Comparison of inflammatory markers as moderators of depression outcomes: A CO-MED study

Inflammatory biomarkers in depression: scoping review

BACKGROUND

Inflammation is increasingly recognised as a fundamental component of the pathophysiology of major depressive disorder (MDD), with a variety of inflammatory biomarkers playing pivotal roles. These markers are closely linked to both the severity of symptoms and the responsiveness to treatments in MDD.

AIMS

This scoping review aims to explore the scientific literature investigating the complex relationships between inflammatory biomarkers and depression, by identifying new studies and critical issues in current research.

METHOD

Following the PRISMA Extension for Scoping Reviews guidelines, we systematically searched databases including PubMed, Scopus, PsycINFO, Open Grey and Cochrane Library. Our search focused on articles published from 1 January 2020 to 1 May 2024. We included studies evaluating inflammatory biomarkers in adult patients with MDD, utilising observational and randomised controlled trial designs, and review studies.

RESULTS

Our analysis examined 44 studies on the complex interplay between inflammation and its multiple effects on MDD. Significant associations between specific inflammatory biomarkers and depression severity were found, requiring cautious interpretation. We also highlight several methodological limitations in the current studies, which warrant caution in directly applying these findings to clinical practice. However, identified methodologies show potential for using these biomarkers as diagnostic tools or therapeutic targets, including anti-inflammatory interventions.

CONCLUSIONS

The findings emphasise the need for sophisticated, integrative research to understand inflammation's role in MDD. Future studies should identify specific biomarker panels for diagnosing depression and bridging peripheral biomarker measurements with central neuroinflammatory processes, leading to better diagnostic and treatment strategies.

A J-shaped association between Dietary Inflammatory Index (DII) and depression: A cross-sectional study from NHANES 2007-2018

BACKGROUND

Growing evidence indicates that depression is more common in people who partake in a pro-inflammatory diet. The objective of our study was to assess the association between the Dietary Inflammatory Index (DII) and depression through a cross-sectional study of the National Health and Nutrition Examination Survey from 2007 to 2018.

METHODS

We used weighted multivariable logistic regression models with subgroup analysis to explore the relationship between DII and depression. Generalized additive models were used to test whether there was a nonlinear association. Then, we constructed a two-piece linear regression model and performed a recursive algorithm to calculate the inflection point.

RESULTS

The study enrolled a total of 30,627 individuals from the United States. In the regression model with full confounding variables adjusted, the OR (95 % CI) for the association between DII and depression was 1.05 (1.04, 1.06). A J-shaped association was found between DII and depression, with a turning point of 2.74. After the turning point, the OR (95 % CI) was 1.60 (1.51, 1.69). Only the interaction in the cardiovascular disease (CVD) analysis was statistically significant.

CONCLUSION

Our study highlighted a J-shaped association between DII and depression in a nationally representative sample of adults from the United States.

Selected Biomarkers of Depression: What Are the Effects of Cytokines and Inflammation?

Depression is one of the leading mental illnesses worldwide and lowers the quality of life of many. According to WHO, about 5% of the worldwide population suffers from depression. Newer studies report a staggering global prevalence of 27.6%, and it is rising. Professionally, depression belonging to affective disorders is a psychiatric illness, and the category of major depressive disorder (MDD) comprises various diagnoses related to persistent and disruptive mood disorders. Due to this fact, it is imperative to find a way to assess depression quantitatively using a specific biomarker or a panel of biomarkers that would be able to reflect the patients' state and the effects of therapy. Cytokines, hormones, oxidative stress markers, and neuropeptides are studied in association with depression. The latest research into inflammatory cytokines shows that their relationship with the etiology of depression is causative. There are stronger cytokine reactions to pathogens and stressors in depression. If combined with other predisposing factors, responses lead to prolonged inflammatory processes, prolonged dysregulation of various axes, stress, pain, mood changes, anxiety, and depression. This review focuses on the most recent data on cytokines as markers of depression concerning their roles in its pathogenesis, their possible use in diagnosis and management, their different levels in bodily fluids, and their similarities in animal studies. However, cytokines are not isolated from the pathophysiologic mechanisms of depression or other psychiatric disorders. Their effects are only a part of the whole pathway.

Innate lymphoid cells in depression: Current status and perspectives

The recent discovery of innate lymphoid cells (ILCs) has provided new insights into our understanding of the pathogenesis of many disease conditions with immune dysregulation. Type 1 innate lymphoid cells (ILC1s) induce type I immunity and are characterized by the expression of signature cytokine IFN-γ and the master transcription factor T-bet; ILC2s stimulate type II immune responses and are defined by the expression of signature cytokines IL-5 and IL-13, and transcription factors ROR-α and GATA3; ILC3s requires the transcription factor RORγt and produce IL-22 and IL-17. ILCs are largely tissue-resident and are enriched at barrier surfaces of the mammalian body. Increasing evidence shows that inflammation is involved in the pathogenesis of depression. Although few studies have directly investigated the role of ILCs in depression, several studies have examined the levels of cytokines produced by ILCs in depressed subjects. This review summarizes the potential roles of ILCs in depression. A better understanding of the biology of ILCs may lead to the development of new therapeutic strategies for the management of depression.