Effects of ethanol and acetaldehyde on rat embryos developing in vitro

Moderate alcohol consumption during pregnancy increases potency of two different drugs (the antifungal fluconazole and the antiepileptic valproate) in inducing craniofacial defects: prediction by the in vitro rat whole embryo culture

The prenatal exposure to ethanol (Eth), fluconazole (FLUCO) and sodium valproate (VPA) is related to effects on development, producing characteristic syndromic pictures. Among embryotoxic effects described for the three molecules, the alteration on craniofacial morphogenesis is a common feature in humans and animal models, including rodent embryos developed in vitro. The aim of the present work is to evaluate the developmental effects of low Eth serum concentration (17 mM, corresponding to the legal limit to drive in UK, USA, Canada, and many other countries) in mixture with increasing realistic concentrations of the antifungal drug FLUCO (62.5-500 µM) or with increasing realistic concentrations of the antiepileptic drug VPA (31.25-250 µM). Groups exposed to Eth alone (17-127.5 mM), FLUCO alone (62.5-500 µM) or VPA alone (31.25-750 µM) were also included. The chosen alternative animal model was the post-implantation rat whole embryo culture (WEC). E9.5 embryos were exposed in vitro to the test molecules during the whole test period (48 h, corresponding to the developmental stages characteristics of any vertebrate, for human embryos post-fertilization days 23-31). Data were statistically analyzed and processed for modelling applying the benchmark dose (BMD) and relative potency factor (RPF) approaches. Concentration-related effects on facial outcomes were observed in all experimental groups, with a significant enhancement in the groups co-exposed with Eth in comparison to the single exposures. Data obtained by the present work suggest an additional alert for the assumption of even low levels of alcohol in pregnant women during FLUCO or VPA therapy.

Modified Xenopus laevis approach (R-FETAX) as an alternative test for the evaluation of foetal valproate spectrum disorder

In compliance to animal welfare 3Rs principle there is a great demand for refined tests alternative to classical mammal teratogenicity tests. We propose a refined alternative amphibian method (R-FETAX) to evaluate chemical induced embryotoxicity. The human foetal valproate spectrum disorder (FVSD) characteristics are morphological defects (including cranio-facial, neural tube defects) and behavioural alterations due to valproate (VPA) exposure in pregnancy. Vertebrate assays to evaluate FVSD include classical and alternative mammal (implying adult sacrifice), and non-mammal developmental models (zebrafish, amphibians, chick). Among these latter only zebrafish assays report in the same test both morphological and behavioural examinations. Compared to zebrafish, the amphibian Xenopus laevis excels having a more comparable organ development and morphology to mammalian systems. We used X. laevis embryos exposed during developmental specific windows to VPA therapeutic concentrations. Different VPA effects were observed depending on the exposure window: concentration-related embryo-lethal and teratogenic effects (neural tube, facial, tail defects) were observed in groups exposed at the organogenetic phylotypic stages. Neurobehavioral deficits were described using a functional swimming test at the highest VPA concentration exposure during the phylotypic stages and at any concentration during neurocognitive competent stages. Malformations were compared to those obtained in a mammalian assay (the rat post-implantation whole embryo culture method, WEC), that we used in the past to evaluate VPA teratogenicity. R-FETAX and WEC data were modelled and their relative sensitivity was calculated. We suggest the amphibian R-FETAX as a refined windowed alternative test for the evaluation of chemicals inducing both morphological and behavioural anomalies, including VPA.

Development of an adverse outcome pathway for cranio-facial malformations: A contribution from in silico simulations and in vitro data

Mixtures of substances sharing the same molecular initiating event (MIE) are supposed to induce additive effects. The proposed MIE for azole fungicides is CYP26 inhibition with retinoic acid (RA) local increase, triggering key events leading to craniofacial defects. Valproic acid (VPA) is supposed to imbalance RA-regulated gene expression trough histone deacetylases (HDACs) inhibition. The aim was to evaluate effects of molecules sharing the same MIE (azoles) and of such having (hypothetically) different MIEs but which are eventually involved in the same adverse outcome pathway (AOP). An in silico approach (molecular docking) investigated the suggested MIEs. Teratogenicity was evaluated in vitro (WEC). Abnormalities were modelled by PROAST software. The common target was the branchial apparatus. In silico results confirmed azole-related CYP26 inhibition and a weak general VPA inhibition on the tested HDACs. Unexpectedly, VPA showed also a weak, but not marginal, capability to enter the CYP 26A1 and CYP 26C1 catalytic sites, suggesting a possible role of VPA in decreasing RA catabolism, acting as an additional MIE. Our findings suggest a new more complex picture. Consequently two different AOPs, leading to the same AO, can be described. VPA MIEs (HDAC and CYP26 inhibition) impinge on the two converging AOPs.

The Ascidian Embryo Teratogenicity assay in Ciona intestinalis as a new teratological screening to test the mixture effect of the co-exposure to ethanol and fluconazole

The aim of this work was to evaluate the Ascidian Embryo Teratogenicity assay (AET) as new alternative invertebrate model to test the developmental effects of the co-exposure to ethanol and fluconazole. Ciona intestinalis embryos were exposed to the azolic fungicide fluconazole, (FLUCO, 7.8-250μM), to ethanol (Eth, 0.01-0.5%) and to their mixture (0.01% Eth+FLUCO 7.8-250μM) from neurula to larval stage. At the end of the exposure period, larvae were morphologically evaluated and benchmark analysis performed by using the PROAST modelling software. Both compounds were teratogenic in a concentration-related manner, particularly affecting the pigmented organs. The co-exposure to Eth enhanced the effects of FLUCO, the additive hypothesis was not rejected by the modelling. The results demonstrated that AET could be considered a good vertebrate-free alternative model for toxicological investigation in embryos.

Alcohol Teratogenesis: Mechanisms of Damage and Strategies for Intervention

There are multiple mechanisms by which alcohol can damage the developing brain, but the type of damage induced will depend on the amount and developmental timing of exposure, along with other maternal and genetic factors. This article reviews current perspectives on how ethanol can produce neuroteratogenic effects by its interactions with molecular regulators of brain development. The current evidence suggests that alcohol produces many of its damaging effects by exerting specific actions on molecules that regulate key developmental processes (e.g., L1 cell adhesion molecule, alcohol dehydrogenase, catalase), interfering with the early development of midline serotonergic neurons and disrupting their regulatory-signaling function for other target brain structures, interfering with trophic factors that regulate neurogenesis and cell survival, or inducing excessive cell death via oxidative stress or activation of caspase-3 proteases. The current understanding of pathogenesis mechanisms suggests several strategic approaches to develop rational molecular prevention. However, the development of behavioral and biologic treatments for alcohol-affected children is crucial because it is unlikely that effective delivery of preventative interventions can realistically be achieved in ways to prevent prenatal damage in at-risk pregnancies. Toward that end, behavioral training that promotes experience-dependent neuroplasticity has been effective in a rat model of cerebellar damage induced by alcohol exposure during the period of brain development that is comparable to that of the human third trimester.

Species extrapolation of life-stage physiologically-based pharmacokinetic (PBPK) models to investigate the developmental toxicology of ethanol using in vitro to in vivo (IVIVE) methods

To provide useful alternatives to in vivo animal studies, in vitro assays for dose-response assessments of xenobiotic chemicals must use concentrations in media and target tissues that are within biologically-plausible limits. Determining these concentrations is a complex matter, which can be facilitated by applying physiologically-based pharmacokinetic (PBPK) models in an in vitro to in vivo extrapolation (IVIVE) paradigm. We used ethanol (EtOH), a ubiquitous chemical with defined metrics for in vivo and in vitro embryotoxicity, as a model chemical to evaluate this paradigm. A published series of life-stage PBPK models for rats was extended to mice, yielding simulations that adequately predicted in vivo blood EtOH concentrations (BECs) from oral, intraperitoneal, and intravenous routes in nonpregnant and pregnant adult mice. The models were then extrapolated to nonpregnant and pregnant humans, replicating BEC data within a factor of two. The rodent models were then used to conduct IVIVEs for rodent and whole-embryo culture embryotoxicity data (neural tube closure defects, morphological changes). A second IVIVE was conducted for exposure scenarios in pregnant women during critical windows of susceptibility for developmental toxicity, such as the first 6-to-8 weeks (prerecognition period) or mid-to-late pregnancy period, when EtOH consumption is associated with fetal alcohol spectrum disorders. Incorporation of data from human embryonic stem cell studies led to a model-supported linkage of in vitro concentrations with plausible exposure ranges for pregnant women. This effort demonstrates benefits and challenges associated with use of multispecies PBPK models to estimate in vivo tissue concentrations associated with in vitro embryotoxicity studies.

Connecting teratogen-induced congenital heart defects to neural crest cells and their effect on cardiac function

Neural crest cells play many key roles in embryonic development, as demonstrated by the abnormalities that result from their specific absence or dysfunction. Unfortunately, these key cells are particularly sensitive to abnormalities in various intrinsic and extrinsic factors, such as genetic deletions or ethanol-exposure that lead to morbidity and mortality for organisms. This review discusses the role identified for a segment of neural crest in regulating the morphogenesis of the heart and associated great vessels. The paradox is that their derivatives constitute a small proportion of cells to the cardiovascular system. Findings supporting that these cells impact early cardiac function raises the interesting possibility that they indirectly control cardiovascular development at least partially through regulating function. Making connections between insults to the neural crest, cardiac function, and morphogenesis is more approachable with technological advances. Expanding our understanding of early functional consequences could be useful in improving diagnosis and testing therapies.

In vitro embryotoxicity study of n,n-dimethylacetamide and its main metabolite N-monomethylacetamide

N,N-Dimethylacetamide (DMAC) is a widely used industrial solvent. Previous teratological studies in vivo reported discording results. Using the postimplantation rat whole embryo culture (WEC) method, the direct embryotoxic effects of DMAC and its main metabolite (N-monomethylacetamide, MMAC) have been investigated in the present work. Both chemicals showed specific embryotoxic and teratogenic effects at similar concentration levels. The no-observed-effect level (NOEL) was 0.85mm.Macroscopically, the main target organs were somites, brain and branchial bars. Histological examination revealed an increase in cell death at the effective concentrations on the neuroepithelium and branchial bars mesenchyme. The results of this work, together with those obtained in in vivo studies, suggest that the exposure limits in workplaces could be inappropriate for the safety of fertile women.

Krox20 is down-regulated following triazole in vitro embryonic exposure: a polycompetitor-based assay

This study was conducted in order to analyse gene-expression alterations in rat embryos following exposure to triazoles, using an easy-handling approach. Triazole derivatives have been shown to alter the morphology of cranio-facial structures and to induce abnormalities in hindbrain patterning and neural crest cell migration. Specification of hindbrain segments is regulated by retinoic acid and the hox code. Krox20 was chosen as molecular marker for its specific distribution in the anterior neural tube. In fact, this zinc-finger protein is expressed in rhombomere 3 and 5. Mis-regulation of Krox20 levels have shown to induce severe alterations in the correct patterning of the rhomboencephalon and the derived structures. In order to analyse Krox20 mRNA levels in rat embryos exposed in vitro to the triazole derivative triadimefon, a semi-quantitative approach utilising the competitive RT-PCR was chosen. A lambda phage-based plasmid construct that could compete with target and internal standard gene at the same time during enzymatic reaction was generated. Results were confirmed by real-time RT-PCR analysis on the same samples. Our data show a down-regulation of Krox20 transcript levels after exposure to the triazole derivative, implying a key role of this molecule in the pathogenic pathway induced by triazole exposure.

Effects of folinic acid and Vitamin B12 on ethanol-induced developmental toxicity in mouse

The objective of this study was to assess whether combined supplementation of folinic acid (FA) and Vitamin B(12) (VB(12)) could suppress ethanol-induced developmental toxicity better than FA alone in mouse embryos cultured in vitro. In this study, exposure to 4.0mg/ml ethanol for 48 h yielded growth retardation and various malformations of the embryos. FA (10(-5), 10(-4)mol/l) or VB(12) (10(-6), 10(-5)mol/l) alone supplementation improved the growth parameters moderately, however combined supplementation of the two vitamins (10(-5)mol/l FA plus 10(-6)mol/l VB(12), 10(-5)mol/l FA plus 10(-5)mol/l VB(12), 10(-4)mol/l FA plus 10(-6)mol/l VB(12) and 10(-4)mol/l FA plus 10(-5)mol/l VB(12)) showed better protective effects, including both the growth and development parameters of the embryos, than either vitamin alone at the same dosage. The present investigation indicated that combined supplementation of folic acid and VB(12) might be a better choice than folic acid alone in the prevention of ethanol-induced birth defects.

Dysmorphogenic effects of some fungicides derived from the imidazole on rat embryos cultured in vitro

Like triazole-derivatives, imidazole-derivatives exert their antifungal and toxicological properties by inhibiting P450 enzymes (Cyps). At the embryonic level, Cyp enzymes are involved also in the catabolism of the retinoic acid. Specific effects of triazole-derivatives have been reported on developing rodent embryos, and were correlated to an imbalance of the retinoid homeostasis. The aim of this work was to investigate if imidazole-derivatives are able to induce specific malformations similar to those observed after triazole-derivative exposure. Post implantation rat embryos were exposed in vitro to 1,000 microM Imidazole and to 5-100 microM of the imidazole-derivatives Ketoconazole and Enilconazole. After 48 h in culture, the embryos exposed to the imidazole-derivatives showed specific malformations, quite similar to those observed after triazole-derivative exposure. The common dysmorphogenic effects of the azole-derivatives of the two classes could be due to the inhibition of retinoid catabolism. From this point of view, the contemporaneous exposure to these substances or their therapeutic use could be considered as potentially dangerous for human conceptuses.

Study on the common teratogenic pathway elicited by the fungicides triazole-derivatives

Triazole-derivatives alter the pharyngeal apparatus morphogenesis of rodent embryos cultured in vitro. The hindbrain segmentation and the rhombencephalic neural crest cell (NCCs) migration are altered by Fluconazole exposure in vitro. The aim of the present work is to identify if a common pathogenic pathway is detectable also for other molecules of this class of compounds. 9.5 days post coitum (d.p.c.) old rat embryos were exposed in vitro to the teratogenic concentrations of Flusilazole, Triadimefon and Triadimenol and cultured for 24, 48 or 60 h. The expression and localisation of Hox-b1 and Krox-20 proteins (used as markers for hindbrain segmentation) were evaluated after 24 h of culture. The localisation and distribution of NCC was evaluated after 24, 30 and 48 h of culture. The morphology of the embryos was analysed after 48 h, while the branchial nerve structures were evaluated after 60 h of culture. Hindbrain segmentation and NCC migration alteration as well as pharyngeal arch and cranial nerve abnormalities were detected after exposure of the tested molecules. A common severe teratogenic intrinsic property for the tested molecules of this chemical class has been found, acting through alteration of the normal hindbrain developmental pattern.

Strain-dependent effects of developmental ethanol exposure in zebrafish

Developmental ethanol exposure from maternal consumption of alcoholic beverages and many other consumer products has been linked to developmental abnormalities in humans and animal models. The sensitivity of an individual to ethanol-induced perturbation of developmental processes is strongly influenced by genetic factors. In this study, we show that there are strain- and dose-dependent differences in sensitivity to developmental ethanol exposure in zebrafish (Danio rerio), suggesting that genetic variation within regulatory factors, influencing critical developmental pathways, is responsible for these differences. Embryos/larvae from genetically distinct strains of zebrafish [Ekkwill (EK), AB, and Tuebingen (TU)] were treated with different concentrations of ethanol. Embryo/larval survival, neurocranial and craniofacial skeletal development, and CNS cell death were analyzed. EK was the most resistant strain to the embryolethal effects of ethanol exposure but had the greatest increase in ethanol-induced cell death. AB survival was affected moderately, as were the neurocranial and craniofacial skeletal structures and ethanol-induced cell death. TU had the lowest survival rate but was the most resistant to alterations in neurocranial and craniofacial skeletal elements. No single strain is the most sensitive or the most resistant to any of the phenotypes examined, suggesting that alcohol influences each of these pathways independently. Further analysis of the molecular and biochemical pathways underlying the strain-dependent differences reported herein could lead to a significant advancement in our mechanistic understanding of the teratogenic effects of ethanol in humans.

Effects of ethanol on mouse embryonic brain development and heat shock protein 73 expression

Effects of ethanol on brain development and heat shock protein 70 (HSP70) expression were investigated in mouse embryos using the whole embryo culture, mid-brain culture, and streptavidin-biotin peroxidase complex (SABC) method. In the whole embryo culture, ethanol (1, 2 and 4 mg/ml) inhibited brain development dose dependently and the most prevalent abnormality was the open cephalic neural tube. At doses of 1 and 2 mg/ml, ethanol significantly decreased constitutive HSP70 (HSP73) expression level compared to control values in embryonic brain areas. In mid-brain culture, ethanol exposure (from 1 to 16 mg/ml) during early neuroblast differentiation inhibited neuronal differentiation and proliferation. These results suggest that ethanol may affect embryonic brain development by decreasing HSP73 expression level as well as inhibiting neuronal differentiation and proliferation during the organogenic period.

Relationship between hindbrain segmentation, neural crest cell migration and branchial arch abnormalities in rat embryos exposed to fluconazole and retinoic acid in vitro

Fluconazole (FLUCO) and retinoic acid (RA) can perturb morphogenesis of the branchial apparatus in rodent embryos exposed in vitro. The aim of the present study was to compare the effects induced by in vitro exposure to FLUCO or to RA on rhombomere organisation, neural crest cell (NCC) migration and cranial nerve differentiation using specific antibodies. For this purpose 9.5 d.p.c. rat embryos were exposed to teratogenic concentrations of FLUCO or RA; another group was exposed to no-effect concentrations of both agents. Expression of Hox-b1 and Krox20 (markers of specific rhombomeres) was altered after FLUCO and RA exposure. Furthermore, FLUCO and RA showed a synergistic effect. These results suggest that the observed branchial abnormalities are due to anomalous NCC migration related to incorrect organisation of specific rhombomeres.

Pathogenic pathways in fluconazole-induced branchial arch malformations

BACKGROUND

A widely-used antimycotic agent, bis-triazole fluconazole (FLUCO), is able to produce abnormalities to the branchial apparatus (hypoplasia, agenesis, and fusion) in postimplantation rodent embryos cultured in vitro. The branchial apparatus is a complex and transient structure in vertebrate embryos and is essential for the development of the face skeleton. Branchial arch mesenchyme is formed by two different cellular populations: paraxial mesenchyme and ectomesenchyme, which originate from rhombencephalic neural crest cell (NCC) migration. We investigated the possible pathogenic pathways involved in FLUCO-related branchial arch abnormalities. Perturbations in physiological apoptosis, cell proliferation, NCC migration and branchial mesenchyme induction have been considered.

METHODS

Rat embryos (9.5-day postcoitum; 1-3 somites) were exposed in vitro to 0 or 500 microM FLUCO. After 24, 36, or 48 hr of culture, embryos were examined for apoptosis (acridine orange method) and cell proliferation (BrdU incorporation and detection method). Rhombencephalic NCC migration was analyzed using immunostaining of NCC (using anti-CRABP antibodies) and the extracellular matrix (using anti-fibronectin antibodies). The differentiative capability of the branchial mesenchymes was investigated using anti-endothelin and anti-endothelin-receptor antibodies.

RESULTS

During the whole culture period, no alterations in physiological apoptosis, cell proliferation, and mesenchymal cell induction were observed in FLUCO-exposed embryos in comparison to controls. On the contrary, severe alterations in NCC migration pathways were observed in FLUCO-exposed embryos.

CONCLUSIONS

The findings suggest that FLUCO produces teratogenic effects by interfering with the cellular and molecular mechanisms that control NCC migration.

Antifungal triazoles induce malformations in vitro

Triazole-derivatives are antimycotics used in agriculture as well as in clinical and veterinary therapy. The aim of the present work is the in vitro comparative study of the teratogenic activity of triazole (the parental compound), flusilazole (an agricultural triazole mono-derivative fungicide), and fluconazole (a clinically used bis-triazole derivative). Rat embryos, 9.5 days old (1 to 3 somites) were exposed in vitro to triazole 500 to 5000 microM, flusilazole 3.125 to 250 microM, or fluconazole 62.5 to 500 microM. After 48 h in culture, the embryos were morphologically examined and processed for histologic and biochemical analysis. Flusilazole and fluconazole showed similar teratogenic effects (abnormalities at the branchial apparatus level and cell death at the level of the branchial mesenchyme) at concentration levels of 6.25 microM and higher for flusilazole and of 125 microM and higher for fluconazole. By contrast, only slight developmental retardation and blood discoloration were observed at the highest concentrations of triazole, suggesting no teratogenic activity for the triazole group.

Acetaldehyde in vitro exposure and apoptosis: a possible mechanism of teratogenesis

Alcohol abuse by pregnant women can result in fetal alcohol effects (FAE) and fetal alcohol syndrome (FAS). Both ethanol itself and its main metabolite, acetaldehyde (Ach), are able to produce specific FAS-related malformations. In previous in vitro studies, we documented that 10-day-old rat embryos exposed to Ach show a characteristic embryonic Ach syndrome, histologically characterized by marked cellular death. As both necrosis and pathological apoptosis are teratological mechanisms, the aim of this work was to evaluate if cellular death, observed in Ach-exposed embryos, can be related to necrotic or apoptotic events. Ten-day-old rat embryos were cultured in the presence of Ach 30-60 microg/ml and stained with the vital dye acridine orange to visualize apoptotic areas. After fixation, the TUNEL [3' terminal deoxynucleotide transferase (TdT)-mediated dUTP-biotin nick end labeling] method was used to histologically identify apoptosis. Both acridine orange and TUNEL staining showed signs of physiological apoptosis in controls and abnormal apoptotic regions in Ach-exposed embryos. Our results show a clear correlation between malformed organs and apoptotic embryonic districts, suggesting the role of apoptosis in Ach-induced abnormalities.

In vitro teratogenic potential of two antifungal triazoles: triadimefon and triadimenol

The teratogenic potential of two antifungal triazoles (Triadimefon and Triadimenol) has been investigated in vitro by the rat postimplantation whole embryo culture method. Rat embryos 9.5 d old were cultured for 48 h in rat serum with Triadimefon (12.5-250 microM) or Triadimenol (6.25-125 microM) and then examined. Some embryos exposed to Triadimenol (6.25-125 microM) were cultured for 12 extra hours in control serum to improve their developmental degree and then immunostain cranial nerves and ganglia. The exposure to the highest doses of triazoles only moderately reduced some morphometrical developmental parameters. By contrast, 25-250 microM Triadimefon and 25-125 microM Triadimenol induced specific concentration-related teratogenic effects at the level of first and second branchial arches. After immunostaining, embryos exposed to 12.5-125 microM Triadimenol showed specific cranial nerve and ganglia abnormalities. The possible implication of neural crest cell alterations on triazole-related abnormalities is discussed.

What research with animals is telling us about alcohol-related neurodevelopmental disorder

The substantial advances in understanding fetal alcohol syndrome over the past 20 years were made in large part because of research with animals. This review illustrates recent progress in animal research by focusing primarily on the central nervous system effects of prenatal alcohol exposure. Current findings suggest further progress in understanding consequences, risk factors, mechanisms, prevention and treatment will depend on continued research with animals.

Interactive dysmorphogenic effects of all-trans-retinol and ethanol on cultured whole rat embryos during organogenesis

Whole rat conceptuses (10.5 gestational days) were explanted into a culture medium containing all-trans-retinol (t-retinol, vitamin A1), ethanol, or combinations of the two alcohols at various concentrations, and were cultured at 37 degrees C for 24 hr. Parameters emphasized in morphological analyses were branchial arch development, closure of neural tube, axial rotation, and development of otic vesicles and of optic cup. Additions of t-retinol alone to the culture medium resulted in significant decreases in viability at concentrations of 7.0 microM and above. A primary target site affected by t-retinol was the second branchial arch. With initial culture medium concentrations of 3.5 microM, 28% of embryos exhibited an underdeveloped second branchial arch, and the effect was concentration dependent. Incubations with t-retinol alone also caused failure of closure of neural tubes, underdevelopment/absence of otic and optic vesicles, and failure of normal axial rotation, but these effects were statistically significant only at the higher concentrations (10.5-14.0 microM). Incubations of conceptuses with ethanol alone resulted in statistically significant decreases in viability and increases of incidence of embryonic abnormalities at 50 mM but not at 10- or 20-mM concentrations. The embryotoxicity of ethanol appeared less site-specific than that of t-retinol. However, ethanol-elicited developmental abnormalities included underdevelopment of the first and second branchial arches, abnormally open neural tubes, abnormally small or absent otic and optic vesicles, and incomplete axial rotation in common with effects elicited by t-retinol. In general, embryos incubated with combinations of t-retinol and ethanol showed lower survival rates and higher incidences of developmental abnormalities when compared to the calculated values expected for simple additive effects; i.e., interactive effects were most frequently greater than additive and probably synergistic but not antagonistic. To assist in the elucidation of possible mechanism(s) for the greater than additive/synergistic dysmorphogenic effects observed, concentrations of all-trans-retinoic acid (t-RA) and all-trans-retinal(t-retinal) in cultured conceptal tissues were determined by high-performance liquid chromatography (HPLC). HPLC analysis showed increases in conceptal tissue levels of both t-RA and t-retinal after conceptuses were exposed to t-retinol (10.5 microM) plus various quantities of ethanol for 24 hr. These observations, in combination with those of previous studies, suggested that the observed greater-than-additive/synergistic dysmorphogenic effects were not due to the inhibition by ethanol of conceptal biosynthesis of t-RA. Whether the increased levels of t-RA and t-retinal caused the observed greater than additive/synergistic dysmorphogenic effects remains to be elucidated.

In vitro comparison of the effects of ethanol and acetaldehyde on dorsal root ganglion neurons

Results of previous experiments designed to investigate the role of acetaldehyde, the primary metabolite of ethanol, have been contradictory. Experiments have provided evidence that supports and refutes the idea that acetaldehyde is responsible for the teratogenic effects observed in fetal alcohol syndrome. In the present study, cell culture techniques were used to examine the effects of acetaldehyde, both independently and in conjunction with ethanol. The purpose was to determine whether acetaldehyde had any effect on survival and process outgrowth of dorsal root ganglion (DRG) neurons cultured in vitro. This study revealed that acetaldehyde was as toxic to DRG survival as is ethanol, but had a lesser effect on neurite outgrowth than ethanol. Also, acetaldehyde and ethanol do not act synergistically to damage neurons in culture. The results indicate that, although acetaldehyde is probably not solely responsible for ethanol neurotoxicity, it does exhibit a secondary toxicity that could be the subject of future studies.

Alterations of mouse embryonic branchial nerves and ganglia induced by ethanol

An immunostaining technique using monoclonal antibodies to a neurofilament protein has allowed us to visualize defects in the development of cranial nerves and ganglia of 10 to 10.5 days mouse embryos following exposure to ethanol in whole embryo culture. Reference patterns for development of cranial nerves and ganglia of control mouse embryos explanted and examined when they had 25 to 34 pairs of somites were established. Additionally, control mouse embryos were grown in whole embryo culture for 48 h, with culture being initiated in embryos having 6 to 7 somite pairs. At the end of the culture period, only minor differences were observed between the control groups. An experimental group of embryos was cultured in the presence of increasing doses (1.6, 3.2, 4, and 4.8 g/l) of ethanol. Defects were observed in the development of the glossopharyngeal and vagus nerves. These abnormalities included absence of the dorsal root (superior ganglion) of IX, star-like shape of inferior ganglion IX, disorganization of the rootlets of nerve X and abnormal fibers between the two nerves and ganglia. These results suggest that the migration and patterning of neural crest cells derived from r6 and r7 may be particularly affected by ethanol. The results also demonstrate the usefulness of this approach in evaluating the susceptibility of the developing cranial nerves to toxicant exposure.

Increased cell death and reduced neural crest cell numbers in ethanol-exposed embryos: partial basis for the fetal alcohol syndrome phenotype

Fetal alcohol syndrome (FAS) is characterized by growth retardation, craniofacial malformations, and heart and neural defects; the cellular and molecular mechanism(s) responsible for ethanol's teratogenicity remains unknown. Although the phenotype suggests that prenatal ethanol exposure perturbs neural crest cell development, direct proof that these cells are an in utero target is still lacking. Previous research suggested that cranial neural crest cells are eliminated by ethanol-induced apoptosis. We tested this hypothesis using a chick embryo model of FAS. A single dose of ethanol, chosen to achieve a concentration of 35-42 mg/dl, was injected in ovo at gastrulation and resulted in growth retardation, craniofacial foreshortening, and disrupted hindbrain segmentation. Ethanol exposure enhanced cell death within areas populated by cranial neural crest cells, particularly in the hindbrain and craniofacial mesenchyme. In contrast, control embryos had limited cell death within these regions. Subsequent immunolabeling with neural crest cell-specific antibody revealed that ethanol treatment resulted in fewer neural crest cell numbers, whereas neural crest migration patterns were unaffected by ethanol. These results suggest that prenatal ethanol exposure leads to loss of cranial neural crest cells. Such a loss could result, in part, in the phenotype characteristic of FAS.

Effect of ethanol on insulin-like growth factor-II release from fetal organs

This study examines the effect of ethanol (ETOH) exposure and nutrient restriction on the release of insulin-like growth factor (IGF)-II from 18- and 20-day explanted fetal organs. Fetuses were exposed to ETOH (E) in utero by feeding dams a 36% (calories derived from ETOH: 6.6% v/v) ETOH liquid diet. Control fetuses were offsprings of dams either pair-fed (P) a control liquid diet or ad libitum (A) fed a standard pelleted lab chow. Brain, heart, kidney, liver, lung, muscle, and placenta of fetuses from the same litter were pooled and explanted, and IGF-II concentration in explanted media was analyzed by radioimmunoassay. Maternal and fetal weights were determined during pregnancy and at sacrifice, respectively, to evaluate the influence of ETOH on growth. Both maternal and fetal weights were substantially reduced by ETOH on 18 and 20 days of gestation compared with both A and P controls. At 18 days of gestation, E fetuses (1.33 +/- 0.03 g) weighed less than either A (1.47 +/- 0.03 g) or P (1.54 +/- 0.04 g) fetuses. By 20 days, A mean fetal weight (4.19 +/- 0.23 g) was significantly greater than both P (3.74 +/- 0.06 g) and E (3.28 +/- 0.06 g) fetuses. IGF-II concentration in media from 18-day fetal explants was highest from E (brain, heart, liver, and placenta) and P tissues (kidney, lung, and muscle). IGF-II in media from A tissues (except placenta) was lower than both E and P levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic disorders of embryogenesis

Prevention of major physical malformations would represent a significant reduction in the burden of mortality and morbidity in infants and young children. However, preventive and therapeutic approaches must be based on a clear understanding of underlying pathogenic mechanisms. While it is estimated that single gene defects account for up to 10% of cases of major malformation, relatively few of these have been identified and analysed in detail. The recognition of characteristic patterns of developmental anomalies associated with specific enzyme defects has highlighted the important role of the metabolic environment in normal development and offers the possibility of correlating biochemical abnormalities with particular teratogenic effects. Once it is generally appreciated that some forms of structural malformation have a specific biochemical basis, metabolic studies should be performed more often in patients with major developmental anomalies. This should lead to identification of other examples of diseases of this type and the elucidation of molecular mechanisms of human teratogenesis.

Effect of alcohol, acetaldehyde, and salsolinol on beta-endorphin secretion from the hypothalamic neurons in primary cultures

The effect of ethanol, acetaldehyde, and salsolinol on hypothalamic beta-endorphin secreting neurons is studied by using rat fetal hypothalamic neurons in primary culture. Exposure of these neuronal cells to different concentrations of ethanol (12.5-50 mM) and acetaldehyde (12.5-50 microM) caused a concentration-dependent increase in the secretion of beta-endorphin. Salsolinol (12.5-50 microM) did not cause any significant change in the secretion of beta-endorphin. Ethanol's effect was short-lasting (2 hr). Acetaldehyde's effect on beta-endorphin secretion was greater and longer lasting, as compared with ethanol. Ethanol and salsolinol do not have any effect on cell viability, whereas higher concentrations of acetaldehyde appear to reduce the number of viable cells after 6 hr of treatment. None of the above treatments has any effect on cellular DNA content. These results suggest that ethanol is a potent stimulator of hypothalamic beta-endorphin. These results also show for the first time that ethanol's metabolite acetaldehyde is more potent in stimulating beta-endorphin secretion and may be significant in the ethanol regulated beta-endorphin secretion.

Ethanol-induced insulin resistance suppresses the expression of embryonic ornithine decarboxylase activity

In utero exposure to ethanol is associated with significant increases in fetal morbidity and mortality as well as with behavioral and learning problems that appear later in life. Growth suppression of the developing child is the most frequent physical effect of ethanol exposure and is correlated with specific molecular changes within the developing organism. The present report suggests that embryonic ethanol exposure suppresses the normal developmental increase in ornithine decarboxylase (ODC) activity. The loss of ODC activity during the early stages of development is dose-dependent and is correlated with the degree of growth suppression. Because ODC is the rate-limiting step for the synthesis of the polyamines and thus appears to be a focal enzyme for the regulation of growth, we have investigated the biochemical consequences of an ethanol-induced inhibition of ODC activity. Using intact chick embryos as well as cultured embryonic tissue, these studies indicate that ethanol-induced changes in tissue putrescine content result in growth suppression because a single dose of exogenous putrescine blocked the growth suppression. In cultured tissue, ethanol exposure inhibited the ability of a known trophic factor (insulin) to induce ODC activity. The loss of insulin-inducible decarboxylase activity as a result of ethanol exposure was specific to ODC, but ethanol per se had no effect on ODC activity in vitro. The data suggest that exposure to ethanol results in a resistance of the embryonic tissue to the action of insulin and thereby disrupts the molecular path by which this mitogenic compound induces the expression of ODC enzymatic activity.