Relationship of Peripheral Inflammatory and Neuroprotective Biomarkers With Response to Intermittent Theta Burst Stimulation in Treatment-Resistant Depression

Major depressive disorder (MDD) is a highly prevalent psychiatric disorder associated with substantial functional impairment, reduced quality of life, increased suicide risk, and significant socioeconomic burden. Despite the availability of pharmacological, psychotherapeutic, and neuromodulation-based treatments, a considerable proportion of patients fail to achieve adequate clinical improvement and develop treatment-resistant depression (TRD). Treatment-resistant depression is commonly defined as inadequate response to at least two antidepressant medications administered at adequate doses and durations. Patients with TRD frequently experience chronic symptoms, recurrent episodes, impaired psychosocial functioning, increased healthcare utilization, and poorer long-term outcomes. Intermittent theta burst stimulation (iTBS) has emerged as an effective, non-invasive neuromodulation treatment for TRD. Compared with conventional high-frequency repetitive transcranial magnetic stimulation (rTMS), iTBS offers substantially shorter treatment sessions while maintaining comparable efficacy. However, the biological mechanisms underlying treatment response remain incompletely understood, and reliable biomarkers predicting therapeutic outcomes have not yet been established. Accumulating evidence suggests that neuroinflammation, impaired neuroplasticity, oxidative stress, and altered immune regulation contribute to the pathophysiology of depression and may influence treatment response. Therefore, investigating biological changes associated with iTBS may improve the understanding of therapeutic mechanisms and facilitate the development of personalized treatment strategies. This single-center, prospective, investigator-initiated clinical study aims to comprehensively evaluate clinical outcomes, executive functions, and peripheral inflammatory and neuroprotective biomarkers in patients with TRD receiving iTBS treatment. A total of 100 participants will be enrolled, including 50 patients with treatment-resistant depression and 50 healthy controls. Patients will receive active iTBS over the left dorsolateral prefrontal cortex using a MagVenture X100 device for 20 sessions administered over four weeks. Healthy controls will not receive any intervention and will participate only in baseline assessments. Clinical outcomes will be evaluated using the 17-item Hamilton Depression Rating Scale (HAM-D-17), Patient Health Questionnaire-9 (PHQ-9), Clinical Global Impression (CGI), and Insomnia Severity Index (ISI). Executive functions will be assessed using the Wisconsin Card Sorting Test (WCST), Trail Making Test A and B (TMT-A and TMT-B), and verbal fluency tests. Peripheral blood samples will be collected before and after treatment. Serum levels of IL-1β, IL-6, IL-10, TNF-α, high-sensitivity C-reactive protein (hs-CRP), brain-derived neurotrophic factor (BDNF), apolipoprotein D (APOD), serum amyloid A1 (SAA1), and serum amyloid A2 (SAA2) will be measured using enzyme-linked immunosorbent assays (ELISA). Gene expression analyses of relevant biomarkers will be performed using quantitative polymerase chain reaction (qPCR). The primary outcome will be the change in HAM-D-17 scores from baseline to week 4. Secondary outcomes will include changes in clinical scales, executive function performance, biomarker levels, and gene expression profiles. Associations between biological markers, cognitive performance, and treatment response will also be examined. The study seeks to identify potential biomarker signatures associated with iTBS response and contribute to the development of biomarker-guided, personalized neuromodulation strategies for treatment-resistant depression.