Microemulsion for Prolonged Release of Fenretinide in the Mammary Tissue and Prevention of Breast Cancer Development.

The need of pharmacological strategies to preclude breast cancer development motivated us to develop a non-aqueous microemulsion (ME) capable of forming a depot after administration in the mammary tissue and uptake of interstitial fluids for prolonged release of the retinoid fenretinide. The selected ME was composed of phosphatidylcholine/tricaprylin/propylene glycol (45:5:50, w/w/w) and presented a droplet diameter of 175.3 ± 8.9 nm. Upon water uptake, the ME transformed successively into a lamellar phase, gel, and a lamellar phase-containing emulsion in vitro as the water content increased and released 30% of fenretinide in vitro after 9 days. Consistent with the slow release, the ME formed a depot in cell cultures and increased fenretinide IC50 values by 68.3- and 13.2-fold in MCF-7 and T-47D cells compared to a solution, respectively. At non-cytotoxic concentrations, the ME reduced T-47D cell migration by 75.9% and spheroid growth, resulting in ∼30% smaller structures. The depot formed in vivo prolonged a fluorochrome release for 30 days without producing any sings of local irritation. In a preclinical model of chemically induced carcinogenesis, ME administration every 3 weeks for 3 months significantly reduced (4.7-fold) the incidence of breast tumors and increased type II collagen expression, which might contribute to limit spreading. These promising results support the potential ME applicability as a preventive therapy of breast cancer.

alpha-Glycosyl Isoquercitrin (AGIQ) and its lack of carcinogenicity in rasH2 mice.

alpha-Glycosyl Isoquercitrin (AGIQ), is used in Japan as a food additive and was granted generally recognized as safe (GRAS) status in 2005 (FEMA) and 2007 (FDA). The safety and toxicity information for AGIQ is sparse and therefore, the carcinogenicity potential of AGIQ was examined in the CByB6F1-Tg(HRAS)2Jic (rasH2) model. One hundred female and male rasH2 mice, each, were allocated to one of four designated dose groups; 0 (control)%, 1.5%, 3.0% or 5.0% AGIQ. Animals were administered the diets for six months and an additional 10 females and 10 males, each, were administered a positive control, N-methyl-N-nitrosourea (MNU). Body weights and clinical observations were collected. A full screen necropsy, organ weights, clinical chemistry, urinalysis and histopathology were performed. The positive control animals elicited appropriate responses specific to this strain (rasH2) of mice. There were statistically significant sporadic non-dose-dependent changes in clinical chemistries without corresponding pathological correlation. No microscopic AGIQ-related findings were noted; the range of pathology observations were all considered background findings, either specific to rasH2 mice or common to inbred strains of mice. Therefore, under the study conditions, the no-observed-adverse-effect level (NOAEL) was determined to be more than 5.0% (7215.4 mg/kg BW/day in male mice and 14685.5 mg/kg/day in female mice).

PD-1 Signaling Promotes Tumor-Infiltrating Myeloid-Derived Suppressor Cells and Gastric Tumorigenesis in Mice.

BACKGROUND & AIMS: Immune checkpoint inhibitors have limited efficacy in many tumors. We investigated mechanisms of tumor resistance to inhibitors of programmed cell death-1 (PDCD1, also called PD-1) in mice with gastric cancer, and the role of its ligand, PD-L1. METHODS: Gastrin-deficient mice were given N-methyl-N-nitrosourea (MNU) in drinking water along with Helicobacter felis to induce gastric tumor formation; we also performed studies with H/K-ATPase-hIL1B mice, which develop spontaneous gastric tumors at the antral-corpus junction and have parietal cells that constitutively secrete interleukin 1B. Mice were given injections of an antibody against PD-1 or an isotype control before tumors developed, or anti-PD-1 and 5-fluorouracil and oxaliplatin, or an antibody against lymphocyte antigen 6 complex locus G (also called Gr-1), which depletes myeloid-derived suppressor cells [MDSCs]), after tumors developed. We generated knock-in mice that express PD-L1 specifically in the gastric epithelium or myeloid lineage. RESULTS: When given to gastrin-deficient mice before tumors grew, anti-PD-1 significantly reduced tumor size and increased tumor infiltration by T cells. However, anti-PD-1 alone did not have significant effects on established tumors in these mice. Neither early nor late anti-PD-1 administration reduced tumor growth in the presence of MDSCs in H/K-ATPase-hIL-1ß mice. The combination of 5-fluorouracil and oxaliplatin reduced MDSCs, increased numbers of intra-tumor CD8+ T cells, and increased the response of tumors to anti-PD-1; however, this resulted in increased tumor expression of PD-L1. Expression of PD-L1 by tumor or immune cells increased gastric tumorigenesis in mice given MNU. Mice with gastric epithelial cells that expressed PD-L1 did not develop spontaneous tumors, but they developed more and larger tumors after administration of MNU and H felis, with accumulation of MDSCs. CONCLUSIONS: In mouse models of gastric cancer, 5-fluorouracil and oxaliplatin reduce numbers of MDSCs to increase the effects of anti-PD-1, which promotes tumor infiltration by CD8+ T cells. However, these chemotherapeutic agents also induce expression of PD-L1 by tumor cells. Expression of PD-L1 by gastric epithelial cells increases tumorigenesis in response to MNU and H felis, and accumulation of MDSCs, which promote tumor progression. The timing and site of PD-L1 expression is therefore important in gastric tumorigenesis and should be considered in design of therapeutic regimens.

Correlation of the Levels of microRNA with Cell Composition of Axillary Lymph Node in Wistar Rats with Breast Cancer.

We studied the levels microRNA (miR-21, miR-221, miR-222, and miR-429) in blood serum, thoracic duct lymph, and breast cancer tissue, as well as the cell composition of the axillary lymph node in Wistar female rats with chemically induced breast cancer. The levels of miR-221 and miR-429 in the tumor tissue and in the lymph correlated with the decrease in lymphocyte number in the medullary cords of the axillary lymph nodes.

Correlation Analysis of Morphological Changes of Structural and Functional Areas of Mesenteric Lymph Nodes with Cytokines of Lymph of Thoracic Lymphatic Duct in Experimental Breast Cancer.

We performed a correlation analysis of the morphometric parameters of mesenteric lymph nodes and cytokine content in the lymph of thoracic duct in rats with chemically induced breast cancer. The study showed that activity of the local immune response in the lymph nodes in breast cancer is aimed at antitumor protection. In breast cancer, the area of the paracortical zone remained at the level of the intact group, while the area of lymphoid nodules with germinative centers and the area of medullary substance increased; the number of macrophages in the thymus-dependent zone and zone responsible for humoral immunity also increased. The following positive correlations were revealed: in germinative centers and medullary substance, number of mitotic cells correlated with cytokine IL-5 content and the number of medium lymphocytes correlated with the content of chemokine MIP-1α; in the germinative centers, the number of immunoblasts correlated with the level of cytokine GRO/KC, in the paracortical zone, the number of macrophages correlated with the level of chemokine MCP-1, the number of reticular cells correlated with IL-6 and M-CSF content; in medullary substance, the number of small lymphocytes and mature cells plasma cells (their content was reduced) correlated with the level of chemokine GRO/KC, which can be caused by their migration from the lymph node.

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 (60 mg/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.

Evaluation of the preventive and therapeutic effects of a recombinant vector co-expressing prostate-specific stem cell antigen and Clostridium perfringens enterotoxin on prostate cancer in rats.

The effects of Clostridium perfringens enterotoxin (CPE) and prostate stem cell antigen (PSCA) on cancer prevention or treatment have been previously studied separately. For the first time, here we have elaborated a recombinant vector to co-express and study the cumulative effects of both of these factors on prostate cancer (PCa) in an animal model. The recombinant pBudCE4.1-cpe-PSCA vector was constructed in large scale. Rats were vaccinated by vector or vector plus chitosan nanoparticles before or after induction of PCa (preventive or therapeutic studies) by N-methyl N-nitrosurea and testosterone. Prostate tumors were weighed and histologically examined. Tumors and infusion site tissues as well as blood samples of all rats were collected and assessed by serological and molecular tests. We showed that vaccination with vector (along with or without nanoparticles) led to lower PCa incidence and tumor weight. The L-1ß, IL6, and TNF-α serum levels and their gene expression accompanied by C-CAM1 gene expression in vaccinated groups were significantly higher than controls while no difference was seen in CK20 expression among all groups. Our findings showed that vector could effectively stimulate the immune system of rats to either prevent or suppress the PCa tumors. Adding chitosan nanoparticles did not affect the results significantly.

Systemic taurine treatment provides neuroprotection against retinal photoreceptor degeneration and visual function impairments.

OBJECTIVE: Retinitis pigmentosa causes progressive photoreceptor degeneration in the subjects while no clinical therapy exists. The present study sought to evaluate the potential protective effects of taurine on a pharmacologically induced RP animal model. METHODS: Photoreceptor degeneration in mice was induced by an intraperitoneal injection of N-methyl-N-nitrosourea (MNU). The MNU-administrated mouse received taurine treatment and then they were examined by electroretinography, spectral-domain optical coherence tomography, optokinetic test, and histological and immunohistochemistry assay. RESULTS: Prominent taurine deficiency was found in the retinas of MNU-administered mice. Intravenous taurine treatment increased significantly the retinal taurine level. Morphological studies showed that taurine could alleviate the retinal disorganizations in the MNU-induced mice. Taurine also ameliorated the visual impairments in the MNU-induced mice as evidenced by functional examinations. Immunostaining experiments demonstrated that both the M-cone and S-cone populations in the degenerative retinas are rescued by taurine. In particular, the M-cone photoreceptors in superior-temporal quadrant and the S-cone photoreceptors in inferior-nasal quadrant were preferentially rescued. Mechanism study showed that the photoreceptor apoptosis and oxidative stress in the degenerative retina were effectively alleviated by taurine treatment. CONCLUSION: Taurine is protective against the MNU-induced photoreceptor degeneration. Systemic taurine administration may act as a promising therapeutic potion for retinopathies with chronic cycle.

Dosage time affects alkylating agents induced micronuclei in mouse peripheral blood reticulocytes through the function of erythropoietin.

Previously, we reported that the frequency of micronucleated reticulocytes (MNRETs) in the peripheral blood of male C3H/He mice intraperitoneally administered ethylnitrosourea (ENU) (25 mg/kg body weight) in the dark period (zeitgeber time, ZT15) was higher than in the light period (ZT3). In this study, to clarify the mechanism underlying this phenomenon, we investigated the differences in micronucleus (MN) induction observed between ZT3 and ZT15 using five chemicals, methylnitrosourea (MNU), ethylmethane sulfonate (EMS), mitomycin C, cyclophosphamide and vincristin. MNU and EMS, monofunctional alkylating agents, showed higher frequencies of MNRETs in the ZT15 than the ZT3 treatment similar to ENU. However, no differences were observed for the other chemicals. In the comet assay, more DNA damage was induced by ENU in the ZT15 than the ZT3 treatment. Furthermore, the plasma erythropoietin (EPO) level, a known effector of MN induction with anti-apoptotic activity mediated by Bcl-xL expression, was higher in the dark than in the light period. EPO did not increase the frequency of MNRETs. However, in the ENU treatment group at ZT3 following EPO injection a significant increase of MNRETs was observed similar to the ZT15 treatment. Higher expression of apoptosis-related genes such as Bcl-xL was induced in bone marrow cells from mice treated with ENU at ZT15 compared with ZT3. From these results, it was speculated that the differences in MN induction in the peripheral blood of mice exposed to monofunctional alkylating agents such as ENU depend on apoptotic or anti-apoptotic conditions related to the circadian rhythms of EPO in bone marrow.

Comparison of Effects of Diet on Mammary Cancer: Efficacy of Various Preventive Agents and Metabolomic Changes of Different Diets and Agents.

To determine the effects of diet, rats were placed on a standard diet (4% fat) or on a modified Western (high-fat diet, HFD) diet (21% fat) at 43 days of age (DOA) and administered methylnitrosourea (MNU) at 50 DOA. Rats were administered effective (tamoxifen, vorozole, and Targretin) or ineffective (metformin and Lipitor) chemopreventive agents either by daily gavage or in the diet beginning at 57 DOA and continuing until sacrifice (190 DOA). Latency period of the tumors was determined by palpation, and multiplicity and cancer weights per rat were determined at final sacrifice. Rats on the HFD versus standard diet had: (i) a 6% increase in final body weights; (ii) significant decreases in tumor latency; and (iii) significant increases in final tumor multiplicity and average tumor weight. Tamoxifen, vorozole, and Targretin were highly effective preventive agents, whereas Lipitor and metformin were ineffective in rats on either diet. Serum was collected at 78 DOA and at sacrifice (190 DOA), and metabolomics were determined to identify the metabolite changes due to diets and effective agents. Rats given the HFD had increased levels of saturated free fatty acids (including myristate) and decreased levels of 2-aminooctanoate. Furthermore, rats on the HFD diet had increased levels of 2-aminobutyrate and decreases in glycine markers previously identified as indicators of prediabetes. Targretin increased long-chain glycophospholipids (e.g., oleyl-linoleoyl-glycerophosphocholine) and decreased primary bile acids (e.g., taurocholate). Tamoxifen increased palmitoyl-linoleoyl-glycophosphocholine and decreased stearoyl-arachidonyl glycophosphocholine. Finally, increased levels of methylated nucleotides (5-methylcytidine) and decreased levels of urea cycle metabolites (N-acetylcitrulline) were associated with the presence of mammary cancers.

Modulating SIRT1 activity variously affects thymic lymphoma development in mice.

SIRT1 is a protein deacetylase with a broad range of biological functions, many of which are known to be important in carcinogenesis, however much of the literature regarding the role of SIRT1 in cancer remains conflicting. In this study we assessed the effect of SIRT1 on the initiation and progression of thymic T cell lymphomas. We employed mouse strains in which SIRT1 activity was absent or could be reversibly modulated in conjunction with thymic lymphoma induction using either the N-nitroso-N-methylurea (NMU) carcinogenesis or the nucleophosmin-anaplastic lymphoma kinase (NPM-ALK) transgene. Decreased SIRT1 activity reduced the development of thymic lymphomas in the NMU-treated mice but was permissive for the formation of lung adenomas. Conversely, in the NPM-ALK transgenic mice, decreased SIRT1 activity had a modest promoting effect in the development of thymic lymphomas. The results of the work presented here add to the growing body of evidence that sirt1 is neither an outright oncogene nor a tumor suppressor. These opposing results in two models of the same disease suggest that the influence of sirt1 on carcinogenesis may lie in a role in tumor surveillance.

Protein Carbonylation-Dependent Photoreceptor Cell Death Induced by N-Methyl-N-nitrosourea in Mice.

Retinal degenerative diseases, such as retinitis pigmentosa, are characterized by night blindness and peripheral vision loss caused by the slowly progressive loss of photoreceptor cells. A comprehensive molecular mechanism of the photoreceptor cell death remains unclear. We previously reported that heat shock protein 70 (HSP70), which has a protective effect on neuronal cells, was cleaved by a calcium-dependent protease, calpain, in N-methyl-N-nitrosourea (MNU)-treated mice retina. Carbonylated HSP70 is much more vulnerable than noncarbonylated HSP70 to calpain cleavage. However, it was not known whether protein carbonylation occurs in MNU-treated mice retina. In this study, we clearly show protein carbonylation-dependent photoreceptor cell death induced by MNU in mice. Therefore, protein carbonylation and subsequent calpain-dependent cleavage of HSP70 are key events in MNU-mediated photoreceptor cell death. Our data provide a comprehensive molecular mechanism of the photoreceptor cell death.

Inhibitory Effect of Filipendula ulmaria on Mammary Carcinogenesis Induced by Local Administration of Methylnitrosourea to Target Organ in Rats.

BACKGROUND: The meadowsweet (Filipendula ulmaria (L.) Maxim.) may have a cancer prophylactic activity, since its extracts exhibit antioxidant, anti-inflammatory and other effects. We investigated the ability of a meadowsweet decoction to inhibit mammary carcinogenesis induced by intramammary injections of Methylnitrosourea (MNU) to the target organ in rats. MATERIALS AND METHODS: The chemical composition of meadowsweet extracts was studied by traditional methods. In animal experiments, adult outbred female rats received single injections of MNU at a dose 1mg directly into the tissue of each mammary gland. After carcinogenic exposure one group (MNU) of rats continued to receive standard feed and tap water throughout life. In another group (MNU+meadowsweet), rats were given daily a decoction of the meadowsweet instead of drinking water and standard feed. RESULTS: Meadowsweet extracts showed a sufficiently high content of flavonoids and tannins and also some individual phenolic compounds. In rats after injections of MNU the overall incidence of tumors was 90% with tumor multiplicity of 3.1. The majority of rats (86%) developed multiple malignant tumors of the mammary gland (most often adenocarcinomas). In rats from the group MNU+meadowsweet, there was a statistically significant decrease of the overall tumor multiplicity-by 1.5 times, and the incidence and multiplicity of breast tumors-by 1.6 and 2.2 times, respectively. CONCLUSIONS: Meadowsweet extract can be considered an effective inhibitor of breast carcinogenesis.

The Impact of Exercise Training on Breast Cancer.

BACKGROUND/AIM: Physical exercise is increasingly considered by many authors to be a factor reducing the risk of cancer development and premature cancer-related death. Data indicate higher cure rates and longer times of survival in cancer patients who regularly exercise. MATERIALS AND METHODS: A total of 50 female Sprague-Dawley rats were used in the experiment. Animals at 1 month of age were intraperitoneally injected with N-methyl-N-nitrosourea. Three months following drug administration, rats underwent supervised physical training. The animals were divided into four groups: control untrained group and 3 groups trained with different intensities - i.e. low, moderate and high. Routine histopathological examination of tumors was performed and mitotic activity was assessed by immunohistochemical expression of the Ki-67 antigen. RESULTS: Ki-67 antigen expression was observed in all analyzed tumors. The increase in Ki-67 antigen expression correlated positively with the increase in training intensity. CONCLUSION: It can be assumed that low-intensity physical training is safe for patients with breast cancer. However, moderate- and high-intensity training may induce tumor cell proliferation worsening patients' prognosis.

Anterior Mediastinal Lymph Nodes in Chemically Induced Breast Cancer.

The anterior mediastinal lymph nodes were analyzed morphometrically in rats with chemically provoked breast cancer. Rats with untreated breast cancer and animals receiving chemotherapy demonstrated decreased volumes of paracortical region and lymphoid nodules with the germinal centers accompanied by extended medullary thymic substance. Resection of largest focus of breast tumor improved the filtration barrier potential of anterior mediastinal lymph nodes, up-regulated the proliferative activity of lymphoid cells in T-cell zones, and down-regulated proliferation of plasmatic cells.

Enhanced Susceptibility of Ogg1 Mutant Mice to Multiorgan Carcinogenesis.

The role of deficiency of oxoguanine glycosylase 1 (Ogg1) Mmh homolog, a repair enzyme of the 8-hydroxy-2'-deoxyguanosine (8-OHdG) residue in DNA, was investigated using the multiorgan carcinogenesis bioassay in mice. A total of 80 male and female six-week-old mice of C57BL/6J background carrying a mutant Mmh allele of the Mmh/Ogg1 gene (Ogg1-/-) and wild type (Ogg1+/+) mice were administered N-diethylnitrosamine (DEN), N-methyl-N-nitrosourea (MNU), N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN), N-bis (2-hydroxypropyl) nitrosamine (DHPN) and 1,2-dimethylhydrazine dihydrochloride (DMH) (DMBDD) to induce carcinogenesis in multiple organs, and observed up to 34 weeks. Significant increase of lung adenocarcinomas incidence was observed in DMBDD-treated Ogg1-/- male mice, but not in DMBDD-administered Ogg1+/+ animals. Furthermore, incidences of lung adenomas were significantly elevated in both Ogg1-/- males and females as compared with respective Ogg1-/- control and DMBDD-treated Ogg1+/+ groups. Incidence of total liver tumors (hepatocellular adenomas, hemangiomas and hemangiosarcomas) was significantly higher in the DMBDD-administered Ogg1-/- males and females. In addition, in DMBDD-treated male Ogg1-/- mice, incidences of colon adenomas and total colon tumors showed a trend and a significant increase, respectively, along with significant rise in incidence of simple hyperplasia of the urinary bladder, and a trend to increase for renal tubules hyperplasia in the kidney. Furthermore, incidence of squamous cell hyperplasia in the forestomach of DMBDD-treated Ogg1-/- male mice was significantly higher than that of Ogg1+/+ males. Incidence of small intestine adenomas in DMBDD Ogg1-/- groups showed a trend for increase, as compared to the wild type mice. The current results demonstrated increased susceptibility of Ogg1 mutant mice to the multiorgan carcinogenesis induced by DMBDD. The present bioassay could become a useful tool to examine the influence of various targets on mouse carcinogenesis.

Visual Responses of Photoreceptor-Degenerated Rats Expressing Two Different Types of Channelrhodopsin Genes.

Optogenetic technologies are expected to be applicable for clinical use in restoring vision. However, the degree of recovered visual function is highly dependent on the function of the chosen optogenetic gene. To investigate the effect on visual function of dual expression of genes with different wavelength sensitivities, we transduced a modified Volvox-derived channelrhodopsin gene (mVChR1) via an adeno-associated virus vector into transgenic rats harbouring the ChR2 gene in retinal ganglion cells. These transgenic rats were given an intraperitoneal injection of N-methyl-N-nitrosourea to induce the degeneration of native photoreceptor cells prior to transduction of mVChR1. Optical coherence tomography images indicated the degeneration of the native photoreceptor cells after the N-methyl-N-nitrosourea injection. Complete loss of function of the native photoreceptor cells was confirmed using electroretinograms. In the ChR2 transgenic rats, visually evoked potentials were clearly detectable in spite of native photoreceptor function abolishment; however the responses were limited to within blue wavelengths. In contrast, the limited wavelength sensitivities were improved by the additional transduction of mVChR1, which exhibited sensitivities to green and red. Thus, the transductions of dual genes encoding channelrhodopsins that exhibit different wavelength sensitivities represents a promising candidate method to expand and to enhance rescued wavelength sensitivities in blind subjects.

Photoreceptor degeneration by intravitreal injection of N-methyl-N-nitrosourea (MNU) in rabbits: a pilot study.

BACKGROUND: Pilot study on the attempt to induce selective photoreceptor degeneration in the rabbit eye by intravitreal injection of MNU, facing the difficulties of the evaluation of retinal degeneration by different in-vivo and in-vitro methods in such a large eye animal model. METHODS: Eight pigmented Chinchilla Bastard rabbits were injected intravitreally with MNU (1 × 1mg/kg body weight (BW), 1 × 2mg/kg BW, 3 × 3mg/kg BW, 1 × 4mg/kg BW, 1 × 6mg/kg BW, and 1 × DMSO + PBS as control). One, 2, and 3 weeks after injection, the effects on the rabbit retina were examined in vivo using clinical observation (macroscopic images, funduscopy, weighing of the animals), measurement of intraocular pressure (IOP), full-field Electroretinography (ffERG), and spectral-domain Optical Coherence Tomography (sd-OCT). After 3 weeks follow-up, blood samples were taken to evaluate the general health status of the animals, and immunohistochemistry (IH) was performed on sections obtained from six different regions throughout the whole retina to evaluate MNU effects in more detail. RESULTS: It was difficult to observe the effects of MNU on retinal structure by OCT in vivo. Only the temporal quadrant of the retina could be visualized. Therefore, it was indispensible to evaluate the effects of MNU on the retina in vitro by examining six areas of the retina using immunohistochemistry. Furthermore, immunohistochemistry plays a decisive role to evaluate the effects on retinal cells other than photoreceptors while in H&E staining, namely the cell count of the ONL can be observed. The results obtained in vivo and in vitro in this study mainly follow the results of a previous study in mice. The low doses of MNU (1, 2 mg/kg BW) had no effects on retinal function and morphology, while high doses (4, 6 mg/kg BW) led to retinal changes in combination with significant side-effects (e.g., cataractous changes). Injection of 3 mg/kg BW MNU induced selective photoreceptor degeneration. However, the degree of degeneration varied between different parts of the same retina and between retinae of different animals. In two of three animals, a complete loss of ERG potentials was observed. Negative effects on the contralateral eye or on general welfare of the animal were never observed. CONCLUSIONS: In rabbits, the intravitreal injection of 3 mg/kg BW MNU leads to selective but inhomogeneous photoreceptor degeneration.

Nitric Oxide Synthase Activation as a Trigger of N-methyl-N-nitrosourea-Induced Photoreceptor Cell Death.

Retinal degeneration (RD) such as retinitis pigmentosa and age-related macular degeneration are major causes of blindness in adulthood. As one of the model for RD, intraperitoneal injection of N-methyl-N-nitrosourea (MNU) is widely used because of its selective photoreceptor cell death. It has been reported that MNU increases intracellular calcium ions in the retina and induces photoreceptor cell death. Although calcium ion influx triggers the neuronal nitric oxide synthase (nNOS) activation, the role of nNOS on photoreceptor cell death by MNU has not been reported yet. In this study, we investigated the contribution of nNOS on photoreceptor cell death induced by MNU in mice. MNU significantly increased NOS activation at 3 day after treatment. Then, we evaluated the effect of nNOS specific inhibitor, ethyl[4-(trifluoromethyl) phenyl]carbamimidothioate (ETPI) on the MNU-induced photoreceptor cell death. At 3 days, ETPI clearly inhibited the MNU-induced cell death in the ONL. These data indicate that nNOS is a key molecule for pathogenesis of MNU-induced photoreceptor cell death.

N-Methyl-N-Nitrosourea-Induced Acute Alteration of Retinal Function and Morphology in Monkeys.

PURPOSE: The purpose of this study was to investigate both functional and morphologic alteration of the retina acutely induced by N-methyl-N-nitrosourea (MNU) in monkeys. METHODS: The MNU was administered intravenously at a single dose of 40 mg/kg to six cynomolgus monkeys, and standard full-field electroretinograms (ERGs) were recorded 1, 3, and 7 days after dosing. In addition, the rod and cone a-waves in response to high-intensity flashes were analyzed by the a-wave fitting model (a-wave analysis). The photopic negative response (PhNR) was also recorded at the same time points. Furthermore, the retinas of two animals each were examined histopathologically 1, 3, or 7 days after dosing. RESULTS: The MNU attenuated all the standard full-field ERGs including the rod-driven and cone-driven responses; in the combined rod-cone response, the b-wave was more affected than the a-wave. In the a-wave analysis, the sensitivity parameters (S) of the rod and cone a-waves had decreased on the day after dosing and remained unchanged thereafter. The maximum response parameter (Rmax) of the rod a-wave gradually decreased. On the other hand, the Rmax in the cone a-wave transiently increased on the day after dosing and decreased thereafter; the PhNR amplitude showed a similar time course change. Histopathologically, the retinal lesion on the day after dosing mainly consisted of pyknosis and karyorrhexis in the photoreceptor nucleus. Depletion of some photoreceptor nuclei, and shortening and disorientation of the photoreceptor segments became prominent at 3 and 7 days after dosing. Localization of degenerated photoreceptors was consistent with that of rhodopsin-positive photoreceptors, resulting in a well-preserved central fovea. CONCLUSIONS: Our results indicated that MNU acutely induced rod-dominant photoreceptor degeneration in monkey retinas, but the photoreceptor function was impaired in both the rods and cones. Functional involvement of the postreceptoral components was also indicated.