Long Sheng Lu

Activation of Estrogen Receptor is Crucial for Resveratrol-stimulating Muscular Glucose Uptake via Both Insulin-dependent and Independent Pathways

OBJECTIVE—Estradiol (E2) is known to modulate insulin sensitivity and, consequently, glucose homeostasis. Resveratrol (RSV), an agonist of estrogen receptor (ER), has exerted antihyperglycemic effects in streptozotocin-induced type 1 diabetic rats in our previous study and was also shown to improve insulin resistance in other reports. However, it remains unknown whether activation of ER is involved in the metabolic effects of RSV via insulin-dependent and -independent mechanisms. RESEARCH DESIGN AND METHODS—Male Sprague-Dawley rats were given a high cholesterol–fructose (HCF) diet for 15 weeks and were treated with RSV for either 15 days or 15 weeks. RESULTS—Here, we show that RSV shifts the metabolic characteristics of rats on an HCF diet toward those of rats on a standard diet. RSV treatment increased insulin-stimulated whole-body glucose uptake and steady-state glucose uptake of soleus muscle and liver in HCF-fed rats as well as enhanced membrane trafficking activity of GLUT4 and increased phosphorylation of insulin receptor in insulin-resistant soleus muscles. Interestingly, the phosphorylated ER level in insulin-resistant soleus muscle was significantly elevated in rats with RSV treatment in both basal and euglycemic-hyperinsulinemic conditions. RSV exerted an insulin-like stimulatory effect on isolated soleus muscle, epididymal fat and hepatic tissue, and C2C12 myotubes. The RSV-stimulated glucose uptake in C2C12 myotubes was dependent on extracellular signal–related kinase/p38 (early phase, 1 h) and p38/phosphoinositide 3-kinase (late phase, 14 h) activation. Inhibition of ER abrogated RSV-induced glucose uptake in both early and late phases. CONCLUSIONS—Collectively, these results indicate that ER is a key regulator in RSV-stimulating insulin-dependent and -independent glucose uptake, which might account for the protective effects of RSV on diet-induced insulin resistance syndrome.

Sympathetic Nerve Sprouting, Electrical Remodeling, and Increased Vulnerability to Ventricular Fibrillation in Hypercholesterolemic Rabbits

Abstract— Whether hypercholesterolemia (HC) can induce proarrhythmic neural and electrophysiological remodeling is unclear. We fed rabbits with either high cholesterol (HC, n=10) or standard (S, n=10) chows for 12 weeks (protocol 1), and with HC (n=12) or S (n=10) chows for 8 weeks (protocol 2). In protocol 3, 10 rabbits were fed with various protocols to observe the effects of different serum cholesterol levels. Results showed that the serum cholesterol levels were 2097±288 mg/dL in HC group and 59±9 mg/dL in S group for protocol 1 and were 1889±577 mg/dL in HC group and 50±21 mg/dL in S group for protocol 2. Density of growth-associated protein 43– (GAP43) and tyrosine hydroxylase– (TH) positive nerves in the heart was significantly higher in HC than S in protocol 1. Compared with S, HC rabbits had longer QTc intervals, more QTc dispersion, longer action potential duration, increased heterogeneity of repolarization and higher peak calcium current (ICa) density (14.0±3.1 versus 9.1±3.4 pA/pF;P <0.01) in protocol 1 and 2. Ventricular fibrillation was either induced or occurred spontaneously in 9/12 of hearts of HC group and 2/10 of hearts in S group in protocol 2. Protocol 3 showed a strong correlation between serum cholesterol level and nerve density for GAP43 (R2=0.94;P <0.001) and TH (R2=0.91;P <0.001). We conclude that HC resulted in nerve sprouting, sympathetic hyperinnervation, and increased ICa. The neural and electrophysiological remodeling was associated with prolonged action potential duration, longer QTc intervals, increased repolarization dispersion, and increased ventricular vulnerability to fibrillation.

Apocynin alleviated hepatic oxidative burden and reduced liver injury in hypercholesterolaemia.

Background: This study addressed the effects of apocynin, a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, on hepatic oxidative burden and liver injury during diet‐induced hypercholesterolaemia.

Downregulated myocardial connexin 43 and suppressed contractility in rabbits subjected to a cholesterol-enriched diet

The effects of hypercholesterolemia on the myocardium per se include electrophysiological and mechanical alterations. Since gap junctions are essential in electromechanical coupling throughout the heart, we examined the correlation between the temporal expression of cardiac connexin 43 (Cx43), contractile function, and conduction velocity in cholesterol-fed rabbits. After a 12-week feeding period, serum cholesterol levels gradually increased (P<0.001). In contrast, expression of cardiomyocyte Cx43 protein progressively decreased (60% reduction at 12 weeks, P<0.001). Such a reduction was also demonstrated by immunoconfocal microscopy, which further showed redistribution of Cx43 gap junctions at the lateral cell membrane. The downregulation of Cx43 protein was associated with increased levels of Cx43 mRNA (3.5 -fold at 12 weeks, P<0.001) and phosphorylated c-Jun N-terminal kinase (three-fold at 12 weeks, P=0.001). Functionally, although fractional shortening of the left ventricle remained unchanged throughout the feeding protocol, the cholesterol-fed rabbits had a reduced cardiac cycle-dependent variation of integrated backscatters, a decreased mitral ring systolic velocity, and an increased modified Tei index (all P<0.001), all of which indicated impaired intrinsic myocardial contractility and attenuated ventricular systolic performance. In Langendorff-perfused hearts of cholesterol-fed rabbits, decreased conduction velocity was observed (P<0.005). Withdrawal of the cholesterol-enriched diet for 18 weeks restored the contractile parameters and Cx43 protein expression. These findings suggest that Cx43 is highly involved in the molecular mechanism of hypercholesterolemia-induced cardiac contractile dysfunction and dysrhythmias.

Myocardial tissue characterization based on the time-resolved Stokes-Mueller formalism.

Time-resolved Stokes vectors of transmitted optical signals were measured to differentiate normal and stunned myocardium tissues. The corresponding Mueller matrices were calculated based on the Stokes-Mueller formalism. Our experimental results indicated that the time-resolved Mueller matrices could provide information about myocardial architectural alteration in stunned myocardium. Thus, the Stokes-Mueller measurement can be a useful method in cardiovascular research.

Optical mapping of myocardial reactive oxygen species production throughout the reperfusion of global ischemia.

Reactive oxygen species (ROS) are short-lived, highly reactive chemical entities that play significant roles in all levels of biology. However, their measurement requires destructive preparation, thereby limiting the continuous measurement of ROS in a living tissue. We develop an optical mapping system to visualize ROS production in an isolated and perfused rat heart. By staining the heart with dihydroethidium (DHE), a 532-nm laser beam is directed to the epicardial surface, where we collect the red fluorescence (>600 nm) for semiquantitative analysis. With this system, ROS production as well as ventricular pressure and ECG in isolated perfused rat hearts are monitored throughout the reperfusion of global ischemia. Ischemia would decrease myocardial ROS production, while reperfusion would immediately result in sustained ROS overproduction. Optical mapping would provide information regarding the spatial distribution and temporal evolution of myocardial ROS production, which would enhance knowledge of the role of free radicals in cardiovascular biology.

Effects of rosiglitazone on native low-density-lipoprotein-induced respiratory burst in circulating monocytes and on the leukocyte-endothelial interaction in cholesterol-fed rats

Low-density lipoprotein (LDL) has been implicated in the initiation and progression of atherosclerotic vascular disease. But whether LDL can elicit similar effects in the microcirculation remain unexplored. To approach this issue, the hypothesis that LDL promotes oxidative stress in monocytes and results in microvascular inflammation was tested. Native LDL was capable of stimulating respiratory burst in rat monocytes, and this was blocked by BAPTA, cytochalasin B, apocynin, and diphenyliodonium. In monocytes from rats on a high-cholesterol (4%) diet, increased intracellular calcium, actin polymerization, respiratory burst, and surface CD18 expression were found. Concurrently, leukocyte–endothelial interaction was enhanced in the cremaster microcirculation. Rosiglitazone, an insulin-sensitizing agent with antiinflammatory properties, was found to suppress native-LDL-induced actin polymerization and respiratory burst in monocytes. It also improved leukocytes activation and leukocyte–endothelial interaction due to the high cholesterol intake. Hence, native LDL stimulation of monocytes contributed to hypercholesterolemia-associated microvascular inflammation, which could be treated by rosiglitazone.

In vivo Depth-resolved Birefringence of the Hyperlipidemic Rat&#8217;s Liver Monitored with Polarization-Sensitive Optical Coherence Tomography

In this paper, we show the first demonstration of in vivo depth-resolved birefringence of the hyperlipidemic rat’s liver with polarization-sensitive optical coherence tomography.

Visualizing inflammatory activity in isolated perfused rat hearts

Inflammation is a defense mechanism against various noxious stimuli. The recruitment of host leukocytes to sites of injury results in increased regional microvascular leakage and reactive oxygen species (ROS) generation. Excessive inflammatory activity not only eliminates offending stimuli but also result in tissue damage, as evidenced in reperfusion injury of the heart. To investigate spatial-temporal evolution of acute inflammation after myocardial reperfusion injury, we monitored microvascular leakage and reactive oxygen species generation with optical mapping technique. Reperfusion injury was performed on isolated blood-perfused rat heart, and it was labeled with dihydroethidium and large molecular weight tetramethylrhodamine conjugated dextran. Tissue was illuminated with a 532 nm laser, and epifluorescence at 580 and 650 nm was collected through 2 separate band pass filters. Our results indicate that 1. Optical mapping of myocardial inflammation is feasible; and 2. Reperfusion injury elicits substantial microvascular leakage and ROS production.