Metabolic disorders, metabolic syndrome and non-alcoholic fatty liver disease, and depression are those of the most common and debilitating disorders worldwide that often coexist further increasing mortality risks. Although the exact mechanisms underlying this association are poorly known, several hypotheses have been proposed: antipsychotic medication and antidepressants use, diet and physical activity or any other lifestyle factors. However, the high co-occurrence rate of depression and metabolic disorders suggests a possible pathophysiological overlap. In this paper I review several raised mechanisms for this overlap which are the hypothalamic-pituitary-adrenal axis dysregulation, immune alterations with chronic inflammation, as well as oxidative stress. In my view, there is one common thread running through all the aforementioned areas of pathophysiology which is microbiota alteration. So far, several possible interventions in our microbiota have been introduced into clinical practice - dietary and other lifestyle changes, supplementation with prebiotics or probiotics, fecal microbiota transplantation – but with vague indications. A better characterization of the above associations may represent a critical step at phenotyping, and a more targeted approach to the treatment of both depressive and metabolic disorders. At the end of the paper, I give several practical applications for future studies.

Depression and metabolic diseases often coexist having several features in common, e.g., chronic low-grade inflammation and intestinal dysbiosis. Different microbiota interventions have been proposed to be used as a treatment for these disorders. In the paper we review the efficacy of probiotics in depressive disorders, obesity, metabolic syndrome and its liver equivalent based on the published experimental studies, clinical trials and meta-analyses. Probiotics seem to be effective in reducing depressive symptoms when administered in addition to antidepressants. Additionally, probiotics intake may ameliorate some of the clinical components of metabolic diseases. However, standardized methodology regarding probiotics clinical trials has not been established yet. In this narrative review we discuss current knowledge on the recently used methodology with its strengths and limitations and propose criteria that may be implemented to create a new study of the effectiveness of probiotics in depressive disorders comorbid with metabolic abnormalities. We put across our choice on type of study population, probiotics genus, strains, dosages and formulations, intervention period, as well as primary and secondary outcome measures.

Tardive dyskinesia (TD) is a phenomenon predominantly observed as a result of the long-term use of dopamine receptor blockers (antipsychotics). TD is a group of involuntary, irregular hyperkinetic movements, mainly in the muscles of the face, eyelid muscles, lips, tongue, and cheeks, and less frequently in the limbs, neck, pelvis, and trunk. In some patients, TD takes on an extremely severe form, massively disrupting functioning, moreover, causing stigmatization and suffering. Deep brain stimulation (DBS), a method used, among others, in Parkinson's disease, is also an effective treatment for TD and often becomes a method of last resort, especially in severe, drug-resistant forms. The procedure is relatively new in TD, so the available reliable clinical studies are few and consist mainly of case reports. Unilateral and bilateral stimulation of two sites has proven efficacy in TD treatment. Most authors describe stimulation of the globus pallidus internus (GPi); less frequent descriptions involve the hypothalamic nucleus (STN). In the present paper, we provide up-to-date information on the stimulation of both mentioned brain areas. We also compare the efficacy of the two methods by comparing the two available studies, which included the largest groups of patients. Although GPi stimulation is more frequently used clinically, our initial analysis indicates comparable results (reduction of involuntary movements) with STN DBS.

There is a huge need to search for new treatment options and potential biomarkers of therapeutic response to antidepressant treatment. Depression and metabolic syndrome often coexist while pathophysiological overlap, including microbiota changes, may play a role. The aim of the study is to assess the effect of probiotic supplementation on symptoms of depression, anxiety and stress, metabolic parameters, inflammation and oxidative stress markers, and faecal microbiota in adult patients with depressive disorders depending on the co-occurance of MetS. The trial will be a four-arm, parallel group, prospective, randomized, double-blind, controlled design that will include 200 participants and will last 20 weeks. The probiotic preparation will contain Lactobacillus helveticus Rosell®-52, Bifidobacterium longum Rosell®-175. We will assess the level of depression, anxiety and stress, quality of life, blood pressure, body mass index and waist circumference, white blood cells count, serum levels of C-reactive protein, HDL cholesterol, triglicerides, fasting glucose, faecal microbiota composition and the level of some faecal microbiota metabolites, as well as inflammation markers and oxidative stress parameters in serum. The trial may establish a safe and easy-to-use treatment option as an adjunct in a subpopulation of depressive patients only partially responsive to pharmacologic treatment. (ClinicalTrials.gov identifier: ).