TYMS and DPYD polymorphisms in a Turkish population

Objective: The thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) enzymes affect the outcome of 5-fluorouracil (5-FU)-based chemotherapy. Genetic polymorphisms of the thymidylate synthase (TYMS) and dihydropyrimidine dehydrogenase (DPYD) genes that may affect chemotherapy are described. The aim of this study was to determine the frequencies of TYMS and DPYD polymorphisms in healthy Turkish individuals. Methods: Genotyping analyses of the promoter enhancer region of TYMS (TSER) and the exon 14-skipping mutation of the DPYD (DPYD*2A) genes were conducted in 250 unrelated, healthy volunteers from the central region of Turkey using a PCR-based assay. Results: The distribution of theTSER*2/*2, *2/*3 and *3/*3 genotypes were 17.6%, 48.8%, and 33.6%, respectively. The frequencies of the TSER*2 and *3 alleles in the Turkish population were 0.42 and 0.58, respectively. No individuals with the variant DPYD*2A allele were identified in the study group. Conclusion: The frequency of the TSER*3 allele among members of the Turkish population was similar to frequencies observed in other Caucasian populations but was lower than those found in Japanese and Chinese populations.     

Paraoxonase 1 mutations in a Turkish population.

Human serum paraoxonase 1 (PON1) catalyzes the hydrolysis of certain organophosphate pesticides and nerve gases and so may alter significantly an individual's susceptibility to the toxicity of these chemicals. Moreover, PON1 hydrolyzes lipid peroxides complexed to low density lipoproteins (LDL) and therefore it was suggested that PON1 may be one of the genes that is involved in the pathogenesis of cardiovascular diseases. Its activity shows interindividual and interethnic variability. At least two mutation sites, namely Gln192Arg (Q/R) and Leu55Met (L/M) were reported responsible for the variations in enzyme activity. The aim of the present study was to determine the frequency of these mutations in Turks and compare the results with other European and Oriental populations. A total of 381 unrelated Turkish individuals were genotyped for Gln192Arg and Leu55Met polymorphisms by PCR-RFLP using AlwI and NlaIII, respectively. Genotype distribution was QQ = 0.49, QR = 0.40, RR = 0.11, and LL = 0.52, LM = 0.39, MM = 0.09. Thus frequencies of high activity alleles R (Arg) and L (Leu) were found as 0.31 and 0.72, respectively. The frequency of these alleles was slightly higher in Turkish subjects than other Caucasian populations but much lower compared to Oriental populations.     

Frequency distribution of thiopurine S-methyltransferase alleles in a polish population

Thiopurine S-methyltransferase (TPMT) is an enzyme that catalyzes the S-methylation of thiopurine drugs such as 6-mercaptopurine, 6-thioguanine, and azathioprine. TPMT activity exhibits an interindividual variability mainly a result of genetic polymorphism. Patients with intermediate or deficient TPMT activity are at risk for toxicity after receiving standard doses of thiopurine drugs. It has previously been reported that 3 variant alleles:TPMT*2, *3A, and *3C are responsible for over 95% cases of lower enzyme activity. The purpose of this study was to determine the frequency of TPMT variant alleles in a Polish population. DNA samples were obtained from 358 unrelated healthy Polish subjects of white origin, and TPMT genetic polymorphism was determined using PCR-RFLP and allele-specific PCR methods. The results showed that allelic frequencies were 0.4% for TPMT*2, 2.7% for TPMT*3A, and 0.1% for TPMT*3C, respectively. A TPMT*3B allele was not found in the studied population. The general pattern of TPMT allele disposition in the Polish population is similar to those determined for other white populations, but the frequency of total variant alleles is lower than in other European populations studied to date.     

Interindividual variability of coumarin 7-hydroxylation in a Turkish population

One hundred healthy Turkish volunteers (70 male, 30 female) aged from 19 to 56 years were given 5 mg coumarin p.o. after an overnight fast. Urine samples were collected before and 2, 4 and 8 h after drug administration. The extent and rate of formation of 7-OH-coumarin (7OHC) was determined by the urinary excretion of the metabolite as measured with the fluorometric method.On average, 80% of 7OHC formed was excreted in 2 h. The total amount of 7OHC formed was 59.8% (21.5%) (mean and SD, n=100, range 17–100%) of the given dose. The percentage of 7OHC excreted during the first 2 h compared with the 7OHC excretion at 8 h was a constant and stable individual characteristic for the rate of the formation of 7OHC (2 h coumarin test).Although four individuals had relatively slow coumarin test values (34–40%), no clear-cut polymorphism in the rate of 7OHC formation was found. However, 7OHC formation was lower in males and in cigarette smokers.The scientific contents of this paper contribute to the goals of the COST B1 project.     

Dihydropyrimidine dehydrogenase activity in a Korean population

Dihydropyrimidine dehydrogenase (DPD) is the major metabolic enzyme in the catabolism of 5-fluorouracil, and the activity in normal tissues shows a wide variation among individuals. Recent studies demonstrate the relevance of DPD in the pharmacokinetics, toxicity, and antitumor efficacy of 5-fluorouracil. We investigated the DPD activity in peripheral blood mononuclear cell form 114 healthy subjects in Korea. The DPD activities in healthy volunteers were shown to follow a unimodal distribution. The mean of the activity was 0.28 +/- 0.16 nmol/min/mg protein. A wide (13-fold) intersubject variability was observed (range, 0.06-0.80 nmol/min/mg protein), and, on average, DPD activity in women (0.26 +/- 0.14) was 13% lower than in men (0.30 +/- 0.16). These findings indicate that the activity of DPD in this study was higher than in reports of research with French and white American populations.     

Frequency and enzyme activity of the butyrylcholinesterase K-variant in a Turkish population

Objective Among variants of the butyrylcholinesterase gene (BChE), the K-variant causing Ala539Thr substitution is the most common one associated with about one-third reduction in the enzyme activity. This study aimed to detect the frequency of the K-variant allele in a Turkish population sample and also to evaluate how the plasma BChE activity was influenced by this variant.Methods Patients administered for elective surgery (n=77) were examined for the presence of the K allele. The enzyme activity was determined in plasma.Results The K-variant of BChE is a common allele with a frequency of 0.266 (CI_95% 0.196–0.336) in our sample from a Turkish population. Mean enzyme activity in subjects homozygous for the K-variant was about 40% lower than other subjects.Conclusion The frequency of the BChE K-variant was significantly higher in a Turkish population than those reported for other populations and it is associated with a diminished enzyme activity.     

Frequencies of CYP2D6 mutant alleles in a normal Japanese population and metabolic activity of dextromethorphan O-demethylation in different CYP2D6 genotypes

AIMS: To determine the frequencies of 11 CYP2D6 mutant alleles (CYP2D6*2, *3, *4, *5, *8, *10, *11, *12, *14, *17 and *18), and their relation to the metabolic capacity of CYP2D6 in Japanese subjects. METHODS: One hundred and sixty-two unrelated healthy Japanese subjects were genotyped with the polymerase chain reaction amplification method and 35 subjects were phenotyped with dextromethorphan. RESULTS: The frequencies of CYP2D6*2,*5, *10 and *14 were 12.9, 6.2, 38.6 and 2.2% in our Japanese subjects, respectively. CYP2D6*3, *4, *8, *11, *12, *17 and *18 were not detected. The mean log metabolic ratio of dextromethorphan in subjects with genotypes predicting intermediate metabolizers was significantly greater than that of heterozygotes for functional and defective alleles. CONCLUSIONS: CYP2D6*5 and CYP2D6*14 are the major defective alleles found in Japanese subjects. In addition, CYP2D6*10 may play a more important role than previously thought for the treatment of Japanese patients with drugs metabolized by CYP2D6.     

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 point mutation (T to A) in codon 160 leads to a single amino acid substitution (Leu to His) and the resulting protein, CYP2A*2 is unable to 7-hydroxylate coumarin. Gene conversion in exons 3, 6, and 8 between the CYP2A6 and the CYP2A7 genes creates another variant, CYP2A6*3. In this study, healthy male and female Turkish volunteers (n = 50) were administered 2 mg coumarin, and urine samples were analyzed for their content of the coumarin metabolite, 7-hydroxycoumarin (7OHC), by high-performance liquid chromatography (HPLC). Genetic polymorphism for CYP2A6 was detected by using two-step polymerase chain reaction (PCR) to identify CYP2A6*1, CYP2A6*2, and CYP2A6*3 in 13 of these subjects. The percentage of the dose excreted of total 7OHC in relation to CYP2A6 genotype and excretion of nicotine/cotinine was also evaluated to demonstrate the role of CYP2A6 in nicotine metabolism. The majority of Turkish subjects (68%) excreted less than 60% of the 2-mg dose as coumarin metabolite. The allelic frequencies were detected as 0.88 for CYP2A6*1 allele; 0.12 for CYP2A6*3 allele in 13 individuals. No heterozygous and homozygous individuals were identified for the CYP2A6*2 allelic variant. Phenotyping and genotyping for drug metabolizing enzymes are of great importance in studies correlating precarcinogen activation or drug metabolism to the CYP2A6 genotype in smoking behavior when populations are investigated.     

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. Since, no information is available on inter-individual variability of COMT genotype in Turkish population, we genotyped 217 healthy, unrelated Turkish individuals. The allelic frequencies of COMT gene in the Turkish population were found to be the same as has been observed in Caucasians, but different from Orientals.     

Proguanil metabolism in relation to S-mephenytoin oxidation in a Turkish population

The oxidation of proguanil was studied in 89 unrelated healthy Turkish volunteers after administration of proguanil (single dose, 200  mg, orally). Based on the distribution of the ratio of proguanil to cycloguanil excreted in urine, and using an antimode value of 15, the prevalence of poor metabolizers in a Turkish population was estimated to be 5.6% (95% confidence interval 2.0%–17.3%) which was similar to that in the other Caucasian populations. The relationship between the oxidative capacities of CYP2C19 for the two substrates, proguanil and mephenytoin, was studied in 39 subjects (two poor and 37 extensive metabolizers of proguanil). The two poor metabolizers of proguanil were also identified as poor metabolizers of S-mephenytoin and no misclassification by the two phenotyping methods was observed. The correlation between the metabolic ratio of proguanil to cycloguanil and the S/R-mephenytoin ratio as assessed by Spearman's rank test, was statistically significant ( r _s=0.50, P <0.001).     

XRCC1 Arg399Gln genetic polymorphism in a Turkish population

Humans are routinely exposed to mutagenic and carcinogenic chemicals. These chemicals can form DNA adducts in vivo and thus lead to DNA damage. The integrity of most of the so-damaged DNAs is typically restored as a consequence of the action of certain DNA-repairing enzymes. In several DNA repair genes, polymorphisms may result in reduced repair capacity, which has been implicated as a risk factor for various types of cancer. XRCC1 is a base-excision repair protein that plays a central role in the repair of DNA base damage and strand breaks. Amongst the known genetic polymorphisms of the DNA-repair genes, X-ray repair cross-complementing groups 1 and 3 (XRCC1 and XRCC3) have been studied most commonly. Inconsistent results have been reported regarding the associations between the Arg399Gln (exon 10) polymorphism of XRCC1 and either functional significance or the risk of tobacco-associated cancers. The Gln allele of this polymorphism was associated with higher levels of DNA adducts. Therefore we genotyped one of the polymorphism of XRCC1, Gln allele. The frequency of the polymorphic alleles varies among populations, suggesting an ethnic distribution of genotypes. There has been no information on interindividual variability of Arg399Gln genotype in the Turkish population. Due to the association between the Arg399Gln polymorphism of XRCC1 and the risk of tobacco-associated cancers, we preferred to evaluate the allelic frequencies of Arg399Gln genotype than the other polymorphisms in XRCC1 gene in healthy Turkish population by polymerase chain reaction-restriction fragment polymorphism (PCR-RFLP) analysis to enable to show interindividual differences and compare to other populations.     

CYP2D6 and GSTM1 genotypes in a Polish population

Objective: The aim of the present study was to investigate the distribution of the CYP2D6 and GSTM1 genotypes in a Polish population. Methods: One hundred and forty-five unrelated healthy individuals from the western region of Poland were studied. The CYP2D6 genotype was analysed by means of polymerase chain reaction (PCR) amplification for the CYP2D6 ^* 3 and CYP2D6 ^* 4 alleles. The GSTM1 genotype was also analysed by means of a PCR assay to determine two genotypes: GSTM1-1 (positive) and GSTM1-0 (negative). Results: Fourteen subjects (9.6%) were classified as poor metabolisers. The frequency of CYP2D6 ^* 4 and CYP2D6 ^* 3 was 23.1% and 2.1%, respectively. The frequency of GSTM1 nulled genotype in a Polish population came to 49%. Conclusion: The frequencies of poor metabolisers for CYP2D6 and GSTM1 nulled genotype among a Polish population were similar to those observed in other Caucasian populations. Received: 29 October 1998 / Accepted in revised form: 15 March 1999     

Effect of alcohol and aldehyde dehydrogenase inhibitors on the toxicity of 3-nitropropanol in rats

The nitrocompounds 3-nitropropanol (NPOH) and 3-nitropropionic acid (NPA) were shown to be equally toxic when injected intraperitoneally into male Wistar rats. The LD50 for NPOH was 0.58 mmol/kg and for NPA it was 0.56 mmol/kg. NPOH was rapidly metabolized to NPA but this conversion was suppressed by prior administration of ethanol or 4-methylpyrazole to inhibit alcohol dehydrogenase. Administration of ethanol or 4-methylpyrazole before NPOH protected rats from intoxication. However, if the alcohol dehydrogenase inhibitors were given after the nitroalcohol, toxicity still occurred. Administration of the aldehyde dehydrogenase inhibitor diethyldithiocarbamic acid had little effect on the conversion of NPOH to NPA and did not alter the toxicity of NPOH. It was concluded that NPOH and NPA are equally toxic to rats but that NPOH is toxic due to its being rapidly converted to NPA.     

High frequency of CYP1A1 mutations in a Turkish population

The frequency distribution of four cytochrome P4501A1 (CYP1A1) gene mutations was investigated in 271 Turks from southeast Anatolia by polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) assay. Allelic linkage of those mutations was proven by peptide nucleic acid-mediated PCR clamping. Mutation m1 (T6235C) forming an MspI restriction site in the 3′-flanking region occurred with 18.1% frequency (95% confidence interval 14.9–21.6%), m2 (A4889G) leading to an Ile/Val exchange in exon 7 had a frequency of 8.9% (6.6–11.6%), and m4 (C4887A; Thr/Asn-exchange also in exon 7) occurred with 5.7% (3.9–8.0%). T5639C (m3) in the 3′-flanking region was not detected. m2 was exclusively found linked with m1 forming allele CYP1A1*2B. The frequency of this allele supposedly at-risk for lung cancer was significantly higher than in Middle European populations, but lower than in the Far East. Received: 11 September 1997 / Accepted: 10 October 1997     

Analysis of the dihydropyrimidine dehydrogenase polymorphism in a British population

Subjects with low or absent dihydropyrimidine dehydrogenase activity (DPD) are at risk of excessive toxicity or death when undergoing fluoropyrimidine chemotherapy. The DPD polymorphism has not been well characterized in the general population and the frequency of the enzyme deficiency is not known. In preparation for a population multicentre analysis of DPD activity, a comparison of sample preparation methods and a pilot study in normal volunteer subjects was performed. The stability of peripheral blood mononuclear cell DPD activity at −70°  C was determined in 35 mm sodium phosphate buffer with 10% glycerol, 100% fetal calf serum (FCS) or as a dry pellet. DPD activity declined in FCS and increased in glycerol buffer, both reaching a plateau value 14 days after blood sampling. The glycerol buffer method was then used to study DPD activity in 50 British subjects (36 M:14F; 20–56 years). A 8.4-fold range in DPD activity was observed (30.4–256  pmol min⁻¹  mg⁻¹ protein). DPD activity was not influenced by age or cigarette smoking. This information will facilitate analysis of the DPD polymorphism in populations from different countries and ethnic groups.