Mutations of TP53 C708T and C748A, oxidative DNA damage, and p53 and OGG1 protein levels in peripheral lymphocytes of the people with Alzheimer's disease

Abstract

Background: We have previously reported an increased susceptibility to cell death of lymphocytes obtained from patients with Alzheimer’s disease (AD) when exposed to oxidative stress induced by hydrogen peroxide (H2O2). Herewe investigated whether the susceptibility to H 2 O 2 -induced death was related to the degree of dementia severity. Methods: Lymphocytes were extracted from peripheral blood from 25 AD patients (9 mildmoderate, CDR 1-2; 6 severe, CDR 3) and 10 healthy controls (all 60 years old) and exposed to H 2 O 2 for 20hrs in the presence or absence of 5 mM 3-aminobenzamide (3-ABA), a PARP-1 inhibitoror to staurosporine, an apoptosis inducer. Cell death was evaluated by flow cytometry and propidium iodide (PI) staining, whereby viable (PI-negative), apoptotic (PI-positive, hypodiploid) and necrotic (PI-positive diploid) cells were distinguished. Results: The dose response curve of lymphocyte viability in the presence of H2O2 was shifted to the left in AD patients compared to healthy controls, with severe dementia showing the highest vulnerability to H 2 O 2 and those with mild to moderate dementia showing intermediate values; i.e. treatment with 50 mM H 2 O 2 (around LD50) for 20 hrs induced death of 68.1% of lymphocytes from patients with severe dementia, 51.1% of those with mild to moderate dementia, and 34.6% of healthy control lymphocytes. The greater susceptibility to death was due to an increase mostly of apoptosis. Staurosporine, an apoptosis inducer, at concentrations between 0.6 6mM provoked death to a similar extent in the three groups of patients. As previously shown, H 2 O 2 -induced death was significantly reduced by PARP inhibition, whereby the extent of protection was less significant in lymphocytes from patients with severe dementia. Conclusions: We confirm our previous results showing that lymphocytes from AD patients are more susceptible to H2O2-induced death, whereby extent of death observed correlated with dementia severity. Moreover, increased susceptibility to death observed for AD lymphocytes was specific for oxidative damage, since no differences between groups were detectable with staurosporine, a kinase inhibitor. These results suggest that measurement of lymphocyte death induced by H 2 O 2 might be exploited to serve as a non-invasive biological marker of the severity of Alzheimer’s disease.