Altered brain metabolites in Parkinson's disease patients

Whole brain NMR spectroscopic imaging has revealed altered levels of certain metabolites in the brains of patients with Parkinson's disease, with increased amounts of creatine particularly notable, say scientists at the University of Miami and its Medical School. Senior reporter Bonnie Levin and colleagues measured the changes in concentrations of several metabolites over a large portion of the brain, including the cortical regions, in the first study of its type using volumetric magnetic resonance spectroscopic imaging, as described in Journal of Neuroimaging. The studies were carried out in conjunction with neuropsychological testing of the 12 patients, who were tested along with 18 controls.

The levels of total creatine (the sum of creatine and phosphocreatine), total choline (the sum of choline, phosphocholine, and glycerophosphocholine) and the neuronal marker N-acetylaspartic acid (NAA) were measured in the grey and white matter of each brain region. The researchers discovered that the ratios of NAA to total creatine and of total choline to total creatine were both reduced in bilateral temporal grey matter compared with the controls, and creatine was increased in right temporal grey matter. This marked increase in creatine might be caused by neuronal degeneration or increased neuronal energy use but it was not possible to deduce which mode of action was dominant at this stage.

Three significant correlations were observed between the cognitive tests and the altered metabolite levels, but none were described as "meaningful." For example, the choline/creatine ratio correlated with the symbol digit modality test [which measures the time to pair abstract symbols with specific numbers] in the temporal lobes. The same metabolite ratio correlated with the Beck depression inventory, which is a measure of depression. However, for all three correlations "interpretation is limited by the lack of a meaningful pattern and the small sample size."

Nevertheless, the study has shown the capabilities of the NMR imaging technique for this type of brain research. Levin concluded: "Future work is needed to replicate our findings and better define the relationship between regional alterations of individual magnetic resonance spectroscopy-observed metabolites and the cognitive and motor changes that characterize Parkinson's disease."