| 1. |
|
|
| 2. |
|
|
| 3. |
- Danielsson, Bengt R., et al.
(författare)
-
Embryonic cardiac arrhythmia and generation of reactive oxygen species : common teratogenic mechanism for IKr blocking drugs
- 2007
-
Ingår i: Reproductive Toxicology. - : Elsevier BV. - 0890-6238 .- 1873-1708. ; 24:1, s. 42-56
-
Tidskriftsartikel (refereegranskat)abstract
- In the adult organism, it is well established that hypoxia followed by reperfusion may be fatal and result in generation of reactive oxygen species (ROS) and subsequent tissue damage. There is also considerable evidence that temporary decrease or interruption in oxygen supply to the embryo and ROS generation during reperfusion result in tissue damage in embryonic tissues. A wide spectrum of different malformations by transient embryonic hypoxia could be produced, depending on the duration, extent, and timing of the hypoxic event. It is the contention of this paper that drugs that block the potassium channel IKr, either as an intended pharmacologic effect or as an unwanted side-effect, are potentially teratogenic by a common ROS related mechanism. Drugs blocking the IKr channel, such as almokalant, dofetilide, phenytoin, cisapride and astemizole, do all produce a similar pattern of hypoxia-related malformations. Mechanistic studies show that the malformations are preceded by embryonic cardiac arrhythmia and periods of hypoxia/reoxygenation in embryonic tissues. Pretreatment or simultaneous treatment with radical scavengers with capacity to capture ROS, markedly decrease the teratogenicity of different IKr blocking drugs. A second aim of this review is to demonstrate that the conventional design of teratology studies is not optimal to detect malformations caused by IKr blocking drugs. Repeated high doses result in high incidences of embryonic death due embryonic cardiac arrhythmia, thus masking their teratogenic potential. Instead, single dosing on specific days is proposed to be a better way to characterize the teratogenic potential of Ikr blocking drugs.
|
|
| 4. |
|
|
| 5. |
- Danielsson, Christian, et al.
(författare)
-
Exploration of human, rat, and rabbit embryonic cardiomyocytes suggests K-channel block as a common teratogenic mechanism
- 2013
-
Ingår i: Cardiovascular Research. - : Oxford University Press (OUP): Policy B. - 0008-6363 .- 1755-3245. ; 97:1, s. 23-32
-
Tidskriftsartikel (refereegranskat)abstract
- Several drugs blocking the rapidly activating potassium (K-r) channel cause malformations (including cardiac defects) and embryonic death in animal teratology studies. In humans, these drugs have an established risk for acquired long-QT syndrome and arrhythmia. Recently, associations between cardiac defects and spontaneous abortions have been reported for drugs widely used in pregnancy (e.g. antidepressants), with long-QT syndrome risk. To investigate whether a common embryonic adverse-effect mechanism exists in the human, rat, and rabbit embryos, we made a comparative study of embryonic cardiomyocytes from all three species. less thanbrgreater than less thanbrgreater thanPatch-clamp and quantitative-mRNA measurements of K-r and slowly activating K (K-s) channels were performed on human, rat, and rabbit primary cardiomyocytes and cardiac samples from different embryo-foetal stages. The K-r channel was present when the heart started to beat in all species, but was, in contrast to human and rabbit, lost in rats in late organogenesis. The specific K-r-channel blocker E-4031 prolonged the action potential in a species- and development-dependent fashion, consistent with the observed K-r-channel expression pattern and reported sensitive periods of developmental toxicity. E-4031 also increased the QT interval and induced 2:1 atrio-ventricular block in multi-electrode array electrographic recordings of rat embryos. The K-s channel was expressed in human and rat throughout the embryo-foetal period but not in rabbit. less thanbrgreater than less thanbrgreater thanThis first comparison of mRNA expression, potassium currents, and action-potential characteristics, with and without a specific K-r-channel blocker in human, rat, and rabbit embryos provides evidence of K-r-channel inhibition as a common mechanism for embryonic malformations and death.
|
|
| 6. |
- Danielsson, Christian, et al.
(författare)
-
Polytherapy with hERG-blocking antiepileptic drugs : Increased risk for embryonic cardiac arrhythmia and teratogenicity
- 2007
-
Ingår i: Birth defects research. Clinical and molecular teratology. - : Wiley. - 1542-0752 .- 1542-0760. ; 79:8, s. 595-603
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The antiepileptic drugs (AEDs) phenytoin, phenobarbital, dimethadione, and carbamazepine cause a similar pattern of malformations in humans, with an increased risk after polytherapy. The teratogenicity has been linked to cardiac rhythm disturbances and hypoxic damage as a consequence of their common potential to inhibit a specific potassium ion current (IKr). The IKr is of major importance for embryonic cardiac repolarization and rhythm regulation. This study investigated whether these AEDs cause irregular rhythm and if various combinations of AEDs result in higher arrhythmia risk than exposure to a single AED. METHODS: The effects on heart rhythm of a single AED (monotherapy), and of various combinations (polytherapy) of AEDs, in gestational day 10 C57BL mouse embryos in culture were analyzed and graphically illustrated during a 25 s recording with a digitalization technique. RESULTS: All of the studied AEDs caused increased intervals between heartbeats (resulting in bradycardia) and large variations in the interval between heartbeats (resulting in irregular rhythm) in a concentration-dependent manner in cultured mouse embryos. Dimethadione caused irregular rhythm at concentrations within and phenytoin slightly above the therapeutic ranges. Polytherapy resulted in more substantial prolongation of the mean interval between heartbeats (>60 ms) than monotherapy at clinically relevant concentrations. CONCLUSIONS: The results suggest that polytherapy more than monotherapy causes substantial prolongation of the cardiac repolarization, a marker associated with high risk of developing irregular rhythm during longer exposure periods (days to months). This supports the idea that the increased risk for malformations following polytherapy is linked to an increased risk for cardiac rhythm disturbances.
|
|
| 7. |
- Karlsson, Miriam, et al.
(författare)
-
New proposals for testing drugs with IKr-blocking activity to determine their teratogenic potential
- 2007
-
Ingår i: Current pharmaceutical design. - : Bentham Science Publishers Ltd.. - 1381-6128 .- 1873-4286. ; 13:29, s. 2979-2988
-
Forskningsöversikt (refereegranskat)abstract
- Drugs blocking the potassium current IKr, either as an intended pharmacologic effect (eg antiarrhythmics dofetilide and almokalant) or as an unwanted side-effect (eg antihistamine astemizole, propulsive drug cisapride, antidepressive drugs and macrolide antibiotics) are potential human teratogens. It is the contention of this paper that the existing repeat dose regimen used in teratology studies to fulfil regulatory requirements, does not properly identify the teratogenic risk of these drugs. Results from conventional studies for dofetilide and almokalant showed high rates of postimplantation embryonic death with few malformed fetuses. For astemizole and cisapride only embryonic death was seen. These latter results were not considered important because they occurred either in the presence of maternal toxicity and/or at high doses. Subsequent studies have shown that IKr-blockers are highly teratogenic when administered on single gestational days (GD) during a sensitive period of rat pregnancy (GD 10-14) when they induce a high incidence of stage-specific malformations. This teratogenic activity of astemizole and cisapride was missed in the original teratology studies. Mechanistically IKr-blockers cause bradycardia and arrhythmia of the embryonic heart and while an embryo may be able to survive a single day exposure to a teratogenic dose, repeat dosing often leads to death of the embryo. With this review we suggest that new drugs identified at the preclinical stage of development as having IKr-blocking properties, should undergo more comprehensive teratology testing including single GD dosing and studies using embryo culture. This would further help identify and characterise their teratogenic potential.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
