Abstract
Major depressive disorder (MDD) is a common mental illness. Evidence suggests that the gut microbiota play an essential role in regulating brain functions and the pathogenesis of neuropsychiatric diseases, including MDD. There are numerous mechanisms through which the gut microbiota and brain can exchange information in a continuous, bidirectional communication. Current research emphasizes the interexchange of signals influenced by the gut microbiota that are detected and transduced in information from the gut to the nervous system involving neural, endocrine, and inflammatory mechanisms, suggesting a relationship between oxidative stress and the pathophysiology of MDD via the hyperactivation of inflammatory responses. Potential sources of inflammation in the plasma and hippocampus of depressed individuals could stem from increases in intestinal permeability. Some nutraceuticals, such as specific probiotics, namely psychobiotics, polyphenols, carotenoids, butyrate, and prebiotics, have been demonstrated to exert an antidepressant activity, but most of them need to be metabolized and activated by gut microorganisms. By inducing changes in the gut microbiota composition, physical exercise might also exert a role in alleviating depression-like symptoms. The mutual relationships among nutraceuticals, exercise, and depression will be discussed, and the potential role of the gut microbiota as a therapeutic target to treat depression will be explored.
Highlights
Major depressive disorder (MDD) is a common psychiatric illness characterized by feelings of guilt, low mood, and cognitive deficits, as well as physical changes, such as weight loss, disturbed sleep, and appetite [1]
In Wistar rats, quercetin and diets high in polyphenols reduced the mRNA expression of corticotropin-releasing factor (CRF) in the hypothalamus area, inhibiting the HPA axis activation generated by acute water immersion restraint, and resulting in decreased depressive-like behavior [115]
Crocin-I supplementation (40 mg/kg for six weeks) decreased the gut microbiota dysbiosis in depressed mice, represented by the decreased abundance of Proteobacteria and Bacteroidetes, Sutterella spp. and Ruminococcus spp., and increased abundances of Firmicutes, Lactobacillus spp., and Bacteroides spp., with an increase of short-chain fatty acids (SCFAs). These results suggested that crocin-I effectively alleviated depression-like behavior, likely depending on the gut microbiota and its modulation of the intestinal barrier and SCFAs [150]
Summary
Major depressive disorder (MDD) is a common psychiatric illness characterized by feelings of guilt, low mood, and cognitive deficits, as well as physical changes, such as weight loss, disturbed sleep, and appetite [1]. Some evidence suggests that the gut microbiota play an essential role in the function of the central nervous system (CNS) and the pathophysiology of several mental diseases, including depression [7]. Gut microbiota imbalance has been observed in people affected by MDD [11]. In this light, recently, it has been demonstrated that “psychobiotics”, a new family of probiotics, can influence gut–brain relationships [12]. Beneficial psychotropic effects of Lactobacillus plantarum ATCC 8014 accompanied with inulin have been reported by Morshedi et al [12] Other nutraceuticals such as polyphenols, carotenoids, and butyrate have demonstrated an antidepressant activity, but most of them need to be metabolized and activated by gut microorganisms. The mutual relationships among nutraceuticals, gut microbiota, exercise, and depression will be discussed, and in perspective, the potential role of the intestinal microbiota as a therapeutic target to treat depression will be explored
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