EDH-mediated Relaxation Research Articles

0051: Lipid emulsions used in parenteral nutrition induce endothelial dysfunction in porcine coronary artery rings: role of oxidative stress and cyclooxygenase-derived vasoconstrictors

Lipid emulsions are used to provide a source of calories and essential fatty acids for patients requiring parenteral nutrition. They have been associated with hypertriglyceridemia, hypercholesterolemia and metabolic stress, which may promote the development of endothelial dysfunction. The aim of the present study was to determine the possibility that five different commercial lipid emulsions affect the endothelial function of coronary arteries, and, if so, to investigate the underlying mechanism. Porcine coronary arteries were incubated with lipid emulsions for 30 minutes before the determination of vascular reactivity in organ chambers and the level of oxidative stress using the redox-sensitive fluorescent dye dihydroethidium (DHE). Incubation of coronary artery rings with either Lipidem ® , Medialipid ® or Smoflipid ® (medium-chain triglycerides), but not with Intralipid ® or Clinoleic ® (long-chain triglycerides), significantly reduced the bradykinin- induced endothelium-dependent relaxations mediated by both nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH). In contrast, Lipidem ® did not affect endothelium-independent relaxations to sodium nitroprusside. The endothelial dysfunction induced by Lipidem ® was significantly improved by indomethacin, a cyclooxygenase (COX) inhibitor, and by inhibitors of oxidative stress (N-acetylcysteine, superoxide dismutase, catalase) and transition metal chelating agents (neocuproine, L-histidine, desferoxamine). Lipidem ® markedly increased the vascular oxidative stress as indicated by increased DHE signal throughout the arterial wall. The present findings indicate that several but not all lipid emulsions induce an endothelial dysfunction in coronary artery rings, involving both blunted NO- and EDH-mediated relaxations. The Lipidem ® -induced endothelial dysfunction is associated with increased vascular oxidative stress and the formation of COX-derived vasoconstrictor prostanoids.

Abstract 298: Chronic Environmental Enrichment Improves Aging-related Endothelial Dysfunction in Rats: Role of Oxidative Stress

Aging is associated with an endothelial dysfunction, which promotes cardiovascular diseases. Physical exercise has beneficial effects on the endothelial function. However, the effect of an enriched environment (EE) promoting physical exercise, on the endothelial function has not been explored during aging. We investigated the endothelial dysfunction in Long-Evans female rats housed in standard conditions (SD, 2 rats per cage) until the age of 18 months. Then, half the rats were transferred to EE (12 rats in one large cage containing various objects, which were changed 5 times per week) for 6 months. A group of 2-month old rats served as young controls. Systolic (SBP), diastolic (DBP) blood pressure and heart rate (HR) were determined by plethysmography. Vascular reactivity was assessed in mesenteric arteries using organ chambers, vascular oxidative stress by dihydroethidine staining, and the proteins expression by immunofluorescence. Aging under SD was associated with increased SBP (by 40 mmHg, P <0.001), DBP (by 12 mmHg, P <0.001) and HR (by 110 bpm, P <0.001) compared to young rats. It was also associated with blunted acetylcholine (ACh)-induced endothelium-dependent nitric oxide (NO)-mediated relaxations (EC50 1.08 10 -8 M vs. 3.08 10 -8 M, P <0.05) and endothelium-derived hyperpolarization (EDH)-mediated relaxation (E max 89.5±11.8% vs. 0.28±0.18%, P <0.001), and the induction of endothelium-dependent contractile responses to ACh (E max 0.004±0.008 g vs. 0.71±0.07 g, P <0.001) in mesenteric artery rings. EE reduced SBP and DBP by 18 and 10 mmHg, respectively ( P <0.05), HR by 30 bpm ( P >0.05), and improved NO-mediated responses to a similar level as in young rats ( P <0.001) without affecting the blunted EDH-mediated relaxation and the increased endothelium-dependent contractile responses in old rats. An excessive oxidative stress and the upregulation of endothelial NO synthase (eNOS), nitrotyrosine and arginase I were observed in the aorta of SD old rats compared to young rats ( P <0.001). EE improved all these effects ( P <0.05). In conclusion, EE retarded the aging-related endothelial dysfunction mostly by improving the NO-mediated relaxation. This effect involves normalization of vascular oxidative stress and possibly also eNOS uncoupling.

Abstract 299: Remodeling of Endothelial Function in Atherosclerotic Mice Overexpressing Endothelin-1 Restricted to Endothelium

Background: In human atherosclerosis , which is associated with elevated plasma and coronary endothelin (ET)-1 levels, ET type A receptor antagonists improved coronary endothelial function. Mice overexpressing ET-1 specifically in the endothelium (eET-1) crossed with apolipoprotein E knockout mice (Apoe-/-) exhibited exaggerated high-fat diet (HFD)-induced atherosclerosis. Since endothelial dysfunction often precedes development of atherosclerosis, we investigated whether endothelium-specific ET-1 overexpression causes endothelial dysfunction in Apoe-/- mice. Methods: Eight-week male old eET-1, Apoe-/-, eET-1/Apoe-/- and wild-type (WT) mice were fed a regular diet or HFD for 8 weeks. Endothelial function was assessed in mesenteric arteries by pressurized myography. Results: In HFD-fed mice, acetylcholine-induced endothelium-dependent relaxation (EDR) was reduced in Apoe-/- and eET-1 compared to WT (Emax: 29.2±2.9% and 51.8±7.9%, respectively, vs. 88.0±2.6%, P<0.05). Surprisingly, EDR was not impaired in eET-1/Apoe-/- (70.9±9.8%) compared to WT. Endothelium-independent relaxation to the nitric oxide (NO) donor sodium nitroprusside and contractile responses to norepinephrine were unaffected. Similar results were observed in regular diet-fed mice. In the presence of inhibitors of either NO synthase (NOS)-mediated relaxation, Nω-nitro-L-arginine methyl ester, or endothelium-dependent hyperpolarization (EDH)-mediated relaxation, apamin plus Tram34, EDR was blunted in WT (Emax: 2.8±0.4% and 35.7±8.4 respectively, P<0.01), whereas relaxation was weakly reduced or unaffected in eET-1/Apoe-/- (Emax: 68.6±9.9, P<0.05 and 80.6±8.0, respectively). However, the concomitant inhibition of NOS- and EDH-mediated relaxation strongly reduced EDR in eET-1/Apoe-/- (Emax: 43.0±8.2%, P<0.05). Conclusions: These results show an interdependence of NOS and EDH pathways in EDR in WT mice. ET-1 overexpression induced development of compensatory mechanisms in pre-atherosclerotic arteries of Apoe-/- mice, which permits either NOS or EDH pathway to mediate independently EDR. Investigation of mechanisms involved in the remodeling of EDR in eET-1/Apoe-/- mice will allow a better understanding of the ET-1 role in atherosclerosis.

Grape-Derived Polyphenols Prevent Doxorubicin-Induced Blunted EDH-Mediated Relaxations in the Rat Mesenteric Artery: Role of ROS and Angiotensin II

This study determined whether doxorubicin, an anticancer agent, impairs endothelium-dependent relaxations mediated by nitric oxide (NO) and endothelium-derived hyperpolarization (EDH) in the mesenteric artery and, if so, the mechanism underlying the protective effect of red wine polyphenols (RWPs), a rich natural source of antioxidants. Male Wistar rats were assigned into 4 groups: control, RWPs, doxorubicin, and doxorubicin + RWPs. Vascular reactivity was assessed in organ chambers; the vascular formation of reactive oxygen species (ROS) using dihydroethidine and the expression levels of small and intermediate conductance calcium-activated potassium channels (SKCa, IKCa) and connexin 40 (Cx40), which are involved in EDH-type relaxations, endothelial NO synthase (eNOS), angiotensin II, and AT1 receptors by immunofluorescence. The doxorubicin treatment impaired EDH-mediated relaxations, whereas those mediated by NO were minimally affected. This effect was associated with reduced expression levels of SKCa, IKCa, and Cx40, increased expression levels of eNOS, angiotensin II, and AT1 receptors, and formation of ROS in mesenteric arteries. RWPs prevented both the doxorubicin-induced blunted EDH-type relaxations and the increased vascular oxidative stress, and they improved the expression levels of target proteins. These findings suggest that polyphenol-rich natural products might be of interest in the management of doxorubicin-induced vascular injury possibly by improving the vascular angiotensin system.