Micronucleus formation, proliferative status, cell death and DNA damage in ethosuximide-treated human lymphocytes

Abstract

Ethosuximide is a T-type Ca2+ channel blocker that has been used as an anticonvulsant to treat absence seizures. Because no data have yet been reported on the cytotoxicity, genotoxicity and cell death effects of this drug, we have investigated ethosuximide-treated human lymphocytes with Fenech's CBMN (cytochalasin-blocked micronucleus cytome) assay and single-cell gel electrophoresis (comet assay). The tests allowed us to examine micronucleus formation, the proliferative status of the viable cells, nuclear blebbing, nucleoplasmic bridge formation, cell death (CBMN assay) and DNA damage (comet assay). The lymphocytes were treated for 24 h with 25, 50 or 100 μg/ml ethosuximide. The cells used for the CBMN assay were examined either immediately or 24 h after the cytochalasin blockade. For the comet assay, cells were examined immediately or 22 h after 2 h ethosuximide treatment. The results indicate that 25 and 50 μg/ml ethosuximide did not induce micronucleus formation, nuclear abnormalities, cell death or DNA damage, nor did they affect cell proliferation, suggesting no cytotoxic or genotoxic effects under such experimental conditions. However, under treatment with 100 μg/ml ethosuximide, an increase in micronucleus formation and nuclear abnormalities, but a decrease in cell proliferation and in DNA damage, and no change in the cell death ratio, were detected. Although apparently contradictory, the data obtained with the 100 μg/ml concentration may indicate that induction of cytotoxicity and genotoxicity are not to be disregarded when considering this drug concentration. The mechanisms underlying the cellular response to ethosuximide remain to be explored.