Shank3 as a potential biomarker of antidepressant response to ketamine and its neural correlates in bipolar depression

BackgroundShank3, a post-synaptic density protein involved in N-methyl-d-aspartate (NMDA) receptor tethering and dendritic spine rearrangement, is implicated in the pathophysiology of bipolar disorder. We hypothesized that elevated baseline plasma Shank3 levels might predict antidepressant response to the NMDA receptor antagonist ketamine.MethodsTwenty-nine subjects with bipolar depression received a double-blind, randomized, subanesthetic dose (.5 mg/kg) ketamine infusion. Of the patients for whom Shank3 levels were collected, 15 completed baseline 3-Tesla MRI and 17 completed post-ketamine [18F]-FDG PET.ResultsHigher baseline Shank3 levels predicted antidepressant response at Days 1 (r=−.39, p=.047), 2 (r=−.45, p=.02), and 3 (r=−.42, p=.03) and were associated with larger average (r=.58, p=.02) and right amygdala volume (r=.65, p=.009). Greater baseline Shank3 also predicted increased glucose metabolism in the hippocampus (r=.51, p=.04) and amygdala (r=.58, p=.02).LimitationsLimitations include the small sample size, inability to assess the source of peripheral Shank3, and the lack of a placebo group for baseline Shank3 levels and comparative structural/functional neuroimaging.ConclusionsShank3 is a potential biomarker of antidepressant response to ketamine that correlates with baseline amygdala volume and increased glucose metabolism in the amygdala and hippocampus.