Post-implantation embryo culture: validation with selected compounds for teratogenicity testing

ECITTS: An Integrated Approach to the Application of In Vitro Test Systems to the Hazard Assessment of Chemicals,

As a result of a workshop held at Täljöviken, Åkersberga, Sweden, on 27–29 May 1991, a multicentre collaborative research project was established, with the purpose of developing the concept of integrated in vitro toxicity testing. The first priority was the selection of tests within eight appropriate areas: basal cytotoxicity, irritancy, developmental toxicity, hepatotoxicity, nephrotoxicity, immunotoxicity, neurotoxicity and biokinetics. An ideal battery of tests for each area was identified. Since it was realised that it would not be feasible to include the full ideal list of tests in the project, a minimum test list was also agreed. For each area, ten calibration chemicals were selected. From these 80 compounds, 30 were selected for inclusion, together with 20 of the OECD test programme chemicals, in a first test set of chemicals. The toxicity of these 50 test set chemicals will be investigated in the minimum integrated test scheme.

The aim of the project is to employ non-animal methods to assess the toxicological properties of chemicals, and to improve this assessment through the use of knowledge about mechanisms of toxic action. The information produced will contribute to the establishment of a more-scientific and more-efficient toxicological procedure for hazard assessment. Questions concerning which parameters need to be investigated and combined to make hazard assessments, and which parameters relevant to in vivo toxicity can be determined in non-whole animal test systems, will also be addressed.

Improvements in Clinical Trials Information Will Improve the Reproductive Health and Fertility of Cancer Patients

There are a number of barriers that result in cancer patients not being referred for oncofertility care, which include knowledge about reproductive risks of antineoplastic agents. Without this information, clinicians do not always make recommendations for oncofertility care. The objective of this study was to describe the level of reproductive information and recommendations that clinicians have available in clinical trial protocols regarding oncofertility management and follow-up, and the information that patients may receive in clinical trials patient information sheets or consent forms. A literature review of the 71 antineoplastic drugs included in the 68 clinical trial protocols showed that 68% of the antineoplastic drugs had gonadotoxic animal data, 32% had gonadotoxic human data, 83% had teratogenic animal data, and 32% had teratogenic human data. When the clinical trial protocols were reviewed, only 22% of the protocols reported the teratogenic risks and 32% of the protocols reported the gonadotoxic risk. Only 56% of phase 3 protocols had gonadotoxic information and 13% of phase 3 protocols had teratogenic information. Nine percent of the protocols provided fertility preservation recommendations and 4% provided reproductive information in the follow-up and survivorship period. Twenty-six percent had a section in the clinical trials protocol, which identified oncofertility information easily. When gonadotoxic and teratogenic effects of treatment were known, they were not consistently included in the clinical trial protocols and the lack of data for new drugs was not reported. Very few protocols gave recommendations for oncofertility management and follow-up following the completion of cancer treatment. The research team proposes a number of recommendations that should be required for clinicians and pharmaceutical companies developing new trials.

Validation of whole chick embryo cultures, whole rat embryo cultures and aggregating embryonic brain cell cultures using six pairs of coded compounds

A comparative study was performed to assess the effects of six pairs of coded compounds using cultures of whole chick and rat embryos as well as aggregating brain cell cultures. Developed originally for basic studies in developmental biology, these three culture systems have been adapted for the screening of chemicals in the field of prenatal toxicology. Chick and rat embryos were cultured for 2 days during the early stages of organogenesis. Aggregating cell cultures were prepared from early foetal rat telecephalon and grown for 14 days in a chemically defined medium. Concentration-response relationships were established by treating whole embryos in vitro for 2 days, and aggregating brain cell cultures for 9 days. After decoding the compounds, the results showed that, in the three test systems, specific effects were induced at comparable concentration levels. Similar compound-related malformations could be observed in both chick and rat whole embryo cultures. In aggregating brain cell cultures, neuron- and glia-specific effects could be distinguished. Based on the results obtained in the three in vitro systems, the following concentration ranges were determined for the teratogenic/toxic potencies of the test compounds (in mol/litre): <10(-6): retinoids (Ro 13-6307, Ro 1-5488), 6-aminonicotinamide, ketoconazole; 10(-6)-10(-3): 4-hydroxypyridine, sulfadiazine, sulfanilamide, caffeine, theophylline, metronidazole, methoxyacetic acid; >10(-3): methoxyethanol. In general, the three in vitro test systems were found to provide concordant and complementary data on the toxicity and teratogenicity of a given compound. These data were also comparable with those available from in vivo studies. It is therefore concluded that such a test battery could contribute significantly to risk assessment and to the reduction of in vivo experimentation in reproductive toxicology.

Organ culture of the fetal mouse palate for screening the developmental toxicity of chemicals: a validation study

Using in vitro organ culture of the fetal mouse palate in a chemically defined serumless medium, the toxicity of 24 chemical compounds was investigated. Explanted palates of day-12.5 mouse fetuses were exposed for 72 h in vitro to various concentrations of each chemical, and the fusion rate and growth parameters were compared between the experimental group and respective controls. The average rate of palate fusion was 84% in vehicle controls. For compounds that are teratogenic in experimental animals in vivo, the fusion rates of palatal shelves decreased as the concentration of the test chemicals increased, showing a dose-dependent relationship. Palate fusion was inhibited by 11 of the 15 in vivo teratogens, and the predictability of in vivo developmental toxicity in this culture system was 73%. Cyclophosphamide itself did not inhibit the growth and fusion of explanted palates, but supplementation of hepatic S-9 fraction and cofactors for a monooxygenase system converted it to a toxic substance, as was shown in other in vitro systems. The 50% inhibitory concentration (IC50) value calculated based on the fusion rate was also found to be a useful parameter for evaluating the developmental toxicity of drugs. The teratogenic risk in the human fetus could be assessed by comparing the minimal toxic concentrations of the test compound on cultured palates with the maximal plasma level in pregnant women under therapeutic conditions and with the plasma concentrations when its minimal teratogenic dose is given to pregnant mice. This organ culture system of the fetal palate should be useful for screening the developmental toxicity of drugs and other environmental agents, and its value should increase when it is used in combination with other battery test systems.

Embryopathic effects of diazoxide and the reduction of sulfonylurea-induced dysmorphogenesis in vitro

Diazoxide is a benzothiadiazine used in oral and intravenous preparations to treat hypertension and hypoglycaemia, but its effect on embryonic development has not been well studied. Previous in vivo work has suggested placental transfer and teratogenicity of diazoxide in humans and laboratory animals, but this study represents the first in vitro investigation of the effect of diazoxide on the embryo. The in vitro method of whole-embryo culture was used to expose mouse embryos to specific levels of diazoxide (0-200 mug/ml) during organogenesis at well-defined (4-6 and 20-25 somite) stages of development. In addition, the combined effect of diazoxide [ATP-sensitive K(+) (K(ATP)) channel opener] and the sulfonylurea oral hypoglycaemic agent chlorpropamide (K(ATP) channel blocker), was evaluated in vitro in embryos with 4-6 somites. Diazoxide produced malformations and growth retardation in mouse embryos exposed to 100 mug/ml or more for 24 hr in vitro at both stages of organogenesis. In addition, a subteratogenic concentration of diazoxide (25 mug/ml) reduced the embryopathic effects of chlorpropamide (130 mug/ml) in embryos with 4-6 somites. A potential mechanism for these effects involves K(ATP) channels.

Comparison of dexamethasone-induced embryotoxicity in vitro in mouse and rat embryos

Previous work demonstrated that rat embryos were more susceptible to the growth retardation effect of the synthetic glucocorticoid dexamethasone (DEX) in vivo than were mouse embryos. The purpose of this study was to examine this species difference using an in vitro system. Embryos of CD rats and CD-1 mice were cultured in a whole embryo culture system with concentrations of DEX from 5 to 250 micrograms/ml. Rat embryos were explanted on day 9 of gestation (GD 9: plug day = GD 0), while mouse embryos were removed on GD 8. After 48 h in culture, each viable embryo was evaluated for morphological score, and the number of somite pairs, crown-rump, and head lengths, as well as DNA and protein concentrations were determined. A reduced morphological score was observed for mouse embryos at 5 micrograms DEX/ml, but a significant decrease in this parameter was only observed at DEX concentrations of > or = 100 micrograms/ml in rat embryos. Significant reductions in the number of somite pairs were observed at 25 micrograms/ml for mouse embryos and 100 micrograms/ml for rat embryos. Crown-rump and head lengths as well as DNA and protein concentrations were significantly decreased at 100 micrograms/ml in mouse embryos and 150 micrograms/ml in rat embryos. Therefore, in vitro mouse embryos were adversely affected by lower concentrations of DEX than were rat embryos for each of the six end points examined in this study. This species sensitivity in vitro could be due to inherent genetic differences or to the slightly different developmental stages evaluated using the culture system.(ABSTRACT TRUNCATED AT 250 WORDS)

Embryonic and fetal development: fundamental research

Much progress has been made over the past decades in the development of in vitro techniques for the assessment of chemically induced effects in embryonic and fetal development. In vitro assays have originally been developed to provide information on the mechanism of action of normal development, and have hence more adequately been used in fundamental research. These assays had to undergo extensive modification to be used in developmental toxicity testing. The present paper focuses on the rat whole embryo culture system, but also reviews modifications that were undertaken for the in vitro chick embryo system and the aggregate cultures of fetal rat brain cells. Today these tests cannot replace the existing in vivo developmental toxicity tests. They can, however, be used to screen chemicals for further development or further testing. In addition, these in vitro tests provide valuable information on the mechanisms of developmental toxicity and help to understand the relevancy of findings for humans. In vitro systems, combined with selected in vivo testing and pharmacokinetic investigations in animals and humans, can thus provide essential information for human risk assessment.

Postimplantation embryo culture for the assessment of the teratogenic potential and potency of compounds

Whole rat embryos cultured during the early stages of organogenesis were subjected to a panel of selected chemicals. Of seventeen known in vivo teratogens, seventeen also induced specific malformations in embryos grown in culture. Of ten chemicals which were reported to be negative in in vivo rat teratogenicity studies, eight also did not provoke dysmorphogenic effects in vitro. Of five additionally tested retinoids, all induced multiple malformations. However, concentrations used to induce these effects varied considerably, isotretinoin inducing malformations at 10(-5) M and arotinoid at 10(-11) M. The results indicate qualitatively as well as quantitatively a high predictability of this in vitro system and suggest that the postimplantation embryo culture system may also be useful in the prospective testing of new drugs and environmental chemicals.