Objectives: To investigate tissue-dependent cerebral energy metabolism by measuring high energy phosphate levels in unmedicated adolescents diagnosed with bipolar I disorder.
Methods: Phosphorus-31 magnetic resonance spectroscopic imaging data were acquired over the entire brain of 24 adolescents with bipolar I disorder and 19 demographically matched healthy comparison adolescents. Estimates of phosphocreatine (PCr) and adenosine triphosphate (ATP, determined from the γ-resonance) in homogeneous gray and white matter in the right and left hemispheres of the cerebrum of each subject were obtained by extrapolation of linear regression analyses of metabolite concentrations vs. voxel gray matter fractions.
Results: Multivariate analyses of variance showed a significant effect of group on high energy phosphate concentrations in the right cerebrum (p=0.0002) but not in the left (p=0.17). Post-hoc testing in the right cerebrum revealed significantly reduced concentrations of PCr in gray matter and ATP in white matter in both manic (p=0.002 and 0.0001, respectively) and euthymic (p=0.004 and 0.002, respectively) bipolar I disorder subjects relative to healthy comparisons.
Limitations: The small sample sizes yield relatively low statistical power between manic and euthymic groups; cross-sectional observations limit the ability to determine if these findings are truly independent of mood state.
Conclusions: Our results suggest bioenergetic impairment - consistent with downregulation of creatine kinase - is an early pathophysiological feature of bipolar I disorder.
Keywords: (31)P MRS; Adolescent; Bioenergetics; Bipolar disorder.
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