Polychlorinated biphenyls (PCB) are persistent environmental contaminants whose chronic exposure can affect nervous system development and function. The cellular and molecular mechanisms underlying neuronal damage are not yet clear. In the present study, we investigated whether
nitric oxide (NO) could be involved in
aroclor 1254 (A1254; a PCB mixture)-induced cytotoxicity in SH-SY5Y human
neuroblastoma cells. Prolonged exposure (24 hr) to A1254 (10-100 microg/ml) caused a dose-dependent reduction of cell viability that was attenuated in the presence of a
calcium entry blocker, gadolinum (
Gd(3+))
at 10 microM, a concentration able to block voltage-sensitive
calcium channels. In addition, A1254 caused an increase of cytosolic
calcium that was dependent on extracellular
calcium, as measured by
fura-2 videomicroscopy. A1254-induced
calcium rise may stimulate NO production through an activation of neuronal NOS (nNOS). Indeed, the concomitant addition of the selective nNOS inhibitor
N(omega)-propyl-L-arginine (NPLA) and A1254 prevented cell injury, suggesting that NO production plays a major role in A1254-evoked cell injury. Furthermore, the exposure (14 hr) to A1254 (30 microg/ml) produced an up-regulation of the expression of beta
isoform of nNOS. This up-regulation was
calcium dependent and was accompanied by an enhancement of NO production as demonstrated by an increase of
nitrite formation. Moreover, A1254-induced cell injury was prevented when
KT 5823, a selective cGMP/PKG inhibitor, was added concomitantly to 30 microg/ml A1254. These results suggest that PCB-induced cell death in
neuroblastoma cells is mediated by an activation of the cGMP/PKG pathway triggered by NO production.