The low-dose ionizing radiation stimulates cell proliferation via activation of the MAPK/ERK pathway in rat cultured mesenchymal stem cells

Hormesis induced by low-dose ionizing radiation (LDIR) is often mirrored by its stimulation of cell proliferation. The mitogen-activated protein kinases (MAPK)/ extracellular-signal- regulated kinases (ERK) pathway is known to play important roles in cell growth. Therefore, this study was to examine the effects of LDIR on rat mesenchymal stem cell (MSC) proliferation and MAPK/ERK signaling pathway. Rat MSCs were isolated from the bone marrow from 6 to 8-week-old male Wistar rats and cultured in vitro. Exponentially growing cells within 4-5 passages were irradiated with low doses of X-rays at 20, 50, 75 and 100 mGy with a dose rate of 100 mGy/min. Cell proliferation was evaluated by counting total viable cell number with trypan-blue staining and MTT assay. Cell cycle changes were also evaluated by flow cytometry and the activation of MAPK/ERK signaling pathway was assayed by Western blotting. Results showed that LDIR at 50 and 75 mGy significantly stimulated the proliferation of rat MSCs with the most stimulating effect at 75 mGy. There was a significant increase in the proportion of S phase cells in MSCs in response to 75 mGy X-rays. Activation of several members in the MAPK/ERK signaling pathway, including c-Raf, MEK and ERK were observed in the cells exposed to 75 mGy X-rays. To define the role of ERK activation in LDIR-stimulated cell proliferation, LDIR-treated MSCs were pre-incubated with MEK specific inhibitor U0126, which completely abolished LDIR-increased phosphorylation of ERK and cell proliferation. These results suggest that LDIR stimulates MSC proliferations in the in vitro condition via the activation of MAPK/ERK pathway.     

低剂量辐射诱导小鼠脾细胞转铁蛋白受体表达的适应性反应

本文采用直接免疫荧光流式细胞术方法,检测了低剂量Ｘ射线全身照射后２４ｈ,小鼠脾脏淋巴细胞转铁蛋白受体（ＴｆＲ）表达的变化及诱导ＴｆＲ表达的适应性反应。结果表明,７５ｍＧｙＸ射线全身照射可增强脾脏淋巴细胞ＴｆＲ的表达,并可明显减轻其后２Ｇｙ照射对小鼠脾脏淋巴细胞ＴｆＲ表达的抑制,诱导ＴｆＲ表达的适应性反应。说明ＴｆＲ可能在低剂量辐射诱导免疫适应性反应中发挥作用。     

Influence on cell proliferation of background radiation or exposure to very low, chronic gamma radiation

Investigations carried out on the protozoan Paramecium tetraurelia and the cyanobacteria Synechococcus lividus, which were shielded against background radiation or exposed to very low doses of gamma radiation, demonstrated that radiation can stimulate the proliferation of these two single-cell organisms. Radiation hormesis depends on internal factors (age of starting cells) and external factors (lighting conditions). The stimulatory effect occurred only in a limited range of doses and disappeared for dose rates higher than 50 mGy/y.     

The combined effects of MRI and X-rays on ICR mouse embryos during organogenesis

The combined effects of X-rays and magnetic resonance imaging (MRI) on mouse embryos at an early stage of organogenesis were investigated. Pregnant ICR mice were irradiated on day 8 of gestation with X-rays at a dose of 1 Gy and/or MRI at 0.5 T for 1 hour. The mortality rates of the embryos or fetuses, the incidence of external malformations, the fetal body weight and the sex ratio were observed at day 18 of gestation. A significant increase in embryonic mortality was observed after exposure to either 1 Gy of X-radiation or 0.5 T MRI. However, the combined X-rays and MRI did not show a statistically significant increase in embryonic mortality compared with the control. External malformations, such as exencephaly, a cleft palate and anophthalmia, were observed in mice irradiated with X-rays and/or MRI. The incidence of each malformation in all treated groups increased with statistical significance compared with the control mice. The incidence in mice irradiated with both X-rays and MRI was lower than in mice irradiated with only X-rays. The combined effects of the combination of radiation and MRI on the external malformations might be antagonistic. There were no statistically significant differences in fetal death, fetal body weight and sex ratio among all experimental groups.     

Damage of genetic material in somatic cells of mice exposed to low doses of X-rays

Pzh:SFIS mice were exposed during 8 weeks, 5 days per week to doses of 0.05 Gy; 0.10 Gy; 0.20 Gy of X-rays. Samples were taken at 24 h and at 72 h after the end of irradiation for micronucleus test, in the case of estimation induction of DNA damages also at 24 h and at 1, 4 and 8 weeks. Subchronic exposure of mice to low doses of ionizing radiation induced damages of genetic material of theirs somatic cells. The enhanced frequency of micronuclei were observed in reticulocytes and polychromatic erythrocytes of bone marrow after each of dose. Subchronic exposure to X-rays induced also DNA single strand breaks in bone marrow lymphocytes. Damage were observed up to 8 weeks after the end of exposure. Results obtained in this study confirmed sensitivity of bone marrow cells to low doses of X-rays.     

Low-dose whole-body irradiation induced radioadaptive response in C57BL/6 mice

Radioadaptive survival responses after relatively low doses of radiation were investigated in C57BL/6 mice. The 8-week-old mice received whole-body mid-lethal challenging irradiation (5.9 Gy) at various intervals after conditioning whole-body irradiation with 50-400 mGy. Thereafter, survival of the mice was observed for 30 days. The mice receiving 400 mGy at 6 h before the challenging dose had a lower survival rate than the control group, but it was not observed when the conditioning 400-mGy irradiation was given 24 h beforehand. The conditioning doses of 100 and 200 mGy did not influence the survival of mice after the challenging dose. The mice receiving 50 mGy at 1 day, 3 days or 1 week before the challenging dose had a higher survival rate than the control, although this adaptive response was not observed when 50 mGy was given 6 h, 12 h, 3.5 weeks, or 5 weeks beforehand. When 50 mGy was given 2 weeks before the challenging dose, the adaptive response was observed in an experiment in which the mice were caged in our laboratory at the age of 5 weeks, whereas it was not observed in another experiment in which the mice were caged at 3 weeks. This study confirmed the presence of radioadaptive survival responses at the dose of 50 mGy given relatively shortly before the challenging dose.     

Dependence of malformation upon gestational age and exposed dose of gamma radiation

In order to evaluate the importance of gestational age and the dose-incidence relationship by gamma radiation, pregnant ICR mice at gestational days from 2.5 to 15.5 days post-coitus (p.c.) were exposed to a single dose of 2.0 Gy and also at day 11.5 after conception, which was the most sensitive stage for the induction of major congenital malformations. The animals were sacrificed on day 18 of gestation and the fetuses were examined for mortality, growth retardation, changes in head size and other morphological abnormalities. The only demonstrable effect of irradiation during the pre-implantation period was an increase in prenatal mortality. Resorptions were maximal on exposure at day 2.5 after conception. The pre-implantation irradiated embryos which survived did not show any major fetal abnormalities. A small head, growth retardation, a cleft palate, dilatation of the cerebral ventricle, a renal pelvis, and abnormalities of the extremities and tail after exposure were prominent during the organogenesis period, especially on day 11.5 of gestation. As for the dose-incidence relationship, the incidence of a small head, growth-retarded fetuses, a cleft palate, dilatation of cerebral ventricle and abnormalities of the extremities in live fetuses rose as the radiation dose increased. The result indicated that the late period of organogenesis in the development of the brain, skull and extremities of a mouse was a particularly sensitive phase. The threshold doses of radiation that induced a cleft palate and dilatation of the cerebral ventricle, and abnormal extremities were between 1.0 and 2.0 Gy, and between 0.5 and 1.0 Gy, respectively.     

Induction of apoptosis by beta radiation from tritium compounds in mouse embryonic brain cells.

Induction of apoptosis by tritium exposure was investigated in both cultured embryonic mid brain cells and brain sections of embryos and of newborns in mice. In the cultures of mid brain cells, addition of methyl-3H-thymidine (3H-TdR) (21 kBq mL(-1)) and tritiated water (5.616 MBq mL(-1)) induced late appearances and low percentages of apoptosis when compared to x-irradiation at the ID50 dose, the inhibitory dose that reduced cellular differentiation by 50% of the control. A significant increase in p53 protein was detected about 2 h before the marked appearance of apoptosis. The pregnant mice were given an intraperitoneal injection of tritiated water at the concentration of 481.8 kBq g(-1) of body weight on gestation day 12.5, by which treatment behavioral changes in the offspring occurred. Increased apoptotic cells were observed in the neural tube of embryos from 1 d after the injection to 1 wk postnatal age. Apoptosis induced by x-rays appeared 2 h after irradiation, with a peak at 4 h. Increase of apoptotic cells was also found in the brain cortexes of newborns. The percentage of apoptosis in the brain was higher in the prenatal tritiated water exposed mice than in the prenatal x-irradiated mice. Possible mechanisms on apoptosis and its relation to the higher relative biological effectiveness value of tritium beta-rays are discussed.     

低剂量辐射对脐血LAK细胞体外抗肿瘤活性的影响

目的 探讨低剂量辐射对脐血LAK细胞体外抗肿瘤活性的影响。方法 新鲜分离的脐血单个核细胞用重组白细胞介素2培养72h获取LAK效应细胞,在培养48h时给予1次不同剂量（分别为62mGy,124mGy,186mGy,248mGy）的γ射线照射,应用^3H－TdR释放实验测定LAK体外杀伤肿瘤靶细胞（K562,HL－60）活性。结果 脐血LAK细胞对K562和HL－60的杀伤活性与成人外周血相比差异无显著性（P＞0．05）。接受低剂量辐射的脐血LAK细胞K562和HL－60的细胞毒性显著高于非照射对照组（P＜0．01）。结论 脐血可作为LAK细胞的一个良好来源。低剂量辐射可增强脐血LAK杀伤肿瘤细胞的细胞毒性,从而可能用于清除微小残留病变及在脐血移植时增强移植物抗白血病效应。     

低剂量CT扫描对青少年副鼻窦疾病的应用价值

目的：探讨低剂量CT扫描对青少年副鼻窦疾病的应用价值。方法：对35例青少年副鼻窦疾病患者分别行低剂量和常规剂量扫描,对比两种剂量扫描所得图像质量与患者的辐射剂量。结果：低剂量和常规剂量扫描两种扫描方法所显示的图像质量没有显著差异（p〉0.05）,低剂量CT扫描单次扫描的辐射剂量加权指数（CTDIvol）为7.6mGy,常规剂量的为28.1mGy,两种扫描方法辐射剂量有显著差异（p〈0.01）。结论：低剂量CT扫描在副鼻窦疾病中是可行的,能保证图像的质量,又有效的降低患者的辐射损伤。     

Estimation of the thyroid doses for ukrainian children exposed in utero after the chernobyl accident

This paper describes methods for estimating thyroid doses to Ukrainian children who were subjects of an epidemiological study of prenatal exposure and presents the calculated doses. Participants were 2,582 mother-child pairs in which the mother had been pregnant at the time of the Chernobyl accident on 26 April 1986 or in the 2-3 mo following when (131)I in fallout was still present. Among these, 1,494 were categorized as "exposed;" a comparison group of 1,088 was considered "relatively unexposed." Individual in utero thyroid dose estimates were found to range from less than 1 mGy to 3,200 mGy, with an arithmetic mean of 72 mGy. Thyroid doses varied primarily according to stage of pregnancy at the time of exposure and level of radioactive contamination at the location of residence. There was a marked difference between the dose distributions of the exposed and comparison groups, although nine children in the latter group had calculated doses in the range 100-200 mGy. For those children who were born after the accident and prior to the end of June 1986, postnatal thyroid doses were also estimated. About 7.7% (200) of the subjects received thyroid doses after birth that were at least 10% of their cumulative doses.     

自动管电流调节低剂量CT在尘肺诊断中的应用

目的 探讨自动管电流调节低剂量CT在尘肺诊断中的可行性及应用价值.方法 45例经专业机构确诊的尘肺患者均行固定管电流（150 mA）常规剂量CT扫描（固定组）和自动管电流调节低剂量CT扫描（ATCM组,固定噪声指数为14,管电流50～200 mA）,记录两组不同扫描条件下患者的容积CT剂量指数（CTDIvol）和剂量长度乘积（DLP）,采用双盲法分别对两种扫描方法所获取图像的质量、尘肺影像特征（阴影大小、阴影密集度、尘肺分期）进行评价,并进行统计学分析.结果 在尘肺的CT影像征象显示率方面,ATCM组可清晰地显示各种尘肺特征性表现,与固定组相比,两者在显示尘肺影像特征（阴影大小、阴影密集度以及尘肺分期）、图像质量方面比较差异均无统计学意义（P＞0.05）.固定组的CTDIvol、DLP分别为13.53 mGy和（337.13±13.53） mGy/cm,ATCM组分别为（7.39±0.45） mGy和（188.78±1.80） mGy/cm,两者比较差异有统计学意义（P＜0.05）.结论 自动管电流调节低剂量CT能全面反映尘肺的特征,图像质量可满足辅助诊断要求,并且能显著降低患者的辐射剂量,可代替常规剂量CT用于尘肺的筛选与辅助诊断.     

Radium-226 dose to a boy from playing on mill tailings

Two boys born in September 1949 played on uranium mill tailings from about ages 8 to 12. One of these boys was diagnosed as having leukemia at age 15.5. The 226Ra body burden of the survivor was measured at age 38. The whole-body 226Ra content measured by counting in vivo was 0 +/- 17 Bq and independently by Rn breath analysis as 4.3 +/- 2.1 Bq. At the same time, a control subject with no known exposure to 226Ra, matched in age, height, and weight, was also measured. The whole-body content was estimated as 4 +/- 15 Bq and independently by Rn breath analysis as 5.5 +/- 3.7 Bq. The body burden of the control subject was not significantly different from that of the exposed person. The radiation dose to the marrow-free skeleton assuming a constant 226Ra:Ca ratio since birth was 0.49 and 1.33 mGy at ages 14 and 38, respectively. The radiation dose to the marrow-free skeleton assuming 226Ra intake only between ages 8 to 12 was 1.4 and 2.8 mGy at ages 14 and 38, respectively. The best estimate is the mean of these two estimates: 0.9 and 2.1 mGy at ages 14 and 38, respectively. The alpha-particle dose to the red marrow from 226Ra and its decay products was 0.05 mGy at age 14 and 0.10 mGy at age 38. Since no excess was found for the radium dial painters whose doses were much higher, the induction of leukemia by doses of this magnitude would seem quite unlikely.     

Induction of somatic mutations by low concentrations of tritiated water (HTO): evidence for the possible existence of a dose-rate threshold

Tritium is a low energy beta emitter and is discharged into the aquatic environment primarily in the form of tritiated water (HTO) from nuclear power plants or from nuclear fuel reprocessing plants. Although the biological effects of HTO exposures at significant doses or dose rates have been extensively studied, there are few reports concerning the biological effects of HTO exposures at very low dose rates. In the present study using a hyper-sensitive assay system, we investigated the dose rate effect of HTO on the induction of mutations. Confluent cell populations were exposed to HTO for a total dose of 0.2 Gy at dose rates between 4.9 mGy/day and 192 mGy/day by incubating cells in medium containing HTO. HTO-induced mutant frequencies and mutation spectra were then investigated. A significant inflection point for both the mutant frequency and mutation spectra was found between 11 mGy/day and 21.6 mGy/day. Mutation spectra analysis revealed that a mechanistic change in the nature of the mutation events occurred around 11 mGy/day. The present observations and published experimental results from oral administrations of HTO to mice suggest that a threshold dose-rate for HTO exposures might exist between 11 mGy/day and 21.6 mGy/day where the nature of the mutation events induced by HTO becomes similar to those seen in spontaneous events.     

Effects of low-dose heavy ions on the postnatal development of mice and the yield of white spots in the mid-ventrum and tail-tips

Effects of prenatal low-dose irradiations of heavy ions on the postnatal development of mice and of melanocytes have not been well studied. Pregnant females of C57BL/10J mice were irradiated whole-body at 9 days of gestation with a single acute dose of γ-rays, silicon (Si, 57 keV/μm), argon (Ar, 100 keV/μm) and iron (Fe, 220 keV/μm) ions. The effects were studied by scoring changes in the postnatal development of mice as well as in the pigmentation of cutaneous coats and tail-tips of their offspring 22 days after birth. The survival to day 22 decreased from the offspring exposed to 0.4 Gy of argon and iron ions and to 0.75 Gy of silicon ions. White spots were found in the mid-ventrum and tail-tips of irradiated offspring. The frequency and size of the white spots in the mid-ventrum in mice exposed to silicon, argon and iron ions were greater than those of γ-rays. Even in the low dose (0.1 Gy), γ-rays and heavy ions increased the frequency of the ventral spots. The RBE estimated by the frequency of the ventral spots was 2.3 (Si), 3.1 (Ar) and 4.5 (Fe). These results suggest that prenatal exposure to heavy ions possesses a greater effect on the postnatal development of mice as well as melanocyte development than does exposure to γ-rays.     

In utero exposure to maternal low protein diets induces hypertension in weanling rats, independently of maternal blood pressure changes

The association between maternal nutrition, fetal growth and the later development of hypertension was investigated in the rat. Animals were habituated to diets containing 18% (control) or 9% (low) protein by weight. The rats were mated and maintained on the diets until the end of pregnancy. Lactating dams were transferred onto standard chow diet. Systolic blood pressure was determined in male and female weanling offspring, using an indirect tail-cuff method. To assess the direct effects of low protein diets upon blood pressure of adult animals, a group of male and female rats were fed 18% or 9% protein for 14 days. Blood pressure was determined at the beginning and end of the feeding period. Blood pressure was additionally assessed over 14 days in pregnant rats fed control or low protein diets. Low protein diets did not alter systolic blood pressure in adult male or female rats. The blood pressures of pregnant females fed 18% or 9% protein diets did not significantly differ at any stage of pregnancy. Rats fed 9% protein diets gave birth to significantly smaller pups. Litter sizes were unaltered, and no differences in perinatal mortality were observed. Pups exposed to maternal low protein in utero had higher systolic blood pressure at the age of 4 weeks, when compared to control pups. The phenomenon was observed in both male and female offspring. Blood pressures at 4 weeks of age were strongly associated with maternal protein intake (r = -0.55). Associations were also noted between blood pressure and maternal weight at mating (r = 0.48), and weight gain in pregnancy (r = -0.30). Fetal exposure to maternal low protein diets induces hypertension in rats. The phenomenon is observed early in life and is independent of sex and the influence of maternal blood pressure. The low protein diet itself did not produce an increase in the blood pressure of adult rats.     

Trp53 activity is repressed in radio-adapted cultured murine limb bud cells

Understanding the effects of of ionizing radiation (IR) at low dose in fetal models is of great importance, because the fetus is considered to be at the most radiosensitive stage of the development and prenatal radiation might influence subsequent development. We previously demonstrated the existence of an adaptive response (AR) in murine fetuses after pre-exposure to low doses of X-rays. Trp53-dependent apoptosis was suggested to be responsible for the teratogenic effects of IR; decreased apoptosis was observed in adapted animals. In this study, in order to investigate the role of Trp53 in AR, we developed a new model of irradiated micromass culture of fetal limb bud cells, which replicated proliferation, differentiation and response to IR in murine embryos. Murine fetuses were exposed to whole-body priming irradiation of 0.3 Gy or 0.5 Gy at embryonic day 11 (E11). Limb bud cells (collected from digital ray areas exhibiting radiation-induced apoptosis) were cultured and exposed to a challenging dose of 4 Gy at E12 equivalent. The levels of Trp53 protein and its phosphorylated form at Ser18 were investigated. Our results suggested that the induction of AR in mouse embryos was correlated with a repression of Trp53 activity.     

Low dose radiation increased the therapeutic efficacy of cyclophosphamide on S(180) sarcoma bearing mice

We examined whether low dose radiation (LDR) exposure (75 mGy) could increase the therapeutic efficacy of cyclophosphamide (CTX) by comparing the effects of tumor suppression, tumor cell apoptosis, cell cycle and proliferation of bone marrow in vivo. Kunming mice implanted with S(180) sarcoma cells were given 75 mGy whole body gamma-ray radiation exposure and CTX (300 mg/kg) by intraperitoneal injection 36 hours after LDR. Proliferation of bone marrow and tumor cells was analyzed by flow cytometry. Cytochrome c leakage from the tumor was measured by Western-blot. We discovered that tumor growth was significantly reduced in the group exposed to CTX add to LDR. The apoptosis of tumor cells increased significantly after LDR. The tumor cells were arrested in G(1) phase in the groups treated with CTX and CTX + LDR, but cell cycle was more significantly arrested in mice exposed to LDR followed by CTX than in mice exposed only to LDR or CTX chemotherapy. Concentration of bone marrow cells and proliferation index in CTX + LDR mice were higher than those in the untreated mice. LDR or CTX + LDR could induce greater cytochrome c levels and caspase-3 activity in tumors. These results suggest that low dose radiation can enhance the anti-tumor effect of the chemotherapy agent CTX markedly. Furthermore, LDR significantly protects hematopoetic function of the bone marrow, which is of practical significance on adjuvant chemotherapy.     

Developmental toxicity potential of paclobutrazol in the rat

Paclobutrazol is used as a fungicide and as a plant growth regulator, but there are few studies about its potential toxic effects. Experiments were conducted to determine whether this compound has adverse effects on the reproduction and development of offspring. The influence of 1.0 mg/kg paclobutrazol (10 x the acceptable daily intake-ADI), by oral exposure during gestational organogenesis of rats, was evaluated on maturational and behavioural aspects of offspring development. This dose did not promote evidence of maternal toxicity and the weight of gravid uterus, fetus, and ovary on days 16 and 20 of pregnancy were not affected. Also, the pesticide did not affect body weight gain of the dams and offspring. However, the pups' survival at weaning was impaired by paclobutrazol. Beyond that, study of the functional state of rat pups' nervous system at different stages of postnatal development revealed some differences in treated ones. Damage was observed in the expression of acoustic startle reflex and altered locomotion and/or rearing in an open-field apparatus in treated pups depending on their age. There were no observed alterations in swimming behaviour. The data support further studies of the potentially toxic effects that exposing mothers to this pesticide may have on their litters.