Cannabidiol impairs neural tube closure in mouse whole embryo culture

BACKGROUND

Cannabidiol (CBD) is a nonpsychoactive constituent of cannabis widely available as a dietary supplement. Previous reports that it impairs the retinoid, sonic hedgehog, and folate metabolism pathways raise concern that it may impair closure of the embryonic neural tube (NT), producing NT defects including spina bifida and exencephaly.

METHODS

We undertook teratogenicity testing of CBD in mouse whole embryo culture.

RESULTS

At concentrations that do not diminish embryo viability, growth, or axial rotation, CBD dose-dependently impairs cranial NT closure, increasing the proportion of embryos that develop exencephaly. It concomitantly diminishes closure of the spinal NT, the posterior neuropore (PNP), producing longer neuropores at the end of culture which is a hallmark of spina bifida risk. Exposure to CBD does not disrupt the formation of long F-actin cables in surface ectoderm cells flanking the PNP or folding of the neuroepithelium at predictable hinge points. At the cellular level, CBD exposure does not alter proliferation or apoptosis of the spinal neuroepithelium.

DISCUSSION

Thus, CBD acts selectively as a neuroteratogen predisposing to spina bifida and exencephaly in mouse whole embryo culture at exposure levels not associated with overt toxicity. Large-scale testing of CBD's effects on NT closure, particularly in at-risk groups, is warranted to inform its marketing to women of childbearing age.

In vitro study of the toxic and teratogenic effects of prednisolone, azathioprine and mycophenolate mofetile on embryological development of rats

This study aimed to evaluate the effects of the glucocorticoid prednisolone, the mycophenolic acid prodrug, azathioprine, and the fungi fermentation end product, mycophenolate mofetile on the embryological development of rats. Nine day-old rat embryos were cultured in rat serum containing prednisolone at varying concentrations (5-30 µg/ml) for 48 h. The test groups were cultured separately in rat serum containing 0.3-10 µg/ml azathioprine and 1-10 µg/ml mycophenolate mofetile. Embryonic development parameter effects of both drugs in combination with prednisolone (20 µg/ml) were studied using morphological methods, with special attention given to the incidence of malformations. The genotoxic effects of agents evaluated with the TUNEL test revealed that prednisolone is not a cause of developmental toxicity. The maximum safe dose of prednisolone that could be used in combination with other immunosuppressive agents was determined to be 20 µg/ml. Azathioprine was found to be toxic and teratogenic for the rat embryos beginning at a dose of 1 µg/ml. Dose-dependent toxic and teratogenic effects of mycophenolate mofetile were detected at doses lower than normal clinical ones.

No developmental toxicity observed with dolutegravir in rat whole embryo culture

BACKGROUND

An in vitro rat whole embryo culture study investigated whether direct exposure to dolutegravir (Tivicay^TM ) during the critical period for neural tube development would result in abnormal development.

METHODS

Dolutegravir (DTG), and HIV integrase inhibitor, was administered at 0 (vehicle), 5.3 μg/mL and 9.3 μg/mL on Gestation Day (GD) 9 through 11 (approximate 40 hour exposure period) along with positive (Valproic Acid) and negative (Penicillin G) controls. The DTG concentrations tested were selected based on clinical exposure at the maximum human recommended dose and maximum feasible concentration that could be formulated under the experimental conditions.

RESULTS

Approximately 6% of DTG present in the culture media was absorbed into the embryos, demonstrating embryonic exposure at a similar level to that observed in a rat DTG placental transfer study. There was no effect in either the DTG or Penicillin G groups on visceral yolk sac size/morphology, embryo size, somite number and embryo morphology at any concentration tested. Valproic Acid, by contrast, produced statistically significant decreases in visceral yolk sac size, embryo size and somite number along with defects in visceral yolk sac and embryonic morphology, including neural tube defects (NTDs), in all embryos.

CONCLUSION

DTG at the maximum human recommended dose administered to rats in a whole embryo culture assay did not produce any abnormal effects, while the positive control Valproic Acid produced abnormal effects, including neural tube defects.

Live Fluorescence Imaging of F-Actin Organization in Chick Whole Embryo Cultures Using SiR-Actin

Morphogenesis is a continuous process of pattern formation so complex that it requires in vivo monitoring for better understanding. Changes in tissue shape are initiated at the cellular level, where dynamic intracellular F-actin networks determine the shape and motility of cells, influence differentiation and cytokinesis and mediate mechanical signaling. Here, we stain F-actin with the fluorogenic probe SiR-actin for live fluorescence imaging of whole chick embryos. We found that 50 nM SiR-actin in the culture medium is a safe and effective concentration for this purpose, as it provides high labeling density without inducing morphological malformations.

Inhibition of glutathione biosynthesis alters compartmental redox status and the thiol proteome in organogenesis-stage rat conceptuses

Developmental signals that control growth and differentiation are regulated by environmental factors that generate reactive oxygen species (ROS) and alter steady-state redox environments in tissues and fluids. Protein thiols are selectively oxidized and reduced in distinct spatial and temporal patterns in conjunction with changes in glutathione/glutathione disulfide (GSH/GSSG) and cysteine/cystine (Cys/CySS) redox potentials (E(h)) to regulate developmental signaling. The purpose of this study was to measure compartment-specific thiol redox status in cultured organogenesis-stage rat conceptuses and to evaluate the impact of thiol oxidation on the redox proteome. The visceral yolk sac (VYS) has the highest initial (0 h) total intracellular GSH (GSH+2GSSG) concentration (5.5 mM) and the lowest Eh (-223 mV) as determined by HPLC analysis. Total embryo (EMB) GSH concentrations ranged lower (3.2 mM) and were only slightly more oxidized than the VYS. Total GSH concentrations in yolk sac fluid (YSF) and amniotic fluid (AF) are >500-fold lower than in tissues and are highly oxidized (YSF E(h)=-121 mV and AF E(h)=-49 mV). Steady-state total Cys concentrations (Cys+2CySS) were significantly lower than GSH in tissues but were otherwise equal in VYS and EMB near 0.5 mM. On gestational day 11, total GSH and Cys concentrations in EMB and VYS increase significantly over the 6h time course while E(h) remains relatively constant. The Eh (GSH/GSSG) in YSF and AF become more reduced over time while E(h) (Cys/CySS) become more oxidized. Addition of L-buthionine-S,R-sulfoximine (BS0) to selectively inhibit GSH synthesis and mimic the effects of some GSH-depleting environmental chemicals significantly decreased VYS and EMB GSH and Cys concentrations and increased Eh over the 6h exposure period, showing a greater overall oxidation. In the YSF, BSO caused a significant increase in total Cys concentrations to 1.7 mM but did not significantly change the E(h) for Cys/CySS. A significant net oxidation was seen in the BSO-treated AF compartment after 6 h. Biotinylated iodoacetamide (BIAM) labeling of proteins revealed the significant thiol oxidation of many EMB proteins following BSO treatment. Quantitative changes in the thiol proteome, associated with developmentally relevant pathways, were detected using isotope coded affinity tag (ICAT) labeling and mass spectroscopy. Adaptive pathways were selectively enriched with increased concentrations of proteins involved in mRNA processing (splicesome) and mRNA stabilization (glycolysis, GAPDH), as well as protein synthesis (aminoacyl-tRNA) and protein folding (antigen processing, Hsp70, protein disulfide isomerase). These results show the ability of chemical and environmental modulators to selectively alter compartmental intracellular and extracellular GSH and Cys concentrations and change their corresponding E(h) within the intact viable conceptus. The altered E(h) were also of sufficient magnitude to alter the redox proteome and change relative protein concentrations, suggesting that the mechanistic links through which environmental factors inform and regulate developmental signaling pathways may be discovered using systems developmental biology techniques.

Convergent extension analysis in mouse whole embryo culture

Mutations have been identified in a non-canonical Wnt signalling cascade (the planar cell polarity pathway) in several mouse genetic models of severe neural tube defects. In each of these models, neurulation fails to be initiated at the 3-4 somite stage, leading to an almost entirely open neural tube (termed craniorachischisis). Studies in whole embryo culture have identified a defect in the morphogenetic process of convergent extension during gastrulation, preceding the onset of neural tube closure. The principal defect is a failure of midline extension, both in the neural plate and axial mesoderm. This leads to an abnormally wide neural plate in which the elevating neural folds are too far apart to achieve closure. In this chapter, we provide details of several experimental methods that can be used to evaluate convergent extension in cultured mouse embryos. We describe analytical methods that can reveal the abnormalities that characterise neurulation-stage embryos with defective planar cell polarity signalling, in particular the loop-tail (Lp; Vangl2) mutant.

Avian models in teratology and developmental toxicology

The avian embryo is a long-standing model for developmental biology research. It also has proven utility for toxicology research both in ovo and in explant culture. Like mammals, avian embryos have an allantois and their developmental pathways are highly conserved with those of mammals, thus avian models have biomedical relevance. Fertile eggs are inexpensive and the embryo develops rapidly, allowing for high-throughput. The chick genome is sequenced and significant molecular resources are available for study, including the ability for genetic manipulation. The absence of a placenta permits the direct study of an agent's embryotoxic effects. Here, we present protocols for using avian embryos in toxicology research, including egg husbandry and hatch, toxicant delivery, and assessment of proliferation, apoptosis, and cardiac structure and function.

Roles of HNK-1 carbohydrate epitope and its synthetic glucuronyltransferase genes on migration of rat neural crest cells

HNK-1 carbohydrate epitope is localized on the surface of avian neural crest cells (NCCs), and is necessary for their migration. However, it is still disputed whether the epitope works in similar ways in mammalian embryos. In this study, we found that HNK-1 carbohydrate epitope was specifically detected in some of the cranial ganglia, migrating trunk NCCs and some non-NCC derivatives in the rat embryo. Two genes encoding glucuronyltransferases that synthesize the HNK-1 epitope in vitro (GlcAT-P and GlcAT-D) were recently identified in the rat. Interestingly, the NCCs in the cranial ganglia expressed the GlcAT-D gene, whereas the migrating trunk NCCs expressed the GlcAT-P gene. To investigate in vivo functions of the GlcATs in the NCC migration further, we overexpressed GlcAT genes by electroporation in the cranial NCCs in cultured rat embryos. Transfection of both GlcAT genes resulted in efficient synthesis of the HNK-1 epitope in the NCCs. GlcAT-P overexpression increased distance of cranial NCC migration, whereas GlcAT-D overexpression did not show this effect. Our data suggest that the HNK-1 epitope synthesized by different GlcATs is involved in migration in the sublineages of the NCCs in the rat embryo, and that GlcAT-P and GlcAT-D mediate different effects on the NCC migration.

The growth promoting effects of bFGF, PD-ECGF and VEGF on cultured postimplantation rat embryos deprived of serum fractions

Serum components in which embryos are cultured in vitro are very important for normal embryonic development. In this study, rat serum was fractionated using Macrosep filters to study the effect of a single growth factor. The fractionated serum, both that containing only material greater than 30 kDa molecular weight (> 30 kDa) and that from which material between 30 kDa and 50 kDa had been removed (< 30 kDa+ > 50 kDa), caused significant embryonic growth retardation. Addition of different concentrations of basic fibroblast growth factor (bFGF, 18 kDa), vascular endothelial growth factor (VEGF, 45 kDa) and platelet-derived endothelial growth factor (PD-ECGF, 45 kDa), to fractionated serum (bFGF to > 30 kDa serum and VEGF or PD-ECGF to < 30 kDa+ > 50 kDa serum) partially restored embryonic growth and development according to a morphological scoring system and protein assay. This restoration was clear by all criteria, as well as in yolk sac vascularisation and heart development. The growth promoting effects of all 3 factors were significant but did not reach the level seen in embryos grown in whole rat serum. The effect of these growth factors was also investigated on anembryonic yolk sac development using a concentration for which maximum whole embryonic growth was seen (128 ng/ml bFGF, 1.6 ng/ml VEGF and 4 ng/ml PD-ECGF), and significant anembryonic yolk sac development was found. These findings suggest that the angiogenic factors may have a growth promoting effect on total embryonic development and vascularisation.

Species-specificity of growth-promoting effects of prolactin during rat embryogenesis

In the early stages of embryonic development, many growth-promoting molecules must be provided by the maternal system. The molecules involved in growth processes may be either hormones or growth factors, or molecules that interact with such factors. The pregnancy related hormone, prolactin (PRL, MW 23 kDa) has been implicated in the control of embryonic growth. The growth-promoting potential of PRL and its species-specificity was investigated by culturing 9.5 d rat embryos in vitro for 48 h in depleted serum in the presence and absence of PRL from 3 different species. The growth-supporting capacity of the serum was reduced by removal of low molecular weight molecules by prolonged filtration of the serum using filters with a molecular weight exclusion of 30 kDa. This method provided a 'semidefined' medium (retenate) in which embryonic growth and development was significantly reduced, demonstrating that the low molecular weight fraction of serum may contain some growth-promoting factors. Addition of PRL (0.4-25.6 ng/ml) from different species (human, sheep and rat) to retenate significantly improved embryonic growth and development, suggesting that the developing embryo may utilise PRL. Amongst PRLs, rat PRL was found to be active at much lower concentrations than either of the other molecules, and human PRL had more effect in low concentrations than sheep PRL suggesting a species-specificity for this hormone. It may be that the PRL receptors of the rat embryos have greater affinity for the rat hormone as different responses for hormones from different species have been shown. These findings suggest that embryos may be able to utilise maternally derived PRL during organogenesis.

The role of maternally derived epidermal growth factor and the epidermal growth factor receptor during organogenesis in the rat embryo

Epidermal growth factor (EGF) has been implicated in the control of embryonic development, but although the receptor is expressed from an early stage, there is little evidence of embryonic expression of EGF. In order to investigate the role of maternally derived EGF during organogenesis, rat embryos were explanted at d 9.5 and cultured in serum depleted of low molecular weight molecules (retenate) which was then supplemented with EGF. Serum depleted of low molecular weight molecules by prolonged filtration loses its capacity to support normal embryonic development, possibly due to the loss of growth promoting factors. The addition of EGF to retenate significantly improved embryonic development with a maximal effect at 8 ng/ml. The addition of an analogue of EGF, long EGF, to retenate also caused a significant increase in development, although at higher concentrations a decrease in its effect was observed, possibly due to down regulation of the EGF receptor. Therefore, embryos may be able to utilise maternally derived EGF during organogenesis. To test the effects of inhibiting the EGF receptor during organogenesis, d 9.5 embryos were cultured in the presence of tyrphostin 47, a specific EGF receptor inhibitor. Tyrphostin 47 caused a significant dose-dependent decrease in the development of embryos which was also observed when tyrphostin 47 was injected into the vitelline circulation at d 11.5 to bypass the effects of the yolk sac. These findings suggest that the EGF receptor is essential for normal organogenesis and may play a role in the control of proliferation and differentiation. Although EGF is not expressed in the rat embryo at this stage, maternally derived EGF may be the ligand for the embryonic EGF receptor.