Many effects of sesamol, an antioxidative constituent of sesame oil, have been reported for human health
benefits due to its antioxidative action. However, we recently isolated two cytotoxic products, trimer and
tetramer of sesamol, from oxidation of sesamol by an assay-guided purification. In this study, we have
revealed some cytotoxic characteristics of these products in rat thymocytes and human leukemia K562
cells. Incubation of cells with trimer or tetramer at 10–30 lM for 24 h significantly increased cell lethality
and population of rat thymocytes containing hypodiploid DNA, suggesting cell death with DNA fragmentation,
while it was not the case for 30 lM sesamol. The cytotoxic action of tetramer was more potent
than that of trimer in rat thymocytes when their concentrations were 10–30 lM. The incubation of cells
with 10 lM tetramer for 24 h increased the population of cells with exposed phosphatidylserine, the
activity of caspases, and the nick of DNA. These results indicate tetramer-induced apoptosis. In K562 cells,
the incubation with tetramer at 10 lM for 72 h significantly inhibited the growth without affecting the
lethality. However, tetramer at 30 lM significantly increased cell lethality. It is likely that tetramer exerts
more cytotoxic action on normal non-proliferative cells (rat thymocytes) rather than proliferative cancer
cells (human leukemia K562 cells). It may be necessary to consider the condition for preservation of sesamol
and the safety of products from in vivo oxidation of sesamol for human health