Pharmacological Screening of Mangifera indica Seeds for Antidepressant-like Action Along with a Mechanistic Study

Prevalence of perturbed gut microbiota in pathophysiology of arsenic-induced anxiety- and depression-like behaviour in mice

Severe toxic effects of arsenic on human physiology have been of immense concern worldwide. Arsenic causes irrevocable structural and functional disruption of tissues, leading to major diseases in chronically exposed individuals. However, it is yet to be resolved whether the effects result from direct deposition and persistence of arsenic in tissues, or via activation of indirect signaling components. Emerging evidences suggest that gut inhabitants play an active role in orchestrating various aspects of brain physiology, as the gut-brain axis maintains cognitive health, emotions, learning and memory skills. Arsenic-induced dysbiosis may consequentially evoke neurotoxicity, eventually leading to anxiety and depression. To delineate the mechanism of action, mice were exposed to different concentrations of arsenic. Enrichment of Gram-negative bacteria and compromised barrier integrity of the gut enhanced lipopolysaccharide (LPS) level in the bloodstream, which in turn elicited systemic inflammation. Subsequent alterations in neurotransmitter levels, microglial activation and histoarchitectural disruption in brain triggered onset of anxiety- and depression-like behaviour in a dose-dependent manner. Finally, to confirm whether the neurotoxic effects are specifically a consequence of modulation of gut microbiota (GM) by arsenic and not arsenic accumulation in the brain, fecal microbiota transplantations (FMT) were performed from arsenic-exposed mice to healthy recipients. 16S rRNA gene sequencing indicated major alterations in GM population in FMT mice, leading to severe structural, functional and behavioural alterations. Moreover, suppression of Toll-like receptor 4 (TLR4) using vivo-morpholino oligomers (VMO) indicated restoration of the altered parameters towards normalcy in FMT mice, confirming direct involvement of the GM in inducing neurotoxicity through the arsenic-gut-brain axis. This study accentuates the potential role of the gut microbiota in promoting neurotoxicity in arsenic-exposed mice, and has immense relevance in predicting neurotoxicity under altered conditions of the gut for designing therapeutic interventions that will target gut dysbiosis to attenuate arsenic-mediated neurotoxicity.

µ-Opioid receptor antagonism facilitates the anxiolytic-like effect of oxytocin in mice

Mood and anxiety disorders are leading causes of disability worldwide and are major contributors to the global burden of diseases. Neuropeptides, such as oxytocin and opioid peptides, are important for emotion regulation. Previous studies have demonstrated that oxytocin reduced depression- and anxiety-like behavior in male and female mice, and opioid receptor activation reduced depression-like behavior. However, it remains unclear whether the endogenous opioid system interacts with the oxytocin system to facilitate emotion regulation in male and female mice. We hypothesized that opioid receptor blockade would inhibit the anxiolytic- and antidepressant-like effects of oxytocin. In this study, we systemically administered naloxone, a preferential μ-opioid receptor antagonist, and then intracerebroventricularly administered oxytocin. We then tested mice on the elevated zero maze and the tail suspension tests, respective tests of anxiety- and depression-like behavior. Contrary to our initial hypothesis, naloxone potentiated the anxiolytic-like, but not the antidepressant-like, effect of oxytocin. Using a selective μ-opioid receptor antagonist, D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2, and a selective κ-opioid receptor antagonist, norbinaltorphimine, we demonstrate that μ-opioid receptor blockade potentiated the anxiolytic-like effect of oxytocin, whereas κ-opioid receptor blockade inhibited the oxytocin-induced anxiolytic-like effects. The present results suggest that endogenous opioids can regulate the oxytocin system to modulate anxiety-like behavior. Potential clinical implications of these findings are discussed.

Implication of Wnt/GSK-3β/β-Catenin Signaling in the Pathogenesis of Mood Disturbances Associated with Hyperthyroidism in Rats: Potential Therapeutic Effect of Naringin

Patients with hyperthyroidism are commonly diagnosed with mood disorders. Naringin, (4',5,7-trihydrocyflavanone-7-O-rhamnoglucoside), a natural bioflavonoid, has many neurobehavioral activities including anxiolytic and antidepressant properties. The role of Wingless (Wnt) signaling in psychiatric disorders is considered substantial but debatable. Recently, regulation of Wnt signaling by naringin has been reported in different disorders. Therefore, the present study aimed to investigate the possible role of Wnt/GSK-3β/β-catenin signaling in hyperthyroidism-induced mood disturbances and explore the therapeutic effects of naringin. Hyperthyroidism was induced in rats by intraperitoneal injection of 0.3 mg/kg levothyroxine for 2 weeks. Naringin was orally administered to rats with hyperthyroidism at a dose of 50 or 100 mg/kg for 2 weeks. Hyperthyroidism induced mood alterations as revealed by behavioral tests and histopathological changes including marked necrosis and vacuolation of neurons in the hippocampus and cerebellum. Intriguingly, hyperthyroidism activated Wnt/p-GSK-3β/β-catenin/DICER1/miR-124 signaling pathway in the hippocampus along with an elevation in serotonin, dopamine, and noradrenaline contents and a reduction in brain-derived neurotrophic factor (BDNF) content. Additionally, hyperthyroidism induced upregulation of cyclin D-1 expression, malondialdehyde (MDA) elevation, and glutathione (GSH) reduction. Naringin treatment alleviated behavioral and histopathological alterations and reversed hyperthyroidism-induced biochemical changes. In conclusion, this study revealed, for the first time, that hyperthyroidism could affect mental status by stimulating Wnt/p-GSK-3β/β-catenin signaling in the hippocampus. The observed beneficial effects of naringin could be attributed to increasing hippocampal BDNF, controlling the expression of Wnt/p-GSK-3β/β-catenin signaling as well as its antioxidant properties.

Antidepressant activity of phytochemicals of Mangifera indica seeds assisted by integrated computational analysis

Mangifera indica L., also known as mango, is a tropical fruit that belongs to the Anacardiaceae family and is prized for its juiciness, unique flavour, and worldwide popularity. The current study aimed to probe into antidepressant power (ADP) of MIS in animals and confirmation of ADP with in silico induced-fit molecular docking. The depression model was prepared by exposing mice to various stressors from 9:00 am to 2:00 pm during 42 days study period. MIS extract and fluoxetine were given daily for 30 min before exposing animals to stressors. ADP was evaluated by various behavioural tests and biochemical analysis. Results showed increased physical activity in mice under behavioural tests, plasma nitrite and malondialdehyde (MDA) levels and monoamine oxidase A (MAO-A) activity decreased dose-dependently in MIS treated mice and superoxide dismutases (SOD) levels increased in treated groups as compared to disease control. With the peculiar behaviour and significant interactions of the functional residues of target proteins with selected ligands along with the best absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties, it is concluded that catechin could be the best MAO-A inhibitor at a binding energy of -8.85 kcal/mol, and two hydrogen bonds were generated with Cys406 (A) and Gly443 (A) residues of the active binding site of MAO-A enzyme. While catechin at -6.86 kcal/mol generated three hydrogen bonds with Ala263 (A) and Gly434 (A) residues of the active site of monoamine oxidase B (MAO-B) enzyme and stabilized the best conformation. Therefore, it is highly recommended to test the selected lead-like compound catechin in the laboratory with biological system analysis to confirm its activity as MAO-A and MAO-B inhibitors so it can be declared as one of the novel therapeutic options with anti-depressant activity. Our findings concluded that M. indica seeds could be a significant and alternative anti-depressant therapy.