Retro-orbital blood acquisition facilitates circulating microRNA measurement in zebrafish with paracetamol hepatotoxicity.

Paracetamol is the commonest cause of acute liver failure in the Western world and biomarkers are needed that report early hepatotoxicity. The liver-enriched microRNA (miRNA), miR-122, is a promising biomarker currently being qualified in humans. For biomarker development and drug toxicity screening, the zebrafish has advantages over rodents; however, blood acquisition in this model remains technically challenging. We developed a method for collecting blood from the adult zebrafish by retro-orbital (RO) bleeding and compared it to the commonly used lateral incision method. The RO technique was more reliable in terms of the blood yield and minimum amount per fish. This new RO technique was used in a zebrafish model of paracetamol toxicity. Paracetamol induced dose-dependent increases in liver cell necrosis, serum alanine transaminase activity, and mortality. In situ hybridization localized expression of miR-122 to the cytoplasm of zebrafish hepatocytes. After collection by RO bleeding, serum miR-122 could be measured and this miRNA was substantially increased by paracetamol 24 h after exposure, an increase that was prevented by delayed (3 h poststart of paracetamol exposure) treatment with acetylcysteine. In summary, collection of blood by RO bleeding facilitated measurement of miR-122 in a zebrafish model of paracetamol hepatotoxicity. The zebrafish represents a new species for measurement of circulating miRNA biomarkers that are translational and can bridge between fish and humans.