Translocator Protein Levels in Brain Predict Response to Anti-Inflammatory Celecoxib in Major Depressive Disorder
Gliosis describes changes in glia that result from damage to the central nervous system. Researchers can use PET scans (positron emission tomography) to measure the extent of gliosis in the brain. But a new study explored whether these PET scans could instead be used to determine who might respond to a given medication.
Researcher Sophia Attwells and colleagues reported in the journal Biological Psychiatry in 2020 that people with high levels of translocator protein (TSPO), a measure of gliosis and inflammation, had a better antidepressant response to the anti-inflammatory drug celecoxib than patients who started out with lower levels of TSPO.
The study participants, who had treatment-resistant depression, all received 200mg of the anti-inflammatory drug celecoxib twice/day for eight weeks on an open (non-blind) basis. Before they began taking celecoxib, the participants received PET scans to measure translocator protein total distribution volume (TSPO VT) in the prefrontal cortex and the anterior cingulate cortex.
Patients with high levels of TSPO showed greater reductions in depression ratings over the course of the study than those with normal levels of TSPO at baseline.
Attwells and colleagues conclude that “this personalized medicine approach of matching a marker of gliosis to [an anti-inflammatory treatment] …should be applied in early development of novel therapeutics, in particular for [treatment-resistant depression].”
Editor’s Note: These findings are of considerable importance, as they are among the first to indicate that measures of inflammation may predict response to an anti-inflammatory medication such as celecoxib. In a 2013 article in the journal JAMA Psychiatry, Charles L. Raison and colleagues reported that patients with high levels of the peripheral inflammatory marker CRP saw marked improvement in their depression when they received the anti-inflammatory treatment infliximab while those with lower or normal levels of inflammation actually worsened.
Longer Periods of Untreated Depression Linked to More Brain Inflammation
A 2018 study by researchers Elaine Setiawan, Sophia Attwells and colleagues reports that inflammation seems to increase with duration of untreated unipolar depression. This implies that depression may be a progressive illness, and later stage depression may require different treatments than early stage depression, such as those that directly target inflammation.
The study published in the journal The Lancet Psychiatry used positron emission tomography (PET scan) to examines levels of translocator protein in the brain. Higher levels of translocator protein indicate activation of microglia, the brain’s immune cells, which can respond to trauma or injury.
The study included 80 participants between the ages of 18 and 75. Ten had a history of more than 10 years of depression, ten had experienced fewer than 10 years of depression, and 30 comprised a healthy comparison group.
The best predictors of high levels of translocator protein were duration of untreated major depressive disorder, total illness duration, and duration of antidepressant exposure. These three factors explained about half of the variation in translocator protein levels. Those participants whose depression went untreated for 10 years or longer had inflammation levels 29–33% higher than those whose depression was untreated for 9 years or less.
Participants who had received antidepressant treatment appeared to avoid an average yearly increase in the extent of their microglial activation.
The study took place at Canada’s Centre for Addiction and Mental Health.
Editor’s Note: Since inflammation is a predictor of poorer response to antidepressants, these data add a further neurochemical rationale to the already strong clinical rationale for earlier and more sustained antidepressant treatment and prevention. Virtually all treatment guidelines suggest that after two or three prior unipolar depressions, patients should receive long-term (lifelong) antidepressant treatment.
There is now a large body of data, including a 2012 article by this editor Robert M. Post and colleagues in the Journal of Psychiatric Research that too many episodes can hurt the brain, and the current study adds to this perspective. Avoiding preventive treatment for too long may actually foster the development of more episodes and more treatment resistance. A good mantra is “prevent episodes, protect the brain.”
Consensus is now also building that comprehensive long-term treatment is indicated after a first manic episode. A 2013 article by Lars Kessing and colleagues in the British Journal of Psychiatry suggested that high quality initial treatment can improve the long-term course of illness. Moreover, a 2016 article by Jan-Marie Kozicky and colleagues and a 2017 article by Christine Demmo and colleagues, both in the journal Bipolar Disorders, suggest that after a first mania, cognition recovers over the next year only if no further episodes occur in that time.
Depression and Suicidal Thoughts Linked to Brain Inflammation
A 2017 article by Sophie E. Holmes and colleagues in the journal Biological Psychiatry reports that people with major unipolar depression, especially those with suicidal thoughts, have higher levels of the inflammatory marker translocator protein than do healthy individuals.
The participants with depression and suicidal thinking had high levels of translocator protein in the anterior cingulate cortex, which suggests that inflammation is affecting microglia.
Many studies have found links between different indicators of inflammation and mood disorders, leading researchers to speculate whether targeting the immune system could be an effective way to treat mood disorders. Patients with high levels of inflammation often fail to respond to typical treatments for depression.
Some previous research has found evidence of microglial activation in the brains of people who died from suicide.
The small study by Holmes and colleagues used positron-emission tomography, or PET scans, to observe evidence of translocator protein levels in the brain in 14 medication-free participants in a major depressive episode and 13 healthy volunteers. Those with depression, and particularly those with suicidal thoughts, showed more evidence of neuroinflammation.
Repeated Sports Injuries Linked to Brain Inflammation
Professional football players face repeated mild traumatic brain injuries throughout their careers, and may face a variety of brain impairments, from depression to dementia, as a result.
A recent study by researcher Jennifer Coughlin and colleagues clarified how these impairments may be caused by repeated brain impacts. The researchers used positron emission tomography (PET) scans to observe the volume of translocator protein, a marker of brain injury and repair, in the brains of seven active or recently retired National Football League (NFL) players. Compared to healthy, athletic volunteers who were age-matched to the NFL players, the NFL players showed greater volume of translocator protein in several brain regions, including the left and right thalamus, the left and right temporal poles, and the brainstem.
It is not yet clear whether the increased volume of translocator protein is a sign of the brain’s attempts to repair itself, or whether it shows deterioration toward chronic traumatic encephalopathy. Translocator protein is also considered a marker of microglial activation, which occurs with inflammation.
High levels of translocator protein have also been seen in patients with depression and schizophrenia.
