Biomedical subjects

N Chernoff

Publications and source records attributed to N Chernoff.

At least 37 records · Page 2Linked to original sources

PubMed1989

An overview of maternal toxicity and prenatal development: considerations for developmental toxicity hazard assessments.

The objective of testing xenobiotics for potential developmental toxicity is to extrapolate laboratory animal information to the human species, thereby deriving biologically rational regulatory policies. One of the problems that significantly contributes to the difficulty of this task is the possibility that general effects on the maternal organism could affect the developing conceptus. Published data have indicated that factors intrinsic to the maternal organism affect developmental outcome. This overview examines factors which may bear directly or indirectly upon developmental outcome, with emphasis on those of greatest relevance to the hazard assessment process. Standard teratology testing protocols often call for dose levels that induce overt maternal toxicity, and the developmental effects of this toxicity (both alone, and with concurrent embryo/fetal insult) continue to present regulators with considerable interpretive difficulties. In response to these problems there have been both research and literature review efforts dealing with the relationship of maternal and developmental toxicity. Relevant studies are reviewed here, and suggestions for avenues of future research are offered including the identification of any syndromes of developmental effects occurring at maternally toxic levels irrespective of the causative agent, and experimental approaches for the characterization of maternal toxicity.

Animals↗

PubMed1989

Cell cycle alterations and cell death in cyclophosphamide teratogenesis.

Litters of pregnant mice treated with cyclophosphamide (CP) exhibit malformations of the limbs ranging from oligodactyly to amelia. Previous studies have indicated that cell death occurs in limb buds shortly after maternal exposure. We have investigated the relationship of cell death, cell cycle perturbation, and embryo/fetal toxicity in the mouse using vital staining and flow cytometry (FCM). CP (20, 30, and 40 mg/kg) was investigated via intraperitoneal administration to Swiss-Webster mice on day 10 of gestation. At 4, 8, or 28 hours later, embryos were removed. Cell death was identified with Nile blue sulphate (NBS). Two embryos per litter were stained with NBS, and the remaining embryos were frozen at -70 degrees C prior to FCM analysis. After thawing, the forelimb buds were removed for the isolation of nuclei. Tissues were dissociated through a wire mesh followed by cytolysis with 0.1% nonidet P-40 in PBS with 0.5 mg/ml RNase. Nuclei were stained with the fluorescent nucleic acid probe propidium iodide and analyzed (10,000 nuclei per sample) for propidium iodide fluorescence by FCM. NBS revealed a dose-related increase in cell death by 8 hours after dosing. CP-induced cell death was greatest in areas of rapid cell proliferation (DNA synthesis). FCM analysis revealed retardation of progression through the S-phase of the cell cycle by 4 hours post-exposure at all doses. This retardation occurred earlier in S-phase with increasing dose and persisted through 8 hours. At 28 hours, cell cycle histograms were normal in the low-dose embryos, but remained perturbed in the intermediate- and high-dose embryos. On day 17 of gestation, the last group of dams was killed. A high incidence of fetal malformations, including limb defects, occurred at the 20 mg/kg dose, and fetal mortality was observed at 30 and 40 mg/kg. The pattern and magnitude of cell death correlated with cell cycle perturbation and fetal toxicity at term, suggesting a relationship between cell cycle perturbation, cell death, and malformations produced by CP.

Animals↗

PubMed1989

Prenatal or postnatal exposure to bis(tri-n-butyltin)oxide in the rat: postnatal evaluation of teratology and behavior.

The results of a series of screening tests to determine the potential teratogenicity and neurotoxicity of developmental exposure to TBTO in rats are presented in this paper. For prenatal exposure, pregnant Long Evans rats were intubated with 0-16 mg/kg/day bis(tri-n-butyltin)oxide TBTO from Days 6 to 20 of gestation (GD 6-20). For postnatal exposure, rat pups were intubated with 0-60 mg/kg TBTO on Postnatal Day 5 (PND 5). Following prenatal exposure, dams were allowed to litter and pups were evaluated using a postnatal teratology screen. Postnatal evaluation for both exposures included motor activity (PND 13-64), the acoustic startle response (PND 22-78), growth, and brain weight. The maximally tolerated dose (MTD) in pregnant rats was 5 mg/kg/day, which is one-third the MTD in nonpregnant rats. There were decreased numbers of live births, and decreased growth and viability at dosages greater than or equal to 10 mg/kg/day. Cleft palate was found in 3% of the 12 mg/kg/day group. There was mortality following postnatal exposure to 60 mg/kg and all prenatal dosages greater than or equal to 10 mg/kg/day. Preweaning body weight was significantly decreased for all postnatal dosages, and all prenatal dosages greater than 2.5 mg/kg/day. Body weight reductions persisted to the postweaning period only in the high dose groups (10 mg/kg/day and 60 mg/kg). Behavioral evaluation demonstrated transient alterations in motor activity development (prenatal exposure only) and the acoustic startle response (postnatal exposure only). Persistent behavioral effects were observed only at dosages that produced overt maternal toxicity and/or postnatal mortality. The demonstration of the teratogenic and neurotoxic potential of TBTO in rats is confounded by associated maternal toxicity and/or pup mortality.

Abnormalities, Drug-Induced↗

PubMed1989

Overview of a workshop on quantitative models for developmental toxicity risk assessment.

A workshop was held to discuss potential advancements to improve the precision of risk estimates for developmental toxicity. This paper presents an overview of the discussions at the workshop, focusing on the risk assessment process and science policy considerations important in the use of quantitative models. Some of the pertinent biological considerations are reviewed, particularly those related to the repair capacity of the developing organism and how this affects the concept of a threshold for developmental toxicity effects, as well as the maternal and litter influences on developmental toxicity outcomes. Finally, the current status of use of quantitative approaches is described, possible short-term approaches are discussed, and future research needs in this area are outlined.

Abnormalities, Drug-Induced↗

PubMed1988

Developmental effects of maternal stress in the CD-1 mouse induced by restraint on single days during the period of major organogenesis.

Maternal stress during gestation can produce significant fetal and/or postnatal effects, and can enhance the teratogenicity of other agents. We have previously shown that restraint stress on gestational day 8 in CD-1 mice produces significant increases in encephaloceles and supernumerary and fused ribs. In the present study we have examined the effects of stress induced by restraint on individual days during the period of major organogenesis (days 6-14). Weight loss and stress-induced analgesia as assessed by the tail-flick method were used to determine the degree of stress induced by a 12-h restraint period. Restrained animals lost significantly more weight and had longer tail-flick latencies than the concurrent food and water deprived controls on all gestational days. Significant increases in embryo/fetal mortality were also observed in the offspring of restrained animals. An increased incidence of supernumerary ribs was found in mice restrained on days 7 and 8. Since maternal toxicity induced by chemical teratogens may be accompanied by a general increase in maternal stress, our data suggest that such stress may be an etiological factor in teratology bioassays in which dose levels are sufficiently high to induce overt maternal toxicity.

Analgesia↗

PubMed1987

Further evaluation of an in vivo teratology screen.

The in vivo teratology screening procedure described previously [Chernoff N, Kavlock RJ: J Toxical Environ Health 10:541-550, 1982] was further evaluated using a total of 46 chemicals in 50 different treatment regimens. Pregnant CD-1 mice were generally treated by oral gavage on days 8-12 of gestation at a dose level predicted from a preliminary range finding study to induce a slight degree of maternal toxicity. The effects on early postnatal growth and viability were compared to results generated from standard mouse teratology bioassays as reported in the literature (there were nine regimens for which no valid comparisons could be made). The procedure correctly categorized 25 of the 30 treatment regimens which were considered developmentally toxic in the mouse, as well as nine of 11 which were considered to be nondevelopmentally toxic in the mouse. Thus, based upon the criteria used in the present study, the assay correctly classified 83% of the chemicals tested as to their effect in a standard mouse bioassay. The five nonconcurring negative findings were likely due to a combination of pharmacokinetic differences between the studies, as well as to the cessation of dosing on day 12, while critical events of organogenesis are still occurring. The assay achieves the requirements for a teratology screening system, but improved predictability would result from the addition of a lower dose level and extension of the dosing period to include later stages of organogenesis.

Animals↗

PubMed1987

Workshop on the Chernoff/Kavlock preliminary developmental toxicity test.

The Chernoff/Kavlock assay, proposed as a preliminary screen for teratogenic potential, was the subject of a 2-day workshop sponsored by the National Institute for Occupational Safety and Health. Data from three large testing programs were presented, representing tests of 165 chemicals, of which 33 were tested at least twice. Applications of the test in industrial laboratories and product development, hazard identification, and risk assessment were discussed. Workshop participants recognized the assay as one of several valid ways to preliminarily evaluate chemicals with unknown developmental toxicity. Other preliminary tests were also discussed in terms of their relationship to this test, which was seen as having the advantage of providing information on neonatal viability. Other techniques, particularly an abbreviated conventional teratology study, were also recognized as appropriate screens. The preferred test in a particular laboratory will be dependent upon the particular skills and objectives of that laboratory. Standardized protocols were suggested, but flexibility in experimental design was considered necessary, and many variations on the basic test could be appropriate. This preliminary test has been used most often as a single-dose test in mice, but might provide more generally useful data if conducted in rats using two dose levels. Workshop participants viewed the test as highly reliable in correctly identifying developmentally toxic chemicals and suggested that a negative finding in a properly conducted Chernoff/Kavlock test could be a sufficient basis for regulatory agencies to determine that conventional teratology tests in the same species are not warranted.

Animals↗

PubMed1987

The potential relationship of maternal toxicity, general stress, and fetal outcome.

Standard 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.

Abnormalities, Drug-Induced↗

PubMed1987

Comparison of the penetration of 14 pesticides through the skin of young and adult rats.

In vivo percutaneous absorption of 14 pesticides was studied in young (33-d-old) and adult (82-d-old) female Fischer 344 rats, at three different dose levels. Carbon-14-labeled pesticides in acetone were applied to previously clipped middorsal skin. The treatment area was 2-3% of the body surface area. Penetration of the pesticides during a 72-h period ranged from approximately 1%-90%, depending on compound, dose, and age of animal. No clear age-related pattern of dermal absorption among compounds was found. Only chlordecone, folpet, and permethrin did not show significant age-dependent differences in skin penetration. Atrazine, carbaryl, chlorpyrifos, and hexachloro-biphenyl had greater absorption in the young, while carbofuran, captan, dinoseb, DSMA, MSMA nicotine, and parathion displayed greater absorption in the adult. The majority of the compounds showed dose-dependent penetration. The dose-response curves for penetration were not parallel for 8 of the 14 compounds studied.

Age Factors↗

PubMed1986

The effects of maternal murine cytomegalovirus infection on the mouse conceptus at different gestational stages.

The effects of murine cytomegalovirus (MCMV) on the prenatal development of the CD-1 mouse were investigated. Two sets of experiments were performed. In the first, mice were inoculated with different doses of MCMV on gestational day 7, and in the second, pregnant animals were inoculated with a subacute injection dose at different gestational stages. The effects of maternal infection on pregnancy in terms of maternal sickness, embryo lethality, date of parturition, litter size, postnatal death, and pups' body weight on d 1 and d 3 postpartum were investigated. High-dose MCMV infection on d 7 of pregnancy resulted in a significant increase in early embryo resorption and also in a reduction of the neonatal body weight of surviving pups. Two gestational stages were identified as being especially susceptible to MCMV infection. Most embryonic death as indicated by resorption rates was found after treatment on d 9, whereas perinatal death was most frequent when treatment was done on d 13 of gestation. Still births and neonatal death within 24 h of birth were found commonly in this latter group, which also showed the most pronounced growth retardation. The phenomenon of delay in time of parturition was noted and found to be most significant in groups of animals that were inoculated on d 3 or d 13. This investigation suggests that the effects of MCMV on the CD-1 mouse vary greatly with the age of the embryo and the course of the infection.

Animals↗

PubMed1986

The induction of supernumerary ribs in rodents: role of the maternal stress.

Increased 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 less than 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.

Animals↗

PubMed1986

Postnatal evaluation of prenatal exposure to p-xylene in the rat.

Pregnant Sprague-Dawley rats were exposed to either 3500 or 7000 mg/m3 p-xylene from days 7-16 of gestation. Dams were allowed to give birth, and litters were counted, weighed, and observed for external malformations on postnatal days (PD) 1 and 3. Litters were normalized to 8 pups (4 males and 4 females +/- 1) on PD4. On PD21 animals were weaned and littermates housed by sex. Body weights were recorded weekly until weaning and once every 2 weeks thereafter. Central nervous system (CNS) development was evaluated by acoustic startle response on PD13, 17, 21, and 63 as well as figure-8 maze activity on PD22 and 65. Maternal weight gain during the treatment period was significantly less in the high-dose group. No effects were seen on litter size or weight at birth or on PD3. There were no effects of xylene exposure on growth rate. There were no treatment-related effects on acoustic startle response or figure-8 maze activity. Thus, p-xylene as administered in this study does not appear to be a selective developmental toxicant in the rat.

Animals↗

PubMed1985

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.

Abnormalities, Drug-Induced↗

PubMed1985

The science of teratology in a regulatory setting.

The science of teratology is discussed from a regulatory point of view. A brief history of this branch of toxicology is presented with emphasis on specific instances of the inadvertent production of birth defects in humans as a result of exposure to exogenous agents. The basic principles of teratology are elucidated as a means of understanding current test protocols and their scientific rationale. A typical, general protocol is given and some of the major shortcomings of such a bioassay are presented. Among these shortcomings are the problems of significance of fetal toxicity and lack of a postnatal component to the teratology test system. The teratogenic and/or fetotoxic potential of selected pesticides are examined with special reference to the bioassay problems alluded to. Pesticides discussed include cacodylic acid, endrin, benomyl, ETU, nitrofen, and mirex. Finally, a brief discussion of a proposed teratology screen using pregnant laboratory animals is presented.

Abnormalities, Drug-Induced↗

PubMed1984

Limited trypsin proteolysis of photoreceptor GTP-binding protein. Light- and GTP-induced conformational changes.

The amphibian photoreceptor rod outer segment contains a guanine nucleotide-binding complex which consists of a 39,000-dalton polypeptide that binds guanine nucleotides (G protein), a 36,000-dalton polypeptide (H protein), and an approximately 6,500-dalton polypeptide. Sensitivity to trypsin proteolysis was utilized as a probe of structure-function relationships for these polypeptides. Digestion of the H protein generated fragments of 26,000 and 15,000 daltons whose proteolytic susceptibility was not altered by guanosine triphosphates, light, or membranes. The approximately 6,500-dalton polypeptide was not trypsin sensitive. When the G protein was eluted from illuminated membranes by GTP, trypsin proteolysis cleaved a terminal 1,000-dalton fragment (G1) to yield a 38,000-dalton fragment (G38). With increased digestion time, a 6,000-dalton fragment (G6) was removed from G38 to yield a 32,000-dalton fragment (G32). G32 was subsequently digested to fragments of 23,000 and 12,000 daltons. However, when the G protein was eluted from illuminated membranes by hydrolysis-resistant analogues of GTP, G32 was protected from further digestion. This is consistent with a GTP-induced conformational change in the G protein which is altered by GTP hydrolysis. Proteolysis of the G protein after covalent labeling with a photoaffinity analogue of GTP demonstrated that the analogue is bound to first G38 and then G32, indicating the GTP-binding site is associated with G32. Fragment G6 was cleaved when the G protein was soluble or bound to unilluminated membranes. However, when bound to illuminated membranes, fragments were generated reflecting the loss of 7,500, 9,000, or 11,000 daltons from the G protein. This light-induced alteration in proteolytic susceptibility indicates there is a light-induced conformational change in the G protein. Fragment G1 was not removed from the G protein when it was membrane bound, suggesting G1 is involved in binding to a membrane structure. These data suggest that the light-induced binding of the G protein to illuminated membranes and the reversal of this binding by GTP are mediated through conformational changes in the G protein and that three conformations exist: 1) a basal, inactive conformation; 2) a primed conformation induced by binding to photolyzed rhodopsin, with a high affinity for GTP; and 3) an active conformation, induced by binding of GTP, which activates the catalytic complex of light-activated phosphodiesterase.

Animals↗

PubMed1983

Activation mechanism of rod outer segment cyclic GMP phosphodiesterase. Release of inhibitor by the GTP/GTP-binding protein.

The physiological regulation of light-activated cyclic GMP phosphodiesterase (EC 3.1.4.17) in rod outer segments has been shown to depend upon a heat-stable inhibitor and upon the reversal of its effect by a specific GTP/GTP-binding protein complex (Hurley, J. B. (1980) Biochem. Biophys. Res. Commun. 92, 505-510; Yamazaki, A., Bartucca, F., Ting, A., and Bitensky, M. W. (1982) Proc. Natl. Acad. Sci. U. S. A. 79, 3702-3706). Washing of illuminated disc membranes with an isotonic buffer released 86% of the peripheral proteins without any release of inhibitor. Subsequent washing with the same isotonic buffer containing GTP released 80% of the inhibitor. When inhibitor was eluted with guanosine-5'-(beta, gamma-imino)triphosphate, it had an apparent molecular weight of 60,000 on Sephadex G-100. The release of inhibitor by guanosine-5'-(beta, gamma-imino)triphosphate was also demonstrated with sucrose density gradient centrifugation. Inhibitor release from the disc membrane by GTP or its analogue was accompanied by the release of the GTP-binding protein and an increased phosphodiesterase activity in the membrane. However, following GTP hydrolysis, both inhibitor and GTP-binding protein returned to the membrane and phosphodiesterase activity in the membrane decreased proportionally. In contrast, incubation of disc membranes with guanosine-5'-(beta, gamma-imino)-triphosphate produced an increase of inhibitor activity in the supernatant and an increase of phosphodiesterase activity in the pellet which remained constant after the initial increase. These data clearly show that the activation of phosphodiesterase by the GTP/GTP-binding protein complex resulted from the release of inhibitor. Hydrolysis of GTP resulted in the reassociation of inhibitor with and concomitant inhibition of disc membrane phosphodiesterase.

3',5'-Cyclic-GMP Phosphodiesterases↗

PubMed1983

Postnatal developmental alterations following prenatal exposure to the herbicide 2,4-dichlorophenyl-p-nitrophenyl ether: a dose response evaluation in the mouse.

Although nitrofen, 2,4-dichlorophenyl-p-nitrophenyl ether, is a relatively nontoxic herbicide, prenatal exposure to doses considerably less than the LD50 value for adult rats and mice produces numerous developmental defects that become apparent as the animals mature. In the present study postnatal development was observed following prenatal exposure during Days 7 to 17 of gestation at doses of 0, 6.25, 12.5, 25, 50, 100, 150, and 200 mg/kg/day. These doses did not cause maternal toxicity as indicated by the viability of the dams or maternal weight gain during pregnancy. By 3 days of age all pups in the two highest dose groups were dead and 50% had died in the 100 mg/kg/day dose group. Some of the dead and moribund pups from the 200 mg/kg/day exposure group necropsied at three days of age had cleft palate (15%) or diaphragmatic hernia (6%). In addition, about 22% of the pups at 200 mg/kg/day developed a distended abdomen from gasping and swallowing air. These pups did not suckle and eventually died. Body weights of offspring were reduced at birth in the 150 and 200 mg/kg/day groups and at 3 days of age in the 100 mg/kg/day group. Growth rates were subsequently retarded at 12.5, 25, 50, and 100 mg/kg. The Harderian glands were reduced or absent in 97, 65, and 4% of the mice in the 100, 50, and 25 mg/kg dosage groups, respectively, and the gland weights were reduced at all dosages, including the lowest dose of 6.25 mg/kg/day. Weights of other organs including lung and liver (at 6.25 and above), seminal vesicle (at 12.5 and above), and testes (at 100 mg/kg/day) were also reduced by prenatal nitrofen exposure. In addition, prenatal treatment with nitrofen produced functional deficits of the reproductive system; puberty was delayed in females and litter sizes were reduced at 50 and 100 mg/kg/day. A cross-fostering experiment with 100 mg/kg/day of nitrofen demonstrated that the effects noted in the present study were produced solely by prenatal exposure; pups exposed to nitrofen in the milk alone as a consequence of any accumulation of nitrofen in the dam during gestation were unaffected.

Abnormalities, Drug-Induced↗

PubMed1982

Prenatal exposure to the herbicide 2,4-dichlorophenyl-p-nitrophenyl ether destroys the rodent Harderian gland.

Exposure of mice to the herbicide 2,4-dichlorophenyl-p-nitrophenyl ether during gestation produces abnormalities that are not readily apparent at birth but become obvious as the pups mature. By 2 weeks after birth there are severe intraorbital defects resulting from destruction of the Harderian glands behind the eyes. This effect is noticeable only postnatally because the Harderian gland does not grow or function until after birth.

Abnormalities, Drug-Induced↗