Zebrafish as an Inflammatory Model
The zebrafish (Danio rerio) has emerged as a powerful model for studying vertebrate development and disease. Its short generation time makes it amenable for genetic manipulation and analysis. Its small size and high fecundity help in large-scale genetic and chemical screening. The rapidly developing zebrafish embryos are transparent, which allows live imaging of various developmental processes in wild-type and mutant animals.
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Inflammation could be a complex biological and pathophysiological cascade of responses to infections and injuries.
It can be mediated by numerous inflammatory cells, including neutrophils, macrophages, eosinophils, and mononuclear phagocytes.
Why is Zebrafish used as an Inflammatory Model ?
Dysregulation of the inflammatory response in humans will cause varied inflammatory diseases, like bronchial asthma, cardiovascular diseases, rheumatic arthritis, inflammatory gut disease, Alzheimer’s disease, and even cancer.
The macrophage and neutrophil play an essential role in all inflammatory diseases. This part of the immune system is well-conserved between humans and therefore the zebrafish, which has emerged as a robust animal model for inflammation, as a result, it offers the chance to create non-invasive and dynamic imaging of the inflammation in vivo at the first life stages.
Mode of Induction:
It can be induced by physical, chemical, and biological stimuli.
Physical stimuli-induced inflammation includes ultraviolet exposure and electroablation
Physical injury-induced inflammation includes optic nerve crush, ventricular resection, hypoxia/reoxygenation cardiac injury, and traumatic bone injury.
Chemical-induced inflammation includes copper sulfate, Tris(1,3-dichloro-2-propyl) phosphanovote (TDCIPP)
Biological stimuli-induced inflammation includes lipopolysaccharide (LPS) exposure in water or injection.
Zebrafish models of inflammation are responsive to treatment with classical steroidal and nonsteroidal anti-inflammatory drugs (NSAIDs)
Fish Behaviour Index – A method to detect nociceptive changes in adult zebrafish, based on general activity and distance swim after mechanical or chemical noxious stimuli.
Estimation of biochemical marker enzymes in liver Enzymes like glutamic pyruvic transaminases (ALT) and glutamic oxaloacetic transaminases (AST) were estimated followed by the estimation of LDH activity.
Determination of the expression level of inflammation mediator genes Reverse transcription and quantitative-PCR (RT-qPCR) assays were carried out to detect the mRNA expression levels of inflammation mediator genes, including cytokines, IL-1β, TNF-α, IL-6 and IFN-γ ; chemokines, IL-8 and CXCL-12a; and neutrophil marker mpx as described in Supplementary Material.
Observation of macrophage accumulation by NR staining NR, an in vivo dye used in zebrafish because of its strong phagocytic activity of macrophages, NR can be phagocytosed by lysosomes and enriched in phagocytic cells.
Histopathology – After 42 days of exposure, adult zebrafish livers were fixed in Bouin’s solution and dehydrated with ethanol. Liver tissue was cleared with xylene and embedded in blocks with paraffin. The blocks were sectioned approximately 5-6 μm using a microtome followed by H&E staining. Photomicrographic examination of liver tissue was done by the computerized trinocular microscope with an image analysis system.
Zebrafish presents a complex immune system featuring mammalian characteristics. Zebrafish for testing inflammation-targeted compounds provides clear advantages over cell culture strategies, enabling the detection of adverse effects in a whole organism.