Maternal toxicity

Although demonstration of some degree of maternal toxicity is required in regulatory developmental toxicology studies, marked maternal toxicity may be a confounding factor in data interpretation. Reduction in maternal body weight gain is the far most frequently used endpoint of toxicity, but alternative endpoints, like organ toxicity or exaggerated pharmacological response, can also be taken into consideration. The following conclusions are based on literature data and discussions at maternal toxicity workshops attended by representatives from regulatory agencies, academia, and industry: (1) Available results do not support that maternal toxicity (defined as clinical signs, decreased body weight gain or absolute body weight loss of up to 15% in rats or 7% in rabbits) can be used to explain the occurrence of major malformations. (2) There is clear evidence that substantial reductions in maternal weight gain (or absolute weight loss) are linked with other manifestations of developmental toxicity. Among these can be mentioned decreased fetal weight, and skeletal anomalies (e.g., wavy ribs) in rats and decreased fetal weights, post implantation loss, abortions, and some skeletal anomalies in rabbits. (3) There are several examples of misinterpretation among companies, where it was incorrectly expected that regulatory authorities would not label chemicals/drugs as "teratogens/developmental toxicants" because embryo fetal adverse effects were only observed at doses also causing signs of maternal toxicity. (4) Similarly, even if mechanistic studies indicate that a substance causes developmental toxicity via exaggerated pharmacological effects in the mother, such a mechanism does not automatically negate the observed fetal adverse effects.From a regulatory perspective, an observed developmental toxic finding is considered to be of potential human relevance (even if it is mediated via maternal pharmacological effects or occur at doses causing signs of maternal toxicity) unless the company can provide appropriate mechanistic and/or other convincing evidence to the contrary.

The enhanced pre- and postnatal development study for monoclonal antibodies

The enhanced pre- and postnatal (ePPND) study design has been developed in response to new scientific knowledge and subsequent guideline changes [ICH M3(R2) and ICH S6(R1)]. The changes in study design were basically driven by the experiences obtained during preclinical development of biopharmaceuticals. The standard ePPND concept does not apply to conventional small molecule pharmaceuticals. In essence, the ePPND design is a pre- and postnatal development (PPND) study in which key elements of an embryo-fetal development study are investigated in newborns and infants rather than in the fetus. The cynomolgus monkey is the current relevant nonhuman primate model. The ICH S6(R1) guideline reached step 5 in June 2011 and provides detailed recommendations on various parameters and the conduct of an ePPND study. This chapter provides working guidance for monitoring menstrual cycles to generate pregnant animals, ultrasound monitoring of pregnancy, morphometric measurements of fetuses and newborns, in vivo skeletal examination, various protocols for evaluation of infants (e.g., neurobehavioral assessment, learning and memory test, grip strength, immune system evaluation) and a comprehensive list of additional infant evaluation parameters for the cynomolgus monkey.

Reproductive toxicity risk assessment for pesticides

Human health risk assessment for pesticides is based mainly on animal studies submitted by the applicant and aims to determine safe exposure levels for operators (farmers and agricultural workers) and consumers of all age groups. Critical effects, including those resulting from reproductive toxicity, are identified during hazard assessment from an evaluation of all studies in the toxicity package. Reproductive or developmental effects are considered critical if they are more severe or occur at lower doses than other toxicities. Reference values for human exposure are then derived from No Adverse Effect Levels for the relevant critical effects by applying safety factors. This paper describes methods and caveats applicable to the evaluation of prenatal toxicity and two-generation studies from the view of a regulator, stressing the importance of individual litter data and the relationship between different endpoints.

Teratology testing under REACH

REACH guidelines may require teratology testing for new and existing chemicals. This chapter discusses procedures to assess the need for teratology testing and the conduct and interpretation of teratology tests where required.

Reporting of teratology studies

The regulatory toxicology report is an unusual document that requires a particular skill to write. The report must be clear, accurate, concise, and focused. A clear and direct writing style is required. The end-users of the report will hope to find the information they seek with as little effort as possible. Few, or none, will read the entire document. The author should aim to appease the user by obliging him to read as little text and turn as few pages as possible. This chapter gives tips and guidance on how to present the experimental data and write the narrative text in the final study report for a teratology study.

Teratology studies in the minipig

The minipig is a suitable species for regulatory teratology testing and may be regarded as an alternative to the rabbit, dog, and primate. The first successful regulatory teratology studies in the minipig were performed in the 1990s. It became clear that minipigs have several benefits over the other non-rodents, as they are purpose-bred for laboratory use, they are sexually mature at approximately 5 months of age, and they produce multiple offspring. The minipig has subsequently gained regulatory acceptance in the teratology testing of new drugs.

Teratology studies in the rat

The rat is the rodent species of choice for the regulatory safety testing of xenobiotics, such as medicinal products, food additives, and other chemicals. Many decades of experience and extensive data have accumulated for both general and developmental toxicology investigations in this species. The high fertility and large litter size of the rat are advantages for teratogenicity testing. The study designs are well defined in the regulatory guidelines and are relatively standardized between testing laboratories across the world. Teratology studies address maternal- and embryo-toxicity following exposure during the period of organogenesis. This chapter describes the design and conduct of a teratology study in the rat in compliance with the regulatory guidelines. The procedures for the handling and housing of the pregnant animals, the caesarean examinations and the sampling of fetuses for morphological examinations are described. The utility and design of preliminary studies and the inclusion of satellite animals in the main study for toxicokinetic sampling are discussed.

Frog embryo teratogenesis assay on Xenopus and predictivity compared with in vivo mammalian studies

Frog embryo teratogenesis assay on Xenopus (FETAX) has been routinely used in our laboratory for the last 12 years as a routine developmental toxicity screening test for pharmaceutical candidate compounds. To date, out of more than 400 candidates tested in FETAX, around 60 have also been evaluated in mammalian embryotoxicity studies according to standard ICH protocols.Compound teratogenic potential in both FETAX and mammalian embryotoxicity studies is determined after analysis of the developmental toxicity characterized by embryotoxicity, growth delay, and/or potential to induce malformations. Based on this experience, the predictivity of FETAX is 81% with a minimal proportion of false positive results.

Teratology studies in the rabbit

The rabbit is generally the non-rodent species or second species after the rat recommended by the regulatory authorities and is part of the package of regulatory reproductive studies for the detection of potential embryotoxic and/or teratogenic effects of pharmaceuticals, chemicals, food additives, and other compounds, including vaccines (see Chapters 1-7).Its availability, practicality in housing and in mating as well as its large size makes the rabbit the preferred choice as a non-rodent species. The study protocols are essentially similar to those established for the rat (Chapter 9), with some particularities. The study designs are well defined in guidelines and are relatively standardized between testing laboratories across the world.As for the rat, large litter sizes and extensive background data in the rabbit are valuable criteria for an optimal assessment of in utero development of the embryo or fetus and for the detection of potential external or internal fetal malformations.

The teratology testing of food additives

The developmental and reproductive toxicity testing (including teratogenicity) of new foods and food additives is performed worldwide according to the guidelines given in the FDA Redbook. These studies are not required for substances that are generally recognized as safe, according to the FDA inventory. The anticipated cumulated human exposure level above which developmental or reproduction studies are required depends on the structure-alert category. For food additives of concern, both developmental (prenatal) and reproduction (multigeneration) studies are required. The developmental studies are performed in two species, usually the rat and the rabbit. The reproduction study is generally performed in the rat. The two rat studies are preferably combined into a single experimental design, if possible. The test methods described in the FDA Redbook are similar to those specified by the OECD for the reproductive toxicity testing of chemicals.

Embryonic cardiac arrhythmia and generation of reactive oxygen species: common teratogenic mechanism for IKr blocking drugs

In the adult organism, it is well established that hypoxia followed by reperfusion may be fatal and result in generation of reactive oxygen species (ROS) and subsequent tissue damage. There is also considerable evidence that temporary decrease or interruption in oxygen supply to the embryo and ROS generation during reperfusion result in tissue damage in embryonic tissues. A wide spectrum of different malformations by transient embryonic hypoxia could be produced, depending on the duration, extent, and timing of the hypoxic event. It is the contention of this paper that drugs that block the potassium channel IKr, either as an intended pharmacologic effect or as an unwanted side-effect, are potentially teratogenic by a common ROS related mechanism. Drugs blocking the IKr channel, such as almokalant, dofetilide, phenytoin, cisapride and astemizole, do all produce a similar pattern of hypoxia-related malformations. Mechanistic studies show that the malformations are preceded by embryonic cardiac arrhythmia and periods of hypoxia/reoxygenation in embryonic tissues. Pretreatment or simultaneous treatment with radical scavengers with capacity to capture ROS, markedly decrease the teratogenicity of different IKr blocking drugs. A second aim of this review is to demonstrate that the conventional design of teratology studies is not optimal to detect malformations caused by IKr blocking drugs. Repeated high doses result in high incidences of embryonic death due embryonic cardiac arrhythmia, thus masking their teratogenic potential. Instead, single dosing on specific days is proposed to be a better way to characterize the teratogenic potential of Ikr blocking drugs.

Gastrulating chick embryo as a model for evaluating teratogenicity: A comparison of three approaches

BACKGROUND

Teratology studies must be carefully designed to minimize potential secondary effects of vehicle and delivery routes. A systematic method to evaluate chick models of early embryogenesis is lacking.

METHODS

We investigated 3 experimental approaches that are popular for studies of early avian development, in terms of their utility for teratogen assessment starting at gastrulation. These included in vitro embryo culture, egg windowing followed by direct application of a carrier vehicle to the embryo, and injection of a carrier vehicle into the egg yolk. We also developed a morphologically based scoring system to assess development of the early embryo.

RESULTS

The in vitro culture and egg windowing approaches both caused an unacceptably high incidence of central nervous system and cardiac abnormalities in vehicle-treated embryos, which made it difficult to identify teratogen-specific defects. In contrast, exposing chick embryos to vehicle via direct egg yolk injection did not induce developmental anomalies.

CONCLUSIONS

Optimization of the exposure route of potential toxicants to the embryo is critical because control treatments can cause developmental anomalies. In ovo yolk injection minimizes perturbation of young embryos and may be appropriate for teratogen delivery.

Teratogenic effects of static magnetic field on mouse fetuses

A short period of exposure of pregnant mice to a strong static magnetic field of 400 mT -- 8000 times that of the earth -- in a dorso-ventral direction had teratogenic effects on developing fetuses. Fetuses were exposed to the static magnetic field in utero for 6 min on 1 day from 7.5 to 14.5 days of pregnancy. Exposed and control groups consisted of 10 pregnant mice each; thus 160 animals were used in total. Various malformations were observed in 15.1%, 13.4%, 15.8%, 16.7%, 20.8%, 24.3%, 24.4%, and 14.1% of fetuses exposed on days 7.5, 8.5, 9.5, I0.5, 11.5, 12.5, 13.5, and 14.5 of pregnancy, respectively. Types of malformations were polydactylism, abdominal fissure, fused rib, vestigial 13th rib, lumbar rib, brain hernia, and curled tail, while only a low incidence (up to 2.8%) of curled tail was detected in control group. These deformations apparently caused by SMF exposure but the effect did not reflect so-called exposure period specificity.

The contribution of new findings and ideas to the old principles of teratology

Although the last generally accepted concept of principles of teratology was issued more than 30 years ago, the cause of less than 50% of all congenital anomalies is known and no substantial change in their incidence has been observed worldwide. In the meantime, powerful techniques of molecular biology as well as many sophisticated preventive measures have been introduced with marginal effects on the overall birth defects numbers. In this paper, we follow the history of basic concepts of teratology starting with Isidore Geoffroy Saint-Hilaire and Dareste, followed in the 20th century by James Wilson. Since that time no bright and completely new idea, which would deserve the name principle, has emerged. The advanced molecular studies support the long-existing principles and disclose the great variability of individuals and their responses to adverse exposures. In this way, the future of teratology counseling may be seen in a deep analysis of any individual case.

Morphological studies in modern teratological investigations

Despite the variety of modern molecular techniques available, examination of foetal anatomy is still a fundamental part of teratological studies in evaluating the developmental toxicity of xenobiotics or other non-chemical factors. The article presents contemporary methods of embryotoxicity and foetotoxicity assessment. A single alizarin red S and double alcian blue followed by alizarin red S staining, as well as various methods of soft tissue examination are discussed.

Radiofrequency fields and teratogenesis

Experimental studies that sought teratologic effects or developmental abnormalities from exposure to radiofrequency electromagnetic fields (RFEMF) in the range 3 kHz-300 GHz are critically reviewed for their possible consequences on human health. Those studies were conducted on beetles, birds, rodents, and nonhuman primates. Collectively, those experimental studies indicate that teratologic effects can occur only from exposure levels that cause biologically detrimental increases in body temperature. No reliable experimental evidence was found for nonthermal teratologic effects; rodents, mouse fetuses, and perinatal mice are more susceptible to such effects than rats. The primary confirmed effect in rats at high RFEMF levels was initial weight deficits in fetuses and neonates that decreased with infant growth. More generally from findings with pregnant mammals, exposures at RFEMF levels far higher than those permitted under the IEEE human exposure guidelines are necessary to reach or exceed cited experimental thresholds for maternal temperature increases. Some results indicated that the levels necessary to cause such effects in pregnant mammals could exceed those lethal to the dams. In a behavioral study of squirrel monkeys, no effects were observed on usual dam-offspring interactions or EEGs, but unexpected deaths of a number of offspring had occurred. However, this finding was not confirmed in a study solely on infant death using a larger number of subjects for greater statistical validity. Also reviewed were epidemiologic studies of various human populations considered to have been chronically exposed to environmental levels of RFEMF. Early studies on the incidence of congenital anomalies yielded no credible evidence that chronic exposure of pregnant women or of fathers exposed to RFEMF from nearby sources at levels below those guidelines would cause any anomalies in their offspring. The findings of studies on pregnancy outcomes of female physiotherapists occupationally exposed while treating patients with RFEMF were mixed, but taken collectively, the findings were negative.

Application of the mouse exo utero development system in the study of developmental biology and teratology

The mouse exo utero development system is useful for analyzing the roles of molecules or interactions between tissues in the histogenesis of organs after the mid-gestational period. In the article presented here, we review the mouse exo utero development system and its specific modifications depending on different purposes as well as its advantages over and limitations compared to other systems in the study of developmental biology and teratology.

Joint models for toxicology studies with dose-dependent number of implantations

Many chemicals interfere with the natural reproductive processes in mammals. The chemicals may prevent the fertilization of an egg or keep a zygote from implanting in the uterine wall. For this reason, toxicology studies with pre-implantation exposure often exhibit a dose-related trend in the number of observed implantations per litter. Standard methods for analyzing developmental toxicology studies are conditioned on the number of implantations in the litter and therefore cannot estimate this effect of the chemical on the reproductive process. This article presents a joint modeling approach to estimating risk in toxicology studies with pre-implantation exposure. In the joint modeling approach, both the number of implanted fetuses and the outcome of each implanted fetus is modeled. Using this approach we show how to estimate the overall risk of a chemical that incorporates the risk of lost implantation due to pre-implantation exposure. Our approach has several distinct advantages over previous methods: (1) it is based on fitting a model for the observed data and, therefore, diagnostics of model fit and selection apply; (2) all assumptions are explicitly stated; and (3) it can be fit using standard software packages We illustrate our approach by analyzing a dominant lethal assay data set (Luning et al., 1966, Mutation Research, 3, 444-451) and compare ourresults with those of Rai and Van Ryzin (1985, Biometrics, 41,1-9) and Dunson (1998, Biometrics, 54, 558-569). In a simulation study, our approach has smaller bias and variance than the multiple imputation procedure of Dunson.

Optimal designs for estimating the effective dose in developmental toxicity experiments

Recent advances in risk assessment have led to the development of joint dose-response models to describe prenatal death and fetal malformation rates in developmental toxicity experiments. These models can be used to estimate the effective dose corresponding to a 5% excess risk for both these toxicological endpoints, as well as for overall toxicity. In this article, we develop optimal experimental designs for the estimation of the effective dose for developmental toxicity using joint Weibull dose-response models for prenatal death and fetal malformation. Based on an extended series of developmental studies, near-optimal designs for prenatal death, malformation, and overall toxicity were found to involve three dose groups: an unexposed control group, a high dose equal to the maximum tolerated dose, and a low dose above or comparable to the effective dose. The effect on the optimal designs of changing the number of implants and the degree of intra-litter correlation is also investigated. Although the optimal design has only three dose groups in most cases, practical considerations involving model lack of fit and estimation of the shape of the dose-response curve suggest that, in practice, suboptimal designs with more than three doses will often be preferred.

Conceptual issues in behavioral teratology and their application in determining long-term sequelae of prenatal marihuana exposure

BACKGROUND

Behavioral teratology, particularly as it is applied to the evaluation of cognition and behavior of children beyond the toddler stage, has become an area of burgeoning activity. In the area of drug abuse, children exposed in utero are often at developmental peril because of non-drug pre- and postnatal risk factors that make a causal association between the drug of interest and a behavioral teratogenic outcome increasingly problematic as the child gets older.

METHODS

In the first portion of this review, the strategies that behavioral teratologists have undertaken to investigate the putative consequences of in utero exposure are discussed in terms of research design, statistical methods and interpretative approaches. In the second part of the paper, the relatively limited literature dealing with the behavioral teratological consequences of prenatal marihuana exposure, particularly in school age offspring, is reviewed.

RESULTS

An emergent theme arising from primarily two longitudinal investigations is that in utero cannabis exposure does not impact upon standardized derived IQ scores but is negatively associated with attentional behavior and visual analysis/hypothesis testing. These findings are interpreted as supporting the hypothesis that, among offspring beyond the toddler stage, prenatal marihuana exposure has a negative influence on aspects of executive function. Executive function is a 'top-down', multifaceted cognitive construct involved in organizing and integrating specific cognitive and output processes over a interval of time and is largely mediated by the late developing, prefrontal region of the brain.

CONCLUSIONS

The results and the interpretation of the prenatal marihuana findings are discussed in terms of the behavioral teratogenic effects (or lack of effects) during the various developmental stages of the offspring, the non-unitary nature of executive function, cannabis receptors, and the consequences of chronic marihuana use in the non-pregnant population.

Exploring extra-binomial variation in teratology data using continuous mixtures

Discrete data from animal teratology experiments are known to exhibit extra-binomial variation. For example, we discuss a dominant lethal assay experiment in which male mice are exposed to various levels of radiation and are then mated to females. The response of interest is the number of resorptions out of the number of implantations. Most statistical work on analyzing such data has focused on modeling response rates as a function of dose of a suspected teratogen (radiation in this case) while accounting for the extra-binomial variability when calculating standard errors of the regression coefficients. Sometimes, however, when an unobserved genetic or exposure variable is suspected, the shape of the mixing distribution is of interest. We propose a mixture of beta-binomials (MBB) family of distributions that includes the non-parametric mixture of binomials model of Laird (1978) as a special case. The MBB family can accommodate a mixing distribution with one or more modes, and we develop a bootstrap test for multimodality. We apply the method to data from a dominant lethal teratology experiment.

Overview of teratology

Teratology is the study of developmental processes to understand the causes and mechanisms of abnormal developmental outcomes. This unit provides an explanation of the basic principles of the field as a context for the more specialized protocol units to follow in the chapter.

Important hints in behavioural teratology of rodents

The paper deals with the most important items regarding the improvement of quality of experimental procedures when testing drug effects on behaviour and development of commonly-used rodent species. Current-used test procedures for immature and adult rodents exposed early developmentally are briefly described and recent advances and difficulties in their hands-on interpretation are highlighted. Comparability of measures in human and animals for drug-effect assessment is also shortly discussed. It is then stressed that studies on rodents carried out in seminaturalistic and naturalistic settings may offer a highly profitable direction for future research in behavioural teratology and toxicology. A final paragraph is dedicated to the bioethical aspects arisen from the use of large number of rodents subjects in behavioural testing.

Dose-dependent number of implants and implications in developmental toxicity

This paper proposes a method for assessing risk in developmental toxicity studies with exposure prior to implantation. The method proposed in this paper was developed to account for a dose-dependent trend in the number of implantation sites per dam, which is a common problem in studies with exposure prior to implantation. Toxins may have the effect of interfering with the early reproductive process, which can prevent implantation in the uterine wall. An imputation procedure is presented for estimating the number of potential fetuses by sampling from the empirical distribution of the number of implants per litter in the control group. The marginal death outcomes and the joint malformation and survival outcomes for each potential fetus can be estimated using multiple imputation or the chained data augmentation algorithm. Logit models can then be fit and used to estimate the effect of dose on reducing the probability of a normal birth. These models accommodate multiple covariate effects and can be applied to low-dose extrapolation. A simulation study is done to evaluate the properties of model-based estimators of the mean response and the virtually safe dose level (VSD). It was found that both estimates were good approximations of the underlying dose effect. A dominant lethal assay data set (Luning et al., 1966, Mutation Research 3, 444-451) is analyzed, and the results are compared with those of Rai and Van Ryzin.

Use of chick embryo in screening for teratogenicity

A teratology screening system would detect agents hazardous to the conceptus before they can perturb embryonic development in humans. The back log of untested chemicals and the rate at which new substances enter the market exceed the developmental effects testing by standard in vivo method. Thus, cheaper, quicker in vitro systems afford a unique opportunity for investigating the direct interaction of substances with developing morphogenetic system (MGSs), since maternal influences are excluded. As a carrier of a complete set of MGSs, the chick embryo in ovo manifests an advantage over those in vitro systems that employ isolated embryos or embryonic tissues that have only limited survival. Under controlled experimental conditions including standardization of subjects, administration technique and mode of evaluation, according to the basic principles of teratology, the chick embryo test is demonstrated to be reliable and to afford quantifiable end points for evaluation. Individual compounds, mixtures of compounds and against and antagonist can easily be administered and tested. The chick embryo possesses its own basic enzyme-catalyzed drug-transformation capacity and moreover, it can be used for screening specific human metabolites. Different newer techniques e.g. chick embryotoxicity screening test (CHEST), Chick embryo blastoderm model etc are described in detail. Chick embryo fulfills all the criteria which a test should have at a lower level of tier system in teratological studies i.e. modest laboratory equipment, moderate skill, minimal expenditure of time and money, ease of accessibility of embryo, known embryological development, possibility of experimenting on a large scale for statistically valid results and whole animals are also not required.

Perspectives on the use of the baboon in embryology and teratology research

This paper summarizes the developmental stages of the baboon during the period of organ formation and provides comparative information for other primates, including the human. Special attention is directed to the early development of the nervous system, eye, ear and nose/palate. The similarity in development of these structures with humans indicates that the baboon is a suitable model for studies of normal and abnormal neurological development. Spontaneous prenatal loss rates in the baboon (2.4-11.2%) are slightly lower than those reported in rhesus and cynomologus monkeys. The baboon, in addition to the cynomologus monkey and macaque, has been used as a model in teratology research to assess the potential risk of thalidomide, sex steroids, Bendectin and rubella virus, as well as to study the pathogenesis of malformations associated with the corticosteroid triamcinolone acetonide. The rate of spontaneous malformations (<1%) in baboons, similar to that reported for other commonly used primates, supports their continued use as a teratological model. In this regard, a sample protocol is provided for the safety evaluation of biotechnology products using nonhuman primates, which are the most appropriate model for those compounds which are bioactive in species closely related to humans.

Methodological considerations in neurobehavioral teratology

Neurobehavioral teratology is a rapidly expanding field benefitting from recent advances in neurobiology and behavior and from the increasing availability of compounds with specific pharmacological actions. There is evidence that data derived from animal studies are clinically pertinent and hence animal studies are useful in extending clinical findings, in anticipating consequences of early drug exposure and, by determining the underlying neural mechanisms, in developing therapeutic approaches. However, the usefulness of animal studies crucially depends on the reliability and sensitivity of the methods used. We highlight the importance of appropriate selection of the route, dose, frequency, duration and timing of drug administration. We also emphasize the importance of not confounding treatment with litter effects and suggest that either the litter be used as the unit of analysis, or that each litter contribute only one pup to each test condition. We discuss the question of the time of testing and of testing, not only under baseline conditions, but also in conditions in which the offspring are exposed to stressful, pharmacological or cognitive challenges. We hope that future studies will benefit from these considerations and avoid the methodological weaknesses that beset some of the early studies in this field.

Cryopreservation of semen from Japanese white rabbits for use in teratological studies

Cryopreservation of semen from Japanese White rabbits was examined to reduce the number of their males for use in teratological studies. Semen was frozen with liquid nitrogen, preserved, thawed, and tested for motility according to the method of Chen et al. Even after cryopreservation an average of 52% of the thawed sperms were motile. In a previous study, frozen- thawed sperms with a motility of 40% resulted in a high conception rate (approximately 88%) on artificial insemination when New Zealand White rabbits were used [5]. These results indicate the possibility that cryopreservation of semen from Japanese White rabbits may be used in teratological studies to reduce the number of males.

Cluster sampling techniques in quantal response teratology and developmental toxicity studies

This paper presents a model-free approach for evaluating teratology and developmental toxicity data involving clustered binary responses. In teratology studies, a major statistical problem arises from the effect of intralitter correlation, or the potential for littermates to respond similarly. Some statistical methods impose strict distributional assumptions to account for extra-binomial variation, while others rely on nonparametric resampling and empirical variance estimation techniques. Quasi-likelihood methods and generalized estimating equations (GEE), which model the marginal mean/variance relationship, also avoid strict distributional assumptions. The proposed approach, often used to analyze complex sample survey data, is based on a first-order Taylor series approximation and a between-cluster variance estimation procedure, yielding consistent variance estimates for binomial-based proportions and regression coefficients from dose-response models. The cluster sample technique, presented here in the context of a logistic dose-response model, incorporates many of the advantages of quasi-likelihood methods, are valid for any underlying nested correlation structure, and are adaptable to a variety of analytical settings. The results of a simulation study show the cluster sample technique to be a viable competitor to GEE methods currently receiving attention.

Toxicological evaluation of u-hEGF

The toxicological evaluation of urinary human epidermal growth factor (u-hEGF) included mutagenicity, single and repeated dose general toxicity, and teratogenicity studies in various animal species. The mutagenic potential of u-hEGF was tested in vitro (Ames test, chromosome aberration in human lymphocytes, unscheduled DNA synthesis in HeLa cells) and in vivo (chromosome aberration in Chinese hamster bone marrow and micronucleus test in rat bone marrow). No mutagenic or clastogenic effects were found. The acute toxicity of u-hEGF was evaluated in mice and rats, using single subcutaneous (sc) or intravenous (i.v.) injection of 15 mg/kg. No toxic effects were observed Four-week i.v. daily administration of u-hEGF at the doses of 0.3, o.9, and 3 mg/kg in the SD rat followed by 2 wk of compound withdrawal induced pronounced and generally dose-related effects (i.e., epithelial hyperplasia) in a wide range of tissues and organs, at all doses. However, these effects were not apparently detrimental to the general health of the rats. The repeated sc administration of u-hEGF to cynomolgus monkeys for 4 wk at the same doses as used in the rat study resulted in lethality after about 7 days of treatment in the 2 higher dose groups or after 14 days at the lowest dose. The main clinical signs observed were gastrointestinal effects, respiratory distress, sedation, marked loss of body weight, and cutaneous desquamation. At histology, hyperplasia of most epithelia was seen in all groups. In addition, atrophy of the ovarian follicles and necrosis of the uterine endometrium were noted. Changes considered secondary to physical distress were atrophy of the hemopoietic and lymphatic system and hepatic steatosis. The embryofetal toxicity and teratogenicity of u-hEGF was tested, using the i.v. route in the SD rat and the i.v. and sc routes in the New Zealand White rabbit. In both species, the compound was administered at the doses of 0, 0.3, 0.9, and 3 mg/kg/day, from day 6 to 15 of pregnancy in rats and 6-18 in rabbits. In the rat, an increase in body weight was noted in the dams and fetuses at the 2 high doses. No embryotoxic or teratogenic effects were observed. In the rabbit studies, mortality and severe clinical signs involving various systems, with marked effects on the eyes, were observed at all doses tested during the first days of treatment by both routes. From the reproductive point of view, most of the surviving treated gravid females showed only resorptions.

On the use of the quasi-likelihood method in teratological experiments

This paper concerns the impact of litter effects on the inference of dose-response relationships in teratological experiments with binary response. Kupper et al. (1986, Biometrics 42, 85-98) concluded that when intra-litter correlations are dose-dependent, the use of a common intra-litter correlation likelihood based on the beta-binomial distribution could lead to severe bias in estimation of the parameter beta, which characterizes the dose-response relationship. We show here that the problems of bias and coverage probability for beta could still be substantial when one uses the likelihood with heterogeneous intra-litter correlations. We then examine through a simulation study the performance of the quasi-likelihood method (Wedderburn, 1974, Biometrika 61, 439-447) and recommend that this method with a common intra-litter correlation parameter be used when the number of litters is small or modest.

Teratologic evaluations of N,N-diethyl-m-toluamide (DEET) in rats and rabbits

The potential for DEET to produce developmental toxicity was evaluated in Charles River CD rats and New Zealand White rabbits. Rats were administered undiluted DEET by gavage on Gestational Days (gd) 6-15 at dosage levels of 0, 125, 250, and 750 mg/kg/day. Rabbits were administered undiluted DEET by gavage on gd 6-18 at dosage levels of 0, 30, 100, and 325 mg/kg/day. Group sizes were 25 females per group for rats and 16 females per group for rabbits. Control rats and rabbits were administered corn oil at the same dosage volumes administered in the high-dose DEET groups. In rats, maternal toxicity in the form of clinical signs including two deaths and depressed body weight and food consumption was observed at the high-dose level of 750 mg/kg/day. Rat fetal body weights per litter also were reduced at 750 mg/kg/day. In rabbits, maternal toxicity in the form of depressed body weight and food consumption was observed at the high-dose level of 325 mg/kg/day. No maternal toxicity was observed at the low- or mid-dose groups for rats or rabbits. With the exception of the reduced fetal weights in rats at 750 mg/kg, there was no evidence of fetal toxicity, no effects on any of the gestational parameters, nor were there any treatment-related increases in external, visceral, or skeletal variations or malformations in the offspring from the rats and rabbits from these studies.