Detection of Paraptosis After Photodynamic Therapy

Photodynamic therapy (PDT) is a procedure for the selective photosensitization of neoplastic tissues. Subsequent irradiation with visible light can lead to cell death along with vascular shutdown and other responses that lead to selective eradication of malignant cells. Among the cellular responses to PDT are necrosis, apoptosis, and autophagy. These pathways have generally been associated with cell death, although autophagy can also be cytoprotective. A fourth effect that has hitherto been somewhat neglected is termed "paraptosis," a lethal response that can be identified by detecting an extensive collection of cytoplasmic vacuoles. Unlike autophagy, these vacuoles are bound by single membranes. Paraptosis has been characterized as a response to misfolded endoplasmic reticulum proteins that must be "cleared" if the affected cell is to survive. At present, there is no simple biochemical test for paraptosis. This chapter describes the procedure for detection of paraptosis using phase-contrast microscopy, along with some confirmatory approaches.