Effects of prenatal nitrofen exposure on cardiac structure and function in the rat

The developmental toxicity of perfluoroalkyl acids and their derivatives

Perfluoroalkyl acids such as perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) have applications in numerous industrial and consumer products. Although the toxicology of some of these compounds has been investigated in the past, the widespread prevalence of PFOS and PFOA in humans, as demonstrated in recent bio-monitoring studies, has drawn considerable interest from the public and regulatory agencies as well as renewed efforts to better understand the hazards that may be inherent in these compounds. This review provides a brief overview of the perfluoroalkyl chemicals and a summary of the available information on the developmental toxicity of the eight-carbon compounds, PFOS and PFOA. Although the teratological potentials of some of these chemicals had been studied in the past and the findings were generally unremarkable, results from recent postnatal studies on developmental and reproductive indices have prompted consideration of their relevance to human health risk. Based on current understanding of the developmental effects of PFOS and PFOA in rodents, several avenues of research are suggested that would further support the risk assessment of these perfluorinated organic chemicals.

Exposure to perfluorooctane sulfonate during pregnancy in rat and mouse. II: postnatal evaluation

The postnatal effects of in utero exposure to perfluorooctane sulfonate (PFOS, C8F17SO3-) were evaluated in the rat and mouse. Pregnant Sprague-Dawley rats were given 1, 2, 3, 5, or 10 mg/kg PFOS daily by gavage from gestation day (GD) 2 to GD 21; pregnant CD-1 mice were treated with 1, 5, 10, 15, and 20 mg/kg PFOS from GD 1 to GD 18. Controls received 0.5% Tween-20 vehicle (1 ml/kg for rats and 10 ml/kg for mice). At parturition, newborns were observed for clinical signs and survival. All animals were born alive and initially appeared to be active. In the highest dosage groups (10 mg/kg for rat and 20 mg/kg for mouse), the neonates became pale, inactive, and moribund within 30-60 min, and all died soon afterward. In the 5 mg/kg (rat) and 15 mg/kg (mouse) dosage groups, the neonates also became moribund but survived for a longer period of time (8-12 h). Over 95% of these animals died within 24 h. Approximately 50% of offspring died at 3 mg/kg for rat and 10 mg/kg for mouse. Cross-fostering the PFOS-exposed rat neonates (5 mg/kg) to control nursing dams failed to improve survival. Serum concentrations of PFOS in newborn rats mirrored the maternal administered dosage and were similar to those in the maternal circulation at GD 21; PFOS levels in the surviving neonates declined in the ensuing days. Small but significant and persistent growth lags were detected in surviving rat and mouse pups exposed to PFOS prenatally, and slight delays in eye opening were noted. Significant increases in liver weight were observed in the PFOS-exposed mouse pups. Serum thyroxine levels were suppressed in the PFOS-treated rat pups, although triiodothyronine and thyroid-stimulating hormone [TSH] levels were not altered. Choline acetyltransferase activity (an enzyme that is sensitive to thyroid status) in the prefrontal cortex of rat pups exposed to PFOS prenatally was slightly reduced, but activity in the hippocampus was not affected. Development of learning, determined by T-maze delayed alternation in weanling rats, was not affected by PFOS exposure. These results indicate that in utero exposure to PFOS severely compromised postnatal survival of neonatal rats and mice, and caused delays in growth and development that were accompanied by hypothyroxinemia in the surviving rat pups.

Prenatal exposure to nitrofen induces Fryns phenotype in mice

Prenatal exposure to nitrofen is known to cause multiple malformations in mice. The reported malformations include lung hypoplasia, diaphragmatic hernia, cardiovascular defects, skeletal malformations, cleft palate, and renal abnormalities. The authors present detailed findings of craniofacial defects after prenatal exposure to nitrofen, and propose that together with the previously reported malformations, nitrofen exposure induces a Fryns phenotype in mice. Fryns syndrome is a rare human genetic syndrome that is an autosomal recessive disorder characterized by lung hypoplasia, diaphragmatic hernia, craniofacial malformations, skeletal malformations, cardiovascular malformations, and genitourinary malformations. Timed-pregnant Swiss Webster mice were gavage-fed 25 mg of nitrofen on day 8 of gestation. Control animals received olive oil. Osteogenesis and chondrogenesis were studied in fetuses recovered on day 17 after Alcian blue-Alizarin red staining. Approximately 26% of the nitrofen-exposed embryos had severe craniofacial defects, and there was generalized delay in chondrogenesis and osteogenesis throughout the skeleton. No such defects were noted in the control group. The authors propose that prenatal exposure to nitrofen induces a Fryns phenotype in mice, and thus speculate that nitrofen may target similar molecular mechanisms to those that lead to Fryns syndrome.

Nitrofen-induced congenital malformations of the heart and great vessels in rats: an animal model

BACKGROUND

Nitrofen (2,4-dichloro-4'-nitrodiphenyl ether), a diapheny ether herbicide, is known to induce in rat fetuses a variety of congenital cardiovascular anomalies, together with diaphragmatic hernia and hydronephrosis. The purpose of the current study was to produce congenital cardiovascular anomalies in rat fetuses by oral nitrofen administration at the indicated doses and days of gestation, and to determine the characteristics of resulting nitrofen-induced cardiovascular anomalies.

METHODS

All the observed fetuses were removed from pregnant Sprague-Dawley rats killed on the 21st day of gestation. They were preserved in 10% formalin, and dissection for examination was carried out under a dissecting microscope.

RESULTS

The following results were based on dissecting microscopic findings of 482 offspring: (1) The 11th day of gestation was the most sensitive for nitrofen induction of congenital cardiovascular anomalies. The incidence of these was dose related. (2) Ventricular septal defect was the most common single cardiovascular anomaly, representing more than half of all such irregularities. The next most common were aortic arch anomalies and tetralogy of Fallot. (3) Cardiac anomalies derived from infundibular maldevelopment such as tetralogy of Fallot and pulmonary atresia with ventricular septal defect were observed only in the group treated with nitrofen on the 11th gestational day. (4) Aortic arch anomalies were very frequent; the great majority were anomalous right subclavian artery with left aortic arch.

CONCLUSION

This animal model is suitable for further embryological investigation of the development of congenital cardiovascular anomalies.

Heart hypoplasia in experimental congenital diaphragmatic hernia

BACKGROUND/PURPOSE

Heart hypoplasia is associated with congenital diaphragmatic hernia (CDH) and decisively influences survival rate. This study examines whether nitrofen-exposed fetal rats have heart hypoplasia.

METHODS

Pregnant rats received either 100 mg nitrofen or vehicle on gestational day 9.5. The hearts recovered near full term were either formalin fixed for anatomic studies or snap-frozen for biochemical studies. Heart weight, ventricular chamber diameters and aortic-to-pulmonary root diameter ratios were measured in fixed hearts. Protein and DNA were determined in frozen hearts. Analysis of variance (ANOVA) and correlation-regression studies were used for statistical assessment.

RESULTS

All control fetuses were normal, whereas 61% of those exposed to nitrofen had CDH. Cardiovascular malformations were found in 73% of CDH and in 50% of non-CDH animals. Wet and fixed heart weights in percent of fetal weight, left-to-right ventricular diameter ratio, and aortic-to-pulmonary root diameter ratio were significantly decreased in fetuses with CDH in comparison with controls. Only wet heart was significantly decreased in nitrofen-treated fetuses without CDH, although all other variables showed a trend in the same direction. Protein to DNA ratios were similar in the three groups. The structure of the myocytes was histologically similar in all groups.

CONCLUSIONS

The spectrum of lesions in the nitrofen model of CDH encompasses heart hypoplasia, further validating its use for research on this condition. Heart hypoplasia is related to cardiopulmonary compression, but its presence in treated animals without CDH demonstrates that the teratogen itself participate directly in its pathogenesis, and this finding invites further research on this line.

[Progress report. What can one expect from a "functional prenatal toxicology?"]

In the strategy of investigation applied and demanded in prenatal toxicology partial aspects have been overstressed until now, although here as well as in postnatal toxicology the problems should be viewed in its complexity (in this case, F1-generation in its several pre- and postnatal stages of development). Therefore, there was the urgent need to summarize the existing methods of functional investigation in the field of prenatal toxicology and to compare them with conventional morphological methods as to their meaningfulness and sensitivity. As a result, the routine introduction of clinical-functional investigations is demanded.

Teratogenic effects of nitrofen on cellular and functional maturation of the rat lung

The herbicide nitrofen was administered to pregnant Sprague-Dawley and Fischer-344 rats on Days 10-13 of gestation (po, 20 or 40 mg/kg daily) and the effects of maturation of the perinatal lung were evaluated. Nitrofen interfered with the ontogenetic acquisition of lung cells as DNA, RNA, and protein content were subnormal. The hypoplastic lungs in the newborns were associated with structural deficits, resulting in a profound reduction of surface area available for gas exchange and depressed lung compliance. Other factors which influence pulmonary function and systemic delivery of oxygen were also considered. Adrenal catecholamines, which play an important role in surfactant production and fluid resorption in the lung during the transition to air-breathing, were markedly reduced. In addition, red blood cell concentration was significantly diminished. Taken together, these results suggest that the neonatal mortality observed in the nitrofen-treated rats is likely associated with respiratory distress caused by a number of cellular and functional aberrations. These include (a) hypoplasia and structural defects in the lung leading to deficient pulmonary function, (b) deficits in adrenal catecholamines potentially impeding the transition of the lung to air-breathing, and (c) impaired systemic delivery of oxygen due to reduced hemoglobin concentration.

Prenatal ethylene glycol monomethyl ether (EGME) exposure produces electrocardiographic changes in the rat

The purpose of the present study was to determine if electrocardiographic (EKG) changes observed in fetuses exposed in utero to ethylene glycol monomethyl ether (EGME) persisted beyond the fetal/neonatal period. Groups of pregnant Sprague-Dawley rats were gavaged on gestation days 7-13 (sperm = day 0) with 0, 50, or 75 mg/kg EGME. Body weight prior to delivery was reduced and gestation was prolonged in EGME-treated dams. EGME treatment reduced the percentage of pregnant dams that delivered, litter size, and pup weight. There were no survivors beyond 3 days of age in the 75 mg/kg EGME group. The number of litters surviving through weaning and weight gain of male and female offspring through 8 weeks of age were reduced in the 50 mg/kg EGME group. In this same group, heart weight was unaffected, but heart/body weight ratios were increased when rats were 8 weeks old. EKGs were obtained from unanesthetized and unrestrained rats at 3 and 6 weeks of age. Prenatal EGME exposure increased the QRS interval in 3- and 6-week-old rats, and increased the T wave in 6-week-old rats. Thirty-six and 54% of 3- and 6-week old litters, respectively, had one or more individuals that were classified as having an intraventricular conduction delay (double R wave and QRS interval of 14 msec or longer). No microscopic heart abnormalities were associated with the observed intraventricular conduction delay.