Semi-quantitative Assessment of Alzheimer's-like Pathology in Two Aged Polar Bears (Ursus maritimus)

Age-associated neurodegenerative changes, including amyloid beta (A beta) plaques, neurofibrillary tangles (NFTs), and amyloid angiopathy comparable to those seen in the brains of human patients with Alzheimer's disease (AD), have been reported in the brains of aged bears. However, the significance of these findings in bears is unclear due to the difficulty in assessing cognitive impairment and the lack of standardized approaches for the semiquantitative evaluation of A beta plaques and NFTs. In this study, we evaluate the neuropathologic changes in archival brain tissue of 2 aged polar bears (Ursus maritimus, ages 28 and 37) using the National Institute of Aging-Alzheimer Association (NIA-AA) consensus guidelines for the neuropathologic assessment of Alzheimer's Disease (AD). Both bears had an A beta (A) score of 3 of 3, Braak stage (B score) of 2 of 3, and neuritic plaque (C) score of 3 of 3. These findings are consistent with the neurodegenerative changes observed in brains of patients with AD. The application of NIA-AA consensus guidelines, as applied to the neuropathologic assessment of the aged bears in this report, demonstrates the use of standardized semiquantitative assessment systems for comparative, translational studies of aging in a vulnerable wildlife species.