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A Weston

Publications and source records attributed to A Weston.

At least 73 records · Page 4Linked to original sources
PubMed1992

Determinants of polycyclic aromatic hydrocarbon-DNA adducts in human placenta.

To determine the relative contributions of tobacco smoking and P-450 metabolism (cytochrome P-450IAI) in the formation of benzo(a)pyrenediol-epoxide and other polycyclic aromatic hydrocarbon-DNA adducts in vivo, 16 human placentas were assayed for aryl hydrocarbon hydroxylase activity and (+/-)r-7,t-8-dihydroxy-c-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene-DN A adduct levels. Immunoaffinity chromatography columns, conjugated with monoclonal antibodies raised against benzo(a)-pyrene-diol-epoxide-deoxyguanosine, were used to concentrate polycyclic aromatic hydrocarbon-DNA adducted nucleotides, and synchronous fluorescence spectroscopy was used specifically to detect r-7,t-8,t-9,c-10-tetrahydroxy-7,8,9,10-tetrahydrobenzo(a)pyrene (BP-tetrol) extracted from acid hydrolysates of immunoconcentrated materials. Data were analyzed for associations with maternal dietary and smoking habits, umbilical cord blood cotinine levels, and placental aryl hydrocarbon hydroxylase levels. Complex mixtures of fluorescent materials were present in organic solvent extracts of acid hydrolysates of immunoconcentrated nucleotide-adducts from all placentas with patterns of fluorescence that may be associated with tobacco smoking determined by generation of spectral fluorescence excitation-emission matrices. BP-tetrols were detected in extracts from 8 placentas: 5 of 7 from smokers and 3 of 9 from nonsmokers. Placental aryl hydrocarbon hydroxylase activity was significantly higher in placentas from which BP-tetrols were extracted [3.9 +/- 2.4 [corrected] (mean +/- SE) pmol 3-hydroxybenzo(a)pyrene mg protein-1 min-1], than among placentas from which BP-tetrols were not extracted (0.4 +/- 0.2 [corrected] pmol 3-hydroxybenzo(a)pyrene mg protein-1 min-1) (P = 0.03, Student's t test). This association was independent of maternal smoking or umbilical cord blood cotinine levels. These results indicate that while maternal tobacco smoking is associated with the accumulation of putative, but as yet unidentified, polycyclic aromatic hydrocarbon-DNA adducts in placenta, metabolic capacity appears to be the principal determinant for the (+/-)r-7,t-8-dihydroxy-c-9,10 epoxy-7,8,9,10-tetrahydrobenzo(a)pyrene-DNA adduct levels detected.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1992

The debrisoquine metabolic phenotype and DNA-based assays: implications of misclassification for the association of lung cancer and the debrisoquine metabolic phenotype.

Debrisoquine is an antihypertensive drug that is metabolized by cytochrome P4502D6. Deficient metabolism is inherited as an autosomal recessive condition. We previously reported in a case-control study that extensive metabolizers of debrisoquine were at greater risk of lung cancer compared to poor and intermediate metabolizers. Cloning of the gene that encodes P4502D6 (CYP2D6) led to the identification of both wild-type and mutant forms of the gene. Subsequently, a DNA-restriction fragment length polymorphism (RFLP) was identified, and a Southern hybridization-based test was developed in an attempt to define the genotype. When the DNA-RFLP test was applied to stored DNA from our study subjects there was neither a significant association with the metabolic phenotype nor an association with lung cancer. Further work has demonstrated that the wild-type gene, which was characterized by a 29-kb allele, can also contain mutations that result in nonfunctional or absent proteins. When these mutations are present, individuals exhibit the poor or intermediate metabolizer phenotype in spite of the presence of the 29-kb putative wild-type allele. Sequence determination of the mutants led to the development of techniques to exploit the polymerase chain reaction, which, together with Southern analysis, have been reported to detect as many as 95% of poor metabolizers. This technique is being used to examine the association of the extensive metabolizer genotype with lung cancer in the subjects from the case-control study. Preliminary results indicate a weak association between the homozygous wild-type genotype and lung cancer; in contrast, the extensive metabolizer phenotype is strongly associated with lung cancer in this subset.(ABSTRACT TRUNCATED AT 250 WORDS)

Case-Control Studies↗
PubMed1992

Polycyclic aromatic hydrocarbon-DNA adducts and the CYP1A1 restriction fragment length polymorphism.

Human cancer risk assessment at a genetic level involves the investigation of carcinogen metabolism and DNA adduct formation. Wide interindividual differences in metabolism result in different DNA adduct levels. For this and other reasons, many laboratories have considered DNA adducts to be a measure of the biologically effective dose of a carcinogen. Techniques for studying DNA adducts using chemically specific assays are becoming available. A modification of the 32P-postlabeling assay for polycyclic aromatic hydrocarbon DNA adducts described here provides potential improvements in quantification. DNA adducts, however, reflect only recent exposure to carcinogens; in contrast, genetic testing for metabolic capacity indicates the extent to which carcinogens can be activated and exert genotoxic effects. Such studies may reflect both separate and integrated risk factors together with DNA adduct levels. A recently described restriction fragment length polymorphism for the CYP1A1, which codes for the cytochrome P450 enzyme primarily responsible for the metabolic activation of carcinogenic polycyclic aromatic hydrocarbons, has been found to be associated with lung cancer risk in a Japanese population. In a subset of individuals enrolled in a U.S. lung cancer case-control study, no association with lung cancer was found.

Blotting, Southern↗
PubMed1992

Relationship of H-ras-1, L-myc, and p53 polymorphisms with lung cancer risk and prognosis.

Proto-oncogenes (H-ras-1 and L-myc) and tumor-suppressor gene (p53) loci have been implicated in lung carcinogenesis. DNA restriction fragment length polymorphisms at these gene loci are being evaluated in a case-control study as markers predictive of risk for cancer or of prognosis when cancer is present. The cases and controls had a cigarette-smoking history of 40 or more pack years or other abnormalities in pulmonary function tests, their ages were closely matched (64 years for cases and 61 years for controls) and the ratio of Caucasians to African Americans was close to unity (cases, 0.95:1.00, controls, 1.00:0.88). The H-ras-1 gene contains an insertion deletion polymorphism. Inheritance of rare H-ras-1 alleles, defined by MspI digestion, confers a relative risk for lung cancer of 2.0 (95% confidence interval, 0.5-7.3) for Caucasians and 3.2 (0.9-11.6) for African Americans (74 cases, 67 controls). The L-myc gene sequence has a restriction site (EcoR1) polymorphism between the second and third exons. Inheritance of restriction site-present alleles was reported to confer poor prognosis (presence of lymph node metastases) in Japanese lung cancer patients. This hypothesis was tested in both case-control study subjects (56 cases, 55 controls) and additional surgical cases (40), but no evidence was found to support the hypothesis in the U.S. population. The p53 gene is a tumor-suppressor gene that can encode either a proline or an arginine in the 72nd residue. No associations was found between the minor allele (proline) and diagnosis of lung cancer (76 cases, 68 controls).(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1991

Measurement of 4-aminobiphenyl-hemoglobin adducts in lung cancer cases and controls.

Hemoglobin adducts of the activated carcinogenic aromatic amine 4-aminobiphenyl have been measured in a case-control study of lung cancer. Data obtained for lung cancer cases are compared to those obtained for controls that consisted of patients with either chronic obstructive pulmonary disease or non-pulmonary cancers. Both simple and multivariate analysis found a positive association of 4-aminobiphenyl-hemoglobin adducts with the quantity of tobacco smoked as determined by either urine cotinine or questionnaire data. No association was found between 4-aminobiphenyl-hemoglobin adducts and cancer diagnosis, and adduct levels were not related to remote tobacco use, i.e., total pack years of smoking. There was no association between the levels of adducts detected and the ability of an individual to metabolize debrisoquine (debrisoquine metabolic phenotype, CYP2D6). Whereas 4-aminobiphenyl-hemoglobin adduct levels reflected recent tobacco smoking, they were not correlated with lung cancer risk.

Aminobiphenyl Compounds↗
PubMed1991

Receptor protein-tyrosine phosphatase gamma is a candidate tumor suppressor gene at human chromosome region 3p21.

PTPG, the gene for protein-tyrosine phosphatase gamma (PTP gamma), maps to a region of human chromosome 3, 3p21, that is frequently deleted in renal cell carcinoma and lung carcinoma. One of the functions of protein-tyrosine phosphatases is to reverse the effect of protein-tyrosine kinases, many of which are oncogenes, suggesting that some protein-tyrosine phosphatase genes may act as tumor suppressor genes. A hallmark of tumor suppressor genes is that they are deleted in tumors in which their inactivation contributes to the malignant phenotype. In this study, one PTP gamma allele was lost in 3 of 5 renal carcinoma cell lines and 5 of 10 lung carcinoma tumor samples tested. Importantly, one PTP gamma allele was lost in three lung tumors that had not lost flanking loci. PTP gamma mRNA was expressed in kidney cell lines and lung cell lines but not expressed in several hematopoietic cell lines tested. Thus, the PTP gamma gene has characteristics that suggest it as a candidate tumor suppressor gene at 3p21.

Animals↗
PubMed1991

Somatic allelic deletion of nm23 in human cancer.

Tumor progression to the metastatic phenotype is accompanied in certain cell types by reduced expression of the nm23 gene. We have localized human nm23-H1 to chromosome 17 by somatic cell hybrid analysis. Regional localization in the CEPH database and in situ hybridization is reported. Somatic allelic deletion of nm23-H1 was observed in human breast, renal, colorectal, and lung carcinoma DNA samples, as compared to DNA from matched normal tissues. A homozygous deletion of nm23-H1 was observed in a lymph node metastasis of a colorectal carcinoma, indicating that nm23-H1 can be recessively inactivated. The data identify nm23-H1 as a novel, independent locus for allelic deletion in human cancer, a characteristic shared with previously described suppressor genes.

Alleles↗
PubMed1991

Racial variation in the distribution of Ha-ras-1 alleles.

Restriction fragment length polymorphism analyses of the Ha-ras-1 proto-oncogene were undertaken in white and black populations residing in the Baltimore-Washington metropolitan area to address whether specific rare alleles of the Ha-ras-1 proto-oncogene locus vary in their distribution among different racial groups. High-molecular-weight genomic DNA samples from the lungs of 80 lung cancer patients and 92 accident victims were digested with appropriate restriction enzymes and subjected to Southern analysis using the 6.6-kb BamHI human Ha-ras-1 recombinant fragment from the plasmid pEC. Thirty allelomorphs of different sizes were detected among the 172 study subjects. An association was observed between race and specific alleles. Rare alleles were more frequent in black cancer patients and trauma victims than in whites. Within each racial category, lung cancer patients had an excess of rare alleles. These data indicate the importance of controlling for racial variation when designing studies to determine human cancer risk factors.

Adult↗
PubMed1991

Fluorescence detection of benzo[a]pyrene--DNA adducts in human lung.

Improved techniques are described for the specific identification of benzo[a]pyrene-diolepoxide (BPDE)--DNA adducts in human tissues. Immunoaffinity chromatography, synchronous fluorescence spectroscopy and second-derivative synchronous fluorescence spectroscopy have previously been used to detect BPDE-DNA adducts in human placenta. Here we report how these methods, together with HPLC and the generation of complete fluorescence excitation--emission matrices, have been used to identify unequivocally BPDE-DNA adducts in samples of human lung. BPDE nucleotide adducts were isolated with immunoaffinity chromatography columns bearing antibodies raised against the (+/-)anti-7,8-diol-9,10-epoxide-deoxyguanosine adduct of benzo[a]pyrene. These adducts were hydrolyzed to tetrahydrotetrols and the hydrolysis products subjected to HPLC. The major product isolated by HPLC, benzo[a]-pyrene-7,10/8,9-tetrahydrotetrol, was determined by fluorescence spectroscopy. Using this method, levels of BPDE-DNA adducts in the range of 1-40 in 10(8) nucleotides were measured in 6 out of 25 samples, with a lower detection limit of one adduct in 10(8) nucleotides. The data may also indicate that adduct levels show regional variation in different parts of the same lung.

Adolescent↗
PubMed1991

Oncogenes and tumor-suppressor genes.

The functional role of oncogenes in human lung carcinogenesis has been investigated by transfer of activated oncogenes into normal cells or an immortalized bronchial epithelial cell line, BEAS-2B. Transfection of v-Ha-ras, Ki-ras, or the combination of myc and raf into BEAS-2B cells produced tumorigenic cell lines, while transfection of raf or myc alone produced nontumorigenic cell lines. In addition to studying the pathogenic role of oncogenes, we are attempting to define negative growth-regulating genes that have tumor-suppressive effects for human lung carcinomas. Our strategy to identify tumor-suppressor genes involves loss of heterozygosity studies, monochromosome-cell fusion, and cell-cell fusion studies. Loss of heterozygosity studies have revealed consistent allelic DNA sequence deletions on chromosome 17p in squamous cell carcinomas, while large cell carcinomas and adenocarcinomas retained this locus. Mutations in p53, a tumor-suppressor gene located on chromosome 17p, have been observed. Cell-cell hybrid clones produced from fusion of nontumorigenic BEAS-2B cells with tumorigenic HuT292DM cells generally are nontumorigenic. The mechanistic role of the known tumor-suppressor genes Rb-1 and p53 in the development of human lung carcinomas is being investigated in this epithelial cell model of human bronchogenic carcinogenesis.

Animals↗
PubMed1991

Role of oncogenes and tumour suppressor genes in human lung carcinogenesis.

Six families of activated protooncogenes, ras, raf, fur, neu, jun and myc have so far been associated with human lung cancer. Human bronchial epithelial cells in vitro are being used to investigate the functional role of these specific oncogenes and growth regulatory genes in carcinogenesis and tumour progression. When transferred into normal human bronchial epithelial cells by the highly efficient protoplast fusion method, the v-Ha-ras oncogene initiates a cascade of events leading to decreased responsiveness of these cells to inducers of squamous differentiation, aneuploidy and, less frequently, 'immortality' and tumorigenicity with metastasis in athymic nude mice. Transfection of the SV40 T antigen gene results in nontumorigenic cell lines that have a nearly normal pathway of terminal squamous differentiation and can be transformed into malignant cells by transfected Ha-ras, N-ras or Ki-ras. The combination of transfected c-myc and c-raf-1 also transforms human bronchial epithelial cells into neoplastic cells that exhibit some phenotypic traits found in small-cell carcinomas. These and other results indicate that proto-oncogenes dysregulate the pathways of growth and differentiation of human bronchial epithelial cells and play an important role in human carcinogenesis. Analyses of allelic deletion and somatic cell hybrids are being used to identify the chromosomal localization of tumour suppressor genes. We have examined 54 non-small-cell bronchogenic carcinomas with 13 polymorphic markers. Loss of heterozygosity was more frequent than among 23 squamous-cell carcinomas than among 23 adenocarcinomas or eight large-cell carcinomas. Loss of heterozygosity for chromosome 17p was found in 89% of cases of squamous-cell carcinoma and 18% of adenocarcinomas. Analysis of chromosome 11 for allelic deletions revealed two commonly deleted regions (11p13 and 11p15.5). Somatic cell hybrids between normal human bronchial epithelial cells and Hut292DM, a lung carcinoma cell line, had a finite lifespan in vitro and were nontumorigenic in athymic nude mice. Tumour suppressive effects of individual or combinations of specific human chromosomes on Hut292DM are being examined by formation of microcell-cell hybrids. Chromosome 11 has tumour suppressor activity in these hybrids. Both of these studies suggest that tumour suppressor genes play a dominant role in lung carcinogenesis and provide in-vitro model systems for isolating these genes by subtraction library and insertional mutagenesis techniques.

Bronchi↗
PubMed1991

Biochemical and molecular epidemiology of cancer.

Examples of practical approaches to molecular epidemiology of human cancer are described. Biomarkers of carcinogen exposure or inherited host factors for cancer susceptibility are discussed. Major advances have been made in the detection of carcinogenmacromolecular adducts through the use of high performance liquid chromatography, immunoaffinity chromatography, the 32P-postlabeling assay, enzyme immunoassays, gas chromatography/mass spectroscopy and synchronous spectrophotofluorimetry. The polycyclic aromatic hydrocarbon-DNA adducts are the most extensively studied in this field and together with antibodies to these adducts found in human serum, they have become useful indicators of exposure to carcinogens. Assays for various kinds of alkyl-DNA adducts have also been developed and the presence of these adducts have been documented in human tissues. Carcinogen-protein adducts have proven to be useful molecular dosimeters of carcinogen exposure. For example, 4-aminobiphenyl hemoglobin adducts are highly correlated with exposure to tobacco smoke. The study of the molecular aspects of interindividual differences in the metabolism and activation of xenobiotics and other genetic markers [DNA-restriction fragment length polymorphisms (RFLPs), mutations, and functional loss of specific genes in carcinogenesis] is an emerging new field that is discussed in the context of genetic susceptibility to cancer. The cytochrome P450 phenotypes and acetylation phenotype are examples of genetic markers that indicate an individual's potential for metabolism of exogenous substances. Further, inherited genetic polymorphic markers, e.g., DNA-RFLPs at protooncogene loci (HRAS-1 and L-myc) have been examined in a case-control study of lung cancer. Data concerning mutations of protooncogenes (H-, K-, and N-RAS) and tumor suppressor genes (retinoblastoma and p53 genes) in various common cancers are providing evidence of multiple genetic lesions that occur during the multistage process of carcinogenesis.

Biomarkers↗
PubMed1991

DNA adduct determination in humans.

Carcinogen-DNA adduct formation, presumed to constitute tumorigenic initiation, provides irrefutable evidence of exposure and some indication of biologically effective dose to target tissues. Carcinogen-DNA adducts, representing a broad spectrum of chemical and physical insult, have been measured in humans using a variety of recently-developed, highly sensitive techniques. Evaluation of the results of these assays relies on detailed understanding of the strengths and weaknesses of the assays themselves. This review is primarily focussed on the application of immunoassays and 32P-postlabeling for human DNA adduct monitoring. Purification of adducts by high performance liquid chromatography or immunoaffinity chromatography, and structural determination by chemically-specific procedures such as synchronous fluorescence spectrometry and gas chromatography/mass spectrometry are also described. In addition, studies in which human DNA adduct dosimetry has been achieved are presented and evaluated.

Carcinogens↗
PubMed1990

Combined high-performance liquid chromatography/32P-postlabeling assay of N7-methyldeoxyguanosine.

A highly sensitive and specific assay for the detection of N7-methyl-2'-deoxyguanosine (N7methyldG) has been developed by combining high-performance liquid chromatography, 32P-postlabeling, and nucleotide chromatography. Separation of normal nucleotides and adducts by high-performance liquid chromatography and then combining a portion of 2'-deoxyguanosine to the N7methyldG allows for quantitation using an internal standard. The directly determined molar ratio is not subject to errors in digestion, variable ATP-specific activity, or assumptions in relative adduct-labeling efficiency. The detection limit was one N7methyldG adduct in 10(7) unmodified 2'-deoxyguanosine bases. N7methyldG adducts have been detected in 5 human lung samples in which O6-methyl-2'-deoxyguanosine adducts had been previously determined. The mean ratio of N7methyldG to O6-methyl-2'-deoxyguanosine was determined to be approximately 10. The current assay complements the high-performance liquid chromatography/32P-postlabeling assay for O6-methyl-2'-deoxyguanosine and increases the detection sensitivity of DNA methylated by exogenous alkylating agents.

Adult↗
PubMed1990

Restriction fragment length polymorphism analysis of the L-myc gene locus in a case-control study of lung cancer.

The L-myc DNA-restriction fragment length polymorphism, revealed by EcoRI, has been studied in both a lung cancer case-control framework and a cohort of 40 non-diseased unrelated individuals. No association was found between the L-myc allelic frequencies and disease status, tumor stage or lung cancer histology. A strong association was, however, observed between the L-myc allelic frequencies and ethnic origin (black or white) of the subjects. Among American whites the allelic distribution at the L-myc proto-oncogene locus was almost identical to that previously reported for Japanese subjects. Among the American black population there was a significantly higher frequency of the presence of the polymorphic EcoRI restriction site in the second intron of the L-myc proto-oncogene. These data emphasize the importance of conducting epidemiologic studies that control for ethnic factors and indicate that L-myc EcoRI allelotypes do not appear to be predictive of lung cancer risk or disease status in American blacks and whites.

Alleles↗
PubMed1990

Association of rare alleles of the Harvey ras protooncogene locus with lung cancer.

The hypothesis that rare variable nucleotide tandem repeat alleles of the Ha-ras-1 polymorphism are an inherited predisposing factor in human lung carcinogenesis has been evaluated in an age, race, and smoking matched case-control study. Twenty-three different alleles were identified by their restriction fragment length in DNA isolated from peripheral blood lymphocytes and were categorized into three groups: common; intermediate; and rare. The frequencies of rare alleles in blacks with either squamous cell carcinoma, large cell carcinoma, or small cell carcinoma were found to be significantly higher than those among groups of control subjects that were comprised of chronic obstructive pulmonary disease patients and patients with cancer at sites other than the lung. A similar trend which did not reach statistical significance was observed in whites. These data are consistent with the hypothesis that inheritance of Ha-ras-1 rare restriction fragment length alleles represents a genetic risk factor for some human lung cancers. The biological basis of this observation remains to be clarified, and it is possible that ethnic variations in rare allele frequencies are responsible for the differences noted. However, the data suggest that further evaluation of the Ha-ras-1 polymorphism as a marker of individual lung cancer susceptibility is warranted.

Adenocarcinoma↗