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Cardiotoxicity is a major problem with numerous pharmaceutical agents and industrial chemicals. Use of zebrafish as an animal model for cardiotoxicity testing can provide more accurate results compared to cell-based assays. Drug effects on heart rates, heart beat rhythm, and contractility can be directly assessed in the transparent zebrafish under a dissecting microscope, providing information on the pharmacological effects of drugs on cardiac function. Visual assessmentAs a rapid assessment of cardiac toxicity, the morphology of the heart and the occurrence of edema, hemorrhage, and necrosis are examined under a dissecting microscope. Cardiac edema may be caused by venous obstruction, increased vascular permeability, or heart failure. Hemorrhage may be caused by blood vessel malformation or rupture of tissues or organs after drug treatment. Cardiac Function AssessmentTransparency of the zebrafish permits rapid measurement of heart rate and examination of cardiac rhythm and contractility. The ventricular and atrial rates, cardiac rhythm, and contractility are assessed.
Changes in relative ventricular rates after drug treatment. Zebrafish embryos at 24 hpf were treated with different drugs for 4 hours, and the ventricular rates were recorded and compared to the control. Isoproterenol (a b-adrenergic agonist) increased ventricular rate, while Propranolol (a b-adrenergic antagonist), Dofetilide (an IKr-channel blocker), Flecainide (a Na+-channel blocker), and Verapamil (an L-type Ca2+-channel blocker) reduced ventricular rate.
In vivo cardiac function assessment: 2-day zebrafish were treated with vehicle (top) or propranolol (bottom), a beta-adrenergic receptor blocker, for 4 hours, and time-lapse recording was used to examine cardiac functions. After propranolol treatment, slow heart rate, irregular atrial/ ventricular beating and prolonged contraction of the ventricle were observed indicating that propranolol treatment causes cardiac arrhythmia in zebrafish. Similar side effects of propranolol have been observed in humans, suggesting the utility of zebrafish for assessing cardiac function after drug treatment. HistologyThe structure of the cardiac chambers, musculature walls, and morphology and condition of the cardiac cells and tissues are analyzed by standard Hematoxylin-Eosin (H&E) staining of sections. Toxicity on the Vascular SystemMicroangiographyFluorescent microspheres are injected into the circulatory system to assess drug effects on blood vessels.
Zebrafish blood vessels labeled by microangiography. The stereotypic pattern of the intersomitic vessels (ISVs) is disrupted by the anti-angiogenic drug SU5416. (A), Normal zebrafish at 72 hpf. (B), Zebrafish treated with SU5416. Note the severe reduction of ISVs after SU5416 treatment. Angiogenesis assay (please refer to the Angiogenesis Assays section for more details)Drug effects on angiogenesis are examined by staining with an angiogenic vessel-specific antibody. |
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