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Pharmacokinetics and drug metabolism in the design and interpretation of developmental toxicity studies
184
Reproductive Toxicology
on the dose of nickel given to the pregnant rat and on the concentration of nickel in the maternal blood. Nickel sulphate did not change the parameters of either systemic (blood pressure, total peripherial resistance, cardiac index) or organ (including placental) blood flow. Authors concluded that nickel crossing the placenta and acting directly on the fetus took part in the pathomechanism of the embryotoxic (weight retardation) and teratogenic (congenital anomalies of the uropoietic system) effects, previously described and confirmed in the present experiments. Since nickel did not influence the maternal and fetal circulations, their alteration could not be the cause of the fetal damage.
Development of the chick embryonic skeleton following the intra-amniotic injection of cyclophosphamide V. Mueller, K. Kosar Department of Biological and Medical Sciences, Faculty of Pharmacy, Charles University, Hradec Kralove, CSFR In our study, the interference with the developing embryonic skeleton of two embryotoxic doses of cyclophosphamide (CP) administered intra-amniotically to the chick embryos on day 3 of incubation was investigated. Dysmorphogenetic effects (growth retardation, affliction of the ossification process, malformations) were assessed on day 14 ofembryogenesis. The doses chosen (3 × 10-5 and 3 × 10-4 mg/embryo) induced growth retardation (P < 0.01), becoming evident through decrease of whole body weight and the low values of the mean bone lengths in the selected anatomic categories of the skeleton. Out of all skeletal afflictions observed, the most characteristic finding seemed to be the damage or the retardation of the ossification in all investigated parts of skeleton (P < 0.01). No statistically significant differences were found between the two experimental dose groups in the response of embryonic skeleton, with the only exception of digiti pedis, pelvis, scapula dx., and mandibula. In the malformation spectrum determined, the absence of os parietal and supraoccipital, spina bifida occulta, dysmorphogenesis of the orofacial complex, abnormally long and "S" shaped radius, ulna, and ossa costalia prevailed, which, moreover, were of a nodule-like hollow shape. The incidence of embryolethality was found to be 47%.
Pharmacokinetics and drug metabolism in the design and interpretation of developmental toxicity studies Heinz Nau Institute of Toxicology and Embryopharmacology, Gary Strasse 3, D-1000 Berlin 33, Germany A direct teratogenic effect will depend on the concentrationtime relationship of the drug or its active metabolite in the placental-embryonic compartment during the sensitive stages of gestation. Pharmacokinetic studies are therefore important for the interpretation and design of teratogenicity experiments, particularly for the problem of species differences, and for attempts to extrapolate experimental findings to the human ("risk assessment"). Pharmacokinetic studies are also crucial in elucidating whether the parent
Volume6, Number 2, 1992 drug or a metabolite is the proximate or ultimate toxic entity. Finally, structure-activity studies can greatly benefit from pharmacokinetic experiments to demonstrate whether the teratogenicity of a substance is related to its intrinsic activity or to the extent of placental transfer or both.
Chick embryo--an optimal model for simultaneous genotoxic and embryotoxic effects analysis Bozena Novotna Institute of Experimental Medicine, Czechoslovak Academy of Sciences, Prague, Czechoslovakia Genotoxic effects of teratogenic doses of two well-known mutagens--cyclophosphamide (CP) and bromodeoxyuridine (BrdU)--were analyzed in the early chick embryo with the aim to contribute to elucidation of the relation between the mutagenic and embryotoxic effects. The embryotoxicity profiles of the two mutagens were estimated using the Chick Embryotoxicity Screening Test (CHEST). Cytogenetic techniques made it possible to evaluate simultaneously chromosomal aberrations and the course of mitotic activity in the circulating primitive erythrocytes as well as in cells of the affected and nonaffected tissues. While in the case of CP the results have confirmed the assumed causal relationship between its genotoxicity and development of heart, face, and/or limb defects, BrdU induced significant increase of aberrant cells accompanied by mitotic inhibition only after the administration of totally embryolethal doses. Gross developmental anomalies resulted from administration of doses 10 times lower, causing no remarkable clastogenic or antiproliferative effects in the affected tissues.
Estimation of isotretinoin embryotoxicity using the chick embryotoxicity test M. Peterka, R. Peterkova Institute of Experimental Medicine, Czechoslovak Academy of Sciences, Prague, Czechoslovakia The chick embryotoxicity screening test (CHEST) was used to evaluate embryotoxicity of 13-cis-retinoic acid. Increasing single doses of 13-cis-retinoic acid were injected subgerminally or intra-amniotically on incubation days 2, 3, or 4. The embryotoxicity range has been found to begin with the doses of 3 to 30 #g per embryo. By extrapolation of our resuits (made according to the conversion used with the CHEST), the beginning ofembryotoxicity of 13-cis-retinoic acid to mammalian species was estimated in the range of 10 to 100 mg/kg maternal body weight. Kistler (1987) found that with mice, rats, and rabbits the lowest teratogenic dose corresponded to 100, 150, and 10 mg/kg maternal body weight, respectively. His data agree with the results of CHEST as both the lowest effective dose and the malformation spectra are concerned. With the chick embryo, the caudal regressions (injection on embryonic day 2), microcephaly, brain frontal hernia, cleft beak, limb defects, and absence of heart vessels (injection on day 3), hydrocephaly, eye defects, cleft beak, and limb defects (injection on day 4) were observed. Malformation spectra in rodents consist of exencephaly, head and eye malformations, cleft palate, and limb defects (Kistler, 1987).
Reproductive Toxicology
on the dose of nickel given to the pregnant rat and on the concentration of nickel in the maternal blood. Nickel sulphate did not change the parameters of either systemic (blood pressure, total peripherial resistance, cardiac index) or organ (including placental) blood flow. Authors concluded that nickel crossing the placenta and acting directly on the fetus took part in the pathomechanism of the embryotoxic (weight retardation) and teratogenic (congenital anomalies of the uropoietic system) effects, previously described and confirmed in the present experiments. Since nickel did not influence the maternal and fetal circulations, their alteration could not be the cause of the fetal damage.
Development of the chick embryonic skeleton following the intra-amniotic injection of cyclophosphamide V. Mueller, K. Kosar Department of Biological and Medical Sciences, Faculty of Pharmacy, Charles University, Hradec Kralove, CSFR In our study, the interference with the developing embryonic skeleton of two embryotoxic doses of cyclophosphamide (CP) administered intra-amniotically to the chick embryos on day 3 of incubation was investigated. Dysmorphogenetic effects (growth retardation, affliction of the ossification process, malformations) were assessed on day 14 ofembryogenesis. The doses chosen (3 × 10-5 and 3 × 10-4 mg/embryo) induced growth retardation (P < 0.01), becoming evident through decrease of whole body weight and the low values of the mean bone lengths in the selected anatomic categories of the skeleton. Out of all skeletal afflictions observed, the most characteristic finding seemed to be the damage or the retardation of the ossification in all investigated parts of skeleton (P < 0.01). No statistically significant differences were found between the two experimental dose groups in the response of embryonic skeleton, with the only exception of digiti pedis, pelvis, scapula dx., and mandibula. In the malformation spectrum determined, the absence of os parietal and supraoccipital, spina bifida occulta, dysmorphogenesis of the orofacial complex, abnormally long and "S" shaped radius, ulna, and ossa costalia prevailed, which, moreover, were of a nodule-like hollow shape. The incidence of embryolethality was found to be 47%.
Pharmacokinetics and drug metabolism in the design and interpretation of developmental toxicity studies Heinz Nau Institute of Toxicology and Embryopharmacology, Gary Strasse 3, D-1000 Berlin 33, Germany A direct teratogenic effect will depend on the concentrationtime relationship of the drug or its active metabolite in the placental-embryonic compartment during the sensitive stages of gestation. Pharmacokinetic studies are therefore important for the interpretation and design of teratogenicity experiments, particularly for the problem of species differences, and for attempts to extrapolate experimental findings to the human ("risk assessment"). Pharmacokinetic studies are also crucial in elucidating whether the parent
Volume6, Number 2, 1992 drug or a metabolite is the proximate or ultimate toxic entity. Finally, structure-activity studies can greatly benefit from pharmacokinetic experiments to demonstrate whether the teratogenicity of a substance is related to its intrinsic activity or to the extent of placental transfer or both.
Chick embryo--an optimal model for simultaneous genotoxic and embryotoxic effects analysis Bozena Novotna Institute of Experimental Medicine, Czechoslovak Academy of Sciences, Prague, Czechoslovakia Genotoxic effects of teratogenic doses of two well-known mutagens--cyclophosphamide (CP) and bromodeoxyuridine (BrdU)--were analyzed in the early chick embryo with the aim to contribute to elucidation of the relation between the mutagenic and embryotoxic effects. The embryotoxicity profiles of the two mutagens were estimated using the Chick Embryotoxicity Screening Test (CHEST). Cytogenetic techniques made it possible to evaluate simultaneously chromosomal aberrations and the course of mitotic activity in the circulating primitive erythrocytes as well as in cells of the affected and nonaffected tissues. While in the case of CP the results have confirmed the assumed causal relationship between its genotoxicity and development of heart, face, and/or limb defects, BrdU induced significant increase of aberrant cells accompanied by mitotic inhibition only after the administration of totally embryolethal doses. Gross developmental anomalies resulted from administration of doses 10 times lower, causing no remarkable clastogenic or antiproliferative effects in the affected tissues.
Estimation of isotretinoin embryotoxicity using the chick embryotoxicity test M. Peterka, R. Peterkova Institute of Experimental Medicine, Czechoslovak Academy of Sciences, Prague, Czechoslovakia The chick embryotoxicity screening test (CHEST) was used to evaluate embryotoxicity of 13-cis-retinoic acid. Increasing single doses of 13-cis-retinoic acid were injected subgerminally or intra-amniotically on incubation days 2, 3, or 4. The embryotoxicity range has been found to begin with the doses of 3 to 30 #g per embryo. By extrapolation of our resuits (made according to the conversion used with the CHEST), the beginning ofembryotoxicity of 13-cis-retinoic acid to mammalian species was estimated in the range of 10 to 100 mg/kg maternal body weight. Kistler (1987) found that with mice, rats, and rabbits the lowest teratogenic dose corresponded to 100, 150, and 10 mg/kg maternal body weight, respectively. His data agree with the results of CHEST as both the lowest effective dose and the malformation spectra are concerned. With the chick embryo, the caudal regressions (injection on embryonic day 2), microcephaly, brain frontal hernia, cleft beak, limb defects, and absence of heart vessels (injection on day 3), hydrocephaly, eye defects, cleft beak, and limb defects (injection on day 4) were observed. Malformation spectra in rodents consist of exencephaly, head and eye malformations, cleft palate, and limb defects (Kistler, 1987).