P11 expression and PET in bipolar disorders

Background: Bipolar disorder (BD) is a common mental disorder, subdivided into BD-I and BD-II. Currently, few biomarkers differentiate BD-I from BD-II. However, it is suggested that peripheral blood mononuclear cell (PBMC) mRNA levels of p11 and positron emission tomography (PET) might be potential biomarkers for BD. Methods: Healthy controls (HCs), BD-I, and BD-II patients in remission (n = 20 in each group) underwent a resting PET study with the radiotracer [ ¹⁸F]-2-deoxy-2-fluoro-d-glucose ( ¹⁸F-FDG). PBMC p11 mRNA levels were determined by quantitative real-time PCR. Results: Comparing BD patients to HCs, normalized glucose metabolism (NGM) was higher in the hippocampus, parahippocampus, and amygdala, but lower in the anterior cingulate cortex (aCC), medial prefrontal cortex (mPFC), dorsolateral prefrontal cortex (dlPFC), insula and thalamus. Compared to BD-II, BD-I had hypometabolism of glucose in the aCC, bilateral middle and inferior gyrus, insula and striatum, and hypermetabolism of glucose in the left parahippocampus. PBMC p11 mRNA was over-expressed in both BD-I and BD-II, although there was no significant difference in its expression levels between BD-I and B-II patients. Further, there were significant positive correlations between PBMC p11 mRNA and NGM in the mPFC, aCC, left insula, bilateral orbitofrontal cortex (OFC), and left middle, inferior and superior temporal gyri. Also, PBMC p11 mRNA was positively correlated to the number of depressive episodes in BD patients, especially in BD-I patients. Discussion: This study demonstrates that PBMC p11 mRNA expression is associated with neural activation in the brain of BD patients and warrants a larger translational study to determine its clinical utility.