MDD Research Roundup: August 25


What is new in research on major depressive disorder?



In this Research Roundup, we explore new studies on major depressive disorder (MDD), with a special focus on the neurobiology of MDD, the potential efficacy of probiotic supplementation, and potentially beneficial combined treatments.

Exploring the Neurobiology of MDD

Investigators aimed to offer a comprehensive view of the neurobiology of MDD by exploring the interactions between several signaling pathways and systems. They discussed several models of MDD neurobiology and suggested some ways future research can help improve general understanding of MDD and its treatments.

“A complete understanding of the associations of the multiple molecular pathways with MDD may be an unrealistic expectation,” the investigators concluded. “Nevertheless, evidence should be noted supporting their effects on key neuronal and synaptic functional measures not only for MDD, but also for other major psychiatric disorders, such as bipolar disorder and schizophrenia.”


Fries GR, Saldana VA, Finnstein J, Rein T. Molecular pathways of major depressive disorder converge on the synapseMol Psychiatry. 2023;28(1):284-297.

Potential Benefits of Probiotic Supplementation in MDD Treatment

Investigators conducted a systematic review exploring evidence of the potential benefits of probiotic supplementation in patients with MDD. They found that probiotic supplementation had limited short-term effects on symptoms of depression and that no signification changes in gut microbiota composition were apparent following 4 to 8 weeks of probiotic treatment.

“To advance this field, further larger-scale and longer-term studies are required,” the investigators concluded. “Future studies could also consider alternative approaches to study gut microbiota, eg, metagenomics and RNA sequencing, which may be more sensitive, have greater resolution, and provide a more comprehensive picture regarding the structure and function of host microbial communities.”


Ng QX, Lim YL, Yaow CYL, et al. Effect of probiotic supplementation on gut microbiota in patients with major depressive disorders: a systematic review. Nutrients. 2023;15(6):1351.

IL-6 Before and After Combined Treatment in MDD

Investigators conducted a first-of-its-kind systematic review exploring and synthesizing changes to IL-6 before and after combined treatment in patients with MDD. In their review, they identified several potentially effective combined treatments for these patients.

“This systematic review identifies several potentially beneficial combined treatments for MDD patients,” the investigators concluded. “However, the small number of effects observed for many adjunctive operating via diverse pathways makes it difficult to determine when differences are due to study design, study population, measurement, or intervention type. Therefore, further evidence is needed to confirm the efficacy of reducing IL-6 levels in patients with treatment-resistant MDD.”


Lombardi AL, Manfredi L, Conversi D. How does IL-6 change after combined treatment in MDD patients? a systematic reviewBrain Behav Immun Health. 2022;27:100579.

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