Showing papers in "Basic life sciences in 1983"
TL;DR: The objective of these experiments was to determine if cancer proneness at the level of the individual is correlated with either hypersensitivity to the lethal effects or hypermutability to the mutagenic effects of DNA damaging agents.
Abstract: Over the past five years we have been examining the mutability of a variety of human fibroblast strains established from both normal individuals and patients suffering from cancer-prone genetic diseases. The objective of these experiments was to determine if cancer proneness at the level of the individual is correlated with either hypersensitivity to the lethal effects or hypermutability to the mutagenic effects of DNA damaging agents. The existence of hypersensitivity and particularly hypermutability implies the presence of defects in repair of DNA damage and underlines the importance of effective repair processes for human health (1).
41 citations
35 citations
TL;DR: Infection of many dicotyledonous plants by the genus Agrobacterium may lead to the plant diseases crown gall, cane gall, and hairy-root disease.
Abstract: Infection of many dicotyledonous plants by the genus Agrobacterium may lead to the plant diseases crown gall, cane gall, and hairy-root disease.
32 citations
TL;DR: I’d like to discuss some of the efforts towards the design of highly specific enzyme inactivators, which can be used in vivo, and hope that such inactivator can be useful as pharmacological agents.
Abstract: I’d like to discuss some of our efforts towards the design of highly specific enzyme inactivators, which can be used in vivo. We hope that such inactivators can be useful as pharmacological agents.
22 citations
TL;DR: This discussion is about tools to analyze the complex relationship between chemicals and mutation in a relatively simple biological system: the exponentially growing single cell population.
Abstract: This discussion is about tools to analyze the complex relationship between chemicals and mutation in a relatively simple biological system: the exponentially growing single cell population. Three assumptions are made about this relationship: that some DNA adducts are premutagenic lesions, that adducted DNA may be repaired, misrepaired or unrepaired at the time of DNA synthesis and that unrepaired DNA may be replicated, misreplicated or unreplicated at the time of mitosis. These three assumptions lead to the definition of variables ascertainable by experimental measurement which, in turn, lead to explicit formulae which should be useful as guides in the analysis of dose(adduct) -response(mutation) relations.
21 citations
TL;DR: Good biological evidence for the existence of an adaptive DNA repair pathway in cultured rodent and human cell lines is provided and recent findings in mammalian cells are outlined.
Abstract: We are continuously exposed to non-toxic levels of carcinogens both from our environment and from our diet. It would therefore seem important to determine how cells respond to this particular kind of treatment. Some years ago, an attempt to simulate this chronic environmental exposure to mutagens revealed the existence of an inducible antimutagenic DNA repair pathway in E. coli — the adaptive DNA repair pathway (1). The obvious progression from finding a new type of DNA repair in E. coli was to ask whether an equivalent pathway exists in mammalian cells, and ultimately whether it exists in human cells. We now have good biological evidence for the existence of an adaptive DNA repair pathway in cultured rodent and human cell lines (2). In order to set the scene for our recent findings in mammalian cells, we should first consider what is presently known about E. coli adaptation.
17 citations
TL;DR: Many types of carcinogens show pronounced differences in effect in different species, often inducing tumors of a certain site in one and being inactive in another and should afford a means of approaching an understanding of the mechanisms of nitrosamine carcinogenesis.
Abstract: Many types of carcinogens show pronounced differences in effect in different species, often inducing tumors of a certain site in one and being inactive in another. N-Nitroso compounds, on the other hand, are commonly carcinogenic in all species examined, but induce tumors of different cell types and in different organs from one species to the next. This variability is particularly true of nitrosamines, whose organ and species specificity are probably due to differences in routes of metabolism and activation. These differences are open to study using biochemical and chemical methods and should afford a means of approaching an understanding of the mechanisms of nitrosamine carcinogenesis.
17 citations
TL;DR: The elucidation of the biological basis of organ-specific tumor induction by chemicals must first be understood to accurately predict the adverse effects of genotoxic agents in humans.
Abstract: The elucidation of the biological basis of organ-specific tumor induction by chemicals is a major objective of cancer research. For many carcinogens, the principal site of tumor induction has been shown to vary with species, dose, route of administration, and age or developmental stage. Some species also exhibit marked differences in their overall susceptibility to certain classes of chemical carcinogens. Accordingly, to accurately predict the adverse effects of genotoxic agents in humans, the basic mechanisms underlying organ and species specificity must first be understood.
16 citations
TL;DR: The potential importance of tumor promotion in human cancer etiology is suggested by a growing body of epidemiological evidence and it is suggested that tumor promotion has been characterized in greatest detail for mouse skin.
Abstract: Tumor promoters are agents that, although not themselves carcinogenic, induce tumors in animals previously treated with a subthreshold dose of a carcinogen (1–3). Although tumor promotion has been characterized in greatest detail for mouse skin, it has also been demonstrated for the liver, bladder, colon, trachea, and mammary gland (4,5). The potential importance of tumor promotion in human cancer etiology is suggested by a growing body of epidemiological evidence (6–8).
16 citations
TL;DR: The technique of tissue and organ culture, especially the culture of organs and buds and the in vitro regeneration of whole plants through them, could be attempted as an alternate method in the propagation in woody plants.
Abstract: A majority of the woody plants are difficult to propagate by vegetative means Traditional methods such as rooting of the excised branches, and grafting, although successful in some instances, still has limitations and cannot be applied for all commercially valuable species The technique of tissue and organ culture, especially the culture of organs and buds and the in vitro regeneration of whole plants through them, could be attempted as an alternate method in the propagation in woody plants (1)
15 citations
TL;DR: Skin tumors can be induced by the sequential application of a single subthreshold dose of a carcinogen followed by repeated treatment with a noncarcinogenic promoter (promotion phase), which is referred to as two-stage carcinogenesis.
Abstract: Topical application of some chemical carcinogens will induce skin tumors on mice. In general, most chemical carcinogens have to be given repeatedly to induce a large number of tumors (complete carcinogenesis). Skin tumors also can be induced by the sequential application of a single subthreshold dose of a carcinogen (initiation phase) followed by repeated treatment with a noncarcinogenic promoter (promotion phase). This second procedure employing initiation and promotion is referred to as two-stage carcinogenesis.
TL;DR: With this compound the guinea pig, cotton rat, monkey, steppe-lemming, and X/Gf mouse, among the mammals, have shown resistance to the carcinogenic effects.
Abstract: Extensive studies on several species of laboratory animals have been done for only a few carcinogenic aromatic amines or amides; those so tested include benzidine, 4-aminobiphenyl, 2-acetylaminofluorene (AAF), and 2-aminonaphthalene (1). Even for these known carcinogens there are sizable variations in species response; the most striking occurs with AAF where at least 15 species have been tested (2). With this compound the guinea pig, cotton rat, monkey, steppe-lemming, and X/Gf mouse, among the mammals, have shown resistance to the carcinogenic effects. Metabolic studies, either in vivo or in vitro, have not always provided satisfactory explanations for these differences (3,4,5).
TL;DR: In an eagerness to obtain reliable data relating to the potential genotoxic and/or carcinogenic potentials, too much emphasis has been placed on procedural details such that sight is lost of the fact that these assays lend themselves to the elucidation of some basic biological problems.
Abstract: It is now well recognized that short-term microbial assays, when run under carefully controlled conditions, have predictive value for the detection of the potential cancer-causing properties of most classes of chemicals. Indeed, our Laboratory has participated both in the development and validation of such assays. However, in an eagerness to obtain reliable data relating to the potential genotoxic and/or carcinogenic potentials, too much emphasis has been placed on procedural details such that sight is lost of the fact that these assays lend themselves — when suitably modified — to the elucidation of some basic biological problems. There is an increasing number of these which can be used to illustrate this point. The present report, however, deals primarily with data obtained in our own Laboratories.
TL;DR: The lacI system of E. coli provides a method for determining UV-induced mutational specificity at a large number of sites and allows the examination of forward mutagenesis at 65† individual sites where nonsense mutations can arise by a single base substitution.
Abstract: The lacI system of E. coli provides a method for determining UV-induced mutational specificity at a large number of sites (1,2,3). In contrast, earlier studies in other systems have generally relied upon the analysis of reversion at a rather limited number of sites (4,5,6). Often, the mutants analyzed in reversion studies were originally induced by the mutagenic treatment (7) and the possibility therefore exists that preferentially mutable sites or hotspots were selected and that these may have behaved atypically. Alternatively, the original mutation may have removed a DNA sequence target and these sites may be in fact partially immutable! Moreover, in studies of the reversion of nonsense mutations, the majority of “revertants” actually occur not in the structural gene but at suppressor loci which behave unusually in their response to UV light (4,8,9). The lacI system allows the examination of forward mutagenesis at 65† individual sites where nonsense mutations can arise by a single base substitution. Since both the DNA sequence and the location of the nonsense mutations have been established (10), each mutation can be attributed to a specific transition or transversion event.
TL;DR: This gene has been isolated from a recombinant human-λ gene library, and the entire gene and 5′ and 3′ flanking regions have been sequenced.
Abstract: Human IFN-γ is encoded by a single gene which, in contrast to the IFN-α and IFN-β genes, contains three introns. This gene has been isolated from a recombinant human-λ gene library, and the entire gene and 5′ and 3′ flanking regions have been sequenced. Southern hybridizations failed to show any polymorphism of the gene or its flanking regions. The first intron contains a repetitive element which is unrelated to the Alu family repeat.
TL;DR: The covalent products formed in DNA of species sensitive and resistant to the biological effects of AFB1 are studied for correlations that may exist between the formation of these products, their removal, and biological responses to their presence.
Abstract: The molecular mechanisms by which aflatoxin B1 (AFB1) produces its biological effects are poorly understood. Many of the biochemical effects of the aflatoxins and other chemical carcinogens are mediated by activation through metabolism by one or more of the mixed-function oxidases and subsequent covalent modification of cellular macromolecules (1). Experimental evidence indicates that AFB1-2,3-oxide is the ultimate reactive metabolite (2,3). It is reasonable that the sites and amount of macromolecular damage play essential roles determining molecular alterations and consequently observable biological effects. The consequences of covalent damage once formed will depend upon the ability of a cell or tissue to repair (correctly or incorrectly) or circumvent damage to essential cellular components before they are lethal or result in permanent change in the molecular program of the cell. For example, cells from patients with xeroderma pigmentosum that are defective in excision repair have increased sensitivity to ultraviolet (UV) light and some chemical agents. Conversely, cells competent for repair that are given adequate time to remove lesions from DNA before critical events exhibit increased survival (4). Thus, the kinetics of formation of this macromolecular damage and its repair are important. We have studied the covalent products formed in DNA of species sensitive and resistant to the biological effects of AFB1 for correlations that may exist between the formation of these products, their removal, and biological responses to their presence.
TL;DR: D dose-response relationships have been demonstrated for Ni3S2 carcinogenesis in rats and hamsters and for transformation of Syrian hamster fetal cells by Ni3s2 in vitro and an experiment in hamsters has indicated that Ni3 S2 may be noncarcinogenic by the oral route.
Abstract: The carcinogenic effects of metal compounds in man and experimental animals have been comprehensively reviewed in several recent articles and monographs (1-7). Four metals (arsenic, cadmium, chromium, and nickel) have been established as human carcinogens on the basis of epidemiological investigations, and compounds of 13 metals (aluminum, beryllium, cadmium, cobalt, chromium, copper, iron, manganese, nickel, lead, platinum, titanium, and zinc) have been shown to induce cancers in experimental animals (5-7). Nickel subsulfide (Ni3S2) is the most potent metallic carcinogen that has been identified to date;Ni3S2 has been evaluated for carcinogenicity much more thoroughly and extensively than any other metal compound (3,8-10). Consequently, Ni3S2 has been selected as the focal point for this exposition of organ and species specificity in metal carcinogenesis.
TL;DR: Because of the acceptance of passive immunization in animal health care as can be demonstrated from the sale of conventional antisera for such use, it was encouraged that monoclonal antibodies could find significant use in veterinary health care.
Abstract: Monoclonal antibody technology, which allows the unlimited production of an antibody with a very defined specificity, has resulted in a renewed interest in passive immunization as a treatment alternative for disease. However, to date, the widespread implementation of monoclonal antibodies for prophylactic or therapeutic use has not occurred. Because of the acceptance of passive immunization in animal health care as can be demonstrated from the sale of conventional antisera for such use, we were encouraged that monoclonal antibodies could find significant use in veterinary health care.
TL;DR: The most cursory inspection of human cancer morbidity tables shows that not all tissues of man are equally at risk for neoplasia, and that for a given tissue, risk varies with age, sex, and genetic background.
Abstract: One of the most central problems in human oncology, as well as in experimental carcinogenesis, is that of organ specificity. The most cursory inspection of human cancer morbidity tables (1) shows that not all tissues of man are equally at risk for neoplasia, and that for a given tissue, risk varies with age, sex, and genetic background (Table 1). Where a specific causative agent is known, characteristically it is linked with a relatively narrow spectrum of diseases, or even with a single clinical entity: 2-aminonaphthalene causes carcinoma of the urinary bladder (2); bis (2-chloromethyl) ether (BCME) causes oat-cell carcinoma of the lung (3); vinyl chloride induces hepatic angiosarcoma (4). Major determinants of organ specificity can be found in some cases in peculiarities of metabolism and excretion of the carcinogen, as in the case of the aromatic amines and the urinary bladder; or in a crude biological form of the chemical Law of Mass Action, that the site of highest local concentration is the most vulnerable, as with pulmonary carcinogenesis in those who inhale the volatile, highly reactive BCME. But neither consideration clearly explains why vinyl chloride, when inhaled, selectively induces tumors of the hepatic endothelium while sparing hepatocytes, in which it is presumably metabolized.
TL;DR: Some of the recent work of the lab on the cellular molecular mechanisms involved in UV and chemical mutagenesis is summarized.
Abstract: The past few years have seen a remarkable increase in our understanding of the strategies employed by cells in dealing with damage to their genetic material Of particular interest has been the recognition that mutagenesis by a variety of agents including UV, methyl methanesulfonate (MMS), and 4-nitroquinoline-1-oxide (NQO) is not a passive process Rather it requires the intervention of a cellular system which processes damaged DNA in such a way that mutations result Mutagenesis is not a necessary consequence of DNA damage since, if this system is inactivated, no mutations result In this paper we would like to summarize some of the recent work of our lab on the cellular molecular mechanisms involved in UV and chemical mutagenesis
TL;DR: The surface area of the lower respiratory tract, approximately 25 m2, is directly exposed to some of these compounds during inhalation, and chemical carcinogens and their metabolites can also reach the lung via the systemic route.
Abstract: Chemical carcinogens are a large group of naturally occurring and man-made compounds of diverse molecular structures. These compounds are ubiquitous in the human environment in the food chain, the water supply, and the atmosphere and they enter the human body through the surface epithelium. The surface area of the lower respiratory tract, approximately 25 m2, is directly exposed to some of these compounds during inhalation. In addition, chemical carcinogens and their metabolites can also reach the lung via the systemic route.
TL;DR: This paper will focus on the direct effects of chemical modification of nucleic acids on mammalian cells or whole animals.
Abstract: Mutagenesis is defined as a heritable change which can occur through indirect as well as direct change in the genetic message. This paper, however, will focus on the direct effects of chemical modification of nucleic acids. Since man is the species we are most concerned about, the effect of modification on mammalian cells or whole animals will be stressed whenever possible.
TL;DR: Results suggest that inducible host functions might decrease the fidelity of replication even on undamaged template, and experiments using animal viruses as a molecular probe have shown that induced mutagenesis could in fact be detected in mammalian cells.
Abstract: The mechanism of induced mutagenesis has been particularly well analyzed in E. coli after UV-irradiation. UV-mutagenesis appears to be an inducible phenomenon which requires the specific cleavage of the lexA gene product by the protease activity of RecA protein and the presence of the umuC gene product. Similar genetic requirements are necessary to detect mutagenesis of UV-irradiated bacteriophages (1, 2, see 3, 4, 5 for review). UV-irradiated λ phage has a better survival in UV-irradiated host cell than in unirradiated one. This UV-reactivation is only associated with mutagenesis of the damaged DNA phage (6). The most likely explanation for UV-mutagenesis mechanism is the induction of some type of DNA replication past pyrimidine dimers which will produce mutations on newly synthesized strand opposite to the lesions on the template strand (7). However, mutations in phage DNA appear to be produced not only in phage containing DNA damages but also in undamaged phage providing that the host cell has been UV-irradiated before infection. This result suggests that inducible host functions might decrease the fidelity of replication even on undamaged template. The exact mechanism of this untargeted mutagenesis is not yet understood. As in bacteria, UV-irradiation of mammalian cells gives rise to mutations.Studies with normal and classical xeroderma pigmentosum human cell lines indicate that excision repair synthesis is an accurate repair process (8). In consequence, mutations seem to be due to the presence of unrepaired UV-damages on DNA, probably pyrimidine dimers. On the other hand, xeroderma pigmentosum variant cells are more mutable by UV-light than normal cells and seem to be deficient in an error-free post-replication repair pathway (9). Experiments carried out in mammalian cells in order to detect any inducible error-prone pathway have been negative so far. For example, no mutagenesis increase has been observed in split dose experiments (10). In contrast, experiments using animal viruses as a molecular probe, in the same way as bacteriophages, have shown that induced mutagenesis could in fact be detected in mammalian cells.
TL;DR: From earliest times, mankind has endowed animals with specific human attributes, but none of these attributions were scientific absolutes; they could be manipulated to suit the current political exigencies.
Abstract: From earliest times, mankind has endowed animals with specific human attributes. Language reflects many of these attributes in phrases such as “wise as an owl,” “cunning as a fox,” or “assinine.” Soothsayers have used the detailed morphological examination of outbred animals to predict man’s fate in the future. It is relevant to our present society that none of these attributions were scientific absolutes; they could be manipulated to suit the current political exigencies. Our current mysticism dictates that we regard all agents that induce cancer in animals as having the same effect in man. Although some evidence for this theory exists, and it represents a cautious view, it is again by no means a scientific absolute.
TL;DR: The phenomena of species, organ, sex, and age specificity in response to chemical carcinogens pose an intriguing problem and may be important for the extrapolation of in vivo and in vitro carcinogenesis data to humans.
Abstract: We have been interested in developing in vitro systems in which the organ and species specificity of chemical carcinogens can be studied (1–6). The phenomena of species, organ, sex, and age specificity in response to chemical carcinogens pose an intriguing problem and may be important for the extrapolation of in vivo and in vitro carcinogenesis data to humans. Many carcinogens exist in the environment in nonreactive form and must be metabolically activated to manifest their biological activity (7,8).
TL;DR: The detoxification response of the organism toward chemical carcinogens is to transform these potentially toxic compounds into more polar, less lipid soluble substances that are readily excretable and therefore harmless.
Abstract: The detoxification response of the organism toward chemical carcinogens is to transform these potentially toxic compounds into more polar, less lipid soluble substances that are readily excretable and therefore harmless. However, it would appear that nature has made a serious mistake in the case of chemical carcinogens. This concept can be stylized by superimposing the steps in metabolic activation upon a chemical energy activation diagram (see Figure 1). It is generally assumed that the parent molecules of an environmentally prevalent chemical carcinogen are structurally stable and relatively inactive metabolically. This assumption is not unreasonable from a teleological point of view since one would expect labile chemical substances to be rapidly degraded or oxidized, due to sunlight and weather, if released in the open environment. Synthetically prepared activated carcinogens, such as polyaromatic epoxides and nitrosamines, have been shown to possess very short half-lives under physiological conditions. Therefore, the parent compound undergoes a decrease in entropy to increase its potential energy for subsequent metabolic degradation. This change requires enzymatic transformation into a reactive intermediate antecedent to further catabolism. Current evidence shows that all known carcinogenic chemicals are electrophilic reagents that seek out nucleophilic sites inside the cells (1). The peak of the curve in Figure 1 is the zone where the electron-deficient reactive metabolite is thought to interact with nucleophilic target sites hypothesized to begin the process of malignant transformation. If no such interaction takes place, the most common reaction is hydroxylation to form a metabolically inactive polar structure that is more hydrophilic and can be readily excreted. Therefore, the major thrust of the detoxification process is to render the parent compound into a structure of greater entropy and consequently less potential to exert a toxic effect.
TL;DR: Sulfur dioxide is unique among environmental substances because of the many routes of human exposure to it and it is rapidly oxidized to sulfate by sulfite oxidase, which releases SO2 into urban atmospheres.
Abstract: Sulfur dioxide is unique among environmental substances because of the many routes of human exposure to it. Combustion of coal and oil releases SO2 into urban atmospheres. It is added to foods, beverages, and pharmaceuticals and we produce it within our bodies as a product of the catabolism of sulfur containing amino acids. It is short-lived within us, as it is rapidly oxidized to sulfate by sulfite oxidase.
TL;DR: To estimate risks to humans from carcinogens requires extrapolation from animal or other data, and there is no shortage of suggested models for this task, but the differences among them can lead to enormously different predictions.
Abstract: To estimate risks to humans from carcinogens requires extrapolation from animal or other data. Any such extrapolation must be made in the context of a model or models, but no current consensus exists as to which models are correct. There is no shortage of suggested models for this task, each motivated by theoretical arguments, but the differences among them can lead to enormously different predictions. Furthermore, they often lack any practical demonstration of validity.
TL;DR: The results underline the significant role that DNA repair may play in preventing a carcinogenesis by alkylating agents and suggest particular emphasis has been placed on the potential role of O 6-alkylguanine.
Abstract: Simple alkylating agents form an interesting class of chemical carcinogens whose interaction with DNA is relatively well understood (1–7). These carcinogens include agents such as alkyl alkanesulfonates, alkylnitrosamides, alkylnitrosoguanidines, and monoalkyltriazines that are direct acting and the chemically-stable nitrosamines, dialkylhydrazines, and dialkyltriazines that require enzymatic activation to generate the alkylating species. The major adducts formed by these agents on reaction with DNA in target and nontarget tissues have been quantitated and their persistence with time measured (1,2,5,6). These studies have suggested that certain adducts are more likely to be responsible for the initiation of tumors than others; particular emphasis has been placed on the potential role of O 6-alkylguanine. O 6-Alkylguanine is known to miscode in nucleic acid synthesis and to lead to mutations. Furthermore, its rate of removal from DNA. differs from tissue to tissue, and the persistence correlates with sensitivity to tumor initiation (1,2,5). These results underline the significant role that DNA repair may play in preventing a carcinogenesis by alkylating agents. Other alkylated bases may also have the potential to initiate tumors, but the rapid removal would minimize their effect.