Molecular Signatures of TMS Response in Treatment-Resistant Depression

This prospective cohort study aims to investigate the relationship between plasma proteomic and metabolomic profiles and the treatment response to transcranial magnetic stimulation (TMS) in patients with treatment-resistant depression (TRD). TRD is defined as a subtype of major depressive disorder (MDD), characterized by an inadequate response to at least two adequate trials of antidepressant therapy. Despite the clinical efficacy of TMS as a non-invasive neuromodulation treatment, the biological underpinnings that determine patient responsiveness remain unclear. This study addresses that gap by evaluating blood-based molecular biomarkers that may predict or reflect TMS treatment outcomes.

A total of 55 TRD patients, diagnosed according to DSM-5-TR criteria and confirmed through the SCID-5 structured clinical interview, will be enrolled. An additional 55 healthy individuals matched for age and sex will serve as a control group for baseline plasma comparisons. Patients will undergo a standardized TMS protocol using the MagVenture™ X100™ device. The protocol includes 20 treatment sessions over four weeks, with each session delivering 1,800 pulses of intermittent theta burst stimulation (iTBS) targeting the left dorsolateral prefrontal cortex (DLPFC). Motor threshold will be assessed weekly to calibrate treatment intensity to 90% of the resting motor threshold.

Blood samples will be collected from TRD patients prior to the first TMS session and after the 20th session, while healthy controls will provide samples at a single time point. Proteomic analysis will be conducted using LC-MS/MS following protein extraction, digestion, and purification. Metabolomic profiling will be carried out using LC-MS coupled with ion mobility spectrometry, enabling the identification of a wide range of plasma metabolites.

Psychiatric assessments, including the Hamilton Depression Rating Scale (HAM-D), Patient Health Questionnaire-9 (PHQ-9), Pittsburgh Sleep Quality Index (PSQI), and the Clinical Global Impression (CGI) scale, will be administered at baseline and post-treatment to monitor clinical outcomes. Data integration and bioinformatics analyses will be performed using MaxQuant, Perseus, and MetaboAnalyst 6.0, enabling the identification of differentially expressed proteins and metabolites associated with treatment response.

The primary objective of the study is to determine whether plasma proteomic and metabolomic profiles differ significantly between TMS responders and non-responders. Secondary objectives include identifying predictive biomarkers for TMS efficacy and assessing biological changes correlated with clinical improvement.

Primary outcomes will focus on identifying molecular signatures that correlate with treatment responsiveness. Secondary outcomes will include changes in depression severity scores, documentation of any adverse effects related to TMS, and examination of correlations between biomarker expression and pharmacological history.

This study is crucial for advancing personalized treatment approaches in psychiatry. By identifying objective, blood-based biomarkers of TMS response, it may become possible to tailor treatment strategies, reduce unnecessary interventions, and improve therapeutic outcomes for individuals suffering from TRD.

Inclusion criteria

• Diagnosis of Major Depressive Disorder (MDD) according to DSM-5-TR criteria.
• Inadequate clinical response to at least two different antidepressants and/or anti-obsessive agents administered at therapeutic doses and durations.
• Clinical symptoms not better explained by metabolic or organic medical conditions.
• No epileptic activity detected on routine electroencephalography (EEG) prior to TMS initiation.
• Routine pre-TMS laboratory tests reveal no abnormalities that may significantly affect treatment response, including:
• Normal thyroid hormone profile
• No significant vitamin deficiencies
• No markedly elevated inflammatory markers
• No history or current evidence of hearing loss on clinical evaluation; if present, evaluation by an otolaryngologist will be obtained.
• Age 18 years and older.
• Ability to provide written informed consent.

Exclusion criteria

• Any contraindication to TMS as identified in the standardized pre-TMS risk assessment form.
• Presence of epileptic focus detected on pre-TMS EEG.
• History of significant head trauma, loss of consciousness, or intracranial surgery.
• Presence of metal implants or foreign bodies incompatible with TMS (e.g., aneurysm clips, surgical clamps, metallic fragments).
• Abnormal thyroid hormone levels in pre-TMS laboratory testing.
• Significantly elevated inflammation markers (e.g., CRP) in pre-TMS bloodwork.
• Vitamin deficiencies associated with cognitive impairment (e.g., B12, folate) in pre-TMS labs.
• Electrolyte imbalances on pre-TMS blood testing.
• History of psychotic disorder or bipolar I/II disorder.
• History of substance-induced psychosis or bipolar disorder.
• Current or past substance use disorder (including alcohol, stimulants, or illicit drugs), unless abstinent from substances (excluding alcohol) for a minimum of 12 months.
• Voluntary discontinuation of TMS during the treatment course.
• Any serious adverse event or unexpected clinical condition during treatment that necessitates discontinuation of TMS.