Current Pharmaceutical Design

ISSN: 1381-6128

Current Pharmaceutical Design
Volume 12, Number 12, 2006

Contents

Recent Advances in Developmental and Reproductive Toxicology
Executive Editor: Gian Mario Tiboni


Editorial Pp. 1429


The Relationship Between Cleft Lip, Maxillary Hypoplasia, Hypoxia and Phenytoin Pp. 1431-1448
W.S. Webster, A.M. Howe, D. Abela and D.J. Oakes
[Abstract]


History and Evolution of Reproductive and Developmental Toxicology Guidelines Pp. 1449-1465
T.F.X. Collins
[Abstract]


Whole Embryo Culture: An Important Tool in Developmental Toxicology Today Pp. 1467-1488
B. Flick and S. Klug
[Abstract]


Mechanisms and Risk of Chemically Induced Aneuploidy in Mammalian Germ Cells Pp. 1489-1504
F. Pacchierotti and R. Ranaldi
[Abstract]


Expression of Estrogen-Regulated Genes During Development in the Mouse Uterus Exposed to Diethylstilbestrol Neonatally Pp. 1505-1520
S. Yamashita
[Abstract]


Fetal Alcohol Syndrome: A Cautionary Note Pp.1521-1529
E.L. Abel
[Abstract]


Teratogenic and Developmental Effects of Lithium Pp. 1531-1541
J.J. Giles and J.G. Bannigan
[Abstract]


General Articles


Pleiotropic Effects of Nifedipine on Atherosclerosis Pp. 1543-1547
S.-i. Yamagishi, K. Nakamura, K. Takenaka, T. Matsui and H. Inoue
[Abstract]


Atorvastatin and Diabetic Vascular Complications Pp. 1549-1554
S.-i. Yamagishi, T. Matsui and K. Nakamura
[Abstract]

Abstracts
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Editorial

Recent Advances in Developmental and Reproductive Toxicology

This collection of papers focuses on environmental forces and their noxious influences on reproductive processes and intrauterine life. In line with previous journal initiatives [1, 2], the issue was designed to provide the reader with timely reviews illustrating novel discoveries and setting new directions in the areas of reproductive and developmental toxicology. As always in science, the presented contributions address several important issues and, in the search for the causal nature of reproductive and developmental alterations, raise many others.

Cleft lip is one of the most common malformations in humans, ranging from 36 per 10,000 live births among native Americans to 3 per 10,000 among Africans. The antiepileptic agent phenytoin is the major known pharmaceutical cause of cleft lip in humans. In the first article, Webster and co-workers [3], review evidence supporting the idea that embryonic hypoxia is involved in the induction of cleft lip by phenytoin.

Thalidomide tragedy in the 1950s and early 1960s, raised the compelling necessity for specific testing strategies to evaluate drugs and environmental chemicals for teratogenicity. In its article, Collins [4] provides an historical perspective describing the major scientific milestones in the complex development of guidelines for animal studies and interpretations for safety assessment.

The review authored by Flick and Klug [5], concentrates on whole embryo culture system. Besides illustrating important methodological aspects and recent developments of the system, the authors summarize the growing literature supporting whole embryo culture as useful tool in assessing the embryotoxic potential of chemicals for regulatory purposes.

Aneuploidy is a pathological condition in which a cell or an individual has a chromosome number different from an exact multiple of the haploid karyotype of its species. Aneuploidy accounts for a significant proportion of spontaneous abortions and congenital malformation syndromes, and is a significant contributor to cancer. The article of Pacchierotti and Ranaldi [6] focuses its attention on the possible role of environmental factors, including endocrine disruptors, in the initiation of aneuploidy in mammalian germ cells.

Diethylstilbestrol is a synthetic estrogen that was widely prescribed to pregnant women to prevent miscarriage and other pregnancy complications between 1938 and 1971. In utero exposure to diethylstilbestrol has been causally linked to clear cell adenocarcinoma of the vagina, breast cancer, and reproductive anomalies. In the paper by Yamashita [7] the current understanding on the molecular basis of diethylstilbestrol-induced uterus anomalies is reviewed. Particular attention is paid to the persistent or temporal changes in the expression of estrogen-regulated genes, especially protooncogenes and growth factors.

Fetal alcohol syndrome is a pattern of congenital anomalies caused by maternal consumption of alcohol during pregnancy. Abel [8] offers an up-to date discussion on the fundamental issues and challenges surrounding the syndrome.

In the final article, the teratogenic effects of lithium are reviewed by Giles and Bannigan [9]. The work also covers the recent findings suggesting that teratogenic effects of lithium are mediated by perturbations of phosphatidyl inositol cycle and Wnt/GSK-3 pathway.

I would like to express my sincere appreciation to the contributors for their effort to prepare the series of review, and to the staff at Bentham Publisher for the excellent editorial support.

References

[1] Recent advances in developmental toxicology. Curr Pharm Design 2001; 7(9): 759-880.

[2] Recent advances in developmental and reproductive toxicology. Curr Pharm Design 2004 10(22): 2657-2767.

[3] Webster WS, Howe A, Abela D, Oakes DA. The relationship between cleft lip, maxillary hypoplasia hypoxia and phenytoin. Curr Pharm Design 2006; 12(12): 1431-1448.

[4] Collins TFX. History and evolution of reproductive and developmental toxicology guidelines. Curr Pharm Design 2006; 12(12): 1449-1465.

[5] Flick B and Klug S. Whole embryo culture: An important tool in developmental toxicology today. Curr Pharm Design 2006; 12(12): 1467-1488.

[6] Pacchierotti F and Ranaldi R. Mechanisms and risk of chemically induced aneuploidy in mammalian germ cells. Curr Pharm Design 2006; 12(12): 1489-1504.

[7] Yamashita S. Expression of estrogen-regulated genes during development in the mouse uterus exposed to diethylstilbestrol neonatally. Curr Pharm Design 2006; 12(12): 1505-1520.

[8] Abel EL. Fetal alcohol syndrome: a cautionary note. Curr Pharm Design 2006; 12(12): 1521-1529.

[9] Giles JJ and Bannigam JG. Teratogenic and developmental effects of lithium. Curr. Pharm Design 2006; 12(12): 1531-1541.

Gian Mario Tiboni, MD
Ostetricia e Ginecologia
Dipartimento di Medicina e Scienze dell'Invecchiamento
Università "G. d'Annunzio"
Presidio Ospedaliero "SS. Annunziata"
Via dei Vestini
66013 - Chieti
Italy
e-mail: tiboni@unich.it

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The Relationship Between Cleft Lip, Maxillary Hypoplasia, Hypoxia and Phenytoin
W.S. Webster, A.M. Howe, D. Abela and D.J. Oakes

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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History and Evolution of Reproductive and Developmental Toxicology Guidelines
T.F.X. Collins

Birth defects and other adverse outcomes of pregnancy have been known since before the industrial age, but the need for guidelines to test chemicals to which pregnant women might be exposed was defined by the thalidomide tragedy in the 1950s and early 1960s. During the five decades that followed the tragedy, guidelines were written to test drugs, foods, and environmental contaminants. The guidelines were written to fulfill national needs, and then were expanded to international levels in order to streamline procedures in the expanding global economy. Multiple sets of animal guidelines were written, based on the need to simulate human experience. It was soon realized that the underlying principles were similar for all guidelines. Guidelines gradually evolved in two directions, in complexity and number of endpoints measured and in the expansion of internationally acceptable guidelines. This manuscript reviews, in chronological order, some of the milestones in the development of guidelines for animal studies and in the interpretations for safety assessment. Guidelines for long-term and short-term studies are reviewed, followed by a discussion of recently added endpoints and the future integration process for the assessment of reproductive toxicity risk.

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Whole Embryo Culture: An Important Tool in Developmental Toxicology Today
B. Flick and S. Klug

The number of candidate chemicals or drugs for registration and authorization is increasing at a fast rate and only few of the existing substances have been tested for teratogenicity to date. Therefore, there is high pressure on authorities to accept models like the whole embryo culture as a screening system for safety evaluation procedures. In view of this background the gradual development of the whole embryo culture into a standardized, scientifically validated tool for developmental toxicology during the last 70 years is summarized. The methodological development of the culture technique is described with the completion, improvement and refinement of the basic culture method as main intention. Special attention was paid to different culture techniques, culture media, gassing schedules, and evaluation strategies. Furthermore the importance of taking “in vitro pharmacokinetics” into consideration when a comparison of in vitro/in vivo results from embryotoxicity testing is intended, is stressed. Additionally, the demonstration of the broad spectrum of useful scientific applications when using this culture system in combination with sophisticated analytical techniques is demonstrated. Finally, an overview on different strategies for the validation of this culture system as an in vitro embryo toxicity test is provided and the officially accepted formal validation process for this application is summarized. The successful validation makes the whole embryo culture a complex in vitro embryotoxicity test with high accuracy and predictability. This robust in vitro system modelling the main phase of rodent organogenesis with a high reproducibility is valuable enough to attract special attention in related scientific fields.



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Mechanisms and Risk of Chemically Induced Aneuploidy in Mammalian Germ Cells
F. Pacchierotti and R. Ranaldi

Aneuploidy is a pathological condition that affects 35% of human spontaneous abortions and 0.3% of livebirths. In spite of the increasing knowledge about molecular mechanisms of meiosis and chromosome segregation, maternal age remains the only ascertained aetiological factor. Genetically modified mouse models have been produced that show increased incidence of aneuploid gametes or abnormalities in meiotic recombination and synapsis. They suggest that genetic polymorphisms might also be involved in the aetiology of human germ cell aneuploidy. Experimental studies in the mouse have identified chemicals that can induce aneuploidy in male and female germ cells. Compounds affecting spindle assembly/dynamics are potent aneugens for oocytes and less so also for spermatocytes. They are active at acute doses during a short time interval preceding the metaphase-to-anaphase transition. Topoisomerase inhibitors are also meiotic aneugens which act on the recombination process; for the first time, the production of viable aneuploid mouse progeny was shown after paternal treatment with etoposide. A comparison between in vitro and in vivo effects of suspect aneugens demonstrates that there are biological mechanisms protecting mammalian oocytes from acute exposures to exogenous chemicals. Endocrine disruptors are a novel group of compounds that might affect chromosome segregation at meiosis. Data on bisphenol-A suggest that such chemicals could be active at low chronic exposure levels, but this hypothesis needs to be confirmed by further experiments. Experiments on cultured mouse oocytes treated with inhibitors of biochemical reactions involved in the regulation of chromosome segregation point to possible new mechanisms of action of environmental aneugens.


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Expression of Estrogen-Regulated Genes During Development in the Mouse Uterus Exposed to Diethylstilbestrol Neonatally
S. Yamashita

Neonatal diethylstilbestrol (DES) exposure elicits a wide range of abnormalities in the female mouse genital tract. This animal model system is suitable for investigating the mechanism of DES syndrome in humans. Accumulated evidence has shown that critical periods in development are present for distinct and permanent alterations in the female genital tract of mice exposed to DES neonatally (DES-mice). These effects of DES and other estrogens are mainly mediated by estrogen receptor α (ERα) through multiple pathways. Induction of ERα by DES exposure in neonatal stromal and epithelial cells, and successive premature activation of estrogen-regulated genes are thought to be essential to induce the abnormalities.

Induction of malformation, permanent changes in estrogen-regulated genes, such as protooncogenes and growth factors, and carcinogenesis are assumed to be interdependent. This review focuses the following topics to discuss the molecular basis of DES-induced abnormalities mainly based on the results by histochemical techniques in the uterus: spatiotemporal expression of ERα and coactivators, proteins relating morphogenesis, and estrogen-regulated protooncogenes and growth factors.



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Fetal Alcohol Syndrome: A Cautionary Note
E.L. Abel

Fetal alcohol syndrome (FAS) is a pattern of anomalies occurring in children born to alcoholic women. The main features of this pattern are pre and/or postnatal growth retardation, characteristic facial abnormalities, and central nervous system dysfunction, including mental retardation. Since its clinical recognition in 1973 it has progressed from an unrecognized condition to a major public health concern with exaggerated and unfounded claims as to causality and impact. This review summarizes some of the basic facts about fetal alcohol syndrome with respect to terminology, prevalence, and mechanisms, in the context of exposure risk.


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Teratogenic and Developmental Effects of Lithium
J.J. Giles and J.G. Bannigan

A review is presented on the effects of lithium in therapeutic doses on the outcome of human pregnancy. The results of various studies including cohort, prospective, retrospective and small number case reports indicate that lithium is a “weak” teratogen in humans. The main effects attributable to lithium are, cardiac malformations and babies with increased birth weight. There is a possibility that, in particular, lithium may be associated with the Ebstein anomaly but present evidence cannot definitely affirm or deny this association. Animal studies with lithium using doses comparable to human therapeutic serum levels have not reported any abnormalities. However, higher doses have produced exencephaly, skeletal and craniofacial defects and abnormalities of blood vessel development. Experiments with other vertebrates have shown that lithium affects dorsoventral specification and inhibition of vasculogenesis. Both these effects can be prevented by pretreatment with myo-inositol indicating that lithium interferes with the phosphatidyl inositol cycle. More recent findings have shown that the effects of lithium on invertebrates may be mediated through inhibition of GSK-3β in the Wnt-GSK-3 pathway.


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Pleiotropic Effects of Nifedipine on Atherosclerosis
S.-i. Yamagishi, K. Nakamura, K. Takenaka, T. Matsui and H. Inoue

Impaired endothelial cell (EC) growth and function have been proposed to be an initial event that leads to the development of atherosclerosis. There is a growing body of evidence that atherosclerosis is an inflammatory-fibroproliferative disease, and ECs are target for cytokines and growth factors released during inflammation. Recently, nifedipine, one of the most widely used dihydropyridine-based calcium antagonists (DHPs) for treatments of patients with hypertension, was shown to inhibit vascular inflammation and subsequently improve endothelial function in many cardiovascular diseases, thus slowing the development and progression of atherosclerosis. However, the molecular mechanisms underlying this are not fully understood, because ECs do not possess voltage-operated L-type calcium channels. In this review, we discuss the pleiotropic effects of nifedipine on atherosclerosis, especially focusing on its anti-oxidative properties.


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Atorvastatin and Diabetic Vascular Complications
S.-i. Yamagishi, T. Matsui and K. Nakamura

Statins inhibit 3-hydroxy-methylglutaryl coenzyme A (HMG-CoA) reductase, a rate-limiting enzyme for cholesterol synthesis, and share the common mechanism of lowering circulating levels of low-density lipoprotein cholesterol. Among various statins, atorvastatin is the most widely used statin for the treatment of hypercholesterolemia. Recent clinical trials show that atorvastatin reduces the risk of cardiovascular events and slows the progression of atherosclerosis in patients with coronary artery diseases. Further, intensive therapy with atorvastatin is also associated with an early clinical benefit in patients with acute coronary syndrome. These observations support the concept that beyond lipid-lowering effects of atorvastatin, that is, pleiotropic effects, could contribute at least in part to cardiovascular event reduction. Diabetic vascular complication is a leading cause of end-stage renal failure, acquired blindness, a variety of neuropathies and accelerated atherosclerosis, which could account for disabilities and high mortality rates in patients with diabetes. However, whether atorvastatin therapy decreases the risk for the development and progression of diabetic vascular complications and the way that it might achieve these effects are not fully elucidated. In this paper, we focus on diabetic vascular complications and review the efficacy and safety of atorvastatin in the treatment of these devastating disorders. We further discuss here the possible vasculoprotective properties of atorvastatin in patients with diabetes.