In situ detection of fragmented dna (tunel assay) fails to discriminate among apoptosis, necrosis, and autolytic cell death: A cautionary note

TLDR

The TUNEL assay, which labels DNA fragments in situ, is widely used to detect apoptosis in tissues. The authors evaluated TUNEL specificity using well‑defined rat liver models of apoptosis, necrosis, and post‑mortem autolysis. TUNEL staining was positive in apoptotic, necrotic, and autolytic hepatocytes, demonstrating that DNA fragmentation is not specific to apoptosis and cannot reliably distinguish cell death types.

Abstract

Detection of DNA fragments in situ using the terminal deoxyribonucleotidyl transferase (TDT)-mediated dUTP-digoxigenin nick end labeling (TUNEL) assay is increasingly applied to investigate active cell death (apoptosis). We studied the specificity of the assay in well-defined models of apoptosis and necrosis as well as in postmortem autolysis in rat liver. During involution of liver hyperplasia, which follows stopping treatment with the hepatomitogens cyproterone acetate (CPA) or nafenopin (NAF), numerous apoptotic hepatocytes could be observed with TUNEL-positive chromatin residues. A similar TUNEL-positive reaction appeared in necrotic hepatocytes after a cytotoxic dose of carbon tetrachloride (CCl 4 ) or N -nitrosomorpholine (NNM). Also, in insufficiently fixed, autolytic livers TUNEL-positive nuclei were observed. Thus, DNA fragmentation is common to different kinds of cell death; its detection in situ should not be considered a specific marker of apoptosis.