Involvement of glutamatergic neurotransmission in the antidepressant-like effect of zinc in the chronic unpredictable stress model of depression

Baicalein induces apoptosis by inhibiting the glutamine-mTOR metabolic pathway in lung cancer

INTRODUCTION

Baicalein, a bioactive component of Scutellaria baicalensis Georgi, has been shown to promote apoptosis in non-small cell lung cancer cells. However, previous studies have not determined if baicalein exerts proapoptotic effects by modulating the metabolic pathways.

OBJECTIVE

To investigate if baicalein induces apoptosis in lung cancer cells by modulating the glutamine-mTOR metabolic pathway.

METHODS

The in vivo anti-lung cancer activity of baicalein (50, 100, and 200 mg/kg) was evaluated using a xenograft model. In vitro experiments were used to assess the efficacy of baicalein (for H1299: 12.5, 25, and 50 μM; for A549: 10, 20, and 40 μM) on lung cancer cell proliferation, colony formation, and apoptosis. Metabolomics analysis was performed using liquid chromatography-mass spectrometry. The binding of baicalein to glutamine transporters and glutaminase was examined using molecular docking. The overexpression of glutamine transporters was validated using qRT-PCR and western blot analyses. The levels of ASCT2, LAT1, GLS1, p-mTOR, mTOR, and apoptosis-related proteins were evaluated using western blot analysis.

RESULTS

Baicalein inhibited lung cancer xenograft tumor growth in vivo and suppressed proliferation and promoted apoptosis in lung cancer cells in vitro. Additionally, baicalein altered amino acid metabolites, especially glutamine metabolites, in H1299 and A549 cells. Mechanistically, baicalein interacted with glutamine transporters as well as glutaminase and inhibited their activation. The expression of mTOR, an apoptosis-related protein and downstream target of glutamine metabolism, was also inhibited by baicalein treatment. Importantly, we next demonstrated the suppression of mTOR signaling and the induction of apoptosis by baicalein were achieved by regulating glutamine metabolism.

CONCLUSION

Baicalein inhibited the mTOR signaling pathway and induced apoptosis by downregulating glutamine metabolism. The potential of baicalein to induce apoptosis in lung cancer cells by selectively targeting the glutamine-mTOR pathway suggests an encouraging approach for treating lung cancer.

Effects of Alcohol Extracts From Ganoderma resinaceum on Sleep in Mice Using Combined Transcriptome and Metabolome Analysis

Ganoderma resinaceum is a valuable Chinese medicine. This study aimed to investigate whether a G. resinaceum alcohol extract (GRAE) improves sleep, and analyze the potential mechanism. After 30 days of continuous administration of GRAE at various doses, GRAE (1,000 mg/kg.bw) prolonged pentobarbital sodium-induced sleep, increased the rate of sleeping in mice treated with a subthreshold dose of pentobarbital sodium, and shortened sleep latency. The mice brain was analyzed using UPLC-MS/MS and RNA-sequencing. Metabolomics analysis revealed that 73 metabolites in the high-dose (HD) group had changed significantly, mainly in amino acids and their derivatives, especially the accumulation of L-glutamine and PGJ2 (11-oxo-15S-hydroxy-prosta-5Z, 9, 13E-trien-1-oic acid). Transcriptome analysis revealed 500 differential genes between HD and control groups, mainly enriched in neuroactive ligand-receptor interaction, amphetamine addiction, and cocaine addiction pathways. The conjoint analysis of the transcriptome and metabolome showed that the biosynthesis of L-glutamine might be regulated by Homer1, Homer3, and Grin3b. This suggests that GRAE may affect L-glutamine accumulation by regulating the expression of these genes. This study showed that GRAE may prolong the sleep time of mice by reducing the accumulation of L-glutamine and deepens our understanding of the regulatory network between certain genes and L-glutamine.

Ursolic acid abrogates depressive-like behavior and hippocampal pro-apoptotic imbalance induced by chronic unpredictable stress

Emerging evidence has shown that ursolic acid exerts antidepressant-like effects, however, its ability to elicit an antidepressant-like response in rodents subjected to stress model that mimics behavioral and neurochemical alterations found in depression remains to be determined. Thus, this study investigated the possible antidepressant-like effect of ursolic acid in mice subjected to chronic unpredictable stress (CUS) for 14 days, and whether this effect could be associated with the modulation of serum corticosterone levels and hippocampal Bcl-2/Bax mRNA expression. Our results indicated that CUS induced a depressive-like behavior, as demonstrated by an increase in the immobility time and latency to first grooming in the tail suspension test and splash test, respectively. Conversely, the repeated administration of ursolic acid (0.1 mg/kg, p.o.) or fluoxetine (10 mg/kg, p.o.) in the last 7 days of CUS completely prevented CUS-induced behavioral alterations, suggesting an antidepressant-like effect. Additionally, CUS significantly increased the mRNA expression of Bax (pro-apoptosis marker), but not Bcl-2 (anti-apoptosis marker) in the hippocampus. Moreover, reduced hippocampal mRNA expression of Bcl-2/Bax ratio was detected in CUS-exposed mice. Ursolic acid, but not fluoxetine, prevented CUS-induced increase in the expression of Bax, but both ursolic acid and fluoxetine prevented CUS-induced reduction on Bcl-2/Bax ratio. Furthermore, neither CUS nor treatments with ursolic acid or fluoxetine altered serum corticosterone levels. Our study unveils the ability of ursolic acid to prevent the depressive-like behavior induced by stress and the modulation of Bcl-2/Bax expression could be associated with this response.

Interaction between zinc, the GPR39 zinc receptor and the serotonergic system in depression

Zinc signalling has a crucial impact on the proper functioning of the brain. Disturbances within the zincergic system may lead to neuropsychological disorders, including major depression. Studying this disease and designing effective treatment is hampered by its heterogeneous etiology and the diversified nature of the symptoms. Over the years, studies have shown that zinc deficiency and disturbances in the expression profile of the zinc receptor - GPR39 - might be a useful neurobiological indicator of a pathological state. Zinc levels and the zinc receptor are altered by classic antidepressant treatment, which indicates possible reciprocity between the monoaminergic system and zinc signalling. Disruptions in this specific interplay might be a cause of a pathological depressive state, and restoring balance and cooperation between those systems might be key to a successful form of pharmacotherapy. In this review, we aim to describe interactions between the serotonergic and zincergic systems and to highlight their significance in the pathophysiology and treatment of depression.

The impact of repetitive transcranial magnetic stimulation and fluoxetine on the brain lipidome in a rat model of chronic unpredictable stress

The antidepressant effect of repetitive transcranial magnetic stimulation (rTMS) has been extensively studied; growing evidence suggests that changes in lipid composition may be involved in the pathogenesis of depression and may be a targeted mechanism for treatment. However, the influence of rTMS on lipid composition and the differences between these effects compared to antidepressants like fluoxetine (Flx) have never been investigated. Using a chronic unpredictable stress (CUS) model in rats, we assessed the antidepressive effects of rTMS and Flx treatments and evaluated changes in lipid composition in the hippocampus and prefrontal cortex (PFC) using a mass spectrometry-based lipidomic approach. Both rTMS and Flx treatments ameliorated depressive-like behaviors induced by CUS. Moreover, changes in lipid composition, especially glycerophospholipids, sphingolipids, and glycerolipids induced by CUS in the hippocampus were more robust than those observed in the PFC. CUS led to decreased levels of 20 carbon-containing fatty acyls and polyunsaturated fatty acyls in the PFC, and decreased levels of acyl carnitines (AcCa) in both the hippocampus and PFC. Notably, rTMS treatment had higher impact than Flx on composition of glycerophospholipids and sphingolipids in the hippocampus that were altered by CUS, while Flx attenuated CUS-induced changes in the PFC to a greater extent than rTMS. However, neither was able to restore fatty acyls and AcCa to baseline levels. Altogether, modulation of the brain lipidome may be involved in the antidepressant action of rTMS and Flx, and the degree to which these treatments induce changes in lipid composition within the hippocampus and PFC might explain their differential antidepressant effects.

EAAT2 as a Research Target in Bipolar Disorder and Unipolar Depression: A Systematic Review

Glutamate is implicated in the neuropathology of both major depressive disorder and bipolar disorder. Excitatory amino acid transporter 2 (EAAT2) is the major glutamate transporter in the mammalian brain, removing glutamate from the synaptic cleft and transporting it into glia for recycling. It is thereby the principal regulator of extracellular glutamate levels and prevents neuronal excitotoxicity. EAAT2 is a promising target for elucidating the mechanisms by which the glutamate-glutamine cycle interacts with neuronal systems in mood disorders. Forty EAAT2 studies (published January 1992-January 2018) were identified via a systematic literature search. The studies demonstrated that chronic stress/steroids were most commonly associated with decreased EAAT2. In rodents, EAAT2 inhibition worsened depressive behaviors. Human EAAT2 expression usually decreased in depression, with some regional brain differences. Fewer data have been collected regarding the roles and regulation of EAAT2 in bipolar disorder. Future directions for research include correlating EAAT2 and glutamate levels in vivo, elucidating genetic variability and epigenetic regulation, clarifying intracellular protein and pharmacologic interactions, and examining EAAT2 in different bipolar mood states. As part of a macromolecular complex within glia, EAAT2 may contribute significantly to intracellular signaling, energy regulation, and cellular homeostasis. An enhanced understanding of this system is needed.

Regulation of Tau Protein on the Antidepressant Effects of Ketamine in the Chronic Unpredictable Mild Stress Model

Tau protein is known to play an important role in maintaining microtubule assembly and stabilization, and maintaining the normal morphology of neurons, but several studies have found that chronic stress leads to Tau hyperphosphorylation. A large number of clinical trials have found that ketamine, which is an N-methyl-D-aspartate receptor antagonist, produces a rapid, long-lasting, and potent antidepressant effect in patients suffering from major depression. This rapid antidepressant effect of ketamine, which involves many mechanisms, has attracted wide attention. However, the relationship between ketamine's antidepressant effects and Tau protein has rarely been examined. We used C57BL/6 and Tau KO mice exposed to 42 days of chronic unpredictable mild stress (the CUMS model) to investigate the effect of ketamine on behavioral changes and synaptic functioning of the hippocampus. The results showed that a single treatment of ketamine rapidly relieved the CUMS-induced anhedonia, depression-like, and anxious behaviors of the C57BL/6 mice. The abnormal behaviors were accompanied by increased levels of specific alterations of hyperphosphorylated Tau protein in cytoplasm and synapse in the hippocampus of the C57BL/6 mice, but ketamine reduced the aggregation of hyperphosphorylated Tau protein only in the synapse. We also found that CUMS exposure reduced the levels of GluA1 and PSD95 in the hippocampus of the C57BL/6 mice and that these deficits were reversed by ketamine. However, the Tau KO mice did not develop any stress-induced depressive behaviors or deficits of hippocampal function. The antidepressant effect of ketamine may decrease the levels of hyperphosphorylated Tau protein in synapse of C57BL/6 mice.

Zinc Chloride Exposure Inhibits Brain Acetylcholine Levels, Produces Neurotoxic Signatures, and Diminishes Memory and Motor Activities in Adult Zebrafish

In this study, we evaluated the acute (24, 48, 72, and 96 h) and chronic (21 days) adverse effects induced by low doses (0.1, 0.5, 1, and 1.5 mg/L) of zinc chloride (ZnCl₂) exposure in adult zebrafish by using behavioral endpoints like three-dimensional (3D) locomotion, passive avoidance, aggression, circadian rhythm, and predator avoidance tests. Also, brain tissues were dissected and subjected to analysis of multiple parameters related to oxidative stress, antioxidant responses, superoxide dismutase (SOD), neurotoxicity, and neurotransmitters. The results showed that ZnCl₂-exposed fishes displayed decreased locomotor behavior and impaired short-term memory, which caused an Alzheimer’s Disease (AD)-like syndrome. In addition, low concentrations of ZnCl₂ induced amyloid beta (amyloid β) and phosphorylated Tau (p-Tau) protein levels in brains. In addition, significant induction in oxidative stress indices (reactive oxygen species (ROS) and malondialdehyde (MDA)), reduction in antioxidant defense system (glutathione (GSH), GSH peroxidase (GSH-Px) and SOD) and changes in neurotransmitters were observed at low concentrations of ZnCl₂. Neurotoxic effects of ZnCl₂ were observed with significant inhibition of acetylcholine (ACh) activity when the exposure dose was higher than 1 ppm. Furthermore, we found that zinc, metallothionein (MT), and cortisol levels in brain were elevated compared to the control group. A significantly negative correlation was observed between memory and acetylcholinesterase (AChE) activity. In summary, these findings revealed that exposure to ZnCl₂ affected the behavior profile of zebrafish, and induced neurotoxicity which may be associated with damaged brain areas related to memory. Moreover, our ZnCl₂-induced zebrafish model may have potential for AD-associated research in the future.

Stereological Study on the Positive Effect of Running Exercise on the Capillaries in the Hippocampus in a Depression Model

Running exercise is an effective method to improve depressive symptoms when combined with drugs. However, the underlying mechanisms are not fully clear. Cerebral blood flow perfusion in depressed patients is significantly lower in the hippocampus. Physical activity can achieve cerebrovascular benefits. The purpose of this study was to evaluate the impacts of running exercise on capillaries in the hippocampal CA1 and dentate gyrus (DG) regions. The chronic unpredictable stress (CUS) depression model was used in this study. CUS rats were given 4 weeks of running exercise from the fifth week to the eighth week (20 min every day from Monday to Friday each week). The sucrose consumption test was used to measure anhedonia. Furthermore, stereological methods were used to investigate the capillary changes among the control group, CUS/Standard group and CUS/Running group. Sucrose consumption significantly increased in the CUS/Running group. Running exercise has positive effects on the capillaries parameters in the hippocampal CA1 and DG regions, such as the total volume, total length and total surface area. These results demonstrated that capillaries are protected by running exercise in the hippocampal CA1 and DG might be one of the structural bases for the exercise-induced treatment of depression-like behavior. These results suggest that drugs and behavior influence capillaries and may be considered as a new means for depression treatment in the future.

Evidence for the involvement of heme oxygenase-1 in the antidepressant-like effect of zinc

BACKGROUND

Considering that heme oxygenase-1 (HO-1) and the brain-derived neurotrophic factor (BDNF)-mediated pathway are involved in the pathophysiology of depression and that zinc has been shown to exert beneficial effects in the management of depression, this study investigated the influence of these targets on the antidepressant-like effect of zinc.

METHODS

Mice were treated with sub-effective or effective doses of zinc chloride (ZnCl₂, 10 mg/kg, po), and 45 min later, they received intracerebroventricular (icv) injections of sub-effective doses of either zinc protoporphyrin IX (ZnPP, 10 μg/mouse, HO-1 inhibitor), cobalt protoporphyrin IX (CoPP, 0.01 μg/mouse, HO-1 inducer) or K-252a (1 μg/mouse, TrkB receptor antagonist). Immobility time and locomotor activity were evaluated through the tail suspension test (TST) and open-field test (OFT), respectively. HO-1 immunocontents were evaluated in the prefrontal cortex and hippocampus 60 min after ZnCl₂ (10 mg/kg, po) treatment.

RESULTS

The antidepressant-like effect of ZnCl₂ was prevented by the treatment with ZnPP and K-252a. Furthermore, sub-effective doses of CoPP and ZnCl₂ produced a synergistic antidepressant-like effect in the TST. None of the treatments altered locomotor activity. ZnCl₂ administration increased HO-1 immunocontents only in the prefrontal cortex.

CONCLUSIONS

The results indicate that the antidepressant-like effect of ZnCl₂ in the TST may depend on the induction of HO-1, and activation of TrkB receptor.

Acute agmatine administration, similar to ketamine, reverses depressive-like behavior induced by chronic unpredictable stress in mice

Agmatine is an endogenous neuromodulator that has been shown to have antidepressant-like properties. We have previously demonstrated that it can induce a rapid increase in BDNF levels after acute administration, suggesting that agmatine may be a fast-acting antidepressant. To investigate this hypothesis, the present study evaluated the effects of a single administration of agmatine in mice subjected to chronic unpredictable stress (CUS), a model of depression responsive only to chronic treatment with conventional antidepressants. The ability of agmatine to reverse CUS-induced behavioral and biochemical alterations was evaluated and compared with those elicited by the fast-acting antidepressant (ketamine) and the conventional antidepressant (fluoxetine). After exposed to CUS for 14days, mice received a single oral dose of agmatine (0.1mg/kg), ketamine (1mg/kg) or fluoxetine (10mg/kg), and were submitted to behavioral evaluation after 24h. The exposure to CUS caused an increased immobility time in the tail suspension test (TST) but did not change anhedonic-related parameters in the splash test. Our findings provided evidence that, similarly to ketamine, agmatine is able to reverse CUS-induced depressive-like behavior in the TST. Western blot analyses of prefrontal cortex (PFC) demonstrated that mice exposed to CUS and/or treated with agmatine, fluoxetine or ketamine did not present alterations in the immunocontent of synaptic proteins [i.e. GluA1, postsynaptic density protein 95 (PSD-95) and synapsin]. Altogether, our findings indicate that a single administration of agmatine is able to reverse behavioral alterations induced by CUS in the TST, suggesting that this compound may have fast-acting antidepressant-like properties. However, there was no alteration in the levels of synaptic proteins in the PFC, a result that need to be further investigated in other time points.

Behavioral Abnormality Induced by Enhanced Hypothalamo-Pituitary-Adrenocortical Axis Activity under Dietary Zinc Deficiency and Its Usefulness as a Model

Dietary zinc deficiency increases glucocorticoid secretion from the adrenal cortex via enhanced hypothalamo-pituitary-adrenocortical (HPA) axis activity and induces neuropsychological symptoms, i.e., behavioral abnormality. Behavioral abnormality is due to the increase in glucocorticoid secretion rather than disturbance of brain zinc homeostasis, which occurs after the increase in glucocorticoid secretion. A major target of glucocorticoids is the hippocampus and their actions are often associated with disturbance of glutamatergic neurotransmission, which may be linked to behavioral abnormality, such as depressive symptoms and aggressive behavior under zinc deficiency. Glucocorticoid-mediated disturbance of glutamatergic neurotransmission in the hippocampus is also involved in the pathophysiology of, not only psychiatric disorders, such as depression, but also neurodegenerative disorders, e.g., Alzheimer’s disease. The evidence suggests that zinc-deficient animals are models for behavioral and psychological symptoms of dementia (BPSD), as well as depression. To understand validity to apply zinc-deficient animals as a behavioral abnormality model, this paper deals with the effect of antidepressive drugs and herbal medicines on hippocampal dysfunctions and behavioral abnormality, which are induced by enhanced HPA axis activity under dietary zinc deficiency.