Mechanisms of Immunotoxicity: Stressors and Evaluators

The immune system defends the body against certain tumor cells and against foreign agents such as fungi, parasites, bacteria, and viruses. One of its main roles is to distinguish endogenous components from non-self-components. An unproperly functioning immune system is prone to primary immune deficiencies caused by either primary immune deficiencies such as genetic defects or secondary immune deficiencies such as physical, chemical, and in some instances, psychological stressors. In the manuscript, we will provide a brief overview of the immune system and immunotoxicology. We will also describe the biochemical mechanisms of immunotoxicants and how to evaluate immunotoxicity.

[Rare-earth metals as a factor in mutagenicity]

Both the regions of the Orenburg Region area and individual examined streams and reservoirs were shown to be characterized by a varying load index for rare earth elements. The total level of rare earth elements was directly correlated with different types of mutations.

On information coded in gene-environment independence in case-control studies

For analysis of case-control genetic association studies, it has recently been shown that gene-environment independence in the population can be leveraged to increase efficiency for estimating gene-environment interaction effects in comparison with the standard prospective analysis. However, for the special case in which data on the binary phenotype and genetic and environmental risk factors can be summarized in a 2 × 2 × 2 table, the authors show here that there is no efficiency gain for estimating interaction effects, nor is there an efficiency gain for estimating the genetic and environmental main effects. This contrasts with the well-known result assuming that rare phenotype prevalence and gene-environment independence in the control population for the same data can lead to efficiency gain. This discrepancy is counterintuitive, since the 2 likelihoods are also approximately equal when the phenotype is rare. An explanation for the paradox based on a theoretical analysis is provided. Implications of these results for data analyses are also examined, and practical guidance on analyzing such case-control studies is offered.

[The cytogenetic status of children living in the vicinity of a pulp-and-paper mill]

To evaluate the cytogenetic and cytotoxic effects of a set of pollutions in the town of Koryazhma, the investigators made a complete karyological analysis (cytogenetic, apoptotic, and indirect proliferation parameters) of buccal and nasal epithelial exfoliative cells in two groups of old school age children living at various distances from a pulp-and-paper mill (PPM). The residential area that is adjacent to the PPM can be considered to be poor in the influence of genotoxic factors since there were 1.6- and 1.65-fold increases in cytogenetic disorders and cells with an atypically shaped nucleus, respectively, with a 1.57-fold reduction in the level of cell apoptosis. Karyological changes were revealed in the nasal mucosa, rather than in the buccal mucosa, which permitted one to recommend for the evaluation of the influence of environmental factors, the impact of ambient air pollution in particular, and to conduct cytogenetic studies on the cells of not only the buccal epithelium (that has been better studied), but also those of the nasal epithelium.

[Effect of toxins of cyanobacteria of the Microcystis genus from the Shershnevo Reservoir on DNA, cell cycle, and apoptosis of bone marrow cells in CBA mice]

The effect of toxins of a Cyanobacterium sample of the Shershnevo Reservoir on DNA, which was presented by cyanobacteria of the Microcystis genera, on the bone marrow of male CBA mice (whose age was 3 months and weight 24 g) was evaluated. With intraperitoneal administration, LD50 and LD16 of this sample for male CBA mice were 48.4 and 42.1 mg/kg, respectively. Administration of Microcystis cyanobacterial sample from the Shershnevo Reservoir in doses of 1/10 of LD16 and 1/2 of LD16, and LD16 was found to cause a dose-dependent reduction in the number of bone marrow nucleated cells, a dose-dependent increase in the rate of cell apoptotic death, a reduction in the duration of a cell cycle (within the first 12 hours), which gave way to an increase in the duration of the cycle 24 hours after administration, a dose-dependent increase in the frequency of micronuclei in the murine bone marrow eryphrocytes, and a dose-dependent decrease in the polychromatophil/normochromatophil ratio in the murine bone marrow.

Sequencing and its consequences: path dependence and the relationships between genetics and medicalization

Both advocacy for and critiques of the Human Genome Project assume a self-sustaining relationship between genetics and medicalization. However, this assumption ignores the ways in which the meanings of genetic research are conditional on its position in sequences of events. Based on analyses of three conditions for which at least one putative gene or genetic marker has been identified, this article argues that critical junctures in the institutional stabilization of phenotypes and the mechanisms that sustain such classifications over time configure the practices and meanings of genetic research. Path dependence is critical to understanding the lack of consistent fit between genetics and medicalization.

[Buccal epithelial micronuclear test in the comprehensive assessment of children's ecological well-being in Moscow]

In the buccal epithelial micronuclear test, only the higher frequency of cells with any nuclear degenerative changes is considered to be attributable to the adverse influence of environmental factors. Comprehensive examination of 223 children of 5-7 years of age, going to kindergartens and schools has indicated that the frequency of cells with nuclear chromatin condensation and incomplete nuclear lysis decreased when ambient air contamination was increased in the territories of children's establishments and when the child's throat was contaminated with Staphylococcus aureus or the pharyngeal resident microflora inhibited. Some poor conditions of the nasal and buccal mucosae were also associated with the increase or decrease of cell frequencies. It is suggested that nuclear chromatin condensation and nuclear lysis (rather than other signs of cell degeneration and death) reflect natural cell aging. A moderate toxic effect causes epitheliocytic physiological development retardation and a more intensive effect accelerates aging of cells and induces their death.

Fibrinogen and CRP in Israeli families: Genetic and environmental sources of concentrations and longitudinal changes

OBJECTIVE

To estimate the genetic and environmental determinants of plasma fibrinogen and C-reactive protein (CRP).

METHODS AND RESULTS

A complex segregation analysis was undertaken in a sample of 142 kindreds residing in Kibbutz settlements in Israel. In addition, included in this analysis were family members who were examined 10 years earlier in the framework of this study. Analysis indicated a major locus in addition to polygenic effect that explained the sex- and age-adjusted levels and longitudinal changes in plasma fibrinogen. A non-transmitted environmental major factor with no polygenic effect explained the adjusted variation in levels and change of CRP. Both the particular genotypes determined by the major genetic factor associated with fibrinogen levels and the particular ousiotypes determined by the major environmental factor associated with CRP levels were sex- and age-dependent. In addition, our results demonstrated significant interactions between polygenotype and gender, age and environmental factors such as smoking and BMI on fibrinogen and CRP levels.

CONCLUSIONS

Our models that consider interactions between genotypes and gender, age and environmental exposures have the potential to improve our understanding of the genetics of fibrinogen and CRP levels.

PopGen: population-based recruitment of patients and controls for the analysis of complex genotype-phenotype relationships

OBJECTIVE

Patient samples used for mapping complex human disease genes are unlikely to be representative of the phenotype spectrum of the respective population as a whole. On the other hand, most ongoing prospective studies are probably too small for evaluating polygenic disease markers.

DESIGN

Precise estimates of population-specific genotypic risks can be obtained efficiently through the complete ascertainment of patients in a geographically confined area. The PopGen project uses the most northern part of Germany as a target region for such a pursuit.

RESULTS

PopGen currently pursues recruitment, sampling and processing activities in close collaboration with a multitude of clinical partners, covering cardiovascular, neuropsychiatric and environmental diseases.

CONCLUSION

PopGen has successfully established itself as a large-scale genetic epidemiological project of international recognition.

[A modification factor of spontaneous chromosomal aberrations in miner's towns and settlements]

The level and qualitative spectrum of spontaneous chromosomal aberrations (CA) were comparatively analyzed in the lymphocytes of 655 children and adolescents from the Kemerovo Region. The presented sample was divided into 3 groups according to the type of an inhabited locality: 1) small miner's towns; 2) large industrial towns; and 3) rural localities. The maximum frequency of CA (3.77 +/- 0.22%) was noted in a group of dwellers in the miner's towns; its minimum frequency (2.68 +/- 0.17%) among the rural inhabitants. The significant clastogenic effects (including the markers of radiation exposure) were detected in the miner's towns located in the southern part of the region, which represented mountain and submountain areas. At the same time, in the northern and western parts of the Kemerovo Region, the average frequencies of CA in children and adolescents did not exceed the control background values. Thus, the residence in the inhabited localities specializing in mining is not a factor of absolute toxicogenetic risk.

[Evaluation of the mutagenic effects of environmental factors using polyorgan micronuclear test]

The author reviews the results of studies in which mutagenic effects of environmental factors were investigated using polyorgan micronuclear test, and substantiates the application of this test. This new approach enables fulfillment of various hygienic tasks, such as evaluation of the mutagenic activity of individual factors and mixtures (evaluation of total mutagenic activity), and detection of the level of human genetic lesions.

[Role of genetic studies in the evaluation of the human influence of environmental factors]

The authors propose to include not only a control of human populations, but also environmental factors (chemical, physical, and biological), and objects (to estimate the cumulative mutagenic activity of water, air, soil, and foodstuffs) in order to ensure human genetic safety. For evaluation of human cell genetic damage, they also propose to use the noninvasive multiple organ micronuclear test, by taking into account additional cardiological parameters. The results of this monitoring makes it possible to define higher genetic risk areas for warranting the necessity, priority, and nature of prophylactic measures and to identify a risk group of individuals to be thoroughly examined and to undergo health-promoting measures.

Genetic aspects of pulmonary responses to inhaled pollutants

Air pollution continues to be a major public health concern in industrialized cities throughout the world. Recent population and epidemiological studies that have associated ozone and particulate exposures with morbidity and mortality outcomes underscore the important detrimental effects of these pollutants on the lung. Inter-individual variation in human responses to air pollutants suggests that some subpopulations are at increased risk to the detrimental effects of pollutant exposure, and it has become clear that genetic background is an important susceptibility factor. Environmental exposures to inhaled pollutants and genetic factors associated with disease risk likely interact in a complex fashion that varies from one population to another. The relationships between the genetic background and disease risk and severity is often evaluated through traditional family-based linkage studies and positional cloning techniques. Case-control studies based on association of disease or disease subphenotypes with candidate genes may have certain advantages over family pedigree studies, and have become useful for understanding complex disease phenotypes. This is based in part on continued development of quantitative analysis and development of mapping technologies. Linkage analyses with genetically standardized animal models are useful to identify genetic determinants of host responses to environmental stimuli. For example, linkage analyses using inbred mice have identified chromosomal segments (quantitative trait loci, QTL) that contain genes that control susceptibility to the lung inflammatory and immune dysfunction responses to ozone, nitrogen dioxide, zinc oxide, and sulfate-associated particles. Candidate genes within the pollutant susceptibility QTLs have been tested for proof-of-concept using gene-targeting and overexpression models. Importantly, significant homology exists between the human and mouse genomes. Therefore, comparative mapping between the human and mouse genomes should yield candidate susceptibility genes that may be tested by association studies in humans. The combined human studies and mouse modeling will provide important insight to understanding genetic factors that contribute to differential susceptibility to pollutants in human populations.

[Current problems of hygiene and epidemiology]

In this review, the data available in the literature concerning determinants of human health from the public health point of view have been summarized. Presented newest concepts of human health include genomic and proteomic perspectives in the complex web of interactions between genes and environment. In 2002 epidemiologist and hygienist also has an access to an almost complete description of a single human genome but the challenges remain to move from the description to understanding the function of the genome. Studying the role of molecular determinants of human health is an area of research that has gained attention, particularly during the past 50 years, since the structure of DNA helix has solved. This field will become more dynamic one in the near future and the important data will rapidly accumulate. Further researches are clearly needed to determine not only carcinogenic potential of human ecosystems, but also to establish new methods of risk assessment. The knowledge gained will be crucial in prophylactic health care systems.

Genetic susceptibility to adverse effects of drugs and environmental toxicants. The role of the CYP family of enzymes

The majority of cytochrome P450 (CYP)-dependent xenobiotic metabolism is carried out by polymorphic and inducible enzymes which can cause abolished, quantitatively or qualitatively altered or enhanced drug metabolism. Stable duplication, multi-duplication or amplification of active genes, most likely in response to dietary components causing a selection of alleles with multiple genes, has been described. Several examples exist where subjects carrying certain alleles suffer from a lack of drug efficacy due to ultra-rapid metabolism caused by multiple genes or by induction of gene expression or, alternatively, adverse effects from the drug treatment due to the presence of defective alleles. The polymorphism of CYP enzymes is expected to influence the individual sensitivity and toxicity for different environmental agents, although there is no real consensus in the literature about specific firm relationships in this regard. Dosage requirements for several commonly used drugs that have a narrow therapeutic range can differ more than 20-fold dependent on the genotype or the enzyme expression status. The incidence of serious and fatal adverse drug reactions has been found to be very high among hospitalised patients and causes over 100,000 deaths per year in the US, making it between the 4th and 6th leading cause of death. It is likely that predictive genotyping could avoid 10-20% of these deaths. In the present contribution, an overview is presented about our present knowledge about the polymorphism of xenobiotic metabolising CYPs and the importance for adverse effects of drugs and metabolic activation of xenobiotics.

Dog exposure in infancy decreases the subsequent risk of frequent wheeze but not of atopy

BACKGROUND

Influence of household pets in the development of childhood asthma or atopy has been controversial.

OBJECTIVE

The purpose of this study was to investigate whether pet exposure in early life decreases the subsequent risk of frequent wheezing and/or allergic sensitization.

METHODS

This was a prospective observational birth cohort study. The setting was a large health maintenance organization in Tucson, Ariz; the subjects were a population sample of 1246 newborns enrolled at birth and followed prospectively to age 13 years. The main outcome measures were as follows: time to first report of frequent wheezing (>3 episodes in the past year), skin prick test reactivity at 6 years and 11 years of age, and total serum IgE at 9 months, 6 years, and 11 years of age.

RESULTS

Children living in households with > or =1 indoor dogs at birth were less likely to develop frequent wheeze than those not having indoor dogs (P =.004). This inverse association was confined to children without parental asthma (hazard ratio = 0.47; P <.001 [Cox regression]) and was not evident for children with parental asthma (hazard ratio = 0.96; P =.87). Adjustment by potential confounders did not change the results. Indoor cat exposure was not significantly associated with the risk of frequent wheezing. Neither cat exposure in early life nor dog exposure in early life was associated with skin prick test reactivity or total serum IgE at any age.

CONCLUSION

Dog exposure in early life might prevent the development of asthma-like symptoms, at least in low-risk children with no family history of asthma. Nevertheless, early pet exposure does not seem to significantly influence the development of allergic sensitization.

Symposium overview: the role of genetic polymorphism and repair deficiencies in environmental disease

A symposium of this title was presented at the 37th Annual Meeting of the Society of Toxicology held in Seattle, Washington during March of 1998. The symposium focused on heritable variations in metabolism, DNA replication, and DNA repair that may predispose humans to environmental diseases. Human metabolic, replication, and repair enzymes function in protective roles. Metabolic enzymes are protective because they detoxify a stream of chemicals to which the body is exposed. Replication and repair enzymes are also protective; they function to maintain the integrity of the human genome. Polymorphisms in the genes that code for some of these enzymes are known to give rise to variations in their protective functions. For example, functional polymorphisms of the N-acetyltransferases, paraoxonases, and microsomal epoxide hydrolases vary in their capacity to metabolize environmental chemicals. Specific isoforms of the N-acetyltransferases and microsomal epoxide hydrolases are increasingly associated with incidences of cancer attributable to exposure to these chemicals. Thus, maintenance of cellular-growth homeostasis, normally and in the face of environmental challenge, is dependent on an inherited assortment of metabolic isoforms. Since replication and repair are also protective cellular functions, and since mutations in genes that code for these functions are associated with tumorigenesis, one can reasonably speculate that common functional polymorphisms of replication and repair enzymes may also impart susceptibility to environmental disease.

[Long-term ecological and genetic consequences of use of dioxin-containing environmental agents]

The long-term consequences of the use of dioxine-containing ecotoxic agents in the USA in 1961-1972 are ecologically and genetically characterized. There were increases in the incidence of pathological reproductive events in the contaminated region. It is concluded that there will be higher probability of abnormalities in the families of individuals born at war or just thereof. An association of impaired reproduction with functional disorders and women's poorer health, with higher incidence of somatic and gynecological diseases (chronic ones in particular) is shown. Cytogenetic changes in the lymphocytes were found in individuals from exposure risk groups. The contribution of chromosomal alterations observed in the contaminated area to immunodeficiency is appreciated. The systemic pattern of the action of biologically active properties of dioxine was demonstrated from the morphofunctional changes of different cell types. Cluster analysis revealed associations of cytogenetic parameters with the integrated index of health status in individuals from different contaminated areas. The ecological and genetic consequences may be regarded as part of homeostatic changes at many levels, as suggested by a correlation between the genetic instability and the changes occurring in other tissues, organs, and systems.

Genes, environments, and sex: factors of importance in atopic diseases in 7-9-year-old Swedish twins

Various atopic manifestations among adults have been shown to be influenced mainly by genetic factors. With the increase in prevalence of atopic diseases in recent years, especially among children, a great deal of attention has been given to environmental causes. In a study of 1480 Swedish twin pairs, 7-9 years old, we examined the importance of genetic and environmental factors in asthma, hay fever, eczema, and urticaria. Structural equation model fitting showed 33-76% of the variation in liability to the diseases to be due to genetic effects. Shared environmental effects were also important for hay fever and urticaria in both sexes and for eczema among girls. The clustering of atopic disease in families was almost entirely due to a common set of genes, but each disease manifestation also seemed to have specific genes of importance. Investigation of unlike-sex twins showed that boys had a higher cumulative incidence of asthma and hay fever than girls, whereas girls had a higher incidence of eczema. Thus, it may be concluded that although genetic factors are of major importance in atopic manifestation in children, both environmental and sex-related factors play a role.

Nontraditional epidemiologic approaches in the analysis of gene-environment interaction: case-control studies with no controls!

Although case-control studies are suitable for assessing gene-environment interactions, choosing appropriate control subjects is a valid concern in these studies. The authors review three nontraditional study designs that do not include a control group: 1) the case-only study, 2) the case-parental control study, and 3) the affected relative-pair method. In case-only studies, one can examine the association between an exposure and a genotype among case subjects only. Odds ratios are interpreted as a synergy index on a multiplicative scale, with independence assumed between the exposure and the genotype. In case-parental control studies, one can compare the genotypic distribution of case subjects with the expected distribution based on parental genotypes when there is no association between genotype and disease; the effect of a genotype can be stratified according to case subjects' exposure status. In affected relative-pair studies, the distribution of alleles identical by descent between pairs of affected relatives is compared with the expected distribution based on the absence of genetic linkage between the locus and the disease; the analysis can be stratified according to exposure status. Some or all of these methods have certain limitations, including linkage disequilibrium, confounding, assumptions of Mendelian transmission, an inability to measure exposure effects directly, and the use of a multiplicative scale to test for interaction. Nevertheless, they provide important tools to assess gene-environment interaction in disease etiology.

Biochemical individuality: the next generation

This paper provides an historical assessment of the development of the concepts of pharmaco- and ecogenetics, including their relationship to major developments in the areas of pharmacology, industrial hygiene, and cancer research in animal models as well as the assessment of inborn metabolic disorders. How this information may be used to evaluate the range of human genetic diversity and its relationship to differential responses to environmental toxins is also considered. The paper concludes by providing a brief summary of several specific conditions in which human genetics traits affect susceptibility to toxic substances.

Interindividual variations in susceptibility and sensitivity: linking risk assessment and risk management

In the past few years, our knowledge of mammalian genomes has increased enormously. Our understanding of the molecular basis of the normal cellular processes of DNA replication and repair and cell cycle control, together with how their fidelity malfunctions as part of tumor development, has increased in parallel. This has led to a clearer appreciation that there are subpopulations that have been generically described as being genetically or otherwise susceptible to the induction of cancer or birth defects. The term susceptibility is a default option, since there clearly will be a very broad range of sensitivities among the so-called susceptible populations, dependent upon the specific underlying mechanism. This could lead to the conduct of risk assessments for each specific situation, involving both genotypes of individuals and agents of concern. This would ideally take into account the effects on response of various modifying factors, genetic and other. One advantage to be gained from this approach is the ability to determine if a particular susceptibility places subpopulations at extreme risk as compared to the overall normal distribution of risk in the population, or whether such a susceptible population presents a slight extension of the upper bound of the risk distribution or lies within the normal distribution. In addition, the specific mechanism of the susceptibility as related to exposure scenarios and the magnitude and demographics of the susceptible populations need to be taken into account. Thus, the management of risk has to be linked to the specific risk assessment. For many of the so-called susceptible populations an uncertainty factor of less than 10, even including 1, would be predicted to bring the risk within the normal distribution. It is hoped that as more mechanistic information on susceptibility becomes available and a specific risk can be defined, the practice of risk management will be considerably improved.

Evaluating human variability in chemical risk assessment: hazard identification and dose-response assessment for noncancer oral toxicity of trichloroethylene

Human variability can be addressed during each stage in the risk assessment of chemicals causing noncancer toxicities. Noncancer toxicities arising from oral exposure to trichloroethylene (TCE) are used in this paper as a case study for exploring strategies for identifying and incorporating information about human variability in the chemical specific hazard identification and dose-response assessment steps. Toxicity testing in laboratory rodents is the most commonly used method for hazard identification. By using animal models for sensitive populations, such as developing fetuses, testing can identify some potentially sensitive populations. A large variety of reproductive and developmental studies with TCE were reviewed. The results were mostly negative and the limited positive findings generally occurred at doses similar to those causing liver and kidney toxicity. Physiologically based pharmacokinetic modeling using Monte Carlo simulation is one method for evaluating human variability in the dose-response assessment. Three strategies for obtaining data describing this variability for TCE are discussed: (1) using in vivo human pharmacokinetic data for TCE and its metabolites, (2) studying metabolism in vitro, and (3) identifying the responsible enzymes and their variability. A review of important steps in the metabolic pathways for TCE describes known metabolic variabilities including genetic polymorphisms, enzyme induction, and disease states. A significant problem for incorporating data on pharmacokinetic variability is a lack of information on how it relates to alterations in toxicity. Response modeling is still largely limited to empirical methods due to the lack of knowledge about toxicodynamic processes. Empirical methods, such as reduction of the No-Observed-Adverse-Effect-Level or a Benchmark Dose by uncertainty factors, incorporate human variability only qualitatively by use of an uncertainty factor. As improved data and methods for biologically based dose-response assessment become available, use of quantitative information about variability will increase in the risk assessment of chemicals.

Ethical aspects of genetic predisposition to environmentally-related disease

Some individuals are highly susceptible to disease caused by chemical exposures and this hypersusceptibility can be genetically determined. Because biomarker technology for the determination of genetic predisposition is at the disposal of researchers, the capability therefore exists to include genetic screening in epidemiologic studies. The application of this technological advance in population-based research is, however, fraught with ethical tensions heretofore unknown. Moral duties alone are of limited use in resolving these problems. Scientific documentation is almost always insufficient to clarify the exact nature of the ethical implications, and ways to deal with uncertainties arising as a result of information generated from genetic screening studies must be considered. The most important tensions relate to autonomy and the right to privacy, fairness and equality, while balancing potential public interest in paternalistic measures. Because no moral framework has been accepted for dealing with this technological advance, an ethical discourse in an open forum is required with all affected parties. Scientists alone, or any other group in isolation, should not expect to resolve these questions, but they should participate in and facilitate the process.

[The ratio of hereditary and environmental factors in the origination of noninfectious human diseases]

Recent investigations in clinical genetics have shown, that manifestations of common nontransmissive diseases in humans are determined by the interactions of hereditary, internal and environmental factors in the same way as it was earlier demonstrated for hereditary diseases and studied on animals and plants for many quantitative and qualitative traits.