analysis of polymorphisms has led to increased understanding of the role of the various forms in the metabolism of clinically important drugs. In particular, the substrate specificity of one form, CYP2D6, is well established. CYP2D6 shows polymorphism, with 5-10% of Caucasians (poor metabolizers) not expressing this enzyme.

Mutant debrisoquine hydroxylation genes in Parkinson's disease.

The frequency of fifteen genotypes of CYP2D6 (debrisoquine 4-hydroxylase) in 53 patients with Parkinson's disease was determined by the polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analyses and compared with the findings in 72 healthy controls. The commonest mutant allele, CYP2D6B, was twice as frequent among patients as in controls, with an approximate relative risk ratio of 2.70 (95% confidence interval 1.