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Published online by Cambridge University Press: 21 December 2023
In the United States, Alzheimer’s disease (AD) is the most common cause of dementia and the seventh leading cause of death. Exercise has demonstrated health benefits in older adults and reduces the risk of developing AD. Exploring underlying biological mechanisms of exercise could aid in identifying therapeutic targets to prevent AD progression, especially for high-risk individuals such as those with Mild Cognitive Impairment (MCI). Many studies of dementia focus on memory; however, executive function and processing speed are also vulnerable to the neuropathology that causes AD. This exploratory study aimed to identify potential mechanisms by which physical activity can facilitate change in cognitive functioning in older adults. This was accomplished by investigating correlations between changes in neurology-related plasma proteins and changes in measures of executive function and processing speed after participation in a water-based exercise intervention.
The sample included 20 older adults with amnestic MCI, ages 55-82 years (mean 68.15 ±7.75). Participants were predominately male (90%), White (70%), and non-Hispanic (85%), with more than high school education (95%). Participants engaged in supervised high-intensity water-based exercise three times per week for six months. Neuropsychological assessments and blood samples were assessed at baseline and after completion of the exercise intervention. Cognitive measures included: the Digit Span subtests from the Wechsler Adult Intelligence Scale, 4th Edition, Trail-Making Test (TMT), Stroop Color Word Test (SCWT), and the Symbol Digit Modalities Test (SDMT). Plasma protein levels were analyzed using the Olink Target 96 Neurology assay (Uppsala, Sweden), selected a priori for the established markers linked to neurobiological processes and diseases. Changes in cognitive measures and protein levels were assessed using paired-sample t-tests, and Pearson’s correlations were calculated for significant findings.
Participants’ cognitive performance significantly improved on the SCWT color trial (t = -2.19, p = 0.042) and SDMT (t = -2.17, p = .043). Significant decreases in plasma proteins levels were found for GDNF family receptor alpha-1 ([GFRA1]: t =2.05, p = 0.055), neuroblastoma suppressor tumorigenicity-1 ([NBL1]: t = 2.13, p= .046), and neuropilin-2 ([NRP2]: t = 2.61 p= 0.017). Correlational analyses showed reductions in NBL1 were significantly associated with changes in both SDMT (r = -.61, p = 0.006) and the color trial of SCWT (r = .48, p = .038), and NRP2 was significantly associated with improvement on the SDMT (r = -.46, p = 0.045). GFRA1 was not significantly associated with change on any cognitive measure.
In a sample of older adults with MCI, participation in high-intensity water-based exercise led to significant improvements in cognitive function as well as changes in neurological plasma proteome. Improved outcomes in processing speed, attention, visuospatial scanning, and working memory were associated with changes in specific plasma protein concentrations. This highlights potential activity-dependent neurobiological mechanisms that may underlie the cognitive benefits derived from physical activity. Future studies should explore these findings in Randomized Control Trials with a comparative condition and larger sample size.
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