2026 ECNP Congress

EP01-1049

Salivary microbiota and epigenetic regulation in major depressive disorder: a protocol to explore non-invasive biomarkers

Joana Cardoso — S. Carvalho, D. Martins, N. Rocha, M. Santos · LAQV REQUIMTE - Associated Laboratory for Green Chemistry - Clean Technologies and Processes, ESS – P.PORTO - School of Health- Polytechnic Institute of Porto, Porto, Portugal

2026 ECNP Congress

Introduction

Major Depressive Disorder is a global health priority, ranked as third leading cause of disease burden [1]. Affecting over 5,7% of adults, Major Depressive Disorder is characterized by the lack of interest or pleasure in doing activities and a persistent low mood [2]. Genetic risk alone is insufficient to fully explain Major Depressive Disorder’s susceptibility. Thus, understanding the mechanisms underlying Major Depressive Disorder is highly relevant, including identifying possible potential biomarkers for accurate diagnosis. Emerging studies suggest that gut and oral microbiota influence neurological and psychiatric disorders [3]. Alterations in bacterial phyla, such as increased Actinobacteriotaand Firmicutesand decreased Bacteroidotaand Proteobacteria, have been observed in Major Depressive Disorder patients. In parallel, circulating microRNAs (miRNAs) have emerged as promising epigenetic biomarkers [4]. While microbial metabolites can influence miRNAs expression, and vice versa, studies integrating salivary microbiome and exosomal miRNA profiles remain scarce [5].

Aims

This project aims to investigate if Major Depressive Disorder is associated with specific alterations in the salivary microbiome and exosomal miRNAs profiles in a sample of Portuguese patients. The project seeks to integrating clinical, molecular, and bioinformatic approaches to identify novel, non-invasive, biomarkers.

Methods

A cross-sectional study will enrol 80 participants (40 Major Depressive Disorder patients and 40 matched healthy controls). Diagnosis will be confirmed via DSM-5 and severity assessed by HAM-D and BDI scales. Cognitive function will be measured via BVMT-R and CVLT-II, and the CANTAB digital battery. Healthy controls will undergo psychiatric screening to exclude undiagnosed conditions. Next, 2 mL of saliva will be collected and genomic DNA sequenced for the 16S rRNA (V3–V4) regions. QIIME2 and LEfSe will be used to explore taxonomical abundance. To analyze the miRNA, we will first isolate exosomes from saliva and then use qRT-PCR to measure the levels of miR-29a-3p and miR-191-5p, using U6, U48, and SNORD44 as controls. Statistical analysis will employ t-tests/Mann-Whitney U and Spearman correlations. We will use generalized linear models and the ComBat (R package) to account for medication, lifestyle, and batch effects.

Preliminary Results:

The project aims to identify unique microbial signatures and dysregulated miRNA profiles in Major Depressive Disorder. Based on the literature, a significant reduction in microbial alpha diversity and a distinct shift in beta diversity are anticipated, potentially indicated by a higher Firmicutes / Bacteroidetes ratio. Regarding epigenetic markers, we expect to find a significant upregulation or downregulation of miR-29a-3p and miR-191-5p in salivary exosomes of the Major Depressive Disorder group. Preliminary analysis is expected to reveal correlations between specific microbial taxa and miRNA expression levels.

Conclusions

Ultimately, we aim to create a multi-marker panel that links multi-omic data to depression severity and cognitive performance. This protocol will connect microbiome-epigenetic interactions with clinical psychiatry using saliva as a non-invasive tool for objective Major Depressive Disorder diagnosis.

References

  1. James, S. L., Abate, D., Abate, K. H., Abay, S. M., Abbafati, C., Abbasi, N., Abbastabar, H., Abd-Allah, F., Abdela, J., Abdelalim, A., Abdollahpour, I., Abdulkader, R. S., Abebe, Z., Abera, S. F., Abil, O. Z., Abraha, H. N., Abu-Raddad, L. J., Abu-Rmeileh, N. M. E., Accrombessi, M. M. K., … Murray, C. J. L. (2018). Global, regional, and national incidence, prevalence, and years lived with disability for 354 diseases and injuries for 195 countries and territories, 1990–2017: A systematic analysis for the Global Burden of Disease Study 2017. The Lancet, 392(10159), 1789–1858. https://doi.org/10.1016/S0140-6736(18)32279-7
  2. World Health Organization. (2025). Depressive disorder (depression). World Health Organization. https://www.who.int/news-room/fact-sheets/detail/depression
  3. Singh, J., Vanlallawmzuali, Singh, A., Biswal, S., Zomuansangi, R., Lalbiaktluangi, C., Singh, B. P., Singh, P. K., Vellingiri, B., Iyer, M., Ram, H., Udey, B., & Yadav, M. K. (2024). Microbiota-brain axis: Exploring the role of gut microbiota in psychiatric disorders - A comprehensive review. Asian Journal of Psychiatry, 97, 104068. https://doi.org/10.1016/j.ajp.2024.104068
  4. Santos, D. A. R., Gaiteiro, C., Santos, M., Santos, L., Dinis-Ribeiro, M., & Lima, L. (2023). MicroRNA Biomarkers as Promising Tools for Early Colorectal Cancer Screening-A Comprehensive Review. International Journal of Molecular Sciences, https://doi.org/10.3390/ijms241311023
  5. Girella, A., Vismara, M., O’Riordan, K. J., Gunnigle, E., Mercante, F., Girone, N., Pucci, M., Gatta, V., Konstantinidou, F., Stuppia, L., Cryan, J. F., Dell’Osso, B., & D’Addario, C. (2025). Distinct Salivary Microbiota Profiles, BDNF Dna Methylation And Mir-16-5p , Mir-29a-3p , Mir-191-5p Alterations In Obsessive-Compulsive Disorder And Major Depressive Disorder. https://doi.org/10.1101/2025.01.24.25321067