Abstract
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.
Keywords: cleft lip, hypoxia, bradycardia, Ikr inhibition, HERG inhibitors, Phenytoin
Current Pharmaceutical Design
Title: The Relationship Between Cleft Lip, Maxillary Hypoplasia, Hypoxia and Phenytoin
Volume: 12 Issue: 12
Author(s): William S. Webster, Andrew M. Howe, Dominique Abela and Diana J. Oakes
Affiliation:
Keywords: cleft lip, hypoxia, bradycardia, Ikr inhibition, HERG inhibitors, Phenytoin
Abstract: 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.
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Cite this article as:
Webster S. William, Howe M. Andrew, Abela Dominique and Oakes J. Diana, The Relationship Between Cleft Lip, Maxillary Hypoplasia, Hypoxia and Phenytoin, Current Pharmaceutical Design 2006; 12 (12) . https://dx.doi.org/10.2174/138161206776389868
DOI https://dx.doi.org/10.2174/138161206776389868 |
Print ISSN 1381-6128 |
Publisher Name Bentham Science Publisher |
Online ISSN 1873-4286 |
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