Objective: To examine whether individuals with PD show greater temporal than frontal high energy phosphate metabolism (31P MRS ATP) that is similar or different from controls

Background: Dysfunctional mitochondria have been implicated in the pathophysiology of Parkinson disease.  We previously used 31P MRS to probe in vivo mitochondrial function in older adults and found greater temporal compared to frontal high energy phosphate (ATP) metabolism. This finding aligns with the high energy consumption of the temporal/hippocampal region.  In this study, we tested whether a similar pattern was present in nondemented PD.  Due to the hypodopaminergic influence of PD on frontal systems, we hypothesized that the temporal-frontal asymmetry would be enhanced in PD relative to controls.  Alternatively, in PD, there might be global blunting of ATP metabolism and we sought to eliminate this possibility.

Method: Twelve idiopathic PD and 70 controls underwent 31P MRS.  The groups were similar in age (early 70’s), education (college), and MoCA scores (26 for both). The PD group was tested off dopa medication and had the following baseline characteristics: duration 7.6 yrs [5.3], on-UPDRS-III of 18.1 [9.6], 67% tremor subtype.  To achieve optimal signal intensity, a single voxel method (bifrontal, left temporal) was used.  Mitochondrial function was estimated by computing a ratio for each voxel: summed ATP to total pooled phosphorous (ATP/TP). This ratio was corrected for voxel size and CSF fraction.  Data were analyzed using ANOVA’s and t-tests.

Results: Results revealed that a 31P MRS marker of phosphate metabolism (ATP/TP) was greater in the left temporal than bifrontal voxel for both PD (p = .004, h²_p = .505) and Controls (p < .001, h²_p = .200).  The groups did not differ in the magnitude of ATP/TP ratios from left temporal and bifrontal voxels (p=.275, d=-.386). However, overall ATP/TP metabolism was greater in controls than PD (p<.0001); though this result may be confounded by scanner differences.

Conclusion: PD participants showed greater ATP/TP metabolism in the temporal than bifrontal region. Magnitudes of findings were similar and consistent with non-PD controls. This study provides preliminary data supporting potential integrity of mesial temporal systems in regional phosphate metabolism.  Future studies should examine how this pattern changes with disease progression to PD-MCI and dementia.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/patterns-of-parkinson-disease-mitochondrial-brain-function-indexed-by-31p-magnetic-resonance-spectroscopy/