Modification and standardization of the culture of early postimplantation embryos for toxicological studies

Verbascoside-enriched fraction from Buddleja cordata Kunth ameliorates the effects of diabetic embryopathy in an animal model

BACKGROUND

The deleterious effects of diabetes mellitus (DM) over development are apparently due to an increase in oxidative stress. Some antioxidants could prevent developmental alterations produced by diabetic state. Extracts of plants of the genus Buddleja are used traditionally for Mexican indigens to ameliorate some diseases. The purpose of this work was to evaluate the effect of the extract of Buddleja cordata over diabetic embryopathy.

METHODS

Two experimental approaches were used: an in vivo study and an in vitro model. In the first, rats were treated with streptozotocin, streptozotocin plus methanolic extract of B. cordata, or none. Females were sacrificed at gestational day (GD) 19, and biochemical clinical parameters were measured; also, the fetuses were obtained and morphologically analyzed. In the in vitro model, a verbascoside-enriched fraction (VEF) of the extract was used in whole embryo culture in order to search for the mechanisms for embryoprotection effect over hyperglycemia-induced malformations.

RESULTS

In the in vivo experiments, B. cordata extract reduces the frequency and severity of fetal malformations produced by chemically induced diabetes, and additionally partially ameliorates the diabetic condition; in the in vitro model, both severity and frequency of embryo dysmorphogenesis were reduced by the VEF; also, this fraction reduces lipoperoxidation without affecting the activity of the antioxidant enzymes.

CONCLUSION

The results suggest that verbascoside of methanolic extract and enriched fraction can directly affect the redox state, and thus, prevents the embryotoxicity mediated by oxidative stress, in embryos of diabetic pregnancy.

Bcl-2 expression in a diabetic embryopathy model in presence of polyamines

The frequency of congenital malformations is 3-5 times higher in mothers with pregestational diabetes mellitus than in general population. Apparently, this problem is due to change in the expression of apoptotic and antiapoptotic genes induced by the oxidative stress derived from the diabetes/hyperglycemia. One of these genes is Bcl-2, which is associated with the control and inhibition of apoptosis. The purpose of the present work was to study the effect of polyamine addition over expression of Bcl-2 gene in a model of diabetic embryopathy. For this, gestational day 10.5 (GD10.5) rat embryos were incubated at 37°C for 24 h in control medium, medium with high glucose, or medium with high glucose and supplemented with spermidine or spermine. Post-cultured embryos were harvested and observed to obtain morphological scores; some of them were subjected to molecular biology studies: DNA isolation plus conventional PCR or RNA isolation plus RT-PCR; other embryos were fixed with paraformaldehyde and used for immunohistochemical detection of Bcl-2 protein. Although Bcl-2 mRNA was similarly expressed in all rat embryo treatments, Bcl-2 protein was found only in control-incubated embryos. In conclusion, it seems that the inhibition of Bcl-2 gene expression induced by glucose was not reversed by polyamines.

Triclabendazole sulfoxide causes stage-dependent embryolethality in zebrafish and mouse in vitro

Background

Fascioliasis and paragonimiasis are widespread foodborne trematode diseases, affecting millions of people in more than 75 countries. The treatment of choice for these parasitic diseases is based on triclabendazole, a benzimidazole derivative which has been suggested as a promising drug to treat pregnant women and children. However, at the moment, this drug is not approved for human use in most countries. Its potential adverse effects on embryonic development have been scarcely studied, and it has not been assigned a pregnancy category by the FDA. Thus, to help in the process of risk-benefit decision making upon triclabendazole treatment during pregnancy, a better characterization of its risks during gestation is needed.

Methodology

The zebrafish embryo test, a preimplantation and a postimplantation rodent whole embryo culture were used to investigate the potential embryotoxicity/teratogenicity of triclabendazole and its first metabolite triclabendazole sulfoxide. Albendazole and albendazole sulfoxide were included as positive controls.

Principal Findings

Triclabendazole was between 10 and 250 times less potent than albendazole in inducing dysmorphogenic effects in zebrafish or postimplantation rodent embryos, respectively. However, during the preimplantation period, both compounds, triclabendazole and triclabendazole sulfoxide, induced a dose-dependent embryolethal effect after only 24 h of exposure in rodent embryos and zebrafish (lowest observed adverse effect concentrations = 10 μM).

Conclusions/Significance

In humans, after ingestion of the recommended doses of triclabendazole to treat fascioliasis and paragonimiasis (10 mg/kg), the main compound found in plasma is triclabendazole sulfoxide (maximum concentration 38.6 μM), while triclabendazole concentrations are approximately 30 times lower (1.16 μM). From our results it can be concluded that triclabendazole, at concentrations of the same order of magnitude as the clinically relevant ones, does not entail teratogenic potential in vitro during the organogenesis period, but its first metabolite triclabendazole sulfoxide has a high embryotoxic capacity in vitro during the preimplantation stage.

Identification of a potent endothelium-derived angiogenic factor

The secretion of angiogenic factors by vascular endothelial cells is one of the key mechanisms of angiogenesis. Here we report on the isolation of a new potent angiogenic factor, diuridine tetraphosphate (Up4U) from the secretome of human endothelial cells. The angiogenic effect of the endothelial secretome was partially reduced after incubation with alkaline phosphatase and abolished in the presence of suramin. In one fraction, purified to homogeneity by reversed phase and affinity chromatography, Up4U was identified by MALDI-LIFT-fragment-mass-spectrometry, enzymatic cleavage analysis and retention-time comparison. Beside a strong angiogenic effect on the yolk sac membrane and the developing rat embryo itself, Up4U increased the proliferation rate of endothelial cells and, in the presence of PDGF, of vascular smooth muscle cells. Up4U stimulated the migration rate of endothelial cells via P2Y2-receptors, increased the ability of endothelial cells to form capillary-like tubes and acts as a potent inducer of sprouting angiogenesis originating from gel-embedded EC spheroids. Endothelial cells released Up4U after stimulation with shear stress. Mean total plasma Up4U concentrations of healthy subjects (N=6) were sufficient to induce angiogenic and proliferative effects (1.34 ± 0.26 nmol L(-1)). In conclusion, Up4U is a novel strong human endothelium-derived angiogenic factor.

The use of whole embryo culture to elucidate teratogenic mechanisms

In the overview presented, only selected examples for the applicability of whole embryo culture, and a few examples for its use and possible misuse, are mentioned. In general, the system has proved suitable for elucidating mechanisms involved in abnormal development at this embryonic stage. However, it should be remembered that only a small window of prenatal development can be judged with this technique, and that the system is not well suited for elucidating many special effects and abnormalities induced at later stages of development. For this reason, no single in vitro system is suitable to study all kinds of problems in prenatal biology or toxicology. As emphasized before, the real significance of the whole embryo culture technique rests on the variety of methodological possibilities that can be modified by any creative scientist. In connection with in vivo and appropriate pharmacokinetic studies, this system will play an important role in the field of developmental biology and toxicology in the future.

Effects of mycophenolic acid alone and in combination with its metabolite mycophenolic acid glucuronide on rat embryos in vitro

Mycophenolic acid (MPA) is an immunosuppressive agent that acts as a selective, non-reversible inhibitor of the enzyme inosine-5'-monophosphate dehydrogenase (IMPDH). Malformations have been described in children after maternal exposure to mycophenolate. However, the causal link is unclear in most cases because women had been treated with a combination of drugs and birth defects may have other causes. Therefore, it is important to study the action of this drug and its main metabolite on embryonic tissue. We studied the teratogenic potential of MPA and its major metabolite, the mycophenolic acid glucuronide (MPAG) in the rat whole-embryo culture. A total of 147 day 9.5 embryos were cultivated for 48 h in the standard medium containing 85 % serum. We tested MPA at concentrations of 0.1; 0.25; 0.5; 0.75 mg/l (0.31; 0.78; 1.56; 2.34 μM) and MPA glucuronide at concentrations of 3; 10; 30; 100 mg/l (6.04; 20.14; 60.43; 201.43 μM). Both substances are highly protein bound, and MPA glucuronide might displace MPA from protein binding. Therefore, we examined whether the effects of MPA can be enhanced when studied in combination with the glucuronide. Furthermore, the focus was on additional endpoints to the standard evaluation of cultivated embryos, such as development of cranial nerves [trigeminal nerve (V), facial nerve (VII), glossopharyngeal nerve (IX), vagus nerve (X)] after staining with an antibody against 2H3 neurofilament. Ultrastructural changes were evaluated by electron microscopy. At a concentration of 0.75 mg MPA/l medium, all embryos showed dysmorphic changes. Embryos exposed to 0.25 mg MPA/l medium showed impaired development of nerves, and at 0.1 mg/l, no effects were detectable. Concentration-dependent ultrastructural changes, such as signs of apoptosis, were found by electron microscopy. The examination of the metabolite in this assay showed that at a concentration of 100 mg MPAG/l, the embryos exhibited distinct malformations. This is probably caused by MPA, which was detectable at 0.6 % in the material used for our experiments. The combination of the parent compound (0.03; 0.1; 0.25 mg/l) with its metabolite MPAG (3 mg/l) did not cause enhanced toxicity under our experimental conditions. IMPDH, the target enzyme of MPA, could be detected in rat embryos on day 9.5 of embryonic development as well as at the end of the culture period 48 h later. In summary, MPA impairs embryonic development at low, therapeutically relevant concentrations, but the glucuronide does not exhibit such a potential. Activity of MPA is not enhanced by MPAG.

Assessment of developmental delay in the zebrafish embryo teratogenicity assay

In this study we analyzed some aspects of the assessment of developmental delay in the zebrafish embryotoxicity/teratogenicity test and explored the suitability of acetylcholinesterase (AChE) activity as a biochemical marker and as a higher throughput alternative to morphological endpoints such as head-trunk angle, tail length and morphological score. Embryos were exposed from 4 to 52 h post-fertilization (hpf) to a selection of known embryotoxic/teratogen compounds (valproic acid, retinoic acid, caffeine, sodium salicylate, glucose, hydroxyurea, methoxyacetic acid, boric acid and paraoxon-methyl) over a concentration range. They were evaluated for AChE activity, head-trunk angle, tail length and several qualitative parameters integrated in a morphological score. In general, the different patterns of the concentration-response curves allowed distinguishing between chemicals that produced growth retardation (valproic and methoxyacetic acid) and chemicals that produced non-growth-delay related malformations. An acceptable correlation between the morphological score, AChE activity and head-trunk angle as markers of developmental delay was observed, being AChE activity particularly sensitive to detect delay in the absence of malformations.

Alternative models in developmental toxicology

In light of various pressures, toxicologists have been searching for alternative methods for safety testing of chemicals. According to a recent policy in the European Union (Regulation, Evaluation Authorisation and Restriction of Chemicals, REACH), it has been estimated that over the next twelve to fifteen years, approximately 30,000 chemicals may need to be tested for safety, and under current guidelines such testing would require the use of approximately 7.2 million laboratory animals [ Hofer et al. 2004 ]. It has also been estimated that over 80% of all animals used for safety testing under REACH legislation would be used for examining reproductive and developmental toxicity [Hofer et al., 2004]. In addition to REACH initiatives, it has been estimated that out of 5,000 to 10,000 new drug entities that a pharmaceutical company may start with, only one is finally approved by the Food and Drug Administration at a cost of over one billion dollars [ Garg et al. 2011 ]. A large portion of this cost is due to animal testing. Therefore, both the pharmaceutical and chemical industries are interested in using alternative models and in vitro tests for safety testing. This review will examine the current state of three alternative models - whole embryo culture (WEC), the mouse embryonic stem cell test (mEST), and zebrafish. Each of these alternatives will be reviewed, and advantages and disadvantages of each model will be discussed. These models were chosen because they are the models most commonly used and would appear to have the greatest potential for future applications in developmental toxicity screening and testing.

Transcriptomic analysis of neurulation and early organogenesis in rat embryos: an in vivo and ex vivo comparison

Cultured embryos mimic the morphological developmental progression of embryos (in vivo) undergoing neurulation and early organogenesis. Using available genomics technologies, comparative molecular-based assessments between cultured embryos and in vivo models may further clarify commonalities and dissimilarities, which contribute to differences between systems. Therefore, in this study, using a transcriptomic approach, we compared cultured whole rat embryos and embryos in vivo at comparable time points in development (gestational day (GD) 10 + 2-48 h, GD 0 = copulatory plug) to assess for commonalities and differences in gene expression in relation to morphology. We reveal strong parallels in time-dependent expression of genes in terms of magnitude, directionality, and functionality between whole embryo culture (WEC) and in vivo (rat). Genes changing in expression over time resemble previously hypothesized mechanisms underlying early development in mammalian systems. Furthermore, at the gene and functional level, we identify genes, which differ in expression between models, including genes related to development, oxygen transport, and metabolism. In summary, our results support the use of WEC for toxicological studies aimed at representing in vivo development during this time window at the molecular level. Additionally, we indicate genes, which differ in expression between models, providing possible insights for improvement of culture conditions.

Fish embryo toxicity of carbamazepine, diclofenac and metoprolol

Frequently measured pharmaceuticals in environmental samples were tested in fish embryo toxicity (FET) tests with Danio rerio, based on the draft OECD test protocol. In this FET test 2-h-old zebrafish embryos were exposed for 72 h to carbamazepine, diclofenac and metoprolol to observe effects on embryo mortality, gastrulation, somite formation, tail movement and detachment, pigmentation, heartbeat, malformation of head, otoliths and heart, scoliosis, deformity of yolk, and hatching success at 24, 48 and 72 h. We found specific effects on growth retardation above 30.6 mg/l for carbamazepine, on hatching, yolk sac and tail deformation above 1.5mg/l for diclofenac, and on scoliosis and growth retardation above 12.6 mg/l for metoprolol. Scoring all effect parameters, the 72-h-EC(50) values were: for carbamazepine 86.5mg/l, for diclofenac 5.3mg/l and for metoprolol 31.0mg/l (mean measured concentrations). In conclusion, our results for carbamazepine and metoprolol are in agreement with other findings for aquatic toxicity, and also fish embryos responded in much the same way as rat embryos did. For diclofenac, the FET test performs comparably to Early Life Stage testing.

Specific Effect of 5-Fluorouracil on α-Fetoprotein Gene Expression During the In Vitro Mouse Embryonic Stem Cell Differentiation

Embryonic stem (ES) cells are considered an important alternative to develop in vitro screening methods for embryotoxicity. Mouse ES cells can be cultured as cell suspension aggregates termed “embryoid bodies” (EBs) in which cells start to differentiate. We have studied the expression of several genes in the presence of a wide range of concentrations of 5-fluorouracil (5-FU). This well-established embryotoxic compound completely inhibited cell viability at 200 nmol/L in monolayer cultures. At lower concentrations, 5-FU led to decrease in the expression of the α-fetoprotein gene, a marker of the visceral endoderm, in the EBs. However, the expression of several mesodermal gene markers was not significantly affected at these concentrations. These results suggest a high sensitivity of the visceral endoderm differentiation to 5-FU. Therefore, the quantification of the α-fetoprotein gene after exposure to potential embryotoxicants should be considered an additional end point in future embryotoxicity assays in vitro with ES cells.

Use of two validated in vitro tests to assess the embryotoxic potential of mycophenolic acid

Mycophenolate mofetil is a widely used immunosuppressive drug that recently has been categorized as a human teratogen. Animal experiments indicate a teratogenic potential of the drug, but so far, it has not been studied in embryotoxicity in vitro assays. The aim of this study was to evaluate the in vitro embryotoxic potential of mycophenolic acid and investigate the ability of such tests to detect its embryotoxic potential. We used two validated assays: the rat whole embryo culture and the murine embryonic stem cell test. Rat embryos cultured from gestational day 9.5 for 48 h with the drug showed dysmorphogenic development already at a concentration of 250 microg mycophenolic acid/l medium. At concentrations of 750 microg/l and more, all rat embryos exhibited malformations. The main effects were defective yolk sac blood circulation, neural tube defects (open cranial neural pore), malformations of the head with missing eye anlagen and heart anomalies. Moreover, the exposed embryos showed a concentration-dependent decrease in protein content, crown-rump length, number of somites and morphological score. The murine embryonic stem cell test was slightly more sensitive. Proliferation and differentiation of the ES-D3-cells were significantly impaired at concentrations of 31 and 125 microg mycophenolic acid/l medium, respectively. In the differentiation assay, at a concentration of 125 microg mycophenolic acid/l medium and more, the number of wells with differentiated cardiomyocytes significantly decreased. Additionally, a cytotoxicity assay with balb/c 3T3 mouse fibroblasts was used to compare the proliferation and vitality of embryonic cells with adult cells. In the balb/c 3T3 cytotoxicity assay, the number of vital mouse fibroblasts significantly decreased at a mycophenolic acid concentration of 62 microg/l and more. In conclusion, by using the two validated in vitro tests, we showed that mycophenolic acid exhibits a pronounced embryotoxic potential at cytotoxic concentrations. This result from validated in vitro tests is of special interest, because it supports the use of the tests to detect human teratogens.

Polyamines protect rat embryo in vitro from high glucose-induced developmental delay and dysmorphogenesis

BACKGROUND

Pregnancy in mammals with diabetes mellitus results in low birth weight, malformations, and intrauterine death. Parenteral application of natural polyamines or their precursor, L-arginine, to diabetic pregnant rats partially prevents the alterations of development caused by diabetes mellitus. This experiment has been designed to understand if this preventive action also occurs in rat whole embryo in culture.

MATERIALS AND METHODS

Rat embryos of gestational day 10 were cultured for 24 h in normal medium, high glucose medium, or high glucose medium supplemented with polyamines or L-arginine, and furthermore embryo growth and development were evaluated.

RESULTS

L-arginine and putrescine partially prevents the dysmorphogenic effects of high glucose, whereas spermidine and spermine prevent these effects almost completely.

CONCLUSIONS

Polyamines directly protect the embryo from the toxic effect of high glucose concentration on growth and development, although the mechanism remains to be elucidated.

Alternative methods for developmental toxicity testing

Alternatives to animal testing in developmental toxicology have been the subject of three decades of research. The aims of these investigations have been to reduce animal experimentation, to refine effect assessment and mechanistic studies, and to accelerate and simplify safety testing in an area of toxicology that uses relatively many animals. Many alternatives have been developed over the years with different compexities, using biologic material ranging from continuous cell lines to complete embryos. The validation of alternatives and their application in testing strategies is still in its infancy, although significant steps towards these aims are currently being made. The introduction of the genomics technology is a promising emerging area in developmental toxicity testing in vitro. Future application of alternatives in testing strategies for developmental toxicity may significantly gain from the inclusion of gene expression studies, given the unique programme of gene expression changes in embryonic and foetal development.

A simple method of culture of 11.5-day-old rat embryos in DMEM/F12 and 20% fetal bovine serum

Post-implantation mouse and rat embryos are usually cultured in sera obtained from various rodents and from humans. We describe here a simple and inexpensive culture medium--Dulbecco's minimal essential medium/Ham's F12 (DMEM/F12) supplemented with 20% fetal bovine serum (FBS)--in which E11.5 rat embryos of the Hebrew University Sabra strain grow for 28 h slightly better than in heat-inactivated 90% rat serum with 10% distilled water and addition of 1 mg mL(-1) glucose. They have good growth and development and a low rate of anomalies, similar to that observed in embryos cultured on rat serum. Their size, total score and olfactory system development is slightly higher than in rat embryos cultured in rat serum. About 7.2% of these embryos exhibit subcutaneous haemorrhages in various areas, but these do not seem to interfere with their growth and development. This method is not appropriate for younger embryos; in E10.5 embryos cultured for 28 h we found increased embryonic death and anomalies.

Effects of ethylene glycol and metabolites on in vitro development of rat embryos during organogenesis

The aim of this study was to investigate in vitro the relative impact of ethylene glycol, a major industrial chemical, and its individual metabolites on the embryonic development of rats. Rat whole embryos were exposed for 48 h (day 9.5-11.5 of gestation) to ethylene glycol (EG) and its metabolites glycolaldehyde (GAl), glycolic acid (GA), glyoxylic acid (GXA), glyoxale (GXAl) and oxalic acid (OXA) at increasing concentrations. Embryotoxic concentrations were achieved within the following range: ethylene glycol (100-200 mM), glycolic acid (3 mM), glyoxal (6 mM), oxalic acid (1-3 mM), glyoxylic acid (0.3-1 mM), glycolaldehyde (0.1-0.2 mM). The pattern of dysmorphogenesis with all compounds including EG showed a general embryotoxicity with diffusely distributed cell necroses with no specific target tissues selectively affected. The results obtained in this study emphasize the hypothesis that the metabolites and not ethylene glycol itself are responsible for the embryotoxicity of ethylene glycol in rats.

Rat embryo cultures for in vitro teratology

Mammalian embryos provide a particular challenge to those who wish to study developmental processes because development takes place inside the mother's body, thus limiting the investigator's ability to directly affect and observe the embryonic stages of development. Fortunately, as this unit illustrates, methods have been developed for in vitro culture of rodent embryos during early postimplantation (gestation days 9 to 11) and early fetal (gestation days 12 to 14) stages, which are the periods during which the major systems of the embryo are established. Embryos at these stages are particularly suitable for screening studies to determine the effects of teratological agents.

Development of a morphologically-based scoring system for postimplantation New Zealand White rabbit embryos

Rodent whole-embryo culture (WEC) systems are well-established, as are several corresponding morphological scoring systems. Recently, WEC techniques for rabbits have been developed, creating the need for a morphological evaluation system in this species. Consequently, we developed a gestational-age-based quantitative morphology evaluation system for rabbit embryos. Detailed descriptions of 21 embryonic structures, as collected from gestational day (gd) 9-13 rabbit embryos, formed the basis for this evaluation system. These descriptions were then developed into specific criteria for assigning numerical scores to quantify the degree of development of each embryonic structure. The overall morphologic score was calculated as the average of the individual structure scores. To make the system as informative as possible, the numerical scale of the scoring system was gestationally age-based (i.e., range of potential scores was 9.0-13.0). The scoring system was then applied in the evaluation of New Zealand White (NZW) rabbit embryos explanted on gd 9 and cultured for 48 hr. Embryos grown in vitro developed normally, but at a slightly slower rate in vitro than in vivo, as evidenced by the lower morphology score (10.4 in vitro, 11.0 in vivo) and measures of growth (somite number, total protein, and head length). This work firmly establishes the normal archetype of embryonic development in the gd 9-13 NZW rabbit and provides an important tool for the advancement of mechanistic studies of rabbit embryos developing both in vivo and in vitro.

Effects of amphetamine on rat embryos developing in vitro

Wistar rat embryos were explanted on Day 10.5 of gestation and exposed in vitro to amphetamine (AMP) at concentrations of 0.1, 0.4, 0.8, 1.2, or 1.6 mM for 24 h, and the direct dysmorphogenic effects of the drug on the embryos were examined by comparisons with a control group. The viability of the cultured embryos was not affected by the AMP treatment. The yolk sac diameter was reduced at AMP concentrations of 1.2 and 1.6 mM. The crown-rump length, the somite number, and the protein content of the embryos were decreased significantly at these two doses, as was the developmental score. The frequency of malformed embryos was increased significantly at the two highest concentrations. The malformations induced in treated embryos included microcephaly, neural tube defects, incomplete rotation of the body axis, and tortuous spinal cord. Abnormal histologic changes, such as derangement and necrosis of the neuroepithelial tissue, were observed in the embryos exposed to the two highest concentrations of the drug. The observed embryotoxic effects appeared to depend on the AMP concentration. Our results demonstrated the direct embryotoxic effects of AMP on rats. The direct dysmorphogenic effect of AMP might be weaker than that of methamphetamine.

A comparison of the in vivo and in vitro response of rat embryos to 5-fluorouracil

This study serves to further define the capabilities of the whole embryo culture system using the well-known teratogen, 5-fluorouracil (5-FU), an antineoplastic agent. An initial in vivo study was performed whereby pregnant rats were injected intraperitoneally with 10-30 mg/kg 5-FU on day 9 of gestation. On day 20 of gestation, the effects of this drug on the growth and development of embryos were evaluated. The number of externally malformed fetuses increased in a dose-related manner, and the most common defect was micro-/anophthalmos in fetuses of dams treated with 5-FU. Growth retardation was also noted in the 5-FU treated groups. An in vitro study was performed in which drug concentrations were varied (0.15-0.30 microg/ml). Externally abnormal embryos were observed in whole embryo culture system from embryonic day 9 to 11. The most common defect was hypoplastic optic vesicles. In the whole embryo culture system, crown-rump length, somite number, protein contents, and morphological score were decreased in a dose-dependent fashion. Finally, histological evaluation and observation of the pattern of cell death of the optic vesicle of 11-day-old embryos in in vivo and in vitro were performed. These parameters revealed no differences in response between in vivo and in vitro embryos treated with 5-FU, suggesting that the whole embryo culture system was an appropriate model for developmental toxicity studies of 5-FU.

The lack of effects of nonthermal RF electromagnetic fields on the development of rat embryos grown in culture

Rat embryos (9.5 days old) were exposed for up to 36 h to various radio frequency (RF) electric and magnetic fields (modulation frequency: 16, 60, 120 Hz; electric field strength: 60, 600 V/m; magnetic induction: 0.2, 2.0 microT). A resonator technique was used to generate standing waves thus fulfilling three conditions: The site of maximum electric and magnetic oscillations could be separated, the field strengths were known exactly and a high homogeneity over the sample volume was achieved. In each frequency region the transmitter power levels were set to give specific absorption rate (SAR) values spreading from far below to far above the values met in the field of telecommunication (0.2, 1.0 and 5.0 W/kg). The criteria used to examine the embryos on day 11.5 for possible structural effects consisted of a scoring system, photographs, histology using both light and electron microscopy and determination of the protein content. All these data have been taken as sets of different intermediate frequency (IF) amplitude modulation of the RF carriers. Neither the electric nor the magnetic fields tested interfered significantly with the normal growth and differentiation of the embryos in vitro.

Rat embryo culture using rabbit serum as a medium for developmental toxicity studies

The usefulness of rabbit serum as a culture medium for postimplantation rat embryos was examined. Rat embryos at day 9.5 of gestation were cultured in a mixture of rat and rabbit sera at various ratios (v/v) for 48 h. In 100% rat serum, a usual medium, rat embryos grew well. On the contrary, rat embryos died with little growth in 100% rabbit serum. In 75% rabbit and 25% rat sera, rat embryos grew but were morphologically abnormal. In 50% rabbit and 50% rat serum, however, rat embryos grew well showing no morphological abnormalities, as in 100% rat serum. It was concluded from these results that rabbit serum could be used at a proportion up to 50% as a medium for postimplantation rat embryo culture in a mixed form with rat serum. The rat embryo culture using rabbit serum as a medium would be useful in developmental toxicity studies, especially those involving species differences and toxicokinetics.

Effects observed on gestational day 13 in rat embryos exposed to albendazole

Albendazole (ABZ) was utilized as a model to investigate the pathogenesis of benzimidazole-induced abnormalities. Pregnant Sprague-Dawley rats were treated po with 0, 10, 20, and 30 mg/kg on gestational days (GD) 10 to 12. The embryos were examined on GD 13, as a window for observing the origin of alterations detected at term. Embryolethality and growth reduction showed dose-related increases at the three dose levels. At 10 mg/kg, an increased developmental delay of limb buds and a less than 5% incidence of embryos with abnormal head or shape were detected. At 20 and 30 mg/kg, > 20% of embryos showed morphologic alterations involving mainly shape abnormalities and the development of forelimb buds, branchial bars, eye, and telencephalon; closure of neuropores was unaffected. Dose-response relationships for morphologic alterations showed steeper slopes than for growth reduction and embryolethality.

Toxicity of beta-blockers in a rat whole embryo culture: concentration-response relationships and tissue concentrations

Beta-adrenoceptor blockers are widely used drugs for the treatment of cardiovascular diseases. Since beta-blockers cross the placenta, it is essential to consider possible adverse effects on the embryo. Six beta-adrenoceptor blockers were tested at various concentrations (10-5000 microM) in a rat whole embryo culture. Although inducing a very similar pattern of dysmorphogenetic effects (incomplete flexure, disturbed development of the neural tube, the head, the heart and the tail bud), the compounds exhibited a wide range of embryotoxic potency. Estimation of the EC50 (median-concentration producing dysmorphogenesis in 50% of the embryos) for the six compounds revealed differences of more than two orders of magnitude: propranolol 25 microM, alprenolol 30 microM, metoprolol 100 microM, pindolol 150 microM, acebutolol 500 microM, atenolol 4000 microM. Measurements of the concentrations of the various drugs in the cultured embryos at corresponding EC50 levels showed differing values: metoprolol 4.5 microM, propranolol 5.2 microM, alprenolol 8.4 microM, pindolol 9.0 microM, acebutolol 12.5 microM and atenolol 77.0 microM. With regard to the EC50 and the degree of substance transfer to the embryo it can be stated that propranolol and metoprolol show a much higher intrinsic potency to interfere with normal in vitro embryonic development than, e.g. atenolol.

In vitro tests for teratogens: desirable endpoints, test batteries and current status of the micromass teratogen test

Information from in vitro tests can be usefully used as a component of the risk/hazard assessment process. In vivo studies will be required to confirm the in vitro data. If the in vitro test system is designed around endpoints that reflect changes following in vivo toxic insult then it may be possible to modify the in vitro system to account for some of the discrepancies observed between in vivo and in vitro outcomes. When the discrepancy can be accounted for by low bioavailability in vivo, pharmacokinetic studies may be required to determine the relevance of the in vitro toxic concentrations. Reproductive hazard, especially teratogenicity, has been the subject of intensive in vitro test development. The observation of teratogenicity may affect the development of new products more significantly than any other type or category of reproductive toxicity. The micromass test, involving culture of differentiating rat embryo limb and midbrain cells exposed to test agents, may be useful as part of a battery of in vitro tests for teratogens. The most recent protocol for the micromass test is described, followed by a summary of validation and mechanistic studies confirming its usefulness. The test is robust in its transfer to new laboratories. Interlaboratory variability is small.

Significance of embryo culture methods for studying the prenatal toxicity of virustatic agents

Culture methods have become important tools for elucidating the prenatal toxicity of drugs and other xenobiotics. In this paper we will review how we used in vitro as well as in vivo approaches to demonstrate the teratogenic potential of aciclovir and other related virustatic agents. In addition, some new data on this topic will be given. The teratogenic potential of the virustatic agent aciclovir was not recognized in routinely performed segment-II-studies, but the first indication came from experiments with the culture of rat embryos. Subsequently, the findings were confirmed in modified in vivo tests and it became clear that out of a group of six related drugs aciclovir exhibited the highest potential for prenatal toxicity. The effects of aciclovir on limb development were not pronounced--this has been shown with in vitro and in vivo experiments as well. In vivo experiments first indicated that the prenatal development of the thymus is disturbed by aciclovir. This effect was further studied with the culture of fetal thymuses and again the effect of aciclovir could be compared with related drugs. In summary, our work with virustatics during the last years has shown that in vivo and in vitro approaches are by no means competitive and that a combination of both approaches can provide a solid basis for a toxicologic evaluation.

Effect of lithium on rat embryos in culture: growth, development, compartmental distribution and lack of a protective effect of inositol

Lithium chloride (LiCl) was tested at various concentrations (50, 100, 150 and 200 micrograms/ml) using a rat whole-embryo culture system beginning on gestation day 9.5 (headfold stage) in order to establish a concentration-response relationship. Open neural tubes--as described in former publications (Tesh 1988)--were not induced by lithium. A significant reduction of embryonic growth and development occurred at the lowest concentration tested (50 micrograms/ml). Clear-cut dysmorphogenetic effects (absence of the eye cup, kink in the spinal anlage, "bleb" at the rostral head region) occurred at a concentration of 150 micrograms/ml LiCl. LiCl concentrations in the embryo, visceral yolk sac, exocoelomic fluid and medium were determined after the embryos had been cultured for 48 h in the presence of a moderately embryotoxic dose of LiCl (3.5 mEq/l or 150 micrograms/ml). Medium supplementation with myo-inositol in different concentrations was ineffective in antagonizing the embryotoxicity induced by LiCl.

Effect of aciclovir on the development of the chick embryo in ovo

The effect of aciclovir (ACV) on embryonic development was investigated using the chick embryo in ovo and treatment during organogenesis. ACV 30-1000 micrograms was applied as single doses prior to or after 24 h of incubation into the yolk sac, and ACV 3-100 micrograms after 2, 3 or 4 days of incubation (DI) directly to the embryo. Data were evaluated after a total of 8 days of incubation. (1) A dose-related increase in the rate of abnormal development was found in the surviving embryos. Depending on the route of drug administration a dose of 300, respectively, 5 micrograms ACV/egg had to be applied to induce 50% abnormal development. (2) Gross structural abnormalities of the surviving embryos mainly concerned the beak and the extremities. With the experimental set-up used a different pattern of abnormalities in the survivors after treatment at various stages could not be observed. The results are compared with data obtained with ACV in rodents in our laboratory. It is suggested that chick embryos are also capable of converting ACV into its triphosphate to interfere with DNA metabolism, probably through a chain break mechanism.

In vitro and in vivo studies on the prenatal toxicity of five virustatic nucleoside analogues in comparison to aciclovir

Several virustatic agents are known to be teratogenic in laboratory animals. Since routinely performed in vivo studies do not always offer the best conditions to detect the teratogenic potential of a drug, we used a combined in vivo/in vitro approach for comparative studies on the prenatal toxicity of five nucleoside analogues. Rat embryos were exposed for 48 h to various concentrations of vidarabine-phosphate (VAP), ganciclovir (GCV), 2',3'-dideoxyadenosine (ddA), 2',3'-dideoxycytidine (ddC) and zidovudine (= azidothymidine, AZT) in a whole-embryo culture system. The steepness of the concentration-response curves as well as the induced abnormality pattern (head, neural tube, shape) were similar for these compounds. However, a wide range in embryotoxic potency was observed: VAP was the most potent compound (100% abnormal embryos at 25 microM) in this in vitro system, while AZT showed the lowest potency to interfere with normal embryonic development (40% abnormal embryos at 3000 microM). In addition to these experiments we treated rats on day 10 of gestation with three s.c. injections (8 a.m.; 12 a.m.; 4 p.m.) of 200 mg of each drug/kg body wt. The embryos were evaluated on day 11.5 of gestation, i.e. at a time of development corresponding to the developmental stage at the end of the whole-embryo culture. The same criteria were used as during the in vitro studies for the evaluation of these in vivo exposed embryos. With VAP and GCV we obtained similar results with both exposure routes (in vitro and in vivo), while no abnormalities were detectable with the other compounds after exposure in utero.(ABSTRACT TRUNCATED AT 250 WORDS)

Interlaboratory evaluation of three culture media for postimplantation rodent embryos

The first aim of the study was to compare the ability of rat serum, human serum, and a mixture of human and rat serum (4:1) to support in vitro development of rodent postimplantation embryos. The comparison was made in three laboratories using rat embryos and in one laboratory using mouse embryos. Batches of sera, initial developmental stage, duration of culture, and endpoints were identical in the laboratories. The second aim of the study was to evaluate if other variables that could not be standardized would significantly influence the results of the laboratories. No reproducible difference was observed among the culture media or among the laboratories except that growth and differentiation were slower in the laboratory using mouse embryos. Further experiments are needed to exclude small differences in performance of the media.

Parameters determining isotretinoin teratogenicity in rat embryo culture

At the in vitro threshold serum concentration of 500 ng/ml, isotretinoin induces defects of visceral arch development in 9.5-day rat embryos grown in culture for 48 h. Experiments were performed to determine the minimum period of exposure necessary to induce these arch defects and whether an increase in concentration of isotretinoin could compensate for reduced exposure time. The results showed that a minimum 6-h exposure to 500 ng/ml immediately prior to cranial neural crest migration was necessary to induce severe defects of the second visceral arch in a majority of embryos. Maximal increase in isotretinoin concentration to 16,000 ng/ml did not compensate for shorter exposure periods. These results suggest that to cause malformations of the visceral arches, the embryo must be exposed to isotretinoin for a minimum period of time regardless of the concentration of isotretinoin above the threshold.

Whole embryo culture: interpretation of abnormal development in vitro

An overview will be given of a number of problems that arise when we attempt an interpretation of data obtained with the whole embryo culture method (WEC). The following aspects will be considered: 1) Types of deviation from normal development in the whole-embryo culture system: (a) problem of "artifacts" (for example, due to preparation mistakes and suboptimal culture conditions), (b) types and frequency of abnormal development in controls, retardation as an abnormal outcome, and the difficulty of assessing its significance, (c) gross-structural defects and, specifically, attempts to answer the following questions: (i) What are the limitations for an assessment of abnormal development with the WEC? (ii) Is a specific abnormality pattern recognizable under specific pathologic conditions? (iii) Is the rate of induced abnormal development concentration-dependent? (2) Problems encountered when interpreting concentration-effect relationships (for example, statistical and pharmacokinetic aspects). (3) Necessity of verifying in vitro effects with in vivo studies.

Effects of calcium channel blockers on the development of early rat postimplantation embryos in culture

Rat embryos (9.5-day-old) were cultured for 48 h in the presence of nifedipine (NIF), nimodipine (NIM), nitrendipine (NIT), gallopamil HCl (GAL), verapamil HCl (VER) and diltiazem HCl (DIL). The effects on growth and morphogenetic differentiation in vitro were monitored. Dose-response relationships were evaluated, including an assessment of the "no-observed-effect-level" (NOEL) or the "lowest-observed-effect-level" (LOEL), and the lowest concentration tested inducing abnormalities in 100% of the embryos ("100% EL"). The morphological alterations observed at the highest concentrations were very similar for all six drugs. The abnormalities concerned yolk sac circulation and morphology, as well as heartbeat, the morphology of the heart, head, neural tube, or forelimbs, and the shape of the embryo. The abnormal embryos were also growth retarded (decrease in protein content and crown-rump length). Interference with calcium channel functions seems to represent an interesting model for studying a special kind of abnormal prenatal development, especially the differentiation of certain mesenchymal structures. The concentration ranges between NOELs and 100% ELs were found to be: NIM = 0.1-1 microgram/ml; NIT and VER = 1-10 micrograms/ml; DIL = 1-30 micrograms/ml, and LOELs-100% ELs were: GAL = 1-10 micrograms/ml; NIF = 10-30 micrograms/ml.

Effects of valproic acid, some of its metabolites and analogues on prenatal development of rats in vitro and comparison with effects in vivo

Using a whole-embryo culture system valproic acid (VPA) and some of its metabolites (2-en-VPA, 4-en-VPA, 4,4'-dien-VPA) and analogues (ethyl-propyl-acetic acid, propyl-butyl-acetic acid, di-butyl-acetic acid, 2-methyl-2-ethyl-hexanoic acid, 1-methyl-1-cyclohexanoic acid) were tested for their potential to induce abnormal development. With regard to embryonic growth, development and abnormality rate, the tested compounds showed a wide range of "teratogenic potency" in vitro. In order to verify some of the in vitro results, in vivo experiments were performed. Pregnant rats were treated subcutaneously on day 10 of gestation with 2 x 330 mg VPA/kg, or 2 x 400 mg 2-en-VPA/kg, respectively. Evaluation of the embryos was performed on day 11.5 of gestation, corresponding to the in vitro experiments. VPA showed a high potential to induce abnormal development in vivo as well as in vitro, whereas 2-en-VPA was inactive under our experimental conditions. Problems connected with the evaluation of the predictive value of an in vitro test system for the detection of embryotoxic effects, such as "validation" and significance of pharmacokinetic data, are discussed.

All-trans retinoic acid and 13-cis-retinoic acid in the rat whole-embryo culture: abnormal development due to the all-trans isomer

9.5-day-old rat embryos were exposed to 3 micrograms 13-cis retinoic acid (13-cis-RA)/ml culture medium or 1 microgram all-trans retinoic acid (all-trans-RA)/ml culture medium for different time intervals of the culture period (test substance-exposure periods alternated with test substance-free periods). These studies were performed to confirm the hypothesis (Klug et al. 1989) that the effect of 13-cis-RA on embryonic development in vitro is predominantly caused by its isomerisation to all-trans-RA. A 12 h exposure of the rat embryos to 13-cis-RA during different periods of culture did not interfere with normal development. However, a 12 h exposure of the embryos to all-trans-RA in the first three quarters of the culture period significantly interfered with normal development and caused clear-cut and typical abnormalities. Embryonic exposure to 13-cis-RA, for periods of more than 12 h, caused severe interference with normal development and led to branchial effects very similar to those observed following to a 12 h exposure to all-trans-RA.