Isolated Erythrocyte Membrane Susceptibility to Photo-oxidative Stress in Alzheimer's Disease

• Malondialdehyde assay [ Time Frame: At the time of recruitment ]
  Isolated and purified red blood cell membranes will be in vitro exposed to oxidative stress by UV-B radiation. The extent of cell membrane damage will be quantified by the fluorometric determination of malondialdehyde.
  
  

• Relationship between urinary excretion of cortisol and levels of malondialdehyde [ Time Frame: At the time of recruitment ]
  Hyperactivity of the hypothalamic pituitary adrenal axis has been frequently described in Alzheimer's disease. Recently published work reported an association between high secretion of cortisol and oxidative stress. We will investigate the relationship between 24 h excretion of urinary cortisol and the level of malondialdehyde, produced by isolated and purified red blood cell membranes, in vitro exposed to oxidative stress by UV-B radiation.
  
  

The study hypothesis is that high lipid peroxidation and decreased antioxidant defenses characterize the natural history of Alzheimer's disease.

It will be evaluated the release of malondialdehyde (MDA) from ex-vivo photo-oxidized erythrocyte ghosts, through a very easy and convenient lab procedure for the preparation of erythrocyte membrane samples.

Isolated and purified red blood cell membranes will be in vitro exposed to oxidative stress by UV-B radiation. The extent of cell membrane damage will be quantified by the fluorometric determination of MDA.

Induction of oxidative stress through ultraviolet rays, unlike that obtained by chemical oxidizing agents, is fully controllable, since it produces effects only during irradiation. Moreover, using isolated erythrocyte membranes allows for a greater specificity in the evaluation of MDA produced, and reduces the amount of blood required for the assay.

A portion of the blood sample (500 µL) will be sent to the laboratory of Lipinutragen (spin-off of CNR- National Research Center Bologna, Italy) where an erythrocyte membrane lipidomic analysis will be performed for the characterization of membrane phospholipids, in order to determinate the different lipid components (saturated fatty acids, monounsaturated and polyunsaturated, trans fatty acids), each one characterized by a different oxidative reactivity.

Recently published papers showed a striking association between urinary excretion of cortisol and the increase of some markers of oxidative damage of DNA and RNA (in humans). This finding provides further support to the idea that chronic psychological stress, who is associated to hypercortisolemia, can lead to an acceleration of the aging process.

The brain is a major target of the effects of glucocorticoids (CCS). The harmful consequences of cortisol on the hippocampus (one of the first brain areas affected by Alzheimer's disease) are well known. Some studies showed inverse correlations between cortisol levels and neuropsychological performance in patients with depression, dementia as well as in people treated chronically with CCS.

Alzheimer's disease is associated with states of hypercortisolism. Nonetheless, so far, its correlation with the level of oxidative stress has not been studied. We will investigate the relationship between 24h excretion of urinary cortisol and the level of malondialdehyde, produced by isolated and purified red blood cell membranes, in vitro exposed to oxidative stress by UV-B radiation.