Biomedical subjects

G D Bennett

Publications and source records attributed to G D Bennett.

At least 19 recordsLinked to original sources

PubMed2000

Ribonucleotide reductase subunit R1: a gene conferring sensitivity to valproic acid-induced neural tube defects in mice.

Neural tube defects (NTDs), although prevalent and easily diagnosed, are etiologically heterogeneous, rendering mechanistic interpretation problematic. To date, there is evidence that mammalian neural tube closure (NTC) initiates and fuses intermittently at four discrete locations. Disruption of this process at any of these four sites may lead to a region-specific NTDs, possibly arising through closure site-specific genetic mechanisms. Although recent efforts have focused on elucidating the genetic components of NTDs, a void persists regarding gene identification in closure site-specific neural tissue. To this end, experiments were conducted to identify neural tube closure site-specific genes that might confer regional sensitivity to teratogen-induced NTDs. Using an inbred mouse strain (SWV/Fnn) with a high susceptibility to VPA- induced NTDs that specifically targets and disrupts NTC between the prosencephalon and mesencephalon region (future fore/midbrain; neural tube closure site II), we identified a VPA-sensitive closure site II-specific clone. Sequencing of this clone from an SWV neural tube cDNA library confirmed that it encodes the r1 subunit of the cell cycle enzyme ribonucleotide reductase (RNR). The abundance of rnr-r1 mRNA was significantly increased in response to VPA drug treatment. This upregulated expression was accompanied by a significant decrease in cellular proliferation in the closure site II neural tube region of the embryos, as determined by ELISA cellular proliferation assays performed on BrdU-pulsed neuroepithelial cells in vivo. We hypothesize that rnr-r1 plays a critical role in the development of VPA-induced exencephaly.

Animals↗

PubMed2000

Microsatellite instability markers in breast cancer: a review and study showing MSI was not detected at 'BAT 25' and 'BAT 26' microsatellite markers in early-onset breast cancer.

Microsatellite markers may provide evidence of faulty DNA mismatch repair (MMR) via the detection of microsatellite instability (MSI). The choice of microsatellite markers may impact on the MSI detection rate. In hereditary non-polyposis colon cancer (HNPCC), several informative microsatellite markers have been recommended. Two of these, BAT 25 and BAT 26, are quasi-homozygous, enabling analysis of tumour DNA in the absence of paired normal DNA. Sixty-six breast cancer patients under 45 years of age at diagnosis were examined for MSI at BAT 25 and BAT 26. Tumour DNA was extracted from paraffin-embedded tissue. No MSI was detected at the BAT 25 or BAT 26 loci. An additional five microsatellite markers, known to be informative for HNPCC, were examined for MSI in these patients. Apparently-normal profiles were achieved. A tabulated survey of 306 microsatellite markers used to detect MSI in breast cancer revealed that only 35.5% of markers detected MSI at an average rate of 2.9%. The MSI detection rate at the specific HNPCC markers varied from 0% to 10% in breast cancer, with D175250 and TP53 being the HNPCC markers most suitable for analysis of breast cancer. The size of the microsatellite marker's repeat unit did not impact on MSI detection rates. Compiled data from large studies (n > 100) revealed D115988 as the marker with the highest MSI detection rate. Genomic instability pathways of carcinogenesis, characterised by MMR defects and MSI, appear to play a role in the genesis of some breast cancer types.

Adult↗

PubMed2000

Stereoselective pharmacokinetic analysis of valnoctamide, a CNS-active chiral amide analogue of valproic acid, in dogs, rats, and mice.

The purpose of this study was to evaluate the stereoselective pharmacokinetics of valnoctamide (VCD) in dogs, rats, and mice; which are the most common animal models for pharmacokinetic, pharmacologic, and toxicologic evaluation; and to compare it with previously published human data. Racemic VCD (mixture of four stereoisomers) was administered intravenously to six mongrel dogs and to rats (five rats per time-point), and intraperitoneally to mice (five mice per time-point). Plasma concentrations of the individual stereoisomers were measured by a stereospecific gas chromatography assay. In dogs, (2S,3R)-VCD had a larger clearance (0.33 L/h x kg) and a larger volume of distribution (0.79 L/kg) than its two diastereomers (0.24-0.25 L/h x kg and 0.65 L/kg, respectively). A tendency toward slightly higher clearance and volume of distribution values for (2S,3R)-VCD was observed in rats and mice as well. Consequently, in all three animal species the half-life (t1/2) of (2S,3R)-VCD was not different from the t1/2 of the other three VCD stereoisomers. The stereoselective pharmacokinetics of VCD as observed in dogs, rats, and mice is in line with the stereoselectivity previously observed in healthy subjects and epileptic patients.

Amides↗

PubMed2000

Genetic basis of susceptibility to environmentally induced neural tube defects.

Neural tube defects (NTDs) are among the most common of all human congenital defects, with multifactorial etiologies comprising both environmental and genetic components. Several murine model systems have been developed in an effort to elucidate genetic factors regulating expression of NTDs. Strain-dependent differences in susceptibility to teratogenic insults and altered patterns of gene expression observed within the neuroepithelium of affected embryos support the hypothesis that subtle genetic changes can result in NTDs. Since several affected genes are folate-regulated, transgenic knockout mice lacking a functional folate receptor were developed. Nullizygous embryos died in utero with significant morphological defects, supporting the critical role of folic acid in early embryogenesis. While epidemiological studies have not established an association between polymorphisms in the human folate receptor gene and NTDs, it is known that folate supplementation reduces infant NTD risk. Continued efforts are therefore necessary to reveal the mechanism by which folate works and the nature of the gene(s) responsible for human NTDs.

Animals↗

PubMed1999

Phenytoin-induced alterations in craniofacial gene expression.

In utero exposure to the anticonvulsant drug phenytoin has been shown to alter normal embryonic development, leading to a pattern of dysmorphogenesis known as the Fetal Hydantoin Syndrome. This embryopathy is characterized by growth retardation, microcephaly, mental deficiency, and craniofacial malformations, although the precise mechanism(s) by which phenytoin alters normal developmental pathways remains unknown. To better understand the molecular events involved in the pathogenesis of phenytoin-induced congenital defects, alterations in gene expression were examined during critical periods of craniofacial development. Pregnant SWV mice were administered phenytoin (60 mg/kg/day) from gestational day 6.5 until they were sacrificed at selected developmental time points. Tissue from the craniofacial region of control and exposed embryos was isolated, and samples were subjected to in situ transcription, antisense RNA amplification, and hybridization on reverse Northern blots to quantitatively assess expression of 36 candidate genes. Chronic phenytoin exposure significantly altered expression of several genes at distinct times during morphogenesis. Results of these studies show that expression of the retinoic acid receptors (RAR) alpha, beta, and gamma were significantly increased by phenytoin exposure. Elevations in gene expression of laminin beta 1, and the growth factors IGF-2, TGF alpha, and TGF beta 1, were also demonstrated in the craniofacial region of phenytoin-exposed embryos. As several of these genes are transcriptionally regulated by retinoic-acid-responsive elements in their promoter regions, phenytoin-induced alterations in expression of the RAR isoforms may have severe downstream consequences in the regulation of events necessary for normal craniofacial development. Such alterations occurring coordinately at critical times during craniofacial development may account for the dysmorphogenesis often associated with phenytoin exposure.

Abnormalities, Drug-Induced↗

PubMed1999

Expression patterns of folate binding proteins one and two in the developing mouse embryo.

Expression patterns of mRNAs coding for the murine folate binding proteins one and two (FBP1 and FBP2) were determined by ribonuclease protection assay (RPA) in highly inbred SWV/Fnn mouse embryos. Tissue samples for RPA were collected from the anterior neural tube throughout the period of embryonic development, as well as from maternal- and fetal-derived term placenta. The peak in expression of FBP1 occurred in term placental tissue compared to neural tissue from any time point. This relative increase in FBP1 expression occurred in placental tissue of embryonic, as opposed to maternal, origin. The expression of FBP2 did not differ statistically between any timepoints or tissues examined. Expression of both FBP1 and FBP2 was slightly elevated throughout the period of neural tube closure (Gestational Days 8 through 10), although not significantly. These data fit the anticipated expression patterns of the homologues of human folate receptors alpha and beta, thus helping to resolve some of the confusion secondary to the nomenclature associated with this gene family. Furthermore, the expression of these two genes in the neural tube closure stage of embryological development supports their involvement in regulatory events related to normal neural tube morphogenesis.

Analysis of Variance↗

PubMed1999

Stereoselective pharmacokinetics and pharmacodynamics of propylisopropyl acetamide, a CNS-active chiral amide analog of valproic acid.

PURPOSE: The purpose of this study was to evaluate there existed stereoselective effects in the pharmacokinetics, anticonvulsant activity, microsomal epoxide hydrolase (mEH) inhibition, and teratogenicity of the two enantiomers of propylisopropyl acetamide (PID), a CNS-active chiral amide analogue of valproic acid. METHODS: Racemic PID, as well as the individual enantiomers, were intravenously administered to six dogs in order to investigate the stereoselectivity in their pharmacokinetics. Anticonvulsant activity was evaluated in mice (ip) and rats (oral), mEH inhibition studies were performed in human liver microsomes, and teratogenicity was evaluated in an inbred susceptible mice strain. RESULTS: Following intravenous administration to dogs of the individual enantiomers, (R)-PID had significantly lower clearance and longer half-life than (S)-PID, however, the volumes of distribution were similar. In contrast, following intravenous administration of racemic PID, both enantiomers had similar pharmacokinetic parameters. In rats (oral), (R)-PID had a significantly lower ED50 in the maximal electroshock seizure test than (S)-PID; 16 and 25 mg/kg, respectively. PID enantiomers were non-teratogenic and did not demonstrate stereoselective mEH inhibition. CONCLUSIONS: (R)-PID demonstrated better anticonvulsant activity, lower clearance and a longer half-life compared to (S)-PID. When racemic PID was administered, the clearance of (S)-PID was significantly reduced, reflecting an enantiomer-enantiomer interaction.

Allylisopropylacetamide↗

PubMed1999

Mice lacking the folic acid-binding protein Folbp1 are defective in early embryonic development.

Periconceptional folic acid supplementation reduces the occurrence of several human congenital malformations, including craniofacial, heart and neural tube defects. Although the underlying mechanism is unknown, there may be a maternal-to-fetal folate-transport defect or an inherent fetal biochemical disorder that is neutralized by supplementation. Previous experiments have identified a folate-binding protein (Folbp1) that functions as a membrane receptor to mediate the high-affinity internalization and delivery of folate to the cytoplasm of the cell. In vitro, this receptor facilitates the accumulation of cellular folate a thousand-fold relative to the media, suggesting that it may be essential in cytoplasmic folate delivery in vivo. The importance of an adequate intracellular folate pool for normal embryogenesis has long been recognized in humans and experimental animals. To determine whether Folbp1 is involved in maternal-to-fetal folate transport, we inactivated Folbp1 in mice. We also produced mice lacking Folbp2, another member of the folate receptor family that is GPI anchored but binds folate poorly. Folbp2-/- embryos developed normally, but Folbp1-/- embryos had severe morphogenetic abnormalities and died in utero by embryonic day (E) 10. Supplementing pregnant Folbp1+/- dams with folinic acid reversed this phenotype in nullizygous pups. Our results suggest that Folbp1 has a critical role in folate homeostasis during development, and that functional defects in the human homologue (FOLR1) of Folbp1 may contribute to similar defects in humans.

Animals↗

PubMed1998

Neurulation abnormalities secondary to altered gene expression in neural tube defect susceptible Splotch embryos.

The murine mutant Splotch (Sp) is a well-established model for studying neural tube closure defects. In the current investigation, the progression through neural tube closure (NTC) as well as the expression patterns of 12 developmentally regulated genes were examined in the neural tissue of wildtype (+/+), Splotch heterozygous (Sp/+), and Splotch homozygous (Sp/Sp) embryos during neurulation. The overall growth of the embryos, as measured by the number of somite pairs, did not differ significantly between the three genotypes at any of the collection time-points. There was, however, a significant delay in the progression through NTC for both the Sp/+ and Sp/Sp embryos. A univariate analysis on the expression of the 12 candidate genes (bcl-2, FBP-2, Hmx-2, Msx-3, N-cam, N-cad, noggin, p53, Pax-3, Shh, Wee-1, wnt-1) revealed that although 11 were statistically altered, across time or by genotype, there were no significant interactions between gestation age and genotype for any of these genes during NTC. However, a multivariate statistical analysis on the simultaneous expression of these genes revealed interactions at both gestation day (GD) 8:12 (day:hour) and 9:00 among Pax-3, N-cam, N-cad, bcl-2, p53, and Wee-1 that could potentially explain the aberrant NTC. The data from these studies suggest that a disruption in the genes that govern the cell cycle or extracellular matrices of the developing neural tube might play a critical role in the occurrence of the NTDs observed in Splotch embryos.

Animals↗

PubMed1997

Strain-dependent alterations in the expression of folate pathway genes following teratogenic exposure to valproic acid in a mouse model.

The molecular basis for the well-established hierarchy of susceptibility to valproic acid-induced neural tube defects in inbred mouse strains was examined using in situ transcription and anti-sense RNA amplification methodologies with both univariate and multivariate analyses of the resulting gene expression data. The highly sensitive SWV strain demonstrated a significant reduction in the expression of the folate binding protein (FBP-1) following the teratogenic insult at gestational day 8:18, while the more resistant LM/Bc embryos were up-regulating this gene in response to valproic acid treatment. More importantly, at all 3 gestational timepoints spanning the period of murine neural tube closure examined in this study, the LM/Bc embryos had significantly higher MTHFR (5,10-methylenetetrahydrofolate reductase) gene expression levels compared to the SWV embryos. As this folate pathway enzyme is important in homocysteine and methionine metabolism, it suggests that the SWV embryos may be hypomethylated, and essential gene expression during critical periods of neural tube closure is compromised by the teratogenic exposure to valproic acid. This study represents the first evidence of a strain difference in transcriptional activity in response to a teratogenic exposure that might be causally related to the development of the teratogen-induced congenital malformations.

5,10-Methylenetetrahydrofolate Reductase (FADH2)↗

PubMed1997

Identification of a growth arrest specific (gas 5) gene by differential display as a candidate gene for determining susceptibility to hyperthermia-induced exencephaly in mice.

Neural tube defects (NTDs) are among the most common congenital malformations, affecting approximately 1 per 1,000 liveborn infants in the United States [Nakano, 1973; Richards et al., 1972]. Maternal exposure to hyperthermia, either through recreational sources or due to an infectious agent, is thought to account for approximately 10% of observed NTD cases. The specific genes conferring susceptibility or resistance to hyperthermia-induced NTDs have not been identified. This study used differential display-polymerase chain reaction (DD-PCR) to characterize alterations in gene expression in the anterior embryonic neural tube of two highly inbred murine strains (SWV/Fnn, LM/Bc/Fnn) known to differ in their genetically determined susceptibility to heat-induced NTDs. Herein, we report the neural tube-specific differential expression of the growth arrest specific (gas 5) gene in the highly susceptible SWV/Fnn strain during neural tube closure (NTC). Although the expression of gas 5 did not appear to be altered by the teratogenic heat treatment, its spatial and strain-specific pattern of expression makes it an excellent candidate gene responsible for the observed genetic differences in NTD susceptibility between these two inbred murine strains.

Animals↗

PubMed1997

Developmental expression of morphoregulatory genes in the mouse embryo: an analytical approach using a novel technology.

The molecular techniques of in situ transcription and antisense RNA amplification (IST/aRNA) have allowed for the monitoring of coordinate changes in the expression of multiple genes simultaneously. However, the analysis of their concurrent behavior during murine embryogenesis has been problematic. Studies involving the investigation of temporal and spatial gene expression during embryogenesis have focused solely on the analysis of isolated, single gene events. Such an approach has failed to provide an integrative picture of genetic control over the varied and complicated cellular processes governing embryogenesis. In order to interpret the enormous amount of gene expression data generated by these procedures, we have attempted to develop an analytical framework by employing the statistical concepts of principal components analysis (PCA). For the current study, we performed IST/aRNA on neural tubes dissected from the highly inbred LM/Bc murine strain collected during four gestational time periods. A subset of these genes, representing a partial signaling pathway in the developing neuroepithelium, was then subjected to PCA. Here, we report that PCA highlighted the transcriptional interplay among the genes p53, wee-1, Tgf beta-2, and bcl-2 such that the combined reciprocal regulation of their gene products is suggestive of a predominant proliferative state for the developing neuroepithelium. The application of PCA to the gene expression data has elucidated previously unknown interrelationships among cell cycle genes, growth, and transcription factors on a transcriptional level during critical stages of neurulation. The information gleaned from this analysis, while not definitive, suggests distinct hypotheses to guide future research.

Analysis of Variance↗

PubMed1997

Phenytoin-induced teratogenesis: a molecular basis for the observed developmental delay during neurulation.

PURPOSE: We wished to determine whether chronic phenytoin (PHT) exposure could impair neural development and if any morphological alterations could be linked to changes in gene expression. METHODS: Pregnant SWV mice were chronically administered PHT 40 mg/kg/day from gestational day (GD) 0:12 (day:h) until they were killed at various timepoints throughout neural tube closure (NTC). At each timepoint, embryos from both treated and control dams were collected and scored for their progression through NTC. The neural tubes were then isolated and subjected to in situ transcription (IST) and antisense RNA amplification procedures. Using these techniques, we examined the expression of 10 genes: N-cadherin (Ncad), collagen type IV (col-IV), bcl-2, c-jun, PAX-3, collular retinol binding protein-2 (CRBP-2), retinoic acid receptor alpha (RAR alpha), transforming growth factor(beta2) (TGF(beta2)), wee-1, and EMX-2. RESULTS: Chronic PHT exposure not only caused a delay in NTC whereby exposed embryos lagged behind the controls at each collection timepoint, but also significantly altered the expression of specific genes at distinct times during NTC. Early in NTC, PHT induced a significant reduction in the expression of N-cad, col-IV, and c-jun in exposed embryos as compared with controls. In contrast, during the midstages of NTC, the only significant molecular alterations observed in the PHT-exposed embryos was the continued decreased expression of col-IV and an increase in CRBP-2 expression. Finally, in the latter stages of NTC, PHT caused a significant reduction in the expression of bcl-2, RAR alpha, TGF(beta2), EMX-2, and PAX-3. CONCLUSIONS: These results show that although the effects of PHT are morphologically subtle, causing a delay in the development of the neural tube, this delay is accompanied by alterations in critical genes at crucial times of neural development that may account for the observed neurological deficits often associated with PHT exposure.

Abnormalities, Drug-Induced↗

PubMed1997

Characterization of carbamazepine metabolism in a mouse model of carbamazepine teratogenicity.

The disposition of carbamazepine (CBZ) was investigated in the SWV mouse. A 14C-CBZ dose was administered to CBZ pretreated mice, and the distribution of radiolabeled material was determined. Twenty-four hours after the 14C-CBZ dose, 92.5% of the dose was accounted for in urine (56%), in the visera and carcass (22%), in feces (11%), and expired as 14CO2 (2%). CBZ metabolites present in hydrolyzed urine were also identified using a combination of spectroscopic techniques. CBZ, CBZ-10,11-epoxide (CBZE), 2- and 3-hydroxy-CBZ, methylsulfonyl-CBZ, and glucuronides of CBZ and CBZE accounted for 64% of total urinary radioactivity (0-24 hr) in CBZ pretreated mice. Minor metabolites of CBZ included novel cysteine and N-acetylcysteine conjugates of CBZ, as well as a methylsulfonyl conjugate of CBZE not previously reported. The urinary excretion of these thioether conjugates was increased in CBZ/phenobarbital pretreated mice and decreased in CBZ/stiripentol pretreated mice in comparison with CBZ-only treated mice. Preliminary studies of the effects of phenobarbital and stiripentol on the urinary abundance of these metabolites are consistent with the modulation of teratogenicity in the SWV mouse by the same pretreatments. These data suggest the formation of thioether metabolites of CBZ may be related to CBZ teratogenicity in the SWV mouse.

Animals↗

PubMed1996

Valproic acid-induced changes in gene expression during neurulation in a mouse model.

The teratogenic potential of valproic acid has been well established both in experimental models and in human clinical studies. As with all human teratogens, there are genetically determined differences in individual susceptibility to the induction of congenital defects. Using a mouse model of valproate-induced neural tube defects, a study was undertaken to examine differential changes in gene expression for selected transcription factor (Pax-3, Emx-1, Emx-2, c-fos, c-jun, creb) and cell cycle checkpoint genes (bcl-2, p53, wee-1) during neural tube closure. In general, exposure to teratogenic concentrations of valproic acid elicited GD 9:12 control levels of transcription factor mRNA expression in GD 9:0 embryos of both strains. This accelerated developmental profile is marked by significant elevation of Emx-1, Emx-2, c-fos, c-jun, and creb expression. There was also a significant over expression of the cell cycle genes p53 and bcl-2 in the LM/Bc embryos in response to the teratogenic insult. Examination of the ratio of expression of these genes clearly favored bcl-2, which supports the hypothesis that altered neuroepithelial cell proliferation rates, rather than increased apoptosis, is the underlying mechanism by which valproic acid alters normal neural tube morphogenesis. An investigation into interactive effects of these genes on the molecular profile of GD 9:0 embryos further validated this observation. That is, the overall proliferative state among the control embryos was prematurely modified into a more differentiated state following teratogenic insult. These results suggest that alterations in the expression of multiple genes are most likely responsible for valproic acid-induced neural tube defects.

Animals↗

PubMed1996

Arsenic-induced alterations in embryonic transcription factor gene expression: implications for abnormal neural development.

We examined the morphological and molecular consequences of acute in utero exposure to teratogenic concentrations of arsenate. The treatment produced a dose-related increase in neural tube defects, along with a significant alteration in the pattern of gene expression for several transcription factors (creb, Hox 3.1, Pax3, and Emx-1) that were examined using in situ transcription and antisense RNA amplification procedures. On gestational day 9:0, there was a significant delay in the embryos progression through neural tube closure, accompanied by a significant downregulation of Hox 3.1 expression and a significant upregulation of Pax3, Emx-1, and creb. As both Hox 3.1 and Pax3 serve to regulate N-CAM expression, it is possible that abnormalities associated with N-CAM may compromise neural crest cell migration and normal neural tube closure.

Animals↗

PubMed1996

Protein-reactive metabolites of carbamazepine in mouse liver microsomes.

The character of reactive metabolites formed from carbamazepine (CBZ) was sought in incubations of [14C]CBZ in hepatic microsomes prepared from adult female mice of a strain (SWV/Fnn) susceptible to CBZ-induced teratogenicity. The formation of radio-labeled protein adducts was used as an index of reactive metabolite exposure. A dependence on cytochrome P450 was shown by a requirement for NADPH and inhibition by carbon monoxide, 1-aminobenzotriazole, piperonyl butoxide, and stiripentol. The addition of ascorbic acid, caffeic acid, N-acetylcysteine, and glutathione decreased the rate of binding of the radiolabel from [14C]CBZ to microsomal protein by more than 50%. The addition of glutathione transferases diminished protein adduct formation beyond that seen with glutathione alone. Evidence for the formation of an arene oxide was sought through the use of inhibitors of epoxide hydrolases, including cyclohexene oxide, chalcone oxides (with the addition of cytosol as appropriate), and by the addition of recombinant human soluble and microsomal epoxide hydrolases and recombinant rat microsomal epoxide hydrolase. The microsomal epoxide hydrolases decreased the velocity of 14C-labeled protein adduct formation by approximately 23%, whereas inhibitors had no effect, most likely because of the low native activity of microsomal epoxide hydrolase in mice. Both DT-diaphorase and catechol-O-methyltransferase diminished 14C-labeled protein adduct formation by 54% and 45%, respectively. The data suggest that the major reactive metabolites formed from CBZ by adult female SWV/Fnn liver microsomes are quinones and arene oxides.

Animals↗

PubMed1996

Teratogenicity of carbamazepine-10, 11-epoxide and oxcarbazepine in the SWV mouse.

The mechanism of carbamazepine (CBZ)-related teratogenicity was investigated in the SWV mouse by contrasting the effects of CBZ-10, 11-epoxide (CBZE) and oxcarbazepine (OXC) treatments. Dietary CBZE administration was initiated 2 weeks before mating and continued through day 18 of gestation. OXC was administered to pregnant dams by gavage on day 6 of gestation and continued through day 18 of gestation. Maternal plasma concentrations of CBZE ranged from 1.4 to 17.7 micrograms/ml and OXC ranged from 6.1 to 15.9 micrograms/ml. In comparison, clinical plasma concentrations of CBZE ranged from 1 to 2 micrograms/ml and OXC plasma concentrations were 1 microgram/ml or less. The incidence of malformation were 14%, 27% and 26% after daily CBZE doses of 300, 600 and 1000 mg/kg, respectively, compared with a 6% incidence in no-drug control mice, P < .05. The incidence of malformation was 8% after exposure at the highest tolerable dose of OXC (1100 mg/kg/day), compared with a 5% incidence in no-drug controls, P > .05. Phenobarbital cotreatment (45 mg/kg/day) with OXC (1100 mg/kg/day) did not lead to changes in the incidence of malformation when compared with OXC (1100 mg/kg/day) dosed alone. These data are consistent with a teratogenic CBZ metabolite, possibly CBZE, or with oxidation of CBZE or CBZ at positions on the aromatic ring leading to the formation of reactive intermediates such as arene oxides or quinones.

Animals↗