Biomedical subjects

H Nau

Publications and source records attributed to H Nau.

At least 19 recordsLinked to original sources

PubMed1992

Differentiation between valproate-induced anticonvulsant effect, teratogenicity and hepatotoxicity. Aspects of species variation, pharmacokinetics, metabolism and implications of structural specificity for the development of alternative antiepileptic agents such as delta 2-valproate.

Valproate is metabolized into a large number of compounds via various metabolic routes. Metabolic profiles depend on species and age. Hepatotoxicity may be correlated with abnormal metabolism, especially in young age. Teratogenicity is associated with specific structural requirements: a free carboxyl atom connected to a carbon atom which also carries a hydrogen, and two carbon chains. This provides a clue for the development of alternative antiepileptic agents.

Abnormalities, Drug-Induced↗

PubMed1992

Methotrexate increases valproic acid-induced developmental toxicity, in particular neural tube defects in mice.

The hypothesis that valproic acid-induced dysmorphogenesis may be due to an interference of this drug with folate metabolic pathways was further investigated by a study of a possible interaction of valproic acid (VPA) and the established folate antagonist methotrexate (MTX). The dihydrofolate reductase inhibitor MTX (1.25 and 2.5 mg/kg, i.p.) was injected 15 min prior to VPA (300 and 400 mg/kg, s.c.) in day 8 pregnant NMRI mice. Fetuses were examined for exencephaly, resorption, and fetal weight retardation on day 18 of gestation. MTX produced no exencephaly or reduction in fetal weight, and the 2.5-mg/kg dose caused 56% resorption. Higher doses (5-20 mg/kg) produced embryolethality and fetal weight retardation, but no exencephaly. VPA (300 and 400 mg/kg) administration resulted in 3.4% and 12.6% exencephaly and 9% and 19% resorptions, respectively. Coadministration of MTX with VPA significantly increased VPA-induced resorption and exencephaly rates as well as fetal weight retardation. Exencephaly induced by VPA 400 mg/kg was increased to 29.5% and 24.1% (P < 0.01 and P < 0.05) when given with 1.25 and 2.5 mg/kg MTX, respectively. MTX (2.5 mg/kg i.p.) did not alter transplacental VPA (400 mg/kg, s.c.) pharmacokinetics. These results support the view that VPA-induced teratogenesis may be mediated by interaction with folate metabolism.

Abnormalities, Drug-Induced↗

PubMed1992

Valproic acid-induced spina bifida: a mouse model.

Prenatal exposure to the antiepileptic drug valproic acid (VPA) has been associated with the formation of spina bifida aperta, meningocele, and meningomyelocele in the human. Until now, a direct relationship between VPA application and spina bifida has not been experimentally demonstrated. VPA was known only to induce exencephaly in mice, a defect of the anterior neural tube. Maximal sensitivity toward production of this defect was on day 8 of gestation (plug day = day 0). The closure of the posterior neuropore occurs later in the development of mice than the closure of the anterior neuropore. To investigate whether there is a direct relationship between VPA application during pregnancy and induction of spina bifida in mice, we administered various doses of the drug on day 9 of gestation, at three time intervals (at 0, 6, and 12 hr). This administration of VPA produced spina bifida aperta and spina bifida occulta in mice. High doses of VPA (3 x 450 and 3 x 500 mg/kg) induced a low rate of spina bifida aperta in the lumbosacral region. High incidences of spina bifida occulta, a less serious form of spina bifida, were induced with lower doses. This malformation was demonstrated in double-stained fetal skeletons by measurements of the distance between the cartilaginous ends of each vertebral arch. The occurrence of this defect and its localization was dose-dependent. The lumbar region was affected by all doses investigated (3 x 300, 3 x 350, 3 x 400, 3 x 450, and 3 x 500 mg/kg). The sacral/coccygeal region was affected additionally, but with higher doses (3 x 400, 3 x 450, and 3 x 500 mg/kg). A comparison of the results obtained with day 16 and 17 control fetuses showed that the pattern of gaps present in the lumbar and sacral region of the spinal cord in treated groups was drug-specific and not related to a developmental delay. Our results indicate that multiple administrations of VPA on day 9 of gestation in mice result in a low incidence of spina bifida aperta and a high incidence of spina bifida occulta, and provides a relevant model for the study of human spina bifida defects.

Abnormalities, Drug-Induced↗

PubMed1992

Spina bifida aperta induced by valproic acid and by all-trans-retinoic acid in the mouse: distinct differences in morphology and periods of sensitivity.

The antiepileptic drug valproic acid (VPA) has been implicated as a human teratogen causing spina bifida aperta. Recently, we developed a mouse model inducing spina bifida aperta with VPA. To elucidate the pathogenesis of VPA-induced spina bifida aperta we now investigated the anatomy and histology of this defect in the mouse. The morphology of spina bifida aperta induced by all-trans-retinoic acid (RA) was used for comparison. Various doses of VPA and RA were administered at different times to determine the periods of sensitivity for inducing spina bifida aperta with these drugs. Each administration regimen consisted of three doses applied at intervals of 6 hr. RA induced spina bifida aperta during an earlier developmental period (day 8 of gestation) than VPA (day 9 of gestation). The most effective regimens for induction of spina bifida aperta in mice were injections of 3 x 500 mg VPA-Na/kg body weight (b.w.) intraperitoneally on day 9 of gestation at 0, 6, and 12 hr; RA (12.5 mg/kg b.w.) was given orally on day 8 of gestation at 12 and 18 hr, day 9 at 0 hr. VPA did not induce spina bifida aperta on day 8 of gestation and RA did not induce this effect on day 9 of gestation. Histological studies of day 18 fetuses carrying spina bifida aperta were performed. The spina bifida aperta induced by VPA shows a disorganized and necrotic spinal cord. In the vertebral canal were observed cell debris, blood cells, capillaries, macrophages, and rests of meninges. These results indicate that the spinal cord is almost destroyed at the affected section. In contrast, the spina bifida aperta induced by RA demonstrates a spinal cord organized in the gray and white matter, the dorsal and ventral horn. But the neural canal does not exist, only a layer of ependymal cells lies on the surface of the spinal cord. Our results indicate that the morphology of spina bifida aperta induced by VPA differed distinctly from that induced by RA in the mouse fetus. Moreover VPA produced a spina bifida aperta with a specific morphology. Also the period of sensitivity for induction of this lesion differed and occurred earlier for RA than for VPA. VPA and RA may possibly induce spina bifida aperta via different mechanisms in the mouse.

Animals↗

PubMed1992

4-Methylpyrazole partially ameliorated the teratogenicity of retinol and reduced the metabolic formation of all-trans-retinoic acid in the mouse.

Oral administration of retinol (50 mg/kg) to NMRI mice on day 11 of gestation (vaginal plug = day 0) led to the metabolic formation of high quantities of all-trans retinoic acid and all-trans-4-oxoretinoic acid, both known as potent teratogenic agents in the mouse. A 96% reduction of the area under the concentration-versus-time-curve (AUC) of metabolically generated all-trans retinoic acid in maternal plasma, and an 84% decrease in the embryonic AUC were observed when mice had been pretreated with the alcohol dehydrogenase inhibitor 4-methylpyrazole. A similar reduction was observed for the major metabolite of all-trans retinoic acid in the mouse, all-trans-4-oxoretinoic acid. However, 4-methylpyrazole pretreatment decreased the AUC of retinol by 10% in maternal plasma and 15% in embryo. Treatment with retinol alone resulted in 55.6%, 43.9% and 56.0% skeletal anomalies of the forelimbs, hindlimbs and craniofacial structures, respectively. Pretreatment with 4-methylpyrazole lowered the retinol induced skeletal defects to 31.3%, 24.0% and 31.3%, respectively, in the forelimb, hindlimb and craniofacial region. Typical retinoid-induced malformations for gestational day 11, e.g. bent or reduced zeugopod or stylopod elements, or cleft palate, were significantly reduced by 4-methylpyrazole pretreatment but were still detected in significantly higher prevalence than in control mice. These data suggest that the teratogenic activity of a single high dose of vitamin A in mouse is partially but not exclusively dependent on the metabolic activation of retinol to all-trans retinoic acid. Thus it could be hypothesized that retinol is either a proximate teratogen or a coteratogen with all-trans retinoic acid.

Abnormalities, Drug-Induced↗

PubMed1992

The disposition of valproate and its metabolites in the late first trimester and early second trimester of pregnancy in maternal serum, urine, and amniotic fluid: effect of dose, co-medication, and the presence of spina bifida.

We have studied 52 pregnancies in epileptic women taking long-term valproate and have measured the concentrations of the parent compound and 13 of its metabolites by gas chromatography-mass spectrometry in amniotic fluid, maternal serum, and 24 h maternal urine samples. All metabolites of valproate present in the serum could also be detected in the amniotic fluid, although at much lower concentrations. Amniotic fluid concentrations of valproate and several of its metabolites ((E) delta 2-valproate, (2E,3'E) delta 2,3'-valproate, and 3-keto-valproate) correlated with total valproate concentrations as well as with unbound valproate concentrations in maternal serum. We suggest that the amniotic fluid acts as a deep compartment, with slow appearance and disappearance of valproate and its main metabolites. The data further suggest that during the first and early second trimesters of pregnancy the beta-oxidation of valproate decreases. In pregnancies associated with fetal neural tube defects (n = 5) significantly higher daily doses of valproate were used compared with normal pregnancies (n = 47). This resulted in higher concentrations of valproate in maternal serum. However, the metabolite patterns in maternal serum, 24 h urine samples, and amniotic fluid did not show any significant differences in pregnancies with neural tube defects.

Amniocentesis↗

PubMed1992

Murine teratology and pharmacokinetics of the enantiomers of sodium 2-ethylhexanoate.

A mouse model for the induction of exencephaly with sodium (+/-)-2-ethylhexanoate has been developed using multiple administration regimes. With three consecutive administrations at one-half-day intervals, the most sensitive time to induce exencephaly was Gestational Days 8-9. Using the racemic substance it was determined that the SWV strain was more sensitive to the induction of exencephaly than the C57BL/6NCrlBR strain. The enantiomers of 2-ethylhexanoic acid were separated via preparative HPLC to greater than 99.8% optical purity, and greater than 99% purity according to a gas chromatographic analysis. It was demonstrated that the (R)-enantiomer is a more potent teratogen than the (S)-enantiomer for the induction of exencephaly as well as malformations of other organ systems. Pharmacokinetic analyses for each of the enantiomers were performed in maternal plasma, maternal muscle, and embryo. The pharmacokinetics showed that the peak concentration (Cmax) for both enantiomers in the three compartments was approximately equivalent and was attained within 15 min following the third administration. The area under the concentration versus time curve values for the two enantiomers were approximately 10% higher for the (R)-antipode because of a slightly slower elimination of this compound. There was negligible (or no) racemization of the two enantiomers in the biological samples. The results suggest that teratologic differences in the enantiomers of sodium 2-ethylhexanoate are not due to differences in the concentrations of these antipodes in the embryo, but more likely result from the specific interaction of the enantiomers with chiral molecules in the embryo.

Abnormalities, Drug-Induced↗

PubMed1992

Quantitative plasma disposition of retinol and retinyl esters after high-dose oral vitamin A administration in the cynomolgus monkey.

A solid-phase extraction technique followed by automated high-performance liquid chromatography sample elution was successfully used to evaluate the effect of three pharmaceutical parameters on the plasma profile of various forms of vitamin A after an oral dose to cynomolgus monkeys. The three parameters evaluated were the chemical form of vitamin A (retinol versus retinyl acetate), the vehicle (acetone/Tween 20/water versus acetone/soybean oil), and the retinol dose (2, 10, and 50 x 10(3) retinol equivalents/kg). The form of the administered compound, retinol or retinyl acetate, appeared to have no major effect on the formation of nonpolar retinoids. The ester profile in plasma differed depending on whether the dose was administered in the water-based or the oil-based vehicle. Irrespective of the vehicle type the predominant retinoid formed was retinyl palmitate/oleate. However, retinol doses in the water-based vehicle formed relatively high concentrations of retinyl laurate and retinyl myristate but no retinyl linolenate. The retinol dose in the oil-based vehicle formed consistent, but relatively minor, concentrations of retinyl linolenate, higher relative concentrations of retinyl linoleate, and no retinyl laurate or myristate. The dose of retinol administered had an impact on the diversity of the nonpolar retinoid profile. The low dose led to the presence of almost exclusively retinyl palmitate/oleate and retinyl stearate, whereas at higher doses the other retinyl esters became major retinol constituents.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗

PubMed1992

Effect of supplementation with folinic acid, vitamin B6, and vitamin B12 on valproic acid-induced teratogenesis in mice.

The effect of administration of folinic acid, vitamin B6 + vitamin B12, and their combination on valproic acid (VPA)-induced teratogenesis was studied in NMRI mice. VPA (500 mg/kg, sc) was injected on Day 8 of gestation and the vitamins (two dose levels) were injected ip 1 hr before, immediately before, and 1 hr after VPA administration. Folinic acid significantly reduced VPA-induced resorptions (21-24%), and palate, rib, and sternebral malformations. Exencephaly and spina bifida occulta were also reduced (14 and 40%, respectively), but the difference was not statistically significant. On the other hand, vitamin B6 + vitamin B12 significantly reduced VPA-induced exencephaly (23%), spina bifida occulta (80%), palate and rib malformations, kidney abnormalities, and fetal weight retardation. A combination of the three vitamins was effective in reducing VPA-induced exencephaly (23-30%), spina bifida occulta (60%), and palate and rib malformations. The protection against VPA-induced malformations was not complete and was not always dose related, and the reduction in exencephaly rate was only significant in the absence of a reduction in resorption rate. Full-length cleft palate, sternebral malformations, and retarded sternebral and caudal ossification were, however, increased by the high dose of combined vitamin administration. The present study supports the view that VPA-induced teratogenesis may be mediated via an interaction with folate metabolism. Although folinic acid and vitamin B6 + vitamin B12 can effectively reduce VPA malformations, the protection was not complete, which may suggest the involvement of other factors. Furthermore, the dose levels should be carefully chosen since high doses of the combined vitamins can actually increase the incidence of certain defects.

Abnormalities, Drug-Induced↗

PubMed1992

The enantioselective teratogenicity of 2-n-propyl-4-pentynoic acid (4-yn-VPA) is due to stereoselective intrinsic activity and not differences in pharmacokinetics.

The present study was designed to investigate whether there are pharmacokinetic reasons for the enantioselective teratogenicity of R(+)-4-yn-VPA (low potency) and S(-)-4-yn-VPA (high potency). A gas chromatographic method was employed to determine 4-yn-VPA enantiomers in maternal plasma, brain, erythrocytes and in the embryo and decidua/extraembryonic membranes of the mouse following a single intraperitoneal dose of 300 mg/kg (+/-)-4-yn-VPA-Na on day 9 of gestation. Furthermore, the pharmacokinetics of R- and S-4-yn-VPA were studied in maternal plasma of day-8 pregnant mice following intraperitoneal administration of 300 and 500 mg (+/-)-4-yn-VPA-Na/kg body wt., respectively. No significant difference in the pharmacokinetic profiles of the two enantiomers was detected in either the maternal organism or in the embryonic compartments. Thus, the two enantiomers reach the embryo in comparable concentrations during the sensitive period of organogenesis, but exhibit very different teratogenic activities. This study therefore indicates that the stereoselective teratogenicity of 4-yn-VPA is due to differences in intrinsic activities and not due to differences in the pharmacokinetics of the enantiomers.

Animals↗

PubMed1992

Effects of valproate and E-2-en-valproate on functional and morphological parameters of rat liver. I. Biochemical, histopathological and pharmacokinetic studies.

E-2-en-Valproate (E-2-en-VPA; trans-2-en-VPA) and VPA were studied for potential hepatotoxicity in young male Sprague-Dawley rats. Both drugs were administered daily at 750 mg/kg i.p. (divided into three doses a day) for 7 consecutive days. Clinical chemistry parameters were studied before and after the period of treatment. Furthermore, the drug pharmacokinetics and metabolism were analyzed at onset and end of the prolonged administration. Treatment with VPA induced hyperammonemia and other alterations in liver function tests which were not observed after treatment with E-2-en-VPA, although plasma levels of both drugs were comparable. The pharmacokinetics of VPA and E-2-en-VPA in young rats were similar, but analysis of metabolites by gas chromatography-mass spectrometry indicated marked differences in the metabolite profile, e.g., a lack of the suspected hepatotoxic metabolite 4-en-VPA in plasma of rats treated with E-2-en-VPA. Histopathological examination of liver sections showed that VPA and E-2-en-VPA did not induce degenerative liver lesions or significant alterations in hepatic content and distribution of lipids and glycogen at the doses administered. Only one of the VPA treated rats showed fatty infiltration (microvesicular steatosis). The data demonstrate that, although E-2-en-VPA is more potent than VPA as an anticonvulsant in rats, it does not exert more potent hepatotoxic effects and does not alter ammonia metabolism. Thus the data substantiate previous experimental studies that E-2-en-VPA might be a valuable substitute for VPA.

Animals↗

PubMed1992

The enantiomers of the valproic acid analogue 2-n-propyl-4-pentynoic acid (4-yn-VPA): asymmetric synthesis and highly stereoselective teratogenicity in mice.

The teratogenic activities of R(+)- and S(-)-2-n-propyl-4-pentynoic acid (R and S-4-yn-VPA), the enantiomers of the highly teratogenic valproic acid (VPA) analogues (+/-)-4-yn-VPA, were investigated in mice. The enantiomers were prepared via asymmetric synthesis, each in three steps employing the chiral auxiliaries (4R,5S)-4-methyl-5-phenyl-2-oxazolidinone and S-4-benzyl-2-oxazolidinone. The determination of the absolute configurations and the optical purities is described. R(+)-4-yn-VPA contained 7%, and S(-)-4-yn-VPA 8%, of the respective antipodes. The aqueous solutions of the sodium salts of R- and S-4-yn-VPA were administered as single i.p. injections during early organogenesis in the mouse (day 8 of gestation) using the induction of exencephaly as the teratological end point. Dose/exencephaly curves indicated that S-4-yn-VPA is 7.5 times more teratogenic than its antipode, 1.9 times more teratogenic than (+/-)-4-yn-VPA and 3.9 times more teratogenic than the parent drug VPA. In contrast, the neurotoxicity (maternal toxicity) of the 4-yn-VPA enantiomers was found to be independent of the stereo-chemical configuration and lower than achieved after VPA administration. Due to its low neurotoxicity and highly stereoselective neural tube-inducing activity, S-4-yn-VPA should prove an important tool for the investigation of molecular mechanism of the teratogenic action in this class of compounds; R-4-yn-VPA could act as the negative control in these studies.

Abnormalities, Drug-Induced↗

PubMed1992

The valproic acid metabolite E-2-n-propyl-2-pentenoic acid does not induce spina bifida in the mouse.

The antiepileptic drug valproic acid (VPA) has been implicated as a human teratogen causing spina bifida aperta. Recently we developed a mouse model inducing spina bifida aperta and occulta with VPA. In a search for novel antiepileptic agents the VPA metabolite E-2-n-propyl-2-pentenoic acid (2-en-VPA) had been developed. In the mouse, 2-en-VPA exhibits anticonvulsive potency similar to VPA but very low teratogenic potency (induction of exencephaly). We have now compared VPA and its metabolite 2-en-VPA in regard to induction of spina bifida in our mouse model. 2-en-VPA was administered 3 times during the period of gestation most sensitive for the induction of spina bifida aperta with VPA: on day 9 of gestation at 0, 6 and 12 h. The following doses were injected (in mmol 2-en-VPA-Na/kg): (a) 3 x 2.1, (b) 3 x 2.7 (the equimolar dose of VPA is the threshold dose for induction of spina bifida aperta) and (c) 3 x 3.0 (the equimolar VPA dose produced spina bifida aperta). 2-en-VPA did not induce spina bifida aperta in the mouse in any of these groups. We then investigated the induction of spina bifida occulta in the three dose groups. Spina bifida occulta is a less serious form of spina bifida and may provide a sensitive method to estimate the potency of a compound to induce more severe forms of spina bifida. This malformation was demonstrated in alcian-blue- and alizarin-red-stained fetal skeletons by measurements of the distance between the cartilaginous ends of each vertebral arch.(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormalities, Drug-Induced↗

PubMed1992

Modulation of myb gene expression in sponges by retinoic acid.

We demonstrate that the cells of the sponge Geodia cydonium are equipped with the basic elements required for a retinoic acid (RA)-dependent response pathway; RA was identified and quantitated, the cellular RA-binding protein (CRABP) was detected and the nuclear RA receptor (RAR) was found. In the isolated cell system the level of CRABP, but not of RAR, is strongly induced after incubating the cells for 10h with the homologous aggregation factor. In induced cells incubation with 0.3 microM RA results in a strong down-regulation of the c-myb (or c-myb-related) proto-oncogene (M(r) 63,000; mRNA 3.3 kb). We postulate that this pathway is also functionally active and that RA acts as a natural morphogen.

Animals↗

PubMed1992

[Irreversible valproate-associated liver failure].

A very severely retarded infant with a Dandy-Walker malformation was treated with valproate since the age of 6 months on account of infantile spasms. Three weeks after start of therapy dexamethasone was applied additionally because valproate was ineffective. Seventy-six days after initiation of valproate therapy the infant died with the clinical signs of fulminant valproate-associated hepatotoxicity despite the discontinuation of valproate. In combination with a febrile otitis media the child had been periodically restless and lethargic during the last week prior to liver coma. Activity of liver enzymes remained within normal limits up to two days before coma occurred. Analysis of valproate metabolites by gas chromatography/mass spectrometry yielded unusually high concentrations of the di-unsaturated metabolite E,E-2,3'-dien-valproate before and during liver failure. The concentrations of the main metabolites E-2-en-valproate und 3-keto-valproate remained within the usual range found during valproate therapy at steady state. The oxydation products 4-en-valproate and E-2,4-dien-valproate which are formed by alternative pathways and are considered to be hepatotoxic were detected in very low concentrations only. The application of carnitine, of antioxidants thought to improve the capacity of the free radical scavenger system (selen, vitamin E), and of N-acetylcysteine which can detoxify reactive drug metabolites could not prevent the fatal outcome.

Dandy-Walker Syndrome↗

PubMed1992

Alteration of embryonic folate metabolism by valproic acid during organogenesis: implications for mechanism of teratogenesis.

The antiepileptic drug valproic acid (2-propylpentanoic acid; [VPA]) is teratogenic in humans and a number of animal species. Using a murine model, we studied the mechanism of VPA-induced teratogenesis during a period of organogenesis sensitive to interference with closure of the neural tube (days 8 to 9). Teratogenic doses of valproic acid altered the pattern of folate metabolites in the embryo: Levels of 5-formyl- and 10-formyl-tetrahydrofolates decreased, and the level of tetrahydrofolate increased. These changes could be explained by VPA-mediated inhibition of transfer of the formyl group via glutamate formyltransferase. Neural-tube defects, alteration of embryonic folate metabolism, and inhibition of the specific enzyme are all produced by comparable doses and levels of the drug. A closely related structural analog of VPA (2-en-VPA, 2-propyl-2-pentenoic acid), which exhibits antiepileptic activity but not teratogenicity, did not influence the embryonic folate metabolism. Our results suggest that interference with embryonic folate metabolism might be an important aspect of the induction of neural-tube defects by VPA. The novel techniques described also should prove useful in studying the teratogenic mechanisms of other drugs.

Animals↗

PubMed1992

Antiepileptic drugs and teratogenesis in two consecutive cohorts: changes in prescription policy paralleled by changes in pattern of malformations.

We analyzed the influence of changes in the prescribing of antiepileptic drugs to pregnant women on frequency and pattern of malformations in their offspring by comparing two consecutive cohorts (1972 to 1979, cohort A; 1980 to 1985, cohort B). In cohort A, 15 (10%) of 151 exposed, live-born infants had one or more congenital anomalies, which consisted primarily of congenital heart defects, facial clefts, and syndromes of dysmorphia with developmental retardation, in association with polytherapy (carbamazepine plus phenobarbitone plus valproate, with or without phenytoin, or phenobarbitone plus phenytoin plus primidone). In cohort B, the prescribing of phenobarbitone, phenytoin, or primidone had dropped markedly, whereas monotherapy with valproate and carbamazepine had increased. Thirteen (7.6%) of 172 exposed, live-born infants had congenital anomalies. The most frequent anomalies were spinal defects (four) and glandular hypospadias (three), all in association with maternal therapy with valproate, carbamazepine, or both. The results underline the need for continuation of prospective studies to monitor the effect of change in prescribing policies and to evaluate the role of metabolic interactions between drugs prescribed in combination.

Abnormalities, Drug-Induced↗

PubMed1991

Isotretinoin (13-cis-retinoic acid) metabolism, cis-trans isomerization, glucuronidation, and transfer to the mouse embryo: consequences for teratogenicity.

It has been reported that fractionated doses of 13-cis-retinoic acid are disproportionately more embryotoxic in pregnant mice than is the same dose given in a single bolus. Here, we examined limited pharmacokinetic profiles of a single (100 mg/kg dose given to NMRI mice on day 11 of gestation) versus multiple (3 x 100 mg/kg, 4 h apart) doses in an effort to assess the relative contribution to teratogenicity made by the drug and/or its metabolites. The major plasma metabolite of 13-cis-retinoic acid in the mouse was 13-cis-retinoyl-beta-glucuronide, followed by the 4-oxo metabolites and all-trans-retinoic acid. Transfer to the mouse embryo was very efficient for all-trans-retinoic acid, whereas, it was tenfold less efficient for 13-cis-retinoic acid and 100-fold less efficient for 13-cis-retinoyl-beta-glucuronide. The isomer all-trans-retinoic acid was found in the placenta at concentrations two- to three-fold higher than in the plasma, suggesting placental accumulation as well as placental cis/trans isomerization. Since 13-cis-retinoyl-beta-glucuronide and 13-cis- and all-trans-retinoic acid were detected in the embryo after this multiple dosing schedule, any of the three or their combinations may have been involved in the induction of malformations, but all-trans-retinoic acid, a well-known potent teratogen detected at concentrations of between 590 and 80 ng/g for 10 critical hours during gestation, could have been the major component.

Administration, Oral↗