[P2–257]: ALBUMIN OXIDATION STATUS IN CSF AND PLASMA SAMPLES FROM ALZHEIMER's DISEASE PATIENTS

Beyond its well-documented role as plasma expander, albumin is the main transporter (e.g., β-amyloid, lipids, free metals and reactive oxygen and nitrogen species) and antioxidant (through a Cys34 residue that can be oxidized) in the human body. In Alzheimer's disease (AD) oxidative stress in brain and peripheral system is considered a major issue. Currently, there is a new therapeutic approach under study for AD (AMBAR Trial, NCT01561053) that includes plasma exchange and replacement with therapeutic albumin (Albutein®, Grifols). In the present study, albumin oxidation status was assessed in both CSF and plasma from AD patients, in comparison with age-matched controls. CSF and plasma samples from AD patients (n=34–37) and age-matched controls (n=10–31) were evaluated. Oxidation status of albumin on Cys34 thiol group was analysed by anionic-exchange chromatography coupled to a fluorescent detector (values expressed as % peak height, median-IQR). Whole post-translational modifications analysis was assessed on the intact mass protein by ultra-high performance liquid chromatography coupled to high resolution mass spectrometry (MS) (values expressed as % relative intensity, median-IQR). The reduced form of albumin (HMA) of CSF from AD patients was significantly decreased when compared with controls (9.6% [6.6%-17.4%] and 67.1% [47.2%-79.9%] respectively, p<0.0001). Interestingly, this marked difference was not observed in plasma samples, although a decrease in HMA content in AD group was also detected (AD 54.1% [47.4%-58.6%] vs. controls 65.4% [63.3%-67.3%], p<0.0001). Of note, the reduced albumin form was remarkably decreased in CSF versus plasma in AD patients, while not in controls. These results were further confirmed by MS, when considering the native form of albumin with the reduced thiol group: CSF (AD (n=11) 28.5% [21.7%-32.0%] vs. controls (n=10) 57.4% [56.8%-60.2%], p<0.001) and plasma (AD (n=9) samples (38.0% [31.6%-43.3%] vs. controls (n=10) 49.0% [45.2%-51.8%], p<0.01). These results show for the first time strong differences in albumin oxidation in the CSF of AD cases compared to controls, which are markedly attenuated in the plasma. Our data confirms that oxidative stress is involved in AD and supports the need of further research to better understand the role of albumin in this pathology.