Genotype-phenotype correlation for thiopurine S-methyltransferase in healthy Italian subjects

Objective: The aim of the present study was to estimate the concordance rate between erythrocyte thiopurine methyltransferase (TPMT) activity and genotype at the TPMT locus in an Italian population sample. Methods: The TPMT phenotype and genotype were determined in an unrelated population of 103 Italian healthy blood donors. Erythrocyte TPMT activity was measured with a radiochemical assay using 12.5 μM S-adenosyl-L-(methyl-14C)-methionine and 4 mM 6-mercaptopurine. The genotyping assay was based on restriction fragment length polymorphism polymerase chain reaction (RFLP-PCR) and allele-specific oligonucleotide polymerase chain reaction (ASO-PCR) methods. Results: All subjects had detectable TPMT activity. The activity of TPMT varied 2.8-fold between the 5th and 95th percentile. This variation was neither age (P=0.63) nor gender (P=0.44) regulated and the frequency distribution of TPMT activity is compatible with a polymorphic distribution. The presence of the four most common defective alleles, i.e. TPMT*2, TPMT*3A, TPMT*3B and TPMT*3C, was examined through the entire phenotyped population. Ninety-two subjects did not carry any of the tested mutations. Eleven individuals were heterozygous for one of the mutant alleles and had a TPMT activity lower than 30 pmol/min/mg. Eight subjects were TPMT*1/TPMT*3A, two TPMTz.ast;1/TPMTz.ast;3C and one was TPMT*1/TPMT*2. The TPMT*3B allele was not detected in the samples analysed. Conclusion: There was a concordance of 97% between genotype and phenotype. All the heterozygotes had an intermediate phenotype. However, the wide variation range in TPMT activity detected in the wild-type homozygotes indicates that other genetic or epigenetic factors influence the TPMT phenotyp

Inhibition of phenol sulfotransferase (SULT1A1) by quercetin in human adult and foetal livers

Quercetin is a potent inhibitor of human adult and foetal liver SULT1A1. It reduces the sulphation rate and intrinsic clearance of 4-nitrophenol in both human adult and foetal livers. This suggests that quercetin may inhibit the sulfation rate of those drugs sulphated by SULT1A1. The inhibition of SULT1A1 is complex and not due solely to competition at the catalytic site of SULT1A1

Thiol methyltransferase activity in colonocytes and erythrocyte membranes.

AimsTo verify the improved thiol methyltransferase (TMT) assay and measure activity in isolated colonocytes and erythrocyte membranes of the same subjects.MethodsHigh performance liquid chromatography with radioactivity detection was used to measure 14C-methylmercaptoethanol formation, the reaction product of cell extracts incubated with mercaptoethanol and 14C-S-adenosylmethionine.ResultsVerification of radiolabelled 14C-methylmercaptoethanol was by exogenous addition of methylmercaptoethanol and simultaneous ultraviolet detection at 214 nm. Using a substrate concentration of 10 mM mercaptoethanol, the Km for S-adenosylmethionine was 25 microM. The sensitivity of the radioactive method was 2 pmol, with coefficients of variation of 7% within assay and 6.4% between assay. TMT activities (mean +/- SE; n = 17) were 471 +/- 64 pmol/hour/mg protein for colonocytes and 73 +/- 7 pmol/hour/mg protein for erythrocyte membranes.ConclusionsThe direct assay of TMT activity is sensitive, specific and eliminates concern over non-enzymatic methylation of thiol compounds. High activities in colonic epithelial cells deserve evaluation in disease states

CYP2D6-related oxidation polymorphism in Italy

The distribution of the oxidation polymorphism related to cytochrome CYP2D6 (debrisoquine type) was determined in 246 healthy Italian volunteers. Phenotyping was based on HPLC determination of the dextrometorphan/dextrorphan concentration ratio (metabolic ratio) in urine samples collected over an 8 h interval following a single oral 30 mg dose of dextromethorphan hydrobromide. Urinary excretion of dextromethorphan showed a wide interindividual variability, ranging from < or = 0.04 to 3.9% and from 0.5 to 79.6% of the dose, respectively. Metabolic ratios ranged from < or = 0.001 to 6.6. Eleven of the 246 subjects showed a metabolic ratio greater than 0.30, indicating that 4.5% of the population could be ascribed to the poor metabolizer status. The frequency of the poor metabolizer phenotype in this population is within the range described for other Caucasian ethnic groups