The site of action of trypan blue in cardiac teratogenesis

Teratogenic effects of suramin on the chick embryo

Suramin, a polysulfonated naphthylamine, has been used for the chemotherapy of trypanosomiasis and onchocerciasis since about the 1920s. Currently, it is also being tested as an anticancer agent. It is hoped that suramin might stop the progression of some kinds of cancer since it has been found to inhibit the proliferation and migration of cells and the formation of new blood vessels. These processes are not only essential for the development and progression of cancer, but also for normal embryonic development. Suramin might, therefore, be a potent teratogen. In the literature, however, we have found only scant information on this subject. In the present study, we demonstrate the teratogenic effects of suramin on chick embryos. Suramin was injected into the coelomic cavity of chick embryos on incubation day (ID) 3. Following reincubation until ID 8, suramin-treated embryos ( n=50) were examined for congenital malformations and compared with a control group ( n=30). The survival rate of suramin-treated embryos was markedly reduced compared with controls (50% vs 90%). Among the 25 survivors the following malformations were recorded: caudal dysgenesia (100%), median facial clefts with hypertelorism (92%), malformations of the aortic arch arteries (88%), hypo-/aplasia of the allantoic vesicle (84%), microphthalmia (52%), abnormalities of the great arterial trunks (44%), unilateral or bilateral cleft lips (40%), heart defects with juxtaposition of the right atrial appendage (36%), persistence of the lens vesicle (32%), median clefts of the lower beak (8%), omphalocele (4%), and cloacal exstrophy (4%). These results show that suramin is a potent teratogen. The possible implications of our findings for human beings and the possible teratogenic mechanisms of suramin are discussed. Use of suramin in experimental teratology might help to clarify the morphogenesis of median facial clefts and of some congenital heart defects.

Hypoplasia of cushion ridges in the proximal outflow tract elicits formation of a right ventricle-to-aortic route in retinoic acid-induced complete transposition of the great arteries in the mouse: scanning electron microscopic observations of corrosion cast models

BACKGROUND

The major morphologic change associated with retinoic acid (RA)-induced complete transposition of the great arteries (TGA), a congenital malformation of the heart, was investigated in a mouse model in which TGA was found in 80% of surviving fetuses.

METHODS

Corrosion casts of embryonic hearts with or without prior exposure to retinoic acid were observed under a scanning electron microscope.

RESULTS

In control hearts, indentations caused by expanded parietal and septal ridges in the outflow tract established right ventricle-to-left ventral pulmonic and left ventricle-to-right dorsal aortic routes before the aorticopulmonary septum completion. In RA-treated hearts, indentations of proximal regions of the parietal and septal ridges were small in the proximal outflow tract, whereas those in the distal regions developed well. These morphological features in the RA-treated hearts elicited right ventricle-to-right ventral aortic and left ventricle-to-left dorsal pulmonic routes in the TGA morphology.

CONCLUSIONS

Hypoplasticity of the proximal regions of parietal and septal ridges in the outflow tract is one of the primary morphological abnormalities of the RA-induced TGA.

Cardiovascular anomalies produced by nimustine hydrochloride in the rat fetus

The cardiovascular teratogenicity of nimustine hydrochloride (ACNU) was studied in rat fetuses. This drug is a nitrosourea derivative anticancer agent and produces alkylation of DNA. Pregnant Donryu rats were treated with single doses of 10, 11 or 13 mg/kg of the teratogen at various stages during gestation. Examination of the hearts was performed by microdissection after sacrificing the animals on the 20th day of gestation. The highest frequency of cardiovascular anomalies was found in the groups treated on the 8th day of gestation, but there was no difference in the rates induced by the three dosages of ACNU administered. The most common cardiovascular anomalies observed were ventricular septal defect (76.8%) and double outlet right ventricle (10.3%). A considerable number of affected fetuses (37/263) showed complex cardiac anomalies with atrioventricular (AV) malalignment and other AV valve anomalies. These anomalies include: double inlet left ventricle, straddling AV valve, atresia or stenosis of the AV valve, and dysplastic AV valve. ACNU appears to be a useful teratogenic agent for inducing complexes of cardiac anomalies which include AV malalignment.

Structural development of endocardial cushions

Development of chick and rat endocardial cushions (cardiac mesenchyme) was studied histologically (using Nomarski differential interference optics on living and unfixed tissue), ultrastructurally (scanning and transmission electron microscopy), cytochemically (using acidified dialyzed iron as a visual probe for polyanionic material) and autoradiographically (using 35S) to elucidate the origin of the mesenchyme, the morphologic sequences leading to cushion formation and secretion of sulfated glycosaminoglycans, if any, by migrating mesenchymal cells. Cushion formation was similar for both species. Mesenchymal cells appeared initially, in 16- to 18-somite embryos, beneath the endothelium (which lacked a basal lamina) of the future atrioventricular canal and outflow tract. The cytoplasm of cushion mesenchymal cells was structurally similar to the ensothelium; probably these cells arose by proliferation of the endothelium. Mitotic figures among the "seeded" cells were also numerous. Cushion cells were initially attached to the endothelium by desmosomes but acquired motile apparatus (pseudopodia and filopodia containing microtubules and microfilamentous bundles). Serial sectioning of successively-aged embryos (20-44 somites) indicated a centrifugal migratory direction. Interaction of the cell processes with extracellular matrix suggested that the latter was used as a migratory substrate. Contact of the advancing wedge of cushion cells with the myocardium produced no alteration in cell structure or mitotic activity. Localization of hyaluronidase-sensitive, dialyzed iron (DI) precipitates in 250-nm Golgi vacuoles and hyaluronidase-sensitive 35S-endangendered silver grains over cushion cells indicated that this tissue contributed sulfated macromolecules to the matrix. Localization of hyaluronidase-labile, DI material in coated, endocytic-like vesicles and caveolae also suggested potential modification or conditioning of the matrix by migrating mesenchymal cells. Altogether, the study established loci in developing cushions where disruption where disruption of the developmental sequence could engender valvular or septal defects.