Biomedical subjects

Douglas A Bell

Publications and source records attributed to Douglas A Bell.

9 recordsLinked to original sources

PubMed2003

Single amino acid mutations, but not common polymorphisms, decrease the activity of CYP1B1 against (-)benzo[a]pyrene-7R-trans-7,8-dihydrodiol.

Genetic differences that underlie inter-individual variation in the metabolism of common carcinogens are important potential sources of cancer susceptibility. Cytochrome P450 1B1 (CYP1B1), a central enzyme in the activation of the ubiquitous environmental carcinogen benzo[a]pyrene (B[a]P), has several genetic variants. This study investigated six rare mutations and four common polymorphisms for their effects on B[a]P metabolism. Five missense mutations associated with congenital glaucoma (Gly61Glu, Gly365Trp, Asp374Asn, Pro437Leu and Arg469Tryp) dramatically decreased the capacity of CYP1B1 to convert (-)benzo[a]pyrene-7R-trans-7,8-dihyrodiol (B[a]P-7,8-diol) to (+/-)benzo[a]pyrene-r-7,t-8-dihydrodiol-9,10-epoxides. These five mutations resulted in enzymes with 3-12% of normal activity when assayed in vitro using an Saccharomyces cerevisiae microsomal expression system. A 10 bp deletion mutation produced no detectable protein or activity. In contrast, proteins containing all possible combinations of four common single nucleotide polymorphisms (Arg48Gly, Ala199Ser, Val432Leu, Asn453Ser) had modest effects on B[a]P-7,8-diol metabolism. Michaelis-Menten analysis suggested that two alleles, Arg48, Ala119, Val432, Ser453 (RAVS) and Arg48, Ala119, Leu432, Ser453 (RALS), have KM values 2-fold lower than Arg48, Ala119, Val432, Ser453 (RAVN): 1.4+/-0.3 and 1.3+/-0.4 microM, respectively, compared with 2.8+/-0.8 microM (P<0.05). However, these differences could not be confirmed with direct measurements of rate at low substrate concentration. There were no significant differences for either of two other kinetic parameters, kcat or kcat/KM. Allele frequency analysis in three populations reveals the Ser453 variant is rare among those of Asian (<1%) and African ancestry (<4%), and more common in individuals of European ancestry (16%). Haplotypes containing the Ser453 variant were uncommon; only RALS was detectable in our small populations. The RALS allele occurred between 0.5% in Asians and 15% in Europeans. Our study demonstrates that rare, disease-associated mutations in CYP1B1 significantly decrease the enzyme's metabolism of B[a]P-7,8-diol; however, our results do not identify any major differences in this metabolism due to four common single amino acid polymorphisms.

Aryl Hydrocarbon Hydroxylases↗

PubMed2003

Sequence context at human single nucleotide polymorphisms: overrepresentation of CpG dinucleotide at polymorphic sites and suppression of variation in CpG islands.

Human polymorphisms originate as mutations, and the influence of context on mutagenesis should be reflected in the distribution of sequences surrounding single nucleotide polymorphisms (SNPs). We have performed a computational survey of nearly two million human SNPs to determine if sequence-dependent hotspots for polymorphism exist in the human genome. Here we show that sequences containing CpG dinucleotides, which occur at low frequencies in the human genome, are 6.7-fold more abundant at polymorphic sites than expected. In contrast, polymorphisms in CpG sequences located within CpG islands, important regulatory regions that modulate gene expression, are 6.8-fold less prevalent than expected. The distribution of polymorphic alleles at CpGs in CpG islands is also significantly different from that in non-island regions. These data strongly support a role for 5-methylcytosine deamination in the generation of human variation, and suggest that variation at CpGs in islands is suppressed.

5-Methylcytosine↗

PubMed2003

Permanent hair dyes and bladder cancer: risk modification by cytochrome P4501A2 and N-acetyltransferases 1 and 2.

We have previously reported permanent hair dye use to be a significant risk factor for bladder cancer in US women. We also have examined N-acetyltransferase-2 (NAT2) phenotype in relation to the hair dye-bladder cancer relationship, and found that the association is principally confined to NAT2 slow acetylators. In the present study, we assessed the possible modifying effects of a series of potential arylamine-metabolizing genotypes/phenotypes (GSTM1, GSTT1, GSTP1, NAT1, NAT2, CYP1A2) on the permanent hair dye-bladder cancer association, among female participants (159 cases, 164 controls) of the Los Angeles Bladder Cancer Study. Among NAT2 slow acetylators, exclusive permanent hair dye use was associated with a 2.9-fold increased risk of bladder cancer (95% CI = 1.2-7.5). The corresponding relative risk in NAT2 rapid acetylators was 1.3 (95% CI = 0.6-2.8). Frequency- and duration-related dose-response relationships confined to NAT2 slow acetylators were all positive and statistically significant. No such associations were noted among NAT2 rapid acetylators. Among CYP1A2 'slow' individuals, exclusive permanent hair dye use was associated with a 2.5-fold increased risk of bladder cancer (95% CI = 1.04-6.1). The corresponding risk in CYP1A2 'rapid' individuals was 1.3 (95% CI = 0.6-2.7). Frequency- and duration-related dose-response relationships confined to CYP1A2 'slow' individuals were all positive and statistically significant. No such associations were noted among CYP1A2 'rapid' individuals. Among lifelong non-smoking women, individuals exhibiting the non-NAT1*10 genotype showed a statistically significant increase in bladder cancer risk associated with exclusive permanent hair dye use (OR = 6.8, 95% CI = 1.7-27.4). The comparable OR in individuals with the NAT1*10 genotype was 1.0 (95%CI = 0.2-4.3). Similarly, all frequency- and duration-related dose-response relationships confined to individuals possessing the non-NAT1*10 genotype were positive and statistically significant. On the other hand, individuals of NAT1*10 genotype exhibited no such associations.

Adult↗

PubMed2003

Genetic polymorphisms in GSTM1, -P1, -T1, and CYP2E1 and the risk of adult brain tumors.

GST and CYP2E1 genes are involved in metabolism of several compounds (e.g., solvents) that may play a role in brain cancer etiology. We evaluated associations between polymorphisms in these genes and adult brain tumor incidence. Cases were 782 patients with brain tumors diagnosed from 1994 to 1998 at three United States hospitals. Controls were 799 patients admitted to the same hospitals for nonmalignant conditions. DNA was extracted from blood samples that had been collected from 1277 subjects (80% of all subjects; 604 controls; 422 gliomas, 172 meningiomas, and 79 acoustic neuromas), and genotyping was successfully conducted for GSTM1 null, GSTT1 null, GSTP I105V, GSTP A114V, CYP2E1 RsaI, and CYP2E1 Ins96. The GSTP1 105 Val/Val genotype was associated with increased glioma incidence [odds ratio (OR), 1.8; 95% confidence limits (CLs), 1.2, 2.7], with the estimated effect following a trend of increasing magnitude by number of variant alleles (Ile/Ile: OR, 1.0; Ile/Val: OR, 1.3; Val/Val: OR, 2.1). The CYP2E1 RsaI variant was weakly associated with glioma (OR, 1.4; 95% CL, 0.9, 2.4) and acoustic neuroma (OR, 2.3; 95% CL, 1.0, 5.3), with some indication of stronger associations among younger subjects. Estimated effects of the gene variants differed by glioma subtype. There was evidence of supermultiplicativity of the joint effect of GSTP1 I105V and CYP2E1 RsaI variants on both glioma and acoustic neuroma, even following adjustment of estimates toward a common prior distribution using hierarchical regression models. Previously reported associations between the GSTT1 null genotype and overall glioma incidence were not replicated, but an association with meningioma was observed (OR, 1.5; 95% CL, 1.0, 2.3). These findings may provide clues to both genetic and environmental determinants of brain tumors.

Adult↗

PubMed2003

Risk of atherosclerosis: interaction of smoking and glutathione S-transferase genes.

BACKGROUND: Cigarette smoking is a well-known risk factor for not only incident events of coronary heart disease, but also preclinical atherosclerosis. Enzymes including glutathione S-transferase mu (GSTM1) and theta (GSTT1) are involved in the metabolism of tobacco smoke chemicals and are expressed in human vessels and smooth muscle cells. METHODS: We estimated the effect of interaction of smoking with the deletion polymorphisms of GSTM1 and GSTT1 on the risk of carotid artery atherosclerosis. We analyzed a stratified random sample of 1394 individuals from the Atherosclerosis Risk in Communities (ARIC) study, which is a prospective cohort study of 15,792 white and black men and women randomly selected from four U.S. communities between 1987 and 1989. As an index of generalized atherosclerosis, we used carotid artery intimal-medial thickness, as determined by B-mode ultrasound at the baseline or first follow-up examination in asymptomatic individuals. RESULTS: We found a suggestion of an interaction between the functional GSTT-1 genotype (GSTT-1) and heavy smoking. For 20 or more pack-years and GSTT1-1, the odds ratio for increased intimal-medial thickness was 4.7 (95% confidence interval = 1.9-11.8); for 20 or more pack-years and GSTT1-0, 1.7 (0.5-5.5); and for nonsmokers and GSTT1-1, 0.7 (0.3-1.5). We found no interaction between smoking and GSTM1. CONCLUSIONS: The results of this analysis of preclinical atherosclerosis extend reports from the ARIC study of an interaction between smoking and GSTT1-1 in relation to the risk of incident coronary heart disease and lower extremity arterial disease.

Arteriosclerosis↗

PubMed2002

Pooled analysis and meta-analysis of glutathione S-transferase M1 and bladder cancer: a HuGE review.

Smoking is a known risk factor for bladder cancer. The product of the GSTM1 gene, glutathione S-transferase M1 (GSTM1), is involved in the detoxification of polycyclic aromatic hydrocarbons found in tobacco smoke; a homozygous deletion of this gene in approximately 50% of Caucasians and Asians results in a lack of GSTM1 enzyme activity. Most studies examining the relation between bladder cancer and GSTM1 have reported an increased risk associated with a lack of GSTM1 activity. The authors performed meta- and pooled analyses of published and unpublished, case-control, genotype-based studies that examined this association (17 studies, 2,149 cases, 3,646 controls) and excluded studies conducted in populations with a high prevalence of exposure to known bladder cancer risk factors other than tobacco smoke. Using random effects models in the meta-analysis, the authors obtained a summary odds ratio of 1.44 (95% confidence interval (CI): 1.23, 1.68) for GSTM1 null status with all studies included. Results from studies with at least 100 cases and 100 controls produced a summary odds ratio of 1.42 (95% CI: 1.26, 1.60). Pooled analyses using original data sets from 10 studies (1,496 cases and 1,444 controls) and adjusting for age, sex, and race produced similar results. There was no evidence of multiplicative interaction between the GSTM1 null genotype and ever smoking in relation to bladder cancer, although there was a suggestion of additive interaction (additive interaction = 0.45, 95% CI: -0.03, 0.93). These results indicate that, among populations studied to date, GSTM1 null status is associated with a modest increase in the risk of bladder cancer.

Benzo(a)pyrene↗

PubMed2002

XRCC1 polymorphisms and head and neck cancer.

Inter-individual differences in DNA repair capacity have been demonstrated using a variety of phenotypic assays, including reduced repair among patients with squamous cell carcinoma of the head and neck (SCCHN). The XRCC1 DNA repair gene may facilitate DNA strand break and base excision repair. A recent case-control study of SCCHN reported associations with two polymorphisms of the XRCC1 including the exon 6, 194Arg/Arg genotype and the exon 10, 399 Gln/Gln genotype. We conducted an analysis of these two XRCC1 polymorphisms using data from a case-control study of SCCHN. Among white subjects, we found a weak elevation in risk associated with the Arg194Trp polymorphism [odds ratio (OR)=1.3; 95% confidence interval (CI)=0.6-2.9] and a decreased risk for the Arg399Gln polymorphism (OR=0.6; CI=0.4-1.1). We found a markedly decreased odds ratio for the Gln/Gln genotype among whites (OR=0.1; CI=0.04-0.6) and blacks (OR=0.01; CI=0.0004-0.3). We also found a suggestion of an interaction between the Arg194Trp and Arg399Gln polymorphisms and tobacco use. Additional epidemiologic and functional studies are needed to resolve the importance of these XRCC1 polymorphisms in SCCHN.

Adult↗

PubMed2002

Associations between carcinogen-DNA damage, glutathione S-transferase genotypes, and risk of lung cancer in the prospective Physicians' Health Cohort Study.

DNA damage from polycyclic aromatic hydrocarbons (PAH) and other aromatic/hydrophobic compounds has been implicated in case-control studies as a risk factor for lung cancer, as have common polymorphisms in the glutathione S-transferase (GST) genes involved in carcinogen detoxification. However, their joint effects have not been evaluated in prospective studies, leaving open questions about predictive value of these biomarkers. In this matched case-control study nested within the prospective Physicians' Health Study, we evaluated whether biomarkers measured in white blood cells (WBC) significantly predicted risk, alone and in combination, after controlling for level of smoking. The biomarkers reported here are aromatic/hydrophobic-DNA adducts and polymorphisms in genes coding for the GSTM1 and GSTP1 enzymes. Our study population was composed of 89 cases of primary lung cancer and 173 controls, matched in a 1:2 ratio on smoking, age and duration of follow up. Adducts were measured in WBC DNA by the nuclease P1-enhanced (32)P-post-labeling method. Genotypes (GSTM1 null versus non-null and GSTP1 Val versus GSTP1 Ile) were determined by genomic amplification and restriction fragment length polymorphism analysis. Among current smokers, adducts were significant predictors of lung cancer risk (after adjusting for GST genotypes, OR = 3.10, 95% CI 1.07, 9.01). The combined GSTM1 null/GSTP1 Val genotype was associated with lung cancer overall and especially among former smokers, before and after adjusting for adducts (OR for former smokers = 4.21, CI 1.08, 16.41; adjusted OR = 4.68, CI 1.17, 18.71). Among cases only, adducts were significantly higher among current or former smokers with the GSTM1 non-null/GSTP1 Ile genotype. The two risk factors (adducts and genotypes) appear to be independent predictors of risk. The findings underscore the complex and important role of biological susceptibility as a determinant of risk from carcinogens found in tobacco smoke and other environmental compounds.

Biomarkers↗

PubMed2002

XPD codon 751 polymorphism, metabolism genes, smoking, and bladder cancer risk.

Cigarette smoking is the main risk factor for bladder cancer, accounting for at least 50% of bladder cancer in men. Cigarette smoke is a rich source of arylamines, which are detoxified by the NAT2 enzyme and activated by the NAT1 enzyme to highly reactive species that can form bulky adducts on DNA. DNA damage from such adducts is mainly repaired by the nucleotide excision repair pathway, in which the XPD protein functions in opening the DNA helix. We hypothesized that an XPD codon 751 polymorphism (Lys-to-Gln amino acid change) could affect the repair of smoking-induced DNA damage and could be associated with bladder-cancer risk. We also hypothesized that allelic variants of the NAT1 and NAT2 genes might modify the effect of the XPD codon 751 polymorphism on smoking-associated bladder-cancer risk. We determined the XPD codon 751 genotype for 228 bladder-cancer cases and 210 controls who were frequency-matched to cases by age, sex, and ethnicity, and we used our previously published data on the NAT1 and NAT2 genotypes for these same individuals (J. A. Taylor et al., Cancer Res., 58: 3603-3610, 1998). We found a slight decrease in risk for the XPD codon 751 Gln/Gln genotype (adjusted odds ratio: 0.8; 95% confidence interval: 0.4-1.3) compared with subjects with the Lys/Lys or Lys/Gln genotypes. The analysis with smoking showed that smokers with the Lys/Lys or Lys/Gln genotypes were twice as likely to have bladder cancer than smokers with the Gln/Gln genotype (test of interaction P = 0.03). The combined presence of the NAT1/NAT2 high-risk genotype and the XPD Lys/Lys or Lys/Gln genotypes ignoring smoking had an odds ratio that was only slightly higher than expected, assuming no genotype-genotype interaction (P = 0.52). We found little evidence for a gene-gene-exposure, three-way interaction among the XPD codon 751 genotype, smoking, and the NAT1/NAT2 genotype.

Aged↗