Early and persistent alterations in prefrontal cortex MAO A and B in Alzheimer's disease

Both monoamine oxidase (MAO) A and MAO B in the brain have been implicated in the etiology of Alzheimer's disease. MAO B is elevated in plaque-associated glia in Alzheimer brain. Elevations in MAO A in Alzheimer neurons have been linked to increases in neurotoxic metabolites and neuron loss. We investigated the relationship between cognitive function in Alzheimer patients and post-mortem prefrontal cortex MAO A and B activities. Prefrontal cortex tissue from 92 Alzheimer patients and 74 neurologically normal subjects was obtained at autopsy and analyzed for activities of MAO A and B by radioenzymatic methods. Mini Mental Status Exam was performed on Alzheimer patients within 1 year of death. Alzheimer brains were analyzed for Braak stage, tangles, plaques and choline acetyltransferase activity. Prefrontal cortex MAO B activity was significantly increased by 16% in Alzheimer patients versus normals, whereas MAO A activity was significantly decreased by 17% in these same patients. Neither MAO A nor MAO B activities correlated with cognitive function (MMSE score), choline acetyltransferase activity, plaques, neurofibrillary tangles, Braak stage, or age of disease onset in the Alzheimer patients. With increasing Alzheimer duration or increasing Braak stage, MMSE scores and choline acetyltransferase activity declined, but levels of MAO A and B in prefrontal cortex were unchanged. Patients in the upper quintile for MAO A or B activity did not differ significantly from those in the lowest quintile with respect to MMSE scores or age of Alzheimer disease onset. We conclude that the changes in MAO A and B in the prefrontal cortex occur very early in Alzheimer's disease and remain relatively constant as the disease progresses.