The effect of caspase-3 inhibition on interdigital tissue regression in explant cultures of developing mouse limbs

Bioluminescence determination of active caspase-3 in single apoptotic cells

Caspase-3 is an executive caspase, in the central position within apoptotic machinery. Apoptosis as a way of programmed cell death is a physiological process that plays an essential role in the development and homeostasis maintenance; moreover, its deregulations are linked to tumor progression or various autoimmune disorders. Therefore, an investigation of apoptosis pathways on the level of individual cells is not only of biological but also medical importance. In this work we report on the development of a high-sensitivity instrumentation and protocol for detection of active caspase-3 in individual mammalian apoptotic cells. The technology is based on the specific cleavage of modified luciferin by caspase-3, an immediate bioluminescence reaction of free luciferin with luciferase followed by emissions of photons and their detection by photomultiplier tube working in the photon counting regime. Three different instrumental arrangements are compared for the determination of caspase-3 in free cells or tissue samples. Thus, in our best miniaturized system the mean amount as low as about 6.5 fg corresponding to 122 000 molecules of caspase-3 can be detected in individual apoptotic mouse leg cells.

Dynamics of caspase-3 activation and inhibition in embryonic micromasses evaluated by a photon-counting chemiluminescence approach

Caspases are key enzymatic components of the intracellular apoptotic machinery, and their role in mammalian systems is often studied using fluoromethylketone (FMK) inhibitors. Despite many advantages of such approach, efficiency of the inhibitor and membrane permeability speed are often questioned. This work therefore focuses on an exact evaluation of caspase-3 FMK inhibition dynamics in camptothecin-induced mesenchymal micromasses. Two parameters of caspase-3 FMK inhibitor were investigated: first, the stability of the inhibitory potential in the time course of cultivation and, simultaneously, the dynamics of caspase-3 FMK inhibition after camptothecin-induced apoptosis peak. A photon-counting chemiluminescence approach was applied for quantification of active caspase-3. The sensitivity of the photon-counting method allowed for evaluation of active caspase-3 concentration in femtogram amounts per cell. The inhibitor penetrated the cells within the first minute after its application, and the peak of caspase-3 started to decline to the blank level after 30 min. The inhibitory effect of the FMK inhibitor was unchanged during the entire 48 h of cultivation.