Schizophrenia is a complex mental disorder characterized by a range of symptoms, including negative symptoms and cognitive impairments. Recent research has indicated the potential benefits of targeting mitochondrial dysfunction, oxidative stress, and inflammatory responses in alleviating symptoms of schizophrenia. However, the results remain inconsistent across various studies. This study aims to evaluate the efficacy of Pyrroloquinoline quinone (PQQ) in reducing negative symptoms and improving cognitive function in patients with chronic schizophrenia. The investigation will focus on changes in severity scores from baseline to endpoint, as well as during an eight-week follow-up period. A double-blind, randomized controlled trial will be conducted involving participants diagnosed with chronic schizophrenia. Participants will be randomly assigned to receive either PQQ or a matched placebo. Data will be collected through questionnaires and neuroimaging techniques, including resting-state scans and multimodal tasks to assess functional connectivity and activation in target brain regions. Statistical analyses will include descriptive statistics, voxel-by-voxel multiple regression, and linear mixed models to account for repeated measurements. Additionally, potential moderating effects of demographic factors such as age and gender will be examined using ANCOVAs. The study will also monitor adverse events and ensure participant safety through a rigorous reporting and unblinding procedure. It is hope to provide insights into the therapeutic potential of PQQ in managing schizophrenia symptoms, contributing to the development of more effective treatment strategies for this challenging condition.

Inclusion criteria:

Eligible male and female patients aged 18 to 50 years, diagnosed with schizophrenia according to the criteria outlined in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5), will be included in the study. Participants are required to meet the following criteria: a Positive and Negative Syndrome Scale (PANSS) total scores of ≥ 60 (indicating an active phase of the illness), a PANSS negative subscale scores of ≥ 20, and a duration of illness of at least 2 years (indicating chronic schizophrenia). Additionally, participants must have been on a stable dose of antipsychotic medication for a minimum of 6 weeks prior to enrollment, and the use of antioxidants or anti-inflammatory medications is prohibited within 2 weeks preceding enrollment.

Exclusion criteria:

Patients with comorbid psychiatric disorders as defined by the DSM-5, such as substance abuse or dependence (excluding nicotine), or intellectual disability (IQ < 70); those with significant depressive symptoms, defined as a score ≥14 on the 17-item Hamilton Depression Rating Scale (HAMD-17) or ≥ 4 on the depression item of PANSS; individuals with severe medical or neurological conditions, or those unable to communicate effectively; patients with a known allergy to PQQ disodium salt, or who are pregnant, breastfeeding, or have severe hepatic or renal impairment; women of childbearing potential who are not using reliable contraception; patients who have received modified electroconvulsive therapy (MECT) or other physical treatments within six months prior to enrollment; and those currently receiving treatments that cannot be discontinued, including antidepressants, mood stabilizers, antihistamines, or combination therapy with two or more antipsychotics (except for low-dose aripiprazole, ≤ 5 mg/day, used solely for prolactin reduction).

Additional exclusion criteria for participants undergoing fMRI scanning:

Participants are required to complete a comprehensive safety questionnaire addressing potential risks associated with exposure to a 3-Tesla magnetic field and the MRI environment. MRI-specific exclusion criteria include: the presence of MRI-incompatible implants (e.g., cochlear implants, insulin pumps, pacemakers, or other metallic implants); a history of possible intraocular metallic foreign bodies due to manual labor without appropriate eye protection; tattoos containing red pigments; claustrophobia; or unwillingness to be informed of any incidental structural brain abnormalities detected during the scan.

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Participants will be randomized to receive either PQQ or a matched placebo in a double-blind, randomized controlled design. Treatment allocation will remain concealed from investigators, clinicians, and statisticians until the completion of data analysis. To ensure blinding, the placebo is matched to PQQ in appearance, odor, and color, and both are dispensed in identically sealed bottles. Each bottle is labeled as trial medication and assigned a random code (1-70) by the trial pharmacist, who maintains exclusive access to the randomization list stored securely until study completion. An independent individual, not involved in any aspect of the trial, generates the random allocation sequence based on the sequential enrollment of participants. Participants are assigned to either the intervention or control group according to this randomization protocol, using a table of random numbers. Participants are interviewed individually to prevent communication about treatment experiences. Medicat