EXTRACELLULAR VESICLES IN MAJOR DEPRESSIVE DISORDER AND THEIR RELATIONSHIP TO TREATMENT OUTCOME

Abstract Background Extracellular vesicles (EVs) play a crucial role in facilitating intercellular communication. Their capacity to traverse the blood-brain barrier, transport, and control the release of diverse neurotransmitters underscores their potential involvement in the pathophysiology of psychiatric disorders (1). The small size and diverse biogenesis of EVs complicates their detection and investigation (2). However, the investigation of exosomal markers, including CD63 and CD9, may provide a convenient method for the investigation of EVs in major depressive disorder (MDD). Aims & Objectives We analyzed the mRNA expression of exosomal markers and characterized EVs isolated from plasma of patients diagnosed with MDD and healthy controls regarding their size and concentration. Methods 37 patients (19 female, mean age ± standard deviation (SD) = 28.0 ± 8.4 years) diagnosed with MDD without antidepressant treatment in three months prior to inclusion and 57 healthy controls (31 female, 27.9 ± 8.3 years) were included. According to a standardized open-label algorithm (3), patients were treated with escitalopram 10 mg daily and were visited biweekly for three months. In case of non- response dosage was increased up to 20 mg escitalopram. In case of side-effects or non-response after 6 weeks, medication was switched to venlafaxine 75 mg, mirtazapine 30 mg or duloxetine 60 mg. For evaluation of severity and treatment response Montgomery-Å sberg Depression Rating Scale (MADRS) was conducted. Total RNA was extracted from blood samples and the mRNA expression of SLC6A4, CD63, CD9 and HSPA1A was determined by quantitative real-time PCR. Samples of 20 patients (10 female, 26.1 ± 2.3 years) and 20 controls (10 female, 26.2 ± 3.5 years) were selected for isolation and analysis of EVs using nanoparticle tracking analysis (NTA) (4). Results Our analysis revealed pronounced changes in mRNA levels of exosomal markers. CD63 expression was significantly reduced (1.08 ± 0.18 vs. 1.74 ± 0.82, t = 5.63, df = 75.37, p <0.0001) and CD9 expression was increased in plasma of MDD patients (1.10 ± 0.51 vs. 0.88 ± 0.50, t = -1.96, df = 84.64, p = 0.05). There was no group difference in HSPA1A levels, but SLC6A4, a gene coding for serotonin transporter, was lower in MDD (4.09 ± 3.00 vs. 7.58 ± 6.04, t = 3.79, df = 69.51, p <0.001). NTA revealed a trend for higher total concentration of nanoparticles in the MDD group compared to controls (14.47 ± 8.23 vs. 10.68 ± 3.89 × 108nanoparticles/ml, t = -1.86, df = 27.09, p = 0.07) with no significant difference in EV diameter. Furthermore, we observed significant relationships between reduction in MADRS and EV concentration (ρ = -0.55, p = 0.03), and CD9 expression (ρ = -0.42, p = 0.02). Discussion & Conclusion We identified changes in mRNA expression of exosomal markers and in EV distribution of MDD patients compared to healthy individuals. Moreover, we demonstrated a relationship between exosomes and antidepressant treatment response. Consequently, an involvement of plasma EVs in the pathophysiology and treatment outcome of MDD seems plausible, emphasizing the need for further investigation. References 1. Saeedi S, Israel S, Nagy C, Turecki G. The emerging role of exosomes in mental disorders. Transl Psychiatry. 2019;9(1):122. 2. Zadka Ł, Grybowski DJ, Dzię giel P. Modeling of the immune response in the pathogenesis of solid tumors and its prognostic significance. Cellular Oncology. 2020 Aug 2;43(4):539–75. 3. Silberbauer LR, Rischka L, Vraka C, Hartmann AM, Godbersen GM, Philippe C, et al. ABCB1 variants and sex affect serotonin transporter occupancy in the brain. Mol Psychiatry. 2022 Nov 1;27(11):4502–9. 4. Zadka Ł, Piotrowska A, Opaliń ska A, Haczkiewicz-Leś niak K, Grybowski D, Ceremuga I, et al. Comparative analysis of exosome markers and extracellular vesicles between colorectal cancer and cancer-associated normal colonic mucosa. Pol Arch Intern Med. 2020 Aug 27;130(7–8):640–8.