Objectives
The therapeutic effects of Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) in patients with major depression have shown promising results; however, there is a lack of mechanistic studies using biological markers (BM) as an outcome. Therefore, our aim was to review non-invasive brain stimulation trials in depression using BM.
Method
The following databases were used for our systematic review: MEDLINE, Web of Science, Cochrane, and SCIELO. We examined articles published before November 2012 that used TMS and tDCS as an intervention for depression and had BM as an outcome measure. The search was limited to human studies written in English.
Results
Of 1234 potential articles, 52 papers were included. Only studies using TMS were found. BM included immune and endocrine serum markers, neuroimaging techniques and electrophysiological outcomes. In 12 articles (21.4%) endpoint BM measurements were not significantly associated with clinical outcomes. All studies reached significant results in the main clinical rating scales. BM outcomes were used as predictors of response, to understand mechanisms of TMS, and as a surrogate of safety.
Conclusions
fMRI, SPECT, PET, MRS, cortical excitability and BDNF consistently showed positive results. BDNF was the best predictor of patients’ likeliness to respond. These initial results are promising; however, all studies investigating BM are small, used heterogeneous samples, and did not take into account confounders such as age, gender or family history. Based on our findings we recommend further studies to validate BM in non-invasive brain stimulation trials in MDD.
Glucagon-like peptide-1 (GLP-1) is a human incretin hormone derived from the proglucagon molecule. GLP-1 receptor agonists are frequently used to treat type 2 diabetes mellitus and obesity. However, the hormone affects the liver, pancreas, brain, fat cells, heart, and gastrointestinal tract. The objective of this study was to perform a systematic review on the use of GLP-1 other than in treating diabetes. PubMed, Cochrane, and Embase were searched, and the PRISMA guidelines were followed. Nineteen clinical studies were selected. The results showed that GLP-1 agonists can benefit defined off-medication motor scores in Parkinson’s Disease and improve emotional well-being. In Alzheimer’s disease, GLP-1 analogs can improve the brain’s glucose metabolism by improving glucose transport across the blood–brain barrier. In depression, the analogs can improve quality of life and depression scales. GLP-1 analogs can also have a role in treating chemical dependency, inhibiting dopaminergic release in the brain’s reward centers, decreasing withdrawal effects and relapses. These medications can also improve lipotoxicity by reducing visceral adiposity and decreasing liver fat deposition, reducing insulin resistance and the development of non-alcoholic fatty liver diseases. The adverse effects are primarily gastrointestinal. Therefore, GLP-1 analogs can benefit other conditions besides traditional diabetes and obesity uses.
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