Control of fetal survival in CBA x DBA/2 mice by lymphokine therapy

In this study, we examined the effect of injecting various cytokines. We report here that tumour necrosis factor (TNF)alpha, gamma-interferon and interleukin 2 (IL-2) can, in some circumstances, increase fetal resorption rates in abortion-prone (CBA/J x DBA/2) and non-abortion prone (CBA/J x BALB/c,C3H x DBA/2) matings: 1000 units TNF enhanced resorptions from 43 to 79% in CBA x DBA/2, from 7 to 89% in CBA x BALB/c, from 5 to 47% in C3H x DBA/2. The effect was both gestational age- and dose-dependent. Gamma interferon and R-IL-2 enhanced resorptions from 38 to 68% and 76% respectively in the CBA/J x DBA/2 mating combination, whereas the rates in CBA/J x BALB/c matings were enhanced from 6 to 44% and 55%. Lipopolysaccharide (LPS), which is known to lead to the release of TNF-alpha, had a similar effect, leading to gestational age- and dose-dependent enhancement of resorptions up to 100%. However, cytokines of the CSF family, including IL-3 and GM-CSF, increased the chances of fetal survival when injected into abortion-prone mice, e.g. reducing resorption rates in the abortion-prone CBA/J x DBA/2 mating combination from 55 to 22% (IL-3), and 47 to 8% (GM-CSF). They also increased fetal and placental weight and, in particular, expanded the spongiotrophoblast zone in the placenta. The latter observations may be due to a direct trophic influence on placental cells, perhaps through a cytokine cascade, or an indirect effect due to inhibition of natural killer (NK)-like cells, or both. Whatever the mechanism, these results may find practical application in influencing reproductive outcome in women and other species.

The fetal alcohol syndrome in mice: an animal model

CBA and C3H female mice were maintained on liquid diets--Metrecal plus ethanol--containing 15-35% ethanol-derived calories. These diets, which resulted in alcohol blood levels of 73-398 mg/100 ml blood in nonpregnant females, were the sole sustenance for the females for at least 30 days before and throughout gestation. Females were killed on day 18 of gestation and offspring examined for skeletal and soft tissue anomalies. Prenatal death and maldevelopment increased with the level of alcohol intake. Deficient occiput ossification, neural anomalies, and low fetal weight occurred with low ethanol diets, and cardiac and eye-lid dysmorphology with higher ethanol diets. This pattern of malformations, which exhibited both a dose-response effect and strain differences in susceptibility, indicated that chronic maternal alcoholism is embryolethal and teratogenic in mice.

Prenatal ethanol exposure in mice: teratogenic effects

C57BL/6J mice were fed a liquid diet in which 17, 25, or 30% of the calories were derived from ethanol from the fifth through the tenth day of gestation. Control mice were fed lab chow or pair-fed identical diets, except that sucrose substituted isocalorically for ethanol. At term the fetuses were removed and, following fixation, examined by microdissection. The incidence of fetal resorptions and congenital malformations increased in a dose-related manner. Anomalies included skeletal, neurological, urogenital, and cardiovascular systems. These data indicate that in mice, an alcohol diet which is adequate in vitamins and protein results in increased fetal wastage and birth defects.

Teratogenic potential of cocaine hydrochloride in CF-1 mice

This investigation revealed that cocaine hydrochloride was teratogenic when administered in nontoxic doses to gravid CF-1 mice on Days 7-12 of gestation. The teratogenic susceptibility of the CF-1 mouse fetus to cocaine hydrochloride was evident throughout this portion of the gestation period. The early appearance of eye defects and the occurrence of skeletal defects later in gestation after cocaine hydrochloride challenge paralleled the sequence of ontogenesis.

Lipopolysaccharide-induced fetal resorption in mice is associated with the intrauterine production of tumour necrosis factor-alpha

Certain strains of mice display an increased frequency of fetal resorption, but little is known about the effector mechanisms involved. We have examined the events associated with lipopolysaccharide (LPS)-induced fetal resorption in mice. Administration of 25 micrograms LPS on Day 12 of gestation resulted in the appearance of tumour necrosis factor-alpha (TNF-alpha) in the amniotic fluid and fetal resorption. Levels of LPS-induced TNF-alpha were reduced by 90% after pretreatment with the TNF-alpha-suppressing drug pentoxifylline (PXF). Treatment of pregnant mice during early gestation with 0.1 micrograms LPS resulted in fetoplacental resorption which was maximal when the LPS was given on Day 8. Resorption induced by 0.1 micrograms LPS on Day 8 of gestation was significantly reduced by pretreatment with PXF. Infiltration of asialo-GM1-positive cells was observed in the decidual-ectoplacental cone area of embryonic units from LPS-treated mice. In addition, treatment with anti-AGM1 antiserum prevented the LPS-induced resorption. Our results suggest that TNF-alpha and asialo-GM1-positive cells are involved in LPS-induced fetal resorption.

The effect of acute maternal toxicity on fetal development in the mouse

The effects of acute alterations in maternal health status upon fetal development were assessed following exposure of pregnant CD-1 mice on day 8 of gestation to one of ten chemicals at doses calculated to exert either a low or a moderate degree of maternal lethality. The dams were killed on day 18 of gestation, and the fetuses were examined by routine teratological techniques. The chemicals were cacodylic acid, caffeine, deltamethrin, dinoseb, ethylene bisisothiocyanate sulfide (EBIS), endrin, guthion, kepone, sodium salicylate, and toxaphene. Three (cacodylic acid, EBIS, and kepone) produced dose-related increases in the incidence of dams with completely resorbed litters. Prenatal mortality in litters that contained live fetuses at term was elevated only for one chemical (cacodylic acid). Fetal weight was reduced in three instances (cacodylic acid, endrin, and guthion), while the incidence of terata was markedly elevated for two (cacodylic acid and kepone). For two other chemicals (endrin and sodium salicylate), a low incidence was found of defects that were similar to defects induced by those chemicals in other species. These effects appear to be chemospecific in nature and not the result of some indirect maternal action. Thus, maternal health status, as measured by the incidence of lethality in the treated groups and by the magnitude of maternal weight gain in surviving females, presents no simple explanation for many manifestations of fetal toxicity. However, for seven chemicals (excluding deltamethrin, EBIS, and kepone) an increased incidence of supernumerary ribs was observed. For three of these seven chemicals (caffeine, dinoseb, and toxaphene), supernumerary ribs was the only observed fetal effect. There was a significant linear inverse relationship between maternal weight gain during gestation and the incidence of extra ribs in the treated groups compared to their respective controls. Under the experimental conditions of this study, it appears that the incidence of supernumerary ribs increased in response to a nonspecific maternal toxicity.

Teratogenic valproic acid concentrations: infusion by implanted minipumps vs conventional injection regimen in the mouse

The dosage-regimen-dependent teratogenicity as well as plasma and tissue levels of the antiepileptic drug valproic acid (VPA) were studied in the mouse by comparing various injection regimens and infusion of the drug via implanted osmotic minipumps. Concentrations of 225-248 micrograms VPA/ml maternal plasma (about 2X above the therapeutic concentration range) and 70-75 micrograms VPA/g gestational material (on gestation Day 8) resulted in a significant incidence of neural tube defects (exencephaly in the mouse). Similar effects were produced if those concentrations were reached several times after multiple injections or by steady-state application via implanted pumps. A single injection was less effective than multiple injections, although drug accumulation did not occur. The doses (or area under the concentration-time curve values) did not correlate with the teratogenic response of the different administration regimens: much higher (factor 10) doses were needed with the infusion regimen to produce exencephaly rates comparable to those obtained with the injection regimen. The pattern of embryotoxicity was also schedule dependent: steady-state concentrations produced predominantly embryolethality and fetal weight retardation, while intermittent injections produced a high incidence of exencephaly (up to 60% of live fetuses). The dose of VPA (and the areas under the concentration-time curves) correlated with the embryolethality and fetal weight retardation of the drug, while the peak or steady-state concentrations reached in mother and gestational material correlated with the incidence of neural tube defects.

Long-term exposure of male and female mice to trivalent and hexavalent chromium compounds: effect on fertility

Sexually mature male and female mice at 50 days of age were exposed to trivalent (Chromium chloride) or hexavalent (potassium dichromate) chromium compounds in drinking water for 12 weeks. The effects of the direct chromium exposure on fertility was assessed at day 140 of age. Fertility was significantly reduced in males exposed to the trivalent chromium compound. The number of implantation sites and the number of viable fetuses was significantly reduced in females impregnated by males exposed to the hexavalent chromium compound. The number of resorptions and dead fetuses was increased in females impregnated by males exposed to trivalent and hexavalent chromium compounds. The exposure of female mice to trivalent and hexavalent chromium compounds significantly reduced the number of implantation sites and the number of viable fetuses. The number of females with resorptions was significantly increased in hexavalent chromium exposed females. The number of resorptions was increased in trivalent and hexavalent exposed females. Body, seminal vesicles and preputial gland weights were significantly reduced in males exposed to trivalent and hexavalent chromium, whereas testes weight was significantly increased in males exposed to these compounds. Furthermore, ovarian weight was significantly increased in females exposed to trivalent and hexavalent chromium, whereas uterine weight was significantly decreased in trivalent chromium exposed females. In conclusion, the ingestion of trivalent and hexavalent chromium compounds by adult male and female mice would cause adverse effects on fertility and reproduction.

Embryotoxicity of the folate antagonist methotrexate in rats and rabbits

The prenatal effects of methotrexate (MTX) in rats and rabbits were assessed. It was found highly embryotoxic in postimplantation rat embryos; 0.3 mg/kg ip or less caused nearly total embryolethality with slight teratogenicity. Rabbit embryos were far more resistant to small doses of MTX than rats, but 19.2 mg/kg iv, when given during days 10 to 15 of gestation, produced little death and a constant spectrum of malformation in a high percentage of offspring. Cleft palate, skull defects, and severe fore- and hindlimb dysplasias, occurred with a high degree of regularity and were strongly dose and developmental-stage specific.

Decreased fertility in mice exposed to environmental air pollution in the city of Sao Paulo

It has largely been shown that air pollution can affect human health. Effects on human fertility have been shown mainly in males by a decrease in semen quality. Few studies have focused on the environmental effects on female fertility. The aim of the present study was to analyze the effects of air pollution in the city of Sao Paulo on mouse female fertility. Four groups of female Balb/c mice were placed in two chambers 10 days (newborn) or 10 weeks (adults) after birth. Mice were maintained in the chambers 24 h a day, 7 days a week, for 4 months. The first chamber received air that had passed through an air filter (clean chamber) and the second received ambient air (polluted chamber). We measured PM10 and NO2 inside both chambers. Mice belonging to the adult groups were bred to male mice after living for 3 months inside the chambers. The newborn groups mated after reaching reproductive age (12 weeks). After 19 days of pregnancy the numbers of live-born pups, reabsorptions, fetal deaths, corpora lutea, and implantation failures were determined. PM10 and NO2 concentrations in the clean chamber were 50% and 77.5% lower than in the polluted chamber, respectively. Differences in fertility parameters between groups were observed only in animals exposed to air pollution at an early age (10 days after birth). We observed a higher number of live-born pups per animal in the clean chamber than per animal from the polluted chamber (median=6.0 and 4.0, respectively; P=0.037). There was a higher incidence of implantation failures in the polluted group than in the clean group (median=3.5 and 2.0, respectively; P=0.048). There were no significant differences in the other reproductive parameters between groups. These results support the concept that female reproductive health represents a target of air pollutants.

The antiabortive effect of progesterone-induced blocking factor in mice is manifested by modulating NK activity

Immunologic effects of progesterone are mediated by a protein named the progesterone-induced blocking factor (PIBF), which inhibits NK activity and displays an antiabortive effect in mice. Our previous data provide indirect evidence for the importance of PIBF in the maintenance of normal gestation. This study was aimed at investigating whether neutralization of endogenous PIBF production influences pregnancy outcome and if so, what are the mechanisms that participate in this process. Syngeneically pregnant Balb/c mice on Day 8.5 of pregnancy were injected ip with 0.3 mg/kg of RU 486 or with 0.5 mg of rabbit anti-PIBF IgG alone, or together with anti-NK monoclonal antibodies. Mice treated with the same amount of normal rabbit serum or untreated mice of similar gestational age were used as controls. On Day 10.5 the ratio of living and resorbed embryos and NK activity of the spleen cells were determined. In mice treated with anti-PIBF the ratio of resorbed fetuses was significantly higher than that in untreated controls. In RU 486-treated mice we also observed significantly increased resorption rate, which was associated with the inability of spleen cells to produce PIBF. Both anti-PIBF treatment and that with progesterone receptor blocker resulted in increased splenic NK activity. There was a positive relationship between NK activity and the rate of resorptions. All the above effects were corrected by simultaneous treatment with anti-NK or anti-NC (natural cytotoxic) antibodies. These data allow the conclusion that PIBF contributes to normal gestation in mice and that the effect of PIBF is manifested via blocking NK and/or NC activity.

A comparative study of the reproductive effects of methadone and benzo[a]pyrene in the pregnant and pseudopregnant rat

Benzo[a]pyrene (BP; 50 mg/kg) or methadone (5 mg/kg) was given subcutaneously to pregnant rats at different stages of gestation. Both BP and methadone affected the reproductive performance of pregnant rats by significantly increasing the number of resorptions and fetal wastage, and by decreasing the fetal weight. The same dosage levels of BP and methadone were also given to pseudopregnant rats (PSP) with an induced decidual cell reaction (DCR) in an attempt to distinguish whether adverse effects occur in the maternal or fetal compartment or both. Since the hormonal requirements for DCR and implantation are similar and the anatomical, histological, cytological, time sequential changes as well as appearance of the vasculature system for DCR and decidua are indistinguishable, PSP with DCR is similar to pregnancy except for the lack of a fetal compartment. BP, in this PSP model, significantly reduced the uterine wet weight and cyclic nucleotide (cAMP) and cGMP) levels whereas methadone was without a detectable effect. Our findings then suggest that BP may exert its effects adversely on both the maternal and fetal compartments, whereas methadone may act primarily in the fetal compartment.

Rat and Rabbit Oral Developmental Toxicology Studies With Two Perfluorinated Compounds

Developmental toxicology (teratology) studies were done on two perfluorinated compounds-perfluorooctanesulfonate (PFOS) and 2-(N-ethylperfluorooctanesulfonamido)ethyl alcohol (N-EtFOSE) in rats and rabbits. Dose selection for these oral developmental toxicity studies were based upon dose-range study results. Dose levels of 0, 1, 5, 10, and 20 mg/kg/day were used for the rat N-EtFOSE study, and dose levels of 0, 0.1, 1.0, 2.5, and 3.75 mg/kg/day were used for both the PFOS and the N-EtFOSE rabbit studies. Although no compound-related deaths occurred in the dosed pregnant females on the developmental toxicity studies, maternal toxicity (reduced body weight gain and feed consumption) was present at higher dose levels in all three studies. At high maternally toxic doses, associated effects occurred in the conceptuses--increased abortions in PFOS and N-EtFOSE rabbits, reduced fetal weights in N-EtFOSE rats and PFOS rabbits, and increased late resorptions in N-EtFOSE rabbits. Detailed external gross, soft tissue, and skeletal fetal examinations failed to reveal any compound-related malformations in either species. Similar results, that is, only effects associated with maternal toxicity, had been found in previously conducted PFOS rat developmental toxicity studies. It was concluded that these perfluorinated compounds were not selective developmental toxicants in either rats or rabbits.

On the embryotoxic effects of benzene and its alkyl derivatives in mice, rats and rabbits

Groups of CFY rats were exposed to inhalation of ethylbenzene at 600, 1200 or 2400 mg/m3 or xylene at 250, 1900 or 3400 mg/m3 or Aromatol at 500, 1000 or 2000 mg/m3 atmospheric concentration for 24 h/day from day 7 to day 15 of pregnancy, or for 2-4 hours only on the 18th or 20th day of gestation. CFLP mice and NZ rabbits were exposed to inhalation of 500 mg/m3 or 1000 mg/m3 benzene, toluene, ortho-, meta-, para-xylene, ethylbenzene, xylene or Aromatol for 24 h/day from day 6 to day 15 of pregnancy. Untreated animals and groups inhaling pure air served as controls. All components of the xylene and Aromatol crossed the placenta and were present in fetal blood and amniotic fluid, as well. The maternal toxic effects at all solvents were moderate and dose dependent. All solvents (at higher concentrations) brought about skeletal and weight retardation in fetuses of rats and mice. At highest concentration some solvents increased the post-implantation loss in rats and mice. All solvents caused spontaneous abortion in rabbits at 1000 mg/m3 atmospheric concentration. Only ethylbenzene and Aromatol increased the malformation rate in rats and mice. No other solvent applied proved to be teratogenic either in mice, rats or rabbits.

Determination of the proximate teratogen of the mouse fetal alcohol syndrome. 1. Teratogenicity of ethanol and acetaldehyde

The proximate teratogen of the fetal alcohol syndrome is unknown. CD-1 mice were treated ip on Day 10 of gestation with 2, 4, 6, or 7 g/kg ethanol. The percentage of resorptions and malformed fetuses was increased and mean fetal weight was decreased in a dose-related manner. Treatment with 7 g/kg ethanol ip on one of gestational Days 7, 8, 9, 10, or 11 significantly increased the percentage of malformed fetuses and decreased fetal weight. In addition, treatment on Days 10 or 11 significantly increased the percentage of resorptions. Coadministration of 100 mg/kg of 4-methylpyrazole, an inhibitor of alcohol dehydrogenase, orally with 6 g/kg ethanol ip on Day 10 of gestation dramatically increased the embryotoxicity of ethanol. Five ip treatments of 200 mg/kg acetaldehyde at 2-hr intervals on Day 10 of gestation did not significantly increase the percentage of resorptions and malformed fetuses or decrease fetal weight. These data suggest that ethanol is the proximate teratogen of the fetal alcohol syndrome in CD-1 mice.

Developmental toxicity of butyl benzyl phthalate in the rat using a multiple dose study design

The developmental toxicity of butyl benzyl phthalate (BBP) was investigated in the rat using ten dose groups between 270 and 2100 mg/kg/day. Exposure was by daily gavage from gestation day 5 through 16 or gestation day 5 through 20. Dose-response data were analyzed using the benchmark approach by fitting dose-response models to the various endpoints. BBP induced increased liver and kidney weights in dams, accompanied by liver enzyme increases in maternal serum. Extramedullary hematopoiesis, which was already substantial in control pregnant animals, was increased after BBP treatment. Fetotoxicity included increased resorptions, reduced fetal weights, increased incidence of skeletal anomalies, and reduced fetal testis weights in the presence of an increased incidence of retarded testicular descent. As embryotoxicity was found at lower dosages compared to observed maternal toxicity, BBP appeared to be a specifically embryotoxic compound. The extended exposure protocol (gestation day 5 through 20) appeared more sensitive for measuring fetotoxic effects. We recommend the use of more doses in toxicity tests, together with the benchmark approach as an appropriate and more accurate method for analyzing dose-response data compared to the NOAEL approach.

Genetically mediated induction of drug-metabolizing enzymes associated with congenital defects in the mouse

Various polycyclic aromatic compounds induce certain monooxygenase activities, including aryl hydrocarbon (benzo[a]pyrene) hydroxylase (EC 1.14.14.2), and cytochrome P1-450 in the liver and many nonhepatic tissues of the mouse. This induction process is controlled by the Ah locus. Genetic differences that have been shown in the past to be associated with the Ah locus include an increased susceptibility to chemical carcinogenesis, mutagenicity in vitro, and drug toxicity--manifested as hepatic necrosis, aplastic anemia, or shortened survival time. Pregnant mice received a single injection of 3-methylcholanthrene or 7,12-dimethylbenz[a] anthracene between day 5 and day 13 of gestation, and the uterine contents were examined on day 18. Striking increases were observed in the incidence of MC-1 and DMBA-induced resorptions and congenital malformations in the aromatic hydrocarbon "responsive" C57BL/6N inbred strain, and of DMBA-induced resorptions in the "responsive" C3H/HeN and BALB/cAnN strains--when compared with the similarly treated genetically "nonresponsive" AKR/N strain. These data suggest but do not prove that an association exists between the Ah locus and developmental toxicity, i.e., teratogenesis. Although numerous teratogenic differences among inbred mouse strains have previously reported, this study is unique in that the genetic differences in teratogenicity observed were predicted in advance on the basis of known differences among these strains in polycyclic hydrocarbon metabolism regulated by the Ah locus.

Protection from ethanol‐induced limb malformations by the superoxide dismutase/catalase mimetic, EUK‐134

Based on previous in vitro studies that have illustrated prevention of ethanol-induced cell death by antioxidants, using an in vivo model, we have tested the anti-teratogenic potential of a potent synthetic superoxide dismutase plus catalase mimetic, EUK-134. The developing limb of C57BL/6J mice, which is sensitive to ethanol-induced reduction defects, served as the model system. On their ninth day of pregnancy, C57BL/6J mice were administered ethanol (two intraperitoneal doses of 2.9 g/kg given 4 h apart) alone or in combination with EUK-134 (two doses of 10 mg/kg). Pregnant control mice were similarly treated with either vehicle or EUK-134, alone. Within 15 h of the initial ethanol exposure, excessive apoptotic cell death was observed in the apical ectodermal ridge (AER) of the newly forming forelimb buds. Forelimb defects, including postaxial ectrodactyly, metacarpal, and ulnar deficiencies, occurred in 67.3% of the ethanol-exposed fetuses that were examined at 18 days of gestation. The right forelimbs were preferentially affected. No limb malformations were observed in control fetuses. Cell death in the AER of embryos concurrently exposed to ethanol and EUK-134 was notably reduced compared with that in embryos from ethanol-treated dams. Additionally, the antioxidant treatment reduced the incidence of forelimb malformations to 35.9%. This work illustrates that antioxidants can significantly improve the adverse developmental outcome that results from ethanol exposure in utero, diminishing the incidence and severity of major malformations that result from exposure to this important human teratogen.

Characterization of the developmental toxicity of di-n-butyl phthalate in rats

The objective of this study was to determine the characterization of the developmental toxicity of di-n-butyl phthalate (DBP) in rats. Pregnant rats were given DBP by gastric intubation at a dose of 0.75, 1.0 or 1.5 g/kg on days 7-9, 10-12 or 13-15 of pregnancy. Postimplantation loss was 100% for each period of dosing at 1.5 g/kg. A significant increase in the postimplantation loss was found in dams given DBP at doses of 0.75 and 1.0 g/kg regardless of the days of treatment. No evidence of teratogenicity was detected when DBP was given on days 10-12. Treatment on days 7-9 with DBP at doses of 0.75 and 1.0 g/kg caused a significant increase in the number of skeletal malformations such as deformity of the vertebral column in the cervical and thoracic regions and of the ribs, but neither external nor internal malformations. Treatment with DBP on days 13-15 at doses of 0.75 and 1.0 g/kg resulted in a significant increase in the incidence of fetuses with external and skeletal malformations such as cleft palate and fusion of the sternebrae. The frequency of malformations increased as the dose of DBP was increased. The highest incidence of malformed fetuses occurred after treatment with DBP on days 13-15. It could be concluded that susceptibility to the teratogenicity of DBP varies with the developmental stage at the time of administration.

The teratogenicity of methoxyacetic acid in the rat

Intraperitoneal (i.p.) administration of methoxyacetic acid (MAA) to rats on Day 8, 10, 12 or 14 of pregnancy was embryolethal and teratogenic. Skeletal anomalies, hydrocephalus and dilatation of the kidney pelvis were the most common malformations. Embryonic response to MAA varied with gestational age and with dosage (0.1 to 2.5 mmol/kg). These actions are similar to those previously reported for 2-methoxyethanol (ME) and dimethoxyethyl phthalate (DMEP). Embryos were also examined on Day 12, 48 h following i.p. administration of 2.5 mmol/kg MAA. Abnormalities were comparable to those previously observed following MAA treatment of rat conceptuses in culture. These data support the conclusion that MAA is the proximal teratogenic metabolite of ME and DMEP.

Correlation between maternal toxicity and embryo/fetal effects

It has been widely debated whether embryo/fetal toxicity is secondary to maternal toxicity. This argument has led to great difficulties for administrative decision makers involved in public health evaluation of drugs or chemicals. The present study sought to characterize whether there is a correlation between maternal toxicity and embryo/fetal toxicity. Developmental data from control and treated animals in our laboratory were collected and evaluated. Maternal toxicity, defined here as maternal body weight change, was statistically correlated with embryo/fetal parameters. The result showed that embryo/fetal parameters did not correlate with the body weight change. It can be concluded that maternal toxicity does not always lead to embryo/fetal toxicity; therefore, findings should be handled on a case by case basis and causal relationships should be established.

Modulation of phenytoin teratogenicity and embryonic covalent binding by acetylsalicylic acid, caffeic acid, and alpha-phenyl-N-t-butylnitrone: implications for bioactivation by prostaglandin synthetase

Teratogenicity of the anticonvulsant drug phenytoin is thought to involve its bioactivation by cytochromes P-450 to a reactive arene oxide intermediate. We hypothesized that phenytoin also may be bioactivated to a teratogenic free radical intermediate by another enzymatic system, prostaglandin synthetase. To evaluate the teratogenic contribution of this latter pathway, an irreversible inhibitor of prostaglandin synthetase, acetylsalicylic acid (ASA), 10 mg/kg intraperitoneally (ip), was administered to pregnant CD-1 mice at 9:00 AM on Gestational Days 12 and 13, 2 hr before phenytoin, 65 mg/kg ip. Other groups were pretreated 2 hr prior to phenytoin administration with either the antioxidant caffeic acid or the free radical spin trapping agent alpha-phenyl-N-t-butylnitrone (PBN). Caffeic acid and PBN were given ip in doses that respectively were up to 1.0 to 0.05 molar equivalents to the dose of phenytoin. Dams were killed on Day 19 and the fetuses were assessed for teratologic anomalies. A similar study evaluated the effect of ASA on the in vivo covalent binding of radiolabeled phenytoin administered on Day 12, in which case dams were killed 24 hr later on Day 13. ASA pretreatment produced a 50% reduction in the incidence of fetal cleft palates induced by phenytoin (p less than 0.05), without significantly altering the incidence of resorptions or mean fetal body weight. Pretreatment with either caffeic acid or PBN resulted in dose-related decreases in the incidence of fetal cleft palates produced by phenytoin, with maximal respective reductions of 71 and 82% at the highest doses of caffeic acid and PBN (p less than 0.05). Caffeic acid and PBN also significantly reduced the incidence of fetal resorptions produced by phenytoin, but not the fetal weight loss. In viable embryos, ASA pretreatment reduced the covalent binding of phenytoin to embryonic protein by 43% (p less than 0.05). Binding of phenytoin to embryonic resorptions was equally high with and without ASA pretreatment, and within each treatment group was 3- to 10-fold higher than that in the respective placentas and associated viable embryos (p less than 0.05). These results suggest that prostaglandin synthetase may contribute to the enzymatic bioactivation of phenytoin to a teratogenic free radical intermediate.