bluuebunny/crossref_metadata_2025_split huggingface dataset:
Twin study methodology and variability in xenobiotic placental metabolism
Authors: Gottlieb Karen , Manchester David K. 
Published: February 2006

AbstractThe present study assesses the contribution of genetic and environmental factors to variability in placental aryl hydrocarbon hydroxylase and glutathione transferase activities using twin study methodology. Twin placentas were collected at the time of delivery. The placenta, except for a single layer of maternal decidua, consists of fetal tissue exhibiting fetal genotype. Microsomal and cytosolic fractions were prepared under stringent protocols to prevent enzyme activity loss. There were two monozygotic‐monochorionic pairs, five monozygotic‐dichorionic pairs, and 21 dizygotic‐dichorionic pairs that showed measurable aryl hydrocarbon hydroxylase activity using the direct fluorometric assay. Most of the mothers were smokers. Aryl hydrocarbon hydroxylase activity was measured with two different substrates, benzo(a)pyrene and 7‐ethoxyresorufin. Glutathione transferase activity was measured using glutathione and 1‐chloro‐2,4‐dinitrobenzene as substrates for a spectrophotometric assay that follows the conversion of the aromatic substrate. Twin pair similarity was calculated with intraclass correlation coefficients. There is a high correlation between the activities of the two aryl hydrocarbon hydroxylase substrates (r = .814), but no correlation between aryl hydrocarbon hydroxylase and glutathione transferase activity levels. There is little evidence of genetic variability underlying the variation in the enzyme activities because monozygotic‐dichorionic twins are no more similar to each other for the three substrate activities than are the dizygotic twins. To delineate the prenatal environmental influences on placental enzyme variability, dichorionic placentation was subdivided further into contiguous and noncontiguous placental position. Lower intraclass correlation coefficients are obtained for the dizygotic twins whose placentas were noncontiguous compared with dizygotic twins with contiguous placentas. The results suggest that most of the variability seen in these placental enzyme systems is due to environmental differences within uteri, rather than genetic variability in the population. This does not negate the possibility that between‐pair, or population, variability may have a genetic component, because even dizygotic twins share a large proportion of their genes. This study points out that a significantly variable environment exists within the human uterus.
Sublethal pH decrease may cause genetic damage to eukaryotic cell: A study on sea urchins andSalmonella typhimurium
Authors: Cipollaro Maria , Corsale Giuliana , Esposito Agostino , Ragucci Enrica , Staiano Norma , Giordano Giovan Giacomo , Pagano Giovanni 
Published: February 2006

AbstractFurther evidence is reported here of genetic and developmental damage that can be induced by a sublethal pH decrease. The effects of three inorganic acids (HCl, H2SO4, and H3PO4) on embryos and sperm from the sea urchinsSphaerechinus granularisandParacentrotus lividuswere evaluated. In addition, acidification of the medium was tested for spontaneous reversion to His+prototrophy inSalmonella typhimurium(strains TA97, TA98, TA100, TA102, TA1535) up to toxic levels, by both liquid incubation and agar plate incorporation.The induction of developmental and mitotic abnormalities inS. granularisconfirmed our previous observations onP. lividus. Embryotoxicity was exerted inS. granularismore severely by H3PO4than by HCl or H2SO4(pH 7 to 6), while the induction of mitotic abnormalities appeared at a pH of ≤ 6.5 irrespective of the acids used. By suspendingS. granularisorP. lividussperm in acidified filtered seawater (fsw) and then inseminating the eggs in natural fsw (pH = 8.0), the offspring showed developmental and mitotic abnormalities. Low‐pH‐induced spermiotoxicity was ruled out in our experiments, since fertilization success of acid‐exposed sperm was actually enhanced, as compared to sperm suspended in untreated fsw.The exposure ofS. typhimuriumto different pH's (ranging from 4 to 9) invariably failed to induce any changes in reversion rates, regardless of the acids (or alkali) being used.These results suggest that extracellular acidification may cause sublethal damage that in turn leads to an impairment of mitotic activity and cell differentiation.
Genetic variation in the susceptibility to mercury and other metal compounds in Drosophila melanogaster
Authors: Magnusson Jan , Ramel Claes 
Published: February 2006

AbstractThe tolerance of Drosophila melanogaster to heavy metal compounds was investigated with special emphasis on methylmercury. A pronounced variation in tolerance to CH3HgOH, HgCl2, (C2H5)3PbCl, (CH3)3SnCl, and CdCl2 was recorded between 12 wild‐type strains. After ranking the tolerance of the strains with respect to the five compounds rank correlations for experiments within and between compounds were calculated. The results showed a high degree of correlation within compounds but no unequivocal indication of a correlation between compounds, indicating that different mechanisms of genetic control for tolerance were operating for the five compounds. Rank correlations for experiments with 12 different mercury, lead, tin, and cadmium compounds and the same 12 wild‐type strains only indicated one significant correlated response, between tripropyltin and tributyltin.A selection experiment for tolerance to methylmercury was performed with a foundation population, synthesized from four wild‐type strains, showing a high initial tolerance. One control and two levels of treatment doses were used. A distinct selection response was obtained and a high tolerance was reached particularly for the high‐dose selection line after 12 generations, when the experiment ended. Genetic analysis of the tolerance indicated a dominant and polygenic inheritance. Investigation of the uptake and excretion of CH3Hg203OH showed that the level of tolerance to methylmercury was correlated with the uptake of the mercury but apparently not with the rate of excretion.Cystein increased the susceptibility to methylmercury. Inorganic mercury and trimethyl lead exhibited a synergistic toxic effect, evidently as the result of an in vitro transmethylation of mercury.A high somatic susceptibility to methylmercury also applied to the induction of nondisjunction and sex‐linked recessive lethals.
Comparative in vivo and in vitro sister chromatid exchange studies in chinese hamster bone marrow and spleen cells
Authors: Krishna G. , Nath J. , Ong T. 
Published: February 2006

AbstractThe sister chromatid exchange (SCE) assay in bone marrow and spleen cells of Chinese hamsters was used to evaluate the differences between in vivo and in vivo/in vitro (exposure of animals to chemical followed by culturing of cells) conditions. Cyclophosphamide, a mutagenic carcinogen, caused dose‐related SCEs both in vivo and in vivo/in vitro. In the in vivo group, both bone marrow and spleen cells showed approximately a five‐fold increase in SCEs over controls following 40 mg cyclophosphamide/kg treatment. The same dose, under in vivo/in vitro conditions, caused about three‐ and six‐fold increases in SCEs over controls in bone marrow and spleen cells, respectively. While the extent of cyclophosphamide‐induced SCEs (after subtraction of baseline level) in bone marrow is approximately the same under both conditions, the response was significantly higher in spleen cells in vivo/in vitro than in vivo. Under in vitro conditions, treatment of bone marrow and spleen primary cell cultures with a direct acting mutagen, trinitrofluorenone, caused significant dose‐related increases in SCEs in both cell types in an equivalent manner. The replicative indices under these experimental conditions remained almost the same. Thus, this study indicates the potential usefulness of Chinese hamster bone marrow and spleen cells for in vivo and in vitro comparative studies with the same tissue to better assess the genotoxic hazard of chemicals.
Karyotype, growth, and cell cycle analysis of human embryonic palatal mesenchymal cells: Relevance to the use of these cells in an in vitro teratogenicity screening assay
Authors: Welsch Frank , Stedman Donald B. , Willis William D. , Pratt Robert M. 
Published: February 2006

AbstractHuman embryonic palatal mesenchyme (HEPM) is an established cell line that is presently under investigation as an in vitro prescreening assay used to determine the teratogenic potential of chemicals. We describe here general growth characteristics, karyotype, and cell cycle analysis of these cells. HEPM cells had plating efficiencies of <95% and displayed notable contact growth inhibition following an exponential growth phase that lasted for approximately 6 days. These cells had the diploid karyotype of a female human embryo. The chromosomal complement showed no dramatic change between passage 5 and 14. Flow cytofluorometry analysis using bromodeoxyuridine (BrdU) pulse labeling and a direct immunofluorescence anti‐BrdU FITC probe revealed that the total cell cycle transit time was approximately 22 hr: the duration of G1 was 12.2 hr, S was 6.1 hr, and G2‐M lasted for 3.7 hr. The results indicate that HEPM cells met the criteria regarding karyotype stability that were assumed by the National Toxicology Program of the USA.
Failure of epoxide formation to influence carbamazepine‐induced teratogenesis in a mouse model
Authors: Finnell Richard H. , Mohl Virginia K. , Bennett Gregory D. , Taylor Stephen M. 
Published: February 2006

AbstractThe teratogenic potential of the anticonvulsant drug carbamazepine was determined following chronic oral administration in two inbred mouse strains (SWR/J and LM/Bc). The drug was administered in the animal's diet in concentrations equivalent to 0, 1,000, 1,500, or 2,000 mg/kg body weight, with treatment starting 2 wks prior to mating and continuing throughout gestation. Fetal examination failed to reveal a significant pattern of malformation in either strain at any treatment level. Levels of plasma carbamazepine and its metabolite, carbamazepine‐10, 11‐epoxide, were determined by high pressure liquid chromatography. There was no correlation with either of these compounds and the incidence of fetal abnormality. The inherent teratogenicity of carbamazepine is significantly lower than that of other anticonvulsant drugs that have been similarly tested in an animal model.
The induction of supernumerary ribs in rodents: Role of the maternal stress
Authors: Beyer Patricia E. , Chernoff Neil 
Published: February 2006

AbstractIncreased incidences of supernumerary ribs (SNR) are a relatively common finding in standard teratology bioassays, and previous studies have indicated a possible correlation between their occurrence and general maternal stress. The present study describes the effects of immobilization stress on the induction of supernumerary ribs. To isolate the sensitive period of SNR induction, Sprague‐Dawley rats and CD‐1 mice were treated with 300 and 1,500 mg/kg, respectively, of sodium salicylate on single days 7–11 of gestation. In the rat, day 10 was found to be the sensitive period of lumbar rib induction (32% SNR vs 10% on other days) while day 9 was critical in the mouse (71% SNR vs <29% on other days). In a second set of experiments, maternal stress was accomplished by restraining two groups of gravid females in the supine position for 12 hours on the predetermined sensitive day. One group was immobilized from 9 am to 9 pm, while the second group was restrained from 9 pm to 9 am. Concurrent controls were food and water deprived for similar periods. Additional untreated controls were also included. An increase in supernumerary ribs was noted in stressed mice but not in rats. The 9 am to 9 pm mouse group exhibited the highest increase in supernumerary ribs (41%) as well as significant incidences of fused ribs and exencephaly. A significant linear relationship between maternal weight loss during treatment and increases in supernumerary ribs was also noted. Results suggest that for some compounds, supernumerary ribs may be the indirect result of agent‐induced, generalized maternal stress in the CD‐1 mouse.
Glucocorticoid receptor‐mediated teratogenesis and cell proliferation in the limbs and face of the chick embryo
Authors: Pavlík Alfred , Novotná Božena , Jelínek Richard 
Published: February 2006

AbstractThe susceptibility of the face region of the chick embryo to the teratogenic action of intraamniotically injected hydrocortisone contrasts with the resistance of the limbs to its action while at the same time their dysmorphogenesis may be induced by other agents. Since glucocorticoid receptors were shown to mediate face teratogenesis, their development was investigated in freshly dissected limb buds of 3‐, 3.5, and 4‐day‐old chick embryos in comparison with the face region. The specific binding of 3H‐dexamethasone to molybdate‐stabilized glucocorticoid receptors was estimated by the dextran‐coated charcoal method and complemented by cytologic analysis of mitotic activity in control and hydrocortisone‐treated embryos. The glucocorticoid receptors were found in both organ anlagen already on day 3 when their concentration in femtomoles per microgram DNA was significantly higher in the face region. Accordingly, on day 3 intraamniotic hydrocortisone inhibited the mitotic activity in the face without affecting the developing limbs. On days 3.5 and 4 the concentration of glucocorticoid receptors was similar in both organ anlagen. Administration of hydrocortisone on day 4 induced mitotic depression in the face as well as in the limbs. However, the degree of inhibition apppeared to be dependent upon the actual mitotic rate. In the face region where the mitotic activity culminated at that time, the inhibition was much deeper and longer‐lasting than in the developing limbs characterized by continuous decrease of proliferation rate in controls. These findings are consistent with a view that glucocorticoid receptors are a prerequisite, but not the only factor in receptor‐mediated teratogenesis.
Evaluation of 60 chemicals in a preliminary developmental toxicity test
Authors: Hardin Bryan D. , Schuler Ronald L. , Burg JeAnne R. , Booth Gary M. , Hazelden Keith P. , MacKenzie Karen M. , Piccirillo Vincent J. , Smith Kirby N. 
Published: February 2006

AbstractThe number of chemicals in commerce which have not been evaluated for potential developmental toxicity is large. Because of the time and expense required by conventional developmental toxicity tests, an abbreviated assay is needed that will preliminarily evaluate otherwise untested chemicals to help prioritize them for conventional testing. A proposed short‐term in vivo assay has been used in a series of studies in which a total of 60 chemicals were tested. Some were independently tested two or four times each. In this preliminaly test, pregnant mice were dosed during mid‐pregnancy and were then allowed to deliver litters. Litter size, birth weight, and neonatal growth and survival to postnatal day 3 were recorded as indices of potential developmental toxicity. Results in this assay and conventional mouse teratology tests were generally concordant. Conventional data were available for 14 chemicals (ten teratogens, one fetotoxin, three nonteratogens), of which 11 (nine teratogens, one fetotoxin, one nonteratogen) produced evidence of developmental toxicity. This included conventional data for three chemicals (ethylene glycol, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether) that were untested before the present study. As high priority candidates for conventional testing on the basis of results here, all were subsequently studied in a standard teratology assay and were confirmed to be teratogenic in mice. Additionally, one of them (ethylene glycol) plus a fourth high priority candidate for conventional study (diethylene glycol monomethyl ether) were subsequently tested in rats and were found to be teratogenic in that species.
Recommendations for the statistical analysis of Chernoff/Kavlock test data
Authors: Burg JeAnne R. , Hardin Bryan D. 
Published: February 2006

AbstractThe statistical analyses of the data related to the teratogenic testing of 60 compounds utilizing the Chernoff/Kavlock test are the basis of this paper. The hypotheses chosen to be tested and the statistical tests utilized to test those hypotheses are discussed. The topics explored are the use of comparisonwise error rate versus experimentwise error rate, the use of nonparametric tests versus more “conventional” parametric tests and the use of “historical data” in assessing and interpreting group difference.
A recommended protocol for the Chernoff/Kavlock preliminary developmental toxicity test and a proposed method for assigning priority scores based on results of that test
Authors: Hardin Bryan D. 
Published: February 2006

AbstractRecommendations are made for a standard protocol for the Chernoff/Kavlock preliminary developmental toxicity test, and a weighted scoring system is proposed to provide a numerical prioritization. Protocol recommendations include use of pregnant animals for dose‐finding studies and, in the testing phase, treatment on gestation days 6–15 at an overtly maternally toxic dose. This treatment period corresponds to the usual timing of a teratology test and provides an improved data base in the event a conventional test is deemed appropriate. Five indices of potential developmental toxicity are: the proportion of pregnant survivors at term that produces a viable litter (at least one liveborn pup), average litter size and pup weight at birth, and average neonatal survival and body weight gain to 3 days of age. Neither systematic examinations of pups (living or dead) for malformations nor counts of dead pups are considered productive. In the proposed method for point scores, each of the five indices is assigned a point value that varies according to broad classes of maternal toxicity. The maximum total point value is 22. When there is no statistically significant difference between treated and control groups, the assigned value is subtracted from 22. If there is a statistically significant treatment effect, or if statistics cannot be applied, then no points are subtracted. The points remaining after all five indices are considered constitute the priority score, which may range from 0 (low) to 22 (high priority).
Application of the preliminary developmental toxicity screen for chemical hazard identification under the toxic substances control act
Authors: Francis Elaine Z. , Farland William H. 
Published: February 2006

AbstractThe Office of Toxic Substances (OTS) within the U.S. Environmental Protection Agency (EPA) is authorized to carry forth the mandates of the Toxic Substances Control Act (TSCA). Included among the provisions of TSCA are the development of requirements for testing of “new” and “existing” chemicals that may present an unreasonable risk of injury to health or the environment. There are over 63,000 “existing” chemicals on the TSCA inventory, and EPA in recent years has been receiving an average of over 1,300 submissions for “new” chemicals a year. Since it is illogical and unrealistic to expect that all of these chemicals should be subjected to detailed testing for all potential adverse health and environmental effects, OTS views screening assays as highly useful tools to assign priorities to chemicals for further testing according to standard methodologies. The Chernoff/Kavlock assay (preliminary developmental toxicity screen) was specifically developed to address the need for a developmental toxicity assay to prioritize for further testing the large number of “new” and “existing” chemicals. OTS has been involved in seeking the development of data through the preliminary developmental toxicity screen for purposes of validating the screen and to obtain critical data necessary for evaluating chemicals. OTS believes that the screen has a role in the risk assessment process and has developed a testing protocol, which is included along with other OTS test guidelines; has provided internal guidance on when the screen may be recommended; and has discussed how the data may be applied in prioritizing chemicals for further study.
Correlations between embryotoxic and genotoxic effects of phenytoin in mice
Authors: Barcellona Patrizio Scorza , Barale Roberto , Campana Alberto , Zucconi Donatella , Rossi Vilma , Caranti Silvia 
Published: February 2006

AbstractThe anticonvulsant drug phenytoin (DPH) has been suspected to produce embryotoxicity through an arene oxide intermediate. This drug was also found to be a genotoxic agent. These hypotheses were tested in pregnant mice modulating the phases I and II metabolizing enzymes. DPH was studied by assessing embryotoxicity, teratogenicity, and genotoxicity, the latter by the micronucleus test on the polychromatic erythrocytes of dams and fetuses.DPH embryotoxicity was potentiated by inhibiting both cytochrome P‐450 and epoxide hydrase and decreased by inducing cytochrome P‐450. Equivocal results were obtained by modulating cytochrome P‐448. The main DPH metabolite, p‐hydroyphenytoin (HPPH), was ineffective both per se and after cytochrome induction or epoxide hydrase inhibition.DPH did not exert genotoxicity on the maternal organism, no matter which modulating agent was used. In the fetus, however, weak genotoxic effects were observed. These effects significantly increased with inhibition of epoxide hydrase; they disappeared with induction of both cytochromes P‐448 and P‐450 or with inhibition of the latter. No genotoxicity was exerted by HPPH, even when the enzymatic pattern was modulated.It is concluded that the major role in DPH embryotoxicity is played by the unchanged drug, while the presence of the arene oxide is determinant for genotoxic effects.
The potential relationship of maternal toxicity, general stress, and fetal outcome
Authors: Chernoff Neil , Kavlock Robert J. , Beyer Patricia E. , Miller Diane 
Published: February 2006

AbstractStandard teratology bioassays generally call for a top dose level which is sufficient to induce some form of overt maternal toxicity such as death or weight loss. The presence of such maternal toxicity is often a confound in the interpretation of experimental results, especially at those dose levels producing the toxicity. While the physiological bases for the toxicity vary widely in a compound‐related fashion, one underlying factor that remains constant for most induced toxicity is the presence of generalized stress in the affected animals. Previous studies have indicated that pregnant animals treated acutely with toxic levels of a variety of pharmacologically unrelated chemicals produced litters without a recognizable syndrome of defects, except for an increased incidence of supernumerary ribs (SNR). The present study reports on the effects of immobilization stress on the production of SNR in the Sprague‐Dawley rat and the CD‐1 mouse. Pregnant animals were immobilized in the supine position for 12‐hour periods during the day of greatest sensitivity to SNR production (days 9 and 10 in the mouse and rat, respectively). Animals were killed immediately before term and the fetuses were examined. An increase in SNR was noted in immobilized mice but not rats. These results suggest that such fetal effects may be the result of general agent‐induced maternal stress.