Resistance of human cerebrospinal fluid to in vitro oxidation is directly related to its amyloid-beta content

Amyloid-beta (A beta) peptide, a major constituent of senile plaques and a hallmark of Alzheimer's disease (AD), is normally secreted by neurons and c an be found in low concentrations in cerebrospinal fluid (CSF) and plasma w here it is associated with lipoproteins. However, the physiological role of A beta secretion remains unknown. We measured the resistance to in vitro o xidation of CSF obtained from 20 control subjects and 30 patients with AD, and correlated it with CSF levels of antioxidants, lipids and A beta. We fo und that the oxidative resistance, expressed as a duration of the oxidation lag-phase, was directly related to CSF levels of A beta (1-40), A beta (1- 42) and ascorbate and inversely to levels of fatty acids. These data sugges t that, besides ascorbate, A beta is another major physiological antioxidan t for CSF lipoproteins.