Every human harbors complex microbial communities (collectively, the human 'microbiome') that cover the skin and the body's mucosal surfaces. There is mounting evidence of an interaction between the intestinal microbiota, the gut, and the central nervous system (CNS) in what is recognized as the microbiome-gut-brain axis. Based on this compelling body of evidence, there is growing enthusiasm for work that is focused on translating this emerging association into novel therapies for psychiatric illness.

Fecal microbiota transplantation(FMT) is a technique in which gut bacteria are transferred from a healthy screened donor to a patient, with the goal to introduce or restore a stable microbial community in the gut.There are no clinical trials examining the impact of FMT on Bipolar Disorder (BD). However, there is biological rationale to support this type of treatment, given the known inflammatory underpinnings of this illness.

The objective of this study is to assess the effectiveness of this very novel therapy targeting the gut-brain axis, FMT, to treat bipolar depression.

Study Hypotheses:

Main hypothesis: FMT from healthy donors to patients with BD depression will improve depression symptoms as an adjunct to approved medication.

Secondary hypotheses:

1. FMT will also reduce anxiety and global function
2. FMT is safe and will be well tolerated by the patients
3. Improvements in clinical parameters will be associated with specific changes in the intestinal microbiome and/or metabolites in stool and serum

The primary goals of this proof of concept study are to determine the effectiveness, safety and tolerability of FMT in adults with BD depression.

Objective 1: To evaluate the effectiveness of the combination of a currently accepted approved therapy for BD depression + FMT in individuals with BD depression. This will be assessed through a change in the Montgomery-Ãsberg Depression Rating Scale (MADRS) total score from baseline (pre-intervention) to the final visit (week 24). The investigators will also assess the proportion of patients withdrawing from study due to inadequate control of depressive symptoms.

Secondary objective 2: To evaluate the effectiveness of FMT on anxiety symptoms and global function/overall improvement in participants with BD depression. Secondary objective 3: To determine the safety and tolerability of FMT in individuals with BD depression. Safety will be evaluated by solicited and unsolicited adverse events, including serious adverse events, throughout the study period. Tolerability will be assessed using the Toronto Side Effect Scale (TSES). This is a 32-item instrument that is designed to establish incidence, frequency, and severity of CNS, gastrointestinal, and sexual side effects.

Secondary objective 4: To assess the effect of FMT on microbiome profile (community structure and functional metagenome) and fecal metabolome. Changes in fecal microbiome profile and fecal metabolome from baseline to the final visit will be assessed using next generation sequencing and nuclear magnetic resonance (NMR) spectrometry, respectively. Changes in mood rating scales will be correlated with a specific microbiome and metabolome signature. Intestinal microbiome and metabolome of healthy donors will also be assessed.

Inclusion Criteria:

1. Between 18-65 years of age
2. Outpatient status
3. Have a diagnosis of bipolar disorder (BD) (type I or II) according to the Mini International Neuropsychiatric Interview (MINI)
4. Have been on a stable first line treatment for BD depression at an adequate dose for at least 8 weeks prior to study entry
5. Suffer from a current depressive episode (Montgomery-Åsberg Depression Rating Scale (MADRS) score at screening and baseline of ≥ 12)

Exclusion Criteria:

1. DSM-IV criteria for substance abuse within the last 6 months or lifetime dependency
2. Active eating disorders
3. Schizophrenia or schizoaffective disorder
4. Current psychotic symptoms
5. A Young Mania Rating Scale (YMRS) score of ≥12 at screening
6. Active suicidality
7. Regular intake of non-steroidal anti-inflammatory drugs or iron supplements in the 3 months prior to study entry
8. Use of prebiotics or probiotics for medical purposes, use of antibiotics or any experimental drug in the 3 months prior to study entry
9. Chronic gastrointestinal diseases
10. Conditions causing immunosuppression
11. A significant bleeding disorder
12. Any contraindication to colonoscopy
13. Pregnancy or breastfeeding

both the descriptive and analyzed data, including individual patient data, will be submitted to the National Database for Clinical Trials related to Mental Illness (NDCT), which is part of the National Institute of Mental Health Data Archive (NDA). The data are de-identified and will be made available to qualified researchers, who have to request access to the dataset.

Data will be uploaded every 6 months through the study and released Within 4 months

Researchers approved for access to NDCT have the ability to download shared data from all clinical trials available in the repository

Both the patient and the study team (clinical team, study coordinator, data analyst) will be blinded to group assignments.