Jian-Dong Luo

Leptin and cardiovascular diseases

1. Leptin is a 16‐kDa hormone, synthesized primarily by adipocyte, which acts as a key factor for maintenance of energy homeostasis in central and peripheral tissues. In most obese individuals, serum leptin levels are increased and correlate with the individual’s body mass index.

Impaired autophagy contributes to adverse cardiac remodeling in acute myocardial infarction.

Objective Autophagy is activated in ischemic heart diseases, but its dynamics and functional roles remain unclear and controversial. In this study, we investigated the dynamics and role of autophagy and the mechanism(s), if any, during postinfarction cardiac remodeling. Methods and results Acute myocardial infarction (AMI) was induced by ligating left anterior descending (LAD) coronary artery. Autophagy was found to be induced sharply 12–24 hours after surgery by testing LC3 modification and Electron microscopy. P62 degradation in the infarct border zone was increased from day 0.5 to day 3, and however, decreased from day 5 until day 21 after LAD ligation. These results indicated that autophagy was induced in the acute phase of AMI, and however, impaired in the latter phase of AMI. To investigate the significance of the impaired autophagy in the latter phase of AMI, we treated the mice with Rapamycin (an autophagy enhancer, 2.0 mg/kg/day) or 3-methyladenine (3MA, an autophagy inhibitor, 15 mg/kg/day) one day after LAD ligation until the end of experiment. The results showed that Rapamycin attenuated, while 3MA exacerbated, postinfarction cardiac remodeling and dysfunction respectively. In addition, Rapamycin protected the H9C2 cells against oxygen glucose deprivation in vitro. Specifically, we found that Rapamycin attenuated NFκB activation after LAD ligation. And the inflammatory response in the acute stage of AMI was significantly restrained with Rapamycin treatment. In vitro, inhibition of NFκB restored autophagy in a negative reflex. Conclusion Sustained myocardial ischemia impairs cardiomyocyte autophagy, which is an essential mechanism that protects against adverse cardiac remodeling. Augmenting autophagy could be a therapeutic strategy for acute myocardial infarction.

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.

Induction of autophagy contributes to the myocardial protection of valsartan against ischemia‑reperfusion injury.

The mechanisms underlying the myocardial protection of valsartan against ischemia/reperfusion (I/R) injury are complicated and remain unclear. The aim of this study was to investigate whether autophagy machinery was involved in the protection against I/R injury that is induced by valsartan. In vivo rat hearts were subjected to ischemia by 30 min ligation of the left anterior descending coronary artery, followed by a 120 min reperfusion. 3‑methyladenine (3‑MA), a specific inhibitor on autophagic sequestration, was used to inhibit autophagy. The hemodynamics, infarct size of the ventricle and LC3B protein were measured. Western blot analysis was performed to investigate the mechanism by which autophagy was induced by valsartan. Valsartan preconditioning resulted in a significant decrease in infarct size and induced autophagy in the rat heart subjected to I/R injury. The hemodynamics assay showed that the valsartan‑induced cardiac functional recovery was attenuated by 3‑MA. By contrast, 3‑MA decreased the improvement induced by valsartan on the histology and infarction of the rat heart subjected to I/R injury. Valsartan preconditioning induced autophagy via the AKT/mTOR/S6K pathway, independent of Beclin1. In conclusion, valsartan preconditioning induced autophagy via the AKT/mTOR/S6K pathway, which contributed to the myocardial protection against I/R injury.

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.

Maternal High-Fat Diet Causes a Sex-Dependent Increase in AGTR2 Expression and Cardiac Dysfunction in Adult Male Rat Offspring

ABSTRACT Maternal high-fat diet (HFD) is associated with cardiovascular disease later in life. This study tested the hypothesis that maternal HFD causes programming of increased cardiac angiotensin II receptor type 2 (AGTR2) expression, resulting in heightened cardiac susceptibility to ischemic injury in male offspring in a sex-dependent manner. Pregnant rats were divided between control and HFD (HFD-fed during gestation) groups. Maternal HFD resulted in cardiac hypertrophy in only male offspring, but had no effect on cardiac systolic and diastolic function in both male and female offspring. In addition, maternal HFD increased heart susceptibility to ischemia-reperfusion injury in adult male offspring, but not female offspring. There was an increase in Agtr2 mRNA and protein abundance in male, but not female offspring. However, maternal HFD had no effect on angiotensin II receptor type 1 (AGTR1) expression in both male and female offspring. HFD resulted in decreased glucocorticoid receptors (GRs) binding to the glucocorticoid response elements at the Agtr2 promoter, which was due to decreased GRs in the hearts of adult male offspring. Inhibition of AGTR2 with PD123319 abrogated maternal HFD-induced increase in cardiac ischemic vulnerability in male adult rats. The results demonstrate that maternal HFD causes programming of increased Agtr2 gene expression in the heart by downregulation of GR, contributing to the heightened cardiac vulnerability to ischemic injury in adult male offspring in a sex-dependent manner.

AMP-activated protein kinase-dependent autophagy mediated the protective effect of sonic hedgehog pathway on oxygen glucose deprivation-induced injury of cardiomyocytes.

Sonic hedgehog (Shh) pathway has been reported to protect cardiomyocytes in myocardial infarction (MI), but the underlying mechanism is not clear. Here, we provide evidence that Shh pathway induces cardiomyocytes survival through AMP-activated protein kinase-dependent autophagy. Shh pathway agonist SAG increased the expression of LC3-II, and induced the formation of autophagosomes in cultured H9c2 cardiomyocytes under oxygen glucose deprivation (OGD) 1 h and 4 h. Moreover, SAG induced a profound AMP-activated protein kinase (AMPK) activation, and then directly phosphorylated and activated the downstream autophagy initiator Ulk1, independent of the autophagy suppressor mammalian target of rapamycin (mTOR) complex 1. Taken together, our results have shown that Shh activates AMPK-dependent autophagy in cardiomyocytes under OGD, suggesting a role of autophagy in Shh-induced cellular protection.

Metabolic profile of puerarin in rats after intragastric administration of puerarin solid lipid nanoparticles

Puerarin has multiple pharmacological effects and is widely prescribed for patients with cardiovascular diseases including hypertension, cerebral ischemia, myocardial ischemia, diabetes mellitus, and arteriosclerosis. We have successfully prepared puerarin-loaded solid lipid nanoparticles (Pue-SLNs) for oral administration. Pue-SLNs are prepared using monostearin, soya lecithin, and poloxamer 188. SLNs may alter the course of puerarin absorption predominantly to and through lymphatic routes and regions, presumably following a transcellular path of lipid absorption, especially by enterocytes and polar epithelial cells of the intestine. The alteration of absorption might influence the metabolic profile of puerarin when incorporated into SLNs. In the present study, we investigated the metabolic profile of puerarin in rat plasma and urine using rapid resolution liquid chromatography–tandem mass spectrometry after a single-dose intragastric administration of Pue-SLNs in comparison with puerarin suspension. Two glucuronidated metabolites of puerarin, puerarin-4′-O-glucuronide and puerarin-7-O-glucuronide, were detected in rat plasma and urine after intragastric administration of Pue-SLNs, with the latter acting as the major metabolite. Similar results were found in rat plasma and urine after intragastric administration of puerarin suspension. The results suggest that incorporation of puerarin into SLNs does not change either the position of glucuronidation or the metabolic pathway of puerarin in rats.

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

Abstract: 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-&kgr;B 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.