Immunohistochemical Study of Four Fish Tumors

Exploring Immunohistochemistry in Fish: Assessment of Antibody Reactivity by Western Immunoblotting

In recent years, research on fish has seen remarkable advancements, especially in aquaculture, ornamental fish industry, and biomedical studies. Immunohistochemistry has become crucial in fish research, aiding in physiological and pathological investigations. However, the use of antibodies originally developed for mammals has raised concerns about their cross-reactivity and specificity in fish. This study systematically evaluated the reactivity of commonly used antibodies for diagnostic purposes, especially in fish pathology, including pan-cytokeratin, vimentin, S-100, glial fibrillary acidic protein, and desmin in the tissue of Sparus aurata, Dicentrarchus labrax, Oncorhynchus mykiss, and Carassius auratus. Western immunoblotting was employed to assess antibody specificity. The results revealed that the pan-cytokeratin and glial fibrillary acidic protein antibodies cross-react with all tested fish species, while S-100 demonstrated specific staining in sea bream, goldfish, and rainbow trout tissues. Conversely, vimentin and desmin antibodies displayed no reactivity. In conclusion, the anti-cytokeratin clone AE1/AE3 and the polyclonal rabbit anti-glial fibrillary acidic protein antibody, which are extensively used in mammals, were validated for fish immunohistochemical studies. Regrettably, D33 anti-desmin and V9 anti-vimentin clones are unsuitable for immunohistochemistry in the tested fish. These findings underscore the need for species-specific antibodies and proper validation for accurate immunohistochemistry analyses in fish research.

Immunohistochemical investigation of epithelial, mesenchymal, neuroectodermal, immune and endocrine markers in sterlet (Acipenser ruthenus), shortnose sturgeon (Acipenser brevirostrum) and common carp (Cyprinus carpio)

Immunohistochemistry (IHC) is a laboratory method widely used to characterize tissue and cell origin, both in human and veterinary medicine. In fish, however, little is known about staining characteristics of most tissue types, and especially for less studied chondrostean fish. The aim of this study was to examine the specificity of various immunohistochemical markers in tissues of chondrostean and teleostean fish and to validate diagnostic tests. Sterlet (Acipenser ruthenus L.), shortnose sturgeon (Acipenser brevirostrum) and common carp (Cyprinus carpio L.) were examined. Markers were chosen as representatives of epithelial (cytokeratin AE1/AE3), mesenchymal (vimentin), neuroectodermal (S-100 protein), lymphoid (leukocyte common antigen, LCA) and endocrine (thyroglobulin, thyroxin) tissues and organs. Applied antibodies were of monoclonal or polyclonal mammalian origin and primarily intended for human medicine research or diagnostic application. No species differences were obvious while examining sterlet, shortnose sturgeon and carp. Cytokeratin AE1/AE3, vimentin, S-100 protein and thyroxin were positive on targeted tissues and structures. Leukocyte common antigen (LCA) and thyroglobulin were negative on targeted structures, however, and with clear cross-reactivity on non-targeted tissues (vascular wall, granulocytes). Conclusive results were obtained when using polyclonal antibodies with dilution adjusted to laboratory practice, while application of ready-to-use (RTU) kits with pre-diluted antibodies or monoclonal antibodies often showed conflicting or inconclusive results.

Histological and Ultrastructural Description of Benign Adipocytic Tumors in Farmed Striped Sea Bream (Lythognathus mormyrus)

Simple Summary

Mesenchymal neoplasms of the skin are common tumors in domestic animals and often reported in fish pathology. Among them, lipomas are frequently observed, but the definition of their different histological features and their classification in fish are still in their primordial stages. In the present work, the authors describe different type of lipomas found in a wild stock of striped seabream and outline their key differential microscopical features. Two new types of lipoma never observed in fish pathology, defined as spindle cell lipoma and atypical spindle cell-like lipoma, are reported.

Abstract

Cutaneous neoplasms affecting wild striped bream (Lythognathus mormyrus) have been recorded after their introduction in a marine aquaculture farm in the Adriatic Sea. The tumors were evident on 24% of the reared fish, showing single or multiple nodules, with a diameter ranging between 0.5–4.0 cm. Histologically, all the neoplastic lesions were located in the stratum spongiosum of the dermis and were surrounded by a thin capsule of connective tissue. The tumors were predominantly composed of adipocytes grouped and surrounded by a thin net of fibroblasts and collagen fibers. In some lipomas a mixture of adipocytes and uniform spindle cells were also observed. Fibroblasts and collagen fibers, or spindle cells, showing few mitotic figures were mainly observed in other nodules. Three of the tumors showed bands of cells with elongated nuclei. Five neoplasms differed from the classic spindle cell lipoma due to the presence of scattered giant cells. These cells presented acidophilic abundant cytoplasm with multiple hyperchromatic nuclei showing a concentric “floret-like” arrangement. The tumors were further characterized by ultrastructural observations that allowed ruling out the presence of virus-like particles within the lesions. Histological features of the masses lead to the identification of four prevalent patterns of neoplasms: lipoma, fibrolipoma, spindle cell lipoma (SCL), and atypical spindle cell-like lipoma (ASCL). The different neoplasms could arise from the transformation of mesenchymal cells of dermal origin. To the author’s knowledge, this is the first report describing key differential histological and ultrastructural features of these neoplasms in striped sea bream.

Peripheral Nerve Sheath Tumors Resembling Human Atypical Neurofibroma in Goldfish (Carassius auratus, Linnaeus, 1758)

Simple Summary

In animals, especially in fish, dermal neoplasms are a common finding. A distinction between peripheral nerve sheath tumors (PNSTs) and other spindle cell tumors (SCTs) is not always possible when relying exclusively on routine cytological and histopathological findings. The current study aims to determine a minimal subset of stains required to correctly identify PNSTs in goldfish and describes, in detail, six dermal nodules that resemble atypical neurofibroma in humans. Interestingly, muscular and fibroblastic tumors were excluded using Azan trichrome staining, while Alcian blue and Gomori’s reticulin stains revealed the presence of intratumoral areas of mucins and basement membrane fragments, respectively. In addition, PAS and PAS with diastase pretreatment confirmed the latter finding and revealed intra- and extracellular glycogen granules. Immunohistochemistry displayed reactivity for S100 protein, CNPase, and phosphorylated and non-phosphorylated neurofilament-positive axons. Altogether, these findings suggested that Azan trichrome staining, Gomori’s reticulin staining, and immunohistochemistry for S100 protein and CNPase represent a useful set of stains to identify and characterize PNSTs in goldfish.

Abstract

Skin spindle cell tumors (SSTs) frequently occur in fishes, with peripheral nerve sheath tumors (PNSTs) being the most commonly reported neoplasms in goldfish. However, distinguishing PNSTs from other SCTs is not always possible when relying exclusively on routine cytological and histopathological findings. Therefore, the aim of this study is to characterize six skin nodules, resembling atypical neurofibromas in humans, found in six cohabiting goldfish (Carassius auratus), and to determine a minimal subset of special stains required to correctly identify PNSTs in this species. Routine cytology and histopathology were indicative of an SCT with nuclear atypia in all cases, with randomly distributed areas of hypercellularity and loss of neurofibroma architecture. Muscular and fibroblastic tumors were excluded using Azan trichrome staining. Alcian blue and Gomori’s reticulin stains revealed the presence of intratumoral areas of glycosaminoglycans or mucins and basement membrane fragments, respectively. PAS and PAS–diastase stains confirmed the latter finding and revealed intra- and extracellular glycogen granules. Immunohistochemistry displayed multifocal, randomly distributed aggregates of neoplastic cells positive for S100 protein and CNPase, intermingled with phosphorylated and non-phosphorylated neurofilament-positive axons. Collectively, these findings are consistent with a PNST resembling atypical neurofibroma in humans, an entity not previously reported in goldfish, and suggest that Azan trichrome staining, reticulin staining, and immunohistochemistry for S100 protein and CNPase represent a useful set of special stains to identify and characterize PNSTs in this species.

Anti-Atherogenic Effect of 10% Supplementation of Anchovy (Engraulis encrasicolus) Waste Protein Hydrolysates in ApoE-Deficient Mice

Fish protein consumption exerts beneficial metabolic effects on human health, also correlating with a decreased risk for cardiovascular disease. Fish waste contains high amount of proteins and utilization may offer the opportunity for generating compounds advantageous for human health. Especially, fish waste protein hydrolysates beneficially influence pathways involved in body composition, exerting anti-inflammatory and antioxidant activities, making their potential supplementation in human disorders of increased interest. This study assessed the effect of a 10% (w/w) anchovy waste protein hydrolysate (APH) diet for 12 weeks in reducing atherosclerosis in ApoE^-/- mice, through histological and immunohistochemical methods. In addition, monitoring of plaque development was performed, using high-frequency ultrasound and magnetic resonance imaging. Overall, the APH diet attenuated atherosclerotic plaque development, producing a regression of arterial lesions over time (p < 0.05). Twelve weeks on an APH diet had an anti-obesity effect, improving lipid metabolism and reducing hepatic enzyme activity. A significant reduction in plaque size and lipid content was observed in the aortic sinus of APH-fed mice, compared to the control (p < 0.001), whereas no differences in the extracellular matrix and macrophage recruitment were observed. Supplementation of APH significantly attenuates atherosclerosis in ApoE^-/- mice, exerting a lipid-lowering activity. The opportunity to use fish waste protein hydrolysates as a nutraceutical in atherosclerosis is worthy of future investigations, representing a low cost, sustainable, and nutritional strategy with minimal environmental impact.

Stages of Granulomatous Response Against Histozoic Metazoan Parasites in Mullets (Osteichthyes: Mugilidae)

Simple Summary

Parasitic diseases represent a common issue in fish and, when histozoic forms are present, this elicits a chronic inflammatory reaction leading to granuloma formation. Despite the large knowledge of granuloma formation due to parasites in visceral organs, little is known about the development and the evolutive stages of granulomas in naturally infected fish. Mullets (Osteichthyes: Mugilidae) are a widespread euryhaline fish species that harbor different parasites, thus representing a suitable model for the study of parasite-induced granulomas. Combining histopathology and immunohistochemical tools, we identified three developmental granuloma stages (pre-granuloma, intermediate, and late stage), that ranged from an intact parasite with mild signs of tissue reaction to the formation of a structured granuloma. The identified histological patterns could be reliable tools in the staging of the granulomatous response associated with histozoic parasites and are an attempt to broaden the knowledge of the inflammatory response in different host–parasite systems.

Abstract

Histozoic parasite–fish host interaction is a dynamic process that leads to the formation of a granuloma, a specific chronic inflammatory response with discernible histological features. Mullets (Osteichthyes: Mugilidae) represent a suitable model concerning the development of such lesions in the host–parasite interface. The present work aimed to identify granuloma developmental stages from the early to the late phase of the infection and to characterize the immune cells and non-inflammatory components of the granuloma in different stages. For this purpose, 239 mullets were collected from 4 Sardinian lagoons, and several organs were examined by combining histopathological, bacteriological, and immunohistochemical methods. Granulomas associated with trematode metacercariae and myxozoan parasites were classified into three developmental stages: (1) pre-granuloma stage, characterized by intact encysted parasite and with no or mild tissue reaction; (2) intermediate stage, with partially degenerated parasites, necrosis, and a moderate number of epithelioid cells (ECs); and (3) late stage, with a necrotic core and no detectable parasite with a high number of ECs and fibroblasts. The three-tier staging and the proposed morphological diagnosis make it conceivable that histopathology could be an essential tool to evaluate the granulomas associated with histozoic parasitic infection in fish.

Expression of acetylcholine, its contribution to regulation of immune function and O2 sensing and phylogenetic interpretations of the African butterfly fish Pantodon buchholzi (Osteoglossiformes, Pantodontidae)

Acetylcholine (Ach) is the main neurotransmitter in the neuronal cholinergic system and also works as a signaling molecule in non-neuronal cells and tissues. The diversity of signaling pathways mediated by Ach provides a basis for understanding the biology of the cholinergic epithelial cells and immune cells in the gill of the species studied. NECs in the gill were not found surprisingly, but specialized cells showing the morphological, histochemical and ultrastructural characteristics of eosinophils were located in the gill filaments and respiratory lamellae. Much remains unknown about the interaction between the nerves and eosinophils that modulate both the release of acetylcholine and its nicotinic and muscarinic receptors including the role of acetylcholine in the mechanisms of O₂ chemosensing. In this study we report for the first time the expression of Ach in the pavement cells of the gill lamellae in fish, the mast cells associated with eosinophils and nerve interaction for both immune cell types, in the gill of the extant butterfly fish Pantodon buchholzi. Multiple roles have been hypothesized for Ach and alpha nAChR in the gills. Among these there are the possible involvement of the pavement cells of the gill lamellae as O₂ chemosensitive cells, the interaction of Ach positive mast cells with eosinophils and interaction of eosinophils with nerve terminals. This could be related to the use of the vesicular acetylcholine transporter (VAChT) and the alpha 2 subunit of the acetylcholine nicotinic receptor (alpha 2 nAChR). These data demonstrate the presence of Ach multiple sites of neuronal and non-neuronal release and reception within the gill and its ancestral signaling that arose during the evolutionary history of this conservative fish species.

Massive infection of Cystidicoloides ephemeridarum in brown trout Salmo trutta with skeletal deformities

We investigated the cause of skeletal deformities found in brown trout from the Aspromonte mountain area in Reggio Calabria, Italy. Toxicological, histopathological and parasitological analyses were carried out on 14 fish with evident macro-morphological alterations from 2 different locations in the same river, and 4 control fish without morphological alterations from a different river (far from the first river but still within the area under study). Histopathological and radiological observations confirmed severe skeletal deformities in the specimens investigated. Parasitological examinations highlighted the presence of the nematode Cystidicoloides ephemeridarum, found only within the gastrointestinal tract of specimens showing deformities. Moreover, a direct correlation between parasite number and fish size was found. Given the low heavy metal levels and the presence of a massive parasitosis in teleosts showing deformities, we postulate a correlation between skeletal deformities and nematode infestation: the parasites caused a serious vitamin and mineral deficiency in the fish, which led to a dysplastic vertebral column. The low calcium levels found in malformed specimens compared with negative controls effectively confirm this hypothesis.

Administration of Protein Hydrolysates from Anchovy (Engraulis Encrasicolus) Waste for Twelve Weeks Decreases Metabolic Dysfunction-Associated Fatty Liver Disease Severity in ApoE-/-Mice

Simple Summary

Metabolic dysfunction-associated fatty liver disease (MAFLD) is an increasing concern worldwide. It currently represents the main cause of chronic liver disease in humans in Western countries. Nutritional strategies based on fish-rich diets are considered helpful in the prevention of MAFLD, and are also thought to be beneficial for human health. In particular, cholesterol- and triacylglycerol-lowering effects are associated with fish-derived proteins or hydrolysates. Our findings suggest that supplementing the diet with 10% (w/w) anchovy protein hydrolysates has an anti-obesity effect together with an improvement in lipid metabolism and a reduction in liver fat content and high-fat diet-induced liver disease. By virtue of their nutritional value and functional proprieties, anchovy by-product protein hydrolysates may be an efficient nutritional strategy in MAFLD prevention and treatment.

Abstract

Metabolic dysfunction-associated fatty liver disease (MAFLD) includes several diseases, ranging from simple steatosis to steatohepatitis, fibrosis and cirrhosis. Fish-rich diets are considered helpful in the prevention of MAFLD, and the enzymatic hydrolysis of fish waste has been explored as a means of obtaining high-value protein hydrolysates, which have been proven to exert beneficial bioactivities including anti-obesity and hypocholesterol effects. This study aimed to assess the effect of the administration of protein hydrolysates from anchovy waste (APH) for 12 weeks on attenuated high-fat diet-induced MAFLD in apolipoprotein E-knockout mice (ApoE^–/–). Thirty ApoE^–/– mice were divided into two groups (n = 15/group) and fed a high-fat diet (HFD), with and without the addition of 10% (w/w) APH. After 12 weeks, serum and hepatic lipid profiles, hepatic enzyme activities, liver histology and immunohistochemistry were analyzed to assess hepatic steatosis, inflammation and fibrosis. Twelve-weeks on a 10% (w/w) APH diet reduces total cholesterol and triglyceride serum levels, hepatic enzyme activity and hepatic triacylglycerol content (p < 0.0001), and results in a reduction in hepatic fat accumulation and macrophage recruitment (p < 0.0001). The results suggest that a 10% APH diet has an anti-obesity effect, with an improvement in lipid metabolism, hepatic steatosis and liver injury as a result of a high-fat diet. Protein hydrolysates from fish waste may represent an efficient nutritional strategy in several diseases, and their use as nutraceuticals is worthy of future investigation.

Testicular leiomyoma and spermatogenic failure syndrome in a seabass from broodstock

Testicular leiomyomas and gonadal dysfunctions are not commonly reported in teleost and particularly in broodstock fish. In the present work, a testicular leiomyoma related to an unusual case of spermatogenic failure syndrome, in a broodstock seabass coming from an Italian aquaculture farm, is reported. At gross pathology, the circumscribed neoplasia showed several white nodular masses, originating from the gonad, deforming the anatomo-physiological shape. From light microscopy, the presence of neoplastic tissue islands with spindle cells with a whirling pattern and the low presence of connective tissue were evident and originated from smooth muscle cells. Seminiferous tubules showed severe azoospermia with the absence of sperm cells even closer to the neoplastic area. Immunohistochemical analysis was positive for alpha-SMA, desmin and vimentin but negative for S-100, confirming a diagnosis of leiomyoma. This is the first report of spermatogenic failure syndrome associated with a testicular leiomyoma in fish from broodstock. More efforts should be made in studying broodstock fish pathologies related to fish maintenance and hormonal treatments that could economically affect aquaculture production.

Insights Into the Albinism Mechanism for Two Distinct Color Morphs of Northern Snakehead, Channa argus Through Histological and Transcriptome Analyses

The great northern snakehead (Channa argus) is one of the most important economic and conservational fish in China. In this study, the melanocytes in the skin of two distinct color morphs C. argus were investigated and compared through employment of the microscopic analysis, hematoxylin and eosin (H&E) and Masson Fontana staining. Our results demonstrated the uneven distribution of melanocytes with extremely low density and most of them were in the state of aging or death. Meanwhile, there was no obvious pigment layer and melanocytes distribution pattern found in the albino-type (AT), while the melanocytes were evenly distributed with abundance in the bicolor-type (BT). The transcriptome analysis through Illumina HiSeq sequencing showed that a total of 34.93 Gb Clean Data was obtained, and Q30 base percentage reached 92.66%. The BT and AT northern snakeheads transcriptome data included a total of 56,039,701 and 60,410,063 clean reads (n = 3), respectively. In gene expression analyses, the sample correlation coefficients (r) were ranged between 0.92 and 1.00; the contribution of PC1 and PC2 were 50.25 and 13.73% by using PCA cluster analysis, the total number of DEGs were 1024 (559 up-regulated and 465 down-regulated), and the number of annotated DEGs was 767 (COG 172, KEGG 262, GO 288, SwissProt 548, Pfam 579 and NR 765). Additionally, 46,363 ± 873 and 44,947 ± 392 single nucleotide polymorphisms (SNPs) were compiled via genetic structure analysis, respectively. Ten key pigment-related genes were screened using qRT-PCR. And all of them revealed extremely higher expression levels in the skin of BT than those of AT. This is the first study to analyze the mechanism of albino characteristics of Channa via histology and transcriptomics, and also provide the oretical and practical support for the protection and development of germplasm resources for C. argus.

Gastric leiomyoma in a sea bass Dicentrarchus labrax broodfish

This report describes a spontaneously arising non-infiltrative neoplasm of gastric tunica muscularis in a broodstock sea bass Dicentrarchus labrax from an Italian aquaculture farm. Microscopically, the mass was circumscribed and non-encapsulated and was composed of spindle cells arranged in parallel interlacing bundles or, occasionally, a whirling pattern. Cells had a small quantity of eosinophilic cytoplasm with distinct cell borders. Neoplastic cells were immuno-reactive with smooth muscle actin, vimentin and desmin; S100 was negative. The mucosal epithelium was intact with no neoplastic involvement. A gastric leiomyoma was diagnosed based on the findings. More efforts should be made to study the possible etiology of leiomyoma affecting fish from aquaculture.

Evidence of Centrocestus formosanus (Nishigori, 1924) in Zebrafish (Danio rerio)

This study reports the presence of cartilaginous cysts in zebrafish gills, purchased at the end of 2012 before the application of the Italian Legislative Decree 26/2014 and used for experimental research. It highlights the importance of using specific pathogen-free organisms from reliable production establishments to avoid obtaining false results in experiments. Of 20 samples analyzed, 4 showed cysts in gills, with abnormal tissue modification and cartilaginous metaplasia induced by prolonged parasitic insult. The results obtained from the periodic health monitoring program showed the presence of metacercariae of digenean trematodes, specifically identified as Centrocestus formosanus.