Inhibition of Akt Attenuates RPO-Induced Cardioprotection

Effects of Red Palm Oil on Myocardial Antioxidant Enzymes, Nitric Oxide Synthase and Heart Function in Spontaneously Hypertensive Rats

The purpose of this study was to investigate the effect of antioxidants rich red palm oil (RPO) supplementation on cardiac oxidative stress known as crucial factor deteriorating heart function in hypertension. 3-month-old, male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) were fed standard rat chow without or with RPO (0.2 mL/day/5 weeks). General characteristic of rats were registered. Left ventricular tissue (LV) was used to determine expression of superoxide dismutases (SOD1, SOD2) and glutathione peroxidases (Gpx) as well as activity of nitric oxide synthase (NOS). Functional parameters of the heart were examined during basal conditions and at the early-phase of post-ischemic reperfusion using Langendorff-perfused system. RPO intake significantly reduced elevated blood pressure and total NOS activity as well as increased lowered expression of mitochondrial SOD2 in SHR hearts during basal condition. Moreover, RPO supplementation resulted in suppression of elevated heart rate, increase of reduced coronary flow and enhancement of systolic and diastolic heart function at the early-phase of post-ischemic reperfusion. It is concluded that SHR benefit from RPO intake due to decrease of blood pressure, amelioration of oxidative stress and protection of heart function that was deteriorated by post-ischemic reperfusion.

Berbamine postconditioning protects the heart from ischemia/reperfusion injury through modulation of autophagy

Pretreatment of berbamine protects the heart from ischemia/reperfusion (I/R) injury. However it is unknown whether it has cardioprotection when given at the onset of reperfusion (postconditioning (PoC)), a protocol with more clinical impact. Autophagy is upregulated in I/R myocardium and exacerbates cardiomyocyte death during reperfusion. However, it is unknown whether the autophagy during reperfusion is regulated by berbamine. Here we investigated whether berbamine PoC (BMPoC) protects the heart through regulation of autophagy by analyzing the effects of BMPoC on infarct size and/or cell death, functional recovery and autophagy in perfused rat hearts and isolated cardiomyocytes subjected to I/R. Berbamine from 10 to 100 nM given during the first 5 min of reperfusion concentration-dependently improved post-ischemic myocardial function and attenuated cell death. Similar protections were observed in cardiomyocytes subjected to simulated I/R. Meanwhile, BMPoC prevented I/R-induced impairment of autophagosome processing in cardiomyocytes, characterized by increased LC3-II level and GFP-LC3 puncta, and decreased p62 degradation. Besides, lysosomal inhibitor chloroquine did not induce additional increase of LC3-II and P62 abundance after I/R but it reversed the effects of BMPoC in those parameters in cardiomyocytes, suggesting that I/R-impaired autophagic flux is restored by BMPoC. Moreover, I/R injury was accompanied by enhanced expression of Beclin 1, which was significantly inhibited by BMPoC. In vitro and in vivo adenovirus-mediated knockdown of Beclin 1 in myocardium and cardiomyocytes restored I/R-impaired autophagosome processing, associated with an improvement of post-ischemic recovery of myocardial contractile function and a reduction of cell death, but it did not have additive effects to BMPoC. Conversely, overexpression of Beclin 1 abolished the cardioprotection of BMPoC as did by overexpression of an essential autophagy gene Atg5. Furthermore, BMPoC-mediated cardioprotection was abolished by a specific Akt1/2 inhibitor A6730. Our results demonstrate that BMPoC confers cardioprotection by modulating autophagy during reperfusion through the activation of PI3K/Akt signaling pathway.

Cholesterol regulates contractility and inotropic response to β2-adrenoceptor agonist in the mouse atria: Involvement of Gi-protein-Akt-NO-pathway

Majority of cardiac β2-adrenoceptors is located in cholesterol-rich microdomains. Here, we have investigated the underlying mechanisms by which a slight to moderate cholesterol depletion with methyl-β-cyclodextrin (MβCD, 1 and 5mM) interferes with contractility and inotropic effect of β2-adrenergic agonist (fenoterol, 50μM) in the mouse atria. Treatment with MβCD itself increased amplitude of Ca²⁺ transient but did not change the contraction amplitude due to a clamping action of elevated NO. Cholesterol depletion significantly attenuated the positive inotropic response to fenoterol which is accompanied by increase in NO generation and decrease in Ca²⁺ transient. Influence of 1mM MβCD on the fenoterol-driven changes in both contractility and NO level was strongly attenuated by inhibition of G_i-protein (pertussis toxin), Akt (Akt 1/2 kinase inhibitor) or NO-synthase (L-NAME). After exposure to 5mM MβCD, pertussis toxin or Akt inhibitor could recover the β2-agonist effects on contractility, NO production and Ca²⁺ transient, while L-NAME only reduced NO level. An adenylyl cyclase activator (forskolin, 50nM) had no influence on the MβCD-induced changes in the β2-agonist effects. Obtained results suggest that slight cholesterol depletion upregulates G_i-protein/Akt/NO-synthase signaling that attenuates the positive inotropic response to β2-adrenergic stimulation without altering the Ca²⁺ transient. Whilst moderate cholesterol depletion additionally could suppress the enhancement of the Ca²⁺ transient amplitude caused by the β2-adrenergic agonist administration in G_i-protein/Akt-dependent but NO-independent manner.

Membrane-tethered AKT kinase regulates basal synaptic transmission and early phase LTP expression by modulation of post-synaptic AMPA receptor level

The serine/threonine kinase AKT/PKB plays a fundamental role in a wide variety of neuronal functions, including neuronal cell development, axonal growth, and synaptic plasticity. Multiple evidence link AKT signaling pathways to regulation of late phase long-term synaptic plasticity, synaptogenesis, and spinogenesis, as well as long-term memory formation. Nevertheless, the downstream effectors mediating the effects of AKT on early phase long-term potentiation (eLTP) are currently unknown. Here we report that using different regimes of pharmacological activation and inhibition of AKT activity in acute hippocampal slices, we found that AKT regulates the post-synaptic expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA) receptors affecting solely the expression of eLTP, with no effect on its induction and maintenance. We further show that both maintenance of basal synaptic activity and expression of eLTP require plasma membrane tethering by activated AKT and that basal synaptic activity may be regulated via the direct effects of AKT1 on the expression level of post-synaptic AMPA receptors bypassing the canonical AKT signaling. Finally, we establish that eLTP expression requires the involvement of both the canonical AKT signaling pathways and the direct effect of AKT1 on AMPA receptor activity/expression in the post-synaptic membrane. © 2016 Wiley Periodicals, Inc.

Modulation of Hypercholesterolemia-Induced Oxidative/Nitrative Stress in the Heart

Hypercholesterolemia is a frequent metabolic disorder associated with increased risk for cardiovascular morbidity and mortality. In addition to its well-known proatherogenic effect, hypercholesterolemia may exert direct effects on the myocardium resulting in contractile dysfunction, aggravated ischemia/reperfusion injury, and diminished stress adaptation. Both preclinical and clinical studies suggested that elevated oxidative and/or nitrative stress plays a key role in cardiac complications induced by hypercholesterolemia. Therefore, modulation of hypercholesterolemia-induced myocardial oxidative/nitrative stress is a feasible approach to prevent or treat deleterious cardiac consequences. In this review, we discuss the effects of various pharmaceuticals, nutraceuticals, some novel potential pharmacological approaches, and physical exercise on hypercholesterolemia-induced oxidative/nitrative stress and subsequent cardiac dysfunction as well as impaired ischemic stress adaptation of the heart in hypercholesterolemia.