MNU Injection Research Articles

Effects of perinatal exposure to bisphenol A on induction of prostate cancer in Sprague Dawley rats by MNU and testosterone

Perinatal and neonatal exposure to bisphenol A (BPA) has been linked to enhancement of prostate carcinogenesis in rats induced by combined treatment with estradiol and testosterone, but human data are lacking. This study aimed to determine the effects of perinatal BPA exposure on induction of prostate cancer in rats by sequential treatment with N-methyl-N-nitrosamine (MNU) and continuous low dose administration of testosterone. Pregnant Sprague Dawley rats were exposed to BPA administered by subcutaneous Alzet minipumps at doses of 2.5 or 25 µg/kg body weight/day from gestational day 9 until postnatal day 28 when pups were weaned providing exposure of offspring in utero and via the mother’s milk. At 10–12 weeks of age, one male offspring per litter was treated with an intraperitoneal injection of MNU after hormonal stimulation of prostatic cell proliferation followed two weeks later by subcutaneous insertion of Silastic implants containing testosterone until the termination of the study 57–58 weeks after MNU injection. The perinatal BPA exposure did not significantly affect the incidence of prostate carcinomas which was slightly lower in exposed rats (33–23 %) than in control animals (40 %). Carcinomas in all accessory sex glands combined were also insignificantly less frequent in exposed (46–48 %) than in control rats (60 %). The incidence of malignant tumors at any site in the body was significantly lower in exposed rats (81–65 %) than in controls (93 %). In conclusion, perinatal BPA exposure did not significantly modify prostate cancer induction by MNU plus testosterone in rats, unlike the enhancement of prostate carcinogenesis induced by treatments involving estradiol administration. Which of the two models of prostate carcinogenesis is more relevant for the human situation is unclear at present.

Mitophagy boosting protects cells against MNU toxicity

Objective: A pharmacological model to study the human disease Retinitis Pigmentosa is N-methyl-N-nitrosourea (MNU) injection which results in retinal degeneration. Our objective is to study the autophagy and mitophagy status of the cells in this disease model. Materials and methods: The mitophagy reporter (MitoQC) and autophagy reporter mice (mCherry-GFP-LC3) have been used to determine the mitophagic and autophagic flux in the retina after MNU injection. Retinal pigment epithelium cell line (ARPE-19) MitoQC has been used to elucidate the cellular and molecular mechanisms after MNU treatment. Results: Neurodegeneration events appear one day after intraperitoneal MNU injection: reduction of photoreceptors thickness layer and increase of TUNEL and GFAP staining. Mitophagosomes and autophagosomes are less frequent in the retina of mice treated with MNU, but they are bigger and they tend to accumulate in the external limiting membrane. ARPE-19 cells are also vulnerable to MNU in a dose-dependent manner producing DNA damage, cytoplasm vacuolization, organelle alterations and cell death. Mitophagy levels depend on the MNU dose: an increase of the mitophagic flux is observed at low doses, whereas it seems to be blocked at high doses. We demonstrate this mitophagy is PINK-Parkin dependent and boosting this pathway makes cells more resistant to MNU. Finally, we achieve to protect MNU-treated retinae explants with the mitophagy inductor, DFP. Conclusion: MNU treatment induces activation of PINK-Parkin dependent mitophagy. We propose that mitophagy could act as a defense mechanism in this disease model.

Ultrastructural changes in the choriocapillaris of N-methyl-N-nitrosourea-induced retinal degeneration in C57BL/6 mice.

N-methyl-N-nitrosourea (MNU) is known to cause apoptosis of photoreceptor cells and changes in retinal pigment epithelium (RPE). However, the changes in choriocapillaris, which nourishes photoreceptor cells by diffusing tissue fluid through RPE, have not been reported in detail. Therefore, we studied the ultrastructural transformation in and around the choriocapillaris to characterize the interdependence between choriocapillaris and surrounding tissue components in a mouse model. Seven-week-old male C57BL/6 mice were given a single intraperitoneal injection of MNU (60mg/kg of body weight). Perfusion-fixed eyeballs were examined chronologically using immunohistochemistry and electron microscopy until the photoreceptor cells were lost. Sequential ultrastructural changes were observed in photoreceptor cells, RPE, Bruch's membrane, choriocapillaris, and choroidal melanocytes after an MNU injection. The lumens of the choriocapillaris narrowed following dilation, and the vascular endothelium showed structural alterations. When the photoreceptor cells were completely lost, the choriocapillaris appeared to be in a recovery process. Our results suggest that transport abnormality through Bruch's membrane and structural changes in the choroid might have influenced the morphology of choriocapillaris. The thin wall of the choriocapillaris appears to be the cause of the vulnerability with its altered morphology.

Aucubin, An Active Ingredient in Aucuba japonica, Prevents N-methyl-N-nitrosourea-induced Retinal Degeneration in Mice.

In the present study, we examined the potent retinoprotective effects of an ethanol-based extract of Aucuba japonica (AJE) and its active ingredient, aucubin, on N-methyl-N-nitrosourea (MNU)-induced retinal degeneration in mice. Retinal degeneration was induced by an intraperitoneal injection of MNU (60 mg/kg). AJE (250 mg/kg) and aucubin (15 mg/kg) were orally administered for 1 week after the MNU injection. Electroretinography (ERG) and histological examinations were performed. Retinal apoptosis and oxidative DNA damage were also quantified. The retinoprotective abilities of AJE and aucubin were also assessed in primary cultured retinal cells. Morphologically, MNU induced a remarkable decrease in the outer nuclear layer, which contains photoreceptor cells. However, this layer was well preserved in the AJE- and aucubin-administered mice. The ERG responses significantly decreased in both a- and b-wave amplitudes in the MNU-injected mice. In the AJE and aucubin-treated mice, ERG responses were significantly increased. In addition, a terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) assay and immunohistochemical staining for 8-hydroxydeoxyguanosine (8-OHdG) revealed that both AJE and aucubin attenuated MNU-induced photoreceptor cell apoptosis and oxidative DNA damage. Furthermore, the in vitro assay also showed that AJE and aucubin have potent anti-oxidative and anti-apoptotic activities in primary cultured retinal cells. These results indicate that AJE and aucubin have potent retinoprotective effects, and that this retinoprotective activity is as a result of the potency of the bioactive compound, aucubin. These pharmacological characteristics suggest the additional application of AJE or aucubin in the treatment of patients with retinal degenerative diseases.

N-Methyl-N-Nitrosourea-Induced Photoreceptor Degeneration Is Inhibited by Nicotinamide via the Blockade of Upstream Events before the Phosphorylation of Signalling Proteins.

N-methyl-N-nitrosourea (MNU), a known carcinogen, is generally used in animal models to chemically induce photoreceptor degeneration. It has been reported that nicotinamide (NAM) exerts a protective effect on MNU-induced photoreceptor degeneration. We investigated the molecular mechanisms on MNU-induced photoreceptor degeneration. Intraperitoneal MNU injection (75 mg/kg) in rats induced selective photoreceptor degeneration in 7 days. NAM administration completely inhibited photoreceptor degeneration. Photoreceptor layer abnormality was observed within 6 hours after MNU injection, whereas it was restored in the NAM-treated retina, as detected by optical coherence tomography. One day following MNU administration, phosphorylation of the cell death-associated signalling proteins c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38) increased, while the apoptosis-related proteins, full-length poly(ADP-ribose) polymerase (PARP) and apoptosis-inducing factor (AIF), were depleted. These changes were not observed in the NAM-treated retinas. Cell survival signalling, such as extracellular signal-regulated kinase (ERK), Akt, and cAMP response element binding protein (CREB) phosphorylation, increased in the MNU- but not in the NAM-treated rat retinas. Increased phosphorylated ERK (p-ERK) levels were observed within 6 hours after MNU administration, suggestive of cell survival signalling activation. This did not occur in NAM-treated retinas. These results indicate that NAM regulates upstream cellular events prior to the activation of cell death-related signalling events, such as JNK and p38 phosphorylation.

Müller Cell Regulated Microglial Activation and Migration in Rats With N-Methyl-N-Nitrosourea-Induced Retinal Degeneration.

During the pathogenesis of retinitis pigmentosa (RP), the roles of retinal microglial cells after activation have not been fully elucidated. Herein, experimental RP was induced in Sprague Dawley rats by intraperitoneal injection of N-methyl-N-nitrosourea (MNU) at 50 mg/kg, and the effects of MNU on the retinas were evaluated, respectively, by retinal histology and electroretinography recordings at serial time points. Time-dependent and gradual loss of photoreceptor cells, disrupted arrangement of the outer nuclear layer (ONL), and significant reductions in both a-wave and b-wave amplitudes were observed. Morphology changes were observed in retinal microglial cells; meanwhile, with time, the number of Iba1-positive microglia and their infiltration into the ONL gradually increased. Furthermore, physical interaction of microglial-Müller cell processes following microglial activation was observed after MNU injection. In addition, Müller cells increased CX3CL1 secretion, enhanced microglial cell migration, and upregulated the CX3CR1 expression of the latter. Our observations implied that, during the pathogenesis of RP by MNU, microglial cells exhibit a prominent morphology change and Müller cells can induce activated microglia infiltration by increasing secretion of the chemotaxis factor, CX3CL1, and promoting the migration of retinal microglial cells. This novel finding highlights a potential therapeutic target aimed at regulating the microglial response.

Abstract 270: Effect of dietary methylseleninic acid and Se-methylselenocysteine on carcinogen-induced, androgen-promoted prostate carcinogenesis in rats

Abstract Selenomethionine (SeMet) did not inhibit development of prostate cancer in the SELECT trial and in preclinical rat models. However, we and others have shown that oral intake of next-generation selenium (Se) forms, especially methylseleninic acid (MSeA) and Se-methylselenocysteine (MSeC), inhibits prostate carcinogenesis in the TRAMP mouse model and growth of human prostate cancer cells xenografted in immunodeficient mice. We recently showed that MSeA suppresses progression of high-grade prostatic intraepithelial neoplasia to adenocarcinoma in pten-deficient mice (Cancer Prev Res 2016;9:35-42). To determine whether next-generation Se forms inhibit prostate carcinogenesis in models driven by a different etiology, we tested the in vivo effect of different Se forms fed to rats undergoing chemically induced androgen-promoted prostate carcinogenesis. We previously established that SeMet was not inhibitory in this model (Cancer Prev Res 2010;3:381-92). Wistar-Unilever (WU) rats (10-12 wks) were sequentially treated with androgen receptor blocker flutamide for 21 days (10 mg/kg/day by gavage), followed by testosterone propionate (TP, 10 mg/kg, s.c) on day 22. Three days after TP, the carcinogen methylnitrosourea (MNU, 30 mg/kg/bw) was administered by i.p. injection. One week later, the rats received slow-release Silastic implants containing testosterone. Rats were then randomized to one of three groups fed the AIN-93M diet supplemented with 3 ppm of Se as MSeA or MSeC or control AIN-93M diet. Moribund animals were euthanized and the study was terminated 400 days after MNU injection. Mean survival (days ± SEM) after MNU was 344±11 in controls (n=31), 354±8 in MSeA fed rats (n=30), and 363±10 in rats given MSeC (n=29). These differences were not statistically significant, which was confirmed by survival analysis using the logrank test. Overall tumor incidence in all accessory sex glands combined (dorsolateral and anterior prostate plus seminal vesicle) was 68% in controls, 83% in MSeA rats, and 72% in MSeC rats. The incidence of large tumors of uncertain origin was 42% in controls, 40% in MSeA rats, and 41% in MSeC rats. The incidence of smaller tumors clearly confined to dorsolateral and/or anterior prostate was 19% in controls, 20% in MSeA rats, and 38% in MSeC rats (some rats had more than one tumor). None of these differences was statistically significant and there were no shifts from large to small tumor or small to large tumors. Thus, MSeA and MSeC were not preventive in this rat prostate carcinogenesis model. The contrast with the inhibitory effects of MSeA in the TRAMP and pten-deficient mouse models may be due to differences in administered dose or fundamental rat-mouse differences in Se metabolism that impact chemoprevention by Se compounds. Supported by NIH grant CA172169. Citation Format: Maarten C. Bosland, Michael J. Schlicht, Yibin Deng, Junxuan Lu. Effect of dietary methylseleninic acid and Se-methylselenocysteine on carcinogen-induced, androgen-promoted prostate carcinogenesis in rats [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 270.

Physical activity induced protection against breast cancer risk associated with delayed parity

Epidemiological evidence indicates that physical activity between menarche and first pregnancy is associated with a lower risk of breast cancer among women with at least 20years between these reproductive events. The mechanism by which physical activity during this interval confers protection is unknown. This study used a novel animal model to assess potentially protective effects of physical activity on tumor development in delayed parity. Thirty-six female Sprague Dawley rats received an i.p. injection of 50mg/kg N-methyl-N-nitrosourea (MNU) at 5weeks of age. Estrogen and progesterone pellets were implanted subcutaneously 1week (early parity, EP, n=8) or 4weeks (delayed parity, DP, n=11) following MNU injection. An additional group of DP rats were progressively exercise trained (Ex+DP, n=9) on a treadmill following MNU injection for 7weeks (up to 20m/min at 15% incline for 30min). We observed the greatest tumor latency and smallest tumor burden in Ex+DP animals. Ductal hyperplasia and inflammation of non-tumor bearing mammary glands were only found in DP, and we detected a significant increase in collagen for DP and Ex+DP compared to EP. Exercise induced differential gene expression of cyclin-dependent kinase-inhibitor 1C (Cdkn1c) and urokinase-plasminogen activator (Plau) in mammary tissue of Ex+DP animals compared to DP alone. While there are delayed parity-induced changes in mammary gland collagen and gene expression levels, Ex+DP animals had longer tumor latency, smaller tumor burden, and glandular tissue resistant to ductal hyperplasia. Exercise may induce protection through beneficial regulation of gene expression profiles.

Abstract 837: Reproducibility of efficacy results for chemopreventive agents in the methylnitrosourea-induced rat mammary cancer model

Abstract Perhaps the greatest question in biological science is: Can results be reproduced? This problem is of particular concern for a group whose primary mission is to screen for potentially effective agents and rank results by activity. The reproducibility of testing specific agents for chemopreventive activity, testing the same agent in various protocols, and testing multiple agents of a given mechanistic class in the MNU-induced model of ER+ breast cancer in Sprague-Dawley rats is presented. The model employs female virgin Sprague-Dawley rats on a standard 4% Teklad diet which develop ER+ mammary cancers (adenocarcinomas) following MNU injection at 50 days of age (DOA). Preventive agents were given by gavage or diet starting at 55 DOA, and animals monitored for tumor development until approximately 170 DOA. Seven agents which we had previously studied and which were strongly positive [tamoxifen, vorozole (an aromatase inhibitor), Targretin, gefitinib] or strongly negative (naproxen, Lipitor, metformin) were examined in the assays presented. These study results confirmed our previous data. We next tested these same agents in animals given a Western diet (high fat, low calcium) and again obtained the same results. We had thought that the altered physiology and potentially altered pharmacokinetics of rats on a Western diet might alter the observed chemopreventive efficacy. These studies show that the direct repetition of clearly positive and negative agents can be achieved and, in fact, repeated with a significant variation in diet. Importantly, in terms of reproducibility, we find that multiple agents of the same mechanistic class give similar results. Thus, various SERMs (tamoxifen, toremifene, Arzoxifene), RXR agonists (targretin, UAB-30, 4Me-UAB-30), EGFR inhibitors (gefitinib, Erlotinib, lapatinib) are all highly positive (70-95% reduction of cancer multiplicity). In contrast, the negative classes COX inhibitors (naproxen, sulindac, aspirin) or statins (atorvastatin or simvastatin) have been consistently negative (<20% reduction). Therefore, reproducibility of efficacy results appears to be quite solid in our chemoprevention agent development program for rat mammary cancer testing, and we can, with significant certainty, trust our results. Citation Format: Vernon E. Steele, Ronald A. Lubet, Clinton J. Grubbs. Reproducibility of efficacy results for chemopreventive agents in the methylnitrosourea-induced rat mammary cancer model. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 837.

Lycium barbarum polysaccharides attenuates N-methy-N-nitrosourea-induced photoreceptor cell apoptosis in rats through regulation of poly (ADP-ribose) polymerase and caspase expression

Ethnopharmacological relevanceLycium barbarum L., popularly known as “Goji berry”, a classic of Traditional Chinese Medicine has long been used to treat ocular diseases and cardiovascular diseases. Recently, the photoreceptor cell protection of Lycium barbarum polysaccharides (LBP), a water extract from Lycium barbarum L. has received more attention. The present study was designed to investigate the effect of LBP on N-methyl-N-nitrosourea (MNU)-induced photoreceptor cell apoptosis, and the involvement of the poly (ADP-ribose) polymerase (PARP) and caspase. Materials and methodsPhotoreceptor cell injury was induced in male Sprague-Dawley rats by an intraperitoneal injection of MNU 60mg/kg. Seven days prior to MNU injection, LBP were intragastrical administered daily, rats were sacrificed at 24h and 7 days after MNU injection. Retinal morphologies, photoreceptor cells apoptosis, and protein expression were evaluated at 24h and 7 days after MNU injection. ResultsMorphologically, the outer nuclear layer was well preserved in the LBP-treated rat retinas throughout the experimental period. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-digoxigenin nick-end labeling (TUNEL) assays showed that LBP could significantly suppress the loss of photoreceptor cells, as determined by the photoreceptor cell ratio at the central retina 24h and 7 days after MNU administration. Western-blot analysis demonstrated the expression levels of procaspase-9, -7, -3 and cleaved caspase-9, -7, -3 were upregulated, and PARP were downregulated both 24h and 7 days after MNU injection. LBP treatment significantly decreased protein levels of procaspase and cleaved caspase, increased the level of PARP and cleaved PARP on 24h and 7 days. ConclusionsLBP inhibits MNU-induced rat photoreceptor cell apoptosis and protects retinal structure via the regulation of the expressions of PARP and caspase.

Leaves of Persimmon (Diospyros kaki Thunb.) Ameliorate N-Methyl-N-nitrosourea (MNU)-Induced Retinal Degeneration in Mice.

The purpose of the study was to investigate the protective effects of the ethanol extract of Diospyros kaki (EEDK) persimmon leaves to study N-methyl-N-nitrosourea (MNU)-induced retinal degeneration in mice. EEDK was orally administered after MNU injection. Retinal layer thicknesses were significantly increased in the EEDK-treated group compared with the MNU-treated group. The outer nuclear layer was preserved in the retinas of EEDK-treated mice. Moreover, EEDK treatment reduced the MNU-dependent up-regulation of glial fibrillary acidic protein (GFAP) and nestin expression in Müller and astrocyte cells. EEDK treatment also inhibited MNU-dependent down-regulation of rhodopsin expression. Quercetin exposure significantly attenuated the negative effects of H2O2 in R28 cells, suggesting that quercetin can act in an antioxidative capacity. Thus, EEDK may be considered as an agent for treating or preventing degenerative retinal diseases, such as retinitis pigmentosa and age-related macular degeneration.

Multiple programmed cell death pathways are involved in N-methyl-N-nitrosourea-induced photoreceptor degeneration.

To identify programmed cell death (PCD) pathways involved in N-methyl-N-nitrosourea (MNU)-induced photoreceptor (PR) degeneration. Adult C57BL/6 mice received a single MNU i.p. injection (60 mg/kg bodyweight), and were observed over a period of 7 days. Degeneration was visualized by H&E overview staining and electron microscopy. PR cell death was measured by quantifying TUNEL-positive cells in the outer nuclear layer (ONL). Activity measurements of key PCD enzymes (calpain, caspases) were used to identify the involved cell death pathways. Furthermore, the expression level of C/EBP homologous protein (CHOP) and glucose-regulated protein 78 (GRP78), key players in endoplasmic reticulum (ER) stress-induced apoptosis, was analyzed using quantitative real-time PCR. A decrease in ONL thickness and the appearance of apoptotic PR nuclei could be detected beginning 3 days post-injection (PI). This was accompanied by an increase of TUNEL-positive cells. Significant upregulation of activated caspases (3, 9, 12) was found at different time periods after MNU injection. Additionally, several other players of nonconventional PCD pathways were also upregulated. Consequently, calpain activity increased in the ONL, with a maximum on day 7 PI and an upregulation of CHOP and GRP78 expression beginning on day 1 PI was found. The data indicate that regular apoptosis is the major cause of MNU-induced PR cell death. However, alternative PCD pathways, including ER stress and calpain activation, are also involved. Knowledge about the mechanisms involved in this mouse model of PR degeneration could facilitate the design of putative combinatory therapeutic approaches.

Testosterone treatment is a potent tumor promoter for the rat prostate.

Testosterone is increasingly prescribed to middle aged and older men, but the safety of this treatment has been called into question, and the possible risk of prostate cancer is unknown. We treated Wistar Cpb: WU rats chronically via slow-release Silastic implants with doses of testosterone that increased circulating levels in a dose-related fashion with or without a preceding single injection of the carcinogen N-nitroso-N-methylurea (MNU). Without MNU, testosterone induced prostate carcinomas in 10%-18% of rats, and after MNU injection, testosterone treatment caused prostate cancer in 50%-71% of rats with a very steep dose response, producing a 50% prostatic tumor incidence even at a testosterone dose that did not elevate circulating testosterone levels. Prostate cancers did not occur in rats given MNU or no treatment, whereas testosterone alone induced a low incidence of prostate cancer and increased the number rats bearing tumors at other sites, particularly malignant tumors. Thus, testosterone was shown to be a weak complete carcinogen and a strong tumor promoter for the rat prostate in this study. These findings have potential significant public health implications for the use of testosterone therapy in men.

Mead acid supplementation does not rescue rats from cataract and retinal degeneration induced by N-methyl-N-nitrosourea.

Fatty acids and their derivatives play a role in the response to ocular disease. Our current study investigated the effects of dietary mead acid (MA, 5,8,11-eicosatrienoic acid) supplementation on N-methyl-N-nitrosourea (MNU)-induced cataract and retinal degeneration in Sprague-Dawley rats. Experiment 1 was designed to inhibit cataract formation, with the dams fed a 2.4% MA or basal (<0.01% MA) diet during lactational periods. On postnatal day 7, male pups received a single intraperitoneal (ip) injection of 50 mg/kg MNU or vehicle. Lens opacity and morphology were examined 7 and 14 days after the MNU injection. Experiment 2 was designed to inhibit retinal degeneration and was performed with female postweaning rats. In this experiment, dams were fed the 2.4% MA or basal diet during the lactational periods. Thereafter, the female pups were continuously fed the same diets during their postweaning periods. On postnatal day 21 (at weaning), pups received a single ip injection of 50 mg/kg MNU. Retinal morphology was examined 7 days after the MNU injection. In experiment 3, six-week-old female rats were fed the 2.4% MA or basal diet starting at one week before the MNU injection and were then continuously fed the same diets until sacrifice. Rats at 7 weeks of age were given a single ip injection of 40 mg/kg MNU, and the retina was then examined morphologically one week after the MNU injection. In experiment 1, mature cataract was found in all of the MNU-treated groups, with or without MA supplementation. In experiments 2 and 3, atrophy of both the peripheral and central outer retina occurred in all rats exposed to MNU, with or without MA supplementation, respectively. The severities of the cataracts and retinal atrophy in the rats were similar regardless of MA supplementation. Dietary mead acid, which is used as a substitute in essential fatty acid deficiency in the body, does not modify MNU-induced cataract and retinal degeneration in rat models.

Green tea extract suppresses N-methyl-N-nitrosourea-induced photoreceptor apoptosis in Sprague-Dawley rats.

Retinitis pigmentosa (RP) is a group of inherited neurodegenerative human diseases characterized by the loss of photoreceptor cells by apoptosis and eventual blindness. A single intraperitoneal (ip) injection of N-methyl-N-nitrosourea (MNU) causes photoreceptor cell apoptosis within 7 days in rats. Green tea extract (THEA-FLAN 90S; GTE) is a common herbal supplement with pluripotent properties including antioxidant activity. The purpose of the present study was to evaluate the efficacy of GTE against photoreceptor apoptosis in 7-week-old female Sprague-Dawley rats that received a single ip injection of 40 mg/kg MNU. The oral administration of 250 mg/kg/day GTE was initiated 3 days prior to MNU injection and continued once daily throughout the experiment. Rats were sacrificed at 12, 24, and 72 h and 7 days after MNU injection, and the eyes were examined morphologically and morphometrically. The photoreceptor cell ratio, retinal damage ratio, and retinal preservation ratio were used to determine the structural and functional alterations. The number of apoptotic photoreceptor cells per mm(2) was determined in situ by TdT-mediated dUTP-digoxigenin nick end labeling (TUNEL). Our results indicated that oral administration of GTE significantly suppressed the loss of photoreceptor cells morphometrically 7 days after MNU injection. The number of TUNEL-positive cells per mm(2) in MNU-exposed rat central retina with or without GTE administration was 981 vs. 2056 at 24 h after MNU injection. GTE structurally and functionally suppressed MNU-induced photoreceptor cell apoptosis. These findings indicate that GTE may help to ameliorate the onset and progression of human RP.

Protective effects of naringenin eye drops on N-methyl-N-nitrosourea-induced photoreceptor cell death in rats.

To investigate the effects of naringenin eye drops on N-methyl-N-nitrosourea (MNU)-induced photoreceptor cell death in rats. Photoreceptor cell death was induced by single intraperitoneal injection of MNU (60 mg/kg) in rats. Both eyes of all animals were instilled with one drop of vehicle, 0.5% or 1.0% naringenin eye drops three times per day from 7d before to 17d after MNU injection. Effects of naringenin on MNU-induced photoreceptor cell death were evaluated by electrophysiological and histological analysis. Flash electroretinography (FERG) and oscillatory potentials (OPs) recordings showed that the vehicle control group had remarkable reduction of amplitudes and prolongation of latency times. FERG and OPs responses were significantly reversed in MNU-induced rats treated with 0.5% or 1.0% naringenin eye drops compared with the vehicle control. The retinal morphological results showed that naringenin dose-dependently preserved the outer nuclear layer, outer retina and total retina. These results indicate that topical treatment with naringenin eye drops prevented retinal neurons from MNU-induced structural and functional damages.

N-Methyl-N-nitrosourea during late gestation results in concomitant but reversible progenitor cell reduction and delayed neurogenesis in the hippocampus of rats

N-Methyl-N-nitrosourea (MNU) is an alkylating agent having genotoxic potential to cause gene mutations and antiproliferative cytotoxic activity on developing brains to cause microcephaly by mid-gestational exposure in rodents. This study investigated the transient genotoxic and cytocidal effect of MNU at the beginning of the subgranular zone (SGZ) formation in the hippocampal dentate gyrus on neurogenesis in later life using rats. Pregnant rats were injected with MNU at 0 (vehicle controls), 1 or 3mg/kg body weight intraperitoneally from gestational day (GD) 18 to GD 20 once a day. In offspring, effects were observed at 3mg/kg. Fetal brains on GD 21 after the last MNU injection increased TUNEL+ apoptotic cells in the tertiary germinal matrices. At postnatal day (PND) 21 on weaning, offspring displayed decrease of doublecortin (Dcx)+ cells and cell proliferation in the SGZ and increase of calbindin (Calb1)+ interneurons in the dentate hilus. Postnatal single bromodeoxyuridine (BrdU) injection on PND 3 resulted in an increase of BrdU+/Dcx+ cells. On PND 77, Dcx+ cells recovered in number, but cell proliferation increased in the SGZ. Thus, late-gestational maternal MNU exposure may induce reversible reductions of type-3 progenitor and/or immature granule cells and cell proliferation on weaning in response to progenitor cell apoptosis, as well as delayed neurogenesis due to cell cycle arrest. Increases of Calb1+ interneurons on weaning and SGZ cell proliferation later on may reflect compensatory mechanism for MNU-induced aberrant neurogenesis. Considering the lack of effects on PND 77, MNU may mainly target transient populations of highly proliferative progenitor cells without affecting their stem cells to undergo progenitor production. Protective and plasticity mechanism may be operated against genotoxic agents on hippocampal neurogenesis.

Effect of sugar concentration mimicking composition of sugars in honey on N-methyl-N-nitrosourea (MNU)-induced breast carcinoma in rats

<h3>Aim</h3> High concentration of sugar is carcinogenic. Honey which is rich in sugars has been shown to have anti-cancer effect. There is no study reported on the effect of sugars mimicking the concentration of sugars of honey (honey-mimic) in inhibiting breast carcinoma in rats. The aim of the study is to investigate if honey-mimic has similar effect as natural honey on experimental breasts tumor induced by N-methyl-N-nitrosourea (MNU) in rats. <h3>Methods</h3> Honey-mimic was made by mixing proportions of fructose, glucose, sucrose and maltose mimicking the sugar composition of honey based on published method. Forty Sprague-Dawley rats were randomly divided into 4 groups with 10 animals per each group. Group 1 rats did not receive MNU injection (negative control). Group 2, 3, 4 rats received a single intraperitoneal dose (80mg/kg body weight) of MNU injection. The size and development of the tumors were monitored. When the tumor size reached 10–12mm² in diameter, rats of Group 3 were given oral honey-sugar mimic 1.0 g/kg while Group 4 was given honey 1.0 g/kg body weight daily. Group 2 was not given honey-sugar mimic nor natural honey (positive control). All rats were allowed to feed on rat chowder ad lib. After 120 days, all rats were sacrificed and tumors were harvested for gross and histopathological examinations. <h3>Results</h3> The mean number of tumors developed per rat in groups 2, 3, 4 was 4.9±0.60, 3.6±0.40 and 3.4±0.30, respectively. The mean tumor weight and volume in the negative and positive control group were significantly larger at 11.85 ± 1.01g and 8.50 ±0.40cm³, respectively; while in the test groups (Groups 3 and 4) were 6.45 ± 0.60 g and 4.50 ±0.20cm³; 4.34 ± 0.35g and 2.50 ± 0.20cm³ (<i>p</i> < 0.05), respectively. Histopathological grading revealed that the majority of rats which received honey-sugar mimic and honey were of grade 1 and 2 compared to control, which were of grade 3. <h3>Conclusion</h3> Sugar concentration mimicking composition of sugars in natural honey has some anti-carcinogenesis modulation properties but not as effective as honey.

Suppression of &amp;lt;i&amp;gt;N&amp;lt;/i&amp;gt;-Methyl-&amp;lt;i&amp;gt;N&amp;lt;/i&amp;gt;-Nitrosourea-Induced Retinal Damage in Mice by Oligonol, an Oligomerized Polyphenol Formulation

Oligonol is a lychee fruit-derived functional food that contains oligomerized polyphenol compounds. Oligonol exhibits a number of beneficial biological effects, primarily due to its antioxidant activity. Retinitis pigmentosa (RP) is an inherited chronic degenerative disease affecting retinal photoreceptor cells. There is currently no effective therapy capable of stopping or reversing the progression of the disease. In RP, apoptosis of photoreceptor cells resulting from oxidative damage is considered to be the final common pathway. In this report, we present an evaluation of the suppressive activity of Oligonol against N-methyl-N-nitrosourea (MNU)-induced retinal damage in mice, which is a commonly used animal model of RP. Both intraperitoneal and oral administration of Oligonol reduced the loss of photoreceptor cells 7 days after MNU injection, as evaluated by histological staining. Photoreceptor cells derived from MNU-treated mice exhibited increased TUNEL-positive staining, suggesting increased DNA fragmentation, a hallmark of apoptosis. Oligonol treatment reduced the number of TUNEL-positive cells. Additionally, Oligonol suppressed MNU-induced retinal production of 8-hydroxydeoxyguanosine (8-OHdG), a marker of oxidative stress. Moreover, Oligonol attenuated the MNU-induced decrease in the visual activity of mice, as evaluated by the visual cliff test. Oligonol, therefore, effectively suppresses NMU-induced retinal degeneration.

Abstract P4-11-02: Mammary tumor formation induced by N-methyl-N-nitrosourea (MNU) is accelerated by natural and synthetic progesterone but suppressed by an anti-progesterone CDB4124

Abstract Background: CDB4124, anti-progesterone suppresses the development of carcinogen-induced ER+/PR+ mammary tumors in rats, and may have implications for prevention and treatment of human breast cancer. We hypothesize that progesterone (P4) and medroxyprogesterone acetate (MPA) will accelerate mammary carcinogenesis induced by MNU, however CDB4124 will efficiently suppress tumor formation stimulated by progesterone. Methods: ovary intact female Sprague Dawley rats received a single intraperitoneal injection of 50mg/kg MNU at 4-5 weeks of age. 30mg of CDB4124 and 25mg of P4 or MPA (90 release pellets, Innovative research of America, Inc) were implanted in dorsal area at 3 weeks and 4 weeks after MNU injection, respectively. 10-11 rats were used for each treatment group. Tumor incidence, latency, multiplicity, and burden were recorded weekly. 9 weeks after MNU injection all the mice were euthanized and mammary tumors and glands were fixed in 10% (v/v) neutral buffered formalin. Plasma concentrations of CDB4124 and its metabolite CDB4453 were determined by LC-MS/MS. Results: The first tumor appeared in the control group at 5 weeks, and in the P4 and MPA treated groups at 6 weeks after MNU injection. 7 weeks after MNU injection, mammary tumor incidence of MPA and P4 treated groups were 80% and 50%, respectively compared to 30% in the control group. 9 weeks after MNU injection all MPA treated mice, 80% of P4 treated mice, and 60% of control mice developed tumors. Tumor incidence, latency, multiplicity, and tumor weight were summarized as mean ± SD in Table 1. [Table 1] Tumor latency, incidence, multiplicity, and burden in mammary tumorsTreatmentsLatency (days)Incidence(%)MultiplicityBurden (g)Control53.7 ± 12.9602.34.25 ± 7.02P453.6 ± 9.6802.64.11 ± 5.32MPA50.8 ± 7.71002.56.02 ± 4.85P4 + CDB412459.3 ± 11.53621.38 ± 0.61MPA + CDB412454.3 ± 10.7732.84.19 ± 4.39 Tumor latency of CDB4124 treated groups was increased; tumor incidence and burden (g) of CDB4124 treated groups were decreased compared to P4 and MPA treated groups. In particular, tumor incidence and burden of CDB4124 + P4 treated group were significantly lower than those of the control group. Plasma CDB4124 and CDB4453 were 11.6 ±5.88 ng/mL and 3.4±1.68 ng/mL, respectively. Histopathology of tumors and mammary glands and immuno-histochemical evaluations of Ki67, activated caspase-3, CD34, ER, and PR are currently underway. Conclusions: Our results indicated that natural progesterone promotes MNU- induced mammary tumor formation similar to synthetic progesterone, MPA in rats. Under this tumor permissive environment, CDB4124 provided excellent prevention efficacy, suggesting good potential as breast cancer prevention agent. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-11-02.