Antidepressant actions of melatonin and melatonin receptor agonist: Focus on pathophysiology and treatment.

Depression has become one of the most commonly prevalent neuropsychiatric disorders, and the main characteristics of depression are sleep disorders and melatonin secretion disorders caused by circadian rhythm disorders. Abnormal endogenous melatonin alterations can contribute to the occurrence and development of depression. However, molecular mechanisms underlying this abnormality remain ambiguous. The present review summarizes the mechanisms underlying the antidepressant effects of melatonin, which is related to its functions in the regulation of the hypothalamic-pituitary-adrenal axis, inhibition of neuroinflammation, inhibition of oxidative stress, alleviation of autophagy, and upregulation of neurotrophic, promotion of neuroplasticity and upregulation of the levels of neurotransmitters, etc. Also, melatonin receptor agonists, such as agomelatine, ramelteon, piromelatine, tasimelteon, and GW117, have received considerable critical attention and are highly implicated in treating depression and comorbid disorders. This review focuses on melatonin and various melatonin receptor agonists in the pathophysiology and treatment of depression, aiming to provide further insight into the pathogenesis of depression and explore potential targets for novel agent development.

The molecular mechanism underlying mitophagy-mediated hippocampal neuron apoptosis in diabetes-related depression.

Diabetes-related depression (DD) is a major complication of diabetes mellitus. Our previous studies indicated that glutamate (Glu) and hippocampal neuron apoptosis are key signal and direct factor leading to diabetes-related depression, respectively. However, the accurate pathogenesis remains to be unclear. We hypothesized that diabetes-related depression might be associated with the mitophagy-mediated hippocampal neuron apoptosis, triggered by aberrant Glu-glutamate receptor2 (GluR2)-Parkin pathway. To testify this hypothesis, here the rat model of DD in vivo and in vitro were both established so as to uncover the potential mechanism of DD based on mitophagy and apoptosis. We found that DD rats exhibit an elevated glutamate levels followed by monoamine neurotransmitter deficiency and depressive-like behaviour, and DD modelling promoted autophagosome formation and caused mitochondrial impairment, eventually leading to hippocampal neuron apoptosis via aberrant Glu-GluR2-Parkin pathway. Further, in vitro study demonstrated that the simulated DD conditions resulted in an abnormal glutamate and monoamine neurotransmitter levels followed by autophagic flux increment, mitochondrial membrane potential reduction and mitochondrial reactive oxygen species and lactic dehydrogenase elevation. Interestingly, both GluR2 and mammalian target of rapamycin (mTOR) receptor blocker aggravated mitophagy-induced hippocampal neuron apoptosis and abnormal expression of apoptotic protein. In contrast, both GluR2 and mTOR receptor agonist ameliorated those apoptosis in simulated DD conditions. Our findings revealed that mitophagy-mediated hippocampal neuron apoptosis, triggered by aberrant Glu-GluR2-Parkin pathway, is responsible for depressive-like behaviour and monoamine neurotransmitter deficiency in DD rats. This work provides promising molecular targets and strategy for the treatment of DD.

[Effect of Baihe Dihuang Decoction on synaptic plasticity of hippocampus in rats with anxious depression].

To explore the effect of Baihe Dihuang Decoction on the synaptic plasticity of hippocampal neurons in rats with anxious depression. Fifty SD rats were randomly divided into normal group, model group, venlafaxine group(6.75 mg·kg~(-1)), high-dose Baihe Dihuang Decoction group(8.64 g·kg~(-1)) and low-dose Baihe Dihuang Decoction group(4.32 g·kg~(-1)). Chronic restraint stress(6 h) combined with corticosterone(ih, 30 mg·kg~(-1)) was used to establish an anxious depression model, and 7 days after modeling, the administration started and continued for 21 days. The anxiety and depression-like behaviors of the rats were evaluated. Golgi-Cox staining and electron microscopy were used to observe the morphology and ultrastructural changes of synaptic dendrites. Immunofluorescence was used to detect the expression of hippocampal synaptic plasticity protein synapsin-1 and postsynaptic density protein 95(PSD-95). Western blot method was used to detect the expression of functional protein synaptophysin(SYP) and synaptic Ras GTPase activating protein(SynGap). The results showed that the rats in the model group had obvious anxiety and depression-like behaviors, the hip-pocampal dendritic spine density and branch length were reduced, the number of synapses was cut, and the internal structure was da-maged. The average fluorescence intensity of synapsin-1 and PSD-95 was significantly reduced and the expression of SYP and SynGap also decreased. High-dose Baihe Dihuang Decoction could significantly improve the anxiety and depression-like behaviors of model rats, relieve synaptic damage, and increase the expression of synapsin-1, PSD-95, SYP, and SynGap proteins. Therefore, we believe that Baihe Dihuang Decoction can improve anxiety and depression behaviors by regulating the synaptic plasticity of hippocampal neurons.

GR/NF-κB signaling pathway regulates hippocampal inflammatory responses in diabetic rats with chronic unpredictable mild stress.

Clinical studies have shown that diabetes can present with underlying depression, and a combination of the two can lead to emotional, memory and cognitive disorders, closely associated with hippocampal neuroinflammation. However, the mechanism underlying the development of hippocampal neuroinflammation under the above condition remains elusive. The aims of this study were to explore the pathogenesis of diabetes combined with depression, and the effect of dexamethasone (Dex), a glucocorticoid receptor (GR) agonist, on hippocampal neuroinflammation in diabetic rats with chronic unpredictable mild stress (CUMS). Therefore, rats were intragastrically fed on a high-fat diet (10% cholesterol 10 ml/kg) for 14 days and thereafter injected with 38 mg/kg of streptozotocin on the 15th day to induce diabetes. Dex treatment of the diabetic and CUMS rats ameliorated the depression-associated behavior in the respective rats. Apart from enhanced depressive behavior, diabetes-depressed condition also up-regulated the expression of hippocampus microglia chemokine Ⅰ receptor (CX3CR1) and secretion of several pro-inflammatory factors, in particular, interleukin 1ß (IL-1ß), interleukin-6 (IL-6), interleukin-8 (IL-8) and tumor necrosis factor - α (TNF-α). Hematoxylin-eosin staining revealed inflammatory damages in the hippocampus. Western blot analysis further revealed repression of GR proteins converse to the nuclear factor kappa-B (NF-κB) proteins, which were up-regulated. Intriguingly, Dex reversed the above events by inhibiting inflammatory reactions in the hippocampus. Consequently, played an antidepressant effect in diabetic and CUMS model rats. Overall, findings of this research suggest that the physiopathology of diabetes with stress cormobity are mediated by inflammatory reactions in the hippocampus. In particular, the responses are associated with regulation of GR/NF-κB signaling pathway.

Molecular Detection and Identification of Candidatus Ehrlichia Hainanensis, A Novel Ehrlichia Species in Rodents from Hainan Province, China.

Ehrlichia (Anaplasmataceae family) are obligatory intracellular bacteria that infect humans and animals. They are hosted by mammals such as canines, bovines and wild rodents, and are vectored by ticks. In this study, we collected 121 rodent samples comprising 67 Niviventer fulvescens, 27 Rattus tanezumi, 24 Chiromyscus sp., 2 Rattus nitidus and 1 Leopoldamys edwardsi from Hainan province, which includes the second largest island in China. The presence and genetic diversity of Ehrlichia species was evaluated and characterized by amplification and sequencing of 16S rRNA, groEL and gltA genes. An Ehrlichia species was detected in 5 of the 67 Niviventer fulvescens samples (7.46%). The 16S rRNA, groEL and gltA genes showed the highest identity to known Ehrlichia sequences (99.20%, 89.87% and 83.86%, respectively). In the phylogenetic trees they formed a cluster distinct from all other species. We propose that this species is a putative novel Ehrlichia species, which we suggest be named Candidatus Ehrlichia hainanensis. Its pathogenicity to humans remains to be further researched, and molecular surveillance in local populations is needed.

Abnormal Glu/mGluR2/3/PI3K pathway in the hippocampal neurovascular unit leads to diabetes-related depression.

Our previous studies have shown that glutamate and hippocampal neuron apoptosis are key signals and direct factors associated with diabetes-related depression, and structural and functional damage to the hippocampal neurovascular unit has been associated with diabetes-related depression. However, the underlying mechanism remains unclear. We hypothesized that diabetes-related depression might be associated with the glutamate (Glu)/metabotropic glutamate receptor2/3 (mGluR2/3)/phosphoinositide 3-kinase (PI3K) pathway, activated by glucocorticoid receptors in the hippocampal neurovascular unit. To test this hypothesis, rat hippocampal neurovascular unit models, containing hippocampal neurons, astrocytes, and brain microvascular endothelial cells, were treated with 150 mM glucose and 200 µM corticosterone, to induce diabetes-related depression. Our results showed that under conditions of diabetes complicated by depression, hippocampal neurovascular units were damaged, leading to decreased barrier function; elevated Glu levels; upregulated glucocorticoid receptor, vesicular glutamate transporter 3 (VGLUT-3), and metabotropic glutamate receptor 2/3 (mGluR2/3) expression; downregulated excitatory amino acid transporter 1 (EAAT-1) expression; and alteration of the balance of key proteins associated with the extracellular signal-regulated kinase (ERK)/glial cell-derived neurotrophic factor (GDNF)/PI3K signaling pathway. Moreover, the viability of neurons was dramatically reduced in the model of diabetes-related depression, and neuronal apoptosis, and caspase-3 and caspase-9 expression levels, were increased. Our results suggest that the Glu/mGluR2/3/PI3K pathway, induced by glucocorticoid receptor activation in the hippocampal neurovascular unit, may be associated with diabetes-related depression. This study was approved by the Laboratory Animal Ethics Committee of The First Hospital of Hunan University of Chinese Medicine, China (approval No. HN-ZYFY-2019-11-12) on November 12, 2019.

Effects of different drying methods on the chemical constituents of Lilium lancifolium Thunb. based on UHPLC-MS analysis and antidepressant activity of the main chemical component regaloside A.

The Lilium lancifolium Thunb. is a herb with multiple functions in both medicine and food in China, and its extracts have shown antidepressant effects. In this study, fresh bulbs of Lilium lancifolium Thunb. were processed to study the effects of different drying processes on changes in its main chemical components. We found that different drying methods can affect the chemical constituents of the herb. Among these components, Regaloside A has been found as the characteristic component. Here, Cell Counting Kit-8 assay, and Western blotting were used to evaluate the neuroprotective antidepressant effects of Regaloside A. The results showed the cell survival rate was improved, the phosphorylation levels of brain-derived neurotrophic factor, tyrosine kinase receptor B, phosphatidylinositol 3 kinase, protein kinase B, and mammalian target of rapamycin were increased after Regaloside A treatment. In general, different drying methods have a significant influence on the chemical composition of the herb, and Regaloside A may be the main chemical component of the herb. It can alleviate the damage of corticosterone in SH-SY5Y cells, and phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin signaling mediated by brain-derived neurotrophic factor/tyrosine kinase receptor B may play an important role in the neuroprotective antidepressant effects of Regaloside A.

[Effects of ELK-1/JNK/c-Fos on apoptosis of rat hippocampal neurons cultured in vitro with Zuogui Jiangtang Jieyu Formula in simulated diabetes mellitus complicated with depression].

OBJECTIVE: To study the effects of Zuogui Jiangtang Jieyu Formula (ZGJTJYF, the Chinese Medicine) on hippocampal neuron apoptosis in diabetes mellitus complicated with depression (DD). METHODS: The primary cultured hippocampal neurons were treated with high glucose (150 mmol/L) and corticosterone (200 micromol/L) to establish the cell model of DD in vitro. The cultured hippocampal neurons were randomly divided into five groups: blank serum group, normal group, Zuogui Jiangtang Jieyu recipe drug-containing serum group, positive drug (metformin + fluoxetine) drug-containing serum group and model group (three compound holes in each group). The model group and the normal group were given the same amount of culture medium, and the other groups were given the corresponding serum with 10% volume fraction for 18 hours. Hoechst staining, high content cell imaging and RT-PCR were used to detect the apoptosis of hippocampal neurons and the expressions of apoptosis-related ETS-like 1 transcription factor(ELK-1), C-Jun N-terminal kinase(JNK) and c-Fos proteins and genes. RESULTS: Compared with the blank group, the apoptotic number of hippocampal neurons in the model group was increased significantly, and the expression levels of ELK-1, JNK and c-Fos were increased significantly (P＜0.05). Compared with the model group, the local bright spots of hippocampal neurons in the Zuogui Jiangtang Jieyu recipe-containing serum group and the positive drug-containing serum group were decreased significantly, and the number of apoptotic cells was decreased significantly. The expressions of JNK, c-fos protein and mRNA were down-regulated significantly (P＜ 0.05), and the neural network and dendritic junction were improved significantly. CONCLUSION: Zuo Gui Jiang Tang Jie Yu Formula can reverse the expressions of ELK-1, JNK and c-Fos signals in hippocampal neurons under DD environment and play an anti-apoptotic effect.

[Damages and its mechanism of the blood brain barrier in rats with diabetes mellitus with depression].

OBJECTIVE: To investigate the expressions of key proteins type IV collagen (CoIV), zonula occludens-1(ZO-1), α-smooth muscle actin(a-SMA) and the mechanisms of the structural injuries of the blood brain barrier in the hippocampus of diabetic rats with depression. METHODS: After 14 days of high-fat diet, the rats were treated with streptozotocin (STZ, 38 mg/kg, iv). Then, the animals were randomly divided into 2 groups (n=15):the diabetic group and the diabetes mellitus with depression group. The normal rats were randomly divided into 2 groups(n=15):the control group and the depression group. Diabetic group and control group were kept in normal conditions. The diabetes mellitus with depression group and the depression group were treated with chronic unpredictable stress for 28 days. The levels of blood glucose were detected. The behavior changes of rats were evaluated by open-field test and Morris test. The blood brain barrier morphological changes were observed under the electron microscope. The expressions of CoIV, ZO-1 and a-SMA in rat hippocampal blood-brain barrier were detected by immunocytochemistry. RESULTS: Compared with control group, the level of blood glucose was increased,the number of autonomic activity was decreased, the escape latencies were significantly longer in the Morris water maze test, as well as the space exploration times were shortened in the diabetes mellitus with depression group (P<0.05, P<0.01). The endothelial cells of the hippocampus were blurred, the capillary lumen was narrow, and the peripheral glial cells were edema, the expressions of ZO-1 and a-SMA were decreased(P <0.05), while the expression of CoIV was increased(P <0.05). Compared with diabetic group, the number of autonomic activity in the diabetes mellitus with depression group was significantly decreased (P<0.01), the escape latencies were longer (P<0.05), the blood brain barrier capillary lumen was more narrow and the glial cell terminal edema was more obvious, the expression of a-SMA was decreased(P<0.05). CONCLUSIONS: The abnormal expressions of ZO-1, CoIV and -SMA, key proteins in the hippocampal blood brain barrier, may be involved in the mechanisms of structural damages of the blood brain barrier in diabetes mellitus with depression.

[Effect of acupuncture on serum MIP-2 and MIP-2 mRNA expressions in isolated Fei and Dachang of severe acute pancreatitis induced acute lung injury rats in the acute phase].

OBJECTIVE: To observe effect of acupuncture on serum macrophage inflammatory protein-2 (MIP-2) and MIP-2 mRNA expressions in isolated Fei and Dachang of severe acute pancreatitis (SAP) induced acute lung injury (ALI) rats in the acute phase. METHODS: Forty male Wistar rats were randomly divided into four groups, i.e., the sham-operation group, the SAP group, the acupuncture treatment group, and the acupuncture control group, 10 in each group. The SAP model was induced by retrograde infusion of 3.5% sodium taurocholate into the pancreatobiliary duct. Under the guidance of "Fei and Dachang exterior-inferiorly related", points were acupunctured along Fei, Dachang, and Pi channels, as well as those points on the back of rats in the acupuncture treatment group 0.5 h after modeling. Besides, points were acupunctured along Fei and Pi channels, as well as those points on the back of rats in the acupuncture control group 0.5 h after modeling. Serum levels of tumor necrosis factor alpha (TNF-alpha) and nitric oxide (NO), and MIP-2 expressions were examined 6 h after modeling. Expressions of MIP-2 mRNA in isolated lung and large intestine tissues were detected by reverse transcription PCR. RESULTS: Compared with the sham-operation group, serum levels of TNF-alpha and NO, and expressions of MIP-2 and MIP-2 mRNA in isolated lung and large intestine tissues were significantly higher in the SAP group (P < 0.05). Each index was lower in the acupuncture treatment group than in the SAP group and the acupuncture control group (P < 0.05). Besides, the serum level of MIP-2 and the MIP-2 mRNA expression in isolated lung and large intestine tissues were positively correlated in all groups except the sham-operation group (P < 0.05). CONCLUSIONS: Under the guidance of "Fei and Dachang exterior-inferiorly related", acupuncture could remarkably reduce the severity of SAP induced ALI rats in the acute phase. Its mechanism might be related to suppressing over-expressions of MIP-2 mRNA in isolated lung and large intestine tissues, and lowering the serum MIP-2 expression level.

[Effects of H2 relaxin on the expression of Epac in a murine model of chronic asthma].

OBJECTIVE: To explore the effects of H(2) relaxin on the expression of exchange protein directly activated by cyclic adenosine monophosphate (Epac) in a murine model of chronic asthma and the roles in the management of airway remodelling. METHODS: Thirty-two BALB/c mice were randomly divided into 4 groups of normal control, asthma, vehicle control and relaxin treatment (n = 8 each). They were sensitized and challenged with ovalbumin to establish a chronic asthmatic model. The vehicle control and relaxin treatment groups were subcutaneously injected with saline and relaxin (0.25 mg×kg(-1)×d(-1)) respectively. Alteration of airway inflammation was observed by hematoxylin-eosin (HE) staining. The airway expressions of proliferating cell nuclear antigen (PCNA) and α-smooth muscle actin (α-SMA) were evaluated by immunohistochemistry. The protein expression of Epac and phosphorylated extracellular signal regulated kinases1/2 (p-ERK1/2) were detected by Western blot. RESULTS: Compared to those in the normal control group, massive infiltration of inflammatory cells, airway stenosis, bronchial smooth muscle hypertrophy were present in the asthmatic and vehicle control groups. The above-mentioned changes were significantly ameliorated in the relaxin treatment group. The percentage of PCNA positive cells (34.8% ± 6.1%, 33.5% ± 6.6%) and the expression of α-SMA ((1.70 ± 0.25), (1.54 ± 0.24) µm(2)/µm) in the asthmatic and vehicle control groups were significantly higher than those in the normal control group (9.9% ± 2.6%, (0.51 ± 0.16) µm(2)/µm) (all P < 0.05) while administration of relaxin decreased the airway expression levels of PCNA and α-SMA (22.9% ± 5.2%, (1.06 ± 0.25) µm(2)/µm) (all P < 0.05). The results of Western blot showed that the expression levels of Epac in the asthmatic and vehicle groups (0.62 ± 0.12, 0.68 ± 0.11) were lower than those in the control group (1.50 ± 0.17) (all P < 0.05) while it significantly increased in the relaxin group (1.08 ± 0.15) (all P < 0.05). The levels of phosphorylation of ERK1/2 in the asthmatic and vehicle groups (1.45 ± 0.13, 1.36 ± 0.09) were higher than those in the control group (0.38 ± 0.17) (all P < 0.05) while it decreased in the relaxin treatment group (0.72 ± 0.06) (all P < 0.05). No differences existed in all parameters between the asthmatic and vehicle groups (P > 0.05). CONCLUSION: Relaxin alleviates the airway inflammation and airway smooth muscle cell proliferation in a murine model of chronic asthma probably through activating Epac and inhibiting the phosphorylation of ERK1/2.