Karyolyse

Karyolysis is the dissolution of a cell’s nucleus during necrotic cell death, characterized by loss of nuclear staining and eventual disappearance of the chromatin. Under light microscopy, the nucleus becomes pale and may ultimately vanish as DNA is degraded.

In the classic sequence of nuclear changes associated with irreversible cell injury, karyolysis follows pyknosis (nuclear condensation) and karyorrhexis (nuclear fragmentation). As necrosis progresses, DNA is degraded by nucleases, leading to fading of nuclear basophilia and, with continued degradation, to the absence of a distinct nuclear structure.

The mechanism involves activation of calcium-dependent endonucleases and other nucleases in necrotic cells, resulting in systematic chromatin breakdown. This degradation also contributes to increased eosinophilia of the cytoplasm due to loss of ribosomes and RNA, which normally bind basophilic dyes.

Karyolysis is observed in various forms of necrosis, including coagulative and liquefactive necrosis, and is commonly associated with ischemic or hypoxic injury, toxin exposure, and severe infections. It denotes late-stage irreversible cell injury and is used in histopathology as a marker of damaged tissue viability, though it is not specific to a particular disease.

Etymology-wise, the term derives from Greek karuon (nucleus) and lysis (dissolution). It is often discussed alongside pyknosis and karyorrhexis as the sequential nuclear changes characteristic of necrotic cell death.