Forskolin Protected against Streptozotocin-Induced Diabetic Cardiomyopathy via Inhibition of Oxidative Stress and Cardiac Fibrosis in Mice.

BACKGROUND: Diabetic cardiomyopathy is one of the cardiac complications in diabetes patients, eventually resulting in heart failure and increasing morbidity and mortality. Oxidative stress is a critical pathological feature in diabetic hearts, contributing to the development of DCM. Forskolin (FSK) was shown to reduce oxidative stress. This study was aimed at investigating the effects of FSK on diabetic hearts and the relevant molecular mechanisms. METHODS: Streptozotocin- (STZ-) induced diabetes in mice was treated with FSK through intraperitoneal injection. Cardiac functions were evaluated by echocardiography. Hematoxylin-eosin and Masson trichrome staining was employed to determine heart morphological changes and cardiac fibrosis, respectively. Cardiac fibrosis-related markers were detected by western blot. Superoxide dismutase activity, reduced/oxidized glutathione ratio, and malondialdehyde concentration in left ventricles were determined using respective commercial kits. RESULTS: Abnormal cardiac diastolic dysfunction and cardiac fibrosis were observed in diabetic hearts. FSK treatment significantly improved the cardiac diastolic function and attenuated the abnormal morphological change in diabetic hearts. Moreover, FSK treatment in diabetic mice decreased the expression of fibronectin, collagen I, TGF-ß, and α-SMA and reduced myocardial fibrosis. Furthermore, we observed that FSK significantly blocked oxidative stress in diabetic hearts. CONCLUSIONS: Our study demonstrates that FSK protects against the development of DCM in STZ-induced diabetes in mice. Our study suggests that FSK might be a potential target for drug development in treating DCM.

Suppression of Kv1.5 protects against endothelial apoptosis induced by palmitate and in type 2 diabetes mice.

AIMS: Palmitate, a common saturated free fatty acid, induces endothelial apoptosis in vitro in culture endothelial cells and in vivo in type 2 diabetes mellitus (T2DM) patients. The present study aimed to investigate whether Kv1.5 regulates palmitate-induced endothelial apoptosis and endothelial dysfunction in T2DM. MAIN METHODS: In vitro experiments were carried out in primary human HUVECs. Apoptosis was analyzed by flow cytometry. Cell viability was determined by Cell Counting Assay Kit-8. The siRNA transfection was employed to knockdown Kv1.5 protein expression. Intracellular and mitochondrial ROS, and mitochondrial membrane potential were detected using fluorescent probes. Male C57BL/6 mice fed with high-sucrose/fat diet were injected with streptozotocin (35mg/kg body weight) to establish T2DM animal model. KEY FINDINGS: We found that palmitate-induced endothelial apoptosis was parallel to a significant increase in endogenous Kv1.5 protein expression in endothelial cells. Silencing of Kv1.5 with siRNA reduced palmitate-induced endothelial apoptosis, intracellular ROS generation, mitochondrial ROS generation and membrane potential (Δψm) alteration and cleaved caspase-3 protein expression; while increased cell viability and ratio of Bcl-2/Bax. Furthermore, we observed that Kv1.5 protein expression increased in endothelial cells of thoracic aorta of T2DM mice. Silencing of Kv1.5 significantly improved the endothelium-dependent vasodilation in thoracic aortic rings of T2DM mice. SIGNIFICANCE: These results demonstrate that suppression of Kv1.5 protects endothelial cells against palmitate-induced apoptosis via inhibiting mitochondria-mediated excessive ROS generation and apoptotic signaling pathway, suggesting that Kv1.5 may serve as a therapeutic target of treatment for endothelial dysfunction induced by palmitate and lipid metabolism in T2DM patients.

Leptin Attenuates the Contractile Function of Adult Rat Cardiomyocytes Involved in Oxidative Stress and Autophagy.

BACKGROUND: Leptin has been identified as an important protein involved in obesity. As a chronic metabolic disorder, obesity is associated with a high risk of developing cardiovascular and metabolic diseases, including heart failure. The aim of this paper was to investigate the effects and the mechanism of leptin on the contractile function of cardiomyocytes in the adult rat. METHODS: Isolated adult rat cardiomyocytes were exposed to leptin (1, 10, and 100 nmol/L) for 1 hour. The calcium transients and the contraction of adult rat cardiomyocytes were recorded with SoftEdge MyoCam system. Apocynin, tempol and rapamycin were added respectively, and Western blotting was employed to evaluate the expression of LC3B and Beclin-1. RESULTS: The peak shortening and maximal velocity of shortening/relengthening (± dL/dtmax) of cell shortening were significantly decreased, and the time to 50% relengthening was prolonged with leptin perfusion. Leptin also significantly reduced the baseline, peak and time to 50% baseline of calcium transient. Leptin attenuated autophagy as indicated by decreased LC3-II and Beclin-1. All of the abnormalities were significantly attenuated by apocynin, tempol or rapamycin. CONCLUSIONS: Our results indicated that leptin depressed the intracellular free calcium and myocardial systolic function via increasing oxidative stress and inhibiting autophagy.

Chloroquine improves left ventricle diastolic function in streptozotocin-induced diabetic mice.

Diabetes is a potent risk factor for heart failure with preserved ejection fraction (HFpEF). Autophagy can be activated under pathological conditions, including diabetic cardiomyopathy. The therapeutic effects of chloroquine (CQ), an autophagy inhibitor, on left ventricle function in streptozotocin (STZ)-induced diabetic mice were investigated. The cardiac function, light chain 3 (LC3)-II/LC3-I ratio, p62, beclin 1, reactive oxygen species, apoptosis, and fibrosis were measured 14 days after CQ (ip 60 mg/kg/d) administration. In STZ-induced mice, cardiac diastolic function was decreased significantly with normal ejection fraction. CQ significantly ameliorated cardiac diastolic function in diabetic mice with HFpEF. In addition, CQ decreased the autophagolysosomes, cardiomyocyte apoptosis, and cardiac fibrosis but increased LC3-II and p62 expressions. These results suggested that CQ improved the cardiac diastolic function by inhibiting autophagy in STZ-induced HFpEF mice. Autophagic inhibitor CQ might be a potential therapeutic agent for HFpEF.

Sonic hedgehog improves ischemia-induced neovascularization by enhancing endothelial progenitor cell function in type 1 diabetes.

The Sonic hedgehog (Shh) pathway is downregulated in type 1 diabetes, and it has been reported that augmentation of this pathway may alleviate diabetic complications. However, the cellular mechanisms underlying these protective effects are poorly understood. Recent studies indicate that impaired function of endothelial progenitor cells (EPCs) may contribute to cardiovascular problems in diabetes. We hypothesized that impaired Shh signaling contribute to endothelial progenitor cell dysfunction and that activating the Shh signaling pathway may rescue EPC function and promote diabetic neovascularization. Adult male C57/B6 mice and streptozotocin (STZ)-induced type 1 diabetic mice were used. Gli1 and Ptc1 protein levels were reduced in EPCs from diabetic mice, indicating inhibition of the Shh signaling pathway. EPC migration, tube formation ability, and mobilization were impaired in diabetic mice compared with non-diabetic controls (p < 0.05 vs control), and all were improved by in vivo administration of the Shh pathway receptor agonist SAG (p < 0.05 vs diabetes). SAG significantly increased capillary density and blood perfusion in the ischemic hindlimbs of diabetic mice (p < 0.05 vs diabetes). The AKT activity was lower in EPCs from diabetic mice than those from non-diabetic controls (p < 0.05 vs control). This decreased AKT activity led to an increased GSK-3ß activity and degradation of the Shh pathway transcription factor Gli1/Gli2. SAG significantly increased the activity of AKT in EPCs. Our data clearly demonstrate that an impaired Shh pathway mediated by the AKT/GSK-3ß pathway can contribute to EPC dysfunction in diabetes and thus activating the Shh signaling pathway can restore both the number and function of EPCs and increase neovascularization in type 1 diabetic mice.

Endogenous glucocorticoids inhibit myocardial inflammation induced by lipopolysaccharide: involvement of regulation of histone deacetylation.

Emerging evidence indicates that myocardial inflammation plays a key role in the pathogenesis of cardiac diseases. But the exact mechanisms for this chronic inflammatory disorder have not been elucidated. Glucocorticoids (GCs) are the most effective anti-inflammatory treatments available for many inflammatory diseases. However, it is unknown whether endogenous GCs are able to exert anti-inflammatory effect on myocardial inflammation. In this study, the potential role of endogenous GCs in the regulation of myocardial inflammation was investigated. We showed that the reduction of endogenous GC level by adrenalectomy promoted the production of basal and lipopolysaccharide (LPS)-induced proinflammatory cytokines, which could be partly reversed by supplementing with exogenous physiological level of hydrocortisone. Inhibition of GC receptor (GR) signaling pathway with GR antagonist mifepristone (RU486) or histone deacetylase inhibitor trichostatin A (TSA) also increased the levels of basal and LPS-induced proinflammatory cytokines. Moreover, blockade of GC-GR signaling pathway by adrenalectomy, RU486 or TSA enhanced LPS-induced myocardial nuclear factor-κB activation and histone acetylation but inhibited myocardial histone deacetylase expression and activity. Cardiac function studies demonstrated that blockade of the GC-GR signaling pathway aggravated inflammation-induced cardiac dysfunction. These findings indicate that endogenous GCs are able to inhibit myocardial inflammation induced by LPS. Endogenous GCs represent an important endogenous anti-inflammatory mechanism for myocardium in rats and such mechanism injury may be an important factor for pathogenesis of cardiac diseases.

Protection of long-term treatment with huang-lian-jie-du-tang on vascular endothelium in rats with type 2 diabetes mellitus.

BACKGROUND: Huang-Lian-Jie-Du-Tang (HLJDT) is the classical traditional Chinese recipe for heat clearance and detoxification and is used in diabetic patients in the clinical practice of traditional Chinese medicine. OBJECTIVE: The aim of this study was to evaluate the protective effects of long-term treatment with HLJDT on vascular endothelial function in rats with type 2 diabetes mellitus (T2DM). METHODS: The male T2DM model rats were induced by intraperitoneal injection of low-dose streptozotocin plus a high-fat and high-calorie laboratory diet. The T2DM animals were randomly divided into the T2DM model group, the low-dose HLJDT group (0.42 g/kg/d), and the high-dose HLJDT group (1.25 g/kg/d). RESULTS: Administration of HLJDT (0.42 or 1.25 g/kg/d) for 8 weeks decreased the levels of serum fasting blood glucose, malondialdehyde, and vascular tissue interleukin 6 but raised the level of serum superoxide dismutase compared with the T2DM model group in a dose-dependent manner. In addition, HLJDT treatment restored the impaired endothelial-dependent vascular relaxation in aortic preparations from the T2DM model group in a dose-dependent manner. CONCLUSIONS: Early and long-term treatments with HLJDT could have anti-inflammatory, antioxidant properties and could protect vascular endothelium from the cardiovascular complications associated with T2DM.

A physiological concentration of glucocorticoid inhibits the pro-inflammatory cytokine-induced proliferation of adult rat cardiac fibroblasts: roles of extracellular signal-regulated kinase 1/2 and nuclear factor-κB.

1. Inflammation-induced proliferation of cardiac fibroblasts plays an important role in cardiac remodelling. Pharmacological doses of exogenous glucocorticoids (GC) are the most effective therapy for inflammatory diseases. Similarly, physiological concentrations of endogenous GC have recently been shown to have anti-inflammatory effects. Therefore, the aim of the present study was to determine whether a physiological concentration of GC could inhibit pro-inflammatory cytokine-stimulated proliferation of cardiac fibroblasts and to explore the mechanisms involved. 2. Cardiac fibroblasts were isolated from adult male Sprague-Dawley rats and cell proliferation was measured using a CCK-8 kit. Western blotting was used to detect protein expression of extracellular-regulated kinase (ERK) 1/2 and nuclear factor (NF)-κB. 3. Cardiac fibroblast proliferation was significantly increased by tumour necrosis factor-α, interleukin (IL)-1ß and angiotensin II and was accompanied by upregulated protein expression of ERK1/2 and NF-κB. A physiological concentration of hydrocortisone (127 ng/mL) not only inhibited the proliferation of cardiac fibroblasts, but also suppressed activation of ERK1/2 and NF-κB. These effects of hydrocortisone were abrogated by the glucocorticoid receptor (GR) antagonist RU-486 (100 nmol/L). Furthermore, inflammation-induced cardiac fibroblast proliferation was also blocked by the mitogen-activated protein kinase kinase 1/2 inhibitor U0126 (100 nmol/L) and the NF-κB inhibitor pyrrolidine dithiocarbamate (1 µmol/L). Cytokine-induced ERK1/2 phosphorylation and cyclin D1 expression were attenuated by U0126, suggesting that the ERK1/2 and NF-κB signalling pathways were involved in cardiac fibroblast proliferation. 4. In conclusion, the results of the present study indicate that a physiological concentration of hydrocortisone can inhibit inflammation-induced proliferation of cardiac fibroblasts by preventing the activation of ERK1/2 and NF-κB.

Leptin induces hypertrophy through activating the peroxisome proliferator-activated receptor α pathway in cultured neonatal rat cardiomyocytes.

1. Our previous study has shown that leptin induces cardiomyocyte hypertrophy; however, the mechanisms are poorly understood. Recent studies have shown that peroxisome proliferator-activated receptor α (PPARα) activation might be responsible for pathological remodeling and severe cardiomyopathy. Leptin, as an endogenous activator of PPARα, regulates energy metabolism through activating PPARα in many cells. Therefore, we hypothesized that leptin induces cardiomyocyte hypertrophy through activating the cardiac PPARα pathway. 2. Cultured neonatal rat cardiomyocytes were used to evaluate the effects of PPARα on hypertrophy. The selective PPARα antagonist GW6471 concentration-dependently decreased atrial natriuretic factor mRNA expression by 23%, 36%, 44% and 59%, and significantly decreased total RNA levels, protein synthesis and cell surface areas, all of which were elevated by 72h of leptin treatment. The augmentation of reactive oxygen species levels in leptin treated cardiomyocytes was reversed by 0.1-10µmol/L GW6471 (40%, 52% and 58%). After 24h of treatment, leptin concentration-dependently enhanced mRNA expression by 7%, 93%, 100% and 256%, and protein expression by 31.2%, 64.2%, 143% and 199%, and the activity of PPARα. Meanwhile, cardiomycytes receiving 72h of treatment with the PPARα agonist, fenofibrate, concentration-dependently increased total RNA levels, atrial natriuretic factor mRNA expression, protein synthesis and cell surface area. Treatment of fenofibrate for 4 h also elevated oxygen species levels in a concentration-dependent manner. 3. In conclusion, these findings show that leptin induces hypertrophy through the activation of the PPARα pathway in cultured neonatal rat cardiomyocytes.

Effects of chronic treatment with honokiol in spontaneously hypertensive rats.

The present study was performed to evaluate the antihypertensive effects of honokiol in vivo in spontaneously hypertensive rats (SHR). The effects of honokiol were investigated by determination of the blood pressure, vascular reactivity, oxidative parameters, and histologic change in the aorta. Long-term administration of honokiol (400 mg/kg/d) to SHR decreased systolic blood pressure significantly. Honokiol (200, 400 mg/kg/d) enhanced the aortic relaxation in response to acetylcholine after 49-d treatment, but had no significant effects on the relaxation to sodium nitroprusside. The oral administration of honokiol significantly increased the plasma level of NO(2(-))/NO(3(-)), but decreased the level of malondialdehyde in liver of SHR compared with the control vehicle. In addition, SHR administered honokiol showed significant reductions in the elastin bands and media thickness in the aorta. These results suggest that chronic treatment with honokiol exerts an antihypertensive effect in SHR, and its vasorelaxant action and antioxidant properties may contribute to reducing the elevated blood pressure.

Inhibitory effects of magnolol on distal colon of guinea pig in vitro.

The influence of plant product magnolol (0-100 microM) on the contractile activity of isolated colonic muscle strips in guinea pig and related mechanism were investigated. Magnolol did not affect the base tone of colon muscle strips, but it dose-dependently inhibited 40 mM KCl-, 1 microM carbachol (CCh)- and 10 microM serotonin (5-HT)-induced contractions at concentrations higher than 10 microM. And also, magnolol inhibited the 5-HT- or CCh-induced muscle contraction in calcium-free buffer. Furthermore, magnolol inhibited the KCl-induced contraction under the condition of procaine. In addition, inhibition rate of nifedipine plus magnolol on muscle strips was lower than that of nifedipine alone. Moreover, magnolol dose-dependently decreased the velocity of pellet propulsion in the concentration range of 0.1-10 microM, and totally inhibited pellet propulsion at the concentration higher than 30 microM. Thus, it can be concluded that magnolol may 1) block receptor-operated cation channels and the voltage dependent Ca2+ channel, and 2) inhibit calcium release from the sarcolemmal membrane (SR) through blocking InsP3-sensitive and ryanodine-sensitive pathways. This explains, at least partially, that Cortex magnoliae officinalis exerts therapeutic effects on gastrointestinal disease through relaxation of GI tract smooth muscles.

Leptin and cardiovascular diseases.

Although obesity is strongly associated with cardiovascular disease (CVD), the endogenous relationship between obesity and CVD is still not fully clear. Emerging evidence from both animal and human studies indicates that leptin may play an important role in obesity-related CVD. Besides modulating appetite and metabolism, leptin has also been shown to increase sympathetic nerve activity, stimulate generation of reactive oxygen species, upregulate endothelin-1 production and potentiate platelet aggregation. These effects of leptin may contribute to hypertension, endothelial dysfunction and atherosclerosis in obese individuals. Better understanding the mechanisms of leptin resistance should facilitate therapeutic approaches to reverse the phenomenon of selective leptin resistance. These recent discoveries could lead to novel strategies for treatment of obesity-associated CVD.

Leptin and cardiovascular diseases.

Although obesity is strongly associated with cardiovascular disease (CVD), the endogenous relationship between obesity and CVD is still not fully clear. Emerging evidence from both animal and human studies indicates that leptin may play an important role in obesity-related CVD. Besides modulating appetite and metabolism, leptin has also been shown to increase sympathetic nerve activity, stimulate generation of reactive oxygen species, upregulate endothelin-1 production and potentiate platelet aggregation. These effects of leptin may contribute to hypertension, endothelial dysfunction and atherosclerosis in obese individuals. Better understanding the mechanisms of leptin resistance should facilitate therapeutic approaches to reverse the phenomenon of selective leptin resistance. These recent discoveries could lead to novel strategies for treatment of obesity-associated CVD.