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.

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.

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.

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.