Influence of the nature of pre-contraction on the responses to commonly employed vasodilator agents in rat-isolated aortic rings

α-Ketoglutarate Attenuates Hyperlipidemia-Induced Endothelial Damage by Activating the Erk-Nrf2 Signaling Pathway to Inhibit Oxidative Stress and Mitochondrial Dysfunction

Aims: α-Ketoglutarate (AKG) is an intermediate of the tricarboxylic acid cycle and a key hub linking amino acid metabolism and glucose oxidation. Previous studies have shown that AKG improved cardiovascular diseases such as myocardial infarction and myocardial hypertrophy through antioxidant and lipid-lowering characteristics. However, its protective effect and mechanism on endothelial injury caused by hyperlipidemia have not been elucidated yet. In this study, we tested whether AKG possesses protective effects on hyperlipidemia-induced endothelial injury and studied the mechanism. Results: AKG administration both in vivo, and in vitro significantly suppressed the hyperlipidemia-induced endothelial damage, regulated ET-1 and nitric oxide levels, and reduced the inflammatory factor interleukin-6 and matrix metallopeptidase-1 by inhibiting oxidative stress and mitochondrial dysfunction. The protective effects were achieved by the mechanism of activating the Nrf2 phase II system through the ERK signaling pathway. Innovation: These results reveal the role of the AKG-ERK-Nrf2 signaling pathway in the prevention of hyperlipidemia-induced endothelial damage, and suggest that AKG, as a mitochondria-targeting nutrient, is a potential drug for the treatment of endothelial damage in hyperlipidemia. Conclusion: AKG ameliorated the hyperlipidemia-induced endothelial damage and inflammatory response by inhibiting oxidative stress and mitochondrial dysfunction. Antioxid. Redox Signal. 39, 777-793.

Mitochondria-Targeted Triphenylphosphonium-Hydroxytyrosol Prevents Lipotoxicity-Induced Endothelial Injury by Enhancing Mitochondrial Function and Redox Balance via Promoting FoxO1 and Nrf2 Nuclear Translocation and Suppressing Inflammation via Inhibiting p38/NF-кB Pathway

Hyperlipidemia results in endothelial dysfunction, which is intimately associated with disturbed mitochondrial homeostasis, and is a real risk factor for cardiovascular diseases (CVDs). Triphenylphosphonium (TPP+)-HT, constructed by linking a mitochondrial-targeting moiety TPP+ to hydroxytyrosol (HT), enters the cell and accumulates in mitochondria and is thus an important candidate drug for preventing hyperlipidemia-induced endothelial injury. In the present study, we found that TPP-HT has a better anti-inflammatory effect than HT. In vivo, TPP-HT significantly prevented hyperlipidemia-induced adverse changes in the serological lipid panel, as well as endothelial and mitochondrial dysfunction of the thoracic aorta. Similarly, in vitro, TPP-HT exhibited similar protective effects in palmitate (PA)-induced endothelial dysfunction, particularly enhanced expression of the mitochondrial ETC complex II, recovered FoxO1 expression in PA-injured human aorta endothelial cells (HAECs) and promoted FoxO1 nuclear translocation. We further demonstrated that FoxO1 plays a pivotal role in regulating ATP production in the presence of TPP-HT by using the siFoxO1 knockdown technique. Simultaneously, TPP-HT enhanced Nrf2 nuclear translocation, consistent with the in vivo findings of immunofluorescence, and the antioxidant effect of TPP-HT was almost entirely blocked by siNrf2. Concomitantly, TPP-HT’s anti-inflammatory effects in the current study were primarily mediated via the p38 MAPK/NF-κB signaling pathway in addition to the FoxO1 and Nrf2 pathways. In brief, our findings suggest that mitochondria-targeted TPP-HT prevents lipotoxicity induced endothelial dysfunction by enhancing mitochondrial function and redox balance by promoting FoxO1 and Nrf2 nuclear translocation.

Punicalagin attenuates endothelial dysfunction by activating FoxO1, a pivotal regulating switch of mitochondrial biogenesis

Accumulating evidence has elucidated that hyperlipidemia is closely associated with an increasing prevalence of CVDs (cardiovascular diseases) because of endothelial dysfunction. In the present study, we investigated the effect and mechanism of PU (Punicalagin), a major ellagitannin in pomegranate, on endothelial dysfunction both in vivo and in vitro. In vivo, PU significantly ameliorated hyperlipidemia-induced accumulation of serum triglyceride and cholesterol as well as endothelial and mitochondrial dysfunction of thoracic aorta. Intriguingly, the FoxO1 (forkhead box O1) pathway was activated, which may account for prevention of vascular dysfunction and mitochondrial loss via upregulating mitochondrial biogenesis. In line, through in vitro cell cultures, our study demonstrated that PU not only increased the total FoxO1 protein, but also enhanced its nuclear translocation. In addition, silencing of FoxO1 remarkably abolished the ability of PU to augment the mitochondrial biogenesis, eNOS (endothelial NO synthase) expression, and oxidative stress, implying the irreplaceable role of FoxO1 in regulating endothelial function in the presence of PU. Conversely, suppression of excessive ROS (reactive oxygen species) secured the PA (palmitate)-induced decrease of FoxO1 expression, implying that there was a cross-talk between FoxO1 pathway and ROS. Concomitantly, the inflammatory response in current study was primarily mediated via p38 MAPK/NF-κB signaling pathway besides of FoxO1 pathway. Taken together, our findings suggest that PU ameliorates endothelial dysfunction by activating FoxO1 pathway, a pivotal regulating switch of mitochondrial biogenesis.

Endothelial nitric oxide attenuates Na+/Ca2+ exchanger-mediated vasoconstriction in rat aorta

BACKGROUND AND PURPOSE

The Na+/Ca2+ exchanger (NCX) may be an important modulator of Ca2+ entry and exit. The present study investigated whether NCX was affected by prostacyclin and nitric oxide (NO) released from the vascular endothelium, as NCX contains phosphorylation sites for PKA and PKG.

EXPERIMENTAL APPROACH

Rat aortic rings were set up in organ baths. Tension was measured across the ring with a force transducer.

KEY RESULTS

Lowering extracellular [Na+] ([Na+]o) to 1.18 mM induced vasoconstriction in rat endothelium-denuded aortic rings. This effect was blocked by the NCX inhibitor KB-R7943 (2-2-[4-(4-nitrobenzyloxy)phenyl] ethyl isothiourea methanesulphonate; 1 microM). In endothelium-intact aortic rings, decreasing [Na+]o did not constrict the aortic rings significantly, but after treatment with the guanylate cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; 1 microM) or the NOS inhibitor L-NAME (N(omega)-nitro-L-arginine methyl ester; 50 microM), a vasoconstriction that was similar in size to that in endothelium-denuded preparations was evident. The vasorelaxation induced by the NO donor sodium nitroprusside sodium nitroprusside dihydrate (30 nM) was the same in the endothelium-denuded aortic rings preconstricted with either low Na+ (1.18 mM), the thromboxane A2 agonist U46619 (9,11-dideoxy-9alpha, 11alpha-methanoepoxy prostaglandin F(2alpha); 0.1 microM) or high K+ (80 mM).

CONCLUSIONS AND IMPLICATIONS

The results suggest that the endothelium inhibits NCX operation via guanylate cyclase/NO. This is stronger than for other constrictors such as phenylephrine and may relate to concomitant NCX-stimulated NO release from the endothelium. This finding may be important where NCX operates in reverse mode, such as during ischaemia, and highlights a new mechanism whereby the endothelium modulates Ca2+ homoeostasis in vascular smooth muscle.

Relaxation effects of ligustilide and senkyunolide A, two main constituents of Ligusticum chuanxiong, in rat isolated aorta

Ligusticum chuanxiong Hort. (Umbelliferae) is a widely prescribed traditional Chinese medicinal herb for cardiovascular diseases in China. However, the cardiovascular actions of ligustilide and senkyunolide A, two of the most abundant Ligusticum chuanxiong constituents, have yet to be examined. The objective of the present study was to investigate the vasorelaxation effects of ligustilide and senkyunolide A and their underlying mechanisms in rat isolated aorta. Both constituents had similar relaxation potencies against contractions to 9,11-dideoxy-9alpha,11alpha-methanoepoxyprostaglandin F(2alpha), phenylephrine, 5-hydroxytryptamine and KCl. Their vasorelaxation effects were not affected by endothelium removal, the adenylate cyclase inhibitor 9-(tetrahydro-2-furanyl)-9H-purin-6-amine, the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, or the non-selective K+ channel blocker tetraethylammonium. This is the first report to demonstrate the vasorelaxation activities of ligustilide and senkyunolide A in contractions to various contractile agents in rat isolated aorta. The underlying mechanisms await further investigations.

Nitric oxide pathway counteracts enhanced contraction to membrane depolarization in aortic rings of rats on high-sodium diet

Vascular smooth muscle cell contraction and endothelium-dependent relaxation was evaluated in aortic rings isolated from weaned, 5-mo-old Sprague-Dawley rats fed a normal (NS; 0.8% NaCl) or high (HS; 8% NaCl) sodium diet. Arterial pressure was 140 +/- 6 (NS) and 145 +/- 6 mmHg (HS). In endothelium-denuded rings, the response to phenylephrine (PE) was not modified by the sodium diet, while that of depolarizing agent KCl and intracellular calcium releasing agent caffeine increased in the HS group. When endothelium was preserved, PE-evoked contraction was reduced in both NS and HS groups, the contraction being yet lower in the HS group. This effect was partially obliterated by addition of N(G)-nitro-L-arginine methyl ester (L-NAME), independently of the sodium diet. Relaxation to ACh in intact rings and to sodium nitroprusside (SNP) and 8-bromoadenosine 3'5' cyclic guanosine monophosphate (8-BrcGMP) in the absence of endothelium was enhanced in rings isolated from HS rats. In addition, the dose-response curve to 8-BrcGMP was shifted to the right in the presence of iberiotoxin, an inhibitor of large conductance, voltage-dependent, and calcium-sensitive potassium channel (BK(Ca)). However, shift was more marked in rings from HS rats. Present results provide evidence that response of vascular smooth muscle cell to nitric oxide/cGMP-related compounds is increased in HS rings and is associated with a greater activation of the repolarizing BK(Ca) channels. Such changes might counterbalance enhanced contractile response to membrane depolarization and thus participate in maintenance of arterial pressure in the present model of early and long-term HS feeding in rats.

Thromboxane A2 induces airway constriction through an M3 muscarinic acetylcholine receptor-dependent mechanism

Thromboxane A2 (TXA2) is a potent lipid mediator released by platelets and inflammatory cells and is capable of inducing vasoconstriction and bronchoconstriction. In the airways, it has been postulated that TXA2 causes airway constriction by direct activation of thromboxane prostanoid (TP) receptors on airway smooth muscle cells. Here we demonstrate that although TXA2 can mediate a dramatic increase in airway smooth muscle constriction and lung resistance, this response is largely dependent on vagal innervation of the airways and is highly sensitive to muscarinic acetylcholine receptor (mAChR) antagonists. Further analyses employing pharmacological and genetic strategies demonstrate that TP-dependent changes in lung resistance and airway smooth muscle tension require expression of the M2 mAChR subtype. These results raise the possibility that some of the beneficial actions of anticholinergic agents used in the treatment of asthma and chronic obstructive pulmonary disease result from limiting physiological changes mediated through the TP receptor. Furthermore, these findings demonstrate a unique pathway for TP regulation of homeostatic mechanisms in the airway and suggest a paradigm for the role of TXA2 in other organ systems.