C-reactive protein in major depressive disorder: Promise and challenge
Angelos Halaris, Danika Prochaska, Ashley Stefanski, Maria Filip
Abstract
Depressive disorders are characterized by persistent low mood, loss of interest and pleasure, decreased energy, varying levels of social and occupational dysfunction. Depressive symptoms include depressed mood, anhedonia, appetite disturbances and changes in weight, loss of libido, sleep disturbances, lack of energy, unwarranted guilt, difficulty in concentration, and even suicidal ideation and intent. Major depressive disorder (MDD) is characterized by the presence of at least five of the abovementioned symptoms during the same two-week period with a change from previous functioning. Depressed mood and/or loss of interest/pleasure must be present and can be further classified from mild to severe (American Psychiatric Association, 2013). MDD can negatively impact a person's life and affects 264 million people globally (GBD, 2018). There is a large body of evidence that many MDD patients have an increased level of inflammation, as indicated by elevated levels of C-reactive protein (CRP) and other proinflammatory biomarkers. CRP is an acute phase reactant produced by the liver in response to infections, inflammatory conditions in the body and stress. CRP has at least two structural isoforms, monomeric and pentameric, and serves as both a proinflammatory and anti-inflammatory protein, depending on the isoform. There is also evidence that polymorphisms within the CRP gene influence the levels of CRP produced. The objective of this review is to highlight current research on the relationship of CRP with MDD, the genetics of CRP, and the possible relationship of CRP structural isoforms specifically in the diagnosis, pathology, and treatment of MDD.