Detection of oxidative DNA damage in lymphocytes of patients with Alzheimer's disease

Abstract

Oxidative damage to DNA may play an important role in both normal ageing and in neurodegenerative diseases. The deleterious consequences of excessive oxidations and the pathophysiological role of reactive oxygen species have been intensively studied in Alzheimer's disease. Although the role of oxidative stress in the aetiology of Alzheimer's disease is still not clear, the detection of an increased damage status in the cells of patients could have important therapeutic implications. The levels of oxidative damage in peripheral lymphocytes of 24 Alzheimer's disease patients and of 21 age-matched controls were determined by comet assay applied to freshly isolated blood samples with oxidative lesion-specific DNA repair endonucleases (endonuclease III for oxidized pyrimidines, formamidopyrimidine glycosylase for oxidized purines). It was demonstrated that Alzheimer's disease is associated with elevated levels of oxidized pyrimidines and purines (p<0.0001) as compared with age-matched control subjects. It was also demonstrated that the comet assay is useful as a biomarker of oxidative DNA damage when used with oxidative lesion-specific enzymes.

Nucleic acid oxidation in Alzheimer disease

“…Higher concentrations of oxidized pyridines and purines were detected in lymphocytes and leukocytes of AD patients compared with controls [6,[112][113][114], and increased levels of 8-oxoG were observed in DNA from ventricular CSF of AD patients [115]. Recent findings indicate increased oxidative damage in leukocytes [6] and brain tissue [17] of subjects with MCI, which suggests that DNA oxidation may constitute an early event in the progression of AD, before cytopathological alterations, and may contribute to the pathogenesis of the disease.…”

Evaluation of DNA Damage in the Lymphocytes of Young, Elderly and Alzheimer’s Disease Patients Treated with β-Estradiol in the Comet Assay

“…Oxidative stress represents the loss of balance between the processes of the creation of free radicals and those that are responsible for the removal of oxidized macromolecules (antioxidative cascade) which again leads to cellular dysfunction (changes in cellular homeostasis) and results in increased genomic instability and eventually in cell death (25). Most likely, the oxidative stress is the essence of a greater DNA damage compared to adequate control (18,26,27) as one of the initial factors that lead to further genomic instability (28)(29)(30). There is substantial evidence supporting the fact that genetic instability is increased in AD lymphocytes compared to corresponding controls.…”

Assessment of DNA Damage in the Peripheral Lymphocytes of Patients with Parkinson's Disease and Multiple Sclerosis Using the Comet Assay

“…[36][37][38][39] Studies related to the role of oxidative stress in neurodegenerative diseases are limited with patients with AD and several studies demonstrated elevated levels of oxidative DNA damage and an impairment in the removal of oxidized purines in the lymphocytes of patients with AD. [16][17][18][19] A significant increase of 8OHG and an oxidized amino acid (nitrotyrosine) were detected in neurons of patients with AD suggesting that increased oxidative damage is an early event in AD that decreases with the progression of the disease. 40 The level of oxidative damage and repair capacity in peripheral lymphocytes of AD patients and their age-matched controls was determined by the comet assay applied to freshly isolated blood samples with oxidative lesion-specific DNA repair endonucleases.…”

“…[11][12][13][14][15][16] A significantly higher levels of basal and oxidative DNA damage were found in the lymphocytes as well as in the polymorphonuclear leukocytes of patients with AD and with mild cognitive impairment (MCI). [17][18][19] Studies in patients with AD showed increased levels of 8-hydroxyguanosine (8OHG) or 8-hydroxy-2'-deoxyguanosine (8OHdG) in addition to decreased levels of plasma antioxidants as compared to controls. 5,11,17,[20][21][22][23] On the other hand, most studies on patients with AD have been performed in post-mortem tissues with advanced disease without clarifying whether oxidative stress is an early event or a common final step secondary to the degenerative process.…”

“…Only relatively small number of studies have been performed in living patients with AD suggesting that oxidative stress in AD is detectable not only in the central nervous system, but also in peripheral cells. 11,[17][18][19]24 PD which is characterized by a severe neurodegeneration of the mesencephalic dopaminergic neurons in the substantia nigra, is one of the most common neurodegenerative diseases affecting about 2% of the population over 60 years. 25 It causes extrapyramidal motor dysfunction as tremor, rigidity, and dyskinesia.…”