OXIDATIVE STRESS IN AUTISM: EXPRESSION OF OXIDATIVE STRESS MARKERS IN A RAT MODEL OF THE HUMAN POSTMORTEM PROCESS

Background: Oxidative stress has been implicated in the autistic pathology. It is supported by our observations of increased levels of oxidative stress markers measured in the postmortem brains, that may be affected by the postmortem process.

Objectives: To evaluate potential contribution of artifacts due to the postmortem interval (PMI) and tissue handling on brain levels of oxidative stress markers.  

Methods: Using a rat model of human postmortem process we compared brain levels of 3-nitrotyrosine (3-NT) in tissue derived from rats exposed to (1) increasing PMI; (2) different storage temperatures; and  (3) between freshly dissected and previously frozen brain tissue. Weanling SD, WKY and SHR rats were euthanized by CO₂ asphyxiation. Cerebellum, brain stem, frontal and other cortical tissues were dissected out. The levels of 3-NT were measured in brain homogenates prepared in the presence of protease inhibitors by a commercial 3-NT ELISA.

Results: Remarkably, the PMI up to 4 hours either at 4^oC or at RT did not significantly affect cerebellar 3-NT levels ranging from 4-7 micromoles/gram. The most significant increase in 3-NT levels occurred between 4 and 8 hours at RT, with no further changes up to 24 hours at RT. On the other hand cortical regions appeared to be more sensitive to the PMI length and storage temperature with 7.8% increase at 4⁰C and 23.5% increase after 4 hours at RT.

Conclusions: Considering the relative mass of animals, that determines the rate of body cooling, the postmortem changes in oxidative stress markers are likely to be relevant only under extremely long PMIs (>48 hours) in humans. Furthermore, the postmortem process appears to be brain region-specific with the cerebellum being relatively spared. Thus our previous data on the increased oxidative stress damage in the autistic cerebellum measured in cases matched for PMI is most likely related to autistic pathology.