*2.10. Hoechst 33258 Staining*

The A549 cells were plated on a 24-well glass slide and incubated for 24 h in media containing 5% CSE in the absence or presence of 10–100 μg/mL YE. After the fixation of A549 cells with ice-cold 4% formaldehyde for 1 h on a glass slides, the nuclear stain Hoechst 33258 (Promega Co., Madison, WI, USA) was added at a final concentration of 10 μg/mL for 15 min to allow uptake and equilibration before microscopic observation. The slides were mounted while wet in aqueous VectaMount mounting solution. Cells containing fragmented or condensed nuclei were considered apoptotic. Images of each slide were taken using an optical microscope system.

#### *2.11. Terminal Deoxynucleotidyl Transferase dUTP Nick End Labeling (TUNEL) Assay*

The transferase dUTP nick end labeling (TUNEL) assay is a common method for detecting DNA fragments. The TUNEL assay was conducted using a commercial fluorometric TUNEL kit (Promega Co., Madison, WI, USA). The A549 cells were plated on a 24-well glass slide and incubated for 24 h in media containing 5% CSE in the absence or presence of 10–100 μg/mL YE. Cells fixed with ice-cold 4% formaldehyde for 20 min were permeabilized with 0.2% Triton X-100, and fragmented DNA was labeled with fluorescein-dUTP at 37 ◦C for 1 h. DAPI was used for counterstaining nuclei, and cells were visualized with an Axiomager optical microscope system.
