ISSN:0270-3211    

DOI:10.1002/tcm.1770010102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractA model system for comparing carcinogen metabolism between human and rat colon has been developed. Tissue explants maintained under chemically defined conditions were treated with radioactively labeled carcinogens. After incubation for 24 hours, the binding of radioactive carcinogen to DNA was quantitated. Further, the carcinogen‐DNA adducts and carcinogen metabolites released into the culture media were identified. Both human and rat colon activate benzo[a]pyrene (BP), aflatoxin B1(AFB), and 1,2‐dimethylhydrazine (DMH) into chemical species that reacted with cellular macromolecules. When human and rat colons were compared, the metabolism of AFB and DMH was qualitatively similar – the same major carcinogen‐DNA adducts and metabolic profile. However, the mean binding levels of DMH and AFB to colonic DNA were higher in rats than in humans. BP‐guanine adducts were the major adducts formed by both rat and human colonic DNA. However, BP‐adenine adducts were observed in rat colonic DNA but not in human colonic DNA. A positive correlation for the binding of BP and DMH to human DNA of different individuals was observed, but no correlation was found between BP and AFB. The data suggest that similar enzyme systems may be involved in the metabolism of BP and DMH, whereas different enzymes might be involved in the metabolic activa

ISSN:0270-3211    

DOI:10.1002/tcm.1770010103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractPrevious studies have shown that the autosomal recessive gene brachymorphic (bm/bm), which is maintained on a C57BL/6J (C57) background, reduces limb growth and sulfation of cartilage proteoglycans. Hydrocortisone administered on gestational days 11–14 resulted in 20% CP in the C57 mouse, but 95% CP in the bm/bm mouse. The bm/bm mouse had a median effective dose for CP of 45 mg/kg, compared to 325 mg/kg for C57 and 40 mg/kg for A/J. Morphometric analysis indicated that the time of palatal elevation was delayed in the bm/bm relative to the C57 mouse both with and without hydrocortisone treatment. The amount of cytoplasmic glucocorticoid receptor protein present in the bm/bm palate on day 14 was the same as the amount found in the C57 palate, and was not elevated as it is in the A/J palate. The levels of cyclic AMP in the bm/bm palate on day 14 were 30–70% higher than that found in the C57 palate with or without hydrocortisone. These results suggest that both bm/bm and A/J exhibit a delay in palatal shelf rotation and elevated levels of cyclic AMP, which appear to be predisposing factors for cortisone‐induced cleft palate. These strains differ in that elevated levels of steroid receptors are present in A/J palate, whereas lower levels are found in the C57 and bm/bm

ISSN:0270-3211    

DOI:10.1002/tcm.1770010104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractDirect in vivo tests of somatic cell mutation in man may provide realism in assessing the genetic risks of potential environmental mutagens. The autoradiographic determination of purine analogue (8‐azaguanine; 6‐thioguanine) resistant (AGr; TGr) peripheral blood lymphocytes (PBLs) arising in vivo in man is proposed as a candidate test. PBLs bearing the naturally occurring Lesch‐Nyhan (LN) mutation are prototype mutant cells. LN PBLs are AGrand TGr, whereas normal PBLs are AG and TG sensitive.When judged by the inhibition of phytohemagglutinin (PHA) stimulated3H‐thymidine incorporation in vitro, analogue‐resistant LN PBLs may be distinguished from analogue‐sensitive normal PBLs by several methods. Early studies quantitating PHA stimulation by scintillation spectrometry detected down to 1% of LN PBLs in artificial mixtures with normal PBLs. Although LN heterozygous females could be identified on the basis of lymphocyte mosaicism, scintillation spectrometry was too insensitive to detect rare “LN‐like” PBLs in non‐LN individuals. Autoradiography, however, detected rare TGrPBLs in normal non‐LN individuals. Their frequencies did not increase with age. With this method, TGrPBL frequencies in LN heterozygous females were found to range from 1 × 10−3to 5 × 10−2, whereas blood samples from LN males showed from 23% to 100% TGrcells. Rare LN PBLs could be detected in artificial mixtures with normal cells.Studies in human patients undergoing various potential mutagenic therapies assessed the effects of these therapies on the TGrPBL variant frequencies (Vf) of non‐LN individuals. Group TGrPBL Vfvalues were higher in treated patient groups than in controls. However, some untreated patient groups (cancer and psoriasis) also had elevated values, suggesting that disease itself may affect TGrPBL frequencies. Nonetheless, one patient group (vitiligo) showed elevated Vfvalues in treated (8‐methoxypsoralen and long‐range UV light = PUVA) but not in untreated patients, suggesting that treatment was responsible for the TGrPBL elevations. Longitudinal studies over time in cancer patients receiving X‐irradiation therapy demonstrated that such exposures also are associated with TGrPBL frequency rises and suggested that longitudinal studies may be necessary to relate TGrPBL Vfelevations to specific environmental influences.Variant TGrPBLs were found at frequencies comparable to those in man in the peripheral blood of rats. They increased in a single study following treatment of the animals with a clinical alkylating agent.Characterization of the TGrPBLs suggests that some of these cells are mutants. Presumably the mutant cells arise in vivo by somatic cell mutation.There also appears to be a population of nonmutant cells that incorporate3H‐thymidine under conditions of the current assay (phenocopies). Current efforts are directed at measures that will allow phenocopies to be distinguished from mutant PBLs.The autoradiographic method is presented as one potentially capable of direct mutagenicity testing in man. It is suggested that its value for this, and the relevance of somatic cell mutation to human health, be tested by correlating sequential mutagenicity test results with eventual clinical outcomes in patients recei

ISSN:0270-3211    

DOI:10.1002/tcm.1770010105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractRegulatory guidelines have produced a need to develop behavioral screening techniques to accompany teratology and reproduction testing. In the repeated use of a provisional test battery, we have found that conclusions about the behavioral teratogenic potential of test compounds are most likely to be revealed using tests having intermediate levels of variability. The results obtained from examining animals exposed developmentally to brominated vegetable oil (BVO as 2.0, 1.0, 0.5, or 0.25 percent of the diet) and comparisons of the tests' co‐efficients of variation, offer an empirical example of this concept. Preweaning tests of locomotion and reflex development demonstrated numerous instances of developmental delay in the BVO‐treated subjects, but postweaning tests revealed few abnormalities. Behavioral testing revealed functional deficits from BVO administration at doses lower than those which have adverse effects on reproduction. Examination of the tests' variability by using coefficients of variation as a comparative index, disclosed that the postweaning test variability was almost twice that of the preweaning tests. Thus, the lack of effects of BVO on most of the postweaning tests should not be conclusively interpreted as indicative of recovery of function, because this pattern is equally likely to have resulted from the lower sensitivity of these tests. An acceptable standard for future behavioral teratology screening requires a close examination of test variability, as it appears to be an important element in the sensitivity and, hence, the interpretation of such procedu

ISSN:0270-3211    

DOI:10.1002/tcm.1770010106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractThe need for efficient methods to screen new chemicals, drugs, and environmental pollutants for their teratogenic activity is obvious. The method currently available, ie, pregnant‐animal testing, is of considerable value but there are certain drawbacks which prevent reliance on this method alone as the predictive device. Nutritional state of the dam, variability in the developmental age of embryos from litter to litter and even within the same litter, metabolic differences between species, placental function, and a host of other factors must be taken into account before data obtained from animal testing can be logically extrapolated to human situation. Many of these variables are either eliminated altogether or at least can be controlled by the use of tissue culture techniques. After surveying a variety of in vitro systems, it is our opinion that organ culture, whole embryo culture, and a combination of the two offer at present the best potential for screening of suspected teratogens. These culture techniques provide a much better simulation of in vivo situations than isolated cells grown as monolayers. Among other advantages, these procedures allow one to exercise control over the effective concentration of the suspected teratogen to which an embryo is exposed and also the duration of this exposure. Since maternal metabolism or modification of the drug is routinely eliminated in these experiments, there is a need for exploring the use of drug‐metabolizing preparations as additives to the culture medium. The choice of limb bud in the screening system is promising since during its development, the limb progresses through a succession of embryonic processes that are generally relevant to other organ systems as well. Hence, such a screening system may not only predict teratogenicity but also provide insight into the mechanisms by which a test chemical is teratoge

ISSN:0270-3211    

DOI:10.1002/tcm.1770010107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractTwo alternative modifications of the experimental protocol for the heritable translocation test are described. One of them proposes to mate F1males and F1females within one experimental group and eliminate normal pairs by a sequential decision procedure based on litter sizes. Pairs that do not meet the criteria for normal litter size have to be separated and tested against normal partners. Male translocation suspects are analyzed cytogenetically for the presence of a reciprocal translocation. Female translocation suspects or XO suspects are verified through analysis of their male and female progeny. The second modification of the heritable translocation test omits fertility testing and proposes to cytogenetically analyze 25 diakineses‐metaphases I from each F1male in the test.Using either one or both protocols it was shown that 20 mg/kg of methyl methanesulfonate (MMS) induced 1.3% heritable translocations in late spermatids and early spermatozoa. With 2.5 mg/kg of mitomycin C, 0.3% and 0.4% translocation carriers were recovered from treated primary spermatocytes and early spermatids, respectively. A dose of 300 R gamma rays resulted in 1.6% translocations in spermatozoa and 4.8% translocations in primary spermatocytes.The advantage of the modified fertility test lies in the doubling of the sample size by including the females. However, a disadvantage is the amount of time and labor that is necessary to verify female translocation carriers. The cytogenetic translocation test protocol with all F1males is considered more reliable and faster. It lacks the possibility of error entailed in the decision procedure by fertility testing, and it requires less time, personnel, and animal spac

ISSN:0270-3211    

DOI:10.1002/tcm.1770010108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractMouse epidermal cell lines have been identified which respond to tumor‐promoting (but not nonpromoting) phorbol esters with an irreversible shift in anchorage independence, an in vitro marker of neoplastic phenotype. This response may be analogous to a later stage of tumor promotion in vivo. The shift occurs at TPA concentrations as low as 0.1 ng/ml (1.6 × 10−10M). The specificity of the soft agar growth response is not limited to phorbol esters but extends to nonphorbol plant diterpenes such as mezerein, to detergents, to polycyclic hydrocarbons present in cigarette smoke, and to some growth factors. All of the above classes of compounds have been previously shown to have tumor‐promoting and/or cocarcinogenic activity in mouse skin in vivo. Clonal heterogeneity for TPA responsiveness has been found. Clones which were highly responsive to phorbol esters were also highly responsive to other classes of promoters, indicating their usefulness both for promoter detection and mechanism studies. The anchorage‐independence response to TPA was inhibited by a series of retinoids whose activity paralleled that for inhibiting tumor promotion in vivo. Both retinoid inhibition and clonal heterogeneity for promoter response are being utilized to study determinants of preneoplastic pro

ISSN:0270-3211    

DOI:10.1002/tcm.1770010109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractExperiments were designed to determine whether DNA conformation and sequence play any role in its methylation by N‐methyl‐N‐nitrosourea, methylmethanesulfonate, and dimethylsulfate, agents that are known to methylate DNA by different mechanisms but yield 7‐methylguanine as the major product. The approach taken was to bind ligands to DNA that interact with it stereospecifically and to study their effect on the formation of 7‐ methylguanine by the three methylating agents. The results indicate that both distamycin A and spermine shielded the formation of 7‐methylguanine in vitro in rat liver DNA by N‐methyl‐N‐nitrosourea but not by methylmethane‐sulfonate or dimethylsulfate; they did not, however, protect 2‐deoxyguanylic acid against methylation by N‐methyl‐N‐nitrosourea. Based on the mechanism by which the methylating agents and the ligands react with DNA, these results are interpreted to suggest that (1) guanines methylatable at the N‐7 position by N‐methyl‐N‐nitrosourea are located at, or close to, the binding sites of the ligands, probably the A‐T‐rich regions, and those methylatable by methyl‐ methanesulfonate and dimethylsulfate are distal to these regions, and/or (2) the conformation DNA assumes in the presence of distamycin A or spermine permits methylation by methylmethanesulfonate and dimethylsulfate but not by N‐methyl‐N‐nitrosourea. The study implicates DNA structure and

ISSN:0270-3211    

DOI:10.1002/tcm.1770010110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY

摘要:

AbstractAt present, experiments with laboratory organisms and epidemiological studies are the major source of information about the genetic toxicology of environmental agents. Laboratory systems are limited in value by difficulties in the interpretation of negative results, in quantitation, and in extrapolation from experimental effects of chemicals to specific levels of activity in man. Epi‐demiologic methods measure effects in man but are weakened by long latency times, confounding environmental factors, imprecise endpoints, and high background levels, which reduce sensitivity. Several methodological improvements in genetic toxicity testing are needed, including increased resolving power, greater relevance of observations to effects in man, techniques for evaluating interactions of compounds in chemically complex systems, and improvements in quantitative risk assessment. Because most genetically toxic agents ultimately react as electrophilic agents with nucleophilic centers in cellular macro‐molecules, the quantitative analysis of the resulting products may be a useful approach to the evaluation of the risks posed by exposure to specific chemicals. The main nucleophilic centers in biological macromolecules are thiol and thioether sulfurs, nitrogens in amino groups and rings, and oxygen atoms. Using the laws of reaction kinetics of alkylation and the observed kinetics of induced mutagenic effects, it is possible to relate the formation of alkylated products in macromolecules to genetic toxicity. The alkylation of amino acids (eg, histidine and cysteine) in hemoglobin can be measured with sufficient sensitivity and accuracy to use it as a monitor of exposure to alkylating agents. By determining the degree of alkylation of a specific center, it is possible to calculate the internal dose of an agent and, because erythrocyte life‐spans are relatively uniform, the incremental daily exposure of an individual to an alkylating agent. Dosimetry can be equated with radiologic dose so that exposure can be expressed in rad‐equivalents and the effects of specific agents compared quantitatively to biologically well‐characterized doses of

ISSN:0270-3211    

DOI:10.1002/tcm.1770010111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1981

数据来源: WILEY