Styrene is the precursor of polystyrene. Human exposure to styrene could occur in
occupational and residential settings and via food intake. Styrene is
metabolized to styrene-7,8-oxide by cytochrome P450 enzyme. In the present
study, we investigated the cytotoxicity mediated by styrene and
styrene-7,8-oxide in TM3 testicular Leydig cells
in vitro
. We
first monitored the nuclear fragmentation in Leydig cells after exposure to
styrene or styrene-7,8-oxide. Hoechst 33258 cell staining showed that styrene
exposure in TM3 Leydig cells did not exhibit nuclear fragmentation at any
concentration. In contrast, nuclear fragmentation was seen in
styrene-7,8-oxide-exposed cells. These results indicate that
cytotoxicity-mediated cell death in Leydig cells is more susceptible to
styrene-7,8-oxide than to styrene. Following styrene treatment, procaspase-3 and
XIAP protein levels did not show significant changes, and cleaved (active) forms
of caspase-3 were not detected. Consistent with the western blot results, the
active forms of caspase-3 and XIAP proteins were not prominently altered in the
cytoplasm of cells treated with styrene. In contrast to styrene,
styrene-7,8-oxide induced cell death in an apoptotic fashion, as seen in
caspase-3 activation and increased the expression of XIAP proteins. Taken
together, the results obtained in this study demonstrate a fundamental idea that
Leydig cells are capable of protecting themselves from cytotoxicity-mediated
apoptosis as a result of styrene exposure
in vitro
. It remains
unclear whether the steroid-producing function, i.e., steroidogenesis, of Leydig
cells is also unaffected by exposure to styrene. Therefore, further studies are
needed to elucidate the endocrine disrupting potential of styrene in Leydig
cells.