Measuring Differences in Brain Metabolism Between Older and Younger Adults

• Anthony Nguyen, Cognitive Science, University of Delaware

• Kevin Decker, , University of Delaware
• Christopher Martens, , University of Delaware

Adenosine triphosphate (ATP) is a critical metabolite, serving as the main energy source for all cells. The phosphocreatine (PCr) system regenerates ATP by donating inorganic phosphate (Pi) from PCr to adenosine diphosphate using creatine kinase. While aging is known to reduce peripheral levels of PCr, less is known about age-related changes in brain PCr. Further, aging is known to reduce cerebral blood flow (CBF), which may affect brain energy metabolism by influencing the delivery and clearance of energy substrates. The purpose of this pilot study was to test the hypothesis that older adults would have lower CBF and brain energy metabolism compared to younger adults. Younger adults (18-35 years) and middle-aged/older adults (50-80 years) underwent MRI brain scans to measure CBF via pseudo-continuous arterial spin labeling (pc-ASL) and to measure brain energy metabolism via phosphorus-31 magnetic resonance spectroscopy (³¹P-MRS). Brain metabolite concentrations of PCr, ATP, and Pi were measured to quantify the ratios of PCr/ATP, Pi/ATP, and PCr/Pi. Differences in CBF and brain energy metabolites were assessed between younger and older adults using unpaired t-tests. In this pilot study, we recruited 9 younger adults (25 ± 5 years; 6 males, 3 females) and 6 middle-aged/older adults (61± 4 years; 3 males, 3 females). Resting CBF (Younger: 68.8 ± 13.6; Older: 67.1± 16.5 ml/100g/min; p = 0.64), PCr/ATP (p = 0.15), and Pi/ATP (p = 0.66) were similar between the groups. However, PCr/Pi tended to be lower in middle-aged/older adults (Younger: 3.526 ± 0.4887; Older: 3.140 ± 0.2759; p = 0.07), suggesting that ATP resynthesis may differ between age groups. A larger sample size is needed to verify our findings. Future research directions will focus on detecting changes in brain energy metabolites, like PCr and Pi, between sex and racial groups, and explore whether brain energy metabolism relates to cognitive function.