Developmental toxicity evaluation of Bendectin in CD rats

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

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

Outcomes of pregnancies complicated by hyperemesis gravidarum

OBJECTIVE

To evaluate maternal and neonatal outcomes among women with hyperemesis during pregnancy.

METHODS

A population-based retrospective cohort study was conducted among women with singleton deliveries between 1988 and 2002. Hyperemetic pregnancies were defined as those requiring one or more antepartum admissions for hyperemesis before 24 weeks of gestation. Severity of hyperemesis was evaluated according to the number of antenatal hospital admissions (1 or 2 versus 3 or more) and according to weight gain during pregnancy (< 7 kg [15.4 lb] versus > or = 7 kg). Maternal outcomes evaluated included weight gain during pregnancy, gestational diabetes, gestational hypertension, labor induction, and cesarean delivery. Neonatal outcomes included 5-minute Apgar score of less than 7, low birth weight, small for gestational age, preterm delivery, and perinatal death. Logistic regression was used to generate adjusted odds ratios for all outcomes, and the odds ratios were converted to relative risks.

RESULTS

Of the 156,091 singleton pregnancies, 1,270 had an admission for hyperemesis. Compared to women without hyperemesis, infants born to women with hyperemesis and with low pregnancy weight gain (< 7 kg [15.4 lb]) were more likely to be low birth weight, small for gestational age (SGA), born before 37 weeks of gestation, and have a 5-minute Apgar score of less than 7. Compared with infants born to women without hyperemesis, rates of low birth weight and preterm delivery were substantially higher among infants born to women with hyperemesis and low pregnancy weight gain (4.2% versus 12.5% and 4.9% versus 13.9%, respectively). The outcomes among infants born to women with hyperemesis with pregnancy weight gain of 7 kg (15.4 lb) or more were not different from the outcomes among women without hyperemesis.

CONCLUSION

The results of this study suggest that the adverse infant outcomes associated with hyperemesis are a consequence of, and mostly limited to, women with poor maternal weight gain.

LEVEL OF EVIDENCE

II-2.

Proconvulsant effects induced by pyridoxine in young rats

High doses of pyridoxine (vitamin B6) can be neurotoxic in adults. Effects of intraperitoneally administered B6 (100, 250 and 400 mg/kg) were studied in 7, 12, 18 and 60 day old rats. B6 elicited epileptiform EEG discharges without any motor correlate in all age groups. In contrast, motor seizures were rare, seen only in 18 day old rats (250 mg/kg of B6). Data indicate that in young rats, B6 may have proconvulsant effects in doses relevant to those sometimes used in pediatric neurology.

Bendectin: review of the medical literature of a comprehensively studied human nonteratogen and the most prevalent tortogen-litigen

OBJECTIVE

to review the extensive literature pertaining to the reproductive and teratogenic effects of Bendectin and the opinions of the scientific experts for the defense and plaintiff. These data were evaluated with regard to the reproductive risks of Bendectin providing a scientific framework for evaluating the views of the experts in the Bendectin litigation.

DESIGN

the Bendectin literature was primarily obtained from articles cited in Research Alert of the Institute for Science Information. Other articles were obtained from Medline, review articles, and colleagues. An attempt was made to be all-inclusive, citing and reviewing all articles related to each subject being discussed. The literature includes epidemiologic studies, animal studies, in vitro studies, and basic science articles related to the principles of teratology and reproductive toxicology. Review articles, meta analyses, editorials, commentaries, articles in the press, and case reports were also included.

METHODOLOGY

the methodology utilized for the evaluation of Bendectin teratogenicity was presented. It consists of a five-part analysis of epidemiologic studies, secular trend analysis, animal studies, dose-response relationships, and biologic plausibility.

CONCLUSION

the five-part analysis of Bendectin reproductive effects indicates that therapeutic use of Bendectin has no measurable teratogenic effects. Presentations by many of the plantiff's experts failed to meet the scientific standards that should be expected of knowledgeable scientists and contributed to the persistence of Bendectin litigation.

Dose-response models for developmental malformations

An empirical dose-response model can generally be found for bioassay data, which provides a mathematical relationship between the incidence of a developmental malformation and dose of a toxicant in the experimental dose range. If biological principles and data can be used in the formulation of the dose-response model, the estimation of the incidence of malformations outside of the experimental dose range may be improved. In this paper, exponential growth of morphological structures in rodents during gestation is assumed. Further, it is assumed that some structural malformations are the result of reduced or delayed growth and the incidence of structurally normal fetuses is proportional to fetal weight raised to a power. When the exponential growth rate constant is reduced by dose raised to a power, a Weibull dose-response function is obtained. When the exponential growth rate constant is modeled by a polynomial function of dose, a polynomial-exponential dose-response model is obtained. The Weibull and the polynomial-exponential model, restricted to degrees from one up to the number of dosed groups, were fit to a database of bioassay data assembled from Teratology Vol. 1 (1968) to Vol. 42 (1990). In general the two models gave similar results and often gave exactly the same fit. The linear term appeared in the polynomial-exponential model in about one-fourth of the cases and was not related to the background incidence.

Vitamin neurotoxicity

Vitamins contain reactive functional groups necessary to their established roles as coenzymes and reducing agents. Their reactive potential may produce injury if vitamin concentration, distribution, or metabolism is altered. However, identification of vitamin toxicity has been difficult. The only well-established human vitamin neurotoxic effects are those due to hypervitaminosis A (pseudotumor cerebri) and pyridoxine (sensory neuropathy). In each case, the neurological effects of vitamin deficiency and vitamin excess are similar. Closely related to the neurological symptoms of hypervitaminosis A are symptoms including headache, pseudotumor cerebri, and embryotoxic effects reported in patients given vitamin A analogs or retinoids. Most tissues contain retinoic acid (RA) and vitamin D receptors, members of a steroid receptor superfamily known to regulate development and gene expression. Vitamin D3 effects on central nervous system (CNS) gene expression are predictable, in addition to the indirect effects owing to its influence on calcium and phosphorus homeostasis. Folates and thiamine cause seizures and excitation when administered in high dosage directly into the brain or cerebrospinal fluid (CSF) of experimental animals but have rarely been reported to cause human neurotoxicity, although fatal reactions to i.v. thiamine are well known. Ascorbic acid influences CNS function after peripheral administration and influences brain cell differentiation and 2-deoxyglucose accumulation by cultured glial cells. Biotin influences gene expression in animals that are not vitamin-deficient and alters astrocyte glucose utilization. The multiple enzymes and binding proteins involved in regeneration of retinal vitamin A illustrate the complexity of vitamin processing in the body. Vitamin A toxicity is also a good general model of vitamin neurotoxicity, because it shows the importance of the ratio of vitamin and vitamin-binding proteins in producing vitamin toxicity and of CNS permeability barriers. Because vitamin A and analogs enter the CNS better than most vitamins, and because retinoids have many effects on enzyme activity and gene expression, Vitamin A neurotoxicity is more likely than that of most, perhaps all other vitamins. Megadose vitamin therapy may cause injury that is confused with disease symptoms. High vitamin intake is more hazardous to peripheral organs than to the nervous system, because CNS vitamin entry is restricted. Vitamin administration into the brain or CSF, recommended in certain disease states, is hazardous and best avoided. The lack of controlled trials prevents us from defining the lowest human neurotoxic dose of any vitamin. Large differences in individual susceptibility to vitamin neurotoxicity probably exist, and ordinary vitamin doses may harm occasional patients with genetic disorders.(ABSTRACT TRUNCATED AT 400 WORDS)