Potential human developmental toxicants and the role of animal testing in their identification and characterization

In vitro models of human development and their potential application in developmental toxicity testing

Recent publications describe the development of in vitro models of human development, for which applications in developmental toxicity testing can be envisaged. To date, these regulatory assessments have exclusively been performed in animal studies, the relevance of which to adverse reactions in humans may be questioned. Recently developed cell culture-based models of embryo-fetal development, however, do not yet exhibit sufficient levels of standardisation and reproducibility. Here, the advantages and shortcomings of both in vivo and in vitro developmental toxicity testing are addressed, as well as the possibility of integrated testing strategies as a viable option in the near future.

Stem cell-based region-specific brain organoids: Novel models to understand neurodevelopmental defects

The study of human brain development and neurodevelopmental defects has remained challenging so far due to unique, specific, and complex underlying processes. Recent advances in the technologies and protocols of in vitro human brain organoid development have led to immense possibilities of understanding these processes. Human brain organoids are stem-cell derived three-dimensional in vitro tissues that resemble the developing fetal brain. Major advances in stem cell techniques pioneering the development of in vitro human brain development include reprogramming human somatic cells into induced pluripotent cells (iPSCs) followed by the targeted differentiation of iPSCs into the cells of three embryonic germ cell layers. The neural progenitor cells produced by the directed differentiation of iPSCs undergo some level of self-organization to generate in vitro human brain like tissue. A three-dimensional differentiation approach applied to create region-specific brain organoids has successfully led to develop highly specialized cortical, forebrain, pallium, and subpallium in vitro human brain organoid models. These stem cell-based brain organoids are novel models to study human brain development, neurodevelopmental defects, chemical toxicity testing, and drug repurposing screening. This review focuses on the fundamentals of brain organoid development and applications. The novel applications of using cortical organoids in understanding the mechanisms of Zika virus-induced microcephaly, congenital microcephaly, and lissencephaly are also discussed.

Maternal pesticide exposure and child neuro-development among smallholder tomato farmers in the southern corridor of Tanzania

BACKGROUND

Exposure to pesticides with its associated effects prenatally and in early childhood has not received much attention. There is little scientific data on this aspect in Tanzania therefore this study was meant to contribute to the deficit in the subject.

METHOD

A cross-sectional study was conducted to a sample of 286 participants of mother to child pair, whereby 172 and 114 were exposed and non-exposed respectively. Mothers who had been working in tomato sprayed farms were exposed and mothers who had not been working in the tomato sprayed farms were un-exposed. Child aged 0-6 years was chosen from each mother sampled but only one child found to be the youngest with the classified age was enrolled. Malawi child development Tool (M-DAT) was employed to assess the child level of development, height, and weight of the children were collected and analyzed by the WHO anthropometric calculator. A checklist and questionnaire were used to observe and assess maternal exposure. Bivariate and Multivariate analysis were conducted to assess the relationship between various factors of exposure.

RESULTS

Overall 15% of the children examined were not well developed and the most used pesticides were those posing neuro-development effects. On the bivariate analysis model, mothers who worked while pregnant were more likely to have a child with neuro-developmental effect OR=5.8(1.29-26.3). On multivariate analyses adjusted for age of the mother, variables which remain in the model were a distance from home [AOR=9.4(4.2-20.5)], and working while pregnancy [AOR=5.8(1.29-26.3)] other were removed due to collinearity effect. None of confounders had a potential significant effect but only nutrition seems to be the effect modifier [AOR=7.8(1.29-36.3)] when analyzed with working while pregnancy.

CONCLUSIONS

The findings from this study have indicated that maternal pesticide exposure among farmworker residents in the SAGCOT area has a potential association with child developmental effect.

Species-specific developmental toxicity in rats and rabbits: Generation of a reference compound list for development of alternative testing approaches

For regulatory information requirements, developmental toxicity testing is often conducted in two mammalian species. In order to provide a set of reference compounds that could be used to explore alternative approaches to supersede testing in a second species, a retrospective data analysis was conducted. The aim was to identify compounds for which species sensitivity differences between rats and rabbits are not caused by maternal toxicity or toxicokinetic differences. A total of 330 compounds were analysed and classified according to their species-specific differences. A lack of concordance between rat and rabbit was observed in 24% of the compounds, of which 10% were found to be selective developmental toxicants in one of the species. In contrast to previously published analyses the presented comparison is based entirely on publically data allowing validating and comparing alternative approaches for developmental toxicity testing. Furthermore, this list could be useful to identify mechanisms leading to species differences.

Embryonic stem cells and the next generation of developmental toxicity testing

INTRODUCTION

The advent of stem cell technology has seen the establishment of embryonic stem cells (ESCs) as molecular model systems and screening tools. Although ESCs are nowadays widely used in research, regulatory implementation for developmental toxicity testing is pending. Areas Covered: This review evaluates the performance of current ESC, including human (h)ESC testing systems, trying to elucidate their potential for developmental toxicity testing. It shall discuss defining parameters and mechanisms, their relevance and contemplate what can realistically be expected. Crucially this includes the question of how to ascertain the quality of currently employed cell lines and tests based thereon. Finally, the use of hESCs will raise ethical concerns which should be addressed early on. Expert Opinion: While the suitability of (h)ESCs as tools for research and development goes undisputed, any routine use for developmental toxicity testing currently still seems premature. The reasons for this comprise inherent biological deficiencies as well as cell line quality and system validation. Overcoming these issues will require collaboration of scientists, test developers and regulators. Also, validation needs to be made worthwhile for academia. Finally we have to continuously rethink existing strategies, making room for improved testing and innovative approaches.

Genomic and in silico analyses of CRBN gene and thalidomide embryopathy in humans

Thalidomide causes Thalidomide Embryopathy (TE), but is largely used to treat several conditions. Investigations with Cereblon, a thalidomide target protein encoded by CRBN gene, have helped to understand thalidomide therapeutic and teratogenic properties. We sequenced CRBN-thalidomide binding region in 38 TE individuals and 136 Brazilians without congenital anomalies, and performed in silico analyses. Eight variants were identified, seven intronic and one in 3'UTR. TE individuals had rare variants in higher frequency than the non-affected group (p=0.04). The genotype rs1620675 CC was related to neurological anomalies in TE individuals (p=0.004). Bioinformatics analysis suggested this genotype leads to potential alterations in splicing sites and binding to transcription factors. Comparison of the Cereblon-thalidomide binding domains in mammals demonstrated that CRBN is highly conserved across species. All the variants require evaluation in functional assays in order to understand their role in Cereblon-thalidomide binding and complex interactions that lead to TE.

Adverse effect of valproic acid on an in vitro gastrulation model entails activation of retinoic acid signaling

Valproic acid (VPA), an antiepileptic drug, is a teratogen that causes neural tube and axial skeletal defects, although the mechanisms are not fully understood. We previously established a gastrulation model using mouse P19C5 stem cell embryoid bodies (EBs), which exhibits axial patterning and elongation morphogenesis in vitro. Here, we investigated the effects of VPA on the EB axial morphogenesis to gain insights into its teratogenic mechanisms. Axial elongation and patterning of EBs were inhibited by VPA at therapeutic concentrations. VPA elevated expression levels of various developmental regulators, including Cdx1 and Hoxa1, known transcriptional targets of retinoic acid (RA) signaling. Co-treatment of EBs with VPA and BMS493, an RA receptor antagonist, partially rescued axial elongation as well as gene expression profiles. These results suggest that VPA requires active RA signaling to interfere with EB morphogenesis.

A Retrospective Appraisal of the Ability of Animal Tests To Predict Reproductive and Developmental Toxicity in Humans

The reproductive and developmental toxicology areas have undergone numerous changes in the 30 years since the thalidomide tragedy. It would be comforting if such changes have resulted in a greatly decreased likelihood that human conceptuses will develop malformations. However, there is little evidence that such testing has better enabled us to identify human reproductive or developmental toxicants. Although there may be justification for performing animal testing on drugs and pesticides, a simple acute toxicity test may be just as predictive as currently employed reproductive and developmental toxicity tests for other synthetic chemicals. Support for this premise is provided by comparing available acute toxicity information on many compounds, identified as (potential) human developmental or reproductive toxicants, with their respective likely human threshold doses. Acute LD50 values of other potential human reproductive or developmental toxicants, not documented as being a threat to humans, also were compared with their time-weighted averages or their lowest teratogenic dose in the same species. The data generated support the premise that most reproductive or developmental toxicants are a potential threat to humans only if exposure levels approach those that are lethal in the rat or mouse. In contrast, unequivocal evidence of developmental toxicity for drugs, such as thalidomide and isotretinoin, to which the human embryo is highly sensitive, were not apparent in the screens used now for routine developmental toxicology testing. Thus, requirements that all chemicals be tested for reproductive and developmental toxicity should await the development of testing methodology capable of better assessing human risk.

Assessment of health risks resulting from early-life exposures: Are current chemical toxicity testing protocols and risk assessment methods adequate?

Abstract Over the last couple of decades, the awareness of the potential health impacts associated with early-life exposures has increased. Global regulatory approaches to chemical risk assessment are intended to be protective for the diverse human population including all life stages. However, questions persist as to whether the current testing approaches and risk assessment methodologies are adequately protective for infants and children. Here, we review physiological and developmental differences that may result in differential sensitivity associated with early-life exposures. It is clear that sensitivity to chemical exposures during early-life can be similar, higher, or lower than that of adults, and can change quickly within a short developmental timeframe. Moreover, age-related exposure differences provide an important consideration for overall susceptibility. Differential sensitivity associated with a life stage can reflect the toxicokinetic handling of a xenobiotic exposure, the toxicodynamic response, or both. Each of these is illustrated with chemical-specific examples. The adequacy of current testing protocols, proposed new tools, and risk assessment methods for systemic noncancer endpoints are reviewed in light of the potential for differential risk to infants and young children.

Elevated titanium levels in Iraqi children with neurodevelopmental disorders echo findings in occupation soldiers

Anthropogenic release of pollutants into the environment is especially harmful to growing fetuses and young children. These populations are at an increased risk of damage because exposure to pollutants during critical periods of development can cause many impairments. Children's exposure to mixtures of metals could be responsible for the rising numbers of neurological disorders surfacing in Iraqi children. Titanium (Ti) and magnesium (Mg) are heavily used in war industries. Exposure to Ti and Mg has been linked to the dust in occupation soldiers' lungs. Hair samples of children in Hawija, Iraq (n = 13) contained significantly higher levels of Ti compared to Iranian children (n = 13) living near the Iraqi border (2080 ± 940 vs 707 ± 421 μg/kg, p < 0.0001). Magnesium was 1.7 times higher in Hawija children compared to Iranian children (115,763 ± 118,155 vs 67,650 ± 46,729 μg/kg). In samples from Hawija, Ti was 1.3 times higher in children with neurodevelopmental disorders (2198 ± 1108 vs 1942 ± 779 μg/kg), and Mg was 1.9 times higher in children without neurodevelopmental disorders (155,618 ± 140,791 vs 81,602 ± 91,940 μg/kg). Lead, arsenic, and cadmium in Hawija children with neurodevelopmental disorders (n = 6) were 2.5, 2.2, and 1.37 times higher compared to non-disabled children (n = 7). To get a clear understanding of the current status of neurodevelopmental disorders in Iraqi children and to determine the magnitude of this suspected global health issue, registries should be set up to compile and aggregate data from hospitals, clinics, and health centers across the country. Functional registries can develop collaborations with researchers toward finding causes of these disorders in Iraqi children and toward preventing them.

Wind of change challenges toxicological regulators

BACKGROUND

In biomedical research, the past two decades have seen the advent of in vitro model systems based on stem cells, humanized cell lines, and engineered organotypic tissues, as well as numerous cellular assays based on primarily established tumor-derived cell lines and their genetically modified derivatives.

OBJECTIVE

There are high hopes that these systems might replace the need for animal testing in regulatory toxicology. However, despite increasing pressure in recent years to reduce animal testing, regulators are still reluctant to adopt in vitro approaches on a large scale. It thus seems appropriate to consider how we could realistically perform regulatory toxicity testing using in vitro assays only.

DISCUSSION AND CONCLUSION

Here, we suggest an in vitro-only approach for regulatory testing that will benefit consumers, industry, and regulators alike.

Assaying embryotoxicity in the test tube: current limitations of the embryonic stem cell test (EST) challenging its applicability domain

Testing for embryotoxicity in vitro is an attractive alternative to animal experimentation. The embryonic stem cell test (EST) is such a method, and it has been formally validated by the European Centre for the Validation of Alternative Methods. A number of recent studies have underscored the potential of this method. However, the EST performed well below the 78% accuracy expected from the validation study using a new set of chemicals and pharmaceutical compounds, and also of toxicity criteria, tested to enlarge the database of the validated EST as part of the Work Package III of the ReProTect Project funded within the 6th Framework Programme of the European Union. To assess the performance and applicability domain of the EST we present a detailed review of the substances and their effects in the EST being nitrofen, ochratoxin A, D-penicillamine, methylazoxymethanol, lovastatin, papaverine, warfarin, β-aminopropionitrile, dinoseb, furosemide, doxylamine, pravastatin, and metoclopramide. By delineation of the molecular mechanisms of the substances we identify six categories of reasons for misclassifications. Some of these limitations might also affect other in vitro methods assessing embryotoxicity. Substances that fall into these categories need to be included in future validation sets and in validation guidelines for embryotoxicity testing. Most importantly, we suggest conceivable improvements and additions to the EST which will resolve most of the limitations.

Cluster of Hodgkin’s lymphoma in residents near a non-operational petroleum refinery

This report examines the prevalence rate of Hodgkin’s disease in an American mid-west town located directly south of a non-operational oil refinery. The refinery has a history of benzene-containing gasoline leaks dating back to the early 1900s. Exposure data were assessed through the Toxic Release Inventory (TRI) data as published by the Environmental Protection Agency (EPA) and supplemented by exposure simulations using variations of residential exposure times and odour levels and the benzene content of the gasoline. Prevalence rates depended on the size of the population in question. The population size varied greatly between sources, with the more conservative and consistent estimates being reported by the local government and United States Census Bureau and the highest population figure being reported by the Agency for Toxic Substances Disease Registry. The prevalence of Hodgkin’s disease for the residents within 1 mile from the refinery was found to be elevated for every population figure, ranging from 72.11 cases per 100,000 using the ATSDR’s population to 182.34 per 100,000, whereas the prevalence for Hodgkin’s disease in all the United States is only 22 cases of Hodgkin’s disease per 100,000 people. The prevalence value reported in this report should be given greater weight than what would have been calculated using data from the ATSDR. Because of its significantly increased value compared with the rest of the United States, it provides evidence of benzene’s role as a causative agent in the etiology of Hodgkin’s disease.

Evidence for carbon monoxide as the major factor contributing to lower fetal weights in rats exposed to cigarette smoke

One of the major effects of cigarette smoking during pregnancy is bearing a child with lower birth weight. It has previously been demonstrated under experimental conditions in rats that exposure to reference cigarette smoke results in reduced birth weight (E. L. Carmines et al., 2003, Toxicol. Sci. 75, 134-147; C. L. Gaworski et al., 2004, Toxicol. Sci. 79, 157-169). The role of various smoke constituents on lower birth weight was evaluated by exposing time-pregnant Sprague-Dawley rats at the concentrations found in cigarette smoke. The rats were exposed for 2 h/day 7 days/week by nose-only inhalation. The target concentrations were designed to produce the same plasma levels of biomarkers as exposure to 2R4F reference cigarette smoke at a concentration of 600 mg/m(3) total particulate matter. The smoke constituents evaluated included carbon monoxide (CO), nicotine, and a mixture of aldehydes (acrolein, acetaldehyde, and formaldehyde). The smoke constituents were tested individually as well as in mixtures to evaluate potential interactions. Exposure to cigarette smoke during gestation produced a reduction in both maternal body weight gain and fetal weights. Exposure to nicotine reduced maternal body weight gain but had no effect on fetal weight. Exposure to CO had no effect on maternal body weight gain but reduced fetal weight to a degree comparable to cigarette smoke. Exposure to a mixture of aldehydes (acrolein, acetaldehyde, and formaldehyde) had no effect on either maternal body weight gain or fetal weight. Exposure to mixtures of nicotine and CO or nicotine, CO, and aldehydes did not demonstrate any interactions. The results of this study suggest that the observed reduction in fetal weight after exposure to cigarette smoke in rats is due to CO toxicity and not nicotine toxicity.

A retrospective analysis of developmental toxicity studies in rat and rabbit: what is the added value of the rabbit as an additional test species?

In contrast to most toxicological tests, developmental studies are usually required in both a rodent and a non-rodent species. This study retrospectively assessed the added value of the rabbit developmental test when a rat developmental test is available. In contrast with previous reviews, we looked at developmental toxicity instead of teratogenicity, and took into account maternal toxicity in the evaluation of developmental toxicity. We analyzed data for 54 substances classified for developmental toxicity and 73 substances considered to be teratogenic in the rabbit and not in the rat in two previous reviews. On average, the rat and the rabbit developmental toxicity studies were similarly sensitive: the average ratio of the NOAELs between the two species was about one, and for most compounds there were no differences between rat and rabbit studies in terms of classification for developmental toxicity. For certain substances the developmental study in either one of the two species appeared to be more sensitive than in the other species. However, these differences are partly due to differences between studies other than the test species used. Overall, our analysis does not clearly indicate that the evaluation of developmental toxicity, as opposed to other types of toxicity, would specifically require the rabbit as an additional test species. The discrimination between direct and indirect (i.e., as a consequence of maternal toxicity) developmental effects was often doubtful, and is one of the factors that could explain the apparent differences between the two species. A more accurate assessment of maternal toxicity might improve the reliability of the results from a single developmental toxicity study. More knowledge about the interaction between maternal and developmental effects is required before decisions on omitting the requirement for the developmental toxicity testing in a second species can be considered.

A comprehensive model for reproductive and developmental toxicity hazard identification: I. Development of a weight of evidence QSAR database

A weight of evidence (WOE) reproductive and developmental toxicology (reprotox) database was constructed that is suitable for quantitative structure-activity relationship (QSAR) modeling and human hazard identification of untested chemicals. The database was derived from multiple publicly available reprotox databases and consists of more than 10,000 individual rat, mouse, or rabbit reprotox tests linked to 2134 different organic chemical structures. The reprotox data were classified into seven general classes (male reproductive toxicity, female reproductive toxicity, fetal dysmorphogenesis, functional toxicity, mortality, growth, and newborn behavioral toxicity), and 90 specific categories as defined in the source reprotox databases. Each specific category contained over 500 chemicals, but the percentage of active chemicals was low, generally only 0.1-10%. The mathematical WOE model placed greater significance on confirmatory observations from repeat experiments, chemicals with multiple findings within a category, and the categorical relatedness of the findings. Using the weighted activity scores, statistical analyses were performed for specific data sets to identify clusters of categories that were correlated, containing similar profiles of active and inactive chemicals. The analysis revealed clusters of specific categories that contained chemicals that were active in two or more mammalian species (trans-species). Such chemicals are considered to have the highest potential risk to humans. In contrast, some specific categories exhibited only single species-specific activities. Results also showed that the rat and mouse were more susceptible to dysmorphogenesis than rabbits (6.1- and 3.6-fold, respectively).

Hazard identification and predictability of children's health risk from animal data

Children differ from adults both physiologically and behaviorally. These differences can affect how and when exposures to xenobiotics occur and the resulting responses. Testing using animal models may be used to predict whether children display novel toxicities not observed in adults or whether children are more or less sensitive to known toxicities. Historically, evaluation of developmental toxicity has focused on gestational exposures and morphological changes resulting from this exposure. Functional consequences of gestational exposure and postnatal exposure have not been as well studied. Difficulties with postnatal toxicity evaluations include divergent differentiation of structure, function and physiology across species, lack of understanding of species differences in functional ontogeny, and lack of common end points and milestones across species.

Proposal for a tiered approach to developmental toxicity testing for veterinary pharmaceutical products for food-producing animals

In order to establish the safety of veterinary drug residues in human food, a number of toxicological evaluations are required, including the assessment of potential risks to development. In the light of the use of developmental toxicity testing for risk characterization, we evaluated whether conducting these tests in more than one species was redundant. Review of the published Summary Reports of recommendations of the EU Committee for Veterinary Medicinal Products supplemented with data from the Joint FAO/WHO Expert Committee on Food Additives (JECFA) reports on veterinary drug residues in food identified 120 compounds, of which 105 had teratogenicity information in more than one species. The analysis of these compounds, representing a variety of chemical and pharmacological classes, provided justification for consideration of the use of a tiered approach for developmental toxicity evaluation of veterinary drugs for food-producing animals. The tiered approach begins with developmental toxicity testing in a rodent species, preferably the rat. If teratogenicity is observed, no testing in a second species would be required, except under specific circumstances where the ADI is determined based on the NOEL from this study. If a negative or an equivocal result for teratogenicity were observed in the rodent, then a developmental test in a second species, preferably the rabbit, would be conducted. The tiered approach provides thorough hazard identification, based on the use of a second species for compounds negative for teratogenicity in the rodent, and maintains maximum public protection based on the extremely low potential for human exposure to these compounds, while making a genuine attempt to limit unnecessary animal testing.

Hazard identification by methods of animal-based toxicology

This paper is one of several prepared under the project "Food Safety In Europe: Risk Assessment of Chemicals in Food and Diet" (FOSIE), a European Commission Concerted Action Programme, organised by the International Life Sciences Institute, Europe (ILSI). The aim of the FOSIE project is to review the current state of the science of risk assessment of chemicals in food and diet, by consideration of the four stages of risk assessment, that is, hazard identification, hazard characterisation, exposure assessment and risk characterisation. The contribution of animal-based methods in toxicology to hazard identification of chemicals in food and diet is discussed. The importance of first applying existing technical and chemical knowledge to the design of safety testing programs for food chemicals is emphasised. There is consideration of the presently available and commonly used toxicity testing approaches and methodologies, including acute and repeated dose toxicity, reproductive and developmental toxicity, neurotoxicity, genotoxicity, carcinogenicity, immunotoxicity and food allergy. They are considered from the perspective of whether they are appropriate for assessing food chemicals and whether they are adequate to detect currently known or anticipated hazards from food. Gaps in knowledge and future research needs are identified; research on these could lead to improvements in the methods of hazard identification for food chemicals. The potential impact of some emerging techniques and toxicological issues on hazard identification for food chemicals, such as new measurement techniques, the use of transgenic animals, assessment of hormone balance and the possibilities for conducting studies in which common human diseases have been modelled, is also considered.

Teratogen update: evaluation of the reproductive and developmental risks of caffeine

Caffeine is a methylated xanthine that acts as a mild central nervous system stimulant. It is present in many beverages, including coffee, tea, and colas, as well as chocolate. Caffeine constitutes 1-2% of roasted coffee beans, 3.5% of fresh tea leaves, and approximately 2% of mate leaves (Spiller, '84; Graham, '84a,b). Many over-the-counter medications, such as cold and allergy tablets, headache medicines, diuretics, and stimulants also contain caffeine, although they lead to relatively minimal intake (FDA, '86). In epidemiological studies, it is assumed that one cup of coffee contains < or =100 mg of caffeine, and soft drinks, such as colas, contain 10-50 mg of caffeine per 12-ounce serving. The per-capita consumption of caffeine from all sources is estimated to be about 3-7 mg/kg per day, or approximately 200 mg/day (Barone and Roberts, '96). Consumption of caffeinated beverages during pregnancy is quite common (Hill et al., '77) and is estimated to be approximately 144 mg/day, or 2.4 mg/kg for a 60-kg human (Morris and Weinstein, '81). However, pregnant women appear to consume slightly less than do other adults, approximately 1 mg/kg per day (Barone and Roberts, '96). This decrease may be interrelated with taste aversion (Hook, '76; Little, '82). The medical literature contains many varied references that appear to indicate that human adverse reproductive/developmental effects are produced by caffeine. If caffeine indeed causes such effects, the reproductive consequences could be very serious because caffeine-containing foods and beverages are consumed by most of the human populations of the world, and consumption in the United States is estimated to be 4.5-kg/person/year (Narod et al., '91). Therefore, the medical literature dealing with developmental and reproductive risks of caffeine was reviewed, and the biological plausibility of the epidemiological and animal findings, as well as the methods and conclusions of previous investigators, were evaluated. The epidemiological studies describe exposures of women to caffeine during pregnancy, as well as the occurrence of congenital malformations, fetal growth retardation, small-for-date babies, miscarriages (spontaneous abortions), behavioral effects, and maternal fertility problems that presumably resulted from the caffeine consumption. A few epidemiological studies were concerned with the genetic effects of preconception exposures to caffeine. Animal studies, conducted mostly in pregnant rats and mice, were designed to produce malformations. The objectives of the present review are to summarize the findings from the various clinical and animals studies, objectively discuss the merits and/or faults inherent in the studies and establish a global reproductive risk assessment for caffeine consumption in humans during pregnancy. It should be noted that evaluation of the developmental risks of caffeine based solely on epidemiological studies is difficult because the findings are inconsistent. Even more important, is the fact that caffeine users are subject to multiple confounding factors that make analyses difficult and prevent investigators from reaching definitive conclusions. For example, the caffeine content of foods and beverages can vary considerably, which can interfere with obtaining valid interpretations from many human studies. Isolated epidemiological studies dealing with the risk of abortion, without evaluating other developmental and reproductive effects, are the most difficult to interpret, because they present special problems that are sometimes ignored in epidemiological studies. The results of animal studies are probably most helpful in solving some of the dilemmas created by the epidemiological studies. An animal study reported in 1960 first focused our attention on the potential developmental effects of caffeine. However, the exposure reported by Nishimura and Nakai ('60) was an intraperitoneal dosage of 250 mg/kg in the mouse, an extremely high dosage that would result in a blood plasma level that could never be obtained from consuming caffeine containing products. More recent animal studies have demonstrated, that depending on the method of administration and species, the developmental NOEL in rodents is approximately 30 mg/kg per day, the teratogenic NOEL is 8,100 mg/kg per day, and the reproductive NOEL approximately 80-120 mg/kg per day. Lack of biological plausibility to support the concept that caffeine has been responsible for human malformations is another important part of this analysis. For example, no one has described the Caffeine "teratogenic syndrome," a cluster of malformations associated with caffeine ingestion. Proven human teratogens have an identifiable syndrome. The malformations described in the animal studies at very high doses fit the description of vascular disruptive types of malformations. (ABSTRACT TRUNCATED)

Assessment of the U.S. Environmental Protection Agency methods for identification of hazards to developing organisms, Part II: The developmental toxicity testing guideline

BACKGROUND

The effects of toxins on developing animals depend not only on the nature of the chemical but also on the timing of exposure and assessment of outcomes. This complicates the task of regulatory agencies such as the U.S. Environmental Protection Agency (EPA), which must comply with the 1996 Food Quality Protection Act to ensure that their standards and policies protect infants and children from environmental toxins. For this task, the Agency relies heavily on scientific data obtained by manufacturers of industrial chemicals and pesticides following protocols collected under EPA's Health Effects Test Guidelines.

METHODS AND RESULTS

This article reviews the protocols included in the EPA guidelines to assess developmental toxicity, which are required for food-use pesticides under the core testing battery. We reviewed these protocols on the basis of their adequacy for identifying hazards to infants and children. Our analysis found limitations in the protocols that hinder their potential for identifying developmental hazards.

CONCLUSIONS

Methods that the EPA currently depends upon to identify developmental toxicity of chemicals have limitations that impede obtaining complete and reliable data on which to base regulatory decisions that protect children. Other methodological approaches need to be explored as alternatives or supplements to the current protocols. Until more accurate testing protocols become available, it may well be necessary under existing laws to employ safety factors that are more protective of the health of children at all stages of development.

ATSDR evaluation of health effects of chemicals. V. Xylenes: health effects, toxicokinetics, human exposure, and environmental fate

Xylenes, or dimethylbenzenes, are among the highest-volume chemicals in production. Common uses are for gasoline blending, as a solvent or component in a wide variety of products from paints to printing ink, and in the production of phthalates and polyester. They are often encountered as a mixture of the three dimethyl isomers, together with ethylbenzene. As part of its mandate, the Agency for Toxic Substances and Disease Registry (ATSDR) prepares toxicological profiles on hazardous chemicals found at Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) National Priorities List (NPL) sites that are of greatest concern for public health purposes. These profiles comprehensively summarize toxicological and environmental information. This article constitutes the release of the bulk of this profile (ATSDR, 1995) into the mainstream scientific literature. An extensive listing of known human and animal health effects, organized by route, duration, and end point, is presented. Toxicological information on toxicokinetics, biomarkers, interactions, sensitive subpopulations, reducing toxicity after exposure, and relevance to public health is also included. Environmental information encompasses physical properties, production and use, environmental fate, levels seen in the environment, analytical methods, and a listing of regulations. ATSDR, as mandated by CERCLA (or Superfund), prepares these profiles to inform and assist the public.

Benzene--a review of the literature from a health effects perspective

A literature review of the impact on human health of exposure to benzene was conducted. Special emphasis in this report is given to the health effects reported in excess of national norms by participants in the Benzene Subregistry of the National Exposure Registry--people having documented exposure to benzene through the use of benzene-contaminated water for domestic purposes. The health effects reported in excess (p < or = .01) by some or all of the sex and age groups studied were diabetes, kidney disease, respiratory allergies, skin rashes, and urinary tract disorders; anemia was also increased for females, but not significantly so.

Translactational exposure of F1 mouse pups to selenium

In an investigation of the modulation of certain neonatal xenobiotic-metabolizing enzymes in liver of mouse pups postnatally exposed to selenium through the transmammary route, sodium selenite was administered in drinking water to lactating dams at the dose levels of 1 or 5 ppm from day 1 of lactation and continued daily for 14 or 21 days. The higher dose of selenium was found to increase the hepatic acid-soluble sulfhydryl content significantly after 21 days of treatment in dams, their pups (P < 0.01) and in the 14-day-old male pups (P < 0.05). Cytochrome b5 content decreased in the livers of dams that received 5 ppm selenium (P < 0.01) and in the F1 pups (P < 0.01) translactationally exposed to selenium for 14 days. Cytochrome P-450 content decreased in dams and pups exposed to 5 ppm selenium for 14 days and either dose for 21 days (P < 0.01). Hepatic glutathione S-transferase decreased in the dam that had received 5 ppm selenium for 14 days (P < 0.05) and in the 14-day-old pups (P < 0.01). Glutathione reductase and glutathione peroxidase activities decreased in both dams and pups (P < 0.01). The overall suppression of neonatal hepatic detoxification enzymes demonstrates that selenium may have far-reaching consequences on neonatal growth, development and drug pharmacokinetics.

Genetic toxicity studies of gossypol

Gossypol, a polyphenolic compound extracted from cotton plants, shows promise for use as a male contraceptive, as well as a treatment for gynecological disorders, cancer, and certain microbial diseases. Before gossypol can be considered safe for widespread human use, particularly by healthy people of childbearing age, its effect on normal genetic processes should be understood. Characterization of gossypol's genotoxic potential has not been approached systematically, although numerous clinical and laboratory studies have addressed issues relating to genetic effects of gossypol. This review summarizes results of relevant studies and offers recommendations for the emphasis of future efforts to understand gossypol's genotoxicity potential. Evidence suggesting that gossypol has any genotoxic effects in mammals under normal physiologic conditions so far is weak, at best. However, several unresolved issues that are important for establishing long-term genetic safety of gossypol were uncovered by this analysis. These include the need for a better understanding of the significance of weak increases in SCE frequency seen in a number of laboratory exposure studies, and more definitive, comprehensive animal tumor bioassay data.

Studies on the prenatal toxicity of toluene in rabbits following inhalation exposure and proposal of a pregnancy guidance value

Prenatal toxicity of toluene was determined in two separate studies by inhalation exposure of Himalayan rabbits. In the first study 15 artificially inseminated females per group were exposed to 30, 100, or 300 ppm and in the second study 20 artificially inseminated females per group inhaled 100 or 500 ppm. In each case the rabbits were exposed for 6 hours per day from day 6 post-insemination (p.i.) to day 18 p.i. The respective controls inhaled conditioned clean air under the same exposure conditions. No signs of maternal toxicity were observed. All data obtained on gestational parameters were found to be within the variation range reported for this rabbit strain. The fetal external, soft tissue and skeletal findings were seen in toluene exposed fetuses in a frequency similar to the corresponding and/or historical controls. Differences observed between the groups were not concentration dependent and were considered incidental rather than compound related. Therefore, toluene was not embryotoxic, fetotoxic, or teratogenic for rabbits exposed during the period of organogenesis. The highest concentration tested under these conditions (500 ppm) was found to be a no-observable-adverse-effect level (NOAEL) for both the adult and the fetal Himalayan rabbit. Based on these and previous results of animal studies of prenatal toxicity, a safety or uncertainty factor approach is considered for setting limits of exposure for women at workplaces. A pregnancy guidance value of 20 ppm is proposed.

Prioritizing candidate reproductive/developmental toxicants for evaluation

To provide a rational method for the timely evaluation of possible reproductive/developmental toxicants, a prioritization scheme was developed by the California Department of Health Services to select chemicals for consideration by the Proposition 65 Scientific Advisory Panel. Initially, four ascertainment methods were used to identify and construct a master list of 164 candidate agents. Using two criteria, the potential for human exposure and the perceived reproductive/developmental hazard as judged by an ad hoc committee of experts, 42 candidates from the master list were identified as priority agents. For practical purposes, the 15 priority agents with the highest rankings will be given the highest priority in the review process. Limitations in the prioritization method used and refinements to be incorporated in an annual update are described.

Dangerous and cancer-causing properties of products and chemicals in the oil refining and petrochemical industry--Part II: Carcinogenicity, mutagenicity, and developmental toxicity of 1,3-butadiene

1,3-butadiene (BD) is present in synthetic rubber and motor fuels (gasoline). BD is shown to cause lymphocytic lymphomas, heart hemangiosarcomas, lung alveolar bronchiolar cancers, forestomach-squamous cell cancers, harderian gland neoplasms, preputial gland adenoma or carcinoma, liver-hepatocellular cancers, mammary gland acinar cell carcinomas, ovary-glanulosa cell carcinoma, brain cancers, pancreas adenoma and carcinoma, testis-Leydig cell tumors, thyroid follicular adenoma and carcinoma, and zymbal gland carcinoma in rodents and to date no exposure level has been established at which this chemical does not cause cancers. In humans BD causes increase in lymphomas, leukemias, and other cancers of hematopoietic systems and organs. BD is also a potent alkylating agent, directly toxic to developing embryos and damages progeny after parental exposure.

Evidence for behavioral teratogenicity in humans

Central to both the scientific development of behavioral teratology and the attention paid to this field as an important area of study is establishing that prenatal exposure of pregnant females to exogenous agents leads to neurobehavioral disorders in their offspring. This tenet may not be questioned by the majority of toxicologists, but others may not be convinced. This paper serves as a brief review of the accumulated evidence that prenatal exposure to a number of drugs and environmental/industrial agents produces behavioral disorders in human infants.

Nonhuman primates in behavioral toxicology: issues of validity, ethics and public health

The small, but vital, niche of nonhuman primates in neurotoxicology is examined. Several models of sensory and cognitive function have been especially useful with primates. Their sensitivity to low doses is clear. The validity of data from these models is indicated by their high correlation with data from intoxicated and normal humans, by the degree to which they approximate job functions and other vital human performances, and by their ability to document specific changes in behavioral function which correlate well with morphological and biochemical effects. The use of primates for this research is justified by the absence of adequate alternatives using nonprimate species, in vitro tests or computer programs. A series of experiments on the effects of methylmercury is used to illustrate ethical and scientific issues concerning research with primates. Recent trends are illustrated by data with trimethyltin.