Clioquinol has been implicated as a causative agent for subacute myelo-optico-neuropathy (SMON) in humans, although the mechanism remains to be elucidated. In this study, we utilized astrocyte-derived cell line, KT-5 cells to explore its potential cytotoxicity on glial cells. KT-5 cells were exposed in vitro to a maximum of 50 μM
clioquinol for up to 24 h. 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenylte trazolium
bromide (MTT) assay of the cells revealed that
clioquinol induced significant cell damage and death. We also found that
clioquinol caused accumulation of
microtubule-associated protein light chain-3 (LC3)-II and sequestosome-1 (p62) in a dose- and time-dependent manner, suggesting the abnormality of autophagy-lysosome pathway. Consistent with these findings, an exposure of 20 μM
clioquinol induced the accumulation of cellular autophagic vacuoles. Moreover, an exposure of 20 μM
clioquinol provoked a statistically significant reduction of intracellular lysosomal
acid hydrolases activities but no change in lysosomal pH. It also resulted in a significant decline of intracellular
ATP levels, enhanced cellular levels of
reactive oxygen species, and eventually cell death. This cell death at least did not appear to occur via apoptosis. 10 μM
Chloroquine, lysosomal inhibitor, blocked the autophagic degradation and augmented
clioquinol-cytotoxicity, whereas
rapamycin, an inducer of autophagy, rescued
clioquinol-induced cytotoxicity. Thus, our present results strongly suggest
clioquinol acts as a potentially
cytotoxic agent to glial cells. For future clinical application of
clioquinol on the treatment of neurological and
cancer disorders, we should take account of this type of cell death mechanism.