Biomarkers that predict suicidal behavior, especially highly lethal behavior, are urgently needed. In cross-sectional studies, individuals with depression who attempt suicide have lower midbrain serotonin transporter binding potential compared with those who do not attempt suicide, and higher serotonin1A binding potential in the raphe nuclei (RN) is associated with greater lethality of past suicide attempts and suicidal intent and ideation.
To determine whether serotonin transporter binding potential in the lower midbrain predicts future suicide attempts and whether higher RN serotonin1A binding potential predicts future suicidal ideation and intent and lethality of future suicide attempts.
Design, Setting, and Participants
In this prospective 2-year observational study, a well-characterized cohort of 100 patients presenting for treatment of a major depressive episode of at least moderate severity underwent positron emission tomography using carbon 11–labeled N-(2-(1-(4-(2-methoxyphenyl)-1-piperazinyl)ethyl))-N-(2-pyridyl)-cyclohexanecarboxamide ([11C]WAY-100635), a serotonin1A antagonist; a subset of 50 patients also underwent imaging with carbon 11–labeled 3-amino-4-(2-dimethylaminomethyl-phenylsulfanyl)- benzonitrile ([11C]DASB), a serotonin transporter radioligand. Imaging was performed at Columbia University Medical Center from May 3, 1999, to March 11, 2008. Follow-up was completed on May 28, 2010, and data were analyzed from August 1, 2013, to March 1, 2016.
Patients were treated naturalistically in the community and followed up for 2 years with documentation of suicidal behavior, its lethality, and suicidal ideation and intent.
Main Outcomes and Measures
Suicide attempt or suicide.
Of the 100 patients undergoing follow-up for more than 2 years (39 men; 61 women; mean [SD] age, 40.2 [11.2] years), 15 made suicide attempts, including 2 who died by suicide. Higher RN serotonin1A binding potential predicted more suicidal ideation at 3 (b = 0.02; t = 3.45; P = .001) and 12 (b = 0.02; t = 3.63; P = .001) months and greater lethality of subsequent suicidal behavior (b = 0.08; t = 2.89; P = .01). Exploratory analyses suggest that the serotonin1A binding potential of the insula (t = 2.41; P = .04), anterior cingulate (t = 2.27; P = .04), and dorsolateral prefrontal cortex (t = 2.44; P = .03) were also predictive of lethality. Contrary to our hypotheses, suicidal intent was not predicted by serotonin1A binding potential in any brain region (F1,10 = 0.83; P = .38), and midbrain serotonin transporter binding potential did not predict future attempts (log-rank χ21 = 0.4; P = .54), possibly owing to low power.
Conclusions and Relevance
Greater RN serotonin1A binding potential predicted higher suicidal ideation and more lethal suicidal behavior during a 2-year period. This effect may be mediated through less serotonin neuron firing and release, which affects mood and suicidal ideation and thereby decision making.