Do Omega-3 Fatty Acids Have an Antidepressant Effect in Patients With Signs of Peripheral Inflammation?

Background

Increased mean levels of peripheral inflammatory markers have repeatedly been reported in individuals with major depression compared to controls, although there is considerable overlap between groups. As further evidence for a role of inflammation in major depression, 20-60% of patients receiving treatment for viral hepatitis and certain forms of cancer with the cytokine interferon-alpha will develop depressive symptoms. Interestingly, some authors have suggested that the association between inflammation and depression is symptom specific, i.e. there might be a subtype of "inflammation-related depression" with a specific phenotype. Although it still remains unclear if the immune abnormalities often seen in depressed subjects derive from changes in the periphery or in the central nervous system (or both), animal studies have shown that by counteracting the effects of pro-inflammatory cytokines in either the blood or the brain, depressive-like behavior in animals can be mitigated. These animal studies, along with data from several clinical studies pertaining to this, suggest that interventions primarily targeting peripheral inflammation may be useful in treating psychiatric symptoms. Although the exact mechanisms by which increased inflammation may give rise to depressive symptoms remain unclear, there are several potential downstream pathways that may be involved including accelerated cellular aging, mitochondrial dysfunction, and oxidative stress.

In search for a potential antidepressant that could be tested in clinical trials in which subjects are selected a priori based on inflammatory markers, the investigators turn to eicosapentaenoic (EPA), an omega-3 (n-3) fatty acid with anti-inflammatory properties. The ability of dietary n-3 fatty acids to mitigate the inflammatory response has been shown in human and animal studies. EPA and Docosahexaenoic acid (DHA) are the two major n-3 fatty acids found in oily fish and fish oil supplements, and both have shown anti-inflammatory properties. Supplementation of EPA and DHA in individuals with cardiovascular disease results in decreased plasma levels of CRP. N-3 fatty acids also have several other anti-inflammatory properties including i) Decreased chemotaxis of neutrophils and monocytes, ii) Decreased expression of adhesion molecules (e.g. ICAM & VCAM) on the surface of immune cells and in the circulation, iii) Decreased production of prostaglandins, iv) Increased synthesis of anti-inflammatory molecules such as resolvins and protectins, and v) Inhibition of T-cell proliferation. The mechanisms underlying these effects are not fully understood but likely involves n-3 fatty acids acting via cell surface and intracellular receptors controlling inflammatory cell signaling and gene expression patterns. In addition to the well-established anti-inflammatory effects of n-3 fatty acids, they may also have beneficial effects on oxidative stress and cell aging parameters such as leukocyte telomere length and telomerase activity. However, more research is needed in order to confirm these relationships, and therefore the investigators will, in addition to assessing inflammatory markers, also study the effects of n-3 fatty acids on markers of cellular aging and oxidative stress.

Some, but not all, previous studies have shown that EPA is superior to placebo in treating unipolar or bipolar depression. Several caveats have, however, been issued when interpreting the results from these studies, including small and perhaps clinically irrelevant effect sizes, as well as potential publication bias. Generally, n-3 preparations with high doses of EPA relative to DHA have been shown to be more efficacious in treating depression. Interestingly, a double blind placebo-controlled RCT showed that that EPA (but not DHA) was effective in preventing interferon-alpha induced depression in hepatitis C subjects, consistent with the notion that EPA may have antidepressant effect in "inflammatory depression". In line with this notion, a recent a proof-of-concept study showed that high inflammation at baseline was associated with a better antidepressant effect of EPA, but not DHA, enriched n-3 compared to placebo. That study stratified subjects post-hoc based on inflammatory markers, whereas our approach will be to select study subjects a priori based on validated cut-offs for CRP. This is the next step in developing a personalized medicine paradigm for depression.

The main aims of the study are to test if i) EPA enriched n-3 (added to stabilized ongoing treatment) is efficacious in treating depressed patients, but only in subjects with prospectively ascertained elevations in baseline CRP, ii) Changes in inflammatory markers over the course of treatment mediate this effect, and iii) Clinical trial designs utilizing prospectively-ascertained biomarkers to predict response are feasible and thereby pave the way for personalized medicine in psychiatry.