Maternal toxicity: a possible etiological factor in embryo-fetal deaths and fetal malformations of rodent-rabbit species

A critical look at adjusted fetal weights in rats

BACKGROUND

A new derived (i.e., calculated) endpoint of developmental toxicology has appeared in a very few studies since 1990. This endpoint is adjusted mean live fetal weight per litter or adjusted fetal weight. Given our lack of familiarity with the endpoint, we evaluated the basis, prevalence, methods, and usefulness in embryo-fetal developmental toxicity (EFDT) studies in rats.

METHODS

Literature searches were performed with key terms using PubMed and Google Scholar. Major textbooks were consulted but lack of any mention of the endpoint. Unpublished EFDT data, which are readily available online, were utilized to test adjustment methods.

RESULTS

Pertinent information on factors that influence fetal weight goes back a century. Four papers utilizing rats were found in which fetal weights were adjusted using either statistical or formula-based methods to adjust fetal weights. Only one study showed a clear benefit to the endpoint when there was a marked decrease in live litter size; this pointed to situations in which the new endpoint might be useful. The lone formula-based adjustment method was found to be lacking adequate testing and justifications. A new experimental alternative formula-based adjustment is shown to produce results very similar to statistical methods.

CONCLUSIONS

From this assessment, we recommend that adjusted fetal weight should not be a routine endpoint at this time. However, there are likely cases where this derived endpoint could aid interpretation. We encourage other investigators to examine previous EFDT study data to establish guidance on the use of adjusted mean live fetal weights.

Genotoxicity and maternal-fetal safety of the dried extract of leaves of Azadirachta indica A. Juss (Meliaceae) in Wistar rats

ETHNOPHARMACOLOGICAL RELEVANCE

Azadirachta indica A. Juss (Meliaceae), popularly known as "neem", is used for the treatment of rheumatism, cancer, ulcers, diabetes, respiratory problems, among others. This species is present on six continents and contains more than 400 bioactive compounds. Practically all parts of the plant are used in the treatment of diseases. Although it is widely used, no study has evaluated the safety of this species throughout the gestational period in Wistar rats.

AIM OF THE STUDY

To evaluate the genotoxicity and the effect of treatment with dried extract of leaves of Azadirachta indica on maternal toxicity and fetal development.

MATERIALS AND METHODS

The dried extract of leaves of A. indica was obtained by spray drying after percolation of the plant material in 30% ethanol (w/w). The total flavonoids and rutin contents of the extract were determined by spectrophotometric method and HPLC-DAD, respectively. Pregnant Wistar rats (n = 40) were divided into four groups (n = 10/group): one control and three groups treated with dried extract of leaves of A. indica at doses of 300, 600 or 1200 mg/kg. Treatments were carried out from gestational day (GD) 0-20. During gestation, clinical signs of toxicity, weight gain, feed and water consumption of the dams were evaluated. On GD 21, rats were euthanized and cardiac blood was collected. Liver, kidneys, lung, heart, uterus, ovaries and bone marrow were collected. Reproductive performance parameters, histopathological analysis, biochemistry and genotoxicity were evaluated. Fetuses were evaluated for external morphology, skeletal and visceral changes.

RESULTS

The total flavonoid content of the extract ranged from 2.64 to 3.01%, and the rutin content was 1.07%. There was no change in body mass gain, food and water consumption between the evaluated groups. There was also no difference between the groups in terms of biochemical parameters, reproductive performance, histopathological analysis of the mother's organs and genotoxicity. Supernumerary ossification sites of the sternum were observed, and other skeletal and visceral alterations were not significant.

CONCLUSIONS

The treatment did not induce maternal toxicity, it was neither embryotoxic nor fetotoxic. The extract was not potentially genotoxic, and at a dose of 1200 mg/kg, it caused changes in the ossification of the sternum.

Article title: Transcriptional profiling efficacy to define biological activity similarity for cosmetic ingredients' safety assessment based on next-generation read-across

The objective of this work was to use transcriptional profiling to assess the biological activity of structurally related chemicals to define their biological similarity and with that, substantiate the validity of a read-across approach usable in risk assessment. Two case studies are presented, one with 4 short alkyl chain parabens: methyl (MP), ethyl (EP), butyl (BP), and propylparaben (PP), as well as their main metabolite, p-hydroxybenzoic acid (pHBA) with the assumption that propylparaben was the target chemical; and a second one with caffeine and its main metabolites theophylline, theobromine and paraxanthine where CA was the target chemical. The comprehensive transcriptional response of MCF7, HepG2, A549 and ICell cardiomyocytes was evaluated (TempO-Seq) after exposure to vehicle-control, each paraben or pHBA, CA or its metabolites, at 3 non-cytotoxic concentrations, for 6 h. Differentially expressed genes (FDR ≥0.05, and fold change ±1.2≥) were identified for each chemical, at each concentration, and used to determine similarities. Each of the chemicals is able to elicit changes in the expression of a number of genes, as compared to controls. Importantly, the transcriptional profile elicited by each of the parabens shares a high degree of similarity across the group. The highest number of genes commonly affected was between butylparaben and PP. The transcriptional profile of the parabens is similar to the one elicited by estrogen receptor agonists, with BP being the closest structural and biological analogue for PP. In the CA case, the transcriptional profile elicited of all four methylxanthines had a high degree of similarity across the cell types, with CA and theophylline being the most active. The most robust response was obtained in the cardiomyocytes with the highest transcriptional profile similarity between CA and TP. The transcriptional profile of the methylxanthines is similar to the one elicited by inhibitors of phosphatidylinositol 3-kinase as well as other kinase inhibitors. Overall, our results support the approach of incorporating transcriptional profiling in well-designed in vitro tests as one robust stream of data to support biological similarity driven read-across procedures and strengthening the traditional structure-based approaches useful in risk assessment.

New framework for a non-animal approach adequately assures the safety of cosmetic ingredients - A case study on caffeine

This case study on the model substance caffeine demonstrates the viability of a 10-step read-across (RAX) framework in practice. New approach methodologies (NAM), including RAX and physiologically-based kinetic (PBK) modelling were used to assess the consumer safety of caffeine. Appropriate animal systemic toxicity data were used from the most relevant RAX analogue while assuming that no suitable animal toxicity data were available for caffeine. Based on structural similarities, three primary metabolites of the target chemical caffeine (theophylline, theobromine and paraxanthine) were selected as its most relevant analogues, to estimate a point of departure in order to support a next generation risk assessment (NGRA). On the basis of the pivotal mode of action (MOA) of caffeine and other methylxanthines, theophylline appeared to be the most potent and suitable analogue. A worst-case aggregate exposure assessment determined consumer exposure to caffeine from different sources, such as cosmetics and food/drinks. Using a PBK model to estimate human blood concentrations following exposure to caffeine, an acceptable Margin of Internal Exposure (MOIE) of 27-fold was derived on the basis of a RAX using theophylline animal data, which suggests that the NGRA approach for caffeine is sufficiently conservative to protect human health.

Repeated dose inhalation developmental toxicity study in rats exposed to cellulose insulation with boric acid additive

Cellulose insulation (CI), a common building material, is a mixture of cellulose fibers and borates. Borates are approximately 20% of the product weight and act as a flame retardant. Given possible exposure to workers and consumers, an inhalation toxicity study was conducted following Organization for Economic Co-operation and Development (OECD) 414 for Prenatal Development Toxicity to evaluate if CI is a developmental toxicant. Pregnant female rats were exposed by nose-only inhalation to CI aerosols containing 20% boric acid for six h/day, from gestational day (GD) 6-19, and fetuses were evaluated for developmental parameters. Respirable CI was produced by grinding to produce respirable particles (MMAD 2.7-2.9 µm, geometric standard deviations (GSD) 1.9-2.6), which were then aerosolized. Target air concentrations were 15, 90, and 270 mg CI/m³. Controls were exposed to air only. Slight body weight reductions (average decrease <7% vs. control) were observed in male and female GD 20 fetuses in the mid and high dose groups. No embryo/fetal developmental toxicity or alterations in any other measured variable were reported at any dose. The no observed adverse effect level (NOAEL) for developmental outcomes was 270 mg/m³.

Developmental Toxicity of Mycotoxin Fumonisin B₁ in Animal Embryogenesis: An Overview

A teratogenic agent or teratogen can disturb the development of an embryo or a fetus. Fumonisin B₁ (FB₁), produced by Fusarium verticillioides and F. proliferatum, is among the most commonly seen mycotoxins and contaminants from stale maize and other farm products. It may cause physical or functional defects in embryos or fetuses, if the pregnant animal is exposed to mycotoxin FB₁. Due to its high similarity in chemical structure with lipid sphinganine (Sa) and sphingosine (So), the primary component of sphingolipids, FB₁ plays a role in competitively inhibiting Sa and So, which are key enzymes in de novo ceramide synthase in the sphingolipid biosynthetic pathway. Therefore, it causes growth retardation and developmental abnormalities to the embryos of hamsters, rats, mice, and chickens. Moreover, maternal FB₁ toxicity can be passed onto the embryo or fetus, leading to mortality. FB₁ also disrupts folate metabolism via the high-affinity folate transporter that can then result in folate insufficiency. The deficiencies are closely linked to incidences of neural tube defects (NTDs) in mice or humans. The purpose of this review is to understand the toxicity and mechanisms of mycotoxin FB₁ on the development of embryos or fetuses.

In vivo toxicity study of quatro stimuli nanocontainers in pregnant rats: Gestation, parturition and offspring evaluation

The aim of the present study was to investigate the impact of intravenous administration of newly fabricated nanocontainers (NCs) on the last third of pregnancy in rats. Fifteen pregnant 3-month-old Wistar rats were separated into 3 groups. On the 15th and 17th day of pregnancy all animals received an intravenous administration of 1 ml of 15 mg of NCs (Group A), 1 ml of 5 mg NCs (Group B) while Control group received 1 ml of 0.9% NaCl. On the 14th and 17th of pregnancy ultrasonography was performed and the parameters evaluated were the width of placenta, the length and width of the embryonic sac, the foetus length and the heart rate. On parturition the number of pups per dam was evaluated. Half of the pups were euthanised the day after parturition and their liver and kidney was histologically evaluated and for the rest of the pups the body growth curve was evaluated until the age of 14 week. At the end of the 14th week the remaining pups were euthanised and their liver and kidney was histologically evaluated. At weaning the dams were euthanised and their liver and kidney was histologically evaluated. Ultrasonography: Baseline measurements of the width of placenta, the length and width of embryonic sac, the foetus length and the heart rate on the 14th day of pregnancy, revealed no statistical significant differences between groups. Comparison of the same values on the 17th day of pregnancy after 2 intravenous administrations of NCs showed no statistical significant effect on the respective parameters. The administration of NCs had no impact on the mean number of pups per dam. Additionally, no impact of the NCs on the body weights of the pups was observed on the 1st day after parturition. Moreover, comparisons between groups, for both sexes showed no difference on growth rate. During the histological evaluation no inflammatory, degenerative or neoplastic lesions were observed as far as the newborn, adult offspring and dams were concerned. According to our results no toxic impact of the low and high doses of the NCs was observed on the parameters selected to be evaluated.

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Nanocontainers toxicity study.

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Toxicological study on pregnant rats, foetuses and offspring.

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Ultrasonographic evaluation.

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Histological evaluation.

Bone development in laboratory mammals used in developmental toxicity studies

Evaluation of the skeleton in laboratory animals is a standard component of developmental toxicology testing. Standard methods of performing the evaluation have been established, and modification of the evaluation using imaging technologies is under development. The embryology of the rodent, rabbit, and primate skeleton has been characterized in detail and summarized herein. The rich literature on variations and malformations in skeletal development that can occur in the offspring of normal animals and animals exposed to test articles in toxicology studies is reviewed. These perturbations of skeletal development include ossification delays, alterations in number, shape, and size of ossification centers, and alterations in numbers of ribs and vertebrae. Because the skeleton is undergoing developmental changes at the time fetuses are evaluated in most study designs, transient delays in development can produce apparent findings of abnormal skeletal structure. The determination of whether a finding represents a permanent change in embryo development with adverse consequences for the organism is important in study interpretation. Knowledge of embryological processes and schedules can assist in interpretation of skeletal findings.

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.

Prenatal Developmental Toxicity Study of Glycosides-based Standardized Fenugreek Seed Extract in Rats

Context:

Glycoside-based standardized fenugreek seed extract (SFSE-G) demonstrated promising efficacy in animal models of immune-inflammatory conditions.

Aim:

The present study was aimed at embryo-fetal development toxicity evaluation of SFSE-G in Wistar rats as per guideline No. 414 of the Organization for Economic Co-operation and Development (OECD).

Material and Methods:

Mated female rats were randomized into four groups of 30 each and received oral doses of either SFSE-G at 250, 500, and 1000 mg/kg or vehicle (water) during the period of gestation (postconception) from gestational day 5 (GD5, an implantation day) until 1 day before cesarean sections (GD19). Maternal food consumption, body weights, and clinical signs were monitored throughout gestation. Cesarean sections were performed on GD20 and fetal observations (gravid uterine weight, implantation sites, early and late resorptions, live and dead fetuses) were recorded. Live fetuses were weighed and examined for external, visceral, and skeletal variations and malformations.

Results:

None of the SFSE-G-treated groups showed maternal and embryo–fetal toxicity. Occasional and incidental skeletal and visceral malformations were observed and found to be spontaneous and unrelated to the treatment.

Conclusion:

Oral exposure of SFSE-G during the prenatal period did not show significant maternal and embryo-fetal toxicity up to a dose of 1000 mg/kg in rats. Therefore, the no-observed-adverse-effect level for SFSE-G for prenatal oral exposure was considered to be 1000 mg/kg.

SUMMARY

Prenatal toxicity of glycoside-based standardized fenugreek seed extract (SFSE-G) was evaluated.

SFSE-G was orally gavaged to rats on gestational days 5-19 with a limit dose of 1000 mg/kg.

SFSE-G did not show maternal or developmental toxicity.

SFSE-G showed NOAEL of 1000 mg/kg for prenatal exposure in female rats.

Abbreviations used: CPCSEA: Committee for the Purpose of Control and Supervision of Experiments on Animals; GD: Gestational day; GRAS: Generally recognized as safe; HED: Human equivalent dose; NOAEL: No-observed adverse effect levels; OECD: Organization for Economic Co-operation and Development; SFSE-G: glycoside-based standardized fenugreek seed extract.

Effects of melatonin in rats in the initial third stage of pregnancy exposed to sub-lethal doses of herbicides

Exposure to the herbicides Paraquat (PQ) and Roundup® may cause cell lesions due to an increase in oxidative stress levels in different biological systems, even in the reproductive system.

OBJECTIVE

Evaluate the possible changes in reproductive parameters and hepatic, as well as its prevention by simultaneous application of melatonin.

METHODS

Thirty-five female rats at the age of 3 months were divided into seven groups: three groups exposed to sub-lethal doses of the herbicides PQ (50mg/kg) and Roundup® (500mg/kg) (n=5, G2, G3 and G4); three groups exposed to herbicides and simultaneous treatment with 10mg/kg of Melatonin (n=5, G5, G6 and G7) and control group (n=5, G1) from the first to the seventh day of pregnancy. On the seventh day of pregnancy, the rats were anesthetized and euthanized, followed by laparotomy to remove their reproductive tissues and liver. Body and ovary weights were taken and the number of implantation sites, corpora lutea, preimplantation losses, implantation rates were counted and histopathology of the implantation sites, morphometry of the surface and glandular epithelia of endometrium and hepatic oxidative stress were undertaken.

RESULTS

The present study shows the decrease in body and ovary weight, decrease in the number of implantation sites, implantation rate, in the total number of corpora lutea and increase of preimplantation percentages were observed when compared to the G1: Fig. 1 and Table 1, (p>0.001 ANOVA/Tukey). The histopathological analysis of the implantation sites showed a disorder of the cytotrophoblast and cell degeneration within the blastocyst cavity in Fig. 4. Morphometry revealed a reduction in surface and glandular epithelia and in the diameter of the endometrial glands (Table 2; p>0.05 ANOVA/Tukey), whereas in liver, serum levels of thiobarbituric acid reactive substances (TBARS) were found to be significantly elevated (Fig. 2; p>0.001; p>0.05 ANOVA/Tukey), and serum level of reduced glutathione (GSH) was significantly lower (Fig. 3; p>0.001 ANOVA/Tukey). However, treatments with melatonin exhibited improvements in reproductive parameters, as well as reduced lesions in the implantation sites (Fig. 4.) and in serum levels TBARS (Fig. 2; p>0.001 ANOVA/Tukey), serum levels GSH (Fig. 3; p>0.001; p>0.05 ANOVA/Tukey).

CONCLUSIONS

These results reveal that melatonin is a protective agent against experimentally induced maternal/embryo toxicity with herbicides and favoring normalization of reproductive parameters and hepatic.

Oral and Dermal Developmental Toxicity Studies of Phenylethyl Alcohol in Rats

Phenylethyl alcohol (PEA) was tested for developmental toxicity. Pregnant rats were fed 0, 83, 266, or 799 mg/kg/d PEA on gestation days (GDs) 6 to 15; only minimal, nonsignificant effects were observed. In dermal studies, PEA (neat) was applied to the skin on GDs 6 to 15 at dosages of 0, 140, 430, or 1400 mg/kg/d and at 0, 70, 140, 280, 430, or 700 mg/kg/d in a corroborative study. Observations included maternal and embryo-fetal toxicity/abnormalities at 1400 mg/kg/d, increased incidences of rudimentary cervical ribs at ≥430 mg/kg/d, and reduced fetal body weights at ≥140 mg/kg/d. Dermal maternal and developmental no-observed-adverse-effect levels are 70 mg/kg/d, based on dermal irritation and reductions (nonsignificant) in fetal body weights. Human exposure from fragrances is 0.02 mg/kg/d, resulting in a margin of safety >2600, when marked differences in dermal absorption between rats and humans are considered. Under normal fragrance use conditions, PEA is not a developmental toxicity hazard for humans.

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.

Regulatory assessment of reproductive toxicology data

This chapter outlines a regulator's personal approach to the assessment of reproductive toxicology data in the context of the assessment of the overall nonclinical data package for pharmaceutical agents. Using as a framework the International Conference on Harmonisation Common Technical Document headings, guidance is provided on the expectations of regulators for the presentation and discussion of the data by the applicant to facilitate the risk assessment process. Consideration is given to the use of reproductive toxicology data in the assessment process for both clinical trial applications (CTAs) and marketing authorization applications (MAAs). Suggestions for some guiding principles in drafting of the various product information documents (for example the Investigator's Brochure (IB) for CTAs and the Nonclinical Overview and Summary of Product Characteristics for MAAs) are included.

Influence of maternal toxicity on the outcome of developmental toxicity studies

The relevance of fetal abnormalities noted at maternally toxic doses is a long-standing issue regarding the interpretation of findings of segment II studies. A number of diseases and conditions during pregnancy are known to adversely affect embryo/fetal development, and along this line many scientists believe that any marked disturbance of maternal homeostasis produced by chemical exposure may eventually produce a teratogenic effect. Although there is little doubt that developmental toxicity may be maternally mediated, the notion that, in principle, any maternal toxicity leads to birth defects is disputed. When embryotoxicity is noted only within the maternally toxic dose range, it is not possible to ascertain whether it is in fact maternally mediated or not (i.e., embryo development may have been impaired by a direct action of the chemical at doses that also adversely affect the mother; in these circumstances it would still be a selective developmental toxicant). However, currently, a chemical is not regarded as a "developmental toxicant" (or "teratogenic agent") if embryotoxicity is apparent only at doses that are also toxic to the mother. In the European Union, developmental hazard identification exerts a strong influence on the classification and labeling of chemicals. In Brazil, registration of any pesticide that proved to be teratogenic in animal studies is strictly forbidden by law (Pesticide Law, Federal Law 7.802, 1989). Therefore, interpretation of findings from developmental toxicity studies in light of maternal toxicity is particularly relevant to regulatory agencies, and becomes even more important when labeling or cutoff decision-making criteria are adopted regarding teratogenicity.

Combined Treatment Potentiates the Developmental Toxicity of Ibuprofen and Acetazolamide in Rats

Aspirin (ASA), an irreversible cyclooxygenase (COX) inhibitor, induces ventricular septal defect (VSD) and diaphragmatic hernia (DH) in rat fetuses when administered on gestation days (GDs) 9-10, a critical period for cardiovascular (CV) and midline development. Evaluation of a spectrum of nonsteroidal antiinflammatory drugs (NSAIDs; reversible COX inhibitors) showed that while some NSAIDs induced VSD in rats, none of the NSAIDs evaluated produced DH. In addition to inhibiting COX, ASA also inhibits carbonic anhydrase. The purpose of this study was to determine whether concurrent inhibition of COX and carbonic anhydrase would produce a teratogenic profile that includes both VSD and DH. To inhibit both COX and carbonic anhydrase, ibuprofen (COX inhibitor) and acetazolamide (carbonic anhydrase inhibitor) were coadministered on GDs 9-10. Groups of 20 female Crl:CD(SD)IGS BR rats were given either 300 mg kg(-1) day(-1) ibuprofen, 1000 mg kg(-1) day(-1) acetazolamide, or both (combination of ibuprofen and acetazolamide). Fetuses were evaluated on GD 21 for external and visceral development. Ibuprofen induced VSD in 3.7% of fetuses per litter; no defects in appendicular skeletal development were noted. Acetazolamide induced VSD in 5.9% of the fetuses per litter and appendicular defects in 41% of the fetuses per litter. Coadministration of ibuprofen and acetazolamide produced VSD in 18.7% of the fetuses per litter and appendicular defects in 77% of the fetuses per litter; however, there were no DH. Therefore, while concurrent inhibition of COX and carbonic anhydrase did not produce DH, potentiation was noted for the induction of VSD and appendicular anomalies.

Intrauterine growth restriction and skeletal variations in mouse fetuses induced by vigabatrin administered at preimplantation stages of development

Epileptic women do not withdraw antiepileptic drug (AED) therapy during pregnancy, therefore, exposure to AED during preimplantation stages might result in considerable embryonic concentrations endangering development. Neither clinical nor experimental research has addressed this important issue adequately. Vigabatrin (VGB), a second generation AED, is both effective and well tolerated as an add-on therapy in epilepsy with partial seizures. However, there is little data on the possible reproductive toxicity of this widely used drug. The objective of the present study was to evaluate the effects of VGB on pregnancy and pregnancy outcome in an experimental model. VGB was administered in single doses of 450 mg/kg intraperitoneally (i.p.) to groups of mice on one of gestation days (GD) 1, 3, or 5. The treated animals consumed moderately reduced amounts of food and water on the day of treatment, so the controls were saline-injected and food and water-restricted to match the amounts consumed by the experimental animals. All animals were killed on GD 18. VGB treatment did not interfere with implantation, nor did it cause significant embryo resorption. However, it caused significant reduction in fetal bodyweight and increased frequency of growth restricted fetuses which weighed two standard deviations (SD) less than the mean of the controls. The VGB group fetuses also had retarded development of the skeletal system in terms of delay in maturity of the suproccipital bone development, cervical and coccygeal vertebral hypoplasia, and poor ossification of the bones of the fore and hind paws. Another major finding was the increased incidence of minor malformations, such as the presence of cervical ribs and sternal anomalies. The results of this study show that VGB administered at preimplantation stages of development causes intrauterine growth restriction (IUGR) and augments minor malformation rates in mice. Future studies must address the mechanisms of VGB-induced IUGR and minor malformations.

Evaluation of the developmental toxicity of lenalidomide in rabbits

BACKGROUND

Lenalidomide, a thalidomide analog, is indicated for treatment of patients with deletion-5q myelodysplastic syndromes or multiple myeloma. NZW rabbits were used because of sensitivity to thalidomide's teratogenicity.

METHODS

Range-finding and pulse-dosing studies preceded a full developmental toxicity study in New Zealand white (NZW) rabbits (25/group) given lenalidomide (0, 3, 10, or 20 mg/kg/day) or thalidomide (180 mg/kg/day) by stomach tube on gestation days (GD) 7-19. Clinical signs, body weights, and feed consumption were recorded daily from GD 7. On GD 29, standard maternal necropsy, uterine content, and fetal evaluations were carried out.

RESULTS

In all studies, thalidomide was selectively toxic to development. In the pulse-dosing study, lenalidomide did not affect development at 100 mg/kg/day. Increases in C(max) and AUC(0-24 hr) values for lenalidomide were slightly less than dose-proportional; lenalidomide occurred in the fetuses. At 10 and 20 mg/kg/day, lenalidomide was maternally toxic (reduced body weight gain and feed consumption; at 20 mg/kg/day, weight loss and one abortion). Developmental toxicity at 10 and 20 mg/kg/day included reduced fetal body weights and increased postimplantation losses and fetal variations (morbidity/purple-discolored skin, undeveloped intermediate lung lobe, irregular nasal-frontal suture, and delayed metacarpal ossification). Thalidomide selectively reduced fetal body weight, increased postimplantation loss and caused characteristic limb and other dysmorphology.

CONCLUSIONS

The maternal and developmental NOAELs for lenalidomide are 3 mg/kg/day. Unlike thalidomide, lenalidomide affected embryo-fetal development only at maternally toxic dosages, confirming that structure-activity relationships may not predict maternal or developmental effects. No fetal malformations were attributable to lenalidomide.

Assessment of the perinatal effects of maternal ingestion of Ipomoea carnea in rats

It is believed that Ipomoea carnea toxicosis induces abnormal embryogenesis in livestock. Studies on rats treated with I. carnea aqueous fraction (AF) during gestation, revealed litters with decreased body weight, but the characteristic vacuolar lesions promoted by swainsonine, its main toxic principle, were observed only in young rats on postnatal day (PND) 7. However, these alterations could have resulted as consequence of swainsonine placental passage and/or damage or even ingestion of the contaminated milk by pups. Thus, this perinatal work was performed to verify the transplacental passage of swainsonine and its excretion into milk employing the cross-fostering (CF) procedure as a tool of study. Females were treated with AF or vehicle during gestation and after birth pups were fostered between treated and untreated dams. Pup body weight gain (BWG) and histopathology to observe vacuolar degeneration were performed on PND 3 and 7. In addition, swainsonine detection was performed in amniotic fluid and milk from rats treated with the AF during gestation or lactation. BWG was significantly lower only in pups from mothers treated with the plant and fostered to other treated mothers (AF-AF group of pups). The histopathology revealed that pups from treated mothers fostered to untreated ones showed the characteristic vacuolar lesions; however, the lesions from the AF-AF pups were more severe in both periods evaluated. Amniotic fluid and milk analysis revealed the presence of swainsonine excretion into these fluid compartments. Thus, the results from CF and the chemical analysis allowed concluding that swainsonine passes the placental barrier and affects fetal development and milk excretion participates in I. carnea perinatal toxicosis.

Uterotrophic, fetotoxic and abortifacient effect of a Malaysian variety of Plumbago rosea L. on isolated rat uterus and pregnant mice

Traditionally Plumbago rosea L. is used as an abortifacient in the Southeast Asian region. Methanolic root extract of a local species of Plumbago rosea L. was studied to evaluate its traditional antifertility claim. Interestingly, it was found to possess dose related inhibitory effect on uterine contractile responses elicited by oxytocic agents on isolated uteri of pregnant and pseudo-pregnant rats. Furthermore, it was found to possess significant (p < 0.05) fetotoxic activity along with mild abortive potential in pregnant mice when given orally at high doses (400 and 800 mg kg(-1)) once daily for ten days starting from day 10 of gestation. The results derived indicated possible presence of utero-active compound (s) in this plant that inhibited oxytocic agents induced uterine motility. Moreover, pronounced fetotoxic and mild abortifacient potentials observed at higher doses in pregnant mice might support its accredited traditional use to avoid unwanted pregnancy.

Developmental toxicity evaluation of triclopyr butoxyethyl ester and triclopyr triethylamine salt in the CD rat

Triclopyr (3,5,6-trichloro-2-pyridyloxyacetic acid) is an herbicide used extensively in the control of woody plants and broadleaf weeds, and is often formulated as a triethylamine salt (T-TEA) or butoxyethyl ester (T-BEE). This study evaluated the developmental toxicity of T-TEA or T-BEE in time-mated CD rats gavaged on gestation days 6-15 with 0, 30, 100 or 300 mg/kg body weight(bw)/day. The doses of each compound were equimolar and equivalent to 22, 76, 216 mg/kg bw/day of triclopyr, based on prior studies indicating rapid cleavage of the salt or ester and equivalent pharmacokinetics for the active ingredient. T-TEA caused maternal toxicity, evidenced by the death of one high-dose dam, reduced body weight gain, increased relative liver and kidney weights (300 mg/kg bw/day), reduced feed consumption, and increased water consumption (100 and 300 mg/kg bw/day). Developmental effects were limited to slightly decreased fetal body weight and reduced skeletal ossification at the high dose level. T-BEE caused similar, albeit slightly more severe, maternal toxicity, with three maternal deaths at 300 mg/kg bw/day, and slight maternal effects at 30 mg/kg bw/day. Due to an equivocal increase in malformations, which were mainly clustered in litters from three high dose dams with marked maternal toxicity, the T-BEE study was repeated using 30 dams/group, investigator-blind fetal evaluations, and an additional dose group (5 mg/kg bw/day). In the repeat study, the only reproducible fetal effect was an increased incidence of 14th thoracolumbar rib at 300 mg/kg bw/day. Overall analysis of the two T-BEE studies suggested that the fetal malformations unique to the initial study likely reflected a combination of spontaneous events, exacerbated by marked maternal toxicity. The combined weight of evidence from these developmental toxicity studies, coupled with their known pharmacokinetic equivalence, indicates that T-BEE and T-TEA are not selectively toxic to the fetus. The respective maternal toxicity no-observed effect levels (NOEL) for T-BEE and T-TEA were 5 and 30 mg/kg bw/day, while the NOEL for developmental toxicity was 100 mg/kg bw/day for both compounds.

Effects of deoxynivalenol (DON, vomitoxin) on in utero development in rats

Deoxynivalenol (DON, vomitoxin), is one of the most common contaminants of cereal grains world-wide. The effects of DON on fetal development were assessed in Charles River Sprague-Dawley rats. Pregnant female rats were gavaged once daily with DON at doses of 0, 0.5, 1, 2.5, or 5 mg/kg body weight on gestation days (GD) 6-19. At cesarean section on GD 20, reproductive and developmental parameters were measured. All females survived to cesarean section. DON caused a dose-related increase in excessive salivation by the pregnant females, a reaction probably linked to the lack of emetic reflex in rats. At 5 mg/kg, feed consumption and mean body weight gain were significantly decreased throughout gestation, mean weight gain (carcass weight), and gravid uterine weight were significantly reduced, 52% of litters (12/23) were totally resorbed, the average number of early and late deaths per litter was significantly increased, average fetal body weight and crown-rump length were significantly decreased, the incidence of runts was significantly increased, and the ossification of fetal sternebrae, centra, dorsal arches, vertebrae, metatarsals, and metacarpals was significantly decreased. At 2.5 mg/kg, DON significantly decreased average fetal body weight, crown-rump length, and vertebral ossification. These effects may be secondary to maternal toxicity and the reduced size of the fetuses. The incidence of misaligned and fused sternebrae was significantly increased at 5.0 mg/kg. No adverse developmental effects were observed at 0.5 and 1.0 mg/kg. Dose-related increases in maternal liver weight-to-body weight ratios were observed in all treated groups (significant at 1, 2.5, and 5 mg/kg). The weight changes were correlated with dose-related cytoplasmic alterations of hepatocytes. The NOEL for maternal toxicity for this study is 0.5 mg/kg based on the dose-related increase in liver-body weight ratio at 1 mg/kg. The NOEL for fetal toxicity is 1 mg/kg based on the general reduction in fetal development at 2.5 and 5 mg/kg. DON is considered a teratogen at 5 mg/kg day in Sprague-Dawley rats based on the anomalous development of the sternebrae.

Effects of feed restriction during organogenesis on embryo-fetal development in rabbit

BACKGROUND

Appropriate maternal nutrition and body weight gain during pregnancy is well established as a major factor in healthy prenatal development in humans. Given the role of nutrition and body weight gain in normal development, pharmaceuticals intended to reduce appetite and promote weight loss will generate developmental toxicity data that may be challenging to interpret. To aid with this, the effects of feed restriction, and subsequent reduction in maternal body weight gain, on embryo-fetal development was investigated in the rabbit.

METHODS

Groups of 15 pregnant New Zealand White rabbits were offered 150 (control), 110, 75, 55, 35, and 15 g feed/day from gestation day (GD) 7-19. Cesarean sections were carried out on GD 29 and fetuses were examined for external, visceral, and skeletal development.

RESULTS

Maternal body weights at the end of the feed restriction period (GD 20) were 0.97, 0.98, 0.93, 0.94, and 0.86 x control for the 110, 75, 55, 35, and 15 g feed/day groups, respectively. Only at 15 g feed/day was there a net maternal body weight loss (the GD 20 body weight was 0.93 x the GD 6 body weight) at the end of the feed restriction period. Six does aborted in the 15 g feed/day group; there were no other abortions associated with feed restriction. Fetal body weight was significantly reduced at 75, 55, 35, and 15 g feed/day (0.95, 0.90, 0.86, and 0.84 x control, respectively). There were no external or visceral malformations or variations, and no skeletal malformations associated with feed restriction. The incidence of fetuses with sternebrae 5 or 6 unossified was increased at feed levels < or = 75 g/day. At a feed level of 35 g/day there was an increase in unossified metatarsals and metacarpals, and an increase in the number of fetuses with a reduced number of caudal vertebrae ossified. Although these findings were not increased at a feed level of 15 g/day, the lack of dose response was likely due to increased abortion and subsequent decrease in fetuses available for evaluation at 15 g feed/day.

CONCLUSION

These data demonstrate that feed restriction to feed levels that produce substantial reductions in maternal body weight gain can result in developmental toxicity expressed by abortion, reduced fetal weight, and alterations in ossification. Abortion only occurred when feed was restricted to an amount that produced maternal body weight loss (15 g feed/day) whereas reduced fetal weight and increased incidence of fetuses with unossified sternebrae, metatarsals, metacarpals, or caudal vertebrae were noted at feed levels of < or = 75 g/day. There were no fetal malformations associated with feed restriction.

Inhibiting matrix metalloproteinases with prinomastat produces abnormalities in fetal growth and development in rats

BACKGROUND

Matrix metalloproteinases (MMPs) play key roles in remodeling of the extracellular matrix during embryogenesis and fetal development. The objective of this study was to determine the effects of prinomastat, a potent selective MMP inhibitor, on fetal growth and development.

METHODS

Prinomastat (25, 100, 250 mg/kg/day, p.o.) was administered to pregnant female Sprague-Dawley rats on gestational days (GD) 6-17. A Cesarian section was carried out on GD 20 and the fetuses were evaluated for viability and skeletal and soft tissue abnormalities.

RESULTS

Prinomastat treatment at the 250 mg/kg/day dose produced a decrease in body weight and food consumption in the dams. A dose-dependent increase in post-implantation loss was observed in the 100 and 250 mg/kg/day-dose groups, resulting in only 22% of the dams having viable litters for evaluation at the 250 mg/kg/day dose. Fetal skeletal tissue variations and malformations were present in all prinomastat treated groups and their frequency increased with dose. Variations and malformation in fetal soft tissue were also increased at the 100 and 250 mg/kg/day doses. Prinomastat also interfered with fetal growth of rat embryo cultures in vitro.

CONCLUSIONS

These data confirm that MMP inhibition has a profound effect on fetal growth and development in vivo and in vitro.

Preclinical Profiling and Safety Studies of ABT-769: A Compound with Potential for Broad-spectrum Antiepileptic Activity

PURPOSE

The objective of this study was to characterize the antiseizure and safety profiles of ABT-769 [(R)-N-(2 amino-2-oxoethyl)spiro[2,5]octane-1-carboxamide].

METHODS

ABT-769 was tested for protection against maximal electroshock and pentylenetetrazol-induced seizures in the mouse and for suppression of electrically kindled amygdala seizures and spontaneous absence-like seizures in the rat. The central nervous system safety profile was evaluated by using tests of motor coordination and inhibitory avoidance. The potential for liver toxicity was assessed in vitro by using a mitochondrial fatty acid beta-oxidation assay. Teratogenic potential was assessed in the mouse.

RESULTS

ABT-769 blocked maximal electroshock, subcutaneous pentylenetetrazol and intravenous pentylenetetrazol-induced seizures with median effective dose (ED50) values of 0.25, 0.38, and 0.11 mmol/kg, p.o., respectively. No tolerance was evident in the intravenous pentylenetetrazol test after twice-daily dosing of ABT-769 (0.3 mmol/kg, p.o.) for 4 days. ABT-769 blocked absence-like spike-wave discharge (ED50, 0.15 mmol/kg, p.o.) and shortened the cortical and amygdala afterdischarge duration of kindled seizures (1 and 3 mmol/kg, p.o.). The protective indices (ED50 rotorod impairment/ED50 seizure protection) were 4.8, 3.2, and 10.9 in the maximal electroshock, subcutaneous pentylenetetrazol and intravenous pentylenetetrazol seizure tests, respectively. ABT-769 did not affect inhibitory avoidance performance (0.1-1 mmol/kg, p.o.). ABT-769 did not affect mitochondrial fatty acid beta-oxidation or induce neural tube defects.

CONCLUSIONS

ABT-769 is an efficacious antiseizure agent in animal models of convulsive and nonconvulsive epilepsy and has a favorable safety profile. ABT-769 has a broad-spectrum profile like that of valproic acid. Its profile is clearly different from those of carbamazepine, phenytoin, lamotrigine, topiramate, vigabatrin, and tiagabine.

Vertebral malformations induced by sodium salicylate correlate with shifts in expression domains of Hox genes

Several embryotoxic agents, which includes sodium salicylate, were reported to induce vertebral variations in the form of supernumerary ribs (SNR) when administered to pregnant rodents. Because the biological significance of SNR in toxicological studies is still a matter of debate, we investigated the molecular basis of this defect by analyzing the possible involvement of Hox genes, known to specify vertebrae identity. Sodium salicylate (300mg/kg) was administered to pregnant rats on gestational day 9 (GD 9). On GD 13, the expression of several Hox genes, selected according to the position of their anterior limit of expression, namely upstream (Hoxa9), at the level (Hoxa10) and downstream (Hoxd9) to the morphological alteration, were analyzed. Posterior shifts in the anterior limit of expression of Hoxa10 and Hoxd9 were observed following exposure to salicylate, which could explain an effect at the level of the axial skeleton. This finding suggests that the appearance of ectopic ribs can be attributed to an anterior transformation of lumbar vertebrae identity into thoracic vertebrae identity. Whether this transformation occurs with all compounds inducing SNR in rats remains to be determined.

The effects of BIS-GMA and TEG-DMA on female mouse fertility

OBJECTIVES

The current study evaluated the effect of bisphenol A glycerolate dimethacrylate (BIS-GMA) and triethyleneglycol dimethacrylate (TEG-DMA) on female mouse fertility.

METHODS

Adult female mice were exposed to BIS-GMA or TEG-DMA (0, 25 and 100 microg/kg) intragastrically daily for 28 d and then mated with sexually mature untreated male mice and after mating their fertility was assessed.

RESULTS

In females exposed to BIS-GMA at both doses significant increases in the total number of resorptions out of the total number of implantations were observed, with a significant increase in the number of animals with resorptions at the higher dose. Significant reductions in body weights and significant increases in ovary weights were also observed. Exposure to TEG-DMA at a dose of 100 microg/kg resulted in significant reductions in pregnancy rates and a significant increase in the total number of embryonal resorptions. Significant reductions in body and uterine weights were also observed in females exposed to TEG-DMA.

SIGNIFICANCE

The results suggest that both BIS-GMA and TEG-DMA have reproductive toxic effects in female mice.

Effects of CKD-602, a new camptothecin anticancer agent, on pregnant does and embryo-fetal development in rabbits

CKD-602 is a newly developed camptothecin anticancer agent. Preclinical studies suggest that it may have greater antitumor activity and lower toxicity than other camptothecin anticancer agents. The potential of CKD-602 to induce developmental toxicity was investigated in the New Zealand White rabbit. Seventy-two artificially inseminated females (artificial insemination=day 0) were distributed among three treatment groups and a control group. CKD-602 was at dose levels of 0, 0.024, 0.048, or 0.096 mg x kg(-1) x day(-1) administered intravenously to pregnant does from days 6 to 18 of gestation. All does were subjected to caesarean section on day 28 of gestation. At 0.096 mg x kg(-1) x day(-1), 2 cases of abortion and 3 cases of death in pregnant rabbits were found in late gestation. In addition, an increase in the embryonic resorptions and a decrease in the litter size were found. At 0.048 mg x kg(-1) x day(-1), a single doe aborted on gestational day 26. An increase in the embryonic resorptions and fetal morphological alterations and a decrease in the litter size were also found. There were no signs of maternal toxicity or developmental toxicity at 0.024 mg x kg(-1) x day(-1). The results show that 13-day repeated intravenous dose of CKD-602 during the major organogenetic period in rabbits produces increased incidence of abortion and death, increased number of embryonic resorptions and fetal morphological alterations, and decreased litter size at dose levels of above 0.048 mg x kg(-1) x day(-1). In the current experimental conditions, the no-observed-adverse-effect levels (NOAELs) of CKD-602 are considered to be 0.048 mg x kg(-1) x day(-1) for does and 0.024 mg x kg(-1) x day(-1) for embryo-fetal development.

Embryotoxic effects of CKD-602, a new camptothecin anticancer agent, in rats

CKD-602 is a newly developed camptothecin anticancer agent. Preclinical studies suggest that it may have greater antitumor activity and lower toxicity than other camptothecin anticancer agents. The potential of CKD-602 to induce embryotoxicity was investigated in the Sprague-Dawley rat. One hundred mated females (sperm in vaginal lavage=day 0) were distributed among three treatment groups and a control group. CKD-602 was administered intravenously at dose levels of 0, 5, 20 and 80 microg/kg/d to pregnant rats from days 6 to 15 of gestation. The vehicle control rats received an equivalent volume of 1 ml distilled water with d-mannitol 50mg and tartaric acid 0.06 mg. All dams were subjected to the caesarean section on day 20 of gestation. There were no signs of maternal toxicity or embryotoxicity at 5 microg/kg/d, but at 20 microg/kg/d, there was an increase in relative brain weight. At 80 microg/kg/d, reduced food intake, suppressed body weight and increased weight of spleen were observed in dams. An increase in the resorptions and dead fetuses, a decrease in litter size, fetal and placental weights were also found. In addition, various types of external, visceral and skeletal malformations occurred. Characteristic malformations included absent eye bulge, agnathia, dilated cerebral ventricle, anophthalmia, absent thoracic centrum, fused vertebral arch, fused rib, among others. Visceral and skeletal variations were observed. Retarded ossification of several skeletal districts and delayed ossification of sternebrae, metatarsals and sacrocaudal vertebrae were also observed. The results show that CKD-602 is embryotoxic and teratogenic at a minimally maternally toxic dose, i.e. at 80 microg/kg/d in rats. The no-observed-adverse-effect level (NOAEL) of CKD-602 for developmental toxicity was considered to be 20 microg/kg/d, however, the NOAEL for maternal toxicity was 5 microg/kg/d.

Effects of Lantana camara (Verbenaceae) on general reproductive performance and teratology in rats

Lantana camara L. (Verbenaceae) possesses several medicinal properties and it is used in folk medicine with antipyretic, antimicrobial and antimutagenic properties. This plant is one of the 10 most noxious weeds in the world. Lantana poisoning have caused severe economic losses and was the major cause of livestock mortality and morbidity. In this article we report the effects of hydroalcoholic extract from Lantana camara var. aculeata leaves on fertility, general reproductive performance and teratology in the rat. The data showed that the extract interfered in the frequency of fetal skeleton anomalies from dams treated with the extract and induced embryotoxicity as indicated by post-implantation loss, without any signs of maternal toxicity. The other parameters evaluated did not suggest modifications.

Developmental toxicity assessment of the new ?uoroquinolone antibacterial DW-116 in rabbits

DW-116 is a newly developed fluoroquinolone antibacterial with a broad spectrum against both Gram-positive and Gram-negative bacteria. We have reported recently that DW-116 is embryotoxic and teratogenic in rats. The present study was conducted to investigate the teratogenicity of DW-116, together with maternal toxicity and developmental toxicity using New Zealand White rabbits. The test chemical was administered by gavage to pregnant rabbits from gestational day (GD) 6 through to GD 18 at dose levels of 0, 5, 19.5 and 76.1 mg kg(-1) day(-1). All does were subjected to caesarean section on day 28 of gestation and their foetuses were examined for external, visceral and skeletal abnormalities. In the 76.1 mg kg(-1) group, a minimal maternal toxicity, as evidenced by decreased body weight gain during treatment period, was observed in pregnant rabbits. Significant embryo-foetal toxicity, including increased number of foetal deaths and delayed foetal ossification, was seen. However, no treatment-related morphological changes were detected in foetal external, visceral and skeletal examinations. There were no adverse effects on either pregnant dams or embryo-foetal development at 19.5 and 5 mg kg(-1). It was concluded that administration of DW-116 during the major organogenetic period in rabbits produced decreased maternal body weight gain, increased number of foetal deaths and foetal developmental delay but no evidence of teratogenicity. The no-observed-adverse-effect levels (NOAELs) of DW-116 are considered to be 19.5 mg kg(-1) day(-1) for does and embryo-foetuses, respectively.

Reproductive toxic effect of bisphenol A dimethacrylate in mice

The current study evaluated the effect of bisphenol A dimethacrylate (Bis-DMA) on mouse fertility. Adult male and female mice were exposed to intragastric Bis-DMA (0, 5, 25, and 100 microg/kg) daily for 28 days and then mated with sexually mature untreated mice and after mating fertility was assessed. Females mated by males that had been exposed to Bis-DMA had significant reductions in pregnancy rates and significant increases in the total number of resorptions out of the total number of implantations. Bis-DMA exposed males had significant reductions in body weights and relative testes weights and significant increases in seminal vesicle and preputial gland weights. Testicular and epididymal sperm counts as well as the efficiency of sperm production were also significantly reduced in these groups. Female mice exposed to Bis-DMA showed significant reductions in pregnancy rates, number of implantation sites, number of viable fetuses, and total number of resorptions out of the total number of implantations. Significant reductions in the body weights were observed at all doses, and significant increases were found in the relative weights of the ovaries and the uterus. The results suggest that Bis-DMA has adverse effects on the fertility and reproductive systems of male and female mice.

Supernumerary ribs in developmental toxicity bioassays and in human populations: incidence and biological significance

Supernumerary or accessory ribs (SNR), either lumbar (LR) or cervical (CR), are a common finding in standard developmental toxicology bioassays. The biological significance of these anomalies within the regulatory arena has been problematic and the subject of some debate. In rodents, the spontaneous incidence of SNR is species and strain related and ranges from <1% to >30%. Compound-induced LR are induced by a wide variety of chemical and physical agents when pregnant animals are exposed during specific gestational periods. A significant portion of the agent-induced LR may be due to maternal factors, as it has been shown that stress alone will induce LR in rodents. SNR are not isolated phenomena and signify basic alterations in the architecture of the axial skeleton. LR are associated with longer ribs, increased numbers of vertebrosternal ribs, and the presence of extra presacral vertebrae ("anteriorization"). CR are associated with reduced numbers of vertebrosternal ribs (posteriorization). It is evident that SNR are not a single anomaly, but consist of two unrelated structures: an extra rib that has a cartilaginous segment at the distal end, and an ossification site that lacks cartilage. These have a bimodal size distribution, with the population of extra ribs being significantly longer than the ossification sites, and 0.6 mm can be used as an approximate length for distinguishing the two populations in mice. Extra ribs are permanent structures in contrast to ossification sites that disappear postnatally, probably becoming part of the lateral transverse vertebral processes. SNR are also found in humans although, in contrast to laboratory species, CR are more commonly noted. SNR are associated with adverse heath effects, and CR with inducing thoracic outlet disease characterized by diminished blood flow and altered position of the ganglia and nerve roots in the area of the C7-T1 vertebrae. LR are associated with lower back pain and L4-5 degeneration. The incidence of CR is greatly reduced in adult humans as compared to fetuses, and it has been hypothesized that fetal "SNR" may be largely composed of ossification sites that disappear postnatally. The mechanisms involved in the formation of extra ribs are not understood at this time, although the fact that the early sensitive periods for their initiation during embryogenesis is coupled with the associated changes in the axial skeleton argues for their induction being due to fundamental changes in gene expression. The sum of the experimental evidence supports the idea of SNR being composed of two different structures: extra ribs that are permanent dysmorphological structures that may be induced by xenobiotics and/or maternal stress, and ossification sites that may be transient variations in the formation of the lateral processes of the vertebrae.