Simple, reliable, and time-efficient colorimetric method for the assessment of mitochondrial function and toxicity.

Mitochondria are organelles involved in the production of cellular energy, regulation of Ca2+ and redox signaling, and are critical for normal functioning of eukaryotic cells. The dysfunction of mitochondria has been implicated in a wide range of diseases, including metabolic and neurodegenerative disorders and different types of cancers. To better understand the role of mitochondria in healthy and disease states, the development of efficient and reliable tools for the assessment of mitochondrial function is particularly important. Janus green B (JG-B) is a supravital lipophilic cationic dye which, in its oxidized form, has a green-blue color. As JG-B is taken up and reduced by metabolically active mitochondria, the dye has been used for assessing the purity, integrity and metabolic activity of mitochondria with microscopy-based methods. Here we present a simple, time- and cost-efficient JG-B-based colorimetric assay for assessing mitochondrial function, activity and toxicity. The method is based upon reduction of JG-B by mitochondrial dehydrogenases to diethylsafranine, which is pink colored and has a maximum absorption at 550 nm. In this proof of principle study, using in vitro mitochondrial preparations isolated from rat brain, we provide evidence that monitoring JG-B conversion to diethylsafranine can be used as a reliable and robust indicator of mitochondrial activity and toxicity. Because of its simplicity and efficiency in terms of costs and time, this assay has a wide potential in analytical as well as therapeutic areas of biomedical research.