Involvement of p53-dependent apoptosis in radiation teratogenesis and in the radioadaptive response in the late organogenesis of mice

The irradiation of fetuses at the late period of organogenesis has been known to induce a dramatic increase in malformations. The mechanisms involved, however, have remained unclear for a long time. Using the mouse limb bud system, we first found that radiation-induced apoptosis is involved in the malformation, namely, radiation-induced apoptosis in the predigital regions of embryonic limb buds is responsible for digital defects in mice. An examination of embryonic C57BL/6J mice with different p53 (trp53) status enabled us to further find that susceptibility to radiation-induced apoptosis in the predigital regions and digital defects depend on both the p53 status and the radiation dose; p53 wild-type mice appeared to be the most sensitive, while p53 knockout mice were the most resistant. These results indicate that p53-dependent apoptosis mediates radiation-induced digital defects in the later organogenesis period. The existence of a radioadaptive response in embryonic mice, which has not been reported so far, was found by irradiating embryos with either 5 cGy or 30 cGy on embryonic day 11 prior to a challenging irradiation at 3 Gy on embryonic day 12. p53-heterozygous embryos did not show the radioadaptive response, indicating the involvement of p53 in the radioadaptive response in embryogenesis.     

Dose and dose-rate effects of X rays and fission neutrons on lymphocyte apoptosis in p53(+/+) and p53(-/-) mice

Following the exposure of mice to X rays or fission neutrons, the frequency (F) of apoptosis was measured after 4 h, and the weight loss or lymphocyte content loss in the thymus and spleen was measured after 24 h. In p53(+/+) mice, F increased linearly with the dose (D (Gy)) and the induced rate per Gy of F (detected by TUNEL staining) was 0.05 and 0.23 for X rays and fission neutrons, respectively. Therefore, the RBE of fission neutrons was 4.6 for apoptosis induction. This indicates that radiation-induced apoptosis is mostly due to double strand breaks (DSBs) in DNA because we previously obtained almost the same RBE value of fission neutrons for the induction of crossover mutations in Drosophila melanogaster, which arise from the recombinational repair of DSBs. In p53(+/+) mice, decreases in the organ weight and the lymphocyte content were observed for the thymus and the spleen 24 h after X-irradiation. These atrophic changes in the thymus and the spleen quantitatively corresponded to the total apoptotic cell deaths occurring in them. However, in p53(-/-) mice, no vigorous apoptosis was induced after X-irradiation, and hyperplastic changes in the weight and the lymphocyte content appeared in the thymus and the spleen 24 h after X-irradiation. In p53(+/+) mice, there was no difference in the induced rate per Gy of reduction in the surviving fraction of lymphocytes between acute (0.4 Gy/min) and chronic (3 mGy/min) gamma-irradiations. Namely, radiation-induced apoptosis in lymphocytes is a dose-rate independent event.     

IFN-γ诱导小鼠颗粒细胞DNA损伤及凋亡的体外研究

目的初步探讨IFN-γ诱导小鼠卵泡颗粒细胞DNA损伤及凋亡的机制。方法体外分离培养小鼠原代颗粒细胞,分为正常对照组、IFN-γ(1 000 U/ml)处理组及NAC(20 mM)+IFN-γ(1 000 U/ml)联合处理组,处理5d后,采用免疫荧光染色、Western blot和流式细胞术检测颗粒细胞的ATM/ATR信号通路中DNA损伤相关蛋白,ROS水平及凋亡相关蛋白的变化。结果 IFN-γ组颗粒细胞表达γ-H2AX,而NAC组未见明显γ-H2AX表达;Western blot发现IFN-γ组颗粒细胞γ-H2AX、Chk2和p-Chk2蛋白以及p53和p-p53、Caspase-3等凋亡相关蛋白水平均明显上调,NAC组中以上蛋白均被抑制;流式细胞术检测发现IFN-γ可诱导颗粒细胞活性氧簇(reactive oxygen species,ROS)水平上调,而NAC组颗粒细胞的ROS下降至对照组水平。结论 IFN-γ可通过DNA氧化损伤信号引起颗粒细胞凋亡。     

Chronic restraint-induced stress has little modifying effect on radiation hematopoietic toxicity in mice

Both radiation and stresses cause detrimental effects on humans. Besides possible health effects resulting directly from radiation exposure, the nuclear plant accident is a cause of social psychological stresses. A recent study showed that chronic restraint-induced stresses (CRIS) attenuated Trp53 functions and increased carcinogenesis susceptibility of Trp53-heterozygous mice to total-body X-irradiation (TBXI), having a big impact on the academic world and a sensational effect on the public, especially the residents living in radioactively contaminated areas. It is important to investigate the possible modification effects from CRIS on radiation-induced health consequences in Trp53 wild-type (Trp53wt) animals. Prior to a carcinogenesis study, effects of TBXI on the hematopoietic system under CRIS were investigated in terms of hematological abnormality in the peripheral blood and residual damage in the bone marrow erythrocytes using a mouse restraint model. Five-week-old male Trp53wt C57BL/6J mice were restrained 6 h per day for 28 consecutive days, and TBXI (4 Gy) was given on the 8th day. Results showed that CRIS alone induced a marked decrease in the red blood cell (RBC) and the white blood cell (WBC) count, while TBXI caused significantly lower counts of RBCs, WBCs and blood platelets, and a lower concentration of hemoglobin regardless of CRIS. CRIS alone did not show any significant effect on erythrocyte proliferation and on induction of micronucleated erythrocytes, whereas TBXI markedly inhibited erythrocyte proliferation and induced a significant increase in the incidences of micronucleated erythrocytes, regardless of CRIS. These findings suggest that CRIS does not have a significant impact on radiation-induced detrimental effects on the hematopoietic system in Trp53wt mice.     

Mechanisms of benzene-induced hematotoxicity and leukemogenicity: cDNA microarray analyses using mouse bone marrow tissue

Although the mechanisms underlying benzene-induced toxicity and leukemogenicity are not yet fully understood, they are likely to be complicated by various pathways, including those of metabolism, growth factor regulation, oxidative stress, DNA damage, cell cycle regulation, and programmed cell death. With this as a background, we performed cDNA microarray analyses on mouse bone marrow tissue during and after a 2-week benzene exposure by inhalation. Our goal was to clarify the mechanisms underlying the hematotoxicity and leukemogenicity induced by benzene at the level of altered multigene expression. Because a few researchers have postulated that the cell cycle regulation mediated by p53 is a critical event for benzene-induced hematotoxicity, the present study was carried out using p53-knockout (KO) mice and C57BL/6 mice. On the basis of the results of large-scale gene expression studies, we conclude the following: (a) Benzene induces DNA damage in cells at any phase of the cell cycle through myeloperoxidase and in the redox cycle, resulting in p53 expression through Raf-1 and cyclin D-interacting myb-like protein 1. (b) For G1/S cell cycle arrest, the p53-mediated pathway through p21 is involved, as well as the pRb gene-mediated pathway. (c) Alteration of cyclin G1 and Wee-1 kinase genes may be related to the G2/M arrest induced by benzene exposure. (d) DNA repair genes such as Rad50 and Rad51 are markedly downregulated in p53-KO mice. (e) p53-mediated caspase 11 activation, aside from p53-mediated Bax gene induction, may be an important pathway for cellular apoptosis after benzene exposure. Our results strongly suggest that the dysfunction of the p53 gene, possibly caused by strong and repeated genetic and epigenetic effects of benzene on candidate leukemia cells, may induce fatal problems such as those of cell cycle checkpoint, apoptosis, and the DNA repair system, finally resulting in hemopoietic malignancies. Our cDNA microarray data provide valuable information for future investigations of the mechanisms underlying the toxicity and leukemogenicity of benzene.     

过氧化氢处理K562细胞中JWA基因的表达及其与DNA损伤和凋亡的关系

目的研究过氧化氢(H2O2)诱导K562细胞氧化应激过程中,JWA蛋白、热休克蛋白(hsp70和hsp27)和p53蛋白的表达特点,探讨JWA参与细胞应答氧化应激的作用和可能机制。方法用0．01、0．1、1mmol／L的H2O2处理K562细胞10、30、60、180min建立氧化损伤模型;用0．1mmol／L H2O2处理不同时间(6～48h)和不同浓度(0．5～1000μmol／L)的H2O2处理48h分别诱导K562细胞凋亡,然后用DNA琼脂糖凝胶电泳鉴定DNA损伤和凋亡,用免疫印迹方法检测热休克蛋白(hsp70和hsp27)、p53以及JWA的蛋白表达水平。结果在DNA损伤模型中,H2O2活跃地调节JWA的表达,JWA对氧化应激的应答比热休克蛋白更快速,JWA和hsp70的表达规律相似;在低剂量H2O2(0．01mmol／L)处理时,JWA和热休克蛋白的表达均显著增高;在细胞凋亡模型中,JWA、hsp70、hsp27和p53的表达均显著增高,其中,JWA、hsp70和p53三者的表达规律相似。结论JWA是一个有效的环境应答基因并活跃地参与细胞应答氧化应激所致的DNA损伤和细胞凋亡的信号通路,其介导的信号通路可能与hsp70和p53有关。     

Induction of apoptosis through the activation of SAPK/JNK followed by the expression of death receptor Fas in X-irradiated cells

A post-irradiation treatment of the human leukemia cell line MOLT-4 with the antioxidant Trolox attenuated caspase-3 dependent apoptosis. The increase in the p53 expression and SAPK/JNK activation after X irradiation was also inhibited by a Trolox treatment, but the expression of BCL-2 and BAX, which would occur downstream from p53, was not changed. Studies on the effects of the intracellular calcium chelator BAPTA-AM on the induction of apoptosis and the activation of SAPK/JNK and caspase-3 proved that the chelation of calcium merely delayed the onset of radiation-induced apoptosis and the activation of SAPK/JNK and caspase-3. When the effects of the protein synthesis inhibitor cycloheximde on the apoptotic signaling pathways, including the activation of caspase family proteins and SAPK/JNK, were investigated, the expression of death receptor Fas through SAPK/JNK activation was found to be required for radiation-induced apoptosis. Finally, the relationship between the amounts of DNA dsb and induction of apoptosis was examined by irradiating BrdU-incorporated cells. An increase in DNA dsb caused by BrdU was found, but the induction of apoptosis was not enhanced. From these data, we could get no positive evidence for DNA as a target of X-rays and p53 as an indispensable factor to induced apoptosis in X-irradiated MOLT-4 cells.     

Pre-irradiation at a low dose-rate blunted p53 response

We investigated whether chronic irradiation at a low dose-rate interferes with the p53-centered signal transduction pathway induced by radiation in human cultured cells and C57BL/6N mice. In in vitro experiments, we found that a challenge with X-ray irradiation immediately after chronic irradiation resulted in lower levels of p53 than those observed after the challenge alone in glioblastoma cells (A-172). In addition, the levels of p53-centered apoptosis and its related proteins after the challenge were strongly correlated with the above-mentioned phenomena in squamous cell carcinoma cells (SAS/neo). In in vivo experiments, the accumulation of p53 and Bax, and the induction of apoptosis were observed dose-dependently in mouse spleen at 12 h after a challenge with X-rays (3.0 Gy). However, we found significant suppression of p53 and Bax accumulation and the induction of apoptosis 12 h after challenge irradiation at 3.0 Gy with a high dose-rate following chronic pre-irradiation (1.5 Gy, 0.001 Gy/min). These findings suggest that chronic pre-irradiation suppressed the p53 function through radiation-induced signaling and/or p53 stability.     

N-Acetylcysteine,vitamin C and vitamin E diminish homocysteine thiolactone-induced apoptosis in human promyeloid HL-60 cells

We showed previously that homocysteine thiolactone (HcyT) is a potent inducer of apoptosis in HL-60 cells. In the present study, the role of some radical scavengers (N-acetylcysteine, vitamin C, vitamin E and folate) on the reduction of HcyT-induced apoptosis was investigated. Preincubation of HcyT-treated HL-60 cells with vitamin C (Vit C; 100 micro mol/L) or vitamin E (Vit E; 100 micro mol/L) for 2 h significantly reduced the proportion of apoptotic cells with hypodiploid DNA contents or with membrane phosphatidylserine exposure, and attenuated the apoptotic DNA fragmentation. Preincubation of cells with N-acetylcysteine (NAC; 5 mmol/L) for 2 h significantly reduced HcyT-promoted apoptosis measured by membrane phosphatidylserine exposure only. The reduction of HcyT-induced apoptosis by NAC, Vit C or Vit E occurred simultaneously with a significant decrease in intracellular H(2)O(2) levels and reduced caspase-3 enzymatic activity. In contrast, folate had no H(2)O(2) scavenging capacity and did not suppress caspase-3 activity 6 h after HcyT treatment, although folate exhibited antioxidant behavior toward superoxide anions, hydroxyl radicals and peroxynitrite. Preincubation of cells with folate (10 micro mol/L) for 3 d did not affect the extent of HcyT-promoted apoptotic damage. Taken together, our findings suggest that antioxidant pretreatment with NAC, Vit C or Vit E exerts more beneficial effects than folate on reducing apoptotic cell damage induced by homocysteine thiolactone.     

氟致人胎肝细胞DNA损伤及其对细胞凋亡和p53蛋白表达的影响

目的　研究氟对L 0 2细胞DNA的损伤作用及其对细胞凋亡和p5 3表达的影响 ,并探讨p5 3表达与细胞凋亡之间的关系。方法　体外培养的L 0 2细胞分别接触 0、4 0、80、1 6 0 μg ml氟化钠 (对照组、A、B、C组 ) 2 4h后 ,检测L 0 2细胞DNA损伤率、细胞凋亡百分率和p5 3蛋白表达水平。结果　染氟各组细胞DNA损伤率均明显高于对照组 (P <0 0 5 )。与对照组相比 ,B组和C组细胞凋亡百分率明显升高 (P <0 0 5 )。B组和C组细胞p5 3蛋白表达量均显著高于对照组 (P <0 0 1 )。结论　氟可导致L 0 2细胞DNA损伤率上升 ,诱导细胞凋亡和p5 3表达 ,并且随着氟浓度的升高 ,细胞凋亡率和p5 3蛋白的表达量均随之升高     

Retrotransposition of limited deletion type of intracisternal A-particle elements in the myeloid leukemia Clls of C3H/He mice

The murine genome has about 1,000 copies of DNA elements for the intracisternal A-particle (IAP) that resembles a retrovirus. We previously reported that the genomic DNA of the cells from radiation-induced acute myeloid leukemia (AML) lines derived from C3H/He inbred mice was frequently rearranged by the integration of the IAP element. In this study, 8 IAP elements from the characteristic integration sites in 6 cell lines of radiation-induced AML from different mice were characterized and compared in structure with 114 IAP elements isolated from the normal C3H/He genome. One of the 8 elements was a full-length type I IAP, and 7 were of type-I Delta 1 with a common deletion site. Although the type I Delta 1 form is a minor population accounting for about 6% of total genomic IAP elements, it is predominantly retrotransposed in the AML cells from different C3H/He mice. This indicates that limited populations of the IAP elements contribute to the unique retrotransposition in AML cells.     

Radioprotective properties of tocopherol succinate against ionizing radiation in mice

Threats of nuclear and other radiologic exposures have been increasing but no countermeasure for acute radiation syndrome has been approved by regulatory authorities. In prior publications we have demonstrated the efficacy of tocopherol succinate (TS) as a promising radiation countermeasure with the potential to protect against lethal doses of ionizing radiation exposure. The aim of this study was to gain further insight regarding how TS protects mice against a lethal dose of radiation. CD2F1 mice were injected subcutaneously with 400 mg/kg of TS, and 24 h later exposed to ⁶⁰Co γ–radiation. Intestinal tissues or spleen/thymus were harvested after irradiation and analyzed for CD68-positive inflammatory cells and apoptotic cells by immunostaining of jejunal cross-sections. Comet assay was used to analyze DNA damage in various tissues. Phospho-histone H3(pH3) and the proliferating cell nuclear antigen (PCNA) were used as mitotic markers for immunostaining jejunal cross-sections. We observed that injecting TS significantly decreased the number of CD68-positive cells, DNA damage and apoptotic cells (BAX, caspase 3 and cleaved poly(ADP-ribose) polymerase-positive cells) as judged by various apoptotic pathway markers. TS treatment also increased proliferating cells in irradiated mice. Results of this study further support our contention that TS protects mice against lethal doses of ionizing radiation by inhibiting radiation-induced apoptosis and DNA damage while enhancing cell proliferation.     

Strain differences in mice highlight the role of DNA damage in neoplasia induced by low dietary folate

In earlier work, we showed that low dietary folate induced intestinal tumors in BALB/c mice. In this study, our goal was to examine the effect of the same diets on a strain that is more resistant to tumorigenesis (C57Bl/6). We also questioned whether supplementation of the folate-deficient diet (FD) with betaine, an alternate methyl donor, would influence tumor formation. C57Bl/6 mice were fed the same diets [control diet (CD) with 2 mg folate/kg diet and FD with 0.3 mg folate/kg diet] as those in our previous study for 1 y, but they did not develop tumors. We also fed BALB/c mice the FD or FD supplemented with betaine for 1 y, but there was no change in tumor incidence. To determine the relative contributions of DNA damage and altered methylation patterns, we measured intestinal dUTP:dTTP ratios, phosphorylated histone H2AX (p-H2AX) staining, and global DNA methylation in both strains. Only BALB/c mice showed changes due to diet in dUTP:dTTP (from 2.19 +/- 0.20 in CD to 2.77 +/- 0.18 in FD; P = 0.05) and in p-H2AX staining (from 14.10 +/- 3.59% in CD to 22.40 +/- 2.65% in FD; P = 0.054). In BALB/c mice only, FD tended to have less (P = 0.06) global DNA methylation than CD. Although the FD increased plasma homocysteine and the betaine-supplemented FD lowered plasma homocysteine, the latter diet did not reduce tumor incidence. We conclude that plasma homocysteine is not likely to be associated with tumorigenesis in our model. However, DNA damage plays a critical role in initiating tumorigenesis when dietary folate is low and methylation changes may also be contributory.     

辛硫磷对大鼠骨髓间充质干细胞DNA损伤、细胞凋亡及P53蛋白表达的影响

目的研究辛硫磷对大鼠骨髓间充质干细胞(BMSCs)DNA的损伤作用及其对氧化损伤、细胞凋亡和P53蛋白表达的影响。方法 Percoll离心法分离培养大鼠BMSCs,正常传代。取第3代BMSCs,调整细胞密度为1.0×106/瓶,当细胞至亚融合状态,分别以0(对照)、0.2、2和20μg/L的辛硫磷浓度染毒24h。采用MTT法检测BMSCs的存活率,分光光度比色法检测BMSCs超氧化物歧化酶(SOD)、过氧化氢酶(CAT)活性和丙二醛(MDA)含量,单细胞凝胶电泳检测BMSCs的DNA损伤,流式细胞术检测大鼠骨髓间充质干细胞凋亡率,Western blotting检测BMSCs的P53蛋白表达水平。结果与对照组相比,0.2～20μg/L辛硫磷染毒24h,可诱发大鼠BMSCs的DNA损伤,且具有剂量-效应关系;各染毒组大鼠BMSCs的存活率、SOD和CAT活性均显著下降(P<0.05),细胞凋亡率和MDA含量均显著升高(P<0.05);辛硫磷染毒可以诱导大鼠BMSCs P53蛋白表达水平的增加(P<0.05)。结论辛硫磷可诱导大鼠BMSCs氧化损伤、DNA损伤、细胞凋亡和P53蛋白表达,且具有剂量-效应关系。     

Amelioration of radiation-induced hematopoietic and gastrointestinal damage by Ex-RAD(R) in mice

The aim of the present study was to assess recovery from hematopoietic and gastrointestinal damage by Ex-RAD^®, also known as ON01210.Na (4-carboxystyryl-4-chlorobenzylsulfone, sodium salt), after total body radiation. In our previous study, we reported that Ex-RAD, a small-molecule radioprotectant, enhances survival of mice exposed to gamma radiation, and prevents radiation-induced apoptosis as measured by the inhibition of radiation-induced protein 53 (p53) expression in cultured cells. We have expanded this study to determine best effective dose, dose-reduction factor (DRF), hematological and gastrointestinal protection, and in vivo inhibition of p53 signaling. A total of 500 mg/kg of Ex-RAD administered at 24 h and 15 min before radiation resulted in a DRF of 1.16. Ex-RAD ameliorated radiation-induced hematopoietic damage as monitored by the accelerated recovery of peripheral blood cells, and protection of granulocyte macrophage colony-forming units (GM-CFU) in bone marrow. Western blot analysis on spleen indicated that Ex-RAD treatment inhibited p53 phosphorylation. Ex-RAD treatment reduces terminal deoxynucleotidyl transferase mediated dUTP nick end labeling assay (TUNEL)-positive cells in jejunum compared with vehicle-treated mice after radiation injury. Finally, Ex-RAD preserved intestinal crypt cells compared with the vehicle control at 13 and 14 Gy. The results demonstrated that Ex-RAD ameliorates radiation-induced peripheral blood cell depletion, promotes bone marrow recovery, reduces p53 signaling in spleen and protects intestine from radiation injury.     

Protective effect of triphlorethol-A from Ecklonia cava against ionizing radiation in vitro

We studied the cytoprotective effect of triphlorethol-A against gamma-ray radiation-induced oxidative stress. In this study, hydrogen peroxide, which is a reactive oxygen species (ROS), was detected using 2',7'-dichlorodihydrofluorescein diacetate (DCF-DA) assay. Triphlorethol-A reduced intracellular hydrogen peroxide generated by gamma-ray radiation. This compound provided protection against radiation-induced membrane lipid peroxidation and cellular DNA damage which are the main targets of radiation-induced damage. Triphlorethol-A protected the cell viability damaged by the radiation through inhibition of apoptosis. Triphlorethol-A reduced the expression of bax and activated caspase 3 induced by radiation, but recovered the expression of bcl-2 decreased by radiation. Taken together, the results suggest that triphlorethol-A protects cells against oxidative damage induced by radiation through reducing ROS.     

TLR4-dependent adjuvant activity of Neisseria meningitidis lipid A

The adjuvant activity of Neisseria meningitidis serogroup B lipopoly(oligo)saccharide (LOS) from wild-type and genetically defined LOS mutants and unglycosylated meningococcal lipid A was assessed in C3H/HeN and C3H/HeJ mice. Meningococcal lipid A, a weak agonist for TLR4/MD-2 in human macrophages, was found to have adjuvant activity similar to that of wild-type and KDO(2)-lipid A LOS in C3H/HeN mice. All meningococcal LOS structures as adjuvants induced high titers of IgG1, IgG2a and IgG2b but very little IgG3 to OMP compared to no adjuvant PBS controls. In addition, induced OMP antibodies were shown to have high bactericidal activity against serogroup B meningococci. Purified LOS and lipid A structures failed to induce any adjuvant activity in C3H/HeJ mice indicating that meningococcal LOS as an adjuvant was TLR4-dependent. Unglycosylated meningococcal lipid A because of its weak agonist activity for human macrophages and retention of adjuvant activity may be a candidate for use in serogroup B meningococcal OMP and OMV vaccines and for use as an adjuvant in other vaccines.     

褪黑素对小鼠淋巴细胞电离辐射损伤的防护作用

目的 探讨褪黑素(MLT)对小鼠淋巴细胞电离辐射损伤的防护作用及其机制。方法 采用流式细胞术和荧光分光光度法在离体和整体条件下分别检测小鼠淋巴细胞凋亡小体百分率和DNA裂解率。在此基础上,腹腔注射MLT,观察2 Gy X射线全身照射后24 h小鼠胸腺、脾脏淋巴细胞数量及胸腺细胞³H-TdR掺入率和Con A、LPS诱导的脾T、B淋巴细胞转化率的变化。结果 离体研究中,小鼠胸腺和脾脏淋巴细胞体外接受0.5~6.0 Gy照射后,凋亡小体百分率、DNA裂解率均呈剂量依赖性增加,而照射前预先加入2 mmol/L MLT,细胞凋亡小体百分率、DNA裂解率与单纯照射组比较均显著降低。整体研究中,2Gy全身照射前腹腔注射MLT,小鼠胸腺和脾脏淋巴细胞凋亡小体百分率和DNA裂解率显著低于单纯照射组,接近或低于假照水平,MLT剂量在0.1~2.5 mg/kg范围内均有作用,但无明显剂量依赖性。小鼠胸腺、脾脏淋巴细胞数量、胸腺细胞³H-TdR掺入率及有丝分裂原诱导的脾脏T、B淋巴细胞转化率在2 Gy全身照射后均显著低于假照组(P <0.001)。0.5~10 mg/kgMLT预先腹腔注射,胸腺、脾脏淋巴细胞数显著高于0 mg/kg体重组(单纯照射),其中0.5 mg/kg体重组增高最显著;胸腺细胞³H-TdR掺入率显著增高(P <0.01或P <0.001),以0.5 mg/kg体重组增高最显著;Con A诱导的T细胞转化率显著增高,也以0.5 mg/kg体重组为著;LPS诱导的B细胞转化率增高,以10mg/kg体重组最显著。结论 MLT在体内和体外均可减轻电离辐射诱导的小鼠淋巴细胞损伤,对免疫功能具有保护作用。     

p53 dependency of radio-adaptive responses in endogenous spleen colonies and peripheral blood-cell counts in C57BL mice

Radio-adaptive responses at a conditioning X-ray dose of 0.45 Gy and a challenging dose of 5.0 Gy on hematopoietic indices were studied in C57BL mice with p53 (Trp53) wild, heterogenous and knockout allele. The conditioning irradiation, given 2 weeks before the challenging irradiation, induced radio-adaptive responses observed as a recovery of the peripheral blood-cell counts of leukocytes, thrombocytes and erythrocytes on day 14 after challenging irradiation in C57BL mice of the wild-type p53(+/+). The pre-irradiation also increased the endogenous spleen colonies (endo-CFU-S) on day 12 and the spleen weight on day 14. On the contrary, the knockout p53(-/-) mice gave no such radio-adaptive response. The heterogenous p53(+/-) mice gave an intermediate response. The radio-adaptive response in hematopoiesis at a challenge dose of 5.0 Gy seems to be a p53-dependent phenomenon. The possible role of induction in radio-resistance through the reduction of p53-drived apoptosis in hematopoietic stem cells in pre-irradiated mice is discussed.     

Supplemental dietary folic acid has no effect on chromosome damage in erythrocyte progenitor cells of mice

Folate deficiency can cause chromosome damage, which could result from reduced de novo thymidylate synthesis or DNA hypomethylation. High folic acid intake has been hypothesized to inhibit folate-dependent one-carbon metabolism, which could also lead to DNA damage. A large proportion of the general population may have high folic acid intakes. In this study, 2 experiments were conducted to examine the effects of folate on chromosome damage. First, male mice were fed folic acid-deficient (D) (0 mg folic acid/kg diet), control (C) (2 mg/kg), or folic acid-supplemented (S) (6 mg folic acid/kg diet) diets from weaning to maturity. Second, female mice were fed the D, C, or S diet throughout pregnancy, lactation, and breeding for 3 generations; male mice from the F3 generation were fed the same diet as their mothers from weaning, producing D, C, and S F3 male mice. RBC micronucleus frequencies, a measure of chromosome damage or aneuploidy, were determined for both experimental groups. In mice fed diets from weaning to maturity, erythrocyte micronucleus frequency was 24% greater in D compared with C mice. F3 mice fed diet D had 260% and 174% greater reticulocyte and erythrocyte micronucleus frequencies compared with F3 C mice, respectively. The S diets did not affect micronucleus frequency, suggesting that excess folic acid at this level does not promote or protect against chromosome damage. The results suggest that chronic exposure to folic acid at the levels similar to those achieved through fortification is unlikely to be clastogenic or aneugenic.