Unveiling the Anti-Inflammatory Effects of Antidepressants: A Systematic Review of Human Studies over the Last Decade

Background/Objectives: Depression ranks among the most prevalent mental health conditions globally, marked by a variety of symptoms that frequently cause significant emotional distress and impairment in individuals, alongside a high recurrence rate. The predominant approach to treating depression revolves around monoamine theory, utilizing SSRIs and SNRIs, with Esketamine emerging as a supplementary option in recent times. Nevertheless, there is a growing focus on exploring the relationship between inflammation and depression, revealing a strong correlation between the two. This insight prompts consideration of the anti-inflammatory properties of current antidepressants in their therapeutic application. Methods: A systematic literature search was conducted using the PubMed database to identify randomized controlled trials (RCTs) and clinical trials (CTs) that assessed the in vivo anti-inflammatory effects of SSRIs (fluoxetine, escitalopram, sertraline, and paroxetine), the SNRI venlafaxine, and esketamine/ketamine in human subjects undergoing treatment for depression. The included studies were evaluated based on changes in levels of pro-inflammatory and anti-inflammatory markers in response to the antidepressant treatments. Results: SSRIs, SNRIs, esketamine, and ketamine (a racemic mixture of S- and R-ketamine not formally approved for the treatment of depression) exhibit anti-inflammatory effects through diverse mechanisms, such as reducing pro-inflammatory cytokines or enhancing anti-inflammatory cytokines in serum or within specific brain regions like the hippocampus and prefrontal cortex. These actions are mediated through various inflammatory pathways, including nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), the brain Nod-like receptor pyrin-containing 3 (NLRP3) inflammasome, the glutamatergic system, the gut-brain axis, the hypothalamic-pituitary axis, impaired neuroplasticity, and the kynurenine pathway. Conclusions: In summary, SSRIs, SNRIs, esketamine, and ketamine exert an anti-inflammatory role alongside their antidepressant effects via these intricate mechanisms.