A neuroendocrine mechanism of co-morbidity of depression-like behavior and myocardial injury in rats

Depression and coronary heart disease: mechanisms, interventions, and treatments

Coronary heart disease (CHD), a cardiovascular condition that poses a significant threat to human health and life, has imposed a substantial economic burden on the world. However, in contrast to conventional risk factors, depression emerges as a novel and independent risk factor for CHD. This condition impacts the onset and progression of CHD and elevates the risk of adverse cardiovascular prognostic events in those already affected by CHD. As a result, depression has garnered increasing global attention. Despite this growing awareness, the specific mechanisms through which depression contributes to the development of CHD remain unclear. Existing research suggests that depression primarily influences the inflammatory response, Hypothalamic-pituitary-adrenocortical axis (HPA) and Autonomic Nervous System (ANS) dysfunction, platelet activation, endothelial dysfunction, lipid metabolism disorders, and genetics, all of which play pivotal roles in CHD development. Furthermore, the effectiveness and safety of antidepressant treatment in CHD patients with comorbid depression and its potential impact on the prognosis of CHD patients have become subjects of controversy. Further investigation is warranted to address these unresolved questions.

The sex-dependent response to psychosocial stress and ischaemic heart disease

Stress is an important risk factor for modern chronic diseases, with distinct influences in males and females. The sex specificity of the mammalian stress response contributes to the sex-dependent development and impacts of coronary artery disease (CAD). Compared to men, women appear to have greater susceptibility to chronic forms of psychosocial stress, extending beyond an increased incidence of mood disorders to include a 2- to 4-fold higher risk of stress-dependent myocardial infarction in women, and up to 10-fold higher risk of Takotsubo syndrome-a stress-dependent coronary-myocardial disorder most prevalent in post-menopausal women. Sex differences arise at all levels of the stress response: from initial perception of stress to behavioural, cognitive, and affective responses and longer-term disease outcomes. These fundamental differences involve interactions between chromosomal and gonadal determinants, (mal)adaptive epigenetic modulation across the lifespan (particularly in early life), and the extrinsic influences of socio-cultural, economic, and environmental factors. Pre-clinical investigations of biological mechanisms support distinct early life programming and a heightened corticolimbic-noradrenaline-neuroinflammatory reactivity in females vs. males, among implicated determinants of the chronic stress response. Unravelling the intrinsic molecular, cellular and systems biological basis of these differences, and their interactions with external lifestyle/socio-cultural determinants, can guide preventative and therapeutic strategies to better target coronary heart disease in a tailored sex-specific manner.

Homocysteine-Induced Disturbances in DNA Methylation Contribute to Development of Stress-Associated Cognitive Decline in Rats

Chronic stress is generally accepted as the main risk factor in the development of cognitive decline; however, the underlying mechanisms remain unclear. Previous data have demonstrated that the levels of homocysteine (Hcy) are significantly elevated in the plasma of stressed animals, which suggests that Hcy is associated with stress and cognitive decline. To test this hypothesis, we analyzed the cognitive function, plasma concentrations of Hcy, and brain-derived neurotropic factor (BDNF) levels in rats undergoing chronic unpredicted mild stress (CUMS). The results showed that decreased cognitive behavioral performance and decreased BDNF transcription and protein expression were correlated with hyperhomocysteinemia (HHcy) levels in stressed rats. Diet-induced HHcy mimicked the cognitive decline and BDNF downregulation in the same manner as CUMS, while Hcy reduction (by means of vitamin B complex supplements) alleviated the cognitive deficits and BDNF reduction in CUMS rats. Furthermore, we also found that both stress and HHcy disturbed the DNA methylation process in the brain and induced DNA hypermethylation in the BDNF promoter. In contrast, control of Hcy blocked BDNF promoter methylation and upregulated BDNF levels in the brain. These results imply the possibility of a causal role of Hcy in stress-induced cognitive decline. We also used ten-eleven translocation (TET1), an enzyme that induces DNA demethylation, to verify the involvement of Hcy and DNA methylation in the regulation of BDNF expression and the development of stress-related cognitive decline. The data showed that TET1-expressing viral injection into the hippocampus inhibited BDNF promoter methylation and significantly mitigated the cognitive decline in HHcy rats. Taken together, novel evidence from the present study suggests that Hcy is likely involved in chronic stress-induced BDNF reduction and related cognitive deficits. In addition, the negative side-effects of HHcy may be associated with Hcy-induced DNA hypermethylation in the BDNF promoter. The results also suggest the possibility of Hcy as a target for therapy and the potential value of vitamin B intake in preventing stress-induced cognitive decline.

Possible cardioprotective role of NaHS on ECG and oxidative stress markers in an unpredictable chronic mild stress model in rats

The protective effect of H₂S against various body organ injuries has been described. The aim of this work is to investigate the potential role of sodium hydrosulfide (NaHS) as an H₂S donor in chronic mild stress induced changes in the rat heart. Forty adult male Sprague Dawley rats were assigned to four groups: control, stressed group, stressed rats treated with aminooxyacetic acid (AOAA), and stressed rats treated with NaHS. Arterial blood pressure (ABP) was recorded. Serum adrenaline, MDA, and GSH levels were measured. Chronic stress significantly increased HR and ABP. AOAA produced similar changes, while NaHS mitigated the rise in HR and ABP. Both stressed and AOAA-treated stressed groups showed a significant decrease in QRS amplitude and a shortening of the RR, QT, and QTc intervals with an elevation of the ST segment. NaHS produced a significant improvement in ECG recordings. Chronic stress produced a significant rise of adrenaline and MDA levels with a significant decline in GSH levels. The AOAA-treated stressed group showed similar elevations. NaHS treatment caused significant reduction in adrenaline and MDA levels but significantly improved GSH levels. In conclusion, H₂S donor has a cardioprotective effect against stress-induced cardiovascular diseases through amelioration of the oxidative stress and raised adrenaline levels induced by chronic stress exposure.

Effect of different charges of modified electroconvulsive seizure on the cognitive behavior in stressed rats: Effects of GluR1 phosphorylation and CaMKIIα activity

Electroconvulsive therapy (ECT) is an efficient therapy for major depression and modern ECT requires anesthesia to enhance safety. However, the commonly used anesthetic, propofol, may weaken the treatment efficacy. A recent study confirmed that ketamine rapidly reduced the symptoms of depression in affected patients. A previous study found that electroconvulsive seizure (ECS), the animal model for ECT, under anesthesia of low-dose ketamine combined with propofol could enhance the antidepressant efficacy and improve the cognitive performance. The present study aimed to investigate the responses to different charges (0, 60, 120, 180 or 240 mC) of ECS under compound anesthetics, ketamine combined with propofol, in stressed rats and the underlying mechanisms to aid in optimization of treatment regimens. The results indicated that ECS exhibited an improved antidepressant effects at 120 mC compared with 60 mC, however, no significant differences in antidepressant effects were identified among the 120, 180 and 240 mC groups. Furthermore, rats subjected to ECS at 120 mC exhibited the best cognitive performance. The phosphorylation levels of calcium/calmodulin-dependent protein kinase IIα (CaMKIIα) at Thr286, glutamate receptor 1 (GluR1) at Ser831 and cAMP-response element-binding protein (CREB) at the Ser133 were higher in the 120-mC group compared with all other groups. These results indicated that the ECS at medium intensity (120 mC) with administration of compound anesthetics may exert an improved therapeutic effect on depression compared with other intensities (0, 60, 180 and 240 mC). The results also suggested that the improvement in cognitive function in stressed rats may be attributed to the phosphorylation of CaMKIIα (Thr286), GluR1 (Ser831) and CREB (Ser133).

The Psycho-cardiac Coupling, Myocardial Remodeling, and Neuroendocrine Factor Levels: The Psychosomatics of Major Depressive Disorder

The association of major depressive disorder (MDD) with myocardial infarction (MI) and vice versa is not unknown. Depression, along with many other systemic factors like atherosclerosis, obesity, diabetes and vascular dysfunction, contributes to the development of adverse cardiac events in the future and, has always been a topic of interest in the fields of cardiology and psychosomatics. We wrote this review article to elaborate this relationship in detail. This article suggests that the individuals with type D personality who already had cardiovascular disease had undergone more serious myocardial damage. In addition, we elucidated the effects of depression on sympathetic activity and remodeling of myocardium after MI. The alterations in the neuroendocrine factors, which included the changes in levels of Serotonin (5-HT), Norepinephrine and Corticosterone, also geared towards the changes associated with depression-induced myocardial injury. However, we need more studies in the near future to further dig into this association process. Therefore, we recommend more research to explore the relationship of psychological factors and adverse cardiac outcomes.

Chronic Unpredictable Mild Stress Causing Cardiac and Thoracic Spinal Cord Electrophysiological Abnormalities May Be Associated with Increased Cardiac Expression of Serotonin and Growth-Associated Protein-43 in Rats

BACKGROUND

The aim of this study was to investigate the potential mechanisms by which chronic unpredictable mild stress (CMS) might induce cardiovascular disease.

METHODS

Twenty male Sprague-Dawley rats (weighing 180-250 g) were divided into the CMS group (CMS for 3 weeks) and control group (n = 10/group). Sucrose solution consumption, sucrose solution preference rate, and the open field test (horizontal and vertical movements) were used to confirm the establishment of the CMS model. Heart rate was determined in Langendorff-perfused hearts, and field action potential duration (FAPD) was measured in cardiac atrial tissue, cardiac ventricular tissue, and thoracic spinal cord segments 1-5. The expressions of serotonin (5-HT) and growth-associated protein-43 (GAP-43) in cardiac ventricular tissue were analyzed using immunohistochemistry and immunofluorescence.

RESULTS

Compared with the control group, sucrose solution consumption, sucrose solution preference rate, horizontal movement, and vertical movement were significantly lower in the CMS group (P < 0.01). The CMS group exhibited significant decreases in atrial and ventricular FAPDs (P < 0.05), as well as significant increases in heart rates (P < 0.05) and T1-5 spinal cord FAPD (P < 0.01), as compared with the control group. The expressions of 5-HT and GAP-43 in cardiac ventricular tissue were significantly higher in the CMS group than in controls (P < 0.01).

CONCLUSIONS

CMS causes cardiac and T1-5 spinal cord electrophysiological abnormalities as well as increased cardiac expression of 5-HT and GAP-43, indicating that CMS could potentially increase the risk of cardiovascular disease.

Hypothalamic-pituitary-adrenal axis hypersensitivity in female rats on a post-weaning high-fat diet after chronic mild stress

A high-fat diet (HFD) is highly correlated to obesity, metabolic diseases and certain behavioral changes. However, the effects of post-weaning HFD in rats during puberty and the role of the hypothalamic-pituitary-adrenal (HPA) axis in this process have remained elusive. The present study hypothesized that the HPA axis mediates the behavioral alterations induced by a post-weaning HFD. To investigate this, female rats were divided into two groups, one of which was fed a HFD from postnatal weeks (PWs) 4-12, while the other group received standard chow. Rats in each group were then subdivided into two subgroups each, and from PW 9-12, animals from one of the two subgroups were subjected to chronic mild stress (CMS), while the other subgroup received no stress. At PW 12, the body weight of rats receiving a HFD but no DMS was significantly higher than that in the control group. The frequency of crossing and rearing in the open field test and the time in the center of the Y-maze were decreased following CMS. Total time to escape was decreased in rats receiving HFD and after CMS. The serum levels of adrenocorticotropic hormone and corticosterone were increased in rats receiving an HFD and after CMS, and the mRNA levels of corticotropin-releasing hormone and arginine vasopressin in the hypothalamus were increased in the HFD + CMS group compared to that in the control group. The mRNA expression of glucocorticoid receptor (GR) in the hippocampi of rats in the HFD + CMS group was significantly decreased and the mineralocorticoid receptor/GR ratio was increased compared to that in the groups receiving either CMS or a HFD. In conclusion, these results indicated that female rats fed a post-weaning HFD showed HPA axis hypersensitivity under CMS, which may mediate behavioral alterations.

Mitochondrial dysfunction bridges negative affective disorders and cardiomyopathy in socially isolated rats: Pros and cons of fluoxetine

Objectives Depression is tightly associated with cardiovascular comorbidity and accounts for high financial and social burden worldwide. Mitochondrial dysfunction contributes to the pathophysiology of depression and cardiovascular disorders; its contribution to depression-cardiovascular comorbidity has not yet been investigated. Methods Adolescent rats were subjected to 4 weeks of isolation (social isolation stress or SIS) or social conditions (control), and then they were divided into treatment (fluoxetine, 7.5 mg/kg/day for 21 days) and non-treatment groups. After different housing conditions and treatment, animals were evaluated by behavioural tests (n = 6-8) and mitochondrial assessments (n = 3) of brain and cardiac tissues. Results We found that juvenile SIS induced behavioural abnormalities and mitochondrial dysfunction in adulthood. We showed that juvenile SIS was associated with impaired respiratory chain complex, which leads to reactive oxygen species formation, oxidative damage and ATP abatement in both brain and heart. Administration of FLX (7.5 mg/kg/day) during the isolation period attenuated the effects of SIS on the brain mitochondria and behavioural abnormalities, but had little or no effect on SIS-induced mitochondrial dysfunction in cardiac tissue. Conclusions This suggests that juvenile SIS predisposes the co-occurrence of depression and cardiovascular disease through mitochondrial dysfunction and that therapeutic effect of fluoxetine is partly mediated by its effect on mitochondrial function.

The involvement of homocysteine in stress-induced Aβ precursor protein misprocessing and related cognitive decline in rats

Chronic stress is a risk factor in the development of cognitive decline and even Alzheimer's disease (AD), although its underlying mechanism is not fully understood. Our previous data demonstrated that the level of homocysteine (Hcy) was significantly elevated in the plasma of stressed animals, which suggests the possibility that Hcy is a link between stress and cognitive decline. To test this hypothesis, we compared the cognitive function, plasma concentrations of Hcy, and the brain beta-amyloid (Aβ) level between rats with or without chronic unexpected mild stress (CUMS). A lower performance by rats in behavioral tests indicated that a significant cognitive decline was induced by CUMS. Stress also disturbed the normal processing of Aβ precursor protein (APP) and resulted in the accumulation of Aβ in the brains of rats, which showed a positive correlation with the hyperhomocysteinemia (HHcy) that appeared in stressed rats. Hcy-targeting intervention experiments were used to verify further the involvement of Hcy in stress-induced APP misprocessing and related cognitive decline. The results showed that diet-induced HHcy could mimic the cognitive impairment and APP misprocessing in the same manner as CUMS, while Hcy reduction by means of vitamin B complex supplements and betaine could alleviate the cognitive deficits and dysregulation of Aβ metabolism in CUMS rats. Taken together, the novel evidence from our present study suggests that Hcy is likely to be involved in chronic stress-evoked APP misprocessing and related cognitive deficits. Our results also suggested the possibility of Hcy as a target for therapy and the potential value of vitamin B and betaine intake in the prevention of stress-induced cognitive decline.

Chronic stress and excessive glucocorticoid exposure both lead to altered Neuregulin-1/ErbB signaling in rat myocardium

Exposure to chronic stress or excess glucocorticoids is associated with the development of depression and heart disease, but the underlying mechanisms remain equivocal. While recent evidence has indicated that Neuregulin-1 (NRG1) and its ErbB receptors play an essential role in cardiac function, much is still unknown concerning the biological link between NRG1/ErbB pathway and the stress-induced comorbidity of depression and cardiac dysfunction. Therefore, we examined the protein expression of NRG1 and ErbB receptors in the myocardium of rats following chronic unpredictable mild stress (CUMS) or rats treated with two different doses (0.2 and 2mg/kg/day, respectively) of dexamethasone (Dex). The stressed rats showed elevated expression of NRG1 and phosphorylated ErbB4 (pErbB4) in the myocardium, whereas ErbB2 and pErbB2 were inhibited. The lower dose of Dex enhanced myocardial NRG1/ErbB signaling, but as the dose is increased, while ErbB4 remained activated, the expression of ErbB2 and pErbB2 became compromised. Both CUMS and 2mg/kg of Dex suppressed the downstream Akt and ERK phosphorylation. Although the lower dose of Dex increased myocardial antiapoptotic Bcl-xl expression, a significant decrease of Bcl-xl expression was found in rats treated with the higher dose. Meanwhile, both CUMS and two different doses of Dex induced proapoptotic Bax level. Combined, our data firstly showed (mal)adaptive responses of NRG1/ErbB system in the stressed heart, indicating the potential involvement of NRG1/ErbB pathway in the stress-induced cardiac dysfunction.

Hyperhomocysteinemia is a result, rather than a cause, of depression under chronic stress

Background

Although the accumulation of homocysteine (Hcy) has been implicated in the pathogenesis of depression, whether Hcy is directly involved and acts as the primary cause of depressive symptoms remains unclear. The present study was designed to clarify whether increased Hcy plays an important role in stress-induced depression.

Results

We employed the chronic unpredictable mild stress model (CUMS) of depression for 8 weeks to observe changes in the plasma Hcy level in the development of depression. The results showed that Wistar rats exposed to a series of mild, unpredictable stressors for 4 weeks displayed depression-like symptoms such as anhedonia (decreased sucrose preferences) and a decreased 5-Hydroxy Tryptophan (5-HT) concentration in the hippocampus. At the end of 8 weeks, the plasma Hcy level increased in the CUMS rats. The anti-depressant sertraline could decrease the plasma Hcy level and improve the depression-like symptoms in the CUMS rats. RhBHMT, an Hcy metabolic enzyme, could decrease the plasma Hcy level significantly, although it could not improve the depressive symptoms in the CUMS rats.

Conclusions

The results obtained from the experiments did not support the hypothesis that the increased Hcy concentration mediated the provocation of depression in CUMS rats, and the findings suggested that the increased Hcy concentration in the plasma might be the result of stress-induced depression.