Psychobiotics have been defined as probiotics, or support to probiotics (ie, prebiotics) that, upon ingestion in adequate amounts, yield positive influence on mental health.1,2 The effect of psychobiotics has been attributed to their impact on the microbiota-gut-brain axis (MGBA), which controls the bidirectional communication between the central nervous system (CNS) and the gut microbiota.2 A solid evidence base in animals now supports the notion that the modulatory effect of the MGBA on brain chemistry and function occurs via an alteration in parameters such as intestinal permeability and inflammation, or in the levels of neurotransmitters and other neurotrophic factors, such as serotonin or brain-derived neurotrophic factor (BDNF).2
BDNF, as a neurotrophin, regulates neurogenesis by promoting cell growth, proliferation, migration, differentiation, and death. BDNF by interacting with its specific receptor, the tyrosine kinase receptor B on CNS target cells interferes in important neurophysiological processes in both central and peripheral nervous systems, and supports neuronal survival3 as well as neuroplasticity and neuroprotection.4,5 BDNF mediates the activation of various signaling pathways such as mitogen-activated protein kinase or phosphatidylinositol-3-kinase pathways, and leads to up-regulation of various neuroprotective proteins6 such as anti-apoptotic protein kinase B and B-cell lymphoma 2.4,7
In recent years, several publications have documented the effects of the intestinal microbiota or probiotics on mood and anxiety in healthy individuals or in populations with depressive symptoms secondary to another condition.8-15 However, in psychiatric populations, studies about psychobiotics are limited.
Overall, as for all probiotics, the benefits and mechanisms of action of psychobiotics appear to be strain- and disease-specific.16,17 Furthermore, whether or not the mechanisms identified in animal models will translate to human psychiatric populations remains to be demonstrated.18 The current psychobiotic formulation (
In humans, the mechanisms of action of psychobiotics on depression in major depressive disorder (MDD) patients remain largely uncharacterized. Hence, the aim of the current
The study population was described previously.23 Briefly, out of the 230 patients screened following referral by a psychiatrist of the psychiatric clinic of the Bahman Hospital (Tehran, Iran), 110 patients (78 women and 32 men) with MDD were included in the trial. Volunteers included in the RCT were aged between 20 years and 50 years, had a current diagnosis of mild to moderate melancholic depression for at least 1 month, and were taking one of the following anti-depressant medications: fluoxetine, citalopram, amitriptyline, or sertraline. Exclusion criteria included any sensitivity reaction to prebiotic and probiotic compounds, refusal to cooperate, any serious changes in diet routine and lifestyle during the study, any changes in medication or its dosage, long term (at least 1 week) inflammatory disease requiring anti-inflammatory pharmacotherapy, pregnancy or lactation, antibiotic intake during the study, history of cancer, diabetes, pancreatitis, or thyroid, kidney, liver, respiratory, or cardiovascular disorders, diagnosis of nutritional allergy by a medical professional, regular consumption of probiotic products within 2 months of study start, dietary supplement intake such as vitamins, antioxidant and/or omega-3’s at least 4-6 weeks before the study, alcohol consumption (alcoholism according to Diagnostic and Statistical Manual of Mental Disorders-IV criteria), smoking (at least 5 cigarettes per day during last 6 months or pipe or hookah at least once in last month), opiate addiction or substance abuse, history of heart attack or stroke, following a specific diet (such as vegetarianism, etc), using hormonal drugs and who participated in another study in the 2 months preceding the study. Participants were instructed to avoid consumption of any other probiotic supplements or vitamins during the study.
As previously described, the PP population of the main trial was composed of 81 participants (probiotics, n = 28; prebiotic, n = 27; and placebo, n = 26). However, for 3 participants, the volume of serum obtained at the last blood collection was insufficient. Hence, for consistency, all analyses, including the Beck’s Depression Inventory (BDI) score, were performed here on the individuals from the PP population for whom BDNF levels were available at both time points (all, n = 78; probiotics, n = 28; prebiotic, n = 25; and placebo, n = 25) (Supplementary Figure).
As previously described,23 randomization was performed by a research assistant not taking part in the project using the method available in www.randomization.com. A permuted block randomization was stratified by (≥ 35 vs < 35). Intervention packs (probiotic, prebiotic, and placebo sachets) were pre-packed and assigned to a code according to the randomization sequence. The codes were concealed from all participants and researchers until the end of the data analysis.
Interventional products were formulated and provided by Lallemand Health Solutions Inc (Mirabel, Quebec, Canada). All supplements were manufactured as orally dispersible powders with similar appearance and taste, and were packaged in 5 g sachets containing 10 billion (≥ 10 × 109) CFU of freeze-dried
Participants were instructed to consume 1 sachet at the same time daily for 8 weeks by directly pouring the powder on the tongue. The remaining sachets were counted at the end of the trial to assess compliance. Subjects were deemed compliant if they consumed a minimum of 80% of the sachets.
Except for BDNF levels measurements, outcome measures were described previously.23 Demographic and general characteristics of the participants, body weight and height measurements, nutritional status, depression severity, and physical activity levels were acquired at the beginning and end of the trial. The nutritional status was evaluated based on 3 dietary records (2 weekdays and 1 weekend) using the software Nutritionist 4 (First Databank, San Bruno, CA, USA) adapted for Iranian foods.
The depression status was measured using the BDI. The BDI is a validated self-reporting scale measuring the emotional, cognitive, somatic, and motivational components of depression. The latest version of the inventory, BDI-II, has been validated among the Iranian population.24 This scale is composed of 21 questions related to a specific symptom of depression, each consisting of 4 answers that express the severity of the symptom, thereby generating a score between 0 and 3 for each question. The sum of all scores indicates BDI score of each participant. The higher total score relates to the more severe grade of depression.
Physical activity was evaluated using the Short International Physical Activity Questionnaire and defined as metabolic equivalents. It was calculated by multiplying the duration of each activity with its specific coefficient. Height and fasting body weight with minimal clothing and no shoes were acquired using a digital scale. The body mass index (BMI, kg/m2) was calculated by dividing the weight (kg) by the squared height (m2).
Blood samples (10 mL) were collected in the fasting state, between 8 AM and 9 AM, at the beginning and end of the 8-week trial. Briefly, blood samples were transferred to test tubes and were immediately centrifuged at 3500 rpm for 10 minutes to extract the serum. Aliquoted serum samples were readily frozen and kept at –80℃ until further analysis. Serum BDNF levels were measured using a commercially available enzyme-linked immunosorbent assay kit (Shanghai Crystal Day Biotech Co, Ltd, Shanghai, China) according to the manufacturer’s instructions.
Statistical analyses of the data obtained in this study were performed using the Statistical Package for Social Science (IBM SPSS, version 22.0; IBM, Armonk, NY, USA). For this
As described previously,23 the trial sample size was determined based on the mean reductions in BDI score obtained in a similar study conducted in a population of patients.25 It was calculated as 27 subjects per group, considering a power of 80%, alpha error of 0.05 and 10% possible lost to follow-up to have mean difference of 5 in BDI scores between intervention and placebo groups. To compensate for unexpected loss to follow-up rates, 110 subjects were included in the initial trial.
As previously described, out of the 110 participants included in the trial and randomized, a total of 32 participants did not complete the study: 10 in the probiotics group, 9 in the prebiotic group, and 10 in the placebo group discontinued the study or were lost to follow up. In addition, for 2 participants in prebiotic and 1 in placebo groups, an insufficient volume serum was recovered at the final time point (8 weeks). Overall, compliance was high, with an average (SD) of 91.90% (5.53%) of the supplements consumed by the participants throughout the study.
The baseline characteristics of the 78 participants included in the
We compared the changes in BDNF levels from baseline to the endpoint for the
Pairwise comparisons of the groups, shown in Table 3, revealed that the increase in BDNF levels in the probiotic group was statistically significant compared to both the prebiotic (
Based on ANOVA/ANCOVA test, there was no difference in weight and BMI among groups at the endpoint (
Despite the lack of significance in some parameters that were previously found different in the intention-to-treat (ITT) population, when compared by pairwise analyses, selenium intake was significantly lower in the probiotic group in comparison to the prebiotic group (
BDI scores analysis was based on the
Furthermore, in accordance with the previously published ITT population analyses,23 pairwise comparisons for the
Furthermore, the BDNF levels and change in BDI scores over the supplementation period were inversely correlated in our population (n = 78). When comparing the correlation between these parameters among the 3 groups, we observed a stronger correlation between BDNF levels and BDI score changes in the probiotics group (
Some adverse events were reported by participants that may be related to the intervention. The most common adverse event was increased appetite, which was reported by 5 participants in the probiotic group and 1 participant in the prebiotic group. This reported adverse event may be reflecting beneficial effect, which was further investigated in a post- hoc analysis.26 Gastrointestinal complaints were the most reported adverse event in the prebiotic group (4 reports); it was also reported by two participants in the probiotic group. Nausea was reported by 1 in the probiotic group and 1 in the prebiotic group. Also 1 participant in the probiotic group reported fever and body aches. There was no adverse event in the placebo group except for 1 report of worse mental state, which was also reported by 1 participant in the probiotic group but was deemed unrelated to the intervention.
The main goal of this
Our findings are consistent with the studies evaluating the effects of these probiotics on BDNF levels in animal models.12,22,30 Liang et al30 found that
As studies on animal models appear to point towards a role of BDNF in the effects of probiotics, studies exploring this hypothesis in depressive patients are limited.34 In a pilot study on irritable bowel syndrome patients,
Here we show that prebiotic GOS administration did not modify BDNF levels significantly in this population, in accordance with the absence of a significant effect on the BDI score. Despite this, it is likely that GOS may have affected the composition of the gut microbiota. A dose of 5 g of GOS was shown to affect microbiota composition in healthy adults, essentially by promoting Bifidobacteria.40 In this study microbiota composition of the participants was not analyzed. The changes in microbiota composition associated with MDD are not yet fully characterized, but differences have been identified compared to healthy individuals.41 Notably, Bifidobacteria,
The strength of this trial is the probiotic strains and prebiotic types which have been previously found psychotropic in human13,39,43 and animal studies.22,30 In addition we used BDI-II to measure depression severity which is well validated in psychiatric studies and in Iranian population.24 However, a number of limitations need to be considered. The major limitation of this study is not addressing the intestinal microbiota composition or sex hormones in the patients which possibly cause interactions.44,45 In addition, the patients were under prescription of different antidepressants. Although the medications belong to the same antidepressant group (SSRI), recruitment of patients who are taking the same medication could be preferable.
It is conceivable that the probiotic may ameliorate depression through a mechanism other than BDNF and the depression improvement can actually mediate the effect of the probiotic on BDNF, and to confirm the BDNF increase as an underlying mechanism of probiotics, further studies with measurement of these parameters in some points between start and end of the study is recommended. It will reveal whether the change in serum BDNF before the depression symptoms is improved. However this seems unlikely, since increase in BDNF levels is found to be independent of depression improvement in a previous study which showed that BDNF levels increased while total depression scores was not significantly different between the control group (conventional drug therapy) and treatment group (probiotic with electroacupuncture).46
This study was supported by the Vice Chancellor of Research, Tehran University of Medical Sciences (Grant No. 94-02-16134937); the experimental products were provided by Lallemand Health Solutions (Mirabel, QC, Canada).
Asma Kazemi and Kurosh Djafarian designed the research study; Nazanin Heidarzadeh-Rad contributed to the design; Nazanin Heidarzadeh-Rad, Asma Kazemi, and Kurosh Djafarian performed the research, analyzed, and interpreted the data; Nazanin Heidarzadeh-Rad drafted the manuscript; Kurosh Djafarian had primary responsibility for the final content; and all authors critically revised the manuscript for important intellectual content and approved the final manuscript.