New trends in biological monitoring: application of biomarkers to genetic ecotoxicology.
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Animals↗
Biomedical subjects
L Shugart
Publications and source records attributed to L Shugart.
Pathology and toxicology of beluga whales from the St. Lawrence Estuary, Quebec, Canada. Past, present and future.
An indigenous population of 450-500 beluga whales (Delphinapterus leucas) inhabiting the St. Lawrence Estuary has been exposed chronically for more than 50 years to a complex mixture of industrial pollutants including organochlorinated compounds (OC), polycyclic aromatic hydrocarbons (PAH) and heavy metals. From 1983 to 1990, we have necropsied 45 well preserved carcasses out of a total of 120 beluga whales reported dead over this period. Of these 45 animals, nine were affected by 10 malignant neoplasms. Fifteen animals (33%) were affected by pneumonia. Milk production was compromised in eight of 17 mature females (41%), by inflammatory changes (seven animals) and cancer (one animal) which affected the mammary glands. Opportunistic bacteria were found in pure culture, and/or in significant amounts in at least two organs in 20 belugas (44%). The concentrations of both total PCBs and highly chlorinated PCB congeners were much higher in St. Lawrence animals than in Arctic beluga whales. OC-induced immunosuppression has been repeatedly demonstrated in a wide variety of animal species. Therefore, it is probable that the immune functions of St. Lawrence beluga whales are impaired. Benzo[a]pyrene adducts were detected in 10 of the 11 St. Lawrence beluga whales of which tissues (six livers, 10/11 brains) were analyzed by a method based on HPLC. No such adducts were found in four Arctic animals. Since benzo[alpha]pyrene is one of the most potent chemical carcinogens known to man, these compounds might be responsible for some of the cancers observed in that population. Overall, our findings contrast vividly with those of others who found that cancers are exceedingly rare in free-ranging odontocete populations and that the major causes for mortalities in these populations are bacteria, parasites, and trauma.
Animals↗
Environmental genotoxicity: probing the underlying mechanisms.
Environmental pollution is a complex issue because of the diversity of anthropogenic agents, both chemical and physical, that have been detected and catalogued. The consequences to biota from exposure to genotoxic agents present an additional problem because of the potential for these agents to produce adverse change at the cellular and organismal levels. Past studies in genetic toxicology at the Oak Ridge National Laboratory have focused on structural damage to the DNA of environmental species that may occur after exposure to genotoxic agents and the use of this information to document exposure and to monitor remediation. In an effort to predict effects at the population, community, and ecosystem levels, current studies in genetic ecotoxicology are attempting to characterize the biologic mechanisms at the gene level that regulate and limit the response of an individual organism to genotoxic factors in their environment.
Animals↗
Genetic and molecular ecotoxicology: a research framework.
Participants at the Napa Conference on Genetic and Molecular Ecotoxicology assessed the status of this field in light of heightened concerns about the genetic effects of exposure to hazardous substances and recent advancements in our capabilities to measure those effects. We present here a synthesis of the ideas discussed throughout the conference, including definitions of important concepts in the field and critical research needs and opportunities. While there were many opinions expressed on these topics, there was general agreement that there are substantive new opportunities to improve the impact of genetic and molecular ecotoxicology on prediction of sublethal effects of exposure to hazardous substances. Future studies should emphasize integration of genetic ecotoxicology, ecological genetics, and molecular biology and should be directed toward improving our understanding of the ecological implications of genotoxic responses. Ecological implications may be assessed at either the population or ecosystem level; however, a population-level focus may be most pragmatic. Recent technical advancements in measuring genetic and molecular responses to toxicant exposure will spur rapid progress. These new techniques have considerable promise for increasing our understanding of both mechanisms of toxicity on genes or gene products and the relevance of detrimental effects to individual fitness.
Animals↗
Quantifying adductive modification of hemoglobin from mice exposed to benzo[a]pyrene.
The present work describes a method for the detection of minute amounts of benzo[a]pyrene, as the diolepoxide metabolite, bound covalently to the hemoglobin of erythrocytes isolated from mice previously exposed to the carcinogen. The technique consists of the acid-induced removal of the pyrenyl moiety from the hemoglobin as the strongly fluorescent free tetrols and their isolation by bonded-phase extraction methods and subsequent quantitation by fluorescence/HPLC. With this procedure as little as 5 pg of tetrol can be detected. The assay was used to determine the amount of benzo[a]pyrene-hemoglobin adduct formation in mice bearing a carcinogen-induced fibrosarcoma.
Animals↗
Quantitating exposure to chemical carcinogens: in vivo alkylation of hemoglobin by benzo[a]pyrene.
Mild acid hydrolysis of globin preparations from erythrocytes of mice, previously exposed topically to benzo[a]pyrene (BaP), releases tetrols which are detectable by HPLC/fluorescence analysis. If the mouse is exposed to radiolabelled BaP, radioactivity can be found in the acid-releasable tetrols. Treatment of the globin preparations prior to acid hydrolysis with proteolytic enzymes, but not enzymes that degrade nucleic acids, followed by dialysis, reduces the amount of tetrols that can be detected. Because the procedure used for the isolation of globin preparations from mouse blood precludes the presence of non-covalently bound BaP or its cellular metabolites, it is concluded that prior to acid hydrolysis, the tetrols were covalently attached to the hemoglobin, most probably as a result of the metabolic conversion of the applied carcinogen to the chemically reactive anti-diol epoxide. There is a dose response relationship between the amount of BaP applied to the skin of the mouse and the occurrence, 24 h later, of BaP adducts to hemoglobin, while the adduct, once formed, disappears with a half-life of 6 days. The amount of anti-benzo[a]pyrene diol epoxide (anti-BaPDE) binding to DNA and hemoglobin at various doses of BaP appears to be qualitatively similar.
Alkylating Agents↗
Adduct formation in hemoglobin of the newborn mouse exposed in utero to benzo[a]pyrene.
The administration of benzo[a]pyrene topically to pregnant mice during days 13-17 of gestation results in adduct formation in the hemoglobin of the mother and progeny. Thus, exposure to a total maternal body burden of 500 micrograms of benzo[a]pyrene during the last 5 days before delivery resulted in an average level of 6.35 (+/- 0.70 S.E.M.) pg of anti-diolepoxide metabolite covalently attached per mg of hemoglobin analyzed in the mother and 1.40 (+/- 0.23 S.E.M.) in the newborn animals. These data indicate that benzo[a]pyrene administered to the skin of the mother passed across the placental membrane, either as benzo[a]pyrene or some metabolite(s), and was present in the fetal tissue as the "ultimate" carcinogenic form (anti-diolepoxide metabolite) before binding to the hemoglobin. Concomitant adduct formation in the DNA of the skin with benzo[a]pyrene in the progeny was not observed and was probably due to the small amount of carcinogen applied to the mother. The data obtained, along with previously published results [Toxicology, 34 (1985) 211], suggest the suitability of hemoglobin as a molecular dosimeter for estimating carcinogenic risk to polycyclic aromatic hydrocarbons.
7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
Covalent binding of benzo[a]pyrene diol epoxide to DNA of mouse skin: in vivo persistence of adducts formation.
In the first 9 d after topical application of a single dose of benzo[a]pyrene to the dorsal skin of C3H mice, the half-lives of benzo[a]pyrene diol epoxide-DNA adducts and of DNA were determined to be approximately 5 d. These data indicate that, in proliferating mouse skin, benzo[a]pyrene diol epoxide-DNA lesions are not repaired, but are diluted from the genome at a rate equivalent to DNA turnover (i.e., replication versus degradation). Subsequent to this initial period, benzo[a]pyrene diol epoxide-DNA adduct removal continues, but at a much reduced rate. At 30 d posttreatment with benzo[a]pyrene, approximately 15% of the adducts are still detectable; however, their half-lives had increased to 30 d. Similar experiments with a hairless mouse showed that, although the amount of adduct formation was lower initially, the kinetics of adduct disappearance and persistence were essentially the same as found with the C3H mouse. The data obtained in this work are consistent with the hypothesis that benzo[a]pyrene diol epoxide adducts persist in a subpopulation of skin cells long after their disappearance by DNA turnover would predict.
7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
Examination of adduct formation in vivo in the mouse between benzo(a)pyrene and DNA of skin and hemoglobin of red blood cells.
We are interested in devising techniques which will allow us to measure and quantitate exposure to chemical carcinogens and which eventually can be used in risk analysis with humans. Our recent research with HPLC/fluorescence has demonstrated that we can detect, identify, and quantitate the binding of benzo(a)pyrene (BaP) with DNA of mouse skin. The technique not only allows femtomole amounts of BaPDE associated with DNA isolated from a single mouse skin to be detected using conventional instrumentation, but also establishes the stereochemical origin of the adduct, and has been employed in the investigation reported here to estimate the concomitant binding of BaP to hemoglobin in vivo. The temporal existence of BaPDE/DNA adducts in mouse skin over a 5-week period showed that at 35 days after treatment, approximately 15% of the initial adducts were still detectable even though DNA turnover would predict that they should have been deleted from the genome. The concentration of the major covalently bound adduct, anti-BaPDE/deoxyguanosine, relative to the total BaPDE/DNA adduct population remained essentially constant during the 5-week period. It is known that topically applied BaP is absorbed, metabolized, and excreted by the mouse. Examination of hemoglobin of mouse RBCs 24 hr after BaP treatment revealed covalent adduct formation exclusively via anti-BaPDE. The dose response of adduct binding to hemoglobin and DNA appeared to be similar.
Animals↗
Effect of ellagic and caffeic acids on covalent binding of benzo[a]pyrene to epidermal DNA of mouse skin in organ culture.
The covalent binding of the anti-diol epoxide of benzo[a]pyrene to cellular DNA of mouse skin in organ culture is affected by the presence of ellagic acid in the culture medium. At 10(-4) M, BaPDE /DNA formation is 40% less than that observed when no ellagic acid is present. Caffeic acid, a similar plant phenolic compound, demonstrates no inhibitory effect on BaPDE /formation. The plant phenolic acids do not drastically interfere with the metabolism of benzo[a]pyrene as shown by the BaP-metabolite profiles of the skin or of the culture medium.
Animals↗
Dosimetry of PAH skin carcinogenesis: covalent binding of benzo[a]pyrene to mouse epidermal DNA.
Benzo[a]pyrene (BaP) is metabolized to the chemically reactive anti and syn isomers of the 7,8-diol-9,10-epoxides of BaP (BPDE) which bind covalently to DNA to form DNA/BPDE complexes. Tetrols liberated from the DNA/BPDE complex by acid hydrolysis are easily quantified by h.p.l.c. using fluorescence detection. This approach allows femtomole amounts of BPDE associated with the DNA isolated from a single mouse to be detected using conventional instrumentation. The usefulness of this technique to estimate the interaction of BaP with DNA of mouse skin, both in the intact animal and in organ culture, was investigated. With mouse skin in organ culture it could be demonstrated that: (i) upon a single topical application of 5 micrograms of BaP, binding to DNA occurred via BPDE at a linear rate for up to 65 h, (ii) the amount of binding was dose dependent at concentrations of BaP less than 10 micrograms.
Animals↗
Poly (ADP-ribosylation) in N, N-diethylnitrosamine-treated mice.
1. Liver nuclei isolated from male mice treated with the carcinogen N, N-diethylnitrosamine were examined for the homopolymer poly(adenosine diphosphate ribose) and for the activity of the conjugate polymerase. 2. At all levels of the carcinogen tested, a concomitant increase in both poly(adenosine diphosphate ribose) content and activity of the enzyme were found. 3. Both responses were transitory and dose dependent.
Animals↗
Kinetic studies of Drosophila melanogaster methylthioadenosine nucleoside phosphorylase.
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Adenosine↗
m7guanosine in tRNA of Escherichia coli.
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Escherichia coli↗
Methylthioadenosine nucleoside phosphorylase activity in Drosophila melangoaster.
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Adenosine↗
Escherichia coli tRNA (uracil-5-)-methyltransferase: Inhibition by analogues of adenosylhomocysteine.
Structural analogues of adenosylhomocysteine (AdoHcy) have been tested as inhibitors of a tRNA(uracil-5-)-methyltransferase preparation obtained from Escherichia coli. All analogues tested gave linear competitive inhibition kinetics with adenosylmethionine (AdoMet) as the variable substrate. Comparison of the Ki values obtained leads to the following conclusions concerning the specificity of the AdoMet-AdoHcy binding site on the enzyme: (i) the terminal amino group of the amino acid moiety is necessary for activity; (ii) both a chiral change of the asymmetric carbon atom of homocysteine and the presence of the terminal carboxyl group contribute little towards inhibitory activity; (iii) analogues in which the amino function of the adenyl moiety is modified or substituted are still potent inhibitors; (iv) inhibitor specificity is considerably reduced when adenine is replaced by a pyrimidine base.
Amino Acids↗
Kinetic studies of Escherichia coli transfer RNA (uracil-5-)-methyltransferase.
The kinetic mechanism of a semipurified tRNA (uracil-5-)-methyltransferase (EC 2.1.1.35) preparation obtained from Escherichia coli has been studied at pH 9.0 in the presence and absence of products. The initial velocity and product inhibition patterns are consistent with a random order of addition of adenosylmethionine and transfer RNA to separate and independent binding sites on the enzyme. Values have been determined for the Michaelis and product inhibitor constants.
Escherichia coli↗
Selective methylation: an incorrect hypothesis.
"Selective methylation," a hypothesis proposed to explain the discrepancy found in the degree of methyl deficiency of transfer ribonucleic acid, cannot be explained on the basis of some biological phenomenon.
Cell-Free System↗