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Acta Histochem. 2018 Apr;120(3):159-167. doi: 10.1016/j.acthis.2018.02.005. Epub 2018 Feb 26.

Tetrazolium salts and formazan products in Cell Biology: Viability assessment, fluorescence imaging, and labeling perspectives.

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Universidad de Buenos Aires, Instituto de Oncología Ángel H. Roffo, Área Investigación, Buenos Aires C1417DTB, Argentina; Universidad de Buenos Aires, Facultad de Ciencias Veterinarias, Instituto de Investigación y Tecnología en Reproducción Animal, Buenos Aires C1427CWO, Argentina. Electronic address:
Chemical Biology and Medicinal Chemistry, School of Chemistry, The University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
Universidad de Buenos Aires, Instituto de Oncología Ángel H. Roffo, Área Investigación, Buenos Aires C1417DTB, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina.
Department of Physics of Materials, Faculty of Sciences, Autonomous University of Madrid, Madrid 28049, Spain.


For many years various tetrazolium salts and their formazan products have been employed in histochemistry and for assessing cell viability. For the latter application, the most widely used are 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT), and 5-cyano-2,3-di-(p-tolyl)-tetrazolium chloride (CTC) for viability assays of eukaryotic cells and bacteria, respectively. In these cases, the nicotinamide-adenine-dinucleotide (NAD(P)H) coenzyme and dehydrogenases from metabolically active cells reduce tetrazolium salts to strongly colored and lipophilic formazan products, which are then quantified by absorbance (MTT) or fluorescence (CTC). More recently, certain sulfonated tetrazolium, which give rise to water-soluble formazans, have also proved useful for cytotoxicity assays. We describe several aspects of the application of tetrazolium salts and formazans in biomedical cell biology research, mainly regarding formazan-based colorimetric assays, cellular reduction of MTT, and localization and fluorescence of the MTT formazan in lipidic cell structures. In addition, some pharmacological and labeling perspectives of these compounds are also described.


Cytotoxicity; Fluorescence imaging; Formazan localization; MTT; Tetrazolium salts; Viability assays

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