2.8. TUNEL staining

Briefly, paraffin sections were washed, permeabilized, and then incubated with 50 μL TUNEL reaction mixtures in a wet box for 60 min at 37°C in the dark. For signal conversion, slides were incubated with 50 μL of peroxidase for 30 min at 37°C, rinsed with PBS, and then incubated with 50 μL diaminobenzidine substrate solution for 10 min at 25°C. Finally, the expression of apoptotic cells was observed under an optical microscope.