Hussain Contractor

Fumarate Is Cardioprotective via Activation of the Nrf2 Antioxidant Pathway

Summary The citric acid cycle (CAC) metabolite fumarate has been proposed to be cardioprotective; however, its mechanisms of action remain to be determined. To augment cardiac fumarate levels and to assess fumarates cardioprotective properties, we generated fumarate hydratase (Fh1) cardiac knockout (KO) mice. These fumarate-replete hearts were robustly protected from ischemia-reperfusion injury (I/R). To compensate for the loss of Fh1 activity, KO hearts maintain ATP levels in part by channeling amino acids into the CAC. In addition, by stabilizing the transcriptional regulator Nrf2, Fh1 KO hearts upregulate protective antioxidant response element genes. Supporting the importance of the latter mechanism, clinically relevant doses of dimethylfumarate upregulated Nrf2 and its target genes, hence protecting control hearts, but failed to similarly protect Nrf2-KO hearts in an in vivo model of myocardial infarction. We propose that clinically established fumarate derivatives activate the Nrf2 pathway and are readily testable cytoprotective agents.

Elevated Blood Pressure in Offspring Born Premature to Hypertensive Pregnancy: Is Endothelial Dysfunction the Underlying Vascular Mechanism?

Offspring born to mothers with hypertensive pregnancy have higher childhood blood pressure. We hypothesized this relates to prenatally programmed differences in the underlying vascular pathophysiology of the offspring and that these would be most apparent in those born preterm because of severe hypertension. We carried out a 20-year follow-up study of 71 subjects born preterm, 19 to a hypertensive pregnancy and 52 to a normotensive pregnancy. Findings were compared with 38 subjects born at term to uncomplicated pregnancies. Peripheral and central blood pressures were measured, and then central arterial stiffness was assessed by carotid-femoral pulse wave velocity using applanation tonometry. Ultrasound was used to assess flow-mediated endothelial-dependent and independent brachial artery responses and common carotid artery intima-media thickness. Offspring born preterm to either hypertensive or normotensive pregnancy had higher peripheral and central blood pressure compared with full-term born offspring (central mean arterial pressure after preterm hypertensive pregnancy: 84.92±7.0 mm Hg; preterm normotensive pregnancy: 84.13±8.9 mm Hg; full-term pregnancy: 76.24±7.96 mm Hg; P=0.0009). However, underlying vascular phenotype differed. Preterm offspring of normotensive pregnancy had greater arterial stiffness than offspring of hypertensive pregnancy (5.92±0.84 versus 5.42±0.73 m/s; P=0.039), whereas offspring of hypertensive pregnancy had greater carotid intima-media thickness (0.52±0.04 versus 0.48±0.06 mm; P=0.013) and 30% lower flow-mediated dilatation (4.25±4.02% versus 6.79±4.38%; P=0.05). Prematurity is associated with elevated blood pressure in later life. However, predominant underlying vascular phenotype depends on maternal pathology. Targeting endothelial function may be particularly important for primary prevention after hypertension in pregnancy.

Glucose-Insulin-Potassium Reduces the Incidence of Low Cardiac Output Episodes After Aortic Valve Replacement for Aortic Stenosis in Patients With Left Ventricular Hypertrophy Results From the Hypertrophy, Insulin, Glucose, and Electrolytes (HINGE) Trial

Background— Patients undergoing aortic valve replacement for critical aortic stenosis often have significant left ventricular hypertrophy. Left ventricular hypertrophy has been identified as an independent predictor of poor outcome after aortic valve replacement as a result of a combination of maladaptive myocardial changes and inadequate myocardial protection at the time of surgery. Glucose-insulin-potassium (GIK) is a potentially useful adjunct to myocardial protection. This study was designed to evaluate the effects of GIK infusion in patients undergoing aortic valve replacement surgery. Methods and Results— Patients undergoing aortic valve replacement for aortic stenosis with evidence of left ventricular hypertrophy were randomly assigned to GIK or placebo. The trial was double-blind and conducted at a single center. The primary outcome was the incidence of low cardiac output syndrome. Left ventricular biopsies were analyzed to assess changes in 5′ adenosine monophosphate–activated protein kinase (AMPK), Akt phosphorylation, and protein O-linked &bgr;-N-acetylglucosamination (O-GlcNAcylation). Over a 4-year period, 217 patients were randomized (107 control, 110 GIK). GIK treatment was associated with a significant reduction in the incidence of low cardiac output state (odds ratio, 0.22; 95% confidence interval, 0.10 to 0.47; P=0.0001) and a significant reduction in inotrope use 6 to 12 hours postoperatively (odds ratio, 0.30; 95% confidence interval, 0.15 to 0.60; P=0.0007). These changes were associated with a substantial increase in AMPK and Akt phosphorylation and a significant increase in the O-GlcNAcylation of selected protein bands. Conclusions— Perioperative treatment with GIK was associated with a significant reduction in the incidence of low cardiac output state and the need for inotropic support. This benefit was associated with increased signaling protein phosphorylation and O-GlcNAcylation. Multicenter studies and late follow-up will determine whether routine use of GIK improves patient prognosis. Clinical Trial Registration— URL: http://www.controlled-trials.com. Reference number: ISRCTN 05758301.

Glucose-Insulin-Potassium Reduces the Incidence of Low Cardiac Output Episodes After Aortic Valve Replacement for Aortic Stenosis in Patients With Left Ventricular Hypertrophy

Background— Patients undergoing aortic valve replacement for critical aortic stenosis often have significant left ventricular hypertrophy. Left ventricular hypertrophy has been identified as an independent predictor of poor outcome after aortic valve replacement as a result of a combination of maladaptive myocardial changes and inadequate myocardial protection at the time of surgery. Glucose-insulin-potassium (GIK) is a potentially useful adjunct to myocardial protection. This study was designed to evaluate the effects of GIK infusion in patients undergoing aortic valve replacement surgery. Methods and Results— Patients undergoing aortic valve replacement for aortic stenosis with evidence of left ventricular hypertrophy were randomly assigned to GIK or placebo. The trial was double-blind and conducted at a single center. The primary outcome was the incidence of low cardiac output syndrome. Left ventricular biopsies were analyzed to assess changes in 5′ adenosine monophosphate–activated protein kinase (AMPK), Akt phosphorylation, and protein O-linked &bgr;-N-acetylglucosamination (O-GlcNAcylation). Over a 4-year period, 217 patients were randomized (107 control, 110 GIK). GIK treatment was associated with a significant reduction in the incidence of low cardiac output state (odds ratio, 0.22; 95% confidence interval, 0.10 to 0.47; P=0.0001) and a significant reduction in inotrope use 6 to 12 hours postoperatively (odds ratio, 0.30; 95% confidence interval, 0.15 to 0.60; P=0.0007). These changes were associated with a substantial increase in AMPK and Akt phosphorylation and a significant increase in the O-GlcNAcylation of selected protein bands. Conclusions— Perioperative treatment with GIK was associated with a significant reduction in the incidence of low cardiac output state and the need for inotropic support. This benefit was associated with increased signaling protein phosphorylation and O-GlcNAcylation. Multicenter studies and late follow-up will determine whether routine use of GIK improves patient prognosis. Clinical Trial Registration— URL: http://www.controlled-trials.com. Reference number: ISRCTN 05758301.

Inhibition of the malate–aspartate shuttle by pre-ischaemic aminooxyacetate loading of the heart induces cardioprotection

AIMS Preserved mitochondrial function is essential for protection against ischaemia-reperfusion (IR) injury. The malate-aspartate (MA) shuttle constitutes the principal pathway for transport of reducing cytosolic equivalents for mitochondrial oxidation. We hypothesized that a transient shut-down of the MA-shuttle by aminooxyacetate (AOA) during ischaemia and early reperfusion modulates IR injury by mechanisms comparable to ischaemic preconditioning (IPC). METHODS AND RESULTS Isolated perfused rat hearts exposed to 40 min global no-flow ischaemia were studied in: (i) control, (ii) pre-ischaemic AOA (0.1 mM), (iii) IPC, and (iv) AOA+IPC hearts. IR injury was evaluated by infarct size and haemodynamic recovery. Tracer-estimated glucose oxidation and metabolic changes in glycogen, lactate, pyruvate, tricarboxylic acid (TCA) cycle intermediates, and ATP degradation products were measured. The effects of AOA on complex I respiration and reactive oxygen species (ROS) production were examined in isolated rabbit mitochondria. Treatment with AOA, IPC, or AOA+IPC induced significant infarct reduction; 28 ± 6, 30 ± 3, and 18 ± 1%, respectively, vs. 52 ± 5% of left ventricular (LV) mass for control (P < 0.01 for all). LV-developed pressure improved to 60 ± 3, 63 ± 5 and 53 ± 4 vs. 31 ± 5 mmHg (P < 0.01 for all) after 2 h reperfusion. Pre-ischaemic AOA administration inhibited glycolysis and increased glucose oxidation during post-ischaemic reperfusion similar to IPC, and suppressed complex I respiration and ROS production in the non-ischaemic heart. Changes in lactate, pyruvate, TCA intermediates, and ATP end products suggested an AOA inhibition of the MA-shuttle during late ischaemia and early reperfusion. CONCLUSION Inhibition of the MA-shuttle during ischaemia and early reperfusion is proposed as a mechanism to reduce IR injury.

Remote ischemic preconditioning with - But not without - Metabolic support protects the neonatal porcine heart against ischemia-reperfusion injury

BACKGROUND While remote ischemic preconditioning (rIPC) protects the mature heart against ischemia-reperfusion (IR) injury, the effect on the neonatal heart is not known. The neonatal heart relies almost solely on carbohydrate metabolism, which is modified by rIPC in the mature heart. We hypothesized that rIPC combined with metabolic support with glucose-insulin (GI) infusion improves cardiac function and reduces infarct size after IR injury in neonatal piglets in-vivo. METHODS AND RESULTS 32 newborn piglets were randomized into 4 groups: control, GI, GI+rIPC and rIPC. GI and GI+rIPC groups received GI infusion continuously from 40 min prior to ischemia. rIPC and GI+rIPC groups underwent four cycles of 5 min limb ischemia. Myocardial IR injury was induced by 40 min occlusion of the left anterior descending artery followed by 2 h reperfusion. Myocardial lactate concentrations were assessed in microdialysis samples analyzed by mass spectrometry. Infarct size was measured using triphenyltetrazolium chloride staining. Systolic recovery (dP/dt(max) as % of baseline) after 2 h reperfusion was 68.5±13.8% in control, 53.7±11.2% in rIPC (p<0.05), and improved in GI (83.6±18.8%, p<0.05) and GI+rIPC (87.0±15.7%, p<0.01). CONCLUSION rIPC+GI protects the neonatal porcine heart against IR injury in-vivo. rIPC alone has detrimental metabolic and functional effects that are abrogated by simultaneous GI infusion.

Human Second Window Pre-Conditioning and Post-Conditioning by Nitrite Is Influenced by a Common Polymorphism in Mitochondrial Aldehyde Dehydrogenase

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Preserved flow-mediated dilation in adults with cyanotic congenital heart disease.

Adults with cyanotic congenital heart disease (CCHD) have been shown to have endothelial dysfunction in the forearm resistance vessels as assessed with venous occlusion plethysmography. Whether these abnormalities are confined to the microvasculature or reflect generalized endothelial dysfunction remain unknown. We used high-resolution ultrasound to compare flow responses and endothelial-dependent flow-mediated dilation (FMD) in the brachial artery of 13 adult patients with CCHD and 14 healthy controls. High-dose vitamin C was infused to evaluate the possible role of reactive oxygen species on endothelial vasomotor function. FMD was measured both prior to and after vitamin C infusion. Sublingual glyceryl nitrate was given to assess endothelium-independent responses. FMD did not differ among patients with CCHD and controls either before (6.2 ± 4.1, 5.1 ± 2.6%, p = 0.44) or after (5.1 ± 2.8, 5.2 ± 3.1%, p = 0.90) vitamin C infusion. Endothelium-independent vasodilatation was similar in both groups (14.3 ± 3.7, 13.2 ± 4.4%). There were no differences in baseline flow or in measures of reactive hyperemia. Adults with CCHD appear to have preserved endothelial function in their conduit arteries. This suggests that these patients are not at an increased risk of premature atherosclerotic cardiovascular events.

Influence of long-term treatment with glyceryl trinitrate on remote ischemic conditioning

Remote ischemic conditioning (RIC) protects against sustained myocardial ischemia. Because of overlapping mechanisms, this protection may be altered by glyceryl trinitrate (GTN), which is commonly used in the treatment of patients with chronic ischemic heart disease. We investigated whether long-term GTN treatment modifies the protection by RIC in the rat myocardium and human endothelium. We studied infarct size (IS) in rat hearts subjected to global ischemia-reperfusion (I/R) in vitro and endothelial function in healthy volunteers subjected to I/R of the upper arm. In addition to allocated treatment, rats were coadministered with reactive oxygen species (ROS) or nitric oxide (NO) scavengers. Rats and humans were randomized to 1) control, 2) RIC, 3) GTN, and 4) GTN + RIC. In protocols 3 and 4, rats and humans underwent long-term GTN treatment for 7 consecutive days, applied subcutaneously or 2 h daily transdermally. In rats, RIC and long-term GTN treatment reduced mean IS (18 ± 12%, P = 0.007 and 15 ± 5%, P = 0.002) compared with control (35 ± 13%). RIC and long-term GTN treatment in combination did not reduce IS (29 ± 12%, P = 0.55 vs. control). ROS and NO scavengers both attenuated IS reduction by RIC and long-term GTN treatment. In humans, I/R reduced endothelial function ( P = 0.01 vs. baseline). Separately, RIC and long-term GTN prevented the reduction in endothelial function caused by I/R; given in combination, prevention was lost. RIC and long-term GTN treatment both protect against rat myocardial and human endothelial I/R injury through ROS and NO-dependent mechanisms. However, when given in combination, RIC and long-term GTN treatment fail to confer protection. NEW & NOTEWORTHY Remote ischemic conditioning (RIC) and long-term glyceryl trinitrate (GTN) treatment protect against ischemia-reperfusion injury in both human endothelium and rat myocardium. However, combined application of RIC and long-term GTN treatment abolishes the individual protective effects of RIC and GTN treatment on ischemia-reperfusion injury, suggesting an interaction of clinical importance.

Adenosine Receptor Activation in the “Trigger” Limb of Remote Pre-Conditioning Mediates Human Endothelial Conditioning and Release of Circulating Cardioprotective Factor(s)

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