The biological and psychological causes of depression are an enduring medical mystery, but a new study claims that inflammation of the blood could be behind some causes of low mood.
In a study published in Molecular Psychiatry, a team from Emory University found that around “one third” of people with depression have high levels of the inflammation markers CRP (C-reactive protein) in their blood. CRP is a protein made by the liver and released into the blood within a few hours after tissue injury, the start of an infection, or other cause of inflammation. Researchers say that this inflammation may be linked to symptoms of depression like anhedonia, which is the inability to experience pleasure.
Anhedonia is one of the most stubborn symptoms of depression, and is often hard to treat even with anti-depressants. “Some patients taking antidepressants continue to suffer from anhedonia,” said Jennifer Felger, lead author of the study in a statement. “Our data suggest that by blocking inflammation or its effects on the brain, we may be able to reverse anhedonia and help depressed individuals who fail to respond to antidepressants.”
In a study of 48 patients with depression, high levels of CRP were linked with a “failure to communicate” between the ventromedial prefrontal cortex and the ventral striatum, two regions of the brain associated with motivation and reward.
“We were interested in these regions of the brain because of their known importance for response to reward,” said Felger. “In addition, we had seen reduced activation of these areas in people receiving immuno-stimulatory treatments for hepatitis C virus or cancer, which suggested that they may be sensitive to inflammation.”
The team think that the “high-inflammation form of depression is distinct”, and hope to develop treatments and diagnostic tests tailored for it. Other depressions work differently, but it’s possible the technique could make a significant difference.
“We hope our investigations may lead to new therapies to treat anhedonia in high-inflammation depression,” she says.
The rest of the medical community is yet to be convinced, however — the journal Brain, Behavior, and Immunity published a meta-analysis of more than fifty clinical studies that found inflammatory molecules in patients with depression, and determined that there was poor consistency between each study about which of these molecules correlated to depression.