Effect of Storage Time, Postmortem Interval, Agonal State, and Gender on the Postmortem Preservation of Glial Fibrillary Acidic Protein and Oxidatively Damaged Proteins in Human Brains

Biochemical analyses of many brain diseases have highlighted that oxidative damage of proteins and astrogliosis are important events associated with pathology. However, human studies on the status of protein oxidation/nitration and astrogliosis [indicated by expression of glial fibrillary acidic protein (GFAP)] heavily depend on postmortem tissues that might be altered by pre and postmortem factors. To evaluate the effect of these variables, we tested whether the status of GFAP expression, oxidized proteins, and nitrated proteins (by protein 3-nitrotyrosine or 3-NT) were affected in postmortem human brains (n = 48) by increased storage time (11.8-104.1 months), postmortem interval (PMI) (2.5-26 h), gender difference, and agonal state (based on Glasgow coma scale: range: 3-15) in different anatomical regions-frontal cortex (FC), cerebellum (CB) and medulla oblongata (MD). We observed that increasing storage time significantly decreased the stability of all 3 markers in MD (oxyblot: P = 0.003; 3-NT: P = 0.01; GFAP: P = 0.03) and that of oxidized proteins in CB (P = 0.04), whereas the status of all markers was not significantly altered in FC. On the other hand, PMI and agonal state did not influence the status of all the markers tested in any of the regions. Similarly, except for the decreased protein 3-NT among women in CB compared with men (P = 0.04), there was no effect due to gender differences in other brain regions for other markers. These data highlight the influence of storage time on preservation of markers of protein damage and astrogliosis and the inherent differences in brain regions, with implications for studies on brain pathology employing stored human samples.