Ultrastructure of hepatic hemangiopericytoma in the medaka (Oryzias latipes)

Therapeutic Intervention with Dietary Chitosan Nanoparticles Alleviates Fish Pathological and Molecular Systemic Inflammatory Responses against Infections

Marine bio-sourced chitosan nanoparticles (CSNP) are antimicrobial and immunomodulatory agents beneficial for fish medicine. Herein, dietary CSNP was investigated for the amelioration of the systemic inflammatory responses of an induced fish model. One hundred and forty-four rainbow trout were assigned to one pathogen-free and non-supplemented group (negative control), and three challenged groups: non-supplemented (positive control), CSNP-preventive, and CSNP-therapeutic. After a feeding experiment extended for 21 days, the organosomatic indices (OSI) and molecular aspects were assessed. After a challenge experiment extended for further 28 days, CSNP-therapeutic intervention was assessed on fish survival and systemic inflammatory responses on pathology, histo-morphology, and molecular aspects. With CSNP administration, OSI nonsignificantly decreased and the relative expression of targeted inflammatory-mediator genes was significantly increased. The CSNP-therapeutic fish showed an RPS of 80% as compared to the positive control group, and CSNP-therapeutic administration retained the highest gene expression augmentation up to 28 days after the challenge. Notably, the splenic reticulin fibers framework of the CSNP-therapeutic group retained the highest integrity among the groups during the infection. After recovery, reticulin fibers density in the CSNP-therapeutic samples was significantly higher than in the negative control group, which indicates high innate immunity. Thus, CSNP showed promising biotherapeutic features enhancing fish resistance against infections.

Multiple tissue gene expression analyses in Japanese medaka (Oryzias latipes) exposed to hypoxia

Due in part to human population growth watersheds and coastal estuaries have been receiving increasing run-off of nutrients and genotoxins. As a consequence, the occurrences of nutrient-driven hypoxia in coastal waters appear to be increasing. Thus, understanding the molecular genetic response to hypoxia by model aquatic organisms is of interest both from environmental and physiological viewpoints. The major objectives of this study are to determine genome-wide gene expression profiles and to better understand how hypoxia influences global gene expression in medaka (Oryzias latipes), a well utilized aquatic model species. Herein we detail our development of a microarray containing 8046 medaka unigenes and describe our experimental results for measuring gene expression changes in the brain, gill, and liver of hypoxia exposed fish. Using conservative selection criteria, we determined that 501 genes in the brain, 442 in the gill, and 715 in the liver were differentially expressed in medaka exposed to hypoxia. These differentially expressed genes fell into a number of biological gene ontology groups related to general metabolism, catabolism, RNA and protein metabolism, etc. Two biological pathways, ubiquitin-proteasome and phosphatidylinositol signaling, were significantly dysregulated in medaka upon hypoxia exposure. Comparative genomics between medaka and human identified several human orthologies associated with known diseases.

An in vivo method for using 5-bromo-2'-deoxyuridine (BrdU) as a marker of chemically-induced hepatocellular proliferation in the Japanese medaka (Oryzias latipes)

Japanese medaka fish (Oryzias latipes) were used to develop an in vivo method to assess hepatocellular proliferation in a nonmammalian model. Proliferative responses were assessed in medaka at 7, 17, 24, and 94 days after a 48-hour exposure to 10 or 100 mg/L diethylnitrosamine (DEN). Subgroups of medaka were exposed to 50 or 75 mg/L of 5-bromo-2'-deoxyuridine (BrdU) in water for 72 hours, sacrificed, and then processed for immunohistochemical staining. Proliferative indices of BrdU-labeled hepatocytes were quantified and compared using both count and area measurements. There was a significant increase (p < 0.05) in hepatocellular proliferation in the 100 mg/L DEN-treated fish as compared to controls and 10 mg/L DEN-treated fish for the first 3 time points. Hepatocarcinogenicity was evaluated 26 weeks post-DEN exposure. There was a significant increase (p < 0.0001) in hepatocellular neoplasms in 100 mg/L DEN-treated fish compared to other fish. Effective BrdU-labeling of S-phase hepatocytes in medaka was achieved by adding BrdU to the aquarium water, and an increase in hepatocellular proliferation using this method was detected 7 days after exposure to a carcinogenic concentration of DEN. Additionally, the new method of area measurement indices of proliferation were as precise as count indices (R2 > or = 0.92).

Diagnostic criteria for degenerative, inflammatory, proliferative nonneoplastic and neoplastic liver lesions in medaka (Oryzias latipes): consensus of a National Toxicology Program Pathology Working Group

Diagnostic criteria are presented for degenerative, inflammatory, nonneoplastic proliferative, and neoplastic lesions in the liver of medaka (Oryzias latipes), a small fish species frequently used in carcinogenesis studies. The criteria are the consensus of a Pathology Working Group (PWG) convened by the National Toxicology Program. The material examined by the PWG was from Medaka exposed to N-nitrosodiethylamine for 28 days, removed to clean water, and sacrificed 4, 6, or 9 mo after initiation of exposure. Degenerative lesions included hepatocellular intracytoplasmic vacuolation, hepatocellular necrosis, spongiosis hepatis, hepatic cysts, and hepatocellular hyalinization. Inflammatory lesions consisted of granulomas, chronic inflammation, macrophage aggregates, and focal lymphocytic infiltration. Nonneoplastic proliferative lesions comprised foci of cellular alteration (basophilic focus, eosinophilic focus, vacuolated focus, and clear cell focus) and bile duct hyperplasia. Neoplastic lesions included hepatocellular adenoma, hepatocellular carcinoma, cholangioma, and cholangiocarcinoma. Two lesions composed mainly of spindle cells were noted, hemangiopericytoma and spindle cell proliferation. Rather than being an exhaustive treatment of medaka liver lesions, this report draws from the published literature on carcinogen-induced liver lesions in medaka and other fish species and attempts to consolidate lesion criteria into a simplified scheme that might be useful to pathologists and other researchers using medaka lesions for risk assessment or regulatory purposes.

Experimental chemical carcinogenesis in fish

Experimental carcinogenesis using fish species as alternative models is a dynamic field of research. The 1940's expansion of synthetic chemical producing industries coincided with a number of pollution-associated fish neoplasia epizootics, with polycyclic aromatic hydrocarbons as significant components of contaminated sediment in several cases. Epizootics of primarily liver and skin neoplasia in benthic species near coastal urban or industrial areas indicated the sensitivity of fish species to known mammalian carcinogens. Stressing a mechanistic approach, investigators have used data compiled from epizootics as the backbone of current research efforts to define carcinogenesis in fish species. With liver as the focus, patterns of neoplastic development similar to those seen in rodent bioassays have been induced in various fish species by genotoxic carcinogens. Similarities between fish and rodent models include chemical and species-specific responses to exposure and the development of predictable preneoplastic and neoplastic lesions. The expression of molecular molecules related to carcinogenesis is currently under investigation, which includes alterations in certain proteins, enzyme activity, and oncogene/tumor suppressor gene function. The potential for the application of research findings to both human and environmental health issues makes fish species attractive and valuable alternative models in carcinogenesis and toxicity research.

N-methyl-N'-nitro-N-nitrosoguanidine-induced neoplasms in medaka (Oryzias latipes)

To test the sensitivity of the small fish species Oryzias latipes to the direct-acting carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), medaka were exposed at 15 days of age to 30 mg/L for 1 hr and followed for up to 16 mo. One hundred neoplasms were diagnosed in 84 of 213 exposed fish, with approximately equal percentages in males and females. Many neoplasms (62%) were of mesenchymal origin and were categorized as blood vascular neoplasms (hemangioma and hemangiosarcoma), invasive sarcomas, and scale-associated neoplasms. Invasive sarcomas included rhabdomyosarcoma, fascial sarcoma, hemangiopericytoma, and undifferentiated sarcoma. A scale-associated neoplasm, termed lepidocytoma, was an unusual neoplasm of scale anlage. Thyroid follicular neoplasms, with a 100% incidence in males, and pancreatic acinar carcinoma were the most common epithelial tumors. Neoplasms of the gills, swim bladder, and olfactory epithelium were also seen as well as teratoma with mixed epithelial and mesenchymal components. The study showed a broad range of neoplasms induced by MNNG in medaka, with a tissue distribution that might support direct action on exposed tissues.

Intermediate filament reactivity in hyperplastic and neoplastic lesions from medaka (Oryzias latipes)

To determine if hyperplastic and neoplastic lesions from medaka showed similar immunoreactivity to intermediate filament antibodies as the tissues of origin, two week old medaka were exposed to 10 or 20 mg/L of methylazoxymethanol acetate for two hours and transferred to clean water for up to six months. Using a streptavidin peroxidase method, paraffin embedded Bouins fixed neoplasms were incubated with cytokeratin, vimentin, or neurofilament antibodies. Like their nonneoplastic cellular counterparts, hepatocellular carcinoma, pancreatic acinar carcinoma and mesenchymal neoplasms including hemangioma and hemangiopericytoma reacted negatively to cytokeratin antibodies. Cholangiocarcinoma, mesothelioma, and proliferative lesions containing biliary epithelial cells reacted positively to cytokeratin antibodies. All neoplasms and proliferative lesions were negative with vimentin and neurofilament antibodies. These data indicate that while some epithelial neoplasms showed cytokeratin reactivity similar to the parent tissues, additional markers are needed to identify mesenchymal tissues and neoplasms.