摘要:

Hydroxyl radical‐induced DNA base lesions of guanine and adenine were originally found in neoplastic and microscopically normal livers of fish exposed to environmental carcinogens. They were later identified in a mammalian tissue—the cancerous female breast. This evidence suggested that the base lesions are broadly present in the cancerous and microscopically normal tissues of a variety of eukaroytic organisms. The base lesion concentrations in both neoplastic tissues frequently exceeded 1 modified base in 1000 normal bases. By contrast, the base lesion:normal base ratios in healthy tissues were generally 10–100 times less. A greater variety of base lesions was found subsequently in the cancerous lung, brain, and other human tissues, although information relating to their biological significance is largely confined to the originally found purine derivatives. The biochemistry of the base lesions and the relationship of ring‐opening (Fapy) derivatives to OH adducts in the DNA of normal and cancerous tissues is discussed with regard to the etiology of cancer and the potential use of the lesions as biomarkers for cancer risk assessment.

ISSN:0098-4108    

DOI:10.1080/15287399309531792

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Activation of gene transcription by radiation has been recently demonstrated in vitro. However, little is known on the specificity of these alterations on gene transcription. Prenatal irradiation is a known teratogen that affects the developing mammalian central nervous system (CNS). Altered neuronal migration has been suggested as a mechanism for abnormal development of prenatally irradiated brains. Fibronectin (FN), an extracellular glycoprotein, is essential for neural crest cell migration and neural cell growth. In addition, elevated levels of FN have been found in the extracellular matrix of irradiated lung. To test whether brain FN is affected by radiation, either FN level in insoluble matrix fraction or expression of FN mRNA was examined pre‐ and postnatally after irradiation. Mice (CD1), at 13 d of gestation (DG), served either as controls or were irradiated with gamma rays at 0.5 or 1 Gy. Control and irradiated animals were killed either at 13 DG, 14 DG, 17 DG, or 5, 6, or 14 d postnatal. Brain and liver were collected from offspring and analyzed for either total FN protein levels or relative mRNAs for FN and tubulin. Results of prenatal irradiation on reduction of postnatal brain weight relative to whole body weight and morphological reduction in cerebral cortex regions of postnatal brains are comparable to that reported by others. Insoluble matrix fraction (IMF) per gram of brain, liver, lung, and heart weight was not significantly different either between control and irradiated groups or between postnatal stages, suggesting that radiation did not affect the IMF. However, total amounts of FN in brain IMF at 17 DG were significantly different (p < .02) between normal (1.66 ± 0.80 μg) and irradiated brains (0.58 ± 0.22 μg). FN mRNA was detectable at 13, 14, and 17 DG, but was not detectable at 6 and 14 d postnatal, indicating that FN mRNA is developmentally regulated. After 0.5 Gy of irradiation, expression of FN mRNA was reduced to 36% ± 22% (1 h), 52% ± 10% (1 d), and 76% ± 10% (4 d) of the control level. After 1 Gy of irradiation, relative FN mRNA was 62% ± 28% (1 h) and 75% ± 3% (4 days) to the control level, respectively. This reduction was comparable to that reported by others for the cytoskeletal protein β‐actin. In contrast, mRNA for tubulin, another cytoskeletal protein, increased at 1 h after irradiation but then approached normal postnatally. The longer lasting alteration of FN may be more directly related to neural development, particularly if the reduction in FN is nonuniform.

ISSN:0098-4108    

DOI:10.1080/15287399309531793

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Chromosome aberration frequency provides the most reliable biological marker of dose to detect acute accidental radiation exposure. Significant radiation‐induced changes in the frequency of chromosome aberrations can be detected at very low doses (Lloyd et al., 1992). In animal studies chromosome aberrations provide a method to relate exposure to cellular dose. Using an in vivo/in vitro approach, aberrations provided a biological marker of dose from radon progeny exposure, which was used to convert exposure, work level months (WLM) to dose in grays (Gy) delivered to rat tracheal epithelial cells. Injection of Chinese hamsters with144Ce, which produced a low‐dose rate exposure of bone marrow to low‐linear energy transfer (LET) radiation, increased the cell sensitivity for the induction of chromatid exchanges by subsequent external60Co exposure. Our paper provides information on using molecular chromosome probes to “paint” chromosomes and score chromosome damage. This approach illustrates how technical advances make it possible to understand the mechanisms involved in the formation of chromosome aberrations. These studies demonstrate the usefulness of chromosome damage as a biological marker of dose and cellular responsiveness.

ISSN:0098-4108    

DOI:10.1080/15287399309531794

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Cytochromes P‐450 (P‐450s) are a large group of heme‐containing proteins that carry out oxidation of numerous chemicals. In mammals, a limited number of P‐450s are involved in metabolic pathways of steroid synthesis, while most of these enzymes are involved in metabolism of foreign compounds. The principal beneficial function of P‐450s is to convert chemicals into derivatives that can be easily eliminated from the body. This generally occurs through P‐450‐mediated oxidations of hydrophobic substances followed by conjugation reactions. For many foreign compounds, P‐450 metabolism results in production of “activated” metabolites that can cause cell death and gene mutations. During the past several years, it has become widely recognized that marked species differences occur among the foreign compound‐metabolizing P‐450s. In addition to this interspecies variability in metabolism, marked intraspecies variability, frequently referred to as drug oxidation polymorphisms, occurs in virtually all mammals examined to date. Based on these observations, it is necessary to develop new human P‐450‐based systems that can be used to study foreign compound metabolism in order to predict human risk. This is being accomplished by use of cDNA‐directed expression in B lymphoblastoid cells. These cells can be used to predict how humans will metabolize a chemical and whether it will be metabolically activated to a toxic or mutagenic metabolite. To study human P‐450 polymorphisms, polymerase chain reaction (PCR) assays have been developed for diagnosis of known mutant P‐450 genes. Molecular probes are also being used to screen populations for levels of expression of carcinogen‐activating P‐45Os in an effort to determine whether expression of certain P‐450 forms is associated with increased risk for development of environmentally based disease.

ISSN:0098-4108    

DOI:10.1080/15287399309531795

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A comparative study of human CYP1A1 genotypes and enzymatic activity was performed in a racially diverse population in order to determine frequencies of CYP1A1 genetic polymorphisms and the relationship between CYP1A1 genotype and function. Restriction fragment length polymorphism analyses revealed significantly higher frequencies of a variant Msp1 polymorphism in Asians versus European‐Americans, while African‐American CYP1A1 genotypic frequencies more closely approximated those of Asians. Comparison of CYP1A1 genotypes at the Msp1 locus to a polymorphic site in exon 7 of the gene revealed a higher frequency of variant genotypes at the Msp1 site. Measurement of lymphocyte CYP1A1 enzyme activity by the ethoxyresorufin O‐deethylase assay revealed significantly elevated levels of inducible enzyme activity among variant exon 7 genotypes when compared to wild‐type genotypic individuals. These results demonstrate racially distinct patterns of CYP1A1 genotypes, and suggest a functional link between genotype and catalytic activity of the cytochrome P‐450 protein responsible for the metabolism of many carcinogenic polycyclic aromatic hydrocarbons.

ISSN:0098-4108    

DOI:10.1080/15287399309531796

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The central nervous system is an important potential target for certain environmental pro‐toxins, but relatively little is known regarding brain‐specific expression of biotransforma‐tion enzyme systems. We undertook the present study to identify regional and cellular expression patterns of individual cytochrome P‐450 genes (CYP) and microsomal epoxide hydrolase (mEH) in human brain. Various regions of normal human brain were isolated and examined with respect to mRNA levels of CYP1A1, CYP1A2, CYP2E1, CPY3A, and mEH, using specific oligomer probes and reverse transcriptase‐coupled polymerase chain reaction analysis. We also used immunohistochemical techniques, with antipeptide‐derived antibodies, to identify specific cells from various regions of the human brain producing CYP1A1 and mEH protein. Relatively equivalent mRNA expression levels of mEH were detected in the cerebellum (C), frontal (F), occipital (O), pons (P), red nucleus (RN), and substantia nigra (SN) regions of brain. The mRNA expression patterns of CYP2E1 and CYPIA2 were similar; although detected in all brain regions examined, the RN and SN exhibited lower levels of CYP2E1 and CYP1A2 mRNA expression compared to other regions. In addition, regional differences in CYP3A and CYP1A1 mRNA expression also were observed, with the highest level of CYP3A mRNA present in the P region compared to the C, F, O, and RN, while no CYP3A mRNA was detected in the SN. CYP1A1 mRNA expression was evident in all brain regions, but the levels of CPY1A1 mRNA in the P and RN were lower than in the C, F, O, and SN. In all cases, the regional mRNA expression levels of these CYP and mEH mRNAs were less than the corresponding levels detected from the same individual's liver. CYP1A1 and mEH immunoreactivity was present in most neurons of the SN, RN, P, median raphae, locus ceruleus, inferior vestibular nucleus, dorsal motor nucleus of the vagus, and thalamus. Some but not all astrocytes within these regions also demonstrated 1A1 and mEH immunoreactivity. These results indicate that many neurons and astrocytes express mEH and CYP1A1 as well as other CYP genes, and suggest that localized biotransformation events within the certain central nervous system may account for toxicities initiated by exposure to certain environmental chemicals.

ISSN:0098-4108    

DOI:10.1080/15287399309531797

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A number of lines of evidence suggest that serum paraoxonase is protective against poisoning by organophosphorus substrates of this enzyme. Birds that have very low levels of paraoxon hydrolyzing activity in their sera are very susceptible to parathion poisoning. Rabbits, which have a sevenfold higher enzyme level compared with rats, have a fourfold higher resistance to paraoxon poisoning than rats. Rabbit paraoxonase hydrolyzes chlorpyrifos‐oxon with a much higher turnover number than does rat paraoxonase, resulting in a very high resistance of rabbits to chlorpyrifos toxicity. Direct tests of paraoxonase protection have been carried out by injecting purified rabbit enzyme into rats. The protection achieved was higher for chlorpyrifos‐oxon than for paraoxon, probably due to the high hydrolytic activity of the rabbit enzyme for chlorpyrifos‐oxon. In humans, a substrate‐dependent polymorphism of serum paraoxonase is observed, where one isoform of paraoxonase has a high turnover number for paraoxon and the other a low turnover number. Both isoforms appear to hydrolyze chlorpyrifos‐oxon and phenylacetate at the same rate. Cloning and sequencing of the human paraoxonase cDNAs has elucidated the molecular basis of the polymorphism. Arginine at position 192 determines high paraoxonase activity, and glutamine at this position, low paraoxonase activity. In addition to the polymorphism, a 13‐fold variation in serum enzyme levels within a given genetic class is seen. The experiments reported here demonstrate that rabbit paraoxonase injected into mice provides protection against the parent insecticide chlorpyrifos as well as the toxic oxon. These results suggest that serum paraoxonase status may serve as a biomarker for insecticide susceptibility in humans.

ISSN:0098-4108    

DOI:10.1080/15287399309531798

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0098-4108    

DOI:10.1080/15287399309531799

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Here we describe new techniques that employ fluorescence in situ hybridization (FISH) with centromeric and chromosome‐specific DNA probes to detect aneuploidy and micronucleus formation in exfoliated human epithelial cells. Micronuclei arise from chromosome breakage or lagging, which results in chromosome fragments and whole chromosomes being left outside of the main nucleus at telophase. By using a centromeric DNA probe to detect the presence of whole chromosomes in micronuclei and propidium iodide as a general DNA stain in exfoliated nasal, buccal, and bladder cells, we have developed a new fluorescent method that can detect micronuclei and determine the mechanism of formation. The new fluorescent technique gave results that were very similar to those obtained with the standard Feulgen‐fast green method. The spontaneous levels of micronuclei in healthy volunteers were buccal, 0.13%, nasal, 0.21%, and urothelial, 0.07%, in approximately 1500 cells per data point. These values are lower than that found in cultured lymphocytes, 0.4–0.8%. Approximately 50% of the exfoliated cell micronuclei contained whole chromosomes (centromeric DNA). FISH was also used to detect aneuploidy in exfoliated buccal and bladder cells. A DNA probe specific for chromosome 9 was used. Average frequencies for 0, 1,2, 3, and 4 hybridization regions were 4.8, 9.3, 84.8, 0.8, and 0.3% for urothelial cells and 8.2, 9.9, 80.1, 1.4, and 0.4% for buccal cells. The estimated frequency of aneuploidy in exfoliated cells is similar to that found in human lymphocytes analyzed by FISH with the same probe for chromosome 9. These techniques are potentially useful for epidemiological studies of exposed populations and are currently being applied in our laboratory for studies of arsenic‐ and formaldehyde‐exposed populations.

ISSN:0098-4108    

DOI:10.1080/15287399309531800

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The promise of biological markers in occupational health research and practice has been described in the scientific literature. The current generation of biological markers has the potential to allow for the earlier detection of disease, for the reduction of misclassification of exposure and outcome, for heightened understanding of mechanisms and etiologic pathways, and for the designation of groups at risk. What is necessary now is a strategy for realizing this potential. The elements of such as a strategy may include the following: (1) a program to validate biomarkers, (2) increased utilization of valid biomarkers in etiologic and prevention research, and (3) developmental programs to encourage interdisciplinary collaboration and train molecular epidemiologists. A framework for linking bio‐markers and epidemiologic study designs has evolved during the part 5 yr. For this progress to continue, it is important that discussion about biomarkers reflect a specificity with regard to both the type of marker and the use for which it is intended.

ISSN:0098-4108    

DOI:10.1080/15287399309531801

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor