Open AccessThapsigargin Enhances Camptothecin‐Induced Apoptosis in Cardiomyocytes
Author(s) -
Kong Jennifer Y.,
Rabkin Simon W.
Publication year - 1999
Publication title -
pharmacology & toxicology
Language(s) - English
Resource type - Journals
eISSN - 1600-0773
pISSN - 0901-9928
DOI - 10.1111/j.1600-0773.1999.tb02011.x
Subject(s) - camptothecin , thapsigargin , propidium iodide , dna fragmentation , apoptosis , fragmentation (computing) , programmed cell death , apoptotic dna fragmentation , viability assay , endoplasmic reticulum , biology , topoisomerase inhibitor , microbiology and biotechnology , chemistry , topoisomerase , biochemistry , dna , ecology
Topoisomerase I inhibitors are promising new chemotherapeutic agents for the treatment of certain malignancies. The present study investigated the impact of the topoisomerase I inhibitor camptothecin on cell death in cardiomyocytes and sought to determine whether the sesquiterpene gamma‐lactone – thapsigargin, that alter sarcoplasmic reticulum calcium flux, modulates the effect of camptothecin on the cardiomyocyte. Camptothecin‐induced cell death was demonstrated in cardiomyocytes maintained in culture, from 7 day old embryonic chick hearts, by the trypan blue and the MTT (3‐[4,5‐dimethylthiazol‐2‐yl]‐2,5‐diphenyl tetrazolium bromide) assay, two independent indicators of the loss of cell viability. The type of cell death was attributed to apoptosis based on cell structure, DNA fragmentation and flow cytometry studies. Camptothecin‐treated cardiomyocytes were shrunken with membrane blebs and nuclear fragmentation. Camptothecin produced a dose‐dependent increase in DNA fragments of 180 base pairs, or multiples thereof, which are characteristic of apoptosis. A two‐fold increase in this type of DNA fragmentation was produced by camptothecin (10 μM) compared to control (diluent‐treated) cells. Flow cytometry analysis of populations of 10,000 cardiomyocytes stained with propidium iodide demonstrated a significant increase in the proportion of the population with alterations of DNA content consistent with apoptosis. Pretreatment of cells with thapsigargin, which selectively inhibits sarcoplasmic reticulum and endoplasmic reticulum Ca +2 ‐dependent ATPase, significantly augmented camptothecin‐induced apoptosis. Exploring further the role of calcium in camptothecin‐induced cell death, we found that the Ca +2 chelator EGTA decreased camptothecin‐induced DNA fragmentation. These data indicate the potential for cardiotoxicity from camptothecin through the process of apoptosis and suggest that agents which affect cellular calcium regulation enhance camptothecin‐induced apoptosis.