Another compound with biochemical redox properties similar to those of methylene blue is resazurin (CAS 550-82-3), a blue oxazine that is reduced to resorufin (pink), and then to hydroresorufin (colorless). Resazurin has been around since at least 1931, is not toxic, and is preferred to methylene blue in some applications.

In recent decades, many researchers have bought resazurin as "alamar blue," a trade name often not recognized as a compound with a traditional trivial name.

If the redox properties of methylene blue and its leuco compound favorably change the formation of Aβ oligomers and fibrils, resazurin might be expected to have the same action. Has anyone tried this?

Should resazurin be shown not to have the predicted effects on Aβ metabolism, an unrelated property of methylene blue probably accounts for its possible therapeutic potential.

Methylene blue and resazurin molecules have similar central parts (thiazine, oxazine) but have very different small side chains.

References:
Carter RA, Ericsson SA, Corn CD, Weyerts PR, Dart MG, Escue SG, Mesta J. Assessing the fertility potential of equine semen samples using the reducible dyes methylene green and resazurin. Arch Androl. 1998 Jan-Feb;40(1):59-66. Abstract

Zhi-Jun Y, Sriranganathan N, Vaught T, Arastu SK, Ahmed SA. A dye-based lymphocyte proliferation assay that permits multiple immunological analyses: mRNA, cytogenetic, apoptosis, and immunophenotyping studies. J Immunol Methods. 1997 Dec 15;210(1):25-39. Abstract

O'brien J, Wilson I, Orton T, Pognan F. Investigation of the Alamar Blue (resazurin) fluorescent dye for the assessment of mammalian cell cytotoxicity. Eur J Biochem. 2000 Sep;267(17):5421-6. Abstract

Also a brief review of the chemistry and applications, with several references, in Conn's Biological Stains 10th ed. pp 278-280(2002) ISBN 1859960995.

For physical and optical properties and traditional applications of resazurin and resorufin see the Sigma-Aldrich Handbook of Stains, Dyes and Indicators, pp 622-623 and 625 (1990) ISBN 0941633225.

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