DIFFERENTIAL EFFECT OF AMYLOID BETA ON THE CYTOCHROME P450 EPOXYGENASE ACTIVITY IN RAT BRAIN

One of the prominent features of Alzheimer's disease is the excessive accumulation of the protein amyloid beta (A beta) in certain areas of the brain leading to neurodegeneration. A beta is cytotoxic and disrupts several cytoprotective pathways. Recent literature has demonstrated that certain cytochrome P450 (CYP) products are neuroprotective, including epoxide metabolites of arachidonic acid (AA), epoxyeicosatrienoic acids (EETs). The action of A beta with respect to regionally produced EETs in the brain has yet to be defined. Epoxygenases metabolize AA into four regioisomers of EETs (14,15-, 11,12-, 8,9- and 5,6-EET). EETs are rapidly degraded into dihydroxyeicosatrienoic acids (DiHETEs) by soluble epoxide hydrolase (sEH). To determine the effect of A beta on the epoxygenase activity in different regions of the brain, microsomes were prepared from the cerebrum and cerebellum of adult Sprague-Dawley rats and incubated with 1 and 10 mu M A beta for 30 min after which epoxygenase activity assay was performed. Mass spectrometry indicated that incubation with A beta reduced 14,15-EET production by 30% as compared to vehicle in the cerebrum, but not in the cerebellum. When we separated the cerebrum into cortex and hippocampus, significant decrease in the production of total EETs and DiHETEs were seen in presence of A beta (81% and 74%) in the cortex. Moreover, 11,12-EET production was decreased to similar to 70% of vehicle in both cortex and hippocampus. Epoxygenase activity in the cultured astrocytes and neurons also showed reduction in total EET and DiHETE production (to 80% and similar to 70% of vehicle respectively) in presence of Ap. Altogether, our data suggest that A beta reduces epoxygenase activity differentially in a region-specific and cell-specific manner. The reduction of cytoprotective EETs by A beta in the cerebrum may make it more prone to degeneration than the cerebellum. Further understanding of these interactions will improve our ability to protect against the pathology of Alzheimer's disease. (C) 2011 IBRO. Published by Elsevier Ltd. All rights reserved.