ApoTox-Glo Triplex Assay
The ApoTox-Glo Triplex Assay combines three assay chemistries to easily assess viability, cytotoxicity and apoptosis events in the same cell-based assay well. First, viability and cytotoxicity are determined by measuring two differential protease biomarkers simultaneously with the addition of a single nonlytic reagent containing two peptide substrates. The live-cell protease activity is restricted to intact viable cells and is measured using a fluorogenic, cell-permeant peptide substrate (GF-AFC Substrate). The substrate enters intact cells, where it is cleaved to generate a fluorescent signal proportional to the number of living cells. This live-cell protease activity marker becomes inactive upon loss of membrane integrity and leakage into the surrounding culture medium. A second, cell-impermeant, fluorogenic peptide substrate (bis-AAF-R110 Substrate) is used simultaneously to measure dead-cell protease activity that has been released from cells that have lost membrane integrity. This results in ratiometric, inversely correlated measures of cell viability and cytotoxicity. The ratio of viable cells to dead cells is independent of cell number and, therefore, can be used to normalize data. A second reagent containing luminogenic DEVD-peptide substrate for caspase-3/7 and Ultra-Glo Recombinant Thermostable Luciferase is added. Caspase-3/7 cleavage of the substrate releases luciferin, which is a substrate for luciferase and generates light. The light output, measured with a luminometer, correlates with caspase-3/7 activation as a key indicator of apoptosis.