The mechanism underlying
sodium arsenite (
arsenite)-induced neurotoxicity was investigated in rat brain.
Arsenite was locally infused in the substantia nigra (SN) of anesthetized rat. Seven days after infusion, lipid peroxidation in the infused SN was elevated and
dopamine level in the ipsilateral striatum was reduced in a concentration-dependent manner (0.3-5 nmol). Furthermore, local infusion of
arsenite (5 nmol) decreased GSH content and increased expression of
heat shock protein 70 and
heme oxygenase-1 in the infused SN. Aggregation of
alpha-synuclein, a putative pathological
protein involved in several CNS
neurodegenerative diseases, was elevated in the
arsenite-infused SN. From the breakdown pattern of
alpha-spectrin, both
necrosis and apoptosis were involved in the
arsenite-induced neurotoxicity. Pyknotic nuclei, cellular shrinkage and cytoplasmic disintegration, indicating
necrosis, and TUNEL-positive cells and
DNA ladder, indicating apoptosis was observed in the
arsenite-infused SN.
Arsenite-induced apoptosis was mediated via two different organelle pathways, mitochondria and endoplasmic reticulum (ER). For mitochondrial activation, cytosolic
cytochrome c and
caspase-3 levels were elevated in the
arsenite-infused SN. In ER pathway,
arsenite increased activating transcription factor-4,
X-box binding protein 1, C/EBP homologues
protein (CHOP) and cytosolic
immunoglobulin binding protein levels. Moreover,
arsenite reduced procaspase 12 levels, an ER-specific
enzyme in the infused SN. Taken together, our study suggests that
arsenite is capable of inducing oxidative injury in CNS. In addition to mitochondria, ER stress was involved in the
arsenite-induced apoptosis.
Arsenite-induced neurotoxicity clinically implies a pathophysiological role of
arsenite in CNS neurodegeneration.