Effects of prenatal X-irradiation on the 14th-18th days of gestation on postnatal growth and development in the rat

Protection of the gametes embryo/fetus from prenatal radiation exposure

There is no convincing evidence of germline mutation manifest as heritable disease in the offspring of humans attributable to ionizing radiation, yet radiation clearly induces mutations in microbes and somatic cells of rodents and humans. Doses to the embryo estimated to be in the range of 0.15-0.2 Gy during the pre-implantation and pre-somite stages may increase the risk of embryonic loss. However, an increased risk of congenital malformations or growth retardation has not been observed in the surviving embryos. These results are primarily derived from mammalian animal studies and are referred to as the "all-or-none phenomenon." The tissue reaction effects of ionizing radiation (previously referred to as deterministic effects) are congenital malformations, mental retardation, decreased intelligence quotient, microcephaly, neurobehavioral effects, convulsive disorders, growth retardation (height and weight), and embryonic and fetal death (miscarriage, stillbirth). All these effects are consistent with having a threshold dose below which there is no increased risk. The risk of cancer in offspring that have been exposed to diagnostic x-ray procedures while in utero has been debated for 55 y. High doses to the embryo or fetus (e.g., >0.5 Gy) increase the risk of cancer. Most pregnant women exposed to x-ray procedures and other forms of ionizing radiation today received doses to the embryo or fetus <0.1 Gy. The risk of cancer in offspring exposed in utero at exposures <0.1 Gy is controversial and has not been fully resolved. Diagnostic imaging procedures using ionizing radiation that are clinically indicated for the pregnant patient and her fetus should be performed because the clinical benefits outweigh the potential oncogenic risks.

Saving lives and changing family histories: appropriate counseling of pregnant women and men and women of reproductive age, concerning the risk of diagnostic radiation exposures during and before pregnancy

Over the past 50 years, our laboratory has provided consultations dealing with the risks of various environmental toxicant exposures during pregnancy. These contacts were primarily by telephone or written communications. Since the year 2000, the primary source of consultations has been via the internet. In 2007, the pregnancy website of the Health Physics Society received 1,299,672 visits. The contacts who downloaded information totaled 620,035. After reading the website information, 1442 individuals who were still concerned contacted me directly. Unfortunately, we have learned that many physicians and other counselors are not prepared to counsel patients concerning radiation risks. Approximately, 8% of the website contacts, who had consulted a professional, were provided inaccurate information that could have resulted in an unnecessary interruption of a wanted pregnancy. Research from our and other investigators' laboratories has provided radiation risk data that are the basis for properly counseling contacts with radiation exposures. Mammalian animal research has been an important source of information that improves the quality and accuracy of estimating the reproductive and developmental risks of ionizing radiation in humans. What are the reproductive and developmental risks of in utero ionizing radiation exposure? 1. Birth defects, mental retardation, and other neurobehavioral effects, growth retardation, and embryonic death are deterministic effects (threshold effects). This indicates that these effects have a no adverse effect level (NOAEL). Almost all diagnostic radiological procedures provide exposures that are below the NOAEL for these developmental effects. 2. For the embryo to be deleteriously affected by ionizing radiation when the mother is exposed to a diagnostic study, the embryo has to be exposed above the NOAEL to increase the risk of deterministic effects. This rarely happens when the pregnant women have x-ray studies of the head, neck, chest or extremities. 3. During the preimplantation and preorganogenesis stages of embryonic development, the embryo is least likely to be malformed by the effects of ionizing radiation because the cells of the very young embryo are omnipotential and can replace adjacent cells that have been deleteriously affected. This early period of development has been designated as "the all-or-none period." 4. Protraction and fractionation of exposures of ionizing radiation to the embryo decrease the magnitude of the deleterious effects of deterministic effects. 5. The increased risk of cancer following high exposures to ionizing radiation exposure to adult populations has been demonstrated in the atomic bomb survivor population. Radiation-induced carcinogenesis is assumed to be a stochastic effect (nonthreshold effect) so that there is theoretically a risk at low exposures. Whereas there is no question that high exposures of ionizing radiation can increase the risk of cancer, the magnitude of the risk of cancer from embryonic exposures following diagnostic radiological procedures is very controversial. Recent publications and analyses indicate that the risk is lower for the irradiated embryo than the irradiated child, which surprised many scientists interested in this subject, and that there may be no increased carcinogenic risk from diagnostic radiological studies. Examples of appropriate and inappropriate counseling will be presented to demonstrate how counseling can save lives and change family histories. The reader is referred to the Health Physics Society website to obtain many examples of the answers to questions posed by women and men who have been exposed to radiation (www.hps.org). Then click on ATE (ask the expert).

Lauriston S. Taylor lecture: fifty years of scientific research: the importance of scholarship and the influence of politics and controversy

Over the past 50 years our laboratory has performed and published many studies in the fields of teratology, radiation biology and radiation embryology. The early work took place when I was a research employee at the University of Rochester Manhattan Project in 1944 and where I had my introduction to embryology and genetics. Over the years our lab has provided consultations dealing with the risks of various environmental toxicant exposures during pregnancy. With the advent of the Internet, consulting has become more rapid and efficient. In the past year our pregnancy Web site of the Health Physics Society received approximately 154,000 hits, of which over a thousand contacts were still quite anxious after reading the Web site answers and requested a personal consultation. From this extensive experience we have learned that many physicians and other counselors are not prepared to counsel patients concerning radiation risks. Approximately 8% of the patient contacts who have consulted a professional have been provided with inaccurate information that would have resulted in an unnecessary interruption of a wanted pregnancy. There are five areas of radiation embryology that are considered to be controversial. 1) Can the fetus be harmed by ionizing radiation if the fetus is not directly exposed? 2) Is the production of mental retardation from radiation during pregnancy a threshold phenomenon? 3) Does fractionation and protraction of radiation decrease the magnitude of the reproductive and developmental risks? 4) Is there a period during pregnancy when radiation will result in an increased mortality but not an increase in malformations? 5) How sensitive is the fetus to the oncogenic effects of radiation? We utilize the scientific information obtained from studies in these five areas to counsel patients concerning pregnancy radiation risks. The willingness and persistence of scientists to debate the controversial aspects of this research and apply the best available scientific information to assist patients in turmoil about the risks of radiation to themselves and their offspring has saved thousand of lives and changed family histories.

Diagnostic Radiation in Pregnancy: Perception Versus True Risks

Significant numbers of therapeutic abortions are performed for radiation-exposed pregnant women because of concerns about the teratogenic risk. However, available data suggest that current diagnostic radiation procedures are not teratogenic.

Effects of Prenatal Irradiation with an Accelerated Heavy-Ion Beam on Postnatal Development in Rats: I. Neurophysiological Alterations

Effects on postnatal neurophysiological development in offspring were studied after exposure of pregnant Wistar rats to accelerated carbon-ion beams with an LET of about 13 keV/ mum at doses ranging from 0.1 Gy to 2.5 Gy on the 15th day of gestation. The age at which four physiological markers appeared and five reflexes were acquired was examined prior to weaning. Gain in body weight was monitored until the offspring were 3 months old. Male offspring were evaluated as young adults using two behavioral tests. The effects of X rays estimated for the same biological end points were studied for comparison. For most of the end points at early age, no significant alterations were observed in offspring that received prenatal irradiation with 0.1 Gy of either accelerated carbon ions or X rays compared to the offspring of sham-irradiated dams. However, all offspring whose dams received 2.5 Gy died prior to weaning. Offspring from dams irradiated with accelerated carbon ions generally showed higher incidences of prenatal death and preweaning mortality, markedly delayed accomplishment in their physiological markers and reflexes, and gain in body weight compared to those exposed to X rays at doses of 0.5 to 2 Gy. Significantly reduced ratios of main organ weight to body weight at the postnatal ages of 30, 60 and 90 days were also observed within this dose range. The results indicate that irradiation with 0.5 to 2 Gy on day 15 of gestation caused permanent alterations in offspring that were dependent on dose. The alterations include permanent growth retardation, morphological malformations in main organs, including microcephaly, diminished reflex attainment, delayed appearance of physiological markers, and changes in adult behavior. Exposure to 1 to 2 Gy of radiation resulted in growth retardation and behavioral alterations that persisted throughout life. Accelerated carbon ions generally induced more detrimental effects than X rays.

Commentary on JAMA article by Hujoel et al

A recent publication by in the April 28, 2004, issue of JAMA raises concern since it suggests that exposure to dental x rays during pregnancy could be responsible for human fetal growth retardation. Furthermore, the article could have a negative impact on the dental care of pregnant women who might fear the effect of dental radiography on their developing embryo. In our initial discussions, John Boice and I decided to communicate our concerns to the scientific and medical community. Boice has published a recent letter concerning the Hujoel paper. The Hujoel publication has very serious deficiencies. This Forum presents analyses of these deficiencies.

Late effect of prenatal irradiation on the hippocampal histology and brain weight in adult mice

We studied the changes in the brain weight and hippocampal histology in adult offspring exposed to 0.25-1.5 Gy of 60Co gamma radiations during day 14 or 17 of gestation. Irradiation with 0.5-1.5 Gy produced a significant decrease in brain weight of the offspring at 6 and 12 months of age. Exposure to 1 Gy at day 14 or 17 of gestation resulted in significant decrease in the number of neurons in the CA3 and CA4 regions of hippocampus of 200 microm length, while 1.5 Gy significantly affected CA1 region also. The fetal period (13-18 days of gestation) of mouse development is an active phase of brain development involving proliferation, migration and differentiation of cerebral cortex and associated structures. The present results show that exposure at this period of mouse development to moderate doses of gamma radiation can induce permanent deficits in the brain histology, which can adversely affect the learning and memory in adults.

Utilization of juvenile animal studies to determine the human effects and risks of environmental toxicants during postnatal developmental stages

BACKGROUND

Toxicology studies utilizing animals and in vitro cellular or tissue preparations have been used to study the toxic effects and mechanism of action of drugs and chemicals and to determine the effective and safe dose of drugs in humans and the risk of toxicity from chemical exposures. Testing in animals could be improved if animal dosing using the mg/kg basis was abandoned and drugs and chemicals were administered to compare the effects of pharmacokinetically and toxicokinetically equivalent serum levels in the animal model and human. Because alert physicians or epidemiology studies, not animal studies, have discovered most human teratogens and toxicities in children, animal studies play a minor role in discovering teratogens and agents that are deleterious to infants and children. In vitro studies play even a less important role, although they are helpful in describing the cellular or tissue effects of the drugs or chemicals and their mechanism of action. One cannot determine the magnitude of human risks from in vitro studies when they are the only source of toxicology data.

METHODS

Toxicology studies on adult animals is carried out by pharmaceutical companies, chemical companies, the Food and Drug Administration (FDA), many laboratories at the National Institutes of Health, and scientific investigators in laboratories throughout the world. Although there is a vast amount of animal toxicology studies carried out on pregnant animals and adult animals, there is a paucity of animal studies utilizing newborn, infant, and juvenile animals. This deficiency is compounded by the fact that there are very few toxicology studies carried out in children. That is one reason why pregnant women and children are referred to as "therapeutic orphans."

RESULTS

When animal studies are carried out with newborn and developing animals, the results demonstrate that generalizations are less applicable and less predictable than the toxicology studies in pregnant animals. Although many studies show that infants and developing animals may have difficulty in metabolizing drugs and are more vulnerable to the toxic effects of environmental chemicals, there are exceptions that indicate that infants and developing animals may be less vulnerable and more resilient to some drugs and chemicals. In other words, the generalization indicating that developing animals are always more sensitive to environmental toxicants is not valid. For animal toxicology studies to be useful, animal studies have to utilize modern concepts of pharmacokinetics and toxicokinetics, as well as "mechanism of action" (MOA) studies to determine whether animal data can be utilized for determining human risk. One example is the inability to determine carcinogenic risks in humans for some drugs and chemicals that produce tumors in rodents, When the oncogenesis is the result of peroxisome proliferation, a reaction that is of diminished importance in humans.

CONCLUSIONS

Scientists can utilize animal studies to study the toxicokinetic and toxicodynamic aspects of drugs and environmental toxicants. But they have to be carried out with the most modern techniques and interpreted with the highest level of scholarship and objectivity. Threshold exposures, no-adverse-effect level (NOAEL) exposures, and toxic effects can be determined in animals, but have to be interpreted with caution when applying them to the human. Adult problems in growth, endocrine dysfunction, neurobehavioral abnormalities, and oncogenesis may be related to exposures to drugs, chemicals, and physical agents during development and may be fruitful areas for investigation. Maximum permissible exposures have to be based on data, not on generalizations that are applied to all drugs and chemicals. Epidemiology studies are still the best methodology for determining the human risk and the effects of environmental toxicants. Carrying out these focused studies in developing humans will be difficult. Animal studies may be our only alternative for answering many questions with regard to specific postnatal developmental vulnerabilities.

Induction of developmental toxicity in mice treated withAlstonia scholaris (Sapthaparna) In utero

BACKGROUND

The teratogenic effect of hydroalcoholic extract of Alstonia scholaris (ASE) was studied in the pregnant Swiss albino mice administered with 0, 60, 120, 240, 360, and 480 mg/kg ASE on Day 11 of gestation.

METHODS

Females were allowed to complete the term and parturiate. The litters were monitored regularly for mortality, growth retardation, congenital malformations, and appearance of physiological markers up to 7 weeks post-parturition (p.p.).

RESULTS

The administration of 60, 120, 180, and 240 mg/kg ASE to the pregnant mice on Day 11 did not induce mortality, congenital malformations, or alter the normal growth patterns. A further increase in the herbal extract dose up to 360 or 480 mg/kg resulted in a dose dependent increase in the mortality, growth retardation, and congenital malformations, characterized mainly by bent tails and syndactyly. The administration of higher doses (360 or 480 mg) of ASE also caused a significant delay in the morphological parameters such as fur development, eye opening, pinna detachment, and vaginal opening. The incisor eruption and testes decent were found to be delayed in litters born to the mothers treated with 240-480 mg/kg ASE.

CONCLUSIONS

Our study indicates clearly that ASE treatment caused teratogenic effect only at doses above 240 mg/kg (>20% of LD(50)). Lower doses had no developmental toxicity.

Effects of Podophyllum hexandrum on radiation induced delay of postnatal appearance of reflexes and physiological markers in rats irradiated in utero

Effect of 2.0 Gy gamma-dose delivered to rats in utero on 17th day of gestation was studied to monitor the radiation induced retardation of neurophysiological development in postnatal young ones. Rhizome of Podophyllum hexandrum which has been well documented for mitigating radiation injuries in adult mice was attempted for modifying radiation damage. Rats were observed from postnatal day 1 to 25 for the age of the appearance of physiological markers (pinna detachment, inscisor's eruption, eye opening) and acquisition of reflexes (surface righting, visual placing, reflex suspension, negative geotaxis). In irradiated groups there was a significant weight reduction in mother rats and offsprings throughout the experimental period. There was radiation-induced delay in the appearance of pinna detachment but not in eye opening and inscisor's eruption. Appearance of the reflexes were also delayed due to irradiation. Preirradiation administration of the extract of Podophyllum hexandrum (i.p., 200 mg/kg/b.w.) mitigated radiation induced postnatal physiological alterations. These studies have implications in protection against damage (in utero) due to planned radiation exposure.

Effect of early fetal irradiation on the postnatal development of mouse

BACKGROUND

An earlier study has shown that irradiation at the late fetal stage of Swiss albino mice disturbed postnatal growth and appearance of physiological markers. The present study was done to determine the effect of irradiation at the early fetal stage on the postnatal development of mouse.

METHODS

Fourteen-day pregnant Swiss albino mice were exposed to 0.1-1.5 Gy of cobalt-60 gamma-rays. F1 pups were observed for < or = 6 weeks of age. Postnatal mortality, body weight and length, head length and width, tail length, and the time of appearance of physiological markers (pinna detachment, eye opening, fur development, vaginal opening and testes descent) were noted.

RESULTS

There was no increase in congenital anomalies. Postnatal mortality and percentage of growth-retarded pups increased significantly at doses of 0.5-1.5 Gy. A significant delay in the appearance of all the physiological markers was also noted at these doses. Body length, head length, and tail length remained significantly lower than in the controls throughout the observation period at doses of 0.3-1.5 Gy, whereas body weight and head width showed such a persistent change only at > or = 0.5 Gy.

CONCLUSIONS

The early fetal day 14 in mouse is sensitive to radiation-induced postnatal mortality and impairment of growth and temporal development of physiological markers, but not to induction of congenital anomalies. While mortality and physiological markers are not affected at <0.5 Gy, growth retardation appears to have a lower threshold of approximately 0.3 Gy.

Influence of gestational age to low-level gamma irradiation on postnatal behavior in mice

The present investigation was carried out to study the effects of in utero exposure to low-level gamma radiation (0.25, 0.35, or 0.50 Gy) on the postnatal neurophysiology and neurochemistry of the mouse. Pregnant Swiss albino mice were irradiated on days 11.5, 12.5, 14.5, or 17.5 post coitus (PC) and allowed to deliver. Locomotor and exploratory activities, learning and memory functions, and emotional activities were tested at 3 months of age using behavior tests. A representative group of animals was killed and hippocampal biogenic amines, noradrenaline, dopamine, serotonin (5-HT), and 5-HT's metabolite 5-hydroxy indoleactetic acid (5-HIAA), were measured. Exposure to 0.25 Gy at any of the gestation days did not produce any significant impairment in brain functions. However, an increase in gamma irradiation to 0.50 Gy on all the gestation days produced significant impairment in locomotor (open-field test) and anxiolytic (light and dark area test) activities, learning (hole board test), memory functions (active avoidance test), and emotional activity (rearings). The late fetal period is relatively resistant to radiation-induced impairment of brain functions. Both of the organogenesis gestation days showed a higher sensitivity than the fetal gestation days studied. Even a lower dose of 0.35 Gy when exposed on the late organogenesis days 11.5 and 12.5 PC, produced significant reduction in locomotor and exploratory activities. Day 11.5 PC showed a higher sensitivity than the other PC days studied. Biogenic amines did not show significant change after any of the exposures on any of the gestation days. The results suggest a threshold between 0.25 to 0.35 Gy for postnatal neurobehavior changes.

Effect of prenatal gamma irradiation during the late fetal period on the postnatal development of the mouse

Pregnant Swiss albino mice were exposed to 0.3, 0.5, 1.0, or 1.5 Gy of gamma radiation on day 17 of gestation. Sham-exposed controls were examined for comparison. Exposed mice as well as controls were left to complete gestation and parturition. Pups were observed up to age 6 weeks; appearance of physiological markers (pinna detachment, eye opening, fur development, vaginal opening, and testes descent), postnatal mortality, body weight, body length, head length, head width, and tail length were recorded. A significant delay in fur development was observed at 0.3 Gy and in other physiological markers at doses above 0.3 Gy, while a significant increase in mortality and growth retardation occurred only at 1.0 and 1.5 Gy. Although congenital anomalies such as syndactyly and bent tail were observed at doses of 0.5-1.5 Gy, only syndactyly showed a statistically significant increase in frequency. A statistically significant lower body weight was observed during the first week of postnatal life, but body weights increased to normal levels by the second week in animals exposed to doses less than 1.0 Gy. At higher doses, low body weight persisted throughout the postnatal period. Head length and tail length showed a significant decrease from controls at 0.5-1.5 Gy, and the effect was evident from birth to age 6 weeks. But a similar effect on body length and head width was noticed only at 1.0 and 1.5 Gy. These studies indicate that even in the absence of any major morphological changes, normal development of physiological landmarks and postnatal growth can be impaired by fetal irradiation at 17 days p.c. (post coitus). Morphological changes appear to have a threshold between 0.3-0.5 Gy, while physiological marker effects may occur with a lower threshold.

Comparative study of behavioral development between high and low shuttlebox avoidance rats

Previously, we reported that high- and low-avoidance animals (HAA and LAA, respectively), selectively bred for different avoidance response rates in a shuttlebox avoidance test, showed additional behavioral differences in wheel cage activity and in water maze performance after weaning. In the present study, physical and behavioral development were examined in HAA and LAA during the preweaning period. As compared to HAA, LAA offspring showed lower body weight, delayed eye opening, poorer performance in pivoting and negative geotaxis, and increased open-field activity. A fostering study indicated that these differences observed in eye opening, pivoting, negative geotaxis, open-field activity, swimming speed, shuttlebox avoidance and wheel cage activity were independent of maternal care. Only the pup weight was strongly dependent on the maternal line. These results indicate that behavioral differences between HAA and LAA observed in the pre- and postweaning periods may be linked to the avoidance genotype, but the difference in pup weight may be caused by maternal care.

Effect of prenatal ultrasound exposure on adult behavior in mice

Pregnant Swiss mice were exposed to diagnostic levels of ultrasound (3.5 MHz, Maximum acoustic output: ISPTP = 1 W/cm2 and ISATA = 240 mW/cm2, acoustic power = 65 mW) for 10 min on days 11.5 or 14.5 postcoitus (PC). At 3 and 6 months postpartum, offspring were subjected to the following behavioral tests: bright and dark arena test for locomotor/exploratory activity and passive avoidance test for learning and memory. Anxiolytic activity and latency in learning were noticed in the ultrasound-treated animals. The effect was more pronounced in the 14.5 days PC group than in the 11.5 days PC group. But memory was not affected in the ultrasound-exposed animals. There was a nonsignificant decrease in the total locomotor activity at 6 months of age in all the exposed animals. Thus, the present data demonstrate that exposure to diagnostic ultrasound during late organogenesis period or early fetal period in mice may cause changes in postnatal behavior as evidence by selected adult offspring behavioral tests. However, any conclusive statement in this regard should await results from more detailed investigations.

Prenatal exposure to gamma/neutron irradiation: sensorimotor alterations and paradoxical effects on learning

The effects of prenatal exposure on gamma/neutron radiations (0.5 Gy at about the 18th day of fetal life) were studied in a hybrid strain of mice (DBA/Cne males x C57BL/Cne females). During ontogeny, measurements of sensorimotor reflexes revealed in prenatally irradiated mice 1) a delay in sensorial development, 2) deficits in tests involving body motor control, and 3) a reduction of both motility and locomotor activity scores. In adulthood, the behaviour of prenatally irradiated and control mice was examined in the open field test and in reactivity to novelty. Moreover, their learning performance was compared in several situations. The results show that, in the open field test, only rearings were more frequent in irradiated mice. In the presence of a novel object, significant sex x treatment interactions were observed since ambulation and leaning against the novel object increased in irradiated females but decreased in irradiated males. Finally, when submitted to different learning tasks, irradiated mice were impaired in the radial maze, but paradoxically exhibited higher avoidance scores than control mice, possibly because of their low pain thresholds. Taken together, these observations indicate that late prenatal gamma/neutron irradiation induces long lasting alterations at the sensorimotor level which, in turn, can influence learning abilities of adult mice.

Development of a useful technique for analyzing behavioral teratologic data

Two measures of postnatal development are described in this paper: the PAC50 and AD50. These measures proved to be more sensitive than the use of means in the evaluation of three radiation studies involving postnatal developmental evaluation. PAC50 is the percent of achievement of a goal by litters or offspring in an experimental group at the age when 50% of the control litters or offspring attain that goal. AD50 is the age (acquisition day) at which 50% of the litters or offspring in each group attain a specified developmental goal. This methodology is a useful technique for analyzing selected behavioral data following in utero X-irradiation and may prove to be a sensitive means of determining postnatal alteration due to prenatal exposure to a variety of suspect agents.