Psychiatrists at the University of Manchester, in the UK, have identified a link between suicidal ideation and neuroinflammation in patients with major depressive disorder (MDD). Using PET scans, they were able to detect elevated levels of microglial activity (an indication of brain inflammation) in individuals with suicidal thoughts.
They now think that neuroinflammation could increase the risk of suicidal thinking and behavior.
This supports earlier research, showing "that there is evidence for inflammation, more specifically microglial activation, in the brains of living patients during a major depressive episode," Peter Talbot, from the Division of Neuroscience and Experimental Psychology at the University of Manchester, said in a statement.
Whereas older studies have looked at brain tissues collected from suicidal patients post-mortem, this is the first to establish a connection in living patients.
Sophie Holmes, first author of the study published in Biological Psychiatry, and colleagues analyzed the levels of translocator protein (TSPO) in fourteen patients who had been diagnosed with moderate to severe depression but weren't taking antidepressants. TSPO is involved in immune response and cell death. Higher levels of the protein is a tell-tale sign that the microglia are activated – something that shouldn't happen under healthy conditions.
Scientists compared their results to those from a control group of thirteen healthy individuals. Then, in a post hoc analysis, they compared levels of TSPO in patients with suicidal thoughts to those without.
Patients experiencing suicidal thinking showed significantly higher levels of TSPO and microglial activity than those without and the healthy test subjects.
The most severe brain inflammation took place in the anterior cingulate cortex. Importantly, this is a part of the brain that helps to regulate mood. Abnormal activity to a lesser amount was also noticed in the insula and prefrontal cortex. These regions play a role in emotions, memory, and forward planning.
"This paper is an important addition to the view that inflammation is a feature of the neurobiology of a subgroup of depressed patients, in this case, the group with suicidal ideation," said John Krystal, Editor of Biological Psychiatry.
"This observation is particularly important in light of recent evidence supporting a personalized medicine approach to depression, i.e., that anti-inflammatory drugs may have antidepressant effects that are limited to patients with demonstrable inflammation."
These results "emphasize the importance of further research into the question of whether novel treatments that reduce microglial activation may be effective in major depression and suicidality," adds Talbot.