Endoderm and mesoderm derivatives in embryonic stem cell differentiation and their use in developmental toxicity testing

Embryonic stem cell differentiation models have increasingly been applied in non-animal test systems for developmental toxicity. After the initial focus on cardiac differentiation, attention has also included an array of neuro-ectodermal differentiation routes. Alternative differentiation routes in the mesodermal and endodermal germ lines have received less attention. This review provides an inventory of achievements in the latter areas of embryonic stem cell differentiation, with a view to possibilities for their use in non-animal test systems in developmental toxicology. This includes murine and human stem cell differentiation models, and also gains information from the field of stem cell use in regenerative medicine. Endodermal stem cell derivatives produced in vitro include hepatocytes, pancreatic cells, lung epithelium, and intestinal epithelium, and mesodermal derivatives include cardiac muscle, osteogenic, vascular and hemopoietic cells. This inventory provides an overview of studies on the different cell types together with biomarkers and culture conditions that stimulate these differentiation routes from embryonic stem cells. These models may be used to expand the spectrum of embryonic stem cell based new approach methodologies in non-animal developmental toxicity testing.

Cell differentiation in the cardiac embryonic stem cell test (ESTc) is influenced by the oxygen tension in its underlying embryonic stem cell culture

Oxygen (O₂) levels in the mammalian embryo range between 2.4% and 8%. The cardiac embryonic stem cell test (ESTc) is a model for developmental toxicity predictions, which is usually performed under atmospheric O₂ levels of 20%. We investigated the chemical sensitivity of the ESTc carried out under 20% O₂, using embryonic stem cells (ESC) cultured under either 20% O₂ or 5% O₂. ESC viability was more sensitive to valproic acid (VPA) but less sensitive to flusilazole (FLU) when cultured under 5% versus 20% O₂. For beating cardiomyocyte differentiation, lower ID₅₀ values were found for FLU and VPA when the ESCs had been cultured under 5% versus 20% O₂. At differentiation day 4, gene expression values were primarily driven by the level of O₂ during ESC culture instead of exposure to FLU. In addition, using ESCs cultured under 5% O₂ tension, VPA enhanced Nes (ectoderm) expression. Bmp4 (mesoderm) was enhanced by VPA when using ESCs cultured under 20% O₂. At differentiation day 10, using ESCs cultured under 5% instead of 20% O₂, Nkx2.5 and Myh6 (cardiomyocytes) were less affected after exposure to FLU or VPA. These results show that O₂ tension in ESC culture influences chemical sensitivity in the ESTc. This enhances awareness of the standard culture conditions, which may impact the application of the ESTc in quantitative hazard assessment of chemicals.

Predicting the safety of medicines in pregnancy: A workshop report

The framework for developmental toxicity testing has remained largely unchanged for over 50 years and although it remains invaluable in assessing potential risks in pregnancy, knowledge gaps exist, and some outcomes do not necessarily correlate with clinical experience. Advances in omics, in silico approaches and alternative assays are providing opportunities to enhance our understanding of embryo-fetal development and the prediction of potential risks associated with the use of medicines in pregnancy. A workshop organised by the Medicines and Healthcare products Regulatory Agency (MHRA), "Predicting the Safety of Medicines in Pregnancy - a New Era?", was attended by delegates representing regulatory authorities, academia, industry, patients, funding bodies and software developers to consider how to improve the quality of and access to nonclinical developmental toxicity data and how to use this data to better predict the safety of medicines in human pregnancy. The workshop delegates concluded that based on comparative data to date alternative methodologies are currently no more predictive than conventional methods and not qualified for use in regulatory submissions. To advance the development and qualification of alternative methodologies, there is a requirement for better coordinated multidisciplinary cross-sector interactions coupled with data sharing. Furthermore, a better understanding of human developmental biology and the incorporation of this knowledge into the development of alternative methodologies is essential to enhance the prediction of adverse outcomes for human development. The output of the workshop was a series of recommendations aimed at supporting multidisciplinary efforts to develop and validate these alternative methodologies.

Workshop on the validation and regulatory acceptance of innovative 3R approaches in regulatory toxicology - Evolution versus revolution

At a joint workshop organized by RIVM and BfR, international experts from governmental institutes, regulatory agencies, industry, academia and animal welfare organizations discussed and provided recommendations for the development, validation and implementation of innovative 3R approaches in regulatory toxicology. In particular, an evolutionary improvement of our current approach of test method validation in the context of defined approaches or integrated testing strategies was discussed together with a revolutionary approach based on a comprehensive description of the physiological responses of the human body to chemical exposure and the subsequent definition of relevant and predictive in vitro, in chemico or in silico methods. A more comprehensive evaluation of biological relevance, scientific validity and regulatory purpose of new test methods and assessment strategies together with case studies that provide practical experience with new approaches were discussed as essential steps to build up the necessary confidence to facilitate regulatory acceptance.

Prenatal exposure to environmental chemical contaminants and asthma and eczema in school-age children

BACKGROUND

Emerging evidence suggests that prenatal or early-life exposures to environmental contaminants may contribute to an increased risk of asthma and allergies in children. We aimed to the explore associations of prenatal exposures to a large set of environmental chemical contaminants with asthma and eczema in school-age children.

METHODS

We studied 1024 mother-child pairs from Greenland and Ukraine from the INUENDO birth cohort. Data were collected by means of an interview-based questionnaire when the children were 5-9 years of age. Questions from the ISAAC study were used to define asthma, eczema, and wheeze. We applied principal components analysis (PCA) to sixteen contaminants in maternal serum sampled during pregnancy, including perfluoroalkyl substances (PFASs), metabolites of diethylhexyl (DEHP) and diisononyl (DiNP) phthalates, PCB-153, and p,p'-DDE. Scores of five principal components (PCs) explaining 70% of the variance were included in multiple logistic regression models.

RESULTS

In a meta-analysis that included both populations, the PC2 score, reflecting exposure to DiNP, was negatively associated with current eczema (OR 0.71, 95% CI 0.52-0.96). Other associations were not consistent between the two populations. In Ukrainian children, the PC3 score (DEHP) was positively associated with current wheeze (adjusted OR 1.56, 95% CI 1.03-2.37), whereas the PC5 score, dominated by perfluorooctanoic acid (PFOA), was inversely associated with current wheeze (OR 0.64, 0.41-0.99). In Greenlandic children, a negative association of PC4 (organochlorines) with ever eczema (OR 0.78, 0.61-0.99) was found.

CONCLUSIONS

We found limited evidence to support a link between prenatal exposure to environmental chemical contaminants and childhood asthma and eczema.

Compound-specific effects of diverse neurodevelopmental toxicants on global gene expression in the neural embryonic stem cell test (ESTn)

Alternative assays for developmental toxicity testing are needed to reduce animal use in regulatory toxicology. The in vitro murine neural embryonic stem cell test (ESTn) was designed as an alternative for neurodevelopmental toxicity testing. The integration of toxicogenomic-based approaches may further increase predictivity as well as provide insight into underlying mechanisms of developmental toxicity. In the present study, we investigated concentration-dependent effects of six mechanistically diverse compounds, acetaldehyde (ACE), carbamazepine (CBZ), flusilazole (FLU), monoethylhexyl phthalate (MEHP), penicillin G (PENG) and phenytoin (PHE), on the transcriptome and neural differentiation in the ESTn. All compounds with the exception of PENG altered ESTn morphology (cytotoxicity and neural differentiation) in a concentration-dependent manner. Compound induced gene expression changes and corresponding enriched gene ontology biological processes (GO-BP) were identified after 24h exposure at equipotent differentiation-inhibiting concentrations of the compounds. Both compound-specific and common gene expression changes were observed between subsets of tested compounds, in terms of significance, magnitude of regulation and functionality. For example, ACE, CBZ and FLU induced robust changes in number of significantly altered genes (≥ 687 genes) as well as a variety of GO-BP, as compared to MEHP, PHE and PENG (≤ 55 genes with no significant changes in GO-BP observed). Genes associated with developmentally related processes (embryonic morphogenesis, neuron differentiation, and Wnt signaling) showed diverse regulation after exposure to ACE, CBZ and FLU. In addition, gene expression and GO-BP enrichment showed concentration dependence, allowing discrimination of non-toxic versus toxic concentrations on the basis of transcriptomics. This information may be used to define adaptive versus toxic responses at the transcriptome level.

Aromatase inhibiting and combined estrogenic effects of parabens and estrogenic effects of other additives in cosmetics

There is concern widely on the increase in human exposure to exogenous (anti)estrogenic compounds. Typical are certain ingredients in cosmetic consumer products such as musks, phthalates and parabens. Monitoring a variety of human samples revealed that these ingredients, including the ones that generally are considered to undergo rapid metabolism, are present at low levels. In this in vitro research individual compounds and combinations of parabens and endogenous estradiol (E(2)) were investigated in the MCF-7 cell proliferation assay. The experimental design applied a concentration addition model (CA). Data were analyzed with the estrogen equivalency (EEQ) and method of isoboles approach. In addition, the catalytic inhibitory properties of parabens on an enzyme involved in a rate limiting step in steroid genesis (aromatase) were studied in human placental microsomes. Our results point to an additive estrogenic effect in a CA model for parabens. In addition, it was found that parabens inhibit aromatase. Noticeably, the effective levels in both our in vitro systems were far higher than the levels detected in human samples. However, estrogenic compounds may contribute in a cumulative way to the circulating estrogen burden. Our calculation for the extra estrogen burden due to exposure to parabens, phthalates and polycyclic musks indicates an insignificant estrogenic load relative to the endogenous or therapeutic estrogen burden.

Mixture effects of estrogenic compounds on proliferation and pS2 expression of MCF-7 human breast cancer cells

Humans are exposed to a variety of food-borne phytochemicals (PC) as well as synthetic chemicals (SC). Some of these compounds have been reported to have estrogenic or anti-estrogenic properties and are therefore suspected endocrine disruptors. Until now it remains unclear if non-additive effects occur in combinations with endogenous estrogens, such as 17beta-estradiol (E(2)). To investigate such interactions, several PC and SC were tested individually, in mixtures and as combinations of mixtures with E(2) for effects on ERalpha receptor mediated cell proliferation and estrogen regulated pS2 expression level in MCF-7(bus) cells. PCs (coumestrol, genistein, naringenin, catechin, epicatechin, quercetin) or SCs (4-nonylphenol, octylphenol, beta-hexachlorocyclohexane, bisphenol A, methoxychlor, dibutyl phthalate) were mixed (PCmix and SCmix) either in concentrations reflecting human serum concentrations or at equipotent concentrations for estrogenicity. EC(50) values were applied in two approaches of the concentration-addition model (the method of isoboles and the cumulative estrogen equivalency method) to assess mixture effects. In both models PCmix and SCmix or combinations of the mixtures with E(2) showed no departure from additivity. In conclusion, the tested PCs and SCs appeared to act as (full) agonists for the estrogen receptor and interacted in mixtures and with estradiol in an additive way. In addition, it is concluded that the possible contribution of food-borne PCs to the estrogenic effect of xenobiotics is likely to be more significant than that caused by food-borne SCs.

(Anti)estrogenic effects of phytochemicals on human primary mammary fibroblasts, MCF-7 cells and their co-culture

In the public opinion, phytochemicals (PCs) present in the human diet are often considered beneficial (e.g. by preventing breast cancer). Two possible mechanisms that could modulate tumor growth are via interaction with the estrogen receptor (ER) and inhibition of aromatase (CYP19). Multiple in vitro studies confirmed that these compounds act estrogenic, thus potentially induce tumor growth, as well as aromatase inhibitory, thus potentially reduce tumor growth. It is thought that in the in vivo situation breast epithelial (tumor) cells communicate with surrounding connective tissue by means of cytokines, prostaglandins and estradiol forming a complex feedback mechanism. Recently our laboratory developed an in vitro co-culture model of healthy mammary fibroblasts and MCF-7 cells that (at least partly) simulated this feedback mechanism (M. Heneweer et al., TAAP vol. 202(1): 50-58, 2005). In the present study biochanin A, chrysin, naringenin, apigenin, genistein and quercetin were studied for their estrogenic properties (cell proliferation, pS2 mRNA) and aromatase inhibition in MCF-7 breast tumor cells, healthy mammary fibroblasts and their co-culture. The proliferative potency of these compounds in the MCF-7 cells derived from their EC(50)s decreased in the following order: estadiol (4*10(-3) nM)>biochanin A (9 nM)>genistein (32 nM)>testosterone (46 nM)>naringenin (287 nM)>apigenin (440 nM)>chrysin (4 microM). The potency to inhibit aromatase derived from their IC(50)s decreased in the following order: chrysin (1.5 microM)>naringenin (2.2 microM)>genistein (3.6 microM)>apigenin (4.1 microM)>biochanin A (25 microM)>quercetin (30 microM). The results of these studies show that these PCs can induce cell proliferation or inhibit aromatase in the same concentration range (1-10 microM). Results from co-cultures did not elucidate the dominant effect of these compounds. MCF-7 cell proliferation occurs at concentrations that are not uncommon in blood of individuals using food supplements. Results also indicate that estrogenicity of these PCs is quantitatively more sensitive than aromatase inhibition. It is suggested that perhaps a more cautionary approach should be taken for these PCs before taken as food supplements.

A category approach for reproductive effects of phthalates

In regulatory toxicology, the experimental assessment of reproductive toxicity is one of the most costly endpoints to perform. Categorizing chemicals is an approach that can be used to reduce animal tests in risk assessments of chemicals, for example, via REACH (Registration, Evaluation, and Authorization of Chemicals). The category approach was tested for reproductive toxicity with a group of 10 ortho-phthalate esters, with different side chain lengths. Three ortho-phthalates were used for testing the category. Phthalates with side-chain lengths C4 to C6 that are commonly known to cause reproductive effects were included, as well as the recently discovered mechanism that indicates antiandrogenic effects. The differences in physicochemical properties, absorption rates, and metabolism between the phthalates investigated could not fully explain the difference in reproductive toxicity. It was concluded that phthalates with the alkyl side-chain length from C4 to C6 produce similar severe reproductive effects in experimental animals. It is expected that phthalates included in the tight boundaries of the proposed category would all show severe reproductive effects, especially the antiandrogenic effects. Further testing might not be needed for phthalates within these boundaries. If necessary, limited testing could focus on the critical endpoints. Detailed mechanistic information is needed on phthalates to apply the categories for regulatory toxicology.

Dietary fatty acid composition during pregnancy and lactation in the rat programs growth and glucose metabolism in the offspring

AIMS/HYPOTHESIS

We investigated of the effects of fatty acid composition of the maternal diet on fetal and postnatal growth, morphology of the pancreas and glucose metabolism and muscle hexosamine concentrations in the adult offspring of rats.

METHODS

High-fat diets enriched with either saturated or unsaturated fatty acids were fed to female adult rats 2 weeks before mating until the end of the weaning period. After weaning, the offspring was maintained on a diet with a balanced fatty acid content. At 3 months of age, pancreatic Langerhans islet size and number were assessed by morphometric analysis and oral glucose tolerance tests (OGTT) were carried out.

RESULTS

The unsaturated fatty acid diet showed lower birth weight and reduced postnatal weight gain. Furthermore, this group showed increased pancreatic islet numbers without affected glucose tolerance at the age of 12 weeks. The offspring of the saturated fatty acid diet group showed a reduced number of large pancreatic islets. Moreover, a faster and higher insulin response was observed after an oral glucose load in these animals. Muscle hexosamine concentrations were not different between groups.

CONCLUSION/INTERPRETATION

Maternal diets enriched with either saturated fatty acids or unsaturated fatty acids had opposite effects on pancreatic islet development in rat offspring, with consequences for the insulin response at 12 weeks of age. Therefore, maternal dietary fatty acid composition plays a role in programming growth, pancreatic development and glucose metabolism in the offspring.

Developmental toxicity but no immunotoxicity in the rat after prenatal exposure to diethylstilbestrol

Studies with dioxins and PCB's have shown that the developing immune system may be especially vulnerable to xenobiotics during the perinatal period. However, current guidelines for reproductive toxicity testing do not include immune parameters. In the present study, we have explored the usefulness of including immune parameters within the prenatal developmental toxicity study in rats, using the treatment protocol as described in the OECD 414 developmental toxicity test guideline. In addition, the experimental protocol was enhanced by including ten dose groups to facilitate dose-response analysis. Diethylstilbestrol (DES) was used as the model compound, as it is known to be toxic both for embryofetal development and for the immune system. The results show developmental toxicity in terms of decreased fetal survival and decreased pup body weight in the presence of reduced maternal food consumption and reduced body weight gain. However, immune parameters, including histopathology, hematology, and antibody responses to sheep red blood cells (SRBC) in pups at 4 weeks of age were uncompromised. It is speculated that rather than the prenatal exposure protocol used here, the generation study design with both pre- and postnatal exposure may be preferable as a general screen to detect developmental immunotoxic injury after xenobiotic exposure.

Developmental toxicity of butyl benzyl phthalate in the rat using a multiple dose study design

The developmental toxicity of butyl benzyl phthalate (BBP) was investigated in the rat using ten dose groups between 270 and 2100 mg/kg/day. Exposure was by daily gavage from gestation day 5 through 16 or gestation day 5 through 20. Dose-response data were analyzed using the benchmark approach by fitting dose-response models to the various endpoints. BBP induced increased liver and kidney weights in dams, accompanied by liver enzyme increases in maternal serum. Extramedullary hematopoiesis, which was already substantial in control pregnant animals, was increased after BBP treatment. Fetotoxicity included increased resorptions, reduced fetal weights, increased incidence of skeletal anomalies, and reduced fetal testis weights in the presence of an increased incidence of retarded testicular descent. As embryotoxicity was found at lower dosages compared to observed maternal toxicity, BBP appeared to be a specifically embryotoxic compound. The extended exposure protocol (gestation day 5 through 20) appeared more sensitive for measuring fetotoxic effects. We recommend the use of more doses in toxicity tests, together with the benchmark approach as an appropriate and more accurate method for analyzing dose-response data compared to the NOAEL approach.

Comparison of in vitro and in vivo developmental toxicity and pharmacokinetics of phenytoin in the rat

The rat whole embryo culture was compared to an in vivo experiment with regard to embryotoxicity as well as exposure characteristics, using phenytoin as a model compound. Intra-embryonic concentrations and their embryotoxic effects were determined on gestation day 11 after in vitro administration of 50-150 microg/ml or in vivo gavage of 500-1500 mg/kg body-weight on gestation day 10. In addition, exposure kinetics were studied in vivo after a single oral dose on gestation day 10, and developmental defects on gestation day 21 were scored. The embryotoxic effects observed on gestation day 11 were more pronounced after in vitro exposure in comparison to in vivo exposure at similar intra-embryonic concentrations. Exposure of phenytoin on gestation day 10 in vitro via the culture medium resulted in general embryotoxicity on gestation day 11, whereas in vivo effects as determined on gestation day 11 were minimal. Plasma concentrations of phenytoin increased and plateaued around 35 microg/ml during the 48 hr monitoring period. Plasma concentration curves and pharmacokinetic parameters did not show remarkable differences between the dose groups, indicating that absorption is the limiting factor at the dose range used. Although the developmental effects were minimal as observed in vivo on gestation day 11, specific malformations (defects encompassing the urogenital. craniofacial and skeletal systems) were observed on gestation day 21. These findings show that with similar intra-embryonic concentrations of phenytoin the embryotoxicity in rat whole embryo culture was not comparable with the in vivo embryotoxicity as determined on gestation day 11. This discrepancy may at least partly be explained by differences in exposure characteristics.

Embryotoxicity of carbamazepine in rat postimplantation embryo culture after in vitro exposure via three different routes

Postimplantation rat embryo culture is used widely for studies of embryotoxic effects on the isolated embryo after in vitro exposure to xenobiotic compounds. In this study, the relevance of three routes of exposure of the embryo in vitro was evaluated using the embryotoxic anticonvulsant carbamazepine. Embryotoxic effects were assessed, and analyses in conceptus tissues were done to reveal uptake and metabolism of the compound. Exposure via the culture medium resulted in neural tube defects and general retardation of growth and development. After injections into the amniotic or exocoelomic space, local membrane adhesions were found. Intra-amniotic exposure caused adhesions of the amniotic membrane with the embryonic neural plate, resulting in trapping of the membrane in the closing neural tube, as well as in open neural tube defects occurring in various areas of the neural tube. Only after exposure via the culture medium were amounts of carbamazepine detectable in the embryonic tissue, correlating with the systemic effects found. It is concluded that uptake from the culture medium via the yolk sac circulation is the relevant exposure route to be used for embryotoxicity effect assessment.

Teratogenicity of a single oral dose of retinyl palmitate in the rat, and the role of dietary vitamin A status

Vitamin A, known for its teratogenic properties, may be present in high concentrations in consumption liver. It is as yet unclear whether congenital malformations can result from a single liver meal. In our first experiment, the teratogenicity of a single dose of retinyl palmitate was tested in the rat. Pregnant rats were treated at day 10 of gestation by gavage with 100, 300 or 1000 mg/kg body weight retinyl palmitate on a dietary background level of 5 mg/kg feed. At gestation day 11 the number of embryos with an open cranial neural tube had increased with the dose. At gestation day 21, the high dose group showed an increase in late resorptions, whereas both the high and the medium dose groups had a high incidence of foetuses with malformations typical of retinoid embryopathy. The data suggest that delayed neural tube closure had occurred in a large proportion of the embryos. In a second experiment, the high oral dose was applied on gestation day 10 in pregnant rats receiving retinyl palmitate at 1.5, 5, 15, or 50 mg/kg feed for 6 weeks. Delayed neural tube closure, post-implantation loss and the nature and incidence of malformations were similar between diet groups, as well as being reminiscent of the high dose group in the first experiment. Thus the dietary status of the animals did not seem to influence the teratogenic potential of a single high dose of retinyl palmitate.

Evaluation of the OECD 421 reproductive toxicity screening test protocol using butyl benzyl phthalate

The OECD421 reproductive toxicity screening test protocol was evaluated using the reproductive and developmental toxicant butyl benzyl phthalate (BBP). Female rats were orally exposed from 14 days premating to 6 days postpartum. Male rats were exposed for 29 days. At 1000 mg/kg bw/day effects were found on body weight gain and food consumption, on spermatogenesis, time to conception, pregnancy rate, postimplantation survival, and litter size and weight. Food consumption and pup weight were slightly affected at 500 mg/kg also. Effects occurred at expected dosages on the basis of literature data. These findings support the conclusion that the OECD421 test scores BBP correctly as a reproductive toxicant, both in a qualitative and in a quantitative sense.

Interlaboratory evaluation of embryotoxicity in the postimplantation rat embryo culture

The embryotoxicity of eight xenobiotic compounds in rat postimplantation whole embryo culture was blindly tested in four laboratories according to a standard protocol. The results show that the four nonteratogens amaranth, penicillin, isoniazid, and saccharin did not affect embryogenesis apart from general toxicity at very high concentrations in culture for amaranth and isoniazid. There was good concordance of results across the laboratories. The four teratogens (retinoic acid, 6-aminonicotinamide, acetylsalicylic acid, and vincristine) induced a variety of specific embryotoxic effects, which were in most cases similar in all laboratories. These results indicate that the definition for specific embryotoxicity used, as well as the culture duration and embryonic age are crucial for concordant scoring. Other methodologic differences did not significantly influence scoring of embryotoxicity. Therefore, within the limits of the end points and embryonic stage represented in the method, embryo culture appears as a useful method for embryotoxicity screening, which can be reproducibly applied in different laboratories.

Evaluation of the OECD 421 reproductive toxicity screening test protocol using 1-(butylcarbamoyl)-2-benzimidazolecarbamate (benomyl)

The OECD 421 reproductive toxicity screening test protocol was evaluated using the fungicide benomyl as a test compound at 10, 30, or 90 mg/kg per day. Male rats showed dose-dependent testicular degeneration after 28 days exposure, as expected on the basis of literature data. Dams in the high dose group, exposed from 14 days premating to postnatal day 6, had pups with decreased weights at postnatal days 1 and 6. Prenatal deaths were increased, but no malformations were found. In contrast, in a developmental toxicity test with exposure between gestation days 6 and 15, 90 mg/kg induced a high level of postimplantation loss, with ophthalmic malformations in the surviving offspring, in agreement with literature data. It is suggested that premating exposure in the OECD 421 protocol may have induced tolerance to the compound, e.g., by modulation of biotransformation in the dam. These findings indicate that the teratogenic potential of a compound need not necessarily be revealed using this screening test. The OECD 421 protocol appeared sufficiently sensitive to reveal the reproductive hazard of benomyl on the basis of prenatal deaths and testicular and pup weight effects. However, the absence of congenital anomalies in the offspring after benomyl treatment according to the OECD 421 protocol underscores the notion that lack of biological activity in the test should not be regarded as evidence of lack of activity of a compound on reproductive parameters.

Minimal immunological changes in structurally malformed rats after prenatal exposure to cyclophosphamide

In order to compare the sensitivities of morphological and immunological parameters in a teratology study, effects in day 20 rat fetuses were studied after a single exposure to the immunosuppressive cytostatic agent cyclophosphamide (CP) on either day 11 or day 15 of gestation. Teratological methods included evaluation of external and skeletal morphology. Furthermore histology, immunohistochemistry and flow cytometry were performed on fetal thymus, liver and spleen. Immune function was assayed using the Trichinella spiralis infection model. Treatment resulted in dose-dependent gross morphological malformations, and in addition in overt skeletal anomalies such as brachygnathia, wavy ribs, and lordosis. In contrast, the immunological parameters tested revealed only minimal differences between treated and control groups. These results suggest either a remarkable recovery of the immune system after treatment, or a relatively high resistance of the immune system to the present treatment.

Cadmium-induced inhibition of proliferation and differentiation of embryonal carcinoma cells and mechanistic aspects of protection by zinc

Murine embryonal carcinoma cells have been used in in vitro models to study the effects of cadmium chloride on proliferation and differentiation of early embryonic cells. This approach allows the various cell types within the early embryo as well as several developmental mechanisms to be dissected and studied in isolation using larger numbers of cells than would be readily available from the embryo itself. The present study shows that both embryonal carcinoma cell proliferation and differentiation into parietal endoderm are inhibited by cadmium chloride. The effects are counteracted by the additional presence of zinc chloride. The uptake of cadmium into the cells is inhibited in the presence of zinc chloride, suggesting that competition between these metals for passage into the cells contributes to the mechanism underlying the protective effect of zinc. In addition, metallothionein gene expression is enhanced more rapidly after simultaneous incubation with zinc chloride, indicating that the attenuating effect of zinc on cadmium toxicity is also partly attributable to detoxification by metallothioneins.

Biotransformation of cyclophosphamide in post-implantation rat embryo culture using maternal hepatocytes in co-culture

The post-implantation rat embryo culture technique is employed to study embryotoxic effects of xenobiotic compounds in the absence of the maternal compartment. For compounds biotransformed in vivo the embryo culture technique must be adapted in order to mimick the in vivo effects. In the present study the possibility of co-culturing metabolically active maternal hepatocytes suspended in the standard culture system with rat serum as a medium was investigated. Cyclophosphamide (CP) was used as a model compound as it needs bioactivation to display embryotoxicity. Morphologic and histologic effects were studied. Neither hepatocytes nor CP alone affected embryo development, whereas in the presence of hepatocytes embryotoxicity was observed at 30 micrograms/ml CP. Embryotoxicity was decreased in the additional presence of metyrapone, a monoxygenase inhibitor. Hepatocyte suspensions prepared via slicing or perfusion of livers were equally effective. In conclusion, co-culture of embryos and suspended hepatocytes can be performed under optimal conditions for embryo development and in the presence of biotransforming activity.

Differentiation of aggregated murine P19 embryonal carcinoma cells is induced by a novel visceral endoderm-specific FGF-like factor and inhibited by activin A

Aggregation of P19 embryonal carcinoma cells in the presence of a factor, secreted by the visceral endoderm-like cell line END-2, induces differentiation to cell types including visceral endoderm, mesoderm-derived muscle tissue and neurons. This factor is different from activin A, type beta transforming growth factors (TGF beta) and fibroblast growth factors (FGF) although its acid- and heat-lability and its stability in the presence of reducing agents resemble the properties of the FGFs. The END-2 factor is completely inhibited in its action by activin A. This inhibitory effect of activin A is not specific for the END-2 factor as retinoic acid (RA)-induced differentiation of aggregated P19 EC cells into neurons (10(-8) M RA) or mesoderm-derived muscle tissue (10(-9) M RA) is also completely inhibited by activin A. The results of this study suggest that the END-2 activity and activin A are intimately involved in the induction and regulation, respectively, of early differentiation processes in vertebrate embryogenesis.

Visceral-endoderm-like cell lines induce differentiation of murine P19 embryonal carcinoma cells

When P19 embryonal carcinoma (EC) cells were cocultured with cells from one of several established visceral-endoderm-like cell lines, the EC cells were rapidly induced to aggregate and differentiate, into cell types including mesoderm-derived cardiac and skeletal muscle. Neither parietal-endoderm- nor mesoderm-like cell lines induced aggregation or differentiation of EC cells in coculture, although a cell line with both parietal and visceral endoderm characteristics induced aggregation but not differentiation. Also, without the feeder cells aggregates of P19 failed to differentiate, provided that serum in the culture medium had been previously passed over dextran-coated charcoal to remove lipophilic substances, which may include endogenous retinoids. All experiments were carried out using serum treated in this way. Taken together, the results demonstrated that aggregation was necessary, but not sufficient, to make P19 EC cells differentiate. Direct contact between the two cell types was not necessary, since even when separated by an agar layer in cocultures, aggregates of P19 still differentiated. Medium conditioned by cells of the END-2 line, a visceral-endoderm-like derivative of P19, was particularly potent in inducing endodermal and mesodermal differentiation of single P19 aggregates, confirming the involvement of a diffusible factor secreted specifically by visceral-endoderm-like cells in this process.

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.

Hemopoiesis on purified bone-marrow-derived reticular fibroblast in vitro

Murine bone-marrow-derived reticular fibroblast cultures were tested for the ability to support hemopoiesis and release hemopoietic growth factors in vitro. The reticular fibroblast cultures employed in these studies were 95%-100% pure on the basis of Mac-1, F4/80, MIV-51, T200, antifactor VIII and ER-TR7 monoclonal antibody staining. Further support for the fibroblastic nature of these cells was obtained from collagen and laminin analyses. Addition of stromal cell-depleted bone marrow cell suspensions to flasks of confluent reticular fibroblasts resulted in production and release of granulocytes, monocyte-macrophages, and granulocyte-monocyte progenitors from the adherent layer for 4-8 weeks. Pluripotent spleen colony-forming units were detected during the first four weeks. Assay of reticular fibroblast conditioned medium for hemopoietic growth factors demonstrated production of granulocyte-macrophage colony-stimulating activity and stem-cell-activating factor. We did not detect any erythroid burst-promoting activity. These results suggest that reticular fibroblasts may play a role in the maintenance of pluripotent stem cells and in the proliferation and differentiation of cells committed to the granulocyte-monocyte lineage.

Migration of fibroblastoid stromal cells in murine blood

This paper describes the kinetics of fibroblastic colony forming units (CFU-f) in murine blood after phenylhydrazine-induced haemolytic anaemia and their subsequent migration into haemopoietic organs. Murine blood contained 5.3 +/- 0.8 CFU-f per 10(6) nucleated cells. Absence of particle ingestion and factor VIII-related antigen in addition to the enzyme pattern in CFU-f-derived cells confirmed that these cells did not have a macrophage-like or endothelial nature. Phenylhydrazine treatment of mice resulted in a 3-fold increase in blood CFU-f numbers which was accompanied by increases in blood cellularity and granulocyte-macrophage progenitor numbers. When both partners of CBA/N and CBA/T6T6 mice in parabiosis had been treated with phenylhydrazine, spleens and femoral bone marrow of both mice were shown to contain partner-derived CFU-f. These data suggest that circulating CFU-f represent a stromal cell population which can migrate into haemopoietic organs.

Recovery of hemopoietic stromal progenitor cells after lethal total-body irradiation and bone marrow transplantation in mice

The recovery of fibroblastic colony-forming units (CFU-F) in murine bone marrow hemopoietic stroma was studied during eighteen months after 9 Gy lethal total-body irradiation and reconstitution with syngeneic bone marrow cells. After an initial depletion, CFU-F numbers increased from 10% of normal values at three months to 40% at 18 months after treatment, irrespective of graft size and presence of CFU-F in the graft. Fourteen months after treatment 35% of all CFU-F present in the recipients' bone marrow was donor-derived independent of graft size. When mice were treated with high-dose lipopolysaccharide-W three months after irradiation and bone marrow transplantation, CFU-F numbers decreased to hardly detectable levels within one day, and then recovered to normal numbers four weeks later--whereas radiation control mice still had low CFU-F numbers. These data suggest that after lethal total-body irradiation the stroma still contained viable fibroblastic cells that had lost their in vitro colony-forming capacity as a result of radiation damage. In consequence there was no need for replacement of these fibroblastic cells by donor-derived or host-derived CFU-F. Only depletion of CFU-F from the bone marrow, as was induced with lipopolysaccharide, stimulated repopulation of the stroma with colony-forming fibroblastic cells.

Characterization of fibroblastic stromal cells from murine bone marrow

Several properties of fibroblastic colony-forming units (CFU-F) from murine bone marrow and their in vitro progeny were evaluated. CFU-F had a high buoyant density relative to total bone marrow cells; they were noncycling in situ and adhered to nylon wool. The fibroblastic cells stained positively for fibronectin, lipid, alkaline phosphatase, and nonspecific esterase, while phagocytosis assays were negative, and ultrastructural analysis failed to reveal desmosomes. These properties contrasted bone-marrow-derived fibroblastic cells to both endothelial cells and macrophages. Fibroblastic cells derived from several hemopoietic organs and skin were screened for antigenic determinants present on hemopoietic cells using monoclonal antibodies. Mac-1 and B220 were absent from all fibroblastic cells studied, whereas the Forsmann and Pgp-1 antigens were always present. Thy-1 was not detected on bone-marrow-derived fibroblasts, but was present on fibroblastic cells derived from other sources. T200 was found on all hemopoietic organ-derived fibroblastic cells, but not on those derived from blood and skin. Thus, analysis of antigenic determinants allowed distinction between fibroblastic cells from different organs.

Stromal cells (CFU-F) in normal and genetically anemic mouse strains

Mice of the Sl/Sld genotype have an approximately 3-fold higher number of fibroblastoid progenitors (CFU-F) in their spleens than their normal +/+ littermates. Experiments were performed to determine whether the elevated Sl/Sld splenic CFU-F numbers were due to compensatory mechanisms acting in the presence of a functionally abnormal CFU-F population or to a nonspecific response to chronic anemia. Comparison of the functional ability of Sl/Sld splenic fibroblasts to produce granulocyte/macrophage colony-stimulating activity with +/+ splenic fibroblasts demonstrated that there was no difference. Similar results were obtained for Sl/Sld and +/+ femoral fibroblasts. Analysis of CFU-F in W/Wv mice revealed an approximately 3-fold higher number of splenic CFU-F than in either +/+ or heterozygous (W/+ and Wv/+) littermates. Since the anemia in W/Wv mice is attributed to a hemopoietic stem cell defect and that of the Sl/Sld mice is attributed to a microenvironmental defect, we suggest that the increased splenic CFU-F number in Sl/Sld mice is not specifically due to the microenvironmental defect, but is part of a general response to hemopoietic stress.

Regulation of in vitro myelopoiesis by a hemopoietic stromal fibroblastic cell line

An adherent cell line (AP63) derived from murine spleen was characterized as fibroblastic, and several of its properties distinguished it from other adherent cells (i.e., macrophages and endothelial cells). The ability of the AP63 cells to regulate in vitro myelopoiesis was investigated. Medium conditioned by the cell line (CM) induced granulocyte-macrophage (GM) colonies, thus demonstrating the production of colony-stimulating activity by AP63 cells. A relatively large proportion of these colonies had a "tight" morphology and contained many early myeloid cells and cells capable of secondary cluster and colony formation. CM also contained a prostaglandinlike inhibitor of colony formation. Furthermore, AP63 cells inhibited GM colony formation by bone marrow cells in their immediate vicinity, whereas colony formation was stimulated at greater distances. These observations may reflect in vivo regulatory properties of hemopoietic stromal fibroblasts with respect to proliferation and differentiation of GM progenitor cells.

A macrophage factor enhancing the systemic anti-tumour effect of T lymphocytes

Spleen cells sensitized to tumour cells have an anti-tumour effect on injected syngeneic lymphosarcoma cells in mice. This study shows that this anti-tumour effect can be enhanced by induced peritoneal macrophages and by macrophage-like tumour cells (macrophages). Addition of macrophages to the intraperitoneally injected sensitized spleen cells stimulated the anti-tumour effect. This was observed both with intraperitoneally injected tumour cells and with subcutaneously transplanted tumour cells. The anti-tumour effect is the result of a cooperation between T cells and macrophages. In vitro incubation of immune T-cells with macrophages or macrophage-like cells enhanced the in vivo anti-tumour activity of the sensitized T-lymphocytes. Neither the presence of antigen nor the proliferation of the immune T-cells were a prerequisite to enhance this anti-tumour effect. Our experiments suggest that a macrophage factor is responsible for the enhancement of the anti-tumour effect. Based on the results of this paper and other studies we propose the following sequence of events to explain the anti-tumour effect of injected sensitized T-lymphocytes and macrophages: injected macrophages enhance the anti-tumour effect of sensitized lymphocytes. These stimulated lymphocytes migrate to the tumour located elsewhere and recognize the tumour antigens. Subsequently, the lymphocytes render (host) macrophages in the tumour cytotoxic to tumour cells.

The nature and function of granulopoietic microenvironments

A significant volume of reviewed literature in combination with observations presented here suggest that fibroblastic reticulum cells of the hematopoietic stroma may play a decisive role in the regulation of granulopoiesis. The histology of both bone marrow and spleen demonstrates an association between granulopoiesis and fibroblastic reticulum cells. Using in vitro cultured primary fibroblastic cells from murine bone marrow (BM) as antigenic source, we have prepared a hybridoma cell line secreting a monoclonal antibody (mAb) to fibroblastic reticular cells of the nonlymphoid domains in the spleen and BM. The mAb (ER-HR1) was demonstrated to exclusively detect primary fibroblastic cells cultured from spleen and bone marrow and in situ reticular cells with characteristic dendritic morphology and a dispersed distribution pattern. These reticular cells had extensive ramifications in the hemopoietic parenchyma. With the exception of some sparse fibroblastic cells in the dermis of the skin, the mAb did not react with any other cell type or extracellular substance elsewhere in the mouse, nor did it cross-react with human hemopoietic tissues. Support for a role of fibroblastic reticular cells in the regulation of granulopoiesis was obtained from in vitro studies. Primary BM fibroblasts produced granulocyte-macrophage colony stimulating activity (CSA). In contrast, we have been unable to detect CSA production by BM macrophages. Rather, we have found that BM macrophages deplete exogenous CSA from their culture medium. It is concluded that CSA may be produced by fibroblastic cells in adherent BM cultures and that the low CSA levels detected in their medium is due to depletion of fibroblastic cell-derived CSA by macrophages. We conclude that fibroblastic reticulum cells of the hemopoietic stroma carry unique antigenic determinants and together with macrophages, endothelial cells, and lymphocytes contribute to a complex network of cellular interactions providing an integrated microenvironmental control of granulopoiesis.

Radiation damage to femoral hemopoietic stroma measured by implant regeneration and quantitation of fibroblastic progenitors

Radiation damage to femoral hemopoietic stroma in mice was measured 6 weeks after irradiation and reconstitution with syngeneic bone marrow by quantitation of fibroblastic progenitor cells (CFUF), and by assaying hemopoietic progenitors and CFUF numbers in regenerated subcutaneous femur implants. A dose-dependent effect of radiation on both preimplantation CFUF numbers and implant regeneration was observed. Changes in bone marrow cell (BMC) graft size did not alter these stromal parameters. Therefore, transplanted CFUF, which were present in the BMC graft, did not alter either the CFUF content of femurs or their regenerative capacity. The strong correlation between CFUF numbers and implant regenerative capacity after irradiation, leads us to suggest a function for CFUF in femoral implant stromal regeneration.

Transplantation of bone marrow fibroblastoid stromal cells in mice via the intravenous route

Kinetics of fibroblastic colony-forming cells (CFU-F) were studied in mouse bone marrow after lethal total body irradiation and intravenous bone marrow transplantation. After an initial decrease, CFU-F numbers recovered, and plateaued 5 weeks post-treatment at 10% of normal values. Using chromosome-marked donor bone marrow cells we found that 1 day after transplantation 72% of donor CFU-F had reached the recipient's bone marrow, indicating a highly specific lodgment of CFU-F. Three months after transplantation donor CFU-F were still detectable and comprised about half of the femoral CFU-F population. It is concluded that CFU-F, a component of the haemopoietic microenvironment, are transplantable via the intravenous route.