The teratogenic effect of dofetilide during rat limb development and association with drug-induced bradycardia and hypoxia in the embryo.

BACKGROUND: Dofetilide is an antiarrhythmic drug that blocks the cardiac repolarizing current IKr ((IKr, rapid component of the delayed rectifying potassium current). Previous studies have shown that (a) IKr is essential for normal cardiac function of the embryonic heart and (b) dofetilide is teratogenic in rodents. This study was undertaken to examine the mechanism by which dofetilide causes limb defects on gestational day 13 (GD 13) in the rat. METHODS: Rats were treated with dofetilide (single oral dose, 5 mg/kg) on GD 13 and embryonic heart rates assessed by ultrasound (Vevo770, VisualSonics, Toronto, Ontario, Canada) 2 hr later. Fetuses were examined for malformations on GD 20. In a separate experiment, dofetilide treatment of GD 13 rats was followed 2, 4, 12, or 24 hr with iv dosing with the hypoxia marker, pimonidazole (60 mg/kg). Embryos were collected and heart rates were assessed in vitro and hypoxia in embryo limbs analyzed. RESULTS: A teratogenic dose of dofetilide at a susceptible stage of development (GD 13) resulted in a period of bradycardia and arrhythmia of the embryonic heart and hypoxia in the developing limbs (GD 13) resulting in limb malformations (GD 20). CONCLUSIONS: Drugs that induce periods of bradycardia and/or arrhythmia of the embryonic heart and cause the embryo to become hypoxic are potential human teratogens.

Calls to a Major Teratogen Information Service Regarding Exposures During Breastfeeding.

Background: MotherSafe is a free telephone-based counseling service for Australian consumers and health care providers concerned about drug exposures during pregnancy and breastfeeding. Calls relating to breastfeeding are relatively common and a source of significant distress to the breastfeeding mother, particularly if there is a lack of clarity regarding possible adverse effects of drug exposure on the infant. This study seeks to identify the medication exposures of concern for breastfeeding mothers and the information available to address these concerns. Aims: To review calls to MotherSafe about breastfeeding drug exposures during the 19-year period from 2000 to 2018 and to highlight drugs of concern and counseling issues. Materials and Methods: A retrospective descriptive assessment of a prospectively collected Access database was undertaken. Phone counseling records identified the medication (and other) exposures of concern regarding breastfeeding. The information about medication exposures via breastfeeding provided in consumer and product information (PI) was also reviewed. Results: Of a total of 315,158 calls received at MotherSafe between 2000 and 2018, 116,876 (37.1%) were regarding drug exposure via breastfeeding; 30% of these calls related to nonsteroidal anti-inflammatory drugs, antihistamines, antidepressants, simple analgesics, and antibiotics, and 5% were regarding an exposure specifically contraindicated when breastfeeding. Conclusions: Queries about medication exposures via breastfeeding represent a significant proportion of all the counseling calls to MotherSafe. This study demonstrates the inconsistent and often misleading information about breastfeeding exposures found in consumer and PI sheets and online and highlights the important role of Teratogen Information Services like MotherSafe in providing evidence-based information to both consumers and health care providers.

Using the Jigsaw Method to Teach Abdominal Anatomy.

This study evaluates a cooperative learning approach for teaching anatomy to health science students incorporating small group and peer instruction based on the jigsaw method first described in the 1970's. Fifty-three volunteers participated in abdominal anatomy workshops. Students were given time to become an "expert" in one of four segments of the topic (sub-topics) by allocating groups to work-stations with learning resources: axial computerized tomography (CT) of abdominal structures, axial CT of abdominal blood vessels, angiograms and venograms of abdominal blood vessels and structures located within abdominal quadrants. In the second part of workshop, students were redistributed into "jigsaw" learning groups with at least one "expert" at each workstation. The "jigsaw" learning groups then circulated between workstations learning all sub-topics with the "expert" teaching others in their group. To assess abdominal anatomy knowledge, students completed a quiz pre- and post- workshop. Students increased their knowledge with significant improvements in quiz scores irrespective of prior exposure to lectures or practical classes related to the workshop topic. The evidence for long-term retention of knowledge, assessed by comparing end-semester examination performance of workshop participants with workshop nonparticipants, was less convincing. Workshop participants rated the jigsaw workshop highly for both educational value and enjoyment and felt the teaching approach would improve their course performance. The jigsaw method improved anatomy knowledge in the short-term by engaging students in group work and peer-led learning, with minimal supervision required. Reported outcomes suggest that cooperative learning approaches can lead to gains in student performance and motivation to learn. Anat Sci Educ 00: 000-000. © 2018 American Association of Anatomists.

Toxicity of landfill leachate to sea urchin development with a focus on ammonia.

Sea urchin gametes and embryos serve as a model system to evaluate toxicity in the marine environment. In this study, the toxicity of complex chemical mixtures in leachate samples to sea urchin development was examined with a focus on ammonia, which was the main contaminant of concern in most samples. Two rapid tests, the submitochondrial particle function and bacterial luminescence tests, were also used. Ammonia is highly toxic to sea urchin embryos with an EC50 of 1.3 mg l(-1) for the embryos of the Australian sea urchin Heliocidaris tuberculata. Leachate ammonia levels were well above these EC50 concentrations. To assess the contribution of ammonia to leachate toxicity in sea urchin development, we compared the predicted toxic units (PTU) and observed toxic units (OTU) for ammonia for each sample. The PTU/OTU comparison revealed that the sensitivity of the sea urchin embryos to ammonia were altered (enhanced or decreased) by other chemicals in the leachates. This result emphasises the need for parallel chemical analyses and a suite bioassays for evaluating the toxicity of complex and variable chemical mixtures.

Early Gestational Hypoxia and Adverse Developmental Outcomes.

Hypoxia is a normal and essential part of embryonic development. However, this state may leave the embryo vulnerable to damage when oxygen supply is disturbed. Embryofetal response to hypoxia is dependent on duration and depth of hypoxia, as well as developmental stage. Early postimplantation rat embryos were resilient to hypoxia, with many surviving up to 1.5 hr of uterine clamping, while most mid-gestation embryos were dead after 1 hour of clamping. Survivors were small and many had a range of defects, principally terminal transverse limb reduction defects. Similar patterns of malformations occurred when embryonic hypoxia was induced by maternal hypoxia, interruption of uteroplacental flow, or perfusion and embryonic bradycardia. There is good evidence that high altitude pregnancies are associated with smaller babies and increased risk of some malformations, but these results are complicated by increased risk of pre-eclampsia. Early onset pre-eclampsia itself is associated with small for dates and increased risk of atrio-ventricular septal defects. Limb defects have clearly been associated with chorionic villus sampling, cocaine, and misoprostol use. Similar defects are also observed with increased frequency among fetuses who are homozygous for thalassemia. Drugs that block the potassium current, whether as the prime site of action or as a side effect, are highly teratogenic in experimental animals. They induce embryonic bradycardia, hypoxia, hemorrhage, and blisters, leading to transverse limb defects as well as craniofacial and cardiovascular defects. While evidence linking these drugs to birth defects in humans is not compelling, the reason may methodological rather than biological. Birth Defects Research 109:1358-1376, 2017.© 2017 Wiley Periodicals, Inc.

The relationship between cleft lip, maxillary hypoplasia, hypoxia and phenytoin.

Cleft lip (CL) is a common malformation that has both genetic and exogenous causes. The main pharmaceutical cause is exposure to phenytoin during early facial development in the 5th to 6th weeks of gestation. Phenytoin also causes CL if administered to pregnant rats during the period of early facial development. Evidence is presented that in the pregnant rat, a teratogenic dose of phenytoin slows the early embryonic heart and causes a prolonged period of embryonic hypoxia. It is proposed that this hypoxia, through an undefined downstream mechanism, leads to the development of CL. The involvement of hypoxia in the pathogenesis of CL is in agreement with studies in mouse strains with a spontaneous rate of CL in which exposure to hypoxia has been shown to increase the rate and hyperoxia to decrease the rate. Other exogenous risk factors during pregnancy for human CL include maternal cigarette smoking, residence at high altitude and exposure to corticosteroids. It is suggested that these exposures all involve an increased risk of embryonic hypoxia. It has been proposed that phenytoin affects the embryonic heart by inhibition of the human-ether-a-go-go (HERG) potassium channel. Phenytoin also inhibits sodium and calcium channels and these properties may also be involved in the observed effect on the embryonic heart. Phenytoin-induced bradycardia leading to embryonic hypoxia may be an important mechanism by which phenytoin causes birth defects.