Hello Anika Dreier

CFDA-AM dye is a non-fluorescent ester that is converted into a fluorescent compound by intracellular esterases found in live cells. If the membrane is compromised, the dye will not be able to enter or remain in the cell, leading to a loss of signal. Since the cells showed 100% viability for CFDA-AM, it means the test substance did not damage the cell membrane in a way that would cause the dye to leak out.

AlamarBlue works by detecting cellular reduction processes that indicate metabolic activity. The test substance might inhibit cellular respiration or other metabolic pathways, reducing the signal from AlamarBlue even if the cells are still technically "alive" and their membranes intact. The cells showing 40% viability for AlamarBlue suggests significant metabolic disruption.

The Neutral Red stain is taken up by living cells and accumulates in lysosomes. It is sensitive to lysosomal damage, which can occur due to various cytotoxic insults, even before significant membrane or metabolic effects are seen. The 70% viability for Neutral Red indicates some degree of lysosomal damage but less severe than the metabolic impact.

So, to summarize, your findings suggest that the test substance is causing significant metabolic disruption, as shown by the low AlamarBlue reading. It is also causing some damage to the lysosomal compartment. However, it is not causing widespread cell death or membrane loss at the concentration tested, which is why CFDA-AM still shows 100% viability.

Best,