Genotoxicity assessment of three reference chemicals in rat hepatocytes by alkaline comet assay / 上海预防医学

Objective:To establish a comet test method for detection of genotoxicity of three reference chemicals in rat liver cells. Methods:6-10 week old Sprague Dawley rats were randomly divided into 4 groups， with normal saline （0.9% NaCl solution） as negative control group. Animals in three test groups were treated， respectively， with ethyl methanesulfonate （EMS） 200 mg/kg， N-methyl-N-nitrosourea （MNU） 50 mg/kg， and D-mannitol 2 000 mg/kg. There were 10 animals in each group， 5 males and 5 females. The animals received two times （21 h interval） of test compounds through intragastric administration， and their clinical symptoms and body weight changes were recorded during the experiment. The rats were sacrificed 3 h after the last exposure. The liver was weighed， then used to prepare single-cell suspensions for the alkaline comet test which determines the average tail DNA content percentage （DNA%） of hepatocytes and other comet indicators. Results:（1） D-mannitol， EMS and MNU did not show significant toxicity in the whole animal. （2） The mean values of tail DNA content percentage （DNA%） of rat hepatocytes in EMS ［（60.07±24.69）%］ and MNU ［（41.66±22.35）%］ groups were higher than that in the negative control group ［（2.32±1.39）%］ and the difference was statistically significant （P<0.05）. The difference between D-mannitol group ［（3.06±3.30）%］ and the negative control group was not significant （P>0.05）. Conclusion:This laboratory has established a comet test method using hepatocytes from treated rats. Among three testing chemicals， EMS and MNU have displayed genotoxicity by this assay， but no genotoxicity was observed in D-mannitol treated animals.

Some Chemical Carcinogens for Leukaemia Induction and Their Animal Models

Animal models have been providing invaluable contributions to the better understanding of mechanisms of cancer (including leukaemias) development and effectiveness of most of the treatments. Chemical carcinogens are generally used to study the biology of cancers including leukaemias in many animal models, including rats and mice. The studies in most cases are aimed at the development and evaluation of cancer treatments and preventions. Some of the most common chemical carcinogens used in animal models for leukaemias include N-ethyl-N-nitrosourea (ENU), N-methyl-N-nitrosourea (MNU), dimethyl benz(a)anthracene (DMBA) and benzo(a)pyrene (BaP). This review provides highlights on different animal models of leukaemia induced by the chemical carcinogens mentioned earlier, at the same time discussing the contributions of these models to the leukaemia diagnosis in laboratory animal models for subsequent development of treatment.

Development of a Post-vitrectomy Injection of N-methyl-N-nitrosourea as a Localized Retinal Degeneration Rabbit Model

Since genetic models for retinal degeneration (RD) in animals larger than rodents have not been firmly established to date, we sought in the present study to develop a new rabbit model of drug-induced RD. First, intravitreal injection of N-methyl-N-nitrosourea (MNU) without vitrectomy in rabbits was performed with different doses. One month after injection, morphological changes in the retinas were identified with ultra-wide-field color fundus photography (FP) and fundus autofluorescence (AF) imaging as well as spectral-domain optical coherence tomography (OCT). Notably, the degree of RD was not consistently correlated with MNU dose. Then, to check the effects of vitrectomy on MNU-induced RD, the intravitreal injection of MNU after vitrectomy in rabbits was also performed with different doses. In OCT, while there were no significant changes in the retinas for injections up to 0.1 mg (i.e., sham, 0.05 mg, and 0.1 mg), outer retinal atrophy and retinal atrophy of the whole layer were observed with MNU injections of 0.3 mg and 0.5 mg, respectively. With this outcome, 0.2 mg MNU was chosen to be injected into rabbit eyes (n=10) at two weeks after vitrectomy for further study. Six weeks after injection, morphological identification with FP, AF, OCT, and histology clearly showed localized outer RD - clearly bordered non-degenerated and degenerated outer retinal area - in all rabbits. We suggest our post-vitrectomy MNU-induced RD rabbit model could be used as an interim animal model for visual prosthetics before the transition to larger animal models.

Helicobacter pylori combined with MNU gavage for preparing balb/c mouse gastric cancer model / 重庆医学

Objective To investigate Helicobacter pylori combined with N-methyl-N-nitrosourea (MNU) gavage for preparing balb/c mouse gastric cancer model.Methods Eighty balb/c mice were randomly divided into four groups after 1-week adaptive feed,normal group,model group Ⅰ,Ⅱ and Ⅲ,20 cases in each group.The model group Ⅰ,Ⅱ and Ⅲ were given Helicobacter pylori bacteria liquid (CFU=109/mL) gavage,once every other day for 5 times;then,the freshly configured MNU solution 0.15,0.3,0.6 mL gavages were in turn given,MNU and pure water allocation ratio was 5mg:3mL.Once gavage per week for continuous 10 weeks.Results The model group II had 66.67% adenocarcinoma,the model group I were gastritis with mild atypical hyperplasia,and all mice in the model group III died.Conclusion This method can prepare the gastric cancer model.

Therapeutic effects of mesenchymal stem cells (MSCs) on N-methyl-N-nitrosourea (MNU)-induced retinitis pigmentosa in C57BL mice / 眼科新进展

Objective To investigate the therapeutic effects of mesenchymal stem cells (MSCs) on N-methyl-N-nitrosourea (MNU)-induced retinal degeneration in C57BL mice.Methods Different doses of MNU (30 mg · kg-1,45 mg · kg-1,60 mg · kg-1,75 mg · kg-1 and 90 mg · kg-1) were injected to C57BL mice for 7 days.Then electroretinogram (ERG) detection and HE staining were performed to examine retinal electrophysiological function and morphological changes on day 1,day 3 and day 7 after MNU treatment,respectively.Then we could explore the optimum condition to establish stable animal model of retinitis pigmentosa.MSCs were transplanted to C57BL mice by intravitreal or tail intravenous injection.Then ERG detection and HE staining were performed to evaluate the effect of MSCs on retinitis pigmentosa induced by MNU.Results When compared with control group,30 mg · kg-1 and 45 mg · kg-1 MNU could cause mild retinal damage in morphology and function in mice;while 60 mg · kg-1 and above dose of MNU induced serious retinal damage,leading to decreased ERG amplitude of the retina (all P ＜ 0.001) and outer nuclear layer (ONL) thickness (all P ＜ 0.001).On day 1 and day 3 after single dose of 60 mg · kg-1 MNU injection,ERG amplitude of the retina was decreased,and outer nuclear layer thickness became thin;while the retinal damage was serious badly in morphological structure on day 7,with the ERG amplitude extinguished (all P ＜ 0.001),ONL thickness thin (all P ＜ 0.001) and internal and external nuclear layer fusion.When compared with MNU alone treatment group,following injection of 60 mg · kg-1 MNU for 1 day MSCs were transplanted to C57BL mice by intravitreal or tail intravenous injection,and the amplitude of ERG and retinal ONL thickness were increased on day 7 after MSCs transplantation (all P ＜ 0.001).Conclusion MSCs transplantation has a certain therapeutic effect on MNU-induced retinitis pigmentosa in C57BL mice.

Nestin Expression in the Adult Mouse Retina with Pharmaceutically Induced Retinal Degeneration

The present study investigated the temporal pattern and cellular localization of nestin in the adult mouse retina with pharmaceutically induced retinal degeneration using N-methyl-N-nitrosourea (MNU). After a single intraperitoneal injection of MNU in 8-week-old C57BL/6 mice, the animals were sacrificed at 1, 3, 5, 7, and 21 days (n = 6, in each stage). The eyes were examined by means of immunohistochemical tests using nestin, ionized calcium-binding adaptor molecule (Iba-1), CD11b, F4/80, and glial fibrillary acidic protein (GFAP). Western blot analysis and manual cell counting were performed for quantification. Nestin expression was increased after MNU administration. Nestin+/Iba-1+ cells were migrated into outer nuclear layer (ONL) and peaked at day 3 post injection (PI). Nestin+/CD11b+ cells were also mainly identified in ONL at day 3 PI and peaked at day 5. Nestin+/F4/80+ cells were shown in the subretinal space and peaked at day 3 PI. Nestin+/GFAP+ cells were distinctly increased at day 1 PI and peaked at day 5 PI. The up-regulation of nestin expression after MNU administration in adult mouse retinal microglia, and monocyte/macrophage suggests that when retinal degeneration progresses, these cells may revert to a more developmentally immature state. Müller cells also showed reactive gliosis and differentiational changes.

Microarray expression analysis of the N-methyl-N-nitrosourea-induced retinal degeneration in rat / 中华实验眼科杂志

Background The rat model of N-methyl-N-nitrosourea (MNU)-induced photoreceptor cell apoptosis is often used to study retinal degeneration.But the changes in the gene expression patterm in retinal degeneration in rats have not been reported.Objective This study was undertaken to investigate regulation of gene expression in the retina of MNU-induced retinal degeneration in rats by performing microarray analysis of retinal RNA.Methods Fifty 6-week-old SD rats were numbered and randomized into the normal group and the model group.The retinal degeneration model was established by a single hypodermic injection of 40 mg/kg of MNU,and the rats in the normal group received equivalent volume of physiological saline in the same way.The rats were sacrificed 12 hours or 24 hours after injection.Retinal sections from the right eyes were prepared for the measurement of the retinal thickness by histopathological examination,and retinas from the left eyes were used to confirm the differential gene expression as detected by microarray (normal group and 12 hours model group).Genes exhibiting changes in expression by ≥2.0 folds were further confirmed using real-time PCR.Results The whole thickness of the retina declined in the rats from the 24 hours model group compared to the normal group and 12 hours model group (t =9.926,P=0.002;t=2.736,P=0.028).The thickness of the outer nuclear layer was (26.58±2.90) μm in the 24 hours model group,showing a significant decrease in comparison with (38.11 ± 1.01) μm in the normal group and (35.07t3.03) μm in the 12 hours model group (t=6.028,P=0.009;t=6.839,P=0.006).However,there was no significant difference in retinal thickness between the normal group and the 12 hours model group (whole thickness:t=1.541,P=0.324;outer nuclear layer thickness:t=2.040,P=0.134).Microarray analysis of the rat genes showed that out of 17 000 genes,142 genes involved in biological process and 94 genes involved in molecular functions were differentially expressed,where most of them participate in the mitogen activated protein kinase signaling pathway,Tolllike receptor signaling pathway and apoptosis pathway.Real-time PCR analysis demonstrated that the expression of CCL2,IL-1b,CCL3,c-fos,c-myc,p53 and MMP3 were consistently up-regulated,conforming with the results from microarray analysis.Conclusions The changes in gene expression pattern appear in the early stage of MNUinduced retinal degeneration.These microarray results provided clues to understanding the molecular pathways underlying photoreceptor degeneration and indicating the directions for future studies.

Morphological and functional evaluation of an animal model for the retinal degeneration induced by N-methyl-N-nitrosourea / 대한해부학회지

The retinal degeneration (RD) is a general cause of blindness. To study its pathophysiology and evaluate the effects of new therapeutic agents before clinical trials, it is essential to establish reliable and stable animal models. This study evaluated a RD animal model in which blindness was induced by N-methyl-N-nitrosourea (MNU), a potent retinotoxin leading to apoptosis of photoreceptors. MNU was applied to the Sprague-Dawley rats by a single intraperitoneal injection in different doses (40, 50, and 60 mg/kg). The retinal functions were examined at 1 week after MNU injection by electroretinogram (ERG). Afterwards, each retina was examined by hematoxylin and eosin stain and immunohistochemistry with anti-glial fibrillary acidic protein antibody. Upon MNU injection of 40, 50 and 60 mg/kg, the ERG amplitude of a-waves showed significant reductions of 7, 26, and 44%, respectively, when compared to that of normal a-waves. The b-wave amplitudes were about 89, 65, and 58% of normal b-waves in the response to scotopic light stimulus. At 1 week, 2 weeks, and 4 weeks after MNU injection (50 mg/kg), all scotopic ERG components decreased progressively. In addition, degeneration of retinal neurons was observed in a time- and dose-dependent manner after MNU injection. Taken together, functional reduction following RD induced by MNU correlates with morphological changes. Thus, this RD rat model may be a useful model to study its pathophysiology and to evaluate the effects of new therapeutic agents before clinical trials.

Damage of photoreceptor cells by N-methyl-N-nitrosourea in cats / 中华实验眼科杂志

Background To establish the ideal animal model of retinitis pigmentosa (RP) is very important for onward relevant study.Previous research determined that N-methyl-N-nitrosourea (MNU) can selectively damage photoreceptors via intravenous injection in mammal.However,whether MNU can be used to create an RP model needs to be investigated.Objective This experiment was designed to evaluate the toxic effect of MNU on photoreceptor cells of cats.Methods MNU was injected into 20 2-year-old cats via femoral vein and randomized into 20mg/kg, 25mg/kg, 30mg/kg, 35mg/kg and 40mg/kg MNU groups,and equal amount of normal saline solution was used in the same way in 4 normal cats as the control group.The activity,pupil size and light reflex were observed after injection of MNU.The cats were sacrificed and eyeballs were enucleated for histological examination to evaluate the structural and morphological changes of photoreceptors at 24 hours,72 hours,7 days and 14 days after the administration of MNU.This experimental study complied with the Statement for the Use of Animals in Ophthalmic and Vision Research.Results Dilated pupil and inertia of light reaction were found in experimental cats on the 7th days in the various groups.In 24 hours after MNU injection,the damage of photoreceptors was primarily characterized by pyknosis and disorder.In 72 hours after MNU injection,attenuation of the outer nuclear layer and disruption of cells were seen.Loss of photoreceptors and disappearance of the outer nuclear layer were observed on the 7th and 14th day.The extent of retinal photoreceptor cell damage was dependent on the dose of MNU.Conclusion MNU can selectively induce serious damage of the photoreceptor cells in cats retina in a time- and dose-dependent manner.

Expression of immediate early gene following N-methyl-N-nitrosourea-induced retinal degeneration in SD rats / 中国药理学通报

Aim To study the molecular mechanism of retinal toxicity induced by N-methyl-N-nitrosourea (MNU) in SD rats. Methods A single intraperitoneal injection of 60 mg?kg~(-1) MNU was given to 50-day-old female SD rats. After MNU treatment for different times, the rats were sacrificed and both eyes were enucleated immediately and processed for histological examination. The apoptotic index of photoreceptor cells was calculated by TUNEL labeling and the expression of c-jun and c-fos genes was detected by RT-PCR technique. Results After the application of MNU for 24 h,the disorientation of photoreceptor outer segments was seen. The outer nuclear layer and photoreceptor layer were almost completely lost at 7 d. Apoptosis had already started at 12 h post-MNU and peaked at 24 h. MNU time-dependently up-regulated the expression of c-jun and c-fos genes. Conclusion MNU has a toxic effect on retina by up-modulating expression of c-jun and c-fos genes to promote photorecptor cells apoptosis.

Targeted therapy with herceptin to rat bladder tumor model / 第三军医大学学报

Objective To investigate the therapeutic effect of herceptin to rat bladder cancer. Methods Totally 50 SD rats were randomly divided into experimental group (n=40) and control group (n=10). The rats of experimental group received a perfusion into the bladder with N-methyl-N-nitrosourea (MNU) at 2.5 mg every time, once per 3 weeks for 4 times in all, while those of the control group underwent a perfusion with normal saline instead of MNU. In 1 week after the last perfusion, the bladders were slited for gross observation and the biopsies were carried out for pathological observation with HE staining. Immunohistochemical SP method and RT-PCR were applied to detect HER-2 protein and mRNA expression in tumor tissues. Then 16 rats with HER-2 positive bladder cancer were randomly and equally divided into treatment group (herceptin, 20 mg/kg by intraperitoneal injection, once per week for 6 weeks) and non-treatment group (normal saline, 0.5 ml). Tumor weight, size and shape were measured and calculated for the inhibitory rate of herceptin. HE staining was carried out for the morphology of the tumor mass. The expression of HER-2 protein was detected with immunohistochemical SP method, and apoptosis in bladder tumor tissues with TUNEL method. Results The results of inhibitory rate was 50.0%, and it showed that the differences were statistically significant in treatment group compared with non-treatment group (P