The
beta amyloid (Abeta), the major
protein component of brain
senile plaques in
Alzheimer's disease, is known to be directly responsible for the production of
free radicals toxic to brain tissue and the redox state of Met-35 residue seems to play a particular and critical role in
peptide's neurotoxic actions. In this study, we investigated, in human
neuroblastoma cells (IMR-32), the relationship between the oxidative state of
methionine, and both neurotoxic and pro-apoptotic actions induced by Abeta-
peptide, comparing the effects of native
peptide, in which the Met-35 is present in the reduced state, with those of a modified
peptide with oxidized Met-35 (Abeta(1-42)(35Met-ox)), as well as an Abeta-derivative with Met-35 substituted with
norleucine (Abeta(1-42)(35Nle)). The obtained results show that Abeta induces a time-dependent decrease in cell viability; Abeta(1-42)(35Met-ox) was significantly less potent, though inducing a remarkable decrease in cell viability compared to control. On the contrary, no toxic effects were observed
after treatment with Abeta(1-42)(35Nle). Abeta-
peptide as well as the
amyloid modified
peptide with oxidized Met-35 induced the pro-apoptotic gene bax over-expression after 24 h, whereas Abeta(1-42)(35Nle) had no effect. Conversely, bcl-2, an anti-apoptotic gene, became highly down-regulated by Abeta
peptide treatment, in contrast to that evidenced by the Abeta(1-42)(35Met-ox)
peptide. Finally, Abeta caused an increase in
caspase-3 activity to be higher with respect to that shown by Abeta(1-42)(35Met-ox) while Abeta(1-42)(35Nle) had no effect. These results support the hypothesis that Abeta-induced neurotoxicity occurs via bax over-expression, bcl-2 down-regulation, and
caspase-3 activation, first indicating that
methionine 35 redox state may alter this cell death pathway.