Apoptosis. Terminal dUTP nick end labeling assay. (a) Fluorescent microscopy images of human gingival fibroblast (HGF) cells exposed to DDs treated with either normal medium (NM) with infusion solution or ZA 1 or 5 μM (green area of fluorescence at the right of the image) and either left unchelated (top rows) or exposed to EDTA 0.001% (chelated) (bottom rows). (b) Alternate TUNEL assay was performed in HaCaT cells using first, DDs treated with either normal medium or 0.5, 1 or 5 μM of ZA and exposed to EDTA 0.001% (chelated). Secondly, the medium from the treated DDs was removed and applied to fresh HaCaT cells for 24 hours, followed by TUNEL assay and images using fluorescent microscopy. Cells were observed over 24 hours with images taken at 24 hours. Original magnification (a) ×200; (b) × 400.