Pathogenesis of craniofacial and body wall malformations induced by ochratoxin A in mice

Accuracy, discriminative properties and reliability of a human ESC-based in vitro toxicity assay to distinguish teratogens responsible for neural tube defects

The poor correlation of developmental toxicity studies in animals with human outcome data has emphasized the need for complementary assays based on human cells and tissues. As neural tube defects represent an important proportion of congenital malformations, we evaluated here the accuracy of a human embryonic stem cell (hESC)-based assay to predict chemically induced disruption of neural tube formation. As teratogenic compounds, we used cyclopamine (CPA), valproic acid (VPA), ochratoxin A (OTA) and mycophenolic acid (MMF), all suspected or known inducers of human neural tube defects, as well as theophylline and saccharin as negative control compounds. We analyzed their effects on the ability of hES cells to give rise to neural precursors (expressing specific marker Nestin), to form neural tube-like structures (rosettes), and to express specific markers (Sox1, Otx2, Lix1, EvI1, Rspo3) during rosette formation. The results showed that various effects of the selected compounds on early neural development could be specifically revealed in vitro through related alterations of neurogenic differentiation of hESC. Furthermore, it was possible to discriminate toxicants acting at different time points during embryonic development and, therefore, responsible for distinct adverse effects on neural tube formation. By comparing four different hESC lines, we observed a significant (up to fivefold) variability of the line-dependent response to toxicants. We highlight at least two sources of variability: one related to the heterogeneity of hESC lines in culture (stemness/commitment profiles); the second to possible genetically determined differences in individual sensitivity to teratogens.

Isl1 mediates mesenchymal expansion in the developing external genitalia via regulation of Bmp4, Fgf10 and Wnt5a

Genital malformations are among the most common human birth defects, and both genetic and environmental factors can contribute to these malformations. Development of the external genitalia in mammals relies on complex signaling networks, and disruption of these signaling pathways can lead to genital defects. Islet-1 (ISL1), a member of the LIM/Homeobox family of transcription factors, has been identified as a major susceptibility gene for classic bladder exstrophy in humans, a common form of the bladder exstrophy-epispadias complex (BEEC), and is implicated in a role in urinary tract development. We report that deletion of Isl1 from the genital mesenchyme in mice led to hypoplasia of the genital tubercle and prepuce, with an ectopic urethral opening and epispadias-like phenotype. These mice also developed hydroureter and hydronephrosis. Identification of ISL1 transcriptional targets via ChIP-Seq and expression analyses revealed that Isl1 regulates several important signaling pathways during embryonic genital development, including the BMP, WNT, and FGF cascades. An essential function of Isl1 during development of the external genitalia is to induce Bmp4-mediated apoptosis in the genital mesenchyme. Together, these studies demonstrate that Isl1 plays a critical role during development of the external genitalia and forms the basis for a greater understanding of the molecular mechanisms underlying the pathogenesis of BEEC and urinary tract defects in humans.

Role of Matrix Gla protein in midface development: Recent advances

Craniofacial development is a delicate process that involves complex interactions among cells of multiple developmental origins, their migration, proliferation, and differentiation. Tissue morphogenesis of the craniofacial skeleton depends on genetic and environmental factors, and on specific signaling pathways, which are still not well understood. Developmental defects of the midface caused by the absence, delays, or premature fusion of nasal and maxillary prominences vary in severity; leading to clefts, hypoplasias, and midline expansion. In the current review, we focus on the importance of the chondrocranium in craniofacial growth and how its impaired development leads to midface hypoplasia. More importantly, we reported how Matrix Gla protein (MGP), a potent inhibitor of extracellular matrix mineralization, facilitates midface development by preventing ectopic calcification of the nasal septum. In fact, MGP may act as a common link in multiple developmental pathologies all showing midface hypoplasia caused by abnormal cartilage calcification. This brief review discusses the gap in knowledge in the field, raises pertinent questions, which remain unanswered, and sheds light on the future research directions.

Linear-No-Threshold Default Assumptions are Unwarranted for Cytotoxic Endpoints Independently Triggered by Ultrasensitive Molecular Switches

Crump's response in this issue to my critique of linear-no-threshold (LNT) default assumptions for noncancer and nongenotoxic cancer risks (Risk Analysis 2016; 36(3):589-604) is rebutted herein. Crump maintains that distinguishing between a low-dose linear dose response and a threshold dose response on the basis of dose-response data is impossible even for endpoints involving increased cytotoxicity. My rebuttal relies on descriptions and specific illustrations of two well-characterized ultrasensitive molecular switches that govern two key cytoprotective responses to cellular stress-heat shock response and antioxidant response element activation, respectively-each of which serve to suppress stress-induced apoptotic cell death unless overwhelmed. Because detailed dose-response data for each endpoint is shown to be J- or inverted-J-shaped with high confidence, and because independent pathways can explain background rates of apoptosis, LNT assumptions for this cytotoxic endpoint are unwarranted, at least in some cases and perhaps generally.

Ochratoxin A and T-2 Toxin Induce Clonogenicity and Cell Migration in Human Colon Carcinoma and Fetal Lung Fibroblast Cell Lines

T-2 toxin and Ochratoxin A (OTA) are toxic secondary metabolites produced by various fungi, and together they contaminate feedstuffs worldwide. T-2 toxin and OTA may exert carcinogenic action in rodent. Despite the various in vivo experiments, carcinogenicity of these two mycotoxins has not yet been proven for human. In this current study, we proposed to investigate, in Human colon carcinoma cells and fetal lung fibroblast-like cells transfected with MYC, the effect of T-2 toxin and OTA on cell clonogenicity and cell migration. Results of the present investigation showed that T2-toxin as well as OTA has an important clonogenic effect in all cell lines, suggesting that these mycotoxins could promote the transcription of c-myc gene. Furthermore, T-2 toxin and OTA enhanced the migration effect of HCT116 cells at very low concentrations, proposing that these mycotoxins may exhibit carcinogenesis-like properties in the studied cells.

MiR-122 partly mediates the ochratoxin A-induced GC-2 cell apoptosis

Ochratoxin A (OTA) is a mycotoxin which has been shown to be nephrotoxic, hepatotoxic, and immunotoxic to animals, and mainly exists in the mildew grain. MicroRNAs (miRNAs) regulate a wide variety of cellular processes. However, the toxic effects of OTA on the germ cell and whether miRNAs mediate the effects of OTA-induced GC-2 cell apoptosis are still not clear. In the present study, OTA treatment resulted in a dose-dependent increase apoptosis in GC-2 cells. MiR-122 was increased in the OTA-treated GC-2 cells. It showed that Bcl-w was down-regulated after OTA treatment, and caspase-3 was obviously activated. Cyclin G1 (CCNG1) was significantly decreased, and inversely the expression of p53 was increased. Inhibition of miR-122 partly relieved the OTA-induced GC-2 cell apoptosis. These results indicate that OTA induces GC-2 cell apoptosis by causing the increase of caspase-3 activity and that miR-122 partly mediates the OTA-induced cell apoptosis.

Ochratoxin A: developmental and reproductive toxicity-an overview

Ochratoxin A (OTA) is nephrotoxic, hepatotoxic, reprotoxic, embryotoxic, teratogenic, neurotoxic, immunotoxic, and carcinogenic for laboratory and farm animals. Male and female reproductive health has deteriorated in many countries during the last few decades. A number of toxins in environment are suspected to affect reproductive system in male and female. OTA is one of them. OTA has been found to be teratogenic in several animal models including rat, mouse, hamster, quail, and chick, with reduced birth weight and craniofacial abnormalities being the most common signs. The presence of OTA also results in congenital defects in the fetus. Neither the potential of OTA to cause malformations in human nor its teratogenic mode of action is known. Exposure to OTA leads to increased embryo lethality manifested as resorptions or dead fetuses. The mechanism of OTA transfer across human placenta (e.g., which transporters are involved in the transfer mechanism) is not fully understood. Some of the toxic effects of OTA are potentiated by other mycotoxins or other contaminants. Therefore, OTA exposure of pregnant women should be minimized. OTA has been shown to be an endocrine disruptor and a reproductive toxicant, with abilities of altering sperm quality. Other studies have shown that OTA is a testicular toxin in animals. Thus, OTA is a biologically plausible cause of testicular cancer in man.

Feeding a diet contaminated with ochratoxin A for broiler chickens at the maximum level recommended by the EU for poultry feeds (0.1 mg/kg). 2. Effects on meat quality, oxidative stress, residues and histological traits

The European Commission Recommendation 2006/576/EC indicates that the maximum tolerable level of ochratoxin A (OTA) in poultry feeds is 0.1 mg OTA/kg. Thirty-six 1-day-old male broiler chicks were divided into two groups, a control (basal diet) and an OTA (basal diet + 0.1 mg OTA/kg) group. The OTA concentration was quantified in serum, liver, kidney, breast and thigh samples. The thiobarbituric acid reactive substances (TBARS) content were evaluated in the liver, kidney, breast and thigh samples. The glutathione (GSH) content, and catalase (CAT) and superoxide dismutase (SOD) activity were measured in the liver and kidney samples. Histopathological traits were evaluated for the spleen, bursa of Fabricius and liver samples. Moreover, the chemical composition of the meat was analysed in breast and thigh samples. In the OTA diet-fed animals, a serum OTA concentration of 1.15 ± 0.35 ng/ml was found, and OTA was also detected in kidney and liver at 3.58 ± 0.85 ng OTA/g f.w. and 1.92 ± 0.21 ng OTA/g f.w., respectively. The TBARS content was higher in the kidney of the ochratoxin A group (1.53 ± 0.18 nmol/mg protein vs. 0.91 ± 0.25 nmol/mg protein). Feeding OTA at 0.1 mg OTA/kg also resulted in degenerative lesions in the spleen, bursa of Fabricius and liver. The maximum tolerable level of 0.1 mg OTA/kg, established for poultry feeds by the EU, represents a safe limit for the final consumer, because no OTA residues were found in breast and thigh meat. Even though no clinical signs were noticed in the birds fed the OTA-contaminated diet, moderate histological lesions were observed in the liver, spleen and bursa of Fabricius.

Ochratoxin A causes oxidative stress and cell death in rat liver

The effect of ochratoxin A (OTA) on oxidant/antioxidant status and on histopathological changes and apoptotic cell death in livers of male Sprague-Dawley rats has been investigated. OTA (0.5 mg/kg body weight/day) was administered by oral route for 14 days. Plasma biochemical parameters, activities of liver selenoenzymes (glutathione peroxidase-1, thioredoxin reductase) and antioxidant enzymes (catalase, superoxide dismutase, glutathione S-transferase), and levels of total glutathione and thiobarbituric acid reactive substance in hepatic tissue were measured. In addition, histopathological examinations were performed and apoptotic cell death of hepatocytes was evaluated by the TdT-mediated dUTP nick-end labelling (TUNEL) assay. OTA exposure was found to induce focal necrosis of hepatocytes and mononuclear cell infiltration. Besides, exposure to OTA caused an imbalance in oxidant and antioxidant parameters in the rat liver, as evidenced by significant decreases in glutathione S-transferase activity and glutathione levels, and marked increases in concentrations of thiobarbituric acid reactive substances. Furthermore, TUNEL analysis revealed a significant ~2.7-fold increase in the number of TUNEL-positive liver cells of rats exposed to OTA compared to the control group. The results of this study showed that oxidative stress is at least one of the mechanisms underlying the hepatic toxicity of OTA, and that both necrosis and apoptosis are types of cell death in the hepatic toxicity of this mycotoxin.

Ochratoxin a and mitotic disruption: mode of action analysis of renal tumor formation by ochratoxin A

The mycotoxin and food contaminant ochratoxin A (OTA) is a potent renal carcinogen in rodents, but its mode of action (MoA) is still poorly defined. In 2006, the European Food Safety Authority concluded that there is a "lack of evidence for the existence of OTA-DNA adducts" and thus insufficient evidence to establish DNA reactivity as a MoA for tumor formation by OTA. In reviewing the available database on OTA toxicity, a MoA for renal carcinogenicity of OTA is developed that involves a combination of genetic instability and increased proliferative drive as consequences of OTA-mediated disruption of mitosis, whereby the organ- and site-specificity of tumor formation by OTA is determined by selective renal uptake of OTA into the proximal tubule epithelium. The proposed MoA is critically assessed with respect to concordance of dose-response of the suggested key events and tumor formation, their temporal association, consistency, and biological plausibility. Uncertainties, data gaps and needs for further research are highlighted.

Toxico-Pathological Effects of In Ovo Inoculation of Ochratoxin A (OTA) in Chick Embryos and Subsequently in Hatched Chicks

This study was designed to investigate the toxico-pathological effects of in ovo inoculation of ochratoxin A (OTA) in chicken embryos and subsequently in the hatching chicks. Nine hundred fertile white leghorn (WL) layer breeder eggs were divided into eight groups (A–H). Group A was maintained as untreated control, whereas group B was kept as sham control (10 µL of 0.1 M NaHCO3 solution). Before incubation, groups C, D, E, F, G, and H were injected with 0.01, 0.03, 0.05, 0.10, 0.50, and 1.00 µg OTA/egg, respectively. At 53 hrs of incubation, crown to rump length, optic cups, and eye lens diameters were significantly ( p ≤ .05) lower, whereas neural tube closure defects were higher in the OTA-treated embryos. Teratogenic defects (studied at day 9 of incubation) and embryonic mortalities were higher in the groups administered high doses of OTA. A significant increase was noted in the serum concentration of ALT, urea, and creatinine, along with higher weights of liver and kidney, in chicks hatched from OTA-contaminated eggs. These findings suggested that there are teratogenic and substantive toxicological risks in the developing chicken embryos and hatched chicks that could be exposed to OTA in ovo.

Limb-body wall defect. Is there a defensible hypothesis and can it explain all the associated anomalies?

Aside from gastroschisis and omphalocele, major defects of the ventral body (thoracoabdominal) wall are relatively uncommon and almost universally lethal. They are most often associated with other anomalies including those of the limbs that may range from amelia to mild positional deformations, unusual craniofacial malformations, and a variety of visceral abnormalities that include the heart, lungs, genitourinary system, and gut. This complex of ventral wall anomalies has been discussed under a broad and changing nomenclature that has included amniotic band disruption complex, amnion rupture sequence, limb-body wall defect (or complex), and simply body wall complex. Three major theories have been suggested to explain this complex: early amnion rupture (operating through uterine pressure and/or disruption by amniotic bands), vascular compromise (primarily hypoperfusion), and an early intrinsic defect of the developing embryo. We present four patients that illustrate the spectrum of ventral body wall defects, and from there critique the current hypotheses of pathogenesis. We conclude that this association of malformations originates as early as the embryonic disc stage, and that some of the observed associated anomalies are secondary complications of the primary disturbance in embryogenesis. We propose a new explanation for the atypical facial clefts and cranial malformations that are often observed.

Embryology and bony and pelvic floor anatomy in the bladder exstrophy-epispadias complex

The exstrophy-epispadias complex is a complex congenital anomaly that, although rare, remains the largest genitourinary birth defect that is surgically correctable. The primary defect in exstrophy is a derangement in midline developmental that presents with a spectrum of severity. In its mildest form, epispadias, the dorsal urethral unit is not fused and has failed to form into a tube. Next, patients with classic bladder exstrophy present with a bladder and urethra open and continuous with the abdominal wall; also associated is a failure of the abdominal muscles, pelvic ring, and pelvic floor musculature to fuse in the midline. Cloacal exstrophy, the most severe variant, includes exstrophied hindgut tube and a more severe degree of concomitant congenital derangements of musculoskeletal, genitourinary, gastrointestinal, and neurological systems. The embryology of the exstrophy-epispadias complex has been long studied, yet debate still exists over the specific origins of the anomaly. This article covers the embryologic theories of this congenital defect and the subsequent bony pelvic and pelvic floor muscular defects characteristic of exstrophy. Primarily, the anatomic focus will be on classic bladder exstrophy because it is the most common and well studied to date.

The embryologic origin of ventral body wall defects

Ventral body wall defects include ectopia cordis, bladder exstrophy, and the abdominal wall malformations gastroschisis and omphalocele. The etiology of ectopia cordis, gastroschisis, and bladder exstrophy is not known, but they may be linked to abnormalities in the lateral body wall folds responsible for closing the thoracic, abdominal, and pelvic portions of the ventral body wall. These folds form in the fourth week (postfertilization) of development as a combination of the parietal layer of lateral plate mesoderm and overlying ectoderm and must move ventrally to meet in the midline. There are differential rates of cell proliferation in the folds and asymmetries in their movement that may be involved in teratogenic effects of toxic factors. Also, the fusion process between the folds is complex, involving cell-to-cell adhesion, cell migration, and cell reorganization and all of these phenomena may be targets for disruption, leading to malformations. In this regard, closure of the ventral body wall is likened to neural tube closure and involves similar processes. It also encompasses a similar time frame during development, such that most neural tube and ventral body wall defects have their origins during the fourth week of development. Omphalocele is a separate entity whose etiology is known. This defect is attributed to a failure of gut loops to return to the body cavity after their normal physiological herniation into the umbilical cord from the 6th to 10th week of development. Thus, the origin of this defect is completely different from that of the ventral body wall malformations.

Genesis of teratogen-induced holoprosencephaly in mice

Evidence from mechanical, teratological, and genetic experimentation demonstrates that holoprosencephaly (HPE) typically results from insult prior to the time that neural tube closure is completed and occurs as a consequence of direct or indirect insult to the rostral prechordal cells that induce the forebrain or insult to the median forebrain tissue, itself. Here, we provide an overview of normal embryonic morphogenesis during the critical window for HPE induction, focusing on the morphology and positional relationship of the developing brain and subjacent prechordal plate and prechordal mesoderm cell populations. Subsequent morphogenesis of the HPE spectrum is then examined in selected teratogenesis mouse models. The temporal profile of Sonic Hedgehog expression in rostral embryonic cell populations and evidence for direct or indirect perturbation of the Hedgehog pathway by teratogenic agents in the genesis of HPE is highlighted. Emerging opportunities based on recent insights and new techniques to further characterize the mechanisms and pathogenesis of HPE are discussed.

Teratogens inducing congenital abdominal wall defects in animal models

Congenital abdominal wall defects are common anomalies which include gastroschisis, omphalocele and umbilical cord hernia. Recent reports indicate that gastroschisis is increasing in prevalence, whereas omphalocele has remained steady, suggesting that environmental factors may play a part in their pathogenesis. The aim of this study is to review animal teratogen studies resulting in abdominal wall defects to investigate their possible causes. Each report was examined not only for the teratogens causing the defects, but also to carefully identify the defect occurring and its correlation with the known clinical anomalies. We found many discrepancies between the nomenclature used by animal teratology investigators and that used by clinicians. We were able to confirm the induction of gastroschisis by 22 teratogens, omphalocele by 9 teratogens and umbilical cord hernia by 8. There is no doubt that environmental factors may be responsible, at least in part, for all three of the clinical abdominal wall defects. Future studies should take care to appreciate the differences between these anomalies and describe them in detail, so that accurate and meaningful conclusions can be obtained.

Seasonal variations in frontoethmoidal meningoencephalocele births in Cambodia

OBJECT

Frontoethmoidal meningoencephalocele (fMEC) is relatively common in many Southeast Asian countries, with devastating aesthetic and social consequences for affected children. No cause has been detected to date. Among other factors, the authors of this paper attempt to identify a statistically significant difference in the spread of fMEC births throughout the year compared with other births. This seasonal variation in the incidence of fMEC births may provide clues to the causes of this condition.

METHODS

From a group of 175 children with fMEC who underwent surgery at the authors' humanitarian institution (Children's Surgical Centre) in Phnom Penh between 2004 and 2008, 86 children were studied. These children were born at full term and had an accurately recorded date of birth. The birth dates of this fMEC group were compared with a group of > 15,000 other live births at one of the main maternity units in Phnom Penh in 2005 and 2006.

RESULTS

Seasonal variation in incidence of fMEC by month of birth was highly statistically significant (p < 0.001), with the peak of births occurring in the dry season (between March and May). This is in contrast to the control group, in which there was an equal distribution of births throughout the year. More than 85% of the parents of children with fMEC who the authors treated were farmers, but this figure reflects the composition of the Cambodian population.

CONCLUSIONS

Uneven spread in the incidence of fMEC births throughout the year suggests that a seasonal factor during the wet season may be suspected in the pathogenesis of fMEC in Cambodia.

The exstrophy-epispadias complex

Exstrophy-epispadias complex (EEC) represents a spectrum of genitourinary malformations ranging in severity from epispadias (E) to classical bladder exstrophy (CEB) and exstrophy of the cloaca (EC). Depending on severity, EEC may involve the urinary system, musculoskeletal system, pelvis, pelvic floor, abdominal wall, genitalia, and sometimes the spine and anus. Prevalence at birth for the whole spectrum is reported at 1/10,000, ranging from 1/30,000 for CEB to 1/200,000 for EC, with an overall greater proportion of affected males. EEC is characterized by a visible defect of the lower abdominal wall, either with an evaginated bladder plate (CEB), or with an open urethral plate in males or a cleft in females (E). In CE, two exstrophied hemibladders, as well as omphalocele, an imperforate anus and spinal defects, can be seen after birth. EEC results from mechanical disruption or enlargement of the cloacal membrane; the timing of the rupture determines the severity of the malformation. The underlying cause remains unknown: both genetic and environmental factors are likely to play a role in the etiology of EEC. Diagnosis at birth is made on the basis of the clinical presentation but EEC may be detected prenatally by ultrasound from repeated non-visualization of a normally filled fetal bladder. Counseling should be provided to parents but, due to a favorable outcome, termination of the pregnancy is no longer recommended. Management is primarily surgical, with the main aims of obtaining secure abdominal wall closure, achieving urinary continence with preservation of renal function, and, finally, adequate cosmetic and functional genital reconstruction. Several methods for bladder reconstruction with creation of an outlet resistance during the newborn period are favored worldwide. Removal of the bladder template with complete urinary diversion to a rectal reservoir can be an alternative. After reconstructive surgery of the bladder, continence rates of about 80% are expected during childhood. Additional surgery might be needed to optimize bladder storage and emptying function. In cases of final reconstruction failure, urinary diversion should be undertaken. In puberty, genital and reproductive function are important issues. Psychosocial and psychosexual outcome depend on long-term multidisciplinary care to facilitate an adequate quality of life.

Developmental toxicity of Ochratoxin A in rat embryo midbrain micromass cultures

Embryonic midbrain micromass cultures were exposed for five days to ochratoxin A (OTA) at seven concentrations (ranging from 0.16 to 10 μg/mL). Cell viability was assessed in neutral red uptake test (NRU), and differentiation – by immunoenzymatic determination of structural proteins (β_III-tubulin, MAP2, GFAP) expression level as well as by computer image analysis. Dose dependent decrease in cell number and differentiation was observed. Concentration-response curves were analysed and the mean inhibition concentrations (μg/mL) for cytotoxicity (IC₅₀) and differentiation (ID₅₀) were calculated. There were no significant differences in the sensitivity of neurons in early and late stage of differentiation and astrocytes to the toxic activity of this compound. For all endpoints ID₅₀ value was very low (< 10 μg/mL) so OTA was classified as a strong teratogen. IC₅₀/ ID₅₀ ratios <2 pointed out that with harmful action of OTA the basic cytotoxicity should be connected.

Ochratoxin A: The Continuing Enigma

The mycotoxin ochratoxin A (OTA) has been linked to the genesis of several disease states in both animals and humans. It has been described as nephrotoxic, carcinogenic, teratogenic, immunotoxic, and hepatotoxic in laboratory and domestic animals, as well as being thought to be the probable causal agent in the development of nephropathies (Balkan Endemic Nephropathy, BEN and Chronic Interstitial Nephropathy, CIN) and urothelial tumors in humans. As a result, several international agencies are currently attempting to define safe legal limits for OTA concentration in foodstuffs (e.g., grain, meat, wine, and coffee), in processed foods, and in animal fodder. In order to achieve this goal, an accurate risk assessment of OTA toxicity including mechanistic and epidemiological studies must be carried out. Ochratoxin has been suggested by various researchers to mediate its toxic effects via induction of apoptosis, disruption of mitochondrial respiration and/or the cytoskeleton, or, indeed, via the generation of DNA adducts. Thus, it is still unclear if the predominant mechanism is of a genotoxic or an epigenetic nature. One aspect that is clear, however, is that the toxicity of OTA is subject to and characterized by large species- and sex-specific differences, as well as an apparently strict structure-activity relationship. These considerations could be crucial in the investigation of OTA-mediated toxicity. Furthermore, the use of appropriate in vivo and in vitro model systems appears to be vital in the generation of relevant experimental data. The intention of this review is to collate and discuss the currently available data on OTA-mediated toxicity with particular focus on their relevance for the in vivo situation, and also to suggest possible future strategies for unlocking the secrets of ochratoxin A.

Development of gastroschisis: review of hypotheses, a novel hypothesis, and implications for research

Gastroschisis, a ventral body wall defect, is a continuing challenge and concern to researchers, clinicians, and epidemiologists seeking to identify its cause(s) and pathogenesis. Concern has been renewed in recent years because, unlike most other birth defects, rates of gastroschisis are reportedly increasing in many developed and developing countries. No tenable explanation or specific causes have been identified for this trend. Rates of gastroschisis are particularly high among pregnancies of very young women. Such an intriguing association, not observed to this degree with other birth defects, may afford clues to the defect's cause. Understanding the causes of gastroschisis may provide insight to the defect's origin. In pursuing such causal studies, it would be helpful to understand the embryogenesis of gastroschisis. To date, four main embryologic hypotheses have been proposed: (1) Failure of mesoderm to form in the body wall; (2) Rupture of the amnion around the umbilical ring with subsequent herniation of bowel; (3) Abnormal involution of the right umbilical vein leading to weakening of the body wall and gut herniation; and (4) Disruption of the right vitelline (yolk sac) artery with subsequent body wall damage and gut herniation. Although based on embryological phenomena, these hypotheses do not provide an adequate explanation for how gastroschisis would occur. Therefore, we propose an alternative hypothesis, based on well described embryonic events. Specifically, we propose that abnormal folding of the body wall results in a ventral body wall defect through which the gut herniates, leading to the clinical presentation of gastroschisis. This hypothesis potentially explains the origin of gastroschisis as well as that of other developmental defects of the ventral wall.

Omphalocele induction in the chick embryo by administration of cadmium

BACKGROUND

Ventral body wall (VBW) defects occur in 1:2000 live births. We examined the association of VBW defect with somite abnormality and lordosis in the chick using in vitro and in ovo methods.

METHODS

Explanted chick embryos were treated at 60 hours with 50 microL sodium acetate or 0.001% cadmium acetate solution to produce VBW defects. Mortality and abnormality rates were assessed. A further cohort of chicks was treated in ovo by dropping 50 microL 0.001% to 0.01% cadmium acetate onto the embryo and allowing development to 16.5 days for further assessment of the defect and skeletal staining with alcian blue and alizarin red.

RESULTS

Cadmium treatment at 24 hours induced VBW defects in chicks treated in both shell-less culture and in ovo. Material herniating through the VBW defects was covered by a membrane in all fresh specimens. Membrane removal revealed large defects containing liver and bowel. These criteria clearly indicate that the defect observed is an omphalocele. Affected embryos had reduced somite numbers within 24 hours. Chicks exhibiting exomphalos at 16.5 days invariably had lumbosacral lordosis.

CONCLUSIONS

The cadmium-treated chick embryo is a reliable model for exomphalos. A positive association was found between exomphalos and lumbar lordosis in the chick.

Ochratoxin A: An overview on toxicity and carcinogenicity in animals and humans

Ochratoxin A (OTA) is a ubiquitous mycotoxin produced by fungi of improperly stored food products. OTA is nephrotoxic and is suspected of being the main etiological agent responsible for human Balkan endemic nephropathy (BEN) and associated urinary tract tumours. Striking similarities between OTA-induced porcine nephropathy in pigs and BEN in humans are observed. International Agency for Research on Cancer (IARC) has classified OTA as a possible human carcinogen (group 2B). Currently, the mode of carcinogenic action by OTA is unknown. OTA is genotoxic following oxidative metabolism. This activity is thought to play a central role in OTA-mediated carcinogenesis and may be divided into direct (covalent DNA adduction) and indirect (oxidative DNA damage) mechanisms of action. Evidence for a direct mode of genotoxicity has been derived from the sensitive 32P-postlabelling assay. OTA facilitates guanine-specific DNA adducts in vitro and in rat and pig kidney orally dosed, one adduct comigrates with a synthetic carbon (C)-bonded C8-dG OTA adduct standard. In this paper, our current understanding of OTA toxicity and carcinogenicity are reviewed. The available evidence suggests that OTA is a genotoxic carcinogen by induction of oxidative DNA lesions coupled with direct DNA adducts via quinone formation. This mechanism of action should be used to establish acceptable intake levels of OTA from human food sources.

Expression of COX-2 and hsp72 in peritoneal macrophages after an acute ochratoxin A treatment in mice

Ochratoxin A (OTA) is a secondary fungal metabolite produced by Aspergillus and Penicillium strains that elicits a broad spectrum of toxicological effects in animals and man. A single oral OTA administration (10 mg/kg) in mice induced after 24 h oxidative damage and polymorphonuclear leukocyte (PMN) infiltration in parenchymal organs. In fact, OTA treatment increased lipid peroxidation (via malondialdehyde formation) in kidney and liver and PMN accumulation in duodenum, as shown by myeloperoxidase activity. Following in vivo OTA treatment an increase of cyclooxygenase-2 and of heat shock protein 72 expression was evidenced in peritoneal macrophage lysates by Western blot. That OTA modulates these proteins involved in the inflammatory process indicates that the mycotoxin is able to activate immune cells. This study suggests that the oxidative stress, the neutrophil accumulation in parenchymal tissues and the modulation of inflammatory parameters in peritoneal macrophages induced by OTA are involved in its toxicity, and represent early events related to several aspects of OTA mycotoxicosis.

Investigation of the teratogenic potential of ochratoxin A and B using the FETAX system

BACKGROUND

Ochratoxin A (OTA) is a mycotoxin produced by certain Aspergillus and Penicillium species. It has been observed to be teratogenic in a number of animal models including rat, mouse, hamster, and chick, with reduced birth weight and craniofacial abnormalities being the most commonly observed malformations. Neither the potential of OTA to cause malformations in humans nor its teratogenic mode of action is known. The FETAX system is an embryotoxicity assay system, with a high correlation to animal models and epidemiological data. Analysis of OTA-mediated teratogenesis using this system could provide a useful tool for the generation of high numbers of samples for mechanistic studies.

METHODS

Using the standard ASTM 96-hr exposure protocol, the effect of OTA and its structural analogue OTB on the development of Xenopus laevis embryos in vitro was assessed. The accumulation of both substances in Xenopus embryos was also examined using tritiated OTA and OTB.

RESULTS

Both OTA and OTB caused craniofacial malformations, while OTA also caused reduced embryo growth. As expected, OTA was far more potent in inducing these effects than OTB. This could at least in part be due to greater levels of OTA being accumulated within the embryos.

CONCLUSIONS

The ability of FETAX to differentiate between close structural analogues indicates the assay has great potential for the elucidation of the embryotoxic and teratogenic mechanisms of action. Hence, the model could provide a suitable system for the investigation of other known teratogens or for the pre-screening of new agents for teratogenic potential.

Toxicokinetics and toxicodynamics of ochratoxin A, an update

Ochratoxin A (OTA) is a mycotoxin produced by fungi of two genera: Penicillium and Aspergillus. OTA has been shown to be nephrotoxic, hepatotoxic, teratogenic and immunotoxic to several species of animals and to cause kidney and liver tumours in mice and rats. Because of differences in the physiology of animal species, wide variations are seen in the toxicokinetic patterns of absorption, distribution and elimination of the toxin. Biotransformation of OTA has not been entirely elucidated. At present, data regarding OTA metabolism are controversial. Several metabolites have been characterized in vitro and/or in vivo, whereas other metabolites remain to be characterized. Several major mechanisms have been shown as involved in the toxicity of OTA: inhibition of protein synthesis, promotion of membrane peroxidation, disruption of calcium homeostasis, inhibition of mitochondrial respiration and DNA damage. The contribution of metabolites in OTA genotoxicity and carcinogenicity is still unclear. The genotoxic status of OTA is still controversial because contradictory results were obtained in various microbial and mammalian tests, notably regarding the formation of DNA adducts. More recent studies are focused on the OTA ability to disturb cellular signalling and regulation, to modulate physiological signals and thereby to influence cells viability and proliferation. The present paper offers an update on these different issues. In addition since humans and animals are likely to be simultaneously exposed to several mycotoxins, especially through their diet, the little information available on the combined effects of OTA and other mycotoxins has also been reviewed.

Effect in rats of simultaneous prenatal exposure to ochratoxin A and aflatoxin B1. I. Maternal toxicity and fetal malformations

Ochratoxin A (OA) and Aflatoxin B1 (AFB1), the food borne mycotoxins are produced by several fungal species of the genera Aspergillus and Penicillium. To determine the teratogenic effects, these mycotoxins were administered orally either individually or in combination to the pregnant Wistar rats on days 6-15 of gestation. OA and AFB1 were dissolved in corn oil and different doses of OA (0.125, 0.25, 0.50, and 0.75 mg/kg), AFB1 (0.125, 0.25, 0.50, and 1.00 mg/kg), and a combination of OA+AFB1 (0.125+0.125; 0.25+0.50; 0.50+0.25 mg/kg) were given by gastric intubation to rats. During dosing period, the body weight and body weight gains significantly decreased at a higher dosage, in both individual and combined treatments. In all the combination treatments, the percent implants resorbed, fetal body weights, and crown-rump lengths were comparable to those of controls and with the individual mycotoxin treatment. The number of dead fetuses was significantly increased in the high OA combination (OA+AFB1 0.50+0.25) group as compared with the other two combinations. OA and AFB1 alone and in combination caused various gross, skeletal, and visceral anomalies. The occurrence was considerably less pronounced in fetuses of AFB1 and combination groups as compared with those of OA group fetuses. The exencephaly, incomplete closure of skull, wavy and fused ribs, agenesis of the ischium bone, and enlarged renal pelvis, recorded in OA treatment and ear abnormality and incomplete ossification of skull bones observed in AFB1 when given individually, were not seen in combination groups. However, new manifestations, such as gastroschisis and syndactyly were observed and the incidence of cardiac defects was increased in fetuses due to the combined treatment. The results of the present study indicated that there is some interaction between these mycotoxins that resulted in reduced teratogenic activity of OA in the presence of AFB1. Apparently, new manifestations observed in combination treatment points to the potential threat of teratogenicity in terms of public health hazards.

Finally, a sense of closure? Animal models of human ventral body wall defects

Malformations concerning the ventral body wall constitute one of the leading categories of human birth defects and are present in about one out of every 2000 live births. Although the occurrence of these defects is relatively common, few detailed experimental studies exist on the development and closure of the ventral body wall in mouse and human. This field is further complicated by the array of theories on the pathogenesis of body wall defects and the likelihood that there is no single cause for these abnormalities. In this review, we summarize what is known concerning the mechanisms of normal ventral body wall closure in humans and mice. We then outline the theories that have been proposed concerning human body wall closure abnormalities and examine the growing number of mouse mutations that impact normal ventral body wall closure. Finally, we speculate how studies in animal models such as mouse and Drosophila are beginning to provide a much-needed mechanistic framework with which to identify and characterize the genes and tissues required for this vital aspect of human embryogenesis.

Loss of AP-2alpha impacts multiple aspects of ventral body wall development and closure

Human birth defects involving the ventral body wall are common, yet little is known about the mechanism of body wall closure in mammals. The AP-2alpha transcription factor knock-out mouse provides an exceptional tool to understand this particular pathology, since it has one of the most severe ventral body wall closure defects, thoracoabdominoschisis. To gain insight into the complex morphological events responsible for body wall closure, we have studied this developmental process in AP-2alpha knock-out mice. Several tissues involved in normal ventral body wall closure are defective in the absence of AP-2alpha, including those associated with the primary body wall, the umbilical ring, and the mesoderm of the secondary body wall. These defects, coupled with the expression pattern of AP-2alpha, suggest that AP-2alpha is involved in multiple developmental mechanisms directing the morphogenesis of the ventral body wall, including cell migration, differentiation, and death. There is a failure of migration and fusion of the body folds at the umbilical ring, as well as in the formation and migration of the abdominal bands and ventral musculature. Furthermore, the mechanism of cell deposition at the umbilical ring is disturbed. Consequently, the mesodermal compartment of the body wall is underdeveloped. We also suggest that AP-2alpha is required for signaling from the surface ectoderm to the underlying mesoderm for proper development and closure of the ventral body wall. These findings provide a fundamental understanding of how AP-2alpha functions in the closure of the ventral body wall, as well as offer insight into related human birth defects.

Inhibitory effects of ochratoxin A on nerve growth factor-induced neurite extension through downregulation of p38 MAP kinase and AP-1 activation in cultured pheochromocytoma cells

Ochratoxin A (OTA) induces microcephaly in animals and in vitro cultured whole embryos. Inhibition of neuronal cell differentiation was proposed as underlying mechanisms responsible for OTA-induced microcephaly. Previously it was found that OTA inhibited differentiation of cultured rat embryonic midbrain cells into neurons. In this study, the influence of OTA on differentiation in PC-12 cells, a widely accepted model cells for study of neuronal differentiation was examined. Cell differentiation was assessed by measurement of neurite extension and quantified by the number of neurites extended. OTA decreased serum and nerve growth factor (NGF)-induced neurite extension in a concentration-dependent manner. Since MAP kinase and transcription factors have been implicated in cell differentiation of neuronal cells, and our previous study demonstrated that p38 MAP kinase and AP-1 are activated during PC 12 cell differentiation, the effect of OTA on NGF-induced p38 MAP kinase and transcription factor activation was examined. Co-treatment of OTA with NGF resulted in inhibition of NGF-induced p38 MAP kinase and AP-1 activation. Moreover, SB203580, a specific inhibitor of p38 MAP kinase blocked p38 MAP kinase and AP-1 activation accompanied by further inhibition of neurite extension. The present study shows that OTA inhibited cell differentiation of PC-12 cells, and this inhibitory effect may be related to inhibition of the activation of the p38 MAP kinase in conjunction with transcription factors AP-1. This finding suggests that the inhibitory effect on neuronal cell differentiation by OTA might be a mechanism responsible for OTA-induced microcephaly.

Apoptosis and oxidative stress induced by ochratoxin A in rat kidney

Ochratoxin A (OTA) is a widespread mycotoxin produced by several species of fungi. OTA induces a tubular-interstitial nephropathy in humans and in animals. It has been implicated as one of the aetiological agents involved in the development of endemic nephropathy. OTA-induced oxidative stress and apoptosis may play key roles in the development of chronic tubulointerstitial nephritis connected to the long-term exposure to this food contaminant. We studied the effects of low doses of OTA on kidney cells. Wistar rats were treated with 120 microg OTA/kg bodyweight daily, for 10, 30 or 60 days. Toxin concentration in kidney was proportional to the time of exposure, and amounted to 547.2, 752.5 and 930.3 ng OTA/g kidney tissue after 10, 30 and 60 days, respectively. OTA treatment caused an increased number of cells undergoing apoptosis in both proximal and distal epithelial kidney cells. The apoptotic cells were visualised using the TUNEL assay and staining with haematoxylin and eosin in situ. The number of apoptotic cells in rats treated for 10, 30 and 60 days increased by 5-, 6.4- and 12.7-fold, respectively, compared with the control cells. However, DNA electrophoresis did not show characteristic fragmentation (DNA laddering). The oxidative stress was evident via increased malondialdehyde formation. The concentration of lipid peroxides showed an increase (36%), but the activity of superoxide dismutase decreased (26%) in 60-day treated rats. In spite of the observed biochemical and morphological changes in the kidney cells, renal functional status was preserved to the end of experiment. This study demonstrates that a combination of morphologic and biochemical markers can be used to monitor early cell death in OTA-induced renal injury. We have shown that the exposure to the relatively low OTA concentrations has activated apoptotic processes and oxidative damage in kidney cells.

Teratogenesis of holoprosencephaly

Teratogenic causes of holoprosencephaly are critically assessed. A brief general review of holoprosencephaly is followed by four tables summarizing etiologic factors. Subjects evaluated here include: 1) maternal diabetes; 2) ethyl alcohol; 3) retinoic acid; 4) mutated genes and teratogens involving the sonic hedgehog signaling network and cholesterol biosynthesis; and 5) cholesterol trafficking, sterol adducts, target tissue response, and sterol sensing domain.

Inhibitory effect of peroxisome proliferator-activated receptor gamma agonist on ochratoxin A-induced cytotoxicity and activation of transcription factors in cultured rat embryonic midbrain cells

The effects of 15-deoxy-delta12,14-prostaglandin J2 (15-deoxy PGJ2) on ochratoxin A (OTA)-induced neurotoxicity and on the activation of transcription factors activator protein-1 (AP-1) and nuclear factor-kappa B (NF-kappaB) were investigated in cultured rat embryonic midbrain cells. Twelve-day rat embryo midbrain cells were cultured for 48 h. OTA (0.5 or 1 microg/ml) and/or 1.5-deoxy PGJ2 (0.5 microM) were then added for 48 h. Cell number and neurite outgrowth were determined to assess the neurotoxicity of OTA. AP-1 and NF-kappaB activation was determined by gel mobility shift assay after 3 h of exposure to OTA and/or 15-deoxy PGI2. OTA caused concentration-dependent reductions in neurite outgrowth and cell number, and induced AP-1 and NF-kappaB activation. Cotreatment with 15-deoxy PGJ2 (0..5 microM) blocked OTA-induced decrease in neurite outgrowth and cell number and inhibited AP-1 and NF-kappaB activation. 15-Deoxy PGJ2 (0.5 microM) caused the expression of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) in the cells. Results show that 1.5-deoxy PGJ2 blocked OTA-induced neurotoxicity by inhibiting AP-1 and NF-kappaB activation in cultured rat embryonic midbrain cells.

AP-2-null cells disrupt morphogenesis of the eye, face, and limbs in chimeric mice

The homozygous disruption of the mouse AP-2 gene yields a complex and lethal phenotype that results from defective development of the neural tube, head, and body wall. The severe and pleiotropic developmental abnormalities observed in the knockout mouse suggested that AP-2 may regulate several morphogenic pathways. To uncouple the individual developmental mechanisms that are dependent on AP-2, we have now analyzed chimeric mice composed of both wild-type and AP-2-null cells. The phenotypes obtained from these chimeras indicate that there is an independent requirement for AP-2 in the formation of the neural tube, body wall, and craniofacial skeleton. In addition, these studies reveal that AP-2 exerts a major influence on eye formation, which is a critical new role for AP-2 that was masked previously in the knockout mice. Furthermore, we also have uncovered an unexpected influence of AP-2 on limb pattern formation; this influence is typified by major limb duplications. The range of phenotypes observed in the chimeras displays a significant overlap with those caused by teratogenic levels of retinoic acid, strongly suggesting that AP-2 is an important component of the mechanism of action of this morphogen.

Formation of DNA adducts in tissues of mouse progeny through transplacental contamination and/or lactation after administration of a single dose of ochratoxin A to the pregnant mother

Ochratoxin A (OTA) is a mycotoxin which has been detected in foods of plant origin, in edible animal tissues, and in human sera, urine, and milk in many countries. OTA is nephrotoxic and carcinogenic in mice and rats and is suspected to play a key role in the etiology of Balkan endemic nephropathy and/or associated urinary tract tumors. In the present study, some early signs of genetic impairment, including the presence of DNA adducts in target tissues from the progeny of mice after administration of a single OTA dose during late pregnancy, have been investigated. By the 32P-postlabeling method, several characteristic DNA adducts with the same Rf values were detected in kidney and liver of both the OTA-treated mice and their progeny the fetus and the offspring. No adduct was found in tissues from control animals. Different adducts were most important in kidney and liver DNA and some were organ-specific. High levels of DNA adducts were detected in the kidneys of male progeny, whereas in the female progeny and the mothers they were detected almost exclusively in the liver. This result correlates well with the carcinogenicity in mice: the target organ for males is the kidney, while for females it is the liver. High levels of DNA adducts were also found in fetuses. These results provide evidence for a direct genotoxic action of OTA in the progeny through transplacental contamination, which constitutes a new serious health hazard of exposure to this toxin.

Pathogenesis of caudal dysgenesis/sirenomelia induced by ochratoxin A in chick embryos

Caudal dysgenesis/sirenomelia is a malformation complex for which the pathogenesis is controversial. This report describes the particular vulnerability of specific caudal structures to Ochratoxin A (OA), a fungal toxin, as the basis for caudal dysgenesis in an avian model. The experimental procedure involved injection of 1 microgram of OA into the air sac of eggs that had been incubated for 48 hours prior to treatment (i.e., embryos that had reached Hamburger and Hamilton stage 9-10 (6-10 somite pairs) [Hamburger and Hamilton (1951) Dev. Dyn. 195:231-272] by the time of treatment). Six to twelve hours following OA injection, excessive cell death, as shown by vital staining and routine histology, was evident in selected cell populations, including cells of the caudal-most mesoderm (the mesoderm that apparently forms the external genitalia and median infraumbilical region), the tail bud, and the neural tube caudal to the wing buds (corresponding to the level of the presomitic mesoderm). The notochord was not severely affected, although there were degenerative changes in the presomitic mesoderm. Except for positional abnormalities, development of the lateral plate mesoderm from which the leg buds are derived appeared relatively normal in most of the treated embryos. Six days post-treatment, varying degrees of caudal dysgenesis, presenting in severely affected specimens as sirenomelia, were observed in approximately 30% of the surviving treated embryos. The potential basis for the differential vulnerability of the affected cell populations and, therefore, the cellular basis for the genesis of caudal dysgenesis/sirenomelia in this model are discussed.

Neural tube, skeletal and body wall defects in mice lacking transcription factor AP-2

The retinoic acid-inducible transcription factor AP-2 is expressed in epithelial and neural crest cell lineages during murine development. AP-2 can regulate neural and epithelial gene transcription, and is associated with overexpression of c-erbB-2 in human breast-cancer cell lines. To ascertain the importance of AP-2 for normal development, we have derived mice containing a homozygous disruption of the AP-2 gene. These AP-2-null mice have multiple congenital defects and die at birth. In particular, the AP-2 knockout mice exhibit anencephaly, craniofacial defects and thoraco-abdominoschisis. Skeletal defects occur in the head and trunk region, where many bones are deformed or absent. Analysis of these mice earlier in embryogenesis indicates a failure of cranial neural-tube closure and defects in cranial ganglia development. We have shown that AP-2 is a fundamental regulator of mammalian craniofacial development.

Prenatal craniofacial development: new insights on normal and abnormal mechanisms

Technical advances are radically altering our concepts of normal prenatal craniofacial development. These include concepts of germ layer formation, the establishment of the initial head plan in the neural plate, and the manner in which head segmentation is controlled by regulatory (homeobox) gene activity in neuromeres and their derived neural crest cells. There is also a much better appreciation of ways in which new cell associations are established. For example, the associations are achieved by neural crest cells primarily through cell migration and subsequent cell interactions that regulate induction, growth, programmed cell death, etc. These interactions are mediated primarily by two groups of regulatory molecules: "growth factors" (e.g., FGF and TGF alpha) and the so-called steroid/thyroid/retinoic acid superfamily. Considerable advances have been made with respect to our understanding of the mechanisms involved in primary and secondary palate formation, such as growth, morphogenetic movements, and the fusion/merging phenomenon. Much progress has been made on the mechanisms involved in the final differentiation of skeletal tissues. Molecular genetics and animal models for human malformations are providing many insights into abnormal development. A mouse model for the fetal alcohol syndrome (FAS), a mild form of holoprosencephaly, demonstrates a mid-line anterior neural plate deficiency which leads to olfactory placodes being positioned too close to the mid-line, and other secondary changes. Work on animal models for the retinoic acid syndrome (RAS) shows that there is major involvement of neural crest cells. There is also major crest cell involvement in similar syndromes, apparently including hemifacial microsomia. Later administration of retinoic acid prematurely and excessively kills ganglionic placodal cells and leads to a malformation complex virtually identical to the Treacher Collins syndrome. Most clefts of the lip and/or palate appear to have a multifactorial etiology. Genetic variations in TGF alpha s, RAR alpha s, NADH dehydrogenase, an enzyme involved in oxidative metabolism, and cytochrome P-450, a detoxifying enzyme, have been implicated as contributing genetic factors. Cigarette smoking, with the attendant hypoxia, is a probable contributing environmental factor. It seems likely that few clefts involve single major genes. In most cases, the pathogenesis appears to involve inadequate contact and/or fusion of the facial prominences or palatal shelves. Specific mutations in genes for different FGF receptor molecules have been identified for achondroplasia and Crouzon's syndrome, and in a regulatory gene (Msx2) for one type of craniosynostosis. Poorly co-ordinated control of form and size of structures, or groups of structures (e.g., teeth and jaws), by regulatory genes should do much to explain the very frequent "mismatches" found in malocclusions and other dentofacial "deformities". Future directions for research, including possibilities for prevention, are discussed.

Omphalocele and gastroschisis in Europe: a survey of 3 million births 1980-1990. EUROCAT Working Group

A total of 732 cases of omphalocele and 274 cases of gastroschisis was registered in 21 regional registers in Europe (EUROCAT registers) during the period 1980-1990. The total prevalence rates were 2.52 per 10,000 for omphalocele and 0.94 per 10,000 for gastroschisis. There was significant heterogeneity in total prevalence rates among regions for omphalocele. Consistently higher than average total prevalence rates of omphalocele were found in the five centers of the British Isles. This was in large part linked to the association between omphalocele and neural tube defects. A significant female excess among the cases of omphalocele associated with neural tube defects, in comparison with an insignificant male excess for other cases of omphalocele, was observed. Geographical differences in the total prevalence of gastroschisis are partly explained by differences in maternal age distributions in the populations surveyed. Omphalocele was an isolated malformation in 46% of cases; gastroschisis was isolated in 79% of cases. The average birthweight and gestational age of both isolated and multiply malformed cases of both omphalocele and gastroschisis were low, especially for multiply malformed cases, and to a greater extent for isolated gastroschisis than for isolated omphalocele. Prenatal diagnosis leading to termination of pregnancy was reported in 33.2% of omphalocele and in 26.5% of gastroschisis cases, demonstrating the considerable impact of current prenatal screening programs. On the basis of clinical manifestations, epidemiologic characteristics, and the presence and type of additional malformations, omphalocele and gastroschisis can be considered heterogeneous conditions.

Prenatal craniofacial development: new insights on normal and abnormal mechanisms

Technical advances are radically altering our concepts of normal prenatal craniofacial development. These include concepts of germ layer formation, the establishment of the initial head plan in the neural plate, and the manner in which head segmentation is controlled by regulatory (homeobox) gene activity in neuromeres and their derived neural crest cells. There is also a much better appreciation of ways in which new cell associations are established. For example, the associations are achieved by neural crest cells primarily through cell migration and subsequent cell interactions that regulate induction, growth, programmed cell death, etc. These interactions are mediated primarily by two groups of regulatory molecules: "growth factors" (e.g., FGF and TGFalpha) and the so-called steroid/thyroid/retinoic acid superfamily. Considerable advances have been made with respect to our understanding of mechanisms involved in primary and secondary palate formation, such as growth, morphogenetic movements, and the fusion/merging phenomenon. Much progress has been made on the mechanisms involved in the final differentiation of skeletal tissues. Molecular genetics and animal models for human malformations are providing many insights into abnormal development. A mouse model for the fetal alcohol syndrome(FAS), a mild form of holoprosencephaly, demonstrates a mid-line anterior neural plate deficiency which leads to olfactory placodes being positioned too close to the mid-line, and other secondary changes. Work on animal models for the retinoic acid syndrome (RAS) shows that there is major involvement of neural crest cells. There is also major crest cell involvement in similar syndromes, apparently including hemifacial microsomia. Later administration of retinoic acid prematurely and excessively kills ganglionic placodal cells and leads to a malformation complex virtually identical to the Treacher Collins syndrome. Most clefts of the lip and/or palate appear to have a multifactorial etiology. Genetic variations in TGF alpha s, RAR alpha s, NADH dehydrogenase, an enzyme involved in oxidative metabolism, and cytochrome P-450, a detoxifying enzyme, have been implicated as contributing genetic factors. Cigarette smoking, with the attendant hypoxia, is a probable contributing environmental factor. It seems likely that few clefts involve single major genes. In most cases, the pathogenesis appears to involve inadequate contact and/or fusion of the facial prominences or palatal shelves. Specific mutations in genes for different FGF receptor molecules have been identified for achondroplasia and Crouzon's syndrome, and in a regulatory gene (Msx2) for one type of craniosynostosis.(ABSTRACT TRUNCATED AT 400 WORDS)